JP7075612B2 - Silicon nitride sintered substrate - Google Patents

Description

The present application relates to a silicon nitride sintered substrate, and more particularly to a silicon nitride sintered group used as a bonding substrate.

In recent years, high-power electronic circuits such as power modules and LEDs have come to be used for various purposes, and an insulating substrate used for mounting such circuits is required. A ceramic substrate is generally used as such an insulating substrate. In particular, the silicon nitride sintered substrate has excellent mechanical strength. For example, Japanese Patent Application Laid-Open No. 6-24850 (Patent Document 1) discloses a silicon nitride sintered substrate having a low dielectric constant, high airtightness, and high productivity, but it is difficult to produce a large-sized substrate.

As one of the methods for manufacturing semiconductors such as LEDs, a bonding method in which an epitaxial layer formed on a single crystal substrate is bonded to an electrode formed on the circuit board via a bump, and the epitaxial layer is electrically connected to the circuit board. Is used. Unlike wire bonding, this bonding does not require wire connection, so that the semiconductor circuit can be made compact. Examples of the circuit board used for this bonding include an aluminum nitride substrate (AlN substrate).

For example, International Publication No. 2005/031882 (Patent Document 2) is a light emitting device in which a light emitting element is mounted on the surface of an aluminum nitride fired substrate, and the surface on which the light emitting element of the aluminum nitride substrate is mounted is 0.3 μmRa. We disclose a luminous device that has the following surface roughness, a metal vapor deposition film is formed, and via holes are formed on an aluminum nitride substrate. Such a configuration enables miniaturization and heat dissipation. It is stated that it is excellent, a larger current can be passed, the luminous efficiency is high, and the brightness can be significantly increased.

The AlN substrate as described in Patent Document 2 is characterized by high heat dissipation because it has high thermal conductivity, but it has a certain thickness due to its low mechanical strength (bending strength and fracture toughness). Is not suitable for applications that require a thin substrate, so there is a limit to further miniaturization.

Japanese Unexamined Patent Publication No. 6-24850 International Publication No. 2005/031882

Therefore, an object of the present invention is to provide a silicon nitride sintered substrate having a large size, excellent thermal conductivity, and excellent mechanical strength (bending strength and fracture toughness).

The silicon nitride sintered substrate according to the embodiment of the present disclosure has a main surface having a shape larger than a square having a side of 120 mm, and the ratio dc / of the density dc of the central portion to the density de of the end portion on the main surface. The de is 0.98 or more and 1.0 or less, the void ratio vc in the central portion of the main surface is 1.80% or less, the void ratio ve at the end portion is 1.00% or less, and the central portion is described. The ratio ve / vc of the void ratio vc of the portion and the void ratio ve of the end portion is 0.50 or more and 1.06 or less, has a thickness of 0.15 mm or more and 2.0 mm or less, and has an insulation of 6 or more. It has a sinter withstand voltage wibble coefficient.

The silicon nitride sintered substrate of the present invention preferably has a dielectric breakdown withstand voltage of 8.0 kV or more.

In the central portion, the carbon content is preferably 0.2% by mass or less.

The silicon nitride sintered substrate of the present invention preferably has a bending strength of 600 MPa or more and a fracture toughness of 5.0 MPa · m ^0.5 or more.

It is preferable that the density dc of the central portion is 3.120 g / cm ³ or more and the density de of the end portion is 3.160 g / cm ³ or more.

Since the silicon nitride sintered substrate of the present application is large and has excellent insulation reliability and mechanical strength (bending strength and breaking toughness), it is used for bonding a semiconductor single crystal substrate or a semiconductor single crystal layer in semiconductor circuit manufacturing. Suitable as a substrate.

It is a perspective view which shows an example of the silicon nitride sintered substrate of this embodiment. It is a schematic diagram which shows the state of cutting out the silicon nitride sintered substrate of this invention from the silicon nitride sintered body obtained by sintering a green sheet. It is a schematic diagram explaining the definition of the central part and the edge part in the silicon nitride sintered substrate which concerns on (a) Example and (b) reference example. It is a schematic diagram which shows the measurement system for measuring a partial discharge voltage. It is (a) plan view and (b) sectional view which shows the shape of the test piece for obtaining a pressure resistance. It is a schematic diagram which shows the manufacturing process of CSP-LED (chip size package LED). It is a flowchart which shows an example of the manufacturing method of the silicon nitride sintered substrate of this embodiment. It is a flowchart which shows the other example of the manufacturing method of the silicon nitride sintered substrate of this embodiment. It is sectional drawing which shows the laminated assembly which has a plurality of green sheets. It is sectional drawing which shows the state which arranges the weight plate on the upper surface of a laminated assembly. It is sectional drawing which shows the appearance which the laminated assembly which put the weight plate is arranged on the multi-stage frame in the container of a double structure. It is sectional drawing which shows the state which one laminated assembly was placed on the lower plate of the inner container and the outer container with the mounting plate. FIG. 3 is a cross-sectional view showing a state in which another mounting plate is placed on the mounting plate shown in FIG. 10 via a vertical frame member, and a second laminated assembly is placed on the mounting plate. It is a graph which shows an example of the temperature profile of the sintering process in the manufacturing method of the silicon nitride sintered substrate of this embodiment. It is a graph which shows the other example of the temperature profile of the sintering process in the manufacturing method of the silicon nitride sintered substrate of this embodiment. 6 is a graph showing the relationship between the void ratio and the carbon content in the silicon nitride sintered substrates of Reference Examples 1 to 28, 51, 52 and Comparative Examples 53 to 55. In the silicon nitride sintered substrate of Reference Examples 1, 3, 5, 10, 12, 14, 51, 52, (a) the relationship between the length of one side and the density of the substrate, and (b) the length of one side and the void ratio. It is a graph which shows the relationship. Reference Examples 1, 3, 5, 10, 12, 14, 51, 52 In the silicon nitride sintered substrate, (a) the relationship between the length of one side and the partial discharge voltage, and (b) the length of one side and the dielectric breakdown withstand voltage. It is a graph which shows the relationship with the Weibull coefficient.

According to a detailed study by the inventor of the present application, when the size of the silicon nitride sintered substrate is increased, various physical properties are different between the vicinity of the center of the substrate and the end portion, and the uniformity of the physical properties in the surface of the substrate is lowered. do. In particular, it was found that the green sheet does not easily shrink during sintering near the center of the substrate, so that the density decreases and the void ratio increases near the center of the substrate.

When a silicon nitride sintered substrate is used for a high power circuit such as mounting a power module, LED or LD (laser diode), it is preferable that the silicon nitride has a high withstand voltage and / or has high insulation reliability. As a result of the examination, it was found that the partial discharge voltage can be used as a characteristic for evaluating the high insulation reliability, and that the partial discharge voltage correlates with the void ratio of the silicon nitride sintered substrate. High insulation reliability means that high insulation characteristics are maintained for a long period of time.

Further, in order to produce a silicon nitride sintered substrate having high in-plane uniformity of density and void ratio and having a large outer shape, the thickness of the boron nitride powder layer laminated together with the green sheet at the time of manufacturing the silicon nitride sintered substrate. It was found that it is important to control the carbon content at the time of sintering. Based on these examination results, the inventor of the present application has a large size, high withstand voltage and high insulation reliability, small in-plane variation thereof, and mechanical strength (bending strength and fracture toughness). I came up with an excellent silicon nitride sintered substrate and its manufacturing method. Hereinafter, an example of the silicon nitride sintered substrate and the manufacturing method thereof according to the present embodiment will be described. The present invention is not limited to the following embodiments, and various modifications or changes may be made.

[1] Silicon Nitride Sintered Substrate As shown in FIG. 1A, the silicon nitride sintered substrate 101 of the present embodiment has a main surface 101a. Here, the main surface refers to the widest surface among the surfaces constituting the silicon nitride sintered substrate 101. In the present embodiment, the surface 101b located on the opposite side of the main surface 101a also has substantially the same size as the main surface 101a. The main surface 101a has a circular shape having a diameter of at least 2 inches or more. That is, the silicon nitride sintered substrate 101 of the present embodiment has a wafer shape having a diameter of 2 inches or more. It is more preferable that the silicon nitride sintered substrate 101 has a shape having a diameter of 4 inches or more.

As shown in FIG. 1 (b), in the silicon nitride sintered substrate 101, the pre-filled portion 102 (shown by hatching) is cut off from the silicon nitride sintered body 101'obtained by sintering the green sheet by processing. It is a board after firing. The silicon nitride sintered body 101'preferably has a shape larger than a square having a side of 120 mm, and preferably has a shape larger than a rectangle having a side of 150 mm × 170 mm.

As long as the density and void ratio of the silicon nitride sintered substrate 101 satisfy the conditions described below, there is no limitation on the size of the main surface 101a. However, as the main surface 101a becomes larger, the difference in the amount of shrinkage between the edge and the center of the green sheet at the time of manufacturing the silicon nitride sintered substrate 101 becomes larger. The variation becomes large. In order to reduce the in-plane variation in pressure resistance and insulation reliability, the main surface 101a is preferably a circle having a diameter of 9.8 inches or smaller, and has a diameter of 8.7 inches or more. More preferably, it is a circle having a smaller shape.

The thickness t of the silicon nitride sintered substrate 101 is preferably 0.15 mm or more and 2.0 mm or less. If the thickness is smaller than 0.15 mm, cracks may occur in the substrate in the process of peeling each silicon nitride sintered substrate 101 from the laminated assembly after sintering at the time of manufacturing the silicon nitride sintered substrate 101. There is a high possibility that the quality of the substrate and the manufacturing yield will be reduced. Further, when the thickness is larger than 2.0 mm, the density difference between the central portion and the end portion of the silicon nitride sintered substrate 101 and the density difference in the thickness direction of the substrate become large, and as a result, the central portion and the edge of the substrate become large. The density difference from the part becomes more remarkable. The thickness t of the silicon nitride sintered substrate 101 is more preferably 0.3 mm or more and 1.0 mm or less.

In the silicon nitride sintered substrate 101, the ratio dc / de of the density dc at the center of the main surface 101a and the density de at the ends is 0.98 or more and 1.0 or less. When the density ratio dc / de is smaller than 0.98, the density variation on the main surface 101a of the silicon nitride sintered substrate 101 becomes large, which is not preferable. Specifically, when the density ratio dc / de is smaller than 0.98, the difference between the density dc in the central portion and the density de in the edge portion is 0.06 g / cm ³ or more. When the ratio dc / de is 1.0, the difference between the density dc in the central portion and the density de in the edge portion becomes zero (substantially dc / de = 1.00). The density dc in the central portion is preferably 3.120 g / cm ^{3 or more, and the density de in the end portion is preferably 3.160 g / cm 3 or} more. When the dc / de is 0.98 or more, the density difference between the central portion and the end portion of the silicon nitride sintered substrate 101 is reduced, and the density uniformity in the silicon nitride sintered substrate 101 is enhanced. Further, since the density dc in the central portion is 3.120 g / cm ³ or more and the density de in the end portion is 3.160 g / cm ³ or more, the silicon nitride sintered with high density and high density uniformity. The substrate 101 is obtained. Further, when the density dc in the central portion is 3.140 g / cm ³ or more and the density de in the end portion is 3.160 g / cm ³ or more, the density of the silicon nitride sintered substrate 101 is higher and the density is higher. The uniformity of is also high. As a result, a silicon nitride sintered substrate 101 having high insulating properties can be obtained. The density of the silicon nitride sintered substrate 101 correlates with the void ratio described below, and is further related to the insulating property of the substrate.

According to the study of the inventor of the present application, the void ratio of the silicon nitride sintered substrate 101 has a correlation with the carbon content, and the larger the residual carbon content, the larger the void ratio. The carbon content of the silicon nitride sintered substrate 101 is preferably 0.2% by mass or less in the central portion. When the carbon content exceeds 0.2% by mass, the void ratio in the central portion becomes larger than 1.80%.

In Patent Document 1, if carbon derived from an organic binder or the like remains in the green sheet during the production of a silicon nitride sintered substrate, silicon carbide is generated by sintering, so that silicon nitride is sintered. It discloses that problems such as an increase in the dielectric constant of a substrate and a decrease in insulation resistance occur. In order to solve this problem, Patent Document 1 discloses that the carbon content in the silicon nitride sintered substrate is 1% by mass or less.

As described above, according to the study of the inventor of the present application, in order to reduce the void ratio of the silicon nitride sintered substrate 101, the carbon content is preferably much smaller than this value. Further, Patent Document 1 also shows a silicon nitride sintered substrate manufactured without using an organic binder, which has a size of 35 mm × 35 mm × 1.1 mm and is a large substrate. is not.

In order to produce a silicon nitride sintered substrate having a low residual carbon content, it is conceivable to produce a green sheet without using an organic binder, but in this case, it is not possible to form a large green sheet. That is, when an organic binder is not used, it is extremely difficult to produce a large-sized silicon nitride sintered substrate in the first place due to the problem of moldability.

The void ratio of the silicon nitride sintered substrate 101 is related to the partial discharge starting voltage. When trying to increase the size of the substrate, the difference in the amount of shrinkage between the edge and the center of the green sheet becomes large, the void ratio becomes large, and the void ratio becomes uniform (specifically, the difference in the void ratio between the center and the end). ) Is low. As a result, the partial discharge voltage is lowered, so that the void ratio vc in the central portion is preferably 1.80% or less, and the void ratio ve in the end portion is preferably 1.00% or less. The void ratio vc in the central portion is more preferably 1.30% or less. When the void ratio vc in the central portion and the void ratio ve in the end portion are larger than these values, both the partial discharge start voltage, more specifically, the partial discharge start voltage and the partial discharge extinction voltage become smaller, and the silicon nitride becomes silicon nitride. The insulation reliability of the sintered substrate 101 is not sufficient. Specifically, when a predetermined high voltage is applied, the period until dielectric breakdown occurs is shortened. In order to secure higher insulation reliability, the ratio ve / vc of the void ratio vc in the central portion and the void ratio ve in the end portion is preferably 0.50 or more. In order to obtain the above-mentioned appropriate central void ratio and edge void ratio, the thickness of the boron nitride powder layer is made appropriate as described later, that is, 3 μm or more and 20 μm or less.

Here, the positions (central portion and edge portion) for measuring the above-mentioned physical properties (density and void ratio) will be described. As described above, the main surface 101a in the silicon nitride sintered substrate of the present invention is a circle having a diameter d of 2 inches or more. The diameter d is a value including a diameter d'of a portion actually used in the manufacture of a semiconductor and a portion such as a processed white. Here, a circle having a diameter d'of a portion used in the manufacture of a semiconductor is defined as a circle 110. That is, the shape of the main surface 101a corresponds to the circular 110 when there is no processed white or the like, and when there is a processed white or the like, it matches the shape obtained by adding the dimensions such as the processed white to the diameter d'of the circular 110.

In a circle 110 having a diameter d'defined in this way, as shown in FIG. 2A, a circle C0 having a diameter of (d' × 0.2) is placed in the center of the circle 110, and further ( Six circles C1 to C6 having a diameter of d'× 0.2) are arranged inscribed in the circumference at equal intervals (every 60 °) in the circumferential direction of the circle 110.

The density and void ratio of the silicon nitride sintered substrate 101 are measured by cutting out the seven circles C0 to C6 arranged as described above from the silicon nitride sintered substrate 101 by laser processing. The density and porosity of the central portion are the densities of the sections of the circle C0, and the density and the void ratio of the end portions are the smallest values measured in the sections of the circles C1 to C6. The density is measured by the Archimedes method. The void ratio is measured by microscopic observation of the sample cross section. That is, a sample of 5 mm × 5 mm was cut out from each section by laser processing, the voids of the sample were filled with resin, and then the measurement sample prepared by polishing the cross section was photographed with a 500 times optical microscope, and the obtained image was obtained. The area of the void within 300 μm × 300 μm is obtained by image analysis, and the void ratio is obtained by the formula: (void area) / (300 μm × 300 μm) × 100.

The carbon content of the silicon nitride sintered substrate 101 is a value obtained by measuring the carbon content in the portion of the circle C0 located in the center of the main surface. The carbon content is a value measured by the non-dispersive infrared absorption method. For example, it can be measured using a CS744 type carbon / sulfur analyzer manufactured by LECO.

In the present application, the density and void ratio of the central portion and the end portion of the circular silicon nitride sintered substrate 101 are, for convenience, the silicon nitride sintered body 101'before the circular silicon nitride sintered substrate 101 is cut off by processing. It can be inferred from the measured values at the center and ends of (a substrate having a shape larger than a square having a side of 120 mm) (measurement by such a method may be performed). That is, since the silicon nitride sintered body 101'has a shape larger than that of the silicon nitride sintered substrate 101, if the densities and void ratios of the central portion and the end portion satisfy the provisions of the present application, the silicon nitride sintered body 101'has a shape larger than that of the silicon nitride sintered substrate 101. A silicon nitride sintered substrate 101 having a smaller shape should also be satisfied.

The density and void ratio of the central portion and the end portion of the silicon nitride sintered body 101'are determined as follows. As shown in FIG. 2B, it is assumed that the silicon nitride sintered body 101'(one side is L1 and the other side is L2) is a quadrangle 110'excluding a portion (1 cm width) that is not used as an insulating substrate. Nine circles C11 to C13, C21 to C23, and C31 to C33 having a diameter of 3 cm are arranged in 3 rows and 3 columns in the quadrangle 110'. Here, the central circle C22 is arranged so that the center of the square, that is, the intersection of the two diagonal lines connecting the two diagonal vertices, coincides with the center of the circle C22, and the other eight circles C11. -C13, C21, C23, C31-C33 arrange circles C11, C13, C31, C33 having a diameter of 3 cm near the apex of the square 110'and in contact with two sides. Further, the circles C12, C21, C23, and C32 are arranged so as to be located in the middle of these circles and in contact with the corresponding sides.

The density and void ratio of the silicon nitride sintered body 101'are measured by cutting out nine circles C11 to C13, C21 to C23, and C31 to C33 arranged as described above from the silicon nitride sintered body 101'by laser processing. .. The density and void ratio at the center are the densities of the sections of the circle C22, and the density and the void ratio at the ends are the values measured for the sections of the circles C11 to C13, C21, C23, and C31 to C33. This is the smallest value.

Since the silicon nitride sintered substrate 101 has the above-mentioned density and void ratio, it is excellent in withstand voltage and insulation reliability, and is excellent in uniformity of density and void ratio on the main surface 101a. Partial discharge of the silicon nitride sintered substrate 101 is a precursor phenomenon of dielectric breakdown, and the higher the partial discharge voltage, the higher the withstand voltage of dielectric breakdown and the longer the period until dielectric breakdown. The silicon nitride sintered substrate 101 of the present embodiment has a partial discharge start voltage of 4 kV or more and a partial discharge extinction voltage of 4 kV or more. In particular, the density dc of the central portion of the silicon nitride sintered substrate 101 is 3.140 g / cm ³ or more, the density de of the end portion is 3.160 g / cm ³ or more, and the void ratio vc of the central portion is 1. If it is 30% or less, the partial discharge start voltage becomes 5 kV or more, and higher insulation reliability can be obtained. The partial discharge start voltage is defined by the voltage value when the discharge charge amount of 10 pC is reached when the voltage applied to the silicon nitride sintered substrate 101 is increased. Further, the partial discharge extinction voltage is defined by the voltage value when the discharge charge amount of 10 pC is reached when the voltage applied to the silicon nitride sintered substrate 101 is reduced.

The measurement can be performed using, for example, a DAC-PD-3 manufactured by Soken Electric Co., Ltd., with a step-up and step-down speed of 100 V / sec and a maximum applied voltage set to 7 kV. Other devices and other measurement conditions may be used.

The measurement system shown in FIG. 3 is used for the measurement. As shown in FIG. 3, a 240 mm × 240 mm back surface side electrode 131 is arranged in the tank 130, and the silicon nitride sintered substrate 101 to be measured is arranged on the back surface side electrode 131. A front electrode 132 having a diameter of 34 mm is arranged on the silicon nitride sintered substrate 101, and one end of the wiring 134 is connected to the back electrode 131 and the front electrode 132, respectively. The other end of the wiring 134 is connected to the measuring device. The tank 130 is filled with a fluorine-based insulating liquid 133, and measurement is performed.

The circuit board produced by using the silicon nitride sintered substrate 101 of the present embodiment has a dielectric breakdown withstand voltage of 8 kV or more and a dielectric breakdown withstand voltage of 6 or more. The dielectric breakdown withstand voltage is a value obtained by measuring the discs cut out at the positions of the central portion and the end portion on the main surface 101a of the silicon nitride sintered substrate 101 according to the above definition, and calculating the average. Specifically, as shown in FIGS. 4 (a) and 4 (b), an Ag paste having a size of 10 mm × 10 mm is applied to the front surface and the back surface of the disk 140 cut out from the silicon nitride sintered substrate 101. Then, it is baked at 500 ° C. to prepare a measurement circuit board with an electrode 141. A DC voltage is applied between the electrodes 141 of the obtained measurement circuit board, and the voltage when the measurement circuit board penetrates the insulation breakdown, that is, the front and back surfaces of the substrate is obtained as the dielectric breakdown withstand voltage.

The circuit board of this embodiment includes a silicon nitride sintered board 101, a metal circuit board (for example, a copper circuit board) provided on one surface of the silicon nitride sintered board 101, and the other of the silicon nitride sintered board 101. It is provided with a metal heat dissipation plate (for example, a copper heat dissipation plate) provided on the surface of the surface. The circuit board may further include a semiconductor element or the like provided on the upper surface of the metal circuit board. For joining the silicon nitride sintered substrate to the metal circuit board and the metal heat sink, for example, an active metal method using a brazing material or a copper direct joining method for directly joining a copper plate can be used.

The Weibull coefficient of dielectric breakdown withstand voltage is obtained by plotting the Weibull distribution with the obtained dielectric breakdown withstand voltage on the horizontal axis and the failure probability on the vertical axis. Specifically, when Ln is a natural logarithm, the insulation failure probability (probability density function) is F, and the insulation withstand voltage is V (kV), Ln (Ln (1 / (1 / ( 1-F))) is on the vertical axis and Ln (V) is on the horizontal axis, and the approximation shown by Ln (Ln (1 / (1-F))) = mLn (V) + constant from the plotted measurement points. Calculate by formula. In this case, m is the Weibull coefficient of dielectric breakdown withstand voltage.

The dielectric constant of the silicon nitride sintered substrate 101 is not particularly limited, and has a dielectric constant according to the application. For example, when used in a power module, the silicon nitride sintered substrate 101 preferably has a dielectric constant of 10 or less, and preferably has a dielectric constant of 7.9 or more and 8.1 or less, for example.

According to the silicon nitride sintered substrate of the present embodiment, in particular, the density and void ratio are controlled within the above-mentioned ranges, so that the size is large, the pressure resistance and insulation reliability, and the mechanical strength (bending strength and fracture) are controlled. It has excellent toughness) and excellent uniformity in the surface of these substrates. By having such characteristics, it is possible to obtain a large-sized silicon nitride sintered substrate having excellent characteristics for high-power applications, which has been difficult to manufacture in the past.

Further, when the silicon nitride sintered substrate of the present embodiment is used as an aggregate substrate and divided, a large number of silicon nitride sintered substrate pieces can be obtained from one large silicon nitride sintered substrate, so that the production is high. The properties can be realized, and the manufacturing cost of the silicon nitride sintered substrate piece can be reduced. Further, there is little variation in characteristics such as density, void ratio, partial discharge voltage, and mechanical strength (bending strength and fracture toughness) among a large number of silicon nitride sintered substrate pieces obtained by division. A plurality of silicon nitride sintered substrate pieces divided or cut into two or more from one silicon nitride sintered substrate of the present embodiment may have, for example, identification information attached to each silicon nitride sintered substrate piece or a substrate. It can be specified by measuring the continuity of the above-mentioned changes in physical properties, the composition, and the continuity of changes in thickness.

The silicon nitride sintered substrate of the present invention can be used as a bonding substrate. Bonding will be described by taking a manufacturing process of CSP-LED (chip size package LED) as an example. A schematic diagram of the manufacturing process of the CSP-LED is shown in FIG. (a) The LED chip is made of (b) GaN or other nitride on a single crystal substrate 201 made of sapphire (Al ₂ O ₃ ), silicon carbide (SiC), aluminum nitride (AlN), silicon (Si), or the like. A single crystal semiconductor 202 such as an object is epitaxially grown (heteroepitaxis) to form an LED chip. (c) The LED chip formed on the single crystal substrate is turned upside down, the surface where the electrode is located faces the silicon nitride sintered substrate 203, and (d) the electrodes and bumps previously provided on the silicon nitride sintered substrate 203 are attached. The gap between the silicon nitride sintered substrate 203 and the LED chip is sealed (underfilled) with a resin. Then, (e) the single crystal substrate 201 is removed by grinding, polishing or etching. (f) The LED chip on the silicon nitride sintered substrate 203 is diced to obtain (g) CSP-LED (204).

Normally, aluminum nitride substrates (AlN substrates) are often used as bonding substrates because of their reliability in insulation and high thermal conductivity. However, if the AlN substrates are thin, there is a risk of breakage during mounting, making them thinner and smaller. It is difficult to make it. Since the silicon nitride sintered substrate of the present invention is excellent in insulating property and thermal conductivity, and also excellent in mechanical strength and fracture toughness, by using it as a bonding substrate, heat dissipation is greatly improved, and miniaturization and labor saving are achieved. It becomes possible to provide a type LED.

The surface of the silicon nitride sintered substrate has a surface roughness Sa of 0.7 μm or less, preferably a surface roughness Sa of 0.3 μm or less. The surface roughness Sa is the arithmetic mean height specified by the international standard ISO 25178. When the surface roughness Sa becomes rougher than 0.7 μm, the adhesion between the silicon nitride sintered substrate and the substrate to be bonded tends to decrease. When Sa is 0.3 μm or less, it is possible to suppress the occurrence of poor bonding in a part of the plurality of LED chips arranged in the plane. The surface roughness Sa is more preferably 0.1 μm or less in order to increase the reliability of the bonding strength after bonding. Such a low surface roughness can be obtained by polishing the surface of the silicon nitride sintered substrate.

The bending strength of the silicon nitride sintered substrate is preferably 600 MPa or more, more preferably 700 MPa or more, and the fracture toughness is preferably 5.0 MPa · m ^0.5 or more, 6.4 MPa · m ^0.5 or more. Is more preferable. Since the bending strength and fracture toughness are high as described above, the possibility of cracking or cracking is reduced even when the silicon nitride sintered substrate is thinned, so that the silicon nitride sintered substrate can be thinned. .. Therefore, it is suitable as a bonding substrate.

The silicon nitride sintered substrate may be formed with via holes that penetrate the front surface and the back surface and conduct the LED chip from the back surface. By providing the via hole in this way and enabling the via connection, it is possible to energize the LED chip on the front surface side from the back surface of the silicon nitride sintered substrate through the via hole. Therefore, the wiring structure is simplified and the LED can be formed thin and compact. In addition to the LED chip, peripheral components such as a diode for preventing reverse current, a resistor, and a thermistor can be mounted on the silicon nitride sintered substrate.

When the silicon nitride sintered substrate is used as the bonding substrate, an orientation flat or a notch may be provided on the periphery in order to match the orientation of the wafer.

[2] Method for Manufacturing Silicon Nitride Sintered Substrate (A) Raw Material Powder The raw material powder for manufacturing the silicon nitride sintered substrate of the present embodiment contains silicon nitride (Si ₃ N ₄ ) as a main component and assists in sintering. Contains more agents. The specific compounding components of the raw material powder are Si _{3N 4 powder} of 80% by mass or more and 98.3% by mass or less, Mg compound powder of 0.7% by mass or more and 10% by mass or less in terms of oxide, and oxide equivalent. Contains a compound powder of at least one rare earth element of 1% by mass or more and 10% by mass or less. From the viewpoint of the density, bending strength and thermal conductivity of the silicon nitride sintered body, the pregelatinization rate of the silicon nitride powder is preferably 20% or more and 100% or less.

When the amount of Si ₃ N ₄ added is less than 80% by mass, the bending strength and thermal conductivity of the obtained silicon nitride sintered substrate are too low. On the other hand, if Si ₃ N ₄ exceeds 98.3% by mass, the sintering aid is insufficient and a dense silicon nitride sintered substrate cannot be obtained. Further, when Mg is less than 0.7% by mass in terms of oxide, the liquid phase formed at a low temperature is insufficient. On the other hand, when Mg exceeds 10% by mass in terms of oxide, the amount of volatilization of Mg increases, and pores are likely to occur in the silicon nitride sintered substrate. Further, when the rare earth element is less than 1% by mass in terms of oxide, the bond between the silicon nitride particles is weakened, and the crack easily extends the grain boundary, so that the bending strength is lowered. On the other hand, when the rare earth element exceeds 10% by mass in terms of oxide, the ratio of the grain boundary phase increases and the thermal conductivity decreases.

The Mg content (oxide equivalent) is preferably 0.7% by mass or more and 7% by mass or less, more preferably 1% by mass or more and 5% by mass or less, and most preferably 2% by mass or more and 5% by mass or less. be. The content of rare earth elements (in terms of oxides) is preferably 2% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. Therefore, the content of Si ₃ N ₄ is preferably 83% by mass or more and 97.3% by mass or less, and more preferably 90% by mass or more and 97% by mass or less. As rare earth elements, Y, La, Ce, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu and the like can be used. Among them, Y is a silicon nitride sintered substrate. It is effective and preferable for increasing the density of. Mg and rare earth elements may be in the form of oxides or compounds other than oxygen. For example, nitrides such as Mg ₃ N ₂ and YN, and silicides such as Mg ₂ Si may be used. Preferably, Mg and rare earth elements are used in the form of oxide powder, respectively. Therefore _, a preferred sintering aid is a combination of MgO powder and _Y2O3 powder.

Si powder may be used as a raw material powder for producing the silicon nitride sintered substrate of the present embodiment. In this case, a silicon nitride sintered substrate can be obtained by nitriding the Si powder before sintering the green sheet. The compounding component (first compounding component) of the raw material powder when Si powder is used as a raw material is, for example, the raw material in the ratio of Si ₃ N ₄ converted to Si in the compounding component when the above-mentioned silicon nitride powder is used. include.

Specifically, the raw material powders are Si powder of 80% by mass or more and 98.3% by mass or less in terms of Si _3N4 , Mg compound powder of 0.7% by mass or more and ₁₀ % by mass or less in terms of oxide, and oxidation. It contains compound powder of at least one rare earth element of 1% by mass or more and 10% by mass or less in terms of material.

Further, Si powder and Si _{3N 4 powder} may be used as the raw material powder for producing the silicon nitride sintered substrate. When all of the silicon nitride in the silicon nitride sintered substrate is synthesized from Si powder, there is a possibility that Si will melt due to the rapid heat generation during the nitriding of Si and the nitriding will be insufficient. On the other hand, if Si _{3N 4 powder} is mixed with the raw material powder, the melting of Si can be suppressed by lowering the calorific value and the calorific value density. In this case, the Si powder and the Si _{3N 4 powder} can be mixed at any ratio. Specifically, the raw material powders are Si powder and Si _{3N 4} powder of 80% by mass or more and 98.3% by mass or less in terms of Si _{3N 4 ,} 0.7% by mass or more and 10% by mass or less in terms of oxide. Mg compound powder and compound powder of at least one rare earth element of 1% by mass or more and 10% by mass or less in terms of oxide.

(B) Manufacturing Process A method for manufacturing a silicon nitride sintered substrate using a laminated assembly of green sheets will be described below. Since a laminated assembly is formed, green sheets are laminated, and the laminated green sheets are sintered at one time, the productivity is excellent. Here, the stacked assembly refers to a temporary laminated structure at the time of sintering, in which a plurality of green sheets are laminated so as not to be welded to each other. After sintering, it is possible to separate individual silicon nitride sintered substrates from the laminated assembly.

FIG. 6A is a flowchart showing an example of a method for manufacturing the silicon nitride sintered substrate of the present embodiment when the silicon nitride raw material powder is used as the raw material powder. Further, FIG. 6B is a flowchart showing an example of a method for manufacturing the silicon nitride sintered substrate of the present embodiment when the silicon raw material powder, or the silicon raw material powder and the silicon nitride raw material powder are used as the raw material powder. .. For the sake of simplification of the explanation, the silicon nitride raw material powder is Si _{3N 4 powder} , the silicon raw material powder is Si powder, the Mg raw material powder is MgO powder, and the rare earth element raw material powder is Y ₂ O ₃ powder. The oxidized state and the nitrided state of the raw material are not limited to these composition formulas, and other oxidized and nitrided raw materials may be used.

(1) Mixing step S1
A plasticizer (for example, a phthalic acid-based plasticizer), an organic binder (for example, polyvinyl butyral) and an organic solvent (for example, ethyl alcohol) are mixed with the raw material powder blended so as to obtain the above sintered composition, and the raw material is mixed with a ball mill or the like. Prepare a containing slurry. The solid content concentration of the slurry is preferably 30% by mass or more and 70% by mass or less. When the Si powder is nitrided as described above, the Si powder, or the Si powder and the Si _{3N 4} powder are used instead of the Si _{3N 4 powder} .

(2) Molding step S2
After defoaming and thickening the slurry, a green sheet is formed, for example, by the doctor blade method. The thickness of the green sheet is appropriately set in consideration of the thickness of the silicon nitride sintered substrate to be formed and the sintering shrinkage rate. Since the green sheet formed by the doctor blade method is usually a long strip, it is punched or cut into a predetermined shape and size. One green sheet has a shape of a square or more with a side of 150 mm or more, and has a size in consideration of the amount of shrinkage due to sintering. The shape of the green sheet is not limited to a square, but may be a circle (wafer shape).

(3) Laminating process S3
In order to efficiently manufacture the silicon nitride sintered substrate 101, it is preferable to stack a plurality of green sheets. As shown in FIG. 7, a plurality of green sheets 1 are laminated via a boron nitride powder layer 12 having a thickness of 3 μm or more and 20 μm or less to form a laminated assembly 10. The boron nitride powder layer 12 is for facilitating the separation of the silicon nitride sintered substrate after sintering, and the boron nitride powder slurry is sprayed, brushed or screen-printed on one surface of each green sheet 1, for example. It can be formed by. The boron nitride powder preferably has a purity of 95% or more and an average particle size of 1 μm or more and 20 μm or less. Here, the average particle size is the value of D50 calculated from the particle size distribution measured by the laser diffraction / scattering method.

The boron nitride powder layer 12 is not sintered in the following sintering step, and shrinkage due to sintering does not occur. Therefore, when the boron nitride powder layer 12 is thicker than 20 μm, the effect of hindering the shrinkage of the green sheet becomes large. In particular, since the shrinkage in the vicinity of the central portion of the green sheet is hindered, the density in the central portion of the obtained silicon nitride sintered substrate 101 tends to decrease and the void ratio tends to increase. On the other hand, when the thickness of the boron nitride powder layer 12 is smaller than 3 μm, the effect as a mold release agent is insufficient, and it becomes difficult to separate each silicon nitride sintered substrate from the laminated assembly after sintering. The thickness of the boron nitride powder layer 12 is more preferably 5 μm or more and 15 μm or less. The thickness of the boron nitride powder layer 12 can be adjusted, for example, by adjusting the average particle size of the boron nitride powder used and / or the viscosity of the slurry. The thickness of the boron nitride powder layer 12 is the thickness in the state where the slurry is applied.

As shown in FIG. 8, in order to suppress warpage and waviness of the obtained silicon nitride sintered substrate, a weight plate 11 is placed on the upper surface of each laminated assembly 10 and a load is applied to each green sheet 1. .. The load acting on each green sheet 1 shall be in the range of 10 to 600 Pa. When the load is less than 10 Pa, warpage is likely to occur in each sintered silicon nitride sintered substrate. On the other hand, when the load exceeds 600 Pa, each green sheet 1 is restrained by the load and smooth shrinkage at the time of sintering is hindered, so that it is difficult to obtain a dense silicon nitride sintered substrate. The load acting on each green sheet 1 is preferably 20 to 300 Pa, more preferably 20 to 200 Pa, and most preferably 30 to 150 Pa.

Assuming that the weight of the weight plate 11 is W ₁ g, the weight and area of each green sheet 1 is W ₂ g and Scm ² , and the number of green sheets 1 in the laminated assembly 10 is n, the top layer The load applied to the green sheet 1a is 98 × (W ₁ / S) Pa, and the load applied to the lowermost green sheet 1b is 98 × [W ₁ + W ₂ × (n-1)] / Spa. For example, if a boron nitride plate having a thickness of 2 mm is used as the weight plate 11 and the laminated assembly 10 is composed of 20 green sheets 1, the load applied to the lowermost green sheet 1b is applied to the uppermost green sheet 1a. It is about 3 to 4 times the applied load. Taking this point into consideration, the weight of the weight plate 11 and the number of green sheets 1 in the laminated assembly 10 are set. It is preferable that the weight W ₁ of the weight plate 11 is set so that even the lowermost green sheet 1b receives a load in the range of 10 to 600 Pa and is sintered without warping and waviness without restraining shrinkage. ..

(4) Degreasing step S4
Since the green sheet 1 contains an organic binder and a plasticizer, the laminated assembly 10 is heated to 400 to 800 ° C. and degreased before the sintering step S5. Since the green sheet 1 after degreasing is brittle, it is preferable to degreas it in the state of the laminated assembly 10.

(5) Sintering step S5
(A) Sintering container FIG. 9 shows an example of a container for simultaneously sintering a plurality of laminated assemblies 10. The container 20 includes a mounting plate assembly 30 in which mounting plates 21 accommodating each laminated assembly 10 are stacked in multiple stages, an inner container 40 accommodating the mounting plate assembly 30, and an outer container 40 accommodating the inner container 40. It consists of a container 50. The vertical frame member 22 holds the space between the mounting plates 21 adjacent to each other in the vertical direction.

By using the double-structured container 20 of the inner container 40 and the outer container 50, it is possible to suppress the decomposition of Si ₃ N ₄ and the volatilization of MgO in the green sheet 1, and the silicon nitride firing is more precise and has less warpage. A knotted substrate can be obtained. Both the inner container 40 and the outer container 50 are preferably made of boron nitride, but the outer container 50 may be made of carbon coated with p-boron nitride by CVD. In the case of the carbon outer container 50 coated with p-boron nitride, the carbon substrate having good thermal conductivity makes it easy to make the temperature distribution uniform at the time of temperature rise, and it is possible to suppress the warp and swell of the silicon nitride sintered substrate, and p. -The boron nitride coating can prevent the formation of a reducing atmosphere due to the carbon substrate. The inner container 40 is composed of a lower plate 40a, a side plate 40b and an upper plate 40c, and the outer container 50 is composed of a lower plate 50a, a side plate 50b and an upper plate 50c.

If the upper surface of the mounting plate 21 is warped or wavy, the green sheet 1b of the lowermost layer that comes into contact with the mounting plate 21 has a portion that contacts the upper surface of the mounting plate 21 and a portion that does not contact. In this case, since the non-contact portion of the green sheet 1b tends to shrink and the contact portion does not easily shrink during sintering, non-uniform shrinkage occurs in the green sheet 1b, causing warpage and waviness. Further, the warp and swell of the lowermost green sheet 1b also spread to the upper green sheet 1, and as a result, warp and swell occur in all the silicon nitride sintered substrates. Therefore, it is preferable that the upper surface of the mounting plate 21 is as flat as possible. Specifically, the warp is preferably 2.0 μm / mm or less, and the swell is preferably 2.0 μm or less. The warp and waviness of the mounting plate 21 can be measured by the same method as the warp and waviness of the silicon nitride sintered substrate.

As shown in FIG. 9, it is preferable to arrange the filling powder 24 in the inner container 40. The filling powder 24 is, for example, 0.1 to 50% by mass of magnesia (MgO) powder, 25 to 99% by mass of silicon nitride (Si _{3N 4 )} powder, and 0.1 to 70% by mass of boron nitride (boron nitride). It is a mixed powder consisting of boron) powder. The silicon nitride powder and magnesia powder in the filling powder 24 volatilize at a high temperature of 1400 ° C. or higher, and the partial pressures of Mg and Si in the sintered atmosphere are adjusted so that the silicon nitride and magnesia volatilize from the green sheet 1. Suppress. The boron nitride powder in the filling powder 24 prevents the silicon nitride powder and the magnesia powder from adhering. By using the stuffing powder 24, it is possible to obtain a silicon nitride sintered substrate that is dense and has little warpage. It is preferable to arrange the filling powder 24 on the mounting plate 21a on the uppermost stage in order to facilitate the handling of the filling powder 24 and prevent the filling powder 24 from coming into contact with the green sheet 1.

As shown in FIG. 10, the lower plate 40a of the inner container 40 is placed on the upper surface of the lower plate 50a of the outer container 50, and the mounting plate 21 is placed on the upper surface of the lower plate 40a of the inner container 40, and a plurality of the mounting plates 21 are placed on the lower plate 40a. The laminated assembly 10 and the weight plate 11 made of the green sheet 1 of the above are placed. As shown in FIG. 11, the vertical frame member 22 is installed on the outer peripheral portion of the mounting plate 21, the mounting plate 21 of the next stage is placed, and the laminated assembly 10 and the weight plate 11 are placed on the mounting plate 21. do. In this way, after the mounting plate assembly 30 on which the laminated assembly 10 and the weight plate 11 of the desired stage are placed is formed, the filling powder 24 is arranged on the upper surface of the mounting plate 21a of the uppermost stage. Next, the side plate 40b and the upper plate 40c of the inner container 40 are assembled, and further, the side plate 50b and the upper plate 50c of the outer container 50 are assembled to complete the container 20 containing the laminated assembly 10. A desired number (eg, 5) of such containers 20 are placed in the sintering furnace (not shown).

(B) Temperature profile and sintering atmosphere When using Si _{3N 4 powder} , sintering of the green sheet 1 is performed according to the temperature profile P shown in FIG. 12 (a). When Si powder or Si powder and Si _{3N 4 powder} are used, the temperature profile P'shown in FIG. 12 (b) is used. The temperature profile P is a temperature having a temperature rise region having a decarbonization region Pc for removing carbon from the green sheet 1 and a heat reduction region P ₀ , and a first temperature holding region P ₁ and a second temperature holding region P ₂ . It consists of a holding area and a cooling area. In FIG. 12A, the temperature shown on the vertical axis is the atmospheric temperature in the sintering furnace. That is, the sintering step includes a decarbonization step using the decarbonization region Pc of the temperature profile P and a sintering step using the _first temperature holding region P1. When Si powder or Si powder and Si 3N ₄ powder are used, a nitriding step ( _S5p ) is included between the decarbonization step and the sintering step. Therefore, the temperature profile P'includes a nitrided region Pn between the decarbonized region Pc and the _first temperature holding region P1.

As the ambient temperature in the sintering furnace in the sintering step, for example, the temperature measured by a radiation thermometer from the peephole provided in the sintering furnace to the target (carbon) in the furnace can be used. Specifically, in the sintering furnace, a container for sintering in which a green sheet is arranged inside, a cylindrical wall made of carbon in which the container for sintering is arranged on the inner peripheral side, and an outer circumference of the tubular wall. A target located near the side can be provided. By measuring the temperature of the target, it can be assumed that the temperature substantially corresponding to the atmospheric temperature in the furnace is measured in the temperature rising range and the temperature holding range.

(C) Decarbonized region Pc
First, the atmospheric temperature in the sintering furnace is raised from room temperature to the temperature range of the decarbonized region Pc. The heating rate is, for example, 60 ° C./hr. When the atmospheric temperature in the sintering furnace reaches a temperature of 900 ° C. or higher and 1300 ° C. or lower, the temperature is maintained within this range for 30 minutes or longer and 2 hours or shorter (holding time t _c ). The inside of the sintering furnace is preferably under reduced pressure. Specifically, the pressure is preferably 80 Pa or less. As described above, if carbon remains during sintering, voids are likely to be generated in the sintered body. Therefore, by holding the green sheet 1 under reduced pressure, carbon in the green sheet 1 is removed. This step is a degreasing step of removing carbon more completely by using a condition in which carbon is more easily volatilized than the degreasing step S4.

If the ambient temperature is lower than 900 ° C, carbon removal may not be sufficient. If the temperature is higher than 1300 ° C., the sintering aid may also be removed. It is more preferable that the atmospheric temperature in the sintering furnace is 1000 ° C. or higher and 1250 ° C. or lower.

Generally, in the manufacturing process of a silicon nitride sintered substrate, sintering is performed in a nitrogen atmosphere in order to suppress the volatilization of nitrogen. However, according to the study of the inventor of the present application, by heating the green sheet 1 in a temperature and atmosphere where nitrogen does not volatilize, carbon can be removed more completely while suppressing the volatilization of nitrogen. It was found that the formation of voids could be suppressed.

(D) Slow heat region After the heating using the decarbonized region Pc is completed, the atmospheric temperature in the sintering furnace is controlled by the temperature profile of the slow heat region P ₀ . The heat-reducing region P ₀ is a temperature region in which the sintering aid contained in the green sheet 1 reacts with the oxide layer on the surface of the silicon nitride particles to form a liquid phase. In the heat-slow region _P0 , the growth of silicon nitride particles is suppressed, and the silicon nitride particles are rearranged and densified in the liquid-phased sintering aid. As a result, a silicon nitride sintered substrate having a small pore diameter and a small porosity and a high bending strength and thermal conductivity can be obtained through the _first and _second temperature holding regions P1 and P2. The temperature T ₀ of the heat-reducing region P ₀ is set within the range of 1400 ° C. or higher and 1600 ° C. or lower, which is lower than the temperature T ₁ of the first temperature holding region P ₁ , and the heating rate in the heat-reducing region P ₀ is 300 ° C./hr or less. The heating time t ₀ is preferably 0.5 hours or more and 30 hours or less. The heating rate may include 0 ° C./hr, that is, it may be a temperature holding range in which the slow heating range P ₀ is held at a constant temperature. The heating rate in the slow heat region P0 is more preferably ₁ to 150 ° C./hr, and most preferably 1 to 100 ° C./hr. The heating time t ₀ is more preferably 1 to 25 hours, and most preferably 5 to 20 hours.

In the heat-reducing region and subsequent steps, it is preferable to fill the inside of the sintering furnace with a nitrogen atmosphere. Specifically, a mixed gas containing nitrogen or nitrogen as a main component and containing an inert gas such as argon, or a mixed gas containing about 3% or less of hydrogen in the nitrogen gas can be used. The pressure in the sintering furnace is preferably 1 atm or more and about 20 atm or less.

When Si powder or Si powder and Si _{3N 4 powder} are used, as shown in FIG. 12 (b), a nitriding region Pn is provided in the heat-reducing region P ₀ , and the nitriding step is performed to obtain the Si powder. Nitriding. For example, after the heating using the decarbonized region Pc is completed, the atmospheric temperature in the sintering furnace is raised and maintained at a temperature Tn in the temperature range of 1350 ° C. or higher and 1450 ° C. or lower. The holding time nt is preferably 3 hours or more and 15 hours or less. By creating a nitrogen atmosphere and holding the green sheet 1 at this temperature, the Si powder reacts with nitrogen, which is the atmosphere in the sintering furnace, to generate silicon nitride.

(E) After the heating using the first temperature holding region P ₀ is completed, the atmospheric temperature in the sintering furnace is controlled by the temperature profile of the first temperature holding region P ₁ . By this step, the raw material in the green sheet is sintered.

In the first temperature holding region P ₁ , the liquid phase generated in the slow heating region P ₀ causes the rearrangement of the silicon nitride particles, the phase transformation from the α-type silicon nitride crystal to the β-type silicon nitride crystal, and the phase transformation of the silicon nitride crystal. It is a temperature range that promotes grain growth and thus further densifies the sintered body. Since the phase transformation from α-type to β-type contributes to the promotion of densification of the sintered body, the raw material silicon nitride powder contains α-type, and the pregelatinization rate is 20% or more and 100% or less. It is preferable to have. Considering the size and aspect ratio (ratio of major axis to minor axis) of β-type silicon nitride particles, formation of pores due to volatilization of sintering aid, etc., the temperature T of the _first temperature holding region P1 It is preferable that ₁ is in the range of 1600 ° C. or higher and 2000 ° C. or lower, and the holding time t ₁ is about 1 to 30 hours. More preferably, the temperature T ₁ is in the range of 1800 ° C. or higher and 2000 ° C. or lower. When the temperature T ₁ of the first temperature holding region P ₁ is less than 1600 ° C., it is difficult to densify the silicon nitride sintered body. On the other hand, when the temperature T ₁ exceeds 2000 ° C., the volatilization of the sintering aid and the decomposition of silicon nitride become severe, and it becomes difficult to obtain a dense silicon nitride sintered body. The heating temperature T ₁ may change (for example, gradually increase) within the first temperature holding region P ₁ as long as it is within the temperature range of 1600 to 2000 ° C.

The temperature T ₁ of the first temperature holding region P ₁ is more preferably in the range of 1750 ° C. or higher and 1950 ° C. or lower, and most preferably in the range of 1800 ° C. or higher and 1900 ° C. or lower. Further, the temperature T ₁ of the first temperature holding region P ₁ is preferably 50 ° C. or higher higher than the upper limit of the temperature T ₀ of the heat-reducing region P ₀ , and more preferably 100 ° C. or higher and 300 ° C. or lower. The holding time t ₁ is 2 hours or more and 20 hours or less, and most preferably 3 hours or more and 10 hours or less.

(F) Second temperature holding region The second temperature holding region P ₂ after the first temperature holding region P ₁ is a temperature slightly lower than the temperature T ₁ of the first temperature holding region P ₁ for the sintered body. By holding the temperature at T ₂ , the liquid phase that has passed through the first temperature holding range P ₁ is maintained as it is or in the state of solid-liquid coexistence. The temperature T ₂ of the second temperature holding region P ₂ is preferably in the range of 1400 to 1700 ° C. and lower than the temperature T ₁ of the first temperature holding region P ₁ . Further, the holding time t ₂ of the second temperature holding region P ₂ is set to 0.5 to 10 hours. When the second temperature holding region P ₂ is provided after the first temperature holding region P ₁ , for example, the warp of the silicon nitride sintered substrate can be kept within 3.2 μm / mm.

After the heating using the first temperature holding region P ₁ is completed, the atmospheric temperature in the sintering furnace is controlled by the temperature profile of the second temperature holding region P ₂ . When the temperature T ₂ of the second temperature holding region P ₂ is less than 1400 ° C., the grain boundary phase tends to crystallize, and the bending strength of the obtained silicon nitride sintered substrate is low. On the other hand, when the temperature T ₂ exceeds 1700 ° C., the fluidity of the liquid phase is too high and the above effect cannot be obtained. The temperature T ₂ is more preferably 1500 ° C. or higher and 1650 ° C. or lower, and most preferably 1550 ° C. or higher and 1650 ° C. or lower. The holding time t ₂ of the second temperature holding region P ₂ is preferably 1 hour or more and 5 hours or less. If the holding time t ₂ of the second temperature holding region P ₂ is less than 0.5 hours, the uniformity of the grain boundary phase is insufficient. In order to suppress the volatilization of the sintering aid and prevent the mechanical properties and thermal conductivity of the silicon nitride sintered substrate from deteriorating, the holding time t ₂ of the second temperature holding region P ₂ is set to 10 hours or less. And.

By using the above-mentioned conditions, the grain boundary phase is uniformly distributed in the thickness direction of the silicon nitride sintered substrate, and segregation of Mg is suppressed. Therefore, it has high mechanical strength (bending strength and fracture toughness) and warpage is suppressed.

(G) Cooling area After the temperature control using the _second temperature holding area P2 is completed _, the atmospheric temperature in the sintering furnace is controlled by the temperature profile of the cooling area P3. The cooling region P ₃ is a temperature region in which the liquid phase maintained in the second temperature holding region P ₂ is cooled and solidified to fix the position of the obtained grain boundary phase. In order to rapidly solidify the liquid phase and maintain the uniformity of the grain boundary phase distribution _, the cooling rate of the cooling region P3 is preferably 100 ° C./hr or more, more preferably 300 ° C./hr or more, and 500 ° C./hr. Most preferred is hr or higher. Practically, the cooling rate is preferably 500 ° C./hr or more and 600 ° C./hr or less. By cooling at such a cooling rate, crystallization of the solidifying sintering aid can be suppressed and a grain boundary phase mainly composed of a glass phase can be formed, so that the bending strength of the silicon nitride sintered substrate can be increased. .. As long as the cooling rate of the cooling region P3 is maintained up to 1200 ° C. _, the cooling rate at a lower temperature is not particularly limited.

(H) Cutting the pre-filled portion By the above steps, the silicon nitride sintered body 101'is manufactured. In the laminated assembly 10, each silicon nitride sintered body 101'is separated by a boron nitride powder layer 12 by a boron nitride powder layer, so that each silicon nitride sintered body 101'is easily separated from the cooled laminated assembly 10. Can be separated into. As described with reference to FIG. 1 (b), the pre-filled portion 102 is cut off from the separated silicon nitride sintered body 101'. As a result, the silicon nitride sintered substrate 101 is obtained.

According to the method for manufacturing a silicon nitride sintered substrate of the present embodiment, the boron nitride powder layer at the time of sintering is selected by selecting the thickness of the boron nitride powder layer interposed when laminating the green sheet within an appropriate range. It is possible to suppress the restraint of the green sheet due to this, and to suppress the decrease in density and the increase in void ratio in the central portion. Further, by removing carbon under reduced pressure when the atmospheric temperature is raised during sintering, residual carbon in the green sheet can be reduced, thereby suppressing the formation of voids during sintering. be able to. Therefore, it is possible to obtain a silicon nitride sintered substrate having high in-plane uniformity of density and void ratio, excellent mechanical strength (bending strength and fracture toughness), and a large outer shape.

The present invention will be described in more detail by way of examples, but the present invention is not limited thereto. Hereinafter, the results of manufacturing silicon nitride sintered substrates under various conditions and investigating their characteristics will be described.

1. 1. Manufacture of Silicon Nitride Sintered Substrate [Reference Examples 1-28, 51, 52]
Doctor blade from a slurry (solid content concentration: 60% by mass) of MgO powder _3.0 % by mass, _Y2O3 powder 2.0% by mass _, balance Si _3N4 powder and raw material powder which is an unavoidable impurity. A green sheet 1 was formed by the method, and 20 sheets were laminated via a boron nitride powder layer to form a laminated assembly 10. As shown in Table 1, the size of the green sheet 1 was changed according to the reference example. Further, as shown in Table 1, the thickness of the boron nitride powder layer was changed according to the reference example.

The weight plate 11 was arranged on each laminated assembly 10, placed on the mounting plate 21, and installed in the container 20 (double container) shown in FIG. The load on the uppermost green sheet 1a by the weight plate 11 was 40 Pa. On the upper surface of the mounting plate 21a on the uppermost stage, a stuffing powder consisting of 15% by mass of magnesia powder, 55% by mass of silicon nitride powder, and 30% by mass of boron nitride powder was placed.

The vessel 20 was placed in a sinter and the sinter was evacuated to a pressure of 10 ^-1 Pa. As shown in Table 1, the holding temperature in the decarbonized region Pc was changed according to the reference example. The holding time ct of each reference example was set to 1 hour. After that, the atmosphere in the sintering furnace was changed to nitrogen at, for example, 7 atm, and the temperature profile in the slow heating region _P0 was heated at a heating rate of 10 ° C./hr (0.166 ° C./min) for 10 hours. Subsequently, the temperature profile of the first temperature holding region P ₁ is held at a temperature T ₁ of 1850 ° C. for 5 hours, and the temperature profile of the second temperature holding region P ₂ is held at a temperature T ₂ of 1600 ° C. It was held for 5 hours. Then, as the temperature profile of the cooling region P3 _, the atmospheric temperature was lowered at a cooling rate of 600 ° C./hr. From the obtained silicon nitride sintered substrate, the prefabricated portion was cut off to obtain a square silicon nitride sintered substrate 101 having a side length shown in Table 1. The thickness of the silicon nitride sintered substrate 101 was 0.32 mm.

[Comparative Examples 53 to 58]
As shown in Table 1, the holding temperature in the decarbonized region Pc, the atmosphere during the decarbonization step, and the thickness of the boron nitride powder layer were changed to prepare a silicon nitride sintered substrate under the same conditions as in the reference example.

2. 2. Measurement of Characteristics The composition of the silicon nitride sintered substrate of the reference example and the comparative example produced under the conditions as described in the above embodiment was confirmed. Specifically, the silicon nitride sintered substrate is subjected to microwave decomposition treatment to form a solution, and then the amount of Mg and the amount of RE are measured by ICP emission analysis, and the magnesium oxide (MgO) content and rare earth element oxide (RE) are measured. ₂ O ₃ ) Converted to content. It was confirmed that the obtained contents were substantially the same as their addition amount (blending composition) (the mass% at the first decimal point was the same).

The density, density ratio, void ratio, void ratio, carbon content, partial discharge start voltage, and partial discharge extinction voltage of the prepared silicon nitride sintered substrate were measured. In addition, the dielectric breakdown withstand voltage was measured, and the Weibull coefficient of the dielectric breakdown withstand voltage was obtained. The results are shown in Table 2-1 and Table 2-2. 13 shows a graph in which the carbon content and the void ratio (center) of the silicon nitride sintered substrates of Reference Examples 1 to 28, 51, 52 and Comparative Examples 53 to 55 are taken on the horizontal axis and the vertical axis. Further, for the silicon nitride sintered substrates of Reference Examples 1, 3, 5, 10, 12, 14, 51, 52, a graph was created in which the external dimensions of the substrate were taken on the horizontal axis and the above-mentioned measurement results were taken on the vertical axis. .. The results are shown in FIGS. 14 (a), 14 (b), 15 (a) and 15 (b).

Further, the bending strength and fracture toughness of the silicon nitride sintered substrate of the reference example were measured as follows, and the average value thereof was obtained. The results are shown in Table 3.

(3-point bending strength)
A test piece with a width of 4 mm and a length of 10 mm was cut out from a silicon nitride sintered substrate manufactured under the same conditions as the reference example, and a three-point bending cure with a support roll-to-support distance (span) of 7 mm in accordance with JIS R1601. It was set on the tool, a load was applied at a crosshead speed of 0.5 mm / min, the load at break was measured, and then the three-point bending strength of the silicon nitride sintered substrate was calculated.

(Fracture toughness)
A Vickers indenter was pushed into the surface of a silicon nitride sintered substrate manufactured under the same conditions as the reference example with a predetermined load (2 kgf), and the indentation size and the size of cracks were calculated by the IF method of JIS R 1607.

3. 3. Results and Discussion In the silicon nitride sintered substrates of Reference Examples 1 to 28, the atmosphere of the decarbonization step is vacuum (80 Pa or less), and the holding temperature is 900 ° C to 1300 ° C. As a result, it is considered that the carbon content of the silicon nitride sintered substrate is 0.20% by mass or less. Further, since the carbon content is small and the thickness of the boron nitride powder layer is in the range of 3.1 μm to 18.5 μm, the values of the density and the void ratio are small, and the uniformity on the main surface is high. It is thought that it is. Specifically, the ratio of the density of the central portion to the density of the edge portion is 0.98 or more, the void ratio of the central portion of the main surface is 1.80% or less, and the void ratio of the end portion is 1.00. % Or less. From FIG. 13, it can be seen that when the carbon content is 0.2% by mass or less, the void ratio in the central portion is 1.52% or less.

Further, since the void ratio is small, it is considered that the partial discharge start voltage and the partial discharge extinction voltage are also 4 kV or more, respectively. Further, it is considered that the dielectric breakdown withstand voltage is 8.0 V or more and the Weibull coefficient of the dielectric breakdown withstand voltage is 10.0 or more because the void ratio is small.

In particular, in the silicon nitride sintered substrates of Reference Examples 1 to 13 and 23 to 25, the holding temperature in the decarbonization step is 1000 ° C. or higher, and the coating thickness of the boron nitride powder layer is about 10 μm or less. As a result of sufficient carbon removal and shrinkage of the green sheet in the laminated assembly, the density of the silicon nitride sintered substrate is increased and the density uniformity is also increased. Specifically, in the silicon nitride sintered substrate, the density dc at the central portion is 3.140 g / cm ³ or more, and the density de at the end portion is 3.160 g / cm ³ or more. Therefore, it is considered that a partial discharge start voltage of 5 kV or more is obtained.

The silicon nitride sintered substrates of Reference Examples 1 to 28 have a square shape having a side of 120 mm (4.7 inches) or more and 220 mm (8.7 inches) or less. Therefore, it can be seen that a silicon nitride sintered substrate having a large size, high withstand voltage, excellent insulation reliability, and excellent mechanical strength (bending strength and fracture toughness) is obtained. Further, the silicon nitride sintered substrates of Reference Examples 51 and 52 have a square shape with a side of 100 mm (3.9 inches) and 110 mm (4.3 inches), and have a density, a void ratio, and a partial discharge voltage. It can be seen that the dielectric breakdown withstand voltage and the dielectric breakdown withstand voltage are about the same as those of Reference Examples 1 to 28. Therefore, from these comparisons, the silicon nitride sintered substrates of Reference Examples 1 to 28 have a large outer shape, but are comparable to small silicon nitride sintered substrates having a side of 100 mm (3.9 inches). It can be seen that the in-plane uniformity of the partial discharge voltage and the dielectric breakdown withstand voltage is high.

On the other hand, in Comparative Example 53, the atmosphere of the decarbonization step is in nitrogen. Further, in Comparative Examples 54 to 56, the atmosphere of the decarbonization step is vacuum, but the holding temperature is low. Therefore, the removal of carbon in the decarbonization step is not sufficient, and the carbon content of the obtained silicon nitride sintered substrate is high. As a result, it is considered that the density and the void ratio are large, and the Weibull coefficient of the partial discharge voltage, the dielectric breakdown withstand voltage and the dielectric breakdown withstand voltage is also small.

In Comparative Example 56, it is considered that the sintering aid has evaporated because the atmospheric temperature in the decarbonization step is too high. Therefore, it is considered that high-density sintering cannot be performed, the density and void ratio are large, and the Weibull coefficient of partial discharge voltage, dielectric breakdown withstand voltage and dielectric breakdown withstand voltage is also small.

In Comparative Examples 57 and 58, it is considered that the thickness of the boron nitride powder layer is too large, so that the shrinkage of the central portion of the silicon nitride sintered substrate is hindered. Therefore, it is considered that the void ratio in the central portion is particularly large, and the Weibull coefficient of the partial discharge voltage, the dielectric breakdown withstand voltage and the dielectric breakdown withstand voltage is also small.

From the above results, according to the silicon nitride sintered substrates of Reference Examples 1 to 28, the holding temperature and atmosphere in the decarbonization step satisfy the above-mentioned conditions, and the thickness of the boron nitride powder layer is within a predetermined range. As a result, it can be seen that a silicon nitride sintered substrate having a large size, high withstand voltage, excellent insulation reliability, and excellent mechanical strength (bending strength and breaking toughness) is obtained.

14 (a) and 14 (b) show the relationship between the length of one side of the silicon nitride sintered substrate of Reference Examples 1, 3, 5, 10, 12, 14, 51, and 52 and the density of the substrate, and one side. The relationship between the length and the void rate is shown. 14 (a) and 14 (b) also show an approximate straight line obtained from the measurement data of the density of the central portion and the density of the end portion, and the void ratio of the central portion and the void ratio of the end portion. As can be seen from these results, the silicon nitride sintered substrate of the reference example has a maximum side of 220 mm (8.7 inches), but has a square shape with a side of 250 mm (9.8 inches). Even if the knotted substrate is manufactured, the void ratio vc in the central portion is 1.80% or less, the void ratio ve in the end portion is 1.00% or less, and the density dc in the central portion is 3.120 g / cm ³ . From the above, it can be estimated that the density de of the end portion can be 3.160 g / cm ³ or more. Further, it can be seen that dc / de is 0.98 or more and ve / vc can be 0.50 or more.

15 (a) and 15 (b) show the relationship between the length of one side of the silicon nitride sintered substrate of Reference Examples 1, 3, 5, 10, 12, 14 and Reference Examples 51 and 52 and the partial discharge voltage, and The relationship between the length of one side and the Weibull coefficient of dielectric breakdown withstand voltage is shown. 15 (a) and 15 (b) also show approximate straight lines obtained from the data of the dielectric breakdown voltage, the partial discharge extinction voltage, the partial discharge start voltage, and the dielectric breakdown withstand voltage. As for these results, when a silicon nitride sintered substrate having a square shape with a side of 250 mm (9.8 inches) was produced, the dielectric breakdown voltage (dielectric breakdown withstand voltage) was 8 kV or more, and the partial discharge extinction voltage and the partial discharge. It is estimated that the starting voltage will be 4 kV or higher. Further, it is estimated that the Weibull coefficient of dielectric breakdown withstand voltage is 6 or more.

Therefore, even when a silicon nitride sintered substrate having a square shape having a side of 220 mm (8.7 inches) or more and 250 mm (9.8 inches) or less is manufactured, the withstand voltage and insulation reliability are excellent, and the surface of these substrates. It is presumed that the uniformity within the inside is excellent.

(Silicon Nitride Sintered Substrate of the Example of the Present Invention)
The silicon nitride sintered substrates of Reference Examples 1 to 28 and 52 produced were processed to obtain a silicon nitride sintered substrate having a circular shape with a diameter of 4 inches and a main surface having a surface roughness Sa of 0.7 or less. Made. Further, the silicon nitride sintered substrates of Reference Examples 5 to 28 were processed to produce silicon nitride sintered substrates having a circular shape with a diameter of 6 inches and a main surface having a surface roughness Sa of 0.7 or less. Further, the silicon nitride sintered substrates of Reference Examples 13 to 18 were processed to produce silicon nitride sintered substrates having a circular shape with a diameter of 8 inches and a main surface having a surface roughness Sa of 0.7 or less. Further, an orientation flat was formed on these circular silicon nitride sintered substrates.

The silicon nitride sintered substrate of the present invention is used as a bonding substrate, and is suitably used for an insulating substrate having a low void ratio and high uniformity.

1, 1a, 1b ... Green sheet 10 ... Laminated assembly 11 ... Plate 12 ... Borbon nitride powder layer 20 ... Container 21 ... Mounting plate 21a ... Mounting plate 22 ... Vertical frame member 24 ... Filling powder 30 ... Mounting plate assembly 40 ... Inner container 40a, 50a ... Lower plate 40b, 50b ... Side plate 40c, 50c ... Upper plate 101 ... Silicon nitride sintered substrate 101'... Silicon nitride sintered body 101a ... Main surface 102 ... Pre-filled portion 110 ... Circular 110' ... Square 130 ... Tank 131.・ ・ Back side electrode 132 ・ ・ ・ Front side electrode 133 ・ ・ ・ Insulating liquid 134 ・ ・ ・ Wiring 140 ・ ・ ・ Disc 141 ・ ・ ・ Electrode 201 ・ ・ ・ Single crystal substrate 202 ・ ・ ・ Single crystal semiconductor 203 ... Silicon nitride sintered substrate 204 ... CSP-LED

Claims (5)

It has a main surface with a shape larger than a square with a side of 120 mm.
When the ratio dc / de of the density dc of the central portion and the density de of the end portion on the main surface is 0.98 or more and 1.0 or less, and the void ratio vc of the central portion on the main surface is 1.80% or less. can be,
The void ratio ve at the end is 1.00% or less, and the ratio ve / vc between the void ratio vc at the center and the void ratio ve at the end is 0.50 or more and 1.06 or less.
It has a thickness of 0.15 mm or more and 2.0 mm or less, and has a thickness of 0.15 mm or more and 2.0 mm or less.
It has a Weibull coefficient of dielectric breakdown withstand voltage of 10.0 or more.
A sintering aid containing 0.7% by mass or more and 10% by mass or less of Mg compound in terms of oxide and at least one rare earth element compound of 1% by mass or more and 10% by mass or less in terms of oxide is used. Manufactured
Silicon nitride sintered substrate. It has a breakdown withstand voltage of 8.0 kV or higher.
The silicon nitride sintered substrate according to claim 1. In the central portion, the carbon content is 0.2% by mass or less.
The silicon nitride sintered substrate according to claim 1 or 2. The bending strength is 600 MPa or more,
Fracture toughness is 5.0 MPa · m ^0.5 or more,
The silicon nitride sintered substrate according to any one of claims 1 to 3. The density dc of the central portion is 3.120 g / cm ³ or more, and the density de of the end portion is 3.160 g / cm ³ or more.
The silicon nitride sintered substrate according to any one of claims 1 to 4.

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