JPH04285073A - Aluminum nitride-based substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a black aluminum nitride substrate having high thermal conductivity, for example, on the surface of which a metal conductor layer is deposited, and particularly relates to improvements in electrical properties such as insulation resistance and dielectric constant. .

0002

[Prior Art] Recently, as the performance and speed of information processing devices have increased, the semiconductor integrated circuits that make up the devices have also rapidly become denser and more highly integrated.As a result, the amount of heat generated by semiconductor integrated circuit elements has increased significantly. The problem is how to efficiently remove the heat generated in order to operate the semiconductor integrated circuit device normally.

[0003]Recently, in order to solve this problem, in place of the alumina substrates used up to now and beryllium oxide substrates, which have long been known as highly thermally conductive substrates,
It has high strength from room temperature to high temperature, and has high electrical insulation.
BACKGROUND ART Aluminum nitride sintered bodies are attracting attention because they have excellent properties such as high thermal conductivity and a thermal expansion coefficient closer to that of silicon single crystal than that of alumina.

However, aluminum nitride is inherently difficult to sinter, and a high-density sintered body with high thermal conductivity cannot be obtained by using aluminum nitride alone. Therefore, rare earth element oxides such as Y2 O3, etc. are used as sintering aids. Alternatively, a method has been adopted in which an alkaline earth element oxide such as CaO is added to increase the density. Among these, JP-A-61-117160 proposes that by adding rare earth element oxides and alkaline earth metal oxides at the same time, it is possible to achieve low temperature firing and high thermal conductivity. There is. Also,
Recently, it has been proposed in Japanese Patent Application Laid-Open No. 153173/1983 to add compounds of elements of groups 4a to 8 of the periodic table to aluminum nitride for the purpose of metallizing properties, light shielding properties, etc.

[0005]

[Problems to be Solved by the Invention] However, although the method disclosed in JP-A-61-117160 has excellent effects in low-temperature firing and high thermal conductivity, A detailed study of the electrical properties revealed that adding rare earth element oxides and alkaline earth element oxides at the same time may cause the sintered body to become semiconducting, resulting in poor electrical insulation and a high dielectric constant. It has been found that a problem arises in that the electrical characteristics deteriorate. Furthermore, it has been found that even in systems to which compounds of elements of Groups 4a to 8 of the periodic table are added, as disclosed in JP-A No. 62-153173, there are elements that significantly deteriorate electrical characteristics depending on the added elements. Ta.

[0006] As described above, aluminum nitride sintered bodies are used as insulators, and as substrate materials on which semiconductor elements are mounted or circuits are formed with metal conductor layers, lead wires, etc., high thermal conductivity is used. Although high insulation properties, low dielectric constant, and low dielectric loss are required as well as electrical properties, sufficient studies have not been made from the viewpoint of such electrical properties.

[0007] Therefore, an object of the present invention is to have high thermal conductivity and to be able to be fired at a temperature of 1700°C or lower,
Another object of the present invention is to provide an aluminum nitride substrate that has no problems in electrical properties such as insulation resistance, dielectric constant, and dielectric loss.

[0008]

[Means for Solving the Problems] As a result of repeated studies on the above problems, the present inventors have found that the deterioration of the electrical properties of the sintered body is caused by alkaline earth elements and rare earth elements contained as sintering aids. It is largely related to the amount ratio with the elements, and by controlling these within specific ranges and selecting specific metal elements as other metal elements and adding them in predetermined amounts, the electrical properties can be improved while maintaining low temperature firing. It was discovered that a highly reliable and excellent substrate material can be obtained without causing deterioration.

That is, the aluminum nitride substrate of the present invention contains a rare earth element and an alkaline earth element, where x is the amount of the rare earth element in terms of oxide, and y is the amount of the alkaline earth element in terms of oxide. Point A (0.1, 3.0) - B (0.1, 0.1) in Figure 1 plotting the (x, y) values at
)-C(1.0,0.1)-D(6.0,1.0)-E
The area surrounded by each point of (6.0, 3.0) or F
(7.0,0.75), G(7.0,0.10), H(
12.0, 0.10), I (12.0, 0.75), and the composition of the region surrounded by the points F-G-H-I-F, as well as Ti, V, Nb, Mo , W, Co and N
At least one element selected from i is 0 in terms of oxide
．． 01 to 5% by weight, and is characterized by having a volume resistivity of 1×10 10 Ω-cm or more at room temperature and a dielectric constant of 10 or less at 1 MHz.

The present invention will be explained in detail below. The substrate of the present invention basically consists of an aluminum nitride sintered body,
Further, the sintered body is characterized in that it contains at least an alkaline earth element and a rare earth element as a sintering aid. Although high thermal conductivity and high densification can be achieved by adding only rare earth element compounds such as rare earth element oxides as sintering aids, it is necessary to set the firing temperature to a high temperature of 1700°C or higher, so the furnace It is not practical due to restrictions such as the structure of the metallization and co-firing with metallization. Therefore, by adding an alkaline earth element compound to this, the firing temperature can be significantly lowered. Specifically, by containing an alkaline earth element in an amount of 0.1% by weight or more in terms of oxide, densification can be achieved by low-temperature firing. However, rare earth elements are 0.1
When the amount is less than % by weight, the sinterability of the system decreases, and densification by low-temperature firing cannot be achieved. On the other hand, if the amount of alkaline earth elements exceeds 3% by weight in terms of oxides, the thermal conductivity will decrease significantly, which is not desirable.

Further, according to the present invention, even if the alkaline earth and rare earth elements are within the desired range from the above-mentioned thermal conductivity and sinterability point of view, the rare earth element oxide and the alkaline earth element oxide can be mixed. It has been found that when they are added simultaneously and fired at a low temperature, there is a phenomenon in which electrical properties are significantly degraded depending on the composition ratio.

According to the present invention, based on this knowledge, when the oxide equivalent amount of the rare earth element is x and the oxide equivalent amount of the alkaline earth element is y, the diagram showing the composition ratio of x and y in FIG. In, the amount of addition is controlled so that (x, y) is an area surrounded by points A-B-C-D-E-A and an area surrounded by points F-G-H-I-F. The electrical characteristics can be improved by

The reason why the amounts of alkaline earth and rare earth elements are limited to the above regions is that in the region below the line segment CD in FIG. Electrical characteristics deteriorate in a region where the amount of rare earth elements is greater than in line segment DE and the amount of alkaline earth elements is greater than in line segment IF. This is also because the electrical characteristics deteriorate even in a region where the amount of rare earth elements is greater than the line segment HI.

[0014] Although it is not clear why the electrical properties deteriorate in areas other than the above-mentioned specific areas, for example, according to ``Research on Aluminum Nitride'' (1973), Research Report No. 4 of the Inorganic Materials Research Institute, For example, it has been described that aluminum nitride can originally have semiconducting properties, and a pale blue single crystal containing carbon or oxygen is 103
It has been shown to exhibit low resistivity values of ~105 Ω-cm. Therefore, it is considered that in composition systems outside the scope of the present invention, trace impurities are solid-dissolved in the aluminum nitride crystal due to some action of the oxides of alkaline earth and rare earth elements and become a semiconductor. In addition, samples with significant deterioration in electrical properties outside the scope of the present invention tend to have stains and color unevenness in appearance, and this phenomenon is thought to be related to the above.

The rare earth elements used in the present invention are most preferably Gd, Ho, Er, and Yb. This is because conventionally used materials such as Y tend to cause stains, color unevenness, etc. in the sintered body, and the mechanical properties and electrical properties of the substrate tend to become unstable. Further, as the alkaline earth elements, Ca, Sr, Ba, etc. are used.

[0016] Furthermore, as other additives to the aluminum nitride sintered body, compounds of elements of Groups 4a, 5a, and 6a of the periodic table are known to be useful, for example, for the purpose of blackening. According to the above, it is important to use at least one element selected from Ti, V, Nb, Mo, W, Co, and Ni in terms of the electrical properties of the substrate. Other metal elements, such as Zr and Ta, have electrical properties (electrical insulation, dielectric constant, dielectric loss) that are not suitable for the substrate, as will be clear from the examples described later. Moreover, no blackening effect is observed for Zr, Ta, Cr, and Fe. In addition, this blackening agent is used in an amount of 0.01 to 5% by weight, especially 0.05% by weight based on the total amount.
It is added in a proportion of ~3% by weight. This addition amount is 0.01
This is because if it is less than 5% by weight, the coloring properties will vary and the light shielding properties will be insufficient, and if it exceeds 5% by weight, the thermal conductivity will decrease significantly. These metal elements can exist in the sintered body in the form of simple metals, oxides, carbides, nitrides, borides, or composite oxides with the rare earth elements, but in particular , carbide, or boride.

Furthermore, from the viewpoint of thermal conductivity, it is desirable that the average crystal grain size of aluminum nitride in the sintered body is 0.8 μm or more, particularly 1.2 μm or more, and the larger the grain size, the higher the thermal conductivity. The particle size can be increased to 0.8μm
If it is smaller, the volume (area) occupied by the grain boundaries between crystal grains is large, so the grain boundaries become obstacles to phonon conduction.
Thermal conductivity decreases.

Next, a method for manufacturing an aluminum nitride substrate according to the present invention will be explained. First, the aluminum nitride raw material powder is manufactured by a known method such as a direct nitriding method or an alumina reduction method, has an impurity oxygen content of 1.5% by weight or less, a carbon content of 0.2% by weight or less, and excludes aluminum. Average particle size 2 with cationic impurity content of 0.1% by weight or less, especially Si content and Fe content of 100ppm or less
Powders with a diameter of .mu.m or less are preferably used.

As sintering aids, rare earth element compounds, especially oxide powders, and alkaline earth element compounds, especially oxides, carbonates, nitrates, etc. that can be converted into oxides by sintering are added to each of the final sintered bodies. They are weighed and mixed so that the amount of elements falls within the specific range shown in FIG. Also, Ti, V, Nb, Mo, W, C
At least one element selected from O and Ni is used as a powder such as an oxide, nitride, boride, or composite oxide with a rare earth element, and the oxide equivalent amount of the above element is 0.1 to 10.
Add and mix in a proportion of weight %.

A mixed powder obtained by adding a sintering aid component to aluminum nitride raw material powder is mixed in an organic solvent if desired. At this time, the amount of water contained in the organic solvent is set to 0.4% by weight or less. This can improve the dispersibility of the aluminum nitride powder and prevent the surface of the aluminum nitride particles from being oxidized due to reaction with moisture.

The obtained mixed powder is molded into a desired shape by a known molding method, such as press molding using a mold or hydrostatic pressure, sheet molding, extrusion molding, etc., and then fired.

By performing the firing in a non-oxidizing atmosphere containing nitrogen gas, densification progresses and the sintered body becomes black. As the firing means, normal pressure firing, hot press firing, nitrogen gas pressure firing, etc. are adopted, but according to the present invention, by setting the firing temperature at this time to 1500°C or higher, the relative density is 90% or higher. It can be densified, and the average crystal grain size of aluminum nitride increases rapidly from the primary grain size of the raw material. As the firing temperature is further increased from 1500°C, the density improves and the average crystal grain size of aluminum nitride gradually increases.
If the temperature exceeds 700° C., the structure of the furnace itself becomes large-scale because of the requirement for heat resistance as a firing furnace. Therefore, when considering mass production, it is desirable to set the firing temperature to 1700°C or lower and to perform normal pressure firing in nitrogen or a mixed atmosphere of nitrogen and hydrogen. Simultaneous firing with the metallized layer becomes possible, and it also becomes possible to use a continuous furnace or the like.

[0023] Further, as a method for depositing and forming a metal conductor layer on the above-mentioned substrate, metal powder such as W, Mo, Mn, Au, Ag, Cu, Ti, etc. is added to the substrate obtained by the above-mentioned method. The conductor layer can be formed by applying a metallizing paste by a screen printing method or the like and heat-treating it at 600 to 1700° C., or by depositing a metal thin film by means such as sputtering or vapor deposition. In addition, in the method for manufacturing the sintered body, W and M are added to the surface of the molded body.
Apply a paste containing metal powder such as 1600~
Co-firing can also be carried out in a non-oxidizing atmosphere at 1800°C. Further, metal lead wires can be bonded to a substrate using low melting point glass, and furthermore, it can be used for semiconductor element heat dissipation, electric circuit substrates, caps, fins, etc.

[0024]

[Function] Alkaline earth elements and rare earth elements are added to aluminum nitride as sintering aid components, and the amounts of alkaline earth elements and rare earth elements are limited to specific areas shown in Figure 1. Ti as a blackening agent
By selecting at least one element selected from , V, Nb, Mo, W, Co, and Ni, densification with a relative density of 95% or more can be achieved at a temperature of 1700°C or less, and a thermal conductivity of 80W. /m・k or higher, and electrical properties of 1×1010 Ω-cm at room temperature.
As described above, excellent electrical properties such as a dielectric constant of 10 or less at 1 MHz and a dielectric loss (tan δ) of 20×10 −4 or less can be obtained.

The invention will now be explained with the following examples.

[Example] Example 1 As aluminum nitride raw material powder, average particle size (BET specific surface area) 3.3 m2 /g, impurity oxygen content 1.1% by weight
, the average particle size is 0.8 μm for commercially available aluminum nitride raw material powder with a carbon content of 0.05% by weight or less and a cationic impurity content excluding aluminum of 0.1% by weight or less.
Erbium oxide powder (Er2O3) and calcium carbonate (CaCO3) powder were added and mixed in the proportions shown in Tables 1 and 2. Moreover, for this system, MoO3
0.5% by weight was added and mixed. Next, add this at room temperature to 100%
Press molding was performed at a pressure of 0 kg/cm2. This molded body was fired at the firing temperature shown in Table 1 under 1 atmosphere of nitrogen gas for 3 hours.

After firing, the relative density of each sintered body was calculated based on the Archimedes method, and the thermal conductivity was measured using the laser flash method. In addition, as electrical properties, we measured the volume resistivity at room temperature using an insulation resistance meter, and measured the dielectric constant (ε) and dielectric loss (tanδ) at room temperature and 1 MHz.
) was measured using a 1KHz/1MHz capacitance meter. Furthermore, the appearance of the sintered body was observed and evaluated. The results are shown in Tables 1 to 4. In addition, the amounts of rare earth elements (in terms of oxides) in Table 1 are plotted on the x-axis, and the amounts of alkaline earth elements (in terms of oxides) are shown on the y-axis, and are plotted in FIG.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

Example 2 In Example 1, 1% by weight of Er2O3, CaCO
3 powder was added in an amount equivalent to 0.75% by weight as CaO, and various metal oxides shown in Table 5 were added and mixed. These were molded and fired at 1650°C for 3 hours. The properties of the obtained sintered body were evaluated in the same manner as in Example 1. The results are shown in Tables 5 and 6. According to Tables 5 and 6, electrical properties deteriorated with Zr and Ta as metal elements, and sufficient blackening effect could not be obtained with Zr, Ta, Fe, and Cr.

[0032]

[Table 5]

[0033]

[Table 6]

Example 3 In Example 1, Er2O was used as the rare earth element oxide.
3 1% by weight, CaCO3 powder as CaO 0.7
An amount equivalent to 5% by weight was added, and the amount of MoO3 powder was shown in Table 7.
After molding, it was baked at 1650°C for 3 hours. The properties of the obtained sintered body were evaluated in the same manner as in Example 1, and the results are shown in Tables 7 and 8. As a result, M
When the amount of oO3 was less than 0.01% by weight, the colorability decreased, and when it exceeded 5% by weight, although there was no problem with sinterability, the electrical properties were significantly deteriorated and the thermal conductivity was also decreased.

[0035]

[Table 7]

[0036]

[Table 8]

Example 4 In Example 1, Table 4 was used instead of Er2 O3 powder.
In addition to CaCO3, BaCO3 and S are used as alkaline earth elements.
Similarly, rCO3 powder and other metal compound powders were weighed and mixed in the proportions shown in Table 4, molded in the same manner as in Example 1, and fired under the conditions shown in the table. The characteristics were measured in the same manner as in Example 1, and the results are shown in Table 9.
and shown in Table 10. According to the results in Tables 9 and 10, the respective amounts of alkaline earth elements and rare earth elements are, in particular, the alkaline earth elements are 2% by weight or less in terms of oxides, and the rare earth elements are 0.3% by weight in terms of oxides. The above value is desirable from the viewpoint of thermal conductivity.

[0038]

[Table 9]

[0039]

[Table 10]

[0040]

Effects of the Invention As detailed above, according to the present invention, aluminum nitride is the main ingredient, alkaline earth elements and rare earth elements are added in a specific range, and a specific metal compound is added to achieve low temperature firing and It is possible to obtain a sintered body having excellent electrical properties such as high insulation, low dielectric constant, and low dielectric loss while maintaining high thermal conductivity. Therefore, by using the sintered body as a substrate with a metal conductor layer deposited on its surface, it is possible to suppress delays in signal propagation speed and reduce power loss, for example, as a circuit board, and as a result, various types of semiconductors can be used. Reliability can be improved as a substrate on which elements are mounted.

[Brief explanation of the drawing]

FIG. 1: Rare earth element content (x) and alkaline earth element content (y) of the aluminum nitride substrate of Example 1 in the present invention.
FIG.

Claims (2)

[Claims] [Claim 1] Mainly made of aluminum nitride, containing rare earth elements and alkaline earth elements as sintering aids,
Point A (0.1, 3.0) in FIG. 1 where the (x, y) values are plotted, where x is the oxide equivalent amount of the rare earth element and y is the oxide equivalent amount of the alkaline earth element. −B(0.1,
0.1)-C(1.0,0.1)-D(6.0,1.0
)-E (6.0, 3.0) and at least one element selected from Ti, V, Nb, Mo, W, Co, and Ni in terms of oxide. An aluminum nitride substrate having a volume resistivity of 1×10 10 Ω-cm or more at room temperature and a dielectric constant of 10 or less at 1 MHz. [Claim 2] Mainly made of aluminum nitride, containing rare earth elements and alkaline earth elements as sintering aids,
When the oxide equivalent amount of the rare earth element is x and the oxide equivalent amount of the alkaline earth element is y, point F (7.0, 0.75) in FIG. 1 where the (x, y) values are plotted. -G(7.0
,0.10)-H(12.0-0.10)-I(12.
0.0, 0.75), and at least one element selected from Ti, V, Nb, Mo, W, Co, and Ni, in an oxide equivalent of 0.01 to 5
The volume resistivity at room temperature contained in the proportion of weight % is 1
×1010Ω-cm or more, dielectric constant at 1MHz is 1
0 or less aluminum nitride substrate.