JP2004241393A - Ceramic heater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heater capable of heating an object such as a silicon wafer to attain uniform temperature over the entire object. <P>SOLUTION: The ceramic heater has a resistive heating element formed inside or on the surface of a ceramic substrate. Variation in thermal conductivity of the ceramic substrate falls within a range of -10 to 10%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

The present invention relates to a ceramic heater (hot plate) mainly used for manufacturing and testing semiconductors.

2. Description of the Related Art In a semiconductor manufacturing / inspection apparatus including an etching apparatus and a chemical vapor deposition apparatus, a heater and a wafer prober using a metal base material such as stainless steel or an aluminum alloy have been used.

However, such a metal heater has the following problems.
First, since it is made of metal, the thickness of the heater plate must be as thick as about 15 mm. This is because, in a thin metal plate, warpage, distortion, and the like are generated due to thermal expansion caused by heating, and the silicon wafer placed on the metal plate is damaged or tilted. However, when the thickness of the heater plate is increased, there is a problem that the weight of the heater increases and the heater becomes bulky.

In addition, the heating temperature is controlled by changing the voltage or current applied to the heating element. However, because the metal plate is thick, the temperature of the heater plate can quickly follow changes in voltage and current. In addition, there was a problem that it was difficult to control the temperature.

Therefore, in Patent Document 1, a nitride ceramic or a carbide ceramic having high thermal conductivity and high strength is used as a substrate, and metal particles are fired on the surface of a plate-shaped body (ceramic substrate) made of these ceramics. There is disclosed a ceramic heater provided with a heating element formed by connection.
JP-A-11-40330

In such a ceramic heater, even when thermally expanded during heating, the ceramic substrate is unlikely to be warped or distorted, and has good temperature followability to changes in applied voltage and current amount.

However, when an object to be heated such as a silicon wafer is heated using this ceramic heater, the temperature of the heated surface tends to vary. If such a temperature variation occurs, the silicon wafer or the like may be subjected to thermal shock. There was a problem of damage.

Also, with the recent increase in the diameter of an object to be heated such as a silicon wafer, a ceramic heater having a larger diameter has been required. However, as the diameter of the ceramic heater increases, the temperature variation of the heating surface of the ceramic substrate increases. Becomes noticeable. In general, the thickness of the ceramic substrate is such that as the thickness increases, the variation in the temperature of the heating surface decreases, but conversely, as the thickness increases, the variation in the temperature of the heating surface increases. was there.

In view of the above-described problems, the present inventors have conducted intensive studies with the aim of obtaining a ceramic heater in which the variation in the temperature of the heating surface is small and the object to be heated such as a silicon wafer is not damaged by thermal shock. As a result, one of the causes of the temperature variation of the heating surface is the variation of the thermal conductivity of the ceramic substrate, and by controlling the variation of the thermal conductivity within a certain range, the heating surface is controlled at a uniform temperature. The inventors have found that the present invention can be performed, and have completed the present invention.

That is, the present invention is a ceramic heater in which the resistance heating element is formed inside or on the surface of the ceramic substrate,
A ceramic heater characterized in that the thermal conductivity of the ceramic substrate varies from -10% to 10%.

When a current is passed through the resistance heating element to generate heat, the heat propagates through the ceramic substrate and reaches the heating surface. If the thermal conductivity of the ceramic substrate is almost uniform, the amount of heat that propagates to the heating surface is almost uniform, but if the thermal conductivity of the ceramic substrate varies, the amount of heat that propagates to the heating surface is limited. It is considered that a difference occurs due to the above, and as a result, a temperature variation occurs on the heating surface.

However, in the ceramic heater of the present invention, as described above, the variation in the thermal conductivity of the ceramic substrate is adjusted within the range of -10 to 10%, so that heat is generated from the resistance heating element to the heating surface of the ceramic substrate. There is almost no difference in the amount of propagation between places, so that the temperature of the heating surface of the ceramic substrate can be made uniform and the object to be heated such as a silicon wafer can be prevented from being damaged by thermal shock. .

In the ceramic heater according to the present invention, the thickness of the ceramic substrate is preferably 20 mm or less, and the ceramic substrate is a disc, and the diameter thereof is preferably more than 190 mm.

In the ceramic heater of the present invention, when the resistance heating element is formed on the surface of the ceramic substrate, it is preferable that the side opposite to the surface on which the resistance heating element is formed be a heating surface, When the resistance heating element is formed inside the ceramic substrate, it is preferable that the resistance heating element is formed at a position of 60% or less in a thickness direction from a surface opposite to a heating surface.

According to the ceramic heater of the present invention, since the variation in the thermal conductivity of the ceramic substrate is -10 to 10%, the variation in the temperature on the heating surface of the ceramic substrate can be suppressed, and the temperature of the object to be heated can be reduced. A certain silicon wafer or the like can be heated to a uniform temperature.

The ceramic heater of the present invention is a ceramic heater in which a resistance heating element is formed inside or on a ceramic substrate,
The thermal conductivity of the ceramic substrate varies from -10% to 10%.

FIG. 1 is a bottom view schematically showing an example of the ceramic heater of the present invention, and FIG. 2 is a partially enlarged sectional view showing a part thereof.
The ceramic substrate 11 is formed in a disk shape, and the resistance heating element 12 is concentrically formed on the bottom surface 11b of the ceramic substrate 11 in order to heat the wafer heating surface 11a of the ceramic substrate 11 so that the entire temperature becomes uniform. It is formed in a pattern of a shape.

The heating elements 12 are connected so that double concentric circles close to each other form a single line, and external terminals 13 serving as input / output terminals are provided at both ends of the heating elements 12 via a metal coating layer 12a. Connected. In a portion near the center, a through hole 15 for inserting a lifter pin 16 for carrying the silicon wafer 9 or the like is formed, and a bottomed hole 14 for inserting a temperature measuring element 18 is formed. I have.

In the ceramic heater 10 shown in FIGS. 1 and 2, the resistance heating element 12 is provided at the bottom of the ceramic substrate 11, but may be provided inside the ceramic substrate 11. Hereinafter, members constituting the ceramic heater of the present invention will be described in detail.

In the ceramic heater 10 of the present invention, in order to control the temperature of the heating surface 11a of the ceramic substrate 11 to be uniform, the variation of the thermal conductivity is adjusted to be -10 to 10%.

Here, “variation in thermal conductivity” refers to the difference between the average value of thermal conductivity and the portion having the largest thermal conductivity or the portion having the smallest thermal conductivity when the thermal conductivity of the ceramic substrate varies from place to place. The difference is defined by the larger absolute value. This “variation in thermal conductivity” occurs due to the firing temperature, the thickness of the ceramic substrate, and the like when manufacturing the ceramic substrate.

The reason why the thermal conductivity of the ceramic substrate varies is not clear, but is considered as follows.
For example, when manufacturing a substrate made of aluminum nitride, a sintering aid such as yttria (Y ₂ O ₃ ) is added to enhance sinterability.
However, these sintering aids move toward grain boundaries and the surface direction of the sintered body during firing, and when there is a certain degree of vapor pressure at the firing temperature, the sintering aids that reach the surface escape. (Escape).

When the sintering temperature is sufficiently high, for example, a considerable amount of the sintering aid (yttria) escapes out of the system, and only the sintering aid that has changed to a part of the compound that is difficult to evaporate is contained in the sintered body (particles). World). Therefore, the amount of remaining yttria is relatively uniform. However, when the sintering temperature is low, the movement of the sintering aid (yttria) is suppressed, and the amount of the remaining yttria increases, so that the variation becomes relatively large. It is considered that variation occurs. Note that the sintering aid only needs to promote sintering at the time of firing, so that there is no particular problem even if the sintering aid does not remain in the fired body.

In addition, even when the ceramic substrate is thick, the yttria inside is difficult to move out of the system, so that the remaining amount increases, and accordingly the variation increases, and the variation in the thermal conductivity of the ceramic substrate increases. it is conceivable that.
Furthermore, the molding conditions of the molded body before sintering are also related, and it was also found that the uniformity of the thermal conductivity is smaller when pressed evenly by the cold isostatic pressing than when the pressing is performed in the uniaxial direction. . This is presumed to be because sintering does not proceed evenly in the uniaxial press.

In the present invention, the minimum value and the maximum value of the thermal conductivity of the ceramic substrate are adjusted so as to fall within a range of −10 to 10% with respect to an average value of these values.
Therefore, there is almost no difference in the amount of heat transmitted from the resistance heating element to the heating surface of the ceramic substrate depending on the location. As a result, the temperature of the heating surface of the ceramic substrate can be made uniform.

In order to suppress the variation in the thermal conductivity as described above, in the present invention, the sintering agent which is easily escaping escapes to the outside of the system by keeping the firing temperature high or reducing the thickness of the ceramic substrate. Thereby, a relatively uniform amount of the sintering aid remains in the sintered body, and the variation in the thermal conductivity of the ceramic substrate can be suppressed.
For example, when manufacturing a ceramic substrate using aluminum nitride as a ceramic material, the firing temperature is preferably 1800 to 2000 ° C.

Further, the thickness of the ceramic substrate is desirably 20 mm or less. This is because if the thickness of the ceramic substrate exceeds 20 mm, the thermal conductivity of the ceramic substrate varies greatly, and the temperature followability decreases. Further, the thickness is desirably 0.5 mm or more. When the thickness is smaller than 0.5 mm, the strength of the ceramic substrate itself is reduced, so that the ceramic substrate is easily broken. More preferably, it is more than 1.5 and 5 mm or less. When the thickness is more than 5 mm, heat becomes difficult to propagate, and the efficiency of heating tends to decrease. On the other hand, when the thickness is less than 1.5 mm, the heat propagating in the ceramic substrate is not sufficiently diffused, so that the temperature on the heating surface becomes lower. This is because variations may occur and the strength of the ceramic substrate may be reduced to cause breakage.

The ceramic substrate desirably has a diameter exceeding 190 mm. This is because the larger the diameter, the greater the variation in temperature on the heating surface, so it is necessary to adjust the firing temperature and thickness to suppress the variation in thermal conductivity.
Further, the ceramic substrate is desirably a disk. Usually, a circular object to be heated such as a silicon wafer is heated.

If the variation in the thermal conductivity of the ceramic substrate 11 is out of the above range, the amount of the heat released from the resistance heating element 12 that propagates to the heating surface 11a varies depending on the location. Variations occur.
The range of the variation in the thermal conductivity is desirably -5 to + 5%.

In the ceramic heater according to the present invention, an object to be heated such as a silicon wafer 9 is placed and heated while being in contact with the heating surface 11a of the ceramic substrate 11, and as shown in FIG. A lifter pin 16 is inserted into the through-hole 15, and the object to be heated such as the silicon wafer 9 is held by the lifter pin 16, so that the object to be heated is separated from the ceramic substrate 11 by a certain distance. May be heated.

Further, by moving the lifter pins 16 up and down, an object to be heated such as the silicon wafer 9 is received from the transfer device, the object to be heated is placed on the ceramic substrate 11, or the object to be heated is heated while being supported. Or you can.

Further, a concave portion, a through hole, or the like is formed in the ceramic substrate, and a pin having a spire or hemispherical tip is inserted and fixed in the concave portion or the like with the tip slightly protruding from the surface of the ceramic substrate. By supporting the object to be heated, such as, with the support pins, the object may be held at a constant distance from the ceramic substrate.

FIG. 3 is a partially enlarged cross-sectional view schematically showing the vicinity of a resistance heating element of a ceramic heater according to another embodiment of the present invention in which a resistance heating element is formed inside a ceramic substrate.

Although not shown, similarly to the ceramic heater shown in FIG. 1, the ceramic substrate 21 is formed in a disk shape, and the resistance heating element 22 is provided inside the ceramic substrate 21 as shown in FIG. It is formed in a pattern similar to the pattern, that is, a concentric pattern.

A through hole 28 is formed immediately below the end of the resistance heating element 22, and a blind hole 27 exposing the through hole 28 is formed in the bottom surface 21 b, and the external terminal 23 is inserted into the blind hole 37. And joined by brazing material 24.
Although not shown in FIG. 3, for example, a socket having a conductive wire is attached to the external terminal 23, and the conductive wire is connected to a power supply or the like.

Even in such a ceramic heater having the resistance heating element 22 formed therein, the variation in the thermal conductivity of the ceramic substrate is adjusted to be -10 to 10%, so that the heating surface of the ceramic substrate can be removed from the resistance heating element. There is no difference in the amount of heat that propagates up to the place, and the temperature of the heating surface of the ceramic substrate can be made uniform.

In the ceramic heater of the present invention, when the resistance heating element is provided on the surface of the ceramic substrate, it is preferable that the heating surface is on the opposite side of the resistance heating element formation surface. This is because the ceramic substrate plays a role of thermal diffusion, so that the temperature uniformity of the heating surface can be improved.

When the resistance heating element is formed inside the ceramic substrate, it is desirable that the resistance heating element is formed at a position of 60% or less in the thickness direction from the surface opposite to the heating surface. If it exceeds 60%, the heat is too close to the heating surface, so that the heat propagating in the ceramic substrate is not sufficiently diffused, and the temperature of the heating surface varies.

When the resistance heating element is formed inside the ceramic substrate, a plurality of resistance heating element formation layers may be provided. In this case, it is desirable that the resistance heating element is formed in some layer so as to complement each other, and that the pattern is formed in any region when viewed from above the heating surface. As such a structure, for example, there is a structure in which the staggered arrangement is provided.
Note that the resistance heating element may be provided inside the ceramic substrate, and the resistance heating element may be partially exposed.

In the ceramic heater 10 of the present invention, ceramic is used as the material of the ceramic substrate 11. This is because ceramic has a smaller coefficient of thermal expansion than metal, and is superior in mechanical strength. Therefore, even if it is thin, it does not warp or warp due to heating, and the ceramic substrate 11 can be made thin and light. Because.

Further, since the thermal conductivity of the ceramic substrate 11 is high and the ceramic substrate 11 itself is thin, the heat capacity is small. As a result, the surface temperature of the ceramic substrate 11 quickly follows the temperature change of the resistance heating element 12. That is, the surface temperature of the ceramic substrate 11 can be controlled well by changing the temperature of the resistance heating element 12 by changing the voltage and the current amount.

The ceramic is not particularly limited, and examples thereof include a nitride ceramic, a carbide ceramic, and an oxide ceramic.
Among these, when a nitride ceramic is used as the material of the ceramic substrate 11, the ceramic heater is particularly excellent in the above characteristics.

Examples of the nitride ceramic include aluminum nitride, silicon nitride, boron nitride, and titanium nitride. Examples of the carbide ceramic include silicon carbide, titanium carbide, boron carbide, and the like. Furthermore, examples of the oxide ceramic include alumina, cordierite, mullite, silica, and beryllia. These may be used alone or in combination of two or more.
Of these, aluminum nitride is most preferred. This is because the thermal conductivity is the highest at 180 W / m · K.

Further, the ceramic material may contain a sintering aid. Examples of the sintering aid include alkali metal oxides, alkaline earth metal oxides, and rare earth oxides. Among these sintering _{aids, CaO, Y 2 O 3,} Na 2 O, Li 2 O, Rb 2 O are preferred. The content of these is preferably 0.1 to 20% by weight. Further, it may contain alumina.

It is preferable that the ceramic substrate has a brightness of N4 or less as a value based on the specification of JIS Z 8721. This is because a material having such brightness is excellent in radiant heat and concealing property. Further, such a ceramic substrate can accurately measure the surface temperature by using a thermoviewer.

Here, N of lightness is 0 for ideal black lightness and 10 for ideal white lightness, and between these black lightness and white lightness, the perception of the lightness of the color is Each color is divided into 10 so as to have a uniform rate, and displayed by symbols N0 to N10.
The actual measurement is performed by comparing the color charts corresponding to N0 to N10. In this case, the first decimal place is 0 or 5.

A ceramic substrate having such characteristics can be obtained by including 100 to 5000 ppm of carbon in the ceramic substrate. There are two types of carbon, amorphous and crystalline.Amorphous carbon can suppress a decrease in volume resistivity of a ceramic substrate at a high temperature. Since the decrease in thermal conductivity at high temperatures can be suppressed, the type of carbon can be appropriately selected according to the purpose of the substrate to be manufactured.

Amorphous carbon can be obtained, for example, by calcining a hydrocarbon consisting of only C, H, and O, preferably a saccharide, in the air, and using graphite powder or the like as the crystalline carbon. be able to.
In addition, carbon can be obtained by thermally decomposing the acrylic resin in an inert atmosphere and then heating and pressurizing. By changing the acid value of the acrylic resin, it is possible to obtain carbon (crystalline). Can be adjusted.

The porosity of the ceramic substrate is preferably 0 or 5% or less. The porosity is measured by the Archimedes method.
This is because a decrease in the thermal conductivity at a high temperature and the occurrence of warpage can be suppressed.

In the present invention, a thermocouple can be embedded in a ceramic substrate as needed. This is because the temperature of the resistance heating element can be measured with a thermocouple, and the temperature can be controlled by changing the voltage and current based on the data.

The size of the joining part of the metal wires of the thermocouple is preferably equal to or larger than the diameter of each metal wire and 0.5 mm or less. With such a configuration, the heat capacity of the junction is reduced, and the temperature is accurately and quickly converted to a current value. For this reason, the temperature controllability is improved, and the temperature distribution on the heated surface of the wafer is reduced.
Examples of the thermocouple include K-type, R-type, B-type, E-type, J-type, and T-type thermocouples as described in JIS-C-1602 (1980).

It is desirable that the resistance heating element formed on the surface or inside of the ceramic substrate is divided into at least two or more circuits. This is because, by dividing the circuit, the amount of heat generated can be changed by controlling the power supplied to each circuit, and the temperature of the heating surface of the silicon wafer can be adjusted.

Examples of the pattern of the resistance heating element include concentric circles, spirals, eccentric circles, bent lines, and the like. However, since the temperature of the entire ceramic substrate can be made uniform, the concentric circles shown in FIG. Or a combination of a concentric shape and a bent shape.

When the resistance heating element is formed on the surface of the ceramic substrate, a conductor paste containing metal particles is applied to the surface of the ceramic substrate to form a conductor paste layer having a predetermined pattern, which is then baked, and then baked on the surface of the ceramic substrate. A method of sintering metal particles is preferred. The sintering of the metal is sufficient if the metal particles and the metal particles and the ceramic are fused.

When the resistance heating element is formed on the surface of the ceramic substrate, the thickness of the resistance heating element is preferably 1 to 30 μm, more preferably 1 to 10 μm. When a resistance heating element is formed inside a ceramic substrate, the thickness thereof is preferably 1 to 50 μm.

When the resistance heating element is formed on the surface of the ceramic substrate, the width of the resistance heating element is preferably 0.1 to 20 mm, more preferably 0.1 to 5 mm. When the resistance heating element is formed inside the ceramic substrate, the width of the resistance heating element is preferably 5 to 20 μm.

Although the resistance value of the resistance heating element can be varied depending on its width and thickness, the above range is most practical. The resistance value increases as the resistance value decreases and the resistance value decreases. When the resistance heating element is formed inside the ceramic substrate, both the thickness and the width are larger, but when the resistance heating element is provided inside, the distance between the heating surface and the resistance heating element becomes shorter, and the heating surface Since the temperature uniformity decreases, it is necessary to increase the width of the resistance heating element itself, and there is no need to consider the adhesion with nitride ceramics, etc. Since a high melting point metal such as molybdenum or a carbide such as tungsten or molybdenum can be used, and the resistance value can be increased, the thickness itself may be increased for the purpose of preventing disconnection or the like. Therefore, it is desirable that the resistance heating element has the above-described thickness and width.

The resistance heating element may have a rectangular or elliptical cross section, but is preferably flat. This is because the flat surface is more likely to dissipate heat toward the heating surface, so that the temperature distribution on the heating surface is less likely.
The aspect ratio of the cross section (the width of the resistance heating element / the thickness of the resistance heating element) is desirably 10 to 5000.
By adjusting to this range, the resistance value of the resistance heating element can be increased, and the uniformity of the temperature of the heating surface can be ensured.

When the thickness of the resistance heating element is constant, if the aspect ratio is smaller than the above range, the amount of heat propagation in the direction of the heating surface of the ceramic substrate is reduced, and the heat distribution approximate to the pattern of the resistance heating element is reduced. Conversely, if the aspect ratio is too large, the temperature immediately above the center of the resistance heating element becomes high, and eventually, a heat distribution similar to the pattern of the resistance heating element is generated on the heating surface. Therefore, in consideration of the temperature distribution, the aspect ratio of the cross section is preferably 10 to 5000.

When the resistance heating element is formed on the surface of the ceramic substrate, the aspect ratio is preferably 10 to 200. When the resistance heating element 12 is formed inside the ceramic substrate, the aspect ratio is preferably 200 to 5000.
When the resistance heating element is formed inside the ceramic substrate, the aspect ratio becomes larger, but this is because if the resistance heating element is provided inside, the distance between the heating surface and the resistance heating element becomes shorter, This is because it is necessary to make the resistance heating element itself flat because the temperature uniformity of the resistance heating element decreases.

The conductive paste is not particularly limited, but preferably contains not only metal particles or conductive ceramic for ensuring conductivity, but also a resin, a solvent, a thickener, and the like.

As the metal particles, for example, noble metals (gold, silver, platinum, palladium), lead, tungsten, molybdenum, nickel and the like are preferable. These may be used alone or in combination of two or more. This is because these metals are relatively hard to oxidize and have a resistance value sufficient to generate heat.
Examples of the conductive ceramic include carbides of tungsten and molybdenum. These may be used alone or in combination of two or more.

The metal particles or the conductive ceramic particles preferably have a particle size of 0.1 to 100 μm. If it is too fine, less than 0.1 μm, it is liable to be oxidized, while if it exceeds 100 μm, sintering becomes difficult and the resistance value becomes large.

The shape of the metal particles may be spherical or scaly. When these metal particles are used, they may be a mixture of the above-mentioned spherical material and the above-mentioned scaly material.
When the metal particles are scaly, or a mixture of spherical and scaly, the metal oxide between the metal particles is easily retained, and the adhesion between the resistance heating element and the nitride ceramic or the like is improved. And the resistance value can be increased, which is advantageous.

Examples of the resin used for the conductor paste include an epoxy resin and a phenol resin. Examples of the solvent include isopropyl alcohol. Examples of the thickener include cellulose and the like.

It is preferable that the conductor paste is obtained by adding a metal oxide to metal particles and sintering the resistance heating element, the metal particles, and the metal oxide. By sintering the metal oxide together with the metal particles in this manner, the ceramic particles, such as a nitride ceramic, and the metal particles can be more closely adhered.

It is not clear why mixing metal oxides improves the adhesion with nitride ceramics, but the surface of metal particles and surfaces of nitride ceramics are slightly oxidized to form oxide films. It is considered that the oxide films are sintered and integrated via the metal oxide, and the metal particles and the nitride ceramics are brought into close contact with each other. When the ceramic constituting the ceramic substrate is an oxide ceramic, the surface is naturally made of an oxide, so that a conductor layer having excellent adhesion is formed.

As the metal oxide, for example, at least one selected from the group consisting of lead oxide, zinc oxide, silica, boron oxide (B ₂ O ₃ ), alumina, yttria, and titania is preferable.

This is because these oxides can improve the adhesion between the metal particles and the nitride ceramic without increasing the resistance value of the resistance heating element 12.

The ratio of the lead oxide, zinc oxide, silica, boron oxide (B ₂ O ₃ ), alumina, yttria, and titania is such that when the total amount of the metal oxide is 100 parts by weight, the lead oxide is 1 to 10 by weight. , Silica is 1 to 30, boron oxide is 5 to 50, zinc oxide is 20 to 70, alumina is 1 to 10, yttria is 1 to 50, titania is 1 to 50, and the total exceeds 100 parts by weight. It is desirable that it be adjusted within a range that does not exist.
By adjusting the amount of these oxides in these ranges, the adhesion to nitride ceramics and the like can be particularly improved.

The amount of the metal oxide added to the metal particles is preferably 0.1% by weight or more and less than 10% by weight. The area resistivity when the resistance heating element 12 is formed using the conductor paste having such a configuration is preferably 1 to 45 mΩ / □.

If the area resistivity exceeds 45 mΩ / □, the amount of heat generated becomes too large with respect to the applied voltage, and it is difficult to control the amount of heat generated in the ceramic substrate 11 having the resistance heating element 12 provided on the surface of the ceramic substrate. It is. If the addition amount of the metal oxide is 10% by weight or more, the sheet resistivity exceeds 50 mΩ / □, the calorific value becomes too large, the temperature control becomes difficult, and the uniformity of the temperature distribution decreases. .

When the resistance heating element is formed on the surface of the ceramic substrate, it is desirable that a metal coating layer be formed on the surface of the resistance heating element. This is to prevent the internal metal sintered body from being oxidized to change the resistance value. The thickness of the metal coating layer to be formed is preferably from 0.1 to 10 μm.

The metal used for forming the metal coating layer is not particularly limited as long as it is a non-oxidizing metal, but specific examples include gold, silver, palladium, platinum, and nickel. These may be used alone or in combination of two or more. Of these, nickel is preferred.

The resistance heating element requires a terminal for connection to a power supply, and this terminal is attached to the resistance heating element via solder. Nickel prevents thermal diffusion of the solder. Examples of the connection terminal include those made of Kovar.

When the resistance heating element is formed inside the ceramic substrate, the surface is not oxidized, and thus no coating is required. When the resistance heating element is formed inside the ceramic substrate, a part of the resistance heating element may be exposed on the surface, and a through hole for connecting the resistance heating element is provided in the terminal portion. The terminals may be connected and fixed.

When the external terminal 13 is connected, an alloy such as silver-lead, lead-tin, and bismuth-tin can be used as the solder. Note that the thickness of the solder layer is preferably 0.1 to 50 μm. This is because the range is sufficient to secure connection by soldering.

Next, a method for manufacturing the ceramic heater of the present invention will be described.
First, a method of manufacturing a ceramic heater in which a resistance heating element is formed on the bottom surface of a ceramic substrate 11 (see FIGS. 1 and 2) will be described with reference to FIGS.

(1) Step of preparing ceramic substrate A slurry obtained by mixing a sintering aid such as yttria (Y ₂ O ₃ ), a compound containing Na and Ca, a binder, or the like with ceramic powder such as aluminum nitride or the like as necessary. After preparing the slurry, the slurry is formed into granules by a method such as spray drying, and the granules are put into a mold or the like and pressed to be formed into a plate shape or the like to produce a formed body (green). Furthermore, by compressing this compact with a cold isostatic press (CIP), sintering proceeds evenly at the time of sintering, thereby reducing the variation in thermal conductivity due to the difference in sintering density. Can be. The pressure at the time of CIP is preferably 0.5 to ⁵ t / cm ² . The thickness of the molded body is adjusted so that the thickness of the fired ceramic substrate is 0.5 to 20 mm.

Next, if necessary, a portion to be a through hole 15 for inserting a lifter pin 16 for carrying a heated object such as a silicon wafer 9 or a temperature measuring element such as a thermocouple is embedded in the molded body. A portion to be the bottomed hole 14 is formed.

Next, this molded body is heated, fired and sintered to produce a ceramic plate. Thereafter, the ceramic substrate 11 is manufactured by processing into a predetermined shape (see FIG. 4A), but may be a shape that can be used as it is after firing. Further, for example, by performing heating and baking while applying pressure from above and below, it becomes possible to manufacture the ceramic substrate 11 without pores. Heating and sintering may be performed at a sintering temperature or higher. For example, in the case of a nitride ceramic, the temperature is preferably 1800 to 2500 ° C., and the pressure is preferably 10 to 20 MPa.

Usually, after firing, a through hole 15 and a bottomed hole 14 for inserting a temperature measuring element are provided. The through holes 15 and the like can be formed by performing blasting such as sand blasting using SiC particles or the like after surface polishing.

(2) Step of Printing Conductor Paste on Ceramic Substrate The conductor paste is generally a high-viscosity fluid composed of metal particles, a resin, and a solvent. This conductor paste is printed on a portion where the resistance heating element is to be provided by screen printing or the like to form a conductor paste layer. Since the resistance heating element needs to have a uniform temperature over the entire ceramic substrate, it is desirable to print it in a concentric pattern as shown in FIG.
The conductor paste layer is desirably formed so that the cross section of the resistance heating element 12 after firing has a rectangular and flat shape.

(3) Firing of the conductive paste The conductive paste layer printed on the bottom surface of the ceramic substrate 11 is heated and fired to remove the resin and the solvent, and sinter the metal particles. 12 (see FIG. 4B). The temperature of the heating and firing is preferably from 500 to 1000C.
If the above-described metal oxide is added to the conductor paste, the metal particles, the ceramic substrate and the metal oxide are sintered and integrated, so that the adhesion between the resistance heating element and the ceramic substrate is improved.

(4) Formation of Metal Coating Layer It is desirable to provide a metal coating layer 12a on the surface of the resistance heating element 12, as shown in FIG. The metal coating layer 12a can be formed by electrolytic plating, electroless plating, sputtering, or the like. However, considering mass productivity, electroless plating is optimal. FIG. 4 does not show the metal coating layer 12a.

(5) Attachment of terminals and the like A terminal (external terminal 13) for connection to a power supply is attached to the end of the pattern of the resistance heating element 12 via solder (see FIG. 4C). Further, a thermocouple is inserted into the bottomed hole 14 and sealed with a heat-resistant resin such as polyimide or the like, and the production of the ceramic heater is completed.

Next, a method for manufacturing a ceramic heater (see FIG. 3) in which the resistance heating element 12 is formed inside the ceramic substrate 11 will be described with reference to FIGS.
(1) Manufacturing Step of Ceramic Substrate First, a ceramic powder such as a nitride ceramic is mixed with a binder, a solvent and the like to prepare a paste, and a green sheet is manufactured using the paste.

As the above-mentioned ceramic powder, for example, aluminum nitride or the like can be used. If necessary, a sintering aid such as yttria, a compound containing Na or Ca, or the like may be added.
The binder is preferably at least one selected from an acrylic binder, ethyl cellulose, butyl cellosolve, and polyvinylal.

Further, as the solvent, at least one selected from α-terpineol and glycol is desirable.
A paste obtained by mixing these is formed into a sheet by a doctor blade method to produce a green sheet 50.
The thickness of the green sheet 50 is preferably 0.1 to 5 mm.

Next, in the obtained green sheet 50, if necessary, a portion serving as a through hole 25 for inserting a lifter pin for transporting an object to be heated such as a silicon wafer, and a temperature measuring element such as a thermocouple are embedded. , A portion serving as a through hole 28 for connecting the resistance heating element to an external terminal pin, and the like. The above processing may be performed after forming a green sheet laminate described later.

(2) Step of Printing Conductive Paste on Green Sheet On the green sheet 50, a conductive paste containing a metal paste or a conductive ceramic for forming a resistance heating element is printed to form a conductive paste layer 220, which is then penetrated. The conductive paste filling layer 280 for the through hole 28 is formed in the hole.
These conductive pastes contain metal particles or conductive ceramic particles.

The average particle diameter of the tungsten particles or molybdenum particles is preferably 0.1 to 5 μm. If the average particle diameter is less than 0.1 μm or exceeds 5 μm, it is difficult to print the conductive paste.
As such a conductive paste, for example, 85 to 87 parts by weight of metal particles or conductive ceramic particles; 1.5 to 10 parts by weight of at least one kind of binder selected from acrylic, ethyl cellulose, butyl cellosolve, and polyvinylal; A composition (paste) in which 1.5 to 10 parts by weight of at least one solvent selected from terpineol and glycol is mixed.

(3) Green Sheet Laminating Step The green sheet 50 on which the conductor paste is not printed is laminated on and under the green sheet 50 on which the conductor paste is printed (see FIG. 5A).
At this time, the green sheets 50 on which the conductive paste is printed are stacked so that they are positioned at 60% or less of the thickness of the stacked green sheets.
The thickness of the green sheet laminate is adjusted so that the thickness of the fired ceramic substrate is in the range of 0.5 to 20 mm. Specifically, the number of stacked green sheets on the upper side is preferably 20 to 50, and the number of stacked green sheets on the lower side is preferably 5 to 20.
Further, after the laminate is calcined at 300 to 1000 ° C. and then compressed by a cold isostatic press (CIP), variation in thermal conductivity due to a difference in sintering density can be reduced. .
The pressure at the time of CIP is preferably 0.5 to ⁵ t / cm ² .

(4) Step of firing green sheet laminate The green sheet laminate is heated and pressed to sinter the ceramic powder in the green sheet and the metal in the internal conductor paste (see FIG. 5B).
For example, in a nitride ceramic, the heating temperature is preferably 1800 to 2000 ° C., and the pressure is preferably 10 to 20 MPa. Heating is performed in an inert gas atmosphere. As the inert gas, for example, argon, nitrogen, or the like can be used.
Usually, after firing, a bottomed hole for inserting a temperature measuring element, a through hole 25 for inserting a lifter pin, and a blind hole 27 exposing a through hole 28 are formed. The through-hole 25 and the bottomed hole can be formed by performing blasting of sand blast or the like after surface polishing.

(5) To connect with the resistance heating element 22 inside the attachment of the terminals and the like, solder paste is applied to the exposed portions of the through holes 28, and then the external terminals 23 are inserted into the blind holes 27 and heated and reflowed. Thus, the external terminal 13 is connected. The temperature at the time of heating is preferably 200 to 500 ° C.
Further, a thermocouple or the like as a temperature measuring element is inserted into the bottomed hole and sealed with a heat-resistant resin such as polyimide or the like, and the production of the ceramic heater is completed.

In the ceramic heater of the present invention, an electrostatic electrode can be provided to be used as an electrostatic chuck, and a chaptop conductor layer can be provided on the surface, and a guard electrode or a ground electrode can be provided inside to serve as a wafer prober. Can be used.

Hereinafter, the present invention will be described in more detail.
(Example 1) Manufacture of a ceramic heater having a resistance heating element outside (see FIG. 4)
(1) A composition comprising 100 parts by weight of aluminum nitride powder (average particle size: 1.1 μm), 4 parts by weight of yttria (average particle size: 0.4 μm), 12 parts by weight of acrylic binder and alcohol is spray-dried, A granular powder was produced.

(2) Next, this granular powder was put into a mold and molded into a flat plate to obtain a molded product (green). Further, using a cold isostatic press (CIP) manufactured by Kobe Steel, compression was performed at a pressure of 3 t / cm ² , and then the surface was polished.

(3) The formed product after the processing was hot-pressed at 1800 ° C. and a pressure of 20 MPa to obtain an aluminum nitride plate having a thickness of approximately 20 mm.
Next, a disk having a diameter of 210 mm was cut out from the plate to obtain a ceramic plate (ceramic substrate 11). Drilling is performed on this molded body, and a portion serving as a through hole 15 for inserting a lifter pin 16 of a silicon wafer and a portion serving as a bottomed hole 14 for embedding a thermocouple (diameter: 1.1 mm, depth: 2 mm) Was formed (FIG. 4A).

(4) Conductive paste was printed on the plate obtained in (3) by screen printing. The printing pattern was a concentric pattern as shown in FIG.
As the conductor paste, Solvest PS603D manufactured by Tokuri Chemical Laboratory, which is used for forming through holes in a printed wiring board, was used.
This conductor paste is a silver-lead paste, and based on 100 parts by weight of silver, lead oxide (5% by weight), zinc oxide (55% by weight), silica (10% by weight), and boron oxide (25% by weight). And 7.5 parts by weight of a metal oxide composed of alumina (5% by weight). The silver particles had a mean particle size of 4.5 μm and were scaly.

(5) Next, the ceramic substrate 11 on which the conductor paste was printed was heated and fired at 780 ° C. to sinter silver and lead in the conductor paste and baked on the ceramic substrate 11 to form the resistance heating element 12 ( FIG. 4 (b)). The silver-lead resistance heating element had a thickness of 5 μm, a width of 2.4 mm, and a sheet resistivity of 7.7 Ω / □.

(6) An electroless nickel plating bath composed of an aqueous solution having a concentration of 80 g / l of nickel sulfate, 24 g / l of sodium hypophosphite, 12 g / l of sodium acetate, 8 g / l of boric acid, and 6 g / l of ammonium chloride as described in (6) above. Was immersed to deposit a 1 μm-thick metal coating layer (nickel layer) 12 a on the surface of the silver-lead resistance heating element 12.

(7) An Ag-Sn solder paste (manufactured by Tanaka Kikinzoku Co., Ltd.) was printed by screen printing on the portion where the external terminal 13 for securing the connection to the power supply was to be attached, to form a solder layer.
Next, an external terminal 13 made of Kovar was placed on the solder layer, and heated and reflowed at 700 ° C. to attach the external terminal 13 to the surface of the resistance heating element 12 (FIG. 4C).

(8) A thermocouple for temperature control was sealed with polyimide to obtain a ceramic heater 10.

(Example 2)
A ceramic heater was manufactured in the same manner as in Example 1, except that the thickness of the formed body was adjusted so that the thickness of the fired ceramic substrate became 10 mm.

(Example 3) Manufacture of a ceramic heater having a resistance heating element inside (see FIG. 5)
(1) 100 parts by weight of aluminum nitride powder (average particle size: 1.1 μm, manufactured by Tokuyama Corporation), 4 parts by weight of yttria (average particle size: 0.4 μm), 11.5 parts by weight of acrylic binder, 0.5 part by weight of dispersant And a paste obtained by mixing 53 parts by weight of alcohol composed of 1-butanol and ethanol with a paste was molded by a doctor blade method to obtain a green sheet having a thickness of 0.47 mm.

(2) Next, after drying the green sheet at 80 ° C. for 5 hours, a portion serving as a through hole for connecting to a terminal pin having a diameter of 1.8 mm, 3.0 mm, or 5.0 mm was provided by punching.

(3) 100 parts by weight of tungsten carbide particles having an average particle diameter of 1 μm, 3.0 parts by weight of an acrylic binder, 3.5 parts by weight of an α-terpineol solvent, and 0.3 parts by weight of a dispersant are mixed to form a conductive paste A. Prepared.

A conductive paste B was prepared by mixing 100 parts by weight of tungsten particles having an average particle diameter of 3 μm, 1.9 parts by weight of an acrylic binder, 3.7 parts by weight of an α-terpineol solvent, and 0.2 parts by weight of a dispersant.
The conductor paste A was printed on a green sheet by screen printing to form a conductor paste layer. The printing pattern was a concentric pattern as shown in FIG. In addition, the conductive paste B was filled in through holes for through holes for connecting terminal pins.

On the green sheet after the above treatment, 37 green sheets on which the tungsten paste was not printed were further laminated on the upper side (heating surface) and 13 on the lower side at 130 ° C. under a pressure of 8 MPa (80 kgf / cm ² ).

(4) Next, the obtained laminate was degreased in nitrogen gas at 600 ° C. for 5 hours, and further compressed at a pressure of 3 t / cm ² using a cold isostatic press (CIP) manufactured by Kobe Steel. Then, hot pressing was performed at 1850 ° C. and a pressure of 15 MPa (150 kgf / cm ² ) for 3 hours to obtain an aluminum nitride plate having a thickness of about 5 mm. This was cut into a 215 mm disk to obtain a ceramic substrate having a 6 μm thick and 10 mm wide conductor layer inside.
Thereafter, a through hole 25 through which the lifter pin is inserted and a bottomed hole (diameter: 1.2 mm, depth: 2.0 mm) were provided by drilling.

(5) Next, a part of the through hole for the through hole is cut out to form a recess, and a gold solder made of Ni-Au is used in the recess, and heated and reflowed at 700 ° C. to connect a Kovar terminal pin. Was. In addition, a plurality of thermocouples for temperature control were embedded in the bottomed holes, and the manufacture of a ceramic heater having a resistance heating element as a conductor layer therein was completed.

Comparative Example 1 A ceramic heater having a resistance heating element on the surface was manufactured at a firing temperature of 1750 ° C., and the thickness of the formed body was adjusted so that the thickness of the ceramic substrate after firing was 25 mm. In the same manner as in Example 1, a ceramic heater was manufactured.

Evaluation method Variations in the thermal conductivity of the ceramic substrate of the ceramic heaters obtained in Examples 1 to 3 and Comparative Example 1, variations in the temperature of the heating surface, and withstand voltage were measured by the following methods. The results are shown in Table 1 below.

(1) Measurement of variation in thermal conductivity a. Equipment used Rigaku laser flash method thermal constant measurement device LF / TCF-FA8510B
b. Test conditions Temperature: normal temperature atmosphere: vacuum c. Measurement method: Twenty samples were cut out evenly from each ceramic substrate, the thermal conductivity of each sample was measured, and the average, maximum and minimum values of the thermal conductivity of each ceramic substrate were calculated from these values.
The temperature detection in the specific heat measurement was performed by a thermocouple (platinel) bonded to the back surface of the sample with a silver paste.
The room temperature specific heat measurement was further performed with a light receiving plate (glassy carbon) adhered to the upper surface of the sample via silicon grease, and the specific heat (Cp) of the sample was determined by the following calculation formula (1).

In the above formula (1), ΔO is the input energy, ΔT is the saturation value of the temperature rise of the sample, and Cp _{G. C} is the specific heat of glassy carbon, WG _{. C} is the weight of glassy carbon, Cp _{S.P. G} is the specific heat of silicon grease, WS _{. G} is the weight of the silicon grease, and W is the weight of the sample.

(2) Measurement of Temperature Variation on Heating Surface After the temperature of the ceramic substrate was raised to 400 ° C., the maximum and minimum temperatures of the heating surface were measured using a thermoviewer (IR-16-0012-0012 manufactured by Nippon Datum). The difference was measured.

(3) Measurement of Withstand Voltage A sample having a thickness of 1 mm was cut out from the obtained ceramic substrate, electrodes were attached to both sides thereof, a voltage was applied until dielectric breakdown, and the value was measured.

In the ceramic substrates of the ceramic heaters obtained in Examples 1 to 3, the variation in the thermal conductivity is −1 to + 8%, and the difference between the maximum temperature and the minimum temperature of the heating surface is as small as 8 ° C. As a result, the silicon wafer placed or separated thereon and supported thereon could be heated substantially uniformly, and its withstand voltage was sufficiently large at 15 kv / mm.
On the other hand, in the ceramic substrate of the ceramic heater obtained in Comparative Example 1, the variation in the thermal conductivity was as large as + 12%, and the difference between the maximum temperature and the minimum temperature of the heating surface was as large as 15 ° C. As a result, the silicon wafer placed on or separated from the silicon wafer cannot be heated uniformly, and the silicon wafer is damaged by thermal shock. The withstand voltage was as small as 5 kv / mm.

It is a top view which shows an example of the ceramic heater of this invention typically. It is an expanded sectional view of the ceramic heater shown in FIG. It is a top view which shows typically another example of the ceramic heater of this invention. (A)-(c) is sectional drawing which shows typically a part of manufacturing process of the ceramic heater shown in FIG. (A)-(d) is sectional drawing which shows typically a part of manufacturing process of the ceramic heater shown in FIG.

Explanation of reference numerals

Reference Signs List 9 silicon wafer 10 ceramic heater 11 ceramic substrate 11a heating surface 11b, 21b bottom surface 12, 22 resistance heating element 13, 23 external terminal 14 bottomed hole 15, 25 through hole 16 lifter pin 24 brazing material 27 bag hole 28 through hole

Claims (5)

A ceramic heater in which a resistance heating element is formed inside or on a surface of a ceramic substrate,
A ceramic heater, wherein the thermal conductivity of the ceramic substrate varies from -10% to 10%. The ceramic heater according to claim 1, wherein the thickness of the ceramic substrate is 20 mm or less. The ceramic heater according to claim 1, wherein the ceramic substrate is a disk, and has a diameter exceeding 190 mm. The resistance heating element is formed on a surface of a ceramic substrate,
The ceramic heater according to claim 1, wherein a side opposite to a side on which the resistance heating element is formed is a heating side. The resistance heating element is formed inside a ceramic substrate,
The ceramic heater according to any one of claims 1 to 3, wherein the resistance heating element is formed at a position 60% or less in a thickness direction from a surface opposite to a heating surface.

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