JP2004273460A - Ceramic heater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heater capable of uniformly heating an object to be heated, such as a silicon wafer. <P>SOLUTION: The ceramic heater has a heating body formed inside or on the surface of a ceramic plate. A not-through hole is provided from the opposite side of a heating surface that heats an object to be heated toward the heating surface. The bottom of the not-through hole is formed closer to the heating surface than the heating body, and the not-through hole is provided with a temperature measuring element. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

The present invention relates to a ceramic heater mainly used in the semiconductor industry for drying, sputtering and the like, and more particularly to a ceramic heater which is easy to control temperature and has excellent temperature uniformity on a heating surface.

Semiconductor products are manufactured through a process of forming a photosensitive resin on a silicon wafer as an etching resist and etching the silicon wafer.
This photosensitive resin is liquid and is applied to the silicon wafer surface using a spin coater or the like, but it must be dried after application, and the applied silicon wafer must be placed on a heater and heated. become.

Conventionally, as a metal heater used for such an application, a heater in which a heating element is arranged on the back surface of an aluminum plate has been adopted.
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, warping or distortion occurs 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, 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.
In view of this, as disclosed in Patent Document 1, for example, a technique has been proposed in which a nitride ceramic having a heating element formed thereon is used, and the temperature is controlled while measuring the temperature in the vicinity of the heating element.
Japanese Patent Publication No. 8-8247

However, when attempting to heat a silicon wafer using such a technique, there has been a problem that the silicon wafer is damaged by thermal shock caused by a temperature difference on the heater surface.
Therefore, the present inventors have conducted intensive studies on the cause of silicon wafer breakage. As a result, even if the temperature is controlled, the silicon wafer breaks even if the temperature near the heating element is measured. Since the temperature does not always reflect the temperature of the heating surface of the silicon wafer, the unexpected fact that the temperature of the silicon wafer varies depending on the location and breaks down was found.
In addition, the inventors have newly found that such non-uniformity in temperature is more remarkable in nitride ceramics and carbide ceramics having higher thermal conductivity.

Therefore, the present inventors have further studied and measured the temperature of a portion closer to the silicon wafer, and performed heating based on the result, so that the temperature difference of the heating surface of the silicon wafer can be reduced, The inventors have found that the ceramic plate can be prevented from being damaged, and have completed the present invention having the following constitution as a summary.

That is, the ceramic heater of the first present invention is a ceramic heater having a heating element formed on the surface or inside of a ceramic plate,
A bottomed hole is provided from the opposite side of the heating surface for heating the object to be heated toward the heating surface, and the bottom of the bottomed hole is formed relatively closer to the heating surface than the heating element. The temperature measuring element is provided.

In the ceramic heater, the distance between the bottom of the bottomed hole and the heating surface is preferably 0.1 mm to 1/2 of the thickness of the ceramic plate.
The ceramic constituting the ceramic heater is desirably a nitride ceramic or a carbide ceramic.

It is desirable that the heating element of the ceramic heater be divided into at least two or more circuits.
The heating element of the ceramic heater desirably has a flat cross section.

The ceramic heater according to the second aspect of the present invention includes a heating element formed on the surface or inside of the ceramic plate, a temperature measuring element for measuring the temperature of the ceramic plate, and a control unit for supplying power to the heating element. A ceramic heater comprising: a storage unit that stores temperature data measured by the temperature measuring element; and a calculation unit that calculates power required for the heating element from the temperature data,
In the ceramic plate, while providing a bottomed hole from the opposite side of the heating surface to heat the object to be heated toward the heating surface, the bottom of the bottomed hole is formed relatively closer to the heating surface than the heating element, The temperature measuring element is provided in the bottomed hole.

In the ceramic heater, it is desirable that the heating element is divided into at least two or more circuits, and each circuit is configured to be supplied with different power.
In the first and second ceramic heaters, it is preferable that the temperature measuring element is a sheath-type thermocouple, which is pressed against the bottom of the bottomed hole.

In addition, it is desirable that the temperature measuring element is press-fitted to the bottom of the bottomed hole with an elastic body or a screw.
Further, it is desirable that the temperature measuring element is sealed in the bottomed hole with an insulator.

According to the first and second ceramic heaters of the present invention, it is possible to accurately measure the temperature of the object to be heated, and by adjusting the heat generation state of the heating element based on the measurement result of the temperature, the entire silicon wafer can be measured. Can be uniformly heated.

The ceramic heater according to the first aspect of the present invention is a ceramic heater having a heating element formed on the surface or inside of a ceramic plate,
A bottomed hole is provided from the opposite side of the heating surface for heating the object to be heated toward the heating surface, and the bottom of the bottomed hole is formed relatively closer to the heating surface than the heating element. The temperature measuring element is provided.

According to the ceramic heater of the first aspect of the present invention, since the temperature measurement location is closer to the heating surface of the object to be heated (silicon wafer) than the heating element, it is possible to more accurately measure the temperature of the object to be heated. By adjusting the heat generation state of the heating element based on the measurement result, the object to be heated can be uniformly heated.

In addition, nitride ceramics and carbide ceramics have a smaller coefficient of thermal expansion than metals and have much higher mechanical strength than metals, so even if the thickness of a ceramic plate (hereinafter referred to as a heater plate) is reduced. Does not warp or warp due to heating. Therefore, the heater plate can be made thin and light. Furthermore, since the heat conductivity of the heater plate is high and the heater plate itself is thin, the surface temperature of the heater plate quickly follows the temperature change of the heating element. That is, the surface temperature of the heater plate can be controlled by changing the voltage and the current value to change the temperature of the heating element.

In the above ceramic heater, the heating element is formed on the surface of one main surface of the heater plate, and the opposite side is a heating surface for heating an object to be heated such as a silicon wafer, or inside the heater plate. It is desirable that the heating element be formed so as to be eccentric to one main surface side from the center, and the surface farther from the heating element be the heating surface.

By setting the formation position of the heating element in this way, while the heat generated from the heating element propagates, it diffuses throughout the heater plate, and the temperature distribution on the surface that heats the object to be heated (silicon wafer) is reduced. The temperature is made uniform in each portion of the object to be heated, as a result.
The heating can be performed by placing the object to be heated on the heater plate, or by holding the object to be heated at a predetermined distance from the heater plate.

FIG. 1 is a bottom view schematically showing one example of the ceramic heater of the first invention.
The heater plate 11 is formed in a disk shape, and the heating element 12 needs to be heated so that the entire temperature of the heating surface (the side opposite to the illustrated bottom surface) of the heater plate 11 is uniform. The heater plate 11 is formed on the bottom surface in a concentric pattern. The heating elements 12 are connected so that double concentric circles close to each other form a single line, and terminal pins 13 serving as input / output terminals are connected to both ends. A through hole 15 for inserting a support pin (not shown) is formed in a portion near the center, and bottomed holes 14a to 14i for inserting a temperature measuring element are formed.

In the ceramic heater 10, the thickness of the heater plate 11 is preferably 0.5 to 5 mm. If the thickness is less than 0.5 mm, the strength is reduced and the material is easily broken. On the other hand, if the thickness is more than 5 mm, heat is difficult to propagate and the heating efficiency is deteriorated.

Preferably, the ceramic constituting the ceramic heater 10 is a nitride ceramic or a carbide ceramic.
Examples of the nitride ceramic include aluminum nitride, silicon nitride, boron nitride, and titanium nitride. These may be used alone or in combination of two or more.
Examples of the carbide ceramic include silicon carbide, zirconium carbide, titanium carbide, tantalum carbide, and tungsten carbide. 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, which is excellent in temperature followability, but tends to cause uneven temperature distribution, and it is necessary to adopt a structure for forming a temperature measuring element as in the present invention.

In the ceramic heater 10 according to the first aspect of the present invention, the distance L between the bottom of the bottomed holes 14a to 14i and the heating surface (see FIG. 2B) is 0.1 mm to 1/2 of the thickness of the ceramic plate. Desirably. If the distance between the bottoms of the bottomed holes 14a to 14i and the heating surface is less than 0.1 mm, heat is radiated and a temperature distribution is formed on the heating surface of the silicon wafer, and on the other hand, １ ／ of the thickness of the ceramic plate. If the temperature exceeds the temperature, the temperature of the heating element is liable to be affected, and a temperature distribution is formed on the heating surface of the silicon wafer.

Examples of the temperature measuring element include a thermocouple, a platinum temperature measuring resistor, a thermistor, and the like.
Examples of the thermocouple include K-type, R-type, B-type, S-type, E-type, J-type, and T-type thermocouples as described in JIS-C-1602 (1980). Of these, a K-type thermocouple is preferred.

It is desirable that the size of the junction of the thermocouple is equal to or larger than the diameter of the strand, and is 0.5 mm or less. This is because, if the junction is large, the heat capacity increases and the responsiveness decreases. It is difficult to make the diameter smaller than the diameter of the strand.
The diameter of the bottomed holes 14a to 14i is desirably 0.3 to 0.5 mm. This is because if the diameter is too large, the heat dissipation increases, and if the diameter is too small, the workability decreases, and the distance to the processed surface cannot be equalized.

The bottomed holes 14a to 14i are desirably arranged symmetrically with respect to the center of the heater plate 11 so as to form a cross, as shown in FIG. By arranging in this way, the temperature of the entire heating surface can be measured.

The temperature measuring element may be adhered to the bottoms of the bottomed holes 14a to 14i using gold brazing, silver brazing, or the like. It may be sealed with an insulator or both may be used together.

Examples of the heat-resistant resin include a thermosetting resin, particularly, an epoxy resin, a polyimide resin, a bismaleimide-triazine resin, and a silicone resin. These resins may be used alone or in combination of two or more. Further, sealing may be performed using a ceramic such as silica sol or alumina sol.

The gold solder is selected from 37-80.5% by weight Au-63-19.5% by weight Cu alloy and 81.5-82.5% by weight Au-18.5-17.5% by weight Ni alloy. At least one is desirable. These are because the melting temperature is 900 ° C. or higher and it is difficult to melt even in a high temperature region.

As the silver solder, for example, an Ag-Cu-based one can be used.
As shown in FIG. 1, the heating element 12 is preferably divided into at least two or more circuits, and more preferably divided into two to ten 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.

4 and 5 are diagrams showing a method of fixing the temperature measuring element, in which (a) is a sectional view showing the vicinity of the bottomed hole, and (b) is an enlarged bottom surface showing the shape of the bottomed hole. FIG.
When fixing the temperature measuring element, as shown in FIG. 4, an elastic body such as a coil spring 65 may be used to crimp the bottom surface of the bottomed hole 610, and as shown in FIG. It may be pressed against the bottom of the bottomed hole 710. As the elastic body, a coil spring, a leaf spring, or the like can be used.

If the temperature measuring element is fixed with resin, ceramic, brazing material, etc., there is a risk that the temperature measuring element will fall off due to thermal degradation. However, if a physical method such as pressure bonding is used, such a problem does not occur, which is advantageous. It is. As shown in FIGS. 4 and 5, when fixing is performed by crimping or the like, and a thermocouple is used as a temperature measuring element, a thermocouple is placed inside a cylindrical body and alumina powder is surrounded by the thermocouple. It is desirable to use a sheath-type thermocouple filled with insulating powder such as. This is because the thermocouple can be prevented from being damaged.

As the pattern of the heating element 12, in addition to the concentric circles shown in FIG. 1, for example, a spiral, an eccentric circle, a bent line, and the like can be given.

In the present invention, when the heating element 12 is formed on the surface of the heater plate 11, a conductive paste containing metal particles is applied to the surface of the heater plate 11 to form a conductor paste layer having a predetermined pattern, which is then baked. Preferably, a method of sintering metal particles on the surface of the heater plate 11 is preferred. The sintering of the metal is sufficient if the metal particles and the metal particles and the ceramic are fused.
As shown in FIG. 1, when the heating element 12 is formed on the surface of the heater plate 11, the thickness of the heating element 12 is preferably 1 to 30 μm, more preferably 1 to 10 μm. When a heating element is formed inside the heater plate 11, its thickness is preferably 1 to 50 μm.

When the heating element 12 is formed on the surface of the heater plate 11, the width of the heating element 12 is preferably 0.1 to 20 mm, more preferably 0.1 to 5 mm. When a heating element is formed inside the heater plate 11, the width of the heating element is preferably 5 to 20 μm.

The resistance of the heating element 12 can be varied depending on its width and thickness, but the above range is the most practical. The resistance value increases as the resistance value decreases and the resistance value decreases. When the heating element 12 is formed inside the heater plate 11, the thickness and the width are larger. However, when the heating element 12 is provided inside, the distance between the heating surface and the heating element becomes shorter, This is because it is necessary to increase the width of the heating element 12 itself because the uniformity of the surface temperature is reduced. In addition, since a heating element is provided inside, there is no need to consider adhesion to nitride ceramics and the like, and high melting point metals such as tungsten and molybdenum and carbides such as tungsten and molybdenum can be used. Since the value can be increased, the thickness itself may be increased for the purpose of preventing disconnection or the like. For the above reasons, it is desirable that the heating element 12 has the above-described thickness and width.
The heating element 12 may be rectangular or elliptical in 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 heating element / the thickness of the heating element) is desirably 10 to 5000.
By adjusting to this range, the resistance value of the heating element 12 can be increased, and the uniformity of the temperature of the heating surface can be ensured.
When the thickness of the heating element 12 is constant and the aspect ratio is smaller than the above range, the amount of heat propagation in the direction of the wafer heating surface of the heater plate 11 decreases, and the heat distribution approximate to the pattern of the heating element 12 is reduced. If the aspect ratio is too large, on the other hand, if the aspect ratio is too large, the temperature immediately above the center of the heating element 12 becomes high, and eventually, a heat distribution similar to the pattern of the heating element 12 occurs on the heating face. I will. Therefore, in consideration of the temperature distribution, the aspect ratio of the cross section is preferably 10 to 5000.

When the heating element 12 is formed on the surface of the heater plate 11, the aspect ratio is desirably 10 to 200. When the heating element 12 is formed inside the heater plate 11, the aspect ratio is desirably 200 to 5000.

When the heating element 12 is formed inside the heater plate 11, the aspect ratio becomes larger. However, when the heating element 12 is provided inside, the distance between the heating surface and the heating element 12 becomes shorter, This is because the heating element 12 itself needs to be flattened because the surface temperature uniformity is reduced.
When the heating element 12 of the present invention is formed eccentrically inside the heater plate 11, the position is close to the opposite side surface (bottom surface) of the heating surface of the heater plate 11, with respect to the distance from the heating surface to the bottom surface. It is desirable that the position be more than 50% and up to 99%.

If it is less than 50%, the temperature distribution is generated because it is too close to the heating surface. Conversely, if it is more than 99%, the heater plate 11 warps and the silicon wafer is damaged. .
When the heating element 12 is formed inside the heater plate 11, a plurality of heating element forming layers may be provided. In this case, it is desirable that the heating element 12 is formed in some layer so that the patterns of the respective layers complement each other, and when viewed from above the heating surface, the pattern is formed in any region. As such a structure, for example, there is a structure in which the staggered arrangement is provided.

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 flakes or a mixture of spheres and flakes, the metal oxide between the metal particles is easily retained, and the adhesion between the heating element 12 and the nitride ceramic or the like is increased. 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.

As described above, it is desirable that the heating element 12 is formed by sintering the metal particles and the metal oxide into the conductor paste, as described above. Thus, by sintering the metal oxide together with the metal particles, the nitride ceramic or carbide ceramic serving as the heater plate can be brought into close contact with the metal particles.

It is not clear why mixing metal oxides improves the adhesion with nitride ceramics or carbide ceramics, but the surface of metal particles, nitride ceramics, and carbide ceramics is slightly oxidized and becomes an oxide film. It is considered that these oxide films are sintered and integrated via the metal oxide, and the metal particles and the nitride ceramic or the carbide ceramic adhere to each other.

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 or the carbide ceramic without increasing the resistance value of the 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 the lead oxide is 1 to 10 by weight when the total amount of the metal oxide is 100 parts 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 amounts of these oxides in these ranges, the adhesion to the nitride ceramic 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 heating element 12 is formed using the conductor paste having such a configuration is preferably 1 mΩ / □ to 10 Ω / □.

When the heating element 12 is formed on the surface of the heater plate 11, it is desirable that a metal coating layer (see FIG. 3) 48 be formed on the surface of the heating element 12. 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 in forming the metal coating layer is not particularly limited as long as it is a non-oxidizing metal, and 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 heating element 12 requires a terminal for connection to a power supply, and this terminal is attached to the heating element 12 via solder. Nickel prevents heat diffusion of the solder. As the connection terminal, for example, a terminal pin 13 made of Kovar is used.

In the case where the heating element 12 is formed inside the heater plate 11, the surface of the heating element is not oxidized, so that the coating is unnecessary. When the heating element 12 is formed inside the heater plate 11, a part of the heating element may be exposed on the surface, and a through-hole for connecting the heating element is provided in a terminal portion. It may be connected and fixed.

When connecting the connection terminals, alloys 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.

In the ceramic heater of the present invention, an electrode can be embedded in a ceramic plate to form an electrostatic chuck, or a chuck top conductor layer can be provided on the surface, and a guard electrode or ground electrode can be formed inside to function as a wafer prober. it can.

Next, a method for manufacturing the ceramic heater according to the first embodiment of the present invention will be described.
First, a method for manufacturing a ceramic heater in which the heating element 12 is formed on the surface of the heater plate 11 shown in FIG. 1 will be described.

(1) Heater plate manufacturing process After preparing a slurry by blending a sintering aid such as yttria or a binder with powder of a nitride ceramic or a carbide ceramic such as aluminum nitride as described above, if necessary, Granules are formed by a method such as spray drying, and the granules are placed in a mold or the like and pressed to be formed into a plate shape or the like, thereby producing a green body (green).

Next, in the formed body, if necessary, a portion serving as a through hole 15 for inserting a support pin for supporting a silicon wafer and bottomed holes 14a to 14i for embedding a temperature measuring element such as a thermocouple are formed. The portion is formed by drilling or blasting. The processing for forming the portion to be the through hole may be performed after the sintered body is manufactured.

Next, the formed body is heated, fired and sintered to produce a ceramic plate. After that, the heater plate 11 is manufactured by processing into a predetermined shape, but may be a shape that can be used as it is after firing. By performing heating and baking while applying pressure, it is possible to manufacture the heater plate 11 having no pores. Heating and firing may be performed at a temperature equal to or higher than the sintering temperature. For a nitride ceramic or a carbide ceramic, the temperature is 1000 to 2500C.

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

(3) Firing of conductive paste The conductive paste layer printed on the bottom surface of the heater plate 11 is heated and fired to remove the resin and the solvent, and sinter the metal particles. To form The temperature of the heating and firing is preferably from 500 to 1000C.

If the above-mentioned metal oxide is added to the conductor paste, the metal particles, the heater plate and the metal oxide are sintered and integrated, so that the adhesion between the heating element and the heater plate is improved.

(4) Formation of Metal Coating Layer It is desirable to provide a metal coating layer on the surface of the heating element 12. The metal coating layer can be formed by electrolytic plating, electroless plating, sputtering, or the like, but in consideration of mass productivity, electroless plating is optimal.

(5) Attachment of Terminals, etc. Terminals (terminal pins 13) for connection to a power supply are attached to the ends of the pattern of the heating element 12 by soldering. Further, a thermocouple is fixed to the bottomed holes 14a to 14i with silver brazing, gold brazing or the like, and the thermocouple is sealed with a heat-resistant resin such as polyimide, and the production of the ceramic heater 10 is completed.
Next, a method of manufacturing a ceramic heater in which a heating element is formed inside a heater plate will be described.

(1) Heater Plate Manufacturing Step First, a paste is prepared by mixing nitride ceramic or carbide ceramic powder with a binder, a solvent, and the like, and a green sheet is manufactured using the paste.
As the above-mentioned ceramic powder, aluminum nitride, silicon carbide, or the like can be used, and a sintering aid such as yttria may be added as necessary.

The binder is preferably at least one selected from an acrylic binder, ethyl cellulose, butyl cellosolve, and polyvinyl alcohol.
Further, as the solvent, at least one selected from α-terpineol and glycol is desirable.
A paste obtained by mixing them is formed into a sheet by a doctor blade method to produce a green sheet.

The thickness of the green sheet is preferably 0.1 to 5 mm.
Next, in the obtained green sheet, if necessary, a portion serving as a through hole for inserting a support pin for supporting a silicon wafer, and a portion serving as a bottomed hole for embedding a temperature measuring element such as a thermocouple. Then, a portion serving as a through hole for connecting the heating element to an external end pin is formed. The above processing may be performed after forming a green sheet laminate described later.

(2) Step of printing conductive paste on green sheet A conductive paste containing a metal paste or a conductive ceramic is printed on the green sheet.

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 size is less than 0.1 μm or more than 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 binder selected from acrylic, ethyl cellulose, butyl cellosolve, and polyvinyl alcohol; A composition (paste) in which 1.5 to 10 parts by weight of at least one solvent selected from α-terpineol and glycol is mixed.

(3) Green Sheet Laminating Step Green sheets on which the conductor paste is not printed are laminated on and under the green sheet on which the conductor paste is printed.
At this time, the number of green sheets stacked on the upper side is made larger than the number of green sheets stacked on the lower side, and the formation position of the heating element is eccentric toward the bottom.
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.

(4) Green Sheet Laminate Firing Step The green sheet laminate is heated and pressed to sinter the ceramic particles in the green sheet and the internal conductor.
The heating temperature is preferably from 1000 to 2000 ° C, and the pressure is preferably from 100 to 200 kg / cm ² . Heating is performed in an inert gas atmosphere. As the inert gas, for example, argon, nitrogen, or the like can be used.

After firing, a bottomed hole for inserting a temperature measuring element may be provided. The bottomed hole can be formed by performing blasting such as sand blasting after surface polishing. A terminal is connected to a through hole for connecting to an internal heating element, and the terminal is heated and reflowed. The heating temperature is preferably from 200 to 500C.

Further, a thermocouple or the like as a temperature measuring element is attached using a silver solder, a gold solder, or the like, and sealed with a heat-resistant resin such as polyimide, thereby completing the manufacture of the ceramic heater.

Next, the second ceramic heater of the present invention will be described.
The ceramic heater of the second aspect of the present invention has a heating element formed on the surface or inside of the ceramic plate, a temperature measuring element for measuring the temperature of the ceramic plate, and a control unit for supplying power to the heating element, A ceramic heater comprising a storage unit that stores temperature data measured by the temperature measuring element, and a calculation unit that calculates power required for the heating element from the temperature data,
In the ceramic plate, while providing a bottomed hole from the opposite side of the heating surface to heat the object to be heated toward the heating surface, the bottom of the bottomed hole is formed relatively closer to the heating surface than the heating element, A temperature measuring element is provided in the bottomed hole.

According to the ceramic heater of the second aspect of the present invention, since the temperature measurement location is closer to the heating surface of the silicon wafer than the heating element, it is possible to more accurately measure the temperature of the silicon wafer. Based on the temperature data stored in the storage unit, the operation unit calculates a voltage to be applied to the heating element for uniform heating, based on the temperature data stored in the storage unit. , It is possible to uniformly heat the entire silicon wafer.
Further, nitride ceramics and carbide ceramics have a smaller coefficient of thermal expansion than metals and have much higher mechanical strength than metals, so that the heater plate can be made thinner and lighter. Furthermore, since the heat conductivity of the heater plate is high and the heater plate itself is thin, the surface temperature of the heater plate quickly follows the temperature change of the heating element.

FIG. 2A is a block diagram schematically showing an example of the second ceramic heater of the present invention, and FIG. 2B is a partially enlarged sectional view showing a part thereof.

As shown in FIG. 2, in the ceramic heater 20, a plurality of through holes 25 (only one in the figure) are provided in the heater plate 21, and a support pin 26 is inserted into the through hole 25. The silicon wafer 19 is mounted on the pins 26. By moving the support pins 26 up and down, the silicon wafer 19 can be transferred to a carrier (not shown) or can be received from the carrier.

The support pins 26 hold the silicon wafer 19 at a predetermined distance from the heater plate 21 so that the silicon wafer 19 can be heated.

On the other hand, heating elements 22 a and 22 b are embedded in the heater plate 21, and the heating elements 22 a and 22 b are connected to terminal pins 23 provided on the bottom surface through through holes 28. In addition, a socket 32 is attached to the terminal pin 23, and the socket 32 is connected to a control unit 29 having a power supply.

A bottomed hole 24 is provided in the heater plate 21 from the bottom surface 21b side, and a thermocouple 27 is fixed to the bottom of the bottomed hole 24. The thermocouple 27 is connected to the storage unit 30 and can measure the temperature of each thermocouple 27 at regular intervals and store the data. The storage unit 30 is connected to the control unit 29 and is connected to the calculation unit 31 to calculate a voltage value and the like controlled by the calculation unit 31 based on the data stored in the storage unit 30. Based on the above, a predetermined voltage is applied from the control unit 29 to each heating element 21 so that the temperature of the heating surface 21a can be made uniform.

Each member (heater plate 21, heating elements 22a and 22b, through hole 28) constituting ceramic heater 20 and bottomed hole 24 formed in heater plate 21 are configured in the same manner as the first ceramic heater. Therefore, the description is omitted here.

Next, the operation of the second ceramic heater 20 of the present invention will be described.
First, when electric power is supplied to the ceramic heater 20 by operating the control unit 29, the temperature of the heater plate 21 itself starts to rise, but the surface temperature of the outer peripheral portion becomes slightly low.
The data measured by the thermocouple 27 is temporarily stored in the storage unit 30. Next, the temperature data is sent to the calculating section 31, where the calculating section 31 calculates the temperature difference ΔT at each measurement point, and further calculates the data ΔW necessary for equalizing the temperature of the heating surface 21a. I do.

For example, if there is a temperature difference ΔT between the heating element 22a and the heating element 22b, and if the heating element 22a is lower, power data ΔW that makes ΔT zero is calculated, and this is transmitted to the control unit 29. Is applied to the heating element 22a to raise the temperature.

Regarding the power calculation algorithm, the simplest method is to calculate the power required for raising the temperature from the specific heat of the heater plate 21 and the weight of the heating area, and a correction coefficient due to the heating element pattern may be added to this. . Alternatively, a temperature rise test may be performed on a specific heating element pattern in advance, and a function of the temperature measurement position, the input power, and the temperature may be obtained in advance, and the input power may be calculated from the function. Then, the applied voltage and the time corresponding to the power calculated by the calculation unit 31 are transmitted to the control unit 29, and the control unit 29 supplies power to each heating element 22 based on the values.

FIG. 3 is a block diagram schematically showing another example of the ceramic heater of the second invention.
In the ceramic heater 40 shown in FIG. 3, the heating elements 42a and 42b are formed on the bottom surface 41b of the heater plate 41, and the metal coating layer 48 is formed around the heating elements 42a and 42b.
Further, terminal pins 43 are connected and fixed to the heating elements 42 a and 42 b via the metal coating layer 48, and a socket 52 is attached to the terminal pins 43. The socket 52 is connected to the control unit 29 having a power source, and is otherwise configured in the same manner as the ceramic heater shown in FIG.

The operation of the ceramic heater 40 shown in FIG. 3 is the same as that of the ceramic heater 20 shown in FIG. 2, and the temperatures of the thermocouples 42a and 42b are measured at regular intervals and stored in the storage unit 50. The calculation unit 51 calculates a voltage value or the like to be controlled. Based on the calculation, the control unit 49 applies a predetermined voltage to the heating elements 42a and 42b to make the temperature of the entire heating surface 41a of the ceramic heater 40 uniform. It has become possible to be.

Hereinafter, the present invention will be described in more detail.

(Example 1) Production of a ceramic heater made of aluminum nitride (see FIG. 1)
(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 an acrylic binder, and alcohol is spray-dried. , To produce a granular powder.

(2) Next, this granular powder was placed in a mold and molded into a flat plate to obtain a formed product (green). Drilling is performed on the formed body to form a portion serving as a through hole 15 for inserting a support pin of a silicon wafer and a portion serving as a bottomed hole 14a to 14i for embedding a thermocouple (diameter: 1.1 mm, depth: 2 mm) ) Was formed.

(3) The green compact after the processing was hot-pressed at 1800 ° C. and a pressure of 200 kg / cm ² to obtain a 3 mm-thick aluminum nitride plate.
Next, a disk having a diameter of 210 mm was cut out from the plate to obtain a ceramic plate (heater plate) 11.

(4) Conductive paste was printed on the heater plate 11 obtained in (3) by screen printing. The printing pattern was a concentric pattern as shown in FIG.
As a conductive 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 heater plate 11 on which the conductor paste was printed was heated and baked at 780 ° C. to sinter silver and lead in the conductor paste and baked the heater plate 11 to form the heating element 12. The silver-lead heating element 12 had a thickness of 5 μm, a width of 2.4 mm, and a sheet resistivity of 7.7 mΩ / □.

(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 was added to the above (5). Was immersed to deposit a metal coating layer (nickel layer) having a thickness of 1 μm on the surface of the silver-lead heating element 12.

(7) A silver-lead solder paste (manufactured by Tanaka Kikinzoku) was printed by screen printing on a portion where a terminal for securing connection to a power supply was to be formed, to form a solder layer.
Next, the terminal pins 13 made of Kovar were placed on the solder layer, and heated and tuffled at 420 ° C. to attach the terminal pins 13 to the surface of the heating element 12.

(8) A thermocouple for temperature control was connected with a gold solder of 81.7 Au-18.3Ni (heated and fused at 1030 ° C.) to obtain a ceramic heater 10.

(Example 2) Manufacture of a ceramic heater made of silicon carbide Silicon carbide having an average particle diameter of 1.0 µm was used, the sintering temperature was 1900 ° C, and the surface of the obtained heater plate was fired at 1500 ° C for 2 hours. A ceramic heater made of silicon carbide was manufactured in the same manner as in Example 1 except that a 1 μm thick SiO ₂ layer was formed on the surface. The thermocouple was sealed by curing it at 120 ° C. using a polyimide resin.

(Example 3) Production of a ceramic heater having a heating element inside
(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 consisting of 1-butanol and ethanol, was molded by a doctor blade method to obtain a green sheet having a thickness of 0.47 mm.

(2) Next, after drying this green sheet at 80 ° C. for 5 hours, a portion to be a through hole 15 into which a silicon wafer support pin having a diameter of 1.8 mm, 3.0 mm, and 5.0 mm is inserted by punching, a terminal A portion serving as a through hole for connecting to a pin was provided.

(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 part by weight of a dispersant were 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 conductive paste A was printed on a green sheet by screen printing to form a conductive 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. and a pressure of 80 kg / cm ² .

(4) Next, the obtained laminate was degreased in nitrogen gas at 600 ° C. for 5 hours, and hot-pressed at 1890 ° C. and a pressure of 150 kg / cm ² for 3 hours to obtain a 3 mm-thick aluminum nitride plate. Was. This was cut into a disk shape of 230 mm to obtain a ceramic heater having a heating element with a thickness of 6 μm and a width of 10 mm inside.

(5) Next, the plate-like body obtained in (4) is polished with a diamond grindstone, a mask is placed on the plate-like body, and a bottomed hole for a thermocouple (diameter: 1.2 mm, depth: 2.0 mm).

(6) Further, a part of the through-hole for the through-hole was cut out to form a concave portion, and a gold solder made of Ni-Au was used in the concave portion, and heated at 700 ° C. and reflowed to connect a Kovar terminal pin. .
The connection of the terminal pins is desirably a structure in which a tungsten support is supported at three points. This is because connection reliability can be ensured.

(8) Next, a plurality of thermocouples for temperature control were embedded in the bottomed holes, sealed with silica sol (Aron Ceramic manufactured by Toagosei Co., Ltd.), and gelled at 120 ° C. to complete the manufacture of the ceramic heater.

(Example 4) Temperature control of ceramic heater
(1) A temperature controller (manufactured by OMRON, E5ZE) including a control unit having a power supply, a storage unit, and a calculation unit is prepared, and the terminal pins 13 are connected to the ceramic heater 10 (see FIG. 1) manufactured in Example 1. The wiring from the control unit was connected via the heater, and the silicon wafer was placed on the ceramic heater 10.

(2) Next, a voltage is applied to the ceramic heater 10 to raise the temperature once to 200 ° C., and then to 200 to 400 ° C., and set in the bottomed holes 14a to 14c shown in FIG. The temperature was measured with a thermocouple. The measurement results are shown in FIG. In FIG. 6, the vertical axis represents temperature, and the horizontal axis represents elapsed time.
FIG. 7 shows the profile of the electric power (expressed by a current value) applied to the heating elements 12a, 12b, and 12c. In FIG. 7, the vertical axis represents current, and the horizontal axis represents elapsed time.
The silicon wafer placed on the ceramic heater 10 was uniformly heated without being damaged during the heating process.

(Example 5)
A ceramic heater was manufactured in the same manner as in Example 1 except for the following points.
That is, first, a K-type thermocouple 67 was placed inside a stainless steel tubular body 66, and a sheath-type thermocouple in which MgO powder and alumina powder were filled around the K-type thermocouple was used as a thermocouple. This tubular body 66 is bent at substantially a right angle as shown in FIG. The bottomed hole 610 has a keyhole shape in a plan view as shown in FIG. 4 (b), and has a structure in which a stainless steel rod 64 is fixed to the tip of a stainless steel coil spring 65. The bent portion of the cylindrical body 66 was pressed against the bottom surface of the bottomed hole 610 with the rod-shaped body 64 and fixed. Note that the coil spring 65 is attached to a bottom plate 63 of a support container (casing) of the ceramic plate 61.

(Example 6)
A ceramic heater was manufactured in the same manner as in Example 1 except for the following points.
That is, as shown in FIG. 5, a sheath-type thermocouple having the same configuration as that of the fifth embodiment is used as the thermocouple, and the bottomed hole 710 is formed into a keyhole shape in a plan view similarly to the fifth embodiment. Further, a thread groove was formed on the side wall surface by drilling. Then, the tubular body 66 having a sheath-type thermocouple is inserted into the bottomed hole 710, and a stainless steel bolt 74 is screwed in to fix the bent portion of the tubular body 66 against the bottom surface of the bottomed hole 610. did.

(Comparative Example 1)
A bottomed hole is formed so that the bottom surface is located at a position 74% of the thickness from the heating surface of the ceramic substrate, that is, the surface at the same level as the heating element forming surface, and a thermocouple is embedded to make Au-Ni. A ceramic heater was manufactured in the same manner as in Example 3, except that the heater was attached.

(Comparative Example 2)
A ceramic heater was manufactured in the same manner as in Example 1 except that a thermocouple was brazed to the heating element forming surface, that is, the bottom surface with Au-Ni.

  With respect to the ceramic heaters according to Examples 1 to 6 and Comparative Examples 1 and 2, the temperature was raised to 200 ° C., and the difference between the maximum temperature and the minimum temperature was measured with a thermoviewer. The sample was placed in a state where the temperature was raised to 200 ° C., and the time until the temperature returned to the original 200 ° C. (recovery time) was measured. The results are shown in Table 1 below.

In the ceramic substrates of Examples 1 to 6, the temperature difference measured by a thermoviewer was as small as 0.5 ° C. or less, and the recovery time up to 200 ° C. was as short as 50 seconds or less. In No. 2, both the recovery time and the temperature difference were long.

It is a bottom view showing typically an example of the ceramic heater of the first present invention. (A) is a block diagram schematically showing an example of the ceramic heater of the second present invention, and (b) is a partially enlarged sectional view of the ceramic heater. It is a block diagram showing typically another example of the ceramic heater of the second present invention. (A) is sectional drawing which shows typically an example of the ceramic heater in which the temperature measuring element was installed, (b) is an enlarged bottom view which shows the shape of a bottomed hole. (A) is sectional drawing which shows typically another example of the ceramic heater in which the temperature measuring element was installed, (b) is an enlarged bottom view which shows the shape of a bottomed hole. 9 is a graph showing a temperature profile of a ceramic heater according to Example 4. 9 is a graph showing a power profile of a ceramic heater according to a fourth embodiment.

Explanation of reference numerals

10, 20, 40 Ceramic heaters 11, 21, 41, 61, 71 Heater plates 12, 22, 42, 62, 72 Heating elements 13, 23, 43 Terminal pins 14, 24, 44 Bottom holes 15, 25, 45 Penetration Hole 19 Silicon wafer 21a, 41a Heating surface 21b, 41b Bottom surface 26, 46 Support pin 27, 47, 67 Thermocouple 28 Through hole 29, 49 Control unit 30, 50 Storage unit 31, 51 Operation unit 66 Tube 610, 710 Bottom Hole

Claims (11)

A ceramic heater having a heating element formed on the surface or inside of a ceramic plate,
A bottomed hole is provided from the opposite side of the heating surface for heating the object to be heated toward the heating surface, and the bottom of the bottomed hole is formed relatively closer to the heating surface than the heating element. A ceramic heater provided with a temperature measuring element. 2. The ceramic heater according to claim 1, wherein the distance between the bottom of the bottomed hole and the heating surface is 0.1 mm to の of the thickness of the ceramic plate. The ceramic heater according to claim 1, wherein the ceramic constituting the ceramic heater is a nitride ceramic or a carbide ceramic. The ceramic heater according to claim 1, wherein the heating element is divided into at least two or more circuits. The ceramic heater according to claim 1, wherein the heating element has a flat cross section. A heating element is formed on the surface or inside of the ceramic plate, a temperature measuring element for measuring the temperature of the ceramic plate, a control unit for supplying power to the heating element, and temperature data measured by the temperature measuring element. A ceramic heater comprising: a storage unit that stores the following, and a calculation unit that calculates the power required for the heating element from the temperature data,
In the ceramic plate, while providing a bottomed hole from the opposite side of the heating surface to heat the object to be heated toward the heating surface, the bottom of the bottomed hole is formed relatively closer to the heating surface than the heating element, A ceramic heater, wherein the temperature measuring element is provided in the bottomed hole. The ceramic heater according to claim 6, wherein the heating element is divided into at least two or more circuits, and each circuit is configured to be supplied with different electric power. The ceramic heater according to any one of claims 1 to 7, wherein the temperature measuring element is a sheath-type thermocouple. The ceramic heater according to any one of claims 1 to 8, wherein the temperature measuring element is pressed against a bottom of the bottomed hole. The ceramic heater according to claim 9, wherein the temperature measuring element is pressed by an elastic body or a screw. The ceramic heater according to any one of claims 1 to 10, wherein the temperature measuring element is sealed in the bottomed hole with an insulator.

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