JP2003229344A - Heater for heating semiconductor product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preventing the contamination of a silicon wafer caused by the thermal diffusion of iron and yttrium to the silicon wafer when heating the silicon wafer by a heater. <P>SOLUTION: In a semiconductor-heating heater 100, a pattern 2 of an electrical heating element is formed on one side of a flat body 1 made of nitride ceramic, and a protection layer 3 covered with silica or the like is formed at least at one portion on the surface of the flat body. Additionally, a planar layer 4 made of a material having high thermal conductivity may be provided on a surface opposite to a surface where the pattern 2 of the electrical heating element is formed to uniformly diffuse heat that is propagated in the thickness direction of the flat body 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater used in a hot plate or an electrostatic chuck, which is mainly used in the semiconductor industry, and more particularly to a heater which is free from contamination due to thermal diffusion of semiconductor products.

[0002]

2. Description of the Related Art Semiconductor products are manufactured by forming a photosensitive resin as an etching resist on a silicon wafer and etching the silicon wafer. The photosensitive resin is applied in liquid form on the surface of the silicon wafer by a spin coater or the like, but it must be dried after application, and the applied silicon wafer is placed on a heater and heated. Conventionally, as such a heater, as disclosed in Japanese Patent Laid-Open No. 1-40330, a heater in which a heating element is wired on the back surface of a nitride ceramic plate is adopted. In this heater, the heater plate itself is thin and excellent in temperature followability.

[0003]

However, such a heater has the following unsolved problems. When this heater is used for heating a silicon wafer, iron and yttrium are thermally diffused in the silicon wafer, and the silicon wafer is contaminated.

The main object of the present invention is to prevent contamination of semiconductor products by iron or yttrium.

[0005]

As a result of intensive studies, the present inventors have found that the cause of iron or yttrium contamination is the nitride ceramic substrate itself. A heating element is formed in the heater, and the nitride ceramic is fixed to the jig when the heating element is formed. At the time of this fixing, the surface of the jig and the nitride ceramic substrate rub against each other and iron adheres to the nitride ceramic substrate, and this iron is thermally diffused into the semiconductor product during heating. Further, when a heating element is provided on one side or inside of the nitride ceramic substrate to be used as a heater, the nitride ceramic is locally heated by the heating element as shown in FIG. 2, so that it is added as a sintering aid. It is considered that the yttria remaining in the world is more likely to be thermally diffused to the surface as compared with the heating in the atmosphere, leading to a semiconductor product.

As a result of further research based on such findings, the present inventors have found that at least a part of the surface of a plate-shaped body (nitride ceramic substrate) made of nitride ceramic,
In particular, by discovering that the heating surface that comes into contact with semiconductor products is protected by a protective layer, it is possible to solve such problems,
The present invention has been completed. The present invention is a heater for heating a semiconductor product, wherein a heating element is formed on one side or inside of a plate-shaped body made of a nitride ceramic, and a protective layer is formed on at least a part of the surface of the plate-shaped body. Is a heater for heating semiconductor products.

In the present invention, at least a part of the surface of a plate-shaped body (nitride ceramic substrate) made of nitride ceramic,
In particular, the heating surface that comes into contact with the semiconductor product is covered with a protective layer to prevent heat diffusion due to iron or yttrium. Further, in the nitride ceramic, since the thin oxide layer on the surface of the nitride ceramic particles is bonded by being bonded through the sintering aid, the nitride ceramic is likely to be shed from the surface even with a slight impact. In the present invention, since the surface is covered with the protective layer, shedding can be prevented. Further, the present invention has an advantage that the reaction between the nitride ceramic and water in the air is prevented by the protective layer, ammonia is not generated, and the photosensitive resist and the silicon wafer are not corroded.

The technique for protecting the surface of the nitride ceramic is described in Japanese Patent Laid-Open No. 9-263453, but this technique does not assume that the nitride ceramic is used as a heater. It does not solve the peculiar problem that occurs when such a nitride ceramic is used as a heater.

The present invention is a heater for heating a semiconductor product, in which a pattern of a heating element is formed on one surface of a plate-shaped body made of a nitride ceramic, and a protective layer is formed on at least a part of the surface of the plate-shaped body. It is a heater for heating semiconductor products characterized by the following.

The protective layer is preferably at least one selected from metal oxides and resins. When the protective layer made of the metal oxide is provided, it is desirable to form the heating element 2 on the surface of the protective layer 3 as shown in FIG. This is because the metal oxide protective layer 3 has excellent adhesion to both the nitride ceramic and the metal heating element 2, and thus improves the adhesion between the plate-shaped body 1 and the heating element 2. In addition, FIG.
As described above, the heating element 2 may be covered with the protective layer 3 made of a metal oxide. Migration of heating elements (metal ions,
This is because the protective layer made of a metal oxide can prevent metal atoms from diffusing in the surface layer of the plate-shaped body 1.
As the metal oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ ,
At least one selected from ZrO ₂ is preferably polyimide as the resin. Among the metal oxides, SiO ₂ which is particularly excellent in water resistance is most suitable. Further, since the heater is remarkably large in stress due to thermal cycles, cracks are likely to occur in the protective layer, but SiO ₂ is not destroyed by such stress, and thus has excellent durability. The thickness of the protective layer is 100 Å (0.0
1 μm) to 1 μm is optimal. If it is too thin, a portion where the protective layer is not formed occurs, and if it is too thick, cracks occur due to the difference in coefficient of thermal expansion, and in any case diffusion of iron or yttrium cannot be prevented, and generation of ammonia cannot be prevented. The protective layer not only covers the entire plate-shaped body,
You may coat a part. In particular, it is desirable to protect the heating surface (the surface opposite to the surface on which the heating element is formed, that is, the surface that contacts the semiconductor product). By protecting the heating surface, it is possible to prevent the diffusion of iron and yttrium and the generation of ammonia.

In the present invention, as shown in FIG. 3, a plane layer 4 made of a material having a higher thermal conductivity than the plate-shaped body 1 may be provided inside the plate-shaped body 1. The heat propagated from the heating element pattern 2 in the thickness direction of the plate-shaped body 1 is diffused in the plane layer 4 to have a uniform temperature, and the surface opposite to the surface on which the heating element pattern 2 is formed (heating surface). Is propagated to.
Therefore, the temperature of the heating surface can be made uniform even in a high temperature region. The plane layer is preferably a continuous plane, but may be divided into a plurality of pieces within a range in which the object of the present invention can be achieved, and may be a mesh having various circular and square openings. The plane layer used in the present invention preferably has a thickness of 1 to 10 ⁴ μm, and optimally 10 to 1000 μm. The reason for this is that if the thickness is too thin, there is no temperature uniforming effect, and if the thickness is too large, temperature distribution occurs in the plane layer itself, and the surface temperature cannot be uniformized. Further, the plane layer only needs to have a higher thermal conductivity than the material of the plate-shaped body, and metal or ceramic can be used. As a plane layer,
At least one ceramic selected from metals selected from tungsten, molybdenum and kovar, tungsten carbide, silicide, and boron nitride is desirable. The plane layer may be a single layer or a plurality of layers.

In the present invention, an insulating nitride ceramic is used as the plate. Nitride ceramic has a smaller coefficient of thermal expansion than metal, and even if it is thin, it warps due to heating,
Does not distort. Therefore, it is possible to make the plate-shaped body forming the heater thin and light. Further, since the plate-shaped body has high thermal conductivity and the plate-shaped body itself is thin, the surface temperature of the heater quickly follows the temperature change of the heating element. That is, the surface temperature of the heater can be controlled by changing the voltage and the amount of current to change the temperature of the heating element. The nitride ceramic is at least one selected from metal nitride ceramics such as aluminum nitride, silicon nitride and boron nitride.
More than one kind is desirable.

The plate-shaped body preferably has a thickness of about 0.5 to 5 mm. This is because if it is too thin, it will break easily.

In the present invention, the plate-like body has the conductor layer 5 for electrostatic chuck between the plane layer 4 and the surface opposite to the surface on which the heating element 2 is provided (that is, the heating surface) as shown in FIG. You may form. This is because the semiconductor wafer can be heated while being fixed by the electrostatic chuck. In the present invention, the heating element can be formed by sintering metal particles in the conductive paste. This is because the surface of the ceramic plate can be baked by heating and baking. It should be noted that the sintering is sufficient if the metal particles are fused to each other or the metal particles and the ceramic are fused. When the heating element is formed on the protective layer, SiO ₂ is preferably used as the protective layer. This is because practical adhesion strength can be obtained. Further, as shown in FIG. 1, since the heating element 2 needs to make the temperature of the entire plate-shaped body 1 uniform, a concentric pattern is preferable. Further, the thickness of the pattern of the heating element 2 is preferably 1 to 20 μm, and the width is preferably 0.5 to 5 mm. The resistance value can be changed depending on the thickness and width, but this range is most practical. The resistance value becomes thin and becomes thin, and becomes large.

The conductive paste generally contains a resin, a solvent, a thickener, etc. in addition to the metal particles. The metal particles are preferably at least one selected from gold, silver, platinum, palladium, lead, tungsten and nickel.
This is because these metals are relatively hard to oxidize and have a resistance value sufficient to generate heat. The particle size of these metal particles is
The thickness is preferably 0.1 to 100 μm. This is because if it is too fine, it is easily oxidized, and if it is too large, it becomes difficult to sinter and the resistance value increases.

As the resin used for the conductive paste,
Epoxy resin and phenol resin are preferable. Further, isopropyl alcohol or the like is used as the solvent.
Examples of the thickener include cellulose and the like.

It is desirable that the conductive paste contains a metal oxide in addition to the metal particles so that the heating element is made by sintering the metal particles and the metal oxide. The reason for this is to bring the nitride ceramic or carbide ceramic into close contact with the metal particles. Although it is not clear why the metal oxide improves the adhesion between the nitride ceramic or the carbide ceramic and the metal particles, a slight oxide film is formed on the surface of the metal particle and the surface of the nitride ceramic or the carbide ceramic. It is presumed that the oxide films may be sintered and integrated with each other through the metal oxide, and the metal particles may adhere to the nitride ceramic or the carbide ceramic.

The metal oxide is preferably at least one selected from lead oxide, zinc oxide, silica, boron oxide (B ₂ O ₃ ), alumina, yttria and titania. 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.

In the present invention, the surface of the heating element is preferably covered with a metal layer. The heating element is a sintered body of metal particles, and if it is exposed, it is easily oxidized and the resistance value changes. Therefore, by coating the surface with a metal layer, oxidation can be prevented. The thickness of the metal layer is
0.1-10 micrometers is desirable. This is because the range is such that oxidation of the heating element can be prevented without changing the resistance value of the heating element.

The metal used for coating may be a non-oxidizing metal. Specifically, at least one selected from gold, silver, palladium, platinum and nickel is preferable.
Of these, nickel is preferable. This is because the heating element needs a terminal for connecting to the power source, and this terminal is attached to the heating element through the brazing material, but nickel prevents the thermal diffusion of the brazing material. A terminal pin made of Kovar can be used as the connection terminal.

As the brazing material, an alloy such as silver-lead, lead-tin or bismuth-tin can be used. The thickness of the brazing material is preferably 0.1 to 50 μm. This is because the range is sufficient to secure the connection with the brazing material. In the present invention, a thermocouple can be embedded in the plate-shaped body if necessary. This is because the temperature of the plate-shaped body can be controlled by measuring the temperature of the plate-shaped body with a thermocouple and changing the voltage and current amount based on the data.

It is also possible to provide a plurality of through holes in the plate-like body, insert the support pins into the through holes, and mount the silicon wafer on the pins. Further, the support pins can be moved up and down to transfer the silicon wafer to the carrier, or to receive the silicon wafer from the carrier.

Next, a method of manufacturing the heater will be described. (1) A step of obtaining a plate-shaped body. Powders of ceramics such as nitride ceramics and carbide ceramics are mixed with a binder and a solvent to obtain a green body. As the above-mentioned ceramic powder, aluminum nitride, silicon carbide or the like can be used, and if necessary, a sintering aid such as yttria may be added. Further, the binder is preferably at least one selected from acrylic binders, ethyl cellulose, butyl cellosolve, and polyvinylal. Further, the solvent is preferably at least one selected from α-terpione and glycol. The paste obtained by mixing these is molded into a sheet by the doctor blade method to produce a green molded body. If necessary, the green body may be provided with a through hole into which a support pin of the silicon wafer is inserted or a recess to embed a thermocouple.

Next, the green body is sintered. When a plain layer is provided, a metal layer is formed on the green body. The metal layer is formed by printing a metal paste. The metal paste contains metal particles, and tungsten or molybdenum is the most suitable as such metal particles. This is because it is difficult to oxidize and the thermal conductivity does not easily decrease. The average particle diameter of the tungsten particles or molybdenum particles is preferably 0.5 to 1.5 μm. This is because it is difficult to print the paste when it is too large or too small. As such a paste, 85 to 97 parts by weight of tungsten particles or molybdenum particles, at least one binder selected from acrylic, ethyl cellulose, butyl cellosolve, and polyvinylal 1.5 to 10 are used.
The tungsten paste or molybdenum paste prepared by mixing 1.5 to 10 parts by weight of at least one solvent selected from parts by weight, α-terpione and glycol is most suitable. Next, the green formed body is further laminated, heated and fired, and sintered to produce a ceramic plate-shaped body. A pressure-free heater plate can be manufactured by pressurizing during heating and firing. The heating and firing may be performed at a temperature equal to or higher than the sintering temperature.
It is 2500 ° C. In the case of providing a plurality of plane layers, a plurality of green molded bodies printed with a metal paste may be laminated. In addition to the method of printing the metal paste, a metal foil may be laminated on the green body, the green body may be further laminated, heated and fired, and then sintered to manufacture a ceramic plate-shaped body. Further, a protective layer is provided. As a method for forming the protective layer, a sol solution prepared by mixing a metal alkoxide with alcohol, water, and an acid is applied by a spin coating method or the like, dried, and then baked at 300 to 1000 ° C. The metal alkoxide undergoes a hydrolytic polymerization reaction by the catalyst to form a sol, and a gel is produced by drying the sol, and a coating layer for the metal oxide film can be provided by firing. As the sol solution,
Metal alkoxide 10-50 parts by weight, alcohol 100
~ 500 parts by weight, water 1 to 50 parts by weight, acid 0.1 to 0.5
A mixture of parts by weight is desirable. As the metal alkoxide, silane-based alkoxide and aluminum-based alkoxide can be used. Tetraethoxysilane and tetramethoxysilane are desirable as the silane-based alkoxide.
Further, aluminum isopropoxide is desirable as the aluminum alkoxide. As alcohol,
Methanol, ethanol, etc. can be used. In addition, the surface of the nitride ceramic is exposed to 0.9 to 1000 ° C. in air at 0.
You may heat-process for 1 to 10 hours and provide a metal oxide layer on the surface. Further, a resin such as polyimide may be used as the protective layer usable in the present invention.

(2) A step of providing a heating element on the plate member. A conductive paste composed of metal particles is printed on the plate. The conductive paste is generally a highly viscous fluid containing metal particles, a resin, and a solvent. This conductive paste is printed by screen printing or the like on the portion where the heating element is to be provided.
Since it is necessary for the heating element to keep the temperature of the entire heater plate uniform, it is desirable to print the heating element in a pattern of concentric circles as shown in FIG. As the conductive paste, a silver paste, a silver / lead paste, the above-mentioned tungsten paste or molybdenum paste can be used.

Further, the conductive paste is sintered by heating to provide a heating element on the surface of the ceramic plate-shaped body. The conductive paste is heated and baked to remove the resin and the solvent and to sinter the metal particles. The heating and firing temperature is 500
~ 1000 ° C. If metal oxide is added to the conductive paste, the metal particles, the ceramic plate and the metal oxide will sinter and be integrated, so the adhesion between the heating element and the ceramic plate Is improved.

Further, it is desirable to coat the surface of the heating element with a metal layer. The coating can be performed by electrolytic plating, electroless plating, or sputtering, but electroless plating is optimal in view of mass productivity. Attach the terminals for connecting to the power supply to the ends of the pattern of the heating element with brazing material. The metal layer is preferably at least one selected from nickel, cobalt and chromium.

After the brazing material paste is printed on the mounting portion, the terminal is placed, and heating is performed for reflow. The heating temperature is preferably 200 to 800 ° C. In addition, thermocouples can be embedded if desired. The thermocouple is preferably chromel-alumel, copper-constantan, or chromel-constantan. Hereinafter, description will be given along with examples.

[0029]

Example 1 SiO ₂ protective layer (1) Aluminum nitride powder (average particle size 1.1 μm) 1
A composition comprising 00 parts by weight, 4 parts by weight of yttria (yttrium oxide having an average particle size of 0.4 μm), 5 parts by weight of an acrylic binder and alcohol was formed with a doctor blade to obtain a green molded body having a thickness of 1.5 mm. It was

(2) A hole for inserting a semiconductor wafer support pin and a recess (not shown) for embedding a thermocouple are provided by drilling the green body. (3) 90 parts by weight of tungsten particles having an average particle diameter of 1 μm, 5 parts by weight of an acrylic binder, and 5 parts by weight of an α-terpione solvent were mixed to prepare a tungsten paste. This tungsten paste is printed on almost the entire surface of the formed body, another formed body on which the tungsten paste is printed is laminated in the same manner, and further, formed bodies on which the tungsten paste is not printed are laminated one by one on top and bottom.
Hot press at 800 ℃, pressure 230kg / cm ² ,
An aluminum nitride plate-like body having a thickness of 3 mm was obtained. This was cut into a circular shape having a diameter of 230 mm to obtain a ceramic plate-shaped body 1 having two plane layers 4 inside. Furthermore, 20.8 parts by weight of tetraethoxysilane and 138 of ethanol
By weight, 23.5 parts by weight of water and 0.3 parts by weight of hydrochloric acid were added to prepare a silica sol solution. This silica sol solution was applied to the surface of the ceramic plate 1 by a spin coater at 1500
The coating was carried out under the conditions of rpm for 20 seconds, dried, and then coated under the same conditions, dried, and then baked at 500 ° C. and 950 ° C. for 1 hour each to form a SiO ₂ film having a thickness of 0.1 μm.
To form a protective layer. The thickness was measured by examining the Si distribution with a fluorescent X-ray analyzer.

(4) A conductive paste was printed on the plate 1 obtained in (3) by screen printing. The print pattern is
The pattern was concentric circles as shown in FIG. As the conductive paste, Solbest PS603 manufactured by Tokuriki Kagaku Kenkyusho was used. This conductive paste is a silver / lead paste and contains a metal oxide. (5) The plate-shaped body on which the conductive paste was printed was heated and baked at 780 ° C. to sinter silver and lead in the conductive paste and to burn the plate-shaped body 1. The pattern of the silver-lead sintered body had a thickness of 5 μm and a width of 2.4 mm.

(6) Nickel sulfate 80 g / l, sodium hypophosphite 24 g / l, sodium acetate 12 g / l,
The plate-like body of (5) was dipped in an electroless nickel plating bath consisting of an aqueous solution of boric acid 8 g / l and ammonium chloride 6 g / l to form a 1 μm thick nickel layer on the surface of the silver-lead sintered body. 5 was deposited to obtain heating element 2.

(7) A tin-lead paste (manufactured by Nippon Solder Co., Ltd.) was printed by screen printing 1 on a portion to which a terminal for securing a connection with a power source was attached to form a brazing material layer. Then, a Kovar-made terminal pin (not shown) was placed on the solder layer, and reflowed by heating at 420 ° C. to attach the terminal pin to the surface of the heating element. (8) A heater 100 was obtained by embedding a plurality of thermocouples for temperature control.

(Example 2) Al ₂ O ₃ protective layer The same as Example 1, except that the SiO ₂ protective layer of Example 1 was replaced by an Al ₂ O ₃ protective layer. As a forming method, the plate-like bodies obtained in (1) to (3) of Example 1 were heated in air at 950 ° C. for 1 hour. The thickness of the Al ₂ O ₃ protective layer was 0.4 μm.

(Comparative Example 1) The same as Example 1 except that no protective layer was provided. For the heaters of Examples 1 and 2 and Comparative Example 1, a silicon wafer was placed and the surface temperature was 60.
After energizing until the temperature reached 0 ° C. and leaving it for 24 hours, it was confirmed whether iron and yttrium (yttrium is an oxide of yttrium) were diffused in the silicon wafer. Confirmation is fluorescent X
A line analyzer (RIGAKU RIX2100) was used. The amount of ammonia eluted by immersing the heater in 1 liter of boiling water at 100 ° C. was measured. further,
For the heater of Example 1, -40 ° C. (1 minute) to 16
After carrying out a heat cycle test at 0 ° C. (1 minute), iron,
The diffusion of yttrium was investigated. The amount of ammonia eluted by immersing the heater in 1 liter of boiling water at 100 ° C. was measured. Further, the adhesive tape was attached to the heating surface of the heater and peeled off, and whether or not the ceramic particles adhered to the adhesive tape was observed with a microscope. The results are shown in Table 1.

[Table 1] The terms “before” and “after” refer to before and after the heat cycle test.
In the heater of Example 1, there was no diffusion of iron and yttrium, and no ammonia was eluted at all, but in Comparative Example 1, 80 ppm of ammonia was detected. Furthermore, after the heat cycle test, 1 liter of the heater of Example 1 was used,
Immersion in boiling water at 100 ° C. showed no elution of ammonia. However, diffusion and ammonia elution were observed in the Al ₂ O ₃ protective layer. Further, in the heaters of Examples 1 and 2, there were no deposits on the adhesive tape, but in the heater of Comparative Example 1, aluminum nitride powder was observed.

[0036]

As described above, the heater of the present invention can prevent the diffusion of contaminant elements. Further, since it is possible to prevent generation of ammonia and prevention of grain breakage, it is most suitable as a heater for heating semiconductor products.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a pattern of a heating element

FIG. 2 is a schematic sectional view of a conventional heater.

FIG. 3 is a schematic sectional view of a heater of the present invention.

FIG. 4 is a schematic sectional view of a heater (conductive layer for electrostatic chuck) of the present invention.

FIG. 5 is a schematic sectional view of a heater of the present invention.

[Explanation of symbols]

1 Ceramic plate 2 heating element 3 protective layer 4 plane layers 5 Conductive layer for electrostatic chuck 100, 101, 102 heaters

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Claims (3)

[Claims] 1. A heater for heating a semiconductor product, wherein a heating element is formed on one side or inside of a plate-shaped body made of a nitride ceramic, and a protective layer is formed on at least a part of the surface of the plate-shaped body. A heater for heating semiconductor products, which is characterized in that 2. The heater for heating a semiconductor product according to claim 1, wherein the protective layer is made of a metal oxide. 3. The protective layer has a thickness of 0.01 to 1
The heater for heating a semiconductor product according to claim 1, wherein the heater has a thickness of μm.