JP2644650B2 - Ceramic heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to plasma CVD and reduced pressure CV.
D, a ceramic heater which can be suitably used in a normal pressure CVD, plasma etching, light etching apparatus and the like.

[0002]

2. Description of the Related Art In a semiconductor manufacturing apparatus requiring a super clean state, corrosive gases such as chlorine-based gas and fluorine-based gas are used as a deposition gas, an etching gas, and a cleaning gas. For this reason, when a conventional heater in which the surface of a resistance heating element is coated with a metal such as stainless steel or Inconel is used as a heating device for heating a wafer in a state of being brought into contact with these corrosive gases, these gases are used. Exposure generates undesirable particles having a particle size of several μm, such as chlorides, oxides and fluorides.

[0003] Therefore, an infrared lamp is installed outside the container exposed to the deposition gas or the like, an infrared transmission window is provided on the outer wall of the container, and infrared rays are radiated to a heated body made of a material having good corrosion resistance such as graphite. A wafer heating apparatus of an indirect heating method for heating a wafer placed on an upper surface of an object to be heated has been developed. However, in this method,
The heat loss is larger than that of the direct heating type, the time required for temperature rise is longer, and the attachment of the CVD film to the infrared transmission window gradually impedes the transmission of infrared rays, causing heat absorption in the infrared transmission window. There were problems such as abnormal heating of the windows.

[0004]

In order to solve the above-mentioned problems, the present inventors newly buried a resistance heating element in a disk-shaped dense ceramic and held the ceramic heater in a graphite case. The heating device was studied. As a result, it has been found that this heating device is an extremely excellent device that has eliminated the problems described above.

[0005] In a heater in which a resistor is embedded in a stainless steel case, even if the heating part is at a high temperature, the electrode part of the heater can be provided outside the low temperature vessel. However, in the above ceramic heater, since the resistance heating element is put into the ceramic powder and press-molded,
The shape must be a simple shape such as a disk shape, and the same applies because the hot press firing is performed even in the firing stage. In addition, the surface of the fired body after firing has a fired deteriorated layer called black scale, and it is necessary to remove this deteriorated layer by processing. At this time,
Grinding with a diamond grindstone is required, and a complicated shape increases the cost. As described above, a ceramic heater in which a resistance heating element is embedded must have a simple shape such as a disk shape due to manufacturing difficulties. Due to its structure, the terminals of the heater are inevitably exposed to high temperatures and corrosive gases. Will be.

[0006] In order to solve this problem, the present applicant has disclosed in Japanese Patent Application No. 2-197817 (filed July 27, 1990, unpublished at the time of filing of this application) a method of forming a disc-shaped substrate made of dense ceramics. The resistance heating element and the columnar terminal are buried, the resistance heating element and the columnar terminal are electrically connected, and the columnar terminal is exposed to the back surface of the disk-shaped base. Are disclosed by a heat-resistant and corrosion-resistant bonding method. These ceramic heaters
In particular, it was extremely effective in a reduced pressure (CVD) apparatus.

[0007] However, it has been newly found that there are cases where such a ceramic heater cannot be used. That is, for example, in a normal pressure CVD apparatus, an oxide film is formed on the surface of a semiconductor wafer by oxygen gas and ozone gas. On the other hand, ceramic heaters for semiconductor devices as described above are intended to be used at a high temperature of usually 400 ° C. or higher, and sometimes 1100 ° C. or higher. Must be used. However, for example, when a tungsten wire is buried inside a disk-shaped substrate, and a ceramic heater is placed in the atmosphere and heated to 400 ° C. or higher, the cylindrical terminals and the resistance heating element made of tungsten are oxidized and disconnected, and the ceramic heater is disconnected. Stopped working.

The present inventor has studied a technique of joining the above-mentioned cylindrical terminal and the electrode body with titanium-evaporated silver solder and covering the exposed surface of the cylindrical terminal with titanium-evaporated silver solder. However, it was found that when the temperature of this portion exceeded 600 ° C., the titanium component and the silver component were oxidized, the bonding strength of the wax was lost, and the coating effect was lost.

[0009] The object of the present invention is to provide the above-mentioned technical background, and furthermore, even when heated to 400 ° C. or more in an apparatus using an oxidizing atmosphere such as a normal pressure CVD apparatus.
An object is to prevent oxidation and disconnection of a resistance heating element and a terminal, and corrosion of a joint portion between a terminal and an electrode body.

[0010]

SUMMARY OF THE INVENTION The present invention provides a substrate formed of dense ceramics; a resistance heating element made of a high melting point metal embedded inside the substrate; and an end portion of the resistance heating element. A terminal that is electrically connected and buried in the base and is exposed to the base; a power supply member heat-bonded to the terminal; and a power supply member installed on the base and including at least the terminal and the heat-resistant joint. The present invention relates to a ceramic heater having a hollow covering material for covering, and configured so that a non-oxidizing gas can be filled inside the covering material.

In the above, the term "heat-resistant bond" means a bond that is stable against repeated temperature drop and temperature rise between room temperature and heater operating temperature. Specifically, it consists of bonding via a high melting point bonding layer and mechanical bonding.
In the case of a conventional stainless steel heater, the heating surface of the semiconductor wafer and the terminal of the resistance heating element are largely separated, and the terminal and the external electrode cable are connected outside the container of the semiconductor manufacturing apparatus. On the other hand, in the ceramic heater according to the present invention, the periphery of the terminal is exposed to a high temperature. Therefore, in order to obtain a ceramic heater with excellent durability and reliability, the melting point of the high melting point bonding layer must be higher than the surface temperature of the heater, and the mechanical bonding is exposed to thermal changes. After that, sufficient bonding strength must be maintained.

The bonding via the high melting point bonding layer includes the following. (1) A high melting point metal powder such as Mo or W is interposed between the massive terminal and the power supply member and diffusion bonded. (2) Join with brazing material. (3) Diffusion bonding with foil interposed. (4) A coating layer is formed on the end face of the block terminal or the end face of the power supply member by plating, CVD, thermal spraying, etc., and then diffusion bonding or friction welding is performed. (5) Welding. Mechanical coupling methods include press-fitting, threading, caulking,
There are embedding and insertion.

[0013]

FIG. 1 is a schematic partial sectional view showing a ceramic heater according to an embodiment of the present invention. Disc-shaped substrate 2
Is made of a dense and gas-tight ceramic, and has a slight step on its side peripheral surface. A resistance heating element 5 is embedded in the disk-shaped base 2. In the present embodiment, the resistance heating element 5 is a linear body, is embedded in a spiral shape when viewed in plan, and is spirally wound when viewed microscopically.
Both ends of the resistance heating element 5 are respectively connected to and electrically connected to the block terminals 6A.

Each block terminal 6A has a shape such as a columnar shape, a quadrangular prism shape, a hexagonal prism shape, or the like. Each block terminal 6A is embedded in the disk-shaped base 2, and the end face of the block terminal 6A is
A female screw 6a is provided to be exposed on the side. Disc-shaped substrate 2
The concave portion 3 is formed on the wafer heating surface 2a side, and the semiconductor wafer W is installed on the wafer heating surface 2a side. A through hole 4 is formed in the center of the disc-shaped base 2, and the through hole 4 communicates with the recess 3. The concave portion 3 is covered with the semiconductor wafer W, and gas is sucked from the through hole 4 as shown by the arrow A, and the semiconductor wafer W is chucked to the wafer heating surface 2a.

The substantially cylindrical hollow covering material 8 is
It is installed on the back surface 2b so as to cover the exposed surface of. An annular packing 9 is interposed between the covering material 8 and the back surface 2b. In this embodiment, a bolt-shaped electrode body 7A is used. The head 7a of the electrode body 7A protrudes outside the coating material 8, and the columnar shaft 7b penetrates the wall surface of the coating material 8 and is inserted into the inner space 8a. A male screw 7c is formed at the tip of the shaft 7b.
Then, the male screw 7c is fitted to the female screw 6a to fix the electrode body 7A.

The covering member 8 covers the exposed portion of the massive terminal 6A, the shaft 7b of the electrode body 7A, and the joint portion between them. A supply pipe 10 for a non-oxidizing gas is provided on a side surface of the coating material 8.
A lead wire 12 is connected to the head 7a of the electrode body 7A, and the pair of lead wires 12 is connected to an AC power supply 13.

A non-oxidizing gas is supplied from the supply pipe 10 as shown by arrow B, and the inner space 8a is pressurized. In the present embodiment, the packing 9 is a ring formed of a heat-resistant metal, and the space between the back surface 2b and the packing 9 is not completely airtightly sealed. Therefore, as indicated by arrow C, the non-oxidizing gas gradually leaks. In this way, by flowing the non-oxidizing gas in one direction, it is possible to prevent external oxygen gas, ozone gas, halogen gas and the like from entering the inner space 8a.

The material of the disk-shaped substrate 2 is silicon nitride,
Sialon, aluminum nitride and the like are preferable, and silicon nitride and sialon are more preferable in terms of thermal shock resistance. It is appropriate to use tungsten, molybdenum, platinum, tungsten carbide, or the like, which has a high melting point and excellent adhesion to silicon nitride or the like, as the material of the resistance heating element 5 and the bulk terminal 6A.

The coating material 8 is preferably formed of a material having resistance to a high-temperature oxidizing atmosphere, and such a material is preferably nickel, inconel, quartz or the like. Electrode body 7A
Is formed of a conductive material that is resistant to a high-temperature oxidizing atmosphere. As such a material, nickel, inconel, platinum and the like are preferable. The packing 9 is preferably formed of a heat-resistant soft metal, such as nickel, platinum, or gold.

When manufacturing a disc-shaped ceramic heater, a resistance heating element 5 provided with a block terminal 6A in advance is embedded in a ceramic molded body, and the ceramic molded body is sintered.
The disk-shaped substrate 2 thus obtained is ground to expose the end face of the massive terminal 6A. When the bulk terminal 6A is formed of tungsten, it is impossible to process with a normal die because tungsten is very hard and brittle. Therefore, thread cutting was performed, particularly by electric discharge machining. In electric discharge machining, machining is performed by causing an electric discharge phenomenon between an electrode and a workpiece, so that the workpiece must be a conductor, and the workpiece needs to be used as an electrode. In this ceramic heater, the resistance heating element 5 itself is used as a current path,
By passing a current from the bulk terminal 6A that is not processed, the embedded bulk terminal 6A is threaded. According to the ceramic heater of this embodiment, it is possible to solve the problems of contamination as in the case of the conventional metal heater and deterioration of the thermal efficiency as in the case of the indirect heating method.

The joint between the bulk terminal 6A and the electrode body 7A is repeatedly exposed to heating and cooling to a high temperature. In this regard, in the present embodiment, since these are screwed together, the joint portion is stably held against heat.

Further, the back of the disc-shaped ceramic heater
An oxidizing gas and various corrosive gases enter the 2b side.
In this regard, in the present embodiment, since the non-oxidizing gas is filled in the inner space 8a of the covering material 8, the end face of the massive terminal 6A,
Neither the joint between the massive terminal 6A and the electrode body 7A nor the minute gap between the massive terminal 6A and the base 2 are exposed to oxidizing gas or corrosive gas. Therefore, these members and the resistance heating element 5 do not oxidize or corrode.

The non-oxidizing gas is preferably an inert gas such as nitrogen gas or argon gas, a reducing gas such as H _2, a halogen gas such as I _2, or a mixture thereof. Oxygen may be mixed into the non-oxidizing gas as an unavoidable impurity, but also in this case, the oxygen concentration is preferably set to 100 ppm or less.

FIG. 2 is a sectional view of a main part of the ceramic heater in which the electrode body 7B and the bulk terminal 6B are diffusion-bonded.
The same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The shape of the block terminal 6B can be, for example, a columnar shape, a quadrangular prism shape, a hexagonal prism shape, or the like. The end of the resistance heating element 5 is connected to the massive terminal 6B.

The flat end face 6b of the block terminal 6B is exposed on the back face 2b. On the other hand, the bolt-shaped electrode body 7B includes a head 7a and a shaft 7b, and the shaft 7b is not provided with a male screw. A thin layer 14 of powder made of a high melting point metal is interposed between the end face 6b of the massive terminal 6B and the tip face of the shaft 7b. Heating is performed in this state to form a diffusion bond. This heating is preferably performed in a non-oxidizing atmosphere in order to prevent the ceramic from deteriorating.

As the powder for forming the thin layer 14, in addition to W powder, for example, Mo, Pb, Ni, Fe, Co, Mn, Au, P
Examples of powders of metals such as t, Y, Ag, Cu, Zr, Cr, Nb, Ti, V, and Ta, whose melting points are not less than (heating element use temperature + 200 ° C.). In addition, even if a metal foil or a coating layer made of these refractory metals is used instead of the powder thin layer,
It has been found that good diffusion bonding can be formed by selecting an appropriate sintering temperature.

In order to reduce the stress due to thermal expansion, it is preferable to use a material having a thermal expansion coefficient equal to that of the bulk terminal or the electrode body as much as possible. When both the bulk terminal and the electrode body are formed of tungsten, it is optimal to use tungsten powder of the same material. Alternatively, the stress may be relaxed by using a soft metal such as gold or nickel. As a method of joining via a joining layer, in addition to the above-described diffusion joining, a method of providing a metal coating layer on a joining surface of a massive terminal or an electrode body and joining by friction welding may be used.

Further, the bulk terminal and the electrode body could be mechanically connected by the press-fitting method. Figure 3 shows a block terminal
FIG. 9 is a cross-sectional view of a main part showing a ceramic heater in which 6C and a bolt-shaped electrode body 7C are joined by a press-fitting method. FIG.
The same reference numerals are given to the same parts as those shown in FIG.

The bolt-shaped electrode body 7C includes a head 7a and a shaft 7b, and a tip of the shaft 7b is formed with, for example, a columnar projection 7d. In addition, a concave portion 6c also having a columnar shape is formed on the exposed surface side of the massive terminal 6C. The results of the actual press-fitting will be described. The bulk terminal 6C and the electrode body 7C were both formed of tungsten. The dimensions of the projection 7d were 3 mm in diameter and 6 mm in length. The dimensions of the recess 6c were 3 mm in diameter and 7 mm in length. When press-fitting was performed at a press-fitting pressure of 1000 kgf / cm ² , a strong bonding state was obtained even when the cooling / heating cycle between room temperature and 800 ° C. was performed 1000 times within the range of interference of 0 to 50 μm. If the interference falls outside this range, loosening may occur,
Cracks occurred in the tungsten terminal.

Before the protrusion 7d is pressed into the recess 6c, a high melting point metal foil can be sandwiched between the two. Further, after the above-described press-fitting or screwing, a high-melting-point metal can be poured between the massive terminal and the electrode body to close a gap between both members.

FIG. 4 is a schematic partial sectional view showing a ceramic heater of another embodiment. Since the overall configuration of the present ceramic heater is substantially the same as that shown in FIG. 1, only the differences will be described. The wafer heating surface 2a of the disc-shaped substrate 2 is flat, and the semiconductor wafer W is set on the wafer heating surface 2a. In the ceramic heater shown in FIG. 1, the semiconductor wafer W is attracted to the wafer heating surface 2a by depressurizing the concave portion 3 and chucked. Therefore, this type of ceramic heater
It cannot be used in a low pressure CVD apparatus or the like in which the degree of vacuum is 1 torr or less. On the other hand, in the ceramic heater shown in FIG. 4, the semiconductor wafer W is chucked by a mechanical chuck or the like.

Next, an actual operation example will be described. FIG.
The following ceramic heater was produced. The disk-shaped substrate 2 was formed from silicon nitride. The resistance heating element 5 and the bulk terminal 6A were formed of tungsten. The electrode body 7A and the covering material 8 were formed by Inconel 600. The packing 9 was formed from nickel. Nitrogen gas having an oxygen concentration of 100 ppm or less was used as the non-oxidizing gas. The supply pressure
1.5 atm. The ceramic heater was held in the air, and the resistance heating element 5 was energized and heated to 1000 ° C., but no disconnection of the resistance heating element 5, an increase in the resistance value, and no change in the heat generation amount were observed.

On the other hand, in FIG. 1, the coating material 8, the packing 9, and the supply pipe 10 were removed. Otherwise, the resistance heating element was energized in the same manner as described above to increase the temperature of the wafer heating surface. As a result, when the temperature reached 450 ° C., the resistance heating element 5 was disconnected.

In FIG. 1, the coating material 8 was formed of silicon nitride, and the packing 9 was formed of platinum. Other than that, when the temperature of the wafer heating surface was increased in the same manner as above, even when the temperature was increased to 1300 ° C., no disconnection of the resistance heating element and no change in the resistance value were observed.

FIG. 5 is a schematic sectional view showing a ceramic heater according to another embodiment. Only the right half of the entire ceramic heater is shown because of the dimensional restrictions in the drawing. On the back surface 2b side of the disc-shaped base 2A, the female screw 6a of the massive terminal 6A
Is exposed. A circular covering material 18 is provided on the back surface 2b in a plan view. The plane dimension of the covering material 18 and the dimension of the back surface 2b are made substantially the same. The packing 9 is interposed between the periphery of the covering material 18 and the periphery of the back surface 2b. The small projection 15a at the end of the presser 15 is hooked on the small projection 2c on the side peripheral edge of the disc-shaped base 2A. Fix the flange 15b of the presser 15 to a flat
Make them face almost parallel to 16. The retainer 16 is brought into contact with the lower surface of the coating material 18, and the flange 15 b and the retainer 16 are
Connect with. As a result, the disc-shaped base 2A and the covering material 18 are integrated so as not to be separated from each other.

The power supply lead 19 has a substantially L-shaped cross section, and includes a vertically extending portion 19a and a horizontally extending portion 19b in FIG. The vertical portion 19a is inserted into the through hole 18b of the covering material 18. The horizontal portion 19b extends substantially parallel to the back surface 2b. Then, the tip of the horizontal portion 19b is fixed to the massive terminal 6A with a bolt 7D. The lead wire 12 is connected to the lead 19 to supply AC power. A supply pipe 10A is provided, for example, near the center of the coating material 18. A non-oxidizing gas is supplied from the supply pipe 10A as shown by an arrow B, and the inner space 18a is filled with the non-oxidizing gas. The non-oxidizing gas slightly leaks from the annular packing 9 as shown by the arrow C.

The ceramic heater shown in FIG. 5 was manufactured and operated. The packing 9 was formed of nickel. The coating material 8 was formed of quartz gas. Holder is Inconel 600
Formed. When nitrogen gas was used as a non-oxidizing gas and the ceramic heater was heated to 1000 ° C., a slight amount of nitrogen gas leaked from the packing 9, but no oxidation of the massive terminals 6A was observed. In each of the above examples, the shape of the disk-shaped substrate is preferably disk-shaped in order to uniformly heat the circular wafer, but may be other shapes, for example, square disk-shaped or hexagonal disk-shaped. In each of the above examples, the block terminals 6A, 6B,
Although 6C is provided on the back surface 2b side, it may be provided on the side peripheral surface of the disk-shaped substrate, or may be provided on a surface other than the wafer installation surface.

[0038]

According to the present invention, since a resistance heating element made of a high melting point metal is buried inside a base made of dense ceramics, contamination such as in the case of a metal heater and indirect heating can be achieved. The problem of deterioration in thermal efficiency as in the case of the method can be solved. In addition, since the power supply member is heat-resistant bonded to the terminal exposed on the surface of the base, even if heating and cooling to a high temperature are repeated, power can be stably supplied to the resistance heating element. it can. In addition, a hollow covering material is provided on the base to cover at least the terminals and the heat-resistant joint, and the inside of the covering material is filled with a non-oxidizing gas.
Accordingly, neither the exposed surface of the terminal nor the above-mentioned heat-resistant joint is oxidized or corroded, especially at high temperatures. Therefore, the ceramic heater can be heated to a high temperature even in an apparatus using an oxidizing gas or a corrosive gas.

[Brief description of the drawings]

FIG. 1 is a schematic partial sectional view showing a ceramic heater according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part showing another ceramic heater.

FIG. 3 is a cross-sectional view of a main part showing still another ceramic heater.

FIG. 4 is a schematic partial sectional view showing a ceramic heater according to still another embodiment.

FIG. 5 is a schematic partial sectional view showing a ceramic heater according to still another embodiment.

[Explanation of symbols]

 2 Disc-shaped substrate made of dense ceramics 2a Wafer heating surface 2b Back surface 5 Resistance heating element made of high melting point metal 6A, 6B, 6C Bulk terminal 7A, 7B, 7C Bolt-shaped electrode body 8 Hollow coating material 8a Coating Inner space of material 9 Packing 19 Lead B, C Flow of non-oxidizing gas

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Claims (2)

(57) [Claims] 1. A substrate formed of dense ceramics; a resistance heating element made of a high melting point metal buried inside the substrate; and said substrate electrically connected to an end of the resistance heating element. Embedded in the terminal and exposed to the substrate;
A power supply member heat-bonded to the terminal; and a hollow covering material installed on the base and covering at least the terminal and the heat-resistant coupling portion, and a non-oxidizing gas is provided inside the covering material. A ceramic heater configured to be able to fill. 2. The method according to claim 1, wherein the non-oxidizing gas is gradually injected into the coating material while being pressurized, and the non-oxidizing gas is gradually leaked from between the coating material and the base. The ceramic heater according to claim 1, wherein