JPH0770491B2 - Ceramics heater for heating semiconductor wafers - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ceramic heater for heating a semiconductor wafer used in plasma CVD, low pressure CVD, plasma etching, a photoetching apparatus and the like.

(Prior art and its problems) In plasma CVD equipment that requires super clean,
A corrosive gas such as a chlorine-based gas or a fluorine-based gas is used as a deposition gas, an etching gas, or a cleaning gas. Therefore, as a heating device for heating the wafer in contact with these corrosive gases, it is possible to use a conventional heater in which the surface of the resistance heating element is coated with a metal such as stainless steel or Inconel. Chloride, oxides, by exposure to gases
Particles such as fluorides and oxides having a particle diameter of several μm are generated, which is not preferable.

Therefore, as shown in FIG. 6, the infrared lamp 20 is installed outside the chamber exposed to the deposition gas and the like, the infrared transmitting window 22 is provided on the outer wall, and the heating target is made of a material having good corrosion resistance such as graphite. An indirect heating type wafer heating device has been developed which emits infrared rays to the body 21 to heat the wafer placed on the upper surface thereof. However, this method has a larger heat loss than the direct heating method, it takes time to raise the temperature, and the infrared transmission window 22
Infrared transmission is gradually hindered by the adhesion of the CVD film to the infrared transmission window 22, heat is absorbed in the infrared transmission window 22 and the window is overheated, and the temperature uniformity of the wafer heating surface and the wafer mounted on the wafer heating surface is poor. There was a problem.

(Process leading to the invention) In order to solve the above problems, it was studied to apply a disk-shaped ceramics heater in which a resistance heating element is embedded inside a ceramics base material to, for example, heating a semiconductor wafer in a thermal CVD apparatus.

However, according to such a heating device, when the resistance heating element is embedded inside the disk-shaped ceramics heater substrate, due to manufacturing problems, the embedded position of the resistance heating element should be viewed in the thickness direction and the radial direction of the substrate. It turns out that it is not always constant. In addition to this, the side surface of the disk-shaped heater is held by a holder such as graphite, but the heat radiation from this side surface is large, and it is difficult to maintain the uniformity of the wafer heating surface.

(Problems to be Solved by the Invention) An object of the present invention is not to cause a problem of contamination such as in the case of a metal heater or a problem such as deterioration of thermal efficiency in the case of an indirect heating method, and further, a semiconductor wafer. It is an object of the present invention to provide a ceramics heater for heating a semiconductor wafer which can enhance the soaking property of the heating surface.

(Means for Solving the Problems) The present invention relates to a plate-shaped ceramics heater having a wafer heating surface, in which a resistance heating element is embedded inside a base material of dense ceramics. Ceramics for heating semiconductor wafers, characterized in that the thickness of the peripheral portion is smaller than the thickness of the central portion, and the thickness between the peripheral portion and the central portion is equal to or less than the thickness of the central portion. It relates to the heater.

(Embodiment) FIG. 1 is a schematic sectional view showing a state in which a ceramic heater for heating a semiconductor wafer according to an embodiment of the present invention is attached to a chamber 1.

In FIG. 1, 1 is a chamber used for thermal CVD for semiconductor manufacturing, 6 is a plate-shaped ceramic heater body for heating a wafer, which is attached to a holder 3 inside the chamber, and its size is, for example, 4 to 8 The size of the wafer is set so that it can be installed in inches.

Gas for thermal CVD is supplied to the inside of the chamber 1 from the gas supply hole 4, and the air inside is exhausted from the suction hole 5 by a vacuum pump. The heater body 6 is a dense, gas-tight ceramic base material such as silicon nitride, in which a resistance heating element 2 of tungsten type is embedded in a spiral shape, and from the outside via a cable 8 at the central portion and the end portion. Electric power is supplied and the heater body 6 can be heated to, for example, about 1100 ° C. Reference numeral 9 is a flange with a water cooling jacket 10 that covers the upper surface of the holder 3, and is sealed between the side wall of the chamber 1 by an O-ring 11 and constitutes the ceiling surface of the chamber 1.

A thermocouple 14 with a stainless steel sheath is inserted into a hollow sheath 12 that is inserted into the chamber 1 through the wall surface of the flange 9 of the chamber 1. Semiconductor wafer W
Is supported from below by a chuck or a pin (not shown), and is heated by heat from the wafer heating surface 6a.

The plate-shaped ceramics heater 6 has a circular plane shape and has a central portion.
At 50, the wall thickness is the largest, and at the peripheral edge portion 30, the wall thickness is extremely small, and the peripheral edge portion 30 holds it by the holder 3. From the central part to the peripheral part, a smooth continuous curve is drawn when viewed in cross section.

According to the heating device of the present embodiment, there is no problem such as contamination as in the case of the metal heater or the indirect heating method. And
Since the wall thickness at the peripheral edge portion 30 is much smaller than the wall thickness at the central portion 50, it is possible to suppress the radiation of heat from the peripheral edge portion 30, and thus the uniform heating at the wafer heating surface 6a can be achieved. Can be increased. That is, by reducing the surface area of the heater peripheral part and reducing the radiation area of this part, the heat loss to the side of the heater is minimized, and as a result, between the central part and the peripheral part of the wafer heating surface 6a. The temperature difference could be kept small.

In particular, if the resistance heating element is embedded evenly inside the disk-shaped ceramics heater with a constant wall thickness and each part of the resistance heating element is made to generate heat evenly, the heat radiation area is small inside and the radiation area is large around the periphery. Often, a gentle temperature decrease curve is drawn from the inner circumference to the outer circumference. In this sense, in this embodiment, the wall thickness is gradually reduced from the central portion 50 toward the peripheral portion 30, and the sectional curve of the heater back surface 6b is a gentle curve. This is effective in counteracting the gentle temperature decrease from the inner peripheral portion to the outer peripheral portion and implementing more precise soaking.

The material of the plate-shaped ceramic heater 6 needs to be a dense body in order to prevent adsorption of the deposition gas, and a material having a water supply rate of 0.01% or less is preferable. Although it is not subjected to mechanical stress, it is required to have thermal shock resistance that can withstand heating and cooling from room temperature to 1100 ° C. From these points, it is most preferable to use silicon nitride and sialon, which are ceramics having high strength at high temperature.

As the resistance heating element 2 embedded in the ceramic heater 6, it is suitable to use tungsten, molybdenum, platinum, or the like, which has a high melting point and has excellent adhesion to silicon nitride. Further, since the lead portion 8 is exposed to the vacuum gas, it is necessary to lower the temperature of the contact portion as much as possible. Further, by coating the lead portion 8 with CVD, the corrosion resistance can be improved.

The following method can be used to manufacture the ceramic heater 6 having a smooth curved surface (back surface) 6b.

(1) First, a disk-shaped ceramics heater (having a constant wall thickness) in which the resistance heating element 2 is embedded is manufactured, and the disk-shaped ceramics heater is manufactured by grinding it with a numerical control machine tool.

(2) It is manufactured by integral sintering with a hot isostatic press or the like.

2 to 5 are sectional views showing plate-shaped ceramic heaters according to other examples. Each of these ceramic heaters is held by the holder 3 (not shown) at the peripheral edge portion 30 and can be manufactured by the methods (1) and (2).

In the ceramic heater 16 of FIG. 2, the resistance heating element 2 is embedded inside a conical base material having the wafer heating surface 16a as the bottom surface, and the thickness of each part of the heater is from the central portion 50 to the peripheral portion. It decreases linearly toward 30. Therefore, since it is possible to suppress the heat loss to the side of the heater and evenly radiate the heat from each portion, the same effect as that of the heating device of FIG. 1 can be obtained.

In the ceramic heater of FIG. 3, basically, the disk-shaped ceramic heater has a trapezoidal cross section, and the side surface (the surface in contact with the holder) 80 is an inclined surface to reduce the area of the side surface 80. Wafer heating surface
We are trying to make the temperature of 26a uniform. In addition, 26b is the back of the heater.

In the example of FIG. 3, without using a complicated, time-consuming, and costly processing method using a numerical control industrial machine,
There is an advantage that it can be done only by grinding, and soaking property can be easily ensured.

In the plate-shaped ceramics heater shown in FIG. 4, an example in which the thickness is further reduced stepwise is shown. That is, the central portion 50
In the vicinity, a thick portion 36b having a relatively large thickness is provided, and the thick portion 3b
On the outer periphery of 6b, a thick part where the wall thickness decreases comparatively gently
36c is provided, and the wafer heating surface 36a is soaked by such two-step discontinuous thickness control.

In the modified example of the first embodiment, the heat radiation area from the side surface is reduced in the side peripheral portion as in the first embodiment, and the heat capacity of the heater itself is reduced to improve the response of the heater in the vicinity of the central portion that does not affect the thermal uniformity. ing.

In addition, in FIG. 4, it is possible to discontinuously change the heater wall thickness in three or more steps.

The example of FIG. 5 is similar to that of FIG. 1 in that the heater wall thickness is gently reduced from the central portion 50 to the peripheral portion 30 of the plate-shaped ceramic heater 46.
Unlike the example of FIG. 1, the shape is not symmetrical, and a thin portion 46c having a smaller thickness is provided on the left side in FIG.

For example, when the resistance heating element 2 is embedded inside the ceramic substrate, the resistance heating element may be displaced to the right side as shown in FIG. 5, for example, and in this case, the heating value on the right side of the heater is increased. Is larger and smaller on the left. Therefore, by providing the thin portion 46c on the left side of the heater, the heat radiation from the side at this portion can be further reduced, which is effective in soaking the wafer heating surface 46a.

The planar shape of the plate-shaped ceramics heater may be a quadrangle, a hexagon, etc., in addition to a circle.

Specific examples will be described below.

First, a resistance heating element 2 made of tungsten was embedded inside a disk-shaped base made of a silicon nitride raw material containing a yttria + alumina-based sintering aid. The resistance heating element 2 has a wire diameter of 0.4 mm and a length of 2.5 m or less.
It is a spiral wound. A tungsten wire having a diameter of 2 mm was used as a wire terminal forming the lead portion 8.

Such a resistance heating element 2 was embedded in a spiral shape in the whole disk-shaped base material and was ground so as to have the shape shown in FIG. This ceramic heater has a conical shape with a diameter of 150 mm and a height of 20 mm. The resistance heating element is 4m from the heating surface of the semiconductor wafer.
It was buried at a depth of m. Regarding the embedding position of the resistance heating element, 5mm, 15mm, 2mm from the center of the heating surface of the semiconductor wafer.
The positions of 5 mm, 35 mm, 45 mm, and 55 mm were embedded so that the resistance heating element wound in a spiral shape could pass through.

Further, a disk-shaped ceramics heater having a diameter of 150 mm and a height of 20 mm was produced in the same manner as above. The material and the embedding position of the resistance heating element were the same as above.

While the heater power source grounds the outer wire terminal,
A voltage is applied to the wire terminal on the center side to further reduce the voltage to prevent discharge in a vacuum, and the power supply is controlled by a thyristor.

Such a heating device was attached to the chamber 1 as shown in FIG. 1 and a wafer heating test in vacuum was conducted. That is,
For each of the above-mentioned conical ceramics heater and conical ceramics heater, on the wafer heating surface
A 4 ^B silicon wafer was placed, and the temperature distribution of this silicon wafer was measured by a thermal imager. The results are shown in FIG. In FIG. 7, the horizontal axis represents the distance from the center of the silicon wafer, and the vertical axis represents the temperature of the silicon wafer. A solid line graph A shows a temperature distribution when a conical ceramics heater is used, and a broken line graph B shows a temperature distribution when a disk-shaped ceramics heater is used. C indicates the range (size) in which the silicon wafer exists. Comparing the graphs A and B, the slope of the graph A is smaller. Then, comparing the temperature difference ΔT at the distances of 0 mm and 50 mm, in graph A, ΔT =
8.7 ° C, and in graph B, ΔT = 11.9 ° C. Therefore, the conical ceramics heater has higher thermal uniformity.

In the indirect heating method, by heating the susceptor,
Both in the case of heating the wafer mainly by conduction and in the case of heating only the wafer by radiation, since infrared converging heating is used, it becomes spot heating and lacks soaking property in a wide range of diameter φ150 mm. Actually, the thermal gradient was about 1100 ° C. ± 4% in the range of diameter 150 mm.

(Effect of the Invention) According to the ceramic heater for heating a semiconductor wafer according to the present invention, since the resistance heating element is embedded inside the base material of the dense ceramics, there is no problem of contamination as in the case of the conventional metal heater. Does not happen. Further, since the plate-shaped ceramics heater has the wafer heating surface, the problem of deterioration of thermal efficiency unlike the case of the indirect heating method does not occur.

The thickness of the peripheral portion of the plate-shaped ceramics heater was made smaller than the thickness of the central portion, and the thickness between the peripheral portion and the central portion was also set to be equal to or less than the central portion. That is, in the case of the flat plate-shaped ceramic heater, the temperature of the base material was gradually decreased from the central portion to the side peripheral surface due to heat radiation from the peripheral portion, that is, the side peripheral surface. However, by making the thickness of the peripheral portion smaller than the thickness of the central portion, it is possible to reduce the surface area in the vicinity of this peripheral portion as compared with the surface area of the peripheral portion of the flat plate-shaped ceramic heater, and The heat radiation area in the peripheral portion can be reduced. Therefore, the heat loss to the side of the heater can be minimized, the temperature difference between the central portion and the peripheral portion of the wafer heating surface can be reduced, and uniform heating can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a state in which a plate-shaped ceramics heater is attached to a container, FIGS. 2, 3, 4, and 5 are sectional views showing other plate-shaped ceramics heaters, respectively. FIG. 7 is a cross-sectional view showing a wafer heating device by an indirect heating method, and FIG. 7 is a graph showing the relationship between the distance from the center of the silicon wafer and the temperature. 2 ... Resistance heating element 3 ... Holder 6,16,26,36,46 ...... Plate ceramic heater 6a, 16a, 26a, 36a, 46a …… Wafer heating surface 6b, 16b, 26b …… Back surface 30… ... peripheral area 50 ... central area

Claims (7)

[Claims] 1. A disk-shaped ceramics heater having a wafer heating surface in which a resistance heating element is embedded inside a dense ceramics substrate, wherein the peripheral wall thickness of the disk-shaped ceramics heater is the central portion. And a thickness between the peripheral portion and the central portion is equal to or less than the thickness of the central portion, the ceramic heater for heating a semiconductor wafer. 2. The ceramic heater for heating a semiconductor wafer according to claim 1, wherein the thickness of the plate-shaped ceramic heater gradually decreases from the central portion toward the peripheral portion. 3. The ceramic heater for heating a semiconductor wafer according to claim 2, wherein the base material has a conical shape. 4. The cross-sectional shape of the base material is trapezoidal,
The ceramic heater for heating a semiconductor wafer according to claim 1, wherein the side surface of the base material is an inclined surface. 5. A thick portion having a relatively large thickness is provided on the center side of the base material, and a thin portion having a relatively small thickness is provided on the peripheral edge side of the base material. The ceramic heater for heating a semiconductor wafer according to claim 1, wherein 6. The ceramic heater for heating a semiconductor wafer according to claim 1, wherein the substrate has a substantially circular planar shape. 7. The ceramic heater for heating a semiconductor wafer according to claim 1, wherein the dense ceramic is silicon nitride or sialon.