JPH04324928A - Heat treatment furnace - Google Patents

Abstract

PURPOSE:To enable the wafers to be excellently oxidized and diffused by a method wherein a heavy metal is prevented form permeating into a furnace core to avoid the pollution of wafers by the metal. CONSTITUTION:The title heat treatment furnace is composed of a thermal resistant quartz tube 1 comprising a furnace core tube, an equalizer 2 formed of a compound of SiC and Si (18%) and heaters 3 formed of Cr-Fe alloy around the outer periphery of said equalizer 2. Next, within an oxidation diffusion furnace A1 (a) to oxidize and diffuse the wafers 5 inside the quartz tube 1 containing a quartz boat 4 whereon multiple wafers 5 to be heat-treated are placed stand in a row and then the quartz tube 1 is heated by the heaters 3 while precisely controlling the temperature of the tube 1 in such a state, a SiC film 6 about 100mum thick is formed on the inner surface of the equalizer 2 e.g. by CVD process.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to heat treatment furnaces, especially oxidation and
Regarding the structure of a diffusion furnace.

0002

2. Description of the Related Art A conventional oxidation/diffusion furnace is constructed by disposing a heater 22 around the outer periphery of a heat-resistant quartz tube 21, as shown in FIG. Then, a large number of wafers 24 to be processed are vertically arranged on a quartz boat 23 and housed in a quartz tube 21, and in this state, a heater 22 is heated while precisely controlling the temperature.
By heating the quartz tube 21, the wafer 24 inside the quartz tube 21 is subjected to oxidation and diffusion treatment.

However, during this oxidation/diffusion process, heavy metals generated from the heater 22 enter the quartz tube 21 through the heater 22 and contaminate the wafer 24, which is disadvantageous. If the wafer 24 is contaminated with heavy metals during this oxidation/diffusion process, various problems occur, such as deterioration of carrier lifetime and reliability of the oxide film.

Therefore, conventionally, as shown in FIG.
A soaking tube 25 made of a material with excellent heat resistance, corrosion resistance, and abrasion resistance is prepared, a quartz tube 21 is housed in the soaking tube 25, and a heater 22 is arranged around the outer periphery of the soaking tube 25. I try to do that. As the material for this soaking tube 25, a material having a small diffusion coefficient with respect to metal impurities, such as S.
By using iC-based material, the quartz tube 21
This is to prevent heavy metals from entering.

[0005]

By the way, when producing the above-mentioned soaking tube 25, since SiC alone cannot be formed, it is formed by impregnating it with about 18% Si. As shown in Table 1, SiC itself has a very small diffusion coefficient for metal impurities, but since Si is included, the overall diffusion coefficient is not small.

[Table 1] Therefore, in the conventional oxidation/diffusion furnace, heavy metals from the heater 22 etc. cannot be effectively blocked by the soaking tube 25, and metal contamination on the wafer 24 cannot be suppressed. be.

The present invention has been made in view of the above problems, and its purpose is to provide a heat treatment that can prevent metal contamination of wafers and can perform oxidation and diffusion treatment on wafers in a good manner. The goal is to provide a furnace.

[0007]

[Means for Solving the Problems] The present invention provides a quartz tube 1 (quartz tubes 1a and 1a having different diameters, respectively) in which a wafer to be processed 5 is housed.
1b) and the quartz tube 1
In the heat treatment furnace A, which has a soaking tube 2 that accommodates a heat soaking tube 2 and a heater 3 arranged around the heat soaking tube 2, the inner or outer surface of the heat soaking tube 2 is coated with a dense material having a small diffusion coefficient for metal impurities. It is constructed by coating a film 6.

In this case, preferably, a spacer 10 is provided on the inner surface of the heat soaking tube 2, and the quartz tube 1 is accommodated in the heat soaking tube 2 via the spacer 10.
0 is formed from a rotating body made of SiC alone.

[0009]

[Operation] According to the above-described structure of the present invention, the inner or outer surface of the soaking tube 2 is coated with a dense film having a small diffusion coefficient for metal impurities, such as the SiC film 6, so that the heater 3, etc. can effectively block heavy metals from Therefore, the quartz tube 1 during oxidation/diffusion treatment
The atmosphere inside can be made cleaner, and metal contamination on the wafer 5 can be reduced. As a result, carrier lifetime and oxide film reliability can be improved.
A high yield of devices formed on the wafer 5 can be achieved.

On the other hand, when the inner surface of the soaking tube 2 is coated with the SiC film 6, when the quartz tube 1 is housed in the soaking tube 2,
Although there is an inconvenience that the SiC film 6 peels off, if a spacer 10 formed of a rotating body made of SiC is provided on the inner surface of the soaking tube 2 and the quartz tube 1 is accommodated through the spacer 10, Peeling of the SiC film 6 can be prevented, and the effects of the SiC film 6 can be fully exhibited.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 9. FIG. 1 is a schematic configuration diagram showing the oxidation/diffusion furnace A1 according to the first embodiment viewed from the front, and FIG. 2 is a schematic configuration diagram shown from the side.

This oxidation/diffusion furnace A1 includes a heat-resistant quartz tube 1 constituting a furnace core tube, a soaking tube 2 housing the quartz tube 1, and a heater 3 arranged around the outer periphery of the soaking tube 2. It is composed of Here, the soaking tube 2 is composed of SiC and Si (18%
), and the heater 3 is made of a Cr-Fe alloy. Then, a large number of wafers 5 to be processed are arranged vertically on a quartz boat 4 and housed in the quartz tube 1, and in this state, the quartz tube 1 is heated with a heater 3 while precisely controlling the temperature.
By heating the wafer 5 inside the quartz tube 1, oxidation and diffusion treatment is performed.

Therefore, in this embodiment, a film is formed on the inner surface of the soaking tube 2, which has a small diffusion coefficient for metal impurities and a coefficient of thermal expansion that is almost the same as the material of which the soaking tube 2 is made. In this example, a SiC film 6 with a thickness of about 100 μm is used.
is formed by, for example, a CVD method. This SiC
Since the film 6 has a very small diffusion coefficient for metal impurities, it can effectively prevent heavy metals from diffusing and entering the quartz tube 1 from the outside (heater 3, etc.). In this case, the amount of intrusion of metal impurities can be reduced to a fraction of that of the conventional case.
It can be reduced to about 1/10.

According to the first embodiment, the inner surface of the soaking tube 2 is coated with the SiC film 6, which has a small diffusion coefficient with respect to metal impurities, thereby effectively blocking heavy metals from the heater 3 and the like. be able to. Therefore, the atmosphere inside the quartz tube 1 during the oxidation/diffusion process can be cleaned, and metal contamination on the wafer 5 can be reduced. As a result, the lifetime of the carrier and the reliability of the oxide film can be improved, and the yield of devices formed on the wafer 5 can be increased.

Next, a second embodiment constructed of double quartz tubes will be described with reference to FIG. 2. Components corresponding to those in FIG. 1 are designated by the same reference numerals.

Oxidation/diffusion furnace A2 according to this second embodiment
Embodiment 1 has almost the same configuration as the first embodiment, but the furnace core tube is composed of two quartz tubes 1a and 1b with different diameters, and during the oxidation/diffusion treatment, HC is
They differ in that they flow l gas.

When HCl gas is flowed between the quartz tubes 1a and 1b in the high temperature state of the oxidation/diffusion treatment, the high temperature causes it to diffuse through the soaking tube 2 and the quartz tubes 1a, 1b from the outside and enter the furnace core. Metal impurities are removed by XC using HCl gas.
It is vaporized as l2 (X: metal element) and exhausted through the exhaust port 7.

Therefore, according to the second embodiment, the synergistic effect of the SiC film 6 formed on the inner surface of the soaking tube 2 and the HCl gas flowing between the quartz tubes 1a and 1b greatly reduces the intrusion of metal impurities from the outside. Therefore, metal contamination on the wafer 5 can be significantly reduced compared to the case of the first embodiment.

In the second embodiment, HCl gas was made to flow between the quartz tubes 1a and 1b;
2. It may be a gas, as long as it can react with metal impurities and reform the metal impurities into a highly sublimable substance.

[0020] Furthermore, in the first and second embodiments, Si
Although the C film 6 is formed on the inner surface of the heat soaking tube 2, it may of course be formed on the outer surface of the heat soaking tube 2.

By the way, the double quartz tubes (hereinafter simply referred to as double tubes) 1a and 1b according to the second embodiment have a weight of about 30K.
It weighs as much as g. Therefore, in the soaking tube 2, there is a double tube 1a,
1b, as shown in FIG. 3A, for example, the double tubes 1a, 1b are lifted manually to the opening 2a of the heat soaking tube 2, and then, as shown in FIG. 3B, the double tubes 1a, 1b are placed in the heat soaking tube 2 and drags the inner bottom of the heat soaking tube 2 over a wide range.

At this time, when the inner surface of the soaking tube 2 is coated with the SiC film 6 as in the first and second embodiments, the SiC film 6 is coated by the dragging of the double tubes 1a and 1b.
The problem arises that the film 6 peels off over a wide area and the original effect of the SiC film 6 cannot be exhibited. In addition, the accommodation state of the double tubes 1a and 1b in the heat soaking tube 2 is as shown in FIG.
Since the center O1 of the double tubes 1a and 1b does not match,
For example, variations in heat conduction within the double tubes 1a and 1b become large, and there is a possibility that a non-uniform oxide film may be formed on the wafer 5 due to this influence. Note that 8 is a holding member that holds the heater 3, and is made of Al2O3.

Therefore, in this example, as shown in the oxidation/diffusion furnace A3 according to the third example in FIG. 5, a ball bearing portion 9 is arranged at a predetermined position on the inner bottom of the soaking tube 2. In the example of FIG. 5, the ball bearing part 9 is
Four locations are arranged in each row at equal intervals (pitch P). As shown in FIG. 6, this ball bearing part 9 has a crater having a ball 10 made of SiC and a circular planar recess 11 that partially exposes the ball 10 and rotatably accommodates the ball 10. It consists of 12.

Next, a method for forming the ball bearing portion 9 will be explained. First, the inner diameter D of the soaking tube 2 and the outer diameter d of the double tubes 1a and 1b are determined. Thereafter, the diameter t of the ball 10 is determined using the formula shown in Equation 1.

t=(D-d)/2 Here, it is assumed that the set position of the wafer 5 in the double tubes 1a, 1b is at the center O1 of the double tubes 1a, 1b. If the set position is shifted from the center O1,
Consider offsetting the difference.

Next, the total length L of the soaking tube 2 is determined. After that, based on the obtained total length L of the soaking tube 2, the crater 12
A design has been completed in which the craters 12 are formed at the inner bottom of the soaking tube 2 in 2 rows of 4 locations (4 locations per row) at equal intervals in the axial direction, and each crater 12 is arranged in a V-shape. let

Next, based on the above design, the soaking tube 2 and the crater 12 are integrally formed from a compound of SiC and Si (18%), and then the inner surface of the soaking tube 2 and the surface of the crater 12 (
A SiC film 6 having a thickness of approximately 100 μm is formed on the surface (including the inner surface of the recess 11) by, for example, the CVD method.

Next, the ball 10 is fitted into the recess 11 of the crater 12 of the completed soaking tube 2. Thereafter, the soaking tube 2 is attached to the oxidation/diffusion furnace body to complete the process. Finally, the double tubes 1a and 1b are housed in the soaking tube 2 using the above-mentioned manual transport method, and while confirming that the wafers 5 in the double tubes 1a and 1b are aligned with the center O2 of the soaking tube 2, It is confirmed that the SiC film 6 formed on the inner surface of the soaking tube 2 is not peeled off.

According to this third embodiment, when the double tubes 1a and 1b are inserted into and taken out from the soaking tube 2, it is possible to prevent the SiC film 6 formed on the inner surface of the soaking tube 2 from peeling off. It is possible to improve the effect of blocking metal impurities due to No. 6. In addition, since the center O1 of the double tubes 1a and 1b (wafer set position) coincides with the center O2 of the soaking tube 2,
The thickness distribution of the oxide film formed on the wafer 5 can be made uniform.

In the third embodiment, the shape of the recess 11 of the crater 12 is circular in plan, but the shape of the recess 11 may be polygonal in plan as shown in FIG. 7, for example. FIG. 7A shows a case where the recess 11 has a triangular shape in plan, and FIG. 7B shows a case where it has a rectangular shape in plan. Further, FIG. 7C shows an example in which the recess 11 is formed into a planar raindrop shape to provide a rolling margin n for the ball 10.

In addition, instead of the crater 12, as shown in FIG.
3 may be provided, and several balls 10 may roll on it. Further, as shown in FIG. 9, iron array type balls 15, which are two balls 10 integrally formed by a rod-shaped connecting member 14, may be arranged at four locations. In this case, as shown in FIG. 9A, one line of trench groove 16
It may be made to slide inside, or may be rotatably accommodated in the crater 12. Furthermore, a guide groove 17 may be provided on the side surface of the trench groove 16 to restrict the movable range of the ball 15.

[0031]

According to the heat treatment furnace according to the present invention, metal contamination of wafers can be prevented and oxidation/diffusion treatments can be performed satisfactorily on wafers.

[Brief explanation of drawings]

FIG. 1A is a schematic configuration diagram of an oxidation/diffusion furnace according to a first embodiment seen from the front. B is a schematic configuration diagram seen from the side.

FIG. 2A is a schematic configuration diagram of an oxidation/diffusion furnace according to a second embodiment, viewed from the front. B is a schematic configuration diagram seen from the side.

FIG. 3 is an explanatory diagram showing the work of accommodating a double pipe into a soaking tube.

FIG. 4 is a front view showing how the double tube is housed in the soaking tube.

FIG. 5A is a schematic configuration diagram of an oxidation/diffusion furnace according to a third embodiment, viewed from the front. B is a schematic configuration diagram seen from the side.

FIG. 6 is a partially cutaway perspective view of the ball bearing section.

FIG. 7 is a perspective view showing a modification of the ball bearing section.

FIG. 8 is a perspective view showing a modification example in which a trench groove is provided.

FIG. 9 is a perspective view showing a modification using iron array type balls.

FIG. 10A is a schematic configuration diagram of a conventional oxidation/diffusion furnace viewed from the front. B is a schematic configuration diagram seen from the side.

FIG. 11A is a schematic configuration diagram of another conventional oxidation/diffusion furnace viewed from the front. B is a schematic configuration diagram seen from the side.

[Explanation of symbols]

A1, A2 and A3 Oxidation/diffusion furnace 1 Quartz tubes 1a, 1b Double tube 2 Soaking tube 3 Heater 4 Quartz boat 5 Wafer 6 SiC film 9 Ball bearing part 10 Ball 11 Recess 12 Crater 13 Trench groove 15 Iron array ball

Claims (5)

[Claims] Claim 1: A quartz tube in which a wafer to be processed is housed;
In a heat treatment furnace comprising a soaking tube that accommodates the quartz tube and a heater arranged around the soaking tube, the inner or outer surface of the soaking tube is coated with a dense material having a small diffusion coefficient for metal impurities. A heat treatment furnace characterized by being coated with a membrane. 2. The heat treatment furnace according to claim 1, wherein the quartz tube is made up of two quartz tubes each having a different diameter. 3. The heat treatment furnace according to claim 1, wherein a spacer is provided on the inner surface of the soaking tube, and the quartz tube is housed within the soaking tube via the spacer. 4. The heat treatment furnace according to claim 3, wherein the spacer is formed of a rotating body. 5. The heat treatment furnace according to claim 4, wherein the rotating body is made of SiC.