JP3035954B2 - Open-tube gallium pre-deposition diffusion method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION A. Field of the Invention The present invention relates to a method for manufacturing a semiconductor, and more particularly to an open-tube gallium pre-deposition diffusion method.

B. Summary of the Invention The present invention provides an open-tube gallium pre-deposition diffusion method in which a silicon wafer dummy is provided on the entrance side of a quartz ampule tube to reduce variations in sheet resistance value within the silicon wafer. is there.

C. Prior Art Gallium (Ga) diffusion for P-type impurity diffusion in a silicon (Si) substrate as a semiconductor is widely used for forming a P base layer and a P emitter layer of a thyristor and a gate turn-off thyristor. I have.

One of the gallium diffusion methods is to form a high-concentration shallow gallium diffusion layer on the surface of a silicon substrate (pre-deposition diffusion of gallium), followed by heat treatment in a mixed gas flow of oxygen and nitrogen to drive-in diffusion. To form a desired gallium diffusion layer.

Here, the pre-deposition diffusion method of gallium includes an open-tube pre-deposition diffusion method in addition to the ion implantation method and the quartz tube sealing method. As shown in FIG. 3, an apparatus configuration using gallium as an impurity is shown in FIG. 3. As shown in FIG. 3, a silicon wafer 3 installed in a boat 2 in a quartz ampoule tube 1 The gallium diffusion source 4 is set on both sides of the tube, and this quartz ampule tube 1 is inserted into the diffusion furnace 6 without setting the quartz cap 5, and then the opening of the quartz ampule tube 1 is located downstream of the flow of the inert gas. A nitrogen gas is flowed into the diffusion furnace 6 in the direction, and the oxygen in the furnace and the quartz tube is expelled and replaced with the nitrogen gas. Then, the quartz cap 5 having a gap partially in the opening of the quartz ampule tube 1 is set and the diffusion furnace is After the lid 7 is replaced with nitrogen gas, the gallium is diffused by heat treatment by heating with a heater 8.

D. Problems to be Solved by the Invention Conventional open-tube gallium pre-deposition diffusion method
There is a problem that the silicon wafer in the quartz ampule tube has a variation in the sheet resistance of the diffusion layer depending on its position.

That is, as shown in FIG. 4, the relationship between the position of the silicon wafer in the quartz ampule tube and the sheet resistance indicates that the silicon wafer closer to the quartz cap 5 (the entrance of the quartz ampule tube 1) has an in-plane variation in the sheet resistance. Becomes larger. This variation is due to the fact that a gap for venting gas is provided between the quartz cap 5 and the quartz ampule tube 1, so that the gallium vapor generated in the ampule tube escapes little by little, and the gallium vapor concentration at the inlet portion is not uniform. It is thought to be.

The above-described variation in the sheet resistance value in the silicon wafer surface deteriorates the yield in manufacturing semiconductor devices, and has been a major problem in the open-tube gallium pre-deposition diffusion method.

An object of the present invention is to provide an open-tube gallium pre-deposition diffusion method in which a variation in sheet resistance value in a silicon wafer surface to be subjected to impurity diffusion is reduced.

E. Means and Action for Solving the Problems In order to achieve the above object, the present invention sets a large number of silicon wafers to be subjected to impurity diffusion in a boat and stores them in a quartz ampule tube together with an impurity diffusion source made of gallium. The quartz ampule tube is installed in a diffusion furnace in which an inert gas flows in one direction such that an opening thereof is located downstream of the flow of the inert gas, and oxygen in the quartz ampule tube is replaced by the inert gas. After that, the opening is provided with a cap having a gap between the quartz ampoule tube and a part thereof, and then, in an open-tube gallium pre-deposition diffusion method for diffusing impurities by heating the diffusion furnace, A quartz dummy having a shape in which a silicon wafer is set in a boat is provided only between the silicon wafer and the opening to diffuse impurities. Nonuniform impurity concentration which occurs at the inlet side of the quartz ampoule is prevented from occurring in the installation position of the silicon wafer to be an impurity diffusion target.

F. Embodiment FIG. 1 is a diagram showing the relationship between the device configuration and sheet resistance showing an embodiment of the present invention. 3 differs from FIG. 3 or FIG. 4 in that a quartz dummy 9 having a shape in which a silicon wafer 3 is mounted on a boat 2 is provided on the entrance side of a quartz ampule tube 1. FIG. 2 shows an enlarged view of the dummy 9.

The number of comb teeth of the quartz dummy 9 is set to be equal to or larger than the number of wafers in which the variation of the sheet resistance value generated on the silicon wafer 3 on the inlet side of the ampule tube by the conventional diffusion method becomes large. This number depends on the diameter (size) of the silicon wafer 3. From experience, the larger the diameter, the larger the number of sheets on which the in-plane sheet resistance value varies, and 3
About 20 to 20 sheets.

Specifically, when the silicon wafer 3 has a diameter of 3 inches, the number of the dummy 9 is 4 to 7, and when the silicon wafer 3 is 4 inches, the number of the dummy 9 is about 12 to 18.

In order to dispose the same number of silicon wafers 3 as the conventional method in order to install the quartz dummy 9, use the quartz ampule tube 1 which is longer by the length of the dummy.

According to the above-described configuration, when performing the diffusion process in the same procedure as the conventional one, the dummy 9 is installed on the inlet side of the quartz ampule tube 1, so that the gallium vapor concentration non-uniformity occurring near the inlet side is caused. Is at the position of the dummy 9, and the variation of the in-plane sheet resistance value of the silicon wafer 3 is extremely reduced.

FIG. 1 shows the variation of the sheet resistance with respect to the position of the silicon wafer 3, and the large variation on the inlet side of the ampule tube which occurs in the conventional method is eliminated.

As an experiment based on the present invention, in the open-tube gallium pre-deposition diffusion using 80 silicon wafers of 4 inches in diameter as one lot, the sheet resistance value of 15 silicon wafers from the side closer to the quartz cap 5 in the conventional method is reduced. The in-plane variation was 4 to 20% in the coefficient of variation.
When a dummy having 14 quartz plates and the boat was installed, the variation could be suppressed to a variation coefficient of 1 to 2%.

G. Effects of the Invention As described above, according to the present invention, a large number of silicon wafers to be subjected to impurity diffusion are accommodated in a quartz ampule tube, and the quartz wafer is set in a boat at the inlet side of the ampule tube. Since the gallium diffusion is performed by setting a dummy made of gallium, the diffusion of gallium, which is an impurity diffusion source, to the silicon wafer near the inlet of the ampoule tube where the vapor concentration becomes uneven, is performed on the dummy, This has the effect of reducing the variation in the in-plane sheet resistance and consequently improving the yield in the manufacture of semiconductor elements.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the device configuration and sheet resistance showing an embodiment of the present invention, FIG. 2 is an enlarged view of a quartz dummy 9 in FIG. 1, and FIG. 3 is an open-tube predeposition diffusion device. FIG. 4 is a diagram showing the relationship between the position of a conventional silicon wafer and the sheet resistance. 1 ... quartz ampoule tube, 2 ... boat, 3 ... silicon wafer, 4 ... gallium diffusion source, 5 ... quartz cap,
6: diffusion furnace, 7: lid, 8: heater, 9: quartz dummy.

Claims (1)

(57) [Claims] 1. A large number of silicon wafers to be subjected to impurity diffusion are set in a boat and housed in a quartz ampule tube together with an impurity diffusion source made of gallium, and the quartz ampule tube is placed in a diffusion furnace in which an inert gas flows in one direction. Is installed so that its opening is located downstream of the flow of the inert gas, and after the oxygen in the quartz ampule tube is replaced by the inert gas, a part of the opening is formed between the quartz ampule tube and the quartz ampule tube. In an open-tube gallium pre-deposition diffusion method in which a cap having a gap is provided and then impurities are diffused by heating the diffusion furnace, a quartz dummy having a shape in which the silicon wafer is set in a boat is placed in the quartz ampule tube. An open-tube gallium predeposit, wherein impurities are diffused by being provided only between the silicon wafer and the opening. Diffusion method.