JP2715645B2 - Semiconductor closed tube diffusion method and closed tube diffusion device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a closed-tube diffusion method for diffusing aluminum or the like into a semiconductor substrate such as silicon, and a closed-tube diffusion device used therefor.

[Conventional technology]

Aluminum diffusion into a silicon semiconductor substrate is used for a semiconductor device requiring a high breakdown voltage, such as a thyristor. When aluminum is diffused by the open-tube diffusion method, outward diffusion occurs, and the aluminum is not diffused into a silicon semiconductor to a required concentration. For this reason, conventionally, a so-called closed tube diffusion method in which a silicon semiconductor substrate and an aluminum diffusion source are put in a quartz ampule, the quartz ampule is sealed under a pressure of 10 ^-6 Torr or less, and the quartz ampule is put into a heating furnace and diffused. Has been taken. FIG. 2 shows an embodiment of such a closed tube diffusion method, in which a silicon substrate 1 and an aluminum diffusion source 2 are housed in a quartz ampule 21 having one end closed, and a quartz cap 22 is welded to the other end under vacuum. And heat-treated at 1250 ° C. in a heating furnace 3.

[Problems to be solved by the invention]

With the recent increase in current capacity of thyristors, some silicon semiconductor substrates have a diameter of 4 inches. For this reason, the quartz ampoule also exceeds the outer diameter of 100 mm, and if the diffusion is performed at 1250 ° C. for about 10 hours under the pressure of 10 ⁻⁶ Torr or less as described above, the quartz ampule 21 is crushed and the silicon substrate is broken. 1 may be destroyed.

One solution to this problem is a quartz ampoule.
There is a method of increasing the thickness of the quartz of 21. In order to prevent the quartz ampoule from being crushed by the above-mentioned diffusion at about 1250 ° C. for about 10 hours, it is necessary to calculate the quartz thickness to be 4.5 mm or more.
However, when the quartz thickness is 4.5 mm or more, there is a problem in that welding at the time of vacuum sealing becomes difficult, and the weight of the quartz ampule increases.

Alternatively, as another method for solving the problem, there is a method in which a vacuum-sealed quartz ampule is subjected to a heat treatment in a reduced pressure furnace of a pressure of about milliTorr with a small pressure difference between the inside and outside of the quartz ampule so that the ampule is not crushed. Currently, the world is decompressed
Although there is a CVD apparatus, its temperature is about 500 ° C, and it is impossible to heat-treat at a temperature of about 1250 ° C because it uses a quartz sealed furnace tube.

An object of the present invention is to provide a semiconductor closed-tube diffusion method for heat-treating a quartz ampoule in which a semiconductor base and a diffusion source are vacuum-sealed to diffuse impurities into the semiconductor base without crushing the quartz ampule, and a closed-tube diffusion apparatus used in the method. Is to do.

[Means for solving the problem]

In order to achieve the above object, a semiconductor tube diffusion method according to the present invention comprises a quartz ampoule in which a semiconductor substrate and a diffusion source are vacuum-sealed and made of silicon carbide (SiC), and an internal pressure of 1%.
It shall be housed in a vacuum hermetic core tube maintained at a vacuum of × 10 ^-3 Torr or more and heat-treated in a heating furnace. It is particularly effective when the semiconductor substrate is made of silicon and the diffusion source contains aluminum. Further, the closed tube diffusion device of the present invention is a heating furnace having a hollow portion, a furnace tube made of SiC longer than the hollow portion, a lid for sealing both ends of the furnace tube in a vacuum-tight manner, and at least one lid. And an exhaust pipe penetrating therethrough and communicating with the vacuum exhaust device. It is effective that the lid has a water cooling mechanism and that the lid is made of stainless steel.

[Action]

By carrying out diffusion while accommodating a quartz ampoule in which a semiconductor substrate and a diffusion source are vacuum-sealed in a vacuum furnace tube made of SiC, deformation at the diffusion temperature is eliminated, and the pressure in the furnace tube is separated from Si by Si. By setting the vacuum to 1 × 10 ⁻³ Torr or more without setting the high vacuum to ^-4 Torr or less, there is no possibility of contamination of the semiconductor substrate. By making the furnace tube longer than the hollow portion of the heating furnace and sealing the lower ends of the furnace tube with, for example, a water-cooled lid, vacuum airtightness can be easily maintained. Therefore, even if stainless steel having a coefficient of thermal expansion close to SiC, which has a larger coefficient of thermal expansion than quartz, is used for the lid for sealing, the temperature of the lid does not increase, so the iron from the stainless steel to the semiconductor substrate is not increased. No risk of contamination by nickel, chromium, etc.

〔Example〕

FIG. 1 shows a closed-tube diffuser according to one embodiment of the present invention, and the same parts as those in FIG. 2 are denoted by the same reference numerals. In the figure, a tube 4 made of SiC is inserted as a furnace tube of the heating furnace 3. The length of the SiC tube 4 was set to be 300 mm longer on one side than the heating furnace 3 so as to prevent a temperature difference between a contact portion between a water-cooled flange and a SiC tube described later from increasing. Flange 5
Is made of stainless steel, and is kept airtight with the SiC pipe by an O-ring 6 interposed between the stainless steel and the SiC pipe 4.
A water cooling tube 7 for preventing seizure is attached to the flange 5. A door 8 is provided outside one of the flanges 5, and an O-ring 6 is inserted between the door 8 and the flange 5 to seal the opening 51 of the flange. An exhaust pipe 9 is connected to the other flange 5 and is connected to an exhaust device 11 via a solenoid valve 10. The interior of the SiC tube 4 may be evacuated to a pressure of 1 × 10 ⁻³ Torr or more.
Is composed of a rotary pump. The exhaust pipe 9 is also connected to an N ₂ gas introduction pipe 13 having a solenoid valve 12. Further, a vacuum gauge 14 is attached to the exhaust pipe 9, and the pressure is reduced.
When a high vacuum of 10 ^-4 Torr or less, at which there is a risk of separation of Si from SiC, the two solenoid valves are automatically operated via the feedback circuit 15 and the solenoid valve 10 on the exhaust pipe 9 side is closed. , since the electromagnetic valve 12 of the N ₂ inlet pipe 13 side is opened, in the range of 10 ^-3 Torr.

FIG. 3 shows an embodiment of a closed pipe diffusion method using this closed pipe diffusion apparatus. The line 31 in FIG. 3 shows the flow chart of the temperature, and the line 32 shows the flow chart of the degree of vacuum. First, with the temperature of the heating furnace 3 at 700 ° C., the door 8 is opened and the quartz ampule 21 as shown in FIG. After the furnace is put in, the exhaust device 11 is operated to make the degree of vacuum 10 ^-3 Torr.
It took about 10 minutes to reach 10 ^-3 Torr. After confirming that the pressure reached 10 ⁻³ Torr, the furnace was heated to 1250 ° C. at a rate of 10 ° C./min, and diffused at 1250 ° C. for 10 hours. After diffusion, the furnace was cooled to -5 ° C /
Allowed to cool minute, cut the furnace upon reaching a 700 ° C., quenched at the same time the exhaust device 11 as switching to natural cooling, the N ₂ gas put into the furnace from the inlet pipe 13, and the atmospheric conditions. Furnace
When the temperature reached 200 ° C. or lower, the quartz ampule was taken out from the door 8.

The quartz ampule 21 used in this embodiment has a 4-inch diameter silicon substrate housed inside, and the diameter of the quartz ampule is 130 mm. The thickness of the quartz was 3 mm. After the quartz ampule was taken out, the crushed state of the quartz ampule was examined, but no crushing occurred. In addition, no trouble was caused by thermal expansion of the SiC tube, and no problem of separation of Si from SiC occurred.

〔The invention's effect〕

According to the present invention, by using SiC for the material of the furnace tube of the decompression furnace, the temperature can be raised to about 1250 ° C., and the quartz ampoule that has been vacuum-sealed is heat-treated in the vacuumed furnace tube to produce quartz. It has become possible to perform semiconductor tube diffusion without crushing the ampoule. Therefore, it is possible to perform closed-tube diffusion on a semiconductor substrate having a large diameter, and it is extremely effective especially for performing Al diffusion on a silicon substrate to which open-tube diffusion cannot be applied. In addition, since a water-cooled lid or a stainless steel lid is used at both ends of the SiC core tube, a hermetic seal that does not hinder high-temperature diffusion can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a closed-tube diffusion apparatus according to one embodiment of the present invention, FIG. 2 is a cross-sectional view showing a conventional closed-tube diffusion method, and FIG. It is a flowchart of a degree. 1: silicon substrate, 2: aluminum diffusion source, 3: heating furnace, 4:
SiC pipe, 5: flange, 6: O-ring, 7: water cooling pipe, 8: door, 9: exhaust pipe, 11: exhaust device, 21: quartz ampule.

Claims (5)

(57) [Claims] A quartz ampoule in which a semiconductor substrate and a diffusion source are vacuum-sealed is made of silicon carbide and has an internal pressure of 1 × 10 4.
A semiconductor closed-tube diffusion method characterized in that it is housed in a vacuum hermetic furnace tube maintained at a vacuum of ^-3 Torr or more and heat-treated in a heating furnace. 2. The method according to claim 1, wherein the semiconductor substrate is made of silicon, and the diffusion source contains aluminum. 3. A heating furnace having a hollow portion, a furnace tube made of silicon carbide longer than the hollow portion, a lid for sealing both ends of the furnace tube in a vacuum-tight manner, and at least one of the lids penetrating therethrough. And a reaction tube provided in the furnace tube for vacuum-sealing the semiconductor substrate and the diffusion source. 4. The closed-tube diffuser according to claim 3, wherein the lid has a water cooling mechanism. 5. The closed-tube diffuser according to claim 3, wherein the lid is made of stainless steel.