JPH04125922A - Semiconductor closed tube diffusion method and closed tube diffusion equipment - Google Patents

Abstract

PURPOSE:To diffuse impurities without crashing an ampoule, by forming a quartz ampoule, in which a semiconductor substrate and a diffusion source are vacuum-sealed, by using silicon carbide, containing said ampoule in a vac uum furnace core tube whose degree of vacuum is lower than or equal to a specified value, and performing heat treatment in a heating furnace. CONSTITUTION:A tube 4 constituted of SiC is used as the furnace core tube of a heating furnace 3. The length of the tube 4 is made longer than that of a hollow part of the furnace 3. A door 8 is installed, via an O ring, on a water cooling frange 5 of one side, and opened and closed. An exhaust tube 9 is connected with a water cooling frange 5 of the other side, and with an exhauster 11. The tube 4 is kept at a degree of vacuum lower than or equal to 1X10<-3>Torr. An ampoule in which a silicon substrate and an Al diffusion source are vacuum-sealed is contained in the tube 4. Thereby semiconductor closed tube diffusion is enabled at a high temperature of about 1250 deg.C, without crashing the ampoule.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor closed tube diffusion method for diffusing aluminum or the like into a semiconductor substrate such as silicon, and a closed tube diffusion device used therein.

[Conventional technology]

Diffusion of aluminum into a silicon semiconductor substrate is used, for example, in semiconductor devices such as thyristors that require high breakdown voltage. When aluminum is diffused using the open tube diffusion method, outward diffusion occurs and the aluminum is not diffused into the silicon semiconductor to the required concentration.For this reason, conventionally, a silicon semiconductor substrate and an aluminum diffusion source are placed in a quartz ampoule. A so-called closed-tube diffusion method is used, in which a quartz ampoule is sealed under a vacuum of 10 -3 Torr or more, and the quartz ampoule is placed in a heating furnace for diffusion. FIG. 2 shows the implementation state of such a closed tube diffusion method, in which the silicon substrates 1 and 22 are welded and sealed, placed in a heating furnace 3, and heated to, for example, 1250°C.
Heat treated with

[Problem to be solved by the invention]

With the recent increase in the current capacity of thyristors, some silicon semiconductor substrates have a diameter of up to 4 inches. For this reason,
The quartz ampoule also has an outer diameter of more than 100 fi, and as mentioned above, it is heated to 1250 m
If the diffusion is carried out at a temperature of about 10 hours, the quartz ampoule 21 may be crushed and the silicon substrate 1 may be destroyed.

One way to solve this problem is to use quartz ampule 2.
There is a method of increasing the thickness of quartz in step 1. 1250℃ above
In order to prevent the quartz ampoule from being crushed during the diffusion for about 10 hours, the total thickness of the quartz directly above must be 4.5 nm or more. However, if the quartz thickness is 451 mm or more, welding becomes difficult during vacuum sealing, and the weight of the quartz ampoule increases.

Alternatively, another method for solving the problem is to heat-treat a vacuum-sealed quartz ampoule in a reduced-pressure furnace at a pressure of about milliTorr with a small pressure difference between the inside and outside of the quartz ampoule so as not to crush the ampoule. Currently, low-pressure CVD equipment exists in the world, but since the temperature is about 500°C and a closed quartz furnace tube is used, it is impossible to perform heat treatment at a temperature of about 1250°C.

An object of the present invention is to provide a semiconductor closed-tube diffusion method for diffusing impurities into the semiconductor substrate by heat-treating a quartz ampoule in which a semiconductor substrate and a diffusion source are vacuum-sealed without crushing the quartz ampoule, and a closed-tube diffusion device used in the method. It's about doing.

[Means for solving R problem]

In order to achieve the above object, the semiconductor closed tube diffusion method of the present invention comprises a quartz ampoule in which a semiconductor substrate and a diffusion source are vacuum-sealed, and is made of silicon carbide (SiC).
It shall be housed in a vacuum-tight furnace tube with a degree of vacuum of 3 Torr or less and heat treated in a heating furnace. This 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 includes a heating furnace having a hollow portion, a core tube made of SiC that is longer than the hollow portion, and a lid body that vacuum-tightly seals both ends of the core tube.
The exhaust pipe is provided with an exhaust pipe that passes through at least one of the lids and communicates with a vacuum exhaust device. It is also effective that the lid body can be cooled with water and that the lid body is made of stainless steel.

[Effect]

By forming the reactor core tube with SiC, deformation at diffusion temperature is eliminated, and the degree of vacuum inside the reactor core tube can be changed from SiC to Si.
There is no risk of contamination of the semiconductor substrate by not creating a high vacuum of more than 10-' Torr, where the Vacuum-tightness can be easily maintained by sealing with a water-cooled lid, for example, in a low-temperature area. Therefore, even if stainless steel, which has a coefficient of thermal expansion close to that of SiC, which has a larger coefficient of thermal expansion than quartz, is used for the lid body for sealing, the temperature of the lid body will not become high, so stainless steel will not be used for the semiconductor substrate. iron, nickel,
There is no risk of contamination with chromium, etc.

〔Example〕

FIG. 1 shows a closed tube diffusion device according to an embodiment of the present invention;
Parts common to those in the figure are given the same reference numerals. In the figure, a tube 4 made of SiC is inserted as a core tube of a 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 not to increase the temperature difference between the contact area between the water cooling flange and the SiC tube, which will be described later. The flange 5 is made of stainless steel, and the O IJ song interposed between the flange 5 and the SiC tube 4 maintains airtightness between the flange 5 and the SiC tube.

A water cooling pipe 7 is attached to the flange 5 to prevent seizure. A door 8 is provided on the outside of one flange 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. Since the inside of the SiC tube 4 may be kept at a vacuum level of 1.times.10@-3 Torr or less, the exhaust device 11 is configured with a rotary pump. Also connected to the exhaust pipe 9 is an N2 gas introduction pipe 13 equipped with a solenoid valve 12. Furthermore, the exhaust pipe 9 has a vacuum gauge 1.
4 is installed, and when the degree of vacuum reaches a high vacuum of 10-3 Torr or higher, which may cause the separation of Si from SiC, the two solenoid valves are automatically activated via the feedback circuit 15 to stop the exhaust gas. Solenoid valve 10 of pipe 9 is closed, N
Since the ii magnetic valve 12 on the 2 introduction pipe 13 side opens, 10-3↑
It will be in the range of orr.

An embodiment of the closed tube diffusion method using this closed tube diffusion device is shown in FIG. 3. Line 31 in FIG. 3 shows a flowchart of temperature, and line 32 shows a flowchart of degree of vacuum. First, when the temperature of the heating furnace 3 reaches 700° C., the door 8 is opened and a quartz ampoule 21 as shown in FIG. 2 is placed in the furnace.

After putting it into the furnace, operate the exhaust system 11 and reduce the temperature to 10”3 Torr.
to a degree of vacuum. It took about 10 minutes to reach 10-3Torr.a After confirming that it had reached 10-3Torr,
The furnace was heated to 1250°C at a rate of 10°C/min,
Diffusion was carried out at 50°C for 10 hours. After the diffusion, the furnace was cooled at a rate of 1°C/min, and when the temperature reached 700°C, the furnace was turned off. At the same time as switching to natural cooling, the exhaust device 11 was stopped, and N2 gas was introduced into the furnace from the inlet pipe 13. It was assumed to be an atmospheric condition. When the temperature of the furnace reached 200°C or below, the quartz ampoule was taken out from door 8.

The quartz ampoule 21 used in this example contains a silicon substrate with a diameter of 4 inches, and the diameter of the quartz ampoule is 130 mm. The thickness of the quartz was 3fi. After taking out the quartz ampoule, the state of crushing of the quartz ampoule was examined, but no crushing had occurred at all. Also, Si
There were no problems caused by thermal expansion of the C-tube, and no problem with separation of Sl from SiC occurred.

〔Effect of the invention〕

According to the present invention, by using SiC as the material for the core tube of the depressurization furnace, it is possible to raise the temperature to a high temperature of about 1250°C. It has become possible to carry out closed-tube diffusion of semiconductors without crushing the ampoule. Therefore, closed-tube diffusion can be performed on large-diameter semiconductor substrates, and it is particularly effective for performing adhesive diffusion on silicon substrates to which open-tube diffusion cannot be applied. In addition, by using water-cooled lids or stainless steel lids at both ends of the SiC reactor core tube, it is possible to achieve a seal that does not interfere with high-temperature diffusion.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a closed tube diffusion device according to an embodiment of the present invention, Fig. 2 is a sectional view showing a conventional closed tube diffusion method, and Fig. 3 is a temperature and vacuum in a closed tube diffusion method according to an embodiment of the present invention. FIG. l: silicon substrate, 2 aluminum diffusion source, 3: heating furnace, 4: SiC tube, 5: flange, 6:. Ring, 7: Water cooling pipe, 8: Door, 9: Exhaust pipe, 11: Exhaust device, 21: Quartz ampoule.

Claims (1)

[Claims] 1) A quartz ampoule in which a semiconductor substrate and a diffusion source are vacuum-sealed is housed in a vacuum-tight core tube made of silicon carbide and has a vacuum level of 1×10^-^3 Torr or less, and then heated in a heating furnace. A semiconductor closed tube diffusion method characterized by heat treatment within a semiconductor tube. 2) The semiconductor closed tube diffusion 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 part, a furnace core tube made of silicon carbide that is longer than the hollow part, a lid body that vacuum-tightly seals both ends of the furnace core tube, and a vacuum pump that penetrates at least one lid body to evacuation. A closed tube diffusion device characterized by comprising an exhaust pipe communicating with the device. 4) The closed tube diffusion device according to claim 3, wherein the lid body can be cooled with water. 5) In the closed tube diffusion device according to claim 3 or 4,
A closed tube diffuser whose lid is made of stainless steel.