JPH05226271A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To inhibit the formation of a compound of platinum and silicon and minimize the variability of forward voltage drop by speeding up the cooling operation after platinum diffusion when heating a semiconductor substrate to a high temperature and diffusing platinum in the substrate. CONSTITUTION:An n-type Si wafer is adopted as a semiconductor substrate. After the formation of a p-n junction, the surface of the substrate is coated with a platinum source. A boat 4 where an Si wafer 3 is loaded is inserted into the center of a furnace by means of a boat loader 5 from one end of a furnace tube 2 of an electric furnace 1 while nitrogen gas 8 is passed into the furnace tube 2 from a gas intake pipe 6 on the other end of the furnace tube 2 where heat treatment is carried out. After the end of Pt diffusion, the boat 4 is pulled out up to a portion of the furnace tube 2 outside the furnace in a short time, say, 1 to 10 seconds, by means of the boat loader 5. Vent holes 7 are bored in this portion of the furnace tube 2. When the N2 gas 8 is sprayed on this portion from the outside, the temperature of the wafer 3 drops immediately. The Si wafers thus obtained are laminated while the forward voltage drop of manufactured diodes is 29V on the average and their variability amplitude is 4V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device including a step of diffusing platinum as a lifetime killer into a semiconductor substrate made of silicon for increasing a switching speed.

[0002]

2. Description of the Related Art Platinum is superior to gold as a lifetime killer to be introduced into the substrate in order to reduce the lifetime of the semiconductor substrate, in terms of softness of reverse leakage current and current change during reverse recovery. It is known that As a method of performing platinum diffusion in a conventional semiconductor device manufacturing process, a platinum source is applied to the surface of a Si wafer having a pn junction, and heat treatment is performed at a high temperature in a diffusion furnace so that the platinum is sufficiently evenly distributed in the wafer. After the diffusion, the wafer was pulled out from the diffusion furnace and cooled to room temperature.

[0003]

In the conventional platinum diffusion method as described above, the heat capacity is different when the number of wafers to be diffused at the same time is different, and the time for pulling out the silicon wafer from the high temperature diffusion furnace and cooling it to room temperature varies, When cooling is slow, a compound of Si and Pt is formed, so that the forward voltage drop of the diode fluctuates.

The object of the present invention is to eliminate these drawbacks.
It is another object of the present invention to provide a method for manufacturing a semiconductor device in which the amount of platinum compound formed does not vary even if the amount of semiconductor substrate on which platinum is diffused is different.

[0005]

In order to achieve the above object, the present invention comprises a step of depositing platinum on the surface of a semiconductor substrate made of silicon and heating it to a high temperature to diffuse platinum in the substrate. In the device manufacturing method, the cooling rate in the temperature range from 750 ° C. to 600 ° C. when cooling the semiconductor substrate after platinum diffusion is set to 20 ° C./min or more. Then, the semiconductor substrate to which platinum is adhered is inserted into the high temperature part of the furnace core tube of the heat treatment furnace and heated for a predetermined time, and then the substrate is pulled out to the low temperature part of the core tube, and the substrate is externally transferred to the low temperature part of the core tube. It is effective to spray the gas, or to open a vent hole at a low temperature portion of the core tube and press an inert gas from the outside into the core tube through the vent hole. It is effective to use nitrogen gas as the inert gas.

[0006]

[Function] Silicon and platinum combine to form a compound in the range of 600 ° C to 750 ° C. Therefore, by quenching in the range of 750 ℃ ~ 600 ℃ at a cooling rate of 20 ℃ / min or more,
The formation of Pt compounds can be prevented. Then, after the semiconductor substrate is drawn out to the low temperature part of the core tube, if a gas is blown from the outside of the core tube at the same time, a large cooling rate can be obtained regardless of the amount of the semiconductor substrate that diffuses platinum at the same time.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. An n-type Si wafer is used as a semiconductor substrate for manufacturing a high-voltage diode, a pn junction is formed by impurity diffusion, and then a platinum source is applied on the surface in the same manner as in the prior art, and the temperature is set in a diffusion furnace at 900 ° C to 930 ° C for 5 The heat treatment was performed for about 15 hours to diffuse Pt. FIG. 1 shows the state of the heat treatment, in which the boat 4 carrying the Si wafer 3 is inserted from one end of the core tube 2 of the electric furnace 1 to the center of the furnace indicated by the dotted line by the boat loader 5, and The heat treatment is performed while flowing the nitrogen gas 8 from the gas introduction pipe 6 at the end into the core tube. After the completion of Pt diffusion, the boat loader 5 pulls out the boat 4 to a portion outside the furnace of the core tube 2 within a short time of 1 to 10 seconds as shown by a solid line. A vent hole 7 is formed in the core tube at this portion. When N ₂ gas 8 is blown to this portion from the outside at a pressure of about 2 kg / cm ² , the gas flows along the surface of the wafer 3 through the vent holes 7, so that the temperature of the wafer 3 suddenly drops, and 750 The temperature in the range of ℃ to 600 ℃ was passed in 7.5 minutes or less. That is, the cooling rate was 20 ° C./minute or more. 15 Si wafers thus obtained
The forward voltage drop of a high voltage diode with a withstand voltage of 12 kV manufactured by stacking and dividing the sheets is 29 V on average and the range of variation is 27 V to 31 V.
V, and the variation width was 4V. Conventional breakdown voltage 12kV
In the high-voltage diode of 3), the average voltage is 30.5V, which varies from 26V to 32V, and the variation width is 6V. Therefore, it can be seen that the variation in the forward voltage drop is reduced.
It should be noted that when the diameter of the core tube is small, even if the gas is blown to the tube wall of the core tube 2 without opening the vent hole 7, the temperature is 20 ° C.
A cooling rate of over min / min was obtained.

[0008]

According to the present invention, the formation of the compound of platinum and silicon can be suppressed by speeding up the cooling after platinum diffusion into the silicon gas, so that a semiconductor device with less variation in forward voltage drop can be obtained. Manufacturing is now possible. Then, such a high cooling rate can be achieved with good reproducibility by drawing the semiconductor substrate from the platinum diffusion furnace inside the core tube and then blowing gas from outside the core tube.

[Brief description of drawings]

FIG. 1 is a sectional view of a platinum diffusion device used in an embodiment of the present invention.

[Explanation of reference symbols] 1 electric furnace 2 core tube 3 Si wafer 4 boat 5 boat loader 7 vent hole 8 N ₂ gas

Claims (4)

[Claims] 1. A method for manufacturing a semiconductor device, which comprises the step of adhering platinum to the surface of a semiconductor substrate made of silicon and heating it to a high temperature to diffuse platinum in the substrate. A method for manufacturing a semiconductor device, characterized in that a cooling rate in a temperature range from ℃ to 600 ℃ is set to 20 ℃ / min or more. 2. A semiconductor substrate to which platinum is adhered is inserted into a high temperature portion of a furnace core tube of a heat treatment furnace and heated for a predetermined time, and then the substrate is pulled out to a low temperature portion of the furnace core tube and externally supplied to the low temperature portion of the furnace core tube. The method for manufacturing a semiconductor device according to claim 1, wherein a gas is blown from the semiconductor device. 3. A method of manufacturing a semiconductor device according to claim 2, wherein a vent hole is opened in a low temperature portion of the core tube, and an inert gas is externally pressed into the core tube through the vent hole. 4. The method of manufacturing a semiconductor device according to claim 3, wherein nitrogen gas is used as the inert gas.