JP2570201B2 - Heat treatment furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment furnace for heat-treating a wafer as a semiconductor substrate to diffuse impurities and form a thin film.

[0002]

2. Description of the Related Art A heat treatment furnace of this type is a kind of electric furnace for storing a plurality of wafers and performing heat treatment at a high temperature. In particular, when performing thermal diffusion for diffusing impurities into a wafer, the temperature in the furnace had to be raised to 1000 ° C. or more. However, raising or lowering the temperature of a large-capacity furnace to a temperature of 1000 ° C. or higher or lowering the temperature requires not only a long time for heating but also a very long cooling time due to natural air cooling. It took a long time. Conventionally, as an improvement measure, the furnace temperature is constantly set to increase the temperature rising rate faster, for example, always 8 before storing the wafer.
At the time of processing the wafer at about 00 ° C., the temperature was raised to 1200 ° C. to shorten the temperature rise time. In addition, various cooling methods have been proposed in order to reduce the time required for cooling down.

FIG. 2 is a diagram showing an example of a conventional heat treatment furnace. An example of the heat treatment furnace in which the above-mentioned temperature decreasing time is shortened is disclosed in Japanese Patent Application Laid-Open No. 57-13736. As shown in FIG. 2, this heat treatment furnace is disposed outside a quartz reaction tube 15 for accommodating a wafer 17 and is made of alumina (Al2 O3).
, A quartz outer tube 14 that supports the heat equalizing tube 13 through claws 18, a heat equalizing tube 13 and a quartz outer tube 1.
An air blowing means 19 for blowing air in the direction shown by the arrow in the gap with the air blower 4 is provided.

[0004] The processing operation of this heat treatment furnace is firstly 800
Slow speed to prevent oxide film growth due to air entrainment in the quartz reaction tube 15 of the heat treatment furnace maintained at 0 ° C. and to prevent warpage due to rapid heat generation of the wafer 17.
For example, a plurality of wafers 17 are stored in the quartz reaction tube 15 by a boat loader at 2-3 cm / min. Next, the temperature of the wafer 17 is increased to 1200 ° C. by the heater 16 over a period of about 40 minutes (4 to 5 ° C./min), and the impurity diffusion process is performed. Next, after a predetermined time has elapsed, the heater 1
6 is cut off, and the gap between the quartz outer tube 15 and the soaking tube 13 is air-cooled by the blowing means 19 so that the wafer 17 is maintained at a uniform temperature of 800 ° C. by the presence of the soaking tube 13. Down to. Then, the wafer 17 is taken out of the furnace by the boat loader.

As a result, in this heat treatment furnace, 1200 ° C.
The cooling time from the temperature up to 800 ° C. was about 40 minutes, which was characterized in that it was reduced to 1/3 of the usual cooling time of 130 minutes without cooling.

[0006]

In the above-mentioned conventional heat treatment furnace, although the time for cooling down to 800.degree. C. is reduced, it takes about 4 to increase to 1200.degree. C. in the next wafer processing.
The disadvantage is that it takes 0 minutes. Also, it is unclear how the heater output is controlled, but usually, if the heater current is simply cut off at the start of the temperature drop,
As the time elapses, the temperature decreases to 800 ° C. or less, and it takes more time until the temperature is raised again to 1200 ° C. and stabilized. In addition, there is a disadvantage that the temperature to be lowered changes depending on the waiting time, and the temperature rise time varies every time the temperature is raised again, and there is no reproducibility. This variation in the temperature rise time will eventually lead to a variation in the processing time, leading to serious defects in quality.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heat treatment furnace capable of shortening the time required for raising and lowering the temperature and improving the processing capacity, and having a reproducible temperature raising time.

[0008]

SUMMARY OF THE INVENTION The present invention is characterized in that a reaction tube for accommodating a plurality of semiconductor wafers, a heat equalizing tube surrounding the reaction tube and having a heater disposed around the outside thereof, A blower for supplying a heat transfer gas medium to the space interposed between the pipe and the heat transfer gas medium and circulating the heat transfer gas medium, connected to the blower via a switching valve and maintaining the heat transfer medium at a high temperature for storage; A heat treatment furnace comprising: a high-temperature gas storage tank and a low-temperature storage tank for storing and storing the heat transfer gas medium at a low temperature; and a temperature control unit for controlling the output of the heater.

Preferably, the temperature control section includes a system for detecting the temperature of the heat equalizing tube and controlling the output of the heater, and a system for detecting the temperature of the heater itself and controlling the output of the heater.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIGS. 1 (a) and 1 (b) show the heat treatment furnace, as shown in FIG. 1 (a), which accommodates a soaking tube 4 surrounded by a heater 5 and a wafer 17 placed on a boat 7. The heat transfer gas medium is introduced into the space 6a between the reaction inner pipe 6 and the pipe 9
a, 9b, a blower 2 for circulating the heat transfer gas medium discharged from the exhaust pipes 8a, 8b, a reservoir 1b connected to the back side of the blower for maintaining and storing the heat transfer gas medium at a high temperature and a heat transfer. A reservoir 1a for maintaining and accumulating a gaseous medium at a low temperature, valves 11a, 12a and valves 11b, 12b for switching to one of supply pipes for reservoirs 1a, 1b, introduction pipes 9a, 9b and exhaust pipes 8a, 8b.
And the temperature is detected by the thermocouples 10a and 10b and the heater 5
And a temperature control unit 10 for controlling the electric current to the heater 5 and adjusting the heating output of the heater 5.

A temperature control unit 10 for controlling the output of the heater 5 includes a temperature control system for detecting the temperature of the soaking tube 4 with a thermocouple 10a and controlling the current of the heater 5, and the heater 5 itself, though not shown in the drawing. And a temperature control system that controls the current of the heater 5 by detecting the temperature of the heater 5 with the thermocouple 10b. The temperature control system including the thermocouple 10a detects the temperature of the soaking tube 4 and controls the output of the heater 5 to increase the temperature, for example,
A generally known PID control is performed with a set temperature of 1200 ° C. On the other hand, the temperature control system including the thermocouple 10b detects the temperature of the heater 5 itself, sets the temperature to a temperature lower than the temperature, for example, 800 ° C., and performs PID control.

Here, as the heat transfer gas medium, for example, inexpensive nitrogen gas is used to fill the respective reservoirs 1a and 1b. The reservoir 1a is a kind of constant temperature bath and includes a chiller unit and is always kept at a temperature lower than normal temperature (for example, 20 ° C.). Then, by opening the valves 11a and 12a, the blower 2 circulates through the space 6a via the pipe. On the other hand, the reservoir 1b is a kind of heat storage tank, in which a heater is wound around the container.
Nitrogen gas at a temperature of about C is stored. The space 6 is opened by opening the valves 11b and 12b.
Supply high temperature nitrogen gas to a and circulate. The valve 11
Although the piping between b and the reservoir 1b is shown short in the drawing, the actual piping is long, so it is desirable to wind the heater 3 around the piping.

Next, the operation of the heat treatment furnace will be described with reference to FIG. First, the valve 11 from the reservoir 1b
The wafer 17 is stored together with the boat 7 in the reaction inner tube 6 maintained at a constant high temperature of, for example, 800 ° C. by the high temperature nitrogen gas sent through the b and 12b and the temperature control system switched to the low temperature side. I do. Of course, as described above, the wafer 17 is transferred into the furnace at a slow speed of 2 to 3 cm / min by a boat loader in order to prevent an oxide film and warpage due to entrainment in the atmosphere.

Next, at time t1 after 10 minutes have passed since the wafer 17 is inserted, the temperature control system is switched to the high temperature side including the thermocouple 10a, and a larger current flows through the heater 5 than in the previous temperature control system. Then, the thermocouple 10a always detects the temperature and supplies a current to the heater 5 so that the temperature in the inner reaction tube 6 becomes 1200 ° C. As a result, the nitrogen gas sent at 800 ° C. is heated to 1200 ° C. or more and heat is transferred to the inner reaction tube 6, and the internal temperature of the inner reaction tube 6 becomes 1200 ° C. By the way, it was 20 minutes when the heating time t1 to t2 was measured.

Next, the processing time from t2 to t3 is maintained at a constant temperature of 1200 ° C. by the temperature control system on the high temperature side, and the impurity of the wafer 17 is diffused. The nitrogen gas heated to 1200 ° C. or more is exhausted from the exhaust pipes 8a and 8b and returns to the reservoir 1b through a long piping path. The nitrogen gas at this time is 800 ° while passing through a long piping route.
It is cooled below C.

Next, when the processing time elapses and reaches t3, the valves 11a and 12a are opened instead of closing the valves 11b and 12b, and low-temperature nitrogen gas at room temperature or lower circulates from the reservoir 1a. At the same time as this operation, the current to the heater 5 is cut off. As a result, the inner reaction tube 6 is cooled to approximately 800 ° C. in the time t4. After t4, the temperature control system is switched to the low temperature side, and the valves 11b and 12b are opened to supply high-temperature nitrogen gas to the space 6a and circulate. As a result, the temperature of the heater 5 does not rise above 800 ° C., and the heater 5 maintains a constant temperature. On the other hand, the interior of the space 6a also becomes a high-temperature nitrogen gas atmosphere of 800 ° C. Will be kept.

Then, the wafer 17 is taken out from the inner reaction tube 6, the unprocessed wafer is stored again, and the wafer is diffused in the same manner as described above. In addition, when the temperature lowering time was measured, it was approximately 30 minutes, which could be shortened by about 10 minutes.
Further, even after the temperature was lowered, the temperature was kept constant without lowering, and the rise time and fall time of the temperature were always constant without fluctuation.

[0019]

As described above, according to the present invention, the temperature equal to the maintenance temperature of the reaction inner tube is provided in the space between the heat equalizing tube in which the heater is disposed on the outer periphery and the reaction inner tube surrounded by the heat equalizing tube. By controlling the output of the heater by detecting the temperature of the heater itself while circulating the heat transfer gas medium, the maintenance temperature of the reaction inner tube is always kept constant regardless of the length of the waiting time of the wafer,
At the time of temperature rise, the temperature of the soaking tube is detected and the output of the heater is controlled to increase the temperature from a constant maintenance temperature to the processing temperature. Therefore, there is an effect that the temperature rise time can be shortened and the reproducibility of the temperature rise time is improved. Further, by supplying and circulating a heat transfer gas medium having a temperature equal to or lower than the room temperature to cool the inner reaction tube from the processing temperature to the maintenance temperature, there is also an effect that the cooling time can be reduced and the processing capacity can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a heat treatment furnace of the present invention and a temperature diagram for explaining the operation.

FIG. 2 is a diagram showing an example of a conventional heat treatment furnace.

[Explanation of symbols]

 1a, 1b Reservoir 2 Blower 3,5,16 Heater 4,13 Heat equalizing tube 6 Reaction inner tube 6a Space 7 Boat 8a, 8b Exhaust tube 9a, 9b Inlet tube 10 Temperature control unit 10a, 10b Thermocouple 11a, 11b, 12a , 12b Valve 14 Quartz outer tube 15 Quartz reaction tube 17 Wafer 18 Claw 19 Blowing means

Claims (2)

(57) [Claims] 1. A reaction tube for accommodating a plurality of semiconductor wafers, a heat equalizing tube surrounding the reaction tube and having a heater disposed around the reaction tube, and a space interposed between the heat equalizing tube and the reaction tube. A blower that supplies a heat transfer gas medium and circulates the heat transfer gas medium; a high-temperature gas storage tank connected to the blower via a switching valve for maintaining and storing the heat transfer medium at a high temperature; A heat treatment furnace comprising: a low-temperature storage tank that maintains and stores a gas medium at a low temperature; and a temperature control unit that controls output of the heater. 2. The temperature control unit includes a system for detecting the temperature of the heat equalizing tube and controlling the output of the heater, and a system for detecting the temperature of the heater itself and controlling the output of the heater. The heat treatment furnace according to claim 1, wherein