JP2002299269A - Device and method for heat treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the throughput of a device while preventing the occurrence of slippages in the heat treatment of an object to be treated such as a semiconductor wafer. SOLUTION: In a process for cooling a process tube wherein, a plurality of semiconductor wafers are packaged on a wafer boat and put into a process tube, and after required treatment is applied to the semiconductor wafers by heating the process tube, cooling air is fed into the outer wall of the process tube, the process tube is gradually cooled by rotating an air blower for feeding the cooling air at a low speed in the case of high temperature. Afterwards, the process tube is quickly cooled by rotating the air blower at a high speed. Thus, the occurrence of slippages on the surface of the semiconductor wafers caused by the in-plane temperature difference expansion of semiconductor wafers caused by quick cooling of semiconductor wafers can be effectively prevented. As a device for providing such a process, the rotational speed of the air blower is controlled by using an inverter circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment apparatus and a heat treatment method particularly suitable for heat treatment of a semiconductor wafer.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor manufacturing process, a CVD apparatus is used for laminating a thin film or an oxide film on a surface of a semiconductor wafer (hereinafter, referred to as a wafer) to be processed or for diffusing impurities. , An oxide film forming device, a diffusion device or the like is used. As one type of such an apparatus, a plurality of wafers are vertically arranged and held in a process tube (processing chamber) such as a reaction vessel heated at a high temperature, and a reaction introduced into the processing chamber. A vertical heat treatment furnace for processing by gas is used.

[0003] As shown in FIG.
A cylindrical bottomed process tube 1 made of quartz glass or the like
And a process tube 1 standing upright with its bottom at the top, with a gap 2 surrounding it and a heat insulating furnace body 4 having a heater 3 as a heating means on its inner wall surface.
The main part is composed of a quartz wafer boat 5 that holds a plurality of wafers W arranged in a vertical direction and a lifting mechanism 6 that moves the wafer boat 5 up and down. In this apparatus, a supply port 7 and an exhaust port 8 are opened in the gap 2, a reaction gas introduction pipe 9 is inserted into the process tube 1, and an exhaust pipe 10 is connected. In addition, the wafer boat 5 has a lid 12 provided below the holding portion for holding the wafers W in a multi-stage manner via a heat retaining tube 11. The lid 12 closes the opening of the process tube 1 so that the process tube 1 is closed. 1
The inside is configured to be sealed. Thus, the process tube 1 can be evacuated using the exhaust pipe 10, and a predetermined reaction gas can be supplied from the reaction gas introduction pipe 9 into the process tube 1 while exhausting the gas from the exhaust pipe 10.

In order to perform the impurity diffusion treatment on the surface of the wafer W using the vertical heat treatment furnace configured as described above, first,
With the shutters 13a and 13b of the supply port 7 and the exhaust port 8 closed, the wafer boat 5 on which the wafers are arranged and arranged is raised to accommodate the wafer W in the process tube 1. Next, the inside of the process tube 1 is
After heating to a predetermined temperature of about 00 to 1000 ° C., a reaction gas is supplied from the reaction gas introduction pipe 9 into the process tube 1 to perform an impurity diffusion process on the wafer W surface. Thereafter, in order to remove the reaction gas remaining in the process tube 1, the reaction gas is removed by supplying a nitrogen gas while evacuating with a vacuum pump, and then the inside of the heat treatment apparatus is cooled and the wafer is taken out.

[0005] In recent years, there has been an increasing demand for improvement in the throughput of a semiconductor processing step.
Various attempts have been made to improve throughput. One of them is a cooling step after the processing step. For example,
When examining the process of forming a film on a semiconductor surface, the process is usually performed in a cycle of a heating process of a processing container, a silicon wafer loading process, a film forming process, and a cooling process. Are a film forming step and a cooling step. By the way, in the film forming process, shortening this time greatly affects the quality of a film to be formed, and thus it is not easy to reduce this time.
On the other hand, in the cooling step, since it is a step after the film formation, it is considered that it is easier to improve the time reduction than the film formation step. In order to shorten the time in the cooling step, it is considered that the cooling rate should be increased,
For this purpose, it is known that a cooling gas is blown around the process tube to cool it (Japanese Patent Laid-Open No. 2000-2000).
100812 and JP-A-7-6955).

However, when the cooling is performed by using the cooling air supply fan 14 as shown in FIG. 9, the temperature difference between the central portion and the peripheral portion of the wafer W becomes large as shown in FIG. That is, as shown in FIG. 6, which is a graph showing a change in the cooling time and the temperature of the central portion and the peripheral portion of the wafer in the cooling step, a temperature curve of the central portion of the wafer when natural cooling is performed is indicated by Cn. Similarly, when the temperature curve of the peripheral portion of the wafer W is indicated by En, in the natural cooling, the temperature difference between the central portion and the peripheral portion of the wafer W is relatively small because the wafer is gradually cooled. On the other hand, the difference between the temperature curve Cf at the central portion of the wafer and the temperature curve Ef at the peripheral portion of the wafer when forced cooling by blowing is larger than that in the case of natural cooling.

[0007] It is known that when the temperature difference between the central portion and the peripheral portion of the wafer W exceeds a certain temperature, slip, which is a kind of crystal defect of silicon single crystal, occurs. FIG. 7 shows a graph in which the lower limit of the in-plane temperature difference in the radial direction of a wafer in which a slip occurs in the heat treatment of an 8-inch silicon wafer is plotted as a function of the temperature at the center of the wafer. As is clear from FIG. 7, the area above the curve in the figure is an area where slip occurs, and the area below the curve is an area where no slip occurs. In other words, it can be seen that the higher the central temperature of the wafer W, the smaller the slip occurs with a smaller temperature difference. This means that the yield stress of the silicon single crystal decreases with increasing temperature. In FIG. 7, the absolute value of the difference between the wafer center temperature and the in-plane temperature at which slip occurs varies depending on conditions such as the diameter and thickness of the wafer and the shape of the wafer support, but this tendency does not change. . And
When this slip, which is a kind of crystal defect of a silicon wafer, occurs, when a semiconductor device is formed using this wafer, the production yield of the semiconductor device is reduced and the productivity is reduced. In the manufacturing process, the occurrence of such a slip is a very worrisome problem.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances. In accelerating cooling of a plate-shaped workpiece, the cooling rate is maintained while maintaining uniformity of the in-plane temperature of the workpiece. A method and apparatus for controlling the temperature of a heat treatment furnace capable of improving the throughput of the processing step of the object to be processed and preventing the occurrence of defects in the object to improve the yield by increasing the temperature. It is. That is, an object of the present invention is to increase the throughput of the apparatus while preventing the occurrence of defects such as slips in the heat treatment of a plate-shaped workpiece such as a semiconductor wafer.

[0009]

According to a first aspect of the present invention, there is provided a heating furnace main body, heating means disposed in the furnace main body, and a plurality of plate-like workpieces disposed in the furnace main body. A heat treatment apparatus, comprising: a processing vessel to be cooled; and a heating device having at least cooling means for bringing a cooling gas into contact with the periphery of the processing vessel to cool the processing vessel, comprising means for controlling a cooling rate by the cooling gas. It is.

In the above heat treatment apparatus, the cooling means is preferably a blower driven by an electric motor, and the means for controlling the cooling rate is preferably a means for controlling the supply amount of the cooling gas. Further, the means for controlling the supply amount of the cooling gas includes a motor speed control means by frequency control using an inverter circuit, a motor speed control means by voltage control, or a motor speed control means by current control. Either can be achieved. further,
In the above heat treatment apparatus, a means for forcibly discharging the cooling gas that has cooled the processing container may be further provided. The means for forcibly discharging the cooling gas may be a blower driven by an electric motor. Further, the means for controlling the cooling rate may be a means for controlling the supply amount and the discharge amount of the cooling gas. As means for controlling the supply and discharge of the cooling gas, the motor speed control means by frequency control using an inverter circuit, the motor speed control means by voltage control, or the motor speed by current control Any of the control means can be employed. The heat treatment apparatus further includes a means for measuring a temperature in the vicinity of the processing container, thereby enabling more accurate control. It is appropriate to use air as the cooling gas.

According to a second aspect of the present invention, there is provided a heat treatment method for accommodating a plurality of plate-like objects in a treatment container and performing heat treatment.
After the heat treatment is completed, when the cooling gas is brought into contact with the outer wall of the processing container in which the plate-like processing object is accommodated to cool the plate-like processing object, the temperature difference between the central part and the peripheral part of each plate-like processing object is reduced A heat treatment method characterized by controlling a cooling rate so as to be equal to or less than a predetermined value.

In the above heat treatment method, the control of the cooling rate can be performed by controlling the supply amount of the cooling gas. Further, the control of the supply amount of the cooling gas is performed by controlling the frequency of the motor rotation speed for driving the blower by the inverter,
This can be realized by voltage control of the motor speed or current control of the motor speed. Further, it is desirable to control the rotation speed of the blower driving motor by the inverter based on a measured value of the temperature near the processing container.

According to a third aspect of the present invention, a plurality of semiconductor wafers are mounted on a wafer boat, loaded into a process tube, and the process tube is heated to perform a required process on the semiconductor wafer. In the heat treatment method of supplying cooling air to the outer wall of the tube and cooling, after slowly cooling a blower for supplying cooling air to a preset temperature, and rapidly cooling by rotating the blower at high speed, This is a heat treatment method for a semiconductor wafer.

As described above, according to the present invention, in order to improve the throughput of the vertical heat treatment apparatus, it is obvious that the plate-like workpiece needs to be forcibly cooled. This is a result of a study on how to prevent the occurrence of slip, and it is possible to improve the throughput while effectively preventing the slip without significantly changing the heat treatment apparatus.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. Here, a case in which the heat treatment apparatus of the present invention is applied to a vertical heat treatment furnace for semiconductor wafers will be described. The same parts as those of the conventional heat treatment furnace shown in FIG.

[First Embodiment] FIG. 1 is a sectional view of a vertical heat treatment furnace having a cooling means according to a first embodiment of the present invention.

The heat treatment furnace of the present embodiment is a process tube 1 having a bottomed cylindrical processing vessel made of quartz glass or the like.
And a process tube 1 standing upright with the bottom part facing upward, with a gap 2 interposed therebetween, and a heat insulating furnace body 4 having a heater 3 as a heating means on its inner wall surface.
And a wafer boat 5 made of quartz for holding a plurality of wafers W arranged in a vertical direction, and an elevating mechanism 6 for elevating the wafer boat 5.

Further, a reaction gas introducing pipe 9 is inserted into the process tube 1 so that the process tube 1
It is configured such that the reaction gas is uniformly supplied to the substrate.
An exhaust pipe 10 is connected to the inside of the process tube 1. The inside of the process tube 1 is evacuated by a suction means such as a vacuum pump (not shown) connected to the exhaust pipe 10, and the exhaust of the reaction gas is performed. You can do it.

On the other hand, the wafer boat 5 is provided with a quartz lid 12 via a heat retaining tube 11 below a holding section for holding the wafers W in a multi-stage manner. The inside of the process tube 1 is sealed by an O-ring provided around the lid 12 by closing the opening. Therefore, the inside of the process tube 1 is evacuated using the exhaust pipe 10, and
A predetermined reaction gas can be supplied into the process tube 1 from the reaction gas introduction pipe 9 while the gas is exhausted from the chamber.

On the other hand, the process tube 1 and the furnace body 4
Are provided at equal intervals in the circumferential direction of the annular space 21 provided in the lower part of the furnace body 4, for example, eight supply ports 7 communicating with the gap 2 provided between The cooling gas supplied from the supply fan 14, which is a blower of, flows uniformly into the gap 2.
The gas used for cooling is the exhaust port 8, the shutter 13
b, and an exhaust fan 1 as a blower as a cooling means
5 and is processed in a predetermined manner.

The cooling air supply fan 14 and the exhaust fan 15 are connected to inverters 16 and 17, respectively. The inverters of these inverters are controlled by a control device 18.

Next, the operation of the heat treatment apparatus will be described by taking as an example a case where the apparatus is used in a step of diffusing impurities into a silicon wafer.

First, the shutter 1 of the supply port 7 and the exhaust port 8
The supply ports 7 and the exhaust ports 8 are closed by closing 3a and 13b. Then, the silicon boat 5 on which the required number of silicon wafers W are aligned and mounted is raised by driving the elevating mechanism 6, and the wafer boat 5 is inserted into the process tube 1. Next, after the heater power is turned on and the inside of the process tube 1 is heated to a predetermined temperature (impurity diffusion temperature) by the heater 3,
A reaction gas is supplied from the reaction gas introduction pipe 9 into the process tube 1 to diffuse impurities on the wafer surface.

After the diffusion process is completed, the power supply to the heater is shut off, and for example, nitrogen (N
₂ ) Purge the reaction gas by introducing a purge gas.
At the same time, the cooling air is fed into the gap 2 between the furnace main body 4 and the process tube 1 through the supply port 7 by using the supply fan 14 and the exhaust fan 15 is driven to Discharge cooling air. Thereby, the temperature in the furnace main body 4 is rapidly cooled, and after the temperature in the process tube 1 decreases to a predetermined temperature (for example, 300 ° C.),
By driving the elevating mechanism 6 to lower the wafer boat 5, the wafer W is taken out, and the processing operation is completed. In the forced cooling step, the present invention performs the following control using an inverter.

In the present invention, as shown in FIG. 8, a wafer center temperature-wafer surface temperature difference curve (cooling temperature history curve) is provided in a region below a slip margin curve (curve S) indicating a slip generation region. The cooling speed is controlled by controlling the frequency of the AC power supplied to the fan by an inverter or the like so that the cooling speed is always present. That is, in FIG. 8, the curve A passes through a region above the slip margin (curve S) because the wafer cooling temperature history curve passes through the region, and a slip occurs in this region. Therefore,
The cooling rate is controlled by an inverter or the like so that the wafer cooling temperature history curve always transitions to the area below the curve S as shown by the curve B in FIG.

More specifically, when forced cooling is performed by bringing cooling air into contact with the outer periphery of a process tube accommodating a wafer boat on which a silicon wafer is placed, the temperature drop at the center of the silicon wafer is caused by the temperature drop at the center of the silicon wafer. The greater the temperature drop and the faster the cooling rate, the greater the difference between the temperature at the center of the wafer and the temperature at the periphery of the wafer. As is clear from the slip margin diagram in FIG. 7, the temperature difference of the slip margin curve is smaller as the temperature of the central portion of the silicon wafer is higher. If the temperature difference between the central portion of the wafer and the peripheral portion of the wafer is reduced, and if the temperature is lowered to some extent, rapid cooling can be performed without causing slip. In order to control the supply amount of the cooling gas so as to realize such a cooling temperature history curve, the driving speed of the cooling gas supply fan and the exhaust fan drive motor, that is, the frequency control of the inverter, or the voltage control or the current control is used to control the drive motor. Is performed. This control process can be calculated in advance based on parameters such as the temperature of the cooling air, the capacity of the supply fan and the exhaust fan, the amount of the silicon wafer mounted, the heat capacity of the furnace internal members, and the like. Operation can be automatically performed by programming the control device.

In this embodiment, the supply fan 14
And the number of rotations of the exhaust fan 15 may be the same,
Different rotation speeds may be used. Further, it is desirable that the pressure in the furnace near the supply port 7 and the vicinity of the exhaust port 8 match. The balance between air supply and exhaust pressure is lost, and the furnace gap 2
If the pressure becomes a pressurized state, the cooling air heated to a high temperature may leak from a portion other than the exhaust port 8 and may damage electric parts and the like constituting the heat treatment apparatus,
On the other hand, when the pressure in the furnace gap is reduced, unclean air flows in from the environment in which the heat treatment apparatus is disposed, and the inside of the furnace may be contaminated.

In the above embodiment, the cooling gas is
Although the gas is supplied only from the lower end of the gap 2, a supply nozzle may be attached to the supply port 7 to supply the cooling gas from a plurality of positions in the height direction of the process tube 1. In this case, the uniformity of cooling at the upper and lower positions of the process tube 1 can be improved, and the control accuracy is further improved.

[Second Embodiment] FIG. 2 is a sectional view showing a vertical heat treatment furnace according to a second embodiment of the present invention.

This heat treatment apparatus controls the blowing capacity of the cooling air by the inverter in the same manner as in the first embodiment. However, a silicon wafer is placed in the process tube 1 by a thermometer 19 such as a thermocouple. The temperature of a portion close to W is measured, and the measured temperature is input to the control device 18, and cooling is performed while correcting the forced cooling process based on the actually measured temperature.

According to this embodiment, even if disturbance occurs due to unpredictable turbulence in the flow of cooling air or the like and an error occurs in the cooling sequence set before the start of the processing step, It is possible to make appropriate corrections to the programmed sequence based on the measured temperature,
The effect of easily converging disturbance due to unpredictable causes is exhibited.

As the thermometer 19, a thermocouple widely used as a thermometer for measuring a high temperature region can be used. However, since it is used in an environment in which the presence of impurities is extremely avoided. It is necessary to cover the surface with a protective tube such as a quartz glass tube. In addition, the measurement location may be one arbitrary location, or may be measured at several locations, such as an upper portion, a central portion, and a lower portion where the silicon wafer is placed. It is better to measure at multiple locations
More precise control becomes possible.

Third Embodiment FIG. 3 is a sectional view of a vertical heat treatment furnace according to a third embodiment of the present invention. In this embodiment, the exhaust fan is omitted from the device in the second embodiment, and forced cooling is performed only by the supply fan 14. According to this device, although a higher-performance fan is required as the supply fan 14, the exhaust fan 15 is not required.
There is no need to consider the balance between the abilities of the supply fan and the exhaust fan, and the simpler control can be realized. The exhaust from the exhaust port 8 is exhausted via the shutter 13b.

Fourth Embodiment FIG. 4 is a sectional view of a vertical heat treatment furnace according to a fourth embodiment of the present invention. In this embodiment, the air supply fan is omitted from the device in the second embodiment, and forced cooling is performed only by the exhaust fan 15. According to this device, although a higher performance fan is required as the exhaust fan 15, the air supply fan 14 is not required, so that
There is no need to consider the balance between the abilities of the supply fan and the exhaust fan, and there is an effect that simpler control can be realized.

[Fifth Embodiment] FIG. 5 is a sectional view of a vertical heat treatment furnace according to a fifth embodiment of the present invention. In this embodiment, the cooling gas supplied from the supply fan 14 passes through the gap 2 in the furnace main body 4 and cools the furnace internal members including the process tube 1 by the exhaust fan 15 while cooling the furnace internal members including the process tube 1. Although exhausted to the outside, the heated exhaust gas is cooled via the heat exchanger 20 and connected to the gas inlet of the supply fan 14 again to be reused as a cooling gas. According to this device, since the cooling gas is circulated and reused, the influence on the environment due to the discharge of the used gas can be reduced. When particles or the like are contained in the used gas, it is desirable to add a purification process to the cooling gas circulation line, to purify and reuse the purified gas. The heat recovered by the heat exchanger 20 is reused by a known method.

In the above embodiment, the case where the heat treatment apparatus of the present invention is applied to a heat treatment apparatus for a semiconductor wafer has been described. If the object to be processed is required to have uniform heat, such as generation of fine cracks in the material due to
Needless to say, the present invention can be applied to a heat treatment apparatus for an object to be processed such as a D substrate.

[0037]

According to the present invention, in the heat treatment step of the object to be processed, the cooling step can be accelerated by forcible cooling and the throughput can be improved without causing defects due to uneven heat in the object to be processed.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a heat treatment apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a heat treatment apparatus according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a heat treatment apparatus according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a heat treatment apparatus according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view of a heat treatment apparatus according to a fifth embodiment of the present invention.

FIG. 6 is a diagram for explaining an in-plane temperature distribution due to a difference in a cooling method of the object to be processed.

FIG. 7 is a diagram showing a relationship between a temperature difference in a silicon wafer surface and occurrence of slip.

FIG. 8 is a diagram for explaining a cooling speed control process according to the present invention.

FIG. 9 is a schematic sectional view of a conventional heat treatment apparatus.

[Explanation of symbols]

 W ... Wafer 1 ... Process tube 2 ... Gap 3 ... Heater 4 ... Heat-insulating furnace body 5 ... Wafer boat 6 ... Elevating mechanism 7 ... Supply port 8. ··· Exhaust port 9 ··· Reaction gas introduction pipe 10 ··· Exhaust pipe 11 · · · Heat retaining cylinder 12 · · · Lids 13a and 13b · · · Shutter 14 · · · Supply fan 15 · · · Exhaust fan 16 , 17 ... Inverter 18 ... Control device 19 ... Temperature measuring device 20 ... Heat exchanger 21 ... Annular space

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tsuyoshi Takizawa F-term (reference) 5F045 BB08 BB11 DP19 EB02 EJ04 EJ10 5-3-6 Akasaka, Minato-ku, Tokyo TBS Release Center Tokyo Electron Limited

Claims (15)

[Claims] 1. A furnace main body of a heating furnace, heating means disposed in the furnace main body, a processing container disposed in the furnace main body and accommodating a plurality of plate-like workpieces, A heat treatment apparatus comprising at least a cooling means for bringing a cooling gas into contact with the surroundings to cool the heating means, comprising means for controlling a rate of cooling by the cooling gas. 2. The heat treatment apparatus according to claim 1, wherein said cooling means is a blower driven by an electric motor. 3. The heat treatment apparatus according to claim 1, wherein the means for controlling the cooling rate is means for controlling a supply amount of a cooling gas. 4. A means for controlling the supply amount of the cooling gas,
The motor speed control means by frequency control using an inverter circuit, the motor speed control means by voltage control, or the motor speed control means by current control. 4. The heat treatment apparatus according to 3. 5. The heat treatment apparatus according to claim 1, further comprising means for forcibly discharging a cooling gas that has cooled the processing container. 6. The heat treatment apparatus according to claim 5, wherein the means for forcibly discharging the cooling gas is a blower driven by an electric motor. 7. The heat treatment apparatus according to claim 5, wherein the means for controlling the cooling rate is means for controlling a supply amount and a discharge amount of the cooling gas. 8. The motor according to claim 5, wherein the means for controlling the supply and discharge of the cooling gas is a means for controlling the number of revolutions of the electric motor by frequency control using an inverter circuit. The heat treatment apparatus according to any one of the above. 9. The heat treatment apparatus according to claim 1, further comprising means for measuring a temperature near the processing vessel. 10. The heat treatment apparatus according to claim 1, wherein the cooling gas is air. 11. A heat treatment method for accommodating a plurality of plate-shaped objects in a processing container and performing heat treatment, wherein after the heat treatment is completed, cooling is performed on an outer wall of the processing container in which the plate-shaped objects are accommodated. A heat treatment method comprising: controlling a cooling rate such that a temperature difference between a central portion and a peripheral portion of each of the plate-shaped workpieces is equal to or less than a predetermined value when cooling by contacting a gas. 12. The heat treatment method according to claim 11, wherein the control of the cooling rate is a control of a supply amount of a cooling gas. 13. The method according to claim 13, wherein the control of the supply amount of the cooling gas is any one of frequency control of a motor speed for driving a blower by an inverter, voltage control of the motor speed, and current control of the motor speed. The heat treatment method according to claim 12, wherein 14. The heat treatment method according to claim 13, wherein the number of rotations of the blower driving motor by the inverter is controlled based on a measured value of a temperature near the processing container. 15. A plurality of semiconductor wafers are mounted on a wafer boat, loaded into a process tube, and the process tube is heated to perform required processing on the semiconductor wafer. A heat treatment method for cooling the semiconductor wafer by bringing a blower for supplying cooling air at a low speed to slowly cool to a preset temperature, and then rapidly rotating the blower to rapidly cool the semiconductor wafer. Method.