JPH0796170A - Temperature controlling method of heat treating device - Google Patents

Abstract

PURPOSE:To provide the temp. controlling method capable of temp. controlling with high controlling responce only by an outside temp. sensor. CONSTITUTION:The FF signal f(t) expressed by formula (1) f(t)=E*exp(-t/T)... (1) (E is max. amplitude manipulated variable, T is a time constant) and the manipulated variable signal for driving the temp. controlling means such as a heating means so as to obtain a desired set temp. signal are mixed, and based on this resultant set temp. signal, an outside temp. is controlled temporarily so as to overshoot, so the controlling responce of an inside temp. is increased as compared with a conventional method. At this time, since it is sufficient to control so as to make this resultant set temp. signal and a detected value by the outside temp. sensor coincide an exact and rapid temp. controlling is possible without using an inside temp. sensor.

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 more particularly to a feedforward temperature control method for the heat treatment apparatus.

[0002]

2. Description of the Related Art Conventionally, in the semiconductor manufacturing process,
A CVD device, an oxide film forming device, a diffusion device, or the like is used for laminating a thin film or an oxide film on the surface of a semiconductor wafer that is an object to be processed, or for diffusing impurities. Vertical heat treatment furnaces are used to achieve high processing. This vertical heat treatment furnace
In general, a tubular furnace for heating is arranged vertically, a reaction tube made of quartz or the like is provided in the tubular furnace (processing chamber), and many objects to be processed such as semiconductor wafers are vertically accommodated in a vertical direction. Is raised by an appropriate elevating device and carried into the reaction tube, and a predetermined heat treatment such as oxide film formation is carried out in the furnace by an appropriate reaction gas introduced into the processing chamber.

By the way, it is necessary to control the processing of the surface of the semiconductor wafer with high accuracy in accordance with the speeding up and high integration of the integrated circuit. For that purpose, it is important to improve the accuracy of temperature control during the heat treatment. is there. For example, a semiconductor wafer, which is an object to be processed, is raised from a predetermined temperature, for example, 500 ° C., to a predetermined temperature, for example, 1000 ° C. in a short time, and is maintained at a predetermined temperature, for example, 1000 ° C. during processing, and again after a processing, a predetermined temperature is predetermined. It is necessary to lower the temperature to, for example, 500 ° C.

[0004]

However, in the structure of the conventional vertical heating furnace, since the object to be processed is heated by the heating means installed outside the processing chamber, the heat transfer from the heating means to the object to be processed is performed. The process has been performed indirectly through a wall of the processing chamber made of quartz or the like, or a heat equalizing means for allowing uniform temperature propagation. Therefore, since there is a difference in the predetermined temperature arrival time between the outside and the inside of the processing chamber, only the temperature control by the external temperature detecting means installed near the heating means outside the processing chamber causes a slow control response of the temperature inside the processing chamber. It was not possible to perform accurate and quick temperature control in the processing chamber. In particular, when inserting a boat on which a wafer is placed into the processing chamber, the temperature inside the processing chamber may temporarily drop. However, the conventional temperature control method has a slow control response and the temperature inside the processing chamber cannot be recovered (temperature recovery). Lateness was also a problem.

Therefore, in the conventional temperature control system,
An internal temperature detecting means for detecting the temperature in the vicinity of the object to be processed is installed in the processing chamber, temperature control is performed according to the internal temperature detected by the internal temperature detecting means, and a method of accelerating temperature recovery has been attempted. There is. However, in this method, since the temperature detecting means itself is installed in the processing chamber, a film of the process adheres to the temperature detecting means during processing, and accurate temperature control cannot be performed, which is a problem.

More recently, a method of controlling the temperature of the processing chamber only by the external temperature detecting means has been developed according to the set temperature recipe obtained by the polygonal line approximation technique, but it is necessary for creating the set temperature recipe. There were many input parameters, and there was a problem in practice because it required skill to create them.

A method has also been developed in which a correction for feedforward control is applied to a preset temperature, and the corrected preset temperature is input to a temperature controller to control the output of the heating means. If the correction signal itself is wrong or the correction signal is abnormal, the temperature control system may be disturbed and the processing may be seriously affected. Therefore, some measures have to be taken.

The present invention has been made in view of various problems of the conventional temperature control method as described above, and an object of the present invention is to set a preset temperature by a correction signal obtained by a very simple method. By correcting the control recipe of (1), it is possible to perform accurate and rapid temperature control of the processing chamber using only the external temperature detecting means without using the internal temperature detecting means, and the correction signal itself has an error. It is an object of the present invention to provide a new and improved feedforward temperature control method for a heat treatment apparatus that can minimize damage to the processing even in the case.

[0009]

In order to solve the above problems, a temperature control method for a heat treatment apparatus according to a first aspect of the present invention is designed such that objects to be processed arranged in a processing chamber are placed outside the processing chamber. Based on the external temperature detected by the installed external temperature detecting means, when heat-treating by the temperature adjusting means installed outside the processing chamber, the temperature adjusting means is driven to bring the external temperature to a set temperature. To generate a preliminary temperature increase signal for preliminarily increasing the temperature for a predetermined time based on the operation amount signal, and for the predetermined time, a temperature based on the external temperature of the processing chamber is generated. The output of the temperature control means is controlled by the output of the control means and the preliminary temperature increase signal.

Further, according to a second aspect of the present invention, the objects to be processed arranged in the processing chamber are adjusted based on the external temperature detected by the external temperature detecting means installed outside the processing chamber. When performing heat treatment by a temperature adjusting means such as a heating means installed outside the processing chamber, an operation amount signal for driving the temperature adjusting means such as the heating means is given in advance so as to bring the external temperature to a set temperature, and The manipulated variable signal and the preliminary temperature increase signal f (t) f (t) = E * exp (-t / T) obtained in advance by the following equation (1) (1) (where E is the maximum amplitude operation) And T represents a time constant) to obtain a combined operation amount signal, and control the output of the temperature adjusting means such as heating means based on the combined operation amount signal and the external temperature of the processing chamber. It is characterized by doing.

According to another aspect of the present invention, the temperature control method for a heat treatment apparatus is applied to a heat treatment apparatus provided with a device for heat-treating a heating region of an object to be treated with at least three heating means, It is also possible to provide a preliminary temperature rising signal for each heating means to raise the temperature.

[0012]

According to the present invention, the predetermined manipulated variable signal for setting the external temperature to the set temperature is corrected by the preliminary temperature increase signal, so that the reaction rate for controlling the internal temperature is increased only by detecting the external temperature. be able to. In particular, according to the knowledge of the inventor of the present application, since the transfer function of the external temperature and the internal temperature of the processing chamber can be well approximated by the first-order lag system, the preliminary temperature increase signal f ( t) f (t) = E * exp (-t / T) (1) (where E represents the maximum amplitude operation amount and T represents the time constant) and drives the temperature adjusting means such as the heating means. It is possible to easily and quickly correct the delay of the temperature control by adding it to the desired manipulated variable. That is, it is possible to speed up the control response of the internal temperature by once overshooting the external temperature according to the feedforward signal. At that time, the maximum amplitude manipulated variable and time constant required for correction are obtained experimentally or by simulation in advance without requiring many control parameters as in the conventional method, and the manipulated variable output from the temperature controller is calculated. In addition, the control reaction rate of the internal temperature of the processing chamber can be easily increased only by monitoring the change in the external temperature detected by the external temperature detecting means without using the internal temperature detecting means. As a result, it is possible to perform finer processing on the surface of the object to be processed, and further improve the control performance of the heat treatment apparatus to improve the yield and throughput of products. Even if the input feedforward signal is improper, the result is fed back to the temperature controller and compared with the preset temperature to be corrected, which is serious for the processing. It is possible to build a fail-safe temperature control system that does not cause damage.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a temperature control method for a heat treatment apparatus constructed according to the present invention is applied to a vertical fast heat treatment furnace for semiconductor wafers will be described in detail below with reference to the accompanying drawings.

The vertical heat treatment furnace shown in FIG. 1 has a substantially cylindrical tubular furnace 2 having a heat insulating top portion vertically supported on a horizontally fixed base 1, and a tubular furnace 2 inside the tubular furnace 2. It is composed of a substantially cylindrical reaction tube 4 having a top made of quartz or the like, which is inserted at a predetermined interval 3 and having a top portion, and a heater such as a resistance heating element spirally arranged on the inner peripheral wall of the tubular furnace 2. The heating means 5, a plurality of objects to be processed, for example, a wafer boat 6 made of quartz or the like capable of holding a large number of semiconductor wafers W in a vertical state in a horizontal state, and an elevating mechanism for elevating the wafer boat 6. The main part is composed of 7 and 7.

Further, at the bottom of the tubular furnace 2, the space 3 is provided.
Is provided with an intake port 8 that communicates with the cooling air, and cooling air can be supplied into the space 3 by an air supply fan 10 connected via an appropriate manifold 9. An exhaust port 11 communicating with the space 3 is also installed at the top of the tubular furnace 2 so that the air in the space 3 can be exhausted.

A reaction gas supply conduit 12 connected to a gas source (not shown) via a flow controller is provided at the bottom of the reaction tube 4, and a predetermined processing chamber 13 inside the reaction tube 4 is provided. It is possible to introduce the reaction gas of Further, an exhaust pipe line 14 connected to an exhaust means such as a vacuum pump (not shown) is connected to the bottom of the reaction tube 4 so that the inside of the processing chamber 13 can be evacuated to a predetermined pressure. It is configured.

Further, the wafer boat 6 is provided with a lid body 16 via a heat retaining cylinder 15 under a holding portion 6a for holding the semiconductor wafers W in multiple stages, and the wafer boat 6 is raised by the elevating mechanism 7. By doing so, the lid 16
Since it is possible to hermetically seal the opening at the bottom of the reaction tube 4, the inside of the processing chamber 13 is evacuated using the exhaust pipe line 14 during processing, and the exhaust gas from the exhaust pipe line 10 is exhausted. It is configured such that a predetermined reaction gas can be introduced into the processing chamber 13 from the reaction gas supply conduit 12 while performing the above.

Next, the temperature control system of the vertical heat treatment furnace configured as described above will be described. A plurality of temperature control systems (in the illustrated example, the upper part,
An upper heater 5a, a central heater 5b, and a lower heater 5c, which are separately arranged in the central portion and the lower portion, and a plurality of locations (upper portion in the illustrated example, corresponding to the heaters of the tubular furnace 2).
Temperature sensors arranged in the central portion and the lower part), for example, temperature sensors 17a and 17b composed of thermocouples,
It is equipped with 17c. As described above, according to the present invention, it is sufficient to install the temperature sensors 17a, 17b, 17c in the vicinity of the heaters 5a, 5b, 5c outside the reaction tube 4, as in the conventional temperature control method. There is no need to install a temperature sensor inside the reaction tube 4. In the illustrated example, three temperature sensors 17a, 17b, 17c are arranged at the upper part, the central part and the lower part, but the number of temperature sensors and the installation location are not limited to this embodiment. When temperature zone control is not performed, it is possible to perform temperature control with a single temperature sensor. Further, in the illustrated example, the internal temperature sensor is not provided only by the external temperature sensor 17, but an internal sensor may be appropriately provided as necessary to obtain a parameter of the correction signal, for example.

The temperature signals detected by the temperature sensors 17a, 17b, 17c are appropriately supplied to the temperature controller 18.
Is transmitted to the heaters 5a and 5a so that the preset temperature and the temperature signal coincide with each other.
Drive signals for driving b and 5c are generated. As described above, this drive signal is processed based on the correction signal formed according to the present invention and sent to the heater power source 19 as a correction drive signal to control the output of the heater 5 or to the inverter 20. The air fan 10 is configured to be frequency-controllable. In the illustrated example, only one heater power supply 19 and one inverter 20 are installed, but the present invention is not limited to this embodiment. For example, when the temperature is zone-controlled as described above, it is also possible to install a plurality of heater power sources corresponding to the heaters installed in each zone,
Alternatively, when a forced exhaust fan (not shown) is installed at the exhaust port 11 to improve the cooling performance, it is possible to provide an inverter for controlling the rotation speed of the exhaust fan.

Next, a method for controlling the temperature of the vertical heat treatment furnace configured as described above according to the present invention will be described. FIG. 2 shows the waveform of the feedforward signal used in the method of the present invention. As shown, the feedforward (FF) signal used by the present invention is an exponential function f (t) f (t) = E * exp (-t / T) (1) ( Here, E represents the maximum amplitude manipulated variable, and T represents the time constant). That is, according to the knowledge of the inventors, since the internal temperature and the external temperature of the processing chamber can be approximated by the transfer function of the first-order lag system, the feedforward signal f (t) approximated by the exponential function as described above.
Can speed up the control response. As the manipulated variable, it is possible to select an optimum numerical value according to the control target, for example, a power value, a voltage value, a current value, a frequency, or the like.

Next, how the operation amount and the correction signal are combined will be described with reference to FIG. 500 as shown
In order to raise the set temperature in the processing chamber from ° C to 1000 ° C, it is necessary to apply the step signal A to the heater power supply 19, for example. However, using the step signal A as it is, the heaters 5a, 5b,
When 5c is driven, the temperature control response in the processing chamber is slow due to the delay in heat transfer from the outside to the inside of the processing chamber, and it is not possible to obtain the desired rising temperature. Therefore, the feedforward signal f obtained by the present invention
(T) B is combined with the step signal A to obtain a combined operation amount signal C, and heaters 5a, 5b, 5
When c is driven, the heater output is increased by the amount of the feedforward signal uniquely determined by the time constant T and the maximum amplitude temperature E, so that the temperature control response in the processing chamber can be increased accordingly. Become.

The maximum amplitude manipulated variable E and the time constant T for obtaining the feedforward signal f (t) can be obtained experimentally or by simulation. Further, in the above example, one feedforward signal B is added to the step signal A, but the present invention is not limited to this embodiment. For example, before the rising edge of the step signal, or at the rising edge of the step signal,
Alternatively, after the step signal rises, it is possible to feed-forward control the set temperature by appropriately adding the optimum feed-forward signal B. Further, when temperature control is performed for each of a plurality of zones, the same or different feedforward signals B1, B2 ... Are applied to the plurality of step signals A1, step signals A2. It is possible.

FIG. 4 is a block diagram showing the flow of the temperature control method according to the present invention. By inputting a desired set temperature 41 that is preset in the temperature controller 42 as shown in the figure, the temperature controller 42 outputs a drive signal that determines an operation amount for driving the power control device 43. The feedforward signal (FF signal) formed by the feedforward signal generator (FF signal generator) 44 is supplied to the drive signal in block 4
In step 5, they are combined to form a combined drive signal. The combined drive signal thus obtained is sent to the power control device 43, and the output of the heater 46 is adjusted according to the signal.
The heating temperature by the heater 46 is appropriately detected by the external temperature sensor 47 and fed back to the temperature controller 42, and the temperature controller 44 outputs the drive signal again so that the temperature signal and the preset temperature may be matched. It outputs and controls the power control device 45 and the heater 46. As described above, according to the method of the present invention, since the feedforward signal 44 is input in a stage subsequent to the temperature controller 42, even if the feedforward signal is erroneous, it is possible to correct the error at the time of feedback from the temperature sensor 47. Therefore, it is possible to construct a fail-safe system that does not seriously damage the processing.

The timing for generating the FF signal and the set temperature can be specified in advance in a recipe of a process controller (not shown), for example. Further, the maximum amplitude value E and the time constant T for producing the FF signal are, for example,
It is possible to store one or more sets of data patterns in the signal generator 42. Further, the FF signal generator 42 is provided as a part of a temperature controller 44 described later, or as a part of the process controller.
Alternatively, it can be configured as an independent device. Further, the function of combining the FF signal and the drive signal can be configured as a part of the temperature controller 44, a part of the power control device 43, or an independent device.

The results of temperature control according to the present invention are shown in FIG. When the normal temperature control is performed as shown in the figure, the external temperature B is controlled so as not to overshoot and is ramped up to a target temperature, for example, 700 ° C. Accordingly, the internal temperature (b) gradually approaches the achieved temperature with a slow control response. However, when the temperature control based on the present invention is performed, the external temperature A once overshoots the target temperature, and the internal temperature (a) responds more quickly than the conventional method according to the overshoot. It can be seen that the target temperature is reached. As described above, according to the method of the present invention, the responsiveness of the internal temperature of the processing chamber is enhanced by simply adding the correction signal that can be easily formed to the set temperature signal and monitoring the temperature detected by the external temperature sensor. It is possible.

Finally, the temperature control method according to the present invention is shown in FIG.
The case where the oxide film forming process is performed by applying the vertical heat treatment apparatus described in 1 above will be briefly described. First, the shutters 21 and 2 of the intake port 9 and the exhaust port 11, respectively.
2 is closed and the wafer boat 6 is raised to accommodate the semiconductor wafer W in the reaction tube 4. Next, the processing chamber 1 in the reaction tube 4 is heated by the heaters 5a, 5b, 5c.
3 is heated to a predetermined temperature, for example 1000 ° C., and in that case, according to the present invention, the drive signal for raising the temperature to a preset set temperature is the temperature controller 18 described above.
Is output, the FF signal is added to the drive signal, and the heater 5 is driven by the correction drive signal, so that the output of the heater 5 once overshoots, and the responsiveness of the internal temperature is improved. It is possible to quickly raise the internal temperature of the processing chamber 13 to a desired set temperature. At that time, the external temperature sensors 17 a, 1
Since the external temperature monitored by 7b and 17c is appropriately fed back to the temperature controller 18 prior to the application of the FF signal, even if an error occurs in the FF signal, the error can be corrected. .

A predetermined reaction gas, for example, oxygen is introduced from the reaction gas introducing pipe 12 into the processing chamber 13 thus heated to a desired temperature, and an oxide film is formed on the surface of the semiconductor wafer W. It is possible to form. After the process is completed, the reaction gas is exhausted from the exhaust pipe line 14, and the shutters 21 and 22 are opened to quickly lower the temperature in the furnace, and the air supply fan 10 is used to open the tubular furnace 2 and the furnace. It is possible to supply cooling air in the space 3 between the reaction tube 4. In this way, the processing chamber 13
After the inner temperature has dropped to a predetermined temperature, the elevating mechanism 7 is lowered to take out the semiconductor wafer W, and the oxide film forming process by the heat treatment apparatus is completed.

In the above embodiment, the case where the step signal for driving the heater is combined with the FF signal for correction has been described as an example, but the method of the present invention is not limited to this embodiment. The method of the present invention can also combine and correct the FF signal with the step signal for driving the cooling device. That is, according to the above example, the frequency of the air supply fan 10 is controlled by the inverter 20 when the inside of the furnace is cooled. At that time, according to the method of the present invention, the inverter 2 is used.
It is also possible to accelerate the cooling response in the furnace by synthetically adding the FF signal formed according to the present invention to the ramp down signal sent to 0. Furthermore, according to the present invention, depending on the type of the manipulated variable signal applied to the controlled object,
It is possible to appropriately select the maximum amplitude value of the FF signal from a negative value to a positive value.

Further, in the above embodiment, the case where the method of the present invention is applied to the vertical heat treatment apparatus for semiconductor wafers has been described, but the present invention is not limited to such an embodiment. In addition to the above, the present invention may be applied to temperature control of a heat treatment apparatus for an object to be processed other than a semiconductor wafer, for example, a glass substrate, an LCD substrate, etc. within a range not departing from the technical idea of the present invention described in the claims. Is possible.

As described above, according to the present invention, the FF signal uniquely determined by only two parameters and the operation amount for driving the temperature adjusting means to achieve the desired set temperature are determined. Since the external temperature is once overshooted by combining with the drive signal, the control response of the internal temperature can be enhanced as compared with the conventional method. In that case, it is sufficient to control so that the desired set temperature and the detected value by the external temperature sensor match, so that accurate and quick temperature control can be performed without using the internal temperature sensor. Further, since the feedback signal from the external temperature sensor is applied before the FF control, even if the feedback signal is erroneous, correction can be performed and a fail-safe temperature control system can be constructed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a vertical heat treatment apparatus to which the method of the present invention can be applied.

FIG. 2 is an explanatory diagram showing a waveform of a feedforward signal (FF signal) formed according to the present invention.

FIG. 3 is an explanatory diagram showing a state of a combined operation amount signal obtained by combining an operation amount signal for driving the temperature adjusting means, a set temperature signal, and an FF signal according to the present invention.

FIG. 4 is a block diagram showing a control flow for implementing the present invention.

FIG. 5 is a graph comparing the results of temperature control according to the present invention and the results of conventional temperature control.

[Explanation of symbols]

 2 Tubular furnace 3 Interval 4 Reaction tube 5 Heater 6 Wafer boat 17 Temperature sensor 18 Temperature controller 19 Heater power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G05D 23/00 F 9132-3H 23/19 G 9132-3H J 9132-3H G06F 19/00 H01L 21 / 22 9278-4M 21/324 Z

Claims (3)

[Claims] 1. A temperature control device for processing objects arranged in a processing chamber based on an external temperature detected by an external temperature detecting device installed outside the processing chamber. When the heat treatment is performed by the means, an operation amount signal for driving the temperature adjusting means is provided in advance so that the external temperature becomes the set temperature, and the temperature is preliminarily raised for a predetermined time for raising the temperature based on the operation amount signal. A preliminary heating signal is generated, and the output of the temperature adjusting means is controlled by the output of the temperature control means based on the external temperature of the processing chamber and the preliminary heating signal over the predetermined time. Temperature control method for heat treatment equipment. 2. The temperature control of the objects to be processed arranged in the processing chamber based on the external temperature detected by the external temperature detecting means installed outside the processing chamber. When the heat treatment is performed by the means, a manipulated variable signal for driving the temperature adjusting means so as to bring the external temperature to the set temperature is given in advance, and the manipulated variable signal and the preliminarily increased temperature calculated in advance by the following equation (1). Temperature signal f (t) f (t) = E * exp (-t / T) (1) (where E represents the maximum amplitude manipulated variable and T represents the time constant), and A temperature control method for a heat treatment apparatus, characterized in that a combined operation amount signal is obtained, and the output of the temperature control means is controlled based on the combined operation amount signal and the external temperature of the processing chamber. 3. The apparatus according to claim 1, further comprising a device for heating the object heating area by at least three heating means, and heating each heating means by giving a preliminary heating signal. A method for controlling the temperature of a heat treatment apparatus according to.