JP2530124B2 - Lamp annealing furnace temperature control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention is directed to activation of an ion implantation layer in a semiconductor wafer process, reflow of phosphosilicate glass, annealing of metal, formation of ohmic contact between Si and metal, etc. The present invention relates to a temperature control device for a lamp annealing furnace (light heating device) used in.

[Prior Art] In a conventional lamp annealing furnace, rod-shaped tungsten halogen lamps (hereinafter abbreviated as lamps) 2, 2 ... The reflecting plate 1 and the lamp 2 are arranged apart from each other (the surface of the reflecting plate 1 may be processed into a curved surface for each lamp in order to enhance the reflection effect). , A quartz glass process tube is arranged between them.

The ion-implanted semiconductor wafer 4 is placed on the quartz susceptor 5 housed in the process tube 3,
In this state, the lamp 2 is irradiated and heated. On the other hand, a processing gas is introduced into and discharged from the processing space formed by the process tube 3 and the lid 6, and the wafer 4 is processed.

FIG. 11 shows an example of a target pattern of the wafer temperature in the heat treatment of the wafer. The temperature of the wafer reaches a constant temperature range of about 1000 ° C. about 8 seconds after the temperature starts to be increased, and the wafer is gradually cooled after about 30 seconds. This pattern is obtained by controlling the lamp output.

By the way, there are an open-loop control method and a closed-loop control method as the lamp output control methods, each of which is implemented as follows.

1) Open loop control method This is a control method that is implemented according to the experimentally obtained lamp output pattern. For example, as shown in Fig. 12, the lamp output is initially large, and after a certain time it is smaller and gradually decreases. Control to do.

2) Closed loop control method A temperature sensor such as a thermocouple is brought into contact with the wafer, and the lamp output is controlled to match the target pattern while measuring the temperature of the wafer.

[Problems to be solved by the invention]

In the conventional temperature control device for the lamp annealing furnace, the lamp output was controlled according to either of the above two methods, but those methods had the following problems.

1) Problems in open-loop control system The wafer temperature is determined by the energy given by the lamp. A) If the wafer initial temperature and absorption rate are different, the temperature rise state will be different even if the same energy is given, The time when the object to be heated reaches a certain temperature varies variously. That is, since the state of the controlled object changes from moment to moment, a pattern with good reproducibility cannot be achieved.

b) If the initial temperature of the process tube or the processing gas is different, the temperature rise state is different even if the same energy is applied.

For the above reasons, the target pattern as shown in FIG. 11 could not be obtained.

2) Problems in closed-loop control method using thermocouples When measuring the temperature of an object using a thermocouple, it is premised that the thermocouple and the object have reached thermal equilibrium. The temperature of the wafer rises in a short time, the thermocouple and the wafer do not reach thermal equilibrium, and the thermocouple does not show the accurate wafer temperature.

Therefore, even if the lamp output is controlled based on the thermocouple output to obtain a thermocouple output that matches the target pattern, it only controls the thermocouple temperature. The pattern will not match the target pattern.

Therefore, in order to avoid the above problems in the open loop control system and the closed loop control system using a thermocouple, a radiation thermometer that does not require time for thermal equilibrium is used,
If the lamp output is controlled according to the target pattern while measuring the wafer temperature, the following problems will occur.

3) Problems in closed-loop control method using radiation thermometer When measuring the temperature of an object with a radiation thermometer, if the object to be measured is opaque at the temperature of its wavelength band and there is no heat radiation around the object to be measured. Although there is no problem, Si, which is one of the objects to be processed in the lamp annealing furnace, is a semi-transparent object in the infrared region (up to about 500 ° C), and the temperature of the process tube itself rises. Thermal radiation passes through the measurement object (Si) and enters the radiation thermometer. As a result, the radiation temperature does not accurately indicate the temperature of the object to be measured.

Generally, there is a limit to the measurement range of the radiation thermometer,
It is difficult to perform measurement over the entire temperature rising process of the measured object.

[Means for solving problems]

According to the present invention, a temperature control device for a lamp annealing furnace includes a lamp group for heating a heated object, a lamp output control device such as a thyristor control device for controlling a lamp output, and a radiation thermometer for measuring the temperature of the heated object. , A thermocouple for measuring the wall temperature of the process tube, a radiation thermometer, and an arithmetic unit for sending a signal to the lamp output control unit in response to the output of the thermocouple and relating to the target temperature at the start of heating and the process. Performs a constant lamp output corrected by the temperature of the tube and maintains a constant value until a predetermined closed loop control start temperature is reached, or controls the lamp output according to a predetermined pattern (open loop control), After that, by controlling the lamp output so that it matches the target pattern (closed loop control), the error during open loop control can be reduced. Moni, can be kept constant the time until the output of the radiation thermometer reaches a certain value.

〔Example〕

FIG. 1 is a vertical cross-sectional side view showing an installation state of a radiation thermometer 9 and a thermocouple 10 in a lamp annealing furnace. Similar to the conventional furnace described with reference to FIG. 10, the lamp annealing furnace is provided with a pair of the flat reflecting surface 1 and the lamp 2 which are vertically or horizontally separated from each other, and the process tube 3 is arranged between them. In addition, the susceptor 5 on which the wafer 4 is placed is housed therein.

Process tube 3 to measure the temperature of the wafer
A hollow tube is welded to the opening on the side surface of the, and the other end is connected to a radiation thermometer 9 through a fixture 8, and the radiation thermometer 9 is
From the opening of the process tube 3 through the hollow tube 7,
The light emitted from the semiconductor wafer 4 is received.

FIG. 2 is a diagram showing an example of a target pattern as described below.

FIG. 3 is a block diagram of a temperature control device for controlling the temperature of the semiconductor wafer 4. The temperature controller comprises a radiation thermometer, a thermocouple for measuring the wall temperature of the process tube, an arithmetic unit, a lamp output controller and a lamp group, and the function of each block is as follows.

1) Radiation thermometer The radiation light of the semiconductor wafer 4 is received and a signal corresponding to the wafer temperature is output.

2) Output a signal corresponding to the wall surface of the thermocouple process tube 3.

3) Arithmetic device Until the output of the radiation thermometer 9 reaches a constant value, the lamp output control device is controlled so that the lamp group generates a constant output or an output according to a predetermined pattern. The temperature of the wall surface of the process tube at the start of heating corrects the constant lamp output determined in relation to the target temperature, so that the time until the output of the radiation thermometer 9 reaches a constant value becomes constant. Control the output controller.

After the output of the radiation thermometer reaches a constant value, the lamp output control device is controlled so as to match the target pattern.

4) Lamp output control device The output of the lamp group is controlled according to the instruction of the arithmetic device, and specifically, the current of the lamp is controlled by a thyristor or a triac.

FIG. 4 shows a circuit diagram of an arithmetic unit for realizing the function of the above item 3), and the configuration and operation of main functional parts will be described below.

1) Process selection switch The process pattern shown in Fig. 2 is a memory (ROM).
A plurality of processing patterns are prepared in the inside, and a processing pattern is selected by this switch. The pattern shown in FIG. 2 is a pattern in which the temperature reaches the constant temperature region temperature T ₂ about t ₁ seconds after the closed loop start temperature T ₁ and the temperature gradually decreases after t ₂ seconds.

2) Memory (ROM) Stores data related to processing patterns. The lower 12 bits of the address bus are accessed by the counter and the upper 4 bits are accessed by the encoder. Therefore, 16 types of patterns can be stored.

3) Connect the ON / OFF status of the 16 processing selection switches of the encoder to the 4-bit data. The output is connected to the upper 4 bits of the memory (ROM).

4) Counter Receives a clock signal from the clock generator through the gate and counts up. The output of the 12-bit counter is connected to the lower 12 bits of the address bus of the memory (ROM). When the start switch is pressed, it is cleared to 0 by the signal issued by the timing control circuit.

5) Comparator The output signal of the radiation thermometer is input through the amplifier and compared with the signal sent from the analog switch 1 (referred to as a reference signal).

When the signal of the radiation thermometer is smaller than the reference signal, a signal of logic level L is sent to the timing control circuit, and when it is larger, it is sent to the timing control circuit.

6) The potentiometer connected to the analog switch 1 input is set to the voltage corresponding to the closed-loop control start temperature defined for each of the 16 types of processing patterns. Then, one of 16 types is selected according to the 4-bit data of the encoder and the voltage is sent to the comparator.

7) The potentiometer connected to the analog switch 2 input is set to the voltage corresponding to the selected processing temperature of 16 types of processing patterns. Then, one of 16 types is selected according to the 4-bit data of the encoder and the voltage is sent to the iP calculator.

8) PiD calculator Performs PiD calculation for the difference between the output voltage of the D / A converter corresponding to the target temperature pattern and the output voltage of the radiation thermometer, and outputs it to the lamp output control device via the analog switch 3. .

9) iP calculator Output at the start of heating by the output voltage of the D / A converter corresponding to the fixed lamp output that is set for the target temperature at the start of heating and the electromotive force of the thermocouple corresponding to the wall temperature of the process tube. The calculation for determining the lamp output to be performed is performed, and the output is output to the lamp output control device through the analog switch 3.

10) Analog switch 3 Output of iP calculator according to the instruction of timing control circuit,
Outputs the PiD calculator output or ground level 0 _V.

11) Amplifier 1 Amplifies the output of the radiation thermometer and sends it to the PiD calculator via the comparator and calculator.

12) Amplifier 2 Amplifies the thermocouple output and sends it to the iP calculator. Next, the arithmetic unit will be described in the order of operation.

1) When the start switch is pressed, the timing control circuit clears the counter to 0 and sends a signal to the analog switch 3 to pass the output of the iP calculation group.

The address of the memory ×××× ○○○○○○○○○○○ B is accessed, and the voltage corresponding to the address data and the electromotive force of the thermocouple corresponding to the wall temperature of the process tube are amplified through the amplifier 2. Voltage, and analog switch 3
The voltage adjusted by the potentiometer corresponding to the XXXXX address is sent to the iP computing unit to calculate the initial output, which is output to the lamp output control device via the analog switch 3 (referred to as the initial output).

2) The wafer is heated by the initial output and the temperature gradually rises. Since analog switch 1 is ×××× address is accessed, the corresponding voltage adjusted by potentiometer (V _R) is applied to the comparator.

The output voltage (V _O ) of the radiation thermometer increases as the temperature of the wafer rises, but the comparator compares this voltage V _O with V _R. Then, a signal of logic level L when V _O <V _R , and a signal of level H when V _O V _R are sent to the timing control circuit.

3) When the timing control circuit receives a signal of logic level H from the comparator, it sends a signal of logic level to the gate and a signal to the analog switch 3 to pass the output of the PiD calculator.

4) As a result, the gate passes the signal of the clock generator and the counter counts up.

Therefore, the memory is ×××× ○○○○○○○○○○
○ The target pattern is generated by sequentially accessing from the first address.

5) This target pattern signal is D / A converted and operated with the above-mentioned signal V _O (referred to as a deviation signal). The deviation signal is subjected to PiD calculation, and the calculation result is given to the lamp output control device through the analog switch 3.

6) On the other hand, the output voltage of the D / A converter is sent to the timing control circuit. When the 0V signal continues for a certain time or longer, the timing control circuit determines the completion of processing and sends a signal to the analog switch 3 to pass the 0V signal.

FIG. 5 is a block diagram of the second embodiment of the arithmetic unit.
This arithmetic unit is composed of an amplifier, an A / D converter, an input unit, a microcomputer, a D / A converter and a display unit, and the function of each block is as follows.

1) Microcomputer The function shown in Fig. 4 is input by the program, and its ROM
It is stored in the area.

2) A / D converter The output of the radiation thermometer (via amplifier 1) and the output corresponding to the electromotive force of the thermocouple (via amplifier 2) are A / D converted,
Send to the micro computer.

3) D / A converter D / A converts the output of the micro computer and sends it to the lamp output controller.

4) Input device This is a device for setting target patterns and setting control parameters.

5) Display device Displays the data input from the input device and the internal state of the microcomputer.

FIG. 6a is a flow chart for explaining the operation of the microcomputer shown in FIG. The functions are as follows.

That is, first, the target pattern is set from the input device, the control parameters are set, and the start switch is pressed. Then, the microcomputer commands to generate the initial output, and outputs the initial output until the output of the radiation thermometer reaches a constant temperature, and the open loop control is performed. When the temperature reaches a certain temperature, PiD calculation is performed so as to match the target pattern, the calculation result is output to the D / A converter, and closed loop control is performed. At this time, the target pattern is stored in a memory such as the ROM or RAM of the microcomputer. When the processing is completed, the state before the start is obtained.

FIG. 6b shows a method of PiD calculation. Here, T _rt is the temperature data at time t on the target pattern, and T _it is the output of the radiation thermometer at time t. e _t , _t , _t , M _t, etc. are defined by the calculation formulas shown in the figure.

 FIG. 7 shows a modified embodiment of FIG.

a) is until the constant temperature is reached, for example at time t _i1
A method of controlling the output in a predetermined pattern, such as from the initial output to the output P _i , at the time t _i2 to the output P ₂ ...
In b), the start of the closed loop control is not the constant temperature described above,
A method of performing with the radiation thermometer having started the temperature rise, c) When the closed loop control is started when the temperature rises by a certain temperature range or more after the temperature rise of the radiation thermometer, for example, the temperature T _it
Temperature T _ito but which rises by the temperature T _C from a raised starting temperature T _ito +
We will show how to do it when the time is over T _C.

In the case of b) and c) among these methods, the basic of the target pattern is given in FIG. 11, but the starting temperature of the closed loop control is, for example, T _X, at which time t _X ′ seconds have elapsed after the initial output output. If so, t _x ′ seconds are set again as t _x seconds and the temperature pattern in the temperature range of T _x or higher is used as the target pattern.

FIG. 8 is a diagram in which a function for calculating and correcting (iP) the initial output based on the wall temperature of the process tube is added to FIG. 6a, and the function is the same as in FIG.

FIG. 9 shows a method of iP calculation. Here, T _ch is the wall temperature of the process Ji Yubu, T _R is set processing temperature and T 'is a predetermined constant, iP _O is a predetermined constant (wall temperature of Chiyubu is normal temperature), iP initial output calculation value ( IP is calculated by the calculation formula in the figure.

〔The invention's effect〕

The present invention performs open-loop control up to a constant temperature and thereafter performs closed-loop control according to a target pattern. 1) A radiation thermometer is used for control from a certain temperature or higher at which a heated portion becomes an opaque object, and closed-loop control Therefore, the desired correct temperature control can be performed.

2) The rise time to the temperature T ₁ (see Fig. 2) due to the difference in the initial state is ignored, so the difference in the initial state is absorbed within this time and does not adversely affect the control over the temperature T ₁ ( The temperature meaningful for heat treatment is from the constant temperature T ₂ to −10
In the range of 0 to -200 ° C, there is no effect below that).

3) Always for a range above a certain temperature T ₁ (Fig. 2)
The coefficient of PiD is adjusted. That is, the reproducibility in the adjustment stage and the actual processing stage is good by adjusting in the range where the influence of the initial state is removed.

4) By correcting the initial output during open-loop control according to the wall temperature of the process tube, the temperature at which closed-loop control shifts becomes constant, the reproducibility of processing after closed-loop shift is good, and the process tube has thermal equilibrium. In addition, the same result as when the initial temperature of the object to be heated is constant and is treated at regular intervals is obtained.

That is, temperature control with good reproducibility after the closed loop start temperature can be performed without being affected by the initial processing conditions such as the wall temperature of the process tube and the initial temperature of the wafer.

[Brief description of drawings]

FIG. 1 is a diagram showing an installation situation of a radiation thermometer and a thermocouple for carrying out the present invention. FIG. 2 is a diagram showing an example of a target pattern. FIG. 3 is a block diagram of the temperature control device. FIG. 4 is a block diagram showing the first embodiment of the arithmetic unit. FIG. 5 is a block diagram showing a second embodiment of the arithmetic unit (which is made into a micro computer). FIG. 6 is a flow chart of the processing in the microcomputer. FIG. 7 is a flow chart showing a modified embodiment thereof. FIG. 8 is a flow chart of an embodiment including correction of initial output. FIG. 9 is a flow chart showing a method of correcting the initial output. FIG. 10 is a vertical sectional side view showing a conventional lamp annealing furnace. FIG. 11 is a diagram showing an example of a target pattern. FIG. 12 is a diagram showing an example of a conventional open loop output signal. 1 ... Reflector, 2 ... Halogen lamp, 3 ... Process tube, 4 ... Wafer, 5 ... Susceptor, 6 ... Lid, 7 ... Hollow tube, 8 ... Fixture, 9 ... Radiant thermometer,
10 ... thermocouple.

Claims (3)

(57) [Claims] 1. A lamp group for heating an object to be heated, a lamp output control device such as a thyristor controller for controlling a lamp output, a radiation thermometer for measuring the temperature of the object to be heated, and a thermoelectric device for measuring the wall temperature of the process tube. Pair, a radiation thermometer, and an arithmetic unit that receives the output of the thermocouple and sends a signal to the lamp output control unit, which is determined in relation to the target temperature at the start of heating and corrected by the wall temperature of the process tube. The lamp output is maintained at a constant value until the temperature reaches the specified closed loop control start temperature, or the lamp output is controlled according to a predetermined pattern (open loop control), and thereafter the target pattern is reached. The temperature control device of the lamp annealing furnace that controls the lamp output so as to match with (closed loop control). 2. The temperature control device according to claim 1, wherein the closed-loop control start temperature is a temperature at which the output of the radiation thermometer starts to rise, or a temperature at which the output has risen by a certain temperature range or more. 3. The temperature control device according to claim 1, wherein a target pattern for the closed loop control is a pattern in a temperature range higher than the closed loop start temperature among patterns determined from 0 ° C.