JP2001085339A - Temperature control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a temperature control method which can control the temperatures of heating objects with high accuracy, even if some of target set temperatures are lower than the lower detection limit of a radiation thermometer. SOLUTION: A control method changeover temperature is set at a value (for instance 650 deg.C), within the detection temperature range (for instance 600 deg.C-1300 deg.C) of a radiation thermometer 31 and near its lower detection limit. If the temperature of a wafer 10, detected by the radiation thermometer 31, is not lower than the control method changeover temperature, the feedback control of the output of a heater 21 is conducted according to the output of the radiation thermometer 31. However, if the temperature of the wafer 10 detected by the radiation thermometer 31 is lower than the control method changeover temperature, the heater output is controlled according to an estimation model, which calculates the temperature of a heating object from a heater output prepared beforehand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the temperature of an object to be heated, and more particularly to a method of heating an object to be heated such as a semiconductor wafer using a heater and detecting the temperature using a radiation thermometer. The present invention relates to a temperature control method for performing feedback control of a heater output based on the output of a radiation thermometer.

[0002]

2. Description of the Related Art FIG. 4 shows an outline of a conventional epitaxial growth apparatus. This apparatus is used for depositing a silicon thin film on the surface of a wafer.

[0003] A ring-shaped susceptor 12 is disposed inside a reaction chamber 11, and the wafer 10 is supported on the susceptor 12 at a peripheral portion thereof. The susceptor 12 is supported at its peripheral edge by a cylindrical drum 13.
Via a rotary drive mechanism (not shown). As the susceptor 12 rotates, the wafer 10 supported thereon rotates.

A first heater 21, a second heater 22, and a third heater 23 are arranged concentrically inside the drum 13 so as to face the lower surface of the wafer 10. As shown in FIG. 5, the first heater 21 has a circular shape as a whole, faces the center of the wafer 10, and is used for heating the center of the wafer 10. A ring-shaped second heater 22 is arranged so as to surround the periphery of the first heater 21. The second heater 22 faces an intermediate portion between the central portion and the peripheral portion of the wafer 10 and is used for heating the intermediate portion. Furthermore,
A ring-shaped third heater 23 is arranged so as to surround the periphery of the second heater 22. The third heater 23 faces the peripheral portion of the wafer 10 and the susceptor, and is used for heating those portions. Note that none of the first heater 21, the second heater 22, and the third heater 23 rotate.

[0005] A reaction gas supply nozzle 15 is provided at the ceiling of the reaction chamber 11, and a reaction gas is blown out from the nozzle to deposit a silicon thin film on the heated wafer 10. The rotation of the wafer 10 promotes the growth of the silicon thin film, and also increases the uniformity of the thickness of the formed silicon thin film.

A radiation thermometer 3 is provided on the ceiling of the reaction chamber 11.
1, 32 and 33 are attached. By measuring the surface temperature at each position on the surface of the wafer 10 using these radiation thermometers 31, 32, 33, the first heater 2
1. Feedback control of the outputs of the second heater 22 and the third heater 23 is performed.

FIG. 6 shows a control block diagram of the output of each heater in the above epitaxial growth apparatus. Each heater is controlled by an individual PID type feedback control loop. That is, the first heater 21,
The outputs of the second heater 22 and the third heater 23 are independently controlled based on the values measured by the radiation thermometers 31, 32, and 33, respectively.

Next, a conventional operation method of the epitaxial growth apparatus shown in FIG. 4 will be briefly described.

This apparatus is an apparatus of the sheet type, and the processing of the wafer 10 is performed one by one as follows. The wafer 10 is moved to a reaction chamber 11 by a transfer robot (not shown).
It is carried in. Next, the wafer 10 is placed in the reaction chamber 11.
Of a silicon thin film on the surface of the substrate. After the deposition of the silicon thin film is completed, the processed wafer 10 is carried out of the reaction chamber 11 by the transfer robot. Next, a new wafer is carried into the reaction chamber 11, and a thin film is deposited again. This process is repeated for the number of wafers to be processed.

In the process of processing one wafer, the temperature of the wafer is program-controlled, for example, according to a pattern as shown in FIG. When the wafer is loaded and unloaded, the feedback method cannot be applied to the control of the heaters 21, 22, and 23 because the wafer 10 is not placed on the susceptor 12. Therefore, when the wafer is loaded and unloaded, the outputs of the heaters 21, 22, and 23 are maintained at a preset constant value. Each heater output is set to a value such that when the wafer 10 is placed on the susceptor 12, the wafer 10 is stabilized at a temperature of, for example, about 700 ° C.

After the wafer 10 is carried into the reaction chamber 11 and placed on the susceptor 12, the temperature of the wafer
The output of the heaters 21, 22, and 23 is maintained at a constant value until the temperature becomes close to ° C. Thereafter, the mode is switched to feedback control, and the target set temperature of the wafer is changed from 700 ° C. to 100 ° C.
Increase linearly to 0 ° C. Set target temperature to 1000
While controlling the heater while maintaining the temperature, the reaction gas is supplied into the reaction chamber 11 through the reaction gas supply nozzle 15 to form a thin film.

After a lapse of a predetermined time, the supply of the reaction gas is stopped, and the target set temperature is set at 700 ° C. to drop linearly. After the temperature of the wafer 10 has dropped to 700 ° C., the outputs of the heaters 21, 22, and 23 are kept at a constant value, and during this time, the wafer 10 on which the thin film formation has been completed is carried out of the reaction chamber. Next, a new wafer is carried into the reaction chamber, and the step of forming a thin film is performed again.

In order to make the thickness of the formed silicon thin film uniform, it is necessary to heat the wafer 10 so that no temperature difference occurs in the plane of the wafer 10. If the temperature difference in the plane of the wafer 10 is large, the thickness of the formed silicon thin film becomes uneven, which adversely affects the quality and yield of the semiconductor device manufactured using the wafer 10.

In recent years, in order to improve the yield of semiconductor devices per unit area of the wafer, the diameter of the wafer is increased to 125
mm, 200 mm, and 300 mm are gradually increasing in diameter. With large-diameter wafers, it has become increasingly difficult to uniformly heat the wafer in-plane.

(Problems of the prior art) Radiation thermometers 21, 2
Reference numerals 2 and 23 detect infrared energy radiated from the wafer and convert it to temperature. For this reason,
If the temperature of the measurement object is lower than the measurable range,
The radiant energy is not sufficient and the temperature of the object to be measured cannot be determined accurately. For example, if the measurement upper limit is 13
When a radiation thermometer is selected as 00 ° C., the lower detection limit may be 600 ° C. in some cases. As described above, when the lower limit of detection by the radiation thermometer is 600 ° C., the range of the target set temperature of the wafer is about 650 ° C. or more in order to stably perform the feedback control of the heater.

If the temperature of the wafer is high and there is a temperature difference in the plane, a crystal defect called a slip occurs, which causes a defect in a semiconductor element to be produced. Generally, the slip is more likely to occur when the temperature is higher. But 600 ° C
Even at a relatively low temperature, a slip occurs if the temperature difference in the plane is large.

When a radiation thermometer having the above specification is used, a temperature measurement error at a temperature of 600 ° C. (lower limit of detection) or less is large. Therefore, it is necessary to precisely control the wafer temperature in the vicinity of the error. Can not. Therefore, it is not easy to make the wafer temperature distribution uniform in a region near the lower limit of detection by the radiation thermometer.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the conventional temperature control method using a radiation thermometer as described above. A temperature control method that can accurately control the temperature of the object to be heated even when the unit is below the lower limit of detection by the radiation thermometer, and as a result, the temperature distribution of the object to be heated can be kept uniform. Is to provide.

[0019]

According to the temperature control method of the present invention, the temperature of an object to be heated is detected by using a radiation thermometer, and the temperature of the object to be heated coincides with a preset target value. In a temperature control method for controlling a heater output based on an output of a radiation thermometer, a control system switching temperature is set within a detection temperature range of the radiation thermometer and near a lower detection limit thereof, When the temperature of the object to be heated detected in the step (c) is equal to or higher than the control system switching temperature, feedback control of the heater output is performed based on the output of the radiation thermometer, and the heating target detected by the radiation thermometer is controlled. When the temperature of the object is lower than the control system switching temperature, the heater output is controlled based on an estimation formula for calculating the temperature of the object to be heated from the heater output prepared in advance.

According to the temperature control method of the present invention, even when the temperature of the object to be heated is close to or lower than the lower limit of detection by the radiation thermometer, the temperature of the object to be heated is set to a value close to the target value. Can be adjusted to Therefore, when the temperature of the object to be heated is increased using the program control, the temperature of the object to be heated can be quickly made to match the target temperature when the target set temperature exceeds the detection lower limit of the radiation thermometer. .

Preferably, the heater comprises a plurality of divided portions which are independently controlled, the radiation thermometer is provided for each of the divided portions, and the object to be heated is provided at a position corresponding to each of the divided portions. It is arranged to detect the temperature of.

As described above, if the temperature control method of the present invention is applied to an apparatus having a plurality of independently controlled heating zones, the temperature of the object to be heated becomes close to the detection lower limit of the radiation thermometer. At some point, the temperature distribution of the object to be heated can be made uniform.

Preferably, the estimating equation is that the heater output is changed at predetermined time intervals in advance in a state where the temperature of the object to be heated is near the control system switching temperature. Is measured, and is created based on the data of the heater output at that time versus the temperature of the object to be heated.

For example, the object to be heated is a semiconductor wafer.

For example, the object to be heated is a semiconductor wafer, which is supported on a susceptor at a peripheral edge thereof, and the heater is disposed at a position facing the lower surface of the semiconductor wafer, and is independently controlled. The radiation thermometer is provided for each of the zones, is disposed above the semiconductor wafer, and detects the temperature of the semiconductor wafer at a position corresponding to each of the zones.

In this case, preferably, before placing the semiconductor wafer on the susceptor, the temperature of the heater is detected using the radiation thermometer, and the estimation formula is corrected based on the detected temperature. .

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a temperature control method according to the present invention will be described.

FIG. 1 shows a block diagram of a temperature control method according to the present invention. When the wafer temperature (specifically, the incident energy to the radiation thermometer) is within the detectable temperature range of the radiation thermometer, the feedback control of the heater output (normal feedback control) is performed based on the output of the radiation thermometer. )I do. When the wafer temperature (specifically, the energy incident on the radiation thermometer) is outside the detectable temperature range of the radiation thermometer, the heater output is directly calculated using an estimation model that calculates the wafer temperature from the heater output. Control. The above estimation model is registered in the control device in the form of a mathematical expression or a table in advance.

Next, an example of a method for creating the above estimation model will be described. In the following, the configuration of the device to be applied and the respective numerical values used are merely examples, and do not limit the content of the present invention.

The epitaxial growth apparatus (FIG. 4) has a three-zone heater configuration as described above,
1, the second heater 22 and the third heater 23 are arranged concentrically. The output of each heater 21, 22, 23 is
Under normal operating conditions, the corresponding radiation thermometer 3
Feedback control is performed based on the outputs of 1, 32 and 33.

The wafer (dummy wafer) is susceptor 1
2, first, the set temperature is set to 700 ° C., and feedback control of the outputs of the heaters 21, 22, and 23 is performed. When the temperature of the wafer is stabilized, the heater output is once fixed. Next, as shown in FIG. 2, the heater output is slightly changed up and down, and the temperature change of the wafer at that time is stored in a controller (not shown), and the temperature is sequentially increased at regular time intervals. This is repeated while approximating the relationship between the heater output and the wafer temperature by a polynomial or transfer function equation, and extending this equation to the area below the lower limit temperature by the radiation thermometer, in the area below this lower limit temperature. A relational expression (estimation formula) between the heater output and the wafer temperature is created.

In the case where the transfer function is approximated, the following equation is used.

Y (t) = b1 · u (t−1) + b2 · u (t−2) +... + Bm · u (t−m) (1) where y (t) is Indicates wafer temperature. u (t) is a heater output, which is discretized by sampling. t indicates the current time. u (t-1) indicates the heater output at the immediately preceding sampling time. m is a certain positive integer value, and u (tm) indicates m heater outputs in the past. b
, Bm are coefficients, and these values are calculated from the measured values of the wafer temperature and the heater output. In this case, the least square method or the like can be used. In the case of the apparatus shown in FIG. 4, since there are three heater zones to be controlled, the above three types of estimation formulas are created in advance.

In addition to the transfer function type expression, an estimation expression using another polynomial or data in a table format can be used.

During the actual operation of the apparatus, the temperature of the wafer is controlled according to the control block shown in FIG. 1 using the estimation formula (estimation model) created as described above.

FIG. 3 shows an example of data when the wafer temperature is controlled based on the method of the present invention. In the drawing, a broken line 41 indicates a target set temperature of the wafer, a dashed line 42 indicates an estimated temperature of the wafer corresponding to the heater output, and a solid line (thick) 43.
Represents a wafer temperature detected by the radiation thermometer, and a solid line (thin) 44 represents a heater output.

The solid line (thick) 45 indicates the surface temperature of the heater detected by the radiation thermometer. In the example shown in FIG. 3, the wafer loading temperature is about 500 ° C., but when the wafer is not placed on the susceptor, the radiation thermometer detects the surface temperature of the heater. In the apparatus shown in FIG. 4, the surface temperature of the heater is about one hundred and several tens degrees Celsius higher than the wafer temperature, and thus appears as the output 45 of the radiation thermometer. As described above, when the surface temperature of the heater can be measured when the wafer is not placed on the susceptor, this is measured.

In this example, the lower limit of detection by the radiation thermometer is 600 ° C. The switching of the control method of the heater output is performed at a wafer temperature of 650 ° C., that is, a temperature having a sufficient margin with respect to the above detection lower limit. Specifically, after the wafer is placed on the susceptor, first, the heater output is controlled based on the above estimation formula, and when the detected value of the wafer temperature reaches 650 ° C., the feedback based on the output of the radiation thermometer is performed. Switch to control.

The lower limit of detection by the radiation thermometer is 60.
Because it is 0 ° C. In the temperature range higher than that, the values measured by the radiation thermometer also have sufficient accuracy. Therefore, when the wafer temperature is between 600 ° C. and 700 ° C., the temperature calculated by the estimation formula is compared with the value detected by the radiation thermometer, and the coefficients (b1, b2,... Correct the value of). In addition, this correction may be performed to the extent that the gain is corrected.

If the heater temperature can be detected before the wafer is loaded, preferably, the heater output is further corrected using the detected value. Normally, after a lapse of time from the start-up of the apparatus, the heater output for maintaining the same temperature becomes smaller than immediately after the start-up. Therefore, the heater output is corrected based on the heater temperature detected by the radiation thermometer so that the temperature of the wafer is stably controlled over a long period of time.

For example, the heater output is corrected as follows. That is, when the heater temperature detected by the radiation thermometer rises by a certain temperature or more compared to the temperature immediately after the start of the furnace, the heater output is reduced by 1% from the value determined based on the estimation formula, Conversely, when the temperature drops below a certain temperature, the heater output is increased by 1%.

[0042]

As described above, when the temperature control method of the present invention is used, even when the target set temperature is lower than the lower limit of detection by the radiation thermometer for feedback control, the temperature of the object to be heated can be reduced. Can be maintained with some accuracy,
When the target set temperature exceeds the detection lower limit of the radiation thermometer, the temperature of the object to be heated can be quickly made to match the target set temperature.

If the temperature control method of the present invention is applied to a semiconductor manufacturing apparatus for heating a wafer using a heater divided into a plurality of zones, such as an epitaxial growth apparatus,
The uniformity of the in-plane temperature distribution of the wafer can be improved. As a result, it is possible to improve the quality and yield of a semiconductor device manufactured using the wafer.

[Brief description of the drawings]

FIG. 1 is a control block diagram showing a temperature control method according to the present invention.

FIG. 2 is a diagram showing an outline of a test for creating a temperature estimation model.

FIG. 3 is a diagram showing an example of data when heater output is controlled using the temperature control method according to the present invention.

FIG. 4 is a diagram showing an example of an epitaxial growth apparatus to which the temperature control method of the present invention is applied.

5 is a top view of a heater portion of the epitaxial growth apparatus shown in FIG.

FIG. 6 is a control block diagram of a conventional heater output.

FIG. 7 is a view showing an example of a wafer set temperature in an epitaxial growth step.

[Explanation of symbols]

Reference Signs List 10: wafer (object to be heated), 11: susceptor, 15: reaction gas supply nozzle, 21: first heater (internal heater) 22: second heater (intermediate heater), 23: Third heater (peripheral heater), 31: Radiation thermometer, 32: Radiation thermometer, 33: Radiation thermometer, 41: Target set temperature, 42: Estimation Temperature, 43: temperature detected by radiation thermometer, 44: heater output, 45: surface temperature of heater detected by radiation thermometer.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideki Ito 2068-3 Ooka, Numazu-shi, Shizuoka Prefecture Inside Toshiba Machine Co., Ltd. (72) Inventor Hidenori Takahashi 2068-3, Ooka, Numazu-shi, Shizuoka Prefecture Toshiba Machine Co., Ltd. Inventor Tadashi Ohashi 30 Soya, Hadano-shi, Kanagawa Pref., Toshiba Ceramics Co., Ltd. 30 Soya, Hadano-shi, Toshiba F-term in Toshiba Ceramics Co., Ltd. Development Research Laboratory (reference) JJ04 KK05 LL01 LL02 LL12 LL18 LL23 LL27 NN03

Claims (6)

[Claims] The temperature of an object to be heated is detected using a radiation thermometer, and the heater output is controlled based on the output of the radiation thermometer so that the temperature of the object to be heated matches a preset target value. In the temperature control method of performing, the control method switching temperature is set within the detection temperature range of the radiation thermometer and near the detection lower limit, the temperature of the object to be heated detected by the radiation thermometer, When the temperature is equal to or higher than the control system switching temperature, feedback control of the heater output is performed based on the output of the radiation thermometer, and the temperature of the object to be heated detected by the radiation thermometer is lower than the control system switching temperature. A temperature control method for controlling the heater output based on an estimation formula for calculating the temperature of the object to be heated from the heater output prepared in advance. 2. The heater comprises a plurality of divided portions which are independently controlled. The radiation thermometer is provided for each of the divided portions, and the radiation thermometer is provided at a position corresponding to each of the divided portions. The temperature control method according to claim 1, wherein the temperature control method is arranged to detect a temperature of the object. 3. The estimating equation is configured such that, in a state where the temperature of the object to be heated is in the vicinity of the control system switching temperature, the temperature of the object to be heated is changed by changing the heater output at regular time intervals. The temperature control method according to claim 1, wherein the temperature control method is created based on data of a measured heater output and a temperature of the object to be heated at that time. 4. The temperature control method according to claim 1, wherein the object to be heated is a semiconductor wafer. 5. The object to be heated is a semiconductor wafer, and is supported on a susceptor at a peripheral portion thereof. The heater is disposed at a position facing a lower surface of the semiconductor wafer, and is independently controlled. Wherein the radiation thermometer is provided for each of the zones, is disposed above the semiconductor wafer, and detects the temperature of the semiconductor wafer at a position corresponding to each of the zones. The temperature control method according to claim 1. 6. The method according to claim 1, wherein before placing the semiconductor wafer on the susceptor, the temperature of the heater is detected using the radiation thermometer, and the estimation formula is corrected based on the detected temperature. The temperature control method according to claim 5, wherein