JPH09260294A - Temperature control method of electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and stably maintain the temperature in an electric furnace at a target temperature when a substrate is introduced in the electric furnace. SOLUTION: This temperature control method of an electric furnace makes a first adjusting equipment 12 and a second adjusting equipment 13 control a heater 7 according to a target temperature inputted from a target temperature setting equipment 9, and heats an electric furnace 1. When a substrate (w) a introduced, a temperature correcting equipment 11 obtains a time variation pattern of temperature difference between the temperature in the electric furnace 1 and the set target temperature. In the case that substrates (w) are introduced in succession, the temperature correcting equipment 11 adds the time variation pattern of temperature difference to a target temperature pattern. The first and the second adjusting equipments 12, 13 control the heater 7, according to the corrected target temperature pattern, and heat the electric furnace 1. As a result, the change of temperature in the electric furnace 1 which is generated at the time of introducing the substrate (w) can be restrained, and the temperature in the electric furnace 1 is quickly and stably maintained at a set target temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control method for an electric furnace used in a semiconductor manufacturing diffusion apparatus, a CVD apparatus or the like, and more particularly to a temperature control method for an electric furnace when a substrate such as a wafer is charged. .

[0002]

2. Description of the Related Art In a semiconductor manufacturing apparatus having an electric furnace such as a CVD apparatus, it is necessary to maintain the temperature in the furnace at an appropriate temperature. Therefore, a control apparatus can be operated based on a temperature change pattern of a preset target temperature. The temperature of the heater is controlled. This temperature control is performed not only when the substrate is subjected to a film forming process or the like, but also when the substrate is put into the electric furnace, and the temperature inside the electric furnace is maintained at a specified value. . An example of a semiconductor manufacturing apparatus that performs such temperature control will be described with reference to FIG. In this semiconductor manufacturing apparatus, the substrate w is held by the boat 2 and is vertically driven by the boat loader 3 to be loaded or withdrawn into the electric furnace 1. When loading this substrate, the first regulator 1
The heater 7 is cascade-controlled based on the PID (proportional, integral, differential) calculation of the second and second controllers 13 to maintain the temperature inside the electric furnace 1.

That is, when the substrate w is put into the electric furnace 1, the first controller 12 measures the temperature measured by the furnace temperature sensor 5 and the preset target temperature inputted by the target temperature setter 9. And PID are calculated to calculate the target value for the second controller, and the second controller 13 calculates the target value and the outside temperature sensor 6
PID calculation is performed on the measured value and the electric power value supplied to the heater 7. Then, the electric power converter 8 supplies electric power to the heater 7 based on the calculated electric power value to maintain the electric furnace 1 at the preset target temperature by the heater 7.

[0004]

Here, in the process of loading the substrate w into the electric furnace 1, the boat 2 outside the electric furnace 1 is loaded with the substrate w to be processed, and the boat 2 is put into the electric furnace 1. It is done by throwing in. In such a substrate w loading process, the substrate w loaded in the boat 2 has a temperature lower than the in-furnace temperature such as room temperature, and thus the boat 2 loaded with the substrate w is loaded into the electric furnace 1. And electric furnace 1
The heat inside is taken away and the temperature inside the furnace falls. In addition, the boat 2 itself for loading the substrate w is also pulled out from the electric furnace 1 and is in a state of lowering the temperature inside the furnace, and when it is loaded in the electric furnace 1, the temperature inside the furnace may be lowered.

Therefore, even if the temperature of the heater 7 is controlled with the specified temperature as the target temperature as described above, the temperature inside the furnace is significantly lowered by the introduction of the substrate w, and the heater 7 actually heats the furnace. It takes a considerable time for the internal temperature to reach the target temperature. That is, as shown in FIG. 8, even when the temperature control is performed based on the specified target temperature, when the loading of the substrate w is started, the temperature inside the furnace of the electric furnace 1 starts to decrease, and the loading of the substrate w is completed. Even at this time, the temperature inside the furnace of the electric furnace 1 is lower than the target temperature, and even if the temperature control by the heater 7 is performed as described above, the temperature inside the furnace is set to the target temperature after the substrate loading is completed. It took me a long time to stabilize.

As described above, since it takes a considerable time for the temperature inside the furnace to stabilize at the target temperature, the processing step after the substrate is put in is delayed and the production efficiency of semiconductor manufacturing is lowered. . In addition, such a delay in controlling the temperature in the furnace causes not only a decrease in production efficiency but also a decrease in the quality of a substrate to be a product, and improvement has been strongly desired. The present invention has been made in view of the above conventional circumstances, and provides a temperature control method for an electric furnace capable of quickly stabilizing the temperature inside the electric furnace to a target temperature that is set after the substrate is put into the electric furnace. With the goal.

[0007]

In order to achieve the above object, a temperature control method according to a first aspect of the present invention is such that when a substrate is put into an electric furnace heated by a heater, the heater is controlled to control the temperature inside the electric furnace. In a temperature control method for an electric furnace that maintains a temperature at a specified target temperature, a temperature change in the electric furnace that occurs when a substrate is charged is measured, and a temporal change pattern of a temperature difference between the target temperature and the measured temperature is obtained. In addition, when the substrate is subsequently inserted, the temperature difference for each time is added to the target temperature, and the heater control is performed based on the corrected target temperature pattern.

In the temperature control method according to the above-mentioned claim 1, the difference between the temperature inside the electric furnace and the prescribed target temperature is continuously obtained in the substrate loading process, and the time change pattern of this temperature difference is obtained. . Then, in the subsequent temperature control at the time of loading the substrate, in order to suppress the change in the temperature inside the furnace that occurs when loading the substrate, the temperature difference pattern obtained above is added to the specified target temperature pattern and the corrected target temperature is corrected. Control the heater based on the pattern.

The temperature control method according to claim 2 is the method according to claim 1.
In the temperature control method described in (1), the time change pattern of the temperature difference is approximated to a pattern formed by a straight line, and when the substrate is subsequently inserted, the temperature difference pattern approximated to the target temperature is added every time, and the correction is performed. The heater is controlled based on the target temperature pattern.

In the temperature control method according to the second aspect, the temperature difference pattern between the furnace temperature and the target temperature is approximated to the temperature difference pattern formed by a straight line. Then, when loading the substrate thereafter, the target temperature pattern is corrected with a temperature difference pattern obtained by linear approximation to control the heater, and this correction control is easily performed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A temperature control method for an electric furnace according to the present invention will be described. First, an example of a semiconductor manufacturing apparatus for carrying out the temperature control method of this embodiment will be described with reference to FIG. The same parts as those in the conventional example shown in FIG. 7 are designated by the same reference numerals. This vertical semiconductor manufacturing apparatus includes an electric furnace 1 for performing a predetermined process on a substrate w, a boat 2 for loading the substrate w,
The boat 2 is moved up and down to be charged into the electric furnace 1 or the electric furnace 1
A boat loader 3 for pulling the boat 2 out of the boat, and an encoder 4 for detecting the vertical movement of the boat 2 by the boat loader 3.
A furnace temperature sensor 5 for measuring the temperature in the electric furnace 1, a furnace temperature sensor 6 for measuring the temperature outside the furnace of the electric furnace 1, a heater 7 for heating the electric furnace 1, and electric power are supplied to the heater 7. A power converter 8, a target temperature setting device 9 for inputting a target temperature in the electric furnace 1, and a control device 10 for controlling the temperature in the electric furnace 1 based on the target temperature are provided.

The boat 2 is made of, for example, high-purity quartz, and is used for loading or unloading a plurality of substrates w (for example, 20 substrates) into the electric furnace 1. The boat loader 3 includes a shaft portion 3a, and the shaft portion 3a is rotationally driven to move the boat 2 up and down to load or unload the electric furnace 1. Encoder 4 is boat loader 3
Detects the drive state of the shaft portion 3a of the boat, controls the drive of the shaft portion 3a of the boat loader 3 based on the detection, and causes the boat 2 to be put into or taken out of the electric furnace 1.
Based on the driving operation, the start and completion of loading the substrate w are detected and notified to the control device 10.

The in-reactor temperature sensor 5 and the in-reactor temperature sensor 6 are composed of temperature sensors such as thermocouples. The in-reactor temperature sensor 5 is provided in the electric furnace 1 to measure the in-reactor temperature and The sensor 6 is provided in the vicinity of the heater 7, measures the temperature of the heater 7, and notifies the control device 10 of the measurement result. The heater 7 is composed of an incandescent wire or the like, and changes the amount of heat generated by the supplied electric power to heat the electric furnace 1. The power converter 8 supplies power to the heater 7 based on the power value sent from the control device 10.

The target temperature setting device 9 sets a target temperature to be maintained by the electric furnace 1 during the semiconductor manufacturing process, and inputs this target temperature to the control device 10. The control device 10 includes a temperature compensator 11, a first controller 12, and a second controller 13.
And a power value is input to the power converter 8 based on the target temperature input from the target temperature setter 9, and the heater 7 is controlled by the power converter 8 to target the furnace temperature of the electric furnace 1. Keep heated to temperature.

The temperature compensator 11 has a function of obtaining a temperature difference pattern from the temperature difference between the furnace temperature measured by the furnace temperature sensor 5 and the target temperature input by the target temperature setting device 9 and approximating it to a straight line. It has a function of adding a temperature difference pattern approximated to a straight line to the target temperature input by the target temperature setting device 9 and correcting the temperature difference pattern. Then, in the case of the former function, the target temperature input by the target temperature setting device 9 is directly supplied to the first controller 12, and in the case of the latter function, the corrected target temperature is supplied to the first controller 12 Supply to. Information such as the temperature difference pattern obtained by both the above-mentioned functions and parameters used when obtaining the temperature difference pattern is appropriately stored in a memory (not shown) in the temperature corrector.

The first controller 12 is a PID calculator, which performs PID calculation on the temperature measured by the furnace temperature sensor 5 and the target temperature supplied by the temperature compensator 11, and outputs a target value to the second controller 13. The calculated target value is calculated and supplied to the second controller 13. The second controller 13 is a PID calculator, which performs PID calculation on the temperature measured by the out-of-furnace temperature sensor 6 and the target value supplied by the first controller 12 to calculate the value of electric power supplied to the heater 7.

In describing the temperature control method of the electric furnace 1 carried out by the above-described semiconductor manufacturing apparatus, first, the operation of the semiconductor manufacturing apparatus for loading the substrate w into the electric furnace 1 will be described. The substrate w to be processed is loaded into the boat 2 located outside the electric furnace 1, the boat loader 3 is driven by the control of the encoder 4, the boat 2 is raised, and the substrate w is put into the electric furnace 1. In this substrate loading process, the encoder 4 notifies the temperature corrector 11 of the loading start of the substrate w and the loading completion of the substrate w based on the ascending / descending position of the boat 2.

Next, a method for controlling the temperature of the electric furnace will be described.
The temperature control method of this electric furnace can be divided into the following two stages, and the temperature of the target temperature and the temperature inside the furnace input from the target temperature setter 9 based on the above-described loading operation of the substrate w. In the preparatory step of approximating the time change pattern of the difference into a temperature difference pattern composed of a straight line, and by adding the temperature difference pattern obtained in the preparatory step to the target temperature to correct the target temperature pattern, in the actual substrate loading process According to the corrected target temperature pattern, it can be divided into an execution stage in which the temperature of the electric furnace 1 is controlled when the substrate w is charged.

In the preparatory stage, when the temperature corrector 11 receives the target temperature set by the target temperature setting device 9, the target temperature is supplied to the first controller 12 as it is. Therefore, the temperature control of the electric furnace 1 is performed according to the target temperature pattern set by the target temperature setting device 9 as in the conventional example, but at the same time, the temperature compensator 11 is based on the target temperature and the actual furnace temperature. As will be described later, processing for creating a temperature difference pattern between the two is performed.

In the present embodiment, the process of creating the temperature difference pattern is repeatedly performed at regular time intervals (for example, every 1 second), and is executed according to the procedure shown in FIG. When the temperature corrector 11 receives the notice of the start of loading the substrate w from the encoder 4 (step S1), it sets the correction set value P1 and the time counter tx to the initial value "0", and the start flag W1ST.
"1" is set in ART (step S2). The start flag W1START is set to “1” from the start of the loading of the substrate w to the end of the creation of the temperature difference pattern, and the start flag W1START is set as if the loading of the substrate was not started. If it is other than "1" (step S3), one cycle of the process is ended.

When the start flag W1START is "1", that is, while the temperature difference pattern is being created (step S3), the target temperature SV input from the target temperature setter 9 is set.
The furnace measured temperature PV measured by the furnace temperature sensor 5 is subtracted from the temperature difference, and the temperature difference WORK at the time counter value tx is obtained.
(Tx) (step S4). Then, the temperature difference WORK (tx) at the time counter value tx is compared with the correction setting value P1 (step S5), and the temperature difference WORK (tx) at the time counter value tx is corrected to the correction setting value P1.
If it is larger, the temperature difference WORK (tx) at the time counter value tx is set as the correction set value P1, and
The value of the time counter tx at that time is set as the correction set time t1, and the two values are stored in the memory in the temperature compensator 11 (steps S6 and S7). When the temperature difference WORK (tx) at the time counter value tx is less than or equal to the correction setting value P1 and when the correction setting time t1 is stored in the memory of the temperature compensator 11, a notification of completion of loading the substrate w is sent from the encoder 4. It is detected whether or not it has been received (step S8),
If not received, the substrate loading completion flag WEN
It is detected that D is not "1" (step S10), "1" is added to the time counter tx (step S17), and one cycle of the temperature difference pattern creation processing is ended. The above-described processing is repeated every cycle from the receipt of the substrate loading start notification to the receipt of the substrate loading completion notification.

When the above process is repeated,
A notice of completion of loading of the substrate w is received from the encoder 4 (step S8), and when it is received, the substrate loading completion flag WEND is set to "1" (step S8).
9). After setting the substrate loading completion flag WEND to "1", it is detected that the substrate loading completion flag WEND is "1" (step S10), and whether the temperature difference WORK (tx) at the time counter value tx is 0 or less. Whether or not, that is, whether or not the furnace temperature has reached the target temperature is detected (step S11).

When only a short time has passed after the completion of loading the substrate, the temperature inside the furnace has not reached the target temperature yet, so that the temperature difference WORK (tx) at the time counter value tx is 0. Since it does not become the following, "1" is added to the time counter tx (step S17), and one cycle of the temperature difference pattern creation processing ends. The above process is repeated every cycle until the temperature in the furnace reaches the target temperature after receiving the notice of the completion of loading the substrate w.

While the above process is repeated, the temperature inside the furnace reaches the target temperature, and it is detected that the temperature difference WORK (tx) at the time counter value tx is 0 or less (step S1).
1). When this detection is performed, the correction setting time t1 stored in the temperature compensator 11 is determined by the steps S5, S6, and S7 that are repeatedly performed for each cycle. Indicates the maximum time, and the correction set value P1 indicates the temperature difference at that time.

Then, the time counter tx at the time of detection
Is stored in the memory of the temperature corrector 11 as the correction setting time t3 indicating the target temperature achievement time (step S12), and the intermediate time between the time when the temperature difference becomes maximum and the time when the target temperature is reached is set as the correction setting. The correction setting time t1 is subtracted from the time t3, and the subtraction result is divided by 2 to obtain the correction setting time t
2 is stored in the memory of the temperature corrector 11 (step S13). Furthermore, the ratio of the time change of the temperature difference from the time when the temperature difference becomes the maximum to the time when the temperature reaches the intermediate time is calculated from the temperature difference WORK (t2) at the time of the intermediate time to the maximum temperature difference WO.
RK (t1) is subtracted, and the result is the difference (t2-
It is obtained by dividing by t1) and stored in the memory of the temperature compensator 11 as the correction set value P2 (step S14).

Next, the rate of temporal change of the temperature difference from the intermediate time to the target temperature attainment time is calculated as the temperature difference WORK (t) at the intermediate time from the temperature difference "0" at the time of achieving the target temperature.
2) is subtracted, the result is divided by the difference between both times (t3-t2), and the result is stored in the memory of the temperature compensator 11 as the correction set value P3 (step S15). Step S15
By completing the above, a temperature difference pattern approximated to a straight line is obtained, and the board loading completion flag WEND and the start flag W
1START is set to "0", and the process of one cycle of the temperature difference pattern creating process is ended.

By the processing of the above-mentioned preparatory step, the information of each point in the actual temperature difference pattern shown in FIG. 3 is obtained, and from this information, the time point when the temperature difference between the target temperature and the furnace temperature becomes maximum (FIG. 3). The time and temperature difference at point A), the time and temperature difference at the time when the furnace temperature reaches the target temperature (point C in FIG. 3), the time at which the temperature difference becomes maximum, and the target temperature arrival time. The time and temperature difference at the intermediate point of time (point B in FIG. 3) can be obtained, and as a result, the temperature difference formed by the straight line shown in FIG. The pattern can be approximated. Further, based on the time and temperature difference at the three points obtained above, the rate of time change of the temperature difference between the time point when the temperature difference becomes maximum and the intermediate time point, and the temperature difference between the intermediate time point and the target temperature arrival time point. Of the time change of
The approximated temperature difference pattern is represented by the time from the wafer loading.

In the execution stage, a correction process is carried out to add the temperature difference pattern obtained in the preparation stage to the pattern of the target temperature input from the target temperature setting device 9 to obtain the target temperature pattern. This correction process of the target temperature pattern is repeatedly performed with a fixed prescribed time period as in the preparation stage, and is performed according to the procedure shown in FIG. When the temperature corrector 11 receives the notice of the start of loading the substrate w from the encoder 4 (step S18), the time counter tx from the loading of the substrate w is initialized to "0", and the start flag W2START is set to "1".
Is set (step S19). The start flag W2
START is set to "1" from the start of the loading of the substrate w to the end of the correction for adding the temperature difference pattern, and when the start flag W2START is other than "1" as after the correction control is completed. (Step S2
0), the target temperature SV supplied by the target temperature setter 9 is set to the first controller target temperature SVX without correction (step S2
1), one cycle of processing ends. Start flag W2STA
When RT is "1", that is, when the target temperature is corrected (step S20), the time counter tx is set to "
1 "is added (step S22).

When the addition is performed, first, the time counter t
When x is less than the correction set time t1, (step S2
3) Then, a value obtained by adding the correction set value P1 to the target temperature SV is supplied as the corrected target temperature SVX to the first controller 12 (step S24), and one cycle of the target temperature pattern correction processing is ended. Then, the above process is repeated until the time counter tx becomes equal to or longer than the correction set time t1, and the target temperature pattern corrected by this repetition becomes a straight line b-1 shown in FIG.

The above process is repeated until the time counter tx reaches the correction setting time t1 or more and the correction setting time t2.
If it is less than (step S25), the corrected target temperature SVX one cycle before is added with the correction set value P2 and supplied to the first controller 12 as a new corrected target temperature SVX (step S26). ), One cycle of the target temperature pattern correction process is completed. Then, the above processing is repeatedly performed until the time counter tx becomes equal to or more than the correction setting time t2,
The target temperature pattern corrected by this repetition becomes a straight line b-2 shown in FIG.

When the time further elapses and the time counter tx reaches the correction setting time t2 or more and is less than the correction setting time t3 (step S27), the correction setting value P3 is set to the corrected target temperature SVX one cycle before. The added value is supplied to the first controller 12 as a new corrected target temperature SVX (step S28), and one cycle of the target temperature pattern correction processing is ended. Then, the time counter tx indicates the correction setting time t3.
The above processing is repeated until the above is reached, and the target temperature pattern corrected by this repetition becomes a straight line b-3 shown in FIG.

When the time counter tx reaches the correction set time t3 or more as the time further elapses, the correction of the target temperature is ended (step S27). Therefore, the target temperature supplied by the target temperature setting device 9 is set. Target temperature S after SV correction
VX is supplied to the first controller 12 (step S2)
At the same time as 9), the start flag W2START is set to "0" (step S30), and one cycle of the target temperature pattern correction processing is ended.

By correcting the target temperature in this way, the target temperature input to the target temperature setter 9 shown in FIG. 6A and the target temperature shown in FIG. The corrected target temperature pattern shown in FIG. 6B, including the temperature difference pattern, is supplied. And
Based on this corrected target temperature pattern, the first controller 12 calculates the target value of the second controller 13 by performing PID calculation on the temperature measured by the furnace temperature sensor 5 and the second controller 1
3 is the PID of the target value and the measured value of the temperature outside the furnace 6
The value of electric power supplied to the heater 7 is calculated. Then, the electric power converter 8 supplies electric power based on the calculated electric power value to the heater 7 to control the temperature of the electric furnace 1.

By performing this temperature control, the electric furnace 1
The temperature in the furnace changes as shown in FIG. 6C, and stabilizes at the target temperature set by the target temperature setter 9 faster than the temperature change in the furnace temperature by the conventional temperature control shown in FIG. 6D. Can be maintained.

It should be noted that in the above-described embodiment, the processing is carried out at the fixed prescribed cycle in the preparation stage and the execution stage. However, the processing is not limited to being carried out at the fixed cycle, and for example, the processing is carried out. The time may be set in advance and the processing may be performed at that time. Further, in the above-described embodiment, the temperature difference for each time in the time change pattern of the temperature difference obtained in the preparatory stage in the execution stage is set as the target temperature setting device 9.
In addition to the target temperature supplied by the target temperature correction, the temperature difference of the temperature difference pattern for each time is multiplied by a fixed value (for example, 1.5 times) and added to the target temperature set by the target temperature setting device 9. Good.

Further, in the above-described embodiment, the temperature difference pattern is approximated to a temperature difference pattern formed by a straight line at the preparation stage and is approximated at the execution stage so that the correction control of the target temperature pattern can be easily performed. The temperature control of the electric furnace 1 was performed by correcting the target temperature pattern based on the obtained temperature difference pattern, but the temperature difference pattern was not approximated to a straight line in the preparatory stage, and the temperature difference pattern was not approximated in the execution stage. Even if the target temperature pattern is corrected based on the temperature control, the furnace temperature of the electric furnace 1 can be quickly and stably maintained at the target temperature.

[0037]

As described above, according to the first aspect of the present invention.
According to the temperature control method of the electric furnace according to the above, the temperature difference pattern between the target temperature and the temperature inside the electric furnace set in advance as the preparation step is obtained, and the target temperature pattern is corrected based on the obtained temperature difference pattern in the execution step. Since the temperature of the electric furnace is controlled to suppress the temperature change that occurs when the substrate is charged, the temperature inside the electric furnace can be quickly and stably maintained at the target temperature. According to the temperature control method of the electric furnace according to claim 2, a temperature difference pattern between the target temperature preset in the preparation stage and the temperature inside the electric furnace is obtained,
This temperature difference pattern is approximated to a temperature difference pattern formed by a straight line, and at the execution stage, the target temperature pattern is corrected based on the approximated temperature difference pattern to control the temperature of the electric furnace, which occurs when the substrate is loaded. Since the temperature change is suppressed, the amount of data required for control can be reduced, the control can be simplified, and the furnace temperature can be stably maintained at the target temperature quickly. Therefore, it is possible to shorten the processing time of semiconductor manufacturing, improve the production efficiency of semiconductor manufacturing, and prevent deterioration of the quality of the substrate.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an electric furnace for carrying out a temperature control method of the present invention.

FIG. 2 is a flowchart showing a processing procedure for creating a corrected target temperature pattern.

FIG. 3 is a diagram showing a temporal change pattern of a temperature difference between a set target temperature and a measured value of a furnace temperature.

FIG. 4 is a diagram approximating a temperature difference pattern formed by a straight line in FIG.

FIG. 5 is a flowchart showing a processing procedure for correcting a target temperature.

FIG. 6 is a diagram showing a furnace temperature of an electric furnace in which the present invention is carried out.

FIG. 7 is a configuration diagram of an electric furnace for implementing a conventional temperature control method.

FIG. 8 is a diagram showing measured values of furnace temperature in a conventional electric furnace.

[Explanation of symbols]

w ... Board, 1 ... Electric furnace, 4 ... Encoder,
5 ... Reactor temperature sensor, 7 ... Heater, 9 ... Target temperature setting device, 10 ... Control device, 11 ... Temperature compensator,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01L 21/324 H01L 21/324 D (72) Inventor Yukio Akita 3-14, Higashi-Nakano, Nakano-ku, Tokyo No. 20 Kokusai Electric Co., Ltd.

Claims (2)

[Claims] 1. A temperature control method for an electric furnace in which a heater is controlled to maintain a temperature inside the electric furnace at a prescribed target temperature when the substrate is put into the electric furnace heated by a heater. The temperature change in the electric furnace that occurs is measured, and the time change pattern of the temperature difference between the target temperature and the measured temperature is obtained in advance, and when the substrate is inserted thereafter, the temperature difference is added to the target temperature every time, A temperature control method for an electric furnace, wherein heater control is performed based on the corrected target temperature pattern. 2. The temperature control method according to claim 1, wherein the time change pattern of the temperature difference is approximated to a straight line pattern, and the temperature difference pattern approximated to the target temperature is set to a time when the substrate is subsequently put in. A temperature control method for an electric furnace, characterized in that heater control is performed based on the corrected target temperature pattern in addition to the above.