JPH07219646A - Internal temperature controller for diffusion furnace - Google Patents

Abstract

PURPOSE:To provide the internal temperature controller for the diffusion furnace which is fast in response speed and converged in a short time. CONSTITUTION:A master controller 10 generates a master controller output PN1 on the basis of the difference between a measured value of the internal temperature of the diffusion furnace 1 heated by a heater 2 and an in-furnace temperature set value. A slave controller 11 generates a slave controller output PN2 for heater operation on the basis of the difference between a measured value of the temperature of the heater 2 and the master controller output PN1. An attenuator 13 is connected between the master controller output PN1 and the input terminal of the slave controller 11, and the master controller output PN1 is attenuated uniformly by the attenuator 13 and then applied to the slave controller 11. An event information detector 16 is preferably connected to the master controller 10 through a PID switch 17 to selectively switch PID constants of the controllers when an event such as expectable disturbance is detected. When the slave controller output PN2 is >=100% or <=0%, an integration suppressor 14 may stops the integrating operation of the master controller 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal temperature control device for a diffusion furnace for diffusing impurities and the like into an article to be processed such as a solid semiconductor. In particular, the internal temperature control device of the diffusion furnace according to the present invention has a master controller and a slave controller,
When the target value changes, it responds without overshooting, and when the temperature changes due to events such as the inflow and outflow of the workpiece, etc., the temperature inside the furnace converges to the target value without overshoot and is maintained at the target value.

[0002]

2. Description of the Related Art Temperature control of a diffusion furnace heated by a heater includes an external temperature control method for controlling the temperature of the heater itself and a furnace temperature control method for controlling the inside of the furnace to a required temperature. The temperature control has the following advantages.

(1) By placing a temperature sensor in the vicinity of an object to be processed such as a semiconductor wafer and controlling it, the temperature of the object to be processed can be brought closer to the required temperature. (2) When inserting the product to be processed into and removing it from the furnace,
Alternatively, a considerable amount of disturbance (temperature decrease) occurs during the entrance and exit of a jig for handling the object to be treated, and the disturbance can be detected and dealt with promptly. (3) Even when a disturbance (temperature rise) such as hydrogen / oxygen combustion (internal burning) occurs in the furnace, the disturbance can be quickly detected and dealt with. (4) Dirt on the furnace wall (evaporation /
The required furnace temperature can be secured without being affected by changes in the thermal conductivity of the furnace wall due to the adhesion of diffusing substances, etc.). (5) It is possible to omit the temperature confirmation work when replacing the reaction tube of the diffusion furnace.

FIG. 2A shows a method of controlling the temperature inside the furnace by simple feedback. In the following description, the following symbols will be used unless otherwise specified. SV: Target value of furnace temperature (sometimes called furnace temperature set value or set value) PV: Furnace temperature (sometimes called furnace temperature measured value or measured value) G _C1 (s): Master The transfer function of the controller is given by equation (1) below for PID control. In equation (1), s is the Laplace operation, K _P1 is the proportional sensitivity of the master controller, T _I1 is the integration time of the master controller, T _D1 is the derivative time of the master controller, and η ₁ is the derivative gain of the master controller. Is. G _C2 (s): Transfer function of slave controller, given by the following equation (2) for PID control. In equation (2), K _P2 is the proportional sensitivity of the slave controller, T _I2 is the integration time of the slave controller, T _D2 is the derivative time of the slave controller, and η ₂ is the derivative gain of the slave controller. G _P1 (s): Transfer function from the heater to the measured temperature in the furnace (equivalently, can be approximated as "waste time + 1st delay") G _P2 (s): Transfer function of the heater (equivalently, "waste time" +1
It can be approximated by "second delay") D ₁ (s): Disturbance generated in the furnace (temperature change due to wafer loading / unloading, burning, etc.) D ₂ (s): Disturbance generated on the heater side (temperature due to power supply fluctuation, etc.) Change) α: Attenuator (may refer to the attenuation factor of the attenuator) I _SUP : Integral suppressor PID-sw: PID switch α-sw: Attenuator switch

[Equation 1] G _C1 (s) = K _P1 [1+ (1 / T _I1 s) + {T _D1 s / (1 + T _D1 η ₁ s)}] (1) G _C2 (s) ＝ K _P2 [1＋ (1 / T _I2 s) ＋ {T _D2 s / (1 ＋ T _D2 η ₂ s)}] ・ ・ ・ ・ ・ ・ (2)

The diffusion furnace 1 has a front heater 2f, a central heater 2c, and a rear heater 2r as heaters 2 for heating, and diffusion gas is supplied from the rear. The temperature inside the diffusion furnace 1 is detected by the furnace temperature sensor 4. Based on the difference between the target value SV and the furnace temperature measurement value PV from the furnace temperature sensor 4, the controller 7 generates an operation signal u for the power control element 8 which is a thyristor in this case, and the heater 2
The heater temperature is controlled by adjusting the power of the heater. The transfer function of the controller 7 is given by equation (3). In equation (3), K _P is the proportional sensitivity of the controller 7, T _I is the integration time of the controller 7, T _D is the derivative time of the controller 7, and η is the derivative gain of the controller 7.

[Formula 2] G _C (s) = K _P [1+ (1 / T _I s) + {T _D s / (1 + T _D ηs)}] (3)

Further, the transfer function G _P1 (s) from the heater temperature to the temperature in the furnace and the transfer function G _P2 (s) between the heater input and output can be expressed by equations (4) and (5), respectively. In equation (4), K
₁ , L ₁ and T ₁ are the process gain, the dead time and the equivalent time constant between the heater temperature and the furnace temperature, respectively. Further, in the equation (5), K ₂ , L ₂ , and T ₂ are the process gain, the dead time, and the equivalent time constant between the heater input and output, respectively. A block diagram of the temperature control device represented by the transfer functions of the equations (4) and (5) is shown in FIG.

[Number 3] _{G P1 (s) = K 1} e -L1s / (1 + T 1 s) ······ (4) G P2 (s) = K 2 e -L2s / (1 + T 2 s) ··· ···(Five)

[0007] FIG. 2 (C), of combined into one transfer from the heater to the furnace temperature function G _P1 (s) and the transfer of the heater function G _P2 (s) below (6) G _P ( It is a block diagram of the control device which was set to s). In the equation (6), G _P (s), K, L, and T are a transfer function, a process gain, a dead time, and an equivalent time constant between the heater input and the furnace temperature.

[ ^Equation 4] _GP (s) = Ke- ^Ls / (1 + Ts) ・ ・ ・ ・ ・ ・ (6)

[0008]

In the prior art of FIG. 2 (A), the waste time L of the above equation (6) is almost always the equation (4) and FIG. 2 (B).
It is determined by the G _P1 (s) part of the above, and the system is a system in which the waste time L is large and difficult to control. For this reason, the sensitivity of the controller 7 has to be reduced, and there is a problem that the rise time is long in response to the target value. Therefore, the convergence time is long. If you try to shorten the rise time, overshoot will always occur. Further, since the response is slow, there is a problem that it is greatly affected by the disturbances D ₁ (s) and D ₂ (s). Here, the disturbance D ₂ (s) of the heater 2 is detected through G _P1 (s) and G _P2 (s), so that the detection is delayed and greatly affected.
The disturbance D ₁ (s) of the diffusion furnace also has a great influence because the response is slow for the above reason.

In order to solve these problems, FIG. 3 (A)
As shown in (1), cascade control has been proposed in which the temperature inside the furnace is controlled by the master controller 10 and the heater temperature detected by the heater temperature sensor 5 is controlled by the slave controller 11.
A block diagram of the standard cascade controller of FIG. 3 (A) is shown in FIG. 3 (B). Even in the cascade control, it is a master that the response speed of the heater 2 given by the transfer function G _P2 (s) is faster than the response speed between the heater temperature and the furnace temperature given by the transfer function G _P1 (s). This is a general condition for accelerating the circuit response and obtaining a more accurate cascade control effect. In the case of a diffusion furnace, the transfer function of G _P1 (s) is better than that of G _P2 (s). However, since the response is fast, an unstable system is likely to occur. Therefore, in order to ensure stability, it is unavoidable that the response to the target value change and the response to the disturbance should be extremely gentle. Therefore, it becomes necessary to add a first-order lag system circuit or to moderate the ramping coefficient with respect to the target value change. Therefore, the problem that the rise in the target value response is slow and the convergence takes a long time cannot be avoided. In addition, depending on the control constant of PID control, a large residual deviation may occur, which makes it difficult to set the control constant of PID control. Further, the recovery with respect to the disturbance D ₁ (s) is slow.

In order to solve the above problems in the standard cascade control device, as shown in FIG. 3 (C), the same target value as the target value SV of the master controller 10 is given to the input of the slave controller 11. A scheme has been proposed. In this case, the problem of the large residual deviation is solved regardless of the set value of the control constant of the PID control of the master controller 10. The SV in the slave controller 11 in this case corresponds to the bias. However, since the system itself is not changed, the points that the target value change response rises slowly, the point that convergence takes time, and the point that recovery to the disturbance D ₁ (s) is slow are not solved.

Therefore, an object of the present invention is to provide an internal temperature control device for a diffusion furnace in which overshoot is extremely small and a response speed is fast in a target value change response and a disturbance response and which converges in a short time.

[0012]

With reference to FIGS. 1 and 4 (A), the internal temperature control device for a diffusion furnace according to the present invention is a method for measuring the internal temperature of a diffusion furnace 1 heated by a heater 2 and the furnace. A master controller 10 that generates a master controller output PN ₁ based on a difference from an internal temperature set value, and a heater operation based on a difference between the measured temperature value of the heater 2 and the master controller output PN ₁ . Slave controller 1 that produces slave controller output PN ₂
In the in-reactor temperature control device having 1, it comprises an attenuator 13 connected between the output end of the master controller and the input end of the slave controller 11, the master controller output PN ₁ It is uniformly attenuated by the attenuator 13 and then added to the slave controller 11.

Referring to FIGS. 1 and 4 (B), the master controller 10 preferably includes a proportional element, an integral element, and a derivative element so that the output of the slave controller and the master controller 10 are When the slave controller output PN ₂ is 100% or more or 0% or less of the predetermined span by connecting an integral suppressor 14 between them, the integral suppressor 14 functions as an integral element of the input signal of the master controller 10. To stop.

[0014]

The internal temperature control device of the diffusion furnace of the present invention adds the master controller output PN ₁ to the slave controller 11 after the master controller output PN ₁ is uniformly attenuated by the attenuator 13 as described above. Input is limited to an amount that can obtain the required rising speed during the input span, and preferably the PID set value with good response is selectively switched to reduce overshoot and improve the rising speed. Can be controlled.

Therefore, the object of the present invention is to provide a "diffusion furnace internal temperature control device which has extremely small overshoot in target value change response and disturbance response, fast response speed, and converges in a short time". It

When the integral suppressor 14 is used, when the slave controller output PN ₂ is 100% or more or 0% or less of the predetermined span, the integral suppressor 14 functions to integrate the input signal of the master controller 10. Since it is prevented, excessive integration can be avoided, time required for canceling the output of the excessive integration can be saved, and recovery to external disturbances, particularly external disturbances such as temperature drop accompanying the entry and exit of the object to be processed, can be accelerated.

FIG. 5 shows the effect of the integral suppressor 14.
FIG. 2 (A) shows a change in the temperature inside the furnace when a disturbance that rapidly lowers the temperature of the front heater 2f of the diffusion furnace 1 by about 100 ° C. occurs and the disturbance is released after about 5 minutes. In the figure, curve 2 shows the result of the conventional PID control, and curve 1 shows the control result when the integral suppressor 14 is added. As is clear from the comparison of both curves, according to the present invention, the overshoot can be suppressed and the target temperature can be reached quickly when recovering from the disturbance.

[0018]

EXAMPLE FIG. 6 (A) shows an event information detector 16 which detects information related to events such as in / out of a semiconductor wafer transfer boat, burning, ramping of temperature in the furnace, and the master controller based on the event information. PI in 10
An example of switching the control constant of D control will be described. The control constants of the PID control are the proportional sensitivity of the controller, the integration time, the differential time, the differential gain, and the like. In order to switch these control constants, the PI between the event information detector 16 and the master controller 10
Connect D switch 17. The PID switch 17 stores appropriate control constants for expected event information, such as target value change response control constants and disturbance response control constants in advance, and responds to the signal from the event information detector 16 according to the signal. To selectively switch control constants.

By adding control constant switching of PID control based on event information, switching to target value change response control constants or disturbance response control constants etc. is performed at appropriate timing when switching target values or disturbances occur. Will be able to do. Therefore, overshoot can be eliminated in the target value change response, and the rise time can be minimized. Further, it is possible to appropriately control the temperature in the furnace with respect to various disturbances and suppress the influence thereof.

FIG. 7A shows a control result when the master controller 10 is switched from the PID control mode to a mode close to the PD control in accordance with the ramping event information of the furnace temperature target value. In the figure, when curve 1 maintains the normal PID control mode, curve 2 responds to the operation of the event information detector 16.
The case where the mode is switched to a mode close to PD control by the PID switch 17 is shown. As is clear from the comparison of both curves, when the above switching is used, the overshoot is almost removed when the target temperature of ramping for temperature increase and temperature decrease is reached.

FIG. 7B shows the master controller 10 in the normal state according to the event information of the incoming of the semiconductor wafer transfer boat.
The control results when switching from the PID control mode to the PID control mode adapted to this furnace disturbance are shown. Curve 3 is normal
When the PID control mode is maintained, the curve 2 is switched to the PID control mode compatible with the incoming furnace disturbance by the PID switch 17 according to the operation of the event information detector 16, and the curve 1 is the outside temperature control by the heater temperature sensor 5 only. In the case of following the temperature inside the furnace under the same conditions as in curve 2. As is clear from the comparison of these curves, controlling the temperature drop due to the above disturbance in the normal PID control mode causes a large overshoot after the completion of the furnace injection, but the PI
It can be seen that the overshoot can be almost eliminated only by switching to the D control mode. As a result, quick target temperature followability can be obtained. The outside temperature control cannot suppress a large decrease in the temperature inside the furnace due to the entering of the product to be processed.

FIG. 6B shows an embodiment in which the attenuation rate α in the attenuator 13 is switched according to the signal from the event information detector 16. To switch the attenuation rate α, an attenuation switch 19 is connected between the event information detector 16 and the attenuator 13. Attenuation switch that is appropriate for the expected event information.
It is stored in advance in 19 and is selectively switched according to the signal from the event information detector 16.

Attenuation rate α of the attenuator 13 according to the event information
By adding switching, it is possible to eliminate the overshoot that occurs each time the target value is switched, and to minimize the rise time. In addition, the overshoot suppressing force when a disturbance occurs can be improved.

FIG. 8 shows that, similarly to the case of FIG. 7B, the switching of the attenuation rate α of the attenuator 13 is selectively added to the switching of the control mode of the master controller 10 according to the event information of the boat entering the furnace. The control results in the case of The curve 1 corresponds to the curve 3 in FIG. 7B, and the curve 2 shows the case where the attenuation rate α is not switched, and the curve 2 shows the case where the attenuation rate α of the attenuator 13 is switched according to the operation of the event information detector 16. As is clear from the comparison of both curves, when the attenuation rate α switching by the attenuator 13 is added, there is an extremely slight overshoot that remains when the temperature drop due to the disturbance is controlled only by switching the PID control mode. It turns out that you can apply the brakes and remove this. As a result, overshoot can be reduced to a substantially negligible amount. Also, by switching the damping rate α, it is possible to obtain a quick target temperature followability.

[0025]

As described above in detail, the internal temperature control device for the diffusion furnace according to the present invention attenuates the output of the master controller under a certain condition, and further, according to the output of the slave controller or the event information. Since the control mode of the master controller and the attenuation rate of its output are switched, the following remarkable effects are obtained.

(A) Since the control is performed by the detected value of the temperature inside the diffusion furnace, it is possible to continuously and stably control from low temperature to high temperature as compared with the control by the heater temperature outside the furnace. (B) Since it can be applied to a case where a diffusion furnace is provided with a plurality of heaters, the temperature inside the furnace can be kept uniform regardless of the position, and variations in processing in a group of processed objects such as wafer rows can be prevented,
Productivity can be increased. (C) Since an appropriate temperature is maintained when entering an object to be processed such as a wafer, it is possible to prevent thermal damage to the object to be processed such as warping of the wafer. (D) Since the control is such that the heater load is suppressed, energy can be saved. (E) Even if the temperature sensor in the diffusion furnace is abnormal, the attenuator can prevent overload on the heater. (F) Optimal furnace temperature control can be realized by general knowledge of controllers without requiring special skill. (G) Since the function of the attenuator and the like avoids severe setting for the heater, the life of the heater and the diffusion furnace can be extended.

[Brief description of drawings]

FIG. 1 is a block diagram of an internal temperature control device for a diffusion furnace according to the present invention.

FIG. 2 is an explanatory diagram of a conventional temperature control device for a diffusion furnace.

FIG. 3 is an explanatory diagram of a conventional cascade control device.

FIG. 4 is an explanatory diagram of an embodiment of the present invention.

FIG. 5 is a graph showing an example of the operation of the above embodiment.

FIG. 6 is an explanatory diagram of another embodiment of the present invention.

FIG. 7 is a graph showing an example of operation of the other embodiment.

FIG. 8 is a graph showing another example of the operation of the other embodiment.

[Explanation of symbols]

1 diffusion furnace 2 heater
4 Furnace temperature sensor 5 Heater temperature sensor 7 Controller
8 Power control element 10 Master controller 11 Slave controller
13 Attenuator 14 Integral suppressor 16 Event information detector 17 PID switch 19 Attenuator switch.

Claims (4)

[Claims] 1. A master controller (10) for generating a master controller output (PN ₁ ) based on a difference between a measured value of an internal temperature of a diffusion furnace (1) heated by a heater (2) and a preset temperature value of the furnace. ) And a slave controller (11) that generates a slave controller output (PN ₂ ) for heater operation based on the difference between the measured temperature value of the heater (2) and the master controller output (PN ₁ ). In the internal temperature control device, an attenuator (13) connected between the output end of the master controller and the input end of the slave controller is provided, and the master controller output (PN ₁ ) is connected to the attenuator (13). The internal temperature control device for the diffusion furnace, which is added to the slave controller (11) after being uniformly attenuated by). 2. The internal temperature control device according to claim 1, wherein the master controller (10) includes a proportional element, an integral element, and a derivative element, and the output terminal of the slave controller and the master controller (10). ) Is connected to the integral element (14), and when the slave controller output (PN ₂ ) is 100% or more or 0% or less of the predetermined span, the integral suppressor (14) An internal temperature control device for a diffusion furnace which blocks the integration function of the integration element of the master controller (10). 3. The internal temperature control device according to claim 2, wherein an event information detector (16) and a PID switcher connected between the event information detector (16) and the master controller (10). (17), the PID switch according to the detected event information including proportional sensitivity, integral time, and derivative time selectable for the proportional element, integral element, and derivative element of the master controller (10). An internal temperature control device for a diffusion furnace, which selects the proportional sensitivity, integration time, and differentiation time predetermined by (17). 4. The internal temperature control device according to claim 3, wherein the event information detector (16) and the attenuator (13).
And an attenuation switching device (19) connected between the attenuation switching device (19) and a plurality of attenuation factors selectable in the attenuator (13). An internal temperature control device for a diffusion furnace, wherein the attenuation factor is selected.