JPS62137605A - Method and device for heat treatment - Google Patents

Abstract

PURPOSE:To improve responsiveness by obtaining a temperature control signal including proportion, integration and differentiation components from the difference between a detected temperature value and a set one, and executing four operations and correcting it so as to input to a power controller. CONSTITUTION:A heat treatment device consists of a heating furnace 11, a temperature detector 12, a temperature setter 13, a temperature controller 14 by proportion, integration and differentiation (PID) controls, the power controller 15 and a heating means 17. At that time, a fourth power corrector 18 is installed at the subsequent stage of the temperature controller 14, and an output B obtained by raising to fourth power to the output signal A of the temperature controller 14 is inputted to the power controller 15. Thus a temperature control signal A is obtained from a temperature difference DELTAT between a target temperature To and a temperature Tr in the heating furnace 11. Then electric power is controlled according to a control signal B to which the four operation corrector 18 applies four operations. If the power controller 15 gives electric power in proportion to the control signal B to the heating means 17, the temperature Tr of an object to be heated in the heating furnace 11 becomes a temperature in proportion to the temperature control signal A.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to semiconductor substrates, etc. (hereinafter referred to as "wafers").
The present invention relates to a heat treatment method and apparatus for heating an object to be heat treated to perform heat treatment.

In particular, the present invention relates to a heat treatment method and apparatus in which a wafer is carried into a heating furnace and subjected to heat treatment at a required temperature by light irradiation.

[Conventional technology]

Generally, the wafer heat treatment process includes heat treatment to activate the ion implantation layer and make the composition uniform, heat treatment to stabilize the silicon film, heat treatment to form ohmic contact, etc. as a post-treatment of ion implantation. , is used very widely.

In any of these heat treatments, it is necessary to uniformly and rapidly heat the surface of the wafer with a required temperature increase characteristic (target temperature).

Therefore, as this heating means, a heating light source such as a halogen lamp is used, and the light irradiation from the heating light source to the wafer is controlled uniformly and rapidly, and with a predetermined desired temperature increase characteristic. Is required.

As a conventional temperature control device for a heat treatment furnace, there is a
As described in Japanese Patent No. 120075, a voltage corresponding to the temperature of the heat treatment furnace in which the wafer is stored is compared with a predetermined reference voltage, and the error signal is processed by an arithmetic device. Disclosed is an apparatus for amplifying the power and controlling the temperature of the heat treatment furnace to a desired temperature in addition to the heating means of the heat treatment furnace.

Furthermore, as a method of uniformly heating a wafer in a conventional heating furnace by irradiating light, the present applicant has proposed, for example, a patent application published in
As disclosed in the specification of No. 5571, before carrying the wafer into the heating furnace, the inside of the furnace is controlled based on an output program for controlling the input to the light source, which is stored in advance in the storage device. There is a heat treatment method in which the wafer is preheated and then carried into a heating furnace within a predetermined temperature range.

[Problem that the invention seeks to solve]

Conventionally, as disclosed by the present applicant in Japanese Patent Application No. 59-105571, for example, the temperature inside the heating furnace,
The temperature is compared with a predetermined set temperature, and depending on the comparison result, the input to the heating means is controlled by proportional (P), integral (I), differential (D), etc., or a combination thereof (hereinafter referred to as PID). control).

FIG. 11 is a block diagram showing an outline of a conventional temperature control method, and FIG. 12 is a block diagram showing an outline of the conventional temperature control method, and FIG. It shows changes over time.

The temperature (Tr″) detected by the temperature detector (2) at a predetermined position in the heating furnace (1) is measured by the curve [■] in Figure 12.
The temperature (target temperature) (To
) change is represented by curve (1) in FIG.

The difference between the temperature (Tr') in the heating furnace (1) at the elapsed time (1) from the start of heating and a predetermined set temperature (To) is PID-controlled by the temperature controller (4), and its output is signal(
A) controls the power controller (5) and the heating means (
7) controls the power CP) injected into the

The changes in the output (A) of the temperature controller (4) and the input power (P) of the heating means (7) at this time are expressed by the curve (m
).

The effect of the input power (P) of the heating means (7) is
), which is detected by the temperature sensor (2) and fed back to the temperature controller (4).

The PID control method in this conventional temperature control is
As shown in the figure, for example, from 200 to 300°C in a few seconds,
The heating response was insufficient for rapid temperature changes such as increases in the range of 1000° C. or higher.

In addition, the proportional coefficient (K
The integral coefficient (K2), integral coefficient (K2), or differential coefficient (K, ) is generally adjusted to the optimum value according to the characteristics of the process. On the other hand, if the target temperature changes in a linear proportional relationship, sufficient control is possible, but the temperature at thermal equilibrium of the heated object and the irradiance from the heating means to the heated object change in a -order proportional It is not a linear relationship, but a fourth-order proportional relationship as described below. Therefore, with conventional PID control, the proportional, integral, and differential coefficients must be uniquely determined, and the relationship can be controlled for any temperature from low to high temperatures. However, it was not possible to obtain optimal control characteristics.

[Means for solving problems]

The present invention provides heat treatment in which an object to be heated is housed in a heating furnace having a radiation heating means, the temperature inside the heating furnace is detected by a temperature detection means, and the energy injected into the radiation heating means of the heating furnace is controlled. In the method, a temperature control signal including proportional, integral, and differential components that controls the injection pattern of heating energy based on the value of the difference between the output value (temperature) of the temperature detection means and the preset temperature in the heating furnace. The temperature control signal is corrected to a required power, and the energy injected into the radiant heating means of the heating furnace is controlled based on a signal obtained by adding a differential component of the temperature control signal to this value as necessary. ing.

In addition, the present invention provides a heating furnace in which an object to be heated is housed in order to realize the above method.

A radiant heating means that is disposed in the heating furnace and applies radiant energy to an object to be heated to heat it; and a temperature detection means that detects the temperature at a suitable location within the heating furnace.

A temperature controller that calculates a temperature control signal including proportional, integral, and component signals based on the difference between the output value of the temperature detection means and the signal corresponding to the heating target temperature, and a power correction that raises the temperature control signal to a required power. and, if necessary, an adder that adds the output value of the power corrector and the differential component value of the temperature control signal, and injects the output signal of the power corrector or the adder to the energy injection controller. The present invention also relates to a heat treatment apparatus having such a structure.

[For production]

A temperature control signal containing proportional, integral, and differential components is obtained from the difference between the temperature at a predetermined position in the heating furnace detected by the temperature detection means and the value set in advance for the desired temperature change. The temperature control signal is corrected to the fourth power, the fourth power correction component and the differential component are added as necessary, and the result is input to the power controller, so that the heating furnace can approximate and follow the desired temperature change set in advance. Temperature changes within can be realized.

〔Example〕

(Basic Principle of the Embodiments) First, the reasons why the desired objectives can be achieved by the embodiments of the present invention will be explained.

Due to Stefan Boltzmann's law, that is, the total amount of radiant energy S emitted per unit time per unit area of the surface of a black body at absolute temperature T (K) is proportional to the fourth power of the absolute temperature T (K). In radiation heating, when the object to be heated is a flat plate and receives radiation heating from both the front and back surfaces, if all the radiant energy projected into the object to be heated is absorbed, the specific gravity (ρ), thickness d), Specific heat (c)
The temperature of the heated object in the thermal equilibrium state dθ/dt=o state after t seconds of the flat plate is 0 (K).

pda'-'=tl-2EaO'+2εage'=
(1) It can be expressed as t.

■ is the irradiance per unit area of the heated object by the radiant heat source, ε is the emissivity of the heated object, Oe is the ambient temperature, σ
is a constant.

Here, the third term on the right side of equation (1) is the column versus energy from the atmosphere inside the furnace, such as the furnace wall of the heating furnace. (0'>
>Oe') and solve it for irradiance (I), ■=L±dan Lee+Sσ04...(2)
ε dt .

That is, it can be seen that the irradiance (I) is proportional to the sum of the temperature θ(K) of the heated object to the fourth power and the time differential dθ/dt of θ(K).

In addition, in a radiant heat source such as an electric heater or a tungsten lamp, the energy density of its radiant flux is approximately proportional to the applied power, so if the proportionality constant is (r) and the applied power is (P), I = rP, and the formula (2) is: P = L ± 2 Li + S θ... (3) r
ε dt r .

The problem with the conventional technology is the poor followability to the target temperature (temperature with preset temperature rise characteristics), which is due to the surface temperature θ (K) of the heated object and the irradiation on the heated object. This is because the radiant energy emitted by the radiant energy was calculated using a -th order proportional relationship.

The means to solve this problem is the second equation on the right side of equation (3).
Based on the term, let θ be the output signal (A) of the temperature controller,
A fourth power corrector that raises this to the fourth power is inserted between the temperature controller and the power control unit.

The difference ΔT between the temperature in the heating furnace (Tr') and the set temperature (To) is ΔT = To-Tr' --(4
), and the output (A) of the temperature controller is.

It is expressed as However, is a coefficient.

In equation (5), the differential component becomes zero in a state of thermal equilibrium. The signal corresponding to the sum of the difference component and the integral component is expressed as (
Corresponding to the second term on the right side of equation (3), the differential component becomes zero in the thermal equilibrium state also in equation (3). Therefore, if some of the proportional and integral components in equation (5) are left unchanged, they are the same as before, so they were treated as 0 in the second term on the right side of equation (3) and raised to the fourth power.

Note that the first term on the right side of equation (3) varies with a coefficient depending on the temperature change according to the temperature change of the object to be heated.

Generally, this temperature coefficient variation is smaller than the second term on the right side of equation (3).

Therefore, the response characteristics can be further improved by making the differential component in the first term on the right side of equation (3) part of the control signal, and using the signal added with the output from the fourth power corrector as the input to the power controller. It can be improved.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention, which includes a heating furnace (11), a temperature detector (12), a temperature setting device (13).
.

A temperature controller (14), a power controller (15), and a heating means (17) using proportional, integral, and differential (PID) control are as follows:
This is the same as the conventional one shown in FIG.

FIG. 1(a) shows a case where a temperature controller (14) that cannot separate differential components is used, and FIG. 1(b) shows a case in which a temperature controller (14) that cannot separate differential components is used.
A case is shown in which the temperature controller (14) can separate differential components.

In this embodiment, a fourth power corrector (18) is provided after the temperature controller (14), and this fourth power corrector (18)
is the output signal (A) of the temperature controller (14) raised to the fourth power B=C0A4 (6) (where C is the same after the coefficient) as the energy injection controller, that is, the power controller (15 ).

The heating furnace (1
1) Internal temperature (Tr) and power (W) of heating means (17)
Figure 2 shows the temporal changes in .

For the target temperature (To) curve [1], the heating furnace (11)
The curve (n) of the temperature (Tr) at a predetermined position in FIG. 12 has a faster response and is more stable from a low temperature range to a high temperature range, compared to the conventional case shown in FIG.

This shows that PID control is optimized by always injecting appropriate radiant energy into the heated object.

Output signal (A) of temperature controller (14) and heating furnace (11)
Comparing and explaining the relationship between the temperature (Tr) in the heating furnace (1
Based on the difference ΔT between the temperature (Tr) in ) and the set temperature (TO), the temperature controller (4) outputs a temperature control signal (A) based on PID control.

Power (P) is controlled by this temperature control signal (A). The energy P added to the heating means (7) of the heating furnace (1) is: P=C2A (
7).

If 0 is replaced with temperature Tr', equation (3) can be rewritten as follows.

The first term on the right side of equation (8) is O, and the temperature inside the heating furnace (1), especially the temperature of the heated object at thermal equilibrium (Tr'), is the fourth root of the injected energy, that is, the electric power (P). Since it is proportional, Tr'=C3P'-(9) Here, P=C2A...(7)(
(reprinted), T rl = C4Au ・= −
(10), and as shown in FIG. 3, the temperature (Tr') of the object to be heated in the heating furnace (1) is maintained in proportion to the fourth root of the temperature control signal.

No matter how much PID control is done in the temperature controller (4),
As a result of controlling the electric power, the temperature (Tr') changes as shown in Figure 3. Therefore, if the temperature control signal (A) remains in the following equation, the heating furnace (1
) indicates that it is difficult to control the temperature within the range.

In the present invention, according to FIG. 1, the temperature difference between the target temperature (To) and the temperature inside the heating furnace (11) (Tr) is determined by the temperature controller (14), for example, by equation (5). , outputs a temperature control signal (A), squares the temperature control signal (A) in a fourth power corrector (18), and outputs a control signal (B).

Power (P) is controlled by the control signal (B).

If the power controller (15) supplies electric power (P) proportional to the control signal (B) to the heating means (17) of the heating furnace (11), the electric power (P) becomes P=C9B... ...(11)
Since the temperature (Tr) of the object to be heated in the heating furnace (11) is Tr=C, P+A (12),
By substituting equations (11) and (6) here, it becomes Tr=C,A --(13).

That is, the temperature of the object to be heated in the heating furnace (11) (T r
) is proportional to the temperature control signal (A) and has the characteristics shown in FIG.

Fig. 4 shows that, compared to the conventional Fig. 3, the temperature can be controlled in linear proportion, and PID control using the temperature controller (14) can be effectively applied.

(Second example) FIG. 5(a) shows a second embodiment of the invention.

Compared to the first embodiment, the temperature change d in equation (2) is
This is done so that θ/dt is treated separately, and an adder (24) is added for this purpose.

The sum of the proportional component and the integral component of the temperature control signal is raised to the fourth power by a quadratic corrector (18), and the differential component of the humidity control signal is added by an adder (24). The signal is input to the power controller (15).

By taking into account the temperature change, Figures 1(a) and (
The accuracy of temperature control is improved compared to the embodiment b).

As shown in Figure 5(b), only the differential components can be separated,
The temperature controller (14) may also output the proportional component, integral component, and differential component as a sum.

(Third Example) In the explanation of the basic principle of the example, from equation (1) to (2)
When converting the equation, e'>>Oe' was set, and the term Oe4 was omitted.

When Oe4 cannot be omitted, equation (2) becomes I = vagina.
+2 a 04-2 σθe' −(14)ε
It should be dt.

FIG. 6 shows a third embodiment of the present invention based on the second and third terms on the right side of equation (14).

FIG. 6 shows (14) the first embodiment shown in FIG.
β, setting device (22
) and subtractor (21), and in order to balance the addition, α setter (20) and adder (21) were added.
I9) was added.

Usually, the furnace wall of the heating furnace (11) is preheated to 200 to 300°C.

The temperature inside the furnace during this heating corresponds to Oe, and according to this temperature, the value of 2αDa' is set in the setting device 13 (22) to perform correction.

Regarding the α setting device (20), originally, the integral component of the PID control corresponding to the preheating state should be output from the temperature controller (14), but the In order to ensure zero output from the temperature controller (14), an integral component of the PID control is added in advance by the α setting device (2o).

In FIG. 6(a), the output A of the temperature controller (14) is A=1ΔT 10KJΔTdt0, .
(5) (Reposted) Since dΔT dt and the output A1 of the adder (19) is A1=A+α, it is passed through the fourth power corrector (18).

The output (B2) of the subtracter (21) is B, =C, (A+α)4-β becomes.

Giving this signal B2 to the power controller (15) corresponds to moving the coordinate origin to (α, β) in FIG. 4, and the situation is shown in FIG.

(Fourth example) FIG. 8 shows a fourth embodiment of the invention.

I =-Li-9-" + 2 a O' -2t a
(?e'-(14) (reprinted) ε dt The first embodiment of FIG. 1 ignores the first and third terms on the right-hand side in equation (14), and the right-hand side in equation (14) is The second embodiment shown in FIG. 5 ignores the third term, and the third embodiment shown in FIG. 6 ignores the first term on the right side of equation (14).

In the fourth embodiment, the equation (14) is almost satisfied.

In the fourth embodiment shown in FIG. 8, the differential component in PID control is sent to the temperature controller (14
), and outputs the sum of the proportional component and the integral component as another independent signal (Api).

Similar to the control signal in FIG. 6, the proportional integral signal (A pi) is generated by setting the offset signal (α) in the α setter (20), adding it in the adder (19), and adding it in the fourth power corrector (18). ), then the offset signal (β) is given to the β setter (22
), subtracted by a subtracter (21), added to the differential signal (Ad) by an adder (24), and inputted to the power controller (15).

As a result, the differential component signal (Ad) acts to always equalize the rate of temperature increase of the object to be heated and the rate of temperature increase of the target temperature ('ro). As described above, the followability of the heating temperature (Tr) to the target temperature (To) is improved.

FIG. 9 shows the relationship among the target temperature (TO), the surface temperature of the heated object (Tr), and the electric power CP in the fourth embodiment.

In addition, due to its good responsiveness and temperature followability, in addition to setting the temperature increase rate of the target temperature (To) constant, it is also possible to program a target temperature (To) with complicated temperature changes in advance to set the target temperature (To). Heat treatment that accurately follows the temperature can also be easily performed. The situation is shown in FIG.

FIG. 10(a) shows an example of a characteristic diagram showing good followability to complicated temperature changes in the fourth embodiment of the present invention, and FIG. 12(b) shows an example of a characteristic diagram in the fourth embodiment of the present invention. An example of a characteristic diagram showing good followability to complicated temperature changes is shown.

(Modification) The fourth power corrector in the embodiment may be exactly the fourth power, or may be a value close to it.

This is because it is feedback control.

Therefore, what used to be 1st power becomes 2nd power, 3rd power, etc.
Good results were obtained by setting ・, and the fourth power showed the best characteristics in the experimental results.

〔effect〕

(1) The output signal of the temperature controller is corrected to a power, the signal obtained by adding a differential component as necessary, and the temperature in the heating furnace are corrected to have a linear proportional relationship. The proportional coefficients, integral coefficients, etc. of the PID control within are fixedly set to optimal values, and control with sufficiently high responsiveness is achieved for any temperature set value or even if the temperature set value fluctuates. be able to.

(2) In the heat treatment equipment, temperature control can be performed with high precision based on preset target temperature rise characteristics, improving quality and productivity.

Significant improvement compared to the past.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of a heat treatment apparatus according to the present invention, FIG. 2 is a heating characteristic diagram of heat treatment according to the embodiment of FIG. 1, and FIG. 3 is a diagram showing conventional temperature control signals and heating. A characteristic diagram showing the relationship between temperature. FIG. 4 is a characteristic diagram showing the relationship between the temperature control signal and heating temperature according to the present invention. FIG. 5 is a diagram showing a second embodiment. FIG. 6 is a diagram showing a third embodiment. 7 is a diagram in which the origin of the characteristic diagram in FIG. 4 has been shifted; FIG. 8 is a diagram showing the fourth embodiment; FIG. 9 is a heating characteristic diagram according to the fourth embodiment;
) is a characteristic diagram showing good followability to complicated temperature changes in the fourth embodiment of the present invention. FIG. 1O(b) is a characteristic diagram showing good followability to complicated temperature changes in the first embodiment of the present invention. FIG. 11 is a diagram of a conventional heat treatment apparatus, and FIG. 12 is a diagram of heating characteristics of heat treatment by the conventional apparatus of FIG. (1) (11) Heating furnace (2) (12) Temperature detector (3) (13) Temperature setting device (4) (14)
Temperature controller (5) (15)'Ki force controller (7)
(17) Heating means (18) Quadrature corrector (19
) Adder (20) α setter (21) Subtractor (22) β setter (24) Adder Figure 9 Figure 10 (a) 6t3. . . , Figure 10(b)

Claims (7)

[Claims] (1) Storing an object to be heated in a heating furnace having a radiation heating means, and detecting the temperature inside the heating furnace with a temperature detection means,
In a heat treatment method for controlling energy injected into a radiation heating means of a heating furnace, proportional, integral, A heat treatment method comprising: obtaining a temperature control signal including a differential component; correcting the temperature control signal to a required power; and controlling energy injected into radiation heating means of a heating furnace based on the correction value. (2) Control the energy injected into the radiation heating means of the heating furnace based on a signal obtained by adding the differential component of the deviation between the output value of the temperature detection means and the set temperature to the value corrected to the required power. A heat treatment method according to claim (1). (3) The heat treatment method according to claim (1) or (2), wherein the required power correction is a fourth power correction. (4) A heating furnace that stores an object to be heated inside, a radiant heating means installed in the heating furnace that applies radiant energy to the object to heat it, and detects the temperature at an appropriate location within the heating furnace. a temperature detecting means; a temperature controller that calculates a temperature control signal including proportional, integral, and differential components based on a value of the difference between an output value of the temperature detecting means and a signal corresponding to a heating target temperature; and the temperature control signal. 1. A heat treatment apparatus comprising: a power corrector which raises the power to a required power; and an energy injection controller which determines the energy to be injected into the heating means based on the output signal of the power corrector. (5) differential calculation means for calculating the differential value of the difference between the output value of the temperature detection means and the signal corresponding to the heating target temperature;
Claim 1, characterized in that the output signal of an adder for adding the output value of the differential calculation means and the output value of the power corrector is input to the energy injection controller.
4) The heat treatment apparatus described in item 4). (6) An adder that adds the temperature controller output and a constant is provided, the output of the adder is input to a power corrector, and a subtractor that subtracts the output of the power corrector and a constant different from the above. The heat treatment apparatus according to claim 4 or 5, characterized in that the output of the subtracter is input to the energy injection controller. (7) The heat treatment apparatus according to any one of claims (4) to (6), wherein the power corrector is a fourth power corrector.