JPH03196206A - Heat treatment equipment - Google Patents

Abstract

PURPOSE:To quickly heighten or lower the temperature by detecting the heat flux given from a heating means piercing through a substance to be treated via a heat flow sensor and estimating and controlling the temperature based on the heat flux. CONSTITUTION:A temperature sensor 6 is provided at a point near the placing surface of a heating plate 1 for a wafer 3, and the output of the sensor 6 is supplied to a temperature control circuit 10 via a thermometer 7. At the same time, a heat flow sensor 8 is provided at a point near the surface of the wafer 3. The output of the sensor 8 is supplied to a heat flow meter 9 for acquisition of a heat flux. This heat flux is supplied to the circuit 10 and the temperature change of the wafer 3 is estimated from the heat flux. The circuit 10 refers to the temperature measurement information given from the sensor 6 only in a temperature setting period and controls a heating resistor 2. Furthermore the circuit 10 obtains an error between a reference temperature and the temperature of the wafer 3 estimated from the heat flux detected by the meter 9 and corrects the error. Thus it is possible to accurately control both temperature rising and dropping periods with high response.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a heat treatment apparatus.

BACKGROUND ART For example, during the manufacturing process of a semiconductor integrated circuit, there are various heat treatment processes such as baking treatment, film formation treatment, and ashing treatment in a photolithography process. Conventionally, this heat treatment, for example, baking treatment, for example, in the case of a single-wafer type, involves placing the substrate to be treated on a heating plate made of, for example, SUS or aluminum and containing a heating resistor such as a nichrome wire, and For example, the processing temperature is controlled by embedding a temperature sensor such as a thermocouple or a resistance temperature detector in the heating plate and monitoring the temperature with this temperature sensor. [Problems to be Solved by the Invention] As described above, the conventional temperature control method for heat treatment equipment is a method of monitoring and controlling the temperature, which causes a delay in control and brings the object to be processed to a predetermined temperature. It has been difficult to perform accurate control with good responsiveness when starting up or cooling down to a predetermined temperature, or in situations where there is a possibility of temperature change due to external disturbances. In other words, the heat flux emitted from a heating element such as a heater (heat flux is the amount of heat per unit area and unit time; the unit is (kc
The heating plate and, by extension, the substrate to be processed are heated by the heating plate (al/m2・h)), but temperature is generally the integral value of the heat flux with respect to time and coordinates (the following thermal diffusion equation ( 1) and Fourier's law equation (2)), after the heat flux is determined, the temperature of the heating plate and the object to be processed is determined as a result, and there is a certain correlation between the heat flux and temperature (see below) Equation (3) of the thermal diffusion equation of Kuuni 1 ・a21 ・・ (1) at pC
p ay2 at pCp ay T; temperature, q; heat flux, t; time, y; coordinate ρ; density,
cp, heat capacity; thermal conductivity Therefore, as a phenomenon change, heat flux is detected earlier than temperature, and if temperature is monitored, there will be a delay in control. Therefore, in the conventional temperature control method using one type of temperature monitor, in situations where there is a possibility of temperature change due to the influence of external disturbances, etc., the temperature change due to the external disturbance is predicted from the set temperature state.
It was not possible to suppress this disturbance. Further, when trying to control the temperature history at the time of starting up or stopping down to a predetermined temperature, it has not been possible to predict and control the temperature so as to follow a predetermined temperature history. Moreover, even if a disturbance occurs during temperature rise or fall and the heat flux differs from the initial one, a single temperature monitor system can only respond to this change after the temperature change occurs. The delay is undeniable. therefore,
With conventional temperature control methods, it has been difficult to accurately and precisely obtain desired temperature increase and decrease patterns. In addition, the baking process removes the solvent in the photoresist after applying the photoresist, exposing the photoresist film to light, developing the photoresist film, etc., and also improves the physical properties of the resist (photosensitivity, etc.) while imparting heat resistance to the resist. A heat treatment performed to control the resolution, etc.), in which a semiconductor wafer, etc., is heated at a desired baking temperature for a predetermined period of time, as disclosed in, for example, Japanese Patent Laid-Open No. 61-201426. It is. For example, as shown in FIG. 2, the substrate to be processed is set to a predetermined temperature T using a heating plate, and heated for a predetermined set time D2 while maintaining this temperature T1. By the way, in FIG. 2, as mentioned above, temperature control was conventionally performed to keep the temperature constant during the period of the set temperature T, but the temperature change pattern during the temperature rising period D1 and q cooling period D3 was The history (temperature change pattern) such as the temperature and the length of the period was not managed at all. Conventionally, the temperature rising and falling patterns are not temperature-controlled, so these patterns vary from substrate to substrate, even if the substrates are of the same type, such as semiconductor wafers. However, there was a problem in that the physical properties of the resist differed depending on the substrate, resulting in a lack of reliability. In addition, resist patterns have recently become finer as semiconductor devices have become more dense and more sophisticated. For this reason, it is no longer possible to ignore the effects of the temperature change patterns during the heating and cooling periods, which were previously ignored in the baking process, on the physical properties such as the resolution and photosensitivity of the photoresist. It is necessary to control the history of temperature drop change patterns and the like to a predetermined value to obtain better resist physical properties. Therefore, it is possible to perform temperature control during the temperature rising period and the temperature falling period, but as mentioned above, the conventional temperature control method is a method of controlling the temperature by monitoring the temperature. In case of change,
Control delays occurred and the temperature could not be predicted to ensure the desired temperature history. In view of the above points, it is an object of the present invention to provide a heat treatment apparatus that improves the above drawbacks by making it possible to predict and control temperature changes.

[Means to solve the problem]

The present invention provides a heat treatment apparatus for heating an object to be processed by a heating means to perform a predetermined treatment, and a heat flux detection means for detecting a heat flux given to the object to be processed from the heating means. The heating means is characterized in that the heating means is controlled based on the output of the means.

[Effect]

As mentioned above, heat flux responds more quickly to changes in phenomena than temperature. Furthermore, since there is a certain correlation between heat flux and temperature, temperature changes can be predicted by monitoring the heat flux (Equation (3) above). Therefore, even in a situation where there is a disturbance, the temperature can always be controlled stably, and the temperature increase or decrease characteristics can be precisely controlled to a desired value.

【Example】

Hereinafter, an embodiment of the heat treatment apparatus according to the present invention will be described with reference to the drawings, taking as an example a case where it is applied to a baking apparatus for a photolithography process. In FIG. 1, a hot plate 1 is made of metal, and a heat generating resistor 2 is embedded therein. A semiconductor wafer 3 is placed on the hot plate 1, and the hot plate 1 allows
Heating is controlled as described below. For example, a switching element, in this example 5SR (Solid 5
Power is supplied via the tate Relay) 5. In this case, the switching of the 5SR5 is controlled by a PWM (pulse width modulation) signal SM from a temperature control circuit 10 including a computer as described later, and the heating resistor 2 is supplied with an alternating current for a time corresponding to the pulse width of the signal SM. A current flows, and the heating resistor 2 generates heat according to the amount of power supplied. Therefore, by changing the pulse width of the PWM signal SM, the amount of power per period T of the signal SM supplied to the heating resistor 2 can be adjusted, and the temperature of the hot plate 1 can be controlled. That is, in this case, the temperature of the hot plate 1 is P
The temperature rises microscopically due to power being supplied to the heat generating resistor 2 during the period of the pulse width W of the WM signal SM, and the power to the heat generating resistor 2 is cut off during the period after the pulse width period. This results in an average temperature with the microscopically decreasing temperature. Therefore, if we assume that the temperature rising and falling characteristics of the hot plate 1 are equal, then for example, the pulse width W in one cycle T of the PWM signal SM is 1/2T, that is, the duty ratio is 50.
%, the temperature of the hot plate 1 does not change, but if the pulse width W of the PWM signal SM becomes wider than 1/2T, the temperature of the hot plate 1 rises at a slope according to the pulse width W, and vice versa. , if the pulse width W of the PWM signal SM becomes narrower than 1/2T, the temperature of the hot plate 1 decreases at a slope according to the pulse width W. thus,
By changing the pulse width W of the PWM signal SM, the temperature of the hot plate 1 can be freely controlled. A temperature sensor 6 made of, for example, a thermocouple or a resistance temperature sensor is provided near the surface of the hot plate 1 on which the wafer 3 is placed, and the output of this temperature sensor 6 is supplied to a thermometer 7 . Then, an output signal corresponding to the temperature detected by the thermometer 7 is sent to the temperature control circuit 1.
0. Further, a heat flow sensor 8 is provided near the surface of the wafer 3, and the output of this heat flow sensor 8 is supplied to a heat flow meter 9.
A heat flux q is determined, and this heat flux q is determined by the temperature control circuit 10.
is supplied to This heat flow sensor 8 is made of a thin plate material (thickness d
), and the heat flux q flowing through this thin plate is
It can be obtained from the following formula. q−＾・ΔT ... (4) Here, Δ
T is the temperature difference between the front and back surfaces of the thin plate, and since λ and d are known, the heat flux q can be obtained from the heat flow meter 9 by measuring this ΔT, for example, with a differential thermocouple provided in the heat flow sensor 8. I can do it. The temperature control circuit 10 predicts the temperature change of the wafer 3 from this heat flux q (based on the principle shown in equation (3) above). Note that the hot plate 1 is provided with a semiconductor wafer 3 supported thereon.
A bottle (not shown) to be lifted from the hole is inserted through the hole. Furthermore, the semiconductor wafer 3 is transported onto the hot plate 1 by a transport mechanism (not shown), and is moved onto the hot plate 1 by raising and lowering the pins.
It is loaded and unloaded. Next, a baking process using a heat treatment apparatus configured as shown in FIG. 1 will be described. First, the aforementioned pin (not shown) is pushed up from the surface of the hot plate 1. Then, the semiconductor wafer 3 that has been transported is placed on these protruding pins. Next, the pin is lowered to place the semiconductor wafer 3 on the hot plate 1 and hold it by suction. Then, by heat conduction from the hot plate 1, the semiconductor wafer 1\3 is heated according to the following temperature control. In this example, as described above, the temperature control circuit 10 is equipped with a computer, and the baking pattern input means 11 such as a keyboard is used to create an appropriate thermal history depending on the type of the object to be processed, such as the semiconductor wafer 3. A specification (recipe) for achieving this is input, stored, and temperature control is performed according to this recipe. Figure 3 shows an example of this recipe, in which the room temperature rises from 20°C to 120°C with a predetermined slope within 60 seconds, then the temperature is maintained at 120°C for 60 seconds, and then the room temperature rises to 120°C for 60 seconds. In order to be able to reproduce the thermal history of cooling to 20°C, for example, as shown in Figure 3, each point PO to P8 is determined, and the time and temperature information at each of these points PO to P8 is input. Enter the recipe by . In the temperature control circuit 10, during the temperature increase period from points PO to P3 and the temperature decrease period from points P5 to P8, two adjacent
From the information of the points (for example, Pi-PO), find the temperature gradient between these two points, and calculate P of the pulse width W that creates this temperature gradient.
WM signal SM is supplied to 5SR5. At this time, the heat flux from the hot plate 1 is detected by the heat flux meter 9 based on an output signal proportional to the temperature difference detected by the heat flux sensor 8, and the correlation between this heat flux and the wafer temperature change determined in advance is (Equation (5) described later), the pulse width W of the signal SM is controlled so as to sequentially correct the error between the temperature calculated from the recipe and the temperature of the wafer 3 estimated from this heat flux. be done. Here, ρCp T; temperature 1t1 hour, q: heat flux, y; coordinate L; distance ρ between the wafer and heat flow sensor; room air density, cp, heat capacity of air; heat flow sensor body, S; wafer 71 surface f ( L,
t); A function expressing a certain relationship between q and qs.
In this step, the temperature information from the temperature sensor 6 is referenced secondarily to verify the control temperature result. During the temperature stabilization period between points P3 and P5, the temperature control circuit 1 refers to the temperature measurement information from only the temperature sensor 6.
0 controls the heating resistor 2. This is because the hot plate 1 has a relatively large heat capacity, and after the temperature has stabilized, disturbances hardly affect it. However, when it is in a state where it is affected by a disturbance, it is better to control the heating resistor 2 by also referring to the heat flux from the heat flux meter 9. In addition, as a temperature control method in this case, for example, a linear control method such as a PID control method can be used. That is, for example, the momentary temperature (reference temperature) is determined based on the slope determined from the above two points of information during the temperature rising period, and the wafer temperature estimated from this reference temperature and the heat flux detected by the heat flux meter 9 is calculated. Find the error from the temperature in step 3, find the amount of power supplied from this temperature error, and calculate P
The pulse width W of the WM signal SM is set accordingly. As described above, the heat flux passing through the wafer 3, which is the object to be processed, is detected by the heat flow meter 9, and the temperature is predicted and controlled from this heat flux, thereby controlling the temperature rising period and the temperature falling period in the baking process. It is possible to control accurately with good response, and resists with uniform physical properties can be obtained from wafers of the same type. Furthermore, since it becomes possible to control the thermal history during the temperature rising period and the temperature falling period, there is also the effect that the physical properties of the resist can be made desired. In the above example, the wafer 3 was placed directly on the hot plate 1, but at least three spherical objects protruding several points above the hot plate 1 were placed.
By providing three points to support the semiconductor wafer 3, the semiconductor tool 3 does not come into direct contact with the hot plate, and even if there is dust on the hot plate 1, the dust will not reach the semiconductor. Adhesion to the back surface of the wafer 3 can be prevented. In this case, since air enters between the wafer 3 and the hot plate, the temperature control for the wafer 3 is delayed by that amount.However, in this invention, instead of monitoring the temperature, the heat flux Since the temperature of the wafer 3 is monitored, heating control that predicts the temperature of the wafer 3 can be performed satisfactorily, and the delay in control can be reduced. The heat flux sensor 8 may be mounted at any position as long as it can detect the heat flux applied to the object to be processed, and may be mounted within the hot plate 1, for example. In addition, the heating means is not limited to one in which a heating resistor is embedded in a heating plate, but can use various heating means, such as one in which a thin film heating element is attached to a heating plate. You can also. In this case, if a hot plate as thin as possible is used in order to reduce the heat capacity of the hot plate, it becomes possible to further exhibit the performance of temperature control using the above-mentioned heat flux. In addition, the object to be processed is not limited to semiconductor wafers, for example, LC
Needless to say, it can also be applied to D substrates, glass substrates, printed circuit boards, etc. Further, although the above example is for a single wafer process, it is of course applicable to a batch process as well. Furthermore, although the above embodiment was applied to baking after resist application, it can also be applied to baking after developer application, baking before processing such as ion implantation, CVD, etching, ashing, etc., and baking during processing. Good too. Furthermore, it is easy to understand that the present invention is applicable not only to baking equipment but also to film forming equipment, ashing equipment, and other heat treatment equipment.

【Effect of the invention】

As explained above, according to the present invention, the heat flux from the heating means penetrating the object to be processed is detected by the heat flux sensor, and the temperature is controlled by presetting δ-1 based on the heat flux. Therefore, the delay in control can be reduced, the temperature can be raised and lowered quickly, and the history of temperature increases and decreases can also be controlled. Further, in a state where a disturbance exists, since the influence of the disturbance can be detected as a change in heat flux before it appears as a phenomenon as a temperature change, stable temperature control can be performed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of applying the heat treatment device according to the present invention to a baking device, FIG. 2 is a diagram showing an example of the temperature history during baking, and FIG. 3 is a diagram showing the temperature during the baking process. FIG. 3 is a diagram for explaining an example of a recipe for control. 1; Hot plate 2; Heating resistor 3; Semiconductor wafer 8; Heat flow sensor 9; Heat flow meter 10; Temperature control circuit

Claims (1)

[Scope of Claims] A heat treatment apparatus that performs a predetermined treatment by heating an object to be processed by a heating means, further comprising a heat flux detection means for detecting a heat flux imparted from the heating means to the object to be processed; A heat treatment apparatus characterized in that the heating means is controlled based on the output of the bundle detection means.