JP2004119804A - Semiconductor manufacturing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always carry out stable feedback control even if a disturbance occurs when a temperature in a furnace is abruptly cooled in order to enhance the productivity of a wafer. <P>SOLUTION: When process sequence information in a constant temperature and raising temperature step is inputted to a switching control part 602 as control loop switching information X, a switching device 601 is switched to the b-point of contact. Thus, by a cascade control loop by a first PID adjustment part 202 for inputting the temperature information of a cascade thermocouple and a second PID adjustment part 204 for inputting the temperature information of a heater thermocouple, a temperature of a heater 101 is controlled in accordance with a power amount Z from an output of the second PID adjustment part 204. When the process sequence information in a compulsory cooling step is inputted to the switching control part 602 as the control loop switching information X, the switching device 601 is switched to the a-point of contact. By an in-furnace temperature direct control loop only by the first PID adjustment part 202, the heater 101 is controlled in accordance with the power amount Z from an output of the first PID adjustment part 202. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor manufacturing apparatus including a heat treatment apparatus such as a diffusion apparatus or a CVD apparatus for processing a substrate such as a semiconductor wafer while controlling the temperature.
[0002]
[Prior art]
When heat treatment is performed on a substrate such as a semiconductor wafer (hereinafter simply referred to as a wafer) by a semiconductor manufacturing apparatus such as a diffusion apparatus or a CVD apparatus, and a film forming process such as thin film formation, impurity doping, and surface treatment is performed, a reaction is performed. The temperature of the tube is maintained at an appropriate temperature by following a target temperature set in advance. Therefore, the temperature of the reaction tube is controlled so as to be able to compensate for a disturbance and follow a change in the target temperature. For example, in a known example (for example, see Patent Literature 1), when a disturbance occurs or a target value fluctuates, the system is switched from the feedback control system to the open loop control system. A temperature control system for switching to a feedback system is disclosed. According to such a temperature control system, even when a disturbance occurs, stable temperature control can be performed by a control system that avoids an unstable factor of the temperature control due to the disturbance. In another known example (see Patent Document 2), when a disturbance occurs in the course of a normal heating process, the disturbance is changed by switching from a feedback control system to a control pattern system calculated based on an approximate function. A technique for avoiding the problem has been disclosed. According to this technique, it is possible to perform temperature control while avoiding sudden and temporary disturbance generated during the temperature raising step.
[0003]
[Patent Document 1]
JP-A-11-305805 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-183072
[Problems to be solved by the invention]
However, when switching to an open-loop control system, even temporarily, when a disturbance occurs, as in the technique disclosed in Patent Document 1, it is no longer possible to perform excellent high-precision temperature control using a feedback loop control system. . Further, the technique disclosed in Patent Document 2 temporarily switches over to a predetermined control pattern system when disturbance occurs when the temperature change speed is relatively slow, such as when loading a wafer on a boat or during a heating process. Therefore, it is possible to perform a desired temperature control while avoiding disturbance. However, in order to reduce the processing time of the wafer, large disturbances that occur when rapid cooling is performed are not stable even if the previous feedback system is switched to the predetermined control pattern system. Can no longer be absorbed, and stable temperature control can no longer be performed.
[0005]
In rapid cooling (forced cooling), a rapid air flow is created near the heater by sending air from outside into the furnace (reaction tube) and rotating the exhaust blower inside the furnace to quickly exhaust air. To lower the heater temperature. When the disturbance of the temperature fluctuation is extremely large as described above, the response speed is slow in the feedback system and the desired temperature control cannot be performed. At this time, the feedback system is switched to the open loop system or the predetermined control pattern system. Even so, it is difficult to control such that the temperature fluctuation due to disturbance is large and the temperature fluctuation can be absorbed. As a result, stable temperature control cannot be performed.
[0006]
The present invention has been made in view of such circumstances, and an object thereof is to perform stable feedback control even when the temperature of a reaction tube is rapidly cooled in order to improve the productivity of a substrate. It is to provide such a semiconductor manufacturing apparatus.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor manufacturing apparatus according to the present invention includes a reaction tube, a heater for heating the reaction tube, first temperature detection means (cascade thermocouple) for detecting a temperature of the reaction tube, Second temperature detection means (heater thermocouple) for detecting the temperature of the heater; and temperature of the reaction tube based on detection information of the first temperature detection means and detection information of the second temperature detection means. Control means for performing temperature control by switching between a pattern for performing control and a pattern for performing temperature control only based on detection information of the first temperature detection means when the temperature of the heater is lowered (temperature controller 108, first PID adjustment Unit 202, a second PID adjusting unit 204, and a switching control unit 602).
[0008]
According to this configuration, the cascade control loop using the second temperature detecting means (heater thermocouple) and the first temperature detecting means (cascade thermocouple) in the normal temperature raising step and the step of maintaining the target temperature. Temperature control is performed, and when the temperature of the heater decreases, the temperature can be controlled by a direct control loop in the furnace using only the first temperature detecting means (cascade thermocouple). Accordingly, when the temperature is unstable due to disturbance caused when the temperature of the heater falls, the detection information of the heater temperature can be removed from the control loop to directly control the furnace temperature. Therefore, stable temperature control can be performed by reducing the instability of control due to disturbance, so that the product yield of substrates such as semiconductor wafers can be improved.
[0009]
Further, the semiconductor manufacturing apparatus of the present invention is provided with a cooling means (rapid cooling system) for improving the cooling efficiency by circulating a cooling medium through the surface of the heater when the temperature of the heater drops.
[0010]
According to this configuration, by providing the quenching system, in the process of lowering the furnace temperature, the heater can be rapidly cooled to a predetermined temperature in a short time. Thus, for example, the time of the wafer heat treatment step can be shortened, so that the productivity of the wafer can be improved. Moreover, when cooling air is flowing through the heater, such as during rapid cooling of the heater, the cooling air also cools the heater thermocouple that is in direct contact with the heater. Although temperature control is no longer possible, in the present invention, by removing the heater thermocouple from the control loop, accurate temperature control can be performed by eliminating the cause of instability in temperature control. Thus, for example, the productivity of the wafer can be improved by shortening the time of the wafer processing process, and the product yield of the wafer can be improved.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a semiconductor manufacturing apparatus according to the present invention will be described in detail with reference to the drawings. In the following embodiment, a general wafer film forming process of a semiconductor manufacturing apparatus is a well-known technique, and therefore, a description thereof is omitted, and a temperature control technique for directly controlling a furnace temperature of the semiconductor manufacturing apparatus. Will be described. In the following embodiments, a vertical diffusion furnace will be described as an example of a semiconductor manufacturing apparatus.
[0012]
FIG. 1 is a conceptual diagram showing the structure of a general vertical diffusion furnace. The vertical diffusion furnace shown in FIG. 1 has a triple structure of a furnace main body 100, a soaking tube 103, and a reaction tube 104. A wafer 107 is mounted on a boat 106 and housed in the reaction tube 104, so that the wafer 107 is During the heat treatment, a film forming process such as thin film formation, impurity doping, and surface treatment is performed. At this time, the inside of the furnace is evenly heated by the heater 101 arranged substantially uniformly between the furnace main body 100 and the soaking tube 103. The temperature of the heater 101 is detected by the heater thermocouples 102 arranged at a plurality of locations and fed back to the temperature controller 108. Further, the temperature between the soaking tube 103 and the reaction tube 104 is detected by the cascade thermocouples 105 arranged at a plurality of positions between the soaking tube 103 and the reaction tube 104 and fed back to the temperature controller 108. The temperature controller 108 controls the amount of power (operating amount) Z to be supplied to the heater 101 based on the detected temperature information from the heater thermocouple 102 and the cascade thermocouple 105 and the target temperature Y to control the temperature of the heater 101. .
[0013]
The heater 101 is divided into zones in order to control the furnace temperature with higher accuracy. For example, in the case of four-zone division, the heaters 101 are called U, CU, CL, L zones, etc. in order from the top. Further, a heater thermocouple 102 and a cascade thermocouple 105 are provided for each zone. In such a vertical diffusion furnace, temperature control is performed so that the detected temperature of the cascade thermocouple 105 installed relatively close to the wafer is equal to the target temperature Y, and the optimal heat treatment is performed on the wafer. Is done.
[0014]
FIG. 2 is a configuration diagram of a temperature control system using a cascade control loop. Normally, in a vertical diffusion furnace as shown in FIG. 1, a cascade control loop as shown in FIG. 2 is formed to perform temperature control. The cascade control loop includes a first adder 201 that outputs a deviation between the target temperature Y and a detected temperature from the cascade thermocouple 105, and a PID (proportional, integral, and differential) according to the output level of the first adder 201. A) a first PID adjusting unit 202 which calculates and controls the temperature detected by the heater thermocouple 102 to follow the temperature, and a deviation between the output level of the first PID adjusting unit 202 and the detected temperature from the heater thermocouple 102. , And a second PID adjusting unit 204 that performs PID calculation according to the output level of the second adder 203 and controls the amount of power Z supplied to the heater 101. I have.
[0015]
FIG. 2 shows a cascade control loop of only one of the heater division zones (U, CU, CL, and L zones) in FIG. 1. However, when the heater 101 is divided into four zones, A cascade control loop having a configuration similar to that of FIG. 2 exists for each zone. In this manner, a cascade control loop as shown in FIG. 2 is configured using the detected temperature of the heater thermocouple 102 having a relatively fast response speed and the detected temperature of the cascade thermocouple 105 having a relatively slow response speed. By doing so, it is generally known that the detected temperature of the cascade thermocouple 105 can be quickly and stably controlled to a target temperature.
[0016]
Next, a processing sequence generally used in the vertical diffusion furnace of FIG. 1 will be described. FIG. 3A shows a flowchart of an example of the process performed in the vertical diffusion furnace, and FIG. 3B shows an outline of a temperature change in the furnace in each step of the process. The symbols S1 to S6 in FIG. 3B correspond to the steps S1 to S6 in FIG. 3A.
[0017]
Step Sl is a process to stabilize at a relatively low temperature T ₀ of the temperature in the furnace. In step Sl, the boat 106 has not yet been inserted into the reaction tube 104 in the furnace. Step S2 is a process (boat loading) of inserting the boat 106 holding the wafer 107 into the reaction tube 104. Since the temperature of the wafer 107 is usually lower than the temperature T ₀ , the temperature in the furnace temporarily becomes lower than T ₀ as a result of inserting the boat 106 into the reaction tube 104. the temperature again stabilizes the temperature T ₀ through some time.
[0018]
Step S3 is a temperature T ₀ to the target temperature T _l for performing the process treatment of the film forming process and the like on the wafer 107 is a process to gradually increase the temperature in the furnace (ramp-up). Step S4 is a process of stabilizing and maintaining the temperature of the furnace in order to perform the process process to the wafer 107 at a target temperature T _l. Step S5 is a process of lowering the temperature gradually in the furnace (ramp down) after the process processing completion from the target temperature T _l to a temperature T ₀ relatively low again. Step S6 is a process of pulling out the boat 106 on which the processed wafer 107 is mounted from the reaction chamber 104. Thereafter, the processed wafer 107 on the boat 106 is replaced with an unprocessed wafer 107. These series of processes (that is, steps S1 to S6) are performed on all the wafers 107.
[0019]
Usually, the processing from step S1 to step S6 is repeatedly performed, so that performing each step in a short time leads to an improvement in productivity. In particular, since the temperature of the heater 101 is easily heated and hardly cooled, how to shorten the time required for the ramp-down step in step S5 is a point of improving productivity. Therefore, a rapid cooling system as shown in FIG. 4 is provided. That is, FIG. 4 is a conceptual diagram showing the structure of a vertical diffusion furnace provided with a quenching system.
[0020]
The quenching system shown in FIG. 4 adjusts the flow of air for forced air cooling to an exhaust blower 401 serving as a driving unit for forced air cooling, a cooling air inlet 402 at a lower part of the apparatus, and an exhaust port 403 at an upper part of the apparatus. And a water-cooled radiator 405 for cooling the exhaust gas.
[0021]
In the vertical diffusion furnace shown in FIG. 4, the temperature control is normally performed with the exhaust blower 401 stopped and the shutters 404 closed, and when the ramp-down step (step S5 in FIG. 3B) is reached, the exhaust blower is used. The heater 401 is driven, each shutter 404 is opened, and the heater 101 is forcibly cooled by an air flow as indicated by an arrow in the drawing. As a result, the time required for the ramp-down step S5 in FIG. 3B can be drastically reduced as compared with the case of natural cooling without the rapid cooling system.
[0022]
However, the problem here is that in the rapid cooling system as shown in the vertical diffusion furnace of FIG. 4, since the heater 101 is directly cooled by forced air cooling, the temperature detected by the heater thermocouple 102 and the temperature of the reaction tube 104 The difference between the detected temperature of the cascade thermocouple 105 installed inside and the temperature fluctuation becomes very large, which makes it difficult to control the temperature by the cascade control loop as shown in FIG. That is, in the vertical diffusion furnace having the quenching system as shown in FIG. 4, the detected temperature of the cascade thermocouple 105 is reduced as quickly as possible, but the detected temperature of the heater thermocouple 102 is more rapidly reduced by forced cooling. Descends. For this reason, the differential operation in the second PID adjustment unit 204 in FIG. 2 works strongly, and an attempt is made to supply a large amount of electric power Z to the heater 101. As a result, the falling speed of the detected temperature of the cascade thermocouple 105 may be reduced. . For this reason, at the time of forced cooling in which the exhaust blower 401 is operated, a special PID parameter for forced cooling may be adjusted and used. However, the time required for the adjustment work is required, and as a result, FIG. The ramp-down time in step S5 of b) cannot be shortened.
[0023]
Further, when the detected temperature of the cascade thermocouple 105 approaches the target temperature, the exhaust blower 401 is stopped, forced cooling is stopped, and normal temperature control is switched, so that more complicated adjustment work is required. May be. There is a limit to performing such an adjustment operation in a short time, and a desired temperature control performance may not be achieved in some cases. For this reason, there is a demand for a control method that does not require a special adjustment time even during forced cooling and can achieve good temperature control.
[0024]
Therefore, in the present invention, in a temperature control system of a semiconductor manufacturing apparatus, a system for detecting a heater temperature (that is, a feedback system of a heater thermocouple) is removed from a control loop during forced cooling while utilizing temperature control by a cascade control loop. It provides a simple control method, shortens the wafer production time, improves the product yield, and improves the productivity. That is, the feedback system is always maintained during the normal temperature raising step and during the target temperature maintenance and also during the forced cooling of the heater, and the cascade thermocouple and the heater thermocouple are connected during the temperature raising step and the target temperature maintenance. While temperature control is performed by the cascade control loop used, at the time of forced cooling, the control is switched to a direct furnace temperature control loop using only a cascade thermocouple so as to eliminate an instability factor of the control system due to forced cooling of the heater.
[0025]
FIG. 5 is a diagram illustrating a configuration example of a furnace temperature direct control loop in the semiconductor manufacturing apparatus of the present invention. That is, FIG. 5 is obtained by omitting the second adder 203 and the second PID adjusting unit 204 from the configuration example of the cascade control loop of FIG. In FIG. 2, the difference between the output level of the first PID adjusting unit 202 and the detected temperature from the heater thermocouple 102 is calculated by the second PID adjusting unit 204 to obtain the electric energy Z. The first adder 201 outputs the deviation between the target temperature Y and the detected temperature from the cascade thermocouple 105, and outputs the result calculated by the first PID adjustment unit 202 as the electric energy Z directly to the heater 101. I have. As a result, even if the detected temperature of the heater thermocouple 102 suddenly drops during forced cooling, the detected temperature information of the heater thermocouple 102 is not fed back, so the second PID adjustment unit 204 as shown in FIG. Does not work strongly, and as a result, it is possible to prevent the falling speed of the detected temperature of the cascade thermocouple 105 from becoming slow.
[0026]
Note that, except for the time of forced cooling, the control by the cascade control loop as shown in FIG. 2 is often excellent in responsiveness and stability. Therefore, in reality, as shown in FIG. It is desirable to construct a control system that can switch the direct control loop of the furnace temperature. That is, FIG. 6 shows a configuration example of a control system capable of switching between the cascade control loop and the direct furnace temperature control loop in the semiconductor manufacturing apparatus of the present invention.
[0027]
6 differs from the circuit configuration of FIG. 2 in that the power amount Z from the output of the first PID adjustment unit 202 is directly output to the heater 101 or the first PID adjustment unit 202 and the second A switch 601 for connecting the PID adjustment unit 204 to switch whether to output the electric energy Z from the output of the second PID adjustment unit 204 to the heater 101, and control loop switching information X such as processing sequence information. The difference is that a switching control unit 602 for inputting and outputting a switching signal to the switching unit 601 is added.
[0028]
According to the configuration of the control system as shown in FIG. 6, in the normal constant temperature and temperature raising steps from step S1 to step S4 in FIG. 3, the switch 601 is switched to the contact b side so that the first PID adjustment unit 202 And the cascade control loop of the second PID adjusting unit 204, and the heater 101 is controlled by the electric energy Z from the output of the second PID adjusting unit 204. Further, in the process at the time of forced cooling in step S5 of FIG. 3, the switch 601 is switched to the a contact side, and the control is performed by switching to the in-furnace temperature direct control loop only by the first PID adjustment unit 202. The heater 101 is controlled by the electric energy Z from the output of the first PID adjustment unit 202.
[0029]
At this time, when the processing sequence information of the temperature raising step and the target temperature maintaining step in steps S1 to S4 shown in FIG. 3 is input to the switching control unit 602 as the control loop switching information X, the switch 601 is switched to the contact b side. And a cascade control loop is formed. Further, when the processing sequence information of the temperature lowering step in step S5 is input to the switching control unit 602 as the control loop switching information X, the switch 601 is switched to the contact a side to form a furnace temperature direct control loop.
[0030]
Also, the direct furnace temperature control loop using only the first PID adjusting unit 202 as shown in FIG. 5 is effective when the detected temperature of the cascade thermocouple 105 is faster than the detected temperature of the heater thermocouple 102. It is. This is a phenomenon seen when the heater has a high output. In such a case, the control effect of the cascade control loop is lost, and conversely, control performance may deteriorate. Therefore, in such a case, the control performance can be improved by using the in-furnace temperature direct control loop in the configuration of the control loop of FIG. 5 or FIG.
[0031]
Further, a temperature control system in the semiconductor manufacturing apparatus of the present invention will be described with reference to FIGS. The temperature control system in the semiconductor manufacturing apparatus according to the present invention includes the temperature of the external temperature sensor (that is, the heater thermocouple 102) installed near the heater 101 which is the heating source of the wafer and the temperature control system inside the soaking tube 103 of the furnace body 100. The first PID adjustment unit 202 and the detected temperature feedback of the heater thermocouple 102 which detect the temperature of the installed internal temperature sensor (that is, the cascade thermocouple 105) and perform temperature control by the detected temperature feedback of the cascade thermocouple 105 The present invention relates to a temperature control system that controls a furnace temperature by forming a cascade control loop with a second PID adjusting unit 204 that performs temperature control according to the present invention. In such a temperature control system, when the temperature is in a temperature control state in which a disturbance occurs in the temperature control system such as by cooling the heater 101, only the cascade thermocouple 105 serving as an internal temperature sensor is used. It is characterized in that temperature control is performed by a direct furnace temperature control loop by only the first PID control unit 202.
[0032]
When cooling the heater 101, the temperature of the heater 101 to be controlled is lowered by a method other than natural cooling, for example, a cooling method such as forced cooling while circulating and exhausting the air in the furnace by the exhaust blower 401. A control system having a forced cooling system is characterized in that the process is switched to a temperature control system based on the above-described furnace temperature direct control loop only in the step of performing forced cooling of the furnace by the exhaust blower 401. That is, in the temperature lowering step, as shown in FIG. 4, each shutter 404 of the exhaust port 403 in the forced cooling system (quick cooling system) is opened to take in air from the cooling air introduction port 402, and at the same time, the exhaust blower 401 is Drive and quickly exhaust air. As a result, rapid air flows near the heater 101 to forcibly cool the heater 101. The air heated by the heater 101 is cooled by a water-cooled radiator 405 and then exhausted to the outside from an exhaust blower 401. At this time, the temperature of the heater 101, whose temperature rapidly changes, is removed from the control loop, and the furnace temperature is directly controlled, thereby reducing control instability and shortening the temperature drop time.
[0033]
Further, the temperature control system in the semiconductor manufacturing apparatus of the present invention is installed in an external temperature sensor (heater thermocouple 102) installed near a heating source (that is, heater 101) and in a soaking tube 103 of the furnace body 100. In the temperature control system that detects the temperature of the internal temperature sensor (that is, the cascade thermocouple 105) and controls the furnace temperature by forming a cascade control loop, the detected temperature of the internal temperature sensor (the cascade thermocouple 105) is detected. If the change speed is faster than the change speed of the detected temperature of the external temperature sensor (heater thermocouple 102), the temperature control by the furnace temperature direct control loop is performed instead of the temperature control by the cascade control loop. It is characterized by performing. That is, if the rate of change of the detected temperature of the cascade thermocouple 105 is faster than the rate of change of the detected temperature of the heater thermocouple 102, the direct control of the furnace temperature by the cascade thermocouple 105 and the first PID adjusting unit 202 as shown in FIG. Sufficiently accurate temperature control can be performed by a control system using a loop.
[0034]
Further, in the temperature control system in the semiconductor manufacturing apparatus of the present invention, when processing sequence information as shown in FIG. 3 is input to the switching control unit 602 as control loop switching information X, the switch 601 automatically switches the control system. It is characterized in that a temperature control system using a direct furnace temperature control loop and a temperature control system using a cascade control loop are switched as needed.
[0035]
The embodiment described above is an example for describing the present invention, and the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention. Although the above embodiment has been described by taking the temperature control system in the vertical diffusion furnace as an example, the present invention is not limited to this. It is needless to say that the present invention can be applied to a temperature control system in the heat treatment step in the above.
[0036]
【The invention's effect】
As described above, according to the present invention, even when a large disturbance occurs, the influence of the disturbance can be suppressed to a small level, and the feedback control system can be maintained, so that the control can always be performed with high accuracy. Accordingly, the productivity of the wafer can be improved by shortening the production time of the wafer, and the production quality of the wafer can be improved.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the structure of a general vertical diffusion furnace.
FIG. 2 is a configuration diagram of a temperature control system using a cascade control loop.
3A is a flowchart illustrating an example of a process performed in a vertical diffusion furnace, and FIG. 3B illustrates a temperature change characteristic in the furnace in each step of the process.
FIG. 4 is a conceptual diagram showing the structure of a vertical diffusion furnace provided with a quenching system.
FIG. 5 is a diagram showing a configuration example of a furnace temperature direct control loop in the semiconductor manufacturing apparatus of the present invention.
FIG. 6 is a configuration example of a control system capable of switching between a cascade control loop and a direct furnace temperature control loop in the semiconductor manufacturing apparatus of the present invention.
[Explanation of symbols]
101 heater, 102 heater thermocouple, 103 soaking tube, 104 reaction tube, 105 cascade thermocouple, 106 boat, 107 wafer, 108 temperature controller, 201 first adder, 202 first PID adjustment unit, 203 second Adder, 204 second PID adjustment unit, 401 exhaust blower, 402 cooling air inlet, 403 exhaust outlet, 404 shutter, 405 cooling radiator, 601 switch, 602 switching control unit, X control loop switching information, Y target temperature , Z power.

Claims (2)

A reaction tube,
A heater for heating the reaction tube;
First temperature detecting means for detecting the temperature of the reaction tube;
Second temperature detecting means for detecting the temperature of the heater;
A pattern for controlling the temperature of the reaction tube based on the detection information of the first temperature detection means and the detection information of the second temperature detection means, and the first temperature detection means when the temperature of the heater decreases. And a control means for performing temperature control by switching between a pattern for performing temperature control only based on the detection information of the semiconductor device. 2. The semiconductor manufacturing apparatus according to claim 1, further comprising: a cooling unit that circulates a cooling medium through a surface portion of the heater when the temperature of the heater drops to improve cooling efficiency. 3.

Images