Concentration control system, concentration control method, and program for concentration control system

Abstract

To provide a concentration control system that can obtain a short delay time and an accurate estimated value for an actual partial pressure of gas in a chamber, and can realize more responsive and accurate partial pressure control than before.SOLUTION: A concentration control system includes: a flow rate control device 1 that is provided on a supply flow path SL for supplying gas into a chamber CN, and controls a flow rate of the gas flowing through the supply flow path SL so as to be an input set flow rate; a partial pressure measuring device 2 that measures a partial pressure of the gas in the chamber; an observer 3 that is equipped with a model 31 for estimating the state of the gas in the chamber CN, and is configured to input an inflow rate of the gas flowing into the chamber and a partial pressure measured by the partial pressure measuring device 2 to the model 31 and to output an estimated partial pressure of the gas in the chamber CN; and a controller 4 that sets a set flow rate in the flow rate control device 1 based on a set partial pressure and the estimated partial pressure of the gas in the chamber CN output by the observer 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a concentration control system used to control the partial pressure of a gas within a chamber. [Background technology]

[0002] In a semiconductor manufacturing process, a mixed gas, for example a mixture of a raw material gas and a carrier gas, is supplied to a process chamber at a predetermined concentration. A mass flow controller, which is a flow control device that controls the flow rate of each gas, is provided in a supply flow path having multiple branch paths connected to the process chamber, and the flow rate of each gas is controlled to a predetermined concentration.

[0003] More specifically, the concentration of the source gas in the mixed gas, i.e., the partial pressure of the source gas, is measured by an absorption spectrometer such as an NDIR (Non Dispersive Infrared) provided on a supply flow path upstream of the process chamber, as shown in Patent Document 1. The partial pressure of the source gas measured by the absorption spectrometer is fed back, and the set flow rate set in the flow rate control device for each gas is appropriately changed based on the deviation between the measured partial pressure and the target set partial pressure.

[0004] However, in the concentration control system described above, the partial pressure of the gas is measured before it enters the chamber, so if gas adsorption or the like occurs in the flow path, a discrepancy will occur between the measured partial pressure and the actual partial pressure in the chamber. Therefore, if the partial pressure is measured in the supply flow path, it cannot be guaranteed that the actual partial pressure of the gas in the chamber is maintained at the set partial pressure. To solve this problem, it is possible to install an NDIR in the chamber to directly measure the gas concentration in the chamber and control the partial pressure more precisely.

[0005] However, NDIR has a large delay with respect to the actual partial pressure and is noisy. Therefore, even if the inside of the chamber is directly measured with NDIR, the actual partial pressure change cannot be obtained quickly and accurately. Therefore, even if the concentration control system described above is constructed, it is difficult to realize partial pressure control with sufficient response speed and accuracy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2010 / 113576 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a concentration control system that can obtain an accurate estimate of the actual partial pressure of a gas in a chamber with a small time delay, thereby realizing partial pressure control with better responsiveness and precision than conventional methods. [Means for solving the problem]

[0008] That is, the concentration control system of the present invention is characterized in comprising a flow control device provided on a supply flow path that supplies gas into a chamber and controls the flow rate of gas flowing through the supply flow path to an input set flow rate; a partial pressure measuring device that measures the partial pressure of the gas in the chamber; an observer having a model that estimates the state of the gas in the chamber, the model being configured to receive as input the inflow flow rate of gas flowing into the chamber and the measured partial pressure of the partial pressure measuring device and output an estimated partial pressure of the gas in the chamber; and a controller that sets the set flow rate for the flow control device based on the set partial pressure and the estimated partial pressure of the gas in the chamber output by the observer.

[0009] Furthermore, the concentration control method of the present invention is a concentration control method using a concentration control system including a flow control device provided on a supply flow path that supplies gas into a chamber and controls the flow rate of the gas flowing through the supply flow path to an input set flow rate, and a partial pressure measuring device that measures the partial pressure of the gas in the chamber, wherein the inflow flow rate of the gas flowing into the chamber and the measured partial pressure of the partial pressure measuring device are input into a model that estimates the state of the gas in the chamber, an estimated partial pressure of the gas in the chamber is estimated, and a set flow rate is set in the flow control device based on the set partial pressure and the estimated partial pressure of the gas in the chamber output by the observer.

[0010] According to such a concentration control system, the observer outputs an estimated partial pressure of the gas in the chamber based on the model, so that a value with a small delay and small noise with respect to the actual partial pressure in the chamber can be obtained compared to the measured partial pressure output by the partial pressure measuring device. In addition, the observer receives not only the inflow flow rate of the gas flowing into the chamber but also the measured partial pressure of the partial pressure measuring device, so that the initial state deviation in the estimated partial pressure and the offset of the partial pressure, etc., are corrected to obtain a correct value. In addition, the controller sets a set flow rate in the flow control device based on the estimated partial pressure of the observer, so that concentration control with better response than that using the measured partial pressure can be realized.

[0011] To enable the model to more accurately reflect the conditions within the chamber based on simple mathematical formulas, the model may model the conductance of the exhaust passage that exhausts the gas within the chamber, and the conductance may be set to a constant value.

[0012] In order to increase the modeling accuracy of the observer even when the conductance is a constant value, an exhaust valve configured to have a controllable opening is provided in the exhaust flow path, and the exhaust valve is fixed at a predetermined opening.

[0013] For example, in order to ensure that a steady-state offset occurs in the actual partial pressure of the gas in the chamber due to a disturbance, the estimated partial pressure is a column vector consisting of a first estimated partial pressure that estimates the actual partial pressure and a second estimated partial pressure that estimates the measured partial pressure by the partial pressure measuring device, and the observer further includes an observer gain H that is a row vector with elements h1 and h2, and the h2 is set to the same value as the conductance. In this case, the conductance becomes a pole of the controlled object, and the steady-state offset is reflected as it is in the first estimated partial pressure by pole placement.

[0014] If the partial pressure measuring device is an NDIR and the model is one in which the delay of the measured partial pressure output by the NDIR relative to the actual partial pressure is modeled as a first-order lag, it becomes possible to perform partial pressure control at a value close to the actual partial pressure in the chamber, which cannot be actually observed.

[0015] In order to realize control with improved responsiveness compared to integrating the deviation between the measured partial pressure output by the partial pressure measuring device and the set partial pressure, the estimated partial pressure may be a column vector consisting of a first estimated partial pressure that estimates the actual partial pressure and a second estimated partial pressure that estimates the measured partial pressure by the partial pressure measuring device, and the controller may be configured to integrate the deviation between the set partial pressure and the first estimated partial pressure. In this way, the change in the actual partial pressure of the gas in the chamber, which cannot be observed, can be fed back without a time delay, thereby improving responsiveness compared to the case of feeding back the measured partial pressure.

[0016] In order to achieve effects substantially equivalent to those of the concentration control system of the present invention by, for example, updating a program in an existing concentration control system, it is sufficient to use a program for a concentration control system that includes a flow control device that is provided on a supply flow path that supplies gas into a chamber and controls the flow rate of gas flowing through the supply flow path to be an input set flow rate, and a partial pressure measuring device that measures the partial pressure of the gas in the chamber, the program being characterized in that it causes a computer to function as: an observer that is equipped with a model that estimates the state of gas in the chamber, the model being configured to input the inflow flow rate of gas flowing into the chamber and the measured partial pressure of the partial pressure measuring device, and outputting an estimated partial pressure of the gas in the chamber; and a controller that sets the set flow rate for the flow control device based on the set partial pressure and the estimated partial pressure of the gas in the chamber output by the observer.

[0017] The program for the concentration control system may be distributed electronically, or may be recorded on a program recording medium such as a CD, DVD, or flash memory. Effect of the Invention

[0018] In this way, according to the concentration control system of the present invention, the observer estimates the partial pressure of the gas in the chamber as an estimated partial pressure based on the model, so a value with less noise and time delay can be obtained compared to the measured partial pressure output by the partial pressure measuring device. Therefore, control that immediately reflects the actual concentration change in the chamber becomes possible, and it becomes possible to improve the responsiveness and accuracy of control compared to the conventional art. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram showing a concentration control system according to an embodiment of the present invention; [Diagram 2] FIG. 4 is a schematic diagram showing state feedback using an observer in the concentration control system according to the embodiment. [Diagram 3] FIG. 4 is a block diagram of state feedback using an observer in the concentration control system according to the embodiment. [Figure 4] 6 is a graph showing a change in conductance for each chamber pressure in the exhaust valve in the embodiment. [Diagram 5] 4 is a block diagram showing details of an observer in the embodiment and a graph of an output. [Figure 6] 6 shows an example of estimation of partial pressure of gas in a chamber by an observer in the embodiment. [Figure 7] 4 shows an example of pole design in observer control in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A concentration control system 100 according to an embodiment of the present invention will be described with reference to the drawings. The concentration control system 100 of this embodiment controls the partial pressure of gas in a process chamber where, for example, plasma processing is performed on a substrate in a semiconductor manufacturing process. As shown in Fig. 1, a supply flow path SL that supplies various gases into the chamber CN and an exhaust flow path EL that exhausts gases in the chamber CN to the outside are connected to the chamber CN.

[0021] The supply flow path SL is composed of a plurality of parallel branch flow paths DL1, DL2, each of which is connected to various gas sources at its upstream side, and a post-merged flow path CL, in which the branch flow paths DL1, DL2 merge to form one flow path and are connected to the chamber CN. In this embodiment, the first branch flow path DL1 is connected to a supply source of N2, which is a diluent gas, and the second branch flow path DL2 is connected to a supply source of CF4, which is a process gas. Note that the type of gas flowing through the supply flow path SL is an example, and other gas types may be used.

[0022] The exhaust flow path EL is connected to the chamber CN on the upstream side and to the vacuum pump VP on the downstream side. An exhaust valve EV is provided on the exhaust flow path EL to control the conductance of the exhaust flow path EL. The opening of the exhaust valve EV can be controlled to any value between 0% and 100%.

[0023] 1, the concentration control system 100 of this embodiment includes two flow control devices 1 provided on the first branch flow path DL1 and the second branch flow path DL2, a partial pressure measuring device 2 provided in the chamber CN for measuring the partial pressure of CF4 gas in the chamber CN, a pressure sensor provided in the chamber CN for measuring the total pressure in the chamber CN, and a control arithmetic device COM for controlling each flow control device 1 and the exhaust valve EV and executing various calculations. Thus, this concentration control system 100 is configured to estimate the actual partial pressure of CF4 gas in the chamber CN, which cannot be observed originally, by an observer 3 realized by the calculation function of the control arithmetic device COM, and to change the set flow rate of each flow control device 1 based on the estimated partial pressure and the set partial pressure set by the user.

[0024] Each part will be described in detail.

[0025] The flow control device 1 is a so-called mass flow controller, and is a package of a flow sensor, a valve, and a control board, which are devices required for flow control. The control board controls the opening of the valve so that the deviation between the measured flow rate measured by the flow sensor and the set flow rate set from the outside becomes small. That is, one flow feedback loop is formed by the flow control device 1 alone. In this embodiment, the set flow rate output by the control arithmetic unit COM is received, and the flow rate of the gas flowing through each branch flow path DL1, DL2 is maintained at the set flow rate. The first flow control device 11 provided in the first branch flow path DL1 is configured to control the flow rate of N2 gas, and the second flow control device 12 provided in the second branch flow path DL2 is configured to control the flow rate of CF4 gas. Various types of flow sensors, such as a thermal flow sensor and a pressure flow sensor, and various types of valves, such as a piezo valve and a solenoid valve, can be used. The flow control device 1 may also be configured using a variable orifice instead of a valve.

[0026] The partial pressure measuring device 2 is a so-called NDIR (Non Dispersive Infrared) and measures the partial pressure of CF4 gas in the chamber CN based on the absorbance. The partial pressure measuring device 2 includes a light source that emits infrared light into the chamber CN, a photodetector that detects the infrared light that has passed through the chamber CN, and a partial pressure calculator (not shown) that calculates the partial pressure of CF4 gas in the chamber CN from the absorbance of CF4 gas in the chamber CN and the total pressure in the chamber CN obtained by the pressure sensor based on the output of the photodetector. The partial pressure calculator is configured, for example, using the calculation function of the control calculation device COM, but the function may be realized by a dedicated calculation board. In addition, an existing algorithm can be used for calculating the partial pressure of CF4 gas in the partial pressure calculator. In the following description, the partial pressure of CF4 gas output as a measurement value in the partial pressure measuring device 2 is also called a measured partial pressure so as to be distinguished from an estimated value output by the observer 3. The measured partial pressure output by the partial pressure measuring device 2 is the actual partial pressure of the CF4 gas in the chamber CN with a certain amount of time delay and, for example, electrical noise superimposed thereon. In other words, the actual partial pressure of the CF4 gas in the chamber CN cannot be directly observed by the partial pressure measuring device 2.

[0027] 2, the control calculation device COM functions as an observer 3 that simulates the state of the partial pressure of CF4 in the chamber CN, which is the object of control, based on a model 31 and outputs the state as an estimated partial pressure, and as a controller 4 that controls the flow control device 1 based on the set partial pressure set by the user and the estimated partial pressure output from the observer 3. Specifically, the control calculation device COM is equipped with a CPU, a memory, an A / D converter, a D / A converter, and various input / output means. A program for the concentration control system 100 stored in the memory is executed, and the functions of the observer 3 and the controller 4 described above are realized by the cooperation of various devices.

[0028] The observer 3 is configured to simulate the physical characteristics related to the partial pressure of CF4 gas in the chamber CN of the plant in Fig. 2 and output the estimated partial pressure of CF4 gas in the chamber CN. Specifically, as shown in the block diagram of Fig. 3, the observer 3 is equipped with a model 31 expressed by the same state equation as the state equation of the plant in Fig. 2, which is the controlled object, and an observer gain 32. In the following description, the estimated partial pressure output by the observer 3 is also called an estimated partial pressure.

[0029] 3, the inflow flow rate of CF4 gas flowing into the chamber CN and the measured partial pressure of the partial pressure measuring device 2 are input to the model 31. Here, the set flow rate input to the second flow control device 12 is used as the inflow flow rate of CF4 gas. Note that the flow rate actually measured by the flow sensor of the second flow control device 12 may be used as the inflow flow rate. In response to the input, the model 31 outputs, as estimated partial pressures, a first estimated partial pressure which estimates the actual partial pressure of CF4 gas in the chamber CN and a second estimated partial pressure which estimates the measured partial pressure of the partial pressure measuring device 2.

[0030] The state equation of model 31 will now be described in detail. Note that the physical model is based on that shown in FIG.

[0031] The total pressure P of the chamber CN is the flow rate Q of the gas flowing into the chamber CN from the supply flow path SL. total and the flow rate Q flowing out from the chamber CN through the exhaust flow path EL. vaccum From the gas state equation for the volume V of the chamber CN, P = 1 / V∫(Q total -Q vaccum )dt (A) In addition, if the conductance of the exhaust valve EV is a constant value Cv, Q vaccum =Cv*P (B)

[0032] 4, the conductance of the exhaust valve EV has a transition region where the exhaust valve EV opening is greatly affected by the total pressure P in the chamber CN, such as the region where the exhaust valve EV opening is 20% to 60%, and a constant conductance region where the opening is 15% or less and the conductance is almost constant regardless of the total pressure P. In this concentration control system 100, the control calculation device COM maintains the exhaust valve EV opening in a constant conductance region of, for example, 15% or less, and prepares conditions so that the conductance is almost unaffected by the total pressure P and can be modeled as a constant value.

[0033] In addition, if we perform a Laplace transform on equation (A) and substitute equation (B), we get V*P*s=Q total -Cv*P...(C) (C) Transform the equation into P=Q total / (V*s+Cv) (D) The flow rate of N2 gas flowing into the chamber CN is Q N2 , the flow rate of CF4 gas flowing into the chamber CN is Q CF4 Then, Q total =Q N2 +Q CF4 (E) From equations (D) and (E), the transfer function of the partial pressure of CF4 gas in the chamber CN is P CF4 (s)=Q CF4 / (V*s+Cv) (F)

[0034] Furthermore, the partial pressure measuring device 2, the NDIR measuring partial pressure Con CF4 (s) is the actual partial pressure P CF4 Since there is a first-order lag with time constant T for (s), Con CF4 (s)=P CF4 (s) / (T*s+1) (G) Based on formulas (F) and (G), the state equation for the partial pressure in the chamber CN represented by A, B, and C in FIG.

[0035]

number

[0036]

number

[0037] As shown in FIG. 5, the control object and the observer 3 are expressed as a state equation with common matrices A, B, and C so that they have the same physical model. CF4 The first estimated partial pressure output by observer 3 is P^ CF4 , the second estimated partial pressure is Con^ CF4 It is written as:

[0038] As shown in the graph of FIG. 4, the measured partial pressure Con CF4 However, no electrical noise is superimposed on the estimated partial pressure estimated by the observer 3. In addition, since the first estimated partial pressure estimates the actual partial pressure of CF4 gas in the chamber CN, which cannot be observed, a value with no time delay is output.

[0039] Next, the observer gain h=[h1;h2] will be described. The observer gain 32 is a value multiplied by the deviation between the measured partial pressure and the second estimated partial pressure, and is fed back to the model 31. The observer gain 32 is designed by pole placement. The actual output steady-state offset Con offset of the controlled object in FIG. 3 is the first estimated partial pressure P^ CF4h2 of the observer gain 32 is set so that it is reflected in the output of the observer 3. Specifically, because the conductance Cv of the exhaust valve EV is the pole of the controlled object, h2 is set to Cv, which is the pole. For example, when Cv=2, the simulation result of the estimated partial pressure when h1=50 is shown in Fig. 6. It can be seen that even if there is an actual output steady-state offset of the controlled object, the offset is reflected in the first estimated partial pressure of the observer 3. Note that h1 is set to a value greater than zero and as large as possible.

[0040] Finally, the configuration of the controller 4 will be described.

[0041] As shown in the block diagram of FIG. 3, in this embodiment, the controller 4 does not integrate the deviation between the set partial pressure set by the user and the measured partial pressure by the partial pressure measuring device 2, but calculates the difference between the set partial pressure and the first estimated partial pressure P^ CF4 This is configured to integrate the deviation of the first estimated partial pressure. In other words, feedback is applied so that the first estimated partial pressure follows the set partial pressure. The poles [f1; f2; -g] are designed to obtain the desired response by pole placement from the state space representation. Specifically, the observer control for V=10, Cv=1, and T=0.5 can be described as the state equation shown in the following formula 3.

[0042]

number

[0043] Figure 7 shows an example of control designed by pole placement based on equation 3. Simulation results of response waveforms are compared between observer control of the partial pressure of CF4 gas in the chamber CN with [f1; f2; -g] = [-100 ; -20 ; -2] and the conventional case of filtering by applying inverse differentiation to the output. It can be seen that with observer control, the effects of noise are eliminated and the partial pressure response is made faster. Robustness is also achieved so that the effects of disturbances are not generated even if they occur.

[0044] In this way, the concentration control system 100 of this embodiment obtains an estimated partial pressure of CF4 gas in the chamber CN that cannot be observed by the observer 3, and performs observer control so that the estimated partial pressure follows the set partial pressure, so that the response is fast, the deviation of disturbance offset is compensated, and noise is reduced. Therefore, the partial pressure of the gas in the chamber CN can be controlled more accurately at a desired value without time delay than in the past.

[0045] Other embodiments will now be described.

[0046] In the above embodiment, the control system is configured so that the partial pressure of CF4 gas is subjected to state feedback. However, the control system may also be configured so that the partial pressure of N2 gas is also subjected to state feedback.

[0047] Instead of fixing the opening of the exhaust valve, the observer model may be constructed by defining the conductance as a function of the total pressure and the opening.

[0048] When modeling the relationship between the measured partial pressure by the partial pressure measuring device and the actual partial pressure that cannot be observed, the model is not limited to a first-order lag model as in the above embodiment. For example, various modeling such as a second-order lag model may be used.

[0049] The number of branched flow paths in the supply flow path is not limited to two, and may be three or more. In this case, the observer model may be modeled by correspondingly modeling the partial pressure in the chamber from the flow rate of the gas supplied from each branched flow path.

[0050] The measurement principle of the partial pressure measuring device is not limited to absorbance, and may be based on other measurement principles, such as an ultrasonic concentration sensor. [Explanation of symbols]

[0051] 100: Concentration control system 1: Flow control device 2: Partial pressure measuring device 3: Observer 4: Controller 11: First flow control device 12: Second flow control device 31: Model 32: Observer Gain CN: Chamber COM: Control and operation unit EL: Exhaust flow path EV: Exhaust valve DL1: First branch DL2: Second branch channel VP: Vacuum pump

Claims

1. a flow rate control device that is provided on a supply flow path that supplies a gas into the chamber and controls the flow rate of the gas flowing through the supply flow path to be a set flow rate that is input; a partial pressure measuring device for measuring a partial pressure of a gas in the chamber; an observer including a model for estimating a state of the gas in the chamber, the model being configured to receive an inflow flow rate of the gas flowing into the chamber and a measured partial pressure of the partial pressure measuring device, and to output an estimated partial pressure of the gas in the chamber; a controller that sets a set flow rate for the flow rate control device based on a set partial pressure and an estimated partial pressure of the gas in the chamber output by the observer.

2. the model models a conductance of an exhaust passage that exhausts gas within the chamber; 2. The concentration control system according to claim 1, wherein the conductance is set to a constant value.

3. 3. The concentration control system according to claim 2, further comprising an exhaust valve, the opening of which is controllable, provided in the exhaust flow path, the exhaust valve being fixed at a predetermined opening.

4. The estimated partial pressure is A first estimated partial pressure obtained by estimating the actual partial pressure; and a second estimated partial pressure obtained by estimating the measured partial pressure of the partial pressure measuring device; The observer further includes an observer gain H, which is a row vector having h1 and h2 as elements; 4. The concentration control system according to claim 2, wherein said h2 is set to the same value as said conductance.

5. The partial pressure measuring device is an NDIR, 5. The concentration control system according to claim 1, wherein the model is a model in which a delay of the measured partial pressure output by the NDIR with respect to an actual partial pressure is modeled as a first-order lag or a second-order lag.

6. The estimated partial pressure is A first estimated partial pressure obtained by estimating the actual partial pressure; and a second estimated partial pressure obtained by estimating the measured partial pressure of the partial pressure measuring device; 6. The concentration control system according to claim 1, wherein the controller is configured to integrate a deviation between the set partial pressure and the first estimated partial pressure.

7. A concentration control method using a concentration control system including a flow control device that is provided on a supply flow path that supplies a gas into a chamber and controls a flow rate of the gas flowing through the supply flow path to be a preset flow rate that is input, and a partial pressure measurement device that measures a partial pressure of the gas in the chamber, comprising: an observer having a model for estimating a state of the gas in the chamber is input with an inflow flow rate of the gas flowing into the chamber and a measured partial pressure of the partial pressure measuring device, and an estimated partial pressure of the gas in the chamber is estimated; A concentration control method comprising: setting a set flow rate in the flow rate controller based on a set partial pressure and an estimated partial pressure of the gas in the chamber output by the observer.

8. A program for use in a concentration control system including a flow control device that is provided on a supply flow path that supplies a gas into a chamber and controls a flow rate of the gas flowing through the supply flow path to be a preset flow rate that is input, and a partial pressure measurement device that measures a partial pressure of the gas in the chamber, an observer including a model for estimating a state of the gas in the chamber, the model being configured to receive an inflow flow rate of the gas flowing into the chamber and a measured partial pressure of the partial pressure measuring device, and to output an estimated partial pressure of the gas in the chamber; a set flow rate for the flow control device based on a set partial pressure and an estimated partial pressure of the gas in the chamber output by the observer.

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