CONCENTRATION CONTROL SYSTEM, CONCENTRATION CONTROL METHOD AND PROGRAM FOR A CONCENTRATION CONTROL SYSTEM

Abstract

Provided is a concentration control system that has only a small time delay, obtains accurate estimated values, and also enables partial pressure control having improved responsiveness and accuracy. The system includes a flow rate control device provided on a supply flow path that supplies gas to a chamber, and controls a flow rate of a gas in the supply flow path to match a set flow rate, a partial pressure measurement device for a gas inside the chamber, an observer having a model which estimates a state of the gas inside the chamber, where a flow rate of the gas flowing into the chamber and measured partial pressures are input into the model, and an estimated partial pressure of the gas within the chamber is output, and a controller that, based on a set partial pressure and on the estimated partial pressure, sets the set flow rate.

Claims

1. A concentration control system comprising: a flow rate control device that is provided on a supply flow path that supplies gas to an interior of a chamber, and performs control such that a flow rate of a gas flowing through this supply flow path matches a set flow rate that has been input; a partial pressure measurement device that measures a partial pressure of a gas inside the chamber; an observer that is equipped with a model which estimates a state of the gas inside the chamber, and that is formed such that an inflow flow rate of a gas flowing into the chamber and measurement partial pressures from the partial pressure measurement device are input into the model, and an estimated partial pressure of the gas within the chamber is output; and a controller that, based on a set partial pressure and on the estimated partial pressure of the gas within the chamber output by the observer, sets the set flow rate in the flow rate control device.

2. The concentration control system according to claim 1, wherein the model simulates a conductance of an exhaust flow path that expels gas from within the chamber, and the conductance is set to a constant value.

3. The concentration control system according to claim 2, wherein an exhaust valve whose valve opening is able to be controlled is provided on the exhaust flow path, and the exhaust valve is fixed at a predetermined valve opening.

4. The concentration control system according to claim 2, wherein the estimated partial pressure is a column vector formed by: a first estimated partial pressure obtained by estimating the actual partial pressure; and a second estimated partial pressure obtained by estimating the measurement partial pressure from the partial pressure measurement device, and wherein the observer is further equipped with an observer gain H which is a row vector whose elements are h1 and h2, and the element h2 is set to the same value as the conductance.

5. The concentration control system according to claim 1, wherein the partial pressure measurement device is an NDIR analyzer, and the model simulates a delay in the measurement partial pressure output by the NDIR analyzer relative to the actual partial pressure as a first order delay.

6. The concentration control system according to claim 1, wherein the estimated partial pressure is a row vector formed by: a first estimated partial pressure obtained by estimating the actual partial pressure; and a second estimated partial pressure obtained by estimating the measurement partial pressure from the partial pressure measurement device, and wherein the controller is formed such that deviations between the set partial pressure and the first estimated partial pressure are integrated.

7. A concentration control method that utilizes a concentration control system that comprises a flow rate control device that is provided on a supply flow path that supplies gas to an interior of a chamber, and performs control such that a flow rate of a gas flowing through this supply flow path matches a set flow rate that has been input, and a partial pressure measurement device that measures a partial pressure of a gas inside the chamber, in which an inflow flow rate of a gas flowing into the chamber and a measurement partial pressure from the partial pressure measurement device are input into a model which estimates a state of the gas inside the chamber, and an estimated partial pressure of the gas within the chamber is estimated, and in which, based on a set partial pressure and on the estimated partial pressure of the gas that has been estimated, the set flow rate is set in the flow rate control device.

8. A program recording medium on which is recorded a program that is used in a concentration control system comprising: a flow rate control device that is provided on a supply flow path that supplies gas to an interior of a chamber, and performs control such that a flow rate of a gas flowing through this supply flow path matches a set flow rate that has been input; and a partial pressure measurement device that measures a partial pressure of a gas inside the chamber, and that is characterized in causing a computer to perform functions of: an observer that is equipped with a model which estimates a state of the gas within the chamber, and that is formed such that an inflow flow rate of a gas flowing into the chamber and a measurement partial pressure from the partial pressure measurement device are input into the model, and an estimated partial pressure of the gas within the chamber is output; and of a controller that, based on a set partial pressure and on the estimated partial pressure of the gas within the chamber output by the observer, sets the set flow rate in the flow rate control device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a schematic view showing a concentration control system according to an embodiment of the present invention.

[0020] FIG. 2 is a schematic view showing state feedback that utilizes an observer of the concentration control system of the same embodiment.

[0021] FIG. 3 is a block line drawing showing state feedback that utilizes the observer of the concentration control system of the same embodiment.

[0022] FIG. 4 is a graph showing changes in conductance at each chamber pressure in an exhaust valve of the same embodiment.

[0023] FIG. 5 contains a block line drawing and output graphs showing details of the observer of the same embodiment.

[0024] FIG. 6 shows an example of an estimation of a partial pressure of a gas within a chamber estimated by the observer of the same embodiment.

[0025] FIG. 7 contains examples of pole designs in the observer control of the same embodiment.

BEST EMBODIMENTS FOR IMPLEMENTING THE INVENTION

[0026] A concentration control system 100 according to an embodiment of the present invention will now be described with reference to the respective drawings. The concentration control system 100 of the present embodiment controls partial pressures of gases within a processing chamber where, for example, plasma processing is performed on substrates in a semiconductor manufacturing process. As is shown in FIG. 1, a supply flow path SL that supplies various types of gases to an interior of a chamber CN, and an exhaust flow path EL that discharges gases within the chamber CN to the outside are connected respectively to the chamber CN.

[0027] The supply flow path SL is formed by a plurality of parallel branch flow paths DL1 and DL2 whose respective upstream sides are connected to individual sources of various types of gas, and a post-convergence flow path CL that is formed by the respective branch flow paths DL1 and DL2 converging into a single flow path, and that is connected to the chamber CN. In the present exemplary embodiment, the first branch flow path DL1 is connected to a supply source for N.sub.2, which is a dilution gas, and the second branch flow path DL2 is connected to a supply source for CF.sub.4, which is a processing gas. Note that the types of gases described above that are supplied to the supply flow path SL are merely examples thereof, and it is also possible for other types of gases to be used.

[0028] An upstream side of the exhaust flow path EL is connected to the chamber CN, while a downstream side thereof is connected to a vacuum pump VP. An exhaust valve VP that controls the conductance of the exhaust flow path EL is provided on the exhaust path EL. The exhaust valve EV is formed such that a valve opening thereof can be controlled to an optional value between 0% and 100%.

[0029] As is shown in FIG. 1, the concentration control system 100 of the present embodiment is provided with two flow rate control devices 1 that are provided respectively on the first branch flow path DL1 and on the second branch flow path DL2, a partial pressure measurement device 2 that is provided in the chamber CN and measures the partial pressure of the CF.sub.4 gas within the chamber CN, a pressure sensor that is provided in the chamber CN and measures the total pressure within the chamber CN, and a control calculation device COM that controls the respective flow rate control devices 1 and the exhaust gas valve EV, and also executes various types of calculations. In this way, the concentration control system 100 is formed so as to estimate an actual partial pressure of the CF.sub.4 gas within the chamber CN, which has not hitherto been observable, using an observer 3 that is realized by the calculation functions of the control calculation device COM, and so as to then alter the set flow rate in each flow rate control device 1 based on the estimated partial pressure and on a set partial pressure that is set by a user.

[0030] Each portion will now be described in detail.

[0031] Each flow rate control device 1 is what is known as a ‘mass flow controller’, and is formed by packaging a flow rate sensor, a valve, and a control board, which are all instruments necessary for performing flow rate control, into a single unit. The control board controls the openings of the valves such that any deviation between the measurement flow rate measured by the flow rate sensor and the set flow rate set from an external unit is reduced. In other words, a single flow rate feedback loop is formed by a single flow rate control device 1. In the present embodiment, each flow rate control device 1 receives set flow rates that are output by the control calculation unit COM, and is operated such that the flow rates of the gas flowing through the respective branch flow rates DL1 and DL2 are maintained at the set flow rates. The first flow rate control device 11, which is provided on the first branch flow path DL1, is formed so as to control the flow rate of the N.sub.2 gas, while the second flow rate control device 12, which is provided on the second branch flow path DL2, is formed so as to control the flow rate of the CF.sub.4 gas. Various sensors such as a thermal flow rate sensor or a pressure flow rate sensor can be used for the flow rate sensor, while various valves such as a piezo valve or a solenoid valve can be used for the valve. Moreover, it is also possible to construct each flow rate control device 1 using a variable orifice instead of a valve.

[0032] The partial pressure measurement device 2 is what is known as an NDIR (Non-Dispersive Infrared) analyzer that measures the partial pressure of the CF.sub.4 gas within the chamber CN based on light absorbance. The partial pressure measurement device 2 is provided with a light source that irradiates infrared light into the interior of the chamber CN, a photodetector that detects infrared light that has passed through the interior of the chamber CN, and a partial pressure calculator (not shown in the drawings) that calculates the light absorbance of the CF.sub.4 gas within the chamber CN based on outputs from the photodetector, and the partial pressure of the CF.sub.4 gas within the chamber CN from the total pressure inside the chamber CN obtained from a pressure sensor. Note that, here, the partial pressure calculator is formed using, for example, the calculation functions of the control calculation device COM, however, it is also possible for the functions thereof to be realized by using a dedicated computing board. An existing algorithm may be used for the algorithm used by the partial pressure calculator to calculate the partial pressure of the CF.sub.4 gas. In the following description, the partial pressure of the CF.sub.4 gas output as a measurement value by the partial pressure measurement device 2 is also referred to as a measurement partial pressure in order to differentiate it from estimated values output by the observer 3. The measurement partial pressure output from the partial pressure measurement device 2 is formed by superimposing a predetermined amount of time delay and, for example, electrical noise and the like onto the actual partial pressure of the actual CF.sub.4 gas within the chamber CN.

[0033] As is shown in FIG. 2, the control calculation device COM functions as the observer 3 that simulates states of the partial pressure of the CF.sub.4 gas within the chamber CN, which is the control subject, based on a model 31, and outputs these partial pressure states as estimated partial pressures, and as a controller 4 that controls the flow rate control devices 1 based on set partial pressures set by a user and on the estimated partial pressures output from the observer 3. More specifically, the control calculation device COM is provided with a CPU, memory, an A/D converter, a D/A converter, and various types of input and output devices. The functions of the above-described observer 3 and controller 4 are realized as a result of a program for the concentration control system 100 that is stored in the memory being executed and causing various instruments to operate in mutual collaboration.

[0034] The observer 3 is formed so as to simulate physical characteristics relating to the partial pressure of the CF.sub.4 gas within the chamber CN of the Plant shown in FIG. 2, and to output an estimated partial pressure for the CF.sub.4 gas within the chamber CN. More specifically, as is shown in the block line drawing in FIG. 3, the observer 3 is equipped with the model 31 that is expressed by the same equation of state as the equation of state of the Plant in FIG. 2, which is the control subject, and with an observer gain 32. In the following description, the estimated partial pressure output by the observer 3 is also referred to as an estimated partial pressure.

[0035] As is shown in FIG. 3, the inflow flow rate of the CF.sub.4 gas flowing into the chamber CN, and the measurement partial pressure from the partial pressure measurement device 2 are input into the model 31. Here, the set flow rate input into the second flow rate control device 12 is used for the inflow flow rate of the CF.sub.4 gas. Note that it is also possible for the flow rate actually measured by the flow rate sensor of the second flow rate control device 12 to be used as the inflow flow rate. In accordance with these inputs, the model 31 outputs as the estimated partial pressure a first estimated partial pressure obtained by estimating the actual partial pressure of the CF.sub.4 gas within the chamber CN, and a second estimated partial pressure obtained by estimating the measurement partial pressure from the partial pressure measurement device 2.

[0036] The equations of state of the model 31 will now be described in detail. Note that the physical model is based on the model shown in FIG. 1.

[0037] A total pressure P inside the chamber CN can be described in the manner shown below from a flow rate Q.sub.total flowing into the chamber CN through the supply flow path S, a flow rate Q.sub.vacuum flowing out from the chamber CN via the exhaust flow path EL, and an equation of state of the gas relative to the volume V of the chamber CN.

P=1/V∫(Q.sub.total−Q.sub.vaccum)dt  (A)

[0038] Moreover, if the conductance of the exhaust valve EV is taken as a constant value Cv, then

Q.sub.vaccum=CV*P  (B)

[0039] Note that, as is shown in the graph in FIG. 4, the conductance of the exhaust valve EV includes a transition area where the effect from the total pressure P within the chamber CN is considerable such as an area where the valve opening of the exhaust valve EV is between 20% and 60%, and a constant conductance area where the valve opening is 15% or less and the conductance remains as a substantially constant value irrespective of the value of the total pressure P. In this concentration control system 100, the control calculation device COM maintains the valve opening of the exhaust valve EV in the constant conductance area of, for example, 15% or less, and establishes conditions that substantially prevent the conductance from being affected by the total pressure P, and enable modeling to be performed with the conductance being taken as a constant value.

[0040] In addition, if a Laplace transform is performed on the above Formula (A) so as to substitute the above Formula (B), then

V*P*s=Q.sub.total−Cv*P  (C)

and if a formula deformation is performed on Formula (C), then

P=Q.sub.total/(V*s+Cv)  (D)

[0041] Moreover, if a flow rate of the N.sub.2 gas flowing into the chamber CN is taken as Q.sub.N2, and a flow rate of the CF.sub.4 gas flowing into the chamber CN is taken as Q.sub.CF4, then,

Q.sub.total=Q.sub.N2+Q.sub.CF4  (E)

[0042] A transfer function of the partial pressure of the CF.sub.4 gas within the chamber CN from the above Formula (D) and Formula (F) is as follows

P.sub.CF4(s)=Q.sub.CF4/(V*s+Cv)  (F)

[0043] Furthermore, because a first order delay of a time constant T relative to the actual partial pressure P.sub.CF4(s) is contained in the measurement partial pressure Con.sub.CF4(s) of the NDIR analyzer, which is serving as the partial pressure measurement device 2,

Con.sub.CF4(s)=P.sub.CF4(s)/(T*s+1)  (G)

[0044] Based on the above Formula (F) and Formula (G), in FIG. 3, an equation of state relating to the partial pressure inside the chamber CN which is expressed using A, B, and C is shown in the following Equation 1.

[00001]$\begin{array}{cc}\left[\begin{array}{c}{\stackrel{.}{P}}_{\mathrm{CF}4}\\ {\stackrel{.}{\mathrm{Con}}}_{\mathrm{CF}4}\end{array}\right]=\left[\begin{array}{cc}-Cv/V& 0\\ 1/T& -1/T\end{array}\right]\left[\begin{array}{c}{P}_{CF4}\\ {\mathrm{CON}}_{\mathrm{CF}4}\end{array}\right]+\left[\begin{array}{c}Cv/V\\ 0\end{array}\right]Q_{CF4}{\mathrm{Con}}_{\mathrm{CF}4+\mathrm{No}ise}=\left[01\right]\left[\begin{array}{c}{P}_{CF4}\\ CO{N}_{\mathrm{CF}4}\end{array}\right]+\mathrm{Noise}& \mathrm{Equation}1\end{array}$

[0045] Accordingly, the matrices A, B, and C that determine the equation of state are shown in the following Equation 2.

[00002]$\begin{array}{cc}A=\left[\begin{array}{cc}-Cv/V& 0\\ 1/T& -1/T\end{array}\right]B=\left[\begin{array}{c}Cv/V\\ 0\end{array}\right]C=\left[01\right]& \mathrm{Equation}2\end{array}$

[0046] As is shown in FIG. 5, the model 31 of the observer 3 is expressed by an equation of state using the common matrices A, B, and C so that the same physical model is used for the control subject and the observer 3. Hereinafter, the partial pressure from the partial pressure measurement device 2 is described as Con.sub.CF4, and the first estimated partial pressure and second estimated partial pressure output by the observer 3 are described as P.sub.CF4 and Con.sub.CF4 respectively.

[0047] As is shown in the graph in FIG. 4, a time delay and electrical noise are generated in the measurement partial pressure Con.sub.CF4 output from the partial pressure measurement device 2, however, no electrical noise is superimposed on the estimated partial pressure estimated by the observer 3. Moreover, because the first estimated partial pressure is obtained by estimating the actual partial pressure of the CF.sub.4 gas within the chamber CN, which it is not possible to observe, a value is output for this first estimated partial pressure from which any time delay has been eliminated.

[0048] Next, the observer gain h=[h1; h2] will be described. The observer gain 32 is a value that is multiplied by the deviation between the measurement partial pressure and the second estimated partial pressure, and is fed back into the model 31. The observer gain 32 is designed by pole placement. The h2 of the observer gain 32 is set such that an actual output constant offset Con offset of the control subject shown in FIG. 3 is also reflected in the output of the first estimated partial pressure P.sub.CF4. More specifically, because a conductance Cv of the exhaust valve EV forms a pole of the control subject, h2 is set to the pole Cv. For example, in a case in which Cv=2, a simulation result of an estimated partial pressure in a case in which h1=50 is shown in FIG. 6. It can be seen from FIG. 6 that, even if there is an actual output constant offset of the control subject, the first estimated partial pressure from the observer 3 is able to reflect this offset. Note that a value that is larger than zero, and is as large as possible is set for the value of h1.

[0049] Lastly, the structure of the controller 4 will be described.

[0050] As is shown in the block line drawing in FIG. 3, in the present embodiment, the controller 4 is formed such that an integration operation is not performed on the deviation between the set partial pressure which has been set by a user, and the measurement partial pressure from the partial pressure measurement device 2, but such that an integration operation is performed on the deviation between the set partial pressure and the first estimated partial pressure P.sub.CF4. In other words, feedback is applied such that the first estimated partial pressure follows the set partial pressure. The poles [f1; f2; −g] are designed such that a desired response is obtained using the pole placement obtained from a state space representation. More specifically, the observer control in a case in which V=10, Cv=1, and T=0.5 is described as an equation of state such as that shown in the following Equation 3.

[00003]$\begin{array}{cc}\left[\begin{array}{c}\stackrel{.}{{\hat{P}}_{\mathrm{CF}4}}\\ {\mathrm{CF}4}_{}\\ \stackrel{.}{z}\end{array}\right]=\left[\begin{array}{ccc}-1/10& 0& 0\\ 1/0.5& -1/0.5& 0\\ -1& 0& 0\end{array}\right]\left[\begin{array}{c}{\hat{P}}_{\mathrm{CF}4}\\ {\mathrm{CF}4}_{}\\ z\end{array}\right]+\left[\begin{array}{c}10\\ 0\\ 0\end{array}\right]Q_{CF4}{Q}_{\mathrm{CF}4}=-\left[f1f2-g\right]\left[\begin{array}{c}{\hat{P}}_{\mathrm{CF}4}\\ {\mathrm{CF}4}_{}\\ z\end{array}\right]& \mathrm{Equation}3\end{array}$

[0051] An example in which control by pole placement is designed based on Equation 3 is shown in FIG. 7. Simulation results of response waveforms are compared between a case in which observer control was performed for the partial pressure of CF.sub.4 gas within the chamber CN in a case in which [f1; f2; −g]=[−100; −20; −2], and a case in which an antiderivative is inserted into the output and filtering is performed, as per the conventional technology. In the case of the observer control, it was found that not only are the effects of noise eliminated, but the speed of the partial pressure response can be improved. Moreover, even if an external disturbance is generated, robustness is improved so that no effects from such an external disturbance are generated.

[0052] In this way, in the concentration control system 100 of the present embodiment, because observer control is performed such that an estimated partial pressure of CF.sub.4 gas within the chamber CN, which is not able to be observed by the observer 3, is obtained, and this estimated partial pressure follows the set pressure, it is possible to increase response speed, compensate for any deviation in the external disturbance offset, and reduce noise. Accordingly, it is possible to control the partial pressure of a gas within the chamber CN to a desired value both more accurately than when the conventional technology is used, and without any time delay.

[0053] Additional embodiments will now be described.

[0054] In the above-described embodiment, a control system is configured that enables state feedback to be performed on the partial pressure of the CF.sub.4 gas, however, it is also possible, for example, to configure a control system that enables state feedback to be performed on the partial pressure of, for example, N.sub.2 gas as well.

[0055] In addition, it is also possible to construct a model of an observer in which the valve opening of the exhaust valve is not fixed, but the conductance is defined as a function of the full pressure and the valve opening.

[0056] In a case in which a relationship between the measurement partial pressure from a partial pressure measurement device and the unobservable, actual partial pressure is modeled, this modeling is not limited to modeling for a first order delay, as is the case in the above-described embodiment. It is also possible to perform various other types of modeling such as, for example, modeling for a secondary delay.

[0057] As far as the supply flow paths are concerned, the number of branch flow paths is not limited to two, and it is also possible for three or more branch flow paths to be provided. In this case, for the observer model as well, a simulation may be made with the partial pressure within the chamber being made to correspond to the observer model from the flow rate of the gas supplied from each branch flow path.

[0058] The measurement principle on which the partial pressure measurement device is based is not limited to light absorbance. It is also possible for a partial pressure measurement device based on another measurement principle, such as an ultrasonic wave concentration sensor, to be used.

[0059] Furthermore, it should be understood that the present invention is not limited to the above-described embodiment, and that various modifications and the like may be made thereto insofar as they do not depart from the spirit or scope of the present invention.

DESCRIPTION OF THE REFERENCE CHARACTERS

[0060] 100 . . . Concentration Control System [0061] 1 . . . Flow Rate Control Device [0062] 2 . . . Partial Pressure Measurement Device [0063] 3 . . . Observer [0064] 4 . . . Controller [0065] 11 . . . First Flow Rate Control Device [0066] 12 . . . Second Flow Rate Control Device [0067] 31 . . . Model [0068] 32 . . . Observer Gain [0069] CN . . . Chamber [0070] COM . . . Control Calculation Device [0071] EL . . . Exhaust Flow Path [0072] EV . . . Exhaust Valve [0073] DL1 . . . First Branch Flow Path [0074] DL2 . . . Second Branch Flow Path [0075] VP . . . Vacuum Pump