JPH05189050A - Positioning device - Google Patents

Abstract

PURPOSE:To suppress a disturbance more by inputting the detection signal regarding the acceleration of a surface plate to a power amplifier through a high-band surface plate acceleration feedback circuit which is set in an optimum state. CONSTITUTION:The signal generated by detecting the acceleration of the surface plate is inputted to the power amplifier 6 through the high-band surface plate acceleration feedback circuit 9 which is set in the optimum state. Further, an acceleration sensor which has high sensitivity in a low frequency range and an acceleration sensor which has high sensitivity above an intermediate frequency band are installed in the surface plate and the frequency band of the feedback circuit 9 is set to a high frequency range. The gains of the sensors are added in parallel after being matched with each other and the output is fed back. Consequently, the frequency characteristics from a surface plate acceleration detection point to the parallel addition output, i.e., to the input point of the power amplifier become flat over the high frequency range. Consequently, restrictions of disturbance suppression effect due to a large time constant of a low-pass filter are reducible and larger suppression performance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to positioning of an XY stage mounted on a surface plate, which is a vibration isolation device, and particularly to high-speed and high-accuracy positioning, and includes a speed control mode during movement for positioning. Therefore, the present invention aims to provide a positioning device in which the response from disturbance is significantly suppressed.

[0002]

2. Description of the Related Art An LSI manufacturing apparatus, such as an electron microscope or a stepper, to which an electron beam is applied employs a structure in which an XY stage is mounted on a vibration isolation device. Such an anti-vibration device has a function of attenuating the vibration by means of a vibration absorbing means such as an air spring, a coil spring, and a vibration isolating rubber. However, the passive vibration isolator has a problem in that the vibration transmitted from the floor can be damped to some extent, but the vibration generated by the XY stage itself mounted therein cannot be damped effectively. That is, the reaction force generated by the high-speed movement of the XY stage itself causes the vibration isolator to oscillate, and this vibration is a disturbance that hinders the high-speed and high-accuracy positioning of the XY stage.

First, a vibration isolation device (hereinafter abbreviated as a surface plate)
Formulation is performed using the dynamic model when the XY stage is mounted on top.

FIG. 5 shows an XY stage 1 mounted on a surface plate 2.
Is a mechanical model in the X or Y horizontal 1-axis direction. As shown in the figure, the mechanical model has two degrees of freedom including the surface plate 2 and the XY stage 1. Here, the equation of motion is expressed as follows using the symbols shown.

[0005]

[Equation 1] However, the meaning of each symbol is as follows.

M ₁ : stage mass [kg] m ₂ : surface plate mass [kg] b ₁ : stage viscous friction coefficient [Ns / m] b ₂ : surface plate viscous friction coefficient [Ns / m] k ₁ : Spring constant of stage [N / m] k ₂ : Spring constant of surface plate [N / m] x ₁ : Stage displacement [m] x ₂ : Surface displacement [m] f: Driving force [N] f _ext : Disturbance [N] Here, the relationship from f, f _ext to x ₁ and x ₂ is first obtained. However, s is a Laplace operator.

[0007]

[Equation 2] Let the denominator of this expression be g (s).

[0008]

[Equation 3] Next, FIG. 6 shows a control block diagram when a position control system is configured in the dynamic model of FIG. In the figure, 3 is the
4 is a position detection conversion means, 5 is a compensator for improving the characteristics of the position control system, 6 is a power amplifier, 7 is a thrust constant of an actuator, and 8 is a platen acceleration feedback circuit. However, it is assumed that the position detection conversion means 4 includes, for example, a laser interferometer as a position detector and a deviation counter.

The operation of the figure will be described below. First, the position (x ₁ -x ₂ ) is detected, and the position gain K _P of the position detection conversion means 4 is multiplied by x _0- (x ₁ -x ₂ ) which is the deviation from the target position x ₀ . Further, the power amplifier 6 is driven through the characteristic improving compensator 5 of the position control system. Finally, the driving force f is generated through conversion by the thrust constant K _t of the actuator that drives the XY stage.

Here, the position feedback detection is (x
_The reason why it is _1- x ₂ ) is that, for example, a laser interferometer which is a position detecting means is usually installed on the surface plate 2. When x ₁ is directly measured, x ₁ becomes the control amount, and there is no particular difference in the essence of positioning control. Further, in the illustrated case, the compensator for improving the characteristics of the position control system is a PID compensator, which means P: proportional operation, I: integral operation, D: derivative operation. Furthermore, the meanings and dimensions of the symbols shown are as follows.

K _P : Position gain [V / m] F _x : P operation gain [V / V] F _i : I operation gain [V / Vsec] F _v : D operation gain [Vsec / V] K _i : Electric power Amplifier gain [A / V] T _d : Power amplifier time constant [sec] K _t : Thrust constant [N / A] A: Surface plate acceleration feedback gain [V / m / sec]
² ] T _a : Time constant of the platen acceleration feedback circuit [se
c] Now, in the position control system of FIG. 6, the relationship between the target position x ₀ and the disturbance f _ext to the position (x ₁ −x ₂ ) is as follows. However, it is assumed here that the surface plate acceleration feedback circuit 8 is not provided yet.

[0012]

[Equation 4] However,

[0013]

[Equation 5] As shown in the above equation, step input x is set as target position x _0.
Given ₀ = x ₀₀ / s, from the theorem of final value

[0014]

[Equation 6] Therefore, the position (x ₁ −x ₂ ) converges to the target value x ₀₀ after the transient phenomenon has settled. However, in equation (3a), the disturbance f
It should be noted that there is also a transfer function for the input of _ext . That is, the positioning time is the sum of the responses from the target position x ₀ and the disturbance f _ext . Therefore, suppressing the influence of the disturbance f _ext on the position (x ₁ −x ₂ ) is only required to shorten the positioning time. Instead, it is also important from the viewpoint of ensuring positioning accuracy.

Conventionally, as a method of suppressing the influence of the disturbance f _ext on the position (x ₁ -x ₂ ), a method of detecting the acceleration signal of the surface plate 2 and feeding it back to the power amplifier input section for driving the XY stage 1. Was known. For example, the literature, the journal of Japan Society for Precision Engineering, "Trial production of high-speed air levitation XY stage (JSPE-52-10, '86 -10-1713)".
Discloses a configuration in which the platen acceleration is detected and fed back to the control system. The following description is made in the document.

"The moving body of the stage moves laterally at a high speed to cause the surface plate to sway. (Omitted) Therefore, the relative displacement of the surface plate due to the vibration is also proportional to the acceleration. Therefore, it is possible to improve the performance by detecting the lateral fluctuation of the surface plate with an accelerometer and feeding it back to the control system. I thought and added the circuit. As described above, the movement of the mechanism is physically grasped and the platen acceleration feedback is adopted.

Therefore, this example will be examined. First,
Based on the dynamic model, the effect of the platen acceleration feedback is shown explicitly using mathematical formulas. After that, the experimental results show the effect of applying the platen acceleration feedback. Again, FIG.
With reference to, the formulation when the platen acceleration feedback circuit 8 functions will be performed here. First, the relationship from the target position x ₀ and the disturbance f _ext to the position (x ₁ −x ₂ ) is expressed by the following equation.

[0018]

[Equation 7] However,

[0019]

[Equation 8] Consider only the response from the disturbance f _ext with x ₀ = 0 in the above equation. Extracting the expression in [] in the numerator polynomial of the disturbance term

[0020]

[Equation 9] Is. Therefore, if the surface plate acceleration feedback gain A is set as in the following equation, the response from disturbance can be considerably reduced.

[0021]

[Equation 10] In summary, when there is no platen acceleration feedback and when its feedback gain is set optimally, that is, when the platen acceleration feedback gain A is set according to equation (7), the transmission from the disturbance f _ext to the position (x ₁ −x ₂ ) The functions are as follows.

(1) When there is no surface plate acceleration feedback
Combined

[0023]

[Equation 11] (2) When the platen acceleration feedback is optimally set
Combined

[0024]

[Equation 12] Here, looking at the numerator polynomials of equations (8) and (9),
It is understood that the equation (8) has a lower order by one. Also, from the results of numerical analysis and measurement of frequency response, it is known that the main roots of the characteristic equation of the position control system hardly change depending on the presence or absence of the platen acceleration feedback. Therefore, if the orders of the numerator polynomials of equations (8) and (9) are compared, the response of the low frequency component is suppressed more effectively by the optimal setting of the platen acceleration feedback than in the case without the feedback. Will be done. To clarify this fact, from the floor vibration x _B to the position (x ₁ −x
Compare the frequency responses up to ₂ ). This index is important because whether or not the criteria for positioning accuracy is satisfied when the vibration level of the floor is given becomes a problem. First, let us consider how floor vibration is incorporated into the two-degree-of-freedom dynamic model of FIG. In the figure, the shaded area represents the floor, and if this vibration is x _B , the equation of motion is

[0025]

[Equation 13] Becomes Therefore, in equation (1),

[0026]

[Equation 14] By replacing with, the transfer function from the floor vibration x _B to the position (x ₁ −x ₂ ) when the position control is applied can be obtained. That is, the following equation is obtained.

[0027]

[Equation 15] Therefore, the frequency response of the vibration transmissibility using the above equation is shown in FIG. FB in the figure is an abbreviation for feedback. In the figure, the shaded portion is the frequency region where the transmission of floor vibration is further suppressed by the optimum setting of the surface plate acceleration feedback. Obviously, with the addition of surface plate acceleration feedback, floor vibrations are more suppressed than without it. In addition, as shown in the figure, if the floor vibration level on which the surface plate 2 is installed is 1 [μm], the 0 [dB] line corresponds to this, and at -20 [dB], the floor vibration is 10 [dB].
This means that the floor vibration is suppressed to 0 [nm] and to -10 [nm] at -40 [dB], and is transmitted to the output of the interferometer, that is, the same as when the floor vibration is attenuated.

Next, the actual measurement result of the step response waveform of the stage is shown to compare with the presence or absence of the platen acceleration feedback. 8A is the deviation output of the position control system when the stage is made to respond in step without the platen acceleration feedback shown in FIG. In this case, a phenomenon occurs in which transient vibration is generated at the natural frequency of the position control system, and then vibration is repeated at the natural frequency of the surface plate mechanism for a long time.
However, in the case of FIG. 7B, the platen acceleration feedback is set almost optimally, and although transient vibration still occurs at the natural frequency of the control system in the initial stage of the step response, after that, the platen mechanism Vibration of natural frequency is suppressed. In summary, the optimum setting of surface plate acceleration feedback has the following advantages.

(1) The response from the disturbance f _ext applied to the surface plate to the position (x ₁ -x ₂ ) can be suppressed.

(2) Position (x ₁ -x ₂ ) from floor vibration x _B
Responses up to may also be suppressed.

(3) It is possible to reduce the influence of the vibration of the surface plate on the positioning time due to the reaction force of the stage drive mounted on the surface plate.

[0032]

[Problems to be Solved by the Invention]
In the conventional example described above, the surface plate acceleration signal is
Time constant T_a And driver time constant T_d Is a finite value
There are limits due to things. This limit is shown in Figure 9.
It The figure shows the time constant T_a And T_d Are both current values at the same time?
Floor vibration when decreasing from 1 to 1/2 and then to 1/3 x
_B Position (x₁ -X ₂ ) Is the vibration transmission rate up to. This
When these time constants are reduced, the vibration transmissibility gradually decreases.
Can be made But in reality T_a To reduce
It was extremely difficult to do. Because the platen acceleration
Sensitive to detect, for example, servo-type acceleration
Frequency sensor must be used and its frequency
Because the band is only up to about 100 [Hz]
It Moreover, it reduces the electrical noise of the acceleration sensor.
In order to set the break frequency at a position lower than the sensor's own band
I had to insert my own low-pass filter. One
Therefore, there is a limit to expanding the frequency band to the higher side.
It was Therefore, the time constant T_a Is relatively large
Then, disturbance, floor vibration, and XY stage were driven.
It is limited to improve the suppression effect against the reaction force when
It was

[0033]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an acceleration sensor having a high sensitivity in a low frequency range and an acceleration sensor having a high sensitivity in a middle range or higher are used as a surface plate. Install each and set the optimum,
Further, the two gains are made to coincide with each other, and then the outputs are fed back by parallel addition. With such a configuration, the frequency characteristic from the surface plate acceleration detection point to the parallel addition output becomes flat over a high band. That is,
It is possible to achieve the same effect as when the time constant of the conventional surface plate acceleration feedback circuit 8 is further reduced.
That is, the above problem can be solved by making the optimum setting of the equation (7) and flattening the frequency characteristic from the surface plate acceleration detection point to the input point of the power amplifier over a high band. Therefore, in this way, the restriction of the disturbance suppression effect due to the large time constant can be reduced, and a larger suppression performance can be obtained.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a positioning device equipped with a high band surface plate acceleration feedback circuit according to the present invention.
In the figure, the transfer function of the high band surface plate acceleration feedback circuit 9 within the broken line is

[0035]

[Equation 16] Is. However, A: Gain of the surface plate acceleration feedback circuit having high sensitivity in the low frequency range [V / m / sec ² ] B: Gain of the surface plate acceleration feedback circuit having high sensitivity in the frequency range above the middle range [V / m / Sec ² ]. Both gains must match, and A = B. Therefore, B is replaced with A in the figure. Even if the detection sensitivities of the acceleration sensors themselves are different, it is not difficult to match the gains with the amplifiers connected after the acceleration sensor. Furthermore, T _a >>
If T _b is given, equation (13) is

[0036]

[Equation 17] Becomes An example of this frequency response is shown in FIG. That is, when the frequency response of the low-pass filter (hereinafter abbreviated as LPF) indicated by the broken line and the output of the band-pass filter (hereinafter abbreviated as BPF) indicated by the alternate long and short dash line are added in parallel, a high frequency is obtained as indicated by the solid line. L with break frequency
It has a PF characteristic. That is, the conventional platen acceleration feedback circuit 8 has the LPF characteristic represented by the transfer function of the following equation having the break frequency at the low frequency.

[0037]

[Equation 18] However, according to the present invention, the LPF characteristic from the platen acceleration to the feedback application point is such that the breakpoint frequency is located at a higher frequency as in the following equation. That is,

[0038]

[Formula 19] Becomes Therefore, conventionally, from the disturbance f _ext to the position (x ₁
The transfer function up to −x ₂ )

[0039]

[Equation 20] However, the form of the transfer function is the same, but T _a in the above equation is replaced with T _b . However, it is known that the main roots of the denominator polynomial hardly change even if this time constant changes. On the other hand, the numerator polynomial is

[0040]

[Equation 21] Therefore, the coefficient for s is obviously small. Therefore, the high band surface plate acceleration feedback circuit 9 further suppresses the influence from the floor vibration x _B. Of course, it goes without saying that the response from the disturbance f _ext is also suppressed.

[0041]

Other Embodiments The high band surface plate acceleration feedback circuit 9 used in the positioning apparatus of the present invention has a LPF characteristic circuit output having high sensitivity in the low frequency range and high detection sensitivity in the middle band or higher. A configuration is adopted in which the circuit output of the BPF characteristic is matched in gain and added in parallel. Among them, the LPF had a first-order frequency characteristic below the transmission point frequency of the first-order lag and above the high-frequency break frequency. But,
It goes without saying that both LPF and BPF may be high-order filters.

Further, in the present invention, the effect of adding the high band surface plate acceleration feedback circuit 9 when the position control system is constructed has been shown. However, even when the speed control system is configured as shown in FIG. 3 and the high band surface plate acceleration feedback circuit 9 is added, it is possible to suppress the influence from disturbance or floor vibration. In the figure, 10 is a speed detection conversion means, and 11 is a PI compensator. This speed control mode may be used as a preceding stage of positioning.
Therefore, this speed control can be considered to be included in the positioning control.

Further, as shown in FIG. 4, even when the high band surface plate acceleration feedback circuit 9 is added only to the controlled object 3, the influence from disturbance or floor vibration can be suppressed. This proof is simple and can be easily understood by formulating it based on the equation (1). Therefore, this control can be configured as a position control for position control or a minor loop for speed control.

[0044]

As described above, according to the present invention, the output of the acceleration sensor having high sensitivity in the low frequency range is passed through the LPF and the output of the acceleration sensor having high sensitivity in the middle band or higher is passed through the BPF. The high-band surface plate acceleration feedback circuit 9 that is optimally set by adding the output to
By adding, the frequency characteristic from the surface plate acceleration to the addition output becomes an LPF characteristic having a break at a high frequency.
Therefore, it is possible to avoid that the effect of suppressing the influence from disturbance or floor vibration to the output of the interferometer is limited due to the large time constant of the LPF with respect to the surface plate acceleration signal. That is, the influence of the disturbance f _ext , the floor vibration x _B , and the reaction force due to the driving of the stage itself on the output of the interferometer can be strongly suppressed as compared with the conventional case where the surface plate acceleration feedback circuit 8 is simply added. effective. Therefore, the positioning time can be shortened and the positioning accuracy can be improved.

However, the decrease of the time constant of the LPF with respect to the acceleration signal causes the increase of the gain in the high frequency range in the response from the target position to the output of the interferometer. Therefore, it should be noted that when the controlled object 3 has a high-frequency dynamics that is not modeled, that is, mechanical resonance or the like, there arises a problem of stimulating the high-frequency dynamics to deteriorate the positioning characteristic.

[Brief description of drawings]

FIG. 1 is a control block diagram showing a configuration of a positioning device including a surface plate acceleration feedback circuit according to an embodiment of the present invention,

FIG. 2 is a diagram showing a frequency characteristic when the gains of the LPF and the output of the BPF are made to coincide with each other and the outputs are added in parallel;

FIG. 3 is a block diagram of a speed control system including a high band surface plate acceleration feedback circuit,

FIG. 4 is a block diagram of an acceleration minor loop including a high band surface plate acceleration feedback circuit,

FIG. 5 is a diagram showing a dynamic model of a horizontal uniaxial direction of an XY stage mounted on a surface plate;

FIG. 6 is a control block diagram when a position control system is configured,

FIG. 7 is a frequency characteristic showing vibration transmissibility from floor vibration to interferometer output,

FIG. 8 is a step response waveform of a stage depending on the presence or absence of surface plate acceleration feedback,

FIG. 9 is a frequency characteristic showing a vibration transmissibility from floor vibration to interferometer output when time constants T _a and T _d are reduced.

[Explanation of symbols]

 1 XY stage 2 surface plate 3 control target 4 position detection conversion means 5 compensator for characteristic improvement 6 power amplifier 7 thrust constant 8 surface plate acceleration feedback circuit 9 high band surface plate acceleration feedback circuit 10 speed detection conversion means 11 PI compensator

Claims (3)

[Claims] 1. A positioning device for an XY stage, comprising a surface plate, which is a vibration isolation device installed on a floor surface, and an XY stage, which is mounted on the surface plate, and detects a signal relating to the position of the XY stage. And a means for detecting the acceleration of the surface plate with respect to the floor surface to form a control system for performing position control of the XY stage by feedback control.
A power amplifier for positioning and driving the XY stage according to a signal based on a difference signal between the command signal and the feedback signal is included in the control system, and a signal from the means for detecting the acceleration of the surface plate is used as the difference signal. In addition to a signal based on which the signal is input to the power amplifier, the signal for detecting the acceleration of the surface plate is input to the power amplifier through an optimally set high-band surface plate acceleration feedback circuit. Positioning device for XY stage. 2. An XY stage positioning device comprising a surface plate, which is a vibration isolation device installed on the floor surface, and an XY stage, which is mounted on the surface plate, and detects a signal relating to the speed of the XY stage. Means and a means for detecting the acceleration of the surface plate with respect to the floor surface are provided to form a control system for performing feedback control of the speed control of the XY stage.
The control system includes a power amplifier for driving the XY stage to control the speed of the XY stage in response to a signal based on the difference signal between the command signal and the feedback signal, and the signal from the means for detecting the acceleration of the surface plate is added to the above In the case where the signal is input to the power amplifier together with the signal based on the difference signal of, the signal detecting the acceleration of the surface plate is input to the power amplifier through the optimally set high band surface plate acceleration feedback circuit. An XY stage positioning apparatus having a speed control mode characterized by the above. 3. The optimally set high-band surface plate acceleration feedback circuit is a feedback circuit in which an output of an acceleration sensor having a low-pass filter characteristic and an output of an acceleration sensor having a band-pass characteristic are matched and added. The XY stage positioning device according to claim 1 or 2.