JP3223542B2 - Positioning method, exposure method, positioning apparatus, and exposure apparatus having the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for manufacturing semiconductors, and more particularly to an improvement in position control of a sample stage.

[0002]

2. Description of the Related Art An original image pattern on a reticle is projected onto a wafer on a sample stage (hereinafter referred to as an XY stage or stage) by a projection lens, and the XY stage is moved to an exposure position while being projected onto the wafer. 2. Related Art An exposure apparatus that sequentially exposes semiconductor chips is known. FIG. 4 is a block diagram showing a drive control unit of an XY stage of this type of exposure apparatus. Here, it is assumed that the stage 1 as a movable body can move one-dimensionally on the guide 2. A nut (not shown) screwed with a feed screw 4 rotationally driven by a motor 3 is fixed to the stage 1, and the stage 1 reciprocates as the motor 3 rotates forward and backward. The moving amount or moving position of the stage 1 is sequentially detected by a length measuring device 5 such as a laser interferometer or an encoder. The position controller 6 has a function of calculating a difference between a command value of a target stop position of the stage 1 and position information (current position of the stage 1) from the length measuring device 5, that is, a position shift amount. The position feedback control is performed through the control.

[0003]

However, in the conventional exposure apparatus described above, the loop gain (control gain) of the position controller is previously set high in order to obtain a predetermined position control accuracy. If mechanical conditions such as friction between the feed screw and the rigidity between the feed screw and the nut change, the feedback control system may become unstable. In order to avoid such control instability, it is conceivable to set the control gain of the position controller low by assuming fluctuations in machine conditions in advance, but doing so will degrade position control accuracy or the time required for positioning. There is a problem that becomes longer.

An object of the present invention is to set an optimum loop gain of a position control system as required, and to position an exposure apparatus capable of accurately positioning a stage at a target position in a short time even when there are fluctuations in machine conditions. It is to provide a control device.

[0005]

The present invention will be described with reference to FIG. 1 showing the configuration of one embodiment. The invention of claim 1 is provided in an exposure apparatus for transferring a pattern of a mask onto a photosensitive substrate, A sample stage 1 that can move while holding a photosensitive substrate;
Driving means 3 for moving the sample table 1, detecting means 5 for detecting the position of the sample table 1, and driving means 3 based on the amount of displacement between the target position for positioning the sample table 1 and the detected position of the detecting means 5. Is applied to a positioning control device of an exposure apparatus including a position control means 6 for feedback-controlling the position. Then, a first calculating means 8 for calculating an average value or a median of the positional deviation amounts for each predetermined time, and a second calculating means for calculating the difference between the minimum value and the maximum value of the positional deviation amounts for each predetermined time 9
And a gain setting means 11 for setting a loop gain of a signal according to the amount of displacement for controlling the driving means 3 based on the calculated average value or median value and the difference. To achieve. Further, the gain setting means 11A of the positioning control device of the exposure apparatus changes the loop gain according to the photosensitive characteristic of the photosensitive substrate.

[0006]

According to the first aspect, the gain setting means 11 sets a loop gain of a signal according to a positional deviation amount for controlling the driving means 3 based on the calculated average value or median value and the difference, The position control unit 6 performs feedback control of the driving unit 3 based on the amount of displacement between the positioning target position of the sample stage 1 and the detection position of the detection unit 5.

[0007] In the means and means for solving the above-mentioned problems which explain the configuration of the present invention, the drawings of the embodiments are used to facilitate understanding of the present invention. However, the present invention is not limited to this.

[0008]

FIG. 1 is a block diagram showing the configuration of one embodiment. Members having the same functions and functions as those of the conventional device shown in FIG. 4 are denoted by the same reference numerals, and the description here will focus on the differences. In FIG. 1, the configuration is such that the image of the pattern of the reticle R is transferred to the wafer W mounted on the stage 1 via the projection optical system PL. Reference numeral 8 denotes an average value calculation unit, which is the target position to be positioned, for example, the exposure position (that is, the position of the optical axis AX of the projection optical system PL).
Alternatively, an average value (or a median value) of the positional deviation amount, which is a difference between a command value such as an alignment position and the current position of the stage 1 detected by the length measuring device 5 every predetermined time, is calculated. Reference numeral 9 denotes a PP value (difference between the minimum value and the maximum value), which calculates the PP value of the positional deviation amount at predetermined time intervals. Reference numeral 10 denotes a timer, which supplies a timing signal to the average value calculation unit 8 and the PP value calculation unit 9 at predetermined time intervals. Note that the timing signal generation time interval is set to a time sufficiently shorter than the exposure time. Upon receiving this timing signal, the average value calculating section 8 and the PP value calculating section 9 calculate the average value and the PP value of the positional deviation amounts from the time of receiving the previous timing signal to the time of receiving this timing signal. Reference numeral 11 denotes a gain adjustment unit that sets a control gain K of the position controller 6 based on the average value of the positional deviation amounts and the PP value calculated by the average value calculation unit 8 and the PP value calculation unit 9. I do.

Next, a method of determining the control gain of the gain adjusting section 11 will be described. FIG. 2 is a time chart showing the command voltage v output from the position controller 6 to the power amplifier 7. The power amplifier 7 applies a drive voltage to the motor 3 according to the command voltage v, and accelerates, runs at a constant speed, and decelerates the motor 3. Position control is performed from the time when the deceleration of the motor 3 is completed (the end of the trapezoidal waveform in the figure), and a command voltage v corresponding to the amount of displacement is output. FIG. 2A shows a case where the control gain K of the position control system is appropriate. The command voltage v converges quickly and positioning is completed. FIG.
(B) shows a case where the control gain K is excessive, and the command voltage v during the position feedback control is oscillating. As a result, the motor 3 vibrates. FIG. 2C shows the control gain K
Is too low, and a steady-state error has occurred.

FIG. 3 shows the amount of positional deviation (a) during position control,
Absolute value (b) of the average value of the displacement amount, P−
6 is a time chart showing a P value (c) and a timing signal (d). As is apparent from the figure, when the displacement amount is oscillating, the absolute value of the average value is small and P
-P value is large. Conversely, when there is a steady-state deviation in the displacement amount, the absolute value of the average value is large and the PP value is small. The vibration of the displacement amount is likely to occur when the position control system is unstable due to, for example, a change in mechanical conditions. Therefore, in this case, the control gain K of the position control system is reduced,
Stabilize the control system. On the other hand, the steady-state deviation of the displacement amount is
This is likely to occur due to insufficient control gain of the position control system. Therefore, in this case, the control gain K of the position control system is increased, and the position control accuracy is increased.

Therefore, a reference amount A is set for the average value, and a reference amount B is set for the PP value. These reference amounts A and B may be determined based on, for example, the photosensitive characteristics of the photosensitive material used. The ratio between the absolute value of the average value and the reference amount A is m (= | average value / A), and the ratio between the PP value and the reference amount B is n (= (PP value). / B), if m is smaller than n, the control gain K is reduced by the gain adjustment unit 11, and conversely, if m is larger than n, the control gain K is increased. That is, every time the timing signal is generated from the timer 10, PP
When the value is relatively larger than the average value, the control gain K
When the average value is larger than the PP value, the control gain K is increased. As a result, the control gain K converges to the optimum value.

As described above, since the optimal control gain is always set according to the degree of change in the amount of displacement, the position control system is stabilized against fluctuations in machine conditions, and high position accuracy can be obtained in a short positioning time. Can be Further, since the optimal control gain is automatically set at the time of use, the gain adjustment at the time of shipment of the exposure apparatus is omitted or simplified.

Further, if the set control gain is corrected in accordance with the photosensitive characteristics of the photosensitive material, position feedback control optimal for exposure conditions can be performed. For example, in the case of an exposure that is loose with respect to the sharpness of the image and severe with respect to the positional deviation, the control gain is set to be high, and the amount of the positional deviation is reduced even in the case of slight vibration. Conversely, when priority is given to the sharpness of the image, the control gain is set low, and the vibration during exposure is reduced as much as possible.

The present invention can be applied to any drive motor and stage drive mechanism, for example, when a stage on an air guide is driven by a linear motor. In this embodiment, the output of the position controller 6 is directly led to the power amplifier 7. However, even in the case where a speed controller (the configuration of the speed controller is arbitrary), the present invention is applied in the same manner. The effect of can be obtained.

In the configuration of the above embodiment, the motor 3 is a driving means, the length measuring device 5 is a detecting means, the position controller 6 is a position controlling means, the average value calculating section 8 is a first calculating means, P
The P value calculation unit 9 sets the second calculation unit to the gain adjustment unit 11
Constitute gain setting means.

[0016]

As described above, according to the present invention, a signal corresponding to the amount of displacement based on the difference between the minimum value and the maximum value and the average value or median value of the displacement amount at predetermined time intervals. Since the feedback control is performed based on the amount of displacement between the positioning target position and the detection position, the optimal loop gain is always set,
The position control system is stabilized against fluctuations in machine conditions, and high position accuracy can be obtained in a short positioning time. Further, since the optimum loop gain is automatically selected at the time of use, the gain adjustment at the time of shipment of the exposure apparatus is omitted or simplified. Further, since the set loop gain is changed in accordance with the photosensitive characteristics of the photosensitive substrate, position feedback control of the sample stage optimal for exposure conditions can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment.

FIG. 2 is a time chart showing a command voltage output from a position controller.

FIG. 3 is a time chart showing a positional deviation amount during position control, an average value of the positional deviation amount, a PP value of the positional deviation amount, and a timing signal.

FIG. 4 is a block diagram showing a conventional exposure apparatus.

[Explanation of symbols]

 Reference Signs List 1 stage 2 guide 3 motor 5 length measuring device 6 position controller 7 power amplifier 8 average value calculation unit 9 PP value calculation unit 10 timer 11 gain adjustment unit

Claims (2)

(57) [Claims] An exposure device for transferring a pattern of a mask onto a photosensitive substrate, the sample stage being movable while holding the photosensitive substrate; a driving unit for moving the sample stage; and a position of the sample stage. A positioning control unit for an exposure apparatus, comprising: a detection unit for detecting; and a position control unit for performing feedback control of the driving unit based on a positional deviation amount between a positioning target position of the sample stage and the detection position of the detection unit. A first calculating means for calculating an average value or a median value of the positional deviation amounts at predetermined time intervals; and a second calculating means for calculating a difference between a minimum value and a maximum value of the positional deviation amounts at predetermined time intervals. And gain setting means for setting a loop gain of a signal corresponding to the displacement amount for controlling the driving means based on the calculated average value or the median value and the difference. Positioning control device of the exposure apparatus characterized by obtaining. 2. A positioning control device for an exposure apparatus according to claim 1, wherein said gain setting means changes said loop gain in accordance with a photosensitive characteristic of said photosensitive substrate. Control device.