JPH09180988A - Automatic reticle positioning apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the exposure time by providing a sensitivity control part for making the sensitivity of a servo control part lower or zero during the non-exposure time. SOLUTION: When information of a non-exposure time start is input from a central control part to a sensitivity control part 17, a gain constant of a servo control part 15 is made smaller. As a result, even if a stage begins to move and thus the whole of an exposure apparatus vibrates, actuators 12 (12X, 12Y, 12Z) do not react excessively or at all to that vibration, and a reticle R remains in the vicinity of a standard position. When information of a non- exposure time end is input to the sensitivity control part 17, the gain constant of the servo control part 15 is returned to the original value. A dislocation amount detected by detection parts 14A, 14B is input to the servo control part 15 and signals are output therefrom to the actuators 12 to position the reticle R at the standard position. The reticle R is returned to the standard position in a short time, because it is in the vicinity of the standard position. In the subsequent exposure, the stage is stationary and there is no vibration of the whole exposure apparatus so that no vibration of the reticle is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device (automatic positioning device) for automatically determining the position of a reticle having an alignment mark.

[0002]

2. Description of the Related Art At present, a step-and-repeat exposure apparatus is used for manufacturing precision devices such as semiconductor devices and liquid crystal devices. This device projects a predetermined pattern drawn on a reticle onto a photosensitive substrate with the same size or reduced size. Photosensitive substrate (hereinafter simply referred to as substrate)
Is a wafer or glass plate coated with a resist. The reticle is a reticle in a broad sense, including a mask.

Generally, the predetermined pattern is formed on a single substrate a plurality of times (100 for a wafer having a substrate diameter of 8 inches).
Project about twice). That is, the substrate is moved (stepped) to a predetermined position, stopped, and exposed. The operation of moving (step) and stopping (exposure) is repeated about 100 times (repeat). This series of operations is called step-and-repeat, and an exposure apparatus that performs this operation is called a step-and-repeat type exposure apparatus.

An exposure apparatus generally comprises a light source for illuminating a reticle, a projection optical system, a stage for mounting a substrate, a stage drive section for moving the stage in the horizontal direction, and a central control section. To complete a precision device, you need multiple reticles with different patterns, which is why
The reticle is replaced. In that case, the positioning of the reticle is very important, and it takes too much time to position it with a human hand, so the exposure apparatus is also equipped with an automatic reticle positioning apparatus (see FIGS. 4 and 5).

After the reticle is positioned, the step and repeat process is started. The process will be described below with reference to FIG. The central control unit moves the substrate to a predetermined position by sending a stage drive signal to the stage drive unit to move (step) the stage every time each exposure is performed. When the drive signal for the stage ends, the central control unit commands the light source or the shutter that blocks the light source to start exposure.

When a heavy stage is moved (stepped) at high speed and stopped in order to move the substrate to a predetermined position, the entire exposure apparatus shakes. This swing causes the reticle to swing. The shaking of this reticle is much larger than the shaking caused by other causes. The central control unit waits for the positioning of the reticle to be completed after the drive signal for the stage is completed, and immediately commands the start of exposure. When the alignment mark (described later) on the reticle stays within a predetermined range with respect to the reference position for a predetermined time or more, it is determined that the positioning of the reticle is completed. If the time from the end of the stage drive signal to the end of reticle positioning is long,
The exposure process time (which will be described later) becomes long, so the user of the exposure apparatus dislikes it.

Conversely, if the exposure start command is issued without waiting for the positioning of the reticle to end, the swaying has not yet stopped, and the reticle will not return to the reference position even if the automatic reticle positioning device is operating. Also, the reticle shakes during the exposure (for example, 0.4 to 2 seconds) even after returning once. As a result, the projected pattern is blurred or misaligned. Currently, the line width of a projected pattern (predetermined pattern) is as thin as 0.5 μm or less, and if the projected pattern is blurred or misaligned, the precision device becomes a defective product.

The automatic reticle positioning device (see FIGS. 4 and 5) includes a reticle holder for holding a reticle having alignment marks, a moving mechanism for moving the holder horizontally, and a position for detecting the alignment marks. And a servo control unit that constantly drives the moving mechanism in a direction in which the displacement amount decreases. With this device, even if the reticle shakes and shifts from the reference position, the reticle is immediately returned to the reference position. As a result, if the start of exposure is commanded after the positioning of the reticle is completed, the projected pattern will not be blurred or will not be displaced.

Referring to FIG. 4, the reticle R is placed on the reticle holder 10. An alignment mark (generally a cross) provided on the reticle R is observed by a detection unit (not shown) provided above the reticle R.
The reticle holder 10 is an alignment actuator 1
It is moved in the horizontal direction by 2X, 12Y, and 12Θ (hereinafter collectively referred to as actuator 12) and positioned at the reference position. This is called alignment. The actuator corresponds to the moving mechanism referred to in the present invention.

FIG. 5 is a circuit block diagram of the positioning device. The detectors 14A and 14B detect the positions of the alignment marks 13A and 13B, and output the amount of deviation between the detected positions and the reference position. This shift amount is input to the servo control unit 15. The servo control unit 15 drives the actuator 12 to reduce the deviation amount (including zero).
The detection of the deviation amount and the driving of the actuator 12 are always (including intermittently) performed during the exposure. Therefore, even if the reticle is displaced during exposure, it is immediately returned to the reference position. In such servo control, the gain constant determines the speed and sensitivity of returning the reticle to the reference position. The gain constant is the ratio of the displacement amount of the alignment mark from the reference position and the output of the servo control unit that drives the moving mechanism (actuator). The gain constant is determined by the circuit design of the servo control unit. When the gain constant is increased (increased), the returning speed is high and the sensitivity is high. On the contrary, if the gain constant is made smaller (lowered), the returning speed becomes slower and the sensitivity becomes lower.

[0011]

Currently, with a wafer diameter of 8 inches, the time required to complete the exposure of a single wafer with the same reticle (hereinafter referred to as the exposure process time) is 1 to 2 minutes. Is. In order to increase the productivity of precision devices, exposure apparatus users are demanding that exposure apparatus manufacturers reduce the exposure process time.

An object of the present invention is to reduce this time.

[0013]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems. Below the reticle is a stage (not shown) having a large mass for mounting the substrate. The mass of the stage varies depending on the model, but is about 200 kilograms. The stage is repeatedly moved and stopped repeatedly to change the exposure position of the substrate. In order to shorten the exposure process time, the stage is moved and stopped with a large acceleration. For this reason, when the stage is moved or stopped, the entire exposure apparatus shakes, which causes the reticle to shake and cause a positional shift. The automatic reticle positioning apparatus is always operating in the conventional exposure apparatus, and tries to recover the positional deviation of the reticle as soon as possible.

Even after the movement of the stage is completed, the shaking of the entire exposure apparatus continues for a while. This time is called the shaking duration. As a result, the reticle also shakes and the position shifts. In order to avoid blurring of the projected pattern and displacement of the reticle, the reticle positioning end is delayed more than the shaking continuation time by the time required to return the reticle from the displaced position to the reference position (hereinafter referred to as recovery time). Since the recovery time differs depending on the size and cycle of the shaking of the exposure apparatus as a whole, it differs from time to time. The sum of the shaking continuation time and the recovery time is defined as the waiting time S. FIG. 6A is the time chart described above.
In practice, the reticle positioning end C and the exposure start D, and the exposure end E and the start F of the next step and repeat process are almost the same.

If the recovery time can be shortened, the exposure process time can be shortened. Therefore, the present inventor carefully studied the recovery process of the reticle displacement. As a result, it was found that if the gain constant of servo control during non-exposure (step time, that is, the total time of the stage movement time and the waiting time S) is decreased (sensitivity is decreased), the recovery time is shortened.
The present invention has been accomplished.

Low gain (low sensitivity) during non-exposure
Then, consider why the recovery time becomes shorter and why. It is presumed that the reason is that the servo controller is too sensitive, and that there is an electrical and / or mechanical time delay in the control system in the positioning device. Due to the time delay of the control system, the reticle may swing in the same direction during the movement of moving the reticle holder in a certain direction. As a result, the reticle moves beyond the distance it should originally move. Moreover, the sensitivity is so high that it goes too far. That is, the reticle goes to a position far away from the reference position. Such a state is just before or after the end of the stage movement (during the shaking duration)
If it occurs, the recovery time will be extended by the time to undo this overshoot. If such a state occurs in the early stage of stage movement, it can be recovered during the subsequent stage movement, so the influence is small.

On the other hand, if the gain constant is made small, even if the reticle sways in the same direction as the moving direction of the reticle, a large overshoot does not occur, so that the recovery time can be shortened. FIG. 6B is a time chart of the present invention. Also in this case, the reticle positioning end C and the exposure start D, and the exposure end E and the start F of the next step and repeat process are almost at the same time.

Therefore, according to the present invention, the reticle holder for holding the reticle having the alignment mark, the moving mechanism for moving the holder in the horizontal direction, the position of the alignment mark, and the deviation between the detected position and the reference position are detected. In an automatic reticle positioning apparatus, which comprises a detection unit that outputs a quantity and a servo control unit that constantly drives the moving mechanism in a direction in which the shift amount decreases, the sensitivity of the servo control unit is reduced during non-exposure, or A sensitivity control unit for zeroing is provided (Claim 1).

In this case, it is preferable that the sensitivity control unit is a changing unit that changes a gain constant of the servo control unit (claim 2). Further, it is preferable that the sensitivity control unit receives a signal from a vibration sensor that detects “swing of the entire exposure apparatus during non-exposure” and changes the gain constant of the servo control unit according to the magnitude of the signal. (Claim 3).

Further, according to the present invention, a reticle holder for holding a reticle provided with an alignment mark, a moving mechanism for moving the holder in a horizontal direction, a position of the alignment mark is detected, and a detected position and a reference position are set. In an automatic reticle positioning device including a detection unit that outputs a deviation amount and a servo control unit that constantly drives the moving mechanism in a direction in which the deviation amount decreases, a "non-contact" is provided between the detection unit and the control unit. A filter for removing a component caused by the shaking of the entire exposure apparatus during exposure is interposed (claim 4).

In this case, the filter receives a signal from a vibration sensor for detecting "swing of the entire exposure apparatus at the time of non-exposure" and operates signal removal according to the magnitude of the signal.
Alternatively, it is preferably inoperative (Claim 5).

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit block diagram of a first embodiment. In addition to the conventional device shown in FIGS. 4 and 5, gain constant changing means 17 is provided, and the servo control unit 15 is provided.
The gain constant of can be changed. When information about the start of non-exposure (during stage movement + waiting time S), that is, the start of stage movement is input to the means 17 from the central control unit (not shown), the means 17 reduces the gain constant. As a result, the signal given from the control unit 15 to the actuator 12 becomes a fraction, a few tenths, or zero. By controlling in this way, even if the stage starts to move, and therefore the entire exposure apparatus shakes, the actuator 12 does not react excessively or at all to the shaking of the entire exposure apparatus, and the reticle R is close to the reference position. Stay in.

Next, when the information about the end of non-exposure is input to the means 17 from the central control section, the means 17 restores the gain constant of the control section 15 to the original value. When the shift amount detected by the detection units 14A and 14B is input to the control unit 15, the control unit 15
Outputs a signal to the actuator 12, which positions the reticle R at the reference position. In that case, since the reticle R is near the reference position as described above, it is returned to the reference position in a short time and held there. Then, after that, exposure is performed. At this time, since the stage is stopped and the shaking of the entire exposure apparatus is stopped, the shaking of the reticle R caused by this does not occur. Even if the reticle R shakes (even if it shifts) during exposure due to other reasons, the shake is generally small and the positioning device is operating with high sensitivity, so the reticle R quickly returns to the reference position.

Even when the means 17 returns the gain constant of the control unit 15 to the original value between the vicinity of the end of the shaking continuation time and the end of the waiting time, the same effect as described above is obtained. Will be obtained. In reality, in order to further shorten the exposure process time, the stage 17 may end the movement of the stage by further advancing the timing at which the gain constant of the control unit 15 is returned to the original value. In this case, since the shake of the entire exposure apparatus has not stopped yet, there is still a risk of the reticle R shaking. This risk and early return of the reticle positioning by quickly returning the gain (If the reticle does not shake in the same direction as the reticle holder moving direction, the higher the gain (the more the gain is returned) The reticle positioning is completed early.) And whether or not to adopt this method is determined. By smoothly changing the speed when the stage is decelerated and stopped, it is difficult for a large shake of the entire exposure apparatus to occur due to the stage decelerated and stopped, and the risk is reduced. In this way, when the means 17 accelerates the timing of returning the gain constant of the control unit 15 to the original value, the information that the non-exposure time ends is moved up at the end of the movement of the stage or after a predetermined time, and is moved to the center. It is input to the means 17 from the control unit.

FIG. 2 shows a second embodiment of the present invention (claim 3).
Is a circuit block diagram of (corresponding to). This embodiment is shown in FIG.
In addition to the conventional device shown in FIG.
4B and the servo control unit 15 between the filters 16A, 16
B is added. Of the signals output from the detection units 14A and 14B to the control unit 15, the components caused by the shake of the entire exposure apparatus are removed by the filters 16A and 16B. This component is known by preliminary experiments, and a filter having a characteristic of removing the component is selected and used. This component has a low frequency (3 to 5 hertz according to the analysis of the present inventor although it varies depending on the structure of the apparatus), so that the detection unit 1 is not exposed during exposure.
It is clearly distinguished from the signals output from 4A and 14B. Therefore, the component caused by the fluctuation of the entire exposure apparatus, which is included in the output signal of the detection unit during the non-exposure, is the filter 16.
Since it is removed in A and 16B and is not input to the control unit 15,
The actuator 12 does not follow the swing, and the reticle R
Stays in the vicinity in place. The outputs from the detection units 14A and 14B other than the non-exposure time are the filters 16A and 1A.
It is input to the control unit 15 with little influence of the component removal by 6B and is positioned with high sensitivity.

FIG. 3 shows a third embodiment of the present invention (claim 4).
Is a circuit block diagram of (corresponding to). In the present embodiment, the second
The filter control unit 1 is provided in the filters 16A and 16B of the embodiment.
The non-exposure information is given from 8 to control the function of the filter. That is, the filter is made to function only during non-exposure to remove the component. In any of the embodiments, the non-exposure information may be generated by the vibration sensor. That is, when the stage moves, the entire exposure apparatus shakes. Therefore, the shake can be detected by the vibration sensor and input to the controller 15 or the filters 16A and 16B.

It is speculated that the present invention can be applied to general positioning devices other than reticles.

[0028]

The present invention does not reduce the sensitivity of servo control during non-exposure, so that the reticle does not needlessly follow. Therefore, at the start of exposure, the reticle is near the reference position. Therefore, the time for returning the reticle to the reference position is shortened. Finally, the exposure process time is shortened and the productivity of semiconductor devices and liquid crystal devices is improved.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a first embodiment of the present invention.

FIG. 2 is a circuit block diagram of a second embodiment of the present invention.

FIG. 3 is a circuit block diagram of a third embodiment of the present invention.

FIG. 4 is a perspective view of a conventional positioning device.

5 is a circuit block diagram of the device of FIG.

6A is a time chart of the conventional device. FIG. 6B is a time chart of the device of FIG.

[Explanation of symbols]

10 ... Reticle holder 12X ... X-axis actuator 12Y ... Y-axis actuator 12.THETA .... THETA.-axis actuator 12X, 12Y, 12.THETA. Alignment mark detection unit (detection unit) 15 ... Servo control unit 16A, 16B ... Filter 17 ... Gain constant changing means (sensitivity control unit) 18 ... Filter control unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyuki Hirachi 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation

Claims (5)

[Claims] 1. A reticle holder for holding a reticle provided with an alignment mark, a moving mechanism for moving the holder in a horizontal direction, a position of the alignment mark is detected, and a deviation amount between a detected position and a reference position is output. In an automatic reticle positioning device including a detection unit and a servo control unit that constantly drives the moving mechanism in a direction in which the displacement amount decreases, the sensitivity of the servo control unit is reduced or made zero at the time of non-exposure. An automatic reticle positioning device having a sensitivity control section. 2. The automatic reticle positioning apparatus according to claim 1, wherein the sensitivity control unit is a changing unit that changes a gain constant of the servo control unit. 3. The apparatus according to claim 2, further comprising a vibration sensor for detecting “swing of the entire exposure apparatus during non-exposure”,
The automatic reticle positioning device, wherein the sensitivity control unit that receives a signal from the vibration sensor changes a gain constant of the servo control unit according to the magnitude of the signal. 4. A reticle holder for holding a reticle provided with an alignment mark, a moving mechanism for moving the holder horizontally, a position of the alignment mark is detected, and a deviation amount between the detected position and a reference position is output. What is claimed is: 1. An automatic reticle positioning device, comprising: a detection unit and a servo control unit that constantly drives the moving mechanism in a direction in which the amount of deviation decreases. An automatic reticle positioning device characterized by interposing a filter that removes a component caused by the overall shake. 5. The apparatus according to claim 4, further comprising a vibration sensor for detecting "swing of the entire exposure apparatus during non-exposure",
An automatic reticle positioning device, wherein the filter receiving a signal from the vibration sensor is configured to activate or deactivate signal removal depending on the magnitude of the signal.