JPH067213B2 - Automatic focus adjustment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing apparatus, and more particularly to an automatic focusing apparatus suitable for industrial cameras such as reduction projection exposure apparatuses.

[Background of the Invention]

Conventionally, when focusing on a photosensitive sample with a high-resolution reduction camera or the like, the sample surface is accurately positioned according to the unevenness and waviness of the sample surface, and the sample surface is positioned at a predetermined focus position. Devices that move and focus are used.

FIG. 5 is a diagram for explaining an example of a conventional device manufactured based on Japanese Patent Publication No. 56-34844. This device is composed of an air micrometer type distance detector, a sample stage that can move in parallel only in the optical axis direction, a drive source that drives the sample stage, and a control system.

In FIG. 5, the lens barrel 1 is partitioned by the reduction lens 2, and the detector 4 having a shape surrounding the projection optical path is provided on the sample side.
The detector 4 is provided with an air supply hole 3, from which a substrate whose pressure is controlled to be constant, for example, air, is supplied and ejected from an opening at the lower end of the detector 4 as indicated by an arrow.

With such a configuration, when the distance between the detector 4 and the sample 6 is gradually increased from a certain value, the pressure inside the detector is decreased, and conversely, the pressure is increased when the distance is decreased. Therefore, the detected pressure according to the distance can be obtained inside the detector.

Therefore, a reference device 7 having the same shape as the detector 4 is made, gas from the same pressure source as that of the detector 4 is added through the air supply hole 8 and ejected from the opening. If the reference plate 9 is provided facing this opening and the distance between them is adjusted to the desired distance between the detector 4 and the sample 6, the internal pressure of the reference device 7 becomes
The internal pressure of the detector 4 becomes the desired pressure. That is,
A reference pressure is obtained inside the reference device 7.

Therefore, the detected pressure obtained by the detector 4 and the reference device 7
So that the reference pressures obtained by
By moving 2 up and down, the distance between the sample 6 and the lens 2 can be controlled to a desired value. Hereinafter, how this is done will be described.

First, when mounting the sample 6 on the sample table 12, the sample table 1
It is necessary to move 2 to the lowest position in the movable range. For this purpose, the analog switch 31 is selected to the B side in the figure by the signal from the computer 17. The descending operation control circuit 23 outputs the descending speed command voltage when the low limit switch 24 is closed.
The output is input to the second amplifier 20 via the analog switch 31 selected to the B side, the servo motor 21 is driven, and the nut 16 moves in the direction of the low limit switch 24. At this time, since the guide surface 14 has a wedge shape, the sample table 12 supported by the leaf spring 13 moves in the descending direction. Immediately after the nut 16 further moves and comes into contact with the low limit switch 24, the low limit switch 24 is opened, the output of the descending motion control circuit 23 becomes zero, the servo motor 21 is stopped, and the sample table 12 is stopped. Stop at position. The position of the sample table 12 at this time will be referred to as a low limit position. In this way, the sample table 12 is lowered to the low limit position, the sample 6 is mounted on the sample table 12, and then the positioning operation to the reference focus position is started.

In order to position the sample surface at the reference focus position, the analog switch 31 is selected to the A side in the figure by the signal from the computer 17. The differential pressure converter 11 detects the pressure difference between the detected pressure introduced through the measurement hole 5 and the reference pressure introduced through the measurement hole 10 and converts it into an electric signal. The output signal of the differential pressure converter 11 is applied to the first amplifier 19 and amplified.
The output is further amplified by the second amplifier 20 through the analog switch 31 selected to the A side, the servo motor 21 is operated, the sample stage 12 is driven in the focus adjustment direction, and the detected pressure and the reference pressure are equal. Control to be.
In this way, the sample surface is positioned at the reference focus position.

The distance between the sample surface and the lens is adjusted by moving the reference plate, but this is not generally sufficient, and fine adjustment centered on the set value by the adjustment of the reference plate is necessary. Moreover, it is desired that this fine adjustment can be performed by a signal from the computer. Computer 1
7. The DA converter 18 does this. The computer 18 uses the DA converter to make the first fine adjustment of the distance.
It is intended to have the same effect as moving the reference plate 9 by applying it to the input of the amplifier 19 of.

After the predetermined processing such as exposure of the sample at the reference focus position is completed, the analog switch 31 is returned to the B side from the computer 17 again to replace the sample in preparation for the next processing, and the sample table 12 is moved to the low limit position. Down to.

As described above, in an actual operating state, the sample table is reciprocated between the low limit position and the reference focus position each time the sample is replaced.

In the conventional device described above, the frictional force existing in the movable part gradually increases near the low limit position and the reference focus position while the sample table is repeatedly reciprocated between the low limit position and the reference focus position. However, there is a problem that the positioning accuracy at the reference focus position deteriorates, and improvement is desired.

This will be described with reference to FIG. FIG. 6 (a) shows the location dependence of the friction torque, where the horizontal axis represents the position Z of the sample table and the vertical axis represents the friction torque τ _F of the movable portion converted into the servo motor axis. In normal operation, the sample is exchanged when the sample table is at the low limit position Z = Z _L, and after the sample exchange, the reference focus position Z = Z _BF is raised and the positioning is performed.
Again, the lower limit position Z is lowered to Z = Z _L for the next sample exchange. Therefore, the normal operating range of the sample table is Z = Z _L
To Z = Z _BF . When the above operation is repeated, fine grinding scraps are formed on the sliding portions between the nut 16 and the feed screw 15 and the guide surface 14 in FIG. 5 corresponding to both ends of the normal operating range of the sample table. As shown in Fig. 6 (a), the friction torque was initially flat with respect to the Z position and was almost constant everywhere due to the accumulation of dust and debris. It locally increases near the low limit position Z = Z _L and the reference focus position Z = Z _BF , which are the ends of the operating range. Fig. 6 (b)
Reference focus position Z = Z is the magnitude of the motor output torque tau _M is
_It shows a linear servo characteristic that it is proportional to the deviation from _BF , and even when using a detector that is non-linear with respect to the detection distance, such as an air micrometer, it can be considered to be almost linear in the minute range. . First, assuming that the values of the friction torque at the reference focus position Z = Z _BF are τ _BFO and −τ _{BFO as} shown in FIG. 6 (a), the motor output torque τ _M is the friction torque in FIG. 6 (b). Torque τ _BFO , −τ
_{In a} region smaller than _BFO , control is impossible, and a dead zone corresponding to δ _ZO , that is, a positioning error occurs. After the repeated operation, a reference focus position Z = Z friction torque in the _BF is locally increased tau _BF, When Natsuta in-tau _BF, dead band increases with the [delta] _Z, resulting deterioration of the positioning accuracy. The value of the dead zone indicates that the focus adjustment operation cannot follow the changes smaller than the dead zone due to the unevenness and waviness of the sample surface. Even if the friction torque increases near the low limit position Z = Z _L during repeated use, there is no mistake if the motor output torque is sufficient to overcome it, but the friction torque increases near the reference focus position Z = Z _BF. Leads to an increase in dead zone, which deteriorates the positioning accuracy.

In a high resolution reduction camera or the like, a dead zone of about submicron is required, and the increase of the dead zone and deterioration of positioning accuracy during use of the apparatus poses a problem since it directly affects deterioration of resolution.

[Object of the Invention]

It is an object of the present invention to provide an automatic focusing device that can maintain high positioning accuracy for a long period of time.

[Outline of Invention]

A feature of the present invention is that the means for stopping the operation of positioning the inclined surface at the reference focus position and the reciprocating operation of the sample table between both ends of the movable range including the reference focus position of the sample table while the positioning operation is stopped. And the reciprocating operation control means.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3.

FIG. 1 is a diagram showing an embodiment of the present invention. In the figure, the parts added according to the present invention are an upgrade switch 25, a reciprocating operation control circuit 26 and an analog switch 27.
C terminal. The upper limit switch 25 is mounted so that when the sample 12 reaches the upper limit of its movable range, the nut 16 comes into contact with it to operate from closed to open.
The reciprocating operation control circuit 26 uses the contact outputs of the upper limit switch 25 and the lower limit switch 24, and when the analog switch 27 is selected to the C side, the sample table 1
2 can be reciprocated between these two limit positions. The second embodiment of the reciprocating operation control circuit 26
It will be described with reference to the drawings.

In FIG. 2, the reciprocating operation control circuit 26 comprises a flip-flop 28 which is set and reset by the contact output of the limit switch, and analog switches 29 and 30 which are controlled by the flip-flop. First, for example, if the sample table is at the low limit position, the low limit switch 24 is open,
The contact output LLMT-P allows flip-flop 2
8 is set, the Q output becomes 1, the analog switch 29 becomes conductive, and the rising speed command voltage V _r is output. At this time, when the analog switch 27 is selected to the C side in FIG. 1, the speed command voltage V _r in the rising direction from the reciprocating operation circuit 26 is amplified by the second amplifier 20 and drives the servo motor 21. The sample table 12 is moved in the ascending direction. At this time, in FIG. 2, since the Q output of the flip-flop 28 is kept at 1, the sample table continues to move upward, and finally the adaptive switch 25 operates from closed to open. Then, since the flip-flop 28 is reset and the Q output changes to 1, the analog switch 30 becomes conductive instead of the analog switch 29, and the speed command voltage −V _{f in the} descending direction is output to reverse the sample table in the descending direction. To move. In this manner, the sample table can be repeatedly reciprocated between the upper limit position and the lower limit position.

Returning to FIG. 1 again, the actual driving method will be described. First,
Analog switch 2 by signal from computer 17
7 is selected on the B side, the sample stage is moved to the low limit position, and the sample is mounted. Next, the analog switch 27 is selected to the A side by the signal from the computer 17,
As described in the example of the conventional apparatus in the figure, the distance detection by the air micrometer and the servo mechanism control the positioning of the sample surface at the reference focal position, and the predetermined processing such as exposure is performed. After the processing is completed, the analog switch 27 is again selected to the B side by the signal from the computer 17, the sample table is lowered to the low limit position, and the processed sample is removed. At this time, in the state where the sample is not mounted on the sample table 12, the analog switch 27 is selected to the C side by the signal from the computer 17, and the sample table 12 is subjected to the self-cleaning operation as described above, and the sample table 12 is set to the preset limit. Position and low limit position repeatedly reciprocating operation,
By moving the sample stage to a range higher than the standard focus position that is not normally used, the sliding position between the nut 16 and the feed screw 15 and the guide surface 14, etc. is stored at a position corresponding to the standard focus position. Sweeping grinding debris, dust, etc. out of the reference focus position to prevent an increase in frictional force at the reference focus position. After performing the self-cleaning operation in this way, the analog switch 27 is selected to the B side by the signal from the computer 17, the sample table is lowered to the low limit position, and the next sample is mounted. Repeat.

The self-cleaning operation described here does not have to be performed every time the sample is replaced, but may be performed at an appropriate frequency, for example, only at the start of work every day.

Next, it will be described with reference to FIG. 3 that high positioning accuracy can be stably realized by this self-cleaning operation.

FIG. 3 (a) shows the location dependence of the friction torque τ _F converted into the servo motor shaft. When the sample table moves only within the conventional normal operating range, the friction torque τ _F locally increases in the vicinity of the low limit position Z = Z _L and the reference focus position Z = Z _BF , which are both ends of the sample table. When the servo characteristic is expressed as in b), the dead zone at the reference focus position is δ _Z corresponding to the friction torques τ _BF and -τ _BF . here,
By performing the self-cleaning operation between the low limit position Z = Z _L and the upper limit position Z = Z _u , the friction torque at the reference focus position decreases like τ _BF ′, −τ _BF ′, and correspondingly the reference torque is reduced. The dead zone at the focal position is reduced to δ _z ′, and deterioration of the positioning accuracy is prevented.

The effect of reducing the friction torque by the self-cleaning operation has been confirmed by experiments by the present inventors. According to it, although the peak of the friction torque about twice as large as that of the other parts appeared in the range of several tens of μm around the reference focus position, the reference focus position was changed by performing the self-cleaning operation. The peak of friction torque in the vicinity almost disappeared, and there was almost no place dependence.

In the embodiment described above, an air micrometer type distance detector is used to detect the position of the sample surface, but in addition to this, an optical reflection type distance detector is used to set the sample surface to the reference focus. It goes without saying that the present invention can also be applied to an apparatus of a type in which positioning control is performed.

FIG. 4 shows another embodiment of the present invention, which is different from FIG. 1 in that the sample stage 12 is driven by the linear servomotor 44. Linear servo motor 44 in the figure
Is incorporated in the slider 41, and applies a horizontal driving force to the field magnet 46. The slider 41 can move horizontally on the guide surface 43, and the sample table 12 supported by the leaf spring 13 can be moved in the vertical direction via the guide surface 42. Also,
The speed generator 45 is incorporated in the slider 41 together with the linear servo motor 44, and is used as a speed detector for forming a speed control system together with the second amplifier 20 and the linear servo motor 44.

In this case as well, as in the case of the embodiment shown in FIG. 1, the repetitive operation, that is, the self-cleaning operation is performed between the upper limit position and the lower limit position, and the sample table is moved to a range higher than the reference focus position which is not normally used. By moving the guide surface 42 and the guide surface 43, the grinding scraps and dust accumulated at the reference focus position are swept out to the outside of the reference focus position to prevent an increase in the frictional force at the reference focus position. It is possible to prevent deterioration of positioning accuracy.

〔The invention's effect〕

According to the present invention, in the automatic focusing apparatus, it is possible to prevent the frictional force from locally increasing at the reference focus position by performing the self-cleaning operation of the sample table beyond the normal operation range, so that it is possible to perform the long-term This has the effect of stably achieving high positioning accuracy.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an embodiment of the present invention, FIG. 2 is a concrete circuit diagram as an embodiment of the reciprocating operation control circuit of FIG. 1, and FIG. 3 is a diagram for explaining the effect of the present invention. FIG. 4 is a conceptual diagram of an essential part of another embodiment of the present invention, FIG. 5 is a diagram showing an example of a conventional device, and FIG. 6 is a diagram explaining problems of the conventional device. 1 ... Lens barrel, 2 ... Reduction lens, 3, 8 ... Air supply hole,
4 ... Detector, 5, 10 ... Measuring hole, 6 ... Sample, 7 ... Reference device, 9 ... Reference plate, 11 ... Differential pressure converter, 12 ... Sample stand, 1
3 ... Leaf spring, 14 ... Guide surface, 15 ... Feed screw, 16 ... Nut, 19 ... First amplifier, 20 ... Second amplifier, 21
... Servo motor, 23 ... Descent operation control circuit, 24 ... Low-limit switch, 25 ... At-limit switch, 2
6 ... Reciprocating operation control circuit, 27, 31 ... Analog switch, 28 ... Flip flop, 29, 30 ... Analog switch, 41 ... Slider, 42, 43 ... Guide surface, 44 ...
Linear servo motor, 45 ... Speed generator, 46 ... Field magnet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01L 21/027 7316-2K G02B 7/11 M 7352-4M H01L 21/30 311 N (56) Reference References JP-A-53-35324 (JP, A) JP-A-52-76590 (JP, A) JP-A-57-196219 (JP, A)

Claims (2)

[Claims] 1. A position of a sample mounted on a sample table is detected,
Based on the detected sample position signal, the sample stage is driven in a focusing direction to position the sample surface at a reference focus position. Means for stopping the operation of positioning at the focus position and reciprocating operation control means for repeatedly reciprocating the sample table between both ends of the movable range including the reference focus position of the sample table while the positioning operation is stopped. An automatic focus adjustment device characterized by being provided. 2. The reciprocating operation control means includes limit switches provided at both ends of the movable range, flip-flops set and reset by opening / closing operations of the limit switches, and analogs controlled by outputs of the flip-flops. An automatic focusing device according to claim 1, further comprising a switch.