JPH0574212B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a positioning device that uses a two-split light-receiving element and performs positioning so that the tolerance for deviation calculated from the output difference between the two is constant. In particular, the present invention relates to a positioning control device suitable for automatic focus control and the like.

[Background of the invention]

In positioning techniques such as automatic focusing, a two-split light receiving element is often used. The light-receiving surface of a two-part light-receiving element generally has a shape as shown in FIG. 1, and the entire light-receiving surface 1 is divided into two parts 1a and 1b so that each part has approximately the same area. Since the amount of light received by each of the light receiving elements 1a and 1b is in the same relationship as the output, the light 3 with equal illuminance as shown in FIG.
When the light beam is incident as a beam so as to be divided into two equal parts at the boundary 4 of 1b, signals (voltages or currents) of the same level appear at the respective outputs 2a and 2b. Therefore, the outputs 2a and 2b of the light receiving elements 1a and 1b receive reflected light or transmitted light from the object.
Positioning is facilitated by determining that the position of the object whose output difference is within a predetermined range is the position of the object to be located.

FIG. 2 is an example of an automatic focusing system using a two-split light receiving element in a semiconductor exposure apparatus. A light beam 3 is formed from the light from the light source 5 through a slit 6, and the slit-shaped light beam 3 is projected as an image onto a wafer 9 via an imaging lens 7 and a reflecting mirror 8, and this reflected light is again passed through a reflecting mirror 10, An image is formed on the light receiving surface of the two-split light receiving element 1 via the imaging lens 11 and the magnifying lens 12. Here, the wafer 9 is connected to a pattern exposure optical system (for example, an optical system of a reduction projection exposure apparatus) 13.
If the setting is made so that the beam 3 is focused on the center of the two-split light receiving element 1 as shown in FIG. 3a when the wafer 9 is at the focused position, The light beam 3 travels in the direction indicated by the dotted line and is projected at a position offset from the center boundary 4 of the two-split light receiving element 1 as shown in FIG. 3b. On the other hand, although not shown in FIG. 2, when the wafer 9 moves upward from the focused position, the light beam 3 moves in the opposite direction to when it moves downward, as shown in FIG. 3c. , the image is formed shifted from the center boundary 4 of the two-split light-receiving element 1. Now, if the electrical outputs obtained from the two divided individual elements 1a and 1b of the two-divided light-receiving element 1 are respectively V _a and V _b , then at the focused point, V _a = V _b
(Fig. 3a), when the wafer 9 is shifted downward from the in-focus position, V _b > V _a (Fig. 3 b), and when it is shifted upward, V _a > V _b (Fig. 3). c). Based on this relationship, the control system includes a differential amplifier 14, a dead band circuit 15, and a wafer 9 as shown in FIG.
It consists of a servo amplifier 16 for driving a motor 19 connected to a mounted Z stage 20. The differential amplifier 14 has an amplification degree k, and the amplification degree k is applied to the difference (V _a −V _b ) between the outputs of the two-split photodetector 1.
A signal V _t =k (V _a −V _b ) is output. The dead band circuit 15 provides a dead band to the motor 19. For example, when the wafer 9 is set at the upper and lower limits of the target accuracy of automatic focusing, the output value appearing at the output V _t of the differential amplifier 14 is input to the input terminal 1.
It works by setting from 7 and 18. Now, assuming that the output of the dead band circuit 15 is _Vs , the relationship between _Vs and the vertical position of the wafer 9 is as shown in FIG. 4a. The servo amplifier 16 receives the output value _Vs of the dead band circuit 15, applies this as speed information to the motor 19, and drives the z stage 20 to move the wafer 9.
to the in-focus position. The output V _s of the dead zone circuit 15 becomes smaller as it moves toward the in-focus position, and when it reaches the dead zone V _d to V _u , the motor 19 stops, the z stage 20 becomes stable, and the wafer 9 is positioned within the target accuracy. It will be done.

In this way, the dead band circuit 15 is provided to provide stability to the z stage 20, but since this dead band has conventionally been fixed, it is susceptible to deterioration of the light source 5 and differences in reflectance of the object to be positioned. As a result, the correspondence between the dead zone and the target accuracy is lost, which has a negative effect on accuracy. That is, as the precision of the light source 5 increases or the reflectance of the object increases, the slope of the characteristic line becomes steeper, as shown in Figure 4b, and when the dead zone V _d to _{V u} is fixed (shaded area) , the actual attainment accuracy is narrower than the target accuracy, making positioning difficult. On the other hand, if the illuminance of the light source 5 decreases or the reflectance of the object decreases, the slope of the characteristic line becomes low, as shown in _{FIG .} )
, the actual attainment accuracy is set lower than the target accuracy, and the positioning accuracy becomes poor.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a highly stable positioning control device that is not affected by variations in illuminance or changes in reflectance of a light source.

[Summary of the invention]

In order to achieve the above object, the positioning control device according to the present invention receives reflected light or transmitted light from an object with a two-split light receiving element, and places the above light at a fixed position where the output difference between the elements shows a certain value. The alignment device for positioning an object further includes dead zone input means for setting a dead zone matching the required accuracy in the vicinity of the constant value of the output difference between the elements;
an addition means for calculating the output sum of the divided light receiving elements; a storage means for storing the output of the addition means; a division means for dividing the current addition output by the addition output stored in the storage means; The gist is to include a multiplier that multiplies the output by the dead zone and uses the result as a new dead zone, and an electric motor that uses the output difference between the elements including the new dead zone as speed information. That is, the present invention quantitatively derives the rate of change in the illumination rate or reflectance of the light source from the total amount of light beam projected onto the two-split light receiving element, and uses this rate of change as the upper and lower limits of the dead zone that have already been set. The objective is to obtain stable positioning control by providing feedback to the user and always forming an appropriate dead zone.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 5 and 6. Figure 5 shows an example in which a DC motor is used to drive the stage, and Figure 6 shows an example in which a pulse motor is used. Compared to Figure 5, only the replacement of necessary components is shown in Figure 6. ing. Both Fig. 5 and Fig. 6 are written as a method of detecting reflected light from an object, and the optical system that images the light beam onto the two-split light receiving element is the same as that shown in Fig. 2, and in this example, It has been omitted.

First, a first embodiment will be described with reference to FIG. In FIG. 5, reference numeral 3 denotes a light beam formed by the optical system, which is reflected by an object 21 and projected onto the two-split light-receiving element 1. 22 is an adder that adds the electric signals 2a and 2b output from the individual elements 1a and 1b of the two-split light receiving element 1; 23 is a storage circuit that stores the output of the adder 22 at the beginning of the operation of the present invention; 24; is a divider that divides the sum signal obtained from the adder 22 by the sum signal stored in the storage circuit 23, and 25 and 26 are the upper limit 17 of the dead zone set at the start of the operation of the present invention.
and a multiplication circuit that multiplies the lower limit 18 by the output of the divider 24 and makes the multiplied outputs new upper and lower limits of the dead band circuit 15, 14 and 16 are differential amplifiers and servo amplifiers, respectively, 19 drives the z stage 20 It is a DC motor.

The positioning control device according to the present invention operates as follows. At the target position of the object 21, the luminous flux 3
The optical system or the two-divided light-receiving element 1 is set so that the light-receiving element 1 is equally divided by the individual light-receiving elements 1a and 1b. With this setting, the two-split light receiving element outputs 1a and 1b in response to changes in the position of the object 21
The change in is as explained in FIG. 3 above.
First, for the first object 21, position the object 21 at the upper and lower limit positions of the target accuracy, read the output from the differential amplifier 14 obtained in each case, and use the smaller voltages V _u and V _d as the reference. Terminal 1 is connected to multipliers 25 and 26 as the dead band width.
Set from 7 and 18. When this preparatory work is completed, the set signal 27 is given, and the sum (V _a +V _b ) of the outputs of the two-split light receiving element 1 obtained by the adder 22 is
is stored in the memory circuit 23. Since the output (V _a +V _b ) of the adder 22 indicates the illuminance (light amount) of the entire luminous flux 3 incident on the two-split light receiving element 1, there is no change in the illuminance of the light source if the object 21 is the same. and as long as the light beam 3 does not cross the light-receiving surface of the two-split light-receiving element 1, it remains constant. Therefore, within the operating range of the z stage 20, the light beam 3 is split into two parts by the light receiving element 1.
If the structure is such that it does not overflow, the addition output (V _a +V _b ) stored in the storage circuit 23 by the set signal 27 will be equal to the dead band width V _d set almost at the same time.
It becomes a reference voltage opposite to ~V _u . Let this reference voltage be _Vr . Considering the case where the servo is turned on by the positioning start signal 28 in the object 21 when the reference dead zone V _d to V _u and the reference voltage V _r are calculated, the output from the adder 22 as long as there is no illuminance fluctuation in the light source. Since the value is the same as the reference voltage V _r stored in the storage circuit 23, the divider 24
The division result is 1, and the multipliers 25 and 2
The results obtained by multiplying the reference dead zones V _u and V _d in step 6 are directly input to the dead zone circuit 15 as actual dead zone values V _u and V _d . This dead zone is a dead zone set for a specific object 21, and is based on the vertical position of the object 21 and the dead zone circuit 1.
The output V _s of 5 forms a characteristic as shown in FIG. 4a.
The subsequent operation is similar to the conventional example shown in FIG. 2, and the DC motor 19 receives commands from the dead band circuit 15.
Drive the z stage 20 and move the object 21 through the dead zone V _d
~ V _u toward the target position.

On the other hand, if we consider changes in the illuminance of the light source or changes in the reflectance of light by objects, these changes nothing but changes in the illuminance of the light beam 3 as a whole. Now, when there is a change in illuminance in the luminous flux 3 due to the combination of the above causes, the area of the luminous flux incident on the two-split light receiving element 1 remains unchanged, and the electrical output is proportional to the illuminance, so calculations are always performed. The current illuminance (V _{a +}
The rate of change R=(V _a +V _b )/V _{r of} V _{b )} can be obtained. The rate of change in illuminance R determined by the divider 24
are then input to multipliers 25 and 26, and multipliers 25 and 26 calculate RV _u and RV _d , respectively, for the reference dead zone values V _u and V _d that have already been determined.
The calculation result is input to the dead band circuit 15 as an actual dead band value. This operation is
It is only necessary to correct the mismatch between the target accuracy and the dead zone caused by a change in illuminance by adjusting or subtracting the dead zone by the rate of change in illuminance. That _is , _{if FIG .} By finding the rate of change R of illuminance (that is, the rate of change of the slope of the straight line) from the output sum (V _a + V _b ) and multiplying this rate of change by the standard dead band values V _u and V _d , the target accuracy and characteristic straight line can be determined. Correct the dead zone at the intersection to obtain a dead zone that meets the target accuracy. This is the fourth
To explain using FIGS. b and c, for high illuminance, the reference dead zones V _d to _{V u} are widened so that the target accuracy and the characteristic straight line intersect. Forming a new dead zone V _q ~ V _p ,
For low illuminance, the reference dead zones V _d to _{V u} are narrowed to form new dead zones V _h to V _g that match the target accuracy.

In FIG. 5, since the memory circuit 23 stores analog values, a sample-and-hold circuit may be used for short-term storage, and an A/D converter that converts the input into digital data for long-term storage. D/A converts the digital value to analog
It can be configured with a converter. In addition, the DC motor 19
Even if the servo amplifier 16 and servo amplifier 16 are replaced with components as shown in FIG. 6, the operation according to the present invention will still work. That is, the V/F converter 29 is connected to the dead band circuit 1.
The polarity determination circuit 30 generates a clock pulse with a frequency proportional to the output V _s of the dead band circuit 1.
5 and _outputs the direction in which the Z stage 20 should move. Inverting circuit 31 and
The AND gates 32 and 33 receive instructions from the polarity determination circuit 30, and for example, when the signal V _s is positive polarity,
With the AND gate 32 open and the AND gate closed, the output of the V/F converter 19 is inputted from the AND gate 32 to the reverse rotation input of the stepping motor 34, and the Z stage 20 is directed toward the target position. When the signal V _s has negative polarity, the operation is opposite to the above, the AND gate 33 is opened, the output pulse of the V/F converter 29 is guided to the positive rotation input of the stepping motor 34, and the Z stage 20
to the target position in the opposite direction from before. Object 21
When the voltage reaches the dead band, the polarity determination circuit 30 outputs V _s
=0 is detected, AND gates 32 and 33 are closed, and stepping motor 34 is stopped. Furthermore, although the embodiments of the present invention discuss a method of detecting reflected light from an object and positioning the object in a fixed position, it may also be applied to a device such as a component insertion machine that detects the position of a hole in a board using transmitted light. It goes without saying that the present invention is applicable.

As described above, according to the present invention, stable positioning control with respect to target accuracy can be realized.

〔Effect of the invention〕

As described above, according to the present invention, a dead zone that matches the target accuracy is always formed in response to changes in the illuminance of the light source or changes in the light reflectance of the object to be positioned, resulting in highly stable positioning. A control device can be realized.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the positional relationship between a two-split light receiving element and incident light, Fig. 2 is a block diagram showing the configuration of a positioning device using a conventional two-split light receiving element, and Fig. 3a
~c are relationship diagrams between the two-split light-receiving element and incident light caused by changes in the position of the object, Figures 4a-c are characteristic diagrams of the differential output of the two-split light-receiving element including a dead zone with respect to the position of the object, and Figure 5 is a block diagram showing the configuration of a positioning control device according to an embodiment of the present invention;
FIG. 6 is a block diagram showing only the constituent elements that are different from FIG. 5 in a positioning device according to another embodiment. 1... 2-split light receiving element, 14... Differential amplifier, 15
... Dead band circuit, 16... Servo amplifier, 17... Reference value for upper limit of dead band, 18... Reference value for lower limit of dead band, 1
9... DC motor, 20... Z stage, 21... Object, 22... Adder, 23... Memory circuit, 24... Divider, 25, 26... Multiplier, 29... V/F converter,
30... Polarity determination circuit, 32, 33... AND gate, 34... Stepping motor.

Claims (1)

[Claims] 1 In an alignment device that receives reflected light or transmitted light from an object with a two-split light receiving element, and positions the object at a fixed position where the output difference between the elements is a certain value, the output between the elements is further adjusted. dead zone input means for setting a dead zone matching the required accuracy in the vicinity of the constant value of the difference; addition means for calculating the sum of the outputs of the two-split light receiving elements; storage means for storing the output of the addition means; a division means for dividing the current addition output by the addition output stored in the means; a multiplication means for multiplying the output of the division means by the dead zone and using the result as a new dead zone; A positioning control device comprising an electric motor that uses an output difference between elements as speed information.