JPS5812563B2 - Positional deviation detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positional deviation detection device, and more particularly to a positional deviation detection device that can be applied to a position detection unit such as an automatic focusing device.

Conventionally, the positional deviation detection device used as the position detection part of an automatic focusing device is an air micro type that uses air pressure, a type that uses changes in capacitance, or an optical type that is used for slide projectors. was known.

Of these, the former two have the disadvantage that the dynamic range is limited because the sensitivity is extremely reduced as the amount of displacement increases.

In comparison, the optical components used for the slide projector have fewer problems with dynamic range.

However, in the case of such optical devices, the light source is an incoherent light source such as a white light bulb, and the light from this incoherent light source is Since the film is irradiated with light and the reflected light is received by a light receiver divided into two, there is a problem in that a sufficient S/N ratio cannot be obtained when detecting minute displacements.

Therefore, especially when observing IC, LSI mask plates, wafers, etc. with a microscope, if you want to attach it to the microscope and automatically detect the amount of movement of the focal point, the S/N is extremely poor with the above-mentioned optical position detection means. It is impossible to put it into practical use.

The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and it is an object of the present invention to provide a position detection device that can detect positional deviation with an accuracy of micron order or less.

The present invention widens the dynamic range by adopting an optical system similar in principle to the conventional optical position detection means described above, and uses a laser light source as a light source.
Moreover, by making the light beam flat and irradiating this flat light beam onto a slit having an opening of an appropriate shape, the S/N ratio is improved, thereby providing a position detection device that enables highly sensitive position detection. It is something to do.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the positional deviation detection device of the present invention.

In this figure, 1 is a laser light source.

The light beam emitted from this laser light source 1 is shaped to some extent by a cylindrical lens 2, and is incident on a sample surface 3 at an incident angle θ.

When θ is set to about 5°, the influence of the surface roughness of the sample surface 3 is reduced, and position detection with good S/N is possible for any sample.

The light beam specularly reflected by the sample surface 3 is further shaped by a spherical lens 4 and a cylindrical lens 6.

At this time, a slit 5 having a pinhole-shaped opening is placed between the spherical lens 4 and the cylindrical lens 6.

This slit 5 is used to increase the S/N of the output signal by excluding light other than the specularly reflected component from the sample surface 3.

The light beam passing through the cylindrical lens 6 becomes a very thin linear flat light beam and enters a slit 7 having a T-shaped opening.

In the device of the present invention, the optical system shown in FIG. 1 (especially the cylindrical lens 6) for creating a flat light beam plays an important role,
The present invention utilizes the flat light beam created by this optical system,
This is to detect the position of the sample surface 3 with high precision.

An example of the positional relationship of each element of the optical system described above and how the laser beam changes will be explained using FIGS. 2a and 2b.

FIG. 2a is shown with respect to the X-axis direction perpendicular to the optical axis number, and FIG. 2b is shown with respect to the Y-axis direction perpendicular to the optical axis and the X-axis.

In this arrangement, the positions of the lenses 2, 4, and 6 are determined so as to satisfy the following conditions as much as possible.

(a) The lenses 2 and 4 constrict the light beam near the slit 5.

(b) In the x-axis direction, the light beam is focused on the slit T.

(c) In the y-axis direction, the light beam is made to spread as much as possible on the slit 7.

(a) The displacement of the light beam on the slit 7 due to the displacement of the sample surface 3 is made as large as possible.

If the focal length of each lens and the spacing between each element are determined to satisfy all these conditions, for example, cylindrical lens 2
The focal length fx in the X-axis direction is 350 mm, the focal length fY in the y-axis direction is infinite, and the focal length of the spherical lens 4 is 5 mm.
0 mm, the focal length fx in the X-axis direction of the cylindrical lens 6 is 150ζ, the focal length fy in the y-axis direction is infinite, the distance between the cylindrical lens 2 and the sample surface 3 is 220 mm, and the distance between the sample surface 3 and the spherical lens 4 is 108 mm. , the distance between the cylindrical lens 6 and the slit 7 is 150 mm, and the slit 5 is connected to the cylindrical lens 2.
and the spherical lens 4 (this combined focal length is approximately equal to the focal length of the spherical lens 4 because fx of the cylindrical lens 2 is long).

However, in FIGS. 2a and 2b, the state of reflection of the laser beam on the sample surface 3 is not shown to simplify the explanation, but the light beam on the left side of the sample surface 3 is the incident light beam on the sample surface 3. This means that the light beam on the right side of the figure is the reflected light beam.

Of course, the focal length of each lens and the spacing between each element described above may be appropriately determined when creating the optical system, and are not limited to the above values.

In this way, each lens 2, 4.6, sample surface 3, and slit 5
, 7, a very thin linear flat light beam is incident on the surface of the slit 7 having a T-shaped opening.

The cylindrical lens 2 is used to spread the light flux on the sample surface 3 to some extent to produce an averaging effect on the sample surface, and also to control the imaging state of the light flux on the slit 7.

FIG. 3 is a diagram showing the shape of the slit 7 and the state of incidence of the laser beam (flat beam) into the slit 7. FIG.

As shown in this figure, the slit 7 is provided with a T-shaped opening that is thick in the horizontal direction and thin in the vertical direction.

In this figure, a straight line 31 indicates the shape of the laser beam incident on the surface of this slit 7.

That is, the flat light beam obtained by the optical system shown in FIG. 2 enters the surface of the slit 7 in the shape shown by a straight line 31.

Next, the case where the sample surface 3 moves downward in the drawing in FIG. 1 will be explained using FIGS. 4a and 4b.

The movement of the sample surface 3 means that the reflected light beam from the sample surface 3 is incident on the spherical lens 4 at a shifted position in the X direction.

The reflected light beam from the sample surface 3 that has entered the spherical lens 4 passes through each element and reaches the slit 7, as shown in FIGS. 4a and 4b.

FIG. 5 is a diagram showing the state of incidence of the flat light beam into the slit 7 at that time.As shown in this figure, the straight line 51 indicating the flat light beam is located in the thick part of the opening that extends in the horizontal direction. ing.

Here, the explanation will be continued using FIG. 1 again.

As described above, when the sample surface 3 moves up and down in the direction of the arrow 8, the flat light beam after passing through the cylindrical lens 6 moves up and down the surface of the slit 7 accordingly.

If this flat light beam hits the narrow aperture extending in the vertical direction in the slit 7, the amount of light passing through the slit 1 will be small, and if the flat light beam hits the thick aperture extending in the horizontal direction in the slit γ, the light will pass through the slit 1. 7, the amount of light passing through increases.

These passing lights are detected by a light receiver 9 placed opposite to the back surface of the slit 7, and converted into electrical signals.

The light receiver 9 is composed of a photodiode such as a PIN diode.

FIG. 6 is a diagram showing the relationship between the amount of movement of the sample surface 3 and the output of the light receiver 9.

In this figure, the horizontal axis indicates the amount of movement (△X) of the sample surface 3,
The vertical axis indicates the voltage conversion value of the output signal of the photoreceiver 9.

As can be seen from this figure, when ΔX is between 550 and 690 μm, the output of the photodetector 9 changes sharply, and the linearity is also quite good.

Therefore, for example, if △X is 620 μm (the output of the optical receiver at that time is 17 mV) as a reference, if a displacement (positional deviation) of ±70 μm occurs from this reference position, the output of the optical receiver 9 will be ±11mV centered on 17mV
Changes almost linearly.

Considering the sensitivity S of positional deviation at this time, it becomes as follows, and it becomes possible to sufficiently detect positional deviation on the order of microns.

Here, the linearity of the output signal shown in FIG.
depends on the shape of the opening.

In the embodiment described above, a case was shown in which a slit having a T-shaped opening was used, but as a result of experiments, it was found that good linearity characteristics could be obtained with other shapes as well.

Figure 7a2b shows examples of the shapes of these slits. Figure 1a shows a slit with a rectangular opening that is long in the horizontal direction (y direction), and Figure 7b shows a slit with a semicircular opening. .

When these slits are used, the characteristics of displacement △X vs. output voltage shown in Fig. 6 are
(in the range of approximately 550 to 690), the slope becomes steeper, and deviation detection can be performed with higher sensitivity.

Further, FIG. 7C is a diagram showing a slit having an opening portion including a hyperbolic shape in a part thereof.

A slit having such a shape is effective when the output of the light receiver 9 is desired to be a logarithmic output, and experiments have confirmed that even when this slit is used, the sensitivity is on the order of microns.

In this way, the shape of the opening of the slit 7 may be determined as appropriate depending on the application.

Next, an example of an electronic circuit for actually detecting the amount of deviation of the sample surface from a predetermined position using the output signal of the light emitter 9 will be described.

FIG. 8 is a block diagram showing the configuration of this electronic circuit, in which the output signal of the light emitter 9 is amplified by an amplifier 91 and then applied to one input terminal 93 of a differential amplifier 92.

Further, the other input terminal 94 of the differential amplifier 92 is connected to the sample 3.
A reference voltage corresponding to the set position is applied.

Therefore, when the input signal deviates from the reference voltage value, the differential amplifier 92 generates an output proportional to the amount of deviation.・Also, it is possible to detect the amount of deviation from the set position.

As described in detail above, according to the present invention, the laser light source 1
The beam from the sample surface 3 is guided to the sample surface 3 at an appropriate angle of incidence, the reflected beam from the sample surface 3 is made into a flat beam, and the amount of light passing through the flat beam changes rapidly depending on the irradiation position of the flat beam. A slit 7 including a shaped opening is provided, and this slit}7
It receives the passing light, converts it into an electrical signal, and detects the amount of deviation of the sample surface 3 from the set position based on the converted output signal; therefore, it is possible to detect displacements on the micron order extremely accurately. can.

Moreover, since the electric signal obtained by the light receiver 9 has an extremely high S/N ratio due to the flat light beam, the positional deviation of the sample surface 3 can be detected with extremely high sensitivity.

In the embodiment described above, the light beam from the laser light source 1 is made into a flat light beam by the subsequent optical system, and this flat beam is guided to the light receiver.

However, if a semiconductor laser is used as a laser light source,
Since the output light beam has a flat shape, a part of the optical system of the previously described embodiment can be simplified.

The positional deviation detection device according to the present invention has a high S/N of 1 μm.
It is possible to reliably detect even slight positional deviations, especially for IC, L.
This is extremely effective when it is desired to detect the amount of movement of a focal point when observing a mask plate such as SI, a wafer, etc. with a microscope, but it can also be applied to various other types of minute position fluctuation reading devices.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the positional deviation detection device of the present invention, FIGS. The figures show the shape of the slit used in the apparatus of the present invention and the state of incidence of the laser beam into the slit, Figure 4 ayb corresponds to Figure 2 ayb when the sample surface moves, and Figure 5 Figure 6 shows the incident state of the laser beam into the slit when the sample surface moves, Figure 6 shows the relationship between the movement of the sample surface and the output of the photodetector, and Figure 7 abyc is based on the present invention. FIG. 8 is a block diagram showing an example of an electric circuit for detecting positional deviation. 1... Laser light source, 2, 6... Cylindrical lens, 3... Sample surface, 4... Spherical lens, 5... Slit, 7... Slit, 9... Light receiver, 91... Amplifier, 92... Differential amplifier, 93...meter.

Claims (1)

[Scope of Claims] 1. A laser light source, a means for guiding a laser beam from the laser light source to a sample surface at a predetermined incident angle, and a means for converting a reflected beam of laser light from the sample surface into a flat beam. a first slit for changing the amount of light passing through the flat light beam obtained by this optical system according to the positional shift of the sample surface; 1. A positional deviation detection device comprising: a light receiver for obtaining a corresponding electric signal; and means for detecting the amount of positional deviation of the sample surface based on the output signal of the light receiver. 2. The positional deviation detection device according to claim 1, wherein the means for guiding the laser beam to the sample surface at a predetermined angle of incidence includes a first cylindrical lens. 3 The optical system for converting the reflected light flux from the sample surface into a flat light flux includes a spherical lens and a second slit having a pinhole-shaped opening placed at a position approximately equal to the focal length of the spherical lens. 2. The positional deviation detection device according to claim 1, further comprising: a second cylindrical lens that receives the light passing through the slit. 4. The positional deviation detection device according to claim 1, wherein the first slit is provided with at least an opening parallel to the longitudinal direction of the flat light beam. 5. The positional deviation detection device according to claim 1, wherein the means for detecting the amount of positional deviation includes a differential amplifier that compares the output signal of the light receiver with a reference signal.