JPH03113309A - Position detector - Google Patents

Abstract

PURPOSE:To measure mean height in a certain area on the surface of a sample with high accuracy by projecting an image of a grating with the certain area on the sample surface and detecting the thickness phase change of the reflected image of the grating from the sample surface. CONSTITUTION:An exciter 9 rotates and vibrates a glass plate 8 at a constant frequency and the angle of incidence on the glass plate 8 is varied to vary the angle of transmitted light, thereby finely vibrating the grating image of the grating 1 formed on a grating 6. Namely, the spatial phase difference between the grating image of the grating 1 and the grating 6 is modulated with the vibration frequency of the glass plate 8 and the modulated light is received by a photodetector 7. Then, the output of an oscillator 10 which drives the exciter 9 is used as a reference signal to detect the phase of the output of the detector 7 by a lock-in amplifier 11, thereby obtaining an output signal indicating the positional deviation of the surface 3 from the amplifier 11. With this signal, the height displacement of the surface 3 is highly accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a position detection device, and particularly to a non-contact type position detection device that can be applied to detect the position of a wafer surface in a semiconductor exposure device or inspection device.

[Conventional technology]

As a conventional technique, for example, as shown in Japanese Unexamined Patent Application Publication No. 56-2632, there is a method in which the wafer surface is irradiated with light from an oblique direction and the position of the wafer surface is detected from the position of the reflected light. be.

A conventional position detection device includes a means for condensing light emitted from a light source onto a sample surface, and a means for focusing reflected light from the sample surface on a detector.

Next, a conventional position detection device will be described in detail with reference to the drawings.

FIG. 4 is a block diagram showing an example of a conventional position detection device.

The position detection device shown in FIG. 4 includes a light source 2, a lens 12 that focuses light emitted from the light source 2 onto a sample surface 3, a lens 13 that focuses reflected light from the sample surface 3, and a lens 13 that focuses light emitted from the light source 2 onto a sample surface 3. and a detector 14 disposed on the imaging plane of the image plane. As this detector 14, a two-split detector, a semiconductor device detection element (hereinafter referred to as PSD), or the like is used, and the position of the beam focused by the lens 13 can be detected.

When the height of the sample surface 3 changes, the spot position on the sample surface 3 moves, and the beam position on the detector 14 changes accordingly. That is, by measuring the beam position on the detector 14, the height of the sample surface 3 can be detected.

When the incident angle of the beam is θ, the positional deviation ΔX of the beam on the detector 14 when the sample surface changes by Δh is expressed by the following equation.

Δx = 2 cosθ0Δh0n n: Magnification of lens 13 Two-split detector or PSD used as detector 14
etc. outputs two signals a and b, and by calculating the difference between these two signals, the position of the beam irradiating the detector 14 can be determined.

However, if the intensity of the beam incident on the detector 14 fluctuates due to changes in the reflectance of the sample surface 30, surface conditions, etc., errors occur, making it impossible to accurately measure the height of the sample surface 3.

Therefore, in the conventional position detecting device shown in FIG. 4, the outputs a and b of the detector 14 are subtracted by a subtracter 15 and added by an adder 16. Then, the output (a − b) of the subtracter 15 is divided by the divider 17 into the output (a − b) of the adder 16 (
By dividing by a+b) and normalizing, a positional deviation signal that is not affected by changes in the intensity of the beam incident on the detector 14 is obtained.

Conventional position detection devices such as those described above are often used to measure the height of the wafer surface in order to match the focal point of the projection lens to the wafer surface in reduction projection type semiconductor exposure equipment. The exposure area is usually about 15 mm x 15 mm, and in order to accurately focus, it is necessary to know the average height of the wafer surface within the exposure area.This is because the wafer has warps and irregularities due to processing. This is because the height within the exposure area is not necessarily constant.

The conventional position detection device shown in FIG. 4 focuses light into a spot and detects changes in the spot position.
Although the height at the spot position on the sample surface 3 can be measured, the average height cannot be measured. If the spot diameter on the sample surface 3 is increased, the average height can be determined accordingly, but the spot diameter formed on the detector 14 also becomes larger, and the resolution of position detection decreases.

Therefore, as a way to more accurately determine the average height of the wafer surface, it is possible to install a plurality of position detection devices as shown in Figure 4 to determine the height of the wafer surface at multiple points. However, the optical system increases and the overall device becomes complex.

[Problem to be solved by the invention]

The conventional position detection device described above can only measure the height at one point on the sample surface because it focuses the beam on the sample surface in the form of a spot. There was a drawback that the height could not be detected accurately. In addition, in order to eliminate this drawback, multiple position detection devices with the same configuration are required, and semiconductor exposure equipment and inspection equipment that use conventional position detection devices have the disadvantage of becoming complicated and expensive. there were.

[Means to solve the problem]

The position detection device of the present invention includes a light source, a projection optical system that forms a first grating image from a first grating projected on the light source onto a sample surface from an oblique direction, and a projection optical system that forms a first grating image projected on the light source on a sample surface, a light-receiving optical system that forms a second grating image by vibrating the second grating image; a modulator that modulates the passing light that has passed through the second grating and outputs a reference signal; a detector that receives the modulated passing light, performs photoelectric conversion and outputs a modulated signal; The modulated signal is configured to include means for phase detecting the modulated signal.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The position detection device shown in FIG.
a light source 2 for projecting a lattice image of the first lattice 1 onto a sample surface 3; a second lattice 6 for forming a lattice image of the first lattice 1 on a sample surface 3; and a photodetector 7 for detecting the amount of light passing through the second lattice 6. , a parallel plane glass plate 8 disposed between the optical axes of the lens 5 and the second grating 6, an exciter 9 that rotationally vibrates the glass plate 8, and an oscillator 10 that provides a drive signal to the exciter 9. and a lock-in amplifier 11 that detects the phase of the output of the photodetector 7 using the output from the oscillator 10 as a reference signal.

Note that the pitch of the grating image of the first grating 1 formed on the second grating 6 is designed to be equal to the pitch of the second grating 6.

If the illumination angle at which the first grating 1 is projected onto the sample surface 3 is θ, then the height change Δh of the sample surface 3 and the change angle ΔX of the grating image of the first grating l on the second grating 6 are The relationship is expressed by the following equation (1), where n is the optical magnification of the lens 5.

ΔX = 2 cosθ・Δh−n
-(1) Also, let the spatial phase change of the grating image of the first grating 1 imaged on the second grating 6 be Δφ, and the pitch of the grating image of the first grating 1 imaged on the second grating 6 If P is Δφ=
2π·Δx/P, and by eliminating ΔX using equation (1), the following equation (2) is obtained.

Δφ=4πncosθ・Δh/Mrad:] −・
・(2) From equation (2), the change in height of the sample surface 3 Δh
As a result, the spatial phase of the grating image of the first grating 1 changes, and the first
It can be seen that the amount of light passing through the second grating 6 having the same pitch as the grating image of the grating 1 changes periodically in accordance with the change in the height Δh of the sample surface 3.

FIG. 2 shows the change in height Δh of the sample surface 3 and the second grid 6.
12 is a graph showing an example of the relationship between the amount of light passing through and the light intensity. As shown in this figure, the light intensity is a periodic curve having a period of P/2 n cos θ with respect to the change Δh in the height of the sample surface 3. Further, by changing the angle of incidence on the glass plate 8 with high precision, the angle of the transmitted light is changed and the grating image of the first grating 1 formed on the second grating 6 is slightly vibrated. That is, the spatial phase difference between the grating image of the first grating and the second grating 6 is modulated by the vibration frequency of the glass plate 8, and the photodetector 7 receives this modified light.

Next, using the output from the oscillator 10 that drives the vibrator 9 as a reference signal, the lock-in amplifier 11 phase-detects the output of the photodetector 7, and outputs an output signal from the lock-in amplifier 11 indicating the positional deviation of the sample surface 3. obtain. From this positional deviation signal, the height displacement of the sample surface 3 can be detected with high precision.

FIG. 3 is a graph showing the relationship between the displacement Δh and the output of the lock-in amplifier 11 when the height of the sample surface is continuously changed. The output of the lock-in amplifier 11 indicating the positional deviation signal shown in FIG. 3 is a differential curve of the light amount change curve shown in FIG. 2, and the maximum and minimum values of the light amount are zero crossing points.

The linearity is good near this zero cross point, and when the position detection device of the present invention is applied to a focusing mechanism of a semiconductor exposure device or an inspection device, for example, the focus point is at the point where the output of the lock-in amplifier 11 becomes zero. Adjust so that

This zero-crossing point does not change even if there is a change in the amount of light due to a change in the reflectance of the sample surface 30, so that high-density focusing that is not affected by the reflectance of the sample surface 3 can be achieved.

In addition, in the above-mentioned embodiment, the first image formed on the second grating 6
Although we have shown an example in which a parallel plane glass plate 8 is used as a means for micro-vibrating the lattice image of the lattice l, the lattice image is transmitted through the lattice image.
Instead of this glass plate 8, a mirror or a prism may be used to reflect the light.

〔Effect of the invention〕

The position detection device of the present invention projects an image of a grating with a certain area onto the sample surface, instead of irradiating the sample surface with a focused beam from an oblique direction in the form of a spot. Since the height of the sample surface is measured by detecting the spatial phase change of the image, the average height within a certain area of the sample surface can be measured with high concentration.

That is, when the position detection device of the present invention is applied to a semiconductor exposure device or an inspection device, it can be configured with one device instead of a plurality of devices, so that the structure can be simplified and the cost can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing an example of the relationship between the change in height of the sample surface Δh in FIG. 1 and the amount of light transmitted through the second grating. FIG. 3 is a graph showing an example of the relationship between the change in height of the sample surface Δh in FIG. 1 and the output of the lock-in amplifier, and FIG. 4 is a block diagram showing an example of the conventional technique. 1...First grating, 2...Light source, 3...
...Sample surface, 4.5, 12, 13...Lens, 6...Second grating, 7...Photodetector, 8...Glass Board, 9...
Exciter, 10... Oscillator, 11... Lock-in amplifier, 14... Detector, 15...
...Subtractor, 16...Adder, 17...
...Divider.

Claims (1)

[Claims] a light source; a projection optical system that forms a first grating image from a first grating projected onto the light source on a sample surface from an oblique direction;
a light-receiving optical system that forms a second grating image by focusing the first grating image reflected on the sample surface; a second grating disposed on an imaging plane of the second grating image; a modulator that vibrates the second grating image to modulate the passing light that has passed through the second grating and outputs a reference signal; and a detection unit that receives the modulated passing light and outputs a photoelectric conversion modulation signal. 1. A position detecting device comprising: a detector; and means for phase-detecting the modulated signal with reference to the reference signal.