JPH03115807A - Position detector - Google Patents

Abstract

PURPOSE:To highly accurately measure average height within a specific area on a specimen surface by projecting a grid image with a specific area on the specimen surface, detecting a fluctuation in a spatial phase of the reflected grid image and measuring the height of the specimen surface. CONSTITUTION:An image of fixed grid 1 is projected on a specimen surface 3 from a slant direction, and the reflected grid image is formed on a vibrating grid 6. Therefore an amount of light transmitting through the grid 6 periodically changes according to a change in height of the specimen 3. Further the grid 6 is subjected to a slight vibration by an exciter 9 and difference in a spatial phase between an image of the grid 1 and the grid 6 is modulated. A photo detector 7 receives the modulated light and amplifies it with an amplifier 8. A lock-in amplifier 11 phase-detects an output of the amplifier 8 with an output from an oscillator 10 driving the shaker 9 as a reference signal. As a result a highly accurate position shift signal can be obtained from the amplifier 11 permitting highly accurate measurement of average height within a specific area on the specimen surface.

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), etc. are used, and the lens 1
3, the position of the imaged beam 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 cos θ・Δh−n n: 2-split detector or PSD used as magnification detector 14 of lens 13
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 detection head device shown in Fig. 4,
The outputs a and b of the detector 14 are subtracted by a subtracter 15 and added together by an adder 16. And divider 17
By dividing the output (a-b) of the subtracter 15 by the output (a+b) of the adder 16 and normalizing it, the detector 1
A positional deviation signal that is not influenced by changes in the beam intensity incident on the beam 4 is obtained.

The conventional position detection device as described above is often used in a reduction projection type semiconductor exposure apparatus (stepper) to measure the height of a wafer surface in order to focus a projection lens on the wafer surface. However, the exposure area of a stepper 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 warpage and unevenness due to processing, and the height within the exposure area is not always 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 of the same +1" configuration are required, and semiconductor exposure equipment and inspection equipment that use conventional position detection devices have complicated structures and become expensive. There was a drawback.

[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 projected on the light source onto a sample surface from an oblique direction, and a light-receiving optical system that forms a first grating image to form a second grating image; a second grating disposed on the imaging plane of the second grating image; a modulator that modulates the passing light that has passed through the grating No. 2 and outputs a reference signal; a detector that receives the modulated passing light, photoelectrically converts it, and outputs a modulated signal; It is configured to include means for phase branching 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. 1 includes a fixed grating 1 as a first grating, a light source 2 for projecting the fixed grating 1, and a lens 4 for forming an image of the fixed grating 1 on a sample surface 3. , a lens 5 that refocuses the image of the fixed grating 1 reflected on the sample surface 3, a vibrating grating 6 that is a second grating placed on the imaging plane of the lens 5, and light transmitted through the vibrating grating 6. , an oscillator 10 that provides a drive signal to the oscillator 9, and a lock-in amplifier 11 that detects the phase of the output of the amplifier 8 by referring to the output signal of the oscillator 10. be done.

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

Assuming that the illumination angle at which the fixed grating l is projected onto the sample surface 3 is θ, the relationship between the change in height of the sample surface 3 Δh and the displacement ΔX of the image of the fixed grating 1 on the vibrating grating 6 is as follows: As the optical magnification n, the following formula (1)% Formula % (1) Also, if the phase change of the image of the fixed grating 1 is △φ, and the pitch of the vibrating grating 6 is P, then Δφ=2π・△x / P, and by substituting equation (1), the following equation (2) can be obtained.

Δφ=4πncosθ・Δh /P Crad]−・・
(2) From equation (2), the spatial phase of the image of the fixed grating 1 changes as the height of the sample surface 3 changes, and therefore the amount of light transmitted through the vibrating grating 6 having the same pitch as the image of the fixed grating 1. It can be seen that changes periodically.

FIG. 2 is a graph showing an example of the relationship between the change Δh in the height of the sample surface 3 and the light tI transmitted through the vibration grating 6. In FIG. As shown in this figure, the light ff1I forms a periodic curve with a period of P/2n cos θ with respect to the change Δh in the height of the sample surface 3.

Furthermore, in order to detect the position of the sample surface 3 with high precision,
The vibrating grating 6 is minutely vibrated at a constant frequency by the vibrator 9, and the spatial phase difference between the grating image of the fixed grating l formed on the vibrating grating 6 and the vibrating grating 6 is modulated.

Next, the photodetector 7 receives the modulated light, and the output thereof is amplified by the amplifier 8.

The lock-in amplifier 11 is an oscillator 1 that drives the exciter 9.
Phase detection is performed on the output of the amplifier 8 using the output of 0 as a reference number. As a result, a positional deviation signal with higher accuracy than that of the lock-in amplifier 11 can be obtained.

FIG. 3 is a graph showing the relationship between the displacement Δh and the output of the lock-in amplifier 11 and 9 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 curve of light amount change shown in FIG. 2, and the maximum and minimum values of the light amount are the zero cross points.

The linearity is good in the vicinity of 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 point where the output of the lock-in 7-block 11 becomes zero is a good value. Adjust so that it is in focus.

This zero-crossing point does not change even if the amount of light varies due to a change in the reflectance of the sample surface 30, so highly accurate focusing can be achieved without being affected by the reflectance of the sample surface 30.

〔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 precision.

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 and the light f transmitted through the vibration grating in FIG. FIG. 3 is a graph showing an example of the relationship between the change Δh in height of the sample surface 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. l...Fixed grating, 2...Light source, 3...
...Sample surface, 4.5, 12.13...Lens, 6...Vibration grating, 7...Photodetector, 8...Amplifier, 9...excillator, lO...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 onto a sample surface from an oblique direction; and a projection optical system that forms an image of the first grating reflected from the sample surface. a light-receiving optical system that forms a second grating image; a second grating disposed on the imaging plane of the second grating image; and a light receiving optical system that vibrates the second grating and passes through the second grating. a modulator that modulates light and outputs a reference signal; a detector that receives the modulated passing light, performs photoelectric conversion and outputs a modulated signal; and detects the phase of the modulated signal with reference to the reference signal. A position detection device comprising: means.