JPH0718699B2 - Surface displacement detector - Google Patents

Description

Description: [Object of the Invention] (Field of Industrial Application) The present invention relates to a surface displacement detection device for detecting displacement of a surface to be inspected, and particularly to a focus position detection device in, for example, a semiconductor manufacturing apparatus. The present invention relates to a surface displacement detection device which is suitable for use in.

(Prior Art) As a focus position detection device in a semiconductor manufacturing apparatus, conventionally, a semiconductor wafer provided at a position where a mask pattern is transferred by an imaging lens is obliquely irradiated with incident light, and the semiconductor wafer An oblique incidence type focus position detection device that detects the reflected light obliquely reflected from the surface and detects the surface position thereof is often used, for example, Japanese Patent Laid-Open No. 56-4220.
It is disclosed in Japanese Patent Publication No. 5 and the like.

This known focus position detection device uses the surface of a semiconductor wafer as a surface to be detected, projects a projection light beam obliquely onto the surface to be detected, forms a slit-shaped optical image on the surface to be detected, and reflects the reflected light. Is re-imaged on the detection unit formed of the photoelectric conversion element provided in the light receiving unit, and the incident position of the reflected light image on the detection unit is detected. Therefore, when the surface of the semiconductor wafer, which is the surface to be detected, is displaced in the vertical direction (moves along the optical axis of the projection lens), the reflected light image incident on the detection unit corresponds to the incident direction in response to the displacement in the vertical direction. And laterally shift in a direction orthogonal to each other. It is possible to determine whether or not the surface of the semiconductor wafer is at the in-focus position with respect to the projection lens by detecting the amount of lateral deviation.

(Problems to be Solved by the Invention) However, when the surface position of the semiconductor wafer is actually detected using the oblique incidence type focus position detection device configured as described above, the position detection accuracy has a certain level. It turns out that there are limits. After examining various causes,
A thin film such as a photoresist is often attached to a semiconductor substrate such as silicon on the surface portion of a semiconductor wafer. When the thickness of the thin film reaches about 1 to 2 μm, the thin film is reflected on the surface of the thin film. The reflected light and the light that has passed through the surface of the thin film and reflected on the surface of the semiconductor substrate cause interference, so that the combined reflected light incident on the detection unit is perpendicular to the optical axis of the detection optical system. It is considered that the light intensity distribution is distorted. By the way, the light transmittance of a material composed of an organic substance such as photoresist is
In general, a wavelength longer than the photosensitive wavelength (for example, red light) is relatively good, and there is a problem that the reflected light from the front surface and the reflected light from the back surface are likely to interfere remarkably and an error is likely to occur.

The present invention considers the influence of the interference of reflected light that may occur in the above-mentioned conventional device, and relatively improves the accuracy of the position detection result of the reflected light, beyond the limit of the conventional device. The purpose is to realize with a simple configuration.

[Structure of Invention]

(Means for Solving the Problems) In order to solve the above problems, in the present invention, the detection light is obliquely incident from a light source onto a test surface having a light-transmissive thin film, and the detected surface is In the grazing incidence type position detector that detects the position of the surface to be detected from the position of the re-formed image by re-imaging the reflected light from The intensity of the P-polarized component parallel to the incident surface of the detection light incident on the detected surface and the intensity of the S-polarized component perpendicular to the detected surface are detected at a predetermined position on the detection optical path between the detected surface and the detection surface. The problem solving means is to provide a polarization optical means arbitrarily changed on the detection surface.

(Function) Of the reflected light which is incident on the thin film on the surface to be detected from the light source and is reflected on the surface to be detected, the surface reflected light reflected on the surface of the thin film and the thin film transmitted through the thin film are reflected on the back surface of the thin film. Internally reflected light that passes through the surface of the thin film interferes according to the thickness of the thin film and forms an interference fringe on the detection surface. The phase of the interference fringes of S-polarized light which is perpendicular to the incident surface of the reflected light forming the interference fringes and the interference fringe of P-polarized light parallel to the incident surface are shifted by 180 ° when the incident angle exceeds the Brewster angle. Therefore,
The change in the light intensity obtained by combining the interference light of the S-polarized component and the interference light of the P-polarized component whose phases are mutually inverted is not proportional to the film thickness, and causes a large disturbance. Therefore, the amount of deviation from the apparent surface on the surface to be detected detected in accordance therewith becomes extremely large. Therefore, a polarization optical means is provided at an appropriate position on the detection optical path to change the ratio of the P-polarized component and the S-polarized component, and the P-polarized component and the S-polarized component are displaced by 180 °. If the intensity of both polarization components is appropriately changed by appropriately rotating the polarization optical means using, the amount of apparent surface deviation on the surface to be detected will be reduced and detection error will be improved. can do.

(Example) Next, the Example of this invention is described in detail based on an accompanying drawing.

FIG. 1 is a schematic configuration diagram of an optical system of a grazing incidence type surface displacement detection apparatus showing an embodiment of the present invention. The path of the light ray shown by the solid line shows the conjugate relationship of the slit image, and the path of the light ray shown by the broken line shows the conjugate relationship of the light source image.

In FIG. 1, detection light from a light source 1 that emits so-called randomly polarized light that does not have a specific polarization direction, such as a light emitting diode (LED) or a halogen lamp, passes through a field lens 2 and a projection slit 3 Irradiate. The projection slit 3 has a slit opening 3A that is long in the direction perpendicular to the paper surface, and the detection light L ₀ projected through this slit opening 3A is condensed by the light-transmitting-side objective lens 4A and An optical slit image is formed on the surface 5A.
The reflected light L ₁ reflected from the surface 5A of the semiconductor wafer 5 is focused by the light-receiving side objective lens 4B, and an optical slit image is re-formed on the light-receiving slit 6. Further, the reflected light L _{1 that} has passed through the slit opening 6A provided in the light receiving slit 6 is condensed as the detection light L ₃ on the light receiving element 8 such as a photoelectric conversion element by the collector lens 7. In addition, the light receiving slit 6,
Photoelectric detector 9 with collector lens 7 and light receiving element 8
Is configured.

The longitudinal direction of the slit opening 6A provided in the light receiving slit 6 is set in the direction perpendicular to the paper surface like the slit opening 3A of the light projecting slit 3. Further, the light receiving slit 6 is
A direction orthogonal to the longitudinal direction of the slit opening 6A,
That is, it is configured to vibrate with a predetermined amplitude in the width direction of the slit opening 6A (direction indicated by arrow a in FIG. 1). As a result, the optical slit image re-formed on the light receiving slit 6 is scanned by the slit opening 6A, and the deviation amount from the reference position of the slit opening 6A when the detection signal from the light receiving element 8 becomes maximum. Therefore, the deviation of the detected surface 5A from the reference plane (focal plane) is detected.

On the optical path between the light-receiving side objective lens 4B and the light-receiving slit 6, a detection error correction optical system 10 which is an essential part of the present invention is arranged rotatably around the optical axis. The detection error correction optical system 10 will be described later in detail.

FIG. 2 is an explanatory diagram showing the displacement amount of the light slit image on the light receiving slit 6 when the detected surface 5A of the semiconductor wafer 5 is displaced along the optical axis Z of the projection lens. When the detection light (incident light) L ₀ is incident on the detected surface 5A at the reference position Z ₀ with the incident angle θ, the light slit image formed at the point Q ₀ is received by the light receiving slit 6 by the light receiving side objective lens 4B. The image is re-imaged at the upper reference position P ₀ . When the surface to be detected 5A is displaced in the direction of the optical axis Z by ΔZ to the position shown by the chain line 5S, the detection light L ₀ is reflected at the Q ₁ point, and the reflected chief ray L _S forming the optical slit image is the receiving side objective lens 4B. Via, to reach point P ₁ on the light-receiving slit 6, and an optical slit image is re-imaged there. In this case, if the displacement amount of the optical slit image from the reference position P ₀ to the point P ₁ on the light receiving slit 6 is Δy and the imaging magnification of the light receiving side objective lens 4B is β, the displacement amount ΔZ of the detected surface 5A is ΔZ. Is given by ΔZ = Δy / (2βsinθ) ………… (1).

On the other hand, when the detected surface 5A of the semiconductor wafer 5 is composed of the surface of the thin film 5C made of, for example, photoresist coated on the semiconductor substrate 5B as shown in FIG. A part of the detection light L0 incident on the point Q ₀ is not only reflected as the reflected light L1A, but also reflected light L2 that is transmitted through the thin film 5C and reflected on the surface of the semiconductor substrate 5B is generated.
Passes through the surface 5A and emerges from the surface 5A as second reflected light L2A. Similarly, based on the reflected light L3 of the reflected light L2 that is not completely transmitted through the surface 5A and is internally reflected by the surface 5A, the third, fourth ... Reflected light L3A, L4A. It is considered that this reaches the light receiving slit 6 after being combined with the first reflected light L1A.

Considering this composite reflected light, it can be considered that the second reflected light L2A reflected once inside the thin film 5C is reflected at a position deeper than the surface 5A by a distance δ, so On the slit 6, with reference to the incident position P ₀ of the regular reflected light L1 on the light-receiving slit 6, ε = 2 · β · sin θ · δ ..... The image will be deviated. Here, the apparent deviation amount δ of the surface 5A is Can be asked as In the formula (3), d is a thin film
The thickness is 5C, and n is the refractive index of the thin film 5C. The expressions (2) and (3) are the positional deviation amounts when the reflected light L2A is reflected only once inside the thin film 5C, but the reflected light L3A obtained by reflecting the light twice, three times ... m times, Similarly for L4A ... L (m + 1) A, the positions are displaced by 2ε, 3ε ... mε.

When such composite light enters the light receiving slit 6, the respective composite lights become coherent with each other based on the conditions of the optical system and the thickness d of the thin film 5C.
The deformation of the shape of the image formed on the top results in the shift of the center of gravity of the amount of light detected by the photoelectric detector 9,
This causes an error in the detection result of the positional deviation amount Δy (see FIG. 2) based on the regular reflected light L1.

A qualitative examination of this phenomenon is shown in FIG.

First, when only the first reflected light L1A arrives at the light receiving slit 6, the photoelectric detector 9 determines this light amount barycentric position to be y _0, and photoelectrically detects the second reflected light L2A reflected once inside the thin film 5C. The device 9 shifts the center of gravity of the light quantity by the amount of displacement ε (Equation (2)).
It is assumed that it is determined that the position is at a position y ₀₁ that is deviated by just that. In this case, if the light intensity of the reflected light L1A is the normalized value 2 as shown in FIG. 4 (A), the light intensity of the second reflected light L2A that is reflected once is weaker than this, and is about 0.5. become.

By the way, if the thickness d of the thin film 5C is sufficiently thick and the detection light L ₀ from the light source 1 has low coherence, the first reflected light L1A and the second reflected light L2A that is reflected once are No interference occurs. Therefore, the light intensity of the light slit image formed on the light receiving slit 6 is, as shown in FIG. 4 (B), the distribution of the light intensity of the reflected light L1A shown by the solid line in FIG. 4 (A), The distribution of the light intensity is represented by the sum of the distribution of the light intensity of the second reflected light L2A of the single reflection shown by the broken line. As a result, the center of gravity of the light intensity distribution of the light slit image formed on the light receiving slit 6 is the center of gravity y ₀ of the light intensity distribution of the reflected light L1A (fourth
Position y ₁ deviated by a slight deviation amount Δy _{1 from} FIG.
Will occur in. However, the amount of deviation Δy ₁ is the film thickness d
Changes in proportion to.

However, in reality, since the film thickness d is as thin as about 1 to 2 μm, the reflected light thereof is likely to interfere, and in many cases, the reflected light L1A and L2A that form the optical slit image on the light receiving slit interfere with each other. , Do they strengthen each other as shown in Fig. 4 (C)?
Or, as a result, as shown in FIG. 4 (d), the results are weakened. Therefore, there occurs a phenomenon that the shape of the combined image formed on the light receiving slit 6 collapses, and the light amount center of gravity of the combined image formed on the light receiving slit 6 deviates greatly from the light amount center of gravity y ₀ of the reflected light L1A. It will be.

For example, when the interference light intensity of the reflected light L2A with respect to the reflected light L1A is maximized, the light intensity of the interference portion L1A + L2A becomes extremely large as shown in FIG. 4 (C) (in the case of this embodiment). The light intensity of the reflected light L1A is 2 while it is 4.5). Therefore, the center of light amount of the image formed on the light receiving slit 6 is moved to the position y ₂ which is displaced by a larger amount of positional deviation Δy ₂ than in the case of FIG. 4B.

On the other hand, when the interference light intensity is the minimum, as shown in FIG. 4 (D), the reflected lights L1A and L2A cancel each other in the range where the reflected light L2A and the regular reflected light L1 overlap. As a result, the light amount center of gravity of the combined image formed on the light-receiving slit 6 is an extremely large amount of positional deviation Δy ₃ compared with the light amount center of gravity y ₀ of the reflected light L1A, which is the opposite of FIG. 4C. This results in moving to a position y ₃ that is offset to the side. Particularly in the case of FIG. 4 (D) in which the reflected lights L1A and L2A cancel each other due to the interference effect, the positional deviation amount Δy ₃ of the light amount center of gravity on the light receiving slit 6 is large, and therefore this positional deviation amount Δy ₃ is a thin film. This causes a very large error in the apparent detection position on the surface to be detected with reference to the surface 5A. Figure 5 shows
FIG. 3 is a diagram schematically showing the influence of the interference of reflected light on the detection position on the detection surface side, where the horizontal axis is the thickness d of the thin film and the vertical axis is the detection target based on the thin film surface 5A. The amount of deviation of the apparent detection position on the surface side is shown. However, a straight line K3 indicated by a chain line indicates the position of the upper surface of the semiconductor substrate 5B coated with the thin film 5C.

In FIG. 3, assuming that the reflected lights do not interfere with each other, the light intensities of the reflected lights from the thin film surface 5A and the semiconductor substrate surface 5D are constant depending on the reflectances on the reflecting surfaces. However, the reflected light from the semiconductor substrate surface 5D
L2A, L3A ... are the thin film surface 5A in proportion to the film thickness d of the thin film 5.
It deviates from the reflected light L1A from. Therefore, the barycentric position of the light slit image on the light receiving slit 6 deviates from the detection reference position P ₀ on the light receiving slit in proportion to the film thickness d. Therefore, on the detected surface side, the position Z _{0 of the} thin film surface 5A is
As a reference, a linear shift proportional to the film thickness d is shown as shown by the solid line K _{1 in} FIG.

However, as described above, when the interference phenomenon occurs in the thin film 5C, it is not proportional to the film thickness d that makes a large wave along the solid line K ₁ due to the influence of interference as shown by the curve (broken line) K ₂ . Misalignment occurs. In particular, as described with reference to FIG. 4 (D), a sharp sharp pointed deviation occurs near the film thickness where the reflected lights cancel each other. Under such a situation, for example, as shown in FIG. 5, the film thickness d of the thin film 5C is in the range of W ₁ to W ₂ (W _{1 to} W ₂ = ΔW) in the manufacturing process.
If the reflected light is non-interfering (solid line K ₁ ), there is only a slight difference in the detection results of the detection position by ΔX ₁ , but the reflected light causes a curve K that causes interference. _In the case of ₂ , the detection result of the detection position greatly varies within the maximum ΔX ₂ range, and this becomes a detection error in the focus position detection.

By the way, in the explanation of the influence of interference in FIG.
Although only the reflected light L1A and the second reflected light L2A have been qualitatively described, in reality, as shown in FIG. 3, the reflection is infinite and extremely complicated. However, the first reflected light L1A and the second reflected light L
Since the light intensity of the other reflected lights L3A, L4A ... Is weaker than that of 2A, it is possible to represent the influence of the interference only by the above reflected lights L1A, L2A without causing a large deviation.

By the way, when the detection light L ₀ is incident on the detected surface 5A as shown in FIG. 1, a part thereof is reflected and the rest is transmitted through the detected surface 5A and refracted as shown in FIG. In this case, generally, the reflected light includes P-polarized light parallel to the incident surface (perpendicular to the detected surface 5A) and S-polarized light perpendicular to the incident surface, and the following Fresnel's equation holds for the amplitude and phase of the light. To do. Assuming that the incident angle is θ _i , the refraction angle is θ _t , the amplitude of P-polarized light is R _P , and the amplitude of S-polarized light is R _S , R _P = −tan (θ _i −θ _t ) / tan (θ _i + θ _{t) ...... (4) R S} = -sin (θ i -θ t) / sin (θ i + θ t) ...... (5) in this case, the incident angle is Brewster's angle (θ _i + θ _r = 90
Tan (θ _i + θ _t ) = ∞.sin (θ
_i + θ _t ) = 1. Therefore, the amplitude R _S of S-polarized light has a value corresponding to the refractive index of the thin film, but the amplitude R _P of P-polarized light is zero (zero), and all the light is transmitted through the detected surface 5A without being reflected. Also, Then, 0 <sin (θ _i + θ _t ) <1, and therefore the sign of the amplitude R _S of the S-polarized light in the equation (5) does not change,
tan (θ _i + θ _t ) 0, and therefore the sign of the amplitude R _P of the P-polarized light in the equation (4) is reversed.

FIG. 6 shows that the phase of the coherent light is approximately 180 for P-polarized light and S-polarized light.
FIG. 9 is a cross-sectional explanatory view for explaining the deviation. First, when the incident angle θ _{i of} the detection light L _{0 on} the sample surface 5A is smaller than the Brewster angle (θ _i + θ _t <90 °), as shown in FIG. Regarding the reflected light L2A that has been transmitted through the surface 5A, then reflected once in the thin film 5C and then transmitted through the sample surface 5A, P-polarized light (arrows p ₁ and p ₂ parallel to the paper surface) and S-polarized light (X perpendicular to the paper surface) There is no phase shift in the same direction as the marks S ₁ and S ₂ ). However, in the case where the incident angle θ _i is larger than the Brewster angle (θ _i + θ _t > 90 °), the S polarization is unchanged as shown in FIG. 6B, but the P polarization is This shows that the P-polarized light of the reflected light L1A is reversed by 180 ° unlike the case of FIG. 6 (A). That is, the P-polarized light in the reflected light L1A shows that the incident angle θ _i is inverted in phase at the Brewster angle.

As for the multi-reflected light L3A, L4A ... Shown in FIG.
It is thought to be reversed. The substrate 5B is usually formed of silicon, aluminum, or the like, and the reflected light from these substances also causes a phase shift when the incident angle is large. However, since the incident angle θ _a is smaller than the Brewster angle in the thin film (resist) 5C, almost no phase shift occurs, and as a result, the incident angle θ _i to the sample surface 5A is larger than the Brewster angle. In this case, P polarized light is 180
° It will be out of phase.

FIG. 7 is a diagram showing an example of the simulation of the P-polarized interference light and the S-polarized interference light in consideration of the multi-reflection light L3A, L4A ... In FIG. 3, and FIG. Is a diagram showing the intensity change of the interference light with respect to the change of the film thickness t of the thin film,
FIG. 7B shows the sample surface based on the position of the center of gravity of the interference light.
FIG. 5 is a diagram showing an apparent amount of surface deviation on the 5A side. The solid line shows the curve for P-polarized light, and the broken line shows the curve for S-polarized light. In this case, the detection light L ₀ from the light source 1 is monochromatic light having a wavelength λ = 740 μm, and the silicon substrate (complex refractive index n _S = 3.71 + 0.01
Aluminum layer (complex refractive index n _AL = 1.44 + 5.
2i) is applied to a thickness of 1 μm, and a photoresist (complex number n _R = 1.64 + 0.002i) is applied to the surface 5A of a semiconductor wafer 5, and the numerical aperture NA is set at an incident angle θ = 70 °. =
It is assumed that the detection light L ₀ is projected using the 0.1 objective lenses 4A and 4B.

As is clear from FIG. 7 (A), the P-polarized light (solid line) and the S-polarized light (dashed line) deviate from each other in the period of the intensity of light due to the interference effect by about half a period (180 °). When the light intensity becomes weak, the position far below the resist (the amount of deviation from the surface is large) is detected as shown in FIG. 7B, which indicates that the detection error is large. For example, looking at the intensity of interference light (see FIG. 7 (A)) and the detection error (see FIG. 7 (B)) at a film thickness of 1.2 μm, the intensity is maximum for P-polarized light (solid line), and the detection error is The amount of (deviation from the surface) is small, and the state is as shown in FIG. 4 (C). However, for S-polarized light, on the contrary, the intensity of the interference light is near the minimum, the detection error is large, and the state shown in FIG. So, these two P
When the polarized light and the S-polarized light are combined, the light amount distributions of (C) and (D) in FIG. 4 are added incoherently, and the light amount centroid has a strong light intensity (for example, FIG. 4C). Direction).

FIG. 8 is a diagram showing the result of synthesizing the P-polarized light and the S-polarized light shown in FIG. 7 above. The broken line curve shows the intensity change of the interference light with respect to the film thickness change, and the solid line curve shows the sample. The amount of apparent deviation (detection error) from the surface on the surface side is shown. As is clear from FIG. 8, the change in the light intensity due to interference is reduced, and the detection error Δ still has a detection error in the range of 0.32 μm in the vicinity of the film thickness of 1.1 μm. However, if the ratio of the intensities of P-polarized light and S-polarized light is changed appropriately by using the means described below, the detection error (change in detection error due to change in film thickness, ΔX _{2 in} FIG. 5) is minimized. It is possible.

In order to improve the detection error of the detection position due to the above interference, a detection error correction optical system 10 is provided between the light receiving side objective lens 4B and the light receiving slit 6 as shown in FIG. The detection error correction optical system 10 is composed of a polarization prism 11 as shown in FIG. The reflecting surface 11R of the polarizing prism 11 is formed by coating a dielectric multilayer film on the mating surface inclined at 45 °, and as shown in the spectral transmission characteristic diagram of FIG.
Almost 100% of the polarized light is transmitted, 50% of the S polarized light is transmitted, and the remaining 5
It is configured to reflect 0%. Therefore, almost 100% of the light passing through the polarizing prism 11 is transmitted through the reflecting surface 11R, but the S-polarized light is reduced to about 50%.
The intensity ratio of P-polarized light and S-polarized light can be set to 2: 1. This ratio is extremely effective for detection error correction when the reflecting surface 5D (see FIG. 6) between the thin film 5C and the semiconductor substrate 5B is made of an aluminum film.

By the way, depending on the refractive index characteristics of the substrate 5B and the thin film 5C, P
In some cases, it may be better to change the ratio of polarized light to S-polarized light to a value different from the above value. In this case, the ratio of P-polarized light and S-polarized light can be freely set by changing the characteristics of the reflecting surface 10R, and further, by rotating this polarizing prism in the α direction about the incident optical axis, detection can be performed. It is possible to change the ratio of the P polarized light and the S polarized light with respect to the incident surface of the light L ₀ .

Further, the detection error correction optical system 10 can be replaced by a polarizing plate 12 as shown in FIG. In this case, the ratio between the P-polarized light and the S-polarized light of the incident light can be changed by rotating the polarization axis in the β direction. That is, the detection light
Polarization axis X with respect to the plane of incidence including L ₀ and perpendicular to sample surface 5A
Is rotated by β, P-polarized light is Cos ² β and S-polarized light is
The transmittance is Sin ² β, and the desired ratio can be obtained by appropriately adjusting the angle β. Further, the transmittance of the P-polarized light of the polarizing prism 11 shown in FIG. 9 T _P = 100%, S
If the transmittance of polarized light is set to T _S = 0%, it can be used in exactly the same way as the polarizing plate 12 described above, and by adjusting the rotation around the incident optical axis, P polarized light and S polarized light can be obtained. The ratio of can be changed.

FIG. 12 shows the polarizing prism 11 of FIG. 9 and the polarizing plate 12 of FIG.
By rotatably providing the detection error correction optical system 10 as shown in FIG. 1 on the detection optical path shown in FIG. 1, the ratio of P polarization to S polarization is set to 1 under the same optical conditions as in FIG. It was synthesized as: 0.35. It specifically shows a change in the intensity of the interference light and a detection error (amount of deviation from the surface) of the detection position on the sample surface side. As is clear from Fig. 12, the thin film 5C
Error range Δ = 0.21μ when the film thickness is around 1.1μm
In m, the accuracy is improved as compared with Δ = 0.32 μm shown in FIG. That is, by relatively weakening the S-polarized light shown in FIG. 7, the detection error due to the S-polarized light is reduced,
The accuracy is improved. Further, it can be seen that the intensity change of the interference light is improved by narrowing the intensity range as compared with the intensity change (broken line) in FIG.

In the above embodiment, the detection error correction optical system 10 is provided on the detection optical path on the light receiving side as shown in FIG. 1, but it is provided on the light transmitting side, that is, between the light source and the sample surface 5A in FIG. Even if it is provided on the detection optical path, a similar correction effect can be obtained. At this time, in the case of the polarization prism 11 like the detection error correction optical system 10, it is desirable to provide the detection error correction optical system 10 on the optical path of a portion as close as possible to the parallel light flux. However, when the opening angle of the light flux is small, the transmittances of the P-polarized component and the S-polarized component do not change so much, so that the installation location is not particularly limited.

Further, in the embodiment of FIG. 1, a randomly polarized light source is used, but when a light source that emits linearly polarized light, such as a semiconductor laser or a linearly polarized laser, is used as the light source 1, the plane of polarization is In order to adjust the rotation with respect to the incident surface of the detection light, instead of the polarizing prism 11 or the polarizing plate 12,
A rotatable λ / 2 plate may be used as the detection error correction optical system 10. In addition, the polarization plane (polarization plane) can be rotated around the optical axis by controlling the magnetic field, or an element having optical rotatory power (natural rotation), such as a crystal plate, can be used to change the polarization plane. The rotation may be adjusted. However, in the case of a crystal plate, in order to rotate the polarization plane by a predetermined amount, a single crystal plate or a plurality of crystal plates having a predetermined thickness are inserted into the optical path.

The polarization plane (polarization plane) from the light source is tilted with respect to the incident plane by using the polarization optical means such as the λ / 2 plate, the Faraday element, and the crystal plate described above, so that the P polarization component is obtained. It is possible to change the relative ratio of the intensities of the and S-polarized components. For example, in the example shown in FIG. 12, P-polarized light and S-polarized light are used.
When setting the intensity ratio of polarized light to 1: 0.35,
5A) and θ as the angle of the plane of polarization. Cos ² θ: Sin ² θ = 1: 0.35
If you choose the angle θ to be set, θ = 30.6 °. In this way, when the light source is polarized, the above-mentioned polarizing prism
It is advantageous in that the loss of light is smaller than that by the polarization optical means such as 11 and the polarizing plate 12.

If a multi-wavelength light source is used as the light source 1 and the coherence of the reflected light is reduced by the polychromatic light, the detection precision can be further improved. In the embodiment shown in FIG. 1, the photoelectric detector 9 including the oscillating light receiving slit 6 is used to detect the reflected light, but this light receiving portion has a CCD type solid-state image sensor or PSD ( A semiconductor position detecting element) or various detectors such as an image pickup tube may be used to detect the light amount centroid.

〔The invention's effect〕

As described above, according to the present invention, since the polarization optical means capable of arbitrarily changing the intensities of the P-polarized component and the S-polarized component on the detection surface is provided on the detection optical path, the detected object having the light-transmissive thin film is provided. It is possible to reduce the surface displacement detection error due to the interference caused by the thin film with respect to the surface with a very simple configuration, and further, the change in the light intensity at the detection destination is small, and the measurement accuracy can be improved. There is.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical system according to an embodiment of the present invention, and FIG.
FIG. 3 is an explanatory view showing changes in the position of the surface to be detected and changes in the position of the optical spot image on the detection surface in the embodiment of FIG. 1, and FIG. 3 is on the surface to be detected in the embodiment of FIG. FIG. 4 is an explanatory view showing the reflected light reflected by the thin film, FIG. 4 is an explanatory view showing the movement of the light amount center of gravity on the detection surface caused by the interference of the reflected light by the thin film in FIG. 3, and FIG. Diagram for explaining the detection error on the detection surface side,
FIG. 6 is an explanatory diagram for explaining that the incident angle of the detection light affects the P-polarized light of the reflected light. (A) is a sectional view when the incident angle is smaller than Brewster's angle, (B) is A cross-sectional view when the incident angle is larger than the Brewster's angle, FIG. 7 is a diagram showing the detection results in the interference state of P-polarized light and S-polarized light by simulation, and (A) is P-polarized light and S-polarized light with respect to the film thickness. FIG. 8B is a diagram showing the amount of deviation from the apparent surface on the detected surface side with respect to the film thickness for P-polarized light and S-polarized light, and FIG. FIG. 9 is a diagram showing a detection result by simulation when the optical means is deleted, FIG. 9 is a perspective view showing a polarizing prism as a detection error correction optical system shown in FIG.
FIG. 11 is a ray transmittance diagram of the polarizing prism in FIG. 9, FIG. 11 is a perspective view showing a polarizing plate as a detection error correction optical system, and FIG.
The drawing is a diagram showing a simulation of the detection result of the present invention shown in FIG. (Explanation of symbols of main parts) 1 ... Light source, 3A ... Light sending slit, 4A ... Light sending objective lens, 4B
... Receiving objective lens, 5 ... Semiconductor wafer, 5A ... Semiconductor wafer surface (detection surface), 5B ... Semiconductor substrate, 5C ... Thin film, 6 ...
Light receiving slit (detection surface) 10 ... Detection error correction optical system (polarizing optical means) 11 ... Polarizing prism (polarizing optical means) 12 ... Polarizing plate (polarizing optical means)

Claims (2)

[Claims] 1. A detection light from a light source is obliquely incident on a surface to be detected having a light-transmissive thin film to form an optical image of a predetermined shape, and then reflected light from the surface to be detected is detected. In the oblique incidence type position detection device for re-imaging on the above, detecting the position of the detected surface by detecting the optical image on the detection surface which is displaced according to the change of the position of the detected surface, From the light source, polarization optical means capable of arbitrarily changing the intensities of the polarization component parallel to the incident surface and the polarization component of the detection light incident on the detection surface after being reflected on the detection surface is provided. A surface displacement detecting device, which is provided at a predetermined position on a detection optical path between the detection surface and the detection surface. 2. The polarization optical means is a polarization prism, a plate-shaped polarization plate, a λ / 2 plate, a Faraday element capable of rotating and adjusting a polarization plane of a light source by controlling a magnetic field, or an optical element having an optical rotatory power. The surface displacement detection device according to claim 1, wherein