JPH09145329A - Level difference measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a level difference accurately when the optical reflectance varies on the opposite sides of level difference. SOLUTION: The level difference measuring apparatus is constructed such that a reflected light arriving at an analyzer is polarized circularly when an object 8 is a mirror face. The analyzer comprises a polarization beam splitter 11 having a predetermined analyzer angle while a two-dimensional image sensor comprises a first two-dimensional image sensor 13 for detecting the light transmitted through the polarization beam splitter 11, and a second two-dimensional image sensor 15 for detecting the light reflected on the polarization beam splitter 11. A measuring means 18 measures a level difference based on the relationship between the difference of output from first and second two-dimensional image sensor 13, 15 for the level difference and the phase difference being imparted between two lights by the level difference which relationship being dependent on the variation of amplitude reflectance on the opposite sides of level difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level difference measuring device, and more particularly to a level difference measuring device suitable for quantitatively measuring a minute level difference existing on an IC pattern or a metal surface.

[0002]

2. Description of the Related Art As a conventional step measuring device, as disclosed in the October 1992 issue of O puls E magazine on pages 70 to 72, a non-contact surface roughness meter to which a laser scanning type step measuring device is applied. It has been known. In this non-contact surface roughness meter, a polarization beam splitter is used instead of the conventional analyzer, and the transmitted light and the reflected light of this polarization beam splitter are simultaneously detected. Then, the step is measured based on the ratio of the difference signal and the sum signal regarding the detection signal of the transmitted light and the detection signal of the reflected light.

[0003]

In the above-mentioned conventional non-contact surface roughness meter, the step is measured based on the ratio of the difference signal and the sum signal regarding the detected transmitted light and reflected light. However, in a measurement based on the ratio of the difference signal and the sum signal,
There is an inconvenience that it is not possible to cope with the case where the light reflectance changes on both sides of the step.

Further, the above-mentioned document describes that the sum signal is not affected by the step. However, the sum signal is not significantly affected by the step only when the phase difference of the light generated by the step is extremely small. That is, in the above-described conventional non-contact surface roughness meter, the sum signal is modulated by diffraction as the step increases, and as a result, the measurement accuracy is impaired.

The present invention has been made in view of the above problems, and provides a step measuring apparatus capable of measuring an arbitrary step with high accuracy even if the light reflectance changes on both sides of the step. Is intended.

[0006]

In order to solve the above problems, in the present invention, a light source, an illumination optical system for illuminating light from the light source onto an object to be inspected, and an image of the object to be inspected are provided. An objective lens for forming an image on a predetermined image plane, and a light from the light source, which is arranged between the objective lens and the light source, is split into two lights by its polarization component, and the two lights reflected by the object to be inspected. A birefringent prism for combining light, an analyzer for selecting the combined two lights as a specific polarization component, and a two-dimensional image sensor arranged on the image plane for receiving light passing through the analyzer And a measuring means for quantitatively measuring a step of an object to be inspected on the basis of a signal output from a two-dimensional image sensor, wherein the step measuring device has a mirror surface of the object to be inspected. So that the reflected light reaching the analyzer becomes circularly polarized when The analyzer has a polarization beam splitter having an analyzer angle of a predetermined angle, and the two-dimensional image sensor includes a first two-dimensional image sensor for detecting light transmitted through the polarization beam splitter and a polarization beam splitter. A second two-dimensional image sensor for detecting the reflected light, and the measuring means includes a step and a difference between the output of the first two-dimensional image sensor and the output of the second two-dimensional image sensor with respect to the step. There is provided a step difference measuring device characterized in that the step difference is measured based on a relationship which is satisfied between a phase difference given to two lights and depends on a change in amplitude reflectance on both sides of the step difference.

According to a preferred aspect of the present invention, the analyzer angle of the polarization beam splitter is n when n is an odd number.
π / 4, and the measuring means sets the phase difference given to the two lights by the step to be Ψ, and outputs the output of the first two-dimensional image sensor and the output of the second two-dimensional image sensor to one region of the step. Is denoted by W _a , the sum of the output of the first two-dimensional image sensor and the output of the second two-dimensional image sensor for the other area of the step is denoted by W _b, and the output of the first two-dimensional image sensor is When the difference from the output of the second two-dimensional image sensor is S and the device-dependent constant is D,

[0008]

(Equation 3)

The step is measured based on the phase difference Ψ obtained by the relationship of In order to solve the above-mentioned problems, in the present invention, a light source, an illumination optical system for illuminating light from the light source onto an object to be inspected, and an image of the object to be inspected are formed on a predetermined image plane. And an objective lens for controlling the light from the light source, which is disposed between the objective lens and the light source.
A birefringent prism for splitting the light into two beams and combining the two lights reflected by the object to be inspected, an analyzer for selecting the two combined lights as a specific polarization component, and an array on the image plane. Step measurement provided with a two-dimensional image sensor that is installed and receives light that has passed through the analyzer, and a measuring unit that quantitatively measures the step of the object to be inspected based on a signal output from the two-dimensional image sensor. The step measuring device is configured so that the reflected light reaching the analyzer is circularly polarized when the object to be inspected is a mirror surface, the analyzer has a variable analyzer angle, and the measuring means is Established between the difference between the outputs of the two-dimensional image sensor when the photon analyzer angle is at two different positions and the phase difference given to the two lights, and depends on the change in amplitude reflectance on both sides of the step. Step difference based on the relationship Providing step measuring apparatus according to claim Rukoto.

According to a preferred embodiment of the invention, the two different positions of the analyzer angle of the analyzer are nπ / 4 and nπ / 4 + mπ / 2, where n and m are odd numbers.
The measuring means sets the phase difference given to the two lights by the step difference to Ψ, and the analyzer angle of the analyzer and the analyzer angle of the two-dimensional image sensor in one of two different positions of the analyzer angle of the analyzer. Is the sum of the output of the two-dimensional image sensor in the other state of the two different positions, and the value of W obtained in one area of the step is W
_a, and the value of W obtained in the other area of the step is W _b
And the output of the two-dimensional image sensor in one of the two positions where the analyzer angle of the analyzer is different from the output of the two-dimensional image sensor in the other state of the analyzer angle of the analyzer being different. Where S is the difference between S and D is a device-dependent constant,

[0011]

(Equation 4)

The step is measured based on the phase difference Ψ obtained by the relationship of

[0013]

As described above, the step measuring device of the present invention has a structure to which a differential interference microscope is applied. In general, a differential interference microscope can give a contrast almost equal to a differential image to a geometrical step existing on an object to be inspected. However, a general step existing on the object to be inspected does not simply consist of surface irregularities (geometric steps). For example, considering the pattern of chrome vapor-deposited on a glass substrate, not only is there a geometric step corresponding to the chrome film thickness at the boundary of the vapor deposition surface, but also the light reflectance changes greatly on both sides of the step. ing.

As described above, a general step has a property of modulating both the phase and the amplitude of incident light.
Therefore, for different steps, the degree of phase and amplitude modulation naturally differs. However, as a result of various studies, the inventors of the present invention have conceived a step measuring device of the present invention capable of highly accurate measurement of any step using the configuration of a conventional differential interference microscope.

The operation of the step measuring device of the present invention will be theoretically described below. In addition, since the step basically has a one-dimensional characteristic, everything including the optical system is treated one-dimensionally in the following analysis. Although an actual optical system has a two-dimensional characteristic, it is needless to say that two-dimensionalization can be easily performed by introducing a coordinate system orthogonal to each equation described later. It is assumed that a one-dimensional coordinate x is set on the object to be inspected and a step exists at the origin x = 0. The object is flat except for x = 0, and the complex amplitude distribution O (x) of the object is given by equation (1).

[0016]

(Equation 5)

In the equation (1), a and b are the square roots (ie, amplitude reflectance) of the reflectance of the object in the region of x≤0 and the region of x> 0, respectively. Further, Ψ is the phase change amount of the incident light caused by the step. Next, the intensity I of the differential interference image at this step position is obtained. At the step position, that is, at x = 0, the two illumination lights formed on the object to be inspected by the step measuring device are symmetrically located on both sides of the step. Focusing on the point image at the center of the illumination light among the point images forming the respective illumination light, the two point images are located at symmetrical positions on both sides of the step, with the step being interposed therebetween. That is, the distance between the centers of the two point images is 2δ
Then, the center of the point image of the first illumination light is at the position x = δ, and the point image of the second illumination light is at x = −δ.

First, consider the point image of the first illumination light. If the amplitude distribution of the point image on the object is u (x), the complex amplitude P _{1 of the} light diffracted in the direction cosine α direction by the diffraction of the point image of the first illumination light is given by ) Is given.

[0019]

(Equation 6)

Similarly, for the point image of the second illumination light, the complex amplitude P ₂ is diffracted in the direction cosine α direction by the diffraction.
Is given by the following equation (3).

[0021]

(Equation 7)

The phase difference given to the first illumination light and the second illumination light by the optical system from the light source to immediately before the analyzer (that is, when the mirror surface is used as the object to be inspected, both illumination lights immediately before the analyzer are detected). When the phase difference) is θ and the azimuth angle (analyzer angle) of the analyzer is φ, the transmitted light intensity i _T and reflected light intensity i _R of the analyzer are given by the following equations (4) and (5), respectively. To be

[0023]

(Equation 8)

[0024]

(Equation 9)

In practice, all diffracted light with a direction cosine smaller than the numerical aperture NA of the lens is received. Therefore, the transmitted light intensity I _T and the reflected light intensity I _R are given by the following equations (6) and (7), respectively.

[0026]

(Equation 10)

[0027]

[Equation 11]

Therefore, the difference signal S between the total intensity I _{T of} transmitted light and the total intensity I _{R of} reflected light is given by the following equation (8).

[0029]

(Equation 12)

By substituting the expressions (1) to (7) into the expression (8), the relationship shown in the following expression (9) is obtained.

[0031]

(Equation 13)

In the present invention, the phase difference θ =
By setting π / 2, the relationship shown in the following expression (10) is established.

[0033]

[Equation 14]

In the equation (10), C is a device constant that does not depend on the object, and is given by the following equation (11).

[0035]

(Equation 15)

The right side of the equation (10) is represented by the inner product of vectors as shown in the following equation (12).

[0037]

(Equation 16)

Therefore, the difference signal S at the step position is
Becomes maximum when the analyzer angle φ satisfies the equation (13).

[0039]

[Equation 17]

Further, referring to the equation (12), the equation (1
It can be seen that the difference signal S at the step position becomes minimum (zero) at the analyzer angle obtained by adding ± π / 4 to φ satisfying 3). Hereinafter, the reason for setting the phase difference θ = π / 2 in the present invention will be described. First, the part cos (θ + Ψ) including the phase difference θ on the right side of Expression (9) is θ =
By setting it as π / 2, it is included in the difference signal S as sin Ψ as shown in equation (10). Thus, the difference signal S with respect to the minute phase difference Ψ corresponding to the minute step
The sensitivity of 1 becomes the best by setting the phase difference θ = π / 2. In other words, by setting the phase difference θ = π / 2, the contrast with respect to the minute step can be increased.

Next, by setting the phase difference θ = π / 2, it is possible to simultaneously maximize the contrast (or the minimum) for the edges on both sides of the step. Assuming that the amplitude reflectance of the step portion is b and the amplitude reflectance of the flat portions on both sides thereof is a, the amplitude reflectance changes from a to b and the phase difference due to the step changes from 0 to Ψ at one edge. . At the other edge, the amplitude reflectance changes from b to a and the phase difference due to the step changes from Ψ to 0.

That is, on the right side of the equation (13), at one edge and the other edge, a and b are interchanged, and the sign of the phase difference Ψ due to the step is opposite. By the way, even if a and b are exchanged and the sign of the phase difference Ψ is reversed, the value on the right side of the equation (13) does not change. This gives the maximum (or minimum) contrast for one edge
It means that the analyzer angle which makes the contrast of the other edge equal to the analyzer angle which makes the contrast of the other edge maximum (or minimum). In other words, by setting the phase difference θ = π / 2, it is possible to simultaneously maximize (or minimize) the contrast for the edges on both sides of the step at the same analyzer angle.

If the phase difference is set to θ = 0 instead of θ = π / 2, the difference signal S at the step position becomes maximum when the analyzer angle φ satisfies the following equation (14).

[0044]

(Equation 18)

In the above equation (14), if a and b are exchanged and the sign of the phase difference Ψ is reversed, the value on the right side will change. That is, unless the phase difference θ = π / 2 is set as in the present invention, even if the contrast for one edge is maximum (or minimum), the contrast for the other edge with respect to the analyzer angle at that time is: It will no longer be the maximum (or minimum).

In the present invention, the phase difference applied to the light corresponding to the two illumination lights by the optical system immediately before the analyzer is π / 2,
That is, the light reaching the analyzer is circularly polarized, and the analyzer angle φ of the analyzer is set to π / 4.
Thus, the difference signal S at the step position is expressed by the following equation (1
5).

[0047]

[Equation 19]

By quantitatively measuring the value of the difference signal S (light amount measurement) in this way, the amount including the phase difference Ψ can be obtained. The right side of Expression (15) includes the amplitude reflectances a and b on both sides of the step in addition to the phase difference Ψ. To obtain the amplitude reflectances a and b, the sum signal W = I _{T at} a position sufficiently distant from the step is obtained as follows.
Find + I _R.

For example, at a position where x <0, which is sufficiently distant from the step position x = 0, the relation expressed by the following equation (16) holds in good approximation.

[0050]

(Equation 20)

By substituting equation (16) into equations (4) to (7) and setting θ = π / 2, the sum signal W _a for the position of x <0 sufficiently far from the step position x = 0 is obtained. , The following equation (17)
Given by

[0052]

(Equation 21)

Thus, the amplitude reflectance a can be obtained by calculating the square root of the sum signal W _a given by the equation (17). That is, the amplitude reflectances a and b are eliminated from the equation (15) using the relationship shown in the equation (17) regarding the sum signal W _{a and the} equation regarding the sum signal W _b [equation corresponding to the equation (17)]. You can As a result, the relationship shown in the following equation (18) is obtained.

[0054]

(Equation 22)

Here, the difference signal S,
In addition to the sum signal W _a and the sum signal W _b , a device-dependent device constant D is included, and this device constant D is a calculable quantity. However, in practice, the device constant D can be obtained by performing calibration using a sample with known steps and reflectance. Thus, the difference signal S
The phase difference Ψ can be calculated based on the equation (18) that is a relational expression that depends on the change in the amplitude reflectance between the phase difference Ψ and the phase difference Ψ. Then, based on the obtained phase difference Ψ, the step Δh can be obtained by the following equation (19).

[0056]

(Equation 23)

Where λ is the wavelength of the light used and n
Is the refractive index of the medium (1 for air). If the complex refractive index is different on both sides of the step, a difference in the amount of phase jump of light occurs between the two corresponding point images. Therefore, it is necessary to measure the amount of phase jump of light in advance and correct the value of the phase difference Ψ obtained according to the equation (18) with the difference in the amount of phase jump measured in advance. However, if the difference in the amount of phase jump of light is within the error range, no correction is necessary.

[0058]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. FIG.
It is a figure which shows roughly the structure of the level | step difference measuring apparatus concerning 1st Example of this invention. Although the light source 1 is shown as a point light source in FIG. 1 for the sake of simplicity, it is actually a light source having a finite size, such as a tungsten lamp.

The light emitted from the light source 1 passes through the collimator lens 2 to become parallel light, and passes through the interference filter 3 to select the wavelength. In the first embodiment, the wavelength is 550n
Selected for m. The light transmitted through the interference filter 3 becomes linearly polarized light at the polarizing plate 4 and enters the half mirror 5. The polarization direction at this time is parallel to the paper surface. The light reflected downward in the figure by the half mirror 5 is the Nomarski prism 6
Incident on. The Nomarski prism 6 is a birefringent prism that has an optical axis that intersects the polarization direction of the incident light at 45 ° and splits the incident light into two lights by the polarization component. A Wollaston prism or the like may be used instead of the Nomarski prism.

The light split into two through the Nomarski prism 6 is condensed through the objective lens 7 and forms two illumination lights on the object 8 to be inspected mounted on the stage 9. As described above, by the action of the Nomarski prism 6, two illumination lights are formed on the object to be inspected 8 with the centers thereof being slightly spaced apart.

2 from the object 8 to be inspected for two illumination lights
After passing through the objective lens 7 again, the two reflected lights are combined via the Nomarski prism 6. Here, the Nomarski prism 6 has its insertion position defined with respect to the optical axis so as to add a phase difference of an integral multiple of π to and from the two illumination lights. Therefore, when the object 8 to be inspected is a flat surface with no change in reflectance, that is, a mirror surface, the phase difference between the two reflected lights that have passed through the Nomarski prism 6 is an integral multiple of π. In other words, the two reflected lights from the object 8 to be inspected for the two illumination lights are the Nomarski prism 6
Is combined into linearly polarized light having polarized light parallel or perpendicular to the paper surface of FIG.

The combined light that has passed through the Nomarski prism 6 enters the half mirror 5. The combined light transmitted through the half mirror 5 enters the quarter wave plate 10. The quarter-wave plate 10 is positioned at an azimuth angle π / 4 with respect to the linear polarization direction of the combined linearly polarized light that enters the quarter-wave plate 10 when the object 8 to be inspected is a mirror surface. Therefore, when the object 8 to be inspected is a mirror surface, the combined light that has passed through the quarter-wave plate 10 becomes circularly polarized light and enters the polarization beam splitter 11 that is an analyzer.

The polarization beam splitter 11 is positioned so that the analyzer angle φ is π / 4, and splits the incident light into transmitted light and reflected light. The light transmitted through the polarization beam splitter 11 is imaged on the two-dimensional image sensor 13 by the lens 12 and photoelectrically converted. On the other hand, the light reflected by the polarization beam splitter is imaged on the two-dimensional image sensor 15 by the lens 14 and photoelectrically converted. The two-dimensional image sensor 13 and the two-dimensional image sensor 15 have the same pixel configuration, and the corresponding pixels are aligned so as to receive the reflected light from the same place on the object 8 to be inspected.

The two-dimensional image sensor is, for example, C
An image sensor such as a CD is used. The electric signals photoelectrically converted by the two-dimensional image sensor 13 and the two-dimensional image sensor 15 are supplied to the two-dimensional subtractor 16 and the two-dimensional adder 17. In the two-dimensional subtractor 16, the difference signal S is obtained for each pixel based on the signal from the two-dimensional image sensor 13 and the signal from the two-dimensional image sensor 15, and the two-dimensional adder 17 uses the two-dimensional image sensor 13 The sum signal W is obtained for each pixel based on the signal from the two-dimensional image sensor 15 and the signal from the two-dimensional image sensor 15. The difference signal S obtained by the two-dimensional subtractor 16 and the sum signal W obtained by the two-dimensional adder 17
Is supplied to the arithmetic unit 18.

The arithmetic unit 18 calculates the step based on the difference signal S and the sum signal W, as already described in the operation of the present invention. The step difference data calculated by the arithmetic unit 18 is supplied to the image forming apparatus 19 together with the difference signal S and the sum signal W. The image forming device 19 supplies the image data based on the difference signal S or the sum signal W to the display device 21 together with the measured value of the step according to the instruction from the selection device 20. That is, the image forming device 19 supplies the differential interference image when the selecting device 20 selects the difference signal S, and supplies the bright field image when the selecting device 20 selects the sum signal W.

In this way, the display device 21 displays the differential interference image or the bright field image according to the switching of the selection device 20 together with the measured value of the step. In this case, the profile of the difference signal S and the profile of the sum signal W are superimposed and displayed on the differential interference image or the bright field image. 2A and 2B are diagrams showing typical profiles of the difference signal S and the sum signal W. As shown in FIG. In FIG. 2, the horizontal axis represents the position along the direction of the positional deviation of the two illumination lights on the object 8 to be inspected (the origin is the step position), and the vertical axis represents the signal intensity at each position.

A concrete step of calculating the step is shown in FIG.
2 and the sum signals W _a and W _{b in} FIG. _2B , the phase difference Ψ is obtained from the equation (18). Incidentally, when the phase difference Ψ is obtained, calibration is performed using an object whose reflectance is known, and the device constant D of the equation (18) is obtained as already described in the operation of the present invention. Also,
When the image of the step is in a certain pixel of the two-dimensional image sensor 13 and the two-dimensional image sensor 15, the sum signal W _a and W _b are used the output of the front and rear or right and left pixels of the pixel. In addition, the front and back or left and right pixels selected at that time are
Appropriate pixels are selected depending on the resolution of the two-dimensional image sensor and the object to be inspected.

Thus, the phase difference Δh can be calculated by substituting the obtained phase difference Ψ into the equation (19). Therefore, in the present invention, even if the light reflectance changes on both sides of the step, it is possible to measure any step with high accuracy. In the embodiment described above, the linearly polarized illumination light enters the quarter-wave plate 10 when the mirror surface is observed. However, if the optical system is adjusted by defining the insertion position of the Nomarski prism 5 with respect to the optical axis so that the illumination light is already circularly polarized immediately before the quarter-wave plate 10, the quarter-wave plate 10 is obtained. It can be omitted.

FIG. 3 is a diagram schematically showing the structure of a step measuring apparatus according to the second embodiment of the present invention. A light source 2 using the same light source and illumination optical system as those of the first embodiment
Reference numeral 2 denotes a tungsten lamp, and the emitted light passes through the collimator lens 23 to become parallel light, and passes through the interference filter 24 to select the wavelength. In this example, the wavelength was chosen to be 550 nm. The light transmitted through the interference filter 24 becomes a linearly polarized light at the polarizing plate 25, and the half mirror 2
It is incident on 6. The polarization direction at this time is parallel to the paper surface.

The light reflected downward in the figure by the half mirror 26 enters a Nomarski prism 27. The Nomarski prism 27 is a birefringent prism that has an optical axis that intersects the polarization direction of the incident light at 45 ° and splits the incident light into two lights by a polarization component. The light split into two via the Nomarski prism 27 is condensed via an objective lens 28 to form two illumination lights on a test object 29 placed on a stage 30.

As described above, due to the action of the Nomarski prism 27, the two illumination lights are formed on the object 29 to be inspected with a slight distance between the centers of the two illumination lights. The two reflected lights from the object 29 to be inspected for the two illumination lights pass through the objective lens 28 again, and then the Nomarski prism 27.
Is synthesized via. Here, Nomarski prism 2
In No. 7, the insertion position with respect to the optical axis is defined so as to add a phase difference of an integral multiple of π to and from the two illumination lights. Therefore, when the object 29 to be inspected is a flat surface without steps, that is, a mirror surface, the Nomarski prism 2
The phase difference between the two reflected lights passing through 7 becomes an integral multiple of π.
In other words, the two reflected lights from the test object 29 with respect to the two illumination lights are combined via the Nomarski prism 27 into linearly polarized light having polarized light parallel or perpendicular to the paper surface of FIG.

The combined light that has passed through the Nomarski prism 27 enters the half mirror 26. The combined light transmitted through the half mirror 26 enters the quarter-wave plate 31. 1/4
The wave plate 31 is 1/4 when the object 29 to be inspected is a mirror surface.
It is positioned at an azimuth angle π / 4 with respect to the linearly polarized direction of the combined linearly polarized light that enters the wave plate 31. Therefore, when the object 29 to be inspected is a mirror surface, the combined light that has passed through the quarter-wave plate 31 becomes circularly polarized light and enters the analyzer 32. The analyzer 32 includes a polarizing plate that is rotatable about the optical axis and a motor that rotates the polarizing plate based on the analyzer angle signal output from the motor driver 33. The motor driver 33 supplies the analyzer angle of the analyzer 32 to the image forming device 34 as an electric signal.

The light transmitted through the analyzer 32 is reflected by the lens 3
At 5, the image is formed on the two-dimensional image sensor 36 and photoelectrically converted. The signal photoelectrically converted by the two-dimensional image sensor 36 is supplied to the image forming apparatus 34. The image forming device 34
Based on the signal of the analyzer angle from the motor driver 33, the electrical signal photoelectrically converted by the two-dimensional image sensor 36 when the analyzer angle is π / 4 (this is φ1) is captured and stored in the image storage device 37. . Next, when the analyzer angle becomes φ1 + mπ / 2 (m is an odd number), the electric signal photoelectrically converted by the two-dimensional image sensor 36 is again taken in, and when the analyzer angle accumulated in the image accumulating device 37 for each pixel is φ1. Difference signal S and sum signal W from the image of
Is calculated.

Further, the image forming device 34 supplies the image data based on the difference signal S or the sum signal W to the display device 39 together with the measured value of the step according to the instruction from the selection device 38. That is, the image forming device 34 supplies the differential interference image when the selecting device 38 selects the difference signal S, and supplies the bright field image when the selecting device 38 selects the sum signal W.

Thus, the display device 39 displays the differential interference image or the bright field image in accordance with the switching of the selection device 38 together with the measured value of the step. In this case, the profile of the difference signal S and the profile of the sum signal W are superimposed and displayed on the differential interference image or the bright field image. Hereinafter, the step Δh can be calculated in the same manner as in the above-described first embodiment of the present invention.

FIG. 4 is a diagram schematically showing the structure of a step measuring apparatus according to the third embodiment of the present invention. Most of the configuration of the step measuring device shown in this embodiment is the second one shown in FIG.
This is the same as the step measuring device of the embodiment. Therefore, the second
The same components as those in the embodiment are designated by the same reference numerals and the description thereof will be omitted. Here, only the difference from the second embodiment will be described.

In this embodiment, a liquid crystal polarization device 40 is used as the analyzer in place of the polarizing plate rotated by the motor in the second embodiment. Liquid crystal polarization device 40
Operates as a polarizing plate whose polarization direction can be arbitrarily changed by arbitrarily changing the voltage applied from the drive device 41, that is, an analyzer whose analyzer angle can be arbitrarily set. The drive device 41 supplies the analyzer angle as an electric signal to the image forming device 34.

The light transmitted through the liquid crystal polarization device 40 is imaged on the two-dimensional image sensor 36 by the lens 35 and photoelectrically converted. The signal photoelectrically converted by the two-dimensional image sensor 36 is supplied to the image forming apparatus 34. The image forming device 34
Based on the analyzer angle signal from the drive device 41,
When the analyzer angle is π / 4 (this is φ1), the electric signal photoelectrically converted by the two-dimensional image sensor 36 is captured and stored in the image storage device 37. Next, when the analyzer angle becomes φ1 + mπ / 2 (m is an odd number), the electric signal photoelectrically converted by the two-dimensional image sensor 36 is again taken in, and when the analyzer angle accumulated in the image accumulating device 37 for each pixel is φ1. The difference signal S from the image and the sum signal W are calculated.

Hereinafter, the step Δh can be calculated in the same manner as in the second embodiment according to the present invention described above.
Incidentally, in each of the above-mentioned embodiments, the display of each azimuth angle of each analyzer and the quarter wave plate is shown only as a representative one, but these angles are all equivalent angles due to the periodicity of the angles. It goes without saying that the angle is included.

[0080]

As described above, according to the present invention, it is possible to realize a step measuring device capable of measuring an arbitrary step with high accuracy even if the light reflectance changes on both sides of the step. .

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a step measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a typical profile of a difference signal S and a sum signal W.

FIG. 3 is a diagram schematically showing a configuration of a step measuring device according to a second embodiment of the present invention.

FIG. 4 is a diagram schematically showing a configuration of a step measuring device according to a third embodiment of the present invention.

[Explanation of symbols]

 1, 22 ... Light source 7, 28 ... Objective lens 6, 27 ... Nomarski prism 8, 29 ... Inspected object 10 ... Quarter wave plate 31 ... 1/2 wave plate 11 ... Polarizing beam splitter 13, 15, 36 ... Two-dimensional image sensor 19, 34 ... Image forming device 33 ... Motor driver 40 ... Liquid crystal polarizing device 21, 39 ... Display device

Claims (14)

[Claims] 1. A light source, an illumination optical system for illuminating light from the light source onto an object to be inspected, an objective lens for forming an image of the object to be inspected on a predetermined image plane, and the objective. A birefringent prism that is arranged between the lens and the light source, divides the light from the light source into two lights by its polarization component, and combines the two lights reflected by the object to be inspected; From the two-dimensional image sensor, an analyzer for selecting the combined two lights as specific polarization components, a two-dimensional image sensor disposed on the image plane for receiving light passing through the analyzer, A step measuring device having a measuring means for quantitatively measuring the step of the object to be inspected based on the output signal, wherein the step measuring device is provided when the object to be inspected is a mirror surface. It is designed so that the reflected light reaching the analyzer is circularly polarized. The analyzer has a polarization beam splitter having an analyzer angle of a predetermined angle, the two-dimensional image sensor includes a first two-dimensional image sensor for detecting light transmitted through the polarization beam splitter, and the polarization beam splitter. A second two-dimensional image sensor for detecting the light reflected by the beam splitter, and the measuring means outputs the output of the first two-dimensional image sensor with respect to the step and the second two-dimensional image sensor. Between the output of the step and the phase difference that the step imparts to the two lights, and the step is measured based on the relationship that depends on the change in the amplitude reflectance on both sides of the step. A characteristic step measuring device. 2. The step measuring apparatus according to claim 1, wherein the light source has a wavelength selection unit that selects light emitted from the light source as light having a specific wavelength. 3. The level difference measuring device according to claim 1, wherein the light source has a polarization selecting unit that selects light emitted from the light source as light of a specific polarization. 4. The birefringent prism reciprocates π with respect to two split light when the object to be inspected is a mirror surface.
Is positioned so as to give a phase difference of an integer multiple of, and linearly polarized light is generated by combining the two lights reflected by the object to be measured, and the birefringence is provided on the incident side of the polarization beam splitter. The step measuring device according to claim 3, further comprising a quarter-wave plate for converting linearly polarized light combined through a prism into circularly polarized light. 5. The insertion position of the birefringent prism with respect to the optical axis is defined so that the combined two lights reaching the polarization beam splitter are circularly polarized when the object to be inspected is a mirror surface. Claim 3 characterized in that
4. The step measuring device according to 4. 6. The analyzer angle of the polarization beam splitter is nπ / 4 when n is an odd number, and the measuring means sets the phase difference given to the two lights by the step difference to Ψ, The first for one area
The sum of the output of the two-dimensional image sensor and the output of the second two-dimensional image sensor is W _a, and the output of the first two-dimensional image sensor and the second two-dimensional for the other area of the step The sum of the output of the image sensor is W _b , and the output of the first two-dimensional image sensor and the second
Where S is the difference from the output of the two-dimensional image sensor and D is a device-dependent constant, 6. The step is measured based on the phase difference Ψ obtained by the relationship of.
4. The step measuring device according to 4. 7. A light source, an illumination optical system for illuminating light from the light source onto an object to be inspected, an objective lens for forming an image of the object to be inspected on a predetermined image plane, and the objective. A birefringent prism that is arranged between the lens and the light source, divides the light from the light source into two lights by its polarization component, and combines the two lights reflected by the object to be inspected; From the two-dimensional image sensor, an analyzer for selecting the combined two lights as specific polarization components, a two-dimensional image sensor disposed on the image plane for receiving light passing through the analyzer A step measuring device comprising a measuring means for quantitatively measuring the step of the object to be inspected based on the output signal, wherein the step measuring device is provided when the object to be inspected is a mirror surface. It is designed so that the reflected light reaching the analyzer is circularly polarized. The analyzer has a variable analyzer angle, and the measuring means is configured such that when the analyzer angle of the analyzer is at two different positions, the difference between the output of the two-dimensional image sensor and the step are the two light beams. The step difference measuring device is characterized in that the step difference is measured based on a relationship that is established between the phase difference given to the step difference and the amplitude reflectance change on both sides of the step difference. 8. The step measuring device according to claim 7, wherein the light source has a wavelength selection unit that selects light emitted from the light source as light having a specific wavelength. 9. The level difference measuring device according to claim 7, wherein the light source has a polarization selecting unit that selects light emitted from the light source as light of a specific polarization. 10. The birefringent prism is positioned so as to impart a phase difference of an integral multiple of π to and from two split light beams when the object to be inspected is a mirror surface, and The two lights reflected by the object to be inspected are combined to generate linearly polarized light, and 1 for converting the linearly polarized light combined through the birefringent prism into circularly polarized light on the incident side of the polarization beam splitter. 10. The level difference measuring device according to claim 9, further comprising a / 4 wavelength plate. 11. The insertion position of the birefringent prism with respect to the optical axis is defined so that the combined two lights reaching the polarization beam splitter are circularly polarized when the object to be inspected is a mirror surface. The step measuring device according to claim 9, wherein 12. The analyzer according to claim 7, wherein the analyzer has a polarizing plate rotatable about an optical axis.
The step measuring device according to 0 or 11. 13. The step measuring device according to claim 7, wherein the analyzer has a liquid crystal polarization device. 14. Two different positions of the analyzer angle of the analyzer are nπ / m, where n and m are odd numbers.
4 and nπ / 4 + mπ / 2, and the measuring means sets the phase difference that the step imparts to the two lights as Ψ, and the analyzer angle of the analyzer is in one of the two different positions. The sum of the output of the two-dimensional image sensor and the output of the two-dimensional image sensor in the other state of the two different positions of the analyzer angle is W, and is obtained in one region of the step. Let the value of W be W
_a, and the value of W obtained in the other region of the step is W
_b , where the analyzer angle of the analyzer is in one of the two different positions and the output of the two-dimensional image sensor and the analyzer angle of the analyzer are in the other of the two different positions. Let S be the difference from the output of the two-dimensional image sensor and D be a device-dependent constant. The step is measured based on a phase difference Ψ obtained by the relationship of
The step measuring device according to 1, 12, or 13.