JPH09145330A - 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 polarization beam splitters 13, 11 having variable analyzer angle while a two-dimensional image sensor comprises a first two-dimensional image sensor 15 for detecting the light transmitted through the polarization beam splitter 13, and a second two-dimensional image sensor 17 for detecting the light reflected on the polarization beam splitter 13. A measuring means 20 measures a level difference based on the analyzer angle of polarization beam splitters 13, 11 when the difference of output from first and second two-dimensional image sensor 15, 17 for the level difference is maximum or minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step measuring apparatus, and more particularly to a step measuring apparatus suitable for quantitatively measuring a minute step 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-mentioned conventional non-contact surface roughness meter, the sum signal is also 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 with a variable analyzer angle, and the two-dimensional image sensor has a first two-dimensional image sensor for detecting light transmitted through the polarization beam splitter and reflection by the polarization beam splitter. A second two-dimensional image sensor for detecting the emitted light, and the measuring means includes a first
And a step measuring device characterized by measuring the step based on the analyzer angle of the polarization beam splitter when the difference between the output of the two-dimensional image sensor and the output of the second two-dimensional image sensor becomes maximum or minimum. provide.

According to a preferred aspect of the present invention, the measuring means is based on the sum of the output of the first two-dimensional image sensor and the output of the second two-dimensional image sensor for one region of the step of the object to be inspected. Then, the first amplitude reflectance of the object to be inspected in one area is obtained, and the output of the first two-dimensional image sensor and the second 2
The second amplitude reflectance of the object to be measured in the other area is obtained based on the sum with the output of the three-dimensional image sensor, and the step is determined based on the analyzer angle, the first amplitude reflectance, and the second amplitude reflectance. The phase difference given to the two illumination lights is calculated, and the step is measured based on the calculated phase difference.

In order to solve the above-mentioned problems, the present invention connects 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 on a predetermined image plane. An objective lens for forming an image, and for dividing the light from the light source arranged between the objective lens and the light source into two lights by its polarization component, and for combining the two lights reflected by the object to be inspected. A birefringent prism, an analyzer for selecting two combined light components as specific polarization components, a two-dimensional image sensor arranged on the image plane for receiving light passing through the analyzer, and a two-dimensional image sensor A step measuring device having a measuring means for quantitatively measuring a step of an object to be inspected based on a signal output from the step measuring device, wherein the step measuring device is an analyzer when the object to be inspected is a mirror surface. Is configured so that the reflected light reaching The analyzer angle is variable, and the measuring means measures the step based on the analyzer angle at which the difference between the outputs of the two-dimensional image sensor becomes maximum or minimum when the analyzer angle of the analyzer is at two different positions. There is provided a step measuring device characterized by the above.

According to a preferred aspect of the present invention, the measuring means is based on the sum of the outputs of the two-dimensional image sensor for one region of the step of the object to be inspected when the analyzer angle of the analyzer is at two different positions. , The first amplitude reflectance of the object to be measured in one area is calculated to obtain the sum of the outputs of the two-dimensional image sensor with respect to the other area of the step of the object to be measured when the analyzer angle of the analyzer is at two different positions. The second amplitude reflectance of the object to be measured in the other area is obtained based on the phase difference based on the analyzer angle, the first amplitude reflectance, and the second amplitude reflectance. Is calculated, and the step is measured based on the calculated phase difference.

[0010]

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).

[0013]

(Equation 1)

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, the first
Consider the point image of the 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.

[0015]

(Equation 2)

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

[0017]

(Equation 3)

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 a 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

[0019]

(Equation 4)

[0020]

(Equation 5)

In practice, all diffracted light having 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.

[0022]

(Equation 6)

[0023]

(Equation 7)

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).

[0025]

(Equation 8)

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

[0027]

(Equation 9)

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

[0029]

(Equation 10)

In the expressions (9) and (10), C is a device constant that does not depend on the object, and is given by the following expression (11).

[0031]

[Equation 11]

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

[0033]

(Equation 12)

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

[0035]

(Equation 13)

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. Let b be the amplitude reflectance of the stepped portion, and a
Then, at one edge, the amplitude reflectance changes from a to b and the phase difference due to the step changes from 0 to Ψ. 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, in the right-hand 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 reversed. 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).

[0040]

[Equation 14]

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).

As described above, according to the present invention, the phase difference applied to the light corresponding to the two illumination lights by the optical system just 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 made variable. In this way, the value on the right side of Expression (13) can be obtained from the analyzer angle when the difference signal S at the step position becomes maximum. Further, the reciprocal of the value on the right side of the equation (13) can be obtained from the analyzer angle when the difference signal S at the step position becomes the minimum.

That is, by measuring the analyzer angle when the difference signal S qualitatively becomes the maximum or the minimum, that is, without measuring the value of the difference signal S quantitatively (directly measuring the light quantity), The amount including the phase difference Ψ can be obtained with high accuracy. In addition, on the right side of the equation (13),
The amplitude reflectances a and b are included in addition to the phase difference Ψ.
To determine the amplitude reflectance a and b are as follows may be obtained sum signal W = I _T + I _R in a position sufficiently away from the step.

For example, x sufficiently separated from the step position x = 0
At the position of <0, the relationship shown in the following equation holds true.

[0045]

(Equation 15)

By substituting the equations (4) to (7) into the equation (15) and setting θ = π / 2, the sum signal W _a for the position of x <0 sufficiently separated from the step position x = 0. Is the following equation (1
Given in 6).

[0047]

(Equation 16)

Thus, the amplitude reflectance a can be obtained by calculating the square root of the sum signal W _a given by the equation (16). Here, the equation (16) includes a device-dependent device constant in addition to the amplitude reflectance a,
This device constant is a calculable quantity. However, practically, the device constant can be obtained by performing calibration using a sample with known steps and reflectance.

Further, x> sufficiently separated from the step position x = 0
By calculating the square root of the sum signal W _b with respect to the position of 0, the other amplitude reflectance b can be similarly obtained. Thus, based on the value on the right side of the equation (13) obtained from the analyzer angle when the difference signal S becomes maximum or minimum and the two amplitude reflectances a and b obtained from the sum signals W _a and W _b , respectively. , The phase difference Ψ can be calculated. Then, based on the calculated phase difference Ψ, the step Δh
Can be calculated by the following equation (17).

[0050]

[Equation 17]

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 phase jump amount of light in advance and correct the value of the phase difference Ψ obtained according to the equation (13) with the difference in the phase jump amount measured in advance. However, if the difference in the amount of phase jump of light is within the error range, no correction is necessary.

[0052]

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. In FIG. 1, the light source 1 is shown as a point light source for ease of explanation, but in reality, a light source having a finite size such as a tungsten lamp is used.

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 this embodiment, the wavelength is 550 nm
Was selected. 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. Half mirror 5
Thus, the light reflected downward in the figure enters the Nomarski prism 6. 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 is rotatable about the optical axis.
It is incident on the half-wave plate 11. The half-wave plate 11 has a drive device for rotating the half-wave plate 11 at an arbitrary angle in response to a signal from the drive control unit 12. The drive control unit 12 is 1
The rotation angle of the 1/2 wavelength plate 11 is supplied to the control device 20.

The light transmitted through the half-wave plate 11 is separated by the polarization beam splitter 13 into transmitted light and reflected light.
As described above, the half-wave plate 11 is an optical rotator whose polarization rotation angle is variable, and the rotatable half-wave plate 11 and the fixed polarization beam splitter 13 allow the polarization beam whose analyzer angle is variable. The splitter is configured.

The light transmitted through the polarization beam splitter 13 is imaged on the two-dimensional image sensor 15 by the lens 14 and photoelectrically converted. On the other hand, the light reflected by the polarization beam splitter 13 is imaged by the lens 16 on the two-dimensional image sensor 17,
It is photoelectrically converted. The two-dimensional image sensor 15 and the two-dimensional image sensor 17 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 15 and the two-dimensional image sensor 17 are supplied to the two-dimensional subtractor 18 and the two-dimensional adder 19. The two-dimensional subtractor 18 obtains the difference signal S for each pixel based on the signal from the two-dimensional image sensor 15 and the signal from the two-dimensional image sensor 17, and the two-dimensional adder 19 calculates the difference signal S for each pixel. The sum signal W is obtained for each pixel based on the signal from the two-dimensional image sensor 17 and the signal from the two-dimensional image sensor 17. The difference signal S obtained by the two-dimensional subtractor 18 and the sum signal W obtained by the two-dimensional adder 19
Are supplied to the control device 20.

The controller 20 controls the drive controller 12 so that the difference signal S from the subtractor 18 becomes maximum (or minimum).
The half-wave plate 11 is rotated around the optical axis via.
The rotation angle (corresponding to half the value of the analyzer angle) of the half-wave plate 11 from the predetermined position when the difference signal S from the subtractor 18 becomes maximum (or minimum) is determined by the drive control unit 12
Is detected by and is supplied to the control device 20.

As already described in the operation of the present invention, the control device 20 is based on the rotation angle (that is, the analyzer angle) of the half-wave plate 11 when the difference signal S becomes maximum (or minimum). , Calculate the step. The calculated step data is supplied to the display device 21. Also, the control device 2
0 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 22. That is, the control device 20
Supplies a differential interference image when the selection device 22 selects the difference signal S, and supplies a bright field image when the selection device 22 selects the sum signal W.

Thus, the display device 21 displays the differential interference image or the bright field image in accordance with the switching of the selection device 22 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.
The value on the right-hand side of equation (13) (or its reciprocal) is determined based on the analyzer angle when the difference signal S of (1) becomes maximum (or minimum). On the other hand, the amplitude reflectance a is obtained from the equation (16) based on the value of the sum signal W _a in FIG. Also,
The amplitude reflectance b is obtained from the equation corresponding to the equation (16) based on the value of the sum signal W _b in FIG.

In obtaining the amplitude reflectance a and the amplitude reflectance b, it is already explained in the operation of the present invention that calibration is performed using an object whose reflectance is known and the device constant of the equation (16) is obtained. On the street. Further, when the image of the step is at a certain pixel of the two two-dimensional image sensors, the sum signals W _a and W _b use the outputs of the pixels before and after or at the left and right of the pixel. It should be noted that the front, rear, left and right pixels selected at that time are appropriately selected depending on the resolution of the two-dimensional image sensor, the object to be inspected and the like.

Thus, the phase difference Ψ is obtained based on the value on the right side of the equation (13) (or its reciprocal) and the amplitude reflectance a and the amplitude reflectance b, and the obtained phase difference Ψ is substituted into the equation (17). Therefore, the step Δh can be calculated. As described above, in this embodiment, the phase difference Ψ is determined by measuring the analyzer angle when the difference signal S qualitatively becomes maximum or minimum, that is, without quantitatively measuring the value of the difference signal S. Find the amount included. Next, the phase difference Ψ is calculated based on the amplitude reflectance a and the amplitude reflectance b on both sides of the step and the amount including the phase difference Ψ. Then, based on the calculated phase difference Ψ,
The step Δh can be calculated. Therefore, in this embodiment, even if the light reflectance changes on both sides of the step, it is possible to measure any step with high accuracy.

In the above embodiment, 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 6 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.

Further, in the above-mentioned embodiment, the analyzer angle of the fixed polarization beam splitter is changed by the action of the half-wave plate 11 rotatable about the optical axis. However, without being limited to the half-wave plate 11, a Faraday rotator using a magneto-optical effect or an optical rotator applying an electro-optical effect can be used as an optical rotator having a polarization rotation action. In the optical rotator applied with the electro-optic effect, the polarization rotation angle can be detected according to the applied voltage.

Furthermore, if the polarization beam splitter 13 and the two-dimensional image sensors 15 and 17 can be integrally rotated, it is possible to omit an optical rotator whose polarization rotation is variable like the half-wave plate 11. Needless to say. FIG. 3 is a diagram schematically showing the configuration of a step measuring apparatus according to the second embodiment of the present invention. The same light source and illumination optical system as those used in the first embodiment were used.

The light source 23 is a tungsten lamp, and the emitted light passes through the collimator lens 24 to become parallel light, and passes through the interference filter 25 to select the wavelength. In this example, the wavelength was chosen to be 550 nm. The light transmitted through the interference filter 25 becomes linearly polarized light at the polarizing plate 26 and enters the half mirror 27. The polarization direction at this time is parallel to the paper surface.

The light reflected downward in the figure by the half mirror 27 enters the Nomarski prism 28. The Nomarski prism 28 is a birefringent prism that has an optical axis that intersects the polarization direction of the incident light at 45 ° and divides the incident light into two lights by a polarization component. The light split into two via the Nomarski prism 28 is condensed via an objective lens 29 to form two illumination lights on an object 30 to be inspected mounted on a stage 31.

As described above, due to the action of the Nomarski prism 28, the two illumination lights are formed on the object 30 to be inspected with a slight distance between the centers of the two illumination lights. The two reflected lights from the object 30 to be inspected for the two illumination lights pass through the objective lens 29 again, and then the Nomarski prism 2
It is synthesized through 8. Here, the Nomarski prism 28 has an 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 30 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 28 is an integral multiple of π. In other words, the object 30 to be inspected for two illumination lights
The two reflected lights from the above are combined through a Nomarski prism 28 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 28 enters the half mirror 27. The combined light transmitted through the half mirror 27 enters the quarter wave plate 32. 1/4
The wave plate 32 is 1/4 when the object 30 to be inspected is a mirror surface.
It is positioned at an azimuth angle of π / 4 with respect to the linear polarization direction of the combined linearly polarized light that enters the wave plate 32. Therefore, when the object 30 to be inspected is a mirror surface, the combined light that has passed through the quarter-wave plate 32 becomes circularly polarized light and enters the analyzer 33. The analyzer 33 is composed of 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 34. The motor driver 34 supplies the analyzer angle of the analyzer 33 as an electric signal to the image forming apparatus 35.

The light transmitted through the analyzer 33 is reflected by the lens 3
At 6, an image is formed on the two-dimensional image sensor 37 and photoelectrically converted. The signal photoelectrically converted by the two-dimensional image sensor 37 is supplied to the image forming apparatus 35. The image forming device 35
Based on the analyzer angle signal from the motor driver 34, the electrical signal photoelectrically converted by the two-dimensional image sensor 37 at a predetermined analyzer angle, for example, φ1, is fetched and stored in the image storage device 38. Then the analyzer angle is φ1
When + π / 2 (or −π / 2) is reached, the electric signal photoelectrically converted by the two-dimensional image sensor 37 is captured again, and the image when the analyzer angle stored in the image storage device 38 for each pixel is φ1 The difference signal S and the sum signal W from and are calculated. The image forming apparatus 35 repeats the capturing and calculation of this electric signal for every φ1.

The image forming device 35 calculates the step difference based on the analyzer angle of the analyzer 33 when the difference signal S reaches the maximum (or minimum), as already described in the operation of the present invention. The calculated step data is displayed on the display device 40.
Supplied to Note that the polarizing plate of the analyzer 33 is always rotated, and the image forming apparatus 35 measures and stores the analyzer angle φ1 when the difference signal S is maximum or minimum, and the analyzer angles φ1 and φ1 + π / 2 (or −). At the time of π / 2), only the electric signal output from the two-dimensional image sensor may be fetched and stored, and the difference signal S and the sum signal W may be calculated from the electric signal.

Further, the image forming device 35 supplies the image data based on the difference signal S or the sum signal W to the display device 40 together with the measured value of the step according to the instruction from the selection device 39. That is, the image forming device 35 supplies the differential interference image when the selecting device 39 selects the difference signal S, and supplies the bright field image when the selecting device 39 selects the sum signal W.

In this way, the differential interference image or the bright field image is displayed on the display device 40 along with the measured value of the step according to the switching of the selection device 39. 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 configuration of a step measuring apparatus according to the third embodiment of the present invention. The structure of the step measuring device shown in this embodiment is almost the same as that of the step measuring device of the second embodiment shown in FIG. Therefore, the same components as those in the second embodiment are designated by the same reference numerals and the description thereof will be omitted. Here, only the points different from the second embodiment will be described.

In this embodiment, a liquid crystal polarization device 41 is used as the analyzer in place of the polarizing plate rotated by the motor in the second embodiment. Liquid crystal polarizing device 41
Operates as a polarizing plate whose polarization direction can be arbitrarily changed by arbitrarily changing the voltage applied from the drive device 42, that is, an analyzer whose analyzer angle can be arbitrarily set. The drive device 42 supplies the analyzer angle as an electric signal to the image forming device 35.

The light transmitted through the liquid crystal polarization device 41 forms an image on the two-dimensional image sensor 37 by the lens 36 and is photoelectrically converted. The signal photoelectrically converted by the two-dimensional image sensor 37 is supplied to the image forming apparatus 35. The image forming device 35
Based on the analyzer angle signal from the drive device 42,
The electrical signal photoelectrically converted by the two-dimensional image sensor 37 is taken in at a predetermined analyzer angle, for example, φ1, and is stored in the image storage device 38. Next, the analyzer angle is φ1 + π
When it becomes / 2 (or -π / 2), the electric signal photoelectrically converted by the two-dimensional image sensor 37 is taken in again,
The difference signal S and the sum signal W from the image when the analyzer angle stored in the image storage device 38 is φ1 are calculated for each pixel. The image forming device 35 repeatedly captures and calculates this electric signal for every φ1.

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

[0080]

As described above, according to the present invention, the phase difference due to the step is calculated based on the analyzer angle when the difference signal S is maximum or minimum and the amplitude reflectance on both sides of the step. The step is obtained based on the phase difference due to the step. Therefore, according to the present invention, it is possible to realize a step measuring device that can measure 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, 23 ... Light source 7, 29 ... Objective lens 6, 28 ... Nomarski prism 8, 30 ... Inspected object 10, 32 ... 1/4 wavelength plate 11 ... 1/2 Wave plate 13 ... Polarizing beam splitter 15, 17, 37 ... Two-dimensional image sensor 20, 35 ... Image forming device 41 ... Liquid crystal polarizing device 21, 40 ... Display device

Claims (18)

[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 with a variable analyzer 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 light reflected by the splitter, wherein 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. A step measuring device, characterized in that the step is measured based on an analyzer angle of the polarization beam splitter when the difference from the output becomes maximum or minimum. 2. The measuring means includes the first measuring device for one area of a step of the object to be measured.
A first amplitude reflectance of the object to be measured in the one area based on a sum of the output of the two-dimensional image sensor and the output of the second two-dimensional image sensor, The first two for the region
A second amplitude reflectance of the object to be measured in the other area based on the sum of the output of the two-dimensional image sensor and the output of the second two-dimensional image sensor, and the analyzer angle, the first amplitude reflection The phase difference that the step imparts to the two illumination lights is calculated based on the rate and the second amplitude reflectance, and the step is measured based on the calculated phase difference. The level difference measuring device according to 1. 3. The analyzer has a polarization beam splitter fixed with respect to the optical axis, and an optical rotator arranged on the incident side of the polarization beam splitter and having a variable polarization rotation angle. The step measuring device according to claim 1. 4. The step measuring device according to claim 3, wherein the polarization rotator having a variable polarization rotation angle is a ½ wavelength plate rotatable with respect to an optical axis. 5. The analyzer has a polarization beam splitter rotatable about an optical axis, and the first two-dimensional image sensor and the second two-dimensional image sensor are integrated with the polarization beam splitter. The step measuring device according to claim 1 or 2, wherein the step measuring device is configured to rotate. 6. The light source according to claim 1, wherein the light source has a wavelength selection unit for selecting light emitted from the light source as light having a specific wavelength. Step measuring device. 7. The light source has polarization selecting means for selecting light emitted from the light source as linearly polarized light having a predetermined polarization direction.
Or the step measuring device described in 6. 8. The birefringent prism reciprocates π with respect to two split light beams when the object to be measured is a mirror surface.
Is positioned so as to provide 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 inspected, and the birefringent prism is provided on the incident side of the analyzer. 8. The level difference measuring device according to claim 7, further comprising a quarter-wave plate for converting the linearly polarized light combined through the light into circularly polarized light. 9. The insertion position of the birefringent prism with respect to the optical axis is defined such that the combined two lights reaching the analyzer are circularly polarized when the object to be inspected is a mirror surface. The step measuring device according to claim 7, wherein 10. 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. The reflected light reaching the analyzer is circularly polarized, and the analyzer has a variable analyzer angle, and the measuring unit is configured to detect the analyzer angle when the analyzer angle is at two different positions. A step measuring device, characterized in that the step is measured based on an analyzer angle when a difference between outputs of a two-dimensional image sensor becomes maximum or minimum. 11. The measuring means, based on a sum of outputs of the two-dimensional image sensor with respect to one region of a step of the object to be inspected when the analyzer angle of the analyzer is at two different positions, The first amplitude reflectance of the object to be inspected in one area is obtained, and the output of the two-dimensional image sensor to the other area of the step of the object to be inspected when the analyzer angle of the analyzer is at two different positions. The second amplitude reflectance of the object to be measured in the other area is calculated based on the sum of, and the step is determined based on the analyzer angle, the first amplitude reflectance, and the second amplitude reflectance. The step difference measuring device according to claim 6, wherein a phase difference given to the two illumination lights is calculated, and the step difference is measured based on the calculated phase difference. 12. The step measuring device according to claim 11, wherein the analyzer has a polarizing plate rotatable about an optical axis. 13. The step measuring device according to claim 11, wherein the analyzer includes a liquid crystal polarization device. 14. Two different positions of the analyzer angle of the analyzer are nπ, where n and m are odd numbers.
14. The level difference measuring device according to claim 10, 11, 12 or 13, wherein / 4 and nπ / 4 + mπ / 2. 15. The light source according to claim 10, 11, 12, 13 or 14, wherein the light source has a wavelength selection unit for selecting light emitted from the light source as light having a specific wavelength. Step measuring device. 16. The light source has a polarization selecting means for selecting light emitted from the light source as linearly polarized light having a predetermined polarization direction.
The step measuring device according to 2, 13, 14 or 15. 17. The birefringent prism is positioned so as to give 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 is provided on the incident side of the analyzer for converting the linearly polarized light combined through the birefringent prism into circularly polarized light. The level difference measuring device according to claim 16, further comprising a / 4 wavelength plate. 18. The insertion position of the birefringent prism with respect to the optical axis is defined such that the combined two lights reaching the analyzer are circularly polarized when the object to be inspected is a mirror surface. The step measuring device according to claim 16, wherein: