JPH10268200A - Interference microscope device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate the phase information indicating the irregular shape of the surface of an observed object with high accuracy by obtaining the differential direction from the information of a differential interference image itself by calculation. SOLUTION: The light on two optical paths reflected from an observed object 20 is again merged on the same optical path by a Nomarski prism 18, and it is made an image signal indicating the interference intensity interfering between components having the same vibration direction by an analyzer 23. This interference image is formed on an image pickup element 24, and the change of the interference intensity is converted into an electric signal and stored in an image memory 28. The image stored in the memory 28 is a differential interference image differentiated with the interference image in one direction. A CPU 26 obtains the differential direction from the differential interference image itself stored in the memory 28 according to a differential direction detecting program P1 stored in a memory 27. When the direction that the high- frequency portion of the space frequency component of the Fourier-transformed image is increased is obtained in the program P1, the differential direction can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an interference microscope apparatus for imaging an uneven shape of an observation object surface using light.

[0002]

2. Description of the Related Art As an apparatus for observing the uneven shape of the surface of an observation object by using the phase of light, V.V. R. Tych
insky, I .; N. Masalov and D.M.
V. Ublinsky: OPTICS Comm. , V
ol. 74, (1989), p. Phase interference microscopes such as those at 37-40 are known.

In this apparatus, as shown in FIG. 7, a laser beam generated by a laser oscillator 1 for generating a coherent plane wave of a constant wavelength is split into two object beams and a reference beam by a half mirror 2, and the object beam is separated. The object beam which is incident on the observation object 4 via the first lens 3 and is reflected on the surface of the observation object 4 is again passed through the first lens 3 and the half mirror 2 to a photodetector 5 composed of, for example, a CCD. Image on top.

On the other hand, the reference light beam split by the half mirror 2 is totally reflected by the standard plane mirror 7 after passing through the second lens 6, and is again reflected by the half mirror 2 through the second lens 6.
To form an image on the photodetector 5 in the same manner as the object light beam.

[0005] The photodetector 5 detects an image signal representing the intensity of interference between the object light beam reflected by the observation object 4 and the reference light beam reflected by the standard plane mirror 7, and the result is not shown. The digital value is converted into a digital value by an A / D converter or the like, and is stored in the image memory 8. This is for obtaining a phase corresponding to the uneven shape.

If the wavelength of the laser beam generated by the laser oscillator 1 is λ [nm] and the phase resolution is m [°], the resolution D of the uneven shape on the surface of the observation object 4 is D = mλ / (4π) Λ = 630 [nm], m = 5
[°] (= 0.087 [rad]), the resolution D
= About 4 [nm], which indicates that the resolution D of the uneven shape is very high.

If the direction perpendicular to the surface of the observation object 4 and parallel to the optical path is the Z axis, and the directions parallel to the surface of the observation object 4 and orthogonal to the optical path are the X and Y axes, respectively, Is very high, but the resolution in each of the X and Y axes is λ, which is the same as that of a normal microscope.
[Nm].

However, X, Y parallel to the surface of the observation object 4
To increase the axial resolution, V.V. R. Tychin
sky: OPTICS Comm. , Vol. 74,
(1989), p. A method using a phase such as that described in R. Tychinsky: OPTIC
S Comm. , Vol. 81, (1991), pp.
A method using polarized light such as 131-137 has also been considered.

This method using polarized light uses a differential interference microscope using a Nomarski prism. When light from a light source is polarized and incident on the Nomarski prism, two rays of an ordinary ray and an extraordinary ray depend on the polarization direction. The light enters the observation object while being split into two light paths and shifted laterally by a certain distance. This laterally displaced distance is referred to as a shear amount, and the two light beams are reflected on the surface of the observation object and again become one optical path via the Nomarski prism, so that the two light beams interfere with each other. Since the image obtained by this interference is a differential interference image, unlike the interference image shown in FIG. 7, a phase image is calculated by performing integration in the shear direction, and a phase corresponding to the uneven shape of the surface of the observation object is calculated. Information can be requested.

[0010]

However, in the method shown in FIG. 7, the light from the laser oscillator 1 is divided into a reference beam and an object beam by the half mirror 2, and the reference beam is divided by the standard plane mirror 7. The light is reflected, and the phase of the observation object 4 is measured based on the phase. In this case, since the optical paths of the two light beams, the reference light beam and the object light beam, are different from each other, not only the entire device tends to have a large and complicated structure, but also vibration such as movement of the mounting position of the standard plane mirror 7, for example. There is a problem that it is easily affected by disturbance.

In the above-described method using polarized light, the light from the light source is divided into two optical paths by the Nomarski prism and both are incident on the object to be observed. Only the difference is almost the same, so that the device can be downsized,
It is difficult to imagine that only one of the optical paths is affected by disturbance or the like, and it is hard to be affected by disturbance or the like.

On the other hand, in the method using the polarized light, since the obtained image is a differential interference image, an accurate phase image cannot be obtained unless integration based on the direction of the shear is performed.

However, in order to integrate the differential phase image obtained from the differential interference image, the differential image is fetched by an image pickup device such as a CCD and digitized, and an image processing section comprising a computer performs integral calculation in the direction of the shear. It is necessary to know the exact direction of the shear for the integral calculation.However, the direction of the shear of the light beam by the Normaski prism and the mounting angle of the CCD chip must be accurately determined. In practice, it is extremely difficult to align or detect them, and so it has not been possible to integrate differential interference images to obtain an accurate phase image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object the purpose of not only being small in size and not easily affected by disturbances, etc. The present invention is to provide an interference microscope apparatus which can obtain the surface roughness of the observation object surface with high accuracy without performing positioning adjustment or measurement.

[0015]

According to the first aspect of the present invention,
A light source that generates light of a certain wavelength, a polarization unit that changes the polarization angle of the light generated by the light source, and the light whose polarization angle has been changed by the polarization unit are split into two and shifted laterally to the observation object. An irradiating means for irradiating, a differential interference image detecting means for causing two reflected lights obtained from an observation object to interfere with each other by the irradiating means, and detecting a differential interference image thereof; and a differential interference image obtained by the differential interference image detecting means. A plurality of direction calculation means for calculating a lateral shift direction of the light split into two by the irradiation means, and a plurality of differential interference image detection means obtained by changing the polarization angle of light generated by the light source by the polarization means by a fixed angle. A phase calculating means for obtaining a plurality of differential phase images by obtaining a differential phase image from the differential interference image; and integrating the plurality of differential phase images in the lateral shift direction calculated by the direction calculating means. And characterized by including an integration means for calculating a phase corresponding to the uneven shape of the observation object surface Te.

As a result, according to the first aspect of the present invention,
Direction calculation means calculates the integral direction necessary for differential interference from the differential interference image itself by calculation, so that accurate integration can be performed without any adjustment of the positioning of the Nomarski prism and the image sensor or measurement of these angles. , The uneven shape of the surface of the observation object can be calculated with high accuracy.

According to a second aspect of the present invention, in the first aspect of the present invention, the direction calculation means performs a Fourier transform on the differential interference image and compares the high-frequency components thereof, thereby dividing the differential interference image into two by the irradiation means. A lateral shift direction of light is calculated.

As a result, according to the second aspect of the present invention,
In addition to the operation of the invention described in claim 1, the lateral shift direction of light is calculated using Fourier transform.
The lateral shift direction of the light can be calculated more quickly.

According to a third aspect of the present invention, in the first aspect of the present invention, the direction calculating means calculates a lateral shift direction of the light obtained by dividing the differential interference image into two by the irradiating means by autocorrelation calculation. It is characterized by.

As a result, according to the third aspect of the present invention,
In addition to the operation of the first aspect of the present invention, the lateral shift direction of light is calculated by using an autocorrelation operation.
The lateral shift direction of light can be calculated with higher accuracy.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the interference microscope apparatus of the present invention will be described with reference to the drawings.

FIG. 1 shows a functional configuration thereof. Reference numeral 10 denotes a white light source 10 which outputs white light as a light source. The white light output from the white light source 10 is, after only a certain wavelength component is extracted by the filter 11, at the rotation position of the filter holder 13 holding the ND filters 12, 12,. The amount of light is adjusted appropriately via the ND filter 12 selectively disposed on the optical path in accordance with the above.

This filter holder 13 arranges and holds a plurality of ND filters 12, 12,... Having different transmittances on the same circumference as shown in FIG.
The ND filter 12 having any transmittance is selectively arranged on the optical path by the rotation drive of the rotation drive unit 14 operating based on the control from 26. The light passing through the ND filter 12 The polarization angle is changed via the polarizing plate 15 disposed on the optical path. This polarizing plate 15
The polarizing plate rotation driving unit 16 changes the polarization angle of the transmitted light to be a desired angle by being rotationally driven by the polarization plate rotation driving unit 16.
It operates based on the control from 26.

However, the light that has passed through the polarizing plate 15 is reflected by the half mirror 17 in the sample direction and then split by the Nomarski prism 18 into two parallel optical paths depending on the polarization direction. Both light beams are radiated via an objective lens 19 onto an observation object 20 mounted on a focus observation mechanism 21 for adjusting the focus.

The light reflected from the observation object 20 passes through the half mirror 17 through the objective lens 19 and the Nomarski prism 18, and is transmitted by the imaging lens 22 to the CCD.
The image is formed on the image sensor 24. An analyzer 23 as a rotatable polarizing element is arranged on an optical path between the imaging lens 22 and the image sensor 24.

The output of the image sensor 24 is converted into a digital signal by the A / D converter 25 and sent to the CPU 26 via the bus B. The bus B also includes a memory 27 storing an operation control program, an image memory 28 storing image signals,
A display unit 2 for displaying images, data, etc., for example, a CRT
9 is connected, and the CPU 26 controls the operation of the entire apparatus based on the operation control program stored in the memory 27.

The memory 27 has the filter holder 13
Rotation drive of the rotation drive unit 14 connected to the rotation drive of the polarization plate rotation drive unit 16 that changes the polarization direction of the polarization plate 15,
In addition to an operation control program such as a focus position adjustment by the focus observation mechanism 21 on which the observation object 20 is placed, a differential direction detection program P1 for obtaining a shear direction from a microscopic interference image obtained by the imaging device 24, and a phase from the differential interference image And an integration program P3 for integrating the shear direction obtained by the differential direction detection program P1 and the differential phase image obtained by the phase operation program P2.

Next, the operation of the above embodiment will be described. The white light output from the white light source 10 is extracted through the filter 11 after extracting only a certain wavelength component.
By arranging the ND filter 12 having the optimum transmittance on the optical path by the rotation drive of the rotation drive unit 14 controlled by the PU 26, the ND filter 12 passes through the ND filter 12 to obtain a light amount suitable for imaging by the image sensor 24. After being restricted, the polarizing plate 15
, Is reflected by the half mirror 17, and is split into two by the Nomarski prism 18 according to the polarization direction.

The two divided light beams pass through different parallel light paths, and pass through an objective lens 19 to a focus observation mechanism 21.
The light impinges on a slightly different position on the surface of the observation object 20 mounted thereon.

Thus, the light of the two optical paths reflected by the observation object 20 is made the same optical path again by the Nomarski prism 18 via the objective lens 19, and transmitted through the half mirror 17, and then detected via the imaging lens 22. An image signal representing the intensity of interference caused by interference between the components having the same vibration direction by the photon 23.
When the image is formed on the chip of the image sensor 24, the image sensor 24 converts the change in the interference intensity into an electric signal and outputs it. The electric signal is converted into a digital signal by the A / D converter 25 and stored in the image memory 28 via the bus B in accordance with an instruction from the CPU 26.

The image stored in the image memory 28 in this manner is a so-called differential interference image obtained by differentiating the interference image obtained by using the standard plane mirror 7 shown in FIG. Is Nomarski prism 18
This is the direction in which the light whose optical path is split into two is shifted laterally on the surface of the observation object 20, that is, the shear direction. The CPU 26 obtains the shear direction from the differential interference image itself stored in the image memory 28 in accordance with the differential direction detection program P1 stored in the memory 27.

For example, as shown in FIG. 3, the differential interference image of the observation object 20 inclined at 45 ° with respect to the shear direction is shown in FIG.
As shown in FIG. 7, an image having interference fringes S in the shear direction is obtained.

Therefore, the differential direction detecting program P1
In the above, the differential interference image is Fourier-transformed to calculate the spatial frequency. Specifically, the differential shear image is differentiated such that the spatial frequency as shown in FIG. 5 is obtained from the differential interference image shown in FIG. In the direction, the high frequency component increases. Therefore, in the differential direction detection program P1,
The differential direction is obtained by obtaining the direction in which the high-frequency portion of the spatial frequency component of the Fourier-transformed image becomes large.

The reason why the Fourier transform is used here is that high-speed operations suitable for computer processing can be performed.
In order to calculate the phase from the interference image, a plurality of interference images in a state where the optical path difference between the two laser beams changes by a fraction of the wavelength, for example, １ ／ wavelength, 波長 wavelength, 3
Interference image 4 having a phase difference of / 4 wavelength and 1 wavelength
You need one. Such a phase difference causes the polarizing plate 15
It can be obtained by rotating by 90 °, 90 °, 135 ° and 180 °.

In order to calculate the differential phase from the phase interference image, the polarizing plate 15 is driven to rotate by the polarizing plate rotation drive unit 16 and the above-described differential interference image is captured. The CPU 26 calculates a differential phase according to the phase calculation program P2 stored in the memory 27.

Using the differential phase image obtained in this way and the differential direction obtained by the differential direction detection program P1, the CPU 26 integrates as follows in accordance with the integration program P3 stored in the memory 27. That is, assuming that the differential phase image data is h '(i, j), the phase image data is h (i, j), and the shear amount is Δx, h (i, j) = {h ′ (i, j) · Δx (2) (where the sum is in the differential direction). Since the phase image thus obtained is a phase image only in the shear direction, the above operation is performed again by rotating the observation object 20 with respect to the Nomarski prism 18 by 90 °, and the two-dimensional phase image is obtained from the two unidirectional phase images. A phase image is obtained.

The phase image thus obtained is converted into height information by the above equation (1), and the result is displayed on the display unit 2 as a representation of the unevenness of the surface of the observation object 20.
Display output at 9.

As described above, according to the first embodiment of the present invention, since the differentiated direction is calculated from the information of the differential interference image itself, the relative direction between the image sensor 24 and the Nomarski prism 18 is determined. It is not necessary to measure or adjust, and it is possible to calculate the phase information representing the uneven shape of the surface of the observation object with high accuracy.

A plurality of ND filters 12, 12,..., Which are rotated by the rotation drive unit 14, and have different transmittances.
The filter holder 13, which is arranged and held in a circumferential shape, receives the image sensor 2 according to the magnification of the objective lens 19 based on the amount of light transmitted from the white light source 10 via the filter 11.
4 prevents the amount of incident light from reaching the saturation level, and is output by changing the driving voltage of the white light source 10 without changing the amount of light emitted by the white light source 10 itself. Since the amount of light incident on the image pickup device 24 is adjusted without changing the color temperature of light, the position of the imaging lens 24 is adjusted in addition to the position shown in FIG. It may be arranged at a position such as between the analyzer 22 and the analyzer 23 or between the analyzer 23 and the imaging device 24.

(Second Embodiment) Hereinafter, a second embodiment of the interference microscope apparatus of the present invention will be described with reference to the drawings.

FIG. 6 shows the functional configuration of the white light source 10 as a light source. A switch (SW) 30 for turning on / off the power source is provided, and a laser oscillator 31 for oscillating and outputting a laser beam is used. The white light output from the white light source 10 is transmitted through the half mirror 32 after extracting only a certain wavelength component by the filter 11, and at the same time, the laser light output from the laser oscillator 31 is reflected by the half mirror 32. 1 is basically the same as the configuration shown in FIG. 1 except that two lights are superimposed and pass through an ND filter 12 selectively disposed on an optical path held by a filter holder 13. Therefore, the same portions are denoted by the same reference numerals and description thereof will be omitted.

Next, the operation of the above embodiment will be described. After only a certain wavelength component is extracted from the white light source 10 through the filter 11, the white light output from the white light source 10 is combined with the coherent laser light having the certain wavelength from the laser oscillator 31 by the half mirror 32, The light amount is adjusted by the ND filter 12. Hereinafter, the imaging device 2
Until the image is captured in step 4, the operation is the same as that of the first embodiment.

The observation object 2 captured by the image sensor 24 with the power of the white light source 10 turned on by the switch 30
It is assumed that the image 0 is displayed on the display unit 29 for observation. The image observed here is a laser interference spot superimposed on the differential interference image by the white light source 10. While observing the image, the observation object 20 is set such that the spot of the laser beam is incident on the observation object 20 at an arbitrary position to be measured.
To move.

When the position is determined, the switch 30
The power of the white light source 10 is turned off by the operation described above, and only the laser light output from the laser oscillator 31 is used as the sole light source to obtain a differential interference image again by the same method as in the first embodiment. From the calculation.

As described above, according to the second embodiment of the present invention, in addition to the effects of the first embodiment, a very high coherent laser beam having a constant wavelength is used. The phase measurement can be performed with high accuracy, and the measurement position can be easily positioned.

In the above embodiment, the method for calculating the direction differentiated from the differential interference image is described as using Fourier transform. However, the present invention is not limited to this. For example, the method using autocorrelation calculation is used. It may be.

For example, the differential interference image data is represented by D (i,
Expressed by j), the autocorrelation E (k, l) is as follows. That is, E (k, l) = ΣD (i, j) D (i + k, j + 1) (3) (where i, j, k, l is a positive integer.) The above calculation is performed by (k ² + l ² ). ^1/2 = m (4) (where m is a constant)
(K, l) is obtained.

Further, while changing m from a small number to a large number, the above E (k, l) is obtained one after another. The calculated E (k, l) is sequentially compared with those satisfying the condition of “l / k = const.”. Among them, E (k, l) showing the maximum value and having the minimum m is defined as E (k, l). Select as _max (m).

When the direction of k and l of the selected E _max (m) having the smallest m is obtained, the direction is the differential direction. In this case, although the calculation speed is slightly lower than when the Fourier transform is used, the differentiated direction can be calculated with higher accuracy. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0050]

As described above in detail, according to the present invention, a more accurate direction of integration can be obtained within a short calculation time without performing any positioning adjustment of the Nomarski prism and the image pickup device or measuring these angles. As a result, the uneven shape of the surface of the observation object can be calculated with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a functional configuration of an interference microscope apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an ND filter and a filter holder of FIG. 1;

FIG. 3 is a view exemplifying a shape of an observation object according to the embodiment;

FIG. 4 is a view exemplifying a differential interference image of the observation object in FIG. 4 according to the embodiment;

FIG. 5 is a view exemplifying a spatial frequency of the differential interference image of FIG. 5 according to the embodiment;

FIG. 6 is a diagram showing a functional configuration of an interference microscope apparatus according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a functional configuration of a conventional interference microscope apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... White light source 11 ... Filter 12 ... ND filter 13 ... Filter holder 14 ... Rotation drive part 15 ... Polarizer 16 ... Polarizer rotation drive part 17 ... Half mirror 18 ... Nomarski prism 19 ... Objective lens 20 ... Observation object 21 ... Focus Observation mechanism 22 ... imaging lens 23 ... analyzer 24 ... image sensor 25 ... A / D converter 26 ... CPU 27 ... memory 28 ... image memory 29 ... display unit 30 ... switch (SW) 31 ... laser oscillator 32 ... half mirror P1: Differential direction detection program P2: Phase calculation program P3: Integration program

Claims (3)

[Claims] 1. A light source for generating light of a certain wavelength, a polarizing means for changing a polarization angle of light generated by the light source, and a light whose polarization angle is changed by the polarizing means is divided into two parts.
Irradiating means for irradiating the observation object laterally, irradiating two reflected lights obtained from the observation object by the irradiating means, detecting a differential interference image thereof, and detecting the differential interference image A direction calculating means for calculating a lateral shift direction of the light split into two by the irradiating means from the differential interference image obtained in the above step, and a polarization angle of the light generated by the light source being changed by a fixed angle by the polarizing means, thereby changing the differential interference image Phase calculating means for obtaining a plurality of differential phase images from the plurality of differential interference images obtained by the detecting means to obtain the plurality of differential phase images; and integrating the plurality of differential phase images in the lateral shift direction calculated by the direction calculating means. And an integrating means for calculating a phase corresponding to the uneven shape of the surface of the observation object. 2. The apparatus according to claim 1, wherein the direction calculating means calculates a lateral shift direction of the two-divided light by the irradiating means by performing a Fourier transform of the differential interference image and comparing high-frequency components thereof. 2. The interference microscope apparatus according to 1. 3. The interference microscope apparatus according to claim 1, wherein the direction calculation means calculates a lateral shift direction of the light obtained by dividing the differential interference image into two by the irradiation means by autocorrelation calculation.