JPH1144517A - Method and instrument for measurement of shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the dimensions of structure smaller than the Rayleigh limit. SOLUTION: The light emitted from a laser source 1 is biased by a Galvanomirror 3, condensed in the exit pupil position of an object lens 6 and introduced onto a sample O as parallel light. The Galvanomirror 3 is swiveled to control the incidence angle of illumination light to the sample O. From the bias angle information of the Galvanomirror 3, the incidence angle of the illumination light on the sample O is calculated and stored together with the intensity of specific part of magnified image. After terminating the total scanning of the Galvanomirror 3, an operator 10 calculates the correlation of incidence angle of the stored illumination light and the intensity of the specific part of magnified image and by using the relation between the sample shape and the correlation obtained by calculation or experience in advance, the sample shape is calculated, which results is displayed on a monitor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape measuring method and a shape measuring instrument, and more particularly to a shape measuring method for measuring and inspecting minute dimensions and a shape measuring apparatus for implementing the method.

[0002]

2. Description of the Related Art In an optical microscope, generally, the limit of Rayleigh, δ = 0.61λ / NA (1) (where δ: limit of Rayleigh λ: wavelength of light NA: numerical aperture of objective lens) ) Cannot be completely resolved.
Therefore, it has not been possible to directly measure the dimensions of structures smaller than this Rayleigh limit.

However, it is possible to detect the presence of a structure smaller than the Rayleigh limit, and to detect and identify minute dust, scratches and specific patterns on the observation sample while changing the irradiation angle of the illumination light. Many methods have been proposed in the past.

[0004] In Japanese Patent Application Laid-Open No. 63-218847,
There is disclosed a method of irradiating an observation sample with illumination light while changing the irradiation angle, and identifying a type of the defect based on a change in an image pattern of the defect on the observation sample with respect to the incident angle. This method utilizes the property that the change in the image pattern with respect to the irradiation angle of the illumination light differs depending on the type of defect.

Japanese Patent Publication No. 5-81883 discloses a method of observing recording fringes of a magnetic recording medium subjected to magnetic development processing with good contrast by changing the irradiation angle of illumination light. This method utilizes the property that the diffraction angle varies depending on the interval between recording stripes.

Japanese Patent Application Laid-Open No. 8-75661 discloses a method of efficiently detecting defects such as dust and scratches on an observation sample by irradiating illumination light from two different directions. This method utilizes the property that the illumination angles of illumination suitable for scattered light, diffracted light, and interference fringes are different.

[0007]

However, these conventional techniques are all devised to detect the presence or absence and type of a defect and a specific pattern, and measure the size of a microstructure of an observation sample. No test method is mentioned. As described above, conventionally, a method for accurately measuring the size of a structure smaller than the Rayleigh limit has not been clearly given.

The present invention has been made in view of such conventional problems, and a first object of the present invention is to provide a shape measuring method capable of accurately measuring a dimension of a structure smaller than the Rayleigh limit. That is.

Further, a second object of the present invention is to provide a shape measuring instrument capable of implementing the above-described shape measuring method with a simple configuration and capable of measuring the dimensions of a microstructure with high accuracy.

[0010]

According to the shape measuring method of the present invention which achieves the above object, the angle of incidence of illumination light from a light source on a sample is variable, an enlarged image of the sample is taken, and the illumination light is measured. Calculating a correlation between an incident angle of the sample on the sample and an image characteristic at a predetermined position determined by the shape of the sample in the enlarged image, and obtaining information related to the shape of the sample from the correlation. Is the way.

According to another aspect of the present invention, there is provided a shape measuring instrument, wherein a light source means, an illumination optical system for guiding illumination light from the light source means to a sample at a certain incident angle, and the incident angle are changed. Incident angle variable means, an enlargement optical system that generates an enlarged image of the specimen, an imaging unit that captures an enlarged image of the specimen generated by the enlargement optical system, and the incident angle and the specimen at the enlarged image. A calculating means for obtaining information related to the shape of the sample from a correlation with an image characteristic at a predetermined position determined by the shape.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION
First, an embodiment of a shape measuring method and a shape measuring instrument capable of achieving the above-described object and the respective effects of the invention will be described, and then a preferable configuration that can be applied to the present invention. And its operation and effect will be described, and then each embodiment will be described.

Therefore, the shape measuring method of the present invention will be described first. In the shape measuring method of the present invention, the angle of incidence of the illumination light from the light source on the sample is variable, an enlarged image of the sample is captured, the angle of incidence on the sample of the illumination light, and the shape of the sample in the enlarged image. This method is characterized in that a correlation with an image characteristic at a predetermined position which is determined further is obtained, and information relating to the shape of the sample is obtained from the correlation.

Here, the predetermined position determined by the shape of the sample in the magnified image is defined by the change (how to change) of image characteristics (intensity or phase) generated by changing the incident angle of illumination. In the image plane from which can be derived.

The principle will be described with reference to FIG. Consider two points A and B at a distance d on the sample surface. It is assumed that the two points are irradiated with coherent illumination light having a wavelength λ at an incident angle θ. At this time, since the optical path length difference of the illumination light between the two points A and B is dsin (θ), the phase difference δφ is given by δφ = 2π ｛dsin (θ)｝ / λ (2)

When the two points A and B are enlarged and observed with an optical microscope, the images of the two points form a point image having a certain extent around the respective geometric optical imaging positions. When the spread of the point images at the two points A and B overlaps, the overlapped portions cause interference according to the phase difference of the light emitted from each point. Therefore, the image observed by the optical microscope differs depending on the phase difference δφ of the light reaching the two points A and B.

Thus, the observed image has two points A and B.
The difference depends on the phase difference δφ between them, and this means that, when the incident angle θ of the illumination light is changed, the observed image changes according to the equation (2). And two points A and B
If there is a condition that causes a specific image characteristic when the phase difference δφ of the light reaching the light has a certain value, the incident angle θ of the illumination light is adjusted to satisfy the predetermined condition, and the image at that time is adjusted. From the estimated phase difference δφ and the incident angle θ,
The distance d between the two points A and B can be obtained by using a modification of the equation (2), d = δφ · λ / {2πsin (θ)} (2 ′).

Although the specification of the image by the two points A and B has been described above, it is considered that any sample is made of a set of points. Therefore, particularly for a sample having a structure as fine as the resolution of a microscope, an image position determined by the shape of the sample if the incident angle θ of the illumination light is changed (in the present embodiment, an intermediate position between the two points A and B). The image observed in changes. By determining the correlation between the incident angle θ of the illumination light and the characteristics of the observed image at that image position, it is possible to obtain information related to the shape of the sample.

In a preferred embodiment of the present invention, observation of intensity as a characteristic of an image is simple and convenient in terms of equipment. The change in the image intensity distribution when the two points A and B are separated from each other by 0.5λ / NA, which is slightly smaller than the Rayleigh limit represented by the equation (1), will be described with reference to FIG. When δφ is an integral multiple of 2π, the two point images overlap in phase with each other, and the intensity distribution of the observed image is as shown in FIG.
As shown in FIG. 9A, one large ellipse is formed (FIG. 9).
(D) Curve 1-1 ′). On the other hand, when δφ is π / 2 + (integer multiple of π), the two point images overlap with a phase shift of π / 2, and the intensity distribution of the observed image is as shown in FIG. It becomes an elongated oblong shape having two gentle peaks (curve 2-2 'in FIG. 9D). And δφ
Is π + (integer multiple of 2π), the two point images are out of phase by π, and the intensity distribution of the observed image is as shown in FIG.
As shown in FIG. 9, two completely separated ellipses are formed (curve 3-3 'in FIG. 9D). Therefore, there is a correlation between the incident angle of the illumination light and the image intensity distribution, and it is possible to obtain information related to the shape of the sample by using the relationship.

In a preferred embodiment of the present invention, it is easy to obtain information relating to the shape of the sample from the rate of change of the intensity at a predetermined position of the image with respect to the incident angle of the illumination light. This is convenient because the correlation between the image characteristics and the incident angle of light can be obtained. In the case of the image formed by the two points A and B shown in FIG. 9, since the image intensity change is large at the intermediate position between the two points A and B, it is necessary to correlate with the incident angle of the illumination light at this intermediate position. desirable.

In a preferred embodiment of the present invention, it is easy to obtain information relating to the shape of the sample from the angle of incidence of the illumination light when the intensity at the predetermined position of the image is minimum. This is convenient because the shape of the sample can be measured quickly. In the case of the image formed by the two points A and B shown in FIG. 9, the image intensity at the intermediate position between the two points A and B is minimum when δφ = π + (integer multiple of 2π). And the interval between the two points A and B can be immediately obtained by using the incident angle θ and (2 ′). Here, the indefinite term of an integral multiple of 2π is obtained by gradually increasing the incident angle of the illumination light from 0 to obtain an angle at which the intensity becomes minimum first, or
Obviously, this can be avoided by determining the angle interval at which the intensity is minimized.

In a preferred embodiment of the present invention, it is convenient to observe the phase distribution as the characteristic of the image because the influence of the fluctuation of the image intensity can be eliminated. In the above, the discussion has focused on the observed image intensity distribution, but it is not only the intensity distribution that can determine the characteristics of the image.
As shown in FIG. 10, the shape of the image phase distribution on the line segment including the two points A and B also changes according to the phase difference δφ. δ
When φ is an integral multiple of 2π, the two point images overlap in phase with each other, so that the observed image phase distribution is a constant. On the other hand, when δφ is π / 2 + (integer multiple of π), the two point images overlap with a phase shift of π / 2, and the observed image phase distribution is gentle from 0 to π except for the constant term. Curve. When δφ is π + (integer multiple of 2π), the two point images have a phase shift of π, and the observed image phase distribution has a phase jump of π (phase singularity) at an intermediate position between the two points A and B. ) Exists. Therefore, the incident angle θ of the illumination light is adjusted so that the image phase distribution satisfies a predetermined condition determined by a certain phase difference δφ, and (2 ′) is obtained from the phase difference δφ estimated from the image at that time and the incident angle θ. ), Two points A,
The interval d of B can also be obtained.

In a preferred embodiment of the present invention, it is easy to obtain information relating to the shape of the sample from the change rate of the phase gradient at a predetermined position of the image with respect to the incident angle of the illumination light. This is convenient because the correlation between the image characteristics and the incident angle of light can be obtained. In the case of the phase distribution by the two points A and B shown in FIG. 10, a change in the phase gradient at an intermediate position between the two points A and B is large, and the correlation with the incident angle of the illumination light is easily obtained.

In a preferred embodiment of the present invention, it is easy to obtain information relating to the shape of the specimen from the angle of incidence of the illumination light when the phase gradient at a predetermined position of the image is maximized. This is convenient because the shape of the sample can be measured quickly. In the case of the phase distribution by the two points A and B shown in FIG. 10, the phase gradient at the intermediate position between the two points A and B is δφ = π + (2
(integral multiple of π), the distance between the two points A and B can be immediately obtained by using the incident angle θ of the illumination light at this time and the equation (2 ′). Here, the indefinite term of an integral multiple of 2π is obtained by gradually increasing the incident angle of the illumination light from 0 to obtain an angle at which the phase gradient becomes maximum first, or an angle at which the phase gradient becomes maximum. Obviously, this can be avoided by determining the interval of.

In a preferred embodiment of the present invention, when the specimen includes at least two adjacent bright spots or two bright lines, the incident angle of the illumination light and the two bright spots or two bright spots are determined.
It is easy to measure the distance between the bright points or the bright lines based on the correlation with the image characteristics of the middle part of the image of the bright line because the change in the image characteristics due to the incident angle of the illumination light is the largest. This is preferable because the interval between the bright lines can be measured.

In a preferred embodiment of the present invention, when the specimen includes at least one dark line, the line width of the dark line is determined from the correlation between the incident angle of the illumination light and the image characteristic of the central portion of the dark line image. The measurement is preferable in that the line width of the dark line can be easily measured because the change in image characteristics due to the incident angle of the illumination light is the largest.

This principle will be described with reference to FIG. FIG.
As shown in FIG. 1, an object having a reflectance of 1 spreads on the xy plane, but a dark line having a width of d (reflectance 0) extends parallel to the y-axis around the position of x = 0. And When a coherent illumination light having a wavelength λ is incident thereon at an incident angle θ, the complex amplitude Q (x) of the illumination light on the x-axis is expressed by: Q (x) = exp {j (2πsinθ) x / λ} Is done. Here, j = √ (−1).
The reflectance R (x) of the object is Therefore, the complex amplitude distribution A (x) on the imaging plane is represented by A (x) = {Q (x) R (x)} * P (x). Here, for the sake of simplicity, the coordinates on the image plane are represented by the coordinates x on the sample plane corresponding to the geometrical optics for simplicity, * is an operator representing convolution, and P
(X) is the line spread function of the imaging optical system. P (x)
Is expressed as P (x) = sinc (2NAx / λ) using the numerical aperture NA of the objective lens to be used. Becomes Here, x ′ {2NAx / λ, d ′ {2NAd / λ, s} (si
nθ / NA). | S | <1, d '> 1.22, x =
There is s≡s ₀ where the image intensity at 0 is 0, and at that time, a phase jump occurs at the x = 0 position (ie, the center of the dark line). FIG. 12 is a graph showing the relationship between the normalized dark line interval d ′ when the image intensity at x = 0 becomes 0 and the normalized incident angle s ₀ of the illumination light. FIG.
As shown in the above, the range of 1.22 <d ′ <1.5 or 2.8
In the range of <d ′ <3.3, the change of s ₀ relative to the change of d ′ is large, so that d ′, that is, d can be accurately obtained from the value of s ₀ . However, 3.1 <d '<
In the range of 5, since there are two values of s ₀ at which the image intensity becomes 0 at the position of x = 0, care must be taken when obtaining the value of d using this region. d '<s ₀ the center intensity of the dark line becomes 0 at 1.22 is not present, the phase gradient in the dark middle, as shown in FIG. 13, s and d'
By measuring the rate of change of the phase gradient at the center of the dark line with respect to s, d ′ can be measured to some extent accurately.

Next, the shape measuring instrument of the present invention will be described. The shape measuring instrument according to the present invention generates a light source means, an illumination optical system for guiding illumination light from the light source means to the sample at a certain incident angle, an incident angle variable means for changing the incident angle, and an enlarged image of the sample. The magnification optical system, the imaging means for imaging a magnified image of the sample generated by the magnifying optical system, and the correlation between the incident angle and the image characteristics at a predetermined position determined by the shape of the sample in the magnified image, Calculating means for obtaining information related to the shape.

As described above, in the shape measuring instrument according to the present invention, the illumination light emitted from the light source is guided at a variable incident angle onto the sample by the illumination optical system and the variable incident angle means, and the magnifying optical system and the image pickup means The information related to the shape of the sample is obtained from the correlation between the incident angle of the illumination light and the enlarged image of the sample by the calculating means. By using the shape, the illumination light, the incident angle, and the correlation of the magnified image, the shape of the sample can be accurately measured.

In a preferred embodiment of the present invention, the calculating means obtains information relating to the shape of the sample by correlating the incident angle of the illumination light with the intensity of the image at a predetermined position. Simple and convenient.

In a preferred embodiment of the present invention, it is easy for the calculating means to obtain the information related to the shape of the sample from the rate of change of the intensity at a predetermined position with respect to the incident angle of the illumination light. This is convenient because the correlation between the image characteristics and the incident angle can be obtained.

In a preferred embodiment of the present invention, it is easy for the calculating means to obtain information related to the shape of the sample from the incident angle of the illumination light when the intensity of the image at the predetermined position is minimum. This is convenient because the shape of the sample can be measured quickly.

In a preferred embodiment of the present invention, the calculating means obtains information relating to the shape of the sample from the correlation between the incident angle of the illumination light and the phase distribution of the image at a predetermined position.
This is convenient because the influence of the fluctuation of the image intensity can be eliminated.

In a preferred embodiment of the present invention, it is easy for the calculating means to obtain the information related to the shape of the sample from the rate of change of the phase gradient at a predetermined position with respect to the incident angle of the illumination light. It is convenient because the correlation of the image characteristics with respect to the incident angle can be obtained.

In a preferred embodiment of the present invention, the calculating means obtains information relating to the shape of the sample from the incident angle of the illumination light when the phase gradient of the image at the predetermined position is maximum. This is convenient because the shape of the sample can be easily measured.

In a preferred embodiment of the present invention, the light source means is a laser light source, which is convenient because a plane wave can be easily illuminated on the sample.

In a preferred embodiment of the present invention, the illumination optical system includes a pupil condenser lens for converging the illumination light emitted from the light source means at the exit pupil position of the magnifying optical system or at a position conjugate to the exit pupil position. This is convenient because the incident angle range of the illumination light and the resolution of the high magnification optical system can be compatible.

In a preferred embodiment of the present invention, the incident angle changing means is preferably a galvanomirror, since the incident angle of the illumination light can be easily and quickly changed.

In a preferred embodiment of the present invention, the incident angle changing means is preferably a polygon mirror in that the incident angle of the illumination light can be easily and quickly changed.

According to a preferred embodiment of the present invention, an interferometer is provided in the illumination optical system, and an interference image corresponding to the phase distribution of the image is generated on the image pickup means. It is preferable because it can be measured.

In a preferred embodiment of the invention, the interferometer is a Michelson-type interferometer, a Millau-type interferometer or a Nomarski-type interferometer,
This is preferable because an interferometer can be easily configured.

In a preferred embodiment of the present invention, there is provided an optical path length difference adjusting means for adjusting an optical path length difference between two divided optical paths in the interferometer, and the optical path length difference adjusting means drives the optical path length difference adjusting means. It is preferable to be connected to a control device that performs fringe scanning in that the phase distribution of the image can be measured with high accuracy.

[0043]

Embodiments of the present invention will be described below with reference to the drawings. The shape measuring apparatus of the first embodiment according to the present invention
As shown in FIG. 1, a laser light source 1, a beam expander 2 for expanding the diameter of a coherent beam emitted from the laser light source 1, and a galvano mirror for deflecting the coherent beam expanded by the beam expander 2 at an angle. 3, a pupil condenser lens 4 for condensing the beam from the galvanometer mirror 3, an optical path splitter 5 for deflecting the convergent light from the pupil condenser lens 4, and the exit pupil position coincides with the convergent position of the convergent light. And an objective lens 6 for generating an enlarged image of the sample O at infinity and an imaging lens 7 for forming an enlarged image of the sample O generated at infinity by the objective lens 6 at a finite position. An imaging device 8 that captures an enlarged image of the specimen O generated by the imaging lens 7; a controller 9 that is electrically connected to the galvanometer mirror 3 and the imaging device 8; Electrically connected to each arithmetic unit 10 to the roller 9, it consists electrically connected to a monitor 11 Metropolitan to the arithmetic unit 10.

In such an apparatus, the coherent beam emitted from the laser light source 1 is expanded in diameter by the beam expander 2, deflected by the galvanomirror 3, and condensed at the exit pupil position of the objective lens 6. Then, the light is incident on the sample O as parallel light. Shake the galvanometer mirror 3,
By changing the beam condensing position at the exit pupil position of the objective lens 6, the angle of incidence of the illumination light on the sample can be adjusted.

The galvanomirror 3 is controlled by the controller 9.
While changing the incident angle of the illumination light on the sample O,
The intensity distribution of the enlarged image of the specimen O is imaged by the imaging device 8. The obtained enlarged image is sent to the arithmetic unit 10 via the controller 9 together with the deflection angle information of the galvanometer mirror 3. The arithmetic unit 10 displays the enlarged image on the monitor 11, calculates the incident angle of the illumination light on the sample O from the deflection angle information of the galvanomirror 3, and stores the angle together with the intensity of the specific portion of the enlarged image. After the scanning of the galvanometer mirror 3 is completed by the controller 9, the arithmetic unit 10 calculates the correlation between the stored incident angle of the illumination light and the intensity of the specific portion of the enlarged image, and obtains the correlation in advance by calculation or experience. The sample shape is measured using the relationship between the sample shape and its correlation, and the result is displayed on the monitor 11.

A flow chart of the procedure for measuring the line width in the present embodiment will be described with reference to FIGS. If the line width of the sample O is large to some extent, it can be measured from the incident angle of the illumination light to the sample O when the intensity of the enlarged image at the center of the line width becomes zero. As shown in FIG. 2, the procedure is as follows. In step ST 1, the measurer monitors the sample O on the monitor 11.
Is set so that the line to be measured enters the vicinity of the center of the magnified image visual field while viewing the image.
Is operated to set the angle of incidence of the illumination light at which the intensity of the magnified image at the center of the line image measured in advance becomes zero, and then sends a measurement start signal to the controller 9. In ST3, the controller 9 captures an enlarged image of the sample O, and in ST4.
, The intensity at the center of the line image is extracted from the enlarged image. In ST5, it is determined whether or not the intensity at the center of the line image is 0. If the intensity at the center of the picked-up line image is not 0, the galvanomirror 3 is driven in ST6, and the sample surface of the illumination light is sampled. By changing the incident angle to
5 are repeated, and when the intensity of the center of the captured line image becomes 0, the driving of the galvanomirror 3 is stopped. In ST7, the deflection angle of the galvanomirror 3 at that time is sent to the arithmetic unit 10. In ST8, the arithmetic unit 10 calculates the incident angle of the illumination light on the sample from the deflection angle of the galvanometer mirror 3 sent from the controller 9, and in ST9, calculates the correlation between the incident angle and the line width previously obtained. The line width is calculated, and the result is displayed on the monitor 11.
However, regarding the actual measurement, there is flare in the optical system and noise in the imaging system. Therefore, it is better to replace the condition of the image intensity 0 with the condition of the minimum image intensity.

Unless the line width of the sample O is thin to some extent and the intensity of the enlarged image at the center of the line width does not become 0, the correlation between the angle of incidence of the illumination light on the sample O and the intensity distribution of the line image will be described. The width can be measured. As shown in FIG. 3, the operator sets the sample O in step ST1 so that the line to be measured enters the vicinity of the center of the enlarged image visual field while watching the monitor 11, and sends a signal to the controller 9 to start the measurement. Send. S
At T2, the controller 9 first adjusts the deflection angle of the galvanometer mirror 3 so that the angle of incidence of the illumination light on the sample O becomes 0, and starts capturing an enlarged image of the sample O at ST3. Next, in ST4, the intensity at the center of the line image is extracted from the enlarged image, and in ST5,
The deflection angle of the galvanometer mirror 3 at that time is calculated by the arithmetic unit 10
Send to In ST6, the arithmetic unit 10 calculates the incident angle of the illumination light to the sample from the deflection angle of the galvanometer mirror 3 sent from the controller 9, and in ST7, the incident angle of the illumination light to the sample and the intensity at the center of the line image. Is recorded, and in ST8, it is determined whether or not the incident angle of the illumination light to the sample O with respect to the sample O is a predetermined maximum incident angle, and the incident angle of the illumination light to the sample is determined in advance. If it is not the determined maximum incident angle, in ST9, the galvanomirror 3 is driven to increase the incident angle of the illumination light on the sample surface,
Steps ST3 to ST8 are repeated, and the galvanomirror 3 is driven until the angle of incidence of the illumination light on the sample O reaches a predetermined maximum value, thereby enlarging the sample O while changing the angle of incidence of the illumination light on the sample O. Take an image. After the driving of the galvanometer mirror 3 by the controller 9 is completed, in ST10,
Arithmetic unit 10 calculates the correlation between the angle of incidence of illumination light on sample O and the intensity of the center of the line image in the magnified image, and calculates the line width from the previously determined relationship between the correlation and the line width in ST11. Then, the result is displayed on the monitor 11.

According to the present embodiment, the angle of incidence of the illumination light on the sample O is changed by the galvanomirror 3, so that the angle of incidence of the illumination light on the sample O can be changed at a high speed. Since the sample O is illuminated coaxially with the light through the objective lens 6, 0 ≦ | s | <
There is an advantage that the angle of incidence of the illumination light on the sample O can be changed in the range of 1. As described above, when measuring a dark line, a condition that the image intensity becomes 0 at x = 0 cannot be obtained unless | s | <1 (that is, coaxial incident illumination). In measurement of dark lines, coaxial epi-illumination is indispensable. Incidentally, it is of course possible to use a polygon mirror instead of the galvanometer mirror 3 as the incident angle variable means.

A shape measuring apparatus according to a second embodiment of the present invention comprises a laser light source 1 and a laser light source 1 as shown in FIG.
A beam expander 2 for expanding the diameter of a coherent beam emitted from the optical system, a galvanomirror 3 for deflecting the coherent beam expanded by the beam expander 2 at a variable angle, and a pupil for condensing the beam from the galvanomirror 3 A part of the convergent light from the condenser lens 4 and the pupil condenser lens 4 is divided into an observation optical path 12 and the other part is divided into a reference optical path 13 and light rays from the observation optical path 12 and the reference optical path 13 are combined. A beam splitter / synthesizer 5 ′, an objective lens 6 that is arranged so that the rear focal position coincides with the convergent position of the convergent light on the observation optical path 12, and generates an enlarged image of the sample O at infinity; A reference lens 14 that is disposed so that the rear focal point position coincides with the convergence position of the convergent light on the reference optical path 13 and is optically equivalent to the objective lens 6;
Reference mirror 15 disposed at the front focal position of reference lens 14
And an optical path length adjusting device 16 that is connected to the reference mirror 15 and moves the reference mirror 15 in the optical axis direction to adjust the optical path length difference between the observation optical path 12 and the reference optical path 13, and is generated at infinity by the objective lens 6. An imaging lens 7 that forms an enlarged image of the sample O at a finite position, an imaging device 8 that captures an enlarged image of the sample O generated by the imaging lens 7, a galvanomirror 3, an imaging device 8, and It comprises a controller 9 electrically connected to the optical path length adjusting device 16, an arithmetic unit 10 electrically connected to the controller 9, and a monitor 11 electrically connected to the arithmetic unit 10.

In such an apparatus, the coherent beam emitted from the laser light source 1 is expanded in diameter by the beam expander 2, deflected by the galvanomirror 3, and turned into convergent light by the pupil condensing lens 4. Are divided into an observation light path 12 and a reference light path 13 by a light beam splitter / combiner 5 '. The convergent light split into the observation optical path 12 is
Is condensed at the rear focal position, and is incident on the sample O as parallel light. On the other hand, the convergent light split into the reference optical path 13 is condensed at the rear focal position of the reference lens 14 and enters the reference mirror 15 as parallel light. The angle of incidence of the illumination light on the sample O can be adjusted by swinging the galvanometer mirror 3 and changing the beam condensing position at the exit pupil position of the objective lens 6.

The light beam reflected by the specimen O and the reference mirror 15 passes through the objective lens 6 and the reference lens 14, respectively.
The light is split again by the beam splitter / combiner 5 'and the image forming lens 7
To form an interference image by the sample image and the reference wavefront on the imaging device 8.

The controller 9 drives the optical path length adjusting device 16 to capture an interference image while changing the phase difference between the sample image and the reference wavefront. The amount of movement of the reference mirror 15 by the optical path length adjusting device 16 and the interference image are obtained. It is sent to the arithmetic unit 10. The arithmetic device 10 calculates the phase distribution of the sample image using a fringe scan method represented by the five bucket method.

Further, the galvanomirror 3 is driven by the controller 9, and the arithmetic device 10 calculates the phase distribution of the sample image while changing the incident angle of the illumination light on the sample O. The deflection angle information of the galvanomirror 3 is sent to the arithmetic unit 10 via the controller 9. The arithmetic unit 10 displays the interference image on the monitor 11, calculates the incident angle of the illumination light on the sample O from the deflection angle information of the galvanometer mirror 3, and stores the calculated angle together with the phase distribution of a specific portion of the interference image. After the controller 9 completes the scanning of the galvanometer mirror 3, the arithmetic unit 10 calculates the correlation between the stored incident angle of the illumination light and the phase distribution of a specific portion of the interference image,
The sample shape is calculated using the relationship between the sample shape and the correlation obtained in advance by calculation or experience, and the result is displayed on the monitor 11.

A flowchart of the procedure for measuring the line width in the present embodiment will be described with reference to FIGS. If the line width of the sample O is large to some extent, it can be measured from the angle of incidence of the illumination light on the sample O when a singular point occurs in the phase distribution at the center of the line width. As shown in FIG. 5, the procedure is as follows. In ST1, the measurer sets the sample O so that the line to be measured enters the vicinity of the center of the enlarged image visual field while watching the monitor 11, and in ST2, the galvanometer mirror 3 is moved. The operation is set to the incident angle of the illumination light at which a singular point occurs in the phase distribution at the center of the line image measured in advance, and then a signal to start measurement is sent to the controller 9. In ST3, imaging of an enlarged image of the specimen O is started. Next, in ST4, the controller 9 performs a fringe scan while driving the optical path length adjusting device 16 to move the reference mirror 15, and
A phase image of the sample O is calculated. In ST5, a phase distribution near the center of the line image is extracted. In ST6, it is determined whether or not there is a phase singular point in the phase distribution. If there is no phase singular point at the center of the line image in the calculated phase image, in ST7, the galvanomirror 3 is driven and the illumination light The angles of incidence on the sample surface are changed, and the above ST3 to ST6 are repeated. When the phase singular point occurs at the center of the captured line image, the driving of the galvanometer mirror 3 is stopped. The deflection angle of the mirror 3 is sent to the arithmetic unit 10. In ST9, the arithmetic unit 10 calculates the incident angle of the illumination light on the sample from the deflection angle of the galvanometer mirror 3 sent from the controller 9, and in ST10,
The line width is calculated from the correlation between the line width of the incident angle and the line width determined in advance, and the result is displayed on the monitor 11.

If the line width of the sample O is small to some extent and no singular point occurs in the phase distribution in the interference image at the center of the line width, the angle between the incident angle of the illumination light to the sample O and the phase distribution of the line image is determined. The line width can be measured from the correlation. As shown in FIG. 6, the measurer sets the sample O in ST1 so that the line to be measured enters the vicinity of the center of the enlarged image field of view while watching the monitor 11, and sends a measurement start signal to the controller 9. Send. In ST2, the controller 9
First, the deflection angle of the galvanometer mirror 3 is adjusted so that the angle of incidence of the illumination light on the sample O becomes 0, and the imaging of the interference image of the sample O is started in ST3. Next, ST4
In, the controller 9 performs a fringe scan while driving the optical path length adjusting device 16 to move the reference mirror 15, and calculates the phase distribution of the sample O. In ST5,
The phase gradient near the center of the line image is extracted, and the deflection angle of the galvanomirror 3 at that time is sent to the arithmetic unit 10 in ST6. In ST7, the arithmetic unit 10 calculates the incidence angle of the illumination light on the sample from the deflection angle of the galvanometer mirror 3 sent from the controller 9, and in ST8, the incidence angle of the illumination light on the sample and the phase near the center of the line image. The gradient is recorded, and in ST9, it is determined whether the incident angle of the illumination light to the sample O with respect to the sample O is a predetermined maximum incident angle, and the incident angle of the illumination light to the sample is determined. If it is not the predetermined maximum incident angle, in ST10, the galvanomirror 3 is driven to increase the incident angle of the illumination light on the sample surface, and the above ST3 to ST9 are repeated to repeat the illumination light sample O
The galvanomirror 3 is driven until the angle of incidence on the sample O reaches a predetermined maximum value, and an interference image of the sample O is captured while changing the angle of incidence of the illumination light on the sample O. Controller 9
ST11 after the driving of the galvanometer mirror 3 by the
, The arithmetic unit 10 calculates the correlation between the angle of incidence of the illumination light on the sample and the phase gradient near the center of the line image in the interference image, and calculates the line based on the relationship between the correlation and the line width determined in advance in ST12. Calculate the width and monitor the result on monitor 1
1 is displayed.

According to the present embodiment, the line width is measured based on the phase distribution of the interference image, so that there is an advantage that the influence of the output fluctuation of the light source can be eliminated and stable measurement can be performed. It is apparent that the above object can be achieved by using a Michelson-type, a Millow-type, or a Nomarski-type interferometer instead of using the above-mentioned linear-type interferometer.

Although only an example of line width measurement has been described above, it is apparent that the present invention is not limited to this as long as the correlation between the angle of incidence of the illumination light on the sample and the image characteristics can be obtained. is there.

In the third embodiment according to the present invention, as shown in FIG. 7, a laser light source 1 and a beam expander 2 are integrally formed, and an illumination unit 17 capable of illuminating a specimen at variable incident angles is provided. An objective lens 6 for generating an enlarged image of the sample O, an imaging device 8 for capturing an enlarged image of the sample generated by the objective lens 6, a controller 9 electrically connected to the illumination unit 17 and the imaging device 8, , An arithmetic unit 10 electrically connected to the controller 9, and a monitor 11 electrically connected to the arithmetic unit 10.

In such an apparatus, the beam expander 2 expands the diameter of the coherent light beam emitted from the laser light source 1 and converts the beam into parallel light for illuminating the sample O. The illumination unit 17 in which the laser light source 1 and the beam expander 2 are integrated is configured to be rotatable about the observation position of the sample O so that the controller 9 can illuminate the sample O at a variable incident angle. I have. The controller 9
The imaging unit 8 captures an enlarged image of the sample O while moving the illumination unit 17 to change the angle of incidence of the illumination light on the sample O, and delivers each angle of incidence of the illumination light and the enlarged image at that time to the arithmetic unit 10. . The arithmetic unit 10 calculates the shape of the sample O from the correlation between the incident angle of the illumination light and the image intensity distribution of a specific portion of the sample O, and displays the result on the monitor 11.

In this embodiment, it is advantageous that the incident angle of the illumination light to the sample O can be made large irrespective of the numerical aperture of the objective lens 6. That is, when the working distance of the objective lens 6 needs to be long depending on the shape of the sample O or the like, the objective lens 6 having a small numerical aperture must be used. However, if the incident light is off-axis as in the present embodiment, the incident angle of the illumination light can be increased regardless of the numerical aperture of the objective lens 6. For example, sample 2
Since the phase difference between the points is determined by the angle of incidence of the illumination light on the sample O, if the angle of incidence of the illumination light on the sample O is increased, the interval between the two points smaller than the resolution of the objective lens 6 is reduced. It is possible to measure with high accuracy.

It should be noted that, even if an interferometer is combined with the configuration of the present embodiment, and a phase distribution is used instead of the intensity distribution of the sample image,
It is clear from the above description that information relating to the shape of the specimen O can be obtained.

The shape measuring method and the shape measuring instrument of the present invention described above can be constituted, for example, as follows. [1] The incident angle of the illumination light from the light source to the sample is variable, an enlarged image of the sample is taken, and determined by the incident angle of the illumination light to the sample and the shape of the sample in the enlarged image. A shape measurement method comprising: obtaining a correlation with an image characteristic at a predetermined position; and obtaining information relating to the shape of the sample from the correlation.

[2] The shape measuring method according to the above [1], wherein the image characteristic is an image intensity.

[3] The shape measuring method according to the above [2], wherein information relating to the shape of the sample is obtained from a rate of change of intensity at the predetermined position with respect to the incident angle.

[4] The shape measuring method according to [2], wherein information related to the shape of the sample is obtained from the incident angle when the intensity at the predetermined position is minimum.

[5] The shape measuring method according to [1], wherein the image characteristic is a phase distribution of an image.

[6] The shape measuring method according to [5], wherein information related to the shape of the sample is obtained from a rate of change of the phase gradient at the predetermined position with respect to the incident angle.

[7] The shape measuring method according to the above [5], wherein information related to the shape of the sample is obtained from the incident angle when the phase gradient at the predetermined position is maximum.

[8] The sample is at least two adjacent
One bright point or two bright lines, and based on a correlation between the incident angle and an image characteristic of an intermediate portion between the two bright points or two bright lines in the enlarged image, the distance between the bright points or the bright lines is determined. The shape measuring method according to any one of the above [1] to [7], wherein the shape is measured.

[0070]

[9] The sample includes at least one dark line, and a line width of the dark line is measured from a correlation between the incident angle and an image characteristic of a central portion of the image of the dark line in the enlarged image. The shape measuring method according to any one of the above [1] to [7].

[10] Light source means, an illumination optical system for guiding illumination light from the light source means to the sample at a certain incident angle, an incident angle variable means for changing the incident angle, and an enlarged image of the sample. A magnifying optical system to generate, imaging means for imaging a magnified image of the sample generated by the magnifying optical system, and image characteristics at a predetermined position determined by the incident angle and the shape of the sample in the magnified image. Calculating means for obtaining information related to the shape of the sample from the correlation.

[11] The arithmetic unit according to [10], wherein information relating to the shape of the sample is obtained from a correlation between the incident angle and the intensity of the image at the predetermined position. Shape measuring instrument.

[12] The shape measurement according to the above [11], wherein the calculating means obtains information related to the shape of the sample from a rate of change in intensity at the predetermined position with respect to the incident angle. vessel.

[13] The arithmetic unit according to [11], wherein the calculating means obtains information related to the shape of the sample from the incident angle at which the intensity at the predetermined position is minimum. Shape measuring instrument.

[14] The above-mentioned [10], wherein the calculating means obtains information relating to the shape of the sample from the correlation between the incident angle and the phase distribution of the image at the predetermined position. Shape measuring instrument.

[15] The shape according to [14], wherein the calculating means obtains information related to the shape of the sample from a change rate of a phase gradient at the predetermined position with respect to the incident angle. Measuring instrument.

[16] The calculating means calculates the angle of incidence at the time when the phase gradient at the predetermined position becomes the maximum.
The shape measuring device according to the above [14], wherein information related to the shape of the sample is obtained.

[17] The shape measuring instrument according to any one of [10] to [16], wherein the light source means is a laser light source.

[18] The illumination optical system includes a pupil condensing lens for converging the illumination light emitted from the light source means to an exit pupil position of the magnifying optical system or a position conjugate thereto. Any one of [10] to [17]
Item.

[19] The shape measuring instrument according to any one of [10] to [18], wherein an interference image corresponding to the phase distribution is generated on the imaging means using an interferometer. .

[20] An optical path length difference adjusting means for adjusting the optical path length difference between the two divided optical paths in the interferometer is provided, and the optical path length difference adjusting means drives the optical path length difference adjusting means to produce a fringe. The shape measuring device according to the above [19], wherein the shape measuring device is connected to a control device for performing scanning.

[0082]

As is apparent from the above description, the use of the shape measuring method and the shape measuring instrument of the present invention makes it possible to accurately measure the dimensions of a structure smaller than the Rayleigh limit.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating a procedure for measuring a line width in the first embodiment.

FIG. 3 is a flowchart showing another procedure for measuring a line width in the first embodiment.

FIG. 4 is a diagram showing a configuration of a shape measuring apparatus according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing a procedure for measuring a line width in the second embodiment.

FIG. 6 is a flowchart showing another measurement procedure of the line width in the second embodiment.

FIG. 7 is a diagram showing a configuration of a shape measuring apparatus according to a third embodiment of the present invention.

FIG. 8 is a diagram for explaining the basic principle of shape measurement according to the present invention.

FIG. 9 is a diagram showing a change of a two-point image due to a phase difference δφ between two points.

FIG. 10 is a diagram illustrating a relationship between a phase difference δφ and an image phase distribution.

FIG. 11 is a diagram for explaining the principle of measuring the line width of a dark line according to the present invention.

FIG. 12 is a graph showing a relationship between a normalized dark line interval d ′ when the image intensity at the center of the dark line is 0 and a normalized incident angle s _{0 of} illumination light.

FIG. 13 is a graph showing a relationship between a parameter s relating to an incident angle and a phase gradient in the middle of a dark line.

[Explanation of symbols]

 O ... Sample 1 ... Laser light source 2 ... Beam expander 3 ... Galvanometer mirror 4 ... Pupil condensing lens 5 ... Optical path splitter 5 '... Light beam splitter / synthesizer 6 ... Objective lens 7 ... Imaging lens 8 ... Imaging device 9 ... Controller Reference Signs List 10 arithmetic unit 11 monitor 12 observation optical path 13 reference optical path 14 reference lens 15 reference mirror 16 optical path length adjusting device 17 illumination unit

Claims (2)

[Claims] An incident angle of illumination light from a light source to a sample is variable, an enlarged image of the sample is captured, and an angle of incidence of the illumination light on the sample and a shape of the sample in the enlarged image. A shape measurement method comprising: obtaining a correlation with an image characteristic at a predetermined position that is determined; and obtaining information related to the shape of the sample from the correlation. 2. A light source means, an illumination optical system for guiding illumination light from the light source means to a sample at a certain incident angle, an incident angle variable means for changing the incident angle, and generating an enlarged image of the sample. A magnifying optical system, imaging means for taking a magnified image of the specimen generated by the magnifying optical system, and a correlation between the incident angle and image characteristics at a predetermined position determined by the shape of the specimen in the magnified image. And a calculating means for obtaining information related to the shape of the sample.