JPH07198591A - Ellipsometer - Google Patents

Abstract

PURPOSE:To provide an extinction type ellipsomer which enables adaptation to a film forming process or the like while allowing the fast detection of a quenching point by eliminating fluctuation in the determination of an extinction point to enhance the measuring accuracy. CONSTITUTION:This apparatus includes a first optical system 1 in which are arranged a light source L for irradiating a sample S various characteristics of which are measured with a parallel luminous flux at an arbitrary incident angle, a polarizer P, a sample S, a 1/4lambda plate and an analyzer A in that order, a second optical to measure the condition of the luminous flux to be emitted from the frist optical system 1 and a calculator section 100 which calculates changes in the state of polarization resulting from the reflection of the luminous flux on the sample S based on azimuths of the individual optical elements while controlling the azimuths of the optical elements based on the measurement of the second optical system 2. The second optical system 2 has a telescope optical system 10 as imaging optical system and a CCD 20 as photodetecting element comprising a plurality of small photodetecting areas, which are arranged in that order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a polarized light for examining various characteristics of a sample by irradiating the sample with a polarized light beam and measuring the change in the polarization state of the light beam when reflected on the sample surface. The present invention relates to an improvement in an analyzer, that is, an ellipsometer, and more particularly, to an extinction type ellipsometer which is a method suitable for highly accurate measurement among ellipsometers.

[0002]

2. Description of the Related Art As is well known, an extinction type ellipsometer uses a quarter wavelength plate (hereinafter abbreviated as "1 / 4.lambda. Plate") for changing the polarization state caused by reflection on a sample surface. By adjusting and canceling the azimuth angle of the two optical elements, the so-called analyzer, which is the polarizing prism through which the light flux passes after the reflection of, the optical state in which the amount of light emitted from the analyzer is zero or minimized is realized. The azimuth angle of each optical element at that time is processed by a computer using an appropriate method, and various characteristics of the sample are obtained. In addition, the extinction type ellipsometer has a 1 /
A method of fixing the azimuth angle of the 4λ plate and adjusting the azimuth angle between the analyzer and the polarizing prism, which is a polarizing prism through which the light beam first transmits, is also often used. In any case, it is very important to accurately determine the combination of the azimuth angles of the optical elements that are in the extinction state, which is a prerequisite for accurately measuring the characteristics of the sample.

The amount of light at the time of extinction in the extinction state is 10 _to ^{6 of} the light source.
Therefore, a photodetector with high sensitivity is used as the light receiving unit for detecting the extinction point. When a laser beam such as a He—Ne laser is used as a light source, the amount of light is relatively large, so a Si photodiode or a GaAs photodiode is used. When monochromatic light extracted from a white light source by a spectroscope is used as a light source, the light source brightness is considerably lower than that of a laser, so the amount of emitted light is extremely small and can only be detected by a photomultiplier tube or the like. become. In any case, the light quantity emitted from the analyzer is extremely small, and the extinction type ellipsometer is
Used near the lower limit of photodetector capability.

FIG. 7 shows an example of the configuration of the conventional extinction type ellipsometer 500 described above. In the figure, reference numeral 1 indicates a first optical system. In the first optical system 1, a light source L, a polarizer P, a sample S, a quarter-wave plate C as a quarter-wave element, and an analyzer A are arranged on the optical axis in this order from the left in the figure. It has a well-known arrangement. Reference numeral D is a photodetector,
Reference numeral 200 indicates a light amount measuring circuit, and reference numeral 300 indicates a computer unit.

As described above, the extinction type ellipsometer 5
In the measurement of the characteristics of the sample S at 00, the light intensity of the light emitted from the analyzer A is detected by the photodetector D, the detected light intensity of the emitted light is converted into an electric signal, and the light amount measurement circuit 200 is measured. The light quantity measuring circuit 200 measures the quantity of the emitted light and sends it to the computer section 300 as a signal. The computer section 300 realizes an optical state in which the quantity of light emitted from the analyzer A is zero or minimum. At this time, the azimuth angle of each optical element is calculated, and the point at which the amount of emitted light is the smallest is defined as the extinction point.

However, as shown in FIG. 8, in the vicinity of the extinction point obtained as described above, there is a region where the change in the amount of emitted light is very gentle, and the minimum point of the amount of emitted light is clearly defined. I can't. Therefore, in the conventional extinction type ellipsometer 500 or the like, in the vicinity of the extinction point shown in the same figure, the extinction point in the region where the rate of change of the emitted light quantity is sufficiently large with respect to the rotation angle of the polarizer P or the analyzer A. Before and after, two points having the same amount of emitted light are taken, and the midpoint thereof is adopted as the extinction point. (Reference: Az
zam and Bashara, North-Hol
land'Ellipsometry and pol
arised Light '(1987); p403,
p497).

[0007]

However, this method has a problem that the factors of estimation are often included in the determination of the extinction point, which greatly deteriorates the accuracy of the extinction type ellipsometer. Specifically, as described above, since the photodetector D is used with the received light amount close to the lower limit with respect to its capability, it is greatly affected by the deterioration of the linearity of the electric signal and the noise with respect to the received light amount. Even if the amount of received light is detected, the fluctuation is considerably large, and the extinction point determined as the midpoint between the two points thus obtained contains such an error. Further, in order to determine the two points of the received light amount with a certain resolution, it is necessary that the change in the light amount is steeper as the resolution is desired to be increased, and the light amount is changed as the resolution for determining the extinction point is requested to be higher. It is necessary to measure the light amount at a steep position, that is, at a position further away from the extinction point, and the fluctuation included in the estimation increases accordingly. That is, since the detection of the extinction point is estimated as the midpoint between the two points of the received light amount, the extinction point determination accuracy does not reach a level sufficient to be required, and no further improvement than the current situation can be expected. .

Another major problem with this method is that it requires a long time to determine the extinction point, which greatly narrows the range of industries to which the extinction type ellipsometer can be applied. . That is, specifically, in this method, the rotation of the polarizer P or the analyzer A is reciprocated at least twice in order to determine the extinction point, and in actuality, several times are performed in order to reduce the error. It is necessary to measure the light quantity with rotation. The extinction point is determined by the polarizer P
Since it is usually performed to find a more complete extinction point by alternately rotating the and the analyzer A, it is necessary to measure the light quantity a very large number of times, which is performed while mechanically rotating the optical element. Therefore, it is difficult to increase the speed, and it takes several seconds to several tens of seconds until the extinction point is finally determined, and this time is so long that the extinction point is accurately determined. That is,
Due to the nature of such a procedure for determining the extinction point, it is in principle impossible to determine the exact extinction point when the measurement target is changing.

Further, as an industrial requirement, there is a great demand for measuring a film thickness change in a film forming process of a semiconductor or the like such as vapor deposition or a dry etching process of a thin film, and the extinction type ellipsometer is as follows. This is one of the most suitable film thickness measurement methods for various applications, and is the only method especially when highly accurate film thickness measurement is required.
With the background of sophistication of semiconductor manufacturing process technology in recent years, expectations for such usage are increasing, but in the conventional extinction type ellipsometer, it takes a considerable time to determine the extinction point as described above, and In the measurement of the film formation process etc., the film thickness changes even during the procedure of determining the extinction point, and the magnitude of the film thickness change is not negligible for the accuracy to be measured. In such cases, the extinction point accuracy will be extremely poor, and the extinction type ellipsometer should be used even though such an extinction point detection method becomes an obstacle and is required for these applications. Could not be done.

Therefore, in order to solve such a problem, the present invention enhances the measurement accuracy by eliminating the fluctuation of the extinction point determination, and can cope with the film forming process and the like, and can detect the extinction point at a high speed. It is an object of the present invention to provide a quenching type ellipsometer that can be used.

[0011]

In order to achieve the above-mentioned object, the invention according to claim 1 provides a light source and a polarizer for irradiating a sample whose various characteristics are to be measured with a parallel light beam at an arbitrary incident angle. A first optical system in which the sample, the quarter-wave element and the analyzer are arranged in this order, and a second optical system for measuring the state of the light beam emitted from the first optical system. A computer unit for controlling the azimuth angle of each optical element based on the measurement of the second optical system and calculating the change of the polarization state due to the reflection of the light flux on the sample from the azimuth angle of each optical element. However, the second optical system has an image forming optical system and a photodetecting element including a plurality of small light receiving regions, and is arranged in this order.

In a second aspect of the present invention, a light source for irradiating a sample whose various characteristics are to be measured with a parallel light beam at an arbitrary incident angle, a polarizer, the sample, a quarter-wave element and an analyzer are provided. The first optical system arranged in this order, the second optical system that measures the state of the light beam emitted from the first optical system, and the azimuth angle of each optical element based on the measurement of the second optical system. And a computer unit for calculating the change of the polarization state due to the reflection of the light flux on the sample from the azimuth angle of each optical element, and the second optical system includes the imaging optical system and the image rotation. It has an optical element and a light detection element consisting of a plurality of small light receiving regions,
Further, it has a first driving device arranged in this order and connected to the image rotating optical element, and the image rotating optical element causes the optical axis of the second optical system to move by the first driving device. It rotates as a rotation axis in synchronization with the signal generated by the computer section.

According to a third aspect of the present invention, there are provided a light source for irradiating a sample whose various characteristics are to be measured with a parallel light beam at an arbitrary incident angle, a polarizer, the sample, a quarter-wave element and an analyzer. A first optical system arranged in this order, a second optical system for measuring a state of a light beam emitted from the first optical system, and a second optical system.
A computer unit that controls the azimuth angle of each optical element based on the measurement of the optical system, and calculates the change in the polarization state due to the reflection of the light flux on the sample from the azimuth angle of each optical element, The second optical system has an imaging optical system, a spatial frequency modulation element, and a photodetection element, and is arranged in this order.

According to the invention of claim 4, claim 1 or 2
In the described ellipsometer, the photodetector element has a two-dimensional array shape in which a large number of independent small light receiving regions are arranged in a lattice in a plane substantially perpendicular to the optical axis.

According to a fifth aspect of the present invention, in the ellipsometer according to the first, second or fourth aspect, an image amplification element and a sub-imaging optical system are provided in front of the photodetection element.

According to the invention of claim 6, claims 1, 2,
In the ellipsometer according to 4 or 5, the size of the small light receiving region is such that the diameter of a circle inscribed in the small light receiving region is
The diameter is set to one fifth or less of the diameter of the beam spot imaged on the photodetector by the imaging optical system.

According to a seventh aspect of the invention, in the ellipsometer according to the third aspect, there is provided a second drive device connected to the spatial frequency modulation element, and the spatial frequency modulation element has a symmetric light transmission. A light transmission plate having a partial pattern, which is synchronized with a signal generated by the computer unit in a plane substantially perpendicular to the optical axis with the optical axis of the second optical system as a rotation axis by the second driving device. Is rotated.

According to an eighth aspect of the present invention, in the ellipsometer according to the third aspect, the spatial frequency modulation elements are two-dimensionally arranged in a plane substantially perpendicular to the optical axis of the second optical system. A plurality of optical shutters whose light transmittances can be individually changed by the computer unit are configured.

According to a ninth aspect of the invention, in the ellipsometer according to the eighth aspect, the size of the optical shutter is
The diameter of the circle inscribed in the optical shutter is set to be ⅕ or less of the diameter of the beam spot imaged on the spatial frequency modulation element by the imaging optical system.

According to a tenth aspect of the present invention, in the ellipsometer according to any one of the first to ninth aspects, the quarter wavelength element is arranged between the polarizer and the sample. It is configured.

[0021]

In the first optical system 1 shown in FIG. 7, the present inventor has focused on changes other than the light quantity of the light beam emitted from the analyzer A during extinction. That is, when the light flux emitted from the analyzer A is observed through an imaging optical system focused at infinity, a beam spot BS having a shape as shown in FIG. 2 appears on the imaging surface at the time of extinction. When the beam spot BS deviates from the extinction point, the shape of the beam spot BS is originally circular, but such a shape is observed only in the vicinity of the extinction point. Then, when the polarizer P or the analyzer A is slightly rotated in the vicinity of the extinction point, corresponding to the rotation angle, in the case of this example, a dark strip shape near the center within the beam spot diameter d of the beam spot BS. Is observed to move laterally. The shape of the beam spot BS is a unique one that is generated by combining the optical state of each part constituting the ellipsometer and the optical characteristics of the sample, and is a stable phenomenon that produces a constant shape in the same measurement. It was confirmed that there is. Then, a new ellipsometer was invented to detect the extinction point by using the change in the shape of the beam spot BS.

According to the invention described in claim 1, paying attention to the above-mentioned phenomenon, the light flux emitted from the analyzer of the first optical system passes through the imaging optical system to form a beam on the photodetecting element. When a certain kind of image that is formed as a spot and appears in the beam spot only in the vicinity of the extinction point is detected by the photodetector, the signal is input to the computer section, and the azimuth angle of each optical element is calculated by the computer section. Is controlled. The controlled optical elements cause a certain kind of image movement, and the movement is detected as a change in signal output from each small light receiving area of the photodetection element via the imaging optical system. From the change state of this signal output and the azimuth angle of each optical element, by the computer unit,
The extinction point is obtained by calculating the change in the polarization state due to the reflection of the light flux on the sample.

According to the second aspect of the invention, the image rotation optical element is rotated by the first drive device with the optical axis of the second optical system as the rotation axis in synchronization with the signal generated by the computer section. Then, the beam spot imaged on the photo-detecting element composed of a plurality of small light receiving regions is rotated at a double rotation speed. When it is far from the extinction point, this beam spot has a simple circular shape, and the light amount as a whole changes only in accordance with the change in the azimuth angle of each optical element, but in the immediate vicinity of the extinction point. An image of some kind is observed, as described above, and that image is rotated by the image rotation optics. Therefore, when the above-mentioned image appears in the beam spot, the photocurrent output of any one of the small light receiving regions forming the photodetection element according to the change of the shape is added to the periodic frequency spectrum due to the rotation. Changes will occur. According to the first aspect of the invention, the beam spot is recognized as an image and it is determined whether or not a certain type of image appears in the beam spot. According to this configuration, the image contains a periodic change so-called AC component. Therefore, even for a finer image or a low-contrast image, the signal is amplified and detected. Further, since the image rotating optical element is rotated in synchronization with the signal generated by the computer section, the frequency of its AC component is also known, and only a specific frequency component is amplified so that a so-called lock with high SN ratio operation is possible. Since the in-detection method can be used, an image can be detected with higher sensitivity than that of the first aspect.

According to the third aspect of the invention, when an image matching the spatial frequency of the spatial frequency modulator appears,
Since the amount of transmitted light sharply decreases or sharply increases, it is possible to detect a certain kind of image with high sensitivity.

According to the invention described in claim 4, the shape of a certain kind of image formed in the beam spot may be changed in the vertical direction depending on the sample, and a large number of independent small light receiving regions are arranged on the optical axis. On the other hand, by having a two-dimensional array shape arranged in a lattice in a plane substantially vertical, whatever shape of the image is detected, the extinction position is determined.

According to the fifth aspect of the present invention, by providing the image amplifying element and the sub-imaging optical system in front of the photodetecting element, it is possible to cope with the case where the light source luminance is low.

According to the sixth aspect of the present invention, in order to determine the extinction point, it is necessary to detect a certain kind of image formed in the beam spot and detect the state in which the image moves to the center of the beam spot. From this point, it is better that the photodetector element is finely divided. On the other hand, as the number of small light-receiving areas of the photodetector increases, the cost increases, and there are many disadvantages such as deterioration of the detection limit due to a decrease in the amount of light received in one small light-receiving area and a decrease in measurement speed due to an increase in calculation time. Occurs. As a result of the experiment, the size of the small light receiving area of the photodetector is
If the diameter of the circle inscribed in the small light receiving area is one-fifth or less of the diameter of the beam spot imaged on the photodetection element by the imaging optical system, a certain type of image can be detected with sufficient accuracy. Therefore, sufficient characteristics can be obtained.

According to the invention of claim 7, there is the same operation as that of the invention of claim 2. When the measurement target of the sample is limited, a spatial frequency modulation element suitable for it is used, and high-speed measurement is possible compared with the invention according to claim 8.
By rotating a slit or the like having a spatial frequency that matches the shape that appears in the beam spot, a certain type of image shape change is detected.

According to the eighth aspect of the invention, it is effective to use an optical shutter array when dealing with various shapes of a certain kind of image formed in the beam spot, and it is effective to use the optical shutter array to detect the optimum spatial frequency. Since the filter can be formed instantaneously and the periodic change can be freely added, it is possible to determine the extinction point with higher sensitivity than the invention according to claim 7.

According to the invention described in claim 9, in addition to the operation of the invention described in claim 8, in order to determine the extinction point, a certain kind of image generated in the beam spot is detected, and the image is the beam. It is necessary to detect the state of movement to the center of the spot. From this point, it is better that the optical shutter is finely divided. On the other hand, as the number of divisions of the optical shutter increases, the cost increases, resulting in many demerits such as deterioration of the detection limit due to a decrease in the amount of light received by one optical shutter and a decrease in measurement speed due to an increase in calculation time. As a result of the experiment, the size of the optical shutter is such that the diameter of the circle inscribed in one optical shutter is 1/5 or less of the diameter of the beam spot imaged on the spatial frequency modulation element by the imaging optical system. For example, a certain type of image can be detected with sufficient accuracy and sufficient characteristics can be obtained.

According to the tenth aspect of the invention, in the configuration of the ellipsometer, the arrangement position of the quarter-wave element is generally 2 between the sample and the analyzer and between the polarizer and the sample. There are various types, and even if a quarter-wave element is arranged between the polarizer and the sample, the same operation is performed.

[0032]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the drawings referred to below, components having the same configurations and functions as those of the components shown in FIG. 7 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 and FIG. 3 show the configuration of an embodiment of the invention described in claim 1. In FIG. 1, reference numeral 150 indicates an ellipsometer. The ellipsometer 150 includes a first optical system 1 described above, a second optical system 2 that measures a state of a light beam emitted from the first optical system 1, and a second optical system 2.
While controlling the azimuth angle of each optical element based on the measurement of
It is mainly composed of a computer section 100 for calculating the change of the polarization state due to the reflection of the light flux on the sample S from the azimuth angle of each optical element.

The second optical system 2 has a telescope optical system 10 as an image forming optical system and a CCD (photoelectric conversion element) 20 as a photo-detecting element composed of a plurality of small light receiving areas 21, and They are arranged in order. The telescope optical system 10
It is composed of a convex lens 11 and a convex lens 12.

Next, the operation of the ellipsometer 150 will be described. The light flux emitted from the analyzer A is the telescope optical system 1
After passing through 0, it is imaged as a beam spot on the CCD 20. At this time, a certain kind of image (for example, a dark strip-shaped portion having a shape as shown in FIG. 2) appears in the beam spot in the vicinity of the extinction point, and the beam spot shape including the certain kind of image becomes the CCD 20. Detected by
It is sent to the computer section 100 as a signal. This CCD2
Based on the signal from 0, the computer unit 100 outputs an optical element rotation feedback signal for controlling the azimuth angle of each optical element (polarizer P or analyzer A) to each optical element (polarizer P or analyzer A). When each optical element (polarizer P or analyzer A) is slightly rotated by this command, the movement of a certain image (for example, a dark strip portion having a shape as shown in FIG. 2) is moved. , CCD 20 detects this as a change in signal output. This signal output is input to the computer unit 100, the change in the polarization state due to the reflection of the light beam on the sample S is calculated from the azimuth angle of each optical element, and the extinction point is obtained.

FIG. 4 shows the configuration of an embodiment of the invention described in claim 2. In FIG. 4, reference numeral 150A indicates an ellipsometer. This ellipsometer 150A differs from the ellipsometer 150 only in that it has a second optical system 2A instead of the second optical system 2.

The second optical system 2A is a telescope optical system 10
A drive as a first drive device in which an image rotating optical element 30, a CCD 20, a gear 31 attached to the image rotating optical element 30, and a drive gear 41 meshing with the gear 31 are attached to its output shaft. It mainly comprises a motor 40, and includes a telescope optical system 10, an image rotation optical element 30, and a CCD 2.
0 and are arranged in this order. The drive motor 40 is connected to the computer section 100 by an electric circuit and is controlled by a command signal from the computer section 100. In FIG. 4, the telescope optical system 10 and the CCD 20 are simply shown.

Next, the operation of the ellipsometer 150A will be described. The image rotation optical element 30 is driven by the drive motor 40.
The computer unit 10 with the optical axis 3 of the second optical system 2A as the rotation axis.
When rotated in synchronization with the signal generated by 0, the CCD 20
The beam spot imaged above is rotated at twice the rotational speed. When it is far from the extinction point, this beam spot has a simple circular shape, and the light amount as a whole changes only in accordance with the change in the azimuth angle of each optical element, but in the immediate vicinity of the extinction point. An image of some kind is observed as described above, and the image is rotated by the image rotation optical element 30. Therefore, when the above-mentioned image of a certain kind appears in the beam spot, the CCD 20 is changed according to the change of the shape.
In the photocurrent output of any one of the small light receiving regions 21 constituting the above, a periodical frequency spectrum change due to the rotation occurs, and the image contains a periodical change so-called AC component. It is easy to amplify and detect the signal of a finer image or a low-contrast image. Further, since the image rotation optical element is rotated in synchronization with the signal generated by the computer unit 100, the frequency of the AC component is also known, and only a specific frequency component is amplified, and operation with a high SN ratio is possible. Since the so-called lock-in detection method can be used,
Certain images are detected with greater sensitivity than the ellipsometer 150.

FIG. 5 shows the configuration of an embodiment of the invention described in claim 3. In FIG. 5, reference numeral 150B indicates an ellipsometer. The ellipsometer 150B differs from the ellipsometer 150 only in that it has a second optical system 2B instead of the second optical system 2. Second optical system 2
B is the telescope optical system 10 and the spatial frequency modulator 50.
And a CCD 20A as a photodetector, and are arranged in this order. Note that C
CD20A is a single element. In FIG. 5, the telescope optical system 10 is shown in a simplified manner.

Next, the operation of the ellipsometer 150B will be described. When a certain type of image that matches the spatial frequency of the spatial frequency modulator 50 appears, the amount of transmitted light sharply decreases or abruptly increases, so that high sensitivity detection of a certain type of image becomes possible. In addition, the CCD 2 as a light detecting element
Since 0A may be a single element, there is an advantage that the configuration is simple.

In the ellipsometer 150 or 150A, the photodetector element is a CC composed of a plurality of small light receiving regions 21.
Not limited to D20, as shown in FIG. 6, a CCD 20B having a two-dimensional array shape in which a large number of independent small light receiving regions 21 are arranged in a lattice shape in a plane substantially perpendicular to the optical axis may be used. (Example of the invention described in claim 4).

CC of ellipsometer 150 or 150A
The use of the CCD 20B instead of the D20 has the following advantages. The shape of a certain image generated in the beam spot may be changed in the vertical direction depending on the sample S, and a large number of independent small light receiving regions 21 are formed in a lattice shape in a plane substantially perpendicular to the optical axis. Due to the arrayed two-dimensional array shape, any shape of the image can be detected and the extinction position can be determined.

Further, in the ellipsometer 150, 150A or the embodiment of the invention described in claim 4, an image amplification element and a sub-imaging optical system (both not shown) may be additionally provided in front of the CCD 20 or CCD 20B. Has an advantage of being able to deal with the case where the light source luminance is low (the embodiment of the invention according to claim 5).

The ellipsometers 150, 150A,
In the embodiment of the invention described in claim 4 or 5, CCD2
0 or the size of the small light receiving area 21 of the CCD 20B, and the diameter of the circle inscribed in the small light receiving area 21 is 1/5 of the diameter of the beam spot imaged on the CCD 20 or CCD 20B by the telescope optical system 10. It may be set as follows (embodiment of the invention described in claim 6).

By setting in this way, there are the following advantages. In order to determine the extinction point, it is necessary to detect a certain type of image formed in the beam spot and detect the state in which the image moves to the center of the beam spot.From this point, the photodetector element is finely divided. The better on the other hand,
The cost increases as the number of small light receiving regions of the photodetector increases, and there are many demerits such as deterioration of the detection limit due to a decrease in the amount of light received in one small light receiving region and a decrease in measurement speed due to an increase in calculation time. Experimental results, CCD20 or C
The size of the small light receiving area 21 of the CD 20B is equal to that of the small light receiving area 2
The diameter of the circle inscribed in 1 is CC by the telescope optical system 10.
About 1/5 of the diameter of the beam spot imaged on the D20 or CCD 20B had good overall balance.
If it is finer than this, a certain type of image can be detected with sufficient accuracy, and sufficient characteristics can be obtained.

Further, not limited to the ellipsometer 150B,
In the ellipsometer 150B, the ellipsometer 15
A second drive unit (not shown) connected to the spatial frequency modulation element according to the configuration of 0B, and the spatial frequency modulation element is a light transmission plate having a symmetrical light transmission section pattern. , The computer unit 100 in a plane substantially perpendicular to the optical axis with the optical axis of the second optical system as the rotation axis by the second drive device.
It may be rotated in synchronism with the signal generated by the above (embodiment 7 of the invention).

According to the embodiment of the invention described in claim 7, there is the same advantage as the ellipsometer 150A. That is, when the measurement target of the sample is limited, a spatial frequency modulation element suitable for it is used, and the following description will be given.
Higher speed measurements are possible than in the described embodiment of the invention. Then, by rotating a slit or the like having a spatial frequency that matches the shape of a certain image appearing in the beam spot, it is possible to detect a change in the shape of the certain image.

Further, in the ellipsometer 150B,
The spatial frequency modulation elements are two-dimensionally arranged in a plane substantially perpendicular to the optical axis of the second optical system, and the computer unit 100
It may be a plurality of optical shutters whose light transmittances can be individually changed by the above method (the embodiment of the invention according to claim 8).

According to the embodiment of the invention described in claim 8, it is effective to use the optical shutter array in the case of dealing with various shapes of a certain kind of image formed in the beam spot.
Since it is possible to instantaneously form the optimum spatial frequency filter for the detection and to freely add the periodical change, it is possible to determine the extinction point with higher sensitivity than the embodiment of the invention described in claim 7. Is.

In the embodiment of the present invention as defined in claim 8, the size of the optical shutter, the diameter of the circle inscribed in the optical shutter, and the diameter of the beam spot imaged by the telescope optical system 10 on the spatial frequency modulation element 50. The diameter may be set to 1/5 or less of the diameter (the embodiment of the invention according to claim 9).

According to the embodiment of the invention described in claim 9, there are the following advantages in addition to the advantages of the embodiment of the invention described in claim 8. In other words, in order to determine the extinction point, it is necessary to detect a certain type of image generated in the beam spot and detect the state in which the image has moved to the center of the beam spot. The better it is. On the other hand, as the number of divisions of the optical shutter increases, the cost increases, resulting in many demerits such as deterioration of the detection limit due to a decrease in the amount of light received by one optical shutter and a decrease in measurement speed due to an increase in calculation time. As a result of the experiment, as for the size of the optical shutter, the diameter of the circle inscribed in one optical shutter is about 1/5 of the diameter of the beam spot imaged on the spatial frequency modulation element 50 by the telescope optical system 10. The overall balance was good. If it is finer than this, a certain type of image can be detected with sufficient accuracy, and sufficient characteristics can be obtained.

In each of the above embodiments, 1 /
Although the 4λ plate C is arranged between the sample S and the analyzer A, the invention is not limited to this, and the 4λ plate C may be arranged between the polarizer P and the sample S instead. Generally, in the configuration of the ellipsometer, the arrangement position of the 1/4 λ plate is 2 between the sample S and the analyzer A and between the polarizer P and the sample S.
There are various types, and even if a ¼λ plate is arranged between the polarizer P and the sample S, the same operation is performed.

(Embodiment 1) A first optical system 1, an embodiment of the invention described in claim 5 as a second optical system, a CCD 20B as a photodetector and an embodiment of the invention described in claim 6, An experiment was conducted using an ellipsometer having a computer section 100, and as shown in Table 1, the extinction point determination accuracy was 0.001 degrees and the required measurement time was 0.
A good result of 01 seconds was obtained. For comparison with the present embodiment, the measurement results by the conventional ellipsometer are shown in the right column of Table 1.

[0054]

[Table 1]

(Embodiment 2) A first optical system 1, an embodiment of the invention described in claim 5 as a second optical system, a CCD 20B as a photodetector and an embodiment of the invention described in claim 6, When an experiment was conducted using an ellipsometer having a computer section 100, the same good results as in Example 1 were obtained.

(Embodiment 3) The first optical system 1, the embodiments of the inventions according to claims 8 and 9 as the second optical system, and the photodetector of all the above embodiments are selectively selected. When an experiment was conducted using an ellipsometer which was used and was equipped with a computer section 100, the same good results as in Example 1 were obtained.

The photo-detecting elements are CCDs 20 and 20B.
Not limited to the above, all the light detection devices can be used in the small light receiving region that constitutes the photodetection element, and these photodetection elements are configured by combining these components, for example, on the same semiconductor substrate. A photodetector formed in a lump may be configured as long as it can separately detect the amount of light received in each small light receiving region.

The photodetector is the CCD of the above embodiment.
Not limited to 20, 20A and 20B, all the photo-detecting elements can be used. For example, a photodiode array or PS
You may use D.

[0059]

As described above, according to the first aspect of the present invention, the light flux emitted from the analyzer of the first optical system passes through the imaging optical system to form a beam on the photodetecting element. When a certain kind of image that is formed as a spot and appears in the beam spot only in the vicinity of the extinction point is detected by the photodetector, the signal is input to the computer section, and the azimuth angle of each optical element by the computer section. Is controlled. The controlled optical elements cause a certain kind of image movement, and the movement is detected as a change in signal output from each small light receiving area of the photodetection element via the imaging optical system. From this change state of the signal output and the azimuth angle of each optical element, the computer unit calculates the change in the polarization state due to the reflection of the light beam on the sample and obtains the extinction point, so by eliminating the fluctuation of the extinction point determination. The measurement accuracy can be increased, the film formation process can be performed, and the extinction point can be detected at high speed.

According to the second aspect of the present invention, the image rotation optical element is rotated by the first drive device with the optical axis of the second optical system as the rotation axis in synchronization with the signal generated by the computer section. Then, the beam spot imaged on the photo-detecting element composed of a plurality of small light receiving regions is rotated at a double rotation speed. When it is far from the extinction point, this beam spot has a simple circular shape, and the light amount as a whole changes only in accordance with the change in the azimuth angle of each optical element, but in the immediate vicinity of the extinction point. An image of some kind is observed, as described above, and that image is rotated by the image rotation optics. Therefore, when the above-mentioned image appears in the beam spot, the photocurrent output of any one of the small light receiving regions forming the photodetection element according to the change of the shape is added to the periodic frequency spectrum due to the rotation. Changes will occur. According to the first aspect of the invention, the beam spot is recognized as an image and it is determined whether or not a certain kind of image appears in the beam spot. According to this configuration, the image contains a periodical change, that is, an AC component. Therefore, even for a finer image or a low-contrast image, the signal is amplified and detected. Further, since the image rotating optical element is rotated in synchronization with the signal generated by the computer section, the frequency of its AC component is also known, and only a specific frequency component is amplified so that a so-called lock with high SN ratio operation is possible. Since the in-detection method can be used, an image can be detected with higher sensitivity than that according to claim 1. Therefore, the fluctuation of determination of the extinction point can be eliminated to improve the measurement accuracy and also to cope with the film forming process. In addition, the extinction point can be detected at high speed.

According to the third aspect of the present invention, when a certain type of image that matches the spatial frequency of the spatial frequency modulator appears, a sharp decrease or a sharp increase in the amount of transmitted light occurs. Since it is possible to detect an image with high sensitivity, it is possible to improve measurement accuracy by eliminating fluctuations in the determination of the extinction point, to cope with a film forming process, and to perform high-speed extinction point detection.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an ellipsometer showing an embodiment of the present invention, in which FIG. 1 (a) shows a first optical system connected and FIG. 1 (b) shows an optical axis of the first optical system. The second optical system and the computer section are shown respectively.

FIG. 2 is an example of a beam spot shape seen at the time of extinction.

FIG. 3 is a front view of a CCD as a photodetecting element including a plurality of small light receiving regions.

FIG. 4 is a configuration diagram of a main part of an ellipsometer showing another embodiment.

FIG. 5 is a configuration diagram of a main part of an ellipsometer showing still another embodiment.

FIG. 6 shows C as a photodetector having a two-dimensional array shape.
It is a front view of CD.

FIG. 7 is a configuration diagram of a conventional extinction type ellipsometer.

FIG. 8 is a graph for explaining a conventional extinction point determination method, in which the vertical axis represents the amount of emitted light near the extinction point and the horizontal axis represents the polarizer azimuth angle.

[Explanation of Codes] 1 First optical system 2 Second optical system 10 Telescope optical system as imaging optical system 20 CCD 100 as a photo-detecting element consisting of a plurality of small light receiving areas Computer section A Analyzer C 4 minutes Λ plate as a one-wavelength device of L L light source P Polarizer S Sample

Claims (10)

[Claims] 1. A light source for irradiating a sample whose various characteristics are to be measured with a parallel light flux at an arbitrary incident angle, a polarizer, the sample, and 4 above.
A first wavelength element and an analyzer arranged in this order
Of the optical system, the second optical system for measuring the state of the light beam emitted from the first optical system, and the azimuth angle of each optical element based on the measurement of the second optical system. And a calculator for calculating a change in polarization state due to reflection of the light flux on the sample from the azimuth angle of the optical element, wherein the second optical system includes an imaging optical system and a plurality of small light receiving regions for light detection. An ellipsometer having elements and arranged in this order. 2. A light source for irradiating a sample whose various characteristics are to be measured with a parallel light flux at an arbitrary incident angle, a polarizer, the sample, and 4 above.
A first wavelength element and an analyzer arranged in this order
Optical system, a second optical system that measures the state of the light flux emitted from the first optical system, and the azimuth angle of each optical element is controlled based on the measurement of the second optical system. And a calculator for calculating a change in polarization state due to reflection of the light flux on the sample from the azimuth angle of the element, wherein the second optical system includes an image forming optical system, an image rotating optical element, and a plurality of small light receiving regions. And a first drive device connected to the image rotation optical element, wherein the image rotation optical element is the first drive device. An ellipsometer that is rotated by the optical axis of the second optical system as a rotation axis in synchronization with a signal generated by the computer section. 3. A light source for irradiating a sample whose various characteristics are to be measured with a parallel light flux at an arbitrary incident angle, a polarizer, the sample, and 4 above.
A first wavelength element and an analyzer arranged in this order
Optical system, a second optical system that measures the state of the light flux emitted from the first optical system, and the azimuth angle of each optical element is controlled based on the measurement of the second optical system. And a calculator for calculating a change in polarization state due to reflection of the light flux on the sample from the azimuth angle of the element, and the second optical system includes an imaging optical system, a spatial frequency modulator and a photodetector. An ellipsometer that has and is arranged in this order. 4. The ellipsometer according to claim 1 or 2, wherein the photodetector element has a two-dimensional array shape in which a large number of independent small light receiving regions are arranged in a lattice in a plane substantially perpendicular to the optical axis. An ellipsometer. 5. The ellipsometer according to claim 1, 2 or 4, wherein an image amplification element and a sub-imaging optical system are provided in front of the photodetection element. 6. The ellipsometer according to claim 1, 2, 4 or 5, wherein the size of the small light receiving area is such that the diameter of a circle inscribed in the small light receiving area is determined by the imaging optical system. An ellipsometer set to be one fifth or less of the diameter of the beam spot imaged above. 7. The ellipsometer according to claim 3, further comprising a second driving device connected to the spatial frequency modulation element, wherein the spatial frequency modulation element has a light transmission part pattern having a symmetrical light transmission part pattern. An ellipsometer, which is a plate and is rotated by a second drive device with the optical axis of the second optical system as a rotation axis in a plane substantially perpendicular to the optical axis in synchronization with a signal generated by the computer section. 8. The ellipsometer according to claim 3, wherein the spatial frequency modulation elements are two-dimensionally arranged in a plane substantially perpendicular to the optical axis of the second optical system, and the spatial frequency modulation elements are individually arranged by the computer section. An ellipsometer, which is a plurality of optical shutters that can change the light transmittance. 9. The ellipsometer according to claim 8, wherein a size of the optical shutter, a diameter of a circle inscribed in the optical shutter, is imaged on the spatial frequency modulation element by the imaging optical system. An ellipsometer set to be 1/5 or less of the spot diameter. 10. The ellipsometer according to claim 1, wherein the quarter wavelength element is arranged between the polarizer and the sample.