JP4153412B2 - Ellipsometry method using ellipsometer - Google Patents

Description

The present invention relates to an optical ellipsometer or an ellipsometer data analysis method for measuring the optical constant and thickness of a thin film using the same.

A typical measurement method for evaluating the characteristics of thin film materials is ellipsometry, a method that has been known for a long time. This is because the reflectance Rp of the component (P-polarized light) whose electric field is parallel to the incident surface of the reflected light of the light incident on the thin film sample, and the reflectance Rs of the component (S-polarized light) whose electric field is perpendicular to the incident surface. This is a method for determining the film thickness and refractive index of the sample by measuring the ratio ρ. Here, ρ is generally a complex number and can be expressed as ρ = Rp / Rs = tan (Ψ) × exp (jΔ). Ψ and Δ are called ellipsometric parameters or ellipsometric angles. In the ellipsometry, the amplitude ratio Ψ and the phase difference Δ are obtained by measurement. Since ρ is a value determined by the optical constant (n) and thickness (d) of the film, it is possible to calculate the optical constant and thickness conversely by obtaining Ψ and Δ.

In conventional ellipsometers, the extinction method, the rotation analyzer method, and the like have been used as a method for obtaining Ψ and Δ by performing polarization analysis of reflected light from a sample (Non-patent Document 1). In the quenching method, reflected light from a sample (generally elliptically polarized light) is passed through a quarter-wave plate and a polarizer in order and received by a light receiver, and the quarter-wave plate and the polarizer are rotated independently. Thus, Ψ and Δ are obtained by reading the rotation angle at which the light intensity is minimum. However, since this method searches for the minimum value using two variables, there is a drawback that a lot of time is required even if only one measurement is performed. On the other hand, the rotational analyzer method is a method of performing polarization analysis using only an analyzer without using a quarter-wave plate. In the rotational analyzer method, if the change in the received light intensity when the polarizer is rotated once is measured and the received light intensity is obtained as a function of the angle, Ψ and Δ can be obtained by calculation. 2π−Δ), that is, it cannot be distinguished whether it is a right-handed elliptically polarized wave or a left-handed elliptically polarized wave. In order to avoid this, it is necessary to perform measurement twice or more with respect to one point measurement by inserting / removing a quarter wavelength plate, etc., and the measurement is complicated and the time required for the measurement is great. That is not much different from the previous quenching method.

A structure that combines a waveplate array, a polarizer array, and a light-receiving element array as a new ellipsometer that eliminates the inconvenience of rotating parts and drive parts of conventional ellipsometers and realizes high-precision and high-speed polarization analysis. Has been proposed (Patent Document 1). This is different from a wave plate array having a plurality of wave plate regions having a constant phase difference (ideally 1/4 wavelength, that is, π / 2 radians) and different optical axis directions, and a main axis direction of polarized light to be transmitted is different. This is an apparatus that superimposes a polarizer array having a plurality of polarizer regions such that the wave plate array is the front surface and the polarizer array is the rear surface, and measures the intensity distribution of the light that has passed through them with the light receiving element array. By using this new ellipsometer, it is possible to instantaneously obtain information about the light intensity with respect to the angle of the wave plate or the angle of the polarizer measured by a conventional ellipsometer as two-dimensional data.

By using a photonic crystal technique, a component having a complicated structure such as a wave plate array or a polarizer array can be produced with high accuracy by a simple process. As the optical element array, a conventional image sensor such as a CCD can be used. Therefore, this new ellipsometer can not only realize a very small and inexpensive device, but also has high device reliability as compared with the conventional product. For this reason, new usage methods that are almost impossible with conventional ellipsometers, such as being introduced into a thin film process apparatus and used as a real-time monitor of film thickness and film quality, are expected.

As described above, the new ellipsometer and ellipsometer using the wave plate array and the polarizer array are expected to have very high performance, but the polarization state of the incident light is accurately determined from the two-dimensional information measured by the light receiving element array. No analysis method has been proposed yet.
Japanese Patent Application No. 2003-363854 Applied Physics Handbook, Applied Physics Society (Maruzen), pp. 20-22, 1990.

In the ellipsometer or ellipsometer of a new method without a driving unit, the present invention uses the wave plate array and the polarizer array described above, and the incident light from the intensity distribution pattern measured by the light receiving element array is used. An algorithm for analyzing the polarization state with high accuracy is provided.

As a means of analyzing the shape of the light intensity distribution pattern measured by the ellipsometer using the wave plate array and the polarizer array, a method of analyzing the contour shape of the intensity distribution pattern or a method of Fourier transforming the intensity distribution and those Adopt a combination of methods.

First, a brief description will be given of a polarization analyzer using a wave plate array and a polarizer array and having no drive unit. This ellipsometer has a configuration as shown in FIG. The wave plate array 101 is formed by arranging a plurality of regions having different optical axis directions in M rows, and the retardation amount of each region is designed to be constant (ideally a quarter wave plate). Yes. In addition, the polarizer array 102 is formed by arranging a plurality of regions having different polarization directions of transmitted light in N rows, and the polarization extinction ratio of each region is designed to be sufficiently high. Such a wave plate array and a polarizer array are bonded so as to be orthogonal to each other, and light beams that have passed through M × N regions formed by superposition of the wave plate array and the polarizer array are individually provided behind the wave plate array and the polarizer array. By disposing the light receiving element array 103 that can receive light, it is possible to realize a polarization analyzer without a drive unit. By producing the wave plate array and the polarizer array with a photonic crystal, a very small and highly accurate device can be realized. Refer to Patent Document 1 for details of such an ellipsometer.

FIG. 2 shows an example of a simulation result of the light intensity distribution observed by the light receiving element array when linearly polarized light or circularly polarized light is incident on the ellipsometer. Here, in the waveplate array used in the ellipsometer, the phase difference of each waveplate region is ¼ wavelength, and the principal axis angle is changed by 12 ° from 0 ° to 180 °. In the array, the principal axis angle of each polarizer region was changed by 12 ° from 0 ° to 180 °. From the results, it can be seen that the light intensity distribution observed with the new ellipsometer changes depending on the polarization state of the incident light. From this, it is expected that the polarization state of incident light can be obtained by analyzing the obtained light intensity distribution shape.

Next, theoretical (mathematical) studies are performed on the light intensity distribution obtained by these ellipsometers. The change in the polarization state of light due to the waveplate and the polarizer can be represented by a Jones matrix, so if the polarization state of the incident light is represented by ellipsometry angles Ψ and Δ, Jones after passing through the waveplate and the polarizer The vector can be expressed as shown in Equation 301 in FIG. Here, θ represents the principal axis angle of the wave plate, α represents the retardation amount of the wave plate, and φ represents the principal axis angle of the polarizer. Here, the polarization state of the incident light is expressed by the expression 302 because it is easier to grasp the image of the polarization state when the polarization state is expressed by the ellipticity (ε) and the inclination (γ) of the elliptical polarization than by the ellipsometry angle. Can be replaced as follows. Therefore, when the above-described ellipsometer is used, the polarization state of the light reaching the light receiving element array can be expressed as Equation 303. For simplicity, -1 ≦ ε ≦ 1 is assumed below, and γ represents the inclination of the major axis of the elliptically polarized wave (an angle with respect to the horizontal direction). In the case of linearly polarized light, ε = 0, and in the case of circularly polarized light, ε = ± 1, and if ε> 0, it represents clockwise elliptically polarized light, and if ε <0, it represents counterclockwise elliptically polarized light. The light intensity finally measured by the light receiving element array can be obtained by the square of the absolute value of the Jones vector, as shown by Expression 304.

As described above, the light intensity measured by the light receiving element array is expressed as a function of the incident polarization state (ε, γ) and the wave plate angle (θ) and the polarizer angle (φ). Become. In this ellipsometer, since θ and φ are known values depending on the device, the polarization state of incident light can be accurately obtained by analyzing the shape of the light intensity distribution observed in the light receiving element array. However, it becomes clear from a theoretical point of view.

The simplest method for analyzing the intensity distribution is a method for detecting the position of the maximum or minimum value of the pattern to be measured. This corresponds to the quenching method in the conventional ellipsometer described above. In the quenching method, the angle of the wave plate and the polarizer are rotated, and the ellipticity and inclination of the incident polarized light can be directly obtained from the angle of the wave plate and the polarizer when the incident light is completely quenched. In the case of a new ellipsometer using a wave plate array and a polarizer array, the position (coordinates, dark point (minimum value, zero point) or bright point (maximum value) generated in the two-dimensional intensity distribution pattern is based on the same principle. In other words, if the main plate angle of the wave plate and the polarizer is detected, the polarization state of the incident light can be obtained. Here, it is easier to detect a dark spot than to detect a bright spot, considering the case where the light intensity incident on the ellipsometer is not uniform in the plane or the light intensity fluctuates over time. It is self-evident.

The light point detection method and the dark point detection method as described above have an advantage that the polarization state of incident light can be analyzed instantaneously by using only a part (one point) of data of a two-dimensional pattern obtained. However, in this method, most of the two-dimensional data to be measured is wasted, and it cannot be said that the advantages of the new ellipsometer are fully utilized. In addition, for example, in the above-described ellipsometer, if the phase difference of the wave plate is deviated from a quarter wavelength, there will be no point of complete extinction depending on the incident polarization. Becomes impossible. The following algorithm is proposed as a method for solving these problems and obtaining the polarization state of incident light with high accuracy by analyzing the shape of the entire pattern using more data points.

An ellipsometry system of the present invention is an ellipsometry system having an ellipsometer and a computer, and the ellipsometer includes a wave plate array having a plurality of wave plates having a constant phase difference and different optical axis directions. A polarizer array on which the light transmitted through the wave plate array is incident, the polarizer array having a plurality of polarizers having different polarization directions to be transmitted, and a wave plate having the wave plate array, And a light receiving element array capable of individually receiving light that has passed through a polarizer of the polarizer array, wherein the angle of the optical axis of the wave plate included in the wave plate array is a first axis. When the angle of the polarized light transmitted through the polarizer included in the polarizer array is a second axis, the photoreceiver array is arranged on the coordinates constituted by the first axis and the second axis. Light intensity observed by And the computer outputs the light intensity distribution, the computer receives the light intensity distribution output from the ellipsometer, and obtains the polarization state of the incident light using the received light intensity distribution. .

The preferred ellipsometry system of the present invention is such that in the ellipsometry system, the sample value is fitted or interpolated using the feature of the pattern shape near the maximum point or minimum point of the intensity distribution pattern observed by the light receiving element array. In this case, the extinction point of the ellipsometry or the minimum point of the light amount is obtained, and the polarization state of the incident light is obtained.

A preferred ellipsometry system of the present invention is characterized in that Fourier transform is adopted as a shape analysis method of the observed intensity distribution pattern in the ellipsometry system.

The preferred ellipsometry system of the present invention detects the phase difference value of the wave plate array used in the ellipsometer by analyzing the shape of the observed intensity distribution pattern, and from the design value. It is characterized by self-correcting the deviation.

In the ellipsometry system of the present invention, in order to remove the influence of scattered light and diffracted light from the boundary portion of each region of the wave plate array or polarizer array, the scattered light and It is characterized in that a signal from a region receiving diffracted light is removed.

By using the polarization analysis method of the present invention, it is possible to analyze the polarization state of incident light with high accuracy from the light intensity distribution observed by a new polarization analyzer using a wave plate array and a polarizer array. Become. Further, even when there is a deviation from the design value in the phase difference of the wave plate array, it is possible to obtain an accurate polarization state by correcting the deviation amount.

An example of the configuration of an apparatus for implementing the ellipsometry system of the present invention is shown in FIG. The CPU 403 receives the light intensity distribution 402 observed by the polarization analyzer 401 using the wave plate array and the polarizer array, and analyzes the two-dimensional pattern shape. At this time, as an analysis algorithm for the pattern shape of the light intensity distribution, either a method of mathematically fitting the pattern shape or a method of analyzing the frequency component by Fourier transforming the pattern is adopted, or they are used. By using together, the polarization state of incident light can be obtained with high accuracy.

Before explaining each pattern shape analysis method, the features of the pattern shape observed in the light receiving element array will be briefly explained. The light intensity distribution measured by the ellipsometer used in the present invention should be expressed as a function of the ellipticity (ε) and the inclination of the ellipse (γ) as shown in Equations 303 and 304 in FIG. Can do. Here, the inclination (γ) of the ellipse is defined with reference to a certain axial direction (in this case, the horizontal direction), but the direction of the reference axis is arbitrary. Therefore, changing the inclination (γ) of the ellipse corresponds to changing the order of the reference axis, that is, the arrangement order of the regions of the wavelength plate array and the polarizer array. For example, as shown in FIG. 5, when the ellipticity of incident polarized light is constant (the value of ε is arbitrary), the intensity obtained when the ellipsometer 501 is horizontally arranged when the inclination of the ellipse is 0 °. The measured results are exactly the same between the distribution and the case where the same ellipsometer 502 is arranged at 45 ° when the inclination of the ellipse is 45 degrees. The ellipsometer 502 is the same as the ellipsometer 503, which corresponds to a case where the arrangement order of the wave plate array and the polarizer array of the ellipsometer 502 is changed. That is, when the inclination of the polarization of incident light is changed, the observed intensity distribution pattern moves horizontally within the plane, and the pattern uneven shape itself does not change. As an example, the light intensity distribution measured when the ellipticity of incident light is constant (ε = 0.5) and the angle (γ) of the ellipse is changed to 0 °, 45 °, and 90 ° is shown in FIG. Show. From this result, it can be seen that even if the angle of the incident polarization is changed, the uneven shape of the pattern does not change, and only the position of the unevenness changes.

On the other hand, when the ellipticity of incident light is changed, it is clear from the results shown in FIG. 2 that the pattern shape changes. As an example, it is measured when the inclination of incident light is constant at γ = 0 ° and the ellipticity ε is changed to 0 (linearly polarized light), 0.2, 0.5, 1 (clockwise circularly polarized light). FIG. 7 shows the light intensity distribution. When the incident light is linearly polarized, the pattern has a “bottom-bottom” periodic shape, whereas the pattern shape is stretched as the ellipticity increases. It turns out that it becomes a shape. From the above, the ellipticity (ε) of the incident polarized light can be obtained from the uneven shape of the light intensity distribution pattern observed in the light receiving element array, and the inclination of the incident polarized light (coordinate) from the position (coordinates) in the plane of the pattern ( γ) can be obtained.

Hereinafter, a method of mathematically fitting an intensity distribution pattern and a method of analyzing each frequency component by performing Fourier transform on the pattern, which are pattern shape analysis methods of the present invention, will be described.

First, as an example of the polarization analysis method by fitting the light intensity distribution of the present invention, a polarization analysis algorithm for analyzing the contour line shape of the measured intensity distribution pattern will be described. The contour shape of the intensity distribution can be easily obtained by extracting points where the intensity becomes equal from the measured intensity distribution data. At this time, if the number of divisions of the wave plate array and the polarizer array is small, in order to obtain a more accurate contour line shape, the contour line is obtained after interpolating the measured jump value by fitting calculation to obtain a smooth intensity distribution. A method for calculating the shape is effective. As shown in FIG. 6 and FIG. 7, the contour lines may be obtained for the entire region of the measured intensity distribution pattern, but may be obtained only for the vicinity of the bright spot or the dark spot where the pattern characteristics are most apparent. If the shape and position of the contour line thus obtained can be analyzed, the polarization state of the incident light can be obtained as described above. Here, as an example of the contour line shape analysis method, a method for analyzing the inclination and position of the contour line shape near the pattern dark spot (minimum value) and a method for comparing the prepared pattern database with a simple method will be described. Explained.

First, a method for detecting the slope and position of contour lines will be described. As an example, as shown in FIGS. 2 and 6, the incident light is linearly polarized light (ε = 0), clockwise circularly polarized light (ε = 1), and clockwise elliptically polarized light (ε = 0.5). 8), the results of drawing contour lines only in the vicinity of the dark spot of the observed intensity distribution pattern are shown together in FIG. In general, when the principal axis angle range of the wave plate array and the polarizer array is 0 ° to 180 °, there are two dark spots in the plane. However, in FIG. Only contour lines are shown. As can be seen from the figure, the contour line shape near the dark spot is almost elliptical, and the shape can be expressed as in Expression 801. Here, A, B, C and D are constants. It can be seen that the position of this dark spot is on a specific straight line determined by the ellipticity (ε) when the ellipticity (ε) of the incident polarization is constant. For example, in the case of linearly polarized light (ε = 1), a dark spot exists on the straight line Pp, and in the case of clockwise circularly polarized light, a dark spot exists on the straight line Qq or Q′-q ′, and ε = 0. The dark spot position for elliptical polarized light of .5 exists on the straight line R-r or R'-r '. Although no contour lines are displayed in the figure, the dark spot position when the counterclockwise circularly polarized light is incident exists on the straight line Ss or S′-s ′ symmetrically with the clockwise direction. When the inclination (γ) of the incident polarized light changes, the dark spot position moves on the straight line determined by the ellipticity (ε).

It can also be seen that the slope of the ellipse obtained as a contour line near the dark spot varies with the ellipticity of the incident light. The contour line in the case of circularly polarized light has a linear shape as the limit where the ellipse becomes infinitely long, but the inclination of the locus of the minimum value is 1, and the inclination of the ellipse of the contour line decreases as the ellipticity decreases. By utilizing this fact, the polarization state of incident light can also be obtained. In any case, if the contour shape of the intensity distribution pattern observed by the ellipsometer can be fitted by the above equation 801, its inclination and position can be obtained accurately, so that the polarization state of incident light (ε and γ ) Can be obtained accurately.

As another example of the contour line shape analysis method, a method of comparing the obtained pattern shape with a database is shown in FIG. In this case, pattern shapes corresponding to various polarization states are stored in a database in advance, the intensity distribution pattern measured by the polarization analyzer 901 is converted into contour data by the CPU 902, and the pattern shapes stored in the database 903 are stored. The polarization state of the incident light is obtained by searching for matching data. Of course, it is also possible to perform more accurate polarization analysis by simultaneously performing the method for detecting the position and inclination of the contour lines described above and the method for comparing with the database.

Next, a polarization analysis algorithm (Fourier analysis method) for obtaining a frequency component by Fourier-transforming the measured intensity distribution pattern of the present invention will be described. When the expression of the light intensity distribution measured by the ellipsometer used in the present invention is described once again, the expression 1001 and the expression 1002 in FIG. 10 are obtained. When this equation is modified and normalized by the incident light intensity, an equation 1003 is obtained. Here, 2φ = Φ and 2θ = Θ are replaced for simplicity. Equation 1003 indicates that the measured two-dimensional intensity distribution is composed of three frequency components Φ, 2Θ−Φ, and Θ−Φ. When the respective frequency components are X, Y, and Z as shown in Expression 1003, Z = 0 when the incident light is linearly polarized light (ε = 0), and when the incident light is linearly polarized light (ε = 1). It can be seen that X = Y = 0. Further, since the inclination (γ) of the incident polarized light appears as the phases of X and Y, it can be seen that the amplitude of each frequency component, that is, the shape of the intensity distribution does not change even when γ changes. Match the result.

From Equation 1003, if the spectrum is calculated by Fourier transforming the intensity distribution observed by the ellipsometer, and the amplitude and phase of each frequency component can be obtained, the polarization state of the incident light can be accurately obtained. I understand. That is, when the values of the frequency components X, Y, and Z are known, the slope (γ) of the incident polarization can be obtained as ½ of the value of the X or Y phase, as shown in Expression 1004. The ellipticity (ε) of incident light can be obtained from the amplitude value of Z as shown in Expression 1005.

As an example of polarization analysis by Fourier transform, the intensity distribution observed by the light receiving element array and the intensity distribution are Fourier-transformed when the ellipticity of the incident polarization changes and when the inclination changes (FIGS. 6 and 7). FIG. 11 and FIG. 12 show the result of the conversion and the result of back-calculating the incident polarization state from each frequency component obtained by Fourier transform. The results in the figure show that the wavelength plate array and polarizer array of the ellipsometer are divided into 64, and the main axis angle is changed from 0 ° to 180 ° (exactly 177.1875 °) by 2.8125 °. This is an analysis of the intensity distribution. Each frequency component obtained by Fourier transform is normalized by the incident light intensity. As is clear from the results, it can be seen that the polarization state calculated backward from the value of each frequency component obtained matches the incident polarization.

However, in an actual ellipsometer, noise is superimposed on the measured intensity distribution due to various electrical noises in addition to the influence of stray light from the outside. In addition, when the light response of the light receiving element array has nonlinearity, a correct intensity distribution cannot be obtained. Therefore, there may be a case where a large error in polarization state is obtained only by the above-described fitting calculation or Fourier analysis. Even in such a case, it is possible to realize more accurate polarization analysis by using both the contour analysis method and the Fourier analysis method in combination. For example, from the result of Fourier analysis of the intensity distribution pattern including noise, a first-order approximation value for the pattern shape near the dark spot of the pattern is obtained, and the sample value is fitted using the approximation value so that accurate contour lines are obtained. If the shape can be obtained, the polarization state of the incident light can be obtained with high accuracy.

In addition, as a noise countermeasure of the ellipsometer, it detects the position of the maximum value (bright point) or the minimum value (dark point) of the pattern, which is the ellipsometry method using contour analysis or Fourier analysis, and the conventional ellipsometry method. It is also effective to use a method (quenching method) in combination. As described above, the extinction method is a very simple polarization analysis method, and the state of incident polarization can be obtained instantaneously from the coordinate information of one point (for example, the minimum point) in the intensity distribution pattern. . Using this, for example, as shown in FIGS. 13C and 13D, the first approximate position of the dark spot obtained by Fourier analysis of the entire observed intensity distribution pattern and the vicinity of the dark spot Using the information of the shape of the intensity distribution quadratic curve, the intensity distribution pattern in the vicinity of the dark spot is accurately fitted to the observed sample value, and the second-order approximate value regarding the position of the dark spot is accurately obtained. If it is possible, the polarization analysis can be performed with very high accuracy as compared with the case of fitting the sample points without having any information as in (b). (Actually, the measurement data is two-dimensional information, but FIG. 13 shows a one-dimensional case for the sake of simplicity.) Further, when analyzing the shape of the entire pattern, the light receiving element array is also at the maximum value. Determine the light intensity and measurement time (gate time) in consideration of not saturating, and when paying attention to the minimum value (dark spot), it is not necessary to worry about saturation of the maximum value, so take a relatively long time. It is also possible to acquire data with a high S / N. By such a method, it is possible to perform fitting with higher accuracy for the shape near the dark spot, and to improve the measurement accuracy of incident polarization.

(Example 1)
The new ellipsometer using the waveplate array and polarizer array used in the present invention has high reliability because it does not have a drive unit, and can significantly reduce the measurement time compared to conventional devices. It has advantages such as. In addition, by using a photonic crystal, not only a sufficiently small device can be realized, but also the direction of the main axis of each array can be controlled with very high accuracy. However, the phase difference (retardation) of the wave plate array is difficult to exactly match the ideal value of ¼ wavelength (π / 2 radians) even when detailed process control is performed. If the structure of the photonic crystal and the preparation method are taken into account, if there is no distribution in the process, the phase difference of each waveplate area of the waveplate array will be a constant value in all areas even if there is a deviation from the design value It is expected that.

It shows a first embodiment of a method for correcting a phase difference shift of such a wavelength plate array 14. This is to obtain the phase difference of the wavelength plate from the intensity distribution information observed when light in a specific polarization state is incident on the ellipsometer, and correct the deviation. As an example, consider a case where linearly polarized light is incident on the polarization analyzer 1402 using a polarizer 1401 having a high extinction ratio such as a Glan-Thompson prism. (At this time, the tilt angle of the polarization is arbitrary.) At this time, the light intensity observed when the phase difference of the wave plate array in the ellipsometer is 70 °, 90 °, and 110 °. Distribution was shown. As already mentioned many times, the intensity distribution pattern when linearly polarized light is incident has a “bottom-bottom” shape. As can be seen from the figure, the elliptical shape (ellipticity) of the bottom is a waveplate array. Varies depending on the phase difference. Therefore, by analyzing the shape of the intensity distribution pattern obtained when linearly polarized light is incident on the polarization analyzer, the phase difference deviation of the wavelength plate array can be accurately evaluated. Here, as a method of analyzing a pattern observed when linearly polarized light is incident, the above-described contour analysis method or Fourier analysis method can be used.

(Example 2)
FIG. 15 shows a second embodiment of the method for correcting the phase difference deviation of the wave plate array. Light of an arbitrary polarization state is incident on the ellipsometer 1501, and the observed light intensity distribution is Fourier transformed by the CPU 1502. At this time, each frequency component obtained by Fourier transform is shown in Expression 1503. When each frequency component is set to X, Y, and Z as before, the phase difference (α) of each wave plate region of the wave plate array can be obtained by Expression 1504. In other words, when Fourier transform is used to analyze the intensity distribution shape, only the ellipticity (ε) and polarization slope (γ) of the incident light are already calculated from the values of each frequency component obtained by the Fourier transform. In addition, the value of the phase difference (α) of the wave plate is also obtained at the same time.

As described above, in the ellipsometry method of the present invention, the magnitude of the phase difference does not matter as long as the phase difference of the waveplate array is constant (uniform) over the entire area of the array. Even if the value of the phase difference is any value (except when α = 0 °), the deviation of the phase difference can be accurately evaluated by analyzing the measured intensity distribution pattern. The correct incident polarization value can be obtained. This is a great advantage compared to the conventional ellipsometer using a single wave plate or polarizer. For example, in the extinction method employed in the conventional ellipsometer, when the phase difference of the wave plate used is slightly deviated from the quarter wavelength, when light in a specific polarization state is incident, Even if the wave plate is rotated, there is no point at which it is completely extinguished, so that accurate polarization analysis becomes impossible.

(Example 3)
Since the wavelength plate array and the polarizer array of the ellipsometer used in the present invention are arranged in a plurality of different regions, the boundary portions between the regions are discontinuous, and light scattering and diffraction occur. Scattered light and diffracted light appear as noise in signal processing and cause deterioration in the accuracy of ellipsometry. For this reason, in order to realize a highly accurate device, a light shielding region is arranged in the wave plate array, polarizer array, or light receiving element array used in the ellipsometer so that scattered light and diffracted light are not received. FIG. 16 shows an example of a signal processing method as a method for removing the influence of scattered light and diffracted light without using such a light shielding structure.

Light that has passed through the wave plate array 1601 and the polarizer array 1602 enters the light receiving element array 1603. Assuming that a general CCD is used as the light receiving element array, the size of a single light receiving element is about several μm, which is sufficiently smaller than the size of each region of the wave plate array and the polarizer array. Therefore, there are a plurality of light receiving elements in each light receiving element region that receives light that has passed through each region formed by the intersection of the wave plate array and the polarizer array. Of the electrical signals output from these light receiving elements, the signals output from the region 1604 that receives scattered light and light including diffracted light from the boundary between the wave plate array and the polarizer array are not used. If the light intensity of each region is obtained by summing or averaging only the signals output from the region 1605 that receives light that is not affected by diffracted light, polarization analysis with high accuracy can be realized. In the figure, regions 1604 where no signal is used are taken for one row of light receiving elements above and below each region, but the manner and size of the regions are arbitrary, and vary depending on the structure of the ellipsometer. Such a signal processing method can be calculated very easily and at high speed by the CPU, and is a very effective method for improving the accuracy of polarization measurement.

Conceptual diagram showing the configuration of an ellipsometer used with a waveplate array and a polarizer array Example of light intensity distribution observed by the ellipsometer of FIG. Theoretical formula of light intensity distribution observed by ellipsometer Configuration example of ellipsometry system for analyzing intensity distribution pattern Conceptual diagram showing the relationship between the slope of the incident polarization and the observed intensity distribution pattern Example of observed intensity distribution pattern (Relationship with ellipticity of incident polarization) Example of observed intensity distribution pattern (Relationship with slope of incident polarization) The figure which shows the contour line shape near the dark spot of the observed intensity distribution pattern Conceptual diagram showing the ellipsometry method for comparing pattern shapes with a database Formula to find the frequency component of the observed intensity distribution pattern Simulation results of Fourier analysis of intensity distribution pattern-Part 1 Simulation results of Fourier analysis of intensity distribution pattern-Part 2 Example of pattern analysis algorithm using both Fourier analysis and dark spot detection The figure which shows 1st Example of the method of correct | amending the phase difference deviation of a waveplate array The figure which shows the 2nd Example of the method of correct | amending the phase-difference of a wavelength plate array. Diagram showing the signal processing method for removing the influence of the boundary of the array

Explanation of symbols

101 Wavelength plate array 102 having different principal axis angles in each region Polarizer array 103 having different principal axis angles in each region Photodetector array 301 Formula for calculating a Jones vector representing a polarization state after passing through the wavelength plate and the polarizer-1
302 Jones vector expression indicating polarization state of incident light 303 Jones vector calculation expression indicating polarization state after passing through wave plate and polarizer-2
304 Expression 401 representing light intensity distribution sensed by light receiving element array Polarization analyzer 402 without drive unit using wavelength plate array and polarizer array Intensity distribution pattern 403 observed by polarization analyzer CPU for pattern analysis
501 Ellipsometer (0 °)
502 Ellipsometer (45 °)
503 Polarization analyzer 801 in which the arrangement order of each array of the ellipsometer 501 is changed. Expression 901 representing a contour line shape near the dark spot. Polarization analyzer 902 having no drive unit using a wavelength plate array and a polarizer array. Intensity distribution 903 Pattern analysis CPU
904 Database for pattern shape comparison 1001 Jones vector 1002 representing polarization state after passing through wave plate and polarizer 1002 representing light intensity distribution perceived by light receiving element array 1003 representing frequency component of light intensity distribution 1004 Each frequency of pattern Calculation formula 1005 for calculating the inclination (γ) of the incident polarization from the components Calculation formula 1402 for calculating the ellipticity (ε) of the incident polarization from each frequency component of the pattern 1402 Polarizer 1402 having a high extinction ratio The phase difference of the wave plate Polarization analyzer 1501 with unknown value Polarization analyzer 1502 with unknown phase difference value of wavelength plate CPU for pattern analysis
1503 Each frequency component obtained by Fourier transform of pattern 1504 Calculation formula 1601 for obtaining the value of the phase difference of the wave plate from the frequency component of the pattern Wave plate array 1602 Polarizer array 1603 Light receiving element array 1604 Diffracted light and scattering by the boundary portion of the array Light receiving element region 1605 for receiving light The light receiving element region not affected by the boundary of the array

Claims (4)

An ellipsometry system having an ellipsometer and a computer,

The ellipsometer is
A wave plate array having a plurality of wave plates having a constant phase difference and different optical axis directions ;
A polarizer array on which light transmitted through the wave plate array is incident, and a polarizer array having a plurality of polarizers having different directions of transmitted polarization ;
The passes through the wavelength plate with a wave plate array and having a light-receiving element array capable of receiving individual light passed through the polarizer with the polarizer array,

The ellipsometer is
The angle of the optical axis of the wave plate included in the wave plate array is a first axis,
When the angle of polarization transmitted by the polarizer included in the polarizer array is the second axis,
Fit the light intensity observed by the photoreceiver array on the coordinates constituted by the first axis and the second axis, and output a light intensity distribution;

The computer receives the light intensity distribution output from the ellipsometer, and determines the polarization state of incident light using the received light intensity distribution.

Ellipsometry system.   The computer
    further,
    A light intensity distribution calculating means for obtaining a contour line of the light intensity distribution using the light intensity distribution;
    From the contours of the light intensity distribution obtained by the light intensity distribution calculating means, a light spot that is the position where the light intensity is the weakest, or a light and dark point calculating means that obtains the dark spot that is the position where the light intensity is the strongest,
    A contour slope calculating means for obtaining a slope of a contour line in the vicinity of a bright spot or a dark spot obtained by the bright spot calculation means;
    A database for storing information on the position of the bright point or dark spot for each polarization state, and storing the slope of the contour line near the bright point or dark point for each polarization state;
    Pattern comparison means for comparing the position of the bright spot or dark spot and the pattern of the slope of the contour line near the bright spot or dark spot;
  Comprising
  Receiving the light intensity distribution output from the ellipsometer;
  The light intensity distribution calculating means obtains a contour line of the light intensity distribution using the received light intensity distribution,
  The light / dark point calculating means obtains a light point where the light intensity is the weakest, or a dark point where the light intensity is the strongest, from the contour lines of the light intensity distribution obtained by the light intensity distribution calculating means,
  The contour line slope calculating means obtains the slope of the contour line in the vicinity of the bright spot or dark spot obtained by the bright spot calculation means,
  The pattern comparison means is
    The pattern stored in the database includes the position of a bright spot or dark spot and the slope of a contour line near the bright spot or dark spot for each polarization state;
    Compare the position of the bright point or dark point obtained by the light / dark point calculating means and the pattern containing the slope of the contour line near the bright point or dark point obtained by the contour slope calculating means,

    This determines the polarization state of the incident light using the received light intensity distribution.

  The ellipsometry system according to claim 1. The computer
    further,
    A light intensity distribution calculating means for obtaining a contour line of the light intensity distribution using the light intensity distribution;
    A database for storing a contour pattern for each polarization state;
    Pattern comparison means for comparing contour line-shaped patterns;
  Comprising

  The computer
    Receiving the light intensity distribution output from the ellipsometer;
    The light intensity distribution calculating means calculates a contour line of the light intensity distribution using the received light intensity distribution,
    Read out the contour pattern for each polarization state stored in the database,
    The pattern comparison means performs fitting between the contour shape of the light intensity distribution calculated by the light intensity distribution calculation means and the contour line pattern for each polarization state read in the previous period,
    This determines the polarization state of the incident light using the received light intensity distribution.
    The ellipsometry system according to claim 1. The computer
    Furthermore, Fourier transform means for Fourier transforming the input light intensity distribution,
    A polarization state calculating means for obtaining a polarization state from each frequency component obtained by Fourier transform of the Fourier transform means;
  Comprising

  The computer
    Receiving the light intensity distribution output from the ellipsometer;
    The Fourier transform means Fourier transforms the received light intensity distribution,
    The polarization state calculating means obtains a polarization state from each frequency component obtained by Fourier transform by the Fourier transform means,
    This determines the polarization state of the incident light using the received light intensity distribution.
  The ellipsometry system according to claim 1.

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