JP2005308612A - Ellipsometer and spectroscopic ellipsometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, quick and precise ellipsometer and spectroscopic ellipsometer without a driving part in a conventional ellipsometer. <P>SOLUTION: This "rotary analyzer type" ellipsometer is constituted by combining one sheet of polarizer array arrayed with a plurality of polarizers different in principal axis directions, and a photoreception element array such as a CCD. Alternatively, the "rotary phaser type" ellipsometer is constituted by arranging one sheet of wave plate arrayed with a plurality of wave plates different in principal axis directions, and one sheet of polarizer having a fixed principal axis direction to be layered overlappedly, and by combining those with the photoreception element array. The small-sized and simple spectroscopic ellipsometer is realized by combining the ellipsometer and a dispersion device such as a diffraction grating. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an optical ellipsometer, and can be applied as an ellipsometer that measures the optical constant and thickness of a thin film by ellipsometry. In addition, according to the present invention, it is possible to realize an ellipsometer having a spectroscopic function, that is, a spectroscopic ellipsometer.

Ellipsometry has long been known as a method for evaluating the properties of thin film samples. Light is incident on the surface of a thin film sample obliquely from above, and the thickness and refractive index of the sample are determined by analyzing the polarization of the reflected light. It is a technique to seek. In other words, in ellipsometry, the ratio of the reflectance (Rp) of a polarized component (p-polarized light) whose electric field is parallel to the incident surface and the reflectance (Rs) of a polarized component (s-polarized light) whose electric field is perpendicular to the incident surface is measured. It will be. The reflectance of each polarization component is generally a complex number and can be expressed as ρ = Rp / Rs = tan (Ψ) × exp (jΔ). Here, Ψ and Δ are called ellipso parameters or ellipsometry angles, and are quantities representing the amplitude intensity ratio and phase difference of the reflected light (light to be measured) from the thin film sample, that is, the polarization state of the reflected light. Since ρ is a value that varies depending on the optical constant (refractive index) and film thickness of the thin film, if the values of Ψ and Δ can be known by measurement, the optical constant (n, k) and film thickness (d) are reversed. Can be calculated.

In conventional ellipsometers, various methods such as “quenching method”, “rotating analyzer method”, “rotating phaser method”, and “phase modulation method” have been adopted as methods for performing polarization analysis of reflected light from a sample ( Non-patent document 1, Non-patent document 2). Among these, the rotation analyzer method is the simplest ellipsometric analysis method, and is a method of measuring a change in transmitted light intensity by making the light to be measured enter a rotating polarizer. In this case, if the relationship between the principal axis angle of the polarizer and the transmitted light intensity is known, the polarization state of the light to be measured can be calculated. Such a rotary analyzer method is still used in many apparatuses because of its advantages such as simple apparatus configuration and low wavelength dependency. However, this method not only has the disadvantage that it is not possible to distinguish between positive and negative Δ (phase difference between p-polarized light and s-polarized light) of the polarization state to be measured, that is, clockwise or counterclockwise polarized light. Since the drive part is essential, it is difficult to reduce the size and accuracy of the device.

While the rotation analyzer method is a polarization analysis method that uses only one polarizer, the rotation phaser method and the quenching method use two elements: a polarizer and a phaser (wave plate). Is the method. The rotating phaser method uses a rotating wave plate (usually a quarter wave plate) and a fixed polarizer. In this method, the light to be measured is passed through the waveplate and the polarizer in this order, and the polarization state of the light to be measured can be determined by measuring the intensity change of the transmitted light accompanying the rotation of the waveplate. One quenching method is a system in which both the wave plate and the polarizer to be used can rotate. Pass the light to be measured in the order of the wave plate and the polarizer, and rotate each element to find the point where it is completely quenched. . In this case, the polarization state of the light to be measured can be known from the principal axis angle of the wave plate and the polarizer at the extinction point. The rotational phaser method and the quenching method as described above have an advantage that all polarization states can be measured without omission, but there are also disadvantages such as a complicated apparatus configuration and a long time for measurement. (Description of the phase modulation method and other methods is omitted.)

In order to eliminate the drive part of the conventional ellipsometer and realize high-accuracy and high-speed polarization analysis, we have proposed a new ellipsometer that combines a waveplate array, polarizer array, and light-receiving element array (patented) Reference 1). These proposals correspond to conventional extinction and phase modulation ellipsometers, which provide two-dimensional information about wave plate angle and polarizer angle (or phase modulation phase difference and polarizer angle). Since it can be measured instantaneously as data, a very high speed measurement is possible. This new ellipsometer can not only realize a compact and highly reliable device by utilizing photonic crystal technology, but also enables highly accurate ellipsometry by adopting an appropriate ellipsometry algorithm (Patent Literature) 2).

On the other hand, with the advancement of device technology such as semiconductor parts and optical parts in recent years, the accuracy required for thin film characteristic evaluation has become stricter year by year, and the need for spectroscopic ellipso is increasing in inline or offline characteristic evaluation. . Spectroscopic ellipsometry is to measure the optical constant (n, k) and film thickness (d) of a thin film sample by measuring the spectrum with respect to the wavelength (λ) of the polarization state (Ψ, Δ) of the light reflected by the sample. This is a method for obtaining with high accuracy. In general, there are only two polarization information, Ψ and Δ, measured by single wavelength ellipsometry, whereas spectral ellipso can use information on wavelength, so three parameters (n, k, It becomes possible to obtain the value of d) with high accuracy. Since the spectrum of the measured Ψ and Δ can be accurately predicted by an optical model, the spectroscopic ellipso is a very effective means for evaluating unknown materials and multilayer films.

However, the conventional spectroscopic ellipsometer is a very large and expensive apparatus because the spectroscope (monochromator) and the ellipsometer such as the rotational analyzer method and the phase modulation method are combined. Furthermore, since the polarization state had to be measured for each wavelength while changing the wavelength of the light to be measured little by little using a spectroscope, it took a lot of time for the measurement. Therefore, the present invention develops the concept of the array-type ellipsometer proposed so far, proposes a new configuration of the ellipsometer, and proposes a method for realizing a compact, high-accuracy and high-speed spectroscopic ellipsometer.
Japanese Patent Application No. 2003-411786 Japanese Patent Application No. 2003-407485 JP-A-10-335758 JP 2001-83321 A Applied Physics Handbook, Applied Physics Society (Maruzen), pp. 20-22, 1990. Spectroscopic ellipsometry, Hiroyuki Fujiwara (Maruzen), pp. 77-98, 2003. Optical waveguide, written by Shojiro Kawakami (Asakura Shoten), pp 126-133, 1980.

As already described, the conventional ellipsometer and spectroscopic ellipsometer require a driving unit and have a complicated configuration. Therefore, (1) the apparatus is large, (2) expensive, and (3) the measurement time is long (4 ) There were problems such as lack of reliability. The present invention solves these problems by using an array technology, and provides a means for realizing a small-sized and highly reliable ellipsometer or ellipsometer that is capable of high-speed measurement without a drive unit. To do.

By combining two optical components, a polarizer array in which a plurality of polarizer regions with different principal axis directions are arranged, and a light receiving element array, or a wavelength plate array in which a plurality of wavelength plate regions with different principal axis directions are arranged and the principal axis direction is By combining three optical components of a fixed polarizer and a light receiving element array, a rotation analyzer type and a rotation phaser type polarization analyzer are configured. In these ellipsometers, since the relationship between the principal axis angle of the polarizer and the wave plate and the light transmission intensity can be obtained instantaneously, the measurement time can be greatly reduced as compared with the conventional apparatus. Further, since the number of parts can be reduced and the drive unit can be omitted, a small and highly reliable device can be realized. Furthermore, by combining these ellipsometers with a dispersion device such as a diffraction grating, a spectroscopic ellipsometer (spectral ellipsometer) that can instantaneously read the polarization state spectrum as two-dimensional data can be realized.

The polarizer array and the wave plate array used in the ellipsometer of the present invention can be manufactured in a small size and with high accuracy by adopting a self-cloning photonic crystal technique (Patent Document 3). As shown in FIG. 1, the self-cloning photonic crystal preserves the shape of the interface between a transparent high-refractive index medium 102 and a low-refractive index medium 103 on a transparent material substrate 101 in which periodic groove arrays are formed. However, it is produced by alternately laminating. The shape of each layer has periodicity in a certain direction (x direction in the figure), but it may be uniform in the direction orthogonal to it (y direction) or periodic or non-longer than the x-axis direction. It may have a periodic structure. In order to perform multilayer film formation while maintaining the uneven shape, it is important to combine sputtering deposition and bias sputtering under optimum conditions. In this way, a fine refractive index periodic structure (photonic crystal) can be industrially produced with high reproducibility and high uniformity.

When light is incident vertically (± z direction) on the self-cloning photonic crystal as shown in FIG. 1, a component having an electric field in the direction parallel to the groove array (TE mode) is present inside the periodic structure. Then, light of a component (TM mode) having an electric field in the orthogonal direction is excited. The propagation constant of each mode can be selected in a wide range depending on the refractive index of the material constituting the periodic structure, the period of unevenness, the lamination period, and the like. As an example, FIG. 2 shows a dispersion curve of a self-cloning photonic crystal formed using Si as a high refractive index material and SiO 2 as a low refractive index material. The vertical axis represents the value obtained by normalizing the light frequency by the stacking period Lz, and the horizontal axis represents the value obtained by normalizing the phase change amount kzLz by π when propagating one period. Such a photonic crystal operates as a polarization separation element (polarizer) that transmits only the TM wave because the TE wave is a cutoff region in the frequency region 201 (Patent Document 3). On the other hand, in the frequency region 202, the TM wave becomes a cut-off region, so that the polarizer transmits only the TE wave. The frequency domain 203 is a propagation band for both modes, but each has a different propagation constant, and therefore operates as a wave plate that gives a phase difference between two polarized waves. By designing the phase difference to be optimum, a quarter wavelength plate or a half wavelength plate can be manufactured.

In the photonic crystal polarizer and the photonic crystal wave plate as described above, the principal axis direction of the device is determined by the direction of the uneven periodic pattern, that is, the direction of the groove on the substrate. Since the periodic pattern of the substrate can be produced by a normal photolithography process, it is easy to provide a plurality of regions on one substrate and change the direction of the groove for each region. That is, the characteristics of the photonic crystal (in this case, the principal axis direction) can be changed for each region. This is called a multi-pattern photonic crystal. The wave plate array and the polarizer array used in the ellipsometer of the present invention can be easily formed by using a multi-pattern photonic crystal technique.

The polarization analyzer of the present invention realized by using a polarizer array and a wave plate array will be briefly described below.

In the ellipsometer according to claim 1, a light receiving element array capable of individually measuring the intensity of light transmitted through each polarizer region is disposed behind the polarizer array composed of a plurality of polarizer regions having different principal axis directions. It is characterized by that. Since the relationship between the principal axis angle of the polarizer and the intensity of the passing light can be instantaneously measured by the light receiving element array, a very high-speed polarization analysis can be performed. This is equivalent to a conventional rotational analyzer type ellipsometer.

In the ellipsometer relating to claim 2, the polarizer array used in the ellipsometer of claim 1 has a periodic concavo-convex shape repeated in a specific direction determined for each region in the in-plane direction. And a dielectric multilayer film in which the shape of each layer is periodically repeated in the stacking direction, that is, a self-cloning photonic crystal. By using a photonic crystal, the principal axis angle of each polarizer region can be strictly controlled, so that a small and highly accurate ellipsometer can be realized.

The ellipsometer relating to claim 3 includes a wave plate array (ideally a quarter wave plate array) comprising a plurality of wave plate regions having different principal axis directions, and a polarizer having a uniform direction of transmitted polarization. Are arranged such that the wave plate array is the front surface and the polarizer is the rear surface, and the light receiving element array is disposed behind the wave plate array. Since the relationship between the principal axis angle of the wave plate and the transmitted light intensity can be instantaneously measured by the light receiving element array, a very high-speed polarization analysis becomes possible. This corresponds to a conventional rotational phaser type ellipsometer.

In the ellipsometer relating to claim 4, the wave plate array used in the ellipsometer according to claim 3 has a periodic concavo-convex shape repeated in a specific direction determined for each region in the in-plane direction. And a dielectric multilayer film in which the shape of each layer is periodically repeated in the stacking direction, that is, a self-cloning photonic crystal. By using a photonic crystal, a small and highly accurate wave plate array can be realized. One polarizer may use a photonic crystal, or may use a conventional technique such as a metal fine particle-dispersed glass or an organic film.

The ellipsometer according to claim 5 has a polarizer array in which a plurality of elongated polarizer regions having different principal axis directions are arranged in stripes, and the ellipsometer according to claim 1 or 2 It is characterized by combining dispersive devices that separate each frequency component. The light to be measured is dispersed in a direction orthogonal to the arrangement direction of the polarizer array by the dispersion device, and then incident on the polarizer array. By collectively measuring the light intensity after passing through the polarizer array with the light receiving element array, two-dimensional information about the polarization state and the wavelength can be obtained, so that high-speed spectroscopic ellipso analysis is possible.

The ellipsometer according to claim 6 has a wave plate array in which a plurality of elongated wave plate regions having different principal axis directions are arranged in a stripe pattern, and the ellipsometer according to claim 3 or 4, It is characterized by combining dispersive devices that separate each frequency component. The light to be measured is dispersed by a dispersion device in a direction orthogonal to the arrangement direction of the wave plate array, and then incident on the wave plate array. Since the light intensity after passing through each region of the wave plate array and the uniform polarizer is collectively measured by the light receiving element array, two-dimensional information about the polarization state and the wavelength can be obtained. Ellipso analysis is possible.

With the configuration of the present invention, a small-sized ellipsometer and a spectroscopic ellipsometer without a drive unit can be realized. In addition, since each component is small and position adjustment is easy, it can be expected to realize a low-cost and highly reliable product. In particular, the ellipsometer and the spectroscopic ellipsometer that can be realized by the present invention are the relationship between the polarization state (Ψ, Δ) of the light to be measured and the wavelength (λ), that is, the optical constant (n, k) and the film thickness (d) of the thin film sample. Can be obtained with high accuracy, so that a new method of use can be made at the manufacturing site of semiconductors and optical components. Conventional expensive and large ellipsometers are assumed to be used off-line, but the present invention makes it possible, for example, to install a small measuring device inside a thin film manufacturing apparatus and measure it online during the process. Become. As described above, the ellipsometer of the present invention is suitable for controlling a thin film manufacturing apparatus or quality control of a thin film product, and not only replaces a conventional apparatus but also realizes a new method of using an ellipsometer.

  Before describing the details of the present invention, a mathematical expression of the polarization state of light will be described. Light is an electromagnetic wave, that is, a “transverse wave”, and has an electric field component perpendicular to the traveling direction. There are two degrees of freedom in the electric field direction, and the two components propagate in different phases, as shown in FIG. Therefore, when measuring light, the electric field vector generally draws an elliptical orbit as shown in FIG. When the amplitudes of the vertical component and horizontal component of the electric field are respectively Ax and Ay, the polarization state of the light traveling in the z direction at each frequency ω can be expressed as Equation 301 in FIG. Here, φx and φy are the phases of the respective polarization components, and k is a value representing the propagation constant of light. At this time, the parameters (Ψ, Δ) measured by ellipsometry can be expressed as Equation 302 using the amplitude and phase values of each component. That is, if the values of Ax and Ay (or Ψ) and Δ of the light to be measured are obtained, the polarization state can be specified.

  As a method for expressing the polarization state of light, a method using an S parameter and a Poincare sphere is also well known. In this method, the polarization state of light is expressed by four parameters S1, S2, S3, and S0, and expressed as a point on a spherical surface having a radius = S0. The Poincare sphere has an advantage that the image on the polarization state can be easily grasped because the coordinates on the spherical surface and the polarization state correspond one-to-one. For example, if the elliptically polarized light (main axis angle is γ and ellipticity angle is η) in FIG. 3B is expressed by a Poincare sphere, as shown in FIG. 4A, longitude 2γ, latitude 2η It becomes the point. Each S parameter can be expressed as an expression 501 in FIG. 4B by using values of amplitude (Ax, Ay) and phase (Δ) of two polarization components. Further, there is a relationship of Formula 502 between S0 and S1, S2, and S3.

  As another method for expressing the polarization state, a method using the ellipticity (ε) of elliptically polarized light and the inclination angle (γ) of the major axis will be described. This method is not necessarily a general method for expressing the polarization state, but it is an easy-to-understand method when theoretically calculating the polarization analysis method of the present invention. As shown in FIG. 5A, the ratio of the major axis to the minor axis length of the ellipse drawn by the electric field vector is 1: ε, and the inclination of the major axis is γ. ε has a value between −1 and 1, and is a positive value for clockwise polarized light and a negative value for counterclockwise polarized light. On the other hand, γ is a value between −90 ° and 90 °. When the relationship between γ and ε is expressed using Ax, Ay and Δ, and Ψ and Δ, which have already been described, an equation 601 in FIG. 5B is obtained. (However, the proportionality coefficient is omitted in Equation 601.)

  Below, the ellipsometry apparatus of this invention is demonstrated using the above three methods. The important point here is that the expression methods of these polarization states are not independent, but all correspond to one to one, and any method can be used to obtain the same result.

  First, FIG. 6 shows the configuration of the “rotating analyzer type” ellipsometer shown in claims 1 and 2. The polarizer array 701 is an array of N (N is an integer of 2 or more) polarizer regions whose main axis angles are changed little by little, and the polarization extinction ratio of each polarizer region is sufficiently high. To do. In the illustrated polarizer array, all the polarizer regions have the same shape, and the respective principal axis angles are gradually changed from 0 ° to 180 ° with respect to the reference axis (x-axis direction), and the horizontal direction (y-axis) The direction of the reference axis, the range of the principal axis angle, the shape of each polarizer, and the arrangement position are all arbitrary. A light receiving element array 702 is arranged behind such a polarizer array. By doing so, it is possible to collectively measure the intensity of the light transmitted through each polarizer region of the polarizer array by the light receiving element array. The polarizer array 701 may be directly bonded to the light receiving element array 702, or the light passing through the polarizer array may be imaged on the light receiving element array using a relay lens.

In order to realize the ellipsometer as shown in FIG. 6, a small polarizer array is essential. In addition, in order to perform highly accurate polarization analysis, it is necessary to accurately grasp the principal axis angle of each polarizer region. However, since each conventional polarizer is an independent component, it has been difficult to strictly manage the angle of each polarizer and to realize a small array by arranging a plurality of elements. On the other hand, if the self-cloning photonic crystal is used, not only can the principal axis angle of the polarizer be strictly controlled by the direction of the groove formed on the substrate, but also the characteristics (in this case, in one substrate by multi-pattern technology) It is also easy to create multiple areas with different spindle angles. Therefore, the polarizer array used in the present invention can be manufactured in a small size and with high accuracy by the photonic crystal technique (claim 2).

A description will be given of the light intensity distribution observed in the light receiving element array when the light to be measured is incident on the "rotating analyzer type" ellipsometer. However, here, it is assumed that the polarizer array and the light receiving element array are sufficiently small, and therefore the light to be measured is irradiated to the array with uniform intensity. When the polarization state of the light to be measured is expressed by the amplitude (Ax, Ay) and the phase difference (Δ) of the two electric field components, the polarization state of the light transmitted through the analyzer (polarizer) having the principal axis angle φ (Jones vector u) Can be described as Equation 801 in FIG. Therefore, the light intensity distribution I measured by the light receiving element array can be obtained as in Expression 802. When the formula 802 is rewritten using the S parameter (formula 501) and further normalized by the intensity of the light to be measured, the light intensity distribution I eventually becomes the formula 803. From Expression 802 and Expression 803, it can be seen that the light intensity distribution observed in the light receiving element array is expressed as a function of the polarization state of the light to be measured and the angle of the polarizer. Therefore, by analyzing the one-dimensional light intensity distribution observed in the light receiving element array, the polarization state of the light to be measured can be specified conversely.

On the other hand, when the polarization state of the light to be measured is expressed by ellipticity (ε) and inclination (γ), the polarization state of the light after passing through the polarizer having the principal axis angle φ can be described as Equation 901 in FIG. The light intensity I observed in the light receiving element array can be obtained as shown in Equation 902 (for simplicity, 2φ = Φ is substituted). When formula 902 is normalized by the intensity of the light to be measured, formula 903 is obtained. From Expression 903, it can be seen that the light intensity distribution observed in the light receiving element array is expressed as a function of the polarization state of the light to be measured and the principal axis angle of the polarizer. This means that the one-dimensional light intensity distribution observed in the rotation analyzer type ellipsometer can be expressed by only a DC component and one frequency component. Therefore, for example, if the light intensity distribution observed in the light receiving element array is Fourier-analyzed and the amplitude and phase values can be obtained for the first-order frequency component of Φ, the values of ε (more precisely, the square of ε) and γ That is, the polarization state of the light to be measured can be known.

As described above, in such a “rotating analyzer type” ellipsometer, it is not possible to distinguish between positive and negative with respect to Δ. That is, in Expression 803, the values of S1 and S2 are obtained from the observed light intensity distribution, and the value of S3 is calculated using Expression 502 (in this case, S0 = 1). Therefore, the sign of S3 cannot be known. Similarly, in Expression 903, what is obtained is the square value of γ and ε, and the sign of ε cannot be determined. As described above, the rotation analyzer type ellipsometer has a drawback that it cannot distinguish clockwise or counterclockwise of the light to be measured. However, as already mentioned, this rotational analyzer type ellipsometer has advantages such as a small number of parts and a simple configuration, and a relatively high-precision measurement with small wavelength dependence. ing.

Next, the "rotary phaser type" ellipsometer described in claims 3 and 4 will be described with reference to FIG. The wave plate array 1001 is an array of N (N is an integer of 2 or more) wave plate (ideally 1/4 wave plate) regions whose main axis angle is changed little by little. In the illustrated waveplate array, each waveplate region has the same shape, and each main axis angle is gradually changed from 0 ° to 180 ° with respect to the reference axis (x-axis direction), and the horizontal direction (y-axis) The direction of the reference axis, the range of the main shaft angle, the shape of each wave plate region, and the arrangement position are all arbitrary. A polarizer 1002 having a uniform principal axis direction is disposed behind such a wave plate array, and a light receiving element array 1003 is disposed further rearward. At this time, the principal axis angle of the polarizer is arbitrary. In such a configuration, the intensity of light transmitted through the wave plate array and the polarizer can be collectively measured by the light receiving element array. The wave plate array 1001 and the polarizer 1002 may be bonded and integrated, or a relay lens may be inserted to form an image of light that has passed through the wave plate array on the polarizer. Similarly, the polarizer 1002 and the light receiving element array may be bonded and integrated, or the light passing through the polarizer may be imaged on the light receiving element array.

In the ellipsometer as shown in FIG. 9, a small wave plate array in which the principal axis angle of each region is accurately managed is essential. However, since the conventional polarizers are still independent components, it is difficult to realize a small array by arranging a plurality of elements while strictly controlling the angle of each polarizer. On the other hand, if self-cloning photonic crystals are used, as already explained, the principal axis angle of each wave plate can be strictly controlled, or multiple wave plates with different principal axis angles can be formed on the same substrate by multi-pattern technology. Since it can be manufactured easily, a small and highly accurate wave plate array can be manufactured. On the other hand, a “rotary phaser type” ellipsometer also requires a polarizer with a uniform principal axis direction. As this polarizer, a conventionally existing polarizer such as a metal fine particle-dispersed glass or an organic film may be used, or a photonic crystal polarizer may be used. When a photonic crystal is used as a polarizer, a polarizer and a wave plate array are sequentially laminated on a single substrate (Example 3), or a wave plate array and a polarization are respectively formed on both sides of the substrate. It is also possible to produce a child (Example 4).

A description will be given of the light intensity distribution observed in the light receiving element array when the light to be measured is incident on this "rotating phaser type" ellipsometer. When the polarization state of the light to be measured is expressed by the amplitude (Ax, Ay) and the phase difference (Δ) of the two electric field components, the Jones vector (u) of the light transmitted through the wave plate having the principal axis angle θ and the polarizer is shown in FIG. Equation 1101 can be described. However, here, for the sake of simplicity, the phase difference of the wave plate array is ¼ wavelength (that is, π / 2 radians), and the principal axis angle of the polarizer is 0 °. At this time, the light intensity I measured by the light receiving element array can be obtained by Expression 1102. If Formula 1102 is rewritten using the S parameter (Formula 501) and is further normalized by the intensity of the light to be measured, I will eventually become Formula 1103. From this, it can be seen that the light intensity distribution observed in the light receiving element array is expressed as a function of the polarization state of the light to be measured and the angle of the wave plate. Therefore, it can be seen that by analyzing the one-dimensional light intensity distribution observed in the light receiving element array, the polarization state of the light under measurement can be specified.

To further generalize the above discussion, let us consider the case where the phase difference of each wave plate of the wave plate array is α and the principal axis angle of the polarizer is φ. When the polarization state of the light to be measured is expressed by ellipticity (ε) and inclination (γ), the polarization state of the light after passing through a wave plate (phase difference: α) with a principal axis angle θ and a polarizer with a principal axis angle φ is shown in FIG. 11 can be expressed as Equation 1201. As a result, the light intensity I (after normalization) observed by the light receiving element array is expressed by Expression 1202. (However, 2φ = Φ, 2θ = Θ have been replaced.) In this case as well, the light intensity distribution observed by the light receiving element array is expressed as a function of the polarization state of the light to be measured and the principal axis angle of the wave plate. . Here, since Φ and α are constants determined by the apparatus, the observed light intensity I can be expressed by a DC component and two frequency components after all. Therefore, for example, if the one-dimensional light intensity distribution observed in the light receiving element array is Fourier-transformed and the magnitude of the DC component and the amplitude and phase values of the two frequency components (X, Y) can be obtained, ε and γ , That is, the polarization state of the light to be measured.

The previous “rotation analyzer type” ellipsometer could not distinguish between clockwise and counterclockwise, whereas the “rotary phaser type” ellipsometer could distinguish all polarization states. That is, as can be seen from Equations 1103 and 1202, it can be seen that all S parameter values or values of ε and γ can be completely obtained from the one-dimensional light intensity distribution observed in the light receiving element array. Further, since the retardation of the wave plate generally has a wavelength dependency, the “rotation phaser type” ellipsometer requires correction of the phase difference. With respect to this as well, the ellipsometer of the present invention can mathematically determine the retardation value (α) of the wave plate from the observed intensity distribution using the formula 1202. Specifically, the observed one-dimensional light intensity distribution is Fourier-analyzed, and the values of the amplitude and phase of each frequency component represented by Expression 1202 are obtained, whereby the value of the phase difference (α) of the wave plate is obtained. It can be obtained and self-corrected.

In the ellipsometer described so far, it is assumed that the light to be measured is monochromatic light such as a laser or the polarization state of the light to be measured has no wavelength dependency. However, in actual ellipsometry, it is known that the polarization state of the reflected light from the thin film greatly depends on the wavelength. Spectroscopic ellipsometry is a technique for accurately obtaining the optical constant and film thickness of a thin film by utilizing the wavelength dependence of the polarization state. With recent advances in semiconductor device technology and optical device technology, the accuracy required for various thin film formations has become stricter year by year, and the need for spectroscopic ellipsometry is increasing in the field of product development and quality control. .

The light intensity distribution observed by the light receiving element array in the ellipsometer of the present invention is one-dimensional information about the principal axis angle of the polarizer or the wave plate. Therefore, if the shape and arrangement of the polarizer array and the wave plate array of the ellipsometer described so far are devised and combined with any dispersive device, for example, the polarization information and the wavelength information are respectively displayed on the vertical axis and the horizontal axis. It is also possible to realize a spectroscopic ellipsometer that can be collectively measured with a light receiving element array as two-dimensional information. The configuration of the spectroscopic ellipsometer will be described below for each of the “rotating analyzer type” and “rotating phaser type” ellipsometers.

First, a configuration example of the “rotating analyzer type” spectroscopic ellipsometer shown in claim 5 is shown in FIG. The polarizer array 1301 is formed by arranging a plurality of polarizer regions having different principal axis angles in one row (stripe shape). The size of each polarizer region of the polarizer array, the range of the principal axis angle, and the order of arrangement are arbitrary, but each region must be arranged in a line in a predetermined direction as shown in the figure. The light receiving element array 1302 is disposed behind such a polarizer array, and the light intensity transmitted through each polarizer can be collectively measured. In this case, white light (light having a wide spectral width) is used as the light to be measured. The light to be measured is dispersed by the diffraction grating 1303 and reaches a predetermined position of the polarizer array 1301 for each wavelength. At this time, it is important to arrange each element so that the wavelength dispersion direction by the diffraction grating 1303 and the arrangement direction of the polarizer array 1301 are orthogonal to each other. With the configuration described above, the light receiving element array can instantaneously measure the polarization information and wavelength information of the light to be measured as two-dimensional data.

The light intensity distribution observed by the spectroscopic ellipsometer as shown in FIG. 12 is obtained by arranging the light intensity distributions given by Expressions 803 and 903 described above for each wavelength. That is, an intensity distribution indicating a polarization state at a specific wavelength is obtained in the arrangement direction (x-axis direction) of the polarizer array, and a spectrum of the polarization state is obtained in a direction orthogonal to that (y-axis direction). . For the wavelength range of the light source, that is, the spectrum range to be measured, an optimum one may be selected depending on the target sample.

  Next, a configuration example of the “rotating phaser type” spectroscopic ellipsometer shown in claim 6 and FIG. 13 are shown. The wave plate array 1401 is formed by arranging a plurality of wave plate (ideally quarter wave plates) regions having different principal axis angles in one row (stripe shape). The size, the range of the principal axis angle, and the arrangement order of each wave plate region of the wave plate array are arbitrary, but each region must be arranged in a line in a determined direction as shown in the figure. Such a wave plate array and a polarizer 1402 having a constant main axis direction are arranged so as to overlap each other, and a light receiving element array 1403 is arranged behind the wave plate array. Therefore, in the light receiving element array, it is possible to collectively measure the intensity distribution of the light that has passed through each wave plate and the polarizer. The light to be measured is white light and is dispersed by the diffraction grating 1404 and then reaches a specific region of the wave plate array 1401 for each wavelength component. At this time, it is important to arrange the elements so that the direction of chromatic dispersion by the diffraction grating 1404 and the arrangement direction of the wave plate array 1301 are orthogonal to each other. With the configuration as described above, the light receiving element array can instantaneously measure the polarization information and wavelength information of the light to be measured as two-dimensional data.

The light intensity distribution observed by the spectroscopic ellipsometer as shown in FIG. 13 is obtained by arranging the light intensity distributions given by Expressions 1103 and 1202 described above for each wavelength. That is, an intensity distribution indicating a polarization state at a specific wavelength is obtained in the arrangement direction (x-axis direction) of the wave plate array, and a polarization state spectrum is obtained in a direction orthogonal to the wavelength plate array (y-axis direction). . For the wavelength range of the light source, that is, the spectrum range to be measured, an optimum one may be selected depending on the target sample.

  The relationship (spectrum) between the polarization state (Ψ, Δ) and the wavelength (or light energy) measured by spectroscopic ellipsometry is theoretically obtained by, for example, creating an optical model as shown in FIG. be able to. In this example, a first thin film layer 1502, a second thin film layer 1503, and a third thin film layer 1404 are formed on a substrate 1501, and light is incident on the surface at an angle ξ. In such a case, the polarization state of the light reflected from the sample can be accurately obtained by, for example, F matrix calculation (Non-Patent Document 3). FIG. 14B shows an example (image diagram) of spectra of Ψ and Δ obtained by calculation. By utilizing this and comparing and analyzing the spectrum obtained by the experiment and the theoretical value, the optical constant and film thickness of each thin film layer on the sample surface can be accurately obtained (Non-patent Document 2). .

(Example 1)
In spectroscopic ellipsometry, in order to evaluate the optical constant, film thickness, and surface roughness of a thin film sample with high accuracy, it is generally desirable that the wavelength range for measurement be wide. For example, many conventional spectroscopic ellipsometers can perform polarization analysis over a wide wavelength range from visible light to infrared light, or from ultraviolet light to infrared light. On the other hand, the transmission wavelength band of self-cloning photonic crystal polarizers and photonic crystal wave plates has been limited to several hundreds of nanometers so far, and cannot be said to be so wide. Therefore, the spectroscopic ellipsometer of the present invention using a photonic crystal polarizer array or a photonic crystal wave plate array is also limited in the usable wavelength band.

FIG. 15 shows a configuration example of a “rotating analyzer type” ellipsometer that solves the above-described problems in the photonic crystal and enables ellipsometry in a wide wavelength band. The polarizer array 1601 is configured not only by arranging a plurality of regions with slightly different principal axis angles in the x-axis direction but also by arranging a plurality of regions with different transmission wavelength bands in the y-axis direction. For example, the polarizer array 1601 shown in the figure integrates five polarizer arrays corresponding to each wavelength region of ultraviolet (UV), blue (B), green (G), red (R), and infrared (IR). It is a thing. By combining such a polarizer array and the light receiving element array 1602, polarization information over a wide wavelength range can be acquired. Since the transmission wavelength band of the photonic crystal polarizer can be arbitrarily designed by controlling the concavo-convex pattern of the substrate, a polarizer array as shown in the figure can be manufactured without much difficulty. The wavelength range (light source) may be optimally selected depending on the sample to be measured.

(Example 2)
FIG. 16 shows a configuration example that enables polarization analysis in a wide wavelength band for a “rotary phaser type” ellipsometer. The wave plate array 1701 is configured not only by arranging a plurality of regions with slightly different principal axis angles in the x-axis direction but also by arranging regions with different transmission wavelength bands in the y-axis direction. Similar to the previous example, the wave plate array 1701 includes five wave plate arrays corresponding to each wavelength region of ultraviolet (UV), blue (B), green (G), red (R), and infrared (IR). Are integrated. For the other polarizer 1702, the transmission wavelength band may be changed for each region if necessary. By combining such a wave plate array with a polarizer and a light receiving element array 1703, it is possible to acquire polarization information over a wide wavelength range. Since the transmission wavelength band of the photonic crystal wave plate can be arbitrarily designed by controlling the concavo-convex pattern of the substrate, a polarizer array as shown in the figure can be manufactured without much difficulty. In addition, since the necessary wavelength range depends on the sample, the optimum number of wavelength divisions for the light source and the array may be selected for the assumed sample.

(Example 3)
FIG. 17 shows an example in which the wavelength plate array and the polarizer array are both made of a photonic crystal and integrated with the “rotary phaser type” ellipsometer of the present invention. First, a photonic crystal polarizer 1803 is stacked on a substrate 1801. At this time, the unevenness of the surface can be flattened by depositing the final layer slightly thicker. Of course, mechanical means such as polishing the surface may be used. Thereafter, the concave / convex pattern for the wave plate array is formed again on the surface, and the photonic crystal wave plate array layer 1802 is laminated, so that the two optical elements can be integrated. By combining this polarizer-integrated wave plate array and the light receiving element array 1804, a small ellipsometer can be realized.

Example 4
FIG. 18 shows another example of integrating the wave plate array and the polarizer array in the “rotary phaser type” ellipsometer of the present invention. In this example, integration is realized by laminating a polarizer layer 1903 and a wave plate array layer 1902 on both surfaces of the substrate 1901, respectively. For pattern alignment, a transparent substrate such as SiO 2 may be used as the substrate 1901 and a marker for alignment may be attached. By combining this polarizer-integrated wave plate array and the light receiving element array 1904, a small-sized polarization analyzer can be realized.

(Example 5)
Since the “rotary phaser type” ellipsometer of the present invention uses two planar devices, a wave plate array and a polarizer, multiple reflection of light between them may be a problem. As a method for solving this problem, an example in which an absorber is inserted between a wave plate array and a polarizer is shown in FIG. FIG. 19 shows a cross section of the wave plate array 2001, the polarizer 2002, the light receiving element array 2003, and the absorber 2004. The same applies to the case where these elements are integrated by bonding them together or by producing each element on both sides of a substrate having loss. In such a configuration, although the light transmission intensity itself becomes weak, there is no practical problem because the intensity of the light to be measured is usually considered sufficiently higher than the sensitivity of the photodetector. Since the light reflected by the polarizer 2002 is absorbed and gradually weakens while propagating through the absorption layer 2004, the component that is reflected again and reaches the detector can be made sufficiently small.

(Example 6)
FIG. 20 shows another configuration example for reducing multiple reflection of light between the wave plate array and the polarizer in the “rotary phaser type” ellipsometer of the present invention. In FIG. 20, the wave plate array 2101 is arranged slightly tilted with respect to the polarizer 2102. In such a configuration, when the light reflected by the polarizer 2102 is reflected again by the wave plate array 2101, the path of the reflected light changes, so that multiple reflections can be suppressed, and noise is received by the light receiving element array 2103. A signal with less can be obtained.

(Example 7)
FIG. 21 shows a configuration example of an ellipsometer and a spectroscopic ellipsometer realized by combining the ellipsometer of the present invention and a laser light source. FIG. 21 is only an example of an ellipsometer using the present invention, and various other configurations for realizing an ellipsometer using the present invention are conceivable. A sample stage 2206 is arranged at the center of the apparatus where the ellipsometer 2203 and the laser light source 2202 of the present invention are arranged. It is assumed that the polarization state of the light emitted from the laser is known in advance. The thin film sample 2201 is set on the sample stage 2206, and the laser beam is condensed on the sample. At the same time, the lens pair 2204 is adjusted so that the reflected light reaches a polarization analyzer 2203 as a parallel beam. The reflected light from the sample is detected by the polarization analyzer 2203, and the polarization state of the reflected light is calculated from the intensity distribution measured by the CPU 2205. In an ellipsometer, the polarization state of light is generally represented by an amplitude intensity ratio (Ψ) and a phase difference (Δ) of P and S waves. Usually, 45 ° linearly polarized light (Ψ = 1, Δ = 0) is used as incident light, and Ψ ′ and Δ ′ of reflected light at this time are measured. From the measurement result, the Fresnel reflectivity (Rp, Rs) of the P wave and S wave in the sample, that is, the film thickness and refractive index of the thin film can be obtained.

(Example 8)
An example in which the ellipsometer of the present invention is used as a film thickness / film quality monitor during a thin film forming process such as vapor deposition or sputtering is shown in FIG. Consider a process apparatus in which a substrate 2301 is set in a vacuum chamber 2306 and a material source 2307 is formed on the substrate by controlling a control circuit 2305. A light source 2302 and a polarization analyzer 2303 of the present invention are installed in the chamber of the film forming apparatus as shown in the figure, and reflected light from the substrate is detected. Although a small light source is installed in the chamber in the figure, it is also possible to arrange the light source outside the chamber and guide the light into the chamber using an optical fiber or the like. The signal from the ellipsometer 2003 is analyzed by the CPU 2304, and the film thickness and refractive index of the thin film being formed can be known in real time from the light intensity distribution.

Such a real-time film thickness / film quality monitor during the thin film formation process is extremely useful for highly accurate film formation management. In other words, the information on the monitored film thickness and film quality is fed back to the apparatus, thereby making it possible to perform strict film formation management. Since the conventional ellipsometer is a large and expensive apparatus, it has been difficult to use it in combination with the process apparatus. On the other hand, the present invention is very promising as an in-situ monitor for a vacuum process because a small and inexpensive ellipsometer or spectroscopic ellipsometer can be realized. As described above, the ellipsometer of the present invention does not require information on the absolute value of the light intensity, and the polarization state can be determined only by the relative intensity distribution. Therefore, monitoring is possible without being affected by fluctuations in light intensity due to adhesion of the film-forming substance to the window.

Conceptual diagram of self-cloning photonic crystal Band diagram showing the propagation characteristics of the photonic crystal shown in FIG. Conceptual diagram showing polarization state of light and mathematical expression expressing polarization state Polarization state expression method using Poincare sphere A method of expressing the polarization state of light by ellipticity and inclination of the ellipse Schematic diagram showing the configuration of the "rotating analyzer type" ellipsometer Theoretical expression (1) representing the light intensity distribution observed with the ellipsometer of FIG. Theoretical expression (2) representing the light intensity distribution observed with the ellipsometer of FIG. Conceptual diagram showing the configuration of a "rotating phaser type" ellipsometer Theoretical expression (1) representing the light intensity distribution observed with the ellipsometer of FIG. Theoretical formula (2) representing the light intensity distribution observed with the ellipsometer of FIG. Schematic diagram showing the configuration of a rotational analyzer type spectroscopic ellipsometer Schematic diagram showing the configuration of a rotational phaser spectroscopic ellipsometer Schematic diagram showing optical model and spectrum of polarization state in spectroscopic ellipsometry Example of a configuration that realizes a wide band of a rotational analyzer type spectroscopic ellipsometer Configuration example for realizing a broadband broadband phase shifter Example (1) in which the wave plate array and the polarizer of the ellipsometer of FIG. 16 are integrated. Example (2) in which the wave plate array and the polarizer of the ellipsometer of FIG. 16 are integrated. Example of configuration for avoiding multiple reflection of light in ellipsometer of FIG. 16 (1) Example (2) of the configuration for avoiding multiple reflection of light in the ellipsometer of FIG. The conceptual diagram showing the structure of the ellipsometer apparatus using this invention Conceptual diagram of on-line film thickness / film quality monitor during thin film process

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate with pattern 102 High-refractive index material layer 103 Low-refractive index material layer 201 Frequency region 202 that operates as a polarizer that reflects TE waves and transmits TM waves A polarizer that transmits TE waves and reflects TM waves The frequency region 203 in which the TE wave also operates The frequency region 301 in which the TE wave also operates as a wave plate that transmits the TM wave Equation 302 expressing the polarization state of light 302 Equation expressing the relationship between the ellipsometry angle and the polarization state 501 S parameter definition equation 502 Relational expression 601 between S parameters Expression 701 expressing polarization state by ellipticity of light and inclination of ellipse 701 Polarizer array 702 in which a plurality of polarizers having different principal axis directions are integrated Light-receiving element array 801 After passing through the polarizer Formula for Jones vector representing the state of polarization (1)
802 Expression (1) representing the light intensity distribution observed in the “rotating analyzer type” ellipsometer
803 Formula (2) representing the light intensity distribution observed in the “rotating analyzer type” ellipsometer
901 Formula for Jones vector representing polarization state after passing through polarizer (Part 2)
902 Expression (3) representing the light intensity distribution observed in the “rotating analyzer type” ellipsometer
903 Expression (4) representing the light intensity distribution observed in the “rotating analyzer type” ellipsometer
1001 Wavelength plate array 1002 in which a plurality of waveplates having different main axis directions are integrated 1002 Polarizer 1003 Light receiving element array 1101 Jones vector equation representing the polarization state after passing through the waveplate and the polarizer (part 1)
1102 Expression (1) representing a light intensity distribution observed in a “rotary phaser type” ellipsometer
1103 Expression (2) representing the light intensity distribution observed in the “rotary phaser type” ellipsometer
1201 Jones vector equation representing polarization after passing through wave plate and polarizer (Part 2)
1202 Expression (3) representing the light intensity distribution observed in the “rotary phaser type” ellipsometer
1301 Polarizer array 1302 Light receiving element array 1303 Diffraction grating 1401 Wavelength plate array 1402 Polarizer 1403 Light receiving element array 1404 Diffraction grating 1501 Substrate 1502 First thin film layer 1503 Second thin film layer 1504 Third thin film layer 1601 A plurality of polarized light having different wavelength bands Polarizer array 1602 with integrated child array Photodetector array 1603 Diffraction grating 1701 Polarizer array 1702 with integrated wave plate arrays with different wavelength bands Polarized light with integrated polarizers with different wavelength bands Child array 1703 Light receiving element array 1704 Diffraction grating 1801 Substrate 1802 Wave plate array layer 1803 Polarizer layer 1901 Substrate 1902 Wave plate array layer 1903 Polarizer layer 2001 Wave plate array 2002 Polarizer 2003 Light receiving element array 2004 Absorbing layer 2101 Wavelength plate array 2102 Polarizer 2103 Light receiving element array 2201 Sample to be measured 2202 Light source 2203 Polarization analyzer 2204 Optical axis adjusting lens 2205 Data analysis CPU of the present invention
2206 Sample stage 2301 Substrate 2302 Light source 2303 Polarization analyzer 2304 Data analysis CPU of the present invention
2305 Deposition control circuit 2306 Chamber 2307 Material source

Claims (6)

Consists of two optical elements, a polarizer array composed of a plurality of polarizer regions having different principal axis directions and a light receiving element array composed of a plurality of light receiving elements, and each of the light passing through each polarizer region of the polarizer array A polarization analyzer characterized in that the light receiving element array is arranged so that light can be received individually. 2. The ellipsometer according to claim 1, wherein the polarizer array has a periodic concavo-convex shape repeated in a specific direction determined for each region in the in-plane direction, and in the stacking direction. Consists of a dielectric multilayer film in which the shape of each layer is periodically repeated. A wave plate array composed of a plurality of wave plate regions having a constant phase difference between two orthogonal polarization components of transmitted light and different principal axis directions, a polarizer having a uniform principal axis direction, and light reception composed of a plurality of light receiving elements Light that is composed of three optical elements, an element array, is arranged so that the wave plate array overlaps with the front surface and the polarizer as a rear surface, and passes through a specific wave plate region and the polarizer of the wave plate array The polarization analysis apparatus is characterized in that the light receiving element array is arranged so that each of the light receiving elements can be individually received. 4. The ellipsometer according to claim 3, wherein the wave plate array has a periodic concavo-convex shape repeated in a specific direction determined for each region in the in-plane direction, and in the stacking direction. Consists of a dielectric multilayer film in which the shape of each layer is periodically repeated. The ellipsometer according to claim 1 or 2, which has a polarizer array in which a plurality of polarizer regions having different principal axis directions are arranged in a stripe shape, and a dispersion device that separates measured light for each wavelength or frequency component The dispersion device and the polarization analysis so that the measured light is dispersed in the direction orthogonal to the arrangement direction of the polarizer array by the dispersion device and then incident on the polarizer array. An apparatus is provided, and the light intensity distribution after passing through the polarizer array is measured by a light receiving element array, thereby obtaining two-dimensional information about the relationship between the polarization state of the light to be measured and the wavelength. Spectroscopic ellipsometer. 5. The ellipsometer according to claim 3, further comprising a wave plate array in which a plurality of wave plate regions having different main axis directions are arranged in a stripe shape, and a dispersion device that separates light to be measured for each wavelength or frequency component The dispersion device and the polarization analysis so that the measured light is dispersed in the direction orthogonal to the arrangement direction of the wave plate array by the dispersion device and then incident on the wave plate array By obtaining a two-dimensional information about the relationship between the polarization state of the light to be measured and the wavelength by measuring the light intensity distribution after being transmitted through the wave plate array and the polarizer with the light receiving element array. A spectroscopic ellipsometer characterized by.

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