JP2009210457A - Spectropolarimetric measurement device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize measurements, by eliminating the influence due to change in the state of bending of an optical fiber on a measurement value, in a spectropolarimetric measuring device for receiving light from a sample incident via the optical fiber by the use of a spectrometer, and measuring the spectropolarimetric parameters of the sample. <P>SOLUTION: The spectropolarimetric measuring apparatus 10 for measuring the spectropolarimetric parameters of the sample 30 by the use of the spectrometer 20 includes a light-receiving optical system 52 for receiving light from the sample 30. The optical system 52 includes the optical fiber 18 for sending a light received with an optical analyzer 16, or the like, to the spectrometer 20, and a diffusion plate 19 which is provided, immediately in front of the optical fiber 18 and makes the light scatter from the sample. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spectroscopic polarimeter, and more particularly to a spectropolarimeter using an optical fiber.

  Light has the property of “transverse wave”. On the premise of three axes (x, y, z) orthogonal to each other, assuming that the traveling direction of light is the z-axis direction, the vibration direction of light is a direction along the xy plane. There is a bias in the vibration direction of light in the xy plane. This polarization of light is called “polarized light”. In this specification, the method of polarization of light is hereinafter referred to as “polarization state”. This polarization state generally varies depending on the wavelength (color) of light.

  When light in a certain polarization state is incident on the measurement target and outgoing light such as transmitted light or reflected light is obtained, if the measurement target has anisotropy with respect to the light, the light is polarized between the incident light and the outgoing light. A change in state is observed. Obtaining information on the anisotropy of the measurement object from this change in polarization state is referred to as “polarization measurement”. Examples of such anisotropy include molecular structure anisotropy, the presence of stress (pressure), the presence of a local electric field and a magnetic field, and the like.

  The change of the polarization state between the incident light and the outgoing light is obtained for each wavelength, and obtaining information on the anisotropy of the measurement object from them is particularly referred to as “spectral polarization measurement”. According to this spectroscopic polarimetry, there is an advantage that much more information can be acquired compared to the case of measurement using a single wavelength (monochrome). In this spectroscopic polarimetry, an apparatus that measures a change in polarization state between incident light and outgoing light, that is, a spectroscopic polarimetry apparatus is a key device.

  As application fields of spectroscopic polarimetry, the spectroscopic ellipsometry field, the medical field, and the like are known. For example, in the spectroscopic ellipsometry field, the film thickness and complex refractive index of a thin film can be measured non-destructively and in a non-contact manner, so that it has been applied to optoelectronic equipment, semiconductor inspection, research, and the like. In the medical field, since some types of cells have polarization characteristics, attempts have been made to early detect glaucoma and cancer cells.

  In this spectroscopic ellipsometry, a measurement object is measured using a parameter used to quantitatively represent a polarization change caused by reflection or transmission of the measurement object, that is, a “spectral polarization parameter”. Ellipsometric parameters Ψ (λ), Δ (λ) and retardation δ (λ) of the birefringent medium are examples of spectral polarization parameters. Here, λ represents the wavelength of light.

  Details of the spectropolarimetry method using the ellipsometric parameters are described in, for example, Japanese Patent Application Laid-Open No. 2006-308550 (Patent Document 1).

  FIG. 9 shows a configuration in the case of obtaining a spectral polarization parameter of a minute region of a sample by a spectral polarization measurement apparatus using a channeled spectral polarization measurement method (channeled type). FIG. 9A shows the overall configuration of the spectroscopic polarimeter 100, and FIGS. 9B to 9E are diagrams showing the optical axes of the optical elements constituting the spectroscopic polarimeter 100. FIG. Referring to FIG. 9A, a spectroscopic polarization measuring device 100 includes a light projecting optical system 101, a light receiving optical system 102 that receives light emitted from the light projecting optical system 101 and reflected by the sample 30, and spectroscopic polarized light. The light receiving optical system 102 and the spectroscope 20 are connected by an optical fiber 18.

  Here, since the reflected light from the sample 30 is used, the spectropolarimeter is used as an ellipsometer.

  The light projecting optical system 101 includes a light source 11, a polarizer 13 for irradiating the sample 11 on the sample mounting table 31 with light from the light source 11, phase shifters R 1 and R 2, and a condenser lens 14. The light emitted from the light source 11 passes through the polarizer 12, the phase shifter R1, and the phase shifter R2 in order. The light transmitted through the two phase shifters R1 and R2 is irradiated onto a minute region on the sample 30 by the condenser lens. The condenser lens 14 operates as a dispersive light projecting unit in order to disperse the traveling direction of the light incident on the sample 30.

  The light receiving optical system 102 includes a collimator lens 15 that collects reflected light from the sample 11, an analyzer 16, and a condenser lens 17. The light reflected by the sample 30 is collimated again by the collimator lens 15, passes through the analyzer 16, enters the optical fiber 18 by the condenser lens 17, and then enters the spectroscope 20.

  As shown in FIGS. 9B to 9E, the fast axis directions of the phase shifter R1 and the phase shifter R2 are inclined by 45 °, and the direction of the transmission axis of the polarizer 13 is the phase shifter R2. It matches the direction of the fast axis. In the figure, the fast axis of the phase shifter is represented as “fast” and the slow axis is represented as “slow”. Also, θ is the azimuth angle of the transmission axis of the analyzer 16 with respect to the fast axis of the phase shifter R2.

  Here, the phase shifters R1 and R2 are elements having a property of changing a phase difference between linearly polarized light components orthogonal to each other before and after transmission through the element. This amount of change in phase difference is called retardation. The coordinate axes taken along the two linearly polarized directions are called main axes, and the axis along the linearly polarized light whose phase advances relatively fast is called the fast axis and the other axis is called the slow axis. The spectroscopic polarimeter 10 having such a configuration is referred to as a channeled spectropolarimeter.

In each of the two phase shifters R1 and R2, the phase difference generated between the orthogonal polarization components depends on the wavelength. For this reason, a channeled spectrum including three carrier components is obtained from the spectroscope 20 functioning as an optical spectrum analyzer. The amplitude and phase of each carrier component are modulated by the spectral polarization parameter of the sample. Therefore, if signal processing using Fourier transform is performed by a computer, ellipsometric parameters Ψ and Δ can be obtained as spectral polarization parameters of the sample. Details of the processing are the same as in Patent Document 1.
JP 2006-308550 A (paragraph number 0217 etc.)

  FIG. 10A shows the characteristics of ellipsometric parameters Ψ and Δ, which are spectral polarization parameters of the thin film sample measured by the spectroscopic polarimetry apparatus 100 shown in FIG. 9, and Ψ (λ) and Δ (λ ) Is a graph showing Ψ (λ). The horizontal axis indicates the wavelength, and the vertical axis indicates the spectral polarization parameter Ψ.

  The measured sample is a SiO2 natural oxide film on the Si substrate. The results of measuring the same point of the same sample four times while plotting various bending states such as the rotation radius and direction of rotation of the optical fiber 18 are plotted on the same graph. As shown in the figure, when the bending state of the optical fiber 18 is changed, it can be seen that the measured values of Ψ (λ) are scattered and shifted up and down. This shift of the measurement value becomes an error in obtaining the film thickness and film quality by fitting the measurement value and the theoretical value.

  FIG. 10B shows the results when the film thickness and the incident angle are obtained from the measured values of the bending state of each optical fiber 18 in FIG. Using the SiO2 film thickness and the incident angle as unknown variables, a combination of the film thickness and the incident angle that minimizes the square error between the measured value and the theoretical value was obtained.

  From this result, it can be seen that there is a maximum variation of 0.15 deg (degrees) between the maximum value and the minimum value of the incident angle, and in particular, a large error appears in the incident angle.

  This phenomenon is a common problem not only for the channeled spectroscopic polarimetry but also for the rotation analyzer method and the rotation phase shifter method.

  The present invention has been made in view of the above-described problems, and is a spectroscope that receives light from a sample incident via an optical fiber using a spectroscope and measures a spectral polarization parameter of the sample. An object of the polarization measurement apparatus is to eliminate the influence on the measurement value due to the change in the bending state of the optical fiber and stabilize the measurement.

The spectral polarization measurement apparatus according to the present invention projects light onto a sample by a light projecting unit, receives light transmitted or reflected by the sample, and measures the spectral polarization parameter of the sample using a spectroscope. The light projecting means includes a dispersion light projecting means for dispersing the traveling direction of the light incident on the sample. The light projecting means receives the transmitted light or reflected light from the sample, and sends the light received by the light receiving means to the spectrometer. The optical fiber includes an optical fiber, and an outlet opening limiting means that limits the exit opening size of the optical fiber so that the spectroscope receives only a part of the light emitted from the optical fiber, and the optical fiber receives the optical fiber. It is provided in the part which receives the light from the means, and includes a diffusing means for dispersing the light from the sample.

  Here, the dispersion projecting means has a function of condensing light on a sample, and generally a lens, a concave mirror or the like is used.

  The exit aperture limiting means is installed behind the optical fiber and limits the aperture (NA) of the light emitted from the optical fiber. A means for blocking light installed at a position several tens of times the slit width. The outer shape of the collimator lens or mirror installed behind the slit may be the aperture limiting means.

  Here, the diffusing unit has a function of transmitting light and dividing it into components in various directions. When the diffusing unit is flat and light is incident on the plane, the light component is perpendicular to the plane. It is preferable to have a function such that is strongest.

  Preferably, the light receiving means includes a light collecting means for collecting light from the sample, and the diffusing means is provided in a light collecting portion by the light collecting means.

  The spectroscopic polarimeter may be an ellipsometer, and the spectropolarimeter may be a channeled spectropolarimeter.

  The light receiving means may receive reflected light from the sample, or may receive transmitted light from the sample.

  In one embodiment of the present invention, the light projecting means, the light receiving means, and the diffusing means are integrally housed in the sensor head, and the diffusing plate means is provided at the light emitting end of the sensor head.

  The spectroscope includes a photoelectric conversion element for measuring light from the sample sent by the optical fiber, and a collimating lens for irradiating the photoelectric conversion element with light from the sample, and on the optical fiber side of the collimating lens An aperture for limiting incident light may be provided so that light from the sample is incident only on the central portion of the collimating lens.

  Because the diffuser that disperses the light from the sample is provided at the incident part of the optical fiber that receives the reflected light from the sample and sends it to the spectroscope, the light reflected or transmitted through the sample, regardless of the angle of incidence on the sample, The light is dispersed over a wide angular range and enters the optical fiber.

  As a result, in the spectroscopic polarimetry apparatus that sends light from the sample to the spectroscope via the optical fiber, the influence on the measurement value due to the change in the bending state of the optical fiber can be removed, and the measurement can be stabilized.

An embodiment of the present invention will be described below. First, the reason why the measured value varies depending on the bending state of the optical fiber, which is the subject of the present invention, will be described.
(1) The reason why the measured values differ depending on the bending state of the optical fiber The inventors have examined why such a phenomenon occurs when the above problems are found. The contents will be described below.

  FIG. 11 is a diagram showing each light component that is collected by the condenser lens and incident on the sample 30 at different angles. The light components A, B, and C in the figure indicate the respective light components incident on the sample at different incident angles of incident angles θ1, θ2, and θ3. Since the spectral polarization parameters Ψ and Δ to be obtained depend on the film structure of the sample 30 and the incident angles θ1, θ2, and θ3 with respect to the sample 30, the light components A, B, and C in FIG. Different information of Ψ and Δ is transmitted and incident on the optical fiber 18. The signal received by the spectroscope 20 is the sum of the components incident at these different angles, and the spectral polarization parameters Ψ and Δ obtained from the sum are different Ψ depending on the incident angles θ1, θ2, and θ3. The information of Δ is a value obtained by weighted averaging with the amount of received light of each incident angle component. Therefore, the amount of light received by each light component incident on the sample at a different angle changes, and the measured value changes if the weighting ratio changes.

  12A and 12B show the light components A and B shown in FIG. 11 incident on the incident end face 18a of the optical fiber 18 from different directions, and the exit end faces 18b of the respective optical fibers 18. FIG. It is a figure which shows the state of the light to radiate | emit, and FIG.12 (c) and (d) are schematic diagrams showing distribution of the incident angle into the optical fiber 18, and an outgoing angle.

  12A to 12D, the broken line represents the light component A, and the solid line represents the light component B. Referring to FIGS. 12A and 12B, the light of A and B is incident on the incident end face 18a of the optical fiber 18 at an incident angle α, and is refracted according to Snell's law when transmitted into the fiber and has an angle β To the inside of the fiber.

  FIG. 12C shows the light intensity distribution for each incident angle into the optical fiber 18 with the axis perpendicular to the incident end face 18a as 0 deg, and FIG. 12D shows the output end face 18b at the time of emission. The intensity distribution for each emission angle at is shown with the axis perpendicular to the emission end face 18b being 0 deg. Since the light A is repeatedly reflected inside the optical fiber 18 and travels while turning, the light A spreads in a hollow conical shape and is emitted. On the other hand, since the light B travels almost without being reflected inside the optical fiber 18, the emission angle is slightly spread around 0 deg.

  If the incident angle to the inside of the optical fiber 18 is different as in the light A and B in FIG. 12C, the traveling path at the time of propagation inside the fiber is different, so that the light A and B in FIG. It has different exit angle distribution. On the other hand, if the incident angle distribution into the optical fiber 18 is the same, the traveling path during propagation inside the fiber is also the same, and therefore the emission angle distribution is also equal.

  FIG. 13 is a diagram showing an internal configuration of the spectrometer 20. Referring to FIG. 13, the spectroscope 20 includes an incident slit 21, a collimating lens 23 for making the light that has passed through the incident slit 21 parallel light, a diffraction grating 24, and diffracted light diffracted by the diffraction grating 24. The condenser lens 25 for condensing the light on the CCD 26 and the CCD 26 are included. The entrance slit 21 is installed immediately after the exit end 18b of the optical fiber 18, and the light beam that has passed through the entrance slit 21 is collimated by the collimator lens 23 and then enters the diffraction grating 24. After being emitted at the diffraction angle, the light is condensed by the condenser lens 25 and is incident on the CCD 26 placed in the wavelength dispersion direction.

  Note that although a collimating lens and a condensing lens are used here, a mirror having the same effect may be used.

  The smaller the F value (the focal length of the collimating lens 23 / the diameter of the diffraction grating 24) indicating the brightness of the optical system, the brighter the spectroscope 20 is. However, since the aberration increases, the imaging performance on the CCD 26 is deteriorated and the resolution is also reduced. descend. For this reason, the structure is generally such that the aperture of the collimating lens 23 is reduced to limit the signal light, and not all of the light from the optical fiber 18 is used. That is, of the light emitted from the optical fiber 18 and transmitted through the entrance slit 21, only the light in a predetermined aperture range of the collimator lens 23 is converted into parallel light, and is split by the diffraction grating 24 and received by the CCD 26. An opening restricting means 22 for restricting the opening 23 is provided. Therefore, when light of a certain wavelength λ incident on the spectroscope 20 is considered, as shown in FIG. 13, only the portion indicated by the central portion 28a of the optical axis that is not blocked by the aperture limiting means 22 is formed on the collimating lens 23. Incident light is finally incident on the CCD 26, and light blocked by the aperture limiting means 22 indicated by the oblique line 28b is not incident.

  FIG. 14 is a diagram illustrating the relationship between the emission angle from the optical fiber 18 and the amount of light that passes through the collimator lens 23 and is collimated. As shown in FIG. 14A, the amount of light emitted from the optical fiber 18 changes through the collimating lens 23 depending on the emission angle from the optical fiber 18.

  FIG. 14B is a graph in which the ratio of the amount of light transmitted through the collimator lens 23 (lens passing rate) out of the light emitted from the optical fiber 18 is plotted for each emission angle from the optical fiber 18. The transmittance distribution of the collimating lens 23 is determined by the width of the entrance slit 21 and the position and size of the collimating lens 23. If the direction perpendicular to the emission end face 18b of the optical fiber 18 is 0 deg, FIG. It looks like the graph shown. This indicates that light whose emission angle from the emission end face 18b of the optical fiber 18 exceeds a certain range (light in a range indicated by 28b in FIG. 13) does not enter the collimating lens 23.

  FIG. 15 is a diagram showing a relationship between components of light A and B incident on the optical fiber 18 at different angles and signals finally received by the spectrometer 20. FIG. 15A is a diagram showing a light path from the optical fiber 18 to the CCD 26, FIG. 15B is a graph showing an emission angle for each light from the optical fiber 18, and FIG. ) Is a graph showing the transmittance of the collimating lens shown in FIG. 15, and FIG. 15D is a graph showing the intensity of light reaching the CCD 26.

  As shown in FIG. 12, when the incident angle to the incident end face 18a of the optical fiber 18 is different as in the light components A and B of FIG. The emission angle of is also different. Further, as shown in FIG. 14, only the light within the opening range of the collimator lens 23 (the range indicated by the dotted line in the figure) is received out of the light emitted from the optical fiber 18 at the emission angle of FIG. To the CCD 26. That is, the relationship between the exit angle from the optical fiber 18 and the amount of light reaching the CCD 26 is represented by the product of the exit angle distribution in FIG. 15B and the lens passage ratio distribution in FIG. The graph is as shown in d).

  That is, the received light amounts of the components A and B that are incident on the optical fiber 18 at different angles in FIG. 15A are obtained by integrating the solid line and the broken line in FIG. 15D with respect to the emission angle from the fiber. expressed.

  Accordingly, each component that is incident on the sample at different incident angles and propagates through different spectral polarization parameters is incident on the optical fiber 18 at different angles as shown in FIG. 15A, and is represented by an integral value in FIG. The measured light amount reaches the CCD 26, but the measured spectral polarization parameter is a value weighted by the light amount of each of these components.

  Based on the above, the influence of bending of the optical fiber 18 will be described. FIG. 16A is a diagram showing the incident intensities of light A and B incident on the optical fiber 18 at different angles for each incident angle, and FIGS. 16B to 16D project the optical fiber 18 upward. FIGS. 16E to 16G are diagrams showing incident and outgoing states of light A and B when bent (bent state X), an outgoing angle from the optical fiber 18, and received light intensity at the CCD. These are figures corresponding to Drawing 16 (b) to (d) at the time of entering optical fiber 18 into fiber of bending state Y in which a bending diameter and a bending direction differ from bending state X.

  As shown in FIG. 16A, the light B enters the optical fiber 18 at an incident angle of 0 deg, and the light A enters the optical fiber 18 at an incident angle β. As shown in FIG. 16B, when the optical fiber 18 is bent as in the state X, the light A repeatedly reflects inside the fiber and travels while turning, so that the light A spreads in a hollow conical shape and is emitted. Since the light B travels with little reflection inside the fiber, the emission angle has a distribution that is slightly spread around 0 deg.

  Here, as shown in FIG. 16 (e), when the optical fiber 18 is bent largely as in the state Y, the reflection condition of the light traveling inside is different from the state X in the bent portion of the fiber. , The lights A and B are emitted from the fiber with an angular distribution different from that in the state X. That is, when the bending state of the optical fiber 18 is changed from the state shown in FIG. 16B to FIG. 16E, the emission angle distribution of each light component is changed from the state shown in FIG. 16C to FIG. The amount of light finally received by the spectroscope 20 also changes from the state shown in FIG. 16D to FIG. 16G, respectively. In the example of FIG. 16, the received light amount of the light component A increases and the received light amount of the component B decreases as shown in FIGS. 16 (d) to 16 (g).

  FIG. 17 is a diagram illustrating a distribution of a signal received by the spectroscope 20 with respect to an incident angle with respect to a sample when the bending state of the optical fiber 18 is changed from X to Y in FIG. In the figure, the solid line is a diagram showing the amount of received light when the bending state of the optical fiber 18 is X, and the dotted line is a diagram showing the amount of received light when the bending state of the optical fiber 18 is Y. In the example shown here, when the bending state of the optical fiber 18 is changed from X to Y, the amount of light received by the component A incident on the sample at the incident angle θ1 increases, and the component B incident on the sample at the incident angle θ2 increases. It shows that the amount of received light decreases.

  Since the measured spectral polarization parameter is an average value obtained by weighting the information of the spectral polarization parameter at each incident angle with the received light intensity at each incident angle, the spectral state in which the bending state of the optical fiber 18 is measured with X and Y is measured. The polarization parameters are different. For this reason, as shown in FIG.10 (b), the measured value of an incident angle varies.

For reference, the received light amount of all light incident on the optical fiber 18 is indicated by a two-dot chain line in the drawing. As shown in the figure, such a problem does not occur when all the light incident on the optical fiber 18 is used.
(2) First Embodiment of the Invention The inventors have considered a spectroscopic polarimeter that is not affected by the bending state of the optical fiber 18 based on the above examination results. FIG. 1 is a diagram showing a spectroscopic polarimetry apparatus according to the first embodiment of the present invention. The spectroscopic polarimetry apparatus 10 according to this embodiment is a channeled ellipsometer. The spectroscopic polarimeter 10 basically has the same configuration as the spectropolarimeter 100 shown in FIG. 9, and emits from the light projecting optical system (light projecting means) 51 and the light projecting optical system 51. And a light receiving optical system (light receiving means) 52 for receiving the light reflected from the sample 30. The light projecting optical system 51 is the same as the light projecting optical system 101 shown in FIG. The light receiving optical system 52 is different from the light receiving optical system 102 shown in FIG. 9 in that a diffusing plate 19 is provided in a condensing portion of the condensing lens 17. The condensing lens operates as a condensing means.

  That is, the spectroscopic polarimetry apparatus 10 according to the embodiment of the present invention is provided with a diffusion plate 19 as a diffusing unit that diffuses light immediately before the optical fiber 18 that receives light from the light receiving optical system 52. Different from the conventional spectropolarimeter 100. The other points are the same as those of the conventional spectropolarimeter 100, and the light from the sample 11 is sent to the analyzer 16 through the collimator lens 15, and the light from the analyzer 16 is collected by the condenser lens 17. The light is incident on the spectroscope 20 through the diffusion plate 19 and the optical fiber 18.

  FIG. 2 is a view for explaining the role of the diffusion plate 19 shown in FIG. FIG. 2A is a diagram showing the incidence and emission states of the light components A and B at the connection portion between the diffusion plate 19 and the optical fiber 18 and the emission end portion 18b of the optical fiber 18. FIG. 2 (b), 2 (c), and 2 (d) respectively show the incident intensities of the light components A and B incident on the diffuser plate 19, and the light components A and B incident on the incident end 18a of the optical fiber 18. 4 is a graph showing the incident intensity of B and the outgoing intensity of light components A and B at the outgoing end portion 18b of the optical fiber 18. FIG. FIGS. 2B and 2D are views corresponding to FIGS. 12C and 12D, respectively, in which the diffusion plate 19 is not provided.

  Here, the diffusing plate 19 serving as a diffusing means has a function of transmitting light and dividing it into components in various directions, and the light incident on the diffusing plate 19 has the light component perpendicular to the surface being the strongest. Diffuse light. The diffuser plate 19 is, for example, like ground glass.

  Therefore, the diffusing means is not limited to the diffusing plate 19 described here, but includes a translucent film or sheet having the above function.

  As shown in FIG. 2A, when light A and B incident from different angles toward the incident end face of the optical fiber 18 pass through the diffusion plate 19 installed in front of the incident end 18a, As shown in c), the light is dispersed almost uniformly over a wide angle range and enters the optical fiber 18. As shown in FIG. 2B, the incident intensity of the light A and the light B is the same. In FIGS. 2C and 2D, the incident intensities of the light A and B overlap.

  As described with reference to FIG. 12, if the incident angle distribution into the optical fiber 18 is the same, the emission angle distribution from the optical fiber 18 is also equal. In this case, due to the effect of the diffusing plate 19, the incident angle distributions of the light A and B into the optical fiber 18 are substantially equal. The amount of light is about the same.

  Furthermore, since the change in the emission angle distribution due to the change in the bending state of the optical fiber 18 also depends on the incident angle distribution into the optical fiber 18, the incident angle distribution into the optical fiber 18 like the light A and B Are the same, the emission angle distributions of the light A and B remain the same regardless of the bending state of the optical fiber 18.

  Next, the effect of the diffusion plate 19 will be described. FIG. 3 is a diagram for explaining the effect of the diffusion plate 19 in a state where the optical fiber 18 is bent when the diffusion plate 19 is not installed and when it is installed. 3 (a) and 3 (c) are diagrams showing the direction of incidence on the diffusion plate 19 or the optical fiber 18 when the diffusion plate 19 is not installed and when it is installed. d) is a diagram showing the emission intensity of light A and B at the emission end portion 18b of the optical fiber 18 in a state in which the optical fiber 18 is bent for each angle of incidence on the sample. FIG. 3B corresponds to FIG.

  As shown in FIG. 3B, the light amounts of the lights A and B received by the spectroscope 20 change depending on the bending state of the optical fiber 18. That is, the weighting ratio of each component of the light A and B in the total amount of light received by the spectroscope 20 changes. Since different spectral polarization information is propagated from A and B, the measurement value also changes when the light quantity of A and B changes and the weighting ratio changes.

  On the other hand, when the diffusing plate 19 is installed, the incident angle distributions into the optical fibers 18 of A and B are substantially equal as shown in FIG. The light receiving amounts at A and B are substantially the same for A and B, and even if the bending state of the optical fiber 18 changes, the weighting ratio of the components A and B does not change. Therefore, the measured value is stable regardless of the change in the bending state of the optical fiber 18. In FIGS. 3B and 3D, the intensity distribution when the entire light incident on the optical fiber 18 is used is also indicated by a two-dot chain line. The intensity shown in FIG. 3D is lower than the intensity shown in FIG. 3B because of the transmittance of the diffusion plate 19.

(3) Verification of effect Next, verification of the effect in this embodiment will be described. FIG. 4 is a diagram showing a result of verifying the effect. FIG. 4A is a diagram showing the spectral polarization parameter Ψ (λ) measured while variously changing the bending state of the optical fiber 18 in the configuration of FIG. 1 in which the diffusion plate 19 is installed in front of the optical fiber 18. This corresponds to the conventional FIG. The horizontal axis indicates the wavelength, and the vertical axis indicates the spectral polarization parameter Ψ.

  As shown in FIG. 4A, the graphs showing all the measured values almost overlap, and it can be seen that the measured values are stable due to the effect of the diffusion plate 19 regardless of the bending state of the optical fiber 18.

  FIG. 4B is a diagram showing the film thickness and the incident angle calculated by fitting Ψ (λ) and Δ (λ) with the theoretical values in the bent state of the optical fiber 18 shown in FIG. 4A. Yes, corresponding to the conventional FIG. Referring to FIG. 4B, it can be seen that both the film thickness value and the incident angle are stable, and in particular, the maximum error of the incident angle is improved to 0.01 deg.

  In addition, it is desirable to use the diffusing plate 19 having the highest possible transmittance so that the amount of light is not impaired by the installation of the diffusing plate 19. If the diffusion angle by the diffusing plate 19 (the spread angle of the light after passing through the diffusing means) is too small, the incident angle distribution into the optical fiber 18 differs depending on the incident angle on the incident end face of the optical fiber 18. Therefore, the measurement stabilization effect is weakened. On the other hand, if the diffusion angle is too large, a diffusion component exceeding the numerical aperture (NA) of the optical fiber 18 is lost, so that a sufficient amount of light cannot be secured. For this reason, it is desirable that the diffusion angle of the diffusion plate 19 is approximately the same as the NA of the optical fiber 18.

Even when the diffusion plate 19 and the incident end face 18 a of the optical fiber 18 are separated, only a part of the diffused light is incident on the optical fiber 18, so that the amount of light cannot be secured. For this reason, it is desirable to install the diffusion plate 19 as close as possible to the optical fiber 18.
(4) Examples Hereinafter, preferred examples of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram showing the main part of the spectropolarimeter 50 in this embodiment. Referring to FIG. 5, the spectroscopic polarimetry apparatus 50 includes a light projecting optical system 51 and a light receiving optical system 52 arranged with the sample 30 interposed therebetween, as shown in FIG. 1.

  The light projecting optical system 51 includes a power source (not shown), a light source 11 that is supplied with power from the power source and is turned on, a pinhole plate 11a disposed on the front side in the emission direction of the light source 11, and a pinhole passing through the pinhole plate 11a. A collimating lens 12 for collimating the light; a shutter 13a on the front side of the collimating lens 12 for opening / closing the passing light; a polarizer 13 on which the passing light of the shutter 13a is incident; and the transmitted light of the polarizer 13 A first phase shifter R1 and a second phase shifter R2 that are sequentially transmitted; and a condenser lens 14 for condensing the light that has passed through the second phase shifter R2 in a minute region on the sample 30; Have

  The light after passing through the condenser lens 14 is emitted from the light projecting optical system 51 and emitted toward the measurement target region, that is, the region where the sample 30 is scheduled to be installed. When the sample 30 is installed in the measurement target region, the reflected light is incident on the light receiving optical system 52.

  On the incident optical path in the light receiving optical system 52, a collimator lens 15, an analyzer 16, a condenser lens 17, a diffusion plate 19, an optical fiber 18, and a spectroscope 20 are installed in this order. Here, the relative angle between the direction of the fast axis of the second phase shifter R2 and the direction of the transmission axis of the analyzer 16 is set to be a known angle.

  In the spectroscope 20, an entrance slit 21, an aperture limiting unit 22, a collimator lens 23, a diffraction grating 24 that splits incident light, and a condenser lens 25 that collects light dispersed by the diffraction grating 24. And a CCD 26 on which the condensed light is incident, and an A / D converter 27 for converting the light reception output of the CCD 26 into a digital signal. A digital light reception output signal obtained from the A / D converter 27 is taken out from the spectroscope 20 and processed by a computer 40 such as a personal computer (PC).

  The computer 40 includes an arithmetic processing unit 41 composed of a microprocessor, a memory unit 42 composed of ROM, RAM, HDD, etc., and a measurement result composed of a display, a printer, various data output devices, a communication device, etc. And an output unit 43.

  Next, the sensor head 55 of the spectroscopic polarimetry apparatus 50 surrounded by a dotted line in FIG. 5 will be described. FIG. 6 is a diagram showing the sensor head 55. Referring to FIG. 6, the sensor head 55 includes a light projecting unit 55 a configured by a main part of the light projecting optical system 51 that emits light, a light receiving unit 55 b that receives light reflected from the sample 30, and these light projects. A housing 56 that protects the portion 55a and the light receiving portion 55b. Here, the light receiving portion 55 b is the same as the light receiving optical system 52.

  The light projecting unit 55a parallels the light projecting optical fiber cable 57 that allows light emitted from a light source (not shown) to pass through, the cable head 58 that allows the transmitted light from the light projecting optical fiber cable 57 to pass through, and the light passing through the cable head 58. The collimating lens 12 to be converted into light, the polarizer 13 on the front side of the collimating lens 12 that transmits the incident light, the first phase shifter R1 and the second phase shifter that sequentially transmit the light emitted from the polarizer 13. The phaser R2 and an optical system holding member and mounting member (shown by hatching in the figure) for mounting these optical systems on the housing 56 are included. The solid line is the light projection axis of light passing through the light projecting unit.

  The light receiving unit 55 b includes an analyzer 16 that transmits the light reflected by the sample 30, a condensing lens 17 that condenses the transmitted light from the analyzer 16, and a cable head 59 that passes the light that has passed through the condensing lens 17. And an optical fiber 18 connected to a spectroscope (not shown), an attachment member for mounting these optical systems on the housing 56, and an optical system holding member (indicated by hatching in the figure). The solid line is the light receiving axis of light reflected or transmitted by the sample.

  Next, a measurement procedure using the spectroscopic polarimeter 50 will be described. FIG. 7 is a flowchart showing a processing procedure when the sample 30 is measured using the spectroscopic polarimetry apparatus 50.

  Referring to FIG. 7, as a measurement procedure, first, in step 11 (abbreviated as S11 in the figure, the same applies hereinafter), light is incident on the spectropolarimeter 50.

  Next, in step 12, after the sample 30 is reflected or transmitted by the spectroscope 20, the spectral light amount of the transmitted light transmitted through the analyzer 16 is measured. At this time, a shutter (shown by 13a in FIG. 5) can be used to reduce the influence of unnecessary light, for example, stray light. Specifically, the spectrum of the unnecessary light is canceled by taking the difference between the spectra measured with the shutter 13a opened and closed.

  Next, in step 13, the spectral light amount of the transmitted light is transferred from the spectroscope 20 to the computer 40 and used for processing in the arithmetic processing unit 41. In step 14, in the computer 40, the arithmetic processing unit 41 outputs the spectral polarization parameter of the sample. Note that the details of the processing performed by the arithmetic processing unit 41 can be applied to the same technique as that of Patent Document 1, and thus the description thereof is omitted here.

  Here, examples of the measurement result output unit 43 include a memory, a hard disk, and other processing units (film thickness, complex refractive index calculation unit, etc.).

  Next, another embodiment of the present invention will be described. In the above-described embodiment, an ellipsometer using light incident on the sample and using the reflected light has been described. In this embodiment, measurement is performed through the sample.

  FIG. 8 is a diagram showing the overall configuration of the transmission-type spectroscopic polarimetry apparatus 60, and corresponds to the part before the spectroscope 20 in the previous embodiment shown in FIG. Referring to FIG. 8, the spectropolarimeter 60 includes a light projecting optical system 61 and a light receiving optical system 62. The only difference from the ellipsometer shown in FIG. 5 is that the light is transmitted through the sample 30, and the description of the other components is omitted.

  The spectral polarization parameter of the sample obtained in this embodiment includes the azimuth angle and retardation of the birefringent medium. In this case as well, as in the case of the reflective arrangement, the signal obtained is the sum of the light components that have entered and passed through the sample at different angles of incidence. Therefore, stable measurement can be realized.

  In the above embodiment, a collimating lens is used as an optical element for condensing light such as condensing light to an incident end to an optical fiber provided in a light receiving optical system that receives reflected light from a sample. Although the example to perform was demonstrated, you may condense not only using this but using a mirror like a concave mirror.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

It is a figure which shows the principal part of the spectroscopic polarimeter which concerns on one embodiment of this invention. It is a figure which shows the incident direction of the light in the connection part of a diffuser plate and an optical fiber. It is a figure for demonstrating the effect of the diffusion plate in one embodiment of this invention. It is a figure for demonstrating the effect of this invention. It is a figure which shows the whole structure of the spectroscopic polarimeter which concerns on one embodiment of this invention. It is a figure which shows a sensor head. It is a figure which shows the measurement procedure of a spectroscopic polarimeter. It is a figure which shows the structure of the principal part of 2nd Example. It is a figure which shows the principal part of the conventional spectroscopic polarimeter. It is a figure for demonstrating the problem of the conventional spectroscopic polarimeter. It is a figure which shows the incident light and reflected light to the conventional sample. It is a figure for demonstrating the problem in the conventional measurement. It is a figure which shows the optical system in the case of transmitting the emitted light from the conventional optical fiber to CCD. It is a figure for demonstrating the lens transmittance | permeability in case the emitted light from the conventional optical fiber permeate | transmits a condensing lens. It is a figure which shows the relationship between the component of the light A and B which injected into the optical fiber from a different angle, and the signal finally received by the spectrometer. It is a figure for demonstrating the influence of the bending of an optical fiber. It is a figure which shows distribution with respect to the incident angle with respect to the sample of the signal received with a spectrometer when the bending state of an optical fiber is changed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Spectral polarization measuring device, 11 Light source, 12 Collimating lens, 13 Polarizer, 15 Collimating lens, 16 Analyzer, 17 Condensing lens, 18 Optical fiber, 19 Diffuser, 20 Spectroscope, 50 Spectral polarization measuring system, 51 Throw Optical optical system, 52 Light receiving optical system, 55 Sensor head.

Claims (8)

A spectropolarimetric measuring device that projects light onto a sample by a light projecting means, receives light transmitted or reflected by the sample, and measures a spectropolarization parameter of the sample using a spectroscope,
The light projecting means includes distributed light projecting means for dispersing the traveling direction of light incident on the sample,
A light receiving means for receiving transmitted light or reflected light from the sample;
An optical fiber for sending the light received by the light receiving means to the spectrometer;
An outlet opening limiting means provided at an outlet of the optical fiber, and limiting an outlet opening size of the optical fiber so that the spectroscope receives only a part of the light emitted from the optical fiber;
The spectroscopic polarimetry apparatus, characterized in that the optical fiber is provided in a portion for receiving light from the light receiving means, and includes a diffusing means for dispersing light from the sample. The spectroscopic polarimetry apparatus according to claim 1, wherein the light receiving unit includes a light collecting unit that collects light from a sample, and the diffusion unit is provided in a light collecting unit of the light collecting unit. The spectroscopic polarimeter according to claim 1 or 2, wherein the spectropolarimeter is an ellipsometer. The spectral polarization measurement apparatus according to claim 1, wherein the spectral polarization measurement apparatus is a channeled spectral polarization measurement apparatus. The spectroscopic polarimetry apparatus according to claim 4, wherein the light receiving means receives reflected light from a sample. The spectroscopic polarimetry apparatus according to claim 4, wherein the light receiving means receives transmitted light from a sample. The light projecting means, the light receiving means, and the diffusing means are integrally housed in a sensor head, and the diffusing plate means is provided at a light emitting end of the sensor head. The spectroscopic polarimetry apparatus described in 1. The spectroscope includes a photoelectric conversion element for measuring light from the sample sent by the optical fiber, and a collimator lens for irradiating the photoelectric conversion element with light from the sample,
8. The aperture according to claim 1, wherein an aperture for limiting incident light is provided on the optical fiber side of the collimating lens so that light from a sample is incident only on a central portion of the collimating lens. 9. Spectroscopic polarimeter.

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