JP2020122680A - Optical measuring system and optical measurement method - Google Patents

Abstract

To provide a configuration capable of more accurately measuring optical characteristics of a sample for which the conventional optical measuring device can be degraded in measurement accuracy.SOLUTION: An optical measuring system includes a light source generating a measuring beam to irradiate a sample, a spectroscopic detector receiving a reflected beam or a transmitted beam generated on the sample by the measuring beam, and a processor for inputting detection result of the spectroscopic detector. The processor is configured to perform the processing of: calculating a first spectrum on the basis of the detection result of the spectroscopic detector; identifying a section in the first spectrum, in which a change in amplitude with respect to the wavelength satisfies a prescribed condition; and using a second spectrum obtained by removing information on the identified section from the first spectrum to calculate optical characteristics of the sample.SELECTED DRAWING: Figure 8

Description

The present invention relates to an optical measurement system and an optical measurement method capable of measuring optical characteristics such as film thickness of a sample.

BACKGROUND ART Conventionally, there is known a technique of measuring optical characteristics such as film thickness of a sample by observing light that appears due to optical interference. For example, Japanese Unexamined Patent Application Publication No. 2009-0924454 (Patent Document 1) discloses a multilayer film analyzer that can measure the film thickness of a multilayer film sample having wavelength dependence with higher accuracy. In addition, Japanese Unexamined Patent Application Publication No. 2018-205132 (Patent Document 2) discloses an optical measuring device and the like that can measure the in-plane distribution of the film thickness of a sample at high speed and with high accuracy.

JP, 2009-092445, A JP, 2018-205132, A

When the film thickness of a sample such as a liquid crystal material or a polymer material (for example, PET film) is measured by using the optical measuring device as described above, the anisotropy of the material reduces the measurement accuracy. There is a problem to do. Further, even when a sample structurally having a plurality of thicknesses is measured, there is a problem that the measurement accuracy is lowered.

An object of the present invention is to provide a configuration capable of measuring optical characteristics with higher accuracy even for a sample in which the measurement accuracy may be lowered in the conventional optical measuring device.

An optical measurement system according to an aspect of the present invention includes a light source that generates measurement light for irradiating a sample, a spectroscopic detector that receives reflected light or transmitted light that is generated in the sample by the measurement light, and a detection result of the spectroscopic detector. Is input to the processing device. The processing device calculates a first spectrum based on a detection result of the spectroscopic detector, identifies a section in the first spectrum in which a change in amplitude with respect to wavelength satisfies a predetermined condition, and The process of calculating the optical characteristics of the sample by using the second spectrum obtained by removing the information of the specified section from the spectrum of is configured to be executable.

The specifying process includes a process of sequentially setting an evaluation window having a predetermined wavelength width for the first spectrum, and each evaluation based on a change in the amplitude of the first spectrum included in each evaluation window. It may include a process of determining whether or not the section corresponding to the window satisfies a predetermined condition.

The process of determining whether or not the section corresponding to each evaluation window satisfies the predetermined condition may include processing of calculating the degree of amplitude variation in the section corresponding to each evaluation window of the first spectrum. ..

When the degree of amplitude variation in the section corresponding to each evaluation window of the first spectrum is lower than the predetermined threshold value, it may be determined that the section corresponding to the evaluation window satisfies the predetermined condition.

The wavelength width of the evaluation window may be predetermined for each type of sample.
The process of calculating the optical characteristics of the sample may include a process of calculating the film thickness based on the peak appearing in the result of Fourier transforming the second spectrum.

The process of calculating the first spectrum may include a process of calculating the reflectance spectrum of the sample based on the detection result of the spectroscopic detector as the first spectrum.

The process of calculating the first spectrum removes information derived from the non-measurement target layer included in the sample from the reflectance spectrum of the sample calculated based on the detection result of the spectroscopic detector as the first spectrum. The process of calculating the reflectance spectrum may be included.

The process of calculating the first spectrum is the process of Fourier transforming the reflectance spectrum of the sample to calculate the third spectrum, and the peak of the third spectrum that is derived from the layer outside the measurement target included in the sample. May be further included, and processing of removing the information of the identified peak and the vicinity of the peak from the third spectrum to calculate the fourth spectrum may be further included.

The process of calculating the first spectrum may further include a process of inverse Fourier transforming the fourth spectrum to calculate the first spectrum.

The optical measurement method according to an aspect of the present invention, based on the detection result obtained by irradiating the sample with measurement light from the light source and receiving reflected light or transmitted light generated in the sample by the measurement light with a spectroscopic detector, A step of calculating the first spectrum, a step of specifying a section in the first spectrum in which a change in the amplitude with respect to the wavelength satisfies a predetermined condition, and a second step of removing information of the specified section from the first spectrum. Calculating the optical properties of the sample using the spectrum of.

According to an aspect of the present invention, it is possible to provide a configuration in which optical characteristics can be measured with higher accuracy even for a sample in which the measurement accuracy of the conventional optical measuring device may be lowered.

It is a schematic diagram which shows the structural example of the optical measurement system according to this Embodiment. It is a schematic diagram which shows the cross-section example of a spectrum detector contained in the optical measurement system according to this Embodiment. It is a schematic diagram which shows the structural example of the processing apparatus contained in the optical measurement system according to this Embodiment. It is a figure for demonstrating the principle of the optical measuring method using the optical interference method. It is a figure which shows an example of the measurement result by the optical measuring method using the optical interference method. It is a figure for demonstrating the birefringence which occurs in the sample which has anisotropy. FIG. 6 is a diagram for explaining a method of removing the influence of a low frequency component in the optical measurement method according to the present embodiment. 6 is a flowchart showing a procedure of the optical measuring method according to the first embodiment. FIG. 9 is a diagram for explaining a process of identifying a bottom section in the optical measurement method according to the first embodiment. 9 is a flowchart showing a more detailed procedure of step S4 of the optical measuring method according to the first embodiment shown in FIG. 8. It is a figure which shows the example of a measurement by the optical measuring method according to 1st Embodiment. 9 is a flowchart showing a procedure of the optical measuring method according to the second embodiment. It is a schematic diagram which shows the constructional example of the sample used as the measurement object. It is a figure which shows the example of a measurement by the optical measuring method according to 2nd Embodiment.

Embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

<A. Optical measurement system>
First, a configuration example of optical measurement system 1 according to the present embodiment will be described.

FIG. 1 is a schematic diagram showing a configuration example of an optical measurement system 1 according to the present embodiment. The optical measurement system 1 includes a light source 10 that generates measurement light for irradiating the sample 2, and a spectroscopic detector 20 that receives observation light (reflected light or transmitted light as described later) generated in the sample 2 by the measurement light. , And the processing device 100 to which the detection result of the spectral detector 20 is input. The processing device 100 calculates the optical characteristic (typically, film thickness) of the sample 2 based on the detection result of the spectroscopic detector 20. The light source 10 and the spectroscopic detector 20 are optically connected via a Y-shaped fiber 4 having an irradiation port toward the sample 2.

In the optical measurement system 1, by irradiating the sample 2 with the measurement light from the light source 10 and observing the light that appears due to the optical interference generated inside the sample 2, the film thickness of one or a plurality of films included in the sample 2 can be measured. To measure.

FIG. 1 shows, as a typical example, a reflection optical system in which the sample 2 is irradiated with the measurement light and the reflected light generated in the sample 2 is observed. However, the measurement light is irradiated to the sample 2 and transmitted through the sample 2. A transmission optical system for observing light may be adopted.

The light source 10 generates measurement light having a predetermined wavelength range. The wavelength range of the measurement light is determined according to the range of wavelength information to be measured from the sample 2. As the light source 10, for example, a halogen lamp or a white LED is used.

FIG. 2 is a schematic diagram showing an example of a sectional structure of spectroscopic detector 20 included in optical measurement system 1 according to the present embodiment. Referring to FIG. 2, the spectroscopic detector 20 includes a diffraction grating 22 that diffracts light incident through the Y-shaped fiber 4, a light receiving section 24 that is arranged in association with the diffraction grating 22, and a light receiving section 24. An interface circuit 26 that is electrically connected and outputs the detection result to the processing device 100. The light receiving unit 24 is composed of a line sensor or a two-dimensional sensor, and can output the intensity of each frequency component as a detection result.

FIG. 3 is a schematic diagram showing a configuration example of processing device 100 included in optical measurement system 1 according to the present embodiment. With reference to FIG. 3, the processing device 100 includes a processor 102, a main memory 104, an input unit 106, a display unit 108, a storage 110, a communication interface 120, a network interface 122, and a media drive 124. Including.

The processor 102 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and reads one or a plurality of programs stored in the storage 110 into the main memory 104 and executes the programs. To do. The main memory 104 is a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory), and functions as a working memory for the processor 102 to execute a program.

The input unit 106 includes a keyboard, a mouse, and the like, and receives an operation from the user. The display unit 108 outputs the execution result of the program by the processor 102 and the like to the user.

The storage 110 is composed of a non-volatile memory such as a hard disk and a flash memory, and stores various programs and data. More specifically, the storage 110 holds an operating system 112 (OS: Operating System), a measurement program 114, a detection result 116, and a measurement result 118.

The operating system 112 provides an environment in which the processor 102 executes programs. The measurement program 114 is executed by the processor 102 to realize the optical measurement method and the like according to the present embodiment. The detection result 116 includes data output from the spectral detector 20. The measurement result 118 includes calculated values of optical characteristics such as film thickness obtained by executing the measurement program 114.

The communication interface 120 mediates data transmission between the processing device 100 and the spectroscopic detector 20. The network interface 122 mediates data transmission between the processing device 100 and an external server device.

The media drive 124 reads out necessary data from a recording medium 126 (for example, an optical disk or the like) storing a program executed by the processor 102 and stores the data in the storage 110. The measurement program 114 or the like executed in the processing device 100 may be installed via the recording medium 126 or the like, or may be downloaded from the server device via the network interface 122 or the like.

The measurement program 114 may be a program module that is provided as a part of the operating system 112 and calls a necessary module in a predetermined array at a predetermined timing to execute a process. In such a case, the measurement program 114 that does not include the module is also included in the technical scope of the present invention. The measurement program 114 may be provided by being incorporated in a part of another program.

Note that all or some of the functions provided by the processor 102 of the processing device 100 executing the measurement program 114 may be realized by dedicated hardware.

<B. Problem and Solution>
Next, a problem that is newly found by the inventors of the present application in the optical measurement method using the optical interferometry will be described.

FIG. 4 is a diagram for explaining the principle of the optical measurement method using the optical interference method. Referring to FIG. 4, as the simplest example, assume Sample 2 (film thickness d ₁₎ consisting of a medium 1 (refractive index n _1). The upper side of the sheet of Sample 2 is in contact with medium 0 (refractive index n ₀ ), and the lower side of the sheet of Sample 2 is in contact with medium 2 (refractive index n ₂ ).

In this state, the sample 2 is irradiated with the measurement light from the light source arranged on the medium 0 side. Part of the measurement light is reflected by the incident surface of the sample 2 (interface between the medium 0 and the medium 1) (reflectance R1). Another part of the measurement light enters the sample 2, propagates in the sample 2, is reflected by the opposite surface (interface between the medium 1 and the medium 2), and further propagates in the sample 2 in the opposite direction. Then, the light is transmitted through the incident surface (reflectance R2). Further, although not shown, multiple reflection occurs in the sample 2, and as a result, reflected light corresponding to the light emitted from the sample 2 is observed.

With respect to such measurement light, the reflectance R012 of the surface of the sample 2 and the entire reflected light generated in the sample 2 is the sum of the reflectances (R1+R2+R3+... ). As shown in the following equation (1-1), the reflectance R012 is the square value of the complex reflectance r ₀₁₂ . The complex reflectance r ₀₁₂ is calculated according to the following equation (1-2). The phase β in the equation (1-2) is calculated according to the following equation (1-3).

It should be noted that the above equations (1-1) to (1-3) show the reflectance with respect to the measurement light having a specific wavelength λ, but in the optical measurement system 1 shown in FIG. Since the reflected light (or the transmitted light) is observed for each wavelength by using the measurement light that it has and the spectral detector 20, the reflectance for each wavelength of the sample 2 (hereinafter, also referred to as “reflectance spectrum”). Can be measured. The reflectance spectrum corresponds to the spectral reflectance.

The film thickness of the target sample 2 or the film thickness of each layer included in the sample 2 can be calculated based on the peak appearing in the power spectrum obtained by Fourier-transforming the measured reflectance spectrum. Note that the film thickness of the target sample 2 or the film thickness of each layer included in the sample 2 can be calculated in the same manner when the transmittance spectrum calculated from the transmitted light is used.

FIG. 5 is a diagram showing an example of a measurement result by an optical measurement method using the optical interference method. FIG. 5A shows an example of a reflectance spectrum measured from a sample having anisotropy, and FIG. 5B shows a power spectrum calculated from the reflectance spectrum of FIG. 5A. An example is shown. The horizontal axis of FIG. 5B represents a value obtained by multiplying the film thickness d by the refractive index n(λ) of each wavelength (hereinafter, also referred to as “optical film thickness” or “nd”).

As shown in FIG. 5A, the reflectance spectrum shows a characteristic that the magnitude of the amplitude periodically changes with respect to the wavelength. In the power spectrum shown in FIG. 5B, three peaks P1, P2 and P3 appear. However, the adjacent peaks P1 and P2 correspond to the same layer, and should essentially appear at the same position. That is, a true peak should appear between the peak P1 and the peak P2. When the peak P1 and the peak P2 are erroneously determined to exist, the respective film thicknesses may be output as the measurement result.

One of the reasons why two peaks occur at such close positions is that the sample has anisotropy.

FIG. 6 is a diagram for explaining birefringence that occurs in a sample having anisotropy. Anisotropy means that the appearance (optical characteristics) varies depending on the observation direction. 6, in the sample having anisotropy, the refractive indices n _x for a certain axial direction (x-axis), a refractive index n _y in the axial direction (y-axis) perpendicular to the axial direction Do not necessarily match (ie, n _x ≠n _y ). Two peaks close as shown in FIG. 5 (B), slight differences _{Δn (= | n x -n y} |) between the axes of such a refractive index can be considered due to the influence.

In addition to the anisotropy, a plurality of adjacent peaks may appear depending on the structure of the sample. Further, when the sample having the multilayer structure has anisotropy, the influence of birefringence occurs in each layer.

As described above, when an anisotropic sample or a sample having a specific structure is measured by the optical interference method, the error included in the measurement result may be large. Further, for samples having a multi-layer structure, such increased error will occur in each layer.

Here, if birefringence (difference in refractive index) due to anisotropy is the only cause, it may be possible to solve it by observing only light in a specific axial direction by using a polarizing plate or the like. .. However, in reality, the components contained in the observed light change depending on the optical positional relationship (angle) between the sample and the polarizing plate, so that the strict adjustment of the optical positional relationship can be performed during measurement. Will be required. Therefore, it is difficult to practically apply it to an application in which a plurality of samples are sequentially measured.

The means for solving the problems that occur in the optical measurement method using the optical interference method as described above will be outlined below.

A beat is generated in the reflectance spectrum of light observed from the sample having anisotropy as described above. Generally speaking, such a “beat” is known as a phenomenon in which the amplitude of a composite wave in which waves having slightly different frequencies are superposed is periodically repeated. For example, regarding a reflectance spectrum measured from a sample having birefringences n _x and n _y , it can be generalized by using a relational expression such as the following expression (2).

(2) As shown in equation, the reflectance spectrum, frequency components that depend on the difference in birefringence index (n x _{-n y)} (hereinafter, also referred to as "low frequency component".) And the birefringence index A frequency component depending on the sum (n _x +n _y ) (hereinafter, also referred to as “high frequency component”) is included. Here, the low frequency component means a component having a relatively long period of amplitude change (wavelength length), and the high frequency component means a component having a relatively short period of amplitude change (wavelength length). To do.

Among these frequency components, the actual measured corresponds to the average value of the film thickness, a high-frequency component depending on the sum of the birefringence _(n x ₊ n _y), the difference in birefringence (n _x -n _The low frequency component depending on _{y 2} ) is pseudo information (that is, error factor) that does not actually exist.

For example, in the case of a wave such as a sound wave whose amplitude changes with time, the low frequency component can be measured by observing for a sufficiently long time. However, since the light wave cannot be observed in the time domain, the observable wavelength range is fixedly determined depending on the performance of the light source and the spectral detector. Moreover, since the wavelength range and the wavelength resolution are determined according to the film thickness (high frequency component) to be measured, it is not easy to observe the wave of the low frequency component in the same measurement.

Therefore, when at least a part of the low frequency component is included in the observable wavelength range, the measurement error may increase. That is, since the observed light is a combination of the low frequency component and the high frequency component, it also affects the high frequency component (that is, information indicating the film thickness) that is an actual measurement target. The frequency of the low-frequency component (cycle of amplitude change) depends on the sample and cannot be known in advance.

FIG. 7 is a diagram for explaining a method of removing the influence of the low frequency component in the optical measuring method according to the present embodiment. 7A shows an example of a low frequency component of the reflectance spectrum, FIG. 7B shows an example of a high frequency component of the reflectance spectrum, and FIG. 7C shows a low frequency component. An example of the reflectance spectrum obtained by multiplying the high frequency component and For convenience of explanation, a simplified waveform is shown in FIG. 7.

Focusing on the bottom section (section) where the amplitude is small among the low-frequency components of the reflectance spectrum shown in FIG. 7A, the amplitude of the high-frequency component (FIG. 7B) of the corresponding reflectance spectrum is Despite the existence, it can be seen that in the reflectance spectrum of the synthetic wave shown in FIG. 7C, the amplitude is small and the information indicating the film thickness is lost. Loss of such information indicating the film thickness may cause a measurement error.

The inventors of the present application have paid attention to the fact that the bottom section (section) occurring in the low frequency component of the reflectance spectrum as described above is a factor of the measurement error, and the bottom of the low frequency component of the measured reflectance spectrum The optical characteristics are calculated after specifying the section and removing information in at least a part of the specified bottom section and/or information in the vicinity of the bottom section. By removing at least a part of such a bottom section and information in the vicinity of the bottom section, a decrease in measurement accuracy is prevented.

Hereinafter, examples of embodying the technical idea found by the inventors of the present application will be described.
<C. First Embodiment>
As the first embodiment, a process when the number of frequency components (peaks) included in the reflectance spectrum measured from the sample is relatively small will be described. The optical measurement method according to the first embodiment is typically applicable to the case of measuring the film thickness of a sample of a single layer film.

(C1: processing procedure)
First, the processing procedure of the optical measurement method according to the first embodiment will be described.

FIG. 8 is a flowchart showing a procedure of the optical measuring method according to the first embodiment. The main steps shown in FIG. 8 are typically realized by the processor 102 of the processing device 100 loading a measurement program 114 (see FIG. 3) into the main memory 104 and executing it.

Referring to FIG. 8, first, optical measurement system 1 is prepared (step S1). In step S1, alignment of the irradiation opening of the Y-shaped fiber 4 included in the optical measurement system 1 and calibration processing in the spectroscopic detector 20 are executed. Then, the sample 2 to be measured is placed at a predetermined position of the optical measurement system 1 (step S2).

Subsequently, a process of irradiating the sample 2 with the measurement light from the light source 10 and calculating a spectrum based on the detection result obtained by receiving the reflected light or the transmitted light generated in the sample 2 by the measurement light with the spectroscopic detector 20. Is executed. In the first embodiment, the process of calculating the spectrum is a process of calculating the reflectance spectrum of the sample 2 based on the detection result of the spectroscopic detector 20.

More specifically, the reflectance spectrum is measured by receiving the reflected light generated by irradiating the sample 2 with the measurement light from the light source 10 by the spectroscopic detector 20 (step S3). The process of calculating the reflectance spectrum of the sample 2 based on the detection result of the spectroscopic detector 20 may be performed by the spectroscopic detector 20 or the processing device 100. The reflectance spectrum measured in step S3 is stored in the storage 110 of the processing device 100 as the detection result 116 (see FIG. 3).

As the process of calculating the spectrum, a process of calculating the transmittance spectrum of the sample 2 based on the detection result of the spectral detector 20 may be adopted.

Subsequently, the processing device 100 executes a process of identifying a section in the calculated spectrum in which the change in the amplitude with respect to the wavelength satisfies a predetermined condition. More specifically, the processing device 100 specifies the bottom section of the low frequency component included in the measured reflectance spectrum, and removes the information of the specified bottom section (step S4).

Then, the processing device 100 executes the process of calculating the optical characteristic of the sample 2 using the spectrum after removing the information of the specified section from the calculated spectrum.

More specifically, the processing device 100 calculates the power spectrum by Fourier transforming the reflectance spectrum from which the information of the bottom section is removed (step S5). Note that FFT (Fast Fourier Transform) may be typically used for the Fourier transform. Furthermore, the processing device 100 searches for a peak included in the power spectrum calculated in step S5 (step S6), and based on the position of the searched peak on the power spectrum, the optical characteristics of the sample 2 are determined as the optical characteristics of the sample 2. The film thickness is calculated (step S7). Then, the optical measurement process ends.

As shown in steps S5 to S7, the process of calculating the optical characteristics of the sample 2 includes the process of calculating the film thickness based on the peak appearing in the result of Fourier transform of the reflectance spectrum from which the information of the bottom section is removed. .. For a more detailed processing procedure for calculating the film thickness of the sample 2 shown in steps S5 to S7, refer to, for example, Japanese Patent Laid-Open No. 2009-092454 (Patent Document 1).

When it is necessary to measure the film thickness of the sample 2 a plurality of times or to measure the film thickness of the sample 2 at a plurality of locations, the processes of steps S3 to S7 are repeatedly performed as many times as necessary.

(C2: Specification of bottom section)
Next, details of the process of identifying the bottom section shown in step S4 of FIG. 8 will be described.

The process of identifying the bottom section corresponds to the process of identifying the section in the reflectance spectrum in which the change in the amplitude with respect to the wavelength satisfies a predetermined condition. Here, the predetermined condition means that the amplitude of the low frequency component included in the reflectance spectrum is relatively small. In other words, the predetermined condition means that the reflectance spectrum corresponds to the node portion of the wave.

In the first embodiment, the bottom section is specified based on the magnitude of amplitude fluctuation in the unit section that occurs in the reflectance spectrum. The closer to the node of the standing wave, the smaller the fluctuation of the amplitude, and the closer to the antinode of the standing wave, the larger the fluctuation of the amplitude. Therefore, the magnitude of the amplitude fluctuation is evaluated for each unit section, and the section in which the amplitude fluctuation is relatively small is specified as the bottom section.

FIG. 9 is a diagram for explaining the process of identifying the bottom section in the optical measurement method according to the first embodiment. FIG. 9A shows an example of the reflectance spectrum measured from the sample. For the reflectance spectrum as shown in FIG. 9A, the evaluation window 30 having a predetermined wavelength width is sequentially set while shifting the wavelength position. Information indicating the magnitude of the amplitude fluctuation is calculated based on the information of the section included in each evaluation window 30 of the reflectance spectrum.

As described above, the process of identifying the bottom section includes the process of sequentially setting the evaluation windows 30 having a predetermined wavelength width with respect to the reflectance spectra and the amplitude of the reflectance spectra included in each evaluation window 30. And a process of determining whether the section corresponding to each evaluation window 30 satisfies a predetermined condition based on the change.

As the change in the amplitude whether or not the predetermined condition is satisfied, the degree of the amplitude variation in the corresponding section in each evaluation window 30 can be used. That is, the processing device 100, as a part of the process of determining whether the section corresponding to each evaluation window 30 satisfies the predetermined condition, the degree of amplitude variation in the section corresponding to each evaluation window of the reflectance spectrum. The process of calculating is executed.

A variance or a standard deviation can be typically used as the degree of amplitude variation. Alternatively, the difference between the maximum value and the minimum value of the amplitude existing in each evaluation window 30 may be used. As described above, an arbitrary value can be used as the information indicating the degree of amplitude variation in the corresponding section in each evaluation window 30. In the following description, an example using “dispersion” will be described as a typical example.

FIG. 9B shows the dispersion for each wavelength (hereinafter, also referred to as “dispersion spectrum”) calculated by sequentially setting the evaluation window 30 for the reflectance spectrum shown in FIG. 9A. The bottom section is specified by evaluating the dispersion spectrum shown in FIG. 9(B).

As a typical example, a threshold value is set in advance for the dispersion spectrum shown in FIG. 9B, and a section in which the dispersion value is below a predetermined threshold value is specified as the bottom section 32. That is, when the degree of amplitude variation (dispersion, for example) in the section corresponding to each evaluation window 30 of the reflectance spectrum is below a predetermined threshold value, the processing apparatus 100 determines that the section corresponding to the evaluation window 30. It is determined that the predetermined condition is satisfied.

The wavelength width of the evaluation window 30 is appropriately determined based on the wavelength range of the entire reflectance spectrum and the wavelength resolution. Alternatively, the wavelength width of the evaluation window 30 may be dynamically adjusted so as to ensure a predetermined measurement accuracy. Further, the threshold value may be a predetermined fixed value, or may be dynamically determined based on the magnitude of the calculated amplitude fluctuation of the entire dispersion spectrum.

Furthermore, the wavelength width of the evaluation window 30 and/or the magnitude of the threshold value may be predetermined for each type of the sample 2. In this case, the processing apparatus 100 may store recipe information for each type of sample 2 in advance and validate the corresponding recipe information according to the type of sample 2 to be measured.

As shown in FIG. 9C, the information of the specified bottom section is removed from the reflectance spectrum. In the process of calculating the film thickness of the sample, the reflectance spectrum is Fourier transformed. Therefore, in the removal of the information of the specified bottom section, a process of updating the amplitude (reflectance) of the corresponding wavelength to zero (or a predetermined reference value) may be executed.

Through the series of processes described above, the identification of the bottom section of the low-frequency component included in the measured reflectance spectrum and the removal of the information of the identified bottom section are completed.

FIG. 10 is a flowchart showing a more detailed procedure of step S4 of the optical measuring method according to the first embodiment shown in FIG. With reference to FIG. 10, the processing apparatus 100 sets the evaluation window 30 at the initial position for the measured reflectance spectrum (step S41). The processing device 100 calculates the variance for the section of the reflectance spectrum within the set evaluation window 30 (step S42). The processing device 100 determines whether or not the setting of the evaluation window 30 for all the positions is completed (step S43).

If the setting of the evaluation window 30 for all positions is not completed (NO in step S43), the processing device 100 sets the evaluation window 30 at the next position (step S44). Then, the processing from step S42 onward is repeated.

If the setting of the evaluation window 30 for all the positions is completed (YES in step S43), the processing device 100 calculates the dispersion spectrum based on the dispersion calculated for each evaluation window 30 (step S45), A section below the threshold value in the calculated dispersion spectrum is specified as the bottom section 32 (step S46). Then, the processing device 100 updates the reflectance of each wavelength included in the identified bottom section 32 to zero (step S47).

As described above, the process of identifying the bottom section of the low-frequency component included in the measured reflectance spectrum and removing the information of the identified bottom section is completed.

(C3: measurement example)
Next, a measurement example by the optical measuring method according to the first embodiment will be described.

FIG. 11 is a diagram showing a measurement example by the optical measurement method according to the first embodiment. FIG. 11A shows an example of a reflectance spectrum measured from a sample having anisotropy. FIG. 11B shows an example of a power spectrum obtained by Fourier transforming the reflectance spectrum shown in FIG. 11A as it is. As shown in FIG. 11B, when the reflectance spectrum measured from the sample having anisotropy is subjected to Fourier transform as it is, a plurality of peaks appear at positions close to each other, and the measurement accuracy deteriorates. obtain.

FIG. 11C shows an example of the dispersion spectrum calculated by sequentially setting the evaluation window 30 for the reflectance spectrum shown in FIG. The section below the threshold value set for the dispersion spectrum shown in FIG. 11C is specified as the bottom section 32. Then, by updating the reflectance of each wavelength included in the bottom section 32 to zero, a reflectance spectrum in which the information of the bottom section is removed as shown in FIG. 11D is obtained.

Fourier transform of the reflectance spectrum from which the information of the bottom section as shown in FIG. 11(D) is removed can suppress the occurrence of adjacent peaks as shown in FIG. 11(E). It can be seen that the reduction in accuracy can be prevented.

(C4: advantage)
According to the optical measuring method according to the first embodiment, the influence of the beat (variation due to the combination of different frequency components) appearing in the spectrum measured from a sample having anisotropy is removed, and then the optical characteristics of the sample are To calculate. Therefore, it is possible to suppress a decrease in measurement accuracy.

<D. Second Embodiment>
In the first embodiment, a sample of a monolayer film having anisotropy has been described as an example. An actual sample is often a multi-layer film including a plurality of layers. When measuring a sample of a multilayer film with anisotropy, not only the influence of the layer that causes the beat (beat) due to the birefringence but also the influence of other layers, the influence of the beat is removed. It can be difficult to do. Therefore, as a second embodiment, an optical measuring method suitable for measuring the film thickness of a multilayer film sample will be described.

(D1: Outline of processing)
First, a processing outline of the optical measurement method according to the second embodiment will be described.

In the optical measuring method according to the second embodiment, among the peaks appearing in the power spectrum obtained by Fourier-transforming the reflectance spectrum measured from the sample having anisotropy, the peak is not the object of film thickness measurement. Information on peaks originating from the layer and in the vicinity of the peaks is removed. Furthermore, by performing inverse Fourier transform on the power spectrum after removing the information of the peak and the vicinity of the peak, the reflectance spectrum from which the information derived from the layer other than the measurement target is removed (hereinafter, also referred to as “noise removal reflectance spectrum”). .) is calculated. Similar to the optical measurement method according to the first embodiment, a process of removing the influence of the low-frequency component is applied to the calculated noise removal reflectance spectrum, so that the measurement target of the measurement target included in the target sample can be obtained. The film thickness for a layer can be calculated.

(D2: processing procedure)
Next, a processing procedure of the optical measuring method according to the second embodiment will be described.

FIG. 12 is a flowchart showing the procedure of the optical measurement method according to the second embodiment. The main steps shown in FIG. 12 are typically realized by the processor 102 of the processing device 100 loading a measurement program 114 (see FIG. 3) into the main memory 104 and executing it. Note that in the flowchart of FIG. 12, the same step numbers are assigned to the processes substantially the same as the processes shown in the flowchart of FIG.

Referring to FIG. 12, first, optical measurement system 1 is prepared (step S1). In step S1, alignment of the irradiation opening of the Y-shaped fiber 4 included in the optical measurement system 1 and calibration processing in the spectroscopic detector 20 are executed. Then, the sample 2 to be measured is placed at a predetermined position of the optical measurement system 1 (step S2).

Subsequently, a process of irradiating the sample 2 with the measurement light from the light source 10 and calculating a spectrum based on the detection result obtained by receiving the reflected light or the transmitted light generated in the sample 2 by the measurement light with the spectroscopic detector 20. Is executed.

In the second embodiment, as the process of calculating the spectrum, the reflectance spectrum of the sample 2 calculated based on the detection result of the spectral detector 20 is derived from the layer other than the measurement target included in the sample 2. A process (steps S3, S11, S12, S13, S14) of calculating a reflectance spectrum (noise-removed reflectance spectrum) from which information has been removed is executed.

More specifically, the reflectance spectrum is measured by receiving the reflected light generated by irradiating the sample 2 with the measurement light from the light source 10 by the spectroscopic detector 20 (step S3). The process of calculating the reflectance spectrum of the sample 2 based on the detection result of the spectroscopic detector 20 may be performed by the spectroscopic detector 20 or the processing device 100. The reflectance spectrum measured in step S3 is stored in the storage 110 of the processing device 100 as the detection result 116 (see FIG. 3).

First, the processing device 100 calculates the power spectrum by performing Fourier transform on the reflectance spectrum measured from the sample 2 (step S11). Then, the processing apparatus 100 identifies the peaks derived from the layer that is not the target for measuring the film thickness included in the calculated power spectrum (step S12). That is, the processing apparatus 100 identifies the peak in the power spectrum, which is derived from the non-measurement target layer included in the sample 2.

Further, the processing device 100 removes the identified peak and information near the peak (step S13). That is, the processing device 100 calculates a power spectrum (noise-removed power spectrum) obtained by removing the identified peak and information near the peak from the power spectrum.

Finally, the processing apparatus 100 calculates the noise-removed reflectance spectrum by performing an inverse Fourier transform on the power spectrum after removing the peak and the information near the peak (step S14).

Subsequently, the processing device 100 executes a process of specifying a section in the calculated noise-removed reflectance spectrum in which a change in amplitude with respect to wavelength satisfies a predetermined condition. More specifically, the processing device 100 specifies the bottom section of the low-frequency component included in the calculated noise removal reflectance spectrum, and removes the information of the specified bottom section (step S4A). The process of step S4A is different from the process of step S4 shown in FIG. 8 in that the spectrum to be removed is different, but the process content itself is substantially the same as that of the first embodiment.

Then, the processing device 100 executes the process of calculating the optical characteristic of the sample 2 using the spectrum after removing the information of the specified section from the calculated spectrum.

More specifically, the processing device 100 calculates the power spectrum by Fourier transforming the reflectance spectrum from which the information of the bottom section is removed (step S5). Further, the processing device 100 searches for a peak included in the power spectrum calculated in step S5 (step S6), and calculates the film thickness of the sample 2 based on the position of the searched peak on the power spectrum (step). S7). Then, the optical measurement process ends.

In addition, when it is necessary to measure the film thickness of the sample 2 a plurality of times, or to measure the film thickness of the sample 2 at a plurality of locations, the number of times that the processes of steps S3 to S7 including steps S11 to S14 are necessary. Only executed repeatedly.

(D3: measurement example)
Next, a measurement example by the optical measuring method according to the second embodiment will be described.

FIG. 13 is a schematic diagram showing a structural example of the sample 2 to be measured. Referring to FIG. 13, Sample 2 as the measurement target has a structure in which a coat layer is arranged on the substrate and a cover layer is arranged on the coat layer. Typically, the coat layer and the cover layer are made of any resin.

As shown in FIG. 13, the measurement target is a layer of the substrate, and the film thicknesses of the coat layer and the cover layer are outside the measurement target.

FIG. 14 is a diagram showing a measurement example by the optical measurement method according to the second embodiment. FIG. 14A shows an example of the reflectance spectrum measured from Sample 2 shown in FIG. In the reflectance spectrum shown in FIG. 14A, the “beat” appearing in the reflectance spectrum measured from the sample of the single layer film (see FIG. 9A) cannot be explicitly confirmed. Can not. However, it does not mean that the “beat” does not exist, but it can be said that the influence of the “beat” is hidden by the influence from other layers.

FIG. 14B shows an example of a power spectrum obtained by Fourier transforming the reflectance spectrum shown in FIG. In the power spectrum shown in FIG. 14B, peaks corresponding to each layer included in Sample 2 appear. The peak derived from the layer (the cover layer in the sample shown in FIG. 13) that is not the measurement target of the film thickness included in the calculated power spectrum is specified. As shown in FIG. 14B, the peak corresponding to the cover layer has the largest power. Then, the identified peak and information near the peak are removed from the power spectrum.

Usually, the structure of the sample 2 is known, and it can be previously determined whether or not each layer included in the sample 2 is a measurement target. Moreover, since the film thickness of the layer that is not the measurement target is already known, it is possible to set in advance which condition in the power spectrum the peak appears as a condition. Therefore, the process of specifying the peak in the power spectrum, which is derived from the layer whose thickness is not measured, can be mechanically executed by using the prior information.

In the example shown in FIG. 14, the measurement target is the layer of the substrate, but since the information corresponding to the coat layer in contact with the substrate of the measurement target is necessary for calculating the film thickness of the measurement target, Not done.

As shown in FIG. 14B, it can be seen that two peaks are generated at positions close to each other with respect to the peaks other than the removed peak. That is, it means that a “beat” has occurred in the measured reflectance spectrum.

FIG. 14C shows an example of the noise-removed reflectance spectrum calculated by performing an inverse Fourier transform on the power spectrum after removing the peak and the information near the peak. For convenience of description, in FIG. 14C, the horizontal axis represents the wave number (=reciprocal of wavelength). By expressing the horizontal axis as the wave number, the “beat” included in the reflectance spectrum can be explicitly confirmed.

In FIG. 14D, the information of the bottom section, which is calculated by applying the optical measurement method according to the first embodiment to the noise-removed reflectance spectrum shown in FIG. 14C, is removed. An example of the reflectance spectrum is shown. Note that since the optical film thicknesses of the substrate and the coat layer are close to each other, two peaks (“substrate” and “coat layer”) are generated at positions close to each other in the reflectance spectrum shown in FIG. However, this is not due to “growing”.

As shown in FIG. 14(D), by removing the information of the bottom section from the noise-removed reflectance spectrum and then performing the Fourier transform again, it is possible to suppress the occurrence of adjacent peaks, thereby reducing the measurement accuracy. You can see that it can be prevented.

(D4: advantage)
According to the optical measurement method according to the second embodiment, in the result of Fourier transforming the spectrum such as the reflectance spectrum measured from the sample, the information derived from the layer that is not the measurement target is removed, and then the original The optical characteristics of the sample are calculated after restoring the spectrum corresponding to the spectrum of. Similar to the optical measurement method according to the first embodiment described above, it is possible to remove the influence of the beat (variation due to the combination of different frequency components) that appears in the restored spectrum, and thus it is possible to suppress the decrease in measurement accuracy.

<E. Summary>
According to the above detailed description of the invention, it is possible to understand a new problem that occurs in the optical measurement method using the optical interferometry found by the inventors of the present application, and the effectiveness of the solution to the problem. Will.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

1 optical measurement system, 2 samples, 4 Y type fiber, 10 light source, 20 spectroscopic detector, 22 diffraction grating, 24 light receiving part, 26 interface circuit, 30 evaluation window, 32 bottom section, 100 processing device, 102 processor, 104 main Memory, 106 input unit, 108 display unit, 110 storage, 112 operating system, 114 measurement program, 116 detection result, 118 measurement result, 120 communication interface, 122 network interface, 124 media drive, 126 recording medium.

Claims (11)

A light source that generates a measurement light for irradiating the sample,
A spectroscopic detector that receives reflected light or transmitted light generated in the sample by the measurement light,
A processing device to which the detection result of the spectral detector is input,
The processing device is
A process of calculating a first spectrum based on the detection result of the spectral detector,
In the first spectrum, a process of identifying a section in which a change in amplitude with respect to wavelength satisfies a predetermined condition,
An optical measurement system configured to execute a process of calculating an optical characteristic of the sample by using a second spectrum obtained by removing the information of the specified section from the first spectrum. The specified process is
A process of sequentially setting an evaluation window having a predetermined wavelength width with respect to the first spectrum;
The process according to claim 1, further comprising: a process of determining whether a section corresponding to each evaluation window satisfies the predetermined condition based on a change in the amplitude of the first spectrum included in each evaluation window. Optical measurement system. The process of determining whether a section corresponding to each evaluation window satisfies the predetermined condition includes a step of calculating a degree of amplitude variation in a section corresponding to each evaluation window of the first spectrum. Item 3. The optical measurement system according to Item 2. When the degree of amplitude variation in a section corresponding to each evaluation window of the first spectrum is lower than a predetermined threshold value, it is determined that the section corresponding to the evaluation window satisfies the predetermined condition. Item 3. The optical measurement system according to Item 3. The optical measurement system according to any one of claims 2 to 4, wherein the wavelength width of the evaluation window is predetermined for each type of sample. The optical measurement system according to claim 1, wherein the process of calculating the optical characteristics of the sample includes a process of calculating a film thickness based on a peak appearing in a result of Fourier transforming the second spectrum. .. The process of calculating the first spectrum includes a process of calculating the reflectance spectrum of the sample based on the detection result of the spectroscopic detector as the first spectrum. An optical measurement system according to item. In the process of calculating the first spectrum, as the first spectrum, from the reflectance spectrum of the sample calculated based on the detection result of the spectroscopic detector, to the layer not included in the measurement target included in the sample. The optical measurement system according to any one of claims 1 to 6, which includes a process of calculating a reflectance spectrum from which derived information is removed. The process of calculating the first spectrum is
Fourier transforming the reflectance spectrum of the sample to calculate a third spectrum;
Of the third spectrum, a process of identifying a peak derived from a non-measurement target layer included in the sample,
9. The optical measurement system according to claim 8, further comprising: a process of removing the identified peak and information near the peak from the third spectrum to calculate a fourth spectrum. The optical measurement system according to claim 9, wherein the process of calculating the first spectrum further includes a process of performing an inverse Fourier transform on the fourth spectrum to calculate the first spectrum. Irradiating the sample with measurement light from the light source, and calculating the first spectrum based on the detection result obtained by receiving reflected light or transmitted light generated by the sample with the measurement light by the spectroscopic detector,
In the first spectrum, identifying a section in which a change in amplitude with respect to wavelength satisfies a predetermined condition;
Calculating the optical characteristic of the sample using a second spectrum obtained by removing the information of the specified section from the first spectrum.

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