TWI867121B - Optical measurement method, optical measurement device and computer program product - Google Patents

Abstract

An optical measurement method, including: a step of measuring the spectrum with respect to a sample; using a first wavelength dispersion formula, the thickness of the sample is calculated for each wavelength represented by a peak or a trough, and the thickness of the sample is calculated based on the calculated thickness under the condition that the evaluation value becomes the maximum, a step of tentatively including the coefficients in the first wavelength dispersion equation, setting the order of the specific peak under multiple conditions, and calculating a second wavelength dispersion formula under the multiple conditions; a step of determining coefficients based on the first wavelength dispersion formula and the second wavelength dispersion formula including the tentative coefficients; and a step of calculating the retardation.

Description

Optical measurement methods, optical measurement devices and computer program products

The present invention relates to an optical measurement method, an optical measurement device and a computer program product.

Traditionally, an optical measurement device is known to obtain the optical degree and delay by rotating the positional relationship between the sample, polarizer, and analyzer in the plane direction of the sample and measuring them simultaneously. (See Patent Documents 1 and 2 below). In addition, when the birefringence of the sample or the thickness of the sample is known, there is another method for measuring the delay (see Patent Document 3 below).

Patent document 1: Japanese Patent Publication No. 11-211656

Patent document 2: Japanese Patent Publication No. 2003-172691

Patent document 3: Japanese Patent Publication No. 2003-240678

As described in Patent Documents 1 and 2, when the angle formed by the sample and the polarization optical system is changed in a plurality of ways for measurement, the measuring device requires a driving mechanism for tilting the sample or the polarization optical system. In addition, especially when the delay of the sample is high, it is difficult to determine the order and it is not easy to accurately measure the delay. In the optical measurement method of Patent Document 3, unless at least one of the birefringence index of the sample or the thickness of the sample is known, the wavelength dispersion of the delay cannot be measured.

The present invention is invented in view of the above situation, and its purpose is to use a simple measuring mechanism to measure the spectrum and determine the order of the peaks or troughs contained in the spectrum, and at the same time measure the accurate delay.

To solve the above problem, the optical measurement method according to the present invention comprises the following steps: measuring a spectrum containing a plurality of peaks and troughs within a predetermined wavelength range relative to a sample; using a first wavelength dispersion formula (wavelength dispersion), calculating the thickness of the sample for each wavelength represented by the peak or the trough, and tentatively determining the coefficient included in the first wavelength dispersion formula under the condition that the evaluation value based on the calculated thickness will become the maximum; setting the order of a specific peak included in the multiple peaks under multiple conditions, and calculating the second wavelength dispersion formula based on the orders and wavelengths of the multiple peaks under the multiple set conditions; determining the coefficient based on the first wavelength dispersion formula and the second wavelength dispersion formula containing the tentative coefficient, under the order of the specific peak, and based on the specified order and the second wavelength dispersion formula; and calculating the delay based on the second wavelength dispersion formula containing the determined coefficient.

In addition, the optical measuring device according to the present invention includes: a measuring unit, which measures a spectrum containing a plurality of peaks and troughs relative to a sample within a predetermined wavelength range; a provisional determination unit, which uses a first wavelength dispersion formula containing coefficients set by a plurality of conditions to calculate the thickness of the sample for each wavelength represented by the peak or the trough, and provisionally determines the coefficients contained in the first wavelength dispersion formula under the condition that the evaluation value based on the calculated thickness will be the maximum; a second wavelength dispersion formula calculation unit, which uses a first wavelength dispersion formula containing coefficients set by a plurality of conditions to calculate the thickness of the sample for each wavelength represented by the peak or the trough, and provisionally determines the coefficients contained in the first wavelength dispersion formula under the condition that the evaluation value based on the calculated thickness will be the maximum; The order of a specific peak included in the plurality of peaks is set under the plurality of setting conditions, and a second wavelength dispersion formula is calculated based on the orders and wavelengths of the plurality of peaks under the plurality of setting conditions; a determination unit determines the coefficient based on the first wavelength dispersion formula and the second wavelength dispersion formula containing the provisional coefficient under the order of the specific peak, and based on the specified order and the second wavelength dispersion formula; and a delay calculation unit calculates the delay based on the second wavelength dispersion formula containing the determined coefficient.

In addition, the computer program product according to the present invention is executed on a computer used in an optical measuring device, and the following steps are executed on the computer: measuring a spectrum containing a plurality of peaks and troughs within a predetermined wavelength range relative to a sample; using a first wavelength dispersion formula containing coefficients set by a plurality of conditions, calculating the thickness of the sample for each wavelength represented by the peak or the trough, and tentatively determining the coefficient contained in the first wavelength dispersion formula under the condition that the evaluation value based on the calculated thickness will become the maximum. Step; setting the order of a specific peak included in the multiple peaks under the multiple conditions, and calculating the second wavelength dispersion formula based on the orders and wavelengths of the multiple peaks under the multiple setting conditions; specifying the order of the specific peak based on the first wavelength dispersion formula containing the tentative coefficient and the second wavelength dispersion formula, and determining the coefficient based on the specified order and the second wavelength dispersion formula; and calculating the delay based on the second wavelength dispersion formula containing the determined coefficient.

100:Optical measuring device

102: Information Processing Department

104: Measurement Department

106: Control Department

108: Memory Department

110: Display unit

112: Input/output department

114: Data bus

116: Wavelength calculation unit

120: Temporary determination department

122: Standardization Department

124: Second wavelength dispersion calculation unit

126: Confirmation Department

128: Delay calculation department

202: Light source

204: Optical fiber

206: Focusing lens

208: Polarizer

210: Rotating sample table

212: Samples

214: Polarizer

216:Multi-channel spectrometer

1202:Objective lens

1204: Semi-reflective mirror

1206: Observation camera

Figure 1 is a schematic diagram showing the schematic structure of the optical measurement device according to this embodiment.

Figure 2 is an example diagram showing the schematic structure of the measuring unit according to this embodiment.

Figure 3 is an example of a measured parallel Nicol spectrum.

Figure 4 is a flow chart showing the method for calculating delay according to this embodiment.

Figure 5 is an example diagram showing the wavelength dependence of thickness.

Figure 6 is a graph showing the first wavelength dispersion type and the second wavelength dispersion type.

Figure 7 is an example diagram showing the experimental results used to verify the effect of the present invention.

Figure 8 is an example diagram showing the experimental results used to verify the effect of the present invention.

Figure 9 is an example diagram showing the experimental results used to verify the effect of the present invention.

Figure 10 is an example diagram showing the experimental results used to verify the effect of the present invention.

Figure 11 is a flow chart showing a method for calculating the phase difference in the thickness direction or the three-dimensional birefringence.

Figure 12 is another example diagram showing the schematic structure of the measuring unit according to this embodiment.

The following will refer to the attached figures and illustrate the embodiments of the present invention.

FIG. 1 is a schematic diagram showing the schematic structure of the optical measuring device 100 of the present embodiment. As shown in FIG. 1, the optical measuring device 100 of the present embodiment includes: an information processing unit 102 and a measuring unit 104. The information processing unit 102 includes a control unit 106, a memory unit 108, a display unit 110, and an input/output unit 112. The information processing unit 102 is, for example, a general computer. The control unit 106, the memory unit 108, the display unit 110, and the input/output unit 112 are connected by a data bus 114 so that electronic signals can be exchanged with each other.

The control unit 106 is a CPU (Central Processing Unit) serving as a processor. Specifically, the control unit 106 functionally includes a wavelength calculation unit 116, a temporary determination unit 120, a normalization unit 122, a second wavelength dispersion calculation unit 124, a determination unit 126, and a delay calculation unit 128. Each unit performs the calculation described below according to the program stored in the memory unit 108.

The memory unit 108 is a main memory device such as RAM (Random Access Memory) that can statically record information and an auxiliary memory device such as HDD (Hard Disk Drive) or SSD (Solid State Drive). In addition to computer program products, the memory unit 108 also stores a program for controlling the operation of each unit included in the information processing unit 102.

The display unit 110 is a cathode ray tube (CRT) or a so-called flat panel display. The display unit 110 visually displays images to the user.

The input/output unit 112 is one or more devices such as a keyboard, a mouse, or a touch panel for a user to input information. The input/output unit 112 is one or more interfaces for the information processing unit 102 to exchange information with external devices such as the measuring unit 104. For example, the input/output unit 112 inputs the result measured by the measuring unit 104. The input/output unit 112 may include various interfaces for wired connection and a controller for wireless connection. In addition, the structure of the information processing unit 102 shown here is an example, and other structures may be used.

FIG. 2 is a schematic diagram showing a schematic structure of the measuring unit 104. As shown in FIG. 2, the measuring unit 104 includes: a light source 202, an optical fiber 204, a condenser 206, a polarizer 208, a rotating sample stage 210, an analyzer 214, and a multi-channel spectrometer 216. In addition, the measuring unit 104 shown in FIG. 2 is an example of measuring a parallel Nicol spectrum.

The light source 202 is, for example, a halogen lamp that emits white light. The light source 202 can be another type of light source 202, as long as it is a light source 202 that emits light within the wavelength range to be measured. The light emitted by the light source 202 passes through the optical fiber 204 and is converted into parallel light by the condenser 206.

Polarizer 208 is a linear polarizer. Polarizer 208 allows only the component in the transmission axis direction of the parallel light converted by focusing lens 206 to pass through.

The sample 212 is arranged on the rotating sample stage 210. When the propagation direction of the light passing through the polarizer 208 is the Z-axis direction, the rotating sample stage 210 is configured so that the angle formed by the surface of the sample 212 arranged on the rotating sample stage 210 and the Z-axis can be changed. FIG. 2 shows a case where the angle formed by the X-axis and the Z-axis and the angle formed by the Y-axis and the Z-axis are both 90 degrees when the surface of the sample 212 is an XY plane. In addition, the rotating sample stage 210 is formed of a material that transmits a component within the wavelength range of the light transmitted through the polarizer 208 as a measurement object. The measuring unit 104 may not have the rotating sample stage 210.

The analyzer 214 is a linear polarizer and is configured to make the polarizer 208 and the transmission axis parallel to each other. The light transmitted through the sample 212 has a phase difference between the X-axis component and the Y-axis component depending on the wavelength. The analyzer 214 allows only the component of the light with phase difference in the transmission axis direction to pass through. The transmitted light is condensed by the condenser 206 and input to the multi-channel spectrometer 216 via the optical fiber 204.

The multi-channel spectrometer 216 distinguishes and measures the intensity of the input light of each wavelength. Specifically, for example, the multi-channel analyzer measures parallel Nicol spectra, as shown in FIG. 3. The vertical axis of FIG. 3 is the transmittance converted from the intensity measured by the multi-channel analyzer, and the horizontal axis is the wavelength. Since the phase of the X-axis component and the Y-axis component of the light after passing through the sample 212 varies depending on the wavelength, the wavelength dependence of the transmittance is in a waveform as shown in FIG. 3.

Next, the delay measurement method according to the present embodiment and the function of each unit included in the control unit 106 will be described using the process shown in FIG. 4. First, the measuring unit 104 measures a spectrum containing a plurality of peaks and troughs within a predetermined wavelength range relative to the sample 212 (S402). Specifically, for example, as shown in FIG. 3, the measuring unit 104 measures a parallel Nicol spectrum containing a plurality of peaks and troughs within a wavelength range of 400 nm to 800 nm.

Next, the wavelength calculation unit 116 calculates the wavelength represented by each peak and trough included in the calculated wavelength range (S404). Specifically, for example, the wavelength calculation unit 116 sets the range of 500nm to 750nm as the calculated wavelength range. In the example of FIG. 3, the wavelength calculation unit 116 calculates the wavelength represented by the seven peaks and seven troughs included in the calculated wavelength range. In addition, the calculated wavelength range can be set by the user inputting into the input/output unit 112.

Next, the provisional determination unit 120 uses the first wavelength dispersion formula including the coefficients set under a plurality of conditions and the calculated thickness to calculate the thickness of the sample for each wavelength represented by the peak or the trough, and provisionally determines the coefficients included in the first wavelength dispersion formula under the condition that the evaluation value based on the calculated thickness becomes the maximum (S406). Specifically, for example, the provisional determination unit 120 provisionally determines the wavelength dispersion coefficients A, B, and C using mathematical formulas 1 to 4. Mathematical formula 1 is a mathematical formula for calculating the thickness as a function of λ _C.

In mathematical formula 1, i is the index of the peak and the trough. For example, for i, among the wavelengths represented by the 14 peaks and the wavelengths represented by the troughs calculated by S404, the index of the peak with the longest wavelength of 740nm is 0, and the index of the trough with the shortest wavelength of 500nm is 13. λ is the wavelength. _λC is the middle wavelength of adjacent peaks or the middle wavelength of adjacent troughs, which is represented by mathematical formula 2.

Δn(λ) is the birefringence at wavelength λ, which can be calculated using the Cauchy wavelength dispersion equation shown in equation 3 and the unknown wavelength dispersion coefficients A, B, and C.

The temporary determination unit 120 temporarily determines the wavelength dispersion coefficients A, B, and C included in the first wavelength dispersion formula so as to maximize the evaluation value based on the thickness calculated by mathematical formula 1. For example, the temporary determination unit 120 uses mathematical formula 1 to calculate the thickness calculated at each peak or trough wavelength, and uses mathematical formula 4 to calculate the standard deviation σ, and uses the reciprocal of the standard deviation σ as the evaluation value.

In mathematical formula 4, d _λC,i , for each index i, is the thickness of the sample 212 calculated for each middle wavelength of the adjacent peaks or the middle wavelength of the adjacent troughs. max is the maximum value of the index within the calculation wavelength range. In the above example, since there are a total of 14 peaks and troughs in the calculation wavelength region, the value of max is 13.

Specifically, the provisional determination unit 120 uses the reciprocal of the standard deviation σ as an evaluation value and uses the nonlinear least square method to calculate the wavelength dispersion coefficients A, B, and C. Again, this algorithm is an example, and if the wavelength dispersion coefficients A, B, and C can be specified under the condition that the evaluation value as the reciprocal of the standard deviation σ becomes the maximum, the wavelength dispersion coefficients A, B, and C are used. Another algorithm may be used for provisional determination.

FIG. 5 shows the relationship between the thickness d and the wavelength calculated under three conditions of the wavelength dispersion coefficients A, B and C that are repeatedly changed before the temporary determination unit 120 temporarily determines the wavelength dispersion coefficients A, B and C. In the example shown in FIG. 5, the standard deviation of the thickness d is the smallest under the condition that the wavelength dispersion coefficient B is 13723. Therefore, the temporary determination unit 120 temporarily determines A, B and C calculated under this condition as the wavelength dispersion coefficients.

In addition, the evaluation value can be calculated by another method. Specifically, the evaluation value can be set so that the smaller the calculated wavelength dependence of the thickness is, the larger the value is. For example, the temporary determination unit 120 can calculate an approximate straight line of a first-order formula relative to the wavelength dependence of the thickness calculated under each condition in step S406. Then, the temporary determination unit 120 can temporarily determine A, B and C as wavelength dispersion coefficients under the condition that the slope included in the approximate formula is the smallest. That is, the temporary determination unit 120 can temporarily determine A, B and C as wavelength dispersion coefficients under the condition that the wavelength dependence of the thickness is the flattest.

Next, the normalizing unit 122 normalizes the first wavelength dispersion coefficient including the tentative wavelength dispersion coefficients A, B, and C (S410). Specifically, the normalizing unit 122 normalizes the first wavelength dispersion coefficient using the mathematical formula 5 based on the delay at the predetermined wavelength λ _n . The predetermined wavelength λ _n can be appropriately set, but is assumed to be 600 nm here. In addition, A', B', and C' included in the mathematical formula 5 are the normalized wavelength dispersion coefficients.

Next, the second wavelength dispersion formula calculation unit 124 calculates a second wavelength dispersion formula based on the order of each peak or trough and the first wavelength dispersion formula under the condition of setting the order in a plurality of ways (S412). Specifically, the second wavelength dispersion formula calculation unit 124 sets the order of a specific peak included in the plurality of peaks under a plurality of conditions, and calculates the second wavelength dispersion formula for the order and wavelength of each peak in the plurality of peaks based on the set plurality of conditions. For example, among the peaks or troughs included in the calculated wavelength range, the wavelength represented by the peak or trough with the longest wavelength is set to λ ₀ , and the order of the peak is set to _m0 . The second wavelength dispersion calculation unit 124 sets the conditions that the peak order _m0 at a wavelength of 740 nm included in the measurement results shown in FIG. 3 is 10, ₁₁ , and 12. The _delay Re.(λ _ι ) at the wavelength represented by each peak and each trough is expressed by mathematical equations 6 and 7.

[Mathematical formula 6] Re.(λ _ι )=(m ₀ +ι)‧λ _ι (λ _ι is the peak wavelength)

[Mathematical formula 7] Re.(λ _ι )=(m ₀ +ι+1/2)‧λ _ι (λ _ι is the trough wavelength)

For example, under the condition that the order of the peak with a wavelength of 740 nm is 10, the delays of λ ₀ , λ ₁ , and λ ₂ are expressed by Mathematical Formulas 8 to 10.

[Mathematical formula 8] Re .( λ ₀ )=(10+0)＊740

[Mathematical formula 10] Re .( λ ₂ )=(10+1)＊690

Similarly, the delay of the wavelength represented by all the peaks and troughs contained in the calculated wavelength range can be calculated using the above mathematical formula 6 or 7. In addition, under the condition that the order is 11 at a wavelength of 740nm and the order is 12, the second wavelength dispersion calculation unit 124 performs the same calculation.

Next, the second wavelength dispersion formula calculation unit 124 includes wavelength dispersion coefficients α _m0 , β _m0 and γ _m0 , and calculates a second wavelength dispersion formula represented by mathematical formula 11. As shown in mathematical formula 11, the second wavelength dispersion formula is a Cauchy wavelength dispersion type formula like the first wavelength dispersion formula.

The second wavelength dispersion calculation unit 124 calculates the wavelength dispersion coefficients α _m0 , β _m0 , and γ _m0 so that the delay values calculated using the mathematical equations 6 and 7 and the delay values calculated using the mathematical equation 11 are minimized under various conditions.

In addition, the normalization unit 122 normalizes the second wavelength dispersion formula with reference to the delay of the predetermined wavelength λn, and the second wavelength dispersion formula includes the wavelength dispersion coefficients α _m0 , β _m0 and γ _m0 calculated under each condition. In addition, the predetermined wavelength λn used in S410 is 600nm. The normalized second wavelength dispersion formula is represented by mathematical formula 12.

Here, α _m0 ' , β _m0 ' and γ _m0 ' are wavelength dispersion coefficients included in the normalized second wavelength dispersion formula. FIG6 is a graph showing the normalized second wavelength dispersion formula calculated under the conditions that the peak order _m0 at a wavelength of 740 nm is 10, 11 and 12.

Next, the determination unit 126 specifies the order of the specific peak based on the first wavelength dispersion formula and the second wavelength dispersion formula including the provisional coefficient, and determines the coefficient based on the specified order and the second wavelength dispersion formula (S414). Specifically, the determination unit 126 compares each second wavelength dispersion formula calculated and standardized in S412 with the first wavelength dispersion formula calculated in S410. Then, the determination unit 126 specifies the order based on the condition of the second wavelength dispersion formula that has been calculated to best match the first wavelength dispersion formula.

FIG. 6 shows the normalized first wavelength dispersion formula calculated in S410 and the normalized second wavelength dispersion formula calculated under each condition. As shown in FIG. 6, the first wavelength dispersion formula calculated in S410 has the highest consistency with the second wavelength dispersion formula calculated under the condition that the peak order _m0 at the wavelength of 740nm is 11. Therefore, the determination unit 126 specifies that the peak order m0 at the wavelength of 740nm is 11. In addition, the determination unit 126 determines α _m0 , β _m0 and γ _m0 included in the second wavelength dispersion formula before normalization calculated under the condition that the order _m0 is 11 as the wavelength dispersion coefficient.

Next, the delay calculation unit 128 calculates the delay based on the second wavelength dispersion equation including the determined coefficients (S416). Specifically, the delay calculation unit 128 calculates the delay of the wavelength required by the user based on the mathematical equation 11 including α _m0 , β _m0 and γ _m0 determined in S414 and the wavelength input by the user.

As described above, according to the present invention, a simple measurement mechanism can be used to measure a spectrum to specify the order of the peaks or troughs contained in the spectrum, and an accurate delay can be measured. Actual measurement data will be used to illustrate the effect of the present invention.

FIG. 7 shows the spectra (in this example, parallel Nicol spectra) of samples 212 (single-layer sample 1 and single-layer sample 2) measured in step S402, wherein sample 212 is two single-layer crystal plates with different delays.

FIG. 8 shows a spectrum (in this example, a parallel Nicol spectrum) of sample 212 (overlapping sample) measured in step 402, wherein sample 212 is made by overlapping two single-layer crystal plates shown in FIG. 7.

FIG. 9 is a graph showing the wavelength dependence of the delay calculated using the measurement results of FIG. 7 and the second wavelength dispersion formula calculated in steps S404 to S416. FIG. 10 is a graph showing the wavelength dependence of the delay calculated using the measurement results of FIG. 8 and the second wavelength dispersion formula calculated in steps S404 to S416. In addition, FIG. 10 also shows the calculated value obtained by adding the wavelength dependence of the delay in the two single-layer crystal plates shown in FIG. 9.

Theoretically, the delay of two single-layer crystal plates and the sum of the delay of the superimposed sample should be consistent. However, in steps S404 to S416, if the wavelength dispersion coefficient included in the second wavelength dispersion formula is not correctly calculated, the sum of the delay of two single-layer crystal plates and the delay of the superimposed sample may be different. According to the present invention, as shown in FIG. 10, the consistency between the calculated value and the measured value is high. Therefore, according to the present invention, it is confirmed that the correct delay can be measured.

In addition, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made. For example, in the present invention, the delay calculated using the flowchart shown in FIG. 4 can calculate the phase difference in the thickness direction of the sample or the three-dimensional refractive index. FIG. 11 is a flowchart showing a method for calculating the phase difference in the thickness direction of the sample or the three-dimensional refractive index.

First, i is set to 0 as a variable (S1102). Next, the tilt angle of the rotating sample stage 210 is set to θ _i degrees corresponding to each value of the variable i (S1104). When the value of the variable i is 0, the tilt angle of the rotating sample stage 210 will be set to θ ₀ degrees.

Then, the delay is measured while the tilt angle of the rotating sample stage 210 is maintained (S1106). Specifically, as in step S402, when the angle between the traveling direction of the light and the surface of the sample 212 is θ ₀ degrees, the measuring unit 104 measures the parallel Nicol spectrum. Then, the delay is calculated based on the coefficient calculated in steps S404 to S416.

Next, determine whether the variable i is consistent with the predetermined constant n (S1108). If the variable i is consistent with the predetermined constant n, proceed to S1112, and if not, proceed to S1110. In addition, the predetermined constant n is appropriately set so that the S1106 step is executed a sufficient number of times to calculate the thickness direction phase difference or the three-dimensional refractive index.

If the variable i does not agree with the predetermined constant n, the variable i is increased (S1110). Then, the tilt angle of the rotating sample stage 210 is changed to the preset θ _i degrees corresponding to each value of the variable i (S1104). Then, similar to step S402, when the angle formed by the forward direction of the light and the surface of the sample 212 is θ _i degrees, the measuring section 104 measures the parallel Nicol spectrum. In addition, the delay is calculated based on the coefficient calculated in steps S404 to S416.

As described above, multiple delays are calculated by repeating the steps of changing the angle and measuring the delay a predetermined number of times. Then, the thickness direction phase difference or three-dimensional refractive index of the sample is calculated based on the calculated multiple delays (S1112). In addition, since the tilt angle of the rotating sample stage 210 is the angle between the forward direction of the light transmitted by the polarizer 208 and the sample surface, the three-dimensional refractive index of the sample can be calculated by the measured delay while changing the angle. Since the calculation method is known, its detailed description will be omitted.

Furthermore, the measuring section 104 according to the present invention may include a microscopic optical system. Specifically, for example, the measuring section 104 may have a structure as shown in FIG. 12. The description of the structure identical to that of FIG. 2 will be omitted. Specifically, the measuring section 104 includes an objective lens 1202, a semi-reflecting mirror 1204, and an observation camera 1206 in addition to the structure shown in FIG. 2. The objective lens 1202 guides light passing through a microscopic region of the measurement object, which is the sample 212, to the analyzer 214. The semi-reflecting mirror 1204 separates light that has passed through the condenser 206. A portion of the separated light is input to the multi-channel spectrometer 216, and another portion is input to the observation camera 1206. As a result, the delay of a micro area which is a measurement object of the sample 212 can be measured, and the micro area can be observed by the observation camera 1206.

In addition, in the above description, the case where the sample 212 is a crystal plate has been described as an example of the experimental results, but the sample 212 can be a liquid crystal panel. According to the present invention, since the thickness of the sample 212 can be calculated in step S406, the cell gap of the liquid crystal panel can be measured.

In addition, although it has been described above that the spectrum measured by the measuring unit 104 is a parallel Nicol spectrum, the spectrum is not limited to the parallel Nicol spectrum. The spectrum can be any spectrum of spectral information obtained by a polarization optical system, for example, an orthogonal Nicol spectrum.

In addition, in the above description, the first wavelength dispersion formula and the second wavelength dispersion formula are described as Cauchy's wavelength dispersion formula, but the first wavelength dispersion formula and the second wavelength dispersion formula are not limited to Cauchy's wavelength dispersion formula. The first wavelength dispersion formula and the second wavelength dispersion formula can be any polynomial used to express the relationship between the birefringence index and the wavelength. For example, it can be Sellmeier's wavelength dispersion formula expressed by mathematical formula 13.

In addition, the method of calculating the delay is not limited to the method shown in the flowchart shown in FIG. 4. Specifically, first, the order of the peak with the longest wavelength included in the calculated wavelength range is set to m ₀ (a predetermined integer). Next, under the condition that the order of the peak is m ₀ , the delay is calculated for the wavelength represented by each peak and each trough included in the calculated wavelength range. Then, using the calculated delay of the wavelength represented by each peak and each trough, the Cauchy wavelength dispersion formula shown in Mathematical Formula 3 is fitted. The remainder δm ₀ of the order calculated by fitting and the set order m ₀ is calculated. Next, the order of the peak with the longest wavelength included in the calculation wavelength range is set to m ₀ +1, and the remainder δm ₀ of the order m ₀ +1 is calculated in the same manner. The remainder of the order is calculated for each order, and at the same time, the order of the peak with the longest wavelength included in the calculation wavelength range is changed from m ₀ to a predetermined value. Among the remainders calculated in the above steps, the order under the condition of the smallest remainder is specified as the order of the peak with the longest wavelength included in the calculation wavelength range. In addition, based on the specified order, the delay is calculated for the wavelength represented by each peak and each trough included in the calculation wavelength range. Each coefficient included in the wavelength dispersion equation is determined by fitting the calculated delay to the wavelength dispersion equation of Cauchy shown in Mathematical Equation 3. Then, the delay at an arbitrary wavelength can be calculated using the wavelength dispersion equation determined by the coefficients.

In summary, although the present invention has been disclosed as above by the embodiments, it is not intended to limit the present invention. Those with common knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of the patent application attached hereto.

S402~S416: Steps

Claims (8)

An optical measurement method comprises the following steps: measuring a spectrum including a plurality of peaks and troughs relative to a sample in a predetermined wavelength range; calculating the thickness of the sample for each wavelength represented by the peak or the trough using a first wavelength dispersion formula including a wavelength dispersion coefficient, and provisionally determining the wavelength dispersion coefficient included in the first wavelength dispersion formula under the condition that the evaluation value based on the calculated thickness is the maximum; setting the wavelength dispersion coefficient included in the plurality of peaks and troughs to the maximum value; The step of determining the order of a peak in the peaks, calculating a second wavelength dispersion formula based on the orders and wavelengths of the plurality of peaks; the step of determining the wavelength dispersion coefficient based on the first wavelength dispersion formula containing the tentative wavelength dispersion coefficient and the second wavelength dispersion formula under the order of the specified peak and based on the specified order and the second wavelength dispersion formula; and the step of calculating the delay based on the second wavelength dispersion formula containing the determined wavelength dispersion coefficient. The optical measurement method as described in claim 1, wherein the first wavelength dispersion formula and the second wavelength dispersion formula are Cauchy wavelength dispersion formulas. An optical measurement method as described in claim 1, wherein the spectrum is a parallel Nicol spectrum. An optical measurement method as described in claim 1, wherein the evaluation value is a value that increases as the wavelength dependence of the calculated thickness decreases. An optical measurement method as described in claim 1, wherein the evaluation value is a value that increases as the calculated standard deviation decreases. The optical measurement method as described in claim 1 further comprises the following steps: a step of changing the angle formed by the propagation direction of light and the surface of the sample; a step of measuring the spectrum while maintaining the angle, and a step of measuring the delay based on the second wavelength dispersion formula including the determined wavelength dispersion coefficient; and a step of calculating the thickness direction phase difference or three-dimensional refractive index of the sample based on a plurality of delays calculated by repeating the steps of changing the angle and measuring the delay for a predetermined number of times. An optical measuring device comprises: a measuring unit, measuring a spectrum containing a plurality of peaks and troughs relative to a sample within a predetermined wavelength range; a provisional determination unit, using a first wavelength dispersion formula containing a wavelength dispersion coefficient, calculating the thickness of the sample for each wavelength represented by the peak or the trough, and provisionally determining the wavelength dispersion coefficient contained in the first wavelength dispersion formula under the condition that an evaluation value based on the calculated thickness is the maximum; and a second wavelength dispersion formula calculation unit, setting the wavelength dispersion coefficient contained in the first wavelength dispersion formula to the value contained in the wavelength dispersion coefficient. The order of a specific peak among the plurality of peaks is used to calculate a second wavelength dispersion formula based on the orders and wavelengths of the plurality of peaks; a determination unit is used to determine the wavelength dispersion coefficient based on the first wavelength dispersion formula including the tentative wavelength dispersion coefficient and the second wavelength dispersion formula under the order of the specific peak and based on the specified order and the second wavelength dispersion formula; and a delay calculation unit is used to calculate the delay based on the second wavelength dispersion formula including the determined wavelength dispersion coefficient. A computer program product is executed on a computer used in an optical measuring device, and executes the following steps on the computer: measuring a spectrum containing a plurality of peaks and troughs within a predetermined wavelength range relative to a sample; using a first wavelength dispersion formula containing a wavelength dispersion coefficient, calculating the thickness of the sample for each wavelength represented by the peak or the trough, and tentatively determining the wavelength dispersion coefficient contained in the first wavelength dispersion formula under the condition that an evaluation value based on the calculated thickness will become maximum.驟; setting the order of a specific peak included in the plurality of peaks, and calculating a second wavelength dispersion formula based on the orders and wavelengths of the plurality of peaks; specifying the wavelength dispersion coefficient based on the first wavelength dispersion formula and the second wavelength dispersion formula containing the tentative wavelength dispersion coefficient under the order of the specific peak, and based on the specified order and the second wavelength dispersion formula; and calculating the delay based on the second wavelength dispersion formula containing the determined wavelength dispersion coefficient.