Film thickness measuring device and film thickness measuring method

Abstract

In this film thickness measurement device (1), a spectroscopic image (P) of measurement light (L) is received through a first pixel region (21A) for a first exposure time (T1), and a spectroscopic image (P) of measurement light (L) is received through a second pixel region (21B) for a second exposure time (T2) that is longer than the first exposure time (T1). Data in a long wavelength region in first measurement spectrum data (S1) obtained from the first pixel region (21A) and data in a short wavelength region in second measurement spectrum data (S2) obtained from the second pixel region (21B) are combined to generate analysis spectrum data (Ds).

Description

Technical Field

[0001] The present disclosure relates to a film thickness measurement device and a film thickness measurement method. Prior Art

[0002] In view of applications such as an on-line film thickness monitor, the development of a spectroscopic film thickness measurement device has been continuously evolving. The change amount of the reflectance spectrum with respect to the film thickness of a multilayer film tends to be larger in the ultraviolet light region than in the visible light region. Therefore, in the current situation of the development of device multilayerization and thinning, from the viewpoint of improving the measurement accuracy, it is considered effective to perform spectroscopy using light in the ultraviolet light region. However, when dealing with light in the ultraviolet light region, there are various technical problems such as stray light, dispersion, scattering, brightness, durability, and cost. In particular, when the intensity of light in the visible light region significantly exceeds that of light in the ultraviolet light region, in the detection system, the exposure time is limited within the range where the sensitivity to light in the visible light region is not saturated, and it is possible that it is difficult to obtain the sensitivity to light in the required ultraviolet light region.

[0003] Regarding such technical problems, for example, the film thickness measurement device described in Patent Document 1 includes: an optical unit having: an input unit to which light having wavelengths in the ultraviolet light region to the visible light region is input; an optical system that converges light in a state where chromatic aberration is generated; and an aperture that forms an image of light having wavelengths in the ultraviolet light region but does not form an image of light having wavelengths in the visible light region among the light in which chromatic aberration is generated. In this optical unit, the spectral intensity of the ultraviolet light region of the light output from the aperture can be relatively increased with respect to the spectral intensity of the visible light region.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication No. 2021 / 106299 Summary of the Invention

[0007] Technical Problems to be Solved by the Invention

[0008] In the film thickness measurement device of Patent Document 1 described above, the significant point is that the sensitivity of the detection system to obtain light in the required ultraviolet light region can form a spectrum most suitable for film thickness measurement. On the other hand, when such a device is applied to on-line film thickness measurement, it is necessary to consider the case where the reflection intensity (reflectivity) of the measurement light varies depending on the sample to be measured. For example, when calculating the film thickness by applying the curve fitting method to the reflectivity data of the measured sample, it is considered that the fitting is performed by taking into account the spectral intensity in the long wavelength region including the visible light region rather than the ultraviolet light region, thereby improving the accuracy of film thickness calculation. On this premise, from the viewpoint of improving the versatility of on-line film thickness measurement, a technique capable of arbitrarily adjusting the wavelength region where the spectral intensity is relatively increased, or the balance of the detection intensity of the measurement light in each wavelength region is required.

[0009] The present disclosure has been completed to solve the above problems, and an object thereof is to provide a film thickness measurement device and a film thickness measurement method capable of improving the versatility of on-line film thickness measurement.

[0010] Means for Solving Technical Problems

[0011] A film thickness measurement device according to an aspect of the present disclosure includes: a spectroscopic unit that spectroscopically disperses measurement light output from a light source and reflected by a sample; a detection unit that detects a spectroscopic image of the measurement light spectroscopically dispersed by the spectroscopic unit; a generation unit that generates analysis spectroscopic data using spectral data obtained from the detection result of the spectroscopic image of the measurement light; and an analysis unit that analyzes the film thickness of the sample based on the analysis spectroscopic data. The spectroscopic unit wavelength-disperses the measurement light in a first direction and images the spectroscopic image of each wavelength in a second direction intersecting the first direction. The detection unit has a first pixel region and a second pixel region divided in the second direction. The spectroscopic image of the measurement light is received through the first pixel region at a first exposure time, and the spectroscopic image of the measurement light is received through the second pixel region at a second exposure time longer than the first exposure time. The generation unit combines data in the long wavelength region in the first measurement spectral data obtained from the first pixel region and data in the short wavelength region in the second measurement spectral data obtained from the second pixel region to generate analysis spectroscopic data.

[0012] In this film thickness measuring device, data in the long wavelength region of the first measurement spectral data obtained with the first exposure time in the first pixel region and data in the short wavelength region of the second measurement spectral data obtained with the second exposure time longer than the first exposure time in the second pixel region are combined to generate spectral data for analysis used to analyze the film thickness of a sample. In the generated spectral data for analysis, data in the short wavelength region is included in a state where the sensitivity of the measurement light in the short wavelength region is sufficiently enhanced. Using such spectral data for analysis, curve fitting is performed on spectral data including the ultraviolet light region and the visible light region, thereby enabling improvement of the measurement accuracy of the film thickness. In addition, in this film thickness measuring device, since the first measurement spectral data and the second measurement spectral data are independently obtained through the first pixel region and the second pixel region, the boundary wavelength of the combination of the first measurement spectral data and the second measurement spectral data can be arbitrarily set when generating the spectral data for analysis. As a result, the intensity balance between the data in the long wavelength region and the data in the short wavelength region can also be arbitrarily adjusted. Therefore, even when the reflection intensity (reflectivity) of the measurement light varies depending on the sample, the acquisition conditions of the spectral data of the sample can be optimized, and the versatility of the on-line measurement of the film thickness can be improved.

[0013] The detection unit may also be a CCD (Charge Coupled Device) photodetector, and this CCD photodetector has: a first horizontal shift register that is transmitted with the charges generated by the respective columns of the first pixel region; and a second horizontal shift register that is transmitted with the charges generated by the respective columns of the second pixel region. According to such a configuration, it is possible to simultaneously perform the reading of the charges of the respective pixels corresponding to the spectroscopic image of the measurement light received in the first pixel region and the reading of the charges of the respective pixels corresponding to the spectroscopic image of the measurement light received in the second pixel region. In addition, by using a CCD photodetector, an increase in read noise when reading the charges generated by the pixels in each column can be avoided.

[0014] The detection unit may also be a CCD photodetector, and this CCD photodetector has: a first accumulation unit that accumulates the charges generated by the respective columns of the first pixel region; a second accumulation unit that accumulates the charges generated by the respective columns of the second pixel region; a first reading unit that outputs an electrical signal for each column corresponding to the magnitude of the charges accumulated by the first accumulation unit; and a second reading unit that outputs an electrical signal for each column corresponding to the magnitude of the charges accumulated by the second accumulation unit. According to such a configuration, it is also possible to simultaneously perform the reading of the charges of the respective pixels corresponding to the spectroscopic image of the measurement light received in the first pixel region and the reading of the charges of the respective pixels corresponding to the spectroscopic image of the measurement light received in the second pixel region. In addition, by using a CCD photodetector, an increase in read noise when reading the charges generated by the pixels in each column can be avoided.

[0015] The detection unit may also be a CMOS (Complementary Metal Oxide Semiconductor) optical detector, which has: a first readout unit that outputs the charges generated by the respective columns of the first pixel region; and a second readout unit that outputs the charges generated by the respective columns of the second pixel region. In such a configuration, it is also possible to simultaneously perform the readout of the charges of each pixel corresponding to the spectral image of the measurement light received in the first pixel region and the readout of the charges of each pixel corresponding to the spectral image of the measurement light received in the second pixel region.

[0016] The generation unit may also set the boundary wavelength between the data in the long wavelength region of the first measurement spectral data and the data in the short wavelength region of the second measurement spectral data when generating the spectral data for analysis, based on the exposure time ratio between the first pixel region and the second pixel region and the estimated value of the reflection spectral data of the sample. By using the exposure time ratio between the first pixel region and the second pixel region and the estimated value of the reflection spectral data of the sample as indicators, the data in the long wavelength region of the first measurement spectral data and the data in the short wavelength region of the second measurement spectral data can be combined in a state where the intensity balance between the first measurement spectral data and the second measurement spectral data is optimized. By performing curve fitting on such spectral data for analysis, the measurement accuracy of the film thickness can be further improved.

[0017] The generation unit may also set the boundary wavelength at a wavelength where the peak intensity of the measurement light contained in the data in the short wavelength region is 80% or more and less than 100% of the saturation intensity. Thereby, a further optimization of the intensity balance between the first measurement spectral data and the second measurement spectral data can be achieved.

[0018] The film thickness measurement method according to an embodiment of the present disclosure includes: a spectroscopic step of splitting the measurement light output from a light source and reflected by a sample; a detection step of detecting the spectral image of the measurement light split in the spectroscopic step; a generation step of generating spectral data for analysis using the spectral data obtained from the detection result of the spectral image of the measurement light; and an analysis step of analyzing the film thickness of the sample based on the spectral data for analysis. In the spectroscopic step, the measurement light is wavelength-dispersed in a first direction, and in a second direction intersecting the first direction, the spectral image of each wavelength is imaged. In the detection step, the first pixel region and the second pixel region divided in the second direction are used, and the spectral image of the measurement light is received by the first pixel region with a first exposure time and by the second pixel region with a second exposure time longer than the first exposure time. In the generation step, the data in the long wavelength region of the first measurement spectral data obtained from the first pixel region and the data in the short wavelength region of the second measurement spectral data obtained from the second pixel region are combined to generate the spectral data for analysis.

[0019] In this film thickness measurement method, data in the long wavelength region of the first measurement spectral data obtained at the first exposure time in the first pixel region and data in the short wavelength region of the second measurement spectral data obtained at the second exposure time longer than the first exposure time in the second pixel region are combined to generate spectral data for analysis for analyzing the film thickness of the sample. In the generated spectral data for analysis, data in the short wavelength region is included in a state where the sensitivity of the measurement light in the short wavelength region is sufficiently improved. Using such spectral data for analysis, curve fitting is performed on spectral data including the ultraviolet light region and the visible light region, thereby improving the measurement accuracy of the film thickness. Further, in this film thickness measurement method, since the first measurement spectral data and the second measurement spectral data can be independently obtained through the first pixel region and the second pixel region, when generating the spectral data for analysis, the boundary wavelength of the combination of the first measurement spectral data and the second measurement spectral data can be arbitrarily set. As a result, the intensity balance between the data in the long wavelength region and the data in the short wavelength region can also be arbitrarily adjusted. Therefore, even when the reflection intensity (reflectivity) of the measurement light varies depending on the sample, the acquisition conditions of the spectral data of the sample can be optimized, and the versatility of on-line measurement of the film thickness can be improved.

[0020] Effects of the Invention

[0021] According to the present disclosure, the versatility of on-line measurement of film thickness can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram showing a film thickness measurement apparatus according to an embodiment of the present disclosure.

[0023] Figure 2 is a schematic diagram showing an imaging state of a spectrogram of measurement light in the detection unit.

[0024] Figure 3 is a diagram showing an example of a CCD light detector constituting the detection unit.

[0025] Figure 4 is a diagram showing another example of a CCD light detector constituting the detection unit.

[0026] Figure 5 is a diagram showing another example of a CCD light detector constituting the detection unit.

[0027] Figure 6 is a diagram showing an example of a CMOS light detector constituting the detection unit.

[0028] Figure 7 is a flowchart showing a film thickness measurement method according to an embodiment of the present disclosure.

[0029] Figure 8(a) is a diagram showing an example of the first measurement spectral data, and (b) is a diagram showing an example of the second measurement spectral data.

[0030] Figure 9 (a) is a diagram showing an example of the first reference spectral data, and (b) is a diagram showing an example of the second reference spectral data.

[0031] Figure 10 (a) is a diagram showing an example of the spectral data for analysis, and (b) is a diagram showing an example of the reference spectral data for analysis.

[0032] Figure 11 (a) is a diagram showing an example of the reflectance spectral data obtained by the method of the comparative example, and (b) is a diagram showing an example of the reflectance spectral data obtained by the method of the example.

[0033] Figure 12 (a) is a schematic diagram showing the reflectance spectral data with respect to the reference specimen, (b) is a schematic diagram showing the approximate reflectance spectral data of the specimen, (c) is a schematic diagram showing the estimated value of the reflectance spectral data of the specimen, and (d) is a schematic diagram showing the relationship between the saturation intensity and the estimated value of the reflectance spectral data of the specimen.

[0034] Figure 13 is a schematic diagram showing an example of the setting of the boundary wavelength.

[0035] Figure 14 is a diagram showing the evaluation result of the reproducibility of the film thickness measurement of the comparative example.

[0036] Figure 15 is a diagram showing the evaluation result of the reproducibility of the film thickness measurement of the example.

[0037] Symbol Explanation

[0038] 1... Film thickness measuring device; 2... Light source; 5... Spectral splitting unit; 6... Detection unit; 7... Generation unit; 8... Analysis unit; 21A... First pixel region; 21B... Second pixel region; 32A... First horizontal shift register; 32B... Second horizontal shift register; 41A... First accumulation unit; 41B... Second accumulation unit; 42A... First readout unit; 42B... Second readout unit; 57A... First readout unit; 57B... Second readout unit; L... Measurement light; D1... First direction; D2... Second direction; M... Specimen; P... Spectral image; V1, V2... CCD photodetector; V3... CMOS photodetector; λr... Boundary wavelength. Detailed Description of the Invention

[0039] Hereinafter, with reference to the accompanying drawings, a preferred embodiment of a film thickness measuring apparatus and a film thickness measuring method according to one aspect of the present disclosure will be described in detail.

[0040] Figure 1 is a schematic diagram showing a film thickness measuring apparatus according to an embodiment of the present disclosure. Figure 1 The illustrated film thickness measuring apparatus 1 is configured, for example, as an apparatus for performing on-line measurement of the film thickness of a specimen M in a film forming step using a film forming chamber. Examples of the specimen M include an optical thin film, a thin film for a display panel, and a thin film for a semiconductor wafer. The film thickness measuring apparatus 1 includes a light source 2, an optical system 3, a measurement head 4, a spectroscopic unit 5, a detection unit 6, a generation unit 7, and an analysis unit 8.

[0041] The light source 2 is a device that outputs measurement light L to the specimen M. As the light source 2, for example, a white light source that outputs light in a wavelength range of 185 nm or more and 2000 nm or less is used. As the light source 2, for example, a light source that outputs pulsed light with a repetition frequency of 1 kHz or more (e.g., a xenon flash lamp) can be used.

[0042] The optical system 3 is a system that guides the measurement light L between the light source 2, the measurement head 4, and the spectroscopic unit 5. In the present embodiment, the optical system 3 includes a first optical fiber 9A and a second optical fiber 9B. The first optical fiber 9A is an optical fiber that guides the measurement light L from the light source 2 to the measurement head 4. The second optical fiber 9B is an optical fiber that guides the measurement light L from the measurement head 4 to the spectroscopic unit 5.

[0043] The measurement head 4 is a part that irradiates the specimen M with the measurement light L. The measurement head 4 is configured to include, for example, a half mirror and a condenser lens. The measurement light L input to the input end of the measurement head 4 from the light source 2 via the first optical fiber 9A is irradiated onto the specimen M via the half mirror and the condenser lens. The measurement light L reflected by the specimen M is output from the output end of the measurement head 4 via the condenser lens and the half mirror, and is input to the spectroscopic unit 5 via the second optical fiber 9B.

[0044] The spectroscopic unit 5 is a part that spectroscopically decomposes the measurement light L output from the light source 2 and reflected by the specimen M. As the spectroscopic unit 5, a spectroscope with good imaging properties is used. Examples of the spectroscope that constitutes the spectroscopic unit 5 include a Czerny-Turner type spectroscope, a Dyson type spectroscope, and an Offner type spectroscope that can perform astigmatism correction.

[0045] The spectroscopic unit 5, for example Figure 2 as shown, wavelength-disperses the measurement light L in the first direction D1, and forms an image of the spectroscopic image P of each wavelength in the second direction D2 that intersects the first direction D1. Here, the first direction D1 and the second direction D2 are orthogonal to each other. In Figure 2In the example, the first direction D1 is along the row direction of the pixel region 21 constituting the detection unit 6, and the second direction D2 is along the column direction of the pixel region 21.

[0046] The detection unit 6 is a part that detects the spectral image P of the measurement light L dispersed by the dispersion unit 5. As shown in Figure 2 , the detection unit 6 has a pixel region 21 that captures the spectral image P. In the pixel region 21, a plurality of pixels 22 are arranged in the row direction and the column direction. Figure 2 In the example, the row direction corresponding to the first direction D1 is along the wavelength dispersion direction of the spectral image P obtained by the dispersion unit 5, and the column direction corresponding to the second direction D2 is along the charge transfer direction of each pixel 22. Each pixel 22 receives the wavelength-dispersed spectral image P and generates and accumulates charges corresponding to the light intensity.

[0047] In Figure 2 's example, the pixel region 21 forms a horizontally long rectangular region in which the number of pixels in the row direction is larger than the number of pixels in the column direction. The pixel region 21 has a first pixel region 21A and a second pixel region 21B that are divided in the second direction D2. Here, the first pixel region 21A and the second pixel region 21B are divided at the center in the column direction. That is, in the pixel region 21, the pixels 22 on one side closer to the center in the column direction belong to the first pixel region 21A, and the pixels 22 on the other side closer to the center in the column direction belong to the second pixel region 21B.

[0048] The spectral image P linearly extends in the column direction of the pixel 22 and is respectively imaged on the first pixel region 21A and the second pixel region 21B in a state of being separated from each other in the row direction. In Figure 2 's example, one-half part of each of the five spectral images P of the measurement light L wavelength-dispersed by the dispersion unit 5 in the second direction D2 is imaged on the first pixel region 21A. In addition, the other half part of each of the five spectral images P of the measurement light L wavelength-dispersed by the dispersion unit 5 in the second direction D2 is imaged on the second pixel region 21B at the same timing as the imaging of the spectral image P in the first pixel region 21A. The detection unit 6 outputs data (first measurement spectral data S1) based on the detection result in the first pixel region 21A and data (second measurement spectral data S2) based on the detection result in the second pixel region 21B to the analysis unit 8.

[0049] The first exposure time T1 of each pixel 22 in the first pixel region 21A and the second exposure time T2 of each pixel 22 in the second pixel region 21B can be set independently of each other. The exposure time ratio T2 / T1 between the first pixel region 21A and the second pixel region 21B is set according to the type of the film of the specimen M and the like. The first exposure time T1 of the first pixel region 21A can also be set to be constant, and the second exposure time T2 of the second pixel region 21B can be adjusted according to the type of the film of the specimen M and the like.

[0050] The detection unit 6 can be constituted by, for example, a CCD photodetector or a CMOS photodetector. Figure 3 It is a diagram showing an example of the CCD photodetector constituting the detection unit. Figure 3 The shown CCD photodetector V1 is configured to include: a pixel region 21 including the above-mentioned first pixel region 21A and second pixel region 21B; a first horizontal shift register 32A corresponding to the first pixel region 21A; a second horizontal shift register 32B corresponding to the second pixel region 21B; and a plurality of dummy pixels 33.

[0051] The charge generated and accumulated by each pixel 22 in the first pixel region 21A is transferred to the first horizontal shift register 32A. At the time of transfer, the charges of the pixels 22 in each column are added up for each column in the first horizontal shift register 32A (vertical transfer), and the charges added up for each column are sequentially read out from the first horizontal shift register 32A (horizontal transfer). A voltage value corresponding to the amount of the charge read out from the first horizontal shift register 32A is output from the amplifier 34A. The voltage value output from the amplifier 34A is converted into a digital value by an AD (Analog-Digital) converter.

[0052] The charge generated and accumulated by each pixel 22 in the second pixel region 21B is transferred to the second horizontal shift register 32B. At the time of transfer, the charges of the pixels 22 in each column are added up for each column in the second horizontal shift register 32B (vertical transfer), and the charges added up for each column are sequentially read out from the second horizontal shift register 32B (horizontal transfer). A voltage value corresponding to the amount of the charge read out from the second horizontal shift register 32B is output from the amplifier 34B. The voltage value output from the amplifier 34B is converted into a digital value by an AD converter.

[0053] In the CCD light detector V1, the first exposure time T1 of the first pixel region 21A and the second exposure time T2 of the second pixel region 21B can be set by an electronic shutter, for example. The electronic shutter can be implemented by using a high-light overflow protection gate, for example. The output operation of the signal from the first pixel region 21A and the output operation of the signal from the second pixel region 21B are independently controlled, but preferably are synchronized with each other. In this case, it is possible to prevent the signal indicating the output operation of one party from repeating as noise with respect to the output signal of the output operation of the other party.

[0054] Figure 4 And Figure 5 FIG. is a diagram showing another example of the CCD light detector constituting the detection unit. Figure 4 And Figure 5 The CCD light detector V2 shown has: a conversion substrate 40; a first accumulation unit 41A that accumulates charges generated by each column of the first pixel region 21A; a second accumulation unit 41B that accumulates charges generated by each column of the second pixel region 21B; a first readout unit 42A that outputs column electrical signals corresponding to the magnitudes of the charges accumulated by the first accumulation unit 41A; and a second readout unit 42B that outputs column electrical signals corresponding to the magnitudes of the charges accumulated by the second accumulation unit 41B.

[0055] The conversion substrate 40 is arranged beside the pixel region 21 in the column direction. A voltage signal (drive signal) for controlling the charge transfer of the pixel 22 is supplied to the conversion substrate 40. The charges of the pixels 22 belonging to each column of the first pixel region 21A are transferred to the first accumulation unit 41A of each column based on the voltage signal supplied to the conversion substrate 40. The charges of the pixels 22 belonging to each column of the second pixel region 21B are transferred to the second accumulation unit 41B of each column based on the voltage signal supplied to the conversion substrate 40.

[0056] The first accumulation unit 41A is arranged at the end in the column direction of the first pixel region 21A for each column, and accumulates the charges generated by the pixels 22 in each column of the first pixel region 21A. The second accumulation unit 41B is arranged at the end in the column direction of the second pixel region 21B for each column, and accumulates the charges generated by the pixels 22 in each column of the second pixel region 21B. The first readout unit 42A is arranged at the rear stage of the first accumulation unit 41A at the end in the column direction of the first pixel region 21A, and the second readout unit 42B is arranged at the rear stage of the second accumulation unit 41B at the end in the column direction of the second pixel region 21B.

[0057] The first readout unit 42A is as Figure 4As shown, for example, it has a transistor 43A and a bonding pad 44A for signal output. The control terminal (gate) of the transistor 43A is electrically connected to the first accumulation unit 41A. One current terminal (drain) of the transistor 43A is electrically connected to the bonding pad 46A via a wiring 45A commonly provided for each column throughout the first pixel region 21A. A voltage of a specified magnitude is always applied to the bonding pad 46A.

[0058] The other current terminal (source) of the transistor 43A is electrically connected to the bonding pad 44A for signal output. A voltage corresponding to the first electrical signal output from the first accumulation unit 41A is applied to the control terminal of the transistor 43A. A current corresponding to the applied voltage is output from the other current terminal of the transistor 43A and taken out to the outside via the bonding pad 44A for signal output.

[0059] The second readout unit 42B is as Figure 5 As shown, for example, it has a transistor 43B and a bonding pad 44B for signal output. The control terminal (gate) of the transistor 43B is electrically connected to the second accumulation unit 41B. One current terminal (drain) of the transistor 43B is electrically connected to the bonding pad 46B via a wiring 45B commonly provided for each column throughout the second pixel region 21B. A voltage of a specified magnitude is always applied to the bonding pad 46B.

[0060] The other current terminal (source) of the transistor 43B is electrically connected to the bonding pad 44B for signal output. A voltage corresponding to the second electrical signal output from the second accumulation unit 41B is applied to the control terminal of the transistor 43B. A current corresponding to the applied voltage is output from the other current terminal of the transistor 43B and taken out to the outside via the bonding pad 44B for signal output.

[0061] Figure 6 This is a diagram showing an example of a CMOS photodetector that constitutes a detection unit. In the CMOS photodetector V3 shown in the figure, each pixel 22 that constitutes the pixel region 21 has a photodiode 51 and an amplifier 52. The photodiode 51 accumulates electrons (photoelectrons) generated by light input as charges. The amplifier 52 converts the charges accumulated in the photodiode 51 into an electrical signal and amplifies the converted signal.

[0062] The electrical signal amplified by the amplifier 52 is transmitted to the vertical signal lines 54 that connect the pixels 22 in the connection row direction through the switching of the selection switches 53 of the respective pixels 22. In each of the vertical signal lines 54, a CDS (correlated double sampling) circuit 55 is arranged. The CDS circuit 55 reduces the readout noise between the respective pixels 22 and temporarily stores the electrical signal transmitted to the vertical signal line 54. The CDS circuit 55 is electrically connected to the conversion unit 56. The conversion unit 56 converts the voltage value output from the amplifier 52 of each pixel 22 into a digital value. In the present embodiment, the conversion unit 56 is constituted by an A / D converter. The A / D converter converts the voltage value stored in the CDS circuit 55 into a digital value (pixel value).

[0063] The CMOS optical detector V3 includes: a first readout unit 57A that outputs the charges generated in each column of the first pixel region 21A; and a second readout unit 57B that outputs the charges generated in each column of the second pixel region 21B. The first readout unit 57A is connected to the A / D converter corresponding to the vertical signal line 54 of each pixel 22 belonging to the first pixel region 21A. The first readout unit 57A outputs the pixel values of each pixel 22 belonging to the first pixel region 21A. The second readout unit 57B is connected to the A / D converter corresponding to the vertical signal line 54 of each pixel 22 belonging to the second pixel region 21B. The second readout unit 57B outputs the pixel values of each pixel 22 belonging to the second pixel region 21B.

[0064] Return to Figure 1 , the generation unit 7 and the analysis unit 8 will be described. The generation unit 7 and the analysis unit 8 are physically constituted by, for example, a computer 9 having a processor such as a CPU (Central Processing Unit), storage media such as a RAM (Random Access Memory) and a ROM (Read only Memory). The computer 9 can also be a smart phone or a tablet terminal integrally equipped with a display unit or an input unit. The computer 9 can also be constituted by a microcomputer or an FPGA (Field-Programmable Gate Array).

[0065] The generation unit 7 is a part that generates analysis spectral data using the spectral data obtained from the detection result of the spectral image P of the measurement light L. The generation unit 7 combines the data S1L in the long wavelength region in the first measurement spectral data S1 obtained from the first pixel region 21A and the data S2S in the short wavelength region in the second measurement spectral data S2 obtained from the second pixel region 21B to generate the analysis spectral data Ds (refer to Figure 10(a)). The generation unit 7 outputs the generated spectral data Ds for analysis to the analysis unit 8.

[0066] In addition, the generation unit 7, for example, previously stores spectral data (reference spectral data) of the measurement light L of a reference specimen (not shown) that is known for the spectral reflectance data. The generation unit 7 combines the data R1L in the long wavelength region in the first reference spectral data R1 obtained from the first pixel region 21A and the data R2S in the short wavelength region in the second reference spectral data R2 obtained from the second pixel region 21B to generate reference spectral data Dr for analysis (see Figure 10 (b)). The generation unit 7 outputs the generated reference spectral data Dr for analysis to the analysis unit 8.

[0067] The analysis unit 8 is a part that analyzes the film thickness of the specimen M based on the spectral data Ds for analysis. The analysis unit 8 previously stores spectral data (reference reflectance spectral data Hr) related to the reflectance of the reference specimen. The analysis unit 8 calculates spectral data (reflectance spectral data Hs for analysis) related to the reflectance of the specimen M, which is the measurement object, based on the spectral data Ds for analysis and the reference spectral data Dr for analysis received from the generation unit 7 and the reference reflectance spectral data Hr. The analysis unit 8 analyzes the film thickness of the specimen M by curve fitting the calculated reflectance spectral data Hs for analysis and the theoretical reflectance spectral data.

[0068] Next, a film thickness measurement method according to an embodiment of the present disclosure will be described. Figure 7 is a flowchart showing a film thickness measurement method according to an embodiment of the present disclosure. As Figure 7 shown, this film thickness measurement method is configured to include a spectroscopic step S01, a detection step S02, a generation step S03, and an analysis step S04. Using the above film thickness measurement device 1, a film thickness measurement method including steps S01 to S04 is implemented.

[0069] The spectroscopic step S01 is a step of spectroscopically analyzing the measurement light L output from the light source 2 and reflected by the specimen M. In the spectroscopic step S01, first, the measurement head 4 is arranged for the specimen M whose film thickness is to be measured. After arranging the measurement head 4, the first exposure time T1 of the first pixel region 21A and the second exposure time T2 of the second pixel region 21B are respectively set. After setting the exposure time, the light source 2 is turned on, and the measurement light L is output from the light source 2. The measurement light L reflected by the specimen M is wavelength-dispersed by the spectroscopic unit 5.

[0070] The detection step S02 is a step of detecting the spectral image P of the measurement light L that has been spectroscopically analyzed by the spectroscopic step S01. In the detection step S02, in the first pixel region 21A and the second pixel region 21B of the detection unit 6, the spectral image P of the measurement light L that has been wavelength-dispersed in the wavelength dispersion direction (first direction D1) is respectively detected. In the detection step S02, the spectral image P of the measurement light L is received by the first pixel region 21A with the first exposure time T1, and the spectral image P of the measurement light L is received by the second pixel region 21B with the second exposure time T2 that is longer than the first exposure time T1. Thereby, the first measurement spectral data S1 from the first pixel region 21A and the second measurement spectral data S2 from the second pixel region 21B are respectively obtained.

[0071] The generation step S03 is a step of generating the analysis spectral data Ds using the spectral data obtained from the detection result of the spectral image P of the measurement light L. More specifically, in the generation step S03, the data S1L in the long wavelength region in the first measurement spectral data S1 obtained from the first pixel region 21A and the data S2S in the short wavelength region in the second measurement spectral data S2 obtained from the second pixel region 21B are combined (joined) to generate the analysis spectral data Ds. In addition, in the generation step S03, the data R1L in the long wavelength region in the first reference spectral data R1 and the data R2S in the short wavelength region in the second reference spectral data R2 are combined (mutually joined) to generate the analysis reference spectral data Dr.

[0072] Figure 8 (a) is a diagram showing an example of the first measurement spectral data S1. Figure 8 (b) is a diagram showing an example of the second measurement spectral data S2. Figure 8 (a) and Figure 8 (b) are examples of the first measurement spectral data S1 and the second measurement spectral data S2 when the sample M is a silicon wafer formed with a SiO2 film as the measurement object. In this case, the measurement light L reflected by the sample M has a certain intensity on the longer wavelength side than the ultraviolet light region, but has a tendency to be weaker in intensity in the ultraviolet light region compared to the long wavelength side.

[0073] The first measurement spectral data S1 is the data obtained by receiving the spectral image P of the measurement light L in the first pixel region 21A with the relatively short first exposure time T1. Figure 8 In the example of the first measurement spectral data S1 shown in (a), on the long wavelength side (for example, 300 nm or more), the intensity of the measurement light L is detected with a certain sensitivity, but on the short wavelength side (for example, less than 300 nm), a weaker intensity compared to the long wavelength side is detected.

[0074] The second measured spectral data S2 is data obtained from the spectral image P of the measurement light L received with a relatively long second exposure time T2 in the second pixel region 21B. Therefore, Figure 8 In the example of the second measured spectral data S2 shown in (b) of, in the long wavelength side (for example, 300 nm or more), the intensity of the measurement light L is saturated in most of it, and in the short wavelength side (for example, less than 300 nm), an intensity sufficient compared to the intensity on the short wavelength side of the first measured spectral data S1 is detected.

[0075] Figure 9 Figure (a) of is a diagram showing an example of the first reference spectral data R1. Figure 9 Figure (b) of is a diagram showing an example of the second reference spectral data R2. As described above, the reference spectral data is spectral data of the measurement light L for a reference specimen (not shown) for which the spectral reflectance data is known. Here, the reference specimen is a bare silicon wafer on which no SiO2 film is formed. In the present embodiment, the measurement light L reflected by the reference specimen is spectroscopically analyzed by the spectroscopic unit 5, and the spectral image is respectively detected in the first pixel region 21A and the second pixel region 21B of the detection unit 6, whereby the first reference spectral data R1 and the second reference spectral data R2 are acquired in advance.

[0076] The waveforms of the first reference spectral data R1 and the second reference spectral data R2 are based on the waveforms of the first measured spectral data S1 and the second measured spectral data S2. That is, Figure 9 In the example of the first reference spectral data R1 shown in (a) of, in the long wavelength side (for example, 300 nm or more), the intensity of the measurement light L is detected with a certain sensitivity, but in the short wavelength side (for example, less than 300 nm), an intensity weaker than that on the long wavelength side is detected. In Figure 9 In the example of the second reference spectral data R2 shown in (b) of, in the long wavelength side (for example, 300 nm or more), the intensity of the measurement light L is saturated in most of it, and in the short wavelength side (for example, less than 300 nm), an intensity sufficient compared to the intensity on the short wavelength side of the first reference spectral data R1 is detected.

[0077] Figure 10 Figure (a) of is a diagram showing an example of the spectral data for analysis, Figure 10 Figure (b) of is a diagram showing an example of the reference spectral data for analysis. Figure 10 In the example of (a) of, the boundary wavelength λr is set to 280 nm, and the data S1L in the long wavelength region of the first measured spectral data S1 and the data S2S in the short wavelength region of the second measured spectral data S2 are combined, whereby the spectral data Ds for analysis is generated. In the spectral data Ds for analysis, the intensity of the measurement light L on the long wavelength side is not saturated, and a state where the intensity of the measurement light L is also sufficiently obtained on the short wavelength side is achieved.

[0078] In the reference spectral data Dr for analysis, the same boundary wavelength λr is also used. Figure 10 In the example of (b), the boundary wavelength λr is set to 280 nm, and the data R1L in the long-wavelength region of the first reference spectral data R1 and the data R2S in the short-wavelength region of the second reference spectral data R2 are combined to generate the reference spectral data Dr for analysis. In the reference spectral data Dr for analysis, the intensity of the measurement light L on the long-wavelength side is also not saturated, and the intensity of the measurement light L is also sufficiently obtained on the short-wavelength side.

[0079] The boundary wavelength λr can be arbitrarily set by the user of the film thickness measuring device 1 according to the type of the specimen M, the reflection intensity (reflectance) with respect to the measurement light L, etc. In the case of a silicon wafer assuming that an SiO2 film is formed as the specimen M, for example, the boundary wavelength λr can be selected from the range of 200 nm or more and 500 nm or less, particularly a wavelength around 300 nm.

[0080] The analysis step S04 is a step of analyzing the film thickness of the specimen M based on the spectral data Ds for analysis. In a general film thickness calculation method, first, the reflectance spectral data of the specimen M is calculated by the following formula (1). Then, the film thickness of the specimen M is analyzed by curve fitting the calculated spectral data related to the reflectance of the specimen M and the theoretical reflectance spectral data.

[0081] Spectral data related to the reflectance of the specimen = (Reflectance spectral data of the specimen / Reflectance spectral data of the reference specimen) × Spectral data related to the reflectance of the reference specimen... (1)

[0082] In the present embodiment, calculating the spectral data related to the reflectance of a general specimen using the above formula (1) is equivalent to, for example, Figure 8 dividing the first measurement spectral data S1 shown in (a) of Figure 9 by the first reference spectral data R1 shown in (a) of Figure 11 and multiplying it by the reference reflectance spectral data Hr. The reflectance spectral data Hs' obtained in this way has a tendency that the S / N ratio is low throughout the entire measurement wavelength region as shown in (a) of

[0083] In contrast, in the present embodiment, the analysis reflectance spectral data Hs of the specimen M is calculated by the following formula (2). And, the film thickness of the specimen M is analyzed by curve fitting the calculated analysis reflectance spectral data and the theoretical reflectance spectral data.

[0084] Analysis reflectance spectral data = (Spectral data for analysis / Reference spectral data for analysis) × Spectral data related to the reflectance of the reference specimen... (2)

[0085] The reflectance spectral data for analysis of the present embodiment calculated using the above formula (2) is equivalent to Figure 10 the spectral data Ds for analysis shown in (a) of Figure 10 (that is, the data generated by combining the data S1L in the long wavelength region of the first measurement spectral data S1 and the data S2S in the short wavelength region of the second measurement spectral data S2) divided by Figure 11 the reference spectral data Dr for analysis shown in (b) of Figure 11 (that is, the data generated by combining the data R1L in the long wavelength region of the first reference spectral data R1 and the data R2S in the short wavelength region of the second reference spectral data R2), and multiplying the result by the reference reflectance spectral data Hr. As

[0086] shown in (b) of

[0087] In the sample M, if the layer structure, the optical characteristics of each layer, and the approximate thickness of each layer are known, the approximate reflectance spectral data can be calculated. Therefore, by multiplying the approximate reflectance spectral data Q1 of the sample M (refer to Figure 12 (b)) by the reflectance spectral data P1 of the reference sample (refer to Figure 12 (a)), the estimated value F of the reflectance spectral data of the sample M can be calculated (refer to Figure 12 (c)). Further, by multiplying the calculated estimated value of the reflectance spectral data of the sample M by the exposure time ratio T2 / T1, the relationship between the saturation intensity and the estimated value F of the reflectance spectral data of the sample M can be obtained (refer to Figure 12 (d)).

[0088] Next, as Figure 13 shown, based on the relationship between the saturation intensity and the estimated value F of the reflectance spectral data of the sample M, the wavelength range λw in which the peak intensity of the measurement light L contained in the data in the short wavelength region is 80% or more and less than 100% of the saturation intensity is calculated, and the boundary wavelength λr is set from the range of λw. Figure 13 In the example of

[0089] The setting of the boundary wavelength λr is not limited to the above method and can be set to any value by the user of the film thickness measuring device 1. In this case, for example, the second measurement spectral data S2 can also be displayed on the monitor, and within the wavelength range where the intensity of the measurement light L is not saturated in the displayed second measurement spectral data S2, the user of the film thickness measuring device 1 can set the boundary wavelength λr.

[0090] As described above, in the film thickness measuring device 1 and the film thickness measuring method of the present embodiment, the data S1L in the long wavelength region of the first measurement spectral data S1 obtained at the first exposure time T1 in the first pixel region 21A is combined with the data S2S in the short wavelength region of the second measurement spectral data S2 obtained at the second exposure time T2 longer than the first exposure time T1 in the second pixel region 21B to generate the analysis spectral data Ds for analyzing the film thickness of the specimen M. In the generated analysis spectral data Ds, the data in the short wavelength region is included in a state where the sensitivity of the measurement light in the short wavelength region is sufficiently improved. By using such analysis spectral data Ds to perform curve fitting on the spectral data including the ultraviolet light region and the visible light region, the measurement accuracy of the film thickness can be improved.

[0091] In addition, in the film thickness measuring device 1 and the film thickness measuring method of the present embodiment, since the first measurement spectral data S1 and the second measurement spectral data S2 are independently obtained through the first pixel region 21A and the second pixel region 21B, when generating the analysis spectral data Ds, the boundary wavelength λr for the combination of the first measurement spectral data S1 and the second measurement spectral data S2 can be arbitrarily set. As a result, the intensity balance between the data S1L in the long wavelength region and the data S2S in the short wavelength region can be arbitrarily adjusted. Therefore, even when the reflection intensity (reflectivity) of the measurement light L varies depending on the specimen M, the acquisition conditions for the spectral data of the specimen M can be optimized, and the versatility of the on-line measurement of the film thickness can be improved.

[0092] In the present embodiment, the detection unit 6 can be constituted by a CCD photodetector V1, and the CCD photodetector V1 has: a first horizontal shift register 32A that transfers the charges generated by each column of the first pixel region 21A; and a second horizontal shift register 32B that transfers the charges generated by each column of the second pixel region 21B. With such a configuration, the reading of the charges of each pixel 22 corresponding to the spectral image P of the measurement light L received in the first pixel region 21A and the reading of the charges of each pixel 22 corresponding to the spectral image P of the measurement light L received in the second pixel region 21B can be simultaneously performed. In addition, by using the CCD photodetector V1, an increase in the reading noise when reading the charges generated by the pixels 22 in each column can be avoided.

[0093] In this embodiment, the detection unit 6 may be constituted by a CCD photodetector V2. The CCD photodetector V2 includes: a first accumulation unit 41A that accumulates charges generated by each column of the first pixel region 21A; a second accumulation unit 41B that accumulates charges generated by each column of the second pixel region 21B; a first readout unit 42A that outputs column electrical signals corresponding to the magnitudes of the charges accumulated by the first accumulation unit 41A; and a second readout unit 42B that outputs column electrical signals corresponding to the magnitudes of the charges accumulated by the second accumulation unit 41B. In such a configuration, the readout of the charges of each pixel 22 corresponding to the spectral image P of the measurement light L received in the first pixel region 21A and the readout of the charges of each pixel 22 corresponding to the spectral image P of the measurement light L received in the second pixel region 21B can be performed simultaneously. In addition, by using the CCD photodetector V2, an increase in readout noise when reading out the charges generated by the pixels in each column can be avoided.

[0094] In this embodiment, the detection unit 6 may be constituted by a CMOS photodetector V3. The CMOS photodetector V3 includes: a first readout unit 57A that outputs charges generated by each column of the first pixel region 21A; and a second readout unit 57B that outputs charges generated by each column of the second pixel region 21B. In such a configuration, the readout of the charges of each pixel 22 corresponding to the spectral image P of the measurement light L received in the first pixel region 21A and the readout of the charges of each pixel 22 corresponding to the spectral image P of the measurement light L received in the second pixel region 21B can be performed simultaneously.

[0095] In this embodiment, the generation unit 7 sets the boundary wavelength λr between the data S1L in the long wavelength region of the first measurement spectral data S1 and the data S2S in the short wavelength region of the second measurement spectral data S2 when generating the analysis spectral data Ds, based on the exposure time ratio T2 / T1 between the first pixel region 21A and the second pixel region 21B and the estimated value F of the reflection spectral data of the specimen M. By using the exposure time ratio T2 / T1 between the first pixel region 21A and the second pixel region 21B and the estimated value F of the reflection spectral data of the specimen M as indices, the data S1L in the long wavelength region of the first measurement spectral data S1 and the data S2S in the short wavelength region of the second measurement spectral data S2 can be combined in a state where the intensity balance between the first measurement spectral data S1 and the second measurement spectral data S2 is optimized. By performing curve fitting on such analysis spectral data Ds, the measurement accuracy of the film thickness can be further improved.

[0096] In the present embodiment, the generation unit 7 sets the boundary wavelength λr at a wavelength at which the peak intensity of the measurement light L contained in the data in the short wavelength region is 80% or more and less than 100% of the saturation intensity. Thereby, further optimization of the intensity balance between the first measurement spectral data S1 and the second measurement spectral data S2 can be achieved.

[0097] The evaluation test results of the film thickness measurement device and the film thickness measurement method of the present disclosure will be described. Figure 14 It is a graph showing the evaluation results of the reproducibility of film thickness measurement in the comparative example. In addition, Figure 15 It is a graph showing the evaluation results of the reproducibility of film thickness measurement in the example. In this evaluation test, a silicon wafer on which a SiO2 film was formed was used as a sample, and after performing film thickness measurement of the SiO2 film 10 times, the average value and standard deviation of the measurement results were calculated. The film thicknesses of the SiO2 films of the samples were set to three types: 1 nm, 5 nm, and 10 nm.

[0098] In the comparative example, reflectance spectral data obtained by a general calculation method (refer to Figure 11 (a)) was used to perform curve fitting between the reflectance spectral data of the sample and the theoretical reflectance spectral data. In the example, reflectance spectral data obtained by the calculation method of the present embodiment (refer to Figure 11 (b)) was used to perform curve fitting between the reflectance spectral data of the sample and the theoretical reflectance spectral data.

[0099] As Figure 14 shown, in the comparative example, the average value of the measurement results for the sample with a film thickness of 1 nm was 0.57, and the standard deviation was 0.25. The average value of the measurement results for the sample with a film thickness of 5 nm was 2.33, and the standard deviation was 0.21. The average value of the measurement results for the sample with a film thickness of 10 nm was 4.9, and the standard deviation was 0.2.

[0100] In contrast, as Figure 15 shown, in the example, the average value of the measurement results for the sample with a film thickness of 1 nm was 1.29, and the standard deviation was 0.09. The average value of the measurement results for the sample with a film thickness of 5 nm was 4.95, and the standard deviation was 0.10. The average value of the measurement results for the sample with a film thickness of 10 nm was 9.85, and the standard deviation was 0.05. From this result, it can be confirmed that the method of the present embodiment improves the measurement accuracy of the film thickness and further contributes to improving the reproducibility.

Claims

1. A film thickness measuring device, wherein, it comprises: a spectroscopic unit that spectroscopically analyzes the measurement light output from a light source and reflected by a specimen; a detection unit that detects the spectroscopic image of the measurement light spectroscopically analyzed by the spectroscopic unit; a generation unit that generates spectroscopic data for analysis using the spectroscopic data obtained from the detection result of the spectroscopic image of the measurement light; and an analysis unit that analyzes the film thickness of the specimen based on the spectroscopic data for analysis, the spectroscopic unit wavelength-disperses the measurement light in a first direction and images the spectroscopic image of each wavelength in a second direction intersecting the first direction; the detection unit has a first pixel region and a second pixel region divided in the second direction, receives the spectroscopic image of the measurement light through the first pixel region with a first exposure time, and receives the spectroscopic image of the measurement light through the second pixel region with a second exposure time longer than the first exposure time; the generation unit combines the data in the long wavelength region in the first measurement spectroscopic data obtained from the first pixel region with the data in the short wavelength region in the second measurement spectroscopic data obtained from the second pixel region to generate the spectroscopic data for analysis.

2. The film thickness measuring device according to claim 1, wherein, the detection unit is a CCD photodetector, and the CCD photodetector has: a first horizontal shift register that is transmitted the charges generated by each column of the first pixel region; and a second horizontal shift register that is transmitted the charges generated by each column of the second pixel region.

3. The film thickness measuring device according to claim 1, wherein, the detection unit is a CCD photodetector, and the CCD photodetector has: a first accumulation unit that accumulates the charges generated by each column of the first pixel region; a second accumulation unit that accumulates the charges generated by each column of the second pixel region; a first readout unit that outputs the electrical signals of each column corresponding to the magnitude of the charges accumulated by the first accumulation unit; and a second readout unit that outputs the electrical signals of each column corresponding to the magnitude of the charges accumulated by the second accumulation unit.

4. The film thickness measuring device according to claim 1, wherein, the detection unit is a CMOS photodetector, and the CMOS photodetector has: a first readout unit that outputs the charges generated by each column of the first pixel region; and a second readout unit that outputs the charges generated by each column of the second pixel region.

5. The film thickness measuring device according to any one of claims 1 to 4, wherein, the generation unit sets the boundary wavelength between the data in the long wavelength region in the first measurement spectroscopic data and the data in the short wavelength region in the second measurement spectroscopic data when generating the spectroscopic data for analysis based on the exposure time ratio between the first pixel region and the second pixel region and the estimated value of the reflection spectroscopic data in the specimen.

6. The film thickness measuring device according to claim 5, wherein, the generation unit sets the boundary wavelength at a wavelength at which the peak intensity of the measurement light contained in the data in the short wavelength region is 80% or more and less than 100% of the saturation intensity.

7. A film thickness measurement method, wherein: Comprising: A spectroscopic step of spectroscopically analyzing the measurement light output from a light source and reflected by a sample; A detection step of detecting the spectroscopic image of the measurement light spectroscopically analyzed by the spectroscopic step; A generation step of generating spectroscopic data for analysis using the spectral data obtained from the detection result of the spectroscopic image of the measurement light; and An analysis step of analyzing the film thickness of the sample based on the spectroscopic data for analysis, In the spectroscopic step, the measurement light is wavelength-dispersed in a first direction, and the spectroscopic image of each wavelength is imaged in a second direction intersecting the first direction; In the detection step, using a first pixel region and a second pixel region divided in the second direction, the spectroscopic image of the measurement light is received by the first pixel region at a first exposure time, and the spectroscopic image of the measurement light is received by the second pixel region at a second exposure time longer than the first exposure time; In the generation step, the data in the long wavelength region in the first measurement spectral data obtained from the first pixel region and the data in the short wavelength region in the second measurement spectral data obtained from the second pixel region are combined to generate the spectroscopic data for analysis.

Images