Level difference measurement device, image processing device, level difference measurement method, and program

Abstract

In the present invention, a conversion unit (311): acquires information on optical path difference and amplitude by performing analysis, which is based on discrete Fourier transform, on spectral interference data regarding a measurement region on the surface of a measurement target, the spectral interference data having been obtained by performing imaging using an optical interference method that employs irradiation light having a plurality of wavelengths; and generates optical path difference information indicating a distribution of a first value based on the optical path difference in the measurement region, and amplitude information indicating a distribution of a second value based on the amplitude in the measurement region A selection unit (312) selects a correction region from among measurement regions on the basis of the amplitude information. A correction unit (313) corrects the first value in the optical path difference information on the basis of a distribution of a first value in the correction region. An output unit (314) outputs output information indicating a distribution of level difference in the measurement region, the output information being generated by the correction made by the correction unit (313).

Description

Step measuring device, image processing device, step measuring method and program

[0001] The present invention relates to a step measurement device, an image processing device, a step measurement method, and a program.

[0002] There are known techniques for measuring unevenness on the surface of an object. For example, a white light interferometer is used to measure the height and depth of unevenness on the surface of an object based on the intensity of light interference caused by an optical path difference. Patent Document 1 (JP-A-2005-102666) discloses an apparatus for performing absolute measurement of two-dimensional optical path distribution using an interferometry method, which can be applied to measuring the surface shape of an object.

[0003] JP 2012-533746 A

[0004] When measuring such steps, errors occur due to vibration, tilt, and the like. In particular, conventional white light interferometers are susceptible to vibration, and therefore require the use of a vibration-damping mechanism such as a vibration-isolating table. Meanwhile, the method disclosed in Patent Document 1 can track vibration, but is difficult to automate, posing a problem of requiring human labor to eliminate the effects of errors. In light of these circumstances, there is a need for a method for measuring steps present on the surface of an object with high accuracy, without the need for a vibration-damping mechanism, and while reducing human labor.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a step measurement device or the like that does not require a vibration control mechanism and is capable of measuring steps present on the surface of an object with high accuracy while reducing human labor.

[0006] In order to achieve the above object, a step measurement device according to a first aspect of the present invention is a step measurement device that measures steps present on a surface of a measurement object, and includes: an imaging unit that acquires spectral interference data of a measurement area on the surface of the measurement object by imaging with an optical interference method using irradiation light having a plurality of wavelengths; a conversion unit that acquires information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on the spectral interference data acquired by the imaging unit, and generates optical path difference information that indicates a distribution of first values ​​based on the optical path difference in the measurement area and amplitude information that indicates a distribution of second values ​​based on the amplitude in the measurement area; a selection unit that selects a correction area from the measurement area based on the amplitude information acquired by the conversion unit; a correction unit that corrects the first value in the optical path difference information acquired by the conversion unit based on the distribution of the first values ​​in the correction area selected by the selection unit; and an output unit that outputs output information that indicates the distribution of steps in the measurement area, generated by the correction by the correction unit.

[0007] In order to achieve the above object, an image processing device according to a second aspect of the present invention comprises: a conversion unit that acquires information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on spectral interference data of a measurement region on the surface of a measurement object, obtained by imaging using an optical interference method using irradiation light having a plurality of wavelengths, and generates optical path difference information indicating a distribution of first values ​​based on the optical path difference in the measurement region and amplitude information indicating a distribution of second values ​​based on the amplitude in the measurement region; a selection unit that selects a correction region from the measurement region based on the amplitude information acquired by the conversion unit; a correction unit that corrects the first value in the optical path difference information acquired by the conversion unit based on the distribution of the first values ​​in the correction region selected by the selection unit; and an output unit that outputs output information that indicates the distribution of steps in the measurement region, generated by the correction by the correction unit.

[0008] In order to achieve the above object, a step measurement method according to a third aspect of the present invention is a step measurement method for measuring steps present on a surface of a measurement object, comprising: an imaging step of acquiring spectral interference data in a measurement area on the surface of the measurement object by imaging with an optical interference method using irradiation light having a plurality of wavelengths; a conversion step of performing an analysis based on a discrete Fourier transform on the spectral interference data acquired in the imaging step to acquire information on optical path difference and amplitude, and generating optical path difference information indicating a distribution of first values ​​based on the optical path difference in the measurement area and amplitude information indicating a distribution of second values ​​based on the amplitude in the measurement area; a selection step of selecting a correction area from the measurement area based on the amplitude information acquired in the conversion step; a correction step of correcting the first value in the optical path difference information acquired in the conversion step based on the distribution of the first values ​​in the correction area selected in the selection step; and a measurement step of measuring the step based on information generated by the correction in the correction step.

[0009] In order to achieve the above object, a program according to a fourth aspect of the present invention causes a computer to function as: a conversion unit that acquires information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on spectral interference data of a measurement region on the surface of a measurement object, obtained by imaging using an optical interference method using irradiation light having a plurality of wavelengths, and generates optical path difference information that indicates a distribution of first values ​​based on the optical path difference in the measurement region and amplitude information that indicates a distribution of second values ​​based on the amplitude in the measurement region; a selection unit that selects a correction region from the measurement region based on the amplitude information acquired by the conversion unit; a correction unit that corrects the first value in the optical path difference information acquired by the conversion unit based on the distribution of the first values ​​in the correction region selected by the selection unit; and an output unit that outputs output information that indicates the distribution of steps in the measurement region, generated by the correction by the correction unit.

[0010] According to the present invention, steps present on the surface of an object can be measured with high accuracy without the need for a vibration damping mechanism and while reducing human effort.

[0011] FIG. 1 is a schematic diagram showing the overall configuration of a step measurement device according to embodiment 1. FIG. 2 is a diagram showing an area where object light is irradiated onto a measurement target in embodiment 1. FIG. 3 is a diagram showing an example of an interference fringe image of one shot in embodiment 1. FIG. 4 is a diagram showing an example of spectral interference data in embodiment 1. FIG. 5 is a block diagram showing the configuration of an image processing device according to embodiment 1. FIG. 6 is a first diagram showing the relationship between data generated in an image processing device according to embodiment 1. FIG. 7 is a diagram showing an example of deriving optical path difference and amplitude information from wavelength information in embodiment 1. FIG. 8 is a diagram showing an example of optical path difference information in embodiment 1. FIG. 9 is a diagram showing an example of amplitude information in embodiment 1. FIG. 10 is a diagram showing an example of deriving a reference range from amplitude information in embodiment 1. FIG. 11 is a diagram showing an example of binarized information in embodiment 1. FIG. 12 is a second diagram showing the relationship between data generated in an image processing device according to embodiment 1. FIG. 13 is a diagram showing an example of vibration correction data in embodiment 1. FIG. 14 is a diagram showing an example of tilt correction data in embodiment 1. FIG. 15 is a diagram showing an example of display of surface height information in embodiment 1. FIG. 16 is a flowchart showing the flow of step measurement processing executed by a step measurement device according to embodiment 1. FIG. 17 is a diagram showing the relationship between data generated in an image processing device according to embodiment 2. FIG. 18 is a diagram showing an example of tilt correction data in embodiment 2. 10A and 10B are diagrams showing the amplitude of an interference fringe pattern depending on the optical path difference when the wavelength resolution is ideal in embodiment 3. FIG. 10B are diagrams showing the amplitude of an interference fringe pattern depending on the optical path difference when the wavelength resolution is high in embodiment 3. FIG. 10C are diagrams showing the amplitude of an interference fringe pattern depending on the optical path difference when the wavelength resolution is low in embodiment 3.

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, in which the same or corresponding parts are designated by the same reference numerals.

[0013] 1 shows the overall configuration of a step measurement device 1 according to embodiment 1. The step measurement device 1 includes a transfer stage 5, an imaging device 10, and an image processing device 30. The step measurement device 1 is a device that captures an image of a measurement object 3 using an optical interference method to obtain an image showing the distribution of the surface height of the measurement object 3, and measures steps present on the surface of the measurement object 3 based on the obtained image.

[0014] <Measurement object 3> The measurement object 3 is an object that is the target of step measurement by the step measurement device 1. One example of the measurement object 3 is a semiconductor wafer having a fine pattern formed on its surface. The fine pattern is, for example, a wiring pattern or a MEMS (Micro Electro Mechanical Systems) structure. The step measurement device 1 measures the fine steps formed by such fine patterns on the surface of the semiconductor wafer. Note that the measurement object 3 is not limited to a semiconductor wafer, and may be any object that has fine steps on its surface.

[0015] More specifically, the measurement target 3 has a plurality of regions formed of different materials on its surface. Here, the plurality of regions formed of different materials refers to, for example, regions formed of metal such as wiring portions, regions formed of silicon such as semiconductor portions, etc. The step measurement device 1 measures steps that exist between such regions of different materials.

[0016] The transfer stage 5 transfers the measurement object 3 along a predetermined transfer path in a predetermined direction (+X direction in the example of FIG. 1 ) at a predetermined transfer speed V. Hereinafter, the transfer direction in which the measurement object 3 is transferred by the transfer stage 5 is defined as the X direction, the width direction of the measurement object 3 transferred by the transfer stage 5 is defined as the Y direction, and the vertical direction is defined as the Z direction. The X direction is also referred to as the time axis direction (first coordinate axis direction), and the Y direction is also referred to as the space axis direction (second coordinate axis direction).

[0017] <Imaging device (imaging section) 10> The imaging device 10 is a unit that captures an image of the measurement target 3 by capturing an image of the measurement target 3. The imaging device 10 is disposed above the measurement target 3 that is being transported by the transport stage 5, and captures an image of the upper surface of the measurement target 3. The imaging device 10 may also be called an imaging section.

[0018] Specifically, the imaging device 10 is an optical interferometer that captures an image of the surface of the measurement target 3 by an optical interference method using irradiation light having a plurality of wavelengths, and obtains an image of an interference fringe pattern. Here, the optical interference method may be a Michelson type or a Mirau type.

[0019] More specifically, as shown in FIG. 1, the imaging device 10 includes an illumination unit 11, a lens unit 12, a reference mirror 13, a spectroscopic unit 14, and an area sensor 15.

[0020] The illumination unit 11 is a unit that irradiates the measurement target 3 with light. The illumination unit 11 includes a light source that emits light having multiple wavelengths, for example, in the wavelength range from visible light to near-infrared. Specifically, the light source is a low-coherence light source that emits low-coherence light. Note that the light source may be a white light source that emits white light, as long as it is a light source that emits light having multiple wavelengths.

[0021] The illumination unit 11 emits low-coherence light, which is irradiation light having a plurality of wavelengths emitted from a light source, to the outside via a light-guiding member and an internal filter of the light source (not shown), and irradiates the light toward the lens unit 12. The light-guiding member guides the low-coherence light emitted from the light source into a linear emission light that extends long in the width direction (Y direction) of the measurement target 3.

[0022] The lens unit 12 is a unit for irradiating the low-coherence light incident from the illumination unit 11 onto the measurement target 3. The lens unit 12 is a coaxial epi-illumination optical system, and is arranged in a direction perpendicular to the surface of the measurement target 3 being transported by the transport stage 5.

[0023] More specifically, the lens unit 12 includes a beam splitter that splits the low-coherence light incident from the illumination unit 11 into object light and reference light. The object light is emitted from the lens unit 12 in the −Z direction and is perpendicularly irradiated onto the upper surface of the measurement target 3 being transported on the transport stage 5. In contrast, the reference light is emitted from the lens unit 12 in the +X direction and is guided to the reference mirror 13.

[0024] 2, the object light emitted from the lens unit 12 is irradiated onto a thin linear irradiation area on the surface of the object 3, which extends elongatedly in the width direction (Y direction) of the object 3 and extends in the conveying direction (X direction). Here, the length of the irradiation area in the conveying direction (X direction) is represented as Dx, and the length of the irradiation area in the width direction (Y direction) is represented as Dy. The irradiation area defined by such lengths Dx and Dy corresponds to the imaging area of ​​one shot by the imaging device 10. The object light irradiated onto the object 3 is reflected by the surface of the object 3, travels in the +Z direction, and enters the lens unit 12 again.

[0025] The reference mirror 13 is disposed in the +X direction with respect to the lens unit 12, and reflects the reference light emitted from the lens unit 12. The reference light reflected by the reference mirror 13 travels in the −X direction and enters the lens unit 12 again.

[0026] The lens unit 12 generates interference light by recombining the object light reflected by the surface of the object 3 and the reference light reflected by the reference mirror 13 in the beam splitter. Interference occurs in the interference light according to the optical path difference between the optical path of the object light and the optical path of the reference light. The lens unit 12 outputs the interference light to the spectroscopic unit 14.

[0027] The spectroscopic unit 14 separates the interference light incident from the lens unit 12 into wavelengths. The spectroscopic unit 14, together with the area sensor 15, constitutes a hyperspectral camera. More specifically, the spectroscopic unit 14 includes a slit for narrowing the interference light incident from the lens unit 12 and a spectroscopic element using a diffraction grating, both of which are not shown. The spectroscopic unit 14 separates the interference light that has passed through the slit using the spectroscopic element. The spectroscopic element diffracts the interference light at different angles depending on the wavelength. This converts the wavelength information of the interference light into position information. In this way, the spectroscopic unit 14 converts the line-shaped interference light incident from the lens unit 12 into two-dimensional information, where the first axis represents spatial information in the width direction (Y direction) of the object 3 and the second axis represents wavelength information, and outputs the information to the area sensor 15.

[0028] The area sensor 15 is an image sensor that is sensitive to the wavelength range of the low-coherence light irradiated from the illumination unit 11. The area sensor 15 is an imaging element such as a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), etc. The area sensor 15 receives the interference light dispersed by the spectroscopic unit 14 with an image sensor and generates an interference fringe image with the width direction (Y direction) of the measurement target 3 as a first axis and wavelength information as a second axis.

[0029] The interference light incident on the area sensor 15 is photoelectrically converted by a photodiode and read out as a signal by a readout circuit (not shown). The readout circuit includes, for example, an A / D (Analog / Digital) converter that converts an analog signal representing an image captured by the area sensor 15 into digital data. The signal read out by the area sensor 15 is output to the image processing device 30.

[0030] With this configuration, the imaging device 10 images the surface of the object 3 by optical interference using irradiation light having multiple wavelengths, and acquires spectral interference data for a measurement region R0 on the surface of the object 3. Fig. 3 shows an example of a one-shot interference fringe image 50 captured by the imaging device 10. The horizontal axis of the interference fringe image 50 represents the position in the spatial axis direction (Y direction), which is the width direction of the object 3, and the vertical axis of the interference fringe image 50 represents the wavelength of the interference light. The length of the interference fringe image 50 in the spatial axis direction (Y direction) corresponds to the length Dy of the object 3 in the width direction.

[0031] The interference fringe image 50 represents an interference fringe pattern caused by interference in the vertical axis direction. In the interference fringe pattern, constructive and destructive wavelengths alternate depending on the optical path difference between the object light and the reference light. As the optical path difference changes, the constructive and destructive wavelengths also change, so the surface height of the measurement target 3 can be derived from the interference fringe pattern.

[0032] 3 shows an example of an interference fringe pattern when a step exists at position P on the surface of the measurement target 3. When a step exists, the optical path difference changes discontinuously with the step as the boundary, and therefore the interference fringe pattern changes discontinuously in the spatial axis direction with position P as the boundary. The step at position P can be measured based on the degree of this change.

[0033] The imaging device 10 repeatedly captures images of linear imaging regions on the surface of the object 3 as the object 3 is transported in a predetermined transport direction, thereby repeatedly acquiring such interference fringe images 50. In this way, the imaging device 10 acquires spectral interference data 51 as shown in Fig. 4. The spectral interference data 51 is three-dimensional array information configured by arranging a plurality of interference fringe images 50 in the time axis direction (X direction), which is the transport direction of the object 3, in the chronological order in which they were acquired.

[0034] More specifically, the imaging device 10 acquires an interference fringe image 50 each time the measurement target 3 is transported by the transport stage 5 a distance Dx. The distance Dx corresponds to one pixel in the time axis direction of the spectral interference data 51. When the spectral interference data 51 includes N interference fringe images 50, the measurement region R0 of the spectral interference data 51 corresponds to a range on the surface of the measurement target 3 whose length in the spatial axis direction (Y direction) is Dy and whose length in the time axis direction (X direction) is Dx×N. By repeatedly capturing images of the measurement target 3 transported by the transport stage 5 in this manner, the imaging device 10 can acquire an interference fringe pattern in a wide measurement region R0 on the surface of the measurement target 3.

[0035] As described above, the imaging device 10 uses low-coherence optical interference technology and a hyperspectral camera in combination to disperse the line-shaped interference light, and obtains spectral interference data 51 by continuously capturing images of the measurement object 3 being transported by the transport stage 5.

[0036] 1 , the image processing device 30 performs image processing based on the spectral interference data 51 acquired by the imaging device 10, and generates information for measuring the surface height and surface step of the measurement target 3. Specifically, the image processing device 30 is an information processing device such as a personal computer or a cloud server. The image processing device 30 may be integrated with the imaging device 10 to form a single unit, or may be located remotely from the imaging device 10.

[0037] More specifically, as shown in FIG. 5, the image processing device 30 includes a control unit 31, a storage unit 32, an operation unit 33, a display unit 34, and a communication unit 35.

[0038] The control unit 31 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU includes a microprocessor and is a central processing unit that executes various processes and calculations. In the control unit 31, the CPU reads out a control program stored in the ROM and controls the overall operation of the image processing device 30 while using the RAM as a work memory. The control unit 31 may also include a processor for image processing, such as a DSP (Digital Signal Processor) or a GPU (Graphics Processing Unit).

[0039] The storage unit 32 is a non-volatile memory such as a flash memory, a hard disk, etc. The storage unit 32 stores programs and data executed by the control unit 31, and data generated by the control unit 31.

[0040] The operation unit 33 includes input devices such as a keyboard, a mouse, and a touch panel, and receives operation inputs from the user.

[0041] The display unit 34 includes a display device such as a liquid crystal display or an organic EL (Electro Luminescence) display, and displays various images under the control of the control unit 31. For example, the display unit 34 displays an image showing the evaluation results obtained by the step measurement device 1.

[0042] The communication unit 35 includes a communication interface for communicating with devices external to the image processing device 30. For example, the communication unit 35 communicates with the external devices in accordance with well-known communication standards such as a local area network (LAN) or a universal serial bus (USB). Here, the external devices include the imaging device 10. For example, the communication unit 35 communicates with the imaging device 10 and acquires the spectral interference data 51 acquired by the imaging device 10.

[0043] The control unit 31 functionally includes a conversion unit 311, a selection unit 312, a correction unit 313, and an output unit 314. In the control unit 31, the CPU reads a program stored in the ROM into the RAM, and executes and controls the program, thereby functioning as each of these units.

[0044] 6 shows the relationship between data generated in image processing executed by the conversion unit 311, selection unit 312, and correction unit 313 of the control unit 31. The image processing executed by the conversion unit 311, selection unit 312, and correction unit 313 will be described below with reference to FIG.

[0045] The converter 311 acquires information about the optical path difference and amplitude by performing a discrete Fourier transform-based analysis on the spectral interference data 51 acquired by the imaging device 10. Here, the optical path difference is the difference in the optical paths between the object light and the reference light, and is an index representing the surface height in the irradiation area irradiated with the object light. The amplitude is an index representing the intensity of the interference light. The discrete Fourier transform includes a fast Fourier transform.

[0046] 7 shows an example of acquiring information on the optical path difference and amplitude from information on wavelength included in the spectral interference data 51. The upper part of Fig. 7 shows the relationship between wavelength and amplitude at one position in the spatial axis direction in one interference fringe image 50. If the optical path difference is represented as L, the intensity is high when the wavelength is equal to one natural fraction of the optical path difference L (L / 1, L / 2, L / 3, L / 4, ...), and the intensity is low for wavelengths in between.

[0047] The converter 311 converts this wavelength information into wavenumber information as shown in the middle of Fig. 7. Since the wavenumber is the reciprocal of the wavelength, the intensity is high when the wavenumber is equal to 1 / L of the optical path difference (1 / L, 2 / L, 3 / L, 4 / L, ...), which is a natural number, and the intensity is low at wavelengths in between. In other words, the wavenumbers at which the intensity is maximum or minimum are arranged at equal intervals in the interference fringe pattern. Note that the wavelength and wavenumber values ​​in Fig. 7 are merely an example and are not necessarily correct values. The same applies to the subsequent figures.

[0048] The converter 311 applies a discrete Fourier transform to such wave number information to obtain values ​​of the optical path difference and the amplitude. In other words, the converter 311 converts the wavelength information included in the spectral interference data 51 into wave number information and then performs analysis based on the discrete Fourier transform. In this way, the converter 311 does not apply a discrete Fourier transform directly to the wavelength information, but rather converts the wavelength information into wave number information and then applies the discrete Fourier transform, thereby making it possible to efficiently perform the discrete Fourier transform process.

[0049] Specifically, the converter 311 applies a discrete Fourier transform to the wave number information shown in the middle part of Fig. 7 to derive the relationship between the optical path difference and the amplitude as shown in the bottom part of Fig. 7. In such a relationship between the optical path difference and the amplitude, the optical path difference when the amplitude shows a peak corresponds to the actual optical path difference at the target position on the surface of the measurement target 3. Therefore, in the derived relationship between the optical path difference and the amplitude, the converter 311 identifies the maximum amplitude Am and the optical path difference L at which the amplitude becomes maximum Am.

[0050] The converter 311 performs a process of acquiring the optical path difference and amplitude values ​​from such wavelength information for each position in the spatial axis direction of one interference fringe image 50, and further performs the process for each of the multiple interference fringe images 50 included in the spectral interference data 51. The converter 311 then generates optical path difference information 52 by two-dimensionally mapping the acquired optical path difference values, and generates amplitude information 53 by two-dimensionally mapping the acquired amplitude values.

[0051] Fig. 8 shows an example of optical path difference information 52. Fig. 9 shows an example of amplitude information 53. In the optical path difference information 52 and the amplitude information 53, the horizontal axis corresponds to the spatial axis direction (y direction) which is the width direction of the measurement object 3, and the vertical axis corresponds to the time axis direction (x direction) which is the transport direction of the measurement object 3.

[0052] 8 is image information showing the distribution of first values ​​based on the optical path difference in the measurement region R0. Here, the first value based on the optical path difference may be the optical path difference value itself, or may be a value converted from the optical path difference to the surface height. In the following, an example will be described in which the optical path difference value itself is used as the first value based on the optical path difference.

[0053] In the example of Figure 8, the optical path difference information 52 shows regions with different optical path differences, i.e., regions with different surface heights, in different colors. A step exists at a position where the optical path difference changes discontinuously. For example, if a step exists between a wiring portion and a semiconductor portion, the optical path difference information 52 shows each region in a distinguishable manner. However, the optical path difference value in the optical path difference information 52 includes error components due to vibration, tilt, etc., because it is before the correction process described below is performed.

[0054] 9 is image information showing the distribution of second values ​​based on amplitude in the measurement region R0. Here, the second values ​​based on amplitude may be the amplitude values ​​themselves, or may be values ​​converted from the amplitudes into another format. Hereinafter, a case where the amplitude values ​​themselves are used as the second values ​​based on amplitude will be described as an example.

[0055] 9, the amplitude information 53 indicates areas with different amplitudes in different colors. The amplitude corresponds to the intensity of the interference light and depends on the reflectance when the object light irradiated onto the measurement target 3 from the lens unit 12 is reflected by the surface of the measurement target 3. The greater the reflectance, the greater the intensity of the interference light, and therefore the greater the amplitude. Conversely, the smaller the reflectance, the smaller the intensity of the interference light, and therefore the smaller the amplitude.

[0056] Furthermore, the reflectance of the object light depends on the material of the region irradiated with the object light. For example, the reflectance differs when the region irradiated with the object light is made of metal compared to when it is made of silicon. Therefore, the amplitude information 53 distinguishes between regions made of different materials on the surface of the measurement target 3.

[0057] Since the optical path difference information 52 and the amplitude information 53 are two-dimensional image information, the value at each position in the optical path difference information 52 and the amplitude information 53 is also referred to as the luminance of each pixel. The same applies to other image information described later.

[0058] 6 , the selection unit 312 selects a correction region R1 from within the measurement region R0 based on the amplitude information 53 acquired by the conversion unit 311. Here, the correction region R1 is a partial region within the measurement region R0 that is used for correction to remove error components such as vibration and tilt that are included in the optical path difference information 52. The selection unit 312 identifies the surface condition within the measurement region R0 based on the amplitude at each position in the amplitude information 53, and selects a correction region R1 that is suitable for evaluating the error components.

[0059] First, the selection unit 312 derives a reference amplitude A0 based on the amplitude at each position in the amplitude information 53. The reference amplitude A0 is an amplitude that serves as a reference for selecting the correction region R1. Specifically, the selection unit 312 derives a representative value of the amplitudes in the amplitude information 53 and sets the derived representative value as the reference amplitude A0. Here, the representative value of the amplitude is specifically the average value, mode, or the like of the amplitudes in the amplitude information 53. Note that if the value to be used as the representative value of the amplitude is known in advance, that value may be used as the reference amplitude A0.

[0060] 10 shows an example of a frequency distribution of luminance (i.e., amplitude) in the amplitude information 53 when two regions of different materials, such as a wiring portion and a semiconductor portion, exist within the measurement region R0. This frequency distribution shows two peaks corresponding to the two different materials. When the mode is used as the representative amplitude value, for example, the selection unit 312 sets the amplitude showing the larger of the two peaks as the reference amplitude A0.

[0061] After deriving the reference amplitude A0, the selection unit 312 sets a reference range based on the derived reference amplitude A0. Specifically, the selection unit 312 sets the reference range to an amplitude range from A0-A1 to A0+A2. Here, the values ​​of A1 and A2 are set to appropriate values ​​in advance. For example, the values ​​of A1 and A2 may be determined as a ratio based on the value of the reference amplitude A0. Note that the absolute values ​​of A1 and A2 may be the same or different.

[0062] In this way, the reference range is set based on the representative value of the amplitude in the amplitude information 53. Since the reference range is set based on the representative value of the amplitude, a region with a large surface area in the measurement region R0 can be selected as the correction region R1.

[0063] Once the reference range is set, the selector 312 selects, as the correction region R1, a region of the measurement region R0 where the amplitude value in the amplitude information 53 falls within the reference range. By selecting a region where the amplitude value falls within the reference range in this manner, it is possible to select, as the correction region R1, a region of the measurement region R0 where the reflectance of the irradiated light is approximately the same. A region where the reflectance of the irradiated light is approximately the same is likely to be a region without steps, such as a region formed of a single material. Therefore, a region suitable for evaluating error components such as vibration and tilt can be selected as the correction region R1.

[0064] When correction region R1 is selected, selector 312 generates binarized information 54 from amplitude information 53. Binarized information 54 is image information that indicates the position of correction region R1 within measurement region R0. Specifically, as shown in Fig. 11 , binarized information 54 represents the luminance of pixels within correction region R1 in measurement region R0 as 1 (white in Fig. 11 ), and represents the luminance of other pixels as 0 (black in Fig. 11 ). Binarized information 54 corresponds to a mask image that masks the value of each position in optical path difference information 52.

[0065] 6 , the correction unit 313 corrects the value of the optical path difference in the optical path difference information 52 acquired by the conversion unit 311, based on the distribution of the optical path difference in the correction region R1 selected by the selection unit 312. Specifically, the correction unit 313 generates vibration correction data 63 and tilt correction data 66, which are correction data, from the optical path difference information 52 and the binarization information 54. The correction data is data generated based on the profile of the optical path difference in the correction region R1 in a predetermined direction. The correction unit 313 then corrects the value of the optical path difference at each position in the optical path difference information 52, based on the generated vibration correction data 63 and tilt correction data 66.

[0066] 12 shows in more detail the relationship between the data generated in the correction process executed by the correction unit 313. The correction process executed by the correction unit 313 will be described below with reference to FIG. 12. The correction process includes (1) a process for correcting vibration components and (2) a process for correcting tilt components.

[0067] (1) First, the correction unit 313 generates vibration correction data 63, which is first correction data, based on the profile of the optical path difference in the correction region R1 in the first direction, that is, the time axis direction (x direction).

[0068] Specifically, the correction unit 313 generates post-mask information 55 by multiplying the optical path difference information 52 by the binarized information 54. Here, the post-mask information 55 is image information after the value of the optical path difference at each position in the optical path difference information 52 has been masked by the binarized information 54. The value at each position in the post-mask information 55 corresponds to the value obtained by multiplying the values ​​at the same coordinates in the optical path difference information 52 and the binarized information 54 together. That is, in the post-mask information 55, the value of a pixel at the same coordinates as a pixel with a value of 0 in the binarized information 54 is changed to 0, and the value of a pixel at the same coordinates as a pixel with a value of 1 in the binarized information 54 remains the value of the pixel at the same coordinates in the optical path difference information 52. As a result, only information from the optical path difference information 52 that is suitable for evaluating the error component remains in the post-mask information 55.

[0069] When the post-mask information 55 is generated, the correction unit 313 generates a time profile 61 by integrating the value of each pixel included in the generated post-mask information 55 in the spatial axis direction (y direction). Here, the time profile 61 is one-dimensional array information for evaluating the tendency of the optical path difference within the correction region R1 in the optical path difference information 52 in the time axis direction corresponding to the transport direction of the measurement object 3. In the time profile 61, by integrating the value of each pixel included in the post-mask information 55 in the spatial axis direction, information on the optical path difference in the spatial axis direction is eliminated, and only information on the optical path difference in the time axis direction remains.

[0070] Furthermore, the correction unit 313 similarly integrates the values ​​of each pixel included in the binarized information 54 in the spatial axis direction to generate a time profile 62. Here, the time profile 62 is one-dimensional array information for averaging each value of the time profile 61 to a value per pixel. The time profile 62 corresponds to a profile of the number of pixels included in the correction region R1 in the time axis direction.

[0071] After generating the time profiles 61 and 62, the correction unit 313 divides the time profile 61 by the time profile 62. Specifically, the correction unit 313 divides each x-coordinate value in the time profile 61 by the value of the same x-coordinate in the time profile 62. In this way, the correction unit 313 generates vibration correction data 63. Here, the vibration correction data 63 is data for correcting vibration components included in the optical path difference information 52.

[0072] 13 shows an example of vibration correction data 63. The vibration correction data 63 represents a change over time in the value of the optical path difference per pixel in the correction region R1. In the example of FIG. 13, the vibration correction data 63 includes a vibration component, which is a periodically fluctuating component. Such a vibration component is caused by vibrations that occur when the measurement target 3 is transported by the transport stage 5.

[0073] 12 , after generating the vibration compensation data 63, the compensation unit 313 compensates the value of the optical path difference in the optical path difference information 52 based on the generated vibration compensation data 63. Specifically, the compensation unit 313 subtracts the value of the optical path difference at a position having the same coordinate in the time axis direction in the vibration compensation data 63 from the value of the optical path difference at each position in the optical path difference information 52. In this way, the compensation unit 313 generates vibration compensation information 56. The vibration compensation information 56 is image information that indicates the distribution of the optical path difference in the measurement region R0, in which the vibration component has been compensated.

[0074] More specifically, the correction unit 313 performs a calculation according to the following equation (1) for each coordinate (x, y) in the measurement region R0. Here, P1(x, y) represents the value of the optical path difference at the coordinate (x, y) in the optical path difference information 52, Q1(x) represents the value at the coordinate x in the vibration correction data 63, and P2(x, y) represents the value at the coordinate (x, y) in the vibration correction information 56. P2(x, y)=P1(x, y)-Q1(x) (1)

[0075] In this way, the correction unit 313 corrects the vibration component included in the optical path difference information 52 based on the vibration correction data 63, and generates the vibration correction information 56. Note that Q1(x) is not limited to being the value at the coordinate x of the vibration correction data 63 itself, but may be a value obtained by adding or subtracting an appropriate offset (such as an overall average value) to or from the value at the coordinate x of the vibration correction data 63.

[0076] (2) Secondly, the correction unit 313 generates tilt correction data 66, which is second correction data, based on the profile of the optical path difference in the correction region R1 in the spatial axis direction (y direction), which is the second direction.

[0077] Specifically, the correction unit 313 generates masked information 57 by multiplying the vibration correction information 56 by the binarized information 54. Here, the masked information 57 is image information after the value of the optical path difference at each position in the vibration correction information 56 has been masked by the binarized information 54. The value at each position in the masked information 57 corresponds to the value obtained by multiplying the values ​​at the same coordinates in the vibration correction information 56 and the binarized information 54 together. That is, in the masked information 57, the value of a pixel at the same coordinates as a pixel with a value of 0 in the binarized information 54 is changed to 0, and the value of a pixel at the same coordinates as a pixel with a value of 1 in the binarized information 54 remains the value of the pixel at the same coordinates in the vibration correction information 56.

[0078] When the post-mask information 57 is generated, the correction unit 313 generates a spatial profile 64 by integrating the value of each pixel included in the generated post-mask information 57 in the time axis direction (x direction). Here, the spatial profile 64 is one-dimensional array information for evaluating the tendency of the optical path difference within the correction region R1 in the optical path difference information 52 in the spatial axis direction corresponding to the width direction of the measurement target 3. In the spatial profile 64, by integrating the value of each pixel included in the post-mask information 57 in the time axis direction, information on the optical path difference in the time axis direction is eliminated, and only information on the optical path difference in the spatial axis direction remains.

[0079] Furthermore, the correction unit 313 similarly integrates the values ​​of each pixel included in the binarized information 54 in the time axis direction to generate a spatial profile 65. Here, the spatial profile 65 is one-dimensional array information for averaging each value of the spatial profile 64 to a value per pixel. The spatial profile 65 corresponds to a profile of the number of pixels included in the correction region R1 in the spatial axis direction.

[0080] After generating the spatial profiles 64 and 65, the corrector 313 divides the spatial profile 64 by the spatial profile 65. Specifically, the corrector 313 divides each y coordinate value in the spatial profile 64 by the value of the same y coordinate in the spatial profile 65. The corrector 313 then approximates the profile obtained by the division with an approximation curve using a method such as the least squares method. In this way, the corrector 313 generates tilt correction data 66. Here, the tilt correction data 66 is data for correcting the tilt component included in the optical path difference information 52.

[0081] FIG. 14 shows an example of tilt correction data 66. In FIG. 14, the solid line represents the division data obtained by dividing spatial profile 64 by spatial profile 65, and the dashed line represents an approximation curve that approximates this division data. Tilt correction data 66 corresponds to this approximation curve and represents the spatial change in the value of the optical path difference per pixel in correction region R1. In the example of FIG. 14, the tilt correction data 66 is tilted in the spatial axis direction. This tilt component is caused by the optical device in imaging device 10 being tilted to one side in the width direction of the object 3.

[0082] Here, the approximation curve that approximates the division data is, for example, a quadratic curve. The reason for using the approximation curve is that if the error component in the spatial axis direction is caused by the tilt of the optical device, the error component does not contain a minute fluctuation component. By using the approximation curve, the minute fluctuation component can be removed from the error component, and therefore, data suitable for correcting the tilt component of the optical device in the spatial axis direction can be generated as tilt correction data 66.

[0083] 12 , after generating the tilt correction data 66, the correction unit 313 corrects the value of the optical path difference in the vibration correction information 56 based on the generated tilt correction data 66. Specifically, the correction unit 313 subtracts the value of the optical path difference at a position in the tilt correction data 66 that has the same coordinate in the spatial axis direction from the value of the optical path difference at each position in the vibration correction information 56. In this way, the correction unit 313 generates tilt correction information 58. The tilt correction information 58 is image information that indicates the distribution of the optical path difference in the measurement region R0, with the tilt component corrected.

[0084] More specifically, the correction unit 313 performs a calculation according to the following equation (2) for each coordinate (x, y) in the measurement region R0. Here, Q2(y) represents the value at the coordinate y in the tilt correction data 66, and P3(x, y) represents the value at the coordinate (x, y) in the tilt correction information 58. P3(x, y)=P2(x, y)-Q2(y) (2)

[0085] In this way, the correction unit 313 corrects the tilt component included in the optical path difference information 52 based on the tilt correction data 66, and generates tilt correction information 58. Note that Q2(y) is not limited to being the value at the y coordinate of the tilt correction data 66 itself, but may be a value obtained by adding or subtracting an appropriate offset (such as an overall average value) to or from the value at the y coordinate of the tilt correction data 66.

[0086] In this way, the correction unit 313 executes (1) a process for correcting the vibration component and (2) a process for correcting the tilt component. As a result, the correction unit 313 generates tilt correction information 58 in which the vibration component and tilt component included in the value of the optical path difference at each position in the optical path difference information 52 have been corrected. The correction unit 313 then converts the optical path difference at each position in the generated tilt correction information 58 into a surface height, thereby generating surface height information 60 shown in FIG. 6 . The surface height information 60 is image information that indicates the distribution of surface heights in the measurement region R0 in which the vibration component and tilt component have been corrected. Because steps exist at positions where the surface height changes discontinuously, the surface height information 60 corresponds to information that indicates the distribution of steps in the measurement region R0.

[0087] 5 , the output unit 314 outputs output information that indicates the distribution of steps in the measurement region R0, which is generated by the correction by the correction unit 313. Specifically, the output unit 314 displays surface height information 60 on the display unit 34 as the output information.

[0088] 15 shows an example of how the surface height information 60 is displayed. As shown in Fig. 15, the output unit 314 displays an image showing the distribution of surface heights within the measurement region R0 of the measurement target 3 on the display unit 34. The user can move the cursor (indicated by an arrow in Fig. 15) to a position where the user wishes to measure the surface height by operating the operation unit 33 while viewing this image.

[0089] The output unit 314 displays the coordinates of the cursor position and the surface height value at those coordinates. By checking this screen, the user can obtain surface height information at any position within the measurement region R0 and can also measure steps at positions where the surface height changes discontinuously. For example, although not shown, when the user designates two positions with the cursor, the output unit 314 outputs the step value, which is the difference in surface height between the two positions, to the display unit 34.

[0090] 15, the surface height information 60 is displayed as a two-dimensional image, but the output unit 314 may display the surface height information 60 as a three-dimensional image so that the user can more easily check the surface height. Also, the output unit 314 may output the surface height information 60 to a device external to the image processing device 30 via the communication unit 35 and display it on a display unit of the external device.

[0091] Next, the flow of the step measurement process executed by the step measurement device 1 will be described with reference to the flowchart shown in Fig. 16. The step measurement process shown in Fig. 16 is an example of a step measurement method.

[0092] When the step measurement process is started, the transfer stage 5 transfers the measurement target 3 along a predetermined transfer path at a constant transfer speed V (step S1). Then, the illumination unit 11 turns on the light source and irradiates the measurement target 3 transferred by the transfer stage 5 with low-coherence light (step S2).

[0093] When the illumination unit 11 irradiates the object 3 with low-coherence light, the imaging device 10 acquires spectral interference data 51 (step S3). Specifically, the imaging device 10 repeatedly captures images of the transported object 3 at a constant time interval Δt, thereby repeatedly acquiring interference fringe images 50 such as those shown in FIG. 3. The imaging device 10 then arranges the acquired interference fringe images 50 in chronological order to acquire spectral interference data 51 such as that shown in FIG. 4. Step S3 is an example of an imaging step.

[0094] Next, the process moves to processing in the image processing device 30. First, in the image processing device 30, the control unit 31 functions as a conversion unit 311 and generates optical path difference information 52 and amplitude information 53 from the spectral interference data 51 acquired by the imaging device 10 (step S4). Specifically, the control unit 31 converts the wavelength information in the spectral interference data 51 into wavenumber information, and then applies a discrete Fourier transform. As a result, the control unit 31 generates, for example, the optical path difference information 52 shown in FIG. 8 and the amplitude information 53 shown in FIG. 9. Step S4 is an example of a conversion step.

[0095] Next, the control unit 31 functions as the selection unit 312 and selects the correction region R1 (step S5). Specifically, the control unit 31 selects, from the measurement region R0, a region in which the representative value of the amplitude in the amplitude information 53 is within a reference range as the correction region R1. Step S5 is an example of a selection step.

[0096] When the correction region R1 is selected, the control unit 31 functions as the selection unit 312 and generates binarized information 54 corresponding to the selected correction region R1 (step S6). Specifically, the control unit 31 generates binarized information 54 in which the brightness of pixels in the correction region R1 in the measurement region R0 is 1 and the brightness of other pixels is 0, as shown in FIG.

[0097] After generating binarized information 54, control unit 31 functions as correction unit 313 and corrects the vibration component in optical path difference information 52 (step S7). Specifically, control unit 31 generates vibration correction data 63 from optical path difference information 52 and binarized information 54, and corrects the value of the optical path difference at each position in optical path difference information 52 based on vibration correction data 63.

[0098] After correcting the vibration component, control unit 31 functions as correction unit 313 and corrects the tilt component in optical path difference information 52 (step S8). Specifically, control unit 31 generates tilt correction data 66 from optical path difference information 52 and binarized information 54, and corrects the value of the optical path difference at each position in optical path difference information 52 based on tilt correction data 66. Steps S7 and S8 are an example of a correction step.

[0099] After correcting the tilt component, the control unit 31 functions as the output unit 314 and outputs surface height information 60 (step S9). The control unit 31 then measures any steps present on the surface of the measurement target 3 (step S10). Specifically, the control unit 31 displays the image shown in FIG. 15 on the display unit 34. When the user operates the cursor to specify a position on the surface of the measurement target 3, the control unit 31 outputs the surface height value at the specified position to the display unit 34. Furthermore, when the user specifies two positions, the control unit 31 outputs the step value, which is the difference in surface height between the two positions, to the display unit 34. Step S10 is an example of a measurement step. This completes the step measurement process shown in FIG. 16.

[0100] As described above, the step measurement device 1 according to the first embodiment acquires spectral interference data 51 in the measurement region R0 on the surface of the measurement object 3 by imaging using the optical interferometry method, and acquires optical path difference information 52 and amplitude information 53 by performing an analysis based on a discrete Fourier transform on the spectral interference data 51. The step measurement device 1 according to the first embodiment then selects a correction region R1 from the measurement region R0 based on the amplitude information 53, and corrects the value of the optical path difference in the optical path difference information 52 based on the distribution of the optical path difference in the correction region R1.

[0101] As described above, the step measurement device 1 according to the first embodiment selects the correction region R1 based on the amplitude information 53. This allows the selection of a region suitable for evaluating error components such as vibration and tilt as the correction region R1 without manual human intervention. While a conventional method requires a human to determine a flat region within the measurement region R0 that does not contain steps and manually select the correction region R1 to correct the error components, the step measurement device 1 according to the first embodiment automates the process of selecting the correction region R1 and correcting the error components. Furthermore, the device configuration can be simplified because error components including vibration components can be removed without a vibration isolation mechanism, such as a vibration isolation table, which is required in conventional step measurement using a white light interferometer. As a result, steps on the surface of the measurement object 3, particularly steps between multiple regions formed of different materials, can be measured with high accuracy without the need for a vibration isolation mechanism and with reduced human effort.

[0102] Furthermore, the step measurement device 1 according to the first embodiment generates vibration correction data 63 based on a profile in the time axis direction corresponding to the transport direction of the transported measurement object 3, and further generates tilt correction data 66 based on a profile in the space axis direction. The step measurement device 1 according to the first embodiment then corrects the vibration component and tilt component included in the optical path difference information 52 based on the vibration correction data 63 and the tilt correction data 66. This makes it possible to correct the vibration component caused by transport of the measurement object 3 and the tilt component of the measurement system, thereby enabling steps to be measured with high accuracy.

[0103] Second Embodiment Next, a second embodiment will be described. Descriptions of the same configurations and functions as those of the first embodiment will be omitted where appropriate.

[0104] In the first embodiment, the correction unit 313 generates the tilt correction information 58 by correcting the vibration component and tilt component included in the optical path difference information 52. However, in actual measurements, slight tilt occurs due to the transportation of the measurement target 3. Therefore, in the second embodiment, the correction unit 313 further corrects such tilt components to further improve the accuracy of the correction.

[0105] In the second embodiment, the correction unit 313 generates the tilt correction information 58 by the correction process shown in Fig. 12, and then further executes the correction process shown in Fig. 17. The correction process executed by the correction unit 313 will be described below with reference to Fig. 17.

[0106] First, the correction unit 313 generates the addition information 71 by uniformly adding an offset to the value of the optical path difference at each position in the tilt correction information 58. Specifically, if the value of the optical path difference in the tilt correction information 58 includes 0, subsequent processing cannot be performed normally, so an inflating process is performed so that the value of each coordinate in the addition information 71 exceeds 0.

[0107] After generating the addition information 71, the correction unit 313 generates a coordinate array 72 representing coordinate values ​​on the spatial axis (y-axis) from the addition information 71. The coordinate array 72 is one-dimensional array information having a number of elements equal to the number of spatial axis coordinate values ​​included in the addition information 71 and the tilt correction information 58, i.e., the number of pixels in the spatial axis direction (y-direction). For example, if the tilt correction information 58 has M pixels in the spatial axis direction, the coordinate array 72 has M elements. The values ​​of the elements of the coordinate array 72 are 1, 2, 3, 4, 5, ..., M-1, M, in order, and correspond to coordinate values ​​in the spatial axis direction. Note that the coordinate array 72 does not include any elements whose value is 0.

[0108] After generating the coordinate array 72, the correction unit 313 executes a process of generating a tilt array 81 based on the addition information 71, the coordinate array 72, and the binarization information 54 (the process surrounded by the dashed line in FIG. 17 ). The correction unit 313 executes the process of generating the tilt array 81 for each of a plurality of different coordinate values ​​in the time axis direction (x direction). Specifically, the correction unit 313 executes the process of generating the tilt array 81 for each coordinate value on the time axis (x axis). The correction unit 313 may execute the process of generating the tilt array 81 sequentially or in parallel.

[0109] 4, when the spectral interference data 51 includes N interference fringe images 50, the number of pixels in the time axis direction included in the tilt correction information 58, i.e., the number of coordinate values ​​on the time axis, is N. The correction unit 313 individually selects the first to N coordinate values ​​and executes a process of generating a tilt array 81 for each of the N coordinate values.

[0110] Below, we will explain the case where the addition information 71 and the binarization information 54 have N coordinate values ​​on the time axis (x-axis) and M coordinate values ​​on the space axis (y-axis) (i.e., N x M pixels), and the correction unit 313 performs a process to generate a slope array 81 using the kth coordinate value (i.e., x-coordinate = k) of the N coordinate values ​​on the time axis.

[0111] The correction unit 313 generates a height array 73 by extracting the value of each pixel at the kth coordinate value from the addition information 71. The height array 73 is one-dimensional array information having values ​​of M pixels at x coordinate=k out of the N×M pixels included in the addition information 71. The height array 73 corresponds to the spatial profile of the addition information 71 at x coordinate=k.

[0112] Next, the correction unit 313 generates a mask array 74 by extracting the value of each pixel at the k-th coordinate value from the binarized information 54. The mask array 74 is one-dimensional array information having values ​​of M pixels at x coordinate=k out of the N×M pixels included in the binarized information 54. The mask array 74 corresponds to the spatial profile of the binarized information 54 at x coordinate=k.

[0113] After generating the height array 73 and the mask array 74, the correction unit 313 generates a masked height array 75 by multiplying the height array 73 and the mask array 74 by the values ​​at the same coordinates. The correction unit 313 then calculates a representative height 77 by dividing the integrated value of the M values ​​included in the mask array 74 by the integrated value of the M values ​​included in the masked height array 75. Here, the representative height 77 corresponds to the average value of the pixel values ​​that exist within the correction region R1 among the M pixels included in the height array 73. In other words, the representative height 77 is the average value of the pixel values ​​that are suitable for evaluating the tilt component at x coordinate = k.

[0114] Furthermore, the correction unit 313 generates a masked coordinate array 76 by multiplying the coordinate array 72 and the mask array 74 by the same coordinate values. The correction unit 313 then calculates a representative coordinate value 78 by dividing the integrated value of the M values ​​included in the mask array 74 by the integrated value of the M values ​​included in the masked coordinate array 76. Here, the representative coordinate value 78 corresponds to the average value of the spatial axis (y axis) coordinate values ​​of pixels present in the correction region R1 at x coordinate = k.

[0115] After calculating the representative height 77 and the representative coordinate value 78, the correction unit 313 replaces the pixel values ​​having a value of 0 in the masked height array 75 with the value of the representative height 77, thereby generating a replaced height array 79. Furthermore, the correction unit 313 replaces the pixel values ​​having a value of 0 in the masked coordinate array 76 with the representative coordinate value 78, thereby generating a replaced coordinate array 80. This replacement is performed to prevent a decrease in the accuracy of approximation due to data having a value of 0 when generating the following tilt array 81.

[0116] After generating the replaced height array 79 and the replaced coordinate array 80, the correction unit 313 performs linear approximation using the least squares method or the like from the replaced height array 79 and the replaced coordinate array 80 to generate the slope array 81. Specifically, the correction unit 313 approximates the value z of each pixel included in the replaced height array 79 and the coordinate value y included in the replaced coordinate array 80 by a linear equation expressed by the following equation (3). As a result, the correction unit 313 obtains the slope a and the intercept b. z = a * y + b (3)

[0117] After determining the slope a and intercept b, the correction unit 313 reflects the slope a and intercept b in each value of the coordinate array 72 to generate a slope array 81. The slope array 81 is one-dimensional array information indicating the degree of slope of the optical path difference in the correction region R1 in the spatial axis direction. The slope array 81 has a height z value expressed by the above formula (3) at the pixel of the coordinate value y on the spatial axis.

[0118] The correction unit 313 executes a process of generating such an inclination array 81 for each of N coordinate values ​​(k=1 to N) on the time axis. Then, the correction unit 313 generates tilt correction data 82 by generating an aggregate of the generated N inclination arrays 81. At this time, the correction unit 313 zero-bases each of the N inclination arrays 81 using the average value of the height z within one inclination array 81.

[0119] The tilt correction data 82 is third correction data for correcting the tilt component included in the optical path difference information 52. The tilt correction data 82 is data that individually indicates the tilt array 81 at each of a plurality of different coordinate values ​​in the time axis direction (in the second embodiment, for example, for each coordinate value on the time axis).

[0120] 18, the tilt correction data 82 is configured by arranging a plurality of tilt arrays 81 at corresponding positions in the time axis direction (x direction). In the tilt correction data 82, the tilt array 81 at x coordinate = k is arranged at the position where the coordinate value on the time axis within the measurement region R0 is k. Each of the plurality of tilt arrays 81 has a value obtained by linearly approximating the tilt component for each pixel in the spatial axis direction.

[0121] 17 , once the tilt correction data 82 is generated, the correction unit 313 subtracts the tilt correction data 82 from the tilt correction information 58 to generate tilt correction information 83. Specifically, the correction unit 313 performs calculations according to the following equation (4) for each of the coordinates (x, y) within the measurement area R0. Here, Q3(x, y) represents the value at the coordinates (x, y) of the tilt correction data 82, P3(x, y) represents the value at the coordinates (x, y) in the tilt correction information 58, and P4(x, y) represents the value at the coordinates (x, y) in the tilt correction information 83. P4(x, y) = P3(x, y) - Q3(x, y) (4)

[0122] In this way, the correction unit 313 corrects the tilt component included in the optical path difference information 52 based on the tilt correction data 82, and generates tilt correction information 83. Then, the correction unit 313 converts the optical path difference at each position in the generated tilt correction information 83 into a surface height, thereby generating surface height information 60. The output unit 314 displays the surface height information 60 on the display unit 34 as output information.

[0123] As described above, in the second embodiment, the correction unit 313 performs (1) a process for correcting the vibration component and (2) a process for correcting the tilt component, and further performs (3) a process for correcting the tilt component. As a result, the correction unit 313 generates tilt correction information 83 in which the tilt component is further corrected in addition to the vibration component and tilt component included in the value of the optical path difference at each position in the optical path difference information 52. This enables correction of the surface height in accordance with actual operation, and makes it possible to measure steps present on the surface of the measurement target 3 with higher accuracy.

[0124] Third Embodiment Next, a third embodiment will be described. Descriptions of the same configurations and functions as those of the first and second embodiments will be omitted as appropriate.

[0125] In the first and second embodiments, the step measurement device 1 selected a correction region R1 suitable for evaluating the error component by utilizing the fact that the amplitude of the interference light differs due to the different reflectivities of the irradiated light between multiple regions formed of different materials. Therefore, in the first and second embodiments, the measurement target 3 has multiple regions formed of different materials within the measurement region R0, and the step measurement device 1 measures the steps existing between the multiple regions formed of different materials. In contrast, in the third embodiment, the measurement target 3 has multiple regions within the measurement region R0 that are formed of the same material or different materials with equivalent reflectivities to the irradiated light. The step measurement device 1 according to the third embodiment can also handle steps existing between such multiple regions with equivalent reflectivities.

[0126] In the third embodiment, the imaging device 10 has an adjustment unit that adjusts the wavelength resolution of the spectroscopic unit 14 when the spectroscopic unit 14 disperses the interference light. Although not shown, the imaging device 10 includes, as the adjustment unit, a drive mechanism that changes the width of a slit that narrows the interference light that has entered the spectroscopic unit 14 from the lens unit 12. The adjustment unit changes the width of the slit to adjust the wavelength resolution of the interference light that passes through the slit and enters the spectroscopic element.

[0127] In this way, by adjusting the wavelength resolution of the spectroscopic unit 14, even if the reflectances for the irradiated light are the same, i.e., even if there is no detectable significant difference in the reflectance, it is possible to generate a difference in amplitude according to the optical path difference, provided that the fluctuation component in height due to the transportation of the measurement object 3 or the like is much smaller than the steps present on the surface of the measurement object 3.

[0128] 19A, 19B, and 19C show the interference fringe patterns in the interference fringe image 50 using solid and dashed lines when the optical path difference is 10,000.0 nm and when the optical path difference is 50,000.0 nm, respectively. When the optical path difference is relatively large, the interfering light constructively interacts with each other at more wavelengths and wave numbers than when the optical path difference is relatively small.

[0129] 19A , when the wavelength resolution of the spectroscopic unit 14 is ideal, that is, when the wavelength resolution is infinite, the amplitude of the interference light is constant regardless of the optical path difference. In contrast, when the wavelength resolution of the spectroscopic unit 14 is not ideal, wavelengths shorter than the wavelength resolution cannot be sufficiently resolved, and therefore, in the interference fringe image 50, interference light of multiple wavelengths whose wavelength differences are smaller than the wavelength resolution mix and weaken each other, reducing the intensity of the interference fringe pattern.

[0130] 19B , when the wavelength resolution of the spectroscopic unit 14 is relatively high at 2.0 nm, the intensity when the optical path difference is 50,000.0 nm is slightly smaller than the intensity when the optical path difference is 10,000.0 nm. Furthermore, when the wavelength resolution of the spectroscopic unit 14 is relatively low at 10.0 nm, the intensity when the optical path difference is 50,000.0 nm is significantly smaller than the intensity when the optical path difference is 10,000.0 nm.

[0131] In this way, by adjusting the wavelength resolution of the spectroscopic unit 14, it is possible to generate differences in the intensity of the interference fringe pattern depending on the optical path difference, even if the reflectance of the irradiated light is the same. Therefore, by adjusting the wavelength resolution to an appropriate value depending on the degree of steps that are likely to exist on the surface of the measurement target 3, it is possible to generate differences in the amplitude acquired from the spectral interference data 51. As a result, even if steps exist between multiple regions with the same reflectance within the measurement region R0, the selector 312 can select the correction region R1 while avoiding the regions where the steps exist. As a result, the corrector 313 can appropriately correct error components such as vibration and tilt included in the optical path difference information 52.

[0132] (Modifications) Although the embodiments of the present invention have been described above, it is possible to combine the embodiments, or to modify or omit the embodiments as appropriate.

[0133] For example, in the first embodiment, the correction unit 313 executes (1) a process for correcting a vibration component and (2) a process for correcting a tilt component. Furthermore, in the second embodiment, the correction unit 313 executes (3) a process for correcting a tilt component in addition to the above processes. However, the correction unit 313 is not limited to executing all of these processes, and may execute only one or two of the correction processes (1) to (3) as necessary. The output unit 314 may output, as the surface height information 60, information in which only one or two of the correction processes (1) to (3) have been executed on the optical path difference information 52.

[0134] Furthermore, the details of the correction processes (1) to (3) above are not limited to those described in the above embodiment. For example, in the above embodiment, the correction unit 313 generates a profile of the optical path difference in the correction region R1 in a predetermined direction and generates correction data based on the generated profile. However, as long as the correction unit 313 can generate correction data based on information about the optical path difference in the correction region R1, it is not necessary to generate a profile in a predetermined direction.

[0135] In the above embodiment, the CPU in the control unit 31 of the image processing device 30 executes a program stored in the ROM or the storage unit 32 to function as the conversion unit 311, the selection unit 312, the correction unit 313, and the output unit 314. However, the control unit 31 may be dedicated hardware. Examples of dedicated hardware include a single circuit, a composite circuit, a programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. When the control unit 31 is dedicated hardware, the functions of each unit may be realized by individual hardware, or the functions of each unit may be realized together by a single piece of hardware.

[0136] In addition, some of the functions of each unit may be realized by dedicated hardware, and other functions may be realized by software or firmware. In this way, the control unit 31 can realize each of the above-mentioned functions by hardware, software, firmware, or a combination of these.

[0137] By applying a program that defines the operation of the above-mentioned image processing device 30 to an existing computer such as a personal computer or a cloud server, it is possible to make the computer function as the above-mentioned image processing device 30.

[0138] Furthermore, the method of distribution of such a program is arbitrary, and for example, it may be stored on a computer-readable recording medium such as a CD-ROM (Compact Disk ROM), a DVD (Digital Versatile Disk), an MO (Magneto Optical Disk), or a memory card and distributed, or it may be distributed via a communication network such as the Internet.

[0139] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to illustrate the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is defined not by the embodiments but by the claims. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of the present invention.

[0140] This application is based on Japanese Patent Application No. 2023-201543 filed on November 29, 2023. The entire specification, claims, and drawings of Japanese Patent Application No. 2023-201543 are incorporated herein by reference.

[0141] 1 Step measurement device, 3 Measurement object, 5 Transfer stage, 10 Imaging device, 11 Illumination unit, 12 Lens unit, 13 Reference mirror, 14 Spectroscopic unit, 15 Area sensor, 30 Image processing device, 31 Control unit, 32 Memory unit, 33 Operation unit, 34 Display unit, 35 Communication unit, 50 Interference fringe image, 51 Spectral interference data, 52 Optical path difference information, 53 Amplitude information, 54 Binarization information, 55, 57 Post-mask information, 56 Vibration correction information, 58 Tilt correction information, 60 Surface height information, 61, 62 Time profile, 63 Vibration correction data, 64, 65 Spatial profile, 66 Tilt correction data, 71 Addition information, 72 Coordinate array, 73 Height array, 74 Mask array, 75 Post-mask height array, 76 Post-mask coordinate array, 77 Representative height, 78 Representative coordinate value, 79 Substituted height array, 80 Substituted coordinate array, 81 Inclination array, 82 Data for tilt correction, 83 Tilt correction information, 311 Conversion unit, 312 Selection unit, 313 Correction unit, 314 Output unit, R0 Measurement area, R1 Correction area

Claims

1. A step measurement device for measuring steps present on a surface of a measurement object, comprising: an imaging unit that acquires spectral interference data of a measurement area on the surface of the measurement object by imaging with an optical interference method using irradiation light having a plurality of wavelengths; a conversion unit that acquires information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on the spectral interference data acquired by the imaging unit, and generates optical path difference information indicating a distribution of first values ​​based on the optical path difference in the measurement area and amplitude information indicating a distribution of second values ​​based on the amplitude in the measurement area; a selection unit that selects a correction area from the measurement area based on the amplitude information acquired by the conversion unit; a correction unit that corrects the first value in the optical path difference information acquired by the conversion unit based on the distribution of the first values ​​in the correction area selected by the selection unit; and an output unit that outputs output information indicating the distribution of steps in the measurement area, generated by the correction by the correction unit.

2. The step measurement device according to claim 1, wherein the correction unit generates correction data based on a profile of the first value in the correction area in a specified direction, and corrects the first value in the optical path difference information based on the generated correction data.

3. The step measurement device of claim 2, wherein the imaging unit acquires the spectral interference data by repeatedly imaging a linear imaging area on the surface of the object to be measured as the object to be measured is transported, the specified direction is a direction corresponding to a transport direction in which the object to be measured is transported, and the correction unit corrects vibration components contained in the optical path difference information based on the correction data.

4. The step measurement device of claim 2, wherein the imaging unit acquires the spectral interference data by repeatedly imaging a linear imaging area on the surface of the object to be measured as the object to be measured is transported, the specified direction is a direction perpendicular to a direction corresponding to a transport direction in which the object to be measured is transported, and the correction unit corrects a tilt component included in the optical path difference information based on the correction data.

5. The step measurement device described in claim 2, wherein the imaging unit acquires the spectral interference data by repeatedly imaging a linear imaging area on the surface of the measurement object as the measurement object is transported, the predetermined direction is a second direction perpendicular to a first direction corresponding to a transport direction in which the measurement object is transported, the correction data is data individually indicating the degree of inclination of the first value in the correction area in the second direction for each of a plurality of different coordinate values ​​in the first direction, and the correction unit corrects a tilt component included in the optical path difference information based on the correction data.

6. A step measurement device as described in any one of claims 1 to 5, wherein the selection unit selects an area of ​​the measurement area in which the second value in the amplitude information is within a reference range as the correction area, and the reference range is set based on a representative value of the second value in the amplitude information.

7. The step measurement device according to any one of claims 1 to 5, wherein the conversion section converts wavelength information included in the spectral interference data into wave number information and then performs the analysis based on the discrete Fourier transform.

8. A step measurement device according to any one of claims 1 to 5, wherein the measurement object has a plurality of regions formed of different materials within the measurement region, and the step exists between the plurality of regions.

9. A step measurement device as described in any one of claims 1 to 5, wherein the imaging unit has an adjustment unit that adjusts the wavelength resolution when acquiring the spectral interference data, the measurement object has multiple regions within the measurement region that are formed of the same material or are formed of different materials that have equivalent reflectance to the irradiated light, and the step exists between the multiple regions.

10. An image processing device comprising: a conversion unit that acquires information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on spectral interference data in a measurement region on a surface of a measurement object obtained by imaging using an optical interference method using irradiation light having multiple wavelengths, and generates optical path difference information indicating a distribution of first values ​​based on the optical path difference in the measurement region and amplitude information indicating a distribution of second values ​​based on the amplitude in the measurement region; a selection unit that selects a correction region from the measurement region based on the amplitude information acquired by the conversion unit; a correction unit that corrects the first value in the optical path difference information acquired by the conversion unit based on the distribution of the first values ​​in the correction region selected by the selection unit; and an output unit that outputs output information indicating the distribution of steps in the measurement region, generated by the correction by the correction unit.

11. A step measurement method for measuring a step present on a surface of a measurement object, comprising: an imaging step of acquiring spectral interference data in a measurement region on the surface of the measurement object by imaging with an optical interference method using irradiation light having a plurality of wavelengths; a conversion step of acquiring information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on the spectral interference data acquired in the imaging step, to generate optical path difference information indicating a distribution of first values ​​based on the optical path difference in the measurement region and amplitude information indicating a distribution of second values ​​based on the amplitude in the measurement region; a selection step of selecting a correction region from the measurement region based on the amplitude information acquired in the conversion step; a correction step of correcting the first value in the optical path difference information acquired in the conversion step based on the distribution of the first values ​​in the correction region selected in the selection step; and a measurement step of measuring the step based on information generated by the correction in the correction step.

12. A program that causes a computer to function as: a conversion unit that acquires information on optical path difference and amplitude by performing an analysis based on a discrete Fourier transform on spectral interference data in a measurement region on the surface of a measurement object obtained by imaging using an optical interference method using irradiation light having multiple wavelengths, and generates optical path difference information indicating a distribution of first values ​​based on the optical path difference in the measurement region and amplitude information indicating a distribution of second values ​​based on the amplitude in the measurement region; a selection unit that selects a correction region from the measurement region based on the amplitude information acquired by the conversion unit; a correction unit that corrects the first value in the optical path difference information acquired by the conversion unit based on the distribution of the first values ​​in the correction region selected by the selection unit; and an output unit that outputs output information indicating the distribution of steps in the measurement region, generated by the correction by the correction unit.

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