TW201812250A - Three-dimensional shape measurement method using scanning white interference microscope that is applicable to measurement of a surface of a sample having a large inclination angle - Google Patents

Abstract

The present invention provides a three-dimensional shape measurement method that uses a scanning white interference microscope. In making a measurement of a three-dimensional shape by using a scanning white interference microscope, appropriate measurement can be conducted on a surface of a measurement object (sample) that shows a large inclination angle. The three-dimensional shape measurement method comprises: acquiring an envelope of an interference signal of light of a light source irradiating the measurement object, determining an observation coherence length 1c' that is an apparent coherence length observed through acquirement of a full width at half maximum of the envelope curve, and conducting measurement of the inclination angle of the surface of the measurement object according to the observation coherence length 1c'.

Description

Three-dimensional shape measurement method using a scanning white interference microscope

The present invention relates to a method for performing three-dimensional shape measurement by interference measurement using a white light source.

A scanning white interference microscope is a device that performs three-dimensional measurement by irradiating a sample with white light and converting the obtained interference signal into height information, and performs various calculations based on the obtained interference signal to perform surface shape, height, and high ground plane. The difference in film thickness, surface roughness, the same material and different materials. For example, Patent Document 1 describes a method of determining a tilt angle of a measurement object by tilting a reference mirror of a scanning white interference microscope. Patent Document 2 describes a method in which, when a thin film is present, interference patterns obtained by scanning white interference microscopes are overlapped and distorted, and peak separation is performed using a template. Patent Document 1: International Publication No. 2014/185133 Patent Document 2: Japanese Patent Application Laid-Open No. 2011-221027 In a three-dimensional measurement using a scanning white interference microscope, the numerical aperture NA of the objective lens provided by light optics is more than The angle determined by the (numerical aperture) is still measured inside, and the apparent coherence length does not change significantly. Therefore, so far, no special attention needs to be paid to the coherence length under such conditions. However, in a high-inclined surface measurement exceeding the numerical aperture NA, the measured apparent coherence length becomes large. In such a case, in Patent Document 1, when the inclination angle is obtained, if the inclination of the reference mirror is increased, for example, if the reference mirror is inclined above the numerical aperture NA, the return light becomes small, and therefore becomes dark. Therefore, it is difficult to measure the inclination angle above the numerical aperture NA. In addition, when a film is formed on the sample, it is impossible to distinguish and detect whether the observed extension of the coherence length is affected by the film or the high-inclined surface in the measurement of the high-inclined surface.

The present invention provides a three-dimensional shape measurement method using a scanning white interference microscope that can appropriately measure a highly inclined surface with a large inclination angle of the surface of a measurement object. The present invention is a three-dimensional shape measurement method using a scanning white interference microscope. The three-dimensional shape measurement method is as follows: obtaining an envelope of an interference signal of light from a light source that irradiates a measurement object, according to a half value of the envelope The width obtains an observed coherence length lc ′ which is an observed apparent coherence length, and measures the inclination angle of the surface of the measurement object based on the observed coherence length lc ′. According to the present invention, the oblique angle of the surface of the measurement object (sample) can be measured on the basis of obtaining the observation coherence length based on the half-value width of the envelope of the interference signal. Therefore, even on a high-inclined surface having a large inclination angle on the surface of the measurement object, the inclination angle can be appropriately measured, and the shape and characteristics of the surface can be grasped.

Hereinafter, a preferred embodiment of a three-dimensional shape measurement method using a scanning white interference microscope according to the present invention will be described in detail with reference to FIGS. 1 to 13. FIG. 1 is an overall configuration diagram of a scanning white interference microscope according to an embodiment of the present invention. The scanning white interference microscope 100 includes an apparatus body 10, a table 20 on which a sample S (a measurement object) of a measurement target is placed, and a computer (processor) 30 that processes the obtained data. The device main body 10 includes a white light source 11, a filter 12, a beam splitter 13, a dual-beam interference objective lens (objective lens) 14, a camera 15, and a piezoelectric actuator 16. As shown by arrow A, the light (white light) emitted from the white light source 11 passes through a filter (eg, a wavelength filter, a polarization filter, etc.) 12 and is guided by a beam splitter 13 to a dual-beam interference objective lens 14 (Arrow B). The light is split by the beam splitter in the two-beam interference objective lens 14 into a first light toward the measurement object (including the sample S itself and the substance inside it) and a second light toward the reference lens (not shown). Daoguang. When the optical distance from the beam splitter in the two-beam interference objective lens 14 disposed opposite to the measurement object to the measurement object is equal to the optical distance from the beam splitter to the reference lens, the measurement signal can interfere with two light beams. The form of the signal is observed. The camera 15 captures the interference signal as an interference fringe (interference pattern), and holds and stores the interference signal in the computer 30. In the embodiment of FIG. 1, since the distance from the beam splitter 13 to a reference mirror (not shown) is fixed, sweeping is performed by using the piezoelectric actuator 16 (movement of the arrow C). Change the distance from the measurement object. Since the scanning type white interference microscope 100 uses a white light source (coherence length to 1 μm) having a short coherence length, the position where the interference signal is obtained is the Z position (depth position) where the measurement object is present. FIG. 2 is a diagram showing the definition of the inclination angle θ of the surface of the sample S as a measurement target, and a part of the overall configuration diagram using the scanning white interference microscope of FIG. 1. An angle viewed from a line extending in the vertical direction of the measurement object to a normal line corresponding to a tangent to the surface of the measurement object is defined as an inclination angle θ. In the example of FIG. 2, the inclination angle at the point P ₁ is θ ₁ , and the inclination angle at the point P ₂ is θ ₂ . On the other hand, under ray optics, the critical angle of the objective lens 14 determined by the inclination angle θ of FIG. When the angle of light) is θ, the numerical aperture NA (numerical aperture) of the objective lens 14 is obtained by the following formula (1). In addition, n is a refractive index (refractive index of a substance in a space on the measurement object side), and is usually 1 when it is air. The higher the numerical aperture NA of the objective lens 14, the higher the horizontal resolution, and the smaller the focal depth, the higher the vertical resolution. FIG. 3 is a graph showing a general interference signal observed with a scanning white interference microscope 100, that is, an interference signal of light (white light) irradiated from a white light source 11 to a measurement object (sample S). . As shown in Equation (2), the signal intensity I observed by the camera 15 of the scanning white interference microscope 100 is an offset term ( ₁₎ from the reference light intensity I ₁ and the reflected light intensity I ₂ from the measurement sample ( First and second) and the third as an interference signal. Δp in the third term is an optical path difference (OPD: Optical Path Difference), which is from a beam splitter (not shown) in the two-beam interference objective lens 14 described in FIG. 1 to a measurement object (including sample S The difference between the optical distance on the side of itself and its internal matter) and the optical distance from the beam splitter (not shown) to the reference mirror side (not shown). The third term, which is the interference term of the formula (2), corresponds to the interference signal shown by the solid line in FIG. 3, and the envelope of the interference signal indicated by the dashed line is composed of three factors of the formula (3). That factor is a three light wavelength spectral characteristics of a white light source 11 is f ₁ (λ _i), wavelength filter (optical filter 12 is included in) spectral characteristics f ₂ (λ _i), as the spectral sensitivity of the camera 15 Characteristics f ₃ (λ _i ). λi is the wavelength of the light source. The half-value width of the envelope of FIG. 3 determined by these is observed as the coherence length. The coherence length lc is given by the formula (4), but the formula (4) is a formula of the inclination angle θ = 0 ° (0 degrees), and is a value of the coherence length of the light source that is not affected by the properties of the surface of the measurement object. . In Equation (4), λ _c is the central wavelength of the light source, Δλ is the half-value width of the wavelength of the light source, c is the speed of light, and Δf is the half-value width of the frequency of the light source. In addition, under the premise of the inclination angle θ = 0 °, this formula represents the characteristics of the wavelength filter (wavelength of the white light source and the transmission wavelength of the wavelength filter, etc.) of the white light source 11 and the filter 12. The unique value to be determined is defined as the basic coherence length (ie, the basic coherence length lc). FIG. 4 is an enlarged view of a region corresponding to one pixel (1 pixel) of the camera 15 in each of the low-inclined surface S ₁ and the high-inclined surface S ₂ of the surface of the sample S as a measurement target. The area corresponding to one pixel here represents the cross-section of the measurement object (the horizontal axis represents the x-coordinate in the radial direction, and the vertical axis represents the z-coordinate in the height direction), and the surface in each area is shown. The surface in this figure conceptually shows the state of the surface changing in one pixel, and is not a signal that is actually recorded. The interference signal obtained during scanning is obtained with respect to the surface of the measurement object, but in the low-inclined surface S ₁ , the position of the surface is in the height direction (z direction) in the horizontal direction (x direction) of one pixel. ). Thus, a mutual enhancing of the input pixel obtained in accordance with the height of the surface of each of the interference signal signals a plurality of frames ₁ each SG close, so that their degree of overlap increases, interference occurs. Therefore, a synthesized interference signal with a smaller half-value width and a larger height, that is, a mountain-shaped envelope EC _{1 is obtained} . On the other hand, in the high-inclined surface S ₂ , the position of the surface greatly changes in the height direction (z direction) in the lateral direction (x direction) of one pixel. Therefore, the signals corresponding to various heights of the interference signal SG ₂ inputted by one pixel and obtained on each surface in a plurality of frames are obtained, so that the degree of overlap with each other is reduced, and it is difficult for interference to enhance each other. Therefore, a synthesized interference signal having a larger half-value width and a smaller height, that is, an envelope EC ₂ having a trapezoidal shape is obtained. That is, it is apparently observed as if the basic coherence length lc is extended. FIG. 5 is a diagram focusing on one pixel of the camera 15. When the pixel size (pixel size; one side of one pixel) of the camera 15 is Wc and the magnification of the objective lens 14 is X, the area actually observed in one pixel It is a square area with Wc / X as one side. Furthermore, it is assumed that different height information (different surface position information) is input at one end and the other end in one pixel (Z ₁ and Z ₂ in FIG. 5). At this time, when the angle connecting the surface at one end and the other end is θ, that is, the inclination angle, Δz (= Z ₂ -Z ₁ ) of the height difference of the amount of variation in the position corresponding to the surface input as one pixel Is given by equation (5). FIG. 6 is a graph plotting the height difference Δz obtained by Equation (5) on the graph corresponding to the tilt angle θ. If the tilt angle θ of the surface is 0 ° (for example, near the low-inclined surface S _{1 of} FIG. 4) ), The height difference input by a pixel is obviously 0. In addition, according to Equation (5), as the tilt angle θ increases, the height difference Δz input by one pixel also obviously increases. That is, when the inclination angle is 0 °, the effect of the apparent coherence length elongation is 0, and the basic coherence length lc of equation (4) is directly observed. On the other hand, as the inclination angle θ becomes larger, the height difference Δz increases according to Expression (5). In this way, the observation coherence length (apparent coherence length) lc ′ obtained by observation using the scanning white interference microscope 100 actually changes according to the tilt angle, and is given by Equation (6). That is, the height difference Δz corresponds to an extension value of the coherence length, which is a value that the basic coherence length lc is extended according to the inclination angle θ. Further, the observation coherence length lc ′ is a value obtained by the basic coherence length lc determined by the wavelength filters of the white light source 11 and the filter 12 of the scanning white interference microscope 100 and the value extended as the basic coherence length lc according to the tilt angle θ. Sum of the extended values Δz. The basic coherence length lc, the pixel size Wc of the camera 15 and the magnification X of the objective lens are known. By measuring the observed coherence length lc ′, the inclination angle θ can be calculated using equations (5) and (6). (Tanθ), height difference Δz. In this way, the shape of the surface of the measurement target, that is, the inclination angle of the surface of the measurement target can be measured. FIG. 7 illustrates a method of determining a local curvature radius of a surface of a measurement object in a pixel by using a position change of a surface captured in a pixel of the camera described with reference to FIGS. 4 and 5. Concept illustration. Let the points at both ends in the pixel be P ₁ and P ₂ , and suppose a circle passing through the points r ₁ and P ₂ with a radius r such that the centers between the respective points r ₁ and r ₂ passing through the points P ₁ and P ₂ The radius (the radius after the angle θ 'is shifted from the radii r ₁ and r ₂ respectively) is located at any imaginary point P on the surface. That is, since it can be assumed that the local curvature radius is the same when measurement is performed in one pixel, r = r ₁ = r _{2 is} established, and the representative point is a radius that divides the radius r ₁ and r ₂ at both ends with an equal angle θ ′. Point P passed by r. If it is assumed that the radius r of the virtual point P is a local curvature radius, the relationship represented by the formula (7) holds. After observing the height difference Δz, the inclination angle θ can be obtained according to the graph in FIG. 6 and Equation (5). Three unknown variables θ ₁ , θ ₂ , and local curvature radius r remain in Equation (7). Each. Therefore, by solving the three simultaneous equations of Equation (7), the local curvature radius r can be calculated and then the local curvature 1 / r can be calculated. That is, the local curvature radius r of the surface of the measurement object can be calculated from the extension value Δz and the inclination angle θ which are the height differences Δz. In addition, if the height z of the surface can be detected, in the field of light optics, the local curvature radius (local curvature) can be obtained by the well-known equation (8). Noise is greater. In contrast, in Equation (7), the local curvature radius is obtained based on the inclination angle θ, so it can be said that it is a strong noise measurement method. Next, a method for setting an appropriate basic coherence length lc will be described. When measuring a high-inclined surface such as the high-inclined surface S ₂ in FIG. 4, if a 90-degree (90 °) inclination angle is measured, a predetermined inclination angle is taken at a point of the 90-degree inclination angle. Among the points of θc, the length corresponding to the distance of one pixel of the camera is given by Equation (9). x ₉₀ is the value of the x-coordinate of a pixel at a point with a tilt angle of 90 °, and x _θc is the value of the x-coordinate of a pixel at a point with a predetermined tilt angle θc. According to the formula (9), the tilt angle θc after shifting the camera by one pixel from the tilt angle of 90 ° is given by the formula (10). In Equation (6), if the basic coherence length lc is unnecessarily excessively increased, the degree of influence of Δz on the apparently extended coherence length (observed coherence length) lc 'becomes small, thereby reducing the measurement accuracy of the tilt angle. It is therefore desirable to suppress the basic coherence length lc to a predetermined size. However, if the basic coherence length lc is too short, disadvantages such as insufficient light amount or minimization of the appearance time of interference fringes may occur. Therefore, based on the premise that a tilt angle of 90 ° can be measured, if the extension value Δz is equal to the basic coherence length lc at the position of the surface shifted by the tilt angle θc (near 88 °, etc.) of one pixel of the camera, The measurement can be performed while maintaining the resolution at all measurable tilt angles. Therefore, the apparently prolonged Δz in the tilt angle θc can be set as a target value of the maximum value of the basic coherence length lc that can be set by the light source and the wavelength filter, and the basic coherence can be set on the condition of equation (11). Length lc. That is, the basic coherence length lc is desirably set to an extension value Δz or less on the surface after the surface of the measurement object corresponding to the tilt angle of 90 ° is shifted from the tilt angle θc corresponding to one pixel of the camera. At a tilt angle θc where the basic coherence length lc is the largest and is offset by one pixel from the camera, lc: Δz = 1: 1 (lc = Δz). Here, the premise is that a tilt angle of 90 ° can be measured, but when it is known that measuring the tilt angle of a sample does not require measurement up to a tilt angle of 90 °, the same can be performed at a tilt angle of 60 °, for example. It is calculated that the basic coherence length lc can also be reduced, so at the cost of a tilt angle that can be measured, the z resolution becomes higher. Next, countermeasures against deterioration of interference signals on a highly inclined surface will be described. FIG. 8 is an enlarged view of the area corresponding to one pixel (1 pixel) of the camera 15 among the surfaces of the low-inclined surface S ₁ and the high-inclined surface S ₂ of the surface of the sample S as the measurement target, as in FIG. 4. Shown figure. However, unlike FIG. 4, the area corresponding to one pixel here shows the surface represented by interference fringes on the xy plane perpendicular to one pixel as the cross-section of the measurement object obtained in FIG. 4. The shape is actually a signal recorded in one pixel (the horizontal axis represents the x-coordinate in the radial direction, and the vertical axis represents the y-coordinate perpendicular to the x-coordinate and the z-coordinate). Conventionally, this phenomenon has not occurred in observations within the numerical aperture NA (observation of the low-inclined surface S ₁ ), but, like the high-inclined surface S ₂ , in a region having a larger inclination angle than that obtained from the numerical aperture NA However, since a plurality of interference fringes are input in one pixel, a phenomenon that interference signals cancel and weaken each other may occur. FIG. 9 is a diagram in which the representation of FIG. 8 is changed, and is a schematic diagram showing a relationship between interference fringes in a wide range and one pixel. The light-to-light width and dark-to-dark width of the interference fringe correspond to one wavelength (λ), and the light-to-dark width corresponds to a half-wavelength λ / 2. As shown in FIG. 9 (a), in the low-inclined surface S ₁ , the height difference Δz corresponding to the widths of the light and dark signals of the interference fringe is λ / 2 smaller than half the wavelength λ of the light source. As a result, in the low-inclined surface S ₁ that satisfies the condition that Δz is smaller than λ / 2, as shown in FIG. 8, signals of interference fringes in one pixel are difficult to cancel each other. On the other hand, as shown in FIG. 9 (b), in the high-inclined surface S ₂ that satisfies the condition that Δz is larger than λ / 2, a plurality of bright and dark interference fringes enter into one pixel and cancel each other out. Since the mutual cancellation occurs in a region of one pixel, as the tilt angle becomes larger, the number of interference fringes increases, and the intensity of the obtained interference signal gradually decreases. FIG. 10 is a graph obtained by plotting Expression (12) that expresses the amplitude value (arbitrary unit) of the luminance input by one pixel at a predetermined tilt angle. Equation (12) expresses the following: Divide the height difference Δz input by one pixel by the wavelength λ as the wave number, and then use the number of interference m. As the number of interference fringes of one pixel entering the camera increases, the brightness The amplitude value, that is, the interference signal is weakened. FIG. 10 also shows a reference example of interference fringes at a maximum value where the intensity of the interference signal becomes large. The amplitude value of the brightness shown in this graph is the intensity of the so-called interference signal. In the angular region where the measured tilt angle exceeds the critical angle determined by the numerical aperture NA of the two-beam interference objective lens, it is intuitively understood that the interference signal is The weakened inclination angle exists with a periodicity determined by equation (12). If the intensity of the interference signal is small, the observed signal strength becomes smaller, that is, the signal-to-noise ratio S / N is deteriorated. Therefore, the deviation may become larger at this tilt angle and accurate shape measurement may not be performed. In order to cope with such a potential problem, the measured tilt angle is obtained from the measured apparently extended observation coherence length lc ′ (refer to equations (5) and (6)). Then, the signal-to-noise ratio S / N can be increased by averaging the vicinity of the tilt angle (tilt angle where the interference signal is weak) or using Fourier analysis to remove the periodic component corresponding to the tilt angle, thereby improving the S / N ratio. Reliability of shape measurement. Next, a method for measuring a measurement target having a film will be described. FIG. 11 is a conceptual diagram illustrating a case where the measurement of the high-inclined surface S ₂ is performed on the sample S having a measurement target having the film f. In the xy coordinates, it is assumed that the coordinates of the outermost surface of the sample S are (x ₁ , z ₂ ), and the coordinates of the inner surface corresponding to the inside of the film f are (x ₁ , z ₁ ). The film thickness t of the film at an inclination angle of 0 ° is expressed as z ₂ -z ₁ at an arbitrary inclination angle, and is given by Equation (13). This formula represents the film thickness t of the film f when observed from the vertical direction. The local curvature radius r is the local curvature radius at the coordinates (x ₁ , z ₁ ) (that is, the local curvature radius at the coordinates (x ₁ , z ₂ ) is r + t). The film f does not necessarily need to exist on the surface of the sample S, and may be a film such as a layer existing inside the sample S. The film f may be a single-layer film or a multilayer film. In the field of optics, as a definition capable of separating two bright spots, for example, there is a known formula having a resolution (0.61 * λ / NA) of Rayleigh. Here, FIG. 12 (a) shows a case where the center of the envelope of an interference fringe that is simply observed is half of the coherence length lc, and FIG. 12 (b) is shown. The corrected situation of the apparent extension value Δz described later is shown. Furthermore, based on equation (6), the following equation (14) will be discussed as a height δ that can be practically separated. FIG. 13 is a graph obtained by plotting equations (13) and (14) under predetermined conditions (the pixel size Wc, the objective lens magnification X, the film thickness t, the local curvature radius r, etc.) are appropriately set. The graph obtained by plotting formula (14) is "the height that can be actually separated" shown by the solid line, and the graph obtained by plotting formula (13) is "from the vertical direction" Film thickness at the time of observation ". The figure shows the following: In a region of a low-inclined surface with a predetermined width centered on an inclination angle of 0 °, the observed coherence length, that is, the height ratio that can be actually decomposed, is observed from the vertical direction. At this time, the film thickness of the film f is still small, so that the observed interference fringes do not overlap. Therefore, the interference signal can be separated from the sample even in the film, and the presence or absence of the film can be determined. In addition, it can be seen that the extension of the coherence length, that is, the height δ that can be separated at approximately ± 23 °, exceeds the film thickness when viewed from the vertical direction. This means that at oblique angles of ± 23 ° or more, it is difficult to determine whether a film exists because the observed interference fringes appear overlapping. Therefore, the correction of the extension value Δz of the coherent length that can be grasped is subtracted from the observed coherence length lc ′ from the equation (5) and FIG. 6. That is, the corrected separable height δ ′ is given by the following formula (15) after subtracting Δz from the formula (14). As a result, the corrected separable height δ 'does not extend apparently and has no tilt angle dependency. Therefore, the corrected separable height δ' does not depend on it as shown by the one-dot chain line in FIG. 13. The inclination angle is determined only by the coherence length of the light source, that is, the basic coherence length lc, so that the measurement target can be judged not only on the low-inclined surface but also on the high-inclined surface (in this example, an area exceeding ± 23 °) Is there a film. As shown by the "correctable separable height δ '" shown by the one-dot chain line in FIG. 13, the difference can be obtained from the signal of the interference fringes of the half-value width obtained by calculation at the tilt angle. To determine the film thickness of the film. Moreover, the measurement of the inclination angle of a film can also be performed on a highly inclined surface. According to the present invention, the oblique angle of the surface of the measurement object (sample) can be measured after obtaining the observation coherence length based on the half-value width of the envelope of the interference signal. Therefore, even on a highly inclined surface with a large inclination angle on the surface of the measurement object, the inclination angle can be appropriately measured, and the shape and characteristics of the surface can be grasped. In particular, according to the present invention, changes in the basic coherence length and the interference fringe waveform of the tilt angle θ = 0 ° determined by a scanning white interference microscope including a light source and a wavelength filter are equivalent to a half of the change. By observing the coherent length of the value width, the inclination angle of the surface of the measurement object (sample) can be measured. In addition, according to the present invention, the local curvature radius of the surface at the measurement position can also be determined. The conventional method of calculating the local curvature radius from the Z position (height position) of the measurement object has a large noise because the second order differential is on the denominator of the calculation formula. However, according to the present invention, the , So the noise is small. In addition, according to the present invention, an appropriate basic coherence length can be set to suppress the influence of the basic coherence length on the observed coherence length. Therefore, an accurate observed coherence length can be obtained, and an accurate tilt angle can be measured. In addition, according to the present invention, since a measurement object having a film has an observation coherence length corresponding to a predetermined inclination angle, it is also possible to perform measurement on a high-inclined surface by correction by subtracting an extension of the coherence length extension. Measurement of the film was performed. For example, the presence or absence of a membrane can be determined when observing interference fringes of a half-value width or more obtained by calculation. In addition, at this time, the film thickness may also be obtained from the interference fringe waveform obtained by taking a difference from the signal of the interference fringes of the half-value width obtained from the calculation of the angle. In addition, the present invention is not limited to the above-mentioned embodiment, and can be appropriately modified, improved, and the like. In addition, as long as the present invention can be realized, the material, shape, size, numerical value, form, number, arrangement position, and the like of each constituent element in the above embodiment may be arbitrary without limitation. INDUSTRIAL APPLICABILITY According to the present invention, in a three-dimensional shape measurement method using a scanning white interference microscope, a surface of a sample having a large inclination angle can be appropriately measured.

10‧‧‧device body

11‧‧‧White light source (light source)

12‧‧‧ filters (including wavelength filters)

13‧‧‧ Beamsplitter

14‧‧‧Double-beam interference objective lens (objective lens)

15‧‧‧Camera

16‧‧‧ Piezo actuator

20‧‧‧Workbench

30‧‧‧Computer

100‧‧‧scanning white interference microscope

S‧‧‧Sample (measurement object)

f‧‧‧ film

FIG. 1 is an overall configuration diagram of a scanning white interference microscope according to an embodiment of the present invention. FIG. 2 is a diagram showing the definition of the inclination angle θ of the surface of the sample. FIG. 3 is a graph showing a general interference signal observed by a scanning white interference microscope. FIG. 4 is an enlarged view of a region corresponding to one pixel (1 pixel) of a camera among each of a low-inclined surface and a high-inclined surface on the surface of the measurement target. FIG. 5 is a diagram showing a height difference in one pixel of a camera. FIG. 6 shows a graph obtained by plotting the height difference corresponding to the tilt angle. FIG. 7 is a conceptual diagram explaining a method of obtaining a local curvature radius of a surface of a measurement object. FIG. 8 is an enlarged view showing interference fringes generated in a region corresponding to one pixel of a camera in each of a low-inclined surface and a high-inclined surface on the surface of the measurement target. FIG. 9 is a schematic diagram showing a relationship between interference fringes and one pixel in a wide range, (a) shows a relationship in a low-inclined plane, and (b) shows a relationship in a high-inclined plane. FIG. 10 is a graph obtained by plotting Equation (12) which expresses the amplitude value of the brightness input by one pixel at a predetermined tilt angle. FIG. 11 is a conceptual diagram illustrating a case where measurement of a highly inclined surface is performed in a measurement target having a film. FIG. 12 is a conceptual diagram explaining whether or not the separation of two bright spots of interference fringes can be performed. (A) It is assumed that the center of the envelope of the observed interference fringes is half of the coherence length lc. (B) is an explanatory diagram of the apparent extension value Δz after correction. FIG. 13 is a graph obtained by plotting equations (5) and (13) under predetermined conditions.

Claims (6)

A three-dimensional shape measurement method is a three-dimensional shape measurement method using a scanning white interference microscope, which is characterized by: obtaining an envelope of an interference signal of light from a light source irradiating a measurement object, and a half value of the envelope Obtain the observed coherence length lc ′, which is the observed apparent coherence length, and measure the inclination angle of the surface of the measurement object based on the observed coherence length lc ′. The three-dimensional shape measurement method according to claim 1, wherein: the observation coherence length lc ′ is a basic coherence length lc determined by the light source and a wavelength filter of the scanning white interference microscope and the basic coherence length lc The sum of the extension values Δz of the values extended according to the aforementioned tilt angle. The three-dimensional shape measurement method according to claim 2, wherein: calculates a local curvature radius of a surface of the measurement object based on the extension value Δz and the tilt angle. The three-dimensional shape measuring method according to claim 3, wherein: the basic coherence length lc is set to be one pixel of a camera that is shifted from the surface of the measurement object corresponding to the tilt angle of 90 degrees and captures the interference signal The amount of elongation Δz in the surface after the inclination angle θc corresponding to the amount is equal to or less than the aforementioned value. The three-dimensional shape measurement method according to claim 1, wherein: the scanning white interference microscope has an objective lens disposed opposite to the measurement object and a camera that captures the interference signal, and exceeds a threshold determined by a numerical aperture of the objective lens. At the tilt angle of the angle, the averaging processing is performed at the nearby tilt angle where the interference signal cancels each other within one pixel of the camera, or the Fourier analysis is used to remove the periodic component corresponding to the tilt angle, thereby improving the signal Noise ratio S / N. The three-dimensional shape measurement method according to claim 2, wherein determines whether the measurement target has a film by subtracting the extension value Δz from the observation coherence length lc '.