JP7742017B2 - Method for adjusting a shape measuring device - Google Patents

Description

The present invention relates to a method for adjusting a shape measuring device, and in particular to a method for adjusting a shape measuring device that measures the shape of a measurement surface of a measurement object.

A scanning white light interferometer is known as a device for measuring the three-dimensional shape of an object. A scanning white light interferometer uses a white light source as a light source and an optical path interferometer such as a Michelson or Mirau type to measure the three-dimensional shape of the object's surface in a non-contact manner.

Patent Document 1 discloses a shape measurement device that measures the height of a surface to be measured in the optical axis direction by causing interference between measurement light that is irradiated from a light source through an objective lens onto the surface of an object to be measured and reflected by the surface, and reference light that is irradiated from a light source through an objective lens onto the reference surface and reflected by the reference surface.

JP 2011-099787 A

In the scanning white light interferometer (white light interference microscope) shown in Figure 15, light L0 from a light source is split by beam splitter 24b into measurement light L1i and reference light L2i, which are reflected by the measurement surface Wa and reference surface 24c of the measurement object W, respectively. The measurement light L1r and reference light L2r reflected by the measurement surface Wa and reference surface 24c, respectively, are superimposed on the same optical path by beam splitter 24b to become combined light L3 (in the following description, measurement light L1i, L1r and reference light L2i, L2r may be collectively referred to as measurement light L1 and reference light L2, respectively). By determining the contrast or phase change of the interference pattern (interference fringes) obtained from this combined light L3, the shape (e.g., three-dimensional shape, height, etc.) of the measurement surface Wa of the measurement object W can be measured.

Figure 15(a) shows an example in which the measurement light L1i collected by the objective lens 24a is focused on the measurement surface Wa of the measurement object W. In the following explanation, the position at which the measurement light L1i is focused on the measurement surface Wa (the positional relationship between the objective lens 24a and the measurement object W when the measurement light L1i is focused on the measurement surface Wa) as shown in Figure 15(a) is referred to as the focusing position. Note that in the example shown in Figure 15(a), the optical path length (measurement optical path length) D1(a) of the measurement light L1 is different from the optical path length (reference optical path length) D2(a) of the reference light L2 (D1(a) ≠ D2(a)).

On the other hand, Figure 15(b) shows an example in which the measurement optical path length D1(b) and the reference optical path length D2(b) are the same (D1(b) = D2(b)). In this case, the phases of the measurement light L1r and the reference light L2r are the same. In the following description, the position where the measurement optical path length D1(b) and the reference optical path length D2(b) are the same (the positional relationship between the objective lens 24a, beam splitter 24b, measurement object W, and reference surface 24c when the measurement optical path length D1(b) and the reference optical path length D2(b) are the same) as shown in Figure 15(b) is referred to as the interference position (position where interference fringes occur). Note that in the example shown in Figure 15(b), the measurement light L1i collected by the objective lens 24a is not focused on the measurement surface Wa of the measurement object W.

As shown in (b) of Figure 15, when the measurement light L1i is not focused on the measurement surface Wa, the shape of the measurement surface Wa obtained from the combined light L3 (measured shape F12 in Figure 16) will be distorted compared to the actual shape (actual shape F10 in Figure 16). Furthermore, because the light intensity of the combined light L3 decreases, a decrease in sensitivity can occur, resulting in a decrease in measurement accuracy or even in the inability to perform measurements.

For this reason, in the white light interference microscope described above, the focal position and the reference position are adjusted to coincide. Specifically, the measurement light L1i collected by the objective lens 24a is focused on the measurement surface Wa of the measurement object W, and the measurement optical path length D1 and the reference optical path length D2 are adjusted to coincide.

When adjusting a white light interference microscope like the one described above, an operator observes a planar substrate on which a pattern is printed, and manually adjusts the position of each optical element while visually checking the focus state. The operator then manually adjusts the position so that the focus position where the objective lens 24a focuses on the pattern matches the interference position, and checks the adjustment results.

To ensure the measurement accuracy of the white light interference microscope described above, it is preferable to frequently adjust and check the white light interference microscope, for example, whenever the measurement object W and the measurement location are changed. However, because the frequency with which the white light interference microscope is adjusted and checked depends on the operator, there are cases where the measurement object W is measured while the microscope is in an improperly adjusted state, which can result in the leakage of low-accuracy, unreliable data.

The present invention was made in consideration of these circumstances, and aims to provide a method for adjusting a shape measurement device that makes it easy to adjust a white light interferometer microscope.

To achieve the above-mentioned objective, a first aspect of the present invention is a method for adjusting a shape measurement device that irradiates light from a light source onto an adjustment master and a reference surface as measurement light and reference light, respectively, and measures the shape of the measurement surface of a measurement object using the combined light of the measurement light and reference light reflected by the adjustment master and the reference surface, respectively. The method includes the steps of acquiring an image of the adjustment master for each of a plurality of scanning positions along a scanning direction perpendicular to the adjustment master, calculating a matching parameter indicating the degree of matching between the focus position and the interference position from the image for each scanning position, and calculating a target setting position of the reference surface based on the matching parameter.

A method for adjusting a shape measuring device according to a second aspect of the present invention is the first aspect, in which the degree of match parameter is calculated based on a first parameter which is the difference in luminance along a direction on the surface of pixels included in an image of the adjustment master for each scanning position, and a second parameter which is the difference in luminance along the scanning direction.

A method for adjusting a shape measuring device according to a third aspect of the present invention is the same as that of the first or second aspect, and includes the steps of calculating a matching parameter for each position of the reference surface, and calculating a target setting position of the reference surface based on the matching parameter calculated for each position of the reference surface.

A fourth aspect of the present invention relates to a method for adjusting a shape measuring device, and in the second aspect, the target setting position of the reference surface is a position obtained by moving the reference surface by the difference between the peak values of the first parameter and the second parameter from the position of the reference surface when the image used to calculate the degree of match parameter was acquired.

According to the present invention, matching parameters can be calculated from images of the adjustment master for each scanning position, making it possible to easily adjust the shape measurement device.

FIG. 1 is a diagram showing a shape measuring device according to an embodiment of the present invention. FIG. 2 shows images of the master acquired at each scanning position. FIG. 3 is a diagram for explaining an example of calculation of the horizontal contrast parameter. FIG. 4 is a diagram for explaining an example of calculation of the vertical contrast parameter. FIG. 5 is a diagram showing an example of calculation of the horizontal contrast parameter. FIG. 6 is a graph showing the relationship between the horizontal contrast parameter and the vertical contrast parameter and the scanning position (Z position). FIG. 7 is a graph showing the relationship between the degree of match parameter and the position of the reference surface. FIG. 8 is a flowchart showing a method for adjusting a shape measuring device according to an embodiment of the present invention. FIG. 9 is a diagram showing an example of interference fringes. FIG. 10 is a graph showing the effect of interference fringes on the calculation of the lateral contrast parameter. FIG. 11 is a diagram illustrating an installation form of the master according to the third embodiment. FIG. 12 is a diagram illustrating an example of a kernel according to the third embodiment. FIG. 13 is a diagram showing a shape measuring device according to the first modification. FIG. 14 is a diagram showing a shape measuring device according to the second modification. FIG. 15 is a diagram showing an example of a white light interference microscope. FIG. 16 is a diagram showing the relationship between the actual shape and the measured waveform.

Below, an embodiment of the method for adjusting a shape measuring device according to the present invention will be described with reference to the accompanying drawings.

[Shape measuring device]
1 is a diagram showing a shape measuring device according to an embodiment of the present invention, in which, of the mutually orthogonal X, Y and Z directions in the figure, the X and Y directions are parallel to the horizontal direction, and the Z direction is parallel to the vertical direction.

As shown in FIG. 1, the shape measurement device 1 includes a white light interferometer microscope 10, a drive mechanism 12, a scale 14, and a data processing unit 100.

The white light interference microscope 10 is a Michelson-type scanning white light interference microscope. It comprises a light source unit 20, a beam splitter 22, an interference objective lens 24, an imaging lens 26, and a camera 28. The interference objective lens 24, the beam splitter 22, the imaging lens 26, and the camera 28 are arranged in this order from the surface Wa to be measured upward in the Z direction. The light source unit 20 is also arranged opposite the beam splitter 22 in the X direction (or the Y direction).

Under the control of the data processing unit 100, the light source unit 20 emits a parallel beam of white light L0 (low-coherence light) toward the beam splitter 22. Although not shown, the light source unit 20 includes a light source capable of emitting white light L0, such as a light-emitting diode, semiconductor laser, halogen lamp, or high-intensity discharge lamp, and a collector lens that converts the white light L0 emitted from this light source into a parallel beam of light.

The beam splitter 22 may be, for example, a half mirror. The beam splitter 22 reflects a portion of the white light L0 incident from the light source unit 20 as measurement light L1i toward the interference objective lens 24 located downward in the Z direction. The beam splitter 22 also transmits a portion of the combined light L3 (described below) incident from the interference objective lens 24 toward the upper side in the Z direction, and emits this combined light L3 toward the imaging lens 26.

The interference objective lens 24 is a Michelson type and includes an objective lens 24a, a beam splitter 24b, and a reference surface 24c. The beam splitter 24b and objective lens 24a are arranged in this order above the measured surface Wa in the Z direction, and the reference surface 24c is arranged opposite the beam splitter 24b in the X direction (or the Y direction). The following explanation will use a Michelson type interference optical system, but the interference optical system is not limited to the Michelson type; known interference optical systems such as the Mirau type and Linnik type can also be used.

The objective lens 24a has a focusing function, and focuses the measurement light L1 incident from the beam splitter 22 onto the measurement surface Wa through the beam splitter 24b.

Beam splitter 24b corresponds to the interference unit of the present invention and is, for example, a half mirror. Beam splitter 24b splits a portion of the white light L0 incident from objective lens 24a as reference light L2i, transmits the remaining measurement light L1i, and emits it to the measurement surface Wa, while reflecting the reference light L2i toward reference surface 24c. Note that symbol D1 in the figure indicates the measurement optical path length, which is the optical path length of measurement light L1 between beam splitter 24b and measurement surface Wa. After transmitting through beam splitter 24b, measurement light L1i is irradiated onto measurement surface Wa, and is reflected by the measurement surface Wa before returning to beam splitter 24b.

Reference surface 24c, for example, is a reflective mirror that reflects reference light L2i incident from beam splitter 24b toward beam splitter 24b. The position of this reference surface 24c in the X direction can be manually adjusted using a position adjustment mechanism (e.g., a ball screw mechanism, actuator, etc.) not shown. This makes it possible to adjust the reference optical path length D2, which is the optical path length of reference light L2 between beam splitter 24b and reference surface 24c. This reference optical path length D2 is adjusted to match (or approximately match) the measurement optical path length D1.

The beam splitter 24b generates combined light L3 from the measurement light L1 returning from the measured surface Wa and the reference light L2 returning from the reference surface 24c, and emits this combined light L3 toward the objective lens 24a located above in the Z direction. This combined light L3 passes through the objective lens 24a and the beam splitter 22 and enters the imaging lens 26.

The imaging lens 26 forms an image of the combined light L3 incident from the beam splitter 22 on the imaging plane (not shown) of the camera 28. Specifically, the imaging lens 26 forms an image of a point on the focal plane of the objective lens 24a as an image point on the imaging plane of the camera 28.

The camera 28 is equipped with a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) imaging element (not shown). The camera 28 captures the combined light L3 imaged on the imaging surface by the imaging lens 26, processes the imaging signal of the combined light L3 obtained by this imaging, and outputs the captured image.

The drive mechanism 12 corresponds to the scanning unit of the present invention. The drive mechanism 12 is composed of a linear motor or a motor drive mechanism, and holds the white light interferometer 10 so that it can move freely in the Z direction, which is the scanning direction. Under the control of the data processing unit 100, this drive mechanism 12 scans the white light interferometer 10 along the Z direction.

The drive mechanism 12 only needs to be able to scan the white light interferometer 10 relative to the measurement surface Wa in the Z direction; for example, it may scan the measurement surface Wa (the support portion that supports the measurement surface Wa) in the Z direction.

The scale 14 is a position detection sensor that detects the Z-direction position of the white light interferometer 10, and is, for example, a linear scale. This scale 14 repeatedly detects the Z-direction position of the white light interferometer 10 and repeatedly outputs the position detection results to the data processing unit 100.

The data processing unit 100 controls the measurement operation of the three-dimensional shape of the measurement surface Wa by the white light interferometer microscope 10 (shape measurement device 1) in response to operation input from the operation unit 108, and performs calculations of the three-dimensional shape of the measurement surface Wa. The data processing unit 100 includes a processor (e.g., a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc.) that performs various calculations, memory (e.g., a ROM (Read Only Memory) and a RAM (Random Access Memory)), etc.) that serves as the processor's working area, and a storage device (e.g., an SSD (Solid State Drive) or an HDD (Hard Disk Drive), etc.) for storing various programs and data.

The data processing unit 100 is able to implement various functions (shape measurement unit 102, match parameter calculation unit 104, and match determination unit 106) described below by executing programs stored in storage using a processor.

The functions of the data processing unit 100 may be realized by a single processor, or by multiple processors of the same or different types. The functions of the data processing unit 100 may also be realized by a general-purpose computer.

The operation unit 108 includes operation members (e.g., a keyboard and mouse) for accepting operation inputs from the operator to the data processing unit 100.

The output unit 110 is a device for outputting the results of program execution by the data processing unit 100, data on the results of calculations, etc. The output unit 110 includes, for example, an operation UI (User Interface) and a monitor (e.g., an LCD display) for displaying the detection results. The output unit 110 may also include a printer, speaker, etc. in addition to or instead of the monitor.

[Procedure for adjusting the shape measuring device]
The data processing unit 100 uses the measurement results of the adjustment master M (hereinafter referred to as master M) to calculate a match parameter indicating the degree of match between the focus position and the interference position (a match parameter indicating the degree of match for the measurement light L1i to be focused on the master M and for the measurement light L1r and reference light L2r to interfere with each other).Then, using this match parameter, it is possible to evaluate the degree of match between the focus position and the interference position and adjust the shape measuring device 1.

(matching parameter)
Next, the procedure for calculating the degree-of-match parameter will be described.

In this embodiment, a master M with a printed pattern is used as the measurement object, and images of the pattern on the surface of the master M are repeatedly acquired while the white light interferometer 10 is scanned in the Z direction by the drive mechanism 12.

The master M can be, for example, a flat plate with an arbitrary shape pattern formed on its surface. The pattern formed on the surface of the master M can be, for example, all or part of the patterns used in various resolution charts, such as a radial (star chart), a checkered pattern, a grid chart, a USAF 1951 target (United States Air Force MIL-STD-150A standard of 1951), or a resolution chart conforming to ISO 12233 (ISO: International Organization for Standardization) (CIPA (Camera & Imaging Products Association) resolution chart). It is also possible to use a roughness standard (e.g., a pseudo-roughness standard, a random-shape roughness standard, etc.) as the master M. The types of shape patterns are not limited to those exemplified above.

The data processing unit 100 acquires an image _Ii of the master M for each scanning position _Zi from the white light interferometer microscope 10. Here, i is a frame number indicating the scanning position in the Z direction, and i = 1, 2, ..., N (N ≥ 2) (see Figure 2).

The match parameter calculation unit 104 calculates a first parameter (a parameter for evaluating horizontal contrast, hereinafter referred to as the horizontal contrast parameter) related to the X and Y directions on the screen (XY plane) of the camera 28, and a second parameter (a parameter for evaluating vertical contrast, hereinafter referred to as the vertical contrast parameter) related to the time axis direction (i.e., frame number or Z direction).The match parameter calculation unit 104 then calculates a match parameter for each scanning position Zi from the correlation between the horizontal contrast parameter and the vertical contrast parameter and the scanning position in the _Z direction.

The degree-of-match determining unit 106 calculates the position of the reference surface 24c at which the degree of match is maximized from the degree-of-match parameters for each scanning position _Zi .

This allows the reference surface 24c to be moved to the position where the degree of match is maximized, making it easy to adjust the shape measuring device 1.

3 and 4 are diagrams for explaining examples of calculation of the horizontal contrast parameter and the vertical contrast parameter, respectively. In the following explanation, the luminance of pixel (x, y) in image _Ii is defined as Pi _{(x, y)} .

When calculating the horizontal contrast parameter, for a pixel (x, y) in image _Ii , the difference in brightness Cp i(x, y) between the pixel and the adjacent pixels ((x-1, y-1), (x-1, y), (x-1, y+1), (x, y-1), (x, y+1), (x+1, y-1), (x+1, y) and (x+1, y+1)) shown in FIG. _3(a) is calculated.

Specifically, Cpi _(x,y) is obtained by multiplying the luminance values Pi(x,y) of the pixel _(x,y ) and its adjacent pixels by the kernel (coefficients) shown in Fig. 3(b). When the kernel (coefficients) shown in Fig. 3(b) is applied, Cpi _(x,y) is expressed by the following formula (1).

Cp _i(x,y) = |4×P _i(x,y) -P _i(x-1,y) -P _i(x+1,y)
-P _{i (x, y-1)} -P _{i (x, y+1)} | ...(1)
When calculating the vertical contrast parameter, the difference Ct _i (x, y) in brightness between a pixel (x, y) in image I i and the pixels at the same position in the previous and next images I _i-1 and I _i+1 in the Z direction shown in Figure 4(a ₎ is calculated.

Specifically, Ct _{i(x, y)} is obtained by multiplying the luminance values Pi(x, y _{) of the pixel (x, y} ) and its adjacent pixels by the kernel (coefficients) shown in Fig. 4(b). When the kernel (coefficients) shown in Fig. 4(b) is applied, Ct _{i(x, y)} is expressed by the following formula (2).

Ct _i(x,y) = |2×P _i(x,y) −P _(i−1)(x,y) −P _(i+1)(x,y) | …(2)
Note that the methods of selecting adjacent pixels shown in Figures 3(a) and 4(b) and the kernels shown in Figures 3(b) and 4(b) are merely examples, and the method of calculating parameters is not limited to the above. For example, for pixels at the ends in the X and Y directions or the end in the Z direction, the method of selecting adjacent pixels or the kernel may be changed.

5 is a diagram showing an example of calculation of the horizontal contrast parameter Cp _{i(x, y)} . For example, as shown in FIG. 5, when calculating Cp _{i(x, y)} , the contrast value (degree of focus) is determined by multiplying the luminance values of the pixel of interest (x, y) by the luminance values of its neighboring pixels ((x-1, y-1), (x-1, y), (x-1, y+1), (x, y-1), (x, y+1), (x+1, y-1), (x+1, y), and (x+1, y+1)).

The above horizontal contrast parameters and vertical contrast parameters (Cp, Ct) can be calculated for all pixels in image Ii or for a subset of pixels, and the sum or median of these values can be used to calculate the matching parameter.

Next, as described above, the horizontal contrast parameters Cp ₁ to Cp _N and the vertical contrast parameters Ct ₁ to Ct _N are calculated for each of the images I ₁ to I _N , and correlations with the scanning position Z _i are calculated.

6 is a graph showing the relationship between the horizontal contrast parameter and the vertical contrast parameter and the scanning position (Z position). In FIG. 6, the curves Cp and Ct are approximate curves (e.g., curves obtained by least squares approximation or polynomial approximation) of the horizontal contrast parameters Cp ₁ to Cp _N and the vertical contrast parameters Ct ₁ to Ct _N , respectively.

The matching parameter calculation unit 104 calculates the scanning positions (Zp, Zt) at which the horizontal contrast parameter Cp and the vertical contrast parameter Ct reach their peaks (maximums). The matching parameter calculation unit 104 then calculates the parameter |Zp-Zt|, which indicates the degree to which Zp and Zt match, as a parameter indicating the degree of match between the in-focus position and the interference position.

Next, similar measurements are performed while changing the position of the reference surface 24c. The match determination unit 106 then calculates the target setting position of the reference surface 24c from the relationship between the position of the reference surface 24c and the match parameter.

Figure 7 is a graph showing the relationship between the degree of match parameter and the position of the reference surface. Figure 7 illustrates the value of the degree of match parameter |Zp - Zt| calculated for each position on the reference surface 24c, along with its approximation curve (e.g., a curve calculated using least-squares approximation or polynomial approximation).

The match determination unit 106 searches for the position on the reference surface 24c where the value of the match parameter |Zp - Zt| is minimum, and adopts that position as the target setting position Ao of the specified reference surface.

In this embodiment, the absolute difference |Zp - Zt| is used as the matching parameter, but the present invention is not limited to this. For example, any parameter indicating the degree to which Zp and Zt match, such as the square of the difference (Zp - Zt), {min(Zp, Zt)/max(Zp, Zt)}, or [1 - {min(Zp, Zt)/max(Zp, Zt)}], can also be used as the matching parameter. Note that when the square of the difference (Zp - Zt) is used as the matching parameter, the position of the reference surface 24c where the matching parameter is minimum can be set as the target setting position. When {min(Zp, Zt)/max(Zp, Zt)} is used as the matching parameter, the position of the reference surface 24c where the matching parameter is closest to 1 can be set as the target setting position. Furthermore, if the matching parameter is [1-{min(Zp,Zt)/max(Zp,Zt)}], the position of the reference surface 24c where the matching parameter is closest to 0 can be set as the target setting position.

(Timing for checking the degree of match)
The timing (time conditions) for checking the degree of match using the master M may be as follows:

(a) A check is performed when the number of measurements performed on the measurement object W exceeds a certain value. In this case, by limiting the number of measurements performed, it is possible to limit the maximum number of measurements performed on the measurement object W in a poorly adjusted state.

(b) A check is performed after a certain period of time or a certain number of days has elapsed. In this case, even if measurement of the measurement object W is performed in a poorly adjusted state, the measurement object W and measurement data measured in a poorly adjusted state can be identified by the measurement date, etc. This makes it easy to trace the measurement data measured in a poorly adjusted state, making it possible to perform re-measurements.

(c) A check is performed at the start of a measurement batch (e.g., a lot). In this case, the measurement objects W that are measured in a misaligned state are limited to the batch. This makes it easy to trace measurement data measured in a misaligned state, allowing for remeasurement.

Note that the timing of confirmation is not limited to the examples listed above. The worker may be able to select or set (a) to (c) above or a combination thereof.

[Method for adjusting a shape measuring device]
FIG. 8 is a flowchart showing a method for adjusting a shape measuring device according to an embodiment of the present invention.

First, the master M is set on the stage ST of the white light interferometer 10 (step S10), and the driving mechanism 12 sets the white light interferometer 10 to its initial position in the Z direction (step S12).

Next, acquisition of an image of the master M (step S14) and scanning in the Z direction of the white light interference microscope 10 (step S18) are repeated, and when scanning in the Z direction is completed (Yes in step S16), a matching parameter is calculated from _the image _Ii at each scanning position Zi (step S20).

Next, the reference surface 24c is scanned in the X direction (step S24), and steps S12 to S20 are repeated. When scanning of the reference surface 24c is completed (Yes in step S22), the target setting position Ao of the reference surface 24c is calculated based on the matching parameter (see Figure 7) (step S26). Then, the reference surface 24c is moved to the target setting position Ao, thereby completing adjustment of the shape measuring device 1.

According to this embodiment, the target setting position of the reference surface 24c can be calculated numerically, allowing the position of the reference surface 24c to be adjusted with high precision. Furthermore, the reproducibility of the adjustment of the position of the reference surface 24c can be improved without relying on individual differences or standards between operators.

[Example 1]
The distance difference between the peak position Zp (indicating the in-focus position) where the horizontal contrast parameter Cp shown in Figure 7 reaches its peak value and the peak position Zt (indicating the interference position) where the vertical contrast parameter Ct reaches its peak value indicates the optical path difference between the measurement optical path length D1 and the reference optical path length D2.

The target setting position Ao of the reference surface 24c can be obtained by moving the position of the reference surface 24c by (Zp - Zt).

According to Example 1, there is no need to perform contrast measurement (the loop of steps S22 to S24) while changing the position of the reference surface 24c, which enables adjustment of the shape measuring device 1 in a shorter time, contributing to improved efficiency of the device.

[Example 2]
When the interference position is close to the in-focus position (for example, when the deviation is within the range of the focal depth), interference fringes appear within the screen of the camera 28 when calculating the horizontal contrast parameter Cp, as shown in Fig. 9. These interference fringes have an adverse effect on the calculation of the horizontal contrast parameter Cp, resulting in a problem of reduced calculation accuracy for Zp, which indicates the in-focus position, as shown in Fig. 10. In Fig. 10, the shape of the horizontal contrast parameter Cp is distorted like Cpf, and the peak position is shifted from Zp to Zpf. In particular, when the installation angle of the master M is to a certain extent, light and dark areas due to interference fringes are more likely to appear within the screen of the camera 28.

In Example 2, when calculating the horizontal contrast parameter Cp, pixels whose brightness is near the maximum or minimum value of the camera 28 are excluded from the calculation of the horizontal contrast parameter Cp. For example, if the resolution of each pixel is 8 bits (0 to 255), calculations are not performed for pixels whose brightness is near 0 (e.g., 0 to 9) or 255 (e.g., 246 to 255), and the value calculated for pixels outside the above range is used.

According to Example 2, the effects of blown-out highlights and blown-out shadows, which can reduce the accuracy of horizontal contrast parameter calculations, can be eliminated, making it possible to calculate the horizontal contrast peak with higher accuracy. This enables the shape measurement device 1 to provide more accurate and reliable three-dimensional shape measurement results.

[Example 3]
In Example 3, as shown in FIG. 11(b), the master M is installed tilted in a specific direction with respect to the measurement optical axis AX. Here, the tilt amount of the master M is preferably set so that, for example, multiple interference fringes occur within one field of view. If the field of view range is 1 mm square, the height per mm is 0.55 μm (approximately the wavelength). In this case, the tilt angle φ shown in FIG. 11(a) is φ = arctan (0.55 μm/1 mm). Note that the field of view range differs depending on the magnification of the objective lens.

Then, as shown in Figure 11(a), the horizontal contrast is calculated in a direction perpendicular to the direction D1 in which the light and dark pattern of interference fringes occurs.

In Figure 11, the direction D1 in which the light and dark patterns of the interference fringes occur is the X direction. In this case, the horizontal contrast parameter Cp is calculated using, for example, a kernel such as that shown in Figure 12. In the kernel shown in Figure 12, the coefficients for pixels adjacent to the central pixel of interest in the X direction are set to 0. By using such a kernel, it is possible to calculate the horizontal contrast in a direction perpendicular to the direction D1 in which the light and dark patterns of the interference fringes occur.

According to Example 3, the influence of contrast caused by interference fringes can be suppressed, making it possible to calculate the peak of horizontal contrast with higher accuracy.

[Modification 1]
FIG. 13 is a diagram showing a shape measuring device according to the first modification.

As shown in FIG. 13, the shape measuring device 1A according to variant example 1 adjusts the position of the reference surface 24c using a temperature regulator (temperature sensor 34 and temperature control unit 112).

As shown in Figure 13, in the shape measurement device 1A, the interference objective lens 24 includes a holder 24d.

Holder 24d is made of a metallic material such as brass, i.e., a material that undergoes reversible thermal deformation. Holder 24d includes lens barrel 24d1 and reference surface storage section 24d2. Lens barrel 24d1 is cylindrical and extends in the Z direction, and stores (holds) objective lens 24a and beam splitter 24b. Reference surface storage section 24d2 is cylindrical and extends in the X direction from the position where beam splitter 24b is held on lens barrel 24d1, and stores reference surface 24c.

The temperature adjustment unit 32 is located near the reference surface storage unit 24d2 and, under the control of the temperature control unit 112, adjusts at least the temperature between the beam splitter 24b and the reference surface 24c, i.e., the temperature of the reference surface storage unit 24d2. For example, a heater or Peltier element may be used as this temperature adjustment unit 32.

The reference surface housing portion 24d2 is made of a material that undergoes reversible thermal deformation, so it undergoes reversible thermal deformation (expands or contracts) in response to temperature changes. This allows the temperature of the reference surface housing portion 24d2 to be changed by the temperature adjustment portion 32, thereby thermally deforming the reference surface housing portion 24d2 and adjusting the X-direction position of the reference surface 24c in response to this thermal deformation.

The temperature sensor 34 corresponds to the temperature measurement unit of the present invention. The temperature sensor 34 is provided near the reference surface storage unit 24d2, and measures the temperature of at least the reference surface storage unit 24d2 (between the beam splitter 24b and the reference surface 24c) within the holder 24d, outputting the temperature measurement result to the temperature acquisition unit 116 of the temperature control unit 112. The measurement result of this temperature sensor 34 is used by the temperature control unit 112 to control the temperature adjustment unit 32.

The thermal insulation material 30 is arranged to cover the entire interference objective lens 24, the temperature adjustment unit 32, and the temperature sensor 34. This prevents the temperature inside the thermal insulation material 30, particularly the temperature of the reference surface storage unit 24d2 and its vicinity, from changing due to external influences.

As shown in FIG. 13, the temperature control unit 112 includes a control target temperature storage unit 114, a temperature acquisition unit 116, a calculation processing unit 118, and an output control unit 120.

The control target temperature storage unit 114 stores a lookup table LUT that indicates the correspondence between the temperature inside the holder 24d (e.g., the temperature of the reference surface storage unit 24d2, the temperature between the beam splitter 24b and the reference surface 24c) and the position of the reference surface 24c (position in the X direction).

The calculation processing unit 118 refers to the LUT stored in the control target temperature storage unit 114 and calculates the output of the temperature adjustment unit 32 required to move the reference surface 24c to the set target position. Specifically, the calculation processing unit 118 reads the temperature (control target temperature) inside the holder 24d corresponding to the set target position of the reference surface 24c from the LUT, and calculates the output of the temperature adjustment unit 32 to bring the temperature inside the holder 24d to the control target temperature.

The output control unit 120 controls the output of the temperature adjustment unit 32 based on the calculation results by the calculation processing unit 118, and sets the temperature inside the holder 24d to the control target temperature. Here, temperature control inside the holder 24d can be performed using, for example, feedback control, PID control (Proportional-Integral-Differential Controller), etc.

In variant 1, the position of the reference surface 24c can be managed using a numerical value, namely temperature, allowing for adjustment with higher precision, higher resolution, and higher reproducibility.

[Modification 2]
FIG. 14 is a diagram showing a shape measuring device according to the second modification.

As shown in Figure 14, the shape measuring device 1B according to variant example 2 adjusts the position of the reference surface 24c using a linear motion mechanism that uses a motor M.

The motor control unit 130 acquires the position of the reference surface 24c in the X direction and controls the amount of rotation of the motor M (feedback control, PID control) to move the reference surface 24c to the set target position.

According to the second modification, the position of the reference surface 24c can be controlled using the motor M, so that adjustment can be performed with higher accuracy, higher resolution, and higher reproducibility.
Although the second modification employs a linear motion mechanism using the motor M, the present invention is not limited to this. For example, it is also possible to employ a linear motion mechanism using an actuator such as a piezoelectric element.

1, 1A, 1B... Shape measurement device, 10... White light interference microscope, 12... Drive mechanism, 14... Scale, 16... Switching mechanism, 20... Light source unit, 22... Beam splitter, 24... Interference objective lens, 24a... Objective lens, 24b... Beam splitter, 24c... Reference surface, 24d... Holder, 26... Imaging lens, 28... Camera, 30... Heat insulating material, 32... Temperature adjustment unit, 34... Temperature sensor, 100... Data processing unit, 102... Shape measurement unit, 104... Matching parameter calculation unit, 106... Matching determination unit, 108... Operation unit, 110... Output unit, 112... Temperature control unit, 114... Control target temperature storage unit, 116... Temperature acquisition unit, 118... Calculation processing unit, 120... Output control unit, 130... Motor control unit

Claims (4)

A method for adjusting a shape measuring device, comprising: irradiating an adjustment master and a reference surface with light from a light source as measurement light and reference light, respectively; and measuring a shape of a surface to be measured of a measurement object using multiplexed light of the measurement light and the reference light reflected by the adjustment master and the reference surface, respectively;
acquiring an image of the adjustment master for each of a plurality of scanning positions along a scanning direction perpendicular to the adjustment master, and calculating a matching degree parameter indicating a matching degree between a focus position and an interference position from the image for each of the scanning positions;
calculating a target set position of the reference surface based on the match parameter;
A method for adjusting a shape measuring device comprising: The method for adjusting a shape measuring device described in claim 1, wherein the degree of match parameter is calculated based on a first parameter that is the difference in luminance along a direction on the surface of pixels included in the image of the adjustment master for each scanning position, and a second parameter that is the difference in luminance along the scanning direction. calculating the degree of match parameter for each position of the reference surface;
calculating the target set position of the reference surface based on the degree of match parameter calculated for each position of the reference surface;
The method for adjusting a shape measuring device according to claim 1 or 2, comprising: The method for adjusting a shape measuring device described in claim 2, wherein the target setting position of the reference surface is a position obtained by moving the reference surface by the difference between the peak values of the first parameter and the second parameter from the position of the reference surface when the image used to calculate the degree of match parameter was acquired.