JP7001947B2 - Surface shape measurement method - Google Patents

Description

The present invention relates to a surface shape measuring method, and more particularly to a surface shape measuring method for measuring the surface shape of a measurement object in a non-contact manner using a scanning white interferometer.

The surface shape measuring device is a device that measures the three-dimensional shape of the surface to be measured of the object to be measured, and is known to use a scanning white interferometer. The scanning white interferometer measures the three-dimensional shape of the measured surface of the object to be measured by non-contact using the interferometer.

The interferometer has an objective lens as a component of an optical microscope, a beam splitter arranged between the objective lens and the surface to be measured, and a reference mirror. The white light incident on the interferometer from the white light source passes through the objective lens and is divided into the measurement light and the reference light by the beam splitter, the measurement light is applied to the surface to be measured, and the reference light is applied to the reference mirror. .. Then, the measurement light returning from the measured surface and the reference light returning from the reference mirror are superposed to generate interference light, and the interference light passes through the objective lens and is emitted from the interference meter to the CCD camera.

As a result, an interference fringe image is formed on the image pickup surface of the CCD camera, and the interference fringe image is acquired by the image pickup element of the CCD camera as interference fringes. Then, the interference fringes are acquired while the interference meter is displaced with respect to the measured surface in the height direction, and the displacement amount when the brightness value shows the maximum value for each pixel of the interference fringes is detected to detect the displacement amount of the measured surface. The relative height of each point is measured.

As described above, in the scanning white interferometer as described above, when the interference fringes are acquired, the scanning white interferometer is scanned in the height direction, but the scanning range in the height direction is not appropriately determined. Then, the range where the interference fringes were not generated was also measured, and it took a long time to measure.

In a non-contact shape measuring machine using light, there are many restrictions on the range that can be measured by one measurement due to the limitation of the field of view of the objective lens used, so multiple measurements are performed and those measurement data are used later. The method of connecting (stitching) is known. In stitching that connects multiple measurements, it takes a long time to measure because the measurements are performed multiple times. For such problems, set the measurement range after visually confirming the disappearance of the interference fringes, or perform preliminary scanning to confirm the generation and disappearance of the interference fringes, and then set the measurement range. Is being done. However, even in these cases, it takes time to prepare for measurement, and the total time required for shape measurement cannot be significantly reduced.

Further, Patent Document 1 below describes a shape measuring device that obtains a moving range in the Z-axis direction at the next measurement position based on an average value of an overlapping region with an adjacent imaging region.

Japanese Unexamined Patent Publication No. 2014-202651

However, in the shape measuring device described in Patent Document 1, since the setting is based on the overlapping range between the imaged region and the adjacent next imaged region, the adjacent region may have a stepped portion. The height was different depending on the step, and it was not possible to cope with it.

The present invention has been made in view of such circumstances, and is a surface shape measuring method capable of estimating a vertical scanning range when measuring a surface shape with a high probability and determining the surface shape in a short time. The purpose is to provide.

In order to achieve the above object, the surface shape measuring method according to the present invention uses a support portion that supports the object to be measured, a light source portion that emits white light, and white light from the light source portion as measurement light and reference light. In addition to irradiating the measured surface of the object to be measured with the measurement light, the reference light is irradiated to the reference surface, and the interference light that interferes with the measurement light returning from the measured surface and the reference light returning from the reference surface is emitted. It has an interfering part to be generated and a plurality of pixels corresponding to each point on the measured surface, and acquires interference fringes from the brightness information of the interference light between the measurement light and the reference light applied to each point on the measured surface. It is a shape measurement method using a shape measuring device including a surface shape acquisition unit for acquiring surface shape data of an object to be measured and an optical unit having the surface shape acquisition unit, and the measurement light applied to each point on the surface to be measured. While changing the optical path length, the interference fringe acquisition step of acquiring interference fringes at an image acquisition interval longer than the center wavelength of white light and the surface shape acquisition corresponding to each point of the measured surface measured in the interference fringe acquisition step. The range in which the interference fringes are generated is estimated from the brightness information of the reference pixel selected from the plurality of pixels of the unit and at least one pixel of the peripheral pixels of the reference pixel, and the scanning range in the axial direction of the measurement light is determined. Interference fringes at shorter image acquisition intervals than the interference fringe acquisition step while changing the optical path length of the measurement light applied to each point on the surface to be measured within the scanning range determined in the scanning range determination step. The present invention comprises a surface shape measuring step of measuring the surface shape of the object to be measured by detecting the position of the interference fringes in the optical axis direction of the measurement light at each point on the surface to be measured based on the interference fringes.

According to the surface shape measuring method of the present invention, the measurement time can be shortened by determining the scanning range of the optical unit when measuring the surface shape before measuring the surface shape of the object to be measured. .. Further, since the image acquisition interval for confirming the generation and disappearance of the interference fringes for determining the scanning range of the optical unit is longer than the center wavelength of the white light, it can be acquired in a short time. By lengthening the image acquisition interval, depending on the pixel, the change in the luminance value due to the interference fringes may be small even in the region where the light and darkness due to the interference fringes is generated. In the present invention, since the scanning range is determined not only by the reference pixel but also by the peripheral pixels thereof, the range in which the interference fringes are generated can be estimated with high probability. Therefore, the scanning range can be determined in a short time, and the surface shape can be measured in a short time, so that the measurement time can be shortened as a whole for the surface shape measurement.

In one aspect of the shape measuring method according to the present invention, it is preferable to randomly select pixels having different distances from the reference pixel as peripheral pixels.

According to this aspect, by selecting pixels whose distances from the reference pixels are randomly different from the peripheral pixels to be selected, the shape of the surface to be measured has a stepped portion, or is extremely inclined. Even when the height displacement is large, the position where the interference fringes are generated can be stably estimated.

One aspect of the shape measuring method according to the present invention is a moving step of relatively moving the positions of the support portion and the optical portion after performing the interference fringe acquisition step, the scanning range determination step, and the surface shape measuring step. , A repeating step of acquiring a plurality of surface shape data by performing an interference fringe acquisition step, a scanning range determination step, and a surface shape measurement step on the surface to be measured after the moving step, and a plurality of surface shape data. It is preferable to have a connection step of connecting the above and acquiring a wide range surface shape data of the object to be measured.

According to the present invention, the time of the surface shape measuring step can be shortened by determining the scanning range of the surface shape measuring step. Therefore, since the measurement time of the entire surface shape measurement can be shortened, the surface of the measurement target is wide, and a plurality of surface shape data are acquired and connected, that is, the surface of the entire region of the measurement target is stitched. When acquiring shape data, it is effective because it can be measured in a short time.

In one aspect of the shape measuring method according to the present invention, in the scanning range determination step, a range including a region in which the sum of the absolute values of the changes in the luminance values of the reference pixel and the peripheral pixels includes a predetermined value or more is determined as the scanning range. Is preferable.

This aspect shows one aspect of the method of determining the scanning range in the scanning range determination step, and includes a vertical scanning position in which the sum of the changes in the luminance values of the reference pixel and the peripheral pixels is equal to or greater than a predetermined value. It can be determined as a scanning range for measuring the range. In this way, even if the generation of interference fringes cannot be confirmed due to the relationship between the interference fringes and the sampling position depending on the reference pixel, if the generation of interference fringes can be confirmed in relation to the peripheral pixels, the surface shape measurement step. Can be the scanning range of.

According to the surface shape measuring method of the present invention, the scanning range for measuring the surface shape can be determined in a short time before measuring the surface shape of the object to be measured, and the scanning range can be determined with high probability. Since it can be estimated, the entire time for measuring the surface shape can be performed in a short time.

It is an overall block diagram of the surface shape measuring apparatus (scanning type white interferometer). It is a figure which showed the pixel array of the interference fringes on the xy coordinate of the image pickup surface of an image pickup element. It is a figure exemplifying the relationship between the z position of an interference part and a luminance value, and an interference fringe curve. It is a figure which exemplifies the relationship between the different z coordinate values of the different points of the measured surface, and the interference fringe curve. It is a figure which exemplifies the relationship between the image acquisition position and the interference fringe curve. It is a figure which exemplifies the relationship between the image acquisition position of a reference pixel and a peripheral pixel, and an interference fringe curve. It is a figure which shows the flowchart of the surface shape measuring method. It is a figure which shows the flowchart of the preliminary scan. It is a figure which showed the pixel arrangement of the interference fringes on the xy coordinate of the image pickup surface of an image pickup element, and is the figure which showed the setting example of a reference pixel. It is a figure which showed the pixel array of the interference fringes on the xy coordinate of the image pickup surface of the image pickup element, and is the figure which showed the selection example of the peripheral pixel. It is a figure which showed the pixel array of the interference fringes on the xy coordinate of the image pickup surface of the image pickup element, and is the figure which showed the other selection example of the peripheral pixel. It is a figure which showed the pixel array of the interference fringes on the xy coordinate of the image pickup surface of the image pickup element, and is the figure which showed the other selection example of the peripheral pixel. It is a figure which shows the example which determines the measurement range using the luminance value of a reference pixel and the peripheral pixel.

Hereinafter, preferred embodiments of the shape measuring method of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram showing an example of a shape measuring device used in the shape measuring method according to the present invention.

The surface shape measuring device 1 in the figure is a so-called Michaelson-type scanning white interferometer (microscope) that measures the surface shape of an object to be measured three-dimensionally by non-contact using a Michaelson-type interferometer. , Various calculations based on the optical unit 2 that acquires the interference image of the measurement object P, the stage 10 on which the measurement object P is placed, each control of the optical unit 2, and the interference image acquired by the optical unit 2. A processing unit 18 or the like including an arithmetic processing device such as a personal computer that performs processing is provided.

In this embodiment, the example of the Michaelson type scanning white interferometer will be described, but a well-known Millow type scanning white interferometer may be used. Further, in the measurement space where the measurement object P is arranged, the two horizontal coordinate axes orthogonal to each other are set as the x-axis (axis orthogonal to the paper surface) and the y-axis (axis parallel to the paper surface), and the x-axis and y-axis. The vertical coordinate axis orthogonal to is the z-axis (measurement optical axis direction). The z-axis is parallel to the measurement optical axis Z-0 described later.

The stage 10 is a flat upper surface substantially parallel to the x-axis and the y-axis, and is a support portion that supports the measurement object P, and has a stage surface 10S on which the measurement object P is placed. Further, the stage 10 has an inclination angle changing means for changing the inclination angle (inclination angle with respect to the z-axis) of the stage surface 10S with respect to the parallel plane, and the stage surface 10S (stage 10) has x by the inclination angle changing means. It is rotatably provided around the x-rotating axis 30 parallel to the axis and around the y-rotating axis 32 parallel to the y-axis. Then, the stage surface 10S rotates around the x rotation axis 30 by driving the x actuator 34, and rotates around the y rotation axis 32 by driving the y actuator 36.

The term actuator in the present specification, such as the x-actuator 34 and the y-actuator 36, means an arbitrary drive device such as a piezo actuator or a motor.

An optical unit 2 integrally housed and held by a housing (not shown) is arranged at a position facing the stage surface 10S, that is, on the upper side of the stage 10.

The optical unit 2 has a light source unit 12 having an optical axis Z-1 parallel to the x-axis and an interference unit having an optical axis Z-0 parallel to the z-axis (hereinafter referred to as “measurement optical axis Z-0”). It has 14 and a photographing unit 16. The optical axis Z-1 of the light source unit 12 is orthogonal to the optical axis Z-0 of the interference unit 14 and the photographing unit 16, and intersects the optical axis Z-0 between the interference unit 14 and the photographing unit 16. The optical axis Z-1 does not necessarily have to be parallel to the x-axis.

The light source unit 12 emits white light having a wide wavelength width (low coherence light with less coherence) as illumination light for illuminating the object P to be measured, and illumination light diffused from the light source 40 and emitted. It has a collector lens 42 that converts light into a substantially parallel light source. The axis at the center of each of the light source 40 and the collector lens 42 is coaxially arranged as the optical axis Z-1 of the light source unit 12.

Further, as the light source 40, any kind of light emitting body such as a light emitting diode, a semiconductor laser, a halogen lamp, and a high-intensity discharge lamp can be used.

The illumination light emitted from the light source unit 12 is arranged between the interference unit 14 and the photographing unit 16, and is a half mirror or the like arranged at a position where the optical axis Z-1 and the measurement optical axis Z-0 intersect. It is incident on the beam splitter 44 of. Then, the illumination light reflected by the beam splitter 44 (the flat light splitting surface (reflecting surface) of the beam splitter 44) travels along the measurement optical axis Z-0 and is incident on the interference portion 14.

The interference unit 14 is composed of a Michelson type interferometer, and divides the illumination light incident from the light source unit 12 into measurement light and reference light. Then, the measurement object P is irradiated with the measurement light, and the reference light is irradiated to the reference mirror 52 to generate interference light in which the measurement light returning from the measurement object P and the reference light returning from the reference mirror 52 interfere with each other. ..

The interference unit 14 includes an objective lens 50 having a light-collecting action, a reference mirror 52 which is a reference surface for reflecting light and has a flat reflection surface, and a flat beam splitter 54 for splitting light. The axis at the center of each of the objective lens 50, the reference mirror 52, and the beam splitter 54 is coaxially arranged as the optical axis Z-0 of the interference unit 14. The reflection surface of the reference mirror 52 is arranged at a lateral position of the beam splitter 54 in parallel with the measurement optical axis Z-0.

The illumination light incident on the interference unit 14 from the light source unit 12 is condensed by the objective lens 50 and then incident on the beam splitter 54.

The beam splitter 54 is, for example, a half mirror, and the illumination light incident on the beam splitter 54 is split into a measurement light that passes through the beam splitter 54 and a reference light that is reflected by the light splitting surface of the beam splitter 54.

The measurement light transmitted through the beam splitter 54 is applied to the measured surface S of the object to be measured P, then returns from the measured surface S to the interference portion 14, and is incident on the beam splitter 54 again. Then, the measurement light transmitted through the beam splitter 54 is incident on the objective lens 50.

On the other hand, the reference light reflected by the beam splitter 54 is reflected by the light reflecting surface of the reference mirror 52 and then incidents on the beam splitter 54 again. Then, the reference light reflected by the beam splitter 54 is incident on the objective lens 50.

As a result, interference light is generated in which the measurement light irradiated from the interference unit 14 to the measured surface S of the object P to be measured and returned to the interference unit 14 and the reference light reflected by the reference mirror 52 are superimposed, and the interference is generated. After the light is focused by the objective lens 50, it is emitted from the interference unit 14 toward the photographing unit 16.

Further, after the illumination light is divided into the measurement light and the reference light, the optical path of the optical path through which each of the measurement light and the reference light passes until the measurement light and the reference light are superimposed is determined by the optical path of the measurement light. The length and the optical path length of the reference light are called, and the difference between them is called the optical path length difference between the measured light and the reference light.

Further, the interference unit 14 is provided in the optical unit 2 so as to be linearly movable in the z-axis direction. Then, the objective lens 50 and the beam splitter 54 move in the z-axis direction by driving the interference unit actuator 56. As a result, the position (height) of the focal plane of the objective lens 50 moves in the z-axis direction, and the distance between the measured surface S and the beam splitter 54 changes, so that the optical path length of the measured light changes, and the measurement is performed. The difference in optical path length between light and reference light changes.

The image pickup unit 16 is a surface shape acquisition unit that acquires surface shape data of the measurement target P from the brightness information of the interference light between the measurement light and the reference light applied to each point of the measured surface S, and is, for example, a CCD (CCD). Charge Coupled Device) Corresponds to a camera, and has a CCD type image pickup element 60 and an image pickup lens 62. The axis at the center of each of the image pickup element 60 and the image pickup lens 62 is coaxially arranged as the optical axis Z-0 of the photographing unit 16. As the image pickup device 60, any imaging means such as a CMOS (Complementary Metal Oxide Semiconductor) type image pickup device can be used.

The interference light emitted from the interference unit 14 is incident on the beam splitter 44 described above, and the interference light transmitted through the beam splitter 44 is incident on the photographing unit 16.

The interference light incident on the photographing unit 16 forms an interference image on the image pickup surface 60S of the image pickup element 60 by the image pickup lens 62. Here, the image pickup lens 62 magnifies an interference image of the measured object P with respect to the region around the optical axis Z-0 of the measured surface S at a high magnification and forms an image on the image pickup surface 60S of the image pickup element 60.

Further, the image pickup lens 62 forms an image of a point on the focal plane of the objective lens 50 of the interference unit 14 as an image point on the image pickup surface of the image pickup element 60. That is, the photographing unit 16 is designed so as to be in focus (focus) on the position of the focal plane of the objective lens 50.

In the following, the position of the focal plane of the object P to be measured in the z-axis direction is simply referred to as the “focus position” or the “focus position of the photographing unit 16”.

The interference image formed on the image pickup surface 60S of the image pickup element 60 is converted into an electric signal by the image pickup element 60 and acquired as an interference image. Then, the interference image is given to the processing unit 18.

As described above, the optical unit 2 including the light source unit 12, the interference unit 14, the photographing unit 16, and the like is provided as an integral unit so as to be movable in a straight line in the z-axis direction. For example, the optical unit 2 is supported by a z-axis guide unit (not shown) erected along the z-axis direction so as to be movable in a straight line. Then, the entire optical unit 2 moves linearly in the z-axis direction by driving the z-actuator 70. As a result, the focus position of the imaging unit 16 can be moved more in the z-axis direction than when the interference unit 14 is moved in the z-axis direction. For example, the imaging unit can be moved according to the thickness of the object P to be measured. The focus position of 16 can be adjusted to an appropriate position.

When measuring the surface shape of the surface S to be measured of the object P to be measured, the processing unit 18 controls the interference unit actuator 56 to move the interference unit 14 of the optical unit 2 in the z-axis direction of the imaging unit 16. Interference images are sequentially acquired from the image sensor 60. Then, based on the acquired interference image, the three-dimensional shape data of the measured surface S is acquired as data indicating the surface shape of the measured surface S.

Here, a process in which the processing unit 18 acquires the three-dimensional shape data of the surface S to be measured based on the interference fringes will be described.

The image sensor 60 of the photographing unit 16 is composed of a large number of light receiving elements (pixels) two-dimensionally arranged along an xy plane (horizontal plane) consisting of an x-axis and a y-axis, and is an interference image received in each pixel. The brightness value, that is, the brightness value of each pixel of the interference image acquired by the image sensor 60 corresponds to the optical path length difference between the measurement light and the reference light reflected at each point of the measured surface S corresponding to each pixel. Indicates the intensity of interference light (brightness information).

Here, as shown in FIG. 2, the pixels in the m-th row and the n-th row of the interference image (the image pickup surface of the image pickup element 60) are represented as (m, n). Then, the x-coordinate value indicating the position of the pixel (m, n) in the x-axis direction (hereinafter, the position in the x-axis direction is referred to as “x position”) is expressed as x (m, n), and the position in the y-axis direction (hereinafter, the position in the y-axis direction). Hereinafter, the y coordinate value indicating the position in the y-axis direction is referred to as “y position”) is expressed as y (m, n).

Further, the x-coordinate value indicating the x-position of the point on the measured surface S of the measurement object P corresponding to the pixel (m, n) is represented by X (m, n), and the y-coordinate value indicating the y-position is Y. It shall be expressed as (m, n), and the point shall be expressed as (X (m, n), Y (m, n)) by the xy coordinate value. The point on the measured surface S corresponding to the pixel (m, n) is the point on the measured surface S on which the image point is formed at the position of the pixel (m, n) in the focused state. Means a point.

At this time, the luminance value of the pixel (m, n) of the interference image acquired by the image sensor 60 is the point (X (m, n), Y () on the measured surface S corresponding to the pixel (m, n). The magnitude corresponding to the optical path length difference between the measurement light and the reference light irradiated to m, n)) is shown.

That is, the interference unit 14 is moved in the z-axis direction by the interference unit actuator 56 in FIG. 1, and the position of the interference unit 14 relative to the optical unit 2 (photographing unit 16) in the z-axis direction (hereinafter referred to as “z position”). ) Is displaced, the focus position of the photographing unit 16 (the focal plane of the objective lens 50) also moves in the z-axis direction, and the focus position is also displaced by the same amount of displacement as the interference unit 14. Further, when the focus position is displaced, the optical path length of the measurement light applied to each point of the surface to be measured S also changes.

Then, while moving the interference unit 14 in the z-axis direction to shift the focus position, that is, while changing the optical path length of the measurement light, the interference images are sequentially acquired from the image pickup element 60, and any pixel of the interference image ( The brightness value of m, n) is detected.

Here, the processing unit 18 may detect the displacement amount of the interference unit 14 from a predetermined reference position (z position of the interference unit 14) by a detection signal from a position detection means (not shown) such as a potentiometer or an encoder. can. Alternatively, when the z position of the interference unit 14 is controlled without using the position detection means, for example, when the interference unit 14 is moved by a constant displacement amount by a drive signal given to the interference unit actuator 56, the total displacement amount thereof. Can be detected by.

Then, the z position of the focus position when the interference portion 14 is the reference position is set as the reference position (origin position) of the z coordinate in the measurement space, and the displacement amount of the interference portion 14 from the reference position is the z coordinate value of the focus position. Can be obtained as. The z-coordinate value has a positive side at a position higher than the origin position (a position closer to the photographing unit 16) and a negative side at a lower position (a position closer to the stage surface 10S). Further, the reference position of the interference unit 14, that is, the origin position of the z coordinate can be set or changed to an arbitrary z position.

3 (A) to 3 (C) are taken when an image is acquired from the image sensor 60 of the photographing unit 16 while raising the object P to be measured of the interference unit 14 from a position close to the measured surface S in the z-axis direction. It is a figure which showed the relationship between the z position of the interference part 14 and a luminance value.

As shown in FIG. 3A, when the optical path length L1 of the measurement light is smaller than the optical path length L2 of the reference light, the interference is small and the luminance value is substantially constant. Then, as shown in FIG. 3B, when the optical path length L1 of the measurement light and the optical path length L2 of the reference light are the same, that is, when the optical path length difference becomes 0, the interference becomes large and the maximum luminance value is shown. .. Further, as shown in FIG. 3C, when the optical path length L1 of the measurement light is larger than the optical path length L2 of the reference light, the interference becomes small again and the luminance value becomes substantially constant. As a result, the luminance value along the interference fringe curve Q shown in FIG. 3D is obtained.

That is, the interference fringe curve Q in any pixel (m, n) is at a point (X (m, n), Y (m, n)) on the measured surface S corresponding to the pixel (m, n). When the optical path length difference between the irradiated measurement light and the reference light is larger than the predetermined value, a substantially constant luminance value is shown, and when the optical path length difference is smaller than the predetermined value, the luminance value increases as the optical path length difference decreases. As it vibrates, its amplitude increases.

Therefore, as shown in FIG. 3D, the interference fringe curve Q shows the maximum value when the optical path lengths of the measurement light and the reference light match (when the optical path length difference is 0), and also shows the maximum value. The maximum value in the envelope of the interference fringe curve Q is shown.

Further, the optical path length between the measurement light and the reference light irradiated to the points (X (m, n), Y (m, n)) on the measurement surface S is such that the focus position of the photographing unit 16 is the measurement surface S. It matches when it matches the z position of the upper point (X (m, n), Y (m, n)).

Therefore, when the interference fringe curve Q shows the maximum value (or when the envelope of the interference fringe curve Q shows the maximum value), the focus position is the point (X (m, n), Y () on the measured surface S. It corresponds to the z position of m, n)), and the z coordinate value of the focus position at that time is the z coordinate of the point (X (m, n), Y (m, n)) on the measured surface S. Indicates a value.

From the above, the processing unit 18 moves the interference unit 14 in the z-axis direction by the interference unit actuator 56 to move the focus position in the z-axis direction (while changing the optical path length of the measurement light). Interference images are sequentially acquired from 60, and the brightness value of each pixel (m, n) is acquired in association with the z-coordinate value of the focus position. That is, the luminance value of each pixel (m, n) of the interference image is acquired while scanning the focus position in the z-axis direction. Then, for each pixel (m, n), the z coordinate value of the focus position when the luminance value of the interference fringe curve Q as shown in FIG. 3D shows the maximum value corresponds to each pixel (m, n). It is detected as a z-coordinate value Z (m, n) of a point (X (m, n), Y (m, n)) on the surface to be measured S.

Note that Z (m, n) indicates the z-coordinate value of the point (X (m, n), Y (m, n)) on the measured surface S corresponding to the pixel (m, n).

Further, a method for detecting the z-coordinate value of the focus position when the luminance value of the interference fringe curve Q indicates the maximum value is well known, and any method may be adopted. For example, by acquiring an interference image at the z-coordinate value for each minute interval of the focus position, it is possible to actually draw the interference fringe curve Q as shown in FIG. 3 (D) for each pixel (m, n). The brightness value can be acquired to some extent, and by detecting the z-coordinate value of the focus position when the acquired brightness value indicates the maximum value, the focus position when the brightness value of the interference fringe curve Q indicates the maximum value. The z-coordinate value of can be detected.

Alternatively, the interference fringe curve Q is estimated by the minimum square method or the like based on the brightness value acquired at each z coordinate value of the focus position, or the envelope of the interference fringe curve Q is estimated and the estimated interference fringe curve Q is estimated. Alternatively, by detecting the z-coordinate value of the focus position when the brightness value shows the maximum value based on the envelope, the z-coordinate value of the focus position when the brightness value of the interference fringe curve Q shows the maximum value is detected. be able to.

As described above, the processing unit 18 has each point (X (m, n), Y) on the measured surface S corresponding to each pixel (m, n) of the interference image (image pickup surface 60S of the image pickup element 60). By detecting the z-coordinate value Z (m, n) of (m, n)), the relative height of each point (X (m, n), Y (m, n)) on the measured surface S Can be detected.

Then, the x-coordinate value X (m, n), y-coordinate value Y (m, n), and z-coordinate value Z (m, n) of each point on the measured surface S are the three-dimensional shapes of the measured surface S. It can be acquired as data (data indicating the surface shape).

For example, as shown in FIG. 4, when the z-coordinate values Z1, Z2, and Z3 at three points on the measured surface S corresponding to the three pixels arranged in the x-axis direction are different, the focus position is scanned in the z-axis direction. While acquiring the brightness values of those pixels of the interference image, the interference fringe curves Q1, Q2, and Q3 showing the maximum brightness values when the focus position is the z coordinate values Z1, Z2, and Z3 for each of those pixels. Is obtained. Therefore, by detecting the z-coordinate value of the focus position when the luminance values of the interference fringe curves Q1, Q2, and Q3 show the maximum values, z at three points on the measured surface S corresponding to those pixels. The coordinate values Z1, Z2, and Z3 can be detected. By acquiring the three-dimensional shape data of the surface to be measured S in this way, the surface shape of the object to be measured P is measured.

When measuring the surface shape of the object P to be measured as described above, as a preparatory work before the measurement, a preliminary scan for determining the scanning range in the z-axis direction in the surface shape measurement is performed. By appropriately determining the scanning range in the z-axis direction of the surface shape measurement, it is possible to omit performing the surface shape measurement in a range where interference fringes do not occur, so that the measurement time can be shortened.

It is preferable to perform this preliminary scan in as short a time as possible in order to improve the measurement efficiency of the surface shape.

However, in order to prepare for measurement in a short time in order to improve the measurement efficiency of the surface shape, it is necessary to widen the image acquisition interval (image sampling interval) in the optical unit 2. However, if the image acquisition interval is widened, Searching for interference fringes becomes difficult. FIG. 5 is a diagram illustrating the relationship between the image acquisition position and the interference fringe curve when the sampling interval is longer than the wavelength. It is assumed that the interference fringe curve Q shown in FIG. 5 can be obtained by acquiring an image at a short sampling interval while raising the image in the z-axis direction (vertical scanning axis direction). However, when the image is acquired at the sampling interval shown in FIG. 5, the image is acquired only at the position where the change in the luminance value is small, and the sampling is not performed at the position where the luminance value is large, and the generation of the interference fringes cannot be confirmed. In some cases.

In the present embodiment, the image acquisition interval is made longer than the measurement wavelength, and the information of the reference pixel and its peripheral pixels is used for preliminary scanning to perform statistical processing, thereby performing z in the surface shape measurement. Appropriately determine the axial scan range. FIG. 6 is a diagram illustrating the relationship between the image acquisition positions of the reference pixel and the peripheral pixels and the interference fringe curve. Similar to the case shown in FIG. 5, in the reference pixel of FIG. 6, even when no change in the luminance value is observed, by using the information of the luminance value of the peripheral pixel, a high luminance value can be obtained in the peripheral pixel. Since it is obtained, the scanning range can be determined to include this range.

The processing unit 18 of the surface shape measuring device 1 according to the embodiment of the present invention is configured to include a measurement preparation control unit 18A for controlling a measurement preparation operation program for preliminary scanning.

FIG. 7 is a flowchart showing an example of a surface shape measuring method, and FIG. 8 is a flowchart showing an example of preliminary scanning.

In the surface shape measuring method, as shown in FIG. 7, first, the object to be measured is placed on the stage 10 (step S10).

Next, the processing unit 18 adjusts the measured light amount and the like so that the luminance value of the interference fringe curve acquired for all the pixels of the interference fringe (the image pickup surface of the image pickup element 60) becomes an appropriate size (step S12). ). That is, the strength of the light source 40 of the light source unit 12, the speed of the electronic shutter in the image sensor 60 (the length of the charge accumulation time), the gain for the image signal obtained by the image sensor 60, and the like are adjusted.

Next, preliminary scanning is performed so that the measurement scanning range (range in which the interference portion 14 is moved in the z-axis direction) of the surface shape measurement (step S16) is shortened (step S14). In this step, the measurement scanning range is shortened to the minimum necessary by grasping the outline of the surface shape of the object to be measured in advance. Preliminary scanning will be described with reference to FIG.

In the preliminary scan, as shown in FIG. 9, first, the reference pixel is selected (step S30). As shown in FIG. 9, the measurement preparation control unit 18A presets the reference pixel 100 as a reference for the generation and disappearance of the interference fringes on the xy coordinates of the image pickup surface 60S of the image pickup element 60. In the case of this embodiment, the reference pixel is a predetermined pixel before the preliminary scan. However, the operator designates the measurement preparation control unit 18A by the input unit 22 while referring to the pixels of the pixel arrangement in the interference fringe (imaging surface 60S of the image pickup element 60) as shown in FIG. 9 displayed on the display unit 20 of FIG. You may try to do it.

Next, the interference unit 14 is scanned and driven in a predetermined range in the z-axis direction, and an interference fringe acquisition step is performed (step S32). In this step, the interval for sampling the interference fringes (image acquisition interval) is set at an interval longer than the center wavelength of the white light to be measured. Further, this image acquisition interval is longer than the image acquisition interval in the surface shape measuring step described later. By lengthening the image acquisition interval, the time for preliminary scanning can be shortened. On the other hand, when the image acquisition interval becomes long, as described above, the image is not acquired at the position where the luminance value becomes large even though the interference fringes are generated, and the interference fringes are generated. It may not be possible to confirm. Therefore, in the present invention, the generation and disappearance of interference fringes can be estimated with high probability and the scanning range can be determined by also using the change in the luminance value of the peripheral pixels. The upper limit of the image acquisition interval is not particularly limited as long as the outline of the surface shape can be grasped by using the luminance value of the peripheral pixels, but it is preferably 2.5 times or less the wavelength. Further, when the wavelength is an integral multiple, the change in the luminance value in the interference fringe curve is the same, so it is preferable to avoid the integer multiple. Here, the defined range means the maximum scanning range in the z-axis direction of the focus position due to the movement of the interference unit 14 with respect to the optical unit 2 in the z-axis direction.

The measurement preparation control unit 18A moves the interference unit 14 in the z-axis direction by the interference unit actuator 56, scans the focus position in the z-axis direction (that is, changes the optical path length of the measurement light) from the image sensor 60. The interference fringes are sequentially acquired, and the brightness value of each pixel is acquired in association with the z-coordinate value of the focus position.

After acquiring the luminance value of each pixel, a scanning range determination step of determining the measurement scanning range in the vertical scanning direction of the main measurement is performed from the luminance values of the reference pixel and its type variation pixel (step S34).

According to the present embodiment, by determining the measurement scanning range using not only the reference pixel but also the luminance values of the peripheral pixels thereof, the sampling interval is lengthened, so that the reference pixel can sufficiently generate and eliminate interference fringes. Even if it cannot be confirmed, it can be estimated from the peripheral pixels.

10 to 12 are diagrams showing a method of selecting the reference pixel 100 and the peripheral pixels 102 of the reference pixel 100. FIG. 10 is an example in which only the pixels adjacent to the reference pixel 100 are used as the peripheral pixels 102. Further, FIG. 11 is an example of selecting peripheral pixels 102 at equal intervals from the reference pixel 100. FIG. 12 is an example of selecting peripheral pixels 102 so that the distance from the reference pixel 100 is random.

The method of selecting peripheral pixels of the reference pixel is not particularly limited. For example, it can be selected by the selection method shown in FIGS. 10 to 12. However, since the preliminary scan widens the sampling interval, when the peripheral pixels 102 are pixels at a certain distance from the reference pixel 100 as shown in FIG. 10 or 11, for example, they are selected from the reference pixels. If the displacement in the z-axis direction is large, such as when the surface shape of the object to be measured corresponding to the peripheral pixels has a stepped portion, it may not be possible to confirm the generation of interference fringes in the preliminary scan. As shown in FIG. 12, by randomly selecting peripheral pixels 102 from the reference pixel 100 and statistically processing using the information of the plurality of peripheral pixels 102, it is possible to stably estimate the outline of the surface shape. Become. The peripheral pixels refer to adjacent pixels adjacent to the reference pixel as shown in FIG. 10 and neighboring pixels located several pixels away from the reference pixel as shown in FIGS. 11 and 12.

Further, in the present embodiment, the measurement scanning range is determined by selecting peripheral pixels and performing statistical processing on them. Generally, when performing a preliminary scan, the frame rate of the camera is set to be as high as possible. Therefore, when an attempt is made to perform statistical processing on all pixels in the imaging surface, there arises a problem that the processing does not fit within the time interval of the frame. Therefore, the time for preliminary scanning is shortened by selecting the reference pixel and the peripheral pixels of the reference pixel and performing statistical processing on them.

Statistical processing for determining the measurement scanning range from the luminance values of the reference pixel and the peripheral pixels will be described. As an example of statistical processing, it can be determined by taking a simple sum as follows, for example.

Let x _i (i: pixel number) be the luminance value of the reference pixel and the selected peripheral pixel when performing the preliminary scan, and let <x> be the average luminance value in the area where no interference fringes are generated. The change in the luminance value due to the interference fringes for the i-th pixel is represented by Δx = | x _i- <x> |.

Then, as statistical processing, the simple sum Σ (Δx _i ) = Σ _i | x _i- <x> | of these values is obtained. This simple sum is calculated while scanning the vertical position of the optical unit (moving in the z direction), and the range including the region where the simple sum is equal to or more than a predetermined value is determined as the scanning range for measuring the surface shape. be able to. When calculating the simple sum, a threshold value may be set so that a value indicating a change in the luminance value below the threshold value is not used in the calculation of the simple sum.

FIG. 13 is a diagram showing an example of determining a measurement range using the luminance values of the reference pixel and the peripheral pixels. When the change in the luminance value of the reference pixel is measured while scanning the optical unit 2 in the vertical direction, for example, the change in the luminance value as shown in the reference pixel in FIG. 13 is shown. In the preliminary scan, since the sampling interval is wider than the wavelength, the change _Δxi of the luminance value may show a small value even in the region where the light and darkness due to the interference fringes is generated.

Peripheral pixels 1 to 3 indicate changes (Δx) in the luminance values of the peripheral pixels selected so that the distance from the reference pixel is random. Although omitted in FIG. 13, a simple sum of changes in the luminance values of the plurality of peripheral pixels is further shown. By obtaining the simple sum and graphing it, the amount of change in the luminance value in the vertical direction (z-axis direction) in the reference pixel and its peripheral pixels can be obtained, and the vertical direction of the surface measurement is included so as to include this range. Scanning range can be determined. In this way, even if a sufficient change in the luminance value cannot be confirmed in the reference pixel, the vertical position of the surface shape can be estimated by using the change in the luminance value of the peripheral pixels, and the scanning range is determined. can do.

As statistical processing, in addition to the method using simple sum, it is possible to create an appearance frequency distribution of luminance value change and determine the range in which the appearance frequency is included in a specific range as the range of this measurement. The method is not limited to one type, and a plurality of types may be used in combination.

Here, the difference between the present invention and autofocus will be described. In general autofocus, when the object to be measured is close to the focal position, the difference in luminance value between adjacent pixels is used by increasing the contrast due to the pattern on the surface of the object to be measured. However, although this method can widen the sampling interval, it has no effect on a smooth surface such as an optical flat, and further, it is not possible to detect the width of the generation and disappearance of interference fringes. Therefore, it does not function as a preliminary scan. In order to reliably obtain the surface shape of the object to be measured, it is necessary to measure the surface shape within the range where interference fringes are generated and disappear.

Returning to FIG. 7, after the measurement scanning range is determined by the preliminary scanning (step S14), the processing unit 18 performs a surface shape measuring step of measuring the surface shape of the measurement object P (step S16). As a method for measuring the surface shape, the measured surface S is measured based on the interference fringes acquired by the photographing unit 16 while changing the optical path length of the measured light applied to each point of the measured surface S of the measurement object P. Any method may be used as long as it is a method of measuring the surface shape of the object P to be measured by detecting the position of the interference fringes in the z-axis direction of each point.

According to the present embodiment, in the surface shape measurement that takes time by narrowing the sampling interval, the scanning range is determined by the preliminary scanning, so that the measurement time can be shortened.

Next, in step S18, if the surface shape data of the entire area of the object to be measured has not been acquired, the process returns to step S14, the stage 10 is moved (movement step), preliminary scanning (step S14), and surface shape measurement. (Step S16) is performed to acquire surface shape data of the entire region of the object to be measured (repeated step).

After acquiring the surface shape data of the entire area of the object to be measured, a wide range of surface shape data is created by connecting the surface shape data as the step of step S20 (connection step), and finally, the processing unit 18 is the surface. The shape measurement result is output to the display unit 20 or the like. Alternatively, if the surface shape of the object to be measured can be measured with one imaging surface, the measurement result of the surface shape is output to the display unit 20 or the like without performing the connection step.

1 ... Surface shape measuring device, 2 ... Optical unit, 10 ... Stage, 10S ... Stage surface, 12 ... Light source unit, 14 ... Interference unit, 16 ... Imaging unit, 18 ... Processing unit, 18A ... Measurement preparation control unit, 20 ... Display unit, 22 ... Input unit, 30 ... x rotation axis, 32 ... y rotation axis, 34 ... x actuator, 36 ... y actuator, 40 ... light source, 42 ... collector lens, 44, 54 ... beam splitter, 50 ... objective lens , 52 ... Reference mirror, 56 ... Interference part actuator, 60 ... Imaging element, 60S ... Imaging surface, 62 ... Imaging lens, 70 ... z actuator, 100 ... Reference pixel, 102 ... Peripheral pixel, L1, L2 ... Optical path length, P ... Object to be measured, Q ... Interference fringe curve, S ... Surface to be measured, Z-0, Z-1 ... Optical axis

Claims (4)

A support part that supports the object to be measured and
The light source unit that emits white light and the white light from the light source unit are divided into measurement light and reference light, and the measurement light is applied to the measured surface of the measurement object, and the reference light is used as the reference surface. It has an interference part that generates interference light that interferes with the measurement light returning from the measured surface and the reference light returning from the reference surface, and a plurality of pixels corresponding to each point of the measured surface. Then, a surface shape acquisition unit that acquires interference fringes from the brightness information of the interference light between the measurement light and the reference light applied to each point of the measurement surface and acquires the surface shape data of the measurement object. It is a surface shape measuring method using a shape measuring device including an optical unit having a light beam.
An interference fringe acquisition step of acquiring the interference fringes while changing the optical path length of the measurement light applied to each point of the measurement surface.
A reference pixel selected from a plurality of pixels of the surface shape acquisition unit corresponding to each point of the measured surface measured in the interference fringe acquisition step, and at least one pixel of peripheral pixels of the reference pixel. A scanning range determination step of estimating the range in which interference fringes are generated from the brightness information and determining the scanning range in the axial direction of the measurement light, and
While changing the optical path length of the measurement light applied to each point of the measured surface within the scanning range determined in the scanning range determination step, interference fringes are acquired at an image acquisition interval shorter than that in the interference fringe acquisition step. A surface having a surface shape measuring step of measuring the surface shape of the object to be measured by detecting the position of the interference fringes in the optical axis direction of the measurement light at each point of the surface to be measured based on the interference fringes. Shape measurement method. The surface shape measuring method according to claim 1, wherein the peripheral pixels randomly select pixels having a different distance from the reference pixel. A moving step of relatively moving the positions of the support portion and the optical portion after performing the interference fringe acquisition step, the scanning range determination step, and the surface shape measurement step.
A repeating step of acquiring a plurality of surface shape data by performing the interference fringe acquisition step, the scanning range determination step, and the surface shape measurement step on the surface to be measured after the movement step.
The surface shape measuring method according to claim 1 or 2, further comprising a connection step of connecting the plurality of surface shape data and acquiring a wide range of surface shape data of the object to be measured. The scanning range determination step is any one of claims 1 to 3 in which a range including a region in which the sum of the absolute values of changes in the luminance values of the reference pixel and the peripheral pixels includes a region of a predetermined value or more is determined as the scanning range. The surface shape measuring method according to item 1.

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