JP2021113832A - Surface shape measurement method - Google Patents

Abstract

To provide a surface shape measurement method capable of shortening whole measurement time.SOLUTION: A surface shape measurement method for measuring a surface shape of a measurement object P from brightness information of interference light obtained by an imaging part 16 while changing an optical path length of measurement light emitted to each point of a measured surface S includes: first light sources 40 and 240 for emitting white light for surface shape measurement; and a second light source 41 for emitting longer light of a coherence region than white light or a bandpass filter 243 for transmitting light having a narrow wavelength width. A surface shape measurement method and a surface shape measurement device include: an interference region acquisition step of acquiring an interference fringe at a longer image acquisition interval than an image acquisition interval in a surface shape measurement step using the long light of the coherence region; a scanning region determination step of determining a scanning range using brightness information of the acquired interference fringe; and a surface shape measurement step of measuring a surface shape within a scanning region determined in the scanning range determination step.SELECTED DRAWING: Figure 5

Description

The present invention relates to a surface shape measuring method and a surface shape measuring device, and more particularly to a surface shape measuring method for measuring the surface shape of an object to be measured 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 uses an interferometer to measure the three-dimensional shape of the surface to be measured of the object to be measured in a non-contact manner.

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 split 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 surface to be measured 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 sensor of the CCD camera as interference fringes. Then, the interference fringes are acquired while the interference meter is displaced with respect to the surface to be measured in the height direction, and the amount of displacement when the brightness value shows the maximum value for each pixel of the interference fringes is detected to detect the amount of displacement of the surface to be measured. 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 interference fringes can be observed in preparation for the measurement. A focusing process is required to drive the scanning axis perpendicular to the position. As the focusing process, focus adjustment that drives the measurement scanning axis so that the surface to be measured comes to the focus position of the optical system where interference fringes can be observed, and the scanning range in the height direction when measuring the surface shape are appropriate. The decision is made. If focusing is not performed and the scanning range in the height direction is not properly determined, the range in which interference fringes are not generated will also be measured, which takes a long time to measure. Further, in order to shorten the measurement time, it is important to shorten the measurement preparation time, and for that purpose, it is also important to shorten the focusing time.

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 the measurement data are collected later. The method of connecting (stitching) is known. In stitching in which a plurality of measurements are connected, the measurement is performed a plurality of times, so that the measurement time is particularly long. For such a problem, the measurement range is set after visually confirming the disappearance of the interference fringes, or the measurement range is set after confirming the generation and disappearance of the interference fringes by performing preliminary scanning. 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.

For example, 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. Further, Patent Document 2 describes a method of separately installing a camera for focus adjustment in addition to a camera that captures interference fringes.

Japanese Unexamined Patent Publication No. 2014-202651 Japanese Unexamined Patent Publication No. 2016-136091

However, in the shape measuring device described in Patent Document 1, since the moving range in the Z-axis direction is set based on the overlapping range between the imaged region and the adjacent next imaged region, the adjacent regions are adjacent to each other. In the case where the stepped portion is provided, it may not be possible to correspond to the height of the stepped portion. In addition, the method of installing a camera separately is not a good method because it leads to an increase in equipment cost.

The present invention has been made in view of such circumstances, and the vertical scanning range when measuring the surface shape can be estimated with a high probability, can be determined in a short time, and has a focus. It is an object of the present invention to provide a surface shape measuring method and a surface shape measuring device capable of performing adjustment in a short time.

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 generates light having different lengths of the coherent region, and light from the light source portion. The measurement light is divided into a measurement light and a reference light, and the measurement light is irradiated to the measured surface of the object to be measured, and the reference light is irradiated to the reference surface. Interference fringes are acquired from the brightness information of the interference portion that generates the interfered interference light and the interference light between the measurement light and the reference light applied to each point on the surface to be measured, and the surface shape data of the object to be measured is acquired. A surface shape measuring method using a surface shape measuring device including a surface shape acquiring unit and an optical unit having a surface shape acquiring unit, and using light having a long coherent region emitted from a light source unit, each of the surfaces to be measured is used. From the interference fringe acquisition step of acquiring the interference fringes while changing the optical path length of the measurement light applied to the point and the brightness information of the interference fringes measured in the interference fringe acquisition step, the interference fringes in the axial direction of the measurement light Each point on the surface to be measured is irradiated using the scanning range determination step of estimating the generated range and determining the scanning range of the measurement light in the axial direction and the short light of the coherent region emitted from the light source unit. The interference fringe acquisition step includes a surface shape measurement step of acquiring interference fringes while changing the optical path length of the measurement light within the scanning range determined in the scanning range determination step and measuring the surface shape of the object to be measured. The image acquisition interval is longer than the image acquisition interval in the surface shape measurement step.

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 determining the scanning range of the optical unit is longer than the image acquisition interval in the surface shape measurement step, the image can be acquired in a short time. Further, by lengthening the image acquisition interval, the change in the luminance value due to the interference fringes may be small in the region where the light and darkness due to the interference fringes is generated. In the present invention, by using light having a long interference region for preliminary scanning for determining the scanning range in the surface shape measurement process, interference occurs in the region where interference fringes are generated even if the image acquisition interval is long. The occurrence of fringes can be confirmed. Further, by using light having a long coherent region, the emission wavelength width is shortened, so that the rate of change of the luminance value of the interference fringes with respect to the change of the optical path length becomes large. Therefore, the image can be acquired at a position equal to or higher than the value at which the generation of the interference fringes can be confirmed, and the range in which the interference fringes are generated can be estimated with high probability. In this way, the scanning range can be determined in a short time, and the surface shape can be measured in a short time. Therefore, the measurement time can be shortened as a whole surface shape measurement.

In one aspect of the shape measuring method according to the present invention, the scanning range determination step includes reference pixels selected from a plurality of pixels of the surface shape acquisition portion corresponding to each point of the surface to be measured measured in the interference fringe acquisition step. It is preferable to determine from the luminance information of at least one pixel of the peripheral pixels of the reference pixel.

According to this aspect, 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.

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.

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

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 of 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 object to be measured is wide, and a plurality of surface shape data are acquired and connected, so-called stitching of the entire area of the object to be measured. When acquiring surface shape data, it is effective because it can be measured in a short time.

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 generates light having different lengths of the coherent region, and light from the light source portion. The measurement light is divided into a measurement light and a reference light, and the measurement light is irradiated to the measured surface of the object to be measured, and the reference light is irradiated to the reference surface. Interference fringes are acquired from the brightness information of the interference portion that generates the interfered interference light and the interference light between the measurement light and the reference light applied to each point on the surface to be measured, and the surface shape data of the object to be measured is acquired. A surface shape measuring method using a surface shape measuring device including a surface shape acquiring unit and an optical unit having a surface shape acquiring unit, and using light having a long coherent region emitted from a light source unit, each of the surfaces to be measured is used. While changing the optical path length of the measurement light applied to the point, adjust so that the focal position of the optical unit matches the position of the interference fringes measured in the interference fringe acquisition step of acquiring the interference fringes and the interference fringe acquisition step. Using the focus adjustment step and the short light in the coherent region emitted from the light source, the optical path length of the measurement light emitted to each point on the surface to be measured is changed within the scanning range determined in the scanning range determination step. However, it has a surface shape measuring step of acquiring interference fringes and measuring the surface shape of the object to be measured, and the image acquisition interval of the interference fringe acquisition step is longer than the image acquisition interval of the surface shape measuring step.

According to the surface shape measuring method of the present invention, the interference fringes used in the focus adjustment step of focusing the optical portion are acquired at an image acquisition interval longer than the image acquisition interval of the surface shape measuring step, so that a short time is required. The focus adjustment process can be performed with. Therefore, the time for the entire surface shape measurement can be shortened. Further, by acquiring the interference fringes used in the focus adjustment step using light having a long interference region, it is possible to acquire a plurality of images in which interference is confirmed even if the image acquisition interval is lengthened. Therefore, the interference fringes required for focus adjustment can be easily and accurately found.

One aspect of the shape measuring method according to the present invention includes a moving step of relatively moving the positions of the support portion and the optical portion after performing the interference fringe acquisition step, the focus adjusting step, and the surface shape measuring step. A repetitive process of acquiring a plurality of surface shape data and 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. It is preferable to have a connection step of connecting and acquiring a wide range surface shape data of the object to be measured.

Since the focus adjustment step can be performed in a short time, the surface of the object to be measured is wide, and a plurality of surface shape data are acquired and connected, so-called stitching is performed to obtain the surface shape data of the entire area of the object to be measured. When acquiring, it is effective because the entire surface shape measurement can be performed in a short time.

In one aspect of the shape measuring method according to the present invention, the light source unit includes a first light source that emits white light and a second light source that emits light having a longer interference region than the white light, and interference fringes. It is preferable that the acquisition step is performed using a second light source and the surface shape measuring step is performed using a first light source.

This aspect shows an example of a light source unit, and by providing two types of light sources, a first light source and a second light source, light from a second light source having a long coherent region can be used for preliminary scanning. , White light having a short coherent region can be used for surface shape measurement.

In one aspect of the shape measuring method according to the present invention, the light source unit includes a first light source that emits white light and a bandpass filter that transmits light having a narrow wavelength width from the white light, and is a step of acquiring interference fringes. Is preferably performed using light transmitted through a bandpass filter, and the surface shape measuring step is preferably performed using white light.

This aspect shows an example of the light source unit, and can generate light having different coherent regions depending on the presence or absence of transmission of the bandpass filter, and can be used for preliminary scanning and surface shape measurement. can.

In order to achieve the above object, the surface shape measuring device according to the present invention emits a support portion that supports the object to be measured, a first light source that emits white light, and light having an interference region longer than that of the white light. The light source unit provided with the second light source to be emitted, the light from the light source unit is divided into the measurement light and the reference light, and the measurement light is irradiated to the measured surface of the measurement object, and the reference light is irradiated to the reference surface. It has an interference unit that generates interference light that interferes with the measurement light returning from the surface to be measured and the reference light returning from the reference surface, and a plurality of pixels corresponding to each point of the surface to be measured. 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 and acquires the surface shape data of the object to be measured, and an optical unit having the optical unit. The interference fringe acquisition operation for acquiring interference fringes and the brightness of the interference fringes measured by the interference fringe acquisition operation while changing the optical path length of the measurement light applied to each point on the surface to be measured using the light source of 2. From the information, the range in which the interference fringes are generated in the axial direction of the measurement light is estimated, and the scanning range determination operation for determining the scanning range in the axial direction of the measurement light and the position of the interference fringes measured by the interference fringe acquisition operation are optically measured. It has a focus adjustment operation that adjusts the focus position of the unit, and a measurement preparation control unit that controls a measurement preparation operation program.

According to the surface shape measuring device of the present invention, it has a measurement preparation control unit that controls a measurement preparation operation program for interference fringe acquisition operation, scanning range determination operation, and focus adjustment operation before measuring the surface shape. Before measuring the surface shape of the object, the scanning range of the optical unit when measuring the surface shape is determined. Therefore, the measurement time when measuring the surface shape can be shortened. Further, a second light source that emits light having a different length of the coherent region and a second light source are provided, and a preliminary scan that determines the scanning range of the surface shape measurement is performed to emit light having a long coherent region. Since the emission wavelength width is shortened by using the light source of the above, the rate of change of the brightness value of the interference fringes with respect to the change of the optical path length becomes large. Therefore, even if the image acquisition interval of the interference fringe acquisition operation is lengthened in order to shorten the preliminary scanning time, the value is equal to or greater than the value at which the generation of the interference fringes can be confirmed in the region where the interference fringes are generated. The image can be acquired at the position, and the range in which the interference fringes are generated can be estimated with high probability. Further, by using light having a long coherence distance, the positions of the interference fringes can be confirmed at a plurality of positions even if the image acquisition interval is lengthened, so that the focus adjustment time can be shortened. In this way, the scanning range can be determined and the focus can be adjusted in a short time, and the surface shape can be measured in a short time. Therefore, the measurement time can be shortened as a whole for the surface shape measurement.

In order to achieve the above object, the surface shape measuring apparatus according to the present invention transmits a support portion that supports an object to be measured, a first light source that emits white light, and light having a narrow wavelength width from the white light. The white light from the light source unit and the white light from the light source unit, or the light transmitted through the band pass filter is divided into measurement light and reference light, and the measurement light is applied to the surface to be measured of the object to be measured. At the same time, an interference unit that irradiates the reference surface with the reference light and generates interference light in which the measurement light returning from the measured surface and the reference light returning from the reference surface interfere with each other, and a plurality of interference parts corresponding to each point on the measured surface. A surface shape acquisition unit that has pixels 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 surface to be measured and acquires the surface shape data of the object to be measured. An interference fringe acquisition operation that acquires interference fringes while changing the optical path length of the measurement light that is applied to each point on the surface to be measured by using the light that has passed through the bandpass filter. From the brightness information of the interference fringes measured by the interference fringe acquisition operation, the scanning range determination operation for estimating the range in which the interference fringes are generated with respect to the axial direction of the measurement light and determining the scanning range in the axial direction of the measurement light, and the interference fringes It has a focus adjustment operation that adjusts the focus position of the optical unit to the position of the interference fringes measured by the acquisition operation, and a measurement preparation control unit that controls the measurement preparation operation program.

According to the surface shape measuring device of the present invention, it has a measurement preparation control unit that controls a measurement preparation operation program for interference fringe acquisition operation, scanning range determination operation, and focus adjustment operation before measuring the surface shape. Before measuring the surface shape of the object, the scanning range of the optical unit when measuring the surface shape is determined. Therefore, the measurement time when measuring the surface shape can be shortened. Further, by using light having a long coherent region through the bandpass filter for the preliminary scan for determining the scanning range of the surface shape measurement, the emission wavelength width is shortened and the brightness value of the interference fringes with respect to the change in the optical path length. The rate of change of is large. Therefore, even if the image acquisition interval of the interference fringe acquisition operation is lengthened in order to shorten the preliminary scanning time, the value is equal to or greater than the value at which the generation of the interference fringes can be confirmed in the region where the interference fringes are generated. The image can be acquired at the position, and the range in which the interference fringes are generated can be estimated with high probability. Further, by using light having a long coherence distance, the positions of the interference fringes can be confirmed at a plurality of positions even if the image acquisition interval is lengthened, so that the focus adjustment time can be shortened. In this way, the scanning range can be determined and the focus can be adjusted in a short time, and the surface shape can be measured in a short time. Therefore, the measurement time can be shortened as a whole for the surface shape measurement.

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

It is an overall block diagram of the surface shape measuring apparatus used in the surface shape measuring method which concerns on 1st Embodiment. 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 device. It is a figure which illustrated the relationship between the z position of the interference part and the luminance value, and the 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 exemplifying the relationship between the image acquisition position and the interference fringe curve when the sampling interval is lengthened by using different light sources. It is a figure which shows the flowchart of the surface shape measuring method of 1st Embodiment. It is a figure which shows the flowchart of the preliminary scanning of 1st Embodiment. It is a figure which showed the pixel arrangement 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 setting example of the reference pixel. It is a figure explaining the difference of the image which can be acquired when the image acquisition interval is lengthened by using the light which has a different coherence region. 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 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 an 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. It is an overall block diagram of the surface shape measuring apparatus used in the surface shape measuring method which concerns on 2nd Embodiment. It is a figure explaining the optical characteristic before and after the bandpass filter transmission. It is a figure which shows the flowchart of the surface shape measuring method of 2nd Embodiment. It is a figure which shows the flowchart of the preliminary scanning of 2nd Embodiment.

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

[First Embodiment]
FIG. 1 is an overall configuration diagram showing an example of a surface shape measuring device used in the surface shape measuring method according to the first embodiment.

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 interferometry 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 interferometry 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 the present embodiment, the example of the Michelson 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 (the axis orthogonal to the paper surface) and the y-axis (the axis parallel to the paper surface), and the x-axis and the y-axis. The coordinate axis in the vertical direction orthogonal to is defined as the z-axis (measurement optical axis direction). The z-axis is parallel to the measurement optical axis Z-0, which will be 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 horizontal plane, and the stage surface 10S (stage 10) is x by the inclination angle changing means. It is rotatably provided around the x-rotating shaft 30 parallel to the axis and around the y-rotating shaft 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.

In addition, when the term "actuator" is used in the present specification as in the case of the x-actuator 34 and the y-actuator 36, it means an arbitrary driving 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 is an interference unit having a light source unit 12 having an optical axis Z-1 parallel to the x-axis and an optical axis Z-0 (hereinafter referred to as “measurement optical axis Z-0”) parallel to the z-axis. It has a 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 has a first light source 40 and a first light source 40 that emit white light (low coherence light with less coherence) having a wide wavelength width for measuring the surface shape as illumination light for illuminating the object P to be measured. It has a second light source 41 used for measurement preparation as a preliminary scan, which emits light having a longer interfering region than the light source 40. It also has a collector lens 42 that converts the illumination light diffused and emitted from the first light source 40 and the second light source 41 into a substantially parallel luminous flux. The central axes of the first light source 40 or the second light source 41 and the collector lens 42 are coaxially arranged as the optical axis Z-1 of the light source unit 12. Note that FIG. 1 shows a diagram in which the first light source 40 and the collector lens 42 are arranged coaxially. When the second light source 41 is used, the second light source 41 is arranged coaxially with the collector lens 42 by a light source changing means (not shown).

As the first light source 40, a low coherence light source such as a light emitting diode (LED), a superluminescent diode (SLD), or an ASE (Amplified spontaneous emission) light source (amplified spontaneous emission light source) is used. Can be used. As the emission wavelength width, it is preferable to use a light source of 20 nm to 100 nm. The center wavelength is not particularly limited, but it is possible to use a light source having a center wavelength in the highly available infrared region, around 660 nm (red), or in the vicinity of 550 nm of a white diode that is compatible with observation of the object to be measured with visible light. preferable.

Further, as the second light source 41, a laser light source such as a laser diode (LD) can be used. It is preferable to use a light source having an emission wavelength width of 5 nm or less. The center wavelength is not particularly limited, but it is preferable to use a wavelength close to the center wavelength of the first light source 40.

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 the above. Then, the illumination light reflected by the beam splitter 44 (the flat light dividing 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 condensing action, a reference mirror 52 which is a reference surface for reflecting light and has a flat reflecting surface, and a flat beam splitter 54 for splitting light. The central axes of the objective lens 50, the reference mirror 52, and the beam splitter 54 are coaxially arranged as the optical axis Z-0 of the interference unit 14. The reflecting 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 focused 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 surface S to be measured of the object P to be measured, then returns from the surface S to be measured 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 that is irradiated from the interference unit 14 to the surface S to be measured of the measurement object P and returns 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 measurement 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 surface S to be measured and the beam splitter 54 changes, so that the optical path length of the measurement light changes, and the measurement is performed. The optical path length difference between the light and the reference light changes.

The image pickup unit 16 is a surface shape acquisition unit that acquires surface shape data of the measurement object P from the brightness information of the interference light between the measurement light and the reference light applied to each point of the surface S to be measured, and is, for example, a CCD (CCD). It corresponds to a Charge Coupled Device) camera and has a CCD type image sensor 60 and an image lens 62. The central axes of the image sensor 60 and the image lens 62 are 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 imaging 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 imaging lens 62. Here, the imaging lens 62 magnifies an interference image with respect to a region around the optical axis Z-0 of the surface S to be measured of the measurement object P at a high magnification and forms an image on the imaging surface 60S of the image sensor 60.

Further, the imaging 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 imaging surface of the image pickup device 60. That is, the photographing unit 16 is designed so that the position of the focal plane of the objective lens 50 is in focus (focused).

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 body so as to be movable in the z-axis direction in a straight line. 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 measurement object P or the like. 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 while moving the interfering unit 14 of the optical unit 2 in the z-axis direction. Interference images are sequentially acquired from the image sensor 60. Then, based on the acquired interference image, the three-dimensional shape data of the surface S to be measured is acquired as data indicating the surface shape of the surface S to be measured.

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 the xy plane (horizontal plane) composed of the x-axis and the y-axis, and is an interference image received by 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 difference in optical path length between the measurement light reflected at each point of the measured surface S corresponding to each pixel and the reference light. 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 (imaging surface of the image pickup device 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 represented by 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 brightness values of the pixels (m, n) of the interference image acquired by the image sensor 60 are the points (X (m, n), Y (X (m, n), Y ( 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 displacement amount as that of 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 S to be measured also changes.

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

Here, the processing unit 18 can 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 detecting means (not shown) such as a potentiometer or an encoder. can. Alternatively, when controlling the z position of the interference unit 14 without using the position detecting means, for example, when moving the interference unit 14 by a constant displacement amount by a drive signal given to the interference unit actuator 56, the total displacement amount. Can be detected by.

Then, the z position of the focus position when the interference unit 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 unit 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) of FIG. 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 brightness 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 brightness value becomes substantially constant. As a result, the luminance value along the interference fringe curve Q shown in FIG. 3D can be obtained.

That is, the interference fringe curve Q at an arbitrary pixel (m, n) is located at a point (X (m, n), Y (m, n)) on the surface to be measured 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 applied 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 ( It matches 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 surface S to be measured. 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), while the image sensor Interference images are sequentially acquired from 60, and the brightness values of each pixel (m, n) are acquired in association with the z-coordinate value of the focus position. That is, the brightness values of each pixel (m, n) of the interference image are 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 brightness 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 the z-coordinate value Z (m, n) of the 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, the interference fringe curve Q as shown in FIG. 3D can be actually drawn for each pixel (m, n). The brightness value can be acquired to a certain 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 (imaging surface 60S of the image sensor 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 surface to be measured S is Can be detected.

Then, the x-coordinate values X (m, n), y-coordinate values Y (m, n), and z-coordinate values 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. In this way, the surface shape of the object P to be measured is measured by acquiring the three-dimensional shape data of the surface S to be 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 of the surface shape measurement in the z-axis direction, 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 scanning in the shortest possible time in order to improve the measurement efficiency of the surface shape. Further, it is preferable to perform the focus adjustment in a short time to adjust the focus of the entire optical unit 2 to a position where the interference fringes can be observed.

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, it becomes difficult to search for interference fringes. FIG. 5 is a diagram illustrating the relationship between the image acquisition position and the interference fringe curve when the sampling interval is lengthened by using different light sources. When an image is acquired at short sampling intervals while raising in the z-axis direction (vertical scanning axis direction) using the first light source 40 used for surface measurement, the interference fringe curve Q shown in FIG. 5A is obtained. It is supposed to be done. However, when the image is acquired at the sampling interval shown in FIG. 5A, 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 interference fringes are generated. May not be confirmed.

In the present embodiment, different light sources are used for the preliminary scanning and the focus adjustment and the surface shape measurement, and the light source used for the preliminary scanning and the focus adjustment is a high coherence light source having a longer coherence region than the light source used for the surface shape measurement. By using it, the scanning range in the z-axis direction in the surface shape measurement is appropriately determined. FIG. 5B is a diagram illustrating the relationship between the image acquisition position and the interference fringe curve when an image is acquired using the second light source 41. As shown in FIG. 5B, by using a high coherence light source, the range in which the light and darkness of the interference fringes appear, that is, the coherent region can be expanded, so that the position of the interference fringes can be expanded even if the sampling interval is widened. Can be confirmed. Further, since the emission wavelength width is short, the rate of change of the interference intensity with respect to the movement in the vertical scanning axis direction (change in the optical path length) becomes large. Therefore, if the sampling interval is not an integral multiple of the wavelength width, different interference intensities can be obtained within the region where the interference fringes are generated, and at a position equal to or higher than the value at which the generation of the interference fringes can be confirmed. Images can be acquired. Therefore, even if the sampling interval is lengthened, the region where the interference fringes are generated can be estimated, and the scanning range can be determined so as to include this region.

The processing unit 18 of the surface shape measuring device 1 according to the embodiment of the present invention interferes while changing the optical path length of the measurement light applied to each point of the surface S to be measured by using light having a long interference wavelength region. From the interference fringe acquisition operation for acquiring fringes and the brightness information of the interference fringes measured by the interference fringe acquisition operation, the range in which the interference fringes are generated with respect to the axial direction of the measurement light is estimated, and the scanning range in the axial direction of the measurement light is determined. Measurement preparation control unit that controls the measurement preparation operation program of the scanning range determination operation to be determined and the focus adjustment operation that adjusts the focus position of the optical unit 2 to the position of the interference fringes measured by the interference fringe acquisition operation. The configuration is such that 18A is built in.

FIG. 6 is a flowchart showing an example of the surface shape measuring method of the present embodiment, and FIG. 7 is a flowchart showing an example of preliminary scanning.

In the surface shape measuring method, as shown in FIG. 6, first, the object to be measured is placed on the stage 10 (step S10).

Next, the processing unit 18 adjusts the amount of measured light and the like so that the brightness values of the interference fringe curves acquired for all the pixels of the interference fringes (imaging surface of the image sensor 60) have an appropriate magnitude (step S12). ). That is, the strength of the first 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 on 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 S20) 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, first, the light source is switched to the second light source 41 by using a light source changing means (not shown) (step S30). If the second light source 41 is already arranged as the light source, this step can be omitted.

Next, as shown in FIG. 8, a reference pixel is selected (step S32). As shown in FIG. 8, 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 array on the interference fringe (imaging surface 60S of the image pickup device 60) as shown in FIG. 8 displayed on the display unit 20 of FIG. You may try to do it.

Next, the interference unit 14 is scanned and driven in the z-axis direction within a specified range to perform an interference fringe acquisition step (step S34). In this step, the interval for sampling the interference fringes (image acquisition interval) is longer than the image acquisition interval in the surface shape measurement step described later. By lengthening the image acquisition interval, the time for preliminary scanning can be shortened. In the present invention, by using a light source having a wide coherent region when performing preliminary scanning, the generation and disappearance of interference fringes can be estimated with high probability, and the scanning range can be determined. The upper limit of the image acquisition interval is not particularly limited as long as the outline of the surface shape can be grasped, but if it is an integral multiple of the wavelength, 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 of the focus position in the z-axis direction 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 to scan the focus position in the z-axis direction (that is, while changing 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 surface shape measuring step from the luminance value of the reference pixel is performed (step S36).

Here, the difference between the present invention and general 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 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 in which interference fringes are generated and disappear.

Returning to FIG. 6, after determining the measurement scanning range by the preliminary scanning (step S14), the processing unit 18 moves the optical unit 2 to the focal position where it is estimated that the interference fringes are generated by the preliminary scanning. The focus adjustment step is performed (step S16).

Focus adjustment before surface shape measurement also needs to be performed in a short time in order to improve the surface shape measurement efficiency. For that purpose, it is necessary to widen the image acquisition interval (image sampling interval) in the optical unit 2. FIG. 9 is a diagram for explaining the difference in images that can be acquired when the image acquisition interval is lengthened by using light having different coherent regions. FIG. 9A is a diagram in which an image is acquired using light having a short coherent region, and FIG. 9B is a diagram in which an image is acquired using light having a long coherent region.

As shown in FIG. 9A, when the image acquisition interval is lengthened by using light having a short coherent region, interference is observed in one image, but no interference is confirmed in the other three images. .. This is because in the case of a white interferometer, the range in the z-axis direction in focus is very small (for example, about 3 μm), and when the image acquisition interval (image sampling interval) is widened, the z-axis position where interference fringes appear is Due to the limitation, it is difficult to confirm the position of the interference fringes.

On the other hand, as shown in FIG. 9B, by using light having a long coherent region, it is possible to increase the number of images in which interference fringes can be acquired even if the image acquisition interval is long. In FIG. 9B, interference fringes can be observed in all four images. By increasing the number of images in which the interference fringes can be observed, the position of the interference fringes required for focus adjustment can be detected.

Next, the measurement preparation control unit 18A acquires the interference fringe curve based on the luminance value associated with the z-coordinate value of the focus position. Further, the measurement preparation control unit 18A obtains the z-coordinate value of the focus position when the luminance value shows the maximum value (maximum value of the envelope) based on the acquired interference fringe curve. Subsequently, the display unit 20 displays an image of the measured interference fringe curve drawn on a graph showing the relationship between the z-coordinate value and the brightness value. Further, it is preferable to display the z-coordinate value of the focus position when the luminance value shows the maximum value in the interference fringe curve and the z-coordinate value which is the center position of the scanning range of the focus position so that it can be easily grasped. ..

Next, the focus adjustment is performed so that the focus position of the optical unit 2 is adjusted to the detected interference fringe position. That is, in the interference fringe curve of the reference pixel 100, the z-coordinate value of the focus position when the brightness value shows the maximum value matches the z-coordinate value which is the center position of the scanning range of the focus position driven by the interference unit actuator 56. As such, the z actuator 70 of FIG. 1 is driven to move the entire optical unit 2 in the z-axis direction. In other words, the z position (z coordinate value), which is the center position of the scanning range of the focus position, and the z position (z coordinate value) of the S-shaped point to be measured corresponding to the reference pixel are optically matched. The position of the entire part 2 in the z-axis direction is adjusted. As a result, the optical unit 2 can be aligned with the focal position.

By adjusting the focus using light with a long coherent region in this way, it is possible to increase the number of images in which interference fringes can be observed even if the image acquisition interval is lengthened. , The position of the interference fringe required for focus adjustment can be detected, and the focus can be adjusted at the position of the found interference fringe. By lengthening the image acquisition interval, the time can be shortened, so that the time can be shortened as a whole for the surface shape measurement.

Although the image acquisition interval is longer than the position of the interference fringe curve shown in FIG. 5 in FIG. 9, the focus adjustment can be performed by using the interference fringes acquired during the preliminary scanning.

Next, the light source is switched to the first light source 40 for measuring the surface shape (step S18). After switching to the first light source 40, the processing unit 18 performs a surface shape measuring step of measuring the surface shape of the measurement object P within the measurement scanning range determined by the preliminary scanning (step S20). 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 measurement 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 S22, if the surface shape data of the entire region of the object to be measured has not been acquired, the process returns to step S14, the stage 10 is moved (movement step), and the surface shape is measured from the preliminary scanning (step S14) (step S14). Step S20) is performed to acquire surface shape data of the entire region of the object to be measured (repetition step).

After acquiring the surface shape data of the entire region 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 S24 (connection step), and finally, the processing unit 18 performs the surface. The shape measurement result is output to the display unit 20 or the like. Alternatively, when 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.

In the surface shape measuring method shown in FIG. 6, both a preliminary scanning for determining the scanning range in the Z-axis direction when measuring the surface shape and a focus adjusting step for moving the optical portion to the focal position are performed. As described above, it is also one aspect of the present embodiment that any of the preliminary scanning and the focusing step is performed.

Further, in the scanning range determination step (step S36) described above, the scanning range of the surface shape measurement step is determined from the brightness value of the reference pixel, but the generation of interference fringes cannot be sufficiently confirmed by the brightness value of the reference pixel. In this case, or if you want to check the position where the interference fringes are generated and improve the accuracy of the scanning range for measurement, you can also use the brightness values of the peripheral pixels of the reference pixel to achieve high accuracy in the vertical scanning direction. The measurement scan range can be determined.

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 in which peripheral pixels 102 are selected at equal intervals from the reference pixel 100. FIG. 12 is an example in which the peripheral pixels 102 are selected so that the distance from the reference pixel 100 is random.

The method of selecting the 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 sampling interval is widened in the preliminary scanning, 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. When the displacement in the z-axis direction is large, such as when the surface shape of the measurement object corresponding to the peripheral pixels has a stepped portion, the generation of interference fringes may not be confirmed in the preliminary scanning. 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.

In addition, the measurement scanning range is determined by selecting peripheral pixels and performing statistical processing on them. Generally, when performing preliminary scanning, the frame rate of the camera should be maximized. Set to. Therefore, when trying to perform statistical processing on all the pixels in the imaging surface, there arises a problem that the processing does not fit within the time interval of the frame. Therefore, the pre-scanning time is shortened by selecting the reference pixel and the peripheral pixels of the reference pixel and performing statistical processing on them.

When the scanning range determination step is performed using peripheral pixels, the scanning range is determined by performing statistical processing on the brightness values of the reference pixel and the peripheral pixels. As an example of statistical processing, it can be determined by taking a simple sum as follows.

_{Let x i} (i: pixel number) be the brightness value of the reference pixel and the selected peripheral pixel when performing preliminary scanning, and let <x> be the average brightness value in the area where no interference fringes are generated. The change in the luminance value due to the interference fringes with respect to 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 in which a measurement range is determined using the luminance values of the reference pixel and the peripheral pixels. When the change in the brightness value of the reference pixel is measured while scanning the optical unit 2 in the vertical direction, for example, the change in the brightness value as shown in the reference pixel in FIG. 13 is shown. In the preliminary scan, since the sampling interval is wider than the surface shape measurement, the change Δx _{i 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 brightness value 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 brightness value in the vertical direction (z-axis direction) of 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 brightness value cannot be confirmed with the reference pixel, the vertical position of the surface shape can be estimated by using the change in the brightness 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 a 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.

In the above description, the method of using peripheral pixels in the preliminary scanning has been described, but peripheral pixels can also be used in the focus adjustment step. in this case. Based on the interference fringe curves acquired for each of the reference pixel and the peripheral pixel, the z-coordinate value of the focus position when the luminance value shows the maximum value (maximum value of the envelope) is obtained. Then, one pixel having the largest z-coordinate value (the most prominent position) is selected. As a result, when the surface S to be measured has a dent such as a scratch, the pixel corresponding to the dent portion can be prevented from being selected. After selecting one pixel from the reference pixel and the peripheral pixels, the focus adjustment step described above is performed based on the selected pixels so that the focus position of the optical unit 2 meets the position of the interference fringes. Can be adjusted.

Further, in the flowchart shown in FIG. 6, the preliminary scan and the surface shape measurement are performed for each imaging surface of the measurement object. However, after the preliminary scan is performed on the entire area of the measurement object, the light source is turned on. Switching and surface shape measurement may be performed on the entire area of the object to be measured.

[Second Embodiment]
FIG. 14 is an overall configuration diagram showing an example of a surface shape measuring device used in the surface shape measuring method according to the second embodiment. In the surface shape measuring device 200 of the second embodiment, the light source unit 212 of the optical unit 202 that acquires the interference image of the measurement object P is white light having a wide wavelength width (interferable) as the illumination light for illuminating the measurement object P. A first light source 240 that emits low-coherence light with less property, and a bandpass filter 243 that transmits white light (light for measurement) from the first light source 240 only to light used for preliminary scanning. It is different from the surface shape measuring device of the first embodiment in that it is provided.

In the second embodiment, the light emitted from the first light source 240 is used properly as light for surface shape measurement and light for preliminary scanning depending on the presence or absence of transmission of the bandpass filter 243. As the first light source 240, 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.

Further, the bandpass filter 243 is not particularly limited as long as light having a wide interferable region for preliminary measurement can be obtained, and it is preferable to use a bandpass filter having a relatively narrow transmission characteristic.

FIG. 15 shows the wavelength characteristic (a) of the light emitted from the light source, the transmission characteristic (b) of the bandpass filter, and the wavelength characteristic (c) of the light after passing through the bandpass filter. The light emitted from the first light source 240 is light used for surface shape measurement, and as shown in FIG. 15A, is low coherence light having a wide emission wavelength region. By using the bandpass filter 243 having the filter transmission characteristic shown in FIG. 15B, the light after being transmitted through the bandpass filter can be the light having the wavelength characteristic shown in FIG. 15C. Light for preliminary scanning can be obtained by using light having a narrow wavelength width as shown in FIG. 15 (c).

According to the surface shape measuring device of the second embodiment, it is not necessary to provide two light sources, a light source for surface shape measurement and a light source for preliminary scanning. Therefore, the cost is low, the configuration is simple, and the preliminary scanning time is reduced. It can be shortened and the measurement range can be determined.

Since the configuration of the surface shape measuring device of the second embodiment other than the light source unit 212 is the same as that of the surface shape measuring device of the first embodiment, the configurations of the light source unit 12, the photographing unit 16, and the like are omitted.

Next, a surface shape measuring method using the surface shape measuring device of the second embodiment will be described. FIG. 16 is a flowchart showing an example of the surface shape measuring method of the second embodiment, and FIG. 17 is a flowchart showing an example of preliminary scanning.

The placement of the object to be measured on the stage 10 (step S50) and the adjustment of the amount of light to be measured (step S52) can be performed by the same method as in steps S10 and S12 of the first embodiment.

Next, a preliminary scan is performed (step S54). Preliminary scanning will be described with reference to FIG. In the preliminary scan, first, the bandpass filter 243 is moved into the light source optical path of the first light source 240 (step S70). If the bandpass filter 243 is already arranged in the light source optical path, this step can be omitted.

The acquisition of the reference pixel (step S72), the acquisition of the interference fringes (step S74), and the determination of the scanning range in the z-axis direction (step S76) can also be performed in the same manner as in steps S32 to S36 of the first embodiment. .. The determination of the scanning range in the z-axis direction (step S76) may be determined using only the selected reference pixel or peripheral pixels thereof, as in the first embodiment. Further, the method of selecting the peripheral pixels to be used can be the same as that of the first embodiment.

Returning to FIG. 16, after determining the measurement scanning range by the preliminary scanning (step S54), the processing unit 18 moves the optical unit 2 to the focal position where it is estimated that the interference fringes are generated by the preliminary scanning. The focus adjustment step is performed (step S56). The focus adjustment step can also be performed by the same method as in the first embodiment. Further, the bandpass filter 243 is moved out of the light source optical path (step S58).

Next, the processing unit 18 performs a surface shape measuring step of measuring the surface shape of the object P to be measured within the measurement scanning range determined by the preliminary scanning (step S60). 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 measurement 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.

Also in the method of the second embodiment, in the surface shape measurement which takes time by narrowing the sampling interval, the scanning range is determined by the preliminary scanning, so that the measurement time can be shortened.

If the surface shape data of the entire region of the object to be measured has not been acquired in step S62, the process returns to step S54, the stage 10 is moved (movement step), and the surface shape is measured from the preliminary scanning (step S54) (step S60). To acquire surface shape data of the entire area of the object to be measured (repeated process).

After acquiring the surface shape data of the entire area of the object to be measured, as the step S64, the step of creating a wide range surface shape data (connection step) and the step of outputting the surface shape measurement result to the display unit 20 or the like are described. It is the same as the first embodiment.

Also in the second embodiment, in the flowchart shown in FIG. 16, preliminary scanning and surface shape measurement are performed for each imaging surface of the measurement object, but preliminary scanning is performed on the entire region of the measurement object. After that, the bandpass filter 243 may be moved out of the light source optical path, and the surface shape may be measured for the entire region of the object to be measured.

1,200 ... Surface shape measuring device, 2,202 ... Optical unit, 10 ... Stage, 10S ... Stage surface, 12,212 ... 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, 240 ... first light source, 41 ... second 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, 243 ... Band path filter, L1, L2 ... Optical path length, P ... Measurement target, Q ... Interference fringe curve, S ... Measured surface, Z-0, Z-1 ... optical axis

Claims (2)

A support part that supports the object to be measured and
A light source unit that generates light having a different length of the interferable region and the light from the light source unit are divided into a measurement light and a reference light, and the measurement light is applied to the surface to be measured of the measurement object. The reference surface is irradiated with the reference light, and the interference portion that generates the interference light in which the measurement light returning from the measurement surface and the reference light returning from the reference surface interfere with each other and each point of the measurement surface are irradiated. Surface shape measurement including an optical unit having 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 and acquires surface shape data of the measurement object. It is a surface shape measurement method using an apparatus.
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 surface to be measured by using the light having a long coherent region emitted from the light source unit. ,
From the luminance information of the interference fringes measured in the interference fringe acquisition step, the scanning range determination step of estimating the range in which the interference fringes are generated with respect to the axial direction of the measurement light and determining the scanning range in the axial direction of the measurement light. ,
Using the short light in the coherent region emitted from the light source unit, the optical path length of the measurement light applied to each point on the surface to be measured is changed within the scanning range determined in the scanning range determination step. A surface shape measuring method comprising a surface shape measuring step of acquiring interference fringes and measuring the surface shape of the object to be measured. A support part that supports the object to be measured and
A light source unit that generates light having a different length of the interferable region and the light from the light source unit are divided into a measurement light and a reference light, and the measurement light is applied to the surface to be measured of the measurement object. The reference surface is irradiated with the reference light, and the interference portion that generates the interference light in which the measurement light returning from the measurement surface and the reference light returning from the reference surface interfere with each other and each point of the measurement surface are irradiated. Surface shape measurement including an optical unit having 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 and acquires surface shape data of the measurement object. It is a surface shape measurement method using an apparatus.
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 surface to be measured by using the light having a long coherent region emitted from the light source unit. ,
From the luminance information of the interference fringes measured in the interference fringe acquisition step, the scanning range determination step of estimating the range in which the interference fringes are generated with respect to the axial direction of the measurement light and determining the scanning range in the axial direction of the measurement light. ,
A focus adjustment step of adjusting the position of the interference fringes measured in the interference fringe acquisition step so that the focal position of the optical unit is aligned with the position of the interference fringes.
Using the short light in the coherent region emitted from the light source unit, the optical path length of the measurement light applied to each point on the surface to be measured is changed within the scanning range determined in the scanning range determination step. A surface shape measuring method comprising a surface shape measuring step of acquiring interference fringes and measuring the surface shape of the object to be measured.

Images