JP6932067B2 - Method for determining the position of the liquid crystal display element in the projection unit of the inspection device - Google Patents

Description

The present invention relates to a method for determining the position of a liquid crystal display element in a projection unit of an inspection device.

In recent years, electronic circuit boards have been mounted on various devices, but in devices on which this type of electronic circuit board is mounted, miniaturization, thinning, etc. have always been issues. From this point of view, it is required to increase the density of mounting of electronic circuit boards. In such an inspection device for inspecting the soldered state of an electronic circuit board, the mounted state of electronic components, and the like, the phase shift method is often used for acquiring height information because of its precision. The phase shift method is configured to acquire height information using a long-period fringe pattern and a short-period fringe pattern (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-053015

However, when the projection unit that projects the stripe pattern for acquiring the height information of the object to be inspected is arranged in the diagonal direction of the rectangular imaging region of the camera unit, the projection region of the projection unit has a rectangular shape. Therefore, there is a problem that the magnification of the stripe pattern becomes large and the accuracy of acquiring the height information cannot be ensured. Another problem is that the contrast of the projected fringe pattern is lowered by simply rotating the projection area of the projection unit by 45 ° in order to reduce the magnification by aligning the directions of the imaging region and the projection region. there were.

The present invention has been made in view of such a problem, and a liquid crystal display element capable of projecting a finer fringe pattern and a high contrast fringe pattern onto an object to be inspected by a projection unit in an inspection device. It is an object of the present invention to provide a method for determining the position of.

In order to solve the above problems, the method for determining the position of the liquid crystal display element in the projection unit of the inspection device according to the present invention reflects light of a camera unit having a rectangular imaging region and illumination light in a predetermined polarized state. A light separation member that transmits light in a polarized state different from the predetermined polarized state, and a rectangular display region in which liquid crystals constituting each of the plurality of pixels are arranged in a two-dimensional manner, and a voltage with respect to the liquid crystal. Whether or not to change the polarization state of the light when the light reflected by the light separating member or the light transmitted through the light separating member passes through the liquid crystal is determined depending on the presence or absence of the application of the light. The emitted light is emitted from the liquid crystal display element that re-enters the light separation member, and the light that is emitted from the liquid crystal display element and transmitted through the light separation member or reflected by the light separation member is projected onto the projection region. It has a projection unit including a projection optical system, each side of the projection region of the projection unit is inclined with respect to each side of the imaging region of the camera unit, and the projection region is the imaging region. In an inspection device configured to include a region, a region composed of liquid crystal to which at least a voltage is applied and a region composed of liquid crystal to which no voltage is applied are formed in the display region of the liquid crystal display element of the projection unit. In a state where the image of the display area is projected onto the projection area of the reference surface, the liquid crystal display element is rotated from a predetermined reference state so that the display area of the liquid crystal display element is located on the same plane. The reference plane is imaged by the camera unit, and the brightness of the image corresponding to the region consisting of the liquid crystal to which the voltage is applied and the brightness of the image corresponding to the region consisting of the liquid crystal to which the voltage is not applied are measured. Then, it is stored in association with the rotation angle of the liquid crystal display element from the reference state, and the brightness of the image corresponding to the region composed of the liquid crystal to which the voltage is applied and the region composed of the liquid crystal to which the voltage is not applied are stored. It is characterized in that the position of the liquid crystal display element is determined so that the rotation angle becomes the minimum value when the brightness that decreases from the brightness in the reference state in accordance with the rotation of the corresponding image brightness becomes the minimum value. ..

In the method for determining the position of the liquid crystal display element in the projection unit of the inspection device according to the present invention, the display area, the projection area, and the main surface of the projection optical system of the liquid crystal display element maintain the conditions of the principle of Scheimpflug. As described above, it is preferable to rotate the liquid crystal display element.

Further, in the method for determining the position of the liquid crystal display element in the projection unit of the inspection device according to the present invention, the liquid crystal display element is preferably LCOS.

Further, in the method for determining the position of the liquid crystal display element in the projection unit of the inspection device according to the present invention, the light separation member is a polarization beam splitter, and the light separation surface of the polarization beam splitter is a P-polarized light and an S-polarized light. It is preferably configured to transmit one of them and reflect the other.

According to the present invention, the projection unit can project a finer fringe pattern and a high contrast fringe pattern onto the object to be inspected. Therefore, the object to be inspected obtained by an inspection device having this projection unit. The accuracy of height information can be improved.

It is a block diagram which shows the structure of an inspection apparatus. It is explanatory drawing which shows the structure of the image pickup unit. It is an enlarged cross-sectional view of a part of a projection unit. It is explanatory drawing which shows the measuring method of the height information by the stripe pattern. It is explanatory drawing which shows the relationship between the image pickup area of a camera unit, the display area of the liquid crystal display element of a projection unit, and a projection area. It is a graph which shows the relationship between the rotation angle of the liquid crystal display element from a reference state, and the brightness of the image of the liquid crystal to which voltage is applied and the liquid crystal to which voltage is not applied. It is explanatory drawing which shows the relationship between the rotation angle of a liquid crystal display element, and the contrast of a fringe pattern. It is a flowchart which shows the flow of the position determination method of the liquid crystal display element in an inspection apparatus.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the inspection device 10 according to the present embodiment will be described with reference to FIGS. 1 to 3. The inspection device 10 is a device that inspects the inspected body 12 by using the image data of the inspected body obtained by imaging the inspected body 12. The object 12 to be inspected is, for example, an electronic circuit board coated with solder. The inspection device 10 determines whether the solder is applied or not based on the image data of the object to be inspected.

The inspection device 10 includes an inspection table 14 for holding the inspected body 12, an imaging unit 20 that illuminates and images the inspected body 12, an XY stage 16 that moves the imaging unit 20 with respect to the inspection table 14, and an image pickup. It includes a control unit 30 for controlling the operation of the unit 20 and the XY stage 16 and performing an inspection of the inspected body 12. For convenience of explanation, as shown in FIG. 1, the object to be arranged surface of the inspection table 14 is set to an XY plane, and the direction perpendicular to the arrangement surface (that is, the image pickup direction by the camera unit 21 constituting the image pickup unit 20 (camera unit). The optical axis direction)) of the optical system of 21 is defined as the Z direction.

The image pickup unit 20 is attached to a moving table (not shown) of the XY stage 16 and can be moved in the X direction and the Y direction by the XY stage 16. The XY stage 16 is, for example, a so-called H-shaped XY stage. Therefore, the XY stage 16 has a Y drive unit that moves the moving table in the Y direction along the Y direction guide extending in the Y direction, supports the Y direction guide at both ends thereof, and supports the moving table and the Y direction guide in the X direction. It includes two movable X-direction guides and an X drive unit. The XY stage 16 may further include a Z movement mechanism for moving the image pickup unit 20 in the Z direction, or may further include a rotation mechanism for rotating the image pickup unit 20. The inspection device 10 may further include an XY stage that allows the inspection table 14 to be moved, and in this case, the XY stage 16 that moves the imaging unit 20 may be omitted. Further, a linear motor or a ball screw can be used for the X drive unit and the Y drive unit.

The imaging unit 20 includes a camera unit 21, a lighting unit 22, and a projection unit 23 that capture images from a direction (Z-axis direction) perpendicular to the inspection surface (board surface) of the object 12 to be inspected. .. In the inspection device 10 according to the present embodiment, the camera unit 21, the lighting unit 22, and the projection unit 23 may be configured as an integrated imaging unit 20. In the integrated imaging unit 20, the relative positions of the camera unit 21, the lighting unit 22, and the projection unit 23 may be fixed, or each unit may be configured to be relatively movable. Further, the camera unit 21, the lighting unit 22, and the projection unit 23 may be separated from each other and may be configured to be movable separately.

The camera unit 21 includes an image pickup element 21a that generates a two-dimensional image of an object, and an optical system (for example, a lens) 21b for forming an image on the image pickup element. The camera unit 21 is, for example, a CCD camera. The maximum field of view of the camera unit 21 may be smaller than the area on which the object to be inspected is placed on the inspection table 14. In this case, the camera unit 21 divides the image into a plurality of partial images and images the entire body 12 to be inspected. The control unit 30 controls the XY stage 16 so that the camera unit 21 is moved to the next imaging position each time the camera unit 21 captures a partial image. The control unit 30 synthesizes the partial images to generate the entire image data of the inspected body 12.

The camera unit 21 may include an image sensor that generates a one-dimensional image instead of the two-dimensional image sensor. In this case, the entire image data of the inspected body 12 can be acquired by scanning the inspected body 12 with the camera unit 21.

The illumination unit 22 is configured to project illumination light for imaging by the camera unit 21 onto the surface of the object to be inspected 12. The illumination unit 22 includes one or a plurality of light sources that emit light in a wavelength or wavelength range selected from the wavelength range that can be detected by the image sensor 21a of the camera unit 21. The illumination light is not limited to visible light, and ultraviolet light, X-rays, or the like may be used. When a plurality of light sources are provided, each light source is configured to project light having a different wavelength (for example, red, blue, and green) onto the surface of the object 12 to be inspected at different projection angles.

In the inspection device 10 according to the present embodiment, the lighting unit 22 is a side illumination source that projects illumination light from an oblique direction with respect to the inspection surface of the inspected body 12, and in the present embodiment, the upper light source 22a, middle It includes a position light source 22b and a lower light source 22c. In the inspection device 10 according to the present embodiment, the side illumination sources 22a, 22b, and 22c are ring illumination sources, respectively, surround the optical axis of the camera unit 21, and are oblique to the inspection surface of the inspected object 12. It is configured to project illumination light to the camera. Each of these side illumination sources 22a, 22b, 22c may be configured by arranging a plurality of light sources in an annular shape. Further, the upper light source 22a, the middle light source 22b, and the lower light source 22c, which are the side illumination sources, are configured to project the illumination light at different angles with respect to the inspection surface, respectively.

The projection unit 23 projects a pattern on the inspection surface of the object to be inspected 12. The object 12 to be inspected on which the pattern is projected is imaged by the camera unit 21. The inspection device 10 determines the height of the inspection surface of the inspected object 12 based on the imaged pattern image data of the inspected object 12 (image data imaged by the camera unit 21 in a state where the pattern is projected on the inspected object 12). Create a map. The control unit 30 detects a local mismatch of the pattern image data with respect to the projection pattern, and acquires height information of the portion based on the local mismatch. That is, the change in the imaging pattern with respect to the projection pattern corresponds to the change in height on the inspection surface.

The projection pattern is preferably a one-dimensional fringe pattern in which bright lines and dark lines are alternately and periodically repeated. The projection unit 23 is arranged so as to project a striped pattern from an oblique direction on the inspection surface of the object to be inspected 12. The discontinuity of height on the inspection surface of the object to be inspected appears as a pattern deviation in the pattern image data. Therefore, the height difference can be obtained from the amount of deviation of the pattern. For example, the control unit 30 creates a height map by the PMP (Phase Measurement Profile) method using a fringe pattern in which the brightness changes according to a sine curve. In the PMP method, the amount of deviation of the fringe pattern corresponds to the phase difference of the sine curve.

The projection unit 23 includes a pattern forming device, a light source device for illuminating the pattern forming device, and a projection optical system for projecting the pattern onto the inspection surface of the object 12 to be inspected. The pattern forming apparatus may be, for example, a variable patterning apparatus capable of dynamically generating a desired pattern such as a liquid crystal display, or a fixed patterning in which a pattern is fixedly formed on a substrate such as a glass plate. It may be a device. When the pattern forming apparatus is a fixed patterning apparatus, the projection position of the pattern is made variable by providing a moving mechanism for moving the fixed patterning apparatus or by providing an adjusting mechanism in the projection optical system for pattern projection. Is preferable. Further, the projection unit 23 may be configured so that a plurality of fixed patterning devices having different patterns can be switched.

In the projection unit 23 according to the present embodiment, as shown in FIG. 3, the pattern forming apparatus is a light separation member and includes a polarization beam splitter 23a having a light separation surface 23b and a reflection type liquid crystal display element 23c. It is composed of. As the reflective liquid crystal display element 23c, LCOS (Liquid crystal on silicon) is used (in the following description, it is assumed that a ferroelectric LCOS is used).

As shown in FIG. 3A, the illumination light emitted from the light source device is converted into substantially parallel light by a collimated lens (not shown) and incident on the light separation surface 23b of the polarizing beam splitter 23a. The light separation surface 23b of the polarization beam splitter 23a transmits P-polarized light and reflects S-polarized light. Therefore, of the illumination light incident on the light separation surface 23b, the P-polarized light passes through the light separation surface 23b, but the S-polarized light is reflected and incident on the liquid crystal display element 23c.

The LCOS, which is the liquid crystal display element 23c, is configured to have a liquid crystal layer in which liquid crystals constituting each of the plurality of pixels are two-dimensionally arranged on a reflective layer (electrode). The liquid crystal that constitutes the pixel has the property of acting as a 1/4 wavelength plate with respect to the light transmitted through the liquid crystal when a voltage is applied, and the light transmitted through the liquid crystal is reflected. It is reflected by the layer, passes through the liquid crystal again, and exits from the liquid crystal layer.

When the projection unit 23 has the above-described configuration, generally, light in the polarization direction separated by the light separation surface 23b of the polarizing beam splitter 23a and incident on the liquid crystal display element 23c (in the present embodiment, S-polarized light). ) On the other hand, when a voltage is applied to the liquid crystal constituting the pixel in the liquid crystal layer, the light incident on the liquid crystal is reflected by the reflective layer and polarized by 90 ° when emitted from the liquid crystal layer. The polarized beam splitter 23a and the liquid crystal display element 23c are arranged so as to (convert to P-polarized light). Therefore, in the case of the above-described configuration, when the S-polarized light reflected by the light separation surface 23b of the polarizing beam splitter 23a is incident on the liquid crystal to which the voltage is applied among the liquid crystals constituting the pixels in the liquid crystal layer, It is converted into P-polarized light and emitted from the liquid crystal layer. On the other hand, when no voltage is applied to the liquid crystal constituting the pixel, the S-polarized light incident on the liquid crystal is emitted as the S-polarized light when emitted from the liquid crystal layer. In the following description, when the light is separated by the light separation surface 23b of the polarization beam splitter 23a and incident on the liquid crystal display element 23c, the light is polarized by 90 ° in the liquid crystal to which the voltage is applied. The arrangement state of the polarization beam splitter 23a and the liquid crystal display element 23c is referred to as a "reference state".

The light emitted from the liquid crystal display element 23c again enters the light separation surface 23b of the polarizing beam splitter 23a, but at this time, no voltage is applied to the liquid crystals constituting the pixels in the liquid crystal layer of the liquid crystal display element 23c. Since the light incident on the liquid crystal is S-polarized light even when it is emitted from the liquid crystal display element 23c, it is reflected by the light separation surface 23b, but it is incident on the liquid crystal to which the voltage is applied and converted into P-polarized light. The light emitted from the display element 23c passes through the light separation surface 23b and is incident on a projection optical system (not shown). The projection optical system projects P-polarized light transmitted through the light separation surface 23b of the polarization beam splitter 23a onto the object 20 to be inspected, thereby projecting the display region of the liquid crystal display element 23c at a magnification set by the projection optical system. (The state of the liquid crystal display, which is an individual pixel constituting the display area) is projected onto the object 12 to be inspected.

From the above, by controlling whether voltage is applied or not applied to each of the liquid crystals constituting the pixels in the liquid crystal layer of the liquid crystal display element 23c, a bright image (bright line) is applied to the pixels to which the voltage is applied. ), And as a dark image (dark line) for pixels to which no voltage is applied (in other words, as an image of the display area of the liquid crystal display element 23c (for example, the surface of the liquid crystal layer)), the projection optical system is used. It can be projected onto the object 12 to be inspected via.

In the above description, the light separation surface 23b of the deflection beam splitter 23a has been described as transmitting P-polarized light and reflecting S-polarized light, but the reverse configuration may be used. Further, it has been described that the incident light is polarized by 90 ° when a voltage is applied to the liquid crystal constituting the pixel in the liquid crystal layer of the liquid crystal display element 23c and is not polarized when the voltage is not applied. It may be. Further, as shown in FIG. 3A, the illumination light emitted from the light source device is reflected by the light separation surface 23b of the polarizing beam splitter 23a to irradiate the liquid crystal display element 23c, and is emitted from the liquid crystal display element 23c. Although the case where the light is configured to be transmitted through the light separation surface 23b of the beam polarizing splitter 23a and incident on the projection optical system has been described, the light transmitted through the light separation surface 23b of the deflection beam splitter 23a is transmitted to the liquid crystal display element 23c. The light incident and emitted from the liquid crystal display element 23c may be reflected by the light separation surface 23b.

As shown in FIG. 2, a plurality of projection units 23 may be provided around the camera unit 21. The plurality of projection units 23 are arranged so as to project a pattern onto the inspected object 12 from different projection directions. In this way, it is possible to reduce the area where the pattern is not projected due to the shadow due to the height difference on the inspection surface.

Further, in the above description, the case where the image pickup unit 20 is fixed and the inspected object 12 is configured to be moved in the XY direction by the XY stage 16 has been described. However, the inspected object 12 is fixed and the image pickup unit 20 is moved. It may be configured to move in the XY direction.

The control unit 30 shown in FIG. 1 controls the entire apparatus in an integrated manner. The hardware is realized by the CPU, memory, or other LSI of an arbitrary computer, and the software is loaded into the memory. It is realized by programs, etc., but here we draw the functional blocks realized by their cooperation. Therefore, it will be understood by those skilled in the art that these functional blocks can be realized in various ways by hardware only, software only, or a combination thereof.

FIG. 1 shows an example of the configuration of the control unit 30. The control unit 30 includes an inspection control unit 31 and a memory 35 which is a storage unit. The inspection control unit 31 includes a height measuring unit 32, an inspection data processing unit 33, and an inspection unit 34. Further, the inspection device 10 includes an input unit 36 for receiving an input from a user or another device, and an output unit 37 for outputting information related to the inspection, and the input unit 36 and the output unit 37. Are each connected to the control unit 30. The input unit 36 includes, for example, an input means such as a mouse or a keyboard for receiving an input from a user, and a communication means for communicating with another device. The output unit 37 includes known output means such as a display and a printer.

The inspection control unit 31 is configured to execute various control processes for inspection based on the input from the input unit 36 and the inspection-related information stored in the memory 35. The inspection-related information includes two-dimensional image data of the object to be inspected 12, a height map of the object to be inspected 12, and substrate inspection data. Prior to the inspection, the inspection data processing unit 33 creates the substrate inspection data using the two-dimensional image data and the height map of the inspected object 12 which is guaranteed to pass all the inspection items. The inspection unit 34 executes the inspection based on the created substrate inspection data, the two-dimensional image data of the object 12 to be inspected, and the height map.

The board inspection data is inspection data created for each type of board. The board inspection data is, so to speak, a collection of inspection data for each solder applied to the board. The inspection data of each solder includes the inspection items required for the solder, the inspection window which is the inspection area on the image data for each inspection item, and the inspection criteria which are the criteria for judging the quality of each inspection item. One or more inspection windows are set for each inspection item. For example, in the inspection item for determining the quality of the solder coating state, the same number of inspection windows as the number of solder coating regions of the component are usually set in an arrangement corresponding to the arrangement of the solder coating regions. In addition, for inspection items that use image data that has undergone predetermined image processing on the image data to be inspected, the content of the image processing is also included in the inspection data.

The inspection data processing unit 33 sets each item of inspection data according to the substrate as a substrate inspection data creation process. For example, the inspection data processing unit 33 automatically sets the position and size of each inspection window for each inspection item so as to match the solder layout of the substrate. The inspection data processing unit 33 may accept input by the user for some items of the inspection data. For example, the inspection data processing unit 33 may accept the tuning of the inspection standard by the user. Inspection criteria may be set using height information.

The inspection control unit 31 executes an imaging process of the object to be inspected 12 as a preprocessing for creating substrate inspection data. As the inspected body 12, one that has passed all the inspection items is used. As described above, the imaging process is performed by illuminating the object 12 to be inspected by the lighting unit 22 and controlling the relative movement between the image pickup unit 20 and the inspection table 14 to sequentially image a partial image of the object 12 to be inspected. .. A plurality of partial images are taken so as to cover the entire body 12 to be inspected. The inspection control unit 31 synthesizes these plurality of partial images and generates image data of the entire surface of the substrate including the entire inspection surface of the object 12 to be inspected. The inspection control unit 31 stores the image data of the entire surface of the substrate in the memory 35.

Further, as a preprocessing for creating a height map, the inspection control unit 31 controls the relative movement between the image pickup unit 20 and the inspection table 14 while projecting a pattern on the inspected body 12 by the projection unit 23, and is inspected. The pattern image of the body 12 is divided and sequentially imaged. The projected pattern is preferably a fringe pattern whose brightness changes according to a sine curve based on the PMP method. The inspection control unit 31 synthesizes the captured divided images and generates pattern image data of the entire inspection surface of the inspected body 12. The inspection control unit 31 stores the pattern image data in the memory 35. It should be noted that the pattern image data may be generated not for the whole but for a part of the inspection surface.

The height measuring unit 32 creates a height map of the entire inspection surface of the inspected body 12 based on the image of the pattern on the pattern image data. First, the height measuring unit 32 obtains a local phase difference between the pattern image data and the reference pattern image data (image data captured by the camera unit 21 in a state where the pattern is projected on the reference plane) for the entire image data. The phase difference map of the inspection surface of the inspected body 12 is obtained. The height measuring unit 32 creates a height map of the object to be inspected 12 based on a reference plane and a phase difference map that serve as a reference for height measurement. The reference plane is, for example, the substrate surface of the electronic circuit board to be inspected. The reference plane does not necessarily have to be a flat surface, and may be a curved surface that reflects deformation such as warpage of the substrate.

Specifically, the height measuring unit 32 obtains the phase difference of the fringe pattern between each pixel of the pattern image data and the pixel of the reference pattern image data corresponding to the pixel. The height measuring unit 32 converts the phase difference into height information. The conversion to height information is performed using the local stripe width in the vicinity of the pixel. This is to compensate for the difference in the stripe width on the pattern image data depending on the location. Since the distance from the projection unit 23 differs depending on the position on the inspection surface, even if the stripe width of the reference pattern is constant, the stripe width changes linearly from one end to the other end of the pattern projection area on the inspection surface. Because it ends up. The height measuring unit 32 acquires height information from the reference plane based on the converted height information and the reference plane, and creates a height map of the object 12 to be inspected.

The inspection control unit 31 creates the inspected body image data having a height distribution by associating the height information of the height map of the inspected body 12 with each pixel of the two-dimensional image data of the inspected body 12. You may. The inspection control unit 31 may perform a three-dimensional modeling display of the inspected body 12 based on the inspected body image data with a height distribution. Further, the inspection control unit 31 may superimpose the height distribution on the two-dimensional image data of the object to be inspected and display it on the output unit 37. For example, the image data of the object to be inspected may be color-coded according to the height distribution.

Hereinafter, a method of projecting a pattern by the projection unit 23 and acquiring height information in such an inspection device 10 will be described.

First, a method of acquiring height information by the PMP method using a striped pattern will be described. Focusing on one measurement point in the fringe pattern projection region, when the fringe pattern is projected while spatially shifting the phase start position (in other words, when the fringe pattern is scanned in the direction in which the fringes repeat), the fringe pattern is projected. The brightness of the measurement point fluctuates periodically. Although the average brightness differs for each measurement point depending on the surface characteristics of the measurement points such as color and reflectance, periodic brightness fluctuations corresponding to the fringe pattern occur at each measurement point. Therefore, for example, the phase of the fringe pattern when the measurement point is brightest represents the height information of the measurement point. Generally speaking, it can be said that the initial phase of the periodic brightness fluctuation gives the height information of each measurement point.

Using the characteristics of such a striped pattern, the height information acquisition method by the PMP method acquires height information using at least two patterns having different periods. Rough height information (rough height) is acquired by the first pattern of long period (that is, thick stripes), and precise height information is acquired by the second pattern of short period (thin stripes). As described above, since the height information is acquired based on the phase in the PMP method, the height information cannot be uniquely specified if the height difference is large and the fringes are deviated by one cycle or more. By obtaining the rough height in combination with the first pattern, it is possible to uniquely specify the height information even when the fringes are deviated by one cycle or more when the second pattern is projected.

In this way, when height information is acquired for each of a plurality of different patterns and the results are integrated to obtain a height map, it is generally considered that each pattern is individually projected and imaged. In principle, the PMP method requires imaging of one type of fringe pattern at least three times, typically four times, with the phase start position shifted. The brightness fluctuation of each measurement point also becomes a sine wave corresponding to the fringe pattern being a sine wave. Since the pitch of the fringes is known, a sine wave representing the variation in brightness can be identified if the average value, amplitude, and initial phase of the brightness are known.

By obtaining the measured value of the brightness of the measurement point from at least three captured image data, three variables of the average value of the brightness, the amplitude, and the initial phase can be determined. Further, assuming that the brightness of a pixel when one fringe pattern is imaged four times by shifting the phase start position by 90 degrees is I0 to I3, the initial phase φ of the measurement point corresponding to the pixel is tan (φ). It is known to be represented by = (I3-I1) / (I2-I0). Assuming that the pitch of the fringe pattern is P, the amount of deviation of the fringe pattern is obtained by P × (φ / 2π). The height information of the position can be obtained from the amount of pattern deviation by using the projection angle of the pattern.

If two types of patterns consisting of a long-period first pattern and a short-period second pattern are used, at least 6 or 8 times of imaging will be performed. In order to inspect one inspected body 12, a plurality of partial regions are imaged to obtain whole image data.

In FIG. 4, as shown in (a), the phase obtained from the image data obtained by projecting the stripe pattern on the reference plane S by the projection unit 23 and capturing the image by the camera unit 21 is shown in (b). As shown in (d), the phase obtained from the image data obtained by projecting the same striped pattern with the object O placed on the reference plane S is shown in (d), and the height of the object O is these. It can be calculated from the amount of phase shift (phase difference = measured phase-phase of reference plane). This phase difference can be calculated for each pixel of the image data captured by the camera unit 21, and the height of the position corresponding to that pixel is calculated by multiplying the phase difference obtained for each pixel by a coefficient. NS. This coefficient is obtained by, for example, tan (projection angle) × stripe pitch / 2π.

As shown in FIG. 5A, the image pickup region (field of view) Rc of the camera unit 21 constituting the image pickup unit 20 of the present embodiment has a rectangular shape. Further, the display area Rs of the liquid crystal display element 23c of the projection unit 23 also has a rectangular area, and as a result, the projection area Rp of the display area Rs also becomes a rectangular area. Note that FIG. 5 shows a case where the rectangular regions Rc, Rs, and Rp are square on the left side, and a case where the rectangular regions Rc, Rs, and Rp are rectangular on the right side.

As shown in FIG. 5, the inspection device 10 according to the present embodiment captures a rectangular shape of the projection unit 23 (display region Rs of the liquid crystal display element 23c) with respect to the imaging region (field of view) Rc of the camera unit 21. It is arranged in the diagonal direction of the region Rc. Although one projection unit 23 is shown in FIG. 5, two projection units 23 may be arranged so as to face each other in the diagonal direction of the imaging region Rc, or the imaging region may be arranged. Four projection units 23 may be arranged for each of the two diagonal lines of Rc, or three projection units 23 may be arranged so as to surround the imaging region Rc.

As is clear from FIG. 5A, when the projection unit 23 is arranged in the diagonal direction of the rectangular imaging region Rc of the camera unit 21, when the above-mentioned polarization beam splitter 23a and the liquid crystal display element 23c are in the reference state, Each side of the rectangular projection region Rp of the projection unit 23 is arranged so as to be oblique with respect to each side of the rectangular imaging region Rc (in FIG. 5A, each side of the imaging region Rc. The case where each side of the projection area Rp is tilted by 45 ° with respect to the side is shown). Therefore, when an image of the display area Rs of the liquid crystal display element 23c of the projection unit 23 is to be projected onto the entire area of the image pickup area Rc, the projection area Rp must be at least a rectangle circumscribing the image pickup area Rc. (In other words, the projection region Rp includes the imaging region Rc), and the area of the projection region Rp is more than double the area of the imaging region Rc. That is, it is necessary to increase the magnification of the projection optical system of the projection unit 23. When the magnification of the projection optical system is increased, the pitch of the fringe pattern formed in the display region Rs of the liquid crystal display element 23c is expanded and projected onto the projection region Rp. The pitch cannot be made thin enough. Further, the height information of the object to be inspected 12 is acquired by imaging the projected fringe pattern with the camera unit 21, but as the magnification of the projection optical system increases, the contrast of the projected fringe pattern decreases. The accuracy of the acquired height information becomes low.

Therefore, in the inspection device 10 according to the present embodiment, as shown in FIGS. 3B and 5B, by rotating the liquid crystal display element 23c of the projection unit 23, each of the rectangular imaging regions Rc is formed. The sides and the sides of the rectangular projection region Rp are arranged so as to face substantially the same direction. Specifically, the projection region Rp is rotated by rotating the display region Rs of the liquid crystal display element 23c. In FIG. 3B, the display area in the reference state is shown as Rs, and the display area after rotation is shown as Rs'. Further, the light separation surface 23b of the polarization beam splitter 23a projected on the same plane as the display region Rs of the liquid crystal display element 23c is shown as Rr. When each side of the rectangular imaging region Rc and the projection region Rp faces substantially the same direction, the areas of the imaging region Rc and the projection region Rp may be substantially the same, and the magnification of the projection optical system can be reduced. .. Therefore, the pitch of the striped pattern projected on the object 12 to be inspected 12 can be made sufficiently thin, and the contrast can be improved.

The display surface (display area Rs) of the liquid crystal display element 23c of the projection unit 23, the projection surface (projection area Rp) on which the fringe pattern formed on the display surface (display area Rs) is projected, and the projection optical system. It is not arranged parallel to the main surface. Therefore, in order to project a fringe pattern in focus on the projection surface (projection region Rp), the display surface, the projection surface, and the main surface of the projection optical system in the projection unit 23 satisfy the conditions of the Scheimpflug principle. Have been placed. Here, when the display area Rs is rotated as shown in FIG. 5B, if the entire projection unit 23 is rotated, the condition of the Scheimpflug principle is not satisfied. Further, if the entire projection unit 23 is rotated, the position of the light source device or the like changes, so that the image pickup unit 20 may not be compactly configured.

Therefore, in the inspection device 10 according to the present embodiment, in order to maintain the conditions of the Scheimpflug principle, the liquid crystal display element 23c is rotated while the display surface (display area Rs) is located on the same plane. It is configured to (rotate around a predetermined axis extending in the normal direction of the display surface (display area Rs)). Even if the liquid crystal display element 23c is rotated, the conditions of the Scheimpflug principle can be maintained as long as the display surfaces (display areas Rs) are on the same plane.

FIG. 6 shows the brightness values when a voltage is applied (when the voltage is on) and when no voltage is applied (when the voltage is off) to the liquid crystal corresponding to the pixels of the liquid crystal display element 23c, which are reference values. When the angle of the liquid crystal display element 23c in the state is 0 ° and the liquid crystal display element 23c is rotated from the reference state, the brightness corresponding to the rotation angle of the image data captured by the camera unit 21 is shown. When the rotation angle is 0 °, as shown in FIG. 5A, it is assumed that each side of the projection region Rp is inclined by 45 ° with respect to each side of the imaging region Rc.

Since the polarization directions of the P-polarized light and the S-polarized light are different by 90 °, when the liquid crystal display element 23c is rotated by 45 ° from the reference state (0 °), the light separation surface 23b of the polarizing beam splitter 23a The S-polarized light reflected in the above is P-polarized light with respect to the liquid crystal display element 23c. In the liquid crystal display element 23c, when a voltage is applied to the liquid crystal with respect to the P-polarized light, the P-polarized light incident on the liquid crystal is of the P-polarized light when emitted from the liquid crystal layer. When the liquid crystal display is not applied with a voltage, it is converted into S-polarized light and emitted from the liquid crystal layer. Since the light separation surface 23b of the polarized beam splitter 23a is not rotating, the P-polarized light emitted from the liquid crystal layer is S-polarized light with respect to the polarized beam splitter 23a, and the S emitted from the liquid crystal layer. The polarized light is P-polarized light with respect to the polarized beam splitter 23a. Therefore, when the liquid crystal display element 23c is rotated by 45 °, the S-polarized light reflected by the light separation surface 23b of the polarizing beam splitter 23a and incident on the liquid crystal display element 23c is the S-polarized light in the liquid crystal to which the voltage is applied. , S-polarized light is again incident on the light separation surface 23b of the polarized beam splitter 23a and reflected by the light separation surface 23b, and in the liquid crystal to which no voltage is applied, the light is changed again as P-polarized light. It is incident on the light separation surface 23b, passes through the light separation surface 23b, and is projected onto the projection surface by the projection optical system. That is, when the rotation angle of the liquid crystal display element 23c is 45 °, the action of converting the polarization direction by the liquid crystal when the voltage is applied and when the voltage is not applied is opposite to that when the rotation angle is 0 °.

Therefore, as is clear from FIG. 6, in the reference state (when the rotation angle of the liquid crystal display element 23c is 0 °), P-polarized light is emitted from the liquid crystal to which the voltage is applied, and the polarized beam splitter is used. It passes through the light separation surface 23b of 23a and is projected as a bright image (white portion of the striped pattern) on the object 12 to be inspected by the projection optical system, but when the rotation angle of the liquid crystal display element 23c approaches 45 °, it is projected. Since S-polarized light is emitted from the liquid crystal to which the voltage is applied, it is reflected by the light separation surface 23b of the polarizing beam splitter 23a and does not enter the projection optical system, so that the image is dark with respect to the object 12 to be inspected. It is projected as (black part of the striped pattern). Similarly, from the liquid crystal to which no voltage is applied, S-polarized light is emitted when the rotation angle is 0 °, and P-polarized light is emitted when the rotation angle approaches 45 °. When the rotation angle is 0 °, it is projected as a dark image (black part of the striped pattern), and when the rotation angle approaches 45 °, it is projected as a bright image (white part of the striped pattern). It becomes.

FIG. 7 shows the relationship between the rotation angle of the liquid crystal display element 23c and the contrast of the projected fringe pattern. The contrast is shown as an MTF (Modulation Transfer Function) value. As is clear from FIG. 7, it can be seen that the MTF value is higher (contrast is better) when the liquid crystal display element 23c is further rotated at 53 ° than when the rotation angle is 45 °. .. In this way, in the state where the MTF value is high, as is clear from FIG. 6, the brightness (brightness of the white part of the striped pattern) in the liquid crystal display to which no voltage is applied (voltage is off) becomes the maximum value. It is not the rotation angle, but the rotation angle at which the brightness (brightness of the black portion of the striped pattern) in the liquid crystal to which the voltage is applied (voltage is on) becomes the minimum value. In other words, of the brightness of the image corresponding to the liquid crystal with voltage applied (voltage on) and the brightness of the image corresponding to the liquid crystal without voltage applied (voltage off), the reference state according to the rotation. The contrast is improved by setting the position of the liquid crystal display element 23c so that the rotation angle corresponds to the minimum value of the brightness that decreases from the brightness of.

As shown in FIG. 5C, when the rotation angle of the liquid crystal display element 23c exceeds 45 °, the projection region Rp becomes slightly larger than when it is 45 °, so that the magnification of the projection optical system increases, but the contrast Therefore, the accuracy of the height information of the object to be inspected 12 can be improved.

Note that FIG. 5 shows a case where both the imaging region Rc of the camera unit 21 and the projection region Rc (display region Rs) of the projection unit 23 are square and rectangular, but one of them is square and the other. The same applies when is rectangular.

Then, the position determination method (rotation angle determination method) of the liquid crystal display element 23c will be described with reference to FIG. A reference plane (for example, a gray chart, hereinafter referred to as a "reference plane") is arranged on the inspection table 14 instead of the object 12 to be inspected. Further, it is assumed that the stripe pattern displayed on the display surface of the liquid crystal display element 23c is a rectangular wave in which white stripes and black stripes change stepwise. Since the line width of the fringe pattern of the square wave is thick, it is easier to find the minimum value of the brightness than the sine wave. In the above-mentioned reference state, the liquid crystal display (pixels) to which the voltage is applied (voltage on) becomes white, and the liquid crystal display (pixels) to which the voltage is not applied (voltage off) becomes black. The position (rotation angle) of the liquid crystal display element 23c will be described in the case where the operator manually rotates the liquid crystal display element 23c. However, an actuator for rotating the liquid crystal display element 23c is provided, and the operation of the actuator is controlled by the control unit 30. It may be configured.

First, the operator sets the liquid crystal display element 23c to the above-mentioned reference state (rotation angle θ = 0 °) (step S100). In the reference state, as described above, each side of the rectangular projection region Rp is arranged at an angle of 45 ° with respect to each side of the rectangular imaging region Rc. Then, the control unit 30 controls the operation of the projection unit 23 to form a rectangular wave fringe pattern on the display surface of the liquid crystal display element 23c, and projects the rectangular wave fringe pattern onto the reference plane to obtain a camera. Image is taken by the unit 21 (step S110). The control unit 30 acquires the brightness of the image corresponding to the voltage-on liquid crystal display and the brightness of the image corresponding to the voltage-off liquid crystal display from the image data captured by the camera unit 21 (step S120). The brightness and the rotation angle θ at that time are associated with each other and stored in the memory 35 (step S130). The rotation angle θ may be input by the operator from the input unit 36, or the liquid crystal display element 23c may be provided with an angle detector so that the control unit 30 acquires the rotation angle θ from the angle detector.

Next, the operator rotates the liquid crystal display element 23c by a predetermined angle Δθ from the current position (step S140), and determines whether or not the rotation angle θ after rotation is 90 ° or more (step S140). Step S150). This is because the state in which the liquid crystal display element 23c is rotated by 90 ° returns to the reference state by rotating the pattern to be displayed on the display surface by 90 °. When the operator determines that the rotation angle θ of the liquid crystal display element 23c is smaller than 90 ° (step S150: NO), the operator returns to step S110 and repeats the process. When the operator determines that the rotation angle θ of the liquid crystal display element 23c is 90 ° or more (step S150: YES), the control unit 30 is composed of the brightness (voltage-applied liquid crystal) stored in the memory. Of the image brightness corresponding to the area and the image brightness corresponding to the area consisting of the liquid crystal to which no voltage is applied), it corresponds to the minimum value of the brightness that decreases from the brightness in the reference state according to the rotation of the liquid crystal display element 23c. The rotation angle to be performed (this is referred to as an "optimal angle") is determined as the position of the liquid crystal display element 23c, and is stored in the memory 35 or output to the output unit 37 (step S160). When the liquid crystal display element 23c is configured to be rotated by the actuator, the control unit 30 controls the operation of the actuator to set the rotation angle of the liquid crystal display element 23c to the optimum angle.

In the present embodiment, as shown in FIG. 6 and the like, the angle corresponding to the minimum value of the voltage-on brightness is determined as the rotation angle of the liquid crystal display element 23c, and the liquid crystal display element 23c is set to the determined rotation angle. .. In the case of FIG. 6, it is desirable that the rotation angle (optimal angle) of the liquid crystal display element 23c is set to 53 °.

In the case of the above configuration, the rotation angle of the liquid crystal display element 23c is approximately between 20 ° and 60 °. Therefore, the initial value of the rotation angle of the liquid crystal display element 23c in step S100 is set to 20 °, and the step is performed. The rotation angle for determining the end of the brightness measurement of S150 may be set to 60 °.

In the inspection device 10 according to the present embodiment, when the rotation angle of the liquid crystal display element 23c of the projection unit 23 from the reference state is determined by the above processing, the area of the projection region (Rp) of the fringe pattern projected by the projection unit 23 is determined. By making the pattern as narrow as possible (lowering the magnification of the projection optical system of the projection unit 23), a finer fringe pattern with high contrast can be projected onto the object 12 to be inspected. It is possible to improve the accuracy of the height information of the object to be inspected 12 measured by the inspection device 10 having the projection unit 23.

When the liquid crystal display element 23c is rotated in the projection unit 23 with the polarization beam splitter 23a fixed (rotated while the display surface (display area Rs) is located on the same plane), it is in the reference state ( When the rotation angle is 0 °) and when the rotation angle is 45 °, the state of the display surface of the liquid crystal display element 23c (the state of whether or not the liquid crystal voltage of the liquid crystal layer is applied) and the image projected on the projection region. The relationship with brightness is reversed. Specifically, the white image (bright line) when the rotation angle is 0 ° becomes a black image (dark line) when the rotation angle is 45 °, and the black image (dark line) when the rotation angle is 0 °. The dark line) becomes a white image (bright line) when the rotation angle is 45 °. Therefore, when the same fringe pattern as the fringe pattern projected on the projection area Rp when the rotation angle is 0 ° is projected, the white and black regions are inverted when the rotation angle is 45 ° (voltage is high). It is necessary to turn off the on region and turn on the voltage off region (if there is an intermediate voltage value, it is inverted with respect to the center value).

In the case of the liquid crystal display element 23c using the LCOS having the above-described configuration, the orientation angle (dynamic switching angle) of the liquid crystal constituting the liquid crystal layer changes according to the voltage, but it is ideal when a voltage is applied. The angle is 45 °. However, in practice, it may not be 45 °, and this angle depends on the temperature. As a result, as shown in FIG. 6, the peak brightness differs between when the voltage is on and when the voltage is off. Therefore, by determining the liquid crystal display element 23c at the optimum angle by the method for determining the position of the liquid crystal display element 23c according to the present embodiment, the contrast of the pattern image data captured by the camera unit 21 is increased, and the pattern image data is increased. The accuracy of the height information calculated from can be increased.

It should be noted that the above embodiments do not limit the invention described in the claims, and all combinations of characteristic matters described in the embodiments are indispensable matters for the solution. It goes without saying that this is not always the case.

10 Inspection device 21 Camera unit 23 Projection unit 23a Polarization beam splitter (optical branching element)
23c liquid crystal display element

Claims (4)

A camera unit with a rectangular imaging area and
A light separation member that reflects light in a predetermined polarized state of illumination light and transmits light in a polarized state different from the predetermined polarized state.
The liquid crystal display constituting each of the plurality of pixels has a rectangular display region arranged in a two-dimensional shape, and depending on whether or not a voltage is applied to the liquid crystal display, the light reflected by the light separation member or the light separation member can be displayed. When the transmitted light passes through the liquid crystal, it is determined whether or not to change the polarization state of the light, and the light emitted from the liquid crystal is re-entered into the light separation member, and the liquid crystal display element.
A projection unit including a projection optical system that emits light from the liquid crystal display element, transmits light through the light separation member, or projects light reflected by the light separation member onto a projection region.
Have,
In an inspection device configured such that each side of the projection region of the projection unit is inclined with respect to each side of the imaging region of the camera unit and the projection region includes the imaging region.
An image of the display region is formed on the display region of the liquid crystal display element of the projection unit by forming at least a region made of liquid crystal to which a voltage is applied and a region made of liquid crystal to which no voltage is applied. Is projected, the liquid crystal display element is rotated from a predetermined reference state so that the display area of the liquid crystal display element is located on the same plane.
The reference plane is imaged by the camera unit, and the brightness of the image corresponding to the region consisting of the liquid crystal to which the voltage is applied and the brightness of the image corresponding to the region consisting of the liquid crystal to which the voltage is not applied are measured. Then, the liquid crystal display element is stored in association with the rotation angle from the reference state.
Of the brightness of the image corresponding to the region consisting of the liquid crystal to which the voltage is applied and the brightness of the image corresponding to the region consisting of the liquid crystal to which the voltage is not applied, the brightness decreases from the brightness of the reference state according to the rotation. A method for determining the position of a liquid crystal display element in a projection unit of an inspection device, which determines the position of the liquid crystal display element so that the rotation angle is such that the brightness becomes the minimum value. The first aspect of the present invention is characterized in that the liquid crystal display element is rotated so that the display area, the projection area, and the main surface of the projection optical system of the liquid crystal display element maintain the conditions of the principle of Scheimpflug. A method for determining the position of a liquid crystal display element in the projection unit of the inspection device described. The method for determining the position of a liquid crystal display element in a projection unit of an inspection device according to claim 1 or 2, wherein the liquid crystal display element is an LCOS. The light separating member is a polarizing beam splitter.
Any one of claims 1 to 3, wherein the light separation surface of the polarization beam splitter is configured to transmit one of P-polarized light and S-polarized light and reflect the other. A method for determining the position of a liquid crystal display element in a projection unit of the inspection device according to the above.

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