JP2012141233A - Detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably and speedily detect a focusing position.SOLUTION: A feed forward control is performed according to predetermined table data so that an adjustment control is performed to reduce light intensity of laser beam at a light point image (a laser spot S) when focusing on line pixels constituting a line sensor 25 and an adjustment control is performed to increase the light intensity of the laser beam at a light point image (a laser spot S) when defocusing that is positioned away from focusing pixels, thereby detection of a focusing position can be performed reliably and speedily. The present invention is applicable to, for example, a position detection unit used for a measuring device for measuring a cross-sectional shape of an object.

Description

  The present invention relates to a detection device.

  2. Description of the Related Art Conventionally, a measuring apparatus that detects the cross-sectional shape of the surface of an object by sampling the displacement position in the vertical direction while scanning the surface of the object is known (see, for example, Patent Document 1).

  In this type of measuring device, when the object is illuminated with light, the light receiving position is deflected due to a change in the relative distance between the surface of the object and the optical system. The in-focus position is detected by electrically performing signal processing.

Japanese Patent Laid-Open No. 11-72311

  When detecting the in-focus position, the amount of light collected per unit area on the light-receiving surface of the light-receiving element increases as it approaches the in-focus position from the out-of-focus position. As a result, the amount of light per unit area may become excessive and become saturated. As a result, when a line sensor or an area sensor is used to detect the focus position, the correct focus position cannot be detected.

  For this reason, it is necessary to perform measurement with a narrowed light amount that has been confirmed not to be saturated in advance, or to perform measurement while adjusting the light amount so as not to be saturated by feedback control.

  However, when measurement is performed with the reduced light amount, the amount of light received by the light receiving element becomes insufficient at a position deviating from the in-focus position, and so-called drawing operation may not be performed. In addition, when the light amount feedback control is performed, the time until the detection of the in-focus position is limited by the response time.

  The present invention has been made in view of such a situation, and makes it possible to detect the in-focus position reliably and at high speed.

  The detection apparatus of the present invention includes an illuminating unit that illuminates an object, an imaging optical system that focuses reflected light from the object, and forms a light spot image of the object, and the imaging optical A light detection means for detecting a focused state of a light spot image of the object focused by a system, a position detection means for detecting a surface position of the object based on a detection result of the light detection means, And adjusting means for adjusting the light amount of the light spot image detected at the detection position according to the detection position of the light spot image in the light detection means.

  According to the present invention, it is possible to detect the in-focus position reliably and at high speed.

It is a figure which shows the structure of one Embodiment of the surface position detection apparatus to which this invention is applied. It is a figure which shows the structure of a sensor unit. It is a figure which shows each state at the time of the focusing of the light spot image condensed on a line pixel, and a non-focusing. It is a figure which shows the example of table data.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an embodiment of a surface position detection apparatus to which the present invention is applied.

  The surface position detection device 1 includes a sensor unit 11, an objective lens 12, an imaging device 13, a stage 14 on which the object 2 is placed, an encoder 15 that detects the amount of movement of the sensor unit 11, and a control unit 16. . The sensor unit 11, the objective lens 12, and the imaging device 13 are attached to the support column 17 via a drive mechanism (not shown), and the relative position with respect to the object 2 can be obtained from the amount of movement detected by the encoder 15. .

  FIG. 2 is a diagram illustrating the configuration of the sensor unit 11. The inside of the broken line in FIG. The laser light beam emitted from the laser illuminating unit 21 is shielded by a knife edge 22 at half of the circular light beam, and the light beam having a semicircular cross section passes through the optical lens 23, and the objective lens 12 by the dichroic mirror 24. Reflected to the side. The laser beam (light beam having a semicircular cross section) reflected by the dichroic mirror 24 passes through a half area (left half area in the drawing) of the pupil surface of the objective lens 12 and irradiates the surface of the object 2. Is done. Thereby, the light beam that has passed through the objective lens 12 forms a light spot image at the in-focus position of the objective lens 12. FIG. 2 shows a case where the surface of the object 2 and the in-focus position of the objective lens 12 match.

  The laser reflected light reflected by the surface of the object 2 passes through a half area (right half area in the figure) of the pupil surface of the objective lens 12 and reaches the dichroic mirror 24, and the dichroic mirror 24 causes the optical lens 23 side. Is reflected. The laser reflected light (light beam having a semicircular cross section) reflected by the dichroic mirror 24 passes through the optical lens 23 and is reflected to the line sensor 25 side by the mirror surface of the knife edge 22.

  The reflected light from the knife edge 22 enters the light receiving surface of the line sensor 25, forms a light spot image on the light receiving surface, and is detected by the line sensor 25. For example, the line sensor 25 includes a plurality of light receiving elements such as photodiodes, and each light receiving element outputs a light reception signal proportional to the amount of light received. The range of the light beam incident on the light receiving surface of the line sensor 25 changes according to the illumination range of the object 2. For example, as shown in FIG. 2, when the object 2 is in an in-focus state, the range of the light beam incident on the light receiving surface is a range centered on the optical axis of the objective lens 12. On the other hand, when the object 2 is in an out-of-focus state, the illumination range of the object 2 extends to the right or left in the figure. It will spread to the left.

  In the following description, a plurality of light receiving elements constituting the line sensor 25 are collectively referred to as line pixels, and one light receiving element among the line pixels is referred to as one pixel. Further, among the line pixels, a pixel on which the light spot image of the object 2 at the in-focus position is formed is referred to as an in-focus pixel.

  The light reception signal detected by the line sensor 25 is amplified by the line sensor preamplifier 26 and supplied to the control unit 16.

  The laser reflected light reflected from the surface of the object 2 is transmitted through the dichroic mirror 24 and guided to the imaging device 13 side. In the imaging device 13, an observation optical system (not shown) forms an image of the laser reflected light that has passed through the dichroic mirror 24 on the imaging device (not shown), and corresponds to the image of the object 2 formed on the imaging device. An image is acquired. This observation image is displayed on a monitor (not shown) by the control unit 16.

  Based on the light reception signal supplied from the line sensor preamplifier 26, the control unit 16 reads the height position (Z-axis direction position) of the sensor unit 11 when the in-focus position is detected from the encoder 15, The position (surface position) of the surface of the object 2 is detected. Thereby, the height, cross-sectional curve, and surface shape of the target object 2 can be measured.

  Further, the control unit 16 controls the focusing operation by performing positioning driving of the focusing mechanism (the sensor unit 11, the objective lens 12, the stage 14, and the like) using the measured height position as a target value. Accordingly, autofocus (AF) is performed on the object 2.

  More specifically, since the sensor unit 11 of FIG. 2 employs a knife edge system, the line sensor 25 receives a light spot image that has passed through the knife edge 22. The position of the light spot image that has passed through the knife edge 22 changes the distance from the reference position on the line pixel (the position of the focused pixel) corresponding to this when the focused position with respect to the object 2 changes. Therefore, for example, the control unit 16 controls the focusing mechanism so that the position of the light spot image in which the focal point of the imaging optical system is focused on the object 2 matches the reference position, or the height position as the stop position. Measure.

  Further, the control unit 16 adjusts the amount of laser light emitted from the laser illumination unit 21 (adjusts the gain of the laser light amount) in accordance with the center of gravity of the amount of light obtained from the light reception signal detected by the line sensor 25. I do.

  Although the details will be described later, the light quantity centroid position means the light quantity centroid position of the light spot image (laser spot) collected on the line pixels constituting the line sensor 25. In this light amount adjustment, adjustment control is performed in which the amount of light is reduced in the vicinity of the focused pixel, and the light amount is increased while moving away from the focused pixel.

  Here, with reference to FIG.3 and FIG.4, the detail of adjustment control of the laser illumination part 21 by the control part 16 is demonstrated.

  FIG. 3 shows respective states when the light spot image collected on the line pixels constituting the line sensor 25 is focused and when it is not focused.

  In FIG. 3, a line pixel in which each rectangular cell has one light receiving element (pixel) is schematically illustrated on the left side in the drawing, and the line pixel on the left side in the drawing and the line pixel are illustrated on the right side in the drawing. The waveform which shows the relationship with the light quantity (light quantity data) light-received by the predetermined pixel is shown in figure. This light quantity data is data corresponding to the light reception signal detected by each pixel of the line pixels constituting the line sensor 25. Note that the vertical axis indicates the position of each pixel of the line pixel, and the approximate center of the axis is the position of the focused pixel, and the position farther away from the focused pixel in the left or right direction in the figure. It means that it becomes the pixel of. Further, although the horizontal axis is not shown, the light amount data received by each pixel of the line pixels is shown, which means that the light amount data becomes larger toward the right in the figure.

As shown in FIG. 3, the light spot images during focusing (laser spot S ₁ on line pixel on the left side of the _figure), since its diameter is in a small area, high density, as shown by the waveform P ₁ In addition, the amount of light received per pixel increases. In this case, there is a possibility that the amount of light received by the in-focus pixel and the pixels near the in-focus pixel may be saturated (saturation), so the control unit 16 determines the amount of laser light emitted from the laser illumination unit 21. Adjustment control to narrow down is performed.

On the other hand, the light spot image at the time of out-of-focus (laser spot S ₂ on the line pixel on the left side in the figure) that is located away from the focused pixel has a large area and low density, as shown by the waveform P _2, the amount of light received per pixel is very small. In this case, since the amount of light received by the pixel at a position away from the focused pixel is very small, there is a possibility that the amount of light cannot be detected by the pixel that received the light spot image. Adjustment control for increasing the amount of laser light emitted from the laser illumination unit 21 is performed.

  More specifically, the light amount of the laser light that is adjusted and controlled by the control unit 16 is prepared, for example, by preparing in advance table data associating the light amount barycenter position and the light amount command as shown in FIG. It is determined. In FIG. 4, the horizontal axis indicates the light intensity barycentric position of the light spot image (laser spot) collected on the line pixels constituting the line sensor 25, and the right or left direction from the focused pixel indicated by the dotted line. Means that the position is farther away from the focused pixel. The vertical axis indicates a light amount command for adjusting the light amount of the laser light emitted from the laser illumination unit 21, and the light amount of the laser light emitted from the laser illumination unit 21 is increased toward the top in the figure. This means that adjustment to increase (adjustment to increase the gain of the laser light amount) is performed.

  In FIG. 4, three types of table data A, B, and C are prepared. These table data are prepared according to the reflectance of the surface of the object 2. That is, when the reflectance of the surface of the target object 2 is small, it is necessary to illuminate the target object 2 with more laser light. Therefore, compared to the case where the reflectance of the surface of the target object 2 is large, A light amount command is instructed so that more laser light is illuminated even at the same light center of gravity. For example, in the example of FIG. 4, the table data A is the table data for the object 2 having the highest reflectance (for example, surface reflectance 100%), and the table data B is the next reflectance (for example, the surface reflectance 50%). Becomes the table data for the object 2 with a large value, and the table data C becomes the table data for the object 2 with the smallest reflectance (for example, the surface reflectance 30%).

  These table data A to C are obtained by, for example, detecting the reflectance of the surface of the object 2 before starting the position detection process by the surface position detection device 1 or at the time of the first position detection process. It is determined according to the reflectance. In addition, the reflectance of the surface of the target object 2 is calculated | required by the well-known reflectance detection method.

And the control part 16 selects the table data according to the reflectance of the target object 2 among the table data A thru | or C. FIG. For example, when the table data A is selected according to the reflectance of the surface of the object 2, the control is performed when the light spot image (laser spot S ₁ ) is received by the focused pixel on the line pixel in FIG. 3. The unit 16 acquires from the table data A a light amount command corresponding to a pixel (focused pixel) in which the light amount center of gravity of the light spot image (laser spot S ₁ ) is received, and instructs the laser illumination unit 21. . As a result, the laser illumination unit 21 emits a laser beam having a light amount in accordance with a light amount command from the control unit 16, so that the light amount of the laser beam in the focused pixel is reduced.

Further, when the table data A is selected according to the reflectance of the surface of the object 2, a light spot image (laser spot S ₂ ) is formed at a pixel away from the focused pixel on the line pixel in FIG. When the light is received, the control unit 16 acquires from the table data A a light amount command corresponding to the pixel whose light point centroid position of the light spot image (laser spot S ₂ ) is received, and instructs the laser illuminating unit 21. To do. As a result, the laser illumination unit 21 emits a laser beam having a light amount in accordance with a light amount command from the control unit 16, so that the laser light at the pixel where the light amount center of gravity of the light spot image (laser spot S ₂ ) has been received. The amount of light is increased more than the amount of laser light in the focused pixel.

  As described above, when the focused pixel is used as a reference and the light intensity center of gravity of the light spot image is received by a pixel near the focused pixel, the light intensity of the laser light emitted from the laser illumination unit 21 is The feed-forward control is performed according to predetermined table data so that the light amount of the laser light is increased as the light amount gravity center position is reduced and received by the pixel at a position away from the focused pixel. . In other words, it can be said that the table data stores correspondence information that associates the light quantity centroid position of the light spot image with the light quantity of the light spot image detected at the light quantity centroid position.

  As a result, a sufficient amount of light can be secured at a position deviating from the in-focus position (in-focus pixel), and the in-focus position can be detected at the in-focus position (in-focus pixel) by the amount of light reduced so as not to be saturated. As a result, it is possible to perform a pull-in operation with a high S / N ratio (Signal to Noise ratio) and a correct in-focus position without saturation.

  In the above description, the amount of light received at the center of gravity of the light spot image (laser spot) collected on the line pixel is adjusted by adjusting the amount of laser light emitted from the laser illumination unit 21. Although an example of adjustment has been described, the amount of light received at the center of gravity of the amount of light may be adjusted by other methods. For example, by controlling the shutter time (exposure time) by controlling the shutter opening / closing operation of each light receiving element constituting the line sensor 25 by the control unit 16, the amount of light received at the light center position can be adjusted. In this case, among the line pixels, the exposure time is adjusted so that the exposure time is shortened at the focused pixel and the pixels near the focused pixel, and the exposure time is increased as the distance from the focused pixel is increased.

  When adjusting the exposure time, table data in which the light intensity barycentric position is associated with the exposure time command is prepared in advance as the table data of FIG. 4 described above. The control unit 16 obtains an exposure time command corresponding to the pixel whose light intensity barycentric position is received from the table data, and instructs the line sensor 25. The plurality of light receiving elements constituting the line sensor 25 operate with a shutter time in accordance with an exposure time command from the control unit 16, and each light receiving element outputs a light reception signal corresponding to the amount of received light. That is, when the focused pixel is used as a reference, when the light intensity centroid position of the light spot image is received by a pixel near the focused pixel, the exposure time is shortened, and the light intensity centroid position is changed from the focused pixel. Feedforward control is performed according to predetermined table data so that the exposure time becomes longer as light is received by pixels at a distant position.

  Further, the adjustment control of the light amount of the laser light emitted from the laser illumination unit 21 and the adjustment control of the shutter time of the plurality of light receiving elements constituting the line sensor 25 are combined, for example, both adjustment control simultaneously or Alternatively, it may be performed while being shifted at a predetermined interval. By combining these adjustment controls, feedforward control with a large dynamic range can be performed.

  In the above description, the example in which the adjustment control is performed according to the movement of the light intensity centroid position of the light spot image collected on the line pixel is described. However, instead of the light intensity centroid position, the light is condensed on the line pixel. Adjustment control may be performed in accordance with the movement of the position (light quantity peak position) at which the light quantity of the light spot image (laser spot) to be peaked. In this case, the amount of laser light and the exposure time are adjusted and controlled in accordance with the movement of the light amount peak position, similarly to the above-described light amount center of gravity.

  In the above description, an example in which three types of table data A, B, and C corresponding to the reflectance of the surface of the object 2 is prepared has been described. However, the types of table data are not limited to three types, and Depending on the reflectance of the surface of the object 2, one or a plurality of table data can be prepared. Furthermore, instead of the table data of FIG. 4, the light quantity gravity center position (light quantity peak position) is used as a variable to obtain the light quantity of the laser light designated by the light quantity command or the shutter time of the light receiving element designated by the exposure time instruction. By preparing a predetermined function and substituting the light quantity centroid position (light quantity peak position) into the variable of the function, a light quantity command or an exposure time command may be obtained.

  As described above, when the focused pixel is used as a reference, the light intensity barycentric position (light intensity peak position) of the light spot image is emitted from the laser illumination unit 21 when received by a pixel near the focused pixel. As the light amount of the laser light is reduced or the exposure time of the line sensor 25 is shortened, and the light center of gravity position (light amount peak position) is received by a pixel away from the focused pixel, the light amount of the laser light is reduced. The feedforward control is performed in accordance with predetermined table data so that the exposure time is increased or the exposure time is increased.

  Thus, conventionally, measurement (detection of the focus position) is performed with the reduced light amount that has been confirmed not to be saturated in advance, but in this embodiment, from the focus position (focus pixel). A sufficient amount of light can be secured at the out-of-position position, and at the in-focus position (in-focus pixel), the in-focus position is detected by the amount of light that has been reduced so as not to saturate. , And a correct in-focus position can be detected without saturation. As a result, the focus position can be reliably detected.

  Conventionally, the feedback control of the light amount has been performed and the measurement (detection of the in-focus position) is performed while adjusting the light amount so that the light amount is not saturated. Since such feedback control is not performed, the in-focus position can be detected reliably and at high speed. For example, in the conventional case, since the feedback control of the light amount is performed, the response time is limited to the feed speed and the time until the surface position detection is limited, but in this embodiment, the feedback response High-speed in-focus position detection is possible without depending on time.

  The embodiment of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

  1 surface position detection device, 11 sensor unit, 12 objective lens, 13 imaging device, 14 stage, 15 encoder, 16 control unit, 17 support, 21 laser illumination unit, 22 knife edge, 23 optical lens, 24 dichroic mirror, 25 lines Sensor, 26 Line sensor preamplifier

Claims (5)

Illumination means for illuminating the object;
An imaging optical system that focuses reflected light from the object and forms a light spot image of the object;
Light detecting means for detecting a focused state of a light spot image of the object collected by the imaging optical system;
Position detecting means for detecting a surface position of the object based on a detection result of the light detecting means;
A detecting device comprising: adjusting means for adjusting a light amount of the light spot image detected at the detection position in accordance with a detection position of the light spot image in the light detection means. The light detection means is a line sensor,
The adjustment means adjusts the light amount of the illumination light emitted from the illumination means so that the detected light amount increases as the pixel is farther away from a preset focus pixel among the line pixels constituting the line sensor. The detection device according to claim 1, wherein the detection device is adjusted. The light detection means is a line sensor,
The adjusting means adjusts the exposure time of the line sensor so that the amount of light detected in a pixel farther from a preset focus pixel among the line pixels constituting the line sensor increases. The detection device according to claim 1 or 2. It further comprises an acquisition means for acquiring correspondence information in which the predetermined detection position is associated with the light amount of the light spot image detected at the detection position.
The detection device according to claim 1, wherein the adjustment unit adjusts the amount of light detected at the detection position based on the acquired correspondence information. A plurality of the correspondence information is prepared according to the reflectance of the object,
The detection device according to claim 4, wherein the acquisition unit acquires the correspondence information according to a reflectance of the object.

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