JP2010072491A - Device and method for measuring height - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve tact time while ensuring accuracy of measurement, when measuring a height of a sample by moving a focusing position for the sample in an optical axis direction. <P>SOLUTION: A device for measuring the height by employing a confocal microscope 12 is equipped with: a Z axis drive unit 125 for varying the focusing position in the optical axis (Z axis) direction; a linear scale 126 for measuring a Z axial coordinate; and a control measurement processor 17. The control measurement processor has: a function for capturing data of the linear scale 126 and an image of the microscope 12, and for leaving a pixel with a higher luminance value and the Z coordinate thereof, while comparing the luminance value of the image with that before one, when moving a sample stand 123 to an end point position from a starting point position on the Z axis; a function for comparing a luminance value of an area on a specified image with a certain specification value; and a function for decelerating a Z axis movement velocity if the comparison value is large, and for returning the Z axis movement velocity to an original velocity if the comparison value is small during deceleration. In this arrangement, a slow mode is set only when obtaining a luminance above a certain level, thereby reducing measuring time without lowering a measurement accuracy. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a height measuring apparatus and a measuring method for measuring the height of a sample having a high contrast by using an optical means such as a confocal microscope used in, for example, medicine or industry.

  In recent years, a height measurement device has been provided that acquires a confocal image of a sample such as an LCD substrate or a semiconductor wafer, measures the height of the sample using the image, and presents the surface shape from a change in the height direction. Yes. This type of measuring apparatus uses, for example, a confocal optical microscope with a shallow depth of field, and an optical image of a sample magnified by the microscope is moved with a camera while moving the focal position of the confocal microscope in the optical axis direction. The captured image data is stored in the memory. Then, the pixel having the maximum luminance is detected from the captured image data, and the pixel having the maximum luminance is collected and a single image is synthesized to obtain an extended focus image. . In addition, by creating one image assuming that the focus position (height) when the maximum luminance is obtained is the position of each pixel, a height image or a cross-sectional profile indicating the shape in the height direction can be obtained. Can be acquired.

  For example, Patent Document 1 is cited as a prior document of the height measuring apparatus as described above. The measurement apparatus described in Patent Document 1 determines whether or not the reception signal level of reflected light from a sample is within a preset appropriate range in order to photograph a sample containing two or more substances having greatly different reflectances. When it is determined that the signal level is out of the proper range, the light receiving gain variable means is controlled to adjust the signal level to be within the proper range.

Japanese Patent No. 3568286

  By the way, in the confocal microscope used in the height measuring apparatus, when the in-focus position is moved in the optical axis direction, the sampling rate is determined by the frame rate of the camera. Since the confocal microscope has an extremely narrow depth of focus, if the speed is increased, an image cannot be captured at each position having a different height, and the measurement accuracy decreases. For this reason, it is necessary to make the measurement with extremely low movement speed and ensure measurement accuracy, and the tact time may be deteriorated.

  The present invention has been made to solve the above-described problem, and improves the tact time while ensuring the measurement accuracy when measuring the height of the sample by moving the in-focus position with respect to the sample in the optical axis direction. An object of the present invention is to provide a height measuring apparatus and a measuring method thereof.

  To achieve the above object, a height measuring apparatus according to the present invention captures a confocal microscope that scans and magnifies an optical image of a sample at a constant rate, and an optical image of the sample that is magnified by the confocal microscope. Camera, a light source that irradiates the sample with light for imaging, and a focal position of the confocal microscope with respect to the sample is moved in the direction of the optical axis. And a control unit that captures an optical image of the sample by the camera while changing the focal position of the confocal microscope with respect to the sample through the drive mechanism, and acquires the captured image. The unit calculates the brightness of the designated area of the captured image and compares it with a reference value, and the brightness value of the designated area is based on the moving range of the focal position. Speed control means for selectively switching the drive mechanism to the high speed mode in a range less than the value, and the drive mechanism to selectively switch to the low speed mode in a range equal to or greater than a reference value, and a captured image acquired in the low speed mode Based on the focal position of the confocal microscope when the pixel area in which the luminance value is included in the maximum range set in advance is extracted, and the image in which the luminance value of the extracted pixel area is in the maximum range is acquired And a calculating means for calculating the height of the sample.

  Further, the height measuring method of the height measuring apparatus according to the present invention scans and enlarges an optical image of a sample at a constant rate with a confocal microscope, and changes the focal position of the confocal microscope with respect to the sample by a driving mechanism. When the optical image of the sample is captured by a camera and the captured image is acquired, the brightness of the designated area of the captured image is calculated and compared with a reference value, and the designated area is within the moving range of the focal position. In the range where the luminance value is less than the reference value, the driving mechanism is selectively switched to the high speed mode, and in the range where the luminance value is equal to or higher than the reference value, the driving mechanism is selectively switched to the low speed mode. The focal position of the confocal microscope when the pixel area whose luminance value is included in the preset maximum range is extracted from the image, and the image in which the luminance value of the extracted pixel area is within the maximum range is acquired And calculates the height of the sample on the basis.

  According to the present invention, when the sample is moved from the start point position to the end point position on the optical axis, the image of the confocal microscope is captured, the pixel area where the maximum luminance is obtained and the focal position thereof are obtained, and Compare the brightness value with the reference value, and if the comparison value exceeds the reference value, the moving speed is set to the low speed mode, and if the comparison value is small in the low speed mode, the moving speed is returned to the original high speed mode. By setting the low-speed mode only when the luminance can be obtained, the measurement time can be shortened without reducing the measurement accuracy.

  According to the present invention, when measuring the height of a sample by moving the in-focus position with respect to the sample in the optical axis direction, the height measuring device capable of improving the tact time while ensuring measurement accuracy, and the measurement A method can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram schematically showing an embodiment of a height measuring apparatus according to the present invention. In FIG. 1, the parallel light emitted from the light source 11 enters the optical processing unit 121 of the confocal optical microscope 12, passes through the objective lens 122 from the optical processing unit 121, and enters the sample 124 placed on the sample stage 123. To reach. The reflected light from the sample 124 passes through the objective lens 122 again, undergoes processing by the optical processing unit 121, and forms an image on the imaging surface of the camera 13. The confocal microscope 12 includes a Z-axis drive unit 125 that moves the sample stage 123 in the direction of the optical axis (hereinafter referred to as Z-axis) of the objective lens 122, and the height thereof is a coordinate value (hereinafter referred to as Z-axis). Z coordinate value) is measured by the linear scale 126.

  The video imaged by the camera 13 is input to the control measurement processing device 14. The control measurement processing device 14 is executed by a program in a computer (PC) 15 and mainly controls the light amount of the light source 11 and the Z-axis drive unit 125. The control measurement processing device 14 measures the height from the image of the camera 13 and the Z coordinate value of the linear scale 126 and outputs the measurement result to the computer 15. In addition, the control measurement processing device 14 controls the Z-axis drive unit 125 in order to control the distance between the sample 124 and the objective lens 122.

  FIG. 2 is a conceptual diagram schematically showing the configuration of the confocal microscope 12 used in the height measuring apparatus. In FIG. 2, the parallel light given from the external light source 11 is incident on the optical processing unit 121 and is focused on a specific pinhole 121c on the Nipkow disc 121b by the imaging lens 121a. A half mirror 121d is arranged in front of the Niipou disc 121b. The half mirror 121d transmits the light from the imaging lens 121a.

  The light that has passed through the pinhole 121 c enters the objective lens 122 and reaches the sample 124. The reflected light from the sample 124 returns to the objective lens 122 and again passes through the pinhole 121c to obtain a confocal effect. This reflected light is incident on the half mirror 121d. The reflected light incident on the half mirror 121d changes direction by 90 degrees, passes through the imaging lens 121e, and forms an image on the imaging surface of the camera 13.

  In the above configuration, the Nipkow disk 121b has thousands of pinholes, and these pinholes rotate, so that thousands of lights scan the sample 124. As a result, the reflected light of the sample 124 scans the imaging surface of the camera 13, whereby one image can be obtained on the imaging surface.

  As described above, the confocal microscope 12 provides the pinhole 121c at a position optically conjugate with the in-focus position and blocks the passage of light other than the in-focus position, thereby obtaining a finer image than a normal optical microscope. However, since it does not transmit light other than the focal point, it has a characteristic that the depth of field is extremely narrower than that of a normal optical microscope.

  On the other hand, the control measurement processing device 14 is basically configured as shown in FIG. That is, the comparison unit 141 that calculates the luminance of the designated area of the captured image obtained by the camera 13 and compares it with the reference value, and within the range where the luminance value of the designated area does not meet the reference value within the moving range of the focal position. A speed control unit 142 that selectively switches the Z-axis drive unit 125 to the low-speed mode in a range that is equal to or higher than the reference value in the Z-axis drive unit 125, and brightness from the captured image acquired in the low-speed mode. A pixel region whose value is included in the preset maximum range is extracted, and the focal position (Z coordinate value) of the confocal microscope 12 when the image in which the luminance value of the extracted pixel region is within the maximum range is acquired is obtained. A calculation unit 143 that calculates the height of the sample 124 is provided. Specifically, the calculation unit 143 obtains an image with the maximum luminance and its height information by comparing the luminance value of the previous image while leaving the pixel with the higher luminance value and its Z coordinate.

Here, a method of measuring the height using the confocal microscope 12 will be briefly described with reference to FIG.
First, as shown in FIG. 4A, a sample 124 having a gentle mountain shape is moved in the Z-axis direction (optical axis direction) from the base to the top, and an image is acquired and the Z coordinate at that time is obtained. Record it. If the luminance value of the dotted line pixel shown in FIG. 4 (a) is the height on the vertical axis and the luminance is on the horizontal axis, as shown in FIG. 4 (b), each Z position (Z1, Z2, Z3,. Z7, Z8) allows the peak of luminance values (I1, I2, I3,..., I7, I8) to be seen. This curve is hereinafter referred to as a Z curve. This Z curve is a steep curve because the depth of field is narrower than that of an optical microscope. Therefore, this peak position can specify the focal position of each Z position. The height information of each pixel position can be obtained by obtaining the Z curve for each pixel on the imaging surface.

Next, the height measurement sequence of the present invention using the confocal microscope 12 will be described with reference to FIGS.
FIG. 5 is a flowchart showing the overall processing flow of height measurement. In FIG. 5, first, a Z coordinate range in which the sample stage 123 is moved along the Z axis is designated in the Z axis movement range setting process (step S11). In the height measurement, the image and its Z-coordinate position are acquired while moving the Z-coordinate within the range of the Z-coordinate set in the Z-axis movement range setting process (step S11). This is a process of leaving a position. Next, the speed at which the sample stage 123 is moved along the Z axis is set to a constant speed by setting the Z axis moving speed (step S12).

  The height measurement sequence (step S13) is a process for determining the height (Z coordinate) corresponding to each pixel position of one image. The height measurement sequence (step S13) will be described in detail with reference to FIG. When the height measurement sequence (step S13) is completed, the result is finally acquired by the acquisition processing (step S14) of the height data 1 and the omnifocal image 1. The height data 1 is height data for all pixels, and the omnifocal image 1 is an image obtained by leaving data with a high luminance value over the Z-axis movement range.

  FIG. 6 is a flowchart showing a specific processing flow of the height measurement sequence (step S13). The height measurement sequence is a sequence for determining the height (Z coordinate) corresponding to each pixel position of one image. As shown in FIG. 6, the process of moving the sample stage 123 to the start position of the Z axis (step In step S131, the sample stage 123 is moved to the start position on the Z axis, the image 1 at the start position is acquired in the image 1 acquisition process (step S132), and the Z coordinate is acquired in the Z coordinate acquisition process (step S133). Next, the Z-axis moving speed is set to the high speed mode in the high speed setting process (step S134).

  At this time, all designated area completion determination processing (step S135) is performed, and it is determined whether the luminance value comparison of the designated area of the image is completed. If not completed, the brightness value of the designated area is calculated in the brightness calculation process (step S136). The luminance value in the designated area designates the average value or peak value of the luminance values of the pixels in the designated area. Subsequently, a process for determining whether or not the brightness of the designated area is high (step S137) is performed. If the brightness value of the designated area is dark, the process proceeds to the Z-axis movement process (step S139), and if the brightness is bright, the low speed setting is performed. In the process (step S138), the Z-axis movement speed is set to the low speed mode, and the process proceeds to the Z-axis movement process (step S139). In the Z-axis movement process (step S139), the movement is performed at the speed of the low-speed mode designated from the start position of the Z coordinate to the end position.

  The image 2 acquisition process (step S1310) updates image 2 with a new image, and the Z coordinate acquisition process (step S1311) acquires the Z coordinate of the image. In the luminance value comparison process (step S1312), the luminance values corresponding to the pixels of the image 1 and the image 2 are compared. The brightness value and Z coordinate update process (step S1313) is a process of updating the image 1 with a pixel having a higher brightness value than the compared brightness value and simultaneously recording the Z coordinate of the updated pixel. The determination process of the Z coordinate end position (step S1314) determines whether or not the Z coordinate is the end position. If it is not the end position, the process returns to the high speed setting process (step S134) to set the Z axis movement to the high speed mode and set the sample stage. 123 is moved at high speed and the sequence is continued. In the case of the end position, it becomes end (step S1315), and image 1 is an image in which only the brightest luminance value remains in the Z-axis movement range corresponding to all pixel positions, and all the pixels have Z coordinate values.

Here, it is assumed that the height of a sample having a three-dimensional shape as shown in FIG. 7 is measured. This sample has a profile having heights A, B, and C in descending order as shown in FIG.
When the Z-axis is moved from the height C to the height A at a constant speed, the sampling rate is determined by the camera frame rate. Since the confocal microscope 12 has an extremely narrow depth of focus, if the speed is high, an image cannot be captured at the positions of heights A, B, and C, and the measurement accuracy decreases. For this reason, conventionally, measurement is performed while ensuring measurement accuracy by extremely reducing the Z-axis movement speed, and the tact time may be deteriorated.

  Therefore, the height measuring device according to the present invention reduces the Z-axis movement speed to the designated speed when the brightness of the designated area in the image exceeds the designated brightness, and falls below the designated brightness during the deceleration. Has a means to return to the original speed. As a result, the tact time can be improved without degrading the accuracy of height measurement using the confocal microscope 12.

Hereinafter, description will be made with reference to specific examples shown in FIGS.
FIG. 9 shows an image of the sample shown in FIG. 7, and hatched lines indicate the designated areas that have been set. FIGS. 10A to 10D are graphs when all of the Z-axis start coordinates Zs are moved once to the end coordinates Ze. FIG. 10A shows the luminance / Z-coordinate curves of the areas A and B. The solid line indicates the area A and the broken line indicates the area B. As shown in the figure, the broken line exceeds the luminance threshold in the interval from height Zb0 to Zb1, and the solid line exceeds the luminance threshold in the interval from height Za0 to Za1. FIG. 10B shows a Z-axis moving speed / Z coordinate curve, where the speed when the luminance threshold is exceeded is V2 (low speed mode), and the speed when the luminance threshold is not exceeded is V1 (high speed mode). FIG. 10B shows a graph.

  FIG. 11 compares the movement time T1 when the Z-axis control of the present invention is performed and the movement time T2 when moving at the speed V2. In FIG. 11, the vertical axis represents the Z coordinate, the horizontal axis represents time, the solid line represents the straight line when moving at the speed V2, and the thin line moved at the speed V1 when the Z-axis control of the present invention is performed. A straight line of time is shown.

As is apparent from FIG. 11, when the Z-axis control of the present invention is performed, the speed V2 is obtained in the zone Zb0 to Zb1 and the zone Za0 to Za1, and the speed V1 is obtained otherwise. When the movement time T1 of the present invention is compared with the movement time T2 of the speed V2, T1 <T2, and it can be seen that by using the present invention, the measurement can be performed at a high speed and the tact time is improved.
In FIG. 10C, the black image indicates the image capturing timing (sampling position) when the speed is constant at the speed V1, and it can be seen that the image cannot be acquired around the peak values of the two luminance values. FIG. 10D shows the image capturing timing (sampling position) of the image when the Z-axis control of the present invention is performed. The black circle indicates the speed around the peak value of the luminance value. An image is acquired around the peak value, and high-precision measurement can be expected. Thus, by using the present invention, the tact time can be improved without degrading accuracy.

  The Z-axis movement range (upper limit, lower limit), Z-axis speed designation (low speed, high speed), and luminance threshold that have been described above are stored in electronic data that saves control parameters called recipes. FIG. 12 shows an example of a user interface screen of application software for setting a recipe. As shown in the figure, the Z-axis movement range (upper limit, lower limit), Z-axis speed designation (low speed, high speed), and luminance threshold can be designated on the screen.

  Therefore, according to the height measuring apparatus having the above configuration, when moving the sample stage 123 from the start position to the end position on the optical axis (Z axis), the data of the linear scale 126 and the image of the microscope 12 are acquired. While comparing the luminance value of the previous image, the pixel having the higher luminance value and its Z coordinate are left, the luminance value of the area on the designated image is compared with a certain designated value, and if the comparison value is large, the Z axis Since the movement speed is decelerated and if the comparison value is small during deceleration, the Z-axis movement speed is returned to the original speed, and the low-speed mode is set only when a certain level of brightness is obtained. Measurement time can be shortened without dropping

  Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can also be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

The block diagram which shows roughly one Embodiment of the height measuring apparatus which concerns on this invention. The conceptual diagram which shows roughly the structure of the confocal microscope 12 used for the height measuring apparatus of the said embodiment. The block diagram which shows the basic composition of the control measurement processing apparatus 14 used for the height measuring apparatus of the said embodiment. The conceptual diagram for demonstrating simply the method of the height measurement using the confocal microscope of the said embodiment. The flowchart which shows the flow of the whole process of the height measurement of the said embodiment. The flowchart which shows the flow of the specific process of the height measurement sequence shown in FIG. In the said embodiment, the three-dimensional figure for assuming measuring the height of the sample which has a three-dimensional shape. The figure which shows the cross-sectional profile of the sample shown in FIG. The figure which shows the picked-up image of the sample shown in FIG. The figure which shows the graph according to conditions at the time of moving to the end coordinate Ze once from the start coordinate Zs of a Z-axis in the state which has acquired the picked-up image shown in FIG. The figure which compared the movement time T2 when moving with the speed V2 and the movement time T1 when performing Z-axis control of the said embodiment. The figure which shows the recipe setting screen of the said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Light source, 12 ... Confocal optical microscope, 121 ... Optical processing part, 122 ... Objective lens, 123 ... Sample stand, 124 ... Sample, 125 ... Z-axis drive part, 126 ... Linear scale, 13 ... Camera, 14 ... Control Measurement processing device, 15 ... computer (PC), 121a ... imaging lens, 121b ... Nipkow disk, 121c ... pinhole, 121d ... half mirror, 121e ... imaging lens, 141 ... comparison unit, 142 ... speed control Part, 143... Height calculation part.

Claims (3)

A confocal microscope that scans and magnifies the optical image of the sample at a constant rate;
A camera that captures an optical image of the sample magnified by the confocal microscope;
A light source for irradiating the sample with light for the imaging;
The focal position of the confocal microscope with respect to the sample is moved in the direction of the optical axis, and a driving mechanism having a low speed mode and a high speed mode as the moving speed;
A control unit for capturing an optical image of the sample by the camera while changing a focal position of the confocal microscope with respect to the sample through the driving mechanism,
The control unit is
Comparing means for calculating the brightness of the designated area of the captured image and comparing it with a reference value;
The drive mechanism is selectively switched to the high speed mode when the luminance value of the designated area is less than the reference value within the moving range of the focal position, and the drive mechanism is selectively switched to the low speed mode when the brightness value is equal to or greater than the reference value. Speed control means,
The confocal microscope when a pixel area whose luminance value is included in a preset maximum range is extracted from the acquired captured image, and an image in which the luminance value of the extracted pixel area is within the maximum range is acquired. And a calculating means for calculating the height of the sample based on the focal position.   The height measuring apparatus according to claim 1, wherein the calculating unit leaves a pixel having a higher luminance value and its Z coordinate than the luminance value of the previous captured image. The optical image of the sample is scanned and enlarged at a constant rate by the confocal microscope, and the optical image of the sample is captured by the camera while changing the focal position of the confocal microscope with respect to the sample by the driving mechanism, and the captured image is acquired. In the measuring method of the height measuring device,
Calculate the brightness of the specified area of the captured image and compare with the reference value,
The drive mechanism is selectively switched to the high speed mode when the luminance value of the designated area is less than the reference value within the moving range of the focal position, and the drive mechanism is selectively switched to the low speed mode when the brightness value is equal to or greater than the reference value. And
The confocal microscope when a pixel area whose luminance value is included in a preset maximum range is extracted from the acquired captured image, and an image in which the luminance value of the extracted pixel area is within the maximum range is acquired. A height measuring device measuring method, wherein the height of the sample is calculated based on the focal position.

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