Surface profile measurement device and surface profile measurement method

Abstract

To provide a surface profile measurement device and surface profile measurement method, which improve measurement accuracy by suppressing the influence of vibration generated while making measurement.SOLUTION: A surface profile measurement device for measuring a surface profile of a measurement target is provided, the device comprising an optical head configured to be scanned relative to the measurement target, image capturing means for capturing an observation image acquired by the optical head, a stage configured to support the measurement target and move in a direction perpendicular to a scanning direction of the optical head, computation means for computing an indicator related to frame drops of the image capturing means for each position of the stage, and setting means for setting measurement conditions for each position of the stage according to the indicator.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a surface profile measuring device and a surface profile measuring method. [Background technology]

[0002] There are known measurement methods for measuring the three-dimensional shape of a measurement surface of an object using a microscope scanning surface profile measuring device, such as a white light interference method or a focus variation method (see Patent Documents 1 and 2). Such scanning surface profile measuring devices measure the three-dimensional shape of the measurement surface by scanning a microscope equipped with a camera along the scanning direction, capturing images of the measurement surface with the camera at regular intervals, and calculating height information for each pixel or calculating the degree of focus (microscope focal position) for each pixel of each observation image based on the observed images for each interval and information from the scale, thereby measuring the three-dimensional shape of the measurement surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-90520 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-99213 Summary of the Invention [Problem to be solved by the invention]

[0004] In scanning surface profile measurement instruments, vibrations during scanning can cause a shift in the relative position between the microscope and the object being measured, resulting in measurement errors. Measurement errors can also occur due to camera frame drops caused by scale vibrations. Furthermore, in surface profile measurement instruments that have an XY stage for measuring workpieces, the center of gravity changes when the stage is moved, which significantly changes the degree of measurement error due to vibration.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a surface profile measuring device and a surface profile measuring method that can suppress the effects of vibrations that occur during measurement and improve measurement accuracy. [Means for solving the problem]

[0006] A first aspect of a surface shape measuring device that acquires an observation image of a measurement object while scanning an optical head relatively in a direction perpendicular to the measurement object includes a camera that captures the observation image acquired by the optical head, a drive unit that scans the optical head relatively in a scanning direction perpendicular to the measurement object, a stage that moves the measurement object relatively to the optical head, an encoder for detecting the scanning direction position of the optical head relative to the measurement object, an image capture command unit that commands the camera to capture an observation image based on a position signal output from the encoder at predetermined intervals, a frame drop occurrence rate calculation unit that calculates a frame drop occurrence rate that indicates the rate at which frame drops occur in the camera for each position of the stage, and a measurement condition setting unit that sets measurement conditions for measuring the surface shape of the measurement object for each position of the stage based on the frame drop occurrence rate.

[0007] In the surface shape measuring apparatus of the second aspect, the measurement condition setting unit sets the field of view of the camera as the measurement condition.

[0008] In the surface shape measuring apparatus of the third aspect, the measurement condition setting unit sets the scanning speed of the optical head relative to the measurement object as the measurement condition.

[0009] In the surface profile measuring apparatus of the fourth aspect, the measurement condition setting unit determines whether or not the measurement conditions need to be changed based on the result of comparing the frame drop occurrence rate with the frame drop occurrence rate threshold.

[0010] In the surface profile measuring device of the fifth aspect, when it is determined that the measurement conditions need to be changed, the measurement condition setting unit changes the measurement conditions so that the frame drop occurrence rate becomes smaller than the frame drop occurrence rate threshold.

[0011] In the sixth aspect of the surface shape measuring device, the measurement condition setting unit can set both the field of view of the camera and the scanning speed of the optical head relative to the object to be measured as measurement conditions, and when it determines that a change in the measurement conditions is necessary, it changes the field of view of the camera with priority over the scanning speed of the optical head so that the frame drop occurrence rate is equal to or less than the frame drop occurrence rate threshold.

[0012] In the surface profile measuring device of the seventh aspect, if the frame drop occurrence rate is FDR, the number of frames of the observation image actually captured by the camera is N, and the planned number of frames of the observation image that the camera should originally capture based on the position signal is M, the frame drop occurrence rate calculation unit calculates the frame drop occurrence rate using the following formula.

[0013] FDR=1-N / M

[0014] In the surface shape measuring apparatus of the eighth aspect, the optical head is a white light interference microscope.

[0015] In a ninth aspect of the surface shape measuring method for measuring a surface shape using a surface shape measuring device comprising: a camera that captures an observation image of the measurement object acquired by the optical head; a drive unit that relatively scans the optical head in a scanning direction perpendicular to the measurement object; an encoder that detects the scanning direction position of the optical head relative to the measurement object; and an imaging command unit that commands the camera to capture an observation image in response to a trigger signal output from the encoder at each sampling interval, a frame drop occurrence rate that indicates the rate at which frame drops occur in the camera for each stage position is calculated, and measurement conditions for measuring the surface shape of the measurement object are set for each stage position based on the frame drop occurrence rate. [Effects of the Invention]

[0016] According to the present invention, it is possible to suppress the influence of vibrations that occur during measurement and improve measurement accuracy. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a surface profile measuring device. [Figure 2] FIG. 2 is a block diagram of the surface shape measuring device. [Figure 3] FIG. 3 is a diagram for explaining the measurement of a plurality of measurement objects. [Figure 4] FIG. 4 is a diagram for explaining the calculation of the three-dimensional shape of the object to be measured by the surface shape measuring device. [Figure 5] FIG. 5 is a diagram for explaining the field of view range. [Figure 6] FIG. 6 is a flowchart showing the setting of measurement conditions in the pre-adjustment mode. [Figure 7] FIG. 7 is a flowchart showing the setting of measurement conditions in the pre-adjustment mode in step S3 shown in FIG. [Figure 8] FIG. 8 is a flowchart showing the measurement mode. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0019] 1 is a schematic diagram of a surface profile measuring device 10 that measures the surface profile of a measurement target W. Of the mutually orthogonal X, Y and Z directions in the figure, the X and Y directions are horizontal directions, and the Z direction is an up-down direction (vertical direction).

[0020] 1, the surface profile measuring apparatus 10 includes an optical head 12, a drive unit 16, an encoder 18, and a control device 20 to measure the three-dimensional shape (surface shape) of the measurement surface of a measurement target W. The surface profile measuring apparatus 10 shown in FIG. 1 also includes a stage 22 and a stage drive unit 24. The optical head 12, camera 14, drive unit 16, and encoder 18 may be collectively referred to as an optical head unit.

[0021] The optical head 12 is configured as a Michelson-type white light interference microscope as shown in FIG.

[0022] The optical head 12 includes a camera 14 , a light source unit 26 , a beam splitter 28 , an interference objective lens 30 , and an imaging lens 32 .

[0023] An interference objective lens 30, a beam splitter 28, an imaging lens 32, and a camera 14 are arranged in this order along the Z-direction upward from the measurement object W. In addition, a light source unit 26 is arranged at a position facing the beam splitter 28 in the X-direction (or the Y-direction).

[0024] Under the control of the control device 20, the light source unit 26 emits a parallel beam of white light (low-coherence light with little coherence) as measurement light L1 toward the beam splitter 28. Although not shown, the light source unit 26 includes a light source capable of emitting measurement light L1, such as a light-emitting diode, a semiconductor laser, a halogen lamp, or a high-intensity discharge lamp, and a collector lens that converts the measurement light L1 emitted from the light source into a parallel beam.

[0025] A half mirror, for example, is used as the beam splitter 28. The beam splitter 28 reflects a portion of the measurement light L1 incident from the light source unit 26 toward the interference objective lens 30 on the lower side in the Z direction. The beam splitter 28 also transmits a portion of the combined light L3 (described below) incident from the interference objective lens 30 toward the upper side in the Z direction, and emits this combined light L3 toward the imaging lens 32.

[0026] The interference objective lens 30 is a Michelson type and includes an objective lens 30A, a beam splitter 30B, and a reference surface 30C. The beam splitter 30B and the objective lens 30A are arranged in this order from the measurement object W upward in the Z direction. The reference surface 30C is also arranged at a position facing the beam splitter 30B in the X direction (or the Y direction).

[0027] The objective lens 30A has a light-collecting effect, and collects the measurement light L1 incident from the beam splitter 28 onto the measurement object W through the beam splitter 30B.

[0028] The beam splitter 30B may be, for example, a half mirror. The beam splitter 30B splits a portion of the measurement light L1 incident from the objective lens 30A as reference light L2, transmits the remaining measurement light L1, and emits it to the measurement object W, while reflecting the reference light L2 toward the reference surface 30C. After transmitting through the beam splitter 30B, the measurement light L1 is irradiated onto the measurement object W, and is then reflected by the measurement object W and returns to the beam splitter 30B.

[0029] The reference surface 30C is, for example, a reflecting mirror, and reflects the reference light L2 incident from the beam splitter 30B toward the beam splitter 30B. The position of the reference surface 30C in the X direction can be manually adjusted by a position adjustment mechanism (not shown). This makes it possible to adjust the optical path length of the reference light L2 between the beam splitter 30B and the reference surface 30C. This reference optical path length is adjusted to match (or approximately match) the optical path length of the measurement light L1 between the beam splitter 30B and the measurement object W.

[0030] The beam splitter 30B generates a combined light L3 from the measurement light L1 returning from the measurement object W and the reference light L2 returning from the reference surface 30C, and emits this combined light L3 toward the objective lens 30A on the upper side in the Z direction. This combined light L3 passes through the objective lens 30A and the beam splitter 28 and enters the imaging lens 32. In the case of a white light interference microscope, the combined light L3 becomes an interference light containing interference fringes.

[0031] The imaging lens 32 forms an image of the combined light L3 incident from the beam splitter 28 on the imaging plane (not shown) of the camera 14. Specifically, the imaging lens 32 forms an image of a point on the focal plane of the objective lens 30A as an image point on the imaging plane of the camera 14.

[0032] Although not shown, the camera 14 is equipped with a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) imaging element. The camera 14 captures the combined light L3 formed on the imaging plane by the imaging lens 32 as an observation image, and outputs the captured observation image 36. Here, the observation image 36 includes interference fringes.

[0033] The drive unit 16 is configured with a known linear motor or motor drive mechanism. The drive unit 16 holds the optical head 12 so that it can be scanned relative to the measurement object W in the Z direction, which is the vertical scanning direction (the optical axis direction of the optical head 12). Under the control of the control device 20, the drive unit 16 moves the optical head 12 relative to the measurement object W within a set scanning speed and scanning direction range.

[0034] The driving unit 16 only needs to be able to relatively scan the optical head 12 with respect to the measurement object W in the scanning direction, and for example, may scan the stage 22 supporting the measurement object W in the scanning direction.

[0035] The stage 22 has a stage surface that supports the measurement target W. The stage surface is composed of a flat surface that is approximately parallel to the X and Y directions. The stage drive unit 24 is composed of a known linear motor or motor drive mechanism, and under the control of the control device 20, moves the stage 22 horizontally relative to the optical head 12 in a plane perpendicular to the scanning direction (X and Y directions).

[0036] The stage driving unit 24 only needs to be able to move the stage 22 in the X and Y directions relative to the optical head 12, and for example, the optical head 12 may be moved in the X and Y directions relative to the stage 22 that supports the measurement object W.

[0037] The encoder 18 is a position detection sensor that detects the scanning direction position of the optical head 12 relative to the measurement object W, and may be, for example, an optical linear encoder (also referred to as a scale). The optical linear encoder is configured, for example, with a linear scale on which slits are formed at regular intervals, and a light receiving element and a light emitting element arranged opposite each other across the linear scale. The encoder 18 repeatedly detects the scanning direction position (Z direction position) of the optical head 12, and repeatedly outputs a position signal 38 including position information indicating the scanning direction position (Z direction position) to the control device 20.

[0038] The control device 20 performs overall control of the surface profile measuring device 10, such as switching between adjustment before measuring the measurement object W (pre-adjustment mode) and measurement of the measurement object W (measurement mode), setting measurement conditions in each mode, and calculating the three-dimensional shape in the measurement mode, in response to input operations on the operation unit 21. The display unit 23 displays various information under the control of the control device 20. do.

[0039] The control device 20 includes an arithmetic circuit configured with various processors, memories, etc. The various processors include a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), and a programmable logic device (e.g., simple programmable logic device (SPLD), complex programmable logic device (CPLD), and field programmable gate array (FPGA)). The various functions of the control device 20 may be realized by a single processor, or may be realized by multiple processors of the same or different types.

[0040] Fig. 2 is a functional block diagram of the control device 20. As shown in Fig. 2, the camera 14 and light source unit 26 of the optical head 12, the drive unit 16, the encoder 18, the stage drive unit 24, and the operation unit 21 are connected to the control device 20.

[0041] 2, the control device 20 includes a storage unit 100, a measurement control unit 102, a trigger signal output unit 104, a three-dimensional shape calculation unit 106, a measurement condition setting unit 108, a frame drop occurrence rate calculation unit 110, a trigger signal number counting unit 112, a camera frame number counting unit 114, and a control unit 116, and realizes each function and performs processing by executing a control program (not shown) read from the storage unit 100. The control unit 116 controls the overall processing of the control device 20.

[0042] As shown in FIG. 2, the measurement control unit 102 includes a light source control unit 120, an imaging command unit 122, a drive control unit 124, and a stage drive control unit 126, and controls the light source unit 26, camera 14, drive unit 16, and stage drive unit 24 of the optical head 12.

[0043] The light source unit control unit 120 starts emitting the measurement light L1 from the light source unit 26. The drive unit control unit 124 controls the drive unit 16 to cause the optical head 12 to scan in the scanning direction at the set scanning speed within the set scanning range.

[0044] While the drive unit 16 scans the optical head 12 in the scanning direction, a position signal 38 is output from the encoder 18, and the position signal 38 is supplied to a trigger signal output unit 104. The trigger signal output unit 104 outputs a trigger signal at predetermined intervals based on the detection result of the position signal 38.

[0045] The photographing command unit 122 commands the camera 14 to photograph an observation image in response to a trigger signal output at predetermined intervals from the trigger signal output unit 104. The photographing command unit 122 commands the camera 14 to photograph an observation image in response to a trigger signal output from the trigger signal output unit 104.

[0046] Based on a trigger signal output from the trigger signal output unit 104, the camera 14 acquires a plurality of observation images 36 of the measurement object W at the predetermined intervals (i.e., sampling intervals) within the scanning range set by the operator via the operation unit 21. The plurality of observation images 36 acquired by the camera 14 at the predetermined intervals (sampling intervals) are output to the control device 20, and the observation images 36 are associated with position signals 38 (including position information indicating the Z-direction position) at the time the observation images 36 were acquired. The three-dimensional shape calculation unit 106 calculates the surface shape of the measurement object W based on the observation images 36 and the position signals 38. The associated observation images 36 and position signals 38 may be stored in the memory unit 100. The three-dimensional shape calculation unit 106 may calculate the surface shape of the measurement object W based on the observation images 36 and the position signals 38 stored in the memory unit 100.

[0047] Fig. 3 is a diagram for explaining the measurement of a plurality of measurement objects W. As shown in Fig. 3, a plurality of measurement objects W are placed on one pallet 25. Pallet 25 on which the plurality of measurement objects W are placed is supported by stage 22. Stage 22 is configured to be movable on two axes parallel to the X direction and Y direction.

[0048] 3A, one of a plurality of measurement objects W is selected as the measurement object, and the measurement object W is aligned with the optical head 12 by moving the stage 22 within the plane. The surface profiler 10 measures the surface profile of the measurement object W.

[0049] 3B, a measurement object W different from 3A is selected as the measurement object, and the measurement object W is aligned with the optical head 12 by moving the stage 22 within the plane. The surface profiler 10 measures the surface profile of the measurement object W different from 3A. A plurality of measurement objects W of the same type are measured by the surface profiler 10.

[0050] 3 shows an example in which multiple measurement objects W are placed on a pallet 25. However, the measurement objects W are not limited to this. For example, a semiconductor wafer and multiple circuit patterns formed on the semiconductor wafer can also be considered as multiple measurement objects of the same type. The semiconductor wafer can correspond to the pallet, and the multiple circuit patterns can correspond to the multiple measurement objects W.

[0051] 3 illustrates an example in which stage 22 is movable along two axes, the X and Y directions. However, stage 22 may be movable along one axis, either the X or Y direction, or may be movable along three axes, the X, Y, and Z directions, or more. While the case in which stage 22 is moved has been described, optical head 12 may also be moved as long as optical head 12 and stage 22 can be moved relative to each other.

[0052] Fig. 4 is an explanatory diagram for explaining the calculation of the three-dimensional shape of the measurement object W by the surface profile measuring apparatus 10. Fig. 4A is a schematic diagram showing the scanning direction of the optical head 12. Fig. 4B shows observation images acquired by the camera 14 at each scanning direction position while the optical head 12 is raised in the scanning direction from a position close to the measurement object WS. Fig. 4C is a diagram illustrating the correlation between the Z direction position (height) and brightness for each pixel, as well as an interference fringe curve.

[0053] The three-dimensional shape calculation unit 106 acquires, from the camera 14, an observation image 36 of the measurement object W photographed at each sampling interval within the field of view of the camera 14 while the optical head 12 is scanning in the scanning direction.

[0054] Next, as shown in 4B and 4C, the three-dimensional shape calculation unit 106 detects the luminance value for each pixel in each observation image 36 where interference fringes are generated. Then, the three-dimensional shape calculation unit 106 compares the luminance values ​​(see symbol Pix1) for each pixel at the same coordinates in each observation image 36 (the image pickup element of the camera 14). The three-dimensional shape calculation unit 106 determines the Z-direction position at which the luminance value is maximized for each pixel at the same coordinates in each observation image 36, thereby calculating height information of the measurement target W for each pixel at the same coordinates.

[0055] The surface profile measuring apparatus 10 calculates height information of a plurality of measurement targets W by moving the stage 22.

[0056] Next, the relationship between the field of view of the camera 14, which is one of the measurement conditions set in the surface profile measuring apparatus 10, and the maximum frame rate will be described.

[0057] 5 is a diagram illustrating the field of view of the camera 14, which is one of the measurement conditions, and is a diagram of the measurement object W observed from the side of the camera 14 along the scanning direction (Z direction). Generally, the field of view of the camera 14 is the range that can measure the measurement object W in one go. Therefore, if the field of view of the camera 14 is reduced, the target measurement location on the measurement object W may not all fit within the field of view of the camera 14, which may result in multiple measurements being required and reduced measurement efficiency.

[0058] Therefore, as shown in FIG. 5, from the viewpoint of measurement efficiency, the field of view of the camera 14 includes the measurement point of the measurement object W and has a maximum field of view P max It is preferable that:

[0059] On the other hand, the maximum frame rate of Camera 14 is F C [fps] is the maximum number of frames (captured images) that the camera 14 can capture in one second. C and the field of view range P of the camera 14 are inversely proportional to each other as shown in the following formula (1).

[0060]

number

[0061] That is, if the viewing range P of the camera 14 is increased, the number of measurements can be reduced, improving the measurement efficiency. However, the maximum frame rate F of the camera 14 is also increased. C Therefore, as will be understood from equation (4) below, frame drops are more likely to occur due to the influence of vibrations, which may lead to a decrease in measurement accuracy. On the other hand, if the field of view P of the camera 14 is reduced, the maximum frame rate F of the camera 14 C Since the field of view P is larger, frame drops are less likely to occur compared to the former case, and measurement accuracy can be improved. However, reducing the field of view P increases the number of measurements, resulting in a decrease in measurement efficiency. Therefore, in order to achieve both measurement efficiency and measurement accuracy, it is important to appropriately set the field of view P of the camera 14. From the viewpoint of measurement efficiency, the field of view P of the camera 14 should be set to the minimum field of view P that includes at least the measurement target W. min The field of view P of the camera 14 is preferably set to the minimum field of view P min and maximum field of view P max It is set between

[0062] Next, the conditions under which frame drops occur in the camera 14 will be described. As already mentioned, while the optical head 12 is scanning in the scanning direction, the observation image is captured by the camera 14 based on the trigger signal output from the trigger signal output unit 104 at predetermined intervals (i.e., the position signal 38 output from the encoder 18 at predetermined intervals). At this time, the interval at which the observation image is captured by the camera 14 is called the sampling interval. Here, the scanning speed of the optical head 12 relative to the measurement object W is V. C [nm / s], and the sampling interval of the camera 14 is D C [nm], and the sampling frequency of the camera 14 is F S If the frequency is in [Hz], the following relationship holds:

[0063]

number

[0064] Sampling frequency F of camera 14 S is the number of observation images captured per second when the camera 14 captures observation images based on the trigger signal output from the trigger signal output unit 104.

[0065] Therefore, the maximum frame rate of camera 14 is F C and sampling frequency F S and satisfy the following formula (3) (maximum frame rate F C Sampling frequency F S is large), the maximum frame rate F C If you issue a command to take a photograph at a speed exceeding V, the excess will be ignored, resulting in a so-called frame drop. This can lead to a decrease in measurement accuracy. C As shown in equation (2), when the sampling frequency F S This increases the chance of frame drops.

[0066]

number

[0067] Therefore, in order not to satisfy equation (3) (i.e., sampling frequency F S is the maximum frame rate F C ), the sampling frequency F of the camera 14 S It is necessary to set the following.

[0068] However, vibrations may occur depending on the environment in which the surface profile measuring apparatus 10 is installed, and these vibrations may affect the measurements performed by the surface profile measuring apparatus 10. For example, sources of vibration include a fan attached to the surface profile measuring apparatus 10, vibrations from the floor, and motors in the workpiece transport system. For example, when vibrations occur during scanning, the vibrations of the measurement object W can cause a shift in the relative position between the measurement object W and the optical head 12, which can result in measurement errors. Furthermore, frame drops in the camera 14 caused by vibrations of the optical head unit can also result in measurement errors. Thus, vibrations can increase the scanning speed of the optical head 12, and frame drops are more likely to occur if the scanning speed of the optical head 12 is too fast. Here, the vibration frequency caused by vibrations occurring during measurements performed by the surface profile measuring apparatus 10 is defined as F. m [Hz], the maximum frame rate of camera 14 is F C and sampling frequency F S and vibration frequency F m If the relationship between the vibration frequency F and the vibration frequency F satisfies the following formula (4), a frame drop occurs. m is based on the amplitude intensity at the same level as the sampling interval of the camera 14.

[0069]

number

[0070] Therefore, in order to prevent a decrease in measurement accuracy due to frame drops even when the above-described vibration occurs during measurement by the surface profile measuring apparatus 10, the vibration frequency F m Considering the sampling frequency F of the camera 14 S You need to set

[0071] From equations (2) and (4), the scanning speed V C is large, the sampling interval D C is small (both are based on the camera sampling frequency F S becomes larger), vibration frequency F mLarge, field of view P is large (maximum frame rate F C In cases such as when the frame rate is low, frame drops are more likely to occur.

[0072] However, the vibration frequency F due to the vibrations occurring during the measurement m Since it is difficult to directly measure the vibration, the influence of the vibration cannot be sufficiently suppressed, and there is a limit to how much the measurement accuracy can be improved.

[0073] In order to solve the above problems, the inventors introduced the concept of frame drop occurrence rate, and by setting the measurement conditions of the surface profile measuring device 10 based on the frame drop occurrence rate, they arrived at the present invention, which makes it possible to suppress the effects of the vibrations and improve measurement efficiency.

[0074] The frame drop occurrence rate will be explained below. This frame drop occurrence rate is calculated from the number of frames planned for measurement and the number of frames actually measured.

[0075] The number of frames to be measured is the number of frames (number of observed images) that should be acquired by the camera 14 if no frame drops occur when the camera 14 performs a photographing operation based on the trigger signal output at predetermined intervals from the trigger signal output unit 104. Let M be the number of frames to be measured, and let F be the sampling frequency of the camera 14. S [fps], sampling interval D C [nm], the scanning range of the optical head 12 is D R [nm], and the scanning speed is V C [nm / s] and the scanning time is t [s], the number of frames to be measured M can be calculated by the following formula (5).

[0076]

number

[0077] The number of measured frames is the number of frames (observed images) actually captured by the camera 14 during measurement. If the number of measured frames is N and the frame drop occurrence rate is FDR, the frame drop occurrence rate FDR can be calculated using the following equation (6).

[0078]

number

[0079] In equation (6), the frame drop rate FDR is calculated by dividing the number of measured frames N by the number of frames planned to be measured M to find the ratio of captured observation images, and then subtracting this ratio from 1. If FDR > 0, it means that frame drops are occurring, and the larger the number, the more frame drops are occurring. Vibrations occurring in the optical head unit can be indirectly detected by calculating the frame drop rate FDR.

[0080] To make it easier to detect vibrations of the measurement object W, it is preferable to design the mass of the white light interferometer (optical head unit) to be smaller than the mass of the base on which the optical head unit is attached. This allows the natural frequency of the white light interferometer to be larger than the natural frequency of the base.

[0081] In this embodiment, as described below, the measurement conditions of the surface profile measuring apparatus 10 are set based on the frame drop rate FDR, which makes it possible to suppress the effects of vibrations that occur during measurement and improve measurement accuracy.

[0082] On the other hand, as shown in Fig. 3, when measuring a plurality of measurement targets W, the optical head 12 and the stage 22 are moved and positioned relative to each other. Therefore, as shown in 3A and 3B, the relative positional relationship between the optical head 12 and the stage 22 varies depending on the position of the measurement targets W. When viewed as a single system including the optical head 12 and the stage 22, the center of gravity of the system differs between 3A and 3B. Due to the difference in the center of gravity position, the susceptibility to vibration varies for each position of the stage 22 (each position of the measurement targets W).

[0083] When setting the measurement conditions, the surface profile measuring apparatus 10 can more reliably suppress a decrease in measurement accuracy by setting the measurement conditions based on the frame drop rate FDR and setting the measurement conditions for each position of the stage 22.

[0084] <Pre-adjustment mode> Next, an example of setting measurement conditions in the pre-adjustment mode using the frame drop rate will be described. In the pre-adjustment mode, a frame drop rate threshold Th is set for the frame drop rate FDR, and the frame drop rate FDR is compared with the frame drop rate threshold Th to determine whether or not the measurement conditions need to be changed. If it is determined that the measurement conditions do not need to be changed, the measurement conditions used when the frame drop rate FDR was calculated are set as the measurement conditions used in the measurement mode.

[0085] On the other hand, if it is determined that a change in the measurement conditions is necessary, the measurement conditions used to calculate the frame drop occurrence rate FDR are changed, and the frame drop occurrence rate FDR is calculated.If it is determined that a change in the measurement conditions is not necessary, the frame drop occurrence rate FDR is calculated while repeatedly changing the measurement conditions.Finally, the measurement conditions used to calculate the frame drop occurrence rate FDR when it is determined that a change in the measurement conditions is not necessary are set as the measurement conditions used in the measurement mode.

[0086] Once the measurement conditions for a certain stage position are set, the stage 22 moves to another position, and the measurement conditions are set for that position. Finally, the measurement conditions to be used in the measurement mode are set for all positions of the stage 22.

[0087] As explained in equation (4), the scanning speed V C When the field of view P is large or the field of view range P is large, frame drops are likely to occur. Therefore, in the pre-adjustment mode, the field of view P and the scanning speed V are set for each position of the stage 22. C Both of these are set as measurement conditions.

[0088] In order to set the measurement conditions, a pallet 25 on which the object W to be measured is placed is set up as a preliminary preparation. As mentioned above, the position of the center of gravity changes depending on the position of the stage 22, and the susceptibility to vibration varies. The surface profile measuring device 10 performs measurements while changing the position of the stage 22 multiple times in the X or Y direction, and calculates the frame drop rate at each position of the stage 22.

[0089] For example, taking the X-axis as an example, assume that the stage 22 can move from 0 to X1. Dividing 0 to X1 into four positions, 0, X1 / 4, 2X1 / 4, 3X1 / 4, and X1 are determined as five positions for setting measurement conditions. At each of the determined positions, the field of view P and the scanning speed V are measured, and a measurement condition map is created and stored, as shown in Table 1 below. The indexes for the field of view P0, P1, P2, P3, and P4 and the scanning speeds V0, V1, V2, V3, and V4 indicate the field of view and scanning speed at each position. The field of view P0, P1, P2, P3, and P4 may be the same field of view or different field of view. Similarly, the scanning speeds V0, V1, V2, V3, and V4 may be the same or different. [Table 1]

[0090] In the measurement mode, the surface profile measuring apparatus 10 measures the surface profile of the measurement object W according to the measurement conditions (map shown in Table 1) set for each position on the stage 22. When measuring a measurement object W that is not on the map and is positioned on the stage 22, the measurement conditions may be estimated by linear interpolation or the like and then measured.

[0091] 6 and 7 are flowcharts showing the setting of measurement conditions in the pre-adjustment mode. In the pre-adjustment mode, the surface profile measuring apparatus 10 executes a process for setting the measurement conditions to be used in the measurement mode.

[0092] In the flowcharts of FIGS. 6 and 7, the location of the stage 22 where the measurement conditions should be set is designated as position X m and the visual field range is P i and the scanning speed is V k The parameter m is an index for identifying each position m, the parameter i is an index for identifying each field of view range P, and the parameter k is an index for identifying each scanning speed V.

[0093] The operator places a plurality of measurement targets W to be used in the pre-adjustment mode on the stage 22 and selects the pre-adjustment mode from the operation unit 21. The operator's selection result is input to the control unit 116, which controls the entire process of the pre-adjustment mode.

[0094] position m Next, the stage is moved to the position X m (Step S2). Next, the surface profile measuring device 10 moves to position X m Then, the measurement condition setting process is executed for the object (step S3).

[0095] FIG. 7 is a flowchart (subroutine) showing an example of the measurement condition setting process of step S3.

[0096] The operator determines the minimum field of view P based on the measurement target W. min(see FIG. 5), and a frame drop occurrence rate threshold Th1 is set (step S11). Step S11 may be performed in step S1 of FIG. 6. Once set in the preliminary measurement mode, the minimum field of view range P min , and the frame drop occurrence rate threshold Th1 do not need to be changed. min means a field of view P of the camera 14 having an area large enough to include the minimum measurement location of the measurement object W. min Since includes the measurement location of the measurement object W, it is possible to avoid a situation where the measurement object W is measured multiple times. The frame drop occurrence rate threshold Th1 is compared with the frame drop occurrence rate FDR in a step described later, and it is determined whether or not to change the measurement conditions. min The frame drop occurrence rate threshold Th1 can be set manually or automatically. min The information on the frame drop occurrence rate threshold Th1 is input to the measurement condition setting unit 108 of the control device 20. min The information about the frame drop occurrence rate threshold Th1 may be stored in the storage unit 100.

[0097] Next, the measurement condition setting unit 108 sets the visual field range P i Set the parameter i, which indicates the index, to i=1, and the scanning speed V k The parameter k indicating the index of the camera 14 is set to k=1 (step S12). Furthermore, the measurement condition setting unit 108 sets the viewing range P1 to the maximum viewing range P of the camera 14 as an initial value. max Set the scanning speed V1 to the maximum scanning speed V max In the flow of Fig. 7, the field of view range P1 and the scanning speed V1 are set as initial values ​​under conditions that prioritize measurement efficiency.

[0098] Next, the measurement control unit 102 sets the visual field range P i , and the scanning speed V kBased on this, the light source unit control unit 120, the photography command unit 122, and the drive unit control unit 124 control the optical head unit. The camera 14 acquires the observed image 36 of the measurement object W, and the control device 20 acquires the position signal 38 from the encoder 18, and the measurement ends (step S13). While the observed image 36 and the position signal 38 are being acquired, the trigger signal number counting unit 112 counts the number of triggers output by the trigger signal output unit 104. The number of triggers counted by the trigger signal number counting unit 112 is a value equivalent to the number of frames M to be measured described above. Note that the sampling interval D C [nm] and scanning range D R When [nm] is acquired or set, the number of frames to be measured may be calculated based on equation (5) in, for example, the frame drop occurrence rate calculation unit 110. In this case, the trigger signal number counting unit 112 is unnecessary. Also, the camera frame number counting unit 114 counts the number of observed images 36 actually acquired by the camera 14 as the number of measured frames N.

[0099] Next, the frame drop occurrence rate calculation unit 110 calculates the frame drop occurrence rate FDR based on the "measurement planned frame M" acquired by the trigger signal number counting unit 112 and the "measured frame number N" acquired by the camera frame number counting unit 114 (step S14).

[0100] Next, the measurement condition setting unit 108 determines whether the frame drop occurrence rate FDR is equal to or less than a frame drop occurrence rate threshold Th1 (FDR≦Th1) (step S15). If the result in step S15 is "Yes," the measurement condition setting unit 108 determines that a change in the measurement conditions is not necessary, and sets the latest (when FDR≦Th1 is satisfied) field of view range P i and scanning speed V k and save the saved field of view range P i and scanning speed V k are set as measurement conditions to be applied in the measurement mode (step S16), and the surface profile measuring apparatus 10 then ends the pre-adjustment mode.

[0101] If the answer is "No" in step S15 (FDR>Th1), the measurement condition setting unit 108 determines that the measurement conditions need to be changed, and changes the measurement conditions (step S17). That is, the measurement condition setting unit 108 indirectly determines that vibrations affect the measurement accuracy of the surface profile measuring apparatus 10 under the set measurement conditions.

[0102] In the flow of FIG. 7, when it is determined that the measurement conditions need to be changed, the measurement condition setting unit 108 changes the field of view range P so that the frame drop occurrence rate FDR becomes smaller than the frame drop occurrence rate threshold Th1. i or scanning speed V k Change the

[0103] In the flow of Figure 7, the visual field range P i and scanning speed V k Both measurement conditions can be set, but the scanning speed V k Camera 14's field of view is i In order to make the frame drop rate FDR smaller than the frame drop rate threshold Th1, the field of view range P i or by reducing the scanning speed V k In the scanning type surface shape measuring device 10, the scanning speed V k Since a decrease (change) in the field of view P i Change it as a priority.

[0104] In step S17, the measurement condition setting unit 108 determines the visual field range P i+1 Calculate the field of view P i In step S17, the measurement condition setting unit 108 changes the visual field range P i Change only.

[0105]

number

[0106] In equation (7), the field of view P iThe rate at which the visual field range P is reduced varies depending on the value of the frame drop occurrence rate FDR calculated in step S14. i By changing the rate at which the field of view P i Compared to multiplying by 0.95, there is no need to repeat the same reduction routine multiple times. This makes it possible to set measurement conditions more efficiently. Although the value "0.95" is used in equation (7), other values ​​may be used. Also, as shown in the following equation (8), the visual field range P i The rate at which the frame rate is reduced may not be changed depending on the value of the frame drop rate FDR.

[0107]

number

[0108] Next, the measurement condition setting unit 108 sets the visual field range P i+1 is the minimum field of view P min That's all (P i+1 ≧P min ) (step S18). If the answer is "Yes" in step S18, the measurement condition setting unit 108 increments the parameter i by 1 (step S19). Next, the processing flow proceeds to step S13.

[0109] In step S13, the measurement control unit 102 sets the visual field range P i , and the maintained scanning speed V k Based on this, the optical head unit is controlled to measure the object W to be measured.

[0110] Field of view P i+1 ≧Minimum field of view P minis satisfied, the processing flow repeats steps S13, S14, S15, S17, and S19 until the frame drop occurrence rate FDR≦frame drop occurrence rate threshold Th1 is satisfied. In step S15, if the frame drop occurrence rate FDR≦frame drop occurrence rate threshold Th1 is satisfied (Yes), the processing flow proceeds to step S16. The measurement condition setting unit 108 sets the latest field of view range P i and the latest scanning speed V k and save the saved field of view range P i and scanning speed V k is set as the measurement condition to be applied in the measurement mode.

[0111] Next, if the answer is "No" in step S18, the measurement condition setting unit 108 sets the visual field range P i In the case of the change of the field of view P i Change the scanning speed V k (Step S20).

[0112] In step S20, the measurement condition setting unit 108 determines the scanning speed V k+1 Calculate the scanning speed V k In step S20, the measurement condition setting unit 108 changes the scanning speed V k Change only.

[0113]

number

[0114] In equation (9), similarly to step S17, the scanning speed V k The rate at which the scanning speed V is reduced varies depending on the value of the frame drop rate FDR calculated in step S14. This allows for more efficient setting of measurement conditions. k The rate at which the frame rate is reduced may not be changed depending on the value of the frame drop rate FDR.

[0115] Next, the measurement control unit 102 determines the field of view range P i+1 , and the scanning speed V changed in step S20 k+1 Based on this, the optical head unit is controlled to measure the measurement object W (step S21).

[0116] Next, the frame drop occurrence rate calculation unit 110 calculates the frame drop occurrence rate FDR based on the "measurement planned frame M" acquired by the trigger signal number counting unit 112 and the "measured frame number N" acquired by the camera frame number counting unit 114 (step S22).

[0117] Next, the measurement condition setting unit 108 determines whether the frame drop occurrence rate FDR is equal to or less than the frame drop occurrence rate threshold value Th1 (FDR≦Th1) (step S23).

[0118] If the answer is "No" in step S23 (FDR>Th1), it is determined that a change in the measurement conditions is necessary, and the parameter k is incremented by 1 (step S24). Next, the processing flow proceeds to step S10. The processing flow repeats steps S20, S21, S22, S23, and S24 until the frame drop occurrence rate FDR≦frame drop occurrence rate threshold Th1 is satisfied.

[0119] In step S23, if the frame drop occurrence rate FDR≦frame drop occurrence rate threshold Th1 is satisfied (Yes), the processing flow proceeds to step S16, and the latest field of view range P i and the latest scanning speed V k and save the saved field of view range P i and scanning speed V k is set as the measurement condition to be applied in the measurement mode.

[0120] 6, when the pre-adjustment mode in step S3 is completed, the process flow proceeds to step S4. In step S4, the latest field of view range and scanning speed set in the pre-adjustment mode are updated to the field of view range P mand scanning speed V m As the position X m and remember it in association with

[0121] The control unit 116 increments the parameter m by 1 (step S5). Next, the control unit 116 determines whether or not measurement of all positions has been completed (step S6). If the answer is "No" in step S6, the processing flow proceeds to step S2. The processing flow repeats steps S2, S3, S4, and S5 until measurement of all positions has been completed.

[0122] If the answer is "Yes" in step S6, the pre-adjustment mode is terminated. When the pre-adjustment mode is terminated, the surface profile measuring apparatus 10 creates a map associating the position X, the field of view P, and the scanning speed V as shown in Table 1, and stores the map in the memory unit 100.

[0123] As described above, the surface profile measuring apparatus 10 has a maximum field of view P max is set as the initial field of view range P1, and the maximum scanning speed V max The surface profile measuring apparatus 10 sets the initial scanning speed V1 to V2 and starts the pre-adjustment mode. m The field of view used in the measurement mode for each P m and scanning speed V m Therefore, it is possible to suppress a decrease in measurement accuracy in the measurement mode.

[0124] <Measurement mode> Next, the measurement mode will be described with reference to Fig. 8. In the measurement mode, the surface profile measuring apparatus 10 performs measurements based on the measurement conditions stored for each position of the stage 22, and determines whether or not the measurement conditions need to be changed based on the frame drop rate FDR. If it is determined that the measurement conditions need to be changed, the measurement object (workpiece) W is measured again (retried) while changing the measurement conditions.

[0125] The operator places multiple workpieces W to be used in the measurement mode at predetermined positions X on the stage 22 and selects the measurement mode from the operation unit 21. The operator's selection result is input to the control unit 116, which controls the entire processing in the measurement mode.

[0126] By the operation of the operator, the measurement condition setting unit 108 sets the scanning speed V k Set the parameter k to 1, which indicates the index of the m A parameter m indicating the index is set to m=1, and a frame drop occurrence rate threshold Th2 in the measurement mode is set (step S31). The frame drop occurrence rate threshold Th2 in the measurement mode may be the same as or different from the frame drop occurrence rate threshold Th1 in the pre-adjustment mode. If the frame drop occurrence rate threshold Th2 is smaller than the frame drop occurrence rate threshold Th1, the surface profile measuring apparatus 10 can reduce the risk of retry.

[0127] Next, the stage driving unit control unit 126 controls the stage driving unit 24 to move the stage 22 to the position X m Located at Work W m to a position facing the optical head 12 (step S32).

[0128] Next, the measurement control unit 102 determines the position X m Measurement conditions corresponding to the field of view P m , scanning speed V k,m ) is read out, for example, from a map stored in the storage unit 100 (step S33). m is position X m is the field of view at k,m Position X in m is the scanning speed at V m This serves as a counter when repeatedly changing the value.

[0129] Next, the measurement control unit 102 sets the read measurement conditions (field of view P m , scanning speed V k,m), the light source control unit 120, the photography command unit 122, and the drive control unit 124 control the optical head unit. m The control device 20 acquires the observed image 36, and the control device 20 acquires the position signal 38 from the encoder 18, ending the measurement (step S34). While the observed image 36 and the position signal 38 are being acquired, the trigger signal number counting unit 112 counts the number of triggers output by the trigger signal output unit 104. Furthermore, the camera frame number counting unit 114 counts the number of frames N measured.

[0130] Next, the frame drop occurrence rate calculation unit 110 calculates the frame drop occurrence rate FDR based on the "measurement planned frame M" acquired by the trigger signal number counting unit 112 and the "measured frame number N" acquired by the camera frame number counting unit 114 (step S35).

[0131] Next, the measurement condition setting unit 108 determines whether the frame drop occurrence rate FDR is equal to or less than a frame drop occurrence rate threshold value Th2 (FDR≦Th2) (step S36).

[0132] If the answer is "No" in step S36 (FDR>Th2), the measurement condition setting unit 108 determines that the measurement conditions for re-measurement need to be changed, and changes the measurement conditions (step S37). That is, the measurement condition setting unit 108 indirectly determines that vibrations affect the measurement accuracy of the surface profile measuring apparatus 10 under the set measurement conditions.

[0133] If it is determined that the measurement conditions need to be changed, the measurement condition setting unit 108 adjusts the scanning speed V of the optical head 12 so that the frame drop occurrence rate FDR becomes smaller than the frame drop occurrence rate threshold Th2. k、m Slow down.

[0134] In step S37, the measurement condition setting unit 108 determines the scanning speed V k+1 Calculate the scanning speed V k Change the

[0135] Next, the measurement condition setting unit 108 increments the parameter k by 1 (step S38). Next, the process flow proceeds to step S34, where the work W m Remeasure.

[0136] Thereafter, the measurement control unit 102 repeats steps S34, S35, S36, S37, and S38 in the processing flow until the frame drop occurrence rate FDR≦frame drop occurrence rate threshold Th2 is satisfied.

[0137] Next, if the answer is "Yes" in step S36, the control unit 116 m It is determined whether the measurement has been completed (step S39).

[0138] If the answer is "No" in step S39, the control unit 116 increments the parameter m by 1, and the measurement condition setting unit 108 sets the parameter k to k=1 (step S40). Next, the processing flow proceeds to step S34.

[0139] All Work W m The process flow repeats steps S32, S33, S34, S35, S36, S37, S38, S39 and S40 until the measurement is completed.

[0140] Next, if the answer is "Yes" in step S39, the surface shape measuring device 10 measures the workpiece W. m End the measurement.

[0141] Since the surface profile measuring apparatus 10 sets the measurement conditions for each stage position in the pre-adjustment mode, in the measurement mode, even if the relative positional relationship between the optical head 12 and the stage 22 changes, the surface profile measuring apparatus 10 is less susceptible to the influence of vibrations, and can suppress a decrease in measurement accuracy. Furthermore, when the frame drop occurrence rate FDR>frame drop occurrence rate threshold Th2, the surface profile measuring apparatus 10 determines that vibrations are affecting the measurement accuracy, and mScanning speed V for each initial measurement condition k By changing the measurement conditions and re-measuring, the influence of vibration can be eliminated and a decrease in measurement accuracy can be prevented.

[0142] In the measurement mode, an example has been shown in which the surface profile measuring apparatus 10 changes the scanning speed V, but the field of view P may be changed instead of the scanning speed V. Furthermore, the surface profile measuring apparatus 10 may change the field of view P and the scanning speed V.

[0143] In addition, although the optical head 12 is a Michelson-type white light interference microscope in the above description, it may be a Mirau-type white light interference microscope or a Linnick-type white light interference microscope. The optical head 12 may also be a focus variation type microscope. [Explanation of symbols]

[0144] 10...surface shape measuring device, 12...optical head, 14...camera, 16...drive unit, 18...encoder, 20...control device, 21...operation unit, 22...stage, 23...display unit, 24...stage drive unit, 25...pallet, 26...light source unit, 28...beam splitter, 30...interference objective lens, 30A...objective lens, 30B...beam splitter, 30C...reference surface, 32...imaging lens, 36...observed image, 38...position signal, 100...memory unit, 102...measurement control unit, 104...trigger signal output unit, 106...three-dimensional shape calculation unit, 108...measurement condition setting unit, 110...frame drop occurrence rate calculation unit, 112...trigger signal number count unit, 114...camera frame number count unit, 116...control unit, 120...light source unit control unit, 122...imaging command unit, 124...drive unit control unit, 126...stage drive unit control unit, L1...measurement light, L2...reference light, L3...combined light, W...measurement object

Claims

1. A surface shape measuring device for measuring the surface shape of a measurement object, an optical head that is scanned relatively to the measurement object; an imaging means for capturing an observation image acquired by the optical head; a stage that supports the measurement object and moves in a direction perpendicular to the scanning direction of the optical head; a calculation means for calculating an index related to a frame drop in the imaging means for each position of the stage; a setting means for setting measurement conditions for each position of the stage based on the index; A surface shape measuring apparatus comprising:

2. the setting means sets a field of view range of the imaging means as the measurement condition. The surface shape measuring apparatus according to claim 1 .

3. the setting means sets a scanning speed of the optical head relative to the measurement object as the measurement condition. The surface shape measuring apparatus according to claim 1 or 2.

4. the indicator is a frame drop occurrence rate indicating an occurrence rate of the frame drop; The surface shape measuring apparatus according to claim 1 .

5. the setting means determines whether or not the measurement conditions need to be changed based on a result of comparing the frame drop occurrence rate with a frame drop occurrence rate threshold. The surface shape measuring apparatus according to claim 4 .

6. When it is determined that the measurement conditions need to be changed, the setting means changes the measurement conditions so that the frame drop occurrence rate becomes smaller than the frame drop occurrence rate threshold. The surface shape measuring apparatus according to claim 5 .

7. the setting means is capable of setting both a field of view of the imaging means and a scanning speed of the optical head relative to the measurement object as the measurement conditions, and when it is determined that a change in the measurement conditions is necessary, the setting means changes the field of view of the imaging means with priority over the scanning speed of the optical head so that the frame drop occurrence rate becomes equal to or less than the frame drop occurrence rate threshold. The surface shape measuring apparatus according to claim 6 .

8. When the frame drop occurrence rate is represented by FDR, the number of frames of the observation image actually captured by the imaging means is represented by N, and the planned number of frames of the observation image that should originally be captured by the imaging means is represented by M, the calculation means calculates the frame drop occurrence rate using the following formula: The surface shape measuring apparatus according to any one of claims 4 to 7. FDR = 1 - N / M

9. The optical head is a white light interference microscope. The surface shape measuring apparatus according to claim 1 .

10. A surface shape measuring method for measuring a surface shape of a measurement object based on a result of imaging an observation image acquired by an optical head while scanning the measurement object relatively with the optical head, the method comprising: a stage supporting the measurement object is moved in a direction perpendicular to the scanning direction of the optical head, and at each position of the stage, an index related to a frame drop in the imaging means is calculated for each position of the stage; setting measurement conditions for each position of the stage based on the index; Surface shape measurement method.

Images