WHITE LIGHT INTERFEROMETER AND METHOD FOR SETTING UP AN INTERFERENCE OPTICS SYSTEM

Abstract

A white light interferometer (1) comprises: an interference optics system (42); an image acquisition unit (52) that acquires an image of a measurement object (W) via the interference optics system (42); a movement mechanism (6) that moves the interference optics system (42) relative to the measurement object (W) in a vertical direction; an adjustment mechanism (43) that sets an optical path length of a reference light in the interference optics system (42);a position detector (723) that detects both a first position (Pa) and a second position (Pb) based on images acquired by the image acquisition unit (52) and which have different height positions of the interference optics system (42) relative to the object being measured (W), wherein the first position (Pa) is a height position of the interference optics system (42) in which a luminance value (Lt) of a target pixel reaches a peak value, and the second position (Pb) is a height position of the interference optics system (42) in which a contrast value (C) reaches a peak value; and a setting amount calculator (724) that calculates a setting amount of the setting mechanism (43) based on a deviation amount (ΔP) between the first position (Pa) and the second position (Pb).

Description

TECHNICAL AREA

[0001] The present invention relates to a white light interferometer and a method for adjusting an interference optics system. STATE OF THE ART

[0002] A white-light interferometer using low-coherence white light is known (see, for example, Publication 1: JP 2018-096869 A). The white-light interferometer comprises an interference optics system that interferes with measurement light reflected from a measurement surface and reference light reflected from a reference surface, and an image acquisition unit that captures an image of the measurement surface via the interference optics system. A surface profile of the measurement surface can be measured by moving the interference optics system along a vertical direction of the measurement surface during scanning and analyzing the interference fringes appearing in the resulting image.

[0003] A typical white-light interferometer is designed so that the difference in optical path length between the measurement light and the reference light is close to zero, allowing interference fringes to be observed with high accuracy when the interference optics system is focused on the measurement surface. However, the optical path length of the reference light can deviate due to aging or temperature changes. For this reason, it is necessary to adjust the optical path length of the reference light within the interference optics system during the manufacture or calibration of the white-light interferometer.

[0004] However, a well-known adjustment method involves precisely tilting and positioning a flat measuring surface of a reference object so that interference fringes appear in an image, and then manually fine-tuning the interference optics system while visually inspecting the interference fringes in the image. This requires considerable time and effort for the adjustment work. Furthermore, it demands a high level of dexterity from the operator performing the adjustment. SUMMARY OF THE INVENTION

[0005] One object of the invention is to provide a white light interferometer with an easily adjustable interference optics system and a method for adjusting the interference optics system.

[0006] A white-light interferometer according to one aspect of the invention comprises: an interference optics system configured to separate light from a light source into a reference light and a measurement light, and to interfere with a return light of the measurement light from a measurement object and a return light of the reference light from a reference surface; an image acquisition unit configured to acquire an image of the measurement object via the interference optics system; a movement mechanism configured to move the interference optics system relative to the measurement object in a vertical direction; and an adjustment mechanism configured to adjust an optical path length of the reference light in the interference optics system.a position detector configured to detect both a first position and a second position based on a multitude of images captured by the image acquisition unit, each exhibiting different height positions of the interference optics system relative to the object being measured, wherein the first position is a height position of the interference optics system at which a luminance value of a target pixel reaches a peak, and the second position is a height position of the interference optics system at which a contrast value reaches a peak; and an adjustment amount calculator configured to calculate an adjustment amount of the adjustment mechanism based on a deviation amount between the first position and the second position.

[0007] A method for adjusting an interference optics system in a white light interferometer according to a further aspect of the invention, wherein the interference optics system is configured to separate light from a light source into a reference light and a measurement light and to allow a return light of the measurement light from a measurement object and a return light of the reference light from a reference surface to interfere with each other, wherein the method comprises: changing a height position of the interference optics system relative to the measurement object and acquiring a plurality of images of the measurement object via the interference optics system;Capturing both a first position and a second position based on the multitude of images exhibiting different height positions of the interference optics system relative to the object being measured, wherein the first position is a height position of the interference optics system in which a luminance value of a target pixel reaches a peak value, and the second position is a height position of the interference optics system in which a contrast value reaches a peak value; and calculating, based on a deviation amount between the first position and the second position, an adjustment amount of the adjustment mechanism configured to set an optical path length of the reference light. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 schematically shows a white light interferometer according to an embodiment of the invention. Fig. Figure 2 schematically shows an interference optics system of the exemplary embodiment. Fig. Figure 3 shows an external side view of an interference objective lens unit of the exemplary embodiment. Fig. Figure 4 shows a block diagram of a control system of the exemplary embodiment. Fig. Figure 5 shows a flowchart to explain a procedure for adjusting the interference optics system of the exemplary embodiment. Fig. Figure 6 shows a diagram that schematically illustrates a change in the luminance value of a target pixel with respect to a change in the Z-position of an optical head of the embodiment. Fig. Figure 7 shows a diagram that schematically illustrates a change in the contrast value of an image with respect to a change in the Z-position of the optical head of the embodiment. Fig. Figure 8 shows a diagram illustrating exemplary changes in luminance and contrast values ​​before adjustment. Fig. Figure 9 shows a diagram illustrating exemplary changes in luminance and contrast values ​​after adjustment. DETAILED DESCRIPTION

[0008] A description of an embodiment of the invention is given with reference to the drawings.

[0009] Fig. Figure 1 shows an overall structure of a white light interferometer 1 of the exemplary embodiment. The white light interferometer 1 of the exemplary embodiment comprises an optical head 2, an image acquisition unit 5, a movement mechanism 6, a control unit 7 and a stage 8.

[0010] The optical head 2 comprises a head body 3 and an interference objective lens unit 4. The optical head 2 is movable in a Z-direction by the movement mechanism 6 described later. In the exemplary embodiment, the Z-direction is defined as the vertical direction of a measurement object W placed on the stage 8. A direction to one side in the Z-direction is designated as the +Z-direction, and a direction to the opposite side is defined as the -Z-direction.

[0011] The head body 3 comprises a light source 31, a collimator lens 32, a beam splitter 33 and a housing 34.

[0012] Light source 31 is a white light source that emits broadband light with low coherence. Examples of light source 31 are halogen lamps and light-emitting diodes (LEDs).

[0013] The collimator lens 32 converts the light incident from the light source 31 into parallel light.

[0014] The beam splitter 33 reflects the parallel light incident from the collimator lens 32, and the reflected light exits the beam splitter 33 towards the interference objective lens unit 4. Furthermore, the beam splitter 33 allows the light incident from the interference objective lens unit 4 to pass through, and the transmitted light exits the beam splitter 33 towards the image acquisition unit 5.

[0015] The housing 34 contains the light source 31, the collimator lens 32 and the beam splitter 33. The housing 34 is supported by the movement mechanism 6.

[0016] The interference objective lens unit 4 comprises an interference optics system 42 and an adjustment mechanism 43 that adjusts the position of an optical element in the interference optics system 42.

[0017] The interference optics system 42 of the exemplary embodiment has a so-called Mirau arrangement. In particular, the interference optics system 42 comprises an objective lens 421, a reference section 422 and a separating / combining section 423, which are arranged on the same optical axis L.

[0018] The objective lens 421 comprises at least one lens. The objective lens 421 focuses the light incident from the beam splitter 33 onto the measuring object W on the stage 8.

[0019] The reference section 422 is arranged between the objective lens 421 and the separating / combining section 423. The reference section 422 includes, for example, a mirror. The reference section 422 has a reference surface 422S that faces the object W being measured (i.e., points in the -Z direction). The reference section 422 is attached to a central portion of a transparent glass plate 424. The reference section 422 is supported over the glass plate 424 by the adjustment mechanism 43.

[0020] The splitting / combining section 423 includes, for example, a beam splitter. The splitting / combining section 423 separates the light incident from the objective lens 421 into a reference light Lr, which is reflected by the splitting / combining section 423, and a measurement light Lm, which passes through the splitting / combining section 423. The reference light Lr is reflected by the reference surface 422S and then reflected again by the splitting / combining section 423. The measurement light Lm is reflected by a surface of the object being measured W (i.e., a measurement surface WS) and then passes through the splitting / combining section 423 as return light. The splitting / combining section 423 thus combines the return light of the reference light Lr from the reference surface 422S and the return light of the measurement light Lm from the measurement surface WS.

[0021] Here, as in Fig. Figure 2 shows a distance in the Z-direction from a reflective surface of the separating / combining section 423 to the reference surface 422S, defined as the reference distance D1, and a distance from the reflective surface of the separating / combining section 423 to the measuring surface WS is defined as the measuring distance D2. A focal length f of the objective lens 421 is greater than the sum of the reference distance D1 and the measuring distance D2.

[0022] An optical path of the reference light Lr in the interference optics system 42 is a path that the reference light Lr travels from the separating / combining section 423 and returns to the separating / combining section 423 via the reference surface 422S. An optical path of the measuring light Lm in the interference optics system 42 is a path that the measuring light Lm travels from the separating / combining section 423 and returns to the separating / combining section 423 via the measuring surface WS. If the reference distance D1 and the measuring distance D2 are equal, the difference in optical path length between the reference light Lr and the measuring light Lm in the interference optics system 42 is zero, which leads to interference in the combined light from the reference light Lr and the measuring light Lm.

[0023] The adjusting mechanism 43 comprises a cylindrical main body 431, which is attached to the housing 34, an annular actuating section 432, which is rotatably mounted on the main body 431, and a slide 433, which is supported by the main body 431 to be movable in the Z-direction, as shown in Fig. 1 shown.

[0024] In the exemplary embodiment, the slide 433 is screwed to an inner circumference of the actuating section 432. A rotation of the actuating section 432 relative to the main body 431 is converted into a movement of the slide 433 in the Z-direction relative to the main body 431. That is, the slide 433 moves in the Z-direction with respect to the main body 431 according to a direction and amount of rotation of the actuating section 432.

[0025] Furthermore, in the exemplary embodiment, the main body 431 carries the reference section 422 over the glass plate 424, and the slider 433 carries the separating / combining section 423. When the slider 433 moves in the Z-direction relative to the main body 431, the separating / combining section 423 moves in the Z-direction relative to the reference section 422 by a distance (the reference distance D1 in Fig. 2) to be set between the reference section 422 and the separating / combining section 423.

[0026] As in Fig. As shown in Figure 3, the actuating section 432 displays a scale 434, and the main body 431 displays a mark 435 indicating a reference position. A graduation mark on the scale 434 indicates the actuation amount of the actuating section 432 and corresponds to a displacement of the separating / combining section 423 in the Z-direction.

[0027] For example, if a worker rotates the actuating section 432 clockwise by a desired number of divisions, the separating / combining section 423 moves in the -Z direction by a distance equal to the number of divisions, resulting in an increase in the reference distance D1. If a worker rotates the actuating section 432 counterclockwise by a desired number of divisions, the separating / combining section 423 moves in the +Z direction by a distance equal to the number of divisions, resulting in a decrease in the reference distance D1.

[0028] The image acquisition unit 5 comprises an imaging lens 51 and an image acquisition section 52, as shown in Fig. 1 shown.

[0029] The imaging lens 51 produces an image of the combined light emitted by the interference objective lens unit 4 and passing through the beam splitter 33 on the image acquisition section 52.

[0030] The image acquisition section 52 comprises, for example, a charge-coupled camera (CCD camera) or the like. The image acquisition section 52 captures an image of the combined light generated by the imaging lens 51, thus producing an image. The control unit 7 receives the image output by the image acquisition section 52 as an electrical signal.

[0031] The movement mechanism 6 comprises a motor, a linear guide, and the like. Based on a movement instruction from the controller 7, the movement mechanism 6 causes the optical head 2 to move in the Z-direction. That is, the movement mechanism 6 changes the position of the interference optics system 42 in the Z-direction relative to the object W on the stage 8.

[0032] The movement mechanism 6 also includes a position sensing sensor 61, which detects a position in the Z-direction (Z-position) of the interference optics system 42. The position sensing sensor 61 includes, for example, a length scale. The position sensing sensor 61 outputs the detected Z-position of the interference optics system 42 to the controller 7, if necessary. The Z-position of the position sensing sensor 61 corresponds to the Z-position of the interference optics system 42.

[0033] Control 7 comprises a basic computer configuration. For example, Control 7 includes, as in Fig. Figure 4 shows a memory 71 with a memory circuit such as main memory and a processor 72 with a computing circuit such as a central processing unit (CPU).

[0034] Memory 71 stores a variety of programs, including a setting program for adjusting the interference optics system 42 and a measurement program for measuring the object W, a variety of data used to execute the various programs, and the like.

[0035] Memory 71 also stores a table or an arithmetic expression that represents a correspondence between a deviation ΔP of an optical arrangement of the interference optics system 42 and a setting value of the adjustment mechanism 43 (i.e., the actuation value of the actuating section 432) to set the deviation ΔP to zero. The deviation ΔP of the optical arrangement of the interference optics system 42 can correspond to a deviation from an optimal value of the optical path length of the reference light Lr (i.e., a deviation of the reference distance D1). It is possible to determine the table or arithmetic expression that represents the correspondence between the deviation ΔP and the setting value of the adjustment mechanism 43 by means of a prior experiment or simulation.

[0036] The processor 72 reads and executes the programs stored in the memory 71 and functions as image acquisition control 721, drive control 722, position detector 723, setting amount calculator 724 and measuring section 725. The details of this will be described later.

[0037] The white light interferometer 1 further comprises a display unit 73 and an operator input unit 74, which are connected to the controller 7. The display unit 73 includes, for example, a display. The display unit 73 outputs a variety of information. The operator input unit 74 includes, for example, a keyboard or a touch panel. The operator input unit 74 receives operator input from a user. Setting up the interference optics system

[0038] The white light interferometer 1 of the exemplary embodiment is constructed such that the reference distance D1 is essentially equal to the measuring distance D2 when a focus position Pf of the objective lens 421 coincides with the measuring surface WS, i.e., when the image acquisition unit 5 is focused on the measuring surface WS, as in Fig. Figure 2 shows that the difference between the reference distance D1 and the measurement distance D2 can increase due to temperature changes or aging.

[0039] Therefore, in the embodiment, the interference optics system 42 is adjusted to reduce the difference between the reference distance D1 and the measurement distance D2.

[0040] The following describes a method for adjusting the interference optics system 42 of the exemplary embodiment with reference to a flowchart in Fig. 5 described.

[0041] First, a worker places a reference object, which is the measurement object W, on the stage 8 (step S1). Here, it is only necessary that the reference object has a flat measurement surface WS. The reference object can have any pattern. The measurement surface WS of the reference object only needs to be substantially perpendicular to the optical axis L and does not require a highly precise adjustment of the inclination of the measurement surface WS. It is therefore assumed that in the exemplary embodiment, no interference fringes will appear in any image acquired in step S2, which is described later.

[0042] Next, the motion mechanism 6, controlled by the drive controller 722, causes the optical head 2 to move along the Z-direction from a scanning start position. Then, the image acquisition unit 52, controlled by the image acquisition controller 721, captures an image of the measurement surface WS each time the optical head 2 moves a predetermined amount in the Z-direction (step S2). In step S2, a multitude of images are captured at different Z-positions of the optical head 2 relative to the measurement object W. The controller 7 instructs the memory 71 to store each of the images captured by the image acquisition unit 52 in conjunction with the Z-position of the optical head 2 as detected by the position sensor 61.

[0043] A scanning area in the Z-direction of the optical head 2 and the distance and number of image acquisition times within the scanning area in step S2 are not particularly limited, as long as it is possible to acquire at least a first position Pa and a second position Pb.

[0044] The position detector 723 calculates a luminance value Lt of the same target pixel in each image recorded in step S2 and detects as the first position Pa the Z-position of the optical head 2 at which the luminance value Lt reaches a peak value (in the embodiment, when the luminance value Lt has a maximum value) (step S3).

[0045] The target pixel is not particularly restricted, and any pixel selected from the image can be used. For example, a pixel in the middle of the image can be used as the target pixel.

[0046] Fig. Figure 6 shows a diagram schematically illustrating a change in the luminance value Lt of the target pixel with respect to a change in the Z-position of the optical head 2. In step S2 described above, the optical head 2 passes through a Z-position (hereinafter referred to as the interference position) where the reference distance D1 is equal to the measurement distance D2 (i.e., the difference in optical path length between the reference light Lr and the measurement light Lm is zero). As the optical head 2 passes near the interference position, light and dark alternate in the target pixel due to the interference between the reference light Lr and the measurement light Lm, so that the luminance value Lt of the target pixel near the interference position exhibits a variety of steep peaks (a positive peak and a negative peak). If the Z-position of the optical head 2 coincides with the interference position, the luminance value Lt of the target pixel reaches a positive maximum peak.

[0047] Therefore, in step S3 described above, the Z-position where the luminance value Lt of the target pixel reaches its maximum value is captured as the first position Pa that corresponds to the interference position.

[0048] Furthermore, the position detector 723 calculates a contrast value C of each image recorded in step S2 and records as the second position Pb the Z-position of the optical head 2 at which the contrast value C reaches a peak value (step S4).

[0049] The 723 position detector is capable of calculating the contrast value C based on the luminance value of each pixel in the image. A specific method for calculating the contrast value C is not particularly limited, and a known technique can be used. For example, assuming that the maximum luminance value of each pixel in the image is denoted by Lmax and the minimum value by Lmin, the contrast value C can be a Michelson contrast value defined by (Lmax - Lmin) / (Lmax + Lmin), or a contrast ratio defined by the ratio Lmax / Lmin.

[0050] Fig. Figure 7 shows a diagram schematically illustrating a change in the contrast value C of the image with respect to a change in the Z-position of the optical head 2. In step S2 described above, the optical head 2 passes through a Z-position (hereinafter referred to as the focus position) in which the focus position Pf of the objective lens 421 coincides with the measurement surface WS (i.e., the image acquisition unit 52 is focused on the measurement surface WS). The image becomes sharp while the optical head 2 is in the focus position, thus maximizing the contrast value C of the image. Therefore, as the optical head 2 passes through the focus position, the contrast value C has a single, gentle peak.

[0051] Accordingly, in step S4 described above, the Z-position, in which the contrast value C has its peak, is recorded as the second position Pb, which corresponds to the focus position.

[0052] The order of steps S3 and S4 described above is not particularly restricted. The luminance value Lt and the contrast value C can be calculated if necessary while step S2 described above is being performed.

[0053] The setting amount calculator 724 then calculates the deviation amount ΔP between the first position Pa recorded in step S3 and the second position Pb recorded in step S4 (step S5). For example, a value obtained by subtracting the first position Pa from the second position Pb is considered the deviation amount ΔP (see Fig. 7) calculated in the exemplary embodiment. The deviation amount ΔP is a value that is proportional to the difference between the reference distance D1 and the measuring distance D2.

[0054] Next, the setting amount calculator 724 determines whether an absolute value of the deviation amount ΔP calculated in step S5 is equal to or less than a threshold value Pth (step S6). The threshold value Pth is a value predetermined, taking into account an acceptable error.

[0055] If YES is selected in step S6, the setting amount calculator 724 determines that the reference distance D1 is almost equal to the measuring distance D2, and ends the flowchart in Fig. 5. At this point, the setting amount calculator 724 can cause the display unit 73 to display a message stating that no setting is required.

[0056] If NO is selected in step S6, the setting amount calculator 724 calculates the actuation amount of the actuation section 432 based on the deviation amount ΔP calculated in step S5 (step S7).

[0057] In particular, the setting amount calculator 724 uses the table or arithmetic expression that represents the correspondence relationship between the deviation amount ΔP and the actuation amount of the actuating section 432 to determine the actuation amount of the actuating section 432 that corresponds to the deviation amount ΔP.

[0058] Here, the actuation amount of the actuating section 432 refers to the direction and amount of rotation of the actuating section 432 to set the deviation amount ΔP to zero. The amount of rotation of the actuating section 432 is indicated by the number of graduations on the scale 434. The direction of rotation (clockwise or counterclockwise) of the actuating section 432 can be indicated by text or an arrow, or by a positive / negative indication on the graduations of the scale 434.

[0059] Next, the setting amount calculator 724 causes the display unit 73 to display the actuation amount of the actuating section 432 calculated in step S7 described above (step S8). The operator then actuates the actuating section 432 according to the actuation amount of the actuating section 432 displayed on the display unit 73 (step S9). This reduces the difference between the reference distance D1 and the measuring distance D2.

[0060] Then the flowchart ends at Fig. 5.

[0061] After the above-described adjustment of the interference optics system 42, the worker can replace the reference object, which is the measurement object W, on the object stage 8 with a measurement target and cause the white light interferometer 1 to start the measurement of the measurement target.

[0062] For example, the drive controller 722 and the image acquisition controller 721 control the motion mechanism 6 and the image acquisition unit 52 as described in step S2 above. In this configuration, the controller 7 captures an image each time the optical head 2 moves in the Z direction by the predetermined amount and instructs the memory 71 to store the image. Based on each image stored in the memory 71, the measurement section 725 detects the Z position of the optical head 2 at which the luminance value of each pixel in the image is at its maximum and instructs the memory 71 to store this Z position as the height of a measurement point. A profile of the measurement target is thus measured.

[0063] The measurement after adjusting the interference optics system 42 can prevent the expansion of the height at each measuring point in the Z direction and thus enable an accurate measurement. Functioning and effects of the exemplary embodiment

[0064] As described above, the white light interferometer 1 of the exemplary embodiment comprises: the interference optics system 42, which separates the light from the light source 31 into the reference light Lr and the measurement light Lm and causes the return light of the measurement light Lm from the object W and the return light of the reference light (Lr) from the reference surface (422S) to interfere with each other; the image acquisition unit 52, which acquires an image of the object W via the interference optics system 42; the movement mechanism 6, which moves the interference optics system 42 relative to the object W in the vertical direction (Z-direction); the adjustment mechanism 43, which adjusts the optical path length of the reference light Lr in the interference optics system 42;the position detector 723, which detects both the first position Pa and the second position Pb based on a plurality of images acquired by the image acquisition unit 52 and which have different height positions (Z-positions) of the interference optics system 42 relative to the object W, wherein the first position Pa is a height position (Z-position) of the interference optics system 42 in which the luminance value Lt of a target pixel reaches a peak value, and the second position Pb is a height position (Z-position) of the interference optics system 42 in which the contrast value C reaches a peak value; and the adjustment amount calculator 724, which calculates the adjustment amount of the adjustment mechanism 43 based on the deviation ΔP between the first position Pa and the second position Pb.

[0065] Such a configuration makes it possible to detect, as the first position Pa, a height position of the interference optics system 42 in which the difference in the optical path length between the reference light Lr and the measurement light Lm is zero, and as the second position Pb, a height position of the interference optics system 42 in which the interference optics system 42 is focused on the measurement surface WS of the measurement object W. Since the deviation ΔP between the first position Pa and the second position Pb corresponds to a deviation from the optimal value of the optical path length of the reference light Lr (i.e., the deviation from the optimal value of the reference distance D1), the adjustment amount of the adjustment mechanism 43 for reducing the deviation of the reference distance D1 can be calculated based on the deviation ΔP between the first position Pa and the second position Pb.Therefore, when adjusting the interference optics system 42, it is only necessary to actuate the adjustment mechanism 43 according to the calculated adjustment amount, without the need to visually check for interference fringes in the image. This reduces the effort and time required for the adjustment work, and a worker performing the adjustment does not need to possess advanced skills. That is to say, the interference optics system 42 in the white-light interferometer 1 of the exemplary embodiment is easy to adjust.

[0066] In the exemplary embodiment, the adjusting mechanism 43 comprises the actuating section 432, which receives an actuation for adjusting the optical path length of the reference light Lr, and the adjusting amount calculator 724 calculates the actuating amount of the actuating section 432 as the adjusting amount of the adjusting mechanism 43.

[0067] Such a configuration makes it easier for a worker to manually adjust the interference optics system 42.

[0068] In the exemplary embodiment, the adjusting mechanism 43 further comprises the scale 434 for measuring the actuation amount of the actuating section 432, and the actuation amount of the actuating section 432 is indicated by the number of graduations on the scale 434.

[0069] Such a configuration further makes it easier for a worker to manually adjust the interference optics system 42.

[0070] The method for adjusting the interference optics system 42 of the exemplary embodiment comprises: step S2 of changing the height position of the interference optics system 42 relative to the object W in the white light interferometer 1 described above and acquiring a plurality of images of the object W via the interference optics system 42; steps S3 and S4 of acquiring both the first position Pa and the second position Pb based on the plurality of images with different height positions of the interference optics system 42 relative to the object W, wherein the first position Pa is a height position (Z-position) of the interference optics system 42 in which the luminance value Lt of a target pixel reaches a peak value, and the second position Pb is a height position (Z-position) of the interference optics system 42 in which the contrast value C reaches a peak value;and steps S5 and S7 of calculating the adjustment amount of the adjustment mechanism 43 based on the deviation amount ΔP between the first position Pa and the second position Pb.;

[0071] Such a method produces effects similar to those of the white light interferometer 1 described above. Modifications

[0072] The invention is not limited to the embodiment described above and modifications and the like, as long as the objective of the invention is achievable. Modification 1

[0073] The embodiment described above describes the case in which no interference fringes appear in any image acquired in step S2 described above. However, interference fringes may still appear in the image. It should be noted that in such a case, if the optical head 2 is positioned near the interference position, the contrast value C of the image will exhibit a multitude of steep peaks, as shown in Fig. Figure 8 is shown, similar to the luminance value Lt of the target pixel. Therefore, in step S4 described above, the position detector 723 can use a known technique such as differentiation or filtering to calculate a trend of change in the contrast value C with respect to a change in the Z-position of the optical head 2, and detect the Z-position of the optical head 2 at which the trend of the contrast value C reaches a peak value as the second position Pb. This makes it possible to detect the second position Pb appropriately regardless of whether interference fringes appear or not.

[0074] If interference fringes appear in the image, a diagram like the one shown in [reference] can be obtained after adjusting the interference optics system 42. Fig. The 9 depicted ones will be obtained. Fig. 9 the Z-position at which the luminance value Lt of the target pixel reaches a positive peak coincides with the Z-position at which the trend of the contrast value C reaches a peak value, so that the difference in optical path length between the reference light Lr and the measurement light Lm is zero when the interference optics system 42 is focused on the measurement surface WS. Modification 2

[0075] The position detector 723 detects as the first position Pa the Z-position of the optical head 2 in which the luminance value Lt reaches a positive maximum peak in step S3 described above. However, the invention is not limited to this. For example, the Z-position of the optical head 2 in which the luminance value Lt reaches a negative maximum peak can be detected as the first position Pa, as long as an accuracy problem is acceptable. Alternatively, the Z-position of the optical head 2 corresponding to any of a plurality of peaks (a positive peak and a negative peak) reached by the luminance value Lt of the target pixel near the interference position can be detected as the first position Pa. Modification 3

[0076] In the embodiment described above, the case is described in which a worker manually adjusts the interference optics system 42. However, the invention is not limited to this. That is, the white-light interferometer 1 can include a drive, such as a motor, that drives the actuating section 432 to automatically adjust the interference optics system 42. In this case, the adjustment amount calculator 724 can calculate a control amount for the drive that actuates the actuating section 432 in step S8 described above, as the adjustment amount of the adjustment mechanism 43. Furthermore, the controller 7 can control the drive based on the calculated control amount in step S9 described above. Modification 4

[0077] In the embodiment described above, the case is described in which the adjusting mechanism 43 adjusts the Z-position of the separating / combining section 423. However, the invention is not limited to this. That is, the adjusting mechanism 43 can adjust the reference section 422 in the Z-direction. In particular, the adjusting mechanism 43 can comprise the main body 431, which carries the separating / combining section 423, and the slide 433, which carries the reference section 422 over the glass plate 424. In such a modification, when the slide 433 moves in the Z-direction relative to the main body 431, the reference section 422 moves in the Z-direction relative to the separating / combining section 423 by a distance (the reference distance D1). Fig. 2) to be set between the reference section 422 and the separating / combining section 423. Modification 5

[0078] The movement mechanism 6 of the embodiment described above causes the interference optics system 42 to move relative to the measuring surface WS by moving the optical head 2 in the Z direction. However, the invention is not limited thereto. For example, the white light interferometer 1 of the embodiment described above can include a movement mechanism that drives the stage 8 instead of the movement mechanism 6, which moves the optical head 2 in the Z direction. Modification 6

[0079] In the embodiment described above, the interference objective lens unit 4 has a Mirau arrangement. However, the interference objective lens unit 4 can also have a Michelson arrangement. In this case, the adjustment mechanism 43 is able to adjust the optical path length of the reference light Lr by setting a position of the reference section 422 along an optical axis of the reference light Lr. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2018-096869 A

[0002]

Claims

[1] White light interferometer (1), comprising: an interference optics system (42) configured to separate light from a light source (31) into a reference light (Lr) and a measurement light (Lm) and to allow a return light of the measurement light (Lm) from a measurement object (W) and a return light of the reference light (Lr) from a reference surface (422S) to interfere with each other; an image acquisition unit (52) configured to acquire an image of the object being measured (W) via the interference optics system (42); a movement mechanism (6) configured to move the interference optics system (42) relative to the object being measured (W) in a vertical direction; an adjustment mechanism (43) configured to adjust an optical path length of the reference light (Lr) in the interference optics system (42); a position detector (723) configured to detect both a first position (Pa) and a second position (Pb) based on a plurality of images acquired by the image acquisition unit (52) which have different height positions of the interference optics system (42) relative to the object being measured (W), wherein the first position (Pa) is a height position of the interference optics system (42) at which a luminance value (Lt) of a target pixel reaches a peak value, and the second position (Pb) is a height position of the interference optics system (42) at which a contrast value (C) reaches a peak value; and a setting amount calculator (724) which is configured to calculate a setting amount of the setting mechanism (43) based on a deviation amount (ΔP) between the first position (Pa) and the second position (Pb). [2] White light interferometer (1) according to claim 1, wherein the position detector (723) is configured to calculate a trend of a change in the contrast value (C) with respect to a change in the height position of the interference optics system (42) and to detect as the second position (Pb) a height position of the interference optics system (42) in which the trend of the contrast value (C) reaches a peak value. [3] White light interferometer (1) according to claim 1, wherein the adjustment mechanism (43) includes an actuation section (432) configured to receive an actuation for adjusting the optical path length of the reference light (Lr), and the setting amount calculator (724) is configured to calculate an actuation amount of the actuation section (432) as the setting amount of the setting mechanism (43). [4] White light interferometer (1) according to claim 3, wherein the adjustment mechanism (43) further comprises a scale (434) with which the actuation amount of the actuating section (432) is measured, and The actuation amount of the actuation section (432) is indicated by the number of graduations on the scale (434). [5] Method for adjusting an interference optics system (42) in a white light interferometer (1), wherein the interference optics system (42) is configured to separate light from a light source (31) into a reference light (Lr) and a measurement light (Lm) and to allow a return light of the measurement light (Lm) from a measurement object (W) and a return light of the reference light (Lr) from a reference surface (422S) to interfere with each other, wherein The procedure includes: Changing the height position of the interference optics system (42) relative to the object being measured (W) and capturing a multitude of images of the object being measured (W) via the interference optics system (42); Capturing both a first position (Pa) and a second position (Pb) based on the multitude of images that have different height positions of the interference optics system (42) relative to the object being measured (W), wherein the first position (Pa) is a height position of the interference optics system (42) at which a luminance value (Lt) of a target pixel reaches a peak value, and the second position (Pb) is a height position of the interference optics system (42) at which a contrast value (C) reaches a peak value; and Calculate, based on a deviation amount (ΔP) between the first position (Pa) and the second position (Pb), an adjustment amount of the adjustment mechanism (43) which is configured to set an optical path length of the reference light (Lr).

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