Interference observation device and optical adjustment method

Abstract

An interference observation device is provided with: a light source that outputs light; an interference optical system which has a movable reference mirror, divides the light output from the light source into first light and second light, and outputs interference light of the first light reflected by the object to be observed and the second light reflected by the reference mirror; an imaging element that detects interference light; and a processing unit that acquires an interference image on the basis of the detection result of the interference light, and performs optical adjustment processing for optical adjustment relating to observation of the object to be observed. The processing unit acquires a first interference image and a second interference image having different optical path length differences between the first light and the second light by changing the optical path length of the second light, and performs optical adjustment processing on the basis of the first interference image and the second interference image.

Description

Technical Field

[0001] One aspect of this disclosure relates to an interferometric observation apparatus and an optical adjustment method for the interferometric observation apparatus. Background Technology

[0002] For example, Patent Document 1 describes an interferometric observation device comprising: a light source; an interferometric optical system that branches the light output from the light source into a first branch light and a second branch light, such that the first branch light is reflected by the object being observed, and combines the first branch light with the second branch light (reference light) and outputs the combined light; a light receiving unit that receives the combined light and outputs a detection signal; and an image acquisition unit that acquires an interferometric image based on the detection signal.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: WO2016-121250 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The aforementioned interferometric observation device is used for surface observation, which is used to observe the surface of an object. On the other hand, internal observation, which is used to observe the interior of an object, can also be considered through interferometric observation. For example, in the case of an object that is a device with a cover member, the surface of the device (the interface between the device and the cover member) can be observed through the cover member by using light of a wavelength that passes through the cover member.

[0008] In either surface or internal observation, optical adjustments are required during observation, such as adjusting the focal position of the objective lens and the optical path length of the reference light. Such optical adjustments must be performed at high speed and with high precision. For example, in internal observation, one method for adjusting the focal position of the objective lens is to scan the entire thickness direction of the object being observed, aligning the focal position with the observation location within the object. However, this method is difficult to scale up quickly. For instance, in this method, after scanning the focal position, it takes several hundred milliseconds for the vibration of the optical path length (the optical path length of the first branch light) on the object side to settle at the nanometer level. This settling time can be a barrier to high-speed observation.

[0009] Therefore, one aspect of this disclosure is to provide an interferometric observation device and optical adjustment method that can perform optical adjustments at high speed and with good accuracy.

[0010] Technical means to solve the problem

[0011] One aspect of the interference observation apparatus disclosed herein is, [1] "An interference observation apparatus comprising: a light source that outputs light; an interference optical system having a movable reference mirror that splits the light output from the light source into a first light and a second light, and outputs interference light of the first light reflected by the object being observed and the second light reflected by the reference mirror; an imaging element that detects the interference light; and a processing unit that acquires an interference image based on the detection result of the interference light and performs optical adjustment processing for optical adjustment associated with the observation of the object being observed, wherein the processing unit acquires multiple interference images with different optical path length differences between the first light and the second light by changing the optical path length of the second light, and performs the optical adjustment processing based on the multiple interference images."

[0012] In this interferometric observation apparatus, optical adjustment can be performed at high speed and with high accuracy because multiple interferometric images with different optical path length differences are obtained based on the change in the optical path length of the second light. In particular, compared to methods such as described above, which scan the focal position of the objective lens across the entire thickness direction of the observed object, optical adjustment can be performed at high speed and with high accuracy.

[0013] One aspect of the interferometric observation apparatus disclosed herein may also be, [2] "the interferometric observation apparatus as described in [1], wherein the processing unit performs the optical adjustment processing on each calculated evaluation value of the plurality of interferometric images based on the evaluation values ​​of the plurality of interferometric images." In this case, the optical adjustment processing may be appropriately performed.

[0014] One aspect of the interferometric observation apparatus disclosed herein may also be, [3] "the interferometric observation apparatus as described in [2], wherein the plurality of interferometric images include a first interferometric image and a second interferometric image with different optical path length differences, and the processing unit performs the optical adjustment processing based on the difference between the evaluation value calculated based on the first interferometric image, i.e., the first evaluation value, and the evaluation value calculated based on the second interferometric image, i.e., the second evaluation value." In this case, the optical adjustment processing can be appropriately performed.

[0015] One aspect of the interference observation apparatus disclosed herein may also be, [4] "the interference observation apparatus as described in [3], wherein after acquiring the first interference image, the second interference image is acquired, and after acquiring the second interference image, the processing unit performs the optical adjustment if the absolute value of the difference is greater than a predetermined value, and does not perform the optical adjustment if the absolute value of the difference is less than the predetermined value." In this case, optical adjustment processing can be appropriately performed.

[0016] One aspect of the interferometric observation apparatus disclosed herein may also be, [5] "the interferometric observation apparatus as described in [4], wherein, when the processing unit performs the optical adjustment after acquiring the second interferometric image, the optical adjustment is performed based on the magnitude relationship between the first evaluation value and the second evaluation value." In this case, optical adjustment processing can be appropriately performed.

[0017] One aspect of the interferometric observation apparatus disclosed herein may also be, [6] "an interferometric observation apparatus as described in [4] or [5], wherein, when the processing unit performs the optical adjustment after acquiring the second interferometric image, the optical adjustment is performed by an amount corresponding to the magnitude of the difference between the first evaluation value and the second evaluation value." In this case, the optical adjustment processing can be suitably performed.

[0018] One aspect of the interferometric observation apparatus disclosed herein may also be, [7] "the interferometric observation apparatus described in any one of [2] to [6], wherein the processing unit calculates the evaluation value based at least on the amplitude image corresponding to the interferometric image." In this case, the evaluation value may be appropriately calculated.

[0019] One aspect of the interferometric observation apparatus disclosed herein may also be, [8] "the interferometric observation apparatus described in any of [2] to [7], wherein the processing unit calculates the evaluation value based at least on the amount of curvature of the interference fringes in the phase image corresponding to the interferometric image." In this case, the evaluation value may be appropriately calculated.

[0020] One aspect of the interference observation apparatus disclosed herein may also be, [9] "an interference observation apparatus as described in any of [1] to [8], wherein the processing unit changes the optical path length of the second light by moving the reference mirror, thereby obtaining multiple interference images with different optical path length differences." In this case, multiple interference images can be appropriately obtained.

[0021] One aspect of the interferometric observation apparatus disclosed herein may also be,

[10] "an interferometric observation apparatus as described in any of [1] to [9], wherein, among the plurality of interferometric images, the change in the optical path length of the second light differs by a value greater than the wavelength of the light output from the light source." In this case, appropriate optical adjustment processing may be performed.

[0022] One aspect of the interferometric observation apparatus disclosed herein may also be,

[11] "an interferometric observation apparatus as described in any of [1] to

[10] , wherein the interferometric optical system further comprises an objective lens, and the optical adjustment includes adjusting the relative position between the objective lens and the object being observed." In this case, the relative position between the objective lens and the object being observed can be adjusted.

[0023] One aspect of the interferometric observation apparatus disclosed herein may also be,

[12] "an interferometric observation apparatus as described in any of [1] to

[11] , wherein the optical adjustment comprises adjusting the optical path length of the second light by moving the reference mirror." In this case, the optical path length of the second light can be adjusted.

[0024] One aspect of the interferometric observation apparatus disclosed herein may also be,

[13] "an interferometric observation apparatus as described in any of [1] to

[12] , wherein the interferometric optical system further comprises a reference objective lens that guides the second light to the reference mirror, and the optical adjustment includes adjusting the position of the reference objective lens." In this case, the position of the reference objective lens can be adjusted.

[0025] One aspect of the interferometric observation apparatus disclosed herein may also be,

[14] , "an interferometric observation apparatus as described in any of [1] to

[13] , wherein, among the plurality of interferometric images, the observation positions relative to the object being observed are the same along a plane intersecting the direction of the first light incident on the object being observed." In this case, optical adjustment processing can be performed based on the plurality of interferometric images obtained at the same observation position.

[0026] One aspect of the interferometric observation apparatus disclosed herein may also be,

[15] "an interferometric observation apparatus as described in any of [1] to

[13] , wherein, among the plurality of interferometric images, the observation positions relative to the object being observed are different along the plane intersecting the direction of the first light incident on the object being observed." In this case, optical adjustment processing can be performed based on the plurality of interferometric images obtained at different observation positions.

[0027] One aspect of the interferometric observation apparatus disclosed herein may also be,

[16] "an interferometric observation apparatus as described in any one of [1] to

[15] , wherein it further comprises: a stage for arranging the object to be observed, which is movable at least along a plane intersecting the direction in which the first light is incident on the object to be observed, and the processing unit performing the optical adjustment processing based on the multiple interferometric images according to the movement of the stage along the plane." In this case, the observation position can be changed by moving the object to be observed while performing optical adjustment.

[0028] One aspect of the interferometric observation apparatus disclosed herein may also be,

[17] "the interferometric observation apparatus as described in

[16] , wherein the interferometric optical system further comprises an objective lens, and the processing unit performs optical adjustment processing for adjusting the relative position between the objective lens and the object being observed based on the multiple interferometric images, according to the movement of the stage along the plane." In this case, the observation position can be changed by moving the object being observed while adjusting the relative position between the objective lens and the object being observed.

[0029] One aspect of the interferometric observation apparatus disclosed herein may also be,

[18] "an interferometric observation apparatus as described in any one of [1] to

[17] , further comprising: a stage for arranging the object to be observed, movable at least along a plane intersecting the direction in which the first light is incident on the object to be observed; the plurality of interferometric images including a first interferometric image and a second interferometric image with different optical path length differences; the processing unit alternately performing a first processing and a second processing; here, in the first processing, the processing unit acquires the first interferometric image, performs the optical adjustment processing based on the first interferometric image and the second interferometric image acquired in the previous second processing, and moves the stage along the plane; in the second processing, the processing unit acquires the second interferometric image, performs the optical adjustment processing based on the second interferometric image and the first interferometric image acquired in the previous first processing, and moves the stage along the plane." In this case, the optical adjustment processing can be performed by successive processing.

[0030] An interferometric observation apparatus according to one aspect of this disclosure may also be,

[19] "an interferometric observation apparatus as described in any one of [1] to

[17] , wherein it further comprises: a stage for arranging the object to be observed, which is movable at least along a plane intersecting the direction in which the first light is incident on the object to be observed; and a first storage area and a second storage area, wherein the plurality of interferometric images include the first interferometric image and the second interferometric image with different optical path length differences, and the processing unit performs the first processing, the second processing and the third processing in parallel, wherein, in the first processing, the processing unit alternately performs: acquiring first data from the imaging element for generating the first interferometric image, storing the first data in the first storage area, and moving the stage along the plane; and acquiring data from the imaging element for generating the first interferometric image. The process of moving the stage along the plane after storing the second data of the 2nd interferometric image in the first storage area, in the second process, the processing unit alternately performs: generating the first interferometric image based on the first data obtained in the first process, storing the first evaluation value corresponding to the first interferometric image in the second storage area; and generating the second interferometric image based on the second data obtained in the first process, storing the second evaluation value corresponding to the second interferometric image in the second storage area. In the third process, whenever the first evaluation value or the second evaluation value is stored in the second storage area in the second process, the processing unit performs the optical adjustment process based on the previously obtained first evaluation value and the second evaluation value. In this case, the optical adjustment process can be performed in parallel.

[0031] One aspect of the interferometric observation apparatus disclosed herein may also be,

[20] "an interferometric observation apparatus as described in any one of [1] to

[19] , wherein it further comprises: a piezoelectric element for moving the reference mirror; and a motor for moving the object to be optically adjusted, wherein the processing unit changes the optical path length of the second light by moving the reference mirror using the piezoelectric element, obtains multiple interferometric images with different optical path length differences, and performs the optical adjustment using the motor." In this case, the piezoelectric element and the motor can be used for optical adjustment processing.

[0032] One aspect of the interferometric observation apparatus disclosed herein may also be,

[21] "an interferometric observation apparatus as described in any one of [1] to

[19] , further comprising: a stepper motor for moving the reference mirror, the stepper motor being driven in a first mode and a second mode with a step angle greater than that of the first mode, the processing unit moving the reference mirror by driving the stepper motor in the first mode to change the optical path length of the second light, thereby obtaining multiple interferometric images with different optical path length differences, and performing the optical adjustment by driving the stepper motor in the second mode." In this case, an optical adjustment process can be performed using a stepper motor.

[0033] One aspect of the interferometric observation apparatus disclosed herein may also be,

[22] "an interferometric observation apparatus as described in any one of [1] to

[21] , wherein the interferometric optical system further comprises an objective lens, and the interferometric observation apparatus further comprises: a surface AF section having an AF light source for outputting light, the interferometric optical system acquiring light output from the AF light source and reflected by the surface of the object being observed, and adjusting the relative position between the objective lens of the interferometric optical system and the surface of the object being observed based on the acquired result." In this case, the relative position between the objective lens and the surface of the object being observed can be adjusted by the surface AF section.

[0034] One aspect of the interferometric observation apparatus disclosed herein may also be,

[23] "the interferometric observation apparatus as described in

[22] , further comprising: a stage for arranging the object to be observed, which is movable at least along a plane intersecting the direction in which the first light is incident on the object to be observed; and a processing unit, based on the movement of the stage along the plane, performing optical adjustment processing for adjusting the relative position between the objective lens and the object to be observed, and optical adjustment processing for adjusting the optical path length of the second light by moving the reference mirror." In this case, optical adjustment processing for adjusting the relative position between the objective lens and the object to be observed, and optical adjustment processing for adjusting the optical path length of the second light, can be performed while the object to be observed is moved.

[0035] One aspect of the optical adjustment method disclosed herein is as follows:

[24] "An optical adjustment method for performing optical adjustments related to the observation of an object in an interferometric observation apparatus, the interferometric observation apparatus comprising: a light source that outputs light; an interferometric optical system having a movable reference mirror that divides the light output from the light source into a first light and a second light, and outputs an interference light of the first light reflected by the object being observed and the second light reflected by the reference mirror; and an imaging element that detects the interference light and obtains an interference image based on the detection result of the interference light, the optical adjustment method comprising: obtaining multiple interference images with different optical path length differences between the first light and the second light by changing the optical path length of the second light, and performing an optical adjustment process for the optical adjustment based on the multiple interference images."

[0036] In this optical adjustment method, since optical adjustment is performed based on multiple interference images with different optical path length differences obtained by changing the optical path length of the second light, optical adjustment can be performed at high speed and with good accuracy. In particular, compared to methods such as those described above, which scan the focal position of the objective lens throughout the thickness direction of the observed object, optical adjustment can be performed at high speed and with good accuracy.

[0037] One aspect of the optical adjustment method disclosed herein may also be,

[25] "the optical adjustment method as described in

[24] , wherein, in the above-mentioned steps, multiple interference images are obtained based on the detection result of the interference light of the first light reflected by the surface of the object being observed and the second light reflected by the reference mirror." In this case, optical adjustment can be performed when observing the surface of the object being observed.

[0038] One aspect of the optical adjustment method disclosed herein may also be,

[26] "the optical adjustment method described in

[24] , wherein, in the above-mentioned steps, multiple interference images are obtained based on the detection result of the interference light of the first light reflected inside the object being observed and the second light reflected by the reference mirror." In this case, optical adjustment can be performed when observing the interior of the object being observed.

[0039] One aspect of the optical adjustment method disclosed herein may also be,

[27] "the optical adjustment method described in any one of

[24] to

[26] , wherein, in the above-mentioned process, the observation position relative to the observation object along the plane is changed by moving the object to be observed along the plane, and the optical adjustment processing is performed based on the multiple interference images according to the movement of the object to be observed along the plane." In this case, the optical adjustment processing can be performed while the object to be observed is being moved.

[0040] One aspect of the optical adjustment method disclosed herein may also be,

[28] "the optical adjustment method described in any of

[24] to

[27] , wherein the interference optical system further comprises a replaceable objective lens, and in the above process, when the objective lens is replaced, an optical adjustment process is performed based on the multiple interference images to adjust the optical path length of the second light by moving the reference mirror." In this case, optical adjustment can be performed when the objective lens is replaced.

[0041] One aspect of the optical adjustment method disclosed herein may also be,

[29] "The optical adjustment method described in any of

[24] to

[28] , wherein the process of obtaining multiple interference images with different optical path length differences between the first light and the second light by changing the optical path length of the second light, and performing optical adjustment processing for the optical adjustment based on the multiple interference images, is defined as a micro-adjustment process; the process of obtaining multiple interference images by scanning the focal position of the objective lens across the entire object of observation along the incident direction with the direction in which the first light is incident on the object of observation as the incident direction, and adjusting the focal position based on the obtained results, is defined as a focal position adjustment process; and the process of performing the micro-adjustment process or the focal position adjustment process is performed according to the observation position relative to the object of observation along the plane as the object of observation moves along the plane." In this case, by intermittently performing the focal position adjustment process, which requires time, the increase in operation time can be suppressed.

[0042] The effects of the invention

[0043] According to one aspect of this disclosure, an interferometric observation device and optical adjustment method capable of high-speed and high-precision optical adjustment can be provided. Attached Figure Description

[0044] Figure 1 This is a structural diagram of the interference observation device according to the implementation method.

[0045] Figure 2 It is a diagram used to illustrate internal observations.

[0046] Figure 3 This is a graph used to illustrate the relationship between the amount of objective lens movement and the change in the optical path length of the second light.

[0047] Figure 4 It is a diagram used to illustrate the adjustment amount when the observed object has multiple layers.

[0048] Figure 5 This is a flowchart illustrating the processes performed in an interferometric observation device.

[0049] Figure 6 This is a diagram used to illustrate the operation of an interferometric observation device.

[0050] Figure 7 This is a diagram showing an example of the obtained interferometric image.

[0051] Figure 8 This is a diagram showing examples of real part images, imaginary part images, amplitude images, and phase images.

[0052] Figure 9 This is a flowchart illustrating the process of calculating evaluation values ​​based on the obtained interferometric images.

[0053] Figure 10 This is a flowchart used to illustrate the focus adjustment process.

[0054] Figure 11 This is a diagram used to illustrate focus adjustment.

[0055] Figure 12 This is a diagram used to illustrate focus adjustment.

[0056] Figure 13 This is a diagram used to illustrate focus locking.

[0057] Figure 14 This is a diagram used to illustrate focus locking.

[0058] Figure 15 Figures (a) and (b) are another example used to illustrate the operation of an interference observation device.

[0059] Figure 16 This is a flowchart illustrating another example of the processing performed in an interferometric observation device.

[0060] Figure 17 This is a flowchart illustrating another example of the processing performed in an interferometric observation device.

[0061] Figure 18 This is a flowchart illustrating another example of the processing performed in an interferometric observation device.

[0062] Figure 19This is a table used to illustrate the methods for obtaining interference images.

[0063] Figure 20 This is another example of a diagram used to illustrate the operation of an interferometric observation device.

[0064] Figure 21 This is another table used to illustrate optical adjustment.

[0065] Figure 22 This is a structural diagram of another example of an interferometric observation device.

[0066] Figure 23 (a)~(c) are used to explain Figure 22 The graph shows the relationship between the amount of focusing movement and the change in optical path length in the interferometric observation device.

[0067] Figure 24 This is a diagram used to illustrate a method for calculating evaluation values ​​based on the amount of curvature in a phase image.

[0068] Figure 25 This is a diagram illustrating an application example of optical adjustment processing.

[0069] Figure 26 It is a diagram used to illustrate surface observation.

[0070] Figure 27 This is another example of a diagram used to illustrate the operation of an interferometric observation device.

[0071] Figure 28 This is another example of a diagram used to illustrate the operation of an interferometric observation device.

[0072] Figure 29 This diagram illustrates the optical adjustments made when changing the objective lens.

[0073] Figure 30 This is a flowchart illustrating an example of the procedure when changing the objective lens.

[0074] Figure 31 This is a diagram showing an example of an objective lens with a coupling mounted on it.

[0075] Figure 32 This is a diagram used to illustrate the adjustment of the telescope barrel's mechanical error. Detailed Implementation

[0076] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements are referred to by the same symbols and repeated descriptions are omitted.

[0077] [Interferometric observation device]

[0078] like Figure 1 and Figure 2As shown, the interferometric observation apparatus 1 includes a light source 2, an interferometric optical system 3, an imaging element 4, a processing unit 5, and a stage S. The interferometric observation apparatus 1 is an interference microscope used to observe an object 8 disposed on the stage S using light interference. The object 8 may be, for example, a semiconductor device, but may also be other industrial samples formed from metals, glass, resins, liquid crystals, polymer compounds, etc. The object 8 may also be a biological sample such as cells or cell blocks. Hereinafter, as... Figure 1 and Figure 2 As shown, the X direction, the Y direction perpendicular to the X direction, and the Z direction perpendicular to both the X and Y directions are explained.

[0079] The interferometric observation device 1 is configured to perform not only surface observation (observation of the outer surface of the object 8) but also internal observation (observation of the interior of the object 8). For example... Figure 1 and Figure 2 As shown, during internal observation, the observation surface R located within the observation object 8 is observed. In this example, the observation object 8 is a semiconductor device with a cover, having a first layer 81, a second layer 82, and a third layer 83.

[0080] Layer 1 81 is a resin layer (cap), layer 2 82 is an air layer, and layer 3 83 is a semiconductor layer (device layer). Layers 1 81 to 3 83 are arranged (stacked) in the order of layer 3 83, layer 2 82, and layer 1 81. The object to be observed 8 is placed on the stage S with layer 3 83 in contact with the stage S. The object surface R is set to any of the interfaces between layers 1 81, 2 82, and 3 83. For example, in Figure 1 In the example, the observed surface R is set as the interface between layer 2 82 and layer 3 83. Figure 2 In the example, the object surface R is set as the interface between layer 1 81 and layer 2 82. By using light of the wavelength that passes through layer 1 81 as light output from light source 2 described below, the object surface R can be observed through layer 1 81.

[0081] Light source 2 outputs incoherent light. Light source 2 can be, for example, a halogen lamp, an LED (Light emitting diode) light source, an SLD (Superluminescent diode) light source, or an ASE (Amplified spontaneous emission) light source.

[0082] In this example, the interferometric optical system 3 (interferometric observation device 1) is configured as a Linnik interferometer. The interferometric optical system 3 includes a lens 11, a beam splitter 12, an objective lens 13, a reference objective lens 14, and a reference mirror 15. The interferometric optical system 3 and the light source 2 are housed together within the housing H, forming the optical module M. The optical module M can be moved along the Z-direction by a predetermined actuator 16. The Z-direction is parallel to the optical axis of the objective lens 13 and is parallel to the direction in which the first light L1 is incident on the object 8.

[0083] Lens 11 collimates the light output from light source 2. Beam splitter 12, for example, is a prism with optical surface 12a, which splits the light collimated by lens 11 into a first beam L1 and a second beam L2 at optical surface 12a. Beam splitter 12 outputs the first beam L1 to objective lens 13 and the second beam L2 to reference objective lens 14. In addition, at optical surface 12a, the first beam L1 reflected from the observation surface R of the observed object 8 is incident through objective lens 13, and the second beam L2 reflected by reference lens 15 is incident through reference objective lens 14. These first beams L1 and second beams L2 are combined at optical surface 12a to become interference light L3. Interference optical system 3 outputs interference light L3 to imaging element 4.

[0084] Objective lens 13 focuses the first light L1 output from beam splitter 12 onto the object 8 positioned on stage S. Additionally, the first light L1 reflected from the object surface R of object 8 is incident on objective lens 13. Objective lens 13 outputs the incident first light L1 to beam splitter 12.

[0085] Reference objective 14 guides the second light L2 output from beam splitter 12 to reference mirror 15 and focuses it onto reference mirror 15. Additionally, reference objective 14 outputs the second light L2 reflected by reference mirror 15 back to beam splitter 12. Reference mirror 15 reflects the second light L2 output from reference objective 14 back to reference objective 14.

[0086] Within the housing H of the optical module M, a stepper motor 17 for moving the reference objective lens 14, a stepper motor 18 for moving the reference mirror 15, and a piezoelectric element 19 are also disposed. The stepper motor 17 moves the reference objective lens 14 along the optical axis direction (e.g., the X direction) of the second light L2 perpendicular to the Z direction. The stepper motor 18 and the piezoelectric element 19 move the reference mirror 15 along the optical axis direction of the second light L2.

[0087] The response times of stepper motors 17 and 18 are greater than 10 ms, while the response time of piezoelectric element 19 is less than 1 ms. That is, the response time of piezoelectric element 19 is shorter than that of stepper motors 17 and 18. The stroke (minimum travel distance) of stepper motors 17 and 18 is several millimeters, while the stroke of piezoelectric element 19 is approximately 2 μm. That is, the stroke of piezoelectric element 19 is shorter than that of stepper motors 17 and 18. The lifespan of stepper motors 17 and 18 is less than 1 million cycles, while the lifespan of piezoelectric element 19 is more than 10 billion cycles. That is, the lifespan of piezoelectric element 19 is greater than that of stepper motors 17 and 18.

[0088] The imaging element 4 is, for example, an image sensor (camera) such as a CCD area image sensor or a CMOS area image sensor. The imaging element 4 detects (captures) the interference light L3 output from the interference optical system 3 (beam splitter 12). A lens 41 and a lens barrel 42 are disposed between the imaging element 4 and the interference optical system 3. The lens 41 images the interference light L3 output from the interference optical system 3 onto the imaging surface of the imaging element 4. The lens 41 is housed within the lens barrel 42. The lens barrel 42 is formed, for example, in a cylindrical shape and is fixed to the imaging element 4 in a manner that surrounds the imaging surface.

[0089] The processing unit 5 is communicatively connected to each part of the interferometric observation apparatus 1, which includes the light source 2, the interferometric optical system 3, the imaging element 4, and the stage S. It acquires an interferometric image based on the detection result of the interferometric light L3 in the imaging element 4. Furthermore, the processing unit 5 performs optical adjustment processing for optical adjustments related to the observation of the object 8 using the interferometric observation apparatus 1. The processing of the interferometric image and the processing performed by the processing unit 5 will be described later. The processing unit 5 is, for example, a computer C including a processor (CPU), storage media such as RAM and ROM. The computer C includes a storage area 51.

[0090] Computer C also includes an input unit 52 for accepting information input and a display unit 53 for displaying information. The input unit 52 is, for example, a device that accepts user input, such as a mouse or keyboard. The display unit 53 is, for example, a monitor that displays images. The input unit 52 and the display unit 53 may also be configured together, for example, a touch panel. Furthermore, in this example, the processing unit 5, the storage area 51, the input unit 52, and the display unit 53 are configured as a single device, but at least one of them may be configured as other devices, such as a portable terminal.

[0091] The stage S is used to position the object 8 to be observed, and it can move along the XY plane perpendicular to the Z direction of the first light L1 incident on the object 8. Thus, in the interferometric observation device 1, the object 8 can be observed (interference image acquired) while the stage S is moved along the XY plane, that is, while the observation position of the object 8 is changed.

[0092] [Example of the operation of an interferometric observation device]

[0093] As described above, in the interferometric observation apparatus 1, the processing unit 5 performs optical adjustment processing for optical adjustments related to the observation of the object 8. This optical adjustment considers the relative position between the objective lens 13 and the object 8, and the adjustment of the optical path length of the second beam L2 (reference beam). For the former adjustment, in the interferometric observation apparatus 1, the position of the objective lens 13 relative to the object 8 is adjusted by moving the objective lens 13 along the Z direction using the actuator 16, thereby adjusting the focal position (focusing position) of the objective lens 13. For the latter adjustment, the optical path length of the second beam L2 (the difference in optical path length between the first beam L1 and the second beam L2) is adjusted by moving the reference objective lens 14 and the reference mirror 15 using stepper motors 17 and 18.

[0094] Such optical adjustments are necessary for reasons such as the following: First, for example, in Figure 1 , 2 In the case of internal observation shown, when observing the interior of the object 8 through the first layer 81, there are deviations between the measured values ​​of the thickness and refractive index of the first layer 81 and the nominal values. Therefore, even if the focusing position of the objective lens 13 and the optical path length of the second beam L2 are adjusted based on the nominal values, this deviation will cause errors in the focusing position of the objective lens 13 and the optical path length of the second beam L2, raising concerns that a good interference image may not be obtained.

[0095] As one example, the first layer 81 is formed of glass. With a nominal refractive index of 1.51 and a nominal thickness of 400 μm, the adjustment calculated based on the nominal values ​​is 256 μm for objective lens 13 and 340 μm for reference lens 15. However, the adjustment calculated based on the measured values ​​is 270 μm for objective lens 13 and 365 μm for reference lens 15. As another example, the first layer 81 is formed of resin. With a nominal refractive index of 1.59 and a nominal thickness of 1000 μm, the adjustment calculated based on the nominal values ​​is 629 μm for objective lens 13 and 961 μm for reference lens 15. However, the adjustment calculated based on the measured values ​​is 590 μm for objective lens 13 and 927 μm for reference lens 15. Thus, there is a deviation between the adjustment amount calculated based on the nominal value and the adjustment amount calculated based on the measured value, and optical adjustment cannot be performed well in adjustment based solely on the nominal value.

[0096] Furthermore, since the thickness and refractive index of the first layer 81 vary depending on the observation position, errors may occur in the focusing position of the objective lens 13 and the optical path length of the second beam L2, raising concerns about obtaining a satisfactory interference image. Therefore, the optical adjustment process described below is performed in the interference observation apparatus 1.

[0097] Reference Figure 3 The relationship between the amount of movement of objective lens 13 and the change in the optical path length of the second beam L2 will be explained. As shown by the dashed line, the state where the focusing position of objective lens 13 is on the surface relative to the object 8 with refractive index n1 and thickness d changes to the state where the distance between the object 8 and objective lens 13 decreases by δd, and the focusing position is on the back surface, as shown by the solid line. In this case, δd = d / n1, and the increase in the optical path length of the first beam L1 is expressed by equation (1). Theoretically, it can be adjusted by extending the optical path length of the second beam L2 by this increase. The adjustment amount based on the nominal value described above can be calculated using this method.

[0098] [Number 1]

[0099]

[0100] Adjustments based on nominal values ​​can also be applied when the observed object 8 has multiple layers. (Refer to...) Figure 4 The relationship between the amount of movement of objective lens 13 and the change in the optical path length of the second beam L2 is explained. Figure 4 In the example shown, the object 8 has 3 layers. In an object with N layers of different refractive indices, when focusing on the lower surface of the Nth layer, compared to focusing on the upper surface of the 1st layer, it is necessary to adjust the distance between the object 8 and the objective lens 13 by narrowing the distance by Δd as expressed by equation (2).

[0101] [Number 2]

[0102]

[0103] At this point, the increase in the optical path length of the first beam L1, ΔOPD, is represented by equation (3). Theoretically, it can be adjusted by extending the optical path length of the second beam L2 by this increase.

[0104] [Number 3]

[0105]

[0106] Through the above calculations, even in the presence of multiple layers with different refractive indices, the distance between the observed object 8 and the objective lens 13, as well as the optical path length, can be adjusted based on the nominal values.

[0107] Reference Figure 5 An example of the processing (optical adjustment method) performed in the interferometric observation apparatus 1 will be described. In general, in this processing, by changing the optical path length of the second light L2, a first interference image and a second interference image with different optical path length differences between the first light L1 and the second light L2 are obtained, and the focusing position of the objective lens 13 is adjusted based on the first and second interference images. The first interference image is obtained when the reference mirror 15 is in a forward position (e.g., a first position close to the reference objective lens 14), and the second interference image is obtained when the reference mirror 15 is in a rear position (e.g., a second position further away from the reference objective lens 14 than the forward position). Hereinafter, following... Figure 5 The flowchart shown illustrates the process. After a general overview of the overall process, details of each process are explained as needed.

[0108] The initial state of the interferometric observation apparatus 1 is not limited, but it can, for example, be a state in which the focusing position of the objective lens 13 and the optical path length of the second beam L2 are adjusted based on the nominal values ​​of the thickness and refractive index of the first layer 81 to the third layer 83 of the object being observed, through coarse adjustment. In coarse adjustment, the focusing position of the objective lens 13 and the optical path length of the second beam L2 are adjusted based on the thickness, refractive index, and arrangement order of the first layer 81 to the third layer 83 in order to obtain an interference image of the object surface R specified by the user. The following description describes a fine adjustment process for optical adjustment with good accuracy compared to the coarse adjustment process.

[0109] After processing begins, firstly, the processing unit 5 moves the reference mirror 15 to the forward position by controlling the piezoelectric element 19 (step S1). Next, the imaging element 4 captures four interference images (step S2). Then, the processing unit 5 constructs (acquires) a first interference image based on the four interference images acquired in step S2 (step S3). Next, the processing unit 5 calculates a first evaluation value based on the first interference image acquired in step S3 (step S4). "f(a=forward)" displays the first evaluation value calculated based on the first interference image acquired with the reference mirror 15 in the forward position. "f" is a function used to calculate the evaluation value based on the interference image, and "a=forward" indicates that the reference mirror 15 is in the forward position. The processing unit 5 overwrites the area in storage region 51 used to store the first evaluation value with the first evaluation value calculated in step S4.

[0110] Next, the processing unit 5 determines whether the absolute value (Abs) of the value obtained by subtracting the second evaluation value (f(a=front)) calculated based on the first interferometric image obtained when the reference mirror 15 is in the front position from the first evaluation value (f(a=front)) calculated based on the second interferometric image obtained when the reference mirror 15 is in the rear position is greater than a predetermined threshold (step S5). The values ​​of f(a=front) and f(a=back) used in step S5 are the values ​​currently stored in the area of ​​storage region 51 used to store the first evaluation value and the second evaluation value. f(a=back) is calculated in step S12 below and stored in the area of ​​storage region 51 used to store the second evaluation value. As will be described later, since the first process consisting of steps S1 to S8 and the second process consisting of steps S9 to S16 are executed alternately, f(a=back) is also calculated and stored in storage region 51 before the execution of step S5.

[0111] If the absolute value of f(a=front) - f(a=back) is greater than the threshold in step S5 (yes in step S5), the processing unit 5 performs focus adjustment (step S6). On the other hand, if the absolute value of f(a=front) - f(a=back) is less than the threshold in step S5 (no in step S5), the processing unit 5 does not perform focus adjustment, but moves the stage S along the XY plane, moving the observation position of the object 8 to the next observation position (step S7). The processing unit 5 also performs step S7 after step S6. Steps S6 and S7 (focus adjustment and stage movement) can also be performed simultaneously in parallel. This also applies to steps S14 and S15 below.

[0112] After step S7, the processing unit 5 determines whether the current observation position is the final observation position (step S8). If the current observation position is the final observation position in step S8 (yes in step S8), the processing ends. On the other hand, if the current observation position is not the final observation position in step S8 (no in step S8), the processing unit 5 proceeds to step S9.

[0113] In step S9, the processing unit 5 controls the piezoelectric element 19 to move the reference mirror 15 from a front position to a rear position. Next, the imaging element 4 captures four interference images (step S10). Then, based on the four interference images acquired in step S10, the processing unit 5 constructs (acquires) one second interference image (step S11). Next, based on the second interference image acquired in step S11, the processing unit 5 calculates a second evaluation value (step S12). The processing unit 5 then overwrites the area in storage region 51 used to store the second evaluation value with the second evaluation value calculated in step S12.

[0114] Next, the processing unit 5 determines whether the absolute value of the value obtained by subtracting f(a=after) from f(a=before) is greater than the aforementioned threshold (step S13). The values ​​of f(a=before) and f(a=after) used in step S13 are the values ​​of the area currently stored in the storage area 51 used to store the first evaluation value and the second evaluation value.

[0115] If the absolute value of f(a=front) - f(a=back) is greater than the threshold in step S13 (yes in step S13), the processing unit 5 performs focus adjustment (step S14). On the other hand, if the absolute value of f(a=front) - f(a=back) is less than the threshold in step S13 (no in step S13), the processing unit 5 does not perform focus adjustment, but moves the stage S along the XY plane, moving the observation position of the object 8 to the next observation position (step S15). The processing unit 5 also performs the processing of step S15 after step S14.

[0116] After step S15, the processing unit 5 determines whether the current observation position is the final observation position (step S16). If the current observation position is the final observation position in step S16 (yes in step S16), the processing ends. On the other hand, if the current observation position is not the final observation position in step S16 (no in step S16), the processing unit 5 returns to the processing of step S1. Thus, in this example, the first processing consisting of steps S1 to S8 and the second processing consisting of steps S9 to S16 are alternately and repeatedly executed until the observation position reaches the final observation position.

[0117] like Figure 6 As shown, in this process, the reference mirror 15 moves between a front position and a rear position (steps S1, S9), and at each position, the imaging element 4 captures images to obtain four interference images (steps S2, S10). Additionally, during the movement of the reference mirror 15, a focus adjustment process (optical adjustment process) is performed (steps S3-S6, S11-S14), and the stage S moves along the XY plane (steps S7, S15). The amount of movement of the stage S is preferably a distance slightly less than the width of a field of view. By configuring the operation in this way, multiple images can be captured simultaneously, and these images can be spatially stitched together to produce a complete image. Figure 6 The camera (exposure) timing of the camera element 4 and the movement timing of the stage S are displayed.

[0118] In addition, Figure 6 This displays the amount of movement of the piezoelectric element 19. For example... Figure 6As shown, the piezoelectric element 19 is precisely moved in time with the imaging sequence of the four interference images. Consequently, the difference in optical path length between the first light L1 and the second light L2 differs between the four interference images. In this example, the change in the optical path length of the second light L2 between the first interference image acquired with the reference mirror 15 in the forward position and the second interference image acquired with the reference mirror 15 in the rear position differs by a value greater than the wavelength λ of the light output from the light source 2. That is, the distance between the forward and rear positions is greater than the wavelength λ. On the other hand, the change in the optical path length of the second light L2 between each of the four interference images acquired at the forward and rear positions differs by a value less than the wavelength λ. That is, the movement of the reference mirror 15 used to acquire the four interference images is less than the wavelength λ and less than the distance between the forward and rear positions. Specifically, in this example, the change in the optical path length of the second light L2 differs by λ / 4 between the four interference images.

[0119] exist Figure 7 This shows an example of the four interferometric images obtained in step S2. Figure 8 This shows an example of the first interferometric image constructed (obtained) from these four interferometric images in step S3. The first interferometric image can be a real part image or an imaginary part image as described below, or it can be an amplitude image (interference fringe amplitude image) or a phase image. The construction of the first interferometric image and the calculation of the first evaluation value based on the first interferometric image (steps S3 and S4) are described here, but the construction of the second interferometric image and the calculation of the second evaluation value based on the second interferometric image (steps S11 and S12) are also described in the same way.

[0120] Reference Figure 9 The process described is as follows: A first interferometric image is obtained from the four interferometric images acquired in step S2, and a first evaluation value is calculated from the acquired first interferometric image (steps S3 and S4). This process is performed by the processing unit 5. First, four interferometric images are acquired (step S21). Next, the real part Re and the imaginary part Im of the first interferometric image are calculated (step S22). In step S22, a complex image is generated as Comp = Re + iIm. The real part Re corresponds to the real part image, and the imaginary part Im corresponds to the imaginary part image. Next, the amplitude image and phase image of the interference fringes are generated (step S23).

[0121] The amplitude image is calculated from the absolute value of the complex number, Abs(Comp), and the phase image is calculated from the deflection angle of the complex number, Arg(Comp). More specifically, if the complex image is denoted as Comp(x, y) = Re(x, y) + iIm(x, y) (where x and y are the coordinates within the image), then Abs(Comp(x, y)) = sqrt(Re(x, y)). 2 +Im (x, y) 2Arg(Comp(x, y)) = atan2(Re(x, y), Im(x, y)). Sqrt is a function that calculates the square root of the numerical value, and atan2 is a function that calculates the skew angle of the 2D vector of the given two independent variables as features. Next, the intra-image mean of the amplitude image Abs(Comp) is calculated as the first evaluation value (step S24).

[0122] Thus, in this example, one first interferometric image is obtained from four interferometric images. The difference in optical path length (phase shift interval) of the second light L2 between the four interferometric images is λ / 4. In this case, in step S22, the real part Re of the complex image is calculated from "I1-I3", and the imaginary part Im is calculated from "I4-I2". I1~I4 correspond to the four interferometric images obtained sequentially. This algorithm is called the "λ / 4 interval 4-point phase shift method" (Reference 1: "Field Guide to Interferometric Optical Testing", SPIEPress, ISBN 978-0-8194-6410-0, 2006, p. 36). λ / 4 can be replaced with π / 2 or 90°.

[0123] Reference Figure 10 The focusing adjustment processes in steps S6 and S14 will be explained. This process is performed by the processing unit 5. First, it is determined whether the first evaluation value f(a=front) is greater than the second evaluation value f(a=back) (step S31). If f(a=front) is greater than f(a=back) in step S31 (yes in step S31), the distance between the objective lens 13 and the object 8 is increased by multiplying the value of f(a=front) - f(a=back) by a predetermined coefficient (step S32). More specifically, in step S32, the actuator 16 is controlled to move the objective lens 13 away from the object 8 by that amount. If f(a=front) is less than or equal to f(a=back) in step S31 (no in step S31), the distance between the objective lens 13 and the object 8 is decreased by multiplying the value of f(a=back) - f(a=front) by the aforementioned coefficient (step S33). More specifically, in step S33, the actuator 16 is controlled by bringing the objective lens 13 close to the object 8 being observed by that amount.

[0124] Based on the processing described above, the focusing position of objective lens 13 is adjusted. Furthermore, in the above processing, while moving the stage S along the XY plane—that is, while changing the observation position of the object 8 to observe it (and acquiring the first and second interferometric images)—the focusing position of objective lens 13 is adjusted. In other words, focusing adjustment processing based on the first and second interferometric images is performed according to the movement of the stage S along the XY plane.

[0125] In this example, the observation positions relative to the observed object 8 along the XY plane are different between the first and second interferograms. That is, the first and second interferograms are obtained from different observation positions. Furthermore, in this description, for simplicity, the focus adjustment is presented as an optical adjustment, but the optical path length of the second light L2 can also be adjusted simultaneously with the focus adjustment. As described later, the adjustment of the optical path length of the second light L2 can be performed simultaneously with the focus adjustment based on a common evaluation value, or it can be performed based on a different evaluation value.

[0126] When the position of the reference mirror 15 is changed between the front and rear positions to obtain the first and second interference images, as in this example, the distortion of the interference fringes in the obtained interference images changes. However, because the focusing position of the objective lens 13 does not change, the S / N ratio decreases, but it can still be used as an interference image. The bowl-shaped distortion generated in the interference fringes can be corrected with simple processing.

[0127] Reference Figures 11-14 The focusing adjustment in the interferometric observation device 1 will be further explained. For example... Figure 11 As shown above, the thickness of the first layer 81 of the observed object 8 varies depending on the observation positions A, B, and C. Figure 12 As shown, in the interferometric observation device 1, because the absolute value of f(a=front) - f(a=back) (the absolute value of the difference between the first evaluation value and the second evaluation value) at position A, for example, is below a predetermined threshold, it is determined that no focusing adjustment is needed. This corresponds to the processing in steps S5 and S13 described above. This determination can be regarded as determining whether the gradient Δf(a) / Δa of the function f(a) at the corresponding position of the reference mirror 15 is greater than a predetermined value. Figure 12 In the diagram, "+Δa" indicates that reference mirror 15 is in the forward position ("a=forward"), and "-Δa" indicates that reference mirror 15 is in the backward position ("a=backward"). This point is related to... Figure 14 The same applies.

[0128] Similar to position A, because the absolute value of f(a=front) - f(a=back) is below a predetermined threshold at position B, for example, it is determined that no focus adjustment is needed. On the other hand, because the absolute value of f(a=front) - f(a=back) is greater than the predetermined threshold at position C, for example, it is determined that focus adjustment is needed. In this case, focus adjustment is performed (S6, S14). Thus, in the interferometric observation device 1, the need for focus adjustment (optical adjustment) is determined based on the gradient (differentiation) of the function f (optimization function), which is used to calculate the evaluation value based on the interferometric image. More specifically, focus adjustment is not performed when the gradient of the function f is small, and focus adjustment is performed when the gradient of the function f is large.

[0129] By performing this process, observation can be conducted while keeping the focusing position of objective lens 13 continuously aligned with the object surface R (while locking the focus). For example, as Figure 13 As shown, consider the case of interface C1 between layer 2 82 and layer 3 83. In this case, it is required to focus on interface C1 rather than interface C2 between layer 1 81 and layer 2 82. On the other hand, for example, as... Figure 14 As shown, in the function f(a), there is a case where the maximum value caused by interface C2 is greater than the maximum value caused by interface C1. In this case, if the function f(a) is maximized by simply moving the position of the reference mirror 15 significantly, the position of the reference mirror 15 may be adjusted to the position corresponding to the maximum value caused by interface C2. In contrast, in the focus adjustment process in the interferometric observation device 1, because the gradient (the difference between the first evaluation value and the second evaluation value) is obtained by moving the reference mirror 15 slightly, and focus adjustment is performed based on this gradient, the position of the reference mirror 15 can be continuously aligned with the position corresponding to the maximum value caused by interface C1 (focus locking).

[0130] [Another example of an action]

[0131] In the above example, during the movement of the reference mirror 15 between the front and rear positions, the stage S moves ( Figure 6 ), but if Figure 15 As shown in (a), after acquiring four interferometric images with the reference mirror 15 in the forward position and four interferometric images with the reference mirror 15 in the rear position, the stage S can be moved along the XY plane. In this case, similar to the example above, based on the four interferometric images in the first half and the four interferometric images in the second half, the difference between the first evaluation value and the second evaluation value is calculated, and focus adjustment processing is performed. In this case, for example, the processing steps S7 and S8 described above are omitted. As the interferometric images used as the observation results at each observation position, for example, an interferometric image constructed based on eight interferometric images can be used.

[0132] Alternatively, seven interferograms can be obtained while varying the phase at λ / 4 intervals. Interferograms numbered 1-4 are used as the first half of the interferograms, and interferograms numbered 4-7 are used as the second half, with the fourth interferogram being used collectively. In this case, the difference can be calculated by obtaining the first evaluation value from the first half of the interferograms and the second evaluation value from the second half of the interferograms, and can be calculated using the following... Figure 19 The λ / 4 interval 7-point phase shift method produces phase images that can be used as observation results at each observation position.

[0133] In addition, such as Figure 15As shown in (b), the acquisition of the first four interferometric images and the second four interferometric images can also be performed consecutively. In this case, the imaging efficiency can be improved.

[0134] In the example above, the first process consisting of steps S1 to S8 and the second process consisting of steps S9 to S16 are alternately and repeatedly executed, performing the process sequentially. However, it can also be done as follows: Figures 16-19 The process is performed in parallel. In this example, the processing unit 5 executes in parallel the first processing S40 (camera thread) related to camera capture, the second processing S50 (image processing thread) related to image processing, and the third processing S60 (motion calculation thread) related to motion calculation.

[0135] like Figure 16 As shown, in the first process S40, firstly, the processing unit 5 controls the piezoelectric element 19 to move the reference mirror 15 to the forward position (step S41). Next, the imaging element 4 captures four interference images corresponding to the first interference image, and the processing unit 5 acquires the first data corresponding to the four interference images from the imaging element 4 and stores the first data in the first storage area (FIFO to be processed) of the storage area 51 (step S42). Next, the processing unit 5 moves the stage S along the XY plane and moves the observation position of the observed object 8 to the next observation position (step S43).

[0136] Next, the processing unit 5 controls the piezoelectric element 19 to move the reference mirror 15 to the rear position (step S44). Then, the imaging element 4 captures four interference images corresponding to the second interference image, and the processing unit 5 acquires the second data corresponding to the four interference images from the imaging element 4 and stores the second data in the first storage area of ​​the storage area 51 (step S45). Next, the processing unit 5 moves the stage S along the XY plane, moving the observation position of the observed object 8 to the next observation position (step S46). After the execution of step S46, the processing unit 5 returns to the processing of step S41. Thus, in the first processing S40, the processing of steps S41-S43 is executed alternately, and the first data and the second data are sequentially stored in the first storage area of ​​the FIFO (First-In First-Out) memory to be processed. The first data and the second data are accompanied by information (flags) indicating which image was captured at the front or rear position.

[0137] like Figure 17As shown, in the second process S50, firstly, the processing unit 5 determines whether first data or second data is stored in the first storage area of ​​the storage area 51 (step S51). If it is determined in step S51 that first data or second data is stored in the first storage area (yes in step S51), the processing unit 5 generates a first interference image or a second interference image based on the first data or the second data by performing image processing (step S52). If it is determined in step S51 that first data or second data is not stored in the first storage area (no in step S51), the processing unit 5 executes the processing in step S51 again.

[0138] Following step S52, processing unit 5 stores the first or second interference image generated in step S52 in storage area 51 (step S53). Next, processing unit 5 calculates a first or second evaluation value based on the first or second interference image generated in step S52 (step S54). Then, processing unit 5 stores the first or second evaluation value calculated in step S54 in the second storage area (data list of evaluation values) of storage area 51 (step S55). After execution of step S55, processing unit 5 returns to the processing of step S51.

[0139] Through the above, in the second process S50, the following processes are executed alternately: generating a first interferometric image based on the first data obtained in the first process S40, and storing the first evaluation value corresponding to the first interferometric image in the second storage area of ​​storage area 51; and generating a second interferometric image based on the second data obtained in the first process S40, and storing the second evaluation value corresponding to the second interferometric image in the second storage area. The second storage area is, for example, a data list of evaluation values, and the first evaluation value and the second evaluation value are stored sequentially in the second storage area.

[0140] like Figure 18 As shown, in the third process S60, firstly, the processing unit 5 waits for the first evaluation value or the second evaluation value to be stored in the second storage area (data list of evaluation values) of the storage area 51 (step S61). If the first evaluation value or the second evaluation value is stored in the second storage area in step S61, the processing unit 5 determines whether the absolute value of f(a=before) - f(a=after) is greater than a threshold based on the previously obtained first evaluation value and second evaluation value (step S62). If the absolute value of f(a=before) - f(a=after) is greater than the predetermined threshold in step S62 (yes in step S62), the processing unit 5 performs a focus adjustment process corresponding to the above steps S6 and S14 (…). Figure 10The processing unit 5 sets the next movement of the objective lens 13 along the Z direction to a predetermined value (step S63). If the absolute value of f(a=front) - f(a=back) in step S62 is below the aforementioned threshold (no in step S62), the processing unit 5 sets the next movement of the objective lens 13 along the Z direction to zero (step S64). After the execution of step S63 or S64, the processing unit 5 returns to the processing of step S61. Through the above, in the third processing S60, whenever the first evaluation value or the second evaluation value is stored in the second storage area in the second processing S50, a focus adjustment process (optical adjustment process) is performed based on the previously obtained first evaluation value and second evaluation value.

[0141] The method for obtaining the first or second interferometric image is not limited to the method described in the example above; for example, it can also be used... Figure 19 The method is shown in the table. Figure 19 In the leftmost column, N indicates the number of interferograms used to construct the first or second interferogram.

[0142] In the method in line 1, either the first or second interferometer image is obtained based on a single interferometer image by spatial multiplexing using a micropolarizer array. In this case, the real part Re of the complex image is calculated by "I1-I3", and the imaginary part Im is calculated by "I4-I2". This algorithm is called "Micropolarizer Array, Phase-Shifting Interferometer" (Reference 1, page 44). In the method in line 2, either the first or second interferometer image is obtained based on a single interferometer image through spatial fringe analysis. In this case, the real part Re of the complex image is calculated by "LPF(I*cos(2πfx))", and the imaginary part Im is calculated by "LPF(I*sin(2πfx))". LPF is a spatial low-pass filter. This algorithm is called "Spatial Synchronous and Fourier Method" (Spatial Fringe Method) (Reference 1, page 43).

[0143] In the method of line 3, the first or second interferogram is obtained based on three interferograms. In this case, the real part Re of the complex image is calculated by “I1-I2”, and the imaginary part Im is calculated by “I3-I2”. This algorithm is called the “λ / 4 interval 3-point phase shift method” (Reference 1, page 36). In the method of line 4, the first or second interferogram is obtained based on three interferograms. In this case, the real part Re of the complex image is calculated by “I1-2I2+I3”, and the imaginary part Im is calculated by “Sqrt(3)*(I1-I3)”. This algorithm is called the “λ / 3 interval 3-point phase shift method” (Reference 2: “Interferogram Analysis for Optical Testing”, CRC Press, ISBN 978-0824799403, (2005), page 269). The method in line 5 is the “λ / 4 interval 4-point phase shift method” of the above example.

[0144] In the method in line 6, either the first or second interferometric image is obtained based on 5 interferometric images. In this case, the real part Re of the complex image is calculated by "-I1+2I3-I5", and the imaginary part Im is calculated by "2(I2-I4)". This algorithm is called the "Schwider-Hariharan 5-point phase shift method" (Reference 1, page 36). In the method in line 7, either the first or second interferometric image is obtained based on 7 interferometric images. In this case, the real part Re of the complex image is calculated by "-I2+4I4-2I6", and the imaginary part Im is calculated by "I1-3I3+3I5-I7". This algorithm is called the "λ / 4 interval 7-point phase shift method" (Reference 3: K. Hibino, BF Oreb, DI Farrant, and KG Larkin, "Phaseshifting for nonsinusoidal waveforms with phase-shift errors," J. Opt. Soc. Am. A 12, 761-768 (1995)). Thus, the method for obtaining the first and second interferograms is not limited; for example, the first or second interferogram can be obtained based on 1, 3, 4, 5, or 7 interferograms.

[0145] For example, in use Figure 19 In the case of the spatial fringe method shown, either the first or second interferometric image is obtained based on a single interferometric image. In this case, it is also possible to... Figure 20As shown, the imaging element 4 performs imaging to acquire one interference image when the reference mirror 15 is in the front position, and the imaging element 4 performs imaging to acquire one interference image when the reference mirror 15 is in the rear position.

[0146] In the example above, the focusing position of the objective lens 13 is adjusted while the stage S is moved along the XY plane, but if... Figure 21 As shown, focus adjustment (focus locking) can also be performed without moving the stage S (without changing the observation position along the XY plane). For example, if the object 8 has a nanostructure inside, consider how the nanostructure changes with temperature over time. In this case, the observation position is throughout the entire observation area and does not change from a specific position, but the focusing conditions are assumed to change due to the thermal expansion of the object 8. In this case, focus can also be locked after the initial adjustment, and the focus position can be continuously aligned on the object surface R of the target. In this case, the observation position relative to the object 8 along the XY plane is the same between the first and second interferograms. That is, the first and second interferograms are obtained from the same observation position.

[0147] Figure 22 Another example of the interferometric observation device 1A shown differs from interferometric observation device 1 in that it also includes a surface AF (Autofocus) section 6. The surface AF section 6 has an AF light source 61 for outputting light L6 and a beam splitter 62, for example, a dichroic mirror. Furthermore, while the light utilization efficiency may decrease, a non-wavelength selective semi-reflective mirror can also be used as the beam splitter 62. The beam splitter 62 splits the light L6 into two, and outputs one of the two split light L6 to the interferometric optical system 3. The light L6 output to the interferometric optical system 3 is reflected by the surface (outer surface) of the object being observed 8 and returns to the surface AF section 6 via the interferometric optical system 3 and the beam splitter 62. The surface AF section 6 detects the returned light, i.e., light L6, from the object being observed 8 and adjusts the relative distance between the objective lens 13 and the surface of the object being observed 8 based on this detection result. For example, the surface AF section 6 maintains the distance between the objective lens 13 and the object being observed 8 at a predetermined distance by moving the objective lens 13 in the Z direction using an actuator 16. In this way, the surface AF section 6 obtains the light L6 reflected from the surface of the object being observed 8 by the interferometric optical system 3, which is output from the AF light source 61. Based on the obtained result, the relative position between the objective lens 13 and the surface of the object being observed 8 is adjusted. The interferometric observation device 1A includes a filter 63, which is disposed between the beam splitter 12 and the reference objective lens 14 and blocks the light L6 reflected by the beam splitter 12.

[0148] In the interferometric observation device 1A, the optical path length of the second beam L2 can be adjusted simultaneously with the aforementioned focus adjustment (steps S6 and S14) based on the evaluation value shared with the focus adjustment. This point will be explained below.

[0149] like Figure 23 of (a), Figure 23 (b) and Figure 23 As shown in (c), assuming that the distance between the objective lens 13 and the object 8 is maintained at a constant level by the surface AF section 6, the thickness of the object 8 changes from d0 to d1. Figure 23 (a) shows the state where, relative to the object 8 with refractive index n1 and thickness d0, the focusing position of the objective lens 13 is on the surface (dashed line), and changes to the state where, as shown by the solid line, the distance between the objective lens 13 and the object 8 decreases by δd0, and the focusing position is on the back surface (solid line). Figure 23 (b) shows the change from the state where the focusing position of the objective lens 13 is on the surface (dashed line) relative to the object 8 with refractive index n1 and thickness d1, to the state where the distance between the objective lens 13 and the object 8 decreases by δd1, and the focusing position is on the back side (solid line), as shown by the solid line. Figure 23 (c) shows that the surface AF part 6 is self- Figure 23 The state shown in (b) is the state after adjusting the distance between the objective lens 13 and the object 8 being observed.

[0150] exist Figure 23 In (a), the distance between objective lens 13 and the object 8 is WD-δd0=WD-d0 / n1. At this time, the correction amount of the optical path length of the second light L2 is represented by (4) below. WD is the working distance of objective lens 13 in air.

[0151] [Number 4]

[0152]

[0153] exist Figure 23 In (c), the distance between the objective lens 13 and the object 8 after adjustment by the surface AF part 6 is WD-δd1=WD-d1 / n1. At this time, the adjustment amount of the optical path length of the second light L2 is represented by (5) below.

[0154] [Number 5]

[0155]

[0156] When the distance between the objective lens 13 and the object 8 is maintained at a constant level by means of the surface AF section 6, in the above-described steps S5 and S13, if the absolute value of f(a=front) - f(a=back) is greater than a predetermined threshold, both the focusing position of the objective lens 13 and the optical path length of the second light L2 are considered as the objects of optical adjustment. At this time, the adjustment amount Δz of the focusing position of the objective lens 13 is positive with respect to the direction in which the objective lens 13 approaches the object 8, and is expressed by equation (6).

[0157] [Number 6]

[0158]

[0159] The adjustment amount ΔOPD of the optical path length of the second beam L2 is positive with reference mirror 15 leaving the beam splitter 12, and is expressed by equation (7).

[0160] [Number 7]

[0161]

[0162] Therefore, in this case, as long as the ratio of the adjustment amount of the optical path length of the second light L2 to the adjustment amount of the focusing position of the objective lens 13 is n1 2 The ratio can be adjusted to -1:1. For example, if the first layer 81 of the observed object 8 is a glass layer (n=1.5), the ratio is 1.25:1; if the first layer 81 is a silicon layer (n=3.5), the ratio is 11.25:1.

[0163] As an example, when using the interferometric observation device 1A, in steps S32 and S33 above, when adjusting the distance between the objective lens 13 and the object 8 by multiplying the difference between the first evaluation value and the second evaluation value by a predetermined coefficient, the ratio of the adjustment amount of the optical path length of the second light L2 to the adjustment amount of the focusing position of the objective lens 13 (the distance between the objective lens 13 and the object 8) is n1. 2 The optical path length of the second beam L2 can be adjusted simultaneously using a ratio of -1:1. Therefore, the optical path length of the second beam L2 can be adjusted concurrently with the focus adjustment, based on a shared evaluation value.

[0164] Alternatively, the optical path length of the second beam L2 can be adjusted based on an evaluation value different from that for focus adjustment. In this case, the adjustment of the optical path length of the second beam L2 is not limited to the interferometric observation device 1A equipped with the surface AF section 6, and can be performed by the interferometric observation device 1 without the surface AF section 6. For example, if in step S31 f(a=front) is greater than f(a=back) (yes in step S31), the processing unit 5 extends the optical path length of the second beam L2 by multiplying the value of f(a=front) - f(a=back) by a predetermined coefficient (step S32). More specifically, in step S32, the stepper motors 17 and 18 are controlled such that the reference objective lens 14 and reference lens 15 move away from the beam splitter 12 by that amount. If in step S31 f(a=front) is less than or equal to f(a=back) (no in step S31), the optical path length of the second beam L2 is shortened by multiplying the value of f(a=back) - f(a=front) by the aforementioned coefficient (step S33). More specifically, in step S33, stepper motors 17 and 18 are controlled so that reference objective lens 14 and reference lens 15 are brought close to beam splitter 12 by that amount. Other processing is the same as for focus adjustment. Thus, the optical path length of the second beam L2 can be adjusted.

[0165] The focus adjustment in this case will be explained. Processing unit 5 uses the average value within the amplitude image Abs(Comp) as the first evaluation value or the second evaluation value, and calculates the curvature of the interference fringes in the phase image Arg(Comp) as the first evaluation value or the second evaluation value, and performs focus adjustment of objective lens 13 based on these first and second evaluation values. That is, in this case, processing unit 5 calculates the curvature of the interference fringes in the phase image as the first evaluation value or the second evaluation value in step S24. The method for calculating the curvature of the interference fringes based on the phase image will be described later. Other processing is the same as described above. Thus, the optical path length of the second light L2 and the focus adjustment of objective lens 13 can be performed. The adjustment of the optical path length of the second light L2 can be performed before or after focus adjustment, or it can be performed in parallel with focus adjustment.

[0166] Alternatively, instead of using only the amplitude or only the curvature of the interference fringes as indicators to set the first and second evaluation values, a new evaluation function can be adopted, using the linear sum or vector sum of the difference in amplitude and the difference in curvature of the interference fringes. This new evaluation function g(a, b) of the interference fringes becomes a bivariate function represented by both the optical path length a and the deviation b in the focusing of the first light L1 (object light) and the second light L2 (reference light). In this case, the differential of the evaluation value when only the optical path length of the reference light path (the optical path length of the second light L2) is moved is denoted as the partial differential of g(a, b) with respect to a, ∂g / ∂a, and the differential of the evaluation value when only the focusing of the reference light path is moved is denoted as the partial differential of g(a, b) with respect to b, ∂g / ∂b (Equation (8)). Furthermore, the gradient vector of the evaluation value is denoted as a 2-dimensional vector with ∂g / ∂a as the first element and ∂g / ∂b as the second element. When the gradient vector of the evaluation function is known, since the steepest descent method or the conjugate gradient method can be used to optimize parameters a and b towards the maximum value of the evaluation function, the optical path length of the second light L2 and the focusing of the objective lens 13 can be adjusted simultaneously based on the adjustment values ​​obtained using these optimization methods, or adjustments can be made at time intervals.

[0167] [Number 8]

[0168]

[0169] Furthermore, when only the reference mirror 15 of the reference optical path is moved, its effect contributes to both the change in optical path length and the change in focus relative to the evaluation function g(a, b). In this case, the optical path length mainly contributes to the amplitude of the interference fringes, and the bending amount mainly contributes to the bending of the interference fringes. Based on this, the optical path length of the second beam L2 and the focus of the objective lens 13 can be adjusted.

[0170] Reference Figure 24 This describes a method for calculating the curvature of interference fringes based on a phase image. For example, a method based on the correlation with a test image having an estimated curvature can be considered. As an example, reference 2 above describes a method for calculating the Zernike polynomial components of the wavefront from a phase image. The curvature of the interference fringes can be established with the components known as "Defocus" in the Zernike polynomial as described below (9).

[0171] [Number 9]

[0172]

[0173] For example, such as Figure 24As shown, the curvature of the interference fringes can be calculated based on the phase image by comparing the acquired phase image with test images having curvatures of +5.0, +10.0, +20.0, etc. However, the method for calculating the curvature from the interference fringes is not limited to this method.

[0174] In the above example, the reference mirror 15 is moved between the front and rear positions by the piezoelectric element 19 (steps S1 and S9). However, the reference mirror 15 can also be moved between the front and rear positions by the stepper motor 18 in steps S1 and S9. In this case, the stepper motor 18 can be configured to be driven in a micro-motion mode (first mode) and a coarse-motion mode (second mode). In micro-motion mode, the step angle (moving distance) of the stepper motor 18 is smaller than that in coarse-motion mode, allowing for micro-step driving, a higher pulse rate, and unrestricted inspection. In coarse-motion mode, the step angle (moving distance) of the stepper motor 18 is larger than that in micro-motion mode, preventing micro-step driving, resulting in a lower pulse rate and limited inspection. The processing unit 5 moves the reference mirror 15 between the front and rear positions by driving the stepper motor 18 in the first mode in steps S1 and S9, obtaining the first interference image and the second interference image (steps S3 and S11). On the other hand, the processing unit 5, after adjusting the determination results based on the first and second interferograms and the optical path length of the second light L2, moves the reference mirror 15 by driving the stepper motor 18 in the second mode. This process allows for optical adjustment in the same manner as described above. In this case, the piezoelectric element 19 can be omitted. This process is particularly effective when using a spatial fringe method that does not require moving the reference mirror 15 using the piezoelectric element 19.

[0175] [Application Examples of Optical Adjustment Processing]

[0176] Reference Figure 25 Examples of optical adjustment processing applications are explained. As a first application example, the initial adjustment of the interferometric observation apparatus 1 is given. Initial adjustment can also be applied to either surface observation or internal observation, adjusting the focusing position of the objective lens 13 and the optical path length of the second beam L2. Because micrometer-level displacement may occur in the housing H of the optical module M due to temperature changes or annual variations, it is advisable to perform initial adjustment periodically (e.g., approximately once a week). Figure 25 In the table, "〇" is displayed when the adjustment is performed using the optical adjustment method based on the first and second interference images described above; "Additionally" is displayed when the adjustment is performed using a method other than the optical adjustment method; and "-" is displayed when no adjustment is performed.

[0177] In the initial adjustment, firstly, the focusing position of objective lens 13 is aligned with the object surface R. This focusing adjustment can be performed using methods such as contrast AF. Contrast AF refers to a method that scans the focal position across the entire optical axis of the object 8 while acquiring multiple interference images, and uses the point with the largest contrast evaluation function of the interference images as the focal position. Next, processing unit 5 uses the average value within the amplitude image as the first evaluation value or the second evaluation value to perform optical adjustment processing to adjust the optical path length (reference optical path length) of the second light L2. Next, processing unit 5 uses the curvature of the interference fringes in the phase image as the first evaluation value or the second evaluation value to adjust the distance between reference objective lens 14 and reference lens 15 (reference-side focusing). More specifically, in this case, stepper motors 17 and 18 are controlled such that the distance between reference objective lens 14 and reference lens 15 is the target distance. Either the adjustment of the optical path length of the second light L2 or the adjustment of the reference-side focusing can be performed first. In the case of the initial adjustment, stage S does not move along the XY plane.

[0178] As a second application example, consider Figure 26 The surface observation is shown. In the case of surface observation, only the focusing position of objective lens 13 needs to be adjusted. Through the above processing ( Figure 5 The focusing position of objective lens 13 can be adjusted. When observing a surface, the focusing position is adjusted while moving the stage S along the XY plane.

[0179] like Figure 27 As shown, in the case of surface observation, the calculation of the first and second evaluation values ​​and the adjustment of the focus position can also be performed separately. For example, in Figure 27 In the example shown, the first and second evaluation values ​​are calculated and the focus position is adjusted every three changes in observation position (field of view) (in this example, this is only done in fields of view #3, #6, #9...).

[0180] In the case of surface observation, the stage S can be driven at a certain speed instead of the method of repeatedly moving and stopping (Stop and Go) as in the example above. That is, in the example above, focus adjustment is performed every time the stage S moves once, but it can also be done as follows: Figure 27As shown in the example, focus adjustment is performed every predetermined number of times the stage S moves, or focus adjustment can be performed while the stage S is continuously moved, as in this example. In either case, the processing unit 5 performs optical adjustment processing based on the first and second interferometric images according to the movement of the stage S along the XY plane. Furthermore, when performing focus adjustment while continuously moving the stage S, it is preferable to use a "Micropolarizer Array, Phase-Shifting Interferometer" or "Spatial Synchronous and Fourier Method" to obtain the first and second interferometric images based on one interferometric image. In addition, in order to suppress the overlap of motion artifacts on the interferometric images, it is preferable to pulse-drive the light source 2.

[0181] like Figure 28 As shown, in situations such as unstable temperature environments, or when the optical path length of the reference side focusing or the second beam L2 may change during observation, the initial adjustment process described above can be combined with the surface observation process. For example, Figure 28 As shown in the example, when observing the object 8 in a zigzag XY scan, initial adjustments can be made in the initial fields of view (fields of view #1, #7, #15, etc.) at each row. Contrast AF requires time, but by performing it intermittently as in this example, the impact on operation time can be suppressed. In other fields of view, the focusing position of the objective lens 13 based on the first and second interferometric images can be adjusted according to the surface observation process. Furthermore, the fields of view for initial adjustments can be selected from those that facilitate contrast AF, such as the edges of the object 8.

[0182] That is, when the process of optical adjustment based on the first and second interference images is defined as the fine adjustment process, and the process of adjusting the focus position of the objective lens 13 by contrast AF is defined as the focus position adjustment process, in the above example, as the object 8 moves along the XY plane, the fine adjustment process or the focus position adjustment process is performed according to the observation position relative to the object 8 along the XY plane. As described above, in the focus position adjustment process (contrast AF), when the direction in which the first light L1 is incident on the object 8 is defined as the incident direction, the focus position of the objective lens 13 is scanned across the entire object 8 along the incident direction while acquiring multiple interference images, and the focus position is adjusted based on the acquired results.

[0183] Refer again Figure 25As a third application example, consider internal observation. In the case of internal observation, both the focusing position of the objective lens 13 and the optical path length of the second beam L2 are adjusted. In this case, as described above, an interferometric observation device 1A equipped with the surface AF section 6 can also be used to adjust the focusing position of the objective lens 13 and the optical path length of the second beam L2 based on a common evaluation value. Alternatively, the average value within the amplitude image can be used as the first or second evaluation value to perform optical adjustment processing for adjusting the optical path length of the second beam L2, and the amount of curvature of the interference fringes in the phase image can be used as the first or second evaluation value to perform optical adjustment processing for adjusting the focusing position of the objective lens 13. The optical adjustment processing for adjusting the optical path length of the second beam L2 and the optical adjustment processing for adjusting the focusing position of the objective lens 13 can be performed each time the field of view is moved (the observation position changes). Alternatively, they can be performed alternately, with only one performed in the odd-numbered fields of view and only the other in the even-numbered fields of view.

[0184] Examples of internal observation include, in addition to the case where the object 8 being observed is a semiconductor device with a cover, as in the example above, observing the semiconductor device through a transparent resin cover, observing the semiconductor device through a glass window, observing the semiconductor device through a semiconductor cover (in which case the light source 2 outputs infrared light), observing the back side of the semiconductor device (in which case the light source 2 outputs infrared light), observing the bonding surface in a laminated wafer (in which case the light source 2 outputs infrared light), observing the pores in the bonding surface in a laminated wafer, observing the joint or bonding surface between glass and resin, observing the laser-processed surface in a component made of glass, resin, or semiconductor, and observing internal defects in a liquid crystal panel.

[0185] As a fourth application example, consider the adjustments made when changing objective lens 13. For example, in Figure 29 In the example shown, objective lens 13 is replaceably mounted in housing H, with one objective lens 13 selected from a plurality of objective lenses 13 (three in this example) with different magnifications mounted in housing H. In such a structure, when objective lens 13 is replaced to change the observation magnification, optical adjustment can be performed quickly and with good accuracy by performing the optical adjustment based on the first and second interferograms as described above.

[0186] like Figure 30As shown, during the adjustment when changing objective lens 13, firstly, objective lens 13 is replaced (step S71). Next, the focusing position of objective lens 13 is aligned with the object surface R. This focusing adjustment can be performed using an adjustment method such as contrast AF (step S72). In parallel with steps S71 and S72, processing unit 5 controls stepper motors 17 and 18 to adjust the optical path length of the second light L2 by the nominal offset of objective lens 13 (step S73) (coarse adjustment). Following steps S72 and S73, processing unit 5 uses the average value within the amplitude image as the first evaluation value or the second evaluation value to perform optical adjustment processing for adjusting the optical path length of the second light L2 (fine adjustment).

[0187] The nominal offset of objective lens 13 refers to the value of the optical path length of the second beam L2, which needs to be corrected according to the different optical path lengths of each objective lens 13, and is determined in advance. However, micrometer-level errors may occur due to changes in the objective lens over time, temperature environment, mechanical errors in the mounting part of the objective lens, etc. Therefore, adjusting only the nominal offset may not yield optimal interference fringes. When a connector is mounted on objective lens 13, the contribution of the connector is also taken into account when setting the nominal offset.

[0188] like Figure 31 As shown, the coupling 13a can also be mounted on at least any one of the plurality of objectives 13. For example, when changing objectives 13, in addition to changes in magnification, the case of changing from a dry objective to an immersion objective (immersion in water, etc.) is also considered. The resolution of the interference observation is determined by the smaller NA of the objective 13 and the reference objective 14. Therefore, the magnification of the reference objective 14 is preferably the same as the magnification of the objective with the highest NA among the plurality of objectives 13. For example, if the plurality of objectives 13 have magnifications of 20X, 10X, and 5X respectively, since the magnification of the objective 13 with the highest NA is 20X, the magnification of the reference objective 14 is preferably 20X.

[0189] Furthermore, in general, even at the same magnification, the NA of a liquid-immersed objective is higher than that of a dry objective. For example, the typical values ​​for a 10X objective are NA=0.25 for the dry type and NA=0.30 for the liquid-immersed type. In this case, if the reference objective 14 is a 10X dry type, then the high resolution of the 10X liquid-immersed objective 13 cannot be utilized. Therefore, it is preferable to set the reference objective 14 to 20X with NA=0.40.

[0190] To shorten the travel distance of the stepper motors 17 and 18 during adjustment when changing objective lenses 13, couplings 13a corresponding to the magnification can be installed on multiple objective lenses 13. The coupling 13a can be a hollow component for extending the optical path length, or a component with a plate containing a transparent dielectric inside. Generally, in 5X, 10X, and 20X objective lenses, since the optical path length in the lens increases in the order 5X < 10X < 20X, by setting the optical path length of the coupling 13a to the opposite order of 5X > 10X > 20X, the travel distance of the stepper motors 17 and 18 during adjustment when changing objective lenses 13 can be shortened. Preferably, the coupling 13a is mechanically connected or bonded to the objective lens 13, allowing for integral disassembly and installation when changing objective lenses 13.

[0191] Refer again Figure 25 As a fifth application example, we consider the adjustment of the lens barrel's mechanical error. For example... Figure 32 As shown, there are cases where the conjugate surface 4b of the imaging surface 4a of the imaging element 4 deviates from the focusing position of the objective lens 13 due to subtle manufacturing errors in the imaging element 4 or the lens barrel 42. This deviation is usually around a few micrometers, but it is a non-negligible size in interferometric observation. Even in this case, the conjugate surface 4b of the imaging surface 4a can be aligned with the focusing position of the objective lens 13 through the optical adjustment process based on the first and second interferometric images described above. The process for adjusting the lens barrel malfunction is the same as the initial adjustment. However, when adjusting the lens barrel malfunction, because the conjugate surface 4b of the imaging surface 4a is offset, it is effective to move only the reference mirror 15 by the stepper motor 18 while keeping the position of the reference objective lens 14 fixed.

[0192] [Functions and Effects]

[0193] The interference observation apparatus 1 includes: a light source 2 that outputs light; an interference optical system 3 having a movable reference mirror 15 that splits the light output from the light source 2 into a first light L1 and a second light L2, and outputs an interference light L3 consisting of the first light L1 reflected by the object under observation 8 and the second light L2 reflected by the reference mirror 15; an imaging element 4 that detects the interference light L3; and a processing unit 5 that acquires an interference image based on the detection result of the interference light L3 and performs optical adjustment processing for optical adjustments related to the observation of the object under observation 8. The processing unit 5 acquires a first interference image and a second interference image with different optical path length differences between the first light L1 and the second light L2 by changing the optical path length of the second light L2, and performs optical adjustment processing based on the first interference image and the second interference image.

[0194] In the interferometric observation apparatus 1, optical adjustment processing is performed on the first and second interferometric images, which have different optical path length differences due to changes in the optical path length of the second light L2. Therefore, optical adjustment can be performed at high speed and with good accuracy. In particular, compared to the case where the focal position of the scanning objective lens 13 is only applied to the entire thickness direction of the object under observation 8, optical adjustment can be performed at high speed and with good accuracy. For example, when scanning the object under observation 8 throughout the Z direction for contrast AF, a large amount of noise remains in the detection results over a period of several hundred msec. Therefore, it is difficult to achieve high speed and is unsuitable for, for example, online measurements. In contrast, in the interferometric observation apparatus 1, optical adjustment can be performed at high speed and with good accuracy, and it can also be suitable for online measurements.

[0195] The processing unit 5 performs optical adjustment processing on the calculated evaluation values ​​(first evaluation value and second evaluation value) of the first and second interferograms (steps S4 and S12), based on the evaluation values ​​of the first and second interferograms. This allows for appropriate optical adjustment processing.

[0196] The processing unit 5 performs optical adjustment processing based on the difference between the evaluation value calculated based on the first interferometric image, i.e., the first evaluation value, and the evaluation value calculated based on the second interferometric image, i.e., the second evaluation value (steps S5 and S12). As a result, optical adjustment processing can be performed appropriately.

[0197] After acquiring the second interference image, the processing unit 5 performs optical adjustment if the absolute value of the difference is greater than a predetermined value, and does not perform optical adjustment if the absolute value of the difference is less than the predetermined value (steps S5 and S12). Thus, optical adjustment processing can be performed appropriately.

[0198] When the processing unit 5 performs optical adjustment after acquiring the second interference image, it performs optical adjustment based on the magnitude relationship between the first evaluation value and the second evaluation value (steps S31 to S33). As a result, the optical adjustment processing can be performed appropriately.

[0199] When the processing unit 5 performs optical adjustment after acquiring the second interference image, it performs optical adjustment by an amount corresponding to the magnitude of the difference between the first evaluation value and the second evaluation value (steps S32 and S33). As a result, the optical adjustment processing can be performed appropriately.

[0200] The processing unit 5 calculates a first evaluation value or a second evaluation value based on the amplitude image corresponding to the first or second interferometric image (step S24). Thus, an evaluation value can be appropriately calculated.

[0201] Processing unit 5 can also calculate and evaluate the curvature of interference fringes in the phase image corresponding to the first or second interference image. Figure 24In this case, an evaluation value may also be appropriately calculated.

[0202] The processing unit 5 changes the optical path length of the second light L2 by moving the reference mirror 15, thereby obtaining a first interference image and a second interference image with different optical path length differences. Thus, the first interference image and the second interference image can be appropriately obtained.

[0203] Between the first and second interferograms, the change in the optical path length of the second light L2 differs by a value larger than the wavelength of the light output from the light source 2. Therefore, appropriate optical adjustment can be performed.

[0204] The optical adjustments performed in the interferometric observation apparatus 1 include adjusting the relative position between the objective lens 13 and the object being observed 8. This allows for adjustment of the relative position between the objective lens 13 and the object being observed 8.

[0205] The optical adjustment involves moving the reference mirror 15 to adjust the optical path length of the second beam L2. Thus, the optical path length of the second beam L2 can be adjusted.

[0206] This optical adjustment includes adjusting the position of the reference objective lens 14. Thus, the position of the reference objective lens 14 can be adjusted.

[0207] Between the first and second interferograms, the observation position relative to the object 8 along the XY plane (the plane intersecting the direction of the first light L1 incident on the object 8) can also be the same. Figure 21 In this case, optical adjustments can be made based on the first and second interferometric images obtained from the same observation position.

[0208] Between the first and second interferometric images, the observation position relative to the observed object 8 along the XY plane can also be different. Figure 5 In this case, optical adjustments can be made based on the first and second interferometric images obtained from different observation positions.

[0209] The processing unit 5 performs optical adjustment processing based on the first and second interference images according to the movement of the stage S along the XY plane. Thus, the observation position can be changed by moving the object 8 while performing optical adjustments.

[0210] The processing unit 5 performs optical adjustment processing to adjust the relative position between the objective lens 13 and the object 8 based on the first and second interference images, according to the movement of the stage S along the XY plane. Thus, the observation position can be changed by moving the object 8 while adjusting the relative position between the objective lens 13 and the object 8.

[0211] Processing unit 5 alternately executes the first process (steps S1-S8) and the second process (steps S9-S16). In the first process, processing unit 5 acquires a first interference image (step S2), performs optical adjustment processing based on the first interference image and the second interference image acquired in the previous second process (steps S5 and S6), and moves the stage S along the plane (step S7). In the second process, processing unit 5 acquires a second interference image (step S10), performs optical adjustment processing based on the second interference image and the first interference image acquired in the previous first process (steps S13 and S14), and moves the stage S along the plane (step S15). Thus, optical adjustment processing can be performed through successive processes.

[0212] The processing unit 5 may also execute the first process S40, the second process S50, and the third process S60 in parallel. In the first process S40, the processing unit 5 alternately executes the following processes: acquiring first data from the imaging element 4 for generating the first interference image, storing the first data in the first storage area of ​​the storage area 51 (step S42), and moving the stage S along the XY plane (step S43); and acquiring second data from the imaging element 4 for generating the second interference image, storing the second data in the first storage area (step S45), and moving the stage S along the XY plane (step S44). In the second process S50, the processing unit 5 alternately performs the following processes: generating a first interference image based on the first data obtained in the first process S40 (step S52), and storing the first evaluation value corresponding to the first interference image in the second storage area of ​​the storage area 51 (steps S54, S55); and generating a second interference image based on the second data obtained in the first process S40 (step S52), and storing the second evaluation value corresponding to the second interference image in the second storage area (steps S54, S55). In the third process S60, whenever the first evaluation value or the second evaluation value is stored in the second storage area in the second process S50 (step S61), the processing unit 5 performs optical adjustment processing based on the previously obtained first evaluation value and second evaluation value. In this case, the optical adjustment processing can be performed in parallel.

[0213] The processing unit 5 moves the reference mirror 15 by using the piezoelectric element 19, thereby changing the optical path length of the second light L2, and obtains a first interference image and a second interference image with different optical path length differences. Optical adjustments are then performed using stepper motors 17 and 18. Thus, optical adjustment processing can be performed using the piezoelectric element 19 and the stepper motors 17 and 18. Because the piezoelectric element 19 has a longer lifespan than the stepper motor 18, obtaining the first and second interference images using the piezoelectric element 19 can extend the lifespan of the device.

[0214] The stepper motor 18 can also be driven in a fine-motion mode (first mode) and a coarse-motion mode (second mode) with a step angle greater than that of the fine-motion mode. In this case, the processing unit 5 drives the stepper motor 18 in fine-motion mode to move the reference mirror 15, thereby changing the optical path length of the second light L2, thus obtaining a first interference image and a second interference image with different optical path length differences, and performs optical adjustment by driving the stepper motor 18 in coarse-motion mode. In this case, optical adjustment processing can be performed using the stepper motor 18, and the structure of the device can be simplified.

[0215] The stepper motors 17 and 18 used for optical adjustment processing can also be other types of motors with a resolution of 1 micrometer to several micrometers. Examples of other types of motors include geared motors with large reduction ratios or servo motors.

[0216] The interferometric observation apparatus 1A includes a surface AF section 6. The surface AF section 6 has an AF light source 61 that outputs light L6. The interferometric optical system 3 acquires the light L6 output from the AF light source 61 and reflected by the surface of the object being observed 8. Based on the acquired result, the relative position between the objective lens 13 of the interferometric optical system 3 and the surface of the object being observed 8 is adjusted. In this case, the relative position between the objective lens 13 and the surface of the object being observed 8 can be adjusted by the surface AF section 6.

[0217] In the interferometric observation apparatus 1A equipped with the surface AF section 6, the processing unit 5 performs optical adjustment processing for adjusting the relative position between the objective lens 13 and the object under observation 8, and optical adjustment processing for adjusting the optical path length of the second light L2 by moving the reference mirror 15, based on the first interference image and the second interference image, according to the movement of the stage S along the XY plane. Thus, optical adjustment processing for adjusting the relative position between the objective lens 13 and the object under observation 8, and optical adjustment processing for adjusting the optical path length of the second light L2, can be performed while the object under observation 8 is being moved.

[0218] In the optical adjustment method using the interferometric observation device 1, a first interference image and a second interference image (surface observation) can also be obtained based on the detection results of the interference light between the first light L1 reflected from the surface of the observed object 8 and the second light L2 reflected by the reference mirror 15. Thus, optical adjustment can be performed in the case of surface observation where the surface of the observed object 8 is observed.

[0219] In the optical adjustment method, a first interference image and a second interference image (internal observation) can also be obtained based on the detection results of the interference light of the first light L1 reflected inside the object 8 and the second light L2 reflected by the reference mirror 15. Thus, optical adjustment can be performed in the case of internal observation to observe the inside of the object 8.

[0220] In optical adjustment methods, optical adjustment processing can also be performed based on the first interference image and the second interference image, according to the movement of the observed object 8 along the XY plane. In this case, optical adjustment processing can be performed while the observed object 8 is being moved.

[0221] In the optical adjustment method, when changing the objective lens 13, optical adjustment processing can also be performed based on the first interference image and the second interference image to adjust the optical path length of the second light L2 by moving the reference mirror 15 (adjustment when changing the objective lens 13). Thus, optical adjustment can be performed when changing the objective lens 13.

[0222] [Variation Example]

[0223] This disclosure is not limited to the examples described above. For instance, various materials and shapes may be used for the materials and shapes of the structures, not limited to those described above.

[0224] In the above example, the first and second interference images are obtained by changing the optical path length of the second light L2 by moving the reference mirror 15. However, the first and second interference images can also be obtained by changing the optical path length of the second light L2 by moving the objective lens 13. In the above example, optical adjustment processing is performed based on two interference images, the first and second interference images. However, optical adjustment processing can also be performed based on three or more interference images.

[0225] In steps S32 and S33 of the above example, the value of the distance change f(a=front) - f(a=back) between the objective lens 13 and the observed object 8 is multiplied by a specified coefficient. However, it is only necessary to make the distance change positively correlated with the value of f(a=front) - f(a=back). The relationship between the value of f(a=front) - f(a=back) and the change is not limited to a proportional relationship.

[0226] The evaluation value based on the amplitude image (either the first or second evaluation value) is not limited to the intra-image average of the amplitude image, but can also be other values ​​calculated based on the amplitude image. Similarly, the evaluation value based on the phase image is not limited to the curvature of the interference fringes in the phase image, but can also be other values ​​calculated based on the phase image. Evaluation values ​​can be calculated based on both the amplitude and phase images. Between the first and second interference images, the optical path length of the second light L2 can differ from a value smaller than the wavelength of the light output from the light source 2. In this case, optical adjustment processing can be performed in the same manner as in the example described above.

[0227] In the example above, the relative position between the objective lens 13 and the object 8 is adjusted by moving the objective lens 13 along the Z direction using the actuator 16. However, alternatively, or in addition to this, the relative position can also be adjusted by moving the stage S along the Z direction. In this case, the stage S is configured to move in the Z direction in addition to the XY direction. In this case, the actuator 16 can also be omitted. The stage S can move in a direction that intersects the direction in which the first light L1 is incident on the object 8, for example, it can move in a direction that is tilted relative to the XY plane. The actuator that drives the reference objective lens 14 and the reference mirror 15 is not limited to stepper motors 17 and 18, but can also be other actuators such as servo motors.

[0228] In the processes of calculating the first evaluation value based on the first interferometric image (step S4) and calculating the second evaluation value based on the second interferometric image (step S12), image processing can also be performed within a subroutine that specifies the evaluation value after spatially separating the interferometric images (low-resolution processing). By generating an interferometric image for inspection using a high-resolution image and calculating the evaluation value from the separated images, image processing can be accelerated.

[0229] In the above example, the interferometric optical system 3 is configured as a Linnicke interferometer, but the interferometric optical system 3 (interferometric observation device 1) can also be configured as a Michelson interferometer or a Mirau interferometer. The reference objective lens 14 can also be omitted.

[0230] Explanation of symbols

[0231] 1, 1A…interference observation device, 2…light source, 3…interference optical system, 4…image sensor, 5…processing unit, 6…surface AF unit, 61…AF light source, 8…observation object, 13…objective lens, 14…reference objective lens, 15…reference mirror, 18…stepper motor, 19…piezoelectric element, 51…storage area, L1…first light, L2…second light, L3…interference light, L6…light, S…stage, S40…first processing, S50…second processing, S60…third processing.

Claims

1. An interferometric observation device, wherein, have: A light source, which outputs light; An interference optical system having a movable reference mirror, splitting light output from the light source into a first light and a second light, and outputting interference light of the first light reflected by the observed object and the second light reflected by the reference mirror; The imaging element detects the interference light; and The processing unit acquires an interference image based on the detection result of the interference light and performs optical adjustment processing for optical adjustments related to the observation of the object being observed. The processing unit obtains multiple interference images with different optical path length differences between the first and second lights by changing the optical path length of the second light, and performs the optical adjustment processing based on the multiple interference images.

2. The interferometric observation device as described in claim 1, wherein, The processing unit performs optical adjustment processing based on the calculated evaluation values ​​of the multiple interferometric images.

3. The interferometric observation device as described in claim 2, wherein, The multiple interference images include a first interference image and a second interference image, each with a different optical path length difference. The processing unit performs the optical adjustment processing based on the difference between a first evaluation value, which is an evaluation value calculated based on the first interference image, and a second evaluation value, which is an evaluation value calculated based on the second interference image.

4. The interferometric observation device as described in claim 3, wherein, After obtaining the first interferometric image, the second interferometric image is obtained. After acquiring the second interference image, the processing unit performs the optical adjustment if the absolute value of the difference is greater than a predetermined value, and does not perform the optical adjustment if the absolute value of the difference is less than the predetermined value.

5. The interferometric observation device as described in claim 4, wherein, When the processing unit performs the optical adjustment after acquiring the second interference image, it performs the optical adjustment based on the magnitude relationship between the first evaluation value and the second evaluation value.

6. The interferometric observation apparatus as described in claim 4 or 5, wherein, When the processing unit performs the optical adjustment after acquiring the second interference image, it performs the optical adjustment by an amount corresponding to the magnitude of the difference between the first evaluation value and the second evaluation value.

7. The interferometric observation apparatus as described in any one of claims 2 to 6, wherein, The processing unit calculates the evaluation value based at least on the amplitude image corresponding to the interference image.

8. The interferometric observation apparatus as described in any one of claims 2 to 7, wherein, The processing unit calculates the evaluation value based at least on the amount of curvature of the interference fringes in the phase image corresponding to the interference image.

9. The interferometric observation apparatus as described in any one of claims 1 to 8, wherein, The processing unit changes the optical path length of the second light by moving the reference mirror, thereby obtaining multiple interference images with different optical path length differences.

10. The interferometric observation apparatus according to any one of claims 1 to 9, wherein, Between the multiple interference images, the change in the optical path length of the second light differs by a value that is larger than the wavelength of the light output from the light source.

11. The interferometric observation apparatus according to any one of claims 1 to 10, wherein, The interference optical system also has an objective lens. The optical adjustment includes adjusting the relative position between the objective lens and the object being observed.

12. The interferometric observation apparatus according to any one of claims 1 to 11, wherein, The optical adjustment includes moving the reference mirror to adjust the optical path length of the second light.

13. The interferometric observation apparatus according to any one of claims 1 to 12, wherein, The interference optical system also includes a reference objective lens that guides the second light towards the reference mirror. The optical adjustment includes adjusting the position of the reference objective lens.

14. The interferometric observation apparatus according to any one of claims 1 to 13, wherein, Among the multiple interference images, the observation positions relative to the object are the same along the plane that intersects the direction of the first light incident on the object.

15. The interferometric observation apparatus according to any one of claims 1 to 13, wherein, Among the multiple interference images, the observation positions relative to the object of observation are different along the plane that intersects the direction of the first light incident on the object of observation.

16. The interferometric observation apparatus according to any one of claims 1 to 15, wherein, It also includes: a stage for positioning the object of observation, which is movable at least along a plane intersecting the direction in which the first light is incident on the object of observation. The processing unit performs the optical adjustment processing based on the multiple interferometric images according to the movement of the stage along the plane.

17. The interferometric observation apparatus as claimed in claim 16, wherein, The interference optical system also has an objective lens. The processing unit performs optical adjustment processing based on the multiple interference images, according to the movement of the stage along the plane, to adjust the relative position between the objective lens and the object being observed.

18. The interferometric observation apparatus as described in any one of claims 1 to 17, wherein, It also includes: a stage for positioning the object of observation, which is movable at least along a plane intersecting the direction in which the first light is incident on the object of observation. The multiple interference images include a first interference image and a second interference image, each with a different optical path length difference. The processing unit alternately performs the first processing and the second processing. Here, in the first process, the processing unit acquires the first interferometric image, performs the optical adjustment process based on the first interferometric image and the second interferometric image acquired in the previous second process, and moves the stage along the plane. In the second process, the processing unit acquires the second interference image, performs the optical adjustment process based on the second interference image and the first interference image acquired in the previous first process, and moves the stage along the plane.

19. The interferometric observation apparatus according to any one of claims 1 to 17, wherein, It also has: A stage for arranging the object of observation, capable of moving at least along a plane intersecting the direction in which the first light is incident on the object of observation; and Storage area 1 and storage area 2 The multiple interference images include a first interference image and a second interference image, each with a different optical path length difference. The processing unit executes the first, second, and third processes in parallel. Here, in the first process, the processing unit alternately executes: a process of acquiring first data from the imaging element for generating the first interference image, storing the first data in the first storage area, and then moving the stage along the plane; and a process of acquiring second data from the imaging element for generating the second interference image, storing the second data in the first storage area, and then moving the stage along the plane. In the second process, the processing unit alternately performs: generating the first interferogram based on the first data obtained in the first process, and storing the first evaluation value corresponding to the first interferogram in the second storage area; and generating the second interferogram based on the second data obtained in the first process, and storing the second evaluation value corresponding to the second interferogram in the second storage area. In the third process, whenever the first evaluation value or the second evaluation value is stored in the second storage area in the second process, the processing unit performs the optical adjustment process based on the previously obtained first evaluation value and the second evaluation value.

20. The interferometric observation apparatus according to any one of claims 1 to 19, wherein, It also has: A piezoelectric element for moving the reference mirror; and A motor, which is used to move the optically adjusted object. The processing unit moves the reference mirror by using the piezoelectric element to change the optical path length of the second light, obtains multiple interference images with different optical path length differences, and performs the optical adjustment using the motor.

21. The interferometric observation apparatus according to any one of claims 1 to 19, wherein, It also includes: a stepper motor for moving the reference mirror. The stepper motor can be driven in a first mode and a second mode with a step angle greater than that of the first mode. The processing unit drives the stepper motor in the first mode, thereby moving the reference mirror and changing the optical path length of the second light, thereby obtaining the multiple interference images with different optical path length differences, and performs the optical adjustment by driving the stepper motor in the second mode.

22. The interferometric observation apparatus according to any one of claims 1 to 21, wherein, The interference optical system also has an objective lens. The interferometric observation device further includes: a surface AF section having an AF light source for outputting light, which acquires light output from the AF light source and reflected by the surface of the object being observed via the interferometric optical system, and adjusts the relative position between the objective lens of the interferometric optical system and the surface of the object being observed based on the acquired result.

23. The interferometric observation apparatus as described in claim 22, wherein, It also includes: a stage for positioning the object of observation, which is movable at least along a plane intersecting the direction in which the first light is incident on the object of observation. The processing unit performs optical adjustment processing to adjust the relative position between the objective lens and the object being observed, and optical adjustment processing to adjust the optical path length of the second light by moving the reference mirror, based on the multiple interference images, according to the movement of the stage along the plane.

24. An optical adjustment method, wherein, It is an optical adjustment method used in interferometric observation devices to make optical adjustments related to the observation of the object being observed. The interferometric observation device includes: a light source that outputs light; An interference optical system comprising a movable reference mirror that splits light output from the light source into a first beam and a second beam, and outputs an interference beam consisting of the first beam reflected by the observed object and the second beam reflected by the reference mirror; and an imaging element that detects the interference beam. The interference observation device obtains an interference image based on the detection result of the interference light. The optical adjustment method includes the steps of obtaining multiple interference images with different optical path length differences between the first light and the second light by changing the optical path length of the second light, and performing optical adjustment processing for the optical adjustment based on the multiple interference images.

25. The optical adjustment method as described in claim 24, wherein, In the process, the multiple interference images are obtained based on the detection results of the interference light between the first light reflected by the surface of the observed object and the second light reflected by the reference mirror.

26. The optical adjustment method as described in claim 24, wherein, In the process, the multiple interference images are obtained based on the detection results of the interference light between the first light reflected from the interior of the observed object and the second light reflected by the reference mirror.

27. The optical adjustment method according to any one of claims 24 to 26, wherein, In the process, the observation position relative to the observation object along the plane is changed by moving the object along the plane, which intersects the direction of the first light incident on the object. Based on the movement of the object along the plane, the optical adjustment process is performed on the multiple interference images.

28. The optical adjustment method according to any one of claims 24 to 27, wherein, The interference optical system also features replaceable objectives. In the process described above, when the objective lens is replaced, an optical adjustment process is performed based on the multiple interference images to adjust the optical path length of the second light by moving the reference mirror.

29. The optical adjustment method according to any one of claims 24 to 28, wherein, The process of obtaining multiple interference images with different optical path length differences between the first and second rays by varying the optical path length of the second ray, and then performing optical adjustment processing based on these multiple interference images for optical adjustment, is designated as the fine adjustment process. The process of taking the direction in which the first light is incident on the object being observed as the incident direction, scanning the focal position of the objective lens across the entire object along the incident direction, acquiring multiple interference images, and adjusting the focal position based on the acquired results is defined as the focal position adjustment process. As the object being observed moves along a plane intersecting the incident direction, the fine-tuning process or the focal position adjustment process is performed based on the observation position relative to the object being observed along the plane.

Images