Interference observation device and interference observation method

Abstract

This interference observation device comprises: a light source; an interference optical system that splits light outputted from the light source into first light and second light and outputs interference light of the first light, which is reflected by an object of observation or transmitted through the object of observation and then reflected, with the second light, which is reflected by a reference mirror; an imaging element; a processing unit; and a mode switching unit that switches an observation mode of an observation surface of the object of observation between an interface observation mode, which is an observation mode in which the first light is reflected by the observation surface, and an internal observation mode, which is an observation mode in which the first light is transmitted through the observation surface and reflected by a reflective surface separate from the observation surface. The mode switching unit switches the observation mode between the interface observation mode and the internal observation mode by controlling the optical path length of the second light such that the optical path length of the second light in the internal observation mode is longer than the optical path length of the second light in the interface observation mode.

Description

Interference Observation Device and Interference Observation Method

[0001] The present disclosure relates to an interference observation device and an interference observation method.

[0002] As technologies related to interference observation devices, Patent Documents 1 and 2 disclose inspection devices that image confocal differential interference images of the surface of a silicon carbide substrate or the surface of an epitaxial layer using a confocal scanning device including a differential interference optical system. In the inspection devices described in Patent Documents 1 and 2, by imaging the confocal differential interference image of the surface of a single crystal substrate, minute uneven defects with a height of about several nm that appear on the surface of the single crystal substrate and the surface of the epitaxial layer formed on the single crystal substrate can be imaged as a luminance distribution image.

[0003] Japanese Patent Application Laid-Open No. 2011-211035, Japanese Patent Application Laid-Open No. 2012-174896

[0004] By the way, depending on the object to be observed, there may be defects inside the object to be observed rather than on the surface (interface) of the object to be observed. Examples of such defects include scratches (SubSurface Damage) etc. that exist near the surface of the object to be observed but do not appear on the surface. With the inspection devices as described above, internal observation of defects existing inside the object to be observed rather than on the surface (interface) cannot be performed. In that case, it is conceivable to perform internal observation of the object to be observed using another inspection device capable of internal observation, but there is a risk that it will be troublesome, such as transporting the object to be observed to another inspection device.

[0005] An object of the present disclosure is to provide an interference observation device and an interference observation method capable of easily performing interface observation and internal observation of an object to be observed.

[0006] The interference observation apparatus of the present disclosure is an interference observation apparatus comprising: [1] a light source that outputs light; an interference optical system having a 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 to be observed or reflected after passing through the object to be observed and the second light reflected by the reference mirror; an image sensor that detects the interference light; a processing unit that acquires an interference image based on the detection result of the interference light; and a mode switching unit that switches the observation mode of the observation surface of the object to be observed between an interface observation mode, which is an observation mode in which the first light is reflected by the observation surface, and an internal observation mode, which is an observation mode in which the first light is passed through the observation surface and reflected by a reflective surface away from the observation surface, wherein the mode switching unit switches the observation mode between the interface observation mode and the internal observation mode by controlling the optical path length of the second light such that the optical path length of the second light in the internal observation mode is longer than the optical path length of the second light in the interface observation mode.

[0007] In this interference observation device, the observation mode can be switched between interface observation mode and internal observation mode by controlling the optical path length of the second light so that the optical path length of the second light in internal observation mode is longer than the optical path length of the second light in interface observation mode. By switching the observation mode in this way, interface observation and internal observation of the object can be performed using the same interference observation device. Furthermore, the switching of observation modes in the interference observation device can be easily performed. Therefore, with this interference observation device, interface observation and internal observation of the object can be easily performed.

[0008] The interference observation apparatus of the present disclosure may also be [2] "the interference observation apparatus according to [1], further comprising a mode selection unit for selecting one of the interface observation mode and the internal observation mode, wherein the mode switching unit switches the observation mode according to the selection by the mode selection unit." In this case, the observation mode can be switched to one of the interface observation mode and the internal observation mode selected by the mode selection unit.

[0009] The interference observation apparatus of the present disclosure may also be [3] "the interference observation apparatus according to [1] or [2], wherein the interference optical system has a reference objective lens that guides the second light to the reference mirror, and the mode switching unit controls the optical path length of the second light by moving the reference mirror and the reference objective lens." In this case, the optical path length of the second light can be easily controlled, and as a result, the observation mode can be easily switched.

[0010] The interference observation apparatus of the present disclosure may also be the interference observation apparatus described in [3], wherein the reference mirror has a reference reflective surface that reflects the second light in each of the interface observation mode and the internal observation mode, and the mode switching unit moves the reference mirror by a distance D1 along a vertical direction perpendicular to the reference reflective surface that satisfies the following formula (1), and moves the reference objective lens by a distance D2 along the vertical direction to the same side as the side to which the reference mirror moves that satisfies the following formula (2). With this interference observation apparatus, the optical path length of the second light can be appropriately controlled when switching observation modes. D1 = t × n ... (1) D2 = t × (n - (1 / n)) ... (2) where, t: distance between the observation surface and the reflective surface of the first light, n: refractive index of the object to be observed

[0011] The interference observation apparatus of the present disclosure may also be the interference observation apparatus described in [4], wherein the mode switching unit is input to the distance t, the refractive index n, and at least one of the material of the object to be observed. In this case, distances D1 and D2 can be automatically calculated from the input information.

[0012] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to any one of [1] to [5], wherein the observation surface is the interface between the surface of the object to be observed and the surrounding atmosphere of the object to be observed. In this case, the surface of the object to be observed can be observed.

[0013] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to any one of [1] to [5], wherein the observation surface is an interface inside the object to be observed. In this case, the interface inside the object to be observed can be observed.

[0014] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to [7], wherein the object to be observed is a bonded wafer, and the observation surface is the bonded surface of the bonded wafer. In this case, the bonded surface of the bonded wafer can be observed.

[0015] The interference observation apparatus of the present disclosure may also be the interference observation apparatus described in [9] "the processing unit determines that there is metal on or near the bonded surface when the brightness of the interference image is greater than a threshold, and the mode switching unit switches the observation mode between the interface observation mode and the internal observation mode based on the determination result by the processing unit." In this case, the bonded wafer can be observed with high accuracy.

[0016] The interference observation apparatus of the present disclosure may also be the interference observation apparatus described in

[10] "the interference observation apparatus described in [9], wherein if the determination result by the processing unit indicates that there is no metal in the interface observation mode, the mode switching unit switches the observation mode from the interface observation mode to the internal observation mode, and if the determination result by the processing unit indicates that there is metal in the internal observation mode, the mode switching unit switches the observation mode from the internal observation mode to the interface observation mode." In this case, even if there is no prior information about the bonded wafer, the bonded wafer can be observed with high accuracy.

[0017] The interference observation apparatus of the present disclosure may also be

[11] "the interference observation apparatus according to any one of [1] to

[10] wherein the mode switching unit acquires position information indicating the position of the reflective surface in a vertical direction perpendicular to the reflective surface of the first light, and controls the optical path length of the second light based on the position information." In this case, even if the position of the reflective surface of the first light differs for each observation range, observation can be performed according to the position (depth) of the reflective surface.

[0018] The interference observation apparatus of the present disclosure may also be

[12] "the interference observation apparatus according to any one of [1] to

[11] , wherein the processing unit acquires a first interference image based on the detection result when the image sensor detects the interference light when the mode switching unit has switched the observation mode to the interface observation mode, acquires a second interference image based on the detection result when the image sensor detects the interference light when the mode switching unit has switched the observation mode to the internal observation mode, and acquires a third interference image by subtracting from the second interference image the first interference image which has been acquired in the same observation range as the second interference image and multiplied by a constant." In this case, pure internal information of the object to be observed can be obtained.

[0019] The interference observation device of the present disclosure may also be

[13] "the interference observation device according to

[12] , further comprising a display unit for displaying the third interference image." In this case, pure internal information of the object to be observed can be displayed.

[0020] The interference observation apparatus of the present disclosure may also be

[14] "an interference observation apparatus according to any one of [1] to

[13] , further comprising a focal plane position adjustment unit provided on the optical path of the interference light from the interference optical system to the imaging surface of the image sensor, wherein the interference optical system has an objective lens that guides the first light to the object to be observed or guides the interference light to the image sensor, and the focal plane position adjustment unit adjusts the position of the focal plane of the objective lens, which is conjugate to the imaging surface, on the optical path of the first light." In this case, the observation depth of the object to be observed can be changed.

[0021] The interference observation apparatus of the present disclosure may also be the interference observation apparatus described in [1] or [2], wherein the light source comprises a first light source that outputs the light and a second light source that outputs the light of a different wavelength from the light output from the first light source, the reference mirror comprises a first reference reflective surface that reflects the second light in the interface observation mode and a second reference reflective surface that reflects the second light that has passed through the first reference reflective surface in the internal observation mode and is located away from the first reference reflective surface, the first reference reflective surface has an anti-reflective film that transmits the light output from the second light source, and the mode switching unit switches the observation mode to the interface observation mode by turning the first light source ON and the second light source OFF, and switches the observation mode to the internal observation mode by turning the first light source OFF and the second light source ON. In this case, the observation mode can be switched without moving the reference mirror. Therefore, the observation mode can be switched at high speed.

[0022] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to

[15] , wherein the reference mirror is a member formed from the same material as the object to be observed and is formed to have the same thickness as the object to be observed. In this case, a configuration that can switch observation modes at high speed can be easily realized.

[0023] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to

[15] , wherein the reference mirror comprises a first reference mirror having the first reference reflecting surface and a second reference mirror having the second reference reflecting surface. In this case, a configuration that can switch observation modes at high speed can be easily realized.

[0024] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to any one of [1] to

[17] , wherein the reference mirror has a reference reflective surface that reflects the second light in the interface observation mode, and in the interface observation mode, the imaging surface of the image sensor and the observation surface are conjugate to each other, and the imaging surface and the reference reflective surface are conjugate to each other. In this case, a useful interference image can be obtained in the interface observation mode.

[0025] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to any one of [1] to

[18] , wherein the reference mirror has a reference reflective surface that reflects the second light in the internal observation mode, and in the internal observation mode, the conjugate surface of the reflective surface of the first light and the reference reflective surface are in a conjugate relationship with each other. In this case, a useful interference image can be obtained in the internal observation mode.

[0026] The interference observation apparatus of the present disclosure may also be

[20] "the interference observation apparatus according to any one of [1] to

[19] , wherein in the internal observation mode, the difference between the optical path length of the first light and the optical path length of the second light is within the coherence length of the light output from the light source." In this case, a useful interference image can be obtained in the internal observation mode.

[0027] The interference observation apparatus of the present disclosure may also be the interference observation apparatus according to any one of items [1] to

[20] , wherein the interference optical system has an objective lens that guides the first light to the object to be observed or guides the interference light to the image sensor, and the position of the focal plane of the objective lens on the optical path of the first light is the same between the interface observation mode and the internal observation mode. In this case, for example, pure internal information of the object to be observed can be obtained by subtracting the interference image acquired in the interface observation mode from the interference image acquired in the internal observation mode.

[0028] The interference observation apparatus of the present disclosure comprises:

[22] a light source that outputs light; an interference optical system having a reference mirror that splits 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 or reflected after passing through the object to be observed and the second light reflected by the reference mirror; an image sensor that detects the interference light; and a processing unit that acquires an interference image based on the detection result of the interference light, wherein the light source has a first light source that outputs the light and a second light source that outputs the light of a different wavelength from the light output from the first light source; the reference mirror has a first reference reflective surface and a second reference reflective surface separated from the first reference reflective surface, the first reference reflective surface has an anti-reflective coating that transmits the light output from the second light source; and the image sensor is separated from the light output from the first light source and reflected by the observation surface of the object to be observed. The interference observation device outputs separately: a first detection result which is the detection result of the interference light between the first light and the second light separated from the light output from the first light source and reflected by the first reference reflection surface; and a second detection result which is the detection result of the interference light between the first light separated from the light output from the second light source, which passes through the observation surface of the object to be observed and is reflected by a reflection surface away from the observation surface; and the second light separated from the light output from the second light source, which passes through the first reference reflection surface and is reflected by the second reference reflection surface. The processing unit acquires a first interference image as the interference image in an interface observation mode for observing the interface of the object to be observed based on the first detection result, and acquires a second interference image as the interference image in an internal observation mode for observing the inside of the object to be observed based on the second detection result.

[0029] In this interference observation device, the image sensor outputs a first detection result and a second detection result separately, allowing the acquisition of a first interference image in interface observation mode and a second interference image in internal observation mode. This enables interface observation and internal observation of an object to be performed using the same interference observation device. Therefore, this interference observation device makes it easy to perform interface observation and internal observation of an object.

[0030] The interference observation apparatus of the present disclosure is an interference observation method comprising:

[23] "an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation mode step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation step comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an observation mode comprising: an

[0031] In this interference observation method, the observation mode is switched between interface observation mode and internal observation mode by controlling the optical path length of the second light so that the optical path length of the second light in internal observation mode is longer than the optical path length of the second light in interface observation mode. By switching the observation mode in this way, interface observation and internal observation of the object can be performed using the same interference observation device. Furthermore, the observation mode can be easily switched in the interference observation device. Therefore, this interference observation method makes it easy to perform interface observation and internal observation of the object.

[0032] The interference observation apparatus of the present disclosure may also be the interference observation method described in

[23] , further comprising a subtraction step, wherein the object to be observed is a bonded wafer having voids on the bonding surface, the observation surface is the bonding surface, and in the interference image acquisition step, when interference light is detected by the interference light detection step while the observation mode has been switched to the interface observation mode by the observation mode switching step, a first interference image is acquired based on the detection result, when interference light is detected by the interference light detection step while the observation mode has been switched to the internal observation mode by the observation mode switching step, a second interference image is acquired based on the detection result, and in the subtraction step, a third interference image showing the voids is acquired by subtracting the first interference image, which has been acquired in the same observation range as the second interference image and multiplied by a constant, from the second interference image. In this case, voids in the bonded wafer can be observed with high accuracy.

[0033] The interference observation apparatus of the present disclosure may also be the interference observation method described in

[23] , further comprising a subtraction step, wherein the object to be observed is a substrate having a scratch near its surface, the observation surface is the surface of the substrate, in the interference image acquisition step, when interference light is detected by the interference light detection step while the observation mode has been switched to the interface observation mode by the observation mode switching step, a first interference image is acquired based on the detection result, when interference light is detected by the interference light detection step while the observation mode has been switched to the internal observation mode by the observation mode switching step, a second interference image is acquired based on the detection result, and in the subtraction step, a third interference image showing the scratch is acquired by subtracting the first interference image, which has been acquired in the same observation range as the second interference image and multiplied by a constant, from the second interference image. In this case, scratches located near the surface of the substrate (e.g., subsurface damage) can be observed with high accuracy.

[0034] The interference observation apparatus of the present disclosure may also be an interference observation method according to any one of

[23] to

[25] , further comprising:

[26] "an interface observation step in which, when the observation mode has been switched to the interface observation mode by the observation mode switching step, the observation range on the object to be observed is moved by moving the stage on which the object to be observed is placed, and the observation step is performed for each of the plurality of observation ranges; and an internal observation step in which, when the observation mode has been switched to the internal observation mode by the observation mode switching step, the observation range on the object to be observed is moved by moving the stage, and the observation step is performed for each of the plurality of observation ranges." In this case, foreign matter in the object to be observed can be inspected with high accuracy for each observation range.

[0035] According to this disclosure, it is possible to provide an interference observation device and interference observation method that can easily perform interface observation and internal observation of an object to be observed.

[0036] Figure 1 is a diagram showing the configuration of the interference observation device according to the first embodiment. Figure 2 is a diagram showing the configuration of the interference observation device of Figure 1 in interface observation mode. Figure 3 is a diagram showing the configuration of the interference observation device of Figure 1 in internal observation mode. Figure 4 is a diagram showing the sensitivity range in interface observation mode and internal observation mode. Figure 5 is a diagram for explaining the movement of the reference mirror and reference objective lens. Figure 6 is a diagram for explaining an example of GUI display. Figure 7 is a diagram for explaining an example of GUI display. Figure 8 is a flowchart for explaining an example of observing an object using the interference observation device. Figure 9 is a diagram showing the configuration of the object to be observed. Figure 10(a) is a diagram showing the first interference image, and Figure 10(b) is a diagram showing the second interference image. Figure 11 is a diagram showing the third interference image. Figure 12 is a diagram schematically showing the sensitivity range of the interference observation device. Figure 13(a) is a diagram showing the reflection of the first light on the surface of the object to be observed in interface observation mode, and Figure 13(b) is a diagram showing the reflection of the first light on the back surface of the object to be observed in internal observation mode. Figure 14 is a diagram illustrating another example of operation of the interference observation device. Figure 15 is a flowchart illustrating yet another example of operation of the interference observation device. Figure 16 is a flowchart illustrating yet another example of operation of the interference observation device. Figure 17 is a diagram schematically showing the operation example shown in Figure 16. Figure 18 is a diagram showing the configuration of the interference observation device in internal observation mode according to the first modification of the first embodiment. Figure 19 is a diagram showing the configuration of the interference observation device in internal observation mode according to the second modification of the first embodiment. Figure 18 is a diagram showing the configuration of the interference observation device in interface observation mode according to the second embodiment. Figure 19 is a diagram showing the configuration of the interference observation device in interface observation mode according to the third embodiment. Figure 18 is a diagram showing the configuration of the interference observation device in internal observation mode according to the third embodiment.

[0037] The embodiments will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0038] [First Embodiment] As shown in Figures 1 and 2, the interference observation apparatus 1 comprises a light source 2, an interference optical system 3, an image sensor 4, a control unit 5, and a stage S. Hereinafter, the X direction, the Y direction perpendicular to the X direction, and the Z direction perpendicular to both the X and Y directions will be used for the explanation.

[0039] The interference microscope 1 is an interference microscope for observing an object 8 placed on a stage S using light interference. The object 8 is, for example, a semiconductor device, but may also be other industrial samples made of metal, glass, resin, liquid crystal, polymer compound, etc. The object 8 may also be a biological sample such as a cell or cell aggregate. The object 8 may be a single wafer or a so-called bonded wafer. The object 8 may also be a substrate made of at least one of silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), and silicon carbide (SiC). In this case, the substrate may contain a dopant. The interference microscope 1 is configured to perform interface observation, which observes the interface of the object 8, as well as internal observation, which observes the inside of the object 8. Details of interface observation and internal observation will be described later.

[0040] Defects in the object 8 observed by the interferometric observation device 1 include, for example, pits, bumps, scratches, foreign matter, dirt, SSD (Subsurface Damage), crystal defects, changes in internal refractive index, foreign matter inclusions, voids, or internal processing marks. SSD is a scratch that exists in the vicinity of the surface of the object 8 but is not visible on the surface. "Nearby" means a peripheral position, a close position, an approaching position, an adjacent position, etc.

[0041] Light source 2 emits incoherent light. Light source 2 is, for example, a lamp-type light source such as a halogen lamp, an LED (Light Emitting Diode) light source, an SLD (Super Luminescent Diode) light source, an ASE (Amplified Spontaneous Emission) light source, etc.

[0042] The interference optical system 3 (interference observation device 1) is configured as a Linnik interference type in this example. The interference 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 interference optical system 3 is disposed in the housing H together with the light source 2 and constitutes the optical module M. The optical module M is movable along the Z direction by a predetermined actuator 16. The Z direction is parallel to the optical axis of the objective lens 13 and parallel to the direction in which the first light L1, which will be described later, is incident on the observation object 8.

[0043] The lens 11 collimates the light output from the light source 2. The beam splitter 12 is, for example, a prism having an optical surface 12a, and splits the light collimated by the lens 11 into the first light L1 and the second light L2 at the optical surface 12a. The beam splitter 12 outputs the first light L1 to the objective lens 13 and the second light L2 to the reference objective lens 14. Further, the first light L1 reflected by the observation object 8 is incident on the optical surface 12a via the objective lens 13, and the second light L2 reflected by the reference mirror 15 is incident on the optical surface 12a via the reference objective lens 14. These first light L1 and second light L2 are combined at the optical surface 12a to become interference light L3. The interference optical system 3 outputs the interference light L3 to the imaging device 4.

[0044] The objective lens 13 guides the first light L1 output from the beam splitter 12 to the observation object 8 disposed on the stage S and condenses it on the observation object 8. Further, the first light L1 reflected by the observation object 8 is incident on the objective lens 13. The objective lens 13 outputs the incident first light L1 to the beam splitter 12. The magnification of the objective lens 13 is, for example, 5 times, 10 times, 20 times, 50 times, etc.

[0045] The reference objective lens 14 guides the second light L2 output from the beam splitter 12 to the reference mirror 15 and condenses it on the reference mirror 15. Further, the reference objective lens 14 outputs the second light L2 reflected by the reference reflection surface 15a of the reference mirror 15 to the beam splitter 12. The reference mirror 15 reflects the second light L2 output from the reference objective lens 14 so as to return it to the reference objective lens 14. The magnification of the reference objective lens 14 is, for example, 5 times, 10 times, 20 times, 50 times, or the like.

[0046] In the housing H of the optical module M, a stepping motor 17 for moving the reference objective lens 14, a stepping motor 18 and a piezo element 19 for moving the reference mirror 15 are further arranged. The stepping motor 17 moves the reference objective lens 14 along the optical axis direction of the second light L2 perpendicular to the Z direction (for example, the X direction). The stepping motor 18 and the piezo element 19 move the reference mirror 15 along the optical axis direction of the second light L2.

[0047] The response times of the stepping motors 17 and 18 are greater than 10 msec, and the response time of the piezo element 19 is less than 1 msec. That is, the response time of the piezo element 19 is shorter than the response times of the stepping motors 17 and 18. The strokes (minimum movement distances) of the stepping motors 17 and 18 are several millimeters, and the stroke of the piezo element 19 is about 2 μm. That is, the stroke of the piezo element 19 is smaller than the strokes of the stepping motors 17 and 18. The number of life driving times of the stepping motors 17 and 18 is less than 1 million times, and the number of life driving times of the piezo element 19 is more than 10 billion times. That is, the number of life driving times of the piezo element 19 is more than the number of life driving times of the stepping motors 17 and 18.

[0048] 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 (images) the interference light L3 output from the interference optical system 3 (beam splitter 12). A lens 41 is arranged between the imaging element 4 and the interference optical system 3. The lens 41 forms an image of the interference light L3 output from the interference optical system 3 on the imaging surface 4a of the imaging element 4.

[0049] The control unit 5 is composed of a computer C, which includes, for example, a processor (CPU), and memory media such as RAM and ROM. The computer C includes a GUI (Graphical User Interface) 6 and a memory area 7. The computer C may also include input devices such as a mouse and a keyboard.

[0050] The control unit 5 is communicatively connected to each part of the interference observation device 1, which includes the light source 2, the interference optical system 3, the image sensor 4, the stepping motors 17 and 18, the piezoelectric element 19, and the stage S. The control unit 5 has a processing unit 51, a mode selection unit 52, a mode switching unit 53, and a stage control unit 54. The processing unit 51 acquires an interference image based on the detection result of the interference light L3 in the image sensor 4.

[0051] The mode selection unit 52 selects the observation mode for the observation surface R (see Figures 2 and 3) of the object to be observed 8 in the interference observation device 1 from an interface observation mode for performing interface observation and an internal observation mode for performing internal observation. The mode selection unit 52 selects the interface observation mode or the internal observation mode selected by, for example, the user's operation on the GUI 6 as the observation mode.

[0052] Next, the interface observation mode and the internal observation mode will be described with reference to Figures 2 and 3. The object to be observed 8 has a surface 8a located on the objective lens 13 side and a back surface (reflective surface) 8b located on the opposite side of surface 8a. The observation surface R of the object to be observed 8 is set at the interface of the object to be observed 8. In this embodiment, the observation surface R is the interface between the surface 8a of the object to be observed 8 and the surrounding atmosphere of the object to be observed 8. The back surface 8b is separated from the observation surface R toward the opposite side of the objective lens 13 (the lower side in Figures 2 and 3). The surrounding atmosphere may be a gas such as air or nitrogen gas, or it may be a vacuum.

[0053] In the interface observation mode shown in Figure 2, the focal plane F1 of the objective lens 13 is located on the observation surface R, and the focal plane F2 of the reference objective lens 14 is located on the reference reflection surface 15a. Furthermore, the imaging surface 4a of the image sensor 4 and the observation surface R are conjugate to each other, and the imaging surface 4a and the reference reflection surface 15a are also conjugate to each other. In other words, the observation surface R and the reference reflection surface 15a are conjugate to each other. A conjugate relationship means, for example, that an image located on one surface is formed on another surface. In addition, the optical path length from the beam splitter 12 through the reference objective lens 14 to the reference reflection surface 15a is approximately the same as the optical path length from the beam splitter 12 through the objective lens 13 to the observation surface R. In this state, the interference light L3 of the first light L1 reflected at the observation surface R and the second light L2 reflected at the reference reflection surface 15a is detected by the image sensor 4. Then, the processing unit 51 acquires a first interference image as an interference image in the interface observation mode. This allows, for example, the defect K on surface 8a to be observed.

[0054] In the internal observation mode shown in Figure 3, the positions of the reference objective lens 14 and the reference mirror 15 have moved from their positions in the interface observation mode. In the example in Figure 3, the position of the reference objective lens 14 in the X direction has moved from position P1 in the interface observation mode to position P2. The position of the reference mirror 15 in the X direction has moved from the position of the focal plane F2 of the reference objective lens 14 to position P3. The movement of the reference objective lens 14 and the reference mirror 15 will be described later.

[0055] In internal observation mode, the focal plane F1 of the objective lens 13 is located on the observation surface R, but the focal plane F2 of the reference objective lens 14 is not located on the reference reflection surface 15a. Furthermore, the conjugate surface 8c of the back surface 8b and the reference reflection surface 15a are conjugate to each other. In other words, the back surface 8b and the reference reflection surface 15a are conjugate to each other. In the example in Figure 3, the conjugate surface 8c is located on the beam splitter 12 (lens 41) side with respect to the imaging surface 4a of the image sensor 4. In this state, interference light L3 of the first light L1 that passes through the observation surface R and is reflected by the back surface 8b of the object to be observed 8, which is away from the observation surface R, and the second light L2 that is reflected by the reference reflection surface 15a is detected by the image sensor 4. Then, the processing unit 51 acquires a second interference image as an interference image in internal observation mode. This allows, for example, the observation of defects K inside the object to be observed 8.

[0056] Referring to Figure 4, the sensitivity range (observable range) for the interface observation mode and the internal observation mode will be explained. In Figure 4, the sensitivity range is shown in grayscale. Figure 4 shows examples of the presence of pits, SSD (Subsurface Damage), bumps, scratches, foreign matter, areas where the internal refractive index changes, and dirt in the object being observed. In the interface observation mode shown on the left side of Figure 4, the sensitivity range includes the area on the observation surface. On the other hand, in the internal observation mode shown on the right side of Figure 4, the sensitivity range includes not only the area on the observation surface but also the area inside the object being observed 8 beyond the observation surface. In both the interface observation mode and the internal observation mode, the observation sensitivity is maximum at the observation surface.

[0057] The mode switching unit 53 shown in Figure 1 switches the observation mode of the observation surface R of the object to be observed 8 between interface observation mode and internal observation mode, according to the selection made by the mode selection unit 52. Specifically, the mode switching unit 53 moves the reference objective lens 14 along the X direction (the direction perpendicular to the reference reflective surface 15a) by controlling the stepping motor 17. The mode switching unit 53 also moves the reference mirror 15 along the X direction by controlling the stepping motor 18.

[0058] Referring to Figure 5, the movement of the reference mirror 15 and the reference objective lens 14 will be explained. In the following explanation, the side approaching the beam splitter 12 (see Figures 1 to 3) in the X direction (right side in Figure 5) will be referred to as the front side X1, and the side moving away from the beam splitter 12 in the X direction (left side in Figure 5) will be referred to as the rear side X2.

[0059] The mode switching unit 53 moves the reference mirror 15 to the rear X2 by a distance D1 and the reference objective lens 14 to the rear X2 (the same side as the reference mirror 15 moves) by a distance D2, thereby moving the reference mirror 15 from the focal plane F2 of the reference objective lens 14 to position P3 and moving the reference objective lens 14 from position P1 to position P2. In this way, the mode switching unit 53 switches the observation mode from interface observation mode to internal observation mode by lengthening the optical path length of the second light L2. In other words, the optical path length of the second light L2 in internal observation mode is longer than the optical path length of the second light L2 in interface observation mode. At this time, the difference between the optical path length of the first light L1 (the optical path length from the beam splitter 12, through the objective lens 13 and the object to be observed 8, reflected by the back surface 8b of the object to be observed 8, and then passing through the object to be observed 8 and the objective lens 13 again to return to the beam splitter 12) and the optical path length of the second light L2 is within the coherence length of the light output from the light source 2.

[0060] The mode switching unit 53 moves the reference mirror 15 forward by a distance D1 X1 and the reference objective lens 14 forward by a distance D2 X1 (the same side as the reference mirror 15), thereby moving the reference mirror 15 from the position P3 of the reference objective lens 14 to the focal plane F2, and moving the reference objective lens 14 from position P2 to position P1. In this way, the mode switching unit 53 switches the observation mode from internal observation mode to interface observation mode by shortening the optical path length of the second light L2. At this time, the difference between the optical path length of the first light L1 (the optical path length from the beam splitter 12, through the objective lens 13, reflected by the surface 8a of the object to be observed 8, and again through the objective lens 13 to the beam splitter 12) and the optical path length of the second light L2 is within the coherence length of the light output from the light source 2.

[0061] As described above, the mode switching unit 53 switches the observation mode between interface observation mode and internal observation mode by controlling the optical path length of the second light L2 in internal observation mode so that the optical path length of the second light L2 in internal observation mode is longer than the optical path length of the second light L2 in interface observation mode. The reason for controlling the optical path length of the second light L2 is as follows: In internal observation mode, the optical path length of the first light L1 is longer than that of the first light L1 in interface observation mode because the back surface 8b is farther away from the observation surface R. Therefore, in internal observation mode, in order for the first light L1 and the second light L2 to interfere (for the optical path lengths of the first light L1 and the second light L2 to be the same), the optical path length of the second light L2 also needs to be made longer.

[0062] The distances D1 and D2 described above satisfy, for example, the following equations (1) and (2). Here, t is the distance between the observation surface R and the back surface 8b (corresponding to the thickness of the object to be observed 8 in this embodiment), and n is the refractive index of the object to be observed 8. In this way, by making the distance D1 that the reference mirror 15 moves longer than the distance D2 that the reference objective lens 14 moves, the reference mirror 15 is positioned behind X2 of the focal plane F2 of the reference objective lens 14. In other words, in interface observation mode, the distance between the reference objective lens 14 and the reference mirror 15 is longer than the focal length of the reference objective lens 14. To put it another way, in interface observation mode, the reference objective lens 14 is focused on the reference mirror 15, whereas in internal observation mode, the reference objective lens 14 is defocused relative to the reference mirror 15. D1 = t × n ... (1) D2 = t × (n - (1 / n)) ... (2)

[0063] The mode switching unit 53 may calculate distances D1 and D2 from equations (1) and (2) above using distance t and refractive index n. In this case, distance t and refractive index n input by the user's operation on GUI 6 are input to the mode switching unit 53. The material of the object to be observed 8 may be input to the mode switching unit 53 instead of refractive index n. In this case, the mode switching unit 53 determines the refractive index n based on the material of the object to be observed 8. The mode switching unit 53 may determine the refractive index n using various known methods.

[0064] The mode switching unit 53 may calculate distances D1 and D2 by another method. For example, the optimal distances D1 and D2 may be measured in advance using a reference sample, and a correction formula may be prepared by polynomial fitting. The mode switching unit 53 may then calculate distances D1 and D2 based on this correction formula.

[0065] The stage control unit 54 controls the movement of the stage S along the XY plane (a plane perpendicular to the Z direction). This allows the stage control unit 54 to move the object to be observed 8 relative to the interference optical system 3. The stage S is a stage on which the object to be observed 8 is placed, and it is movable along the XY plane. By controlling the movement of the stage S by the stage control unit 54, the interference observation device 1 can observe the object to be observed 8 (acquire interference images) while changing the observation range (field of view) of the object to be observed 8.

[0066] The GUI (display unit) 6 displays interference images and the like acquired by the processing unit 51. The GUI 6 includes, for example, a touch panel display. Various settings related to observation conditions are input to the GUI 6 through user operations such as touching.

[0067] An example of the GUI 6 display will be explained with reference to Figures 6 and 7. In the example in Figure 6, the object to be observed 8 is a substrate. As shown in Figure 6, the user can input the observation mode, substrate type (material), and substrate thickness in the GUI 6. When the user clicks the "Internal Observation Mode" button and then clicks the button to start processing (not shown), the mode switching unit 53 controls the positions of the reference mirror 15 and the reference objective lens 14 according to the input substrate type and substrate thickness. The interference image acquired in internal observation mode is then displayed in the GUI 6. The display of the interference image in the GUI 6 is performed by the processing unit 51.

[0068] In the example shown in Figure 7, GUI 6 displays the first interference image in interface observation mode and the second interference image in internal observation mode side by side. GUI 6 may also display the first and second interference images acquired in the same observation range of the object 8 side by side. GUI 6 may also display the first and second interference images superimposed on each other using different color channels (they may overlap). GUI 6 may highlight the location of defects in the interference images. In this case, the processing unit 51 may detect the location of defects based on the first and second interference images. When highlighting the location of defects, the type of defect may be indicated by text or color differences based on the distinction between internal defects and surface defects described later.

[0069] [Example of operation of the interference observation device] Referring to Figure 8, an example of observing the object to be observed 8 with the interference observation device 1 will be explained. First, in step S1, the object to be observed 8 is placed on the stage S.

[0070] Next, in step S2, for example, based on the imaging result from the image sensor 4, the position of the objective lens 13 is adjusted so that the focal plane F1 of the objective lens 13 is positioned on the surface 8a (observation surface R) of the object to be observed 8. In other words, it is focused on the surface 8a of the object to be observed 8.

[0071] Next, in step S3, the optical path length of the second light L2 is adjusted so that an interference image of the observation surface R is acquired (so that interference fringes are visible). Specifically, the positions of the reference objective lens 14 and the reference mirror 15 are adjusted based on the thickness, refractive index, and arrangement order of the object to be observed 8. For example, the positions of the reference objective lens 14 and the reference mirror 15 are adjusted so that the focal plane F2 of the reference objective lens 14 is positioned on the reference reflective surface 15a of the reference mirror 15. After adjustment, the next step S4 is executed as an observation process in interface observation mode.

[0072] In step S4 (observation step), a first interference image (interference image in interface observation mode) is acquired. Specifically, first, incoherent light is output from the light source 2 (light output step). This light is collimated by the lens 11 and split into a first light L1 and a second light L2 by the beam splitter 12. The first light L1 is focused onto the object to be observed 8 by the objective lens 13, reflected by the observation surface R of the object to be observed 8, and input to the beam splitter 12 via the objective lens 13. The second light L2 is focused onto the reference mirror 15 by the reference objective lens 14, reflected by the reference reflective surface 15a of the reference mirror 15, and input to the beam splitter 12 via the reference objective lens 14. The beam splitter 12 combines the input first light L1 and second light L2 and outputs interference light L3 (interference light output step). The output interference light L3 is detected by the image sensor 4 (interference light detection step). Based on the detection results of the image sensor 4, the processing unit 51 acquires an interference image (interference image acquisition step).

[0073] In step S4, the image sensor 4 takes images to acquire four interference images. The piezoelectric element 19 moves the reference mirror 15 precisely in accordance with the timing of the acquisition of the four interference images. This causes the difference in optical path length between the first light L1 and the second light L2 to differ between the four interference images. The amount of movement of the reference mirror 15 to acquire the four interference images is smaller than the wavelength λ of the light output from the light source 2. In this example, the difference in optical path length (phase shift interval) of the second light L2 between the four interference images is λ / 4. Furthermore, this amount of movement is smaller than the distances D1 and D2. Note that the number of interference images required to calculate the real part image, imaginary part image, amplitude image, phase image, or optical path length image described later is not limited to four, but may be taken and used for more than five, seven, or eight images. Also, the phase shift interval is not limited to λ / 4, but may be any value smaller than the distances D1 and D2.

[0074] The processing unit 51 constructs (acquires) a single first interference image based on the four acquired interference images. The first interference image may be a phase image or an optical path length image. For example, the processing unit 51 calculates the real part Re and the imaginary part Im of the first interference image and generates a complex number image Comp as Comp = Re + iIm. Here, i is the imaginary unit. The real part Re corresponds to the real part image, the imaginary part Im corresponds to the imaginary part image, the deflection angle of Comp corresponds to the phase image, and the absolute value of Comp corresponds to the amplitude image of the interference fringes. If the phase image is Φ and the optical path length image is OPD, the optical path length image OPD is calculated as a constant multiple of Φ using the formula OPD = λ × Φ / (4π). Therefore, in the following description, substantially the same effect can be obtained whether the calculation is performed using OPD or Φ.

[0075] Next, in step S5, the mode switching unit 53 calculates the travel distance of the reference mirror 15 (distance D1) and the travel distance of the reference objective lens 14 (distance D2). The mode switching unit 53 calculates distances D1 and D2 from the above formulas (1) and (2) based on, for example, the distance t input by the user's operation on the GUI 6, the refractive index n, and at least one of the material of the object to be observed 8.

[0076] Next, in step S6, the mode switching unit 53 switches the observation mode from interface observation mode to internal observation mode according to the selection by the mode selection unit 52 (observation mode switching step). Specifically, the mode switching unit 53 lengthens the optical path length of the second light L2 by moving the reference mirror 15 a distance D1 to the rear X2 (see Figure 5) and moving the reference objective lens 14 a distance D2 to the rear X2. At this time, the position of the focal plane F1 of the objective lens 13 does not move, and the focal plane F1 remains located on the surface 8a (observation surface R) of the object to be observed 8. In other words, the position of the focal plane F1 of the objective lens 13 on the optical path of the first light L1 is the same between interface observation mode and internal observation mode.

[0077] Next, in step S7 (observation step), a second interference image (interference image in internal observation mode) is acquired in the same manner as in step S2. In step S7, the interference light L3 of the first light L1 reflected from the back surface 8b of the object to be observed 8 and the second light L2 reflected from the reference reflective surface 15a is detected by the image sensor 4. In step S7, the image sensor 4 takes images to acquire four interference images in the same manner as in step S2. The processing unit 51 constructs (acquires) one second interference image based on the four acquired interference images. The second interference image may be a phase image or an optical path length image, similar to the first interference image. Thus, in step S7, the second interference image is acquired in the same observation range as the first interference image.

[0078] For the first interference image, which is an interference image in interface observation mode, and the second interference image, which is an interference image in internal observation mode, the distortion and undulation components, which are low spatial frequency fluctuation components in the phase image or optical path length image, may be subtracted in advance before use. The distortion and undulation in the phase image or optical path length image reflect the aberration components of the observation optical system itself and the gradual minute changes in refractive index inside the object being observed 8, and are not caused by internal defects or surface defects. Therefore, by subtracting these fluctuation components in advance before use, it becomes possible to further emphasize internal defects and surface defects during image processing.

[0079] In step S8, the processing unit 51 acquires a third interference image using the first interference image and the second interference image. Specifically, the processing unit 51 acquires the third interference image by subtracting from the second interference image a first interference image, which was acquired within the same observation range as the second interference image and multiplied by a constant (subtraction step). This constant is, for example, the refractive index n of the object being observed 8. The reason for using the refractive index n will be explained later.

[0080] Referring to Figures 9, 10(a), 10(b), and 11, examples of the first, second, and third interference images will be explained. In the locations indicated by "A" to "C" in Figure 9, abnormalities exist as follows: A: There is an abnormality on the surface and a larger abnormality inside. B: There is no abnormality on the surface, but an abnormality is seen only in internal observation. C: There is an abnormality only on the surface.

[0081] In the first interferometric image shown in Figure 10(a), surface anomalies at "A" and surface anomalies at "C" are detected. In the second interferometric image shown in Figure 10(b), anomalies are detected at each of "A" through "C". In contrast, in the third interferometric image shown in Figure 11, internal anomalies at "A" and an anomaly at "B" are detected. In the third interferometric image, surface anomalies at "A" and surface anomalies at "C" are not detected. In other words, the third interferometric image shows purely internal information.

[0082] Figure 12 schematically shows the sensitivity range as a graph. In internal observation mode, the sensitivity range includes the region on the observation surface and the region inside the object 8 beyond the observation surface, whereas in interface observation mode, the sensitivity range includes only the region on the observation surface. Therefore, in the third interference image obtained by subtracting the first interference image, which has been multiplied by a constant, from the second interference image, pure internal information is obtained when the sensitivity range includes only the region inside the object 8 beyond the observation surface.

[0083] Referring to Figures 13(a) and 13(b), the reason for using the refractive index n as a constant multiplied by the first interference image will be explained. The surface 8a of the object to be observed 8 shown in Figures 13(a) and 13(b) has an uneven shape. Figure 13(a) shows the reflection of the first light L1 at the surface 8a of the object to be observed 8 in interface observation mode, and Figure 13(b) shows the reflection of the first light L1 at the back surface 8b of the object to be observed 8 in internal observation mode.

[0084] In the interface observation mode shown in Figure 13(a), only the surface shape of the object 8 is observed. In the internal observation mode shown in Figure 13(b), the optical path length of the first light L1 that passes through a recessed area D on the surface 8a of the object 8 is shorter than the optical path length of the first light L1 that passes through a flat area F on the surface 8a of the object 8. This is because the distance that passes through the object 8 with refractive index n is shorter due to the recessed surface 8a. Also, the optical path length of the first light L1 that passes through a protruding area E on the surface 8a of the object 8 is longer than the optical path length of the first light L1 that passes through area F. Here, if the surface shape distribution obtained in the interface observation mode is H(x,y), then the optical path length in the internal observation mode is contributed by a value n × H(x,y) derived from the shape of the object 8. Therefore, by subtracting n × H(x, y) from the optical path length measured in internal observation mode, the optical path length can be obtained as pure internal information, calibrated for the influence of the surface shape. Based on the above, for example, the refractive index n is used as the constant multiplied by the first interference image.

[0085] Returning to Figure 8, in step S9, the processing unit 51 displays and / or saves the interference image. The processing unit 51 displays at least one of the first interference image, the second interference image, and the third interference image on the GUI 6 and / or saves it in the storage area 7.

[0086] [Operation and Effects] In the interference observation device 1 and interference observation method, the observation mode is switched between the interface observation mode and the internal observation mode by controlling the optical path length of the second optical light L2 so that the optical path length of the second optical light L2 in the internal observation mode is longer than the optical path length of the second optical light L2 in the interface observation mode. By switching the observation mode in this way, interface observation and internal observation of the object to be observed 8 can be performed using the same interference observation device 1. Furthermore, the observation mode in the interference observation device 1 can be easily switched. Therefore, the interference observation device 1 and interference observation method make it easy to perform interface observation and internal observation of the object to be observed 8.

[0087] The interference observation device 1 includes a mode selection unit 52 for selecting either an interface observation mode or an internal observation mode, and the mode switching unit 53 switches the observation mode according to the selection made by the mode selection unit 52. In this case, the observation mode can be switched to either the interface observation mode or the internal observation mode selected by the mode selection unit 52.

[0088] In the interference observation device 1, the mode switching unit 53 controls the optical path length of the second optical fiber L2 by moving the reference mirror 15 and the reference objective lens 14. In this case, the optical path length of the second optical fiber L2 can be easily controlled, and as a result, the observation mode can be easily switched.

[0089] In the interference observation device 1, the mode switching unit 53 moves the reference mirror 15 along the X direction by a distance D1 satisfying equation (1) above, and moves the reference objective lens 14 along the X direction to the same side as the reference mirror 15 moves by a distance D2 satisfying equation (2) above, thereby switching the observation mode between interface observation mode and internal observation mode. In this case, the optical path length of the second light can be appropriately controlled when switching observation modes.

[0090] In the interference observation device 1, the mode switching unit 53 receives input of distance t, refractive index n, and at least one of the material of the object to be observed 8. In this case, distances D1 and D2 can be automatically calculated from the input information.

[0091] In the interference observation device 1, the observation surface R is the interface between the surface 8a of the object to be observed 8 and the surrounding atmosphere of the object to be observed 8. In this case, the surface 8a of the object to be observed 8 can be observed.

[0092] In the interference observation device 1, the processing unit 51 obtains a third interference image by subtracting from the second interference image a first interference image, which is obtained within the same observation range as the second interference image and multiplied by a constant (in this embodiment, the refractive index n of the object being observed 8). In this case, pure internal information of the object being observed 8 can be obtained.

[0093] The interference observation device 1 is equipped with a GUI 6 for displaying a third interference image. In this case, the user can visually perceive the pure internal information of the object being observed 8.

[0094] In the interferometry observation device 1, in interface observation mode, the imaging surface 4a and the observation surface R of the image sensor 4 are conjugate to each other, and the imaging surface 4a and the reference reflection surface 15a are also conjugate to each other. In this case, a useful interference image can be obtained in interface observation mode.

[0095] In the interference observation device 1, in internal observation mode, the conjugate surface 8c of the back surface 8b of the object to be observed 8 and the reference reflective surface 15a are in a conjugate relationship with each other. In this case, a useful interference image can be obtained in internal observation mode.

[0096] In the interference observation device 1, in internal observation mode, the difference between the optical path length of the first light L1 and the optical path length of the second light L2 is within the coherence length of the light output from the light source 2. In this case, a useful interference image can be obtained in internal observation mode.

[0097] In the above interference observation method, if the object to be observed 8 is a substrate having a scratch (SSD) near the surface 8a, a third interference image showing the SSD is acquired in step S8 (subtraction step). In this case, the SSD can be observed with high accuracy.

[0098] [Another Operation Example of the Interferometry Observation Device] Next, another operation example of the interferometry observation device 1 will be described with reference to Figure 14. In this example, a bonded wafer is used as the object to be observed 8. This bonded wafer has a void V on the bonded surface 8d, and the observation surface R is set on the bonded surface 8d. The bonded surface 8d is also the internal interface of the object to be observed 8. In Figure 14, the position of the objective lens 13 when acquiring interference images in each of the observation ranges OR1 to OR4 is shown for convenience.

[0099] In observation range OR1, a void V is present on the bonded surface 8d. When observing observation range OR1, in interface observation mode, interference light L3 is detected between the first light L1 (directly reflected light) reflected by the bonded surface 8d and the second light L2 reflected by the reference reflective surface 15a. In internal observation mode, interference light L3 is detected between the first light L1 (back surface reflected light) reflected by the back surface 8b and the second light L2 reflected by the reference reflective surface 15a. In regions of a bonded wafer where bonding is properly performed, there is little directly reflected light, making it difficult to focus on the bonded surface 8d. Therefore, when observing void V, it is useful to use internal observation mode.

[0100] In observation range OR1, back-reflected light could be used in internal observation mode, but an example where back-reflected light cannot be used is described below. In observation range OR2, a metallic ME exists on the bonding surface 8d, and in observation range OR3, a metallic ME exists between the bonding surface 8d and the back surface 8b. The metallic ME is, for example, a pattern of a functional element. In this case, the first light L1 is reflected by the metallic ME without reaching the back surface 8b. The optical path length of the first light L1 reflected by the metallic ME is shorter than the optical path length of the first light L1 reflected by the back surface 8b. Therefore, when observing observation ranges OR2 and OR3 in internal observation mode, the mode switching unit 53 controls the optical path length of the second light so that it is the same as the optical path length of the first light L1 reflected by the metallic ME. In this way, the reflective surface of the first light L1 in internal observation mode is set to the metallic ME. Then, interference light L3 is detected between the first light L1 reflected by the metal ME and the second light L2 reflected by the reference reflective surface 15a.

[0101] In the observation range OR4, an anti-reflective coating (not shown) is provided on the back surface 8b to prevent reflection of the first light L1. In this case, sufficient reflection of the first light L1 on the back surface 8b cannot be expected, so a mirror MR is placed below the back surface 8b. The mirror MR reflects the first light L1 that has passed through the back surface 8b, that is, the first light L1 that has passed through the object to be observed 8. In this case, the reflective surface of the first light L1 is set to the mirror MR. Then, interference light L3 is detected between the first light L1 reflected by the mirror MR and the second light L2 reflected by the reference reflective surface 15a.

[0102] As described above, depending on the type of object to be observed 8, the position of the reflective surface of the first light L1 in the Z direction may differ for each observation range of the object to be observed 8. In other words, the optical path length of the first light L1 may differ for each observation range. In the interferometry observation device 1, the mode switching unit 53 may acquire position information indicating the position of the reflective surface of the first light L1 in the Z direction (the vertical direction perpendicular to the reflective surface of the first light L1), and control the optical path length of the second light L2 based on the position information. For example, the processing unit 51 may acquire the position information based on the image of the object to be observed 8 acquired by the image sensor 4, and input the position information to the mode switching unit 53. Alternatively, the position information may be input by user operation on the GUI 6. By controlling the optical path length of the second light L2 based on the position information in this way, observation can be performed according to the position (depth) of the reflective surface even if the position of the reflective surface of the first light L1 differs for each observation range.

[0103] As shown in Figure 14, when the observation surface R is the bonding surface 8d (internal interface of the object being observed 8), the bonding surface 8d (internal interface of the object being observed 8) can be observed with high accuracy regardless of whether or not the object being observed 8 includes a reflective surface.

[0104] As shown in Figure 14, metal may be present in the object 8, which is a bonded wafer. Another example of operation in this case will be explained with reference to Figure 15. In this example, it is determined whether the reflective surface is metal based on the captured image of the object 8, which is a bonded wafer, and processing is performed based on the determination result.

[0105] First, in step S11, the image sensor 4 acquires an image of the object to be observed 8 in interface observation mode or internal observation mode.

[0106] Next, in step S12, the processing unit 51 determines that if the brightness of the captured image is greater than a threshold, there is metal on or near the bonding surface 8d, and if the brightness of the captured image is less than or equal to the threshold, there is no metal on or near the bonding surface 8d. The threshold may be a value that has been set in advance. The threshold may be a fixed value or a variable value that can be changed by user input, for example. If the determination result by the processing unit 51 indicates that there is metal in the interface observation mode (step S12: NO), the process proceeds to step S14, which will be described later. Also, if the determination result by the processing unit 51 indicates that there is no metal in the internal observation mode (step S12: NO), the process proceeds to step S14.

[0107] On the other hand, if the determination result by the processing unit 51 indicates that there is no metal in the interface observation mode (step S12: YES), the process proceeds to step S13. Also, if the determination result by the processing unit 51 indicates that there is metal in the internal observation mode (step S12: YES), the process proceeds to step S13. If the result in step S12 is YES, it means that the conditions for switching the observation mode are met. The switching conditions in step S12 can be summarized as follows: <If the switching conditions are not met (if the result in step S12 is NO)> - The observation mode is the interface observation mode and there is metal. - The observation mode is the internal observation mode and there is no metal. <If the switching conditions are met (if the result in step S12 is YES)> - The observation mode is the interface observation mode and there is no metal. - The observation mode is the internal observation mode and there is metal.

[0108] In step S13, the mode switching unit 53 switches the observation mode from interface observation mode to internal observation mode by moving the reference mirror 15 and the reference objective lens 14. Alternatively, the mode switching unit 53 switches the observation mode from internal observation mode to interface observation mode by moving the reference mirror 15 and the reference objective lens 14. In this way, the mode switching unit 53 switches the observation mode between interface observation mode and internal observation mode based on the determination result by the processing unit 51.

[0109] In step S14, if the answer in step S12 is YES, the image sensor 4 acquires multiple interference images in the observation mode set in step S13. In step S14, if the answer in step S12 is NO, the image sensor 4 acquires multiple interference images in the observation mode set in step S11. The processing unit 51 constructs (acquires) a single interference image based on the acquired multiple interference images. In step S14, multiple interference images and a single interference image are acquired in the same manner as in steps S4 and S7 shown in Figure 8.

[0110] In step S15, the processing unit 51 displays and / or saves the interference image acquired in step S14. The processing unit 51 may add information to the interference image indicating whether it was acquired in interface observation mode or internal observation mode.

[0111] In step S16, the control unit 5 determines whether imaging has been completed in all observation areas. If the control unit 5 determines that imaging has been completed in all observation areas (step S16: YES), the process ends. If the control unit 5 determines that imaging has not been completed in all observation areas (step S16: NO), the process proceeds to step S17.

[0112] In step S17, the stage control unit 54 controls the movement of the stage S, causing it to move to the next range. Then, step S11 is executed again.

[0113] As demonstrated by the operation example above, even when no prior information about the bonded wafer is available, the bonded wafer can be observed with high accuracy. For example, even if the location of metal on the bonded wafer is unknown beforehand, the presence or absence of metal can be determined from the brightness of the interference image, and the observation mode is switched based on the determination result, thereby acquiring interference images in both interface observation mode and internal observation mode. This allows for accurate observation of the bonded wafer.

[0114] Next, another example of operation will be explained with reference to Figures 16 and 17. In this example, the observation range of the object being observed 8 is moved, and interference images of each observation range are acquired.

[0115] First, in step S21 (interface observation step), the mode switching unit 53 switches the observation mode to interface observation mode. In this state, step S2 shown in Figure 8 is executed and a first interference image is acquired. Next, the stage control unit 54 moves the stage S on which the object to be observed 8 is placed, thereby moving the observation range of the object to be observed 8 to a different observation range. Then, step S2 is executed again and a first interference image of the new observation range is acquired. In step S21, the movement of the observation range and the acquisition of the first interference image of the new observation range are repeated. As a result, in step S21, a first interference image of each of the multiple observation ranges is acquired.

[0116] Next, in step S22, the mode switching unit 53 switches the observation mode from interface observation mode to internal observation mode.

[0117] Next, in step S23 (internal observation step), step S7 shown in Figure 8 is executed, and a second interference image is acquired. Subsequently, the stage control unit 54 moves the stage S on which the object to be observed 8 is placed, thereby moving the observation range of the object to be observed 8 to another observation range. Then, step S7 is executed again, and a second interference image of the new observation range is acquired. In step S23, the movement of the observation range and the acquisition of the second interference image of the new observation range are repeated. As a result, in step S23, a second interference image of each of the multiple observation ranges is acquired. The stage control unit 54 moves the stage S so that the multiple observation ranges in step S23 coincide with the multiple observation ranges in step S21.

[0118] Next, in step S24 (display step), the processing unit 51 displays the first interference image and the second interference image on the GUI 6 for each observation range.

[0119] As shown in Figure 17, according to the above example of operation, surface defects K are observed in multiple observation ranges in interface observation mode. After observing multiple observation ranges in interface observation mode, the observation mode switches to internal observation mode. Then, in internal observation mode, internal defects K are observed in the same multiple observation ranges as in interface observation mode.

[0120] According to the operation example described above, foreign objects in the object 8 can be accurately inspected for each observation range. Furthermore, even when imaging multiple observation ranges using both interface observation mode and internal observation mode, the dead time associated with switching observation modes can be reduced. In the above operation example, the observation mode is switched only once, between step S21 and step S23. This allows for efficient observation of multiple observation ranges in the object 8.

[0121] In the above example, steps S21, S22, and S23 were executed in this order, but steps S23, S22, and S21 may also be executed in this order. In other words, imaging in internal observation mode for multiple observation ranges, switching of observation modes, and imaging in interface observation mode for multiple observation ranges may be executed in this order.

[0122] [First Modified Example According to the First Embodiment] Next, a first modified example according to the first embodiment will be described. The difference between the interference observation device 1A of the first modified example shown in Figure 18 and the first embodiment is that the interference observation device 1A is equipped with a variable focus lens 9 (focal plane position adjustment unit) instead of the lens 41. In the interference observation device 1A shown in Figure 18, the observation mode is switched to internal observation mode.

[0123] The variable-focus lens 9 is positioned on the optical path of the interference light L3 from the interference optical system 3 to the imaging surface 4a of the image sensor 4. The variable-focus lens 9 takes the interference light L3 output from the beam splitter 12 as input and outputs the interference light L3 to the image sensor 4. The variable-focus lens 9 is a lens that changes its focal length according to, for example, the input current value. In the internal observation mode, the variable-focus lens 9 adjusts the position of the focal plane F1 (observation surface R) of the objective lens 13, which is conjugate to the imaging surface 4a of the image sensor 4, on the optical path of the first light L1. Specifically, the variable-focus lens 9 adjusts the position of the focal plane F1 in the Z direction on the optical path of the first light L1 from the beam splitter 12 as a branching section to the beam splitter 12 as a multiplexing section. The variable-focus lens 9 adjusts the position of the focal plane F1 so that the defect K in the object to be observed 8 is located around the focal plane F1.

[0124] At this time, the variable focus lens 9 simultaneously adjusts the position of the focal plane F2 of the reference objective lens 14, which is conjugate to the imaging surface 4a of the image sensor 4, on the optical path of the second optical beam L2 in the internal observation mode. Specifically, the variable focus lens 9 adjusts the position of the focal plane F2 in the X direction on the optical path of the second optical beam L2 from the beam splitter 12 as a branching section to the beam splitter 12 as a multiplexing section. By adjusting the focal plane F1 and the focal plane F2 simultaneously, the conjugate relationship between the back surface (reflective surface) 8b in the optical path of the first optical beam L1 and the reference reflective surface 15a in the optical path of the second optical beam L2 is maintained even when the position of the focal plane F1 in the Z direction is changed.

[0125] The interference observation device 1A of the first modified example described above also allows for easy observation of the interface and interior of the object to be observed 8. Furthermore, in the interference observation device 1A, in the interior observation mode, the position of the focal plane F1 of the objective lens 13, which is conjugate to the imaging surface 4a of the image sensor 4, on the optical path of the first light L1 is adjusted by the variable focus lens 9, thereby changing the observation depth of the object to be observed 8. This allows the object to be scanned in the Z direction.

[0126] [Second Modification According to the First Embodiment] Next, a second modification according to the first embodiment will be described. The difference between the interference observation device 1B of the second modification shown in Figure 19 and the first embodiment is that the interference observation device 1B is equipped with one objective lens 13B instead of the objective lens 13 and the reference objective lens 14. In the interference observation device 1B shown in Figure 19, the observation mode is switched to internal observation mode.

[0127] The objective lens 13B is positioned between the beam splitter 12 and the lens 41. The objective lens 13B guides the interference light L3 output from the beam splitter 12 to the lens 41. The magnification of the objective lens 13B is, for example, 2x, 5x, 10x, etc. The focal plane F1 of the objective lens 13B is located on the optical path of the first light L1 from the beam splitter 12 as a branching section to the beam splitter 12 as a multiplexing section. The focal plane F2 of the objective lens 13B is located on the optical path of the second light L2 from the beam splitter 12 as a branching section to the beam splitter 12 as a multiplexing section.

[0128] In the interference observation device 1B, when switching the observation mode between interface observation mode and internal observation mode, the mode switching unit 53 controls the stepping motor 18 to move the reference mirror 15 along the X direction. When switching the observation mode from interface observation mode to internal observation mode, the mode switching unit 53 moves the reference mirror 15 to the rear X2 (see Figure 5) so that the reference mirror 15 is located behind the focal plane F2 of the objective lens 13B. When switching the observation mode from internal observation mode to interface observation mode, the mode switching unit 53 moves the reference mirror 15 to the front X1 (see Figure 5) so that the focal plane F2 of the objective lens 13B is located on the reference mirror 15. The focal plane F1 of the objective lens 13B is located on the observation plane R in both interface observation mode and internal observation mode.

[0129] The interference observation device 1B of the first modified example described above also allows for easy observation of the interface and interior of the object to be observed 8. Furthermore, the interference observation device 1B has a relatively small number of objective lenses, which allows for miniaturization of the interference observation device 1B, easier adjustment of the interference observation device 1B, and reduction of wavefront distortion.

[0130] [Second Embodiment] Next, an interference observation device 201 according to the second embodiment will be described. The interference observation device 201 of the second embodiment shown in Figures 20 and 21 differs from the first embodiment in that the interference observation device 201 includes a first light source 21 and a second light source 22 that outputs light of a different wavelength from the light output from the first light source 21, the interference optical system 3 includes a reference mirror 215 instead of a reference mirror 15 (see Figure 1), and the interference optical system 3 includes an anti-reflective coating AR. The first light source 21 and the second light source 22 have the same configuration as, for example, the light source 2.

[0131] In the interference observation device 201 shown in Figure 20, the observation mode is switched to interface observation mode, while in the interference observation device 201 shown in Figure 21, the observation mode is switched to internal observation mode. In Figure 20, of the first light source 21 and the second light source 22, only the first light source 21 is shown, and the second light source 22 is omitted. In Figure 21, of the first light source 21 and the second light source 22, only the second light source 22 is shown, and the first light source 21 is omitted. The same applies to Figures 22 and 23, which will be described later.

[0132] As shown in Figure 20, the beam splitter 12 splits the light output from the first light source 21 into a first beam L11 and a second beam L21. The beam splitter 12 outputs the first beam L11 to the objective lens 13 and the second beam L21 to the reference objective lens 14. As shown in Figure 21, the beam splitter 12 splits the light output from the second light source 22 into a first beam L12 and a second beam L22. The beam splitter 12 outputs the first beam L12 to the objective lens 13 and the second beam L22 to the reference objective lens 14.

[0133] The reference mirror 215 is a component formed from the same material as the object to be observed 8 and with the same thickness. The reference mirror 215 has a surface (first reference reflective surface) 215a located on the side of the reference objective lens 14 and a back surface (second reference reflective surface) 215b located on the opposite side of the surface 215a. The back surface 215b is separated from the surface 215a toward the opposite side of the reference objective lens 14 (the left side in Figures 20 and 21). The focal plane F2 of the reference objective lens 14 is located on the surface 215a in both the interface observation mode and the internal observation mode. The surface 215a has an anti-reflective coating AR.

[0134] The anti-reflective film AR is a film that transmits light output from the second light source 22. Specifically, the anti-reflective film AR transmits the second light L22 separated from the second light source 22 and reflects the second light L21 separated from the first light source 21. As a result, the second light L22 is transmitted through the surface 215a. The anti-reflective film AR is formed, for example, from a dielectric multilayer film.

[0135] The mode switching unit 53 switches the on / off state of the first light source 21 and the second light source 22, respectively. When the mode switching unit 53 turns the first light source 21 on and turns the second light source 22 off (the state shown in Figure 20), the interference light L3 of the first light L11 reflected from the observation surface R and the second light L21 reflected from the surface 215a of the reference mirror 215 is detected by the image sensor 4. As a result, the mode switching unit 53 switches the observation mode to interface observation mode.

[0136] On the other hand, when the mode switching unit 53 turns off the first light source 21 and turns on the second light source 22 (as shown in Figure 21), the interference light L3 between the first light L12 reflected from the back surface 8b of the object to be observed 8 and the second light L22 transmitted through the surface 215a of the reference mirror 215 by the anti-reflective film AR and reflected from the back surface 215b is detected by the image sensor 4. In this state, the optical path length of the second light L22 is longer than the optical path length of the second light L21 by at least the amount by which the second light L22 passes inside the reference mirror 215. As a result, the mode switching unit 53 switches the observation mode to the internal observation mode. In this way, in the second embodiment, the optical path length of the second light is controlled by the mode switching unit 53 switching the on / off states of the first light source 21 and the second light source 22, respectively.

[0137] Alternatively, instead of alternately switching the on / off states of the first light source 21 and the second light source 22 included in the light source 2, imaging may be performed using an image sensor 4 that can output separate images for the wavelength of the first light source 21 and the wavelength of the second light source 22 while keeping both the first light source 21 and the second light source 22 constantly lit. In other words, with both the first light source 21 and the second light source 22 lit, the image sensor 4 may output separately the detection result of interference light L3 between the first light L11 reflected from the observation surface R and the second light L21 reflected from the surface 215a of the reference mirror 215 (first detection result), and the detection result of interference light L3 between the first light L12 reflected from the back surface 8b of the object to be observed 8 and the second light L22 reflected from the back surface 215b of the reference mirror 215 (second detection result). Such an image sensor 4 may be a color camera in which a color filter that transmits the wavelength of a first light source 21 and a color filter that transmits the wavelength of a second light source 22 are arranged in a periodic pattern on a single semiconductor image sensor chip, or it may be a camera in which light with color split by a dichroic mirror is incident on two semiconductor image sensors whose fields of view substantially coincide. The processing unit 51 may acquire a first interference image as an interference image in interface observation mode based on the first detection result, and acquire a second interference image as an interference image in internal observation mode based on the second detection result. The interference image in interface observation mode and the interference image in internal observation mode may be acquired simultaneously. In other words, interface observation and internal observation of the object to be observed 8 may be performed simultaneously.

[0138] In the second embodiment, a moving mechanism MM1 for moving the reference mirror 215 is provided. The moving mechanism MM1 may include a stepping motor for adjusting the position of the reference mirror 215 or a piezoelectric element for finely moving the reference mirror 215 in accordance with the timing of interference image acquisition.

[0139] The interference observation device 201 of the second embodiment described above also allows for easy observation of the interface and interior of the object to be observed 8. Furthermore, as mentioned above, by devising the material and coating of the reference mirror 215, the observation mode can be switched without moving the reference mirror 215 and the reference objective lens 14. This allows for high-speed switching of the observation mode and makes it easy to realize such a configuration.

[0140] [Third Embodiment] Next, an interference observation device 301 according to the third embodiment will be described. The difference between the interference observation device 301 of the third embodiment shown in Figures 22 and 23 and the second embodiment is that the interference optical system 3 of the interference observation device 301 is equipped with a first reference mirror 315 and a second reference mirror 415 instead of the reference mirror 215 (see Figures 20 and 21). In the interference observation device 301 shown in Figure 22, the observation mode is switched to interface observation mode, and in the interference observation device 301 shown in Figure 23, the observation mode is switched to internal observation mode.

[0141] The first reference mirror 315 has a reference reflective surface (first reference reflective surface) 315a. The second reference mirror 415 has a reference reflective surface (second reference reflective surface) 415a. The first reference mirror 315 is positioned on the reference objective lens 14 side relative to the second reference mirror 415. The reference reflective surface 415a is separated from the reference reflective surface 315a toward the opposite side of the reference objective lens 14 (left side in Figures 22 and 23). The focal plane F2 of the reference objective lens 14 is located on the reference reflective surface 315a in both interface observation mode and internal observation mode. The reference reflective surface 315a has an anti-reflective coating AR.

[0142] The anti-reflective film AR is a film that transmits light output from the second light source 22. Specifically, the anti-reflective film AR transmits the second light L22 separated from the second light source 22 and reflects the second light L21 separated from the first light source 21.

[0143] The mode switching unit 53 switches the on / off state of the first light source 21 and the second light source 22, respectively. When the mode switching unit 53 turns the first light source 21 on and turns the second light source 22 off (the state shown in Figure 22), the interference light L3 of the first light L11 reflected from the observation surface R and the second light L21 reflected from the reference reflection surface 315a of the first reference mirror 315 is detected by the image sensor 4. As a result, the mode switching unit 53 switches the observation mode to interface observation mode.

[0144] On the other hand, when the mode switching unit 53 turns off the first light source 21 and turns on the second light source 22 (the state shown in Figure 23), the interference light L3 between the first light L12 reflected from the back surface 8b of the object to be observed 8 and the second light L22 that is transmitted through the reference reflective surface 315a of the first reference mirror 315 by the anti-reflective film AR and reflected by the reference reflective surface 415a of the second reference mirror 415 is detected by the image sensor 4. In this state, the optical path length of the second light L22 is longer than the optical path length of the second light L21 by at least the amount by which the second light L22 passes inside the first reference mirror 315. As a result, the mode switching unit 53 switches the observation mode to the internal observation mode. Thus, in the third embodiment, reference mirrors are provided for use in the interface observation mode and the internal observation mode, respectively.

[0145] In addition, similar to the second embodiment, instead of alternately switching the on / off states of the first light source 21 and the second light source 22 included in the light source 2, imaging may be performed using an image sensor 4 that can output separate images for the wavelength of the first light source 21 and the wavelength of the second light source 22 while keeping the first light source 21 and the second light source 22 constantly lit. In other words, with both the first light source 21 and the second light source 22 lit, the image sensor 4 may output separately the detection result of interference light L3 between the first light L11 reflected from the observation surface R and the second light L21 reflected from the reference reflection surface 315a of the first reference mirror 315 (first detection result), and the detection result of interference light L3 between the first light L12 reflected from the back surface 8b of the object to be observed 8 and the second light L22 reflected from the reference reflection surface 415a of the second reference mirror 415 (second detection result). Such an image sensor 4 may be a color camera in which a color filter that transmits the wavelength of a first light source 21 and a color filter that transmits the wavelength of a second light source 22 are arranged in a periodic pattern on a single semiconductor image sensor chip, or it may be a camera in which light with color split by a dichroic mirror is incident on two semiconductor image sensors whose fields of view substantially coincide. The processing unit 51 may acquire a first interference image as an interference image in interface observation mode based on the first detection result, and acquire a second interference image as an interference image in internal observation mode based on the second detection result. The interference image in interface observation mode and the interference image in internal observation mode may be acquired simultaneously. In other words, interface observation and internal observation of the object to be observed 8 may be performed simultaneously.

[0146] In the third embodiment, a moving mechanism MM2 is provided for moving the first reference mirror 315. The moving mechanism MM2 may include a stepping motor for adjusting the position of the first reference mirror 315, a piezoelectric element for precisely moving the first reference mirror 315 in accordance with the timing of interference image acquisition. In the third embodiment, a moving mechanism MM3 is provided for moving the second reference mirror 415. The moving mechanism MM3 may include a stepping motor for adjusting the position of the second reference mirror 415, a piezoelectric element for precisely moving the second reference mirror 415 in accordance with the timing of interference image acquisition.

[0147] The interference observation device 301 of the third embodiment described above also allows for easy observation of the interface and interior of the object to be observed 8. Furthermore, the interference observation device 301 of the third embodiment, like the second embodiment, allows for high-speed switching of observation modes, and such a configuration can be easily realized.

[0148] [Modifications] The embodiments described above are not limited to the embodiments and modifications described above.

[0149] In the above embodiments and modifications, various objects may be used as the object to be observed 8. For example, according to the above embodiments and modifications, by using a substrate containing a compound semiconductor such as silicon (Si) or gallium nitride (GaN) as the object to be observed 8, the substrate can be inspected with high accuracy. Furthermore, if the main material of the object to be observed 8 is silicon (Si), by using a near-infrared light source as the light source 2, the object to be observed 8 can be inspected with high accuracy.

[0150] In the above embodiments and modifications, the interference optical system 3 was configured as a Linick interference type, but the interference optical system 3 may also be configured as a Mirau interference type. In the above embodiments and modifications, the number of interference images used to construct the first interference image and the second interference image is not particularly limited and may be one or more.

[0151] In the second embodiment described above, the reference mirror 215 was formed from the same material and with the same thickness as the object to be observed 8. However, in the internal observation mode, the material and thickness of the reference mirror 215 are not limited as long as the optical path length of the first light L12 and the optical path length of the second light L22 are the same.

[0152] The components in the above embodiments and modifications are not limited to the materials and shapes described above, and various materials and shapes can be applied. Furthermore, the components in the above embodiments and modifications can be arbitrarily applied to the components in other embodiments or modifications.

[0153] 1, 1A, 1B, 201, 301... Interferometry observation device, 2... Light source, 3... Interferometry optical system, 4... Image sensor, 4a... Imaging surface, 6... GUI (Display unit), 8... Object to be observed, 8a... Front surface, 8b... Back surface (reflective surface), 8c... Conjugate surface, 8d... Bonding surface, 9... Variable focus lens (Focal plane position adjustment unit), 13, 13B... Objective lens, 14... Reference objective lens, 15, 215... Reference mirror, 15a... Reference reflective surface, 21... First light source, 22... Second light source, 51... Processing unit, 52... Mode selection unit, 53...Mode switching section, 215a...Front surface (first reference reflective surface), 215b...Back surface (second reference reflective surface), 315...First reference mirror, 315a...Reference reflective surface (first reference reflective surface), 415...Second reference mirror, 415a...Reference reflective surface (second reference reflective surface), AR...Anti-reflective coating, D1, D2, t...Distance, F1, F2...Focal plane, L1, L11, L12...First light, L2, L21, L22...Second light, L3...Interference light, ME...Metal, R...Observation surface, S...Stage, V...Void.

Claims

A light source that emits light, An interference optical system having a reference mirror, which splits the light output from the light source into a first beam and a second beam, and outputs interference light of the first beam reflected by the object being observed or reflected after passing through the object being observed and the second beam reflected by the reference mirror, An image sensor for detecting the aforementioned interference light, A processing unit that acquires an interference image based on the detection result of the interference light, The observation mode of the observation surface of the object to be observed is selected from between an interface observation mode, in which the first light is reflected by the observation surface, and an internal observation mode, in which the first light is transmitted through the observation surface and reflected by a reflective surface located away from the observation surface. Interferometry observation device, wherein the mode switching unit switches the observation mode between the interface observation mode and the internal observation mode by controlling the optical path length of the second light such that the optical path length of the second light in the internal observation mode is longer than the optical path length of the second light in the interface observation mode. 　 The system further includes a mode selection unit for selecting one of the interface observation mode and the internal observation mode. The interference observation apparatus according to claim 1, wherein the mode switching unit switches the observation mode according to the selection made by the mode selection unit. 　 The interference optical system has a reference objective lens that guides the second light to the reference mirror, The interference observation apparatus according to claim 1 or 2, wherein the mode switching unit controls the optical path length of the second light by moving the reference mirror and the reference objective lens. 　 The reference mirror has a reference reflective surface that reflects the second light in both the interface observation mode and the internal observation mode. The interference observation apparatus according to claim 3, wherein the mode switching unit moves the reference mirror a distance D1 along a vertical direction perpendicular to the reference reflective surface that satisfies the following formula (1), and moves the reference objective lens a distance D2 along the vertical direction to the same side as the side on which the reference mirror moves that satisfies the following formula (2). D1 = t × n ... (1) D2=t×(n-(1 / n))...(2) however, t: distance between the observation surface and the reflective surface of the first light, n: refractive index of the object being observed. The interference observation apparatus according to claim 4, wherein the mode switching unit receives input the distance t, the refractive index n, and at least one of the material of the object to be observed. 　 The interference observation apparatus according to any one of claims 1 to 5, wherein the observation surface is the interface between the surface of the object to be observed and the surrounding atmosphere of the object to be observed. 　 The interference observation apparatus according to any one of claims 1 to 5, wherein the observation surface is an interface inside the object to be observed. 　 The object to be observed is a bonded wafer, The interference observation apparatus according to claim 7, wherein the observation surface is the bonding surface of the bonded wafer. 　 The processing unit determines that there is metal on or near the bonding surface when the brightness of the interference image is greater than a threshold, The interference observation apparatus according to claim 8, wherein the mode switching unit switches the observation mode between the interface observation mode and the internal observation mode based on the determination result by the processing unit. 　 If the determination result by the processing unit indicates that there is no metal in the interface observation mode, the mode switching unit switches the observation mode from the interface observation mode to the internal observation mode. The interference observation apparatus according to claim 9, wherein if the determination result by the processing unit indicates that the metal is present in the internal observation mode, the mode switching unit switches the observation mode from the internal observation mode to the interface observation mode. 　 The interference observation apparatus according to any one of claims 1 to 10, wherein the mode switching unit acquires position information indicating the position of the reflective surface in a vertical direction perpendicular to the reflective surface of the first light, and controls the optical path length of the second light based on the position information. 　 The aforementioned processing unit, When the mode switching unit switches the observation mode to the interface observation mode and the image sensor detects the interference light, a first interference image is acquired based on the detection result. When the observation mode is switched to the internal observation mode by the mode switching unit and the interfering light is detected by the image sensor, a second interfering image is acquired based on the detection result. An interference observation device according to any one of claims 1 to 11, wherein a third interference image is obtained by subtracting the first interference image, which is obtained in the same observation range as the second interference image and multiplied by a constant, from the second interference image. 　 The interference observation device according to claim 12, further comprising a display unit for displaying the third interference image. 　 The system further includes a focal plane position adjustment unit provided on the optical path of the interference light from the interference optical system to the imaging surface of the image sensor, The interference optical system has an objective lens that guides the first light to the object to be observed, or guides the interference light to the image sensor. The interference observation apparatus according to any one of claims 1 to 13, wherein the focal plane position adjustment unit adjusts the position of the focal plane of the objective lens, which is conjugate to the imaging plane, on the optical path of the first light in the internal observation mode. 　 The light source comprises a first light source that outputs the light, and a second light source that outputs the light of a different wavelength from the light output from the first light source. The reference mirror has a first reference reflective surface that reflects the second light in the interface observation mode, and a second reference reflective surface that reflects the second light that has passed through the first reference reflective surface in the internal observation mode, and is located away from the first reference reflective surface. The first reference reflective surface has an anti-reflective coating that transmits the light output from the second light source, The mode switching unit is By turning the first light source ON and the second light source OFF, the observation mode is switched to the interface observation mode. The interference observation apparatus according to claim 1 or 2, wherein the observation mode is switched to the internal observation mode by turning off the first light source and turning on the second light source. 　 The interference observation apparatus according to claim 15, wherein the reference mirror is a member formed from the same material as the object to be observed and is formed to have the same thickness as the object to be observed. 　 The interference observation apparatus according to claim 15, wherein the reference mirror comprises a first reference mirror having a first reference reflective surface and a second reference mirror having a second reference reflective surface. 　 The reference mirror has a reference reflective surface that reflects the second light in the interface observation mode, An interference observation apparatus according to any one of claims 1 to 17, wherein in the interface observation mode, the imaging surface of the image sensor and the observation surface are conjugate to each other, and the imaging surface and the reference reflective surface are conjugate to each other. 　 The reference mirror has a reference reflective surface that reflects the second light in the internal observation mode, The interference observation apparatus according to any one of claims 1 to 18, wherein in the internal observation mode, the conjugate plane of the first light reflecting surface and the reference reflecting surface are in a conjugate relationship with each other. 　 The interference observation apparatus according to any one of claims 1 to 19, wherein in the internal observation mode, the difference between the optical path length of the first light and the optical path length of the second light is within the coherence length of the light output from the light source. 　 The interference optical system has an objective lens that guides the first light to the object to be observed, or guides the interference light to the image sensor. The interference observation apparatus according to any one of claims 1 to 20, wherein the position of the focal plane of the objective lens on the optical path of the first light is the same between the interface observation mode and the internal observation mode. 　 A light source that emits light, An interference optical system having a reference mirror, which splits the light output from the light source into a first beam and a second beam, and outputs interference light of the first beam reflected by the object being observed or reflected after passing through the object being observed and the second beam reflected by the reference mirror, An image sensor for detecting the aforementioned interference light, The system includes a processing unit that acquires an interference image based on the detection result of the interference light, The light source comprises a first light source that outputs the light, and a second light source that outputs the light of a different wavelength from the light output from the first light source. The reference mirror has a first reference reflective surface and a second reference reflective surface located away from the first reference reflective surface. The first reference reflective surface has an anti-reflective coating that transmits the light output from the second light source, The aforementioned imaging sensor is The first detection result is the detection result of the interference light between the first light, which is separated from the light output from the first light source and reflected from the observation surface of the object to be observed, and the second light, which is separated from the light output from the first light source and reflected from the first reference reflection surface. The first light, which is separated from the light output from the second light source, passes through the observation surface of the object being observed and is reflected by a reflective surface away from the observation surface, and the second detection result, which is the detection result of the interference light between the first light and the second light, which is separated from the light output from the second light source, passes through the first reference reflective surface and is reflected by the second reference reflective surface, are output separately. The aforementioned processing unit, Based on the first detection result, a first interference image is acquired as the interference image in the interface observation mode for observing the interface of the object to be observed. An interference observation device that, based on the second detection result, acquires a second interference image as the interference image in an internal observation mode for observing the inside of the object to be observed. 　 An observation step comprising: a light output step of outputting light from a light source; an interference light output step of splitting the 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 object to be observed or reflected after passing through the object to be observed and the second light reflected by a reference mirror; an interference light detection step of detecting the interference light; and an interference image acquisition step of acquiring an interference image based on the detection result of the interference light, The observation mode switching step includes switching the observation mode of the observation surface of the object to be observed between an interface observation mode, in which the first light is reflected from the observation surface, and an internal observation mode, in which the first light is transmitted through the observation surface and reflected from a reflective surface away from the observation surface. Interferometry method, wherein in the observation mode switching step, the optical path length of the second light is controlled such that the optical path length of the second light in the internal observation mode is longer than the optical path length of the second light in the interface observation mode, thereby switching the observation mode between the interface observation mode and the internal observation mode. 　 With an additional subtraction step, The object to be observed is a bonded wafer having voids on the bonding surface, The observation surface is the bonding surface, In the aforementioned interference image acquisition step, When the observation mode is switched to the interface observation mode by the observation mode switching step, and interference light is detected by the interference light detection step, a first interference image is acquired based on the detection result. When the observation mode is switched to the internal observation mode by the observation mode switching step, and interference light is detected by the interference light detection step, a second interference image is acquired based on the detection result. In the subtraction step, The interference observation method according to claim 23, wherein a third interference image showing the void is obtained by subtracting the first interference image, which is obtained in the same observation range as the second interference image and multiplied by a constant, from the second interference image. 　 With an additional subtraction step, The object to be observed is a substrate having a scratch near its surface. The observation surface is the surface of the substrate, In the aforementioned interference image acquisition step, When the observation mode is switched to the interface observation mode by the observation mode switching step, and interference light is detected by the interference light detection step, a first interference image is acquired based on the detection result. When the observation mode is switched to the internal observation mode by the observation mode switching step, and interference light is detected by the interference light detection step, a second interference image is acquired based on the detection result. In the subtraction step, The interference observation method according to claim 23, wherein a third interference image showing the defect is obtained by subtracting the first interference image, which is obtained from the second interference image within the same observation range as the second interference image and multiplied by a constant, from the second interference image. 　 In the state in which the observation mode has been switched to the interface observation mode by the observation mode switching step, the observation range of the object to be observed is moved by moving the stage on which the object to be observed is placed, and the observation step is performed for each of the multiple observation ranges, Interference observation method according to any one of claims 23 to 25, further comprising: an internal observation step in which, in a state in which the observation mode has been switched to the internal observation mode by the observation mode switching step, the observation range on the object to be observed is moved by moving the stage, and the observation step is performed for each of the plurality of observation ranges.

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