Observation device and observation method

Abstract

To provide an observation device and an observation method for achieving tact improvement.SOLUTION: A laser processing device 1 includes: an imaging unit 4 having a light source, an objective lens, and a light detection part; a drive unit 7 for moving the imaging unit 4 in a Z direction being a vertical direction; an actuator for moving the objective lens in the Z direction; and a control part 8. The control part 8 executes first control for controlling the drive unit 7 so as to move the imaging unit 4 to a position at which a rear face becomes a condensation position, and second control for controlling the actuator so as to move the objective lens to a position at which a first region being a region between the rear face and a front face becomes a condensation position, and controlling the actuator so as to move the objective lens to a position at which a second region being a region of an opposite side from the front face with respect to the rear face becomes a condensation position after the first control.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] One aspect of the present invention relates to an observation device and an observation method. [Background technology]

[0002] A laser processing device is known that cuts a wafer, which includes a semiconductor substrate and a functional element layer formed on the semiconductor substrate, along each of a plurality of lines by irradiating the wafer with laser light from one surface side of the semiconductor substrate, thereby forming a plurality of rows of modified regions inside the semiconductor substrate along each of the plurality of lines. The laser processing device described in Patent Document 1 includes an imaging unit (e.g., an infrared camera), and makes it possible to observe the modified regions formed inside the semiconductor substrate and processing damage formed in the functional element layer from one surface side of the semiconductor substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-64746 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of observing information related to the modified region (for example, a crack extending from the modified region) in the laser processing device as described above, for example, the tip of a crack extending from the modified region toward the other surface (the surface opposite to the surface irradiated with the laser light) cannot be detected by making the tip the focal point, but can be detected by making a point symmetrical to the tip with respect to the other surface the focal point. In this way, when it is necessary to make a point symmetrical with respect to the other surface the focal point, the imaging area becomes wide. Usually, the imaging section is moved in the vertical direction (Z direction) by a control unit that moves the entire imaging section, but when the imaging area is wide, the focal position cannot be moved at a sufficiently high speed. The time required to move the focal position becomes longer than the imaging rate, which causes a decrease in tact time. In addition, even if the focal position can be moved at high speed, the vibration is difficult to settle after the movement by moving the entire imaging section at high speed, and imaging cannot be performed until the vibration settles, which results in a decrease in tact time.

[0005] One aspect of the present invention has been made in view of the above-mentioned circumstances, and relates to an observation device and an observation method that can improve takt time. [Means for solving the problem]

[0006] An observation device according to one embodiment of the present invention is an observation device for observing a wafer having a first surface and a second surface, in which a modified region is formed by irradiating laser light from the first surface side, and includes an imaging section having a light source that outputs light that is transparent to the wafer, a focusing lens that focuses the light output from the light source at a focusing position on the wafer, and a light detection section that detects the light that has propagated through the wafer, a drive unit that supports the imaging section and moves the imaging section in the Z direction, which is the vertical direction, an actuator provided on the focusing lens that moves the focusing lens in the Z direction, and a control section, and the control section is configured to execute a first control that controls the drive unit so that the imaging section moves to a position where the second surface is at the focusing position, and a second control that controls the actuator after the first control so that the focusing lens moves to a position where at least a portion of the first region, which is the region between the second surface and the first surface, is at the focusing position, and so that the focusing lens moves to a position where at least a portion of the second region, which is the region on the opposite side of the first surface with respect to the second surface, is at the focusing position.

[0007] In the observation device according to one aspect of the present invention, in the observation of a wafer on which a modified region is formed, a drive unit that moves the imaging unit in the Z direction is controlled so that the imaging unit moves to a position where the second surface (rear surface) of the wafer becomes the focusing position, and then, the condenser lens moves to a position where the first region, which is the region between the second surface and the first surface, becomes the focusing position, and an actuator that moves the condenser lens in the Z direction is controlled so that the condenser lens moves to a position where the second region, which is the region on the opposite side of the first surface with respect to the second surface, becomes the focusing position. In this way, by moving the condenser lens so that both the first region and the second region become the focusing positions, it is possible to appropriately perform both direct observation of cracks and the like from the modified region when the first region is the focusing position, and observation using the back surface (second surface) reflection of cracks and the like when the second region is the focusing position. And, since the movement of the condenser lens to focus the first region and the second region is performed by an actuator that moves only the condenser lens of the imaging unit, the focusing position can be moved at a high speed compared to, for example, the case where the entire imaging unit is moved, and vibration after the movement can also be suppressed. Here, the observation device according to one aspect of the present invention has a drive unit that moves the entire imaging section in the Z direction, and an actuator that moves the condenser lens of the imaging section in the Z direction. By providing both the drive unit and the actuator in this way, for example, it is possible to perform rough alignment by the drive unit and detailed alignment by the actuator, and it is possible to perform alignment (such as condenser alignment in the imaging range) that requires precision with high accuracy while suppressing the device cost. In the observation device according to one aspect of the present invention, first, the imaging section is controlled by the drive unit so that the second surface, which is the boundary surface between the first area and the second area, becomes the condenser position, and then the condenser lens is controlled by the actuator so that the first area and the second area become the condenser positions. Before the control by the actuator is started, the condenser position is aligned with the second surface (the boundary surface between the first area and the second area), so that the high-speed movement of the condenser lens with the first area and the second area as the condenser position can be appropriately performed by making the most of the movable range of the actuator.As described above, according to an observation device according to an aspect of the present invention, the focusing position can be moved at high speed, thereby improving the tact time.

[0008] The control unit may further execute a pre-control before the first control, which controls the actuator so that the actuator is fixed at the center position of the movable range of the actuator in the Z direction. This allows the second control to be executed in a state in which the actuator can be sufficiently moved in both directions (up and down) in the Z direction, and makes the most of the movable range of the actuator to appropriately perform high-speed movement of the focusing lens with the first region and the second region as focusing positions.

[0009] The control unit may be configured to execute a third control in which, in the second control, the actuator is controlled so that the position of the condenser lens moves in the Z direction in a state where the region near the second surface is the condensing position, the detailed position of the second surface is specified based on the light detection result by the light detection unit in this state, and the actuator is controlled so that the condenser lens moves to a reference position where the specified detailed position of the second surface is the condensing position, and a fourth control in which the actuator is controlled so that the condenser lens moves from the reference position to a position where at least a part of the first region is the condensing position and the actuator is controlled so that the condenser lens moves from the reference position to a position where at least a part of the second region is the condensing position. Even with the first control, it is considered that the condensing position may deviate from the second surface, for example, when the actual wafer thickness is different from the expected one. In this case, there is a risk that the imaging of the first region and the second region cannot be realized by making the most of the movable range of the actuator described above. In this regard, in the second control, the exact position of the second surface is identified based on the light detection results and set as the reference position (third control), and the focusing lens is moved from the reference position to the imaging range of the first and second areas by the actuator (fourth control).Therefore, even if the focusing position deviates from the second surface in the first control, the reference position can be appropriately set to realize imaging of the first and second areas making maximum use of the movable range of the actuator.

[0010] The control unit may be configured to execute a third control for controlling the actuator in the second control so that the position of the condenser lens moves in the Z direction in a state where the region near the second surface is the condensing position, specifying a detailed position of the second surface based on a result of light detection by the light detection unit in this state, and controlling the actuator so that the condenser lens moves to a reference position where the specified detailed position of the second surface is the condensing position, and may further execute a fifth control for controlling the drive unit to move the imaging unit to a position where at least a part of an unimaged region, which is a region in the first region or the second region and is not set as the condensing position when specifying the detailed position of the second surface in the third control, becomes the condensing position, and a sixth control for controlling the actuator to move to a position where the condenser lens of the imaging unit after the fifth control is set as a new reference position and the region included in the unimaged region becomes the condensing position. According to the third control, imaging of the vicinity of the second surface can be performed in the process of specifying the detailed position of the second surface. Therefore, in the present observation device, the drive unit is controlled so that the imaging section moves to a position where the unimaged region becomes the focusing position in the third control (fifth control), and the position of the focusing lens after the fifth control is set as a new reference position, and the actuator is controlled so that the focusing lens moves to a position where the unimaged region becomes the focusing position (sixth control). According to this configuration, the unimaged region is controlled to become the focusing position in the third control, so that imaging can be performed more efficiently without performing unnecessary imaging. Also, according to this configuration, even if the region to be imaged does not fit within the movable range of the actuator at the initial reference position, the region to be imaged can be reliably imaged by changing the reference position.

[0011] An observation method according to one aspect of the present invention is a method for observing a wafer having a first surface and a second surface, in which a modified region is formed by irradiating a laser beam from the first surface side, and includes a first step of moving an imaging unit to a position where the second surface is a focusing position by a drive unit that moves the imaging unit in the Z direction, which is the vertical direction, and a second step of moving a focusing lens included in the imaging unit to a position where at least a part of a first region, which is a region between the second surface and the first surface, is a focusing position by an actuator that moves a focusing lens included in the imaging unit in the Z direction, and moving the focusing lens to a position where at least a part of a second region, which is a region on the opposite side of the first surface with respect to the second surface, is a focusing position. According to the observation method according to one aspect of the present invention, the focusing position can be moved at high speed, thereby improving the tact time.

[0012] The observation method may further include, before the first step, a preliminary step of controlling the actuator so that the actuator is fixed at a center position of its movable range in the Z direction. With this configuration, the movable range of the actuator can be fully utilized to appropriately perform high-speed movement of the condenser lens with the first and second regions as condensing positions. Effect of the Invention

[0013] According to one aspect of the present invention, even when the imaging area is wide, the focusing position can be moved at high speed, thereby improving the tact time. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a configuration diagram of a laser processing apparatus according to one embodiment. [Diagram 2] FIG. 2 is a plan view of a wafer of one embodiment. [Diagram 3] 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2. [Figure 4] FIG. 2 is a configuration diagram of a laser irradiation unit shown in FIG. [Diagram 5] FIG. 2 is a configuration diagram of an inspection imaging unit shown in FIG. [Figure 6] FIG. 2 is a configuration diagram of an alignment correction imaging unit shown in FIG. [Figure 7] 6A to 6C are cross-sectional views of a wafer for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and images at various locations by the inspection imaging unit. [Figure 8] 6A to 6C are cross-sectional views of a wafer for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and images at various locations by the inspection imaging unit. [Figure 9] 1 is a SEM image of modified regions and cracks formed within a semiconductor substrate. [Figure 10] 1 is a SEM image of modified regions and cracks formed within a semiconductor substrate. [Figure 11] 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. [Figure 12] 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. [Figure 13] FIG. 1 is a diagram illustrating the configuration of an objective lens equipped with an actuator. [Figure 14] FIG. 1 is a diagram illustrating the configuration of an objective lens equipped with an actuator. [Figure 15] 1A and 1B are diagrams for explaining an overview of movement of a focusing position using a drive unit and an actuator. [Figure 16] 11A and 11B are diagrams for explaining details of movement of the focusing position using a drive unit and an actuator. [Figure 17] 11 is a flowchart illustrating an example of an observation method. [Figure 18] 11A and 11B are diagrams for explaining details of movement of the focusing position using a drive unit and an actuator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted. [Laser processing equipment configuration]

[0016] 1, the laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3, a plurality of imaging units 4, 5, 6, a drive unit 7, a control unit 8, and a display 150. The laser processing apparatus 1 is an apparatus that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L. The laser processing apparatus 1 is also an observation apparatus that observes the object 11 (a wafer 20 described later) on which the modified region 12 has been formed.

[0017] The stage 2 supports the object 11, for example, by adsorbing a film attached to the object 11. The stage 2 is movable along both the X direction and the Y direction, and is rotatable about an axis parallel to the Z direction. The X direction and the Y direction are a first horizontal direction and a second horizontal direction that are perpendicular to each other, and the Z direction is a vertical direction.

[0018] The laser irradiation unit 3 focuses laser light L, which is transparent to the object 11, and irradiates the object 11. When the laser light L is focused inside the object 11 supported by the stage 2, the laser light L is particularly absorbed in a portion corresponding to a focusing point C of the laser light L, and a modified region 12 is formed inside the object 11.

[0019] The modified region 12 is a region that differs from the surrounding non-modified region in terms of density, refractive index, mechanical strength, and other physical properties. Examples of the modified region 12 include a melting treatment region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 has a property that cracks tend to extend from the modified region 12 to the incident side of the laser light L and to the opposite side. Such a property of the modified region 12 is utilized for cutting the target object 11.

[0020] As an example, when the stage 2 is moved along the X direction and the focal point C is moved along the X direction relative to the object 11, multiple modified spots 12s are formed in a row along the X direction. One modified spot 12s is formed by irradiating one pulse of laser light L. One row of modified regions 12 is a collection of multiple modified spots 12s lined up in a row. Adjacent modified spots 12s may be connected to each other or separated from each other depending on the relative moving speed of the focal point C with respect to the object 11 and the repetition frequency of the laser light L.

[0021] The imaging unit 4 is an imaging section that captures an image of the modified region 12 formed in the target object 11 and the tip of the crack extending from the modified region 12.

[0022] Under the control of the control unit 8, the imaging units 5 and 6 capture an image of the object 11 supported on the stage 2 by light transmitted through the object 11. The images obtained by the imaging units 5 and 6 are used, for example, to align the irradiation position of the laser light L.

[0023] The drive unit 7 supports the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6. The drive unit 7 is a Z axis that moves the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6 along the Z direction.

[0024] The control unit 8 controls the operations of the stage 2, the laser irradiation unit 3, the multiple imaging units 4, 5, and 6, and the drive unit 7. The control unit 8 is configured as a computer device including a processor, a memory, a storage, a communication device, etc. In the control unit 8, the processor executes software (programs) loaded into the memory, etc., and controls the reading and writing of data in the memory and storage, as well as communication by the communication device.

[0025] The display 150 functions as an input unit that accepts information input from the user, and as a display unit that displays information to the user.

[0026] [Object composition] The object 11 in this embodiment is a wafer 20, as shown in FIG. 2 and FIG. 3. The wafer 20 includes a semiconductor substrate 21 and a functional device layer 22. In this embodiment, the wafer 20 is described as having the functional device layer 22, but the wafer 20 may or may not have the functional device layer 22, and may be a bare wafer. The semiconductor substrate 21 has a back surface 21a (second surface) and a front surface 21b (first surface). The semiconductor substrate 21 is, for example, a silicon substrate. The functional device layer 22 is formed on the back surface 21a of the semiconductor substrate 21. The functional device layer 22 includes a plurality of functional devices 22a arranged two-dimensionally along the back surface 21a. The functional device 22a is, for example, a light receiving device such as a photodiode, a light emitting device such as a laser diode, a circuit device such as a memory, or the like. The functional device 22a may be configured three-dimensionally by stacking a plurality of layers. Although the semiconductor substrate 21 has a notch 21c indicating the crystal orientation, an orientation flat may be provided instead of the notch 21c.

[0027] The wafer 20 is cut into functional elements 22a along each of the lines 15. The lines 15 pass between the functional elements 22a when viewed from the thickness direction of the wafer 20. More specifically, the lines 15 pass through the center (the center in the width direction) of the street region 23 when viewed from the thickness direction of the wafer 20. The street region 23 extends in the functional element layer 22 so as to pass between adjacent functional elements 22a. In this embodiment, the functional elements 22a are arranged in a matrix along the rear surface 21a, and the lines 15 are set in a lattice pattern. The lines 15 are virtual lines, but may be lines that are actually drawn.

[0028] [Laser irradiation unit configuration] As shown in Fig. 4, the laser irradiation unit 3 has a light source 31, a spatial light modulator 32, and a condenser lens 33. The light source 31 outputs laser light L, for example, by a pulse oscillation method. The spatial light modulator 32 modulates the laser light L output from the light source 31. The spatial light modulator 32 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 32. The condenser lens 33 may be a correction ring lens.

[0029] In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with laser light L from the front surface 21b side of the semiconductor substrate 21 along each of the multiple lines 15, thereby forming two rows of modified regions 12a, 12b inside the semiconductor substrate 21 along each of the multiple lines 15. The modified region 12a is the modified region closest to the back surface 21a among the two rows of modified regions 12a, 12b. The modified region 12b is the modified region closest to the modified region 12a among the two rows of modified regions 12a, 12b, and is the modified region closest to the front surface 21b.

[0030] The two rows of modified regions 12a, 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20. The two rows of modified regions 12a, 12b are formed by moving the two focusing points C1, C2 along the line 15 relative to the semiconductor substrate 21. The laser light L is modulated by the spatial light modulator 32, for example, so that the focusing point C2 is located on the rear side of the focusing point C1 in the traveling direction and on the incident side of the laser light L. The modified regions may be formed by a single focus or multiple focuses, and may be formed by one pass or multiple passes.

[0031] The laser irradiation unit 3 irradiates the wafer 20 with laser light L from the front surface 21b side of the semiconductor substrate 21 along each of the multiple lines 15. As an example, <100> The two focal points C1 and C2 are aligned at positions 54 μm and 128 μm from the back surface 21a of the semiconductor substrate 21, respectively, and the laser light L is irradiated from the front surface 21b of the semiconductor substrate 21 along each of the multiple lines 15 to the wafer 20. At this time, for example, when the condition is that the cracks 14 across the two rows of modified regions 12a and 12b reach the back surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099 nm, the pulse width is 700 nsec, and the repetition frequency is 120 kHz. The output of the laser light L at the focal point C1 is 2.7 W, the output of the laser light L at the focal point C2 is 2.7 W, and the relative moving speed of the two focal points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm / sec. In addition, for example, when the number of processing passes is 5, ZH80 (position 328 μm from the back surface 21a), ZH69 (position 283 μm from the back surface 21a), ZH57 (position 234 μm from the back surface 21a), ZH26 (position 107 μm from the back surface 21a), and ZH12 (position 49.2 μm from the back surface 21a) may be set as processing positions for the above-mentioned wafer 20. In this case, for example, the wavelength of the laser light L may be 1080 nm, the pulse width may be 400 nsec, the repetition frequency may be 100 kHz, and the moving speed may be 490 mm / sec.

[0032] The formation of the two rows of modified regions 12a, 12b and the cracks 14 is performed in the following case: that is, in a later process, for example, by grinding the surface 21b of the semiconductor substrate 21 to thin the semiconductor substrate 21 and expose the cracks 14 on the surface 21b, and cut the wafer 20 into a plurality of semiconductor devices along each of the plurality of lines 15.

[0033] [Configuration of the inspection imaging unit] As shown in FIG. 5, the imaging unit 4 (imaging section) has a light source 41, a mirror 42, an objective lens 43 (a condensing lens), and a light detection section 44. The imaging unit 4 captures an image of the wafer 20. Here, only an overview of the imaging unit 4 is described, and a more detailed configuration of the imaging unit 4 (specifically, the configuration of the objective lens 43 on which the actuator 70 (see FIG. 13) is mounted) will be described later. The light source 41 outputs light I1 that is transparent to the semiconductor substrate 21 of the wafer 20. The light source 41 is composed of, for example, a halogen lamp and a filter, and outputs light I1 in the near-infrared region. The light I1 output from the light source 41 is reflected by the mirror 42 and passes through the objective lens 43, and is irradiated onto the wafer 20 from the surface 21b side of the semiconductor substrate 21. The objective lens 43 functions as a condensing lens that condenses the light I1 output from the light source 41 at a condensing position on the wafer 20. At this time, the stage 2 supports the wafer 20 on which the two rows of modified regions 12a, 12b have been formed as described above.

[0034] The objective lens 43 passes the light I1 reflected by the back surface 21a of the semiconductor substrate 21. That is, the objective lens 43 passes the light I1 propagated through the semiconductor substrate 21. The numerical aperture (NA) of the objective lens 43 is, for example, 0.45 or more. The objective lens 43 has a correction collar 43a. The correction collar 43a corrects aberrations occurring in the light I1 in the semiconductor substrate 21, for example, by adjusting the distances between the multiple lenses constituting the objective lens 43. Note that the means for correcting the aberrations is not limited to the correction collar 43a, and may be other correction means such as a spatial light modulator. The light detection unit 44 detects the light I1 transmitted through the objective lens 43 and the mirror 42 (i.e., the light propagated through the wafer 20). The light detection unit 44 is, for example, configured by an InGaAs camera, and detects the light I1 in the near-infrared region. The means for detecting (capturing) the light I1 in the near-infrared region is not limited to an InGaAs camera, and may be any other imaging means that captures images in a transmission type, such as a transmission confocal microscope.

[0035] The imaging unit 4 can capture images of each of the two rows of modified regions 12a, 12b and the tips of each of the multiple cracks 14a, 14b, 14c, and 14d (details will be described later). The crack 14a is a crack that extends from the modified region 12a to the back surface 21a. The crack 14b is a crack that extends from the modified region 12a to the front surface 21b. The crack 14c is a crack that extends from the modified region 12b to the back surface 21a. The crack 14d is a crack that extends from the modified region 12b to the front surface 21b.

[0036] [Configuration of the imaging unit for alignment correction] 6, the imaging unit 5 has a light source 51, a mirror 52, a lens 53, and a light detection unit 54. The light source 51 outputs light I2 that is transparent to the semiconductor substrate 21 of the wafer 20. The light source 51 is composed of, for example, a halogen lamp and a filter, and outputs light I2 in the near-infrared region. The light source 51 may be shared with the light source 41 of the imaging unit 4. The light I2 output from the light source 51 is reflected by the mirror 52 and passes through the lens 53, and is irradiated onto the wafer 20 from the surface 21b side of the semiconductor substrate 21.

[0037] The lens 53 passes the light I2 reflected by the rear surface 21a of the semiconductor substrate 21. That is, the lens 53 passes the light I2 propagated through the semiconductor substrate 21. The numerical aperture of the lens 53 is 0.3 or less. That is, the numerical aperture of the objective lens 43 of the imaging unit 4 is larger than the numerical aperture of the lens 53. The light detection unit 54 detects the light I2 that has passed through the lens 53 and the mirror 52. The light detection unit 54 is configured by, for example, an InGaAs camera, and detects the light I2 in the near-infrared region.

[0038] The imaging unit 5, under the control of the control unit 8, irradiates the wafer 20 with light I2 from the front surface 21b side and detects the light I2 returning from the rear surface 21a (functional element layer 22), thereby capturing an image of the functional element layer 22. Similarly, under the control of the control unit 8, the imaging unit 5, under the control of the control unit 8, irradiates the wafer 20 with light I2 from the front surface 21b side and detects the light I2 returning from the positions where the modified regions 12a and 12b are formed in the semiconductor substrate 21, thereby acquiring an image of the region including the modified regions 12a and 12b. These images are used for alignment of the irradiation position of the laser light L. The imaging unit 6 has a similar configuration to the imaging unit 5, except that the lens 53 has a lower magnification (for example, 6x in the imaging unit 5 and 1.5x in the imaging unit 6), and is used for alignment in the same manner as the imaging unit 5.

[0039] [Principle of imaging by inspection imaging unit] Using the imaging unit 4 shown in FIG. 5, the focal point F (the focal point of the objective lens 43) is moved from the front surface 21b side to the back surface 21a side with respect to the semiconductor substrate 21 in which the cracks 14 extending across the two rows of modified regions 12a, 12b reach the back surface 21a as shown in FIG. 7. In this case, when the focal point F is adjusted from the front surface 21b side to the tip 14e of the crack 14 extending from the modified region 12b to the front surface 21b side, the tip 14e can be confirmed (the image on the right side in FIG. 7). Hereinafter, such a method of adjusting the focal point F to the tip 14e of the crack 14 and observing the tip 14e may be referred to as direct observation. However, even if the focal point F is adjusted from the front surface 21b side to the cracks 14 themselves and the tip 14e of the cracks 14 reaching the back surface 21a, they cannot be confirmed (the image on the left side in FIG. 7). It should be noted that when the focal point F is adjusted from the front surface 21b side to the back surface 21a of the semiconductor substrate 21, the functional element layer 22 can be confirmed.

[0040] 5, the focal point F is moved from the front surface 21b side to the back surface 21a side of the semiconductor substrate 21 in which the cracks 14 extending across the two rows of modified regions 12a, 12b have not yet reached the back surface 21a, as shown in FIG. 8. In this case, even if the focal point F is aligned from the front surface 21b side to the tip 14e of the crack 14 extending from the modified region 12a to the back surface 21a side, the tip 14e cannot be confirmed (the image on the left side in FIG. 8). However, when the focal point F is aligned from the front surface 21b side to the region on the opposite side of the back surface 21a from the front surface 21b (i.e., the region on the functional element layer 22 side of the back surface 21a) with respect to the back surface 21a, the tip 14e can be confirmed by the reflected light from the back surface 21a (the image on the right side in FIG. 8). The virtual focal point Fv is a point symmetrical with the focal point F in terms of the back surface 21a, taking into account the refractive index of the semiconductor substrate 21. Hereinafter, the method of observing the tip 14e by focusing F on the area on the back surface 21a opposite to the front surface 21b and utilizing back surface reflection may be referred to as back surface reflection observation.

[0041] As described above, the reason why the crack 14 itself cannot be confirmed is assumed to be because the width of the crack 14 is smaller than the wavelength of the light I1, which is the illumination light. Figures 9 and 10 are SEM (Scanning Electron Microscope) images of the modified region 12 and the crack 14 formed inside the semiconductor substrate 21, which is a silicon substrate. (b) of Figure 9 is an enlarged image of the region A1 shown in (a) of Figure 9, (a) of Figure 10 is an enlarged image of the region A2 shown in (b) of Figure 9, and (b) of Figure 10 is an enlarged image of the region A3 shown in (a) of Figure 10. Thus, the width of the crack 14 is about 120 nm, which is smaller than the wavelength (e.g., 1.1 to 1.2 μm) of the light I1 in the near-infrared region.

[0042] Based on the above, the imaging principle is assumed to be as follows. As shown in FIG. 11(a), when the focal point F is located in air, the light I1 does not return, and a dark image is obtained (the image on the right side of FIG. 11(a)). As shown in FIG. 11(b), when the focal point F is located inside the semiconductor substrate 21, the light I1 reflected by the back surface 21a returns, and a whitish image is obtained (the image on the right side of FIG. 11(b)). As shown in FIG. 11(c), when the focal point F is aligned with the modified region 12 from the front surface 21b side, the modified region 12 absorbs, scatters, or the like a part of the light I1 reflected by the back surface 21a and returned, and an image is obtained in which the modified region 12 appears dark against a whitish background (the image on the right side of FIG. 11(c)).

[0043] As shown in (a) and (b) of FIG. 12, when the focal point F is focused on the tip 14e of the crack 14 from the surface 21b side, for example, due to optical singularities (stress concentration, distortion, discontinuity of atomic density, etc.) occurring near the tip 14e, light confinement occurring near the tip 14e, etc., a part of the light I1 reflected by the back surface 21a and returned is scattered, reflected, interfered, absorbed, etc., and an image in which the tip 14e appears black on a whitish background is obtained (the right image in (a) and (b) of FIG. 12). As shown in (c) of FIG. 12, when the focal point F is focused on a part other than the vicinity of the tip 14e of the crack 14 from the surface 21b side, at least a part of the light I1 reflected by the back surface 21a is returned, and a whitish image is obtained (the right image in (c) of FIG. 12).

[0044] [Configuration of objective lens equipped with actuator] 13 and 14, the actuator-mounted objective lens 43 included in the imaging unit 4 will be described below. Fig. 13 is a configuration diagram of the objective lens 43 on which an actuator 70 is mounted.

[0045] 13, the imaging unit 4 further includes an actuator 70 in addition to the components shown in FIG. 5. The actuator 70 is provided (attached) to the objective lens 43, and moves the objective lens 43 in the Z direction, which is the up-down direction. The actuator 70 is configured to be movable in the Z direction, and moves the objective lens 43 in the Z direction by moving in the Z direction. The movable range required for the actuator 70 is determined, for example, according to the size of the imaging area. The movable range of the actuator 70 is set, for example, so that the tip of the crack 14 extending from the modified area 12 is imaged when the imaging unit 4 is fixed to a predetermined position by the drive unit 7 (details will be described later).

[0046] Now, as shown in FIG. 13, it is assumed that two modified regions 12a, 12b are formed inside the wafer 20, and a crack 14 extends from the two modified regions 12a, 12b to the front surface 21b side and the back surface 21a side of the wafer 20. In the example shown in FIG. 13, the crack 14 does not reach the front surface 21b and the back surface 21a of the wafer 20. In such a case, in order to properly image the tip of the crack 14 extending from the modified region 12, it is required that the tip of the crack 14 on the front surface 21b side extending from the modified region 12b on the front surface 21b side can be directly observed (the tip of the crack 14 on the front surface 21b side can be the focusing position), and that the back surface reflection observation can be performed by focusing on a point on the opposite side of the tip of the crack 14 on the front surface 21b side with respect to the back surface 21a (the point on the opposite side can be the focusing position). In this case, the movable range required for the actuator 70 is the "ACT movable range" shown in FIG. 13.

[0047] In addition, when the modified region 12 is formed so that the crack 14 reaches at least the front surface 21b, such as when the modified region 12 is formed so that the crack 14 in the wafer 20 is in a full cut state in which the crack 14 reaches the front surface 21b and the back surface 21a, in order to properly image the tip of the crack 14 extending from the modified region 12, as shown in Fig. 14, it is required that the tip of the crack 14 on the front surface 21b side extending from the modified region 12d closest to the front surface 21b among the modified regions 12a, 12b, 12c, and 12d can be directly observed (the front surface 21b can be used as the focusing position), and that the back surface reflection can be observed by focusing on a point on the opposite side of the front surface 21b with respect to the back surface 21a (the point on the opposite side can be used as the focusing position). In this case, the movable range required for the actuator 70 is the "ACT movable range" shown in Fig. 14. For example, when the thickness of the wafer 20 made of a silicon substrate is 400 μm and the wafer 20 is in a fully cut state, the imaging range in the silicon is 400 μm+400 μm=800 μm (including the area on the opposite side of the back surface 21a from the front surface 21b). In this case, taking into account the difference in refractive index, the movable range of the actuator 70 in the air is preferably about 100 μm+100 μm=200 μm.

[0048] [Imaging control using drive units and actuators] In the following, with reference to Figs. 15 to 18, imaging control by the imaging unit 4 using the drive unit 7 (see Fig. 1) and the actuator 70 will be described. In the laser processing device 1, the control unit 8 (see Fig. 1) controls the drive unit 7 and the actuator 70 to move the focusing position in the imaging unit 4, thereby causing the imaging unit 4 to capture an image of the inside of the wafer 20. In such imaging control, the drive unit 7 performs rough alignment of the focusing position related to imaging, and the actuator 70 performs detailed alignment of the focusing position related to imaging. The drive unit 7 is configured to support the entire imaging unit 4 and to move the entire imaging unit 4 in the Z direction. The actuator 70 is attached to the objective lens 43 of the imaging unit 4 and is configured to move the objective lens 43 in the Z direction.

[0049] FIG. 15 is a diagram for explaining an outline of the movement of the focusing position using the drive unit 7 and the actuator 70. The control unit 8 is configured to execute a first control (see FIG. 15(a)) for controlling the drive unit 7 so that the imaging unit 4 moves to a position where the back surface 21a becomes the focusing position, and a second control (see FIG. 15(b)) for controlling the actuator 70 so that the objective lens 43 moves to a position where at least a part of the first region 28, which is a region between the front surface 21b and the back surface 21a, becomes the focusing position after the first control, and to control the actuator 70 so that the objective lens 43 moves to a position where at least a part of the second region 29, which is a region on the opposite side of the back surface 21a from the front surface 21b, becomes the focusing position (see FIG. 5(1c)). Note that the back surface 21a becoming the focusing position may include the vicinity of the back surface 21a (for example, a region within a range of ±10 μm from the back surface 21a) becoming the focusing position.

[0050] Furthermore, before executing the first control, the control unit 8 executes a preliminary control to control the actuator 70 so that the actuator 70 is fixed (center-fixed) at the center position in the Z direction of the movable range of the actuator 70. The center position of the operating range may be near the center position of the movable range, and for example, when the movable range of the actuator 70 is 80 μm, it may be a position of 40 μm±10 μm.

[0051] In the first control, as shown in FIG. 15(a), the drive unit 7 moves the entire imaging unit 4 in response to the control by the control unit 8 so that the light collection position is the back surface 21a. That is, the Z axis is dropped near the back surface 21a. As described above, the actuator 70 is fixed at the center with respect to the Z direction. Since the first area 28 and the second area 29, which are the imaging areas, are located symmetrically with respect to the back surface 21a (that is, the back surface 21a is the center of the imaging area in the Z direction), it can be said that the state in which the light collection position is the back surface 21a with the actuator 70 fixed at the center is the state in which the area in which imaging can be performed by the operation of the actuator 70 is maximized.

[0052] In the second control, as shown in FIG. 15(b), the actuator 70 first moves only the objective lens 43 in response to the control by the control unit 8 so that the focusing position is the first region 28. Next, as shown in FIG. 15(c), the actuator 70 moves only the objective lens 43 in response to the control by the control unit 8 so that the focusing position is the second region 29. The control unit 8 may move the objective lens 43 by the actuator 70 so that the entire first region 28 and the entire second region 29 in the Z direction are sequentially focused positions, or may move the objective lens 43 by the actuator 70 so that only a part of the first region 28 and a part of the second region 29 are sequentially focused positions. The control unit 8 may also move the objective lens 43 by the actuator 70 so that the second region 29 is first focused and then the first region 28 is focused. By executing the second control, imaging of the inside of the wafer 20 in the first region 28 and the second region 29 is performed.

[0053] FIG. 16 is a diagram for explaining the details of the movement of the focusing position using the drive unit 7 and the actuator 70. As shown in FIG. 16(a), when the thickness of the wafer 20 is different from the expected thickness, it is considered that the focusing position after the first control may deviate from the back surface 21a. For this reason, in the second control after the first control, the control unit 8 first controls the actuator 70 so that the position of the objective lens 43 moves in the Z direction with the region near the back surface 21a being the focusing position, specifies the detailed position of the back surface 21a based on the light detection result by the light detection unit 44 in this state, and executes the third control to control the actuator 70 so that the objective lens 43 moves to a reference position where the specified detailed position of the back surface 21a is the focusing position (see FIG. 16(b)). The region near the back surface 21a here may be a region including the entire range of the focusing position that may deviate from the back surface 21a after the first control.

[0054] In the third control, the actuator 70 moves only the objective lens 43 in response to the control by the control unit 8 so that the focusing position after the first control moves in the Z direction. In this way, the focusing position is continuously changed in the Z direction, thereby imaging the vicinity of the back surface 21a. The control unit 8 may detect a device pattern on the back surface 21a based on a signal from the light detection unit 44, which is the imaging result, and specify a detailed position of the back surface 21a based on the device pattern. Alternatively, the control unit 8 may specify the results of direct observation and back surface reflection observation of the cracks 14 from the modified region 12 in the vicinity of the back surface 21a based on the signal from the light detection unit 44, and specify a detailed position of the back surface 21a from the specified information. Then, in response to the control by the control unit 8, the actuator 70 moves the objective lens 43 to a reference position where the detailed position of the back surface 21a becomes the focusing position. By moving the objective lens 43 to the reference position in this way, a fourth control described later can be executed starting from the reference position where the focusing position is appropriately set to the back surface 21a.

[0055] The control unit 8 is configured to execute a second control in which the actuator 70 is controlled so that the objective lens 43 moves from the reference position described above to a position where at least a part of the first region 28 becomes the focusing position (see FIG. 16(d)), and a fourth control in which the actuator 70 is controlled so that the objective lens 43 moves from the reference position to a position where at least a part of the second region 29 becomes the focusing position (see FIG. 16(c)). The control unit 8 may move the objective lens 43 by the actuator 70 so that the entire first region 28 and the entire second region 29 in the Z direction become the focusing position sequentially, or may move the objective lens 43 by the actuator 70 so that only a part of the first region 28 and a part of the second region 29 become the focusing position sequentially.

[0056] Thus, in the aspect shown in FIG. 16, the objective lens 43 is moved to a reference position, which is the starting position for imaging, by the first control and the third control, and then an imaging process is performed by the fourth control to image the inside of the wafer 20, and information related to the modified region 12 is derived (e.g., detection of the tip position of the crack 14).

[0057] Fig. 17 is a flowchart showing an example of an observation method carried out by the laser processing apparatus 1. Hereinafter, the example of the observation method will be described with reference to Figs.

[0058] 17, first, the control unit 8 controls the actuator 70 so that the actuator 70 is fixed to the center position of the movable range of the actuator 70 in the Z direction (step S1: pre-step). Note that such center fixing of the actuator 70 may be performed manually.

[0059] Next, the control unit 8 controls the drive unit 7 so that the imaging unit 4 moves to a position where the rear surface 21a becomes the light collecting position, as shown in FIG. 16(a) (step S2: first step).

[0060] Next, the control unit 8 controls the actuator 70 so that the position of the objective lens 43 moves in the Z direction with the area near the back surface 21a being the focusing position, and the detailed position of the back surface 21a is specified based on the detection result of the light detection unit 44 in this state, and the actuator 70 is controlled so that the objective lens 43 moves to a reference position where the specified detailed position of the back surface 21a is the focusing position, as shown in Fig. 16(b). That is, the focusing position is corrected based on the detection result (step S3: second process).

[0061] Next, the control unit 8 controls the actuator 70 so that the objective lens 43 moves to a position where the second region 29, which is the region on the back surface observation side, becomes the focusing position, as shown in Fig. 16(c) (step S4: second process). Then, the control unit 8 controls the actuator 70 so that the objective lens 43 moves to a position where the first region 28, which is the region on the front surface observation side, becomes the focusing position, as shown in Fig. 16(d) (step S5: second process). This is one example of the observation method.

[0062] The observation method performed by the laser processing apparatus 1 is not limited to the embodiments shown in FIGS. 16 and 17. FIG. 18 is a diagram for explaining details of another example of the movement of the focusing position using the drive unit 7 and the actuator 70. The embodiment shown in FIG. 18 is similar to the embodiment shown in FIG. 16 in that the first control described above is executed (see FIG. 18(a)) and the third control described above is executed in the second control after the first control (see FIG. 18(b)). That is, the control shown in FIG. 18(a) corresponds to the control shown in FIG. 16(a), and the control shown in FIG. 18(b) corresponds to the control shown in FIG. 16(b). Here, in the embodiment shown in FIG. 16, in the third control (see FIG. 16(b)) for determining the reference position, the imaging result near the back surface 21a is obtained, but the imaging result is used only to determine the reference position and is not used as information related to the derivation of information related to the modified region 12 of the wafer 20. 18, the imaging results of the vicinity of the back surface 21a obtained in the third control (see FIG. 18(b)) are used not only as information for deriving the reference position but also as information for deriving information related to the modified region 12 of the wafer 20. In this way, by effectively utilizing the imaging results in the third control, it is possible to avoid performing duplicate imaging processes on the same region, and imaging can be performed more efficiently.

[0063] Now, suppose that an imaging result of the area A1 (see FIG. 18(c)) near the back surface 21a is obtained in the third control (see FIG. 18(b)) for determining the reference position. In this case, the control unit 8 executes a fifth control for controlling the drive unit 7 so that the entire imaging unit 4 moves to a position where at least a part of an unimaged area, which is an area in the first area 28 or the second area 29 and was not set as a light collecting position when identifying the detailed position of the back surface 21a in the third control, i.e., an area other than the above-mentioned area A1, becomes a light collecting position. In the example shown in FIG. 18, it is assumed that the unimaged area of ​​the second area 29 is an area that does not require imaging. In this case, the control unit 8 controls the drive unit 7 so that the entire imaging unit 4 moves (is pushed up) to a position where the area A2, which is an unimaged area of ​​the first area 28, becomes a light collecting position. More specifically, the control unit 8 controls the drive unit 7 so that the entire imaging unit 4 moves to a position where the area A2 becomes a light collecting position by a sixth control (to be described later) in which the objective lens 43 is moved by the actuator 70, taking into consideration the movable range of the actuator 70.

[0064] Then, the control unit 8 executes a sixth control in which the actuator 70 is controlled to move the objective lens 43 to a position where the region A2, which is included in the unimaged region, becomes the focusing position, with the position of the objective lens 43 of the imaging unit 4 after the fifth control being set as a new reference position. The control unit 8 may move the objective lens 43 by the actuator 70 so that the entire region A2 in the Z direction becomes the focusing position sequentially, or may move the objective lens 43 by the actuator 70 so that only a part of the region A2 becomes the focusing position sequentially.

[0065] 18, the imaging results acquired during the third control are used not only as information for deriving the reference position but also as information for deriving information related to the modified region 12 of the wafer 20, and the fifth control and sixth control are performed to image only the region for which imaging results could not be acquired in the third control, thereby enabling efficient imaging. Also, even if the entire desired imaging region does not fit within the movable range of the actuator 70, for example, the fifth control and sixth control are performed (performed multiple times as necessary) to sequentially expand the imaging region and image the entire desired imaging region.

[0066] [Effects] Next, the effects of the laser processing apparatus 1 (observation apparatus) and the observation method according to this embodiment will be described.

[0067] The laser processing apparatus 1 according to this embodiment is an observation apparatus for observing a wafer 20 having a front surface 21b and a back surface 21a, in which a modified region 12 has been formed by irradiating the wafer 20 with laser light from the front surface 21b side, and includes an imaging unit 4 having a light source 41 that outputs light that is transparent to the wafer 20, an objective lens 43 that focuses the light output from the light source 41 at a focusing position on the wafer 20, and a light detection unit 44 that detects the light that has propagated through the wafer 20, a drive unit 7 that supports the imaging unit 4 and moves the imaging unit 4 in the Z direction, which is the up and down direction, and a drive unit 8 that is provided on the objective lens 43 and moves the objective lens 43 in the Z direction. The control unit 8 is configured to execute a first control for controlling the drive unit 7 so that the imaging unit 4 moves to a position where the back surface 21a becomes a focusing position, and a second control for controlling the actuator 70 after the first control so that the objective lens 43 moves to a position where at least a portion of a first region 28, which is a region between the back surface 21a and the front surface 21b, becomes a focusing position, and for controlling the actuator 70 so that the objective lens 43 moves to a position where at least a portion of a second region 29, which is a region on the opposite side of the back surface 21a to the front surface 21b, becomes a focusing position.

[0068] In such a laser processing apparatus 1, in observing the wafer 20 on which the modified region 12 is formed, the driving unit 7 that moves the imaging unit 4 in the Z direction is controlled so that the imaging unit 4 moves to a position where the back surface 21a of the wafer 20 becomes the focusing position, and then the actuator 70 that moves the objective lens 43 in the Z direction is controlled so that the objective lens 43 moves to a position where the first region 28, which is the region between the back surface 21a and the front surface 21b, becomes the focusing position, and the actuator 70 that moves the objective lens 43 in the Z direction is controlled so that the objective lens 43 moves to a position where the second region 29, which is the region on the opposite side of the back surface 21a from the front surface 21b, becomes the focusing position. In this way, by moving the objective lens 43 so that both the first region 28 and the second region 29 become the focusing positions, it is possible to appropriately perform both direct observation of the cracks 14, etc. from the modified region 12 when the first region 28 is the focusing position, and observation of the cracks 14, etc. using back surface reflection when the second region 29 is the focusing position. The movement of the objective lens 43, which focuses the first region 28 and the second region 29, is performed by the actuator 70 that moves only the objective lens 43 of the imaging unit 4, so that the focus position can be moved at high speed and vibration after the movement can be suppressed, compared to the case where the entire imaging unit 4 is moved. Here, the laser processing device 1 according to the present embodiment has a drive unit 7 that moves the entire imaging unit 4 in the Z direction and an actuator 70 that moves the objective lens 43 of the imaging unit 4 in the Z direction. By providing both the drive unit 7 and the actuator 70 in this way, it is possible to perform rough alignment by the drive unit 7 and detailed alignment by the actuator 70, for example, and it is possible to perform alignment that requires precision (such as focusing alignment in the imaging range) with high precision while suppressing the device cost compared to the case where all the movement in the Z direction is performed by an actuator capable of detailed alignment. In the laser processing apparatus 1 according to this embodiment, first, the imaging unit 4 is controlled by the drive unit 7 so that the rear surface 21a, which is the boundary surface between the first region 28 and the second region 29, becomes the focusing position, and then the objective lens 43 is controlled by the actuator 70 so that the first region 28 and the second region 29 each become the focusing position.By aligning the focusing position with the rear surface 21a (the boundary surface between the first region 28 and the second region 29) before control by the actuator 70 is started, it is possible to maximize the movable range of the actuator 70 and appropriately perform high-speed movement of the objective lens 43 with the first region 28 and the second region 29 as focusing positions. As described above, according to the laser processing device 1 of this embodiment, it is possible to quickly move the focusing position and improve the tact time.

[0069] Before the first control, the control unit 8 may further execute a pre-control for controlling the actuator 70 so that the actuator 70 is fixed at the center position of the movable range in the Z direction of the actuator 70. In this way, the second control is executed in a state in which the actuator 70 can be sufficiently movable in both directions (up and down) in the Z direction, and the movable range of the actuator 70 can be fully utilized to appropriately perform high-speed movement of the objective lens 43 with the first region 28 and the second region 29 as focusing positions.

[0070] The control unit 8 may be configured to execute a third control in which the actuator 70 is controlled so that the position of the objective lens 43 moves in the Z direction in a state where the region near the back surface 21a is the light-collecting position in the second control, the detailed position of the back surface 21a is specified based on the light detection result by the light detection unit 44 in this state, and the actuator 70 is controlled so that the objective lens 43 moves to a reference position where the specified detailed position of the back surface 21a is the light-collecting position, and a fourth control in which the actuator 70 is controlled so that the objective lens 43 moves from the reference position to a position where at least a part of the first region 28 is the light-collecting position, and the actuator 70 is controlled so that the objective lens 43 moves from the reference position to a position where at least a part of the second region 29 is the light-collecting position. Even with the first control, for example, when the actual thickness of the wafer 20 is different from the expected thickness, it is considered that the light-collecting position may deviate from the back surface 21a. In this case, there is a risk that the imaging of the first region 28 and the second region 29 cannot be realized by making the most of the movable range of the actuator 70 described above. In this regard, in the second control, the exact position of the back surface 21a is identified based on the light detection results and set as a reference position (third control), and the objective lens 43 is moved from the reference position to the imaging range of the first region 28 and the second region 29 by the actuator 70 (fourth control). Therefore, even if the focusing position deviates from the back surface 21a in the first control, the reference position can be appropriately set to realize imaging of the first region 28 and the second region 29 by making maximum use of the movable range of the actuator 70.

[0071] The control unit 8 is configured to execute a third control in which, in the second control, the actuator 70 is controlled so that the position of the objective lens 43 moves in the Z direction in a state where the area near the back surface 21a becomes the light collecting position, the detailed position of the back surface 21a is specified based on the light detection result by the light detection unit 44 in this state, and the actuator 70 is controlled so that the objective lens 43 moves to a reference position where the specified detailed position of the back surface 21a becomes the light collecting position, and may further execute a fifth control in which the drive unit 7 is controlled so that the imaging unit 4 moves to a position where at least a part of an unimaged area, which is an area in the first area 28 or the second area 29 and is not specified as the light collecting position when the detailed position of the back surface 21a is specified in the third control, becomes the light collecting position, and a sixth control in which the actuator 70 is controlled so that the objective lens 43 moves to a position where an area included in the unimaged area becomes the light collecting position, with the position of the objective lens 43 of the imaging unit 4 after the fifth control being set as a new reference position. According to the third control, imaging of the area near the back surface 21a can be performed in the process of specifying the detailed position of the back surface 21a. Therefore, in this observation device, the drive unit 7 is controlled so that the imaging unit 4 moves to a position where the unimaged region becomes the focusing position in the third control (fifth control), and the position of the objective lens 43 after the fifth control is set as a new reference position, and the actuator 70 is controlled so that the objective lens 43 moves to a position where the unimaged region becomes the focusing position (sixth control). According to this configuration, the unimaged region is controlled to become the focusing position in the third control, so that imaging can be performed more efficiently without performing unnecessary imaging. Also, according to this configuration, even if the region to be imaged does not fit within the movable range of the actuator 70 at the initial reference position, the region to be imaged can be reliably imaged by changing the reference position.

[0072] The observation method according to the present embodiment is an observation method for observing a wafer 20 having a front surface 21b and a back surface 21a and having a modified region 12 formed therein by irradiation of laser light from the front surface 21b side, and includes a first step of moving the imaging unit 4 to a position where the back surface 21a becomes a light collecting position by a drive unit 7 that moves the imaging unit 4 in the Z direction, which is the vertical direction, and a second step of moving the objective lens 43 included in the imaging unit 4 in the Z direction by an actuator 70 that moves the objective lens 43 to a position where at least a part of a first region 28, which is a region between the back surface 21a and the front surface 21b, becomes a light collecting position, and moving the objective lens 43 to a position where at least a part of a second region 29, which is a region on the opposite side of the back surface 21a to the front surface 21b, becomes a light collecting position. According to the observation method according to the present embodiment, the light collecting position can be moved at high speed, thereby improving the tact time.

[0073] The observation method may further include, before the first step, a preliminary step of controlling the actuator 70 so that the actuator 70 is fixed at the center position of the movable range in the Z direction of the actuator 70. With such a configuration, it is possible to appropriately perform high-speed movement of the objective lens 43 with the first region 28 and the second region 29 as focusing positions by making the most of the movable range of the actuator 70. [Explanation of symbols]

[0074] 1...laser processing apparatus (observation apparatus), 4...imaging unit (imaging section), 7...driving unit, 8...control section, 12...modified region, 20...wafer, 21a...rear surface (second surface), 21b...front surface (first surface), 28...first region, 29...second region, 41...light source, 43...objective lens (collecting lens), 44...light detection section, 70...actuator.

Claims

1. 1. An observation apparatus for observing a wafer having a first surface and a second surface, the wafer having a modified region formed therein by irradiating the wafer with laser light from the first surface side, the observation apparatus comprising: an imaging unit including a light source that outputs light that is transparent to the wafer, a condenser lens that condenses the light output from the light source at a condensing position on the wafer, and a light detection unit that detects the light that has propagated through the wafer; a drive unit that supports the imaging unit and moves the imaging unit in a Z direction that is a vertical direction; an actuator provided on the condenser lens and configured to move the condenser lens in the Z direction; A control unit, The control unit is a first control for controlling the drive unit so that the imaging unit moves to a position where the second surface is at the light collecting position; the observation device is configured to execute a second control, which controls the actuator so that, after the first control, the focusing lens moves to a position where at least a portion of a first region, which is a region between the second surface and the first surface, becomes the focusing position, and which controls the actuator so that the focusing lens moves to a position where at least a portion of a second region, which is a region on the opposite side of the second surface from the first surface, becomes the focusing position.

2. The observation device according to claim 1 , wherein the control unit further performs a pre-control, before the first control, to control the actuator so that the actuator is fixed at a central position of a movable range of the actuator in the Z direction.

3. The control unit is In the second control, a third control for controlling the actuator so that a position of the condensing lens is moved in the Z direction with a region near the second surface being the condensing position, identifying a detailed position of the second surface based on a detection result of the light by the light detection unit in this state, and controlling the actuator so that the condensing lens is moved to a reference position where the identified detailed position of the second surface is the condensing position; 3. The observation device according to claim 1 or 2, wherein the observation device is configured to execute a fourth control of controlling the actuator so that the condensing lens moves from the reference position to a position where at least a portion of the first region becomes the condensing position, and a fourth control of controlling the actuator so that the condensing lens moves from the reference position to a position where at least a portion of the second region becomes the condensing position.

4. The control unit is In the second control, a third control is configured to execute a third control of controlling the actuator so that a position of the condensing lens moves in the Z direction in a state where an area near the second surface becomes the condensing position, identifying a detailed position of the second surface based on a light detection result by the light detection unit in this state, and controlling the actuator so that the condensing lens moves to a reference position which is a position of the condensing lens where the identified detailed position of the second surface becomes the condensing position, a fifth control for controlling the drive unit so that the imaging unit moves to a position where at least a part of an unimaged region, which is a region within the first region or the second region and which was not set as the light-collecting position when a detailed position of the second surface was specified in the third control, becomes the light-collecting position; and a sixth control for controlling the actuator so that the condenser lens moves to a position where an area included in the unimaged area becomes the condensing position, using a position of the condenser lens of the imaging unit after the fifth control as a new reference position.

5. 1. A method for observing a wafer having a first surface and a second surface, the method comprising: a first step of moving the imaging unit to a position where the second surface is a light collecting position by a drive unit that moves the imaging unit in a Z direction that is a vertical direction; a second step of moving the focusing lens by an actuator that moves a focusing lens included in the imaging unit in the Z direction to a position where at least a portion of a first region, which is a region between the second surface and the first surface, is at the focusing position, and moving the focusing lens to a position where at least a portion of a second region, which is a region on the opposite side of the second surface from the first surface, is at the focusing position.

6. 6. The observation method according to claim 5, further comprising a preliminary step of controlling the actuator so that the actuator is fixed at a central position of a movable range of the actuator in the Z direction, before the first step.

Images