JP2019147191A - Confirmation device and confirmation method for laser material processing region - Google Patents

Abstract

The present invention provides a confirmation apparatus and confirmation method for a laser processing apparatus capable of nondestructively confirming the formation position and processing damage of a laser processing region formed inside a workpiece.
An illumination light source that outputs illumination light in a wavelength range that passes through a workpiece, an observation objective lens that collects the illumination light on the workpiece and receives reflected light from a condensing point, and The focusing point of the observation objective lens 46 is changed in the depth direction of the workpiece, and the reflected light received by the observation objective lens 46 is imaged. And an infrared camera 50 for acquiring a plurality of captured images.
[Selection] Figure 1

Description

  The present invention provides a laser that forms a modified region in a wafer along a planned cutting line of the wafer by irradiating a laser beam with a condensing point aligned inside the wafer having a plurality of devices formed on the surface. The present invention relates to a processing apparatus and a laser processing method.

  Conventionally, in order to divide a wafer with a plurality of devices on the surface into individual chips, the wafer is cut by inserting grinding grooves into the wafer with a thin grindstone with a thickness of about 30 μm formed of fine diamond abrasive grains. A dicing machine was used.

  In the dicing apparatus, a thin grindstone (hereinafter referred to as a dicing blade) is rotated at a high speed of, for example, 30,000 to 60,000 rpm to grind the wafer, and the wafer is completely cut (full cut) or incompletely cut (half cut or semi-full). Cut).

  However, in the case of grinding with this dicing blade, since the wafer is a highly brittle material, it becomes brittle mode processing, chipping occurs on the front and back surfaces of the wafer, and this chipping is a factor that degrades the performance of the divided chips. It was.

  In response to such a problem, instead of cutting with a conventional dicing blade, the wafer is irradiated with a laser beam with a converging point aligned inside, thereby modifying a modified region (modified layer) by multiphoton absorption inside the wafer. ) And dividing into individual chips have been proposed (see, for example, Patent Documents 1 and 2).

JP 2009-34723 A JP 2010-58128 A

  However, in the technique as described above, when forming the modified region by condensing the laser beam inside the wafer, the formation position (particularly the position in the wafer depth direction) of the modified region formed inside the wafer is determined. In order to confirm or measure, there was only a method of observing a cross section of the cut wafer with a microscope after the wafer was cut along a cutting line. For this reason, verification with a product wafer is difficult, and it is necessary to make the wafer easy for verification. Regarding processing damage, after processing using a wafer with tin or gold deposited on the back side, the wafer must be observed with another microscope, for example, to detect troubles in the middle of a lot. I couldn't.

  The present invention has been made in view of such circumstances, and provides a laser processing apparatus and a laser processing method capable of nondestructively confirming and measuring the formation position and processing damage of a modified region formed inside a wafer. For the purpose.

  In order to achieve the above object, the laser processing apparatus according to the first aspect of the present invention irradiates the interior of the wafer along the planned cutting line of the wafer by irradiating the laser beam with the focusing point inside the wafer. A laser processing apparatus for forming a modified region in an illumination light source that outputs illumination light in a wavelength region that passes through the wafer, and an objective that condenses the illumination light on the wafer and receives reflected light from the focal point. A lens, a condensing point changing means for changing the condensing point of the objective lens in the wafer depth direction, and an image of the reflected light received by the objective lens, and for each condensing point changed by the condensing point changing means Imaging means for acquiring a plurality of captured images.

  The laser processing apparatus according to a second aspect of the present invention is the laser processing apparatus according to the first aspect, wherein the focusing point changing means changes the focusing point of the objective lens in the wafer depth direction by moving the objective lens in the optical axis direction. It has an objective lens moving means.

  The laser processing apparatus according to a third aspect of the present invention is the laser processing apparatus according to the first aspect or the second aspect, wherein the condensing point changing means is a tunable lens disposed on the optical path between the imaging means and the objective lens, Tunable lens curvature changing means for changing the focal point of the objective lens in the wafer depth direction by changing the curvature of the tunable lens.

  A laser processing apparatus according to a fourth aspect of the present invention is the laser processing apparatus according to any one of the first to third aspects, wherein the condensing lens that condenses the laser light inside the wafer and the wafer relative to the laser light. And a moving means for moving, and the focusing point of the objective lens is arranged downstream of the focusing point of the focusing lens in the moving direction of the wafer.

  A laser processing apparatus according to a fifth aspect of the present invention is the laser processing apparatus according to any one of the first to fourth aspects, wherein the spatial light modulator that modulates the laser light and the depth from the laser light irradiation surface inside the wafer are mutually different. The spatial light modulator is configured separately from the controller that controls the spatial light modulator so that the laser light is simultaneously focused at a plurality of positions that are different from each other in the wafer moving direction. And an aberration correction unit that corrects the aberration of the laser beam to be equal to or less than a predetermined aberration at a plurality of positions where the condensing points of the laser beam are aligned.

  A laser processing apparatus according to a sixth aspect of the present invention is the laser processing apparatus according to the fifth aspect, wherein the control unit condenses the laser light at the first position in the wafer depth direction, and the first position is the wafer depth. The spatial light modulator is controlled so that the laser light is condensed at a second position different in the direction.

  In the laser processing method according to the seventh aspect of the present invention, a laser that forms a modified region in the wafer along the planned cutting line of the wafer by irradiating the laser beam with the focusing point inside the wafer. A processing method, in which illumination light in a wavelength region that passes through a wafer is condensed on the wafer by an objective lens, and light reflected from the focal point is received by the objective lens, and the focal point of the objective lens is the wafer. Imaging process for changing the focal point in the depth direction and imaging the reflected light received by the objective lens with an imaging means and acquiring a plurality of captured images for each focal point changed in the focal point changing process And a process.

  In the laser processing method according to the eighth aspect of the present invention, in the seventh aspect, in the focusing point changing step, the focusing point of the objective lens is changed in the wafer depth direction by moving the objective lens in the optical axis direction. Process.

  In the laser processing method according to the ninth aspect of the present invention, in the seventh aspect or the eighth aspect, the condensing point changing step includes the curvature of the tunable lens disposed on the optical path between the imaging means and the objective lens. By changing the focal point of the objective lens in the wafer depth direction by changing.

The laser processing method according to the tenth aspect of the present invention is the laser processing method according to any one of the seventh to ninth aspects, wherein the objective lens is collected by a condensing point changing step while forming a modified region inside the wafer by laser light. While changing the light spot in the wafer depth direction, a plurality of captured images are acquired for each condensing point changed in the condensing point changing step by the imaging step.

  A laser processing method according to an eleventh aspect of the present invention is the laser processing method according to any one of the seventh to tenth aspects, wherein the modulation step modulates the laser light with the spatial light modulator, and the laser light modulated with the spatial light modulator. The condensing process for condensing the inside of the wafer, the moving process for moving the wafer relative to the laser light, and the depth from the laser light irradiation surface inside the wafer are different from each other and in the moving direction of the wafer. A control process for controlling the spatial light modulator so that the laser light is simultaneously focused at a plurality of positions separated from each other, and the spatial light modulator are configured separately, and the focal point of the laser light is aligned inside the wafer. And an aberration correction step of correcting the aberration of the laser beam to be equal to or less than a predetermined aberration at a plurality of positions.

  The laser processing method according to a twelfth aspect of the present invention is the laser processing method according to the eleventh aspect, in which the control step focuses the laser light at a first position in the wafer depth direction, and the first position is the wafer depth. The spatial light modulator is controlled so that the laser light is condensed at a second position different in the direction.

  According to the present invention, it is possible to confirm and measure the formation position and processing damage of the modified region formed inside the wafer in a non-destructive manner.

The block diagram which showed the outline of the laser processing apparatus which concerns on the 1st Embodiment of this invention Schematic showing how the modified region is formed inside the wafer Conceptual diagram showing how cracks extend in the wafer depth direction from the modified region formed inside the wafer Schematic showing multiple captured images obtained with an infrared camera The figure which showed an example of the captured image containing an upper side modified layer and a lower side modified layer Graph showing the relationship between aberration correction amount and total crack length Graph showing the relationship between aberration correction amount and crack bottom length It is the conceptual diagram which showed a mode that the modification | reformation area | region was formed in the inside of a wafer, and the figure for demonstrating other forms of two positions (condensing position) where a laser beam is condensed The block diagram which showed the outline of the laser processing apparatus concerning the 2nd Embodiment of this invention The block diagram which showed the outline of the laser processing apparatus concerning the 3rd Embodiment of this invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a configuration diagram showing an outline of a laser processing apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the laser processing apparatus 1 according to the present embodiment is mainly composed of a wafer moving unit 11, a laser head 20, a control unit 60, and the like.

  The wafer moving unit 11 includes a suction stage 13 that sucks and holds the wafer W, and an XYZθ table 12 that is provided on the main body base 16 of the laser processing apparatus 1 and moves the suction stage 13 precisely in the XYZθ direction. The wafer moving unit 11 moves the wafer W precisely in the XYZθ direction in the figure. The wafer moving unit 11 is an example of a moving unit.

  Wafer W is mounted on suction stage 13 such that a back grind tape (hereinafter referred to as BG tape) having an adhesive material is attached to the surface on which the device is formed, and the back surface is directed upward. The thickness of the wafer W is not particularly limited, but is typically 700 μm or more, more typically 700 to 800 μm.

  Note that the wafer W may be placed on the suction stage 13 in a state where a dicing sheet having an adhesive material is attached to one surface and the wafer W is integrated with the frame via the dicing sheet.

  The laser head 20 includes a processing optical system for irradiating the wafer W with a processing laser beam L, and observation optics for confirming or measuring the formation position of the modified region formed in the wafer W and processing damage. System.

  The processing optical system of the laser head 20 includes a laser light source 22, a spatial light modulator 28, a condenser lens 38, and the like.

The laser light source 22 outputs a processing laser beam L for forming a modified region inside the wafer W under the control of the control unit 60. As conditions for the laser beam L, for example, the light source is a semiconductor laser excitation Nd: YAG laser, the wavelength is 1.1 μm, the laser beam spot cross-sectional area is 3.14 × 10 ⁻⁸ cm ² , and the oscillation mode is a Q switch pulse. The repetition frequency is 80 to 120 kHz, the pulse width is 180 to 380 ns, and the output is 8 W.

  The spatial light modulator 28 is of a phase modulation type, and receives a laser beam L output from the laser light source 22 and modulates the phase of the laser beam L in each of a plurality of pixels arranged two-dimensionally. The pattern is presented, and the laser light L after the phase modulation is output. This hologram pattern is a superposition of a plurality of Fresnel lens patterns with different condensing positions. Thereby, as will be described later in detail, the depths from the laser light irradiation surface (the back surface of the wafer W) are different from each other inside the wafer W, and the wafer moving direction (processing feed direction) parallel to the X direction in FIG. The laser beam L is simultaneously condensed by the condenser lens 38 at two positions M apart from each other.

As the spatial light modulator 28, for example, reflective liquid crystal (LCOS: Liquid Crystal on Silicon)
) Spatial Light Modulator (SLM). The operation of the spatial light modulator 28 and the hologram pattern presented by the spatial light modulator 28 are controlled by the control unit 60. Note that a specific configuration of the spatial light modulator 28 and a hologram pattern presented by the spatial light modulator 28 are already known, and thus detailed description thereof is omitted here.

  The condensing lens 38 is an objective lens (infrared objective lens) that condenses the laser light L inside the wafer W. The condensing lens 38 has a numerical aperture (NA) of 0.6 to 0.8 (for example, 0.65).

  The condensing lens 38 is composed of an objective lens with a correction ring in order to correct the aberration of the laser light L generated inside the wafer W. A correction ring (not shown) provided in the condenser lens 38 is configured to be manually rotatable. When the correction ring is rotated in a predetermined direction, the interval between the lens groups constituting the condenser lens 38 is changed. Then, the aberration can be corrected so that the aberration of the laser light L is equal to or less than the predetermined aberration at a predetermined depth from the laser light irradiation surface (back surface) of the wafer W. The correction ring of the condenser lens 38 is an example of an aberration correction unit.

  Note that the correction ring of the condensing lens 38 may be configured to be electrically rotated by a correction ring driving unit (not shown). In this case, the control unit 60 controls the operation of the correction ring driving unit to perform correction so that the aberration of the laser light L becomes a desired state by rotating the correction ring.

  The processing optical system of the laser head 20 includes a beam expander 24, a λ / 2 wavelength plate 26, a reduction optical system 36, and the like in addition to the above configuration.

  The beam expander 24 expands the laser light L output from the laser light source 22 to an appropriate beam diameter for the spatial light modulator 28. The λ / 2 wavelength plate 26 adjusts the polarization plane of incidence of laser light on the spatial light modulator 28. The reduction optical system 36 is an afocal optical system (bilateral telecentric optical system) including a first lens 36 a and a second lens 36 b, and collects the laser light L modulated by the spatial light modulator 28. Reduce the projection.

  The observation optical system of the laser head 20 includes an illumination light source 42, a half mirror 44, an observation objective lens 46, an actuator 48, an infrared camera 50, and the like.

  The illumination light source 42 includes, for example, an LD (Laser Diode) light source, an SLD (Super Luminescent Diode) light source, and the like, and outputs illumination light (infrared light) in a wavelength region (infrared region) that passes through the wafer W.

  The illumination light output from the illumination light source 42 passes through the half mirror 44 arranged on the optical path, and is irradiated onto the wafer W via the observation objective lens 46. The observation objective lens 46 has a numerical aperture (NA) of 0.5 to 0.9 (preferably 0.6 to 0.8). Further, the position of the condensing point in the Z direction (wafer depth direction position) by the observation objective lens 46 is moved by the actuator 48 in the Z direction (the optical axis direction of the observation objective lens 46). Adjusted by. The actuator 48 is an example of an objective lens moving unit.

  The reflected light reflected by the wafer W (that is, the reflected light from the condensing point by the observation objective lens 46) is received by the observation objective lens 46. Further, the reflected light received by the observation objective lens 46 is reflected by the half mirror 44 and enters the infrared camera 50.

  The infrared camera 50 is an example of an imaging unit, and images the wafer W from the laser light incident surface (back surface) side of the wafer W. The infrared camera 50 includes an image sensor (not shown) having sensitivity to the wavelength range of infrared light. Accordingly, the infrared camera is operated in a state where the observation objective lens 46 is moved in the Z direction (the optical axis direction of the observation objective lens 46) by the actuator 48 and the condensing point by the observation objective lens 46 is set inside the wafer W. When the wafer W is imaged by 50, the internal state of the wafer W can be confirmed. In addition, the internal state of the wafer W can be confirmed by aligning the focal point of the observation objective lens 46 with the surface of the wafer W (the surface opposite to the laser light incident surface). A captured image captured by the infrared camera 50 is stored in a storage unit (not shown) of the laser processing apparatus 1.

  As the infrared camera 50, for example, a camera (near infrared camera) having high sensitivity in the near infrared region (wavelength region of 1 μm or more) typified by an InGaAs (indium gallium arsenide) camera is preferably used.

  In this embodiment, as shown in FIG. 1, the observation position of the wafer W by the observation optical system, that is, the imaging position of the wafer W by the infrared camera 50 (the condensing point of the observation objective lens 46) is the processing optical system. The wafer W is disposed in a straight line on the downstream side (right side in FIG. 1) in the wafer movement direction M with respect to the processing position of the wafer W (the condensing point of the laser light L by the condensing lens 38). With this configuration, the infrared camera 50 can take an image of the wafer W on the same cutting scheduled line as the processing position of the wafer W by the processing optical system, and the formation position of the modified region formed inside the wafer W It is possible to check and measure processing damage in real time.

  Although not shown, the laser head 20 includes an alignment optical system for performing alignment with the wafer W, and an auto for maintaining a constant distance (working distance) between the wafer W and the condenser lens 38. A focus unit and the like are provided.

  The control unit 60 includes a CPU, a memory, an input / output circuit unit, and the like, and controls the operation of each unit of the laser processing apparatus 1. Specifically, the thickness of the wafer W and the feeding speed of the wafer W are controlled, and the operation of each part (wafer moving part 11, laser head 20, etc.) is controlled under optimum conditions to form a modified region.

  In addition, the control unit 60 controls the operation of the spatial light modulator 28 and causes the spatial light modulator 28 to present a predetermined hologram pattern. Specifically, two positions different from each other inside the wafer W (that is, two positions having different depths from the laser light irradiation surface and separated from each other in the wafer moving direction M parallel to the X direction in FIG. 1). The spatial light modulator 28 is caused to present a hologram pattern for modulating the laser light L so that the laser light L is simultaneously condensed by the condenser lens 38. Note that the hologram pattern is derived in advance based on the formation position of the modified region, the wavelength of the laser beam L to be irradiated, the refractive index of the condenser lens 38 and the wafer W, and the like, and is stored in the control unit 60.

  Further, when the control unit 60 confirms or measures the formation position of the modified region formed inside the wafer W and the processing damage, the condensing point by the observation objective lens 46 is a minute step (for example, 2 μm). The driving of the actuator 48 is controlled so as to move at intervals.

  In addition to this, the laser processing apparatus 1 includes a wafer transfer means, an operation plate, a television monitor, an indicator lamp, and the like (not shown).

  On the operation plate, switches and a display device for operating operations of each part of the laser processing apparatus 1 are attached. The television monitor displays a captured image (wafer image) captured by the infrared camera 50, or displays program contents and various messages. The indicator lamp displays an operation status such as processing end or emergency stop during the processing of the laser processing apparatus 1.

  The operation of the laser processing apparatus 1 of the present embodiment configured as described above will be described. Here, a case where a silicon substrate having a thickness of 775 μm is processed as the wafer W will be described as an example.

  First, the correction ring provided in the condensing lens 38 is rotated manually (or electrically) so that the laser light L is focused at the position where the laser light L is condensed inside the wafer W (processing depth of the modified region). The amount of aberration correction is adjusted so that the aberration becomes less than a predetermined aberration. In this specification, the “aberration correction amount” is a value converted into the depth of the wafer W from the laser light irradiation surface. That is, for example, when the aberration correction amount is 500 μm, it means that the aberration of the laser light is minimized at a position where the depth of the wafer W from the laser light irradiation surface is about 500 μm. In this example, as will be described in detail later, when the thickness of the wafer W is 775 μm, the aberration correction amount by the correction ring is preferably set to 500 μm.

  Next, after placing the wafer W to be processed on the suction stage 13, the wafer W is aligned using an alignment optical system (not shown).

  Next, while processing and feeding the XYZθ table 12 in the wafer movement direction M (that is, while moving the wafer W relative to the laser light L in the wafer movement direction M), the laser head 20 moves toward the wafer W. Laser light L is irradiated.

  At this time, the laser light L output from the laser light source 22 is expanded in beam diameter by the beam expander 24, reflected by the first mirror 30, and the polarization direction is changed by the λ / 2 wavelength plate 26 to modulate the spatial light. Is incident on the device 28.

  The laser light L incident on the spatial light modulator 28 is modulated according to a predetermined hologram pattern presented on the spatial light modulator 28. At that time, the controller 60 spatially modulates the hologram pattern for modulating the laser light L so that the laser light L is simultaneously condensed by the condenser lens 38 at two different positions inside the wafer W. Control to be presented to the device 28 is performed.

  The laser light L emitted from the spatial light modulator 28 is sequentially reflected by the second mirror 31 and the third mirror 32, then passes through the first lens 36a, and further by the fourth mirror 33 and the fifth mirror 34. The light is reflected, passes through the second lens 36 b, and enters the condenser lens 38. Thereby, the laser light L emitted from the spatial light modulator 28 is reduced and projected onto the condenser lens 38 by the reduction optical system 36 including the first lens 36a and the second lens 36b. The laser light L incident on the condenser lens 38 is condensed by the condenser lens 38 at two different positions inside the wafer W.

  FIG. 2 is a conceptual diagram showing how the modified region is formed inside the wafer W. FIG. As shown in FIG. 2, the laser light L modulated by the spatial light modulator 28 has different depths from the laser light irradiation surface (back surface of the wafer W) inside the wafer W by the condenser lens 38, and Condensation is simultaneously performed at two positions separated from each other in the wafer moving direction M. Thus, modified regions P1 and P2 by multiphoton absorption are formed in the vicinity of the respective condensing positions. Further, when the modified regions P1 and P2 are formed, cracks K1 and K2 extending from the respective modified regions P1 and P2 in the wafer depth direction (wafer thickness direction) are formed.

  Here, the two positions (condensing positions) where the laser beam L is condensed will be described in detail. In the present embodiment, the first position Q1 in the wafer depth direction inside the wafer W (right side in FIG. 2). The laser beam L is condensed at the second focal point Q2 (the left focal point in FIG. 2) different from the first position Q1 in the wafer depth direction. The

  Furthermore, in the present embodiment, the second position Q2 is disposed upstream of the first position Q1 in the wafer movement direction M (left side in FIG. 2), and the first position Q2 from the laser light irradiation surface of the wafer W is the first position Q2. It is arranged at a position deeper than the position Q1. An example of the distance (interval) between the first position Q1 and the second position Q2 is 50 μm in the wafer depth direction. The distance in the wafer moving direction M is 30 μm.

  When the wafer W moves relative to the laser beam L in this state, as shown in FIG. 3, along the movement locus of the two condensing points (condensing positions Q1, Q2) of the laser beam L. Inside the wafer W, modified regions P1 and P2 are formed. Thereby, along the planned cutting line of the wafer W, the modified region P1 and the modified region P2 are formed one line at a time in a state where the modified region P1 and the modified region P2 are overlapped at a predetermined interval.

  Thus, when the modified region P1 and the modified region P2 are formed in a state of being overlapped at a predetermined interval, the two modified regions P1 and P2 overlapping in the wafer depth direction are delayed in time. As shown in FIG. 3, due to the impact at the time of forming the modified region P1 to be formed, the crack K1 of the modified region P1 and the crack K2 of the modified region P2 are connected, and a crack K2 extending from the modified region P2 further forms a wafer. It extends toward the surface (the surface of the wafer W) opposite to the laser light irradiation surface of W.

  That is, by modulating the laser light L by the spatial light modulator 28, the laser light L is simultaneously condensed at different positions inside the wafer W, so that the throughput from the surface of the wafer W can be reduced without reducing the throughput. The crack can be extended to a desired position between the target surface indicating the position of the final thickness T2 of the wafer W and the surface of the wafer W. 2 and 3, T1 represents the initial thickness of the wafer W (in this example, 775 μm).

  When the reformed regions P1 and P2 are formed one line at a time along the planned cutting line, the XYZθ table 12 is indexed and fed by one pitch in the Y direction, and the reformed regions P1 and P2 are similarly formed on the next line. .

  When the modified regions P1 and P2 are formed along all the planned cutting lines parallel to the X direction, the XYZθ table 12 is rotated by 90 °, and all the lines orthogonal to the previous line are similarly modified region P1. , P2 is formed.

  As a result, the modified regions P1 and P2 are formed along all the planned cutting lines. The modified regions P1 and P2 have the same position on the plane (the position viewed from the back surface or the front surface of the wafer W) and are formed along the planned cutting line, but the thickness direction of the wafer W (wafer Only the position in the depth direction) is different.

  After the modified regions P1 and P2 are formed along the scheduled cutting line as described above, the back surface of the wafer W is ground using a grinding apparatus (not shown), and the thickness (initial thickness) T1 of the wafer W is obtained. The back surface grinding process which processes this to predetermined thickness (final thickness) T2 (for example, 30-50 micrometers) is performed.

  After the back surface grinding process, an expand tape (dicing tape) is applied to the back surface of the wafer W, the BG tape applied to the front surface of the wafer W is peeled off, and then the expanded tape applied to the back surface of the wafer W is tensioned. The expanding process of adding and stretching is performed.

  Thereby, the wafer W is cut | disconnected from the crack (crack) extended to the surface side of the wafer W as the starting point. That is, the wafer W is cut along the cutting line and divided into a plurality of chips.

  Here, in the laser processing apparatus 1 in the present embodiment, as shown in FIG. 1, the laser beam L is formed inside the wafer W while forming a modified region along the planned cutting line inside the wafer W. Wafer processing confirmation processing for confirming the formation position of the modified region and processing damage is performed in real time.

  In the wafer processing confirmation processing, an image is taken by the infrared camera 50 from the laser light incident surface (back surface) side of the wafer W on the same cutting scheduled line as the modified region formed inside the wafer W by the processing optical system.

  At this time, the control unit 60 controls the driving of the actuator 48 to move the observation objective lens 46 in the optical axis direction (Z direction) in a minute step (for example, about 2 μm) (that is, the observation objective lens 46 is moved). The image is picked up by the infrared camera 50 while the position of the focal point (focal point) is moved in a minute step in the wafer depth direction. In the present embodiment, the position of the condensing point of the observation objective lens 46 is changed from the laser light incident surface (back surface) of the wafer W to the device surface (front surface). Accordingly, as shown in FIG. 4, a plurality of captured images (XY images at the positions of the respective condensing points) 62 (62-1, 62-2,... 62-n) are sequentially acquired by the infrared camera 50. A plurality of captured images 62 sequentially acquired by the infrared camera 50 are stored in a storage unit (not shown) of the laser processing apparatus 1. Each captured image stored in the storage unit can be displayed on a television monitor in accordance with a user operation.

  An example of a captured image including an upper modified layer (modified region P1) and a lower modified layer (modified region P2) among a plurality of captured images obtained by the infrared camera 50 in the wafer processing confirmation process is shown in FIG. Shown in

  When the modified region P1 and the modified region P2 are appropriately formed in the wafer depth direction (Z direction), as shown in FIG. The modified region can be confirmed in the captured image at the wafer depth direction position.

  On the other hand, when the modified region P1 and the modified region P2 are not properly formed in the wafer depth direction, the modified region cannot be confirmed in the captured image at the desired position in the wafer depth direction.

  Therefore, it is determined whether or not the captured image in which the modified region P1 and the modified region P2 are confirmed is a captured image at a desired position in the wafer depth direction from a plurality of captured images captured by the infrared camera 50. Thus, it is possible to confirm whether or not the modified region forming positions such as the wafer depth direction positions of the modified regions P1 and P2 and the intervals between the modified regions P1 and P2 are appropriate.

  In the present embodiment, this determination process is automatically performed by the control unit 60. The control unit 60 detects the three-dimensional positional relationship between the modified regions P1 and P2 inside the wafer W by performing image processing on each captured image with an image processing unit 60a provided therein. Thereby, not only the wafer depth direction position (Z direction position) of each modified region P1, P2 but also the processing feed direction position (X direction position) and the index feed direction position (Y direction position) are formed at appropriate positions. It can be easily determined whether or not it is done. Accordingly, it is possible to confirm a positional deviation in the horizontal direction (X direction and Y direction) of the incident point of the laser beam L with respect to the cutting line to be cut.

  In addition, processing damage caused on the device surface side of the wafer W is confirmed from an image captured by the infrared camera 50 when the position of the condensing point of the observation objective lens 46 is set at or near the device surface of the wafer W. can do.

  As described above, according to the present embodiment, the formation position and processing of the modified region formed inside the wafer W while forming the modified region along the line to be cut inside the wafer W by the laser light L. Wafer processing confirmation processing for confirming and measuring damage is performed in real time. In this wafer processing confirmation process, as described above, for each condensing point of the observation objective lens 46 by the infrared camera 50, the position of the condensing point (focal point) of the observation objective lens 46 is changed in the wafer depth direction. A plurality of captured images are sequentially acquired. Thereby, it is possible to confirm and measure the formation position and processing damage of the modified region formed inside the wafer W from the plurality of captured images acquired by the infrared camera 50 without destroying the wafer W. it can.

  Further, in the present embodiment, it is possible to preferably employ a configuration in which the result confirmed or measured in the wafer processing confirmation process is feedback-controlled to the formation position of the modified region and the laser processing conditions. According to this configuration, it is possible to form a modified region suitable for wafer division and prevent processing damage while automatically modifying the modified region forming position and laser processing conditions. Stable quality chips can be obtained.

  In the present embodiment, as an example, an aspect in which the above-described determination process is automatically performed by the image processing unit 60a provided in the laser processing apparatus 1 is shown. However, the present invention is not limited to this. A plurality of captured images may be displayed on a television monitor, and the user may check and measure the formation position of the modified region formed inside the wafer W and the processing damage.

  Further, in the present embodiment, the laser light L is condensed at a plurality of positions using the spatial light modulator 28 at the same time by the condenser lens 38, and the laser light L is condensed using the correction ring of the condenser lens 38. Since the aberration at the point alignment is corrected so as to be equal to or less than the predetermined aberration, the laser beam L can be efficiently condensed at a deep position in the wafer depth direction even when the wafer W is thick. Is possible. Further, it is possible to sufficiently extend the crack generated when the modified regions P1 and P2 overlapping in the wafer depth direction are formed to the surface (the surface of the wafer W) opposite to the laser light irradiation surface of the wafer W. it can. Therefore, the wafer W can be efficiently divided into chips, and stable quality chips can be obtained efficiently.

  Here, an experiment conducted by the present inventors in order to verify the above effect will be described.

  In this experiment, the laser processing apparatus 1 according to the above-described embodiment was used as an example. As a comparative example, an apparatus having the same configuration as that of Patent Document 2 described above, that is, using a spatial light modulator, condensing laser light at two different positions inside the wafer, Apparatus for correcting aberrations (first comparative example), and apparatus for correcting aberrations using a correction ring without using a spatial light modulator (that is, condensing laser light at one condensing position) (Second Comparative Example) was used.

  As an experimental condition, the total crack length (crack of the crack) generated in the wafer depth direction when the modified region is formed while changing the aberration correction amount with each apparatus for a wafer (silicon substrate) having a thickness of 775 μm. The total length) and the crack lower end length (the crack length extending from the lower end of the modified region to the wafer surface side) were measured (see FIG. 3).

  FIG. 6 is a graph showing the relationship between the aberration correction amount and the total crack length. FIG. 7 is a graph showing the relationship between the aberration correction amount and the crack lower end length. 6 and 7, the horizontal axis indicates the aberration correction amount, and the vertical axis indicates the total crack length and the crack lower end length generated by each device, respectively.

  As can be seen from FIGS. 6 and 7, in the example, compared to the first comparative example and the second comparative example, the total crack length is increased over all aberration correction amounts, and the crack lower end length is also increased. Results were obtained.

  In particular, when the aberration correction amount is 500 μm, in the example, the total crack length is about 250 μm, and the crack lower end length is about 80 μm, which is a result superior to the first comparative example and the second comparative example. Has been obtained. From this result, in the laser processing apparatus 1 of this embodiment, when processing a wafer W having a thickness of 775 μm, the aberration correction amount by the correction ring is 500 μm (that is, the laser light irradiation surface of the wafer W (wafer W It is preferable to set the aberration at a position where the depth from the back surface is 500 μm. Then, the laser light L is modulated by the spatial light modulator 28 so that the laser light L is simultaneously condensed by the condenser lens 38 at two positions having different depths in the vicinity of this depth (500 μm). The crack extending in the wafer depth direction from the modified region formed inside the wafer W can be sufficiently extended. As a result, the wafer can be efficiently divided into chips, and stable quality chips can be obtained efficiently.

  In the present embodiment, the aberration correction unit is configured by the correction ring provided in the condenser lens 38. However, the present invention is not limited to this, and the aberration correction unit includes the condenser lens 38 and the spatial light modulator 28. A correction optical system may be arranged on the optical path of the laser light L between them (for example, between the condensing lens 38 and the second lens 36b). In this case, the aberration of the laser light L generated inside the wafer W can be corrected by changing the interval between the plurality of lens groups constituting the correction optical system by a driving unit (not shown).

  Further, instead of using an objective lens with a correction ring, a correction function is incorporated in advance as a condenser lens 38 so that the aberration of the laser beam L is minimized at a predetermined position in the wafer depth direction inside the wafer W. An objective lens (infrared objective lens) may be used. In this case, the aberration correction amount is fixed in accordance with the thickness of the wafer W and the condensing position of the laser beam (processing depth of the modified region). For example, aberration occurs at a position where the aberration correction amount is 500 μm. By using the smallest objective lens, the crack can be sufficiently extended from the modified region in the wafer depth direction.

  In the present embodiment, the laser light L is simultaneously condensed at two positions different from each other in the wafer depth direction inside the wafer W, and the modified regions P1 and P2 are simultaneously formed at the respective condensing positions. After performing the two-stage processing, a back surface grinding process for grinding the back surface of the wafer W is performed, and a method of dividing the wafer W into individual chips is adopted. However, the present invention is not limited to this. The laser processing may be performed a plurality of times while changing the position (the processing depth of the modified region) where the laser beam L is focused inside. At this time, a correction pattern for correcting the aberration inside the wafer W (in this case, in a direction to cancel the correction by the correction ring) is applied to the hologram pattern to be presented to the spatial light modulator 28 according to the processing depth of the modified region. By superimposing the pattern), appropriate aberration correction can be performed even on a relatively deep portion of the wafer W from the laser light irradiation surface.

  In the present embodiment, as shown in FIG. 2, the second position Q2 is the first position Q2 as the positional relationship between the two positions (collection positions) Q1 and Q2 where the laser light L is collected. A configuration is adopted in which it is arranged upstream of the position Q1 in the wafer movement direction M (left side in FIG. 2) and deeper than the first position Q1 from the laser light irradiation surface of the wafer W. The present invention is not limited to this, and as shown in FIG. 8, a configuration opposite to the configuration shown in FIG. 2 may be used. That is, the second position Q2 is disposed upstream of the first position Q1 in the wafer movement direction M (left side in FIG. 8), and is shallower than the first position Q1 from the laser light irradiation surface of the wafer W. The structure arrange | positioned in a position may be sufficient.

  In the present embodiment, the spatial light modulator 28 modulates the laser light L so that the laser light L is simultaneously condensed by the condenser lens 38 at two different positions inside the wafer W. The positions for condensing the laser light L are not limited to two, and may be three or more.

  In this embodiment, a reflective spatial light modulator (LCOS-SLM) is used as the spatial light modulator 28. However, the present invention is not limited to this, and a MEMS-SLM or DMD (deformable mirror device) is used. There may be. Further, the spatial light modulator 28 is not limited to the reflective type, and may be a transmissive type. Furthermore, as the spatial light modulator 28, a liquid crystal cell type, an LCD type or the like can be cited.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. Hereinafter, description of parts common to the first embodiment will be omitted, and description will be made focusing on characteristic parts of the present embodiment.

  FIG. 9 is a configuration diagram showing an outline of a laser processing apparatus according to the second embodiment. In FIG. 9, components that are the same as or similar to those in FIG.

  In the second embodiment, in the observation optical system of the laser head 20, a tunable lens 52 is disposed on the optical path of reflected light between the half mirror 44 and the infrared camera 50. The tunable lens 52 changes the converging point of the observation objective lens 46 in the wafer depth direction (Z direction) by changing the curvature according to the control of the control unit 60. The control unit 60 is an example of a tunable lens curvature changing unit.

  According to the second embodiment, the focusing point of the observation objective lens 46 is moved in the wafer depth direction at a high speed by the tunable lens 52 and the focusing point of the observation objective lens 46 is moved by the actuator 48 to the wafer. It is possible to move with a small distance in the depth direction with high accuracy. Therefore, compared with the case where the focusing point of the observation objective lens 46 is changed only by the actuator 48 as in the first embodiment, the focusing point of the observation objective lens 46 can be moved at high speed and with high accuracy. Therefore, the imaging time of the wafer W by the infrared camera 50 can be shortened, and the throughput for the wafer processing confirmation process can be improved.

  In the second embodiment, as an example, a mode in which the tunable lens 52 and the actuator 48 are used in combination as a means for changing the condensing point of the observation objective lens 46 (condensing point changing means) is shown. However, the present invention is not limited to this. For example, the focusing point of the observation objective lens 46 may be changed using only the tunable lens 52 without including the actuator 48.

(Third embodiment)
Next, a third embodiment of the present invention will be described. Hereinafter, description of parts common to the first embodiment will be omitted, and description will be made focusing on characteristic parts of the present embodiment.

  FIG. 10 is a configuration diagram showing an outline of a laser processing apparatus according to the third embodiment. In FIG. 10, components that are the same as or similar to those in FIG.

  In the third embodiment, a part of the observation optical system in the laser head 20 is arranged coaxially with the optical axis of the processing optical system. Specifically, a half mirror 44 is disposed between the condensing lens 38 and the second lens 36b on the optical path of the processing optical system, and the condensing lens 38 is shared by the processing optical system and the observation optical system. Has been. For this reason, the laser light L output from the laser light source 22 is condensed inside the wafer W by the condenser lens 38 via the spatial light modulator 28 and the like, and the laser reflected inside the wafer W. The reflected light of the light L is reflected by the half mirror 44 via the condenser lens 38 and enters the infrared camera 50. Further, the Z direction position (wafer depth direction position) of the condensing point by the condensing lens 38 is adjusted by moving the condensing lens 38 in the Z direction (optical axis direction of the condensing lens 38) by the actuator 54. The

  According to the third embodiment, since a part of the observation optical system in the laser head 20 is arranged coaxially with the optical axis of the processing optical system, the imaging position of the wafer W by the infrared camera 50 is processed. It is set at the same position as the processing position of the wafer W by the optical system. Therefore, when the modified region is formed inside the wafer W by the laser beam L, the formation position of the modified region can be instantaneously confirmed and measured with the infrared camera 50 simultaneously with the formation of the modified region. Become.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the scope of the present invention. .

  DESCRIPTION OF SYMBOLS 10 ... Laser processing apparatus, 11 ... Wafer moving part, 12 ... XYZtheta table, 13 ... Adsorption stage, 20 ... Laser head, 22 ... Laser light source, 24 ... Beam expander, 26 ... λ / 2 wavelength plate, 28 ... Spatial light Modulator, 36 ... reduction optical system, 38 ... condensing lens, 42 ... illumination light source, 44 ... half mirror, 46 ... observation objective lens, 48 ... actuator, 50 ... infrared camera, 52 ... tunable lens, 54 ... actuator 60 ... control unit, 60a ... image processing unit

Claims (6)

A device for confirming a laser processing area formed inside a workpiece,
An illumination light source that outputs illumination light in a wavelength range that passes through the workpiece;
An objective lens for condensing the illumination light on the workpiece and receiving reflected light from a condensing point;
A condensing point changing means for changing the condensing point of the objective lens in the depth direction of the workpiece;
Imaging means for imaging the reflected light received by the objective lens and acquiring a plurality of captured images for each condensing point changed by the condensing point changing means;
An apparatus for confirming a laser processing area. The condensing point changing means includes objective lens moving means for changing the condensing point of the objective lens in the depth direction by moving the objective lens in the optical axis direction.
The laser processing region confirmation device according to claim 1. The condensing point changing means changes the curvature of the tunable lens and the tunable lens disposed on the optical path between the imaging means and the objective lens, thereby changing the condensing point of the objective lens. Tunable lens curvature changing means for changing in the depth direction,
The apparatus for confirming a laser processing region according to claim 1 or 2. A method for confirming a laser processing region formed inside a workpiece,
A light receiving step of condensing illumination light in a wavelength range that passes through the workpiece with the objective lens and receiving reflected light from a focal point with the objective lens;
A condensing point changing step of changing the condensing point of the objective lens in the depth direction of the workpiece; and
An imaging step of capturing the reflected light received by the objective lens with an imaging unit and acquiring a plurality of captured images for each condensing point changed in the condensing point changing step;
A method for confirming the laser processing area, including The condensing point changing step includes a step of changing the condensing point of the objective lens in the depth direction by moving the objective lens in the optical axis direction.
The method for confirming a laser processing region according to claim 4. The condensing point changing step changes the condensing point of the objective lens in the depth direction by changing the curvature of the tunable lens disposed on the optical path between the imaging means and the objective lens. Including the step of
The method for confirming a laser processing region according to claim 4 or 5.