JP6531345B2 - Laser processing apparatus and laser processing method - Google Patents

Description

  The present invention is a laser that forms a modified region inside the wafer along a line to be cut of the wafer by irradiating the laser light with the focusing point aligned on the inside of 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 having a plurality of devices formed on its surface into individual chips, the wafer is cut by putting a grinding groove in the wafer with a thin grindstone of about 30 μm in thickness formed of fine diamond abrasive grains. A dicing machine was used.

  In a dicing machine, 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 a wafer, and the wafer is completely cut (full cut) or incompletely cut (half cut or semi full) Do the cut).

  However, in the case of grinding using this dicing blade, the wafer is a highly brittle material and therefore brittle mode processing is performed, chipping occurs on the front and back surfaces of the wafer, and this chipping causes the performance of divided chips to be degraded. The

  To solve these problems, instead of cutting with a conventional dicing blade, the laser light is irradiated to the inside of the wafer with the focusing point aligned, and the modified region (modified layer) by multiphoton absorption inside the wafer There has been proposed a technology of forming and dividing into individual chips (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 (especially the position in the wafer depth direction) of the modified region formed inside the wafer is determined. In order to confirm or measure, there has been only a method of observing the cross section of the cut wafer with a microscope after cutting the wafer at a line to cut. For this reason, verification with a product wafer is difficult, and it was necessary to separately facilitate the wafer for verification. Also, with regard to processing damage, after processing is performed using a wafer having 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 could not.

  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 of a modified region formed inside a wafer and processing damage. The purpose is

  In order to achieve the above object, a laser processing apparatus according to a first aspect of the present invention aligns a focusing point on the inside of a wafer and irradiates a laser beam to the inside of the wafer along a planned cutting line of the wafer. An illumination light source that outputs illumination light in a wavelength range that transmits the wafer, and an objective that condenses the illumination light on the wafer and receives reflected light from a light collection point A lens, a focusing point changing means for changing the focusing point of the objective lens in the wafer depth direction, and an image of reflected light received by the objective lens, and for each focusing point changed by the focusing point changing means And imaging means for acquiring a plurality of captured images.

  In the laser processing apparatus according to the second aspect of the present invention, in the first aspect, 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.

  In the laser processing apparatus according to the third aspect of the present invention, in the first aspect or the second aspect, the focusing point changing means is a tunable lens disposed on an optical path between the imaging means and the objective lens; Tunable lens curvature changing means for changing the condensing 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 a condensing lens for condensing the laser beam inside the wafer and the wafer relative to the laser beam And a moving means for moving the focusing point of the objective lens is disposed downstream of the focusing point of the focusing lens in the moving direction of the wafer.

  In the laser processing apparatus according to the fifth aspect of the present invention, in any one of the first to fourth aspects, the spatial light modulator for modulating the laser light and the depth from the laser light irradiation surface inside the wafer are mutually different A control unit that controls the spatial light modulator so that the laser light is simultaneously condensed to a plurality of different positions that are different from each other in the moving direction of the wafer, and the spatial light modulator are configured separately inside the wafer And Aberration correction means for correcting the aberration of the laser beam to be equal to or less than a predetermined aberration at a plurality of positions where the focusing points of the laser beam are aligned.

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

  A laser processing method according to a seventh aspect of the present invention is a laser that forms a modified region in the interior of a wafer along a line to be cut of the wafer by irradiating the laser light while aligning the condensing point inside the wafer. In the processing method, illumination light in a wavelength range that transmits the wafer is condensed on the wafer by the objective lens, and the reflected light from the condensing point is received by the objective lens, and the condensing point of the objective lens is Focusing point changing step to change in the depth direction, Reflected light received by the objective lens is imaged by the imaging means, and imaging is performed to obtain a plurality of captured images for each focusing point changed in the focusing point changing step And a process.

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

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

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

  In the laser processing method according to an eleventh aspect of the present invention, in any one of the seventh to tenth aspects, a modulation step of modulating the laser light by the spatial light modulator, and the laser light modulated by the spatial light modulator A condensing step of condensing light inside the wafer, a moving step of moving the wafer relative to the laser light, and a 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 step of controlling the spatial light modulator so that the laser light is simultaneously collected at a plurality of mutually separated positions, and a separate process from the spatial light modulator, adjust the focusing points of the laser light inside the wafer 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.

  In a laser processing method according to a twelfth aspect of the present invention, in the eleventh aspect, the controlling step includes focusing the laser light at a first position in the wafer depth direction and the first position being the wafer depth. The spatial light modulator is controlled such that the laser light is focused to a second position different in direction.

  According to the present invention, it is possible to nondestructively check and measure the formation position of the modified region formed inside the wafer and the processing damage.

The block diagram which showed the outline of the laser processing apparatus which concerns on the 1st Embodiment of this invention Conceptual diagram showing how the reformed area is formed inside the wafer A conceptual view of how a crack extends in the wafer depth direction from the modified region formed inside the wafer A schematic diagram showing a plurality of captured images acquired by an infrared camera The figure which showed an example of the captured image containing an upper modified layer and a lower modified layer Graph showing relationship between aberration correction amount and total crack length Graph showing relationship between aberration correction amount and crack bottom length FIG. 16 is a conceptual view showing how a reformed area is formed inside a wafer, for illustrating another form of two positions (focusing positions) where laser light is focused. The block diagram which showed the outline of the laser processing apparatus which concerns on 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 attached drawings.

First Embodiment
FIG. 1 is a schematic view showing a laser processing apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the laser processing apparatus 1 of the present embodiment mainly includes a wafer moving unit 11, a laser head 20, a control unit 60, and the like.

  The wafer moving unit 11 is provided with a suction stage 13 for holding the wafer W by suction, and an XYZθ table 12 provided on the main body base 16 of the laser processing apparatus 1 for precisely moving the suction stage 13 in the XYZθ directions. The wafer moving unit 11 precisely moves the wafer W in the XYZθ direction in the drawing. The wafer moving unit 11 is an example of a moving unit.

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

  The wafer W may be mounted on the suction stage 13 in a state in which a dicing sheet having an adhesive material is attached to one surface and integrated with the frame through the dicing sheet.

  The laser head 20 is a processing optical system for irradiating the wafer W with the laser light L for processing, and an observation optical for confirming or measuring the formation position of the modified region formed inside the wafer W and processing damage. It is equipped with a 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 laser light L for processing for forming a modified region inside the wafer W according to the control of the control unit 60. As the conditions for the laser light L, for example, the light source is a semiconductor laser pumped Nd: YAG laser, the wavelength is 1.1 μm, the laser light spot cross-sectional area is 3.14 × 10 ^-8 cm ² , and the oscillation mode is 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. The spatial light modulator 28 modulates the phase of the laser beam L in each of a plurality of two-dimensionally arranged pixels. The pattern is presented, and the laser light L after the phase modulation is output. This hologram pattern is obtained by superimposing a plurality of Fresnel lens patterns having different focusing positions. Thereby, as described in detail later, the wafer moving directions (processing feed direction) different from each other in depth from the laser beam irradiation surface (the back surface of the wafer W) inside the wafer W and parallel to the X direction in FIG. The laser light L is simultaneously condensed by the condensing lens 38 at two positions separated from each other by M.

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

  The focusing lens 38 is an objective lens (infrared objective lens) for focusing the laser beam L on the inside of the wafer W. The numerical aperture (NA) of the condenser lens 38 is 0.6 to 0.8 (e.g., 0.65).

  The condenser lens 38 is configured of an objective lens with a correction ring in order to correct the aberration of the laser light L generated inside the wafer W. The correction ring (not shown) provided on the condenser lens 38 is manually rotatable, and when the correction ring is rotated in a predetermined direction, the distance between the lens groups constituting the condenser lens 38 is changed. Thus, the aberration can be corrected so that the aberration of the laser beam L becomes equal to or less than the predetermined aberration at the position of the predetermined depth from the laser beam irradiation surface (rear surface) of the wafer W. The correction ring of the focusing lens 38 is an example of an aberration correction unit.

  The correction ring of the condenser 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 drive unit, and corrects the aberration of the laser light L to be in a desired state by rotating the correction ring.

  The processing optical system of the laser head 20 is provided with 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 into an appropriate beam diameter for the spatial light modulator 28. The λ / 2 wavelength plate 26 adjusts the laser light incident polarization plane to the spatial light modulator 28. The reduction optical system 36 is an afocal optical system (both-side telecentric optical system) including a first lens 36 a and a second lens 36 b, and the condensing lens 38 is a laser light L modulated by the spatial light modulator 28. Project to a reduced size.

  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) of a wavelength range (infrared range) transmitting the wafer W.

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

  The reflected light reflected by the wafer W (that is, the reflected light from the focal 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 (rear surface) side of the wafer W. The infrared camera 50 includes an imaging device (not shown) having sensitivity to the wavelength range of infrared light. Therefore, the infrared camera is moved in a state in which the objective lens 46 for observation is moved in the Z direction (direction of the optical axis of the objective lens 46 for observation) by the actuator 48 and the condensing point by the objective lens 46 for observation is aligned inside the wafer W. When the wafer W is imaged by 50, the internal state of the wafer W can be confirmed. Further, 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). The 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) represented by an InGaAs (indium gallium arsenide) camera is preferably used.

  In the present 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) The wafer W is disposed on a straight line on the downstream side (right side in FIG. 1) of the wafer moving direction M with respect to the processing position of the wafer W (the condensing point of the laser light L by the condenser lens 38). With this configuration, the infrared camera 50 can image the wafer W on the same planned cutting 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 confirm and measure processing damage etc. 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 etc. 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 feed rate of the wafer W are controlled, and the operation of each part (the wafer moving part 11 and the laser head 20 etc.) is controlled under optimum conditions to form a modified region.

  Further, 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 different positions within the wafer W (that is, two positions different from each other in the wafer moving direction M parallel to the X direction in FIG. 1 and different in depth from the laser light irradiation surface) The spatial light modulator 28 presents a hologram pattern for modulating the laser light L so that the laser light L is simultaneously condensed by the condensing lens 38. 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 condensing lens 38 or the wafer W, and the like, and is stored in the control unit 60.

  In addition, when confirming or measuring the formation position of the modified region formed inside the wafer W and the processing damage, the control unit 60 microsteps the focusing point by the observation objective lens 46 in the Z direction (for example, 2 μm The drive of the actuator 48 is controlled to move in the interval).

  The laser processing apparatus 1 further includes wafer transfer means, an operation plate, a television monitor, and an indicator light, which are not shown.

  Switches and a display device for operating the operation of each part of the laser processing apparatus 1 are attached to the operation plate. The television monitor displays a captured image (wafer image) captured by the infrared camera 50 or displays program content, various messages, and the like. The indicator light indicates the operation status such as processing end, emergency stop, etc. during 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, the case of processing a silicon substrate having a thickness of 775 μm as the wafer W will be described as an example.

  First, by rotating the correction ring provided on the condenser lens 38 manually (or electrically), the laser light L is focused at the position (the processing depth of the modified region) where the laser light L is condensed inside the wafer W The aberration correction amount is adjusted so that the aberration of the lens is smaller than or equal to a predetermined aberration. In the present specification, the “aberration correction amount” is a value converted to the depth from the laser light irradiation surface of the wafer W. That is, for example, when the aberration correction amount is 500 μm, it means that the aberration of the laser light becomes minimum at a position near the depth of 500 μm from the laser light irradiation surface of the wafer W. In this example, as 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 the wafer W to be processed is mounted on the suction stage 13, the alignment of the wafer W is performed using an alignment optical system (not shown).

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

  At this time, the beam diameter of the laser light L output from the laser light source 22 is expanded 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 perform spatial light modulation. Is incident on the

  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 this time, the control unit 60 performs spatial light modulation on the hologram pattern for modulating the laser light L so that the laser light L is simultaneously condensed by the condensing lens 38 at two different positions in the inside of the wafer W. Control to be displayed on the display unit 28.

  The laser beam L emitted from the spatial light modulator 28 is sequentially reflected by the second mirror 31 and the third mirror 32, passes through the first lens 36a, and is further reflected by the fourth mirror 33 and the fifth mirror 34. The light is reflected, passes through the second lens 36 b, and is incident on the condensing lens 38. As a result, the laser beam 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 36 a and the second lens 36 b. Then, the laser light L incident on the condensing lens 38 is condensed at two different positions inside the wafer W by the condensing lens 38.

  FIG. 2 is a conceptual view showing how a reformed region is formed inside the wafer W. As shown in 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 (the back surface of the wafer W) inside the wafer W by the condensing lens 38, and The light is collected simultaneously at two positions separated from each other in the wafer movement direction M. As a result, modified regions P1 and P2 are formed by multiphoton absorption in the vicinity of the respective focusing positions. Further, when the modified regions P1 and P2 are formed, cracks (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 (focusing positions) where the laser light L is focused will be described in detail. In this embodiment, the first position Q1 in the wafer depth direction inside the wafer W (right side in FIG. 2) The laser light L is collected at the light collection point), and the laser light is collected at the second position Q2 (light collection point on the left side in FIG. 2) different from the first position Q1 in the wafer depth direction. Ru.

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

  In this state, as the wafer W moves relative to the laser beam L, as shown in FIG. 3, along the movement locus of two focusing points (focusing positions Q1 and Q2) of the laser beam L. The reformed regions P1 and P2 are formed inside the wafer W. As a result, along the line to cut the wafer W, the modified region P1 and the modified region P2 are formed one by one in the wafer W in a state of being overlapped at a predetermined interval.

  As described above, when the modified region P1 and the modified region P2 are formed in a state of being overlapped at a predetermined interval, time delay is caused among the two modified regions P1 and P2 overlapping in the wafer depth direction. By the impact at the time of formation of the formed modified region P1, as shown in FIG. 3, the crack K1 of the modified region P1 and the crack K2 of the modified region P2 are connected, and the crack K2 extending from the modified region P2 is a wafer It extends toward the surface (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 mutually different positions in the wafer W, thereby reducing the throughput from the surface of the wafer W. 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 indicates the initial thickness of the wafer W (775 μm in this example).

  When the reformed regions P1 and P2 are formed one by one along the lines to be cut, 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 in the next line. .

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

  Thereby, the modified regions P1 and P2 are formed along all the lines to be cut. The modified regions P1 and P2 have the same position on the plane (the position seen from the back surface or the front surface of the wafer W) and are both formed along the line to be cut, but the thickness direction of the wafer W Only the position in the depth direction) differs.

  After the reformed regions P1 and P2 are formed along the lines to be cut as described above, the back surface of the wafer W is ground using a grinding device (not shown) to obtain the thickness (initial thickness) T1 of the wafer W. Is processed to a predetermined thickness (final thickness) T2 (for example, 30 to 50 .mu.m).

  After the back surface grinding step, an expand tape (dicing tape) is attached to the back surface of the wafer W, and after the BG tape attached to the front surface of the wafer W is peeled off, tension is applied to the expanded tape attached to the back surface of the wafer W An expansion step is performed to add and stretch.

  As a result, the wafer W is cut starting from the crack extending to the surface side of the wafer W. That is, the wafer W is cut along a line to cut and divided into a plurality of chips.

  Here, in the laser processing apparatus 1 according to the present embodiment, as shown in FIG. 1, the laser beam L is formed inside the wafer W while forming the modified region along the line to be cut inside the wafer W. A wafer processing confirmation process for confirming the formation position of the modified region and the processing damage is performed in real time.

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

  At this time, the control unit 60 controls the drive of the actuator 48 to move the observation objective lens 46 in the optical axis direction (Z direction) in minute steps (for example, about 2 μm) (ie, for the observation objective lens 46). While moving the position of the focusing point (focus point) in the wafer depth direction in minute steps, the image is captured by the infrared camera 50. 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). As a result, as shown in FIG. 4, a plurality of captured images (XY images at the positions of the respective focusing points) 62 (62-1, 62-2 to 62-n) are sequentially acquired by the infrared camera 50. The 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. In addition, each captured image stored in the storage unit can be displayed on the television monitor in accordance with the user's operation.

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

  When the modified region P1 and the modified region P2 are properly formed in the wafer depth direction (Z direction), as shown in FIG. 5 among the plurality of captured images captured by the infrared camera 50, the desired ones The modified region can be confirmed in the captured image at the position in the wafer depth direction of

  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 can not be confirmed in the captured image at the desired position in the wafer depth direction.

  Therefore, it is determined from the plurality of captured images captured by the infrared camera 50 whether the captured image in which the modified region P1 or the modified region P2 is confirmed is a captured image at a desired wafer depth direction position. Thus, it is possible to confirm whether or not the formation positions of the modified regions, such as the positions in the wafer depth direction 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 in the inside of the wafer W by performing image processing on each captured image by the image processing unit 60a provided therein. Thereby, not only the wafer depth direction position (Z direction position) of each of the modified regions P1 and 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 has been done. Therefore, positional deviation in the horizontal direction (X direction and Y direction) of the incident point of the laser beam L with respect to the planned cutting line can also be confirmed.

  In addition, 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, processing damage occurring on the device surface side of the wafer W is confirmed from the captured image captured by the infrared camera 50 can do.

  As described above, according to the present embodiment, the formation position and processing of the modified region formed in the inside of the wafer W while forming the modified region along the line to be cut in the inside of the wafer W by the laser light L Wafer processing confirmation processing is performed in real time to confirm and measure damage. In this wafer processing confirmation process, as described above, every focusing point of the observation objective lens 46 with the infrared camera 50 while changing the position of the focusing point (focus) of the observation objective lens 46 in the wafer depth direction. The plurality of captured images are sequentially acquired. Thereby, the formation position and processing damage of the modified region formed inside the wafer W can be nondestructively confirmed and measured without destroying the wafer W from a plurality of captured images acquired by the infrared camera 50. it can.

  Further, in the present embodiment, a configuration in which the result of confirmation or measurement in the wafer processing confirmation processing is feedback-controlled to the formation position of the modified region and the laser processing conditions can be preferably adopted. According to this configuration, it is possible to form a modified region suitable for dividing the wafer while automatically correcting the formation position of the modified region and the laser processing conditions, and it is also possible to prevent processing damage. , You can get stable quality chips.

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

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

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

  In this experiment, the laser processing apparatus 1 of the embodiment described above was used as an example. In addition, as a comparative example, an apparatus having the same configuration as that of Patent Document 2 described above, that is, a spatial light modulator is used to condense laser light at two mutually different positions inside the wafer while the respective positions are separated. (1st comparative example) which performs the aberration correction in (1), and the device which performs the aberration correction using the correction ring without using the spatial light modulator (that is, the laser beam is condensed at one light collecting position) (Second comparative example) was used.

  As experimental conditions, for a wafer (silicon substrate) having a thickness of 775 μm, the total crack length (the crack length) generated in the wafer depth direction when the modified region is formed while changing the aberration correction amount with each device The total length) and the crack lower end length (the length of the crack 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 amount of aberration correction and the total crack length. FIG. 7 is a graph showing the relationship between the aberration correction amount and the crack lower end length. In FIG. 6 and FIG. 7, the horizontal axis shows the aberration correction amount, and the vertical axis shows the total crack length generated by each device and the crack lower end length, respectively.

  As can be seen from FIGS. 6 and 7, in the example, the total crack length is longer over all aberration correction amounts and the crack lower end length is also longer than in the first comparative example and the second comparative example. The 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 very superior result than the first comparative example and the second comparative example It is obtained. From this result, in the laser processing apparatus 1 of the present 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 it so that the aberration is minimized at a position of 500 μm from the back surface of Then, by modulating the laser light by the spatial light modulator 28 so that the laser light L is simultaneously condensed by the condensing lens 38 at two positions different from each other in depth 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 chips of stable quality can be efficiently obtained.

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

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

  Further, in the present embodiment, the laser light L is simultaneously condensed at two different positions 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-step processing, the back surface grinding step of grinding the back surface of the wafer W is performed, and the method of dividing the wafer W into individual chips is adopted, but it is not limited thereto. The laser processing may be performed a plurality of times while changing the position (processing depth of the modified region) of condensing the laser light L in the inside of. At that time, according to the processing depth of the modified region, a correction pattern for correcting the aberration inside the wafer W (in this case, in the direction to cancel the correction by the correction ring) on the hologram pattern to be presented to the spatial light modulator 28 By superimposing the pattern, appropriate aberration correction can be performed even on a portion relatively deep from the laser beam irradiation surface of the wafer W.

  Further, in the present embodiment, as shown in FIG. 2, the second position Q2 is a first position relation as an arrangement relationship between two positions (light collection positions) Q1 and Q2 at which the laser light L is collected. A configuration is employed that is disposed upstream of the position Q1 in the wafer moving direction M (left side in FIG. 2) and is disposed deeper than the first position Q1 from the laser beam irradiation surface of the wafer W The configuration is not limited to this, and as shown in FIG. 8, the configuration may be reverse to the configuration shown in FIG. 2. That is, the second position Q2 is disposed on the upstream side (left side in FIG. 8) of the wafer moving direction M than the first position Q1 and is shallower than the first position Q1 from the laser light irradiation surface of the wafer W. It may be arranged at a position.

  Further, in the present embodiment, 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 different positions in the inside of the wafer W. The position at which the laser light L is condensed is not limited to two, and may be three or more.

  Further, in the present 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 MEMS-SLM or DMD (deformable mirror device) or the like is used. It 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 or an LCD type may, for example, be mentioned.

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

  FIG. 9 is a configuration diagram schematically showing a laser processing apparatus according to the second embodiment. In FIG. 9, the same or similar components as or to those of FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the second embodiment, in the observation optical system of the laser head 20, the tunable lens 52 is disposed on the optical path of the reflected light between the half mirror 44 and the infrared camera 50. The tunable lens 52 changes the curvature in accordance with the control of the control unit 60 to change the condensing point of the observation objective lens 46 in the wafer depth direction (Z direction). 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 largely in the wafer depth direction by the tunable lens 52 at high speed, and the focusing point of the observation objective lens 46 is detected by the actuator 48 It is possible to move with high precision in the depth direction by a minute distance. Therefore, as 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 is described in which the tunable lens 52 and the actuator 48 are used in combination as a means (focusing point changing means) for changing the focusing point of the observation objective lens 46. However, the present invention is not limited to this. For example, the focusing point of the observation objective lens 46 may be changed only by the tunable lens 52 without providing the actuator 48.

Third Embodiment
Next, a third embodiment of the present invention will be described. Hereinafter, the description of the parts common to the first embodiment will be omitted, and the characteristic parts of the present embodiment will be mainly described.

  FIG. 10 is a configuration diagram schematically showing a laser processing apparatus according to the third embodiment. In FIG. 10, components common or similar to those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

  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, the half mirror 44 is disposed between the condensing lens 38 and the second lens 36 b 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. It is done. Therefore, the laser light L output from the laser light source 22 is condensed on the inside of the wafer W by the condensing lens 38 via the spatial light modulator 28 and the like, and the laser reflected on the inside of 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 (the optical axis direction of the condensing lens 38) by the actuator 54. Ru.

  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 forming the modified region inside the wafer W by the laser light L, it is possible to instantaneously and precisely confirm and measure the formation position of the modified region with the infrared camera 50 simultaneously with the formation of the modified region. Become.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above examples, and it goes without saying that 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 ... XYZθ table, 13 ... Adsorption stage, 20 ... Laser head, 22 ... Laser light source, 24 ... Beam expander, 26 ... λ / 2 wavelength plate, 28 ... Space light Modulator 36: Demagnification optical system 38: Condenser lens 42: Illumination light source 44: Half mirror 46: Objective lens for observation 48: Actuator 50: Infrared camera 52: Tunable lens 54: Actuator , 60 ... control unit, 60 a ... image processing unit

Claims (12)

A laser processing apparatus for forming a modified region in the interior of a wafer along a line to cut the wafer by aligning a condensing point inside the wafer and irradiating a laser beam,
An illumination light source that outputs illumination light in a wavelength range that transmits the wafer;
An objective lens that condenses the illumination light onto the wafer and receives the reflected light from the condensing point;
Focusing point changing means for changing the focusing point of the objective lens in the wafer depth direction;
Imaging means for imaging the reflected light received by the objective lens and acquiring a plurality of captured images for each of the focusing points changed by the focusing point changing means;
Laser processing equipment. The focusing point changing means has an objective lens moving means for changing the focusing point of the objective lens in the wafer depth direction by moving the objective lens in the optical axis direction.
The laser processing apparatus according to claim 1. The focusing point changing means changes the curvature of the tunable lens disposed on the optical path between the imaging means and the objective lens, and the focusing point of the objective lens by changing the curvature of the tunable lens. And Tunable lens curvature changing means for changing in the wafer depth direction.
The laser processing apparatus of Claim 1 or 2. A condensing lens that condenses the laser beam inside the wafer;
Moving means for moving the wafer relative to the laser light;
Equipped with
The focusing point of the objective lens is disposed downstream of the focusing point of the focusing lens in the moving direction of the wafer.
The laser processing apparatus of any one of Claims 1-3. A spatial light modulator that modulates the laser light;
The spatial light modulator is controlled such that the laser light is simultaneously collected at a plurality of positions which are different from each other in depth from the laser light irradiation surface inside the wafer and are mutually separated in the moving direction of the wafer. A control unit,
An aberration correction unit configured separately from the spatial light modulator to correct the aberration of the laser light to be equal to or less than a predetermined aberration at the plurality of positions where the focusing points of the laser light are aligned inside the wafer; ,
The laser processing apparatus of any one of Claims 1-4 provided with these. The controller condenses the laser light at a first position in the wafer depth direction, and the laser light collects at a second position different from the first position in the wafer depth direction. Control the spatial light modulator to be illuminated,
The laser processing apparatus according to claim 5. A laser processing method for forming a modified region in the interior of the wafer along a planned cutting line of the wafer by aligning a condensing point inside the wafer and irradiating it with laser light,
A light receiving step of condensing illumination light in a wavelength range that transmits the wafer onto the wafer with an objective lens and receiving reflected light from a condensing point by the objective lens;
A focusing point changing step of changing the focusing point of the objective lens in the wafer depth direction;
An imaging step of imaging the reflected light received by the objective lens by an imaging unit and acquiring a plurality of captured images for each of the focusing points changed in the focusing point changing step;
Laser processing method including: The focusing point changing step includes the step of changing the focusing point of the objective lens in the wafer depth direction by moving the objective lens in the optical axis direction.
The laser processing method according to claim 7. In the focusing point changing step, the focusing point of the objective lens is made in the wafer depth direction by changing the curvature of a tunable lens disposed on the optical path between the imaging means and the objective lens. Including the step of changing
A laser processing method according to claim 7 or 8. While forming a modified region inside the wafer by the laser light, changing the light collection point of the objective lens in the wafer depth direction by the light collection point changing process, the light collection point by the imaging process Acquire a plurality of captured images for each of the focusing points changed in the changing step,
The laser processing method of any one of Claims 7-9. A modulation step of modulating the laser light with a spatial light modulator;
A focusing step of focusing the laser light modulated by the spatial light modulator inside the wafer;
Moving the wafer relative to the laser beam;
The spatial light modulator is controlled such that the laser light is simultaneously collected at a plurality of positions which are different from each other in depth from the laser light irradiation surface inside the wafer and are mutually separated in the moving direction of the wafer. Control process,
An aberration correction step, which is configured separately from the spatial light modulator, and corrects the aberration of the laser light to be equal to or less than a predetermined aberration at the plurality of positions where the focusing points of the laser light are aligned inside the wafer; ,
The laser processing method according to any one of claims 7 to 10, comprising In the control step, the laser beam is collected at a first position in the wafer depth direction, and the laser light is collected at a second position different from the first position in the wafer depth direction. Control the spatial light modulator to be illuminated,
The laser processing method according to claim 11.