JP2017064747A - Laser processing device and laser processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing device which enables an operation state of a spatial light modulator to be easily checked, and to provide a laser processing method.SOLUTION: A laser processing device 1 includes: a laser light source 22; a spatial light modulator 28 which modules laser light L output from the laser light source 22; a half mirror 40 which is disposed on an optical path of the laser light L modulated by the spatial light modulator 28; a condenser lens 38 which condenses the laser light L, which has penetrated through the half mirror 40, into a wafer W; control means which controls a modulation pattern of the spatial light modulator 28; a wafer moving part 11 which moves the wafer W relative to the laser light L; a power meter 44 which measures power of reflection light reflected by the half mirror 40; and determination means which determines an operation state of the spatial light modulator 28 on the basis of the power of the reflection light measured by the power meter 44.SELECTED DRAWING: 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 a 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 technology as described above, a spatial light modulator is used to suppress the aberration generated inside the wafer, and it is confirmed in real time whether or not this spatial light modulator is operating normally. There is no way to do it. For this reason, in order to confirm the operating state of the spatial light modulator, it is necessary to stop the laser processing and then divide the wafer along the planned cutting line and observe the processing cross section.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a laser processing apparatus and a laser processing method capable of easily confirming the operation state of the spatial light modulator.

  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, a laser light source that outputs laser light, a spatial light modulator that is disposed on an optical path of the laser light output from the laser light source and modulates the laser light, An optical path branching unit that is disposed on the optical path of the laser light modulated by the spatial light modulator and branches the optical path of the laser light into at least a first branched optical path and a second branched optical path, and disposed on the first branched optical path. The condensing lens that condenses the laser light branched into the first branching optical path inside the wafer, and the spatial light so that the condensing point of the laser light condensed by the condensing lens is formed at a desired position. modulation The control means for controlling the modulation pattern of the laser, the moving means for moving the wafer relative to the laser light, and the power of the laser light that is disposed on the second branch optical path and branched to the second branch optical path is measured. Power measuring means, and control means for judging the operating state of the spatial light modulator based on the power of the laser light measured by the power measuring means.

  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 determining means confirms a change in the power of the laser light measured by the power measuring means when the modulation pattern of the spatial light modulator is switched. By doing so, the operating state of the spatial light modulator is determined.

  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 control means have different depths from the laser light irradiation surface inside the wafer and are separated from each other in the movement direction of the wafer. This is a means for controlling the modulation pattern of the spatial light modulator so that the laser light is simultaneously condensed by a condenser lens at a plurality of positions, and is configured separately from the spatial light modulator. 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 condensing points are aligned is provided.

  A laser processing apparatus according to a fourth aspect of the present invention is the laser processing apparatus according to the third aspect, wherein the control means focuses the laser beam at a first position in the wafer depth direction, and the first position is the wafer depth. The modulation pattern of 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 fifth 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, a modulation step of modulating laser light output from a laser light source with a spatial light modulator, and an optical path of the laser light modulated by the spatial light modulator to at least a first branch optical path and a second branch optical path The optical path branching step for branching, the condensing step for condensing the laser light branched to the first branch optical path inside the wafer by the condensing lens, and the condensing point of the laser light condensed by the condensing lens are desired. A control process for controlling the modulation pattern of the spatial light modulator, a movement process for moving the wafer relative to the laser light, and a laser beam branched into the second branch optical path so as to be formed at the position Comprising a power measuring step of measuring the power, based on the power of the measured laser light power measuring step, a determination step of determining the operating state of the spatial light modulator, a.

  The laser processing apparatus according to a sixth aspect of the present invention is the laser processing apparatus according to the fifth aspect, wherein the determination step confirms a change in the power of the laser beam measured in the power measurement step when the modulation pattern of the spatial light modulator is switched. By doing so, the operating state of the spatial light modulator is determined.

  The laser processing method according to a seventh aspect of the present invention is the laser processing method according to the fifth aspect or the sixth aspect, wherein the control step has different depths from the laser light irradiation surface inside the wafer and is separated from each other in the moving direction of the wafer. This is a process to control the modulation pattern of the spatial light modulator so that the laser beam is simultaneously focused by a condensing lens at a plurality of positions. It is performed separately from the modulation process, and the laser beam is focused inside the wafer. An aberration correction step is included 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 points are aligned.

  In the laser processing method according to the eighth aspect of the present invention, in the seventh aspect, in the control step, the laser beam is condensed at the first position in the wafer depth direction, and the first position is the wafer depth. The modulation pattern of 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 easily confirm the operating state of the spatial light modulator by branching a part of the laser light modulated by the spatial light modulator and measuring the power of the branched laser light. It becomes.

The block diagram which showed the outline of the laser processing apparatus which concerns on one 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 The flowchart figure which showed the flow of the operation check processing performed with the laser processing equipment 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

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

  FIG. 1 is a configuration diagram showing an outline of a laser processing apparatus according to an 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 mainly includes a laser light source 22, a spatial light modulator 28, a condenser lens 38, a half mirror 40, an aperture 42, a power meter 44, 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 10 W.

  The spatial light modulator 28 is disposed on the optical path of the laser light L output from the laser light source 22. 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. A pattern (modulation 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, a reflective liquid crystal (LCOS) spatial light modulator (SLM) 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. 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 half mirror 40 is disposed on the optical path of the laser light L modulated by the spatial light modulator 28, and transmits a part of the light and reflects the remaining light. That is, the half mirror 40 branches the optical path of the laser beam L into at least a first branch optical path and a second branch optical path. Of the laser light L incident on the half mirror 40, the laser light L transmitted through the half mirror 40 (laser light L branched to the first branch optical path) is guided to the condenser lens 38 and reflected by the half mirror 40. The light L (laser light L branched to the second branch optical path) is guided to the power meter 44 through the aperture 42. The half mirror 40 is an example of an optical path branching unit.

  The condenser lens 38 is disposed on the first branch optical path. 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 aperture 42 is disposed on the second branch optical path. The aperture 42 shields the peripheral portion of the laser light L reflected by the half mirror 40 and transmits the central portion. That is, the aperture 42 passes a part of the laser light L branched to the second branch optical path by the half mirror 40. As a result, the laser light L that has passed through the aperture 42 is limited to an appropriate beam diameter (light beam diameter) and enters the power meter 44.

  The power meter 44 is an example of a power measuring unit, and measures the power of the laser light L that has passed through the aperture 42. The measurement result of the power meter 44 is given to the control unit 60, and the operation state of the spatial light modulator 28 is judged by the control unit 60.

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

  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.

  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, the control unit 60 is based on the power of the laser light L measured by the power meter 44.
The control unit 60 is an example of a control unit and a determination unit, and these units may be configured separately.

  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 wafer image captured by a CCD camera (not shown) 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 condensing lens 38 via the half mirror 40 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, an operation confirmation process for confirming the operation state of the spatial light modulator 28 is performed in real time while performing the laser processing described above.

  FIG. 4 is a flowchart showing the flow of the operation confirmation process performed by the laser processing apparatus 1 in the present embodiment. Hereinafter, the flow of the operation check process will be described.

  First, the control unit 60 constantly monitors the power of the laser beam measured by the power meter 44 (step 10).

  Next, the control unit 60 determines whether or not the switching of the hologram pattern presented by the spatial light modulator 28 has occurred (step S12). When the hologram pattern is not switched, the process returns to step S10 and the power of the laser beam L is continuously monitored. On the other hand, when the hologram pattern is switched, the process proceeds to the next step S14.

  Next, the control unit 60 determines whether or not the power of the laser light L has changed when the hologram pattern is switched (step S14). If the change in the power of the laser light L is greater than or equal to the threshold value, it is determined that the operation state of the spatial light modulator 28 is normal (step S16), and the process returns to step S10 to continue monitoring the power of the laser light L. . On the other hand, when the change in the power of the laser light L is less than the threshold value, it is determined that the operation state of the spatial light modulator 28 is abnormal (step S18).

  If the control unit 60 determines in step S18 that the operation state of the spatial light modulator 28 is abnormal, the control unit 60 notifies the user of the operation state of the spatial light modulator 28 using a notification means such as a television monitor or an indicator lamp. Notification is made (step S20). Therefore, the user can quickly grasp the abnormality of the spatial light modulator 28 and can take appropriate measures.

  As described above, according to the present embodiment, the laser light L modulated by the spatial light modulator 28 is branched by the half mirror 40, and the laser light L branched to one branching optical path (first branching optical path) is collected. The light is condensed inside the wafer W by the lens 38, and the power of the laser light L branched to the other branched optical path (second branched optical path) is measured by the power meter 44 through the aperture 42. Thereby, it is possible to easily confirm the operation state of the spatial light modulator 28 while performing laser processing.

  In the present embodiment, the operation of the spatial light modulator 28 is determined from the change in the power of the laser light L measured by the power meter 44 using the switching of the hologram pattern of the spatial light modulator 28 as a trigger in the operation confirmation process described above. Although the state is judged, it is not restricted to this. For example, when the hologram pattern of the spatial light modulator 28 is not switched (that is, when the hologram pattern is the same), the change in the power of the laser light L measured by the power meter 44 is greater than or equal to the threshold value. May determine that the operational state of the spatial light modulator 28 is abnormal.

  Further, the switching of the hologram pattern of the spatial light modulator 28 is not only for switching the normal hologram pattern accompanying the change of the condensing position of the laser light L and the laser processing conditions, but also for operation check as an interruption process during laser processing. A process of temporarily switching to the hologram pattern may be added.

  Further, the above-described operation confirmation process is not limited to being performed in real time during laser processing, but may be performed before or after the start of laser processing, or may be performed periodically during laser processing. Moreover, you may make it implement suitably according to the request | requirement from a user.

  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. 5 is a graph showing the relationship between the aberration correction amount and the total crack length. FIG. 6 is a graph showing the relationship between the aberration correction amount and the crack lower end length. 5 and 6, 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. 5 and 6, 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 configuration is not limited to the above, and as shown in FIG. 7, the configuration shown in FIG. 2 may be reversed. That is, the second position Q2 is disposed upstream of the first position Q1 in the wafer movement direction M (left side in FIG. 7), 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.

  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, 40 ... half mirror, 42 ... aperture, 44 ... power meter, 60 ... control unit

Claims (8)

A laser processing apparatus for forming a modified region in the wafer along the planned cutting line of the wafer by irradiating a laser beam with a condensing point inside the wafer,
A laser light source for outputting the laser light;
A spatial light modulator that is disposed on an optical path of the laser light output from the laser light source and modulates the laser light;
An optical path branching unit that is disposed on the optical path of the laser light modulated by the spatial light modulator and branches the optical path of the laser light into at least a first branching optical path and a second branching optical path;
A condenser lens disposed on the first branch optical path and condensing the laser beam branched into the first branch optical path inside the wafer;
Control means for controlling a modulation pattern of the spatial light modulator so that a condensing point of the laser light condensed by the condenser lens is formed at a desired position;
Moving means for moving the wafer relative to the laser beam;
A power measuring means disposed on the second branch optical path and measuring the power of the laser beam branched into the second branch optical path;
Control means for judging the operating state of the spatial light modulator based on the power of the laser beam measured by the power measuring means;
A laser processing apparatus comprising: The determination means confirms a change in power of the laser light measured by the power measurement means when the modulation pattern of the spatial light modulator is switched, thereby operating the spatial light modulator. To judge,
The laser processing apparatus according to claim 1. The control means is configured to simultaneously collect the laser light by the condenser lens at a plurality of positions having different depths from the laser light irradiation surface inside the wafer and separated from each other in the moving direction of the wafer. Means for controlling the modulation pattern of the spatial light modulator,
Aberration correction means configured separately from the spatial light modulator and configured to correct the laser light aberration to be equal to or less than a predetermined aberration at the plurality of positions where the laser light condensing points are aligned inside the wafer. Prepare
The laser processing apparatus according to claim 1 or 2. The control means condenses the laser light at a first position in the wafer depth direction, and condenses the laser light at a second position different from the first position in the wafer depth direction. Controlling the modulation pattern of the spatial light modulator to be
The laser processing apparatus according to claim 3. A laser processing method for forming a modified region in the wafer along the planned cutting line of the wafer by irradiating a laser beam with a focusing point inside the wafer,
A modulation step of modulating the laser light output from the laser light source with a spatial light modulator;
An optical path branching step of branching the optical path of the laser light modulated by the spatial light modulator into at least a first branch optical path and a second branch optical path;
A condensing step of condensing the laser beam branched into the first branch optical path inside the wafer with a condensing lens;
A control step of controlling a modulation pattern of the spatial light modulator so that a condensing point of the laser light condensed by the condenser lens is formed at a desired position;
A moving step of moving the wafer relative to the laser beam;
A power measurement step of measuring the power of the laser beam branched into the second branch optical path;
A determination step of determining an operating state of the spatial light modulator based on the power of the laser beam measured in the power measurement step;
Including laser processing method. The determining step confirms a change in power of the laser light measured in the power measuring step when the modulation pattern of the spatial light modulator is switched, thereby operating the spatial light modulator. To judge,
The laser processing method according to claim 5. In the control step, the laser light is simultaneously condensed by the condenser lens at a plurality of positions having different depths from the laser light irradiation surface inside the wafer and separated from each other in the movement direction of the wafer. The step of controlling the modulation pattern of the spatial light modulator,
An aberration correction step, which is performed separately from the modulation step, 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 condensing points of the laser light are aligned inside the wafer.
The laser processing method according to claim 5 or 6. In the control step, the laser light is condensed at a first position in the wafer depth direction, and the laser light is condensed at a second position different from the first position in the wafer depth direction. Controlling the modulation pattern of the spatial light modulator to be
The laser processing method according to claim 7.

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