WO2011016296A1

WO2011016296A1 - Laser machining method

Info

Publication number: WO2011016296A1
Application number: PCT/JP2010/060666
Authority: WO
Inventors: 一弘渥美; 雅春星川; 浩之岩城; 誠中野
Original assignee: 浜松ホトニクス株式会社
Priority date: 2009-08-03
Filing date: 2010-06-23
Publication date: 2011-02-10
Also published as: JP2011031284A; TW201105444A; JP5451238B2; TWI560015B

Abstract

Provided is a laser machining method by which a precisely modified region can be stably formed in an object to be machined. The laser beam (L) is modulated by a spatial light modulator and is converged onto the object to be machined. Upon convergence, the position of the laser beam (L) is detected and the position of a modulation pattern (H) in the spatial light modulator is changed on the basis of the detected position of the laser beam (L). Therefore, even if the position of the laser beam (L) incident upon the spatial light modulator is deviated, or the like, it is possible to change the position of the modulation pattern (H) in accordance with the deviation, so that the laser beam (L) can be always appropriately modulated by the spatial light modulator. Thus, it is possible to stably suppress aberrations of the laser beam (L) converged onto the object to be machined.

Description

Laser processing method

The present invention relates to a laser processing method for forming a modified region on a workpiece.

As a conventional laser processing method, there is known a method in which a modified region is formed on a processing target by irradiating a laser beam with a focusing point inside the processing target (for example, Patent Document 1). , 2). In such a laser processing method, a laser beam emitted from a laser light source is modulated by a reflective spatial light modulator.

International Publication No. 2005/106564 Pamphlet JP 2006-68762 A

Here, in the conventional technology as described above, an accurate modified region is stably formed on the workpiece due to, for example, a shift in the optical system caused by a machine difference between laser processing apparatuses (so-called machine difference). May be difficult to do.

Therefore, an object of the present invention is to provide a laser processing method capable of stably forming an accurate modified region on a workpiece.

In order to solve the above-described problems, a laser processing method according to the present invention includes a laser processing method in which a modified region is formed in a processing target by irradiating a laser beam with a focusing point inside the processing target. A modulation step of modulating the laser light with the spatial light modulator, a condensing step of condensing the modulated laser light on the workpiece, and a detection step of detecting the position of the laser light, and modulating In the process, laser light is incident on the modulation pattern displayed on the display unit of the spatial light modulator, the laser light is modulated according to the modulation pattern, and based on the position of the laser light detected in the detection process, The position of the modulation pattern is changed.

In this laser processing method, the position of the modulation pattern in the spatial light modulator is changed based on the position of the laser light. Therefore, for example, even when the position of the laser light incident on the spatial light modulator is shifted, the position of the modulation pattern can be changed according to the shift. Therefore, the laser beam can always be suitably modulated by the spatial light modulator, and the aberration of the laser beam focused on the workpiece can be stably suppressed. That is, it is possible to stably form a modified region with high accuracy on the workpiece.

In the detection step, the amount of change in position of the laser beam with respect to the reference position is detected. In the modulation step, the laser beam and the modulation pattern are predetermined based on the amount of change in the position of the laser beam detected in the detection step. It is preferable to change the position of the modulation pattern so that the positional relationship is established. In this case, the above-described effect of stably forming an accurate modified region on the workpiece can be preferably exhibited.

At this time, in the modulation step, the position of the modulation pattern may be changed using a data table regarding the position change amount of the modulation pattern associated with the position change amount of the laser beam. In the modulation step, the modulation pattern position change amount may be calculated based on the laser beam position change amount, and the modulation pattern position may be changed according to the calculated modulation pattern position change amount.

Further, as a configuration that favorably exhibits the above-described effects, specifically, the modulation pattern represents the refractive index for each of the plurality of pixels of the display unit. In the modulation step, the modulation pattern is moved to a predetermined position and moved. There is a configuration in which the refractive index of a plurality of pixels is calculated in accordance with the modulated pattern, and the refractive index of the pixel is controlled so as to have a refractive index in accordance with the calculated value.

At this time, the amount of movement for moving the modulation pattern may be less than or equal to one pixel size of the display unit.

According to the present invention, an accurate modified region can be stably formed on a workpiece.

It is a schematic block diagram of the laser processing apparatus used for formation of a modification area | region. It is a top view of the processing target object used as the object of formation of a modification field. FIG. 3 is a cross-sectional view taken along the line III-III of the workpiece in FIG. 2. It is a top view of the processing target after laser processing. FIG. 5 is a cross-sectional view taken along the line VV of the workpiece in FIG. 4. FIG. 5 is a cross-sectional view taken along line VI-VI of the workpiece in FIG. 4. It is a schematic structure figure showing a laser processing device concerning one embodiment of the present invention. It is a fragmentary sectional view of a reflection type spatial light modulator. It is a flowchart which shows the procedure of the laser processing method. It is a conceptual diagram which shows an example of the positional information on the laser beam detected by PSD. It is a figure which shows the data table regarding the coordinate value of a laser beam, and the position variation | change_quantity of a modulation pattern. It is a conceptual diagram which shows the relationship between the modulation pattern displayed on the liquid crystal layer, and the laser beam which injected into the liquid crystal layer. It is an enlarged photograph figure which shows the cut surface state at the time of forming and forming a modification area | region in a workpiece. It is a schematic block diagram which shows the other example of the laser processing apparatus of FIG. It is a figure for demonstrating the movement of the modulation pattern of 1 pixel or less.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent element in each figure, and the overlapping description is abbreviate | omitted. Further, the terms “upper”, “lower”, “left”, and “right” are based on the state shown in the drawings for convenience.

In the laser processing apparatus according to the present embodiment, the modified region is formed in the processing target by irradiating the processing target with the laser beam with the focusing point inside the processing target. First, the formation of the modified region by the laser processing apparatus of this embodiment will be described with reference to FIGS.

As shown in FIG. 1, a laser processing apparatus 100 includes a laser light source 101 that oscillates a laser beam L, a dichroic mirror 103 that is arranged so as to change the direction of the optical axis (optical path) of the laser beam L, and A condensing lens 105 for condensing the laser light L. The laser processing apparatus 100 also includes a support 107 for supporting the workpiece 1 irradiated with the laser light L collected by the condensing lens 105, and the support 107 in the X, Y, and Z axis directions. A stage 111 for moving the light source, a laser light source control unit 102 for controlling the laser light source 101 to adjust the output and pulse width of the laser light L, and a stage control unit 115 for controlling the movement of the stage 111. I have.

In this laser processing apparatus 100, the laser light L emitted from the laser light source 101 is changed in the direction of its optical axis by 90 ° by the dichroic mirror 103, and is placed inside the processing object 1 placed on the support base 107. The light is condensed by the condensing lens 105. At the same time, the stage 111 is moved, and the workpiece 1 is moved relative to the laser beam L along the planned cutting line 5. As a result, a modified region along the planned cutting line 5 is formed on the workpiece 1.

As the processing object 1, a semiconductor material, a piezoelectric material, or the like is used, and as shown in FIG. 2, a cutting scheduled line 5 for cutting the processing object 1 is set in the processing object 1. The planned cutting line 5 is a virtual line extending linearly. When forming a modified region inside the workpiece 1, as shown in FIG. 3, the laser beam L is projected along the planned cutting line 5 in a state where the focused point P is aligned with the inside of the workpiece 1. It moves relatively (that is, in the direction of arrow A in FIG. 2). As a result, as shown in FIGS. 4 to 6, the modified region 7 is formed inside the workpiece 1 along the planned cutting line 5, and the modified region 7 formed along the planned cutting line 5 is formed. It becomes the cutting start area 8.

In addition, the condensing point P is a location where the laser light L is condensed. Further, the planned cutting line 5 is not limited to a straight line, but may be a curved line, or may be a line actually drawn on the surface 3 of the workpiece 1 without being limited to a virtual line. In addition, the modified region 7 may be formed continuously or intermittently. Further, the modified region 7 may be in the form of a line or a dot. In short, the modified region 7 only needs to be formed at least inside the workpiece 1. In addition, a crack may be formed starting from the modified region 7, and the crack and modified region 7 may be exposed on the outer surface (front surface, back surface, or outer peripheral surface) of the workpiece 1.

Incidentally, here, the laser beam L passes through the workpiece 1 and is particularly absorbed in the vicinity of the condensing point inside the workpiece 1, whereby a modified region 7 is formed in the workpiece 1. (Ie, internal absorption laser processing). Therefore, since the laser beam L is hardly absorbed by the surface 3 of the workpiece 1, the surface 3 of the workpiece 1 is not melted. In general, when a removed portion such as a hole or a groove is formed by being melted and removed from the front surface 3 (surface absorption laser processing), the processing region gradually proceeds from the front surface 3 side to the back surface side.

By the way, the modified region formed by the laser processing apparatus according to the present embodiment refers to a region where the density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings. Examples of the modified region include a melt treatment region, a crack region, a dielectric breakdown region, a refractive index change region, and the like, and there is a region where these are mixed. Furthermore, as the modified region, there are a region where the density of the modified region in the material to be processed is changed compared to the density of the non-modified region, and a region where lattice defects are formed. Also known as the metastatic region).

In addition, the area where the density of the melt treatment area, the refractive index change area, the modified area has changed compared to the density of the non-modified area, and the area where lattice defects are formed are further divided into these areas and the modified area. In some cases, cracks (cracks, microcracks) are included in the interface with the non-modified region. The included crack may be formed over the entire surface of the modified region, or may be formed in only a part or a plurality of parts. Examples of the processing object 1 include those containing or consisting of silicon, glass, LiTaO ₃ or sapphire (Al ₂ O ₃ ).

Next, an embodiment of the present invention will be described in detail.

FIG. 7 is a schematic configuration diagram illustrating a laser processing apparatus that performs a laser processing method according to an embodiment of the present invention. As shown in FIG. 7, the laser processing apparatus 200 includes a laser light source 202, a reflective spatial light modulator 203, a 4f optical system 241 and a condensing optical system 204 in a housing 231.

The laser light source 202 emits laser light L. For example, a fiber laser is used as the laser light source 202. The laser light source 202 here is fixed to the top plate 236 of the housing 231 with screws or the like so as to emit laser light in the horizontal direction (X direction).

The reflective spatial light modulator 203 modulates the laser light L emitted from the laser light source 202. As the reflective spatial light modulator 203, for example, a reflective liquid crystal (LCOS: liquid crystal on silicon) spatial light modulator (SLM: Spatial light modulator) is used. The reflective spatial light modulator 203 reflects the laser light L incident from the horizontal direction obliquely upward with respect to the horizontal direction, and is condensed inside the workpiece 1 (that is, the condensed light). Modulation is performed so that the aberration of the laser beam L) at the position is less than or equal to a predetermined aberration (ideally substantially zero).

FIG. 8 is a partial cross-sectional view of the reflective spatial light modulator of the laser processing apparatus of FIG. As shown in FIG. 8, the reflective spatial light modulator 203 includes a silicon substrate 213, a drive circuit layer 914, a plurality of pixel electrodes 214, a reflective film 215 such as a dielectric multilayer mirror, an alignment film 999a, a liquid crystal layer (display). Part) 216, an alignment film 999b, a transparent conductive film 217, and a transparent substrate 218 such as a glass substrate, which are laminated in this order.

The transparent substrate 218 has a surface 218 a along the XY plane, and the surface 218 a constitutes the surface of the reflective spatial light modulator 203. The transparent substrate 218 mainly includes a light transmissive material such as glass. The transparent substrate 218 transmits the laser light L having a predetermined wavelength incident from the surface 218 a of the reflective spatial light modulator 203 into the reflective spatial light modulator 203. The transparent conductive film 217 is formed on the back surface 218a of the transparent substrate 218, and mainly includes a conductive material (for example, ITO) that transmits the laser light L.

The plurality of pixel electrodes 214 are two-dimensionally arranged according to the arrangement of the plurality of pixels, and are arranged on the silicon substrate 213 along the transparent conductive film 217. The plurality of pixel electrodes 214 are formed of a metal material such as aluminum, for example. In addition, the surface 214a of the electrode 214 is processed flat and smooth. The plurality of pixel electrodes 214 are driven by an active matrix circuit provided in the drive circuit layer 914.

The active matrix circuit is provided between the plurality of pixel electrodes 214 and the silicon substrate 213, and controls the voltage applied to each pixel electrode 214 in accordance with the optical image to be output from the reflective spatial light modulator 203. . Such an active matrix circuit includes, for example, a first driver circuit that controls the applied voltage of each pixel column arranged in the X-axis direction (not shown) and a first driver circuit that controls the applied voltage of each pixel column arranged in the Y-axis direction. 2 driver circuits. The active matrix circuit is configured such that a predetermined voltage is applied to the pixel electrode 214 of the pixel designated by the control unit 250 in both driver circuits.

Note that the

alignment films

999a and 999b are arranged on both end faces of the liquid crystal layer 216, and the liquid crystal molecule groups are arranged in a certain direction. The

alignment films

999a and 999b are made of a polymer material such as polyimide. As the

alignment films

999a and 999b, those in which a rubbing process or the like is performed on a contact surface with the liquid crystal layer 216 are used.

The liquid crystal layer 216 is disposed between the plurality of pixel electrodes 214 and the transparent conductive film 217, and modulates the laser light L in accordance with an electric field formed by each pixel electrode 214 and the transparent conductive film 217. That is, when a voltage is applied to a certain pixel electrode 214 by the active matrix circuit, an electric field is formed between the transparent conductive film 217 and the pixel electrode 214.

This electric field is applied to each of the reflective film 215 and the liquid crystal layer 216 at a rate corresponding to the thickness of each. Then, the alignment direction of the liquid crystal molecules 216a changes according to the magnitude of the electric field applied to the liquid crystal layer 216. When the laser light L passes through the transparent substrate 218 and the transparent conductive film 217 and enters the liquid crystal layer 216, the laser light L is modulated by the liquid crystal molecules 216 a while passing through the liquid crystal layer 216 and reflected by the reflective film 215. Then, the light is again modulated by the liquid crystal layer 216 and taken out.

At this time, a voltage is applied to each pixel electrode part 214a facing the transparent conductive film 217 by the controller 250 (described later), and each pixel electrode part facing the transparent conductive film 217 in the liquid crystal layer 216 according to the voltage. The refractive index of the portion sandwiched between 214a is changed (the refractive index of the liquid crystal layer 216 at the position corresponding to each pixel is changed). With the change in the refractive index, the phase of the laser light L can be changed for each pixel of the liquid crystal layer 216 in accordance with the applied voltage. That is, phase modulation corresponding to the hologram pattern can be applied to each pixel by the liquid crystal layer 216 (that is, a modulation pattern as a hologram pattern for applying modulation is displayed on the spatial light modulator 203). As a result, the wavefront of the laser beam L that is incident on the reflective spatial light modulator 203 and is modulated and reflected is adjusted, and each light beam constituting the laser beam L is shifted in phase to a component in a predetermined direction orthogonal to the traveling direction. And at least one of the intensity, amplitude, phase, polarization, etc. of the laser beam L is adjusted.

Returning to FIG. 7, the 4f optical system 241 adjusts the wavefront shape of the laser light L modulated by the reflective spatial light modulator 203. The 4f optical system 241 includes a first lens 241a and a second lens 241b.

The

lenses

241a and 241b are arranged between the reflective spatial light modulator 203 and the condensing optical system 204 so as to have the following configuration. That is, in the

lenses

241a and 241b, the distance between the reflective spatial light modulator 203 and the first lens 241a is the focal length f1 of the first lens 241a, and the distance between the condensing optical system 204 and the second lens 241b. Is the focal length f2 of the lens 241b, the distance between the first lens 241a and the second lens 241b is f1 + f2, and the reflective spatial light so that the first lens 241a and the second lens 241b are both-side telecentric optical systems. It is arranged between the modulator 203 and the condensing optical system 204.

In this 4f optical system 241, it is possible to prevent the laser light L modulated by the reflective spatial light modulator 203 from changing its wavefront shape due to spatial propagation and increasing aberrations. In the 4f optical system 241 here, the laser light L is adjusted so that the laser light L incident on the condensing optical system 204 becomes parallel light.

The condensing optical system 204 condenses the laser light L modulated by the 4f optical system 241 inside the workpiece 1. The condensing optical system 204 includes a plurality of lenses and is installed on the bottom plate 233 of the housing 231 via a drive unit 232 including a piezoelectric element and the like.

The laser processing apparatus 200 includes a surface observation unit 211 for observing the surface 3 of the processing object 1 and an AF (AutoFocus) unit for finely adjusting the distance between the condensing optical system 204 and the processing object 1. 212 in the housing 231.

The surface observation unit 211 includes an observation light source 211a that emits visible light VL1, and a detector 211b that receives and detects the reflected light VL2 of the visible light VL1 reflected by the surface 3 of the workpiece 1. ing. In the surface observation unit 211, the visible light VL1 emitted from the observation light source 211a is reflected and transmitted by the mirror 208 and the

dichroic mirrors

209, 210, and 238, and is condensed toward the object to be processed by the condensing optical system 204. The In the surface observation unit 211, the reflected light VL2 reflected by the surface 2 of the workpiece 1 is collected by the condensing optical system 204 and transmitted and reflected by the

dichroic mirrors

238 and 210, and then the dichroic mirror 209. And is received by the detector 211b.

The AF unit 212 emits the AF laser beam LB1 and receives and detects the reflected light LB2 of the AF laser beam LB1 reflected by the surface 3 of the workpiece 1, thereby detecting the surface along the planned cutting line 5 3 displacement data is acquired. Then, when forming the modified region 7, the AF unit 212 drives the drive unit 232 based on the acquired displacement data, and moves the condensing optical system 204 along the waviness of the surface 3 of the workpiece 1. Reciprocate in the optical axis direction.

Furthermore, the laser processing apparatus 200 includes a control unit 250 including a CPU, a ROM, a RAM, and the like for controlling the laser processing apparatus 200. The control unit 250 controls the laser light source 202 and adjusts the output, pulse width, and the like of the laser light L emitted from the laser light source 202. Further, when the control unit 250 forms the modified region 7, the condensing point P of the laser light L is located at a predetermined distance from the surface 3 of the workpiece 1 and moves relatively along the scheduled cutting line 5. Thus, the position of the housing 231 and the stage 111 and the drive of the drive unit 232 are controlled.

Further, when forming the modified region 7, the control unit 250 applies a predetermined voltage to each electrode portion 214 a of the pixel electrode 214 and the transparent electrode film 217 in the reflective spatial light modulator 203, thereby reflecting the reflective spatial light. The refractive index of each element of the liquid crystal layer 216 in the modulator 203 is changed, and a predetermined modulation pattern is displayed on the liquid crystal layer 216. As a result, the aberration of the laser light L emitted from the reflective spatial light modulator 203 and condensed inside the workpiece 1 is controlled to be equal to or less than a predetermined aberration (details will be described later).

When cutting the workpiece 1 using the laser processing apparatus 200 configured as described above, first, for example, an expand tape is attached to the back surface of the workpiece 1 and the workpiece 1 is placed on the stage 111. Place.

Subsequently, a condensing point is aligned from the surface 3 of the workpiece 1 to the inside of the silicon wafer 11, and the laser light source 202 irradiates the laser beam L (S1 in FIG. 9). The emitted laser light L travels in the horizontal direction in the housing 231, is reflected downward by the mirror 205 a, and the light intensity is adjusted by the attenuator 207. Then, the laser beam L is reflected in the horizontal direction by the mirror 205 b, the intensity distribution is made uniform by the beam homogenizer 260, and is incident on the reflective spatial light modulator 203.

The laser beam L incident on the reflective spatial light modulator 203 is modulated so as to be focused inside the workpiece 1 with an aberration equal to or less than a predetermined aberration (S4). Specifically, the incident laser beam L transmits through the modulation pattern displayed on the liquid crystal layer 216, is modulated according to the modulation pattern, and is emitted obliquely upward with respect to the horizontal direction. Then, after the laser beam L is reflected upward by the mirror 206a, the polarization direction is changed by the λ / 2 wavelength plate 228 so that the polarization direction is along the line 5 to be cut, and is reflected by the mirror 206b in the horizontal direction to be 4f. The light enters the optical system 241.

The wavefront shape of the laser light L incident on the 4f optical system 241 is adjusted so as to be incident on the condensing optical system 204 as parallel light (S5). Specifically, the laser light L is transmitted and converged through the first lens 241a, reflected downward by the mirror 219, diverged through the confocal O, and transmitted through the second lens 241b to become parallel light. Will converge again.

Thereafter, the laser light L sequentially passes through the

dichroic mirrors

210 and 218 and enters the condensing optical system 204, and is condensed by the condensing optical system 204 inside the workpiece 1 placed on the stage 111. (S6). Thereby, the modified region 7 is formed inside the workpiece 1 along the planned cutting line 5. Then, by expanding the expanded tape, the workpiece 1 is cut along the scheduled cutting line 5 with the modified region 7 as a starting point of cutting, and separated from each other as a plurality of semiconductor chips.

Here, the laser processing apparatus 200 of the present embodiment includes PSDs (Position Sensitive Detectors) 270a and 270b as optical sensors for detecting the position (pointing) of the laser light L. These

PSDs

270 a and 270 b are connected to the control unit 250 and output the detected position information of the laser light L to the control unit 250.

The PSD 270a is connected between the mirror 205a and the attenuator 207 in the optical path of the laser beam L. Here, the PSD 270a reflects the laser light L reflected by the mirror 205a in order by the

mirrors

271 and 272 and guides it to the PSD 270a. As a result, the PSD 270a two-dimensionally detects the barycentric position (center position) of the spot of the laser light L before the light intensity is adjusted by the attenuator 207 as a coordinate value.

The PSD 270b is connected between the mirror 205b and the beam homogenizer 260 in the optical path of the laser light L. Here, the PSD 270b guides the laser light L reflected by the mirror 205b to the PSD 270b by sequentially reflecting it by the

mirrors

273 and 274. Thereby, the PSD 270b two-dimensionally detects the position of the center of gravity of the spot of the laser light L before the intensity distribution is made uniform by the beam homogenizer 260 as the coordinate value.

FIG. 10 is a conceptual diagram showing an example of position information of laser light detected by PSD. In the example in the figure, the coordinate value Q of the detected laser beam L is set on a coordinate axis with the center of gravity of the laser beam L in the initial state (at the time of initial adjustment) as the origin (reference position). As shown in FIG. 10, according to the

PSDs

270a and 270b, the coordinate value of the laser beam L is detected, that is, the position change amount with respect to the reference value (initial value) of the laser beam L is detected.

Therefore, in this embodiment, the coordinate value Q of the laser light L emitted from the laser light source 202 and before entering the reflective spatial light modulator 203 is constantly monitored by

PSDs

270a and 270b (S2). Based on the coordinate value Q of the laser beam L input from at least one of the

PSDs

270a and 270b, the voltage applied to the electrode unit 214a and the transparent conductive film 217 of the reflective spatial light modulator 203 is controlled by the control unit 250. Then, the position of the modulation pattern displayed on the liquid crystal layer 216 is automatically changed (corrected) (S3).

Specifically, a data table relating to the position change amount of the modulation pattern associated with the coordinate value of the laser beam L is stored in the control unit 250 in advance. As shown in FIG. 11, in the data table Tb here, the coordinate value Q of the laser light L is maintained so that the laser light L and the modulation pattern maintain a predetermined positional relationship (for example, the centroids coincide with each other). And the position change amount of the modulation pattern are associated with each other for each X and Y coordinate (see FIG. 8). Then, using this data table Tb, the position change amount of the modulation pattern is derived from the coordinate values of the laser light L detected by the

PSDs

270a and 270b, and the position of the modulation pattern is changed by this position change amount.

Alternatively, the position change amount of the modulation pattern may be calculated by the following equation (1) based on the coordinate value of the laser beam L, and the position of the modulation pattern may be changed by this position change amount.
ΔX = PSDx × a
ΔY = PSDy × b (1)
Where ΔX is the amount of change in the position of the modulation pattern (X coordinate),
ΔY: position change amount (Y coordinate) of the modulation pattern,
PSDx: Coordinate value of laser beam L (X coordinate)
PSDy: Coordinate value of laser beam L (Y coordinate)
a, b: predetermined set values

Thereby, the positional relationship between the laser beam L incident on the liquid crystal layer 216 and the modulation pattern H displayed on the liquid crystal layer 216 is matched with the predetermined positional relationship with a high accuracy of about one pixel. As a result, in the reflective spatial light modulator 203, the laser light L is reliably and accurately modulated so that the aberration of the laser light L condensed inside the workpiece 1 is equal to or less than a predetermined aberration. Become.

FIG. 12 is a conceptual diagram showing the relationship between the modulation pattern displayed on the liquid crystal layer and the laser light incident on the liquid crystal layer. FIG. 12 shows the liquid crystal layer 216 when viewed from the Z-axis direction (see FIG. 8), and the modulation pattern H is circular. As shown in FIG. 12A, even when the center of gravity of the displayed modulation pattern H and the center of the incident laser beam L are shifted from each other due to, for example, a shift of the optical system, they do not match each other. ), The position of the modulation pattern H is automatically moved based on the coordinate value of the laser beam L, and the center of gravity of the modulation pattern H and the center of gravity of the laser beam L coincide with each other.

As described above, in the present embodiment, the position of the modulation pattern H in the reflective spatial light modulator 203 is changed based on the position of the laser light L, and the positional relationship between the laser light L and the modulation pattern H is as high as about 1 pixel. It is put together in. Therefore, the laser beam L can always be suitably modulated by the reflective spatial light modulator 203, and the aberration of the laser beam L focused on the workpiece 1 can be stably suppressed.

Therefore, according to the present embodiment, it is possible to stably form the modified region 7 with high accuracy in the workpiece 1. As a result, the machine difference between apparatuses can be suppressed, and the processing quality can always be kept high.

FIG. 13 is an enlarged photograph showing a state of a cut surface when a modified region is formed on a workpiece and cut. Note that the pixel size (pixel size) of the reflective spatial light modulator 203 is 20 μm × 20 μm, and the number of pixels (number of pixels) is 792 in the horizontal (X) direction, and 792 × 600 of 600 in the vertical (Y) direction. Has been. In the drawing, the liquid crystal layer 216 is shown when the position of the aberration correction pattern H, which is a modulation pattern, is changed along the X direction.

In the example shown in FIG. 13, when the amount of change in the position of the modulation pattern H is 0 (reference position) and +4 μm, the positional relationship between the laser light L and the modulation pattern H is a predetermined positional relationship, and the quality of the cut surface is good. You can see that It can also be seen that when the amount of change in the position of the modulation pattern H is +24 μm, the quality of the cut surface is poor, and otherwise, the quality of the cut surface is normal. Moreover, it can be seen from the example shown in FIG. 13 that, when the modified region 7 is formed with high accuracy, high-precision alignment is required for the positional relationship between the laser light L and the modulation pattern H.

Moreover, a sufficient effect appears with a movement amount of 1 pixel or less (that is, a movement amount of the pixel size in the vertical and horizontal directions). If the desired processing quality cannot be obtained by the movement within the range of one pixel, it is desirable to readjust the setting of the optical system.

The movement of the modulation pattern of 1 pixel or less will be described. FIG. 15 is a diagram for explaining movement of a modulation pattern of one pixel or less. In FIG. 15, the refractive index corresponding to the modulation pattern (for example, relating to aberration correction) in each pixel (liquid crystal) in one direction which is a predetermined X direction is shown by a bar graph. That is, the modulation pattern is represented by the refractive index for each of a plurality of pixels. Here, for explanation, the two-dimensional pattern is simplified and described as a one-dimensional pattern.

First, as shown in FIG. 15 (a), a modulation pattern curve (in the case of FIG. 13, an aberration correction pattern curve) W1 representing the refractive index of each pixel is set. In order to explain in one dimension, the refractive index of each pixel is expressed as a modulation pattern curve. However, in the case of two dimensions, this modulation pattern curve is a modulation pattern representing the refractive index for each pixel.

Then, as shown in FIG. 15B, the modulation pattern curve W1 is shifted rightward by a predetermined movement amount (for example, +4 μm as in FIG. 13). Next, the refractive index (the circle in W2) of each pixel corresponding to the shifted modulation pattern curve W2 is recalculated. Next, a refractive index corresponding to the recalculated value is given to each pixel. For example, in the example shown in FIG. 13, the refractive index given according to each pixel is 8 bits (256 gradations).

The modulation pattern H is shifted as described above. Therefore, it is possible to correct even a shift of 1 pixel or less, and it is possible to shift the modulation pattern (aberration correction pattern) more precisely.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, although the above embodiment includes

PSDs

270a and 270b for detecting the position of the laser beam, only one of these may be included.

Furthermore, instead of or in addition to the

PSDs

270a and 270b, other PSDs may be provided. For example, as shown in FIG. 14, between the dichroic mirror 238 and the condensing optical system 204 in the optical path of the laser light L, A PSD 370 may be connected. In this case, the laser light L transmitted through the dichroic mirror 238 is sequentially reflected by the

mirrors

371 and 372 and guided to the PSD 370. Therefore, the position of the laser beam L immediately before being focused on the workpiece 1 is detected. Accordingly, when a deviation or the like occurs in the optical system related to the laser light L, the position of the modulation pattern H is always detected as a deviation of the position of the laser light L, and the positional relationship between the laser light L and the modulation pattern H is changed. It will be appropriate.

In the above embodiment, the beam homogenizer 260 is provided, and the laser light L whose intensity distribution is uniformed by the beam homogenizer 260 is incident on the reflective spatial light modulator 203. Instead, a beam expander is provided. The laser beam L whose beam diameter has been expanded by the beam expander may be incident on the reflective spatial light modulator 203. In this case, in order to improve the position detection of the laser beam L, it is preferable to detect the position of the laser beam L before the beam diameter is expanded by the beam expander by PSD.

Further, the laser light incident surface when forming the modified region 7 is not limited to the surface 3 of the workpiece 1 and may be the back surface of the workpiece 1. In the above-described embodiment, a plurality of rows of modified regions 7 may be formed along the planned cutting line 5.

DESCRIPTION OF SYMBOLS 1 ... Processing object, 7 ... Modified area | region, 203 ... Reflection type spatial light modulator (spatial light modulator), 216 ... Liquid crystal layer (display part), H ... Modulation pattern, L ... Laser beam, P ... Condensing point.

Claims

A laser processing method for forming a modified region on the processing object by irradiating a laser beam with a focusing point inside the processing object,
A modulation step of modulating the laser light with a spatial light modulator;
A condensing step of condensing the modulated laser beam on the workpiece;
Detecting the position of the laser beam,
In the modulation step,
The laser light is incident on the modulation pattern displayed on the display unit of the spatial light modulator, and the laser light is modulated according to the modulation pattern, and
A laser processing method, wherein the position of the modulation pattern is changed based on the position of the laser beam detected in the detection step.
In the detection step, a position change amount in which the laser beam has changed with respect to a reference position is detected,
In the modulation step, the position of the modulation pattern is changed based on the position change amount of the laser beam detected in the detection step so that the laser beam and the modulation pattern have a predetermined positional relationship. The laser processing method according to claim 1.
3. The laser processing according to claim 2, wherein, in the modulation step, the position of the modulation pattern is changed using a data table related to the position change amount of the modulation pattern associated with the position change amount of the laser beam. Method.
In the modulation step, a position change amount of the modulation pattern is calculated based on a position change amount of the laser light, and the position of the modulation pattern is changed according to the calculated position change amount of the modulation pattern. The laser processing method according to claim 2.
The modulation pattern represents a refractive index for each of the plurality of pixels of the display unit,
In the modulation step, the modulation pattern is moved to a predetermined position, a refractive index of the plurality of pixels is calculated according to the moved modulation pattern, and the refractive index of the pixel is set to be a refractive index according to the calculated value. 3. The laser processing method according to claim 1, wherein the refractive index is controlled.
6. The laser processing method according to claim 5, wherein a movement amount for moving the modulation pattern is equal to or smaller than one pixel size of the display unit.