JP5844089B2 - Laser processing method - Google Patents

Description

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

  As a conventional laser processing method in the above technical field, for example, by irradiating a plate-shaped processing target with laser light having a wavelength of 1300 nm, a modified region serving as a starting point of cutting along a planned cutting line of the processing target is formed. What is formed in a processing object is known (for example, refer to patent documents 1).

Japanese Patent Laid-Open No. 2006-108459

  Here, the processing object is not directly irradiated with laser light, but the processing object is irradiated with laser light through a member having a refractive index different from that of the processing object, and the modified region is formed inside the processing object. There is a demand to form.

  Therefore, the present invention provides a laser processing method capable of forming a modified region inside a processing object even with laser light irradiated through a member having a refractive index different from that of the processing object. For the purpose.

  Therefore, in the laser processing method according to the present invention, in a state where the first member and the second member having different refractive indexes are stacked, the first processing is performed so that the light is condensed at a predetermined position inside the second member. By irradiating laser light along the planned cutting line of the second member from the side on which the member is arranged, a modified region that becomes the starting point of cutting along the planned cutting line is formed inside the second member And a step of correcting the aberration of the laser beam so that the laser beam is condensed at a predetermined position.

  In this laser processing method, even when the first member and the second member having different refractive indexes are laminated, the laser beam passes through the first member and is generated inside the second member. Condensate. Thereby, even if it is the laser beam irradiated through the 1st member which has a refractive index different from a 2nd member, a modification area | region is formed inside the 2nd member where a laser beam condenses. be able to.

Further, the correction of the aberration of the laser beam is performed in a state where the laser beam is transmitted only through the first member, and at the position of the laser beam emission surface of the first member or the position where the laser beam is transmitted through the first member. A first correction pattern for correcting the aberration of the laser beam so that the light is condensed, and a predetermined region for forming a modified region inside the second member in a state where the laser beam is transmitted only through the second member The aberration of the laser beam is corrected based on the second correction pattern for correcting the aberration of the laser beam so that the laser beam is condensed at the position . Thereby , the aberration of the laser beam is corrected based on the first correction pattern and the second correction pattern, and the laser beam inside the second member is desired to be condensed without causing the laser beam to be condensed. The laser beam can be reliably condensed at the position. Therefore , the modified region can be reliably formed at a predetermined position.

  The first correction pattern is calculated based on the refractive index of the first member and the distance from the laser light incident surface to the output surface of the first member, and the second correction pattern is It can be calculated based on the refractive index of the second member and the distance from the laser light incident surface of the second member to a predetermined position for forming the modified region.

  Further, it is preferable that the correction of the aberration of the laser beam is performed based on a third correction pattern obtained by combining the first correction pattern and the second correction pattern. Thus, by correcting the aberration of the laser beam using the third correction pattern obtained by synthesizing the first correction pattern and the second correction pattern, it is possible to easily suppress the condensing blur of the laser beam. can do.

  Further, it is preferable that correction of the aberration of the laser beam is performed by a spatial light modulator that corrects the aberration of the laser beam. In this case, the aberration of the laser beam can be easily corrected by the spatial light modulator.

  In addition, the first member is preferably an adhesive tape having a base material and an adhesive layer and having a transmittance of 90% or more with respect to laser light, and is preferably attached to the second member. In this case, the modified region can be formed inside the second member by condensing the laser light transmitted through the adhesive tape inside the second member. Moreover, since the adhesive tape has a transmittance with respect to the laser beam of 90% or more, the modified region can be formed inside the second member while suppressing the attenuation of the laser beam power.

  In addition, it is preferable that, after the modified region is formed by the laser beam, the first member is expanded to cause the second member to be cracked starting from the modified region and to cut the second member. . In this case, by expanding the first member, the second member can be easily cut by causing a crack starting from the modified region.

  Moreover, it is preferable that the 1st member is comprised from the several member from which the refractive index mutually differs laminated | stacked along the axial direction of a laser beam. As described above, even if the second member is irradiated with the laser light transmitted through the plurality of members constituting the first member, the modified region can be formed inside the second member. .

  According to the present invention, it is possible to form a modified region inside a processing object even with laser light irradiated through a member having a refractive index different from that of the processing object.

It is a block diagram of the laser processing apparatus used for formation of a modification area | region. It is a top view of the process target object used as the formation object of a modification | reformation area | region. It is sectional drawing along the III-III line of FIG. It is a top view of the processing target object after formation of a modification field. It is sectional drawing along the VV line of FIG. It is sectional drawing along the VI-VI line of FIG. It is a figure which shows the processing target object used as implementation object of one Embodiment of the laser processing method which concerns on this invention. It is a block diagram of the laser processing apparatus used for implementation of one Embodiment of the laser processing method concerning this invention. It is a fragmentary sectional view of the reflection type spatial light modulator of the laser processing apparatus of FIG. It is a figure for demonstrating the correction pattern which correct | amends the spherical aberration of a laser beam. It is a schematic block diagram of the other laser processing apparatus which concerns on this embodiment.

  DESCRIPTION OF EMBODIMENTS 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.

  Prior to the description of the embodiment of the laser processing method according to the present invention, the formation of the modified region on the object to be processed 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 to change the direction of the optical axis (optical path) of the laser beam L by 90 °, and And a condensing lens 105 for condensing the laser light L. Further, the laser processing apparatus 100 moves the support base 107 for supporting the workpiece (second member) 1 to which the laser light L condensed by the condensing lens 105 is irradiated, and the support base 107. A stage 111 for controlling the laser 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. Yes.

  In this laser processing apparatus 100, the laser light L emitted from the laser light source 101 has its optical axis changed by 90 ° by the dichroic mirror 103, and the inside of 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.

  A semiconductor material, a piezoelectric material, or the like is used as the material of the processing object 1. As illustrated in FIG. 2, a scheduled cutting line 5 for cutting the processing object 1 is set in the processing object 1. ing. The planned cutting line 5 is a virtual line extending linearly. When the modified region is formed inside the workpiece 1, the laser beam L is cut in a state where the condensing point (condensing position) P is aligned with the inside of the workpiece 1 as shown in FIG. 3. It moves relatively along the planned line 5 (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 laser light incident 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 row or a dot, and 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 the modified region 7 may be exposed on the outer surface (front surface, back surface, or outer peripheral surface) of the workpiece 1.

  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, thereby forming a modified region 7 in the workpiece 1 ( That is, internal absorption laser processing). Therefore, since the laser beam L is hardly absorbed by the laser beam incident surface 3 of the workpiece 1, the laser beam incident surface 3 of the workpiece 1 is not melted. Generally, when a removal portion such as a hole or a groove is formed by being melted and removed from the laser light incident surface 3 (surface absorption laser processing), the processing region is gradually opposite from the laser light incident surface 3 side. Progress toward the surface.

  By the way, the modified region refers to a region in which 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 in which the density of the modified region in the material to be processed is changed as compared with the density of the non-modified region, and a region in which lattice defects are formed (collectively these are high-density regions). 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 included in these areas and the modified areas. In some cases, cracks (cracks, microcracks) are included in the interface between the non-modified region and 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 silicon, glass, LiTaO ₃ or sapphire (Al ₂ O ₃ ), or those made of these.

  Further, here, the modified region 7 is formed by forming a plurality of modified spots (processing marks) along the planned cutting line 5. The modified spot is a modified portion formed by one pulse shot of pulsed laser light (that is, one pulse of laser irradiation: laser shot). Examples of the modified spot include a crack spot, a melting treatment spot, a refractive index change spot, or a mixture of at least one of these. Considering the required cutting accuracy, required flatness of the cut surface, thickness of the workpiece, type, crystal orientation, etc., the size of the modified spot and the length of the crack to be generated are appropriately determined. It is preferable to control.

  Next, an embodiment of a laser processing method according to the present invention will be described. Fig.7 (a) is a top view of the processed object used as the implementation object of one Embodiment of the laser processing method based on this invention, FIG.7 (b) is a VIIb-VIIb line | wire in Fig.7 (a). It is sectional drawing along. In FIG. 7B, hatching indicating a cross section is omitted. As shown in FIGS. 7A and 7B, the plate-like workpiece 1 includes a silicon substrate 11 and a functional element layer 16 formed on the surface 11a of the silicon substrate 11. ing. Further, an expanded tape (adhesive tape) 20 is attached to the back surface 11 b of the processing object 1, and the processing object 1 and the expanding tape 20 are laminated. In the present embodiment, the processing target 1 is irradiated with laser light from the back surface 11 b side of the processing target 1. That is, the workpiece 1 is irradiated with laser light that has passed through the expanded tape 20.

  The expanded tape 20 is a stealth dicing tape having a base material 20a (see FIG. 10A) and an adhesive layer 20b (see FIG. 10A). As the expanded tape 20, for example, a tape of Lintec Adwill D series can be used. In addition, it is preferable to use the expandable tape 20 having a laser light transmittance of, for example, 90% or more. Moreover, the expandable tape 20 and the workpiece 1 have different refractive indexes.

  The functional element layer 16 includes a plurality of functional elements 15 formed in a matrix in a direction parallel to and perpendicular to the orientation flat 6 of the silicon substrate 11. The functional element 15 is, for example, a semiconductor operation layer formed by crystal growth, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element formed as a circuit.

  In the workpiece 1, cutting lines 5 are set in a lattice shape so as to pass between the adjacent functional elements 15. The workpiece 1 is cut along the planned cutting line 5, and each cut chip becomes a semiconductor device having one functional element 15.

  FIG. 8 is a configuration diagram of a laser processing apparatus used for carrying out an embodiment of the laser processing method according to the present invention. As shown in FIG. 8, the laser processing apparatus 200 includes a support base 201 that supports the plate-shaped workpiece 1, a laser light source 202 that emits laser light L, and laser light L emitted from the laser light source 202. A reflective spatial light modulator 203 that modulates; and a condensing optical system 204 that condenses the laser light L modulated by the reflective spatial light modulator 203 inside the workpiece 1 supported by the support table 201. And a control unit 205 that controls the reflective spatial light modulator 203. The laser processing apparatus 200 aligns the condensing point P inside the workpiece 1 and irradiates the laser beam L with the laser beam L, so that the modified region that becomes the starting point of cutting along the planned cutting line 5 of the workpiece 1 7 is formed.

  The processing object 1 is placed on the support table 201 so that the back surface 11b of the processing object 1 faces the condensing optical system 204 side. That is, the workpiece 1 is irradiated with the laser light L that has passed through the expanded tape 20.

  The reflective spatial light modulator 203 is installed in the housing 231, and the laser light source 202 is installed on the top plate of the housing 231. The condensing optical system 204 includes a plurality of lenses, and is installed on the bottom plate of the housing 231 via a drive unit 232 including a piezoelectric element and the like. And the laser engine 230 is comprised by the components installed in the housing | casing 231. FIG. Note that the control unit 205 may be installed in the housing 231 of the laser engine 230.

  The housing 231 is provided with a moving mechanism that moves the housing 231 in the thickness direction of the workpiece 1 (not shown). Thereby, since the laser engine 230 can be moved up and down according to the depth of the workpiece 1, the position of the condensing optical system 204 is changed, and the laser beam L is changed to a desired depth of the workpiece 1. It is possible to condense at this position. Instead of installing a moving mechanism in the housing 231, a moving mechanism that moves the supporting table 201 in the thickness direction of the workpiece 1 may be provided on the supporting table 201. Further, the condensing optical system 204 may be moved in the thickness direction of the workpiece 1 using an AF unit 212 described later. It is also possible to combine these.

  The control unit 205 controls the reflection type spatial light modulator 203 and also controls the entire laser processing apparatus 200. For example, when the control unit 205 forms the modified region 7, the condensing point P of the laser light L is located at a predetermined distance from the back surface 11 b of the workpiece 1, and the condensing point P of the laser light L is The laser engine 230 including the condensing optical system 204 is controlled so as to move relatively along the scheduled cutting line 5. The control unit 205 controls the support base 201 instead of the laser engine 230 including the condensing optical system 204 in order to move the condensing point P of the laser light L relative to the workpiece 1. Alternatively, both the laser engine 230 including the condensing optical system 204 and the support base 201 may be controlled.

  The laser light L emitted from the laser light source 202 is sequentially reflected by the mirrors 206 and 207 in the housing 231, and then reflected by the reflecting member 208 such as a prism and enters the reflective spatial light modulator 203. The laser beam L incident on the reflective spatial light modulator 203 is modulated by the reflective spatial light modulator 203 and emitted from the reflective spatial light modulator 203. The laser light L emitted from the reflective spatial light modulator 203 is reflected by the reflecting member 208 along the optical axis of the condensing optical system 204 in the housing 231 and sequentially passes through the beam splitters 209 and 210. Then, it enters the condensing optical system 204. The laser light L incident on the condensing optical system 204 is condensed by the condensing optical system 204 inside the workpiece 1 placed on the support table 201.

  In addition, the laser processing apparatus 200 includes an observation unit 211 for observing the back surface 11 b side of the workpiece 1 in the housing 231. The observation unit 211 emits visible light VL reflected by the beam splitter 209 and transmitted through the beam splitter 210, collected by the condensing optical system 204, and reflected by the back surface 11 b side of the workpiece 1. Is detected, an image on the back surface 11b side of the workpiece 1 is acquired.

  Furthermore, the laser processing apparatus 200 is an AF for accurately aligning the condensing point P of the laser beam L at a predetermined distance from the back surface 11b even when the back surface 11b of the workpiece 1 has waviness. A (autofocus) unit 212 is provided in the housing 231. The AF unit 212 emits the AF laser light LB reflected by the beam splitter 210, and detects the AF laser light LB condensed by the condensing optical system 204 and reflected by the back surface 11 b of the workpiece 1. Thus, the displacement data of the back surface 11b along the planned cutting line 5 is acquired using, for example, an astigmatism method. The AF unit 212 drives the drive unit 232 based on the acquired displacement data when forming the modified region 7, so that the condensing optical system is along the undulation of the back surface 11 b of the workpiece 1. 204 is reciprocated in the optical axis direction to finely adjust the distance between the condensing optical system 204 and the workpiece 1.

  Here, the reflective spatial light modulator 203 will be described. FIG. 9 is a partial cross-sectional view of the reflective spatial light modulator of the laser processing apparatus of FIG. As shown in FIG. 9, 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 216, An alignment film 999b, a transparent conductive film 217, and a transparent substrate 218 such as a glass substrate are provided, and these are stacked 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 contains a light transmissive material such as glass, for example, and the laser light L having a predetermined wavelength incident from the surface 218 a of the reflective spatial light modulator 203 is converted into the interior of the reflective spatial light modulator 203. To penetrate. The transparent conductive film 217 is formed on the back surface 218b 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. Each pixel electrode 214 is made of a metal material such as aluminum, for example, and the surface 214a is processed flat and smoothly. 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. And a predetermined voltage is applied to the pixel electrode 214 of the pixel designated by both of the driver circuits by the control unit 250.

  Note that the alignment films 999a and 999b are disposed on both end surfaces of the liquid crystal layer 216, and align liquid crystal molecule groups in a certain direction. The alignment films 999a and 999b are made of, for example, a polymer material such as polyimide, and the contact surface with the liquid crystal layer 216 is subjected to a rubbing process or the like.

  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 the 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.

  Thereby, in each of the plurality of light beams constituting the laser light L, a phase shift occurs in a component in a predetermined direction orthogonal to the traveling direction of each light beam, and the laser light L is shaped (phase modulated). .

  Returning to FIG. 8, when forming the modified region 7, the control unit 205 faces each other so that the laser light L is condensed at a position where the modified region 7 is formed inside the workpiece 1. The reflective spatial light modulator 203 is controlled by applying a voltage to each of the pair of electrode portions 214a and 217a. Specifically, the control unit 205 transmits the laser light L at a predetermined position that forms the modified region 7 inside the processing target 1 while the laser light L is transmitted through the expanding tape 20 and the processing target 1. A correction pattern for correcting the spherical aberration of the laser light L so as to be condensed is input to the reflective spatial light modulator 203. Hereinafter, a correction pattern (hereinafter, referred to as “third correction pattern”) for correcting the spherical aberration input to the reflective spatial light modulator 203 will be described.

  The third correction pattern used when the control unit 205 controls the reflective spatial light modulator 203 is a first correction pattern for correcting spherical aberration that occurs when the laser light L passes only through the expanded tape 20; It is obtained by combining the second correction pattern for correcting the spherical aberration when the laser light L is transmitted only through the workpiece 1.

  FIG. 10A is a diagram for explaining a first correction pattern for correcting spherical aberration that occurs when the laser light passes only through the expanded tape, and FIG. 10B shows the laser light to be processed. It is a figure for demonstrating the 2nd correction pattern which correct | amends the spherical aberration produced when transmitting only an object, FIG.10 (c) is a figure for demonstrating a 3rd correction pattern.

  As shown in FIG. 10A, the first correction pattern is the back surface (laser light L) of the expanded tape 20 in a state where the laser light L is transmitted only through the expanded tape 20 (a state where the processed object 1 does not pass through). The spherical aberration of the laser beam L is corrected so that the laser beam L is condensed at the position of the emission surface 20d). Note that the spherical aberration of the laser light L may be corrected so as to focus on a point in the air that has passed through the expanded tape 20 instead of the position on the back surface of the expanded tape 20. This first correction pattern can be calculated by the thickness of the expanded tape 20 (the distance from the laser light incident surface 20c to the output surface 20d of the expanded tape 20) and the refractive index of the expanded tape 20. In FIG. 10A, the left diagram shows the locus of the laser beam L before the correction pattern is applied, and the right diagram shows the locus of the laser beam L after the correction pattern is applied (FIG. 10). 10 (b) and FIG. 10 (c) are the same as FIG. 10 (a).

  As shown in FIG. 10B, the second correction pattern is a modification of the inside of the workpiece 1 in a state where the laser light L is transmitted only through the workpiece 1 (a state where the laser beam L does not pass through the expanded tape 20). The spherical aberration of the laser beam L is corrected so that the laser beam L is condensed at a predetermined position that forms the region 7. This second correction pattern depends on the distance from the surface (back surface 11b) on which the laser beam L is incident on the workpiece 1 to a predetermined position for forming the modified region 7, and the refractive index of the workpiece 1 Can be calculated.

  The control unit 205 controls the reflective spatial light modulator 203 using the third correction pattern obtained by combining the first correction pattern and the second correction pattern obtained as described above. . Thus, as shown in FIG. 10C, when the processing object 1 is irradiated with the laser light L via the expanding tape 20 in a state where the expanding tape 20 is attached to the processing object 1, the modified region The laser beam L is condensed at a predetermined position where the number 7 is formed.

  Strictly speaking, the laser light L modulated (corrected) by the reflective spatial light modulator 203 changes its wavefront shape by propagating through the space. In particular, when the laser light L emitted from the reflective spatial light modulator 203 or the laser light L incident on the condensing optical system 204 is light having a predetermined spread (that is, light other than parallel light), The wavefront shape in the reflective spatial light modulator 203 and the wavefront shape in the condensing optical system 204 do not coincide with each other, and as a result, there is a possibility that the intended precise internal processing may be hindered. Therefore, it is important to match the wavefront shape in the reflective spatial light modulator 203 with the wavefront shape in the condensing optical system 204. For this purpose, a change in the wavefront shape when the laser beam L propagates from the reflective spatial light modulator 203 to the condensing optical system 204 is obtained by measurement or the like, and wavefront shaping (aberration correction) considering the change in the wavefront shape. It is more desirable to input pattern information to the reflective spatial light modulator 203.

  Alternatively, in order to make the wavefront shape in the reflective spatial light modulator 203 coincide with the wavefront shape in the condensing optical system 204, as shown in FIG. 11, the reflective spatial light modulator 203 and the condensing optical system 204 are used. The adjusting optical system 240 may be provided on the optical path of the laser light L traveling between the two. This makes it possible to accurately realize wavefront shaping.

  The adjustment optical system 240 has at least two lenses 241a and 241b. The lenses 241a and 241b are for making the wavefront shape in the reflective spatial light modulator 203 and the wavefront shape in the condensing optical system 204 similar. In the lenses 241a and 241b, the distance between the reflective spatial light modulator 203 and the lens 241a is the focal length f1 of the lens 241a, the distance between the condensing optical system 204 and the lens 241b is the focal length f2 of the lens 241b, and the lens 241a. And the lens 241b are disposed between the reflective spatial light modulator 203 and the reflective member 208 so that the lens 241a and the lens 241b form a double-sided telecentric optical system.

  By arranging in this way, even with the laser light L having a small divergence angle of about 1 ° or less, the wavefront in the reflective spatial light modulator 203 and the wavefront in the condensing optical system 204 can be matched. it can. In order to obtain more accuracy, it is desirable that the distance between the reflective spatial light modulator 203, the liquid crystal layer 216, and the principal point of the lens 241a is f1. However, since the reflective spatial light modulator 203 is very thin and the distance between the liquid crystal layer 216 and the transparent substrate 218 is extremely small, the degree of change in the wavefront shape between the liquid crystal layer 216 and the transparent substrate 218 is also extremely small. . Therefore, simply, on the configuration of the reflective spatial light modulator 203, the distance between the position where the focal length can be easily set (for example, the surface of the reflective spatial light modulator 203 (near the surface) and the like) and the lens 241a is f1. In this way, adjustment becomes easy. In order to obtain more accuracy, it is desirable to set the distance between the principal point of the condensing optical system 204 and the principal point of the lens 241b to be f2. However, the condensing optical system 204 is configured to include a plurality of lenses, and it may be difficult to align the principal point. In this case, simply, the distance between the lens 241b and a position where the focal length can be easily set (for example, the surface (near the surface) of the condensing optical system 204) due to the configuration of the condensing optical system 204 is set to f2. It may be set, and adjustment becomes easy by doing in this way.

  The beam diameter of the laser light L is determined by the ratio of f1 and f2 (the beam diameter of the laser light L incident on the condensing optical system 204 is determined by the laser light L emitted from the reflective spatial light modulator 203. F2 / f1 times the beam diameter). Therefore, regardless of whether the laser light L is parallel light or light having a small spread, the laser incident on the condensing optical system 204 while maintaining the angle emitted from the reflective spatial light modulator 203. A desired beam diameter in the light L can be obtained.

  Here, the case where the workpiece 1 is processed using the laser processing apparatus 200 will be described. As an example, the modified region 7 that is the starting point of cutting is cut along the planned cutting line 5 by irradiating the laser beam L with the condensing point P inside the plate-shaped processing target 1. The case of forming inside 1 will be described.

  First, the expand tape 20 is affixed to the back surface 11 b of the workpiece 1, and the workpiece 1 is placed on the support table 201. At this time, the processing object 1 is placed on the support table 201 so that the back surface 11b of the processing object 1 faces the condensing optical system 204 side. Subsequently, the workpiece 1 and the laser beam L are relatively moved along the planned cutting line 5 while irradiating the workpiece 1 with the laser beam L in a pulsed manner with the back surface 11b of the workpiece 1 as the laser beam irradiation surface ( Scan). As a result, the modified region 7 is formed at a predetermined depth in the thickness direction in the workpiece 1.

  Then, after the modified region 7 is formed, the expanded tape 20 is expanded to cut the workpiece 1 along the planned cutting line 5 using the modified region 7 as a starting point of cutting, and the plurality of cut chips are cut. Obtained as a semiconductor device (eg, memory, IC, light emitting element, light receiving element, etc.).

  The present embodiment is configured as described above, and even when the processing object 1 and the expanding tape 20 having different refractive indexes are laminated, the laser light L passes through the expanding tape 20 and is processed. Condensed inside 1. Thereby, even if it is the laser beam L irradiated through the expanded tape 20 which has a refractive index different from the process target object 1, the modification area | region 7 is formed in the process target object 1 where the laser beam L condenses. Can be formed.

  Further, the first correction pattern for correcting the spherical aberration that occurs when the laser beam L passes through the expanded tape 20 and the spherical aberration that occurs when the laser beam L passes through the workpiece 1 are corrected. The spherical aberration of the laser light L is corrected based on the second correction pattern. Thereby, the laser beam L can be reliably condensed at a predetermined position where the laser beam L inside the workpiece 1 is desired to be condensed without causing the laser beam L to be defocused. Therefore, the modified region 7 can be reliably formed at a predetermined position where the modified region 7 is desired to be formed.

  Further, by correcting the spherical aberration of the laser light L using the third correction pattern obtained by combining the first correction pattern and the second correction pattern, the condensing blur of the laser light L can be easily performed. Can be suppressed.

  Further, by correcting the aberration of the laser light L by the reflective spatial light modulator 203, the aberration of the laser light L can be easily corrected.

  Moreover, since the expandable tape 20 has a transmittance with respect to the laser beam of 90% or more, the modified region 7 can be formed inside the workpiece 1 while suppressing the attenuation of the power of the laser beam L.

  Further, since the modified region 7 can be formed with the expanded tape 20 attached to the workpiece 1, the expanded tape 20 can be easily expanded along the planned cutting line 5 by expanding the expanded tape 20. Can be cut.

  The present invention is not limited to the above embodiment. For example, instead of the expanded tape 20 laminated on the workpiece 1, a member (such as a silicon substrate) different from the expanded tape 20 may be used. Even in this case, the modified region 7 can be formed inside the workpiece 1 through the members stacked on the workpiece 1. Moreover, the member laminated | stacked on the workpiece 1 (equivalent to the expanded tape 20 in the said embodiment) may be contact | abutted to the workpiece 1, and is arrange | positioned by providing the workpiece 1 and the predetermined clearance gap. May be. Moreover, the member laminated | stacked on the workpiece 1 is not restricted to one member, The some member from which the refractive index mutually laminated | stacked along the axial direction of the laser beam L may be sufficient.

  DESCRIPTION OF SYMBOLS 1 ... Processing object (1st member), 7 ... Modified area | region, 11b ... Back surface (incident surface of a laser beam), 20 ... Expanding tape (2nd member, adhesive tape), 20a ... Base material, 20b ... Adhesive layer, 20c... Entrance surface, 20d exit surface, L... Laser beam, 200. 203: Reflective spatial light modulator (spatial light modulator).

Claims (7)

From the side where the first member is arranged so that the first member and the second member having different refractive indexes are stacked at a predetermined position inside the second member in a state where the first member and the second member are stacked. Irradiating a laser beam along the planned cutting line of the second member to form a modified region in the second member as a starting point of cutting along the planned cutting line;
When irradiating the laser beam, the aberration of the laser beam is corrected so that the laser beam is condensed at the predetermined position ,
In the correction of the aberration of the laser beam, the laser beam is transmitted through only the first member, and the position of the laser beam emission surface of the first member or the laser beam passes through the first member. The first correction pattern for correcting the aberration of the laser beam so that the laser beam is condensed at the transmitted position, and the laser beam transmitted only through the second member, Correcting the aberration of the laser beam on the basis of a second correction pattern for correcting the aberration of the laser beam so that the laser beam is condensed at the predetermined position forming the internal modified region. A featured laser processing method. The first correction pattern is calculated based on a refractive index of the first member and a distance from an incident surface to an emission surface of the laser light in the first member,
The second correction pattern is based on the refractive index of the second member and the distance from the laser light incident surface of the second member to the predetermined position that forms the modified region. Calculated,
The laser processing method according to claim 1 . Correction of aberration of the laser beam, a first correction pattern is performed based on the third correction pattern obtained by combining the a second correction pattern according to claim 1 or, characterized in that 2. The laser processing method according to 2. Correction of aberration of the laser light, the laser processing method according to any one of claims 1 to 3, wherein the performing by the spatial light modulator for correcting aberration of the laser light, it is characterized. The first member is a pressure-sensitive adhesive tape having a base material and an adhesive layer and having a transmittance of 90% or more with respect to the laser beam, and is attached to the second member. The laser processing method according to any one of claims 1 to 4 . After the formation of the modified region by the laser beam, the first member is expanded to cause a crack in the second member to start from the modified region and cut the second member. The laser processing method according to claim 5 . Said first member, according to any one of claims 1 to 6, wherein said laser beam to each other refractive index are laminated along the axial direction of the is composed of a plurality of different members, it Laser processing method.

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