JP2013128088A - Laser processing method and laser processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit damages of metal wiring without deteriorating cutting performance.SOLUTION: A laser processing method comprises a step of forming modified regions 7 inside a workpiece 1 along scheduled cutting lines 5 by radiating laser beams L to the workpiece 1 having a semiconductor substrate 2 and a lamination part 4 including metal wiring 4b from a rear face 21 opposite to a surface 3 on the lamination part 4 side. The step of forming the modified regions 7 includes a first modified region formation step of forming first modified regions 7a in the workpiece 1 at positions on the surface 3 side by radiating laser beams L, and a second modified region formation step of forming second modified regions 7b in the workpiece 1 at positions on the rear face 21 side than the first modified regions 7a by radiating laser beams L. A pulse width of the laser beams L irradiated when the first modified regions 7a are formed is smaller than a pulse width of the laser beams L irradiated when the second modified regions 7b are formed.

Description

  The present invention relates to a laser processing method and a laser processing apparatus for cutting a workpiece.

  As a conventional laser processing method, there is known a method in which a laser beam is condensed on a processing object and a plurality of rows of modified regions are formed along the planned cutting line in the thickness direction in the processing object (for example, , See Patent Document 1). In such a laser processing method, an object to be processed is cut using the modified region as a starting point of cutting, and thereby a plurality of chips are obtained.

JP 2006-68816 A

  Here, the laser processing method as described above may be performed on an object to be processed that includes a semiconductor substrate and a stacked portion that is stacked on the semiconductor substrate and includes metal wiring. In this case, for example, if the street width of the object to be processed (distance between a plurality of obtained chips, also referred to as cut width) is narrowed, the metal wiring may be damaged, such as elution of the metal wiring. Further, as the laser processing method as described above, a method having a high cutting ability is desired with the recent popularization and expansion.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the laser processing method and laser processing apparatus which can suppress the damage of metal wiring, without reducing cutting capability.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, have obtained knowledge that damage to metal wiring is caused by irradiation of laser light on a workpiece. Further, as a result of further intensive studies, it was found that the damage to the metal wiring is reduced when the pulse width of the laser beam when forming the modified region on the laminated portion side is reduced. Then, if the said tendency can be utilized suitably in relation to cutting ability, it will be thought that it becomes possible to suppress damage to metal wiring, without reducing cutting ability, and came to complete this invention.

  That is, in the laser processing method according to the present invention, a processing object having a semiconductor substrate and a stacked portion including metal wirings stacked on the semiconductor substrate is opposite to the surface on the stacked portion side in the processing target. A laser processing method for irradiating a laser beam from the back surface of the workpiece and forming a modified region as a starting point of cutting inside the workpiece along the planned cutting line. A first modified region forming step of forming a first modified region at a position on the front surface side in the laser beam and a second modification at a position on the back surface side of the first modified region inside the workpiece by irradiating with laser light. A second modified region forming step of forming a quality region, and the pulse width of the laser beam irradiated when forming the first modified region is determined by the laser beam irradiated when forming the second modified region It is characterized by being smaller than the pulse width.

  In addition, the laser processing apparatus according to the present invention provides a processing object having a semiconductor substrate and a stacked portion including metal wirings stacked on the semiconductor substrate, and is opposite to the surface on the stacked portion side in the processing target. This is a laser processing apparatus for forming a modified region, which is a starting point of cutting, inside a processing object along a scheduled cutting line by irradiating the processing object with laser light, and irradiates the processing object with laser light A laser light source unit; a moving unit for moving a condensing point position of the laser light irradiated by the laser light source unit; and a control unit for controlling the laser light source unit and the moving unit. A first modified region formation control for irradiating a laser beam so that the first modified region is formed at a position on the front side in the interior of the workpiece, and a position on the back side of the first modified region in the workpiece Second modified region formed in The second modified region forming control for irradiating the laser beam so that the pulse width of the laser beam irradiated when forming the first modified region is formed. It is characterized in that it is made smaller than the pulse width of the laser beam irradiated on the substrate.

  In the laser processing method and the laser processing apparatus, when the first modified region is formed, the occurrence of the damage can be prevented by using the above tendency of the pulse width of the laser beam and the damage of the metal wiring. And the cutting ability, such as the straightness of the object to be processed at the time of cutting and the ratio (division ratio) at which the object to be processed can be accurately cut, can be maintained by forming the second modified region. Therefore, damage to the metal wiring can be suppressed without reducing the cutting ability.

  The laser beam preferably has a wavelength of 1080 nm to 1200 nm. Moreover, it is preferable that a laser light source part irradiates a workpiece with the laser beam which has a wavelength of 1080 nm-1200 nm.

  In this case, the above-described effect of suppressing damage to the metal wiring without lowering the cutting ability is suitably achieved. This is because if the wavelength of the laser beam is smaller than 1080 nm, the laser beam is not sufficiently transmissive to the object to be processed, and it becomes difficult to form the modified region with high accuracy, while the wavelength of the laser beam is more than 1200 nm. If it is too large, the transmittance of the laser beam with respect to the workpiece will be too high, and the laser beam may adversely affect the metal wiring.

  In addition, a plurality of scheduled cutting lines are provided, and the second modified region is formed along the plurality of scheduled cutting lines after or before the first modified region forming step is performed along the plurality of scheduled cutting lines. It is preferable to include a step of performing the forming step. Further, a plurality of scheduled cutting lines are provided, and the control unit performs the first cutting along the plurality of scheduled cutting lines after or before executing the first modified region formation control along the plurality of scheduled cutting lines. It is preferable to execute the 2-modified region formation control.

  Thereby, for example, in the case where the first and second modified regions are formed using one laser light source, the number of times of switching the pulse width of the laser light can be suppressed, and the processing time can be shortened. Become.

  In addition, a plurality of scheduled cutting lines are provided, and a step of performing a line process for performing the first and second modified region forming processes along one scheduled cutting line in order for the plurality of scheduled cutting lines is included. It is preferable. In addition, a plurality of scheduled cutting lines are provided, and the control unit sequentially performs line control for performing the first and second modified region forming controls along the one scheduled cutting line on the plurality of scheduled cutting lines. It is preferable to execute control.

  When the modified region is formed along a plurality of planned cutting lines, the modified region is shifted from the planned cutting line due to, for example, the expansion due to the formation of the modified region or the opening of a crack extending from the modified region. A phenomenon (hereinafter referred to as “index shift”) may occur. In this regard, as described above, the index shift can be suppressed by sequentially performing the line process or the line control on the plurality of cutting scheduled lines.

  According to the present invention, it is possible to suppress damage to the metal wiring without reducing the cutting ability.

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. It is sectional drawing along the III-III line of the workpiece of FIG. It is a top view of the processing target after laser processing. It is sectional drawing along the VV line of the workpiece of FIG. It is sectional drawing along the VI-VI line of the processing target object of FIG. It is a schematic block diagram which shows the laser processing apparatus which implements embodiment. It is a fragmentary sectional view of a reflection type spatial light modulator. It is a top view which shows the process target object used as the object of the laser processing by 1st Embodiment. (A) is a flowchart of the laser processing method in the present embodiment, (b) is a flowchart showing a continuation of FIG. 10 (a), and (c) is a flowchart showing a continuation of FIG. 10 (b). (A) is a flow chart showing the continuation of FIG. 10 (c), (b) is a flow chart showing the continuation of FIG. 11 (a), and (c) is a flow chart showing the continuation of FIG. 11 (b). It is a schematic sectional drawing for demonstrating the process of forming a modification area | region. It is a schematic sectional drawing for demonstrating formation of the 1st-3rd modified area | region in 1st Embodiment. It is a photograph figure which illustrates the cut surface of the processing target after laser processing by a 1st embodiment. It is a general | schematic expanded sectional view for demonstrating the damage of metal wiring. It is the table | surface which compared the damage of metal wiring by processing conditions. (A) is a graph illustrating the correlation between the distance from the surface of the modified region and the damage of the metal wiring, (b) is a graph illustrating the correlation between the pulse width of the laser beam and the damage of the metal wiring, (c). These are graphs illustrating the correlation between the output of laser light and the damage of metal wiring. It is a figure for demonstrating the relationship between the escape light of a laser beam, and the condensing point position of a laser beam. It is a figure for demonstrating the relationship between the pulse width of a laser beam, and the energy amount of a missing light. It is a figure for demonstrating the relationship between the pulse waveform of a laser beam, and the damage of metal wiring. It is a table | surface which illustrates the correlation with the damage and cutting | disconnection performance of a metal wiring about the distance from the surface of a modification area | region, and a pulse width. It is another photograph figure which illustrates the cut surface of the processed object after the laser processing by this embodiment. It is a schematic sectional drawing for demonstrating formation of the 1st-3rd modification area | region in 2nd Embodiment. It is a schematic block diagram which shows the laser processing apparatus which enforces the laser processing method which concerns on 3rd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted.

  In the laser processing method according to the present embodiment, the laser beam is focused on the object to be processed, and the modified region is formed along the planned cutting line. First, the formation of the modified region will be described with reference to FIGS.

  As shown in FIG. 1, the laser processing apparatus 100 is arranged so that the direction of the laser light source (laser light source unit) 101 that oscillates the laser light L and the optical axis (optical path) of the laser light L is changed by 90 °. A dichroic mirror 103 and a condensing lens 105 for condensing the laser light L are provided. 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 a stage (moving) for moving the support 107. Part) 111, a laser light source control part (control part) 102 for controlling the laser light source 101 to adjust the output, pulse width, pulse waveform, etc. of the laser light L, and a stage control part (control part) for controlling the movement of the stage 111 Control unit) 115.

  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. Thereby, a modified region along the planned cutting line 5 is formed on the workpiece 1. Here, the stage 111 is moved in order to move the laser light L relatively, but the condensing lens 105 may be moved, or both of them may be moved.

  As the processing object 1, a plate-like member (for example, a substrate, a wafer, or the like) including a semiconductor substrate formed of a semiconductor material is used. As shown in FIG. 2, a scheduled cutting line 5 for cutting the workpiece 1 is set in the workpiece 1. The planned cutting line 5 is a virtual line extending linearly. When the modified region is formed inside the workpiece 1, as shown in FIG. 3, the laser beam L is scheduled to be cut in a state where the focusing point (focusing position) P is aligned with the inside of the workpiece 1. It moves relatively along the line 5 (that is, in the direction of arrow A in FIG. 2). Thereby, 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, a three-dimensional shape in which these lines are combined, or a coordinate designated. Further, the planned cutting line 5 is not limited to a virtual line but may be a line actually drawn on the surface 3 of the workpiece 1. 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 the modified region 7 may be exposed on the outer surface (front surface 3, back surface 21, or outer peripheral surface) of the workpiece 1. Good. Further, the laser light incident surface when forming the modified region 7 is not limited to the front surface 3 of the workpiece 1 but may be the back surface 21 of the workpiece 1.

  Incidentally, the laser light L here passes through the workpiece 1 and is particularly absorbed near the condensing point inside the workpiece 1, thereby forming the modified region 7 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 7 formed in 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 7 include a melt treatment region (meaning at least one of a region once solidified after melting, a region in a molten state, and a region in a state of being resolidified from melting), a crack region, and the like. In addition, there are 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 of the workpiece 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-processed area, the refractive index changing area, the modified area is changed compared to the density of the non-modified area, or the area where lattice defects are formed is 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 those containing or consisting of silicon (Si), glass, LiTaO ₃ or sapphire (Al ₂ O ₃ ).

  Further, in the present embodiment, 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, this embodiment will be described in detail.

[First Embodiment]
FIG. 7 is a schematic configuration diagram illustrating a laser processing apparatus that performs the laser processing method according to the first embodiment. As illustrated in FIG. 7, the laser processing apparatus 300 according to the present embodiment includes a laser light source (laser light source unit) 202, a reflective spatial light modulator 203, a 4f optical system 241, and a condensing optical system 204 in a housing 231. I have. The laser light source 202 emits laser light L having a wavelength of, for example, 1080 nm to 1200 nm, and for example, a fiber laser is used. 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 the laser light L in the horizontal direction.

  The reflective spatial light modulator 203 modulates the laser light L emitted from the laser light source 202. For example, a reflective liquid crystal (LCOS) spatial light modulator (SLM: Spatial Light Modulator) is used. Is used. The reflective spatial light modulator 203 here modulates the laser beam L incident from the horizontal direction to correct aberrations, and reflects it obliquely upward with respect to the horizontal direction.

  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 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 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. 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 according to 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.

  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 to be modulated is displayed on the reflective spatial light modulator 203).

  As a result, the wavefront of the laser light L that enters and passes through the modulation pattern is adjusted, and the phase of a component in a predetermined direction orthogonal to the traveling direction is shifted in each light beam constituting the laser light L. Accordingly, the laser beam L can be modulated (for example, the intensity, amplitude, phase, polarization, etc. of the laser beam L can be modulated) by appropriately setting the modulation pattern to be displayed on the reflective spatial light modulator 203. Here, the spherical aberration correction (aberration correction) for correcting the spherical aberration occurring at the condensing point P is performed on the laser light L irradiated to the workpiece 1.

  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. 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 lens 241b is the focal length f2 of the lens 241b. Thus, the reflective spatial light modulator 203 and the condensing optics are set so that the distance between the first lens 241a and the second lens 241b is f1 + f2 and the first lens 241a and the second lens 241b are both-side telecentric optical systems. It is arranged between the system 204. In the 4f optical system 241, it is possible to suppress the laser beam L modulated by the reflective spatial light modulator 203 from changing its wavefront shape due to spatial propagation and increasing aberration.

  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.

  In the laser processing apparatus 300 configured as described above, the laser light L emitted from the laser light source 202 travels in the horizontal direction in the housing 231, is then reflected downward by the mirror 205 a, and is reflected by the attenuator 207. Strength is adjusted. Then, the light 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 in accordance with the modulation pattern by passing through the modulation pattern displayed on the liquid crystal layer 216, corrected for aberrations, and then reflected upward by the mirror 206a. Then, the polarization direction is changed by the λ / 2 wavelength plate 228, reflected by the mirror 206b in the horizontal direction, and incident on the 4f 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. 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. Then, 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 in the workpiece 1 placed on the stage 111.

  In addition, the laser processing apparatus 300 according to the present embodiment finely adjusts the distance between the surface observation unit 211 for observing the laser light incident surface of the processing target 1 and the condensing optical system 204 and the processing target 1. And an AF (AutoFocus) unit 212.

  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 laser light incident surface of the workpiece 1. Have. In the surface observation unit 211, the visible light VL 1 emitted from the observation light source 211 a is reflected and transmitted by the mirror 208 and the dichroic mirrors 209, 210, and 238, and condensed toward the workpiece 1 by the condensing optical system 204. Is done. Then, the reflected light VL2 reflected by the laser light incident surface of the workpiece 1 is condensed by the condensing optical system 204, transmitted and reflected by the dichroic mirrors 238 and 210, and then transmitted through the dichroic mirror 209. Light is received by the detector 211b.

  The AF unit 212 emits the AF laser light LB1, receives and detects the reflected light LB2 of the AF laser light LB1 reflected by the laser light incident surface, thereby detecting the laser light incident surface along the planned cutting line 5 Get the displacement data. 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 in the optical axis direction so as to follow the undulation of the laser light incident surface. Move back and forth.

  Furthermore, the laser processing apparatus 300 according to the present embodiment includes a control unit 250 including a CPU, ROM, RAM, and the like and a pulse width variable control unit 251 as control units for controlling the laser processing apparatus 300. The control unit 250 controls the laser light source 202 and adjusts the output of the laser light L emitted from the laser light source 202 and the like.

  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 position in the workpiece 1, and the condensing point P of the laser light L is the cutting scheduled line 5. The position of the housing 231 and the stage 111 and the drive of the drive unit 232 are controlled so as to move relatively along the axis. Here, the control unit 250 performs first modified region formation control for irradiating the laser beam L so that the first modified region 7a is formed at a position opposite to the laser beam incident surface in the workpiece 1. The second modified region formation control for irradiating the laser beam L so that the second modified region 7b is formed at a position closer to the laser beam incident surface side than the first modified region 7a in the workpiece 1; The third modified region formation control for irradiating the laser beam L so that the third modified region 7c is formed at a position closer to the laser beam incident surface side than the second modified region 7b in the object 1 is executed. (Details will be described later).

  Further, when forming the modified region 7, the control unit 250 applies a predetermined voltage to the electrode units 214 a and 217 a in the reflective spatial light modulator 203 and causes the liquid crystal layer 216 to display a predetermined modulation pattern. As a result, the laser beam L is modulated as desired by the reflective spatial light modulator 203, and desired aberration correction is performed on the laser beam L applied to the workpiece 1.

  The modulation pattern depends on, for example, the position where the modified region 7 is to be formed, the wavelength of the laser beam L to be irradiated, the material of the processing target 1, the refractive index of the condensing optical system 204 and the processing target 1, and the like. This is derived in advance and stored in the control unit 250. This modulation pattern includes an individual difference correction pattern for correcting individual differences generated in the laser processing apparatus 300 (for example, distortion generated in the liquid crystal layer 216 of the reflective spatial light modulator 203), and a spherical surface for correcting spherical aberration. An aberration correction pattern is included.

  The pulse width variable control unit 251 controls the laser light source 202 and varies the pulse width of the laser light L emitted from the laser light source 202. Specifically, the pulse width variable control unit 251 applies the pulse width of the laser beam L irradiated when forming the first modified region 7a to the laser beam L irradiated when forming the second modified region 7b. Less than the pulse width. “Pulse width” usually means a half width (FWHM (Full Width at Half Maximum)), which is a time width when the pulse waveform has a value of ½ or more of the peak value.

  Next, a laser processing method using the laser processing apparatus 300 will be described in detail. The laser processing method of this embodiment is used as a manufacturing method for manufacturing an image sensor such as a CIS device, for example, and cuts the workpiece 1 into a plurality of chips. First, the overall flow of the laser processing method will be outlined.

  FIG. 9 is a plan view showing an object to be processed by the laser processing according to the present embodiment, FIGS. 10 and 11 are diagrams showing respective flows of the laser processing method in the present embodiment, and FIG. 12 forms a modified region. It is sectional drawing for demonstrating a process. As illustrated in FIGS. 9 and 12, the workpiece 1 includes a semiconductor substrate 2 such as a silicon substrate and a stacked portion 4 stacked on the surface 2 a of the semiconductor substrate 2 and has a plate shape. . The thickness of the workpiece 1 is preferably 150 μm to 350 μm, and more preferably 200 μm or 250 μm here.

The stacked portion 4 includes an insulating layer 4a, a metal wiring 4b, and a surface layer film 4c. The insulating layer 4 a is formed on the surface 2 a of the semiconductor substrate 2. The insulating layer 4a is made of, for example, SiO ₂ and has an insulating property. The metal wiring 4b is provided in the functional element formation region 15 arranged in a matrix on the surface 2a of the semiconductor substrate 2 so as to be covered with the insulating layer 4a. The metal wiring 4b is made of a metal such as aluminum. The surface layer film 4c is provided so as to cover the outer surface of the insulating layer 4a, and is formed of, for example, metal.

  A plurality of scheduled cutting lines 5 extending so as to pass between adjacent functional element formation regions 15 are set on the surface 3 of the workpiece 1 on the stacked portion 4 side. The plurality of planned cutting lines 5 extend in a lattice shape, and the planned cutting line 5a along a direction substantially parallel to the orientation flat 6 of the workpiece 1 and the planned cutting line 5b along a substantially vertical direction. Is included. In a direction along the surface 3 (a direction perpendicular to the thickness direction), the distance D between the planned cutting line 5 and the metal wiring 4b is, for example, within 25 μm.

  When performing laser processing on the workpiece 1, first, a BG tape 31 is attached to the surface 3 of the workpiece 1 as shown in FIG. Subsequently, as illustrated in FIG. 10B, the workpiece 1 is placed on the support base 107 of the stage 111 so that the back surface 21 opposite to the front surface 3 is a laser light incident surface. Thereafter, as shown in FIG. 10C and FIG. 12, the laser processing apparatus 300 is controlled by the control unit 250 and the variable pulse width control unit 251, and the aberration-corrected laser beam L along the plurality of scheduled cutting lines 5. Is irradiated from the back surface 3 of the workpiece 1. Thereby, a plurality of rows (here, 3 rows) of first to third modified regions 7 a to 7 c having different thickness direction positions are formed inside the workpiece 1 along the plurality of scheduled cutting lines 5. To do.

  Subsequently, as shown in FIGS. 10 (c) and 11 (a), after the dicing tape 32 is attached to the back surface 21 of the workpiece 1, the workpiece 1 is turned upside down so that the front surface 3 faces upward. The BG tape 31 is removed. Subsequently, as shown in FIG. 11 (b), the knife edge 33 is pressed against the workpiece 1 from the back surface 21 side through the dicing tape 32 along the planned cutting line 5, and the cutting target line 5 is touched. A force is applied to the workpiece 1 along the outside. Thus, the workpiece 1 is cut into a plurality of chips 10 using the modified region 7 as a starting point for cutting. Subsequently, as shown in FIG. 11C, in order to easily pick up a plurality of chips, the dicing tape 32 is irradiated with UV light (ultraviolet rays), and the adhesive layer of the dicing tape 32 is cured to reduce the adhesive strength. Let Then, a plurality of chips 10 are picked up.

  Next, the formation of the first to third modified regions 7a to 7b will be described in detail with reference to FIG.

  First, the pulse width of the laser light L is set to a first pulse width that is smaller than the pulse width of the laser light L in the subsequent second modified region forming step, for example, 150 ns. Further, the focusing point of the laser beam L is aligned with the position on the surface 3 side inside the workpiece 1 and the liquid crystal layer 216 of the reflective spatial light modulator 203 is adjusted so that the spherical aberration of the laser beam L is corrected. A predetermined modulation pattern is displayed. Then, while irradiating the workpiece 1 with the laser beam L having the first pulse width at an output of 15 μJ, the condensing point of the laser beam L is set to 360 mm / long along one (arbitrary) planned cutting line 5a. The relative movement is performed at the speed of s.

  Thereby, the 1st modification area | region 7a is formed in a line along the one cutting plan line 5a in the position by the side of the surface 3 in the workpiece 1 (1st modification area | region formation process). Subsequently, as shown in FIG. 13A, the first modified region forming step is repeatedly performed along a plurality of other scheduled cutting lines 5a and repeatedly performed along the plurality of scheduled cutting lines 5b. To do. Thus, the first modified region 7a is formed along the plurality of scheduled cutting lines 5a and 5b at the position on the surface 3 side in the workpiece 1.

  Thereafter, the pulse width of the laser light L is set to a second pulse width that is larger than the pulse width of the laser light L in the first modified region forming step, for example, 500 ns. In addition, the reflective spatial light is set so that the condensing point of the laser light L is aligned with the position on the back surface 21 side of the first modified region 7a inside the workpiece 1 and the spherical aberration of the laser light L is corrected. A predetermined modulation pattern is displayed on the liquid crystal layer 216 of the modulator 203. Then, while irradiating the workpiece 1 with the laser beam L having the second pulse width with an output of 15 μJ, the condensing point of the laser beam L is relatively moved along the one scheduled cutting line 5a at a speed of 360 mm / s. . As a result, the second modified region 7b is formed in a row along the one scheduled cutting line 5a at a position closer to the back surface 21 than the first modified region 7a in the workpiece 1 (second modified region formation). Process).

  Subsequently, the focusing point of the laser beam L is set to a position closer to the back surface 21 side than the second modified region 7b inside the workpiece 1, and the reflection type space is adjusted so that the spherical aberration of the laser beam L is corrected. A predetermined modulation pattern is displayed on the liquid crystal layer 216 of the optical modulator 203. Then, while irradiating the workpiece 1 with the laser beam L having the second pulse width with an output of 10 μJ, the condensing point of the laser beam L is relatively moved along the one scheduled cutting line 5a at a speed of 360 mm / s. . As a result, the third modified region 7c is formed in a row along the one scheduled cutting line 5a at a position closer to the back surface 21 than the second modified region 7b in the workpiece 1 (third modified region formation). Process).

  Subsequently, the second and third modified region forming steps are performed along the plurality of other scheduled cutting lines 5a and along the plurality of scheduled cutting lines 5b. As described above, the second modified region 7b is formed along the plurality of scheduled cutting lines 5a and 5b at a position closer to the back surface 21 than the first modified region 7a in the processed object 1, and the inside of the processed object 1 The third modified region 7c is formed along the plurality of scheduled cutting lines 5a and 5b at a position closer to the back surface 21 than the second modified region 7b.

  FIG. 14 is a photograph illustrating the cut surface of the workpiece after laser processing according to the present embodiment. As shown in FIG. 14, in this embodiment, it can be confirmed that the workpiece 1 can be cut with high accuracy. Furthermore, it turns out that generation | occurrence | production of the twist hackle which reaches | attains the surface 3 from the 1st modification | reformation area | region 7a is suppressed, and the deterioration of the straightness of the workpiece 1 is suppressed.

  By the way, when the street width of the workpiece 1 is narrowed, for example, in the chip 10 cut by the conventional laser processing method, as shown in FIG. 15, the metal wiring 4b penetrates the insulating layer 4a and is eluted (outflow). There is a risk of damage (characteristic failure) of the metal wiring 4b in which wiring failure occurs.

  Here, basic condition machining in which the workpiece 1 is cut by a conventional laser machining method, dummy run machining in which the workpiece 1 is cut under conditions where emission of the laser beam L is stopped with respect to the basic condition machining, and basic condition machining. On the other hand, the damage of the metal wiring 4b was compared in the static elimination processing in which the workpiece 1 was cut by performing the static elimination treatment using an antistatic tape or an ionizer. The result is shown in FIG.

  “Distance from the surface of the modified region” in FIG. 16 indicates the distance from the surface 3 to the first modified region 7a (that is, the lower end distance of the first modified region 7a). “Determination of damage to metal wiring” is “◯ (suitable)” when the metal wiring 4b is not damaged in a predetermined number of chips (for example, 30 chips), and “× ( Not suitable) ”, and the number of damage occurrences is shown in parentheses. These are the same in the following description.

  As shown in FIG. 16, it is found that damage to the metal wiring 4b occurs only when the laser beam L is irradiated, and it occurs even when countermeasures against static electricity are taken. As a result, it is found that the metal wiring 4b is damaged due to the irradiation of the laser beam L on the workpiece 1. In particular, laser light that passes through the workpiece 1 until the workpiece 1 starts to be absorbed after the laser beam L is irradiated (that is, the formation of the modified region 7 starts) (so-called, It is estimated that “missing light”) is a cause of damage to the metal wiring 4b. Note that even when only one row of the modified region 7 is formed on the workpiece 1, the metal wiring 4 b is damaged, and it is confirmed that a characteristic defect occurs only by laser processing for one scan.

  FIG. 17 is a graph illustrating the correlation between each parameter and damage to the metal wiring. In FIG. 17A, the wavelength of the laser beam L is 1080 nm, the pulse width is 500 ns, the output is 15 μJ, and aberration correction is performed. In FIG. 17B, the wavelength of the laser beam L is 1080 nm, the output is 15 μJ, the aberration is corrected, and the distance from the surface 3 to the first modified region 7 a is 0 μm. In FIG. 17C, the wavelength of the laser beam L is 1080 nm, the aberration is corrected, and the distance from the surface 3 to the first modified region 7a is 20 μm.

  As shown in FIG. 17A, it can be seen that the damage to the metal wiring 4b tends to be less likely to occur as the distance from the surface 3 to the first modified region 7a increases. This is considered to be due to the following mechanism. In other words, when the laser beam L escapes the metal wiring 4b, the influence range Ar of the laser beam L escape and the energy density ρE of the escape light vary depending on the formation depth of the first modified region 7a. . For example, as shown in FIGS. 18A and 18B, when the distance between the surface 3 and the condensing point P is halved, the influence range Ar of the laser beam L is 1/2 (radius). However, the energy density ρE increases four times. It is considered that the damage of the metal wiring 4b is caused by the energy density ρE, not the influence range Ar. Therefore, the formation position of the first modified region 7a (the laser beam L when forming the first modified region 7a) It is more difficult for the metal wiring 4b to be damaged when the condensing point P position is further away from the surface 3.

  Further, as shown in FIG. 17B, it can be seen that damage to the metal wiring 4b tends to be less likely to occur as the pulse width of the laser light L becomes smaller. The reason why the metal wiring 4b is more likely to be damaged when the pulse width is larger is assumed to be the following two points, for example. That is, as a first example, as shown in FIG. 19, for example, it is confirmed that the laser light L having a pulse width of 500 ns generates twice as much escape light as compared to the pulse width of 150 ns. For this reason, it is presumed that the laser light L having a long pulse width with a large amount of energy of light leakage is likely to damage the metal wiring 4b.

Note that, in the workpiece 1 having a thickness of 300 μm, the amount of energy necessary for forming the modified region 7 and the pulse width of the laser light L have the following relationship. This also shows that the amount of energy necessary for forming the modified region 7 is larger for the laser light L having a long pulse width.
Pulse width: 150 ns Required energy: 1.25 μJ Ratio: 1
Pulse width: 250 ns Required energy: 1.5 μJ Ratio: 1.2
Pulse width: 350 ns Required energy: 2 μJ Ratio: 1.6
Pulse width: 500 ns Required energy: 2.5 μJ Ratio: 2

  Secondly, the state of the laser beam L is different depending on the difference in the pulse width, and a peak output is high at a pulse width of 150 ns, but a short light is generated in terms of time, whereas a peak is generated at a pulse width of 500 ns. Although the output is low, a long passage of light is generated. It is presumed that the damage to the metal wiring 4b is caused not by the peak output but by the long time passage of light.

  Further, as shown in FIG. 17C, it can be seen that the damage to the metal wiring 4b is not affected even if the output is changed in the output region of the laser light L that is normally used for laser processing. When the output of the laser beam L is 6 μJ or less, the metal wiring 4b is not damaged but is not practical as laser processing.

  FIG. 20 is a diagram showing the relationship between the pulse waveform of the laser beam and the damage of the metal wiring 4b. In each pulse waveform shown in FIGS. 20A to 20D, the horizontal axis represents time, the vertical axis represents the output value, and the pulse widths (half-value widths) are equal to each other. As shown in FIG. 20, in a plurality of pulse waveforms having the same pulse width, it is presumed that the earlier rising waveform has less influence on the damage to the metal wiring 4b. Therefore, in the present embodiment, the pulse waveform of the laser beam L preferably has a steep rise.

  Moreover, in the laminated part 4 which apply | coated the photosensitive resin (for example, melting | fusing point 230 degreeC) which absorbs all the laser beams L, the result that the metal wiring 4b might not be damaged might be obtained. In addition, it was obtained that there was a case where the metal wiring 4b was not damaged even in the laminated portion 4 where the aluminum used for the metal wiring 4b was applied to the entire surface. Therefore, in particular, when the laminated portion 4 includes the insulating layer 4a and the metal wiring 4b as in the present embodiment, the light emitted from the laser light L interferes or reflects on the insulating layer 4a and the metal wiring 4b. However, there is a possibility that damage has occurred at the place where the light is intensified.

  FIG. 21 is a table illustrating the correlation between the distance from the surface of the first modified region and the pulse width, and the damage and cutting performance of the metal wiring. In FIG. 21, the wavelength of the laser beam L is 1080 nm, the frequency is 95 kHz, the processing speed is 360 mm / sec, and aberration correction is performed. In each cell of the graph in the figure, “determination of damage of metal wiring”, “determination of straightness”, and “determination of division rate” are shown in order from the top. “Straightness” indicates straightness when the workpiece 1 is cut, and is “◯ (appropriate)” when it is within 3 μm, “X (unsuitable)” when it is larger than 3 μm, and enclosed in parentheses The length is shown.

  The “division rate” in FIG. 21 indicates the ratio of chips that have been cut accurately in a predetermined number of chips (for example, 30 chips), and is “◯ (suitable)” if it is within 100%, otherwise “× (unsuitable)”, and the division rate is shown in parentheses. Incidentally, the correlation shown in FIG. 21 is exemplified with respect to the workpiece 1 having a thickness of 200 μm, but the workpiece 1 having a thickness of 250 μm also has the same correlation, and further, the thickness of 150 μm to The workpiece 1 having a thickness of 350 μm has the same correlation.

  As shown in FIG. 21, when the pulse width of the laser beam L is 450 ns and 500 ns, it can be seen that the metal wiring 4b is damaged. It can also be seen that when the pulse width of the laser beam L is 200 ns and 150 ns, the cutting ability is reduced, and the straightness and the cutting rate are inappropriate. On the other hand, it can be seen that when the pulse width of the laser beam L is 250 ns to 400 ns, damage to the metal wiring 4b can be suppressed without reducing the cutting ability. Therefore, in this embodiment, the pulse width of the laser light L is preferably 250 ns to 400 ns.

It can also be seen that when the distance from the surface 3 of the first modified region 7a is 16 μm or less, the metal wiring 4b is damaged and the cutting ability is reduced. On the other hand, in the following case, it can be seen that damage to the metal wiring 4b can be suppressed without reducing the cutting ability.
Pulse width: 250 ns, distance from the surface 3 of the first modified region 7a: 20 μm to 40 μm
Pulse width: 300 ns, distance from the surface 3 of the first modified region 7a: 28 μm to 40 μm
Pulse width: 350 ns, distance from surface 3 of first modified region 7a: 28 μm to 48 μm
Pulse width: 400 ns, distance from the surface 3 of the first modified region 7a: 36 μm to 48 μm

  Therefore, the distance from the surface 3 as the formation position of the first modified region 7a is 20 μm to 40 μm when the pulse width is 250 ns, 28 μm to 40 μm when the pulse width is 300 ns, and the pulse width is 350 ns. In this case, it is found that it is preferably 28 μm to 48 μm, and preferably 36 μm to 48 μm when the pulse width is 400 ns.

  Here, each numerical value of the pulse width of the laser beam L has errors in processing, manufacturing, design, and the like. Therefore, in the example shown in FIG. 21, for example, the distance from the surface 3 of the first modified region 7a is preferably 20 μm to 40 μm when the pulse width is 225 ns to 275 ns, and the distance is 275 ns to 325 ns. 28 μm to 40 μm, 28 μm to 48 μm when the pulse width is 325 ns to 375 ns, and 36 μm to 48 μm when the pulse width is 375 ns to 425 ns.

Further, as shown below, it can be seen that the pulse pitch of the laser light L has no effect on the damage to the metal wiring 4b.
Pulse pitch: 2.25μm, damaged part of metal wiring 4b: 14 points
Pulse pitch: 3.75 μm, damage to metal wiring 4b: 17
Pulse pitch: 5.25 μm, damaged part of metal wiring 4 b: 15 However, pulse width 500 ns, output 15 μJ, distance from surface 3 to first modified region 7 a 20 μm

Further, as shown below, it can be seen that the presence or absence of the correction of the aberration of the laser light L does not affect the damage of the metal wiring 4b.
Pulse width: 500 ns, aberration correction: yes, damaged part of metal wiring 4b: 17 points Pulse width: 500 ns, aberration correction: none, damaged part of metal wiring 4b: 12 places Pulse width: 150 ns, aberration correction: yes, metal wiring Damaged part of 4b: 0 places Pulse width: 150ns, Aberration correction: None, Damaged parts of metal wiring 4b: 0 places

  If the wavelength of the laser beam L is smaller than 1080 nm, the laser beam L is not sufficiently transmissive to the workpiece 1 and it is difficult to form the modified region 7 with high accuracy. Further, for example, when the wavelength of the laser beam L is 1064 nm, which is smaller than 1080 nm, the number of scans (modified region 7 in the thickness direction) is maintained in order to maintain the division rate due to the material, thickness, and the like of the workpiece 1. The number of columns) must be increased. That is, the cutting ability may be reduced, which is not preferable. On the other hand, if the wavelength of the laser beam L is larger than 1200 nm (for example, 1300 nm), the transmittance of the laser beam L with respect to the workpiece 1 is increased, so that the possibility that the laser beam L adversely affects the metal wiring 4b increases. In a predetermined number of chips (for example, 30 chips), damage to the metal wiring 4b may occur in 100 places or more, which is not preferable. Therefore, the wavelength of the laser beam L is preferably 1080 nm to 1200 nm.

  As described above, the formation position of the first modified region 7a in the first modified region forming step is preferably the following position. That is, when the pulse width is 250 ns, the distance from the surface 3 is 20 μm to 40 μm. When the pulse width is 300 ns, the distance from the surface 3 is 28 μm to 40 μm. When the pulse width is 350 ns, When the distance from the surface is 28 μm to 48 μm and the pulse width is 400 ns, it is preferable that the distance from the surface is 36 μm to 48 μm. Thereby, not only the above-mentioned tendency between the pulse width of the laser beam L and the damage of the metal wiring 4b when forming the first modified area 7a, but also the position of the first modified area 7a and the damage of the metal wiring 4b. The above-mentioned tendency (that is, the tendency that the damage of the metal wiring 4b is reduced when the position of the first modified region 7a is moved away from the surface 3) can be suitably used in relation to the cutting ability. it can. As a result, it is possible to effectively exhibit the above-described effect of suppressing damage to the metal wiring 4b without reducing the cutting ability.

  The distance from the surface 3 of the first modified region 7a is, for example, 20 μm to 40 μm when the pulse width is 225 ns to 275 ns due to an error in processing of each numerical value of the pulse width. It may be 28 μm to 40 μm in the case of 275 ns to 325 ns, 28 μm to 48 μm in the case of the pulse width of 325 ns to 375 ns, and 36 μm to 48 μm in the case of the pulse width of 375 ns to 425 ns.

  FIG. 22 is another photographic diagram illustrating the cut surface of the workpiece after laser processing according to the present embodiment. In the example shown in FIG. 22, a plurality of microcavities V are formed on the surface 3 side (opposite to the laser light incident surface side) with the modified region 7b interposed therebetween so as to be separated from each other along the planned cutting line 5. Has been. That is, in the second modified region forming step of the present embodiment, the second modified region 7b is formed so that the microcavity V is generated. As a result, unnecessary cracks deviating from the scheduled cutting line 5 are less likely to occur, and the cleaving control is facilitated, and the workpiece 1 is easily cut by the stress distribution between the modified region 7 and the microcavity V. can do.

  The microcavity V is formed only inside the workpiece 1 and the surrounding crystal structure is not substantially changed. When the workpiece 1 has a silicon single crystal structure, there are many portions around the microcavity V that remain in the silicon single crystal structure. The microcavity V may be formed continuously with the modified region 7.

  Incidentally, it is found that the closer the cutting line 5 is to the metal wiring 4b, the more easily the metal wiring 4b is damaged. Therefore, the distance D between the cutting line 5 and the metal wiring 4b (see FIG. 12) is within 25 μm. In the case of the embodiment, the metal wiring 4b is particularly easily damaged. Therefore, in the present embodiment, the above-described effect of suppressing damage to the metal wiring 4b becomes remarkable.

  As described above, in the present embodiment, the pulse width of the laser beam L is varied, and the pulse width of the laser beam L irradiated when forming the first modified region 7a is irradiated when forming the second modified region 7b. It is made smaller than the pulse width of the laser beam L. Thus, when forming the first modified region 7a, the above-described tendency between the pulse width of the laser light L and the damage of the metal wiring 4b is utilized to prevent the occurrence of the damage while the second modified region 7b is formed. The cutting ability can be maintained by forming. Therefore, damage to the metal wiring 4b can be suppressed without reducing the cutting ability.

  In the present embodiment, the laser beam L has a wavelength of 1080 nm to 1200 nm. Thereby, the said effect which suppresses the damage of the metal wiring 4b, without reducing cutting ability is suitably show | played. As described above, when the wavelength of the laser beam L is smaller than 1080 nm, the laser beam L is not sufficiently transmissive to the workpiece 1 and it is difficult to form the modified region 7 with high accuracy. On the other hand, if the wavelength of the laser beam L is larger than 1200 nm, the transmittance of the laser beam L with respect to the workpiece 1 is excessively increased, and the possibility that the laser beam L and the light emitted from the laser beam L adversely affect the metal wiring 4b increases. .

  Further, in the present embodiment, after the first modified region forming step is performed along the plurality of scheduled cutting lines 5a and 5b and the formation of the first modified region 7a at the same depth position is completed, a plurality of modified regions are formed. The second and third modified regions are formed along the scheduled cutting lines 5a and 5b to form the second and third modified regions 7b and 7c. That is, the control unit 250 and the pulse width variable control unit 251 execute the first modified region formation control along the plurality of scheduled cutting lines 5, and then perform the second and third along the plurality of scheduled cutting lines 5. The reformed area formation control is executed. As a result, the number of times of pulse width switching by the pulse width variable control unit 251 can be suppressed (here, it can be made once), and the processing time can be shortened.

  Since the pulse width of the laser light L is extremely difficult to change instantaneously, the above effect of suppressing the number of switching of the pulse width is particularly effective. Incidentally, in this embodiment, since the laser light source 101 is comprised by one, the apparatus structure can be simplified.

  Incidentally, in the present embodiment, in the first modified region forming step, the first modified region 7a is formed so that a crack (so-called BHC) reaching the surface 3 does not occur from the first modified region 7a. . Also in this point, in this embodiment, damage to the metal wiring 4b can be suppressed. On the other hand, in the second modified region forming step, the second modified region 7b is formed such that a crack reaching the surface 3 occurs from the second modified region 7b. Thereby, the workpiece 1 can be reliably cut using the crack, and high cutting ability can be secured.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the description of the present embodiment, differences from the first embodiment will be mainly described.

  FIG. 23 is a schematic cross-sectional view for explaining the formation of the first to third modified regions in the second embodiment. As shown in FIG. 23, the present embodiment is different from the first embodiment with respect to the formation order of the first to third modified regions 7a to 7c. Specifically, first, the pulse width of the laser light L is set to a first pulse width that is smaller than the pulse width in the subsequent second modified region forming step, for example, 150 ns. Then, as shown in FIG. 23A, the processing object 1 is irradiated with the laser beam L having the first pulse width by aligning the condensing point of the laser light L with the position on the surface 3 side inside the processing object 1. However, the condensing point of the laser beam L is relatively moved along the one scheduled cutting line 5. Thereby, the 1st modification area | region 7a is formed in a line along the one cutting plan line 5 in the position by the side of the surface 3 in the workpiece 1 (1st modification area | region formation process).

  Subsequently, the pulse width of the laser light L is set to a second pulse width larger than the pulse width in the first modified region forming step, for example, 500 ns. And as shown in FIG.23 (b), the condensing point of the laser beam L is matched with the position of the back surface 21 side rather than the 1st modification | reformation area | region 7a inside the workpiece 1, and the laser beam of the 2nd pulse width While irradiating the workpiece 1 with L, the condensing point of the laser beam L is relatively moved along one scheduled cutting line 5. As a result, the second modified regions 7b are formed in a row along the one scheduled cutting line 5 at a position closer to the back surface 21 than the first modified region 7a in the workpiece 1 (second modified region formation). Process).

  Subsequently, as shown in FIG. 23 (c), the condensing point of the laser beam L is aligned with the position on the back surface 21 side of the second modified region 7b inside the workpiece 1, and the laser having the second pulse width. While irradiating the processing object 1 with the light L, the condensing point of the laser light L is relatively moved along one scheduled cutting line 5. As a result, the third modified region 7c is formed in a row along the one cutting scheduled line 5 at a position closer to the back surface 21 than the second modified region 7b in the workpiece 1 (third modified region formation). Process). Thus, the formation of the first to third modified regions 7a to 7c along the one scheduled cutting line 5 is completed (line process).

  Subsequently, as shown in FIG. 23 (d), the above line process is performed on a plurality of other scheduled cutting lines 5. Thereby, a plurality of first to third modified regions 7 a to 7 c having different thickness direction positions are formed inside the workpiece 1 along the plurality of scheduled cutting lines 5.

  As described above, also in this embodiment, the same effect as that of the above embodiment, that is, the effect of suppressing damage to the metal wiring 4b without reducing the cutting ability is achieved.

  Here, when the modified region 7 is formed along the plurality of planned cutting lines 5, the index shift that the modified region 7 formed shifts from the planned cutting line 5 and the amount of shift gradually increases as the processing proceeds. May occur. For example, this index shift is caused when a crack extending to the front surface 3 or the back surface 21 of the workpiece 1 (half cut) or a crack extending to the front surface 3 and the back surface 21 (full cut) occurs in laser processing. It is considered that this occurs because the workpiece 1 opens at the crack. In addition, this index deviation occurs because, for example, the modified region 7 formed by laser processing expands so that the back side moves to the back and the near side moves to the near side. I think that. This phenomenon is more likely to occur when the formation region of the modified region 7 becomes shallower than the front surface 3 and the rear surface 21 when it is connected to a crack at a deeper position.

  In this regard, in the present embodiment, the first to third modified regions 7 a to 7 b are continuously formed along one scheduled cutting line 5, and this is repeated along the plurality of scheduled cutting lines 5. Specifically, the line process for forming the first to third modified regions 7 a to 7 c along one scheduled cutting line 5 is sequentially performed on the plurality of scheduled cutting lines 5. That is, the control unit 250 and the variable pulse width control unit 251 sequentially perform line control for performing the first to third modified region formation control along the one scheduled cutting line 5 on the plurality of scheduled cutting lines 5. doing. As a result, the adverse effect of the index deviation can be suppressed. As a result, the frequency of index correction can be reduced, the processing time in laser processing can be shortened, and the processing efficiency can be improved.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the description of the present embodiment, differences from the first embodiment will be mainly described.

  FIG. 24 is a schematic configuration diagram illustrating a laser processing apparatus that performs the laser processing method according to the third embodiment. As shown in FIG. 24, the laser processing apparatus 500 of this embodiment includes a mounting table 510 on which the workpiece 1 is mounted horizontally, a laser unit 520, and movement control for moving the mounting table 510 and the laser unit 520. Part 530. The movement control unit 530 moves the mounting table 510 in the horizontal direction (X-axis direction and Y-axis direction), and moves the laser unit 520 in the vertical direction (Z-axis direction).

  The laser unit 520 includes a first laser light source 501 that pulsates the first laser light L1 and a second laser light source 502 that pulsates the second laser light L2. The first laser light L1 has a pulse width larger than that of the second laser light L2, and has a pulse width of 500 ns, for example. The first laser light L1 passes through an attenuator 503a as an attenuator for adjusting the amount of light, and then passes through a shutter 504a for passing or blocking the laser light L1, a beam expander 505a for expanding the beam size, and a dichroic mirror 506. The light is sequentially guided, condensed by the condensing lens 507a, and irradiated onto the workpiece 1.

  The second laser light L2 has a smaller pulse width than the first laser light L1, and has a pulse width of 150 ns, for example. The second laser light L2 passes through an attenuator 503b as an attenuator for adjusting the amount of light, and is sequentially guided to a shutter 504b for passing or blocking the laser light L2 and a beam expander 505b for expanding the beam size. Then, the light is condensed by the condensing lens 507b and irradiated onto the object 1 to be processed.

  A piezo element 508a is attached to the condensing lens 507a, and the position of the condensing lens 507a in the Z-axis direction is adjusted by the piezo element 508a. Similarly, a piezo element 508b is also attached to the condensing lens 507b, and the position of the condensing lens 507b in the Z-axis direction is adjusted by the piezo element 508b. The condensing lenses 507a and 507b are juxtaposed with the condensing lens 31 by a predetermined distance D in the X-axis direction, and the distance D here is 35 mm.

  The control unit 250 controls the first and second laser light sources 501 and 502, and the first and second laser beams L1 emitted from these. The output and pulse width of each L2 are adjusted. The control unit 250 also collects the first and second laser beams L1 collected by the focusing lenses 31 and 32 based on the displacement data of the laser beam incident surface along the scheduled cutting line 5 acquired by the AF unit 212. , L2 are controlled so that the focusing points of L2 and L2 are in a predetermined position with respect to the surface 3, respectively.

  In the laser processing apparatus 500 configured as described above, the second or third modified region forming step can be performed simultaneously with the first modified region forming step. Specifically, the second laser light source 502 emits the second laser light L2 to form the first modified region 7a along the planned cutting line 5, and at the same time from the first laser light source 501 to the first laser light. The second modified region 7b or the third modified region 7c can be formed along the planned cutting line 5 by irradiation with L.

  Accordingly, switching of the pulse width of the laser light L can be suppressed, and the processing time can be shortened. In addition, since a plurality of modified regions 7 are formed for each line 5 to be cut, adverse effects of index deviation can be suppressed.

  In the present embodiment, the second laser light L may be pulsed from the first laser light source 501 and the first laser light L1 may be pulsed from the second laser light source 502. Further, the AF unit 212 may be provided corresponding to each of the first and second laser beams L1 and L2 (condensing lenses 507a and 507b).

  Furthermore, in the present embodiment, one condenser lens may be used instead of the condenser lenses 507a and 507b. In this case, the first and second laser beams L1 and L2 are guided to the one condenser lens by appropriately switching the optical paths of the first and second laser beams L1 and L2.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. The present invention can be modified without departing from the scope described in the claims or applied to other embodiments. May be.

  For example, in the first embodiment, the reflective spatial light modulator 203 is not provided, and the correction of the aberration of the laser light L by the reflective spatial light modulator 203 may not be performed. Further, the second and third modified region forming steps may be performed before the first modified region forming step is performed along the plurality of scheduled cutting lines 5.

  Moreover, in the said laminated part 4, the 1 or several metal wiring different from the metal wiring 4b may be further laminated | stacked. The present invention can also be understood as a laser processing apparatus that manufactures a chip by the laser processing method, and can also be understood as a chip manufactured by the laser processing method. In the above embodiment, the second and third modified regions 7b and 7c may be formed before the first modified region 7a is formed. Further, the third modified region 7c may be formed before the second modified region 7b is formed.

  In addition, in the above, the order of the planned cutting lines 5 that form the modified region 7 among the plurality of planned cutting lines 5 is not limited, but for example, the front side of the workpiece 1 in the thickness direction view The line process may be performed along the planned cutting line 5 extending to each region in the order of the region, the back region, and the central region. In this case, the index deviation can be effectively acted to cancel each other, and the index deviation can be further suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Processing object, 2 ... Semiconductor substrate, 3 ... Surface, 4 ... Laminate part, 4b ... Metal wiring, 5, 5a, 5b ... Planned cutting line, 7 ... Modified area | region, 7a ... 1st modified area | region (modified) Quality region), 7b ... second modified region (modified region), 7c ... third modified region (modified region), 21 ... back surface, 100, 300, 500 ... laser processing apparatus, 101 ... laser light source (laser) Light source unit), 111 ... Stage (moving unit), 202 ... Laser light source (laser light source unit), 232 ... Drive unit, 250 ... Control unit, 251 ... Pulse width variable control unit (control unit), 501 ... First laser light source (Laser light source part), 502 ... second laser light source (laser light source part), 508a, 508b ... piezo element, 530 ... movement control part (moving part, control part), L ... laser light, L1 ... first laser light ( Laser beam), L2 ... second laser beam (laser beam)

Claims (8)

Irradiating a laser beam from a back surface opposite to the surface on the side of the laminated part in the object to be processed, which includes a semiconductor substrate and a laminated part including metal wiring laminated on the semiconductor substrate. According to the laser processing method of forming a modified region that is a starting point of cutting along the planned cutting line inside the workpiece,
A first modified region forming step of irradiating the laser beam and forming a first modified region at a position on the surface side inside the workpiece;
A second modified region forming step of irradiating the laser beam and forming a second modified region at a position closer to the back surface than the first modified region inside the workpiece;
Laser processing characterized in that a pulse width of the laser light irradiated when forming the first modified region is smaller than a pulse width of the laser light irradiated when forming the second modified region. Method.   The laser processing method according to claim 1, wherein the laser beam has a wavelength of 1080 nm to 1200 nm. A plurality of the planned cutting lines are provided,
After performing the first modified region forming step along the plurality of planned cutting lines or before performing the first modified region forming step, including performing the second modified region forming step along the plurality of planned cutting lines. The laser processing method according to claim 1 or 2, wherein A plurality of the planned cutting lines are provided,
The line process which performs the said 1st and 2nd modified region formation process along the said one cutting plan line includes the process of implementing in order with respect to the said some cutting plan line. 2. The laser processing method according to 2. Irradiating a laser beam from a back surface opposite to the surface on the side of the laminated part in the object to be processed, which includes a semiconductor substrate and a laminated part including metal wiring laminated on the semiconductor substrate. According to the laser processing apparatus for forming a modified region that is a starting point of cutting along the planned cutting line inside the workpiece,
A laser light source unit for irradiating the workpiece with the laser beam;
A moving unit for moving a condensing point position of the laser beam irradiated by the laser light source unit;
A control unit for controlling the laser light source unit and the moving unit,
The controller is
First modified region formation control for irradiating the laser beam so that the first modified region is formed at a position on the surface side in the processing object;
And a second modified region forming control for irradiating the laser beam so that the second modified region is formed at a position closer to the back surface than the first modified region inside the workpiece. With
A laser characterized in that a pulse width of the laser beam irradiated when forming the first modified region is made smaller than a pulse width of the laser beam irradiated when forming the second modified region. Processing equipment.   The laser processing apparatus according to claim 5, wherein the laser light source unit irradiates the processing object with the laser light having a wavelength of 1080 nm to 1200 nm. A plurality of the planned cutting lines are provided,
The control unit performs the second modified region formation control along the plurality of planned cutting lines after or before executing the first modified region formation control along the plurality of planned cutting lines. The laser processing apparatus according to claim 5, wherein the laser processing apparatus is executed. A plurality of the planned cutting lines are provided,
The control unit executes control for sequentially performing line control for performing the first and second modified region formation control along one cutting planned line with respect to the plurality of cutting planned lines. The laser processing apparatus according to claim 5 or 6.