Laser processing apparatus

Abstract

To provide an optical modulator and a laser machining device with which it is possible to eliminate the time and effort of Faraday rotator position adjustment and prevent losses due to the attenuation of light by the Faraday rotator.SOLUTION: The present invention comprises: a separation element which has a light branching plane for separating incident light having entered along a first direction into first incident light and second incident light and passing the first incident light through and reflecting the second incident light in a first reflection direction which is parallel or inclined with respect to a second direction; a first spatial light modulator arranged directly facing the separation element in the first direction, for modulating the first incident light having passed through the light branching plane to generate first modulated light and returning the first modulated light to the light branching plane; and a second spatial light modulator arranged directly facing the separation element in the first reflection direction, for modulating the second incident light having been reflected by the light branching plane to generate second modulated light and returning the second modulated light to the light branching plane. The light branching plane synthesizes the first modulated light entering from the first spatial light modulator and the second modulated light entering from the second spatial light modulator.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an optical modulation device that separates and modulates incident light, and a laser processing device including this optical modulation device.

Background Art

[0002] There is known a laser processing device that forms a laser processing region inside a wafer along a cutting planned line of the wafer by irradiating laser light with a condensing point aligned by a condensing lens inside a workpiece such as a silicon wafer (hereinafter abbreviated as a wafer) (see, for example, Patent Document 1 and Patent Document 2). Here, the laser processing region refers to a region where physical properties such as density, refractive index, and mechanical strength inside the wafer become different from those of the surroundings due to irradiation with laser light, and the intensity is lower than that of the surroundings.

[0003] The laser processing devices described in Patent Document 1 and Patent Document 2 simultaneously condense laser light at two positions different from each other in the thickness direction inside the wafer by the condensing lens while relatively moving the condensing lens along the cutting planned line with respect to the wafer, and simultaneously form a pair of laser processing regions. As a result, two rows of laser processing regions can be formed inside the wafer for one cutting planned line in one scan.

[0004] Such a laser processing device is provided with an optical modulation device in order to simultaneously condense laser light at two positions different from each other in the thickness direction inside the wafer by the condensing lens (see, for example, Patent Documents 2 to 4 above). This optical modulation device includes a polarization beam splitter, a first reflective optical spatial modulator, a second reflective optical spatial modulator, a first Faraday rotator, and a second Faraday rotator (see particularly FIG. 1 of Patent Document 2 above).

[0005] The polarization beam splitter separates the laser light emitted from the laser light source into P-polarized light and S-polarized light. The first reflective spatial light modulator phase-modulates the P-polarized light transmitted through the polarization beam splitter to generate first modulated light, and reflects this first modulated light toward the polarization beam splitter. Also, the second reflective spatial light modulator phase-modulates the S-polarized light reflected by the polarization beam splitter to generate second modulated light, and reflects this second modulated light toward the polarization beam splitter.

[0006] The first Faraday rotator is disposed between the polarization beam splitter and the first reflective spatial light modulator, and rotates the polarization plane of the P-polarized light emitted from the polarization beam splitter toward the first reflective spatial light modulator and the polarization plane of the first modulated light reflected from the first reflective spatial light modulator toward the polarization beam splitter by 45 degrees each. The second Faraday rotator is disposed between the polarization beam splitter and the second reflective spatial light modulator, and rotates the polarization plane of the S-polarized light emitted from the polarization beam splitter toward the second reflective spatial light modulator and the polarization plane of the second modulated light reflected from the second reflective spatial light modulator toward the polarization beam splitter by 45 degrees each. As a result, the first modulated light (S-polarized light) and the second modulated light (P-polarized light) are incident on the polarization beam splitter. Then, the polarization beam splitter combines the first modulated light and the second modulated light and reflects them in a direction perpendicular to the incident direction of the laser light (the direction opposite to the second reflective spatial light modulator).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, in the optical modulation devices described in Patent Documents 2 to 4 above, it is necessary to arrange a first Faraday rotator between a polarization beam splitter and a first reflective spatial light modulator, and to arrange a second Faraday rotator between the polarization beam splitter and a second reflective spatial light modulator. In this case, adjustment of the position of each Faraday rotator is required, and furthermore, losses due to attenuation of each light and each modulated light occur in each Faraday rotator.

[0009] The present invention has been made in view of such circumstances, and an object thereof is to provide an optical modulation device and a laser processing device capable of saving the trouble of adjusting the position of a Faraday rotator and preventing losses due to attenuation of light by the Faraday rotator.

Means for Solving the Problems

[0010] An optical modulation device for achieving the object of the present invention includes, among a first direction, a second direction, and a third direction that are orthogonal to each other, a separation element having an optical branching surface that separates incident light incident along the first direction into a first incident light and a second incident light, transmits the first incident light, and reflects the second incident light in a first reflection direction that is parallel or inclined with respect to the second direction when viewed from the third direction; a first spatial light modulator disposed directly opposite to the separation element in the first direction, modulating the first incident light that has passed through the optical branching surface to generate a first modulated light, and returning the first modulated light to the optical branching surface; and a second spatial light modulator disposed directly opposite to the separation element in the second direction, modulating the second incident light reflected by the optical branching surface to generate a second modulated light, and returning the second modulated light to the optical branching surface. The first spatial light modulator reflects the first modulated light in a second reflection direction parallel to a plane perpendicular to the second direction and inclined with respect to the incident light when viewed from the second direction, and makes the first modulated light incident on the optical branching surface. The second spatial light modulator reflects the second modulated light toward the incident point of the first modulated light with respect to the optical branching surface. The optical branching surface combines the first modulated light incident from the first spatial light modulator and the second modulated light incident from the second spatial light modulator, and emits the combined light in the second reflection direction.

[0011] According to this optical modulation device, it is no longer necessary to provide a Faraday rotator between the separation element and the first spatial light modulator, and between the separation element and the first spatial light modulator, respectively.

[0012] In the optical modulation device according to another aspect of the present invention, the separation element is a cube-type polarization beam splitter, and in the polarization beam splitter, the surface on which incident light is incident and the surface from which the first modulated light and the second modulated light are emitted from the optical branching surface are the same. Thereby, it is no longer necessary to provide a Faraday rotator in the optical modulation device.

[0013] In the optical modulation device according to another aspect of the present invention, the polarization beam splitter separates incident light into P-polarized light, which is the first incident light, and S-polarized light, which is the second incident light.

[0014] In the optical modulation device according to another aspect of the present invention, the polarization directions of the P-polarized light and the first modulated light are maintained between the optical branching surface and the first spatial light modulator, and the polarization directions of the S-polarized light and the second modulated light are maintained between the optical branching surface and the second spatial light modulator.

[0015] In the optical modulation device according to another aspect of the present invention, the distance until the first incident light transmitted through the optical branching surface reaches the first spatial light modulator and the distance until the second incident light reflected by the optical branching surface reaches the second spatial light modulator are the same.

[0016] A laser processing apparatus for achieving the object of the present invention is a laser processing apparatus that forms a laser processing region inside a workpiece along a planned cutting line of the workpiece by irradiating the laser light with a condensing point inside the workpiece. The laser processing apparatus includes a laser light source that outputs laser light, and the laser light output from the laser light source enters as incident light, separates the incident light into a first incident light and a second incident light, generates a first modulated light obtained by modulating the first incident light and a second modulated light obtained by modulating the second incident light, and outputs a combined first modulated light and second modulated light. The optical modulation device according to any one of claims 1 to 5, a condenser lens that condenses the first modulated light and the second modulated light inside the workpiece, a relative movement unit that relatively moves the condenser lens along the planned cutting line with respect to the workpiece, and controls the first spatial light modulator and the second spatial light modulator to make the condensing points of the first modulated light and the second modulated light condensed inside the workpiece by the condenser lens different from each other in the thickness direction of the workpiece and equal to each other in the relative movement direction of the condenser lens. And a control unit that forms at positions.

Advantages of the Invention

[0017] The present invention saves the trouble of adjusting the position of the Faraday rotator and prevents losses due to light attenuation by the Faraday rotator.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0019] FIG. 1 is a schematic diagram of a laser processing apparatus 10 including an optical modulation device 28 of the present invention. In the figure, the XYZ directions are orthogonal to each other, the XY direction is the horizontal direction, and the Z direction is the vertical direction. Also, θ is the direction around an axis having an axis parallel to the Z direction as the rotation axis. This laser processing apparatus 10 forms two rows of laser processing regions inside the wafer W for one planned cutting line in one scan while relatively moving the condensing lens 38 in the X direction along the planned cutting line with respect to the wafer W which is the workpiece.

[0020] As shown in FIG. 1, the laser processing apparatus 10 includes a stage 11, a laser processing head (also referred to as a laser engine) 20, and a control unit 50. In this embodiment, the laser processing head 20 and the control unit 50 are configured separately, but the laser processing head 20 may include a part or all of the control unit 50.

[0021] Stage 11 corresponds to the relative moving part of the present invention and adsorbs and holds the wafer W. Stage 11 includes a stage moving mechanism (not shown) and is configured to be movable in the XYZθ directions by this stage moving mechanism. Thereby, the wafer W can be relatively moved in the XYZθ directions with respect to the laser processing head 20 (condensing lens 38) described later. As this stage moving mechanism, for example, it is constituted by various mechanisms (actuators) such as a ball screw mechanism and a linear motor mechanism. In the present embodiment, stage 11 is configured to be movable in the XYZθ directions, but it is not particularly limited as long as the wafer W can be relatively moved in the XYZθ directions with respect to the laser processing head 20. For example, stage 11 may be configured to be movable in the XYθ directions and the laser processing head 20 may be configured to be movable in the Z direction.

[0022] The wafer W is partitioned into a plurality of regions by dicing planned lines arranged in a grid pattern, and various devices constituting semiconductor chips are formed in each of the partitioned regions. A back grinding tape having an adhesive material is attached to the surface (device surface) of the wafer W on which the devices are formed, and the wafer W is placed on the stage 11 with its back surface facing upward. Note that a dicing tape having an adhesive material may be attached to one surface of the wafer W, and the wafer W may be placed on the stage 11 in a state of being integrated with the frame via this dicing tape.

[0023] The laser processing head 20 simultaneously condenses the first modulated light L1 and the second modulated light L2 of the laser light L at two positions different from each other in the thickness direction within the wafer W by the condensing lens 38 under the control of the control unit 50 to simultaneously form a pair of laser processing regions. The laser processing head 20 includes a laser light source 22, a beam expander 24, a mirror 25, a λ / 2 wavelength plate 26, an optical modulator 28, mirrors 30, 31, a first lens 32a (4f optical system 32), mirrors 33, 34, a second lens 32b (4f optical system 32), and a condensing lens 38, which are arranged along the optical path of the laser light L (the first modulated light L1 and the second modulated light L2) emitted from the laser light source 22.

[0024] The laser light source 22 emits a laser beam L used for forming a laser processing region inside the wafer W toward the beam expander 24. As this laser light source 22, for example, a semiconductor laser-excited Nd:YAG (Yttrium Aluminum Garnet) laser is used. As conditions of the laser beam L, for example, the wavelength is wavelength: 1.1 μm, the cross-sectional area of the laser beam spot is 3.14×10 -8 cm 2 , the oscillation mode is Q-switch pulse, the repetition frequency is 80 to 120 kHz, the pulse width is 180 to 280 ns, and the output is 8 W.

[0025] The beam expander 24 expands the laser beam L output from the laser light source 22 to an appropriate beam diameter for phase modulation in the optical modulation device 28 described later, and then emits it toward the mirror 25. The mirror 25 reflects the laser beam L incident from the beam expander 24 toward the λ / 2 wavelength plate 26. The λ / 2 wavelength plate 26 adjusts the incident polarization plane of the laser beam L incident on the optical modulation device 28. Note that the λ / 2 wavelength plate 26 may be omitted.

[0026] The optical modulation device 28, which will be described in detail later, polarization-separates the laser beam L that has passed through the λ / 2 wavelength plate 26, performs phase modulation on each of the polarization-separated laser beams L to generate a first modulated light L1 and a second modulated light L2, and further synthesizes the first modulated light L1 and the second modulated light L2 and outputs them to the mirror 30.

[0027] The mirrors 30 and 31 sequentially reflect the first modulated light L1 and the second modulated light L2 incident from the optical modulation device 28 and guide them to the first lens 32a (4f optical system 32).

[0028] The 4f optical system 32 is an afocal optical system (both-side telecentric optical system) including a first lens 32a and a second lens 32b, and reduces and projects (enlarged projection is also possible) the first modulated light L1 and the second modulated light L2 modulated by the optical modulation device 28 onto the condenser lens 38.

[0029] The mirrors 33 and 34 sequentially reflect the first modulated light L1 and the second modulated light L2 that have passed through the first lens 32a and guide them to the second lens 32b. As a result, the first modulated light L1 and the second modulated light L2 that have passed through the second lens 32b are reduced and projected onto the condenser lens 38.

[0030] The condenser lens 38 is an objective lens (infrared objective lens) that condenses the first modulated light L1 and the second modulated light L2 inside the wafer W, and condenses the first modulated light L1 and the second modulated light L2 at two positions that are different from each other in the Z direction inside the wafer W. The numerical aperture (NA) of this condenser lens 38 is, for example, 0.65.

[0031] Further, the condenser lens 38 is provided with a correction ring 40 in order to correct the aberration of the first modulated light L1 and the second modulated light L2 generated inside the wafer W. This correction ring 40 is configured to be manually rotatable, and when the correction ring 40 is rotated in a predetermined direction, the interval of the lens group constituting the condenser lens 38 is changed. Thereby, the aberration correction amount can be adjusted so that the aberration of the first modulated light L1 and the second modulated light L2 becomes equal to or less than a predetermined aberration at a position having a predetermined depth from the irradiation surface (back surface) of the wafer W. Note that the "aberration correction amount" is a value converted into the depth from the irradiation surface of the wafer W. Here, since the aberration correction using the correction ring 40 is a known technique, a specific description thereof is omitted.

[0032] Note that the correction ring 40 may be configured to be rotationally driven electrically by a correction ring driving unit (not shown). In this case, the control unit 50 controls the correction ring driving unit to correct the aberration of the first modulated light L1 and the second modulated light L2 to a desired state by rotating the correction ring 40.

[0033] The control unit 50 is a control device that controls the operations of each part of the laser processing apparatus 10, and has, for example, a CPU (Central Processing Unit) that functions as a controller for executing various processes, a RAM (Random Access Memory) that functions as a memory for storing various information, a ROM (Read Only Memory), and the like. Based on the processing information (processing conditions, etc.) specified by the operator, the control unit 50 comprehensively controls the operations of each part of the laser processing apparatus 10, including the movement of the stage 11, the control of the laser light source 22, and the control of the first spatial light modulator 46 and the second spatial light modulator 48 of the optical modulation device 28 described later, thereby controlling the formation of the laser processing region inside the wafer W.

[0034] [Optical Modulation Device] FIG. 2 is a perspective view of the optical modulation device 28. FIG. 3 is a top view of the optical modulation device 28 shown in FIG. 2 as viewed from the upper side. FIG. 4 is a side view of the optical modulation device 28 shown in FIG. 2 as viewed from the side. In each figure, the X1 direction is a direction parallel to the incident direction of the laser light L with respect to the optical modulation device 28 (corresponding to the first direction), the Z1 direction (corresponding to the second direction) is a direction parallel to the reflection direction of the reflected light LS by the polarization beam splitter 44 described later, and the Y1 direction (corresponding to the third direction) is a direction perpendicular to both the X1 direction and the Z1 direction.

[0035] As shown in FIGS. 2 to 4, the optical modulation device 28 includes a cube-type polarization beam splitter 44, a first spatial light modulator 46, and a second spatial light modulator 48.

[0036] The polarization beam splitter 44 corresponds to the separation element of the present invention and has an optical input / output surface 44a, an optical branching surface 44b, a first opposing surface 44c, and a second opposing surface 44d.

[0037] The light input / output surface 44a is located on one end side in the X1 direction and is a surface perpendicular to the X1 direction. This light input / output surface 44a functions as an incident surface through which the laser light L from the λ / 2 wavelength plate 26 is incident along the X1 direction, and also functions as an output surface that emits the first modulated light L1 and the second modulated light L2, which will be described later, toward the mirror 30. Note that reference sign SA1 in FIG. 2 indicates the incident point of the laser light L within the light input / output surface 44a, and reference sign SA2 indicates the output points of the first modulated light L1 and the second modulated light L2 within the light input / output surface 44a.

[0038] The light branching surface 44b is located between the light input / output surface 44a and the first opposing surface 44c in the X1 direction and is a surface inclined at 45 degrees when viewed from the Y1 direction side, and is a surface that functions as a beam splitter. The light branching surface 44b polarization-separates the laser light L incident at the incident point SB1 along the X1 direction from the light input / output surface 44a into transmitted light LP (corresponding to the first incident light) that is P-polarized and reflected light LS (corresponding to the second incident light) that is S-polarized, emits the transmitted light LP toward the first opposing surface 44c side, and reflects the reflected light LS toward the second opposing surface 44d side. Here, the reflected light LS is reflected in a reflection direction perpendicular to the X1 direction by the light branching surface 44b, in other words, in a direction parallel to the Z1 direction when viewed from the Y1 direction (the first reflection direction of the present invention). At this time, when the laser light L is linearly polarized, the ratio of the transmitted light LP and the reflected light LS can be adjusted by adjusting the rotation angle of the λ / 2 wavelength plate 26 to adjust the angle of the polarization plane (polarization direction) of the laser light L.

[0039] Also, as will be described in detail later, the light branching surface 44b combines the first modulated light L1 reflected back by the first spatial light modulator 46 and the second modulated light L2 reflected back by the second spatial light modulator 48, and emits the first modulated light L1 and the second modulated light L2 toward the output point SA2 of the light input / output surface 44a. Note that reference sign SB2 in FIG. 2 indicates the incident points of the first modulated light L1 and the second modulated light L2 within the light branching surface 44b.

[0040] The first opposing surface 44c is a surface located on the other end side in the X1 direction and perpendicular to the X1 direction, and faces the first spatial light modulator 46 described later. This first opposing surface 44c functions as an emission surface that emits the transmitted light LP transmitted through the optical branching surface 44b toward the first spatial light modulator 46, and also functions as an incident surface on which the first modulated light L1 reflected by the first spatial light modulator 46 is incident. Note that reference sign SC1 in FIG. 2 indicates the emission point of the transmitted light LP within the first opposing surface 44c, and reference sign SC2 indicates the incident point of the first modulated light L1 within the first opposing surface 44c.

[0041] The second opposing surface 44d is a surface perpendicular to the Z1 direction and faces the second spatial light modulator 48 described later. This second opposing surface 44d functions as an emission surface that emits the reflected light LS reflected by the optical branching surface 44b toward the second spatial light modulator 48 side, and also functions as an incident surface on which the second modulated light L2 reflected by the second spatial light modulator 48 is incident. Note that reference sign SD1 in FIG. 2 indicates the emission point of the reflected light LS within the second opposing surface 44d, and reference sign SD2 indicates the incident point of the second modulated light L2 within the second opposing surface 44d.

[0042] FIG. 5 is an explanatory diagram showing an example of hologram patterns 52 and 54 presented by the first spatial light modulator 46 and the second spatial light modulator 48. As shown in FIG. 5 and FIGS. 2 to 4 described above, the first spatial light modulator 46 and the second spatial light modulator 48 are of the phase modulation type, and for example, a spatial light modulator (SLM) of a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) is used. The first spatial light modulator 46 performs phase modulation of the transmitted light LP, and the second spatial light modulator 48 performs phase modulation of the reflected light LS. When the first spatial light modulator 46 and the second spatial light modulator 48 are LCOS-type SLMs, only the linearly polarized light component whose vibration direction is parallel to the liquid crystal alignment direction is modulated. Therefore, the first spatial light modulator 46 is arranged in accordance with the angle of the polarization plane (polarization direction) of the transmitted light LP, and the second spatial light modulator 48 is arranged in accordance with the angle of the polarization plane of the reflected light LS.

[0043] The first spatial light modulator 46 is disposed directly opposite the first facing surface 44c of the polarization beam splitter 44. Also, the second spatial light modulator 48 is disposed directly opposite the second facing surface 44d of the polarization beam splitter 44. Here, "directly opposite" indicates that no optical element for rotating the polarization plane of light, such as a Faraday rotator, is disposed between the first spatial light modulator 46 and the first facing surface 44c, and between the second spatial light modulator 48 and the second facing surface 44d.

[0044] The first spatial light modulator 46 has a reflective surface (modulation surface) on which a plurality of pixels are two-dimensionally arranged and which has a positional relationship conjugate to the pupil plane of the condenser lens 38. A hologram pattern 52 for modulating the phase of the transmitted light LP incident from the first facing surface 44c is presented on the reflective surface of the first spatial light modulator 46 under the control of the control unit 50. Thereby, the reflective surface of the first spatial light modulator 46 phase-modulates the transmitted light LP by the hologram pattern 52 to generate the first modulated light L1, and reflects this first modulated light L1 toward the optical branching surface 44b through the first facing surface 44c.

[0045] Also, the first spatial light modulator 46 is held so as to be position-adjustable in the X1 direction by a moving mechanism (not shown) and is held so as to be rotation-adjustable about a rotation axis parallel to the Z1 direction by a rotating mechanism (not shown). Then, the first spatial light modulator 46 is position-adjusted and rotation-adjusted by the moving mechanism and the rotating mechanism so that the distance until the transmitted light LP that has passed through the optical branching surface 44b reaches the first spatial light modulator 46 becomes a predetermined distance d (see FIG. 4).

[0046] Furthermore, the first spatial light modulator 46 is position-adjusted and rotation-adjusted by the moving mechanism and the rotating mechanism so as to reflect the first modulated light L1 in the reflection direction RD (see FIGS. 2 and 3). This reflection direction RD (corresponding to the second reflection direction of the present invention) is a direction parallel to the X1Y1 plane (corresponding to the plane perpendicular to the second direction of the present invention), which is a plane perpendicular to the Z1 direction, and is a direction inclined with respect to the X1 direction (the incident direction of the laser light L) when viewed from the Z1 direction side, and is further a direction passing through the optical branching surface 44b and the light input / output surface 44a.

[0047] As described above, since no Faraday rotator or the like is disposed between the first spatial light modulator 46 and the first opposing surface 44c, the transmitted light LP (P-polarized light) emitted from the first opposing surface 44c enters the reflecting surface of the first spatial light modulator 46 while maintaining its polarization plane (polarization direction). Also, with respect to the first modulated light L1 (P-polarized light) reflected by the reflecting surface of the first spatial light modulator 46, it enters the incident point SB2 of the optical branching surface 44b from the first opposing surface 44c while maintaining its polarization plane (polarization direction). For this reason, the first modulated light L1 passes through the optical branching surface 44b as it is and is emitted from the light input / output surface 44a.

[0048] The second spatial light modulator 48 has a reflecting surface similar to that of the first spatial light modulator 46. A hologram pattern 54 for modulating the phase of the reflected light LS incident from the second opposing surface 44d is presented on the reflecting surface of the second spatial light modulator 48 under the control of the control unit 50. Thereby, the reflecting surface of the second spatial light modulator 48 phase-modulates the reflected light LS by the hologram pattern 54 to generate the second modulated light L2, and reflects this second modulated light L2 toward the optical branching surface 44b through the second opposing surface 44d.

[0049] Also, the second spatial light modulator 48 is held so as to be position-adjustable in the Z1 direction by a moving mechanism (not shown) and is held so as to be rotation-adjustable about a rotation axis parallel to the X1 direction by a rotating mechanism (not shown). Then, the second spatial light modulator 48 is position-adjusted and rotation-adjusted by the moving mechanism and the rotating mechanism so that the distance until the reflected light LS reflected by the optical branching surface 44b reaches the second spatial light modulator 48 becomes a predetermined distance d (see FIG. 4). Thereby, the distance until the transmitted light LP reaches the first spatial light modulator 46 from the optical branching surface 44b and the distance until the reflected light LS reaches the second spatial light modulator 48 from the optical branching surface 44b both become the same at the predetermined distance d.

[0050] Furthermore, the second spatial light modulator 48 is position - adjusted and rotation - adjusted by a moving mechanism and a rotating mechanism so that the second modulated light L2 is incident on the incident point SB2 of the optical branching surface 44b, that is, the incident point SB2 of the first modulated light L1 with respect to the optical branching surface 44b, and further, the second modulated light L2 is reflected in the reflection direction RD at this incident point SB2.

[0051] As described above, since no Faraday rotator or the like is arranged between the second spatial light modulator 48 and the second opposing surface 44d, the reflected light LS (S - polarized light) emitted from the second opposing surface 44d enters the reflection surface of the second spatial light modulator 48 while maintaining its polarization plane (polarization direction). Also, with respect to the second modulated light L2 (S - polarized light) reflected by the reflection surface of the second spatial light modulator 48, it enters the incident point SB2 of the optical branching surface 44b from the second opposing surface 44d while maintaining its polarization plane (polarization direction). For this reason, the second modulated light L2 is reflected in the reflection direction RD by the optical branching surface 44b. As a result, after the first modulated light L1 and the second modulated light L2 are combined at the incident point SB2 of the optical branching surface 44b, they are emitted from the emission point SA2 of the light input / output surface 44a along the reflection direction RD.

[0052] The hologram patterns 52 and 54 are derived in advance based on the formation position of the laser processing region, the wavelength of the laser light L, the refractive index of the condenser lens 38, the wafer W, etc., and are stored in the control unit 50.

[0053] The hologram pattern 52 is a modulation pattern for modulating the phase of the transmitted light LP. Specifically, the hologram pattern 52 is a superposition of a focusing hologram pattern for making the focusing position of the first modulated light L1 focused by the condenser lens 38 different from the focusing position of the second modulated light L2 in the thickness direction of the wafer W, and a correction hologram pattern for correcting the aberration of the first modulated light L1 generated inside the wafer W. Note that the correction hologram pattern may include a pattern for correcting the aberration generated by the optical system of the laser processing head 20.

[0054] The hologram pattern 54 is a modulation pattern for modulating the phase of the reflected light LS, and is a correction hologram pattern for correcting the aberration of the second modulated light L2 generated inside the wafer W.

[0055] Note that the hologram pattern 52 and the hologram pattern 54 may be reversed. Also, the hologram pattern 54 may be a superimposition of a condensing hologram pattern and a correction hologram pattern in the same manner as the hologram pattern 52. That is, the hologram patterns 52 and 54 are not particularly limited as long as the condensing positions of the first modulated light L1 and the second modulated light L2 condensed inside the wafer W by the condenser lens 38 can be adjusted to different positions in the thickness direction of the wafer W from each other.

[0056] As described above, in this embodiment, by individually performing phase modulation of the transmitted light LP and the reflected light LS using the two first spatial light modulators 46 and the second spatial light modulator 48, the amount of light incident on the first spatial light modulator 46 and the second spatial light modulator 48 can be reduced. As a result, the temperature rise of the first spatial light modulator 46 and the second spatial light modulator 48 can be suppressed, and suppression of distortion due to heat and reduction of the risk of breakage of the first spatial light modulator 46 and the second spatial light modulator 48 can be achieved.

[0057] Note that instead of using the two first spatial light modulators 46 and the second spatial light modulator 48 as in this embodiment, it is also conceivable to divide the reflection surface of one spatial light modulator into two, and individually perform phase modulation of the transmitted light LP and the reflected light LS for each divided region of this reflection surface. However, in this case, since the first modulated light L1 and the second modulated light L2 individually condensed for each divided region cannot occupy the aperture of the condenser lens 18 in the same manner, the condensing property of the first modulated light L1 and the second modulated light L2 decreases and the processing quality also decreases.

[0058] In contrast, in the present embodiment, by individually performing phase modulation of the transmitted light LP and the reflected light LS using the two first spatial light modulators 46 and the second spatial light modulator 48, the first modulated light L1 and the second modulated light L2 are multiplexed and overlap with each other, so that each occupies the aperture of the condenser lens 18 in the same manner. As a result, a decrease in the condensing property and a decrease in the processing quality of the first modulated light L1 and the second modulated light L2 are suppressed.

[0059] [Laser Processing by Laser Processing Apparatus] Next, the flow of the laser processing of the wafer W by the laser processing apparatus 10 having the above configuration will be described. First, aberration correction is performed as necessary using the correction ring 40 of the condenser lens 38. Next, after the wafer W is adsorbed and held on the stage 11, the control unit 50 controls an alignment optical system (not shown) and the stage 11 (stage moving mechanism) to perform alignment so that the optical axis of the condenser lens 38 is aligned with the processing start position of the cutting planned line.

[0060] When the alignment is completed, the control unit 50 starts the emission of the laser light L from the laser light source 22, the presentation of the hologram pattern 52 by the first spatial light modulator 46, and the presentation of the hologram pattern 54 by the second spatial light modulator 48, and drives the stage 11 to relatively move the condenser lens 38 in the X direction (processing feed direction) with respect to the wafer W.

[0061] The laser light L emitted from the laser light source 22 enters the light modulation device 28 through the beam expander 24, the mirror 25, and the λ / 2 wavelength plate 26.

[0062] The laser light L incident on the optical modulation device 28 is incident on the light input / output surface 44a of the polarization beam splitter 44, and then is polarization-separated into transmitted light LP and reflected light LS at the light branching surface 44b. The transmitted light LP passes through the light branching surface 44b and is emitted from the first opposing surface 44c toward the first spatial light modulator 46, and enters the first spatial light modulator 46 while maintaining its polarization plane (polarization direction). As a result, the transmitted light LP is phase-modulated into first modulated light L1 by the hologram pattern 52 presented on the reflection surface of the first spatial light modulator 46. Then, the first modulated light L1 is reflected by the reflection surface of the first spatial light modulator 46, and while maintaining its polarization plane, passes through the first opposing surface 44c along the reflection direction RD and enters the incident point SB2 of the light branching surface 44b.

[0063] On the other hand, the reflected light LS is emitted from the second opposing surface 44d toward the second spatial light modulator 48 after being reflected by the light branching surface 44b, and enters the second spatial light modulator 48 while maintaining its polarization plane (polarization direction). As a result, the reflected light LS is phase-modulated into second modulated light L2 by the hologram pattern 54 presented on the reflection surface of the second spatial light modulator 48. Then, the second modulated light L2 is reflected by the reflection surface of the second spatial light modulator 48, and while maintaining its polarization plane, passes through the second opposing surface 44d and enters the incident point SB2 of the light branching surface 44b.

[0064] The first modulated light L1 and the second modulated light L2 are combined at the incident point SB2, and then proceed along the reflection direction RD and are emitted from the emission point SA2 of the light input / output surface 44a toward the mirror 30. Thus, in this embodiment, by adjusting the arrangement of the first spatial light modulator 46 and the second spatial light modulator 48 with respect to the polarization beam splitter 44 so that the first modulated light L1 and the second modulated light L2 are emitted from the light input / output surface 44a where the laser light L is incident, it is possible to omit the arrangement of a Faraday rotator or the like between the polarization beam splitter 44 and each spatial light modulator 46, 48.

[0065] The first modulated light L1 and the second modulated light L2 emitted from the light input / output surface 44a enter the condenser lens 38 through the mirrors 30, 31, the first lens 32a, the mirrors 33, 34, and the second lens 32b. Then, the first modulated light L1 and the second modulated light L2 are condensed by the condenser lens 38 at two different positions inside the wafer W.

[0066] FIG. 6 is a diagram showing a state in which the first modulated light L1 and the second modulated light L2 are individually condensed inside the wafer W. FIG. 7 is a diagram showing a state in which laser processing regions P1 and P2 are formed at the condensing points Q1 of the first modulated light L1 and Q2 of the second modulated light L2 shown in FIG. 6. FIG. 8 is a diagram showing a state in which two rows of laser processing regions P1 and P2 are formed inside the wafer W along the planned cutting line.

[0067] As shown in FIG. 6, the first modulated light L1 and the second modulated light L2 are simultaneously condensed by the condenser lens 38 at two positions (condensing point Q1, condensing point Q2) that are different from each other in the thickness direction and equal to each other in the X direction (corresponding to the relative movement direction) inside the wafer W. As a result, as shown in FIG. 7, a pair of laser processing regions P1 and P2 are formed in the vicinity of the two condensing points Q1 and Q2. Also, cracks K1 and K2 (also referred to as cracks) extending in the thickness direction of the wafer W starting from the laser processing regions P1 and P2 are formed. Then, when one scan is performed along the planned cutting line, as shown in FIG. 8, two rows of laser processing regions P1 and P2 are formed inside the wafer W along the planned cutting line.

[0068] Next, under the control of the control unit 50, the stage 11 is fed by one pitch in the Y direction, and laser processing regions P1 and P2 are formed in the same manner for the next planned cutting line.

[0069] Then, when the laser processing regions P1 and P2 are formed along all the planned cutting lines parallel to the X direction, under the control of the control unit 50, the stage 11 is rotated by 90°, and the laser processing regions P1 and P2 are similarly formed along all the planned cutting lines orthogonal to the previous planned cutting lines. As a result, the laser processing regions P1 and P2 are formed along all the planned cutting lines.

[0070] After the laser processing regions P1 and P2 are formed along the planned cutting lines as described above, a back grinding process is performed using a grinding device (not shown) to grind the back surface of the wafer W so that the thickness (initial thickness) T1 of the wafer W is processed to a predetermined thickness (final thickness) T2 (for example, 30 to 50 μm).

[0071] After the back grinding process, an expand process is performed in which an expand tape (dicing tape) is attached to the back surface of the wafer W, the BG tape attached to the front surface of the wafer W is peeled off, and then tension is applied to the expand tape attached to the back surface of the wafer W to stretch it. As a result, the wafer W is cut starting from the cracks (cracks) that have spread to the device surface (front surface) side of the wafer W. That is, the wafer W is cut along the planned cutting lines and divided into a plurality of chips.

[0072] As described above, in this embodiment, the Faraday rotator can be omitted from the optical modulation device 28, so that the trouble of adjusting the position of the Faraday rotator as in the prior art can be saved, and the loss due to the attenuation of light by the Faraday rotator can be prevented.

[0073] [Others] FIG. 9 is a perspective view showing a modified example of the optical modulation device 28. In the above embodiment, the cube type polarization beam splitter 44 is provided in the optical modulation device 28. However, as shown in FIG. 9, a plate type polarization beam splitter 60 may be provided in the optical modulation device 28 instead of the cube type. This polarization beam splitter 60 has a light branching surface 44b similar to that of the polarization beam splitter 44 in the above embodiment. Similar to the above embodiment, the polarization separation of the laser beam L, the emission of the transmitted light LP to the first spatial light modulator 46, the emission of the reflected light LS to the second spatial light modulator 48, the combination of the first modulated light L1 and the second modulated light L2, and the emission of the first modulated light L1 and the second modulated light L2 to the mirror 30 are performed.

[0074] In the above embodiment, the laser beam L is polarization-separated by the polarization beam splitters 44 and 60. However, for example, as a separation element of the present invention, a half mirror may be used to separate the laser beam L into a first incident light and a second incident light, and the first incident light may be emitted to the first spatial light modulator 46 and the second incident light may be emitted to the second spatial light modulator 48. However, when the first spatial light modulator 46 and the second spatial light modulator 48 are LCOS type SLMs, only the linearly polarized light component whose vibration direction is parallel to the liquid crystal alignment direction is modulated. Therefore, when a half mirror is used, the light utilization efficiency will decrease. For this reason, it is preferable to use the polarization beam splitters 44 and 60.

[0075] In the above embodiment, after performing two-stage processing of simultaneously forming the laser processing regions P1 and P2 at two condensing points Q1 and Q2 that are different from each other in the thickness direction inside the wafer W, the back grinding process and the expand process are executed. However, the present invention is not limited to this. For example, if necessary, a plurality of laser processes may be performed while changing the positions (processing depths of the laser processing regions P1 and P2) where the first modulated light L1 and the second modulated light L2 are condensed inside the wafer W. At that time, according to the processing depths of the laser processing regions P1 and P2, a correction pattern (in this case, a pattern in a direction that cancels the correction by the correction ring 40) for correcting the aberration inside the wafer W is superimposed on the hologram patterns 52 and 54, so that appropriate aberration correction can be performed even for relatively shallow portions from the back surface of the wafer W.

[0076] FIG. 10 is a top view of a modified example of the optical modulation device 28 as viewed from above. FIG. 11 is a top view of a modified example of the optical modulation device 28 as viewed from above. Note that, in order to prevent complication of the drawing, illustration of the second spatial light modulator 48 is omitted in FIG. 10.

[0077] In the above embodiment, the reflected light LS is reflected in the direction perpendicular to the X1 direction (Z1 direction) by the optical branching surface 44b, but the present invention is not limited thereto. For example, as shown in FIGS. 10 and 11, by adjusting the positions and postures of the polarization beam splitter 44 and the spatial light modulators 46 and 48, when viewed from the Y1 direction, the reflected light LS may be reflected by the optical branching surface 44b in a reflection direction inclined with respect to the Z1 direction (corresponding to the first reflection direction of the present invention). Also in this case, the second modulated light L2 reflected by the reflection surface of the second spatial light modulator 48 enters the optical branching surface 44b while maintaining its polarization plane, is combined with the first modulated light L1 in the same manner as in the above embodiment, and then travels along the reflection direction RD together with the first modulated light L1.

[0078] In the above embodiment, an LCOS type SLM is used as each of the spatial light modulators 46 and 48, but an MEMS (Micro Electro Mechanical Systems) type SLM or a deformable mirror device or the like may be used. Further, each of the spatial light modulators 46 and 48 is not limited to a reflection type, and may be a transmission type. Furthermore, examples of each of the spatial light modulators 46 and 48 include a liquid crystal cell type or an LCD (Liquid Crystal Display) type.

Description of Reference Numerals

[0079] 10 Laser processing apparatus 11 Stage 18 Condensing lens 20 Laser processing head 22 Laser light source 24 Beam expander 25 Mirror 26 Two-wavelength plate 28 Optical modulation device 30 Mirror 31 Mirror 32 4f Optical System 32a First Lens 32b Second Lens 33 Mirror 34 Mirror 38 Condensing Lens 40 Correction Ring 44 Polarizing Beam Splitter 44a Light Input / Output Surface 44b Light Branching Surface 44c First Opposing Surface 44d Second Opposing Surface 46 First Spatial Light Modulator 48 Second Spatial Light Modulator 50 Control Unit 52 Hologram Pattern 54 Hologram Pattern 60 Polarizing Beam Splitter K1 Crack K2 Crack L Laser Light L1 First Modulated Light L2 Second Modulated Light LP Transmitted Light LS Reflected Light Nd Semiconductor Laser Excitation P1 Laser Processing Area P2 Laser Processing Area Q1 Focus Point Q2 Focus Point RD Reflection Direction W Wafer d Predetermined Distance

Claims

In a laser processing apparatus that forms a laser processing region inside a workpiece along a planned cutting line of the workpiece by irradiating the workpiece with laser light while aligning a condensing point inside the workpiece, a laser light source that outputs the laser light; a light modulation device into which the laser light output from the laser light source enters as incident light, separates the incident light into a first incident light and a second incident light, generates a first modulated light obtained by phase-modulating the first incident light and a second modulated light obtained by phase-modulating the second incident light, and synthesizes and outputs the first modulated light and the second modulated light; a condenser lens that condenses the first modulated light and the second modulated light inside the workpiece; a relative movement unit that relatively moves the condenser lens along the planned cutting line with respect to the workpiece; a control unit; and includes: the light modulation device includes: a separation element that separates the incident light incident along the first direction among the first direction, the second direction, and the third direction that are orthogonal to each other into a first incident light and a second incident light, transmits the first incident light, and reflects the second incident light in a first reflection direction that is parallel or inclined with respect to the second direction when viewed from the third direction, and has a light branching surface; a first spatial light modulator that is disposed directly opposite to the separation element in the first direction, phase-modulates the first incident light that has passed through the light branching surface to generate the first modulated light, and returns the first modulated light to the light branching surface; a second spatial light modulator that is disposed directly opposite to the separation element in the first reflection direction, phase-modulates the second incident light reflected by the light branching surface to generate the second modulated light, and returns the second modulated light to the light branching surface; and includes: the first spatial light modulator reflects the first modulated light in a second reflection direction that is parallel to a plane perpendicular to the second direction and inclined with respect to the incident light when viewed from the second direction, and makes the first modulated light enter the light branching surface; the second spatial light modulator reflects the second modulated light toward an incident point of the first modulated light with respect to the light branching surface; the light branching surface synthesizes the first modulated light incident from the first spatial light modulator and the second modulated light incident from the second spatial light modulator, and emits the synthesized light in the second reflection direction; A laser processing apparatus in which the control unit controls the first spatial light modulator and the second spatial light modulator to form the condensing points of the first modulated light and the second modulated light that are condensed inside the workpiece by the condenser lens at positions that are different from each other in the thickness direction of the workpiece and equal to each other in the relative movement direction of the condenser lens.

2. The separating element is a cube-type polarizing beam splitter, The laser processing apparatus according to claim 1, wherein, in the polarizing beam splitter, the surface on which the incident light is incident and the surface from which the first modulated light and the second modulated light from the optical branching surface are emitted are the same.

3. The laser processing apparatus according to claim 2, wherein the polarizing beam splitter separates the incident light into P-polarized light which is the first incident light and S-polarized light which is the second incident light.

4. The laser processing apparatus according to claim 3, wherein the polarization directions of the P-polarized light and the first modulated light are maintained between the optical branching surface and the first spatial light modulator, and the polarization directions of the S-polarized light and the second modulated light are maintained between the optical branching surface and the second spatial light modulator.

5. The laser processing apparatus according to any one of claims 1 to 4, wherein the distance until the first incident light transmitted through the optical branching surface reaches the first spatial light modulator is the same as the distance until the second incident light reflected by the optical branching surface reaches the second spatial light modulator.

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