JP2023019078A - Optical modulator and laser processing device - Google Patents

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

The present invention relates to an optical modulator that separates and modulates incident light, and a laser processing apparatus that includes this optical modulator.

Laser processing is performed inside the wafer along the scheduled cutting line of the wafer by irradiating the inside of the workpiece such as a silicon wafer (hereinafter abbreviated as wafer) with a laser beam by aligning the focal point with a condenser lens. A laser processing device that forms a region is known (see, for example, Patent Documents 1 and 2). The term “laser processing region” as used herein refers to a region where physical properties such as density, refractive index, mechanical strength, etc. inside the wafer become different from those of the surroundings due to the irradiation of laser light, and the strength is lower than that of the surroundings. .

In the laser processing apparatuses described in Patent Documents 1 and 2, while relatively moving the condenser lens with respect to the wafer along the planned cutting line, two positions different from each other in the thickness direction in the wafer by the condenser lens A pair of laser processing regions are simultaneously formed by simultaneously condensing laser beams on both sides. As a result, it becomes possible to form two rows of laser-processed regions inside the wafer for one line to be cut by one scan.

Such a laser processing apparatus is provided with an optical modulator for simultaneously condensing the laser light at two different positions in the thickness direction within the wafer by means of a condensing lens (for example, Patent Document 2 above). to 4). This optical modulation device includes a polarizing beam splitter, a first reflective spatial optical modulator, a second reflective spatial optical modulator, a first Faraday rotator, and a second Faraday rotator (in particular, 2, Figure 1).

The polarizing beam splitter splits 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 polarizing beam splitter to generate first modulated light, and reflects this first modulated light toward the polarizing beam splitter. 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.

The first Faraday rotator is arranged between the polarizing beam splitter and the first reflective spatial light modulator, and the plane of polarization of the P-polarized light emitted from the polarizing beam splitter toward the first reflective spatial light modulator is and the polarization plane of the first modulated light reflected from the first reflective spatial light modulator toward the polarization beam splitter are rotated by 45 degrees. The second Faraday rotator is arranged between the polarizing beam splitter and the second reflective spatial light modulator, and the plane of polarization of the S-polarized light emitted from the polarizing beam splitter toward the second reflective spatial light modulator is and the plane of polarization of the second modulated light reflected from the second reflective spatial light modulator toward the polarization beam splitter are rotated by 45 degrees. As a result, the first modulated light (S-polarized light) and the second modulated light (P-polarized light) enter the polarization beam splitter. The polarizing 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 (direction opposite to the second reflective spatial light modulator). do.

JP 2011-051011 A JP 2014-202956 A JP 2014-202957 A JP 2014-202958 A

By the way, in the optical modulation devices described in Patent Documents 2 to 4, the first Faraday rotator is arranged between the polarizing beam splitter and the first reflective spatial light modulator, and the polarizing beam splitter and the second reflective light modulator are arranged. A second Faraday rotator needs to be placed between the spatial modulator. In this case, it is necessary to adjust the position of each Faraday rotator, and furthermore, each Faraday rotator causes a loss due to attenuation of each light and each modulated light.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical modulation device and a laser processing device that can save the trouble of adjusting the position of the Faraday rotator and prevent loss due to attenuation of light by the Faraday rotator. aim.

An optical modulation device for achieving the object of the present invention divides incident light incident along the first direction into the first incident light and the third 2 incident light, transmits the first incident light, and reflects the second incident light in a first reflection direction parallel or inclined to the second direction when viewed from the third direction. a separation element having a surface, arranged directly opposite the separation element in a first direction, modulating the first incident light transmitted through the light splitting surface to generate the first modulated light, and generating the first modulated light; A first spatial light modulator that returns to the light splitting surface and is arranged directly opposite the separation element in the second direction and modulates the second incident light reflected by the light splitting surface to generate the second modulated light. and a second spatial light modulator for returning the second modulated light to the optical splitting surface, wherein the first spatial light modulator directs the first modulated light to a plane perpendicular to the second direction in parallel to the plane perpendicular to the second direction. When viewed from the second direction, the second spatial light modulator reflects the second modulated light in a reflecting direction that is inclined with respect to the incident light, and makes the second modulated light incident on the light branching surface. The light branching surface reflects the first modulated light incident from the first spatial light modulator and the second modulated light incident from the second spatial light modulator. , and emitted in the second reflection direction.

According to this optical modulator, it is not 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.

In the optical modulation device according to another aspect of the present invention, the separating element is a cubic polarizing beam splitter, and in the polarizing beam splitter, the plane on which the incident light is incident, the first modulated light from the light splitting plane, and the second modulated light from the light splitting plane. and the surface from which modulated light is emitted. This eliminates the need to provide a Faraday rotator in the optical modulator.

In a light modulation device according to another aspect of the present invention, a polarizing beam splitter splits incident light into P-polarized light as the first incident light and S-polarized light as the second incident light.

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 light splitting surface and the first spatial light modulator, and the light splitting surface and the second spatial light are maintained. The polarization directions of the S-polarized light and the second modulated light are maintained with the modulator.

In the optical modulation device according to another aspect of the present invention, the distance between the first incident light transmitted through the light branching surface and reaching the first spatial light modulator and the second incident light reflected by the light branching surface are is the same as the distance to reach the second spatial light modulator.

A laser processing apparatus for achieving the object of the present invention irradiates a laser beam with a focal point aligned with the interior of the workpiece, thereby cutting the workpiece along the planned cutting line of the workpiece. A laser processing apparatus for forming a laser processing region, comprising: a laser light source that outputs a laser beam; 2. generating a first modulated light obtained by modulating the first incident light and a second modulated light obtained by modulating the second incident light, and combining and outputting the first modulated light and the second modulated light. 6. The light modulation device according to any one of 1 to 5, a condenser lens for condensing the first modulated light and the second modulated light inside the workpiece, and the condenser lens is cut with respect to the workpiece Controlling the relative movement part that relatively moves along the planned line, the first spatial light modulator and the second spatial light modulator, and the first modulated light focused inside the workpiece by the condenser lens a controller for forming the condensing point and the condensing point of the second modulated light at different positions in the thickness direction of the workpiece and equal to each other in the relative movement direction of the condensing lens.

The present invention saves the trouble of adjusting the position of the Faraday rotator and prevents loss due to attenuation of light by the Faraday rotator.

It is a schematic diagram of a laser processing apparatus. 1 is a perspective view of an optical modulator; FIG. 3 is a top view of the optical modulation device in FIG. 2 as seen from above; FIG. FIG. 3 is a side view of the optical modulation device in FIG. 2 as seen from the lateral side; FIG. 4 is an explanatory diagram showing an example of a hologram pattern presented by a first spatial light modulator and a second spatial light modulator; FIG. 4 is a diagram showing a state in which first modulated light and second modulated light are separately focused inside a wafer; 7 is a diagram showing a state in which laser processing regions are formed at the condensing position of the first modulated light and the condensing position of the second modulated light shown in FIG. 6; FIG. FIG. 4 is a diagram showing a state in which two rows of laser-processed regions are formed inside a wafer along a line to cut; It is a perspective view showing a modification of the optical modulation device. It is the top view which looked at the modification of the optical modulation device from the upper side. It is the side view which looked at the modification of the optical modulation device from the side side.

FIG. 1 is a schematic diagram of a laser processing apparatus 10 equipped with a light modulating device 28 of the present invention. The XYZ directions in the drawing are orthogonal to each other, the XY directions are horizontal directions, and the Z directions are vertical directions. Also, θ is the direction around the axis with the axis parallel to the Z direction as the axis of rotation. This laser processing apparatus 10 relatively displaces the condenser lens 38 in the X direction along the planned cutting line with respect to the wafer W, which is a workpiece, while moving two lines inside the wafer W for one planned cutting line. is formed in one scan.

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 section 50 . In this embodiment, the laser processing head 20 and the controller 50 are configured separately, but the laser processing head 20 may include part or all of the controller 50 .

The stage 11 corresponds to the relative moving part of the present invention, and holds the wafer W by suction. The stage 11 includes a stage moving mechanism (not shown), and is configured to be movable in the XYZθ directions by this stage moving mechanism. As a result, the wafer W can be relatively moved in the XYZ.theta. This stage moving mechanism is composed of, for example, various mechanisms (actuators) such as a ball screw mechanism and a linear motor mechanism. In this embodiment, the stage 11 is configured to be movable in the XYZθ directions, but there is no particular limitation as long as the wafer W can be moved in the XYZθ directions relative to the laser processing head 20. For example, the stage 11 may be configured to be movable in the XY[theta] directions, and the laser processing head 20 may be configured to be movable in the Z direction.

The wafer W is partitioned into a plurality of regions by cutting lines arranged in a grid pattern, and various devices constituting semiconductor chips are formed in each partitioned region. A back grind 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 so that the back surface thereof faces upward. A dicing tape having an adhesive material may be applied to one surface of the wafer W, and the wafer W may be mounted on the stage 11 in a state integrated with the frame through the dicing tape.

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

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

The beam expander 24 expands the laser light L output from the laser light source 22 to an appropriate beam diameter for phase modulation by the light modulation device 28 described later, and then emits it toward the mirror 25 . The mirror 25 reflects the laser light 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 light L entering the optical modulator 28 . Note that the λ/2 wavelength plate 26 may be omitted.

Although the details will be described later, the optical modulator 28 polarization-separates the laser light L transmitted through the λ/2 wavelength plate 26, and performs phase modulation for each polarization-separated laser light L to obtain the first modulated light L1 and the second modulated light L1. The modulated light L2 is generated, and the first modulated light L1 and the second modulated light L2 are combined and output to the mirror 30.

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

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. is projected on the condensing lens 38 in a reduced scale (enlarged projection is also possible).

The mirrors 33 and 34 sequentially reflect the first modulated light L1 and the second modulated light L2 transmitted 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 projected onto the condensing lens 38 in a reduced scale.

The condenser lens 38 is an objective lens (infrared objective lens) for condensing the first modulated light L1 and the second modulated light L2 inside the wafer W, and collects the first modulated light L1 and the second modulated light L2 into the wafer W. The light is condensed at two different positions in the Z direction inside W. The numerical aperture (NA) of this condenser lens 38 is, for example, 0.65.

The condenser lens 38 also includes a correction ring 40 for correcting aberrations of the first modulated light L1 and the second modulated light L2 that occur inside the wafer W. As shown in FIG. The correction ring 40 is manually rotatable, and when the correction ring 40 is rotated in a predetermined direction, the interval between the lens groups forming the condenser lens 38 is changed. As a result, the amount of aberration correction can be adjusted so that the aberrations of the first modulated light L1 and the second modulated light L2 are less than or equal to a predetermined aberration at a predetermined depth from the irradiated surface (back surface) of the wafer W. . The "aberration correction amount" is a value converted into the depth from the irradiation surface of the wafer W. FIG. Here, since the aberration correction using the correction ring 40 is a well-known technique, a detailed description thereof will be omitted.

The correction ring 40 may be configured to be electrically rotatable by a correction ring drive section (not shown). In this case, the control unit 50 controls the correction ring drive unit to rotate the correction ring 40, thereby correcting the aberrations of the first modulated light L1 and the second modulated light L2 to desired states.

The control unit 50 is a control device that controls the operation of each unit of the laser processing apparatus 10. For example, the control unit 50 includes a CPU (Central Processing Unit) functioning as a controller that executes various processes, and a RAM (Random Processing Unit) functioning as a memory that stores various information. Access Memory) and ROM (Read Only Memory). The control unit 50 moves the stage 11, controls the laser light source 22, and controls the first spatial light modulator 46 and the second spatial light modulator 46 of the light modulation device 28, which will be described later, based on processing information (processing conditions, etc.) specified by the operator. The formation of the laser processing area inside the wafer W is controlled by integrally controlling the operation of each part of the laser processing apparatus 10 including the control of the spatial light modulator 48 .

[Optical Modulator]
FIG. 2 is a perspective view of the optical modulator 28. As shown in FIG. FIG. 3 is a top view of the light modulation device 28 in FIG. 2 as seen from above. FIG. 4 is a side view of the optical modulator 28 in FIG. 2 as seen from the lateral side. Note that the X1 direction in each drawing is parallel to the incident direction (corresponding to the first direction) of the laser light L to the optical modulator 28, and the Z1 direction (corresponding to the second direction) is the polarization beam splitter 44 described later. is parallel to the reflection direction of the reflected light LS. Also, the Y1 direction (corresponding to the third direction) is a direction perpendicular to both the X1 direction and the Z1 direction.

As shown in FIGS. 2 to 4 , the optical modulator 28 includes a cube-shaped polarizing beam splitter 44 , a first spatial light modulator 46 and a second spatial light modulator 48 .

The polarizing beam splitter 44 corresponds to the separating element of the present invention, and has a light input/output surface 44a, a light splitting surface 44b, a first opposing surface 44c, and a second opposing surface 44d.

The light entrance/exit surface 44a is a surface located on one end side in the X1 direction and perpendicular to the X1 direction. The light incidence/emission surface 44a functions as an incidence surface on which the laser light L from the λ/2 wavelength plate 26 is incident along the X1 direction, and the mirror 30 receives the first modulated light L1 and the second modulated light L2, which will be described later. It functions as an emission surface that emits light toward. 2 indicates the incident point of the laser beam L within the light incident/emission surface 44a, and the code SA2 indicates the emission of the first modulated light L1 and the second modulated light L2 within the light incident/exiting surface 44a. point.

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

Further, the light branching surface 44b, which will be described later in detail, has the first modulated light L1 reflected back from the first spatial light modulator 46 and the second modulated light reflected back from the second spatial light modulator 48. L2 are synthesized, and the first modulated light L1 and the second modulated light L2 are emitted toward the emission point SA2 of the light incidence/emission surface 44a. 2 indicates the incident point of the first modulated light L1 and the second modulated light L2 within the light splitting surface 44b.

The first facing 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, which will be described later. The first opposing surface 44 c functions as an emission surface for emitting the transmitted light LP that has passed through the light splitting surface 44 b toward the first spatial light modulator 46 , and also functions as an emission surface for emitting the transmitted light LP that has been reflected by the first spatial light modulator 46 . It functions as an incident surface on which the 1-modulated light L1 is incident. 2 indicates the exit point of the transmitted light LP within the first opposing surface 44c, and the reference SC2 indicates the incident point of the first modulated light L1 within the first opposing surface 44c.

The second facing surface 44d is a surface perpendicular to the Z1 direction and faces a second spatial light modulator 48, which will be described later. The second opposing surface 44 d functions as an emission surface for emitting the reflected light LS reflected by the light branching surface 44 b toward the second spatial light modulator 48 , and also functions as an emission surface for emitting the reflected light LS reflected by the second spatial light modulator 48 . 2 functions as an incident surface on which the modulated light L2 is incident. 2 indicates the exit point of the reflected light LS within the second opposing surface 44d, and the reference SD2 indicates the incident point of the second modulated light L2 within the second opposing surface 44d.

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. FIG. As shown in FIG. 5 and FIG. 2 to FIG. 4 already described, the first spatial light modulator 46 and the second spatial light modulator 48 are phase modulation type, for example, reflective liquid crystal (LCOS). on Silicon) Spatial Light Modulator (SLM) is used. The first spatial light modulator 46 phase-modulates the transmitted light LP, and the second spatial light modulator 48 phase-modulates 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 alignment direction of the liquid crystal is modulated. The light modulator 46 is arranged to match the angle of the polarization plane (polarization direction) of the transmitted light LP, and the second spatial light modulator 48 is arranged to match the angle of the polarization plane of the reflected light LS.

The first spatial light modulator 46 is arranged to directly face the first facing surface 44 c of the polarizing beam splitter 44 . Also, the second spatial light modulator 48 is arranged to directly face the second facing surface 44 d of the polarization beam splitter 44 . Here, "directly facing" means that light such as a Faraday rotator is placed 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. indicates that there is no optical element that rotates the plane of polarization of .

The first spatial light modulator 46 has a reflection surface (modulation surface) in which a plurality of pixels are arranged two-dimensionally and which has a conjugate positional relationship with the pupil plane of the condenser lens 38 . A reflecting surface of the first spatial light modulator 46 presents a hologram pattern 52 that modulates the phase of the transmitted light LP incident from the first opposing surface 44 c under the control of the control unit 50 . As a result, the reflecting surface of the first spatial light modulator 46 phase-modulates the transmitted light LP with the hologram pattern 52 to generate the first modulated light L1, which is transmitted through the first opposing surface 44c. The light is reflected toward the light branching surface 44b.

The first spatial light modulator 46 is held by a moving mechanism (not shown) so as to be positionally adjustable in the X1 direction, and is also rotatably adjustable around a rotation axis parallel to the Z1 direction by a rotating mechanism (not shown). held. The first spatial light modulator 46 is controlled by a moving mechanism and a rotating mechanism so that the transmitted light LP transmitted through the light splitting surface 44b reaches the first spatial light modulator 46 by a predetermined distance d (see FIG. 4). ) are adjusted in position and rotation.

Further, the first spatial light modulator 46 is positionally and rotationally adjusted by a moving mechanism and a rotating mechanism so as to reflect the first modulated light L1 in the reflection direction RD (see FIGS. 2 and 3). The reflection direction RD (corresponding to the second direction of reflection of the present invention) is parallel to the X1Y1 plane (corresponding to the plane perpendicular to the second direction of the present invention) perpendicular to the Z1 direction, and It is a direction that is inclined with respect to the X1 direction (the incident direction of the laser beam L) when viewed from the Z1 direction side, and is a direction that passes through the light branching surface 44b and the light incident/exiting surface 44a.

As described above, since no Faraday rotator or the like is arranged 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 is The light enters the reflecting surface of the first spatial light modulator 46 while maintaining the plane of polarization (direction of polarization). Further, the first modulated light L1 (P-polarized light) reflected by the reflecting surface of the first spatial light modulator 46 is also diverted from the first opposing surface 44c to the light branching surface 44b while maintaining its plane of polarization (polarization direction). Incident at the incident point SB2. Therefore, the first modulated light L1 is transmitted through the light branching surface 44b as it is and is emitted from the light incident/exiting surface 44a.

The second spatial light modulator 48 has reflective surfaces similar to those of the first spatial light modulator 46 . A hologram pattern 54 that modulates the phase of the reflected light LS incident from the second opposing surface 44 d is presented on the reflecting surface of the second spatial light modulator 48 under the control of the control unit 50 . As a result, the reflecting surface of the second spatial light modulator 48 phase-modulates the reflected light LS with the hologram pattern 54 to generate the second modulated light L2, which is transmitted through the second opposing surface 44d. The light is reflected toward the light branching surface 44b.

The second spatial light modulator 48 is held by a moving mechanism (not shown) so as to be positionally adjustable in the Z1 direction, and is also rotatably adjustable around a rotation axis parallel to the X1 direction by a rotating mechanism (not shown). held. Then, the second spatial light modulator 48 is controlled by the moving mechanism and the rotating mechanism so that the reflected light LS reflected by the light splitting surface 44b reaches the second spatial light modulator 48 by a predetermined distance d (FIG. 4). ) are adjusted in position and rotation. As a result, the distance for the transmitted light LP to reach the first spatial light modulator 46 from the light branching surface 44b and the distance for the reflected light LS to reach the second spatial light modulator 48 from the light branching surface 44b are , become the same at a predetermined distance d.

Further, the second spatial light modulator 48 uses a moving mechanism and a rotating mechanism to make the second modulated light L2 incident on the incident point SB2 of the light branching surface 44b, that is, the incident point SB2 of the first modulated light L1 on the light branching surface 44b. Further, the position and rotation are adjusted so that the second modulated light L2 is reflected in the reflection direction RD at this incident point SB2.

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 is The light enters the reflecting surface of the second spatial light modulator 48 while maintaining the plane of polarization (direction of polarization). Further, the second modulated light L2 (S-polarized light) reflected by the reflecting surface of the second spatial light modulator 48 is also diverted from the second opposing surface 44d to the light branching surface 44b while maintaining its plane of polarization (polarization direction). Incident at the incident point SB2. Therefore, the second modulated light L2 is reflected in the reflection direction RD by the light 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 light splitting surface 44b, they are emitted from the emitting point SA2 of the light incident/exiting surface 44a along the reflection direction RD.

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

The hologram pattern 52 is a modulation pattern for modulating the phase of the transmitted light LP. Specifically, the hologram pattern 52 is designed to make the condensing position of the first modulated light L1 condensed by the condensing lens 38 different from the condensing position of the second modulated light L2 in the thickness direction of the wafer W. A condensing hologram pattern and a correction hologram pattern for correcting the aberration of the first modulated light L1 occurring inside the wafer W are superimposed. The correction hologram pattern may include a pattern for correcting aberration generated by the optical system of the laser processing head 20 .

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 occurring inside the wafer W. FIG.

Note that the hologram pattern 52 and the hologram pattern 54 may be reversed. Also, the hologram pattern 54 may be formed by superimposing a condensing hologram pattern and a correction hologram pattern, similar to the hologram pattern 52 . That is, the hologram patterns 52 and 54 differ from each other in the thickness direction of the wafer W at the respective condensing positions of the first modulated light L1 and the second modulated light L2 condensed inside the wafer W by the condensing lens 38. There is no particular limitation as long as the position can be adjusted.

As described above, in this embodiment, the two first spatial light modulators 46 and the second spatial light modulators 48 are used to separately perform phase modulation of the transmitted light LP and the reflected light LS, thereby performing the first spatial light modulation The amount of light incident on the 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 the distortion and breakage of the first spatial light modulator 46 and the second spatial light modulator 48 due to heat can be suppressed. It is possible to reduce the risk.

In addition, instead of using the two first spatial light modulator 46 and the second spatial light modulator 48 as in the present embodiment, the reflecting surface of one spatial light modulator is divided into two, and the divided areas of this reflecting surface It is also conceivable to perform the phase modulation of the transmitted light LP and the reflected light LS separately for each. However, in this case, the first modulated light L1 and the second modulated light L2 individually condensed for each divided region cannot occupy the same aperture of the condensing lens 18, so the first modulated light L1 In addition, the convergence of the second modulated light L2 is degraded, and the processing quality is also degraded.

On the other hand, in the present embodiment, by using the two first spatial light modulators 46 and the second spatial light modulators 48 to separately perform phase modulation of the transmitted light LP and the reflected light LS, the first modulated light Since L1 and the second modulated light L2 are combined and overlapped, they occupy the aperture of the condenser lens 18 in the same way. As a result, the deterioration of the convergence of the first modulated light L1 and the second modulated light L2 and the deterioration of the processing quality are suppressed.

[Laser processing by laser processing equipment]
Next, the flow of laser processing of the wafer W by the laser processing apparatus 10 configured as described above will be described. First, the correction ring 40 of the condensing lens 38 is used to correct aberrations as required. Next, after the wafer W is held by suction on the stage 11, the controller 50 controls the alignment optical system (not shown) and the stage 11 (stage movement mechanism) to process the line to be cut along the optical axis of the condenser lens 38. Perform alignment to match the starting position.

When the alignment is completed, the controller 50 causes the laser light source 22 to emit the laser light L, the first spatial light modulator 46 to present the hologram pattern 52, and the second spatial light modulator 48 to present the hologram pattern 54. , is started, the stage 11 is driven to move the condenser lens 38 relative to the wafer W in the X direction (processing feed direction).

A laser beam L emitted from the laser light source 22 passes through the beam expander 24 , the mirror 25 and the λ/2 wavelength plate 26 and enters the optical modulator 28 .

The laser beam L incident on the light modulator 28 is incident on the light input/output surface 44a of the polarizing beam splitter 44, and then polarized and separated into the transmitted light LP and the reflected light LS by the light splitting surface 44b. The transmitted light LP is transmitted through the light splitting surface 44b and emitted from the first opposing surface 44c toward the first spatial light modulator 46, and is subjected to the first spatial light modulation while maintaining its polarization plane (polarization direction). incident on the device 46 . As a result, the transmitted light LP is phase-modulated into the first modulated light L1 by the hologram pattern 52 presented on the reflecting surface of the first spatial light modulator 46 . Then, the first modulated light L1 is reflected by the reflecting surface of the first spatial light modulator 46, and while maintaining its plane of polarization, is transmitted through the first opposing surface 44c along the reflection direction RD to be optically split. It is incident on the incident point SB2 of the surface 44b.

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 splitting surface 44b, and is maintained in its plane of polarization (polarization direction). Enters spatial light modulator 48 . Thereby, the reflected light LS is phase-modulated into the second modulated light L2 by the hologram pattern 54 presented on the reflecting surface of the second spatial light modulator 48 . Then, the second modulated light L2 is reflected by the reflecting surface of the second spatial light modulator 48, and while maintaining its plane of polarization, passes through the second opposing surface 44d and reaches the incident point SB2 of the light branching surface 44b. incident on

After being combined at the incident point SB2, the first modulated light L1 and the second modulated light L2 travel along the reflection direction RD and are emitted toward the mirror 30 from the emission point SA2 of the light incidence/emission surface 44a. As described above, in this embodiment, the arrangement of the first spatial light modulator 46 and the second spatial light modulator 48 with respect to the polarization beam splitter 44 is adjusted, and the first modulation is performed from the light incidence/emission surface 44a on which the laser light L is incident. By emitting the light L1 and the second modulated light L2, the arrangement of a Faraday rotator or the like between the polarization beam splitter 44 and the spatial light modulators 46 and 48 can be omitted.

The first modulated light L1 and the second modulated light L2 emitted from the light entrance/exit surface 44a enter the condenser lens 38 via the mirrors 30 and 31, the first lens 32a, the mirrors 33 and 34, and the second lens 32b. do. The first modulated light L1 and the second modulated light L2 are condensed at two different positions inside the wafer W by the condensing lens 38 .

FIG. 6 is a diagram showing a state in which the first modulated light L1 and the second modulated light L2 are separately condensed inside the wafer W. As shown in FIG. FIG. 7 is a diagram showing a state in which the laser processing regions P1 and P2 are formed at the focal point Q1 of the first modulated light L1 and the focal point Q2 of the second modulated light L2 shown in FIG. FIG. 8 is a diagram showing a state in which two rows of laser-processed regions P1 and P2 are formed inside the wafer W along the lines to be cut.

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

Next, under the control of the control unit 50, the stage 11 is indexed and fed in the Y direction by one pitch, and laser processing areas P1 and P2 are similarly formed on the next line to be cut.

Then, when the laser processing regions P1 and P2 are formed along all the planned cutting lines parallel to the X direction, the stage 11 is rotated by 90° under the control of the control unit 50, and is perpendicular to the planned cutting lines. The laser processing regions P1 and P2 are formed on all of the planned cutting lines in the same manner. Thereby, the laser processing regions P1 and P2 are formed along all the planned cutting lines.

After the laser-processed regions P1 and P2 are formed along the planned cutting lines as described above, the back surface of the wafer W is ground using a grinding device (not shown) to obtain the thickness (initial thickness) T1 of the wafer W. is processed to a predetermined thickness (final thickness) T2 (for example, 30 to 50 μm).

After the back surface grinding process, an expanding tape (dicing tape) is attached to the back surface of the wafer W, and after the BG tape attached to the front surface of the wafer W is peeled off, the expanding tape attached to the back surface of the wafer W is tensioned. An expanding step is performed by adding and stretching. As a result, the wafer W is cut starting from the crack extending to the device surface (front surface) side of the wafer W. As shown in FIG. That is, the wafer W is cut along the planned cutting lines and divided into a plurality of chips.

As described above, in the present embodiment, the Faraday rotator can be omitted from the light modulation device 28. Therefore, the labor for adjusting the position of the Faraday rotator as in the conventional art can be saved, and the loss due to the attenuation of light by the Faraday rotator can be prevented. be able to.

[others]
FIG. 9 is a perspective view showing a modification of the light modulation device 28. As shown in FIG. In the above embodiment, the light modulation device 28 is provided with the cube-shaped polarizing beam splitter 44, but as shown in FIG. good too. This polarizing beam splitter 60 has an optical splitting surface 44b similar to that of the polarizing beam splitter 44 of the above-described embodiment. emission of the transmitted light LP to the second spatial light modulator 48, emission of the reflected light LS to the second spatial light modulator 48, synthesis of the first modulated light L1 and the second modulated light L2, and emission of the first modulated light L1 and the second modulated light L2 to the mirror 30 and emitting the second modulated light L2.

In the above embodiment, the laser beam L is polarized and split by the polarization beam splitters 44 and 60. For example, a half mirror is used as the splitting element of the present invention to divide the laser beam L into the first incident light and the second incident light. Separately, the first incident light may be directed to the first spatial light modulator 46 and the second incident light may be directed 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 alignment direction of the liquid crystal is modulated. If it is used, the light utilization efficiency will decrease. For this reason, it is preferable to use the polarizing beam splitters 44 and 60 .

In the above-described embodiment, two-stage processing is performed in which the laser processing regions P1 and P2 are simultaneously formed at two focal points Q1 and Q2 that are different from each other in the thickness direction inside the wafer W, and then the back surface grinding step and the expanding step are performed. However, it is not limited to this. ), laser processing may be performed a plurality of times. At that time, a correction pattern for correcting aberration inside the wafer W (in this case, a pattern in the direction of canceling the correction by the correction ring 40) is added to the hologram patterns 52 and 54 according to the processing depth of the laser processing regions P1 and P2. ) is superimposed, appropriate aberration correction can be performed even for a relatively shallow portion from the back surface of the wafer W. FIG.

FIG. 10 is a top view of a modification of the light modulation device 28 viewed from above. FIG. 11 is a top view of a modification of the light modulating device 28 as viewed from above. It should be noted that the second spatial light modulator 48 is omitted from FIG. 10 in order to avoid complication of the drawing.

In the above embodiment, the reflected light LS is reflected in the direction (Z1 direction) perpendicular to the X1 direction by the light branching surface 44b, but the present invention is not limited to this. For example, as shown in FIGS. 10 and 11, by adjusting the positions and attitudes of the polarizing beam splitter 44 and the spatial light modulators 46 and 48, when viewed from the Y1 direction, the light is reflected by the light splitting surface 44b. LS may be reflected in a reflection direction (corresponding to the first reflection direction of the present invention) inclined with respect to the Z1 direction. In this case as well, the second modulated light L2 reflected by the reflecting surface of the second spatial light modulator 48 enters the light branching surface 44b while maintaining its plane of polarization, and is subjected to the first modulation as in the above embodiment. After being synthesized into the light L1, it travels along the reflection direction RD together with the first modulated light L1.

Although LCOS type SLMs are used as the spatial light modulators 46 and 48 in the above embodiment, they may be MEMS (Micro Electro Mechanical Systems) type SLMs or deformable mirror devices. Moreover, each of the spatial light modulators 46 and 48 is not limited to the reflective type, and may be of the transmissive type. Furthermore, the spatial light modulators 46 and 48 may be of liquid crystal cell type or LCD (Liquid Crystal Display) type.

10 laser processing device 11 stage 18 condenser lens 20 laser processing head 22 laser light source 24 beam expander 25 mirror 26 two-wave plate 28 optical modulator 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 Polarization beam splitter 44a Light input/output surface 44b Light splitting surface 44c First opposing surface 44d Second opposing surface 46 First spatial light modulator 48 Second spatial light modulator 50 Controller 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 Condensing point Q2 Condensing light Point RD Reflection direction W Wafer d Predetermined distance

Claims (6)

In a first direction, a second direction, and a third direction that are orthogonal to each other, incident light incident along the first direction is separated into first incident light and second incident light, and the first incident light a separation element having a light branching surface that transmits 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;
arranged directly opposite to the separation element in the first direction, modulating the first incident light transmitted through the light splitting surface to generate a first modulated light, and converting the first modulated light into the light a first spatial light modulator returning to the branch plane;
arranged directly facing the separation element in the first reflection direction, modulating the second incident light reflected by the light splitting surface to generate a second modulated light, and generating the second modulated light a second spatial light modulator returned to the light branching surface;
with
The first spatial light modulator irradiates the first modulated light with respect to the incident light in a reflection direction parallel to a plane perpendicular to the second direction and when viewed from the second direction. reflected in a second slanted reflection direction to be incident on the light branching surface;
the second spatial light modulator reflects the second modulated light toward a point of incidence of the first modulated light on 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 directs the light in the second reflection direction. Emitting light modulator. the separating element is a cube-shaped polarizing beam splitter,
2. The optical modulator according to claim 1, wherein, in the polarization beam splitter, a plane on which the incident light is incident and a plane from which the first modulated light and the second modulated light from the light splitting plane are emitted are the same. Device. 3. The optical modulation device according to claim 2, wherein the polarizing beam splitter splits the incident light into P-polarized light as the first incident light and S-polarized light as the second incident light. The polarization directions of the P-polarized light and the first modulated light are maintained between the light branching surface and the first spatial light modulator, and the polarization directions of the P-polarized light and the first modulated light are maintained between the light branching surface and the second spatial light modulator. 4. The optical modulation device according to claim 3, wherein the polarization directions of the S-polarized light and the second modulated light are maintained. The distance until the first incident light transmitted through the light branching surface reaches the first spatial light modulator, and the second incident light reflected by the light branching surface reaches the second spatial light modulator. 5. The optical modulation device according to any one of claims 1 to 4, wherein the reaching distance and the distance are the same. A laser processing apparatus for forming a laser processing area inside a workpiece along a planned cutting line of the workpiece by irradiating a laser beam with a focal point aligned with the inside of the workpiece, ,
a laser light source that outputs the laser light;
The laser light output from the laser light source is incident as incident light, the incident light is separated into first incident light and second incident light, and the first modulated light obtained by modulating the first incident light and the first modulated light are separated. 6. The light modulation device according to any one of claims 1 to 5, wherein a second modulated light is generated by modulating two incident lights, and the first modulated light and the second modulated light are synthesized and output;
a condensing lens condensing the first modulated light and the second modulated light inside the workpiece;
a relative movement unit that relatively moves the condenser lens along the line to cut with respect to the workpiece;
controlling the first spatial light modulator and the second spatial light modulator to converge the first modulated light into the inside of the workpiece by the condensing lens and the second modulation; a control unit that forms light condensing points at positions that are different from each other in the thickness direction of the workpiece and are equal to each other in the relative movement direction of the condensing lens;
A laser processing device comprising:

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