WO2022249541A1 - レーザ加工装置及びレーザ加工方法 - Google Patents
レーザ加工装置及びレーザ加工方法 Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
- H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/50—Working by transmitting the laser beam through or within the workpiece
- B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/0006—Working by laser beam, e.g. welding, cutting or boring taking account of the properties of the material involved
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/03—Observing, e.g. monitoring, the workpiece
- B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
- B23K26/044—Seam tracking
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
- B23K26/046—Automatically focusing the laser beam
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
- B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/073—Shaping the laser spot
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/08—Devices involving relative movement between laser beam and workpiece
- B23K26/083—Devices involving movement of the workpiece in at least one axial direction
- B23K26/0853—Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
- B23K26/0861—Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane in at least in three axial directions
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/67005—Apparatus not specifically provided for elsewhere
- H01L21/67011—Apparatus for manufacture or treatment
- H01L21/67092—Apparatus for mechanical treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/36—Electric or electronic devices
- B23K2101/40—Semiconductor devices
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
- B23K2103/56—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26 semiconducting
Definitions
- One aspect of the present invention relates to a laser processing apparatus and a laser processing method.
- a laser beam is applied to the wafer from the other surface side of the semiconductor substrate in order to cut the wafer including the semiconductor substrate and the functional element layer formed on one surface of the semiconductor substrate along a plurality of lines.
- a plurality of rows of modified regions for division (cutting) are formed inside a semiconductor substrate along each of a plurality of lines (see, for example, Patent Document 1).
- a semiconductor chip having high bending strength can be produced by grinding the modified region after processing for forming the modified region.
- the modified regions for division may be sequentially formed along a plurality of lines that intersect each other.
- the warping of the wafer occurs due to the formation of the modified region along the line (first line) that is first irradiated with the laser beam, and the warping of the wafer causes the intersecting line that is later irradiated with the laser beam.
- (Second line) processing accuracy may be degraded. That is, when processing of a line (second line) to be irradiated with laser light is performed later in a state in which the warp occurs, autofocus or the like for adjusting the focused spot of the laser light during processing of the second line is performed. It becomes difficult to ensure the accuracy of the modification, and there is a possibility that the formation of the modified region or the like cannot be performed appropriately.
- One aspect of the present invention has been made in view of the above circumstances, and an object of the present invention is to appropriately form a modified region for dividing an object and improve laser processing accuracy.
- a laser processing apparatus includes a laser irradiation unit that irradiates a laser beam onto an object using a first surface of the object including a first surface and a second surface opposite to the first surface as an incident surface. and a control unit, wherein the control unit relatively moves the condensed spot of the laser light along each of the plurality of first lines extending in the first direction along the plane of incidence, by irradiating the laser light First control for controlling the laser irradiation part so that a first modified region for division is formed inside the object and a crack extends from the first modified region in the direction of the second surface, and after the first control, While relatively moving the condensed spot of the laser light along each of a plurality of second lines that intersect the first direction and extend in the second direction along the plane of incidence, the object is divided inside by irradiation with the laser light.
- a plurality of third modified regions for suppressing warpage are formed inside the article, and the cracks extending from the third modified regions reach the first surface and are formed without being continuous with the cracks extending from the first modified region. and a third control for controlling the laser irradiation unit.
- the first modified region for division is formed along each of the plurality of first lines extending in the first direction along the plane of incidence by the irradiation of the laser beam.
- a crack extending in the direction of the second surface is formed from the modified region, and then, along each of a plurality of second lines that intersect the first direction and extend in the second direction along the plane of incidence, by irradiation with laser light.
- a splitting second modified region is formed and a crack extending from the second modified region in the second plane direction is formed.
- the formation of the first modified region along the line (first line) that is first irradiated with the laser light causes the target to be changed.
- An object warps, and the effect of the warp of the object may reduce the processing accuracy of a line (second line) to be irradiated with a laser beam later.
- the warp of the object is caused by the formation of the first modified region and the formation of cracks extending from the first modified region in the direction of the second surface of the object (here, the direction in which the cracks mainly extend).
- a plurality of third warp-suppressing warp-suppressing laser beams are irradiated to the inside of the object by laser light irradiation.
- a modified region is formed such that cracks extending from the third modified region reach the first surface and are not continuous with cracks extending from the first modified region.
- control unit may control the laser irradiation unit so that the third modified region is formed at a position different from the formation position of the first modified region in the second direction.
- the control unit controls the laser irradiation unit so that the third modified region is formed in the middle position in the second direction between the formation positions of the two first lines that are adjacent in the second direction.
- the laser irradiation unit has a spatial light modulator that modulates the laser light according to the set modulation pattern, and the control unit determines, in the third control, the formation position of the first modified region in the second direction and The modulation pattern may be set such that the third modified regions are formed at different positions. In this way, by adjusting the formation position of the third modified region by setting the modulation pattern of the spatial light modulator, the processing time is shortened compared to the case where the formation position of the modified region is changed by stage operation. can be shortened.
- the laser irradiation unit has a spatial light modulator that modulates the laser light according to the set modulation pattern, and the control unit performs the first modification in at least one of the first control and the third control.
- the modulation pattern may be set such that the position of the first surface side end of the crack extending from the region is different from the position of the second surface side end of the crack extending from the third modified region. In this way, by adjusting the position of the ends of the cracks extending from the modified region by setting the modulation pattern of the spatial light modulator, the positions of the ends of the cracks are appropriately adjusted, and the cracks are connected to each other. It is possible to more preferably suppress the occurrence of unintended cracks in the object.
- control unit may control the laser irradiation unit so that the crack extending from the third modified region is shorter than the crack extending from the first modified region.
- the cracks extending from the third modified region for suppressing warpage are not cracks that are desired to contribute to splitting, so the cracks are made continuous by shortening them. It is possible to more preferably suppress the occurrence of unintended cracks in the object.
- the control unit may control the laser irradiation unit so that the third modified regions are formed in a larger number than the first modified regions in the second direction.
- the crack extending from the third modified region is shortened, there is a possibility that the effect of suppressing warpage will not be sufficiently exhibited.
- the cracks extending from the large number of third modified regions have a sufficient effect of suppressing warpage. It is possible to suppress the occurrence of unintended cracks in the object while exerting the force.
- the control unit compares the third modified region at the central portion of the object in the second direction with the third modified region at both ends, and determines that the third modified region at both ends is the third modified region in the second direction.
- the third modified region is formed so as to satisfy at least one of the fact that the number of modified regions is increased and the length of cracks extending from the third modified region is longer at both ends.
- the laser irradiation unit may be controlled. Warpage of the object due to the formation of the first modified region becomes more pronounced toward both end portions in the second direction.
- the control unit causes the laser irradiation unit to alternately perform formation of the first modified region related to any first line in the first control and formation of the third modified region in the third control. may be controlled. Warping of the object due to the formation of the first modified regions progresses gradually as the formation of the first modified regions related to the plurality of first lines progresses. Therefore, the influence of the machining of the first line, which is processed first, affects the machining of the first line, which is processed later. That is, in the processing of the first line in which processing is performed relatively late among the plurality of first lines, the first modified region is formed in a state in which the object is warped.
- the formation of the first modified region for division and the formation of the third modified region for suppressing warpage are alternately performed, so that the influence of the previously performed processing of the first line is carried out later. It is possible to suppress the influence on the processing of the first line to be performed, and to appropriately form the first modified region for dividing the object.
- the control unit forms a plurality of fourth modified regions for suppressing warpage inside the object by irradiating the laser beam, and the cracks extending from the fourth modified regions reach the first surface and the second modified region. It is configured to further execute a fourth control for controlling the laser irradiation unit so that the crack extending from the region is formed discontinuously, and the second modification related to any second line in the second control is configured to be performed.
- the laser irradiation unit may be controlled so as to alternately form the modified region and the fourth modified region in the fourth control. In this way, the formation of the second modified region related to the second line and the formation of the fourth modified region for suppressing warpage are alternately performed, thereby reducing the previously performed processing of the second line.
- the second modified region for division can be appropriately formed on the object by suppressing the influence on the processing of the second line which is performed later.
- a laser processing method includes irradiating a laser beam on an object with a first surface of the object including a first surface and a second surface opposite to the first surface as an incident surface, A laser processing method for performing laser processing of the object by irradiating the laser beam while relatively moving the focused spot of the laser beam along each of a plurality of first lines extending in the first direction along the incident surface a first step of forming a first modified region for division inside the object and forming a crack extending in a second plane direction from the first modified region; and after the first step, crossing the first direction.
- the third modified region may be formed at a position different from the formation position of the first modified region in the second direction.
- the third modified region may be formed at an intermediate position in the second direction between respective formation positions of two first lines adjacent in the second direction.
- the third modified region may be formed at a position different from the formation position of the first modified region in the second direction by setting the modulation pattern of the spatial light modulator that modulates the laser light. .
- the position of the end of the crack extending from the first modified region on the first surface side is determined by setting the modulation pattern of the spatial light modulator that modulates the laser beam. and the position of the end of the crack extending from the third modified region on the second surface side.
- the third modified region may be formed so that the crack extending from the third modified region is shorter than the crack extending from the first modified region.
- more third modified regions than the first modified regions may be formed in the second direction.
- the both ends are the third modified region in the second direction.
- the third modified regions may be formed so as to satisfy at least one of the requirement that the number of cracks increases and that the cracks extending from the third modified regions are longer at both ends.
- the formation of the first modified region related to any first line in the first step and the formation of the third modified region in the third step may be alternately performed.
- the laser processing method forms a plurality of fourth modified regions for suppressing warpage inside the object by irradiating the laser beam, and reaches the first surface from the fourth modified region and the second modified region Further comprising a fourth step of forming a crack discontinuous to the crack extending from, forming a second modified region related to any second line in the second step, and forming a fourth modified region in the fourth step may be performed alternately.
- FIG. 1 is a plan view of a wafer in one embodiment
- FIG. 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2
- FIG. FIG. 2 is a configuration diagram of a laser irradiation unit shown in FIG. 1
- Figure 5 shows the 4f lens unit shown in Figure 4
- Figure 5 shows the spatial light modulator shown in Figure 4
- 2 is a configuration diagram of an imaging unit for inspection shown in FIG. 1
- FIG. 2 is a configuration diagram of an imaging unit for alignment correction shown in FIG. 1.
- FIG. It is a figure explaining the generation
- FIG. 10 is a diagram showing warpage in the CH2 processing progress direction after CH1 processing, for each formation mode of a modified region for suppressing warpage. It is a figure explaining the processing position shift by modulation pattern setting of a spatial light modulator.
- the laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3, a plurality of imaging units 4, 5, 6, a driving unit 9, a control unit 8, a display 150 (display unit ) and
- the laser processing apparatus 1 is an apparatus that forms a modified region 12 on an object 11 by irradiating the object 11 with a laser beam L. As shown in FIG.
- the stage 2 supports the object 11 by, for example, sucking a film attached to the object 11 .
- the stage 2 is movable along each of the X and Y directions, and is rotatable about an axis parallel to the Z direction. Note that the X direction and the Y direction are the first horizontal direction and the second horizontal direction perpendicular to each other, and the Z direction is the vertical direction.
- the laser irradiation unit 3 condenses a laser beam L having transparency to the object 11 and irradiates the object 11 with the laser beam L.
- the laser beam L is focused inside the object 11 supported by the stage 2, the laser beam L is particularly absorbed in the part corresponding to the focused spot C of the laser beam L, and the inside of the object 11 is reformed. A textured region 12 is formed.
- the modified region 12 is a region that differs in density, refractive index, mechanical strength, and other physical properties from the surrounding unmodified regions.
- the modified region 12 includes, for example, a melting process region, a crack region, a dielectric breakdown region, a refractive index change region, and the like.
- the modified region 12 has a characteristic that cracks tend to extend from the modified region 12 to the incident side of the laser light L and the opposite side. Such properties of the modified region 12 are used for cutting the object 11 .
- the plurality of modified spots 12s are aligned along the X direction. formed in rows.
- One modified spot 12s is formed by one pulse of laser light L irradiation.
- a row of modified regions 12 is a set of a plurality of modified spots 12s arranged in a row. Adjacent modified spots 12 s may be connected to each other or separated from each other depending on the relative moving speed of the focused spot C with respect to the object 11 and the repetition frequency of the laser beam L.
- the imaging unit 4 is configured to be capable of imaging the modified region 12 formed in the object 11 and the tips of cracks extending from the modified region 12 . Although the imaging unit 4 is not an essential component, the laser processing apparatus 1 has the imaging unit 4 in this embodiment.
- the imaging unit 5 and the imaging unit 6 image the object 11 supported by the stage 2 with light passing through the object 11 under the control of the control unit 8 . Images obtained by imaging by the imaging units 5 and 6 are used for alignment of the irradiation position of the laser light L as an example. Note that the imaging units 5 and 6 are not essential components, but in the present embodiment, the laser processing apparatus 1 has the imaging units 5 and 6 .
- the drive unit 9 supports the laser irradiation unit 3 and multiple imaging units 4, 5, 6.
- the driving unit 9 moves the laser irradiation unit 3 and the plurality of imaging units 4, 5, 6 along the Z direction.
- the control unit 8 controls the operations of the stage 2, the laser irradiation unit 3, the plurality of imaging units 4, 5, 6, and the driving unit 9.
- the control unit 8 is configured as a computer device including a processor, memory, storage, communication device, and the like.
- the processor executes software (program) read into the memory or the like, and controls reading and writing of data in the memory and storage, and communication by the communication device.
- the display 150 has a function as an input unit for accepting input of information from the user and a function as a display unit for displaying information to the user.
- the object 11 of this embodiment is a wafer 20, as shown in FIGS.
- the wafer 20 includes a semiconductor substrate 21 and functional element layers 22 .
- the wafer 20 is described as having the functional element layer 22, but the wafer 20 may or may not have the functional element layer 22, and may be a bare wafer.
- the semiconductor substrate 21 has a front surface 21a and a back surface 21b.
- the semiconductor substrate 21 is, for example, a silicon substrate.
- the functional element layer 22 is formed on the surface 21 a of the semiconductor substrate 21 .
- the functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along the surface 21a.
- the functional element 22a is, for example, a light receiving element such as a photodiode, a light emitting element such as a laser diode, a circuit element such as a memory, or the like.
- the functional element 22a may be configured three-dimensionally by stacking a plurality of layers.
- the semiconductor substrate 21 is provided with the notch 21c indicating the crystal orientation, an orientation flat may be provided instead of the notch 21c.
- the wafer 20 is cut along each of the plurality of lines 15 into functional elements 22a.
- the plurality of lines 15 pass through each of the plurality of functional elements 22a when viewed from the thickness direction of the wafer 20 . More specifically, line 15 passes through the center of street region 23 (the center in the width direction) when viewed from the thickness direction of wafer 20 .
- the street region 23 extends between adjacent functional elements 22 a in the functional element layer 22 .
- the plurality of functional elements 22a are arranged in a matrix along the surface 21a, and the plurality of lines 15 are set in a lattice.
- a plurality of lines 15 (first lines) extending in the X direction and a plurality of lines 15 (second lines) extending in the Y direction are set.
- the line 15 is a virtual line, it may be an actually drawn line.
- the laser irradiation unit 3 has a light source 31 (laser irradiation section), a spatial light modulator 7, a condenser lens 33, and a 4f lens unit .
- the light source 31 outputs laser light L by, for example, a pulse oscillation method.
- the spatial light modulator 7 modulates the laser light L output from the light source 31 .
- the spatial light modulator 7 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator).
- a condenser lens 33 collects the laser light L modulated by the spatial light modulator 7 . Note that the condenser lens 33 may be a correction ring lens.
- the laser irradiation unit 3 irradiates the wafer 20 with the laser light L from the rear surface 21 b side of the semiconductor substrate 21 along each of the plurality of lines 15 , thereby causing the semiconductor wafer 20 to be irradiated along each of the plurality of lines 15 .
- a modified region 12 (for example, two rows of modified regions 12 a and 12 b ) is formed inside the substrate 21 .
- the modified region 12a is the modified region closest to the surface 21a among the two rows of modified regions 12a and 12b.
- the modified region 12b is the modified region closest to the modified region 12a and the modified region closest to the rear surface 21b.
- the two rows of modified regions 12a and 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20.
- the two rows of modified regions 12 a and 12 b are formed by relatively moving the two focused spots C 1 and C 2 along the line 15 with respect to the semiconductor substrate 21 .
- the laser beam L is modulated by the spatial light modulator 7 so that the focused spot C2 is located behind the focused spot C1 in the traveling direction and on the incident side of the laser beam L, for example.
- the formation of the modified region it may be single focus or multifocal, and even if one row of modified regions is formed on one planned cutting line (one pass), multiple rows of modified regions may be formed.
- a modified region may be formed (multiple passes).
- the 4f lens unit 34 has a pair of lenses 34A and 34B arranged on the optical path of the laser light L from the spatial light modulator 7 to the condenser lens 33.
- a pair of lenses 34A and 34B constitute a double-telecentric optical system in which the modulation surface 7a of the spatial light modulator 7 and the entrance pupil surface (pupil surface) 33a of the condenser lens 33 are in an imaging relationship.
- the image of the laser light L on the modulation surface 7a of the spatial light modulator 7 (the image of the laser light L modulated by the spatial light modulator 7) is transferred to the entrance pupil plane 33a of the condenser lens 33 ( image).
- Fs in the figure indicates the Fourier plane.
- the spatial light modulator 7 is a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator).
- LCOS Liquid Crystal on Silicon
- SLM Spatial Light Modulator
- a drive circuit layer 72, a pixel electrode layer 73, a reflective film 74, an alignment film 75, a liquid crystal layer 76, an alignment film 77, a transparent conductive film 78 and a transparent substrate 79 are arranged on a semiconductor substrate 71 in this order. It is configured by being laminated with
- the semiconductor substrate 71 is, for example, a silicon substrate.
- the drive circuit layer 72 constitutes an active matrix circuit on the semiconductor substrate 71 .
- the pixel electrode layer 73 includes a plurality of pixel electrodes 73 a arranged in a matrix along the surface of the semiconductor substrate 71 .
- Each pixel electrode 73a is made of, for example, a metal material such as aluminum. A voltage is applied by the drive circuit layer 72 to each pixel electrode 73a.
- the reflective film 74 is, for example, a dielectric multilayer film.
- the alignment film 75 is provided on the surface of the liquid crystal layer 76 on the reflecting film 74 side, and the alignment film 77 is provided on the surface of the liquid crystal layer 76 opposite to the reflecting film 74 .
- Each of the alignment films 75 and 77 is made of, for example, a polymer material such as polyimide, and the contact surface of each of the alignment films 75 and 77 with the liquid crystal layer 76 is subjected to, for example, a rubbing treatment.
- the alignment films 75 and 77 align the liquid crystal molecules 76a contained in the liquid crystal layer 76 in a certain direction.
- the transparent conductive film 78 is provided on the surface of the transparent substrate 79 on the alignment film 77 side, and faces the pixel electrode layer 73 with the liquid crystal layer 76 and the like interposed therebetween.
- the transparent substrate 79 is, for example, a glass substrate.
- the transparent conductive film 78 is made of, for example, a light-transmissive and conductive material such as ITO. The transparent substrate 79 and the transparent conductive film 78 allow the laser light L to pass therethrough.
- the spatial light modulator 7 when a signal indicating a modulation pattern is input from the control section 8 to the driving circuit layer 72, a voltage corresponding to the signal is applied to each pixel electrode 73a. An electric field is formed between the pixel electrode 73 a and the transparent conductive film 78 .
- the electric field is formed, in the liquid crystal layer 76, the arrangement direction of the liquid crystal molecules 76a changes in each region corresponding to each pixel electrode 73a, and the refractive index changes in each region corresponding to each pixel electrode 73a.
- This state is the state where the modulation pattern is displayed on the liquid crystal layer 76 .
- the modulation pattern is for modulating the laser light L.
- the laser light L is incident on the liquid crystal layer 76 from the outside through the transparent substrate 79 and the transparent conductive film 78, is reflected by the reflective film 74, and is reflected by the liquid crystal layer.
- the laser light L is modulated according to the modulation pattern displayed on the liquid crystal layer 76 .
- the spatial light modulator 7 by appropriately setting the modulation pattern displayed on the liquid crystal layer 76, the laser light L can be modulated (for example, the intensity, amplitude, phase, polarization, etc. of the laser light L can be modulated). ) is possible.
- the modulating surface 7a shown in FIG. 5 is, for example, a liquid crystal layer 76. As shown in FIG.
- the laser light L output from the light source 31 is incident on the condenser lens 33 via the spatial light modulator 7 and the 4f lens unit 34, and is condensed into the object 11 by the condenser lens 33.
- a modified region 12 and a crack extending from the modified region 12 are formed in the object 11 at the focused spot C.
- the control unit 8 controls the stage 2 to move the focused spot C relative to the wafer 20, thereby forming the modified region 12 and the crack along the movement direction of the focused spot C. It will happen.
- the laser irradiation unit 3 further has an AF (autofocus) unit 91 (measurement section, measurement unit).
- the AF unit 91 places the focused spot of the laser beam L at a position at a predetermined distance from the back surface 21b of the wafer 20 even when there is displacement (undulation) in the thickness direction (Z direction) on the back surface 21b, which is the incident surface of the wafer 20.
- This is a configuration for matching with high accuracy.
- the AF unit 91 measures the displacement on the back surface 21b (surface to be measured) in order to adjust the focused spot of the laser light L irradiated onto the wafer 20 by the light source 31 .
- the AF unit 91 irradiates the back surface 21b with the AF laser beam LA (measurement light), and receives and detects the reflected light of the AF laser beam LA on the back surface 21b, thereby determining the displacement of the back surface 21b. Acquire data (measure displacement).
- the AF unit 91 has an AF light source 91a that outputs an AF laser beam LA, and a displacement detector 91b that receives and detects the reflected light of the AF laser beam LA.
- the AF laser beam LA emitted from the AF light source 91a is reflected by the AF dichroic mirror 92, passes through the condenser lens 33, and is irradiated onto the rear surface 21b. In this way, the AF laser beam LA and the laser beam L are irradiated onto the wafer 20 from the same condenser lens 33 (they are coaxial).
- the reflected light of the AF laser beam LA on the back surface 21b is reflected by the AF dichroic mirror 92 and detected by the displacement detection section 91b.
- the displacement detector 91b is configured including, for example, a four-part split photodiode.
- the 4-split photodiode is configured to split and receive the condensed image of the reflected light of the AF laser beam LA, and output a voltage value corresponding to each light amount. Since astigmatism is added to the reflected light of the AF laser beam LA, the focused image depends on the position of the rear surface 21b of the wafer 20 with respect to the focused spot of the AF laser beam LA.
- the shape vertical, perfect circle, horizontal
- the focused image changes according to the position of the rear surface 21b of the wafer 20 with respect to the focused spot. Therefore, the voltage value output from the quadrant photodiode changes according to the position of the rear surface 21b of the wafer 20 with respect to the focused spot of the AF laser beam LA.
- the voltage value output from the four-divided photodiode of the displacement detection section 91b is input to the control section 8.
- the control unit 8 calculates a calculated value as position information regarding the position of the rear surface 21b of the wafer 20 with respect to the condensed spot of the AF laser beam LA, based on the voltage value output from the four-divided photodiode of the displacement detection unit 91b. .
- the control unit 8 controls the drive unit 9 (actuator) based on the calculated value so that the position of the focused spot of the laser light L emitted from the light source 31 is at a constant depth from the back surface 21b.
- the position of the condenser lens 33 is finely adjusted in the vertical direction.
- control based on the distance measurement result by the AF unit 91 is performed together with the laser processing by the laser beam L (prior to the laser processing).
- the condensed spot of the laser beam L can be accurately aligned at a position at a predetermined distance from the rear surface 21b.
- the imaging unit 4 (imaging section) has a light source 41 , a mirror 42 , an objective lens 43 , and a light detection section 44 .
- the imaging unit 4 images the wafer 20 .
- the light source 41 outputs light I ⁇ b>1 having transparency to the semiconductor substrate 21 .
- the light source 41 is composed of, for example, a halogen lamp and a filter, and outputs light I1 in the near-infrared region.
- the light I1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and is irradiated onto the wafer 20 from the rear surface 21b side of the semiconductor substrate 21.
- FIG. At this time, the stage 2 supports the wafer 20 on which the two rows of modified regions 12a and 12b are formed as described above.
- the objective lens 43 allows the light I1 reflected by the surface 21a of the semiconductor substrate 21 to pass therethrough. That is, the objective lens 43 allows the light I1 propagated through the semiconductor substrate 21 to pass therethrough.
- the numerical aperture (NA) of the objective lens 43 is, for example, 0.45 or more.
- the objective lens 43 has a correction ring 43a.
- the correction ring 43a corrects the aberration occurring in the light I1 within the semiconductor substrate 21 by adjusting the mutual distances of the plurality of lenses constituting the objective lens 43, for example.
- the means for correcting aberration is not limited to the correction ring 43a, and other correction means such as a spatial light modulator may be used.
- the photodetector 44 detects the light I1 transmitted through the objective lens 43 and the mirror 42 .
- the photodetector 44 is composed of, for example, an InGaAs camera, and detects light I1 in the near-infrared region.
- the means for detecting (imaging) the light I1 in the near-infrared region is not limited to the InGaAs camera, and other imaging means such as a transmission confocal microscope may be used as long as they perform transmission imaging.
- the imaging unit 4 can image the two rows of modified regions 12a and 12b and the tips of the plurality of cracks 14a, 14b, 14c and 14d.
- the crack 14a is a crack extending from the modified region 12a toward the surface 21a.
- Crack 14b is a crack extending from modified region 12a toward back surface 21b.
- the crack 14c is a crack extending from the modified region 12b toward the surface 21a.
- the crack 14d is a crack extending from the modified region 12b toward the rear surface 21b.
- the imaging unit 5 has a light source 51, a mirror 52, a lens 53, and a photodetector .
- the light source 51 outputs light I ⁇ b>2 that is transmissive to the semiconductor substrate 21 .
- the light source 51 is composed of, for example, a halogen lamp and a filter, and outputs light I2 in the near-infrared region.
- the light source 51 may be shared with the light source 41 of the imaging unit 4 .
- the light I2 output from the light source 51 is reflected by the mirror 52, passes through the lens 53, and is irradiated onto the wafer 20 from the rear surface 21b side of the semiconductor substrate 21.
- the lens 53 allows the light I2 reflected by the surface 21a of the semiconductor substrate 21 to pass therethrough. That is, the lens 53 allows the light I2 propagated through the semiconductor substrate 21 to pass therethrough.
- the numerical aperture of lens 53 is 0.3 or less. That is, the numerical aperture of the objective lens 43 of the imaging unit 4 is larger than the numerical aperture of the lens 53 .
- the photodetector 54 detects the light I2 that has passed through the lens 53 and the mirror 52 .
- the photodetector 54 is composed of, for example, an InGaAs camera, and detects light I2 in the near-infrared region.
- the light detection unit 54 may be an SD camera, or may detect non-transmissive light.
- FIG. Imaging unit 6 has a configuration similar to that of imaging unit 5, except that lens 53 has a lower magnification (e.g., 6x in imaging unit 5 and 1.5x in imaging unit 6). , is used for alignment in the same manner as the imaging unit 5 .
- the back surface 21b of the wafer 20 (object) including the back surface 21b (first surface) and the surface 21a (second surface) opposite to the back surface 21b is used as an incident surface.
- This laser processing method includes a first step and a second step performed after the first step. As described above, the wafer 20 is cut along each of the plurality of lines 15 into functional elements 22a.
- first step laser irradiation is performed along each of a plurality of lines 15 (first lines, see FIG. 2) extending in the X direction (first direction) along the back surface 21b.
- second step laser irradiation is performed along each of a plurality of lines 15 (second lines, see FIG. 2) extending in the Y direction (second direction) along the back surface 21b.
- the processing in the first step may be described as CH1 processing
- the processing in the second step may be described as CH2 processing.
- the wafer 20 is irradiated with the laser beam L while relatively moving the focused spot of the laser beam L along each of the plurality of lines 15 extending in the X direction.
- a dividing modified region 12 (first modified region) is formed in the interior of the , and a crack 14 extending from the modified region 12 in the direction of the surface 21a is formed.
- the controller 8 controls the laser irradiation unit 3 so that such a crack 14 is formed (first control).
- the modified region 12 is formed so that the crack 14 reaches the surface 21a in a so-called BHC (bottom side half-cut) state.
- the modified region 12 may be formed so as to be in a so-called ST (Stealth) state in which the crack 14 does not reach the surface 21a.
- ST Stepth
- the inside of the wafer 20 is irradiated with the laser beam L while the focused spot of the laser beam L is relatively moved along each of the plurality of lines 15 extending in the Y direction.
- a modified region 12 (second modified region) for division is formed in the second modified region 12, and a crack 14 extending from the modified region 12 toward the surface 21a is formed.
- the controller 8 controls the laser irradiation unit 3 so that such a crack 14 is formed (second control).
- the modified region 12 is formed such that the crack 14 reaches the surface 21a and is in a so-called BHC state.
- the modified region 12 may be formed so as to be in a so-called ST state in which the crack 14 does not reach the surface 21a.
- FIG. 9 is a diagram for explaining the principle of warping of the wafer 20.
- the warp of the wafer 20 is caused by the formation of the modified region 12 and the formation of the crack 14 extending from the modified region 12 in the direction of the surface 21a. It is caused by the concentration of stress on the surface 21a) reached by the crack 14.
- FIG. 9 In the example shown in FIG.
- modified regions 12 are sequentially formed in a plurality of lines 15 (first lines) extending in the X direction and adjacent to each other in the Y direction in CH1 processing, and cracks 14 are formed in the direction of the surface 21a. Due to the extension, the amount of warp is increased especially at both ends of the wafer 20 in the Y direction. That is, the CH1 machining causes warping in the Y direction, which is the machining advancing direction in the CH2 machining. Such warpage of the wafer 20 becomes particularly noticeable when the wafer 20 is a microchip or when a relatively large crack 14 is formed in the wafer 20 .
- FIG. 10 is a diagram showing the warp in the CH2 processing progress direction after CH1 processing and before CH2 processing.
- the horizontal axis indicates the processing progress direction of CH2 (the width direction of the wafer 20), and the vertical axis indicates the amount of displacement indicated by the voltage value.
- a voltage value of 1 V on the vertical axis corresponds to, for example, a displacement amount of about 8 ⁇ m.
- FIG. 11 is a diagram for explaining AF (autofocus) follow-up failure during CH2 processing after CH1 processing.
- the AF unit 91 detects the reflected light from the back surface 21b to acquire the displacement data of the back surface 21b.
- the amount of warpage at the wafer edge portion is large as described above, and AF tracking failure occurs, and even the AF unit 91 may not be able to acquire accurate displacement data of the back surface 21b.
- the accuracy of forming the modified region 12 (second modified region) during CH2 processing may deteriorate.
- the third step for suppressing warpage is performed before the second step.
- a modified region 12 (third modified region) for suppressing warpage is formed inside the wafer 20 by irradiating the laser beam L, and from the modified region 12 on the incident surface, A crack 114 (see FIG. 12) that reaches a certain back surface 21b and is not continuous with the crack 14 extending from the modified region 12 for division is formed.
- the controller 8 controls that a plurality of modified regions 12 for suppressing warpage are formed by the irradiation of the laser beam L, the cracks 114 extending from the modified regions 12 reach the back surface 21b, and the modified regions 12 for splitting are formed.
- the laser irradiation unit 3 is controlled so that the crack 14 extending from is formed discontinuously (third control).
- FIG. 12 is a diagram explaining formation of the modified region 12 for suppressing warpage.
- a modified region 12 for division is formed in CH1 processing, and a crack 14 is formed from the modified region 12 in the direction of the surface 21a.
- the modified region 12 for division in CH1 processing and the crack 14 extending from the modified region 12 are formed, for example, in the center of the street region 23 where the line 15 (first line) extending in the X direction is formed.
- the third step as shown in FIG.
- the modified region 12 for suppressing warpage (the modified region 12 related to the crack 114) is formed at the position where the crack 114 is located. That is, in the third control, the control unit 8 controls the laser irradiation unit 3 so that the modified region 12 for suppressing warpage is formed at a position different from the formation position of the modified region 12 for division in the Y direction. do.
- the modified region 12 for suppressing warpage is formed so that the crack 114 reaches the back surface 21b, which is a so-called HC (half-cut) state.
- warpage originating from the warp-suppressing modified region 12 is generated, and warping originating from the dividing modified region 12 can be further reduced (details will be described later).
- the method of shifting the position of the modified region 12 for division and the position of the modified region 12 for suppressing warpage is not limited, for example, the operation of stage 2, or It is implemented by the Y shift pattern of the spatial light modulator 7 (details will be described later).
- the modified region 12 for suppressing warpage may be formed in the Y-direction intermediate position between the formation positions of the two lines 15 (first lines) adjacent in the Y-direction.
- the control unit 8 forms the modified region 12 for suppressing warpage at the intermediate position in the Y direction between the formation positions of the two lines 15 (first line) adjacent in the Y direction.
- the laser irradiation unit 3 is controlled as follows. As described above, in the line 15 (first line) adjacent in the Y direction and extending in the X direction, the modified region 12 for division and the crack 14 extending from the modified region 12 are formed in CH1 processing.
- FIG. 13 is a diagram illustrating formation of the modified region 12 for suppressing warpage in the vicinity of the center position of the chip.
- the modified region 12 for suppressing warpage is formed at the center position of the chip.
- the separation distance from the extending cracks 14 can be maximized and the risk of wafer cracking due to continuation of these cracks can be reduced.
- the modified region for suppressing warpage is formed on the active area.
- the distance from the condensed spot to the functional element 22a in the third step can be made sufficiently long, so the functional element 22a is damaged by the escaped light associated with the laser irradiation in the third step. never.
- the modified region 12 for suppressing warpage is removed in subsequent grinding, the modified region 12 for suppressing warpage is formed on the active area in the third step. Even if it is, it does not affect the chipped semiconductor device.
- the crack 114 may be formed so that the crack 114 extending from the modified region 12 for suppressing warpage is shorter than the crack 14 extending from the modified region 12 for splitting. Furthermore, in the third step, while shortening the length of the crack 114 as described above, a larger number of modified regions 12 for suppressing warpage than the modified regions 12 for splitting are formed in the second direction.
- FIG. 14 is a diagram illustrating formation of modified regions for suppressing warpage by multi-point branching.
- a modulation pattern Multi-point branch processing using a multi-point branch pattern
- the control unit 8 controls the modulation pattern so that the crack 114 is shorter than the crack 14 and more modified regions 12 for suppressing warpage than the modified regions 12 for division are formed.
- (multipoint branch pattern) is set in the spatial light modulator 7 .
- a large number of modified regions 12 for suppressing warpage are formed at once by multi-point branching processing of the spatial light modulator 7 .
- the vertical crack 114 can be shortened (the risk of wafer cracking can be reduced). According to such multi-point branching processing using the modulation pattern (multi-point branching pattern) set in the spatial light modulator 7, it is possible to reduce the risk of cracking the wafer without reducing the takt time.
- the method of making the crack 114 shorter than the crack 14 and forming a larger number of modified regions 12 for suppressing warpage than the modified regions 12 for division is multipoint branching processing by the spatial light modulator 7.
- the table may be fed and processed line by line.
- the modified region 12 for suppressing warpage is formed so as to intensively suppress the warp of the outer peripheral portion of the wafer 20 (the wafer edge portion, which is both end portions in the CH2 processing progress direction) where the amount of warp is large.
- may 15A and 15B are diagrams for explaining a processing method for mainly suppressing warpage in the outer peripheral portion of the wafer 20. FIG. As shown in FIG.
- the modified regions 12 for suppressing warpage may be formed by changing the processing index depending on the location so that the number of modified regions 12 for suppressing warpage in the second direction is greater at both ends.
- the controller 8 controls the laser irradiation unit 3 so that the number of modified regions 12 for suppressing warpage is greater at both ends in the Y direction. Further, as shown in FIG.
- the modified region 12 for suppressing warpage in the central portion of the wafer 20 in the Y direction is compared with the modified region 12 for suppressing warpage at both ends.
- the modified region 12 for suppressing warpage may be formed such that the length of the crack 114L, which is the crack 114 at both ends, is longer than the length of the crack 114S, which is the crack 114 at the central portion.
- the controller 8 controls the laser irradiation unit 3 so that the length of the crack 114 extending from the modified region 12 for suppressing warpage is longer at both ends in the Y direction.
- FIG. 16 is a diagram showing warpage in the CH2 processing progress direction after CH1 processing, for each formation mode of the modified region for warpage suppression.
- the horizontal axis indicates the processing progress direction of CH2 (the width direction of the wafer 20), and the vertical axis indicates the amount of displacement indicated by the voltage value.
- a voltage value of 1 V on the vertical axis corresponds to, for example, a displacement amount of about 8 ⁇ m.
- FIG. 16 shows the case where only the modified regions 12 for division are formed (pattern 1), and the case where the modified regions 12 for division are formed and the same number of modified regions 12 for suppressing warpage are formed (pattern 2).
- the warpage amount (displacement amount) is It is shown. As shown in FIG. 16, when pattern 3 is employed, the amount of warpage can be suppressed even in the outer peripheral portion of the wafer 20 where the amount of warp tends to increase.
- the modified regions 12 for suppressing warpage are formed so that the modified regions 12 for suppressing warpage in the central portion of the wafer 20 are thinned out.
- the modified region 12 for suppressing warpage at the central portion of the wafer 20 is formed. is thinned out, warping of the wafer 20 can be appropriately suppressed.
- the warp occurs at a position different from the modified region 12 for splitting in the Y direction.
- Modified region 12 for suppression may be formed. That is, in the third control, the control unit 8 sets the modulation pattern so that the modified region 12 for suppressing warpage is formed at a position different from the formation position of the modified region 12 for division in the Y direction.
- 17A and 17B are diagrams for explaining the processing position shift due to the modulation pattern setting of the spatial light modulator 7. FIG. In the example shown in FIG.
- the focused spot of the modified region 12 for splitting is shifted in the -Y direction from the reference focused position in the first step
- the modified region 12 for suppressing warpage is shifted in the third step. is shifted in the +Y direction from the reference condensing position.
- the modified regions 12 for division and the modified regions 12 for suppressing warpage can be shifted in the opposite direction in the Y direction, and the positions of these modified regions 12 and the positions extending from these modified regions 12 can be changed.
- the cracks 14, 114 can be sufficiently spaced apart.
- the processing position can be shifted only by switching the modulation pattern, so that the processing time required for processing can be shortened compared to the case where the stage 2 is operated.
- the control unit 8 determines that the position of the end of the crack 14 extending from the modified region 12 for splitting on the back surface 21b side is set to the modified region for suppressing warpage.
- the modulation pattern may be set so as to be different from the position of the end of crack 114 extending from 12 on the side of surface 21a.
- the position of the end of the crack 14 on the back surface 21b side is made different from the position of the end of the crack 114 on the front surface 21a side. do.
- the first step by forming the crack 14 inclined with respect to the Z direction and the Y direction, the position of the end of the crack 14 on the back surface 21b side and the end of the crack 114 on the front surface 21a side are changed. position (see FIG. 18(a)).
- FIG. 18 is a diagram explaining the formation of oblique cracks by setting the modulation pattern of the spatial light modulator.
- the first step in the first step, two rows of modified regions 12 for division are formed, and cracks 14A extending from the modified region 12 on the side of the surface 21a are formed along the line 15.
- the crack 14B extending from the modified region 12 on the back surface 21b side is formed as an oblique crack that continues to the crack 14A and is inclined with respect to the Z and Y directions.
- the position of the end of the crack 14 (specifically, the crack 14B) extending from the modified region 12 for division on the back surface 21b side and the position of the end of the crack 114 on the front surface 21a side can be different. Since the crack 14A leading to the crack 14B extends along the line 15, the crack 14 (specifically, the crack 14A) can be extended appropriately in the position and direction required for the splitting crack 14.
- a crack 14A is formed extending along it. Further, by setting the modulation pattern of the spatial light modulator 7 (setting of Y shift and coma aberration), the middle modified region 12 (SD2 in FIG. 18B) is shifted from SD1 in the Y direction and from there An oblique crack 14B extends, and the modified region 12 (SD3 in FIG. 18B) on the side of the rear surface 21b is further softened in the Y direction from SD2, and an oblique crack 14C extends therefrom.
- the diagonal crack 14B is continuous with the crack 14A and the diagonal crack 14C, and the diagonal crack 14B and the diagonal crack 14C extend in the same direction (diagonal direction).
- the wafer was bent in the third step before the second step.
- Formation of the modified region 12 (third modified region) for suppressing warpage in the interior of 20 has been described.
- the warpage of the wafer 20 due to the formation of the modified regions 12 in the CH1 processing progresses gradually as the formation of the divided modified regions 12 related to the plurality of lines 15 progresses. Therefore, in the CH1 machining, the machining of the line 15 which is machined first affects the machining of the line 15 which is machined later.
- FIG. 19 is a diagram for explaining deterioration of machining stability during the second half machining of CH1.
- the wafer 20 is warped when the modified regions 12 are already formed for a plurality of lines and the cracks 14 extend from the modified regions 12 .
- the crack 14 extends diagonally with respect to the device surface of the wafer 20, and the processing position accuracy is reduced.
- the problem is that it gets worse.
- the wafer 20 may be improperly chucked to the stage 2 . As described above, it may be difficult to perform machining stably and accurately during the second half machining of CH1.
- the formation of the modified region 12 for division according to one of the lines 15 in the first step and the modified region for suppressing warpage in the third step 12 may be alternately performed. That is, the control unit 8 alternately forms the modified regions 12 for division in any of the lines 15 in the first control and forms the modified regions 12 for suppressing warpage in the third control.
- the laser irradiation unit 3 is controlled as follows. Alternating here means not only the case of completely alternately performing one-to-one, but also the formation of a plurality of modified regions 12 for division and the formation of a plurality of modified regions 12 for suppressing warpage. Includes alternating implementations.
- FIG. 20 is a diagram illustrating a processing method for alternately forming the modified regions 12 for division and the modified regions 12 for suppressing warpage.
- numbers 1 to 9 indicate the processing order.
- the modified region 12 for suppressing warpage and the crack 114 extending from the modified region 12 are formed in the third step (processing order 1), and then the second step is performed.
- Formation of the modified region 12 for division and the crack 14 extending from the modified region 12 in one step (processing order 2) is performed, and then the third step and the first step are sequentially performed one by one. .
- the machining locations in each machining are arranged in the order of machining in the Y direction.
- processing orders 1 and 2 are performed to form the modified region 12 for suppressing warpage and the crack 114 extending from the modified region 12 in the third step
- processing orders 3 and 4 the formation of the modified region 12 for division and the crack 14 extending from the modified region 12 in the first step is performed in two processes (processing orders 3 and 4), and then such two processes are performed.
- the machining locations in each machining are arranged in order of machining order in the Y direction.
- the formation of the modified region 12 for suppressing warpage and the crack 114 extending from the modified region 12 in the third step is performed in three steps (processing order 1, 2, 3). Then, the formation of the modified regions 12 for division and the cracks 14 extending from the modified regions 12 in the first step are carried out in three steps (processing order 4, 5, 6). In this case, when looking at each of the first step and the third step individually, the machining locations in each machining are arranged in order of machining order in the Y direction.
- the following fourth step may be further performed. That is, in the laser processing method according to the present embodiment, a plurality of modified regions 12 (fourth modified regions) for suppressing warpage are formed inside the wafer 20 by irradiating laser light, and from the modified regions 12 to the back surface 21b and forming a crack 114 discontinuous to the crack 14 extending from the modified region 12 for division formed by the CH2 processing. In this case, the formation of the modified regions 12 for division in any of the lines 15 in the second step and the formation of the modified regions 12 for suppressing warpage in the fourth step may be performed alternately.
- a laser processing apparatus 1 includes a laser irradiation unit 3 and a control unit 8.
- the control unit 8 emits a laser beam L along each of a plurality of lines 15 extending in the X direction along the back surface 21b. While relatively moving the focused spot, the laser irradiation unit 3 is irradiated with the laser light L so that the modified region 12 for division is formed inside the wafer 20 and the crack 14 extends from the modified region 12 toward the surface 21a.
- a second control for controlling the laser irradiation unit 3 so that the modified region 12 for division is formed inside the wafer 20 by the irradiation of the laser beam L and the crack 14 extends from the modified region 12 toward the surface 21a;
- a plurality of modified regions 12 for suppressing warpage are formed inside the wafer 20 by irradiation with the laser beam L, and cracks 114 extending from the modified regions 12 reach the back surface 21 b and split the wafer.
- a third control for controlling the laser irradiation unit 3 so that the crack 14 extending from the modified region 12 is formed discontinuously.
- the modified regions 12 for division are formed along each of the plurality of lines 15 extending in the X direction along the back surface 21 b by irradiation with the laser beam L. Cracks 14 extending in the direction of the surface 21a are formed from the surface 21a, and then the modified regions 12 for division are formed along each of a plurality of lines 15 extending in the Y direction by irradiation with the laser beam L. A crack 14 extending in the direction of the surface 21a is formed. In this way, when the modified regions 12 are sequentially formed along a plurality of lines 15 that intersect with each other, the modified regions 12 are first formed along the line 15 (first line) irradiated with the laser light L.
- the wafer 20 is warped by the formation (CH1 processing), and the influence of the warp of the wafer 20 may reduce the processing accuracy of the line 15 (second line) to which the laser beam L is later irradiated. More specifically, the warpage of the wafer 20 is caused by the formation of the modified region 12 and the formation of the crack 14 extending from the modified region 12 toward the surface 21a. It is caused by stress concentration on one surface 21a). Such warping of the wafer 20 becomes particularly noticeable when the wafer 20 is a microchip or when a relatively large crack is formed.
- a plurality of modified regions 12 for suppressing warpage are formed inside the wafer 20 by irradiation with the laser light L prior to control (second control) related to CH2 processing.
- the crack 114 that is formed and extends from the modified region 12 is formed so as not to reach the rear surface 21b and to be continuous with the crack 14 that extends from the modified region 12 for division.
- the modified region 12 for suppressing warpage is formed so that the crack 141 reaches the back surface 21b opposite to the front surface 21a where stress is concentrated by forming the modified region 12 for division, Localization of stress is relieved, and warping of the wafer 20 can be reduced.
- the crack 141 extending from the modified region 12 for suppressing warpage is formed so as not to be continuous with the crack 14 extending from the modified region 12 for splitting, so that the modified region 12 for suppressing warpage is formed.
- unintended cracking of the wafer 20 can be appropriately suppressed.
- the laser processing apparatus 1 according to the present embodiment it is possible to appropriately form the modified region 12 for dividing the wafer 20 while suppressing unintended cracking of the wafer 20. It is possible to improve the laser processing accuracy.
- FIG. 21 is a diagram for explaining the effects of the laser processing apparatus 1 according to the present embodiment, and is a diagram showing warpage in the CH2 processing progress direction after CH1 processing.
- the horizontal axis indicates the processing progress direction of CH2 (the width direction of the wafer 20), and the vertical axis indicates the amount of displacement indicated by the voltage value.
- a voltage value of 1 V on the vertical axis corresponds to, for example, a displacement amount of about 8 ⁇ m.
- FIG. 21 shows the amount of warpage after CH1 processing and before CH2 processing.
- the modified region 12 for suppressing warpage is formed, and the crack 114 extending from the modified region 12 for suppressing warpage reaches the back surface 21b, thereby forming an HC state. It is possible to greatly reduce the warp of the wafer 20 due to the BHC associated with the formation of the modified region 12 for .
- FIG. 22 is a diagram for explaining the effects of the laser processing apparatus 1 according to this embodiment, and is a diagram showing the warp of the wafer 20 after CH1 processing and CH2 processing.
- the horizontal axis indicates the position in the width direction of the wafer 20, and the vertical axis indicates the surface displacement.
- the surface displacement here is measured with a microscope.
- FIG. 22 shows the surface displacement indicating the amount of warpage of the wafer 20 after CH1 processing and CH2 processing. Only”), and when the modified region 12 for suppressing warpage is formed in the center of the chip (described as "SD for division + warp suppression SD (processed at the center of the chip)" in FIG. 22). , the surface displacement indicating the amount of warpage is shown.
- SD division + warp suppression SD (processed at the center of the chip)
- the wafer 20 If the amount of warpage at both ends of the wafer 20 is large, the wafer 20 cannot be properly attracted to the transfer arm after processing, and there is a risk that the wafer 20 will drop or cause a transfer failure. In this respect, the wafers 20 whose warp amount was reduced to half or less by the modified region 12 for warp suppression as described above could be properly transferred. Moreover, no cracks occurred in the wafer 20 after transfer.
- the control unit 8 controls the laser irradiation unit 3 so that the modified region 12 for suppressing warpage is formed at a position different from the formation position of the modified region 12 for division in the Y direction. good too.
- the crack 14 from the modified region 12 for splitting and the crack 114 from the modified region 12 for suppressing warpage can be more suitably suppressed.
- the control unit 8 controls the laser irradiation unit 3 so that the modified region 12 for suppressing warpage is formed in the middle position in the Y direction between the formation positions of the two lines 15 adjacent in the Y direction. may be controlled.
- the distance between any of the modified regions 12 for division and the modified region 12 for suppressing warpage is can be increased, and continuation of the crack 14 and the crack 114 can be appropriately avoided. As a result, it is possible to suitably suppress the occurrence of unintended cracking of the wafer 20 .
- control unit 8 may set the modulation pattern so that the modified region 12 for suppressing warpage is formed at a position in the Y direction different from the position where the modified region 12 for division is formed. In this way, when the formation position of the modified region 12 for suppressing warpage is adjusted by setting the modulation pattern of the spatial light modulator 7, the formation position of the modified region 12 is changed by the operation of the stage 2. Machining time can be shortened compared to
- the control unit 8 changes the modulation pattern such that the position of the end of the crack 14 on the back surface 21b side is different from the position of the end of the crack 114 on the front surface 21a side. may be set. In this way, by adjusting the positions of the ends of the cracks 14 and 114 extending from the modified region 12 by setting the modulation pattern of the spatial light modulator 7, the positions of the ends of the cracks 14 and 114 are appropriately adjusted. However, unintended cracking of the wafer 20 due to continuous cracks 14 and 114 can be more preferably suppressed.
- the control unit 8 controls the laser irradiation unit 3 so that the crack 114 extending from the modified region 12 for suppressing warpage is shorter than the crack 14 extending from the modified region 12 for division. good.
- the crack 114 extending from the modified region 12 for suppressing warpage is not a crack that is desired to contribute to splitting. Unintended cracking of the wafer 20 can be more suitably suppressed by the continuation.
- the control unit 8 controls the laser irradiation unit 3 so that the number of modified regions 12 for suppressing warpage is greater than the number of modified regions 12 for division in the Y direction.
- the controller 8 determines that At least one of the increase in the number of modified regions 12 for suppressing warpage in the Y direction and the length of the cracks 114 extending from the modified regions 12 for suppressing warpage at both ends.
- the laser irradiation unit 3 may be controlled such that the modified region 12 for suppressing warpage is formed so as to satisfy the condition. Warpage of the wafer 20 due to the formation of the modified regions 12 for division becomes more pronounced toward both ends in the Y direction.
- either the number of modified regions 12 for suppressing warpage is increased at both ends of the wafer 20 compared to the central portion in the Y direction, or the length of the crack 114 extending from the modified region 12 for suppressing warpage is By increasing the length of , it is possible to effectively suppress warping of the wafer 20 at both ends in the Y direction where the warping is conspicuous.
- the control unit 8 performs the formation of the modified region 12 for division and the formation of the modified region 12 for suppressing warpage according to one of the lines 15 in the first control so as to alternately perform the laser irradiation unit. 3 may be controlled.
- the warpage of the wafer 20 due to the formation of the modified regions 12 for division progresses gradually as the formation of the modified regions 12 for division according to the plurality of lines 15 progresses. Therefore, the machining of the line 15 that is machined first affects the machining of the line 15 that is machined later. That is, in the processing of the line 15 that is processed relatively late among the plurality of lines 15, the modified region 12 is formed with the wafer 20 warped.
- the formation of the modified regions 12 for division and the formation of the modified regions 12 for suppressing warpage are alternately performed, so that the influence of the previously performed processing of the line 15 is 15 is suppressed, and the modified region 12 for division can be formed more appropriately on the wafer 20 .
- FIG. 23 is a diagram showing the warp in the CH1 processing progress direction after CH1 processing.
- the horizontal axis indicates the CH1 machining advancing direction
- the vertical axis indicates the amount of displacement indicated by the voltage value.
- a plurality of modified regions 12 for suppressing warpage are formed inside the wafer 20 by the irradiation of the laser beam L, and the control unit 8 causes the cracks 114 extending from the modified regions 12 to reach the back surface 21b and cause splitting in CH2 processing. It is configured to further perform a fourth control for controlling the laser irradiation unit 3 so that the crack extending from the modified region 12 (second modified region) for the second is formed discontinuously.
- the laser irradiation unit 3 may be controlled so as to alternately perform the formation of the modified region 12 related to any line 15 in the control and the formation of the modified region 12 in the fourth control.
- the formation of the modified region 12 in the CH2 machining and the formation of the modified region 12 for suppressing warpage are alternately performed, so that even in the CH2 machining, the previously performed machining of the line 15 is improved.
- the effect on the processing of the line 15 to be performed later is suppressed, and the modified region 12 for dividing the wafer 20 can be appropriately formed.
- SYMBOLS 1 Laser processing apparatus, 3... Laser irradiation unit (laser irradiation part), 7... Spatial light modulator, 8... Control part, 12... Modification area (1st modification area, 2nd modification area, 3rd modification texture area), 14, 114... crack, 15... line (first line, second line), 20... wafer (object).
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Abstract
Description
図1に示されるように、レーザ加工装置1は、ステージ2と、レーザ照射ユニット3と、複数の撮像ユニット4,5,6と、駆動ユニット9と、制御部8と、ディスプレイ150(表示部)とを備えている。レーザ加工装置1は、対象物11にレーザ光Lを照射することにより、対象物11に改質領域12を形成する装置である。
本実施形態の対象物11は、図2及び図3に示されるように、ウエハ20である。ウエハ20は、半導体基板21と、機能素子層22と、を備えている。なお、本実施形態では、ウエハ20は機能素子層22を有するとして説明するが、ウエハ20は機能素子層22を有していても有していなくてもよく、ベアウエハであってもよい。半導体基板21は、表面21a及び裏面21bを有している。半導体基板21は、例えば、シリコン基板である。機能素子層22は、半導体基板21の表面21aに形成されている。機能素子層22は、表面21aに沿って2次元に配列された複数の機能素子22aを含んでいる。機能素子22aは、例えば、フォトダイオード等の受光素子、レーザダイオード等の発光素子、メモリ等の回路素子等である。機能素子22aは、複数の層がスタックされて3次元的に構成される場合もある。なお、半導体基板21には、結晶方位を示すノッチ21cが設けられているが、ノッチ21cの替わりにオリエンテーションフラットが設けられていてもよい。
図4に示されるように、レーザ照射ユニット3は、光源31(レーザ照射部)と、空間光変調器7と、集光レンズ33と、4fレンズユニット34と、を有している。光源31は、例えばパルス発振方式によって、レーザ光Lを出力する。空間光変調器7は、光源31から出力されたレーザ光Lを変調する。空間光変調器7は、例えば反射型液晶(LCOS:Liquid Crystal on Silicon)の空間光変調器(SLM:Spatial Light Modulator)である。集光レンズ33は、空間光変調器7によって変調されたレーザ光Lを集光する。なお、集光レンズ33は、補正環レンズであってもよい。
図7に示されるように、撮像ユニット4(撮像部)は、光源41と、ミラー42と、対物レンズ43と、光検出部44と、を有している。撮像ユニット4はウエハ20を撮像する。光源41は、半導体基板21に対して透過性を有する光I1を出力する。光源41は、例えば、ハロゲンランプ及びフィルタによって構成されており、近赤外領域の光I1を出力する。光源41から出力された光I1は、ミラー42によって反射されて対物レンズ43を通過し、半導体基板21の裏面21b側からウエハ20に照射される。このとき、ステージ2は、上述したように2列の改質領域12a,12bが形成されたウエハ20を支持している。
図8に示されるように、撮像ユニット5は、光源51と、ミラー52と、レンズ53と、光検出部54と、を有している。光源51は、半導体基板21に対して透過性を有する光I2を出力する。光源51は、例えば、ハロゲンランプ及びフィルタによって構成されており、近赤外領域の光I2を出力する。光源51は、撮像ユニット4の光源41と共通化されていてもよい。光源51から出力された光I2は、ミラー52によって反射されてレンズ53を通過し、半導体基板21の裏面21b側からウエハ20に照射される。
以下では、レーザ加工装置1が実施するレーザ加工方法の詳細について説明する。本実施形態に係るレーザ加工方法は、裏面21b(第1面)と、裏面21bの反対側の表面21a(第2面)とを含むウエハ20(対象物)の裏面21bを入射面としてウエハ20にレーザ光Lを照射し、ウエハ20のレーザ加工を行うレーザ加工方法である。本レーザ加工方法は、第1工程と、該第1工程よりも後に実施される第2工程と、を含んでいる。上述したように、ウエハ20は複数のライン15のそれぞれに沿って機能素子22aごとに切断される。第1工程では、裏面21bに沿うX方向(第1方向)に延びる複数のライン15(第1ライン,図2参照)のそれぞれに沿って、レーザ照射を行う。第2工程では、裏面21bに沿うY方向(第2方向)に延びる複数のライン15(第2ライン,図2参照)のそれぞれに沿って、レーザ照射を行う。以下では、第1工程の加工をCH1加工、第2工程の加工をCH2加工として説明する場合がある。
Claims (20)
- 第1面と前記第1面の反対側の第2面とを含む対象物の前記第1面を入射面として前記対象物にレーザ光を照射するレーザ照射部と、
制御部と、を備え、
前記制御部は、
前記入射面に沿う第1方向に延びる複数の第1ラインのそれぞれに沿って、前記レーザ光の集光スポットを相対移動させながら、前記レーザ光の照射によって前記対象物の内部に分割用の第1改質領域が形成され該第1改質領域から前記第2面方向に亀裂が延びるように前記レーザ照射部を制御する第1制御と、
前記第1制御後において、前記第1方向に交差すると共に前記入射面に沿う第2方向に延びる複数の第2ラインのそれぞれに沿って、前記レーザ光の集光スポットを相対移動させながら、前記レーザ光の照射によって前記対象物の内部に分割用の第2改質領域が形成され該第2改質領域から前記第2面方向に亀裂が延びるように前記レーザ照射部を制御する第2制御と、
前記第2制御前において、前記レーザ光の照射によって前記対象物の内部に反り抑制用の複数の第3改質領域が形成され該第3改質領域から延びる亀裂が、前記第1面に到達すると共に前記第1改質領域から延びる亀裂に連続せずに形成されるように、前記レーザ照射部を制御する第3制御と、を実行するように構成されている、レーザ加工装置。 - 前記制御部は、前記第3制御において、前記第2方向における前記第1改質領域の形成位置と異なる位置に前記第3改質領域が形成されるように、前記レーザ照射部を制御する、請求項1記載のレーザ加工装置。
- 前記制御部は、前記第3制御において、前記第2方向で隣り合う2つの前記第1ラインそれぞれの形成位置の前記第2方向における中間の位置に前記第3改質領域が形成されるように、前記レーザ照射部を制御する、請求項2記載のレーザ加工装置。
- 前記レーザ照射部は、設定された変調パターンに応じて前記レーザ光を変調する空間光変調器を有しており、
前記制御部は、前記第3制御において、前記第2方向における前記第1改質領域の形成位置と異なる位置に前記第3改質領域が形成されるように前記変調パターンを設定する、請求項2又は3記載のレーザ加工装置。 - 前記レーザ照射部は、設定された変調パターンに応じて前記レーザ光を変調する空間光変調器を有しており、
前記制御部は、前記第1制御及び前記第3制御の少なくともいずれか一方において、前記第1改質領域から延びる亀裂の前記第1面側の端部の位置が、前記第3改質領域から延びる亀裂の前記第2面側の端部の位置と異なるように、前記変調パターンを設定する、請求項1~4のいずれか一項記載のレーザ加工装置。 - 前記制御部は、前記第3制御において、前記第1改質領域から延びる亀裂よりも前記第3改質領域から延びる亀裂が短くなるように、前記レーザ照射部を制御する、請求項1~5のいずれか一項記載のレーザ加工装置。
- 前記制御部は、前記第3制御では、前記第2方向において、前記第1改質領域の数よりも多くの数の前記第3改質領域が形成されるように、前記レーザ照射部を制御する、請求項6記載のレーザ加工装置。
- 前記制御部は、前記第3制御において、前記対象物の前記第2方向における中央部の前記第3改質領域と両端部の前記第3改質領域とを比較した場合に、前記両端部のほうが前記第2方向における前記第3改質領域の数が多くなること、及び、前記両端部のほうが前記第3改質領域から延びる亀裂の長さが長くなること、の少なくともいずれか一方が満たされるよう前記第3改質領域が形成されるように、前記レーザ照射部を制御する、請求項1~7のいずれか一項記載のレーザ加工装置。
- 前記制御部は、前記第1制御におけるいずれかの前記第1ラインに係る前記第1改質領域の形成と、前記第3制御における前記第3改質領域の形成とを、交互に実施するように、前記レーザ照射部を制御する、請求項1~8のいずれか一項記載のレーザ加工装置。
- 前記制御部は、
前記レーザ光の照射によって前記対象物の内部に反り抑制用の複数の第4改質領域が形成され該第4改質領域から延びる亀裂が、前記第1面に到達すると共に前記第2改質領域から延びる亀裂に連続せずに形成されるように、前記レーザ照射部を制御する第4制御を更に実行するように構成されており、
前記第2制御におけるいずれかの前記第2ラインに係る前記第2改質領域の形成と、前記第4制御における前記第4改質領域の形成とを、交互に実施するように、前記レーザ照射部を制御する、請求項9記載のレーザ加工装置。 - 第1面と前記第1面の反対側の第2面とを含む対象物の前記第1面を入射面として前記対象物にレーザ光を照射し、前記対象物のレーザ加工を行うレーザ加工方法であって、
前記入射面に沿う第1方向に延びる複数の第1ラインのそれぞれに沿って、前記レーザ光の集光スポットを相対移動させながら、前記レーザ光の照射によって前記対象物の内部に分割用の第1改質領域を形成し、該第1改質領域から前記第2面方向に延びる亀裂を形成する第1工程と、
前記第1工程後において、前記第1方向に交差すると共に前記入射面に沿う第2方向に延びる複数の第2ラインのそれぞれに沿って、前記レーザ光の集光スポットを相対移動させながら、前記レーザ光の照射によって前記対象物の内部に分割用の第2改質領域を形成し、該第2改質領域から前記第2面方向に延びる亀裂を形成する第2工程と、
前記第2工程前において、前記レーザ光の照射によって前記対象物の内部に反り抑制用の複数の第3改質領域を形成し、該第3改質領域から前記第1面に到達すると共に前記第1改質領域から延びる亀裂に連続しない亀裂を形成する第3工程と、を備えるレーザ加工方法。 - 前記第3工程では、前記第2方向における前記第1改質領域の形成位置と異なる位置に前記第3改質領域を形成する、請求項11記載のレーザ加工方法。
- 前記第3工程では、前記第2方向で隣り合う2つの前記第1ラインそれぞれの形成位置の前記第2方向における中間の位置に前記第3改質領域を形成する、請求項12記載のレーザ加工方法。
- 前記第3工程では、前記レーザ光を変調する空間光変調器の変調パターンを設定することにより、前記第2方向における前記第1改質領域の形成位置と異なる位置に前記第3改質領域を形成する、請求項12又は13記載のレーザ加工方法。
- 前記第1工程及び前記第3工程の少なくともいずれか一方では、前記レーザ光を変調する空間光変調器の変調パターンを設定することにより、前記第1改質領域から延びる亀裂の前記第1面側の端部の位置と、前記第3改質領域から延びる亀裂の前記第2面側の端部の位置とを異ならせる、請求項11~14のいずれか一項記載のレーザ加工方法。
- 前記3工程では、前記第1改質領域から延びる亀裂よりも前記第3改質領域から延びる亀裂が短くなるように、前記第3改質領域を形成する、請求項11~15のいずれか一項記載のレーザ加工方法。
- 前記第3工程では、前記第2方向において、前記第1改質領域の数よりも多くの数の前記第3改質領域を形成する、請求項16記載のレーザ加工方法。
- 前記第3工程では、前記対象物の前記第2方向における中央部の前記第3改質領域と両端部の前記第3改質領域とを比較した場合に、前記両端部のほうが前記第2方向における前記第3改質領域の数が多くなること、及び、前記両端部のほうが前記第3改質領域から延びる亀裂の長さが長くなること、の少なくともいずれか一方が満たされるよう前記第3改質領域を形成する、請求項11~17のいずれか一項記載のレーザ加工方法。
- 前記第1工程におけるいずれかの前記第1ラインに係る前記第1改質領域の形成と、前記第3工程における前記第3改質領域の形成とを、交互に実施する、請求項11~18のいずれか一項記載のレーザ加工方法。
- 前記レーザ光の照射によって前記対象物の内部に反り抑制用の複数の第4改質領域を形成し、該第4改質領域から前記第1面に到達すると共に前記第2改質領域から延びる亀裂に連続しない亀裂を形成する第4工程を更に備え、
前記第2工程におけるいずれかの前記第2ラインに係る前記第2改質領域の形成と、前記第4工程における前記第4改質領域の形成とを、交互に実施する、請求項19記載のレーザ加工方法。
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