CN116135407A - Wafer processing method - Google Patents

Wafer processing method Download PDF

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Publication number
CN116135407A
CN116135407A CN202211395683.6A CN202211395683A CN116135407A CN 116135407 A CN116135407 A CN 116135407A CN 202211395683 A CN202211395683 A CN 202211395683A CN 116135407 A CN116135407 A CN 116135407A
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CN
China
Prior art keywords
wafer
processing
laser beam
processing conditions
dividing
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Pending
Application number
CN202211395683.6A
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Chinese (zh)
Inventor
佐藤友亮
村田研二
王楠
竹生田利正
池永幸次
马场夏树
铃木孝雅
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Disco Corp
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Disco Corp
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Publication date
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Publication of CN116135407A publication Critical patent/CN116135407A/en
Pending legal-status Critical Current

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    • 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
    • B23K26/36—Removing material
    • B23K26/38—Removing material by boring or cutting
    • 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
    • B23K26/02—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
    • B23K26/36—Removing material
    • B23K26/40—Removing material taking account of the properties of the material involved
    • B23K26/402—Removing material taking account of the properties of the material involved involving non-metallic material, e.g. isolators
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q3/00—Devices holding, supporting, or positioning work or tools, of a kind normally removable from the machine
    • B23Q3/02—Devices holding, supporting, or positioning work or tools, of a kind normally removable from the machine for mounting on a work-table, tool-slide, or analogous part
    • B23Q3/06—Work-clamping means
    • B23Q3/08—Work-clamping means other than mechanically-actuated
    • B23Q3/088—Work-clamping means other than mechanically-actuated using vacuum means
    • 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
    • H01L21/683—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 for supporting or gripping
    • H01L21/6835—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 for supporting or gripping using temporarily an auxiliary support
    • H01L21/6836—Wafer tapes, e.g. grinding or dicing support tapes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2221/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof covered by H01L21/00
    • H01L2221/67—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere
    • H01L2221/683—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L2221/68304—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L2221/68327—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support used during dicing or grinding
    • H01L2221/68336—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support used during dicing or grinding involving stretching of the auxiliary support post dicing

Abstract

The invention provides a wafer processing method, which is used for carrying out laser processing on a wafer according to proper processing conditions corresponding to thickness deviation of the wafer. The wafer processing method comprises the following steps: a holding step of sucking and holding a wafer by a chuck table having a permeability to a laser beam; and a laser beam irradiation step of irradiating laser beams along a plurality of division predetermined lines, the laser beam irradiation step including the steps of: a proper condition selecting step of changing the processing conditions stepwise from the processing conditions that do not penetrate the wafer to the processing conditions that penetrate the wafer when processing is performed along at least one predetermined dividing line, thereby selecting the processing conditions when the light detecting means detects the laser beam penetrating the wafer as proper processing conditions; and a dividing step of dividing the wafer into a plurality of device chips by irradiating the laser beam along the other predetermined dividing line using the processing conditions selected by the appropriate condition selecting step.

Description

Wafer processing method
Technical Field
The present invention relates to a wafer processing method for irradiating a pulsed laser beam having a wavelength absorbed by a wafer along each predetermined dividing line of the wafer to divide the wafer into a plurality of device chips.
Background
In a process for manufacturing a semiconductor device chip, in order to thin the semiconductor device chip, a back surface side of a semiconductor wafer (hereinafter, simply referred to as a wafer) having a plurality of devices formed on a front surface side thereof may be ground by a grinding device before singulation (for example, refer to patent document 1).
After grinding, the wafer thinned to a prescribed finished thickness is divided into a plurality of semiconductor device chips. For example, the wafer is divided by a laser processing apparatus. In order to divide the wafer, a dicing tape is first stuck to the back surface side of the wafer, and then the back surface side is sucked and held by a chuck table with the dicing tape interposed therebetween.
Next, a laser beam having a wavelength absorbed by the wafer is irradiated along a predetermined line for dividing the wafer to form a processing groove (full-cut) penetrating the wafer from the front surface to the back surface, thereby dividing the wafer into a plurality of semiconductor device chips (for example, refer to patent document 2).
In such laser processing, the processing conditions such as the output of the laser beam and the processing feed rate are predetermined according to the type of wafer by test dicing, and therefore the same processing conditions are uniformly applied to the same type of wafer to process the wafer.
However, when wafers manufactured in different lots are compared with each other, for example, the thickness of the wafers may slightly vary due to manufacturing variations of devices, variations in the finished thickness after grinding, and the like.
Therefore, when ablation processing is performed by a laser beam according to predetermined processing conditions, defects may occur due to thickness variation of the wafer. Specifically, in a relatively thick wafer, a non-through region in which the wafer is not completely cut may be generated in the entire wafer.
In addition, in a relatively thin wafer, after cutting the wafer, the dicing tape may be excessively heated by a laser beam to melt, and the melted residues may adhere to a chuck table. The molten residue may reduce the flatness of the holding surface of the chuck table, and may clog the suction holes of the holding surface.
Patent document 1: japanese patent laid-open No. 2009-90389
Patent document 2: japanese patent application laid-open No. 2018-125448
Disclosure of Invention
The present invention has been made in view of the above-described problems, and an object of the present invention is to perform laser processing on a wafer under appropriate processing conditions corresponding to thickness variations of the wafer when the wafer is cut by ablation processing.
According to one aspect of the present invention, there is provided a method for processing a wafer having devices formed in regions defined by a plurality of dividing lines set in a lattice shape on a front surface, respectively, the method comprising the steps of: a tape adhering step of adhering a central portion of a tape to a back surface of the wafer on a side opposite to the front surface, and adhering one surface of an annular frame to an outer peripheral portion of the tape; a holding step of holding the wafer by suction through the tape by a chuck table having a permeability to the laser beam after the tape attaching step; and a laser beam irradiation step of relatively moving a converging point of the laser beam and the chuck table in a predetermined direction after the holding step, thereby irradiating the laser beam along the plurality of division lines while changing a processing position, the laser beam irradiation step comprising the steps of: a proper condition selecting step of changing the processing conditions stepwise from the processing conditions that do not penetrate the wafer to the processing conditions that penetrate the wafer when processing is performed along at least one predetermined dividing line until the laser beam penetrating the wafer is detected by a light detecting means disposed on the opposite side of the wafer with respect to the chuck table, whereby the processing conditions when the laser beam penetrating the wafer is detected by the light detecting means are selected as proper processing conditions; and a dividing step of dividing the wafer into the plurality of device chips by irradiating the laser beam along another division line different from the at least one division line using the processing conditions selected by the appropriate condition selecting step.
Preferably, the suitable condition selection step comprises the following process: the average output is increased stepwise with the relative movement in the predetermined direction, whereby the processing conditions are changed from those which do not penetrate the wafer to those which do penetrate the wafer.
In addition, preferably, the appropriate condition selecting step includes the following process: the processing feed speed is gradually reduced in accordance with the relative movement in the predetermined direction, whereby the processing conditions are changed from those which do not penetrate the wafer to those which do penetrate the wafer.
In addition, the wafer processing method preferably further comprises the following re-irradiation step: and re-irradiating the laser beam to an unperforated area formed in the proper condition selection step until the light detection unit detects the laser beam penetrating the wafer.
In addition, the wafer processing method preferably further includes the following tape expanding step: after the laser beam irradiation step, the band is expanded.
In the wafer processing method according to one aspect of the present invention, when processing is performed along at least one predetermined dividing line, the processing conditions are changed stepwise from those which do not penetrate the wafer to those which penetrate the wafer until the light detection means detects the laser beam penetrating the wafer, whereby the processing conditions when the light detection means detects the laser beam penetrating the wafer are selected as appropriate processing conditions (appropriate condition selecting step).
Accordingly, since an appropriate processing condition corresponding to the thickness of the wafer can be selected, by performing laser processing in accordance with the selected processing condition, it is possible to prevent the occurrence of a non-penetrated region in the entire wafer and the adhesion of the molten residue to the chuck table.
Drawings
Fig. 1 is a flow chart of a method of processing a wafer.
Fig. 2 (a) is a perspective view of a wafer, and fig. 2 (B) is a perspective view of a wafer unit.
Fig. 3 is a perspective view of the laser processing apparatus.
Fig. 4 is a side view of a chuck table or the like.
Fig. 5 (a) is a diagram showing a case where laser processing is performed at the 1 st average output, fig. 5 (B) is a diagram showing a case where laser processing is performed at the 2 nd average output, and fig. 5 (C) is a diagram showing a case where a laser beam penetrates a wafer.
Fig. 6 is a perspective view of a plurality of device chips and the like.
Fig. 7 (a) is a flowchart of a method for processing a wafer according to modification 1, and fig. 7 (B) is a flowchart of a method for processing a wafer according to modification 2.
Fig. 8 (a) is a partially cross-sectional side view of the expanding device and the like, and fig. 8 (B) is a view showing a tape expanding step.
Fig. 9 (a) is a diagram showing a case of performing laser processing at the 1 st processing feed rate, fig. 9 (B) is a diagram showing a case of performing laser processing at the 2 nd processing feed rate, and fig. 9 (C) is a diagram showing a case where a laser beam penetrates a wafer.
Description of the reference numerals
2: a laser processing device; 4: a base station; 6: a guide rail; 8: a Y-axis direction moving plate; 10: a screw shaft; 12: a Y-axis direction driving source; 14: guide railA rail; 11: a wafer; 11a: a front face; 11b: a back surface; 11c: a processing groove; 11d: an unperforated region; 13: dividing a predetermined line; 15: a device; 17: dicing tape; 19: a frame; 16: a mobile station; 16a: a top plate; 16b: a side plate; 16c: a bottom plate; 16d: a space; 18: a screw shaft; 20: an X-axis direction driving source; 22: a chuck table; 21: a wafer unit; 23: a device chip; 24: a holding plate; 24a: one face; 24b: another face; 24c 1 : a 1 st suction path; 24c 2 : a 2 nd suction path; 24c 3 : a center; 24d: an opening portion; 24e: a peripheral suction path; 26: a frame; 26a: a belt wheel part; 28: a rotation driving source; 28a: a belt wheel; 28b: an endless belt; 30: a laser beam irradiation unit; 32: a condenser; 34: a light detection mechanism; 36: an arm; 38: a light detection unit; 40: a control unit; 42: an expansion device; 44: a drum; 46: a roller; 48: a frame support table; 50: a clamp; 52: a leg portion; l: a laser beam; p: a converging point; s10: a tape sticking step; s20: a holding step; s30: a laser beam irradiation step; s32: a step of selecting appropriate conditions; s34: a segmentation step; s40: a re-irradiation step; s50: and a band expanding step.
Detailed Description
An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flowchart of a processing method of a wafer 11 (see fig. 2 a) according to embodiment 1. In embodiment 1, the tape application step S10, the holding step S20, the appropriate condition selection step S32, the dividing step S34, and the re-irradiation step S40 are sequentially performed.
In this specification, the appropriate condition selecting step S32 and the dividing step S34 may be collectively referred to as a laser beam irradiating step S30. First, a wafer 11 subjected to laser processing will be described.
Fig. 2 (a) is a perspective view of the wafer 11. The wafer 11 is mainly made of a semiconductor material such as silicon, and has a disk shape. A circuit layer (not shown) including an insulating layer made of a Low-k interlayer insulating film material (so-called Low-k material) and a metal wiring layer (metallization layer) is formed on the front surface 11a side of the wafer 11.
A plurality of lines (streets) 13 for dividing each having a straight line shape are set in a lattice shape on the front surface 11a of the wafer 11. Devices 15 such as ICs (Integrated Circuit, integrated circuits) are formed in a plurality of rectangular regions divided by a plurality of lines 13, respectively.
The back surface 11b side of the wafer 11 opposite to the front surface 11a has been ground, and the wafer 11 has been thinned to a substantially uniform predetermined finished thickness (for example, a predetermined thickness of 50 μm or less).
When laser processing is performed on the wafer 11, first, a wafer unit 21 is formed (see fig. 2B). Fig. 2 (B) is a perspective view of the wafer unit 21.
When the wafer unit 21 is manufactured, a center portion of a dicing tape (tape) 17 having a larger diameter than the wafer 11 is attached to the back surface 11b, and one surface of an annular frame 19 having an opening having a larger diameter than the wafer 11 is attached to an outer peripheral portion of the dicing tape 17 (tape attaching step S10).
The dicing tape 17 is substantially transparent, and has a laminated structure of a base layer made of a resin such as polyolefin or polyester and an adhesive layer (paste layer) made of an uncured adhesive resin such as a thermosetting resin or an ultraviolet curing resin.
However, the dicing tape 17 may have only the base material layer. In this case, the wafer unit 21 is formed by, for example, thermocompression bonding the dicing tape 17 to the wafer 11 and the frame 19.
Next, the laser processing apparatus 2 used in the holding step S20 and the like after the tape application step S10 will be described with reference to fig. 3 and 4.
Fig. 3 is a perspective view of the laser processing apparatus 2. In fig. 3, the laser beam irradiation unit 30 and the light detection mechanism 34 (see fig. 4) are omitted. Fig. 4 is a side view of the chuck table 22 and the like. In fig. 4, hatching is omitted for convenience of explanation.
The X-axis direction, the Y-axis direction, and the Z-axis direction shown in fig. 3 and 4 are directions perpendicular to each other. For example, the X-Y plane corresponds to a horizontal plane, and the Z-axis direction corresponds to a vertical direction. Each component of the laser processing apparatus 2 is supported on the base 4.
A pair of guide rails 6 are fixed to the upper surface of the base 4 along the Y-axis direction. A Y-axis direction moving plate 8 is slidably attached to the pair of guide rails 6. A nut portion (not shown) is provided on the lower surface side of the Y-axis direction moving plate 8.
A screw shaft 10 disposed substantially parallel to the Y-axis direction is rotatably coupled to the nut portion. The nut portion and the screw shaft 10 constitute a ball screw. A Y-axis direction drive source 12 such as a pulse motor is connected to one end of the screw shaft 10.
When the screw shaft 10 is rotated by the Y-axis direction drive source 12, the Y-axis direction moving plate 8 moves along the guide rail 6. The guide rail 6, the nut portion, the screw shaft 10, the Y-axis direction drive source 12, and the like constitute a Y-axis direction moving mechanism.
A pair of guide rails 14 are fixed along the X-axis direction on the upper surface of the Y-axis direction moving plate 8. A mobile station 16 is slidably mounted on the pair of guide rails 14. A nut portion (not shown) is provided on the lower surface side of the bottom plate 16c of the mobile station 16.
A screw shaft 18 disposed substantially parallel to the X-axis direction is rotatably coupled to the nut portion. The nut portion and the screw shaft 18 constitute a ball screw. An X-axis direction drive source 20 such as a pulse motor is connected to one end of the screw shaft 18.
When the screw shaft 18 is rotated by the X-axis direction drive source 20, the moving table 16 moves along the guide rail 14. The guide rail 14, the nut portion, the screw shaft 18, the X-axis direction drive source 20, and the like constitute an X-axis direction moving mechanism.
The mobile station 16 has a top plate 16a, side plates 16b, and a bottom plate 16c each having a rectangular plate shape. An upper end of the side plate 16b is connected to one end of the top plate 16a in the X-axis direction, and a lower end of the side plate 16b is connected to one end of the bottom plate 16c in the X-axis direction.
A space 16d is formed by the top plate 16a, the side plates 16b, and the bottom plate 16c, in which the other end portion in the X-axis direction and the both end portions in the Y-axis direction are open. A chuck table 22 is provided on the top plate 16a.
The chuck table 22 has a disk-shaped holding plate 24. The holding plate 24 is made of a transparent material such as quartz glass, and has a permeability to a laser beam L (see fig. 4) described later. The holding plate 24 includes: a substantially flat one face 24a; and the other surface 24b (see fig. 4) located on the opposite side of the one surface 24a.
A plurality of gas flow passages are formed in the holding plate 24. For example, in a plan view of the holding plate 24, the 1 st suction paths 24c are each linear 1 And a 2 nd suction path 24c 2 Formed in the center 24c of one face 24a 3 Perpendicular.
1 st suction path 24c 1 And a 2 nd suction path 24c 2 Formed at the same depth of the retaining plate 24 at the center 24c 3 Is connected to each other directly below. A plurality of openings 24d are formed in the outer peripheral portion of the one surface 24a at substantially equal intervals in the circumferential direction of the one surface 24a.
A plurality of openings 24d are formed in the 1 st suction path 24c 1 The second suction passage 24c 2 And the both ends of (a) are provided. The openings 24d are formed from one surface 24a to a predetermined depth short of the other surface 24b, and are connected to each other by an outer peripheral suction path 24e formed at the outer peripheral portion of the holding plate 24.
A suction passage (not shown) is formed radially outward of the opening 24d of the holding plate 24, and a suction source (not shown) such as an ejector is connected to the suction passage. When the suction source is operated to generate negative pressure, the negative pressure is transmitted to each opening 24d. Thus, the one surface 24a functions as a holding surface.
An annular frame suction plate (not shown) having a plurality of suction ports formed discretely along the circumferential direction of the chuck table 22 is provided on the outer peripheral portion of the chuck table 22, and the frame 19 is sucked and held by the frame suction plate.
In addition, in the 1 st suction path 24c 1 The 2 nd suction path 24c 2 In the flow path of the holding plate 24, such as the opening 24d and the outer Zhou Xi guide 24e, a part of the incident light is scattered or reflected. Therefore, the flow path of the holding plate 24 may not be completely transparent to the laser beam L, but may be light-transmissive or opaque.
However, a predetermined region other than these flow paths is transparent from one surface 24a to the other surface 24 b. For example by the 1 st suction path 24c 1 And (d)2 suction path 24c 2 The region divided into 4 portions and located inside the outer peripheral suction path 24e in the radial direction of the holding plate 24 is transparent to the laser beam L from one surface 24a to the other surface 24 b.
A cylindrical frame 26 made of a metal such as stainless steel is provided on the outer periphery of the holding plate 24. The holding plate 24 is fixed to the housing 26 so as to seal a through-opening (not shown) of the housing 26.
The frame 26 is rotatably supported by the top plate 16a of the mobile station 16. A through opening (not shown) having substantially the same diameter as the holding plate 24 is formed in the top plate 16a, and light irradiated to the one surface 24a enters the space 16d of the moving table 16 through the through opening.
The cylindrical side surface of the housing 26 functions as a pulley portion 26 a. The pulley portion 26a is located above the top plate 16a in a state where the frame 26 is supported by the top plate 16a. The side plate 16b is provided with a rotation drive source 28 such as a motor. A pulley 28a is provided on the rotation shaft of the rotation drive source 28.
An endless belt 28b is suspended over the pulley portion 26a and the pulley 28a. When the pulley 28a is rotated by the rotation drive source 28, the frame 26 rotates about a rotation axis substantially parallel to the Z-axis direction by a force transmitted through the endless belt 28b.
In this way, by controlling the rotation of the pulley 28a, the chuck table 22 can be rotated by an arbitrary angle about the rotation axis substantially parallel to the Z-axis direction. As shown in fig. 4, a laser beam irradiation unit 30 is disposed above the one surface 24a.
The laser beam irradiation unit 30 has a laser oscillator (not shown) having a power supply consisting of Nd: YAG, nd: YVO 4 Etc. The pulsed laser beam L emitted from the laser oscillator and then converted by a wavelength conversion unit (not shown) so that the main peak becomes a predetermined wavelength is incident on the condenser 32.
The condenser 32 has a condenser lens (not shown). The condenser 32 irradiates the laser beam L toward the one surface 24a so as to converge on the wafer 11 sucked and held by the one surface 24a. The wavelength of the main peak of the laser beam L is the wavelength absorbed by the wafer 11 (for example, 355 nm).
A light detection mechanism 34 is provided in the space 16d. The light detection mechanism 34 has an arm 36 with a long side portion arranged along the X-axis direction. A light detection unit 38 is provided at the front end of the arm 36.
The light detection unit 38 has, for example, a power sensor or a power meter each having a photodiode as a light receiving element. However, the light detection unit 38 may be a camera with a light reduction filter including a light receiving element such as a photodiode and a light reduction filter for reducing the amount of light taken into the light receiving element.
The light detection unit 38 is disposed directly below the condenser 32 with the chuck table 22, the wafer 11, and the like interposed therebetween with the condenser 32. Therefore, the laser beam L penetrating the wafer 11 and passing through the dicing tape 17 and the holding plate 24 is incident on the light detection unit 38.
The respective components of the laser processing apparatus 2 are controlled by the control unit 40. The control unit 40 is constituted by, for example, a computer, and the control unit 40 includes: a processor (processing device) represented by a CPU (Central Processing Unit ); main memory devices such as DRAM (Dynamic Random Access Memory ); auxiliary storage devices such as flash memory.
The auxiliary storage device stores software including a predetermined program. The function of the control unit 40 is realized by operating the processing device or the like in accordance with the software.
The holding step S20 to the re-irradiation step S40 shown in fig. 1 are performed using the laser processing apparatus 2. First, in the holding step S20, the dicing tape 17 of the wafer unit 21 is arranged on one surface 24a of the chuck table 22.
Then, negative pressure is transmitted to the opening 24d, and suction and holding are performed on the back surface 11b side of the wafer 11 through the dicing tape 17 (holding step S20). After the holding step S20, an image of the front face 11a is acquired using a photographing unit (not shown), and alignment is performed.
The chuck table 22 is oriented using a rotation drive source 28 or the like so that the line 13 to be divided along one direction is substantially parallel to the X-axis direction. Then, a laser beam irradiation step S30 of irradiating the laser beam L along each planned division line 13 is performed.
The processing conditions are generally predetermined in accordance with the thickness, type, etc. of the wafer 11, but when the predetermined processing conditions are directly employed, a non-penetrated region in which the wafer 11 is not completely cut may be generated in the wafer 11 as a whole in a relatively thick wafer 11.
In the relatively thin wafer 11, after the wafer 11 is cut, the dicing tape 17 may be melted, and the melted residue may be stuck to the one surface 24a of the holding plate 24. Therefore, in the laser beam irradiation step S30, first, the appropriate condition selection step S32 is performed by performing laser processing on at least one line 13 to be divided.
In the appropriate condition selection step S32 of embodiment 1, for example, the appropriate condition selection step S32 is first performed on the first wafer 11 among the 25 wafers 11 processed in one lot, whereby processing conditions more appropriate than predetermined processing conditions are selected.
In addition, instead of using one wafer 11 of the plurality of wafers 11 to select appropriate processing conditions as in embodiment 1, the appropriate condition selecting step S32 may be performed for each wafer 11 subjected to laser processing.
When the appropriate condition selection step S32 is performed on each wafer 11, the processing conditions can be optimized for each wafer 11, although the time required for processing becomes longer, compared to the case where the appropriate condition selection step S32 is performed on only one wafer 11 among the plurality of wafers 11.
In the appropriate condition selection step S32 of embodiment 1, the machining feed speed is made constant, and the average output of the laser beam L is increased stepwise. Thus, the processing conditions are changed stepwise from those that do not penetrate the wafer 11 to those that do penetrate the wafer until the laser beam L is detected by the light detection unit 38. The processing conditions are as follows, for example.
Laser medium: nd: YAG (yttrium aluminum garnet)
Wavelength: 355nm
Average output: 5.0W (when starting irradiation of the wafer 11)
Variation of average output: every 0.1s up by 0.1W (i.e., 1.0W/s)
Repetition frequency: 20kHz
Spot diameter of condensing light: 5.0 μm
Processing feed rate: 100 mm/sec (constant value)
Fig. 5 (a) to 5 (C) show the case where the appropriate condition selecting step S32 is performed when processing is performed along one line of division scheduled 13. The direction of the arrow indicates the direction in which the chuck table 22 is moved, and the length of the arrow corresponds to the magnitude of the machining feed speed.
In the appropriate condition selection step S32, the converging point P of the laser beam L is first positioned at one end portion of one line 13 for dividing in the X-axis direction. Subsequently, the moving stage 16 is subjected to processing feed, whereby the converging point P of the laser beam L and the chuck table 22 are relatively moved in the X-axis direction (predetermined direction).
Thus, the laser beam L is irradiated along the one line of division scheduled 13 while changing the processing position, and ablation processing is performed. Fig. 5 (a) is a diagram showing a case of performing laser processing according to the 1 st average output (about 5.0W).
Fig. 5 (B) is a diagram showing a case of performing laser processing according to the 2 nd average output (about 5.1W). The depth of the processing groove 11c formed in the wafer 11 by the ablation processing gradually increases as the average output increases.
Fig. 5C is a diagram showing a case where laser processing is performed at the 3 rd average output (about 5.3W) and the laser beam L passes through the wafer 11. When the laser beam L passes through the wafer 11 and is detected by the light detection unit 38, the control unit 40 stores the XY coordinates of the condenser 32 at that time and fixes the average output of the laser beam L.
The processing groove 11c is formed to the other end portion of the one line 13 in the X axis direction at a fixed average output. The control unit 40 selects and stores the average output at the time when the laser beam L is detected by the light detection unit 38 as the average output of the appropriate processing conditions.
In the present specification, when the power (W) or the light quantity of the laser beam L received by the light detection unit 38 exceeds a predetermined threshold value, it is assumed that the light detection unit 38 detects the laser beam L.
The predetermined threshold is set appropriately for the purpose of not selecting the processing condition at the time of penetration when the laser beam L accidentally penetrates the locally thin region of the wafer 11 due to the in-plane deviation of the thickness.
The appropriate condition selection step S32 may be performed by using a relatively short line 13 to be divided, which is located on the outer peripheral side of the wafer 11, among the plurality of lines 13 to be divided along one direction, or the appropriate condition selection step S32 may be performed by using a relatively long line 13 to be divided, which is located on the central side of the wafer 11.
The appropriate condition selecting step S32 is preferably performed using one line of division scheduled 13, but in the case where the laser beam L is not detected by the light detecting unit 38 using the first line of division scheduled 13, the appropriate condition selecting step S32 may be performed using a second line of division scheduled 13 different from the first one.
In this way, the appropriate condition selection step S32 can be performed using two or more lines 13, but in embodiment 1, the appropriate condition selection step S32 is performed using one line 13.
The machining groove 11c is formed to the other end in the X-axis direction on one of the dividing lines 13 subjected to the appropriate condition selection step S32, and then the moving table 16 is index-fed by a predetermined length. Next, laser processing is performed on the other lines to be divided 13 adjacent to the line to be divided 13 in the Y-axis direction according to the selected processing conditions.
By performing laser processing under the selected processing conditions, appropriate processing conditions corresponding to the thickness of the wafer 11 can be selected, and therefore, the occurrence of a non-penetrated region and adhesion of molten residues to the chuck table 22 can be prevented in the entire wafer 11.
The chuck table 22 is rotated 90 degrees after the laser processing is performed according to the selected processing conditions along all the lines to be divided 13 in one direction different from the lines to be divided 13 subjected to the laser processing in the appropriate condition selection step S32.
Then, laser processing is performed along each line 13 along the other direction perpendicular to the one direction, in accordance with the selected processing conditions. Thereby, the wafer 11 is divided into a plurality of device chips 23 (see fig. 6) (dividing step S34).
Fig. 6 is a perspective view of the plurality of device chips 23 and the like after the dividing step S34. In fig. 6, one device chip 23 is shown enlarged for convenience of explanation.
In embodiment 1, after the dividing step S34, the laser beam L is irradiated again to the non-penetrated region 11d (see fig. 5C) of the line to be divided 13 formed in the appropriate condition selecting step S32 (re-irradiation step S40).
The non-penetrated region 11d is formed on one of the dividing lines 13 subjected to the appropriate condition selection step S32 until the light detection unit 38 detects the laser beam L penetrating the wafer 11 from the time of starting irradiation of the laser beam L.
In the non-penetrated region 11d, 90% or more and 98% or less of the wafer 11 has been removed in the thickness direction, and therefore, in the re-irradiation step S40, the average output is adjusted to be high enough to enable ablation processing and low enough not to melt the dicing tape 17.
In embodiment 1, since an appropriate processing condition corresponding to the thickness of the wafer 11 can be selected, the occurrence of the non-penetrated region 11d and the adhesion of the molten residues to the chuck table 22 can be prevented in the entire wafer 11.
Further, by performing laser processing on the remaining 24 wafers 11 under the selected processing conditions, it is possible to prevent the occurrence of the non-penetrated region 11d and the adhesion of the molten residues to the one surface 24a in the entire remaining 24 wafers 11.
Next, a modification of embodiment 1 will be described. Fig. 7 (a) is a flowchart of a processing method of the wafer 11 according to modification 1, and fig. 7 (B) is a flowchart of a processing method of the wafer 11 according to modification 2.
In modification 1, the band expanding step S50 is performed after the re-irradiation step S40 using the expanding device 42 (see fig. 8 (a)). In contrast, in modification 2, the band expanding step S50 is performed without the re-irradiation step S40 after the dividing step S34.
Fig. 8 (a) is a partially cut-away side view of the expansion device 42 and the like. The expanding device 42 has a cylindrical drum 44, and the drum 44 has a diameter larger than that of the wafer 11. A plurality of rollers 46 are provided at the upper end portion of the drum 44 at substantially equal intervals along the circumferential direction of the drum 44.
An annular frame support table 48 is provided on the outer side of the drum 44 in the radial direction of the drum 44. A plurality of jigs 50 for clamping the frames 19 of the wafer units 21 placed on the frame support table 48 are provided on the upper surface side of the frame support table 48.
The frame support table 48 is supported by a plurality of leg portions 52 arranged at substantially equal intervals along the circumferential direction of the frame support table 48. Each leg 52 can be lifted and lowered by a lifting mechanism such as an air cylinder.
In the tape expanding step S50, as shown in fig. 8 (a), the upper end of the drum 44 and the upper surface of the frame support table 48 are set to substantially the same height position, and then the wafer unit 21 after the laser beam irradiation step S30 is placed on the drum 44 and the frame support table 48.
Next, when each elevator is operated to pull down the leg portion 52, the frame support table 48 is pulled down with respect to the drum 44. Thereby, as shown in fig. 8 (B), the dicing tape 17 expands in the radial direction, and the intervals of the respective device chips 23 expand. Fig. 8 (B) is a diagram showing the band expanding step S50.
In the case where the non-through region 11d is not completely penetrated even after the re-irradiation step S40 (modification 1 of fig. 7 (a)) and in the case where the re-irradiation step S40 is not performed after the division step S34 (modification 2 of fig. 7 (B)), the non-through region 11d can be divided by the band expansion step S50.
In the tape expansion step S50, the wafer 11 can be divided into a plurality of device chips 23 by dividing the undivided region in the wafer 11 that has undergone the dividing step S34 and/or the re-irradiation step S40. In addition, by expanding the interval between the device chips 23, the pickup of the device chips 23 becomes easier than the case where the interval is not expanded.
Next, embodiment 2 will be described with reference to fig. 9 (a) to 9 (C). In embodiment 2, the appropriate condition selecting step S32 is different from embodiment 1. In the appropriate condition selection step S32 of embodiment 2, the machining feed speed is gradually reduced in accordance with the relative movement of the converging point P and the chuck table 22 in the X-axis direction.
The lower the processing feed speed is, the higher the ratio of the overlapping area of the condensed spots of the pulsed laser beam L (also referred to as the overlapping ratio or the like) is. Therefore, the processing conditions can be changed from the processing conditions under which the laser beam L does not pass through the wafer 11 to the processing conditions under which the laser beam L passes through the wafer 11. The processing conditions are as follows, for example.
Laser medium: nd: YAG (yttrium aluminum garnet)
Wavelength: 355nm
Average output: 5.0W (constant value)
Repetition frequency: 20kHz
Spot diameter of condensing light: 5.0 μm
Processing feed rate: 100 mm/sec (when starting to irradiate the wafer 11)
Variation of processing feed rate: reduced by 0.2mm/s per 0.1s (i.e., -2.0 mm/s)
Fig. 9 (a) is a diagram showing a case of performing laser processing at a 1 st processing feed rate (about 100 mm/s), and fig. 9 (B) is a diagram showing a case of performing laser processing at a 2 nd processing feed rate (about 98 mm/s).
Fig. 9C is a diagram showing a case where laser processing is performed at the 3 rd processing feed rate (about 96 mm/s) and the laser beam L passes through the wafer 11. In fig. 9 (a) to 9 (C), the direction of the arrow indicates the direction in which the chuck table 22 is moved, and the length of the arrow corresponds to the magnitude of the machining feed speed.
When the laser beam L passes through the wafer 11 and the light detection unit 38 detects the laser beam L, the control unit 40 stores the XY coordinates of the condenser 32 at that time, and fixes the processing feed speed.
The processing groove 11c is formed to the other end portion of the one line 13 in the X axis direction at a fixed processing feed rate. The control unit 40 selects and stores the machining feed rate at the time when the laser beam L is detected by the light detection unit 38 as the machining feed rate of the appropriate machining condition.
The machining groove 11c is formed to the other end in the X-axis direction on one of the dividing lines 13 subjected to the appropriate condition selection step S32, and then the moving table 16 is index-fed by a predetermined length.
Next, laser processing is performed on the other lines to be divided 13 adjacent to the line to be divided 13 in the Y-axis direction according to the selected processing conditions. Similarly, the other lines 13 are processed at the processing feed speed selected in the appropriate condition selection step S32.
In embodiment 2, since an appropriate processing condition corresponding to the thickness of the wafer 11 can be selected, the occurrence of the non-penetrated region 11d and the adhesion of the molten residues to the chuck table 22 can be prevented in the entire wafer 11.
In embodiment 2, the appropriate condition selection step S32 may be performed on the first wafer 11 out of the 25 wafers 11 processed in one lot, or the appropriate condition selection step S32 may be performed on each wafer 11 subjected to laser processing.
In embodiment 2, the band expansion step S50 may be performed as described in the above-described modification 1 and modification 2. In addition, the structure, method, and the like of the above embodiment can be modified and implemented as appropriate without departing from the scope of the object of the present invention.
For example, when the thickness of the wafer 11 is 50 μm or less, the wafer 11 can be cut by irradiating the laser beam L from one end portion to the other end portion of one line 13 for cutting (that is, passing the converging point P once (that is, passing once)).
However, when the thickness of the wafer 11 exceeds 50 μm, laser processing may be required to pass the converging point P two or more times (i.e., two or more passes) along one line of intended dividing lines 13 in order to cut the wafer 11. The above embodiments and modifications can be applied also when laser processing is required to be performed twice or more.
Specifically, when cutting the wafer 11 by the laser processing of N passes (where N is a natural number of 2 or more), the laser processing is performed along each planned dividing line 13 from the first pass to the (N-1) th pass according to processing conditions predetermined according to the thickness, the type, and the like of the wafer 11.
Then, at the time of the nth pass laser processing, the above-described proper condition selection step S32 is performed on at least one line 13 for dividing. For example, the appropriate condition selection step S32 is performed on one line 13 to be divided. Thus, more appropriate processing conditions than predetermined processing conditions are selected.
Then, the moving stage 16 is fed by indexing by a predetermined length, and the nth pass laser processing is performed on the other planned dividing line 13 adjacent to the one planned dividing line 13 in the Y-axis direction after the processing is completed, in accordance with the processing conditions selected in step S32.
Similarly, the nth pass laser processing is performed along all the remaining lines of division scheduled 13 in one direction according to the processing conditions selected in step S32 selected by appropriate conditions, and then the chuck table 22 is rotated by 90 degrees.
The nth pass laser processing is performed along each line 13 to be divided along the other direction perpendicular to the one direction, similarly to the processing conditions selected in step S32, by selecting appropriate conditions. This can divide the wafer 11 into a plurality of device chips 23, and prevent the occurrence of a non-penetrated region in the entire wafer 11 and the adhesion of the molten residues to the chuck table 22.
For example, a protective film (not shown) having a water-soluble resin may be uniformly formed on the front surface 11a after the tape application step S10 and before the holding step S20, and then the laser beam irradiation step S30 may be performed.
By performing the ablation process in a state where the protective film is formed, the melt (chipping) of the wafer 11 can be prevented from adhering to the front surface 11a, and the protective film can be cleaned after the ablation process to be removed together with the chipping.

Claims (5)

1. A method for processing a wafer having devices formed in regions defined by a plurality of dividing lines set in a lattice shape on the front surface, respectively, by irradiating a pulsed laser beam having a wavelength absorbed by the wafer along each dividing line of the wafer to divide the wafer into a plurality of device chips,
the wafer processing method comprises the following steps:
a tape adhering step of adhering a central portion of a tape to a back surface of the wafer on a side opposite to the front surface, and adhering one surface of an annular frame to an outer peripheral portion of the tape;
a holding step of holding the wafer by suction through the tape by a chuck table having a permeability to the laser beam after the tape attaching step; and
a laser beam irradiation step of relatively moving a converging point of the laser beam and the chuck table in a predetermined direction after the holding step, thereby irradiating the laser beam along the plurality of dividing predetermined lines while changing a processing position,
the laser beam irradiation step includes the steps of:
a proper condition selecting step of changing the processing conditions stepwise from the processing conditions that do not penetrate the wafer to the processing conditions that penetrate the wafer when processing is performed along at least one predetermined dividing line until the laser beam penetrating the wafer is detected by a light detecting means disposed on the opposite side of the wafer with respect to the chuck table, whereby the processing conditions when the laser beam penetrating the wafer is detected by the light detecting means are selected as proper processing conditions; and
a dividing step of dividing the wafer into the plurality of device chips by irradiating the laser beam along another division line different from the at least one division line using the processing conditions selected by the appropriate condition selecting step.
2. The method for processing a wafer according to claim 1, wherein,
the appropriate condition selection step comprises the following procedures:
the average output is increased stepwise with the relative movement in the predetermined direction, whereby the processing conditions are changed from those which do not penetrate the wafer to those which do penetrate the wafer.
3. The method for processing a wafer according to claim 1, wherein,
the appropriate condition selection step comprises the following procedures:
the processing feed speed is gradually reduced in accordance with the relative movement in the predetermined direction, whereby the processing conditions are changed from those which do not penetrate the wafer to those which do penetrate the wafer.
4. A method for processing a wafer according to any one of claim 1 to 3, wherein,
the wafer processing method also comprises the following re-irradiation steps: and re-irradiating the laser beam to an unperforated area formed in the proper condition selection step until the light detection unit detects the laser beam penetrating the wafer.
5. A method for processing a wafer according to any one of claims 1 to 4, wherein,
the wafer processing method further comprises the following band expanding steps: after the laser beam irradiation step, the band is expanded.
CN202211395683.6A 2021-11-17 2022-11-09 Wafer processing method Pending CN116135407A (en)

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