CN114535839A

CN114535839A - Laser processing method for workpiece

Info

Publication number: CN114535839A
Application number: CN202111312150.2A
Authority: CN
Inventors: 田中圭
Original assignee: Disco Corp
Current assignee: Disco Corp
Priority date: 2020-11-10
Filing date: 2021-11-08
Publication date: 2022-05-27
Also published as: JP2022076905A

Abstract

The invention provides a laser processing method of a processed object, which can inhibit the damage of a device and the undivided of the processed object caused by the bending of an interval channel. The laser processing method of the processed object comprises the following steps: a positioning step, wherein positioning is carried out in a mode that the spacing channels are parallel to the machining feeding direction; a first laser processing step of performing a predetermined number of processes inward from an unprocessed outermost street among streets from one edge to one half-plane region at the center in the index feeding direction; and a second laser processing step of performing a predetermined number of processes inward from the unprocessed outermost streets in the other half-plane region.

Description

Laser processing method for workpiece

Technical Field

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

Background

As a method for dividing a plate-shaped workpiece such as a semiconductor wafer into chips, the following methods are known: a laser beam having permeability to a workpiece is focused and irradiated into the workpiece to form a modified layer, and the modified layer is divided by applying an external force (see, for example, patent document 1).

In such a machining method, when the modified layer is formed along the streets formed in the workpiece, the workpiece slightly expands in a direction perpendicular to a direction in which the streets extend. As a result, a cumulative positional deviation occurs in the positional relationship between the condensed point of the laser beam and the street, and therefore, there is a problem as follows: an alignment operation for correcting the positional deviation must be performed during the machining, and productivity is reduced.

In order to solve the problem, the following laser processing method is proposed: the center region having the largest area is finally processed by utilizing a phenomenon that the object expands in the relatively small area when the modified layer or the laser-processed groove is formed along the streets (see patent document 2). This method can reduce the correction of the positional deviation (alignment work) due to the expansion of the workpiece.

Patent document 1: japanese patent No. 3408805

Patent document 2: japanese laid-open patent publication No. 2008-60164

However, with the recent miniaturization of chips, the influence of compressive stress generated from a processed region on an unprocessed region cannot be ignored. That is, if a method of processing from the outer side toward the center of the workpiece is used as in patent document 2, the streets in the unprocessed region may be bent due to the break in symmetry between the processed region and the unprocessed region, and the device may be damaged during processing. In addition, there are also problems as follows: the formation of the modified layer is inhibited by the compressive stress applied to the central region of the workpiece, and therefore, the workpiece is likely to be undivided in the central region.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a laser processing method for a workpiece, which can suppress damage to a device and undivided workpiece due to bending of streets.

According to the present invention, there is provided a laser processing method for processing a workpiece by laser processing along streets on a front surface of the workpiece, the method including: a chuck table for sucking and holding the workpiece; a laser beam irradiation unit having a condenser for irradiating the workpiece held by the chuck table with a laser beam; a machining feed unit that relatively moves the chuck table and the laser beam irradiation unit in a machining feed direction; an index feeding unit that relatively moves the chuck table and the laser beam irradiation unit in an index feeding direction; and a control unit for controlling the above units, wherein the laser processing method of the processed object comprises the following steps: a protective member attaching step of attaching a protective member to the front or back of the workpiece; a suction holding step of performing suction holding on the protective member side of the workpiece by using the chuck table; a positioning step of positioning the object to be processed such that a direction in which the streets extend is parallel to a processing feed direction; a first laser processing step of, after the positioning step is performed, positioning a converging point of the laser beam on an unprocessed outermost lane among a plurality of lanes set in a half-plane region from one edge to the center in an index feed direction of the workpiece, repeating a processing feed for relatively moving the converging points of the workpiece and the laser beam in the processing feed direction and an index feed for relatively moving the converging points of the workpiece and the laser beam in the index feed direction perpendicular to the processing feed direction in this order, and performing laser processing on a predetermined number of lanes facing the inside of the unprocessed outermost lane among the plurality of lanes set in the half-plane region; and a second laser processing step of, after the first laser processing step is performed, positioning a converging point of the laser beam on an unprocessed outermost lane among a plurality of lanes set from the other edge in the index feeding direction of the workpiece to the other half-plane area at the center, and repeating in sequence a processing feed for relatively moving the converging points of the workpiece and the laser beam in the processing feeding direction and an index feed for relatively moving the converging points of the workpiece and the laser beam in the index feeding direction perpendicular to the processing feeding direction, the laser processing is performed on a predetermined number of streets, from among the plurality of streets set in the other half area, toward the inside of the street that is not processed and is located on the outermost side, and the laser processing is performed on all the streets set in the workpiece by alternately repeating the first laser processing step and the second laser processing step.

Preferably, the method of laser processing a workpiece further includes the steps of: a suction holding releasing step of releasing the suction holding of the chuck table to the workpiece after the first laser processing step and the second laser processing step are performed, and releasing the compressive stress generated in the workpiece; and a re-suction holding step of re-suction holding the workpiece by the chuck table after the suction holding releasing step.

The invention can restrain the damage of the device and the undivided processed object caused by the bending of the spacing channel.

Drawings

Fig. 1 is a perspective view showing a configuration example of a laser processing apparatus according to an embodiment.

Fig. 2 is a flowchart illustrating a flow of a laser processing method of the embodiment.

Fig. 3 is a perspective view showing an example of the protective member attaching step shown in fig. 2.

Fig. 4 is a side view showing one state of the first laser processing step shown in fig. 2.

Fig. 5 is a plan view of the workpiece in fig. 4.

Fig. 6 is a side view showing a state after the first laser processing step shown in fig. 2.

Fig. 7 is a plan view of the workpiece in fig. 6.

Fig. 8 is a plan view of the workpiece in a state of the second laser processing step shown in fig. 2.

Fig. 9 is a plan view of the workpiece after the second laser processing step shown in fig. 2.

Fig. 10 is a diagram showing the distribution of compressive stress in the cross section of the workpiece before the suction holding release step shown in fig. 2.

Fig. 11 is a diagram showing the distribution of compressive stress in the cross section of the workpiece after the suction holding releasing step shown in fig. 2.

Fig. 12 is a plan view of the workpiece in a state of the first laser processing step after the re-suction holding step shown in fig. 2.

Fig. 13 is a plan view of the workpiece in a state of the second laser processing step after the re-suction holding step shown in fig. 2.

Fig. 14 is a plan view of the workpiece in a state after the second laser processing step after the re-suction holding step shown in fig. 2.

Fig. 15 is a plan view schematically showing a dummy wafer in the laser processing method of comparative example 1.

Fig. 16 is a view showing a bent state of the dummy wafer shown in fig. 15.

Fig. 17 is a plan view schematically showing a dummy wafer in the laser processing method of comparative example 2.

Fig. 18 is a view showing a bent state of the dummy wafer shown in fig. 17.

Fig. 19 is a plan view schematically showing a dummy wafer of the laser processing method of the embodiment.

Fig. 20 is a view showing a bent state of the dummy wafer shown in fig. 19.

Description of the reference symbols

1: a laser processing device; 10: a chuck table; 20: a laser beam irradiation unit; 21: a laser beam; 22: a light-focusing point; 40: a processing feeding unit; 50: an indexing feed unit; 90: a control unit; 100: a workpiece; 101: a substrate; 102: a front side; 103: a spacing channel; 104: a device; 105: a back side; 106. 107: a half-plane area; 110: a protective member; 111: a frame; 120: and modifying the layer.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. The components described below include substantially the same contents as those easily conceivable by those skilled in the art. The following structures can be combined as appropriate. Various omissions, substitutions, and changes in the structure can be made without departing from the spirit of the invention.

First, the structure of a laser processing apparatus 1 used in a laser processing method according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view showing a configuration example of a laser processing apparatus 1 according to an embodiment. In the following description, the X-axis direction is a direction on a horizontal plane. The Y-axis direction is a direction perpendicular to the X-axis direction on a horizontal plane. The Z-axis direction is a direction perpendicular to the X-axis direction and the Y-axis direction. In the laser processing apparatus 1 of the embodiment, the processing feed direction is the X-axis direction, and the indexing feed direction is the Y-axis direction.

As shown in fig. 1, the laser processing apparatus 1 has a chuck table 10, a laser beam irradiation unit 20, a processing feed unit 40, an index feed unit 50, a focal point position adjustment unit 60, a photographing unit 70, a display unit 80, and a control unit 90. The laser processing apparatus 1 of the embodiment is an apparatus that processes a workpiece 100 by irradiating the workpiece 100 held by a chuck table 10 with a laser beam 21 by a laser beam irradiation unit 20. The machining of the workpiece 100 by the laser machining apparatus 1 is, for example, modified layer forming machining for forming a modified layer inside the workpiece 100 by stealth dicing.

The workpiece 100 is made of silicon (Si) or sapphire (Al)₂O₃) And a wafer such as a disc-shaped semiconductor device wafer or an optical device wafer having a substrate 101 (see fig. 3) made of gallium arsenide (GaAs) or silicon carbide (SiC). The workpiece 100 is not limited to the embodiment, and may not be a circular plate shape in the present invention. In the embodiment, the workpiece 100 is held on the chuck table 10 while being supported by the protective member 110 and the annular frame 111.

The chuck table 10 holds the workpiece 100 by the holding surface 11. The holding surface 11 is a disk shape formed of porous ceramics or the like. In the embodiment, the holding surface 11 is a plane parallel to the horizontal direction. The holding surface 11 is connected to a vacuum suction source via a vacuum suction path, for example. The chuck table 10 sucks and holds the workpiece 100 placed on the holding surface 11. A plurality of clamping portions 12 for clamping a frame 111 for supporting the workpiece 100 are arranged around the chuck table 10.

The chuck table 10 is rotated by the rotating unit 13 about an axis parallel to the Z-axis direction. The rotating unit 13 is supported by the X-axis direction moving plate 14. The rotation unit 13 and the chuck table 10 are moved in the X-axis direction by the process feeding unit 40 by moving the plate 14 in the X-axis direction. The rotation unit 13 and the chuck table 10 are moved in the Y-axis direction by the index feeding unit 50 via the X-axis direction moving plate 14, the work feeding unit 40, and the Y-axis direction moving plate 15.

The laser beam irradiation unit 20 is a unit that irradiates the workpiece 100 held by the chuck table 10 with a pulse-shaped laser beam 21. The laser beam irradiation unit 20 has at least a condenser for converging and irradiating the laser beam 21 to the workpiece 100 held by the chuck table 10.

The processing feed unit 40 is a unit that relatively moves the chuck table 10 and the laser beam irradiation unit 20 in the X-axis direction as a processing feed direction. In the embodiment, the machining feed unit 40 moves the chuck table 10 in the X-axis direction. In the embodiment, the processing and feeding unit 40 is provided in the apparatus main body 2 of the laser processing apparatus 1.

The machining feed unit 40 supports the X-axis direction moving plate 14 to be movable in the X-axis direction. The machining feed unit 40 includes a known ball screw 41, a known pulse motor 42, and a known guide rail 43. The ball screw 41 is provided to be rotatable about the axial center. The pulse motor 42 rotates the ball screw 41 around the axis. The guide rail 43 supports the X-axis direction moving plate 14 to be movable in the X-axis direction. The guide rail 43 is fixedly provided to the Y-axis direction moving plate 15.

The index feeding unit 50 is a unit that relatively moves the chuck table 10 and the laser beam irradiation unit 20 in the Y-axis direction as the index feeding direction. In the embodiment, the index feeding unit 50 moves the chuck table 10 in the Y-axis direction. In the embodiment, the index feeding unit 50 is provided in the apparatus main body 2 of the laser processing apparatus 1.

The index feeding unit 50 supports the Y-axis direction moving plate 15 to be movable in the Y-axis direction. The indexing-feed unit 50 includes a well-known ball screw 51, a well-known pulse motor 52, and a well-known guide rail 53. The ball screw 51 is provided to be rotatable about the axial center. The pulse motor 52 rotates the ball screw 51 about the axis. The guide rail 53 supports the Y-axis direction moving plate 15 to be movable in the Y-axis direction. The guide rail 53 is fixedly provided on the apparatus main body 2.

The focal point position adjusting unit 60 is a unit that moves the focal point 22 of the laser beam 21 focused by the condenser of the laser beam irradiation unit 20 in the optical axis direction perpendicular to the holding surface 11 of the chuck table 10. More specifically, the focal point position adjusting unit 60 relatively moves the chuck table 10 and the laser beam irradiation unit 20 in the Z-axis direction which is a focal point position adjusting direction. In the embodiment, the focal point position adjusting unit 60 moves the condenser of the laser beam irradiation unit 20 in the Z-axis direction. In the embodiment, the focal point position adjusting means 60 is provided on the column 3 that is erected from the apparatus main body 2 of the laser processing apparatus 1.

The focal point position adjusting unit 60 supports at least the condenser in the laser beam irradiation unit 20 to be movable in the Z-axis direction. The focal point position adjusting unit 60 includes a known ball screw 61, a known pulse motor 62, and a known guide rail 63. The ball screw 61 is provided to be rotatable around the axial center. The pulse motor 62 rotates the ball screw 61 around the axis. The guide rail 63 supports the laser beam irradiation unit 20 to be movable in the Z-axis direction. The guide rail 63 is fixedly provided to the column 3.

The imaging unit 70 is arranged to image the lower side from directly above the condenser of the laser beam irradiation unit 20, for example. The photographing unit 70 includes a coaxial camera, a CCD (Charge Coupled Device) camera, or an infrared camera.

The display unit 80 is a display unit including a liquid crystal display device or the like. The display unit 80 includes a display surface for displaying the image captured by the imaging unit 70, a setting screen of the machining condition, a state of the machining operation, and the like. When the display surface includes a touch panel, the display unit 80 may include an input unit. The input unit can accept various operations such as an operator registering processing content information. The input unit may be an external input device such as a keyboard. The display unit 80 switches information and images displayed on the display surface by an operation from an input unit or the like. The display unit 80 may include a notification unit. The notification unit emits at least one of sound and light to notify an operator of the laser processing apparatus 1 of predetermined notification information. The notification unit may be an external notification device such as a speaker or a light emitting device.

The control unit 90 controls each of the above-described components of the laser processing apparatus 1, and causes the laser processing apparatus 1 to perform a processing operation on the workpiece 100. The control unit 90 controls the chuck table 10, the laser beam irradiation unit 20, the processing feed unit 40, the index feed unit 50, the focal point position adjustment unit 60, the photographing unit 70, and the display unit 80.

The control unit 90 is a computer including an arithmetic processing device as arithmetic means, a storage device as storage means, and an input/output interface device as communication means. The arithmetic Processing Unit includes a microprocessor such as a CPU (Central Processing Unit). The storage device includes a Memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The arithmetic processing device performs various calculations based on a predetermined program stored in the storage device. The arithmetic processing device outputs various control signals to the above-described components via the input/output interface device in accordance with the arithmetic result, and controls the laser processing device 1.

Next, a laser processing method of the workpiece 100 according to the embodiment will be described. Fig. 2 is a flowchart illustrating a flow of a laser processing method of the embodiment. The laser processing method of the workpiece 100 includes a protective member attaching step 201, a suction holding step 202, a positioning step 203, a first laser processing step 204, a second laser processing step 205, a suction holding releasing step 206, an end determining step 207, and a re-suction holding step 208.

(protective member attaching step 201)

Fig. 3 is a perspective view showing an example of the protective member attaching step 201 shown in fig. 2. The protective member attaching step 201 is a step of attaching the protective member 110 to the front surface 102 or the back surface 105 of the workpiece 100. In the protective member attaching step 201 of the embodiment, the protective member 110 is attached to the back surface 105 of the workpiece 100.

First, the workpiece 100 according to the embodiment will be described in more detail. As shown in fig. 3, the workpiece 100 includes streets 103 set in a grid pattern on the front surface 102 of the substrate 101 and devices 104 formed in regions defined by the streets 103. The device 104 is, for example, an Integrated Circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration), or an image sensor such as a CCD or a CMOS (Complementary Metal Oxide Semiconductor).

In the embodiment, the object 100 is formed with the modified layer 120 along the streets 103 (see fig. 6). The workpiece 100 is divided into devices 104 along the modified layer 120 formed on the streets 103, and is singulated into chips. The workpiece 100 according to the embodiment has an outer diameter of 8 inches and a thickness of 100 μm. In the embodiment, the chip has a square shape, but in the present invention, the chip may have a rectangular shape.

In the protective member attaching step 201, first, the protective member 110 is attached to the back surface side of the frame 111. The frame 111 has an opening larger than the outer diameter of the workpiece 100. Next, the workpiece 100 is positioned at a predetermined position of the opening of the frame 111, and the rear surface 105 is attached to the protective member 110. Thereby, the workpiece 100 is fixed to the protective member 110 and the frame 111.

The protective member 110 includes, for example, a base layer made of a synthetic resin and a paste layer laminated on the base layer and made of an adhesive synthetic resin. The protection component 110 may also have extensibility. In this case, after the modified layer 120 (see fig. 6) is formed along the streets 103 in the workpiece 100, the protective member 110 is spread in the planar direction, whereby the workpiece 100 can be divided into individual chips by applying an external force thereto.

(suction holding step 202)

The suction holding step 202 is a step of performing suction holding on the protective member 110 side of the workpiece 100 by the chuck table 10. In the suction holding step 202 of the embodiment, first, the holding surface 11 of the chuck table 10 of the laser processing apparatus 1 shown in fig. 1 holds the back surface 105 side of the workpiece 100 via the protective member 110. Next, the frame 111 supporting the workpiece 100 is clamped by the clamping portion 12. Next, negative pressure is applied from a vacuum suction source connected to the holding surface 11 through the vacuum suction path, thereby sucking and holding the workpiece 100 placed on the holding surface 11.

(positioning step 203)

The positioning step 203 is a step of positioning the direction in which the streets 103 extend so as to be parallel to the machining feed direction (X-axis direction). Here, the streets 103 parallel to the machining feed direction are streets 103 on which the modified layers 120 are formed by the machining method of the embodiment, among the plurality of streets 103 set in the lattice shape on the front surface 102 of the workpiece 100. In the embodiment, the alignment in the direction in which the streets 103 extend is performed by rotating the chuck table 10 about the vertical axis by the rotating means 13. When the positioning step 203 is completed, the process shifts to a first laser processing step 204.

(first laser processing step 204)

Fig. 4 is a side view showing one state of the first laser processing step 204 shown in fig. 2. Fig. 5 is a plan view of the workpiece 100 in fig. 4. Fig. 6 is a side view showing a state after the first laser processing step 204 shown in fig. 2. Fig. 7 is a plan view of the workpiece 100 in fig. 6.

The first laser machining step 204 is performed after the positioning step 203 is performed. The first laser processing step 204 is a step of performing a predetermined number of laser processings in one direction of the index direction on the streets 103 parallel to the processing feed direction. In the first laser processing step 204 of the embodiment, the modified layers 120 are formed on a predetermined number of the streets 103 parallel to the processing feed direction in one direction of the index direction.

The modified layer 120 is a region in which the density, refractive index, mechanical strength, or other physical properties are different from those of the surroundings. The modified layer 120 is, for example, a melt-processed region, a crack region, an insulation breakdown region, a refractive index change region, a region in which these regions coexist, or the like. The modified layer 120 has a mechanical strength or the like lower than that of the other parts of the workpiece 100.

In the first laser processing step 204, the object 100 is first imaged by the imaging unit 70, and the streets 103 are detected. If the streets 103 are detected, alignment for positioning the streets 103-1 of the work 100 and the focal points 22 of the laser beams 21 is performed as shown in FIG. 5. The streets 103-1 are the outermost streets 103-1 among the plurality of streets 103 set from one edge (upper end in fig. 5) in the index direction (Y-axis direction) of the workpiece 100 to one half area 106 at the center.

In the first laser processing step 204, as shown in fig. 6, the pulsed laser beam 21 is converged into the workpiece 100 from the laser beam irradiation unit 20 and irradiated. The laser beam 21 is a laser beam having a wavelength that is transparent to the workpiece 100.

Next, the machining feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the machining feed direction and the indexing feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the indexing feed direction perpendicular to the machining feed direction are sequentially repeated. That is, the laser beam 21 is irradiated from the streets 103-1 of the workpiece 100 toward the inside (downward in fig. 5) to the portions corresponding to the predetermined number of streets 103-2 (see fig. 7) while relatively moving the chuck table 10 with respect to the laser beam irradiation unit 20.

As a result, as shown in fig. 7, a predetermined number of streets 103-2 are laser-machined from the unprocessed outermost streets 103-1 toward the inside of the plurality of streets 103 set in the first half area 106 from the first edge to the center in the index direction of the workpiece 100, thereby forming modified layers 120. When the first laser processing step 204 is completed, the process shifts to a second laser processing step 205.

(second laser processing step 205)

Fig. 8 is a plan view of the workpiece 100 in a state of the second laser processing step 205 shown in fig. 2. Fig. 9 is a plan view of the workpiece 100 after the second laser processing step 205 shown in fig. 2.

The second laser machining step 205 is performed after the first laser machining step 204 is performed. The second laser processing step 205 is a step of performing a predetermined number of laser processings in the other direction of the index direction on the streets 103 parallel to the processing feed direction. In the second laser processing step 205 of the embodiment, the modified layers 120 are formed on a predetermined number of the streets 103 parallel to the processing feed direction in the other direction of the index direction.

In the second laser processing step 205, first, as shown in fig. 8, alignment for positioning the streets 103-3 of the work 100 and the focal points 22 of the laser beams 21 is performed. The streets 103-3 are the outermost streets 103-3 among the plurality of streets 103 set from the other edge (lower end in fig. 5) in the index direction (Y-axis direction) of the workpiece 100 to the other half-plane area 107 at the center.

In the second laser processing step 205, the pulsed laser beam 21 is converged into the workpiece 100 from the laser beam irradiation unit 20 and irradiated (see fig. 6 and the like). Next, the machining feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the machining feed direction and the indexing feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the indexing feed direction perpendicular to the machining feed direction are sequentially repeated. That is, the laser beam 21 is irradiated from the streets 103-3 of the workpiece 100 toward the inside (upper side in fig. 8) to the portions corresponding to the predetermined number of streets 103-4 (see fig. 9) while relatively moving the chuck table 10 with respect to the laser beam irradiation unit 20.

As a result, as shown in fig. 9, laser processing is performed on a predetermined number of streets 103-4 from the unprocessed street 103-3 located outermost toward the inside among the plurality of streets 103 set in the other half-plane region 107 from the other edge to the center in the index direction of the workpiece 100, thereby forming modified layers 120. The number of streets 103 to be laser-machined in the second laser machining step 205 is preferably the same as the number of streets 103 to be laser-machined in the first laser machining step 204. When the second laser processing step 205 is completed, the process proceeds to a suction hold releasing step 206.

(suction holding releasing step 206)

Fig. 10 is a diagram showing the distribution of compressive stress in the cross section of the workpiece 100 before the suction/hold releasing step 206 shown in fig. 2. Fig. 11 is a diagram showing the distribution of compressive stress in the cross section of the workpiece 100 after the suction/hold releasing step 206 shown in fig. 2. The suction holding release step 206 is performed after the first laser processing step 204 and the second laser processing step 205 are performed. The suction holding releasing step 206 is a step of releasing the suction holding of the chuck table 10 to the workpiece 100 and releasing the compressive stress generated in the workpiece 100.

In the first laser processing step 204 and the second laser processing step 205, the modified layer 120 is formed on the streets 103-2 and 103-4, whereby the object 100 is expanded in the index feeding direction (Y-axis direction). Thus, as shown in fig. 10, the compressive stress becomes large in the central region 101-1 of the substrate 101 where the modified layer 120 is not formed on the streets 103.

In the suction holding release step 206, the vacuum suction source connected to the holding surface 11 of the chuck table 10 is controlled to release the suction holding of the workpiece 100 placed on the holding surface 11. Thereby, as shown in fig. 11, the compressive stress generated in the central region 101-1 of the substrate 101 where the modified layer 120 is not formed on the streets 103 is released. When the suction holding release step 206 is completed, the process proceeds to an end determination step 207.

(end judgment step 207)

The end determination step 207 is a step of determining whether or not to end the machining method according to the embodiment shown in the flowchart of fig. 2. Specifically, it is determined whether or not the formation of the modified layer 120 is completed for all the streets 103 on which the modified layer 120 is formed by the processing method of the embodiment. When the modified layer 120 is formed on all the streets 103, the process of the flowchart shown in fig. 2 is terminated. When the streets 103 where the modified layers 120 are not formed remain in the center portion of the workpiece 100, the process proceeds to the re-suction holding step 208.

(re-suction holding step 208)

The re-suction holding step 208 is performed after the suction holding releasing step 106 when the streets 103 where the modified layers 120 are not formed remain in the center portion of the workpiece 100. The re-suction holding step 208 is a step of performing suction holding of the workpiece 100 by the chuck table 10 again.

In the re-suction holding step 208, the vacuum suction source connected to the holding surface 11 of the chuck table 10 via the vacuum suction path applies a negative pressure, thereby re-sucking and holding the workpiece 100 placed on the holding surface 11. When the re-suction holding step 208 is completed, the first laser processing step 204 is returned to. In the embodiment, the frame 111 supporting the workpiece 100 is clamped by the clamping portion 12, but when the workpiece 100 is shifted in the horizontal direction with respect to the chuck table 10 in the suction/holding releasing step 206, the process returns to the positioning step 203, and the positioning is performed again.

For example, when the vacuum suction path of the chuck table 10 is divided into a plurality of areas of the holding surface 11, the holding surface 11 can be sucked for each area. That is, the suction holding is released in the suction holding releasing step 206 only for the region of the chuck table 10 corresponding to the region where the laser processing is performed in the first laser processing step 204 and the second laser processing step 205, and the suction holding is performed again in the re-suction holding step 208. According to such a method, since the horizontal displacement is suppressed by maintaining the suction holding of the area including the unprocessed streets 103, the alignment work for correcting the positional displacement can be omitted.

(first laser processing step 204 after re-suction holding step 208)

Fig. 12 is a plan view of the workpiece 100 in a state of the first laser processing step 204 after the re-suction holding step 208 shown in fig. 2.

In the first laser processing step 204 after the re-attraction holding step 208, first, as shown in fig. 12, alignment for positioning the streets 103-5 of the work 100 and the focal points 22 of the laser beams 21 is performed. The streets 103-5 are the unmachined and outermost streets 103-5 among the plurality of streets 103 set in the one half area 106 of the workpiece 100. That is, the street 103-5 is a street 103-5 inside the street 103-2 processed in the previous first laser processing step 204.

In the first laser processing step 204 after the re-suction holding step 208, the pulsed laser beam 21 is converged into the workpiece 100 from the laser beam irradiation unit 20 and irradiated, similarly to the previous first laser processing step 204. Next, the machining feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the machining feed direction and the indexing feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the indexing feed direction perpendicular to the machining feed direction are sequentially repeated. That is, the laser beam 21 is irradiated from the streets 103-5 of the workpiece 100 toward the inside (downward in fig. 12) to the portions corresponding to the predetermined number of streets 103-6 (see fig. 13) while relatively moving the chuck table 10 with respect to the laser beam irradiation unit 20.

As a result, a predetermined number of the streets 103-6 extending inward from the unprocessed street 103-5 located outermost in the plurality of streets 103 set in the half-plane region 106 are laser-processed to form modified layers 120 (see fig. 13). When the first laser processing step 204 is completed, the process shifts to a second laser processing step 205.

(second laser processing step 205 after re-suction holding step 208)

Fig. 13 is a plan view of the workpiece 100 in a state of the second laser processing step 205 after the re-suction holding step 208 shown in fig. 2. Fig. 14 is a plan view of the workpiece 100 in a state after the second laser processing step 205 after the re-suction holding step 208 shown in fig. 2.

In the second laser processing step 205 after the re-suction holding step 208, first, as shown in fig. 13, alignment for positioning the streets 103-7 of the object to be processed 100 and the focal point 22 of the laser beam 21 is performed. The streets 103-7 are the unmachined and outermost streets 103-7 among the plurality of streets 103 set in the other half area 107 of the workpiece 100. That is, the street 103-7 is a street 103-7 located inside the street 103-4 processed in the previous second laser processing step 205.

In the second laser processing step 205 after the re-suction holding step 208, the pulsed laser beam 21 is converged into the workpiece 100 from the laser beam irradiation unit 20 and irradiated, as in the second laser processing step 205 of the previous time. Next, the machining feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the machining feed direction and the indexing feed for relatively moving the workpiece 100 and the converging point 22 of the laser beam 21 in the indexing feed direction perpendicular to the machining feed direction are sequentially repeated. That is, the laser beam 21 is irradiated from the streets 103-7 of the workpiece 100 toward the inside (upper side in fig. 13) to the portions corresponding to the predetermined number of streets 103-8 while relatively moving the chuck table 10 with respect to the laser beam irradiation unit 20.

As a result, as shown in fig. 14, a predetermined number of streets 103-8 are laser-processed from the unprocessed street 103-7 located outermost in the other half surface region 107 toward the inside, thereby forming modified layers 120. When the second laser processing step 205 is completed, the process again proceeds to the suction holding release step 206.

In this way, in the method of processing the workpiece 100 according to the embodiment, the first laser processing step 204 and the second laser processing step 205 are alternately repeated, and laser processing is performed on all the streets 103 set on the workpiece 100. When it is determined in the end determination step 207 that the laser processing has been completed for all the streets 103, the process of the flowchart shown in fig. 2 is ended.

As described above, in the laser processing method of the workpiece 100 according to the embodiment, the processing from one end portion side of the workpiece 100 (the first laser processing step 204) and the processing from the other end portion side (the second laser processing step 205) are alternately performed. This maintains the balance (symmetry) of the compressive stresses generated from the processed streets 103, thereby suppressing the bending of the streets 103, and as a result, the damage of the devices 104 can be suppressed. In addition, since the lane 103 in the unprocessed region can be suppressed from shifting in one direction, the following effects are obtained: the alignment work for correcting the positional deviation can be omitted, or the frequency of the alignment work can be reduced.

After a predetermined number of the streets 103 are machined in the workpiece 100, the suction holding of the chuck table 10 to the workpiece 100 may be released, thereby releasing the compressive stress applied to the central region 101-1 of the workpiece 100. This can eliminate the compressive stress that interferes with the formation of the modified layer 120, and therefore, when the chips are divided, the undivided chips can be suppressed.

Conventionally, in order to divide an undivided region, an operation of assisting the division of a workpiece by pressing with a blade or the like is performed, but by suppressing undivided, this operation step can be omitted, so that man-hour reduction and space saving can be achieved, and generation of particles at the time of pressing with a blade can be suppressed.

Next, the effects of the embodiment were verified. Fig. 15 is a plan view schematically showing a dummy wafer 300 in the laser processing method of comparative example 1. Fig. 16 is a view showing a bent state of the dummy wafer 300 shown in fig. 15. Fig. 17 is a plan view schematically showing a dummy wafer 300 in the laser processing method of comparative example 2. Fig. 18 is a view showing a bent state of the dummy wafer 300 shown in fig. 17. Fig. 19 is a plan view of a dummy wafer 300 schematically illustrating the laser processing method of the embodiment. Fig. 20 is a diagram illustrating a bent state of the dummy wafer 300 illustrated in fig. 19.

The inventors of the present invention confirmed the effect of the laser processing method according to the embodiment by performing laser processing on the dummy wafers 300 of comparative examples 1 and 2 and the products of the present invention shown in fig. 15, 17 and 19. The dummy wafer 300 is a wafer formed only of the substrate 301 without forming a device (for example, the device 104 of the workpiece 100 shown in fig. 3), and a wafer having an outer diameter of 8 inches and a thickness of 100 μm was used in the experiment.

In addition, in the experiment, the bending state of the dummy wafer 300 was confirmed by measuring the positions in the Y-axis direction at the respective positions in the machining feed direction (X-axis direction) on the front surfaces of the first position 400 and the second position 500. The first position 400 is a position of 50mm from one edge toward the center in the one half area 306 from one edge (upper end in fig. 15 and the like) to the center in the index feeding direction (Y-axis direction) of the dummy wafer 300, and is shown by a solid line in the figure. The second position 500 is a position 50mm from the other edge toward the center in the other half area 307 from the other edge (lower end in fig. 15 and the like) to the center in the index feeding direction (Y-axis direction) of the dummy wafer 300, and is shown by a one-dot chain line in the figure.

In the graphs shown in fig. 16, 18, and 20, the horizontal axis represents each position in the machining feed direction (X-axis direction), and the vertical axis represents the position in the Y-axis direction of the front surface of the dummy wafer 300. In the vertical axis, the position of the front surface of the dummy wafer 300 before laser processing in the Y-axis direction is zero, and a positive value indicates a position above the position before laser processing, and a negative value indicates a position below the position before laser processing.

In the 1 st comparative example showing the laser processing method in fig. 15 and the curved state in fig. 16, the laser processing is performed from the other edge of the other half surface region 307 toward the one edge of the one half surface region 306 with the index feed set to 0.2mm up to the first position 400 described above.

In the 2 nd comparative example showing the laser processing method in fig. 17 and the curved state in fig. 18, the laser processing is performed with the index feed set to 0.2mm from one edge of one half surface region 306 to the position 400 described above, and then the laser processing is performed with the index feed set to 0.2mm from the other edge of the other half surface region 107 to the center of the dummy wafer 300.

In the example of the embodiment in which the laser processing method is shown in fig. 19 and the curved state is shown in fig. 20, the first laser processing step 204 in which the index feed is set to 0.2mm from one edge of one half surface region 306 toward the center of the dummy wafer 300 and the second laser processing step 205 in which the index feed is set to 0.2mm from the other edge of the other half surface region 307 toward the center of the dummy wafer 300 are alternately repeated five times, and the laser processing of the laser processing method shown in the embodiment is carried out until the first position 400 and the second position 500 described above.

In the 1 st comparative example showing the bent state in fig. 16, the maximum bending amount 401 at the first position 400 is about 12 μm, and the maximum bending amount 501 at the second position 500 is about 4.5 μm. In comparative example 2 showing the bent state in fig. 18, the maximum bending amount 402 at the first position 400 is about 6 μm, and the maximum bending amount 502 at the second position 500 is about 3 μm.

In contrast to comparative example 1 and comparative example 2, in the example of the embodiment showing the bent state in fig. 20, the maximum bent amount 403 at the first position 400 is about 3 μm, and the maximum bent amount 503 at the second position 500 is about 3 μm.

Therefore, as shown in fig. 16, 18 and 20, the following experimental results were obtained: the dummy wafer 300 processed by the processing method of the embodiment has less warpage after processing than the dummy wafer 300 processed by the processing method of each comparative example. That is, it is found that by alternately performing the processing from one end portion side of the workpiece 100 (the first laser processing step 204) and the processing from the other end portion side (the second laser processing step 205), the meandering of the streets 103 can be suppressed, and as a result, the damage of the devices 104 can be suppressed.

The present invention is not limited to the above embodiments. That is, various modifications can be made without departing from the scope of the present invention. For example, the suction holding release step 206 and the re-suction holding step 208 may not necessarily be included. In the drawings used in the description of the embodiment, the device 104 of the workpiece 100, that is, the divided chip, has a square shape, but in the present invention, the divided chip may have a rectangular shape.

For example, the machining method of the present invention may not be used for the streets 103 having a large indexing amount in the indexing direction, and the machining method of the present invention may be used for the streets 103 having a small indexing amount in the indexing direction. For example, when the chip size is 0.223mm × 10mm, the laser processing apparatus 1 may process a large index side of 10mm without using the processing method of the present invention in the first pass and process a small index side of 0.223mm using the processing method of the present invention in the second pass.

In this case, the second channel can be divided into individual chips by simply expanding the second channel by performing the processing by repeating the first laser processing step 204, the second laser processing step 205, and the suction holding releasing step 206, for example, 12.5mm each from the end of the workpiece 100.

Further, the division ratio is about 50% in the case where the machining of the streets to the predetermined positions on the one edge side from the one edge toward the center in the index feeding direction is performed, and then the machining of the remaining streets is performed from the other edge toward the one edge. The division ratio when processing was performed by repeating the first laser processing step 204, the second laser processing step 205, and the suction holding release step 206 for 50mm each was about 70%. The division ratio when the processing was performed by repeating the first laser processing step 204, the second laser processing step 205, and the suction holding release step 206 for 25mm each was about 75%.

In addition, the laser processing apparatus 1 may process each of the first laser processing step 204 and the second laser processing step 205 by several mm, that is, the timing of switching the processing direction may be automatically determined by the control unit 90. The control means 90 may acquire the position of a target set at the center of the workpiece 100 from the imaging means 70 or the like, and perform control to switch the machining direction when the target is offset by a predetermined amount (for example, 2 μm) or more.

The target set at the center of the workpiece 100 may be, for example, an element included in the pattern surface of the front surface 102 of the workpiece 100, a grinding mark present on the rear surface 105, an element included in the front surface of the protective member 110, or the like. When the target faces the chuck table 10, the object is observed from below the workpiece 100 using a visible light camera, and when the surface opposite to the surface on which the target is set faces the chuck table 10, the object is observed from below the workpiece 100 using an IR (infrared) camera.

In addition, when the surface opposite to the surface on which the target is set faces the chuck table 10, the image may be taken from above the workpiece 100 using a visible light camera. In the case of imaging from above the workpiece 100, it is not necessary to add an imaging means for imaging from below the workpiece 100, which can contribute to cost reduction.

On the other hand, when the image is taken from below the workpiece 100, the target offset can be constantly monitored while the processing is performed, and therefore, time for offset confirmation is not required, which contributes to improvement in yield.

As described above, by automatically controlling the switching of the machining direction, the positional deviation of the workpiece 100 can be quantitatively determined, and the machining direction can be switched at an appropriate timing. This can suppress the lane 103 in the unprocessed region from shifting in one direction, and therefore, the alignment work for correcting the positional shift can be omitted, or the frequency of the alignment work can be reduced.

In addition, by automatic control of switching of the machining direction, a minimum correction distance in the Y-axis direction that can suppress positional deviation can be calculated. This can suppress a decrease in throughput due to an increase in the movement processing in the Y-axis direction accompanying switching of the machining direction.

In the mass production process, when a plurality of workpieces 100, which are wafers having the same thickness and the same chip size, are sequentially processed, it can be estimated that appropriate timings for switching the processing direction are substantially the same. Therefore, the data of the switching timing calculated when the first workpiece 100 is machined may be applied to the second and subsequent workpieces 100. This further contributes to shortening the processing time.

Claims

1. A laser processing method for processing a workpiece, the workpiece having a plurality of streets formed on a front surface thereof along streets, the method comprising the steps of:

a chuck table for sucking and holding the workpiece;

a laser beam irradiation unit having a condenser for irradiating the workpiece held by the chuck table with a laser beam;

a processing feeding unit which relatively moves the chuck worktable and the laser beam irradiation unit in a processing feeding direction;

an index feeding unit that relatively moves the chuck table and the laser beam irradiation unit in an index feeding direction; and

a control unit for controlling the above units,

wherein,

the laser processing method of the processed object comprises the following steps:

a protective member attaching step of attaching a protective member to the front or back of the workpiece;

a suction holding step of performing suction holding on the protective member side of the workpiece by using the chuck table;

a positioning step of positioning the object to be processed such that a direction in which the streets extend is parallel to a processing feed direction;

a first laser processing step of, after the positioning step is performed, positioning a converging point of the laser beam on an unprocessed outermost lane among a plurality of lanes set in a half-plane region from one edge to the center in an index feed direction of the workpiece, repeating a processing feed for relatively moving the converging points of the workpiece and the laser beam in the processing feed direction and an index feed for relatively moving the converging points of the workpiece and the laser beam in the index feed direction perpendicular to the processing feed direction in this order, and performing laser processing on a predetermined number of lanes facing the inside of the unprocessed outermost lane among the plurality of lanes set in the half-plane region; and

a second laser processing step of, after the first laser processing step is performed, positioning a converging point of the laser beam on an unprocessed outermost lane among a plurality of lanes set from the other edge of the object in the index feeding direction to the other half-plane area at the center, repeating a processing feed for relatively moving the object and the converging point of the laser beam in the processing feeding direction and an index feed for relatively moving the object and the converging point of the laser beam in the index feeding direction perpendicular to the processing feeding direction in this order, and performing laser processing on a predetermined number of lanes from the unprocessed outermost lane among the plurality of lanes set in the other half-plane area toward the inside,

the first laser processing step and the second laser processing step are alternately repeated to perform laser processing on all the streets set on the object to be processed.

2. The laser processing method of a workpiece according to claim 1,

the laser processing method of the processed object further comprises the following steps:

a suction holding releasing step of releasing the suction holding of the chuck table to the workpiece after the first laser processing step and the second laser processing step are performed, and releasing the compressive stress generated in the workpiece; and

and a re-suction holding step of re-suction holding the workpiece by the chuck table after the suction holding releasing step.