CN111162042A

CN111162042A - Method for processing wafer

Info

Publication number: CN111162042A
Application number: CN201911079501.2A
Authority: CN
Inventors: 中村胜
Original assignee: Disco Corp
Current assignee: Disco Corp
Priority date: 2018-11-08
Filing date: 2019-11-07
Publication date: 2020-05-15
Also published as: TW202018797A; KR20200053427A; JP2020077782A

Abstract

To provide a wafer processing method that reliably generates cracks from the modified layer to the front surface when the modified layer is formed along the dividing line. The wafer processing method includes at least the following steps: a step of forming a starting point for division, and positioning a light-converging point of a laser beam (LB) having a wavelength transparent to the wafer (10) from the back surface (10b) of the wafer (10) on the The predetermined interior is irradiated to form a division starting point consisting of a modified layer (100) and a crack (110) extending from the modified layer (100) to the front surface (10a) along the planned division line (14); the protective tape is arranged Steps are provided, after the step of forming the starting point of division, a protective tape (T) is arranged on the front surface (10a) of the wafer (10); and in the step of dividing, a grinding wheel ( 76) Grinding the back surface (10b) of the wafer (10) to thin the wafer (10), and dividing the wafer (10) into individual device chips (12').

Description

Method for processing wafer

Technical Field

The present invention relates to a wafer processing method for dividing a wafer into device chips, the wafer being divided by planned dividing lines and having a plurality of devices formed on a front surface thereof.

Background

A wafer having a plurality of devices such as ICs and LSIs formed on its front surface divided by lines to be divided is divided into individual devices by a dicing apparatus and used for electronic devices such as mobile phones and personal computers.

In addition, the following techniques are proposed: a wafer is divided into device chips by irradiating a wafer with a laser beam having a wavelength that is transparent to the wafer while locating a converging point of the laser beam inside the wafer from the back surface of the wafer, forming a modified layer along a line to be divided, grinding the back surface of the wafer to thin the wafer, and growing a crack from the modified layer to the front surface (see, for example, patent document 1).

In order to effectively form cracks from the modified layer formed along the lines to be divided to the front surface, the present applicant has proposed a technique of heating a wafer on which the modified layer is formed (see patent document 2).

Patent document 1: japanese patent laid-open publication No. 2009-290148

Patent document 2: japanese patent laid-open publication No. 2016-

According to the method for processing a wafer described in patent document 2, a modified layer is formed and cracks are also generated. When an external force is applied to the wafer on which the modified layer and the cracks are formed, and the wafer is divided into the device chips along the lines to be divided, the division can be performed more favorably than the case where only the modified layer is formed.

However, there are also problems as follows: when forming a modified layer on a wafer, even if a crack extending from the modified layer to the front surface is intended to be generated, the crack is not easily and reliably generated, and the wafer cannot be reliably divided into individual device chips depending on the generation state of the crack, and the quality of each device chip varies.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and a main technical object thereof is to provide a wafer processing method capable of reliably generating cracks extending from a modified layer to a front surface when forming the modified layer along a line to be divided, and reliably dividing a wafer into device chips in a dividing step.

In order to solve the above-described main technical problem, the present invention provides a method of processing a wafer, the method dividing a wafer into device chips, the wafer having a plurality of devices formed on a front surface thereof and partitioned by planned dividing lines, the method including at least the steps of: a division starting point forming step of positioning a converging point of a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer into a predetermined interior and irradiating the wafer with the converging point, and forming division starting points, each of which is composed of a modified layer and a crack extending from the modified layer to the front surface, along the lines to divide; a protective tape arranging step of arranging a protective tape on the front surface of the wafer after the division starting point forming step; and a dividing step of thinning the wafer by grinding the back surface of the wafer with a grinding wheel having a grinding wheel in an annular shape, and dividing the wafer into individual device chips.

Preferably, in the dividing start point forming step, a protective member for protecting the front surface of the wafer is disposed on the front surface of the holding table for holding the front surface side of the wafer.

The method for processing a wafer according to the present invention includes at least the steps of: a division starting point forming step of positioning a converging point of a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer into a predetermined interior and irradiating the wafer with the converging point, and forming division starting points, each of which is composed of a modified layer and a crack extending from the modified layer to the front surface, along the lines to divide; a protective tape arranging step of arranging a protective tape on the front surface of the wafer after the division starting point forming step; and a dividing step of thinning the wafer by grinding the back surface of the wafer with a grinding wheel having a grinding wheel in an annular shape, and dividing the wafer into individual device chips, wherein a protective tape is disposed on the front surface of the wafer after the division starting point forming step. In this way, since the dividing start point forming step is performed in a state where the protective tape is not provided on the front surface of the wafer, the contraction force of the tape does not act on the wafer when the dividing start point forming step is performed, and cracks from the modified layer to the front surface can be appropriately grown, and the wafer can be reliably divided into the respective device chips by performing the dividing step.

Drawings

Fig. 1 is an overall perspective view of the laser processing apparatus according to the present embodiment.

Fig. 2 is a view showing a wafer as a workpiece processed in fig. 1 and a mode in which the wafer is placed on a holding table.

Fig. 3 (a) is a view showing an embodiment in which the division start point forming step is performed by the laser processing apparatus shown in fig. 1, and fig. 3 (b) is a partially enlarged cross-sectional view showing a modified layer and a crack formed in a wafer.

Fig. 4 is a diagram showing an embodiment of the protective tape arranging step of the present embodiment.

Fig. 5 (a) is a diagram showing an embodiment of the dividing step of the present embodiment, and fig. 5 (b) is a diagram showing a state in which the wafer is divided into the respective device chips by performing the dividing step shown in fig. 5 (a).

Description of the reference symbols

1: a laser processing device; 2: a base station; 10: a wafer; 10 a: a front side; 10 b: a back side; 12: a device; 12': a device chip; 14: dividing the predetermined line; 20: a holding unit; 21: a movable plate in the X-axis direction; 22: a Y-axis direction movable plate; 24: a holding table; 26: an adsorption chuck (protective member); 30: a mobile unit; 31: an X-axis feeding unit; 32: a Y-axis feeding unit; 50: a laser beam irradiation unit; 52: a condenser; 55: a shooting unit; 60: a grinding device; 62: a chuck table; 70: a grinding unit; 72: rotating the main shaft; 78: grinding the grinding tool; 100: a modified layer; 110: cracking; 120: dividing the lines; t: provided is a protective tape.

Detailed Description

Hereinafter, a laser processing apparatus 1 preferred in the method of processing a wafer according to the present invention will be described in detail with reference to the drawings.

Fig. 1 is a perspective view of the entire laser processing apparatus 1. The laser processing apparatus 1 includes: a holding unit 20 for holding a circular workpiece (wafer); a moving unit 30 that moves the holding unit 20; a laser beam irradiation unit 50 that irradiates a laser beam on the workpiece held by the holding unit 20; an imaging unit 55 that images the workpiece held by the holding unit 20; and a display device M.

The holding unit 20 is disposed on a base 2 as a base of the laser processing apparatus 1, and the holding unit 20 includes: a rectangular X-axis movable plate 21 mounted movably in the X-axis direction indicated by an arrow X in the figure; a rectangular Y-axis movable plate 22 movably mounted on the X-axis movable plate 21 in the Y-axis direction indicated by an arrow Y in the figure; a holding table 24 disposed on an upper surface of the Y-axis direction movable plate 22 and configured to be rotatable in a direction indicated by an arrow by a driving unit not shown; and an adsorption chuck 26 which constitutes the front surface of the holding table 24 and is formed of a soft resin sheet having air permeability such as foamed polyurethane. A porous ceramic having air permeability, not shown, is disposed on the lower surface side of the suction chuck 26. The holding table 24 is connected to a suction unit, not shown, and the plate-like member placed on the holding table 24 is sucked and held via the porous ceramic and the suction chuck 26.

The mobile unit 30 includes: an X-axis feeding unit 31 that feeds the holding unit 20 in the X-axis direction; and a Y-axis feeding unit 32 that index-feeds the holding unit 20 in the Y-axis direction. The X-axis feed unit 31 converts the rotational motion of the pulse motor 33 into linear motion by the ball screw 34, transmits the linear motion to the X-axis movable plate 21, and advances and retracts the X-axis movable plate 21 in the X-axis direction along the

guide rails

2a and 2a on the base 2. The Y-axis feed unit 32 converts the rotational motion of the pulse motor 35 into linear motion via the ball screw 36, and transmits the linear motion to the Y-axis movable plate 22, so that the Y-axis movable plate 22 advances and retreats in the Y-axis direction along the guide rails 21a, 21a on the X-axis movable plate 21. A position detecting means, not shown, is disposed on the moving means 30, and the position of the holding table 24 in the X-axis direction, the Y-axis direction, and the rotational direction is detected and fed back to a control means, not shown, so that the holding table 24 can be moved to a desired position.

The frame 4 is erected on a side of the moving means 30. The frame 4 includes a vertical wall 4a disposed on the base 2 and a horizontal wall 4b extending horizontally from an upper end of the vertical wall 4 a. An optical system, not shown, including a laser oscillator of the laser beam irradiation unit 50 is built in the horizontal wall portion 4b of the housing 4. A condenser 52 constituting a part of the laser beam irradiation unit 50 is disposed on the lower surface of the distal end portion of the horizontal wall portion 4b, and a condenser lens, not shown, for condensing the laser beam is built in the condenser 52. The laser beam oscillated from the laser oscillator of the laser beam irradiation unit 50 is condensed by the condenser 52 via an optical system not shown, and a condensed spot is formed in a predetermined inner portion of the workpiece held by the holding table 24 of the holding unit 20.

The imaging unit 55 is disposed at a position adjacent to the condenser 52 in the X-axis direction on the lower surface of the front end portion of the horizontal wall portion 4b, and images the workpiece held by the holding unit 20 from a direction facing the holding unit 20. The imaging unit 55 includes an infrared imaging device (infrared CCD) that images by infrared rays, not shown, and an infrared irradiation unit, not shown, that irradiates the workpiece with infrared rays, and the imaging unit 55 is connected to a control unit, not shown, that controls each operating unit of the laser processing apparatus 1. A signal of the image captured by the capturing unit 55 is sent to the control unit. The imaging unit 55 may include a visible light ray irradiation unit and a normal imaging device (CCD) for imaging visible light rays, depending on the type of the workpiece.

The display device M is disposed on the horizontal wall portion 4b, is connected to a control unit (not shown), displays various kinds of processing information (for example, the wavelength, repetition frequency, condensing point position, and spot diameter of the laser beam) output from the control unit, image information of the wafer captured by the imaging unit 55, and the like, and has a touch panel function of receiving an operation by an operator and transmitting the operation to the control unit.

The laser processing apparatus 1 has substantially the above-described configuration, and a method of processing a wafer by using the laser processing apparatus 1 will be described below.

First, as shown in the upper part of fig. 2, a wafer 10 to be processed in the wafer processing method according to the present embodiment is prepared. The wafer 10 is a circular semiconductor wafer made of, for example, a silicon substrate. The wafer 10 is divided by the lines to divide 14 and has a plurality of devices 12 formed on the front surface.

When the wafer 10 is prepared, the front surface 10a is placed downward and the back surface 10b is placed upward on the suction chuck 26 of the holding table 24 of the laser processing apparatus 1. At this time, no protective member such as a protective tape is pasted on the front surface 10a of the wafer 10, and the front surface 10a is placed in direct contact with the holding table 24. Here, the suction chuck 26 is formed of a soft resin sheet having air permeability such as foamed urethane as described above, and functions as a protective member for protecting the front surface 10a of the wafer 10 placed on the suction chuck 26. When the wafer 10 is placed on the holding table 24 in this manner, a suction unit, not shown, is operated to suck and hold the wafer 10 on the holding table 24.

(starting point of division Forming step)

When the wafer 10 is sucked and held on the holding table 24, a division starting point forming step is performed in which the laser beam LB is irradiated from the laser beam irradiation unit 50 included in the laser processing apparatus 1, and division starting points composed of a modified layer and cracks extending from the modified layer to the front surface 10a are formed along the lines to divide 12 inside the wafer 10. More specifically, first, the back surface 10b of the wafer 10 is irradiated with infrared rays from the imaging unit 55 and imaged, and alignment is performed such that the position to which the laser beam LB is irradiated coincides with the position of the lines to divide 12 of the wafer 10, and the lines to divide 14 coincide with the X-axis direction and the Y-axis direction. When the alignment is performed, the laser beam irradiation unit 50 of the laser processing apparatus 1 is started to irradiate the laser beam LB having a wavelength that is transparent to the wafer 10 from the back surface 10b side of the wafer 10, as shown in fig. 3 (a). The converging point of the laser beam LB is positioned in a predetermined interior of the wafer 10 by a condenser 52 disposed in the laser beam irradiation unit 50, and the chuck table 24 is moved in the X-axis direction indicated by the arrow X at a predetermined processing feed speed while the laser beam LB is irradiated from the condenser 52 along the planned dividing lines 12. The laser beam irradiation unit 50, the X-axis feed unit 31 and the Y-axis feed unit 32 that move the chuck table 24, a rotation unit, not shown, that rotates the chuck table 24, and the like are controlled, and the modified layer 100 is formed along all the lines to divide 14 on the wafer 10. The laser beam LB thus irradiated is set to the following laser processing conditions as shown in fig. 3 (b) by enlarging a partial cross section of the wafer 10: the modified layer 100 is formed inside the wafer 10, and a crack 110 extending from the modified layer 100 in the direction of the front surface 10a is generated, thereby forming a division starting point (modified layer 100+ crack 110). In this way, the division start point forming step is completed.

As described above, in the present embodiment, the division start point forming step is performed, and the protective tape or the like is not disposed on the front surface 10a of the wafer 10, but the front surface 10a side is directly placed on the holding table 24 and suction-held. This is because the inventors of the present invention have found that, when laser processing is performed so as to form the modified layer 100 in this state, the contraction force of the protective tape or the like does not act on the wafer 10, and the crack 110 extending from the modified layer 100 toward the front surface 10a side can be formed satisfactorily. In the present embodiment, the suction chuck 26 that holds the table 24 is formed of a protective member made of a soft resin sheet having air permeability such as foamed polyurethane. Thus, even if the front surface 10a of the wafer 10 on which the devices 12 are formed is directly placed on the holding table 24 without a protective tape or the like interposed therebetween and the division start point forming step is performed, the devices 12 are not damaged.

The laser processing conditions to be performed in the above-described division start point forming step are set as follows, for example.

(protective tape disposing step)

After the above-described division starting point forming step is completed, the wafer 10 is carried out from the holding table 24, and as shown in the upper part of fig. 4, a protective tape T is disposed on the front surface 10a side of the wafer 10. The protective tape T is bonded to the front surface 10a of the wafer 10 by applying adhesive force thereto. The protective tape T is selected from a synthetic resin sheet that can be stretched, such as polyvinyl chloride or polyolefin.

(dividing step)

After the protective tape arranging step is completed, the wafer is transported to a grinding apparatus 60 (not shown in the overall drawing) shown in fig. 4 and 5, and the protective tape T side, i.e., the front surface 10a side of the wafer 10 is placed on a chuck table 62 of the grinding apparatus 60 shown in fig. 4 with the front surface facing downward. The suction chuck 63 constituting the front surface of the chuck table 62 is made of porous ceramic having air permeability, and is connected to a suction unit not shown. When the wafer 10 is placed on the chuck table 62, a suction unit, not shown, is operated to suck and hold the wafer 10 on the chuck table 62.

As shown in fig. 5, the grinding apparatus 60 includes a grinding unit 70, and the grinding unit 70 grinds and thins the back surface 10b of the wafer 10 placed on the chuck table 62. The grinding unit 70 has: a rotation main shaft 72 rotated by a rotation driving mechanism not shown; a mount 74 mounted on a lower end of the rotary main shaft 72; and a grinding wheel 76 attached to the lower surface of the mounting seat 74, and a grinding wheel 78 is annularly disposed on the lower surface of the grinding wheel 76.

When the wafer 10 is held by suction on the chuck table 62 as described above, the spindle 72 is rotated at, for example, 3000rpm in the direction indicated by the arrow R1 in fig. 5 (a), and the chuck table 62 is rotated at, for example, 300rpm in the direction indicated by the arrow R2 in fig. 5 (a). The grinding stone 78 is brought into contact with the back surface 10b of the wafer 10, and is ground and fed downward, i.e., in a direction perpendicular to the chuck table 62, at a grinding feed speed of, for example, 1 μm/sec. In this case, the wafer 10 can be ground while the thickness thereof is measured by a not-shown gauge. As shown in fig. 5 (b), the back surface 10b side of the wafer 10 is ground to thin the wafer 10 to a thickness of the modified layer 100, so that the wafer 10 is completely divided into the device chips 12' by the dividing lines 120. As described above, since the wafer 10 is ground in a state where the start points of division composed of the modified layer 100 and the good cracks 110 are formed along all the lines to divide 14, the grinding is performed to the thickness, and as a result, the device 12 is reliably divided into the device chips 12' without impairing the quality of the device 12, and the dividing step is completed. When the dividing step is completed, the wafer 10 is transported to the next step, for example, a step of transporting each device chip 12' to a pickup step, while being held by the protective tape T.

Claims

1. A wafer processing method for dividing a wafer into device chips, the wafer having a plurality of devices formed on a front surface thereof and divided by planned dividing lines,

the wafer processing method at least comprises the following steps:

a division starting point forming step of positioning a converging point of a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer into a predetermined interior and irradiating the wafer with the converging point, and forming division starting points, each of which is composed of a modified layer and a crack extending from the modified layer to the front surface, along the lines to divide;

a protective tape arranging step of arranging a protective tape on the front surface of the wafer after the division starting point forming step; and

and a dividing step of thinning the wafer by grinding the back surface of the wafer with a grinding wheel having a grinding wheel in an annular shape, and dividing the wafer into individual device chips.

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

in the dividing start point forming step, a protective member for protecting the front surface of the wafer is disposed on the front surface of the holding table for holding the front surface side of the wafer.