TW201635358A - Wafer processing method - Google Patents

Abstract

The topic of the present invention is to provide a wafer processing method, which is to irradiate a pulse laser beam with a predetermined 1300~1400 nm wavelength onto a silicon wafer for suppressing transmission light for causing damage of the devices on the wafer surface a modified layer is formed inside the wafer. The solution is a wafer processing method to process a silicon wafer whose surface is divided by plural predetermined division lines and formed with plural devices. It has: a wavelength setting step to set the wavelength of pulse laser beam having penetrability to wafer in the range of 1300nm~1400nm; a step of forming the modified layer, after the implementation of wavelength setting step, position the focal point of pulse laser beam to the interior of wafer, and irradiate a pulse laser beam onto the region of back side of wafer corresponding to the predetermined division line, also, process and feed the holding mechanism and the laser beam irradiation mechanism relatively for forming a modified layer inside the wafer; and a division step, after implementing the step of forming the modified layer, apply external force to the wafer so as to use the modified layer as the starting point of division to divide the wafer along the predetermined division line. The forming step of modified layer comprises the step of irradiating a first pulse laser light beam having less energy of each pulse to form the first modified layer, and the step of irradiating a second pulse laser light beam having larger energy of each pulse to form the second modified layer stacked on the first modified layer.

Description

Wafer processing method Field of invention

The present invention relates to a pulsed laser beam that illuminates a wavelength that is transparent to a wafer to form a modified layer inside the wafer, and then applies an external force to the wafer to divide the wafer into plural numbers starting from the modified layer. A method of processing a wafer of device wafers.

Background of the invention

A germanium wafer (hereinafter, simply referred to as a wafer) which is divided into a plurality of devices, such as an IC and an LSI, which are divided by a predetermined dividing line and formed on a surface, is divided into individual device wafers by a processing device, and The divided device wafers are widely used in various electrical appliances such as mobile phones and personal computers.

In the division of wafers, a cutting method using a cutting device called a dicing saw is widely used. In the dicing method, when a cutter having a thickness of about 30 μm formed by fixing a diamond or the like with a metal or a resin is rotated at a high speed of about 30,000 rpm, the wafer is cut into a wafer to cut the wafer and divide it into One device wafer.

On the other hand, in recent years, there has been a spotlighting point of a pulsed laser beam that has a wavelength that is transparent to the wafer, corresponding to the division schedule. Inside the wafer of the line, a method of forming a modified layer inside the wafer by irradiating a pulsed laser beam along a predetermined dividing line, and then applying an external force to divide the wafer into individual device wafers is proposed (refer to, for example, a Japanese patent) Bulletin No. 4402708).

The so-called modified layer refers to a region in which the density, the refractive index, the mechanical strength, or other physical properties become different from the surroundings, and includes cracks in addition to the molten resolidified region, the refractive index change region, and the dielectric breakdown region ( Crack) area and the area where these are mixed.

The optical absorption end of the crucible is near the wavelength of 1050 nm of light corresponding to the energy band gap of 矽 (1.1 eV), and on the bulk silcon, the light having a shorter wavelength is absorbed.

In the conventional reforming layer forming method, a Nd:YAG pulsed laser doped with a neon (Nd) having a wavelength of 1064 nm which is close to the optical absorption end is generally used (refer to, for example, Japanese Patent Laid-Open Publication No. 2005). -95952 bulletin).

However, since the wavelength of the Nd:YAG pulsed laser is close to the optical absorption end of the crucible, a portion of the laser beam will be absorbed in the region where the converging point is trapped, and a sufficient reforming layer will not be formed. The case where the wafer cannot be divided into individual device wafers.

Therefore, the Applicant of the present invention has found that when a modified layer is formed by using a YAG pulse laser having a wavelength of 1,342 nm, which is set in the range of 1300 to 1400 nm, to form a modified layer, the region of the condensed spot is included. The absorption of the laser beam can be reduced to form a good modified layer, and the wafer can be smoothly divided into individual device wafers (refer to Japanese Patent Special Japanese Patent Publication No. 2006-108459).

Prior technical literature Patent literature

Patent Document 1: Japanese Patent No. 4402708

Patent Document 2: Japanese Patent Laid-Open Publication No. 2005-95952

Patent Document 3: Japanese Patent Laid-Open Publication No. 2006-108459

Summary of invention

However, it has been found that a new problem arises in that the spot of the pulsed laser beam is positioned inside the wafer for illumination while being adjacent to the newly formed modified layer along the predetermined line of division, while on the wafer. When the reforming layer is formed inside, the surface formed on the surface is attacked and damaged by the laser beam scattering on the surface opposite to the surface on which the pulsed laser beam is irradiated (that is, on the surface of the wafer).

In verifying this problem, it is speculated that there may be a fine crack from the newly formed modified layer to the surface side of the wafer, and the crack causes the penetrating light of the subsequently irradiated pulsed laser beam to refract or reflect and attack the device. To.

The present invention has been made in view of such a problem, and an object of the invention is to provide a pulsed laser beam having a wavelength set in the range of 1300 to 1400 nm for a germanium wafer to form a modified layer inside the wafer. A method of processing a wafer that can damage a device that penetrates light on a wafer surface.

A method for processing a wafer according to the present invention is to borrow A laser processing apparatus for processing a wafer processed wafer having a plurality of devices formed by dividing a predetermined number of lines on a surface by a laser processing apparatus, the laser processing apparatus having a workpiece to be processed a holding mechanism, a laser beam that irradiates a pulsed laser beam having a penetrating wavelength to the workpiece held by the holding mechanism, a laser beam irradiation mechanism that forms a modified layer inside the workpiece, and the holding mechanism A processing feed mechanism for processing a feed relative to the laser beam irradiation mechanism, the wafer processing method characterized by: a wavelength setting step of setting a wavelength of a pulsed laser beam having transparency to a wafer a range of 1300 nm to 1400 nm; a reforming layer forming step, after performing the wavelength setting step, positioning a condensing point of the pulsed laser beam to the inside of the wafer, and an area corresponding to the dividing line from the back side of the wafer Irradiating the pulsed laser beam, and processing the holding mechanism opposite to the laser beam irradiation mechanism to form a reforming layer inside the wafer; and dividing the step to implement the After the reforming layer forming step, an external force is applied to the wafer, and the modified layer is used as a dividing starting point, and the wafer is divided along the dividing line; wherein the modifying layer forming step includes: a first modifying layer forming step, Irradiating the energy per pulse is a first pulsed laser beam having a first value that suppresses the formation of cracks to form a first modified layer; and a second modifying layer forming step, irradiating energy per pulse is a ratio The second pulsed laser beam of the second value having a larger first value is overlapped on the first modified layer to form a second modified layer.

Preferably, the energy (first value) per pulse of the first pulsed laser beam is 1.5 to 4.0 μJ, and the energy per second pulse of the second pulse laser beam (second value) is 6.5 to 10 μJ.

According to the processing method of the wafer of the present invention, since the reforming layer forming step includes the first modifying layer forming step and the second modifying layer forming step, the first modifying layer forming step is to irradiate the energy per pulse Forming a first modified layer by a first pulsed laser beam having a first value that suppresses the formation of a crack, the second modifying layer forming step of irradiating the energy per pulse to be greater than the first value The second-valued second-pulse laser beam is superposed on the first modified layer to form a second modified layer, so when the first pulse of the first value is smaller by the energy per pulse When the first modified layer formed by the irradiation of the beam of light overlaps to irradiate the second pulsed laser beam whose energy per pulse is a relatively large second value, the second pulsed laser beam having a relatively large energy is subjected to The first modified layer is induced to suppress the formation of fine cracks to be superposed on the first modified layer to form a second modified layer, so that the pulsed laser beam that is subsequently irradiated is not affected by the crack. Can solve the problem formed on the surface of the wafer The problem of damage to the piece.

2‧‧‧ Laser processing equipment

4‧‧‧Standing abutment

6‧‧‧1st slider

8, 18‧‧‧ ball screw

10, 20‧‧‧ pulse motor

11‧‧‧Semiconductor wafer

11a‧‧‧ surface

11b‧‧‧Back

12‧‧‧Processing feed mechanism

13a‧‧‧1st dividing line

13b‧‧‧2nd dividing line

14, 24 ‧ ‧ rails

15‧‧‧Device

16‧‧‧2nd slider

19‧‧‧Modified layer

19a‧‧‧Second modified layer

21‧‧‧Device Chip

22‧‧‧Dividing feed mechanism

26‧‧‧Cylinder support members

28‧‧‧Working table

30, 88‧‧‧ fixture

32‧‧‧Cylinder

33‧‧‧shells

34‧‧‧Laser beam irradiation unit

35‧‧‧Laser beam generating unit

37‧‧‧ concentrator

39‧‧‧ camera unit

40‧‧‧Controller (control agency)

42‧‧‧Central Processing Unit (CPU)

44‧‧‧Reading Memory (ROM)

46‧‧‧ Random Access Memory (RAM)

48‧‧‧ counter

50‧‧‧Input interface

52‧‧‧Output interface

54, 58‧‧‧ linear ruler

56‧‧‧Processing feed detection unit

60‧‧‧Divided feed detection unit

62‧‧‧Laser oscillator

64‧‧‧Repetition frequency setting mechanism

66‧‧‧ pulse width adjustment mechanism

68‧‧‧Power adjustment mechanism

68‧‧‧Mirror

72‧‧‧ Concentrating lens

74‧‧‧Attenuator

80‧‧‧Splitting device

82‧‧‧Frame keeping agency

84‧‧‧ tape expansion mechanism

86‧‧‧Frame holding components

86a‧‧‧Loading surface

90‧‧‧Expansion cylinder

92‧‧‧ cover

94‧‧‧Support flange

96‧‧‧ drive mechanism

98‧‧‧ cylinder

100‧‧‧ piston rod

F‧‧‧Ring frame

LB ₁ ‧‧‧first pulsed laser beam

LB ₂ ‧‧‧second pulsed laser beam

P‧‧‧ spotlight

T‧‧‧ cutting tape

1 is a perspective view of a laser processing apparatus suitable for carrying out the method of processing a wafer of the present invention.

2 is a block diagram of a laser beam generating unit.

3 is a perspective view of a surface side of a tantalum wafer.

Figure 4 is a view showing that the surface side of the germanium wafer is attached to the outer peripheral portion. A perspective view of the situation on the dicing tape of the annular frame.

Fig. 5 is a rear perspective view of the tantalum wafer supported by the annular frame through the dicing tape.

Fig. 6 is a schematic view showing an optical path of a laser beam.

Fig. 7 is a perspective view showing a step of forming a modified layer.

Fig. 8(A) is a schematic cross-sectional view illustrating a first modifying layer forming step, and Fig. 8(B) is a schematic cross-sectional view illustrating a second modifying layer forming step.

Figure 9 is a perspective view of the dividing device.

10(A) and (B) are cross-sectional views showing the dividing step.

Form for implementing the invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to Fig. 1, there is shown a schematic perspective view of a laser processing apparatus 2 suitable for carrying out the method of processing a wafer of the present invention.

The laser processing apparatus 2 includes a first slider 6 that is mounted on the stationary base 4 so as to be movable in the X-axis direction. The first slider 6 is moved in the machining feed direction (that is, the X-axis direction) along the pair of guide rails 14 by the machining feed mechanism 12 including the ball screw 8 and the pulse motor 10.

A second slider 16 that is movable in the Y-axis direction is mounted on the first slider 6. In other words, the second slider 16 is moved along the pair of guide rails 24 in the indexing feed direction (that is, the Y-axis direction) by the index feed mechanism 22 including the ball screw 18 and the pulse motor 20.

The working slider 28 is mounted on the second slider 16 through the cylindrical support member 26, and the working chuck 28 can be rotated and processed by the machining feed mechanism 12. The indexing mechanism 22 is movable in the X-axis direction and the Y-axis direction. A clamp 30 that holds an annular frame that supports the wafer held by the work chuck 28 is provided on the work chuck 28.

A column 32 is erected on the stationary base 4, and a laser beam irradiation unit 34 is mounted on the column 32. The laser beam irradiation unit 34 is composed of a laser beam generating unit 35 shown in Fig. 2 housed in the casing 33, and a concentrator 37 attached to the front end of the casing 33.

As shown in FIG. 2, the laser beam generating unit 35 includes a laser oscillator 62 that oscillates to generate a YAG pulse laser, a repetition frequency setting mechanism 64, a pulse width adjusting mechanism 66, and a power adjustment mechanism 68. In the present embodiment, as the laser oscillator 62, a YAG pulse laser oscillator which can oscillate to generate a pulsed laser having a wavelength of 1342 nm is used.

At the front end portion of the casing 35, an image pickup unit 39 that is lined with the concentrator 37 in the X-axis direction to detect a processing area for laser processing is disposed. The imaging unit 39 includes an imaging element such as a general CCD that photographs a processing region of the semiconductor wafer 11 by visible light.

The imaging unit 39 further includes an infrared irradiation unit that irradiates infrared rays to the workpiece, an optical system that captures infrared rays that are irradiated by the infrared irradiation unit, and an electrical signal that outputs infrared rays that are captured by the optical system. An infrared imaging device including an infrared imaging device such as an infrared CCD can transmit the captured image signal to a controller (control mechanism) 40.

The controller 40 is composed of a computer, and includes a central processing unit (CPU) 42 that performs calculation processing in accordance with a control program, a storage control program, and the like. A read-only memory (ROM) 44, a readable and writable random access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 for storing calculation results.

Reference numeral 56 denotes a machining feed amount detecting unit including a linear ruler 54 disposed along the guide rail 14 and a reading head (not shown) disposed on the first slider 6, and the detection of the machining feed amount detecting unit 56. The signal will be input to the input interface 50 of the controller 40.

60 is an indexing feed amount detecting unit composed of a linear ruler 58 disposed along the guide rail 24 and a reading head (not shown) disposed on the second slider 16, and the indexing feed amount detecting unit 60 The detection signal is input to the input interface 50 of the controller 40.

The image signal captured by the camera unit 39 is also input to the input interface 50 of the controller 40. On the other hand, the control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam generating unit 35, and the like.

Referring to Fig. 3, there is shown a front side perspective view of a semiconductor wafer 11 to be processed by the processing method of the present invention. The semiconductor wafer 11 shown in FIG. 3 is composed of, for example, a germanium wafer having a thickness of 100 μm.

The semiconductor wafer 11 has a plurality of first divided planned lines (cutting streets) 13a extending in the first direction and a plurality of second extending in the second direction perpendicularly intersecting the first direction on the surface 11a. The predetermined line 13b is divided, and the device 15 such as an IC or an LSI is formed in each of the areas divided by the first dividing line 13a and the second dividing line 13b.

In the method of processing a wafer according to the embodiment of the present invention, a semiconductor wafer (hereinafter simply referred to as a wafer) 11 is attached to the surface 11a side as shown in FIG. The dicing tape T to which the outer periphery has been attached to the annular frame F is attached, and the back surface 11b of the wafer 11 is exposed as shown in FIG.

In the method of processing a wafer of the present invention, first, the wavelength of a pulsed laser beam having transparency to the germanium wafer 11 is set in a range of 1300 nm to 1400 nm (wavelength setting step). In the present embodiment, as the laser oscillator 62 of the laser beam generating unit 35 shown in Fig. 2, a YAG laser oscillator capable of oscillating a pulsed laser having a wavelength of 1342 nm is used.

Next, the wafer 11 is sucked and held by the dicing tape T on the work chuck 28 of the laser processing apparatus 2, and the back surface 11b of the wafer 11 is exposed. Then, calibration is performed in which the wafer 11 is imaged from the side of the back surface 11b by the infrared imaging element of the image pickup unit 39, and the region corresponding to the first division planned line 13a and the concentrator 37 are in the X-axis direction. In a row. In this calibration, image processing such as well-known pattern matching is utilized.

After the alignment of the first division planned line 13a is performed, the operation table 28 is rotated by 90 degrees, and then the same calibration is performed on the second division planned line 13b extending in the direction perpendicular to the first division planned line 13a. .

After performing the calibration step, the reforming layer forming step is performed, and the concentrating layer forming step is to position the condensing point of the pulsed laser beam having a wavelength of 1342 nm to the first dividing line by the concentrator 37 as shown in FIG. 13a corresponds to the inside of the wafer, irradiating the pulsed laser beam from the side of the back surface 11b of the wafer 11, and processing the working chuck 28 in the direction of the arrow X1, thereby forming the modified layer 19 inside the wafer 11. .

As shown in FIG. 6, the pulsed laser beam emitted from the laser beam generating unit 35 passes through an attenuator 74 at the concentrator 37. After being reflected by the mirror 68, it is condensed inside the wafer 11 by the condensing lens 72.

The reforming layer forming step of the embodiment includes: a first modifying layer forming step of irradiating a first pulsed laser beam having a relatively small (first value) energy per pulse to form a first modifying layer; a second reforming layer forming step of irradiating a second pulsed laser beam having a relatively large energy (a second value greater than the first value) per pulse to overlap on the first modified layer to form a second modification Quality layer.

Here, the first value which is relatively small in energy per pulse means energy for suppressing the formation of cracks propagating from the reforming layer, and in the present embodiment, it is in the range of 1.5 to 4.0 μJ. ideal. The energy per pulse is a relatively large second value to be in the range of 6.5 to 10 μJ.

In the first reforming layer forming step, the pulsed laser beam emitted from the laser beam generating unit 35 is attenuated by the attenuator 74 to a first pulsed laser beam having an energy per pulse of 1.5 to 4.0 μJ.

Then, by concentrating the energy of each pulse as the condensed spot P of the attenuated first pulsed laser beam LB ₁ , the condensing lens 72 of the concentrator 37 is positioned to correspond to the first dividing line 13a. Inside the wafer, the first pulsed laser beam LB _{1 is} irradiated from the back surface 11b side of the wafer 11, and the working chuck 28 is processed and fed in the direction of the arrow X1 in FIG. 7 as shown in FIG. 8(A). A first modifying layer 19 is formed inside the wafer 11.

The work chuck 28 is indexed in the Y-axis direction, and a first reforming layer 19 is formed inside the wafer 11 corresponding to all of the first divided planned lines 13a. Next, the work chuck 28 is rotated 90 degrees, and then along with the first score All of the second division planned lines 13b perpendicularly intersecting the predetermined line 13a form the same modified layer 19.

The reforming layer 19 refers to a region in which the density, the refractive index, the mechanical strength, or other physical properties have become different from the surroundings. For example, a molten resolidification region, a crack region, an insulation failure region, a refractive index change region, and the like are also included, and a region in which these regions are mixed is also included.

The processing conditions of the first modified layer forming step are set as follows, for example.

Light source: YAG pulse laser

Wavelength: 1342nm

Average output: 0.15~0.4W

Repeat frequency: 100kHz

Spot diameter: φ3.0μm

Feeding speed: 300mm/s

After the first modifying layer forming step is performed, a second modifying layer forming step may be performed, in which the second pulsed laser beam LB _{2 having a} relatively large energy per pulse is superposed on the first modifying layer 19 to form a first The second modified layer 19a. In the second reforming layer forming step, since the second modifying layer 19a is formed by being superposed on the first modifying layer 19, the conditions other than the average output are the processing conditions of the first modifying layer forming step described above. same.

In the second reforming layer forming step, the pulsed laser beam emitted from the laser beam generating unit 35 is slightly attenuated by the attenuator 74 to be converted into a relatively large second value of energy per pulse. The second pulsed laser beam LB ₂ .

Thereafter, by positioning the condensed spot P of the second pulsed laser beam LB ₂ on the first modifying layer 19, and illuminating the second pulsed laser beam LB ₂ from the side of the back surface 11b of the wafer 11, the working clip is The stage 28 is fed in the direction of the arrow X1 in Fig. 7, and as shown in Fig. 8(B), the first modified layer 19 is superposed on the first modified layer 19 to form the second modified layer 19a.

In the second reforming layer forming step, the condensing point P of the second pulsed laser beam LB ₂ having a relatively large energy per pulse is superposed on the first modifying layer 19, and from the wafer 11 The second pulsed laser beam LB _{2 is} irradiated on the back surface 11b side, and as shown in FIG. 8(B), the first modified layer 19 is superposed to form the second modified layer 19a.

Since the condensed spot P of the second pulsed laser beam LB ₂ is superposed on the first modified layer 19 and then irradiated with the second pulsed laser beam LB ₂ , the second pulsed laser beam having a relatively large energy can be obtained. LB ₂ is induced by the modified first layer 19, and fine cracks are formed can be suppressed to the second modified layers 19a is formed in the overlap 19 of the modified layer.

Therefore, the second pulsed laser beam LB _{2 to} be irradiated is not affected by the crack, and the problem of damage to the device 15 formed on the surface 11a of the wafer 11 can be solved.

The working chuck 28 is indexed in the Y-axis direction, and is overlapped on the first modifying layer 19 to form the second modifying layer 19a inside the wafer 11 corresponding to all the first dividing lines 13a. .

Next, the work chuck 28 is rotated by 90 degrees, and then all the second divided planned lines 13b perpendicularly intersecting the first divided planned line 13a are superposed on the first modified layer 19 to form the second modified layer 19a. .

The processing conditions of the second modified layer forming step are set as follows, for example.

Light source: YAG pulse laser

Wavelength: 1342nm

Average output: 0.65~1.0W

Repeat frequency: 100kHz

Spot diameter: φ3.0μm

Feeding speed: 300mm/s

In the embodiment shown in FIG. 6, the power of the pulsed laser beam emitted from the laser beam generating unit 35 is attenuated by the attenuator 74 to be converted into the first pulsed laser beam and the second pulsed laser beam. However, other output adjusters may be used instead of the attenuator 74.

In this case, the power adjustment mechanism 68 and the output adjuster can be adjusted by appropriately adjusting the laser beam generating unit 35 to generate the first pulsed laser beam and the second pulsed laser beam.

After the reforming layer forming step is performed, a dividing step of dividing the wafer 11 into individual device wafers 21 by applying an external force to the wafer 11 using the dividing device 80 shown in FIG. 9 is performed. The dividing device 80 shown in FIG. 9 includes a frame holding mechanism 82 that holds the annular frame F, and a tape expanding mechanism 84 that expands the dicing tape T attached to the annular frame F held by the frame holding mechanism 82.

The frame holding mechanism 82 is composed of an annular frame holding member 86 and a plurality of jigs 88 arranged as fixing means disposed on the outer circumference of the frame holding member 86. The upper surface of the frame holding member 86 is formed with a ring frame The mounting surface 86a of the frame F can mount the annular frame F on the mounting surface 86a.

Further, the annular frame F placed on the mounting surface 86a is fixed to the frame holding mechanism 86 by the jig 88. The frame holding mechanism 82 thus constructed is supported by the tape expanding mechanism 84 so as to be movable in the vertical direction.

The tape expansion mechanism 84 is provided with an expansion cylinder 90 disposed inside the annular frame holding mechanism 86. The upper end of the expansion cylinder 90 is closed by a cover 92. This expansion cylinder 90 has an inner diameter smaller than the inner diameter of the annular frame F and larger than the outer diameter of the wafer 11 attached to the dicing tape T attached to the annular frame F.

The expansion cylinder 90 has a support flange 94 integrally formed at a lower end thereof. The tape expansion mechanism 84 further includes a drive mechanism 96 that moves the annular frame holding member 86 in the vertical direction. The drive mechanism 96 is constituted by a plurality of cylinders 98 disposed on the support flange 94, and the piston rod 100 is coupled to the lower surface of the frame holding member 86.

The drive mechanism 96 composed of a plurality of cylinders 98 expands the annular frame holding member 86 at a reference position at a substantially equal height between the mounting surface 86a and the surface of the cover 92 at the upper end of the expansion cylinder 90, and the distance expansion. The expansion position below the predetermined amount of the upper end of the cylinder 90 moves in the vertical direction.

The dividing step of the wafer 11 performed using the dividing device 80 configured as above will be described with reference to FIG. As shown in FIG. 10(A), the annular frame F supporting the wafer 11 through the dicing tape T is placed on the frame holding member. The mounting surface 86a of the 86 is placed and the frame holding member 86 is fixed by the jig 88. At this time, the frame holding member 86 is positioned at a reference position at which the mounting surface 86a and the upper end of the expansion cylinder 90 have substantially the same height.

Next, the cylinder 98 is driven to lower the frame holding member 86 to the expanded position shown in Fig. 10(B). Thereby, the annular frame F fixed to the mounting surface 86a of the frame holding member 86 is also lowered, so that the dicing tape T attached to the annular frame F abuts against the upper end edge of the expansion cylinder 90. It is expanded in the radial direction.

As a result, the tensile force acts radially on the wafer 11 attached to the dicing tape T. When the tensile force is radially applied to the wafer 11, the second modified layer 19a formed along the first and second divided planned lines 13a and 13b is divided into the starting point, and the wafer 11 is placed. The first and second divided planned lines 13a and 13b are cut and divided into individual device wafers 21.

11‧‧‧Semiconductor wafer

11b‧‧‧Back

T‧‧‧ cutting tape

P‧‧‧ spotlight

19‧‧‧Modified layer

19a‧‧‧Second modified layer

LB ₁ ‧‧‧first pulsed laser beam

LB ₂ ‧‧‧second pulsed laser beam

Claims (2)

A method for processing a wafer, which is a wafer processing method for forming a wafer processed by a plurality of devices by dividing a predetermined line on a surface by a laser processing apparatus, the laser The processing apparatus includes a laser beam having a holding mechanism for holding the workpiece and a wavelength of a laser beam that is transparent to the workpiece held by the holding mechanism, so as to form a laser beam of the modified layer inside the workpiece. An irradiation mechanism and a processing feed mechanism that feeds the holding mechanism to the laser beam irradiation mechanism, wherein the wafer processing method is characterized by: a wavelength setting step to be transparent to the wafer The wavelength of the pulsed laser beam is set in the range of 1300 nm to 1400 nm; the reforming layer forming step is performed, and after the wavelength setting step is performed, the concentrating point of the pulsed laser beam is positioned inside the wafer, and is aligned from the back side of the wafer. The area corresponding to the dividing line is irradiated with a pulsed laser beam, and the holding mechanism and the laser beam irradiation mechanism are relatively processed to feed to form a modified layer inside the wafer. And the dividing step, after performing the reforming layer forming step, applying an external force to the wafer and dividing the wafer along the dividing line by using the modified layer as a starting point of the dividing line; wherein the reforming layer forming step includes: a reforming layer forming step of irradiating the energy of each pulse to a first pulsed laser beam having a first value that suppresses the formation of the crack to form a first modified layer; a second reforming layer forming step of irradiating a second pulsed laser beam having a second value greater than the first value, so that the first modified layer overlaps to form a second modified layer . The processing method of the wafer of claim 1, wherein the first value is 1.5 to 4.0 μJ, and the second value is 6.5 to 10 μJ.