TW201625374A - Wafer processing method - Google Patents

Abstract

A subject of this invention is to provide a wafer processing method. As the wafer is irradiated by pulse laser beam with a determined wavelength ranging from 1300nm to 1400nm to form a modified layer inside the wafer, penetrated light is suppressed from damaging components on the surface of the wafer. A solution of this invention is a wafer processing method that processes a silicon wafer whose surface is divided by a plurality of predetermined division lines to form a plurality of components. The method is characterized in including a wavelength setting step where a wavelength of a pulse laser beam that is of penetrability to the wafer within a range of 1300nm~1400nm, a beam correction step where, after the wavelength setting step, a power distribution of the pulse laser beam of each pulse is modified to form a cap shape, a modified layer forming step where, after the beam correction step, a converging point of the pulse laser beam is positioned inside the wafer to irradiate the areas corresponding to the predetermined division lines with the pulse laser beam from the back side of the wafer, and the retaining mechanism and the laser beam irradiating mechanism are processed and fed relative to each other to form a modified layer inside the wafer, and a splitting step, where, after the modified layer forming step, an external force is applied to the wafer to cut the wafer along the predetermined division lines with the modified layer serving as a start point of cutting.

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 sometimes referred to simply as a wafer) in which a plurality of devices such as an IC and an LSI are divided into predetermined dividing lines and formed on a surface thereof is divided into individual device wafers by a processing device. The device wafers that have been divided can be widely used in various electronic devices 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 cutting method, when a cutting blade having a thickness of about 30 μm is fixed by grinding a metal such as a metal or a resin to form a cutting blade having a thickness of about 30 μm , the wafer is cut into the wafer, thereby cutting and dividing the wafer. Into a device wafer.

On the other hand, in recent years, there has been a concentrating point of a pulsed laser beam that has a wavelength that is transparent to a wafer, and a predetermined line is divided. In the interior of the corresponding wafer, a method of forming a modified layer inside the wafer by irradiating the 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, Japan). Patent 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 deuterated region, and the insulating breakage 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 band gap (1.1 eV) of the crucible, 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 ytterbium (Nd) which can oscillate a laser having a wavelength of 1064 nm close to the optical absorption end is generally used (refer to, for example, Japanese Patent Laid-Open) Bulletin 2005-95952).

However, since the wavelength of the Nd:YAG pulsed laser is close to the optical absorption end of the 矽, the laser beam is partially absorbed in the region of the condensed spot, and a sufficient reforming layer is not formed. The case where the wafer is 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 when it is adjacent to the newly formed modified layer along the dividing line, and is on the wafer. When the reforming layer is formed inside, the surface formed on the surface is attacked and damaged by the scattering of the laser beam on the surface opposite to the surface of the laser beam irradiated with the pulsed laser beam (that is, on the surface of the wafer). .

After 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 the device and attack the device. Caused.

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 forming a modified layer in a wafer. A method of processing a wafer that inhibits damage to a device on the surface of the wafer by penetrating light.

The method for processing a wafer according to the present invention is a wafer processed by a laser processing device for forming a wafer composed of a plurality of devices formed by dividing a predetermined number of lines on a surface by a laser processing device. A processing method, wherein the laser processing apparatus includes a pulsed laser beam having a holding mechanism for holding a workpiece and a wavelength that is transparent to a workpiece held by the holding mechanism to form a modified inside the workpiece A laser beam irradiation mechanism of the mass layer and a processing feed mechanism that feeds the holding mechanism to the laser beam irradiation mechanism. The wafer processing method is characterized by comprising: a wavelength setting step of setting a wavelength of a pulsed laser beam having transparency to a wafer in a range of 1300 nm to 1400 nm; and a beam correcting step, after performing the wavelength setting step, The power distribution of the pulsed laser beam per pulse is formed into a top hat shape; the reforming layer forming step, after performing the beam correcting step, positioning the concentrated spot of the pulsed laser beam inside the wafer, Irradiating a pulsed laser beam from a back surface of the wafer corresponding to the predetermined dividing line, and processing the feeding mechanism relative to the laser beam irradiation mechanism to form a modified layer inside the wafer; And the dividing step, after the reforming layer forming step is performed, an external force is applied to the wafer, and the wafer is divided along the dividing line by using the modified layer as a dividing starting point.

According to the processing method of the wafer of the present invention, since the power distribution of the pulsed laser beam per pulse is formed into a top hat shape in the beam correcting step, there is no slight power of the hillside such as a Gaussian distribution. In the case of a wafer, a modified layer can be formed inside the wafer with only a relatively high power.

Therefore, since the formation of fine cracks due to weak power can be suppressed, the pulsed laser beam to be irradiated is not affected by the crack, and the problem of damage to the device formed on the surface of the wafer can be solved. .

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

17‧‧‧ gap

19‧‧‧Modified layer

21‧‧‧Device Chip

22‧‧‧Dividing feed mechanism

26‧‧‧Cylinder support member

28‧‧‧Working table

30‧‧‧Clamp

32‧‧‧ pillar

33‧‧‧shells

34‧‧‧Laser beam irradiation unit

35‧‧‧Laser beam generating unit

37‧‧‧ concentrator

39‧‧‧Photographic 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

70‧‧‧beam expander

72‧‧‧ mirror

74‧‧‧ Concentrating lens

75‧‧‧Power distribution

75a, 75b‧‧‧ hillside section

80‧‧‧Splitting device

82‧‧‧Frame keeping agency

84‧‧‧ tape expansion mechanism

86‧‧‧Frame holding components

86a‧‧‧Loading surface

88‧‧‧ fixture

90‧‧‧Expansion roller

92‧‧‧ cover

94‧‧‧Support flange

96‧‧‧ drive mechanism

98‧‧‧ cylinder

100‧‧‧ piston rod

T‧‧‧ cutting tape

F‧‧‧Ring frame

X, Y, Z‧‧ Direction

X1‧‧‧ arrow

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.

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

4 is a perspective view showing a state in which the surface side of the crucible wafer is attached to a dicing tape that attaches the outer peripheral portion to the annular frame.

Fig. 5 is a perspective view showing the back side of a crucible wafer supported by an annular frame through a dicing tape.

Fig. 6 is a schematic view showing a beam correcting step.

Fig. 7 is a graph showing the power distribution of a laser beam per one pulse formed into a top hat shape.

Fig. 8 is a perspective view showing a step of forming a modified layer.

Figure 9 is a cross-sectional view showing a modified layer formed under predetermined processing conditions.

Figure 10 is a perspective view of the dividing device.

11(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.

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

The second slider 16 is provided with a working chuck 28 through the cylindrical support member 26, and the working chuck 28 is rotatable and can be rotated in the X-axis direction by the machining feed mechanism 12 and the indexing feed mechanism 22. Move in the Y-axis direction. A clamp 30 for holding the annular frame for supporting the wafer held by the work chuck 28 is provided on the work chuck 28.

A pillar 32 is erected on the stationary base 4, and a laser beam irradiation unit 34 is mounted on the pillar 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 this embodiment As the laser oscillator 62, a YAG pulsed laser oscillator which can oscillate to generate a pulsed laser having a wavelength of 1342 nm is used.

As shown in Fig. 1, at the end of the casing 33, an image pickup unit 39 which is aligned 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 ray irradiation mechanism that irradiates the workpiece with infrared rays, an optical system that can capture the infrared ray that is irradiated by the infrared ray irradiation mechanism, and an electrical signal that corresponds to the infrared ray captured by the optical system. An infrared imaging device including an infrared imaging device such as an infrared CCD that is outputted 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 according to a control program, a read-only memory (ROM) 44 that stores a control program, and the like, and a readable and writable random such as a storage calculation result. The memory (RAM) 46, the counter 48, the input interface 50, and the output interface 52 are accessed.

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

The image signal captured by the imaging unit 39 is also input to the input interface 50 of the controller 40. On the other hand, a 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 silicon 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. Further, on the outer circumference of the semiconductor wafer 11, a notch 17 as a mark indicating the crystal orientation of the germanium wafer is formed.

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. 4, and the outer periphery is attached to the annular frame F. The dicing tape T is formed and formed by exposing the back surface 11b of the wafer 11 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, the A pulsed laser YAG laser oscillator with a wavelength of 1342 nm can be oscillated.

After the wavelength setting step has been performed, a beam correcting step is performed which corrects the shape of the pulsed laser beam emitted from the laser beam generating unit 35. In this beam correcting step, the power distribution of the pulsed laser beam per pulse is formed into a top hat shape.

An embodiment in which the power distribution of the pulsed laser beam per pulse is formed into a top hat shape will be described with reference to FIG. In this embodiment, the beam expander 70 corrects the pulsed laser beam emitted from the laser beam generating unit 35 in such a manner as to enlarge the beam diameter.

The beam expander 70 is easily implemented by, for example, passing a pulsed laser beam through two convex lenses. The pulsed laser beam having the beam diameter expanded by the beam expander 70, although reflected on the mirror 72 of the concentrator 37, is condensed by the collecting lens 74 to the inside of the wafer 11 held by the working chuck 28. However, since the peripheral portion of the beam cross section does not pass through the collecting lens 74, it does not contribute to the formation of the reforming layer.

That is, as shown in FIG. 7, in the beam correcting step, among the power distributions 75 of the pulsed laser beams per pulse, the hill portions 75a, 75b having weaker power at both ends do not pass through the collecting lens. 74, so the formation of the modified layer 19 will be discarded without contributing. That is, in the beam correcting step, the beam shape of the pulsed laser beam is formed into a top hat shape using only a portion of the central portion where the power is strong.

Next, as shown in FIG. 8, the wafer holder 11 is sucked and held by the working tape 28 of the laser processing apparatus 2 via the dicing tape T, and the back surface of the wafer 11 is placed. 11b exposed. Then, the calibration is performed, and the wafer 11 is imaged from the back surface 11b side 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 aligned in the X-axis direction. In this calibration, image processing such as well-known pattern matching is utilized.

After the calibration 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. .

In the reforming layer forming step, since the reforming layer 19 is formed inside the wafer 11 by the pulsed laser beam formed in the shape of a top hat, there is no partial illumination of the weak power of the hillside such as the Gaussian distribution. In the case of a wafer, the reforming layer 19 can be formed only with a relatively high power of the central portion.

Therefore, since the formation of fine cracks due to weak power can be suppressed, the pulsed laser beam to be irradiated is not affected by the crack, and thus the pulsed laser beam can be prevented from being scattered and damaged on the wafer 11. The case of the device 10 of the surface 11a.

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

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

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

Light source: YAG pulse laser

Wavelength: 1342nm

Average output: 0.5W

Repeat frequency: 100kHz

Spot diameter: φ 2.5 μ m

Feeding speed: 300mm/s

Referring to Fig. 9, there is shown a cross-sectional view showing the reforming layer 19 formed inside the wafer 11 under the above processing conditions. Under the above processing conditions, the interval between adjacent reforming layers 19 and 19 was 3 μm.

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. 10 is performed. The dividing device 80 shown in Fig. 10 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 an annular frame holding member 86, and A plurality of jigs 88, which are arranged as fixing means on the outer circumference of the frame holding member 86, are formed. A mounting surface 86a on which the annular frame F is placed is formed on the upper surface of the frame holding member 86, and the annular frame F can be placed 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 roller 90 disposed inside the annular frame holding mechanism 86. The upper end of the expansion drum 90 is closed by a cover 92. The expansion drum 90 has an outer 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 mounted on the annular frame F.

The expansion drum 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 composed of 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 the plurality of cylinders 98 sets the annular frame holding member 86 at a reference position at which the mounting surface 86a and the surface of the cover 92 at the upper end of the expansion drum 90 are substantially the same height, and the distance expansion roller The expansion position below the predetermined amount of the upper end of 90 moves in the up and down direction.

The division step of the wafer 11 implemented by the dividing device 80 configured as described above will be described with reference to FIG. As shown in Figure 11 (A), The annular frame F that supports the wafer 11 through the dicing tape T is placed on the mounting surface 86a of the frame holding member 86, 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 drum 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. 11(B). Thereby, since the annular frame F fixed to the mounting surface 86a of the frame holding member 86 is also lowered, the dicing tape T attached to the annular frame F abuts on the upper end of the expansion drum 90. The cover 92 is mainly 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 acts radially on the wafer 11, the modified layer 19 formed along the first and second divided planned lines 13a and 13b becomes the starting point of the division, and the wafer 11 is along the wafer 11. The first and second divided planned lines 13a and 13b are cut and divided into individual device wafers 21.

According to the above embodiment, since the power distribution of the pulsed laser beam per pulse is formed into a top hat shape in the beam correcting step, the weak power of the hillside such as the Gaussian distribution is not irradiated onto the wafer, and only Since the reforming layer is formed with a strong power at the center of the beam, it is possible to suppress the formation of fine cracks caused by weak power, so that the pulsed laser beam to be irradiated is not affected by the crack, and thus can be prevented. The pulsed laser beam is scattered to damage the device 15 formed on the surface 11a of the wafer 11.

11‧‧‧Semiconductor wafer

28‧‧‧Working table

35‧‧‧Laser beam generating unit

37‧‧‧ concentrator

70‧‧‧beam expander

72‧‧‧ mirror

74‧‧‧ Concentrating lens

Claims (1)

A method for processing a wafer by using a laser processing apparatus to process a wafer formed by a plurality of devices formed by dividing a predetermined number of lines on a surface by a laser processing apparatus, wherein the wafer is processed by a laser processing apparatus The laser processing apparatus includes a pulsed laser beam having a holding mechanism for holding a workpiece and a wavelength that is transparent to the workpiece held by the holding mechanism, so as to form a modified layer of the inside of the workpiece. a beam irradiation mechanism and a processing feed mechanism for processing the holding mechanism opposite to the laser beam irradiation mechanism, the wafer processing method is characterized by comprising: a wavelength setting step of wearing the wafer The wavelength of the permeable pulsed laser beam is set in the range of 1300 nm to 1400 nm; the beam correcting step, after performing the wavelength setting step, the power distribution of the pulsed laser beam per pulse is formed into a top hat shape; the reformed layer is formed. Step, after performing the beam correcting step, positioning a concentrating point of the pulsed laser beam inside the wafer to face the area corresponding to the dividing line from the back side of the wafer Irradiating the pulsed laser beam, and processing the feeding mechanism opposite to the laser beam irradiation mechanism to form a modified layer inside the wafer; and dividing the step, performing the reforming layer forming step, and then performing the crystal modification The circle imparts an external force and divides the wafer along the dividing line by using the modified layer as a starting point of division.