TWI697040B - Wafer processing method - Google Patents

Abstract

The object of the present invention is to provide a method for irradiating a silicon wafer with a pulsed laser beam whose wavelength has been set in the range of 1300 to 1400 nm to form a modified layer inside the wafer, which can suppress the device damage caused by the penetrating light on the front side of the wafer Wafer processing method. The solution is a wafer processing method for processing a wafer composed of silicon formed by dividing a plurality of predetermined lines on the front side and forming a plurality of devices. It is characterized by including a wavelength setting step, a modified layer forming step and a dividing step. The wavelength setting step is to set the wavelength of the pulsed laser beam penetrating the wafer in the range of 1300 nm to 1400 nm. The reforming layer forming step is to implement the wavelength setting step, position the condensing point of the pulsed laser beam inside the wafer to irradiate the pulsed laser beam from the back of the wafer toward the area corresponding to the predetermined dividing line and keep The mechanism is processed and fed relative to the laser beam irradiation mechanism to form a modified layer inside the wafer. In 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 planned dividing line with the modified layer as a dividing starting point. In the step of forming the modified layer, the fragile part is avoided to locate the condensing point of the pulsed laser beam. The fragile part is the pulsed laser irradiated by the device that is formed adjacent to the planned dividing line due to scattering The damage caused by the beam.

Description

Wafer processing method Field of invention

The present invention relates to irradiating a pulsed laser beam with a wavelength penetrating to a wafer to form a modified layer inside the wafer, applying an external force to the wafer, and dividing the wafer into a plurality of layers starting from the modified layer Wafer processing method for each device wafer.

Background of the invention

A plurality of devices such as ICs and LSIs are divided by a predetermined dividing line to form a silicon wafer (hereinafter sometimes simply referred to as a wafer) that is divided into individual device chips by a processing device, and The divided device wafers are widely used in various electrical appliances such as mobile phones and personal computers.

For the division of wafers, a cutting method using a cutting device called a dicing saw is widely used. In the cutting method, the wafer is cut and divided by cutting the wafer with a thickness of about 30 μm while fixing the abrasive grains such as diamonds with metal or resin at a high speed of about 30,000 rpm. Into a device wafer.

On the other hand, in recent years, there has been a The converging point of the pulsed laser beam of a specific wavelength is positioned inside the wafer corresponding to the planned dividing line to irradiate the pulsed laser beam along the planned dividing line to form a modified layer inside the wafer, and then external force is applied A method of dividing a wafer into individual device wafers has been proposed (see, for example, Japanese Patent No. 4402708).

The so-called modified layer refers to the area where density, refractive index, mechanical strength and other physical properties have formed differently from the surroundings, and in addition to the melt rehardening area, the refractive index change area, and the insulation breakdown area, it also contains crack areas Or a mixture of these areas.

The optical absorption end of silicon is near the wavelength of 1050nm, which is equivalent to the energy band gap (1.1eV) of silicon. On bulk silcon, light with a wavelength shorter than this is absorbed.

Conventional modified layer formation methods generally use a Nd:YAG pulsed laser doped with neodymium (Nd) that can oscillate a laser with a wavelength of 1064 nm near the optical absorption end (see, for example, Japanese Patent Laid-Open No. 2005-95952 Bulletin).

However, because the wavelength of the Nd:YAG pulse laser is 1064 nm, which is close to the optical absorption end of silicon, a part of the laser beam is absorbed in the region between the condensed light spots, and a sufficient modification layer cannot be formed. The case where the circle is divided into individual device wafers.

Therefore, the inventors of the present invention have found that when a YAG pulsed laser with a wavelength of 1342 nm, for example, set in the wavelength range of 1300 to 1400 nm is used to form a modified layer inside the wafer, the light spot can be sandwiched in the region The absorption of the laser beam is reduced to form a good modification layer, and can be The wafer is successfully divided into individual device wafers (refer to Japanese Patent Laid-Open No. 2006-108459).

Prior technical literature Patent Literature

Patent Document 1: Japanese Patent No. 4402708

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

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

Summary of the invention

However, it was found that the following new problems were formed: the condensing point of the pulsed laser beam was positioned inside the wafer adjacent to the reforming layer just formed to irradiate along the predetermined dividing line, and the reformation was formed inside the wafer After the layer, on the surface opposite to the surface irradiated with the pulsed laser beam (that is, on the front surface of the wafer), the device formed on the front surface will be attacked and damaged due to the scattering of the laser beam.

After verifying this problem, it is presumed that the newly formed modified layer may cause a fine crack to propagate to the front side of the wafer, and the crack refracts or reflects the penetrating light of the pulsed laser beam irradiated subsequently. Caused by the device.

The present invention is made in view of this problem, and its object is to provide a pulsed laser beam with a wavelength set in the range of 1300 to 1400 nm to a silicon wafer to form a modified layer inside the wafer. Wafer processing method to suppress penetrating light from damaging devices on the front side of the wafer.

According to the wafer processing method provided by the present invention, a laser processing apparatus is used to process a wafer composed of silicon formed with a plurality of devices divided by a plurality of predetermined dividing lines on the front surface Processing method, wherein the laser processing device includes a holding mechanism for holding the object to be processed, irradiating a pulsed laser beam with a wavelength that is transparent to the object to be held by the holding mechanism to form a modification inside the object A laser beam irradiating mechanism for the mass layer and a processing and feeding mechanism for processing and feeding the holding mechanism relative to the laser beam irradiating mechanism. The processing method of the wafer is characterized by including: a wavelength setting step, setting the wavelength of a pulsed laser beam penetrating the wafer in the range of 1300 nm to 1400 nm; a reforming layer forming step, after performing the wavelength setting step , Positioning the condensing point of the pulsed laser beam inside the wafer to irradiate the pulsed laser beam from the back of the wafer toward the area corresponding to the predetermined dividing line, and the holding mechanism is opposed to the laser beam irradiation mechanism Processing and feeding to form a modified layer inside the wafer; and a dividing step, after the step of forming the modified layer, an external force is applied to the wafer and the modified layer is used as a division starting point to divide the wafer along the planned dividing line.

In the step of forming the modified layer, the fragile part is avoided to locate the condensing point of the pulsed laser beam. The fragile part is the pulsed laser irradiated by the device formed by the device adjacent to the planned dividing line due to scattering The damage caused by the beam.

According to the wafer processing method of the present invention, even if there are fine cracks propagating from the reformed layer just formed, the pulse laser beam to be irradiated next is irradiated to avoid the fragile part of the device, so it is not The pulsed laser beam may scatter and attack the fragile part of the device, which can solve the problem of damaging the device formed on the front side of the wafer.

2: Laser processing device

4: Static abutment

6: 1st slider

8, 18: Ball screw

10, 20: pulse motor

11: Semiconductor wafer (silicon wafer)

11a: front side of the wafer

11b: the back of the wafer

12: Processing feed mechanism

13a: The first division plan line

13b: 2nd division plan line

14, 24: rail

15: Device

16: 2nd slider

17: Fragile part of laser beam

19: Modified layer

21: Device wafer

22: Indexing feed mechanism

26: cylindrical support member

28: Work clamp table

30, 88: fixture

32: cylinder

33: Shell

34: Laser beam irradiation unit

35: Laser beam generating unit

37: Concentrator

39: Camera unit

40: controller (control mechanism)

42: Central Processing Unit (CPU)

44: Read Only 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: Indexing feed amount detection unit

62: Laser Oscillator

64: Repetition frequency setting mechanism

66: Pulse width adjustment mechanism

67: Power adjustment mechanism

68: Mirror

72: Condenser lens

74: Acousto-optic device (AOD)

76: buffer

80: Split device

82: Frame holding mechanism

84: tape expansion mechanism

86: Frame holding member

86a: Mounting surface

90: Expansion roller

92: lid

94: Support flange

96: Drive mechanism

98: cylinder

100: Piston rod

F: ring frame

T: cutting tape

X1: Arrow

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

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

3 is a front perspective view of a silicon wafer.

FIG. 4 is an enlarged view illustrating a part of the device that is weak to the laser beam.

5 is a perspective view showing a state where the front side of a silicon wafer is attached to a dicing tape that attaches an outer peripheral portion to a ring frame.

6 is a perspective view of the back side of a silicon wafer supported by a ring frame through dicing tape.

7 is a schematic diagram showing the optical path of a laser beam.

FIG. 8 is a perspective view illustrating a step of forming a modified layer.

9 is a cross-sectional view showing the relationship between a modified layer formed inside a wafer and a portion that is weak to a laser beam.

Fig. 10 is a perspective view of a dividing device.

11(A) and (B) are cross-sectional views showing the division steps.

Forms for carrying out the invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, a schematic perspective view of a laser processing apparatus 2 suitable for implementing the wafer processing method of the present invention is shown.

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

The first slider 6 is mounted with a second slider 16 movable in the Y-axis direction. That is, the second slider 16 is moved in the indexing feed direction (that is, the Y-axis direction) along the pair of guide rails 24 by the indexing feed mechanism 22 composed of the ball screw 18 and the pulse motor 20.

The second slider 16 is mounted with a work clamp table 28 through a cylindrical support member 26. The work clamp table 28 is rotatable and can be moved in the X-axis direction by the machining feed mechanism 12 and the index feed mechanism 22 Move in the Y axis direction. The work chuck table 28 is provided with a jig 30 that chucks a ring frame for supporting the wafers attracted and held by the work chuck table 28.

A column 32 is provided upright 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 condenser 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 a YAG pulse laser, a repetition frequency setting mechanism 64, a pulse width adjusting mechanism 66, and a power adjusting mechanism 67. In this embodiment, the laser oscillator 62 is a YAG pulsed laser oscillator that oscillates a pulsed laser with a wavelength of 1342 nm.

An image pickup unit 39 that is aligned with the condenser 37 in the X-axis direction to detect the processing area for laser processing is arranged at the front end portion of the casing 33. The imaging unit 39 includes an imaging element such as a general CCD that images the processing area of the semiconductor wafer 11 with visible light.

The imaging unit 39 further includes an infrared irradiation mechanism that irradiates infrared rays to the workpiece, an optical system that captures infrared rays irradiated by the infrared irradiation mechanism, and outputs electrical signals corresponding to the infrared rays captured by the optical system An infrared imaging mechanism composed of an infrared imaging element such as an infrared CCD and the like, and transmits the captured image signal to a controller (control mechanism) 40.

The controller 40 is composed of a computer, including a central processing unit (CPU) 42 that performs calculation processing according to a control program, a read-only memory (ROM) 44 that stores control programs, etc., and a readable and writable random number that stores calculation results, etc. Access memory (RAM) 46, counter 48, input interface 50, and output interface 52.

56 is a processing feed amount detection unit composed of a linear ruler 54 arranged along the guide rail 14 and a reading head not shown on the first slider 6, and the processing feed amount detection unit 56 detects The signal will be input to the input interface 50 of the controller 40.

60 is an indexing feed amount detection unit composed of a linear ruler 58 arranged along the guide rail 24 and a reading head not shown on the second slider 16, and the indexing feed amount detection 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 control 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.

3 is a front perspective view of the 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 with a thickness of 100 μm.

The semiconductor wafer 11 has a plurality of first planned dividing lines (dicing lines) 13a extending in the first direction and a plurality of second lines extending in the second direction perpendicular to the first direction on the front surface 11a The planned dividing line 13b is formed with devices 15 such as IC and LSI in each area defined by the first planned dividing line 13a and the second planned dividing line 13b.

Referring to FIG. 4, an enlarged view of the front side of the silicon wafer is shown. In the device 15 formed by dividing the planned dividing lines 13a and 13b, there may be a plurality of portions 17 that are damaged by the laser beam and are vulnerable to the irradiation of the laser beam.

In the wafer processing method of the present invention, the portion 17 that is weak to the laser beam is specified in advance, and the position of the portion 17 that is weak to the laser beam is detected in the calibration step described later, and its X-axis coordinate is It is stored in the RAM 46 of the controller 40 in advance.

In the wafer processing method according to the embodiment of the present invention, a semiconductor wafer (hereinafter simply referred to as a wafer) 11 is attached to the front surface 11a side thereof as shown in FIG. As shown in FIG. 6, the dicing tape T is formed in a state where the back surface 11b of the wafer 11 is exposed and processed.

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

Next, the wafer 11 is sucked and held by the work chuck 28 of the laser processing apparatus 2 via the dicing tape T, and the back surface 11 b of the wafer 11 is exposed. Then, the infrared imaging element of the imaging unit 39 images the wafer 11 from the back surface 11b side, and aligns the area corresponding to the first planned dividing line 13a with the condenser 37 in the X-axis direction. In this calibration, well-known image processing such as pattern matching is used.

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

During this calibration, the portion 17 that is vulnerable to laser beam irradiation as shown in FIG. 4 is detected, and the X coordinate value of this vulnerable portion is stored in the RAM 46 of the controller 40.

After the calibration step is performed, a reforming layer forming step is performed. The reforming layer forming step is to position the condensing point of the pulsed laser beam with a wavelength of 1342 nm with the condenser 37 as shown in FIG. In the wafer 13a, a pulsed laser beam is irradiated from the back surface 11b side of the wafer 11 and the work clamp 28 is processed and fed in the direction of arrow X1, thereby forming the modified layer 19 inside the wafer 11.

As shown in FIG. 7, the pulsed laser beam emitted from the laser beam generating unit 35 passes through the acousto-optic element (AOD) 74 and is applied to the mirror of the condenser 37 After being reflected on the sub 68, it is condensed inside the wafer 11 by the condensing lens 72. The pulsed laser beam changes its refractive index when a voltage is applied to the AOD74, and is refracted at the AOD74 as shown by the broken line and absorbed by the buffer 76.

In the modified layer forming step of this embodiment, during the processing and feeding of the work holder 28 in the direction of the arrow X1, as shown in FIG. 9, when the X coordinate value of the portion 17 that is vulnerable to the irradiation of the laser beam is detected After that, a voltage is applied to the AOD74 shown in FIG. 7 so that the pulsed laser beam emitted from the laser beam generating unit 35 is refracted at the AOD74 and absorbed by the buffer 76.

After passing through the fragile part 17, the application of voltage to the AOD74 is stopped. In this way, the focusing point of the pulsed laser beam can be positioned inside the wafer 11 to form the modified layer 19 inside the wafer again.

The work chuck table 28 is divided and fed in the Y-axis direction, and the modified layer 19 is formed while avoiding all the portions 17 in the wafer 11 corresponding to the first planned dividing line 13a that are weak to the laser beam. Next, the work clamping table 28 is rotated by 90°, and thereafter, the same modified layer 19 is formed along all the second planned dividing lines 13b perpendicularly crossing the first planned dividing line 13a.

The modified layer 19 refers to a region in which the density, refractive index, mechanical strength, and other physical properties have become different from the surroundings. For example, it may include a melt rehardening region, a crack region, a dielectric breakdown region, a refractive index change region, etc., and may also include a region obtained by mixing these regions.

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

Light source: YAG pulsed laser

Wavelength: 1342nm

Average output: 0.5W

Repetition frequency: 100kHz

Light spot diameter: φ 2.5μm

Feeding speed: 300mm/s

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 ring-shaped frame F, and a tape expansion mechanism 84 that expands the cutting tape T mounted on the ring-shaped frame F held by the frame holding mechanism 82.

The frame holding mechanism 82 is composed of a ring-shaped frame holding member 86 and a plurality of jigs 88 as fixing mechanisms disposed on the outer periphery of the frame holding member 86. On the upper surface of the frame holding member 86, a mounting surface 86a for mounting the ring-shaped frame F is formed, and the ring-shaped frame F can be mounted on this mounting surface 86a.

The ring frame F placed on the mounting surface 86a is fixed to the frame holding mechanism 86 by a jig 88. The frame holding mechanism 82 configured in this way is supported by the tape expansion mechanism 84 so as to be movable in the vertical direction.

The tape expansion mechanism 84 includes an expansion drum 90 arranged inside the ring-shaped frame holding mechanism 86. The upper end of the expansion drum 90 is closed by the lid 92. This expansion drum 90 has an inner diameter smaller than the inner diameter of the ring frame F and larger than the outer diameter of the wafer 11 attached to the dicing tape T mounted on the ring frame F path.

The expansion drum 90 has a support flange 94 integrally formed at the lower end thereof. The tape expansion mechanism 84 further includes a drive mechanism 96 that moves the ring-shaped frame holding member 86 in the vertical direction. The driving mechanism 96 is composed of a plurality of cylinders 98 arranged on the support flange 94 and connects the piston rod 100 to the lower surface of the frame holding member 86.

The driving mechanism 96 composed of a plurality of air cylinders 98 causes the ring-shaped frame holding member 86 to have the placement surface 86a and the front surface of the cover 92 at the upper end of the expansion drum 90 at a reference position of approximately the same height and distance from the expansion drum The expansion positions below the upper end of 90 at a predetermined amount move up and down.

With reference to FIG. 11, the process of dividing the wafer 11 using the dividing device 80 configured as described above will be described. As shown in FIG. 11(A), the ring-shaped frame F supporting the wafer 11 through the dicing tape T is placed on the mounting surface 86a of the frame holding member 86, and is fixed to the frame holding member 86 by a jig 88. At this time, the frame holding member 86 is positioned at a reference position where the placement surface 86a and the upper end of the expansion drum 90 are substantially the same height.

Next, the air cylinder 98 is driven to lower the frame holding member 86 to the expanded position shown in FIG. 11(B). As a result, the ring frame F fixed on the mounting surface 86a of the frame holding member 86 will also be lowered, so the cutting tape T mounted on the ring frame F will abut on the upper end edge of the expansion drum 90 and mainly face The radial direction is expanded.

As a result, a tensile force acts radially on the wafer 11 attached to the dicing tape T. In this way, the tensile force acts radially on the wafer At 11, the modified layer 19 formed along the first and second planned dividing lines 13a, 13b becomes the starting point of the division, and the wafer 11 is cut along the first and second planned dividing lines 13a, 13b. Divided into device wafers 21 one by one.

According to the above-mentioned embodiment, in the reforming layer forming step, the pulsed laser beam is irradiated from the back surface 11b side of the wafer 11 while avoiding the portion vulnerable to the irradiation of the laser beam. The fine cracks propagated by the mass layer 19 will also irradiate the laser beam away from the part 17 of the device 15 that is vulnerable to the laser beam, without the pulsed laser beam scattering and attacking the fragile part of the device 15 In the case of 17, it is possible to prevent the device 15 from being damaged.

11: Semiconductor wafer (silicon wafer)

11b: the back of the wafer

28: Work clamp table

35: Laser beam generating unit

37: Concentrator

68: Mirror

72: Condenser lens

74: Acousto-optic device (AOD)

76: buffer

T: cutting tape

Claims (1)

A wafer processing method is a wafer processing method for processing a wafer composed of silicon in which a plurality of devices are formed by dividing a plurality of predetermined dividing lines on the front surface by a laser processing device, wherein The laser processing apparatus includes a holding mechanism for holding the object to be processed, and a laser beam that irradiates a pulsed laser beam with a wavelength that is transparent to the object to be held by the holding mechanism to form a modified layer inside the object The beam irradiation mechanism and the processing feeding mechanism that processes and feeds the holding mechanism relative to the laser beam irradiation mechanism. The processing method of the wafer is characterized by including a wavelength setting step, which will have transparency to the wafer The wavelength of the pulsed laser beam is set in the range of 1300nm~1400nm; after the step of forming the modified layer, after the implementation of the wavelength setting step, the condensing point of the pulsed laser beam is positioned inside the wafer to face from the back of the wafer Irradiate a pulsed laser beam to the area that should be divided into predetermined lines, and process and feed the holding mechanism and the laser beam irradiation mechanism to form a modified layer inside the wafer; and a dividing step to implement the modified layer formation After the step, an external force is applied to the wafer and the modified layer is used as a starting point to split the wafer along the planned dividing line. In the step of forming the modified layer, the focused portion of the pulsed laser beam is positioned to avoid the weak part Point, the fragile part is caused by the pulsed laser beam irradiated by scattering by the device formed adjacent to the planned dividing line The damaged part.

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