JP6529404B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a method of processing a wafer such as a silicon wafer.

  A wafer such as a silicon wafer on which a plurality of devices such as IC and LSI are divided by dividing lines and formed on the surface is divided into individual device chips by a processing device, and the divided device chips are mobile phones, personal computers, etc. Are widely used in various electronic devices.

  A dicing method using a cutting device called a dicing saw is widely adopted for dividing the wafer. In the dicing method, a cutting blade with a thickness of about 30 μm is solidified by grinding abrasive particles such as diamond with metal or resin, and the wafer is cut by rotating it at a high speed of about 30,000 rpm to cut the wafer. Divide into device chips.

  On the other hand, in recent years, a method of dividing a wafer into individual device chips using a laser beam has been developed and put to practical use. First and second processing methods described below are known as methods for dividing a wafer into individual device chips using a laser beam.

  In the first processing method, the focusing point of a laser beam of a wavelength having transparency to the wafer is positioned inside the wafer corresponding to the planned dividing line, and the laser beam is irradiated along the planned dividing line. In this method, a modified layer is formed inside, and then an external force is applied to the wafer by a dividing device to divide the wafer into individual device chips using the modified layer as a dividing starting point (see, for example, Japanese Patent No. 3408805).

  In the second processing method, a laser beam of a wavelength (for example, 355 nm) having absorption to the wafer is irradiated to a region corresponding to the planned dividing line to form a processing groove by ablation processing, and then an external force is applied. This is a method of dividing a wafer into individual device chips with a processing groove as a dividing starting point (see, for example, JP-A-10-305420).

  The first processing method described above has merits such as minimization of cut lines and anhydrous processing as compared to dicing using a cutting blade that has generally been used without any generation of processing waste, and is actively used. There is.

  In addition, the dicing method using laser beam irradiation has an advantage that it can process a wafer having a discontinuous configuration in which a planned dividing line (street) is substituted for a projection wafer (for example, see JP-A-2010-123723). ). In processing a wafer in which the planned dividing line is discontinuous, processing is performed by turning on / off the laser beam output according to the setting of the planned dividing line.

Patent No. 3408805 JP 10-305420 A JP, 2010-123723, A

  However, there is the following problem in the vicinity of the intersection point where the planned dividing line extending in the second direction abuts on the dividing planned line continuously extending in the first direction as a T-junction.

  (1) The first divided line in which the first modified layer is previously formed inside the first divided line parallel to one side of the device forms a T-shaped intersection with the first divided line. (2) When the reformed layer is formed, a part of the laser beam for processing the second dividing scheduled line is irradiated to the already formed first modified layer as the focusing point of the laser beam approaches the intersection of the T-junction There is a problem that reflection or scattering of a laser beam occurs, light leaks to the device area, and the leak light damages the device and degrades the quality of the device.

  (2) On the contrary, before forming the modified layer in the first planned dividing line parallel to one side of the device, the wafer is arranged along the second planned dividing line which comes into contact with the first planned dividing line as a T-shaped path. If a reformed layer is first formed inside, a reformed layer that blocks the progress of a crack generated from the reformed layer formed in the vicinity of the intersection of the T-junction is not present at the intersection of the T-junction. There is a problem that the crack extends about 1 to 2 mm from the intersection of the T-shaped passage to reach the device and the quality of the device is degraded.

  The present invention has been made in view of these points, and it is an object of the present invention to laser-work a wafer on which at least one planned dividing line is discontinuously formed. It is suppressed that the laser beam is irradiated to the modified layer which has already been formed near the intersection point where the end portion becomes a T-shaped path to the other dividing planned line and the reflection or scattering of the laser beam in the modified layer It is an object of the present invention to provide a method of processing a wafer that can prevent and prevent damage to devices due to leakage light.

  According to the present invention, each of the plurality of first planned division lines formed in the first direction and the plurality of second planned division lines formed in the second direction intersecting the first direction A method of processing a wafer in which devices are formed in a region and a wafer on which at least the second planned dividing line among the first planned dividing line and the second planned dividing line is discontinuously divided into individual device chips A laser beam of a wavelength having transparency to the wafer is condensed from the back side of the wafer into the interior of the wafer and irradiated along the first planned dividing line to the inside of the wafer; After performing a first direction modified layer forming step of forming a plurality of first direction modified layers along a predetermined line, and performing the first direction modified layer forming step, along the second divided planned line , Versus wafer A laser beam of a wavelength having transparency is condensed and irradiated from the back side of the wafer into the interior of the wafer to form a plurality of second direction modified layers along the second planned dividing line inside the wafer. After performing the second direction modified layer forming step, the first direction modified layer forming step, and the second direction modified layer forming step, an external force is applied to the wafer to form the first direction modified layer and the first direction modified layer. And c) dividing the wafer along the first planned dividing line and the second planned dividing line with the second direction modified layer as the fracture start point, and dividing the wafer into individual device chips. The formation step includes the step of forming a second direction modified layer inside the second planned division line intersecting with the first planned division line on which the first direction modified layer is formed as a T-shaped passage. A step of forming a T-shaped path including a step of forming a curved side Is the wafer processing method characterized in that the wavelength is irradiated to the laser beam 1064nm is provided.

  Preferably, in the first direction modified layer forming step and the second direction modified layer forming step other than the T-junction processing step, a laser beam having a wavelength of 1300 nm or more is irradiated. More preferably, the wavelength of the laser beam irradiated in steps other than the T-shaped step is 1342 nm.

  According to the wafer processing method of the present invention, since the laser beam with a wavelength of 1064 nm is irradiated in the T-junction processing step, the laser beam is formed earlier than in the case where the laser beam with a wavelength of 1300 nm or more is irradiated. Even if light leaks due to scattering or reflection of the laser beam due to collision with the first direction modification layer, the amount of leaked light is small, so the problem of leaked light attacking the device and damaging the device Can be suppressed. Therefore, an appropriate modified layer can be formed on the inside of the wafer along the planned dividing line without degrading the quality of the device.

FIG. 1 is a perspective view of a laser processing apparatus suitable for carrying out the wafer processing method of the present invention. It is a block diagram of a laser beam generation unit. FIG. 1 is a perspective view of a semiconductor wafer suitable for being processed by the wafer processing method of the present invention. It is a perspective view which shows a 1st direction modification layer formation step. It is a typical sectional view showing the 1st direction modification layer formation step. It is a schematic plan view which shows a 2nd direction modification layer formation step. It is a schematic side view which shows the structure which switches the laser oscillator used between a 1st and 2nd direction modification layer formation step and a T-junction processing step. It is a perspective view of a dividing device. It is sectional drawing which shows a division | segmentation step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a perspective view of a laser processing apparatus 2 suitable for carrying out the method of processing a wafer according to an embodiment of the present invention is shown. The laser processing apparatus 2 includes a pair of guide rails 6 which are mounted on a stationary base 4 and extend in the Y-axis direction.

  The Y-axis movement block 8 is moved by the Y-axis feed mechanism (Y-axis feed unit) 14 composed of the ball screw 10 and the pulse motor 12 in the indexing feed direction, that is, the Y-axis direction. A pair of guide rails 16 extending in the X-axis direction is fixed on the Y-axis moving block 8.

  The X-axis movement block 18 is guided by the guide rail 16 by the X-axis feed mechanism (X-axis feed unit) 28 composed of the ball screw 20 and the pulse motor 22 and moved in the processing feed direction, that is, the X axis direction. Ru.

  A chuck table 24 is mounted on the X-axis moving block 18 via a cylindrical support member 30. The chuck table 24 is provided with a plurality of (four in the present embodiment) clamps 26 for clamping an annular frame F shown in FIG. 4.

  A column 32 is erected behind the base 4. The casing 36 of the laser beam irradiation unit 34 is fixed to the column 32. The laser beam irradiation unit 34 includes a first laser beam generation unit 35 housed in a casing 36, and a light collector (laser head) 38 having a condensing lens 39 (see FIG. 7) attached to the tip of the casing 36. Contains. The condenser 38 is attached to the casing 36 so as to be finely movable in the vertical direction (Z-axis direction).

  The first laser beam generation unit 35, as shown in FIG. 2, includes a first laser oscillator 42A such as a YAG laser oscillator or YVO4 laser oscillator that oscillates a pulsed laser with a wavelength of 1064 nm, repetition frequency setting means 44, and pulse width adjustment. And means 46 and power adjusting means 48 for adjusting the power of the pulsed laser beam oscillated from the laser oscillator 42.

  Furthermore, as shown in FIG. 7, the second laser beam generation unit (not shown) is provided with a second laser oscillator 42B such as a YAG laser oscillator or a YVO4 laser oscillator that oscillates a pulsed laser with a wavelength of 1342 nm.

  Similarly to the first laser beam generation unit 35 shown in FIG. 2, the second laser beam generation unit also includes repetition frequency setting means, pulse width adjustment means and power adjustment means, but these components are shown in FIG. It is omitted.

  At the tip of the casing 36 of the laser beam irradiation unit 34, an imaging unit 40 equipped with a microscope and a camera for imaging the wafer 11 held by the chuck table 24 is mounted. The condenser 38 and the imaging unit 40 are disposed in alignment in the X-axis direction.

  Referring to FIG. 3, there is shown a surface side perspective view of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11 suitable for being processed by the wafer processing method of the present invention. On the surface 11a of the wafer 11, a plurality of first planned dividing lines 13a formed continuously in the first direction and a plurality of first planned non-continuously formed in the direction orthogonal to the first dividing plan line 13a A two-divided line 13 b is formed, and a device 15 such as an LSI or the like is formed in a region divided by the first divided line 13 a and the second divided line 13 b.

  In carrying out the method of processing a wafer according to the embodiment of the present invention, as shown in FIG. 4, the wafer 11 is attached to a dicing tape T, which is an adhesive tape whose outer surface is attached to an annular frame F. In the form of a frame unit, the wafer 11 is mounted on a chuck table 24 in the form of a frame unit and suction-held through a dicing tape T, and an annular frame F is clamped and fixed by a clamp 26.

  Although not illustrated, in the wafer processing method of the present invention, first, the wafer 11 held by suction on the chuck table 24 is positioned directly below the imaging unit 40 of the laser processing apparatus 2 and the imaging unit 40 images the wafer 11 , Align the first planned division line 13a with the light collector 38 in the X-axis direction.

  Next, after rotating the chuck table 24 by 90 °, the same alignment is performed on the second dividing lines 13b extending in the direction orthogonal to the first dividing lines 13a, and the alignment data of the laser processing apparatus 2 is obtained. Store in the controller's RAM.

  Since the imaging unit 40 of the laser processing apparatus 2 is usually equipped with an infrared camera, the first and second planned division lines 13a, 13b formed on the surface 11a by the infrared camera through the wafer 11 from the back surface 11b side of the wafer 11 13b can be detected.

  After the alignment is performed, a first direction modified layer forming step is performed to form a first direction modified layer 17 inside the wafer 11 along the first planned dividing line 13a. In this first direction modified layer forming step, as shown in FIG. 4 and FIG. 5, the condensing point of the laser beam having a wavelength having transparency to the silicon wafer 11 is placed inside the wafer 11 by the light collector 38. Positioning and irradiation from the back surface 11b side of the wafer 11 to the first planned dividing line 13a, and processing feed of the chuck table 24 in the direction of arrow X1 in FIG. 5, along the first planned dividing line 13a inside the wafer 11. The first direction modified layer 17 is formed.

  Here, since the optical absorption edge of the silicon wafer is about 1050 nm, a laser beam with a wavelength of 1300 nm or more is preferable as a laser beam of a wavelength having transparency to the silicon wafer 11.

  The oscillation wavelength of the YAG pulse laser is usually 1064 nm, but by adjusting the composition of YAG, lasers of 1342 nm, 1550 nm and 2940 nm can be oscillated.

  In the present embodiment, a laser beam with a wavelength of 1342 nm is used as a laser beam used in the first direction modified layer forming step. The laser beam with a wavelength of 1342 nm has high permeability to the silicon wafer 11 as compared with the laser beam with 1064 nm, so that a good first modified layer 17 can be formed inside the wafer.

  Preferably, the light collector 38 is moved stepwise upward to form a plurality of first direction modified layers 17, for example, five first direction modified layers along the first planned dividing line 13a inside the wafer 11. The quality layer 17 is formed.

  The modified layer 17 is a region in which the density, refractive index, mechanical strength, and other physical properties are different from those in the surrounding area, and is formed as a molten resolidified layer. The processing conditions in this first direction modified layer forming step are set, for example, as follows.

Light source: LD pumped Q-switched Nd: YAG pulsed laser Wavelength: 1342 nm
Repetition frequency: 50kHz
Average power: 0.5W
Focused spot diameter: φ 3 μm
Processing feed rate: 200 mm / s

  After carrying out the first direction modified layer forming step, the wafer 11 is extended along the second planned dividing line 13b where the end in the extending direction (extension direction) collides with the first planned dividing line 13a as a T-shaped path. A second direction modified layer 19 along the second planned dividing line 13 b is formed by condensing and irradiating a laser beam of a wavelength having transparency to the inside of the wafer 11. Implement a directionally modified layer formation step.

  In this second direction modified layer forming step, after rotating the chuck table 24 by 90 °, a plurality of second direction modified layers 19 are formed inside the wafer 11 along the second dividing lines 13b.

  In the present embodiment, a laser beam with a wavelength of 1342 nm is used as the laser beam used in the second direction modified layer forming step as in the first direction modified layer forming step. FIG. 6 shows a schematic plan view showing the step of forming a second direction modified layer. The processing conditions of the second direction modified layer forming step are the same as the processing conditions of the first direction modified layer forming step described above.

  In the second direction modified layer forming step, the second direction modified layer is formed in the second divided line 13b intersecting with the first divided line 13a on which the first direction modified layer 17 is formed as a T-shaped passage. 19 includes a tee machining step to form 19.

  In the T-curve processing step, as shown in FIG. 7, the reflecting mirror 43 is moved by the moving mechanism 47, and the laser beam having a wavelength of 1064 nm oscillated from the first laser oscillator 42A is reflected by the reflecting mirror 43 and collected. The light is incident on the lens 39. The moving mechanism 47 is constituted of, for example, an air cylinder, and a piston rod of the air cylinder 47 is connected to a support member 45 which supports the reflection mirror 43.

  As described above, in the T-junction processing step, the laser beam with the wavelength of 1064 nm oscillated from the first laser oscillator 42A is continuously provided to the second direction modified layer 19 formed by the laser beam with the wavelength of 1342 nm shown in FIG. The second direction modified layer 19 is formed inside the wafer along the second planned dividing line 13b, and the T-shaped processing step is stopped just before crossing the first direction modified layer 17.

  The coordinates of the point to be switched from the second laser oscillator 42B to the first laser oscillator 42A in the T-curve processing step are stored in advance in the memory of the controller of the laser processing apparatus 2. Then, when the x-coordinate value of the laser beam irradiated from the condenser 38 matches the coordinate value stored in advance, the moving mechanism 47 is driven to irradiate the laser beam with a wavelength of 1064 nm from the laser beam of wavelength 1342 nm. Switch to the laser beam and carry out the T-curve processing step.

  The processing conditions of the T-shaped path processing step are set as follows, for example.

Light source: LD pumped Q-switched Nd: YAG pulsed laser Wavelength: 1064 nm
Repetition frequency: 50kHz
Average power: 0.5W
Focused spot diameter: φ 3 μm
Processing feed rate: 200 mm / s

  As described above, since the optical absorption edge of the silicon wafer is about 1050 nm, the step of forming the first modified layer and the second modification are performed using a laser beam having a wavelength of 1300 nm or more that is highly transparent to the silicon wafer. By performing the layer forming step, it is possible to form good first direction modified layer 17 and second direction modified layer 19.

  However, the laser beam having a wavelength of 1300 nm or more has excess transmittance after forming the modified layer due to good transmittance, and the device 15 formed on the surface 11 a of the wafer 11 leaks. It may attack and damage the circuit.

  Therefore, in the method of processing a wafer according to the present invention, the second direction modified layer 19 is formed by using a laser beam having a wavelength of 1064 nm close to the optical absorption edge of the silicon wafer although it has transparency for the T-junction processing step. The excess laser beam after absorption is absorbed on the way to the surface 11 a of the wafer 11 to be quenched and attacking the device 15 is suppressed.

  After performing the first direction modified layer forming step and the second direction modified layer forming step, an external force is applied to the wafer 11 to make the wafer the first direction modified layer 17 and the second direction modified layer 19 as the fracture origin. 11 is broken along the first planned dividing line 13a and the second planned dividing line 13b to carry out the dividing step of dividing into individual device chips.

  This division step is performed using, for example, a division device (expand device) 50 as shown in FIG. The dividing device 50 shown in FIG. 8 comprises a frame holding means 52 for holding the annular frame F, and a tape expanding means 54 for expanding the dicing tape T mounted on the annular frame F held by the frame holding means 52. There is.

  The frame holding means 52 comprises an annular frame holding member 56 and a plurality of clamps 58 as fixing means disposed on the outer periphery of the frame holding member 56. The upper surface of the frame holding member 56 forms a mounting surface 56a on which the annular frame F is mounted, and the annular frame F is mounted on the mounting surface 56a.

  The annular frame F mounted on the mounting surface 56 a is fixed to the frame holding means 52 by the clamp 58. The frame holding means 52 configured in this manner is vertically movably supported by the tape expanding means 54.

  The tape expansion means 54 comprises an expansion drum 60 disposed inside the annular frame holding member 56. The upper end of the expansion drum 60 is closed by a lid 62. The expansion drum 60 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 mounted on the annular frame F.

  The expansion drum 60 has a support flange 64 integrally formed at its lower end. The tape expanding means 54 further comprises driving means 66 for moving the annular frame holding member 56 in the vertical direction. The drive means 66 comprises a plurality of air cylinders 68 disposed on the support flange 64, and the piston rod 70 is connected to the lower surface of the frame holding member 56.

  The driving means 66 composed of a plurality of air cylinders 68 extends the annular frame holding member 56 at a reference position where the mounting surface 56a is substantially the same height as the surface of the lid 62 which is the upper end of the expansion drum 60 It moves in the vertical direction between the upper end of the drum 60 and the extended position which is lower by a predetermined amount.

  The dividing step of the wafer 11 performed using the dividing device 50 configured as described above will be described with reference to FIG. As shown in FIG. 9A, the annular frame F supporting the wafer 11 through the dicing tape T is placed on the mounting surface 56a of the frame holding member 56, and fixed to the frame holding member 56 by the clamp 58. Do. At this time, the frame holding member 56 is positioned at a reference position at which the mounting surface 56 a is substantially flush with the upper end of the expansion drum 60.

  Next, the air cylinder 68 is driven to lower the frame holding member 56 to the expanded position shown in FIG. 9 (B). Thereby, in order to lower the annular frame F fixed on the mounting surface 56 a of the frame holding member 56, the dicing tape T mounted on the annular frame F abuts on the upper end edge of the expansion drum 60 and mainly the radius Expanded in the direction.

  As a result, a tensile force acts radially on the wafers 11 attached to the dicing tape T. As described above, when tensile force acts radially on the wafer 11, the first direction modified layer 17 formed along the first planned dividing line 13a and the second direction break formed along the second planned dividing line 13b. The quality layer 19 serves as the dividing start point, and the wafer 11 is broken along the first dividing planned line 13 a and the second dividing planned line 13 b and divided into individual device chips 21.

11 semiconductor wafer 13a first division planned line 13b second division planned line 15 device 17 first direction modification layer 19 second direction modification layer 24 chuck table 34 laser beam irradiation unit 35 laser beam generation unit 38 condenser (laser (laser (laser) head)
39 condensing lens 40 imaging unit 42A first laser oscillator 42B second laser oscillator 43 reflection mirror 47 moving mechanism 50 dividing device

Claims (3)

A device is formed in each area divided by a plurality of first planned division lines formed in a first direction and a plurality of second planned division lines formed in a second direction intersecting the first direction. A method of processing a wafer in which at least the second planned dividing line among the first planned dividing line and the second planned dividing line is discontinuously divided into individual device chips,
Along the first planned dividing line, a laser beam of a wavelength having transparency to the wafer is condensed and irradiated from the back side of the wafer to the inside of the wafer, and along the first planned dividing line inside the wafer. Forming a first direction modified layer forming a plurality of first direction modified layers;
After performing the first direction modified layer forming step, a laser beam of a wavelength having transparency to the wafer is condensed from the back side of the wafer to the inside of the wafer along the second planned dividing line and irradiated. A second direction modified layer forming step of forming a plurality of second direction modified layers along the second planned dividing line inside the wafer;
After the step of forming the first direction modified layer and the step of forming the second direction modified layer, an external force is applied to the wafer, and the first direction modified layer and the second direction modified layer are set as fracture starting points. Splitting the wafer along the first planned dividing line and the second planned dividing line and dividing it into individual device chips;
In the second direction modified layer forming step, a second direction modified layer is formed in the second divided line which intersects the first divided line on which the first direction modified layer is formed as a T-shaped passage. Including a T-step processing step to form a layer,
A method of processing a wafer, wherein a laser beam with a wavelength of 1064 nm is irradiated in the T-junction processing step.   The wafer processing method according to claim 1, wherein a laser beam having a wavelength of 1300 nm or more is irradiated in the first direction modified layer forming step and the second direction modified layer forming step other than the T-shaped path processing step.   3. The method of processing a wafer according to claim 2, wherein the wavelength of the laser beam irradiated in steps other than the T-shaped step is 1342 nm.

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