JP2017069287A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method that can prevent damage of a device due to reflection or scattering in a reformed layer which has been already formed in the vicinity of a cross point at which a parting scheduled line abuts against another parting scheduled line as a T-shaped path when laser processing is performed on a wafer on which at least one parting scheduled line is discontinuously formed.SOLUTION: A processing method divides, into individual device chips 15, a wafer 11 on which a second parting scheduled line 13b formed orthogonally to a first parting scheduled line 13a is formed discontinuously, and comprises a thinning step of grinding the back surface and performing processing to achieve a predetermined thickness, a step of forming a reformed layer 17 inside the wafer along the first parting scheduled line, and a step of forming the reformed layer 19 in the interior along the second parting scheduled line. Even when a part of a laser beam LB which is conically converged in a second-direction reformed layer forming step collides with the first direction reformed layer, and leak light occurs due to scattering, most of the leak light scatters to the first parting scheduled line, and the device does not suffer damage.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method for processing a wafer such as a silicon wafer or a sapphire wafer.

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

  A dicing method using a cutting device called a dicing saw is widely used for dividing the wafer. In the dicing method, a cutting blade having a thickness of about 30 μm formed by solidifying abrasive grains such as diamond with a metal or resin is cut into the wafer while rotating at a high speed of about 30000 rpm, and the wafer is cut individually. 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 into practical use. As methods for dividing a wafer into individual device chips using a laser beam, first and second processing methods described below are known.

  In the first processing method, a condensing point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer corresponding to the division line, and the wafer is irradiated with the laser beam along the division 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 having a wavelength (for example, 355 nm) having absorptivity with respect to the wafer is irradiated to a region corresponding to the division planned 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 using a processing groove as a division starting point (see, for example, JP-A-10-305420).

  In the first processing method, there is no generation of processing waste, and there are merits such as minimization of the cut line and anhydrous processing as compared with dicing with a cutting blade that has been generally used in the past, and it is actively used. Yes.

  In addition, the dicing method by laser beam irradiation has an advantage that a wafer having a structure in which the division lines (streets) substituted for the projection wafer are discontinuous can be processed (see, for example, JP 2010-123723 A). ). In processing a wafer in which the division lines are discontinuous, the laser beam output is turned on / off according to the setting of the division lines.

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

  However, there are the following problems in the vicinity of the intersection where the planned division line extending in the second direction and the planned division line continuously extending in the first direction hit a T-junction.

  (1) The second division planned line intersects with the first division planned line in which the first modified layer is first formed inside the first division planned line parallel to one side of the device as a T-junction. When the two modified layers are formed, as the laser beam condensing point approaches the intersection of the T-junction, the already formed first modified layer is irradiated with a part of the laser beam for processing the second divided line. There is a problem that reflection or scattering of the laser beam occurs, light leaks into the device region, and this leaked light damages the device and degrades the quality of the device.

  (2) On the other hand, before forming the modified layer on the first division line parallel to one side of the device, the wafer is moved along the second division line that hits the first division line as a T-junction. When the reforming layer is formed inside, the reforming layer that blocks the progress of cracks generated from the reforming layer formed in the vicinity of the intersection of the T-junction does not exist at the intersection of the T-junction. The crack extends from the intersection of the T-junction by about 1 to 2 mm to reach the device, and there is a problem that the quality of the device is lowered.

  The present invention has been made in view of the above points, and the object of the present invention is to perform the laser processing of a wafer in which at least one of the planned dividing lines is discontinuously formed. The laser beam is suppressed from being irradiated to the modified layer that has already been formed near the intersection where the end hits the other splitting line as a T-junction, and reflection or scattering of the laser beam at the modified layer is prevented. It is an object of the present invention to provide a wafer processing method capable of preventing and preventing damage to a device due to light leakage.

  According to the present invention, the surface partitioned by a plurality of first division planned lines formed in the first direction and a plurality of second division planned lines formed in the second direction intersecting the first direction. A wafer is formed in which a device is formed in each of the regions, and a wafer in which at least the second scheduled division line among the first scheduled division line and the second scheduled division line is formed discontinuously is divided into individual device chips. A processing method comprising: a wafer thinning step in which a wafer is ground to a predetermined thickness by grinding the back surface of the wafer; and after performing the wafer thinning step, the wafer is formed along the first division line. On the other hand, a laser beam having a wavelength having transparency is condensed and irradiated on the inside of the wafer from the back side of the wafer to form a first direction modification layer along the first scheduled division line inside the wafer. After performing the direction-modified layer forming step and the first direction-modified layer forming step, a laser beam having a wavelength that is transmissive to the wafer is applied from the back side of the wafer along the second division line. A second direction modified layer forming step for forming a second direction modified layer along the second division planned line inside the wafer, and condensing and irradiating the inside of the wafer, and forming the first direction modified layer After performing the step and the second direction modified layer forming step, an external force is applied to the wafer, and the wafer is divided into the first division planned line with the first direction modified layer and the second direction modified layer as the break starting point. And a dividing step of breaking along the second scheduled dividing line and dividing into individual device chips, wherein the second direction modified layer forming step includes the step of forming the first direction modified layer. T-junction on the first division line A condensing point of a laser beam that includes a T-shaped machining step for forming a second direction modification layer inside the second line to be divided and condenses in a conical shape from the back surface of the wafer in the T-shaped machining step Even if a portion of the conical laser beam collides with the first direction modification layer formed earlier and leakage light is generated by scattering of the laser beam, most of the leakage light A wafer processing method is provided in which the thinly formed wafer is scattered on the first scheduled division line, and leakage light is prevented from attacking and damaging the device.

  According to the wafer processing method of the present invention, since the wafer thinning step for grinding the back surface of the wafer is performed, the first direction modified layer forming step and the second direction modified layer forming step are performed. Part of the laser beam focused in a conical shape in the T-junction processing step, which is a part of the direction modification layer forming step, collides with the first direction modification layer formed earlier, and the laser beam is scattered. Alternatively, even if leakage light is generated due to reflection, most of the leakage light is scattered on the first division line of the thinly formed wafer, and the leakage light is prevented from reaching the device and damaging the device. .

It is a perspective view of the laser processing apparatus suitable for implementing the processing method of the wafer of this invention. It is a block diagram of a laser beam generation unit. 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 the wafer thinning step which grinds the back surface of a wafer and thins a wafer. It is a perspective view which shows a 1st direction modified layer formation step. It is typical sectional drawing which shows a 1st direction modified layer formation step. FIG. 7A is a schematic plan view showing the T-junction machining step, and FIG. 7B is a cross-sectional view showing the T-junction machining 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, there is shown a perspective view of a laser processing apparatus 2 suitable for carrying out the wafer processing method of the embodiment of the present invention. The laser processing apparatus 2 includes a pair of guide rails 6 that are mounted on a stationary base 4 and extend in the Y-axis direction.

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

  The X-axis moving block 18 is guided by the guide rail 16 and moved in the machining feed direction, that is, the X-axis direction, by an X-axis feed mechanism (X-axis feed means) 28 including a ball screw 20 and a pulse motor 22. The

  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 (four in this embodiment) of clamps 26 for clamping the annular frame F shown in FIG.

  A column 32 is erected on the rear side of the base 4. A casing 36 of a laser beam irradiation unit 34 is fixed to the column 32. The laser beam irradiation unit 34 includes a laser beam generation unit 35 housed in a casing 36 and a condenser (laser head) 38 attached to the tip of the casing 36. The condenser 38 is attached to the casing 36 so as to be finely movable in the vertical direction (Z-axis direction).

  As shown in FIG. 2, the laser beam generating unit 35 includes a laser oscillator 42 such as a YAG laser oscillator or a YVO4 laser oscillator that oscillates a pulse laser having a wavelength of 1342 nm, a repetition frequency setting means 44, a pulse width adjusting means 46, Power adjusting means 48 for adjusting the power of the pulsed laser beam oscillated from the laser oscillator 42.

  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 on the chuck table 24 is mounted. The condenser 38 and the imaging unit 40 are arranged in alignment in the X-axis direction.

  Referring to FIG. 3, there is shown a front side perspective view of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11 suitable for processing by the wafer processing method of the present invention. The wafer 11 has a thickness of about 700 μm.

  On the surface 11a of the wafer 11, a plurality of first division planned lines 13a formed continuously in the first direction and a plurality of first division lines formed discontinuously in the direction perpendicular to the first division planned lines 13a. A two-division line 13b is formed, and a device 15 such as an LSI is formed in an area partitioned by the first division line 13a and the second division line 13b.

  In the wafer processing method of the present invention, first, a wafer thinning step is performed in which the back surface 11b of the wafer 11 is ground to thin the wafer 11 to a predetermined thickness. The wafer thinning step will be described with reference to FIG.

  A wheel mount 31 is fixed to the tip of the spindle 29 of the grinding unit 27, and a grinding wheel 33 is detachably attached to the wheel mount 31 by a plurality of screws 39. The grinding wheel 33 includes an annular wheel base 35 and a plurality of grinding wheels 37 fixed to the outer periphery of the lower end of the wheel base 35.

  In the wafer thinning step, the protective tape 23 is attached to the front surface 11a of the wafer 11, and the wafer 11 is sucked and held by the chuck table 25 of the grinding apparatus via the protective tape 23, so that the back surface 11b of the wafer 11 is exposed.

  Then, while rotating the chuck table 25 in the direction of arrow a at 300 rpm, for example, the grinding wheel 33 is rotated in the same direction as the chuck table 25, that is, in the direction of arrow b at 6000 rpm, for example, and a grinding unit feed mechanism (not shown) is operated. Then, the grinding wheel 37 is brought into contact with the back surface 11 b of the wafer 11.

  Then, the grinding wheel 33 is ground and fed by a predetermined amount at a predetermined grinding feed speed, and the back surface 11b of the wafer 11 is ground. The wafer 11 is ground to a desired thickness between 50 μm and 150 μm while measuring the thickness of the wafer 11 with a contact or non-contact thickness gauge not shown.

  After carrying out the wafer thinning step, the surface protective tape 23 is peeled off from the surface of the wafer 11, and the surface 11a of the wafer 11 is attached to a dicing tape T which is an adhesive tape having an outer peripheral portion attached to the annular frame F. Thus, the frame unit shown in FIG.

  In the form of this frame unit, the wafer 11 is placed on the chuck table 24 and sucked and held via the dicing tape T, and the annular frame F is clamped and fixed by a clamp 26.

  Although not particularly illustrated, in the wafer processing method of the present invention, after performing the wafer thinning step, the wafer 11 sucked and held by the chuck table 24 is positioned directly below the imaging unit 40 of the laser processing apparatus 2, and the imaging unit The wafer 11 is imaged by 40, and alignment is performed in which the first scheduled division line 13a is aligned with the condenser 38 in the X-axis direction.

  Next, after the chuck table 24 is rotated by 90 °, the same alignment is performed on the second division planned line 13b extending in the direction orthogonal to the first division planned line 13a, and the alignment data is obtained from the laser processing apparatus 2. Store in the RAM of the controller.

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

  After the alignment, a first direction modified layer forming step is performed in which the first direction modified layer 17 is formed in the wafer 11 along the first division planned line 13a. In this first direction modified layer forming step, as shown in FIGS. 5 and 6, a condensing point of a laser beam having a wavelength (for example, 1342 nm) having transparency to the wafer is focused on the wafer 11 by the condenser 38. Positioned inside, the first division planned line 13a is irradiated from the back surface 11b side of the wafer 11, and the chuck table 24 is processed and fed in the direction of the arrow X1 in FIG. A first direction modification layer 17 is formed along the line.

  Depending on the thickness of the wafer thinned in the wafer thinning step described above, the number of first directionally modified layers 17 is different. For example, when the thickness of the wafer 11 is reduced to about 50 μm in the wafer thinning step, it is sufficient to form only one first direction modification layer 17 along the first division line 13a. When the thickness of the wafer 11 is about 150 μm, for example, two first direction modified layers 17 along the first division planned line 13a are formed.

  The modified layer 17 is a region in which density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings, and is formed as a melt-resolidified layer. The processing conditions in the first direction modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1342 nm
Repetition frequency: 50 kHz
Average output: 0.5W
Condensing spot diameter: φ3μm
Processing feed rate: 200 mm / s

  After performing the first direction modified layer forming step, the wafer 11 extends along the second division planned line 13b where the end in the extending direction (extension direction) hits the first division planned line 13a as a T-junction. A laser beam having a wavelength that is transparent (eg, 1342 nm) is condensed and irradiated on the inside of the wafer 11, and the second direction modification layer 19 along the second division planned line 13 b is formed inside the wafer 11. A second direction modified layer forming step is performed.

  In this second direction reformed layer forming step, after the chuck table 24 is rotated by 90 °, one layer or two along the second division planned line 13b is formed inside the wafer 11 according to the thickness of the thinned wafer 11. A second direction reforming layer 19 of the layer is formed.

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

  This T-junction machining step will be described with reference to FIG. FIG. 7A is a schematic plan view of the T-junction machining step, and FIG. 7B is a cross-sectional view thereof. As shown in FIG. 7B, the thickness of the wafer 11 thinned in the wafer thinning step is about 150 μm, for example, and the first direction reforming layer 17 has two layers along the first division line 13a. Is formed.

  As shown in FIG. 7B, when the T-direction machining step is performed to form the second direction modified layer 19 close to the first direction modified layer 17, a part of the conical laser beam LB is formed. Irradiation to the first direction modification layer 17 causes leakage light due to scattering or reflection of the laser beam.

  However, each of the first scheduled division line 13a and the second scheduled division line 13b has a width of about 50 μm, and the first direction modification layer 17 is formed at substantially the center of the first scheduled division line 13a. The leakage light generated when the conical laser beam LB collides with the first direction modification layer 17 is formed so that the wafer 11 is thin. A small amount of light leaks onto the device 15. Therefore, even if the slight leakage light is applied to the device 15, the device 15 is not fatally damaged.

  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, and the wafer is started with the first direction modified layer 17 and the second direction modified layer 19 as the starting point of breakage. 11 is broken along the first division planned line 13a and the second division planned line 13b, and a division step is performed for dividing the device into individual device chips.

  This dividing step is performed using, for example, a dividing device (expanding device) 50 as shown in FIG. 8 includes a frame holding unit 52 that holds the annular frame F, and a tape expansion unit 54 that extends the dicing tape T attached to the annular frame F held by the frame holding unit 52. Yes.

  The frame holding means 52 includes an annular frame holding member 56 and a plurality of clamps 58 as fixing means arranged on the outer periphery of the frame holding member 56. An 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 placed on the placement surface 56 a is fixed to the frame holding means 52 by a clamp 58. The frame holding means 52 configured as described above is supported by the tape extending means 54 so as to be movable in the vertical direction.

  The tape expansion means 54 includes an expansion drum 60 disposed inside an annular frame holding member 56. The upper end of the expansion drum 60 is closed with a lid 62. The expansion drum 60 has an inner diameter that is 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 drum 60 has a support flange 64 integrally formed at the lower end thereof. The tape expanding means 54 further includes driving means 66 for moving the annular frame holding member 56 in the vertical direction. The driving means 66 includes 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 includes an annular frame holding member 56, 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, and an expansion. It moves in the vertical direction between the extended position below the upper end of the drum 60 by a predetermined amount.

  A dividing step of the wafer 11 performed using the dividing apparatus 50 configured as described above will be described with reference to FIG. As shown in FIG. 9A, the annular frame F that supports the wafer 11 via the dicing tape T is placed on the placement surface 56 a of the frame holding member 56, and is fixed to the frame holding member 56 by the clamp 58. To do. At this time, the frame holding member 56 is positioned at a reference position where the placement surface 56 a is substantially the same height as the upper end of the expansion drum 60.

  Next, the air cylinder 68 is driven to lower the frame holding member 56 to the extended position shown in FIG. As a result, the annular frame F fixed on the mounting surface 56a of the frame holding member 56 is lowered, so that the dicing tape T attached to the annular frame F abuts on the upper end edge of the expansion drum 60 and mainly has a radius. Expanded in the direction.

  As a result, a tensile force acts radially on the wafer 11 adhered to the dicing tape T. When a pulling force is applied to the wafer 11 in a radial manner in this way, the first direction reforming layer 17 formed along the first division planned line 13a and the second direction modification formed along the second division planned line 13b. The material layer 19 serves as a division starting point, and the wafer 11 is broken along the first division planned line 13 a and the second division planned line 13 b to be divided into individual device chips 21.

  In the above-described embodiment, the semiconductor wafer 11 has been described as the wafer to be processed by the processing method of the present invention. However, the wafer to be processed of the present invention is not limited to this, and light using sapphire as a substrate. The processing method of the present invention can be similarly applied to other wafers such as device wafers.

11 Semiconductor wafer 13a First division planned line 13b Second division planned line 15 Device 17 First direction modified layer 19 Second direction modified layer 24 Chuck table 33 Grinding wheel 34 Laser beam irradiation unit 35 Laser beam generating unit 37 Grinding wheel 38 Condenser (laser head)
40 Imaging unit 50 Dividing device

Claims (2)

Device in each region of the surface partitioned by a plurality of first division planned lines formed in a first direction and a plurality of second division planned lines formed in a second direction intersecting the first direction And a wafer processing method for dividing a wafer in which at least the second scheduled division line among the first scheduled division line and the second scheduled division line is formed discontinuously into individual device chips. ,
A wafer thinning step for grinding the back surface of the wafer to thin the wafer to a predetermined thickness;
After performing the wafer thinning step, a laser beam having a wavelength that is transmissive to the wafer is condensed and irradiated from the back surface side of the wafer along the first division planned line. A first direction modified layer forming step for forming a first direction modified layer along the first division planned line inside;
After carrying out the first direction modified layer forming step, a laser beam having a wavelength that is transparent to the wafer is condensed and irradiated from the back side of the wafer to the inside of the wafer along the second division line. A second direction modified layer forming step for forming a second direction modified layer along the second division planned line inside the wafer;
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, and the first direction modified layer and the second direction modified layer are used as starting points of breakage. A dividing step of breaking the wafer along the first scheduled dividing line and the second scheduled dividing line to divide the wafer into individual device chips,
In the second direction reformed layer forming step, a second direction reformed layer is formed inside the second planned division line that intersects the first planned division line on which the first direction modified layer is formed as a T-junction. Including a T-junction machining step to form a layer;
The first direction modification layer in which a part of the conical laser beam is formed first when the condensing point of the laser beam condensing in a conical shape from the back surface of the wafer is positioned in the T-junction processing step. Even if leakage light is generated due to scattering of the laser beam due to collision with the laser beam, most of the leakage light is scattered on the first division line of the thin wafer, and the leakage light attacks the device to the device. A method for processing a wafer, wherein damage is suppressed.   The wafer processing method according to claim 1, wherein in the wafer thinning step, the wafer is thinned to 50 μm to 150 μm.

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