JP5939769B2 - Processing method of plate - Google Patents

Description

  The present invention irradiates a plate-like material such as a wafer with a laser beam having a wavelength that is transparent to form a modified layer inside the plate-shaped material, and then divides the plate-shaped material starting from the modified layer. The present invention relates to a processing method of a plate-like object for forming a plurality of chips.

  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 devices by a processing apparatus, and the divided devices are mobile phones, Widely used in various electrical equipment such as 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 wafer is cut by cutting a wafer into a wafer while rotating a cutting blade having a thickness of about 30 μm by solidifying abrasive grains such as diamond with a metal or a resin at a high speed of about 30000 rpm. Divide into chips.

  On the other hand, in recent years, a condensing point of a laser beam having a wavelength (for example, 1064 nm) having transparency to the wafer is positioned inside the wafer corresponding to the division line, and the laser beam is irradiated along the division line. A method has been proposed in which a modified layer is formed inside a wafer and then an external force is applied to divide the wafer into individual device chips (see, for example, Japanese Patent No. 3408805).

  The modified layer is a region where the density, refractive index, mechanical strength and other physical properties are different from the surroundings, in addition to the melt rehardened region, refractive index changing region, dielectric breakdown region, A crack region and a region where these are mixed are also included.

  The formation of the modified layer using a laser processing apparatus can increase the processing speed compared to the dicing method using a dicing saw, and relatively easily process even a wafer made of a material having high hardness such as sapphire or SiC. can do. In addition, since the modified layer can have a narrow width of, for example, 10 μm or less, the amount of devices taken per wafer can be increased as compared with the case of processing by the dicing method.

Japanese Patent No. 3408805

  However, divided waste often remains on the side surface (divided cross section) of the chip formed by dividing by the dividing method disclosed in Patent Document 1. If the divided waste remains on the side surface of the chip, the inside of the apparatus may be contaminated with the divided waste in a subsequent process such as a pick-up process, and the wafer to be processed later may be contaminated.

  In the case where a device is formed on the surface of the wafer, there is a problem in that, if the debris adheres to the surface of the device, the device quality is deteriorated and the bonding and packaging in the subsequent process are hindered.

  Since there is almost no space between the chips after an external force is applied to the wafer and divided into individual chips, it is very difficult to remove the divided waste remaining on the side surfaces of the chips even if the wafer is cleaned after the division.

  In addition, MEMS (Micro Electro Mechanical Systems) device wafers made of silicon wafers generally have a very fine and fragile structure, so cleaning with a general fluid cannot be performed, and adhesion of divided waste is a major problem. Become.

  The present invention has been made in view of these points, and an object of the present invention is to provide a processing method of a plate-like object that can reduce the division waste remaining on the side surface of the chip after division more than before. It is.

According to the present invention, a plate-like object that forms a plurality of chips by dividing a plate-like object having a plurality of chip regions partitioned by a plurality of intersecting scheduled lines set on the surface along the scheduled dividing line. A focusing point of a laser beam having a wavelength that is transmissive to the plate-like object is positioned in a region that does not reach the finished thickness of the chip inside the plate-like object, and is along the line to be divided A first modified layer forming step of forming a first modified layer as a starting point of division by irradiating the laser beam with a first output, and before or after performing the first modified layer forming step A condensing point of a laser beam having a wavelength that is transmissive to the object is positioned in the finished thickness region of the chip inside the plate, and the laser beam is made to be more than the first output along the division line. Irradiate with a low second power to induce splitting A second modified layer forming step for forming a modified layer; and an external force is applied to the plate-like material on which the first modified layer and the second modified layer are formed to form chips along the scheduled division line A dividing step for dividing, a tape adhering step for adhering an adhesive tape to the surface of the plate at least at any timing until the dividing step is performed, and after performing the dividing step, thinned to finish the thickness of the chip by grinding the back surface, the processing of the platelet, characterized by comprising a thinning step of leaving the second reforming layer to remove said first modified layer, the A method is provided.

  Preferably, the second output is not more than 1/2 times the first output.

  In the processing method of the present invention, first, a first modified layer serving as a division starting point is formed in a region that does not reach the finished thickness of the chip, and a second modified layer formed at a lower output is formed in the finished thickness region of the chip. Form a quality layer. Next, an external force is applied to the plate-like material to divide the plate-like material starting from the first modified layer.

  At this time, since the second modified layer is formed on the surface side of the plate-like material, cracks extending from the first modified layer generated at the time of division are guided by the second modified layer and scheduled to be divided. A plate-like object can be divided along the line.

  After dividing the plate-like material into individual chips, the area that does not reach the finished thickness of the chip where a large amount of divided waste remains is removed by grinding. Compared to a significant reduction.

1 is a schematic perspective view of a laser processing apparatus suitable for forming a modified layer inside a wafer. It is a block diagram of a laser beam irradiation unit. It is a surface side perspective view of a semiconductor wafer. It is a disassembled perspective view which shows a tape sticking step. It is sectional drawing which shows a 2nd modified layer formation step. It is sectional drawing which shows a 1st modified layer formation step. It is a longitudinal cross-sectional view of the division | segmentation apparatus which shows a division | segmentation step. It is a partial cross section side view which shows a thinning 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 schematic perspective view of a laser processing apparatus 2 suitable for forming the first and second modified layers in the plate-like material processing method of the present invention.

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

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means 22 constituted by the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 that clamps an annular frame that supports the wafer sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a casing 35 for accommodating the laser beam irradiation unit 34 is attached to the column 32. As shown in FIG. 2, the laser beam irradiation unit 34 includes a laser oscillator 62 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 64, a pulse width adjustment unit 66, and a power adjustment unit 68. .

  The pulse laser beam adjusted to a predetermined power by the power adjusting means 68 of the laser beam irradiation unit 34 is reflected by the mirror 70 of the condenser 36 attached to the tip of the casing 35 and further collected by the condenser objective lens 72. The light is applied to the optical device wafer 11 held on the chuck table 28.

  At the tip of the casing 35, an image pickup unit 38 that detects the processing region to be laser processed in alignment with the condenser 36 in the X-axis direction is disposed. The imaging unit 38 includes an imaging element such as a normal CCD that images the processing region of the optical device wafer 11 with visible light.

  The imaging unit 38 further outputs an infrared irradiation unit that irradiates the optical device wafer 11 with infrared rays, an optical system that captures infrared rays irradiated by the infrared irradiation unit, and an electrical signal corresponding to the infrared rays captured by the optical system. Infrared imaging means including an infrared imaging device such as an infrared CCD is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  A machining feed amount detection unit 56 includes a linear scale 54 disposed along the guide rail 14 and a reading head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes an index feed amount detection unit composed of a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal captured by the imaging unit 38 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 irradiation unit 34, 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. A semiconductor wafer 11 shown in FIG. 3 is made of, for example, a silicon wafer having a thickness of 700 μm. A plurality of division lines (streets) 13 are formed in a lattice shape on the surface 11a, and the plurality of division lines are arranged. A device 15 such as an IC or LSI is formed in each region (chip region) partitioned by 13.

  The semiconductor wafer 11 configured as described above includes a device region 17 in which the device 15 is formed and an outer peripheral surplus region 19 surrounding the device region 17 in a flat portion of the surface 11a. A notch 21 is formed on the outer periphery of the semiconductor wafer 11 as a mark indicating the crystal orientation of the silicon wafer.

  In the following description, the semiconductor wafer 11 (hereinafter also referred to as a wafer) will be described as an object to be processed by the processing method of the present invention. The processing method of the present invention is an optical device wafer in which a light emitting layer is laminated on a sapphire substrate. The present invention can be applied to a plate-like workpiece (plate-like object) such as a wafer on which no device is formed on the surface.

  In the plate-like material processing method of the present invention, as shown in FIG. 4, a tape adhering step of adhering the adhesive tape T to the surface 11 a of the wafer 11 is performed. The outer peripheral portion of the adhesive tape T is attached to the annular frame F.

  Thereby, after implementation of a tape sticking step, the wafer 11 is supported by the annular frame F via the adhesive tape T, and the back surface 11b is exposed upward. The tape attaching step is performed at any timing after the first modified layer forming step and the second modified layer forming step, which will be described later, or until the dividing step is performed. Also good.

  After performing the tape attaching step, as shown in FIG. 5, the semiconductor wafer 11 is sucked and held by the chuck table 28 of the laser processing apparatus 2 via the adhesive tape T, and the back surface 11b of the semiconductor wafer 11 is exposed.

  Then, the wafer 11 is imaged from the back surface 11b side by the infrared imaging element of the imaging unit 38, and the alignment corresponding to the area 36 corresponding to the planned division line 13 is aligned with the condenser 36 in the X-axis direction. For this alignment, well-known image processing such as pattern matching is used.

  After the alignment of the planned dividing line 13 extending in the first direction is performed, the chuck table 28 is rotated 90 degrees, and then the planned dividing line 13 extending in the second direction orthogonal to the first direction is aligned. To do.

  After the alignment, as shown in FIG. 5, the condensing point P of the laser beam having a wavelength transmissive to the semiconductor wafer 11 is positioned in the finished thickness region t1 of the chip inside the wafer, and the chuck table 28 is moved in the direction of arrow X1. Is sent to the rear surface 11b side of the wafer 11 along the planned division line 13 to induce division into the finished thickness region t1 of the chip of the wafer 11. A quality layer 23 is formed.

  While indexing and feeding the chuck table 28 in the Y-axis direction, the second modified layer 23 is formed in the finished thickness region t1 of the chip corresponding to all the division lines 13 extending in the first direction.

  Next, after the chuck table 28 is rotated by 90 degrees, the same second modification is applied to the finish thickness region t1 of the corresponding chip along all the planned dividing lines 13 extending in the second direction orthogonal to the first direction. A quality layer 23 is formed.

  The second modified layer 23 is a region where the density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings. For example, it includes a melt rehardening region, a crack region, a dielectric breakdown 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 second modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 80 kHz
Pulse output: 0.25W
Processing feed rate: 300 mm / s

  After performing the second modified layer forming step, a first modified layer serving as a starting point of division is formed inside the wafer using a laser beam having an output larger than that used in the second modified layer forming step. 1 Perform the modified layer forming step.

  In this first modified layer forming step, as shown in FIG. 6, the condensing point P of the laser beam having a wavelength transmissive to the wafer 11 is positioned in a region t2 that does not reach the finished thickness of the chip inside the wafer. Then, by feeding the chuck table 28 in the direction of the arrow X1, the laser beam is irradiated with the first output larger than the second output along the scheduled division line 13, and the first reforming that becomes the starting point of the division is performed. The layer 25 is formed in a region t2 that does not reach the finished thickness of the chip.

  The first modified layer 25 is formed in the region t2 that does not reach the finished thickness of the chip along all the division lines 13 that extend in the first direction while indexing and feeding the chuck table 28 in the Y-axis direction.

  Next, after the chuck table 28 is rotated 90 degrees, the same first region t2 that does not reach the finished thickness of the chip corresponding to all the division lines 13 extending in the second direction orthogonal to the first direction. The modified layer 25 is formed.

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

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 80 kHz
Pulse output: 1.2W
Processing feed rate: 300 mm / s

  In the first modified layer forming step and the second modified layer forming step described above, a plurality of first modified layers 25 and second modified layers 23 may be formed. In particular, considering that the thickness of the wafer 11 is 700 μm and the finished thickness of the chip is 100 μm or less, the first modified layer 25 that is the starting point of the division is formed in a plurality of layers in the region t2 that does not reach the finished thickness of the chip. It is preferable to do this.

  In the embodiment described above, the front surface 11a side of the wafer 11 is attached to the adhesive tape T, and the laser beam is incident from the rear surface 11b side of the wafer 11. However, the front surface 11a of the wafer 11 is not attached to the adhesive tape T. When the first modified layer forming step and the second modified layer forming step are performed, a laser beam is incident from the surface 11a side of the wafer 11 so that the first modified layer 25 and the second modified layer 23 are formed. You may make it form.

  When there is a TEG (Test Element Group), a passivation film, or the like on the division line 13, it is preferable that the laser beam is incident from the back surface. In the case of incidence from the front surface side, the first modified layer forming step is performed before the second modified layer forming step, and the modified layers are formed in order from the back surface 11b side of the wafer 11 to the front surface 11a side. By doing (forming in order of distance from the incident surface), the modified layers 23 and 25 can be formed with more stable quality.

  That is, by forming the modified layers in this order, it is possible to prevent the laser beam irradiation from being hindered by the modified layers existing before the condensing point of the laser beam. However, the order of forming the modified layers is not limited to this, and the modified layers may be formed from the side closer to the laser beam incident surface.

  After the first and second modified layer forming steps are performed, an external force is applied to the wafer 11 on which the first modified layer 25 and the second modified layer 23 are formed to divide the wafer along the scheduled dividing line 13. A dividing step of dividing into chips is performed.

  When the first modified layer forming step and the second modified layer forming step are performed without attaching the adhesive tape T to the surface 11a of the wafer 11, the surface 11a of the wafer 11 is performed before the dividing step is performed. Adhesive tape T is adhered to the outer periphery, and the outer peripheral portion of adhesive tape T is adhered to annular frame F.

  This dividing step is preferably performed by a dividing device 76 as shown in FIG. 7A, the dividing device 76 includes a frame holding unit 78 that holds the annular frame F, and an expansion drum 80 that expands the adhesive tape T attached to the annular frame F held by the frame holding unit 78. ing.

  The frame holding unit 76 includes an annular frame holding member 82 and a plurality of clamps 84 as fixing means disposed on the outer periphery of the frame holding member 82. The upper surface of the frame holding member 82 is formed on a placement surface 82a on which the annular frame F is placed, and the annular frame F is placed on the placement surface 82a.

  The frame holding unit 78 is driven by a driving means 86 including an air cylinder 88, and a reference position where the mounting surface 82 a of the annular frame holding member 82 is substantially flush with the upper end of the expansion drum 80, and the expansion drum 80. It moves in the vertical direction between the extended positions below the upper end by a predetermined amount. A piston rod 90 of the air cylinder 88 is connected to the lower surface of the frame holding member 82.

  In the dividing step, as shown in FIG. 7A, the annular frame F that supports the wafer 11 via the adhesive tape T is placed on the placement surface 82 a of the frame holding member 82, and the frame is held by the clamp 84. The member 82 is fixed. At this time, the frame holding member 82 is positioned at a reference position where the mounting surface 82 a is substantially the same height as the upper end of the expansion drum 80.

  Next, the air cylinder 88 is driven to lower the frame holding member 82 to the extended position shown in FIG. As a result, the annular frame F fixed on the mounting surface 82a of the frame holding member 82 is also lowered, so that the adhesive tape T adhered to the annular frame F abuts on the upper end edge of the expansion drum 80 and mainly. Expanded radially.

  As a result, a radial tensile force acts on the wafer 11 adhered to the adhesive tape T. When a tensile force is applied to the wafer 11 in a radial manner in this way, the wafer 11 is broken along the scheduled division line 13 with the first modified layer 25 as a division starting point, and is divided into individual device chips 15A.

  In this division, cracks extending from the first modified layer 25 generated at the time of division are guided by the second modified layer 23, and the wafer 11 can be divided into individual devices 15 along the planned division line 13. .

  When the wafer 11 is divided into the individual device chips 15, a large amount of divided waste adheres to the region t 2 that does not reach the finished thickness of the chip on the side surface of the device chip 15, but the second modification formed in the finished thickness region t 1 of the chip. Since the quality layer 23 is formed with an output of 1/2 times or less than the output at the time of forming the first modified layer, it is possible to reduce the divided dust adhering to the finished thickness region t1 of the chip.

  After performing the dividing step, a thinning step is performed in which the back surface 11b of the wafer 11 is ground to reduce the thickness to the finished thickness of the chip. In this thinning step, as shown in FIG. 8, the wafer 11 is sucked and held by the chuck table 92 of the grinding device via the adhesive tape T, and the back surface 11b of the wafer 11 is exposed.

  In FIG. 8, a grinding wheel 100 is detachably attached to a wheel mount 98 fixed to the tip of a spindle 96 of a grinding unit 94 by a plurality of screws (not shown). The grinding wheel 100 is configured by arranging a plurality of grinding wheels 104 in an annular shape at a free end (lower end) of a wheel base 102.

  In the thinning step, while rotating the chuck table 92 in the direction indicated by the arrow a at 300 rpm, for example, the grinding wheel 100 is rotated in the direction indicated by the arrow b at, for example, 6000 rpm, and the grinding unit feed mechanism is driven to drive the grinding wheel 100. The grinding wheel 104 is brought into contact with the back surface 11 b of the wafer 11. Then, the grinding wheel 100 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed.

  While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness measurement gauge, the wafer 11 is ground to a desired thickness t1. When the wafer 11 is ground to a desired thickness t1, the first modified layer 25 is completely removed by grinding.

  In the processing method of the plate-like object of this embodiment, a large amount of divided waste remains and an area that does not reach the finished thickness of the chip is removed by grinding, so that the divided waste remaining on the side surface of the finally formed chip is removed. Can be greatly reduced as compared with the prior art.

2 Laser processing device 11 Semiconductor wafer 13 Scheduled division line 15 Device 23 Second modified layer 25 First modified layer 28 Chuck table 34 Laser beam irradiation unit 36 Condenser 38 Imaging unit 76 Dividing device 94 Grinding unit 100 Grinding wheel 104 Grinding wheel T Adhesive tape F Annular frame P Focus point t1 Finished thickness area of chip t2 Area not reaching the finished thickness of chip

Claims (3)

A processing method for a plate-like object in which a plate-like object having a plurality of chip regions defined by a plurality of intersecting scheduled lines set on the surface is divided along the scheduled dividing lines to form a plurality of chips. And
A condensing point of a laser beam having a wavelength that is transmissive to the plate-like object is positioned in a region that does not reach the finished thickness of the chip inside the plate-like object, and the laser beam is guided along the division line to the first A first modified layer forming step of forming a first modified layer as a starting point of division by irradiation with an output;
Before or after performing the first modified layer forming step, the condensing point of the laser beam having a wavelength that is transparent to the plate-like object is positioned in the finished thickness region of the chip inside the plate-like object, and the division is performed. A second modified layer forming step of forming a second modified layer that irradiates the laser beam along a predetermined line with a second output lower than the first output to induce division;
A dividing step in which an external force is applied to the plate-like object on which the first modified layer and the second modified layer are formed, and divided into chips along the planned division line;
A tape adhering step of adhering an adhesive tape to the surface of the plate-like object at least at any timing until the division step is performed;
After performing the dividing step, by grinding the back surface of the platelet thinned to finish the thickness of the chip, and the thinning step leaving the second reforming layer to remove said first modified layer,
The processing method of the plate-shaped object characterized by comprising.   The plate-like material processing method according to claim 1, wherein the second output is an output equal to or less than ½ times the first output.   The plate-like material processing method according to claim 1, wherein the plate-like material is formed of a silicon wafer.

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