JP2011151070A - Processing method for wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a processing method for a wafer that removes an altered layer on a side face without cracking peripheral edges of individual devices. <P>SOLUTION: The processing method includes a wafer grinding process of grinding a reverse surface of the wafer 2 so that the wafer has a predetermined thickness, an altered layer forming process of forming the altered layer having a depth, which does not reach a finish thickness of a device, in the wafer 2 from a top surface of the wafer along a street by irradiating the reverse surface side of the wafer 2 with a laser light beam which is transmissive in the wafer 2 along the street, a wafer dividing process of dividing the wafer 2 into the individual devices 22 along the street where the altered layer is formed by applying external force to the wafer 2, and an altered layer removing process of removing the altered layer by grinding the reverse surface of the wafer 2 to form the devices to the finish thickness, the altered layer removing process being performed using a grinding wheel 321 having diamond abrasive grains of 0.5 to 7 μm in grain size fixed with a vitrified bond. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wafer processing method in which a wafer in which devices are formed in a plurality of regions partitioned by streets formed in a lattice shape on the surface is divided into individual devices along the streets.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer, and devices such as ICs, LSIs, etc. are partitioned in the partitioned regions. Form. Then, the semiconductor wafer is cut along the streets to divide the region in which the device is formed to manufacture individual devices. In addition, an optical device wafer in which a gallium nitride compound semiconductor or the like is laminated on the surface of a sapphire substrate or silicon carbide substrate is also divided into optical devices such as individual light emitting diodes and laser diodes by cutting along the streets. Widely used.

  As a method of dividing the wafer along the street, a laser processing method has been attempted in which a pulsed laser beam having transparency to the wafer is used, and the focused laser beam is aligned within the region to be divided and irradiated with the pulsed laser beam. . The dividing method using this laser processing method is to irradiate the inside of the wafer with a pulsed laser beam having a wavelength that is transparent to the wafer by aligning the condensing point from one side of the wafer to the inside. An altered layer is continuously formed along the street, and an external force is applied along the street whose strength is reduced by the formation of the altered layer, thereby dividing the wafer into individual devices. (For example, refer to Patent Document 1.)

  However, since the deteriorated layer remains on the side surfaces of the individual devices divided by the dividing method described in Patent Document 1, there is a problem that the bending strength of the device is lowered and the quality of the device is lowered. In particular, in the optical device, when the deteriorated layer remains on the side surface, there is a problem that the light emitted from the optical device is absorbed by the deteriorated portion and the luminance is lowered.

  In order to solve such problems, an altered layer having a predetermined thickness was formed from the back surface of the wafer by irradiating the wafer with a laser beam having transparency to the wafer, and the altered layer was formed on the wafer. A wafer processing method has been proposed in which after dividing along the street, the rear surface of the wafer is ground to remove the deteriorated layer. (For example, see Patent Document 2.)

Japanese Patent No. 3408805 JP 2005-86161 A

  When the back surface of a wafer that has already been divided into individual devices is ground with a grinding wheel as in the wafer processing method disclosed in Patent Document 2 above, the impact force of the grindstone acting on the peripheral edge of the divided device causes The device may be damaged by cracking at the periphery. In addition, as described above, a wafer formed of quartz is irradiated with a laser beam having a wavelength that is transmissive to the wafer along the street, thereby forming an altered layer having a predetermined thickness from the back surface of the wafer, thereby altering the wafer. The same problem occurs when manufacturing a cover glass by grinding the back surface of the wafer and removing the deteriorated layer after dividing along the street where the layer is formed.

  The present invention has been made in view of the above-mentioned facts, and its main technical problem is to provide a wafer processing method capable of removing a deteriorated layer on the side surface without causing cracks in the peripheral edge of each device. It is in.

In order to solve the above-mentioned main technical problem, according to the present invention, a wafer processing method for dividing a wafer in which devices are formed in a plurality of regions partitioned by streets formed in a lattice shape on the surface along the streets. There,
A wafer grinding process in which the back surface of the wafer is ground to form a wafer having a predetermined thickness;
A laser beam that is transparent to the wafer is irradiated along the street from the back side of the wafer on which the wafer grinding process has been performed, and the depth inside the wafer along the street does not reach the finished thickness of the device from the wafer surface. A deteriorated layer forming step for forming a deteriorated layer;
Wafer dividing step of applying an external force to the wafer on which the deteriorated layer forming step has been performed and dividing the wafer into individual devices along the street on which the deteriorated layer is formed;
A deteriorated layer removing step of removing the deteriorated layer by grinding the back surface of the wafer subjected to the wafer dividing step and forming the wafer in a finished thickness of the device,
The deteriorated layer removing step is performed using a grinding wheel in which diamond abrasive grains having a particle diameter of 0.5 to 7 μm are fixed with vitrified bonds.
A method for processing a wafer is provided.

  In the present invention, the deteriorated layer is removed by grinding the back surface of the wafer that has been subjected to the dividing process of dividing into individual devices along the street where the deteriorated layer is formed, and forming the wafer to the finished thickness of the device. Since the deteriorated layer removing step is performed using a grinding wheel in which diamond abrasive grains having a particle diameter of 0.5 to 7 μm are fixed with vitrified bonds, even if the wafer is divided into individual devices, Since the impact force of the grindstone acting on the peripheral edge is small, the device does not crack.

The perspective view and principal part expanded sectional view which show the semiconductor wafer as a wafer. The perspective view which shows the state which affixed the surface of the semiconductor wafer shown in FIG. 1 on the dicing tape with which the cyclic | annular flame | frame was mounted | worn. Explanatory drawing of the wafer grinding process in the processing method of the wafer by this invention. The principal part perspective view of the laser processing apparatus for implementing the deteriorated layer formation process in the processing method of the wafer by this invention. Explanatory drawing of the deteriorated layer formation process in the processing method of the optical device wafer by this invention. The perspective view of the dividing apparatus for implementing the wafer division | segmentation process in the processing method of the wafer by this invention. Explanatory drawing of the wafer division | segmentation process in the processing method of the wafer by this invention. Explanatory drawing of the deteriorated layer removal process in the processing method of the wafer by this invention. Sectional drawing which expands and shows the principal part of the semiconductor wafer in which the deteriorated layer removal process in the processing method of the wafer by this invention was implemented. Explanatory drawing of the wafer transfer process in the processing method of the wafer by this invention. The perspective view of the pick-up apparatus for implementing the pick-up process in the processing method of the wafer by this invention. Explanatory drawing of the pick-up process in the processing method of the wafer by this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a perspective view of a semiconductor wafer as a wafer processed by the wafer processing method according to the present invention and a cross-sectional view showing an enlarged main part. A semiconductor wafer 2 shown in FIGS. 1A and 1B is made of a silicon wafer. For example, a plurality of device layers 21 are formed by laminating an insulating film and a functional film for forming a circuit on the surface of a silicon substrate 20 having a thickness of 600 μm. The devices 22 such as IC and LSI are formed in a matrix. Each device 22 is partitioned by streets 23 formed in a lattice shape. The device layer 21 is formed with a thickness of 10 μm, for example. Hereinafter, a processing method for dividing the semiconductor wafer 2 into the individual devices 22 along the streets 23 will be described.

  First, in order to protect the device formed on the surface of the semiconductor wafer, a protective member attaching step for attaching a protective member to the surface of the semiconductor wafer is performed. That is, as shown in FIG. 2, the surface 2a of the semiconductor wafer 2 is adhered to the surface of a dicing tape T as a protective member mounted on an annular frame F formed of a metal material. In the illustrated embodiment, the dicing tape T has an acrylic resin paste of about 5 μm thick on the surface of a sheet base material made of polyvinyl chloride (PVC) having a thickness of 100 μm. This glue has a property of reducing the adhesive strength when irradiated with ultraviolet rays.

  If the surface 2a of the semiconductor wafer 2 is attached to the dicing tape T attached to the annular frame F by carrying out the protective member attaching step described above, the back surface of the wafer is ground to obtain a predetermined thickness of the wafer. A wafer grinding process is performed to form a thickness. This wafer grinding process is carried out using a grinding apparatus 3 shown in FIG. A grinding apparatus 3 shown in FIG. 3 includes a grinding wheel 32 including a chuck table 31 that holds a workpiece and a grinding wheel 321 for grinding the workpiece held on the chuck table 31. . Note that the chuck table 31 is formed such that the central portion for holding the workpiece is high and the outer peripheral portion is lower than the central portion. As the grinding wheel 321, a grinding wheel is used in which diamond abrasive grains having a particle size of 40 to 50 μm and a concentration degree of 50 are fixed with vitrified bonds. In order to perform the wafer grinding process using the grinding apparatus 3 configured as described above, the dicing tape T side of the semiconductor wafer 2 is placed on the chuck table 31 of the grinding apparatus 3 as shown in FIG. At the same time, the annular frame F is placed on the outer periphery of the chuck table 31 and the suction means (not shown) is operated to suck and hold the semiconductor wafer 2 and the annular frame F on the chuck table 31. Accordingly, in the semiconductor wafer 2 held on the chuck table 31, the back surface 20b of the silicon substrate 20 is on the upper side. When the semiconductor wafer 2 is sucked and held on the chuck table 31 in this manner, the grinding wheel 32 is rotated in the direction indicated by the arrow 32a at, for example, 6000 rpm while the chuck table 31 is rotated in the direction indicated by the arrow 31a at, for example, 300 rpm. It rotates and contacts the back surface 20b of the silicon substrate 20 constituting the semiconductor wafer 2, and the grinding wheel 32 is ground and fed, for example, 410 μm at a grinding feed rate of 3 μm / second in the direction indicated by the arrow 32b. As a result, the back surface 20b of the silicon substrate 20 is ground, and the semiconductor wafer 2 is formed to a predetermined thickness (200 μm in the illustrated embodiment).

  When the wafer grinding process described above is performed, a laser beam having transparency to the wafer is irradiated along the street from the back side of the wafer, and the finished thickness of the device is reached from the wafer surface along the street inside the wafer. A deteriorated layer forming step for forming a deteriorated layer having no depth is performed. This deteriorated layer forming step is performed using a laser processing apparatus 4 shown in FIG. The laser processing apparatus 4 shown in FIG. 4 has a chuck table 41 that holds a workpiece, laser beam irradiation means 42 that irradiates a workpiece held on the chuck table 41 with a laser beam, and a chuck table 41 that holds the workpiece. An image pickup means 43 for picking up an image of the processed workpiece is provided. The chuck table 41 is configured to suck and hold a workpiece. The chuck table 41 is moved in a processing feed direction indicated by an arrow X in FIG. 4 by a processing feed means (not shown) and is also shown in FIG. 4 by an index feed means (not shown). It can be moved in the index feed direction indicated by the arrow Y.

  The laser beam application means 42 includes a cylindrical casing 421 arranged substantially horizontally. In the casing 421, pulse laser beam oscillation means including a pulse laser beam oscillator and repetition frequency setting means (not shown) are arranged. A condenser 422 for condensing the pulse laser beam oscillated from the pulse laser beam oscillating means is attached to the tip of the casing 421. The laser beam irradiating unit 42 includes a condensing point position adjusting unit (not shown) for adjusting the condensing point position of the pulsed laser beam condensed by the condenser 422.

  An image pickup means 43 for picking up an image of the processing area of the workpiece held on the chuck table 41 is disposed at the tip of the casing 421 constituting the laser beam irradiation means 42. In the illustrated embodiment, the imaging unit 43 includes, in addition to a normal imaging device (CCD) that captures an image with visible light, an infrared illumination unit that irradiates a workpiece with infrared rays, and an infrared ray that is irradiated by the infrared illumination units. And an imaging device (infrared CCD) that outputs an electrical signal corresponding to infrared rays captured by the optical system, and sends the captured image signal to a control means described later.

Using the laser processing apparatus 4 described above, a laser beam having a wavelength that is transmissive to the silicon substrate 20 constituting the semiconductor wafer 2 is positioned from the back surface 20b side of the silicon substrate 20 at a condensing point inside the silicon substrate 20. FIG. 4 and FIG. 5 are referred to in regard to a deteriorated layer forming step of irradiating along the street 23 to form a deteriorated layer having a depth that does not reach the finished thickness of the device from the surface of the semiconductor wafer 2 inside the silicon substrate 20. I will explain.
First, the dicing tape T side on which the semiconductor wafer 2 is adhered is placed on the chuck table 41 of the laser processing apparatus 4 shown in FIG. 4 described above. Then, the semiconductor wafer 2 is held on the chuck table 41 via the dicing tape T by operating a suction means (not shown) (wafer holding step). Accordingly, the semiconductor wafer 2 held on the chuck table 41 has the back surface 20b of the silicon substrate 20 on the upper side. In FIG. 4, the annular frame F on which the dicing tape T is mounted is omitted, but the annular frame F is held by an appropriate frame holding means provided on the chuck table 41. In this way, the chuck table 41 that sucks and holds the optical device wafer 2 is positioned directly below the imaging unit 43 by a processing feed unit (not shown).

  When the chuck table 41 is positioned immediately below the image pickup means 43, an alignment operation for detecting a processing region to be laser processed on the wafer 2 is executed by the image pickup means 43 and a control means (not shown). That is, the image pickup means 43 and the control means (not shown) align the streets 23 formed in a predetermined direction of the semiconductor wafer 2 and the condenser 422 of the laser beam irradiation means 42 that irradiates the laser beams along the streets 23. Image processing such as pattern matching is performed to perform the laser beam irradiation position alignment (alignment process). Similarly, the alignment of the laser beam irradiation position is performed on the street 23 formed on the semiconductor wafer 2 in a direction orthogonal to the predetermined direction. At this time, the surface of the device layer 21 on which the streets 23 are formed in the semiconductor wafer 2 is located on the lower side. However, the imaging means 43 is compatible with the infrared illumination means and the optical system for capturing infrared rays as described above. Since the image pickup unit (infrared CCD) that outputs the electrical signal is provided, the street 23 can be imaged through the back surface 20b of the silicon substrate 20.

  If the street 23 formed on the surface of the device 21 constituting the semiconductor wafer 2 held on the chuck table 41 as described above is detected and the laser beam irradiation position is aligned, ( As shown in a), the chuck table 41 is moved to the laser beam irradiation region where the condenser 422 of the laser beam irradiation means 42 is located, and one end of the predetermined street 23 (the left end in FIG. 5A) is moved to the laser beam irradiation means 42. It is positioned directly below the light collector 422. Then, the condensing point P of the pulsed laser beam irradiated from the condenser 422 is adjusted to a position, for example, 80 μm above the surface 2 a (lower surface) of the semiconductor wafer 2. In order to position the condensing point P of the pulsed laser beam irradiated from the concentrator 422 at a predetermined position of the semiconductor wafer 2, for example, a workpiece to be processed held on a chuck table described in JP-A-2009-63446. A height position of the upper surface of the semiconductor wafer 2 held on the chuck table 41 is detected using an object height position detection device, and a light condensing point (not shown) is used on the basis of the detected height position of the upper surface of the semiconductor wafer 2. By operating the position adjusting means, the condensing point P of the pulse laser beam is positioned at a predetermined position. Next, the chuck table 41 is irradiated in a direction indicated by an arrow X1 in FIG. 5A while irradiating a pulse laser beam having a wavelength having transparency to the silicon substrate 20 constituting the semiconductor wafer 2 from the condenser 422. Move at the machining feed rate of. When the irradiation position of the condenser 422 of the laser beam irradiation means 42 reaches the position of the other end of the street 23 (the right end in FIG. 5B) as shown in FIG. And the movement of the chuck table 41 is stopped. As a result, an altered layer 210 continuous along the street 23 is formed in the silicon substrate 20 constituting the semiconductor wafer 2 as shown in (b) of FIG. 5 and (c) of FIG. Layer forming step). The altered layer 210 is formed on the silicon substrate 20 at a depth that does not reach the finished thickness of the device (for example, 20 μm) from the surface 2 a of the semiconductor wafer 2. The above-described deteriorated layer forming step is performed along all the streets 23 formed on the semiconductor wafer 2.

The processing conditions in the above-mentioned deteriorated layer forming step are set as follows, for example.
Light source: LD excitation Q switch Nd: YVO4 laser Wavelength: 1064 nm pulse laser Repetition frequency: 80 kHz
Pulse width: 120 ns
Average output: 1.2W
Condensing spot diameter: φ2μm
Processing feed rate: 100 mm / sec

  When the above-described deteriorated layer forming step is performed under the above processing conditions, the deteriorated layer 210 having a depth of about 100 μm in the vertical direction is formed around the condensing point P of the pulse laser beam. Therefore, by performing the above-described deteriorated layer forming step, the deteriorated layer 210 having a depth of about 100 μm is formed on the back surface 20b (upper surface) side of the silicon substrate 20 from a position 30 μm from the front surface 2a (lower surface) of the semiconductor wafer 2. Is done. That is, an altered layer 210 having a depth that does not reach the finished thickness (for example, 20 μm) of the device from the surface 2 a of the semiconductor wafer 2 is formed along the street 23 inside the silicon substrate 20. As described above, the deteriorated layer forming step removes the deteriorated layer by grinding the back surface of the silicon substrate 20 constituting the semiconductor wafer 2 to form the wafer to the finished thickness of the device (for example, 20 μm). Since it is performed in a thick state (for example, 200 μm) before the layer removal step, the focused point P of the pulse laser beam can be easily positioned at a desired position, and the altered layer 210 is not damaged without damaging the device layer 21. Can be formed.

  If the above-described deteriorated layer forming step is performed, an external force is applied to the wafer on which the deteriorated layer forming step has been performed, and a dividing step is performed in which the wafer is divided into individual devices along the street on which the deteriorated layer is formed. . This wafer dividing step is performed using a wafer dividing apparatus 5 shown in FIG. 6 includes a base 51 and a moving table 52 disposed on the base 51 so as to be movable in a direction indicated by an arrow Y. The base 51 is formed in a rectangular shape, and two guide rails 511 and 512 are arranged in parallel with each other in the direction indicated by the arrow Y on the upper surfaces of both side portions. A moving table 52 is movably disposed on the two guide rails 511 and 512. The moving table 52 is moved in the direction indicated by the arrow Y by the moving means 53. On the moving table 52, frame holding means 54 for holding the annular frame F is disposed. The frame holding means 54 includes a cylindrical main body 541, an annular frame holding member 542 provided at the upper end of the main body 541, and a plurality of clamps 543 as fixing means disposed on the outer periphery of the frame holding member 542. It is made up of. The frame holding means 54 configured in this manner fixes the annular frame F placed on the frame holding member 542 with the clamp 543. Further, the wafer dividing device 5 shown in FIG. 6 includes a rotating means 55 for rotating the frame holding means 54. The rotating means 55 is wound around a pulse motor 551 disposed on the moving table 52, a pulley 552 mounted on a rotation shaft of the pulse motor 551, and the pulley 552 and a cylindrical main body 541. An endless belt 553 is included. The rotation means 55 configured in this manner rotates the frame holding means 54 via the pulley 552 and the endless belt 553 by driving the pulse motor 551.

  The wafer dividing device 5 shown in FIG. 6 applies a tensile force in a direction perpendicular to the street 23 to the semiconductor wafer 2 supported by the annular frame F held by the annular frame holding member 542 via the dicing tape T. There is provided tension applying means 56 to be applied. The tension applying means 56 is disposed in the annular frame holding member 54. The tension applying means 56 includes a first suction holding member 561 and a second suction holding member 562 having a rectangular holding surface that is long in a direction orthogonal to the arrow Y direction. A plurality of suction holes 561 a are formed in the first suction holding member 561, and a plurality of suction holes 562 a are formed in the second suction holding member 562. The plurality of suction holes 561a and 562a communicate with suction means (not shown). Further, the first suction holding member 561 and the second suction holding member 562 can be moved in the arrow Y direction by a moving means (not shown).

  The wafer dividing apparatus 5 shown in FIG. 6 has a detection means 57 for detecting the street 23 of the semiconductor wafer 2 supported by the annular frame F held by the annular frame holding member 542 via the dicing tape T. It has. The detection means 57 is attached to an L-shaped support column 571 disposed on the base 51. The detection means 57 is composed of an optical system, an image sensor (CCD), and the like, and is disposed above the tension applying means 56. The detection means 57 configured in this manner images the street 23 of the semiconductor wafer 2 supported by the annular frame F held by the annular frame holding member 542 via the dicing tape T, and this is electrically captured. It converts into a signal and sends it to the control means which is not illustrated.

Wafer breakage performed using the wafer breaker 6 described above will be described with reference to FIG.
An annular frame F that supports the semiconductor wafer 2 on which the above-described deteriorated layer forming step has been performed via the dicing tape T is placed on the frame holding member 542 as shown in FIG. To the frame holding member 542. Next, the moving means 53 is actuated to move the moving table 52 in the direction indicated by the arrow Y (see FIG. 6). As shown in FIG. The street 23 (the leftmost street in the illustrated embodiment) is positioned between the holding surface of the first suction holding member 561 and the holding surface of the second suction holding member 562 constituting the tension applying means 56. At this time, the street 23 is imaged by the detection means 57, and the holding surface of the first suction holding member 561 and the holding surface of the second suction holding member 562 are aligned. In this way, if one street 23 is positioned between the holding surface of the first suction holding member 561 and the holding surface of the second suction holding member 562, the suction means (not shown) is operated to perform suction. By applying a negative pressure to the holes 561a and 562a, the semiconductor wafer 2 is sucked and held via the dicing tape T on the holding face of the first suction holding member 561 and the holding face of the second suction holding member 562 ( Holding step).

  When the holding step described above is performed, the moving means (not shown) constituting the tension applying means 56 is operated, and the first suction holding member 561 and the second suction holding member 562 are as shown in FIG. Move them away from each other. As a result, a tensile force acts in a direction perpendicular to the street 23 on the street 23 positioned between the holding surface of the first suction holding member 561 and the holding surface of the second suction holding member 562, and the semiconductor In the wafer 2, the altered layer 210 formed on the silicon substrate 20 is broken along the streets 23 (wafer dividing step). By performing this wafer dividing step, the dicing tape T slightly extends. In this wafer dividing step, the semiconductor wafer 2 has a deteriorated layer 210 formed along the streets 23 to reduce its strength, so that the first suction holding member 561 and the second suction holding member 562 are separated from each other. By moving about 0.5 mm in the direction, the altered layer 210 formed on the silicon substrate 20 of the semiconductor wafer 2 can be broken along the street 23 as a starting point of breakage.

  As described above, when the wafer splitting process is performed along the one street 23 formed in a predetermined direction, the semiconductor wafer 2 by the first suction holding member 561 and the second suction holding member 562 described above is used. Release suction hold. Next, the moving means 53 is operated to move the moving table 52 in the direction indicated by the arrow Y (see FIG. 6) by an amount corresponding to the interval between the streets 23, and the street 23 adjacent to the street 23 on which the above-described breaking process is performed. Is positioned between the holding surface of the first suction holding member 561 and the holding surface of the second suction holding member 562 constituting the tension applying means 56. Then, the holding step and the wafer dividing step are performed.

  As described above, when the holding process and the wafer dividing process are performed on all the streets 23 formed in a predetermined direction, the rotating means 55 is operated to rotate the frame holding means 54 by 90 degrees. . As a result, the semiconductor wafer 2 held by the frame holding member 542 of the frame holding means 54 also rotates 90 degrees, and is formed in a direction perpendicular to the street 23 formed in a predetermined direction and subjected to the wafer dividing step. The street 23 thus formed is positioned in a state parallel to the holding surface of the first suction holding member 561 and the holding surface of the second suction holding member 562. Next, the semiconductor wafer 2 extends along the street 23 by performing the above-described holding step and wafer dividing step on all the streets 23 formed in a direction orthogonal to the street 23 on which the wafer dividing step is performed. Are divided into individual devices 22.

  When the wafer dividing step described above is performed, the deteriorated layer removing step of removing the deteriorated layer by grinding the back surface of the wafer subjected to the wafer dividing step and forming the wafer to the finished thickness of the device is performed. This deteriorated layer removing step is performed using a grinding device substantially similar to the grinding device 3 shown in FIG. The grinding wheel 321 of the grinding wheel 32 provided in the grinding apparatus 3 shown in FIG. 8 for performing the deteriorated layer removing step is a diamond having a particle size of 0.5 to 7 μm and a concentration of 30 to 70, preferably a concentration of 50. It is important to use a grinding wheel with abrasive grains fixed with vitrified bonds. The particle size of the diamond abrasive grains constituting the grinding wheel 321 varies depending on the type of wafer (silicon wafer, sapphire wafer, crystal wafer, GaAs wafer, GaN wafer, GaP wafer). 0.5 to 2 μm for silicon wafers, 5 to 7 μm for sapphire wafers, 3 to 6 μm for quartz wafers, 1 to 3 μm for GaAs wafers, and 2 to 2 for GaN wafers. In the case of a 5 μm GaP wafer, it is preferably 1.5 to 4 μm. The lower limit of the diamond abrasive grains constituting the grinding wheel 321 is a lower limit value that enables the workpiece to be ground, and the upper limit is ground without causing cracks in the peripheral edge of the device when performing the deteriorated layer removing step described later. It is the upper limit that can be done. Therefore, in the illustrated embodiment, since the semiconductor wafer 2 as a workpiece is a silicon wafer, the grain size of diamond abrasive grains constituting the grinding wheel 321 is set to 0.5 to 2 μm and the degree of concentration is set to 50. .

  In order to perform the deteriorated layer removing process using the grinding apparatus 3 described above, as shown in FIG. 8, the semiconductor wafer 2 (individual devices 22) in which the wafer dividing process described above is performed on the chuck table 31 of the grinding apparatus 3 is performed. The dicing tape T side of the semiconductor wafer 2 is placed on the chuck table 31 by placing the annular frame F on the outer periphery of the chuck table 31 and operating a suction means (not shown). The annular frame F is sucked and held. Accordingly, in the semiconductor wafer 2 held on the chuck table 31, the back surface 20b of the silicon substrate 20 is on the upper side. When the semiconductor wafer 2 is sucked and held on the chuck table 31 in this way, the grinding wheel 32 is rotated in the direction indicated by the arrow 32a while rotating the chuck table 31 in the direction indicated by the arrow 31a, for example, at 40 to 300 rpm. The wafer is rotated at 1000 to 3500 rpm to come into contact with the back surface 20b of the silicon substrate 20 constituting the semiconductor wafer 2, and the grinding wheel 32 is ground and fed at a grinding feed rate of 0.3 μm / second, for example, 180 μm in the direction indicated by the arrow 32b. As a result, the back surface 20b of the silicon substrate 20 constituting the semiconductor wafer 2 is ground to remove the altered layer 210 remaining on the side surfaces of the devices 22 that are individually divided as shown in FIG. The thickness of the wafer 2 is formed to the finished thickness of the device (20 μm in the illustrated embodiment). Thus, the deteriorated layer removal step is performed using a grinding wheel in which diamond grains having a particle size of 0.5 to 2 μm and a concentration of 50 are fixed by vitrified bonds, so that the semiconductor wafer 2 is divided into individual devices 22. However, since the impact force of the grindstone acting on the peripheral edge of the divided device 22 is small, the device 22 is not cracked.

  If the deteriorated layer removing step described above is performed, the back surface of the wafer divided into individual devices is attached to the surface of the protective tape attached to the annular frame, and the surface of the wafer is attached. A wafer transfer process is performed in which the dicing tape T is peeled off and the annular frame F is removed. In this wafer transfer process, as shown in FIG. 10 (a), the dicing tape T mounted on the annular frame F (the semiconductor wafer 2 divided into individual devices 22 is attached) is irradiated with ultraviolet rays. The container 6 is irradiated with ultraviolet rays. As a result, the adhesive paste of the dicing tape T is cured and the adhesive strength is reduced. Next, as shown in FIG. 10B, the back surface 20b of the silicon substrate 20 constituting the semiconductor wafer 2 attached to the dicing tape T attached to the annular frame F (in FIG. 10B). The surface (the lower surface in FIG. 10B) of the dicing tape Ta attached to the annular frame Fa is adhered to the upper surface. The annular frame Fa and the dicing tape Ta may have substantially the same configuration as the annular frame F and the dicing tape T. Next, as shown in FIG. 10C, the semiconductor wafer 2 (divided into individual devices 22) whose surface is bonded to the dicing tape T is peeled off from the dicing tape T. At this time, as shown in FIG. 10 (a), the dicing tape T is irradiated with ultraviolet rays, and the adhesive paste of the dicing tape T is cured to reduce the adhesive force, so that the semiconductor wafer 2 (individual device 22) is reduced. Can be easily peeled from the dicing tape T. Then, by removing the annular frame F on which the dicing tape T is attached, the semiconductor divided into individual devices on the surface of the dicing tape Ta attached to the annular frame Fa as shown in FIG. Wafer 2 has been transferred. Thus, in the wafer transfer process, the wafer grinding process, the altered layer process, the wafer dividing process, and the altered layer removing process are performed with the wafer surface adhered to the dicing tape T mounted on the annular frame F. Then, since the semiconductor wafer 2 is divided into the individual devices 22, the semiconductor wafer 2 can be reversed and replaced with the dicing tape Ta mounted on the annular frame Fa without breaking the semiconductor wafer 2. Accordingly, the continuity test of the device 22 can be performed in a state where the semiconductor wafer 2 divided into the individual devices 22 is replaced with the dicing tape Ta mounted on the annular frame Fa.

  Once the wafer transfer process has been performed as described above, a pick-up process is performed in which the individually divided devices attached to the surface of the protective tape attached to the annular frame are separated from the protective tape and picked up. To do. This pickup process is performed using the pickup device 7 shown in FIG. The pickup device 7 shown in FIG. 11 includes a frame holding means 71 for holding the annular frame Fa, and a tape extending means 72 for expanding the dicing tape Ta attached to the annular frame Fa held by the frame holding means 71. And a pickup collet 73. The frame holding means 71 includes an annular frame holding member 711 and a plurality of clamps 712 as fixing means provided on the outer periphery of the frame holding member 711. An upper surface of the frame holding member 711 forms a mounting surface 711a on which the annular frame Fa is mounted, and the annular frame Fa is mounted on the mounting surface 711a. The annular frame Fa placed on the placement surface 711 a is fixed to the frame holding member 711 by the clamp 712. The frame holding means 71 configured as described above is supported by the tape expanding means 72 so as to be able to advance and retreat in the vertical direction.

  The tape expansion means 72 includes an expansion drum 721 disposed inside the annular frame holding member 711. The expansion drum 721 has an inner diameter and an outer diameter that are smaller than the inner diameter of the annular frame Fa and larger than the outer diameter of the semiconductor wafer 2 (divided into individual devices 22) mounted on the annular frame Fa. Yes. The expansion drum 721 includes a support flange 722 at the lower end. The tape expansion means 72 in the illustrated embodiment includes support means 723 that can advance and retract the annular frame holding member 711 in the vertical direction. The support means 723 includes a plurality of air cylinders 723 a disposed on the support flange 722, and the piston rod 723 b is connected to the lower surface of the annular frame holding member 711. As described above, the support means 723 including the plurality of air cylinders 723a is configured such that the mounting position of the annular frame holding member 711 is substantially the same as the upper end of the expansion drum 721 as shown in FIG. Then, as shown in FIG. 12 (b), it is moved in the vertical direction between the extended positions below the upper end of the expansion drum 721 by a predetermined amount.

  A pickup process performed using the pickup apparatus 7 configured as described above will be described with reference to FIG. That is, an annular frame Fa on which a dicing tape Ta to which a semiconductor wafer 2 (divided into individual devices) is attached is configured as a frame holding means 71 as shown in FIG. It is mounted on the mounting surface 711a of the frame holding member 711 to be fixed, and is fixed to the frame holding member 711 by the clamp 712 (frame holding step). At this time, the frame holding member 711 is positioned at the reference position shown in FIG. Next, the plurality of air cylinders 723a as the supporting means 723 constituting the tape expanding means 72 are operated to lower the annular frame holding member 711 to the extended position shown in FIG. Accordingly, the annular frame Fa fixed on the mounting surface 711a of the frame holding member 711 is also lowered, so that the dicing tape Ta mounted on the annular frame Fa as shown in FIG. It is expanded in contact with the upper edge of 721 (tape expansion process). As a result, since the semiconductor wafer 2 adhered to the dicing tape Ta is divided into individual devices 22 along the streets 23, the space between the individual devices 22 is widened and a space S is formed. In this state, the pickup collet 73 is actuated to suck and hold the surface (upper surface) of the device 22 and peel off from the dicing tape Ta to pick up. At this time, as shown in FIG. 12B, the device 22 can be easily peeled from the dicing tape Ta by pushing up the device 22 from the lower side of the dicing tape Ta with the push-up needle 74. The push-up needle 74 acts on the back surface of the device 22 and pushes it up, so that the surface of the device 22 is not damaged. In the pickup process, since the gap S between the individual devices 22 is widened as described above, the pickup can be easily performed without contacting the adjacent devices 22. Thus, since the optical device 23 picked up by the pickup collet 73 has its surface (upper surface) held by suction, it is not necessary to reverse the front and back of the device 22 thereafter.

  Although the present invention has been described based on the illustrated embodiment, the present invention is not limited to the embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in the embodiment described above, an example is shown in which the wafer grinding step, the altered layer step, the wafer dividing step, and the altered layer removing step are performed in a state where the wafer surface is attached to a dicing tape attached to an annular frame. However, a protective tape is applied to the surface of the wafer, the wafer grinding process and the altered layer process are performed, and then the back surface of the wafer is applied to a dicing tape attached to an annular frame, and the protective tape is peeled off. In this state, the wafer dividing step may be performed, and then the deteriorated layer removing step may be performed by attaching a protective tape to the front surface of the wafer and peeling the dicing tape from the back surface of the wafer.

2: Semiconductor wafer 20: Silicon substrate 21: Device layer 5: Grinding device 51: Chuck table of grinding device 52: Grinding wheel 521: Grinding wheel 4: Laser processing device 41: Chuck table of laser processing device 42: Laser beam irradiation means 5 : Wafer dividing device 56: Tension applying means 7: Pickup device
F: Ring frame
T: Dicing tape

Claims (1)

A wafer processing method for dividing a wafer in which devices are formed in a plurality of regions partitioned by a street formed in a lattice shape on the surface, along the street,
A wafer grinding process in which the back surface of the wafer is ground to form a wafer having a predetermined thickness;
A laser beam that is transparent to the wafer is irradiated along the street from the back side of the wafer on which the wafer grinding process has been performed, and the depth inside the wafer along the street does not reach the finished thickness of the device from the wafer surface. A deteriorated layer forming step for forming a deteriorated layer;
Wafer dividing step of applying an external force to the wafer on which the deteriorated layer forming step has been performed and dividing the wafer into individual devices along the street on which the deteriorated layer is formed;
The wafer includes a deteriorated layer removing step of removing the deteriorated layer by grinding the back surface of the wafer subjected to the division step and forming the wafer to a finished thickness of the device,
The deteriorated layer removing step is performed using a grinding wheel in which diamond abrasive grains having a particle diameter of 0.5 to 7 μm are fixed with vitrified bonds.
A method for processing a wafer.

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