JP2017107988A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a high quality device chip from a WL-CSP wafer.SOLUTION: A wafer processing method includes: forming a groove 19 having a depth equivalent to a finishing thickness of a device chip along a division schedule line; covering a surface 11a of a wafer with a mold resin 21 and embedding the mold resin in the groove; arranging a protective member on the mold resin; sucking and holding the wafer with a chuck table through the protective member, grinding a rear face 11b of the wafer, and exposing the mold resin embedded in the groove to the rear face; sticking the rear face of the wafer to an adhesive tape T of which the outer peripheral portion is stuck to an annular frame having an opening that accommodates the wafer therein, in the opening, and supporting the wafer by the annular frame through the adhesive tape; forming a division starting point 25 in the center of the mold resin corresponding to the division schedule line from the surface of the wafer; and moving a ball 42 over the whole surface while pressing the ball from the rear face through the adhesive tape, and dividing the wafer into individual device chips having the outer periphery surrounded by the mold resin with a pressing force of the ball.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a wafer processing method for dividing a wafer into individual device chips.

  In the manufacturing process of semiconductor device chips, grid-like division lines called streets are formed on the surface of a wafer made of silicon or a compound semiconductor, and devices such as ICs and LSIs are formed in each area partitioned by the division lines. Is done. After these wafers are ground and thinned to a predetermined thickness, the individual semiconductor device chips are manufactured by being divided by a cutting device along a predetermined division line.

  In recent years, a technology called WL-CSP (Wafer-Level Chip Size Package) has been actively used in the field of semiconductor devices. WL-CSP is a technology that forms a rewiring layer and electrodes (metal posts) in a wafer state, then seals the wafer surface with a resin, and divides the wafer into individual packages with a cutting blade or the like. Since the size of the package becomes the size of the semiconductor device chip, it is widely adopted from the viewpoint of miniaturization and weight reduction.

  The following processes are known as processes for manufacturing individual device chips with WL-CSP.

  (1) A cutting groove corresponding to the finished thickness of the device chip is formed on the division line of the wafer.

  (2) Cover the entire surface of the wafer with mold resin and embed the mold resin in the cutting groove.

  (3) After a protective member is attached to the front surface of the wafer, the back surface of the wafer is ground to expose the mold resin in the cutting groove to the back surface of the wafer.

  (4) The wafer back surface is attached to a dicing tape whose outer peripheral portion is attached to an annular frame, and the wafer is cut along a planned dividing line with a cutting blade having a thickness smaller than the thickness of the cutting blade used in the cutting groove forming process. Cut into individual device chips.

JP 2006-1000053 A

  However, when the back surface of the wafer whose surface is coated with the mold resin is ground to expose the cutting grooves on the back surface, the cutting grooves along the line to be divided are formed only by the mold resin, and the wafer is divided in the dividing process. When the line to be divided is cut, there is a problem that the cutting blade of the cutting blade is bent by the resistance of the mold resin, and the side surface of the device chip is damaged.

  The present invention has been made in view of these points, and an object of the present invention is to provide a wafer processing method capable of generating a high-quality device chip from a WL-CSP wafer.

  According to the present invention, there is provided a wafer processing method for dividing a wafer in which a device is formed in each region of a surface partitioned by a plurality of division lines formed in a lattice shape into individual device chips, the device chip A groove forming step for forming a groove having a depth corresponding to the finished thickness along the line to be divided, and after performing the groove forming step, the surface of the wafer is coated with a mold resin and the groove is molded resin After performing the molding process, the protective member disposing process for disposing a protective member on the mold resin coated on the surface of the wafer, and the protective member disposing process The wafer is sucked and held by the chuck table through the protective member, the back surface of the wafer is ground, and the mold resin embedded in the groove is removed from the wafer. After carrying out the back surface grinding step to be exposed to the surface and the back surface grinding step, the back surface of the wafer is adhered within the opening to the adhesive tape whose outer peripheral portion is adhered to the annular frame having the opening for accommodating the wafer, A frame supporting step for supporting the wafer with the annular frame via the adhesive tape, and after performing the frame supporting step, the dividing line is formed in the center of the mold resin corresponding to the dividing line from the surface of the wafer. A split starting point forming step for forming the split starting point along the split start point forming step, and then moving the entire surface of the wafer while pressing the ball from the back surface of the wafer via the adhesive tape. And a dividing step of dividing the wafer into individual device chips each having an outer periphery surrounded by the mold resin. Method for processing Doha is provided.

  Preferably, in the division start point forming step, the division start point is formed by any one of a cutting blade, a scriber, and laser beam irradiation.

  According to the wafer processing method of the present invention, after the division starting point forming step is performed, the wafer is moved from the back surface of the wafer through the adhesive tape while pressing the ball over the entire surface of the wafer, and the wafer is surrounded by the mold resin by the pressing force of the ball. Therefore, the problem that the cutting blade of the cutting blade bends and damages the side surface of the device chip is solved, and the device chip whose outer periphery is reliably surrounded by the mold resin can be generated.

It is a surface side perspective view of a semiconductor wafer. It is a perspective view of the groove | channel formation process implemented with a cutting blade. 3A is a front perspective view of the semiconductor wafer after the groove forming step, and FIG. 3B is an enlarged sectional view taken along line 3B-3B of FIG. 3A. 4A is a front perspective view of the semiconductor wafer showing the molding process, and FIG. 4B is an enlarged sectional view taken along line 4B-4B of FIG. 4A. It is a perspective view which shows a back surface grinding process. It is a perspective view which shows a flame | frame support process. It is a perspective view of an embodiment which carries out a division starting point formation process with a cutting blade. It is sectional drawing which shows a division | segmentation process. It is sectional drawing of CSP.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a front side perspective view of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11. The wafer 11 has a thickness of about 700 μm.

  The wafer 11 has a front surface 11a and a back surface 11b. A plurality of scheduled division lines 13 are formed on the front surface 11a so as to be orthogonal to each other. The device 15 is formed.

  As shown in the enlarged view of FIG. 1, each device 15 has a plurality of protruding electrodes (bumps) 17 protruding on the surface thereof. In this way, the wafer 11 having the bumps 17 on the surface is divided into flip chip bonding in which the wafer 11 is divided into individual device chips having the devices 15 and the bumps 17 are directly bonded to the electrodes formed on the wiring board. It is mounted on a wiring board by a so-called mounting technique.

  Referring to FIG. 2, a perspective view of an embodiment in which a groove forming process is performed by a cutting blade is shown. In FIG. 2, reference numeral 10 denotes a cutting unit of the cutting apparatus. The cutting unit 10 includes a cutting blade 14 attached to the tip of a spindle housed in a spindle housing 12 and a blade cover 16 that covers the upper half of the cutting blade 14. ing. The blade cover 16 is provided with a blade cooler nozzle 18 that ejects cutting water toward the wafer 11 and the cutting blade 14 that are being cut.

  In the groove forming process, the cutting blade 14 having a cutting blade having a predetermined width and rotating at high speed in the direction of arrow A is cut from the surface 11a of the wafer 11 to a depth corresponding to the finished thickness of the device chip, and the wafer 11 is held. By cutting and feeding a chuck table (not shown) in the direction of the arrow X1, a cutting groove 19 having a depth corresponding to the finished thickness of the device chip is formed along the planned dividing line 13.

  While indexing and feeding the wafer 11 in the Y-axis direction, similar cutting grooves 19 are formed one after another along the planned dividing line 13 extending in the first direction. Next, after the chuck table holding the wafer 11 is rotated by 90 °, similar cutting grooves 19 are formed one after another along the division line 13 extending in the second direction orthogonal to the first direction.

  FIG. 3A shows a front perspective view of the wafer 11 after completion of the groove forming step. As shown in FIG. 3B, which is an enlarged cross-sectional view taken along line 3B-3B in FIG. 3A, the cutting groove 19 formed in the groove forming step corresponds to a predetermined width W1 and a finished thickness of the device chip. Depth d1.

  Here, when the thickness of the wafer 11 is t1 = 700 μm, in this embodiment, the predetermined width W1 = 40 μm and the depth d1 = 300 μm corresponding to the finished thickness of the device chip. However, the predetermined width W1 and the depth d1 corresponding to the finished thickness of the device chip are not limited to these values.

  After performing the groove forming process, a molding process is performed in which the surface 11a of the wafer 11 is coated with a mold resin and the mold resin is embedded in the cutting groove 19 formed in the wafer 11.

  In this molding process, as shown in FIG. 4A, a liquid mold resin 21 containing a filler is dropped onto the surface 11a of the wafer 11, and a chuck table (not shown) for sucking and holding the wafer 11 is rotated to perform spin coating. Thus, the surface 11 a of the wafer 11 is covered with the mold resin 21 as shown in the enlarged sectional view of FIG. 4B, and the mold resin 21 is embedded in the cutting groove 19. The liquid mold resin 21 is cured when left at room temperature.

  In this embodiment, the thickness t2 of the mold resin 21 coated on the surface 11a of the wafer 11 is about 100 μm, and the heads of the bumps 17 are slightly exposed from the surface of the mold resin 21. When the heads of the bumps 17 are completely covered with the mold resin 21, the heads of the bumps 17 are exposed from the surface of the mold resin 21 by grinding or polishing.

  Here, when the width of the division line 13 of the wafer 11 in this embodiment is 50 μm, the width W1 of the cutting groove 19 is preferably about 40 μm, and the mold resin 21 is a mixture of silica as a filler in an epoxy resin. Is preferred.

Further, a mold resin containing silica (SiO ₂ ) 9 as a filler in a volume ratio with respect to the epoxy resin 1 is preferable, and an average particle diameter of silica is preferably 30 μm or less, more preferably 20 μm or less.

  After the molding process is performed, a protective member disposing process for disposing a protective member on the surface 11a of the wafer 11 is performed. Actually, since the surface 11 a of the wafer 11 is covered with the mold resin 21, a protective member such as a protective tape is stuck on the mold resin 21.

  After performing the protective member disposing step, a back surface grinding step is performed in which the back surface 11b of the wafer 11 is ground to expose the mold resin 21 embedded in the cutting groove 19 to the back surface 11b of the wafer 11.

  This back grinding process will be described with reference to FIG. In the back surface grinding process, the front surface 11a side of the wafer 11 is sucked and held via the protective tape 23 by the chuck table 20 of the grinding device, and the back surface 11b side of the wafer 11 is exposed.

  The grinding unit 22 of the grinding apparatus includes a spindle 24 that is rotationally driven by a motor, a wheel mount 26 that is fixed to the tip of the spindle 24, and a grinding wheel 30 that is detachably fixed to the wheel mount 26 with a plurality of screws 28. Is included. The grinding wheel 30 includes an annular wheel base 32 and a plurality of grinding wheels 34 that are annularly fixed to the outer periphery of the lower end of the wheel base 32.

  In the back grinding process, the grinding wheel 30 is rotated in the same direction as the chuck table 20, that is, in the arrow b direction, for example, at 6000 rpm while rotating the chuck table 20 in the direction indicated by the arrow a, for example, and a grinding unit (not shown). The feed mechanism is operated to bring the grinding wheel 34 into contact with the back surface 11 b of the wafer 11.

  Then, the grinding wheel 30 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed (for example, 1 μm / s), and the back surface grinding of the wafer 11 is performed. When the grinding is continued and the wafer 11 is thinned to the finished thickness of the device chip, the mold resin 21 embedded in the cutting groove 19 is exposed on the back surface 11b of the wafer 11 as shown in FIG.

  After performing the back surface grinding step, as shown in FIG. 6, the wafer 11 is placed in the dicing tape T, which is an adhesive tape having an outer peripheral portion attached to an annular frame F having an opening F1 for accommodating the wafer. A back surface 11b is attached, the wafer 11 is supported by the annular frame F via the dicing tape T, and a frame support process is performed to remove the protective tape 23 from the front surface 11a of the wafer 11.

  In this frame support process, since the protective tape 23 is peeled off from the surface 11a of the wafer 11, the mold resin 21 coated on the surface 11a of the wafer 11 is exposed on the surface. After carrying out the frame supporting step, for example, as shown in FIG. 7, the cutting unit 10 of the cutting apparatus moves along the planned dividing line 13 from the surface 11 a of the wafer 11 to the center of the mold resin 21 corresponding to the planned dividing line 13. A division starting point forming step for forming the division starting point 25 is performed.

  The cutting blade 14a employed in the division starting point forming step needs to be thinner than the cutting blade 14 employed in the groove forming step. For example, a cutting blade 14a having a cutting blade thickness of 20 μm is used.

  In the division starting point forming step, the cutting blade 14a that rotates at high speed in the direction of arrow A is slightly cut (for example, 30 μm) from the surface 11a of the wafer 11 into the center of the mold resin 21 corresponding to the planned division line 13 to hold the wafer. By dividing and feeding a chuck table (not shown) in the direction of the arrow X1, the division start point 25 is formed along the planned division line 13 extending in the first direction.

  While indexing and feeding the wafer 11 in the Y-axis direction, the same division start points 25 are formed one after another along the planned division line 13 extending in the first direction. Next, after the chuck table holding the wafer 11 by suction is rotated by 90 °, the same division starting points 25 are formed one after another along the planned division line 13 extending in the second direction orthogonal to the first direction. As shown in the cross-sectional view of FIG. 8A, the dividing starting point 25 is formed on the surface of the mold resin 21 embedded in the cutting groove 19 formed along the dividing line 13.

  In the embodiment described above, the divided starting point forming step is performed by cutting using the cutting blade 14a. However, the divided starting point forming step is not limited to cutting with the cutting blade, and the divided starting point 25 is formed by a scriber. You may do it.

  As another embodiment, a central portion of the mold resin 21 embedded in the cutting groove 19 is irradiated with a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to the mold resin 21 along the division line 13. The division starting point 25 may be formed by ablation.

  After performing the division start point forming step, as shown in FIG. 8A, the ball 42 is rotatably accommodated in the hemispherical ball cage 40, and the ball cage 40 is moved in the direction of the arrow Z to move the ball. 42 is pressed against the dicing tape T adhered to the back surface 11b of the wafer 11, the ball 42 is rotated in the direction of arrow A while pressing the ball 42 against the dicing tape T, and the ball holder 40 is moved in the direction of arrow B.

  As shown in FIG. 8B, when the ball 42 moves to a position immediately below the dividing starting point 25 formed in the mold resin 21 embedded in the cutting groove 19 of the wafer 11, the mold resin 21 in the cutting groove 19 is divided. The starting point 25 is broken into two parts. In FIG. 8B, t4 = 20 μm.

  The mold resin embedded in the cutting groove 19 of the wafer 11 by the pressing force of the ball 42 by moving the ball 42 over the entire surface of the wafer 11 while pressing the ball 42 against the back surface 11b of the wafer 11 via the dicing tape T. The wafer 11 can be divided into individual device chips 27 having outer peripheries surrounded by the mold resin 21 from the division starting points 25 formed on the substrate 21.

  When carrying out this dividing step, the annular frame F is fixed by fixing means such as a clamp. Then, the wafer 11 can be divided into individual device chips 27 as shown in FIG. 9 by moving the ball 42 across the entire surface of the wafer 11 while pressing the ball 42 against the dicing tape T from below the dicing tape T. . In FIG. 9, the device chip 27 is covered on the surface side and both side surfaces with the mold resin 21, so that the wafer 11 is divided into chip size packages (CSP) 31.

DESCRIPTION OF SYMBOLS 10 Cutting unit 11 Semiconductor wafer 13 Scheduled division lines 14 and 14a Cutting blade 15 Device 17 Bump 19 Cutting groove 21 Mold resin 22 Grinding unit 23 Protection tape 25 Division start point 27 Device chip 30 Grinding wheel 31 CSP
42 balls

Claims (4)

A wafer processing method for dividing a wafer in which a device is formed in each region of a surface defined by a plurality of division lines formed in a lattice shape into individual device chips,
A groove forming step of forming a groove having a depth corresponding to the finished thickness of the device chip along the planned dividing line;
After performing the groove forming step, a molding step of covering the surface of the wafer with a mold resin and embedding the mold resin in the groove;
A protective member disposing step of disposing a protective member on the mold resin coated on the surface of the wafer after performing the molding step;
After performing the protective member disposing step, the wafer is sucked and held by the chuck table through the protective member, and the back surface of the wafer is ground to expose the mold resin embedded in the groove to the back surface of the wafer. Grinding process;
After carrying out the back surface grinding step, the back surface of the wafer is adhered within the opening to an adhesive tape having an outer peripheral portion attached to an annular frame having an opening that accommodates the wafer, and the wafer is attached via the adhesive tape. A frame support process for supporting by an annular frame;
After performing the frame support step, a split starting point forming step for forming a split starting point along the planned split line from the wafer surface to the center of the mold resin corresponding to the split planned line;
After carrying out the division starting point forming step, the wafer moves across the entire surface of the wafer while pressing the ball from the back surface of the wafer via the adhesive tape, and has an outer periphery surrounded by the mold resin by the pressing force of the ball. And a dividing step of dividing the wafer into device chips.   The wafer processing method according to claim 1, wherein in the division starting point forming step, the division starting point is formed by a cutting blade.   The wafer processing method according to claim 1, wherein in the division starting point forming step, the division starting point is formed by a scriber.   2. The wafer processing method according to claim 1, wherein in the division starting point forming step, the division starting point is formed by laser beam irradiation.