JP2017112269A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a device chip of good quality from a WL-CSP wafer.SOLUTION: A wafer processing method comprises the steps of: forming a groove 19 having a depth representing a finished thickness of device chips along each scheduled division line in a wafer 11; covering a surface 11a of the wafer with a mold resin 21 including a filler 33 to fill the mold resin in the groove; providing a protective member on the mold resin on the resultant surface of the wafer; holding, by suction, the wafer on a chuck table through the protective member and grinding a backside 11b of the wafer to expose the mold resin filled in the groove from the backside of the wafer; forming a division-start point at a center of a part of the mold resin corresponding to each scheduled division line from the wafer surface or backside; and applying an external force to the wafer to divide the wafer into individual device chips each having a periphery surrounded by the mold resin. In the groove-forming step, the width of the groove is in a range from double the average particle diameter of the filler for constituting the mold resin up to the width of the scheduled division line.SELECTED DRAWING: Figure 4

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 containing a filler. Molding step of embedding a 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, and 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 and embedded in the groove. After performing the back surface grinding step for exposing the resin to the back surface of the wafer, and the back surface grinding step, the dividing starting point along the planned dividing line from the front or back surface of the wafer to the center of the mold resin corresponding to the planned dividing line A dividing starting point forming step for forming the dividing step, and a dividing step for dividing the wafer into individual device chips having an outer periphery surrounded by the mold resin by applying an external force to the wafer after performing the dividing starting point forming step. And a groove processing step in which the width of the groove is not less than twice the average particle size of the filler constituting the mold resin and not more than the width of the line to be divided. The

  Preferably, in the division start point forming step, the molding step is performed when the division start point is formed along the planned division line from the wafer surface to the center of the mold resin corresponding to the planned division line. Thereafter, the split starting point forming step is performed before the back grinding step.

  In another preferred embodiment, in the split starting point forming step, when the split starting point is formed along the planned split line from the back surface of the wafer to the center of the mold resin corresponding to the split planned line, The divided starting point forming step is performed after the grinding step.

  In still another preferred embodiment, after the division starting point forming step is performed and before the division step is performed, the opening is formed in an adhesive tape having an outer peripheral portion attached to an annular frame having an opening for accommodating a wafer. The wafer further includes a frame supporting step of attaching the back surface of the wafer and supporting the wafer with the annular frame via the adhesive tape and peeling the protective member from the surface of the wafer.

  In yet another embodiment, before the split starting point forming step is performed, the back surface of the wafer is adhered within the opening to an adhesive tape having an outer peripheral portion adhered to an annular frame having an opening for accommodating the wafer. The wafer is supported by the annular frame via the adhesive tape, and further includes a frame support step for peeling the protective member from the surface of the wafer. In the dividing starting point forming step, The division starting point is formed along the planned division line in the center of the corresponding mold resin.

  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 performing the split starting point forming step for forming the split starting point along the planned split line at the center of the mold resin corresponding to the planned split line from the front or back surface of the wafer, By applying external force and dividing the wafer into individual device chips (chip size package) surrounded by mold resin, the problem that the cutting blade of the cutting blade bends and damages the side surface of the device chip is solved and surely A device chip whose outer periphery is surrounded by a mold resin can be generated.

  The width of the groove in which the mold resin is embedded is set to be twice or more the average particle size of the filler contained in the mold resin. Therefore, when the dividing step is performed, the filler divided on the right and left of the groove is avoided. Thus, it is possible to easily generate a device chip in which a crack runs around the center of the mold resin from the division starting point, the mold resin is divided at the center, and the outer periphery is surrounded by the mold resin.

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 of an embodiment which carries out a division starting point formation process with a cutting blade. It is sectional drawing of the wafer by which the protective tape was stuck on the surface after division | segmentation starting point formation process implementation. It is a perspective view which shows the frame support process which supports a wafer with an annular frame via a dicing tape. It is a perspective view which shows a mode that a protective tape is peeled from the surface of a wafer. It is a partial cross section side view which shows the division | segmentation process of 1st Embodiment. It is a partial cross section side view which shows the division | segmentation process of 2nd Embodiment. 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, the liquid mold resin 21 containing filler is applied to the surface 11a of the wafer 11 so that the thermal expansion coefficient of the wafer 11 and the thermal expansion coefficient of the mold resin 21 are substantially the same. The chuck 11 (not shown) for sucking and holding the wafer 11 is rotated, and the surface 11a of the wafer 11 is coated with the mold resin 21 as shown in the enlarged sectional view of FIG. 4B by spin coating. 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 the average particle diameter of silica is set to 20 μm or less in the present embodiment.

  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, a split start point forming step is performed in which a split start point 25 is formed along the planned split line 13 in the center of the mold resin 21 embedded in the cutting groove 19 and exposed on the back surface 11b of the wafer 11.

  This division starting point forming step is performed by a cutting unit 10 of a cutting apparatus as shown in FIG. 6, for example. 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, a cutting blade 14a that rotates at high speed in the direction of arrow A is slightly cut (for example, 30 μm) into the center of the mold resin 21 that is embedded in the cutting groove 19 and exposed on the back surface 11b of the wafer 11. By dividing and feeding a chuck table (not shown) that holds the head in the direction of the arrow X1, a split starting point 25 is formed along the planned split 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.

  Referring to FIG. 7, there is shown an enlarged cross-sectional view of the wafer 11 in a state in which the division starting point 25 is formed by the cutting blade 14a on the mold resin 21 embedded in the cutting groove 19 and exposed on the back surface 11b of the wafer 11. Here, since the thickness of the mold resin 21 coated on the surface 11a of the wafer 11 is 100 μm, t3 = 400 μm.

  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. In addition, after implementing a molding process, you may implement a separation starting point formation process from the surface of a wafer before implementing a back surface grinding process.

  After performing the division start point forming step, as shown in FIG. 8, the outer peripheral portion of the dicing tape T, which is an adhesive tape, is adhered to the annular frame F having the opening F1 for accommodating the wafer 11, and the back surface 11b of the wafer 11 is opened to the opening F1. The frame is supported on the dicing tape T and the wafer 11 is supported by the annular frame F via the dicing tape T.

  After performing the frame supporting process shown in FIG. 8, a protective tape peeling process for peeling the protective tape 23 from the surface 11a of the wafer 11 is preferably performed as shown in FIG. However, this protective tape peeling step is not essential, and the protective tape 23 may remain adhered to the surface 11 a of the wafer 11.

  After carrying out the protective tape peeling step, a dividing step is performed in which an external force is applied to the wafer 11 to divide the wafer 11 into individual device chips having an outer periphery surrounded by the mold resin 21.

  In the dividing step, for example, as shown in FIG. 10, the wafer 11 is mounted on the pair of support bases 42 of the splitting device 40 so that the split starting point 25 is positioned between a pair of support bases 42 spaced apart by a predetermined distance. Then, the wedge-shaped division bar 44 having an acute-angled tip 44a is moved in the direction of arrow A, and the division bar 44 is pressed against the surface 11a of the wafer 11, thereby being embedded in the cutting groove 19 from the division starting point 25. The mold resin 21 is cut along the planned dividing line 13.

  The division bar 44 is driven by, for example, an air cylinder. Since the division starting point 25 is formed in the mold resin 21 embedded in the cutting groove 19, two mold resins 21 embedded in the cutting groove 19 are relatively smoothly pressed by the wedge-shaped division bar 44. Cleaved.

  When the cutting along one split starting point 25 is completed, the wafer 11 is moved by one pitch in the horizontal direction, the next split starting point 25 is positioned at the middle part of the pair of support bases 42, and the split bar 44 is driven. Then, the wafer 11 is cleaved from the next division starting point 25.

  When division along all the planned division lines 13 extending in the first direction is completed, the wafer 11 is rotated by 90 ° in the second direction orthogonal to the division planned lines 13 extending in the first direction. The wafer 11 is divided from the division starting point 25 along the planned division line 13 that extends.

  Thus, the wafer 11 is divided into individual device chips 27 as shown in FIG. The device chip 27 is divided into chip size packages (CSP) 31 because the surface side and both side surfaces thereof are covered with the mold resin 21.

  When the protective tape 23 is not peeled off from the surface of the wafer 11 after the frame supporting process shown in FIG. 8, the wedge-shaped dividing bar 44 having an acute angle tip 44a is provided in the dividing process as shown in FIG. Is moved in the direction of arrow A, and the dividing bar 44 is pressed against the surface 11 a of the wafer 11 via the protective tape 23.

  Thereby, the mold resin 21 embedded in the cutting groove 19 from the division starting point 25 can be cleaved along the division planned line 13. Preferably, the width of the cutting groove 19 is not less than twice the average particle size of the filler contained in the mold resin 21 and not more than the width of the division planned line 13.

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
33 Filler 40 Dividing device 42 Support base 44 Dividing bar

Claims (8)

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 containing a filler 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;
A split starting point forming step for forming a split starting point along the planned split line at the center of the mold resin corresponding to the split planned line from the front or back surface of the wafer after performing the back surface grinding step;
A step of dividing the wafer into the individual device chips having outer peripheries surrounded by the mold resin by applying an external force to the wafer after performing the division starting point forming step; and
In the groove forming step, the width of the groove is not less than twice the average particle diameter of the filler constituting the mold resin and not more than the width of the line to be divided.   In the split starting point forming step, when forming the split starting point along the planned split line from the wafer surface to the center of the mold resin corresponding to the planned split line, the molding step is performed, The wafer processing method according to claim 1, wherein the split starting point forming step is performed before the back grinding step.   In the dividing starting point forming step, when the dividing starting point is formed along the planned dividing line from the back surface of the wafer to the center of the mold resin corresponding to the planned dividing line, The wafer processing method according to claim 1, wherein the division starting point forming step is performed.   After carrying out the division start point forming step and before carrying out the division step, the back surface of the wafer is adhered to the adhesive tape whose outer peripheral portion is adhered to an annular frame having an opening for accommodating the wafer. The wafer processing method according to claim 1, further comprising a frame supporting step of supporting the wafer with the annular frame via the adhesive tape and peeling the protective member from the surface of the wafer. Before carrying out the split starting point forming step, the back surface of the wafer is stuck in an adhesive tape having an outer peripheral part attached to an annular frame having an opening for accommodating the wafer, and the adhesive tape is interposed through the adhesive tape. A frame supporting step of supporting the wafer with the annular frame and peeling the protective member from the surface of the wafer;
2. The wafer processing method according to claim 1, wherein, in the division starting point forming step, the division starting point is formed along the planned dividing line from the wafer surface to the center of the mold resin corresponding to the planned dividing line.   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.