JP2018113394A - Method for processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing a wafer with which the possibility of the generation of cracks in a wafer can be reduced.SOLUTION: A method for processing a wafer includes: a grinding step of grinding a rear surface Wb of a wafer W to form a concave part 2 and form an annular convex part 3 that surrounds the concave part 2; a metal layer forming step of forming a metal layer 4 in the concave part 2; a filling step of filling the concave part 2 with filler 5; a groove forming step of forming grooves 6 dividing the metal layer 4 along a division scheduled line S from a surface Wa of the wafer W; and a dividing step of grinding or polishing the rear surface Wb of the wafer W to expose the metal layer 4 and dividing the wafer into individual chips C. Even when the thickness of a device area W1 is reduced, for example, to 50 μm or less, since the annular convex part 3 is formed and the concave part 2 is filled with the filler 5, the risk of breakage of the wafer W can be reduced and the possibility of the generation of cracks in the wafer W can be reduced when the wafer W is divided into the individual chips after the execution of the groove forming step.SELECTED DRAWING: Figure 6

Description

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

  A wafer formed by dividing a discrete device (individual semiconductor element) such as a power transistor or IGBT (Insulated Gate Bipolar Transistor) by a line to be divided is provided with a metal film for an electrode on the back surface (for example, the following) (See Patent Document 1). Such a wafer is divided into individual chips along a division line by cutting with a cutting blade or irradiation with a laser beam, and is used for various electronic devices.

JP 2006-294913 A

  In order to reduce the size of electronic equipment, the wafer as described above is ground on the back surface before being divided into individual chips, and the thickness of the wafer is reduced to, for example, 5 to 50 μm. As described above, when the thickness of the wafer is reduced to 50 μm or less, in the cutting in which the wafer is completely cut (full cut) by the cutting blade, the wafer back surface or the interface between the metal film and the substrate (for example, silicon substrate) constituting the wafer is used. Cracks will occur. Further, if the thickness of the wafer is as thin as 25 μm or less, for example, the cutting blade breaks due to the impact that enters the wafer. Furthermore, for example, even if a dicing tape is stuck and fixed to the wafer, the glue layer of the dicing tape is soft, so that there is a problem that the wafer moves during cutting and cracks occur. On the other hand, even when a full cut is performed by laser beam irradiation, there are problems that cracks occur in the wafer due to insufficient strength, and metal film debris scatters and adheres to the surface of the wafer. In particular, in order to obtain a device having a metal film on the back surface, the above problem occurs because dicing must be performed with the wafer thinned and the metal film formed on the back surface.

  The present invention has been made in view of the above circumstances, and there is a problem to be solved by the wafer processing method that can reduce the possibility of cracks occurring in the wafer.

  The present invention is a processing method of a wafer having a surface including a device region in which devices are formed in regions divided by a plurality of intersecting scheduled lines and an outer peripheral surplus region surrounding the device region, Grinding the back surface of the wafer corresponding to the device region to form a concave portion and forming an annular convex portion corresponding to the outer peripheral surplus region surrounding the concave portion; and after performing the grinding step, the concave portion A metal layer forming step for forming a metal layer on the substrate, a filling step for filling the concave portion with a filler after performing the metal layer forming step, and a line to be divided from the surface of the wafer after performing the filling step. A groove forming step for dividing the metal layer along the groove, and after performing the groove forming step, the back surface of the wafer is ground or polished to form the metal layer. A dividing step of dividing into individual chips causes exposed, with a.

  In the wafer processing method of the present invention, the back surface of the wafer corresponding to the device region is ground to form a recess, and the grinding step to form the annular protrusion corresponding to the outer peripheral surplus region surrounding the recess, and the grinding step are performed. Then, after performing the metal layer forming step for forming the metal layer in the recess, the filling step for filling the recess with a filling material after performing the metal layer forming step, the line to be divided from the surface of the wafer after performing the filling step. A groove forming step for forming a groove for dividing the metal layer along the step, and a dividing step for performing the groove forming step and then grinding or polishing the back surface of the wafer to expose the metal layer and to divide the wafer into individual chips. The device region is thinned to, for example, 50 μm or less to form an annular convex portion, and then the concave portion is filled with a filler, so that the wafer breaks. Risk can be reduced. That is, according to the present invention, the filling step is performed and the lower portion of the device region is reinforced with the filling material, and then the groove forming step is performed by the cutting blade, for example, so that the cutting blade enters the wafer with the impact. Since the device region is divided by half-cutting, for example, a dicing tape is not necessary, and it is possible to prevent the occurrence of cracks due to the movement of the wafer during cutting. In addition, after forming a groove that divides the metal layer, the risk of cracks occurring in the wafer when the back surface of the wafer reinforced by the filler is ground or polished and divided into individual chips is reduced. Can do.

It is a perspective view which shows a surface protection member arrangement | positioning step. It is a perspective view which shows a grinding step. It is sectional drawing which shows the structure of the wafer after a grinding step. It is sectional drawing which shows a metal layer formation step. It is sectional drawing which shows a filling step. It is sectional drawing which shows a groove | channel formation step. It is sectional drawing which shows the structure of the wafer after a groove | channel formation step. It is sectional drawing which shows a division | segmentation step. It is sectional drawing which shows the structure of the wafer after a division | segmentation step.

  A wafer W shown in FIG. 1 is an example of a workpiece, and has, for example, a circular plate-like silicon substrate. The surface Wa of the silicon substrate includes a device region W1 in which devices D are formed in regions partitioned by a plurality of intersecting scheduled lines S, and an outer peripheral surplus region W2 that surrounds the device region W1. The back surface Wb opposite to the front surface Wa is a surface to be ground that is ground by a grinding wheel or the like. The device D is, for example, a discrete device such as an LED, a power transistor, or an IGBT. Hereinafter, a wafer processing method for dividing the wafer W into individual chips will be described with reference to the accompanying drawings. Note that the thickness of the wafer W before grinding is not particularly limited, and is several hundred μm (for example, 625 μm).

(1) Surface Protection Member Arrangement Step As shown in FIG. 1, the surface protection member 1 is adhered to the surface Wa of the wafer W. The surface protection member 1 is formed at least approximately the same diameter as the wafer W. When the entire surface Wa of the wafer W is covered with the surface protection member 1, the device D is protected. The surface protection member 1 is made of, for example, an adhesive heat resistant tape. Further, a substrate made of glass, silicon, or metal may be attached to the surface Wa of the wafer W with an adhesive or a double-sided tape.

(2) Grinding Step As shown in FIG. 2, the surface protection member 1 side is placed on a holding table 10 that holds the workpiece and can rotate so that the back surface Wb of the wafer W is exposed upward. A suction source (not shown) is connected to the holding table 10. On the upper side of the holding table 10, there is disposed a grinding means 20 for grinding a central portion of the wafer W to form a concave portion and forming an annular convex portion on an outer peripheral portion. The grinding means 20 includes a spindle 21 having a vertical axis, a spindle housing 22 that rotatably surrounds the spindle 21, a grinding wheel 23 attached to the lower end of the spindle 21, and an annular ring below the grinding wheel 23. And a grinding wheel 24 fixed to the head, and the whole can be moved up and down while rotating the grinding wheel 23. The diameter of the outer peripheral edge of the grinding wheel 24 is set to be approximately the same as the radius of the device region W1 of the wafer W shown in FIG.

  When the wafer W is sucked and held by the holding table 10, the direction in which the grinding means 20 approaches the back surface Wb of the wafer W while rotating the holding table 10 in the direction of arrow A and rotating the grinding wheel 23 in the direction of arrow A, for example. Then, the rotating grinding wheel 24 is brought into contact with the central portion of the back surface Wb of the wafer W and is ground to a desired thickness. That is, during grinding of the wafer W, the outer peripheral edge of the grinding wheel 24 always passes through the center of the wafer W, while grinding the back surface Wb of the wafer W corresponding to the device region W1 shown in FIG. In addition, the annular convex portion 3 corresponding to the outer peripheral surplus region W2 surrounding the concave portion 2 is formed. The wafer W shown in FIG. 3 shows a state where the recess 2 is thinned to a desired thickness T. The desired thickness T is, for example, 25 μm. The annular convex portion 3 is formed by remaining a portion corresponding to the outer peripheral surplus region W2 without being ground, and has a thickness before grinding.

(3) Metal Layer Formation Step After performing the grinding step, the metal layer 4 is formed in the recess 2 formed in the wafer W as shown in FIG. For forming the metal layer 4, for example, a reduced pressure film forming apparatus shown in FIG. 7 of Japanese Patent No. 4749849 can be used. The metal layer 4 functions as an electrode and is made of, for example, gold or titanium. And the wafer W in which the metal layer 4 was formed is finally divided | segmented with the device D in the division | segmentation step mentioned later, and is formed as a chip | tip with a metal layer.

(4) Filling Step After performing the metal layer forming step, the filling material 5 is filled into the recess 2 formed in the wafer W as shown in FIG. As the filler 5, for example, a thermosetting mold resin such as epoxy is used. The filler 5 is supplied to the recess 2 until it reaches at least the same position as the height of the back surface Wb of the wafer W. Thereafter, the filler 5 is cured by heating with, for example, a heater. Thus, when the concave portion 2 is filled with the filler 5 so that the metal layer 4 is embedded, the thickness of the concave portion 2 becomes approximately the same as the thickness of the wafer W before grinding. Can be increased.

  Here, the filler 5 may be mixed with the filler 5 in order to make the thermal expansion coefficient of the mold resin the same as that of silicon. Thereby, even if the filler 5 is hardened, it is possible to prevent the wafer W from being warped. As the filler, fine particles made of silica are preferably used. In addition, after the filler 5 is cured, if the wafer W is not warped by shrinkage, a UV curable resin or the like may be used as the filler 5.

(5) Groove Forming Step After performing the filling step, as shown in FIG. 6, for example, the wafer W is transferred to a cutting apparatus including a cutting means 30 for cutting the wafer W. The cutting means 30 includes at least a spindle 31 having an axis parallel to the surface Wa of the wafer W, and a cutting blade 32 attached to the tip of the spindle 31, and when the spindle 31 rotates. The cutting blade 32 can be rotated. The cutting means 30 is connected to an elevating means (not shown), and the cutting means 30 can be raised and lowered in the vertical direction.

  While moving the wafer W below the cutting means 30 and rotating the spindle 31, the cutting blade 32 is rotated about the axis parallel to the surface Wa of the wafer W, for example, in the direction of arrow B, The cutting means 30 is lowered in a direction approaching the surface Wa of the wafer W, and the cutting blade 32 is cut from the surface Wa side of the wafer W to cut along the scheduled division line S shown in FIG. In the illustrated example, the surface protection member 1 is peeled from the surface Wa of the wafer W, and then the cutting process is performed.

  At this time, the cutting blade 32 is cut to reach the filler 5 formed in the recess 2 and is cut to form the groove 6 in which at least the metal layer 4 is completely divided. In this way, the same cutting is repeated along all the division lines S shown in FIG. 1 to form a plurality of grooves 6 on the surface Wa of the wafer W as shown in FIG.

  In the groove forming step, the case where the groove 6 is formed on the surface Wa of the wafer W by the cutting means 30 has been described. For example, the metal layer 4 is completely divided on the surface Wa of the wafer W by irradiating a laser beam. Laser processing grooves may be formed. In this case, the surface Wa of the wafer W is previously coated with a protective film or the like. In addition, the groove forming step may be performed in a state where the annular frame and the wafer W are formed integrally with a dicing tape.

(6) Dividing Step After performing the groove forming step, as shown in FIG. 8, for example, the grinding means 50 disposed on the upper side of the holding table 40 while holding the wafer W on the rotatable holding table 40. Thus, the back surface Wb of the wafer W is ground and thinned to a desired thickness. The grinding means 50 includes a spindle 51 having a vertical axis, a grinding wheel 53 attached to the lower part of the spindle 51 via a mount 52, and a grinding wheel 54 fixed to the lower part of the grinding wheel 53 in a ring shape. The whole can be moved up and down while rotating the grinding wheel 53.

  As shown in FIG. 8, after the surface protection member 1a is stuck to the surface Wa of the wafer W, the surface protection member 1a side is held by the holding table 40 and the back surface Wb of the wafer W is exposed upward. That is, the filler 5 formed in the recess 2 is exposed upward. Subsequently, the holding table 40 is rotated, for example, in the direction of the arrow A, and the grinding means 50 is lowered at a predetermined grinding feed speed while rotating the grinding wheel 53, for example, in the direction of the arrow A. Grinding is performed by feeding the grinding wheel 54 at least to a depth position at which the metal layer 4 is exposed while pressing the back surface Wb side.

  Here, the determination of whether or not the metal layer 4 is exposed can be made, for example, by controlling the current value of the spindle 51. In this case, when the grinding by the grinding wheel 54 proceeds and the annular protrusion 3 and the filler 5 are scraped and the grinding wheel 54 comes into contact with the metal layer 4, the current value of the spindle 51 increases. When the current value exceeds a threshold value set in advance in a control unit (not shown), it can be determined that the metal layer 4 is exposed. By thinning the wafer W and exposing the metal layer 4 in this way, the wafer W can be divided into individual chips C with the metal layer 4 as shown in FIG. Since grinding traces are formed on the exposed surface of the metal layer 4, the grinding traces may be removed by polishing the surface of the metal layer 4 with a polishing pad, for example.

  In the dividing step, as described above, the metal layer 4 may be exposed by grinding alone and divided into individual chips C with the metal layer 4, or while supplying slurry between the wafer W and the polishing pad, for example. The metal layer 4 may be exposed only by CMP (Chemical Mechanical Polishing) for polishing the wafer W and divided into individual chips C with the metal layer 4.

  Further, for example, while measuring the thickness of the wafer W using a thickness measuring instrument such as a height gauge, the wafer W is ground to a predetermined thickness by the grinding means 50, and then the thickness of the wafer W is measured by the thickness measuring instrument. However, when the back surface Wb side of the wafer W is polished by the polishing pad and the thickness of the wafer W reaches a predetermined thickness, it may be determined that the metal layer 4 is exposed.

  As described above, in the wafer processing method according to the present invention, the back surface Wb of the wafer W corresponding to the device region W1 is ground to form the concave portion 2, and the annular convex portion corresponding to the outer peripheral surplus region W2 surrounding the concave portion 2. 3, a metal layer forming step for forming the metal layer 4 in the concave portion 2, a filling step for filling the concave portion 2 with the filler 5, and a metal along the planned division line S from the surface Wa of the wafer W. A groove forming step for forming the groove 6 for dividing the layer 4; and a dividing step for grinding or polishing the back surface Wb of the wafer W to expose the metal layer 4 and to divide the chip into individual chips C. Is reduced to, for example, 50 μm or less, and an annular convex portion 3 is formed around it, and then the concave portion 2 is filled with the filler 5, thereby reducing the risk of damage to the wafer W. Can. That is, according to the present invention, the filling step is performed to reinforce the lower portion (recess 2) of the device region W1 shown in FIG. Thus, the wafer W thinned by the impact of the cutting blade 32 entering the wafer W can be prevented from cracking, and the device region W1 is divided by half-cutting. It is possible to prevent cracks from occurring due to the movement of the wafer W. In addition, after forming the groove 6 that divides the metal layer 4, when the back surface Wb of the wafer W reinforced by the filler 5 is ground or polished and divided into individual chips C, cracks are generated in the wafer W. The possibility of occurrence can be reduced.

DESCRIPTION OF SYMBOLS 1,1a: Surface protection member 2: Concave part 3: Annular convex part 4: Metal layer 5: Filler 6: Groove 10: Holding table 20: Grinding means 21: Spindle 22: Spindle housing 23: Grinding wheel 24: Grinding wheel 30 : Cutting means 31: Spindle 31: Cutting blade 40: Holding table 50: Grinding means 51: Spindle 52: Mount 53: Grinding wheel 54: Grinding wheel

Claims (1)

A method of processing a wafer having a surface including a device region in which devices are formed in regions divided by a plurality of intersecting scheduled lines and an outer peripheral surplus region surrounding the device region,
Grinding the back surface of the wafer corresponding to the device region to form a recess and forming an annular protrusion corresponding to the outer peripheral surplus region surrounding the recess;
A metal layer forming step of forming a metal layer in the recess after the grinding step;
After performing the metal layer forming step, a filling step of filling the recess with a filler;
After performing the filling step, a groove forming step for forming a groove for dividing the metal layer along the division line from the surface of the wafer;
A wafer processing method comprising: a dividing step of performing the groove forming step and then grinding or polishing the back surface of the wafer to expose the metal layer and dividing the wafer into individual chips.