JP2017193010A - Grinding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to satisfactorily grind a rear face of a wafer without damaging a device area.SOLUTION: In a wafer (W) to be ground by this grinding method, there is a step between a device area (W1) comprising a convex-shaped device (D) on a front face (Wa) and an outer peripheral excess area (W2) which surrounds the device area. First, a division groove (W4), which has a depth to a thickness direction middle of the wafer and divides the device area and the outer peripheral excess area, is formed along a boundary between the device area of the wafer and the outer peripheral excess area. Next, a protective tape (T) is bonded to a front face side of the wafer. Thereafter, the protective tape (T) side is held on a chuck table (21), and grinding from a rear face (Wb) side to a finish thickness is performed by a grinding wheel (25). By this grinding, the division groove is appeared on the rear face side of the wafer, the wafer is divided into the device area and the outer peripheral excess area, and the outer peripheral excess area of the wafer is dropped and held on the chuck table.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method for grinding a wafer having a plurality of convex devices on the surface.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets formed in a lattice pattern on the surface of a substantially disk-shaped semiconductor wafer, and devices such as ICs and LSIs are placed in each partitioned region. Form.

  A semiconductor wafer is ground to a predetermined thickness by grinding the backside with a grinding machine, and then divided into individual devices by a cutting machine or a laser machining apparatus. The divided devices are widely used in various electronic devices such as mobile phones and personal computers. It's being used. Before grinding the back surface of the semiconductor wafer, a protective tape is attached to the surface of the semiconductor wafer in order to protect the devices formed on the surface of the semiconductor wafer. A semiconductor wafer is sucked and held through a protective tape by a chuck table of a grinding apparatus, and the back surface of the semiconductor wafer is ground.

JP 2006-303051 A

  In a semiconductor wafer, when a plurality of devices on the surface are formed in a convex shape, the outer peripheral surplus region surrounding the device region is formed to be recessed as compared with the device region. Therefore, when the protective tape is attached to the surface side of the semiconductor wafer, a step is generated between the outer peripheral surplus area and the device area in the protective tape, and the part attached to the outer peripheral extra area of the protective tape is recessed. Become. In this state, when the semiconductor wafer is sucked and held by the chuck table through the protective tape to perform the back surface grinding, the protective tape is removed from the chuck table surface by the amount of the outer peripheral surplus area which is recessed compared to the device area. The suction holding force is weak and away. As a result, as the semiconductor wafer is thinned by grinding from the back side of the semiconductor wafer, the outer peripheral surplus region flutters because the suction holding force is weak. This fluttering causes a problem that cracks are generated from the outer peripheral surplus region, and as a result, the crack reaches the device region and cannot be ground.

  The present invention has been made in view of such points, and even if there is a step between the device region and the outer peripheral surplus region of the attached protective tape, the device region is not damaged and the wafer is satisfactorily obtained. It aims at providing the grinding method which can carry out back surface grinding.

  The grinding method of the present invention is a grinding method for thinning the back side of a wafer having a step between a device region having a convex device on the surface and an outer peripheral surplus region surrounding the device region to a finished thickness. A dividing groove forming step for forming a dividing groove that divides the device area and the outer peripheral surplus area at least halfway along the thickness direction of the wafer along the boundary between the device area and the outer peripheral surplus area, and a dividing groove formation; After carrying out the steps, after carrying out the protective tape attaching step for attaching the protective tape to the front surface side of the wafer and the protective tape attaching step, the protective tape side is held on the chuck table, and the grinding wheel is started from the back side of the wafer. And a grinding step for grinding to a finished thickness.

  According to this configuration, the dividing groove deeper than the finished thickness is formed at the boundary between the device region and the outer peripheral surplus region before attaching the protective tape. For this reason, when the wafer is ground from the back surface side and thinning proceeds until the back surface reaches the dividing groove, the outer peripheral surplus region is separated from the device region by the dividing groove and falls onto the surface of the chuck table. As a result, the protective tape attached to the outer peripheral surplus area comes into contact with the chuck table and the suction holding force is sufficiently applied, and the outer peripheral surplus area flutters and cracks can be prevented. . As a result, cracks do not reach the device region, and it is possible to perform good grinding so that the device region is not damaged. In addition, since the outer peripheral surplus region remains on the chuck table even after the back surface grinding, the diameter of the wafer does not change after grinding and can be used without changing the existing transport mechanism.

  According to the present invention, even if there is a step between the device region and the outer peripheral surplus region of the adhered protective tape, the wafer can be ground properly without damaging the device region.

It is a schematic sectional drawing of the wafer which concerns on this Embodiment. It is a figure which shows an example of the dividing groove formation step which concerns on this Embodiment. It is a figure which shows an example of the protective tape sticking step which concerns on this Embodiment. It is a figure which shows an example of the grinding step which concerns on this Embodiment. It is a figure which shows an example of the grinding step which concerns on this Embodiment. It is explanatory drawing of the grinding method of the wafer which concerns on a comparative example. It is explanatory drawing of the grinding method of the wafer which concerns on a comparative example.

  Hereinafter, the grinding method according to the present embodiment will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of a wafer according to the present embodiment. FIG. 2 is a diagram showing an example of the dividing groove forming step according to the present embodiment. FIG. 3 is a diagram showing an example of the protective tape attaching step according to the present embodiment. 4 and 5 are diagrams showing an example of a grinding step according to the present embodiment.

  As shown in FIG. 1, the wafer W is formed in a substantially disc shape, and a plurality of devices D are formed in a convex shape in the center so as to protrude from the surface Wa. The wafer W has a device region W1 in which a plurality of devices D are formed, and an outer peripheral surplus region W2 that surrounds the device region W1. The device region W1 and the outer peripheral surplus region W2 have different upper surface height positions in FIG. 1, and there are steps at their boundaries W3. Note that the device D is not formed on the back surface Wb opposite to the front surface Wa of the wafer W. The wafer W may be a semiconductor wafer such as silicon or gallium arsenide as long as the device D is formed on the surface Wa, or may be a ceramic, glass, or sapphire optical device wafer.

  As shown in FIG. 2, a dividing groove forming step is first performed. In the dividing groove forming step, the cutting means 10 is used to form the dividing groove W4 at the boundary W3 on the surface Wa of the wafer W held on the chuck table 11. The chuck table 11 holds the wafer W with the upper surface serving as a holding surface, and can rotate around the rotation shaft 12. The cutting means 10 includes a cutting blade 15 attached to the tip of a spindle (not shown), and can rotate the cutting blade 15 at a predetermined rotational speed.

  In the dividing groove forming step, first, the back surface Wb side of the wafer W is placed on the chuck table 11 to expose the front surface Wa upward. Thereafter, the wafer W is sucked and held by the chuck table 11 by operating a suction source (not shown). Then, while rotating the cutting blade 15 of the cutting means 10, the cutting blade 15 is lowered in a direction approaching the boundary W <b> 3 of the wafer W, and the cutting edge of the cutting blade 15 is cut into the surface Wa of the wafer W. Subsequently, when the chuck table 11 rotates at least once around the axis of the rotary shaft 12, the cutting blade 15 cuts around the center of the wafer W along the boundary W3, and the device region W1 and the outer peripheral surplus region W2 A ring-shaped dividing groove W4 is formed. Here, the dividing groove W4 is formed at a groove depth d at least halfway in the thickness direction so as not to penetrate to the back surface Wb, and the groove depth d is obtained when the wafer W is ground to a finished thickness in a grinding step described later. It is set at least so as to be exposed on the back surface Wb, and is preferably set to about 2/3 of the total thickness of the wafer W.

  The dividing groove forming step may be performed by ablation processing using a laser beam in addition to the cutting means 10 as described above. Specifically, a laser beam having a wavelength having an absorptivity with respect to the wafer W is irradiated in a ring shape from the surface Wa side of the wafer W to the boundary W3 to form the dividing groove W4.

  As shown in FIG. 3, a protective tape sticking step is performed after the dividing groove forming step. In the protective tape attaching step, the protective tape T is attached to the surface Wa of the wafer W. For example, the sticking roller rolls on the protective tape T while feeding the protective tape T from the outer peripheral edge side of the wafer W to the surface Wa of the wafer W, and the protective tape T is applied to the entire surface Wa of the wafer W. Affix. As described above, since there is a step at the boundary W3 between the device region W1 and the outer peripheral surplus region W2, a step is also formed at a position corresponding to the boundary W3 of the protective tape T. The protective tape T is not particularly limited, and a protective tape having an adhesive layer on the surface side in contact with the surface Wa of the wafer W is used.

  As shown in FIGS. 4 and 5, a grinding step is performed after the protective tape attaching step. In the grinding step, the wafer W is ground from the back surface Wb side to the finished thickness by grinding the wafer W held on the chuck table 21 using the grinding means 20. The chuck table 21 holds the wafer W with the upper surface as a holding surface, and can rotate around the rotation shaft 22. The grinding means 20 includes a spindle 24 having a vertical axis, a grinding wheel 25 attached to the lower end of the spindle 24, and a grinding wheel 26 fixed in an annular shape to the lower part of the grinding wheel 25. The grinding means 20 can rotate the grinding wheel 25 at a predetermined rotational speed by rotating the spindle 24 with a motor (not shown).

  In the grinding step, first, as shown in FIG. 4, the protective tape T side is placed on the chuck table 21 to expose the back surface Wb of the wafer W upward. Thereafter, the wafer W is sucked and held by the chuck table 21 via the protective tape T by the operation of a suction source (not shown), and the chuck table 21 is rotated around the rotation shaft 22. Subsequently, while rotating the grinding wheel 25 of the grinding means 20, the grinding means 20 is lowered in a direction approaching the back surface Wb of the wafer W, and the rotating grinding wheel 26 is brought into contact with the back surface Wb. Then, as shown in FIG. 5, by grinding to the depth reaching the dividing groove W4 while pressing the back surface Wb of the wafer W with the grinding wheel 26, the dividing groove W4 is exposed from the back surface Wb, and the dividing groove W4 is bordered. As a result, the device region W1 and the outer peripheral surplus region W2 are separated. After these are separated, grinding by the grinding wheel 26 is continued until the wafer W is thinned to the finished thickness.

  Here, in the grinding step, the protective tape T attached to the outer peripheral surplus region W2 by the step of the protective tape T in the state of FIG. 4 before the back surface Wb of the wafer W reaches the dividing groove W4 is applied to the chuck table 21. The suction holding force becomes weaker away from the upper surface. However, in the state shown in FIG. 4, the protective tape T attached to the device region W1 receives a suction force from the chuck table 21 over a wide area, so that the state where the wafer W is satisfactorily held is maintained. When the grinding progresses from the state of FIG. 4 and the device region W1 and the outer peripheral surplus region W2 are separated from each other with the dividing groove W4 as a boundary, the outer peripheral surplus region W2 falls as shown in FIG. As a result, the protective tape T attached to the outer peripheral surplus area W2 comes into contact with the upper surface of the chuck table 21, and the outer peripheral surplus area W2 of the wafer W is held so that the suction force by the chuck table 21 is not reduced.

  Here, for comparison with the present invention, a wafer grinding method according to a comparative example will be briefly described with reference to FIGS. 6 and 7. 6 and 7 are explanatory views of a wafer grinding method according to a comparative example. The wafer grinding method according to the comparative example is different from the grinding method according to the present embodiment in that the dividing groove forming step is not performed, that is, the dividing groove is not formed. In addition, about the protective tape sticking step, since it is the same as that of this Embodiment, description is abbreviate | omitted. Further, in the comparative example, for convenience of explanation, the same name is given the same name for explanation.

  As shown in FIG. 6, also in the grinding method of the wafer W according to the comparative example, the rotating grinding wheel 26 is rotated while rotating the chuck table 21 and rotating the wafer W, as in the grinding step of the present embodiment. The wafer W is ground in contact with the back surface Wb of the wafer W. As shown in FIG. 7, even when the wafer W is thinned by grinding, the protective tape T attached to the outer peripheral surplus region W <b> 2 is in a state of being separated from the upper surface of the chuck table 21. For this reason, the state where the suction holding force on the outer peripheral surplus area W2 side of the wafer W is weak is maintained, and if grinding is performed in this state, the outer peripheral surplus area W2 thinned by the rotation of the grinding stone 26 or the like flutters. As a result, a crack is generated from the outer peripheral surplus area W2, and the crack reaches the device area W1 and cannot be ground.

  Thus, in the grinding method for the wafer W according to the comparative example, as the wafer W is thinned by grinding, the outer peripheral surplus region W2 flutters, and the grinding must be stopped.

  On the other hand, in the method for grinding the wafer W according to the present embodiment, as shown in FIG. 5, the device region W1 and the outer peripheral surplus region W2 are separated from each other with the dividing groove W4 as a boundary. And since the protective tape T stuck to the outer periphery surplus area | region W2 contact | abutted and hold | maintained by attracting | sucking to the upper surface of the chuck table 21, the flutter of the outer periphery surplus area | region W2 like a comparative example can be suppressed. Thereby, generation | occurrence | production of the crack of the outer periphery excess area | region W2 resulting from flapping can be prevented.

  As described above, according to the grinding method according to the present embodiment, since no cracks are generated in the outer peripheral surplus region W2, cracks do not reach the device region W1, and good grinding is performed without damaging the device region W1. Can be performed. In addition, as shown in FIG. 5, even if grinding is performed in the grinding step, the outer peripheral surplus region W <b> 2 remains around the device region W <b> 1 on the chuck table 21. Thereby, before and after the grinding method according to the present embodiment, the diameter of the wafer W can be maintained so as not to change, and the existing mechanism capable of transporting the wafer W as a transport mechanism for unloading the ground wafer W. Can be used without changing. As a result, an increase in equipment cost for the transport mechanism can be suppressed and economical.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, direction, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  As described above, the present invention has an effect that the device area can be satisfactorily ground without damaging the device area, and there is a step between the device area and the outer peripheral surplus area in the attached protective tape. It is useful for existing wafer grinding methods.

21 Chuck table 25 Grinding wheel D Device T Protection tape W Wafer W1 Device area W2 Peripheral surplus area W3 Boundary W4 Dividing groove Wa Surface Wb Back

Claims (1)

A grinding method for thinning a back surface side of a wafer having a step between a device region having a convex device on a surface and a peripheral excess region surrounding the device region to a finish thickness,
A dividing groove forming step for forming a dividing groove that divides the device area and the outer peripheral surplus area at least halfway in the thickness direction of the wafer along the boundary between the device area and the outer peripheral surplus area,
After performing the dividing groove forming step, a protective tape attaching step of attaching a protective tape to the front surface side of the wafer;
A grinding method comprising: after carrying out the protective tape attaching step, holding the protective tape side on a chuck table and grinding from the wafer back side to the finished thickness with a grinding wheel.

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