Wafer processing method

A wafer processing method including a protective plate attaching step of attaching a protective plate to the front side of a wafer, a support member providing step of providing a support member on the back side of the wafer, a protective plate cutting step of cutting the protective plate along an area corresponding to each division line formed on the front side of the wafer, thereby exposing each division line, and a plasma etching step of performing plasma etching through the protective plate to each division line of the wafer, thereby etching each division line to divide the wafer into individual device chips.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wafer processing method for processing a wafer having a plurality of devices formed on the front side so as to be separated by a plurality of division lines.

Description of the Related Art

A plurality of devices such as integrated circuits (ICs) and large-scale integrations (LSIs) are formed on the front side of a wafer so as to be separated by a plurality of division lines. The wafer thus having the plural devices on the front side is divided into individual device chips by using a dicing apparatus, for example. The device chips are used in various electric equipment such as mobile phones and personal computers.

In the case that the wafer is divided into the individual device chips by using a cutting blade included in the dicing apparatus, there is a problem such that minute chipping occurs on the periphery of each device chip to cause a reduction in die strength. To cope with this problem, the present applicant has proposed a processing method which can improve the die strength of each device chip, and this processing method has been put to practical use. This processing method includes the steps of entirely covering the front side of a wafer with a resist film, next removing the resist film from the division lines by exposure, and next removing the division lines by plasma etching to thereby divide the wafer into the individual device chips (see Japanese Patent Laid-open No. 2006-114825, for example).

SUMMARY OF THE INVENTION

However, in the above processing method, a high-precision mask and exposure apparatus are required in performing the exposure to the resist film entirely covering the front side of the wafer to remove the resist film from the division lines. Accordingly, there is a problem such that the cost is increased and the productivity of the device chips is reduced.

Further, the resist film formed on the division lines of the front side of the wafer is removed by a toxic developer such as tetra methyl ammonium hydroxide (TMAH) in the exposure process, and the resist film after ending the plasma etching is removed from the whole of the front side of the wafer by using an organic solvent such as N-methyl pyrrolidone (NMP). Accordingly, there is a possibility of environmental pollution. To cope with this problem, any dedicated disposal equipment is needed, so that there is an additional problem such that the costs for installation and maintenance of equipment are increased and the production efficiency is also reduced.

It is therefore an object of the present invention to provide a wafer processing method which can reduce the cost and improve the productivity of the device chips in dividing the wafer into the individual device chips by plasma etching.

In accordance with an aspect of the present invention, there is provided a wafer processing method for dividing a wafer into individual device chips, the wafer having a plurality of devices formed on the front side so as to be separated by a plurality of division lines, the wafer processing method including a protective plate attaching step of attaching a protective plate to the front side of the wafer; a support member providing step of providing a support member on the back side of the wafer; a protective plate cutting step of cutting the protective plate along an area corresponding to each division line formed on the front side of the wafer, thereby exposing each division line; and a plasma etching step of performing plasma etching through the protective plate to each division line of the wafer after performing the protective plate cutting step, thereby etching each division line to divide the wafer into the individual device chips.

Preferably, the wafer processing method further includes a back grinding step of grinding the back side of the wafer to thereby reduce the thickness of the wafer after performing the protective plate attaching step and before performing the support member providing step. Preferably, the protective plate is formed of any one of silicon, glass, and polyethylene terephthalate. In the case that the protective plate is formed of silicon, an SiO2film is formed on the surface of the protective plate. Preferably, the protective plate is attached through a wafer-soluble resin to the front side of the wafer in the protective plate attaching step.

According to the present invention, it is unnecessary to use any high-precision mask and exposure apparatus in dividing the wafer, thereby reducing the cost and improving the productivity of the device chips. Further, in the case that the wafer processing method further includes the back grinding step of grinding the back side of the wafer to thereby reduce the thickness of the wafer after performing the protective plate attaching step and before performing the support member providing step, higher-quality device chips can be produced.

In the case that the protective plate is formed of silicon, an SiO2film is formed on the surface of the protective plate. Accordingly, the progress of plasma etching to the protective plate in the plasma etching step can be retarded, so that the wafer can be reliably divided into the individual device chips. Further, in the case that the protective plate is attached through a water-soluble resin to the front side of the wafer in the protective plate attaching step, the protective plate can be removed from the front side of the wafer by using a pure water, for example, after performing the plasma etching step. Accordingly, no dedicated disposal equipment is needed. As a result, the cost can be reduced and the production efficiency of the device chips can be improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1A, a wafer W is shown as an example of a disk-shaped workpiece. The wafer W has a front side Wa and a back side Wb opposite to the front side Wa. The front side Wa of the wafer W is partitioned by a plurality of crossing division lines S to form a plurality of separate devices D. The back side Wb of the wafer W is not especially formed with anything, but it is a work surface to be ground by abrasive members in thinning the wafer W, for example. There will now be described a wafer processing method for dividing the wafer W into individual device chips by plasma etching, with reference to the attached drawings.

(1) Protective Plate Attaching Step

As shown inFIG. 1A, a protective plate1is attached to the front side Wa of the wafer W. The protective plate1is a circular member having a diameter equal to or greater than the diameter of the wafer W, so that the front side Wa of the wafer W can be entirely covered with the protective plate1. The protective plate1is formed of any one of silicon, glass, and polyethylene terephthalate (PET). In the case that the protective plate1is formed of silicon, an SiO2film is preferably formed on the surface of the protective plate1. By forming the SiO2film on the surface of the protective plate1, the progress of the plasma etching to the protective plate1in a plasma etching step to be hereinafter described can be retarded, so that the wafer W can be reliably divided into individual device chips.

As shown inFIG. 1B, the protective plate1is preferably attached through a water-soluble resin2to the front side Wa of the wafer W. An acrylic resin may be used in place of the water-soluble resin2. Accordingly, the front side Wa of the wafer W is entirely covered with the protective plate1. As the water-soluble resin2, a liquid resin such as polyvinyl alcohol (PVA) may be used.

(2) Back Grinding Step

After performing the protective plate attaching step and before providing a support member to be hereinafter described, the back side Wb of the wafer W is ground until a predetermined thickness of the wafer W is reached, by using grinding means4shown inFIG. 2. The grinding means4includes a spindle40having a vertical axis of rotation, a grinding wheel42mounted through a mount41to the lower end of the spindle40, and a plurality of abrasive members43fixed to the lower surface of the grinding wheel42so as to be annularly arranged along the outer circumference thereof. The grinding wheel42is rotatable and the grinding means4is vertically movable as a whole.

In grinding the back side Wb of the wafer W, the wafer W with the protective plate1is placed on a rotatable holding table3for holding a workpiece in the condition where the protective plate1attached to the front side Wa of the wafer W is in contact with the upper surface of the holding table3. Thereafter, a suction source (not shown) is operated to hold the wafer W on the holding table3under suction in the condition where the back side Wb of the wafer W is oriented upward, or exposed. Thereafter, the holding table3is rotated in the direction shown by an arrow A inFIG. 2at a predetermined speed (e.g., 300 rpm). Further, the spindle40of the grinding means4is rotated by a drive source (not shown) to thereby rotate the grinding wheel42in the direction shown by an arrow B inFIG. 2at a predetermined speed (e.g., 6000 rpm). At the same time, the grinding wheel42is lowered until the abrasive members43come into contact with the back side Wb of the wafer W at a predetermined feed speed (e.g., 1 μm/second). Thereafter, the abrasive members43being rotated are pressed on the back side Wb of the wafer W to thereby grind the back side Wb until a predetermined thickness of the wafer W is reached.

(3) Protective Plate Cutting Step

After performing the back grinding step, the protective plate1is cut along an area corresponding to each division line S shown inFIG. 1to thereby form a groove along each division line S, by using cutting means5shown inFIG. 3. The cutting means5includes a spindle50having a horizontal axis of rotation, a cutting blade51mounted on the spindle50at its front end portion, and a blade cover52for covering the cutting blade51. Accordingly, the cutting blade51is rotated by rotating the spindle50.

The wafer W with the protective plate1is held on a holding table3aunder suction in the condition where the protective plate1is oriented upward, or exposed as shown inFIG. 3. In this condition, alignment known in the art is performed to detect the division lines S. Thereafter, the holding table3ais moved in the direction (X direction) shown by an arrow X inFIG. 3. At the same time, the spindle50of the cutting means5is rotated by a drive source (not shown) to thereby rotate the cutting blade51, and the cutting blade51is lowered toward the protective plate1in the direction (Z direction) shown by an arrow Z inFIG. 3. Accordingly, the cutting blade51being rotated is lowered to cut the protective plate1along an area corresponding to a predetermined one of the division lines S extending in a first direction, which coincides with the X direction. In this manner, the protective plate1is cut along the area corresponding to the predetermined division line S extending in the first direction by using the cutting blade51, thereby forming a groove G along the predetermined division line S extending in the first direction, wherein the bottom of the groove G is exposed to the predetermined division line S. In other words, the depth of the groove G is the same as the thickness of the protective plate1.

After forming the groove G along the predetermined division line S extending in the first direction, the cutting means5is indexed in the direction (Y direction) shown by an arrow Y inFIG. 3by the pitch of the division lines S to repeat the cutting operation along all of the other division lines S extending in the first direction, thus cutting the protective plate1along the areas corresponding to all the division lines S extending in the first direction to thereby form similar grooves G in the protective plate1. The depth of cut by the cutting blade51may be set so that at least the protective plate1can be fully cut. Further, in the case that a test element group (TEG) is formed on each division line S, the TEG may also be cut off by the cutting blade51.

After cutting the protective plate1along all the division lines S extending in the first direction, the holding table3ais rotated 90 degrees, so that the other division lines S extending in a second direction perpendicular to the first direction becomes parallel to the X direction. Thereafter, the cutting operation mentioned above is similarly performed to cut the protective plate1along the areas corresponding to all the other division lines S extending in the second direction, thereby forming similar grooves G. As a result, all the division lines S formed on the front side Wa of the wafer W are exposed to the respective grooves G formed in the protective plate1. Thus, the division lines S to be removed by plasma etching can be exposed by using the protective plate1cut along the area corresponding to each division line S, without performing high-precision exposure and development. As a modification, the back grinding step may be omitted and this protective plate cutting step may be performed immediately after performing the protective plate attaching step.

(4) Support Member Providing Step

After performing the protective plate cutting step, a support member6is provided so as to support the back side Wb of the wafer W as shown inFIG. 4. More specifically, polyvinyl alcohol (PVA), for example, is interposed between the back side Wb of the wafer W and the support member6, and the support member6is attached to the back side Wb of the wafer W, thereby supporting the back side Wb (lower surface) of the wafer W to the support member6.

(5) Plasma Etching Step

After performing the support member providing step, the division lines S of the wafer W are etched (removed) by plasma etching through the protective plate1having the grooves G to thereby divide the wafer W into individual device chips, by using an etching gas supply unit7shown inFIG. 5. The etching gas supply unit7is provided in a chamber (not shown) and connected to a gas source (not shown) for supplying a fluorine-based gas such as SF6to a target to be etched. Reference numeral70inFIG. 5denotes an etching gas to be discharged from the etching gas supply unit7. The etching gas70discharged from the etching gas supply unit7is dissociated to form a plasma by applying a radio frequency (RF) power from an RF power source (not shown), so that the target is plasma-etched by this plasma.

More specifically, the wafer W is first loaded into the chamber. Thereafter, the etching gas supply unit7is operated to discharge the etching gas70such as SF6toward the protective plate1at a predetermined processing pressure (e.g. 20 Pa). On the other hand, an RF power of 3000 W (13.5 MHz) is applied from the RF power source (not shown) to the etching gas70, thereby dissociating the etching gas70to form a plasma. Thus, an etching effect is exhibited to etch the division lines S. That is, the protective plate1attached to the front side Wa of the wafer W is formed with the grooves G corresponding to the division lines S formed on the front side Wa of the wafer W, wherein the division lines S are exposed to the grooves G of the protective plate1. Accordingly, the division lines S of the wafer W are etched off through the grooves G of the protective plate1by the plasma of the etching gas70. As a result, the wafer W is divided into individual device chips having the devices D shown inFIG. 1.

(6) Protective Plate Removing Step

After performing the plasma etching step, the protective plate1is removed from the front side Wa of the wafer W as shown inFIG. 6A. For example, a nozzle8for spraying a pure water80is located above the wafer W as shown inFIG. 6A. That is, the pure water80is sprayed from the nozzle8toward the wafer W, thereby removing the protective plate1from the front side Wa of the wafer W. As described above, the protective plate1is attached through the water-soluble resin2to the front side Wa of the wafer W. Accordingly, the water-soluble resin2can be dissolved in the pure water80sprayed from the nozzle8, so that the protective plate1can be removed from the front side Wa of the wafer W.

When the protective plate1is removed from the front side Wa of the wafer W, the device chips having the individual devices D are kept supported on the support member6as shown inFIG. 6B. These individual device chips are next picked up from the support member6and transferred to the next step (e.g., packaging step).

As described above, the wafer processing method of the present invention essentially includes the protective plate attaching step of attaching the protective plate1to the front side Wa of the wafer W, the protective plate cutting step of cutting the protective plate1along the area corresponding to each division line S after performing the protective plate attaching step, thereby forming the groove G along each division line S so that each division line S is exposed to the corresponding groove G, and the plasma etching step of performing plasma etching to each division line S through the corresponding groove G of the protective plate1after performing the protective plate cutting step, thereby dividing the wafer W into the individual device chips having the devices D. Accordingly, it is unnecessary to use any high-precision mask, exposure apparatus, and developer in dividing the wafer W, thereby reducing the cost and improving the productivity of the device chips. Further, in the case that the wafer processing method of the present invention further includes the back grinding step of grinding the back side Wb of the wafer W to thereby reduce the thickness of the wafer W after performing the protective plate attaching step and before performing the support member providing step, higher-quality device chips can be produced.

In this preferred embodiment, the protective plate1is attached through the water-soluble resin2to the front side Wa of the wafer W in the protective plate attaching step. Accordingly, in performing the protective plate removing step, the protective plate1can be easily removed by using the pure water80. That is, no organic solvent is needed in removing the protective plate1, so that environmental pollution can be prevented and no dedicated disposal equipment is needed. Accordingly, the costs for installation and maintenance of equipment can be reduced and the disposal time can also be reduced. As a result, the device chips can be produced efficiently.