Method of processing workpiece and resin sheet unit

A method of processing a workpiece includes sticking an adhesive layer side of a resin sheet having a layered structure that includes an adhesive layer and a base material layer, to an annular frame having an opening in covering relation to the opening, forming surface irregularities on a face side of the base material layer that is opposite the adhesive layer, placing the face side of the workpiece and the face side of the base material layer in facing relation to each other and pressing the workpiece against the resin sheet or pressing the resin sheet against the workpiece, thereby bringing the workpiece into intimate contact with the resin sheet to fix the workpiece to the resin sheet, holding the face side of the workpiece fixed to the resin sheet on a holding surface of a chuck table, and grinding the reverse side of the workpiece with a grinding stone.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of processing a workpiece secured to an annular frame through a resin sheet.

Description of the Related Art

In a process of processing a wafer made of a semiconductor material or the like, it is known to stick a resin sheet for protecting devices formed on a face side of the wafer to the face side of the wafer, then to hold the face side of the wafer under suction on a chuck table, and to grind i.e., process, a reverse side of the wafer (see, for example, JP 2003-209080A). For example, before the reverse side of the wafer is ground, the face side of the wafer where the devices are formed in respective areas demarcated by a plurality of projected dicing lines i.e., streets, is cut along the projected dicing lines to form cut grooves in the wafer to a predetermined depth short of the reverse side of the wafer. Thereafter, the reverse side of the wafer is ground until the cut grooves are reached or exposed.

SUMMARY OF THE INVENTION

The resin sheet is normally of a layered structure including a base material layer and an adhesive layer. The resin sheet is stuck to the wafer by the adhesive layer that adheres to the face side of the wafer. However, when the resin sheet is peeled off from the wafer, the adhesive may be left on the face side of the wafer, i.e., adhesive residue may remain on the face side of the wafer. Particularly, wafers with bumps on the face sides thereof or wafers to be divided into small-size device chips need to have resin sheets firmly secured thereto. Therefore, the resin sheet contains an adhesive with strong adhesive power used in its adhesive layer, and hence the adhesive tends to remain on the face sides of the wafers. The present invention has been made in view of the above problems. It is an object of the present invention to provide a method of processing a workpiece without securing a resin sheet to the workpiece with an adhesive made of an adhesive resin.

In accordance with an aspect of the present invention, there is provided a method of processing a workpiece with devices formed on a face side thereof by grinding a reverse side of the workpiece until the workpiece is thinned to a predetermined finished thickness, including: sticking an adhesive layer side of a resin sheet having a layered structure that includes an adhesive layer and a base material layer, to an annular frame having an opening in covering relation to the opening; before or after sticking the adhesive layer side, forming surface irregularities on a face side of the base material layer that is opposite the adhesive layer; after sticking the adhesive layer side and forming the surface irregularities, placing the face side of the workpiece and the face side of the base material layer in facing relation to each other, and pressing the workpiece against the resin sheet or pressing the resin sheet against the workpiece, thereby bringing the workpiece into intimate contact with the resin sheet to fix the workpiece to the resin sheet; holding the face side of the workpiece fixed to the resin sheet on a holding surface of a rotatable chuck table; and after holding the face side of the workpiece, grinding the reverse side of the workpiece with a grinding stone mounted on a grinding wheel disposed in facing relation to the holding surface.

In accordance with another aspect of the present invention, there is provided a method of processing a workpiece with devices formed on a face side thereof by polishing a reverse side of the workpiece, including: sticking an adhesive layer side of a resin sheet having a layered structure that includes an adhesive layer and a base material layer, to an annular frame having an opening in covering relation to the opening; before or after sticking the adhesive layer side, forming surface irregularities on a face side of the base material layer that is opposite the adhesive layer; after sticking the adhesive layer side and forming the surface irregularities, placing the face side of the workpiece and the face side of the base material layer in facing relation to each other, and pressing the workpiece against the resin sheet or pressing the resin sheet against the workpiece, thereby bringing the workpiece into intimate contact with the resin sheet to fix the workpiece to the resin sheet; holding the face side of the workpiece fixed to the resin sheet on a holding surface of a rotatable chuck table; and after holding the face side of the workpiece, polishing the reverse side of the workpiece with a polishing pad disposed in facing relation to the holding surface.

In accordance with still another aspect of the present invention, there is provided a resin sheet unit for fixing a workpiece in intimate contact therewith, including: a resin sheet having an adhesive layer and a base material layer that is positioned opposite the adhesive layer, with surface irregularities formed on a face side of the base material layer that is opposite the adhesive layer, the surface irregularities being defined by grooves in the face side of the base material layer and remaining portions of the face side of the base material layer; and an annular frame having an opening larger in diameter than the workpiece, an adhesive layer side of the resin sheet being stuck to the annular frame in covering relation to the opening, in which the resin sheet unit fixes the workpiece to the annular frame by placing the face side of the workpiece and the face side of the base material layer in facing relation to each other and bringing the face side of the workpiece into intimate contact with the face side of the base material layer on which the surface irregularities are formed.

With the methods of processing workpieces according to the aspects of the present invention, the adhesive layer side of the resin sheet that includes the adhesive layer and the base material layer is stuck to the annular frame. Then, the surface irregularities are formed on the face side of the base material layer that is positioned opposite the adhesive layer. Thereafter, the workpiece is pressed against the resin sheet and hence is brought into intimate contact with the resin sheet and fixed thereto. Since no adhesive is used to fix the resin sheet to the workpiece, no adhesive remains on the workpiece when the workpiece is peeled off from the resin sheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter be described below with reference to the accompanying drawings.FIG. 1illustrates in perspective a workpiece11to be processed by the preferred embodiments of the present invention. As described later, the preferred embodiments of the present invention include a first embodiment and a second embodiment. As illustrated inFIG. 1, the workpiece11is in the form of a disk-shaped wafer primarily made of a material such as silicon or the like, for example. The workpiece11has a face side11ademarcated into a plurality of areas by a grid of projected dicing lines i.e., streets13, with devices15such as integrated circuits (ICs) or the like disposed respectively in the areas. The workpiece11may be made of a semiconductor or an insulator other than silicon. Furthermore, the workpiece11is not limited to any shapes, structures, sizes, etc., and the devices15are not limited to any kinds, numbers, shapes, structures, sizes, layouts, etc.

FIG. 2illustrates in perspective a resin sheet21used in the methods of processing workpieces according to the preferred embodiments of the present invention. The resin sheet21is in the form of a circular film that is larger in diameter than the workpiece11, and has a layered structure including a base material layer23and an adhesive layer25. According to the preferred embodiments of the present invention, a surface, i.e., a face side, of the base material layer23that is opposite the adhesive layer25is referred to as a face side21aof the resin sheet21, whereas a surface of the adhesive layer25that is opposite the base material layer23as a reverse side21bof the resin sheet21. The face side21aacts as an outer surface of the resin sheet21on the base material layer23side, and the reverse side21bas an outer surface of the resin sheet21on the adhesive layer25side.

The base material layer23is in the form of a film-like solid layer having a circular shape. The base material layer23has a predetermined thickness ranging from 100 μm to 200 μm, and is made of a resin material such as polyolefin (PO), polyvinyl chloride (PVC), polyethylene terephthalate (PET), or the like, for example. The adhesive layer25is disposed in an annular pattern in the vicinity of an outer circumference of the other surface of the base material layer23, i.e., a surface of the base material layer23that is opposite the face side21a(SeeFIG. 3). The adhesive layer25is not limited to the annular pattern, but may be disposed entirely on the other surface of the base material layer23. In this case, however, a non-adhesive cover layer of resin is additionally disposed on a predetermined area, e.g., an area corresponding to an opening29cof an annular frame29to be described later. The adhesive layer25is in the form of a layer including an adhesive, i.e., a sticky compound, and is made of a material such as silicone rubber, acrylic resin, epoxy resin, or the like, for example. The adhesive layer25has such a nature that it will lose stickiness and be hardened upon exposure to an external stimulus such as ultraviolet rays or heat.

A method of processing the workpiece11, or a workpiece processing method, according to the first embodiment of the present invention will hereinafter be described below with reference toFIGS. 3 through 11. In the workpiece processing method, initially, an annular frame29of metal is prepared. The annular frame29has an opening29cthat is larger in diameter than the workpiece11and smaller in diameter than the resin sheet21. Then, the reverse side21bof the resin sheet21is stuck to the annular frame29in covering relation to the opening29cof the annular frame29(seeFIG. 3), integrally combining the resin sheet21and the annular frame29with each other (sticking step (S10) (seeFIG. 11)). According to the present embodiment, a surface of the annular frame29to which the resin sheet21is stuck is referred to as a face side29aof the annular frame29, whereas a surface of the annular frame29that is opposite the face side29aas a reverse side29bof the annular frame29.

In the sticking step (S10), the annular adhesive layer25that is positioned on the reverse side21bside of the resin sheet21is stuck to the face side29aof the annular frame29using a sticking apparatus, not illustrated. The sticking apparatus has a support table, not illustrated, that supports the annular frame29thereon. The annular frame29is placed on the support table such that the reverse side29bof the annular frame29is held in contact with a face side of the support table. A moving mechanism, not illustrated, such as a ball screw or the like is mounted on a reverse side of the support table. The support table can be moved along a predetermined direction by the moving mechanism. A cylindrical pressing roller, not illustrated, for pressing the resin sheet21toward the support table is disposed over the support table. The cylindrical pressing roller is rotatable about a central longitudinal axis thereof that extends perpendicularly to the predetermined direction referred to above along which the support table can be moved.

The sticking apparatus has a feed mechanism, not illustrated, that feeds a tape assembly, not illustrated, including a release sheet, not illustrated, stuck to the adhesive layer25side of the resin sheet21toward the pressing roller. The sticking apparatus also has a peeling unit, not illustrated, that peels off the resin sheet21from the release sheet when the resin sheet21is supplied to the region between the pressing roller and the annular frame29. The release sheet peeled off from the tape assembly by the peeling unit is wound by a take-up mechanism, not illustrated. The take-up mechanism and the feed mechanism are adjusted such that the take-up mechanism winds the release sheet and the feed mechanism feeds the tape assembly at the same speed.

In the sticking step (S10), initially, the annular frame29is placed on the support table such that the face side29aof the annular frame29faces upwardly. Then, the resin sheet21is placed between the pressing roller and the annular frame29such that the surface of the base material layer23side, i.e., the face side21aof the resin sheet21, is held in contact with the pressing roller and the surface of the adhesive layer25side, i.e., the reverse side21bof the resin sheet21, faces the support table. Then, the resin sheet21is delivered to the peeling unit by the feed mechanism and the take-up mechanism, and then peeled off from the release sheet by the peeling unit. Thereafter, the resin sheet21is pressed downwardly by the pressing roller and stuck to a portion of the annular frame29on the support table. Next, the feed mechanism and the take-up mechanism deliver the resin sheet21to the peeling unit, and the support table is moved along the predetermined direction referred to above while the resin sheet21is being pressed downwardly by the pressing roller. The feed mechanism, the take-up mechanism, and the moving mechanism referred to above are adjusted such that the resin sheet21is delivered over the support table and the support table is moved at the same speed.

While a region of the resin sheet21that is pressed by the pressing roller is being moved with respect to the support table, the reverse side21bof the resin sheet21is brought into intimate contact with the face side29aof the annular frame29, so that the resin sheet21is stuck to the annular frame29in covering relation to the opening29cof the annular frame29. Now, a resin sheet unit31is jointly made up of the resin sheet21and the annular frame29. The resin sheet21, whose outer circumferential portion is fixed to the annular frame29, is kept taut in radial directions of the resin sheet21. Therefore, the resin sheet21is prevented from flexing under its own weight compared with the case in which the resin sheet21is not stuck to the annular frame29. In the sticking step (S10) according to the present embodiment, the sticking apparatus is used as described above. However, the resin sheet21may be stuck to the annular frame29manually by a worker.

After the sticking step (S10), surface irregularities are formed on the face side21aof the resin sheet21using a cutting apparatus40(surface irregularity forming step (S20)).FIG. 4illustrates in partial cross-sectional side elevation the surface irregularity forming step (S20).FIG. 5illustrates in perspective the surface irregularity forming step (S20). The cutting apparatus40has a chuck table50having a substantially hollow cylindrical shape for holding the reverse side21bof the resin sheet21of the resin sheet unit31under suction thereon. The chuck table50is coupled to a rotating mechanism having a rotary actuator, not illustrated, such as an electric motor or the like disposed therebelow. The chuck table50can be rotated about a rotational axis generally parallel to a vertical Z-axis by the rotating mechanism. The cutting apparatus40also includes a table moving mechanism, not illustrated, including a ball screw, etc., disposed beneath the chuck table50. The chuck table50can be moved along a horizontal direction, e.g., a processing-feed direction indicated by the arrow52, perpendicular to the Z-axis by the table moving mechanism. The chuck table50has an upper surface as a holding surface50afor holding under suction the other surface side of the base material layer23of the resin sheet21, i.e., the reverse side21bside, thereon. The holding surface50ais in the form of a disk-shaped surface of a porous plate that is made of a porous material. The porous plate is connected to a fluid channel, not illustrated, that is connected to a suction source, not illustrated, such as an ejector or the like.

A plurality of clamp mechanisms, not illustrated, are disposed laterally of the chuck table50in a manner to project from the chuck table50. For example, four clamp mechanisms are disposed at circumferentially equal intervals around the chuck table50. Each of the clamp mechanisms has a frame support, not illustrated, for placing the reverse side29bof the annular frame29thereon. The frame supports are disposed in positions lower than the holding surface50a.When the annular frame29is placed on the frame supports, the outer circumferential portion of the resin sheet21and the annular frame29are disposed in positions lower than the holding surface50a.

The frame supports include rotational drive sources such as rotary actuators or the like. Arms are coupled respectively to the rotational drive sources. The arms are angularly movable in a predetermined angular range by the rotational drive sources. Frame pressers, not illustrated, are fixed to respective tips of the arms. The frame pressers are selectively disposed in a pressing position for pressing the face side29aof the annular frame29placed on the frame supports and an open position for opening regions above the frame supports. When the annular frame29is to be placed onto the frame supports or the annular frame29is to be removed from the frame supports, the frame pressers are disposed in the open position.

The cutting apparatus40also includes a cutting tool unit42disposed above the chuck table50. The cutting tool unit42has a tubular spindle housing44athat is fixed to a Z-axis movable plate, not illustrated, that is movable along the Z-axis. The Z-axis movable plate is supported by a Z-axis moving mechanism, not illustrated. The spindle housing44ahouses a spindle44brotatably disposed therein that is coupled to a rotary actuator, not illustrated, such as an electric motor or the like. The spindle44bhas a lower end portion exposed out of a lower surface of the spindle housing44a.

A disk-shaped wheel mount44cis fixed to the lower end of the lower end portion of the spindle44b.A disk-shaped cutting wheel46made of metal such as stainless steel, aluminum, or the like is mounted on a lower surface of the wheel mount44c.A cutting tool48is mounted on a lower surface of the cutting wheel46. The cutting tool48includes a substantially prism-shaped base48amounted on the cutting wheel46and a cutting blade48bmade of diamond or the like and fixed to the end of the base48athat is opposite the cutting wheel46.

In the surface irregularity forming step (S20), the resin sheet unit31is placed on the chuck table50such that the reverse side21bof the resin sheet21is held in contact with the holding surface50aand the reverse side29bof the annular frame29is held in contact with the frame supports. At this time, the frame pressers are disposed in the open position. Thereafter, the suction source is actuated to generate and apply a negative pressure to the holding surface50a,thereby holding the reverse side21bside of the resin sheet21under suction on the chuck table50. Then, the rotational drive sources of the frame supports are actuated to move the frame pressers to the pressing position. The annular frame29is now gripped and secured in position by the clamp mechanisms. At this time, the outer circumferential portion of the resin sheet21and the annular frame29are disposed in the positions lower than the holding surface50a.The central portion of the resin sheet21positioned on the holding surface50ais of a flat shape, whereas the outer circumferential portion of the resin sheet21is inclined downwardly from the central portion radially outwardly.

Then, the Z-axis moving mechanism is actuated to adjust the height of the cutting tool unit42along the Z-axis to position a lower cutting edge of the cutting blade48bat a height where it contacts the face side21aof the resin sheet21. The rotary actuator is energized to rotate the cutting wheel46about its own vertical central axis. Then, the table moving mechanism moves the chuck table50under the cutting tool unit42, causing the cutting tool48to cut the central portion of the face side21aof the resin sheet21.

Particularly, the chuck table50is moved linearly along the processing-feed direction so that the resin sheet unit31goes from one diametrical side of the cutting wheel46across an area directly below the spindle44bto another opposite diametrical side of the cutting wheel46. At this time, the chuck table50is not rotated about its own axis during movement along the processing-feed direction. The central portion of the face side21aof the resin sheet21is thus cut by the cutting blade48b.Specifically, the cutting tool48leaves a plurality of arcuate cut marks on the face side21aof the resin sheet21. To leave the cut marks, the cutting tool48scratches the face side21awhile being frictionally dragged over the face side21aof the resin sheet21that is soft. Each of the arcuate cut marks includes a plurality of minute discrete grooves27(seeFIGS. 5 and 6) that are separate along arcuate directions.

Each of the grooves27has a depth ranging from 0.1 μm to 0.3 μm from the face side21athough it may have a depth of several micrometers or less, e.g., ranging from approximately 2 μm to 3 μm or may have a depth that is 3% or less of the thickness of the resin sheet21. The grooves27are recessed in the face side21awhereas the remaining portions of the face side21aare protruded between the grooves27. Therefore, the resin sheet21has surface irregularities on the face side21athat are defined by the grooves27and the remaining portions of the face side21a.FIG. 6illustrates in perspective the face side21aof the resin sheet21after the surface irregularity forming step (S20). InFIG. 6, the resin sheet unit31is illustrated as removed from the chuck table50. According to the present embodiment, the surface irregularities are formed on the face side21aby the cutting tool48. However, the face side21amay be scratched to form surface irregularities thereon by sandblasting, i.e., a step of forcibly applying an abrasive material on a stream of compressed air to the face side21a.Alternatively, the face side21amay be etched by plasma etching to form surface irregularities thereon.

According to still another way, while a disk-shaped grinding wheel, not illustrated, coupled to a lower end of a spindle, not illustrated, is being rotated by the spindle about the central axis of the spindle, a grinding stone, not illustrated, mounted on a bottom of the grinding wheel may be held in contact with the face side21ato grind the face side21a,thereby scratching the face side21ato form surface irregularities thereon. In the surface irregularity forming step (S20), surface irregularities may be formed on a portion of the face side21aof the resin sheet21rather than on the entire face side21a.For example, surface irregularities may be formed on only a region of the face side21awhere the workpiece11will be placed in a workpiece fixing step (S30) to be described below.

After the surface irregularity forming step (S20), the workpiece11is pressed against the resin sheet21such that the face side11aof the workpiece11and the face side21aof the base material layer23face each other, so that the workpiece11is fixed to the resin sheet21in intimate contact therewith (workpiece fixing step (S30)).FIG. 7illustrates in partial cross-sectional side elevation the workpiece fixing step (S30). The workpiece fixing step (S30) is carried out using a pressing apparatus60illustrated inFIG. 7. The pressing apparatus60includes a chuck table62having a porous plate, not illustrated, in an upper surface thereof.

The porous plate is connected to a fluid channel, not illustrated, connected to a suction source, not illustrated, such as an ejector or the like. When the suction source is actuated, it generates and applies a negative pressure to the porous plate. An upper surface of the porous plate now functions as a holding surface62aof the chuck table62that holds the resin sheet unit31under suction thereon. A substantially disk-shaped flat pressing plate66made of metal or the like is disposed in facing relation to the chuck table62. The pressing plate66is larger in diameter than the workpiece11, for example. The pressing plate66has a surface remote from the chuck table62and connected to a lower end of a cylindrical rod64extending along the Z-axis. The rod64has an upper end that is opposite the pressing plate66and that is coupled to a lifting and lowering mechanism, not illustrated, including an electric motor, etc. When the rod64is lifted or lowered by the lifting and lowering mechanism, the pressing plate66is lifted away from or lowered toward the holding surface62aof the chuck table62.

In the workpiece fixing step (S30), initially, the resin sheet unit31is placed on the holding surface62aof the chuck table62such that the face side21aof the resin sheet21faces upwardly. Then, the suction source is actuated to hold the reverse side29bof the resin sheet unit31under suction on the holding surface62a.Then, the workpiece11is placed on the face side21asuch that the face side11aof the workpiece11is held in contact with the face side21a.The lifting and lowering mechanism lowers the pressing plate66, pressing the pressing plate66against the reverse side11bof the workpiece11. The pressing plate66is pressed against the reverse side11bof the workpiece11by a force ranging from several newtons (N) to several tens of newtons (N). At this time, heat may be applied to at least one of the workpiece11and the resin sheet21.

When the disk-shaped flat pressing plate66presses the workpiece11for a period of time ranging from several seconds to several tens of seconds, for example, a substantially uniform force is applied along the Z-axis to the workpiece11. The face side11aof the workpiece11thus pressed is brought into intimate contact with the face side21aof the resin sheet21. After having pressed the workpiece11, the pressing plate66is lifted away from the workpiece11. The face side11aof the workpiece11and the face side21aof the resin sheet21remain in intimate contact with each other or air has been removed from between them, creating a vacuum therebetween. Therefore, even after the pressing plate66has been separated from the workpiece11, the workpiece11and the resin sheet21remain pressed against each other under the atmospheric pressure.

At this time, the grooves27function as suction cups, keeping the workpiece11fixed to the annular frame29through the resin sheet21thereby to form a workpiece unit33. In the workpiece unit33, the workpiece11is disposed on the face side21aside and the annular frame29on the reverse side21bside. This layout is unique to the present embodiment in which the resin sheet21and the workpiece11are not fixed to each other by the adhesive layer25. The resin sheet21is not stuck to the workpiece11by an adhesive layer, but stuck to the workpiece11through the surface irregularities formed on the face side21aof the base material layer23of the resin sheet21. Consequently, even if the workpiece11is peeled off from the resin sheet21, no adhesive remains on the workpiece11. The workpiece unit33is also advantageous in that the resin sheet21can be manufactured inexpensively as a protective tape because it does not contain an adhesive to be applied to the workpiece11. In the workpiece fixing step (S30), the workpiece11is not permanently fixed to the resin sheet21, but temporarily fixed to the resin sheet21. The workpiece11and the resin sheet21are fixed to each other thicknesswise by being pressed against each other under the atmospheric pressure. However, when air is introduced between the workpiece11and the resin sheet21, the resin sheet21can easily be peeled off from the workpiece11.

According to the present embodiment, the pressing apparatus60is used to press the workpiece11and the resin sheet21against each other. However, the workpiece11may be pressed against the face side21aof the resin sheet21manually by a worker. Alternatively, the chuck table62and the pressing plate66may be positioned upside down, i.e., in a vertically reversed layout, and the reverse side lib of the workpiece11may be held under suction on the chuck table62in a manner for the workpiece11to be suspended from above. Then, the resin sheet unit31placed on the pressing plate66may be lifted and pressed against the workpiece11such that the face side11aof the workpiece11and the face side21aof the resin sheet21face each other.

After the workpiece fixing step (S30), the workpiece11is processed. For processing, i.e., grinding, the reverse side11bof the workpiece11according to the present embodiment, the face side11aof the workpiece11is held on a holding surface72a(seeFIG. 8A) of a chuck table72of a grinding apparatus70(seeFIG. 9) (holding step (S40)), to be described later.FIG. 8Aillustrates the holding step (S40) in cross section, andFIG. 8Billustrates the holding step (S40) in perspective. The chuck table72has a porous plate74in its upper surface. The porous plate74is connected to a fluid channel, not illustrated, that is connected to a suction source, not illustrated, such as an ejector or the like. When the suction source is actuated, it generates and applies a negative pressure to the porous plate74. An upper surface of the porous plate74now functions as the holding surface72aof the chuck table72. The chuck table72is coupled to a rotating mechanism having a rotary actuator, not illustrated, such as an electric motor or the like disposed therebelow. The chuck table72can be rotated about a rotational axis generally parallel to a vertical Z-axis by the rotating mechanism. A plurality of clamp mechanisms, not illustrated, are disposed laterally of the chuck table72in a manner to project from the chuck table72. Since the clamp mechanisms are identical to the clamp mechanisms of the cutting apparatus40, their description will be omitted below.

In the holding step (S40), initially, the workpiece unit33is placed on chuck table72such that the reverse side21bof the resin sheet21is held in contact with the holding surface72aand the reverse side29bof the annular frame29is held in contact with the frame supports. At this time, the frame pressers are disposed in the open position. The suction source then applies a generated negative pressure to the holding surface72ato hold the reverse side21bof the resin sheet21under suction on the chuck table72.

Then, the rotational drive sources of the frame supports are actuated to move the frame pressers to the pressing position. The face side29aand reverse side29bof the annular frame29are now gripped and secured in position by the clamp mechanisms. At this time, since the outer circumferential portion of the resin sheet21and the annular frame29are disposed in the positions lower than the holding surface72a,the central portion of the resin sheet21positioned on the holding surface72ais of a flat shape, whereas the outer circumferential portion of the resin sheet21is inclined downwardly from the central portion radially outwardly. After the holding step (S40), the reverse side11bof the workpiece11is ground (grinding step (S50)).FIG. 9illustrates the grinding step (S50) in partial cross-sectional side elevation, andFIG. 10illustrates the grinding step (S50) in perspective.

The grinding step (S50) is carried out using the grinding apparatus70. The grinding apparatus70includes, in addition to the chuck table72, a grinding unit80disposed in facing relation to the holding surface72aof the chuck table72. The grinding unit80has a tubular spindle housing82a.The spindle housing82ahas a side surface including a portion fixed to a Z-axis movable plate, not illustrated, that is movable along the Z-axis. The spindle housing82ahouses therein a spindle82bthat is rotatable about its own vertical central axis. The spindle82bhas an upper end portion coupled to a rotary actuator, not illustrated, such as an electric motor or the like for rotating the spindle82babout its own vertical central axis. The spindle82bhas a lower end portion exposed out of a lower surface of the spindle housing82a.A disk-shaped wheel mount82cis fixed to the lower end of the lower end portion of the spindle82b.

A grinding wheel84is mounted on a lower surface of the wheel mount82cthat is opposite the spindle82b.The grinding wheel84is generally equal in diameter to the wheel mount82cand has an annular wheel base84amade of metal such as stainless steel or the like. The wheel base84ahas an annular surface as a mount surface mounted on the wheel mount82c.The wheel base84aalso has another annular surface that is positioned opposite the mount surface and that supports a plurality of grinding stones84bsecured thereto in an annular array. The grinding stones84bare made of a binder such as of metal, ceramics, resin, or the like mixed with abrasive grains of diamond, cubic boron nitride (cBN), or the like. The binder and the abrasive grains are not limited to any particular materials and may be made of materials selected according to the specifications of the grinding stones84b.

In the grinding step (S50), the grinding unit80is lowered along the Z-axis while the chuck table72and the grinding unit80are being rotated in one direction about their own axes. When respective lower surfaces of the grinding stones84bthat are in turning motion are brought into contact with the reverse side11bof the workpiece11, the grinding stones84bstart grinding the reverse side11bof the workpiece11. When the reverse side11bhas been ground to thin the workpiece11to a predetermined finished thickness, the grinding step (S50) is finished. In a case where the workpiece11is to be peeled off from the resin sheet unit31after the grinding step (S50), an external stimulus such as ultraviolet rays or heat is applied to the adhesive layer25to harden the adhesive layer25, which then loses its stickiness. The annular frame29can now easily be peeled off from the resin sheet21. Then, an end of the resin sheet21is turned up, and air is introduced between the workpiece11and the resin sheet21. The resin sheet21is now peeled off from the workpiece11.FIG. 11is a flowchart illustrating the workpiece processing method according to the first embodiment as described above.

According to a first modification of the surface irregularity forming step (S20) according to the first embodiment, the surface irregularity forming step (S20) may be carried out to form surface irregularities on the face side21aof the resin sheet21prior to the sticking step (S10). For example, while the release sheet side of the resin sheet21to which the release sheet is stuck, i.e., the reverse side21bside thereof, is being held under suction on the holding surface50aof the chuck table50, the cutting tool unit42cuts the face side21aof the resin sheet21, forming surface irregularities on the face side21a.Thereafter, the sticking step (S10) is carried out, followed successively by the workpiece fixing step (S30), the holding step (S40), and the grinding step (S50).

A method of processing the workpiece11, or a workpiece processing method, according to the second embodiment of the present invention will hereinafter be described below with reference toFIGS. 12 and 13. The method of processing the workpiece11according to the second embodiment includes a polishing step (S55) for polishing the reverse side11bof the workpiece11instead of the grinding step (S50) according to the first embodiment. The method of processing the workpiece11according to the second embodiment includes a sticking step (S10), a surface irregularity forming step (S20), a workpiece fixing step (S30), and a holding step (S40) which are similar to those according to the first embodiment. The polishing step (S55) is carried out after the holding step (S40) in which a chuck table92(seeFIG. 12) of a polishing apparatus90holds the workpiece unit33.FIG. 13is a flowchart illustrating the workpiece processing method according to the second embodiment. The processing step (S55) is carried out using the polishing apparatus90having the chuck table92. The chuck table92has a porous plate, not illustrated, in an upper surface thereof. The porous plate is connected to a fluid channel, not illustrated, that is connected to a suction source, not illustrated, such as an ejector or the like.

When a negative pressure generated by a suction source acts on the porous plate, an upper surface of the porous plate functions as a holding surface92aof the chuck table92. The chuck table92is coupled to a rotating mechanism having a rotary actuator, not illustrated, such as an electric motor or the like disposed therebelow. The chuck table92can be rotated about a rotational axis generally parallel to a vertical Z-axis by the rotating mechanism. The chuck table92is identical in structure to the chuck table72of the grinding apparatus70, and its description will be omitted below. The polishing apparatus90has, in addition to the chuck table92, a polishing unit94disposed in facing relation to the holding surface92aof the chuck table92. The polishing unit94has a tubular spindle housing96a.The spindle housing96ahas a side surface including a portion fixed to a Z-axis movable plate, not illustrated, that is movable along the Z-axis. The Z-axis movable plate is supported on a Z-axis moving mechanism, not illustrated. The spindle housing96ahouses therein a spindle96bthat is rotatable about its own vertical central axis.

The spindle96bhas an upper end portion coupled to a rotary actuator, not illustrated, such as an electric motor or the like for rotating the spindle96babout its own vertical central axis. The spindle96bhas a lower end portion exposed out of a lower surface of the spindle housing96a.A disk-shaped wheel mount96cis fixed to the lower end of the lower end portion of the spindle96b.A polishing wheel98is mounted on a lower surface of the wheel mount96cthat is opposite the spindle96b.The polishing wheel98is generally equal in diameter to the wheel mount96cand has a disk-shaped wheel base98amade of metal such as stainless steel or the like. The wheel base98ahas a disk-shaped surface as a mount surface mounted on the wheel mount96c.The wheel base98aalso has another disk-shaped surface that is positioned opposite the mount surface and that supports a disk-shaped polishing pad98bsecured thereto. The polishing pad98bis made of abrasive grains dispersed in urethane foam and secured by a bonding agent. The abrasive grains are made of green silicon carbide (GC), white fused alumina (WA), diamond, cBN, or the like. The urethane foam may be replaced with nonwoven fabric.

In the polishing step (S55), the polishing unit94is lowered along the Z-axis while the chuck table92and the polishing unit94are being rotated in one direction about their own axes. When a lower surface of the polishing pad98bthat is in rotation is brought into contact with the reverse side11bof the workpiece11, the polishing pad98bstarts polishing the reverse side11bof the workpiece11. According to a first modification of the second embodiment, the surface irregularity forming step (S20) may be carried out to form surface irregularities on the face side21aof the resin sheet21prior to the sticking step (S10). After the surface irregularity forming step (S20), the sticking step (S10) may be carried out, followed successively by the workpiece fixing step (S30), the holding step (S40), and the polishing step (S55).

In the first embodiment and the second embodiment described above, one workpiece11is fixed to the face side21aof the resin sheet unit31. However, a plurality of workpieces11may be fixed to the face side21aof the resin sheet unit31.FIG. 14Aillustrates in perspective a plurality of disk-shaped workpieces11that are fixed to the resin sheet21in the holding step (S40), illustrating the workpiece unit33as removed from the chuck table62used in the workpiece fixing step (S30). InFIG. 14A, three workpieces11are fixed to the resin sheet21. However, two or four or more disk-shaped workpieces11may be fixed to the resin sheet21. The workpieces11may not necessarily be disk-shaped, but may be of a rectangular shape.FIG. 14Billustrates in perspective a plurality of rectangular workpieces11, as viewed in plan, that are fixed to the resin sheet21in the holding step (S40), illustrating the workpiece unit33as removed from the chuck table62used in the workpiece fixing step (S30). Two or four or more rectangular workpieces11may be fixed to the resin sheet21.

The structural details, the methods, etc., according to the above embodiments may be changed or modified within the scope of the present invention. For example, after each step of the workpiece processing methods has been carried out from the sticking step (S10) to the holding step (S40) according to their sequence, the workpiece11supported on the annular frame29may be observed, measured, or conveyed in another step instead of the grinding step (S50) or the polishing step (S55). In the step of observing, measuring, or conveying the workpiece11that is included in the workpiece unit33, the workpiece11can be handled easily compared with the workpiece11handled alone, i.e., not supported on annular frame29. As described above, when the workpiece11is peeled off from the resin sheet21, no adhesive remains on the workpiece11. The resin sheet21that has been used once may be reused. However, on the used resin sheet21, the grooves27tend to have become wider than when they were formed and are less likely to function as suction cups. Consequently, if the used resin sheet21is to be reused, it is preferable to perform the surface irregularity forming step (S20) on the reused resin sheet21to regenerate surface irregularities on the face side21athereof.