POLISHING PAD AND POLISHING METHOD

BACKGROUND OF THE INVENTION
Field of the Invention

The present invention relates to a polishing pad for polishing a workpiece such as a wafer and a polishing method for polishing a workpiece with the polishing pad.

Description of the Related Art

In a manufacturing process of semiconductor devices such as integrated circuits (ICs) or large-scale integration (LSI) circuits, wafers are ground on back surfaces thereof to be thinned to a predetermined thickness for the purpose of reducing the size and weight of the semiconductor devices. In recent years, especially, in order to meet demands for the size and weight reduction of electronic equipment, it is required to grind wafers to obtain a very small thickness of not more than 100 μm or not more than 50 μm, for example.

Meanwhile, wafers are ground by use of a grinding apparatus. In this grinding apparatus, grinding is carried out by grinding stones being rotated at high speed while the grinding stones are being pressed against a back surface of a wafer. When the back surface of the wafer is ground with such a grinding method, a strained layer including a microcrack (grinding mark) having a depth of approximately 1 μm is formed in the back surface of the wafer, and this strained layer causes lowering in flexural strength of the wafer.

To cope with this problem, the back surface of the wafer is polished by use of a polishing apparatus to remove the strained layer (refer to Japanese Patent Laid-open No. 2010-069601, for example). In this case, the polishing apparatus rotates a polishing pad mounted to a tip end of a spindle while pressing the polishing pad against the back surface of the wafer, thereby polishing the back surface of the wafer.

Here, the polishing pad to be mounted to the spindle includes a disc-shaped base to be mounted to the tip end of the rotatable spindle and a pad portion fixed to one end surface of the base. Until before being mounted to the spindle, the polishing pad is housed in a case formed of synthetic resin such as polypropylene for protection of the pad portion. When the polishing is to be carried out, an operator takes out the polishing pad from the case and mounts the polishing pad thus taken out to the tip end of the spindle of the polishing apparatus.

SUMMARY OF THE INVENTION

As described above, the polishing pad is housed in the case formed of synthetic resin until before being mounted to the spindle, and when the polishing of a workpiece such as a wafer is to be carried out, the operator takes out the polishing pad from the case and mounts the polishing pad thus taken out to the spindle. In the polishing apparatus, there are provided various mechanisms such as a chuck table for holding a workpiece being polished, a dressing unit for dressing the polishing pad, and a processing chamber cover for defining a processing chamber. Therefore, there is the possibility that the pad portion is unintentionally brought into contact with any of the various mechanisms when the operator mounts the polishing pad taken out from the case to the spindle, causing a damage to the polishing pad or causing a foreign matter to stick to the pad portion.

Accordingly, it is an object of the present invention to provide a polishing pad and a polishing method that make it possible to prevent the pad portion from being damaged or prevent a foreign matter from sticking to the pad portion at the time of mounting the polishing pad to the spindle.

In accordance with an aspect of the present invention, there is provided a polishing pad including a disc-shaped base to be mounted to a tip end of a rotatable spindle and a pad portion fixed to one end surface of the base, at least a polishing surface of the pad portion being coated with a resin film until before the polishing pad is mounted to the spindle.

In accordance with another aspect of the present invention, there is provided a polishing method for polishing a workpiece with the polishing pad, the polishing method including a polishing pad mounting step of mounting the polishing pad to the tip end of the spindle, a separating step of separating the resin film from the pad portion, a holding step of holding the workpiece on a holding surface of a chuck table, and a polishing step of polishing the workpiece by individually rotating the polishing pad and the chuck table while the pad portion and the workpiece are brought into contact with each other.

In the polishing pad according to the aspect of the present invention, since at least the polishing surface of the pad portion of the polishing pad is coated with the resin film to protect the pad portion until before the polishing pad is mounted to the spindle, defects such as damages to at least the polishing surface of the pad portion do not occur even if the pad portion makes contact with any of the various mechanisms such as the chuck table, the dressing unit, and the processing chamber cover when the polishing pad is taken out from a case and mounted to the spindle for polishing of the workpiece.

Moreover, with the polishing method according to the aspect of the present invention, the polishing pad whose pad portion has at least its polishing surface coated with the resin film is mounted to the tip end of the spindle in the polishing pad mounting step, and then, the resin film coating at least the polishing surface of the pad portion of the polishing pad is separated in the separating step. Accordingly, the workpiece held on the holding surface of the chuck table in the subsequent holding step can normally be polished by the pad portion of the polishing pad in the subsequent polishing step.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side elevation view illustrating a polishing apparatus including a polishing pad according to an embodiment of the present invention;

FIG. 2 is a perspective view illustrating the polishing pad according to the embodiment of the present invention upside down;

FIG. 3A is a side elevation view illustrating the polishing pad according to the embodiment of the present invention upside down;

FIG. 3B is a sectional side elevation view illustrating the polishing pad according to the embodiment of the present invention upside down;

FIG. 4A is a cutaway side elevation view illustrating a polishing pad mounting step in a polishing method according to the embodiment of the present invention;

FIG. 4B is a cutaway side elevation view illustrating a separating step in the polishing method according to the embodiment of the present invention;

FIG. 4C is a cutaway side elevation view illustrating a holding step in the polishing method according to the embodiment of the present invention;

FIG. 4D is a cutaway side elevation view illustrating a polishing step in the polishing method according to the embodiment of the present invention;

FIG. 5 is a cutaway side elevation view illustrating a modification of the polishing step in the polishing method according to the embodiment of the present invention; and

FIG. 6 is a cutaway side elevation view illustrating a state in which a resin film formed of a thermoplastic resin sheet is being peeled off in the polishing method according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described below with reference to the attached drawings. First, description will be made about a configuration of a polishing apparatus including a polishing pad according to the embodiment of the present invention with reference to FIG. 1.

The polishing apparatus, denoted by 1 in FIG. 1, is an apparatus that polishes a disc-shaped wafer W (refer to FIGS. 4C and 4D) as a workpiece, and includes the following constituent elements. Specifically, the polishing apparatus 1 includes, as its main constituent elements, a chuck table 10 for holding the wafer W thereon and rotating about its central axis, a polishing unit 20 that polishes the wafer W held under suction on the chuck table 10, a polishing feed mechanism 30 that moves the polishing unit 20 up and down in a direction perpendicular to a holding surface 11a of the chuck table 10, a pure water supply unit 40 that jets pure water upward, a slurry supply unit 50 that supplies slurry as an abrasive from a central part of a polishing pad 25 toward the wafer W being polished, and an inclination adjustment mechanism 60 that adjusts the inclination of the chuck table 10.

Here, the wafer W (refer to FIGS. 4C and 4D) includes single crystal silicon as a base material and is formed with a plurality of unillustrated devices on a surface thereof facing downward in the state illustrated in FIGS. 4C and 4D. These devices are protected by an unillustrated protective tape attached to the surface of the wafer W.

Next, description will be made about each of the configurations of the chuck table 10, the polishing unit 20, the polishing feed mechanism 30, the pure water supply unit 40, the slurry supply unit 50, and the inclination adjustment mechanism 60, which are the main constituent elements of the polishing apparatus 1.

The chuck table 10 is a disc-shaped member and incorporates a porous member 11 at an upper central portion thereof. Here, the porous member 11 is formed of porous ceramic or the like, and an upper surface of the porous member 11 serves as the holding surface 11a for holding the disc-shaped wafer W under suction thereon.

The chuck table 10 is driven to rotate at a predetermined speed about a rotational axis 12 extending vertically downward from a central part thereof by an electric motor 13 that is a rotational drive source coupled to the rotational axis 12. It is to be noted that the porous member 11 of the chuck table 10 is selectively connected to an unillustrated suction source such as a vacuum pump.

The polishing apparatus 1 according to the present embodiment further includes a base 2 in the shape of a rectangular box elongated in a front-rear direction (left-right direction in FIG. 1), and the base 2 is provided therein with an unillustrated horizontal movement mechanism that moves the chuck table 10 in a direction (left-right direction in FIG. 1) horizontal to the holding surface 11a.

The polishing unit 20 includes a spindle motor 22 that is a rotational drive source housed in a holder 21, a spindle 23 that extends vertically and is rotationally driven by the spindle motor 22, a disc-shaped mount 24 attached to a lower end of the spindle 23, and the polishing pad 25 according to the present embodiment detachably mounted to a lower surface of the mount 24.

The polishing pad 25 according to the present embodiment is now described in detail with reference to FIGS. 2, 3A, and 3B. The polishing pad 25 includes a disc-shaped base portion 25a formed of aluminum alloy or the like and a disc-shaped pad portion 25b attached to a lower surface (upper surface in FIGS. 2, 3A, and 3B) of the base portion 25a. The base portion 25a and the pad portion 25b are formed at respective central parts thereof with passages 25al and 25b1 in the shape of circular holes for allowing slurry to pass therethrough. Here, the pad portion 25b is formed of a pad material such as non-woven fabric or urethane containing abrasive grains.

Until before the polishing pad 25 is mounted to the mount 24 attached to the lower end of the spindle 23 in a polishing pad mounting step to be described later, the pad portion 25b of the polishing pad 25 has its entire surface coated with a resin film 26 formed of water-soluble resin or a thermoplastic resin sheet. Here, as the water-soluble resin, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, polyethylene oxide, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyacrylic acid, a polyvinyl alcohol-polyacrylic acid block copolymer, a polyvinyl alcohol-polyacrylic acid ester block copolymer, polyglycerin, or the like is used. As the thermoplastic resin sheet, a polyethylene (PE) sheet, a polypropylene (PP) sheet, a polystyrene (PS) sheet, or the like is used.

The polishing feed mechanism 30 is a mechanism that moves the polishing unit 20 up and down along a direction (up-down direction) perpendicular to the holding surface 11a of the chuck table 10, and is disposed on a rectangular-box-shaped column 3 standing vertically at an end portion (rear end portion) in a +Y axis direction on an upper surface of the base 2 as illustrated in FIG. 1. The polishing feed mechanism 30 moves the holder 21 of the polishing unit 20 up and down along a left and right pair of guide rails 31 (only one of them is illustrated in FIG. 1) together with the spindle motor 22 held by the holder 21, the spindle 23, and the polishing pad 25. “Left and right” in this case represents a direction perpendicular to the plane of FIG. 1, and the paired guide rails 31 are disposed vertically and parallel to each other on an end surface (front surface) of the column 3.

On a rear surface of the holder 21, a slider 32 in the shape of a block is provided in the manner protruding horizontally, and a vertically extending ball screw 33 is inserted in screw engagement with the slider 32. To an upper end of the ball screw 33, an output shaft of a servo motor 35 that is a rotational drive source and that is installed vertically and attached to an upper surface of the column 3 through a bracket 34 is coupled. A lower end of the ball screw 33 is rotatably supported by a bearing 36 to the column 3. It is to be noted that a scale 37 is vertically attached to a side end surface of the column 3 along the ball screw 33 and that a reading part 38 for reading the scale of the scale 37 is attached to a rear surface of the slider 32.

With such a configuration, when the servo motor 35 is activated to rotate the ball screw 33 normally and reversely, the slider 32 in screw engagement with the ball screw 33 moves up and down together with the polishing unit 20 along the pair of guide rails 31, so that the polishing unit 20 moves up and down to set a polishing amount (polishing margin) of the polishing pad 25 relative to the wafer W.

The pure water supply unit 40 is a unit that, in the case where the resin film 26 (refer to FIGS. 2, 3A, and 3B) coating the entire surface of the pad portion 25b of the polishing pad 25 is formed of water-soluble resin, jets pure water toward the resin film 26 to dissolve the resin film 26, thereby separating the resin film 26 from the pad portion 25b. The pure water supply unit 40 includes a jetting nozzle 41 for jetting the pure water upward and a pure water supply source 42 for supplying the jetting nozzle 41 with the pure water, and the jetting nozzle 41 and the pure water supply source 42 are connected to each other by a pipe 43. Here, the jetting nozzle 41 is disposed on the chuck table 10 and is movable in the left-right direction in FIG. 1 together with the chuck table 10 by the unillustrated horizontal movement mechanism. It is to be noted that, in the polishing apparatus 1 according to the present embodiment, the chuck table 10, part of the spindle 23, the mount 24, and the polishing pad 25 of the polishing unit 20, the inclination adjustment mechanism 60, and the like are housed in a processing chamber S defined by a rectangular-box-shaped processing chamber cover 4 disposed on the base 2.

The slurry supply unit 50 is a unit that supplies slurry as an abrasive from the central part of the polishing pad 25 toward the wafer W being polished, and includes a slurry supply source 51 and a supply route for supplying the slurry from the slurry supply source 51 to the central part of the polishing pad 25. Here, the supply route includes a supply passage 52 vertically extending through axial centers of the spindle motor 22 and the spindle 23, a supply passage 53 formed at an axial center of the mount 24, and the passages 25al and 25b1 formed at respective axial centers of the base portion 25a and the pad portion 25b of the polishing pad 25. The supply passage 52 formed through the axial centers of the spindle motor 22 and the spindle 23 is connected to the slurry supply source 51 by a pipe 55. It is to be noted that pure water is preferably used as grinding water.

The inclination adjustment mechanism 60 is a mechanism that adjusts the inclination of the chuck table 10, and is disposed between the chuck table 10 and the base 2 as illustrated in FIG. 1. Specifically, the inclination adjustment mechanism 60 includes two actuators 61 (only one of them is illustrated in FIG. 1) and a pivot 62, and the actuators 61 and the pivot 62 are arranged at equal angular intervals (at pitches of 120°) in a circumferential direction.

Here, the actuators 61 are each configured such that, when an electric motor 64 is activated to rotate a screw shaft 63 normally and reversely and thus move the screw shaft 63 up and down, the chuck table 10 is tilted about the pivot 62, thereby adjusting the inclination of the holding surface 11a of the chuck table 10 relative to a horizontal surface.

Next, description will be made about a polishing method of the wafer W according to the present embodiment carried out in the polishing apparatus 1 configured described above.

The polishing method according to the present embodiment is a method for polishing the wafer W by sequentially carrying out 1) polishing pad mounting step, 2) separating step, 3) holding step, and 4) polishing step. Each of the steps will hereinafter be described.

1) Polishing Pad Mounting Step:

The polishing pad mounting step is a step in which an operator takes out the polishing pad 25 (the polishing pad 25 whose pad portion 25b has its entire surface coated with the resin film 26) from an unillustrated case formed of synthetic resin such as polypropylene and mounts the polishing pad 25 to the mount 24 fixed at a tip end of the spindle 23.

Specifically, the operator raises the polishing pad 25 taken out from the case toward the mount 24 as indicated by a thick arrow in FIG. 4A to bring the polishing pad 25 into close contact with the lower surface of the mount 24. At a plurality of positions in a circumferential direction of the mount 24, a plurality of circular bolt insertion holes 24a (only one of them is illustrated in FIG. 4A) are formed in the manner extending through the mount 24. At a plurality of positions in a circumferential direction of the base portion 25a of the polishing pad 25 corresponding to the positions of the bolt insertion holes 24a, a plurality of female threaded holes 25a2 (only one of them is illustrated in FIG. 4A) the number of which is the same as the number of the bolt insertion holes 24a are formed. By inserting bolts 27 (only two of them are illustrated in FIG. 4A) from above through the plurality of bolt insertion holes 24a formed in the mount 24 and screwing the bolts 27 into the female threaded holes 25a2 formed in the base portion 25a of the polishing pad 25, the polishing pad 25 is mounted to the lower surface of the mount 24. It is to be noted that, in this state, the entire surface of the pad portion 25b of the polishing pad 25 is coated with the resin film 26.

In this polishing pad mounting step, since the pad portion 25b of the polishing pad 25 taken out from the unillustrated case by the operator has its entire surface protected by the resin film 26, defects such as damages to the pad portion 25b do not occur even if the pad portion 25b makes contact with any of the various mechanisms such as the chuck table 10 and the processing chamber cover 4 when the polishing pad 25 is mounted to the mount 24 as described above.

2) Separating Step:

The separating step is a step of separating and removing, from the pad portion 25b of the polishing pad 25 mounted to the mount 24 in the polishing pad mounting step, the resin film 26 coating the pad portion 25b. In the case where the resin film 26 is formed of water-soluble resin, the pure water supplied from the pure water supply source 42 to the jetting nozzle 41 through the pipe 43 of the pure water supply unit 40 is jetted upward from the jetting nozzle 41 as illustrated in FIG. 4B. At this time, the polishing pad 25 above the jetting nozzle 41 is being rotated at a predetermined speed in a direction indicated by an arrow in FIG. 4B by the spindle motor 22 (refer to FIG. 1), while the jetting nozzle 41 moves back and forth in a direction (left-right direction) indicated by a thick arrow in FIG. 4B by the unillustrated horizontal movement mechanism together with the chuck table 10. Therefore, the pure water jetted upward from the jetting nozzle 41 dissolves the resin film 26 coating the entire surface of the pad portion 25b of the polishing pad 25, thereby separating and removing the resin film 26 from the pad portion 25b.

3) Holding Step:

The holding step is a step of holding the wafer W to be polished on the holding surface 11a of the chuck table 10. In this holding step, as illustrated in FIG. 4C, the wafer W is placed on the holding surface 11a of the chuck table 10 with the unillustrated protective tape facing downward. The porous member 11 of the chuck table 10 is connected to the unillustrated suction source such as a vacuum pump. When the porous member 11 is vacuum-drawn, a negative pressure acts on the porous member 11, so that the wafer W is held under suction on the holding surface 11a of the chuck table 10 by the negative pressure.

4) Polishing Step:

The polishing step is a step of polishing the wafer W held on the holding surface 11a of the chuck table 10 in the holding step, by use of the pad portion 25b of the rotating polishing pad 25. In this polishing step, as illustrated in FIG. 4D, the chuck table 10 and the polishing pad 25 are individually driven to rotate at predetermined speeds in directions indicated by arrows, while the chuck table 10 moves back and forth in a direction (left-right direction) indicated by a thick arrow in FIG. 4D by the unillustrated horizontal movement mechanism relative to the polishing pad 25. In this state, the polishing feed mechanism 30 illustrated in FIG. 1 lowers the polishing pad 25 such that the pad portion 25b of the polishing pad 25 is brought into contact with the wafer W held on the rotating chuck table 10. Thus, the back surface (upper surface in FIG. 4D) of the wafer W is polished by the pad portion 25b.

During the polishing of the wafer W in the polishing step, the slurry supply unit 50 illustrated in FIG. 1 supplies slurry from the slurry supply source 51 through the pipe 55, the supply passages 52 and 53, and the passages 25a1 and 25b1 toward the wafer W, and this slurry enables effective polishing of the back surface of the wafer W.

In this polishing step, when the polishing of the wafer W by the polishing pad 25 is completed, the polishing feed mechanism 30 illustrated in FIG. 1 raises the polishing pad 25 to separate the pad portion 25b of the polishing pad 25 from the wafer W. The series of steps of polishing the wafer W is now completed.

As described above, in the polishing method of the wafer W according to the present embodiment, the polishing pad mounting step mounts the polishing pad 25 whose pad portion 25b has its entire surface coated with the resin film 26 to the tip end (mount 24) of the spindle 23, and then, the separating step separates the resin film 26 coating the entire surface of the pad portion 25b of the polishing pad 25. Accordingly, the wafer W held on the holding surface 11a of the chuck table 10 in the subsequent holding step can normally be polished by the pad portion 25b of the polishing pad 25 in the subsequent polishing step.

Incidentally, in a case where a dressing unit 70 is installed on the chuck table 10 as illustrated in FIG. 5, the jetting nozzle 41 for jetting pure water (cleaning water) toward the pad portion 25b of the polishing pad 25 to be dressed is disposed on the chuck table 10. In the above-described separating step in the polishing method of the wafer W, the pure water may be jetted from the jetting nozzle 41 toward the pad portion 25b to dissolve the resin film (water-soluble resin film) coating the entire surface of the pad portion 25b, thereby separating the resin film from the pad portion 25b.

It is to be noted that, since, in the separating step in the polishing method described above, the resin film 26 coating the pad portion 25b of the polishing pad 25 is formed of water-soluble resin, pure water is jetted to the resin film 26 to dissolve the resin film 26 with the pure water. In the case where the resin film 26 is formed of a thermoplastic resin sheet, the operator can separate the resin film (thermoplastic resin sheet) 26 from the pad portion 25b by manually peeling off the resin film 26 from the pad portion 25b as illustrated in FIG. 6.

While the above embodiment adopts the configuration in which the entire surface of the pad portion 25b of the polishing pad 25 is coated with the resin film 26, a configuration in which at least a polishing surface (lower surface) of the pad portion 25b is coated with the resin film 26 may alternatively be adopted to obtain effects same as those achieved by the embodiment described above.

It is to be noted that, while the polishing pad for polishing a wafer as a workpiece and the wafer polishing method using this polishing pad have been described thus far, the present invention is similarly applicable to a polishing pad to be used for polishing any workpiece other than a wafer and a workpiece polishing method carried out in a polishing apparatus including this polishing pad.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

POLISHING PAD AND POLISHING METHOD

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Description

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Priority Claims (1)