METHOD OF PROCESSING WORKPIECE

BACKGROUND OF THE INVENTION
Field of the Invention

The present invention relates to a method of processing a plate-shaped workpiece by grinding and polishing the workpiece to thin down the workpiece to a predetermined thickness.

Description of the Related Art

Device chips including devices such as electronic circuits, for example, are components that are indispensable for various electronic appliances represented by cellular phones and personal computers. Such device chips are manufactured by demarcating a plurality of areas on a wafer made of a semiconductor material such as silicon with a grid of projected dicing lines also known as streets, constructing devices respectively in the areas, and thereafter dividing the wafer along the projected dicing lines into pieces referred to as device chips. By thinning down such a wafer before it is divided, thinner device chips can eventually be fabricated from the wafer when the wafer is divided.

Plate-shaped workpieces such as wafers are thinned down using an annular grinding wheel to which grindstones that contain abrasive grains are fixed (see Japanese Patent Laid-open No. 2000-288881). Generally, when grindstones grind a surface of a workpiece, they leave miniscule surface irregularities such as processing marks and processing strains on the ground surface. After the workpiece is ground, it has been customary to perform a polishing process such as chemical mechanical polishing (CMP) on the ground surface of the workpiece in order to remove the surface irregularities therefrom (Japanese Patent Laid-open No. Hei 8-99265). A workpiece is ground and polished in sequence using a grinding and polishing apparatus that includes a grinding unit and a polishing unit (see Japanese Patent Laid-open No. 2002-283243). When the grinding and polishing apparatus is in operation, it grinds the workpiece while monitoring the thickness of a particular area of the workpiece, and stops grinding the workpiece when it confirms that the workpiece has been ground to a predetermined thickness. Then, the grinding and polishing apparatus polishes the ground workpiece under predetermined conditions.

SUMMARY OF THE INVENTION

In recent years, there has been an increasing tendency for electronic appliances incorporating device chips to be smaller in size and higher in functionality. For example, wafers that have been thinned down are required to have higher total thickness uniformity, i.e., lower total thickness variation (TTV), for stabilization of device chip quality. However, when a surface of a workpiece is ground under predetermined conditions by a grinding and polishing apparatus, the ground surface of the workpiece may not be planarized due to thickness variations of the workpiece itself and the state of the grinding and polishing apparatus. In other words, the ground surface of the workpiece may have height variations at various sites thereof. When the ground surface of the workpiece whose height is not even is polished under predetermined conditions, the polished surface also suffers height irregularities.

For the above reasons, there has been a demand for a method of processing a workpiece to make the workpiece even in thickness. Different workpieces that have been processed have processed surfaces whose height variations are not uniform. Even when workpieces of the same kind are processed under common processing conditions by the same grinding and polishing apparatus, the workpieces tend to have different thickness variations. It is thus not easy to process workpieces to have thickness uniformity.

It is therefore an object of the present invention to provide a method of processing a plate-shaped workpiece to thin down the workpiece to a uniform thickness.

In accordance with an aspect of the present invention, there is provided a method of processing a workpiece using a chuck table for holding the workpiece, a grinding unit including a grinding wheel for grinding a processed surface of the workpiece, a polishing unit including a polishing pad for polishing the surface of the workpiece held on the chuck table, and a measuring unit for measuring a thickness of the workpiece, including a grinding step of grinding the workpiece from the surface thereof with the grinding unit, after the grinding step, a measuring step of measuring thicknesses of the workpiece at a plurality of measurement sites thereon with the measuring unit and acquiring information with respect to a thickness distribution of the workpiece with the measuring unit, and a polishing step of polishing the workpiece from the surface thereof with the polishing unit, in which the polishing step includes determining polishing conditions on the basis of the information with respect to the thickness distribution of the workpiece acquired in the measuring step and polishing the workpiece under the determined polishing conditions.

Preferably, the method of processing a workpiece further uses a controller for controlling the polishing unit, the controller having a storage section in which a plurality of kinds of polishing conditions are registered, and, in the polishing step, the controller reads polishing conditions favorable for uniformizing the thickness of the workpiece from among the kinds of polishing conditions registered in the storage section, on the basis of the information with respect to the thickness distribution of the workpiece acquired in the measuring step, and controls the polishing unit to keep polishing the workpiece under the polishing conditions thus read.

More preferably, the polishing pad of the polishing unit is larger in diameter than the workpiece, in the polishing step, the workpiece is polished with the polishing pad while the chuck table that is holding the workpiece and the polishing pad are being oscillated relatively to each other along directions parallel to the surface of the workpiece, and, in the polishing step, a distance that the chuck table and the polishing pad are oscillated relatively to each other and a central position across which the chuck table and the polishing pad are oscillated relatively to each other are determined, on the basis of the polishing conditions read from the storage section.

Much more preferably, the polishing conditions registered in the storage section include a distance between a reference position representing relative positions of the polishing pad and the workpiece at the time when the workpiece has an outer circumferential edge inscribed in an outer circumferential edge of the polishing pad on the processed surface of the workpiece and the central position across which the chuck table and the polishing pad are oscillated relatively to each other and the distance that the chuck table and the polishing pad are oscillated relatively to each other.

In the method of processing a workpiece according to the aspect of the invention, the workpiece is ground from the surface thereof, the thickness of the workpiece is measured to acquire information with respect to a thickness distribution of the workpiece, and the workpiece is polished from the surface under polishing conditions selected on the basis of the acquired information with respect to the thickness distribution of the workpiece. Thickness distributions of a plurality of workpieces that have been ground can individually be acquired and assessed, and optimum polishing conditions can be selected in a manner to match the shapes of the ground workpieces, so that the workpieces can be polished under the selected optimum polishing conditions. Therefore, the workpieces can be polished under polishing conditions that take into account variations of the thicknesses thereof, unlike a situation where workpieces are polished under the same polishing conditions.

According to the aspect of the present invention, consequently, there is provided a method of processing a plate-shaped workpiece to thin down the workpiece to a uniform thickness.

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 perspective view schematically illustrating a grinding and polishing apparatus, i.e., a processing apparatus, that carries out a method of processing a workpiece according to an embodiment of the present invention;

FIG. 2 is a plan view schematically illustrating a turntable, a grinding unit, and a polishing unit of the grinding and polishing apparatus;

FIG. 3 is a perspective view schematically illustrating the manner in which a grinding step of the method is carried out;

FIG. 4 is a side elevational view, partly in cross section, schematically illustrating the workpiece that is available immediately after the grinding step has started;

FIG. 5 is a side elevational view, partly in cross section, schematically illustrating the workpiece that has been thinned down in the grinding step;

FIG. 6 is a plan view schematically illustrating the positional relation between a measuring instrument and the workpiece in a measuring step of the method;

FIG. 7 is a side elevational view, partly in cross section, schematically illustrating the workpiece whose thickness is measured by a measuring unit;

FIG. 8A is a cross-sectional view schematically illustrating a workpiece whose processed surface has been ground into a recessed shape with its center lower than a peripheral portion thereof;

FIG. 8B is a cross-sectional view schematically illustrating a workpiece whose processed surface has been ground into a protruding shape with its center higher than a peripheral portion thereof;

FIG. 9 is a side elevational view, partly in cross section, schematically illustrating the manner in which a polishing step of the method is carried out;

FIG. 10A is a plan view schematically illustrating, by way of example, the positional relation between a polishing pad and the workpiece at the time when the workpiece has its outer circumferential edge inscribed in the outer circumferential edge of the polishing pad on the processed surface of the workpiece;

FIG. 10B is a plan view schematically illustrating, by way of example, the positional relation between a polishing pad and the workpiece at the time when the workpiece has its outer circumferential edge not inscribed in the outer circumferential edge of the polishing pad on the processed surface of the workpiece;

FIG. 11 is a graph illustrating the results of an experiment; and

FIG. 12 is a flowchart of the sequence of the steps of the method of processing a workpiece according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method of processing a workpiece according to a preferred embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 3 schematically illustrates, in perspective, the manner in which a grinding step of the method is carried out. FIG. 3 also schematically illustrates a workpiece 1 to be processed by the method according to the present embodiment. The workpiece 1 includes, for example, a wafer shaped as a circular plate made of a semiconductor. More specifically, the workpiece 1 is made of silicon (Si), silicon carbide (Sic), or sapphire (Al₂O₃), for example. The workpiece 1 has a face side 1a including a plurality of small areas demarcated thereon by a grid of projected dicing lines also known as streets and a plurality of devices such as integrated circuits (ICs) constructed in the respective small areas. The workpiece 1 has a reverse side 1b opposite the face side 1a, and the reverse side 1b is processed as a processed surface. A film-like protective member 3 (see FIGS. 3, 4, and 5, for example) is affixed to the face side 1a for protecting the devices thereon. The protective member 3 includes a circular base and an adhesive layer, i.e., a glue layer, provided on the base. The base is made of resin such as polyolefin, polyvinyl chloride, polyethylene terephthalate, for example, whereas the adhesive layer is made of an adhesive such as an epoxy-based adhesive, an acryl-based adhesive, or a rubber-based adhesive, for example. Alternatively, the adhesive layer may be made of an ultraviolet-curable resin that can be cured upon exposure to ultraviolet rays.

However, the workpiece 1 is not limited to any particular materials, shapes, structures, and sizes. For example, a substrate made of another material, e.g., any of semiconductors, ceramics, resin, or metal may be used as the workpiece 1. Similarly, the devices on the workpiece 1 are not limited to any particular kinds, quantities, shapes, structures, sizes, and layouts, for example. The workpiece 1 may even be free of devices with no protective member 3 affixed to the face side 1a thereof.

A grinding and polishing apparatus 2 as a processing apparatus for carrying out the method of processing a workpiece according to the present embodiment will be described below primarily with reference to FIG. 1. The grinding and polishing apparatus 2 operates to perform a grinding process and a polishing process on the workpiece 1. As illustrated in FIG. 1, the grinding and polishing apparatus 2 is illustrated in reference to a three-dimensional XYZ coordinate system having an X-axis indicated by the arrow X, a Y-axis indicated by the arrow Y, and a Z-axis indicated by the arrow Z. The X-axis represents horizontal forward and rearward directions, the Y-axis represents horizontal leftward and rightward directions, and the Z-axis represents vertical upward and downward directions. The X-axis, the Y-axis, and the Z-axis extend perpendicularly to each other.

The grinding and polishing apparatus 2 includes a foundation base 4 supporting various components thereof. The foundation base 4 has a cavity 4a defined in an upper surface of a front end portion thereof. A delivery unit or mechanism 6 is disposed in the cavity 4a. The grinding and polishing apparatus 2 includes a cassette rest 4b for supporting a cassette 8 placed thereon and a cassette rest 4c for supporting a cassette 10 placed thereon. The cassette rests 4b and 4c are mounted on a front end of the base 4 forwardly of the cavity 4a. Each of the cassettes 8 and 10 houses therein a plurality of workpieces 1 each with a protective member 3 affixed thereto. While the grinding and polishing apparatus 2 is in operation, workpieces 1 housed in the cassettes 8 and 10 are successively removed therefrom, processed, and then returned into the cassettes 8 and 10.

The grinding and polishing apparatus 2 includes a positioning mechanism, i.e., an alignment mechanism, 12 disposed on the base 4 obliquely behind the cavity 4a. A workpiece 1 stored in one of the cassettes 8 and 10 is delivered to the positioning mechanism 12 by the delivery unit 6. The positioning mechanism 12 that has received the workpiece 1 positions the workpiece 1 as desired, i.e., aligns the workpiece 1 with a predetermined position. A delivery unit, i.e., a delivery mechanism or a loading arm, 14 for holding and turning a workpiece 1 is disposed at a position adjacent to the positioning mechanism 12. The delivery unit 14 includes a suction pad for attracting under suction an upper surface, i.e., the reverse side 1b, of a workpiece 1. The delivery unit 14 holds, with the suction pad, under suction a workpiece 1 that has been positioned by the positioning mechanism 12 and delivers the workpiece 1 held by the suction pad rearwardly away from the positioning mechanism 12. The grinding and polishing apparatus 2 also includes a disk-shaped turntable 16 disposed on the base 4 behind the delivery unit 14. The turntable 16 is coupled to a rotary actuator, not depicted, such as an electric motor and is rotatable about a central axis thereof that extends vertically parallel to the Z-axis. The turntable 16 supports on its upper surface a plurality of, e.g., four in FIG. 1, chuck tables 18 each for holding a workpiece 1 thereon. The chuck tables 18 are angularly spaced by substantially equal intervals circumferentially around the turntable 16.

FIG. 2 schematically illustrates, in plan, the four chuck tables 18 disposed on the turntable 16. Each of the chuck tables 18 has an upper surface acting as a holding surface 18a for holding a workpiece 1 thereon. The holding surface 18a is of a planar shape similar to the workpiece 1 and is approximately of the same size as the workpiece 1. The holding surface 18a is fluidly connected to a suction source, not depicted, such as an ejector, for example, through a fluid channel, not depicted, defined in the chuck table 18. Each of the chuck tables 18 for holding workpieces 1 thereon is not limited to any particular kinds and structures. For example, a chuck table for holding a workpiece 1 by way of mechanical or electrical means may be used instead of each of the chuck tables 18.

Each of the chuck tables 18 is coupled to a rotary actuator, not depicted, such as an electric motor and is rotatable about a central axis thereof that extends vertically parallel to the Z-axis. The turntable 16 is rotatable counterclockwise, i.e., in the direction indicated by the arrow a, as viewed in plan, to position each of the chuck tables 18 successively in a delivery position A, a coarse-grinding position B, a finish-grinding position C, and a polishing position D. The delivery unit 14 delivers a workpiece 1 that has been positionally adjusted by the positioning mechanism 12 onto the chuck table 18 that has been positioned in the delivery position A.

Two columnar support structures 20 are disposed on the base 2 behind the turntable 16, or specifically, respectively behind the coarse-grinding position B and the finish-grinding position C. A Z-axis moving mechanism 22 is mounted on a front face of each of the support structures 20 that faces the turntable 16. The Z-axis moving mechanism 22 includes a pair of Z-axis guide rails 24 mounted on the front face of the support structure 20 and extending essentially along the Z-axis and a Z-axis movable plate 26 movably mounted on the Z-axis guide rails 24 for sliding movement along the Z-axis guide rails 24. A nut, not depicted, is mounted on a rear face of the Z-axis movable plate 26 and operatively threaded over a Z-axis ball screw 28 disposed between and extending essentially parallel to the Z-axis guide rails 24. The Z-axis ball screw 28 has an upper end coupled to a Z-axis stepping motor 30. When the Z-axis stepping motor 30 is energized, it rotates the Z-axis ball screw 28 about its own vertical central axis, causing the nut to move the Z-axis movable plate 26 along the Z-axis guide rails 24 along the Z-axis.

A grinding unit 32a for performing a coarse-grinding process on a workpiece 1 held on the chuck table 18 in the coarse-grinding position B is mounted on a front face of the Z-axis movable plate 26 on the support structure 20 behind the coarse-grinding position B. Similarly, a grinding unit 32b for performing a finish-grinding process on a workpiece 1 held on the chuck table 18 in the finish-grinding position C is mounted on a front face of the Z-axis movable plate 26 on the support structure 20 behind the finish-grinding position C. The grinding units 32a and 32b are movable vertically along the Z-axis respectively by the Z-axis moving mechanisms 22 on the respective support structures 20. Each of the grinding units 32a and 32b includes a tubular housing 34 mounted on the Z-axis movable plate 26. A cylindrical spindle 36 that acts as a rotatable shaft extending vertically along the Z-axis is rotatably housed in the tubular housing 34. The spindle 36 has a distal lower end portion protruding downwardly from the lower end of the housing 34. As illustrated in FIG. 3, a wheel mount 37 with a grinding wheel 38a or 38b fixed thereto is disposed on the lower end of the spindle 36.

The grinding wheel 38a for coarsely grinding the workpiece 1 held on the chuck table 18 in the coarse-grinding position B is mounted on the wheel mount 37 on the lower end of the spindle 36 of the grinding unit 32a. The grinding wheel 38b for finish-grinding the workpiece 1 held on the chuck table 18 in the finish-grinding position C is mounted on the wheel mount 37 on the lower end of the spindle 36 of the grinding unit 32b. The grinding wheels 38a and 38b of the respective grinding units 32a and 32b include respective annular bases 39a and 39b mounted on the respective lower surfaces of the wheel mounts 37 and made of a metal material such as stainless steel or aluminum, for example. The grinding wheels 38a and 38b also include respective annular arrays of grindstones 40a and 40b for grinding workpieces 1 on the chuck tables 18 in the coarse-grinding position B and the finish-grinding position C. The grindstones 40a and 40b are mounted on the respective lower surfaces of the bases 39a and 39b and angularly spaced at substantially equal intervals circumferentially around the bases 39a and 39b. Each of the grindstones 40a and 40b is made of abrasive grains made of diamond or cubic boron nitride (CBN), and bound together by a binder such as a metal bond, a resin bond, or a vitrified bond. However, the grindstones 40a and 40b are not limited to any particular materials, shapes, structures, and sizes. The number of the grindstones 40a and 40b of the grinding wheels 38a and 38b is optional.

The spindle 36 of each of the grinding units 32a and 32b has a proximal upper end connected to a rotary actuator, not depicted, such as an electric motor. When the rotary actuator is energized, it generates rotary power that is transmitted through the spindle 36 to each of the grinding wheels 38a and 38b, rotating the grinding wheels 38a and 38b about their vertical central axes substantially parallel to the Z-axis. The grinding units 32a and 32b have respective grinding liquid supply passages, not depicted, for supplying a grinding liquid such as pure water therethrough. When workpieces are held on the chuck tables 18 in the coarse-grinding position B and the finish-grinding position C, the grinding liquid is supplied from the grinding liquid supply passages to the workpieces 1 and the grindstones 40a and 40b. The grinding unit 32a grinds the workpiece 1 held on the chuck table 18 in the coarse-grinding position B with the grindstones 40a, thereby performing the coarse-grinding process on the workpiece 1. The grinding unit 32b grinds the workpiece 1 held on the chuck table 18 in the finish-grinding position C with the grindstones 40b, thereby performing the finish-grinding process on the workpiece 1.

A measuring unit 72 (see FIG. 3) for measuring the thickness of the workpiece 1 held on the chuck table 18 is disposed on the base 4 in the vicinity of each of the coarse-grinding position B and the finish-grinding position C. The measuring unit 72 includes, for example, a non-contact-type measuring unit for measuring the thickness of the workpiece 1 by applying a laser beam or light to the upper surface of the workpiece 1 and detecting a reflected laser beam or light from the upper surface of the workpiece 1, thereby measuring the height of the upper surface of the workpiece 1. However, the measuring unit 72 is not limited to such a non-contact-type measuring unit, and may be a contact-type measuring unit that includes a probe for contacting the upper surface of the workpiece 1. The measuring unit 72 as a non-contact-type measuring unit includes, for example, a shaft 74 disposed radially outwardly of the turntable 16 and extending upwardly from the base 4 along the Z-axis, and an arm 76 extending from the upper end of the shaft 74 horizontally along an XY plane along the X-axis and the Y-axis. The measuring unit 72 also includes a measuring instrument 78 fixedly mounted on the distal end of the arm 76 for measuring the height of the upper surface of the workpiece 1. The measuring instrument 78 includes, for example, a laser beam or light emitter for applying a laser beam or light to the upper surface, i.e., the reverse side 1b, of the workpiece 1 and a sensor for detecting a reflected laser beam or light from the upper surface of the workpiece 1. The shaft 74 is rotatable about its vertical central axis to move the measuring instrument 78 over the upper surface of the workpiece 1, thereby changing the position where the measuring unit 72 measures the height of the upper surface of the workpiece 1.

As illustrated in FIG. 1, a columnar support structure 41 is disposed on the base 2 laterally of the turntable 16, or specifically, laterally of the polishing position D. An XZ-axis moving mechanism 42 is mounted on a front face of the support structures 41 that faces the turntable 16. The XZ-axis moving mechanism 42 includes a pair of first guide rails 44 mounted on the front face of the support structure 41 and extending essentially along the X-axis and a first movable plate 46 movably mounted on the first guide rails 44 for sliding movement along the first guide rails 44. A nut, not depicted, is mounted on a rear face of the first movable plate 46 and operatively threaded over a first ball screw 48 disposed between and extending essentially parallel to the first guide rails 44. The first ball screw 48 has an end coupled to a first stepping motor 50. When the first stepping motor 50 is energized, it rotates the first ball screw 48 about its own horizontal central axis, causing the nut to move the first movable plate 46 along the first guide rails 44 along the X-axis.

A pair of second guide rails 52 extending substantially parallel to the Z-axis are mounted on a front face of the first movable plate 46 that faces the turntable 16. A second movable plate 54 is movably mounted on the second guide rails 52 for sliding movement along the second guide rails 52. A nut, not depicted, is mounted on a rear face of the second movable plate 54 that faces the first movable plate 46 and operatively threaded over a second ball screw 56 disposed between and extending essentially parallel to the second guide rails 52. The second ball screw 56 has an upper end coupled to a second stepping motor 58. When the second stepping motor 58 is energized, it rotates the second ball screw 56 about its own vertical central axis, causing the nut to move the second movable plate 54 along the second guide rails 52 along the Z-axis. A polishing unit 60 for polishing the workpiece 1 held on the chuck table 18 in the polishing position D is mounted on a front face of the second movable plate 54 that faces the turntable 16. The XZ-axis moving mechanism 42 moves the polishing unit 60 along the X-axis and the Z-axis.

The polishing unit 60 includes a tubular housing 62 mounted on the second movable plate 54. A cylindrical spindle 64 that acts as a rotatable shaft extending vertically along the Z-axis is rotatably housed in the tubular housing 62. The spindle 64 has a distal lower end portion protruding downwardly from the lower end of the housing 62. FIG. 9 schematically illustrates the polishing unit 60. As illustrated in FIG. 9, a pad mount 80 with a polishing pad 66, to be described below, fixed thereto is disposed on the lower end of the spindle 64. The polishing pad 66 that is disk-shaped for polishing the workpiece 1 held on the chuck table 18 in the polishing position D is mounted on the pad mount 80. The polishing pad 66 is larger in diameter than the workpiece 1 to be polished. The spindle 64 has a proximal upper end connected to a rotary actuator, not depicted, such as an electric motor. When the rotary actuator is energized, it generates rotary power that is transmitted through the spindle 64 to the polishing pad 66, rotating the polishing pad 66 about its vertical central axis substantially parallel to the Z-axis.

The polishing pad 66 includes a disk-shaped base 82 fixed to the lower surface of the pad mount 80. The base 82 is made of a metal material such as stainless steel or aluminum, for example. The polishing pad 66 also includes a polishing layer 84 fixed to the lower surface of the base 82 for polishing the workpiece 1. The polishing layer 84 is of a disk shape essentially equal in diameter to the base 82 and affixed to the lower surface of the base 82 by an adhesive, for example. The polishing layer 84 has a lower surface acting as a polishing surface for polishing the workpiece 1. The polishing layer 84 includes a base member made of unwoven cloth or foamed urethane that contains abrasive grains of silicon oxide (SiO₂), green carborundum (GC), or white alundum (WA), for example. The abrasive grains contained in the polishing layer 84 have an average particle size ranging from 0.1 to 10 μm, for example. However, the material of the polishing layer 84 and the particle size and material of the abrasive grains may be changed depending on the material of the workpiece 1.

While a workpiece 1 is being polished by the polishing unit 60, the workpiece 1 and the polishing pad 66 are not supplied with a liquid chemical, i.e., a slurry, and liquid such as pure water, i.e., a polishing liquid. In other words, the workpiece 1 is processed, i.e., polished, in a dry polishing process using the polishing pad 66 that contains the abrasive grains. However, the workpiece 1 may alternatively be processed in a wet polishing process during which a polishing liquid free of abrasive grains is supplied to the workpiece 1 and the polishing pad 66. The polishing liquid may be a liquid chemical such as an acidic polishing liquid or an alkaline polishing liquid or pure water, for example. The acidic polishing liquid includes an acidic solution with permanganate dissolved therein, for example, and the alkaline polishing liquid includes an alkaline solution with sodium hydroxide or potassium hydroxide dissolved therein. According to the wet polishing process, a liquid chemical containing abrasive grains, i.e., a slurry, may be supplied to the workpiece 1 and the polishing pad 66. The liquid chemical contains abrasive grains made of SiO₂or alumina (Al₂O₃), for example, as free abrasive grains. When the liquid chemical is used, the polishing pad 66 does not contain abrasive grains. The polishing unit 60 may have a supply passage 86 defined through the spindle 64 along the Z-axis, so that the liquid chemical may be supplied via the supply passage 86 to the workpiece 1 and the polishing pad 66.

The polishing unit 60 polishes the workpiece 1 held on the chuck table 18 in the polishing position D with the polishing pad 66. In this manner, the polishing unit 60 performs a polishing process on the workpiece 1.

Another delivery unit, i.e., a delivery mechanism or an unloading arm, 68 for holding and turning a workpiece 1 is disposed at a position adjacent to the delivery unit 14. The delivery unit 68 includes a suction pad for attracting under suction an upper surface, i.e., the reverse side 1b, of a workpiece 1. The delivery unit 68 holds, under suction with the suction pad, a workpiece 1 that has been placed on the chuck table 18 in the delivery position A and delivers the workpiece 1 held by the suction pad forwardly away from the chuck table 18. A cleaning unit, i.e., a cleaning mechanism, 70 for cleaning a processed workpiece 1 delivered by the delivery unit 68 with a cleaning liquid such as pure water is disposed on the base 4 forwardly of the delivery unit 68. The workpiece 1 that has been cleaned by the cleaning unit 70 is picked up and delivered by the delivery unit 6 to one of the cassettes 8 and 10 where it is stored back again. Therefore, the cassettes 8 and 10 store workpieces 1 to be processed by the grinding units 32a and 32b and the polishing unit 60 and also store workpieces 1 that have been processed by the grinding units 32a and 32b and the polishing unit 60.

The grinding and polishing apparatus 2 further includes a controller, i.e., a control unit, 88 that has functions to control the components thereof described above. The controller 88 is electrically connected to the components. The controller 88 controls operation of the components to process workpieces 1 appropriately. The controller 88 typically includes a computer including a processing device such as a central processing unit (CPU) and a storage device such as a flash memory, for example. The processing device runs software, i.e., programs, stored in the storage device to perform the functions of the controller 88.

The controller 88 functionally includes a storage section 90 for storing various pieces of information and a processing control section 92 for controlling the grinding units 32a and 32b, the polishing unit 60, and other components. The storage section 90 registers therein a plurality of processing conditions for processing various workpieces 1. The processing conditions include parameters for operating the components of the grinding and polishing apparatus 2. The processing control section 92 reads processing conditions suitable for the kind and state of a workpiece 1 to be processed and the result to be achieved by processing the workpiece 1 from the storage section 90 and controls the various components under the processing conditions.

Operation of the grinding and polishing apparatus 2 to grind and polish a workpiece 1 will now be described below. For processing workpieces 1, a plurality of workpieces 1 to be processed are stored in the cassettes 8 and 10, and the cassettes 8 and 10 are placed on the respective cassette rests 4b and 4c. Then, one of the workpieces 1 stored in the cassettes 8 and 10 is removed and delivered to the positioning mechanism 12 by the delivery unit 6. The workpiece 1 is then positioned, i.e., aligned with a predetermined position, by the positioning mechanism 12. The positioned workpiece 1 is then delivered to a position over the chuck table 18 in the delivery position A by the positioning mechanism 12.

The workpiece 1 is placed on the chuck table 18 in the delivery position A with the lower surface, i.e., the face side 1a, facing the holding surface 18a and the upper surface, i.e., the reverse side 1b, exposed upwardly. Then, a negative pressure from the suction source is applied via the holding surface 18a to the workpiece 1 thereon, thereby holding the workpiece 1 under suction on the holding surface 18a with the protective member 3 interposed therebetween.

The turntable 16 is turned about its central axis to bring the chuck table 18 from the delivery position A to the coarse-grinding position B. Then, the workpiece 1 held on the chuck table 18 in the coarse-grinding position B is ground by the grindstones 40a of the grinding unit 32a. Specifically, while the chuck table 18 and the grinding wheel 38a are being rotated about their respective axes in respective directions at respective speeds, the grinding wheel 38a is lowered toward the chuck table 18 by the Z-axis moving mechanism 22. The speed at which the grinding wheel 38a is lowered is so adjusted as to press the grindstones 40a against the workpiece 1 under an appropriate force. When the lower surfaces of the grindstones 40a of the rotating grinding wheel 38a are brought into abrasive contact with the upper surface of the workpiece 1, the upper surface of the workpiece 1 is coarsely ground off. In this manner, a coarse-grinding process is performed on the workpiece 1, thereby thinning down the workpiece 1. When the workpiece 1 is thinned down to a predetermined thickness, the coarse-grinding process is completed. While the workpiece 1 is being ground by the grindstones 40a, the workpiece 1 and the grindstones 40a are supplied with a grinding liquid such as pure water, for example. The grinding liquid thus supplied is effective to cool the workpiece 1 and the grindstones 40a and wash away debris, i.e., swarf, produced by the grinding of the workpiece 1.

Then, the turntable 16 is turned to bring the chuck table 18 that is holding the workpiece 1 to the finish-grinding position C. The workpiece 1 held on the chuck table 18 brought to the finish-grinding position C is then ground by the grindstones 40b of the grinding unit 32b. The grinding unit 32b is structurally and operatively similar to the grinding unit 32a except that the grindstones 40b of the grinding wheel 38b are smaller than the grindstones 40a of the grinding wheel 38a in terms of average abrasive grain particle size. When the lower surfaces of the grindstones 40b of the rotating grinding wheel 38b are brought into abrasive contact with the upper surface of the workpiece 1, the upper surface of the workpiece 1 is finish-ground off. When the workpiece 1 is thinned down to a predetermined thickness, the finish-grinding process is completed.

When the grinding and polishing apparatus 2 grinds the workpiece 1 with each of the grinding units 32a and 32b, the grinding and polishing apparatus 2 monitors the thickness of the workpiece 1. Specifically, as described above, the grinding and polishing apparatus 2 includes the measuring unit 72 (see FIG. 3) for measuring the thickness of the workpiece 1 held on the chuck table 18 in the vicinity of each of the coarse-grinding position B and the finish-grinding position C. The measuring unit 72 measures the height of the upper surface, i.e., the reverse side 1b, of the workpiece 1 held on the chuck table 18 from the holding surface 18a, thereby measuring the thickness of the workpiece 1. The grinding and polishing apparatus 2 is thus able to confirm that the workpiece 1 has been thinned down to a predetermined thickness with the measured data from the measuring unit 72.

Then, the turntable 16 is turned to bring the chuck table 18 that is holding the workpiece 1 to the polishing position D. The workpiece 1 held on the chuck table 18 brought to the polishing position D is then polished by the polishing unit 60. Specifically, when the chuck table 18 is placed in the polishing position D, the workpiece 1 on the chuck table 18 is positioned below the polishing unit 60.

For performing a polishing process on the workpiece 1 with the polishing unit 60, the polishing pad 66 is positioned such that the polishing layer 84 lies over the workpiece 1 in its entirety, as illustrated in FIG. 9. Specifically, while the chuck table 18 and the polishing pad 66 are being rotated about their respective axes in respective directions at respective speeds, the polishing pad 66 is lowered toward the chuck table 18 by the XZ-axis moving mechanism 42. The speed at which the polishing pad 66 is lowered is so adjusted as to press the polishing layer 84 against the workpiece 1 under an appropriate force. When the rotating polishing pad 66 is pressed against the workpiece 1, the upper surface of the workpiece 1 is polished. When the workpiece 1 has been polished a predetermined degree, the polishing process on the workpiece 1 is completed. In the polishing process, processing marks, i.e., grinding marks, and fractured layers formed in the workpiece 1 when the workpiece has been ground by the grinding units 32a and 32b are removed, and the upper surface of the workpiece 1 is planarized. While the workpiece 1 is being polished, the workpiece 1 and the polishing pad 66 may be supplied with a liquid chemical, i.e., a slurry, and liquid such as pure water, i.e., a polishing liquid. The liquid chemical is supplied via the supply passage 86 to the workpiece 1 and the polishing pad 66.

Thereafter, the turntable 16 is turned to bring the chuck table 18 that is holding the workpiece 1 to the delivery position A. Then, the workpiece 1 that has been ground and polished is delivered from the chuck table 18 in the delivery position A to the cleaning unit 70 by the delivery unit 68. The processed workpiece 1 is cleaned by the cleaning unit 70. The workpiece 1 that has been cleaned by the cleaning unit 70 is stored back into one of the cassettes 8 and 10 by the delivery unit 6. In this manner, the grinding and polishing apparatus 2 successively processes workpieces 1 removed from the cassettes 8 and 10 and returns the processed workpieces 1 to the cassettes 8 and 10. When all the workpieces 1 from the cassettes 8 and 10 have been processed and then stored back in the cassettes 8 and 10, the cassettes 8 and 10 are unloaded from the grinding and polishing apparatus 2.

Workpieces 1 such as semiconductor wafers, for example, that have been thinned down by the grinding and polishing apparatus 2 are divided into individual device chips. The device chips will be incorporated in electronic appliances such as smartphones and personal computers (PCs). In recent years, since such electronic appliances have a greater tendency to be smaller in size and higher in functionality, it is important that the device chips to be incorporated therein be of highly stable quality. For example, a workpiece 1 that has been thinned down is required to have high total thickness uniformity or low TTV. However, when the grinding units 32a and 32b grind a workpiece 1 under predetermined conditions, the processed surface, i.e., the reverse side 1b of the ground workpiece 1 may not be flat as desired due to its own thickness variations or the state of the grinding and polishing apparatus 2. For example, the processed surface of the ground workpiece 1 may be of a protruding shape with its center higher than a peripheral portion thereof or may be of a protruding shape with its center lower than a peripheral portion thereof.

FIG. 8A schematically illustrates, in cross section, a workpiece 5 whose processed surface, i.e., reverse side 5b, has been ground into a recessed shape with its center 5c lower than a peripheral portion thereof. FIG. 8B schematically illustrates, in cross section, a workpiece 7 whose processed surface, i.e., reverse side 7b, has been ground into a protruding shape with its center 7c lower than a peripheral portion thereof. In FIGS. 8A and 8B, the cross-sectional shape of the processed surfaces 5b and 7b is illustrated as obliquely straight from the centers 5c and 7c toward their outer circumferential edges. However, the cross-sectional shape of the processed surfaces 5b and 7b may not necessarily be straight. The processed surfaces, i.e., the reverse sides 5b and 7b, that are recessed and protruding in shape have no uniform thickness, and hence the distances between the reverse sides 5b and 7b and corresponding face sides 5a and 7a of the workpieces 5 and 7 are not uniform. If a workpiece 1 having a processed surface whose height is not uniform is polished under general conditions by the polishing unit 60, the polished processed surface thereof has a height that is not uniform and hence is not flat. Therefore, it has been desirous, in the art of processing a workpiece 1, of the thickness of the workpiece 1 uniform.

The processed surfaces of workpieces 1 have uneven height variations. Consequently, when workpieces 1 of one type are processed under the same processing conditions, the processed surfaces of the workpieces 1 cannot be made flat. With the method of processing a workpiece according to the present embodiment, polishing conditions for a workpiece 1 that has been ground are selected in a manner to match the state of the workpiece 1, and then the workpiece 1 is polished under the selected polishing conditions. The method of processing a workpiece according to the present embodiment will be described in detail below.

In the method of processing a workpiece according to the present embodiment, a workpiece 1 is processed using the chuck table 18, the grinding units 32a and 32b, the polishing unit 60, and the measuring unit 72. The method of processing a workpiece according to the present embodiment is carried out on the grinding and polishing apparatus, i.e., a processing apparatus, 2. An example in which the workpiece 1 is processed on the grinding and polishing apparatus 2 will be described below. However, the method of processing a workpiece according to the present embodiment may not be carried out on the grinding and polishing apparatus 2. FIG. 12 is a flowchart of the sequence of the steps of the method of processing a workpiece according to the embodiment.

The method of processing a workpiece according to the embodiment begins with a grinding step S10. FIG. 3 schematically illustrates, in perspective, the manner in which the grinding step S10 is carried out. FIG. 4 schematically illustrates, in side elevation, partly in cross section, the workpiece 1 immediately after the grinding step S10 has started. FIG. 5 schematically illustrates, in side elevation, partly in cross section, the workpiece 1 that has been thinned down in the grinding step S10. In the grinding step S10, the workpiece 1 is ground from the processed surface, i.e., the reverse side 1b, thereof by the grinding units 32a and 32b. The workpiece 1 is thinned down to a predetermined thickness by carrying out the grinding step S10. The grinding step S10 is carried out in two stages involving a coarse-grinding process and a finish-grinding process. The grinding unit 32a performs the coarse-grinding process on the workpiece 1, whereas the grinding unit 32b performs the finish-grinding process on the workpiece 1.

The grinding step S10 will be described in detail below. The grinding and polishing apparatus 2 operates to remove a workpiece 1 from one of the cassettes 8 and 10 and place the workpiece 1 on the holding surface 18a of the chuck table 18 in the delivery position A. In the course of moving the workpiece 1 from one of the cassettes 8 and 10 to the chuck table 18, the positioning mechanism 12 adjusts the position of the workpiece 1 and the delivery unit 14 delivers the workpiece 1, bringing the center of the workpiece 1 and the center of the holding surface 18a of the chuck table 18 into alignment with each other. The workpiece 1 is then held under suction on the chuck table 18 with the protective member 3 interposed therebetween. Thereafter, the turntable 16 is turned counterclockwise as viewed in plan about its central axis, bringing the chuck table 18 that is holding the workpiece 1 under suction into the coarse-grinding position B. In other words, the chuck table 18 is moved to a position below the grinding unit 32a.

Thereafter, while grinding water such as pure water is being supplied to the workpiece 1 and the grinding wheel 38a, the workpiece 1 and the grinding wheel 38a are rotated relatively to each other, and the grindstones 40a of the grinding wheel 38a are brought into abrasive contact with the reverse side 1b of the workpiece 1. In this manner, the coarse-grinding process is performed on the workpiece 1. Then, the turntable 16 is turned to bring the chuck table 18 that is holding the workpiece 1 to the finish-grinding position C. In other words, the chuck table 18 is moved to a position below the grinding unit 32b. Thereafter, while grinding water such as pure water is being supplied to the workpiece 1 and the grinding wheel 38b, the workpiece 1 and the grinding wheel 38b are rotated relatively to each other, and the grindstones 40b of the grinding wheel 38b are brought into abrasive contact with the reverse side 1b, i.e., the upper surface, of the workpiece 1. In this manner, the finish-grinding process is performed on the workpiece 1.

When the workpiece 1 is ground in the two stages, the grinding unit 32a performs the coarse-grinding process on the workpiece 1 at a high speed, and the grinding unit 32b performs the finish-grinding process on the workpiece 1 with precision. Specifically, in each of the two stages of the grinding step S10, the thickness of the workpiece 1 may be monitored by the measuring unit 72, and the grinding units 32a and 32b may stop grinding the workpiece 1 when the workpiece 1 has been ground to predetermined thicknesses in the coarse-grinding process and the finish-grinding process. For thinning down the workpiece 1 to a predetermined finished thickness on the grinding and polishing apparatus 2, the coarse-grinding process is performed on the workpiece 1 by the grinding unit 32a to grind off most of a total workpiece material planned to be removed from the workpiece 1, and then the finish-grinding process is performed on the workpiece 1 by the grinding unit 32b to remove a damaged layer produced in the coarse-grinding process from the workpiece 1, thereby thinning down the workpiece 1 to the predetermined finished thickness.

In the grinding step S10, the measuring unit 72 measures the thickness of the workpiece 1 in an annular range thereon that is spaced a constant distance from the center of the reverse side 1b of the workpiece 1. Specifically, the measuring unit 72 measures the height of the reverse side 1b of the workpiece 1 in an annular range thereon that underlies the measuring instrument 78 of the measuring unit 72, and measures the thickness of the workpiece 1 in the annular range. Stated otherwise, the measuring unit 72 does not measure the thickness of the workpiece 1 in an entire range thereon in the grinding step S10. Particularly, while the grinding of the workpiece 1 is in progress, since the grindstones 40a and 40b keep contacting the workpiece 1 in the vicinity of the center of the processed surface, i.e., the reverse side 1b, thereof, the measuring instrument 78 is unable to move in overlapping relation to an area of the workpiece 1 in the vicinity of the center of the processed surface thereof. In other words, the measuring unit 72 is unable to measure the thickness of the workpiece 1 in the vicinity of the center thereof during the grinding of the workpiece 1.

When the grinding step S10 is completed, the reverse side 1b of the workpiece 1 may not necessarily be flat. In other words, the thickness of the workpiece 1 may not necessarily be uniform over the entire area of the workpiece 1. One solution would be to correct the shape of the processed surface of the workpiece 1 in a polishing step S30 to be subsequently carried out. However, as the shape of the processed surface of the workpiece 1 varies depending on the quality accuracy of the workpiece 1 and the state of the grinding and polishing apparatus 2, the shape of the processed surface is not rendered constant. In view of these difficulties, the grinding step S10 is followed by a measuring step S20 to be described below. In the measuring step S20, the measuring unit 72 measures the thicknesses of the workpiece 1 at a plurality of measurement sites thereon to acquire information with respect to a thickness distribution of the workpiece 1. FIG. 6 schematically illustrates, in plan, the positional relation between the measuring instrument 78 and the workpiece 1 in the measuring step S30. FIG. 7 schematically illustrates in side elevation, partly in cross section, the workpiece 1 whose thickness is measured by the measuring unit 72.

When the measuring unit 72 is used to measure the height of the processed surface, i.e., the reverse side 1b, of the workpiece 1, the measuring unit 72 cannot make measurements simultaneously on the entire processed surface of the workpiece 1. In the first place, it is not necessary to measure the height of the processed surface of the workpiece 1 in the entire range thereof in acquiring information with respect to a thickness distribution of the workpiece 1. Instead, by measuring the thicknesses of the workpiece 1 at a plurality of measurement sites on the processed surface thereof and obtaining the thicknesses of the workpiece 1 at the measurement sites, it is possible to infer the shape of the processed surface of the workpiece 1 and acquire sufficient information with respect to a thickness distribution of the workpiece 1.

In the measuring step S20, the measuring instrument 78 is positioned in overlying relation to the processed surface, i.e., the reverse side 1b, of the workpiece 1, as illustrated in FIGS. 6 and 7. For measuring the thickness of the workpiece 1 using the measuring unit 72 at the finish-grinding position C, the grinding wheel 38b of the grinding unit 32b is retracted away from the space above the workpiece 1 so that the measuring instrument 78 can be positioned in vertical alignment with the center of the processed surface of the workpiece 1. Then, the measuring instrument 78 is energized to measure the height of the processed surface of the workpiece 1 in the vicinity of the center of the processed surface of the workpiece 1. The thickness of the workpiece 1 can be calculated by subtracting the height of the holding surface 18a of the chuck table 18 from the height of the processed surface of the workpiece 1. Stated otherwise, measuring the height of the processed surface in the vicinity of the center of the workpiece 1 is synonymous with measuring the thickness of the workpiece 1 in that area.

Then, the measuring instrument 78 of the measuring unit 72 is moved. For example, the measuring instrument 78 is moved to a position overlying an area between the center of the processed surface of the workpiece 1 and an outer circumferential portion of the workpiece 1, as indicated by a two-dot chain line circular spot that is spaced radially outwardly from the center in FIG. 6. Then, the measuring instrument 78 is energized to measure the height of the processed surface of the workpiece 1 at the circular spot. In other words, the thickness of the workpiece 1 is measured at the circular spot. Thereafter, the measuring instrument 78 of the measuring unit 72 is further moved. For example, the measuring instrument 78 is further moved to a position near an outer circumferential edge of the workpiece 1, as indicated by another two-dot chain line circular spot at the outer circumferential edge of the workpiece 1. In other words, the thickness of the workpiece 1 is measured at the other circular spot.

In this manner, the measuring unit 72 measures the thicknesses of the workpiece 1 at a plurality of measurement sites thereon, thereby acquiring information with respect to a thickness distribution of the workpiece 1. In the measuring step S20, the measuring instrument 78 may be moved to positions overlying other areas of the workpiece 1 for measuring the height of the processed surface of the workpiece 1 and hence the thickness of the workpiece 1 at those areas of the workpiece 1.

While the thickness of the workpiece 1 is being measured in the measuring step S20, the chuck table 18 may be rotated about its central axis perpendicular to the holding surface 18a thereof. For example, the chuck table 18 may be rotated at a rotational speed ranging from approximately 60 to 750 rpm. Because of the nature of the grinding processes performed on the workpiece 1 in the grinding step S10, the height of the processed surface of the workpiece is likely to become even in areas that are spaced equal distances from the center of the processed surface. Therefore, the measuring instrument 78 should make a plurality of measurements while the chuck table 18 is rotated, and the obtained measured values should be averaged. The averaged value represents a value that better reflects the real height of the processed surface of the workpiece 1 at an area spaced a certain distance from the center of the processed surface, i.e., a value where the adverse effect of thickness variations is reduced. However, the chuck table 18 may not be rotated about its central axis in the measuring step S20.

When the measuring step S20 is carried out, it can be found from the measured values whether the processed surface, i.e., the reverse side 1b, of the workpiece 1 is of a recessed shape with its center lower than a peripheral portion thereof or of a protruding shape with its center higher than a peripheral portion thereof. It can also be found how much the center of the ground reverse side 1b of the workpiece 1 is lower or higher than the peripheral portion thereof. In this manner, the measuring step S20 is able to acquire information with respect to a thickness distribution of the workpiece 1. However, the information with respect to the thickness distribution of the workpiece 1 is not limited to the type described above, and may be of other types. For example, the information with respect to the thickness distribution of the workpiece 1 may be represented by a cluster of the positions of a plurality of measurement sites on the reverse side 1b of the workpiece 1 and the heights of the reverse side 1b at the measurement sites. Alternatively, the information with respect to the thickness distribution of the workpiece 1 may be represented otherwise. At any rate, the information with respect to the thickness distribution of the workpiece 1 that has been acquired from the measuring step S20 may be registered in the storage section 90 of the controller 88 of the grinding and polishing apparatus 2. In the method of processing a workpiece according to the present embodiment, the information with respect to the thickness distribution of the workpiece 1 will be used in the polishing step S30 to be described below.

In the method of processing a workpiece according to the present embodiment, the polishing step S30 is carried out after the measuring step S20. In the polishing step S30, the workpiece 1 is polished from the processed surface, i.e., the reverse side 1b, thereof by the polishing unit 60. The workpiece 1 that has been ground may be polished for the purpose of removing miniscule surface irregularities formed on the processed surface of the workpiece 1 upon being ground, thereby planarizing the processed surface to a mirror finish. In the method of processing a workpiece according to the present embodiment, moreover, a relatively thick portion of the workpiece 1 is polished with a high level of intensity and a relatively thin portion of the workpiece 1 is polished with a low level of intensity to make the thickness of the workpiece 1 closer to uniformity.

FIG. 9 schematically illustrates in side elevation, partly in cross section, the manner in which the polishing step S30 is carried out. In the polishing step S30, the turntable 16 is turned to bring the chuck table 18 that is holding the workpiece 1 under suction from the finish-grinding position C to the polishing position D. In other words, the workpiece 1 is moved to a position below the polishing unit 60. Then, the chuck table 18 and the polishing pad 66 are rotated relatively to each other, and the lower surface of the polishing pad 66 is brought into polishing contact with the processed surface, i.e., the reverse side 1b, of the workpiece 1 that is exposed upwardly. The processed surface of the workpiece 1 is now polished by the polishing pad 66. At this time, the workpiece 1 and the polishing pad 66 may be supplied with a polishing liquid containing abrasive grains via the supply passage 86. Alternatively, while the workpiece 1 is being polished, the workpiece 1 and the polishing pad 66 may not be supplied with a polishing liquid containing abrasive grains. In the method of processing a workpiece according to the present embodiment, the XZ-axis moving mechanism 42 may be actuated to continuously move the polishing pad 66 along directions generally parallel to the X-axis, i.e., the processed surface of the workpiece 1. Specifically, the polishing pad 66 may be periodically oscillated with respect to the workpiece 11 by moving the spindle 64 back and forth between opposite ends of a stroke diametrically across the workpiece 1, as indicated by the double-headed arrow in FIG. 9.

Particularly, in the polishing step S30, the workpiece 1 is polished under polishing conditions that are determined on the basis of the information with respect to the thickness distribution of the workpiece 1 that has been acquired in the measuring step S20. For example, the controller 88 reads polishing conditions favorable for uniformizing the thickness of the workpiece 1 from among the polishing conditions registered in the storage section 90, on the basis of the information with respect to the thickness distribution of the workpiece 1 that has been acquired in the measuring step S20. Then, the controller 88 controls the polishing unit 60 to keep polishing the workpiece 1 under the polishing conditions thus read.

More specifically, the storage section 90 stores various examples of thickness distributions of workpieces 1 and polishing conditions favorable for uniformizing the thicknesses of the workpieces 1 having the thickness distributions according to the examples, registered in association with each other. The controller 88 compares the thickness distribution represented by the information acquired in the measuring step S20 with the various examples of thickness distributions stored in the storage section 90. The controller 88 selects and reads polishing conditions favorable for uniformizing the thickness of the workpiece 1 having the thickness distribution represented by the information from among the polishing conditions stored in the storage section 90. Then, the controller 88 determines a rotational speed for the polishing pad 66, a rotational speed for the chuck table 18, a rate at which to supply the polishing liquid, and a speed at which to lower the polishing unit 60, for example, according to the polishing conditions read from the storage section 90. Thereafter, the processing control section 92 of the controller 88 controls the polishing unit 60 and other components according to the read polishing conditions or parameters to polish the workpiece 1. The method of processing a workpiece according to the present embodiment is thus able to polish the processed surface of the workpiece 1 to uniformize the thickness thereof in a manner to match the state of the processed surface, i.e., the reverse side 1b, of the workpiece 1, so that the workpiece 1 will finally have a uniform level of thickness.

In a case where the workpiece 1 is to be polished by the polishing pad 66 while the chuck table 18 that is holding the workpiece 1 and the polishing pad 66 are being oscillated relatively to each other along directions generally parallel to the X-axis, i.e., the processed surface of the workpiece 1, conditions for oscillating the workpiece 1 and the polishing pad 66 relatively to each other are established. For example, the polishing conditions stored in the storage section 90 include distances by which the workpiece 1 and the polishing pad 66 are to be oscillated relatively to each other and central positions across which the workpiece 1 and the polishing pad 66 are to be oscillated relatively to each other. For polishing the workpiece 1, a distance by which the workpiece 1 and the polishing pad 66 are to be oscillated relatively to each other and a central position across which the workpiece 1 and the polishing pad 66 are to be oscillated relatively to each other are determined from the polishing conditions read from the storage section 90. In the polishing step S30, the processing control section 92 controls the polishing pad 66 to be oscillated according to the distance and the central position that have been thus determined. The workpiece 1 and the polishing pad 66 that are thus oscillated relatively to each other contribute to making the thickness of the workpiece 1 more uniform in the polishing step S30.

The polishing conditions may not include values that are directly indicative of the distances and the central positions referred to above. The polishing conditions that include the distances and the central positions refer to polishing conditions represented in formats that make it possible to derive distances and central positions. For example, the polishing conditions may include the positions of opposite ends of a stroke along which the polishing pad 66, i.e., the spindle 64, is to oscillate diametrically across the workpiece 1. From the positions of the opposite ends, there can be derived a stroke along which the polishing pad 66, i.e., the spindle 64, is to oscillate, a distance that the polishing pad 66, i.e., the spindle 64, is to move, and a central position across which the polishing pad 66, i.e., the spindle 64, is to oscillate. In other words, distances that the polishing pad 66, i.e., the spindle 64, is to move and central positions across which the polishing pad 66, i.e., the spindle 64, is to oscillate may be registered in the storage section 90 as values for deriving the positions of opposite ends of strokes along which the polishing pad 66, i.e., the spindle 64, is to oscillate and central positions across which the polishing pad 66, i.e., the spindle 64, is to oscillate.

Moreover, a central position across which the polishing pad 66, i.e., the spindle 64, is to oscillate may be represented by the distance between a reference position to be described below and such a central position. The distance may be registered in the storage section 90 as a value for deriving the central position. The reference position refers to the relative positions of the polishing pad 66 and the workpiece 1 at the time when the workpiece 1 has its outer circumferential edge inscribed in the outer circumferential edge of the polishing pad 66 on the processed surface of the workpiece 1, for example.

FIG. 10A schematically illustrates, in plan, by way of example, the positional relation between the polishing pad 66 and the workpiece 1 at the time when the workpiece 1 has its outer circumferential edge inscribed in the outer circumferential edge of the polishing pad 66 on the processed surface of the workpiece 1. In the example illustrated in FIG. 10A, the diameter of the workpiece 1 is one half of the diameter of the polishing pad 66. As viewed vertically along the Z-axis, the outer circumferential edge, denoted by 1d, of the workpiece 1 is inscribed in the outer circumferential edge, denoted by 66d, of the polishing pad 66, and overlies the center, denoted by 66c, of the polishing pad 66. The positional relation between the workpiece 1 and the polishing pad 66 as illustrated in FIG. 10A, for example, is referred to as a reference position. The storage section 90 registers therein the distances between reference positions and central positions across which the polishing pad 66, i.e., the spindle 64, is to oscillate as values indicative of central positions across which the polishing pad 66, i.e., the spindle 64, is to oscillate as well as distances that the polishing pad 66, i.e., the spindle 64, is to oscillate. However, the method of processing a workpiece according to the present embodiment is not limited to such details, and central positions across which the polishing pad 66, i.e., the spindle 64, is to oscillate may be stored in another format in the storage section 90.

The relation between relative oscillating movement of the polishing pad 66 and the chuck table 18 at the time when the polishing process is performed on workpieces 1 and results of the polishing process will be described below. Specifically, changes caused in the results of the polishing process on workpieces 1 by different modes of oscillating movement will be described in detail below. Particularly, an experiment conducted to polish workpieces 1 while the polishing pad 66 is being oscillated under various conditions will be described below. In the experiment, a plurality of semiconductor wafers shaped as circular plates, each having a diameter of 150 mm, were prepared as workpieces 1 and polished by a polishing pad 66 having a diameter of 300 mm. Polished-off quantities removed from portions of the workpieces 1 were calculated by subtracting the thicknesses of the portions, i.e., the heights of processed surfaces, of the workpieces 1 that were polished from the thicknesses of the portions of the workpieces 1 to be polished. The polished-off quantities were assessed when the workpieces 1 were polished while the polishing pad 66 was being oscillated and when the workpieces 1 were polished while the polishing pad 66 was not being oscillated.

FIG. 11 is a graph illustrating the results of the experiment. The graph of FIG. 11 has a horizontal axis representing positions on the workpieces 1 shaped as circular plates. Specifically, the horizontal axis of the graph represents the coordinates of measurement sites or positions along a straight line passing through the center 1c of the processed surface, i.e., the reverse side 1b, of the workpiece 1, where the center 1c is indicated by position 0 and the straight line includes a portion extending from a position of 0 to the right through positive positions in a positive direction and a portion extending from the position of 0 to the left through negative positions in a negative direction. A position of 75 mm (+75 mm) on the horizontal axis represents one outer circumferential edge 1d of the workpiece 1 on the straight line, and a position of −75 mm on the horizontal axis represents a diametrically opposite outer circumferential edge 1d of the workpiece 1 on the straight line. The graph of FIG. 11 has a vertical axis representing polished-off quantities removed from the workpiece 1 when it is polished. For example, a polished-off quantity of 4.5 μm on the vertical axis at a certain measurement site means that a thickness of 4.5 μm has been removed from the workpiece 1 at the measurement site. Stated otherwise, it means that the height of the processed surface of the workpiece 1 has been reduced by 4.5 μm after the workpiece 1 was polished at the measurement site. The larger the polished-off quantity is on the vertical axis, the more the material is removed from the workpiece when the workpiece is polished. Conversely, the smaller the polished-off quantity is on the vertical axis, the less the material is removed from the workpiece when the workpiece is polished.

First, an instance where the polishing pad 66 polished the workpiece 1 without being oscillated will be described below. In particular, the results of the polishing process in a case where the workpiece 1 has its outer circumferential edge 1d inscribed in the outer circumferential edge 66d of the polishing pad 66 as viewed in plan in FIG. 10A will be described below. In this case, if the direction oriented from the center 1c of the workpiece 1 toward the center 66c of the polishing pad 66 is regarded as a positive direction and the center 66c of the polishing pad 66 is at a position of 0 mm, then the center 1c of the workpiece 1 is at a position of −75 mm. In other words, the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 are spaced apart from each other by a distance 94 (see FIG. 10A) of 75 mm. In the graph of FIG. 11, the measured results of the instance are represented by solid triangular dots. As can be understood from the graph, these results indicate that the polished-off quantities are relatively larger in the vicinity of the center 1c of the workpiece 1 and progressively smaller toward the outer circumferential edges 1d of the workpiece 1.

Next, the results of a polishing process in a case where the center 1c of the workpiece 1 is shifted farther from the center 66c of the polishing pad 66 to the extent that a portion of the outer circumferential edge 1d of the workpiece 1 is not covered with the polishing pad 66, as illustrated in FIG. 10B, will be described below. For example, if the center 66c of the polishing pad 66 is at the position of 0 mm, then the center 1c of the workpiece 1 is at a position of −100 mm. In other words, the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 are spaced apart from each other by a distance 96 (see FIG. 10B) of 100 mm. In this case, the polishing pad 66 is not oscillated either. In the graph of FIG. 11, the measured results of this instance are represented by solid square dots. As can be understood from the graph, these results indicate that the polished-off quantities are relatively smaller in the vicinity of the center 1c of the workpiece 1 and progressively larger toward the outer circumferential edges 1d of the workpiece 1.

It can be seen from these results that even if the polishing pad 66 is not oscillated, the results of the polishing processes are opposite each other depending on the positional relation between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66. Since the results of the polishing processes tend to vary greatly when the positional relation between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 are changed, it is not easy to adjust the positional relation in order to achieve desired polishing process results.

Now, an instance where the polishing pad 66 is oscillated will be described below. First, described is a case in which the polishing pad 66 is oscillated to move the position of the center 1c of the workpiece 1 in the range of −75 to −95 mm when the center 66c of the polishing pad 66 is in the position of 0 mm. In this case, the polishing pad 66 is oscillated to keep the distance between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 in the range of 75 to 95 mm. In the graph of FIG. 11, the measured results of this instance are represented by negative marks (−). In this case, it can be understood from the graph that the polished-off quantities are relatively larger in the vicinity of the center 1c of the workpiece 1 and progressively smaller toward the outer circumferential edges 1d of the workpiece 1. However, when the distance 94 between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 is 75 mm, the polished-off quantities tend to be smaller as a whole than if the polishing pad 66 is not oscillated, resulting in a relatively small difference between the polished-off quantities in an area where the polished-off quantities are maximum and the polished-off quantities in an area where the polished-off quantities are minimum.

Next, described is a case in which the polishing pad 66 is oscillated to move the position of the center 1c of the workpiece 1 in the range of −75 to −100 mm when the center 66c of the polishing pad 66 is in the position of 0 mm. In this case, the polishing pad 66 is oscillated to keep the distance between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 in the range of 75 to 100 mm. In the graph of FIG. 11, the measured results of this instance are represented by lozenge-shaped marks. In this case, it can be understood from the graph that the polished-off quantities are relatively larger in the vicinity of the center 1c of the workpiece 1 and progressively smaller toward the outer circumferential edges 1d of the workpiece 1. However, the polished-off quantities tend to be further smaller as a whole, resulting in a further smaller difference between the polished-off quantities in an area where the polished-off quantities are maximum and the polished-off quantities in an area where the polished-off quantities are minimum.

Next, described is a case in which the polishing pad 66 is oscillated to move the position of the center 1c of the workpiece 1 in the range of −75 to −105 mm when the center 66c of the polishing pad 66 is in the position of 0 mm. In this case, the polishing pad 66 is oscillated to keep the distance between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 in the range of 75 to 105 mm. In the graph of FIG. 11, the measured results of this instance are represented by positive marks (+). In this case, it can be understood from the graph that the polished-off quantities exhibit no significant differences in the overall ground surface of the workpiece 1. If anything, the polished-off quantities are slightly larger in the vicinity of the center 1c of the workpiece 1 than surrounding areas.

Next, described is a case in which the polishing pad 66 is oscillated to move the position of the center 1c of the workpiece 1 in the range of −75 to −110 mm when the center 66c of the polishing pad 66 is in the position of 0 mm. In this case, the polishing pad 66 is oscillated to keep the distance between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 in the range of 75 to 110 mm. In the graph of FIG. 11, the measured results of this instance are represented by cross marks (x). In this case, it can be understood from the graph that the polished-off quantities exhibit no significant differences in the overall ground surface of the workpiece 1. If anything, the polished-off quantities are slightly smaller in the vicinity of the center 1c of the workpiece 1 than surrounding areas.

Next, described is a case in which the polishing pad 66 is oscillated to move the position of the center 1c of the workpiece 1 in the range of −75 to −115 mm when the center 66c of the polishing pad 66 is in the position of 0 mm. In this case, the polishing pad 66 is oscillated to keep the distance between the center 1c of the workpiece 1 and the center 66c of the polishing pad 66 in the range of 75 to 115 mm. In the graph of FIG. 11, the measured results of this instance are represented by blank circular dots. In this case, it can be understood from the graph that the polished-off quantities are relatively smaller in the vicinity of the center 1c of the workpiece 1 and progressively larger toward the outer circumferential edges 1d of the workpiece 1.

As described above, when the conditions for oscillating the polishing pad 66 are changed, the polished-off quantities of portions of the processed surface, i.e., the reverse side 1b, of the workpiece 1 vary. Even if the thickness of the workpiece 1 is not uniform after the grinding step S10, the shape of the processed surface of the workpiece 1 can be corrected by selecting polishing conditions, in the polishing step S30, that match the shape of the processed surface of the workpiece 1.

For example, if the information with respect to the thickness distribution of the workpiece 1 that has been acquired in the measuring step S20 indicates that the area of the workpiece 1 in the vicinity of the center 1c is thicker than the surrounding areas, then it is preferable to relatively reduce the range of oscillating movement of the polishing pad 66 in the polishing step S30. Conversely, if the information with respect to the thickness distribution of the workpiece 1 that has been acquired in the measuring step S20 indicates that the area of the workpiece 1 in the vicinity of the center 1c is thinner than the surrounding areas, then it is preferable to relatively increase the range of oscillating movement of the polishing pad 66 in the polishing step S30. The range of oscillating movement of the polishing pad 66 may be selected depending on the difference between the height of a highest area of the processed surface of the workpiece 1 and the height of a lowest area of the processed surface of the workpiece 1.

In the experiment described above, one end of the stroke of oscillating movement is shared by all the cases whereas the other end the stroke of oscillating movement is different in all the cases. However, it is not necessary to keep one end of the stroke of oscillating movement at a fixed position. Rather, various results of polishing processes can be acquired by varying the opposite ends of strokes of oscillating movement. Specifically, by oscillating the polishing pad 66 in the polishing step S30, the polished-off quantities of portions of the workpiece 1 can be adjusted more finely to correct the shape of the processed surface of the workpiece 1 that has been ground in greater detail.

The experiment described above is by way of example only, and the results of polishing processes are variable depending on the material, size, and thickness of the workpiece 1, the material, size, and thickness of the polishing pad 66, i.e., the polishing layer 84, the rotational speed of the chuck table 18, the rotational speed of the polishing pad 66, and the temperature of a processing chamber in which polishing processes take place. It is therefore preferable for the grinding and polishing apparatus, i.e., the processing apparatus, 2 to process workpieces 1 under varying polishing conditions in test-run polishing processes, assess the results of the processing processes, and register the assessed results in the storage section 90. The manufacturer of the grinding and polishing apparatus 2 may process workpieces 1 in test-run polishing processes and register the polishing process results in the storage section 90 in advance. Alternatively, the user of the grinding and polishing apparatus 2 may periodically process workpieces 1 in test-run polishing processes and register the polishing process results in the storage section 90. At any rate, once the results of various test-run polishing processes together with polishing conditions used therein have been registered in the storage section 90, it is possible to select polishing conditions for achieving polishing process results closer to desired polishing process results.

As described above, the method of processing a workpiece according to the present embodiment makes it possible to polish workpieces 1 to uniformize the thicknesses thereof by determining polishing conditions based on the thickness distributions of the individual workpieces 1, i.e., the distribution of the heights of the processed surfaces of the workpieces 1.

When a workpiece 1 is polished, the thickness of the workpiece 1 is uniformized and surface irregularities of the processed surface, i.e., the reverse side 1b, of the workpiece 1 are removed, thereby planarizing the processes surface to a mirror finish. Thereafter, the turntable 16 is turned about its central axis to move the chuck table 18 that is holding the workpiece 1 to a position where the delivery unit 68 can gain access to the workpiece 1. Then, the chuck table 18 releases the workpiece 1 from its suction-assisted hold, and the delivery unit 68 delivers the workpiece 1 to the cleaning unit 70. The cleaning unit 70 then cleans the workpiece 1. Thereafter, the delivery unit 6 stores the workpiece 1 back into one of the cassettes 8 and 10. When the workpieces 1 stored in and supplied from the cassettes 8 and 10 are successively processed in the method of processing a workpiece according to the present embodiment, since the workpieces 1 are polished in a manner to match the shapes of the individual workpieces 1 that have been ground, the polished workpieces 1 have their thicknesses highly uniformized.

The present invention should not be limited to the details of the embodiment described above, and covers various changes and modifications thereof. According to the above embodiment, for example, workpieces 1 are processed, i.e., polished, in test-run polishing processes, polishing process results are stored in the storage section 90, and the stored polishing process results are used in selecting polishing conditions for use in the polishing step S30. According to the present invention, the method of processing a workpiece is not limited to such details of the embodiment. For example, when the grinding and polishing apparatus 2 processes a large number of workpieces 1, it acquires information with respect to thickness distributions of the workpieces 1 in the measuring step S20 before and after the polishing step S30. In this fashion, information with respect to changes in the thickness distributions of the workpieces 1 after the polishing step S30 can be accumulated. In other words, rather than performing test-run polishing processes, real polishing processes are performed on the workpieces 1 under polishing conditions, and the results of the polishing processes and the polishing conditions are accumulated in the storage section 90. The stored information can be used in selecting appropriate polishing conditions for polishing workpieces 1 subsequently.

According to the above embodiment, moreover, the method of processing a workpiece that is carried out by the processing apparatus, i.e., the grinding and polishing apparatus 2, that includes both the grinding units 32a and 32b and the polishing unit 60 has been described by way of example. However, the present invention is not limited to the method described above. The method of processing a workpiece according to an aspect of the present invention may be carried out using both a grinding apparatus including the grinding units 32a and 32b and a polishing apparatus including the polishing unit 60. In the latter case, the grinding step S10 and the measuring step S20 are performed by the grinding apparatus, after which the polishing step S30 is performed by the polishing apparatus. Specifically, a workpiece 1 is ground and information with respect to a thickness distribution of the workpiece is acquired by the grinding apparatus, and thereafter the workpiece 1 is transferred to the polishing apparatus and polished by the polishing apparatus. The information acquired by the grinding apparatus is transmitted to the polishing apparatus via a wired or wireless communication link or a storage medium such as a nonvolatile memory. The polishing apparatus polishes the workpiece 1 under polishing conditions that are determined on the basis of the information.

In this case, the grinding apparatus and the polishing apparatus that have their components disposed in their respective housings that are separate from each other function as one processing apparatus, i.e., one processing system to carry out the method according to the aspect of the invention. The grinding apparatus and the polishing apparatus may be installed respectively in factories built on sites that are different from each other or may be installed in one factory. In a case where the grinding apparatus and the polishing apparatus function as one processing apparatus, the controller 88 that includes the storage section 90 may be included in the grinding apparatus or the polishing apparatus, or two controllers may be included respectively in the grinding apparatus and the polishing apparatus. Further alternatively, the controller 88 may not be included in the grinding apparatus and the polishing apparatus, and may be included in a managing apparatus connected to apparatuses that belong to a factory or factories that include the grinding apparatus and the polishing apparatus. In the latter case, the grinding apparatus, the polishing apparatus, and the managing apparatus function as a processing apparatus, i.e., a processing system, used to carry out the method of processing a workpiece according to an aspect of the present invention.

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.

METHOD OF PROCESSING WORKPIECE

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