Method of processing wafer

A method of processing a wafer having a first surface and a second surface opposite the first surface is provided. The method includes the steps of: holding the second surface of the wafer such that the first surface thereof is exposed; processing an exposed first surface side of an outer circumferential edge portion of the wafer with a processing tool including a grinding stone made of abrasive grains bound together by a bonding material, thereby forming on the outer circumferential edge portion a slanted surface that is inclined to the first surface so as to be progressively closer to the second surface in a direction from a central area of the wafer toward an outer circumferential edge thereof; and coating the first surface of the wafer with a liquid material according to a spin coating process, thereby forming a resist film on the first surface of the wafer.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of processing a wafer.

Description of the Related Art

Electronic devices represented by mobile phones and personal computers include as indispensable components device chips having devices such as electronic circuits. Device chips are fabricated by demarcating the face side of a wafer made of a semiconductor such as silicon into a plurality of areas along projected dicing lines known as streets, forming devices in the respective areas, and then dividing the wafer along the projected dicing lines.

The devices described above are generally formed by stacking metal films, insulating films, etc. on the wafer in a thickness direction thereof and processing the stacked films according to predetermined patterns corresponding to the devices. The metal films, the insulating films, etc. are processed, for example, by an etching process in which an etchant such as a highly reactive gas, a chemical solution, or the like is applied to a target film through a mask in the form of a resist film produced by coating the target film with a liquid material by a spin coating process (see, for example, Japanese Patent Laid-Open No. Hei 8-44064).

SUMMARY OF THE INVENTION

When the resist film is formed on the wafer by the spin coating process, the resist film tends to swell in a thicker shape or a granular shape on an outer circumferential edge portion of the wafer, and hence is highly likely to decrease in planarity. In the thicker swelling portion of the resist film, the solvent is not sufficiently removed by a subsequent prebaking process. Therefore, in a case where a contact-type exposure process is carried out to expose the resist film to light through a photomask held in contact with the resist film, the material of the resist film is liable to stick to the photomask.

In addition, a gas may be also trapped in the thicker swelling portion of the resist film. In a case where the gas is trapped in the thicker swelling portion of the resist film, the trapped gas tends to expand in a subsequent heating process, i.e., a heating process that is carried out to paste the wafer with the resist film formed thereon to another wafer, possibly bursting the thicker swelling portion of the resist film and contaminating the environment with resist film fragments.

It is therefore an object of the present invention to provide a method of processing a wafer in a manner to make it less likely to have a resist film swell on an outer circumferential edge portion of the wafer.

In accordance with an aspect of the present invention, there is provided a method of processing a wafer having a first surface and a second surface opposite the first surface, including the steps of: holding the second surface of the wafer such that the first surface thereof is exposed; after holding the second surface of the wafer, processing an exposed first surface side of an outer circumferential edge portion of the wafer with a processing tool including a grinding stone made of abrasive grains bound together by a bonding material, thereby forming on the outer circumferential edge portion a slanted surface that is inclined to the first surface so as to be progressively closer to the second surface in a direction from a central area of the wafer toward an outer circumferential edge thereof; and after forming the slanted surface, coating the first surface of the wafer with a liquid material according to a spin coating process, thereby forming a resist film on the first surface of the wafer.

Alternatively, in accordance with an aspect of the present invention, the processing tool includes a frustoconical cutting blade including a first side surface having a circular outer circumferential edge, a second side surface having a circular outer circumferential edge that is larger in diameter than the first side surface and positioned opposite the first side surface, and an outer circumferential surface formed of the grinding stone and connecting the outer circumferential edge of the first side surface and the outer circumferential edge of the second side surface to each other, the outer circumferential surface being inclined to the first side surface and the second side surface, and the step of forming the slanted surface includes the step of causing the cutting blade to cut into the outer circumferential edge portion of the wafer such that the second side surface of the cutting blade is positioned closer to the outer circumferential edge of the wafer.

Alternatively, in accordance with an aspect of the present invention, the processing tool includes a disk-shaped cutting blade including a first side surface having a circular outer circumferential edge, a second side surface having a circular outer circumferential edge and positioned opposite the first side surface, and an outer circumferential surface formed of the grinding stone and connecting the outer circumferential edge of the first side surface and the outer circumferential edge of the second side surface to each other, and the step of forming the slanted surface includes the step of causing the cutting blade to cut into the outer circumferential edge portion of the wafer while the cutting blade is being rotated by a rotational shaft inclined to the first surface of the wafer.

Further alternatively, in accordance an aspect of the present invention, the processing tool includes a grinding wheel having the grinding stone.

In the method of processing a wafer according to an aspect of the present invention, since the slanted surface that is inclined to the first surface so as to be progressively closer to the second surface in the direction from the central area of the wafer toward an outer circumferential edge thereof is formed on the first surface side of the outer circumferential edge portion of the wafer, when a liquid material that is to turn into a resist film is applied to the first surface of the wafer by a spin coating process, it is easy for the liquid material to flow down the slanted surface and drain off from the wafer11to the outside thereof, upon flowing from the central area of the wafer toward the outer circumferential edge thereof. In other words, as the liquid material is less likely to accumulate on the outer circumferential edge portion of the wafer, the possibility that the resist film formed from the applied liquid material will swell on the outer circumferential edge portion of the wafer is reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1illustrates in perspective a wafer11to be processed by a method of processing a wafer according to a first embodiment of the present invention. As illustrated inFIG. 1, the wafer11is made of a semiconductor such as silicon and is of a disk shape having a first surface11aand a second surface11bopposite the first surface11a, i.e., on the back side of the wafer11. Each of the first surface11aand the second surface11bis of a generally flat circular shape. In addition, the first surface11aand the second surface11bare joined to each other by an outer circumferential edge surface11ccurved by beveling.

The wafer11is free of devices such as electronic circuits. However, the method of processing a wafer according to the present embodiment is also able to process a wafer with devices formed thereon. The wafer11is not limited to any materials, structures, sizes, etc. For example, wafers made of other semiconductors, ceramics, resins, metals, or the like can be processed by the method of processing a wafer according to the present embodiment. Furthermore, the wafer11may be pasted to another wafer, a substrate, or the like in a subsequent step.

In the method of processing a wafer according to the present embodiment, the second surface lib of the wafer11is held in place such that the first surface11athereof is exposed (holding step).FIG. 2illustrates in cross section a manner in which the wafer11is held in place. InFIG. 2, some components are represented by symbols and a functional block.

The wafer11is held in place using a processing apparatus2illustrated inFIG. 2, for example. The processing apparatus2includes a chuck table, i.e., holding table,4configured to be able to hold the wafer11thereon. The chuck table4includes a cylindrical frame6made of a metal material such as stainless steel, for example, and having a recess defined in an upper surface thereof. The frame6has a fluid channel6adefined therein for transmitting a negative pressure to be used for attracting the wafer11under suction on the chuck table4.

The chuck table4also includes a porous plate8securely placed in the recess of the frame6. The porous plate8is made of ceramics and hence is rendered porous thereby. The porous plate8has an upper surface, i.e., holding surface,8afor holding the wafer11thereon. A suction source12such as a vacuum pump is connected through a valve10to the fluid channel6ain the frame6. When the valve10is opened while the suction source12is in operation, a vacuum pressure generated by the suction source12is transmitted through the valve10and the fluid channel6aand acts on the upper surface8aof the porous plate8.

A rotary actuator, not depicted, such as an electric motor is coupled to the frame6of the chuck table4. When the rotary actuator is energized, it generates and transmits rotational power to the frame6, rotating the chuck table4about a central axis generally perpendicular to the upper surface8aof the porous plate8. In addition, the frame6of the chuck table4is supported on a table moving mechanism, not depicted. The table moving mechanism moves the frame6in a first direction, i.e., a first horizontal direction, generally parallel to the upper surface8aof the porous plate8.

For holding the wafer11on the chuck table4, the second surface11bof the wafer11is brought into contact with the upper surface8aof the porous plate8, for example, as illustrated inFIG. 2. Then, the valve10is opened while the suction source12is in operation, allowing the vacuum pressure from the suction source12to act on the upper surface8aof the porous plate8. Accordingly, the second surface11bof the wafer11is attracted under suction to the upper surface8aof the porous plate8. In other words, the second surface11bof the wafer11is held under suction on the chuck table4with the first surface11aexposed upwardly.

According to the present embodiment, the second surface11bof the wafer11is held in direct contact with the upper surface8aof the porous plate8. However, a protective member such as a tape may be affixed to the second surface11bof the wafer11in advance. With the protective member affixed to the second surface11b, the second surface11bof the wafer11is held on the chuck table4with the protective member interposed therebetween and can be hence protected against damage due to contact with the porous plate8or the like.

After the second surface lib of the wafer11has been held on the chuck table4, an outer circumferential edge portion of the first surface11aof the wafer11is processed to form a slanted surface thereon (processing step).FIG. 3illustrates in cross section a manner in which a slanted surface11dis formed on the wafer11. InFIG. 3, some components are represented by symbols and a functional block.

The slanted surface11dis formed also using the processing apparatus2. As illustrated inFIG. 3, a cutting unit, i.e., a processing unit,14is disposed above the chuck table4. The cutting unit14includes a spindle16that has a central axis generally parallel to the upper surface8aof the porous plate8and generally perpendicular to the first direction. A cutting blade, i.e., a processing tool,18including a grinding stone made of abrasive grains bound together by a bonding material is mounted on one end of the spindle16.

The other end of the spindle16is coupled to a rotary actuator, not depicted, such as an electric motor. When the rotary actuator is energized, it generates and transmits rotational power to the spindle16, rotating the cutting blade18mounted on the other end of the spindle16about the central axis thereof. The cutting unit14is supported on a cutting unit moving mechanism, not depicted. The cutting unit moving mechanism moves the cutting unit14in a second direction, i.e., a second horizontal direction, generally parallel to the upper surface8aof the porous plate8and generally perpendicular to the first direction, and in a third direction, i.e., a vertical direction, generally perpendicular to the first direction and the second direction.

The cutting blade18is of a frustoconical shape including a first side surface18ahaving a circular outer circumferential edge and a second side surface18bhaving a circular outer circumferential edge that is larger in diameter than the first side surface18aand positioned opposite the first side surface18a, i.e., on the back side of the cutting blade18, for example. The outer circumferential edge of the first side surface18aand the outer circumferential edge of the second side surface18bare connected to each other by an outer circumferential surface18cinclined to both the first side surface18aand the second side surface18b. In addition, at least the outer circumferential surface18cis formed of a grinding stone made of abrasive grains such as diamond or the like bound together by a bonding material such as a resin.

The cutting blade18is mounted on the one end of the spindle16such that the first side surface18aand the second side surface18blie generally perpendicular to the axis of the spindle16. In other words, the first side surface18aand the second side surface18blie generally perpendicular to the second direction.

The width or thickness of the cutting blade18, i.e., the distance between the first side surface18aand the second side surface18b, is optionally set to a value matching the desired width of the slanted surface11dto be formed. For example, the slanted surface11dthat is of a sufficient width can easily be formed on the wafer11by using the cutting blade18whose width is in a range from 0.5 mm to 3.0 mm, typically of 1 mm.

For forming the slanted surface11don the wafer11, as illustrated inFIG. 3, the cutting blade18as it is rotated by the spindle16about the axis thereof is caused to cut into the outer circumferential edge portion of the wafer11that includes the boundary between the first surface11aand the outer circumferential edge surface11cof the wafer11. At this time, the cutting blade18is caused to cut into the outer circumferential edge portion of the wafer11such that the first side surface18aof the cutting blade18is positioned closer to the center of the wafer11and the second side surface18bof the cutting blade18is positioned closer to the outer circumferential edge of the wafer11. Then, the chuck table4is rotated to make one revolution about its own central axis.

The height of the cutting unit14at the time that the cutting blade18cuts into the wafer11is adjusted in such a range that only the outer circumferential surface18cof the cutting blade18contacts the wafer11. Specifically, for example, the height of the cutting unit14is adjusted such that the height of the lower end of the first side surface18aof the cutting blade18is equal to or larger than the height of the first surface11aof the wafer11and the height of the lower end of the second side surface18bof the cutting blade18is smaller than the height of the first surface11a.

The cutting blade18is thus allowed to cut into the first surface11aside of the outer circumferential edge portion of the wafer11, forming the slanted surface11dthat is joined to the first surface11awithout abrupt height differences. The slanted surface11dthus formed is inclined to the first surface11aso as to be progressively closer to the second surface lib of the wafer11in a direction from a central area of the wafer11toward an outer circumferential edge thereof.

Specifically, the height of the slanted surface11dis smaller on the outer circumferential edge surface11cside, i.e., on an outer side of the wafer11, than on the first surface11aside, i.e., on an inner side of the wafer11. The thickness of the wafer11in the outer circumferential edge portion thereof where the slanted surface11dis formed is smaller on the outer circumferential edge surface11cside than on the first surface11aside.

FIG. 4illustrates in enlarged fragmentary cross section the wafer11with the slanted surface11dformed thereon. As illustrated inFIG. 4, the angle Θ formed between the first surface11aand the slanted surface11dshould preferably be adjusted in a range from 10° to 25°, for example. The angle Θ thus adjusted is effective to keep sufficiently low the possibility that a resist film to be formed on the first surface11aof the wafer11will swell on the outer circumferential edge portion of the wafer11. Meanwhile, the width W of the slanted surface11d, i.e., the length of the slanted surface11dalong radial directions of the wafer11, is adjusted in a range from 0.5 mm to 3.0 mm. However, there is no particular limitation on the width W.

After the slanted surface11dhas been formed on the wafer11, a liquid material is applied to the first surface11aof the wafer11by a spin coating process, thereby forming a resist film on the first surface11aof the wafer11(resist film forming step).FIG. 5illustrates in cross section a manner in which a resist film is formed on the wafer11. The resist film is formed using a spin coater22illustrated inFIG. 5, for example.

As illustrated inFIG. 5, the spin coater22includes a hollow cylindrical housing24that houses the wafer11and the like therein. The housing24has therein a space24aas a processing chamber in which a resist film will be formed on the wafer11. A disk-shaped spinner table26that is smaller in diameter than the wafer11is disposed centrally in the space24a. The spinner table26has an upper surface, i.e., a holding surface,26afor holding the wafer11thereon.

A suction source, not depicted, such as a vacuum pump is connected to the upper surface26aof the spinner table26through a fluid channel, not depicted, defined in the spinner table26and a valve, not depicted. When the valve is opened while the suction source is in operation, a vacuum pressure generated by the suction source can be transmitted through the valve and the fluid channel and act on the upper surface26aof the spinner table26. A rotary actuator30such as an electric motor is coupled to a lower portion of the spinner table26through a spindle28. When the rotary actuator30is energized, it generates and transmits rotational power through the spindle28to the spinner table26, rotating the spinner table26about its own central axis.

The spin coater22also includes a nozzle32disposed above the spinner table26, for dropping a liquid material13from its distal end onto the first surface11aof the wafer11. The nozzle32has a proximal end coupled to a rotary actuator34such as an electric motor. When the rotary actuator34is energized, it generates and transmits rotational power to the nozzle32, moving the distal end of the nozzle32to follow an arcuate path over the spinner table26. When the liquid material13is to be dropped onto the wafer11, the distal end of the nozzle32is moved from a retracted region at an end of the space24ato a dropping region directly above the spinner table26.

For forming a resist film on the first surface11aof the wafer11, the second surface11bof the wafer11is brought into contact with the upper surface26aof the spinner table26, as illustrated inFIG. 5, for example. Then, the valve is opened while the suction source is in operation, applying the vacuum pressure to the upper surface26aof the spinner table26. The second surface11bof the wafer11is now attracted under suction to the upper surface26aof the spinner table26. In other words, the second surface11bof the wafer11is held under suction on the spinner table26with the first surface11aexposed upwardly.

Next, the distal end of the nozzle32is moved to the dropping region directly above the spinner table26. The nozzle32then drops the liquid material13from the distal end thereof onto the first surface11aof the wafer11held on the spinner table26. More specifically, the distal end of the nozzle32is positioned above a central area of the wafer11and drops the liquid material13onto the upper surface11aof the central area of the wafer11.

Then, the spinner table26is rotated about its own central axis by the rotary actuator30. The spinner table26is rotated at a rotational speed in a range from 1000 rpm to 3000 rpm, for example. The spinner table26is rotated for a period of time in a range from 10 seconds to 60 seconds, for example. However, there is no particular limitation on the conditions under which to rotate the spinner table26, for example.

For example, the spinner table26may be rotated at a combination of different rotational speeds, e.g., a high rotational speed in a range from 1000 rpm to 3000 rpm and a low rotational speed in a range from 10 rpm to 300 rpm. The rotation of the spinner table26causes the liquid material13that has been dropped on the wafer11to be spread all over the first surface11athereof. In other words, the first surface11aof the wafer11is coated in its entirety with the liquid material13.

According to the present embodiment, an epoxy resin such as SU-8 or the like that is suitable for forming a resist film is used as the liquid material13. However, there is no particular limitation on the liquid material13as well. The liquid material13may be changed depending on properties required for the resist film to be formed, for example.

After the liquid material13has been spread all over the first surface11aof the wafer11, the applied liquid material13is dried to evaporate the solvent and water contained in the liquid material13. For example, the wafer11with the liquid material13spread thereon is placed on a hot plate that has been heated to a temperature in a range from 80° C. to 120° C. and left on the hot plate for approximately 60 seconds, drying the liquid material13together with the wafer11. When the liquid material13is dried, it turns into a resist film15(seeFIG. 6) covering the first surface11ain its entirety. However, there is also no particular limitation on the conditions under which to dry the liquid material13.

For example, after the nozzle32has stopped supplying the liquid material13, the spinner table26may be continuously rotated to dry the liquid material13applied to the first surface11aof the wafer11. Alternatively, an oven, i.e., a drying furnace, a heater, a lamp, or the like may be used in place of the hot plate to heat and dry the liquid material13. For example, the wafer11coated with the liquid material13may be introduced into an oven heated to a temperature in a range from 80° C. to 120° C. to dry the liquid material13. The oven may heat the wafer11for a period of time in a range from approximately 10 minutes to approximately 20 minutes, in this case.

FIG. 6illustrates in enlarged fragmentary cross section the wafer11with the slanted surface11dformed thereon and the resist film15formed on the wafer11. As illustrated inFIG. 6, according to the present embodiment, since the slanted surface11dis formed on the first surface11aside of the outer circumferential edge portion of the wafer11, when the liquid material13that is to turn into the resist film15is applied to the first surface11aof the wafer11by the spin coating process, it is easy for the liquid material13to flow down the slanted surface11dand drain off from the wafer11to the outside thereof, upon flowing from the central area of the wafer11toward the outer circumferential edge thereof.

In other words, as the liquid material13is less likely to accumulate on the outer circumferential edge portion of the wafer11, the possibility that the resist film15will swell on the outer circumferential edge portion of the wafer11is reduced.FIG. 7illustrates in enlarged fragmentary cross section a wafer21with no slanted surface and with a resist film25formed on the wafer21.

The wafer21is similar to the wafer11except that no slanted surface is formed thereon. Specifically, the wafer21is of a disk shape having a first surface21aand a second surface21bopposite the first surface21a, i.e., on the back side of the wafer21. The first surface21aand the second surface21bare joined to each other by an outer circumferential edge surface21ccurved by beveling.

If a resist film25is formed on the first surface21aof the wafer21by a spin coating process, as illustrated inFIG. 7, the resist film25is highly likely to form a thicker swelling portion25aon the outer circumferential edge portion of the wafer21. Specifically, since no slanted surface is formed on the wafer21, the liquid material13tends to accumulate on the outer circumferential edge portion of the wafer21. When the spinner table26is rotated, the accumulated liquid material13on the outer circumferential edge portion of the wafer21is locally dried by an air stream, i.e., turbulence, produced on the outer circumferential edge portion of the wafer21by the rotation of the spinner table26, resulting in the thicker swelling portion25athereon.

In the method of processing a wafer according to the present embodiment, as described above, inasmuch as the slanted surface11dthat is inclined to the first surface11aso as to be progressively closer to the second surface lib of the wafer11in the direction from the central area of the wafer11toward the outer circumferential edge thereof is formed on the first surface11aside of the outer circumferential edge portion of the wafer11, when the liquid material13that is to turn into the resist film15is applied to the first surface11aof the wafer11by the spin coating process, it is easy for the liquid material13to flow down the slanted surface11dand drain off from the wafer11to the outside thereof, upon flowing from the central area of the wafer11toward the outer circumferential edge thereof.

In other words, as the liquid material13is less likely to accumulate on the outer circumferential edge portion of the wafer11, the possibility that the resist film15will swell on the outer circumferential edge portion of the wafer11is reduced even in a situation where the liquid material13applied to the wafer11is liable to be locally dried by an air stream, i.e., turbulence, produced around the wafer11by the rotation of the wafer11.

Second Embodiment

A method of processing a wafer according to a second embodiment of the present invention will be described in detail below. According to the second embodiment, a slanted surface11dis formed on a wafer11in a manner different from the first embodiment described above. Other details of the method according to the second embodiment than the processing step of forming the slanted surface11don the wafer11are the same as those of the method according to the first embodiment. Therefore, different details of the method according to the second embodiment will mainly be described below.

FIG. 8illustrates in cross section a manner in which the slanted surface11dis formed on the wafer11in the method according to the present embodiment. InFIG. 8, some components are represented by symbols and a functional block.

The method of processing a wafer according to the present embodiment is carried out using a processing apparatus42illustrated inFIG. 8. Specifically, the second surface lib of the wafer11is held on the chuck table4of the processing apparatus42(holding step), and thereafter, the slanted surface11dis formed on the wafer11by the processing apparatus42(processing step). Some components of the processing apparatus42are identical to those of the processing apparatus2described above. Therefore, those components of the processing apparatus42that are identical to those of the processing apparatus2are denoted by identical reference characters, and their description will be omitted below.

As illustrated inFIG. 8, a cutting unit, i.e., a processing unit,54is disposed above the chuck table4. The cutting unit54includes a spindle, or a rotational shaft,56that is capable of changing the angle of its own central axis with respect to the upper surface8aof the porous plate8, for example. A cutting blade, i.e., a processing tool,58including a grinding stone made of abrasive grains bound together by a bonding material is mounted on one end of the spindle56.

The other end of the spindle56is coupled to a rotary actuator, not depicted, such as an electric motor. When the rotary actuator is energized, it generates and transmits rotational power to the spindle56, rotating the cutting blade58on the spindle56about the central axis thereof. The cutting unit54is supported on a cutting unit moving mechanism, not depicted, for example. The cutting unit moving mechanism moves the cutting unit54in a second direction, i.e., a second horizontal direction, generally parallel to the upper surface8aof the porous plate8and generally perpendicular to the first direction in which the chuck table4is movable, and in a third direction generally perpendicular to the first direction and the second direction.

The cutting blade58is of a disk shape including a first side surface58ahaving a circular outer circumferential edge and a second side surface58bhaving a circular outer circumferential edge that is of the same diameter as the first side surface58aand positioned opposite the first side surface58a, i.e., on the back side of the cutting blade58. The outer circumferential edge of the first side surface58aand the outer circumferential edge of the second side surface58bare connected to each other by an outer circumferential surface58c. In addition, at least the outer circumferential surface58cis formed as a grinding stone made of abrasive grains such as diamond bound together by a bonding material such as a resin.

The cutting blade58is mounted on the one end of the spindle56such that the first side surface58aand the second side surface58blie generally perpendicularly to the central axis of the spindle56. The width or thickness of the cutting blade58, i.e., the distance between the first side surface58aand the second side surface58b, is optionally set to a value matching the desired width of the slanted surface11dto be formed. For example, the slanted surface11dthat is of a sufficient width can easily be formed on the wafer11by using the cutting blade58whose width is in a range from 0.5 mm to 3.0 mm, typically of 1 mm.

For forming the slanted surface11don the wafer11, the spindle56as the rotational shaft is inclined with respect to the upper surface8aof the porous plate8, as illustrated inFIG. 8. In other words, the spindle56is inclined with respect to the first surface11aand the second surface11bof the wafer11. Thereafter, the cutting blade58as it is rotated about the central axis thereof by the spindle56is caused to cut into the outer circumferential edge portion of the wafer11that includes the boundary between the first surface11aand the outer circumferential edge surface11cof the wafer11. Then, the chuck table4is rotated to make one revolution about its own central axis.

The first side surface58aof the cutting blade58is positioned closer to the outer circumferential edge of the wafer11, and the second side surface58bof the cutting blade58is positioned closer to the center of the wafer11. Then, the spindle56is inclined such that the height of the lower end of the first side surface58ais smaller than the height of the lower end of the second side surface58b. However, in a case where the second side surface58bis positioned closer to the outer circumferential edge of the wafer11and the first side surface58ais positioned closer to the center of the wafer11, the spindle56is inclined such that the height of the lower end of the second side surface58bis smaller than the height of the lower end of the first side surface58a.

The height of the cutting unit54at the time that the cutting blade58cuts into the wafer11is adjusted in such a range that only the outer circumferential surface58cof the cutting blade58contacts the wafer11. Specifically, for example, the height of the cutting unit54is adjusted such that the height of the lower end of the first side surface58aof the cutting blade58is smaller than the height of the first surface11aof the wafer11and the height of the lower end of the second side surface58bof the cutting blade58is equal to or larger than the height of the first surface11a.

The cutting blade58is thus allowed to cut into the first surface11aside of the outer circumferential edge portion of the wafer11, thereby forming the slanted surface11dthat is joined to the first surface11awithout abrupt height differences. The slanted surface11dthus formed is inclined to the first surface11aso as to be progressively closer to the second surface lib of the wafer11in a direction from the central area of the wafer11toward the outer circumferential edge thereof.

Specifically, the height of the slanted surface11dis smaller on the outer circumferential edge surface11cside, i.e., on an outer side of the wafer11, than on the first surface11aside, i.e., on an inner side of the wafer11. Also, the thickness of the wafer11in the outer circumferential edge portion thereof where the slanted surface11dis formed is smaller on the outer circumferential edge surface11cside than on the first surface11aside.

The angle Θ formed between the first surface11aand the slanted surface11dand the width W of the slanted surface11d, i.e., the length of the slanted surface11dalong radial directions of the wafer11, may be the same as those according to the first embodiment described above. After the slanted surface11dhas been formed on the wafer11, the liquid material13is applied to the first surface11aof the wafer11by the spin coating process, forming the resist film15on the first surface11aof the wafer11(resist film forming step).

Also in the method of processing a wafer according to the present embodiment, since the slanted surface11dis formed on the first surface11aside of the outer circumferential edge portion of the wafer11, when the liquid material13that is to turn into the resist film15is applied to the first surface11aof the wafer11by the spin coating process, it is easy for the liquid material13to flow down the slanted surface11dand drain off from the wafer11to the outside thereof, upon flowing from the central area of the wafer11toward the outer circumferential edge thereof.

In other words, as the liquid material13is less likely to accumulate on the outer circumferential edge portion of the wafer11, the possibility that the resist film15will swell on the outer circumferential edge portion of the wafer11is reduced even in a situation where the liquid material13applied to the wafer11is liable to be locally dried by an air stream, i.e., turbulence, produced around the wafer11by the rotation of the wafer11.

Third Embodiment

A method of processing a wafer according to a third embodiment of the present invention will be described in detail below. According to the third embodiment, a slanted surface11dis formed on a wafer11in a manner different from the first and second embodiments described above. Other details of the method according to the third embodiment than the processing step of forming the slanted surface11don the wafer11are the same as those of the methods according to the first and second embodiments. Therefore, different details of the method according to the third embodiment will mainly be described below.

FIG. 9illustrates in cross section a manner in which the slanted surface11dis formed on the wafer11in the method according to the present embodiment. InFIG. 9, some components are represented by symbols and a functional block.

The method of processing a wafer according to the present embodiment is carried out using a processing apparatus62illustrated inFIG. 9. Specifically, the second surface lib of the wafer11is held on the chuck table4of the processing apparatus62(holding step), and thereafter, the slanted surface11dis formed on the wafer11by the processing apparatus62(processing step). Some components of the processing apparatus62are identical to those of the processing apparatus2and42described above. Therefore, those components of the processing apparatus62that are identical to those of the processing apparatus2and42are denoted by identical reference characters, and their description will be omitted below.

As illustrated inFIG. 9, a grinding unit, i.e., a processing unit,64is disposed above the chuck table4. The grinding unit64includes a spindle66whose central axis extends generally perpendicularly to the upper surface8aof the porous plate8, for example. A disk-shaped mount68is fixed to a lower end of the spindle66.

A grinding wheel, i.e., a processing wheel,70that is annular in shape which has a diameter generally equal to the diameter of the mount68is mounted on a lower surface of the mount68. The grinding wheel70includes an annular wheel base72made of a material such as stainless steel, aluminum, or the like. The wheel base72has a lower surface to which there are fixed a plurality of grinding stones74each made of abrasive grains such as diamond or the like bound together by a bonding material such as a resin.

A rotary actuator, not depicted, such as an electric motor is coupled to an upper end of the spindle66. When the rotary actuator is energized, it generates and transmits rotational power through the spindle66and the mount68to the grinding wheel70on the mount68on the lower end of the spindle66, rotating the grinding wheel70about a central axis thereof. The grinding unit64is supported on a lifting and lowering mechanism, not depicted, for example. The grinding unit64can be moved in directions generally perpendicular to the upper surface8aof the porous plate8by the lifting and lowering mechanism.

For forming the slanted surface11don the wafer11, first, the chuck table4and the grinding unit64are moved relatively to each other to position an end of the grinding wheel70above the outer circumferential edge portion of the wafer11that includes the boundary between the first surface11aand the outer circumferential edge surface11cof the wafer11held on the chuck table4.

Then, as illustrated inFIG. 9, while the chuck table4and the grinding wheel70are being rotated about their respective central axes, the grinding unit64is lowered. After at least the grinding stones74of the grinding wheel70have contacted the wafer11, the chuck table4is relatively moved in a direction away from the grinding unit64. Specifically, the grinding wheel70is moved with respect to the wafer11in a direction indicated by the arrow inFIG. 9, i.e., a direction from the central area of the wafer11toward the outer circumferential edge thereof.

Accordingly, the grinding stones74of the grinding wheel70grind the first surface11aside of the outer circumferential edge portion of the wafer11, forming the slanted surface11dthat is joined to the first surface11awithout abrupt height differences. The slanted surface11dthus formed is inclined to the first surface11aso as to be progressively closer to the second surface11bof the wafer11in a direction from the central area of the wafer11toward the outer circumferential edge thereof.

Specifically, the height of the slanted surface11dis smaller on the outer circumferential edge surface11cside, i.e., on an outer side of the wafer11, than on the first surface11aside, i.e., on an inner side of the wafer11. The thickness of the wafer11in the outer circumferential edge portion thereof where the slanted surface11dis formed is smaller on the outer circumferential edge surface11cside than on the first surface11aside.

The angle Θ formed between the first surface11aand the slanted surface11dand the width W of the slanted surface11d, i.e., the length of the slanted surface11dalong radial directions of the wafer11, may be the same as those according to the first and second embodiments described above. After the slanted surface11dhas been formed on the wafer11, the liquid material13is applied to the first surface11aof the wafer11by the spin coating process, thereby forming the resist film15on the first surface11aof the wafer11(resist film forming step).

Also in the method of processing a wafer according to the present embodiment, since the slanted surface11dis formed on the first surface11aof the wafer11, when the liquid material13that is to turn into the resist film15is applied to the first surface11aof the wafer11by the spin coating process, it is easy for the liquid material13to flow down the slanted surface11dand drain off from the wafer11to the outside thereof, upon flowing from the central area of the wafer11toward the outer circumferential edge thereof.

In other words, as the liquid material13is less likely to accumulate on the outer circumferential edge portion of the wafer11, the possibility that the resist film15will swell on the outer circumferential edge portion of the wafer11is reduced even in a situation where the liquid material13applied to the wafer11is liable to be locally dried by an air stream, i.e., turbulence, produced around the wafer11by the rotation of the wafer11.

Fourth Embodiment

A method of processing a wafer according to a fourth embodiment of the present invention will be described in detail below. According to the fourth embodiment, a slanted surface11dis formed on a wafer11in a manner different from the first, second, and third embodiments described above. Other details of the method according to the fourth embodiment than the processing step of forming the slanted surface11don the wafer11are the same as those of the methods according to the first, second, and third embodiments. Therefore, different details of the method according to the fourth embodiment will mainly be described below.

FIG. 10illustrates in cross section a manner in which the slanted surface11dis formed on the wafer11in the method according to the present embodiment. InFIG. 10, some components are represented by symbols and a functional block.

The method of processing a wafer according to the present embodiment is carried out using a processing apparatus82illustrated inFIG. 10. Specifically, the second surface11bof the wafer11is held on the chuck table4of the processing apparatus82(holding step), and thereafter, the slanted surface11dis formed on the wafer11by the processing apparatus82(processing step). Some components of the processing apparatus82are identical to those of the processing apparatus2,42, and62described above. Therefore, those components of the processing apparatus82that are identical to those of the processing apparatus2,42, and62are denoted by identical reference characters, and their description will be omitted below.

As illustrated inFIG. 10, a grinding unit, i.e., a processing unit,84is disposed above the chuck table4. The grinding unit84includes a spindle, i.e., a rotational shaft,86that is capable of changing the angle of its own central axis with respect to the upper surface8aof the porous plate8, for example. A disk-shaped mount88is fixed to a lower end of the spindle86.

A grinding wheel, i.e., a processing wheel,90that is annular in shape which has a diameter generally equal to the diameter of the mount88is mounted on a lower surface of the mount88. The grinding wheel90includes an annular wheel base92made of a material such as stainless steel, aluminum, or the like. The wheel base92has a lower surface to which there are fixed a plurality of grinding stones94each made of abrasive grains such as diamond bound together by a bonding material such as a resin.

A rotary actuator, not depicted, such as an electric motor is coupled to an upper end of the spindle86. When the rotary actuator is energized, it generates and transmits rotational power through the spindle86and the mount88to the grinding wheel90on the mount88on the lower end of the spindle86, rotating the grinding wheel90about a central axis thereof. The grinding unit84is supported on a lifting and lowering mechanism, not depicted, for example. The grinding unit84can be moved in directions generally perpendicular to the upper surface8aof the porous plate8by the lifting and lowering mechanism.

For forming the slanted surface11don the wafer11, the spindle86as the rotational shaft is inclined with respect to the upper surface8aof the porous plate8, as illustrated inFIG. 10. In other words, the spindle86is inclined with respect to the first surface11aand the second surface11bof the wafer11. Thereafter, the chuck table4and the grinding unit84are moved relatively to each other to position an end of the grinding wheel90above the outer circumferential edge portion of the wafer11that includes the boundary between the first surface11aand the outer circumferential edge surface11cof the wafer11held on the chuck table4.

Then, as illustrated inFIG. 10, while the chuck table4and the grinding wheel90are being rotated about their respective central axes, the grinding unit84is lowered to bring the grinding stones94of the grinding wheel90into contact with the outer circumferential edge portion of the wafer11. The spindle86has been inclined with respect to the upper surface8aof the porous plate8such that the height of the lower surfaces of the grinding stones94which is brought into contact with the wafer11is lower on the outer circumferential edge side of the wafer11than on the center side thereof.

Accordingly, the first surface11aside of the outer circumferential edge portion of the wafer11is now ground by the grinding stones94of the grinding wheel90, forming the slanted surface11dthat is joined to the first surface11awithout abrupt height differences. The slanted surface11dthus formed is inclined to the first surface11aso as to be progressively closer to the second surface11bof the wafer11in a direction from the central area of the wafer11toward the outer circumferential edge thereof.

The height of the slanted surface11dis smaller on the outer circumferential edge surface11cside, i.e., on an outer side of the wafer11, than on the first surface11aside, i.e., on an inner side of the wafer11. The thickness of the wafer11in the outer circumferential edge portion thereof where the slanted surface11dis formed is smaller on the outer circumferential edge surface11cside than on the first surface11aside.

The angle Θ formed between the first surface11aand the slanted surface11dand the width W of the slanted surface11d, i.e., the length of the slanted surface11dalong radial directions of the wafer11, may be the same as those according to the first, second, and third embodiments described above. After the slanted surface11dhas been formed on the wafer11, the liquid material13is applied to the first surface11aof the wafer11by the spin coating process, forming the resist film15on the first surface11aof the wafer11(resist film forming step).

Also in the method of processing a wafer according to the present embodiment, since the slanted surface11dis formed on the first surface11aof the wafer11, when the liquid material13that is to turn into the resist film15is applied to the first surface11aof the wafer11by the spin coating process, it is easy for the liquid material13to flow down the slanted surface11dand drain off from the wafer11to the outside thereof, upon flowing from the central area of the wafer11toward the outer circumferential edge thereof.

In other words, as the liquid material13is less likely to accumulate on the outer circumferential edge portion of the wafer11, the possibility that the resist film15will swell on the outer circumferential edge portion of the wafer11is reduced even in a situation where the liquid material13applied to the wafer11is liable to be locally dried by an air stream, i.e., turbulence, produced around the wafer11by the rotation of the wafer11.

The present invention is not limited to the embodiments described above, but various changes and modifications may be made therein. For example, the methods of processing a wafer according to the above embodiments use two types of apparatus including the processing apparatus2and the like and the spin coater22. However, the method of processing a wafer according to the present invention may use a single composite apparatus that has both the function of the processing apparatus2and the like and the function of the spin coater22.

Structural and functional details according to the above embodiments and modifications may be changed and modified without departing from the scope of the present invention.