JP4937700B2 - Dry polishing equipment - Google Patents

Description

  The present invention relates to a dry polishing apparatus for dry polishing a semiconductor wafer as a workpiece, and more particularly to a technique for polishing a semiconductor wafer without charging.

  In general, a wafer having a plurality of semiconductor devices formed on the surface is finished to a required thickness by a back grinding process or the like, and then attached to a dicing tape, and then divided into individual device chips by a dicing apparatus or the like. . In order to cope with the recent downsizing of electronic devices, the necessary thickness is 100 μm or less, and the maintenance of the strength as a chip after being formed into a chip is a problem. Therefore, a technique is used in which mechanical damage due to back grinding is removed by polishing or etching the processed surface after back grinding. As such a technique, for example, Patent Document 1 discloses a technique using a dry polishing grindstone that can be polished without using a chemical or slurry for etching.

JP 2000-343440 A

  In the case of dry polishing, since polishing is performed by rubbing a polishing grindstone and a semiconductor wafer as a workpiece while maintaining a dry state, static electricity is charged on the semiconductor wafer. If this charged static electricity is applied to a device formed on the surface of the semiconductor wafer at some timing, the device may be destroyed.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide a dry polishing apparatus capable of preventing the wafer being processed from being charged.

The present invention is a dry polishing apparatus for dry polishing a semiconductor wafer, comprising: a holding unit that rotatably holds a semiconductor wafer; a polishing unit that rotatably holds a polishing grindstone; and a polishing unit that holds the polishing unit. A feed unit that allows the holding unit to approach and separate in a direction perpendicular to the holding surface; and a moving unit that relatively moves the holding unit and the polishing unit in a direction parallel to the holding surface of the holding unit. A polishing grindstone that is opposed to the holding surface is fixed to one surface of a disk-shaped frame, and the polishing grindstone includes a polishing portion that includes polishing abrasive grains and forms a polishing surface, and contacts the frame, and is attached to the polishing surface. and a static eliminator which comprises an electrically conductive material composed of equally spaced carbon or carbon fibers in the circumferential direction in a state of being separated from the polishing unit while exposed, the static electricity generated in the semiconductor wafer, the discharger It is characterized for discharge flowing to the frame.

According to the present invention, static electricity generated in the semiconductor wafer flows from the static eliminating portion including the conductive material of the polishing means through the frame to the apparatus main body, and is dissipated therefrom as a ground current. Therefore, in the present invention, it is possible to prevent the occurrence of destruction of the device caused by electrified static electricity passing through the device.

The grinding wheel is composed of a polishing part made of abrasive grains and a binder and a charge removal part made of a conductive material and a binder, and the charge removal parts are arranged at equal intervals in the circumferential direction in the polishing part. Is done. In this case, it can be configured such that the static eliminating portions are scattered in an island shape or extend radially.

According to the present invention, the static electricity generated in the semiconductor wafer is neutralized through the static eliminating portion including the conductive material of the polishing means. Can be prevented.

Hereinafter, an embodiment of a dry polishing apparatus according to the present invention will be described with reference to the drawings.
[1] Semiconductor Wafer Reference numeral 1 in FIG. 1 indicates a disk-shaped semiconductor wafer (hereinafter abbreviated as a wafer) whose back surface is polished by the dry polishing apparatus of one embodiment. The wafer 1 is a silicon wafer or the like, and the back surface is processed to a thickness of, for example, 600 to 700 μm to 100 μm or less by a grinding process. A plurality of rectangular semiconductor chips 3 are defined on the surface of the wafer 1 by grid-like division lines 2, and electronic circuits (not shown) such as ICs and LSIs are formed on the surface of the semiconductor chips 3. Has been.

  A V-shaped notch 6 indicating the crystal orientation of the semiconductor is formed at a predetermined location on the peripheral surface of the wafer 1. The wafer 1 is finally cut and divided along the planned division line 2 and separated into a plurality of semiconductor chips 3. When the wafer 1 is back-ground and dry-polished, a protective tape 7 is attached to the surface on which the electronic circuit is formed as shown in FIG. 1 for the purpose of protecting the electronic circuit. The protective tape 7 has a structure in which an adhesive of about 5 to 20 μm is applied to one side of a soft resin base sheet such as polyolefin having a thickness of about 70 to 200 μm, and the adhesive is applied to the back surface of the wafer 1. It is pasted together.

[2] Polishing Apparatus FIG. 2 shows a dry polishing apparatus according to an embodiment. The dry polishing apparatus 10 includes a rectangular parallelepiped base 11. At one end in the longitudinal direction of the base 11, a wall portion 12 erected vertically with respect to the horizontal upper surface of the base 11 is integrally formed. In FIG. 2, the longitudinal direction, the width direction, and the vertical direction of the base 11 are shown as a Y direction, an X direction, and a Z direction, respectively. On the base 11, the wall 12 side from the substantially middle part in the longitudinal direction is a processing area 11A where the wafer 1 is processed, and the opposite side supplies the unprocessed wafer 1 to the processing area 11A. An attachment / detachment area 11B for collecting the wafer 1 is used.
Hereinafter, the processing area 11A and the attachment / detachment area 11B will be described.

(A) Mechanism of machining area As shown in FIG. 2, rectangular pits 13 are formed in the machining area 11A. A vacuum chuck type disk-like chuck table (holding means) 15 is provided in the pit 13 so as to be movable in the Y direction via a table base (moving means) 14. The table base 14 is slidably provided on a guide rail disposed in the pit 13 and extending in the Y direction. The table base 14 is reciprocated in the same direction by an appropriate drive mechanism (not shown). Further, the chuck table 15 is made of alumina, silicon carbide, or the like, and electrical insulation with the wafer 1 is ensured to prevent the semiconductor chip 3 from being energized.

  One end of bellows-like covers 16 and 17 are attached to both ends of the table base 14 in the moving direction. The other ends of the covers 16 and 17 are the pits facing the inner surface of the wall portion 12 and the wall portion 12. Each is attached to the inner wall surface of 13. These covers 16 and 17 cover the moving path of the table base 14 and prevent the polishing dust and the like from dropping on the moving path, and expand and contract as the table base 14 moves. The chuck table 15 is supported on the table base 14 so that the upper surface as a holding surface of the wafer 1 is in a horizontal state and is rotatable about a rotation axis (not shown) along the Z direction (vertical direction). Has been. The chuck table 15 can be rotated clockwise or counterclockwise by a rotation driving mechanism (not shown).

  As shown in FIG. 2, the chuck table 15 is moved together with the table base 14 toward the wall 12 and is positioned at a predetermined polishing position. A polishing unit 20 is disposed above the polishing processing position. The polishing unit 20 is attached to the wall 12 of the base 11 through a moving plate 32 and a guide rail 31 so as to be movable up and down, and is lifted and lowered by a feed mechanism (feed means) 33 driven by a motor 30.

  As shown in FIGS. 2 and 3, the polishing unit 20 has a cylindrical spindle housing 21 whose axial direction extends in the Z direction, and is coaxially and freely rotatable in the spindle housing 21 by an air bearing mechanism (not shown). A spindle shaft 22 supported by the spindle housing 21, a motor 23 fixed to the upper end portion of the spindle housing 21 and rotationally driving the spindle shaft 22, a disk-like flange 24 coaxially fixed to the lower end of the spindle shaft 22, and a flange And a polishing tool (polishing means) 50 fixed to the lower surface of 24. As shown in FIG. 2, in the polishing unit 20, the spindle housing 21 is fixed to the moving plate 32 via a block 34.

  As shown in FIG. 4, the polishing tool 50 has a disk-shaped polishing pad (polishing grindstone) 52 fixed to the lower surface of a disk-shaped frame 51 whose outer diameter is substantially the same as that of the flange 24. A through hole 51 a is formed at the center of the frame 51, and a through hole 52 a having the same shape and size is formed at the center of the polishing pad 52. The frame 51 and the polishing pad 52 are concentric with the flange 24. It is arranged in. The polishing pad 52 is formed into a disk shape by impregnating polishing abrasives such as alumina and cerium oxide into a polishing cloth made of a nonwoven fabric or the like and bonding them with an appropriate binder. Most of the polishing pad 52 is a polishing portion 52P used for polishing, and a plurality of (four in this embodiment) static elimination portions 52R are arranged at equal intervals in the circumferential direction in the polishing portion 52P. .

  The neutralization unit 52R is embedded by cutting the polishing unit 52P into a circular shape in the axial direction. The static eliminating portion 52R is formed by impregnating a non-woven fabric or the like with carbon powder and bonding them with a binding material, or solidifying carbon fibers with a binding material. As shown in FIG. 4 and FIG. It is flush with the portion 52P and the other end surface is in contact with the frame 51. Thus, when the wafer 1 is dry-polished by the polishing pad 52, the wafer 1 and the frame 51 are electrically connected.

  The polishing pad 52 configured as described above is fixed to the frame 51 by an adhesive means or the like. The polishing tool 50 is detachably set to the polishing unit 20 by attaching the frame 51 to the flange 24 by screwing or the like.

(B) Mechanism of attachment / detachment area As shown in FIG. 2, a rectangular pit 18 is formed at the center of the attachment / detachment area 11B, and a two-bar link type transfer robot that moves up and down at the bottom of the pit 18 60 is installed. Around the transfer robot 60, a supply cassette 61, an alignment table 62, a swing arm type supply arm 63, a recovery arm 64 having the same structure as the supply arm 63, a spinner A cleaning device 65 and a recovery cassette 66 are arranged.

  The supply cassette 61, the alignment table 62, and the supply arm 63 are means for supplying the wafer 1 to the chuck table 15. The recovery arm 64, the cleaning device 65, and the recovery cassette 66 remove the polished wafer 1 from the chuck table 15. It is a means to collect. Each of the cassettes 61 and 66 stores a plurality of wafers 1 in a stacked state, and is set at a predetermined position on the base 11.

  When one wafer 1 is taken out from the supply cassette 61 by the transfer robot 60, the wafer 1 is placed on the alignment table 62 with the surface to be processed facing upward, and is determined at a certain position. Next, the wafer 1 is attracted and picked up from the alignment table 62 by the supply arm 63 and placed on the chuck table 15 waiting at the attachment / detachment position with the processing surface facing upward. On the other hand, the surface to be processed is polished by the polishing unit 20, and the wafer 1 on the chuck table 15 positioned at the attachment / detachment position is attracted and picked up by the recovery arm 64, transferred to the cleaning device 65, washed with water and dried. The wafer 1 cleaned by the cleaning device 65 is transferred and accommodated in the collection cassette 66 by the transfer robot 60.

  A nozzle 67 that cleans the chuck table 15 by spraying cleaning water and high-pressure air onto the chuck table 15 is disposed between the supply arm 63 and the recovery arm 64. The processing position of the wafer 1 by the polishing unit 20 is a range moved by a predetermined distance from the attaching / detaching position to the wall 12 side, and the chuck table 15 is moved between the processing position and the attaching / detaching position by the movement of the table base 14. Go back and forth. Cleaning of the chuck table 15 by the nozzle 67 and supply of water are performed at the attachment / detachment position.

[3] Polishing Operation Next, a method for dry polishing the thin plate wafer 1 using the dry polishing apparatus 10 will be described. First, a large number of wafers 1 are accommodated in the supply cassette 61. One of the wafers 1 is transferred to the alignment table 62 by the transfer robot 60 and positioned. Subsequently, the wafer 1 is placed on the chuck table 15 that stands by at the attachment / detachment position and is operated in a vacuum by the supply arm 63 so that the processing surface to be polished is exposed upward. The wafer 1 is sucked and held on the upper surface of the chuck table 15. The suction area of the chuck table 15 is desirably set to a shape corresponding to the shape of the wafer 1. Although the chuck table 15 of this embodiment is a vacuum chuck type, any type of chuck system may be used as long as the wafer 1 can be held with the surface to be processed exposed.

  Next, the table base 14 moves in the direction of the wall 12, and the wafer 1 is sent to a polishing position below the polishing unit 20. Then, the chuck table 15 is rotated and the wafer 1 is rotated. The polishing unit 20 lowered by the feeding mechanism 33 is brought close to the wafer 1 and the spindle shaft 22 of the motor 23 is rotated at a high speed so that the polishing tool 50 is rotated. The polishing pad 52 is pressed against the processing surface of the wafer 1, and the processing surface of the wafer 1 is dry-polished by the polishing pad 52.

  The operating conditions such as the rotation speed and rotation direction of the wafer 1, that is, the chuck table 15, the rotation speed and rotation direction of the polishing tool 50, and the load of the polishing pad 52 on the wafer 1 are arbitrarily set depending on the material of the wafer 1. For example, the wafer 1 and the polishing pad 52 rotate in directions opposite to each other, and the polishing process is performed under the condition that the rotation speed of the wafer 1 is 100 to 300 rpm and the rotation speed of the polishing pad 52 is 1000 to 3000 rpm. The pressing force of the polishing pad 52 against the wafer 1 is set to 50 to 500N. The pressing force can be controlled while being measured, for example, by a force sensor (for example, Nippon Kistler Co., Ltd .: thin force sensor 9135B) arranged below the chuck table 15.

  In FIG. 3, the polishing pad 52 is larger than the wafer 1 and covers and covers the entire surface of the wafer 1, but the size of the polishing pad 52 may be smaller than the wafer 1. However, it is preferable that the polishing pad 52 is as large as possible from the viewpoint of processing efficiency.

  When the processing surface of the wafer 1 is polished to a desired degree, the polishing unit 20 is raised to separate the polishing pad 52 from the wafer 1, and the rotation of the chuck table 15 is stopped. Then, the table base 14 is moved to the attachment / detachment position, and the vacuum operation of the chuck table 15 is stopped. Thereafter, the wafer 1 is transferred into the cleaning device 65 by the recovery arm 64 and washed with water, and then the water is removed. Then, the wafer 1 is transferred and accommodated in the recovery cassette 66 by the transfer robot 60. Further, cleaning water and high-pressure air are sprayed from the nozzle 67 toward the chuck table 15 stopped at the supply / recovery position, and the chuck table 15 is cleaned.

[4] Effects of One Embodiment When the work surface of the wafer 1 is dry-polished by the polishing pad 52 as described above, static electricity is generated by friction between the two. In this case, as shown in FIG. 3, since the static eliminator 52R of the polishing pad is always in contact with the wafer 1, the generated static electricity flows to the frame 51 via the static eliminator 52R, and from the frame 51 to the spindle shaft 22 Is dissipated as ground current. Here, the spindle shaft 22 is supported by the air bearing mechanism in the spindle housing 21 in a floating state, but static electricity can be conducted. In other words, a carbon plate or the like is embedded in the surface of the thrust bearing of the air bearing mechanism to prevent seizure, and the clearance of the thrust bearing is extremely small. And since it is highly conductive and the gap is extremely small, static electricity can be easily conducted, and each part of the dry polishing apparatus 10 is conducted and dissipated. Therefore, it is possible to prevent the occurrence of destruction of the semiconductor chip 3 caused by the charged static electricity flowing through the semiconductor chip 3 of the wafer 1.

[5] Modification Examples The static elimination unit 52R is not limited to the above embodiment, and various modifications can be made. For example, as shown in FIG. 5, the static eliminating portion 52 </ b> R can be configured to extend radially from the center portion of the polishing pad 52. Moreover, the static elimination part 52R is not restricted to a lump shape as shown in FIG. 4 and FIG. 5, but can be comprised by a planar body (linear shape by planar view) as shown in FIG. In the example shown in FIG. 6, a cylindrical static elimination unit 52 </ b> R and a plate-like static elimination unit 52 </ b> R extending across from the inner peripheral edge to the outer peripheral edge are provided. Further, the static elimination unit 52R does not necessarily need to be in constant contact with the wafer 1 during dry polishing, and may be disposed so as to be in intermittent contact with the wafer 1.

  In the above embodiment, the polishing pad 52 in which polishing abrasive grains such as alumina and cerium oxide are impregnated in the polishing cloth is employed as the polishing wheel of the present invention, but the polishing wheel is not limited to this example. For example, a polishing grindstone in which similar abrasive grains are dispersed in a rubber-based binder such as NBR (acrylonitrile-butadiene rubber), SBR (styrene-butadiene rubber), polyurethane-polyurea rubber, silicone rubber, fluorine rubber or the like is used. be able to.

1A is a perspective view of a wafer dry-polished by a dry-polishing apparatus according to an embodiment of the present invention, and FIG. 1 is a perspective view of a dry polishing apparatus that can suitably carry out an embodiment of the present invention. It is a partial cross section side view of the grinding | polishing unit which a dry-type grinding | polishing apparatus comprises. It is a perspective view of the polishing tool provided with the polishing pad. It is a perspective view which shows the other example of the grinding | polishing tool. It is a perspective view which shows the further another example of a grinding | polishing tool. It is side sectional drawing of the polishing tool provided with the polishing pad.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wafer 10 ... Dry-type polisher 14 ... Table base (moving means)
15 ... Chuck table (holding means)
33 ... Feed mechanism (feed means)
50: Polishing tool (polishing means)
52. Polishing pad (polishing wheel)
52P: Polishing part 52R: Static elimination part

Claims (1)

A dry polishing apparatus for dry polishing a semiconductor wafer,
Holding means for rotatably holding the semiconductor wafer by suction;
Polishing means for rotatably holding the polishing wheel;
Feeding means that enables the polishing means to approach and separate in a direction perpendicular to the holding surface of the holding means;
Moving means for moving the holding means and the polishing means relatively closer to and away from each other in a direction parallel to the holding surface of the holding means;
The polishing means is formed by fixing the polishing grindstone opposed to the holding surface on one surface of a disc-shaped frame, the polishing grindstone including polishing grains and forming a polishing surface; and the frame A charge removing portion including a conductive material made of carbon or carbon fibers arranged at equal intervals in the circumferential direction in a state separated from the polishing portion while being in contact with the polishing surface,
Dry grinding apparatus, characterized by neutralizing the static electricity generated in the semiconductor wafer by flowing the frame through the charge eliminating unit.

Images