JP6541476B2 - Wafer polishing method - Google Patents

Description

  The present invention relates to a method of polishing a wafer, such as a semiconductor wafer or an optical device wafer, which polishes the back surface of the wafer.

  In an optical device wafer, an epitaxial layer (light emitting layer) such as gallium nitride (GaN) is formed on the surface of a sapphire substrate, SiC substrate or the like, and a plurality of optical devices such as LEDs are formed in a lattice on the epitaxial layer. It is divided and formed by a schedule line.

  A sapphire substrate is suitable for the growth of a GaN epitaxial layer because it has a lattice constant close to that of GaN and is an essential material for producing an optical device, but after the epitaxial layer is grown, weight reduction and miniaturization of electrical devices The back side of the sapphire substrate is ground by a grinding device to improve the brightness of the optical device.

  When the back surface of the wafer is ground by the grinding device, grinding marks remain on the back surface and fine cracks are formed, which causes a problem of lowering the bending strength of the device diced by the dicing device or the laser processing device.

  Therefore, in order to remove fine cracks and the like generated on the surface to be ground after grinding to improve the bending strength of the device, polishing is performed while pressing the rotating polishing pad while supplying the slurry solution to the surface to be ground of the wafer. Chemical mechanical polishing (CMP) is known.

JP 2012-106293 A Unexamined-Japanese-Patent No. 2010-120130 JP, 2011-173198, A

  However, when a sapphire wafer or SiC wafer having a Mohs hardness higher than that of a silicon wafer is polished by CMP, polishing takes time because the polishing rate (removal amount per time) is low. As a result, the amount of the slurry solution to be used also increases, and there is a problem that the processing cost is high.

  The present invention has been made in view of these points, and an object thereof is to provide a wafer polishing method capable of suppressing the amount of use of a slurry solution while preventing the polishing pad from being dried.

According to the present invention, there is provided a method of polishing a wafer using a polishing pad having a polishing surface larger than the diameter of the wafer and a slurry solution, the step of holding the wafer on the holding surface of the chuck table, A polishing step of rotating the held chuck table and pressing the polishing surface of the polishing pad against the wafer held by the chuck table while rotating the polishing pad, and polishing the wafer while supplying a slurry solution; In the polishing step, polishing is performed while supplying the slurry solution from a slurry solution supply hole facing the wafer and opening to the polishing surface while supplying pure water to a region of the polishing surface not in contact with the wafer. The slurry solution of the polishing pad is supplied in the pure water supply range of the polishing pad to which the pure water is supplied. Method of polishing wafer, comprising surrounding the slurry solution supply range is provided.

  Preferably, the wafer is composed of a sapphire wafer or a SiC wafer, and the flow rate of the slurry solution supplied in the polishing step is smaller than the flow rate of pure water.

  According to the wafer polishing method of the present invention, the slurry solution used for polishing is supplied to the area corresponding to the wafer, and polishing is performed while supplying pure water to the area of the polishing pad not in direct contact with the wafer. The amount of use of the slurry solution can be minimized while preventing the drying of the slurry, and an increase in processing cost can be prevented.

FIG. 2 is a perspective view of an optical device wafer. It is a perspective view which shows a protection member arrangement | positioning step. 1 is a perspective view of a polishing apparatus according to an embodiment of the present invention. It is a longitudinal cross-sectional view which shows a grinding | polishing step. It is a schematic plan view explaining a slurry solution supply range and a pure water supply range.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a front side perspective view of the optical device wafer 11 is shown. The optical device wafer 11 is configured by laminating an epitaxial layer (light emitting layer) 15 such as gallium nitride (GaN) on a sapphire substrate 13. The optical device wafer 11 has a surface 11 a on which the epitaxial layer 15 is stacked and a back surface 11 b on which the sapphire substrate 13 is exposed.

  The sapphire substrate 13 has its back surface ground by a grinding apparatus to be thinned to about 100 μm, and the epitaxial layer 15 has a thickness of 5 μm, for example. A plurality of optical devices 19 such as LEDs are formed on the epitaxial layer 15 by being divided by planned dividing lines (streets) 17 formed in a lattice.

  In carrying out the wafer polishing method according to the embodiment of the present invention, as shown in FIG. 2, to protect the device 19 formed on the surface of an optical device wafer (hereinafter sometimes simply referred to as a wafer). Then, a protection member adhesion step is performed in which a protection member 21 such as a protection tape is adhered to the surface 11a of the wafer 11 with an adhesive such as a thermoplastic resin. In the present embodiment, the protective member 21 having a diameter larger than the diameter of the wafer 11 is attached to the surface 11 a of the wafer 11, but a protective member having the same diameter as the wafer 11 may be attached.

  Next, with reference to FIG. 3, a polishing apparatus 2 suitable for carrying out the wafer polishing method of the present invention will be described. Reference numeral 4 denotes a base of the polishing apparatus 2, and a column 8 is erected at the rear of the horizontal base 6.

  A pair of guide rails 12 and 14 extending in the vertical direction is fixed to the column 8. The polishing unit 16 is mounted movably in the vertical direction along the pair of guide rails 12 and 14. The polishing unit 16 is attached to a movable base 18 that moves in the vertical direction along the pair of guide rails 12 and 14 via the support portion 20.

  The polishing unit 16 includes a housing 22 attached to a support 20, a spindle 24 rotatably housed in the housing 22, and a servomotor 28 for rotationally driving the spindle 24.

  As best shown in FIG. 4, a wheel mount 30 is fixed to the tip of the spindle 24, and a polishing wheel 32 is detachably attached to the wheel mount 30 by a plurality of screws 31. The polishing wheel 32 includes a base 34 and a polishing pad 36 attached to the lower surface of the base 34. The polishing pad 36 is formed of non-woven fabric or soft urethane.

  A slurry solution supply hole 26 is formed in the spindle 24, and as shown in FIG. 3, the slurry solution supply hole 26 is connected to a slurry solution supply source 74 via a slurry solution supply passage 72. Slurry solution supply holes 35 and 37 communicating with the slurry solution supply hole 26 of the spindle 24 are formed in the base 34 and the polishing pad 36 of the polishing wheel 32, respectively.

  As a slurry solution, a mixed solution obtained by mixing an alkaline solution such as colloidal silica, tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH) and a hydrophilizing agent such as hexaethylene cellulose can be used.

  Referring again to FIG. 3, the polishing unit 16 includes a polishing unit feed mechanism 38 which moves the polishing unit 16 up and down along the pair of guide rails 12 and 14. The polishing unit feed mechanism 38 comprises a ball screw 40, a pulse motor 42 fixed to one end of the ball screw 40, and a nut screwed on the ball screw 40 disposed on the movable base 18. When the pulse motor 42 is driven, the ball screw 40 is rotated, and the polishing unit 16 is moved in the vertical direction.

  A chuck table unit 44 is disposed in the recess 10 of the horizontal base portion 6. The chuck table unit 44 includes a chuck table 46. The chuck table 46 is rotatably disposed and moved in the front-rear direction of the apparatus, that is, in the Y-axis direction by a horizontal movement mechanism (chuck table movement mechanism) not shown. Be done. The chuck table 46 has a suction holding surface 46 a formed of porous ceramics or the like.

  The chuck table unit 44 includes a chuck table cover 48 disposed to surround the chuck table 46 and a bellows 50 disposed at both ends of the chuck table cover 48.

  In front of the horizontal base portion 6, a positioning mechanism having a cassette 52 for storing wafers before polishing, a cassette 54 for storing wafers after polishing, a wafer transfer robot 56, and a plurality of positioning pins 58 60, a wafer loading mechanism (loading arm) 62, a wafer unloading mechanism (loading arm) 64, a spinner cleaning unit 68 having a spinner table 66, and an operation panel 70 for the operator to input polishing conditions and the like. ing.

  The pure water supply nozzle 76 is disposed in the recess 10 of the horizontal base portion 6, and as shown in FIG. 4, the jet nozzle 76a of the pure water supply nozzle 76 is positioned below the polishing wheel 32, and the polishing pad Pure water is supplied to the outer peripheral portion 36, that is, the area of the polishing surface 36 a of the polishing pad 36 not in contact with the wafer 11.

  As apparent from FIG. 4, the polishing pad 36 has a diameter larger than the diameter of the wafer 11 to be polished, and preferably, the polishing pad 36 has a diameter twice or more the diameter of the wafer 11. doing.

  In the method of polishing a wafer according to the embodiment of the present invention, first, the holding step of holding the wafer 11 on the holding surface 46 a of the chuck table 46 is performed. Then, the chuck table 46 holding the wafer 11 is moved in the Y-axis direction in FIG. 1 and positioned at the polishing position as shown in FIG. 4 with respect to the polishing wheel 32.

  In this polishing position, the central axis of the chuck table 46 and the central axis of the polishing wheel 32 are eccentric, and the slurry solution supply hole 37 formed in the polishing pad 36 is disposed near the outer peripheral portion of the wafer 11 held by the chuck table 46. It is positioned to be set up. As described above, the jet nozzle 76a of the pure water supply nozzle 76 is positioned to supply pure water to the area of the polishing surface 36a not in contact with the wafer 11.

  In the polishing step, while rotating the chuck table 46 in the direction of arrow a at, for example, 300 rpm, while rotating the polishing wheel 32 in the direction of arrow b at, for example, 600 rpm, the polishing surface 36a of the polishing pad 36 is subjected to a predetermined polishing pressure. It presses on back side 11b.

  Then, while the slurry solution is continuously supplied from the slurry solution supply hole 37 of the polishing pad 36 to the back surface 11 b of the wafer 11, the pure water supply nozzle 76 in a region not contacting the inner wafer 11 of the polishing surface 36 a of the polishing pad 36. The backside 11 b of the wafer 11 is polished while supplying pure water.

  In an actual polishing process, a sapphire wafer 11 of φ4 inch was polished by a polishing pad 36 having a diameter of 300 mm. The flow rate of the slurry solution at the time of polishing was 0.1 liter / minute or less, and pure water was supplied from the pure water supply nozzle 76 at 0.2 liter / minute or more.

  The supplied slurry solution was supplied with the undiluted solution without being diluted with pure water. The flow rate of the slurry solution supplied at the time of polishing of the wafer 11 is preferably smaller than the flow rate of pure water. As a result, the amount of use of the slurry solution can be minimized, and an increase in processing cost can be prevented.

  When pure water is not supplied to the polishing pad 36, the polishing pad 36 is dried, and the slurry solution supplied from the slurry solution supply hole 37 penetrates to the outer periphery of the polishing pad 36. The amount of slurry solution to be supplied must be increased.

  However, according to the wafer polishing method of the present invention, as shown in the schematic view of FIG. 5, pure water is supplied from the pure water supply nozzle 76 to the polishing surface 36 a not in contact with the wafer 11. Since the outer peripheral portion becomes the pure water supply range 80 and the polishing pad 36 is wetted by the pure water, the slurry solution supply range 78 surrounded by the pure water supply range 80 can be suppressed to a small area, and the usage amount of the slurry solution It could be reduced to less than 0.1 liter per minute.

  As for the slurry solution, the polishing rate increases as the concentration of colloidal silica that is the slurry increases. Therefore, it is desirable to use a thick slurry solution as much as possible, but a thick slurry solution directly leads to an increase in slurry cost.

  In the present invention, since polishing is performed while supplying pure water to the area of the polishing surface 36 a not contacting the wafer 11, the flow rate of the slurry solution used without drying the outer peripheral portion of the polishing pad 36 by supplying pure water. It could be kept to a very low value.

  It is also possible to intermittently carry out the supply of pure water, and supply the minimum amount of pure water maintaining the area of the pure water supply range 80 to such an extent that the slurry solution supply range 78 does not expand and the polishing rate can be maintained. By doing this, the amount of pure water used can also be reduced. As a result, the polishing cost of the sapphire substrate 13 required for a long time for polishing can be reduced.

  In the embodiment described above, an example in which the polishing method of the present invention is applied to the sapphire substrate 13 has been described, but the effect is large when the present invention is applied to a SiC substrate having a high Mohs hardness like the sapphire substrate 13.

11 Optical Device Wafer 13 Sapphire Substrate 15 Epitaxial Layer 19 Optical Device 21 Protective Member 24 Spindle 26, 35, 37 Slurry Solution Supply Hole 32 Polishing Wheel 36 Polishing Pad 46 Chuck Table 74 Slurry Container Supply Source 76 Pure Water Supply Nozzle 78 Slurry Solution Supply Range 80 pure water supply range

Claims (3)

A method of polishing a wafer, comprising the steps of: polishing a wafer using a polishing pad having a polishing surface larger in diameter than a wafer and a slurry solution,
A holding step for holding the wafer on the holding surface of the chuck table;
A polishing step of rotating the chuck table holding a wafer and pressing the polishing surface of the polishing pad against the wafer held by the chuck table while rotating the polishing pad to polish the wafer while supplying a slurry solution; , And
In the polishing step,
While supplying the slurry solution from a slurry solution supply hole opened to the polishing surface facing the wafer,
Polishing is performed while supplying pure water to the area of the polishing surface not contacting the wafer ,
A method for polishing a wafer, comprising: enclosing a slurry solution supply range of the polishing pad to which the slurry solution is supplied within a pure water supply range of the polishing pad to which the pure water is supplied .   2. The method of polishing a wafer according to claim 1, wherein the flow rate of the slurry solution supplied in the polishing step is smaller than the flow rate of pure water.   The method for polishing a wafer according to claim 1, wherein the wafer is composed of a sapphire wafer or a SiC wafer.

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