EP1004400A1

EP1004400A1 - Method for polishing a notch of a wafer

Info

Publication number: EP1004400A1
Application number: EP99122257A
Authority: EP
Inventors: Shunji Hakomori
Original assignee: SpeedFam-IPEC Co Ltd
Current assignee: SpeedFam-IPEC Co Ltd
Priority date: 1998-11-27
Filing date: 1999-11-08
Publication date: 2000-05-31
Also published as: KR20000047734A; TW415880B; JP2000158315A

Abstract

A method for notch polishing by a notch-polishing unit (20) of an edge polisher is provided, in which evenness of polishing can be ensured by rotating a pad (32) for notch polishing in positive and reverse directions to polish a notch in a wafer (W). When the notch is polished by the pad (32) for notch polishing in the notch-polishing unit (20) formed of a sucking portion (30) for sucking a wafer (W) placed on the top surface thereof and the pad (32) for notch polishing rotatable by a driving source (33), the notch is evenly polished by rotating the pad (32) for notch polishing in positive and reverse directions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for notch polishing by a notch-polishing unit of an edge polisher and more specifically relates to a method for notch polishing by a notch-polishing unit of an edge polisher in which a notch is polished by a polishing pad for notch polishing rotating in the positive and reverse directions.

2. Description of the Related Art

A semiconductor wafer such as a silicon wafer is generally chamferred in its peripheral portion so as to prevent chipping of edges, crowning during epitaxial growing, and so forth.
This chamferring is performed by grinding using a diamond grindstone. After the grinding, a work strain layer is prone to remain, so that the work strain layer may cause to produce flaws in a crystal during repetitions of the heat treatment in a device process.
Therefore, the work strain layer is generally removed by etching. However, wavelike or scale-like bumps and dips are produced on the surface after the etching treatment, so that dirt is prone to remain therein. These dirty things spread across the wafer in a device process to be a leading cause of characteristic deterioration.
Accordingly, a technique for smoothing chamferred edges of a wafer by mirror polishing is recently established as a completely different technique from that of grinding a wafer surface. Various edge polishers for mirror polishing wafer edges are proposed.
In a notch-polishing unit of an edge polisher, a notch of a wafer fed in succession is polished by a rotary pad. The pad is soft to some extent so as to swell slightly outwardly during rotation. Therefore, the outer periphery of the pad can be urged enough in contact with the surface of the notch before it touches the notch. After the abutment, the outer periphery of the pad is separated from the surface of the notch compared with before the abutment so as not to abut enough the surface of notch. Therefore, the preceding surface of the notch in the rotational direction of the pad is always not polished enough so that a problem that polishing evenness cannot be secured is involved.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method for polishing a notch by a notch-polishing unit of an edge polisher in which whole surfaces of the notch are sufficiently and evenly polishable when the notch is polished by a polishing pad of the notch-polishing unit of the edge polisher.
In order to solve the above-described problem, a method for notch polishing according to the present invention using a notch-polishing unit of an edge polisher provided with a feeding section for feeding a wafer accommodated in a cassette, a notch-polishing section for notch polishing of the supplied wafer, an edge-polishing section for polishing the peripheral surface of the wafer, and a discharging section having a cassette for accommodating wafers polished by the edge-polishing section, the method for notch polishing comprises the steps of providing a notch-polishing unit in the notch-polishing section, formed of a sucking portion for horizontally placing the wafer and a polishing portion contactable with and separable from the sucking portion; and polishing the notch in the wafer by rotating the pad for notch polishing in positive and reverse directions.
In the present invention, the step of polishing the notch in the wafer may be performed by using a driving source disposed in the polishing portion rotatable in positive and reverse directions.
In the present invention, the step of polishing the notch in the wafer may be also performed by using a driving source disposed in the polishing portion and a reversible rotational direction mechanism disposed in a driving-force-transmission system between the driving source and the pad for notch polishing.
When the notch is polished, the pad for notch polishing swells, so that the upstream side thereof in the rotational direction is sufficiently polished while the downstream side thereof is not sufficiently polished. Therefor, when the pad is rotated in one direction, unevenness of polishing is produced in front and rear of the rotation so that evenness of polishing cannot be secured. In accordance with the present invention, by using the method of the invention described above, the pad for notch polishing is rotated in positive and reverse directions, so that unevenness of polishing cannot be produced in front and rear of the rotation, resulting in ensuring of evenness of polishing.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic plan view showing an entire edge polisher in which a method for polishing a notch by a notch-polishing unit according to the present invention is adopted;
Fig. 2 is a schematic front elevation showing the entire edge polisher;
Fig. 3 is a schematic elevation viewed along the lineC-C of Fig. 1;
Fig. 4 is a schematic plan view of the notch-polishing unit;
Fig. 5 is a schematic front view of the notch-polishing unit;
Fig. 6 is a schematic elevation viewed along the lineD-D of Fig. 1;
Fig. 7 is a schematic front view of an edge-polishing unit arranged in the edge polisher;
Fig. 8 is a schematic side view of the edge-polishing unit arranged in the edge polisher;
Fig. 9 is a schematic front view showing the vicinity of a sucking portion of the edge-polishing unit arranged in the edge polisher;
Fig. 10 is a schematic plan view showing one line of the edge-polishing section arranged in the edge polisher;
Fig. 11 is a schematic front view showing one line of the edge-polishing section arranged in the edge polisher;
Fig. 12 is a schematic plan view of a feeding section; and
Fig. 13 is a schematic representation showing the state that a notch-polishing pad abuts a notch of a wafer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention illustrated in the drawings will be described below.
Fig. 1 shows an entire edge polisher in which a method for polishing a notch by a notch-polishing unit according to the present invention is adopted.
The edge polisher comprises a feeding section 10 for taking out a wafer from a cassette accommodating wafers stacked therein to align it in the predetermined direction and further to reverse the alignment for feeding to the next process, a notch-polishing section 20 for receiving a wafer from the feeding section 10 to polish the notch formed in the wafer, an edge-polishing section 50 for receiving the wafer with the notch polished by the notch-polishing section 20 to polish the edge of the wafer with the front surface directed upward at first and further to polish the edge of the wafer similarly in the state the wafer is turned upside-down, and a discharge section 100 having cassettes for accommodating wafers with polished edges and notches.
A notch-polishing unit 22 arranged in the notch-polishing section 20, in which a method for polishing a notch by a notch-polishing unit according to the present invention is adopted, will be described.
As shown in Fig. 1, in the notch-polishing section 20, a pair of notch- polishing units 22 and 22 opposing each other and wafer-delivering portions 21 and 21 sandwiched between the pair of notch- polishing units 22 and 22 are arranged. Furthermore, as shown in Fig. 2, in the notch-polishing section 20 are arranged three-hooks members 23, each three-hooks member 23 disposed above each of the pair of notch- polishing units 22 and 22, being capable of going up and down and movable between the wafer-delivering portion 21 and the notch-polishing unit 22 along a rail 29 arranged in the "X" direction, so that in the down-position the three-hooks member 23 receives a wafer "W" in the wafer-delivering portion 21 to go up and move in the "X" direction toward above the notch-polishing unit 22 and then goes down to deliver the wafer to a sucking disc 36 of the notch-polishing unit 22.
The notch-polishing unit 22 comprises a sucking portion 30 with the top surface capable of sucking a wafer thereon and a polishing portion 34 capable of contacting with and separating from the wafer sucked by the sucking portion 30, as shown in Figs. 4 and 5. The polishing portion 34 comprises a cover 31 with an opened portion opposing a notch, a pad 32 for notch-polishing placed in the cover 31 and exposed so as to abut the notch, and a driving source 33 for rotating the pad 32 for notch polishing.
The sucking portion 30 includes a disc-shaped sucking disc 36 having circumferential-shaped sucking openings 35 formed on the top surface thereof and a vacuum source connected thereto.
In the polishing portion 34, a base 39 having a main shaft 38 disposed penetrating therethrough and arranged toward the direction of the sucking portion 30 is formed on a bed 37 of the notch-polishing unit 22. A frame board 40 is vertically arranged on the base 39. The cover 31 containing the pad 32 for notch polishing therein is attached to the upper portion of the frame board 40 while the driving source 33 is disposed in the lower portion thereof. A belt 41 is looped around between the driving source 33 and a rotation axis of the pad 32 for notch polishing.
On the other hand, a connecting member 42 with a length of wire 43 connected thereto is attached to the base 39, and a weight 45 is suspended from the length of wire 43 via a pulley 44 disposed in the bed.
Therefore, owing to the weight 45, the base 39 is moved along the main shaft 38 so that the pad 32 for notch polishing disposed in the frame board 40 of the base 39 is urged to a notch of a wafer "W" sucked to the sucking disc 36.
In addition, a cylinder 46 can place the movable part to a separated position from the notch by moving the base 39 against the weight 45 using an actuating portion 46a of the cylinder 46.
In the notch-polishing section 20, two of the notch-polishing units 22 configured as described above are arranged sandwiching the wafer-delivering portions 21.
In the notch-polishing unit 22, the three-hooks member 23 for supplying a wafer has a hook portion 24 hanging downward which is shown in Fig. 3 as a state viewed along the lineC-C of Fig. 1.
The hook portion 24 has three hooks and one of them enters into the notch of the wafer while other two urge peripheral edges of the wafer during gripping the wafer "W".
Each hook is capable of gripping and releasing by opening up due to the driving source and the wafer is restrained from rotation because the one hook is placed in the notch during gripping.
The hook portion 24 is formed so as to be moveable vertically and in the direction "X" by the driving source and also rotatable horizontally. When it moves in the direction "X", it is to be positioned above the sucking disc 36 of the notch-polishing unit 22 shown in Fig. 4.
Next, the operation of the notch-polishing unit 22 formed as above will be described.
Poly-articulated arms 13 with wafers placed thereon of a transferring member 14 in the feeding section 10, which will be described later, are positioned in the wafer-delivering portions 21 and 21.
Then, the hook portion 24 of the three-hooks member 23 grips the wafer to transfer it to the sucking portion 30 for placing it on the sucking disc 36. When the cylinder 46 is not actuated, the base 39 is moved along the main shaft 38 by the effect of the weight 45 such that the pad 32 for notch polishing of the frame board 40 disposed in the base 39 is urged to the notch "a" of the wafer "W" sucked by the sucking disc 36.
The driving source 33 is driven simultaneously with urging the pad 32 for notch polishing exposed from the cover 31 to the notch "a" in this manner. Then, since the driving force of the driving source 33 is transmitted to the pad 32 for notch polishing via the belt 41, the pad 32 for notch polishing starts to rotate while abutting the notch "a" of the wafer "W".
During the rotation, as shown in Fig. 13, since the pad 32 for notch polishing has elasticity to some extent, it swells slightly outwardly. Therefore, the portion of the pad in the upstream side of the rotational direction before the abutting point "x" with the notch "a" as a boundary can be urged enough in contact with the notch "a", while the portion of the pad in the downstream side of the rotational direction displaces in the separating direction from the notch "a".
That is, since the portion of the pad 32 for notch polishing in the proximal side of the rotational direction across the abutting point "x" with the notch "a" as the boundary swells, while the portion of the pad in the front side of the rotational direction sinks, the notch "a" is always excellently polished in the proximal side of the abutting point "x".
In this condition, since the driving source 33 of the pad 32 for notch polishing can rotate in the positive and reverse directions, any portion of the notch "a" can be excellently polished.
The notch "a" of the wafer "W" is cup-shaped, that is, in top plan thereof, the width of the mouth is roughly the same as the thickness of the pad 32 for notch polishing and the width decreases toward the inner side. Any portion of the notch "a" can be securely and evenly polished by rotating the pad 32 for notch polishing in the positive and reverse directions as the same as described above.
The driving source 33 may be in itself reversible in the rotational direction or may be reversible through a reversible rotational direction mechanism disposed between the driving source 33 and the pad 32 for notch polishing rotated through the belt 41.
Next, the feeding section 10 for feeding wafers to the notch-polishing section 20 formed as described above will be described below.
As shown in Fig. 12, the feeding section 10 comprises two cassettes 11 and 11 accommodating wafers stacked therein, an aligner 12 for taking out a wafer successively from the cassette 11 to align the notch formed in the wafer peripheral surface in a predetermined direction, and the transferring member 14 having the poly-articulated arms 13 for transferring a wafer from the cassette 11 to the aligner 12 and transferring an aligned wafer taken out from the aligner 12 to a notch-polishing process as well.
The two cassettes 11 and 11 and the aligner 12 are arranged on a mounting base 110, and the transferring member 14 is formed so as to move along the mounting base 110 by a robot 111.
The transferring member 14 is reciprocatable between the position indicated by the solid line in the drawing and the position indicated by the phantom line, and has two poly-articulated arms 13 and 13, each arm having a fork portion 15 in its end. The two fork portions 15 of the transferring member 14 can transfer the wafers "W" in accordance with expansion and contraction of the poly-articulated arms 13 by placing a wafer on the top surface of each fork portion.
In addition, a circle in the outside of the transferring member 14 indicated by the phantom line shows the rotatable-regional-boundary of the fork portion 15.
The aligner 12 is described in Japanese Patent Publication No. 2729297, for example, and is formed so as to receive the wafer "W" transferred by the fork portion 15 of the poly-articulated arms 13 in the transferring member 14 to align the notch formed in the peripheral surface of the wafer "W" in the predetermined position relative to the fork portion 15 of the poly-articulated arms 13.
Therefore, the transferring member 14 takes out the wafer "W" from the cassette 11 to transfer it to the aligner 12 and receives the aligned wafer "W" again from the aligner to transfer to wafer-delivering portions 21 and 21.
The wafer-delivering portions 21 and 21 are arranged in respective two positions so as to correspond to the notch-polishing units 22 arranged in the notch-polishing section 20 which will be described later, as indicated by phantom lines (see Fig. 1).
On the other hand, the edge-polishing section 50 for polishing the peripheral surface of the wafer is arranged in succession to the notch-polishing section 20.
The edge-polishing section 50 comprises two transferring members 51 and 52 successively arranged in series in the "Y" direction of the center portion, each member having two poly-articulated arms reciprocatable in the "Y" direction, edge-polishing units 53 arranged in two lines sandwiching the two transferring members 51 and 52 and opposing each other, two edge-polishing units 53 being arranged in series in the "Y" direction in each line, and a wafer-counter-turning member 80 furthermore.
The wafer-counter-turning member 80 has a pair of wafer-counter-turning mechanisms 81 capable of wafer-counter-turning and movable in the "Y" direction along rails 82 as well, each rail 82 being disposed in the upper portion of each line of the edge-polishing section 50.
The wafer-counter-turning mechanisms 81 receive the both wafers placed on the top surfaces of poly-articulated arms 13 of one of the transferring members 51 and deliver them to the both sucking discs 54 of one of edge-polishing units 53, respectively.
After edge polishing by the edge-polishing unit 53 of the feeding section 10 side, the wafer-counter-turning mechanisms 81 further receive the both wafers on the sucking discs 54 and move upward to make them counter-turning and deliver them to the both sucking discs 54 of the other edge-polishing unit 53, respectively. After edge polishing by the other edge-polishing unit 53, the wafer-counter-turning mechanisms 81 deliver the both wafers to both the poly-articulated arms 13 of the other of the transferring members 52, respectively.
In addition, two transferring members 51 and 52 arranged successively in the "Y" direction of the center portion are formed just like the transferring member 14 used in the feeding section 10.
On the other hand, the edge-polishing unit 53 comprises a pair of polishing drums 55 disposed in the center portion, each drum with a drum pad 55a wound thereon, and wafer-urging mechanisms 60 arranged in both sides of the polishing drums 55 in the "Y" direction, respectively.
Each wafer-urging mechanism 60 is arranged in the direction ("A" direction) inclined by a predetermined angle toward the "Y" direction, in top plan thereof (see Fig. 10). Above the wafer-urging mechanism 60, the sucking disc 54 vertically swingable between the horizontal state and the inclined state is arranged.
As shown in Figs. 7 to 9, the wafer-urging mechanism 60 comprises a first body 61 for holding the sucking disc 54 for vacuum sucking of a wafer and a second body 63 for holding the first body 61 to be swingable about a supporting shaft 62. The second body 63 is supported by a supporting mechanism 65 so as to be movable in the radius direction of a turn table 64, i.e., the direction of contacting with and separating from the polishing drum 55, and also in the perpendicular direction to the radius direction of the polishing drum 55, i.e., the parallel direction to the line connecting centers of two adjacent polishing drums 55.
The supporting mechanism 65 comprises a first rail 67 disposed in a mounting base 66 fixed to the bottom surface of the turn table 64 in the direction of contacting with and separating from the polishing drum 55 (the "A" direction), a first slide member 68 movable along the first rail 67, a second rail 69 disposed on the first slide member 68 in the perpendicular direction to the first rail 67 (the "B" direction), and a second slide member 70 movable along the second rail 69. To the second slide member 70, the second body 63 is fixed through a leg 71.
To the bottom surface of the mounting base 66, a pulley 72 with a length of wire 72a strung thereabout is fixed. The one end of the length of wire 72a is fixed to an arm 73 extended downwardly from the first slide member 68 while a weight 74 is suspended from the other end of the length of wire 72a.
Owing to the weight 74, the first slide member 68 is always urged toward the polishing drum 55 on the first rail 67.
A length of wire 92 with a weight 91 suspended from the one end thereof is fixed to the second slide member 70 through a pulley 90. Owing to the weight 91, the sucking disc 54 is urged so that the wafer sucked thereby is substantially evenly abutted to the two polishing drums 55 and 55.
This is an attempt for roughly unifying the unevenness of abutting forces to both the polishing drums 55 and 55 resulted from the wafer itself rotates when it abuts the rotating polishing drums 55 and 55.
The tip of a rod 75a of an air cylinder 75 attached to the bottom surface of the mounting base 66 abuts the arm 73 such that the first slide member 68 is urged in the separating direction from the polishing drum 55 against the weight 74 owing to the air cylinder 75.
Plural sucking holes are bored in the surface of the sucking disc 54, to which a vacuum source (not shown) is connected through ports and piping 77 disposed in the first body 61, the second body 63, etc., as shown in Fig. 9.
This sucking disc 54 is rotated at extremely slow speed by a driving source disposed in the first body 61 during polishing.
As described above, the first body 61 is swingable about the supporting shaft 62 between the horizontal state and the inclined state of the sucking disc 54 using a rotary actuator 78. At the horizontal state, the sucking disc 54 is separated from the polishing drum 55 to receive or deliver a wafer.
At the inclined state of the sucking disc 54, it is urged in contact with both the polishing drums 55, i.e., drum pads 55a wound onto the two polishing drums 55, respectively, owing to an operating force of the weight 74, so that two portions of the peripheral surface of the wafer are simultaneously polished.
In addition, at the horizontal state, i.e., no polishing position, the first body 61 is retracted by the cylinder 75 against the weight 74 in the separating direction from the polishing drums 55.
The polishing drums 55 are formed to be rotatable by a driving source 76 disposed in the base of the polishing unit.
Furthermore, an abrasive (slurry) is sprayed during polishing of the wafer "W" attached to the sucking disc 54, and the abrasive is recovered for recycling.
As described above and shown in Figs. 2 and 6, the wafer-counter-turning member 80 is movably formed above the two edge-polishing units 53 in the one side.
That is, the wafer-counter-turning member 80 comprises the rail 82 disposed above the two edge-polishing units 53 of the one side in the "Y" direction and a pair of wafer-counter-turning mechanisms 81 attached to the rail 82 having a space corresponding to that of a pair of sucking discs 54 opposing each other and sandwiching the polishing drums 55.
The wafer-counter-turning mechanisms 81 of the wafer-counter-turning member 80 are disposed above the positions corresponding to those of the sucking discs 54 in the horizontal state opposing each other and sandwiching the polishing drums 55 of the edge-polishing unit 53, respectively.
The wafer-counter-turning mechanism 81 can grip the water and is vertically rotatable by a driving source. It comprises an embayed hook portion 83 formed of a pair of embayed arms capable of wafer-counter-turning by the rotation in the wafer gripping state, an elevating arm 84 being capable of rising and falling the embayed hook portion 83 by a cylinder, etc., and a movable base 85 which fixes the elevating arm 84 thereto.
The movable base 85 is movable by a driving source disposed thereto along the rail 82 in the "Y" direction.
Therefore, as shown in Fig. 2, the wafer-counter-turning mechanisms 81 (81a and 81b), each having the embayed hook portion 83a, are movable along the rail 82 disposed above in the "Y" direction from above the sucking discs 54 and 54 in the horizontal state opposing each other and sandwiching the polishing drums 55 of the edge-polishing unit 53 in the feeding section 10 side toward the position above the sucking discs 54 and 54 in the horizontal state opposing each other and sandwiching the polishing drums 55 of the edge-polishing unit 53 in the other side.
Among the sucking discs 54 of both the edge-polishing units 53, the sucking discs 54a in the feeding section 10 side upwardly oppose the same wafer-counter-turning mechanisms 81 (81a) while the sucking discs 54b in the opposite side to the feeding section 10 among the sucking discs 54 of both the edge-polishing units 53 upwardly oppose also the same water-counter-turning mechanisms 81 (81b) accordingly.
Thereby, the same wafers "W" are supplied to the sucking discs 54a in the feeding section 10 side of both the edge-polishing units 53 and the sucking discs 54b in the opposite side to the feeding section 10, respectively.
In addition, the rail 82 and the wafer-counter-turning member 80 are also arranged above the other two edge-polishing units 53 opposingly disposed across the two transferring members 51 and 52.
Thereby, two lines of edge-polishing section 50 are formed, each line being formed of the two edge-polishing units 53 successively disposed in the "Y" direction and the wafer-counter-turning member 80, using the transferring members 51 and 52 in common.
The discharge section 100 for accommodating wafers after polishing in cassettes is arranged adjacent to the edge-polishing section 50.
In the discharge section 100, two cassettes 11 just like the cassettes 11 disposed in the feeding section 10 are arranged. The portion of the cassette 11 ahead the inserting direction is closed to be prevented from further insertion.
The position in which each cassette 11 is disposed is a position accommodatable the wafers "W" after polishing by both poly-articulated arms of the transferring member 52 arranged in the edge-polishing section 50.
Furthermore, both the cassettes 11 are attached to bases 101 which are fixed to the top surfaces of base boards 103 being swingable in the vertical direction between the horizontal position and the perpendicular position by a driving source 102. A storing portion of water 104 is formed in the discharge section 100 so that the cassette 11 disposed on the top surface of the base board 103 are sunk into the water when the base board 103 is in the vertical position (see Fig. 2).
In addition, since the portions of both the cassettes 11 ahead the inserting direction are closed to be prevented from further insertion of wafers, even when the base board 103 is sunk into the water by the rotation thereof by the driving source 102 so that the portion ahead the inserting direction is to be the under side, there is no fear of jumping out of the wafer in the cassette 11.
When the cassette 11 is sunk into water, the wafer after polishing accommodated therein is to be sunk into water from the edge thereof, such that it can be smoothly sunk into water without effect of the water resistance. Furthermore, when the cassette 11 is sunk into water and pulled up therefrom, it takes effect that the surface thereof is washed out by the water.
Next, the operations of the edge-polishing unit configured as described above will be described.
A wafer "W" is carried out by the transferring member 14 from the cassette 11 securely placed on the mounting base 110 by means of a cassette-evenness-retaining mechanism according to the present invention to transfer it to the aligner 12. In the aligner 12, the wafer "W" is aligned so that the notch is aligned in the definite position.
Then, the wafer "W" is transferred by the poly-articulated arm 13 of the transferring member 14 to be reversed before and behind; the wafer "W" is gripped by the hook portion 24 of the three-hooks member 23 to be delivered to the sucking disc 36 of the notch-polishing unit 22 to be notch-polished in the notch-polishing unit 22.
As described above, the notch is securely polished by the rotation in the positive and reverse directions of the pad 32 for notch polishing of the notch-polishing unit 22.
After notch polishing, the wafer is transferred by the transferring member 51 to the opposing sucking discs 54 of the edge-polishing unit 53 to be edge-polished by two polishing drums 55 in the edge-polishing unit 53.
Since the edge-polishing is performed in the state inclined vertically relative to a level by a predetermined angle, the wafer is edge-polished in the first edge-polishing unit 53 at first; then the wafer is transferred to the next edge-polishing unit 53.
Since the wafer-counter-turning member 80 is arranged above between the first edge-polishing unit 53 and the next edge-polishing unit 53, the wafer edge-polished in the first edge-polishing unit 53 is counter-turned by the wafer-counter-turning member 80 to be transferred to the next edge-polishing unit 53 for edge-polishing again. That is, the edge of the wafer "W" is polished twice in the inclined state by urging to the polishing drums 55.
Since the edge of a wafer has been chamferred when it is polished, the center portion of the edge and the chamferred edge in the front surface are polished in the front surface polishing while the center portion of the edge and the chamferred edge in the back surface are polished in the back surface polishing.
The wafer "W" polished respectively in the front and back sides is transferred to the discharge section 100 by the arm of the transferring member 52 to be accommodated into the cassette 11 disposed therein.
Accordingly, the wafers "W" notch-polished and edge-polished are accommodated in the cassette 11 of the discharge section 100 in the stacked state, so that the polishing operations are completed.
In accordance with the present invention, by using the method of the invention described above, when the notch in the wafer supplied from the feeding section is polished, the pad for notch polishing is rotated in positive and reverse directions, so that evenness of polishing by the pad for notch polishing can be ensured with the entire surface of the notch.
By using a motor rotatable in positive and reverse directions as means for rotating the pad for notch polishing in positive and reverse directions, the pad for notch polishing can be securely rotated in positive and reverse directions.
Even when the driving source rotating in the one direction is used, by arranging a switching mechanism of the rotational direction, the pad for notch polishing can be also securely rotated in positive and reverse directions.

Claims

A method for notch polishing using a notch-polishing unit of an edge polisher provided with a feeding section for feeding a water accommodated in a cassette, a notch-polishing section for notch polishing of the supplied wafer, an edge-polishing section for polishing the peripheral surface of the wafer, and a discharging section having a cassette for accommodating wafers polished by the edge-polishing section, the method for notch polishing comprising the steps of:

providing a notch-polishing unit in the notch-polishing section, formed of a sucking portion for horizontally placing the wafer and a polishing portion contactable with and separable from the sucking portion; and

polishing the notch in the wafer by rotating the pad for notch polishing in positive and reverse directions.
A method according to Claim 1, wherein said step of polishing the notch in the wafer is performed by using a driving source disposed in the polishing portion rotatable in positive and reverse directions.
A method according to Claim 1, wherein said step of polishing the notch in the wafer is performed by using a driving source disposed in the polishing portion and a reversible rotational direction mechanism disposed in a driving-force-transmission system between the driving source and the pad for notch polishing.