JP2613081B2 - Mirror polishing method for wafer periphery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror polishing method for mirror polishing an outer peripheral portion of a disk-shaped semiconductor wafer having a linear portion on an outer peripheral portion.

[Prior Art] For example, a semiconductor wafer such as a silicon wafer is usually chamfered at its peripheral edge in order to prevent edge chipping and crown during epitaxial growth. This chamfering is performed by grinding with a diamond grindstone, but a work-strained layer tends to remain after the grinding, and if such a work-strained layer remains, crystal defects will occur when heat treatment is repeated in the device process. May occur.

Therefore, usually, the work strained layer is usually removed by etching, but the etched surface is likely to have wavy or scaly irregularities and dirt is likely to remain. But when it remains,
In the device process, the dirt spreads over the entire wafer, deteriorating the characteristics of the wafer.

Therefore, in order to improve the accuracy of the wafer, it is necessary to completely remove dirt by mirror-polishing the outer peripheral portion of the wafer such as the chamfered portion and the peripheral side surface parallel to the axis. The same precision is required as in the case of polishing the surface of a wafer so that there is no partial difference in state.

Conventionally, as a method of processing the outer peripheral portion of the wafer,
The methods described in JP-B-57-10568 and JP-A-62-37925 are known. The former is a method of finishing the wafer to a certain size according to the master, and the latter is to store the shape of the workpiece in a computer in advance and process the wafer according to it, It is of substantially the same type as the former using a master.

However, all of these methods process a wafer according to a master shape, and thus are suitable for processing with a relatively large amount of grinding such as chamfering processing and finishing processing. If there is a difference of several microns between them, it is impossible to finish the outer peripheral portion of the wafer to a desired mirror state, and therefore, it is not suitable for the above-mentioned mirror polishing requiring precision.

In view of this, the present inventors have proposed, in Japanese Patent Application No. 62-230398, an apparatus capable of precisely mirror-polishing the outer peripheral portion of a wafer. According to this apparatus, while rotating a disc-shaped wafer around an axis, a rotating polishing drum is pressed against the outer peripheral portion of the wafer with a constant force and polished, whereby the outer peripheral portion is adjusted according to the shape of the wafer. Can be accurately polished.

However, as shown in FIG.
When polishing the wafer 1 provided with the (orientation flat), when the polishing drum 2 moves from the arc-shaped portion 1b to the linear portion 1a of the wafer 1 due to the rotation of the wafer 1, the polishing drum 2 changes its shape. Cannot be displaced enough to follow the wafer 1 and the wafer 1 at the end 1c of the linear portion 1a.
There is a possibility that the contact with the metal becomes slow and the polishing becomes insufficient.

[Problems to be Solved by the Invention] An object of the present invention is to grind a disc-shaped wafer having a linear portion on the outer periphery while pressing the rotating polishing drum against the outer periphery of the wafer while rotating the wafer around the axis. In doing so
An object of the present invention is to ensure that a linear portion formed on the outer peripheral portion of the wafer can be mirror-polished.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a method for rotating a wafer and a polishing drum in one direction, and polishing at least one of the wafer and the polishing drum in the opposite direction. It is characterized by rotating and polishing.

[Specific Examples of the Invention] Hereinafter, the method of the present invention will be described in more detail.

FIG. 1 shows an example of a mirror polishing apparatus which can be suitably used for carrying out the method of the present invention. This polishing apparatus has the following configuration. That is, a table support member 11 is provided on the machine base 10, and on the table support member 11,
A chuck table 13 for holding a disk-shaped wafer 12 having one or more linear portions 12a (see FIG. 2) on the outer peripheral portion
The drive shaft 13a of the chuck table 13 is connected to a drive source 16 such as a motor, which can be rotated forward and backward, via a timing pulley 14 and a timing belt 15, and a computer or the like. The control means 18 can be driven in a forward direction and a reverse direction at a low speed of, for example, about 1 to 10 rpm according to a predetermined program. A chuck means for vacuum chucking the wafer 12 is provided on the upper surface of the chuck table 13, and this chuck means is connected to a suction pump (not shown) through a suction pipe 17 passing through the drive shaft 13a.

Further, on the machine base 10, there is provided a slide table 20 which is slid by a cylinder 22 along a slide rail 21, and the slide table 20 is slid by interposing air on a sliding portion. A polishing drum mounting member 24 is movably mounted in the direction of the chuck table 13 via an air slide mechanism 23 having a reduced dynamic resistance, and a screw rod 25 is driven at the tip of the polishing drum mounting member 24 to drive it. Guide bracket 27 screwed onto screw bar 25
An elevating motor 28 for elevating the wafer 12 is mounted on the bracket 26. A polishing drum 29 for mirror-finishing the outer peripheral portion of the wafer 12 is supported on the bracket 26 so as to be rotatable around an axis. A drum drive motor 30 for driving the drum in the forward and reverse directions is attached, and the drum drive motor 30, that is, the polishing drum 29, is controlled by the control unit 18,
The chuck table 13 is driven in the forward / reverse direction in accordance with the forward / reverse rotation.

The polishing drum 29 is obtained by sticking a polishing cloth to the outer surface of a cylindrical drum member.

In order to constitute urging means for pressing the polishing drum 29 against the outer peripheral portion of the wafer 12 with a constant force during processing, two pulleys 31, 32 are attached to the slide table 20, and these pulleys 31, 32 A rope 34 whose one end is engaged with a protrusion 33 of the polishing drum mounting member 24 is wound around the rope 34, and a weight 35 is suspended from the other end of the rope 34. When the chuck drum 13 advances toward the chuck table 13 by the operation of 22, the polishing drum 29 comes into contact with the wafer 12 immediately before reaching the stroke end, and the polishing drum mounting member 24 lifts the weight 35 to the slide table 20. The pressing force is generated by the gravity of the weight 35 acting on the polishing drum mounting member 24 at this time. The magnitude of the pressing force differs depending on the processing conditions, but is usually set to an appropriate force in consideration of the balance with the holding force of the wafer 12 by the chuck table 13 and the strength of the polishing pad.

Although not shown, a chemical polishing agent supply nozzle is provided at a portion where the polishing drum 29 contacts the wafer 12, and the chemical polishing agent is supplied from the nozzle during processing. .

Next, a method of mirror-polishing the outer peripheral portion of the wafer by the mirror-polishing apparatus having the above configuration will be described.

When the wafer 12 is sucked and held in a predetermined direction on the chuck table 13 by the chuck means, the cylinder 22 is operated to move the slide table 20 forward, and the polishing drum 29 which has started to rotate in the forward direction moves around the outer periphery of the wafer 12. Abut the part. Then, the chuck table 13 is driven at a low speed (1
1 rotation in the forward direction at about 10 rpm, and the outer peripheral portion of the wafer 12 is mirror-polished by the polishing drum 29 (FIGS. 2A to 2H).
reference).

When the polishing in the normal rotation is completed, the polishing drum 29 is temporarily separated from the wafer 12, and the rotation direction is reversed. Then, when the polishing drum 29 comes into contact with the wafer 12 again, the chuck table 13 makes one rotation in the reverse direction at a low speed, and the same polishing as in the above-described normal rotation is performed (see FIGS. 3A to 3H). ).

Thus, by performing the polishing in the case where the wafer 12 and the polishing drum 29 are rotated in the forward direction and the case in which the polishing drum 29 is rotated in the opposite direction, the entire circumference of the wafer 12 is evenly mirror-polished.

That is, at the time of the above-mentioned polishing, the polishing drum 29 causes the wafer 12 having the linear portion 12a
While appropriately displacing in the radial direction of the wafer 12 according to the outer peripheral shape of the
However, when the polishing drum 29 extends from the arc-shaped portion 12b of the wafer 12 to the linear portion 12a (FIG. 2C), the polishing drum 29 cannot sufficiently follow the shape change of the wafer 12, and At the end of 12a, contact with the wafer 12 becomes slow, and it is difficult to perform sufficient polishing. Therefore, by rotating the wafer 12 in the reverse direction and performing the same polishing, the above-mentioned portion which is hard to be polished by the forward rotation is sufficiently polished by the reverse rotation.

If the rotation speed of the polishing drum 29 is sufficiently higher than the rotation speed of the wafer 12, at least one of the wafer 12 and the polishing drum 29 may be rotated in the normal or reverse direction. If it is not enough to rotate the 12 one turn in the forward and reverse directions, a plurality of turns can be made in each direction.

Further, in the above example, the peripheral side surface parallel to the axis of the wafer is mirror-polished, but as shown in FIG.
When the chamfered portion 39 formed on the outer peripheral portion is mirror-polished, the axis of the wafer 38, that is, the chuck table 40 or the axis of the polishing drum 41 may be inclined according to the chamfer angle θ.

[Effect of the Invention] As described above, according to the present invention, after the wafer and the polishing drum are rotated in one direction and polished, at least one of them is rotated in the opposite direction and polished again. The linear portion of the wafer, which is difficult to be polished by only one rotation, can be surely mirror-polished by the reverse rotation.

[Brief description of the drawings]

FIG. 1 is a side view showing an example of a polishing apparatus used for carrying out the method of the present invention. FIGS. 2A to 2H are step-by-step explanatory diagrams of the polishing method of the present invention. FIG. 4 is a partial side view of the case where the chamfered portion of the chamfered wafer is mirror-polished, and FIG.
The figure is an explanatory view of a case where the outer peripheral portion of a wafer having a linear portion is mirror-polished. 12,39: Wafer 12, 12a: Linear portion, 29,41: Polishing drum.

Claims (1)

(57) [Claims] 1. A method for polishing by rotating a disk-shaped wafer having a linear portion on the outer periphery and pressing a rotating polishing drum against the outer periphery of the wafer while rotating the wafer around an axis.
A mirror polishing method for an outer peripheral portion of a wafer, comprising: rotating the wafer and the polishing drum in one direction, respectively, and polishing the wafer, and then rotating at least one of the wafer and the polishing drum in the opposite direction.