EP0877418A2

EP0877418A2 - Edge-polishing apparatus and method

Info

Publication number: EP0877418A2
Application number: EP98108249A
Authority: EP
Inventors: Taketoshi Kato
Original assignee: SpeedFam Co Ltd
Current assignee: SpeedFam Co Ltd
Priority date: 1997-05-09
Filing date: 1998-05-06
Publication date: 1998-11-11
Also published as: JPH10309666A; EP0877418A3

Abstract

An edge-polishing apparatus and method are provided which are capable of not only preventing the surfaces of workpieces such as silicon wafers from being smeared, stained, soiled, damaged or marred by forming hydrophilic oxide films thereon, and but also of storing the workpieces in a dry state. A workpiece W stored in a cassette 10 in a dry state is taken out by means of a first robot 12 of a first transportation section 1, and transported to an oxide-film forming section 2 where it is immersed in ozone water 21 in an oxidation water tank 20 so as to form a hydrophilic oxide film on the surfaces of the workpiece W. The workpiece W thus formed with the hydrophilic oxide film is cleaned with a shower 29 of pure water by means of a cleaning device 28, and then transported to an edge-polishing section 4 by means of a second robot 32 of a second transportation section 3. At the edge-polishing section 4, the edges of the workpiece W are mirror finished by a polishing drum 41. Thereafter, the workpiece W is cleaned with a shower 53 of pure water while being brushed by means of a pair of brushes 51, 51. The workpiece W thus cleaned is transported to a drying section 7 by means of a third robot 60 of a third transportation section 6, and dried there. Subsequently, the dried workpiece W is kept or stored in a cassette 79 in a dry state.

Description

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an edge-polishing apparatus and method for automatically mirror finishing edges of a workpiece such as a semiconductor wafer which has been subjected to chamfering.

Description of the Prior Art

Fig. 8 is a block diagram showing an edge-polishing apparatus known to the inventor.

The edge-polishing apparatus illustrated, generally designated at 100, comprises an edge-polishing section 101, a cleaning or washing section 102 and a storage section 103. A plurality of workpieces in the form of silicon wafers W stored in a cassette in their dry state are transported one by one to the edge-polishing section 101 where edges of each silicon wafer W are subjected to mirror finishing while being supplied with slurry. The silicon wafers W thus having been mirror finished are then transported to the cleaning section 102, where pure water is showered on the silicon wafers W to clean or wash off slurry and the like attached thereto. Thereafter, the silicon wafers W thus cleaned are transferred to the storage section 103 in which they are soaked or immersed in the pure water in a tank.

In this manner, the edge polishing, cleaning and storing of the silicon wafers W are carried out in a continuous manner by means of a single edge-polishing apparatus, thus improving efficiency in the wafer-processing operations.

With the above-mentioned edge-polishing apparatus, however, there is the following problem.

In the processing operations, surfaces of the silicon wafers W are liable to be smeared, stained, soiled or contaminated. That is, the surfaces of the silicon wafers W are hydrophobic, so that pure water is attached to the silicon wafers W in a droplet state, as shown in Fig. 9. In the water droplets, impurities such as abrasive grains of slurry or the like supplied to the wafers W at the edge-polishing section 101 are aggregated and appear on the surfaces of the silicon wafers W as smear, stain, soil, blur or the like during drying thereof.

In order to cope with such a problem, it is considered that the silicon wafers W are subjected to scrub cleaning or washing at the cleaning section 102. Specifically, the silicon wafers W are subjected not only to simple showering of pure water but also scrubbing so that the silicon wafers W are supplied with a shower of pure water while at the same time being scrubbed by means of brushes to remove or scrape off the impurities thereon. In this manner, it is possible to achieve substantially complete cleaning of the silicon wafers W without producing any smear, stain, soil or the like.

In this approach, however, there is a fear that the surfaces of the silicon wagers W might be damaged or marred by the blushes.

Moreover, with the known edge-polishing apparatus, since the silicon wafers W are stored in a wet state in the storage section 103, it is necessary to clean and dry the silicon wafers W before they are transported to a clean room for the next processing thereof. Thus, the silicon wafers W having once been processed by means of the edge-polishing apparatus can not directly be transported to the clean room.

SUMMARY OF THE INVENTION

In view of the above, the present invention is intended to obviate the above-mentioned problems, and has for its object to provide a novel and improved edge-polishing apparatus and method which are capable of not only preventing the surfaces of workpieces such as silicon wafers from being smeared, stained, soiled, damaged or marred by forming hydrophilic oxide films thereon, and but also of storing the workpieces in a dry state.

Bearing the above object in mind, according to a first aspect of the present invention, there is provided an edge-polishing apparatus comprising:

an oxide-film forming means for covering surfaces of a workpiece with a hydrophilic oxide film, the workpiece having a chamfered edge; and

an edge-polishing means for mirror finishing the chamfered edge of the workpiece covered with the oxide film.

With the above arrangement, the surfaces of the workpiece are covered with the hydrophilic oxide film in the oxide-film forming means, and the chamfered edge of the workpiece is mirror finished by the edge-polishing means.

In a preferred form of the edge-polishing apparatus, the oxide-film forming means forms the oxide film on the workpiece surfaces by immersing the workpiece into ozone water.

In another preferred form of the edge-polishing apparatus, the oxide-film forming means forms the oxide film on the workpiece surfaces by immersing the workpiece into electrolytically oxidized water.

In a further preferred form of the edge-polishing apparatus, a cleaning means is provided at a downstream side of the edge-polishing means for cleaning the workpiece having its edge mirror finished by the edge-polishing means.

With this arrangement, mirror finishing of the workpiece edge and cleaning of the workpiece can be effected by use of the single apparatus.

In a still further preferred form of the edge-polishing apparatus, the cleaning means comprises a scrub cleaning means for cleaning the workpiece by spraying thereto a shower of pure water while brushing the workpiece by means of rotating brushes.

With this arrangement, it is possible to achieve substantially complete cleaning of the workpiece.

In a yet further preferred form of the edge-polishing apparatus, a drying means is provided at a downstream side of the cleaning means for drying the workpiece which has been cleaned by the cleaning means.

With this arrangement, it is possible to achieve mirror finishing of the workpiece edge, cleaning and drying of the workpiece by use of the single apparatus, and hence it is possible to provide the workpiece in a dry state.

According to a second aspect of the present invention, there is provided an edge-polishing method comprising:

an oxide-film forming step for covering surfaces of a workpiece with a hydrophilic oxide film, the workpiece having a chamfered edge; and

an edge-polishing step for mirror finishing the edge of the workpiece which has been subjected to the oxide-film forming step.

In a preferred form of the edge-polishing method, the oxide-film forming step comprises forming the oxide film on the workpiece surfaces by immersing the workpiece into ozone water.

In another preferred form of the edge-polishing method, the oxide-film forming step comprises forming the oxide film on the workpiece surfaces by immersing the workpiece into electrolytically oxidized water.

In a further preferred form of the edge-polishing method, a cleaning step is provided for cleaning the workpiece having its edge mirror finished in the edge-polishing step.

In a still further preferred form of the edge-polishing method, the cleaning step comprises a scrub cleaning step for cleaning the workpiece by spraying thereto a shower of pure water while brushing the workpiece by means of rotating brushes.

In a yet further preferred form of the edge-polishing method, a drying step is provided for drying the workpiece which has been cleaned by the cleaning means.

The above and other objects, features and advantages `of the present invention will become more readily apparent from the following detailed description of a presently preferred embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic illustration showing the construction of an edge-polishing apparatus in accordance with the present invention;

Fig. 2 is a side elevational view of a silicon wafer;

Fig. 3 is a side elevational view of a silicon wafer covered with an oxide film;

Fig. 4 is a schematic view of an edge-polishing section of the apparatus;

Fig. 5 is a schematic view of a cleaning section of the apparatus;

Fig. 6 is a schematic view of a drying section of the apparatus;

Fig. 7 is a side elevational view showing a underwater dispersion state of impurities due to an oxide film;

Fig. 8 is a block diagram showing a known edge-polishing apparatus; and

Fig. 9 is a side elevational view showing an aggregated state of impurities.

PREFERRED EMBODIMENT OF THE INVENTION

Now, a preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

Fig. 1 schematically illustrates an edge-polishing apparatus which is constructed in accordance with principles of the present invention.

The edge-polishing apparatus illustrated includes a first transportation section 1, an oxide-film forming means in the form of an oxide-film forming section 2, a second transportation section 3, an edge-polishing means in the form of an edge-polishing section 4, a cleaning means in the form of a cleaning or washing section 4, a third transportation section 6 and a drying means in the form of a drying section 7.

The first transportation section 1 is to transport a plurality of workpieces in the form of silicon wafers W stored in a cassette 10 to the oxide-film forming section 2 one by one. The first transportation section 1 is constructed of a first robot 12 which is movable on and along a pair of first rails 11, 11 (only one rail is illustrated).

Specifically, as shown in Fig. 2, each silicon wafer W of a circular or disk-shaped configuration has peripheral edges which are chamfered or beveled to provide a pair of wafer edges Wa, Wb by means of a chamfering device (not shown) in a preceding process step. In the cassette 10 of Fig. 1, there are beforehand stored the plurality of such chamfered silicon wafers W in a dry state.

The first robot 12 is equipped with an articulated arm 12a having a chuck 12b provided at its distal end, and it operates as follows. The arm12a is extended toward the cassette 10 so as to attach a silicon wafer W thereto under the action of suction by means of the chuck 12b. The first robot 12 carrying the silicon wafer W thus attached to the chuck 12b is driven by an unillustrated drive means such as an electric motor incorporated therein to move along the

first rails

11, 11 to the oxide-film forming section 2 where it places the silicon wafer W onto a table 30.

The oxide-film forming section 2 comprises an oxidizing water tank 20 and a cleaning or washing device 28.

The oxidizing water tank 20 is filled with an ozone-containing water 21 having a predetermined concentration of ozone. The silicon wafers W, which have been transported to the oxidizing water tank 20 by means of the first robot 12, are soaked or immersed in the ozone water 21 for a predetermined period of time, so that a hydrophilic oxide film S is formed on the entire surfaces of each silicon wafer W. The hydrophilic oxide film S is composed of silicon dioxide and has a thickness of about 10 - 20 angstroms.

The cleaning device 28 is to clean or wash off the ozone water 21 attached to the silicon wafers W by spraying a shower 29 of pure water onto the silicon wafers W inserted into the cleaning device 28.

The second transportation section 3 is to transport the silicon wafers W placed on the table 30 by means of the first robot 12 to the edge-polishing section 4 and the cleaning section 5. The second transportation section 3 comprises a second rail 31 and a second robot 32 which is movable on the second rail 31.

Specifically, the second robot 32 is equipped with an articulated arm 32a having a chuck 32b provided at its distal end, and it operates as follows. The arm 32a is extended toward a silicon wafer W on the table 30 so as to attach the silicon wafer W thereto under the action of suction by means of the chuck 32b. The second robot 32 carrying the silicon wafer W thus attached to the chuck 32b is driven by an unillustrated drive means such as an electric motor incorporated therein to move along the second rail 31 to a rotary vacuum chuck 40 of the edge-polishing section 40 to be described later in detail where the silicon wafer W carried by the second robot 32 is sucked to the vacuum chuck 40, and a silicon wafer W having been mirror finished is taken out of the rotary vacuum chuck 40 and carried by the second robot 32 which is then moved along the second rail 31 to the cleaning section 5.

The edge-polishing section 4 is to mirror finish or polish the edges of each silicon wafer W.

Fig. 4 schematically illustrates the edge-polishing section 4.

As shown in Fig. 4, the edge-polishing section 4 comprises a rotary vacuum chuck 40 and a polishing drum 41.

The rotary vacuum chuck 40 is to vacuum draw or suck a silicon wafer W and is driven to rotate by means of a motor (not shown) built in a mounting member 42.

The mounting member 42 is vertically rotatably or swingably mounted on a base 43 which is slidable on and along a rail 45.

On the other hand, the polishing drum 41 is mounted on an rotation shaft of a motor 44 so that it is driven to rotate by the motor 44.

Specifically, the mounting member 42 is caused to rotate or sing in the vertical direction in such a manner that the upper wafer edge Wa of the silicon wafer W attached under suction to the rotary vacuum chuck 40 forms a predetermined angle with respect to the cylindrical peripheral surface of the polishing drum 41. In this state, with the rotary vacuum chuck 40 being driven to rotate by means of the unillustrated motor, the mounting member 42 is caused to slide in a direction toward the polishing drum 41 so as to place the upper wafer edge Wa of the silicon wafer W into contact with the rotating polishing drum 41, whereby the upper wafer edge Wa is mirror finished by the polishing drum 41 while slurry G is supplied to the mutual contacting portions of the upper wafer edge Wa and the polishing drum 41.

Also, with the rotary vacuum chuck 40 being rotated to an upright position, as shown at the alternate long and two short dashes line in Fig. 4, a cylindrical peripheral side portion Wc of the silicon wafer W is able to be mirror finished by means of the polishing drum 41. Moreover, the silicon wafer W can be turned over or upside down by means of an unillustrated wafer turn-over mechanism, and the rotary vacuum chuck 40 carrying the silicon wafer W thus turned over is rotated or swung to an inclined position as shown at the solid line in Fig. 4, whereby the lower wafer edge Wb of the silicon wafer W can be subjected to mirror finishing or polishing by means of the polishing drum 41.

In Fig, 1, the cleaning section 5 is to scrub clean or wash a silicon wafer W transported thereto by means of the second robot 32.

Fig. 5 schematically illustrates the cleaning section 5.

As shown in Fig. 5, the cleaning section 5 serves to transport a silicon wafer W placed on a conveyor 50 by means of the second robot 32 to a pair of

brushes

51, 51 under the action of the conveyor 50. A pair of

rollers

52, 52 are disposed at an upstream or entrance side of the paired brushes 51, 51 for clamping therebetween the silicon wafer W conveyed there by the conveyor 50 and feeding it into the pair of

brushes

51, 51.

The pair of

brushes

51, 51 are caused to rotate in opposite directions with respect to each other by means of unillustrated drive means such as motors, so as to brush or scrub the opposite side surfaces of the silicon wafer W fed therein by the pair of

rollers

52, 52 with a shower of pure water 53 being supplied thereto. The silicon wafer W having been scrubbed or brushed and cleaned by means of the pair of

brushes

51, 51 are discharged onto a table 55 through a pair of

rollers

54, 54.

As shown in Fig. 1, the third transportation section 6 is to transport the silicon wafer W on the table 55 to the drying section 7. The third transportation section 6 comprises a third robot 60.

Specifically, the third robot 60 is equipped with an articulated arm 60a having a chuck 60b provided at its distal end, and it operates as follows. The arm 60a is extended toward the silicon wafer W on the table 55 so as to attach the silicon wafer W thereto under the action of suction by means of the chuck 60b. The third robot 60 transports the silicon wafer W thus attached to the chuck 60b toward a spinner 70 of the drying section 7 to be described later in detail where the silicon wafer W thus transported is sucked by the spinner 70, and a silicon wafer W having been dried at the drying section 7 is taken out of the spinner 70 and stored in the cassette 79 by means of the third robot 60.

The drying section 7 is to dry the silicon wafer W having been cleaned at the cleaning section 5.

Fig. 6 schematically illustrates the drying section 7.

As shown in Fig. 6, the drying section 7 is equipped with the spinner 70 and a mounting member 71.

The spinner 70 is to draw or suck a silicon wafer W under the action of vacuum. The spinner 70 is driven to rotate at a high speed by means of an unillustrated motor incorporated in the mounting member 71.

Now, reference is made to the operation of the edge-polishing apparatus according to the present invention.

It is to be noted that the edge-polishing apparatus in operation achieves an edge-polishing method of the present invention in a concrete manner. Also, the operations of the first robot 12 of the first transportation section 1, the cleaning device 28 of the oxide-film forming section 2, the second robot 32 of the second transportation section 3, the edge-polishing section 4, the cleaning section 5, the third robot 60 of the third transportation section 6, and the drying section 7 are all controlled by an unillustrated control unit such as a computer.

First, an oxide-film forming process is carried out.

Specifically, as shown at the solid line in Fig. 1, the silicon wafers W stored in the cassette 10 in a dry state are taken out one by one by means of the first robot 12 and transported to the oxidizing water tank 20 of the oxide-film forming section 2 where the silicon wafers W thus transported there are soaked or immersed into the ozone water in the oxidizing water tank 20 by means of the second robot 12 for a predetermined period of time, as shown at the alternate long and shot dash line in Fig. 1. Thereafter, when a hydrophilic oxide film S having a thickness of about 10 - 20 angstroms is formed on the surfaces of a silicon wafer W, the silicon wafer W is taken out of the ozone water 21 and transported to the cleaning device 28, as shown at the broken line in Fig. 1, where the ozone water 21 attached to the silicon wafer W is removed or cleaned off by means of a shower 29 of pure water.

The silicon wafers W, which have been cleaned to a sufficient extent, are transferred to and placed onto the table 3 by means of the first robot 12. Thus, the oxide-film forming process ends.

Subsequently, the silicon wafers having been subjected to the oxide-film forming process are transferred to the edge-polishing process.

Specifically, a silicon wafer W on the table 30 is transported to the edge-polishing section 4 by means of the second robot 32 and attached under suction to the rotary vacuum chuck 40.

Then, as shown in Fig. 4, the upper wafer edge Wa, the cylindrical peripheral side portion Wc and the lower wafer edge Wb of the silicon wafer W are in sequence subjected to mirror finishing or polishing by means of the rotating polishing drum 41. During this process, slurry G is continuously supplied to the mutual contacting portions of the silicon wafer W and the polishing drum 41.

When the mirror finishing process of the silicon wafer W ends in this manner, the suction force of the rotary vacuum chuck 40 acting against the silicon wafer W is released so that the silicon wafer W is taken out by means of the second robot 32. Thus, the edge-polishing process ends.

Thereafter, the silicon wafer W having been subjected to the edge-polishing process is transported to the cleaning section 5, as shown at the alternate long and two short dashes line in Fig. 1, where it is subjected to a cleaning process.

Although at this time, impurities such as the slurry G and the like are attached to the silicon wafer W, the silicon wafer W is covered with the hydrophilic oxide film S so water is attached to the surfaces of the silicon wafer W in a uniform manner, as shown in Fig. 7. As a result, impurities such as abrasive grains in the slurry G and the like hardly aggregate in the water attached to the wafer surfaces, thus diffusing therein substantially in a uniform manner.

Such a silicon wafer W is placed onto the conveyor 50 of the cleaning section 5 by means of the second robot 32, and then transported toward the pair of

brushes

51, 51 under the action of the conveyor 50.

As the silicon wafer W is fed into the pair of

brushes

51, 5, it is brushed or scrubbed by means of the pair of

brushes

51, 51 while being sprayed with a shower 53 of pure water, whereby impurities adhered to the surfaces of the silicon wafer W are removed or cleaned off to a substantially complete extent. That is, even if the impurities are adhered to the oxide film S on the surfaces of the silicon wafer W in an aggregated stage, they are cleaned off by brushing and hence do not at all remain as smear, stain, soil or the like on the surfaces of the silicon wafer W.

Also, during the brushing, the pair of

brushes

51, 51, being in contact with the hard oxide film S covering the silicon wafer W, do not damage or mars the surfaces of the silicon wafer W.

Finally, a drying process is carried out.

Specifically, the silicon wafer W having been scrub cleaned on the table 55 is transported to the drying section 7 by means of the third robot 60 where it is placed on the spinner 70.

Thereafter, the silicon wafer W is sucked to the spinner 70 which is then driven to rotate at a high speed so that pure water attached to the surfaces of the silicon wafer W is scattered off under the action of a centrifugal force of the wafer W rotating with the spinner 70.

When the pure water on the surfaces of the silicon wafer W has been completely scattered off to thereby make the silicon wafer W
in a dry state, the spinner 79 is caused to stop rotating, and to release its suction force against the silicon wafer W, thus finishing the drying process.

As a result, the silicon wafer W having been dried without including any smear, stain, soil or the like is taken out of the spinner 70 by means of the third robot 60 and stored in the cassette 79 in a dry state.

Thus, according to the edge-polishing apparatus of the present invention, it is constructed such that a silicon wafer W covered with a hydrophilic oxide film S is mirror finished, cleaned and dried at the edge-polishing section 4, the cleaning section 5 and the drying section 7, respectively. With such a construction, there will be no fear that impurities such as abrasive grains of the slurry G and the like might appear as smear, stain, soil or the like on the surfaces of the silicon wafer W.

Moreover, since the silicon wafer W is covered with the hard oxide film S, the surfaces of the silicon wafer W are not damaged or marred at all during scrub cleaning thereof at the cleaning section 5.

In addition, dry silicon wafers W having been dried at the drying section 7 are kept or stored in the cassette 79, so that they can be directly transferred to a clean room for subsequent processing.

Here, it is to be noted that the present invention is not limited to the above-described embodiment, but can be varied or modified in various ways within the spirit and scope of the invention as defined in the accompanying claims.

For example, in the above embodiment, the edge-polishing section 4, the cleaning section 5 and the drying section 7 have been so constructed as shown in Fig. 4, Fig. 5 and Fig. 6, respectively, but at the edge-polishing section 4, all the possible techniques can be utilized which are capable of mirror finishing or polishing the edges of a silicon wafer W; similarly, at the cleaning section 5, all the possible techniques can be used which are capable of scrub cleaning the silicon wafer W; and at the drying section 7, every suitable drying technique such as heat drying and the like can be employed instead of the spin drying technique.

As described in detail in the foregoing, according to the present invention, there are obtained a variety of advantages as referred to below.

Since the surfaces of a workpiece such as a silicon wafer are covered with a hydrophilic oxide film prior to mirror finishing of edges of the workpiece, even if impurities such as slurry and the like are attached to the workpiece, these impurities are diffused over the entire surface of the oxide film, and hence do not aggregate at localized spots thereof. As a result, there are provided clean workpieces including substantially no smear, stain, soil or the like contaminations.

Furthermore, the oxide film is formed on the surfaces of the workpiece by use of ozone water, electrolytically oxidized water or the like, so a desired oxide film can readily be formed without adversely affecting the workpiece.

Moreover, mirror finishing of the edges of the workpiece and cleaning thereof can be carried out in a continuos manner without generating smear, stain, soil or the like contaminations on the surfaces of the workpiece.

In addition, the workpiece covered with the oxide film is cleaned through brushing of rotating brushes, so substantially complete cleaning of the workpiece can be effected without damaging the surfaces thereof.

Still further, it is possible to perform mirror finishing of the workpiece edges, cleaning and drying of the workpiece in a continued manner without producing any smear, stain, soil or the like on the surfaces of the workpiece, so that the workpiece can be provided in a dry state. As a result, the workpiece can directly be transported from one clean room to another without requiring any particular processing.

Claims

An edge-polishing apparatus comprising:

an oxide-film forming means for covering surfaces of a workpiece with a hydrophilic oxide film, said workpiece having a chamfered edge; and

an edge-polishing means for mirror finishing the chamfered edge of said workpiece covered with said oxide film.
The edge-polishing apparatus according to claim 1, wherein
said oxide-film forming means forms said oxide film on said workpiece surfaces by immersing said workpiece into ozone water.
The edge-polishing apparatus according to claim 1, wherein
said oxide-film forming means forms said oxide film on said workpiece surfaces by immersing said workpiece into electrolytically oxidized water.
The edge-polishing apparatus according to claim 1, further comprising a cleaning means provided at a downstream side of said edge-polishing means for cleaning said workpiece having its edge mirror finished by said edge-polishing means.
The edge-polishing apparatus according to claim 4, wherein said cleaning means comprises a scrub cleaning means for cleaning said workpiece by spraying thereto a shower of pure water while brushing said workpiece by means of rotating brushes.
The edge-polishing apparatus according to claim 4 or 5, further comprising a drying means provided at a downstream side of said cleaning means for drying said workpiece which has been cleaned by said cleaning means.
An edge-polishing method comprising:

an oxide-film forming step for covering surfaces of a workpiece with a hydrophilic oxide film, said workpiece having a chamfered edge; and

an edge-polishing step for mirror finishing the edge of said workpiece which has been subjected to said oxide-film forming step.
The edge-polishing method according to claim 7, wherein
said oxide-film forming step comprises forming said oxide film on said workpiece surfaces by immersing said workpiece into ozone water.
The edge-polishing method according to claim 7, wherein
said oxide-film forming step comprises forming said oxide film on said workpiece surfaces by immersing said workpiece into electrolytically oxidized water.
The edge-polishing method according to claim 7, further comprising a cleaning step for cleaning said workpiece having its edge mirror finished in said edge-polishing step.
The edge-polishing method according to claim 10, wherein said cleaning step comprises a scrub cleaning step for cleaning said workpiece by spraying thereto a shower of pure water while brushing said workpiece by means of rotating brushes.
The edge-polishing method according to claim 10 or 11, further comprising a drying step for drying said workpiece which has been cleaned by said cleaning means.