JP2002043257A - Method of polishing work - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a dull peripheral edge of a circular work for providing a very precise flatness such as semiconductor wafers, thereby stably manufacturing a wafer having a very high flatness of 0.15 μm or less in surface reference SFQRmax, especially including regions within 2 mm from the edge. SOLUTION: In the method of polishing a circular work held with a holder plate using a polishing cloth slidably contracted to the work surface, a coat film made of a material having a lower polishing rate than the work is formed at least on a peripheral portion of the work surface, such that a central portion of the work surface is exposed or the film is formed thinner on this portion than on the peripheral portion. The work surface is polished while the backside of the work is held. The coat film is preferably a silicon oxide film, a silicon nitride film or a resin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing technique for a circular workpiece which requires a high degree of flatness, and more particularly to a polishing method for producing a mirror-polished wafer to a high level up to the peripheral portion of the wafer.

[0002]

2. Description of the Related Art Among thin circular workpieces, semiconductor wafers used for manufacturing devices are required to have very high flatness. In general, a method for manufacturing a silicon wafer includes a slicing step of slicing a single crystal ingot to obtain a thin disk-shaped wafer, and chamfering an outer peripheral portion of the wafer obtained by the slicing step to prevent cracking and chipping. Chamfering step, lapping step for flattening the wafer surface, etching step for removing processing strain remaining on the chamfered and wrapped wafer, polishing step for mirror polishing the wafer surface, and cleaning the polished wafer. It comprises a cleaning step for removing abrasives and foreign matter adhering thereto. The above steps show the main steps, and a heat treatment step or the like is added, or the order of the steps is changed.

[0003] Among the above-mentioned processes, the polishing process for mirror-finishing the wafer surface is very important because it is a process for determining the final shape of the wafer, that is, the quality of the wafer. Polishing is performed in a plurality of stages, such as performing secondary polishing before finish polishing.

A polishing apparatus used for polishing a circular workpiece such as a silicon wafer is generally designed to combine rotation and revolution so that the momentums of the center and the periphery of the workpiece (wafer) are equalized. ing. For example, as shown in FIG. 5, a work W is held by a vacuum suction or the like on a holding plate 16 attached to a rotatable holder 11, and a polishing cloth 13 attached to a rotatable surface plate 12 from an abrasive supply device 14. While supplying the abrasive 15 on the top,
Surface polishing is performed by sliding the surface of the work W (the surface to be polished) against the rotating polishing cloth 13 while applying a load.

[0005] Incidentally, as a method of holding a work, a method of providing a backing pad on a holding surface of a holding plate made of metal or the like to fix the work, or a method of holding a holding plate made of ceramics or glass via an adhesive or wax is used. There is also a method of attaching a work.

A silicon wafer is turned into a mirror-finished wafer by polishing as described above. When a semiconductor device is manufactured by forming a circuit on the surface of the mirror-finished wafer, it is possible to obtain as many devices as possible from one wafer. Desirably, for this purpose, it is required that the shape be as flat as possible over the entire surface of the wafer, particularly near the outer peripheral end. More specifically, according to the current standard, it is sufficient that high flattening is performed in a region excluding a certain region (for example, 3 mm in outer periphery) from the outer peripheral end of the wafer. Wafers having high flatness in the region up to are being demanded.

However, when the wafer is polished as shown in FIG. 5, the peripheral portion of the wafer becomes excessively large due to various factors such as the peripheral portion coming into contact with a newer abrasive than the central portion of the wafer surface. There has been a problem that polishing results in so-called peripheral sagging. FIG. 6 is a graph showing the shape change of the peripheral portion of the wafer measured by the present inventors after the primary polishing with reference to a position 10 mm from the outer peripheral edge, and a so-called change from about 6 mm from the outer peripheral edge of the wafer. Peripheral sagging has occurred. Such peripheral sagging often starts from a position about 6 mm from the outer peripheral edge regardless of the diameter of the wafer.

As a method for suppressing the peripheral sag, for example, a jig called a retainer ring is provided on the outer periphery of the holding plate so as to protrude from the holding surface by the thickness of the wafer.
A method has been proposed in which an abrasive cloth is sunk from the outer peripheral portion of the wafer, or a peripheral portion of the wafer is floated by using a holding plate having a smaller diameter than the wafer to suppress excessive polishing. Further, a method in which a retainer ring and a small-diameter holding plate are combined has been proposed as in Japanese Patent Application Laid-Open No. 8-257893.

[0009]

By devising the structure of the holding plate as described above, the peripheral sag can be somewhat improved, but the peripheral sag at a position 2 mm from the outer peripheral end is suppressed to 0.2 μm or less. It is very difficult.
In particular, high integration of semiconductor devices has been advanced in recent years, and high flatness is required over the entire surface of the wafer as described above. However, it is difficult to stably manufacture a wafer having a surface-based SFQRmax of 0.15 μm or less. Met.
In addition, SFQR (Site Front Least-
sQuares Range) is a value representing the maximum range of unevenness with respect to the surface by calculating an average plane based on the surface with respect to the flatness for each site, and SFQRmax is the maximum value among the SFQRs of all the sites on the wafer. Represents a value.

The present invention has been made in view of the above problems, and suppresses peripheral sagging when polishing a circular workpiece such as a semiconductor wafer that requires very precise flatness. An object of the present invention is to stably manufacture a wafer having a very high flatness having a surface-based SFQRmax of 0.15 μm or less including a region within 2 mm from an end.

[0011]

According to the present invention, a circular work is held by a holding plate.
In the method of polishing by bringing the surface of the work into sliding contact with a polishing cloth, a coat film made of a material having a lower polishing rate than the work is formed at least at a peripheral portion of the work surface and a work film is formed at a central portion of the work surface. A method of polishing a work, characterized in that the surface is formed to be exposed or thinner than a peripheral portion, and the work surface is polished while holding the back surface of the work (claim 1).

By performing polishing after forming the coating film in this manner, the polishing of the peripheral portion of the work can be substantially delayed, and the peripheral portion is excessively polished, causing peripheral sagging. Can be prevented. In addition, since the coat film is formed on the work, the work surface can be highly flattened stably regardless of the structure of the holding plate or the like.

The polishing method according to the present invention can be suitably applied when the work is a silicon wafer (claim 2). In particular, if the polishing method according to the present invention is applied in a polishing step of a silicon wafer where high flatness is required, a high flatness can be achieved including a region within 2 mm from the outer peripheral end, and for example, a surface-based A wafer having an SFQRmax of 0.15 μm or less can be stably manufactured.

In this case, it is preferable that the coat film is formed on a peripheral portion within 10 mm from the outer peripheral end of the surface of the wafer. In this manner, if the polishing is performed by forming the coat film on the peripheral portion within 10 mm from the outer peripheral edge of the wafer surface, the peripheral sag can be surely suppressed.

It is preferable that a silicon oxide film, a silicon nitride film or a resin film is formed as the coat film. Such a coat film has a polishing rate that is appropriately lower than that of a silicon wafer, the rate of which can be precisely controlled, and can be formed relatively easily on the peripheral portion of the wafer surface.

The formation of the silicon oxide film or silicon nitride film is performed by CVD (Chemical Vapor D).
After an oxide film or a nitride film is formed on at least the wafer surface by deposition (e.g., chemical vapor deposition) or heat treatment, the peripheral portion of the wafer surface is masked and etched to thereby form an oxide film at the central portion of the wafer. Alternatively, it is possible to remove the nitride film and expose the work surface or make the work surface thinner than the peripheral portion. As described above, a desired oxide film or nitride film can be easily formed on the peripheral portion of the wafer surface by combining the CVD or the heat treatment with the etching process.

Further, the resin film can be formed by applying the resin to a peripheral portion of the wafer surface by spin coating and then performing a heat treatment (claim 6). That is, after a resin or a thermosetting resin dissolved in an organic solvent is applied to the peripheral portion of the wafer surface by spin coating, a heat treatment such as a drying heat treatment for evaporating the organic solvent or a curing heat treatment for curing the resin is performed. By combining spin coating and heat treatment in this manner, a desired resin film can be easily formed on the peripheral portion of the wafer surface.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings, but the present invention is not limited thereto. The polishing method according to the present invention can be applied to any case where a thin circular work requiring high flatness is polished, but a case where a silicon wafer is polished will be described as a preferable specific example.

When manufacturing a silicon wafer, an ingot grown from a silicon raw material melt by a Czochralski method (CZ method), a floating zone melting method (FZ method), or the like is sliced, and the obtained wafer is rough-chamfered. After lapping, to remove processing distortion etc. on the wafer surface,
Etching is performed. In some cases, surface grinding may be performed instead of lapping.

The wafer having undergone such a process is subjected to surface polishing in order to make the surface more flat and mirror-finished. In the present invention, first, a coat film made of a material having a lower polishing rate than the wafer is formed. Forming at least a peripheral portion of the wafer surface and forming the wafer surface in a central portion of the wafer surface such that the wafer surface is exposed or thinner than the peripheral portion, and then holding the back surface of the wafer and polishing the wafer surface I do.

If a coat film made of a material having a lower polishing rate than the wafer is formed on at least the peripheral portion of the wafer surface and then the surface is polished, the peripheral portion of the coat film is polished, so that the peripheral portion of the wafer is polished. It can delay the silicon from starting to be polished. That is, after the silicon in the central portion is removed to some extent by polishing until the coat film in the peripheral portion of the wafer is removed, substantial polishing of the silicon in the peripheral portion is started. Therefore, even if the peripheral portion of the wafer is removed at a higher polishing rate than the central portion after the coat film is removed by polishing, overpolishing of the peripheral portion can be prevented and generation of peripheral sag can be suppressed.

By forming the coat film at least on the peripheral portion within 10 mm from the outer peripheral edge of the wafer surface to be polished, peripheral sag can be suitably prevented. As described above, in the polishing of the silicon wafer, the drop easily starts from a position about 6 mm from the outer peripheral end regardless of the diameter of the wafer, so that it is formed in the peripheral part within 15 mm, preferably 10 mm or less from the outer peripheral end, particularly If a coat film is formed and polished to about 5 to 7 mm from the outer peripheral end, peripheral sag can be effectively prevented. Further, it is more preferable that the coating film is formed so as to gradually become thinner from the outer peripheral end portion to the central portion.

The coating film formed in the present invention is not particularly limited as long as it is made of a material having a lower polishing rate than a work, that is, a silicon wafer, but a silicon oxide film, a silicon nitride film or a resin film is preferable. The polishing rate of these coat films is several times lower than that of silicon.
To several tens of minutes, which is advantageous in that the start of polishing of the silicon around the wafer can be effectively delayed, and that it can be formed relatively easily.

The method of forming the silicon oxide film or the silicon nitride film is not particularly limited. After forming an oxide film or a nitride film on at least the wafer surface by CVD or heat treatment, the peripheral portion of the wafer surface is masked and etched. By performing the treatment, a silicon oxide film or a silicon nitride film can be easily formed on the peripheral portion of the wafer surface.

For example, after a heat treatment is performed on an etched raw material wafer in an oxidizing atmosphere to form a thermal oxide film on the entire surface of the wafer, the peripheral portion is masked by attaching a tape or forming a resist on the peripheral portion, and the like. By etching with hydrofluoric acid (HF) or the like, the central portion of the thermal oxide film can be removed. After an oxide film (CVD oxide film) is formed on the wafer by CVD instead of heat treatment, the oxide film can be formed only on the peripheral portion according to the same procedure as described above. By performing CVD after masking the central portion, a CVD oxide film may be formed only on the peripheral portion.

The method for forming the resin film is not particularly limited, either.
A resin film diluted with an organic solvent is applied to a peripheral portion of the wafer surface by spin coating, and then heat-treated, whereby a resin film can be easily formed. The resin is not particularly limited, but may be a thermosetting resin such as an epoxy resin.

For example, as shown in FIG. 2, the wafer W is fixed on the turntable 2 so that the center thereof is located on the rotary shaft 3. Then, while rotating the wafer W, a thermosetting resin such as an epoxy resin dissolved in an appropriate solvent is applied to the peripheral portion of the wafer through the supply nozzle 4, and then this is subjected to a thermosetting treatment, so that only the peripheral portion of the wafer is applied. The epoxy resin coat film 1 can be easily formed. The resin is not limited to an epoxy resin, and any resin can be used as long as it has a polishing rate lower than that of the work after curing.

In forming any of the coating films,
The coat film is formed such that the wafer surface is exposed at the central portion of the wafer surface or is thinner than the peripheral portion, but if the coat film 1 is formed such that the wafer surface 5 is exposed at the central portion, the coat film 1 is formed. Is preferred because it can be thinner and the subsequent polishing time can be shortened.

Further, it is not essential to form a coat film on a portion other than the peripheral portion of the wafer surface, for example, on the back surface of the wafer. However, as shown in FIG. If performed, it is possible to prevent excessive etching and contamination of the wafer back surface due to abrasives and the like, and also possible to prevent generation of scratches due to holding of the back surface. The prevention of such stains and scratches is particularly effective when a resinous coating film is formed.

The wafer shown in FIG. 1 is an example in which a coat film according to the present invention is formed, and a coat film may be formed only on the peripheral portion of the wafer surface or only on the peripheral portions of the front and back surfaces of the wafer. As described above, the working efficiency can be improved by reducing the portion where the coat film is formed. After the polishing of the front surface, the coat film remaining on the back surface or the chamfered portion is washed and removed using a solution capable of dissolving and removing the coat film. Alternatively, the film may be removed by polishing, etching, mirror polishing, or the like for removing the coat film.

Although a desired coat film can be easily formed by the above-described method, the thickness of the coat film formed on the peripheral portion is determined by a simple method as follows, for example. Can be. Peripheral sag amount when polished by a conventional polishing method: Y, Silicon polishing rate: Rsi Polishing rate of coat film: Rc Thickness of coat film in peripheral portion: TH, and time until the coat film is removed. : T1 is
It is expressed as t1 = TH / Rc, and the thickness TH of the coat film can be determined so that the amount of silicon removed from the central portion during the time t1 matches the peripheral sag amount Y.

Therefore, Y = Rsi × (TH / Rc). When this is further modified, TH = Y × (Rc / Rsi), so that the peripheral sag amount (Y), the polishing rate of silicon (Rsi), If the polishing rate (Rc) of the coat film is measured in advance, the thickness (TH) of the coat film in the peripheral portion can be easily determined.

The polishing rate varies depending on the polishing conditions. According to the experiments conducted by the present inventors, polishing was performed under normal polishing conditions in which the polishing rate of the silicon wafer itself was 0.6 to 0.7 μm / min. When performing the polishing, the respective polishing rates are as follows. Thermal oxide film: 0.01 to 0.02 μm / min. CVD oxide film: 0.04 to 0.06 μm / min. Epoxy resin film: 0.02 to 0.04 μm / min. Polishing conditions, such as
Alternatively, the value varies depending on the coating film preparation conditions and the like, but can be easily obtained by conducting an experiment under the same conditions in advance.

FIG. 3 shows the results of an experiment on the polishing rate performed by the present inventors. As is clear from this graph, each coating film has a polishing rate of 1/10 or less as compared with that of a silicon wafer, and is much less polished than silicon. Therefore, polishing of the silicon in the peripheral portion can be delayed by only thinly coating the peripheral portion of the wafer, and the peripheral sag can be effectively prevented.

Note that the above calculation formula for deriving the thickness of the coat film is an example, and the thickness of the coat film is determined by the shape of the wafer (raw material wafer) after lapping or etching as described above. In consideration of the polishing allowance, the material and preparation conditions of the coating film, the polishing conditions such as the polishing agent and polishing pressure used, or the change in hardness due to the dope amount of the wafer to be polished, the polishing rate is previously confirmed by experiments, etc. And determine it appropriately.

After forming a coat film on the peripheral portion, FIG.
Can be polished using a conventional holding plate as shown in FIG. That is, the wafer W is vacuum-adsorbed and held in the holding plate 16 provided with a large number of through-holes through the through-holes, the abrasive 15 is supplied to the polishing cloth 13, and a predetermined pressing force is applied to the surface of the wafer against the polishing cloth 13. Polish while sliding. By performing such polishing, in the initial stage of polishing, silicon is directly polished in the central portion of the wafer, while a coat film having a low polishing rate is polished in the peripheral portion, so that the central portion of the wafer is once thinned. . After that, when the coat film in the peripheral portion is removed, the silicon in the peripheral portion is polished at a higher polishing rate than in the central portion. You only have to end.

The polishing method of the present invention can be applied at any stage in the polishing process. However, since the peripheral sag is almost always generated by the primary polishing, which has the largest polishing allowance, it is preferably applied to the primary polishing. be able to. Therefore,
After the primary polishing according to the method of the present invention, the secondary polishing is performed as necessary, and the finish polishing is further performed, whereby a mirror-finished wafer having a very high flatness over the entire surface can be obtained.

In the above-mentioned polishing method, the case of single-wafer polishing has been described. However, the present invention is not particularly limited with respect to the type of holding plate, the method of holding a wafer, and the like, and is applicable to the case of batch-type polishing. be able to. That is, the back surfaces of a plurality of wafers on which a desired coat film has been formed can be attached to a glass or ceramic plate via an adhesive or wax, and the plurality of wafers can be polished simultaneously.

The silicon wafer polished by the polishing method of the present invention is a mirror-polished wafer having excellent flatness over the entire surface of the wafer, in which peripheral sag is suppressed.
The yield rate of wafers can be remarkably improved. In particular, it is possible to stably manufacture a wafer having a very high flatness having a surface-based SFQRmax of 0.15 μm or less including a region within 2 mm from the outer peripheral end irrespective of the structure of the holding plate and the like. Further, by using such a wafer, a circuit can be formed on the entire surface, and the productivity and yield of semiconductor devices can be significantly improved.

[0040]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. (Example) A silicon wafer (diameter: 8 inches) after etching was formed into a film by CVD and C
A VD oxide film was formed. Next, the peripheral portion from the outer peripheral edge of the wafer to 5 mm was masked and etched, and the central portion of the oxide film was removed to leave the CVD oxide film only in the peripheral portion. The thickness of the CVD oxide film was calculated by the above equation, and the CVD oxide film was formed based on the calculated value. That is, the polishing rate Rs of silicon
i: 0.6 μm / min, polishing rate Rc of the coat film (CVD oxide film): 0.06 μm / min, peripheral sag amount Y: about 0.3
μm (value obtained by polishing by a conventional method), the thickness of the coat film TH = Y × (Rc / Rsi) = 0.3 μm
× (0.06 / 0.6) = 30 nm.

Using the wafer on which the coating film was formed as described above, primary polishing was performed under the following polishing conditions. Polishing device: Vacuum adsorption type single wafer polishing device Polishing cloth: SUBA600 (trade name, manufactured by Rodale) Polishing agent: Colloidal silica polishing Polishing load: 300 gf / cm ² Relative speed: 50 m / min Polishing allowance: 10 μm

(Comparative Example) A silicon wafer having the same size as the wafer used in the example was polished under the same polishing conditions as in the example 1 without forming a coat film.

The wafers polished in the examples and comparative examples were measured for 10 m from the outer peripheral edge using a capacitance type thickness measuring instrument.
The thickness distribution of the peripheral part based on the position of m (exclusion area:
2 mm) and the results are shown in FIG.

The wafer polished in the embodiment (with a coating film) achieved very high flatness to the peripheral portion, the displacement was 0.1 μm or less even at a position 2 mm from the outer peripheral edge, and the SFQRmax was 0.1 mm. It was 09 μm. On the other hand, although the wafer polished in the comparative example (without the coating film) is improved more than the peripheral sag of the raw material wafer, peripheral sag starts around 6 mm from the outer peripheral end and 2 m from the outer peripheral end.
At the position of m, there was a displacement of about 0.3 μm. Also, SFQ
Rmax was about 0.20 μm.

As shown in FIG. 4, peripheral sagging had already occurred in the peripheral portion of the raw material wafer measured in advance after etching. Normally, when polishing a wafer on which peripheral sag has occurred in the etching process, in the very initial stage of polishing, the peripheral portion of the wafer has a lower polishing pressure and a lower polishing rate because the thickness is thinner than the central portion. , The whole surface of the wafer is almost the same condition (polishing speed)
Or the peripheral portion of the wafer is excessively polished. Therefore, when polishing with a polishing allowance of about 10 μm in the polishing process,
A new peripheral sag as shown in FIG. 6 occurs. However, in the example, since the coat film was formed on the peripheral portion of the wafer, it was possible to prevent the peripheral sag in the polishing process as described above.

The present invention is not limited to the above embodiment. The above embodiment is merely an example, and has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same function and effect,
Anything is included in the technical scope of the present invention.

For example, in the above-described embodiment, a case where a silicon wafer is polished has been described as an example. However, the object to be polished to which the present invention can be applied is not limited to a silicon wafer, and a circle requiring high flatness of the entire surface is required. Applicable to polishing of shaped workpieces. In addition, since peripheral sagging occurs regardless of the diameter of the work, the present invention is not particularly limited with respect to the size of the work.

In the embodiment, the method of controlling the thickness of the coat film is controlled so as to obtain a high flatness after one-stage polishing. However, when polishing is performed in a plurality of stages, final polishing is performed. It is necessary to have high flatness later. As described above, the present invention is optimally used in primary polishing where peripheral sagging is most likely to occur. However, in the subsequent polishing such as secondary polishing and finish polishing, a slight sag may occur in the periphery. Therefore, the thickness of the coating film is not determined so as to completely achieve high flatness by the primary polishing. In consideration of the amount of sag in the final polishing, the thickness of the coat film may be controlled and polished in the first polishing so that the outer peripheral portion is slightly jumped up (the peripheral portion is slightly thickened). That is, the present invention may be used so that a high flatness wafer can be obtained in a final product. Of course, a coat film as in the present invention may be formed and polished at each polishing step.

[0049]

As described above, when polishing a circular workpiece such as a semiconductor wafer that requires extremely high flatness, the surface of the workpiece is polished after forming the coat film according to the present invention. Thereby, overpolishing of the peripheral portion of the work can be substantially suppressed.

In particular, if the present invention is applied to polishing that requires extremely high flatness, such as a semiconductor wafer, there is no need to improve the structure of the holding plate, and the wafer is held using the conventional holding plate. By polishing the wafer, peripheral sag is prevented, very high flatness is achieved over the entire surface up to near the outer peripheral edge of the wafer, and a mirror-finished wafer having excellent surface characteristics can be obtained. Such a mirror-finished wafer can form a circuit on the entire surface, and can improve the productivity and yield of semiconductor devices.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a wafer before polishing on which a coat film according to the present invention is formed.

FIG. 2 is a schematic view showing a part of a process of forming a thermosetting resin film according to the present invention.

FIG. 3 is a graph showing a polishing rate of a silicon wafer and various coating films.

FIG. 4 is a graph showing the amount of displacement of the thickness of the peripheral portion of the wafer measured in Examples and Comparative Examples.

FIG. 5 is a schematic view showing an example of a wafer polishing apparatus.

FIG. 6 is a graph showing a displacement amount of a thickness of a peripheral portion of a wafer after polishing by a conventional method.

[Explanation of symbols]

1 ... coat film, 2 ... rotary table, 3 ... rotary axis,
4 ... supply nozzle, 5 ... wafer front surface, 6 ... wafer back surface, 11 ... holder, 12 ... surface plate, 13 ... polishing cloth, 14 ... abrasive supply device, 15 ... abrasive, 16
... holding plate, W ... work (wafer).

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Michito Sato 150 Odakura Osaikura, Nishigo-mura, Nishishirakawa-gun, Fukushima Prefecture

Claims (6)

[Claims] 1. A method of holding a circular work with a holding plate and polishing the surface of the work by bringing the surface of the work into sliding contact with a polishing cloth,
A coat film made of a material having a polishing rate lower than that of the work is formed at least in a peripheral portion of the work surface, and is formed such that the work surface is exposed or thinner in a central portion of the work surface than in the peripheral portion, A polishing method for a work, comprising polishing the work surface while holding the back surface of the work. 2. The polishing method according to claim 1, wherein the workpiece is a silicon wafer. 3. The polishing method according to claim 2, wherein the coat film is formed on a peripheral portion within 10 mm from an outer peripheral end of the surface of the wafer. 4. A silicon oxide film as the coat film,
4. The polishing method according to claim 1, wherein a silicon nitride film or a resin film is formed. 5. The method according to claim 1, wherein the silicon oxide film or the silicon nitride film is formed by forming an oxide film or a nitride film on at least the wafer surface by CVD or heat treatment.
5. The polishing method according to claim 4, wherein the polishing is performed by masking a peripheral portion of the wafer surface and performing an etching process. 6. The polishing method according to claim 4, wherein the resin film is formed by applying the resin to a peripheral portion of the surface of the wafer by spin coating and then performing a heat treatment.