JP2003133273A - Raw material wafer for polishing and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a raw material wafer for polishing that can be produced without the use of a special jig during a polishing process into a mirror-surfaced wafer with little peripheral sagging and the high flatness of at least 0.15 μm or below in SFQR, and is shaped to have, if necessary, a little sagging or rather a little bound in the peripheral portion thereof. SOLUTION: A raw material wafer 1 for polishing, wherein there exists a film such as an oxide film 2 or the like comprising a material which takes longer time for polishing than the wager at a chamfered portion which contacts at least a main surface, and there does not exist the film at the main surface. For example, after the oxide film is formed on the entire wafer, the oxide film on at least the main surface of the wafer is removed by surface grinding, etching, or wrapping, thus making it possible to produce the wafer which has the oxide film at a chamfered portion contacting at least the main surface of the wafer and no oxide film on the main surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing raw material wafer before performing mirror polishing, and more particularly to a polishing raw material wafer in which excessive polishing of the peripheral portion of the wafer is suppressed during polishing, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the field of semiconductors, memory devices have been highly integrated and miniaturized year by year, and pattern dimensions have been reduced and semiconductor wafers serving as substrates have been increased in diameter. A silicon wafer is generally used as a semiconductor substrate material used for memory devices and the like.

As shown in FIG. 8, the procedure for manufacturing a silicon wafer is as shown in Czochralsk (Czochralsk).
i; CZ) method for producing a single crystal ingot, and a wafer processing step for slicing the single crystal ingot into a wafer and processing it into a wafer having at least one principal surface of a mirror surface (mirror surface wafer) It is divided into

Further, as a wafer processing step, FIG.
As shown in Fig. 1, a slice step of slicing a single crystal ingot to obtain a thin disk-shaped wafer, a cracking of the wafer, a chamfering step of chamfering its outer peripheral portion to prevent chipping, and a flattening of the wafer. Lapping process, etching process to remove processing strain remaining on the wafer, polishing (polishing) process to mirror the surface of the wafer, and cleaning the polished wafer to remove abrasives and foreign substances adhering to the surface There is a cleaning process. The above steps show the main steps, and other steps such as a heat treatment step may be added, the same step may be performed in multiple steps, or the order of steps may be changed. The wafer may be flattened by surface grinding instead of lapping. The mirror-finished wafer that has undergone the above steps is then sent to the device manufacturing step.

Conventionally, with respect to the flatness of a polished wafer, a flatness equal to or smaller than the wiring width is required from the viewpoint of control of a film forming process such as lithography in a device manufacturing process. For example, the conventionally required flatness is SFQ.
Although R was 0.18 μm or less, recently, a wafer having SFQR of 0.15 μm or less, or 0.13 μm or less, and further 0.10 μm or less has been required. In addition, SFQR (Site Front)
“Least Squares Range” is a value that represents the maximum value of the unevenness on the surface by calculating the surface-referenced average plane for the flatness for each site. Generally, the size of the site is evaluated as about 25 mm × 25 mm.

Even if the wafer is processed into a high flatness through a flattening step such as a lapping step or a surface grinding step, the flatness may be deteriorated in the subsequent etching step or polishing step. In particular, in the polishing step, when the stock removal (polishing stock) increases, the peripheral portion of the wafer is excessively polished from the central portion, so-called peripheral sag (peripheral sag) may occur, and flatness may deteriorate.

As a method for suppressing the outer peripheral sag, for example, a jig called a retainer ring that protrudes from the holding surface by the thickness of the wafer is provided on the outer periphery of a holding plate that holds the wafer during polishing, and the outer peripheral portion of the wafer is polished during polishing. Have proposed a method of sinking a polishing cloth, or a method of suppressing excessive polishing of the peripheral portion of the wafer by floating the peripheral portion of the wafer by using a holding plate having a diameter smaller than that of the wafer.

[0008]

The silicon wafer polishing step is generally carried out in a plurality of stages of polishing, for example, after primary polishing,
Secondary polishing and further final polishing are performed, and the polishing allowance is about 10 μm in the entire polishing process. However, when polishing is performed to this extent by a normal polishing method, the SFQR which has been recently required.
It is difficult to manufacture a mirror-finished wafer having a grain size of 0.15 μm or less.

It is usually important to obtain a mirror-finished wafer having a high flatness. However, depending on the subsequent manufacturing of the device, it may be better if the peripheral portion of the wafer is slightly sagged, or vice versa. In some cases, it may be preferable to use a retainer ring or a small-diameter holding plate, but it is difficult to control how the polishing cloth is submerged and how much the wafer is floated, and the quality varies. There's a problem.

In view of the above problems, according to the present invention, it is possible to obtain a mirror-finished wafer having a high flatness with a small peripheral sag and an SFQR of 0.15 μm or less without using a special jig or the like. It is an object of the present invention to provide a polishing raw material wafer and a method for manufacturing the same, which can be a mirror-finished wafer in which the peripheral portion of the wafer is slightly sagged or, on the contrary, is slightly shaved, if necessary.

[0011]

To achieve the above object, according to the present invention, there is provided a polishing raw material wafer,
Provided is a raw material wafer for polishing, characterized in that a chamfered portion in contact with at least one main surface has a film made of a material whose polishing rate is slower than that of the wafer, and the film does not exist on the one main surface. (Claim 1).

Originally, the outer peripheral portion of the wafer is excessively polished and the outer peripheral sag is apt to occur. However, when the raw material wafer having the above film is polished, the peripheral portion of the wafer is polished in the vicinity of the chamfered portion. Since the speed becomes slower, the polishing margins at the central portion where the semiconductor material is exposed and at the peripheral portion near the chamfered portion are almost the same, and the outer peripheral sag is suppressed.

The film made of a material having a low polishing rate is not particularly limited, but an oxide film can be preferably used. That is, according to the present invention, the polishing raw material wafer is characterized in that an oxide film is present in at least a chamfered portion in contact with one main surface, and no oxide film is present in the one main surface. A raw material wafer for polishing is provided (Claim 2).

For example, when polishing a silicon wafer,
In the case of the raw material wafer as described above, the presence of the silicon oxide film in the chamfered portion of the wafer causes a difference in polishing rate between the central portion and the peripheral portion of the wafer as polishing progresses. That is, originally, the peripheral portion of the wafer is excessively polished and the outer peripheral sagging is more likely to occur.However, in the case of the silicon oxide film and silicon, the polishing rate by the polishing liquid is much slower in the silicon oxide film. The polishing rate in the vicinity of the formed chamfered portion is slightly reduced. It is also possible that the chamfered oxide film acts like a retainer ring.

When polishing is performed using such a raw material wafer for polishing, as a result, the polishing allowance in the central portion where the silicon is exposed and in the peripheral portion near the chamfered portion where the silicon oxide film is formed are about the same. Becomes Therefore, it is not necessary to use a special jig such as a retainer ring or a small diameter holding plate,
Outer peripheral sagging is suppressed even with normal polishing, and SFQR is 0.1
A highly flat mirror-finished wafer of 5 μm or less can be obtained. Further, if the thickness of the oxide film at the chamfered portion is adjusted, it is possible to process it into any shape after polishing, such as a slight sag in the peripheral portion or conversely a raised shape.

Further, according to the present invention, there is provided a method of manufacturing a raw material wafer for polishing, which comprises forming a film made of a material having a slower polishing rate than the wafer on the entire surface of the wafer,
By removing the film on at least one main surface of the wafer, a film made of a material having a polishing rate slower than that of the wafer exists in the chamfered portion in contact with at least one main surface, and the film is formed on the one main surface. There is provided a method of manufacturing a raw material wafer for polishing, which comprises manufacturing a wafer which does not exist.

As described above, after the film made of a material having a slow polishing rate is formed on the entire surface of the wafer, and then the film other than the chamfered portion is removed, the film made of a material having a slower polishing rate than the wafer is formed in the chamfered portion. However, it is possible to easily manufacture a polishing raw material wafer having no film formed on the polishing surface.

The oxide film can be suitably used also in the case of manufacturing such a raw material wafer for polishing. That is, according to the present invention, there is provided a method for producing a raw material wafer for polishing, which comprises forming an oxide film on the entire surface of the wafer,
By removing the oxide film on at least one main surface of the wafer by surface grinding, a wafer having an oxide film on the chamfered portion in contact with at least one main surface and having no oxide film on the one main surface can be obtained. A method for producing a raw material wafer for polishing, which is characterized in that it is produced (claim 4).

For example, an oxide film is formed on the entire surface of a silicon wafer (wafer before polishing) that has been highly flattened through an etching process or the like, and then one or both main surfaces are ground. This makes it possible to easily manufacture a wafer having a polished surface (silicon) in which an oxide film remains in the chamfered portion. It is a simple method to form the oxide film on the entire surface of the wafer, but when the surface to be polished is one side, it is only necessary to form the oxide film on the chamfered portion on the polished surface side and one main surface. But good. In any case, the oxide film may be formed on the chamfered portion in contact with the polishing surface.

Since the surface grinding can be processed with a very high degree of flatness, it is possible to improve the waviness and the like caused by the etching in the previous step. That is, it is possible to manufacture the raw material wafer with the surface layer removed of the oxide film on the main surface and less waviness. Therefore,
By polishing such a raw material wafer, it is possible to obtain a mirror-finished wafer having extremely high flatness with almost no waviness and sagging on the outer periphery.

As another method, after an oxide film is formed on the entire surface of the wafer, the oxide film on at least one main surface of the wafer is removed by etching so that the oxide film exists on the chamfered portion in contact with at least one main surface. Also, a wafer having no oxide film on the one main surface can be manufactured (Claim 5). For a silicon wafer (wafer before polishing) that has undergone an etching process, etc., if the oxide film on at least one main surface of the oxide film formed on the entire surface of the wafer is removed by etching, silicon appears on the etched surface and the chamfered portion It is possible to manufacture a wafer in which the oxide film remains.

As yet another method, after forming an oxide film on the entire surface of the wafer, the oxide film on at least one main surface of the wafer can be removed by lapping (claim 6). In this way, when removing the oxide film on at least one main surface of the wafer by lapping, it is more difficult to remove the oxide film than in the case of surface grinding, but since the oxide films on both sides can be removed simultaneously, only the chamfered portion can be removed. A wafer on which an oxide film is formed can be efficiently obtained.

Further, according to the present invention, there is provided a method for producing a raw material wafer for polishing, wherein an oxide film is formed on a plurality of wafers in a state where the main surfaces of the wafers are superposed on each other, whereby at least one main surface is formed. It is also possible to manufacture a wafer in which an oxide film is present in the chamfered portion in contact with the chamfered portion and the oxide film is not present in the one main surface (claim 7). According to such a method, it is possible to simultaneously form an oxide film on the chamfered portion of the wafer for a plurality of wafers, and then it is possible to omit the removal of the oxide film existing on the main surface. A raw material wafer for polishing can be manufactured extremely efficiently.

The thickness of the oxide film may be appropriately set depending on the polishing conditions and the like, but it is particularly preferable to form it to a thickness of 30 nm to 1 μm (claim 8). An oxide film having such a thickness can be easily formed, and the polishing rate at the peripheral portion can be surely delayed to prevent the occurrence of peripheral sag, so that a wafer having a very high flatness can be obtained. Can be manufactured.

It is preferable that a thermal oxide film is formed as the oxide film. Regarding the thermal oxide film, for example, in the case of a silicon wafer, the thermal oxide film can be uniformly formed on the silicon surface by heat treatment in an atmosphere containing water vapor and oxygen, and the film thickness can be easily controlled.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below. The semiconductor wafer used in the present invention is not particularly limited, and the film formed on the chamfered portion of the wafer is not particularly limited as long as it is made of a material whose polishing rate is slower than that of the wafer, but the preferred embodiment is described below. As an example, a raw material wafer for polishing in which an oxide film is formed on a silicon wafer will be described. 1 (a)-
(D) is a schematic view showing a raw material wafer for polishing according to the present invention, in which an oxide film is present in at least one chamfered portion in contact with one main surface, and no oxide film is present in the one main surface. Shows a wafer.

The wafer 1 of FIG. 1 (a) is a raw material wafer mainly for double-side polishing, in which the oxide film 2 exists only in the chamfered portion. The wafer 1 shown in FIG. 1B is a raw material wafer for single-side polishing in which an oxide film 2 exists on the chamfered portion and the back surface. Oxide film exists in such chamfered part,
And if the raw material wafer has no oxide film on at least one main surface, excessive polishing of the peripheral portion is suppressed in the polishing process, and a wafer with high flatness without sagging in the peripheral portion of the wafer can be obtained. .

FIG. 6 shows a mode in which the polishing wafer as shown in FIG. 1 (b) is polished by using a single-side polishing apparatus. The apparatus and the polishing conditions in the polishing step may be any conventional ones and are not particularly limited in the present invention. However, as shown in FIG. The back side of the wafer 1 is chucked to the polishing head (holding plate) 14 which is supported. Then, the wafer 1 is pressed against the polishing cloth 12 adhered to the surface plate (polishing surface plate) 13 and the wafer 1 and the surface plate 13 are rotated while supplying the polishing liquid, so that the wafer 1 is applied to the polishing cloth 12. The polishing surface can be made into a mirror-finished surface by sliding contact. The polishing step is not limited to the single-side polishing apparatus as shown in FIG. 6, and when polishing both sides of the wafer, the double-side polishing apparatus can be used for polishing.

When the raw material wafer for polishing according to the present invention is polished as described above, a difference in polishing rate occurs between the central portion and the peripheral portion of the wafer as the polishing progresses. The polishing rate for silicon is about 0.6 μm /
If it is an oxide film, the polishing rate is about 0.
There is a difference of about 10 times the polishing rate from about 06 μm / min. Therefore, if a silicon wafer having an oxide film formed on the chamfered portion is polished, excessive polishing of the peripheral portion of the wafer near the chamfered portion is suppressed. Further, as the polishing progresses, the oxide film in the chamfered portion slightly protrudes from the main surface of the wafer, and this oxide film has a function similar to that of a retainer ring and serves to slightly sink the polishing cloth. It is considered that this also suppresses the peripheral sag.

The wafer 1 of FIG. 1C is a raw material wafer for double-sided polishing, but the oxide film 2 in the chamfered portion in contact with the main surface (surface to be polished) is thinner than the wafer of FIG. 1A. Has become. In addition, the wafer 1 shown in FIG.
Is a raw material wafer for single-side polishing, but the oxide film 2 in the chamfered portion in contact with the surface to be polished is thicker than the wafer shown in FIG. 1 (b). If the thickness of the oxide film at the chamfered portion is adjusted in this manner, a mirror-finished wafer having an arbitrary shape with a peripheral edge slightly shaved or sagging can be formed by polishing according to the purpose.

That is, as shown in FIG. 1C, if the wafer 1 has a thin oxide film 2 in the chamfered portion, excessive polishing of the peripheral portion of the wafer is suppressed, but the effect is small,
The peripheral portion of the wafer after polishing may have a slightly sagging shape. On the other hand, the wafer 1 having the thick oxide film 2 in the chamfered portion as shown in FIG. 1 (d) has a strong effect of delaying the polishing rate of the peripheral portion of the wafer. It can be a specular wafer with a slightly raised edge.

A method of manufacturing the above-mentioned polishing raw material wafer and the like will be described below. In the method for manufacturing a polishing raw material wafer according to the present invention, for example, as shown in FIG.
A semiconductor ingot is sliced into a wafer, and a chamfering step, a flattening step, and an etching wafer obtained by subjecting the wafer to an etching step and the like are performed to form an oxide film on the chamfered portion of the wafer (hereinafter, “chamfering”). "Partial oxide film forming step"). Through these steps, it is possible to obtain a wafer in which an oxide film exists at least in the chamfered portion in contact with one main surface (surface to be polished) of the wafer and the oxide surface does not exist in the surface to be polished.

Note that FIG. 7 is an example, and the steps before the chamfered oxide film forming step are not particularly limited and are arbitrary, and any of the commonly used methods can be used. However, before forming an oxide film on the chamfered portion, the shape should be kept as flat as possible. This is because the present invention can prevent the sagging of the outer periphery due to polishing, and the better the shape before polishing, the higher the flatness of the wafer can be obtained.

The chamfered oxide film forming step will be described more specifically below. As a method of forming the oxide film on the chamfered portion, for example, after forming the oxide film on the entire front and back surfaces including the chamfered portion of the wafer, the oxide film on one main surface or both main surfaces may be removed. Regarding how to form an oxide film,
Chemical vapor deposition (CVD method), heat treatment, application of a solution of a silicon compound dissolved in an organic solvent and baking, or an oxide film formed by baking, or an oxide film formed by ozone water is not particularly limited, but a silicon wafer is used. It is preferable to form a thermal oxide film by heat treatment in an atmosphere containing water vapor or oxygen.

For example, if the wafer is heat-treated in an atmosphere containing oxygen, a thermal oxide film can be uniformly formed on the entire surface of the wafer, and the film thickness can be made sufficiently thick.
Further, according to the atmospheric pressure chemical vapor deposition method, the CVD oxide film is mainly formed on one main surface and the chamfered portion of the wafer, and is hardly formed on the other main surface. Further, regarding the oxide film of the chamfered portion, a sufficient thickness can be obtained on the side where the CVD oxide film is formed, but the portion contacting the back surface side (the other main surface) may not be sufficient. In such a case, a raw material wafer for single-side polishing can be used. At this time, if a sufficient oxide film can be formed also on the chamfered portion on the other main surface side, it can be used as a raw material wafer for double-side polishing.

Further, the CVD oxide film may be formed on the entire surface (both sides) of the wafer by reversing the wafer, etc., whereby the oxide film thickness of the chamfered portion in contact with the front and back main surfaces can be surely made uniform. it can. Also, reduced pressure CVD or other methods may be used.

The oxide film thickness may be set according to the conditions in the polishing process to be performed later, the chamfering angle of the chamfered portion of the wafer, and the like. It suffices to set an appropriate oxide film thickness. Although it depends on the polishing conditions and the like, it is preferable to form an oxide film of about 30 nm to 1 μm (300 Å to 10000 Å) in order to obtain a flat wafer. An oxide film having a thickness in this range can be easily formed, and at the same time, the polishing rate at the peripheral portion of the wafer can be reliably delayed to prevent the occurrence of peripheral sag. If the oxide film in the chamfered portion is thinner than 30 nm, excessive polishing of the peripheral portion of the wafer may not be suppressed, whereas if an oxide film having a thickness of more than 1 μm is formed, the oxide film formation process will take time. The productivity falls, so the above range is preferable.

After forming the oxide film on the wafer as described above, the oxide film on one side or both sides of the side to be polished is removed.
The oxide film can be easily removed by surface grinding or etching. As another method, the oxide film can be removed by lapping.

(Removal of oxide film by surface grinding) When the oxide film is removed by surface grinding, a double-sided grinding machine or a single-side grinding machine is used. FIG. 5 shows an example of a single-side grinding machine for removing an oxide film on one main surface. The wafer 1 having the oxide film 2 formed on the entire surface is adsorbed on a wafer holding plate (adsorption chuck) 3, and a cup-type wheel grindstone 5 fixed to a grinding head 4 supported by a spindle 6 is pressed against the wafer 1 to The holding plate 3 and the spindle 6 are rotated to grind one side of the wafer. After finishing the grinding of one surface, the oxide film on both main surfaces can be removed by turning over the wafer and grinding the opposite surface, if necessary. In this step, the number of the grindstone used for the cup-type wheel grindstone is # 20 in order to reduce damage.
It is preferably set to 00 or more, particularly about # 4000.
The grinding device is not limited to this, and a double-head grinding device capable of grinding both surfaces at the same time may be used if the oxide film on both surfaces is removed.

In the present invention, the surface is ground so that an oxide film remains on the chamfered portion and the oxide film is removed on at least one main surface. FIG. 2A shows a raw material wafer for polishing only one surface, which is an example of a stock removal when only one surface of the oxide film is removed by surface grinding. Figure 2
(B) is a raw material wafer for polishing both surfaces, and is an example of a stock removal for removing the oxide film on both surfaces by surface grinding (or lapping). As shown in these figures, preferably, the oxide film on the main surface is removed, and further, grinding is performed to such an extent that the silicon is slightly scraped. Specifically, considering the stability of the grinding machine, the normal wafer surface may be ground by about 5 to 20 μm. The chamfered portion itself is also slightly ground by such grinding, but if it is this level, it does not cause a problem. The chamfered shape may be adjusted in advance in the chamfering step so that the chamfered shape is within the standard after grinding.

The surface grinding process has a high processing ability, and the oxide film and the silicon surface can be removed at the same grinding speed, and the grinding itself does not cause sagging on the outer periphery. This grinding also has an advantage that undulations on the surface of the wafer can be removed. By grinding as described above, it is possible to reliably obtain a polishing raw material wafer in which an oxide film is formed on a chamfered portion in contact with at least one main surface and an oxide film is not formed on at least one main surface.

(Removal of Oxide Film by Lapping) Instead of the surface grinding, the oxide film can be removed by lapping. Although lapping is not as high in processing capacity as surface grinding, it is possible to simultaneously process both surfaces of the wafer by using an ordinary lapping apparatus, which is suitable for mainly removing oxide films on both main surfaces. At the same time, there is an advantage that surface undulations can be removed.

In this lapping, both surfaces are simultaneously processed using, for example, free abrasive grains of Al ₂ O ₃ . Similar to surface grinding, the oxide film on the main surface is removed, and the wafer main surface (silicon)
Is carried out to such an extent that it is slightly wrapped. 4 on both sides
About 30 μm is sufficient. By doing so, it is possible to reliably manufacture a wafer having an oxide film on the chamfered portion in contact with at least one main surface of the wafer and having no oxide film on both main surfaces. In addition, undulations on the surface of the wafer can be removed.

(Removal of Oxide Film by Etching) As still another method, an oxide film may be formed on the entire surface of the wafer and then the oxide film on at least one main surface may be removed by etching.
For example, the oxide film on at least one main surface of the wafer is removed by a wet etching method, a dry etching method, or the like so that the oxide film remains only on the chamfered portion to expose silicon.

Specifically, as shown in FIG. 3, the chamfered portion of the wafer 1 on which the oxide film 2 is formed, and if necessary, one main surface (back surface) is covered with a film or resin to form a mask. Form 7. Then, the unmasked one main surface (surface to be polished) of this wafer is subjected to, for example, HF treatment,
The oxide film may be removed by etching (dissolving and removing). This makes it possible to manufacture a wafer in which an oxide film is present in the chamfered portion in contact with the one main surface (surface to be polished) and no oxide film is present in the one main surface. Note that FIG. 3 shows a case where the oxide film is removed on only one side. If the oxide films on both sides are removed by etching, only the chamfered portion may be masked and the both sides are subjected to HF treatment.

Hydrofluoric acid (HF) is preferable as the etching liquid, and the oxide film on the unmasked surface can be easily removed by etching. In particular, if the raw material wafer before etching removal is a high flatness wafer with less waviness, by removing the oxide film on the main surface by etching as described above,
It is possible to obtain a highly flat wafer equivalent to the case of performing surface grinding.

(Formation of oxide film only on chamfered portion) In the present invention, the oxide film on the main surface is removed so that the oxide film on the chamfered portion remains after the oxide film is formed on the entire surface of the wafer as described above. Besides, an oxide film may be formed only on the chamfered portion from the beginning. As such a method, if an oxide film is formed in a state where the main surfaces of a plurality of wafers are superposed, an oxide film exists in a chamfered portion in contact with at least one main surface, and the oxide film is present on the one main surface. Wafers that do not exist can be manufactured.

For example, as shown in FIG. 4, a plurality of wafers having the same size are superposed so that their principal surfaces coincide with each other, and an oxide film is formed on the wafer while maintaining the state. At this time, the oxide film is formed only on the exposed portion of the wafer, that is, on the chamfered portion of each wafer and on the outer principal surfaces of both ends of the wafer. Therefore, if the superposed wafers are peeled one by one after the oxide film is formed, the other wafers except the two wafers at both ends become raw material wafers for polishing in which the oxide film exists only in the chamfered portion. Further, the two wafers at both ends are also wafers having an oxide film in the chamfered portion in contact with the one main surface, and having no oxide film on the one main surface, and can be used as raw material wafers for polishing. .

By polishing the raw material wafer for polishing produced as described above, a mirror-finished wafer having a high flatness in which the peripheral sag is suppressed can be obtained. However, after polishing, the oxide film remaining on the chamfered portion of the wafer may be removed by cleaning with hydrofluoric acid. As a result, a mirror-finished wafer having no oxide film on the entire surface of the wafer can be obtained. If the oxide film remains even if it does not cause a problem in product specifications, the oxide film may be left as it is without being removed. For example, there are many product specifications in which an oxide film is formed on the back surface in order to prevent so-called autodoping. Therefore, an oxide film is formed on the chamfered portion and the back surface of the wafer as shown in FIG. 1 (b) and FIG. 1 (d). The raw material wafer for polishing also has an advantage that it can be made into a product even after the one-side polishing, with the oxide film left on the back surface.

Polishing is usually carried out in a plurality of stages, and usually, in order to improve extremely minute irregularities (surface roughness and haze), the polishing is repeated by changing the polishing conditions such as the hardness of the polishing cloth and the polishing agent supplied. (So-called secondary, finish polishing). However, the polishing allowance and the peripheral sag that influence the flatness are
The second polishing) has the greatest effect. Therefore, in the primary polishing, if the polishing raw material wafer provided by the present invention is used for polishing, it is possible to manufacture a highly flat polished wafer with less peripheral sag. In addition, if the thickness of the oxide film formed on the chamfered portion is adjusted, a mirror-finished wafer having an arbitrary shape can be obtained in which the peripheral portion is slightly shaved or sagged after polishing.

Furthermore, after polishing, water cleaning or alkali cleaning and / or acid cleaning can be performed, and then rinse cleaning with water can be performed. A brush or ultrasonic vibration may be used as an auxiliary means for cleaning. After the cleaning is finished, for example, spin drying is performed to obtain a mirror-finished wafer free from dirt and cleaning liquid.

The case where an oxide film is formed on a silicon wafer has been described above. As the film formed on the chamfered portion of the wafer, PET (polyethylene terephthalate), acrylic, PVB (polyvinyl butyral),
In addition to a resin film such as an epoxy resin, a film made of a material that has a lower polishing rate than silicon, has no metal contamination, has good adhesiveness to silicon, and is easily removed after polishing can be suitably used. . In particular, the oxide film is particularly preferable because it is easy to form, does not peel off during polishing, and can be easily removed by HF after polishing.

[0053]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. (Example 1) 25 silicon wafers having a diameter of 200 mm sliced from a silicon single crystal ingot with a wire saw were chamfered, then single-sided ground with a surface grinder, the wafers were washed, and then the front and back surfaces were washed. Reversely, the back side of the wafer was ground to remove about 25 μm each from the front and back sides. Further, it was washed with water to obtain a ground wafer with high flatness.

Next, as an etching process, alkali etching and acid etching with phosphoric acid were performed. NaO
A cassette containing 25 ground wafers was immersed in an etching bath containing an alkaline etching solution containing H, and etching was performed on both sides at about 20 μm at 80 ° C. Next, using a mixed acid composed of hydrofluoric acid, nitric acid, phosphoric acid and water, both surfaces were similarly etched at 25 ° C. to about 10 μm. After the etching, the wafer was washed with water and spin-dried to obtain an etching wafer.

Next, in the chamfered oxide film forming step, a film was formed on the entire surface of the silicon wafer after etching by thermal oxidation to form a thermal oxide film on the entire surface of the wafer. Here, the wafer was heat-treated at 1100 ° C. in an oxygen atmosphere to form an oxide film having a thickness of about 5000 Å (0.5 μm).

The main surface of the wafer to be polished was 10 μm single-sided using an in-feed type single-sided grinding machine with a grindstone number # 2000. As a result, an oxide film was formed only on the chamfered portion and the back surface of the wafer (remained).
A raw material silicon wafer for polishing was obtained.

In the polishing step, polishing was performed using a single-sided polishing machine as shown in FIG. The back surface side of the polishing raw material wafer having the oxide film formed on the chamfered portion as described above was adsorbed and held by the polishing head (holding plate). Then, a polishing liquid containing a colloidal silica-based abrasive is dropped on the polishing cloth (nonwoven fabric) on the rotating surface plate, and the polishing head is lowered to apply a pressure of 20 kPa to the polishing surface plate to which the polishing cloth is attached. The surface of the wafer was pressed and brought into sliding contact with the polishing cloth to carry out primary polishing.

After that, the polishing conditions were changed, and the secondary polishing and the final polishing were sequentially performed. After finishing polishing, the polished wafer is brush washed, rinsed and dried in order,
A wafer having a mirror-finished surface (one surface) was obtained. The polishing stock removal of the wafer in the polishing step was about 8 μm.

For the mirror-finished wafer obtained as described above, a capacitance size flatness measuring instrument Ultra Gauge 9500 manufactured by ADE was used, and the site size was 25 mm ×
The flatness (SFQR) was measured at 25 mm.

Here, the flatness (SFQR) is defined as the maximum displacement amount on each of the + side and the-side from the plane, which is the in-site plane calculated by the least square method of the data in the set site. It is the sum of absolute values, and the maximum value of SFQR obtained on the wafer surface by evaluating each site is SFQRm.
ax. SFQRmax of the obtained mirror surface wafer
Was 0.13 μm or less for all wafers, and most of the wafers was 0.10 μm or less.

(Example 2) As the chamfered oxide film forming step, a film was formed by thermal oxidation on the entire surface of the etched silicon wafer in the same manner as in Example 1 to form a thermal oxide film on the entire surface of the wafer. Heat treatment was performed at 1100 ° C. in an oxygen atmosphere. The thickness of the obtained oxide film is about 5000Å (0.5μ
m).

In order to remove the oxide film on both sides and leave the oxide film on the chamfered portion, 20 μm lapping was performed on both sides using a double-sided lapping device. As a result, a polishing raw material wafer in which an oxide film remained only on the chamfered portion could be obtained.

(Example 3) As a chamfered oxide film forming step, a film was formed on the entire surface of the etched silicon wafer by thermal oxidation in the same manner as in Example 1 to form a thermal oxide film on the entire surface of the wafer. Heat treatment was performed at 1100 ° C. in an oxygen atmosphere. The thickness of the obtained oxide film is about 5000Å (0.5μ
m).

In order to remove the oxide film on one surface and leave the oxide film on the chamfered portion, one main surface (surface, surface to be polished) was etched. In the etching, the back surface of the wafer and the chamfered portion were masked (protected) with a resin, and only the front surface of the wafer was etched with HF vapor. After that, the resin was removed by washing. As a result, a polishing raw material wafer in which an oxide film remained only on the back surface and the chamfered portion of the wafer could be obtained.

(Example 4) In the chamfered oxide film forming step, 20 silicon wafers after etching were stacked in the same manner as in Example 1 so that the main surfaces of the wafers were in contact with each other, and both ends were dummy wafers. In that state, a film formation process was performed by thermal oxidation to form a thermal oxide film. It heat-processed at 800 degreeC in oxygen atmosphere. After forming the oxide film on the wafer, the superposed wafers were peeled off one by one to obtain a polishing raw material wafer in which the oxide film remained only on the chamfered portion of the wafer.

When the wafers of Examples 2 to 4 were also polished, a mirror-finished wafer of high flatness with less peripheral sag was obtained as in Example 1.

The present invention is not limited to the above embodiments and examples. The above-described embodiment is merely an example, and it has substantially the same configuration as the technical idea described in the scope of the claims of the present invention, and has the same operational effect It is included in the technical scope of the invention.

For example, when a resin or the like is used as a material having a slower polishing rate than a semiconductor wafer, a resin dissolved in a solvent is applied to the chamfered portion. For example, in the case of a thermosetting resin, a heat treatment is performed after the application to remove the resin. The film may be formed by curing. In addition, silicon compounds (generally R _n Si (O
H) _4-n ) and additives (organic binder, vitreous forming agent) dissolved in an organic solvent are applied to at least the chamfered portion of the wafer by using a spinner or the like, and then subjected to heat treatment to evaporate the solvent and A film (oxide film) using a dehydration / polymerization reaction may be formed. In the above embodiments, the case of a silicon wafer has been described as an example, but it goes without saying that the present invention can be applied to a semiconductor wafer other than a silicon wafer.

[0069]

According to the present invention, at least a chamfered portion in contact with one main surface has a film made of a material having a slower polishing rate than that of the semiconductor wafer, such as an oxide film, and the one main surface has the film. A raw material wafer for polishing, which is characterized by not existing, is provided.By using such a wafer, a normal polishing can be performed without using a special jig such as a retainer ring or a small-diameter holding plate during polishing. Therefore, a wafer with high flatness can be obtained. Further, by adjusting the thickness of the oxide film or the like in the chamfered portion, it is possible to obtain a mirror-finished wafer having an arbitrary shape in which the peripheral portion is slightly shaved or sagged after polishing.

[Brief description of drawings]

FIG. 1 is a schematic view showing a polishing raw material wafer according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a machining allowance by surface grinding or lapping.

FIG. 3 is a schematic view showing an example in which an oxide film on one main surface of a wafer is removed by etching.

FIG. 4 is a schematic view of forming an oxide film on chamfered portions of a plurality of wafers.

FIG. 5 is a diagram showing a mode in which an oxide film on the front surface side is removed by using a single-side grinding device (surface grinding device).

FIG. 6 is a diagram showing an aspect in which a polishing raw material wafer according to the present invention is polished using a single-side polishing apparatus.

FIG. 7 is a flowchart showing an example of a method for manufacturing a polishing raw material wafer according to the present invention.

FIG. 8 is a flowchart showing general steps in manufacturing a semiconductor device.

[Explanation of symbols]

1 ... Wafer, 2 ... Oxide film, 3 ... Wafer holding plate (suction chuck), 4 ... Grinding head, 5 ... Cup wheel grindstone, 6 ... Spindle, 7 ... Mask, 1
2 ... Polishing cloth, 13 ... Surface plate (polishing surface plate), 14 ... Polishing head (holding plate), 16 ... Spindle.

Continued front page    (72) Inventor Tadahiro Kato             Odaira, Odakura, Saigo Village, Nishishirakawa-gun, Fukushima Prefecture             No. 150 Shin-Etsu Semiconductor Co., Ltd. Semiconductor Shirakawa             In the laboratory (72) Inventor Hisashi Oshima             596 Shironokoshi Nitta             Address 2 Naoetsu Electronics Co., Ltd. F-term (reference) 3C049 AA04 AA07 CA01 CB01

Claims (9)

[Claims] 1. A raw material wafer for polishing, wherein a film made of a material having a polishing rate slower than that of the wafer is present in at least a chamfered portion in contact with the one main surface, and the film is present in the one main surface. Raw material wafer for polishing, characterized by not having. 2. A polishing raw material wafer, wherein an oxide film is present on at least a chamfered portion in contact with one main surface, and no oxide film is present on the one main surface. Waha. 3. A method of manufacturing a raw material wafer for polishing, comprising forming a film made of a material having a slower polishing rate than the wafer on the entire surface of the wafer, and then removing the film on at least one main surface of the wafer. Thereby, a wafer having a film whose polishing rate is slower than that of the wafer is present in the chamfered portion in contact with at least one main surface, and the wafer in which the film is not present on the one main surface is manufactured. Method of manufacturing raw material wafer for polishing. 4. A method of manufacturing a raw material wafer for polishing, which comprises forming an oxide film on the entire surface of a wafer and then removing the oxide film on at least one main surface of the wafer by surface grinding to remove at least one main material. A method for producing a raw material wafer for polishing, characterized by producing a wafer having an oxide film on a chamfered portion in contact with the surface and having no oxide film on the one main surface. 5. A method of manufacturing a raw material wafer for polishing, which comprises forming an oxide film on the entire surface of a wafer and then removing the oxide film on at least one main surface of the wafer by etching to remove the oxide film on at least one main surface. A method for producing a raw material wafer for polishing, characterized in that a wafer having an oxide film on a chamfered portion in contact therewith and having no oxide film on the one main surface is produced. 6. A method of manufacturing a raw material wafer for polishing, comprising forming an oxide film on the entire surface of a wafer, and then removing the oxide film on at least one main surface of the wafer by lapping, thereby forming at least one main surface. A method for producing a raw material wafer for polishing, characterized in that a wafer having an oxide film on the chamfered portion in contact with the wafer and having no oxide film on the one main surface is produced. 7. A method of manufacturing a raw material wafer for polishing, wherein an oxide film is formed on a plurality of wafers in a state where the main surfaces of the wafers are overlapped with each other, whereby a chamfered portion in contact with at least one main surface is oxidized. A method for producing a raw material wafer for polishing, which comprises producing a wafer having a film and having no oxide film on the one main surface. 8. The method of manufacturing a raw material wafer for polishing according to claim 3, wherein the oxide film is formed to have a thickness of 30 nm to 1 μm. 9. The method for producing a raw material wafer for polishing according to claim 3, wherein a thermal oxide film is formed as the oxide film.