JP2003039310A - Wafer polishing method and wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for finishing and polishing wafer by preventing generation of a polish line and wafer having an extremely excellent surface state. SOLUTION: This method is for brushing abrasive cloth and finishing and polishing wafer after brushing. Brushing is performed by supplying an alkali solution, and subsequently polishing is performed in a state of pH of the alkali solution on the abrasive cloth maintained to more than 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer polishing method, and more particularly to a wafer final polishing method in which dressing of a polishing cloth before final polishing is improved, and a wafer having a good surface condition.

[0002]

2. Related Art A silicon wafer will be described as a typical example of the wafer. Conventionally, a manufacturing method of a silicon wafer used as a semiconductor substrate material is generally a Czochralski (CZ) method or a floating zone melting (Float) method.
ing zone: FZ) method or the like for producing a single crystal ingot, and a wafer processing step of slicing the single crystal ingot and processing at least one main surface into a mirror surface. The device is then formed in the semiconductor substrate material. To show the wafer processing step in more detail, a slicing step for slicing a single crystal ingot to obtain a thin disk-shaped wafer, and a wafer obtained by the slicing step are cracked and chamfered on the outer peripheral portion thereof to prevent chipping. Chamfering step, a lapping step for flattening the wafer, an etching step for removing the processing strain remaining on the chamfered and lapped wafer, a polishing step for mirror-finishing the wafer surface, and a polishing step for polishing It has a cleaning step of cleaning the wafer and removing the abrasives and foreign substances adhering to the wafer. The above-mentioned wafer processing step shows the main steps, and other steps such as a heat treatment step may be added, the same step may be performed in multiple stages, or the order of steps may be changed.

Of these processes, there are various forms of polishing in the polishing process. For example, a silicon wafer mirror polishing method includes a double-sided polishing method in which both surfaces are simultaneously mirror-finished, such as lapping, a single-wafer method in which wafers are vacuum-adsorbed and held on a plate one by one, and an adhesive such as wax is used to bond the wafers. There are various methods such as a wax-free polishing method in which a backing pad and a template are used for polishing without using. At present, a wax mount batch type single-side polishing apparatus that affixes a plurality of wafers to a plate made of glass, ceramics or the like with wax and polishes one side is the mainstream. The plate holding the wafer is placed on a surface plate on which a polishing cloth is attached, a load is applied to the upper top ring, and polishing is performed while rotating the surface plate and the top ring.

As the polishing cloth used in these polishing, a non-woven cloth-type polishing cloth or a suede-type polishing cloth is generally used. Nonwoven cloth type polishing cloth is made by impregnating polyurethane into polyester felt (texture is random structure), has porosity and moderate elasticity, and has high polishing rate and flatness, and can be processed with less sagging. It is like this. Widely used for primary polishing of silicon substrates. Suede type polishing cloth is made of polyester felt impregnated with polyurethane.
A material in which a foam layer is grown in polyurethane, a surface portion is removed, and an opening is provided in the foam layer (this layer is called a nap layer). In particular, the polishing agent, which is used for finishing and is held in the foam layer, acts between the workpiece and the inner surface of the foam layer, so that the polishing proceeds. It is often used for chemical mechanical polishing to obtain a surface without damage. There is also a polishing cloth such as urethane foam sheet.

[0005]

In the polishing process, it is important to keep the quality of the polished wafer constant. For that purpose, the stability of the polishing cloth is important, but before the start of polishing (or after the completion of polishing), brush the polishing cloth while flowing pure water to remove foreign matters and to prevent clogging or dressing of the polishing cloth. To do. Further, in JP-A-7-108453, an alkaline solution such as caustic soda or ethanolamine is used to effectively remove clogging and foreign matter, dressing a polishing cloth with a brush, and switching from alkaline solution to water. Further, an example in which dressing with a brush is performed is disclosed. As a result, it is possible to reliably remove the clogging of the polishing cloth, prevent deterioration of the polishing cloth, reduce the polishing rate, change the shape of the polishing cloth surface, and prevent scratches, and obtain a wafer with high processing accuracy. ing. These are particularly useful for primary polishing and the like, which requires a large amount of polishing.

However, in the final polishing, when the wafer is polished after such treatment, the polished wafer has a depth of 20 nm or less, which is called a polish line.
A large number of linear irregularities having a width of 500 μm or less and a length of several mm or more may occur. The unevenness of the polish line is very small and has existed conventionally. Conventionally, such a polish line has not been a level of concern so much, and even if it exists on the wafer surface, there is no problem. However, as the device becomes finer, it sometimes becomes a problem. Therefore, it has become important to reduce or not generate polish lines at all.

In order to erase the formed polish line, it is possible to eliminate it by increasing the polishing allowance. However, if the polishing allowance is increased, the productivity will be significantly reduced. It also leads to deterioration of flatness. Therefore, the wafer is often finished in a certain polishing time at present and the polishing line remains.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of preventing polishing lines from being generated in finish polishing and polishing, and a wafer having an extremely good surface condition.

[0009]

In order to solve the above-mentioned problems, a method for polishing a wafer according to the present invention is a method for brushing a polishing cloth and, after brushing, performing a final polishing on the wafer. It is characterized in that it is supplied to carry out the above-mentioned brushing, and then the polishing is carried out while the pH of the alkaline solution on the polishing cloth is maintained at 8 or more.

As described above, by polishing the polishing cloth with an alkaline solution and then shifting to polishing the wafer without lowering the pH, the polishing line is eliminated from the beginning, and the polishing line is very few even if the polishing time is short. Can be polished. As the alkaline solution at this time, a polishing agent used for polishing the wafer, specifically, an alkaline solution containing colloidal silica may be used, but a polishing agent for finish polishing in which colloidal silica is finely dispersed is particularly preferable. The pH of the solution is preferably about 9-11. Ammonia is generally used as the alkaline component of this alkaline solution.

As described above, the polishing line can be effectively suppressed by brushing the polishing cloth while flowing the alkaline solution before (immediately before) polishing instead of the conventional pure water.

On the other hand, when the polishing cloth is dressed with water before the polishing and immediately after that, the polishing agent on the polishing cloth is replaced with water to be thinned and held on the polishing cloth. When polished with, the occurrence of polish lines was remarkable. It was also confirmed that the polish line was formed at the beginning of polishing and then removed as the polishing was performed.

Although the clear cause of the formation of the polish line in the initial stage of polishing is unknown, the etching action is insufficient due to the thinning of the polishing agent at the start of polishing the wafer, or pure water is used. When polishing the polishing cloth with a brush, the polishing agent on the polishing cloth flows out, and the foreign substances in the polishing cloth come into contact with the wafer through pure water when the wafer is polished. To be That is, it is considered that polishing with a polishing agent having a low concentration causes a polish line due to the influence of minute foreign substances mixed in during the manufacture of the polishing pad.

The conventional treatment with a brush may be omitted so as to prevent the polishing agent from flowing out, but the treatment with a brush cannot be abolished because it is usually for the purpose of removing foreign matters and preventing clogging. Therefore, even if the treatment with a brush is performed, it is sufficient to treat the polishing cloth so that the abrasive, especially the alkaline component is present. That is, the processing is performed while supplying the polishing agent even during the brushing before the polishing. Further, it is preferable that water is not always used during the brushing or other processing so that the polishing agent having a low concentration does not come into contact with the polishing cloth and the wafer at the polishing step.

For example, as in the method described in Japanese Patent Laid-Open No. 7-108453, even if the material is previously treated with an alkaline solution to effectively remove the clogging and the like, if dressing (brushing) with water is performed thereafter, the initial polishing is performed. Since the polishing agent in a thin state comes into contact with the wafer, the polish line is likely to occur. Dressing for removing clogging and foreign matter may be performed by any method, but finally, as in the present invention, brushing with an alkaline solution immediately before polishing is performed to adjust the concentration change on the polishing cloth, particularly pH for wafer polishing. It is preferable to keep the same as the above, and then continuously shift to polishing. That is, the polishing line can be prevented by treating the polishing cloth with as little pure water as possible and shifting to polishing of the wafer without lowering the concentration of the polishing agent on the polishing cloth, especially the alkaline component.

It is preferable to suppress the pH change of the alkaline solution on the polishing cloth used for the final polishing to within ± 1. Since the pH of the polishing agent required for polishing a wafer is about 9 to 11, it is preferable to treat the polishing cloth so that the pH change can be maintained at about 9 to 12, especially at pH = 10 to 11. . Particularly, the pH on the polishing cloth before (immediately before) polishing is set within the above range.

Among polishing, it is effective to perform brushing while supplying an alkaline solution during dressing performed before final polishing. Particularly in the finish polishing, the polishing allowance is very small and the wafer surface is mirror-finished, and since it is the final stage of the polishing process, the surface condition is not improved thereafter. Therefore, the polish line generated in the initial stage of finish polishing is a very serious problem.

That is, in the polishing using a suede type polishing cloth or the like, the ripple level Rrms = 0.35 nm or less,
It is a problem that such a polish line remains at the time of polishing (finish polishing) for forming a surface state having a haze level of 50 bits or less.

Ripple means 0.25 mm square (0.25
(mm × 0.25 mm) area observed with a non-contact optical roughness meter (Roughness root mean sq)
uare: Rrms), which is unevenness with a period of several tens to several hundreds of μm. In this embodiment, a phase shift interference type WYK is used.
It was measured with TOPO-3D manufactured by O company.

The haze is expressed as a mean square surface roughness (Rrms) when observing an extremely small area with an atomic force microscope, and is a minute surface roughness having a period of several to several tens nm. That's it. Usually, the haze level is quasi-quantitatively evaluated by a particle counter having a function of measuring a weak diffuse reflection intensity due to a minute surface roughness. Therefore, although the value obtained varies depending on the evaluation method, in this example, the evaluation was performed by LS-6500 manufactured by Hitachi Electronics Engineering Co., Ltd., which is a laser surface inspection device. With this evaluation device, haze is evaluated in bit units. The smaller this value, the better the finished surface.

The wafer of the present invention is characterized in that the wavy level on the wafer surface is Rrms 0.35 nm or less and the haze level is 50 bit or less, and no polish line exists.

As described above, when polishing is started with a polishing agent having a low concentration, a polish line is formed in the initial stage, and the polish line cannot be removed depending on the polishing time and exists on the wafer surface. .
By always holding the alkaline solution on the polishing cloth as in the method of the present invention, it is possible to prevent the polish line from being generated from the beginning even when the wafer is polished with such a polishing cloth. If no polish line is generated, the stock removal can be reduced.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION A polishing apparatus used in a method for polishing a wafer according to the present invention will be described below with reference to the accompanying drawings. However, the illustrated example is shown as an example and deviates from the technical idea of the present invention. It goes without saying that various modifications are possible unless they are done. That is, the polishing apparatus used in the method of the present invention is not limited to the illustrated example.

FIG. 1 shows an example of a polishing apparatus used in the method for polishing a wafer according to the present invention, and is an explanatory view for explaining the outline of the construction of a polishing apparatus for a work equipped with a single-wafer polishing head. is there. However, the polishing apparatus may be a batch type polishing apparatus.

In FIG. 1, the present polishing apparatus 10 is constructed as an apparatus for polishing one side of a work, for example, a semiconductor wafer W. The polishing apparatus 10 includes a rotating surface plate (rotary table) 12, a polishing work holding plate 16 mounted on the lower surface of a polishing head 14, and a polishing agent supply pipe 18. A polishing cloth 20 is attached to the upper surface of the surface plate 12. The surface plate 12 is rotated at a predetermined rotation speed by a rotating shaft 22. The polishing head 14 is rotated by a rotating shaft 15 at a predetermined rotation speed.

The polishing work holding plate 16 holds the work (wafer) W on its work holding surface 16a by vacuum suction or the like. The polishing work holding plate 16 is
The work W is mounted on the lower surface of the polishing head 14 and is rotated by the polishing head 14 and simultaneously presses the work W against the polishing cloth 20 with a predetermined load. The abrasive 24 is supplied by the abrasive supply pipe 18
Is supplied to the polishing cloth 20 at a predetermined flow rate from
The work W is polished by supplying 4 between the work W and the polishing cloth 20.

More specifically, the polishing work holding plate 16 has a structure as shown in FIG. In FIG. 2, the polishing work holding plate 16 has a work holding surface 16a and a hard work holding plate body 16b such as SiC having a high flatness and having a number of through holes h for vacuum suction.

These through holes h are connected to a vacuum device (not shown) from the vacuum passage 17, and the work W is sucked and held on the work holding surface 16a by the generation of vacuum. Further, the work holding surface 16 of the work holding board body 16b.
You may coat | cover a with the resin film 19 which has a through hole.

When polishing the work W, the work W is held on the work holding surface 16a of the work holding plate 16 for polishing or the surface of the resin film 19 by vacuum suction or the like, and mounted on the polishing head 14 having the rotating shaft 15. And then polishing head 1
The work W is pressed against the polishing cloth 20 affixed on the surface plate 12 which is rotated by 4 and simultaneously rotates with a predetermined load.

Reference numeral 21 denotes an air supply passage provided in parallel with the vacuum passage 17, and by supplying air to the pressurizing space 23 provided inside the work holding board 16 and above the work holding board body 16b. The work holding plate body 16b swingably supported by the work holding plate 16 by the elastic support portion 27 such as rubber can be pressed downward to press the work W against the polishing cloth 20 of the surface plate 12 under pressure. .

A brush device 25 is installed in the polishing apparatus 10. The brush device 25 includes a brush base 26 provided near the outer peripheral surface of the surface plate 12 and the brush base 2
6 has a brush arm 28 rotatably attached and a brush 30 provided at the tip of the brush arm 28. The brush device 25 functions to dress the polishing cloth 20 between polishing (batch). The brush 30 is made of nylon, and when not in operation, the brush arm 28 rotates in the outer peripheral direction of the surface plate 12,
The brush 30 is located at the end of the surface plate 12, while in operation,
That is, before and after polishing, the brush arm 28 is mounted on the surface plate 1.
2 inwardly to position the brush 30 at the center of the surface plate 12, and then gradually rotate the brush arm 28 in the outer peripheral direction of the surface plate 12 to move the brush 30 to the surface plate 12.
The polishing pad 20 is brushed while being moved in the outer peripheral direction.

In the method of the present invention, when dressing with the brush 30, an abrasive 24 for finish polishing, which is an alkaline solution containing dispersed colloidal silica or ammonia, is used instead of pure water. That is, brushing is performed while supplying the polishing agent 24. The polishing agent 24 used at this time may be the same as that used for normal wafer polishing. As a result, since polishing can be performed from the initial stage of polishing without lowering the concentration of the polishing agent 24 on the polishing cloth 20, the occurrence of polish lines can be suppressed.

According to the above-described polishing method of the present invention, it is possible to obtain a wafer having an extremely good surface condition, for example, a wafer having a ripple level Rrms of 0.35 nm or less and a haze level of 50 bits or less and having no polish line.

[0034]

The present invention will be described in more detail with reference to the following examples, but it goes without saying that these examples are shown by way of illustration and should not be construed as limiting.

(Example 1) Final polishing was carried out by using the polishing apparatus as shown in FIGS. The wafer is an 8-inch silicon wafer that has undergone primary polishing and secondary polishing.

As the polishing cloth, a suede type polishing cloth for finishing was used FS-7 manufactured by Daiichi Lace Co., Ltd., and the above polishing was carried out at a polishing load of 20 kPa.

As a polishing procedure, the polishing cloth was first brushed. Brushing was performed for 30 seconds by supplying an abrasive as an alkaline solution at 1.5 L / min. At this time, a colloidal silica-containing alkaline solution (containing ammonia) having a pH of about 10.5 was added as an abrasive. After the completion of the brushing, the polishing agent was continuously supplied at 0.7 L / min, and the wafer was polished.

As a result, no polish line was observed from the beginning, and polishing for about 1 minute and 30 seconds was sufficient to achieve a mirror surface. The haze level of the wafer after polishing is 50
A finish-polished surface having a bit or less was obtained. Specifically, 0.
The area of 25 mm square (0.25 mm × 0.25 mm) is T
The mean square surface roughness (roughness level Rrms) when observed with OPO-3D (manufactured by WYKO) is about 0.31 nm, and LS-6500 manufactured by Hitachi Electronics Engineering Co., Ltd.
It was found that the haze level evaluated in step 3 was 30 bits or less, and that a good finish-polished surface was formed.

(Example 2) The polishing was repeated under the same polishing conditions as in Example 1. Polishing # 2 for each batch # 1
5 batches of 5 are performed, and brushing is performed for 30 seconds between each batch. For brushing, 1.5 L of colloidal silica-containing alkaline solution (abrasive) with a pH of about 10.5
/ Min. The polishing cloth is a two-layered polishing cloth [FS-7 polishing cloth manufactured by Daiichi Lace Co., Ltd.
Polishing load was 20 kPa, and the above polishing was performed. The polishing time was 1 minute and 30 seconds.

The results are shown in FIG. FIG. 3 is a map of the results measured by LS-6500 manufactured by Hitachi Electronics Engineering Co., Ltd. In FIG. 3, the entire surface of the wafer is evaluated with high sensitivity, and the unevenness present on the wafer is observed. It is the polish line that appears linear. Polish lines were hardly observed and there was no problem. Even if there are polish lines, the number is very small, and about 70% of the wafers have no polish lines at all, which shows that the polishing method is preferable. When the pH of the solution (abrasive) on the polishing cloth after brushing when the polishing was repeatedly performed in this way was confirmed, pH = 10.1 to
It was 10.7. The pH was maintained at almost the same level as during polishing. The ripple level and the haze level were almost the same as in Example 1, and the ripple level was 0.32 to 0.29 nm and the haze level was about 28.9 bits on average.

(Comparative Example 1) Polishing was performed under the same polishing conditions as in Example 1 except that pure water was supplied instead of an abrasive at the time of brushing for dressing.

As a result, when the wafer surface was confirmed by polishing for 1 minute and 30 seconds, a polish line was observed.
It took about 10 minutes of polishing before the polish line disappeared.

Comparative Example 2 Five batches # 1 to # 5 were repeatedly polished under the same polishing conditions as in Example 2 except that pure water was used during brushing.

The results are shown in FIG. FIG. 4 shows the results of measurement performed in the same manner as in Example 2. Fine lines correspond to polish lines. Polish lines were found on every batch of wafers. Also, the number of polish lines is very large, which may become a problem as the device becomes finer. When the pH of the solution (abrasive) on the polishing cloth after brushing when the polishing was repeatedly performed in this way was confirmed, it was found that the pH was 7 to 7.8 and the actual polishing state (p
It can be seen that the pH is lower than H = 10 to 11). It can be seen that the alkaline component is replaced by pure water and the concentration is lowered. Ripple level is 0.32-0.3
The average haze level was 0 nm, and the haze level was about 30.6 bits.

As described above, when the polishing is performed after the brushing with the finishing abrasive, the generation of the polish line can be prevented and the polishing time can be set short, so that the polishing can be performed with high productivity.

Since the brushing in the present invention is performed only by brushing while supplying the abrasive, the conventional apparatus can be used and the apparatus can be easily dealt with. The present invention is not limited to the above embodiment. The above-mentioned embodiment is merely an example, and it has substantially the same configuration as the technical idea described in the scope of claims of the present invention, and has any similar effect to the present invention. It is included in the technical scope of the invention.

Although polishing of a silicon wafer has been described as a preferred example of the present invention, the present invention is not limited to this and can be applied to a wafer of a compound semiconductor or the like. Further, in the present embodiment, the brushing with the abrasive also serves as the dressing for preventing the clogging and the removal of the foreign matter, and although this has a sufficient dressing effect, the polishing cloth is brushed by another method before the brushing with the abrasive. You can dress it. At this time, even if pure water or the like is used, the occurrence of a polish line can be prevented by continuously brushing with an alkaline solution as in the present invention and then continuously shifting to finish polishing. Further, after brushing, an alkaline solution (other than an abrasive) may be supplied for a while and then the polishing may be started.

[0048]

As described above, according to the wafer polishing method of the present invention, the production of polish lines is prevented in the final polishing step, and the polishing time is shortened. The effect that a wafer having an extremely good upper surface condition can be manufactured is achieved.

[Brief description of drawings]

FIG. 1 is a polishing apparatus used in the method of the present invention.
It is a side surface explanatory view showing an example.

FIG. 2 is a schematic cross-sectional explanatory view of a polishing work holding plate in the polishing apparatus shown in FIG.

FIG. 3 is a map showing a surface state of a polished wafer in Example 2.

FIG. 4 is a map showing a surface state of a polished wafer in Comparative Example 2.

[Explanation of symbols]

10: polishing device, 12: surface plate, 14: polishing head, 1
5: rotary shaft, 16: work holding board, 16a: work holding surface, 16b: work holding board body, 17: vacuum passage,
18: Abrasive supply pipe, 19: Resin film, 20: Abrasive cloth,
21: Air supply path, 22: Rotating shaft, 23: Pressurized space, 2
4: Abrasive, 25: Brush device, 26: Brush base, 2
7: elastic support, 28: brush arm, 30: brush,
h: through hole, W: wafer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Suzuki             Odaira, Odakura, Saigo Village, Nishishirakawa-gun, Fukushima Prefecture             No. 150 Shin-Etsu Semiconductor Co., Ltd. Semiconductor Shirakawa             In the laboratory F-term (reference) 3C058 AA07 AA19 AC04 CB01 DA17

Claims (4)

[Claims] 1. A method of brushing a polishing cloth, followed by final polishing of a wafer after brushing, wherein an alkaline solution is supplied to perform the brushing, and then the pH of the alkaline solution on the polishing cloth is adjusted to 8 or more. A method for polishing a wafer, which comprises performing polishing while maintaining it. 2. The method of polishing a wafer according to claim 1, wherein the pH change of the alkaline solution on the polishing cloth is controlled to be within ± 1. 3. The final polishing of the wafer is polishing for the purpose of removing haze, and has a ripple level Rrms.
The method for polishing a wafer according to claim 1 or 2, wherein polishing is performed to form a surface state having a haze level of 0.35 nm or less and a haze level of 50 bits or less. 4. The rippling level of the wafer surface is Rrm.
A wafer having a s of 0.35 nm or less and a haze level of 50 bits or less and having no polish line.