TWI727165B - Method for polishing silicon wafer - Google Patents

Abstract

The present invention provides a method for polishing a silicon wafer. The polishing slurry is used between the silicon wafer and the polishing pad to grind the silicon wafer. As the polishing slurry, colloidal silica and alkali are used to satisfy the following requirements: the conditions were: [(hydroxide ion concentration [OH in the slurry ^{-] (mol / l))} ( colloidal silicon dioxide to the mass fraction of the slurry mass) /] ≧ 0.1 (mol / l). In this way, even if a hard gasket is used, low defectivity can be achieved.

Description

Method for polishing silicon wafer

The invention relates to a polishing method for silicon wafers.

As semiconductor devices become lighter and thinner, silicon wafers as substrates are required to have further flatness and low defects. Generally, a silicon wafer is manufactured by slicing a single crystal silicon block lifted by the Czochralski (CZ) method and then performing multi-stage polishing (refer to Patent Document 1).

In particular, in a polishing step using a resin-made gasket, the flatness of the outer peripheral edge is easily impaired due to edge collapse or the like, and as a result, the device yield in the outer peripheral portion of the wafer deteriorates. At the same time, since the introduction of surface defects such as scratches will also cause deterioration of the yield of the device, peripheral flatness and low defectivity are pursued in the polishing step. [Prior technical literature]

Patent Document 1: Japanese Patent Application Laid-Open No. 2008-205147

[Problems to be Solved by the Invention] As described above, although flatness and low defectivity are pursued in the polishing step, it is generally known that it is extremely difficult to achieve both. It is very important to use a hard polishing pad in order to maintain good peripheral flatness in the polishing step. This is because the use of a hard polishing pad can suppress the displacement of the outer periphery of the pad and suppress the concentration of pressure on the outer periphery of the wafer.

However, it is difficult to achieve low defectivity when using a hard polishing pad. Since the gasket is hard, there is a possibility that the gasket itself will be scratched to the wafer, and when foreign matter invades the wafer/pad, even if it is the same foreign matter, the damage of the hard gasket to the wafer is greater than that of the soft one. Therefore, the possibility of bringing in scratches is increased.

It can be seen from the above that the flatness of the outer periphery and the low defectivity are a trade-off relationship between the hardness of the polishing pad, and it is a problem to achieve low defectivity even if a hard pad is used.

In view of the above-mentioned problems, the present invention aims to provide a method for polishing a silicon wafer that can achieve improved flatness and low defects. 〔Technical means to solve the problem〕

In order to solve the above-mentioned problems, the present invention provides a method for polishing a silicon wafer. A polishing slurry exists between a silicon wafer and a polishing pad to polish the silicon wafer. The polishing slurry is used as the polishing slurry. contains colloidal silicon dioxide and a base thereof and satisfies the following condition: (hydroxide ion concentration in the slurry ^{[OH -] (mol / l} )) [ mass / (the slurry of the colloidal silicon dioxide is Mass fraction)] ≧0.1 (mol/l).

In this way, using a polishing slurry that satisfies the above-mentioned conditions to polish a silicon wafer makes it possible to achieve low defectivity even if a hard pad is used.

At this time, as the polishing pad, a polishing pad having a Shore A hardness of 60 or more is preferably used.

Furthermore, as the polishing pad, a polishing pad having a Shore A hardness of 70 or more is preferably used.

By polishing using a hard polishing pad in this way, a silicon wafer that achieves both flatness and low defectivity can be obtained. [Compare the effects of previous technologies]

Based on silicon wafer polishing method of the present invention, as an index of the strength with respect to the chemical action of the mechanical polishing action, focusing on the slurry concentration of hydroxide ions [OH ^-] divided by the mass of the polishing slurry The value of the mass fraction of colloidal silica can achieve low defects by using a polishing slurry with a value of 0.1 or more. Therefore, even if a hard polishing pad is used, since low defects can be achieved, a silicon wafer that achieves both flatness and low defects can be obtained.

As mentioned above, the prior art seeks to have a polishing method for silicon wafers that can achieve low defects even if hard pads are used.

In order to solve the problem, the inventor of this case focused on the chemical effect in polishing. Although there are many conventional technologies that focus on mechanical effects such as gasket hardness, gasket surface roughness, abrasive grain size, grinding pressure, or grinding speed, there are few examples that focus on chemical effects.

The chemical effect in polishing is expected to be caused by the reaction between silicon oxide and alkali. Specifically, it is caused by Si+OH ^­ →SiOH reaction, which shows that Si crystals in contact with alkali are deteriorated by OH groups.

The inventors of the present case envisioned that by increasing the chemical effect during polishing, the surface of the wafer is deteriorated, and a buffer layer is provided between the polishing pad and the Si crystal part, which can reduce the hard pad or the hard pad. Damage caused by some foreign objects.

In addition, the inventors of the present case believe that the metamorphic layer (buffer layer) formed by the chemical action is quickly removed by the mechanical action, so the strength of the chemical action during polishing should not be used as the pH value, etc. The index of absolute strength should be an index of the strength of chemical action relative to mechanical action. Here, in the present invention, the strength of the chemical action is the concentration of hydroxide ions, and the strength of the mechanical action is the mass fraction of colloidal silica in the mass of the slurry (hereinafter also referred to as the concentration of abrasive grains). The value of the concentration of hydroxide ions divided by the concentration of abrasive particles is used as an index of chemical action with respect to mechanical action. It is only necessary that this index falls within the specified range when using hard gaskets.

Further, the present inventors, as in the polishing action of chemical indicators of intensity, focusing on the hydrogen ion concentration [OH ^-] in the slurry divided by the concentration of the abrasive grains was found that the polishing slurry by the modulation value If it is 0.1 or more, it is used for polishing, so that even if a hard polishing pad is used, low defectivity can be achieved, and the invention can be achieved.

That is, the present invention provides a method for polishing a silicon wafer, in which a polishing slurry exists between a silicon wafer and a polishing pad to polish the silicon wafer, wherein, as the polishing slurry, colloidal dioxide is used. and a silicon base material and satisfies the following condition: [(hydroxide ion concentration in the slurry ^{[OH -] (mol / l} )) / ( mass of the slurry of the colloidal silicon dioxide in a mass fraction) ]≧0.1(mol/l).

Hereinafter, the polishing method of the silicon wafer of the present invention will be described in detail.

The polishing device used in the silicon wafer polishing method of the present invention may be any one of a double-sided polishing device and a single-sided polishing device. For example, as shown in FIG. 3, a single-sided polishing apparatus 10 provided with a table 2 to which a polishing pad 1 is attached, and a polishing head 3 for supporting a silicon wafer W can be used. In this single-side polishing device 10, the surface of the silicon wafer W supported by the polishing head 3 is slidably contacted with the polishing pad 1 for polishing while the polishing slurry is supplied from the nozzle 4 onto the polishing pad 1.

In the present invention, the silicon wafer is polished by allowing a polishing slurry to exist between the silicon wafer W and the polishing pad 1. Among them, as the polishing slurry supplied from the nozzle 4, a combination containing colloidal silica and alkali is used. thereof satisfy the following condition: [(hydroxide ion concentration in the slurry ^{[OH -] (mol / l} )) / ( mass of colloidal silicon dioxide slurry mass fraction)] ≧ 0.1 (mol / l ).

In this way, the strength of the chemical action is the concentration of hydroxide ions, and the strength of the mechanical action is the mass fraction of colloidal silica in the mass of the slurry, and the concentration of hydroxide ions is divided by the concentration of abrasive particles as the relative value. It is used as an index of mechanical action and chemical action, and a slurry with this value of 0.1 or more can be used to achieve low defectivity.

Conventional polishing slurry, [(hydroxide ion concentration in the slurry ^{[OH -] (mol / l} )) / ( mass of colloidal silicon dioxide slurry mass fraction)] is less than 0.1 No polishing slurry with the above value of 0.1 or more, that is, a slurry with a high hydroxide ion concentration relative to the concentration of abrasive grains, has not been used.

If it is ^- a value less than 0.1 in slurry [(hydroxide ion concentration in the slurry [OH] (mol / l) ) / ( mass of the slurry colloidal silicon dioxide mass fraction)], and However, since the chemical action relative to the mechanical action becomes weak, surface defects such as scratches are introduced when a hard polishing pad is used, and low defectivity cannot be achieved.

If it is a polishing slurry that satisfies the above-mentioned conditions, the type of alkali, pH, concentration and particle size of colloidal silica are not particularly limited. For example, pH 9-13, colloidal silica particle size of 15-17 nm, and colloidal silica concentration of 0.01 to 1 wt% can be used, which satisfies the above conditions. As the base, KOH, tetramethylammonium hydroxide (TMAH), etc. can be used.

[(Hydroxide ion concentration in the slurry ^{[OH -] (mol / l} )) / ( mass of colloidal silicon dioxide slurry mass fraction)] The upper limit is not particularly limited, it can be, for example, 10mol / l or less.

Although there are no particular limitations on the polishing pad 1, it is preferable to use a polishing pad (for example, a non-woven fabric) having a Shore A hardness of 60 or more, particularly 70 or more. At this time, the upper limit of the Shore A hardness of the polishing pad 1 is not particularly limited, but it can be, for example, 98 Shore A hardness or less. By using such a hard polishing pad for polishing, it is possible to obtain a silicon wafer that achieves both flatness and low defectivity. However, since low defectivity is achieved by the present invention, it is not necessary to use such a hard polishing pad. According to the purpose, it can also be applied to the situation where soft gaskets are used.

In addition, the polishing pressure, plate rotation speed, head rotation speed, and polishing time during polishing can be selected under general conditions, and are not particularly limited. (Example)

Although examples and comparative examples are shown below to specifically describe the present invention, the present invention is not limited to these examples.

(Examples 1 to 4, Comparative Example 1) A single-sided polishing device using a hard gasket with a Shore A hardness of 60 was used to verify and evaluate the chemical action against the mechanical action. First, maintain the mass fraction (abrasive grain concentration) in the slurry of high-purity colloidal silica with a particle size of 35nm at 0.01 (ie 1%), and change the alkali concentration (hydroxide ion concentration) of the slurry to perform silicon Grinding of wafers. The pH adjustment is carried out by potassium hydroxide and tetramethylammonium hydroxide (TMAH). The grinding pressure was 20 kPa, the rotation speed of the platen and the head were 30 rpm, and the grinding was performed for 3 minutes.

After the polishing step with the hard polishing pad, the final finishing polishing step with the soft polishing pad is performed, and then the polishing evaluation is performed. The polishing evaluation was performed by measuring the number of localized light scattering (Localized Light Scattering, LLS) defects (at least 37 nm) with SP2 manufactured by KLA Tencor.

Table 1 shows respective conditions in the display [OH ^-] in FIG. 1 showing the relationship between the value of the scale / mass fraction of colloidal silicon dioxide and the number of defects LLS. If that [OH ^-] / colloidal silicon dioxide mass fraction value of 0.1mol / l or more, reducing the number of LLS defects.

【Table 1】

(Examples 5 to 8, Comparative Examples 2, 3) Next, the alkali concentration of the polishing slurry was maintained at a constant (pH 10.5), and the mass fraction (abrasive grain concentration) of colloidal silica was changed to perform polishing evaluation. The other conditions are the same as in Examples 1 to 4 and Comparative Example 1. Each condition in Table 2 show, the display [OH ^-] in FIG. 2 shows the relationship between the scale value of mass fraction / colloidal silicon dioxide and the number of defects LLS. Also here that if [OH ^-] / colloidal silicon dioxide mass fraction value of 0.1mol / l or more, reducing the number of LLS defects.

【Table 2】

From the above results, that the non-rigid cushion on the use, the use of indicators in the chemical polishing action with respect to the mechanical action of [OH ^-] Value / abrasive concentration of 0.1 in the above slurry (Embodiment Examples 1 to 8), compared with Comparative Examples 1 to 3, LLS defects are reduced. And, as mentioned above, the resulting wafer flatness (SFQR) is also high.

In addition, the present invention is not limited by the foregoing embodiments. The foregoing embodiments are examples, and those that have substantially the same structure as the technical idea described in the scope of the patent application of the present invention and achieve the same effects are included in the technical scope of the present invention.

FIG. 1 is a scale diagram showing the relationship between the value of the mass fraction ^{of [OH −} ]/colloidal silica and the number of LLS defects in Examples 1 to 4 and Comparative Example 1. Fig. 2 is a scale diagram showing the relationship between the value ^{of the [OH-} ]/colloidal silica mass fraction in Examples 5 to 8 and Comparative Examples 2 and 3 and the number of LLS defects. 3 is a schematic diagram showing an example of a single-side polishing apparatus that can be used in the polishing method of the silicon wafer of the present invention.

Claims (1)

A method for polishing a silicon wafer is to make a polishing slurry exist between a silicon wafer and a polishing pad to polish the silicon wafer, wherein, as the polishing slurry, a combination containing colloidal silica and alkali is used A substance that satisfies the following conditions: [(The concentration of hydroxide ion in the slurry [OH ^- ](mol/l))/(The mass fraction of the colloidal silica in the mass of the slurry)] ≧1.0( mol/l). As the polishing pad, a polishing pad with a Shore A hardness of 70 or more was used.

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