TW201900333A - 矽 wafer grinding method - Google Patents

Abstract

The present invention provides a silicon wafer polishing method of polishing a silicon wafer with a polishing slurry interposed between the silicon wafer and a polishing pad, the silicon wafer polishing method being characterized in that the polishing slurry used for polishing comprises a choroidal silica and an alkali and satisfies (hydroxide ion concentration [OH-] in the polishing slurry (mol/l))/(mass fraction of the choroidal silica in the mass of the polishing slurry) ≥ 0.1 (mol/l). In this way, a silicon wafer polishing method with which low defect performance can be achieved even when a hard pad is used is provided.

Description

矽 wafer grinding method

The present invention relates to a method of polishing a tantalum wafer.

With the thinning of semiconductor devices, germanium wafers as substrates are required to have further flatness and low defects. In general, a tantalum wafer is produced by slicing a single crystal block lifted by a Czochralski (CZ) method and then performing multi-stage polishing (see Patent Document 1).

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

Patent Document 1: Japanese Laid-Open Patent Publication 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 combine both. It is important to use a hard polishing pad in order to maintain good peripheral flatness in the grinding step. This is because the use of a hard polishing pad can suppress the displacement of the spacer on the outer circumference and suppress the pressure concentration on the outer peripheral portion of the wafer.

However, when a hard polishing pad is used, it is difficult to achieve low defect. Since the gasket is hard, the gasket itself brings the possibility of scratching to the wafer, and when the foreign matter invades the wafer/gasket, even if the same foreign matter, the hard gasket has a greater damage to the wafer than the soft cushion. The film, so the possibility of bringing in scratches is increased.

From the above, it is understood that the outer peripheral flatness and the low defect are the mutual trade-off relationship between the hardness of the polishing pad, and even if a hard gasket is used, it is possible to achieve low defect.

The present invention has been made in view of the above problems, and it is an object of the invention to provide a polishing method for a tantalum wafer which can achieve improvement in flatness and low defect. [Technical means to solve the problem]

In order to solve the above problems, the present invention provides a method for polishing a tantalum wafer by grinding a tantalum wafer between a wafer and a polishing pad, wherein the slurry is used as the slurry. a substance containing colloidal cerium oxide and a base and satisfying the following conditions: [(the concentration of hydroxide ions in the slurry [OH ^- ] (mol/l)) / (the mass of the slurry is the colloidal cerium oxide Mass fraction)] ≧ 0.1 (mol/l).

As described above, by polishing the tantalum wafer with the slurry satisfying the above conditions, it is possible to achieve low defect even by using a hard spacer.

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

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

By using a hard polishing pad as described above, it is possible to obtain a tantalum wafer which achieves both flatness and low defect. [Compared with the efficacy of prior art]

According to the polishing method of the tantalum wafer according to the present invention, as an index of the strength of the chemical action relative to the mechanical action in the polishing, attention is paid to dividing the concentration of hydroxide ions [OH ^- ] in the slurry by the mass of the slurry. The value of the mass fraction of the colloidal cerium oxide can be low defect by using the slurry having a value of 0.1 or more. Therefore, even if a hard polishing pad is used, since a low defect can be achieved, a tantalum wafer which achieves both flatness and low defect can be obtained.

As described above, it has been conventionally known to have a polishing method for a tantalum wafer which can achieve low defects even when a hard gasket is used.

The inventor of the present invention focused on the chemical action in grinding in order to solve the problem. Although many techniques have been focused on mechanical effects such as gasket hardness, gasket surface roughness, abrasive grain size, grinding pressure or grinding speed, there are few examples of chemical effects.

The chemical action in the grinding is expected to be caused by the reaction of cerium oxide with a base, specifically, due to Si+OH. ^­ → Reaction of SiOH, which shows that Si crystals in contact with a base are deteriorated by an OH group.

The inventors of the present invention have conceived that the surface of the wafer is deteriorated by increasing the chemical action during polishing, and a buffer layer is provided between the polishing pad and the Si crystal portion, thereby reducing the hardness of the hard gasket or the hard gasket. Some damage caused by foreign bodies.

Moreover, the inventors of the present invention believe that the metamorphic layer (buffer layer) formed by chemical action is rapidly removed by mechanical action, so the strength of the chemical action in the grinding should not be taken as the pH value, etc. The indicator of absolute strength, but should be an indicator of the strength of the chemical action relative to the mechanical action. Here, in the present invention, the intensity of the chemical action is the concentration of the hydroxide ions, and the strength of the mechanical action is the mass fraction of the colloidal ceria in the mass of the slurry (hereinafter also referred to as the abrasive concentration). The concentration of the hydroxide ion divided by the value of the abrasive grain concentration is used as an index of the chemical action against the mechanical action, and it is desirable to enter the specified range when using a hard gasket.

Further, the inventor of the present invention, as an index of the strength of the chemical action in the polishing, focused on dividing the hydroxide ion concentration [OH ^- ] in the slurry by the value of the abrasive grain concentration, and found that the value was obtained by modulating the slurry. The present invention is achieved by using 0.1 or more for polishing, whereby low defects can be achieved even by using a hard polishing pad.

That is, the present invention provides a method for polishing a tantalum wafer by grinding a tantalum wafer between a wafer and a polishing pad, wherein the slurry is used for colloidal dioxide oxidation. An anthracene and a base satisfying the following conditions: [(Hydroxide ion concentration [OH ^- ] (mol/l) in the slurry) / (mass fraction of the colloidal ceria in the mass of the slurry) ]≧0.1 (mol/l).

The method of polishing the tantalum wafer of the present invention will be described in detail below.

The polishing apparatus used in the polishing method of the tantalum wafer of the present invention may be either a double-side polishing apparatus or a single-side polishing apparatus. For example, the single-sided polishing apparatus 10 including the fixed disk 2 to which the polishing pad 1 is attached and the polishing head 3 for supporting the silicon wafer W can be used. In the single-side polishing apparatus 10, the slurry is supplied from the nozzle 4 to the polishing pad 1, and the surface of the silicon wafer W supported by the polishing head 3 is slidably attached to the polishing pad 1 to be polished.

In the present invention, the slurry is placed between the silicon wafer W and the polishing pad 1 to polish the silicon wafer. The slurry supplied from the nozzle 4 is made of colloidal ceria and alkali. The following conditions are satisfied: [(Hydroxide ion concentration [OH ^- ] (mol/l) in the slurry) / (mass fraction of colloidal cerium oxide in the mass of the slurry)] ≧ 0.1 (mol/l ).

Thus, the intensity of the chemical action is the concentration of the hydroxide ion, the strength of the mechanical action is the mass fraction of the colloidal ceria in the mass of the slurry, and the concentration of the hydroxide ion is divided by the value of the abrasive concentration as a relative It is used as an index of the chemical action of mechanical action, and the slurry of this value of 0.1 or more is used, and low defect can be achieved.

The conventional slurry, [(the concentration of hydroxide ions in the slurry [OH ^- ] (mol / l)) / (mass fraction of colloidal ceria in the mass of the slurry)] is less than 0.1 The slurry having the above value of 0.1 or more, that is, the slurry having a high hydroxide ion concentration with respect to the concentration of the abrasive grains, has not been used.

If [(the hydroxide ion concentration [OH ^- ] (mol / l) in the slurry) / (mass fraction of the colloidal ceria in the mass of the slurry)] is a slurry of less than 0.1, Then, since the chemical action with respect to the mechanical action becomes weak, surface defects such as scratches are brought in when the hard polishing pad is used, and low defect property cannot be achieved.

In the case of the slurry which satisfies the above conditions, the type of the alkali, the pH, the concentration of the colloidal cerium oxide, and the particle diameter are not particularly limited. For example, pH 9 to 13, colloidal cerium oxide having a particle diameter of 15 to 17 nm and colloidal cerium oxide having a concentration of 0.01 to 1% by weight, which satisfy the above conditions, can be used. As the base, KOH, tetramethylammonium hydroxide (TMAH) or the like can be used.

[(The hydroxide ion concentration [OH ^- ] (mol/l) in the slurry) / (the mass fraction of the colloidal ceria in the mass of the slurry)] The upper limit is not particularly limited, and can be, for example, 10 mol / l below.

The polishing pad 1 is not particularly limited, but is preferably a polishing pad (for example, a nonwoven 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 may be, for example, a Shore A hardness of 98 or less. By using such a hard polishing pad for polishing, it is possible to obtain a tantalum wafer which achieves both flatness and low defect. However, since the low defect is achieved by the present invention, it is not necessary to use such a hard polishing pad. It can also be applied to the condition of using a soft gasket for the purpose.

Moreover, the polishing pressure, the number of rotations of the disk, the number of rotations of the head, and the polishing time at the time of polishing can be selected according to general conditions, and are not particularly limited. (Example)

Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the examples.

(Examples 1 to 4, Comparative Example 1) A chemical evaluation of the chemical action with respect to the mechanical action was performed using a one-side polishing apparatus using a hard gasket having a Shore A hardness of 60. First, the mass fraction (abrasive concentration) in the slurry of high-purity colloidal ceria having a particle diameter of 35 nm is maintained at 0.01 (that is, 1%), and the alkali concentration (hydrogen-oxygen ion concentration) of the slurry is changed to carry out hydrazine. Grinding of the wafer. The pH adjustment was carried out by using potassium hydroxide and tetramethylammonium hydroxide (TMAH). The grinding pressure was 20 kPa, the fixing speed and the head rotation speed were 30 rpm, and the grinding was performed for 3 minutes.

After the polishing step by the hard polishing pad, the final finishing polishing step by the soft polishing pad was performed, and the polishing evaluation was performed. The polishing evaluation was carried out by measuring the number of localized light scattering (LSL) defects (37 nm or more) by SP2 manufactured by KLA Tencor.

Table 1 shows the respective conditions, and Fig. 1 shows a scale chart showing the relationship between the value of the mass fraction of [OH ^- ] / colloidal ceria and the number of LLS defects. It is found that if the value of the mass fraction of [OH ^- ] / colloidal ceria is 0.1 mol/l or more, the number of LLS defects is decreased.

【Table 1】

(Examples 5 to 8, Comparative Examples 2 and 3) Next, the alkali concentration of the slurry was maintained at a fixed value (pH 10.5), and the mass fraction (abrasive concentration) of the colloidal cerium oxide was changed to carry out polishing evaluation. Other conditions were the same as those of Examples 1 to 4 and Comparative Example 1. Table 2 shows the respective conditions, and Fig. 2 shows a scale chart showing the relationship between the value of the mass fraction of [OH ^- ] / colloidal ceria and the number of LLS defects. Here, it is also known that if the mass fraction of [OH ^- ] / colloidal ceria is 0.1 mol/l or more, the number of LLS defects is decreased.

【Table 2】

From the above results, it was found that the slurry having a value of [OH ^- ] /abrasive concentration of 0.1 or more using an index of the chemical action against mechanical action during polishing was used. In Examples 1 to 8), LLS defects were reduced as compared with Comparative Examples 1 to 3. Also, as described above, the resulting wafer flatness (SFQR) is also high.

Further, the present invention is not limited by the foregoing embodiments. The above-described embodiments are exemplified, and have substantially the same configuration as the technical idea described in the patent application scope of the present invention, and the same effects are achieved in the technical scope of the present invention.

Fig. 1 is a graph showing the relationship between the value of the mass fraction of [OH ^- ] / colloidal ceria in Examples 1 to 4 and Comparative Example 1 and the number of LLS defects. Fig. 2 is a graph showing the relationship between the value of the mass fraction of [OH ^- ] / colloidal cerium oxide and the number of LLS defects in Examples 5 to 8, Comparative Examples 2 and 3. Fig. 3 is a schematic view showing an example of a single-side polishing apparatus which can be used in the polishing method of the tantalum wafer of the present invention.

Claims (3)

A method for polishing a tantalum wafer by grinding a tantalum wafer between a wafer and a polishing pad, wherein the slurry is a colloidal ceria and a base The following conditions are met: [(Hydroxide ion concentration [OH ^- ] (mol/l) in the slurry) / (mass fraction of the colloidal ceria in the mass of the slurry)] ≧ 0.1 ( Mol/l). A method of polishing a tantalum wafer according to claim 1, wherein a polishing pad having a Shore A hardness of 60 or more is used as the polishing pad. A method of polishing a tantalum wafer according to claim 1 or 2, wherein a polishing pad having a Shore A hardness of 70 or more is used as the polishing pad.