JP2001237203A - Silicon wafer polishing liquid and polishing method by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive polishing liquid which is used for polishing a semiconductor wafer, capable of eliminating contamination by metal especially copper in a rough polishing process. SOLUTION: A polishing liquid contains abrasive particles of 0.01 to 10 wt.%, chelating agent of 1×10-5 to 0.3 mol/l, hydrogen peroxide of 0.03 to 3 wt.%, and ammonia of 0.029 to 2.9 wt.% when it is used for polishing a silicon wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing solution for mechanically and chemically polishing a silicon wafer formed by the Czochralski method (hereinafter referred to as CZ method) and a polishing method using the same.

[0002]

2. Description of the Related Art A silicon wafer cut and sliced from a silicon single crystal ingot is subjected to mechanical polishing (lapping), chemical etching, and other processes, and is then combined with mechanical or physical polishing and chemical polishing. Mechanical and chemical polishing (mechanochemical polishing) is performed.
In this mechanical and chemical polishing step, the silicon wafer attached to the holder is pressed against a soft polishing pad such as a polyester felt or a laminate stuck on a rotating platen, and the polishing pad is rotated while the polishing liquid is dropped. Thus, the wafer surface is polished to a mirror surface. The polishing liquid used in this polishing step is, for example, silica (SiO ₂ ).
Abrasive particles such as alkaline aqueous solution (potassium hydroxide: KO)
H, sodium hydroxide: NaOH, amines, etc.).

In the conventional polishing process, metal contamination occurs on the surface of a silicon wafer. The cause of this contamination is mainly metal impurities contained in the polishing liquid used in the polishing process, and it is also conceivable that the contamination from the process or equipment may occur. Metal contamination on the wafer surface that occurs during the polishing process occurs when metal dissolved in the polishing solution is adsorbed on the silicon wafer and then diffuses into the wafer using the pressure and temperature generated when the polishing apparatus is driven as a driving force. it is conceivable that. Therefore, methods such as suppressing the contamination of impurities by purifying the polishing liquid, and adding a large excess of a chelating agent having an action of reducing contaminants attached to the wafer surface to the polishing liquid have been adopted.

[0004]

However, the high purity of the polishing liquid has a problem of increasing the price of the polishing liquid, and has no effect on mixing impurities from the process or equipment. There is also a problem that a large excess of a chelating agent added to the polishing liquid increases the price of the polishing liquid. The object of the present invention is inexpensive,
An object of the present invention is to provide a polishing liquid for a silicon wafer and a polishing method using the same, which reduce metal contamination, particularly copper contamination, generated in the polishing step.

[0005]

The invention according to claim 1 is
It is a polishing liquid for silicon wafers containing a chelating agent, hydrogen peroxide and ammonia in a slurry containing abrasive particles.
In the invention according to claim 1, by adding a chelating agent to the polishing liquid, the impurity metal dissolved in the polishing liquid is captured by coordination bonds with the chelating agent. This can prevent metal ions released from the wafer from being re-adsorbed to the wafer surface. The potential of the polishing liquid is increased by adding hydrogen peroxide to the polishing liquid. As a result, the impurity metal dissolved in the polishing liquid is in an oxidized state, and has an effect of hardly being precipitated on the surface of the silicon wafer. Since hydrogen peroxide has a large oxidizing power, it oxidizes the wafer surface to form a thin chemical oxide film of about 1 μm. The chemical oxide film formed on the wafer surface has an effect of inhibiting metal adsorption. Ammonia has a property of forming a complex with a metal, and forms an ammine complex with a metal dissolved in a polishing liquid (for example, when forming an ammine complex with Cu [Cu (N
H _{3) 4]} take the ²⁺ form. ) Is formed and stabilized, so that it is difficult to adsorb to the wafer surface. Therefore chelating agents,
By adding hydrogen peroxide and ammonia to the polishing liquid, both the wafer and the impurity metal have a reducing effect, so that metal contamination can be more effectively reduced.

The invention according to claim 2 is the invention according to claim 1, wherein the abrasive particles are used in an amount of 0.01 to 10% by weight and the chelating agent is used in an amount of 1 × 10 ^{−5 to} 0.
It is a polishing liquid for silicon wafers containing 3 mol / l, 0.03 to 3% by weight of hydrogen peroxide, and 0.029 to 2.9% by weight of ammonia. According to the second aspect of the present invention, the polishing liquid containing the abrasive particles, the chelating agent, the hydrogen peroxide, and the ammonia in the above ratio can more effectively remove contaminants.

In the first aspect, the term "polishing liquid" refers to not only a so-called polishing slurry (polishing liquid stock) immediately after the polishing liquid is manufactured, but also a polishing slurry (polishing liquid stock) at the time of processing a silicon wafer. It means both polishing liquids diluted with water.

[0008]

Embodiments of the present invention will be described.
The polishing liquid of the present invention is a polishing liquid used in mechanical chemical polishing, and is formed in a slurry form in which abrasive particles are dispersed in an aqueous alkaline solution or the like. This embodiment is characterized in that the slurry contains a chelating agent, hydrogen peroxide and ammonia.

As the abrasive particles, for example, silica,
A (CeO_Two), Alumina (Al_TwoO _Three) Etc. are alkaline
As aqueous solution, potassium hydroxide, sodium hydroxide, etc.
Respectively. Polished with this alkaline aqueous solution
The pH of the solution is adjusted to 10 to 11.5. pH not 10
When it is full, the polishing rate decreases, and when it exceeds 11.5, the polishing rate decreases.
Polishing particles such as silica may dissolve or the wafer may become rough.
The problem that it becomes easy to rub occurs.

[0010] When used in a polishing apparatus, a slurry-like polishing liquid (polishing stock solution) is diluted 2 to 50 times with pure water.
When the diluted polishing liquid is 100% by weight, the abrasive particles are 0.01 to 10% by weight, and the chelating agent is 1 × 10 ^{−5 to} 0.1%.
3 mol / l, hydrogen peroxide at 0.03 to 3% by weight, and ammonia at 0.029 to 2.9% by weight. Examples of the chelating agent include ethylenediaminetetraacetic acid (hereinafter, referred to as EDTA), diethylenetriaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA). EDTA and DTPA are particularly preferable for reducing copper contamination of the wafer. The preferred concentration of the chelating agent is 0.1.
001 to 0.2 mol / l. 1 × 10 ⁻⁵ mol /
If less than 1, the effect of reducing contamination is insufficient,
Even if it exceeds 0.3 mol / l, no improvement in the effect of reducing contamination can be expected. The preferred concentration of hydrogen peroxide is 0.1-1.
0% by weight. If it is less than 0.03% by weight, the effect of reducing contamination is insufficient, and if it exceeds 3% by weight, no improvement in the effect of reducing contamination can be expected. The preferred concentration of ammonia is 0.1-1.0% by weight. If it is less than 0.029% by weight, the effect of reducing contamination is insufficient,
Even if it exceeds 2.9% by weight, no improvement in the effect of reducing contamination can be expected.

The polishing method for roughly polishing a silicon wafer using the polishing liquid of the present invention includes a single-side polishing method and a double-side polishing method. FIG. 1 shows a single-side polishing apparatus 10. The polishing apparatus 10 includes a rotary platen 11 and a wafer holder 12. The rotating surface plate 11 is a large disk, and is rotated by a shaft 15 connected to the center of the bottom surface. A polishing pad 13 is attached to the upper surface of the rotary platen 11. The wafer holder 12 includes a pressure head 12a and a shaft 12b connected to the pressure head 12a to rotate the pressure head 12a.
A polishing plate 14 is attached to the lower surface of the pressure head 12a. A plurality of silicon wafers are attached to the lower surface of the polishing plate 14. A pipe 18 for supplying a slurry-like polishing liquid 17 is provided at an upper portion of the rotary platen 11.

When the silicon wafer 16 is polished by the polishing apparatus 10, the pressure head 12a is lowered and a predetermined pressure is applied to the silicon wafer 16 to polisher the wafer 1.
Hold down 6. While supplying the polishing liquid 17 to the polishing pad 13 from the pipe 18, the pressing head 12 a and the rotary platen 11
Are rotated in the same direction to polish the surface of the wafer 16 into a flat shape.

[0013]

Next, examples of the present invention will be described together with comparative examples. <Example 1> First, a silicon wafer cut and sliced from a silicon single crystal ingot grown by the CZ method was wrapped, chamfered, chemically etched, and then subjected to a mechanical and chemical polishing step. As a polishing liquid used in the rough polishing step, a pH of 10. wherein abrasive particles of SiO ₂ are dispersed in an aqueous solution of alkali (sodium hydroxide).
9 was prepared, and the polishing slurry 1 was diluted with pure water so that the SiO ₂ concentration was 2.0% by weight. EDT was added to this diluted solution as a chelating agent.
A has a concentration of 0.1 mol / l and hydrogen peroxide (hereinafter, H ₂
That O _2. ) And ammonia (hereinafter referred to as NH ₃ ) at a concentration of 0.68% by weight, respectively, to obtain a polishing liquid. A standard copper solution for atomic absorption analysis (copper concentration 1000 ppm)
Of the polishing solution was forcibly contaminated with copper so that the copper concentration became 1000 ppb. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes by the polishing apparatus 10 shown in FIG. Hereinafter, rough polishing of Example 2 and Comparative Examples 1 to 9 was similarly performed by the polishing apparatus shown in FIG.

Comparative Example 1 A silicon wafer obtained in the same manner as in Example 1 was prepared, and diluted with the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 10.5) as in Example 1. This diluent was used as a polishing liquid without any addition. This polishing liquid was forcibly contaminated with copper as in Example 1. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes. Comparative Example 2 A silicon wafer obtained in the same manner as in Example 1 was prepared, and EDTA was added to the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 10.5) as in Example 1. A polishing liquid was prepared by adding and mixing so as to be 0.1 mol / l. This polishing liquid was forcibly contaminated with copper as in Example 1. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes.

Comparative Example 3 A silicon wafer obtained in the same manner as in Example 1 was prepared, and E was added to the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 10.5) as in Example 1.
DTA at a concentration of 0.1 mol / l and NH ₃ at a concentration of 0.1 mol / l.
Each was added and mixed so as to be 58% by weight to obtain a polishing liquid. This polishing liquid was forcibly contaminated with copper as in Example 1. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes. Comparative Example 4 A silicon wafer obtained in the same manner as in Example 1 was prepared, and EDTA was added to the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 10.5) as in Example 1. 0.1 mol / l and H ₂ O ₂ were added and mixed so as to have a concentration of 0.6% by weight to prepare a polishing liquid. This polishing liquid was forcibly contaminated with copper as in Example 1. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes.

Example 2 A silicon wafer obtained in the same manner as in Example 1 was prepared, and SiO ₂ was polished with an alkaline aqueous solution (aqueous solution of sodium hydroxide and amines) as a polishing liquid used in the rough polishing step. PH 1 with dispersed particles
A polishing slurry 2 (polishing stock solution) of 1.2 was prepared, and the polishing slurry 2 was diluted with pure water so that the SiO ₂ concentration was 2.0% by weight. The diluted solution has a concentration of EDTA of 0.1 mol / l, a concentration of H ₂ O ₂ of 0.6% by weight,
₃ was added and mixed so that the concentration became 0.58% by weight to obtain a polishing liquid. A standard copper solution for atomic absorption analysis (a copper nitrate solution having a copper concentration of 1000 ppm) was added to the polishing solution to forcibly contaminate the polishing solution with copper so that the copper concentration became 10 ppb. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes.

Comparative Example 5 A silicon wafer obtained in the same manner as in Example 1 was prepared, and diluted with the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 11.0) as in Example 2. This diluent was used as a polishing liquid without any addition. This polishing liquid was forcibly contaminated with copper as in Example 2. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes. <Comparative Example 6> A silicon wafer obtained in the same manner as in Example 1 was prepared, and the concentration of EDTA was adjusted to the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 11.0) as in Example 2. A polishing liquid was prepared by adding and mixing so as to be 0.1 mol / l. This polishing liquid was forcibly contaminated with copper as in Example 2. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes.

Comparative Example 7 A silicon wafer obtained in the same manner as in Example 1 was prepared, and H was added to the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 11.0) as in Example 2. _Two
O ₂ was added and mixed to a concentration of 0.6% by weight to obtain a polishing liquid. This polishing liquid was forcibly contaminated with copper as in Example 2. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes. Comparative Example 8 A silicon wafer obtained in the same manner as in Example 1 was prepared, and NH ₃ was concentrated in the same diluent as in Example 2 (SiO ₂ concentration: 2.0% by weight, pH = 11.0). Was adjusted to 0.58% by weight to obtain a polishing liquid. This polishing liquid was forcibly contaminated with copper as in Example 2. Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes.

Comparative Example 9 A silicon wafer obtained in the same manner as in Example 1 was prepared, and H was added to the same diluent (SiO ₂ concentration: 2.0% by weight, pH = 11.0) as in Example 2. _Two
O ₂ was added at a concentration of 0.6% by weight and NH ₃ was added and mixed at a concentration of 0.58% by weight to prepare a polishing liquid. This polishing liquid was forcibly contaminated with copper as in Example 2.
Using the polishing liquid thus mixed, the silicon wafer was roughly polished for 30 minutes. <Comparative Evaluation> The concentration of Cu after the surface of a silicon wafer was roughly polished was measured. Table 1 shows the results of Example 1 and Comparative Examples 1 to 4, and Table 2 shows the results of Example 2 and Comparative Examples 5 to 9, respectively. Note that the concentration of Cu is as described in JP-A-9-0641.
The measurement was carried out using the method disclosed in JP-A-33-33. That is, the silicon wafer was heat-treated at a temperature of 400 ° C. for 15 minutes, and after the heat treatment, the Cu concentration was measured by total reflection X-ray fluorescence analysis.

[0020]

[Table 1]

Table 1 shows that the chelating agents EDTA and H ₂ O ₂
And NH ₃ are used alone or in combination to examine the effect of suppressing contamination. Chelating agent, H ₂
O ₂ and a chelating agent in Comparative Examples 2 to 4 is added to one of NH _3, H ₂ O ₂ and pollutant concentration of Cu in comparison with Comparative Example 1, neither the addition of NH ₃ is slightly decreased ing. In Example 1 in which all of the chelating agent, H ₂ O ₂ and NH ₃ were added, the Cu concentration was about 1 compared to Comparative Examples 2 to 4.
It has been reduced from 1/00 to about 1/1000. In addition, the Cu concentration was at a very low level of the order of 10 ¹⁰ atoms / cm ² , indicating that Cu was effectively reduced.

[0022]

[Table 2]

Table 2 shows that the chelating agents EDTA and H ₂ O ₂
And NH ₃ are used alone or in combination to examine the effect of suppressing contamination. In Comparative Examples 6 to 9, the Cu contamination concentration was not much reduced as compared with Comparative Example 5 in which nothing was added. Example 2 is Example 1 of Table 1.
Similarly to the above, the Cu concentration is at a very low level of the order of 10 ¹⁰ atoms / cm ^2, and it can be seen that Cu is effectively reduced.

[0024]

As described above, by polishing a slurry containing abrasive particles with a polishing liquid containing a chelating agent, hydrogen peroxide and ammonia, the impurity metal is stabilized in the polishing liquid, and Since an environment in which adsorption to a wafer is suppressed is realized, metal contamination, particularly copper contamination, caused by contamination from various processes and facilities can be reduced.
Further, since metal contamination is reduced by using hydrogen peroxide and ammonia in addition to the chelating agent, the addition of the chelating agent is smaller than in the conventional case, so that an inexpensive polishing liquid can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a single-side polishing apparatus for roughly polishing a silicon wafer using the polishing liquid of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Single-side polishing apparatus 11 Rotary surface plate 12 Wafer holder 12a Pressurizing head 12b Shaft 13 Polishing pad 14 Polishing plate 16 Silicon wafer 17 Polishing liquid 18 Piping

Continued on the front page (72) Inventor Masaaki Tominaga 1-297 Kitabukurocho, Omiya-shi, Saitama Mitsubishi Materials Silicon Research Center (72) Inventor Hideki Sakamoto 1-297 Kitabukurocho, Omiya-shi, Saitama Mitsubishi Materials Corporation Silicon Research Center F term (reference) 3C058 AA07 CB05 CB06 CB10 DA02 DA17

Claims (4)

[Claims] 1. A polishing liquid for silicon wafers containing a chelating agent, hydrogen peroxide and ammonia in a slurry containing abrasive particles. 2. When polishing a silicon wafer (16), 0.01 to 10% by weight of abrasive particles and 1 × 10 ⁻⁵ to ⁵ % by weight of a chelating agent.
0.3 mol / l, 0.03 to 3% by weight of hydrogen peroxide,
2. The polishing liquid for silicon wafer according to claim 1, wherein the polishing liquid contains ammonia in a proportion of 0.029 to 2.9% by weight. 3. A method for polishing a silicon wafer, comprising polishing a silicon wafer (16) using a polishing liquid (17) containing a chelating agent, hydrogen peroxide and ammonia in a slurry containing abrasive particles. 4. An abrasive particle of 0.01 to 10% by weight, a chelating agent of 1 × 10 ^{−5 to} 0.3 mol / l, hydrogen peroxide of 0.03 to 3% by weight, and ammonia of 0.029 to 2%. .9
4. The method for polishing a silicon wafer according to claim 3, wherein the polishing is performed using a polishing liquid (17) containing the respective components in a proportion of% by weight.