JPH09316431A - Slurry for polishing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a slurry for polishing, having a polishing ability equal to those of conventional polishing slurries, low in the affection with an alkali metal, capable of being repeatedly used, contributing to the reduction of costs and useful for polishing semiconductor substrates, magnetic recording media, etc., by dispersing a polishing agent in a specific aqueous solution. SOLUTION: This slurry for polishing is obtained by dispersing (B) a polishing agent such as fumed silica in (A) an aqueous solution containing (A1 ) cesium hydroxide and, if necessary, further (A2 ) a cesium salt such as cesium chloride or cesium formate. The slurry is obtained e.g. adding the 50% aqueous solution of the component A1 having a purity of 99.6wt.% and, if necessary, further the 80% aqueous solution of the cesium formate having a purity of >=98.4wt.% or the powder of the cesium chloride having a purity of >=99.98wt.% to ultrapure water having an electric resistance of >=17MΩ so as to give a final slurry pH of 10.0-13.0, especially 11.5-12.5, and subsequently suspending the component B in the mixture in such an amount as to give a concentration of 5-15wt.%, especially 6.5-8.5wt.%, under stirring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing slurry for polishing a semiconductor substrate, a semiconductor device or a magnetic recording medium.

[0002]

2. Description of the Related Art Semiconductor devices and magnetic recording media are manufactured by polishing a substrate into a mirror surface and then forming a functional layer. For example, in the mirror polishing step of a semiconductor wafer, a lapping step (coarse polishing) for removing a cutting strain layer and surface waviness generated when a single crystal ingot is cut into a wafer shape (rough polishing), a surface for a wrapped wrapped wafer There is a polishing process (precision polishing) that finishes to roughness. The polishing agent used at that time is SiO ₂ , Al.
An alkaline aqueous solution in which ₂ O ₃ , ZrO ₂ , TiO ₂ , CeO ₂ , Fe ₂ O _{3 and the} like are dispersed is used. In recent years, the mirror surface quality required for ULSI devices and memory hard disks has become increasingly severe. Above all, as the density of ULSI devices has increased and the multi-layering of devices has been introduced, it has become necessary to flatten the interlayer insulating film between the layers. This interlayer insulating film is usually formed of silicon oxide. The object to be polished has also been changed to a silicon oxide film rather than silicon itself.

As a polishing method for polishing the interlayer insulating film, a so-called CMP (Chemical and Mechanical Poli) is used.
shing: Chemical mechanical polishing) is used. This method is described in, for example, Journal of Electrochemical Society Vol.1.
38 No.6 1991, potassium hydroxide (KO
The colloidal silica having a particle diameter of about 30 nm stabilized by H) is diluted with pure water to adjust the pH to about 9.5. In this polishing composition, the colloidal silica easily gels in the presence of water,
Potassium hydroxide (KOH) is added for the purpose of preventing gelation. However, since silicon oxide generally has high hygroscopicity, potassium oxide (K
OH) diffuses into the silicon oxide. Normally, when an alkali metal such as sodium or potassium penetrates into the gate oxide film of a MOS transistor, the threshold voltage fluctuates, resulting in deterioration of transistor characteristics, resulting in deterioration of device characteristics and deterioration of reliability. It has a problem of bringing it. Further, there is also a problem that after polishing, the colloidal silica fine particles in the polishing agent remain attached to the semiconductor substrate and are difficult to remove. Further, when the abrasive is dried, it causes generation of fine particles containing an alkali metal, which causes a decrease in device yield and device reliability.

For the purpose of improving these drawbacks, fluorine-containing silicon dioxide is used (Japanese Patent Laid-Open No. 7-17345).
6), silicon dioxide as an abrasive is obtained by an ion exchange method or by hydrolyzing an organic silicon compound. In addition, amines for promoting processing and organic polymers for suppressing haze are added (New Ceramics 1995 No. 2). Further, as a slurry capable of increasing the polishing rate, suppressing the occurrence of surface defects such as orange peel, and flattening with high quality, there has been proposed a slurry containing a hydrazine compound as a polishing accelerator (Japanese Patent Laid-Open No. 7-
228863). Desirable properties required for a polishing slurry mother liquor are: 1) It is possible to suspend the polishing agent in the mother liquor as evenly as possible. 2) Does not act chemically or physically to impair the function such as reacting with an abrasive or gelling. 3) Be stable against temperature changes. 4) Good wettability to the processed surface. 5) Contain as few components as possible that have a negative effect on the post-process of device fabrication. 6) Easy cleaning after polishing. 7) Do not include harmful substances that have a harmful effect on the human body or environment in the polishing and cleaning processes. 8) It is cheap. And so on. The development of polishing slurries that satisfy these conditions is still ongoing.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a polishing slurry which is excellent in polishing ability and cleaning ability and has little deterioration in polishing ability even after repeated use. In CMP, the ratio of the polishing slurry to the wafer product cost is very high. These costs differ depending on the type and consumption of the polishing slurry, but are generally said to account for 30 to 40% of the entire CMP process, and how to reduce the cost is a major issue ( Electronic Materials May 1996, p. 57). As one of the solutions, there is a proposal to regenerate the polishing slurry, but it is technically difficult and has not yet been put into practical use (Monthly Semiconduct
or World 1996. February issue P.22). As a solution to this problem, the present invention is a novel polishing slurry which does not deteriorate the polishing performance even when it is repeatedly used a plurality of times, at least three times or more, instead of throwing away the conventional polishing slurry once. To find out.

[0006]

In the present invention, a means for adding cesium hydroxide (CsOH) to the mother liquor is adopted.
Cesium hydroxide (CsOH) is the strongest alkaline as an inorganic base, and cesium has the lowest electronegativity of Pauling compared to other alkaline metals, and the basicity can be adjusted with a small amount of use, so the chemical polishing ability is deteriorated. Therefore, the alkali metal can be easily removed by washing. Further, since the cesium salt has a high specific gravity, it has excellent dispersibility on the polishing pad surface during polishing work, and therefore uniform polishing is possible and the polishing ability is high. Furthermore, in another invention, cesium hydroxide (CsO
In addition to H), a means of using cesium salt together was adopted. The polishing slurry containing a cesium salt has a large specific gravity and excellent dispersibility on the polishing pad, so uniform polishing is possible and excellent in polishing ability, and it is effective in suppressing deterioration of polishing ability even when repeatedly used. .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As the abrasive used in the present invention,
SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ , CeO ₂ , Fe ₂ O _{3 and the} like. Among them, fumed silica is most suitable for CMP. An example of the characteristics of fumed silica is as follows: (1) Specific surface area by BET method: 130 ± 25 m ² / g (2) Average particle size: about 16 nm (3) Apparent specific gravity: about 50 g / l (4) Loss on ignition at 1000 ° C x 2 hrs: 1% or less (5) SiO ₂ content: 99.9% or more (6) Al ₂ O ₃ content: 0.01% or less (7) Fe ₂ O ₃ content : 0.001% or less (8) TiO ₃ content: 0.01% or less (9) HCl content: 0.007% or less

Cesium hydroxide (CsO used in the present invention
H) has a molecular weight of 149.9 and usually has a purity of 99.6% by weight.
It is available as a colorless and transparent 50% aqueous solution (specific gravity: 1.789). An example of the impurity content is as follows;

[Table 1]

Cesium chloride (CsC) used in the present invention
l) has a molecular weight of 168.4 and usually a purity of 99.98 wt.
% White powder is available. An example of the impurity content is as follows;

[Table 2]

Cesium formate (CsCO used in the present invention
OH) has a molecular weight of 177.9 and is usually 98.4% pure.
It is available as the above colorless and transparent 80 wt% aqueous solution (specific gravity: 2.30). An example of the impurity content is as follows;

[Table 3]

As the mother liquor, ultrapure water having an electric resistance of 17 MΩ or more is used. Cesium hydroxide (CsOH) is appropriately added to ultrapure water to make it alkaline, and an abrasive is added and suspended therein while stirring. The final polishing slurry pH is 1
It is 0.0 to 13.0, preferably 11.5 to 12.5. If the pH is lower than this, chemical polishing is not promoted and the polishing rate does not increase. If it is higher than this, stains are likely to occur on the polished surface. The concentration of the abrasive is 5 to 15 wt%, preferably 6.5 to 8.5 wt%. If it is thinner than this, the polishing rate does not increase, and if it is thick, it becomes viscous and the workability deteriorates.

When a cesium salt is used in addition to cesium hydroxide (CsOH), p of the final polishing slurry is used.
H is 10.0 to 13.0, preferably 11.5 to
12.5. Cesium hydroxide is a strong base and is almost 100% ionized. Now, if 1 gram equivalent of ions is present in 1 liter of the aqueous solution, the concentration is 1 normal and pH = 1.
Equivalent to 4. That is, in the wt% concentration, (133 + 16 + 1)
× 100/1000 = 15 wt%. Therefore, pH =
13 is 1.5 wt%, pH = 12 is 0.15 wt%, pH =
In the case of No. 11, the target basicity is achieved at an extremely thin concentration of 0.015 wt%, which alone reduces the cleaning load for removing the alkali metal. The advantage of using cesium salt in combination is that the polishing slurry has a long life and can be used repeatedly, and the specific gravity of the polishing slurry can be increased so that the dispersion on the pad is better and uniform polishing is possible. Is.

In order to confirm the storage stability of the polishing slurry, cesium hydroxide alone or cesium hydroxide was used under the compounding conditions shown in Table 4, and 7 wt% of fumed silica was added to a mother liquor whose pH was adjusted to 11 to 13. Stir and stir to adjust the polishing slurry, put it in a test tube with a stopper, and keep at 30 ℃.
It was stored for 14 days in a thermostat and the appearance was visually observed.

[0014]

[Table 4]

The results after storage for 14 days showed no change in the case of using cesium hydroxide alone. Also,
In the case where the cesium salt was used in combination, no change was observed in the case where the pH was made to be 12 or 13 and strongly alkaline. However, when the pH was set to 11, a part of gelation started after 7 days and completely gelated after 14 days and could not be used for polishing.

[0016]

In the present invention, the use of cesium hydroxide, which has the highest Pauling electronegativity, makes it possible to use a small amount to provide high alkalinity, high chemical polishing ability, and excellent detergency. It was done. Further, by utilizing the large specific gravity of the cesium salt, the dispersibility on the polishing pad is improved, uniform polishing is achieved, and a long-life polishing slurry that withstands repeated use is provided. is there.

[0017]

EXAMPLES The contents of the present invention will be specifically described below with reference to examples. (Example 1) Example 1 shows an example in which cesium hydroxide (CsOH) is used as a polishing accelerator. 50% cesium hydroxide (CsOH) was appropriately added to ultrapure water (electrical resistance: 18 MΩ or more) at room temperature to adjust the pH to 12. An average particle diameter of 16n, which was previously weighed
m, fumed silica having a specific surface area of 130 m ² / g according to the BTE method was added with stirring and suspended. The amount of fumed silica added was 7 wt%. Since the pH of the mother liquor shifts slightly to the acidic side by the addition of fumed silica, a small amount of cesium hydroxide was added to maintain pH = 12.

The polishing slurry thus prepared was used to polish a 5-inch silicon wafer.
The polishing conditions were as follows. Polishing machine: Single-wafer single-side polishing machine Wafer: Silicon oxide film of about 3 μm formed on the surface by thermal oxidation method Polishing pad: Hard urethane pad Polishing pressure: 250 g / cm ² Rotation speed: 100 rpm Polishing time: 20 minutes Polishing liquid temperature: 25 ° C Polishing liquid supply: Continuous

After polishing, the polishing rate was calculated by the gravimetric method.
Regarding surface defects, the presence or absence of orange peel and micro scratches was observed with a microscope. As a result, the polishing rate was 0.141 μm / min,
No peels or micro scratches were observed. Further, the polishing slurry was collected and the polishing test was repeated twice and three times to measure the polishing ability. As a result, in the second polishing test, the polishing rate was 0.108 μm / min, and no orange peel or micro scratch was observed. In the third polishing test, the polishing rate was 0.07.
At 5 μm / min, no orange peel or micro scratch was observed. The results are shown in Table 5 and FIG.

(Comparative Example) For comparison, the same test was conducted on a polishing slurry using conventional potassium hydroxide (KOH). The polishing slurry is cesium hydroxide (Cs
Example 1 was repeated except that potassium hydroxide (KOH) was used instead of OH). The conditions for the polishing test are also those of Example 1.
Same as As a result, the polishing rate was 0.108 μm /
No orange peel or micro scratches were observed at min. In the second polishing test, the polishing rate was 0.092 μm / min, and no orange peel or micro scratch was observed. In the third polishing test, the polishing rate was 0.069 μm / min.
So no orange peel or micro scratches were observed. The results are shown in Table 5 and FIG.

Example 2 As Example 2, cesium hydroxide (CsOH) and cesium chloride (Cs) were used as polishing accelerators.
An example using Cl) is shown. Ultrapure water at room temperature (electrical resistance:
Cesium hydroxide (CsO) of 50% concentration in 18 MΩ or more)
H) and cesium chloride (CsCl) 5 wt% (No. 2-
1) or 10 wt% (No.2-2) added, pH = 12
I adjusted it to be. An average particle diameter of 16 nm and a specific surface area measured by the BTE method of 130 m ² /
g of fumed silica was added with stirring and suspended. The amount of fumed silica added was 7 wt%. Since the pH of the mother liquor shifts slightly to the acidic side by the addition of fumed silica, add a small amount of cesium hydroxide to add p.
It was kept at H = 12. Using the polishing slurry thus prepared, the same polishing test as in Example 1 was conducted. The results are also shown in Table 5. The relationship between the number of times the polishing liquid is used and the polishing rate is shown in FIG. As is clear from these results, it is understood that the deterioration of the polishing ability can be suppressed by using cesium chloride (CsCl) together.

Example 3 As Example 3, cesium hydroxide (CsOH) and cesium formate (Cs) were used as polishing accelerators.
An example using (COOH) is shown. 50% cesium hydroxide (C) in ultrapure water (electrical resistance: 18 MΩ or more) at room temperature
sOH) and cesium formate (CsCOOH) 5 wt% (N
o.3-1) or 10wt% (No.3-2) added, pH
It was adjusted so that = 12. An average particle size of 16 nm and a specific surface area of 130 according to the BTE method, which were weighed in advance.
m ² / g fumed silica was added with stirring and suspended. The amount of fumed silica added was 7 wt%. Since the pH of the mother liquor shifts slightly to the acidic side by the addition of fumed silica, a small amount of cesium hydroxide was added to maintain pH = 12. Using the polishing slurry thus prepared, the same polishing test as in Example 1 was conducted. The results are also shown in Table 5. The relationship between the number of times the polishing liquid is used and the polishing rate is shown in FIG.

[0023]

[Table 5]

As is clear from Table 5 and FIG. 1, it was found that when a cesium salt is used, the polishing rate does not deteriorate even after repeated use and the life is long. The larger the amount of cesium salt used, the longer the life.

[0025]

According to the present invention, the polishing ability is comparable to that of the conventional polishing slurry using KOH, the polishing finish is good, and the influence of alkali metal is small. In particular, when a cesium salt is used in combination, the polishing performance is not deteriorated even if it is repeatedly used, so that it greatly contributes to the cost reduction of the polishing process.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between the number of times a polishing slurry is repeatedly used and a polishing rate.

Claims (4)

[Claims] 1. A polishing slurry in which an abrasive is dispersed in an aqueous solution containing cesium hydroxide. 2. A polishing slurry in which an abrasive is dispersed in an aqueous solution containing cesium hydroxide and a cesium salt. 3. The polishing slurry according to claim 2, wherein the cesium salt is one of cesium chloride and cesium formate. 4. The polishing slurry according to claim 1, wherein the polishing agent is fumed silica.