US20070039246A1

US20070039246A1 - Method for preparing polishing slurry

Info

Publication number: US20070039246A1
Application number: US11/493,450
Authority: US
Inventors: Zhendong Liu
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-08-17
Filing date: 2006-07-26
Publication date: 2007-02-22

Abstract

The method for manufacturing polishing slurries is useful for polishing electronic substrates. The method includes preparing an aqueous intermediate dispersion, the aqueous intermediate dispersion containing solid particles; and introducing an azole compound into the aqueous intermediate dispersion to prevent biological activity and to form a stable intermediate dispersion. Then storing the stable intermediate dispersion; and introducing additional components to the stable intermediate dispersion to form a final polishing slurry.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/709,036 filed Aug. 17, 2005.

BACKGROUND OF THE INVENTION

The invention relates to chemical mechanical polishing formulations for polishing substrates, such as silicon, magnetic media, glass displays and patterned wafers. In particular, the invention relates to a method for preparing and storing polishing slurries useful for nonferrous metal patterned wafers.
Chemical mechanical polishing is an enabling technology for copper damascene processes. It allows global planarization of interconnect metals and dielectrics before the lithography step. Copper polishing usually occurs in at least a two-step process. The first step is for bulk copper removal, which needs high copper removal rate and low barrier and dielectric removal rates. The second step, also called barrier polishing, clears the diffusion barrier layer. It often requires a high barrier rate with specific copper and dielectric removal rates. Corresponding to these two steps, there are at least two types of slurries employed in CMP processing, namely the first-step copper slurry and the second-step barrier slurry.
Conventional barrier slurries rely upon an alkaline pH regime for better abrasive stability and higher dielectric removal rate. Recently, acidic barrier slurries such as those disclosed by Liu et al. in US Pat. Pub. No. 2004/0147118 have demonstrated performance advantages by achieving a higher barrier removal rate that allows the polishing process to operate at low down forces. Unfortunately, the intermediate acidic abrasive particle products used to formulate these polishing slurries can suffer from detrimental biological activity. For example, silica particles at acidic pH levels have high levels of biological activities when stored for a few months at room temperature. Specifically, these particles tend to undergo an irreversible agglomeration from biological activity; and because this agglomeration of slurry particles affects polishing performance, it is unacceptable for most polishing applications. In summary, this irreversible agglomeration from biological activity renders control of the manufacturing process most difficult.
Typically, slurry formulations rely upon biocides such as Kordek™ MLX manufactured by Rohm and Haas Company (9.5-9.9% methyl-4-isothiazolin-3-one, 89.1-89.5% water and ≦1.0% related reaction product). Ideally, these biocides should improve the polishing slurry as follows: 1) kill bacteria in its working concentration range; 2) do not significantly affect polishing performance of the slurry; and 3) do not cause slurry stability issues. Unfortunately, these biocides can lose their effectiveness at low pH levels.
In view of the above, there exists a need to provide a method of manufacture that controls or eliminates biological activity and the irreversible agglomeration associated with acidic particle sources. In addition, there exists a need for a biocide that does not adversely affect the slurry's polishing performance or cause detrimental slurry stability issues.

STATEMENT OF THE INVENTION

An aspect of the invention includes a method for manufacturing polishing slurries useful for polishing patterned integrated circuit substrates comprising the steps of: preparing an aqueous intermediate dispersion, the aqueous intermediate dispersion containing solid particles and having an acidic pH; introducing an azole compound into the aqueous intermediate dispersion to prevent biological activity and to form a stable intermediate dispersion; storing the stable intermediate dispersion for at least one day; and introducing additional components to the stable intermediate dispersion to form a final polishing slurry, the final polishing slurry having an acidic pH.
Another aspect of the invention includes a method for manufacturing polishing slurries useful for polishing patterned integrated circuit substrates, the patterned integrated circuit substrates having nonferrous interconnects, comprising the steps of: preparing an aqueous intermediate dispersion, the aqueous intermediate dispersion containing solid particles and having a pH less than 5; introducing at least 0.1 weight percent benzotriazole into the aqueous intermediate dispersion to prevent biological activity and to form a stable intermediate dispersion; storing the stable intermediate dispersion at least one week; and introducing additional components to the stable intermediate dispersion to form a final polishing slurry, the final polishing slurry having a pH less than 5.

DETAILED DESCRIPTION

It was found that azole compounds can effectively function as a biocide at higher concentrations for abrasive intermediates used to produce polishing slurries. Azole compounds such as benzotriazole are chemically quite inert and do not cause any slurry stability concerns at high concentration levels. Most importantly, benzotriazole is a useful corrosion inhibitor ingredient in most copper slurries. Pre-adding the azole compound as an abrasive biocide to raw abrasive particle dispersion can provide the additional benefit of not introducing contamination to the final slurry products when the azole compound remain in a final slurry formulation component. Under these circumstances, the azole compound functioning as a biocide in an intermediate abrasive product will not adversely affect the slurry's final polishing performance. Furthermore, for polishing non-copper and non-silver substrates, the presence of azole compounds can have limited impact upon polishing rates and selectivity because it often is a chemically inert material in these polishing systems. For purpose of this specification chemically inert refers to an azole compound that does not react with the final polishing ingredients to produce sufficient detrimental byproducts to render polishing unacceptable. Most preferably, the amount of azole compound has less than five percent affect on removal rate of the integrated circuit substrate as measured in Angstroms per minute. For purposes of this specification the final polishing slurry refers to formulations prepared in advance useful for polishing electronic substrates. Electronic substrates include silicon wafers, patterned wafers, magnetic media disks and display panels. The method is particulary effective in preparing slurries useful for preparing patterned integrated circuit substrates, such as patterned wafers. For example, patterned wafers including aluminum, copper or silver interconnects.
The azole compound stabilizes the abrasive dispersion for at least several months or greater than one year without any detrimental biological activity. Preferably, the abrasive particle manufacturer adds the azole compound at the point of manufacture to prevent significant biological activity from occurring. For purposes of this specification, storing the intermediate dispersion refers to maintaining the aqueous intermediate product for at least one day. Preferably, storing refers to maintaining the aqueous intermediate product for at least one week. Most preferably, storing refers to maintaining the aqueous intermediate product for at least one month. For example, significant biological activity occurs when the biological activity begins to agglomerate particles. After preparing the azole compound-stabilized intermediate product, the slurry manufacturer is free to prepare the final slurry formulation with consistent and predictable polishing performance.
For purposes of this specification azole compound refers to any organic compounds having a five-member heterocyclic ring with two double bonds. For example, specific Azole compounds include compounds selected from at least one of the group of 1,2,4-triazole, 3-methyl-1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole, 1-amino-1,2,4-triazole, 3-amino-1,2,4-triazole, 5-amino-3-methyl-1,2,4-triazole, 3-isopropyl-1,2,4-triazole, 1,2,3-triazole, 1-methyl-1,2,3-triazole, 1-amino-1,2,3-triazole, 1-amino-5-methyl-1,2,3-triazole, 4,5-dimethyl-1,2,3-triazole, 1-amino-5-n-propyl-1,2,3-triazole, 1-(β-aminoethyl)-1,2,3-triazole, 1-methyltetrazole, 2-methyltetrazole, 5-amino-1H-tetrazole, 5-amino-1-methyltetrazole, 1-(β-aminoethyl)tetrazole, a substituted triazole and tetrazole compounds having an electron-donating substituent. Preferably the azole compounds include at least one of benzotriazole, mercaptobenzothiazole, tolytriazole and imidazole. Most preferably, the azole compound is benzotriazole. Benzotriazole provides the additional efficacy of being an effective corrosion inhibitor for polishing slurries designed for polishing patterned wafers having copper or silver interconnects.
The intermediate abrasive product includes a sufficient amount of azole compound to prevent the formation of biological growth detrimental to abrasive's shelf life and polishing performance. The amount of azole compound sufficient to control biological activity will vary with pH levels, abrasive type, temperature and specific azole compound or mixture used. Typically, a concentration of at least 0.2 weight percent azole compound is sufficient to prevent the formation of biological activity in the aqueous intermediate dispersion. This specification refers to all concentrations in term of weight percent, unless expressly noted otherwise. Preferably, the abrasive intermediate includes at least 0.4 weight percent azole compound. The intermediate slurry product will have a typical azole compound concentration of 0.5 to 2 weight percent in the aqueous intermediate dispersion.
In addition, when mixing these intermediate slurries into their final formulation, it is often advantageous to maintain the level of the azole compound at a level that prevents biological activity. Preferably, the final composition maintains an azole compound concentration of at least 0.2 weight percent. Most preferably, the final concentration of the azole compound is at least 0.4 weight percent with a typical final azole concentration being 0.5 to 2 weight percent. For purposes of this specification, final slurry refers to a mixture that upon little or no adjustment, such as final dilution, pH adjustment or oxidizer addition (such as adding the instable hydrogen peroxide before use) is ready for polishing.
These concentrations are suitable for both acidic and basic slurries of intermediate abrasive product. But the azole compounds are particularly effective at preventing biological activity for acidic dispersions where conventional biocides can lose their effectiveness. For example, the azole compounds can operate at a pH of less than 5 or even less than 3 to prevent biological growth in the intermediate abrasive dispersion and the final polishing slurry. In particular, the azole additive forms a stable abrasive dispersion that allows storage at room temperature for several months without detrimental biological activity. Final polishing slurriess having a pH of at least 5 such as basic copper polishing slurries may optionally include biocides, such as Kathon® ICP III, containing active ingredients of 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one (Kathon is a registered trademark of Rohm and Haas Company) or Kordek™ MLX manufactured by Rohm and Haas Company (9.5-9.9% methyl-4-isothiazolin-3-one, 89.1-89.5% water and ≦1.0% related reaction product).
The slurry intermediate composition includes an abrasive for “mechanical” removal of substrate materials. For example, the CMP composition may include an abrasive for “mechanical” removal of barrier layers, such as tantalum, tantalum nitride, titanium and titanium nitride. The abrasive is preferably a colloidal abrasive. Example abrasives include the following: inorganic oxide, metal boride, metal carbide, metal hydroxide, metal nitride, or a combination comprising at least one of the foregoing abrasives. Suitable inorganic oxides include, for example, silica (SiO₂), alumina (Al₂O₃), zirconia (ZrO₂), ceria (CeO₂), manganese oxide (MnO₂), and mixtures thereof. Alumina is available in many forms such as alpha-alumina, gamma-alumina, delta-alumina, and amorphous (non-crystalline) alumina. Other suitable examples of alumina are boehmite (AlO(OH)) particles and mixtures thereof. Modified forms of these inorganic oxides such as polymer-coated inorganic oxide particles may also be utilized if desired. Suitable metal carbides, boride and nitrides include, for example, silicon carbide, silicon nitride, silicon carbonitride (SiCN), boron carbide, tungsten carbide, zirconium carbide, aluminum boride, tantalum carbide, titanium carbide, and mixtures comprising at least one of the foregoing metal carbides, boride and nitrides. Diamond may also be utilized as an abrasive if desired. Alternative abrasives also include polymeric particles and coated polymeric particles. The preferred abrasive is silica.
The intermediate slurry product typically has a concentration of 1 to 95 percent abrasive with the balance being water and azole compound. Preferably the intermediate slurry product typically has a concentration of 5 to 75 percent abrasive with the balance being water and azole compound. Mixing this intermediate abrasive compound into a final slurry formulation with other constituents forms the final polishing slurry. In the final polishing slurry, the abrasive typically has a concentration in the aqueous phase of the polishing composition of 0.01 to 50 weight percent. Preferably, the abrasive concentration is 0.1 to 40 weight percent. And most preferably, the abrasive concentration is 0.25 to 35 weight percent. Typically, increasing abrasive concentration increases the removal rate of dielectric materials; and it especially increases the removal rate of low-k dielectric materials, such as carbon-doped oxide. For example, if a semiconductor manufacturer desires an increased low-k dielectric removal rate, then increasing the abrasive content can increase the dielectric removal rate to the desired level.
For patterned wafer substrates, the abrasive preferably has an average particle size of less than 250 nm for preventing excessive metal dishing and dielectric erosion. For purposes of this specification, particle size refers to the colloidal particles average particle size. Most preferably, the abrasive has an average particle size of less than 100 nm to further reduce metal dishing and dielectric erosion. In particular, an average abrasive particle size less than 50 nm removes the barrier metal an acceptable rate without excessive removal of the dielectric material. For example, the least dielectric erosion and metal dishing occur with a colloidal silica having an average particle size is 2 to 50 nm. Decreasing the size of the colloidal abrasive, such as silica tends to improve the selectivity of the slurry; but it also tends to decrease the barrier removal rate. In addition, the preferred colloidal silica may include additives, such as dispersants to improve the stability of the silica at acidic pH ranges. One such abrasive is colloidal silica that is available from AZ S.A., of Puteaux, France.
Optionally, the removal rate of interconnects such as copper or barrier layers, such as tantalum, tantalum nitride, titanium and titanium nitride are preferably optimized by the use of an oxidizing agent. Suitable oxidizers in the final polishing slurry include, for example, hydrogen peroxide, monopersulfates, iodates, magnesium perphthalate, peracetic acid and other peracids, persulfates, bromates, periodates, nitrates, iron salts, cerium salts, manganese (Mn) (III), Mn (IV) and Mn (VI) salts, silver salts, copper salts, chromium salts, cobalt salts, halogens, hypochlorites, or combinations comprising at least one of the foregoing oxidizers. The preferred oxidizer is hydrogen peroxide. It is to be noted that the oxidizer is typically added to the polishing composition just prior to use and in these instances the oxidizer is contained in a separate package. Adjusting the amount of oxidizer, such as peroxide can also control the metal interconnect removal rate. For example, increasing the peroxide concentration increases the copper removal rate. Excessive increases in oxidizer, however, provide an adverse impact upon polishing rate.
Optionally, the slurry contains complexing agent for the nonferrous metal when forming polishing slurries for patterned wafers. Most preferably, the dispersion contains 0.05 to 1 weight percent complexing agent for the nonferrous metal. Typical complexing agents include at least one of carboxylic acids, multi-carboxylic acids, aminocarboxylic acids, multi-amine compounds and mixtures thereof. Specific complexing agents include the following: acetic acid, alanine, aspartic acid, ethyl acetoacetate, ethylene diamine, trimethylene diamine, ethylenediaminetetraacetic acid (EDTA), citric acid, lactic acid, malic acid, maleic acid, malonic acid, oxalic acid, triethylenetetramine, diethylene triamine, glycine, glycolic acid, gluteric acid, salicylic acid, nitrilotriacetic acid, ethylenediamine, hydroxyethylenethylenediaminetetraacetic acid, hydroxyqunoline, tartaric acid, sodium diethyl dithiocarbamate, succinic acid, sulfosalicylic acid, triglycolic acid thioglycolic acid, 3-hydroxybutyric acid, propionic acid, phthalic acid, isophthalic acid, 3-hydroxy salicylic acid, 3,5-dihydroxy salicylic acid, gallic acid, gluconic acid, pyrocatechol, pyrogallol, tannic acid, salts thereof and mixtures thereof. Some organic acids, such as citric acid may serve as both a complexing agent and a pH adjusting agent. Adding the complexing agent accelerates copper removal, but excessive complexing agent can adversely impact polishing rate.
In addition, the dispersions most preferably rely upon a balance of deionized water to limit incidental impurities. The final pH adjustment of the slurry can include organic or inorganic compounds. Example organic acids include at least one of acetic acid, citric acid, malic acid, maleic acid, glycolic acid, phthalic acid, oxalic acid, malonic acid, lactic acid, succinic acid, tartaric acid and mixtures thereof. Examples of basic compounds include the following: sodium hydroxide, potassium hydroxide, ammonium hydroxide and organic amines. Preferably, the pH adjusting occurs with an inorganic acid or base. Examples of inorganic acids include nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid and phosphoric acid. The polishing composition can also optionally include buffering agents such as various organic and inorganic acids, and amino acids or their salts with a pKa in the pH range of 1.5 to less than 4.
The polishing composition can further optionally include defoaming agents, such as non-ionic surfactants including esters, ethylene oxides, alcohols, ethoxylate, silicon compounds, fluorine compounds, ethers, glycosides and their derivatives, and the like. The defoaming agent can also be an amphoteric surfactant.

EXAMPLE

The test relied upon an inoculation technique to verify the biological control of several formulations in silica slurries. The silica slurry contained 30 weight percent silica particles (balance water) at a pH of 2.2 and an average particle size of 25 nm. In particular, the testing relied upon first placing a 10-gram sample of the slurry into a sterile vial and then inoculating the sample with 0.1 mL of the inoculum. The inoculum included a mixture of active bacteria (5), yeasts (2) and molds (2) that are known to be common in industrial environments. Table 1 contains the specific inoculum microorganisms as follows:

	TABLE 1


	Microorganisms

	Gram Negative Bacteria:	Pseudomonas aeruginosa
		Pseudomonas fluorescens
		Enterobacter cloacae
		Alcaligenes faecalis
		Proteus vulgaris
	Yeast:	Candida albicans
		Rhodotorula rubra
	Mold:	Aspergillus niger
		Penicillium ochrochloron

The 0.1 mL: 10 gram ratio of inoculum-to-slurry achieved approximately 10⁶-10⁷Colony Forming Units of microbes per mL of test sample [CFU/mL]. The inoculated sample incubated in the vial for one week in a chamber maintained at a temperature of 30° C. After one week, 0.1 mL streaks of the incubated samples on agar plates divided the sample for further testing. Then incubating the “streaked” agar plates for one week in the chamber at a temperature of 30° C. provided additional opportunity for biological growth. During this second week, visual inspection also confirmed the presence or absence of biological activity.
After preparing the streaks, introducing a second 0.1 mL of the inoculum into the remainder of the slurry and repeating the two week procedure described above confirmed the biocide's effectiveness.

The data below provide a measure of the total number of colonies observed per plate.

TABLE 2


BIOACTIVITY TESTING OF THE SLURRY
SAMPLES WITH DIFFERENT ADDITIVES

	Colonies Observed on	Colonies Observed on
	Streaked Plate After	Streaked Plate After
Biocide additives	1st Inoculation	2nd Inoculation

Control	10³-10⁵	Not Tested
100 ppm	10³-10⁴	Not Tested
Kordek ™ MLX
300 ppm	10²-10³	10³-10⁴
Kordek ™ MLX
100 ppm H₂O₂	10³-10⁵	Not Tested
200 ppm H₂O₂	10³-10⁴	Not Tested
0.05% BTA	10²-10³	10²-10³
0.1% BTA	10²-10³	10-10²
0.5% BTA	None	None
1% BTA	None	None

Kordek ™ MLX manufactured by Rohm and Haas Company (9.5-9.9% methyl-4-isothiazolin-3-one, 89.1-89.5% water and ≧1.0% related reaction product).

The data show that hydrogen peroxide (“H₂O₂”) and Kordek™ MLX biocide would not work in their normal concentration ranges. And increased concentrations of these biocides could adversely impact the slurry's polishing performance. For example, too much Kordek™ MLX biocide can react with the oxidizer in the slurry, causing the slurry to change color and have a very short time before it loses effectiveness or “pot-life”. In addition, higher levels of Kordek™ MLX biocide can also change the polishing rates and the selectivity of different films. Similarly, excessive hydrogen peroxide will cause slurry stability issues and safety concerns. Hydrogen peroxide slowly decomposes under normal conditions and generates oxygen gas. If the dosage of hydrogen peroxide is too large, then there could be sufficient gas accumulated inside a sealed container to cause an explosion. It was found however that benzotriazole effectively function as a biocide at concentrations of 0.5 and 1 weight percent.

Claims

1. A method for manufacturing polishing slurries useful for polishing patterned integrated circuit substrates comprising the steps of:

preparing an aqueous intermediate dispersion, the aqueous intermediate dispersion containing solid particles and having an acidic pH;

introducing an azole compound into the aqueous intermediate dispersion to prevent biological activity and to form a stable intermediate dispersion;

storing the stable intermediate dispersion for at least one day; and

introducing additional components to the stable intermediate dispersion to form a final polishing slurry, the final polishing slurry having an acidic pH.

2. The method of claim 1 wherein the azole compound is selected from at least one of the group of 1,2,4-triazole, 3-methyl-1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole, 1-amino-1,2,4-triazole, 3-amino-1,2,4-triazole, 5-amino-3-methyl-1,2,4-triazole, 3-isopropyl-1,2,4-triazole, 1,2,3-triazole, 1-methyl-1,2,3-triazole, 1-amino-1,2,3-triazole, 1-amino-5-methyl-1,2,3-triazole, 4,5-dimethyl-1,2,3-triazole, 1-amino-5-n-propyl-1,2,3-triazole, 1-(β-aminoethyl)-1,2,3-triazole, 1-methyltetrazole, 2-methyltetrazole, 5-amino-1H-tetrazole, 5-amino-1-methyltetrazole, 1-(β-aminoethyl)tetrazole, a substituted triazole and tetrazole compound having an electron-donating substituent.

3. The method of claim 1 including the step of adding additional azole compound with the additional components to maintain concentration of the azole compound above a level that prevents biological activity.

4. The method of claim 1 including the additional step of adding an oxidizer to the final polishing slurry.

5. A method for manufacturing polishing slurries useful for polishing patterned integrated substrates, the patterned dielectric substrates having nonferrous interconnects, comprising the steps of:

preparing an aqueous intermediate dispersion, the aqueous intermediate dispersion containing solid particles and having a pH less than 5;

introducing at least 0.1 weight percent benzotriazole into the aqueous intermediate dispersion to prevent biological activity and to form a stable intermediate dispersion;

storing the stable intermediate dispersion at least one week; and

introducing additional components to the stable intermediate dispersion to form a final polishing slurry, the final polishing slurry having a pH less than 5.

6. The method of claim 5 including the step of adding additional benzotriazole with the additional components to maintain concentration of the benzotriazole above at least 0.2 weight percent to prevent biological activity.

7. The method of claim 5 including the additional step of adding an oxidizer to the final polishing slurry.

8. The method of claim 5 wherein the nonferrous interconnects are copper and including the additional step of polishing the patterned wafer.

9. The method of claim 8 wherein the benzotriazole decreases removal rate of the copper nonferrous interconnects.

10. The method of claim 5 wherein the pH is less than 5 and the solid particles include silica.