HK1027590A

HK1027590A - Composition for oxide cmp

Info

Publication number: HK1027590A
Application number: HK00105995.4A
Authority: HK
Inventors: 高坦‧S‧格罗弗; 布赖恩‧L‧米勒
Original assignee: 卡伯特微电子公司
Priority date: 1996-12-30
Filing date: 1997-12-19
Publication date: 2001-01-19

Description

Composition for oxide CMP

Background

The present invention relates to a chemical mechanical polishing slurry for a semiconductor integrated circuit substrate. The present invention specifically relates to CMP slurries having unique chemical properties particularly suited for chemical mechanical planarization, where high silicon dioxide removal rates and low silicon nitride removal rates are required for the same substrate.

Description of the related Art

Integrated Circuits (ICs) are made up of millions of active elements formed in or on a silicon substrate. The active elements form functional circuits and components. These elements are connected by using multi-layer metal interconnects and vias. The interconnect structure typically has a first metallization layer, an interconnect plug, a second metallization layer, and sometimes a third or interconnecting further metallization layer. Intermediate dielectric layers (ILD) such as doped and undoped SiO₂With different interconnect layers than electrical isolation.

Shallow Trench Isolation (STI) is a technique for element isolation of a given layer in an IC manufacturing process. In the STI process, silicon nitride is deposited on a thermally grown oxide. After nitride deposition, shallow trenches are etched into the substrate using a mask. Oxide is then deposited in the trenches so that the trenches form insulating dielectric regions that function to isolate the elements in the wafer and thereby reduce cross-talk between active elements. The excess deposited oxide must be polished away and the slots flattened to produce the next metallization layer. Coating silicon nitride on silicon has prevented the silicon dioxide of the masking element from being polished.

In a typical mechanical polishing process, a substrate is brought into direct contact with a rotating polishing pad. A load weight is used to apply pressure to the back of the substrate. During polishing, the pad and the platen rotate while maintaining a downward force on the back side of the substrate. An abrasive and a chemically active solution (commonly referred to as a "slurry") are applied to the pad during polishing. The chemicals and particles in the slurry begin the polishing process by contacting the wafer being polished. The polishing process is facilitated by the rotational motion of the pad relative to the substrate under the application of the slurry at the wafer/pad interface. Polishing is continued in this manner until the desired film thickness on the insulator is removed.

When polishing oxide, it is required that the slurry used has a high removal rate for the oxide layer and a low removal rate for other layers, such as a silicon nitride layer, which may be exposed during CMP. The polishing slurry should be conditioned to provide effective polishing within the desired polishing range for the particular thin layer material selected, while at the same time minimizing surface defects, imperfections, corrosion, erosion and removal of silicon nitride and other stop layers.

CMP slurries for polishing oxides typically contain an alkaline or high pH abrasive. These slurries rely on potassium hydroxide or ammonium hydroxide to effectively buffer high pH. When these slurries polish at high rates, they also polish silicon nitride at high rates. Typically, the ratio of these removal rates (i.e., selectivity) is at most about 5 to 1 for silicon oxide to silicon nitride. It is believed that the mechanism of silicon nitride polishing is the oxidative hydrolysis of nitrides to oxides in an aqueous environment. At alkaline pH, oxides and nitrides similarly etch at high rates. Thus, existing CMP polishes at unacceptably high rates.

There remains a need in the semiconductor industry for CMP polishing slurries having an oxide to nitride selectivity greater than 5 to 1. Therefore, to overcome the problems in current production, increase throughput, and reduce the production cost of CMP, it is desirable to selectively remove oxide at a high rate while keeping the silicon nitride stop layer relatively intact with new CMP slurries. This is due to the fact that the low selectivity process, when used in the manufacturing industry, necessarily results in over-polishing in the thinner film portions of the silicon wafer, and the nitride stop layer will not prevent penetration into the underlying film

Summary of the invention

The present invention relates to a chemical mechanical polishing composition capable of polishing silica at a high rate.

The invention also relates to a chemical mechanical polishing composition for inhibiting polishing of a silicon nitride film.

In addition, the invention relates to a method for selectively removing silicon dioxide from a substrate using a chemical-mechanical polishing composition while leaving a silicon nitride layer attached to the substrate substantially intact.

In one embodiment, the invention is directed to a chemical-mechanical polishing composition comprising a carboxylic acid, a salt, and a soluble cerium compound. The composition has a pH of about 3.0 to about 11, preferably about 3.8 to about 5.5, and is suitable for selectively removing silica from a substrate forming a layer.

In another embodiment, the present invention is directed to a chemical mechanical polishing slurry comprising the above-described chemical mechanical polishing composition and an abrasive. The slurry is particularly suitable for polishing a silicon dioxide film.

In yet another embodiment, the invention is directed to a method of selectively removing an overlying oxide in preference to a silicon nitride film during the manufacture of integrated circuits and semiconductors using a chemical mechanical polishing composition having a pH of about 3.0 to about 11 comprising a carboxylic acid, a salt, and a water-soluble cerium compound in an aqueous solution.

Brief description of the drawings

FIG. 1 is a graph of pH versus PETEOS removal rate and nitride removal rate

Description of embodiments of the invention

The invention relates to a chemical mechanical polishing composition having a pH of about 3.0 to 11.0 comprising a carboxylic acid, a salt, and a soluble cerium compound. The chemical mechanical polishing composition can be used alone or can be mixed with a metal oxide abrasive to form a slurry. The compositions and slurries of the present invention polish oxide layers, such as silica layers, attached to a substrate at high rates. In addition, the compositions of the present invention have been found to inhibit silicon nitride polishing. The invention also relates to a novel method for polishing an oxide layer using the composition and slurry of the invention.

Before describing in detail various preferred embodiments of the present invention, a definition of a term used herein is provided. A "chemical-mechanical polishing (CMP) composition" relates to a composition of at least one carboxylic acid, at least one salt, and at least one water-soluble cerium compound that can cooperate with an abrasive pad to remove one or more layers of a substrate. The term "slurry" or "chemical mechanical polishing slurry" refers to a mixture of a chemical mechanical polishing slurry composition and at least one abrasive.

Carboxylic acids suitable for use in the CMP slurry of the present invention include mono-functional and di-functional carboxylic acids and salts thereof. The carboxylic acid is preferably selected from the group consisting of acetic acid, adipic acid, butyric acid, capric acid, caproic acid, caprylic acid, citric acid, glutaric acid, glycolic acid, formic acid, fumaric acid, lactic acid, lauric acid, malic acid, maleic acid, malonic acid, myristic acid, oxalic acid, palmitic acid, phthalic acid, propionic acid, pyruvic acid, stearic acid, succinic acid, tartaric acid, valeric acid, 2- (2-methoxyethoxy) acetic acid, 2- [2- (2-methoxyethoxy) ethoxy ] acetic acid, poly (ethylene glycol) bis (carboxymethyl) ether and derivatives thereof, including salts thereof. The most preferred carboxylic acid is acetic acid.

In the composition of the present invention, the carboxylic acid may comprise more than 10% of the slurry. In a preferred embodiment, the carboxylic acid is present in the composition in an amount of about 0.05 to about 10 weight percent. However, in a more preferred embodiment, the carboxylic acid is present in the composition in an amount of from about 0.1 to about 3%.

The chemical mechanical composition of the present invention may include a salt. The term "salt" refers to any water-soluble salt, including organic and inorganic salts, such as nitrates, phosphates, and sulfates. Soluble salts are salts which are only partially or mostly soluble in water. The preferred salt is the nitrate.

The term "nitrate" includes nitric acid. Suitable nitrates include those commonly used (M)_n(NO₃)_mWherein n and m are both integers. When n ═ M, M is monovalent and can be an alkaline earth metal such as Li, Na, K, and H, NH₄、NR₄Wherein R is an alkyl group having 1 to 10 or more carbon atoms or mixtures thereof, including NMe₄、NB_uAnd the like. When n ≠ M, M is a multivalent cation or a metal or a combination of multivalent and monovalent cations. One known preferred nitrate salt is ammonium cerium nitrate, (NH)₄)₂Ce(NO₃)₆。

The salt may be present in the composition in an amount of about 0.05 to about 6% by weight of the composition. Most preferably, the salt may be present in the composition in an amount of from about 0.1 to about 4% wt.

The inventive chemical mechanical composition comprises at least one soluble cerium compound. For the purposes of the present invention, the term "water-soluble cerium" includes both added soluble forms of cerium and cerium dissolved from colloidal or abrasive particles. Non-limiting examples of soluble cerium compounds that may be used in the compositions of the present invention include cerium (Ce (OH) hydroxide₄) Water-soluble hydrated and non-hydrated salt of (a), cerium ammonium sulfate (NH)₄)₂SO₄Ce₂(SO₄)₃(ii) a Cerium acetate, Ce (O)₂CH₃)₃(ii) a Cerium sulfate, Ce (SO)₄)₂(ii) a Bromic acidCerium, Ce (BrO)₃)₃·9H₂O; cerium bromide, CeBr₃(ii) a Cerium carbonate, Ce (CO)₃)₂(ii) a Cerium chloride, CeCl₃(ii) a Cerium oxalate, Ce (C)₂O₄)₃(ii) a Cerium nitrate, Ce (NO)₃)₃(OH)·6H₂O and any other known water-soluble cerium compound. The preferred water-soluble cerium compound is cerium ammonium nitrate, (NH)₄)₂Ce(NO₃)₆. The soluble cerium compound is present in the compositions of the present invention in an amount of from about 0.05% to about 10.0% by weight, preferably from about 0.1 to about 4.0% by weight.

A preferred embodiment of the inventive chemical mechanical composition comprises cerium ammonium nitrate in the form of a salt and a soluble cerium compound. Other soluble cerium nitrate salts may be included in the compositions of the present invention as soluble cerium compounds and salts. Ammonium cerium nitrate may be present in the compositions of the present invention in an amount of about 0.05 to about 6 weight percent, based on the total weight of the composition. A more preferred range of cerium ammonium nitrate is from about 0.1 to about 4.0 wt%.

Commercially available cerium salts usually contain dissolved Ce^4-And Ce³⁺A mixture of ions. The preferred dissolved cerium salt is Ce³⁺In ionic form. Addition of Ce to the reaction mixture⁴⁺Oxidation to Ce^3-Ionic oxidizing agents into the compositions of the present invention can produce products that exhibit high oxide selectivity and low nitride selectivity. The oxidant used must have a specific Ce ratio^4-High oxidation potential. The preferred oxidizing agent is ammonium persulfate. The oxidizing agent may be used in an amount of about 0.05 to about 5.0 wt.%. The oxidizing agent is preferably used in an amount of about 0.1 to about 2.0 wt.%.

The inventive chemi-mechanical composition may optionally comprise at least one chelating agent. It has been found that the addition of an agent to the inventive chemical mechanical composition improves the cleanability of a substrate polished with the inventive composition. It is believed that the cleanability of the substrate is enhanced by the chelating agent binding to free ions of the composition of the present invention that would otherwise deposit on the silicon wafer.

Suitable chelating agents include any chelating agent that can bind to the free ions in the compositions of the present invention. Examples of suitable chelating agents include, but are not limited to, polycarboxylic acids such as citric acid, EDTA, triethanolamine, benzonitrile, adipic acid, malic acid, oxalic acid, phosphonic acid, phosphoric acid, and salts thereof. If used, the chelating agent is present in the composition in an amount of about 0.05 to about 5.0% by weight, preferably about 0.1 to about 1.5% by weight.

The chemical mechanical compositions of the present invention can be used alone or in combination with abrasives to provide chemical mechanical polishing "slurries". Abrasives that can be used in combination with the compositions of the present invention include metal oxides. The metal oxide abrasive is selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria and mixtures thereof. Further, suitable abrasives may be the result of mixing two or more metal oxide precursors, thereby resulting in a chemical blend of mixed metal oxide abrasives. For example, alumina may be intergrown with silica, or a combination of alumina/silica.

Suitable metal oxide abrasives may be produced by any process known to those skilled in the art, including high temperature methods such as sol-gel, hydrothermal or plasma methods, or by methods that produce fumed or precipitated metal oxides. Powdered or crushed metal oxide abrasives are also suitable for use in the CMP slurries of the present invention and can be prepared by conventional manufacturing techniques such as jet milling, ball milling, bead milling, and other milling and pulverizing techniques and methods known to those skilled in the art.

Preferred abrasives suitable for the CMP slurries of the present invention are silica and ceria, with fumed silica being most preferred. Other suitable silica abrasives may be produced by methods such as sol-gel, hydrothermal, plasma, flame pyrolysis, or by other methods of making metal oxides.

Powdered abrasives are also suitable for the present invention. Any powdered metal oxide abrasive can be used in the CMP slurries of the present invention. However, powdered cerium oxide is preferred. And grinding the cerium oxide abrasive in a medium mill to obtain the powdered zirconium oxide. The starting material for the cerium oxide particles may be mined cerium oxide or precipitated and calcined cerium oxide or a mixture thereof. Milling can be accomplished in an aqueous medium using any type of milling device, such as by jet milling or ball milling. The preferred milling machine is a media mill using Yttria Tetrahedral Zircon (YTZ) or zirconium silicate media. The milling process may use a dispersant or steric stabilizer.

Preferred powdered metal oxide abrasives will have a narrow particle size distribution with an average particle size (aggregate or single particle) below 0.5 μm. The particles may be diluted and filtered after milling. After filtration, the particle size of the powdered metal oxide abrasive is preferably from about 40 to about 1000nm, preferably from about 100 to about 300 nm. Preferred powdered abrasives should contain less than about 10% by weight of particles having an average particle size greater than 0.6 μm.

The precipitated ceria is suitable as an abrasive for oxide CMP. Precipitated cerium oxide particles are prepared from various precursors including acetates, carbonates, hydroxides, and nitrates of cerium. The average particle size of the precipitated cerium oxide particles may be from about 10nm to about 500nm, with a preferred size of the precipitated cerium oxide particles being from about 30 to about 300 nm.

Another preferred abrasive is fumed silica. The production of fumed metal oxides is a well-known process that involves the hydrolysis of a suitable feedstock vapor, such as silicon tetrachloride for the production of silica abrasives, in a hydrogen and oxygen flame. Approximately spherical molten particles are formed during combustion. The diameter of these particles can be varied by process parameters and the fused spheres of silica or similar oxides (often referred to as primary particles) are fused to each other at their points of contact by collision to form branched, three-dimensional, chain-like aggregates. The force required to break the aggregate is considerable and is generally considered irreversible. During cooling and collection, the aggregates are subjected to further collisions, which may cause some mechanical entanglement, thereby forming aggregates.

Preferred metal oxides may have a surface area of about 5m²G to about 430m²A/g, preferably about 30m²G to about 170m²(ii)/g, the surface area is determined by the methods of S.Brunauer, P.H.Emmet and I.Teller, commonly known as BET (American society of chemistry, Vol.60, p 309 (1938)). Due to the stringent purity requirements in the IC industry, the preferred metal oxides should be of high purity. By high purity is meant that the total impurity content from sources such as feed impurities and trace process contaminants is generally less than 1%, preferably less than 0.01% (i.e., 100 ppm).

In a preferred embodiment, the metal oxide abrasive consists of metal oxide aggregates having 99 weight percent particle diameters of less than about 1.0 μm, average aggregate diameters of less than about 0.4 μm, and sufficient to repel and overcome van der Waals forces between the abrasive aggregates. These metal oxide abrasives are effective in minimizing or avoiding scratches, micro-spotting, divot and other surface defects during polishing. The aggregate size distribution of the present invention can be determined by known techniques such as Transmission Electron Microscopy (TEM). The aggregate mean diameter refers to the mean isosphere diameter when analyzed with TEM images, i.e., the diameter based on the aggregate cross-section. The surface potential or hydration force of the metal oxide particles must be sufficient to repel and overcome the van der Waals forces between the particles.

In another preferred embodiment, the metal oxide particles may be formed of particles having a particle diameter of less than 0.5 μm (500nm) and a surface area of about 10m²G to about 250m²(iv) isolated individual metal oxide particles in grams.

The CMP slurry of the present invention comprises about 2 to about 25 wt.%, preferably about 2 to about 15 wt.%, of the metal oxide abrasive.

The metal oxide abrasive used in the CMP slurries of the present invention is added to the aqueous medium of the polishing slurry as a concentrated aqueous dispersion of the metal oxide, which typically contains about 3% to about 55%, preferably 30% to 50%, solids. The aqueous metal oxide dispersions can be produced by conventional techniques, such as by slowly adding the metal oxide abrasive to a suitable medium (e.g., deionized water) to form a colloidal dispersion. The dispersion is typically prepared by subjecting it to high shear mixing as known to those skilled in the art.

The abrasive used in the CMP slurry of the present invention may be a mixture of the above-mentioned abrasives. For example, precipitated ceria, powdered ceria, and fumed silica can be added to the CMP slurry of the invention. Other abrasive mixtures are also suitable for use in the CMP slurries of the present invention. Further, the abrasive mixtures may include any relative proportion between abrasive and abrasive. For example, it has been found that a combination of about 5 to 100 weight percent of the above powdered oxide abrasive with about 0 to about 95 weight percent of a precipitated abrasive is effective as an abrasive for CMP slurries in STI applications.

Commercially available precipitated ceria at a pH of about 1.5 is not effective for CMP slurries. However, we have found that raising the pH of commercially available slurries to a large extent, to about 3.5, yields CMP slurries suitable for STI polishing. Furthermore, we have also surprisingly found that CMP slurries having the compositions and pH disclosed above exhibit high oxide layer removal rates and low nitride layer removal rates.

The CMP slurry of the present invention must have a ph of about 3.0 to about 11.0 to be effective. More preferably, the pH of the slurry is from about 3.5 to about 6.0, most preferably from about 3.8 to about 5.5. The pH of the slurry can be adjusted by adding any base to the composition, preferably by adding a non-metallic base such as ammonium hydroxide to the slurry.

The chemical mechanical compositions of the present invention may contain one or more buffering agents. The buffering agent functions to help maintain the pH of the composition in the desired range, most preferably in the range of about 3.8 to about 5.5.

Any buffer capable of maintaining the pH of the composition within the desired range may be used. Most preferred buffers are ammonium formate or formic acid. The buffer used in the composition is typically from about 0.01 to about 5.0 wt%, most preferably from 0.05 to about 0.5 wt%.

To further stabilize the polishing slurry of the present invention against settling, flocculation, and decomposition by oxidizing agents, various optional auxiliary additives, such as surfactants, polymeric stabilizers, or other surface active dispersing agents, may be used. The surfactant may be an anionic, cationic, nonionic, zwitterionic surfactant or a mixture of two or more surfactants. In addition, the added surfactant can be used to improve the within-wafer non-uniformity (WIWNU) of the wafer, thereby improving the surface of the wafer and reducing wafer defects.

The amount of additives, such as surfactants, generally useful in the present invention should be sufficient to achieve effective steric stabilization of the slurry and will generally vary depending on the particular surfactant selected and the surface properties of the metal oxide abrasive. For example, if insufficient amounts of surfactant are selected, there is little or no effect on stability. On the other hand, too much surfactant can lead to improper foaming and/or flocculation in the slurry. Thus, stabilizers such as surfactants should generally be present in an amount of about 0.001% to 10% by weight. In addition, the additives may be added directly to the slurry or the surface of the metal oxide abrasive may be treated by known techniques. In each case, the amount of additive is adjusted to achieve the desired concentration in the polishing slurry.

The chemical mechanical polishing composition and slurry of the present invention are capable of selectively removing silicon dioxide from a layered substrate at very high rates. In addition, the inventive compositions and slurries inhibit polishing silicon nitride from a layered substrate. One important use of the chemical mechanical polishing compositions and slurries of the present invention is in the manufacture of integrated circuits and semiconductors. In such polishing applications, the compositions and slurries of the present invention are effective in removing silicon dioxide for shallow trench isolation purposes.

The compositions and slurries of the present invention preferably exhibit an oxide removal rate of about 1200 a/min to about 6000 a/min or greater with a selectivity of oxide to nitride removal rate of about 5 to about 100 or greater, preferably about 15 to about 50 or greater.

The compositions and slurries of the present invention may be included in a packaged system comprising an aqueous composition at a desired pH comprising at least one carboxylic acid, a soluble cerium compound, a salt, optionally an abrasive, and optionally additives. To avoid degradation of the activity of the slurry over time, it is preferred to use at least two package systems, wherein the first package comprises at least one carboxylic acid, salt and soluble compound at any pH and the second package comprises the optional abrasive at any pH. These packages are designed in such a way that: when they are mixed, useful compositions are in the desired pH range. Furthermore, the components in one container may be in dry form, while the components in the other container may be in the form of an aqueous dispersion. Other two-container combinations of the CMP slurry components of the present invention are within the knowledge of one skilled in the art.

At the desired pH, the compositions and slurries of the present invention do not significantly increase the removal rate of silicon nitride. However, the compositions and slurries of the present invention significantly increase the removal rate of silica compared to known slurries. The polishing slurry of the present invention can be used at various stages in the manufacture of semiconductor integrated circuits, thereby efficiently removing a silicon dioxide layer at a desired rate while minimizing surface defects and flaws.

Example 1

The following examples illustrate preferred embodiments of the present invention and preferred methods of using the compositions of the present invention. All compositions and slurries were used in the STI polishing protocol described below.

The CMP slurry was used to chemically mechanically polish the overburden PETEOS and silicon nitride using an IC1000/SUBAIV polishing pad manufactured by Rodel, Inc. IPEC/WESTECH 472 CMP tool for polishing at 9 lbs/inch down force²(psi), slurry flow rate 140 ml/min, bench speed 35rpm and jack stand speed 24 rpm.

Example 2

Powdered cerium oxide formulation

Powdered ceria slurries were prepared to evaluate their ability to polish silicon wafers covered with silicon dioxide and silicon nitride. Rhodite grade 400HS cerium oxide (particle size about 2-4 μm) was purchased from Universal Photonics, Hicksville, New York and pulverized to an initial average particle size of 150 μm using a ball mill with a stirrer. The pulverization is carried out under wet conditions so that the pH of the resulting slurry after the pulverization process is about 7.5 to 8.5, with 20 to 30% solids.

The slurry was then diluted and pH adjusted to produce the slurry listed in table 1. These slurries were used to polish substrates according to the method described in example 1.

TABLE 1

Slurry No.	pH	% of solids	PETEOS RR (Angel/min)	Nitride RR (Angstrom/min)	Selectivity is
Slurry No.	pH	% of solids	PETEOS RR (Angel/min)	Nitride RR (Angstrom/min)	Selectivity is	1	8	4.0	925	1050	0.89
2	8	5.0	4337	1137	3.81	1	8	4.0	925	1050	0.89
2	8	5.0	4337	1137	3.81	3	8	7.5	4800	1130	4.25
4	8	10.0	5145	1153	4.46	3	8	7.5	4800	1130	4.25
4	8	10.0	5145	1153	4.46	5	10	4.0	4342	1101	3.95
6	10	10.0	4344	1015	4.28	5	10	4.0	4342	1101	3.95

The powdered cerium oxide was used for polishing. This data demonstrates that the powdered ceria slurry produces a very high PETEOS (silica layer) removal rate.

Example 3

Precipitated cerium nitrate formula

Nitrate-stabilized ceria slurries containing precipitated ceria particles, nitric acid, acetic acid at pH 1.8 and 20% solids were purchased from Nyacol RRoducts (Ashland, MA). The pH of the slurry was adjusted to about 4.2-6.8 by the addition of ammonium hydroxide. These slurries were used to polish substrates according to the method described in example 1. The polishing results are given in table 2.

TABLE 2

Slurry No.	pH	% of solids	Additive agent	PETEOS RR (Angel/min)	Nitride RR (Angstrom/min)	Selectivity is
Slurry No.	pH	% of solids	Additive agent	PETEOS RR (Angel/min)	Nitride RR (Angstrom/min)	Selectivity is	7	4.2	20	406	14.5	28
8	5.8	20		281	208	1.35	7	4.2	20	406	14.5	28
8	5.8	20		281	208	1.35	9	6.1	20	241	281	0.86
10	6.2	20		163	354	0.46	9	6.1	20	241	281	0.86

Polishing data shows high selectivity at the lowest pH (4.2), but low total oxide removal rate.

Example 4

Precipitated cerium acetate formulations

Including soluble Ce^3-And Ce⁴⁺And colloidal cerium acetate slurry of acetic acid (pH 1.8 and 20% solids) was purchased from Nyacol RRoducts (Ashland, MA). The pH of the slurry was adjusted to 4.5 and the solids content was adjusted to 15%. The slurry was applied to a substrate as described in example 1 and showed an oxide layer removal rate of 117 a/min, a nitride layer removal rate of 10.5 a/min and an oxide to nitride selectivity of 11.1.

Example 5

Pulverized/precipitated cerium oxide formulations

Ceria slurries consisting of various weight percentages of the powdered ceria prepared in example 2 and precipitated ceria purchased from Nyacol RRoducts (Ashland, MA) were formulated as shown in table 3. These slurries were used to polish substrates according to the method described in example 1, with the results given in table 3.

TABLE 3

Slurry No.	pH	% of the total solids	Pulverized cerium oxide% in the slurry	PETEOS RR (Angel/min)	Nitride RR (Angstrom/min)	Selectivity is
Slurry No.	pH	% of the total solids	Pulverized cerium oxide% in the slurry	PETEOS RR (Angel/min)	Nitride RR (Angstrom/min)	Selectivity is	11	4	8	20	1595	108.4	14.71
12	4	8	40	2168	183.4	11.82	11	4	8	20	1595	108.4	14.71
12	4	8	40	2168	183.4	11.82	13	4	8	60	3356	826.5	4.06
14	4	8	80	4785	209.1	22.88	13	4	8	60	3356	826.5	4.06

The results show that CMP slurries comprising 80% powdered ceria and 20% precipitated ceria produced the most suitable high PETEOS rate, low nitride rate and high selectivity.

Example 6

Chemical formulation using powdered cerium oxide

Slurries consisting of various percentages of L-90 fumed silica particles (manufactured by cabot corporation and sold under the trademark CAB-O-SIL ), cerium ammonium nitrate, acetic acid, and deionized water were formulated as shown in table 4. All slurries were adjusted to pH4 after addition of the additives. These slurries were applied to a substrate as described in example 1.

TABLE 4

Slurry material	Silica wt.%	Cerium ammonium nitrate by weight%	Weight of acetic acid	Nitride RR (Angstrom/min)	PETEOS RR (Angel/min)	Selectivity is
Slurry material	Silica wt.%	Cerium ammonium nitrate by weight%	Weight of acetic acid	Nitride RR (Angstrom/min)	PETEOS RR (Angel/min)	Selectivity is	20	4	0.1	0.1	58	280	4.83
21	4	0.1	1	52	253	4.87	20	4	0.1	0.1	58	280	4.83
21	4	0.1	1	52	253	4.87	22	4	0.65	0.5	59	619	10.49
23	4	1	0.1	44	1535	34.89	22	4	0.65	0.5	59	619	10.49
23	4	1	0.1	44	1535	34.89	24	4	1	1	312	1524	4.88
25	4	1	0	104.62	1337.9	12.79	24	4	1	1	312	1524	4.88
25	4	1	0	104.62	1337.9	12.79	26	4	2	0.05	57.51	1103	19.18
27	4	3	0.1	89.99	835.8	9.29	26	4	2	0.05	57.51	1103	19.18
27	4	3	0.1	89.99	835.8	9.29	28	4	1	0.5	71.5	803.1	11.23
29	4	2	0.1	24.1	346.6	14.38	28	4	1	0.5	71.5	803.1	11.23
29	4	2	0.1	24.1	346.6	14.38	30	4	2	0.5	71.1	768.0	10.8

High PETEOS removal rates and low nitride removal rates were obtained with high nitrate (1% nitrate) and low (0.1%) acetic acid content.

Example 7

Chemical batch-pH test Using silica

Slurries consisting of 4 wt% CAB-O-SIL  L-90 fumed silica, 1.8 wt% ceric ammonium nitrate, and 0.6 wt% acetic acid were prepared as shown in Table 5. The pH of the slurry varied between 4.0 and 5.0. These slurries were applied to a substrate as described in example 1.

TABLE 5

Slurry material	Silica wt.%	pH	Acetic acid wt.%	Nitride RR (Angstrom/min)	PETEOS RR (Angel/min)	Selectivity is
Slurry material	Silica wt.%	pH	Acetic acid wt.%	Nitride RR (Angstrom/min)	PETEOS RR (Angel/min)	Selectivity is	31	4	4.0	0.6	114	1713.7	15.03
32	4	4.3	0.6	141	1988.9	14.11	31	4	4.0	0.6	114	1713.7	15.03
32	4	4.3	0.6	141	1988.9	14.11	33	4	4.7	0.6	199	2810.5	14.12
34	4	5.0	0.6	219	2355	10.75	33	4	4.7	0.6	199	2810.5	14.12

High PETEOS removal rates were obtained with very good selectivity for each slurry. The results show that the pH of the slurry has a large effect on PETEOS removal rate, with the optimum removal rate of oxides being obtained at a pH of about 4.7 (fig. 1).

Example 8

A composition consisting of 1.8 wt.% cerium ammonium nitrate, 0.8 wt.% cerium acetate, and deionized water was used to polish PETEOS and silicon nitride wafers according to the method of example 1. The pH of the slurry was adjusted to 4.5. The composition polished PETEOS at 690 angstroms per minute and silicon nitride at 23 angstroms per minute. A PETOS selectivity of 30 was obtained.

Example 9

By mixing appropriate amounts of (1) a 20 wt% colloidal cerium solution (manufactured by Nyacol RRoducts (Ashland, MA) and described in example 4); (2) l-90 fumed silica particles (manufactured by Cabot corporation and sold under the trademark CAB-O-SIL ); and (3) deionized water, a CMP slurry having a ph of 4.5 consisting of 4.0 wt.% cerium and 4.0 wt.% silicon oxide was prepared. The pH of the slurry was adjusted to 4.5 with ammonium hydroxide. The slurry included 0.15 wt% ammonium persulfate.

Various amounts of EDTA or citric acid chelating agents were added to the slurry prior to testing. The slurry was then tested as in example 1. The test results are given in table 6 below.

TABLE 6

Chelating agents	Chelating agent (% by weight)	Oxide removal rate	Nitride removal rate	post-CMP cleaning (LPD)
Chelating agents	Chelating agent (% by weight)	Oxide removal rate	Nitride removal rate	post-CMP cleaning (LPD)	EDTA-k	0	3870	19	＞20,000
EDTA-k	0.1	2731	11	977	EDTA-k	0	3870	19	＞20,000
EDTA-k	0.1	2731	11	977	EDTA-k	0.2	1806	12	169
EDTA-k	0.3	1381	11	45	EDTA-k	0.2	1806	12	169
EDTA-k	0.3	1381	11	45	Citric acid	0	4241	20	3772
Citric acid	0.10％	2095	34	516	Citric acid	0	4241	20	3772
Citric acid	0.10％	2095	34	516	Citric acid	0.20％	1625	68	28

Increasing the amount of dipotassium EDTA in the slurry decreases the oxide removal rate. However, increasing the concentration of dipotassium EDTA significantly reduced the Light Point Defects (LPD) on the silicon wafers after post-CMP cleaning: number of particles on the wafer.

Example 10

This example evaluates the polishing effect of the inventive compositions in the absence and presence of an oxidizing agent. Formulated with 4.0 wt.% including Ce according to the method of example 9⁴⁺Ionic colloidal ceria and 4.0 wt% silica with a slurry of 4.5. According to the examplesMethod 2 these slurries were tested without and with the addition of 0.15 wt.% ammonium persulfate. The test results are given in table 7 below.

TABLE 7

No oxidant				With an oxidizing agent
No oxidant				With an oxidizing agent			Batches of	Oxide rate (angstroms/minute)	Nitride rate (angstroms/minute)	Selectivity is	Oxide rate (angstroms/minute)	Nitride rate (angstroms/minute)	Selectivity is
1	2822	472	5.98	3255	28.9	112.6	Batches of	Oxide rate (angstroms/minute)	Nitride rate (angstroms/minute)	Selectivity is	Oxide rate (angstroms/minute)	Nitride rate (angstroms/minute)	Selectivity is
1	2822	472	5.98	3255	28.9	112.6	2	3394	373	9.10	3513	22.8	154.1
3	3640	319	11.42	3428	25.8	132.9	2	3394	373	9.10	3513	22.8	154.1
3	3640	319	11.42	3428	25.8	132.9	4	2929	473	6.19	3711	36.1	102.8
5	1734	856	2.02	3880	46.5	83.4	4	2929	473	6.19	3711	36.1	102.8

The data presented in table 7 illustrates that batches of ceria exhibited different polishing rates and acceptably low nitride selectivity in the absence of ammonium sulfate oxidizer. The performance of the same batch was more consistent after the addition of 0.15 wt%, and these slurries showed high nitride selectivity.

While the invention has been described with reference to specific embodiments, it will be appreciated that substitutions may be made without departing from the spirit of the invention. It is intended that the scope of the invention be limited not by this description of the specification and examples, but rather by the claims that follow.

Claims

1. An aqueous chemical mechanical polishing composition comprising:

a salt;

soluble cerium; and

a carboxylic acid, wherein the composition has a pH of about 3 to about 11.

2. The aqueous chemical mechanical polishing composition of claim 1 wherein the pH is about 3.8 to about 5.5.

3. The aqueous chemical mechanical polishing composition of claim 1 wherein the salt is a nitrate salt.

4. The aqueous chemical mechanical polishing composition of claim 3 wherein the nitrate salt is a compound of the formula:

(M)_n(NO₃)_m

wherein n and M are both integers, wherein when n ═ M, M is an alkaline earth metal, H, NH₄Or NR₄Wherein R is an alkyl group having 1 to 10 carbon atoms, wherein when n ≠ M, M is a polyvalent cation or a metal or a combination of a polyvalent cation and a monovalent cation.

5. The aqueous chemical mechanical polishing composition of claim 3 comprising about 0.05 to about 6.0 wt.% nitrate.

6. The aqueous chemical mechanical polishing composition of claim 3 wherein the nitrate salt is cerium ammonium nitrate.

7. The aqueous chemical mechanical polishing composition of claim 1 wherein the carboxylic acid is selected from the group consisting of monofunctional acids, difunctional acids, and salts thereof.

8. The aqueous chemical mechanical polishing composition of claim 1 wherein the carboxylic acid is at least one compound selected from the group consisting of acetic acid, adipic acid, butyric acid, capric acid, caproic acid, caprylic acid, citric acid, glutaric acid, glycolic acid, formic acid, fumaric acid, lactic acid, lauric acid, malic acid, maleic acid, malonic acid, myristic acid, oxalic acid, palmitic acid, phthalic acid, propionic acid, pyruvic acid, stearic acid, succinic acid, tartaric acid, valeric acid, 2- (2-methoxyethoxy) acetic acid, 2- [2- (2-methoxyethoxy) ethoxy ] acetic acid, and poly (ethylene glycol) bis (carboxymethyl) ether, and mixtures thereof.

9. The aqueous chemical mechanical polishing composition of claim 1 wherein the carboxylic acid is acetic acid.

10. The aqueous chemical mechanical polishing composition of claim 1 comprising about 0.05 to about 10.0 wt.% of the carboxylic acid.

11. The aqueous chemical mechanical polishing composition of claim 10 comprising about 0.1 to about 3.0 wt.% of the carboxylic acid.

12. The aqueous chemical mechanical polishing composition of claim 1 comprising about 0.05 to about 10 wt.% soluble cerium.

13. The aqueous chemical mechanical polishing composition of claim 1 wherein the soluble cerium is at least one compound selected from the group consisting of cerium ammonium sulfate, cerium acetate, cerium sulfate hydrate, cerium hydroxide, cerium bromate, cerium bromide, cerium chloride, cerium oxalate, cerium nitrate, cerium carbonate, and mixtures thereof.

14. The aqueous chemical mechanical polishing composition of claim 1 wherein the salt and soluble cerium is cerium ammonium nitrate.

15. The aqueous chemical mechanical polishing composition of claim 14 comprising about 0.1 to about 4.0 wt.% of the cerium ammonium nitrate.

16. A chemical mechanical polishing slurry comprising:

a salt;

soluble cerium;

a carboxylic acid; and

the abrasive material is coated on the surface of the substrate,

wherein the composition has a pH of about 3 to about 11.

17. The chemical mechanical polishing slurry of claim 16 comprising about 1 to about 25 wt% abrasive.

18. The chemical mechanical polishing slurry of claim 16 wherein the abrasive is a metal oxide.

19. The chemical mechanical polishing slurry of claim 18 wherein the metal oxide abrasive is at least one compound selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria, or mixtures and chemical blends thereof.

20. The chemical mechanical polishing slurry of claim 19 wherein the abrasive is a physical mixture of oxides of at least two elements selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria.

21. The chemical mechanical polishing slurry of claim 16 wherein the abrasive is abraded.

22. The chemical mechanical polishing slurry of claim 17 comprising about 2 to about 15 weight percent metal oxide abrasive.

23. The aqueous chemical mechanical polishing slurry of claim 17 comprising about 0.5 to about 10 wt.% of a nitrate salt, about 0.5 to about 10 wt.% of a carboxylic acid, and about 0.5 to about 10 wt.% of soluble cerium.

24. The aqueous chemical mechanical polishing slurry of claim 17 comprising about 0.1 to about 3.0 wt.% acetic acid and about 0.1 to about 4.0 wt.% cerium ammonium nitrate, wherein the slurry has a pH of about 3.8 to about 5.5.

25. A chemical mechanical polishing slurry comprising about 2 to about 15 wt.% of a metal oxide abrasive, about 0.5 to about 10 wt.% of a nitrate salt, about 0.5 to about 10 wt.% of a carboxylic acid, and about 0.5 to about 10 wt.% of soluble cerium, wherein the slurry has a pH of about 3 to about 11.

26. The chemical mechanical polishing slurry of claim 25 comprising about 0.1 to about 3.0 wt.% acetic acid, about 0.1 to about 4.0 wt.% cerium ammonium nitrate, and about 1.0 to about 15 wt.% fumed silica, wherein the slurry has a pH of about 3.8 to about 5.5.

27. The chemical mechanical polishing slurry of claim 25 comprising about 0.1 to about 3.0 wt.% acetic acid, about 0.1 to about 4.0 wt.% cerium ammonium nitrate, and about 1.0 to about 15 wt.% abrasive cerium oxide, wherein the slurry has a pH of about 3.8 to about 5.5.

28. A method of removing at least a portion of a silicon dioxide layer from a substrate, comprising:

mixing a salt, a soluble cerium compound, a carboxylic acid, and deionized water to prepare a chemical-mechanical polishing composition having a pH of about 3.0 to about 11.0;

applying the chemical-mechanical polishing composition to a substrate; and

at least a portion of the silicon oxide layer is removed by contacting the pad with the substrate and moving the pad and the substrate relative to each other.

29. The method of claim 28, wherein the substrate is a layered substrate comprising at least one silicon dioxide layer and at least one silicon nitride layer.

30. The method of claim 29 wherein the silicon oxide is removed at a rate at least 5 times greater than the rate at which the silicon nitride is removed.

31. The process of claim 28 wherein the carboxylic acid is acetic acid.

32. The method of claim 28, wherein the salt and soluble compound is cerium ammonium nitrate.

33. The method of claim 28, comprising at least one metal oxide abrasive selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria, and mixtures thereof.

34. The method of claim 33, wherein the metal oxide abrasive is silica.

35. A method of removing at least a portion of a silicon dioxide layer deposited on a silicon wafer comprising a silicon nitride layer, comprising:

mixing about 2 to about 15 wt.% silicon dioxide, about 0.1 to about 4.0 wt.% cerium ammonium nitrate, about 0.1 to about 3.0 wt.% acetic acid, and deionized water to prepare a chemical-mechanical polishing composition having a pH of about 3.8 to about 5.5;

applying the chemical-mechanical polishing composition to a pad;

rotating the spacer; and

at least a portion of the silicon oxide layer is removed by contacting the spinning pad with the silicon wafer and rotating the silicon wafer relative to the spinning pad.

36. A package containing a chemical-mechanical polishing composition comprising a salt, a carboxylic acid, and a soluble cerium compound.

37. A multi-pack system for preparing a chemical mechanical polishing slurry, comprising:

a first container containing a water-soluble salt, a nitrate salt, a soluble cerium compound, and a carboxylic acid; and

a second container holding a dispersed metal oxide abrasive.

38. An aqueous chemical mechanical polishing composition comprising:

including Ce⁴⁺Ionic soluble cerium; and

oxidation potential greater than Ce⁴⁺An oxidizing agent of (1).

39. The aqueous chemical mechanical polishing composition of claim 38 having a pH of about 3.8 to about 5.5.

40. The aqueous chemical mechanical polishing composition of claim 38 including a nitrate salt.

41. The aqueous chemical mechanical polishing composition of claim 40 wherein the nitrate salt is a compound having the general formula:

(M)_n(NO₃)_m

wherein n and M are both integers, and wherein when n ═ M, M is an alkaline earth metal, H, NH₄Or NR₄Wherein R is an alkyl group having 1 to 10 carbon atoms, and wherein when n ≠ M, M is a polyvalent cation or a metal or a combination of a polyvalent cation and a monovalent cation.

42. The aqueous chemical mechanical polishing composition of claim 40 comprising about 0.05 to about 6.0 wt.% nitrate.

43. The aqueous chemical mechanical polishing composition of claim 40 wherein the nitrate salt is cerium ammonium nitrate.

44. The aqueous chemical mechanical polishing composition of claim 38 comprising about 0.05 to about 10.0 wt.% of the at least one carboxylic acid or salt thereof.

45. The aqueous chemical mechanical polishing composition of claim 44 wherein the carboxylic acid or salt thereof is selected from the group consisting of monofunctional acids, difunctional acids, and salts thereof.

46. The aqueous chemical mechanical polishing composition of claim 45 wherein the carboxylic acid is acetic acid.

47. The aqueous chemical mechanical polishing composition of claim 38 wherein the oxidizing agent is ammonium persulfate.

48. The aqueous chemical mechanical polishing composition of claim 47 comprising about 0.05 to about 5.0 wt.% ammonium persulfate.

49. The aqueous chemical mechanical polishing composition of claim 38 comprising about 0.05 to about 10 weight percent colloidal cerium.

50. The aqueous chemical mechanical polishing composition of claim 38 wherein the soluble cerium is at least one compound selected from the group consisting of cerium ammonium sulfate, cerium acetate, cerium sulfate hydrate, cerium hydroxide, cerium bromate, cerium bromide, cerium chloride, cerium oxalate, cerium nitrate, cerium carbonate, and mixtures thereof.

51. The aqueous chemical mechanical polishing composition of claim 38 wherein the soluble cerium is cerium ammonium nitrate.

52. The aqueous chemical mechanical polishing composition of claim 38 comprising about 0.5 to about 10 weight percent cerium ammonium nitrate.

53. The aqueous chemical mechanical polishing composition of claim 38 including at least one chelating agent.

54. The aqueous chemical mechanical polishing slurry of claim 53 comprising about 0.05 to about 5.0 wt.% of the chelating agent.

55. The aqueous chemical mechanical polishing slurry of claim 38 comprising a chelating agent selected from the group consisting of EDTA salts, citric acid, and mixtures thereof.

56. The aqueous chemical mechanical polishing slurry of claim 38 including at least one buffering agent.

57. A chemical mechanical polishing slurry comprising:

including Ce⁴⁺Ionic soluble cerium;

oxidation potential greater than Ce⁴⁺An oxidizing agent of (1);

at least one chelating agent; and

at least one abrasive, wherein the composition has a pH of about 3 to about 11.

58. The chemical mechanical polishing slurry of claim 57 comprising about 1 to about 25 weight percent abrasive.

59. The chemical mechanical polishing slurry of claim 58 wherein the abrasive is at least one metal oxide.

60. The chemical mechanical polishing slurry of claim 59 wherein the metal oxide abrasive is at least one compound selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria, or mixtures and chemical blends thereof.

61. The chemical mechanical polishing slurry of claim 59 wherein the abrasive is a physical mixture of oxides of at least two elements selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria.

62. The chemical mechanical polishing slurry of claim 59 comprising about 2 to about 15 weight percent metal oxide abrasive.

63. The aqueous chemical mechanical polishing slurry of claim 57 comprising about 0.05 to about 5.0 wt.% ammonium persulfate, about 0.05 to about 5.0 wt.% of at least one chelating agent, and about 0.5 to about 10 wt.% soluble cerium.

64. The aqueous chemical mechanical polishing slurry of claim 57, comprising about 0.05 to about 10 weight percent cerium ammonium nitrate, about 2.0 to about 15.0 weight percent fumed silica, about 0.05 to about 5.0 weight percent of at least one chelating agent, and about 0.05 to about 5.0 weight percent ammonium persulfate, wherein the slurry has a pH of about 3.8 to about 5.5.

65. The aqueous chemical mechanical polishing slurry of claim 64 wherein the chelating agent is selected from the group consisting of EDTA salts, citric acid, and mixtures thereof.

66. The aqueous chemical mechanical polishing slurry of claim 57, packaged with a buffer.

67. A method of removing at least a portion of a silicon dioxide layer from a substrate, comprising:

a salt, including Ce⁴⁺Ionic soluble cerium compound with cerium oxide greater than Ce^4-And deionized water to provide a chemical mechanical polishing composition having a pH of about 3.0 to about 11.0;

applying the chemical-mechanical polishing composition to a substrate; and

at least a portion of the silicon oxide layer is removed by contacting the pad with the substrate and moving the pad relative to the substrate.

68. The method of claim 67, wherein the substrate is a layered substrate comprising at least one silicon dioxide layer and at least one silicon nitride layer.

69. The method of claim 67, wherein the silicon dioxide is removed from the substrate at a rate at least 5 times greater than the rate of silicon nitride removal.

70. The method of claim 67, wherein the oxidizing agent is ammonium persulfate.

71. The method of claim 67, wherein the salt and soluble cerium compound is cerium ammonium nitrate.

72. The method of claim 67, comprising at least one metal oxide abrasive selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria, and mixtures thereof.

73. The method of claim 67, wherein the metal oxide abrasive is silica.

74. A method of removing at least a portion of a silicon dioxide layer deposited on a silicon wafer comprising a silicon nitride layer, comprising:

mixing about 2 to about 15 wt.% silica, about 0.05 to about 10 wt.% cerium ammonium nitrate, about 0.05 to about 5.0 wt.% ammonium persulfate, at least one chelating agent, and deionized water to prepare a chemical-mechanical polishing composition having a pH of about 3.8 to about 5.5;

applying the chemical mechanical polishing slurry to a pad;

rotating the spacer; and

at least a portion of the silicon dioxide layer is removed by contacting the spin pad with the silicon wafer and moving the silicon wafer relative to the spin pad.