This invention pertains to polishing systems and methods for polishing substrates.
The trend in the semiconductor industry continues to concentrate on reducing the size of semiconductor devices while improving the planarity of their surfaces. More specifically, it is desirable to achieve a surface of even topography by decreasing the number and allowable size of surface imperfections. A smooth topography is sought-after because it is difficult to lithographically image and pattern layers applied to rough surfaces. A conventional way of planarizing the surfaces of these devices is to polish them with a polishing system.
During polishing, it is often useful to polish one wafer surface material faster than another. For example, in shallow-trench isolation (STI), it is important to polish away an overlayer of silicon dioxide, until a silicon nitride layer is exposed, and then to remove as little of the exposed silicon nitride layer as possible. This can be accomplished by a polishing system that polishes away silicon dioxide at a faster rate than silicon nitride. The difference in the rate of polishing between two materials, such as silicon dioxide and silicon nitride, is called selectivity. Increased silicon dioxide-silicon nitride selectivity is a highly desirable property in STI polishing systems.
An accepted method of polishing (e.g., planarizing) semiconductor devices involves polishing the surface of the semiconductor with a polishing composition and/or a polishing pad, such as is accomplished by chemical-mechanical polishing (CMP). In a typical CMP process, a wafer is pressed against a polishing pad in the presence of a slurry under controlled chemical, pressure, velocity, and temperature conditions. The slurry generally contains small, abrasive particles that abrade the surface of the wafer in a mixture with chemicals that etch and/or oxidize the newly formed surface of the wafer. The polishing pad generally is a planar pad made from a continuous phase matrix material such as polyurethane. Thus, when the polishing pad and/or the wafer moves with respect to the other, material is removed from the surface of the wafer mechanically by the abrasive particles and chemically by the etchants and/or oxidants in the slurry.
While the aqueous chemicals desirably react chemically with the substrate, they also are reactive with the abrasive particles. This reaction can xe2x80x9csoftenxe2x80x9d the abrasive particle surfaces, rendering the abrasive less abrasive. Moreover, the reaction of the chemical component with the abrasive particle surface lowers the concentration of that component available for reaction with the substrate surface during polishing. As a result, the polishing performance of premixed CMP slurries may not be optimal for the polishing of solid surfaces, including IC wafer surfaces, rigid disk surfaces, glass surfaces, magnetic media, etc. Furthermore, because CMP slurries must be stable for the extended periods over which they arc typically stored before use, the chemical additives available for use in slurries is limited by their reactivity with other components in the slurry. This consideration also limits the concentration of additives that can be incorporated into slurries.
Thus, there remains a need for improved polishing systems and methods. The invention provides such a polishing system and method These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The invention provides polishing systems that comprise a liquid carrier, an alkali metal ion, a compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom (hereinafter referred to as an xe2x80x9camine-containing, compoundxe2x80x9d), and a polishing pad and/or an abrasive. The abrasive can be dispersed in the liquid carrier of the polishing system or bound to the polishing pad. In a first embodiment, the alkali metal ion and the amine-containing compound desirably are present in a concentration such that the total ion concentration of the polishing system is above the critical coagulation concentration. In a second embodiment, the polishing system comprises about 0.05 wt. % to about 0.15 wt. % KOH and about 0.4 M to about 0.8 M of the amine-containing compound. The invention further provides polishing a portion of a substrate with a polishing system of the invention, preferably beginning about 6 hours or less after the polishing system is prepared.
The invention provides polishing systems and methods for polishing a substrate. Generally, the polishing systems comprise, consist essentially of, or consist of (a) a liquid carrier, (b) an alkali metal ion, (c) a compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom, and (d) a polishing pad and/or an abrasive. In a first embodiment, the polishing system has a total ion concentration, which is above the critical coagulation concentration. In a second embodiment, the polishing system comprises about 0.05 wt. % to about 0. 5 wt. % KOH and about 0.4 M to about 0.8 M of the compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom. The polishing methods generally comprise contacting a surface of a substrate with a polishing system and polishing at least a portion of the substrate. In a first embodiment, the polishing system used in the polishing method is one of the aforementioned polishing systems. In a second embodiment, the polishing system used in the polishing method comprises (a) a liquid carrier, (b) an alkali metal ion, (c) a compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom, and (d) a polishing pad and/or an abrasive, and a portion of the substrate is polished with the polishing system before the polishing system components reach a chemical equilibrium after the system is prepared.
Typically, each polishing system is used about 6 hours or less after the polishing system is prepared, which generally will be before the polishing system reaches a chemical equilibrium. Preferably, the polishing system is used about 4 hours or less (e.g., about 2 hours or less, about 1 hour or less, about 30 minutes or less, about 10 minutes or less, about 5 minutes or less, or even about 1 minute or less) after the polishing system is prepared. Indeed, the polishing system can be used seconds (e.g., about 30 seconds, or less or about 10 seconds or less) after the polishing system is prepared, such as when the polishing system components are mixed very near or at the point-of-use of the polishing system (e.g., on the polishing pad and/or substrate being polished).
The term xe2x80x9ccomponentxe2x80x9d as used herein includes individual ingredients (e.g., acids, bases, oxidizers, water, etc.) as well as any combination of ingredients (e.g., aqueous compositions, abrasive slurries, mixtures and solutions of oxidizers, acids, bases, complexing agents, etc.) that are stored separately and combined to form a polishing system.
The polishing systems and methods of the invention can be used to polish any suitable substrate. Suitable substrates are typically wafers used in the semiconductor industry that are in need of polishing or planarizing. They comprise, for example, a metal, metal oxide, metal composite, metal alloy, or mixtures thereof. The substrate can comprise metals such as copper, aluminum, titanium, tungsten, gold, and combinations (e.g., alloys or mixtures) thereof. The substrate also can comprise metal oxides such as, alumina, silica, titania, ceria, zirconia, germania, magnesia, and co-formed products thereof, and mixtures thereof. In addition, the substrate can comprise metal composites and/or alloys such as metal nitrides (e.g., silicon nitride, tantalum nitride, titanium nitride, and tungsten nitride), metal carbides (e.g., silicon carbide and tungsten carbide), nickel-phosphorus, alumino-borosilicate, borosilicate glass, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), silicon-germanium alloys, and silicon-germanium-carbon alloys. The substrate also can comprise semiconductor base materials such as single-crystal silicon, poly-crystalline silicon, amorphous silicon, silicon-on-insulator, and gallium arsenide. The polishing systems and methods of the invention are not limited to semiconductor polishing, they also can be applied to glass substrates, including technical glass, optical glass, and ceramics, of various types known in the art.
The polishing systems and methods of the invention can be used to polish any part of a substrate (e.g., a semiconductor device) at any stage in the production of the substrate. For example, a particularly effective use of the polishing systems and methods of the invention is in polishing a semiconductor device in conjunction with shallow trench isolation (STI) processing or in conjunction with the formation of an interlayer dielectric (ILD) as is known in art.
The polishing systems described herein comprise an abrasive, a polishing pad, or both. Preferably, the polishing systems comprise both an abrasive and a polishing pad. The abrasive can be fixed on the polishing pad and/or can be in particulate form and suspended in the liquid carrier. The polishing pad can be any suitable polishing pad. The liquid carrier and substances dissolved or suspended (e.g., dispersed) therein, such as the alkali metal ion, the compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom, and the abrasive (when present and suspended in the liquid carrier), form the polishing composition, upon which all concentrations (e.g., weight percentage and molarity values) are based as recited therein. Thus, the concentrations recited herein are not based upon substances not dissolved or suspended in the liquid carrier (such as the polishing pad and any abrasive embedded therein).
Any suitable abrasive can be used in conjunction with the inventive polishing systems. Suitable abrasives are capable of polishing a substrate surface without introducing deleterious scratches or other imperfections in the substrate surface. The abrasive preferably is a metal oxide. Suitable metal oxide abrasives include, for example, alumina, silica, titania, ceria, zirconia, and magnesia, as well as co-formed products thereof, mixtures thereof, and chemical admixtures thereof. Silica is the preferred abrasive, with fumed silica being more preferred.
The abrasive can have any suitable abrasive particle characteristics depending on the desired polishing effects. In particular, the abrasive can have any suitable surface area. A suitable abrasive surface area, for example, is a surface area ranging from about 5 m2/g to about 430 m2/g (e.g., about 5-200 m2/g), as calculated from the method of S. Brunauer, P. H. Emmet, and I. Teller, J. Am. Chem. Soc., 60, 309 (1938). Desirably, the surface area of the abrasive used in conjunction with the invention is about 90 m2/g or more.
The abrasive can be combined with (e.g., suspended in) any suitable liquid carrier to form a dispersion or suspension (i.e., a xe2x80x9cslurryxe2x80x9d). Suitable liquid carriers generally include polar solvents, preferably water or an aqueous solvent. Where the abrasive is included in a dispersion, the dispersion can have any concentration of abrasive that is suitable for polishing. Generally, about 0.1 wt. % silica or more is contemplated. Desirably the polishing system will have 5-30 wt. % silica. Polishing systems containing 10-25 wt. % silica are preferred.
Alternatively, the abrasive in the polishing systems can be fixed (e.g., embedded) in or on a polishing pad. The aforementioned considerations as to the type of abrasive particle suitable for dispersions are applicable to embedded abrasives. Any suitable amount of abrasive can be embedded in the pad. A suitable amount is any amount sufficient to provide for polishing of a substrate surface at a suitable rate without introducing deleterious scratches or other imperfections in the substrate surface.
The alkali metal ion present in the polishing systems can be any suitable alkali metal ion. Suitable alkali metal ions include any of the univalent basic metals of group I of the periodic table. For example, sodium, potassium, rubidium, and cesium ions can be used. Potassium and cesium ions are preferred, with potassium ions being more preferred. Any suitable source of alkali metal ion can be used. For example, alkali metal salts or alkali metal hydroxides (e.g., KCI or KOH) are suitable sources of alkali metal ions.
The alkali metal ion can be present in the polishing systems in any suitable concentration, desirably such that the total ion concentration of the polishing system is above the critical coagulation concentration. Preferably, the alkali metal ion is present in the polishing system in a concentration of about 0.15 M or more (e.g., about 0.2 M or more). More preferably, the alkali metal ion is present in the polishing system in a concentration of 0.25 M or more, about 0.3 M or more, about 0.35 M or more, about 0.4 M or more, or even about 0.45 M or more. Generally, the alkali metal ion is present in the polishing system in an amount that does not exceed 1.5 M, preferably an amount that does not exceed 0.75 M (e.g., about 0. 15-0.75 M, or more preferably, about 0.2 M-0.5 M).
The amine-containing compound, which, as previously described, is a compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom (e.g., amino acids, amino alcohols, and the like) can be any suitable such compound in the polishing systems of the invention. Suitable amine-containing compounds include dimethylpropanolamine (also know as 2-dimethylamino-2-methyl-1-propanol or DMAMP), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol, 2-(isopropylamino)ethanol, 2-(methylamino)ethanol, 2-(diethylamino)ethanol, 2-(2-(dimethylamino)ethoxy)ethanol, 1,1xe2x80x2-[[3-(dimethylamino)propyl]imino]-bis-2-propanol, 2-(butylamino)ethanol, 2-(tert-butylamino)ethanol, 2-(diisopropylamino)ethanol, N-(3-aminopropyl)morpholine, and mixtures thereof.
The amine-containing compound can be present in the polishing systems in any suitable concentration, desirably such that the total ion concentration of the polishing system is above the critical coagulation concentration. Preferably, the amine-containing compound is present in the polishing system in a concentration of about 0.2 M or more (e.g., about 0.5 M or more). More preferably, the amine-containing compound is present in the polishing system in a concentration of about 0.7 M or more, about 0.8 M or more, about 0.9 M or more, or even about 1 M or more. It is also suitable for the amine-containing compound to be present in the polishing system in a concentration of about 1.1 M or more (e.g., about 1.5 M or more). Generally, the amine-containing compound is present in the polishing system in a concentration that does not exceed 3 M, preferably in an amount that does not exceed 1.4 M (e.g., about 0.2-1.4 M, or more preferably, about 0.7-1.1 M).
In a first embodiment, the polishing system contains both an alkali metal ion and a compound comprising an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom, wherein the total ion concentration of the polishing system is above the critical coagulation concentration. The combination of the alkali metal ion and the amine-containing compound has a synergistic effect on the polishing rate achieved by the polishing system when the total ion concentration of the system is above the critical coagulation concentration.
The critical coagulation concentration (CCC) is defined herein as the lowest total ion concentration of the polishing system required to induce the coagulation of a stable colloidal suspension (e.g., to form a gel). In the context of the invention, coagulation can be described as the process by which the dispersed phase of a colloid (e.g., a slurry) is made to aggregate and thereby separate from the continuous phase, eventually forming a gel. This occurs when the ions present in the polishing system gather closely around the colloidal particles, effectively neutralizing the overall charge of the individual particles. Once this occurs, the particles can move closer together and eventually aggregate. Thus, the CCC is a function of the colloidal particle size as well as a function of the valences of the ions present in the polishing system. The stronger the counterion, the more tightly packed the colloidal particles will become, and thus the more likely the particles will agglomerate.
Since the CCC is related to the total ion concentration present in the polishing system, it varies both with the specific alkali metal ion and the specific amine-containing compound used in the polishing system. For example, a concentration of about 0.15 M or more of the alkali metal ion and a concentration of about 0.2 M or more of the amine-containing compound generally are sufficient to raise the total ion concentration of the polishing system above the CCC.
The CCC can be determined by any suitable method, many of which are known in the art and can be readily employed. One such method, for example, involves the Schulze-Hardy rule, which states that the CCC of counterions is found to be inversely proportional to the sixth power of its valence. Other suitable methods for calculating the CCC, including the Schulze-Hardy rule, are set forth, for example, in Hsu and Kuo, J. Colloid Interface Sci., 185, 530-537 (1997).
Although the polishing system of the first embodiment desirably utilizes a total ion concentration well above the CCC, no agglomeration or sedimentation effects will be observed in the polishing system as used in the polishing method of the invention because the mixing of the components takes place at or near the time of use (i.e., polishing). In effect, this invention allows for higher concentrations of all components to be present in the polishing system without adverse gelling consequences. As a result, superior polishing rates can be achieved as compared to similar conventional CMP slurries.
In a second embodiment, the alkali metal ion is KOH that is present in the final polishing system (after mixing) in a concentration of about 0.05 wt. % to about 0.15 wt. % (e.g., about 0.08 wt. % to about 0.12 wt. %) and the amine-containing compound is present in the final polishing system (after mixing) in a concentration of about 0.4 M to about 0.8 M (e.g., about 0.5 M to about 0.7 M).
The polishing systems optionally further comprise ammonium salts (e.g., tetramethylammonium hydroxide (TMAH) and quaternary ammonium compounds). The ammonium salt can be any suitable cationic amine-containing compound, such as, for example, hydrogenated amines and quaternary ammonium compounds, that adsorbs to the silicon nitride layer present on the substrate being polished and reduces, substantially reduces, or even inhibits (i.e., blocks) the removal of silicon nitride during polishing. A preferred polishing system comprises a 1:1 equal weight ratio mixture of dimethylpropanolamine and tetramethylammonium hydroxide.
The polishing systems can have any pH that provides suitable polishing rates. Generally, the pH of the polishing system is about 7 or more (e.g., about 8 or more). Preferably, the pH of the present polishing system is about 9 or more (e.g., about 9-14). More preferably, the pH of the polishing system will be in the range of about 10-13 or even about 10-12. Because the inventive method disclosed herein provides for use of the polishing system at about 6 hours after mixing or less and preferably at the point-of-use, a higher pH can be used than would otherwise be possible for polishing systems that are allowed to reach chemical equilibrium, which systems must be stable upon storage for extended periods such as days, weeks, or months before use. The present polishing system is largely free of this constraint, requiring only that it be stable enough to provide suitable polishing in about 6 hours or less after it is prepared.
At its simplest, the polishing system consists essentially of a liquid carrier, an alkali metal ion, a compound containing an amine group and at least one polar moiety, wherein the polar moiety contains at least one oxygen atom, and a polishing pad and/or an abrasive. In this polishing system, the total ion concentration desirably is above the critical coagulation concentration. As mentioned previously, the liquid carrier is preferably a polar solvent, particularly water.
A variety of other additives can be used in conjunction with the polishing systems. For example, film-forming agents, complexing agents, surfactants, rheological control agents, polymeric stabilizers or dispersing agents, and/or halide ions can be present in the polishing system.
Any suitable film-forming agent (i.e., corrosion-inhibitor) can be used in conjunction with the polishing systems. For example, in STI polishing methods, suitable film-forming, agents generally include surface-active agents (i.e., surfactants) that preferentially adsorb to and prevent polishing of silicon nitride. Therefore, suitable film-forming agents include, for example, alkylamines, alkanolamines, hydroxylamines, phosphate esters, sodium laurylsulfate, fatty acids, polyacrylates, polymethacrylates, polyvinylphosphonates, polymalate, polystyrenesulfonate, and polyvinylsulfonate. Other film-forming agents include, for example, benzotriazole, triazole, benzimidazole, and mixtures thereof.
Any suitable complexing agent (i.e., chelating agent or selectivity enhancer) can be used in conjunction with the polishing systems. Suitable complexing agents include, for example, carbonyl compounds (e.g., acetylacetonates and the like), simple carboxylates (e.g., acetates, aryl carboxylates, and the like), carboxylates containing one or more hydroxyl groups (e.g., glycolates, lactates, gluconates, gallic acid and salts thereof, and the like), di-, tri-, and poly-carboxylates (e.g., oxalates, phthalates, citrates, succinates, tartrates, malates, edetates (e.g., disodium EDTA), mixtures thereof, and the like), and carboxylates containing one or more sulfonic and/or phosphonic groups. Suitable chelating or complexing agents also can include, for example, di-, tri-, or poly-alcohols (e.g., ethylene glycol, pyrocatechol, pyrogallol, tannic acid, and the like) and phosphate-containing compounds (e.g., phosphonium salts and phosphonic acids).
Any suitable surfactant and/or rheological control agent can be used in conjunction with the polishing systems, including viscosity enhancing agents and coagulants. Suitable rheological control agents include polymeric rheological control agents, such as, for example, urethane polymers (e.g., urethane polymers with a molecular weight greater than about 100,000 Daltons), acrylates comprising one or more acrylic subunits (e.g., vinyl acrylates and styrene acrylates), and polymers, copolymers, and oligomers thereof, and salts thereof Preferably, the rheological control agent is a low molecular weight carboxylate base or a high molecular weight polyacrylamide agent. Suitable surfactants include, for example, cationic surfactants, anionic surfactants, anionic polyelectrolytes, nonionic surfactants, amphoteric surfactants, fluorinated surfactants, mixtures thereof, and the like.
The polishing systems can contain any suitable polymeric stabilizer or other surface-active dispersing agent. Suitable stabilizers include, for example, phosphoric acid, organic acids, tin oxides, organic phosphonates, mixtures thereof, and the like.
The compounds recited herein have been classified for illustrative purposes, and there is no intent to limit the uses of these compounds to their noted classifications. As those of skill in the art will recognize, certain compounds may perform differently in different contexts and/or perform more than one function. For example, some compounds can function both as a chelating agent and an oxidizing agent (e.g., certain ferric nitrates and the like).
Any of the components used in conjunction with the invention can be provided in the form of a mixture or solution in an appropriate carrier liquid or solvent (e.g., water or an appropriate organic solvent). Furthermore, the compounds, alone or in any combination, can be used as components of the polishing system. Two or more components then desirably are individually stored and subsequently mixed to form the polishing system. In this regard, it is suitable for the polishing system to be prepared (e.g., for all the components to be mixed together) no more than 6 hours prior to delivery to the polishing pad or to the surface of the substrate. It is also suitable for the polishing system to be prepared on the surface of the polishing pad or on the surface of the substrate, through delivery of the components of the polishing system from two or more distinct sources, whereby the components of the polishing system meet at the surface of the polishing pad or at the surface of the substrate (e.g., at the point-of-use). In either case, the flow rate at which the components of the polishing system are delivered to the polishing pad or to the surface of the substrate (i.e., the delivered amount of the particular components of the polishing system) can be altered prior to the polishing process and/or during the polishing process, such that the polishing characteristics, such as rate, selectivity, and/or viscosity of the polishing system is altered.
When two or more of the components are combined prior to reaching the point-of-use, the components can be combined in the flow line and delivered to the point-of-use without the use of a mixing device. Alternatively, one or more of the flow lines can lead into a mixing device to facilitate the combination of two or more of the components. Any suitable mixing device can be used. For example, the mixing device can be a nozzle or jet (e.g., a high pressure nozzle or jet) or an in-line mixer through which two or more of the components flow. Alternatively, the mixing device can be a container-type mixing device comprising one or more inlets by which two or more components of the polishing slurry are introduced to the mixer, and at least one outlet through which the mixed components exit the mixer to be delivered to the point-of-use, either directly or via other elements of the apparatus (e.g., via one or more flow lines). Furthermore, the mixing device can comprise more than one chamber, each chamber having at least one inlet and at least one outlet, wherein two or more components are combined in each chamber. If a container-type mixing device is used, the mixing device preferably comprises a mixing mechanism to further facilitate the combination of the components. Mixing mechanisms are generally known in the art and include stirrers, blenders, agitators, paddled baffles, gas sparger systems, vibrators, etc.
A component can have any pH appropriate in view of the storage and contemplated end-use, as will be appreciated by those of skill in the art. Moreover, the pH of a component used in conjunction with the invention can be adjusted in any suitable manner, e.g., by adding a pH adjuster, regulator, or buffer. Suitable pH adjusters, regulators, or buffers include acids, such as, for example, inorganic acids (e.g., hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid) and organic acids (e.g., acetic acid, citric acid, malonic acid, succinic acid, tartaric acid, and oxalic acid). Suitable pH adjusters, regulators, or buffers also include bases, such as, for example, inorganic hydroxide bases (e.g., sodium hydroxide, potassium hydroxide, ammonium hydroxide, cesium hydroxide, and the like) and carbonate bases (e.g., sodium carbonate and the like).
A substrate can be polished (e.g., planarized) by contacting the surface of the substrate with the polishing systems using any suitable technique. For example, in one typical CMP process, a wafer is pressed against a polishing pad using the inventive polishing system under controlled chemical, pressure, velocity, and temperature conditions and the pad and the wafer are moved with respect to each other. Material is then removed from the surface of the wafer.
A substrate can be polished with the polishing systems with any suitable polishing pad (e.g., polishing surface). Suitable polishing pads include, for example, woven and non-woven polishing pads. Moreover, suitable polishing pads can comprise any suitable polymer of varying density, hardness, thickness, compressibility, ability to rebound upon compression, and compression modulus. Suitable polymers include, for example, polyvinylchloride, polyvinylfluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, and coformed products thereof, and mixtures thereof. As discussed above, the abrasive of the polishing system can be fixed (e.g., embedded) in whole or in part, in or on the polishing pad. Such fixation on the polishing pad can be accomplished, for example, by blending the abrasive into the aforementioned polymers during the formation of the polishing pad or by adhering the abrasive to the pad after the pad is formed using such adherents as are known.
The polishing systems are particularly well suited for polishing a substrate that has undergone shallow trench isolation (STI) processing. STI processing typically involves providing a silicon substrate on which is deposited a layer of silicon dioxide and a layer of silicon nitride. Trenches are etched following photolithography and are filled with silicon dioxide. The excess silicon dioxide is planarized until the silicon nitride is fully exposed, such that the silicon oxide remaining in the trenches is approximately level with the silicon nitride level on the mesa regions or with the pad oxide level. Desirably, the polishing is carried out in such typical STI processing with the polishing systems and/or methods of the invention, preferably such that the silicon dioxide is removed and planarization stops at the silicon nitride layer.
Preferred formulations of the polishing systems can provide selective polishing of silicon oxide surfaces relative to silicon nitride surfaces. The selectivity can be controlled, to some extent, by altering the relative concentrations of the components of the polishing system. Without wishing to be bound by any particular theory, it is believed that cationic species (i.e., amines, such as hydrogenated amines, and quaternary ammonium compounds) adsorb to the silicon nitride layer and reduce, substantially reduce, or even inhibit (i.e., block) the removal of silicon nitride during polishing. The alkali metal ion of the polishing system neutralizes the cationic amine, thereby reducing its ability to adsorb to, and inhibit the removal of, the silicon nitride layer. Accordingly, silicon nitride removal by the polishing system can be controlled by altering the relative concentrations of the alkali metal ion and the amine-containing compound in the polishing system, as well as by altering the pH of the polishing system.
When desirable, the polishing systems and methods of the invention can be used to polish a substrate with a polishing selectivity of silicon oxide to silicon nitride (i.e., oxide:nitride) of about 2:1 or more (e.g., about 5:1 or more), or even an oxide:nitride selectivity of about 10:1 or more (e.g., about 15:1 or more). Certain formulations can exhibit even higher oxide:nitride selectivities, such as about 25:1 or more, or even about 35:1 or more (e.g., about 45:1 or more), and when very high selectivity is required even about 55:1 or more, about 65:1 or more, or even about 75:1 or more (e.g., about 90:1 or more).
The polishing methods desirably utilize at least one dispenser, which simultaneously or sequentially dispenses one or more components of a polishing system from the flow lines onto the polishing surface (e.g., the substrate surface or the polishing pad). A single dispenser can be used, from which a single component or any combination of components of the polishing system can be dispensed. Alternatively, the polishing methods can utilize more than one dispenser from which the components of the polishing system are independently dispensed (e.g., one dispenser for each component). Generally, however, the polishing methods utilize more than one dispenser from each of which different combinations or ratios of components can be dispensed. For example, two or more dispensers can be utilized, each delivering different components simultaneously or sequentially to the same polishing surface.
Following polishing of a composite substrate, the used polishing system can be combined with any compound(s) suitable for enhancing the disposability of the polishing system. Suitable compounds include, for example, acids which will decrease the pH of the used polishing system, calcium-containing salts which will act as complexing agents to fluoride ions, and other compounds known to ordinary artisans. These compounds can be added to the polishing system in any suitable manner. It is suitable, for example, for the compound to be added to the waste stream by which the polishing system exits the polishing surface.