Patent Description:
Exemplary embodiments of the present invention relate to an etching composition, and more particularly, to a high-selectivity etching composition capable of selectively removing a nitride film while minimizing the etch rate of an oxide film and to a method for fabricating a semiconductor, which includes an etching process employing the etching composition.

Selective Si<NUM>N<NUM> sacrificial removal is one of the critical steps for 3D NAND memory device fabrication. After the etch process, Si<NUM>N<NUM> is removed, leaving the SiO<NUM> core with SiO<NUM> fins unchanged. Traditionally, an Si<NUM>N<NUM> etch could be accomplished by hot phosphoric acid at <NUM>, however, the selectivity of the Si<NUM>N<NUM> etch relative to a silicon or silicon oxide material is generally low.

As semiconductor devices become more highly integrated, the reliability and electrical characteristics of the semiconductor devices are more susceptible to damage or deformation of the layers constituting the semiconductor device. Therefore, when an etching process is performed to remove a specific material layer selectively using an etchant, it is desirable that the etchant should have a higher etch selectivity with respect to other material layers and the etching process generate less byproduct to reduce process defects.

With such high integration, therefore, the material selectivity requirement for selective Si<NUM>N<NUM> sacrificial removal in 3D NAND fabrication becomes more critical - to the point where it is desired to effectively leave the SiO<NUM> layer unchanged while etching the Si<NUM>N<NUM> layer. Thus, there is a need in the art to further suppress the SiO<NUM> etch rate to achieve an even higher Si<NUM>N<NUM> to SiO<NUM> selectivity.

<CIT> discloses discloses an etching solution suitable for selective removal of silicon nitride over silicon oxide comprising water, phosphoric acid and solvent.

<CIT> discloses a phosphoric etch bath comprising methyltriethoxysilane for use in selectively etching silicon nitride without unduly impacting other silicon containing underlying layers e.g. silicon oxide.

The present invention provides an etching solution according to claim <NUM> for the selective removal of silicon nitride over silicon oxide from a microelectronic device. The etching solution comprises water, aqueous phosphoric acid solution and a hydroxyl group-containing water-miscible solvent which is a saturated aliphatic monohydric alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, isopropyl alcohol, <NUM>-butanol, <NUM>-butanol, isobutyl alcohol, tert-butyl alcohol, <NUM>- pentanol, t-pentyl alcohol, and <NUM>-hexanol.

In another aspect, the present invention provides a method of selectively enhancing the etch rate of silicon nitride relative to silicon dioxide on a composite semiconductor device (or microelectronic device) comprising silicon nitride and silicon dioxide, the method comprising the steps of: contacting the composite semiconductor device (or microelectronic device) comprising silicon nitride and silicon dioxide with a composition according to claim <NUM>; and rinsing the composite semiconductor device (or microelectronic device) after the silicon nitride is at least partially removed, wherein the selectivity of the etch for silicon nitride over silicon oxide is over about <NUM>.

The embodiments of the invention can be used alone or in combinations with each other.

This invention provides high selectivity for silicon nitride over silicon oxide, which is particularly important as the numbers of alternating layers of silicon nitride and silicon oxide in memory devices during their fabrication increases to above <NUM>, or above <NUM> or above <NUM>, or more.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention.

The present invention relates generally to compositions useful for the selective removal of silicon nitride over silicon oxide from a microelectronic device having such material(s) thereon during its manufacture.

For ease of reference, "microelectronic device" corresponds to semiconductor substrates (wafers), flat panel displays, phase change memory devices, solar panels and other products including solar substrates, photovoltaics, and microelectromechanical systems (MEMS), manufactured for use in microelectronic, integrated circuit, or computer chip applications. Solar substrates include, but are not limited to, silicon, amorphous silicon, polycrystalline silicon, monocrystalline silicon, CdTe, copper indium selenide, copper indium sulfide, and gallium arsenide on gallium. The solar substrates may be doped or undoped. It is to be understood that the term "microelectronic device" is not meant to be limiting in any way and includes any substrate that will eventually become a microelectronic device or microelectronic assembly. The term "semiconductor device" may be used interchangeably with microelectronic device. The term "composite" may be used to describe either semiconductor device or microelectronic device to indicate that there are more than one type of material present in one or more layers, films, patterns, vias, etc in or on the semiconductor device, one layer may be the substrate, which may be a silicon wafer.

As defined herein, "low-k dielectric material" corresponds to any material used as a dielectric material in a layered microelectronic device, wherein the material has a dielectric constant less than about <NUM>. Preferably, the low-k dielectric materials include low-polarity materials such as silicon-containing organic polymers, silicon-containing hybrid organic/inorganic materials, organosilicate glass (OSG), TEOS, fluorinated silicate glass (FSG), silicon dioxide, and carbon-doped oxide (CDO) glass. It is to be appreciated that the low-k dielectric materials may have varying densities and varying porosities.

As defined herein, the term "barrier material" corresponds to any material used in the art to seal the metal lines, e.g., copper interconnects, to minimize the diffusion of said metal, e.g., copper, into the dielectric material. Preferred barrier layer materials include tantalum, titanium, ruthenium, hafnium, and other refractory metals and their nitrides and silicides.

"Substantially free" is defined herein as less than <NUM> wt. %, preferably less than <NUM> wt. %, more preferably less than <NUM> wt. % and more preferably less than <NUM> wt %. "Substantially free" also includes <NUM> wt. The term "free of" means <NUM> wt.

As used herein, "about" is intended to correspond to ±<NUM>% of the stated value.

In all such compositions, wherein specific components of the composition are discussed in reference to weight percentage ranges including a zero lower limit, it will be understood that such components may be present or absent in various specific embodiments of the composition, and that in instances where such components are present, they may be present at concentrations as low as <NUM> weight percent, based on the total weight of the composition in which such components are employed.

In the broad practice of this aspect, the etching solution of the present development comprises, consists essentially of, or consists of water, phosphoric acid, an organosilicon compound as disclosed herein, and a hydroxyl group-containing water-miscible solvent.

In some embodiments, the etching solution compositions disclosed herein may be formulated to be substantially free of at least one of the following chemical compounds: hydrogen peroxide and other peroxides, ammonium ions, ammonium salts, for examples, ammonium citrate, ammonium acetate and ammonium sulfate, fluoride ions, hydrofluoric acid, ammonium fluoride, fluorine-containing compounds, sulfurcontaining compounds and abrasives.

In other embodiments, the etching solution compositions disclosed herein are formulated to be free of at least one of the following chemical compounds: hydrogen peroxide and other peroxides, ammonium ions, fluoride ions, and abrasives.

The etching compositions of the present development comprise water. In the present invention, water functions in various ways such as, for example, to dissolve one or more components of the composition, as a carrier of the components, as an aid in the removal of residue, as a viscosity modifier of the composition, and as a diluent. Preferably, the water employed in the etching composition is de-ionized (DI) water. In some embodiments, the water will be added to the composition only by introducing other components to the composition that are typically or only commercially available in an aqueous solution, for example the phosphoric acid, described below.

It is believed that, for most applications, water will comprise, for example, from about <NUM>% to about <NUM>% by wt. of the etching composition. Other preferred embodiments of the present invention could comprise from about <NUM>% to about <NUM>% by wt. Still other preferred embodiments of the present invention could include water in an amount to achieve the desired weight percent of the other ingredients. The amount of water in the composition of this invention may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In alternative examples, water will comprise from about <NUM>% to about <NUM>% by wt. or from about <NUM>% to about <NUM>% by wt. of the etching composition.

The etching compositions of the present invention comprise phosphoric acid. The phosphoric acid functions primarily to etch silicon nitride. Commercial grade phosphoric acid can be used. Typically, the commercially available phosphoric acid is available as <NUM>% to <NUM>% aqueous solutions. In a preferred embodiment electronic grade phosphoric acid solutions are employed wherein such electronic grade solutions typically have a particle count below <NUM> particles/ml, and wherein the size of the particles is less than or equal to <NUM> microns and metallic ions are present in the acid in the low parts per million to parts per billion level per liter. In certain embodiments, no other acids such as, for example, hydrofluoric acid, nitric acid or mixtures thereof are added to the solution of the present invention.

It is believed that, for most applications, the amount of phosphoric acid (aqueous solution) can comprise from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition. The amount of phosphoric acid on a neat basis, that is, excluding the water in the phosphoric acid solution added to the composition of this invention may be from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition. Alternatively, the amount of phosphoric acid added to the composition on a neat basis may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, such as, from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition. For the purpose of clarity, if <NUM> grams of an <NUM>% aqueous phosphoric acid solution is added to the composition, then <NUM> grams of phosphoric acid and <NUM> grams of water will be added to the composition; therefore, on a neat basis, <NUM> grams of phosphoric acid was added to the composition and <NUM> grams of water is added to the total amount of water in the composition.

The etching compositions of the present invention comprise a hydroxyl group-containing water-miscible solvent, namely a saturated aliphatic monohydric alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, isopropyl alcohol, <NUM>-butanol, <NUM>-butanol, isobutyl alcohol, tert-butyl alcohol, <NUM>- pentanol, t-pentyl alcohol, and <NUM>-hexanol. The hydroxyl group-containing water-miscible solvent functions primarily to protect the silicon oxide such that the silicon nitride is etched preferentially and selectively and may also enhance the miscibility between the phosphoric acid and any other components added to the composition.

Classes of hydroxyl group-containing water-miscible solvents include, but are not limited to, alkane diols and polyols (including, but not limited to, alkylene glycols), glycols, alkoxyalcohols (including but not limited to glycol monoethers), saturated aliphatic monohydric alcohols, unsaturated non-aromatic monohydric alcohols, and low molecular weight alcohols containing a ring structure.

Examples of water soluble alkane diols and polyols such as (C<NUM>- C<NUM>) alkanediols and (C<NUM>- C<NUM>) alkanetriols including, but are not limited to, <NUM>-methyl-<NUM>,<NUM>-propanediol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, and pinacol.

Examples of water soluble alkylene glycols include, but are not limited to, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol and tetraethyleneglycol.

Examples of water soluble alkoxyalcohols include, but are not limited to, <NUM>-methoxy-<NUM>-methyl-<NUM>-butanol, <NUM>-methoxy-<NUM>-butanol, <NUM>-methoxy-<NUM>-butanol, and water soluble glycol monoethers.

Examples of water soluble glycol monoethers include, but are not limited to, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-propyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutylether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, <NUM>-methoxy-<NUM>-propanol, <NUM>-methoxy-<NUM>-propanol, <NUM>-ethoxy-<NUM>-propanol, <NUM>-ethoxy-<NUM>-propanol, propylene glycol mono-n-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monomethyl ether and ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, and mixtures thereof.

Examples of water soluble saturated aliphatic monohydric alcohols include, but are not limited to methanol, ethanol, n-propyl alcohol, isopropyl alcohol, <NUM>-butanol, <NUM>-butanol, isobutyl alcohol, tert-butyl alcohol, <NUM>-pentanol, t-pentyl alcohol, <NUM>-hexanol, and mixtures thereof.

Examples of water soluble unsaturated non-aromatic monohydric alcohols include, but are not limited to allyl alcohol, propargyl alcohol, <NUM>-butenyl alcohol, <NUM>-butenyl alcohol, <NUM>-penten-<NUM>-ol, and mixtures thereof.

Examples of water soluble, low molecular weight alcohols containing a ring structure include, but are not limited to, alpha-terpineol, tetrahydrofurfuryl alcohol, furfuryl alcohol, <NUM>,<NUM>-cyclopentanediol, and mixtures thereof.

It is believed that, for most applications, the amount of hydroxyl group-containing water-miscible solvent will comprise from about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% by weight of the composition. When employed, the hydroxyl group-containing water-miscible solvent may comprise from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition. Additionally, the amount of hydroxyl group containing water-miscible solvent in the composition of this invention may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. Additional embodiments may comprise the hydroxyl group-containing water-miscible solvent in an amount from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition.

The etching compositions of the present invention comprise an organosilicon compound, namely trimethoxymethylsilane TMMS. The organosilicon compound functions primarily to protect the silicon oxide such that the silicon nitride is etched selectively and substantially exclusively.

The organosilicon compound is at least one organosilicon compound having a chemical structure represented by Formula A:.

wherein R<NUM> and R<NUM> are each independently selected from a hydrogen atom, a C<NUM> to C<NUM> linear alkyl group, a C<NUM> to C<NUM> branched alkyl group, a C<NUM> to C<NUM> cyclic alkyl group, a C<NUM> to C<NUM> aryl group, a C<NUM> to C<NUM> linear or branched alkenyl group, a C<NUM> to C<NUM> linear or branched alkynyl group, and a functional group-containing moiety, wherein the functional group is at least one selected from the group consisting of vinyl, epoxy, styryl, methacyloxy, acyloxy, amino, ureide, isocycanate, isocyanurate, and mercapto; R<NUM> is selected from a C<NUM> to C<NUM> linear alkyl group, a C<NUM> to C<NUM> branched alkyl group, a C<NUM> to C<NUM> cyclic alkyl group, a C<NUM> to C<NUM> linear or branched alkenyl group, and a C<NUM> to C<NUM> linear or branched alkynyl group, a C<NUM>-C<NUM> aryl group and wherein m =<NUM>, <NUM>, or <NUM>. Exemplary compounds of Formula A include, but are not limited to, trimethoxymethylsilane, dimethoxydimethylsilane, triethoxymethylsilane, diethoxydimethylsilane, trimethoxysilane, dimethoxymethylsilane, di-isopropyldimethoxysilane, diethoxymethylsilane, dimethoxyvinylmethylsilane, dimethoxydivinylsilane, diethoxyvinylmethylsilane, and diethoxydivinylsilane. According to the invention, the organosilicon compound must include at least TMMS.

Examples of compounds of Formula A where R<NUM>, for example, is a functional group-containing moiety, wherein the functional group is at least one selected from the group consisting of vinyl, epoxy, styryl, methacyloxy, acyloxy, amino, ureide, isocycanate, isocyanurate, and mercapto include vinyltrimethoxysilane and vinyltriethoxysilane which are vinyl-functional-group-containing examples of Formula A; <NUM>-(<NUM>,<NUM> epoxycyclohexyl) ethyltrimethoxysilane, <NUM>-Glycidoxypropyl methyldimethoxysilane, <NUM>-Glycidoxypropyl trimethoxysilane, <NUM>-Glycidoxypropyl methyldiethoxysilane and <NUM>-Glycidoxypropyl triethoxysilane which are epoxy-functional-group-containing examples of Formula A; p-styryltrimethoxysilane which is a styryl-functional-group-containing example of Formula A; <NUM>-methacryloxypropyl methyldimethoxysilane; <NUM>-methacryloxypropyl trimethoxysilane; <NUM>-methacryloxypropyl methyldiethoxysilane and <NUM>-Methacryloxypropyl triethoxysilane which are methacryloxy-functional-group-containing examples of Formula A; <NUM>-Acryloxypropyl trimethoxysilane which is an acryloxy-functional-group-containing example of Formula A; N-<NUM>-(Aminoethyl)-<NUM>-aminopropylmethyldimethoxysilane, N-<NUM>-(Aminoethyl)-<NUM>-aminopropyltrimethoxysilane, <NUM>-Aminopropyltrimethoxysilane, <NUM>-Aminopropyltriethoxysilane, <NUM>-Triethoxysilyl-N-(<NUM>,<NUM> dimethyl-butylidene) propylamine, N-Phenyl-<NUM>-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-<NUM>-aminoethyl-<NUM>-aminopropyltrimehoxysilane hydrochloride which are amino- functional-group-containing examples of Formula A; and <NUM>-ureidopropyltrialkoxysilane which is an ureide-functional-group-containing example of Formula A; <NUM>-isocyanatepropyltriethoxysilane which is an isocyanate-functional-group-containing example of Formula A; tris-(trimethoxysilylpropyl)isocyanurate which is an isicyanurate-functional-group-containing example of Formula A; and <NUM>-mercaptopropylmethyldimethoxysilane and <NUM>-mercaptopropyltrimethoxysilane which are mercapto-functional-group-containing examples of Formula A.

Without intending to be bound by a particular theory, it is believed that the organosilicon compound once added reacts with the water and forms a hydrolysis product once in the presence of water. The rate of hydrolysis of etch group on silicon typically depends on the solution pH and water concentration. For example, hydrolysis of trimethoxymethylsilane can proceed both under acidic and basic conditions. It is believed that the hydroxyl groups in the hydrolyzed organosilicon compound either react with or associate somehow with the hydroxyl groups on the surface of the silicon substrate to generate a protective layer thus allowing for significantly increased selectivity for silicon nitride.

It is believed that, for most applications, the amount of the organosilicon compound will comprise from about <NUM>% to about <NUM>% by weight of the composition. Preferably, when employed, the organosilicon compound comprises from about <NUM>% to about <NUM>% by weight of the composition. The amount of organosilicon compound in the composition of this invention may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, for examples, from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition.

The etching compositions disclosed herein optionally include silicic acid. If employed, the silicic acid aids in protecting the silicon oxide and increasing the selectivity of the silicon nitride etch.

If employed, the amount of silicic acid will typically comprise from about <NUM>% to about <NUM>% by weight of the composition and, preferably, from about <NUM>% by weight to about <NUM>% by weight. In other embodiments, when employed, the silicic acid comprises from about <NUM>% to about <NUM>% by weight of the composition. The amount of silicic acid in the composition of this invention may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, for examples, from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>% by weight of the composition.

The etching compositions disclosed herein optionally include a phosphate compound, such as, for example, triethyl phosphate (TEPO) and/or trimethyl phosphate (TMPO). If employed, the phosphate compound functions as a supplemental solvent.

If employed, the amount of phosphate compound, such as, triethyl phosphate will typically comprise from about <NUM>% to about <NUM>% by weight of the composition and, preferably, from about <NUM>% by weight to about <NUM>% by weight. In other embodiments, when employed, the triethyl phosphate comprises about <NUM>% by weight of the composition. The amount of phosphate compound in the composition of this invention may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, for examples, from about <NUM>% to about <NUM>% or from about <NUM>% to about <NUM>% by weight of the composition. In yet other embodiments, the compositions may be substantially free of or free of added phosphorus-containing components other than the phosphoric acid.

The compositions of the present invention optionally comprise at least one water-soluble nonionic surfactant. Surfactants serve to aid in the removal of residue.

Examples of the water-soluble nonionic dispersing agents include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene steary ether, polyoxyethylene oleyl ether, polyoxyethylene higher alcohol ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene derivatives, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbit tetraoleate, polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene alkylamine, polyoxyethylene hardened castor oil, alkylalkanolamide, and mixtures thereof.

It is believed that for most applications, if present the surfactant will comprise from about <NUM> wt. % to about <NUM> wt. % of the composition, preferably from about <NUM> wt. % to about <NUM> wt. % and, most preferably, from about <NUM> wt. % to about <NUM> wt. % of the composition. The amount of surfactant in the composition of this invention may be any amount defined by a range having any combination of the endpoints selected from the following weight percents: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>,<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, for examples, from about <NUM> wt. % to about <NUM> wt. %, or from about <NUM> wt. % to about <NUM> wt. % of the composition.

In some embodiments the compositions of this invention will be free of or substantially free of any or all of the above-listed surfactants added to the composition.

The etching composition of the present invention may also include one or more metal chelating agents. Metal chelating agents may function to increase the capacity of the composition to retain metals in solution and to enhance the dissolution of metallic residues. Typical examples of chelating agents useful for this purpose are the following organic acids and their isomers and salts: ethylenediaminetetraacetic acid (EDTA), butylenediaminetetraacetic acid, (<NUM>,<NUM>-cyclohexylenediamine)tetraacetic acid (CyDTA), diethylenetriaminepentaacetic acid (DETPA), ethylenediaminetetrapropionic acid, (hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), N, N,N', N'-ethylenediaminetetra(methylenephosphonic) acid (EDTMP), triethylenetetraminehexaacetic acid (TTHA), <NUM>,<NUM>-diamino-<NUM>-hydroxypropane-N,N,N',N'-tetraacetic acid (DHPTA), methyliminodiacetic acid, propylenediaminetetraacetic acid, nitrotriacetic acid (NTA), citric acid, tartaric acid, gluconic acid, saccharic acid, glyceric acid, oxalic acid, phthalic acid, maleic acid, mandelic acid, malonic acid, lactic acid, salicylic acid, propyl gallate, pyrogallol, <NUM>-hydroxyquinoline, and cysteine. Preferred chelating agents are aminocarboxylic acids such as EDTA, CyDTA and aminophosphonic acids such as EDTMP.

It is believed that, for most applications, the chelating agent will be present in the composition in an amount of from about <NUM> wt. % to about <NUM> wt. %, preferably in an amount of from about <NUM> wt. % to about <NUM> wt. % of the composition.

In some embodiments the compositions of this invention will be free of or substantially free of any or all of the above-listed chelating agents added to the composition.

The etching solution composition of the present invention is typically prepared by mixing the components together in a vessel at room temperature until all solids have dissolved in the aqueous-based medium.

In another aspect there is provided herein a method of selectively enhancing the etch rate of silicon nitride relative to silicon dioxide on a composite semiconductor device (or microelectronic device) comprising silicon nitride and silicon dioxide, the method comprising the steps of: contacting the composite semiconductor device (or microelectronic device) comprising silicon nitride and silicon dioxide with a composition comprising, consisting essentially of, or consisting of: water, aqueous phosphoric acid solution and a hydroxyl group-containing water-miscible solvent which is a saturated aliphatic monohydric alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, isopropyl alcohol, <NUM>-butanol, <NUM>-butanol, isobutyl alcohol, tert-butyl alcohol, <NUM>- pentanol, t-pentyl alcohol, and <NUM>-hexanol; and rinsing the composite semiconductor device (or microelectronic device) after the silicon nitride is at least partially removed, wherein the selectivity of the etch for silicon nitride over silicon oxide is over about <NUM>. An additional drying step may also be included in the method. "At least partially removed" means removal of at least <NUM>% of the material, preferably at least <NUM>% removal. Most preferably, at least <NUM>% removal using the compositions of the present development.

The contacting step can be carried out by any suitable means such as, for example, immersion, spray, or via a single wafer process. The temperature of the composition during the contacting step is preferably from about <NUM> to <NUM> and more preferably from about <NUM> to <NUM>. Even more preferably, the temperature of the composition during the contacting step is about <NUM>.

In preferred embodiments, the etch selectivity of silicon nitride over silicon oxide observed with the composition of the present invention is typically over from about <NUM>, more preferably over from about <NUM>, and most preferably over from about <NUM>.

The rinsing step is carried out by any suitable means, for example, rinsing the substrate with de-ionized water by immersion or spray techniques. In preferred embodiments, the rinsing step is carried out employing a mixture of de-ionized water and a water-miscible organic solvent such as, for example, isopropyl alcohol.

The drying step is carried out by any suitable means, for example, isopropyl alcohol (IPA) vapor drying, heat, or by centripetal force.

In some embodiments, the wafers may be pretreated by contacting them with a diluted hydrofluoric acid (DHF) which may be a H2O:HF = <NUM>:<NUM> composition for <NUM> seconds to <NUM> minutes. In some embodiments the pretreatment may be performed for <NUM> minutes.

The features and advantages are more fully shown by the illustrative examples discussed below.

The examples of Table <NUM> are according to the invention.

All compositions which are the subject of the present Examples were prepared by mixing the components in a <NUM> beaker with a <NUM>" Teflon-coated stir bar. Typically, the first material added to the beaker was deionized (DI) water. Phosphoric acid is typically added next followed by the hydroxyl-containing water-miscible solvent and then the remaining components.

Each test <NUM> x <NUM> coupon employed in the present examples comprised a layer of silicon nitride, Si<NUM>N<NUM>, on a silicon substrate. Additional examples comprised a layer of silicon oxide, SiO<NUM>, on a silicon substrate to determine the etch rate of the silicon oxide.

Etching tests were run using <NUM> of the etching compositions in a <NUM> beaker with a ½" round Teflon stir bar set at <NUM> rpm. The etching compositions were heated to a temperature of about <NUM> on a hot plate. The test coupons were immersed in the compositions for about <NUM> (SiNx) to <NUM> (SiOx) minutes while stirring. The SiN test coupons were pretreated with <NUM>:<NUM> DHF in a beaker at room temperature for 3mins, rinsing and drying and afterwards to contact the test coupons with the etching composition for <NUM> minutes at <NUM>.

The segments were then rinsed for <NUM> minutes in a DI water bath or spray and subsequently dried using filtered nitrogen. The silicon nitride and silicon oxide etch rates were estimated from changes in the thickness before and after etching and was measured by spectroscopic ellipsometry (MG-<NUM>, Nano-View Co. , South Korea). Typical starting layer thickness was <NUM>Å for Si<NUM>N<NUM> and <NUM>Å for SiO<NUM>.

The following series of Tables show the evaluation of several aspects of the compositions evaluated.

The process conditions for Table <NUM> test coupons were <NUM> for <NUM> minutes.

The results in Table <NUM> show that, with the addition of various solvents, etching of SiO<NUM> was suppressed. Addition of DMSO decreased etch rates of both Si<NUM>N<NUM> and SiO<NUM> without change of selectivity. Addition of Sulfolane more decreased etch rate of SiO<NUM> with a selectivity increase to <NUM>. Addition of PG and DPGME which have -OH groups greatly suppressed the etching rate of SiO<NUM> with increases of selectivity to <NUM> and <NUM>, respectively. However, when PG and DPGME were added, the etchant became viscous and sticky after heating. Amount of PG and DPGME addition was reduced to <NUM> wt% to reduce etchant viscosity. The decrease in the etching of SiO<NUM> was smaller with <NUM> wt% than with <NUM> wt% addition. Since the etching of Si<NUM>N<NUM> was not significantly affected, etch selectivity was still higher than just <NUM>% H<NUM>PO<NUM>, but much lower than that with <NUM> wt% addition of PG and DPGME. Although the amount of additives were reduced to <NUM> wt%, the etchant solutions were still viscous and sticky.

The etching rates of Si<NUM>N<NUM> and SiO<NUM> decreased with addition of EG and Glycol. However, the suppression of etching of SiO<NUM> was not as huge as observed in PG and DPGME. Addition of α-terpineol did not significantly change etching rates of both Si<NUM>N<NUM> and SiO<NUM>. Finally, the gain of etch selectivity was not as huge as observed in PG and DPGME. With the addition of EG, bubbling occurred in the etchant solution. With the addition of glycol, the solution became sticky when the temperature was raised, but less than that of PG or DPGME.

The process conditions for contacting each composition with the coupons tested for which the results are reported in Table <NUM> were <NUM> for <NUM> minutes. SiN wafers were pretreated with DHF for 3mins and after rinsing and drying.

(NH<NUM>)<NUM>SiF<NUM> contains Si with a large amount of F, thus the etching rates were very fast. The SiO<NUM> film was completely removed in two minutes with <NUM> addition. With the addition of silicic acid and TEOS, etching rate of SiO<NUM> greatly decreased with selectivities of <NUM> and <NUM>, respectively. This is due to their similar chemical structures to SiO<NUM>. Without intending to be bound by a particular theory, silicic acid and TEOS may contribute to the formation of SiO<NUM> and reduce the etching of SiO<NUM>.

Si(OH)<NUM> → SiO<NUM> + <NUM><NUM>O (Equilibrium in water).

Si(OC<NUM>H<NUM>)<NUM> + <NUM><NUM>O → Si(OH)<NUM> + 4C<NUM>H<NUM>OH (hydrolysis).

Si(OH)<NUM> → SiO<NUM> + <NUM><NUM>O (condensation).

Since high etch selectivities were obtained with the addition of silicic acid and TEOS, HF (<NUM>) was added in the presence of silicic acid and TEOS to increase the etching rate of Si<NUM>N<NUM>. The addition of HF in silicic acid and TEOS increased the etching rate of SiO<NUM> twice. However, since the etching rate of Si<NUM>N<NUM> increased more, the selectivity increased to <NUM> and <NUM>. Addition of both HF and Si-based additives successfully increased etching rate of Si<NUM>N<NUM> with a high etch selectivity of Si<NUM>N<NUM> to SiO<NUM>. Thus far, etching rate of Si<NUM>N<NUM> at ~<NUM>Å/min and etch selectivity of <NUM> are the best.

For the results reported in Table <NUM>, the process for treating the SiN test coupons was to pretreat with <NUM>:100DHF in a beaker at room temperature for 3mins and after rinsing and drying to contact the test coupons with the etching composition for <NUM> minutes at <NUM>. The process for treating the SiOx test coupons was to contact the test coupons with each etching composition for <NUM> minutes at <NUM>.

With the decrease in silicic acid concentration from <NUM> to <NUM> wt%, Si<NUM>N<NUM> increased, but SiO<NUM> ER increased more, thus Si<NUM>N<NUM>/SiO<NUM> selectivity decreased. H<NUM>PO<NUM> + <NUM> wt% silicic acid increased SiO<NUM> ER by x20 and Si<NUM>N<NUM> ER by ~<NUM> %, as compared to H<NUM>PO<NUM> + <NUM> wt% silicic acid. It is concluded that the concentration of silicic acid should be around <NUM> wt% to have <NUM>:<NUM> etch selectivity. However, the silicic acid contained chemicals showed oxide regrowth (on the silicon oxide) causing a clogging problem (which means that the silicon nitride layer was blocked by the regrowth preventing the etching composition from reaching the silicon nitride layers on the patterned structure.

For the results reported in Table <NUM>, the process for treating the SiN test coupons was to pretreat with <NUM>:100DHF in a beaker at room temperature for 3mins and then after rinsing and drying to contact the test coupons with each etching composition for <NUM> minutes at <NUM>. The process for treating the SiOx test coupons was to contact the test coupons with each etching composition for <NUM> minutes at <NUM>.

With the <NUM> wt%, TMMS etch selectivity was higher than the target selectivity, <NUM>:<NUM>. H<NUM>PO<NUM> + <NUM> wt% TMMS did not meet selectivity <NUM>:<NUM>, because the ER of SiO<NUM> increased more. No oxide regrowth and clogging problem was observed on pattern structure by processing with TMMS contained chemicals.

For the results reported in Table <NUM>, the process for treating the SiN test coupons was to pretreat with <NUM>:100DHF in a beaker at room temperature for 3mins, rinsing and drying the test coupons and then contacting the test coupons with each etching composition for <NUM> minutes at <NUM>. The process for treating the SiOx test coupons was to contact the test coupons with each etching composition for <NUM> minutes at <NUM> without a pretreatment step.

As-prepared Examples YL-<NUM> and YL-<NUM> without A1 were transparent, but became slightly opaque after <NUM> stirring. Both became transparent after boiling at <NUM>. YL-<NUM> showed selectivity of <NUM>,<NUM>, which was higher than target selectivity, <NUM>:<NUM>. YL-<NUM> showed selectivity of <NUM>, which was lower than target because SiO<NUM> ER was x3 higher than YL-<NUM>. As-prepared, Example 119A was transparent but became slightly opaque after <NUM> stirring. It became transparent after boiling at <NUM> and it was still transparent after cooling down to RT. Example 119B contains <NUM> wt % TMMS, it was transparent at all four time points. Example 119A and B showed selectivity of <NUM>,<NUM> and <NUM>, respectively, which was lower than the target selectivity, <NUM>:<NUM>. As the concentration of TMMS added to H<NUM>PO<NUM> + <NUM> wt % TEPO decreased, both Si<NUM>N<NUM> and SiO<NUM> ER increased. Because increase in the SiO<NUM> ER was larger than that of Si<NUM>N<NUM> ER, etch selectivity decreased with lower TMMS concentration.

For the results reported in Table <NUM>, the process for treating the SiN test coupons was to pretreat with <NUM>:100DHF in a beaker at room temperature for 3mins and then after rinsing and drying the test coupons to contact the test coupons with each etching composition for <NUM> minutes at <NUM>. The process for treating the SiOx test coupons was to contact the test coupons with each etching composition for <NUM> minutes at <NUM> without a pretreatment step.

Example <NUM> was opaque and became cloudy after <NUM> stirring. It became transparent after boiling at <NUM> and it was still transparent after cooling down to RT. Example 119E was transparent but became cloudy after <NUM> stirring. It became transparent after boiling at <NUM> and it was still transparent after cooling down to RT. Example 119N was transparent but became opaque after <NUM> stirring. It became transparent after boiling at <NUM> and it was still transparent after cooling down to RT. Example <NUM> showed selectivity of <NUM>, which was lower than target selectivity. Example 119E showed selectivity of <NUM> which was higher than target selectivity, <NUM>:<NUM>. Example 119N showed selectivity of <NUM> which was higher than target selectivity, <NUM>:<NUM>. The added solvent with lower polarity showed better miscibility (ethyl acetate>ethanol>acetic acid), but Ex. 119E showed better selectivity, so we focused on studying the effects from alcohols in the following tests. In some embodiments, solvents having a polarity less than <NUM>, or less than <NUM> or less than <NUM> or less than <NUM> or less than <NUM> or less than <NUM> were preferred, where water has a polarity of <NUM>. Additionally or alternatively, in some embodiments, solvents having fewer than <NUM> carbons may be preferred or fewer than <NUM> carbons or fewer than <NUM> carbons.

Example <NUM> was slightly opaque and it became more opaque after stirring for <NUM>. It was still opaque and yellowish after boiling at <NUM> and even after cooling down to room temperature. Example 119P was transparent but became opaque after stirring for <NUM> hours. It became transparent after boiling at <NUM> and it was still transparent after cooling down to room temperature (RT). Example 119Q was transparent and it was still transparent after stirring for <NUM> hours. It was also transparent, but became slightly yellowish after boiling at <NUM> and cooling down to RT. Example <NUM> showed selectivity of <NUM>, which was higher than target selectivity, <NUM>:<NUM>. Example 119P showed selectivity of <NUM>Å/min, which was lower than target selectivity. Example 119Q showed selectivity of <NUM>Å/min, which was higher than target selectivity, <NUM>:<NUM>. Example 119Q met the target selectivity and showed good miscibility. Additionally, the performance of Example 119Q on a patterned structure showed that no thinning of SiOx layer and no oxide regrowth while SiN layer is totally removed.

Claim 1:
An etching solution suitable for the selective removal of silicon nitride over silicon oxide from a microelectronic device, which comprises:
water;
aqueous phosphoric acid solution;
trimethoxymethylsilane; and
a hydroxyl group-containing water-miscible solvent which is a saturated aliphatic monohydric alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, isopropyl alcohol, <NUM>-butanol, <NUM>-butanol, isobutyl alcohol, tert-butyl alcohol, <NUM>-pentanol, t-pentyl alcohol, and <NUM>-hexanol.