WO2012154498A2

WO2012154498A2 - Removal of metal impurities from silicon surfaces for solar cell and semiconductor applications

Info

Publication number: WO2012154498A2
Application number: PCT/US2012/036329
Authority: WO
Inventors: Li-Min CHEN (Raymond); Emanuel I. Cooper; Jeffrey A. Barnes; Jun Liu; Laisheng SUN; Thomas Baum; Michael Korzenski; Ben LOCHTENBERG; Lawrence Dubois
Original assignee: Advanced Technology Materials, Inc.
Priority date: 2011-05-06
Filing date: 2012-05-03
Publication date: 2012-11-15
Also published as: TW201308627A; WO2012154498A3

Abstract

Removal compositions and processes for removing at least one metal impurity from a substrate (e.g., a silicon-containing substrate) having same thereon. Advantageously, the compositions remove metal impurities, e.g., iron, from silicon-containing substrates used as semiconductor devices and solar cell devices.

Description

REMOVAL OF METAL IMPURITIES FROM SILICON SURFACES FOR SOLAR CELL AND SEMICONDUCTOR APPLICATIONS

FIELD

[0001] The present invention generally relates to compositions and processes useful for the removal of metal contamination from a silicon-containing substrate or article having said metal thereon as well as to minimize metal impurities that may impact the fabrication process.

DESCRIPTION OF THE RELATED ART

[0002] The majority (>80%) of photovoltaic cells are based on either single or multi-crystalline silicon substrates, with the single-crystalline ones delivering 1-2% higher efficiencies than their multi- crystalline counterparts. The cell performance and degradation depends in large measure on silicon crystallite size, amount and distribution of impurities, surface passivation, etc. The extent of these impurities is determined by the quality of the silicon-containing starting materials, the cleanliness of the furnace(s), the heating and cooling cycle(s), etc. and, of course, the fabrication techniques employed.

[0003] Metals (e.g., Fe, Cr, Cu, and Ni) segregate much more effectively than shallow dopants (e.g., B and P) and are known to severely affect the minority carrier diffusion length and therefore the solar cell efficiency (Istratov, A.A., et al., Mat. Sci. Eng. B, 134 (2006) 282-286). For a given impurity level, metals may be dispersed throughout the silicon or concentrated in fewer, larger clusters at grain boundaries and/or at intragranular defects as a result of previous fabrication processes (e.g., ingot growth, wire-saw, contact with chemical solutions, etc.). Although carrier lifetimes can vary by an order of magnitude across even a few millimeters of a multicrystalline silicon substrate (Proc. 22nd European PV Solar Energy Conf. (2007) Milan 1519), only a small fraction of the metal atoms (<10%) are actually "active" controlling the minority carrier diffusion length (Istratov, A.A., et al., J. Appl. Phys. 94 (2003) 6552-6559). Note that minority carrier recombination at "clean" dislocations is relatively weak, but increases dramatically when transition metal precipitates are present. Metals may be elemental (interstitial defects) or in the form of silicides, oxides/silicates, and/or borides.

[0004] For example, in order to manufacture a high-performance photovoltaic cell from mono/multi- crystalline silicon substrates, it must be etched after the saw-wafering process. This etch removes both the surface and sub-surface damage caused by the sawing process and creates surface roughness to minimize optical reflections. This texturing process is followed by phosphorous (typically POCl₃ or H₃P0₄) or boron doping and interdiffusion by heating to ~900°C to form a p-n junction. Alternatively, phosphorous or boron may be added by ion implantation. Disadvantageously, metal precipitates may dissolve in the silicon and reduce the carrier lifetime (see, for example, Macdonald, Proc. 29th IEEE Photovoltaics Specialist Conf. (2002) and Schwaderer, Proc. 22nd European PV Solar Energy Conf. (2007) Milan), and the gettering process to de-activate these recombination centers from the impurities are relatively ineffective, particularly for multi- crystalline silicon. Thus there is a need to remove as much trace metal impurities as possible in order to optimize the performance of mono/multi-crystalline silicon photovoltaic cells.

[0005] The phosphorous doping step forms a phosphosilicate glass (PSG) layer on the top surface of the silicon substrate. This PSG layer contains a large amount of electrically-inactive phosphor dopants and creates a so-called "dead layer" that is not fully transparent and also contains a large amount of recombination centers that needs to be removed. The current industry standard of removing this PSG layer is submerging the wafer in a HF bath for a few minutes. (A. F. Stassen et al., Photovoltaics International (2010)).

[0006] Recent research has shown that the recombination activity per metal atom for clusters is reduced compared to that of interstitially dissolved metals (see, for example, Buonassissi, et al., Nature Mat, 4 (2005) 676-679; Istratov, A.A., et al., Mat. Sci. Eng. B, 134 (2006) 282-286). Nevertheless, there is a direct correlation between impurity precipitates and regions of low light- induced current (McHugo, S.A., et al., J. Appl. Phys. 89 (2001) 4282-4288). Subsequent processing of the silicon substrate may change the quantity and distribution of these metals and therefore their removal may improve solar cell performance (see, for example, Proc. 29th IEEE Photovoltaics Specialist Conf. (2002) 285, Bentzen, A., et al., J. Appl. Phys. 99 (2006) 093509-1-093509-6, Schwaderer, Proc. 22nd European PV Solar Energy Conf. (2007) Milan). Having said that, iron precipitates in the form of oxides or silicates are highly stable and are not removed using standard silicon processing and thus the recombination lifetime at these sites does not change dramatically (McHugo, S.A., et al., J. Appl. Phys. 89 (2001) 4282-4288; Bentzen, A., et al., J. Appl. Phys. 99 (2006) 093509-1-093509-6).

[0007] Further, once removed from a surface, these metal surface impurities /contaminants can be re-deposited onto the same (or a different) surface, cannot be simply washed off by a rinse and tend to be carried over into the diffusion process, thus deteriorating solar cell performance.

[0008] The well-known RCA-clean (Surface Clean-2 or SC-2; a mixture of HC1 and hydrogen peroxide) is commonly used in the semiconductor industry as a final cleaning step to remove metal impurities from bare silicon wafers. The hydrogen peroxide oxidizes the metal impurities, while the hydrochloric acid serves as a metal ion chelator. Due to the instability of the mixture, it must be formulated point-of-use (POU) and has a short bath-life as the chloride ions initiate decomposition of the peroxide. More typically in the solar industry a mixture of HF and HC1 is used as the final cleaning solution. While low-cost, its performance is not very effective and metal impurities are often available to deposit back on the surface. Clearly a stable, use-as-is, metal contamination cleaner would be advantageous as long as the cost of ownership is kept low and performance requirements are met. [0009] Accordingly, there is a continuing need in the art to provide a composition and method that effectively removes trace metal impurities from a substrate, e.g., a silicon-containing substrate, as well as prevents re-adhesion of said metal impurity at said substrate surface. In other words, the composition must effectively remove metal impurities from a surface as well as sequester the metal impurities within the removal bath. In addition, the incorporation of metal chelating agents also has the advantage of extending bath life to lower the cost of ownership.

SUMMARY

[0010] Compositions and processes are disclosed herein, wherein said compositions and processes are useful for the removal of trace metal impurities from a substrate (e.g., a silicon- containing substrate) having said material thereon, as well as a process for sequestering metal impurities in the removal bath so as to substantially minimize re-adhesion of the metal impurities at a substrate surface.

[0011] In one aspect, a method of removing metal impurities from a substrate is described, said method comprising contacting the substrate comprising said metal impurities with a metal impurity removal composition to substantially remove said metal impurities from the substrate, wherein said metal impurity removal composition comprises at least one etchant, at least one chelating agent, and water.

[0012] In another aspect, a method of removing metal impurities from a substrate is described, said method comprising contacting the substrate comprising said metal impurities with a metal impurity removal composition to substantially remove said metal impurities from the substrate, wherein said metal impurity removal composition comprises at least one etchant, at least one chelating agent, at least one oxidizing agent, at least one surfactant, and water.

[0013] In still another aspect, a method of removing metal impurities from a liquid is described, said method comprising combining a liquid comprising said metal impurities with a composition to substantially sequester and remove said metal impurities from the liquid, wherein the composition comprises at least one etchant, at least one chelating agent, water, optionally at least one chloride salt, optionally at least one surfactant, optionally at least one oxidizing agent, optionally a buffer system, optionally at least one capping agent, and optionally at least one fluoride activity agent.

[0014] Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 corresponds to the concentration of Cu, Fe, Na and Ti in compositions following the immersion of "as-cut" wafers in said compositions.

[0016] Figure 2 corresponds to the schematic of the process of preparing the coupon for lifetime measurements.

[0017] Figure 3 A illustrates the QSSPC effective lifetime of the coupons following immersion in the respective compositions.

[0018] Figure 3B illustrates the normalized lifetime results whereby each composition was normalized relative to SC-2.

[0019] Figure 3C illustrates the implied Voc of the coupons based on QSSPC lifetime measurements.

[0020] Figure 4 illustrates the lifetime of coupons following immersion in the respective compositions.

[0021] Figure 5 illustrates the results of the TXRF analysis of textured silicon wafers before and after immersion in the compositions described herein.

[0022] Figure 6 illustrates the results of the ICP analysis in the compositions subsequent to immersion of textured silicon wafers therein.

[0023] Figure 7 illustrates the results when as-cut or textured silicon surfaces are cleaned using the compositions described herein.

[0024] Figure 8 illustrates the results when a coupon comprising a PSG layer is immersed in a composition described herein relative to the present industry standard.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS THEREOF

[0025] The present invention generally relates to compositions and processes useful for the removal of trace metal impurities from a substrate having said impurities thereon. More particularly, the present invention relates to compositions and processes useful for the removal of metal impurities from silicon-containing substrates (e.g., microelectronic device substrates, solar cell substrates, etc.) having said impurities thereon. Further, the present invention relates to compositions and processes for sequestering metal impurities in solution so as to substantially minimize the adhesion or re- adhesion of metal impurities at a substrate surface (e.g., a silicon-containing substrate surface). Preferably, the substrate surface is not damaged during the metal impurity removal and the surface remains passivated to subsequent oxidation.

[0026] As defined herein, a "substrate" corresponds to a microelectronic device or a solar cell device.

[0027] "Microelectronic device" corresponds to semiconductor substrates, phase change memory devices, and microelectromechanical systems (MEMS), manufactured for use in microelectronic, integrated circuit, or computer chip applications. It is to be understood that the terms "microelectronic device," "microelectronic substrate" and "microelectronic device structure" are not meant to be limiting in any way and include any substrate or structure that will eventually become a microelectronic device or microelectronic assembly. The microelectronic device can be patterned, blanketed, a control and/or a test device.

[0028] "Solar cell device" corresponds to flat panel displays, solar panels and other products including solar substrates and photovoltaics, manufactured for use in the solar industry.

[0029] The "silicon-containing substrate" can comprise, consist of, or consist essentially of bare silicon; polysilicon; polycrystalline silicon (doped or undoped); mono crystalline silicon (doped or undoped); amorphous silicon, and combinations thereof. It should be appreciated that the term "single crystalline Si" or "single crystal Si" is synonymous with the term "monocrystalline Si." Further, it should be appreciated that the term "polycrystalline Si" is synonymous with the term "multicrystalline Si." The silicon-containing substrate can be as-cut, textured, patterned, doped or undoped, as readily understood by the person skilled in the art. The silicon can be commercially available solar grade or electronic-grade.

[0030] As defined herein, a "capping agent" corresponds to a component which disperses and/or stabilizes metal particles and/or metal ions, hence aiding in the removal of same from a surface. Although not wishing to be bound by theory, it is thought that capping agents work sterically, electrosterically or electrostatically. Steric effects correspond to the obstruction effect caused by the adsorption of non-ionic bulky species (e.g., polymers, fatty acids, etc.) at the surface of particles, thereby forming a layer that prevents said particles from approaching one another. Electrosteric effects correspond to the adsorption of charged species at the surface of particles which lead to a mixed electrosteric/ electrostatic mechanism.

[0031] As defined herein, "chelating agent" includes those compounds that are understood by one skilled in the art to be complexing agents, chelating agents, sequestering agents, and combinations thereof. Chelating agents will chemically combine with or physically hold the metal atom and/or metal ion to be removed using the compositions described herein.

[0032] As used herein, "about" is intended to correspond to + 5 % of the stated value.

[0033] As defined herein, "substantial removal" or "substantially remove" corresponds to the removal of at least 90 wt.% of the metal impurities desired to be removed, more preferably, at least 95 wt.%, even more preferably, at least 97 wt.%, even more preferably, at least 98 wt.%, and most preferably at least 99 wt.%.

[0034] As defined herein, "substantially devoid" corresponds to less than about 1 wt. %>, more preferably less than 0.5 wt. %>, and most preferably less than 0.1 wt. % of the composition, based on the total weight of said composition.

[0035] As defined herein, a "metal impurity" corresponds to elemental metal, metal ions, metal silicides, metal oxides, metal silicates, metal borides, and any combination thereof. Metals include Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Te, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg.

[0036] Removal compositions may be embodied in a wide variety of specific formulations, as hereinafter more fully described. [0037] 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 0.001 weight percent, based on the total weight of the composition in which such components are employed.

[0038] In a first aspect, an aqueous composition is described, said aqueous composition comprising at least one etchant, at least one chelating agent, optionally at least one oxidizing agent, optionally at least one chloride salt, optionally at least one surfactant, optionally a buffer system, optionally at least one capping agent, and optionally at least one fluoride activity agent. The composition is useful for removing metal impurities from the surface of a substrate. The composition is also useful for sequestering metal impurities from a liquid comprising same, for example, a bath comprising metal impurities which can be removed prior to reuse or disposal. Advantageously, when the metal impurities are removed from the liquid, the metal impurities are no longer available to adhere or re-adhere to the surface of a substrate and the bath life (loading) is extended.

[0039] In one embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, and water. In another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, and at least one chloride salt. In another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, and at least one surfactant. In yet another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, at least one chloride salt, and at least one surfactant. In yet another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, at least one surfactant, and at least one capping agent. In yet another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, at least one surfactant, at least one chloride salt, and at least one capping agent. In still another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, and at least one capping agent. In another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, water, at least one chloride salt, and at least one capping agent. In every one of the foregoing embodiments, an oxidizing agent can be added. Moreover, in every one of the foregoing embodiments, a buffer system can be added to achieve and maintain the desired pH. Further, at least one fluoride activity agent can be added at any of the foregoing embodiments.

[0040] The compositions of the first aspect have a pH value in a range from about -1 to about 7, more preferably about 2.5 to about 4.5, most preferably about 3 to about 3.5, when diluted 20: 1 with deionized water.

[0041] Although not wishing to be bound by theory, it is thought that the mechanism of action of the etchant is to etch of the substrate surface slightly, thereby assisting with the removal of metal impurities. Etchants contemplated herein include, but are not limited to, fluorides, ammonium salts thereof, and any combination thereof, including at least one of: hydrogen fluoride (HF); xenon difluoride (XeF₂); ammonium fluoride (NH₄F); tetraalkylammonium fluoride (NR₄F); alkyl hydrogen fluoride (NRH₃F); ammonium hydrogen bifluoride (NH₅F₂); dialkylammonium hydrogen fluoride (NR₂H₂F); trialkylammonium hydrogen fluoride (NR₃HF); trialkylammonium trihydrogen fluoride (NR₃:3HF); anhydrous hydrogen fluoride pyridine complex; anhydrous hydrogen fluoride triethylamine complex, where R may be the same as or different from one another and is selected from the group consisting of straight-chained or branched Ci-C₆ alkyl groups (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl). Preferably, the etchant comprises hydrogen fluoride, ammonium chloride, hydrogen chloride, or any combination thereof. Even more preferably, the etchant comprises hydrogen fluoride or ammonium fluoride.

[0042] At least one chelating agent is added to chelate/complex metal impurities in the baths or on the substrate surface. Chelating agents contemplated herein include, but are not limited to, hydroxyethylidene diphosphonic acid (HEDP), ethylendiamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DPTA), (1,2- cyclohexylenedinitrilo)tetraacetic acid (CDTA), glycine, salicylic acid, sulfosalicylic acid, glucoronic acid, tartaric acid, citric acid, ammonium gluconate, humic acid, fulvic acid, iminodiacetic acid, hydroxyethyl iminodiacetic acid (HEIDA), ascorbic acid, gallic acid, acetic acid, benzoic acid, alanine, ammonium citrate tribasic, pyrophosphoric acid, Dequest 2000, Dequest 2010, Dequest 2060s, Dequest 2000EG, Dequest 7000 (2-phosphonobutane-l,2,4-tricarboxylic acid (PBTCA)), nitrilo-tris(methylenephosphonic acid) (NTMPA), ethylene diamine tris(methylenephosphonic acid) (EDTMPA), serine, proline, leucine, alanine, asparagine, aspartic acid, glutamine, valine, and lysine, maleic acid, oxalic acid, malonic acid, succinic acid, phosphonic acid, l -hydroxyethane-1,1 - diphosphonic acid, nitrilo-tris(methylenephosphonic acid), nitrilotriacetic acid, uric acid, propylenediamine tetraacetic acid, 2-hydroxypyridine 1 -oxide, methane sulfonic acid, (MSA), formamidinesulfmic acid (FASA), tetraethylenetetramine (TETA), tetraethylenepentamine (TEPA), phenanthrolines, bypyridyls, and combinations thereof. Preferably, the at least one chelating agent comprises a phosphonic acid derivative, more preferably HEDP. In another preferred embodiment, the at least one chelating agent comprises a carboxylic acid such as oxalic acid.

[0043] Surfactants contemplated include nonionic, anionic, cationic (based on quaternary ammonium cations) and/or zwitterionic surfactants. For example, suitable non-ionic surfactants may include fluoroalkyl surfactants, ethoxylated fluorosurfactants, polyethylene glycols, polypropylene glycols, polyethylene or polypropylene glycol ethers, carboxylic acid salts, dodecylbenzenesulfonic acid or salts thereof, polyacrylate polymers, dinonylphenyl polyoxyethylene, silicone or modified silicone polymers, acetylenic diols or modified acetylenic diols, alkylammonium or modified alkylammonium salts, and alkylphenol polyglycidol ether, as well as combinations comprising at least one of the foregoing. In a preferred embodiment, the nonionic surfactant may be an ethoxylated fluorosurfactant such as ZONYL® FSO-100 fluorosurfactant (DuPont Canada Inc., Mississauga, Ontario, Canada). Anionic surfactants contemplated in the compositions of the present invention include, but are not limited to, fluorosurfactants such as ZONYL® UR and ZONYL® FS-62 (DuPont Canada Inc., Mississauga, Ontario, Canada), sodium alkyl sulfates such as sodium ethylhexyl sulfate (NIAPROOF® 08), ammonium alkyl sulfates, alkyl (C io-Cis) carboxylic acid ammonium salts, sodium sulfosuccinates and esters thereof, e.g., dioctyl sodium sulfosuccinate, alkyl (Cio-Cis) sulfonic acid sodium salts, and the di-anionic sulfonate surfactants DowFax™ (The Dow Chemical Company, Midland, Mich., USA) such as the alkyldiphenyloxide disulfonate DowFax™3B2. Cationic surfactants contemplated include alkylammonium salts such as cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium hydrogen sulfate. Suitable zwitterionic surfactants include ammonium carboxylates, ammonium sulfates, amine oxides, N-dodecyl-N,N-dimethylbetaine, betaine, sulfobetaine, alkylammoniopropyl sulfate, and the like. Alternatively, the surfactants may include water soluble polymers including, but not limited to, polyethylene glycol (PEG), polyethylene oxide (PEO), polypropylene glycol (PPG), polyvinyl pyrrolidone (PVP), cationic polymers, nonionic polymers, anionic polymers, hydroxyethyl cellulose (HEC), acrylamide polymers, poly(acrylic acid), carboxymethyl cellulose (CMC), sodium carboxymethylcellulose (Na CMC), hydroxypropylmethylcellulose, polyvinylpyrrolidone K30, BIOCARE™ polymers, DOW™ latex powders (DLP), ETHOCEL™ ethylcellulose polymers, KYTAMER™ PC polymers, METHOCEL™ cellulose ethers, POLYOX™ water soluble resins, SoftCAT™ polymers, UCARE™ polymers, UCON™ fluids, PPG-PEG-PPG block copolymers, PEG-PPG-PEG block copolymers, ethylene oxide/propylene oxide block copolymers such as Pluronic® (BASF®) products (e.g., Pluronic®17R2, Pluronic®17R4, Pluronic®31Rl and Pluronic®25R2), and combinations thereof. The water soluble polymers may be short-chained or long-chained polymers and may be combined with the nonionic, anionic, cationic, and/or zwitterionic surfactants of the invention. In addition, the surfactants can include amphiphilic compounds such as tetraglyme, acetylacetone, hexafluoroacetylacetone, 2- butoxyethanol and the glycol ethers such as diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether (i.e., butyl carbitol), triethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether (DPGME), tripropylene glycol methyl ether, dipropylene glycol dimethyl ether, dipropylene glycol ethyl ether, propylene glycol n-propyl ether (PPGPE), dipropylene glycol n-propyl ether (DPGPE), tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, and combinations thereof. Preferably, the surfactants comprise di-anionic sulfonate surfactants, PPG-PEG-PPG block copolymers, PEG-PPG-PEG block copolymers, tetraglyme, or combinations thereof. When present, the amount of surfactant may be in a range from about 0.01 wt % to about 15 wt %, based on the total weight of the composition.

[0044] In one preferred embodiment, the water is deionized.

[0045] Oxidizing agents contemplated herein include, but are not limited to, hydrogen peroxide (H₂0₂), nitric acid (HN0₃), sulfuric acid (H₂S0₄), iodic acid (HI0₃); nitromethane; aromatic nitro- containing compounds such as nitrobenzene, nitrobenzoic acid, nitrophenols, having one, two or three nitro substituents; inorganic peracids such as perboric acid, perchloric acid, periodic acid, persulfuric acid, perboric acid, peroxomonosulfuric acid, peracetic acid, and salts thereof; peroxydiphosphoric acid; peroxydisulfuric acid; FeCl₃ (both hydrated and unhydrated); oxone (2KHSO5 KHSO4 K2SO4); ammonium polyatomic salts (e.g., ammonium peroxomonosulfate, ammonium chlorite (NH₄C10₂), ammonium chlorate (NH₄CIO₃), ammonium iodate (NH₄IO₃), ammonium perborate (NH₄BO₃), ammonium perchlorate (NH₄CIO₄), ammonium periodate (NH₄IO₃), ammonium persulfate ((NH₄)₂S₂0₈), ammonium hypochlorite (NH₄CIO)); sodium polyatomic salts (e.g., sodium persulfate (Na₂S₂0₈), sodium hypochlorite (NaCIO)); potassium polyatomic salts (e.g., potassium iodate (KJO₃), potassium permanganate (KMn0₄), potassium persulfate, potassium persulfate (K₂S₂0₈), potassium hypochlorite (KCIO)); nitric acid (HNO₃); tetramethylammonium polyatomic salts (e.g., tetramethylammonium chlorite ((N(CH₃)₄)C10₂), tetramethylammonium chlorate ((N(CH₃)₄)C10₃), tetramethylammonium iodate ((N(CH₃)₄)I0₃), tetramethylammonium perborate ((N(CH₃)₄)B0₃), tetramethylammonium perchlorate ((N(CH₃)₄)C10₄), tetramethylammonium periodate ((N(CH₃)₄)I0₄), tetramethylammonium persulfate ((N(CH₃)₄)S₂08)); tetrabutylammonium polyatomic salts (e.g., tetrabutylammonium peroxomonosulfate); ferric nitrate (Fe(N0₃)₃); urea hydrogen peroxide ((CO(NH₂)₂)H₂0₂); N-methylmorpholine-N-oxide (NMMO); trimethylamine-N-oxide; triethylamine- N-oxide; pyridine-N-oxide; p-benzoquinone; p-toluquinone; isatin; alloxane; ninhydrin; and combinations thereof. The oxidizing agent may be introduced to the composition at the manufacturer, prior to introduction of the composition to the substrate, or alternatively at the substrate, i.e., in situ. Preferably, the oxidizing agent comprises nitric acid.

[0046] It is known in the art that HF in the presence of metallic contaminants, including copper, causes pitting of microelectronic device substrates including silicon. To substantially eliminate this detrimental pitting effect, chloride sources such as, but not limited to, hydrochloric acid, alkali metal chlorides (e.g., NaCl, KCo, RbCl, CsCl, etc.), alkaline earth metal chlorides (e.g., MgCl₂, CaCl₂, SrCl₂, BaCl₂, etc.), ammonium chloride, alkylammonium chlorides having the formula NR'R²R³R⁴C1 (where R¹, R², R³ and R⁴ may be the same as or different from one another and may be H or a branched or straight- chained Ci-C₆ alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, or hexyl)) and combinations thereof, may be added to the removal composition to minimize pitting of the microelectronic device substrate during the reclamation process. Preferably, the chloride source comprises ammonium chloride. [0047] Capping agents contemplated herein include, but are not limited to, cysteine, 2- mercaptobenzimidazole, 1 -butanethiol, ammonium citrate tribasic, cetyltrimethylammonium bromide (CTAB), polyacrylic acid, polycarboxylic acids, polyethyleneimine, oxalic acid, malonic acid, succinic acid, glutaric acid, phthalic acid, maleic acid, citric acid, and combinations thereof. When present, the amount of capping agent may be in a range from about 0.01 wt % to about 10 wt %, based on the total weight of the composition.

[0048] Buffering agents are well known in the art and can include, for example, phosphate buffer such as monosodium phosphate/disodium phosphate or monopotassium phosphate/dipotassium phosphate.

[0049] Although not wishing to be bound by theory, fluoride activating agents are thought to self-passivate the surface thus controlling the etch rate of said surface. For example, organic acids such as boric acid and citric acid, or the salts thereof (e.g., sodium, potassium, ammonium salts) can be added to the composition disclosed herein to reduce the etch rate and self-passivate the surface. When present, the amount of fluoride activating agent may be in a range from about 0.01 wt % to about 5 wt %, based on the total weight of the composition.

[0050] The composition of the first aspect is preferably substantially devoid of organic solvents including ethylene groups, e.g., ethylene, diethylene, triethylene, etc., and other HAP organic solvents.

[0051] In a preferred embodiment, the composition of the first aspect comprises, consists of, or consists essentially of at least one etchant, at least one chloride source, at least one chelating agent, and water. In still another preferred embodiment, the composition of the first aspect comprises, consists of, or consists essentially of at least one etchant, at least one chloride source, at least one phosphonic acid chelating agent, and water. In another preferred embodiment, the composition of the first aspect comprises, consists of, or consists essentially of at least one etchant, at least one chloride source, at least one chelating agent, at least one surfactant, and water. In another embodiment, the composition of the first aspect comprises, consists of, or consists essentially of at least one etchant, at least one chloride source, at least one phosphonic acid chelating agent, at least one surfactant, and water. In yet another preferred embodiment, the composition of the first aspect comprises, consists of, or consists essentially of HF, ammonium chloride, HEDP, and water. An oxidizing agent such as hydrogen peroxide may be introduced to the composition at the manufacturer, prior to introduction of the composition to the device wafer, or alternatively at the device wafer, i.e., in situ.

[0052] The composition of the first aspect may further include metal impurities. Preferably, the metal impurities are sequestered in the composition and the composition remains viable for its intended use.

[0053] In one embodiment, the compositions of the first aspect are formulated in the following concentrated embodiments, wherein all percentages are by weight, based on the total weight of the formulation: component of % by weight preferably (% by weight) most preferably (% by weight)

etchant about 0.01% to about about 2% to about 40% about 5% to about 30%

50%

chelating agent(s) about 0.01% to about about 0.1% to about 20% about 2% to about 10%

25%

water about 25% to 99.9% about 40% to 98% about 60% to 95% surfactant(s) 0 to about 15% 0 to about 5% 0 to about 4% chloride source(s) 0 to about 25% about 0.1% to about 10% about 1% to about 10% capping agent(s) 0 to about 10% 0 to about 5% 0 to about 2% fluoride activity 0 to about 5% 0 to about 3% 0 to about 1% agent(s)

oxidizing agent(s) 0 to about 20% 0 to about 5% Oto about 2%

The concentrated embodiment can optionally include about 0.01 % to about 20%o, more preferably about 1 %> to about 15%> by weight of at least one oxidizing agent that may be added prior to and/or at the removal locus.

[0054] In each embodiment of the first aspect, the composition can be substantially devoid of at least one of nitric acid, sulfuric acid, lactams (e.g., piperidones and/or pyrrolidones), supercritical fluids, amines, polymers prepared by the polycondensation of at least one aldehyde and at least one aromatic compound, and abrasive material typically used during CMP processing prior to contact of the compositions with the substrate.

[0055] In a second aspect, an aqueous composition is described, said aqueous composition comprising at least one chelating agent, at least one oxidizing agent, optionally at least one chloride salt, optionally at least one etchant, optionally at least one surfactant, optionally a buffer system, and optionally at least one capping agent. When the composition of the second aspect includes a fluoride etchant, a fluoride activity agent can be included, as described herein. The composition is useful for removing metal impurities, i.e., trace metal impurities, from the surface of a substrate. The composition is also useful for sequestering metal impurities from a liquid comprising same, for example, a bath comprising metal impurities which can be removed prior to reuse or disposal. Advantageously, when the metal impurities are removed from the liquid, the metal impurities are no longer available to adhere or re-adhere to the surface of a substrate and the bath life (loading) is extended.

[0056] In one embodiment, the composition of the second aspect comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, at least one oxidizing agent, and water. In another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, at least one oxidizing agent agent, water, and at least one chloride salt. In another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, at least one oxidizing agent, water, and at least one surfactant. In yet another embodiment, the composition comprises, consists of, or consists essentially of at least one etchant, at least one chelating agent, at least one oxidizing agent, water, at least one chloride salt, and at least one surfactant. In every one of the foregoing embodiments, a buffer system can be added to achieve and maintain the desired pH.

[0057] The etchant(s), chelating agent(s), oxidizing agent(s), chloride salt(s), and surfactant(s) for the composition of the second aspect were previously enumerated with regards to the composition of the first aspect.

[0058] The compositions of the second aspect have a pH value in a range from about 0 to about 7, more preferably about 2.5 to about 4.5, most preferably about 3 to about 3.5, when diluted 20: 1 with deionized water.

[0059] The composition of the second aspect is preferably substantially devoid of organic solvents including ethylene groups, e.g., ethylene, diethylene, triethylene, etc., and other HAP organic solvents. In each embodiment of the second aspect, the composition can be substantially devoid of at least one of sulfuric acid, lactams (e.g., piperidones and/or pyrrolidones), supercritical fluids, amines, polymers prepared by the polycondensation of at least one aldehyde and at least one aromatic compound, and abrasive material typically used during CMP processing prior to contact of the compositions with the substrate.

[0060] In a particularly preferred embodiment, the composition of the second aspect comprises, consists of, or consists essentially of HEDP and hydrogen peroxide. In another preferred embodiment, the composition of the second aspect comprises, consists of, or consists essentially of HF, HN0₃, oxalic acid, water, and tetraglyme. In still another preferred embodiment, the composition of the second aspect comprises, consists of, or consists essentially of HF, HNO₃, oxalic acid, water and dipropylene glycol propyl ether.

[0061] The composition of the second aspect may further include metal impurities. Preferably, the metal impurities are sequestered in the composition and the composition remains viable for its intended use.

[0062] In one embodiment, the compositions of the second aspect are formulated in the following concentrated embodiments, wherein all percentages are by weight, based on the total weight of the formulation: component of % by weight preferably (% by weight) most preferably (% by weight)

chelating agent(s) about 0.01% to about about 0.1 % to about 30% about 1% to about 10%

50%

oxidizing agent(s) about 0.01% to about about 0.1 % to about 30% about 1% to about 10%

50%

Etchant(s) about 0.01% to about about 0.1 % to about 10% about 0.5%o to about 5%> 25%

Water about 1 % to about about 10% to 99% about 70% to 97.5%

99.9%

surfactant(s) 0 to about 15% 0 to about 12% 0 to about 12% chloride source(s) 0 to about 25% 0 to about 10% 0 to about 10% capping agent(s) 0 to about 10% 0 to about 5% 0 to about 2%

[0063] In one embodiment, the composition of the second aspect is used to remove trace metal impurities from a substrate (e.g., a microelectronic device or a solar cell device). In another embodiment, the composition of the second aspect is used to sequester metal impurities present in a solution. It should be appreciated by the skilled artisan that the composition of the second aspect may be used to simultaneously remove metal impurities from a substrate and sequester metal impurities in a solution. Advantageously, due to the low viscosity and low surface energy of the compositions described herein, the composition can easily penetrate small features and grain boundaries thereby reaching metal impurities in the substrate (i.e., impregnated within the substrate). Further, the compositions are easily rinsed off the substrate using water (e.g., deionized water)

[0064] The compositions described herein are easily formulated by simple addition of the respective ingredients and mixing to homogeneous condition. Furthermore, the compositions may be readily formulated as single-package formulations or multi-part formulations that are mixed at the point of use. The individual parts of the multi-part formulation may be mixed at the tool, in a storage tank upstream of the tool, or both. The concentrations of the respective ingredients may be widely varied in specific multiples of the composition, e.g., more dilute or more concentrated, and it will be appreciated that the compositions can variously and alternatively comprise, consist or consist essentially of any combination of ingredients consistent with the disclosure herein.

[0065] Concentrated formulations of the compositions described herein are contemplated with low amounts of water, or alternatively without water, wherein water may be added prior to use to form the compositions. The concentrated formulations may be diluted in a range from about 1 : 10 to 1000: 1 solvent to concentrate, wherein the solvent can be water.

[0066] A third aspect relates to a kit including, in one or more containers, one or more components adapted to form the compositions described herein. In one embodiment, the kit may include, in one or more containers, at least one etchant, at least one chelating agent, optionally at least one oxidizing agent, optionally at least one chloride salt, optionally at least one surfactant, optionally a buffer system, optionally at least one capping agent, and optionally at least one fluoride activity agent for combining as is or with diluent (e.g., water) at the fab. Alternatively, the kit may include at least one etchant, at least one chelating agent, at least one chloride salt, and water for combining as is or with diluent (e.g., water) at the fab. In another alternative, the kit may include at least one etchant, at least one chelating agent, at least one chloride salt, at least one surfactant, and water for combining as is or with diluent (e.g., water) at the fab. In still another alternative, the kit may include at least one etchant, at least one chelating agent, at least one oxidizing agent, at least one surfactant, and water for combining as is or with diluent (e.g., water) at the fab.

[0067] The containers of the kit should be chemically rated to store and dispense the component(s) contained therein. For example, the containers of the kit may be NOWPak® containers (Advanced Technology Materials, Inc., Danbury, Conn., USA). The one or more containers which contain the components of the removal composition preferably include means for bringing the components in said one or more containers in fluid communication for blending and dispense. For example, referring to the NOWPak® containers, gas pressure may be applied to the outside of a liner in said one or more containers to cause at least a portion of the contents of the liner to be discharged and hence enable fluid communication for blending and dispense. Alternatively, gas pressure may be applied to the head space of a conventional pressurizable container or a pump may be used to enable fluid communication. In addition, the system preferably includes a dispensing port for dispensing the blended composition to a process tool.

[0068] Substantially chemically inert, impurity-free, flexible and resilient polymeric film materials, such as high density polyethylene, are preferably used to fabricate the liners for said one or more containers. Desirable liner materials are processed without requiring co-extrusion or barrier layers, and without any pigments, UV inhibitors, or processing agents that may adversely affect the purity requirements for components to be disposed in the liner. A listing of desirable liner materials include films comprising virgin (additive-free) polyethylene, virgin polytetrafluoroethylene (PTFE), polypropylene, polyurethane, polyvinylidene chloride, polyvinyl chloride, polyacetal, polystyrene, polyacrylonitrile, polybutylene, and so on. Preferred thicknesses of such liner materials are in a range from about 5 mils (0.005 inch) to about 30 mils (0.030 inch), as for example a thickness of 20 mils (0.020 inch).

[0069] Regarding the containers for the kits, the disclosures of the following patents and patent applications are hereby incorporated herein by reference in their respective entireties: U.S. Patent No. 7,188,644 entitled "APPARATUS AND METHOD FOR MINIMIZING THE GENERATION OF PARTICLES IN ULTRAPURE LIQUIDS;" U.S. Patent No. 6,698,619 entitled "RETURNABLE AND REUSABLE, BAG-IN- DRUM FLUID STORAGE AND DISPENSING CONTAINER SYSTEM;" International Application No. PCT/US08/63276 entitled "SYSTEMS AND METHODS FOR MATERIAL BLENDING AND DISTRIBUTION" filed on May 9, 2008 in the name of John E.Q. Hughes; and International Application No. PCT/US08/85826 entitled "SYSTEMS AND METHODS FOR DELIVERY OF FLUID-CONTAINING PROCESS MATERIAL COMBINATIONS" filed on December 8, 2008 in the name of John E.Q. Hughes et al.

[0070] In a fourth aspect, a method of removing metal impurities from a substrate is described, said method comprising contacting a substrate comprising said metal impurities with a composition described herein to substantially remove said metal impurities from the substrate. The compositions include the composition of the first aspect or the composition of the second aspect described herein. The method of removing metal impurities from a substrate can be performed before or after the diffusion step. Moreover, the method of removing metal impurities from a substrate can be an inline process or a batch process. Preferably, the substrate a silicon-containing substrate (i.e., a microelectronic device or a solar cell device).

[0071] In application, a composition as described herein is contacted in any suitable manner to the substrate having metal impurities thereon, e.g., by spraying a composition on the surface of the substrate, by dipping (in a volume of a composition) of the substrate including the metal impurities optionally with stirring or agitation, by contacting the substrate with another material, e.g., a pad, or fibrous sorbent applicator element, that has a composition absorbed thereon, by contacting the substrate including the metal impurities with a recirculating composition, or by any other suitable means, manner or technique, by which a composition is brought into contact with the metal impurities to be removed. The contacting conditions include a period of time and conditions sufficient to remove the metal impurities. The process using the compositions may include a static clean, a dynamic clean, or sequential processing steps including dynamic cleaning and static cleaning of the substrate in a composition. Any of the contacting options disclosed herein may further comprise soni cation to assist with the removal of the metal impurities to be removed from the substrate.

[0072] When removing metal impurities from a substrate having same thereon, a composition typically is contacted with the substrate for a time of from about 30 seconds to about 60 minutes, more preferably about 75 sec to about 5 min, at temperature in a range of from about 20°C to about 90°C, preferably about 20°C to about 70°C, most preferably about 20°C to about 50°C. The contacting time may be in a range of from about 5 minutes to about 3 hours at temperature in a range of from about 20°C to about 80°C. Such contacting times and temperatures are illustrative, and any other suitable time and temperature conditions may be employed that are efficacious to substantially remove the material(s) from the device structure, within the broad practice of the invention.

[0073] Following the achievement of the metal impurities removal, the composition can be readily removed from the substrate to which it has previously been applied, e.g., by rinse, wash, drying, or other removal step(s), as may be desired and efficacious in a given end use application of the compositions disclosed herein. For example, the substrate may be rinsed with deionized water, or isopropanol in deionized water. In addition, the microelectronic device may be dried with nitrogen gas, isopropanol, or SEZ (spin process technology).

[0074] In one embodiment of the fourth aspect, prior to contact with the compositions described herein, the substrate is contacted with an organic contaminant removal composition such as SC-1 (NH₄OH and H₂O₂). Although not wishing to be bound by theory, with the removal of the organic contaminants, the metal impurity removal becomes more effective. Accordingly, in another embodiment, a method of removing metal impurities from a substrate is described, said method comprising contacting a substrate comprising said metal impurities with an organic contaminant removal composition to substantially remove said organic contaminants from the substrate, and contacting said substrate with a composition of the first aspect or a composition of the second aspect to substantially remove said metal impurities from the substrate. The substrate can be rinsed (e.g., with water) between the organic contaminant removal step and the metal impurity removal step. It should be appreciated that during the organic contaminant removal step, some metal impurities may be removed and that during the metal impurity removal step, some organic contaminants may be removed.

[0075] In a fifth aspect, a method of removing metal impurities from a liquid is described, said method comprising combining a liquid comprising said metal impurities with a composition described herein to substantially sequester and remove said metal impurities from the liquid. The compositions include the composition of the first aspect or the composition of the second aspect described herein. The liquid includes any bath used in the microelectronic device fabrication industry or the solar cell fabrication industry that has metal impurities therein. For example, the bath can comprise the composition subsequent to completion of the fourth aspect of the invention, wherein the composition comprises metal impurities.

[0076] In still another aspect, an article is described, wherein said article comprises a substrate, metal impurities, and a composition of the invention. For example, the article can comprise a silicon- containing substrate (i.e., a semiconductor device or a solar cell device), metal impurities, and a composition comprising at least one etchant, at least one chelating agent, optionally at least one oxidizing agent, optionally at least one chloride salt, optionally at least one surfactant, optionally a buffer system, optionally at least one capping agent, and optionally at least one fluoride activity agent. Alternatively, the article can comprise a silicon-containing substrate (i.e., a semiconductor device or a solar cell device), metal impurities, and a composition comprising at least one etchant, at least one chelating agent, at least one oxidizing agent, optionally at least one chloride salt, optionally at least one surfactant, optionally a buffer system, and optionally at least one capping agent.

[0077] In another aspect, the compositions described herein are formulated to clean a silicon- containing substrate prior to texturing, i.e., a pre-texturing clean, or subsequent to texturing, to ensure the removal of surface organic/metal contaminants therefrom. Organic contamination may exist on the wafer surface before/after the texturing process or after storage in common plastic containers, thus compositions containing an oxidizing agent can ensure the removal of metal contamination removal before the texturing step to facilitate uniform texturing or before the emitter formation step.

[0078] Furthermore, these compositions can also function as the PSG removal solutions after the diffusion process to remove this dead layer. Owing to the synergestic effect of both the oxidizer and HF, the PSG removal rate is much faster than the industry standard (i.e., diluted HF) alone, and can also prevent metal impurity redeposition in the PSG removal process.

[0079] The features and advantages of the invention are more fully shown by the illustrative examples discussed below. Example 1

[0080] Solutions were prepared including SC-1 (NH₄OH and H₂0₂), SC-2 (HC1 and H₂0₂), an HF dip, HF/HCl (1 :1 : 100 in deionized water), and HF/NH₄C1 (1 : 1 : 100 in deionized water). In addition, Formulation A comprising 69.394 wt% deionized water, 6.75 wt% ammonium chloride, 0.156 wt% Pluronic 25R2, 9 wt% HEDP, and 14.7 wt% HF was prepared. In addition, Formulation B comprising 67.342 wt% deionized water, 6.75 wt% ammonium chloride, 0.156 wt% Pluronic 25R2, 2.052 wt% DOWFAX 3B2, 9 wt% HEDP, and 14.7 wt% HF was prepared. Lastly, Formulation C comprising 69.45 wt% deionized water, 6.75 wt% ammonium chloride, 9 wt% HEDP, and 14.7 wt% HF was prepared.

[0081] "As-Cut" wafers (two p-Si and one n-Si) were dipped in the HF/HCl solution and formulation A for 10 minutes at room temperature and the solutions were analyzed for the presence and concentration of copper, iron, sodium and tantalum using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). It can be seen in Figure 1 that Formulation A was more efficient at chelating Cu, Fe and Na impurities from the wafers than the HF/HCl solution. Additional data is provided in Table 1, which includes the concentration of Ca, Cr, Cu, Fe, Ni, Mg, Mn, Sn and Zn following immersion of monocrystalline Si textured wafers for 10 min at room temperature in HF/HCl solution, Formulation A, and Formulation A diluted 1 : 10 with deionized water. Again, it can be seen that Formulation A was more efficient than HF/HCl at chelating metal impurities from a wafer surface.

Table 1 : Metal concentration in solutions measured using ICP-AES

Example 2

[0082] Lifetime measurements were performed using Quasi-Steady State Photoconductance (QSSPC) analysis, which was performed to ascertain how long a minority carrier could travel. Long lifetimes are preferred, which is indicative of increased efficiency.

[0083] The process of preparing the coupon for QSSPC analysis is illustrated schematically in Figure 2. The wafer clean consisted of an immersion of the textured wafer coupon (Float Zone (FZ) and Czochralski (CZ)) in the different chemistries at room temperature. Following the wafer clean, the coupon was either (i) annealed in nitrogen gas only (at 850°C), (ii) diffused with POCl₃ (at 850°C for 15 minutes, then drive-in) or (iii) annealed with oxygen at 1060°C to form a thermal oxide. Annealing in both oxygen and nitrogen will drive the remaining surface metal impurities into the wafer and degrade the carrier lifetime. Thermal oxidation has the benefit of both annealing and passivating the wafer, and as such the wafer does not require further passivation by SiN_x deposition prior to the lifetime measurement. The results of the lifetime measurements are provided in Table 2 and shown schematically in Figure 3B. Notably, the much lower lifetime after the N₂ anneal suggests that the furnace was contaminated.

Table 2: Lifetime measurements

[0084] The lifetime results were normalized relative to the SC-1 + SC-2 + HF dip clean and shown schematically in Figure 3A. It can be seen that Formulation C provides a higher lifetime than the industry standard HF/HC1, consistent with the ICP-AES results. Although not wishing to be bound by theory, it is thought that the SC-1 + SC-2 + HF dip clean was higher because formulation C may not remove surface organics, wherein said surface organics may inhibit effective metal impurity removal.

[0085] Figure 3C illustrates the implied open circuit voltage (Voc) as derived from QSSPC, which is a good estimation of final cell performance, wherein an increased Voc is indicative of an increased cell efficiency. Again, it can be seen that overall, Formulation C should have a higher performance than the industry standard HF/HC1.

Example 3

[0086] Two mono-silicon coupons that were passivated with thermal oxide were contacted with SC-1 + SC-2, HF/HC1, SC-1 + SC-2 + Formulation C, SC-1 + Formulation C, Formulation C, Formulation C with H₂0₂, and Formulation B with H₂0₂ at 70°C for 10 min for SC-1 and SC-2, respectively, and at 20°C for 10 min for HF/HC1 and Formulation B, and C. The lifetime results are shown in Figure 4, wherein it can be seen that the SC-1 + Formulation C removal provided the coupon with the highest lifetime. Example 4

[0087] Formulations D-G were prepared as follows:

Formulation D: 30 wt% HF (49%), 6.75 wt% NH₄C1, 15 wt% HEDP, 48,25 wt% water

Formulation E: 10 wt% HF (49%), 32.43 wt% HC1 (37%), 0.475 wt% pyridine-N-oxide, 57.1 wt% water

Formulation F: 2 wt% HF (49%), 6.87 wt% HN0₃, 6.3 wt% oxalic acid, 1 1.12 wt% tetraglyme, 73.71 wt%> water

Formulation G: 0.5 wt% HF (49%), 6.87 wt% HN0₃, 6.3 wt% oxalic acid, 0.236 wt% PPGPE, 86.094 wt% water

Formulation H: 5 wt% HF (49%), 12 wt% HC1 (37%), 83 wt% water

Formulation I: SC-1 (1 NH₄OH: 1 H₂0₂: 5 H₂0)

[0088] Textured silicon wafers were analyzed in three different spots using Total Reflection x- ray Fluorescence (TXRF) to identify the metals present on the surface. Thereafter, coupons of the wafers were immersed in 15 mL of the following compositions at 20°C for 30 seconds unless indicated otherwise.

1. Formulation H

2. Formulation I (10 min, 70°C)/DIW rinse + Formulation H

3. Formulation 1 (10 min, 70°C)/DIW rinse + Formulation D

4. Formulation E

5. Formulation G

6. Formulation F

Following immersion, the solutions were analyzed for metal concentration change (in ppb) using ICP and the surfaces of the silicon wafers were re-analyzed using TXRF.

[0089] The results of the TXRF are shown in Figure 5 where it can be seen that iron is one of the principal trace metal impurities found on the surface of the wafer. Comparing Figures 5 and 6, it can be seen that the surface iron concentration (Figure 5) correlates well with the ICP results (Figure 6) whereby Formulations F and G were effective at removing said iron.

[0090] Although not shown, the Formulations F and G were effective at removing trace metal impurities from as-cut silicon wafers as well.

Example 5

[0091] A total of ten (10) as-cut and textured silicon coupons were immersed in both Formulations F and G at room temperature for 30 seconds and the change in the concentration of metal contaminants determined. Referring to Figure 7, it can be seen that metal impurities are removed from both as-cut and textured wafers using the compositions described herein, even with the existence of possible surface organic contaminants. Example 6

[0092] A coupon containing a layer of PSG was immersed in Formulation F as well as a 5% HF solution. The results are shown in Figure 8. It can be seen that the PSG removal rate when using Formulation F is constant up to 5 minutes, while the removal rate of PSG in the presence of 5% HF significantly decreases. This indicates the higher bath loading capability of formulation F.

Example 7

[0093] Additional formulations contemplated herein for the removal of trace metal impurities from silicon-containing substrates and the sequestration of said metal impurities in solution are shown in Table 1 below.

Table 1 : Compositions for the removal of trace metal impurities from silicon-containing substrates.

* * *

[0087] Accordingly, while the invention has been described herein in reference to specific aspects, features and illustrative embodiments of the invention, it will be appreciated that the utility of the invention is not thus limited, but rather extends to and encompasses numerous other aspects, features, and embodiments. Accordingly, the claims hereafter set forth are intended to be correspondingly broadly construed, as including all such aspects, features, and embodiments, within their spirit and scope.

Claims

THE CLAIMS What is claimed is:

1. A method of removing metal impurities from a substrate, said method comprising contacting the substrate comprising said metal impurities with a metal impurity removal composition to substantially remove said metal impurities from the substrate, wherein said metal impurity removal composition comprises at least one etchant, at least one chelating agent, and water.

2. The method of claim 1, wherein the metal impurities comprise a species selected from the group consisting of elemental metal, metal ions, metal silicides, metal oxides, metal silicates, metal borides, and any combination thereof.

3. The method of claims 1 or 2, wherein the metal impurities comprise a metal selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Te, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, and combinations thereof.

4. The method of claims 1 or 2, wherein the metal impurities comprise iron.

5. The method of any of the preceding claims, wherein the at least one etchant comprises a species selected from the group consisting of hydrogen fluoride (HF); xenon difluoride (XeF₂); ammonium fluoride (NH₄F); tetraalkylammonium fluoride (NR₄F); alkyl hydrogen fluoride (NRH₃F); ammonium hydrogen bifluoride (NH₅F₂); dialkylammonium hydrogen fluoride (NR₂H₂F); trialkylammonium hydrogen fluoride (NR₃HF); trialkylammonium trihydrogen fluoride (NR₃:3HF); anhydrous hydrogen fluoride pyridine complex; anhydrous hydrogen fluoride triethylamine complex, and combinations thereof, where R may be the same as or different from one another and is selected from the group consisting of straight-chained or branched Ci-C₆ alkyl groups.

6. The method of any of the preceding claims, wherein the at least one etchant comprises hydrogen fluoride.

7. The method of any of the preceding claims, wherein the at least one chelating agent comprises a species selected from the group consisting of hydroxyethylidene diphosphonic acid (HEDP), ethyl endiamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DPT A), (l ,2-cyclohexylenedinitrilo)tetraacetic acid (CDTA), glycine, salicylic acid, sulfosalicylic acid, glucoronic acid, tartaric acid, citric acid, ammonium gluconate, humic acid, fulvic acid, iminodiacetic acid, hydroxyethyl iminodiacetic acid (HEIDA), ascorbic acid, gallic acid, acetic acid, benzoic acid, alanine, ammonium citrate tribasic, pyrophosphoric acid, Dequest 2000, Dequest 2010, Dequest 2060s, Dequest 2000EG, Dequest 7000, nitrilo-tris(methylenephosphonic acid) (NTMPA), ethylene diamine tris(methylenephosphonic acid) (EDTMPA), serine, proline, leucine, alanine, asparagine, aspartic acid, glutamine, valine, and lysine, maleic acid, oxalic acid, malonic acid, succinic acid, phosphonic acid, l-hydroxyethane-l,l-diphosphonic acid, nitrilo- tris(methylenephosphonic acid), nitrilotriacetic acid, uric acid, tetraglyme, propylenediamine tetraacetic acid, 2-hydroxypyridine 1 -oxide, methane sulfonic acid, (MSA), formamidinesulfmic acid (FASA), phenanthrolines, bypyridyls, tetraethylenetetramine (TETA), tetraethylenepentamine (TEPA), and combinations thereof.

8. The method of any of the preceding claims, wherein the at least one chelating agent comprises hydroxyethylidene diphosphonic acid or oxalic acid.

9. The method of any of the preceding claims, wherein the metal impurity removal composition further comprises at least one surfactant.

10. The method of claim 9, wherein that at least one surfactant comprises a species selected from the group consisting of fluoroalkyl surfactants, ethoxylated fluorosurfactants, polyethylene glycols, polypropylene glycols, polyethylene glycol ethers, polypropylene glycol ethers, carboxylic acid salts, dodecylbenzenesulfonic acid, salts of dodecylbenzenesulfonic acid, polyacrylate polymers, dinonylphenyl polyoxyethylene, silicone polymers, modified silicone polymers, acetylenic diols, modified acetylenic diols, alkylammonium salts, modified alkylammonium salts, alkylphenol polyglycidol ether, fluorosurfactants sodium alkyl sulfates, ammonium alkyl sulfates, alkyl (Cio-Cis) carboxylic acid ammonium salts, sodium sulfosuccinates and esters thereof, alkyl (Ci₀-Ci₈) sulfonic acid sodium salts, di-anionic sulfonate surfactants cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium hydrogen sulfate, ammonium carboxylates, ammonium sulfates, amine oxides, N-dodecyl-N,N-dimethylbetaine, betaine, sulfobetaine, alkylammoniopropyl sulfate, polyethylene glycol (PEG), polyethylene oxide (PEO), polypropylene glycol (PPG), polyvinyl pyrrolidone (PVP), cationic polymers, nonionic polymers, anionic polymers, hydroxyethylcellulose (HEC), acrylamide polymers, poly(acrylic acid), carboxymethylcellulose (CMC), sodium carboxymethyl cellulose (Na CMC), hydroxypropylmethylcellulose, polyvinylpyrrolidone K30, BIOCARE™ polymers, DOW™ latex powders (DLP), ETHOCEL™ ethyl cellulose polymers, KYTAMER™ PC polymers, METHOCEL™ cellulose ethers, POLYOX™ water soluble resins, SoftCAT™ polymers, UCARE™ polymers, UCO ™ fluids, PPG-PEG-PPG block copolymers, PEG-PPG-PEG block copolymers, ethylene oxide/propylene oxide block copolymers, tetraglyme, acetylacetone, hexafluoroacetylacetone, 2-butoxyethanol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether (DPGME), tripropylene glycol methyl ether, dipropylene glycol dimethyl ether, dipropylene glycol ethyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether (DPGPE), tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n- butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, and combinations thereof.

1 1. The method of claim 9, wherein the at least one surfactant comprises tetraglyme.

12. The method of any of the preceding claims, wherein the metal impurity removal composition further comprises at least one oxidizing agent.

13. The method of claim 12, wherein the at least on oxidizing agent comprises a species selected from the group consisting of hydrogen peroxide, nitric acid, sulfuric acid, iodic acid; nitromethane, nitrobenzene, nitrobenzoic acid, nitrophenols, perboric acid, perchloric acid, periodic acid, persulfuric acid, perboric acid, peroxomonosulfuric acid, peracetic acid, peroxydiphosphoric acid; peroxydisulfuric acid; FeCl₃, oxone (2KHSO5 KHSO4 K2SO4), ammonium peroxomonosulfate, ammonium chlorite, ammonium chlorate, ammonium iodate, ammonium perborate, ammonium perchlorate, ammonium periodate, ammonium persulfate, ammonium hypochlorite, sodium persulfate, sodium hypochlorite, potassium iodate, potassium permanganate, potassium persulfate, potassium persulfate, potassium hypochlorite, tetramethylammonium chlorite, tetramethylammonium chlorate, tetramethylammonium iodate, tetramethylammonium perborate, tetramethylammonium perchlorate, tetramethylammonium periodate, tetramethylammonium persulfate, tetrabutylammonium peroxomonosulfate, ferric nitrate, urea hydrogen peroxide, N-methylmorpholine-N-oxide (NMMO), trimethylamine-N-oxide, triethylamine-N-oxide, pyridine-N-oxide, p-benzoquinone, p-toluquinone, isatin, alloxane, ninhydrin, and combinations thereof.

14. The method of claim 12, wherein the at least on oxidizing agent comprises nitric acid.

15. The method of any of the preceding claims, wherein the metal impurity removal composition further comprises at least one additional component selected from the group consisting of optionally at least one chloride salt, optionally a buffer system, optionally at least one capping agent, and optionally at least one fluoride activity agent.

16. The method of any of the preceding claims, wherein the method further comprises diffusion of a gettering element into the substrate.

17. The method of any of the preceding claims, wherein the method further comprises contacting the substrate with an organic contaminant removal composition prior to contacting the substrate with the metal impurity removal composition.

18. The method of claim 17, wherein the organic contaminant removal composition comprises ammonium hydroxide and hydrogen peroxide.

19. The method of any of the preceding claims, wherein the substrate comprises silicon.

20. The method of claim 19, wherein the silicon is as-cut or textured or doped.

21. The method of any of the preceding claims, wherein the substrate is rinsed subsequent to contacting with the metal impurity removal composition.

22. The method of any of the preceding claims, wherein the metal impurity removal composition comprises hydrofluoric acid, nitric acid, oxalic acid, tetraglyme, PPGPE, and water.

23. The method of any of the preceding claims, wherein the metal impurity removal composition has pH in a range from about -1 to about 7.

24. The method of any of the preceding claims, wherein the metal impurity removal composition further comprises metal impurities.

25. A method of removing metal impurities from a liquid, said method comprising combining a liquid comprising said metal impurities with a composition to substantially sequester and remove said metal impurities from the liquid, wherein the composition comprises at least one etchant, at least one chelating agent, water, optionally at least one chloride salt, optionally at least one surfactant, optionally at least one oxidizing agent, optionally a buffer system, optionally at least one capping agent, and optionally at least one fluoride activity agent.