Patent Grant
7553803
The present invention relates to supercritical fluid-based compositions containing polymeric alcohols such as polyvinyl alcohol, polymeric amines such as polyvinyl amine, and other polyalcohol or polyamine species, useful for the removal of silicon-containing particulate material, e.g., silicon nitrides and silicon oxides, generated in situ during plasma-assisted processes, from the surface of patterned semiconductor wafers.
Particle contamination on the surface of semiconductor wafers is known to have deleterious effects on the morphology, performance, reliability and yield of the semiconductor device. For example, it has been reported that a particle larger than about one-quarter of the minimum line-width may cause fatal device defects. Clearly, with the continuing and rapid decrease in the critical dimensions of microelectronic device structures, the effective removal of particulates from the surface of semiconductor wafers is increasingly essential.
Well known sources of particle contamination during device production include plasma-assisted processes such as plasma-enhanced chemical vapor deposition (PECVD). The particle contamination may occur in situ during continuous plasma operation or following the termination of the plasma process (Setyawan, H., Shimada, M., Imajo, Y., Hayashi, Y., Okuyama, K., J. Aerosol Sci., 34, 923-936 (2003); Selwyn, G. S., Singh, J., Bennett, R. S., J. Vac. Sci. Tech. A, 77, 2758-2765 (1989)). Because of the importance of the PECVD method for the fabrication of very large-scale integration (VLSI) circuits and thin-film transistors (TFTs), the future viability of the PECVD method, especially as critical dimensions continue to decrease, requires that the particles deposited during and/or at the termination of the PECVD process be removed prior to subsequent processing.
Traditional particle removal techniques used within the semiconductor industry include at least one of megasonic agitation, brush scrubbing, wet cleaning, and aerosol jet dry cleaning. Wet cleaning techniques utilize cleaning compositions such as ammonium hydroxide-hydrogen peroxide-water (APM, also referred to as “standard clean” 1 or SC-1) solutions to form soluble compounds of surface contaminants. A disadvantage of wet cleaning techniques include the disposal and/or treatment of large volumes of waste solvents following treatment of the wafer surface.
Megasonic agitation involves the application of energy in the 500-1000 kHz frequency range to the liquid in which particle-containing wafers are immersed (such as the APM solution) to remove said particles. Disadvantages of megasonic agitation include reports that the removal of particles smaller than 100 nm should not be theoretically possible (Olim, M., J. Electrochem. Soc., 144, 3657-3659 (1997)), which renders the technique useless as the dimensions of the devices, and hence the contaminating particles, get smaller and smaller.
Aerosol jet dry cleaning uses solid water, carbon dioxide or argon particles in a high velocity gas stream to collide with and remove the contaminating particles from the surface. A disadvantage of aerosol jet dry cleaning includes the potential for dislodging delicate features, such as MEMS (Micro Electro Mechanical Systems) devices and wafer patterns, with the high velocity gas stream.
Recently, supercritical carbon dioxide (SCCO2) compositions containing co-solvents have been used to enhance particle removal, both organic and inorganic in nature, from silicon and silicon dioxide regions of both blanketed and patterned wafers. However, compositions containing only SCCO2 and alkanol co-solvents have proven to be incapable of removing 100% of the particulates from the wafer surface.
There is therefore a continuing need in the field for improved particle removal compositions and methods, since the removal of contaminating particulate material from semiconductor wafer surfaces is critical to ensure the production of semiconductor devices having exemplary performance, reliability and yields.
The present invention relates to supercritical fluid-based compositions useful for the removal of silicon-containing particulate material from the surface of patterned semiconductor wafers, and methods of using such compositions for removal of same.
In one aspect, the invention relates to a composition for removing silicon-containing particulate material from the surface of a semiconductor wafer, said composition comprising a supercritical fluid (SCF), at least one co-solvent, at least one etchant species, at least one surface passivator, a binder interactive with said silicon-containing particulate material to enhance removal thereof, deionized water, and optionally at least one surfactant.
In another aspect, the invention relates to a method of removing silicon-containing particulate matter from a semiconductor wafer surface having same thereon, said method comprising contacting the wafer surface with a SCF-based composition comprising a SCF, at least one co-solvent, at least one etchant species, at least one surface passivator, a binder interactive with said silicon-containing particulate material to enhance removal thereof, deionized water, and optionally at least one surfactant, for sufficient time and under sufficient contacting conditions to remove the silicon-containing particulate matter from the surface of the semiconductor wafer.
In yet another aspect, the invention relates to a composition for removing silicon-containing particulate material from the surface of a semiconductor wafer, said composition comprising about 85.0% to about 99.0% SCF, about 0.01% to about 15.0% co-solvent, about 0.25% to about 5.0% etchant, and optionally about 0% to about 3.0% surfactant, based on the total weight of the composition.
In a further aspect, the invention relates to a method of removing silicon-containing particulate matter from a semiconductor wafer surface having same thereon, said method comprising:
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.
The present invention is based on the discovery of supercritical fluid (SCF)-based compositions that are highly efficacious for the removal of particulate material from the surface of patterned semiconductor wafers. The compositions and methods of the invention are effective for removing silicon-containing particulate material including, but not limited to, silicon nitride (Si3N4), silicon oxide and hydrogenated silicon nitride (SixNyHz), from the surface of patterned silicon-containing wafers, e.g., Si/SiO2 wafers. The particulate material is generated in situ during plasma-assisted processes including, but not limited to, sputtering and PECVD.
The PECVD of silicon oxide films is often carried out using gaseous mixtures containing silane in nitrogen (SiH4/N2), nitrous oxide and ammonia. In addition to the deposition of silicon dioxide onto the substrate, highly hydrogenated silicon nitride particles are formed that can settle out onto the wafer surface, either during plasma operation or following the completion of the PECVD process. It is speculated that the source of the hydrogen on the surface of the silicon nitride particles is the silane precursor and/or the ammonia oxidant. In addition to silazane (Si2—NH) groups at the surface of the silicon nitride particles, silanol (Si—OH) groups may also be present. The proportion of these functional groups on the surface of the silicon nitride particles varies according to the conditions under which the particles are generated.
Because of its readily manufactured character and its lack of toxicity and negligible environmental effects, supercritical carbon dioxide (SCCO2) is a preferred SCF in the broad practice of the present invention, although the invention may be practiced with any suitable SCF species, with the choice of a particular SCF depending on the specific application involved. Other preferred SCF species useful in the practice of the invention include oxygen, argon, krypton, xenon, and ammonia. Specific reference to SCCO2 hereinafter in the broad description of the invention is meant to provide an illustrative example of the present invention and is not meant to limit same in any way.
SCCO2 is an attractive reagent for removal of particle contaminants, since SCCO2 has the characteristics of both a liquid and a gas. Like a gas, it diffuses rapidly, has low viscosity, near-zero surface tension, and penetrates easily into deep trenches and vias. Like a liquid, it has bulk flow capability as a “wash” medium. SCCO2 also has the advantage of being recyclable, thus minimizing waste storage and disposal requirements.
Ostensibly, SCCO2 is an attractive reagent for the removal of Si3N4 particles, because both compounds are non-polar. However, neat SCCO2 has not proven to be an effective medium for solubilizing silicon nitride particles. Furthermore, the addition of a polar co-solvent, e.g., alkanols, to the SCCO2 has not substantially improved the solubility of the silicon nitride particles in the SCCO2 composition. Accordingly, there is a continuing need to modify the SCCO2 composition to enhance the removal of particulate material from the semiconductor wafer surface.
It is known that polymeric alcohols, such as polyvinyl alcohol, adsorb onto the surface of silicon nitride particles, thus lowering the surface potential of the particles. It is speculated that the silanol (Si—OH) and the silazane (Si2—NH) groups at the surface of the silicon nitride particles participate in the transfer of protons in water to be Bronsted acid points, e.g., H+ donation points, and Bronsted base points, e.g., H+ receiving points. As such, the polyvinyl alcohol hydroxyl groups may adsorb onto the surfaces of the silicon nitride particles at the Bronsted acid points, thus enhancing the removal of the particles from the wafer surface. Additionally, hydrogen bonding between the polyvinyl alcohol hydroxyl groups and the silanol or silazane groups may participate in removal enhancement. Advantageously, once the contaminating particles are removed from the wafer surface, polyvinyl alcohol can stabilize the dispersion of silicon nitride particles in the fluid, thus minimizing flocculation.
The present invention combines the advantages associated with SCCO2 and other SCFs, with the particle binding efficiency of polymeric alcohols such as polyvinyl alcohol, by using appropriately formulated SCF-based compositions as hereinafter more fully described. The removal of silicon nitride particles from a wafer surface using these SCF-based compositions is upwards of 100% efficient, while maintaining the structural integrity of the Si/SiO2 layers.
In one aspect, the invention relates to SCF-based compositions useful in removing particulate contaminants including, but not limited to, silicon nitride, silicon oxide and hydrogenated silicon nitride, from a semiconductor wafer surface. The formulation of the present invention comprises a SCF, at least one co-solvent, at least one surface passivator, at least one etchant, a binder interactive with said silicon-containing particulate material to enhance removal thereof, deionized water, and optionally at least one surfactant, present in the following ranges, based on the total weight of the composition:
In the broad practice of the invention, the SCF-based etching formulations may comprise, consist of, or consist essentially of a SCF, at least one co-solvent, at least one surface passivator, at least one etchant, a binder interactive with said silicon-containing particulate material to enhance removal thereof, deionized water, and optionally at least one surfactant. In general, the specific proportions and amounts of SCF, co-solvent, surface passivator, etchant, binder, surfactant, and deionized water, in relation to each other, may be suitably varied to provide the desired removal of the silicon-containing particulate material from the wafer surface, as readily determinable within the skill of the art without undue effort.
The inclusion of the co-solvent with the SCF serves to increase the solubility of the binder in the SCF. The co-solvents contemplated for use in the SCF-based composition include alkanols, dimethylsulfoxide, sulfolane, catechol, ethyl lactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone, an alkyl carbonate such as butylene carbonate, ethylene carbonate and propylene carbonate, a glycol amine such as N-methylpyrrolidone (NMP), N-octylpyrrolidone and N-phenylpyrrolidone, or a mixture of two of more of such species. The alkanol co-solvent is preferably a straight-chain or branched C1-C6 alcohol (i.e., methanol, ethanol, isopropanol, etc.), or a mixture of two or more of such alcohol species. In a preferred embodiment, the alkanol is methanol or isopropanol (IPA).
“Surface passivator” is defined herein as a substance that protects the wafer surface from additional oxidation, while simultaneously being capable of hydrogen bonding to the silicon-containing particulate surface to improve the removal of particles from the wafer surface. The surface passivator may comprise boric acid, triethyl borate and triethanolamine. In a preferred embodiment, the surface passivator is boric acid.
Species capable of etching silicon-containing species such as silicon nitride are well known in the art, and include hydrofluoric acid (HF), ammonium fluoride (NH4F) and triethylamine trihydrofluoride ((C2H5)3N.3HF). Additionally, salts of bifluorides may be used, including ammonium difluoride ((NH4)HF2), tetraalkylammonium difluorides ((R)4NHF2, where R is methyl, ethyl, butyl, phenyl or fluorinated C1-C4 alkyl groups) and alkyl phosphonium difluorides ((R)4PHF2, where R is methyl, ethyl, butyl, phenyl or fluorinated C1-C4 alkyl groups). The fluoride source aids in particle removal by chemically reacting with the silicon nitride and silicon oxide particles, undercutting the particles, thus reducing their size while concomitantly enhancing the ability of the binder to remove the particle from the wafer surface. In a preferred embodiment, the etchant is ammonium fluoride.
“Binders” are defined herein as species that interact with the silicon-containing particulate material to enhance removal from the semiconductor wafer. The binder may have moieties, e.g., hydroxyl or amine groups, capable of interacting with the Bronsted acid and/or Bronsted base points present on the surface of the contaminating particulate material. Additionally, the binders may be capable of hydrogen bonding with the surface of the silicon-containing particulate material. The combined effect of these intermolecular interactions is a reduction of the surface potential of the particulate material and concomitantly, the enhanced removal of the particulate material from the wafer surface. The binder of the present invention may be derived from at least one ethylenically unsaturated reactant. In a preferred embodiment, the binder is a polymeric alcohol, a polymeric amine, a polymeric acetate or a enzymatically decomposed sugar. In a particularly preferred embodiment, the polymeric alcohol is polyvinyl alcohol, which is commonly made by the polymerization of vinyl acetate followed by hydrolysis of the polyvinyl acetate polymer. In another particularly preferred embodiment, the polymeric amine is polyvinyl amine, which is commonly made from vinyl formamide.
The surfactants contemplated in the SCF-based composition of the present invention may include nonionic surfactants, such as 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, and alkylammonium or modified alkylammonium salts, as well as combinations comprising at least one of the foregoing. In a preferred embodiment, the surfactant is an ethoxylated fluorosurfactant such as ZONYL® FSO-100 fluorosurfactant (DuPont Canada Inc., Mississauga, Ontario, Canada).
Alternatively, the surfactants may include anionic surfactants, or a mixture of anionic and non-ionic surfactants. Anionic surfactants contemplated in the SCF-based composition 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, ammonium alkyl sulfates, alkyl (C10-C18) carboxylic acid ammonium salts, sodium sulfosuccinates and esters thereof, e.g., dioctyl sodium sulfosuccinate, and alkyl (C10-C18) sulfonic acid sodium salts.
In one embodiment, the SCF-based composition of the invention includes SCCO2, methanol, ammonium fluoride, boric acid, a fluorosurfactant, polyvinyl alcohol and deionized water.
In another aspect, the invention relates to methods of particulate material contaminant removal including, but not limited to, silicon nitride and silicon oxide, from a semiconductor wafer surface using the SCF-based composition described herein.
Particle removal by conventional wet chemical techniques, e.g., using SC-1 or SC-2 solutions, has not proven wholly satisfactory in effecting complete removal of particulate material from the wafer surface. Further, these conventional cleaning approaches require substantial amounts of chemical reagents and produce substantial quantities of chemical waste.
The SCF-based compositions of the present invention overcome the disadvantages of the prior art particle removal techniques by minimizing the volume of chemical reagents needed, thus reducing the quantity of waste, while simultaneously providing a composition and method having recyclable constituents, e.g., the SCFs.
The appropriate SCF-based composition can be employed to contact a wafer surface having particulate material contaminants, e.g., silicon nitride and silicon oxide, thereon at a pressure in a range of from about 1200 to about 4500 psi for sufficient time to effect the desired removal of the particulate matter, e.g., for a contacting time in a range of from about 2 minutes to about 20 minutes and a temperature of from about 30° C. to about 100° C., although greater or lesser contacting durations and temperatures may be advantageously employed in the broad practice of the present invention, where warranted. In a preferred embodiment, the contacting temperature is in the range of from about 40° C. to about 70° C., preferably about 50° C.
The removal process in a particularly preferred embodiment includes sequential processing steps including dynamic flow of the SCF-based composition over the contaminated wafer surface, followed by a static soak of the wafer in the SCF-based composition, with the respective dynamic flow and static soak steps being carried out alternatingly and repetitively, in a cycle of such alternating steps.
A “dynamic” contacting mode involves continuous flow of the composition over the wafer surface, to maximize the mass transfer gradient and effect complete removal of the particulate material from the surface. A “static soak” contacting mode involves contacting the wafer surface with a static volume of the composition, and maintaining contact therewith for a continued (soaking) period of time.
For example, the dynamic flow/static soak steps may be carried out for four successive cycles in the aforementioned illustrative embodiment, as including a sequence of 2.5 min-10 min dynamic flow, 2.5 min-5 min high pressure static soak, e.g., about 3000 psi to about 4500 psi, 2.5 min-10 min dynamic flow, and 2.5 min-10 min low pressure static soak, e.g., about 1200 psi to about 2900 psi. In a preferred embodiment, the sequence consists of a 2.5 min dynamic flow, a 2.5 min static soak at 4400 psi, a 2.5 min dynamic flow, and a 2.5 min static soak at 1500 psi.
Following the contacting of the SCF-based composition with the wafer surface, the wafer thereafter preferably is washed with copious amounts of SCF/methanol/deionized water solution in a first washing step, to remove any residual precipitated chemical additives from the region of the wafer surface in which particle removal has been effected, and finally with copious amounts of pure SCF, in a second washing step, to remove any residual methanol and/or precipitated chemical additives from the wafer surface. Preferably, the SCF used for washing is SCCO2.
The SCF-based compositions of the present invention are readily formulated by simple mixing of ingredients, e.g., in a mixing vessel under gentle agitation.
Once formulated, such SCF-based compositions are applied to the wafer surface for contacting with the particulate material contaminants thereon, at suitable elevated pressures, e.g., in a pressurized contacting chamber to which the SCF-based composition is supplied at suitable volumetric rate and amount to effect the desired contacting operation for removal of the particulate material from the wafer surface.
It will be appreciated that specific contacting conditions for the SCF-based compositions of the invention are readily determinable within the skill of the art, based on the disclosure herein, and that the specific proportions of ingredients and concentrations of ingredients in the SCF-based compositions of the invention may be widely varied while achieving desired removal of the particulate material from the wafer surface.
In yet another aspect, the invention relates to a second SCF-based composition for particulate material, e.g., silicon nitride and silicon oxide, removal from a semiconductor wafer surface, said second SCF-based composition being devoid of the binder and surface passivator. The formulation comprises a SCF, at least one co-solvent, at least one etchant, and optionally at least one surfactant, present in the following ranges, based on the total weight of the composition:
The contemplated compositional components are the same as those disclosed hereinabove. In a particularly preferred embodiment, the SCF is SCCO2, the co-solvent is NMP, the fluoride source is triethylamine trihydrofluoride and the surfactant is dioctyl sodium sulfosuccinate.
The methods of particulate material removal using the second SCF-based composition are the same as those disclosed hereinabove. Notably, the sample containing the particulate matter to be removed may have to be “pre-cleaned” prior to exposure to the second SCF-based composition to reoxidize the surface. An effective SCF-based “pre-cleaning” formulation includes 95-100 wt % SCCO2 and 0-5 wt % aqueous-based pre-cleaning formulation, wherein the aqueous-based pre-cleaning formulation includes 0-10 vol % ammonium hydroxide, 0-20 vol % tertbutyl hydrogen peroxide and 70-95 vol % water. The pre-cleaning method includes a static soak of the sample in the SCF-based pre-cleaning formulation at pressures in a range from about 1200 psi to about 2800 psi and temperatures in a range from about 40° C. to about 60° C. for about 2 to about 30 minutes.
The features and advantages of the invention are more fully shown by the illustrative example discussed below.
The sample wafers examined in this study were Si/SiO2 patterned wafers contaminated with Si3N4 particles. Various chemical additives, as described herein, were added to the SCF-based composition and particle removal efficiency evaluated. The temperature of the SCF-based composition was maintained at 50° C. throughout the particle removal experiments. Following particle removal, the wafers were thoroughly rinsed with copious amounts of SCCO2/methanol/deionized water and pure SCCO2 in order to remove any residual solvent and/or precipitated chemical additives. The results are shown in
The above-described photographs thus evidence the efficacy of SCF-based compositions in accordance with the invention, for removal of silicon-containing particulate material, e.g., silicon nitride particles, from wafer surfaces.
The following formulation resulted in substantial removal of silicon nitride particles from the patterned Si/SiO2 surface. “Substantial removal” is defined as greater than about 98% removal of the particulate material from the semiconductor device, as determined by optical microscopy. In this specific embodiment, 100% cleaning of the particles was observed in all areas in 4 minutes at 50° C.
Another formulation found to substantially remove particles at lower pressures, e.g., 2800 psi, and 50° C. includes:
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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5068040 | Jackson | Nov 1991 | A |
| 5676705 | Jureller | Oct 1997 | A |
| 5709910 | Argyle | Jan 1998 | A |
| 5866005 | DeSimone et al. | Feb 1999 | A |
| 5868862 | Douglas | Feb 1999 | A |
| 5962390 | Flynn et al. | Oct 1999 | A |
| 6306564 | Mullee | Oct 2001 | B1 |
| 6309425 | Murphy | Oct 2001 | B1 |
| 6500605 | Mullee | Dec 2002 | B1 |
| 6623355 | McClain et al. | Sep 2003 | B2 |
| 6669785 | DeYoung | Dec 2003 | B2 |
| 6735978 | Tom et al. | May 2004 | B1 |
| 6764552 | Joyce | Jul 2004 | B1 |
| 6777337 | Yasui et al. | Aug 2004 | B2 |
| 6800142 | Tipton | Oct 2004 | B1 |
| 6943139 | Korzenski | Sep 2005 | B2 |
| 6958123 | Reid et al. | Oct 2005 | B2 |
| 6989358 | Korzenski et al. | Jan 2006 | B2 |
| 7018481 | Hayasaki et al. | Mar 2006 | B2 |
| 7022655 | Brask et al. | Apr 2006 | B2 |
| 7044143 | DeYoung et al. | May 2006 | B2 |
| 7119052 | Korzenski et al. | Oct 2006 | B2 |
| 20030125225 | Xu et al. | Jul 2003 | A1 |
| 20040087174 | Korzenski et al. | May 2004 | A1 |
| 20040087456 | Korzenski | May 2004 | A1 |
| 20040087457 | Korzenski | May 2004 | A1 |
| 20040171502 | Clark et al. | Sep 2004 | A1 |
| 20040224865 | Roeder et al. | Nov 2004 | A1 |
| 20040266635 | Korzenski | Dec 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20050192193 A1 | Sep 2005 | US |
