Patent Application
20080254218
The semiconductor fabrication industry continues to use metal source containing precursors for chemical vapor deposition processes including atomic layer deposition for fabricating conformal metal-containing films on substrates such as silicon, silicon oxide, metal nitride, metal oxide and other metal-containing layers using these metal source containing precursors. In the fabrication process, a particularly advantageous way of delivering multiple source containing precursors is to employ neat liquid source containing liquid metal precursors or solutions of metal source precursors dissolved in a solvent, flash to vaporize the mixture, and then deliver the resulting vapors to the reactor. If in the fabrication process the reactions convert the metal source containing precursor to an insoluble or non-volatile product, or to a material of different chemical or physical properties, the elements contained in that product may not reach the substrate and the stoichiometry of the deposited film may not be correct.
In certain instances, such problems can be avoided sometimes by using identical ligands coordinated to the metals to make ligand exchange a degenerate reaction (i.e., where the exchanging ligand is identical to the original ligand). The foregoing problems also may be encountered where the precursor is provided in a liquid solution and the solvent contains moieties which react with the metal or ligands of the precursor to produce undesirable reaction by-products.
The following references are illustrative of metal source containing precursor solutions for use in preparing conformal metal-containing films: U.S. Pat. No. 5,820,664; U.S. Pat. No. 6,225,237; U.S. Pat. No. 6,984,591; US2006/0269667; Lee, D.-J., S.-W. Kang and S.-W. Rhee (2001). “Chemical vapor deposition of ruthenium oxide thin films from Ru(tmhd)3 using direct liquid injection.” Thin Solid Films 413: 237; U.S. Pat. No. 6,111,122; Moshnyaga, V., I. Khoroshun, A. Sidorenko, P. Petrenko, A. Weidinger, M. Zeitler, B. Rauschenbach, R. Tidecks and K. Samwer (1999). “Preparation of rare-earth manganite-oxide thin films by metalorganic aerosol deposition technique.” Applied Physics Letters 74(19): 2842-2844; U.S. Pat. No. 5,900,279; U.S. Pat. No. 5,916,359; and JP 06234779.
The present invention generally relates to an improvement in metal source containing precursor solutions suitable for use in chemical vapor deposition processes, including cyclic chemical vapor deposition as well as atomic layer deposition, for fabricating conformal metal-containing films on substrates and to such processes. More specifically, the metal source precursor solutions are comprised of (i) at least one metal coordination complex including a metal, to which is coordinatively bound to at least one ligand in a stable complex and (ii) a solvent comprised of an organic amide for such metal source containing precursors. Preferably the ligand for metal complex is selected from the group consisting of: β-diketonates, β-ketoiminates, β-ketoesters, alkyl, carbonyl, alkylcyclopentadineyl, and alkoxy.
Some of the advantages which may be available through the use of these solutions include the following:
an ability to provide metal source precursor compositions in liquid solution form to simultaneously deliver the constituent metal(s) to a deposition locus such as a chemical vapor deposition or atomic layer deposition chamber;
an ability to provide solutions which are resistant to deleterious ligand exchange reactions;
an ability to provide a solution containing a high boiling linear or cyclic organic amide;
an ability to stabilize a metal complex in both liquid and gas phase via coordinating the organic amide to the metal center, an ability to promote the vaporization of the metal complex via a direct liquid injection device; and,
an ability to tune the physical properties of the precursor solution such as viscosity for easy delivery.
In reference to the above, the broadly based metal source precursor solutions are comprised of (i) at least one metal coordination complex including a metal, to which is coordinatively bound to at least one ligand in a stable complex. Representative metal complexes include β-diketonates, β-ketoiminates, β-diiminates, alkyl metal, metal carbonyl, alkyl metal carbonyl, aryl metal, aryl metal carbonyl, cyclopentadienyl metal, alkylcyclopentadienyl metal, cyclopentadienyl metal isonitrile, cyclopentadienyl metal nitrile, carbonyl cyclopentadienyl metal, metal alkoxide, metal ether alkoxide, and metal amides. The ligand can be monodentate, bidentate and multidentate coordinating to the metal atom and the metal is selected from group 2 to 14 elements. Generally the valence of the metal is from 2 to 5.
Variations of the above metal source containing precursors are represented by the generalized formulas:
(a) Metal β-diketonates having the formula:
wherein M is selected from Group 2 to 14, e.g., those having a valence from 2 to 5 and specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Ti, Zr, Hf, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, Sn, and Pb; wherein R1-3 are linear, branched, or cyclic independently selected from the groups consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C3-10 alkylsilyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein x is the integer 2, 3, or 4 based upon the valence of the metal.
Illustrative β-diketonate ligands employed in metal source complexes of the present invention include: acetylacetonate or more specifically 2,4-pentanedionate (acac), hexafluoroacetylacetonate or more specifically 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (hfacac); trifluoroacetylacetonate or more specifically 1,1,1-trifluoro-2,4-pentanedionate (tfacac); tetramethylheptanedionate or more specifically 2,2,6,6-tetramethyl-3,5-heptanedionate (thd); fluorodimethyloctanedionate or more specifically 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate (fod); and heptafluoro-dimethyloctanedionate. Exemplary metal complexes include Sr(thd)2, Ba(thd)2, Co(acac)2, Ni(acac)2, Cu(acac)2, Ru(thd)3, La(thd)3, Y(thd)3, Ti(thd)4, Hf(thd)4, and Zr(thd)4.
(b) Metal β-ketoiminates having the formula:
wherein M is selected from Group 2 to 14, and specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Ti, Zr, Hf, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, Sn, and Pb; wherein R1-3 are linear, branched or cyclic independently selected from the groups consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein x is the integer 2, 3, or 4 consistent with the valence of M; R4 is linear, branched or cyclic selected from the group consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl.
(c) Metal β-diiminates having the formula:
wherein M is selected from Group 2 to 13, and specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Ti, Zr, Hf, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, Sn, and Pb; wherein R1-3 are linear, branched or cyclic independently selected from the groups consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein x is the integer 2, 3, or 4. R4-5 also can contain unsaturation bonds and are linear, branched or cyclic independently selected from the groups consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl.
(d) Metal Alkoxy β-diketonates having the formula:
wherein M is a metal ion selected from Group 4 and 5 metals including titanium, zirconium, hafnium, vanadium, niobium, and tantalum; wherein R1-3 are linear, branched or cyclic independently selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl R4 is linear, branched or cyclic selected from the group consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein m and n are at least 1 and the sum of m plus n is equal to the valence of the metal M. Exemplary metal complexes include Ti(thd)2(OBut)2, Hf(thd)2(OBut)2, and Zr(thd)2(OBut)2.
(e) Alkyl Metal β-diketonates having the formula:
wherein M is a metal ion selected from Group 8, 9, and 10 metals including iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum; wherein R1-3 are liner, branched or cyclic selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein R4 is linear, branched or cyclic selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C6-10 cycloalkene, C6-12 cycloalkyne, C6-12 aryl, and fluorinated C1-10 alkyl; wherein m and n are at least 1 and the sum of m plus n is equal to the valence of the metal M and n is equal to the valence of the metal M if R4 is a neutral ligand. Exemplary metal complexes but not limited bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(1,5-cyclo-octadiene)ruthenium(II).
(f) Metal Alkoxy β-ketoiminates with the formula:
wherein M is a metal ion selected from Group 4 and 5 metals including titanium, zirconium, hafnium, vanadium, niobium, and tantalum; wherein R1-5 are linear, branched or cyclic independently selected from the group consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein m and n are at least 1 and the sum of m plus n is equal to the valence of the metal M.
(g) Metal β-ketoiminates with the formula:
wherein M is a metal ion selected from Group 11 metals including copper, silver, and gold; wherein R1-2 are linear, branched or cyclic independently selected from the groups consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl or halogen; R3-4 are linear or branched independently selected from the groups consisting of C1-6 alkyl, C1-6 alkenyl, C1-6 alkynyl and fluorinated C1-6 alkyl, preferably R4 is a 2 to 4 carbon atom linkage; R5-6 are linear, branched or cyclic independently selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C6-12 aryl, fluorinated C1-10 alkyl or connected to form a ring containing carbon, oxygen, or nitrogen atoms; X is either a carbon or a silicon, and Y is either an oxygen, or a nitrogen substituted with a hydrogen, C1-6 alkyl or C6-10 aryl group. Exemplary metal complexes include Cu(CF3C(O)CHC(NCH2CH2OSiMe2C2H3)CF3), Cu(CF3C(O)CHC(NCH2CH2OSiMe2C2H3)Me), Cu(MeC(O)CHC(NCH2CH(Me)OSiMe2C2H3)Me), Cu(MeC(O)CHC(NCH2CH2OSiMe2C2H3)Me), Cu(MeC(O)CHC(NCH2CH2N(Me)SiMe2C2H3)Me), Cu(MeC(O)CHC(NCH(Et)CH2OSiMe2C2H3)Me).
(h) Metal alkyl having the formula:
MR1xR2y
wherein M is selected from Group 2 to 14 where specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, and Pb; wherein R1 and R2 are linear, branched or cyclic independently selected from the groups consisting of hydrogen, C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C3-10 alkylsilyl, C6-12 aryl, and fluorinated C1-10 alkyl, cyclopendienyl (Cp) and alkylcyclopendienyl; and wherein x is the integer 0, 1, 2, 3, or 4; y is the integer 0, 1, 2, 3, or 4 and x+y=the valence of M; and Me represents —CH3. Exemplary metal complexes include CoCp2, SrCp2, Sr(iPrCp)2, Sr(iPr3 Cp)2, BaCp2, Ba(iPrCp)2, Ba(iPr3 Cp)2, RuCp2, Ru(EtCp)2, Ru(MeCp)(EtCp), Ru(DMPD)(EtCp), NiCp2, Cp2HfMe2, and Cp2ZrMe2.
(i) Alkyl metal carbonyl having the formula:
(CO)yMRx
wherein M is selected from Group 2 to 14 where specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, and Pb; wherein R is linear, branched or cyclic selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C3-10 alkylsilyl, C6-12 aryl, and fluorinated C1-10 alkyl, cyclopendienyl (Cp) and alkylcyclopendienyl; wherein x=2, 3, 4; y=1, or, 2, or 3, or 4 and x=the valence of M. Exemplary metal complexes include Cp2Ru(CO)2, (1,3-cyclohexdiene)Ru(CO)3, CpRe(CO)3, CpCo(CO)2 and iPrCpRe(CO)3.
(j) Metal carbonyl with the formula:
Mx(CO)y
wherein M is selected from Group 8 to 10 where specific examples of metals include Fe, Co, Ni, Ru, Ir, and Rh; wherein x is an integer 1, 2, or 3; y is an integer 4 to 12. Exemplary metal complexes include Ru3(CO)12, W(CO)6, Mo(CO)6, CO2(CO)8, and Ni(CO)4.
(k) Metal alkoxide with the formula:
M(OR)n
wherein M is selected from Group 2 to 14 where specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, and Pb; wherein R is linear, branched or cyclic selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein n is an integer 2, 3, 4 or 5, comprising the valence of M. Exemplary metal complexes include Ti(iPrO)4, Hf(OBut)4, Zr(OBut)4, and Ta2(OEt)10.
(i) Metal amides with the formula:
M(NR1R2)n
wherein M is selected from Group 2 to 14 where specific examples of metals include Mg, Ca, Sr, Ba, Y, La, Ce, Sm, Tb, Er, Yb, Lu, Fe, Co, Ni, Ru, Ir, Rh, Cu, Al, and Pb; wherein R1-2 are liner, branched or cyclic independently selected from the groups consisting of C1-10 alkyl, C1-10 alkenyl, C1-10 alkynyl, C3-10 alkylsilyl, C5-C10 cycloaliphatic, C6-12 aryl, and fluorinated C1-10 alkyl; wherein n is the integer 2, 3, 4, or 5, comprising the valence of M.
Exemplary metal complexes include tetrakis(dimethylamino)titanium (TDMAT), tetrakis(diethylamino)titanium (TDEAT), tetrakis(ethylmethyl)titanium (TEMAT), tetrakis(dimethylamino)zirconium (TDMAZ), tetrakis(diethylamino)zirconium (TDEAZ), tetrakis(ethylmethyl)zirconium (TEMAZ), tetrakis(dimethylamino)hafnium (TDMAH), tetrakis(diethylamino)hafnium (TDEAH), tetrakis(ethylmethyl)hafnium (TEMAH), tert-butylimino tri(diethylamino)tantalum (TBTDET), tert-butylimino tri(dimethylamino)tantalum (TBTDMT), tert-butylimino tri(ethylmethylamino)tantalum (TBTEMT), ethyllimino tri(diethylamino)tantalum (EITDET), ethyllimino tri(dimethylamino)tantalum (EITDMT), ethyllimino tri(ethylmethylamino)tantalum (EITEMT), tert-amylimino tri(dimethylamino)tantalum (TAIMAT), tert-amylimino tri(diethylamino)tantalum, pentakis(dimethylamino)tantalum, tert-amylimino tri(ethylmethylamino)tantalum, bis(tert-butylimino)bis(dimethylamino)tungsten (BTBMW), bis(tert-butylimino)bis(diethylamino)tungsten, bis(tert-butylimino)bis(ethylmethylamino)tungsten.
Summarizing, the ligand groups of the metal source containing precursor complexes in the broad practice of the present invention may be variously substituted to produce a wide variety of materials to optimize volatility, stability and film purity. Preferably, when the metal source precursor comprises two or more metal source containing precursor complexes, the ligands of the various metal source containing precursor complexes should be either: (a) identical, to result in degenerative ligand exchange (wherein any ligand exchange involves replacement of the ligand group by the same type ligand from another constituent of the multicomponent solution); or, (b) resistant to any detrimental non-degenerative ligand exchange in relation to one another, which would substantially impair or preclude the efficacy of the metal source complex for its intended purpose.
The metal source containing precursors generally are selected for solution applications on the basis of the following criteria: (i) the metal centers in the coordinated complexes should be as coordinatively saturated as possible, and in such respect multidentate ligands are preferred which occupy multiple coordination sites in the source precursor complex; (ii) the ligands preferably comprise sterically bulky groups such as isopropyl, t-butyl, and neopentyl, which prevent intermolecular interaction of the metal centers and thus hinder ligand exchange reaction and (iii) each of the individual metal source precursors in the solution should have a suitable vapor pressure characteristic, e.g., a vapor pressure of at least 0.001 Torr at the temperature and pressure conditions involved in their volatilization.
The solvent medium employed in formulating the metal source precursor solutions in accordance with the present invention is the organic amide class of the form, RCONR′R″, wherein R and R′ are linear or branched alkyl having from 1-10 carbon atoms or R and R′ can be connected to form a cyclic group (CH2)n, wherein n is from 4-6, preferably 5, and R″ is alkyl having from 1 to 4 carbon atoms and cycloalkyl. N-methyl, N-ethyl and N-cyclohexyl 2-pyrrolidinones are examples of the preferred solvents of the organic amide class.
The metal source precursor solutions of the present invention may be readily employed in chemical vapor deposition (CVD) applications including atomic layer deposition (ALD) for forming a metal-containing film on a substrate by the steps of volatilizing the metal source precursor liquid solution to yield a metal source vapor, and contacting the metal source vapor with the substrate, to deposit the metal-containing film thereon.
The following examples illustrate the preparation of the metal-containing complexes as precursor solutions in metal-containing film deposition processes and their use in a chemical vapor deposition process.
To a 2 mL vial, a faint yellow orange solution of titanium isopropoxide (0.10 g, 0.35 mmol) and 0.35 mL N-methyl-2-pyrrolidinone (NMP) was prepared. The solution was kept at room temperature over night and did not show any visible change.
To a 2 mL vial, a clear solution of La(thd)3) (0.05 g, 0.07 mmol) and 0.78 mL NMP was prepared.
Three solutions of tetrakis(ethylmethylamino)zirconium (TEMAZ) in NMP were prepared according to Table 1. All are clear yellow solutions.
The procedure of Example 1 is followed in preparing the above solution.
To a 2 mL vial, a clear orange solution of tetrakis(diethylamino)zirconium (TDEAZ) (0.05 g, 0.07 mmol) and 0.27 g of N-cyclohexyl-2-pyrrolidinone was prepared. The TGA graph indicates the solution is volatile and can be used as precursor source in a CVD or ALD process.
To a 2 mL vial, a clear yellow solution of tungsten carbonyl (0.10 g, 0.17 mmol) and 12 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph indicates the solution is volatile and can be used as precursor source for CVD or ALD.
To a 2 mL vial, a clear orange solution of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(1,5-cyclo-octadiene)ruthenium(II) (0.10 g, 0.28 mmol) and 20 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph indicates the solution is volatile and can be used as precursor source for CVD or ALD.
Table 2 below shows the weights of the copper metal complex Cu-KI3 (i.e., (CF3C(O)CHC(NCH2CH2OSiMe2C2H3)CF3)Cu) mixed with dry deoxygenated NMP solvent under nitrogen. After thoroughly mixing, three solutions 1, 2 and 3 were individually tested in a TGA/DSC (Differential Scanning Calorimetry) apparatus.
In this system, a small sample of 1, 2 or 3 was placed in a microbalance and a steady flow of nitrogen passed over the sample as it was steadily heated. Evaporation is registered as weight loss, manifest as a smooth curve down to almost complete evaporation. Since all three samples do not show two stages of evaporation per sample, i.e., the solvent evaporates first and then the copper complex evaporates, it is evident that these mixtures represent excellent blends for Direct Liquid Injection (DLI) type delivery for a CVD or ALD process. The TGA graphs are shown in
To a 2 mL vial, an amber solution of bis(ethylcyclopentadienyl)ruthenium (1.00 g, 2.88 mmol) and 2.97 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph indicates the solution is completely vaporized, leaving no residue.
To a 2 mL vial, a clear yellow solution of bis(n-propyltetramethyl cyclopentadienyl)barium (0.14 g, 0.30 mmol) and 1.24 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph shows the solution is more volatile than pure bis(n-propyltetramethylcyclopentadienyl)barium, suggesting NMP enhances the vaporization of bis(n-propyltetramethylcyclopentadienyl)barium.
To a 2 mL vial, a clear solution of tris(i-propylcyclopentadienyl)lanthanum (0.21 g, 0.46 mmol) and 0.94 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph indicates the solution is volatile and can be used as precursor source for CVD or ALD.
To a 2 mL vial, a yellow solution of bis(2,2,6,6-tetramethyl-3,5-heptanedionate)strontium (0.23 g, 0.51 mmol) and 1.38 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph shows the solution is more volatile than pure bis(2,2,6,6-tetramethyl-3,5-heptanedionate)strontium, suggesting NMP enhances the vaporization of bis(2,2,6,6-tetramethyl-3,5-heptanedionate)strontium.
To a 2 mL vial, a foggy white solution of bis(2,2,6,6-tetramethyl-3,5-heptanedionate)barium (0.14 g, 0.28 mmol) and 1.14 g of N-methyl-2-pyrrolidinone was prepared. The TGA graph indicates the solution is volatile and can be used as precursor source for CVD or ALD.
Process details: A Gartek single wafer CVD reactor fitted with a Direct Liquid Injector (DLI) system was used to individually process ruthenium and titanium coated silicon wafers at a process chamber pressure of 1 Torr and wafer temperature of 150° C. The copper precursor was utilized as a 3:1 by weight ratio of KI3 dissolved in dry N-methylpyrolidone (NMP) and injected into the vaporizer at a rate of 41 mg/min using an evaporation temperature of 100° C. with an argon carrier gas flow of 250 sccm. Formic acid vapor was delivered by the DLI of 82 mg of liquid formic acid/min using an evaporation temperature of 65° C. with an argon carrier gas flow rate of 100 sccm. Run time was 30 minutes.
Results: Ruthenium: 427.5 nm of copper (as confirmed by EDX (energy dispersive x-ray) analysis) were deposited to give, after correcting for the ruthenium underlayer conductivity, a resistivity of 2.6 μΩcm.
Results: Titanium nitride: 386.7 nm of copper (as confirmed by EDX analysis) were deposited to give, after correcting for the titanium nitride underlayer, a resistivity of 2.3 μΩcm.
This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/911,970 filed 16 Apr. 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60911970 | Apr 2007 | US |
