Vapor source using solutions of precursors in terpenes

Abstract

This disclosure relates to terpene solutions of metal precursors used for chemical vapor deposition, atomic layer deposition, spray pyrolysis or misted deposition. The terpenes do not supply impurities such as oxygen or halogens to the material being produced, nor do they etch or corrode them. In spray pyrolysis or misted deposition, small droplets provide uniform coating. Terpenes have high flash points and low flammability, reducing the risk of fires. Terpenes have low toxicity and are biodegradable. They are available in large amounts from renewable, natural plant sources, and are low in cost.

Claims

1. A liquid solution comprising: an acyclic, terpene solvent; and a precursor containing at least one metal or metalloid atom; wherein the terpene solvent is a liquid; wherein the terpene solvent and the precursor have vaporization rates in which the T.sub.1/2 values of the terpene solvent and the precursor differ by less than 100° C., as determined by thermogravimetric analyses; and wherein the liquid solution is suitable for use in one of chemical vapor deposition and atomic layer deposition.

2. The solution of claim 1, wherein the terpene is alloocimene.

3. The solution of claim 1, wherein the terpene is farnesene.

4. The solution of claim 1, wherein the terpene is a monoterpene.

5. The solution of claim 1, wherein the terpene is a sesquiterpene.

6. The solution of claim 1, wherein the terpene is a diterpene.

7. The solution of claim 1, wherein the terpene is a triterpene.

8. The solution of claim 4, wherein the monoterpene has the formula, ##STR00014##

9. The solution of claim 4, wherein the monoterpene has the formula, ##STR00015##

10. The solution of claim 4, wherein the monoterpene has the formula, ##STR00016##

11. The solution of claim 5, wherein the sesquiterpene has the formula, ##STR00017##

12. The solution of claim 5, wherein the sesquiterpene has the formula, ##STR00018##

13. The solution of claim 6, wherein the diterpene has the formula, ##STR00019##

14. The solution of claim 7, wherein the triterpene has the formula, ##STR00020##

15. The solution of claim 1, wherein the precursor is bis(N,N′-di-tert-butylacetamidinato) nickel(II) and the acyclic terpene solvent is alloocimene.

16. The solution of claim 1, wherein the precursor is bis(N,N′-di-tert-butylacetamidinato)nickel(II) and the acyclic terpene solvent is famesene.

17. The solution of claim 1, wherein the concentration of the solution is from 0.25 to 0.50 molar.

18. The solution of claim 1, wherein the concentration of the solution is from 0.5 to 1.0 molar.

19. The solution of claim 1, wherein the concentration of the solution is greater than 1 molar.

20. The solution of claim 1, wherein the T.sub.1/2 values of the precursor and the solvent differ by less than 50° C., as determined by thermogravimetric analyses.

21. The solution of claim 1, wherein the T.sub.1/2 values of the precursor and the solvent differ by less than 25° C., as determined by thermogravimetric analyses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a thermogravimetric analysis of alloocimene.

(2) FIG. 2 shows a thermogravimetric analysis of mixed isomers of farnesenes.

(3) FIG. 3 shows a thermogravimetric analysis of a nickel amidinate precursor.

DETAILED DESCRIPTION

Definitions

(4) The term “terpene” is used in this disclosure to mean an organic molecule containing at least one unit of isoprene. One or more isoprene units may be linked together “head to tail” or “head to head” to form linear chains or they may be arranged to form rings. The terpene may be oxygenated.

(5) The term “monoterpene” is used in this disclosure to mean a terpene containing two isoprene units.

(6) The term “sesquiterpene” is used in this disclosure to mean a terpene containing three isoprene units.

(7) The term “diterpene” is used in this disclosure to mean a terpene containing four isoprene units.

(8) The term “triterpene” is used in this disclosure to mean a terpene containing six isoprene units.

(9) The term “isoprene” is used in this disclosure to mean a molecule having the formula C.sub.5H.sub.8.

Solvents

(10) In one or more embodiments, the monoterpene 7-methyl-3-methyleneocta-1,6-diene, also called beta-myrcene, is used as a solvent. It has formula 1, shown below:

(11) ##STR00001##
It may be used as a mixture of various isomers of structure 1.

(12) In one or more embodiments, the monoterpene 3,7-dimethylocta-1,3,6-triene, also called beta-ocimene, is used as a solvent. It has formula 2,

(13) ##STR00002##
It may be used as a mixture of various isomers of structure 2.

(14) In one or more embodiments, the monoterpene 2,6-dimethylocta-2,4,6-triene, also called alloocimene, is used as a solvent. It has formula 3,

(15) ##STR00003##
It may be used as a mixture of various isomers of structure 3.

(16) In one or more embodiments, the sesquiterpene 3,7,11-trimethyldodeca-1,3,6,10-tetraene, also called alpha-farnesene, is used as a solvent. It has formula 4,

(17) ##STR00004##
It may be used as a mixture of various isomers of structure 4.

(18) In one or more embodiments, the sesquiterpene 7,11-dimethyl-3-methylenedodeca-1,6,10-triene, also called beta-farnesene, is used as a solvent. It has formula 5,

(19) ##STR00005##
It may be used as a mixture of various isomers of structure 4. Commercial sources usually supply mixtures of farnesenes 4 and 5.

(20) In some embodiments, a diterpene 3,7,11,15-tetramethylhexadeca-1,3,6,10,14-pentaene, also called alpha-springene, is used as a solvent. It has formula 6,

(21) ##STR00006##
It may be used as a mixture of various isomers of structure 6.

(22) In other embodiments, a triterpene, 2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene, also called squalene, is used as a solvent. It has formula 7,

(23) ##STR00007##
It may be used as a mixture of various isomers of structure 7.

Solutions

(24) Many types of metal or metalloid precursors may be dissolved in terpenes and their solutions then used in CVD, ALD, SP and/or MD. The metals include, but are not limited to, any of the transition metals, main-group metals, lanthanide metals. Transition metals of interest include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt and Au. Main group metals of interest include Li, Na, K, Mg, Ca, Sr, Ba, Al, Ga, In, Sn, Pb, Sb and Bi. Lanthanide metals of interest include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Metalloids of interest include B, Si, Ge, As and Te. The metal precursor compounds may contain metals bonded to anionic ligands that form amidinates, β-diketonates, β-thioketonates, β-ketoiminates, β-diiminates, alkoxides, dialkylamides, alkyls, cycloalkyls, cycloalkenyls such as cyclopentadienyls, halides, and/or neutral ligands such as carbonyls, trialkylamines, pyridines, trialkylphosphines, ethers, thioethers, nitriles, isonitriles, as well as heteroleptic compounds containing two or more of these ligands.

(25) As a guide to the choice of a terpene solvent whose vaporization rate matches that of a metal precursor, thermogravimetric analysis (TGA) is useful. In TGA, a small amount (typically 10 to 20 milligrams) of the solvent or metal precursor is evaporated into a flowing stream of nitrogen gas. The remaining mass of the sample is recorded as a function of temperature. TGA data for alloocimene is plotted in FIG. 1. One half of its mass is lost by a temperature of 112° C., which is known as T.sub.1/2. TGA data for farnesenes is plotted in FIG. 2. One half of its mass is lost by a temperature of 177° C. TGA of the nickel precursor, bis(N,N′-di-tert-butylacetamidinato)nickel(II), is shown in FIG. 3. One half of its mass is lost by 197° C. Comparison of these data show that farnesene solvent provides a good match to the vaporization rate of this nickel precursor, in that the difference between farnesene's T.sub.1/2 and the nickel precursor's T.sub.1/2 is only 20° C. Alloocimene vaporizes somewhat more quickly than the nickel precursor (T.sub.1/2 for alloocimene is 85° C. below that of the nickel precursor), but it is still a useful solvent for use in vaporization of this precursor. In some embodiments, when matching a terpene solvent and a metal precursor based on vaporization rates, the difference in T.sub.1/2 values between precursor and solvent is less than 100° C. In other embodiments, the difference in T.sub.1/2 values between precursor and solvent is less than 50° C. In still other embodiments, the difference in T.sub.1/2 values between precursor and solvent is less than 25° C.

(26) Useful concentrations of the solutions are larger than 0.25 molar in some embodiments, larger than 0.5 molar in other embodiments, and larger than 1 molar in still other embodiments.

(27) As a first step in the use of these solutions in CVD, ALD, SP or MD processes, they may be nebulized into a mist of small droplets. Conventional nebulization or spray equipment may be used. For example, U.S. Pat. No. 6,180,190 describes an ultrasonic nebulizer suitable for use with these solutions. Commercial systems for vaporization of solutions are sold by Brooks Instrument Company, MKS Instruments, Kemstrean and other companies. In some cases, the solution may be vaporized for use in CVD or ALD without nebulization; see for example the method described in the Review of Scientific Instruments, volume 74, pages 3879-3980 (2008), in which the solution flows down a heated tube along with a carrier gas.

Example 1

Solution of a Nickel Amidinate in Alloocimene

(28) A nickel precursor, bis(N,N′-di-tert-butylacetamidinato)nickel(II),

(29) ##STR00008##
was dissolved in alloocimene. Its solubility was found to be over 40 weight percent. The density of the solution is 0.97 g cm.sup.−3, corresponding to a volume concentration over 1.0 molar.

Example 2

Solution of a Nickel Amidinate in Farnesene Isomers

(30) The nickel precursor, bis(N,N′-di-tert-butylacetamidinato)nickel(II), of Example 1, was dissolved in mixed isomers of farnesene. Its solubility was found to be over 37 weight percent. The density of the solution is 0.96 g cm.sup.−3, corresponding to a volume concentration over 0.9 molar.

Comparative Example 1

Solution of a Nickel Amidinate in a Saturated Hydrocarbon

(31) Examples 1 and 2 were repeated except that dodecane was used as a solvent in place of alloocimene or farnesenes. The solubility was around 0.25 molar.

Example 3

Solution of a Copper Amidinate in Farnesene Isomers

(32) A copper amidinate precursor, copper(I) (N,N′-di-sec-butylacetamidinate),

(33) ##STR00009##
is dissolved in mixed isomers of farnesene. Its solubility is high.

Example 4

Solution of a Yttrium Amidinate in Farnesene Isomers

(34) A yttrium precursor, tris(N,N′-diisopropylacetamidinato)yttrium(III),

(35) ##STR00010##
is dissolved in mixed isomers of farnesenes. Its solubility is high.

Example 5

Solution of a Lanthanum Amidinate in Farnesene Isomers

(36) A lanthanum precursor, tris(N,N′-diisopropylformamidinato)lanthanum(III),

(37) ##STR00011##
is dissolved in mixed isomers of farnesenes. Its solubility is high.

Example 6

Solution of a Cobalt Amidinate in Alloocimene

(38) A cobalt amidinate precursor, bis(N,N′-diisopropylacetamidinato)cobalt(II),

(39) ##STR00012##
is dissolved in alloocimene. Its solubility is high.

Example 7

Solution of a Manganese Amidinate in Farnesene Isomers

(40) A manganese amidinate precursor, bis(N,N′-diisopropylpentamidinato)manganese(II),

(41) ##STR00013##
is dissolved in mixed isomers of farnesene. Its solubility is high.

Example 8

CVD of Nickel Nitride Using a Solution in Alloocimene

(42) A solution prepared as in Example 1 is flowed at a rate of 0.1 g min.sup.−1 and vaporized into a 60 sccm flow of pure nitrogen gas, and mixed with a flow of 30 sccm ammonia gas and 30 sccm hydrogen gas. This gas mixture is passed into a cylindrical deposition chamber with 3.5 cm inner diameter held at a temperature of 160° C. and a total pressure of 5 Torr. Substrates of silicon and glass resting on a half-cylinder in the deposition chamber are coated with nickel nitride.

(43) It is recognized, of course, that those skilled in the art may make various modifications and additions to the processes and solutions of this disclosure without departing from the spirit and scope of the present contribution to the art. Accordingly, it is to be understood that the protection sought to be afforded hereby should be deemed to extend to the subject matter of the claims and all equivalents thereof fairly within the scope of this disclosure.