COMPOUNDS AND PROCESSES FOR EXTREME ULTRAVIOLET LITHOGRAPHY

Abstract

The present disclosure includes the preparation of mixed-ligand compounds, such as tin(II) cyclopentadienylide complexes. The compounds of the present disclosure can be used as atomic layer deposition (ALD) precursors for extreme ultraviolet (EUV) lithography. The compounds of the present disclosure can also be used as plasma chemical vapor deposition (CVD) precursors for EUV lithography.

Claims

1. A cyclopentadienylide tin(II) compound of formula (I) comprising: ##STR00021## wherein each R.sup.2 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4, wherein ##STR00022## and wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4.

2. The compound of claim 1, wherein each R.sup.2 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

3. The compound of claim 1, wherein each R.sup.2 is a methyl group.

4. The compound of claim 1, wherein each R.sup.2 is a C.sub.1-C.sub.4alkyl group.

5. The compound of claim 1, wherein the C.sub.1-C.sub.4 is branched or unbranched.

6. The compound of claim 1, wherein the C.sub.1-C.sub.4 is substituted or unsubstituted.

7. The compound of claim 1, wherein each R.sup.3-R.sup.7 is hydrogen.

8. The compound of claim 1, wherein each R.sup.2 is hydrogen and each R.sup.3-R.sup.7 is hydrogen.

9. A method of forming a cyclopentadienylide tin(II) compound of formula (I): ##STR00023## wherein each R.sup.2 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4 group, wherein ##STR00024## wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4, and wherein the method comprises: contacting [Sn(N(R.sup.2).sub.2).sub.2].sub.2 with Cp.sub.2Sn or CpH.

10. The method of claim 9, wherein [Sn(N(R.sup.2).sub.2).sub.2].sub.2 is dissolved in tetrahydrofuran before the contacting step.

11. The method of claim 10, wherein R.sup.2 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

12. The method of claim 9, wherein Cp.sub.2Sn or CpH is dissolved in tetrahydrofuran before the contacting step.

13. A cyclopentadienylide tin(II) compound of formula (II): ##STR00025## wherein each R.sup.1 is independently hydrogen, C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4, and wherein ##STR00026## and wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4.

14. The compound of claim 13, wherein each R.sup.1 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

15. The compound of claim 13, wherein each R.sup.1 is a methyl group.

16. The compound of claim 13, wherein each R.sup.1 is a C.sub.1-C.sub.4alkyl group.

17. The compound of claim 13, wherein each R.sup.3-R.sup.7 is hydrogen.

18. The compound of claim 13, wherein each R.sup.1 is hydrogen and each R.sup.3-R.sup.7 is hydrogen.

19. A method of forming a cyclopentadienylide tin(II) compound of formula (II): ##STR00027## wherein each R.sup.1 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4 group, wherein ##STR00028## wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4, and wherein the method comprises: contacting [Sn(O(R.sup.1)).sub.2].sub.2 with Cp.sub.2Sn.

20. The method of claim 19, wherein [Sn(O(R.sup.1)).sub.2].sub.2 is dissolved in tetrahydrofuran before the contacting step.

Description

DRAWINGS

[0042] Some embodiments of the disclosure are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the embodiments shown are by way of example and for purposes of illustrative discussion of embodiments of the disclosure. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the disclosure may be practiced.

[0043] FIG. 1 depicts a non-limiting embodiment of a method 100 for the synthesis of cyclopentadienylide tin(II) amides described herein.

[0044] FIG. 2 depicts a non-limiting embodiment of a method 200 for the synthesis of cyclopentadienylide tin(II) alkoxides described herein.

[0045] FIG. 3 depicts a non-limiting example of a method 300 for the synthesis of cyclopentadienyl tin(II) amides using Cp.sub.2Sn described herein.

[0046] FIG. 4 depicts a solid-state structure of [CpSn(N(CH.sub.3).sub.2)].sub.2 as determined by X-ray crystallographic analysis.

[0047] FIG. 5 depicts a non-limiting example of a method 600 for the synthesis of cyclopentadienyl tin(II) amides using CpH described herein.

DETAILED DESCRIPTION

[0048] Among those benefits and improvements that have been disclosed, other objects and advantages of this disclosure will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the disclosure that may be embodied in various forms. In addition, each of the examples given regarding the various embodiments of the disclosure which are intended to be illustrative, and not restrictive.

[0049] All prior patents and publications referenced herein are incorporated by reference in their entireties.

[0050] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases in one embodiment, in an embodiment, and in some embodiments as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases in another embodiment and in some other embodiments as used herein do not necessarily refer to a different embodiment, although it may. All embodiments of the disclosure are intended to be combinable without departing from the scope or spirit of the disclosure.

[0051] As used herein, the term based on is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of a, an, and the include plural references. The meaning of in includes in and on.

[0052] The present disclosure relates to compounds of, including the preparation of, mixed-ligand compounds. The mixed-ligand compounds include tin(II) cyclopentadienylide complexes including cyclopentadienylide amides and cyclopentadienylide alkoxides. The compounds of the present disclosure can be used as atomic layer deposition (ALD) precursors for EUV lithography. For example, the compounds of the present disclosure can be used for EUV hard mask applications. The tin compounds can be used in other applications as well (e.g., polyvinyl chloride (PVC) stabilizers, biocides, precursors for tin(IV) oxide coatings, and catalysts for organic transformations).

[0053] FIG. 1 depicts a non-limiting embodiment of a method 100 for the synthesis of cyclopentadienylide tin(II) amides described herein. In some embodiments, the present disclosure includes contacting [Sn(N(R.sup.2).sub.2).sub.2].sub.2 with Cp.sub.2Sn 110 or CpH 120. In some embodiments, the method 100 includes dissolving [Sn(N(R.sup.2).sub.2).sub.2].sub.2 in tetrahydrofuran (THF) before the contacting step. In some embodiments, the method 100 includes dissolving Cp.sub.2Sn or CpH in tetrahydrofuran (THF) before the contacting step.

[0054] In some embodiments, using Cp.sub.2Sn 110 in the method 100 can include loading [Sn(N(R.sup.2).sub.2).sub.2].sub.2 into a container (e.g., a vial) and dissolving in tetrahydrofuran (THF). In a separate container, Cp.sub.2Sn can be added and dissolved in tetrahydrofuran (THF). The solution with [Sn(N(R.sup.2).sub.2).sub.2].sub.2 dissolved in THF can then be added to the solution with Cp.sub.2Sn dissolved in THF. The combined solution of [Sn(N(R.sup.2).sub.2).sub.2].sub.2, Cp.sub.2Sn, and tetrahydrofuran (THF) can be stirred for a period of time. The combined solution can be stirred for an extended period of time, e.g., between one to twelve hours. For example, the combined solution can be stirred for greater than one hour, greater than three hours, greater than six hours, greater than nine hours, less than twelve hours, less than nine hours, less than six hours, or less than three hours. After stirring the combined solution, the combined solution can then be dried. In some examples, the combined solution can be dried under reduced pressure to yield a solid mass. The reduced pressure can be selected from a range of reduced pressures, e.g., 100 mTorr-760 Torr (atm). For example, the reduced pressure can be greater than 100 mTorr, greater than 1 torr, greater than 10 torr, greater than 100 torr, greater than 300 torr, greater than 500 torr, greater than 700 torr, less than 760 torr, less than 700 torr, less than 500 torr, less than 300 torr, less than 100 torr, less than 10 torr, or less than 1 torr. In some examples, the stirred solution can be dried under dynamic vacuum, including at the reduced pressure values described herein. X-ray quality crystals can be grown by slow evaporation of a solution, such as a NMR solvent, including a concentrated benzene (C.sub.6D.sub.6) solution, Tetrahydrofuran (THF), diethyl ether (Et.sub.2O), or toluene (PhMe).

[0055] In some embodiments, using CpH 120 in the method 100 can include diluting cyclopentadiene with tetrahydrofuran (THF). The solution of cyclopentadiene with tetrahydrofuran (THF) can then be added to a stirred solution of THF and [Sn(N(R.sup.2).sub.2).sub.2].sub.2. The combined solution of [Sn(N(R.sup.2).sub.2).sub.2].sub.2, CpH, and tetrahydrofuran (THF) can be stirred for a period of time. The combined solution can be stirred for an extended period of time, e.g., between one to twelve hours. For example, the combined solution can be stirred for greater than one hour, greater than three hours, greater than six hours, greater than nine hours, less than twelve hours, less than nine hours, less than six hours, or less than three hours. After stirring the combined solution, the combined solution can then be dried. In some examples, the stirred solution can be dried under reduced pressure to yield a solid mass. For example, the reduced pressure can be greater than 100 mTorr, greater than 1 torr, greater than 10 torr, greater than 100 torr, greater than 300 torr, greater than 500 torr, greater than 700 torr, less than 760 torr, less than 700 torr, less than 500 torr, less than 300 torr, less than 100 torr, less than 10 torr, or less than 1 torr. In some examples, the stirred solution can be dried under dynamic vacuum, including at the reduced pressure values described herein.

[0056] In some embodiments, using Cp.sub.2Sn 110 or CpH 120 in the method 100 of the present disclosure includes a cyclopentadienylide tin(II) compound of formula (I):

##STR00009##

[0057] In some embodiments, each R.sup.2 is independently hydrogen or C.sub.1-C.sub.4.

[0058] In some embodiments, each R.sup.2 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group. In some embodiments, each R.sup.2 is a methyl group. In some embodiments, each R.sup.2 is a C.sub.1-C.sub.4 alkyl group.

[0059] In some embodiments, the cyclopentadienylide (Cp) has the formula (1):

##STR00010##

[0060] In some embodiments, R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4. In some embodiments, each R.sup.3-R.sup.7 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group. In some embodiments, each R.sup.2 is a methyl group.

[0061] In some embodiments, the C.sub.1-C.sub.4 is branched or unbranched. In some embodiments, the C.sub.1-C.sub.4 is substituted or unsubstituted.

[0062] In some embodiments, each R.sup.2 is a methyl group and each R.sup.3-R.sup.7 is hydrogen. In some embodiments, each R.sup.2 is hydrogen and each R.sup.3-R.sup.7 is hydrogen.

[0063] In some embodiments, the present disclosure includes forming a cyclopentadienylide tin(II) compound of formula (I). In some embodiments, each R.sup.2 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4 group.

[0064] In some embodiments, the cyclopentadienylide (Cp) has the formula (1). In some embodiments, R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4. In some embodiments, the method 100 includes forming a cyclopentadienylide tin(II) compound of formula (I) by contacting [Sn(N(R.sup.2).sub.2).sub.2].sub.2 with Cp.sub.2Sn or CpH. In some embodiments, the method 100 includes dissolving [Sn(N(R.sup.2).sub.2).sub.2].sub.2 in tetrahydrofuran (THF) before the contacting step. In some embodiments, the method 100 includes dissolving Cp.sub.2Sn or CpH in tetrahydrofuran (THF) before the contacting step.

[0065] FIG. 2 depicts a non-limiting embodiment of a method 200 for the synthesis of cyclopentadienylide tin(II) alkoxides described herein. In some embodiments, the present disclosure includes contacting [Sn(O(R.sup.1)).sub.2].sub.2 with Cp.sub.2Sn. In some embodiments, the method 200 includes dissolving [Sn(O(R.sup.1)).sub.2].sub.2 in tetrahydrofuran (THF) before the contacting step. In some embodiments, the method 200 includes dissolving Cp.sub.2Sn in tetrahydrofuran (THF) before the contacting step.

[0066] In some embodiments, using Cp.sub.2Sn in the method 200 of the present disclosure includes a cyclopentadienylide tin(II) compound of formula (II):

##STR00011##

[0067] In some embodiments, each R.sup.1 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4.

[0068] In some embodiments, each R.sup.1 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group. In some embodiments, each R.sup.1 is a methyl group. In some embodiments, each R.sup.1 is a C.sub.1-C.sub.4 alkyl group. In some embodiments, each R.sup.1 is a C.sub.1-C.sub.4 alkyl group that contains at least one halide (e.g., fluorine (F), chlorine (CI), bromine (Br), or iodine (I)). For example, R.sup.1 can be OCH.sub.2CF.sub.3 (trifluoro ethoxide).

[0069] In some embodiments, the cyclopentadienylide (Cp) has the formula (1):

##STR00012##

[0070] In some embodiments, R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4. In some embodiments, each R.sup.3-R.sup.7 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group. In some embodiments, each R.sup.1 is a methyl group.

[0071] In some embodiments, the C.sub.1-C.sub.4 is branched or unbranched. In some embodiments, the C.sub.1-C.sub.4 is substituted or unsubstituted.

[0072] In some embodiments, each R.sup.1 is a methyl group and each R.sup.3-R.sup.7 is hydrogen. In some embodiments, each R.sup.1 is hydrogen and each R.sup.3-R.sup.7 is hydrogen.

[0073] In some embodiments, the present disclosure includes forming a cyclopentadienylide tin(II) compound of formula (II). In some embodiments, each R.sup.1 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4 group.

[0074] In some embodiments, the cyclopentadienylide (Cp) has the formula (1). In some embodiments, R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4. In some embodiments, the method 200 includes forming a cyclopentadienylide tin(II) compound of formula (II) by contacting [Sn(O(R.sup.1)).sub.2].sub.2 with Cp.sub.2Sn. In some embodiments, the method 200 includes dissolving [Sn(O(R.sup.1)).sub.2].sub.2 in tetrahydrofuran (THF) before the contacting step. In some embodiments, the method 200 includes dissolving Cp.sub.2Sn in tetrahydrofuran (THF) before the contacting step.

EXAMPLES

Example 1

[0075] FIG. 3 depicts a non-limiting example of a method 300 for the synthesis of cyclopentadienyl tin(II) amides using Cp.sub.2Sn described herein. [Sn(N(CH.sub.3).sub.2).sub.2].sub.2 (1.0 g, 3.98 mmol) was loaded into an amber 40 mL vial and dissolved in tetrahydrofuran (10 mL). Cp.sub.2Sn was loaded into a separate amber 40 mL vial equipped with a magnetic stir bar and dissolved in THF (10 mL). The [Sn(N(CH.sub.3).sub.2).sub.2].sub.2 solution was added to the Cp.sub.2Sn solution with stirring over the course of five minutes. The resulting pale-yellow solution was stirred overnight at room temperature. The next day the pale-yellow solution was dried under reduced pressure to yield [CpSn(N(CH.sub.3).sub.2)].sub.2 as an off-white/yellow solid (Mass: 1.63 g, Yield: 89.5%). X-ray quality crystals were grown by slow evaporation of a concentrated C.sub.6D.sub.6 solution. .sup.1H-NMR (400 MHz, d.sub.8-THF, 298K): 2.65 (s, 6H); 2.73 (s, 6H); 6.12 (s, 10H) ppm; .sup.13C{.sup.1H}-NMR (100 MHz, d.sub.8-THF, 298K): 44.06 ppm; .sup.119Sn{.sup.1H}-NMR (149 MHz, d.sub.8-THF, 298K): 287.3, 306.12 ppm.

[0076] FIG. 4 depicts a solid-state structure of [CpSn(N(CH.sub.3).sub.2)].sub.2 as determined by X-ray crystallographic analysis.

[0077] Table 1 depicts crystal data and structure refinement for [CpSn(N(CH.sub.3).sub.2)].sub.2.

TABLE-US-00001 Empirical formula C20 H22 D6 N2 Sn2 Molecular formula C14 H22 N2 Sn2, C6 D6 Formula weight 539.86 Temperature 100.00 K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 5.7015(2) ; = 109.2680(10) b = 8.8255(2) ; = 90.5790(10) c = 11.3321 (3) ; = 106.5100(10) Volume 512.67(3) .sup.3 Z 1 Density (calculated) 1.749 Mg/m.sup.3 Absorption coefficient 2.440 mm.sup.1 F(000) 262 Crystal size 0.18 0.16 0.11 mm.sup.3 Crystal color, habit colorless block Theta range for data 2.567 to 26.365 collection Index ranges 7 <= h <= 7, 11 <= k <= 11, 14 <= l <= 14 Reflections collected 16961 Independent reflections 2079 [R(int) = 0.0308] Completeness to theta = 99.9% 25.242 Absorption correction None Max. and min. transmission 0.2607 and 0.2204 Refinement method Full-matrix least-squares on F.sup.2 Data/restraints/parameters 2079/0/115 Goodness-of-fit on F.sup.2 1.119 Final R indices [I > R1 = 0.0107, wR2 = 0.0267 2sigma(I)] R indices (all data) R1 = 0.0109, wR2 = 0.0268 Extinction coefficient 0.0049(8) Largest diff. peak and hole 0.315 and 0.280 e..sup.3

Example 2

[0078] FIG. 5 depicts a non-limiting example of a method 600 for the synthesis of cyclopentadienyl tin(II) amides using CpH described herein.

[0079] Cyclopentadiene (0.158 g, 2.40 mmol) was diluted with 3 mL of tetrahydrofuran and added dropwise over the course of five minutes to a stirred 3 mL THF solution of [Sn(N(CH.sub.3).sub.2).sub.2].sub.2 (0.500 g, 1.20 mmol) and the resulting pale-yellow solution stirred overnight. The next day the volatiles were removed under reduced pressure to yield [CpSn(N(CH.sub.3).sub.2)].sub.2 as a pale-yellow solid. .sup.1H-, .sup.13C-, and .sup.119Sn-NMR collected on a d.sub.8-THF solution of the product are consistent with that obtained by combining Cp.sub.2Sn and [Sn(N(CH.sub.3).sub.2).sub.2].sub.2.

ASPECTS

[0080] Various Aspects are described below. It is to be understood that any one or more of the features recited in the following Aspect(s) can be combined with any one or more other Aspect(s).

[0081] Aspect 1. A cyclopentadienylide tin(II) compound of formula (I) comprising:

##STR00013## [0082] wherein each R.sup.2 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4, [0083] wherein

##STR00014##

and [0084] wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4.

[0085] Aspect 2. The compound of Aspect 1, wherein each R.sup.2 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

[0086] Aspect 3. The compound of Aspect 1, wherein each R.sup.2 is a methyl group.

[0087] Aspect 4. The compound of Aspect 1, wherein each R.sup.2 is a C.sub.1-C.sub.4alkyl group.

[0088] Aspect 5. The compound as in any one of the preceding Aspects, wherein the C.sub.1-C.sub.4 is branched or unbranched.

[0089] Aspect 6. The compound as in any one of the preceding Aspects, wherein the C.sub.1-C.sub.4 is substituted or unsubstituted.

[0090] Aspect 7. The compound as in any one of the preceding Aspects, wherein each R.sup.3-R.sup.7 is hydrogen.

[0091] Aspect 8. The compound of Aspect 1, wherein each R.sup.2 is hydrogen and each R.sup.3-R.sup.7 is hydrogen.

[0092] Aspect 9. A method of forming a cyclopentadienylide tin(II) compound of formula (I):

##STR00015## [0093] wherein each R.sup.2 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4 group, [0094] wherein

##STR00016## [0095] wherein R.sup.3-R.sup.7 is hydrogen or 1-4, an [0096] wherein the method comprises: contacting [Sn(N(R.sup.2).sub.2).sub.2].sub.2 with Cp.sub.2Sn or CpH.

[0097] Aspect 10. The method of Aspect 9, wherein [Sn(N(R.sup.2).sub.2).sub.2].sub.2 is dissolved in tetrahydrofuran before the contacting step.

[0098] Aspect 11. The method of Aspect 9 or Aspect 10, wherein R.sup.2 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

[0099] Aspect 12. The method as in one of Aspects 9-11, wherein Cp.sub.2Sn or CpH is dissolved in tetrahydrofuran before the contacting step.

[0100] Aspect 13. A cyclopentadienylide tin(II) compound of formula (II):

##STR00017## [0101] wherein each R.sup.1 is independently hydrogen, C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4, and [0102] wherein

##STR00018##

and [0103] wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4.

[0104] Aspect 14. The compound of Aspect 13, wherein each R.sup.1 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

[0105] Aspect 15. The compound of Aspect 13, wherein each R.sup.1 is a methyl group.

[0106] Aspect 16. The compound of Aspect 13, wherein each R.sup.1 is a C.sub.1-C.sub.4alkyl group.

[0107] Aspect 17. The compound as in any one of the preceding Aspects, wherein the C.sub.1-C.sub.4 is branched or unbranched.

[0108] Aspect 18. The compound as in any one of the preceding Aspects, wherein the C.sub.1-C.sub.4 is substituted or unsubstituted.

[0109] Aspect 19. The compound as in any one of the preceding Aspects, wherein each R.sup.3-R.sup.7 is hydrogen.

[0110] Aspect 20. The compound of Aspect 13, wherein each R.sup.1 is hydrogen and each R.sup.3-R.sup.7 is hydrogen.

[0111] Aspect 21. A method of forming a cyclopentadienylide tin(II) compound of formula (II):

##STR00019## [0112] wherein each R.sup.1 is independently hydrogen, a C.sub.1-C.sub.4, or a halide containing C.sub.1-C.sub.4 group, [0113] wherein

##STR00020## [0114] wherein R.sup.3-R.sup.7 is hydrogen or C.sub.1-C.sub.4, and wherein the method comprises: contacting [Sn(O(R.sup.1)).sub.2].sub.2 with Cp.sub.2Sn.

[0115] Aspect 22. The method of Aspect 21, wherein [Sn(O(R.sup.1)).sub.2].sub.2 is dissolved in tetrahydrofuran before the contacting step.

[0116] Aspect 23. The method of Aspect 21 or Aspect 22, wherein R.sup.1 is independently a methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, or sec-butyl group.

[0117] Aspect 24. The method as in one of Aspects 21-23, wherein Cp.sub.2Sn is dissolved in tetrahydrofuran before the contacting step.

[0118] It is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size, and arrangement of parts without departing from the scope of the present disclosure. This Specification and the embodiments described are examples, with the true scope and spirit of the disclosure being indicated by the claims that follow.