UNITED STATES PATENT APPLICATION FOR

SILICON POLYMERS, METHODS OF POLYMERIZING SILICON COMPOUNDS, AND METHODS OF FORMING THIN FILMS FROM SUCH

SILICON POLYMERS

Inventors:

Dmitry KARSHTEDT

Joerg ROCKENBERGER

Fabio ZURCHER

Brent RIDLEY

Erik SCHER

Docket No.: IDR0884WO

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

60/850,094, filed October 6, 2006 (Attorney Docket No. IDR0881), and U.S. Provisional Application No. 60/905,403, filed March 5, 2007 (Attorney Docket No. IDR0883).

FIELD OF THE INVENTION

[0002] The present invention relates to poly- and/or oligosilane compositions, methods for the oligomerization and/or polymerization of hydro(aryl)silanes, methods of forming a thin silicon-containing film from such poly- and/or oligosilanes, thin silicon- containing films formed by such methods and from such poly- and/or oligosilanes, and structures containing such thin films.

BACKGROUND OF THE INVENTION

[0003] Cyclopentasilane is a known compound that is liquid at ambient temperatures and can form silicon films with useful photovoltaic or electrical properties. However, cyclopentasilane is relatively volatile, and there has been a recent interest in methods of forming higher molecular weight silanes that have similar chemical properties, but that are less volatile at ambient temperatures.

[0004] FIG. IA shows an equation for the catalytic dehydrogenative polymerization of cyclopentasilane by a Zr catalyst such as Cp ₂ ZrR ₂ (Cp = cyclopentadienyl; R = H, alkyl, aryl or trialkylsilyl). The product is a polysilane with relatively high molecular weight, but which can be intractable or insoluble, even in nonpolar organic solvents. It is believed that Zr complexes (and other early transition metal-based catalysts) tend to form polysilanes with an undesirably high degree or incidence of branching, which can make the polysilane less soluble, and in the extreme case, insoluble.

[0005] FIG. IB shows an equation for the idealized catalytic dehydrogenative polymerization of cyclopentasilane. The polymerized product contains substantially linear poly(cyclopentasilane), with a minimum (or no) branching. Such a poly(cyclopentasilane) is

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expected to be relatively soluble in nonpolar solvents, and could increase the viscosity of an ink containing the poly(cyclopentasilane) to further facilitate processes of coating or printing the ink on a substrate. However, in practice, actual cyclopentasilane polymers have appreciable and/or significant branching and/or cross-linking. Thus, a need and/or desire for an improved (cyclo)silane polymerization process is felt.

SUMMARY OF THE INVENTION

[0006] An object of the invention is to provide a composition comprising an oligosilane or polysilane consisting essentially of (i) hydrogen and (ii) silicon and/or germanium, having a molecular weight of from 450 to about 2300 g/mol, which, after coating or printing the composition (optionally with simultaneous or immediately subsequent UV irradiation) and forming an oligo- and/or polysilane film, then curing, forms an amorphous, hydrogenated semiconductor film having a carbon content of not greater than 0.1 at%. In alternative embodiments, the oligosilane or polysilane may have a chain length of from 10 to 10,000, 100,000 or 1,000,000 silicon and/or germanium atoms.

[0007] Another object of the invention is to provide a composition comprising an oligosilane or polysilane of consisting essentially of (i) hydrogen and (ii) silicon and/or germanium, having a molecular weight of from 450 to about 2300 g/mol and a polydispersity index of < 2.5. In alternative embodiments, the oligosilane or polysilane may have a polydispersity index of > 2.5 (e.g., < 4), and/or the oligosilane or polysilane (e.g., having such polydispersity or other characteristic or property) may have a chain length ranging from 10 to 10,000, 100,000 or 1,000,000 silicon and/or germanium atoms. In any case, the resulting oligo-/polysilanes can be linear, branched or crosslinked, and may contain essentially random linear and/or cyclic blocks, sections or chains.

[0008] Another object of the invention is to provide a polysilane of the formula H- [( AHR) _n (C- A _m R ¹ _2m-2 ) _q ]-H, where each instance of A is independently Si or Ge; each instance of R and R ¹ is independently H, -A _b H _b+ iR ² _b (where R ² is H or aryl), or aryl, but if q = 0 and A is Si, R is not phenyl; (n + b) > 10 if q = 0, q > 2 if n = 0, and (n + q) > 2 if both n and q ≠ 0; and each instance of m is independently from 4 to 6.

Docket No.: IDR0884WQ

[0009] Yet another object of the invention is to provide a method of making an oligosilane or polysilane, comprising combining a silane compound of the formula A _n H _2n+2 and/or a cyclosilane compound of the formula C-AmH _2n , with a heterogeneous catalyst consisting essentially of an elemental Group 7-12 transition metal (or a substrate-anchored derivative thereof) to form the oligosilane or polysilane, where each instance of A is independently Si or Ge, n is an integer of from 1 to 10, and m is an integer of from 4 to 6; and removing the catalyst from the oligosilane or polysilane. t

[0010] Another embodiment of the invention provides a method of making a polysilane, comprising (a) combining a silane compound of the formula A _a H _2a + _2- bR _b and/or the formula c-A _m Hp _m R ¹ ,™ with an elemental metal catalyst or a catalyst of the formula R ³ _x R ⁴ yR ⁵ _z MX _w (or a multinuclear or substrate-anchored derivative thereof) to form a polysilane of the formula H-[(A _a H _2a - _b R _b ) _n -(c-A _m H( _pm . ₂ )R ¹ _rm )q]-H, where each instance of A is independently Si or Ge, 1 < a < 100, and each instance of R and R ¹ is independently hydrogen, aryl or -A _c H _2C+Ud R ² _C i (where R ² is aryl, alkyl or H, and c is an integer from 1 to 4); n*a > 6 if q = 0, q > 2 if n = 0, and (n + q) > 2 if both n and q ≠ 0; m is an integer from 3 to 8, p = 2 - r, and r is 0 or 1 or 2; M is a metal selected from the group consisting of Rh, Fe, Ru, Os, Co, Ir, Ni, Pd, and Pt, each of x, y, z and w is an integer of from 0 to 5, and 3 < (w + x + y + z) < 6; each instance of R ³ , R ⁴ and R ⁵ is independently a substituted or non-substituted cyclopentadienyl, indenyl, fluorenyl, allyl, benzyl, silyl, (per)alkylsilyl, germyl, (per)alkylgermyl, hydride, phosphine, amine, sulfide, carbon mon-oxide, nitrile, isonitrile, siloxyl, germoxyl, hydrocarbyl, hydrocarbyloxy, hydrocarbylphosphino, hydrocarbylamino, or hydrocarbylsulfido ligand, or two or more of R ³ , R ⁴ and R ⁵ together may be a polydentate phosphine, amine, oxo and/or carbido ligand; and X is a halogen or halogen-equivalent; and (b) removing the catalyst from the poly(aryl)silane.

[0011] It is yet another object of the present invention to provide a method of forming a semiconductor film from a composition containing an oligosilane or polysilane, comprising (1) coating or printing the composition onto a substrate, optionally with simultaneous and/or immediate subsequent UV irradiation; (2) heating the coated or printed composition sufficiently to form an amorphous, hydrogenated semiconductor; and optionally (3) annealing

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and/or irradiating the amorphous, hydrogenated semiconductor sufficiently to at least partially crystallize and/or reduce a hydrogen content of the amorphous, hydrogenated semiconductor and form the semiconductor film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. IA is a chemical equation showing the polymerization reaction of cyclopentasilane by Zr catalysts.

[0013] FIG. IB is a chemical equation showing an idealized catalytic polymerization reaction of cyclopentasilane.

[0014] FIG. 2 shows gel permeation chromatography (GPC) data for polysilanes made by Rh-black catalyzed oligo- and/or polymerization of cyclopentasilane in accordance with an embodiment of the present invention.

[0015] FIG. 3 shows proton nuclear magnetic resonance (NMR) data for poly(cyclopentasilane) made by Rh-black catalyzed oligo- and/or polymerization in accordance with an embodiment of the present invention.

[0016] FIG. 4 A shows silicon NMR data for poly(cyclopentasilane) according to an embodiment of the present invention, and FIG. 4B shows silicon NMR data for a polyhydrosilane prepared by a comparative method.

[0017] FIG. 5 shows GPC data for poly(cyclopentasilane) made by polymerization of cyclopentasilane using Ru black as a catalyst in accordance with an embodiment of the present invention.

[0018] FIG. 6 shows GPC data for poly(heptasilane) made by Rh-black catalyzed oligo- and/or polymerization in accordance with an embodiment of the present invention.

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[0019] FIG. 7 shows GPC data demonstrating variations in the molecular weight distribution of poly(cyclopentasilane) according to the reaction time in accordance with embodiments of the present invention.

[0020] FIG. 8 shows chemical formulas for various Rh catalysts useful in certain homogeneous catalysis embodiments of the present method.

[0021] FIG. 9 shows GPC data on polycyclopentasilanes made by oligo- and/or polymerization using various Rh catalysts containing phosphine-based ligands in accordance with embodiments of the present invention.

[0022] FIG. 10 shows GPC data on polycyclopentasilanes made by oligo- and/or polymerization using a Rh catalyst containing a bidentate amine ligand in accordance with an embodiment of the present invention.

[0023] FIG. 11 shows proton NMR data on a polycyclopentasilane made by oligo- and/or polymerization using a Rh catalyst containing a bidentate phosphine ligand in accordance with an embodiment of the present invention.

[0024] FIG. 12 shows impurity data from SIMS analysis of poly(cyclopentasilane) films prepared from Rh black-catalyzed oligo-/polymerization of cyclopentasilane according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended

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claims. Furthermore, in the following disclosure numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail, to avoid unnecessarily obscuring aspects of the present invention.

[0026] For the sake of convenience and simplicity, the terms "coupled to," "connected to," and "in communication with" (and variations thereof) mean direct or indirect coupling, connection or communication, unless the context clearly indicates otherwise. These terms are generally used interchangeably herein, and wherever one such term is used, it also encompasses the other terms, unless the context clearly indicates otherwise. In the present disclosure, the term "deposit" (and grammatical variations thereof) is intended to encompass all forms of deposition, including blanket deposition (e.g., CVD and PVD), coating, and printing. Furthermore, with regard to certain materials, the phrase "consisting essentially of does not exclude intentionally added dopants, which may give the material to which the dopant is added (or the element or structure formed from such material) certain desired (and potentially quite different) physical and/or electrical properties. The term "(poly)silane" refers to compounds or mixtures of compounds that consist essentially of (1) silicon and/or germanium and (2) hydrogen, and that predominantly contain species having at least 15 silicon and/or germanium atoms. Such species may contain one or more cyclic rings. The term "(cyclo)silane" refers to compounds or mixtures of compounds that consist essentially of (1) less than 15 silicon and/or germanium atoms and (2) hydrogen, and that may contain one or more cyclic rings. In a preferred embodiment, the (poly)- and/or (cyclo)silane has a formula Si _x Hy, where x is from 3 to about 200, and y is from x to (2x+2), where x may be derived from an average number molecular weight of the silane. The term "hetero(cyclo)silane" refers to compounds or mixtures of compounds that consist essentially of (1) silicon and/or germanium, (2) hydrogen, and (3) dopant atoms such as B, P, As or Sb that may be substituted by one or more conventional hydrocarbyl, silyl or germyl substituents and that may contain one or more cyclic rings. Also, a "major surface" of a structure or feature is a surface defined at least in part by the largest axis of the structure or feature (e.g., if the structure is round and has a radius greater than its thickness, the radial surface[s] is/are the

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major surface of the structure; however, where the structure is square, rectangular or oval, the major surface of the structure is typically a surface defined by the two largest axes, generally the length and width).

[0027] Divided metal powders (e.g., having an average particle size of < 100 microns, preferably ~ 10 microns or less), including those of Rh and Ru (commonly called "Rh black" and "Ru black"), efficiently catalyze the dehydrogenative coupling of silanes such as cyclopentasilane, pentasilane and heptasilane to oligo- and polysilanes. In addition, Rh complexes such as (PPh ₃ ) ₃ RhCl (known as Wilkinson's catalyst) and other Rh (I) complexes, such as [(CO) ₂ RhCl] ₂ , catalyze the polymerization and/or oligomerization of (cyclo)silanes to dimers, trimers and higher order polymers and/or oligomers.

[0028] The polysilane materials of the present invention have low carbon content and excellent physical properties for making silicon thin films via spincoating or printing (e.g., inkjet printing). These materials are uniquely suited for making printed semiconductor devices (e.g., transistors, capacitors, diodes, etc.) and circuits including the same on various substrates, including but not limited to glass (e.g., quartz, amorphous silicon dioxide, etc.) sheets, wafers or slips, plastic and/or metal foils or slabs (e.g., polyimide or polyethylene sheets, or stainless steel or aluminum foils), silicon wafers, etc., all of which may carry one or more additional layers thereon (e.g., providing one or more dielectric, buffer, planarization and/or mechanical support functions, etc.). Applications for such films and devices (and products made therefrom on such substrates) include, but are not limited to displays (e.g., flat panel, plasma, LCD, organic or inorganic LED, etc.), RF and/or RFID devices, EAS devices, so-called "smart" tags (high frequency devices such as toll booth tags), sensors, and photovoltaics.

[0029] The present method(s) enable controlled polymerization and/or oligomerization of cyclic and linear hydrosilanes (e.g., of the general formula Si _n H _2n or Si _n H _2n+2 , respectively). The present methods can also be applied to arylsilanes of the general formula Si _n Ar _p H _q (e.g., Si _n Ar _n H _n+2 ), where Ar is an aryl group, n is 1-10 (preferably 1-5), and (p + q) = 2n or (2n + 2). Exemplary starting materials include cyclohydrosilanes, such as

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cyclopentasilane (Si ₅ H ₁₀ ), linear silanes, such as heptasilane (Si ₇ H ₁₆ ), pentasilane (Si ₅ Hi ₂ ), trisilane (Si ₃ Hg), etc., to produce a soluble polyhydrosilane-containing material for use as a precursor to silicon thin films with very low carbon content. It is also contemplated that alkyl- and/or aryl-substituted hydrosilanes can also be polymerized and/or oligomerized using the present methodology, and that polyarylsilanes made according to the present method(s) can be de-arylated (e.g., by halogenation and reduction; see U.S. Pat. Appl. Nos. 10/789,317, 11/246,014 and 11/249,167, respectively filed on February 27, 2004, October 6, 2005 and October 11, 2005 [Attorney Docket Nos. IDR0020, IDR0422, and IDR0423, respectively]) to provide high molecular weight, low volatility polysilanes. For example, an oligo- /polyarylsilane can be de-arylated to provide an oligo-/polysilane by (i) reacting the oligo- /polyarylsilane with a halogen source and (optionally) a Lewis acid, or trifluoromethanesulfonic acid (HOTf), to form a halopolysilane; and (ii) reducing the halopolysilane with a metal hydride to form the oligo-/polysilane. The metal hydride may comprise a compound of the formula M ¹ ₈ M ² _b H _c R _d (where M ¹ and M ² are independently first and second metals, each R in the metal hydride compound is independently a ligand bound to at least one of M ¹ and M ² by a covalent, ionic or coordination bond, at least one of a and b is at least 1, c is at least 1, and d is 0 or any integer up to one less than the number of ligand binding sites available on the (a + b) instances of M ¹ and M ² , e.g. lithium aluminum hydride [LAH], calcium aluminum hydride, sodium borohydride, aluminum hydride, gallium hydride, and aluminum borohydride), and the oligo-/polysilane may be washed with a washing composition comprising an immiscible polar solvent (e.g., deionized water) to remove metal contaminants therefrom (e.g., sufficiently to remove a substantial amount of the metal contaminants).

Catalytic Heterogeneous Dehvdrogenative Coupling of Silanes

[0030] hi one aspect of the present invention, finely divided metal powders (e.g., having an average particle size of ~ 10 microns), including those of Rh and Ru (commonly called "Rh black" and "Ru black") efficiently catalyze polymerization of fully hydrogenated silanes, such as cyclopentasilane and heptasilane. The catalytic polymerization reactions of such hydrosilanes with Rh black are reproducible, and provide control of product molecular

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weight via reaction time. Finely divided powders of other metals also have polymerization activity.

[0031] In general, the method of heterogeneously making an oligosilane or polysilane includes combining a silane compound of the formula A _n H _2n+2 and/or a cyclosilane compound of the formula c-A _m H _2m with a heterogeneous catalyst consisting essentially of an elemental Group 7-12 transition metal or a substrate-anchored or -supported derivative thereof to form the oligosilane or polysilane, where each instance of A is independently Si or Ge; n is an integer of from 1 to 10; and m is an integer of from 4 to 6; and removing the catalyst from the oligosilane or polysilane. Suitable Group 7-12 transition metals are Rh, Fe, Ru, Os, Co, Ir, Ni, Pd, and Pt. Preferably, the Group 7-12 transition metal is selected from the group consisting of Rh and Ru.

[0032] FIG. 2 shows representative GPC data for polysilanes made by Rh-catalyzed cyclopentasilane polymerization for two different runs. Reaction conditions included use of 1 mol% Rh black, a 2 h reaction time, and reaction quenching/extraction of the polymer product with cyclohexane. The workup included drying under vacuum for 2 h. The GPC trace shows the area-normalized refractive index signal (y-axis) as a function of the number of Si repeat units (i.e., Si atoms, x-axis). The polymerization reaction shows acceptable reproducibility.

[0033] One major advantage of polymerizing fully hydrogenated silanes is that no further steps (e.g., post-polymerization) are required to convert the polymeric material into polyhydrosilane, thereby minimizing chances of introducing contaminants into the system, particularly carbon impurities. The use of metal powders as catalysts is also advantageous for producing polyhydrosilanes with low carbon impurity levels because the catalyst has no carbon-based ligands that may leach into, react with or otherwise contaminate the reaction mixture, and the catalyst can be easily removed at the end of the reaction by filtration through an inert adsorbent, such as Celite. These features make the present invention an effective alternative to other polysilane synthesis techniques that involve post-polymerization chemistry (e.g., dephenylation of polyphenylsilane) and/or homogeneous catalysis (e.g., using

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a soluble organometallic catalyst that has carbon- and/or other impurity-containing ligands). The purity difference is most clearly seen in the carbon levels in films derived from polysilanes synthesized by the present method vs. prior methods (e.g., 0.03-0.05 at% C for present invention vs. > 0.15 at% C [typically] via the chloro-dephenylation/reduction methodology, as determined by SIMS analysis).

[0034] As further shown in FIG. 3, the ¹ H NMR spectrum of an oligo-

/poly(cyclopentasilane) mixture made by a typical process shows Si-H shift values between 3- 4 ppm that are typical or comparable to shift values of other hydrosilanes. (The peaks at about 1.4 ppm correspond to cyclohexane and deuterated cyclohexane.) FIG. 4A is the ²⁹ Si NMR spectrum of an oligo-/poly(cyclopentasilane) mixture made by a typical process, showing peaks in the -80 to -140 ppm range, typical of the chemical shifts for Si atoms of hydrosilanes. A comparative ²⁹ Si NMR spectrum of an oligo-/poly(cyclopentasilane) mixture made by a process involving catalytic dehydrogenative coupling of phenylsilane, followed by chloro-dephenylation and reduction, is shown in FIG. 4B. The differences in shift values and relative peak intensities appear to reflect different polymer microstructures for the respective products of the different polymerization reactions.

[0035] In one embodiment of the method, the starting silane compound is combined with a rhodium metal catalyst. Preferably, the rhodium metal catalyst comprises rhodium black, in particular wherein the rhodium metal catalyst comprises a powder having a mean or average particle size of one hundred microns or less. The rhodium metal catalyst may consist essentially of rhodium powder having a size distribution where at least 90% of the powder has a particle size of less than one hundred microns; in particular wherein at least 99% of the powder has a particle size of less than one hundred microns. In further embodiments, the powder has a particle size of ten (10) microns or less. In another embodiment, the rhodium metal catalyst consists essentially of rhodium nanoparticles or nanoparticles of another late transition metal (see the following paragraph). Such nanoparticles may be passivated or unpassivated, but if passivated with a species other than hydrogen, the passivation should be at least partially removed immediately prior to use. Such passivation removal may be done in situ.

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[0036] Alternative embodiments utilize other pure late transition metals (groups 7-12) such as Pt, Pd, Ir, Ru, and Os, as well as late transition metals supported on silica, alumina, silicates, aluminates, aluminosilicates (e.g., zeolites), or other stationary phases (for example, Rh on Al ₂ O ₃ ). Thus, suitable heterogeneous catalysts may be selected from the elemental Group 7-12 transition metals, in particular a powder of such metals having a mean or average particle size of 100 microns or less, preferably a powder having a mean or average particle size of 10 microns or less.

[0037] For example, FIG. 5 shows GPC data for the polymerization of cyclopentasilane by Ru black (0.2 at% Ru atoms, relative to total Si atoms in the reaction mixture) for 24 h. The data in FIG. 5 shows consumption of most of the monomer (> 70 wt%) and a relatively controlled molecular weight distribution of product, from about 10 Si atoms (i.e., dimer) to about 200 atoms (e.g., 40-mer). Most of the product distribution is in the range of from 15 to about 110 Si atoms, with a maximum at about 60-70 Si atoms.

[0038] The catalyst may be activated or pre-treated prior to the polymerization reaction. Thus, the present method may also include washing the catalyst with one or more organic solvents (e.g., with one or more nonpolar solvents such as a C ₅ -C ₁₀ alkane or cycloalkane, a C ₆ -C ₁₀ arene, a C ₄ -Cg dialkyl ether, etc., and/or one or more polar solvents such as a C ₃ -C ₆ alkyl ketone or cycloalkyl ketone, a C ₄ -C ₆ cyclic ether such as tetrahydrofuran or dioxane, a C ₁ -C ₁₀ alkanol or cycloalkanol, etc.), and heating the catalyst under vacuum or in an inert and/or reducing atmosphere to dry it, prior to combining it with the silane and/or cyclosilane compound. In particular, the catalyst may be washed with a polar solvent, and separately, with a non-polar solvent. For example, the polar solvent may be acetone, and the non-polar solvent may be toluene. In another embodiment, the activation of the catalyst may include a similar heat treatment in air to "burn off' organic impurities, followed by a subsequent reduction of any oxidized catalyst in forming gas (e.g., H ₂ , optionally in the presence of CO, in the optional further presence of an inert gas such as N ₂ ,

He, Ar, etc.).

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[0039] In preferred embodiments, the silane compound has the formula A _n H _2n+2 , wherein A is Si and n is an integer of from 1 to 10, especially wherein n is an integer of from 1 to 3. In other embodiments, the silane compound has the formula c-A _m H _2m , in particular where A is Si and m is 5. In addition to heptasilane, Si ₇ Hj ₆ , and cyclopentasilane, C-Si ₅ Hi ₀ , other silane starting materials that may be used include monosilane, disilane, trisilane, cyclotetrasilane, pentasilane, cyclohexasilane, and polysilanes. Thus, linear, cyclic, or branched silanes of the general formulae Si _n H ₂ n ₊₂ or -Si _n H _2n -, where n is an integer of 1, 2, 3, 4, 5, or 6, up to 10, 15 or 20, or any range of values therein (particularly where n is 1 to 5 or 1 to 3) may be polymerized and/or oligomerized by the present method.

[0040] FIG. 6 shows GPC data for the polymerization of heptasilane by Rh black (0.2 at% Rh atoms, relative to total Si atoms in the reaction mixture) for 24 h. The data in FIG. 6 shows substantially complete consumption of monomer (> 90%) and relatively even distribution of product, from about 14 Si atoms (i.e., dimer) to about 100 atoms (e.g., 12-mer to 14-mer). A significant fraction of product is identified at the size exclusion limit of the GPC column (e.g., at about 150 Si atoms).

[0041] The use of monosilane, disilane or trisilane instead of heptasilane or cyclopentasilane has significant economical advantages, although such low molecular weight starting silanes advantageously employ a process comprising passing the silane gas over a supported catalyst such as rhodium on alumina or ruthenium on alumina, under high pressure (e.g., at least 5 or 10 atm, up to 15, 20 or 30 atm) or autoclave conditions, and recovering a liquid-phase product therefrom. The supported catalysts rhodium on alumina or ruthenium on alumina are commercially available in powder (5 wt% metal) or pellet (0.5 wt% metal) forms from Sigma-Aldrich Chemical Co., Milwaukee, Wisconsin. In various alternative embodiments, the oligo-/polymerization of low molecular weight starting silanes can be conducted using an unsupported catalyst, optionally in a relatively nonpolar solvent, and/or at a pressure of at least 1, 2, 3 atm or any value > 1 atm.

[0042] Furthermore, the ability to polymerize small linear silanes (e.g., Si ₃ H ₈ , Si ₂ H ₆ , or, potentially, SiH ₄ ) differentiates the present invention from other approaches that rely on

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UV polymerization of cyclic silanes. Since cyclic silanes (such as C-S1 ₅ H ₁₀ ) are not commercially available and are generally challenging to purify to semiconductor-grade quality, the present method offers a route to polysilane materials (from relatively low molecular weight silanes) that is cheaper and that produces materials of potentially higher purity than approaches based on UV polymerization of cyclic silanes. In addition, the present method may provide better control of the product molecular weight distribution and molecular weight range than UV polymerization, and may provide oligo-/polysilanes with greater stability (neat and/or in solution) and longer shelf life (e.g., at a variety of temperatures and/or other storage conditions).

[0043] In further embodiments, the starting materials may advantageously include one or more dopant species, preferably including compounds containing (or consisting essentially of) silicon and/or germanium, hydrogen, and a dopant atom such as B, Ga, P, As, Sb, etc. For example, a dopant species particularly suitable for use in the present methods of making oligo- and/or polysilanes includes compounds of the formula D(A _x H _2x+1 ) ₃ (e.g., D(AH ₃ ) ₃ ), where D is selected from the group consisting of B, Ga, P, As and Sb, A is Si or Ge, and each x is independently an integer of from 1 to 4. Another species includes compounds of the formula AH _y (DH ₂ ) _z (e.g., A(DH ₂ ) ₄ ), where A and D are as described herein and (y + z) = 4.

[0044] In various embodiments, the catalyst is present in an amount of from 0.01 to

10 transition metal atoms to 100 atoms of silicon, or any range of values therein. For example, the catalyst may be present in an amount of from 0.1 to 5 or from 0.5 to 3 transition metal atoms to 100 silicon atoms.

[0045] In one embodiment of the method, the silane compound and the Group 7-12 transition metal are combined and reacted for a length of time sufficient to form the oligosilane or polysilane (e.g., as described herein). Generally, the present polymerization reaction is conducted at ambient temperatures (e.g., without applied heating or cooling; from about 15 to less than 30 ⁰ C, or any range of values therein). However, it is anticipated that the silane compound and the Group 7-12 transition metal may be combined and reacted at a temperature of from about -196 ⁰ C (e.g., the temperature of liquid nitrogen), at least about -

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78 ⁰ C (e.g., the temperature of dry ice baths), or O ⁰ C (e.g., the temperature of ice) to ambient temperature or higher (e.g., at a temperature of > 20 ⁰ C), or any range of temperatures therein, for a length of time sufficient to form the oligosilane or polysilane. For example, the reaction may be conducted at a temperature of up to the boiling point of the silane monomer (e.g., when the monomer is liquid at ambient temperature), or in some cases up to 300-500 ⁰ C (e.g., for gas-phase silane monomers such as silane [SiH ₄ ], disilane [Si ₂ H ₆ ] or trisilane [Si ₃ Hg], and/or when the reaction is conducted at a pressure > 1 atm).

[0046] In general, when the reaction is conducted in a solvent or when coupling liquid-phase silane monomers neat, the reaction time may be at least 1 min, 10 min, or 1 h. For example, the reaction may be conducted for a length of time of from 1 to 96 h., 1 to 48 h., 1.5 to 24 h., or any range of values therein. For many metals (e.g., Rh and Ru) and silanes (e.g., cyclopentasilane and heptasilane), a reaction time of 2 h. is sufficient to consume most of the monomer (e.g., at least 60%, 65% or 70%), increase the average molecular weight (e.g., the weight-average or number average molecular weight, but preferably expressed as an average number of silicon atoms) by at least 100%, 200%, or more, and/or increase the viscosity of an ink consisting essentially of 1-20 wt.% of the polysilane product in a C ₆ -C ₁₀ cycloalkane solvent to form a substantially uniform silicon film after drying and curing the ink (e.g., relative to an otherwise identical ink in which the silicon component comprises at least 80% of the corresponding monomer). Alternatively, when the reaction is run in the gas phase, contact time between the gas-phase silane monomer and the catalyst may be quite short, although the total time for passing the gas-phase reactants over the catalyst may be relatively long.

[0047] FIG. 7 shows GPC data for polymerization reactions run under identical conditions, except for the reaction time. The data in FIG. 7 show that the average molecular weight increase with reaction time, but that the peak of the polymeric product (at about 50 Si atoms) does not appear to change significantly after 24 h. In the data of FIG. 7, residual monomer (cyclopentasilane) was not removed under vacuum. The monomer content of the 2 h. reaction is about 20% as shown by integration of the area under the curve (i.e., about 80% conversion to polymer).

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[0048] Although generally not necessary, the present polymerization reaction may be conducted at a higher or lower temperature. For example, the higher molecular weight and/or more highly branched polysilanes may be formed when the reaction is conducted at a temperature of at least 30 ⁰ C (e.g., 30-100 ⁰ C, or any range of values therein). For example, the reaction can be conducted at a temperature > 5O ⁰ C. Alternatively, the present polymerization reaction may be conducted at a temperature of < O ⁰ C.

[0049] Other embodiments with regard to reaction conditions include conducting the polymerization in a solvent, or modifying the pressure and temperature at which the reaction is carried out. For example, solvents for the present polymerization reaction generally include nonpolar organic solvents such as C ₅ -C ₁₀ alkanes and cycloalkanes such as cyclohexane, cyclooctane and decalin, C ₆ -C] ₀ arenes such as benzene, toluene and tetralin, C ₄ -Cg dialkyl ethers such as diethyl ether and methyl t-butyl ether, etc.

[0050] In general, the catalyst may be immobilized on and/or anchored to a support or substrate, and removing the catalyst from the oligosilane or polysilane may comprise filtering the immobilized and/or anchored catalyst. Suitable supports/substrates include silica, alumina, a silicate, an aluminate, and/or an aluminosilicate. Alternatively, the catalyst may be removed by filtering the reaction mixture. In one embodiment, filtering comprises passing the reaction mixture through a pad or bed of adsorbent. Suitable adsorbents include a chromatography gel or finely divided oxide of silicon and/or aluminum (including silicates, aluminates and/or aluminosilicates) that is substantially unreactive with the oligosilane or polysilane. A preferred adsorbent is Celite. In other embodiments, filtering comprises passing the reaction mixture through a PTFE membrane filter with pore size less than 0.45 μm (e.g., 0.2 μm, or other value therein or therebelow) or a metal removing and/or purification filter and/or resin (such as is conventionally used for removing Pd and Rh catalysts from reaction mixtures).

[0051] Once polymerized, the polymer (or polymer mixture) may be characterized

(e.g., to determine the molecular weight distribution, the identity and/or quantity of one or more impurity atoms, etc.). Characterization techniques for establishing microstructural

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features of the polymers may include mass-spectrometric methods (e.g., FAB-MS or ESI- MS), gas and/or gel permeation chromatography, nuclear magnetic spectroscopy (e.g., ¹ H and/or ²⁹ Si), SIMS analysis (e.g., of deposited polysilane films after being converted to amorphous silicon upon curing), etc.

Catalytic Homogeneous Dehvdrogenative Coupling of Silanes

[0052] Rhodium complexes such as (PPh ₃ ) ₃ RhCl (commonly known as Wilkinson's catalyst) and other Rh(I) complexes, such as [(CO) ₂ RhCl] ₂ , also catalyze the polymerization and/or oligomerization of (cyclo)silanes such as cyclopentasilane to dimers, trimers, and higher order poly-/oligomers, similar to the catalytic activity of Rh metal (as described above and elsewhere herein). As for the heterogeneous catalysis method, the homogeneous catalysis method involves formation of silicon-silicon bonds between (cyclo)silane monomers, with concomitant release of hydrogen gas. Generally, polysilane polymers and/or oligomers made by the present method are soluble in nonpolar solvents such as hexane, cyclohexane, cyclooctane and decalin.

[0053] Methods for producing polysilanes via homogeneous catalytic dehydrocoupling of phenylsilane (or other arylsilanes, such as tolylsilane) using Rh(I) or Ru complexes, with subsequent chlorination/dearylation and reduction, yield polysilanes but perhaps of lesser purity than can be obtained by dehydrogenative coupling of (cyclo)hydrosilanes by heterogeneous catalysis (e.g., using elemental late transition metal catalysts). Such oligo-/polysilanes may be particularly suitable for formation of thin films where atomic purity is less critical, such as the formation of silicon dioxide films (e.g., by annealing a dried and/or cured thin film from the present oligo-/polysilane in an oxygen source gas, such as dioxygen, ozone, nitrous oxide, nitric oxide, NO, etc.). Oxidative annealing to form oxide films from similar precursor materials is described at least in part in U.S. Pat. Appl. No. 10/616,147, 11/452,108, 11/888,949 and 11/818,078, filed on July 8, 2003, June 12, 2006, June 11, 2007, and July 31, 2007 (Attorney Docket Nos. KOV-004, IDR0502, IDRO813 and IDR0742, respectively).

Docket No.: IDR0884WO

[0054] In general, oligo-/polysilanes can be made by combining a compound of the formula A _a H _2a+2-b Rb and/or the formula c-AmHpmR ¹ ™ with an elemental metal catalyst (as described in the section above) or a catalyst of the formula R ³ _x R ⁴ _y R ⁵ _z MX _w (or a multinuclear or substrate-anchored derivative thereof) to form a polysilane of the formula H-[(A _a H _2a _ _b R _b ) _n - (c-A _m H _(pm-2) R ¹ _πn ) _q ]-H, where each instance of A is independently Si or Ge, 1 < a < 100, and each instance of R and R ¹ is independently hydrogen, aryl or -A _c H _2c+ i. _d R ² _d (where R ² is aryl, alkyl or H, and c is an integer from 1 to 4); n*a > 6 if q = 0, q > 2 if n = 0, and (n + q) > 2 if both n and q ≠ 0; m is an integer from 3 to 8, p = 2 - r, and r is 0 or 1 or 2; M is a metal selected from the group consisting of Rh, Fe, Ru, Os, Co, Ir, Ni, Pd, and Pt, each of x, y, z and w is an integer of from 0 to 5, and 3 < (w + x + y + z) < 6; each instance of R ³ , R ⁴ and R ⁵ is independently a substituted or non-substituted cyclopentadienyl, indenyl, fluorenyl, allyl, benzyl, silyl, (per)alkylsilyl, germyl, (per)alkylgermyl, hydride, phosphine, amine, sulfide, carbon monoxide, nitrile, isonitrile, siloxyl, germoxyl, hydrocarbyl, hydrocarbyloxy, hydrocarbylphosphino, hydrocarbylamino, or hydrocarbylsulfido ligand, or two or more of R ³ , R ⁴ and R ⁵ together may be a polydentate phosphine, amine, oxo and/or carbido ligand; and X is a halogen or halogen-equivalent such as phenylsulfonyl, tolylsulfonyl, trifluoromethylsulfonyl, tetraphenylborate, tetrafluoroborate, hexafluorophos-phate, etc.; and removing the catalyst from the poly(aryl)silane. In certain embodiments, the method includes combining a compound of the formula A _a H _2a+2 and/or the formula c-A _m H _2m to form a polysilane of the formula H- [(A _a H _2a ) _n -(c- A _m H _(2m-2) ) _q ] -H.

[0055] Alternative embodiments for catalytic dehydrogenative coupling of silanes to produce the present oligo-/polysilanes utilize other late transition metals (e.g., from Groups 7- 12 of the Periodic Table). Suitable metal complexes may contain chelating neutral or monoanionic phosphorus- or nitrogen-based ligands, such as bis-dialkylphosphinoalkanes (e.g., l,2-bis-(diisopropylphosphino)ethane), diamines (e.g., bis-(dialkylamino)ethane and - propane), and bidentate heterocyclic ligands such as α,α'-bipyridyl and 2-(2'-pyridyl)indole. In addition, metal salts such as RhCl ₃ that can be reduced in situ to more reactive states (e.g., Rh(I) species) are also useful. Ligand types such as triaryl- and trialkylphosphines and - amines, carbon monoxide [CO], π-coordinated allyl ligands, benzyl ligands, σ-alkyl groups, σ-aryl groups, alkoxy or aryloxy groups, alkylthio or arylthio groups, and trialkylsilyl groups

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are particularly suitable. Also, aluminum-containing compounds may act as co-catalysts in these reactions, such as AICl ₃ , AlMe ₃ , and MAO (methylalumoxane).

[0056] Among Rh complexes, preferred catalysts include [(CO) ₂ RhCl] ₂ ,

(NN)RhH ₂ (SiEt ₃ ) ₂ and (PP)Rh(benzyl), where (NN) is a bidentate nitrogen-containing ligand such as 2-(2'-pyridyl)indole (see FIG. 8) and (PP) is a bidentate phosphine ligand such as bis- (di-t-butylphosphino)methane (see FIG. 8). Other ligands for coordination to the late transition metal may include tridentate phosphorus-, nitrogen-, oxygen and/or carbon-based ligands and mixed bidentate ligands (e.g., PN, PC, PO, NO, NC, OC).

[0057] In preferred embodiments, x is 1, 2 or 3, and R ³ is triphenylphosphine or CO. In general, two or three units of R ³ , R ⁴ and R ⁵ may comprise a multidentate nitrogen-, phosphorus-, oxygen- and/or carbon-based ligand. In particular, two of R ³ , R ⁴ and R ⁵ may comprise a bidentate ligand, bound to the metal through nitrogen and/or phosphorous atoms. In another embodiment x = 1, y = 1, and R ³ and R ⁴ together comprise 1,2- bis(diphenylphosphino)ethane. In another embodiment w = 1 and X is Cl. In another example, w = 0, z = 1 , and R ⁵ is hydrocarbyl or hydride.

[0058] A preferred catalyst M is Rh. M may comprise a Rh(O), Rh(I), Rh(III) or

Rh(V) precursor. The catalyst may comprise a dimer, a binuclear species or a multinuclear species. In one embodiment x = 1, y = 1, and R ³ and R ⁴ together comprise 2-(2'- pyridyl)indolide. In another example, z = 2, and R ⁵ is carbon monoxide (CO). In a preferred embodiment of the method, z is at least 1, and R ⁵ is H, C ₃ -C ₇ allyl, aryl, benzyl, SiR ² ₃ , or Si(SiR ² ₃ ) ₃ , where R ² is H or C ₁ -C ₄ alkyl. In another example w is 1, 2 or 3, and X is Cl. Among alternative heterogeneous Rh complexes, there are grafted/bound complexes (e.g., attached to a silica surface, as described herein).

[0059] Preferred arylsilane starting compounds have the formula AH ₈ R _4-3 , especially where A is Si, R is phenyl, tolyl, mesitylyl, benzyl or naphthyl (particularly phenyl or tolyl), and a is 2 or 3 (particularly 3). In other embodiments, the silane compounds have the formula A _n H _2n + ₂ , preferably where A is Si and/or Ge (particularly Si) and n is from 3 to 7, or the formula c-A _m H _2m , preferably where A is Si and m is 5.

Docket No.: IDR0884WO

[0060] Other silane starting materials that may be polymerized and/or oligomerized by this method include monosilane, disilane, trisilane, cyclotetrasilane, cyclohexasilane, and oligo-/polysilanes (linear, cyclic, or branched silanes of the general formulae Si _n H _2n+2 or - Si _n H _2n -, where n is an integer of 1, 2, 3, 4, 5, or 6, up to 10, 15 or 20, or any range of values therein, particularly where n is 1 to 5 or 1 to 3). Preferred embodiments include the polymerization and/or oligomerization of trisilane, Si ₃ H ₈ , heptasilane, Si ₇ Hi ₆ , and cyclopentasilane, C-Si ₅ Hi _0. Additionally, other arylsilane starting materials, such as oligo- /poly(phenylsilane), may be dehydrogenatively coupled using a late transition metal complex as described herein. The present method (both homogeneous and heterogeneous) may be particularly advantageous for oligo-/polymerization of linear hydrosilanes, such as Si ₃ H ₈ , n- Si ₄ Hi ₀ , n-Si ₅ Hi ₂ , n-Si ₇ Hi ₆ , etc.

[0061] Alternative starting materials include higher cyclosilanes, as well as other mono- and diaryl- and -alkyl(oligo)silanes, such as H ₃ SiSi(Ph)HSiH ₃ . Also, higher-molecular weight aryl- and alkyl-substituted oligosilanes (e.g., containing at least 3, and up to about 20, silicon atoms) can be used in the present method.

[0062] In a typical process, a solution of 1 mol% (PPh ₃ ) ₃ RhCl (or other homogeneous catalyst) in neat cyclopentasilane is stirred at room temperature for 2-48 h. The catalyst is then precipitated with hexane, which generally dissolves the polysilane/oligosilane products. The resulting mixture is filtered through an adsorbent such as Florisil ^® , and the solvent is evaporated to give a clear oil or gel-like material. As shown by the data in FIG. 9, the molecular weight distribution (shown as the number of Si atoms, or "Si Repeat Units" in the oligo-/polymer) includes substantial amounts of dimers and higher-order oligo-/polysilanes, up to 70-80 Si atoms in the case of (PPh ₃ ) ₃ RhCl and up to 140-150 Si atoms in the case of methylenebis-(di-t-butylphosphinyl)rhodium complexes (see, e.g., "(PP)RhCl" in FIG. 8).

[0063] Generally, polysilanes prepared according to the present method have a broader molecular weight distribution than polysilanes prepared from PhSiH ₃ , the corresponding GPC data for which is shown by the dashed line in FIG. 9. It is believed that a broader molecular weight distribution may, in some cases, facilitate printing an ink

Docket No.: IDR0884 WO

containing such a polysilane mixture. Following evaporative work-up to remove some, most or substantially all of the relatively volatile components (e.g., monomer; see "An Exemplary Method of Removing Low-Molecular Weight Silanes from OligoVPolysilane Mixtures" below), in some cases (e.g., the catalysts employing bidentate ligands), the present method may provide a polysilane mixture having a greater average molecular weight (which may be a weight or number average molecular weight, and/or which can be reflected in the average number of silicon atoms in the polysilane chains) than the comparative polysilanes prepared from PhSiH ₃ .

[0064] In a variation of the typical process, FIG. 10 shows GPC data for various polycyclopentasilanes made by oligo-/polymerization using various Rh catalysts containing a bidentate amine ligand. As for the oligo-/polysilane mixtures of FIG. 9, the oligo-/polysilane mixtures of FIG. 10 also generally show a broader molecular weight distribution than polysilanes prepared from PhSiH ₃ (see the trace labeled "baseline" in FIG. 10). Also, following evaporative work-up, the oligo-/polysilane mixtures of FIG. 10 may also provide a polysilane mixture having a greater average molecular weight than the comparative polysilanes prepared from PhSiH ₃ .

[0065] The polymeric products of the invention have been analyzed by NMR and

GPC, demonstrating the formation of poly-/oligomeric (cyclo)pentasilane materials (as shown in FIGS. 10-12). For example, FIG. 11 shows the ¹ H NMR spectrum of an oligo- /poly(cyclopentasilane) mixture made by a typical process using (PP)RhCl as the catalyst (see FIG. 8). For the polysilane in FIG. 10, the catalyst was precipitated from the reaction mixture by adding hexane, and the precipitated catalyst was removed by filtration through Florisil ^® . The H NMR spectrum shows Si-H shift values between 3-4 ppm, typical and/or comparable to shift values of other hydrosilanes, such as the relatively intense, narrow peak from the unreacted cyclopentasilane monomer. (The peaks at about 1.4 ppm correspond to hexane, cyclohexane and deuterated cyclohexane.) A ³¹ P NMR spectrum of a polysilane mixture prepared by the same process showed substantially no significant phosphorous-containing residues, either from the catalyst or from free phosphine.

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[0066] Variations of reaction conductions, such as the selection of catalyst type and ligand, reaction time (from 1 sec to 1 week for either liquid- or gas-phase coupling; e.g., 1 - 24 hours, and preferably 2 - 8 hours in liquid-phase coupling/polymerization), and temperatures above ambient (from 25 to 85 ⁰ C), and below ambient (-78 °C to 15 ⁰ C) may be used. Preferably, the reaction temperature is ambient (generally, no additional/external heating or cooling; e.g., from 15 to 25 ⁰ C). Variations of other reaction conditions, such as pressure (e.g., for gas-phase silane starting materials, from 1, 5 or 10 atm, up to 15, 20 or 30 atm), catalyst loading (0.01 to 1000 transition metal atoms to 100 silicon atoms, more preferably 0.1 to 10 transition metal atoms to 100 silicon atoms), and solvent can control the production of long-chain poly-/oligomers of (cyclo)silanes with respect to a higher weight- average and/or number-average molecular weight (a higher average number of silicon atoms).

[0067] In other embodiments, hydrogen gas generated during the reaction is continuously removed with an argon stream or via a dynamic vacuum, or by increasing the liquid-gas phase interface area to promote an increased hydrogen removal rate (e.g., using a reaction vessel with a flat surface). Also, in some cases, fresh catalyst may be advantageously added after completion of an initial reaction period (e.g., from about 1 sec, 1 min, or 1 h. to about 50% of the total reaction time) to continue consuming monomer. Unreacted monomer may be removed and recycled (e.g., by washing the reaction mixture with tetramethylsilane or by distilling off the monomer under vacuum). In the case of tetramethylsilane washing, the tetramethylsilane phase may be separated using a separatory funnel, and the starting silane recovered by evaporation of the tetramethylsilane solvent.

[0068] In all cases, the catalyst from the reaction mixture may be recycled, reconditioned if necessary or desired, and reused (in part or in total) in one or more subsequent reactions. Moreover, it is possible to remove and/or recover the unreacted monomer (such as cyclopentasilane or other monomer that is liquid at ambient temperature) from the reaction mixture by evaporation or washing with tetramethylsilane, and use (or recycle) it in subsequent reactions.

Docket No.: IDR0884 WO

[0069] Removing the catalyst from the poly(aryl)silane reaction product in general involves contacting the polysilane reaction product with an adsorbent. Suitable adsorbents include chromatography gels, or finely divided silicon oxide and/or aluminum oxide, that are substantially unreactive with the poly(aryl)silane. Alternatively, the catalyst may be removed from the poly(aryl)silane product by adding a solvent in which the poly(aryl)silane is soluble and the catalyst is insoluble, to precipitate the catalyst, then filtering the precipitated catalyst. A suitable solvent for removing catalysts of the invention from the reaction products is hexane.

[0070] In addition to or instead of filtration through an adsorbent such as Florisil ^® or Celite ^® , the catalyst may be removed with a metal-scavenging column containing immobilized ligand functionalities such as thiol and/or thiourea groups. In an alternative embodiment, the catalyst may be supported on a stationary gel or polymer phase such as silica, alumina or polystyrene beads, so as to facilitate isolation of the polyhydrosilane products and/or recovery of the catalyst. Thus, the catalyst may be immobilized on and/or anchored to a substrate, and removing such a catalyst from the product (e.g., poly(aryl)silane) may comprise filtering the immobilized and/or anchored catalyst and/or decanting the poly(aryl)silane. Alternatively, removing the catalyst from the poly(aryl)silane may comprise solid phase extraction of the catalyst using a column having thiol or thiourea groups thereon.

In one further alternative embodiment, removing the catalyst from a poly(aryl)silane comprises extracting the catalyst from an organic phase comprising the poly(aryl)silane with a water-soluble thiol in an aqueous phase.

[0071] Other reaction conditions, such as solvent, dopant species, and characterization method or technique may be used, varied and/or optimized as described above for the heterogeneous catalysis method.

An Exemplary Method of Removing Low-Molecular Weight Silanes from

Oligo-/Polvsilane Mixtures

[0072] A typical reaction workup for a crude reaction mixture of polysilane includes dilution with cyclohexane, followed by filtration and gentle drying (e.g., with relatively low

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vacuum, such as house vacuum; for example, greater than 10, 20, or 30 Torr, or any value therein), preferably in a drybox (glove box). However, such relatively low vacuum does not necessarily remove the residual monomer. In the typical polymerization of cyclopentasilane as described above, ~ 20% of the reaction mixture remains, and the polymeric material (formulated as a 20% solution by weight in cis-decalin) may not provide ideal properties for inkjet printing. Instead of forming silicon islands (see, e.g., in U.S. Pat. Appl. No. 11/452,108, 11/818,078 and 11/888,949, filed on June 12, 2006, June 12, 2007, and August 3, 2007 [Attorney Docket Nos. KOV-004, IDR0502, IDR0813 and IDR0742, respectively]), the material may form beads, or "ball up," on the substrate.

[0073] It is thought that residual silane starting material may interfere with the printing process, perhaps by reducing the viscosity of the ink and/or increasing the surface tension of the ink to a value that leads to increased bead formation. Thus, excess silane can be removed by drying under high vacuum (e.g., < 1 Torr, 500 mTorr, 200 mTorr, 50 mTorr or any value therein, down to a value that also significantly decreases the amount of oligomers having 10 or more Si atoms, such as 1, 2, or 5 mTorr) for about 2 hours or more. In one example, such high vacuum can be provided by a conventional Schlenk line. In this manner, the amount of cyclopentasilane left in the reaction mixture can be reduced to less than 10%, 8%, or 5% (e.g., by weight). An ink including the resulting material, for example formulated as a cis-decalin solution, is printable on wafers. The wafer has a contact angle with the ink in a range of from 0 to 15°. Such a range of contact angles enables a wide process window for printing, and thus, promotes reproducible silicon island formation. However, depending on the specific printing surface and its surface energy, a composition containing more than 10% by weight of volatile silanes may be preferable. Alternatively, a minimum amount of silane monomer (e.g., cyclopentasilane or low-molecular weight oligosilane may be helpful for solubility of the higher molecular weight polysilanes in the composition. For example, at least 5 wt%, 10 wt%, 15 wt%, etc. (or any minimum value therein) of (cyclo)silane having 15 silicon atoms or less (e.g., 10 Si atoms, 7 Si atoms, 5 Si atoms, or Ge atoms if a Ge- containing monomer is used) may remain in the product mixture.

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[0074] Other embodiments for the workup method include drying the oligo-

/polysilane for a longer period of time, such as for 12, 16, 24, 48 hours or more. Further, drying under vacuum can be assisted by gentle heating (e.g., at 30-40 ⁰ C, which can be performed using a Schlenk tube containing the material). These approaches may remove silane monomer substantially completely. However, merely reducing silane content (e.g., when the silane monomer contains 7 or fewer silicon atoms) appears to be sufficient for improving the printability (e.g., for inkjetting) of the oligo-/polysilane. For example, in one embodiment, excess cyclopentasilane is removed by drying under a vacuum of < 50 niTorr for 2 - 24 hours, whereby the amount of cyclopentasilane left in the reaction mixture is reduced to less than 10% by weight. In other embodiments, the excess monomer and/or volatile oligosilanes can be removed by applying milder vacuum conditions (i.e. > 1 Torr) in combination with passing an inert gas stream over the mixture. This approach may result in better control of the polysilane composition (e.g., the ratio between volatile oligosilanes [i.e., having 10 Si units or less] and polysilanes).

Exemplary Oligo-ZPolysilanes

[0075] Another aspect of the invention includes oligo- and/or polysilanes ("oligo-

/poly-silanes") having an atomic purity of greater than 90% with respect to silicon, germanium and hydrogen (i.e., greater than 90% of the atoms in the polysilane are either Si or H). In particular, the present oligo-/polysilanes may have an atomic purity of at least 95%, at least 99%, or any value therein, with respect to silicon, germanium and hydrogen. In one embodiment in which the oligo-/polysilane is made from silane monomers of the formula Si _n H _2n+2 and/or cyclo-Si _m H _2m , the oligo-/polysilane has an atomic purity of greater than 90% with respect to silicon and hydrogen (i.e., greater than 90% of the atoms in the polysilane are either Si or H). Preferably, such oligo-/polysilanes have an atomic purity of at least 95%, at least 99%, or any value therein, with respect to silicon and hydrogen. In a particularly preferred embodiment, the purity is at least 99.9% with respect to Si and H.

[0076] A preferred oligosilane and/or polysilane composition consists essentially of

(i) hydrogen and (ii) silicon and/or germanium, and has a molecular weight of from 450 to

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about 2300 g/mol, which, after coating and/or printing the composition (optionally with simultaneous or immediately subsequent UV irradiation) and forming a oligo- or polysilane film, then curing, forms an amorphous, hydrogenated semiconductor film having a carbon content of not greater than 0.1 at%. In alternative embodiments, the oligosilane or polysilane may have a chain length of from 10 to 10,000, 100,000 or 1,000,000 silicon and/or germanium atoms. In further embodiments, the molecular weight (which may be a molecular weight distribution or an average molecular weight) is from about 500 to about 1500 g/mol, preferably from about 500 to about 1300 g/mol. In further embodiments, the chain length (which may be a chain length distribution or an average chain length) is from about 15 to about 1000 silicon and/or germanium units, preferably from about 15 to about 100 silicon and/or germanium units. For example, the composition may include or consist essentially of a mixture of oligosilanes and/or polysilanes, each oligosilane or polysilane therein consisting essentially of (i) hydrogen and (ii) silicon and/or germanium, and having the prescribed molecular weight and/or chain length.

[0077] Another composition of oligo-/polysilanes consists essentially of (i) hydrogen and (ii) silicon and/or germanium, has a molecular weight of from 450 to about 2300 g/mol, and has a polydispersity index of < 2.5, preferably < 4. This latter composition may further have any demonstrable or theoretically possible polydispersity index < 2.5 or higher.

[0078] In one embodiment, at least 50 mol% of the composition consists of the oligo- /polysilane. hi further embodiments, at least 65 mol%, 70 mol%, 75 mol%, or 80 mol% (or any value therein or thereabove) of the composition consists of the oligo-/polysilane.

[0079] The present oligo-/polysilane composition is noteworthy for its capability to form printed thin semiconductor films with very high purity levels. Thus, in some embodiments of the present composition, the carbon content of the thin semiconductor film(s) is not greater than 0.05 at%. Preferably, the carbon content (as well as the content of other impurity atoms) is determined by SIMS analysis. In further embodiments, the film made from the oligo-/polysilane composition has a transition metal content of not greater than 0.1 parts per million, preferably not greater than 0.05 parts per million, more preferably not

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greater than 0.02 parts per million. In still further embodiments, the film made from the oligo-/polysilane composition has an oxygen content is < 0.05 at% and/or a nitrogen content of not greater than 100 parts per million.

[0080] In another aspect of the invention, the present oligo-/polysilane may have the formula H-[(AHR) _p (c-A _m R ¹ _2m-2 ) _q ]-H, where each instance of A is independently Si or Ge; each instance of R and R ¹ is independently H, -A|,H _b+ iR ² _b (where R ² is H or aryl), or aryl, but if q = 0 and A is Si, R is not phenyl; (p + b) > 10 if q = 0, q > 2 if p = 0, and (p + q) > 2 if both p and q ≠ 0; and each instance of m is independently from 4 to 6. Alternatively, the present oligo-/polysilane may have the formula H-[(A _n H _2n ) _p (c-A _m R ¹ _2m-2 ) _q ]-H or H- [(A _n H _n R _n ) _p (c-A _m R ¹ _2m . ₂ ) _q ]-H, where A, n, p, m, q, R and R ¹ are as described herein. In various embodiments, A is Si, n is an integer of from 3 to 7, R is H, phenyl or tolyl (preferably H or phenyl, more preferably H), and R ¹ is H. In other embodiments (which may be combined with one or more other embodiments), at least one A is Ge, and/or p or q = 0. hi the latter embodiment, when q = 0, p is at least 2, 3, 4 or more, and p can be up to 20, 25, 30 or more; and when p = 0, q is at least 2, 3, 4 or more, and q can be up to 20, 25, 30 or more.

[0081] One oligo-/polysilane has the formula H-(AHR) _n -H. In certain embodiments, when R = -A _b H _2b +i, n*(b+l) has an average value of < 1000 (e.g., < 200, < 100, < 50 or any value < 1000) according to or as calculated from a number average molecular weight Mn of the polysilane. In another embodiment, the polysilane has the formula H-(c-A _m H _2m . ₂ ) _q -H, where each instance of m is independently 5 or 6, and q is from 2 to 30 (preferably 4 to 30, or any range of values therein). In further embodiments, the present polysilane contains up to 1000 or 10,000, 100,000 or 1,000,000 A units.

Exemplary Inks Including Oligo-ZPolvsilanes

[0082] hi general, one composition contains an oligosilane and/or polysilane (as described herein) and a solvent in which the oligosilane and/or polysilane is soluble. The solvent may include any of a wide variety of solvents, such as those described in U.S. Pat. Appl. Nos. 10/616,147, 10/789,317, 10/950,373, 10/949,013, 10/956,714, 11/246,014 and 11/249,167, respectively filed on July 8, 2003, February 27, 2004, September 24, 2004,

Docket No.: IDR0884WO

September 24, 2004, October 1, 2004, October 6, 2005 and October 11, 2005 [Attorney Docket Nos. KOV-004, IDR0020, IDR0301, IDR0302, IDR0303, IDR0422, and IDR0423, respectively]. However, for reasons relating to ease and/or completeness of removal, properties facilitating spincoating and printing, and compositional stability, preferred solvents include linear alkanes, cycloalkanes, polycycloalkanes, and mixtures thereof. For example, the solvent may be a linear (C ₃ - Ci ₂ ) alkane (e.g., pentane, hexane, heptane, octane, decane), a (C ₅ - Cio) cycloalkane (e.g., cyclopentane, cyclohexane, cyclooctane), a (Cg - Ci ₄ ) polycyclo-alkane, or a mixture thereof. Polycycloalkanes include cis- and trans- bicycloalkanes, such as m-decalin, trans-dec&hn, and mixtures thereof.

[0083] The composition may contain the oligosilane and/or polysilane in an amount of from about 0.5 to about 50% by weight or by volume (e.g., from about 1 to about 30% or about 5 to about 25% by weight or by volume, or any range of values between 0.5 and 50%). Furthermore, to improve the purity of a semiconductor thin film produced from the composition, the ink composition preferably consists essentially of the oligo-/polysilane and the solvent.

[0084] In another preferred embodiment, the oligo-/polysilane component of the present ink composition contains < 10% by weight of monomer (or of silanes having < 10, 8, 7 or 5 silicon atoms, optionally depending on the identity of the monomer).

An Exemplary Method of Making Silicon-Containing Thin Films

[0085] A general method of forming a semiconductor film from a low-carbon composition of the invention includes coating or printing the composition onto a substrate; heating the coated or printed composition sufficiently to form an amorphous, hydrogenated semiconductor; and optionally annealing and/or irradiating the amorphous, hydrogenated semiconductor sufficiently to at least partially crystallize and/or reduce a hydrogen content of the amorphous, hydrogenated semiconductor and form the semiconductor film. The method may include irradiating the composition with UV radiation, simultaneously with or immediately subsequent to coating or printing the composition onto a substrate, substantially as disclosed in U.S. Pat. Appl. Nos. 10/789,274, 10/950,373, 10/949,013, 10/956,714,

Docket No.: IDR0884WO

11/246,014, 11/249,167, 11/452,108, 11/818,078 and 11/888,949, respectively filed on February 27, 2004, September 24, 2004, September 24, 2004, October 1, 2004, October 6, 2005, October 11, 2005, June 12, 2006, June 12, 2007, and August 3, 2007 (Attorney Docket Nos. IDR0080, IDR0301, IDR0302, IDR0303, IDR0422, IDR0423, IDR0502, IDR0813 and IDR0742, respectively).

[0086] The composition may further include one or more dopants. The dopants are generally compounds containing one or more dopant atoms, for example selected from the group consisting of B, Al, Ga, P, As and Sb. For example, the dopant compounds may be selected from those disclosed in the preceding paragraph. However, in preferred embodiments, the dopant compounds consist essentially of the dopant atom(s), silicon and/or germanium atoms, and hydrogen and/or t-butyl (-C[CHa] ₃ ) groups. Therefore, preferred dopants may have the formula (where n is from 2 to 12, m is 1 or 2, each of the n instances of z is independently 1 or 2, and each of the m instances of R ¹ is alkyl [e.g., t-butyl], aryl, aralkyl, or AR ² ₃ , where R ² is hydrogen or A _y H _2y+ i [e.g., 1 < y < 4], such as SiH ₃ and Si(SiH ₃ ) ₃ ), (where n is from 3 to 12, z' is from (n-q) to (2n+2-q), m is from 1 to 3, q is from 1 to n [preferably 1 or 2], and each of the (3-m) instances of R ¹ is independently H, alkyl [e.g., t-butyl], or AR ² ₃ ), (AHp) _n (DR ¹ ₂ ) ₂ (where n is from 3 to 12, each of the n instances of p is independently 1 or 2, and each R ¹ is independently H, alkyl [e.g., t- butyl], or AR ² ₃ ), D _a R ^J _b (where a is from 1 to 20, each of the b instances of R ¹ is independently H, alkyl [e.g., t-butyl], or AR ² ₃ , at least one of the b instances of R ¹ is alkyl or AR ² ₃ , and b is an integer corresponding to the number of binding sites available on the a instances of D), (R^A^A _c φR ¹ ^ (where c is 1 to 4, r + s = 2c + 2, s > 1 [preferably s > 3], and R ¹ and R ² are as described for D ₃ R ¹ _I ,), or (as described above) D(A ₁ H _2x .^ or AHy(DH ₂ ) _z , where D is selected from the group consisting of B, Al, Ga, P, As and Sb (preferably B, P, As and Sb), and A is Si or Ge.

Silicon-Containing Thin Films

[0087] A semiconductor film may be formed from compositions of the invention by: coating or printing the composition onto a substrate; heating the coated or printed

Docket No. : IDR0884 WO

composition sufficiently to form an amorphous, hydrogenated semiconductor; and optionally annealing and/or irradiating the amorphous, hydrogenated semiconductor sufficiently to at least partially crystallize and/or reduce a hydrogen content of the amorphous, hydrogenated semiconductor and form the semiconductor film. This method may include irradiating the composition with UV radiation, simultaneously with or immediately subsequent to coating or printing the composition onto the substrate. The composition may further comprise one or more dopants.

[0088] A preferred thin film in accordance with the invention consists essentially of hydrogen and silicon. Another thin film consists essentially of hydrogen, silicon and germanium. In preferred embodiments, the carbon content of the thin film is not greater than 0.05 at% as determined by SIMS analysis. Preferred films made from the present polysilane compositions have a transition metal content of not greater than 0.1 parts per million, in particular where the film has a transition metal content of not greater than 0.05 parts per million, not greater than 0.02 parts per million, or any value therein or therebelow. Also, the film may have an oxygen content of not greater than 0.1 at%. In particular, the oxygen content may be < 0.05 at%. The film may have a nitrogen content of not greater than 100 parts per million.

[0089] The above semiconductor film methods may be employed to make a thin film transistor, capacitor, diode and/or resistor device and/or a circuit comprising such a device, e.g., an EAS (electronic article surveillance) or RFID (radio frequency identification) tag, display backplane, sensor and/or photovoltaic device or circuit. Thus, the invention includes a film transistor, capacitor, diode and/or resistor device and/or circuit, comprising the semiconductor film as described herein and/or made using the materials and/or methods described herein. The invention also further relates to and includes a method of making an EAS or RFID tag, display backplane, sensor and/or photovoltaic device or circuit, comprising forming a semiconductor thin film for a transistor, capacitor, diode and/or resistor device in such a tag, backplane, sensor, device and/or circuit.

Docket No.: IDR0884 WO

Example 1 - Synthesis of Polyfcyclopentasilane) by Heterogeneous Catalysis

[0090] Neat cyclopentasilane (1.0 g) was added to a 4 mL amber vial containing 1 mol% Rh black (6.9 mg) under an inert atmosphere, and this reaction mixture was allowed to stir for 2 h in the loosely capped vial. Then, the reaction was quenched with 2 g of distilled cyclohexane, and the resulting mixture transferred to a 40 mL amber vial (equipped with a stir bar) and further diluted with 5 g of cyclohexane. After 30 min of stirring, insoluble materials were allowed to settle for about 15 min, and the mixture then filtered through a short plug of Celite (primed with distilled cyclohexane), ensuring that the black Rh particles stayed on top of the filter bed. The solution was then transferred to a Schlenk tube and the volatile materials removed by applying high vacuum (< -300 mTorr) for about 2 h. This drying step should reduce the cyclopentasilane (monomer) content in the resulting product to < 10% (monomer content can be checked by GPC). If the cyclopentasilane content exceeds 10% of the reaction mixture, the solution should be further dried under vacuum. The overall procedure typically yields 0.6-0.7 g of poly(cyclo-pentasilane) (60-70% yield), although higher yields have been obtained. The product material can be stored as a 20 wt % solution in dried, distilled cis-decalin.

[0091] FIG. 12 shows data from SIMS analysis of three different films identically prepared from an ink containing about 15 wt% of each of three different poly(cyclopentasilane) mixtures in the same cycloalkane solvent. The films were prepared identically, in accordance with the UV-spincoating and curing procedures described in U.S. Pat. Appl. No. 10/789,274, filed on February 27, 2004. The impurity levels are remarkably similar across all three examples. In each case, the carbon content and the oxygen content are each less than 0.05 at%, a level suitable for semiconductor-grade films. Nitrogen impurities are at a level of about 10 ppm or less, and typical metal impurities (e.g., Na, K, Al, Mg) are less than 0.01 ppm. Even the level of catalyst metal (Rh) in the film is remarkably low (<0.02 ppm; see the third row of SIMS data in FIG. 12).

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Example 2 - Synthesis of Polysilane Mixtures by Heterogeneous Catalysis

[0092] Polymerization reactions similar to Example 2 above were conducted using (1) cyclopentasilane with Ru black as the catalyst and (2) linear heptasilane as the monomer, with Rh black as the catalyst. Using the polymerization of cyclopentasilane by 1 mol% Rh black as the baseline reaction, the method can provide polymeric materials in the MW range of 700- 1300 (or 20-45 Si units, as determined by Gel Permeation Chromatography), with the MW increasing at longer reaction times. Furthermore, formation of polymeric products was confirmed by ¹ H and ²⁹ Si NMR spectroscopy. The purified polymer is then mixed with distilled, degassed cyclohexane, and the solution stored in a freezer at a temperature below the melting point of cyclohexane until use, at which time the frozen cyclohexane is removed by vacuum. Printability of inks containing polyhydrosilanes produced by the present process has been established.

[0093] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.