TECHNICAL FIELD

The present invention relates to processes of area selective deposition (ASD) of a metal containing film using a metal containing precursor. In particular, the metal is a Group 12, Group 13, Group 14, Group 15, Group IV or Group V metal.

BACKGROUND

Due to continuous scaling down of semiconductor devices, typical lithography is about to reach its physical limitation at which structural flaws will become unaviodable, such as misalignment of contacts. Difficulty of accurate pattern alignment is increasingly difficult and the biggest issue has been “edge placement error (EPE)”. Hence, the current top-down technology needs to be changed to bottom-up technology using area selective deposition (ASD) techniques in combination with self-assembled monolayers (SAMs) or inhibitor formation on surface.

In practice, it is extremely difficult to achieve perfect growth selectivity. This translates by a parasitic growth on a blocked surface, which starts on defects of an inhibited surface (available active sites like —OH, etc.). This effect limits the maximum thickness grown on a non-protected surface before a film growth happens on the inhibited surface. To be of industrial interest, such thickness on a non-protected surface should be maximized, and parasitic growth on the inhibited surface (i.e. that translates into defect islands at the early stage of the growth) should be suppressed at least to a degree that avoids imparment of the resulting strycture's function within the finished device and ideally to the maximum extent possible.

Metal oxides are commonly used materials for their specific physical properties (insulating properties, high dielectric constant, etch resistance, refractive index, etc.) and the selective growth of metal oxide is of interest in the semiconductor industry. Al2O3is a common metal oxide material. A common precursor for forming Al2O3is Al2Me6(TMA), as it has almost all the requirements of a perfect atomic layer deposition (ALD) precursor, such as, volatile, fast saturation, high surface reactivity, etc. However, for the ASD, TMA suffers from its extreme reactivity and oxophilic character, as it tends to react with oxygen that bridges the surface to the SAM, thus starting the growth of a film on the protected region. As such, the usage of O-containing inhibitor, such as carboxylic acids, phosphonic acids, acetates, beta-diketonate, etc. or O-binded SAMs, such as —O-TMS (trimetylsilane), O-DMS (dimethylsilane)-O, O—Si—R, etc. is not compatible with the usage of highly oxophilic precursors like TMA.

Discovery of new and novel precursors that are applicable to the ASD is challenging due to the difficulties described above. Thus, there are needs to provide such precursors to meet the requirements of the ASDs.

US2006193984 discloses processes for producing the organoaluminum precursor compounds and a method for producing a film or coating from the organoaluminum precursor compounds. The organoaluminum precursor compound represented by the formula:


wherein R1, R2, R3and R4are the same or different and each represents hydrogen or an alkyl group having from 1 to about 3 carbon atoms, and R5represents an alkyl group having from 1 to about 3 carbon atoms.

US2015266904 discloses a compound has a low melting temperature, sufficient volatility, and high thermal stability suited for use as a material for thin film formation by CVD. The aluminum compound represented by a general formula:


wherein R1and R2each independently represent a straight or branched alkyl group having 2 to 5 carbon atoms; and R3represents a methyl group or an ethyl group.

Beachly et al. (Inorganic Chemistry, Vol. 15, No. 9, 1976, 2110-2115) discloses chelation in organoaluminum-nitrogen chemistry including the chelated monomer for the compounds (CH3)2Al(C2H5)NC2H4N(C2H5)2, (C2H5)2Al(CH3)NC2H4N(CH3)2, (C6H5)2Al(C2H5)NC2H4N(CH3)2, Cl2Al(C2H5)NC2H4N(CH3)2, and (CH3)2AlSC2H4N(CH3)2, having the structure:



Barry et al. (Mat. Res. Soc. Symp. Proc., Vol. 606, p 83-89, 2000) discloses monomeric chelated amides of aluminum and gallium: volatile, miscible liquid precursors for CVD. The aluminum nitride (AlN) and gallium nitride (GaN) have the following structure:



Blakeney et al. (Inorganic. Nucl. Chem. Lett., 9, 423 (1973)) discloses ALD of aluminum metal films using a thermally stable aluminum hydride reducing agent, in which volatile dimeric Al dihydride complexes coordinated by simple amido-amine ligands of the formula (RN)CH2CH2(NMe2) (R=Me, Et) have the following structure.



McMahon et al. (J. Chem., Soc., Dalton Trans., 1999, 67-72) discloses aluminium compounds containing bidentate ligands: ligand base strength and remote geometric control over degree of association, in which (tBu)2Al[N(Me)CH2CH2NMe2] is yielded and has the structure:



Choi et al. (Chem. Mater., 10, 2323-2325, 1998) discloses volatile Amidoalane Compounds for CVD of Aluminum, H2Al{N(Et)C2H4NMe2} (1, DMEEDA), H2Al{N(Me)C2H4NMe2} (2, TRMEDA) and H2Al{N(Et)C2H4NEt2} (3, TREEDA),



Wissing et al. (Journal of Organometallic Chemistry, 459, 11-16, 1993) discloses 1,2-alkyl shift within a chelate bonded organoaluminium-enamine 1c-3c,



SUMMARY

Disclosed is a process of selectively depositing a metal-containing film comprising the steps of:a) providing a surface having a plurality of materials exposed thereon simultaneously; andb) exposing the surface to a vapor of a metal-containing film-forming composition that contains a precursor having the formula:
LxM(—N(R)—(CR′2)n—NR″2)wherein M is a Group 12, Group 13, Group 14, Group 15, Group IV or Group V element; x+1 is the oxidation state of the M; L is an anionic ligand; R, R″ each are independently a C1-C10linear, branched or cyclic alkyl, alkenyl, or trialkylsilyl group; R′ is H or a C1-C10linear, branched or cyclic alkyl, alkenyl or trialkylsilyl group; n=1-4; andc) preferentially or selectively depositing a film on one or more of, but less than all of, the plurality of materials on the surface in a vapor deposition process,wherein at least one of the materials on the surface is at least partially blocked by a blocking agent thereby reducing or preventing a deposition of the metal-containing film on said blocked material.

Also, the disclosed is a process of selectively depositing Al2O3film comprising the steps of:a) providing a surface having at least one dielectric material and at least one metal material exposed thereon simultaneously;b) exposing the surface to a vapor of (NMe2)2Al(—NEt-(CH2)2—NEt2); andc) exposing the surface to a co-reactant H2O;wherein the at least one dielectric material is at least partially blocked by a blocking agent dimethyldichlorosilane (DMDCS) from the deposition of the Al2O3film through an ALD process.

The disclosed processes may include one or more of the following aspects:the vapor deposition process being an ALD process;the process further comprising exposing the surface to a co-reactant selected from an oxidizer agent or a nitrigen agent;the co-reactant being selected from O3, O2, H2O, H2O2, D2O, ROH wherein R═C1-C10linear or branched hydrocarbon or combinations thereof;the co-reactant being selected from NH3, NO, N2O, hydrazines, amines or combinations thereof;the co-reactant being H2O;the blocking agent forming a SAM layer on the at least one of the materials by dipping the surface in the blocking agent or vapor spraying the surface with the blocking agent;the plurality of the materials including at least a dielectric material and at least a metal material on the surface;the metal-containing film being deposited on the dielectric film but not deposited on the metal film by blocking the reactivity of the metal film by a metal blocking agent;the metal blocking agent being selected from a alkyl or fluoroalkyl compounds having a surface reactive chemical function group selected from phosphonic acids, carboxylic acids, thiols, or triazoles;the metal-containing film being deposited on the metal material but not deposited on the dielectric material by blocking the reactivity of the dielectric material by a dielectric blocking agent;the dielectric blocking agent being a compound having the formula R4-aSiXa, wherein each X are independently a surface hydroxyl reactive group (halide, alkylamino, alkoxy, acetamide, etc.), and each R are selected from H, a C1-C20alkyl or fluoroalkyl group or mixture thereof;a the surface being exposed to the precursor at a temperature raging from room temperature to approximately 500° C.;the process further comprising the steps ofrepeating the exposing to the vapor of the metal-containing film-forming composition and the exposing to the co-reactant until a desired thickness of the metal-containing film is formed; andpurging excess vapor of the metal-containing film-forming composition and excess co-reactant using an inert gas, respectively, to separate each exposure, wherein the inert gas is N2, Ar, Kr or Xe;the precursor being (NMe2)2Al(—NEt-(CH2)2—NEt2);the blocking agent being dimethyldichlorosilane (DMDCS); andthe metal-containing film being an Al2O3film.

Also, disclosed is a composition for selective deposition of a metal-containing film comprising a precursor having the formula:
LxM(—N(R)—(CR′2)n—NR″2)
wherein M is a Group 12, Group 13, Group 14, Group 15, Group IV or Group V element; x+1 is the oxidation state of the M; L is an anionic ligand, independently selected from dialkylamine, alkoxy, alkylimine, bis(trialkylsilylamine), amidinate, betadiketonate, keto-imine, halide, or the like; R, R″ each are independently a C1-C10linear, branched or cyclic alkyl, alkenyl, or trialkylsilyl group; R′ is H or a C1-C10linear, branched or cyclic alkyl, alkenyl or trialkylsilyl group; n=1-4.

The disclosed compositions include one or more of the following aspects:M=Al;M=B, Ga, In, lanthanide elements, P, As, Sb or Bi;x=2;L being a dialkylamino ligand —NR1R2wherein R1, R2each independently are a linear or branched alkyl group having 1 to 5 carbon atoms;R1=R2=Me;n=2;R=Me, Et, Pr, Bu;R′═H;R″=Me, Et;the precursor being (NMe2)2Al(—NEt-(CH2)2—NEt2);the Al-containing precursor being selected from (NMe2)2Al(—NMe-(CH2)2—NMe2), (NMe2)2Al(—NEt-(CH2)2—NMe2), (NMe2)2Al(—NiPr—(CH2)2—NMe2), (NMe2)2Al(—NnPr—(CH2)2—NMe2), (NMe2)2Al(—NiBu-(CH2)2—NMe2), (NMe2)2Al(—NnBu-(CH2)2—NMe2), (NMe2)2Al(—NtBu-(CH2)2—NMe2), (NMe2)2Al(—NsBu-(CH2)2—NMe2), (NEt2)2Al(—NMe-(CH2)2—NMe2), (NEt2)2Al(—NEt-(CH2)2—NMe2), (NEt2)2Al(—NiPr—(CH2)2—NMe2), (NEt2)2Al(—NnPr—(CH2)2—NMe2), (NEt2)2Al(—NiBu-(CH2)2—NMe2), (NEt2)2Al(—NnBu-(CH2)2—NMe2), (NEt2)2Al(—NtBu-(CH2)2—NMe2), (NEt2)2Al(—NsBu-(CH2)2—NMe2), (NiPr2)2Al(—NMe-(CH2)2—NMe2), (NiPr2)2Al(—NEt-(CH2)2—NMe2), (NiPr2)2Al(—NiPr—(CH2)2—NMe2), (NiPr2)2Al(—NnPr—(CH2)2—NMe2), (NiPr2)2Al(—NiBu-(CH2)2—NMe2), (NiPr)2Al(—NnBu-(CH2)2—NMe2), (NiPr2)2Al(—NtBu-(CH2)2—NMe2), (NiPr)2Al(—NsBu-(CH2)2—NMe2), (NnPr2)2Al(—NMe-(CH2)2—NMe2), (NnPr2)2Al(—NEt-(CH2)2—NMe2), (NnPr2)2Al(—NiPr—(CH2)2—NMe2), (NnPr2)2Al(—NnPr—(CH2)2—NMe2), (NnPr2)2Al(—NiBu-(CH2)2—NMe2), (NnPr2)2Al(—NnBu-(CH2)2—NMe2), (NnPr)2Al(—NnBu-(CH2)2—NMe2), (NnPr2)2Al(—NsBu-(CH2)2—NMe2), (NiBu2)2Al(—NMe-(CH2)2—NMe2), (NnBu2)2Al(—NEt-(CH2)2—NMe2), (NnBu2)2Al(—NiPr—(CH2)2—NMe2), (NnBu2)2Al(—NnPr—(CH2)2—NMe2), (NnBu2)2Al(—NiBu-(CH2)2—NMe2), (NnBu2)2Al(—NnBu-(CH2)2—NMe2), (NnBu2)2Al(—NtBu-(CH2)2—NMe2), (NnBu2)2Al(—NsBu-(CH2)2—NMe2), (NiBu2)2Al(—NMe-(CH2)2—NMe2), (NiBu2)2Al(—NEt-(CH2)2—NMe2), (NiBu2)2Al(—NiPr—(CH2)2—NMe2), (NiBu2)2Al(—NnPr—(CH2)2—NMe2), (NiBu2)2Al(—NsBu-(CH2)2—NMe2), (NiBu2)2Al(—NnBu-(CH2)2—NMe2), (NiBu2)2Al(—NtBu-(CH2)2—NMe2), (NiBu2)2Al(—NsBu-(CH2)2—NMe2), (NiBu2)2Al(—NMe-(CH2)2—NMe2), (NtBu2)2Al(—NEt-(CH2)2—NMe2), (NtBu2)2Al(—NiPr—(CH2)2—NMe2), (NtBu2)2Al(—NnPr—(CH2)2—NMe2), (NtBu2)2Al(—NiBu-(CH2)2—NMe2), (NtBu2)2Al(—NnBu-(CH2)2—NMe2), (NtBu2)2Al(—NtBu-(CH2)2—NMe2), (NtBu2)2Al(—NsBu-(CH2)2—NMe2), (NsBu2)2Al(—NMe-(CH2)2—NMe2), (NsBu2)2Al(—NEt-(CH2)2—NMe2), (NiBu2)2Al(—NiPr—(CH2)2—NMe2), (NsBu2)2Al(—NnPr—(CH2)2—NMe2), (NsBu2)2Al(—NiBu-(CH2)2—NMe2), (NsBu2)2Al(—NnBu-(CH2)2—NMe2), (NsBu2)2Al(—NiBu-(CH2)2—NMe2), (NsBu2)2Al(—NsBu-(CH2)2—NMe2), (NMe2)2Al(—NMe-(CH2)2—NEt2), (NMe2)2Al(—NEt-(CH2)2—NEt2), (NMe2)2Al(—NiPr—(CH2)2—NEt2), (NMe2)2Al(—NnPr—(CH2)2—NEt2), (NMe2)2Al(—NsBu-(CH2)2—NEt2), (NMe2)2Al(—NnBu-(CH2)2—NEt2), (NMe2)2Al(—NiBu-(CH2)2—NEt2), (NMe2)2Al(—NsBu-(CH2)2—NEt2), (NEt2)2Al(—NMe-(CH2)2—NEt2), (NEt2)2Al(—NEt-(CH2)2—NEt2), (NEt2)2Al(—NiPr—(CH2)2—NEt2), (NEt2)2Al(—NnPr—(CH2)2—NEt2), (NEt2)2Al(—NtBu-(CH2)2—NEt2), (NEt2)2Al(—NnBu-(CH2)2—NEt2), (NEt2)2Al(—NiBu-(CH2)2—NEt2), (NEt2)2Al(—NsBu-(CH2)2—NEt2), (NiPr2)2Al(—NMe-(CH2)2—NEt2), (NiPr2)2Al(—NEt-(CH2)2—NEt2), (NiPr2)2Al(—NiPr—(CH2)2—NEt2), (NiPr2)2Al(—NnPr—(CH2)2—NEt2), (NiPr2)2Al(—NiBu-(CH2)2—NEt2), (NiPr2)2Al(—NnBu-(CH2)2—NEt2), (NiPr2)2Al(—NtBu-(CH2)2—NEt2), (NiPr2)2Al(—NsBu-(CH2)2—NEt2), (NnPr2)2Al(—NMe-(CH2)2—NEt2), (NnPr2)2Al(—NEt-(CH2)2—NEt2), (NnPr2)2Al(—NiPr—(CH2)2—NEt2), (NnPr2)2Al(—NnPr—(CH2)2—NEt2), (NnPr2)2Al(—NiBu-(CH2)2—NEt2), (NnPr2)2Al(—NnBu-(CH2)2—NEt2), (NnPr2)2Al(—NtBu-(CH2)2—NEt2), (NnPr2)2Al(—NsBu-(CH2)2—NEt2), (NnBu2)2Al(—NMe-(CH2)2—NEt2), (NnBu2)2Al(—NEt-(CH2)2—NEt2), (NnBu2)2Al(—NiPr—(CH2)2—NEt2), (NnBu2)2Al(—NnPr—(CH2)2—NEt2), (NnBu2)2Al(—NiBu-(CH2)2—NEt2), (NnBu2)2Al(—NnBu-(CH2)2—NEt2), (NnBu2)2Al(—NtBu-(CH2)2—NEt2), (NnBu2)2Al(—NsBu-(CH2)2—NEt2), (NiBu2)2Al(—NMe-(CH2)2—NEt2), (NtBu2)2Al(—NEt-(CH2)2—NEt2), (NiBu2)2Al(—NiPr—(CH2)2—NEt2), (NiBu2)2Al(—NnPr—(CH2)2—NEt2), (NiBu2)2Al(—NtBu-(CH2)2—NEt2), (NiBu2)2Al(—NnBu-(CH2)2—NEt2), (NiBu2)2Al(—NtBu-(CH2)2—NEt2), (NiBu2)2Al(—NiBu-(CH2)2—NEt2), (NtBu2)2Al(—NMe-(CH2)2—NEt2), (NtBu2)2Al(—NEt-(CH2)2—NEt2), (NtBu2)2Al(—NiPr—(CH2)2—NEt2), (NtBu2)2Al(—NnPr—(CH2)2—NEt2), (NtBu2)2Al(—NiBu-(CH2)2—NEt2), (NtBu2)2Al(—NnBu-(CH2)2—NEt2), (NtBu2)2Al(—NtBu-(CH2)2—NEt2), (NtBu2)2Al(—NsBu-(CH2)2—NEt2), (NsBu2)2Al(—NMe-(CH2)2—NEt2), (NsBu2)2Al(—NEt-(CH2)2—NEt2), (NsBu2)2Al(—NiPr—(CH2)2—NEt2), (NsBu2)2Al(—NnPr—(CH2)2—NEt2), (NsBu2)2Al(—NiBu-(CH2)2—NEt2), (NsBu2)2Al(—NnBu-(CH2)2—NEt2), (NsBu2)2Al(—NtBu-(CH2)2—NEt2), or (NiBu2)2Al(—NsBu-(CH2)2—NEt2);the composition comprising between approximately 95% by weight or w/w and approximately 100.0% w/w of the precursor;the composition comprising between approximately 99% by weight or w/w and approximately 99.999% w/w of the precursor;the composition comprising between approximately 99% by weight or w/w and approximately 100.0% w/w of the precursor;the composition comprising between approximately 0.0% by weight or w/w and approximately 5.0% w/w impurities;the composition comprising between approximately 0.0% by weight or w/w and approximately 0.1% w/w impurities; andthe composition comprising between approximately 0 ppbw and approximately 500 ppbw metal impurities.

NOTATION AND NOMENCLATURE

The following detailed description and claims utilize a number of abbreviations, symbols, and terms, which are generally well known in the art, and include:

As used herein, the indefinite article “a” or “an” means one or more.

As used herein, “about” or “around” or “approximately” in the text or in a claim means ±10% of the value stated.

As used herein, “room temperature” in the text or in a claim means from approximately 20° C. to approximately 25° C.

The term “ambient temperature” refers to an environment temperature approximately 20° C. to approximately 25° C.

As used in the disclosed embodiments, the term “independently” when used in the context of describing R groups should be understood to denote that the subject R group is not only independently selected relative to other R groups bearing the same or different subscripts or superscripts, but is also independently selected relative to any additional species of that same R group. For example in the formula MR1x(NR2R3)(4-x), where x is 2 or 3, the two or three R1groups may, but need not be identical to each other or to R2or to R3. Further, it should be understood that unless specifically stated otherwise, values of R groups are independent of each other when used in different formulas.

The term “substrate” refers to a material or materials on which a process is conducted. The substrate may refer to a wafer having a material or materials on which a process is conducted. The substrates may be any suitable wafer used in semiconductor, photovoltaic, flat panel, or LCD-TFT device manufacturing. The substrate may also have one or more layers of differing materials already deposited upon it from a previous manufacturing step. For example, the wafers may include silicon layers (e.g., crystalline, amorphous, porous, etc.), silicon containing layers (e.g., SiO2, SiN, SiON, SiCOH, etc.), metal containing layers (e.g., copper, cobalt, ruthenium, tungsten, platinum, palladium, nickel, ruthenium, gold, etc.) or combinations thereof. Furthermore, the substrate may be planar or patterned. The substrate may be an organic patterned photoresist film. The substrate may include layers of oxides which are used as dielectric materials in MEMS, 3D NAND, MIM, DRAM, or FeRam device applications (for example, ZrO2based materials, HfO2based materials, TiO2based materials, rare earth oxide based materials, ternary oxide based materials, etc.) or nitride-based films (for example, TaN, TiN, NbN) that are used as electrodes. One of ordinary skill in the art will recognize that the terms “film” or “layer” used herein refer to a thickness of some material laid on or spread over a surface and that the surface may be a trench or a line. Throughout the specification and claims, the wafer and any associated layers thereon are referred to as substrates.

The term “aspect ratio” refers to a ratio of the height of a trench (or aperture) to the width of the trench (or the diameter of the aperture).

Note that herein, the terms “film” and “layer” may be used interchangeably. It is understood that a film may correspond to, or related to a layer, and that the layer may refer to the film. Furthermore, one of ordinary skill in the art will recognize that the terms “film” or “layer” used herein refer to a thickness of some material laid on or spread over a surface and that the surface may range from as large as the entire wafer to as small as a trench or a line.

The terms “via”, “aperture” and “hole” are sometimes used interchangeably, and generally mean an opening in an interlayer insulator.

As used herein, the abbreviation “NAND” refers to a “Negated AND” or “Not AND” gate; the abbreviation “2D” refers to 2 dimensional gate structures on a planar substrate; the abbreviation “3D” refers to 3 dimensional or vertical gate structures, wherein the gate structures are stacked in the vertical direction.

The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements may be referred to by these abbreviation (e.g., Si refers to silicon, N refers to nitrogen, O refers to oxygen, C refers to carbon, H refers to hydrogen, F refers to fluorine, etc.).

The unique CAS registry numbers (i.e., “CAS”) assigned by the Chemical Abstract Service are provided to identify the specific molecules disclosed.

The term “wafer” or “patterned wafer” refers to a wafer having a stack of silicon-containing films on a substrate and a patterned hardmask layer on the stack of silicon-containing films formed for pattern etch. The term “wafer” or “patterned wafer” may also refers to a trench wafer having an aspect ratio.

Note that herein, the terms “film” and “layer” may be used interchangeably. It is understood that a film may correspond to, or related to a layer, and that the layer may refer to the film. Furthermore, one of ordinary skill in the art will recognize that the terms “film” or “layer” used herein refer to a thickness of some material laid on or spread over a surface and that the surface may range from as large as the entire wafer to as small as a trench or a line.

Note that herein, the terms “deposition temperature” and “substrate temperature” may be used interchangeably. It is understood that a substrate temperature may correspond to, or related to a deposition temperature, and that the deposition temperature may refer to the substrate temperature.

Note that herein, the terms “precursor” and “deposition compound” and “deposition gas” may be used interchangeably when the precursor is in a gaseous state at room temperature and ambient pressure. It is understood that a precursor may correspond to, or related to a deposition compound or deposition gas, and that the deposition compound or deposition gas may refer to the precursor.

As used herein, the abbreviation “NAND” refers to a “Negated AND” or “Not AND” gate; the abbreviation “2D” refers to 2 dimensional gate structures on a planar substrate; the abbreviation “3D” refers to 3 dimensional or vertical gate structures, wherein the gate structures are stacked in the vertical direction.

The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements might be referred to by these abbreviation (e.g., Si refers to silicon, N refers to nitrogen, O refers to oxygen, C refers to carbon, H refers to hydrogen, F refers to fluorine, etc.).

The unique CAS registry numbers (i.e., “CAS”) assigned by the Chemical Abstract Service are provided to identify the specific molecules disclosed.

As used in the disclosed embodiments, the term “hydrocarbyl group” refers to a functional group containing carbon and hydrogen; the term “alkyl group” refers to saturated functional groups containing exclusively carbon and hydrogen atoms. The hydrocarbyl group may be saturated or unsaturated. Either term refers to linear, branched, or cyclic groups. Examples of linear alkyl groups include without limitation, methyl groups, ethyl groups, propyl groups, butyl groups, etc. Examples of branched alkyls groups include without limitation, t-butyl. Examples of cyclic alkyl groups include without limitation, cyclopropyl groups, cyclopentyl groups, cyclohexyl groups, etc.

As used in the disclosed embodiments, the abbreviation “Me” refers to a methyl group; the abbreviation “Et” refers to an ethyl group; the abbreviation “Pr” refers to a propyl group.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. Any and all ranges recited herein are inclusive of their endpoints (i.e., x=1 to 4 or x ranges from 1 to 4 includes x=1, x=4, and x=any number in between), irrespective of whether the term “inclusively” is used.

Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

