WO2001066816A1

WO2001066816A1 - Liquid sources for cvd of group 6 metals and metal compounds

Info

Publication number: WO2001066816A1
Application number: PCT/US2001/007045
Authority: WO
Inventors: Roy G. Gordon; Sean T. Barry; Randy N.R. BROOMHALL-DILLARD
Original assignee: President And Fellows Of Harvard College
Priority date: 2000-03-03
Filing date: 2001-03-05
Publication date: 2001-09-13

Abstract

A chemical vapor deposition process is provided for the formation of conformal layers containing metals, metal nitrides or metal oxides. The process includes contacting a vapor or vapor mixture comprising one or more metal compounds having both carbonyl and Lewis base ligands, such as tungsten pentacarbonyl 1,2-dimethylpropylisonitrile as shown in (Figure 1), with a heated surface in a deposition process to deposit a material containing one or more metals. The process can be used to form diffusion barrier layers between copper and silicon in computer microcircuits, or gate electrodes compatible with ultrathin dielectric layers.

Description

LIQUID SOURCES FOR CND OF GROUP 6 METALS AND METAL

COMPOUNDS

This invention was made with the support of the United States

government under National Science Foundation Grant Nos. ECS-9975504 and CTS-9974412. The United States may have certain rights in the

invention.

Background of the Invention

1. Field of the Invention

This invention relates to an improved process for chemical vapor deposition (CND) of thin films of tungsten metal, tungsten nitride or

tungsten oxide. One application of the process is to form semiconductor microcircuits in which the film acts as a barrier preventing diffusion of

metals such as copper into silicon transistors. Another application is to deposit tungsten gate electrodes on thin insulating oxide layers in metal- oxide-semiconductor (MOS) microelectronic devices.

2. Description of the Related Art

In computer processors and memory chips, metal circuits connect the

transistors and capacitors formed near the surface of the silicon. Aluminum and copper are the metals commonly used for these circuits. In order to provide a functional and durable computer, the metals must be separated from the silicon by a barrier layer. In the absence of such a barrier layer,

aluminum alloys with the silicon, producing etch pits that can short out the

electrical circuits, or copper diffuses into the silicon and provides

deleterious recombination centers for the electrons and holes. An effective barrier should be impermeable even when it is very thin (less than about 10

rrm). It must have a very low electrical resistance (less than about 200

micro-ohm-cm). It must also be mechanically and chemically stable to the

conditions (mechanical polishing, etchant solutions, water, heating to

around 400 °C in oxidizing or reducing atmospheres) encountered during

further processing and final use of the device.

Tantalum nitride is a material that is being used as a barrier to

diffusion of copper. The tantalum nitride is ordinarily formed by the

process of reactive sputtering of a tantalum target in a low pressure of nitrogen gas. The sputtered material has been satisfactory for the

production of computer chips with feature sizes down to about 0.2 micron.

As the industry tries to make the circuits operate faster and store more

information, the feature sizes are being reduced further. The complexity of

features that can be acceptably coated using sputtering techniques is limited

because sputtering is a "line-of-sight" deposition method. For feature sizes

less than about 0.2 micron, sputtering may not cover adequately the sides and bottoms of the narrow holes and trenches that are etched about a micron

deep into the substrates.

It is desirable that the coverage of the side walls and bottom of the

etched features has a film thickness similar to that on the upper surface.

"Step coverage" is defined as the ratio of the thickness of the deposited film

at the bottom of the holes to the thiclαiess of the film deposited on the top of

the layer. It is desirable for a barrier film to have step coverage close to

one. Thus a need is perceived for barrier layers deposited by a process that

has better step coverage than sputtering.

Chemical vapor deposition (CND) is a widely-used process for

forming solid materials, such as coatings, from reactants in the vapor phase.

Often, CVD processes produce better step coverage than sputtering. The

deposition of tungsten using CND techniques is known, most typically

using tungsten hexafluoride, WF₆, as the tungsten source. However, use of

hexafluoride compounds often leaves residual fluoride contamination in the

films. However, the byproduct hydrogen fluoride is highly corrosive and

can damage substrates. Residual fluoride contamination in the films can

cause problems such as loss of adhesion, or diffusion of fluorine into gate

oxides causing threshold voltage shifts.

CVD of tungsten-containing films from vapors of tungsten

hexacarbonyl, W(CO)₆, have been reported by J. Haigh, G. Burkhardt and K. Blake, J. Cryst. Growth,. 155:266 (1995). Gate electrodes of tungsten

have been formed by CVD from W(CO)₆ onto ultra-thin dielectrics needed

for high speed/high density MOS and CMOS devices, according to US

Patent 5,789,312 and D. A. Buchanan, F. R McFeely and J. J. Yurkas, in

Appl. Phys. Lett, 73:1676 (1998).

CVD using both (CO)₆ vapor and oxygen gas, O₂, has produced

electrochromic films of tungsten oxide. See D. Davazoglou, Chimica

Chronica, New Series, 23:423 (1994). W(CO)₆ has also been used to

deposit tungsten nitride, W₂N, with properties suitable for barriers to

diffusion of copper in microelectronics.

However, these CVD processes have a practical disadvantage in that

tungsten hexacarbonyl is a solid. Sublimation from solid W(CO)₆ is not as

reproducible or convenient a source of vapor as a liquid source would be, ,

since the surface area of a solid changes as the solid evaporates. W(CO)₆ is

highly toxic and has sufficient vapor pressure at room temperature that

toxic concentrations of vapor can be emitted from any spilled material.

Also, the carbon monoxide byproduct from its CVD reactions is highly

toxic and lacks any warning odor.

Summary of the Invention

A feature of the present invention is to provide a reproducible and

convenient liquid source for a process for the chemical vapor deposition of films with effective diffusion barrier properties, good step coverage, high electrical conductivity and high stability.

A particular feature of the invention is to provide a reproducible and

convenient liquid source for a process for the chemical vapor deposition of

group 6 metals, metal nitrides, metal carbides, and metal oxides, and in

particular, tungsten metal, metal nitrides and metal oxides, in layers with

effective diffusion barrier properties, good step coverage, high electrical conductivity and no fluoride contamination.

An additional feature of the invention is to provide a process for

chemical vapor deposition of conformal films from the vapors of stable, volatile liquids.

A related feature of the invention is to deposit conformal layers containing several metal nitrides in a single chemical vapor deposition

process.

Another particular feature of the invention is to provide a process for

depositing conformal tungsten metal or tungsten nitride films having strong

adhesion to silicon and silicon dioxide.

A further particular feature of the invention is to provide conformal

tungsten metal or tungsten nitride films onto which subsequently deposited

metal films adhere strongly. Another particular feature of the invention is to provide a process for depositing conformal, electrically conductive molybdenum metal or

molybdenum nitride films having good resistance to diffusion of materials

through the films.

Another feature of the invention is to provide a process for

depositing tungsten metal films that are suitable as gate electrodes for microelectronic circuits.

A further feature of the invention is to provide a process for

depositing tungsten oxide films that have electrochromic properties.

Other features of the invention will be obvious to those skilled in the art on reading the instant invention.

The above features have been substantially achieved by use of a

chemical vapor deposition process in which a gaseous mixture, comprising

the vapors of a metal carbonyl compound substituted with a Lewis base, and, optionally, ammonia gas or other reactive vapor, are brought in contact with a hot surface on which a film comprising a metal nitride or other metal

compound is deposited. With suitable choices of the alkyl group, these

compounds are low-viscosity liquids at room temperature and can be

vaporized and distilled at higher temperatures (typically 50 to 80 °C under

vacuum). These liquids have negligible vapor pressure at room

temperature, so they are safer to handle than tungsten hexacarbonyl. They are stable to air and water. Their CVD byproducts have a pungent odor

even at low concentrations, so any failure of the exhaust scrubbing system

can easily be identified before toxic concentrations of carbon monoxide are

released.

In one aspect of the invention, a metal-containing film is obtained by

contacting vapor or vapor mixture comprising one or more metal

compounds having both carbonyl and Lewis base ligands with a heated

surface in a deposition process to deposit a material containing one or more

metals. In preferred embodiments, a conformal film which closely matches

the features of the underlying substrate is obtained. For example, tungsten

pentacarbonyl 2-methylbutylisonitrile vapor and ammonia gas are flowed

onto a patterned substrate held at 300 °C, on which a film of tungsten

nitride deposits and uniformly covers holes and trenches in the substrate.

The metal carbonyl Lewis base compounds used in the process of the

invention have the general formula M(CO)_m(L)_n, where L stands for a

Lewis base that is not CO, M stands for a metal, and m and n are integers.

Preferred compounds contain the group 6 metals of the periodic table of the

elements, and more preferably include tungsten or molybdenum. Preferred

compounds have the general formula M(CO) ._n(L)_n with n = 1, 2 or 3.

A Lewis base includes any compound which functions as an electron

donor, such as nitriles, isonitriles, amines, phosphines, phosphites, and other nucleophilic compounds. Particularly preferred Lewis bases are

isonitriles, which have the general formula L = RNC, where R is an alkyl

group or a substituted alkyl group. Other preferred Lewis bases are the nitriles, which have the general formula RCN. Other preferred Lewis bases

may be chosen from the group comprising compounds of the general

formula R^JR²R³E, where "E" is a group 15 nonmetal, preferably nitrogen or

phosphorus, and where R¹, R² and R³ are independently chosen from the

class of alkyl groups or a substituted alkyl groups containing heteroatoms such as nitrogen. Other preferred Lewis bases include trimethylphosphite,

triethylphosphine, tripropylphosphine, phenyldimethylphosphine,

phenyldimethoxyphosphine, phenyldiethylphosphine, and

phenyldiethoxyphosphine. Still other preferred Lewis bases include sulfur-

containing compounds such as diethylsulfide, dipropylsulfide, and dibutylsulfide.

The Lewis base is preferably chosen such that the metal carbonyl

Lewis base compound is a liquid at room temperature, taken to be about 20

°C. While not being bound by any particular mode of operation, it is postulated that coordination of one or more Lewis base compounds at the metal disrupts symmetry, thereby reducing the melting point of the

compound. Examples of preferred compounds include tungsten(O) pentacarbonyl

3-methyl-2-butylisonitrile, tungsten(O) pentacarbonyl 3-pentylisonitrile,

tungsten(O) pentacarbonyl 2-pentylisonitrile, tungsten(O) pentacarbonyl 2- methylbutylisonitrile, tungsten(O) pentacarbonyl isoamylisonitrile,

tungsten(O) pentacarbonyl 2-isonitrile-3,3-dimethylbutane, tungsten(O)

pentacarbonyl n-pentylisonitrile, tungsten(O) pentacarbonyl 1,3- dimethylbutylisonitrile, tungsten(O) pentacarbonyl 2-hexylisonitrile,

tungsten(O) pentacarbonyl 1,4-dimethylpentylisonitrile, tungsten(O)

pentacarbonyl n-hexylisonitrile, tungsten(O) pentacarbonyl 2-

heptylisonitrile, tungsten(O) pentacarbonyl n-heptylisonitrile, tungsten(O)

pentacarbonyl 1,3-dimethylpentylisonitrile, tungsten(O) pentacarbonyl 1,5-

dimethylhexylisonitrile, tungsten(O) pentacarbonyl 2-octylisonitrile, tungsten(O) pentacarbonyl 2-ethylhexylisonitrile, tungsten(O) pentacarbonyl

n-octylisonitrile and tungsten(O) tricarbonyl tri(n-propylisonitrile). Further

examples of preferred compounds include tungsten(O) pentacarbonyl

triethylphosphite, W(CO)₅P(OEt)₃, tungsten(O) pentacarbonyl tributylphosphine, W(CO)₅P(n-Bu)₃, and tungsten(O) pentacarbonyl N-

isopropyl-dimethylamine, W(CO)₅ PrMe₂.

The method of the invention is useful in the formation of metal,

metal oxide, metal carbide, and metal nitride films and mixed-metal

derivatives thereof. In one embodiment, the invention provides a process for the

chemical vapor deposition of metals, using reactant vapors produced by the

vaporization of a liquid compound of a metal carbonyl and a Lewis base.

This vapor is then brought in contact with a heated substrate. This process

may be used to form films of metals including, but not limited to, tungsten

and molybdenum.

In another embodiment, the invention provides a process for the

chemical vapor deposition of metal nitrides, using reactant vapors produced

by the vaporization of a liquid compound of a metal carbonyl and a Lewis

base. This vapor is then mixed with a source of nitrogen, such ammonia gas or hydrazine and, optionally, an inert carrier gas. This vapor mixture is

brought into contact with a substrate heated to a temperature sufficient to

deposit a material comprising a metal nitride. This process may be used to

form films including, but not limited to, tungsten and molybdenum nitrides.

In another embodiment of the invention, mixed metal nitrides are formed by vaporizing two or more metal carbonyl Lewis base compounds,

and mixing their vapors with ammonia gas and, optionally, an inert carrier

gas. This vapor mixture is brought into contact with a substrate heated to a

temperature sufficient to deposit a material comprising two or more metal

nitrides. The process may be used to form multi-metal nitride films including, but not limited to, chromium, molybdenum and tungsten nitrides. In another embodiment, the invention provides a process for the

chemical vapor deposition of metal oxides, using reactant vapors produced

by the vaporization of a liquid compound of a metal carbonyl and a Lewis

base. This vapor is then mixed with oxygen gas or another oxygen-

containing gas and, optionally, an inert carrier gas. This vapor mixture is brought into contact with a substrate heated to a temperature sufficient to

deposit a material comprising a metal oxide. This process may be used to

form films including, but not limited to, tungsten and molybdenum oxides.

Another embodiment of the invention provides a process for the

CVD of metal-containing materials, using reactant vapors comprising vapors of a liquid solution comprising a liquid solvent and a compound of a

metal carbonyl and a Lewis base.

In another aspect of this invention includes novel metal-isonitrile-

containing compounds. In preferred embodiments, the novel metal- isonitrile-containing compounds are liquids at 50 °C, and preferably at 20

°C.

The present invention provides a metal-containing films having good

step coverage, low resistivity and forming a good barrier against diffusion

of materials such as copper. Brief Description of the Drawings

The invention is described with reference to the figures, which are

presented for illustration purposes only and are not intended to be limiting

of the invention, and in which: Figure 1 is a molecular structure of solid tungsten(O) pentacarbonyl

1,2-dimethylpropylisonitrile; and

Figure 2 is a Rutherford Backscattering (RBS) spectrum of a CVD

tungsten oxide film deposited on glassy carbon.

Detailed Description of the Invention

The method of the invention includes a chemical vapor deposition

, process in which a gaseous mixture, comprising the vapors of a metal

carbonyl Lewis base compound and ammonia, is brought in contact with a

hot surface to deposit a conformal metal-containing film. The vapor may additionally contain other reactive components, such as a reactive nitrogen-

or oxygen-containing compound of as to obtain metal nitride or metal oxide

films, respectively. For example, tungsten pentacarbonyl n-hexylisonitrile

vapor and ammonia gas are flowed onto a patterned substrate held at 300 °C, on which a film of tungsten nitride is deposited which imiformly covers holes and trenches in the substrate. Specific embodiments of this invention

may require the use of one or more metal carbonyl Lewis base compounds. The metal carbonyl Lewis base compounds used in the process of the

invention may have the general formula M(CO)_m(L )_n where L is a Lewis

base. In preferred embodiments, the Lewis base is chosen such that the metal carbonyl Lewis base compound is a liquid at 20 °C, and is

vaporizable without significant decomposition. In addition, it may be

selected to be reactive with any additional components of the vapor. For

example, M(CO)_mL_n may be selected to react with ammonia under suitable

CVD conditions to form a metal nitride deposit. Preferred Lewis bases include alkyl isonitriles, alkyl nitriles, alkyl amines, alkyl phosphines and

alkyl phosphites.

The compounds of this invention may be formed by reacting a metal

carbonyl compound with a suitable Lewis base. In a particularly convenient

method, tungsten hexacarbonyl is dissolved in a solvent, such as tetrahydrofuran, along with the Lewis base, such as an alkyl isonitrile.

Reaction is induced by the addition of a small amount of a catalyst, such as

palladium oxide. Carbon monoxide is evolved rapidly at room temperature as the Lewis base replaces one or more of the carbon monoxide ligands.

Other catalysts, such as cobalt chloride, may also be used. Exemplary

catalysts for this type of reaction are found in M. O. Albers and N. J.

Coville, Coord. Chem. Rev., 53:227 (1984). The reaction may also be induced by heating, or by a reactant such as

trimethylamine oxide, as described by T.-Y. Luh, in Coord. Chem. Rev., 60:255 (1984). Another method of synthesis converts the metal

hexacarbonyl to a tetraalkylammonium halide salt, which is then displaced

by the Lewis base. See H. D. Murdoch and R. Henzi, J. Organometal.

Chem., 5:166 (1966). Alternatively, a solution of tungsten carbonyl and the Lewis base in tetrahydrofuran may be irradiated by ultraviolet light to

induce reaction. See Darensbourg et al., JACS, 95: 5919 (1973).

Some of the preferred Lewis bases are not commercially available,

particularly the isonitriles. Isonitriles may be synthesized from

commercially available amines according to the following reaction scheme. First, the amine is refluxed with ethyl formate to form an alkyl formamide

according to eq (1).

RNH₂ + HC(=O)OEt -> RNHC(=O)H + EtOH (1)

See J. Moffat, M. V. Newton and G. J. Papenmeier in the Journal of

Organic Chemistry (27:4058 (1962)), for further detail. Then the resulting

alkyl formamide is dehydrated by distillation from a solution of p-

toluenesulfonyl chloride in quinoline according to eq (2). RNHC(=O)H -> RNC + H₂O (2)

The byproduct water reacts with the p-toluenesulfonyl chloride and

quinoline. A procedure for carrying out this dehydration reaction is given

by R. E. Schuster, J. E. Scott and J. Casanova, Jr., in Organic Syntheses, collective volume 5, pages 772-774 (1973).

The new tungsten compounds are readily synthesized by reacting the

alkyl isonitrile with tungsten hexacarbonyl according to (eq) 3 :

RNC + W(CO)₆ — RNCW(CO)₅ + CO (3)

The tungsten hexacarbonyl is dissolved in tetrahydrofuran, THF, and the

liquid alkyl isonitrile is added dropwise with stirring at room temperature. A small amount of palladium oxide (0.1% by weight of the tungsten hexacarbonyl) is used to catalyze the reaction. See N. J. Coville and M.O.

Albers, Inorg. Chim. Ada., 65:L7 (1982) for further details. Carbon

monoxide gas is evolved, and the reaction is complete within about 15

minutes. Slightly longer reaction times are needed for the isonitriles with larger alkyl groups. The solution is filtered to remove the palladium oxide,

and the THF is removed under vacuum. The crude product is generally over 95% pure. Purification is then done by falling film molecular

distillation under high vacuum (typically 0.01 Torr).

This method is a considerable improvement on previous synthetic

techniques for this type of compound. Previously, replacement of a

carbonyl ligand with an isonitrile was done in refluxing toluene. These

conditions generally lead to considerable amounts of unwanted byproducts,

such as bis- and tris-substituted isonitrile compounds, as well as cluster

compounds containing two or more tungsten atoms.

During the reaction replacing carbon monoxide by isonitrile, the

temperature of the solution stayed constant to within + 0.1 °C. Thus the

bond strengths of W-CO and W-CNR are practically identical. The reaction

is driven to completion by the entropy generated by the release of the

carbon monoxide gas.

Some physical properties of the new tungsten compounds are given

in Table I. The last six compounds in Table I are liquids at room temperature, having melting points below 20 °C. All of the compounds

with alkyl groups having four or fewer carbons are solids at room temperature. All of these compounds with alkyl groups having six or more carbons are liquids at room temperature. Of the eight isomeric compounds

with 5-carbon alkyl groups, two are liquid and the other six are solids with

low melting points. The molecular masses of these new compounds were determined by cryoscopy in p-xylene solution. Their "molecular complexities," defined as

the ratio of the cryoscopic molecular mass to the theoretical monomeric

value, generally fall between about 0.9 and 1.1. Thus the compounds are

monomeric in solution.

Table I. Physical properties of some tungsten(O) pentacarbonyl alkylisonitrile compounds

Density of solid determined from X-ray data.

The crystal structure (shown in Figure 1) verifies the monomeric nature of tungsten(O) pentacarbonyl 1,2-dimethylpropyl-isonitrile. The

tungsten atoms have nearly perfect octahedral coordination by the six

bonded carbon atoms. The tungsten-carbon bond to the isonitrile is 2.12

Angstroms long and the tungsten-carbon bonds to the carbonyls range from 2.03 to 2.05 Angstroms. These lengths are within the range of values

previously observed for similar types of bonds.² The two enantiomers of

the isonitrile ligand, whose chiral center is at carbon C2, appear to be

disordered in the centrosymmetric crystal. Deposition of oxide layers is accomplished by chemical vapor

deposition (CVD) using the liquid group 6 metal precursors prepared as

described herein. The process of the invention can be carried out in

standard equipment well known in the art of chemical vapor deposition (CVD). The CVD apparatus brings the vapors of the reactants into contact

with a heated substrate on which the material deposits. The CVD process is preferably carried out at very low pressures. Low-pressure CVD equipment

is made by Applied Materials (Santa Clara, California), Spire Corporation

(Bedford, Massachusetts), Materials Research Corporation (Gilbert, Arizona), Novellus (San Jose, California), Emcore Corporation (Somerset,

NJ) and NZ Applied Technologies (Woburn, Massachusetts). The vapors of the liquid precursors may be formed in a suitable evaporator. Commercial equipment for direct vaporization of liquids is

made by MKS Instruments (Andover, Massachusetts), ATMI (Danbury, Connecticut), Novellus (San Jose, California) and COVA Technologies

(Tiburton, California). Ultrasonic nebulizers are made by Sonotek

Corporation (Milton, New York) and Cetac Technologies (Omaha,

Nebraska).

The precursors may also be vaporized by flash evaporation. For this

purpose a low viscosity liquid is desired, which may be obtained by

addition of solvent, e.g. liquid mesitylene, to either liquid or solid precursors. The solution is then nebulized into tiny droplets, e.g., less than

about 20 microns, by a high-frequency (1.4MHz) ultrasonic system, such as

that described by Gordon et al. in WO 99/28532.

Gaseous reactants, such as oxygen or ammonia, may be introduced

into the vapor through a mass flow controller, with or without an inert

carrier gas, to provide the desired partial pressure of the gas in the

deposition system.

Typical deposition temperatures lie in the range of about 200 to 600

°C. The deposition reaction may also be accelerated by light, or by the

electrical energy of a plasma discharge, as well as by heat. Typical deposition pressures range from 0.1 to 10 milli-Torr for metal deposition,

and 0.1 to 760 Torr for metal nitride, metal carbide, or metal oxide

deposition.

Conformal films and improved step coverage of the films described

herein may be obtained over the conventionally deposited films using sputtering techniques, which rely upon line-of-sight for coverage.

Conformal tungsten metal or tungsten nitride films demonstrate

strong adhesion to silicon and silicon dioxide. In addition, subsequently deposited metal films adhere strongly to the CVD-deposited tungsten metal

or tungsten nitride films. These advantages of the invention may be due, in part, to the absence of fluorine in the reactants. By way of contrast, the

conventional CVD process using tungsten hexafluoride leaves fluorine

residues that can interfere with adhesion. Byproduct hydrogen fluoride from the conventional process also etches silicon dioxide, causing damage

to substrates, such as gate insulators, containing silicon dioxide. No such

damage is caused by the process of the invention.

The invention is illustrated in the following examples, which are not intended to be limiting of the invention.

Example 1. Synthesis of n-hexylformamide, CH₃(CH₂)₅NHC(=O)H.

n-Hexylamine (50.0 g, 0.49 mol) and ethyl formate (38.4 g, 0.52

mol) were added to a schlenk flask, degassed, and refluxed at 85°C for 12 hours. The excess ethyl formate and ethanol by-product were removed by vacuum distillation to yield crude, colorless n-hexylformamide (31.1 g,

52%), which was used without further purification. IR ^m^"1): 1663,

NC(=O). Η NMR (C₆D₆) δ: 8.09, s, 1H, RNHC(O)H; 6.95, v br s, 1H,

RNHC(O)H; 3.15, q, 2H; 1.35, q, 2H; 1.13 br m, 4H; 0.84, t, 3H. ¹³C NMR (C₆D₆) δ: 161.4; 38.2; 31.8; 29.8; 26.8; 22.9; 14.2.

Example 2. Synthesis of n-hexylisonitrile, CH₃(CH₂)₅NC.

A dark brown solution of p-toluenesulfonylchloride (58.6 g, 0.31

mol) dissolved in quinoline (132.3 g, 1.02 mol) was heated to 85°C in a

three-neck round bottom flask equipped with a distillation head to a condenser and schlenk flask, and an addition funnel with n-hexylformamide

(31.0 g, 0.26 mol). The system was evacuated (80 mtorr) and the n-

hexylformamide was added over 20 min. A clear, colorless liquid distilled from the reaction and was collected in the schlenk flask chilled in liquid

nitrogen. The volatiles were collected for 20 minutes after addition completed and the crude product contained large quantities of quinoline.

The product was distilled under low pressure (59-62°C at 19 torr) using a vigreux column producing clear, colorless n-hexylisonitrile (23.0 g, 81%).

IR ^m^"1): 2146, RN=C. Η NMR (C₆D₆) δ: 2.61, br m, 2H; 1.08, br m, 4H; 1.00 m, 2H; 0.93, q, 2H; 0.78, t, 3H. ¹³C NMR (C₆D₆) δ: 158.8, t, RNC; 41.1, t, C₅H„CH₂NC; 31.0; 29.11; 26.1; 22.6; 14.1. Example 3. Synthesis of tungsten(O) pentacarbonyl 2-

methylbutylisonitrile, (CO)₅ W(CNCH₂CH(CH₃)CH₂CH₃).

Tungsten hexacarbonyl (10.0 g, 0.028 mol) and palladium (II) oxide (0.02 g, 0.00016 mol) were charged in a 250-mL schlenk flask and the flask

was evacuated and backfilled with dry nitrogen gas three times. Dry

tetrahydrofuran (150 mL) was added by cannula and the mixture was

slightly heated to facilitate the dissolution of the tungsten hexacarbonyl. To this, 2-methylbutylisonitrile (3.00 g, 0.031 mol) was added drop-wise over

10 minutes. The solution effervesced vigorously and was allowed to stir for

15 minutes after addition was complete. The yellow solution was filtered

through celite to remove the palladium oxide, and volatiles were removed in

vacuo. A low viscosity orange liquid (11.2 g) resulted. Purification by falling molecular film distillation at 65 °C and <3 x 10^"3 Torr gave bright yellow tungsten pentacarbonyl 2-methylbutylisonitrile (4.40 g, 37% yield).

Η NMR (C₆D₆) δ: 2.28, multiplet, 2H, CNCH₂CH(CH₃)CH₂CH₃; 0.87,

multiplet., 2H, CNCH₂CH(CH₃)CH₂CH₃; 0.72, multiplet, 1H,

CNCH₂CH(CH₃)CH₂CH₃; 0.49, overlaid doublet and triplet, 6H, CNCH₂CH(CH₃)CH₂CH₃. ¹³C NMR (C₆D₆) δ: 196.51; 194.80; 48.98;

34.44; 26.22; 16.40; 10.82. Molecular weight: 421.05 (calc); 453 (found). Example 4. Tungsten metal films were made by very low-pressure chemical vapor deposition.

Tungsten pentacarbonyl 2-methylbutylisonitrile was placed in a

syringe pump, from which the liquid was delivered at a controlled rate

through a back-pressure regulator into a low-pressure CVD chamber similar

to the one shown in US Patent 5,789,312, whose walls were heated to about

100 °C. As the liquid enters the chamber it is warmed and vaporized. The

liquid pumping rate is adjusted to maintain the chamber pressure at 0.4

milliTorr. A thin, conformal, adherent coating of tungsten metal is deposited on an oxidized and patterned silicon substrate heated to 500 °C.

Example 5. Tungsten nitride films were made by low-pressure

chemical vapor deposition.

Tungsten pentacarbonyl 2-methylbutylisonitrile was vaporized at 60

°C by an MKS Model LDS 100 liquid delivery and vaporization system into a hydrogen carrier gas purified of water and oxygen by a Nanochem

purifier. In the reactor chamber, this gas mixture was mixed with a flow of

purified ammonia gas, with a molar flow rate 20 times larger than the tungsten compound.

The substrate was a silicon wafer previously coated with a layer of

silicon dioxide 2.4 microns thick, into which holes 0.7 microns in diameter

had been etched. The substrate was preheated to 300 °C and exposed to the vapor mixture for 10 minutes at a pressure of 0.4 Torr. A conformal film of tungsten nitride was deposited on the substrate.

Example 6. Tungsten metal films were made by low-pressure

chemical vapor deposition using a tungsten(O) pentacarbonyl 1 -

methylbutylisonitrile precursor..

Tungsten(O) pentacarbonyl 1 -methylbutylisonitrile (prepared as described for tungsten(O) pentacarbonyl 2-methylbutylisonitrile in Example

3) was evaporated from a reservoir at 80 °C into a stainless steel vacuum

chamber initially at 10^"7 Torr. Tungsten metal films were deposited on

silicon wafers, glass and glassy carbon substrates placed on a substrate holder heated to 500 °C. Rutherford Backscattering Spectroscopy (RBS)

showed that the films were tungsten metal with about 1% molybdenum

impurity derived from the starting tungsten hexacarbonyl. X-ray

Photoelectron Spectroscopy detected some carbon and oxygen impurities.

X-ray diffraction shows that the films are polycrystalline.

Example 7. Tungsten nitride films were made by low-pressure

chemical vapor deposition using a tungsten(O) pentacarbonyl 1-

methylbutylisonitrile precursor.

Tungsten(O) pentacarbonyl 1 -methylbutylisonitrile was vaporized by

flash evaporation. For this purpose, liquid tungsten(O) pentacarbonyl 1- methylbutylisonitrile was mixed with liquid mesitylene to lower its viscosity below about 3 centipoise. At this viscosity the solution could be

nebulized easily into tiny droplets (less than about 20 microns in diameter)

by a high-frequency (1.4 MHz) ultrasonic system. The resulting fog was entrained by a flow of nitrogen and ammonia carrier gas at atmospheric

pressure into a tube furnace with substrates placed on a heated aluminum

substrate holder in the tube. Tungsten nitride films were deposited on

substrates at 250 to 400 °C. RBS analysis showed that the films have a

composition near to W₂N. X-ray diffraction showed that these films are

amorphous.

Example 8. Tungsten oxide films were made by low-pressure

chemical vapor deposition using a tungsten(O) pentacarbonyl 1-

methylbutylisonitrile precursor.

A tungsten oxide film was deposited according to Example 7, with

the following modifications. Oxygen gas was used in place of ammonia gas

in the deposition process to give films of amorphous tungsten oxide. RBS

analysis gave a composition of WO_3,5C_0,025 (Fig. 2).

Example 9. Example 4 is repeated with molybdenum pentacarbonyl 2-methylbutylisonitrile in place of the tungsten pentacarbonyl 2-

methylbutylisonitrile. A molybdenum film with excellent step coverage is

obtained. Example 10. Example 5 is repeated with molybdenum pentacarbonyl 2-methylbutylisonitrile in place of the tungsten

pentacarbonyl 2-methylbutylisonitrile. A molybdenum nitride film with

excellent step coverage is obtained.

Example 11. Example 5 is repeated with oxygen in place of the

ammonia gas, and nitrogen as the carrier gas in place of hydrogen. An film

of tungsten oxide is obtained, having electrochromic properties.

The liquids and solutions disclosed in these examples all appeared to

be non-pyrophoric by the methods published by the United States

Department of Transportation. One test calls for placing about 5 milliliters of the liquid or solution on an non-flammable porous solid, and observing

that no spontaneous combustion occurs. Another test involves dropping 0.5

milliliters of the liquid or solution on a Whatman No. 3 filter paper, and observing that no flame or charring of the paper occurs. The compounds

are air and moisture stable, however, some of these precursor liquids do

react in the presence of light.

Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific

embodiments of the invention described specifically herein. Such equivalents are intended to be encompassed in the scope of the following

claims. The contents of all patents, applications and publications made

references to herein are included in their entirety.

What is claimed is:

Claims

1. A process for forming a material containing one or more

metals, comprising: contacting vapor or vapor mixture comprising one or more metal

compounds having both carbonyl and Lewis base ligands with a heated

surface in a deposition process to deposit a material containing one or more

metals.

2. The process of claim 1 in which the metal or metals are

selected from the group consisting of tungsten, molybdenum and

chromium.

3. The process of claim 2 in which the metal is tungsten.

4. The process of claim 2 in which the metal is molybdenum.

5. The process of claim 1 wherein the Lewis base is chosen such that the metal carbonyl Lewis base compound is a liquid at 20 °C.

6. The process of claim 5, wherein the Lewis base is an alkyl

isonitrile.

7. The process of claim 5, wherein the Lewis base is an alkyl

nitrile or an alkylamine.

8. The process of claim 5 wherein the Lewis base is an

alkylphosphine or an allylphosphite.

9. The process of claim 1 wherein the Lewis base is chosen such

that the metal carbonyl Lewis base compound has a vapor pressure of at

least 0.1 milliTorr at a temperature less than 200 °C.

10. The process of claim 1 wherein the Lewis base has the

formula R'R^E, where "E" is a group 15 nonmetal, preferably nitrogen or

phosphorus, and where R¹, R² and R³ are independently chosen from the

class of alkyl groups or a substituted alkyl groups containing hetero-atoms

such as nitrogen.

11. The process of claim 1, wherein the surface is heated to a

temperature in the range of about 300-600 °C.

12. The process of claim 1, wherein the metal compound is

selected from the group consisting of tungsten(O) pentacarbonyl 3-methyl- 2-butylisonitrile, tungsten(O) pentacarbonyl isopropylisonitrile, tungsten(O) pentacarbonyl propylisonitrile, tungsten(O) pentacarbonyl sec-

butylisonitrile, tungsten(O) pentacarbonyl isobutylisonitrile, tungsten(O)

pentacarbonyl n-butylisonitrile, tungsten(O) pentacarbonyl

isopentylisonitrile, tungsten(O) pentacarbonyl 3-pentylisonitrile, tungsten(O) pentacarbonyl 2-pentylisonitrile, ttxngsten(O) pentacarbonyl 2-

methylbutylisonitrile, tungsten(O) pentacarbonyl isoamylisonitrile,

tungsten(O) pentacarbonyl 2-isonitrile-3,3-dimethylbutane, tungsten(O)

pentacarbonyl n-pentylisonitrile, tungsten( ) pentacarbonyl 1,3- dimethylbutylisonitrile, tungsten(O) pentacarbonyl 2-hexylisonitrile,

tungsten(O) pentacarbonyl 1,4-dimethylpentylisonitrile, tungsten(O) pentacarbonyl n-hexylisonitrile, tungsten(O) pentacarbonyl 2-

heptylisonitrile, tungsten(O) pentacarbonyl n-heptylisonitrile, tungsten(O)

pentacarbonyl 1,3-dimethylpentylisonitrile, tungsten(O) pentacarbonyl 1,5-

dimethylhexylisonitrile, tungsten(O) pentacarbonyl 2-octylisonitrile,

tungsten(O) pentacarbonyl 2-ethylhexylisonitrile, tungsten(O) pentacarbonyl

n-octylisonitrile, tungsten(O) tricarbonyl tri(n-propylisonitrile), tungsten(O)

pentacarbonyl triethylphosphite, tungsten(O) pentacarbonyl

tributylphosphine, and tungsten(O) pentacarbonyl N-isopropyl-

dimethylamine.

13. A process for forming a material containing one or more

metal nitrides, comprising: providing a vapor comprising ammonia or other reactive nitrogen

source and one or more metal compounds having both carbonyl and Lewis

base ligands, and

contacting the vapor mixture with a heated surface in a deposition process to deposit a material containing one or more metals.

14. The process of claim 13 in which the metal or metals are selected from the group consisting of tungsten, molybdenum and clxromium.

15. The process of claim 14 in which the metal is tungsten.

16. The process of claim 14 in which the metal is molybdenum.

17. The process of claim 15 wherein the Lewis base is chosen such that the metal carbonyl Lewis base compound is a liquid at 20 °C.

18. The process of claim 17, wherein the Lewis base is an alkyl

isonitrile.

19. The process of claim 17, wherein the Lewis base is an alkyl

nitrile or an alkyl amine.

20. The process of claim 17 wherein the Lewis base is an

alkylphosphine or an alkylphosphite.

21. The process of claim 13 wherein the Lewis base is chosen

such that the metal carbonyl Lewis base compound has a vapor pressure of

at least 0.1 milliTorr at a temperature less than 200 °C.

22. The process of claim 13 wherein the Lewis base has the

formula R^!R²R³E, where "E" is a group 15 nonmetal, preferably nitrogen or

phosphorus, and where R¹, R² and R³ are independently chosen from the

class of allcyl groups or a substituted allcyl groups containing hetero-atoms

such as nitrogen.

23. The process of claim 13, wherein the surface is heated to a

temperature in the range of about 200-600 °C.

24. The process of claim 13, wherein the metal compound is

selected from the group consisting of tungsten(O) pentacarbonyl 3-methyl-

2-butylisonitrile, tungsten(O) pentacarbonyl isopropylisonitrile, tungsten(O) pentacarbonyl propylisonitrile, tungsten(O) pentacarbonyl sec-

butylisonitrile, tungsten(O) pentacarbonyl isobutylisonitrile, tungsten(O)

pentacarbonyl n-butylisonitrile, tungsten(O) pentacarbonyl

isopentylisonitrile, tungsten(O) pentacarbonyl 3-pentylisonitrile, tungsten(O)

pentacarbonyl 2-pentylisonitrile, tungsten(O) pentacarbonyl 2-

methylbutylisonitrile, tungsten(O) pentacarbonyl isoamylisonitrile,

tungsten(O) pentacarbonyl 2-isonitrile-3,3-dimethylbutane, tungsten(O)

heptylisonitrile, tungsten(O) pentacarbonyl n-heptylisonitrile, tungsten(O)

pentacarbonyl 1,3-dimethylpentylisonitrile, tungsten(O) pentacarbonyl 1,5- dimethylhexylisonitrile, tungsten(O) pentacarbonyl 2-octylisonitrile, tungsten(O) pentacarbonyl 2-ethylhexylisonitrile, tungsten(O) pentacarbonyl

n-octylisonitrile, tungsten(O) tricarbonyl tri(n-propylisonitrile), tungsten(O) pentacarbonyl triethylphosphite, tungsten(O) pentacarbonyl

tributylphosphine, and tungsten(O) pentacarbonyl N-isopropyl-

dimethylamine.

25. A process for forming a material containing one or more

metal nitrides, comprising:

providing a vapor comprising ammonia and one or more metal

compounds having both carbonyl and Lewis base ligands, and

26. The process of claim 25 in which the metal or metals are

selected from the group consisting of tungsten, molybdenum and

chromium.

27. The process of claim 26 in which the metal is tungsten.

28. The process of claim 26 in which the metal is molybdenum.

29. The process of claim 25 wherein the Lewis base is chosen

such that the metal carbonyl Lewis base compound is a liquid at 20 °C.

30. The process of claim 25, wherein the Lewis base is an allcyl isonitrile.

31. The process of claim 25, wherein the Lewis base is an allcyl

nitrile or an alkyl amine.

32. The process of claim 25 wherein the Lewis base is an alkylphosphine or an alkylphosphite.

33. The process of claim 25 wherein the Lewis base is chosen such that the metal carbonyl Lewis base compound has a vapor pressure of

at least 0.1 milliTorr at a temperature less than 200 °C.

34. The process of claim 25, wherein the surface is heated to a

temperature in the range of about 200-500 °C.

35. The process of claim 25 wherein the Lewis base has the

formula R¹R²R³E, where "E" is a group 15 nonmetal, preferably nitrogen or

phosphorus, and where R¹, R² and R³ are independently chosen from the

class of allcyl groups or a substituted alkyl groups containing hetero-atoms

such as nitrogen.

36. The process of claim 25, wherein the metal compound is

selected from the group consisting of tungsten(O) pentacarbonyl 3-mefhyl-

2-butylisonitrile, tungsten(O) pentacarbonyl isopropylisonitrile, tungsten(O)

pentacarbonyl propylisonitrile, tungsten(O) pentacarbonyl sec-

butylisonitrile, tungsten(O) pentacarbonyl isobutylisonitrile, tungsten(O) pentacarbonyl n-butylisonitrile, tungsten(O) pentacarbonyl

isopentylisonitrile, tungsten(O) pentacarbonyl 3-pentylisonitrile, tungsten(O)

pentacarbonyl 2-pentylisonitrile, tungsten(O) pentacarbonyl 2- methylbutylisonitrile, tungsten(O) pentacarbonyl isoamylisonitrile, tungsten(O) pentacarbonyl 2-isonitrile-3,3-dimethylbutane, tungsten(O)

tungsten(O) pentacarbonyl 1,4-dimethylpentylisonitrile, tungsten(O)

pentacarbonyl n-hexylisonitrile, tungsten(O) pentacarbonyl 2- heptylisonitrile, tungsten(O) pentacarbonyl n-heptylisonitrile, tungsten(O)

pentacarbonyl 1,3-dimethylpentylisonitrile, tungsten(O) pentacarbonyl 1,5-

dimethylhexylisonitrile, tιxngsten(O) pentacarbonyl 2-octylisonitrile,

tungsten(O) pentacarbonyl 2-ethylhexylisonitrile, tungsten(O) pentacarbonyl

n-octylisonitrile, tungsten(O) tricarbonyl tri(n-propylisonitrile), tungsten(O)

pentacarbonyl triethylphosphite, tungsten(O) pentacarbonyl tributylphosphine, and tungsten(O) pentacarbonyl N-isopropyl-

dimethylamine.

37. A tungsten carbonyl compound selected from the group consisting of:

tungsten(O) pentacarbonyl 3-methyl-2-butylisonitrile, tungsten(O)

pentacarbonyl isopropylisonitrile, tungsten(O) pentacarbonyl

propylisonitrile, tungsten(O) pentacarbonyl sec-butylisonitrile, tungsten(O)

pentacarbonyl isobutylisonitrile, tungsten(O) pentacarbonyl n-

butylisonitrile, tungsten(O) pentacarbonyl isopentylisonitrile, tungsten(O) pentacarbonyl 3-pentylisonitrile, tungsten(O) pentacarbonyl 2- pentylisonitrile, tungsten(O) pentacarbonyl 2-methylbutylisonitrile, tungsten(O) pentacarbonyl isoamylisonitrile, tungsten(O) pentacarbonyl 2-

isonitrile-3,3-dimethylbutane, tungsten(O) pentacarbonyl n-pentylisonitrile,

tungsten(O) pentacarbonyl 1,3-dimethylbutylisonitrile, tungsten(O)

pentacarbonyl 2-hexylisonitrile, tungsten(O) pentacarbonyl 1,4-

dimethylpentylisonitrile, tungsten(O) pentacarbonyl n-hexylisonitrile, tungsten(O) pentacarbonyl 2-heptylisonitrile, tungsten(O) pentacarbonyl n-

heptylisonitrile, tungsten(O) pentacarbonyl 1,3-dimethylpentylisonitrile,

tungsten(O) pentacarbonyl 1,5-dimethylhexylisonitrile, tungsten(O)

pentacarbonyl 2-octylisonitrile, tungsten(O) pentacarbonyl 2- ethylhexylisonitrile, tungsten(O) pentacarbonyl n-octylisonitrile, and

tungsten(O) tricarbonyl tri(n-propylisonitrile).

38. The tungsten carbonyl compound of claim 37, wherein the compound has a melting point below 50 °C.

39. The tungsten carbonyl compound of claim 37, wherein the compound has a melting point below 20 °C.