Organometallic compounds - Patent Review 7390360

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This invention relates generally to the field of organometallic compounds. In particular, this invention relates to organometallic compounds used in the manufacture of compound semiconductors.

Trialkyl Group IIIA metal compounds are used as precursors in the vapor deposition of Group IIIA metal-containing films. In the manufacture of III/V compound semiconductors, such as gallium nitride (GaN), using metalorganic chemical vapor deposition ("MOCVD") techniques, trimethyl gallium and ammonia (a Group V precursor) are conveyed in the vapor phase to a deposition chamber at elevated temperature, the compounds are decomposed and a film of GaN is deposited on a substrate heated at temperatures as high as 1000.degree. C. or greater. In such process, a large amount of ammonia must be used as the incorporation of nitrogen in the film is inefficient in that only a small amount of ammonia is consumed. Usual quantity of ammonia used in the growth of Group III nitrides is several thousand folds molar excess of Group III organometallic employed. Highly pure ammonia, which is required in semiconductor manufacture, is quite expensive and ammonia can be difficult to handle in large amounts. Unreacted ammonia exits the deposition chamber as a waste stream and may enter the environment. Similar issues exist with the use of other Group V precursors such as phosphine such as used in the manufacture of InP and arsine such as used in the manufacture of GaAs.

Efforts have been made to improve these deposition processes. For example, hydrochloric acid has been used in conjunction with trimethyl gallium, trimethyl aluminum and arsine in the metalorganic chemical vapor deposition of Al.sub.xGa.sub.1-xAs films, such as is disclosed in Fujii et al., Surface Orientation Dependency for AlGaAs growth rate with/without HCl in MOCVD, Journal of Crystal Growth, vol 259, pp 327-334, 2003. The presence of HCl produced complicated results, but the HCl was found to increase the amount of aluminum in the film. No effect on the amount of arsine employed was noted.

A problem in fabricating GaN-based microelectronic devices is the fabrication of GaN semiconductor layers having low defect densities. The substrate on which the gallium nitride layer is grown is a major contributor to defect density issue. Accordingly, although GaN layers have been grown on sapphire substrates, aluminum nitride buffer layers formed on silicon carbide substrates reduce defect density in GaN layers deposited thereon. Despite these advances, continued reduction in defect density is desirable and not yet fulfilled, since alternatives to sapphire substrates are very expensive.

Molecular beam epitaxy has been used to selectively grow GaAs films on a GaAs substrate using arsenic metal (As.sub.4), triethyl gallium and either dimethyl gallium chloride or diethyl gallium chloride. The triethyl gallium and either dimethyl gallium chloride or diethyl gallium chloride were used in approximately equimolar amounts. This method achieved selective area epitaxial growth of the GaAs film on masked and patterned substrates, depositing polycrystalline GaAs only on the exposed GaAs substrate. This approach was not attempted with arsine, a gaseous Group VA compound.

There is a need for an improved method for manufacturing Group III/V semiconductors using thermal decomposition techniques, such as chemical vapor deposition ("CVD") and particularly MOCVD techniques. There remains a need to reduce the amount of hazardous Group VA compound sources used in the manufacture of III/V compound semiconductors with substantially reduced defect density, using CVD techniques.

The present invention addresses the above shortcomings by providing a method of depositing a film including a Group IIIA metal on a substrate including the steps of: a) conveying a Group IIIA metal compound having the formula R.sub.3M, where M is a Group IIIA metal and each R is independently a (C.sub.1-C.sub.10) organic radical or hydrogen in a gaseous phase to a deposition chamber containing the substrate; b) conveying a catalytic amount of a catalyst compound in a gaseous phase to the deposition chamber containing the substrate; c) conveying a Group VA gaseous compound to the deposition chamber containing the substrate; d) decomposing the Group IIIA metal compound and the Group VA gaseous compound in the deposition chamber; and e) depositing the film comprising the Group IIIA metal on the substrate, wherein the catalyst compound catalyzes the decomposition of the Group VA gaseous compound. Preferably, the film deposited on the substrate contains a Group IIIA metal and a Group VA element, such as a III/V compound semiconductor.

Also provided by the present invention is a vapor delivery device including a vessel having an elongated cylindrical shaped portion having an inner surface having a cross-section, a top closure portion and a bottom closure portion, the vessel having an inlet opening for the introduction of a carrier gas and an outlet opening for the exiting of the carrier gas, the elongated cylindrical shaped portion having a chamber including a Group IIIA metal compound having the formula R.sub.3M, where M is a Group IIIA metal and each R is independently a (C.sub.1-C.sub.10) organic radical or hydrogen and a catalyst compound capable of catalyzing decomposition of a Group VA gaseous compound; the inlet opening being in fluid communication with the chamber and the chamber being in fluid communication with the outlet opening. The catalyst compound is capable of catalyzing the decomposition of a Group VA gaseous compound.

As used throughout this specification, the following abbreviations shall have the following meanings, unless the context clearly indicates otherwise: .degree. C.=degrees centigrade; mol=moles; g=gram; ca.=approximately; mol %=mole percent; ppm=parts per million; .mu.m=micrometer; Me=methyl; Et=ethyl; iPr=iso=propyl, iBu=iso-butyl; nPr=n-propyl; nBu=n-butyl; tBu=tert-butyl; Bz=benzene and Cp=cyclopentadienyl.

"Halogen" refers to fluorine, chlorine, bromine and iodine and "halo" refers to fluoro, chloro, bromo and iodo. "Alkyl" includes linear, branched and cyclic alkyl. Likewise, "alkenyl" and "alkynyl" include linear, branched and cyclic alkenyl and alkynyl, respectively. As used herein, "CVD" is intended to include all forms of chemical vapor deposition such as MOCVD, metalorganic vapor phase epitaxy ("MOVPE"), organometallic vapor phase epitaxy ("OMVPE"), organometallic chemical vapor deposition "(OMCVD") and remote plasma chemical vapor deposition ("RPCVD"). The articles "a" and "an" refer to the singular and the plural.

Unless otherwise noted, all amounts are percent by weight and all ratios are molar ratios. All numerical ranges are inclusive and combinable in any order except where it is clear that such numerical ranges are constrained to add up to 100%.

The present invention provides a method of depositing a film including a Group IIIA metal on a substrate including the steps of: a) conveying a Group IIIA metal compound having the formula R.sub.3M, where M is a Group IIIA metal and each R is independently a (C.sub.1-C.sub.10) organic radical or hydrogen in a gaseous phase to a deposition chamber containing the substrate; b) conveying a catalytic amount of a catalyst compound in a gaseous phase to the deposition chamber containing the substrate; c) conveying a Group VA gaseous compound to the deposition chamber containing the substrate; d) decomposing the Group IIIA metal compound and the Group VA gaseous compound in the deposition chamber; and e) depositing the film comprising the Group IIIA metal on the substrate, wherein the catalyst catalyzes the decomposition of the Group VA gaseous compound.

A wide variety of Group IIIA metal compounds may be used in the present invention. In such compounds, the R groups may be the same or different, i.e. the compounds may be homoleptic or heteroleptic, respectively. Suitable groups for R include alkyl, alkenyl, alkynyl and aryl. The R groups may optionally be substituted with one or more dialkylamino groups of the formula NR'R'', wherein R' and R'' are independently a (C.sub.1-C.sub.4)alkyl. By "substituted", it is meant that one or more hydrogens of the organic radical are replaced with a dialkylamino group. Typically, R is a (C.sub.1-C.sub.6)alkyl group, optionally substituted with one or more dialkylamino groups. In one embodiment, the Group IIIA metal compound has the formula R.sub.3M, wherein each R is independently a (C.sub.1-C.sub.6)alkyl and M is chosen from indium, gallium and aluminum. Exemplary R groups include, without limitation, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, iso-pentyl, neo-pentyl, allyl, vinyl and phenyl.

Exemplary Group IIIA metal compounds include, but are not limited to, trimethyl indium, triethyl indium, tri-n-propyl indium, tri-iso-propyl indium, dimethyl iso-propyl indium, dimethyl ethyl indium, dimethyl tert-butyl indium, methyl di-tert-butyl indium, methyl di-isopropyl indium, allyl dimethyl indium, methyl diallyl indium, trimethyl gallium, triethyl gallium, tri-iso-propyl gallium, tri-tert-butyl gallium, dimethyl iso-propyl gallium, diethyl tert-butyl gallium, allyl dimethyl gallium, methyl di-iso-propyl gallium, dimethyl tert-butyl gallium, dimethyl neo-pentyl gallium, methyl ethyl isopropyl gallium, trimethyl aluminum, triethyl aluminum, tri-n-propyl aluminum, tri-iso-propyl aluminum, tri-tert-butyl aluminum, dimethyl iso-propyl aluminum, dimethyl ethyl aluminum, dimethyl tert-butyl aluminum, methyl di-tert-butyl aluminum, methyl di-iso-propyl aluminum, allyl dimethyl aluminum, and methyl diallyl aluminum.

The Group IIIA metal compounds of the invention are generally commercially available or may be prepared by methods described in the art, see e.g., U.S. Pat. Nos. 5,756,786, 6,680,397 and 6,770,769. Such compounds may be used as is or may be further purified prior to use.

Suitable catalyst compounds are any compounds that catalyze the decomposition of a Group VA gaseous compound, which in turn suitably enhances the incorporation of a Group VA element in a III/V compound semiconductor film, particularly using techniques of thermal decomposition of vapor phase compounds. While not wishing to be bound by theory, it is believed that the catalyst compound will also reduce the mole ratio of Group VA element to Group IIIA metal compounds in the vapor phase necessary to prepare III/V compound semiconductor films. Exemplary catalyst compounds include, but are not limited to, compounds including one or more of a Group IIIA metal, a Group VA element or both. In one embodiment, the catalyst compound is a compound of the formula R.sup.1.sub.aMY.sub.b, wherein M is a Group IIIA metal, each R.sup.1 is independently chosen from (C.sub.1-C.sub.10) organic radical and hydrogen, each Y is independently chosen from halogen and hydrogen, a is an integer from 0 to 2, b is an integer from 1-3, and a+b=3. Such compounds typically contain 1-3 halogens, such halogens may be the same or different. In another embodiment, R.sup.1 is a typically a (C.sub.1-C.sub.6) alkyl.

Group VA element-containing compounds useful as a catalyst compound may include one or more elements chosen from nitrogen, phosphorus, arsenic, antimony and bismuth. In one embodiment, the catalyst compound includes one or more elements chosen from nitrogen, phosphorus and arsenic. Such catalyst compounds include, without limitation, primary amines, secondary amines, tertiary amines, primary phosphines, secondary phosphines, tertiary phosphines, primary arsines, secondary arsines, tertiary arsines, primary stibines, secondary stibines, tertiary stibines, primary bismuthines, secondary bismuthines and tertiary bismuthines.

Exemplary catalyst compounds include, without limitation, indium trichloride, methyl indium dichloride, dimethyl indium chloride, tert-butyl indium dichloride, indium tribromide, methyl indium dibromide, ethyl indium dibromide, iso-propyl indium dibromide, gallium trichloride, methyl gallium dichloride, ethyl gallium dichloride, gallium tribromide, methyl gallium dibromide, iso-propyl gallium dichloride, aluminum trichloride, methyl aluminum dichloride, dimethyl aluminum chloride, ethyl aluminum dichloride, aluminum tribromide, methyl aluminum dibromide, aluminum triflouride, hydrazine, unsymmertrical dimethyl hydrazine, phenyl hydrazine, isobutyl hydrazine, di-isopropyl amine, hydrazoic acid, phosphorus trichloride, methyl phosphorus dichloride, phenyl phosphorus dichloride, phosphorus tribromide, methyl phosphorus dibromide, tertiarybutyl phosphine, bisphosphinoethane, arsenic trichloride, methyl arsenic dichloride, methyl arsenic dibromide, ethyl arsenic dichloride, propyl arsenic dibromide, monoethyl arsine, diethyl arsine, tertiarybutyl arsine, methyl antimony dichloride, ethyl antimony dichloride, antimony tribromide, methyl antimony dibromide, diethyl beryllium, triethyl boron, n-butyl lithium, bis(n-butyl) magnesium, bis(cyclopentadienyl) magnesium, tris(dimethylamino) gallium, bis(ethylcyclopentadienyl) nickel, tetrakis(diethylamino) molybdenum, pentakis(dimethylamino) tantalum, tetrakis(ethylmethylamino) zirconium and titanium tetrachloride.

In one embodiment, a Group IIIA metal-containing catalyst compound has the same metal as that used in the Group IIIA metal compound. In another embodiment, a catalyst compound including a Group VA element contains nitrogen when ammonia is used, phosphorus when phosphine is used and arsenic when arsine is used in the reaction. In yet another embodiment, the use of catalyst compounds containing different isoelectronic elements from the Group IIIA metal or from the gas (ammonia, phosphine or arsine) used offers certain advantages. As an example, but not wishing to be bound by any theory, the use of catalyst compounds containing isoeletronic elements different from those used to grow the desired film may enable modulation of the bandgap energy during film growth by modifying the surface reconstruction process and/or improving incorporation efficiency.

In general, the catalyst compound is present in a catalytic amount, which is an amount of .ltoreq.5 mol %, based on the moles of Group IIIA metal compound. Typically, the catalyst compound is present in an amount of .ltoreq.4 mol % and more typically .ltoreq.3 mol %. While any amount of catalyst compound is expected to provide the benefits of the invention, a minimum of an amount greater than the typical level of impurities in the Group IIIA metal compound is typically used, although lesser amounts may also be useful. For example, the catalytic amount of the catalyst is at least 5 ppm, more typically at least 10 ppm and still more typically at least 20 ppm, based on the weight of Group IIIA metal compound. A useful range of catalyst compounds is from 5 ppm to 5 mol %, and more typically 10 ppm to 5 mol %.

The catalyst compounds are generally commercially available or may be prepared by methods which are well-known in the art. Such compounds may be used as is or may be further purified prior to use.

A variety of Group VA gaseous compounds may be suitably employed in the present invention. Exemplary Group VA gaseous compounds include, but are not limited to ammonia, phosphine and arsine, which are generally commercially available and may be used as is or may be further purified.

In chemical vapor deposition processes, the Group IIIA metal compound, the catalyst compound and the Group VA gaseous compound are conveyed to a deposition chamber (reactor) in the gas phase. Once in the reactor, the compounds thermally dissociate and a desired film is deposited on a substrate.

The Group IIIA metal compounds and the catalyst compounds may be solids, liquids or gases. When the Group IIIA metal compounds and the catalyst compounds are solids, liquids or gases, they may be combined into a single delivery device, such as a bubbler. For example, two or more gases, two or more liquids, two or more solids, or a combination of liquid and solid compounds may be combined into a single delivery device. Alternatively, multiple delivery devices may be used. For example, a Group IIIA metal compound may be added to a first delivery device and a catalyst compound may be added to a second delivery device. When a gaseous catalyst compound is to be used with a solid and/or liquid Group IIIA metal compounds it is preferred that the gaseous catalyst compound is not in the same delivery device as the solid and/or liquid Group IIIA metal compound.

In one embodiment, films including a Group IIIA metal and a Group VA element are deposited by first placing a desired Group IIIA metal compound, i.e. source compound, and a catalyst compound in a vapor delivery device having an outlet connected to a deposition chamber. The present invention provides a composition including a Group IIIA metal compound having the formula R.sub.3M, where M is a Group IIIA metal and each R is independently a (C.sub.1-C.sub.10) organic radical or hydrogen and a catalyst compound including one or more Group VA elements. In such composition, the Group VA element may be used in the catalyst compound. In particular, the catalyst compound may include one or more of nitrogen, phosphorus and arsine. The catalyst compound is typically present in the compositions in an amount of from 5 ppm to 5 mol %, based on the Group IIIA metal compound.

In another embodiment, a Group IIIA metal compound may be placed in a first vapor delivery device and a catalyst compound may be placed in a second vapor delivery device. Each vapor delivery device is then connected to the same deposition apparatus. Each of the compounds is then conveyed from its respective delivery device into the deposition chamber to provide the Group IIIA metal compound and the catalyst compound in the vapor phase. It will be appreciated that more than one vapor delivery device containing Group IIIA metal compounds may be used in order to provide more than one Group IIIA metal compounds in the vapor phase. In an alternate embodiment, two Group IIIA metal compounds are placed in a single delivery device.

Alternatively, when the catalyst compound is a gas, it may be placed in the same delivery device as the Group VA gaseous compound. In yet another embodiment, each of the Group IIIA metal compound, the catalyst compound and the Group VA gaseous compound may be placed in a separate delivery device.

A wide variety of vapor delivery devices may be used, depending upon the particular deposition apparatus used. When the precursor compound mixture is a solid, the devices disclosed in U.S. Pat. No. 6,444,038 (Rangarajan et al.) and U.S. Pat. No. 6,607,785 (Timmons et al.), as well as other designs, may be used. For liquid precursor compound mixtures, the devices disclosed in U.S. Pat. No. 4,506,815 (Melas et al) and U.S. Pat. No. 5,755,885 (Mikoshiba et al) may be used, as well as other liquid precursor vapor delivery devices. The source compound is maintained in the vapor delivery device as a liquid or solid. Solid source compounds are typically vaporized or sublimed prior to transportation to the deposition chamber.

The present invention further provides a vapor delivery device including a vessel having an elongated cylindrical shaped portion having an inner surface having a cross-section, a top closure portion and a bottom closure portion, the vessel having an inlet opening for the introduction of a carrier gas and an outlet opening for the exiting of the carrier gas, the elongated cylindrical shaped portion having a chamber including a Group IIIA metal compound having the formula R.sub.3M, where M is a Group IIIA metal and each R is independently a (C.sub.1-C.sub.10) organic radical or hydrogen and a catalyst compound, the catalyst compound being capable of catalyzing the decomposition of a Group VA gaseous compound; the inlet opening being in fluid communication with the chamber and the chamber being in fluid communication with the outlet opening. In one embodiment, the top closure portion contains the inlet opening. In another embodiment, the top closure portion contains the inlet opening and the outlet opening.

In another embodiment, the present invention provides an apparatus for chemical vapor deposition of III/V compound semiconductor films including one or more of the vapor delivery devices for feeding a fluid stream saturated with the Group IIIA metal compound and the catalyst compound described above. Such vapor delivery devices may be used to provide the Group IIIA metal compound and the catalyst compound in the vapor phase to a single deposition chamber or to a plurality of deposition chambers.

Group VA gaseous compounds, such as ammonia, phosphine and arsine, are provided in appropriate delivery devices. Such delivery devices are well-known in the art. These gases are transported to the deposition chamber using conventional techniques.

The source compound and catalyst compound are typically transported to the deposition chamber by passing a carrier gas through the vapor delivery device. Suitable carrier gases include nitrogen, hydrogen, and mixtures thereof. In general, the carrier gas is introduced above or below the surface of a compound, and passes through the compound either to the headspace above it or a chamber below it, entraining or carrying vapor of the compound in the carrier gas. The entrained or carried vapor then passes into the deposition chamber. When the source compound and catalyst compound are in the same delivery device, the carrier gas entrains the vapor of both the source