WO1993004212A1 - Preparation of group iii element-group vi element compound films - Google Patents

Preparation of group iii element-group vi element compound films Download PDF

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WO1993004212A1
WO1993004212A1 PCT/US1992/007106 US9207106W WO9304212A1 WO 1993004212 A1 WO1993004212 A1 WO 1993004212A1 US 9207106 W US9207106 W US 9207106W WO 9304212 A1 WO9304212 A1 WO 9304212A1
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group
group iii
compound
formula
iii element
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PCT/US1992/007106
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French (fr)
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Henry James Gysling
Alex A. Wernberg
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Eastman Kodak Company
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G15/00—Compounds of gallium, indium or thallium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B19/00—Selenium; Tellurium; Compounds thereof
    • C01B19/007—Tellurides or selenides of metals
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F5/00—Compounds containing elements of Groups 3 or 13 of the Periodic Table
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F5/00—Compounds containing elements of Groups 3 or 13 of the Periodic Table
    • C07F5/06—Aluminium compounds
    • C07F5/061—Aluminium compounds with C-aluminium linkage
    • C07F5/066—Aluminium compounds with C-aluminium linkage compounds with Al linked to an element other than Al, C, H or halogen (this includes Al-cyanide linkage)
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides

Definitions

  • This invention relates to the preparation of Group III element- Group VI element compound films.
  • Group IV elements primarily germanium and silicon
  • Group III element-Group V element compounds that is, compounds consisting of Group III and Group V elements.
  • Group III element-Group VI element compounds that is those consisting of Group III and Group VI elements— have similarly been recognized for their useful electronic properties, including semiconductivity, photoconductivity, and luminescence, as well as their optical properties.
  • Interest has, consequently, turned to methods for preparing films of Group III element-Group VI element compounds which offer stringent control of film stoichiometry, purity, uniformity and thickness which is required in electronic and optical applications.
  • Group III element-Group VI element compound film preparation has centered on conventional high temperature methods.
  • Sen and others. "Preparation and Electrical Properties of Ga 2 Te 3 Thin Films," Phys. Stat. Sol. (a) 66, K117 (1981) describes the preparation of thin films of Ga 2 Te 3 by electron beam evaporation of bulk Ga 2 Te 3 previously prepared by a high temperature fusion reaction between the elements. Romeo, and others., "Memory Effects in GaTe Films", Journal of Non- Crystalline Solids 237-11 (1977) prepares GaTe films by a three temperature method in which the two component elements are evaporated at the same time from two sources at different temperatures onto a substrate maintained at the third temperature. These methods are undesirable, however, because of the potential for obtaining films which are stoichiometrically unbalanced as the result of the introduction of the Group III and Group VI elements as separate vapors.
  • MOCVD multisource organometallic chemical vapor deposition
  • Group III element-Group V element compound films have, alternatively, been prepared by two single source methods.
  • a thin film of a liquid carrier and a Group III element-Group V element precursor compound is applied to a substrate.
  • the film is heated to remove the liquid carrier and the precursor's thermally volatilizable ligands, leaving a Group III element-Group V element compound as a monophasic layer on the substrate.
  • a Group III element-Group V element precursor compound is applied to a substrate by solution spin coating.
  • the precursor is thermally vaporized and decomposes upon deposition on a receiving layer held at the decomposing temperature and positioned a short distance above the source layer.
  • the film produced may contain a minor amount of a Group III element-Group VI element compound which acts as a dopant, imparting N type conductivity to the film.
  • a minor amount of a Group III element-Group VI element compound in the film does not transform the film into Group III element-Group VI element compound film.
  • the doped film is rather a Group III element-Group V element compound film with a minor amount of a Group III element-Group VI element compound as a dopant.
  • This invention relates to a method of preparing a film, particularly a Group III element-Group VI element compound film, from a single source precursor in which the Group III and Group VI atoms are joined by thermally stable bonds.
  • a film produced by the method of the invention comprises a thin layer of crystals of a Group III element-Group VI element compound in monophasic form with the crystals of this single phase having a substantially single orientation.
  • the method of the invention employs a spray single source organometallic vapor deposition technique. This involves nebulizing a solution of a Group III element-Group VI element precursor compound to form a mist and sweeping the mist into a heated chamber containing a heated substrate, preferably with an inert carrier gas. Because the solvent does not chemically react with the substrate, the solvent is not deposited on the substrate. The precursor compound is deposited onto the heated substrate as a film, and is thermally decomposed to a Group III element-Group VI element compound of the formula A x By, wherein x and y are determined by the oxidation states of A and B.
  • Useful precursor compounds are of formula I or II as follows:
  • A is Al, Ga, or In
  • B is S, Se, or Te
  • R and R' independently are substituted or unsubstituted alkyl or aryl groups
  • a is zero to two
  • b is one to three
  • c is one to three
  • A is Al, Ga, or In
  • B is S, Se, or Te
  • X is -COR, -CNR 2 , -CR, -PR 2 , or -P(OR) 2 , wherein each R is independently a substituted or unsubstituted alkyl or aryl group.
  • This technique has significant advantages over the earlier film preparation techniques. For example, the need for separate gaseous sources of the desired elements and the accompanying exposure to toxic and pyrophoric substances is eliminated. Because the method employs precursors in which the desired Group III and Group VI elements are present and joined with thermally stable bonds, it is inherently biased toward the desired stoichiometric balance of the elements. The non-metal elements of the precursor ligands are removed entirely during the thermal decomposition step, leaving Group III element- Group VI element compound layers of high purity, despite the use of moderate temperatures, that is, between 350-650°C. Finally, the monophasic state of the Group III element-Group VI element films produced by this method have superior electrical properties because they are formed as crystals of a substantially single orientation.
  • the steps of the spray single source organometallic chemical vapor deposition technique include nebulizing a solution of a Group III element- Group VI element precursor compound to form a mist, and sweeping the mist into a heated chamber containing a heated substrate, preferably with a carrier gas.
  • the precursor compound is deposited onto the heated substrate as a film, and is thermally decomposed to a Group III element-Group VI element compound of the formula A x B y , wherein x and y are determined by the oxidation states of A and B.
  • the method of the present invention can be carried out with a spray pyrolysis reactor like that shown in DeSisto and others., "Preparation and Characterization of Copper (II) Oxide Thin Films Grown by a Novel Spray Pyrolysis Method” Mat. Res. Bull, 24, 753 (1989), hereby incorporated by reference, modified by sealing the ultrasonic transducer directly to the solvent reservoir.
  • This device includes a Holmes commercial ultrasonic transducer connected by a passage for gas flow to a reactor heated by a two-zone mirror furnace (Transtemp Co., Chelsea, MA).
  • the temperature of the first zone is maintained at a level sufficient to vaporize the precursor solution.
  • the temperature of the substrate in the higher temperature (second) zone is maintained at a level sufficient for decomposition of the precursor compound to form a Group III element-Group VI element compound.
  • the films produced by the practice of the invention are compounds formed of Group III (aluminum, gallium, and indium) and Group VI (sulfur, selenium, and tellurium) elements.
  • An important aspect of the process of the present invention lies in the selection, from among known compounds and new compositions, of the precursor of the Group III element-Group VI element compound.
  • Group III element-Group VI element compound precursors herein employed are those represented by formula I: [R a A-(BR') b ] c
  • A is Al, Ga, or In
  • B is S, Se, or Te
  • R and R' independently are substituted or unsubstituted alkyl or aryl groups, a is zero to two,
  • b is one to three
  • c is one to three.
  • Group III element-Group VI element compound precursors are compounds represented by formula II:
  • A is Al, Ga, or In
  • B is S, Se, or Te
  • X is -COR, -CNR 2 , -CR, -PR 2 , or -P(OR) 2
  • each R is independently a substituted or unsubstituted alkyl or aryl group.
  • Group III and Group VI elements are joined by thermally stable bonds.
  • Specifically preferred Group III and Group VI element combinations are gallium with sulfur, selenium or tellurium, and indium with sulfur, selenium or tellerium.
  • Suitable R and R' groups are volatilizable substituted and unsubstituted hydrocarbon ligands, including alkyl and aryl groups.
  • Exemplary R and R' groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n- pentyl, neopentyl, n-hexyl, cyclohexyl, phenyl, tolyl and anisyl groups, as well as fluorine-substituted versions of the same groups.
  • hydrocarbon ligands can have up to 20 or more carbons, it is generally preferred to employ hydrocarbon and substituted
  • hydrocarbon ligands containing from 1 to 10 carbon atoms containing from 1 to 10 carbon atoms.
  • R and R' groups are those in which aliphatic moieties consist of 1 to 6 carbon atoms and aromatic moieties consist of from 6 to 10 carbon atoms.
  • Group III element-Group VI element precursor compounds contemplated for use in the practice of this invention are the following:
  • Ph is phenyl, Et is ethyl, np is neopentyl, n-Bu is n-butyl and i-Bu is isobutyl;
  • A is Ga or In
  • R and R' independently are methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, n-pentyl, -CF 2 CF 3 , -CF 3 , -CF 2 CH 3 , or
  • A is Ga or In, and R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or n-pentyl group;
  • A is Ga or In
  • R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, -CF 3 , -C 2 F 5 , -C 3 F 7 , -C 4 F 9 , phenyl, p-tolyl, p- anisyl and -C 6 F 5 ;
  • A is Ga or In
  • R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, phenyl, p-tolyl, p-anisyl, -C 6 F 5 , -CF 3 , -C 2 F 5 , or -C 3 F 7 group; either A(SR) 3 , A(SeR) 3 , or A(TeR) 3 , wherein A is Ga or In, and R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-hexyl, phenyl, p-tolyl, p-anisyl, -C 6 F 5 , -C 2 F 5 , or -CF 3 group; and either A(
  • Specifically preferred precursor compounds include In(S 2 CN(n- Bu) 2 ) 3 , In(SePh) 3 , Me 2 lnSePh, In(S 2 CNEt 2 ) 3 , In(S 2 P(i-Bu) 2 ) 3 ,
  • Ga(S 2 CNEt 2 ) 3 ⁇ Np 2 Ga(TePh) ⁇ 2 , Me 2 InTePh, MeIn(SePh) 2 , and MeIn(TePh) 2 .
  • A is Al, Ga, or In
  • B is S, Se, or Te
  • R and R' independently are substituted or unsubstituted alkyl or aryl groups, as described above,
  • a is zero to two
  • n one to three
  • the single source precursor (Neopentyl) 2 GaTePh has been shown by single crystal x-ray diffraction to be dimeric with bridging phenyl telluride ligands (that is, N p2 Ga(u-TePh) 2 GaNp 2 as described in Banks and others., Organometallics, 9, 1979 (1990)).
  • Group III and Group VI elements can be prepared by synthetic methods described in the literature such as, Cowley and others. "Single-Source III/V Precursors: A New Approach to Gallium Arsenide and Related Semiconductors” Angew. Chem., Internat. Edit., 28, 1208 (1989) and in U.S. Patent No.4,833,103 to Agostinelli and others., which are hereby incorporated by reference. Although these references describe the preparation of Group III element-Group V element precursor compounds, the synthetic routes for Group III element-Group VI element precursor compounds are analogous to those described.
  • the synthetic methods useful for the preparation of single-source Group III element-Group VI element compound precursors include the following:
  • the method of the invention is carried out with the exclusion of oxygen (that is, under a flow of an inert gas such as nitrogen or argon) to preclude the formation of any oxides in the final films.
  • a solution of the Group III element-Group VI element precursor compound is prepared.
  • the solution may be prepared from any inert solvent which is compatible with the solubility of the precursor compound.
  • suitable solvents are hydrocarbons such as pentane, hexane, octane, benzene and toluene, and halocarbons such as chloroform, methylene chloride and dichlorobenzene.
  • Preferred solvents include hydrocarbons such as hexane, benzene, and toluene, and mixtures thereof.
  • the concentration of the precursor compound in the solution can range from 1 x 10 -4 to 1 molar, with optimum results obtained with concentrations of 1 x 10 -3 to 1 x 10 -1 molar.
  • the solution of the precursor compound is then nebulized to form a mist, which is swept into the heated reaction chamber, typically by an inert carrier gas.
  • carrier gases include argon and nitrogen.
  • the carrier gas can be a mixture of argon and hydrogen sulfide when the Group VI element in the precursor compound is sulfur.
  • the carrier gas can be a mixture of argon and hydrogen selenide or a dialkyl selenide such as dimethyl selenide or diethyl selenide.
  • the carrier gas flows through the heated chamber at a flow rate of 0.1 to 100 standard liters per minute (SLM), preferably at a rate of 1 to 10 SLM.
  • SLM standard liters per minute
  • the reaction chamber containing the substrate is preheated to equilibrate the temperature of the substrate and the chamber.
  • Substrate temperatures are selected according to the Group III element-Group VI element compound selected for deposition and the precursor chosen.
  • substrate temperatures in which ligand volatilization can be effected without cleaving the bonds between the Group III and Group VI elements can range from temperatures of 250°C to 650°C. It is usually preferred to heat the Group III element-Group VI element precursor compound to a temperature in the range of from 350°C to 450°C. With more thermally resistant Group III element-Group VI element compounds, this range can be increased, and, with more readily volatilizable ligands the lower temperature can approach 250°C as a lower limit
  • any conventional substrate for a Group III element-Group VI element compound film can be used for the present invention.
  • the Group III element-Group VI element compound film be formed on an insulative, or, particularly, a semiconductive substrate.
  • Useful insulative substrates include silicon nitride, aluminum oxide (particularly monocrystalline aluminum oxide, that is, sapphire), and silicon dioxide (including amorphous, monocrystalline, and glass forms). Glasses containing elements in addition to silicon and oxygen are contemplated.
  • Semiconductive elements are highly useful substrates for the practice of the invention.
  • any of the single crystal Group IV or III-V compound wafers conventionally employed in the manufacture of semiconductor elements can be employed as substrates for the deposition of a Group III element-Group VI element compound layer according to the present invention.
  • a major face lying in a (111), (110), or (100) crystal plane of a silicon or III-V compound (for example, gallium arsenide, gallium phosphide, or indium phosphide) wafer can serve as an ideal substrate for a Group III element- Group VI element compound layer.
  • Substrate surfaces which match or at least approximate the crystal habit of the Group III element-Group VI element compound forming the layer to be deposited are particularly advantageous for forming Group III element-Group VI element compound layers which are monocrystalline and an epitaxial extension of the original substrate.
  • the Group III element-Group VI element compound layer and its substrate can be brought back to ambient temperature by any convenient method.
  • thermal stress on the product article it is generally preferred to return to ambient temperatures gradually.
  • the magnitude of thermal stress increases with the area of the layer being prepared.
  • annealing and slow rates of cooling are desirable. It is also desirable to maintain the layer in contact with the inert or reducing atmosphere until temperatures below 100°C are reached.
  • the process may be carried out at a pressure ranging from 1 mTorr to 10 atm. It is usually preferred to work at a pressure of 0.1 to 10 arm, most preferably at 1 atm.
  • Group III element-Group VI element compound films of 100 to 100,000 Angstroms in thickness can be deposited in a single iteration of the process of the present invention.
  • the film thickness can be controlled by varying process parameters such as the carrier gas flow rate, the concentration of the precursor solution and the temperature of the substrate. Repetition of the process may be undertaken to build up still thicker layers, if desired.
  • the composition of the Group III element-Group VI element compound layer deposited according to the method of the invention matches that of the substrate on which it is deposited, the Group III element-Group VI element compound layer can form an epitaxial extension of the initially present substrate.
  • a single iteration of the process of the present invention can result in a Group III element-Group VI element compound layer of any thickness.
  • the Group III element-Group VI element compound layer can be formed with a mixture of Group III element- Group VI element compounds, if desired.
  • the monophasic film layer usually contains minor amounts of one or more dopants intended to impart n or p type conductivity.
  • N type conductivity can be achieved by substituting for some of the group III elements in the Group III element-Group VI element compound an element such as silicon or tin, or by substituting for some of the group VI elements chlorine, bromine, or iodine.
  • P type conductivity is achieved by substituting for some of the group III elements in the Group III element-Group VI element compound an element such as zinc, cadmium, beryllium, or magnesium, or by substituting for some of the group VI elements phosphorus or arsenic.
  • Dopant levels are generally limited to amounts sufficient to impart
  • dopant levels of from 10 15 to 10 18 ions per cc being common.
  • semiconductor dopant levels of from 10 15 to 10 18 ions per cc being common.
  • degenerate dopant levels can be used, but in no event would the dopant level exceed 10 20 ions per cc.
  • the present invention may be practiced to reproducibly achieve all dopant
  • Examples 1 to 8 illustrate the synthesis of Group III element- Group VI element precursor compounds useful in the practice of the invention, while Examples 4 to 8 further illustrate the fabrication of Group III element- Group VI element compound films by the method of the invention.
  • a molecular weight of 727.95 was expected, calculating for In(S 2 CN(n-Bu) 2 ) 3 (C 27 H 54 InN 3 S 6 ).
  • the molecular weight found by FDMS (115-In) was 727.
  • Expected (theoretical) relative amounts of carbon (C), hydrogen (H), nitrogen (N) and sulfur (S) were C- 44.44%, H-7.48%, N-5.77%, and S-26.43%.
  • the values found by elemental analysis were: C-44.83%, H-7.30%, N-5.61%, and S-25.86%.
  • the solvent was then removed under vacuum and the residue was extracted with 200 ml of hot hexane.
  • the hexane extract was filtered through a medium porosity glass frit in an argon atmosphere, concentrated to 35 ml under vacuum, and cooled to -20°C to produce a white precipitate. After the supernatant solution was removed by cannula, the white solid was vacuum dried to yield 3.2 grams of product, a 70.9% yield.
  • the product was characterized as described in EXAMPLE 1.
  • the molecular weight found for the product by FDMS was 559, compared with a calculated value (for C 15 H 30 N 3 S 6 In) of 559.63.
  • the theoretical and found percentages, respectively, of carbon, hydrogen, nitrogen and sulfur are as follows:
  • TGA Thermal gravimetric analysis
  • a film of In 2 S 3 was prepared by a spray single source organometallic chemical vapor deposition process, using silicon (100) as a substrate.
  • the reactor used was that described above.
  • a 3 x 10 -3 M solution of the precursor in toluene was nebulized using ultrasonic energy and the resulting mist was moved into the reactor using an argon carrier gas at a flow rate of
  • the film obtained at a deposition temperature of 350°C was shown to be (111) oriented In 2 S 3 by X-ray diffraction (pattern match with authentic In 2 S 3
  • JCPDS #32-456 The JCPDS file is a compilation of x-ray patterns for various materials. It is the reference against which measured x-ray diffraction patterns are made to establish phase identification in the solid state chemistry and film fabrication arts.
  • the resulting films contained both a low level of the above pseudo diamond-like cubic phase and a major level of the known hexagonal InSe phase (JCPDS # 34-1431: 3.41A, 2.94A, 2.40A and 1.97A).
  • the melting point of the product was 135°C.
  • a film of In 2 S 3 was prepared from this precursor by a spray single source organometallic vapor deposition process on a silicon (100) substrate, using the reactor identified in EXAMPLE 4.
  • the temperature of the first (low temperature) zone was held at 320°C while the second (high temperature) zone, containing the substrate, was maintained at 550°C.
  • a toluene solution of the precursor 200 mg/100 ml solution
  • was nebulized using ultrasonic energy was carried into the reactor with an argon carrier gas at a flow rate of 4.5 SLM.
  • the film obtained after a thirty minute deposition time was determined by X-ray diffraction to be (111) oriented In 2 S 3 (JCPDS #25-390).
  • This complex was prepared by a metathetical reaction of
  • the product was characterized as described in EXAMPLE 1.
  • the molecular weight determined by FDMS (115-In) was 513, compared with a calculated value (for C 15 H 30 N 3 S 6 Ga) of 514.53.
  • the theoretical and found relative amounts of carbon, hydrogen, nitrogen, and sulfur were as follows: C- 35.02%, 34.65%; H-5.88%, 5.73%; N-8.17%, 8.02%; and S-37.39%, 37.55%.
  • a film of Ga 2 S 3 was prepared from this single source precursor by the spray pyrolysis technique described in EXAMPLE 6.
  • the precursor solution in toluene (220 mg/100 ml solution) was carried into the reactor using an argon flow rate of 4.5 SLM.
  • the film was prepared by the spray single source organometallic vapor deposition technique described above using a solution of 260 mg of the In(SePh) 3 prepared in EXAMPLE 2 in 100 ml toluene.
  • the first zone in the reactor was held at 320°C and the zone containing the substrate was maintained at
  • the film obtained after a 25 minute deposition was identified as (001) In 2 Se 3 (JCPDS #23-294).

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Abstract

A Group III element-Group VI element compound film is prepared by nebulizing a solution of a Group III element-Group VI element precursor compound of formula (I): [RaA-(BR')b]c, wherein A is Al, Ga, or In, B is S, Se, or Te, R and R' independently are substituted or unsubstituted alkyl or aryl groups, a is zero to two, b is one to three, and c is one to three; or formula (II) wherein A is Al, Ga, or In, B is S, Se, or Te, and X is -COR, -CNR2, -CR, -PR2, or -P(OR)2, wherein each R is independently a substituted or unsubstituted alkyl or aryl group; sweeping the mist into a heated chamber containing a heated substrate, depositing the precursor compound onto the heated substrate, and thermally decomposing the precursor compound to yield a Group III element-Group VI element compound film, wherein the Group III element-Group VI element compound has the formula AxBy, wherein x and y are determined by the oxidation states of A and B. Films produced by the method of the invention are of superior quality, in that the crystals of a given film are monophasic and exhibit a substantially single orientation.

Description

PREPARATION OF GROUP III ELEMENT-GROUP VI ELEMENT
COMPOUND FILMS
This invention relates to the preparation of Group III element- Group VI element compound films.
References to Group III, IV, V, and VI elements follow art established designations of elements found in groups 13, 14, 15, and 16, respectively, of the Periodic Table of Elements as adopted by the American Chemical Society.
Group IV elements, primarily germanium and silicon, have long been recognized for their useful semiconductor properties. Subsequent attention has focused on the useful and, for many applications, superior semiconductor properties of Group III element-Group V element compounds - that is, compounds consisting of Group III and Group V elements. More recently, Group III element-Group VI element compounds— that is those consisting of Group III and Group VI elements— have similarly been recognized for their useful electronic properties, including semiconductivity, photoconductivity, and luminescence, as well as their optical properties. Interest has, consequently, turned to methods for preparing films of Group III element-Group VI element compounds which offer stringent control of film stoichiometry, purity, uniformity and thickness which is required in electronic and optical applications.
Besides these desirable properties, it is known that optimum electronic properties of Group III element-Group VI element compound films, such as high electron mobility and photoluminescent lifetimes, are associated with a high degree of crystal orientation, as measured by X-ray diffraction studies. In polycrystalline materials (that is those in which the crystals exhibit random orientation), on the other hand, the ability of "oriented" crystals to conduct electrons is diluted or even cancelled by the presence of various dissimilar crystal orientations.
Much of the work regarding Group III element-Group VI element compound film preparation has centered on conventional high temperature methods. For example, Sen and others., "Preparation and Electrical Properties of Ga2Te3 Thin Films," Phys. Stat. Sol. (a) 66, K117 (1981) describes the preparation of thin films of Ga2Te3 by electron beam evaporation of bulk Ga2Te3 previously prepared by a high temperature fusion reaction between the elements. Romeo, and others., "Memory Effects in GaTe Films", Journal of Non- Crystalline Solids 237-11 (1977) prepares GaTe films by a three temperature method in which the two component elements are evaporated at the same time from two sources at different temperatures onto a substrate maintained at the third temperature. These methods are undesirable, however, because of the potential for obtaining films which are stoichiometrically unbalanced as the result of the introduction of the Group III and Group VI elements as separate vapors.
An alternative to films prepared by elemental fusion or by the three temperature method is multisource organometallic chemical vapor deposition ("MOCVD"). MOCVD is widely used in the fabrication of Group III element-Group V element semiconductor films, such as GaAs, through the reaction of alkyls of Group III elements with Group V element hydrides.
Complexity results, however, because these reactants require precise
stoichiometric control and are both toxic and pyrophoric.
Group III element-Group V element compound films have, alternatively, been prepared by two single source methods. In one method, described in U.S. Patent No. 4,833,103 to Agostinelli and others., a thin film of a liquid carrier and a Group III element-Group V element precursor compound is applied to a substrate. The film is heated to remove the liquid carrier and the precursor's thermally volatilizable ligands, leaving a Group III element-Group V element compound as a monophasic layer on the substrate.
In a second method, described in U.S. Patent No.4,975,299 to Mir and others., a Group III element-Group V element precursor compound is applied to a substrate by solution spin coating. The precursor is thermally vaporized and decomposes upon deposition on a receiving layer held at the decomposing temperature and positioned a short distance above the source layer.
In either of these single source methods for producing Group III element-Group V element compound films, the film produced may contain a minor amount of a Group III element-Group VI element compound which acts as a dopant, imparting N type conductivity to the film. The presence of a minor amount of a Group III element-Group VI element compound in the film does not transform the film into Group III element-Group VI element compound film.
The doped film is rather a Group III element-Group V element compound film with a minor amount of a Group III element-Group VI element compound as a dopant.
The use of a one-source system for the preparation of a Group III element-Group VI element compound, In2S3 has been investigated in Nomura and others., "Single-Source Organometallic Chemical Vapor Deposition Process for Sulphide Thin Films: Introduction of a New Organometallic Precursor BunIn(SPri)2 and Preparation of In2S3 Thin Films, Thin SolidFilms, 198 (1991) 339-345. In this method, a thin film of indium sulfide (In2S3) was deposited on a substrate from a single source organometallic precursor comprising both elements in a single source MOCVD process. In Nomura and others., "Useful and
Accessible Organometallic Precursors for Preparation of Zinc Sulfide and Indium Sulfide Thin Films Via Solution Pyrolysis Method", Applied Organometallic Chemistry (1990) 4.607-610, indium (II) sulfide (InS) and indium (III) sulfide ( In2S3) thin films were prepared from a single source precursor by solution pyrolyis. This technique involved solution spin-coating of a single source organometallic precursor on a substrate followed by pyrolysis of the coated precursor layer. Although these single source precursor methods eliminate the problems associated with multisource techniques, X-ray diffraction studies of the resulting films revealed a polycrystalline structure which, as noted above, has inferior electrical properties.
This invention relates to a method of preparing a film, particularly a Group III element-Group VI element compound film, from a single source precursor in which the Group III and Group VI atoms are joined by thermally stable bonds. A film produced by the method of the invention comprises a thin layer of crystals of a Group III element-Group VI element compound in monophasic form with the crystals of this single phase having a substantially single orientation.
The method of the invention employs a spray single source organometallic vapor deposition technique. This involves nebulizing a solution of a Group III element-Group VI element precursor compound to form a mist and sweeping the mist into a heated chamber containing a heated substrate, preferably with an inert carrier gas. Because the solvent does not chemically react with the substrate, the solvent is not deposited on the substrate. The precursor compound is deposited onto the heated substrate as a film, and is thermally decomposed to a Group III element-Group VI element compound of the formula AxBy, wherein x and y are determined by the oxidation states of A and B.
Useful precursor compounds are of formula I or II as follows:
[RaA-(BR')b]c
(I) wherein
A is Al, Ga, or In,
B is S, Se, or Te,
R and R' independently are substituted or unsubstituted alkyl or aryl groups,
a is zero to two,
b is one to three, and
c is one to three;
Figure imgf000006_0001
(II) wherein
A is Al, Ga, or In,
B is S, Se, or Te and
X is -COR, -CNR2, -CR, -PR2, or -P(OR)2, wherein each R is independently a substituted or unsubstituted alkyl or aryl group.
In one aspect of the invention, the Group III element-Group VI element compounds prepared by the method of the invention are compounds of the formula AxBy wherein x= 1 or 2, when x= 1, y=1 and when x=2, y=3.
This technique has significant advantages over the earlier film preparation techniques. For example, the need for separate gaseous sources of the desired elements and the accompanying exposure to toxic and pyrophoric substances is eliminated. Because the method employs precursors in which the desired Group III and Group VI elements are present and joined with thermally stable bonds, it is inherently biased toward the desired stoichiometric balance of the elements. The non-metal elements of the precursor ligands are removed entirely during the thermal decomposition step, leaving Group III element- Group VI element compound layers of high purity, despite the use of moderate temperatures, that is, between 350-650°C. Finally, the monophasic state of the Group III element-Group VI element films produced by this method have superior electrical properties because they are formed as crystals of a substantially single orientation. The steps of the spray single source organometallic chemical vapor deposition technique include nebulizing a solution of a Group III element- Group VI element precursor compound to form a mist, and sweeping the mist into a heated chamber containing a heated substrate, preferably with a carrier gas. The precursor compound is deposited onto the heated substrate as a film, and is thermally decomposed to a Group III element-Group VI element compound of the formula AxBy, wherein x and y are determined by the oxidation states of A and B.
The method of the present invention can be carried out with a spray pyrolysis reactor like that shown in DeSisto and others., "Preparation and Characterization of Copper (II) Oxide Thin Films Grown by a Novel Spray Pyrolysis Method" Mat. Res. Bull, 24, 753 (1989), hereby incorporated by reference, modified by sealing the ultrasonic transducer directly to the solvent reservoir. This device includes a Holmes commercial ultrasonic transducer connected by a passage for gas flow to a reactor heated by a two-zone mirror furnace (Transtemp Co., Chelsea, MA).
In the method of the invention, the temperature of the first zone, a low temperature inlet zone, is maintained at a level sufficient to vaporize the precursor solution. The temperature of the substrate in the higher temperature (second) zone is maintained at a level sufficient for decomposition of the precursor compound to form a Group III element-Group VI element compound.
The films produced by the practice of the invention are compounds formed of Group III (aluminum, gallium, and indium) and Group VI (sulfur, selenium, and tellurium) elements. An important aspect of the process of the present invention lies in the selection, from among known compounds and new compositions, of the precursor of the Group III element-Group VI element compound. In one aspect of the invention, Group III element-Group VI element compound precursors herein employed are those represented by formula I: [RaA-(BR')b]c
(I)
wherein
A is Al, Ga, or In,
B is S, Se, or Te,
R and R' independently are substituted or unsubstituted alkyl or aryl groups, a is zero to two,
b is one to three, and
c is one to three.
Also useful as Group III element-Group VI element compound precursors are compounds represented by formula II:
Figure imgf000008_0001
(II) wherein
A is Al, Ga, or In,
B is S, Se, or Te, and
X is -COR, -CNR2, -CR, -PR2, or -P(OR)2
wherein each R is independently a substituted or unsubstituted alkyl or aryl group.
In each of formulas I and II, the Group III and Group VI elements are joined by thermally stable bonds. Specifically preferred Group III and Group VI element combinations are gallium with sulfur, selenium or tellurium, and indium with sulfur, selenium or tellerium.
Suitable R and R' groups are volatilizable substituted and unsubstituted hydrocarbon ligands, including alkyl and aryl groups. Exemplary R and R' groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n- pentyl, neopentyl, n-hexyl, cyclohexyl, phenyl, tolyl and anisyl groups, as well as fluorine-substituted versions of the same groups.
The solubility of the Group III element-Group VI element precursor compound in the solvent selected for the nebulization step, as well as the viscosity of the resulting solution, can be controlled through the selection of hydrocarbon ligands. Hydrocarbon ligands of excessive bulk should be avoided, as they may raise the viscosity of the solution of the Group III element-Group VI element precursor compound beyond acceptable levels for nebulization. While hydrocarbon and substituted hydrocarbon ligands can have up to 20 or more carbons, it is generally preferred to employ hydrocarbon and substituted
hydrocarbon ligands containing from 1 to 10 carbon atoms. Specifically preferred R and R' groups are those in which aliphatic moieties consist of 1 to 6 carbon atoms and aromatic moieties consist of from 6 to 10 carbon atoms.
Specific illustrations of Group III element-Group VI element precursor compounds contemplated for use in the practice of this invention are the following:
Figure imgf000009_0001
wherein Ph is phenyl, Et is ethyl, np is neopentyl, n-Bu is n-butyl and i-Bu is isobutyl;
Figure imgf000010_0001
wherein A is Ga or In, and R and R' independently are methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, n-pentyl, -CF2CF3, -CF3, -CF2CH3, or
-C H2CH2OH groups;
Figure imgf000010_0002
wherein A is Ga or In, and R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or n-pentyl group;
Figure imgf000010_0003
wherein A is Ga or In, and R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, -CF3, -C2F5, -C3F7, -C4F9, phenyl, p-tolyl, p- anisyl and -C6F5;
Figure imgf000010_0004
wherein A is Ga or In, and R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, phenyl, p-tolyl, p-anisyl, -C6F5, -CF3, -C2F5, or -C3F7 group; either A(SR)3, A(SeR)3, or A(TeR)3, wherein A is Ga or In, and R is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-hexyl, phenyl, p-tolyl, p-anisyl, -C6F5, -C2F5, or -CF3 group; and either RA(SR')2, RA(SeR')2, RA(TeR')2, R2A(SR'), R2A(SeR'), or R2A(TeR'), wherein A is Ga or In, and R and R' independently represent methyl, ethyl, n- propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, -CF3, -C2F5, - C3F7, phenyl, p-tolyl, p-anisyl, or -C6F5 groups.
Specifically preferred precursor compounds include In(S2CN(n- Bu)2)3, In(SePh)3, Me2lnSePh, In(S2CNEt2)3, In(S2P(i-Bu)2)3,
Ga(S2CNEt2)3, {Np2Ga(TePh)}2, Me2InTePh, MeIn(SePh)2, and MeIn(TePh)2.
It is understood that the exact structure (that is, degree of association) of the precursor compounds of formula (I) will be determined by the steric properties of the organic radicals, and compositions of the general formula
[RaA(BR')3-a]n
wherein
A is Al, Ga, or In,
B is S, Se, or Te,
R and R' independently are substituted or unsubstituted alkyl or aryl groups, as described above,
a is zero to two, and
n is one to three,
are included in the scope of this invention as useful single source precursors.
Such organometallic derivatives of Ga and In generally achieve coordination numbers of four by formation of dimers (n=2) or trimers (n=3) unless the steric bulk of the organic radicals precludes such structures and imposes a monomeric formulation. For example, the single source precursor (Neopentyl)2 GaTePh has been shown by single crystal x-ray diffraction to be dimeric with bridging phenyl telluride ligands (that is, Np2Ga(u-TePh)2GaNp2 as described in Banks and others., Organometallics, 9, 1979 (1990)). Although the latter compound is the only single source Group III element-Group VI element compound precursor molecule that has been structurally characterized, the importance of the steric properties of ligands in determining the degree of association of such precursor molecules has been well established in Group III element-Group V element single source precursor molecules. The phenomenon is described, for example, in Cowley and others., Angew. Chem., Internat. Edit. Engl., 28, 1208 (1989).
The single source precursors incorporating bonds between
Group III and Group VI elements can be prepared by synthetic methods described in the literature such as, Cowley and others. "Single-Source III/V Precursors: A New Approach to Gallium Arsenide and Related Semiconductors" Angew. Chem., Internat. Edit., 28, 1208 (1989) and in U.S. Patent No.4,833,103 to Agostinelli and others., which are hereby incorporated by reference. Although these references describe the preparation of Group III element-Group V element precursor compounds, the synthetic routes for Group III element-Group VI element precursor compounds are analogous to those described.
The synthetic methods useful for the preparation of single-source Group III element-Group VI element compound precursors include the following:
A. Metathetical or Salt Elimination Reaction
2 R 2 G o C I + 2 L i
Figure imgf000012_0001
E q u a t i o n 1
2 GoCI3 + 4 LiBu + 2 Li
Figure imgf000013_0001
Equotion 2
lnCI3 + 3 Li
Figure imgf000013_0002
Equation 3
ln(NO3)3 + 3 NoS2CNEt2
Figure imgf000013_0003
Equation 4
B. Redistribution Reaction
4 InEt 3 + 2 ln(TeBu)3
Figure imgf000013_0004
Equotion 5
Hydrocarbon Thermal Elimination Reaction 2 GoBu3 + 2 HSe-t-Bu 4
Figure imgf000014_0001
Equation 6
D. Chlorotrimethylsilane Elimination Reaction
2 Bu2GoC I + 2 Me3SiTe-t-Bu
Figure imgf000014_0002
Equat ion 7
E. Oxidative Addition Reaction Between a Group III Metal and a
Diorpanodichalcogenide
I n + 3/2 PhSeSePh
Figure imgf000014_0003
Equat ion 8
Although the single source precursor reagents have a range of aerial stability (that is they range from extremely air-sensitive organometallic reagents to air stable coordination complexes), the method of the invention is carried out with the exclusion of oxygen (that is, under a flow of an inert gas such as nitrogen or argon) to preclude the formation of any oxides in the final films.
In the practice of the method of the invention, a solution of the Group III element-Group VI element precursor compound is prepared. In general, the solution may be prepared from any inert solvent which is compatible with the solubility of the precursor compound. Examples of suitable solvents are hydrocarbons such as pentane, hexane, octane, benzene and toluene, and halocarbons such as chloroform, methylene chloride and dichlorobenzene.
Preferred solvents include hydrocarbons such as hexane, benzene, and toluene, and mixtures thereof. The concentration of the precursor compound in the solution can range from 1 x 10-4 to 1 molar, with optimum results obtained with concentrations of 1 x 10-3 to 1 x 10-1 molar.
The solution of the precursor compound is then nebulized to form a mist, which is swept into the heated reaction chamber, typically by an inert carrier gas. Preferred carrier gases include argon and nitrogen. The carrier gas can be a mixture of argon and hydrogen sulfide when the Group VI element in the precursor compound is sulfur. Similarly, when the Group VI element in the precursor compound is selenium, the carrier gas can be a mixture of argon and hydrogen selenide or a dialkyl selenide such as dimethyl selenide or diethyl selenide.
The carrier gas flows through the heated chamber at a flow rate of 0.1 to 100 standard liters per minute (SLM), preferably at a rate of 1 to 10 SLM. The reaction chamber containing the substrate is preheated to equilibrate the temperature of the substrate and the chamber. Substrate temperatures are selected according to the Group III element-Group VI element compound selected for deposition and the precursor chosen. In general, substrate temperatures in which ligand volatilization can be effected without cleaving the bonds between the Group III and Group VI elements can range from temperatures of 250°C to 650°C. It is usually preferred to heat the Group III element-Group VI element precursor compound to a temperature in the range of from 350°C to 450°C. With more thermally resistant Group III element-Group VI element compounds, this range can be increased, and, with more readily volatilizable ligands the lower temperature can approach 250°C as a lower limit
Any conventional substrate for a Group III element-Group VI element compound film can be used for the present invention. For semiconductor applications, it is preferred that the Group III element-Group VI element compound film be formed on an insulative, or, particularly, a semiconductive substrate. Useful insulative substrates include silicon nitride, aluminum oxide (particularly monocrystalline aluminum oxide, that is, sapphire), and silicon dioxide (including amorphous, monocrystalline, and glass forms). Glasses containing elements in addition to silicon and oxygen are contemplated.
Semiconductive elements, particularly single crystal semiconductor wafers, are highly useful substrates for the practice of the invention. For example, any of the single crystal Group IV or III-V compound wafers conventionally employed in the manufacture of semiconductor elements can be employed as substrates for the deposition of a Group III element-Group VI element compound layer according to the present invention. For example, a major face lying in a (111), (110), or (100) crystal plane of a silicon or III-V compound (for example, gallium arsenide, gallium phosphide, or indium phosphide) wafer can serve as an ideal substrate for a Group III element- Group VI element compound layer. Substrate surfaces which match or at least approximate the crystal habit of the Group III element-Group VI element compound forming the layer to be deposited are particularly advantageous for forming Group III element-Group VI element compound layers which are monocrystalline and an epitaxial extension of the original substrate.
Following heating, the Group III element-Group VI element compound layer and its substrate can be brought back to ambient temperature by any convenient method. To rnmimize thermal stress on the product article, it is generally preferred to return to ambient temperatures gradually. Generally, the magnitude of thermal stress increases with the area of the layer being prepared. Thus, in working with larger diameter wafers, annealing and slow rates of cooling are desirable. It is also desirable to maintain the layer in contact with the inert or reducing atmosphere until temperatures below 100°C are reached.
The process may be carried out at a pressure ranging from 1 mTorr to 10 atm. It is usually preferred to work at a pressure of 0.1 to 10 arm, most preferably at 1 atm.
Group III element-Group VI element compound films of 100 to 100,000 Angstroms in thickness can be deposited in a single iteration of the process of the present invention. The film thickness can be controlled by varying process parameters such as the carrier gas flow rate, the concentration of the precursor solution and the temperature of the substrate. Repetition of the process may be undertaken to build up still thicker layers, if desired. Additionally, where the composition of the Group III element-Group VI element compound layer deposited according to the method of the invention matches that of the substrate on which it is deposited, the Group III element-Group VI element compound layer can form an epitaxial extension of the initially present substrate. Thus, depending on the thickness of the substrate chosen, a single iteration of the process of the present invention can result in a Group III element-Group VI element compound layer of any thickness.
It is also contemplated that the Group III element-Group VI element compound layer can be formed with a mixture of Group III element- Group VI element compounds, if desired. For semiconductor applications, the monophasic film layer usually contains minor amounts of one or more dopants intended to impart n or p type conductivity. N type conductivity can be achieved by substituting for some of the group III elements in the Group III element-Group VI element compound an element such as silicon or tin, or by substituting for some of the group VI elements chlorine, bromine, or iodine. P type conductivity is achieved by substituting for some of the group III elements in the Group III element-Group VI element compound an element such as zinc, cadmium, beryllium, or magnesium, or by substituting for some of the group VI elements phosphorus or arsenic.
Dopant levels are generally limited to amounts sufficient to impart
semiconductive properties. The exact proportions of dopant will vary depending on the intended application, with semiconductor dopant levels of from 1015 to 1018 ions per cc being common. For some applications, such as those requiring conductivity above semiconductive levels, higher, degenerate dopant levels can be used, but in no event would the dopant level exceed 1020 ions per cc. The present invention may be practiced to reproducibly achieve all dopant
concentration levels conventionally found in Group III element-Group VI element compound films.
Examples 1 to 8 illustrate the synthesis of Group III element- Group VI element precursor compounds useful in the practice of the invention, while Examples 4 to 8 further illustrate the fabrication of Group III element- Group VI element compound films by the method of the invention.
EXAMPLES EXAMPLE 1-Synthesis of In(S2CN(n-Bu)2)3
A solution of 3.91 grams (10 mmoles) of In(NO3)3 ·5 H2O in
250 ml of water was added to a solution of 8.1 grams (35.6 mmoles) of
NaS2CNBu2 dissolved in 600 ml of water to produce a milky white solution.
After stirring this solution at room temperature for 1 hour, the solution was extracted four times with 300 ml. of methylene chloride each time. The combined methylene chloride extracts were dried over MgSO4 and the solvent was removed on a rotary evaporator. The resulting gummy yellow residue was extracted with ether and the filtered ether solution was dried to a gummy yellow solid. Recrystallization of the yellow solid from methylene chloride-ethanol produced white crystals when cooled to -15°C. A 17% yield was obtained. The product was characterized by field description mass spectrometry (FDMS) and elemental analysis. A molecular weight of 727.95 was expected, calculating for In(S2CN(n-Bu)2)3 (C27H54InN3S6). The molecular weight found by FDMS (115-In) was 727. Expected (theoretical) relative amounts of carbon (C), hydrogen (H), nitrogen (N) and sulfur (S) were C- 44.44%, H-7.48%, N-5.77%, and S-26.43%. The values found by elemental analysis were: C-44.83%, H-7.30%, N-5.61%, and S-25.86%.
EXAMPLE 2-Synthesis of In(SePh)3
A suspension of 1.33 grams (11.58 mg atoms) of In metal was refluxed in a solution of 5.42 grams (17.4 mmoles) of diphenyldiselenide
(Ph2Se2), in 225 ml of toluene for 4.5 hours under an atmosphere of argon. The reaction solution was filtered from a small amount of unreacted indium and concentrated to 100 ml to give a heavy yellow precipitate. The solid was then dissolved by heating the solution carefully and the resulting clear orange solution was cooled overnight at -15°C to form pale orange crystals. The toluene supernatant solution was decanted off in an argon atmosphere with a cannula. The product was washed with 200 ml of pentane and vacuum dried. A 46.5% yield (3.14 grams) was obtained.
The product was characterized as described in EXAMPLE 1. A molecular weight of 586 was found by FDMS (115-In), in agreement with the theoretical molecular formula. The theoretical and found percentages,
respectively, of carbon, hydrogen, indium (In) and selenium (Se) were as follows: C-37.08%, 37.17%; H-2.59%, 2.47%; In-19.69%, 19.37%; and Se-40.63%, 40.56%.
EXAMPLE 3-Synthesis of Me2InSePh
1.59 grams (10 mmoles) of trimethyl indium and 2.91 grams (5 mmoles) of In(SePh)3 (prepared as described in EXAMPLE 2) were loaded into a Schlenk flask in a glove box. After removal of the flask from the glove box, 150 ml of dry toluene was added to the flask in an argon atmosphere. The resulting solution was refluxed for 30 minutes and then stirred at room
temperature for 10 hours to effect the following redistribution reaction:
2 Me3ln + In(SePh)3 → 3 Me2lnSePh
The solvent was then removed under vacuum and the residue was extracted with 200 ml of hot hexane. The hexane extract was filtered through a medium porosity glass frit in an argon atmosphere, concentrated to 35 ml under vacuum, and cooled to -20°C to produce a white precipitate. After the supernatant solution was removed by cannula, the white solid was vacuum dried to yield 3.2 grams of product, a 70.9% yield.
The product was characterized by elemental analysis. The theoretical (calculated for C8H11InSe) and found percentages, respectively, of carbon, hydrogen, and indium are as follows: C-31.93%, 32.37%; H-3.68%, 3.67%; andIn-38.15%, 37.73%. EXAMPLE 4-Synthesis of In(S2CNEt2)3 and Its Use As a Single Source Precursor for the Fabrication of In2S3 Films by a Solution Spray Single
Source Organometallic Chemical Vapor Deposition Technique
A solution of 6.75 grams (30 mmoles) of NaS2CNEt2 in 450 ml of water was added to a solution of 3.91 grams (10 mmoles) of In(NO3)3 ·5 H2O in
250 ml of water to form an immediate heavy white precipitate. After stirring at room temperature for 30 min., the reaction solution was filtered and the white solid was washed well with water and dried under vacuum. This product was then dissolved in 150 ml of warm CH2CI2 and filtered. The filtrate was diluted to 325 ml with ethanol. When this solution was cooled overnight at -10°C, a crop of white crystals was formed.
The product was characterized as described in EXAMPLE 1. The molecular weight found for the product by FDMS was 559, compared with a calculated value (for C15H30N3S6In) of 559.63. The theoretical and found percentages, respectively, of carbon, hydrogen, nitrogen and sulfur are as follows:
C-32.19%, 32.20%; H-5.40%, 5.20%; N-7.51%, 7.23%; and S-34.38%, 34.89%.
Thermal gravimetric analysis (TGA) of this material in a flowing nitrogen atmosphere showed that it began to decompose above ca 310°C with a final weight residue at 450°C of 26.3% (theoretical weight residue for In2S3 = 29.11 %). The low result in the TGA analysis suggests that the compound is somewhat volatile.
A film of In2S3 was prepared by a spray single source organometallic chemical vapor deposition process, using silicon (100) as a substrate. The reactor used was that described above. A 3 x 10-3M solution of the precursor in toluene was nebulized using ultrasonic energy and the resulting mist was moved into the reactor using an argon carrier gas at a flow rate of
3.7 SLM. The film obtained at a deposition temperature of 350°C was shown to be (111) oriented In2S3 by X-ray diffraction (pattern match with authentic In2S3
(JCPDS #32-456)). The JCPDS file is a compilation of x-ray patterns for various materials. It is the reference against which measured x-ray diffraction patterns are made to establish phase identification in the solid state chemistry and film fabrication arts.
EXAMPLE 5-Fabrication of InSe Thin Films by a Spray Single Source Organometallic Chemical Vapor Deposition Process Using Me2InSePh as a
Single Source Precursor
A solution of 0.773 grams of Me2lnSePh in 300 ml of toluene
(0.0086M solution) was loaded, in a glove box, into a nebulization chamber. After attachment of this chamber to the reactor assembly identified in
EXAMPLE 4, a mist of the solution was passed into the heated zone of the reactor using ultrasonic nebulization and an argon flow rate of 4.5 SLM. With a GaAs (001) substrate at 309°C, a film of highly oriented cubic InSe Gattice constant a = 5.72A) was obtained. This form of InSe has not been previously described in the literature. Using a substrate temperature of 365°C an essentially identical film was obtained.
When the substrate temperature was held at 408°C - 477°C, the resulting films contained both a low level of the above pseudo diamond-like cubic phase and a major level of the known hexagonal InSe phase (JCPDS # 34-1431: 3.41A, 2.94A, 2.40A and 1.97A).
EXAMPLE 6-Synthesis of In(S2P(i-Bu)2)3 and Its Use as a Single Source Precursor for the Fabrication of In2S3 Thin Films To a solution of 3.91 grams (10 mmoles) of In(NO3)3 -5H2O in
250 ml of water, 15.4 grams of a 50% aqueous solution of 33 mmoles of
NaS2P(i-Bu)2 was added; (Aerophine-3418A, Cyanamide) to immediately form a milky, white solution. After stirring the reaction solution for 1 hour at room temperature, it was extracted with 4 portions of CH2CI2 (200 ml each). The combined extracts were dried over MgSO4 and filtered, and the filtrate was removed on a rotary evaporator to form a white powder. Recrystallization from CH2Cl2-EtOH gave the analytically pure complex. A 27% yield was obtained.
The melting point of the product was 135°C.
The product was characterized as described in EXAMPLE 1. The molecular weight determined by FDMS (115-In, 31-P) was 742, compared with a calculated value of 742.82. The theoretical and found percentages of carbon, hydrogen, and phosphorus (P) are as follows: C-38.81%, 39.08%; H-7.33%,
7.16%; and P-12.51%, 12.70%.
The TGA scan of this complex in a nitrogen atmosphere showed weight loss above 250°C, with a weight residue at 410°C of 1.5% which indicates that the compound underwent significant sublimation (that is, theoretical weight residue for In2S3 = 21.93%). This shows the complex's usefulness as a precursor for the method of the invention.
A film of In2S3 was prepared from this precursor by a spray single source organometallic vapor deposition process on a silicon (100) substrate, using the reactor identified in EXAMPLE 4. The temperature of the first (low temperature) zone was held at 320°C while the second (high temperature) zone, containing the substrate, was maintained at 550°C. A toluene solution of the precursor (200 mg/100 ml solution) was nebulized using ultrasonic energy and the resulting mist was carried into the reactor with an argon carrier gas at a flow rate of 4.5 SLM. The film obtained after a thirty minute deposition time was determined by X-ray diffraction to be (111) oriented In2S3 (JCPDS #25-390).
EXAMPLE 7-The Synthesis of Ga(S2CNEt2)3 and Its Evaluation as a Single Source Precursor for Ga2S3
This complex was prepared by a metathetical reaction of
Ga(NO3)3 and NaS2CNEt2, as described for the In analog in EXAMPLE 4.
Recrystallization from CH2Cl2-EtOH gave the analytically pure complex as white crystals. The melting point of the product was 247°C.
The product was characterized as described in EXAMPLE 1. The molecular weight determined by FDMS (115-In) was 513, compared with a calculated value (for C15H30N3S6Ga) of 514.53. The theoretical and found relative amounts of carbon, hydrogen, nitrogen, and sulfur were as follows: C- 35.02%, 34.65%; H-5.88%, 5.73%; N-8.17%, 8.02%; and S-37.39%, 37.55%. A film of Ga2S3 was prepared from this single source precursor by the spray pyrolysis technique described in EXAMPLE 6. The precursor solution in toluene (220 mg/100 ml solution) was carried into the reactor using an argon flow rate of 4.5 SLM. The temperature of the first zone was held at 300°C and the zone containing the substrate was maintained at 500°C. The film obtained after a 30 minute deposition was identified as Ga2S3 by X-ray diffraction by comparison with the X-ray pattern in Hahn and others., Z. Anorg. Allg. Chem., 259, 135 (1949). EXAMPLE 8--Fabrication of an In2Se3 Film by a Spray Single Source Organometallic Vapor Deposition Process Using In(SePh)3 as a Precursor
The film was prepared by the spray single source organometallic vapor deposition technique described above using a solution of 260 mg of the In(SePh)3 prepared in EXAMPLE 2 in 100 ml toluene. The first zone in the reactor was held at 320°C and the zone containing the substrate was maintained at
550°C. The film obtained after a 25 minute deposition was identified as (001) In2Se3 (JCPDS #23-294).

Claims

1. A method of preparing a film, comprising:
nebulizing a solution of a precursor compound of formula I or II to form a mist, wherein formula I is:
[RaA-(BR')b]c
(I)
wherein
A is Al, Ga, or In,
B is S, Se, or Te,
R and R' independently are substituted or unsubstituted alkyl or aryl groups,
a is zero to two,
b is one to three, and
c is one to three, wherein formula II is:
Figure imgf000023_0001
(II) wherein
A is Al, Ga, or In,
B is S, Se, or Te and
X is -COR, -CNR2, -CR, -PR2, or -P(OR)2, wherein each R is independently a substituted or unsubstituted alkyl or aryl group;
sweeping the mist into a heated chamber containing a heated substrate;
depositing the precursor compound onto the heated substrate; and thermally decomposing the precursor compound to form a
Group III element-Group VI element compound film, wherein the Group III element-Group VI element compound has the formula AxBy, wherein x and y are determined by the oxidation states of A and B.
2. The method of claim 1, wherein said sweeping is carried out with a carrier gas.
3. The method of claim 2, wherein the carrier gas is argon or nitrogen.
4. The method of claim 2, wherein B in formula I or II is S, and the carrier gas is a mixture of argon and hydrogen sulfide.
5. The method of claim 1, wherein the solution is made from hexane, benzene, or toluene, or a mixture thereof.
6. The method of claim 1, wherein the substrate is selected from the group consisting of silicon, gallium arsenide, sapphire, quartz, and glass.
7. The method of claim 1, wherein the precursor compound is selected from the group consisting of In(S2CN(n-Bu)2)3, In(SePh)3, Me2lnSePh,
In(S2CNEt2)3, In(S2P(i-Bu)2)3, Ga(S2CNEt2)3, {Np2Ga(TePh)}2, Me2InTePh,
MeIn(SePh)2, and MeIn(TePh)2.
8. The method of claim 1, wherein the Group III element- Group VI element compound film further comprises a dopant
9. The product by the process of claim 1.
10. A mediod of preparing a film, comprising:
nebulizing a solution of a precursor compound of formula I or II to form a mist wherein formula I is:
[RaA-(BR')b]c (I) wherein
A is Al, Ga, or In,
B is S, Se, or Te,
R and R' independently are substituted or unsubstituted alkyl or aryl groups,
a is zero to two,
b is one to three, and
c is one to three, wherein formula II is:
Figure imgf000025_0001
(II) wherein
A is Al, Ga, or In,
B is S, Se, or Te, and
X is -COR, -CNR2, -CR, -PR2, or -P(OR)2, wherein each R is independently a substituted or unsubstituted alkyl or aryl group;
sweeping the mist into a heated chamber containing a heated substrate;
depositing the precursor compound onto the heated substrate; and thermally decomposing the precursor compound to form a
Group III element-Group VI element compound film, wherein the Group III element-Group VI element compound has the formula AxBy, wherein x and y are determined by the oxidation states of A and B, and said sweeping is carried out with an argon carrier gas at a flow rate of 1 to 10 SLM through the heated chamber, the solution is made from hexane, benzene, or toluene, or a mixture thereof with a 1 x 10-3 to 1 x 10-1 molar concentration of the precursor compound, the substrate is selected from the group consisting of silicon, gallium arsenide, sapphire, quartz, and glass and is heated to a temperature of 250°C to
650°C, the heated chamber has a pressure of 0.1 to 10 atm, and the precursor compound is selected from the group consisting of In(S2CN(n-Bu)2)3,
In(SePh)3, Me2InSePh, In(S2CNEt2)3, In(S2P(i-Bu)2)3, Ga(S2CNEt2)3, {Np2Ga(TePh)}2, Me2lnTePh, MeIn(SePh)2, and MeIn(TePh)2.
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