WO2014013214A1

WO2014013214A1 - An alkyltelluroether precursor for use in the single source chemical vapour deposition of a metal telluride

Info

Publication number: WO2014013214A1
Application number: PCT/GB2013/000307
Authority: WO
Inventors: Gillian REID; William Levason; Cornelis Hendrik de Groot
Original assignee: University of Southampton
Current assignee: University of Southampton
Priority date: 2012-07-17
Filing date: 2013-07-16
Publication date: 2014-01-23
Anticipated expiration: 2015-01-17
Also published as: GB201212729D0

Abstract

An alkyltelluroether precursor for use in the single source chemical vapour deposition of a metal telluride, which alkyltelluroether precursor comprises an alkyltelluroether ligand bonded to a metal halide, which alkyltelluroether precursor comprises at least one alkyl group containing at least two carbon atoms, and which alkyltelluroether precursor has the general formula: MX_n(alkyltelluroether)y where M = metal X = a halide n = 3 or 4, and y = 1, 2 or 3 alkyl = butyl, propyl, ethyl, trimethylsilyl, cyclohexyl, cyclopentyl or benzyl.

Description

AN ALKYLTELLUROETHER PRECURSOR FOR USE IN THE

SINGLE SOURCE CHEMICAL VAPOUR DEPOSITION OF A METAL

TELLURIDE

This invention relates to an alkyltelluroether precursor and, more especially, this invention relates to an alkyltelluroether precursor which is for |use in the single source chemical vapour deposition of a metal telluride, and Which has at least one alkyl group containing at least two carbon atoms.

There is a significant demand for chemical reagents to produce electronic materials for applications in electronic devices. The production of the electronic devices may advantageously be performed with chemical yapour deposition from the reagent, which ideally is easily handled because it is usually a stable solid, has low toxicity and is not pyrophoric. Often the Chemical vapour deposition is not sufficiently selective.

It is an aim of the present invention to reduce the above mentioned problems.

Accordingly, in one non-limiting embodiment of the present invention there is provided an alkyltelluroether precursor for use in the single source bhemical vapour deposition of a metal telluride, which alkyltelluroether precursor comprises an alkyltelluroether ligand bonded to a metal halide, which alkyltelluroether precursor comprises at least one alkyl group containing at least two carbon atoms, and which alkyltelluroether precursor has the general formula:

MX_n(alkyltelluroether)y where M = metal

X = a halide

n = 3 or 4, and

y = 1 , 2 or 3

alkyl = butyl, propyl, ethyl, trimethylsilyl,

cyclohexyl, cyclopentyl or benzyl.

The alkyltelluroether precursor of the present invention is advantageous in that it enables selective chemical vapour deposition. The alkyltelluroether precursor may be used for the production of electronic devices, with selective deposition being effected onto a patterned substrate with small holes in a very selective manner. Hitherto, chemical vapour deposition would normally lead to deposition everywhere. In contrast, the alkyltelluroether precursor of the present invention enables selective deposition onto certain substrate types, for example only onto the TiN within the shallow holes in lithographically patterned substrates formed of TiN/Si02. The alkyltelluroether precursor may further be advantageous in that it is a single source precursor which means that only one entity rather than multiple sources are required. Still further, known compounds that are currently used in chemical vapour deposition in the production of metal tellurides for electronic devices are usually highly unstable, toxic, volatile and flammable. The alkyltelluroether precursor of the present invention avoids or reduces these undesirable properties because it is more stable, less toxic and not pyrophoric. The alkyltelluroether precursor may be one in which n = 3, and in which M = a p-block element. The p-block element may be Ga, In, Al, As, Sb or Bi.

Alternatively, the alkyltelluroether precursor may be one in which n = 4, and in which M = a p-block element. The p-block element may be Sn or Ge.

The alkyltelluroether precursor may be one in which X = a chloride or a bromide.

The alkyltelluroether precursor may be one in which the jalkyltelluroether is a mono-telluroether TeR₂, a di-telluroether RTe(CH₂)_nTeR jwhere n = 1 , 3, 4 or 5, or a tri-telluroether MeE(CH₂TeR)₃ where E = C or Si; |or RTe(CH2)₃Te(CH₂)₃TeR, and where R for all of the said alkyltelluroethers = alkyl, cycloalkyl, trimethylsilyl or substituted alkyl. The alkyl may be butyl, propyl, ethyl, trimethylsilyl, cyclohexyl, cyclopentyl or benzyl. The butyl may be n-butyl, t-butyl, or s-butyl. The propyl may be n-propyl or i-propyl. When the alkyltelluroether is a di-telluroether, then it may be for example EtTe(CH₂)_nTeEt where n = 1 , 3 or 4.

The alkyltelluroether precursor may be one in which the alkyltelluroether is a di-telluroether and in which the di-telluroether is BuTe(CH₂)_nTeBu, where Bu = n-butyl, t-butyl or s-butyl.

The alkyltelluroether precursor may be one in which the alkyltelluroether is a di-telluroether, and in which the di-telluroether is PrTe(CH₂)_nTePr, where Pr = i-propyl or n-propyl.

The present invention also provides a process of producing a metal telluride using at least one of the alkyltelluroether precursors, which process

I comprises of placing the precursor together with a substrate into a chemical 'vapour deposition apparatus, and heating to a predetermined temperature and pressure until the precursor has evaporated and the metal telluride has |been deposited on the substrate.

The process of the invention may be one in which the pre-determined |temperature and pressure of 600-900 K, 0.1 mmHg, until the precursor had [completely evaporated.

The process of the invention may be one in which the substrate is ilithographically patterned TiN/Si02 or Si/Si0₂. In such a process the quantity pf the single source metal alkyltelluroether precursor may be limited to only deposit onto the desired areas of the substrate and prevent complete {coverage of the substrate surface.

The process may be one in which there is only one of the jalkyltelluroether precursors. Alternatively, the process may be one in which there are two of the alkyltelluroether precursors.

The process may be one in which the metal telluride is a senide-doped metal telluride, and in which the process comprises using the alkyltelluroether precursor together with the analogous alkylselenoether precursor.

The number of alkyltelluroethers bonded to the metal halide in the reagent may depend upon the choice of metal. For example, for GaCI₃, it will fjsually be one per metal, while for larger metals, two or even three telluroether ligands may be present. For AIX₃, GaX₃ and ASX3 usually it will be only one telluroether per MX₃. For lnX₃, SbX₃ and BiX₃ there may be 1 , 2 lor 3 Te ligands per metal depending on how bulky the R groups are on TeF<2. In order to further illustrate the present invention, reference will now be made to the following Examples which are given for the purposes of illustration only.

For the precursor preparation and characterisation in the Examples 1 - 18 all reactions were conducted using Schlenk, vacuum line and glove-box techniques and under a dry nitrogen atmosphere. The reagents were stored at -18°C (in a freezer) and manipulated using a glove box. Hexane, toluene, [diethyl ether and tetrahydrofuran were dried by distillation over 'sodium/benzophenone. Dichloromethane was dried over Cahfe. SnCU, GaC , iBiCI₃, "BuLi (1.6 mol dm^-3 in diethyl ether) and 'BuLi (1.7 mol dm^-3 in pentane) were obtained from Aldrich and used as received. TeⁿBu2 was prepared by the literature procedure (D. H. O'Brien, N. Dereu, C. K. Huang, K. J. Irgolic and F. F. Knapp Jr., Orgamometallics, 1983, 2, 305-307). IR spectra were recorded as Nujol mulls between Csl plates using a Perkin Elmer Spectrum 100 instrument. Raman spectra on the molecular complexes Were obtained using a Perkin-Elmer FT2000R with a Nd:YAG laser. ¹H NMR spectra were recorded from solutions in CD₂CI₂ on a Bruker AV300, ^l25Te{¹H}, ⁷¹Ga, ⁷⁷Se{¹H} and ¹¹⁹Sn NMR spectra on a Bruker DPX400 and referenced to external neat TeMe2, [Ga(H₂O)6]³⁺ in water, external neat SeMe₂ and SnMe₄ respectively. Microanalytical results were from Medac Ltd. or from London Metropolitan University.

EXAMPLE 1

†BuTe(CH₂)₃Te"Bu This is an alkyltelluroether ligand for forming a complex with a metal halide. Freshly ground tellurium powder (8.9 g, 0.07 mol) in dry tetrahydrofuran (140 mL) was frozen in a liquid nitrogen bath. "BuLi (44 mL of 1.6 mol dm^-3 solution in diethyl ether, 0.07 mol) was added and the mixture allowed to thaw. When all the tellurium had dissolved, the clear solution was refrozen (-196°C) and 1 ,3-dichloropropane (3.6 mL, 4.28 g, 0.036 mol) added slowly dropwise. The mixture was allowed to warm to room temperature and hydrolyzed with deoxygenated water, followed by separation, extraction with diethyl ether and drying (MgS0₄), under an inert atmosphere. The solvent was removed by distillation and the residue fractionated in vacuo to give an air-sensitive red oil. Yield: 8 g, 53%. ¹H NMR (CDCI₃) δ/ppm: 0.91 (t, [6H], CH₃), 1.39 (m, [4H], CH₂), 1.72 (m, [4H], CH₂), 2.13 (m, [2H], 2.68 (m, [8H], CH₂TeCH₂). ³C{¹H} NMR (CDCI₃) δ/ppm: 3.85 (CH₂Te, ¹J_Tec = 150 Hz), 5.60 (CH₂Te, ¹J_Tec = 150 Hz), 14.48 (CH₃), 26.16 (CH₂), 35.42 (CH₂), 35.48 (CH₂). 2⁵Te{¹H} NMR (neat) δ/ppm: 289.

EXAMPLE 2

tBuTe(CH₂)₃Te^tBu

This is an alkyltelluroether ligand for forming a complex with a metal halide. Freshly ground Te (12.76 g, 0.1 mol) was suspended in anhydrous THF (150 mL) and frozen in a liquid N₂ bath. *BuLi (63 mL, 0.1 mol) was added and the solution allowed to warm to room temperature with stirring. After 30 minutes a yellow solution formed, which was frozen in a liquid N₂ bath and 1 ,3-dichloropropane added. The solution was allowed to warm to room temperature with stirring. After 30 minutes the solution had turned brown and a white precipitate had formed. After a further 30 minutes all solvent was removed in vacuo. The brown oil was extracted with anhydrous hexane (2 x 75 mL) and filtered through Celite. The hexane was removed in vacuo to give an orange oil, which was purified by vacuum distillation. 'BuTeiCH^Te'Bu was collected as an orange-brown oil at 120°C at 0.1 mmHg. Yield 16.2 g, (78%). ¹H NMR (CDCI₃, 295 K) δ/ppm: 1.48 (s, [18H], CH₃), 2.11 (m, [2H], TeCH₂), 2.63 (t, [4H], TeCH₂CH₂). ¹³C{¹H} NMR (CDCI₃,

295 K) δ/ppm: 35.73 (CTe), 34.28 (TeCH₂), 23.08 (TeCH₂CH₂), 5.75 (CH₃).

¹²⁵Te{¹H} NMR (CDCI₃, 295 K) δ/ppm: 612.

EXAMPLE 3

[GaCI₃(TeⁿBu₂)]

This is an example of an alkyltelluroether precursor for depositing a metal telluride. GaCI₃ (0.29 g, 1.7 mmol) was dissolved in anhydrous CH₂CI₂ (10 mL) and a solution of TeⁿBu₂ (0.40 g, 1.7 mmol) in anhydrous CH₂CI₂ (10 mL) was added with stirring. After 30 minutes, all solvent was removed in vacuo to give an orange oil, which was washed with cold hexane (5 mL). Yield 0.55 g (80%). ¹H NMR (CDCI₃, 295 K) δ/ppm: 0.99 (t, [6H]), 1.48 (m,

[4H]), 1.88 (m, [4H]), 3.08 (t, [4H]). ⁷¹Ga NMR (CDCI₃, 295 K) δ/ppm: 234 (W_1/2 = 3500 Hz). IR (cm^-1, Nujol): 387 (s,br), 349 (s). EXAMPLE 4

[(GaCI₃)₂{ⁿBuTe(CH₂)3TeⁿBu}]

This is an example of an alkyltelluroether precursor for depositing a metal telluride. GaCI₃ (0.44 g, 2.5 mmol) was dissolved in anhydrous CH₂CI₂ (10 mL) and a solution of ⁿBuTe(CH₂)₃TeⁿBu (prepared according to Example 1) (0.51 g, 2.5 mmol) in anhydrous CH₂CI₂ (10 mL) was added with stirring to form an orange solution. After 30 minutes, all solvent was removed in vacuo to give a viscous brown oil, which was washed with cold hexane (5 mL). Yield 0.67 g (73%). ¹H NMR (CDCI₃, 295 K) δ/ppm: 1.00 (m, [6H]), 1.50 (m, [4H]), 1.90 (m, [4H]), 2.47 (m, [2H]), 3.09 (m, [4H]), 3.17 (m, [4H]). ⁷¹Ga NMR (CDCI₃₎ 295 K) δ/ppm: 234 (W_1/2 = 6000 Hz). IR (cm^-1, Nujol): 387 (s.br), 349 (s).

EXAMPLE 5

This is an example of an alkyltelluroether precursor for depositing a metal telluride. GaCI₃ (0.44 g, 2.5 mmol) was dissolved in anhydrous CH₂CI₂ (10 mL) and a solution of

(prepared according Example 2) (0.51 g, 2.5 mmol) in anhydrous CH₂CI₂ (10 mL) was added with stirring to form an orange solution. The volume of solvent was reduced in vacuo to 10 mL and stored at 5°C overnight. Yellow, needle like crystals grew from the solution. Yield 0.63 g (69%). Anal. Calcd for CiiH₂₄CI₆Ga₂Te₂: C, 17.3; H, 3.2. Found: C, 17.5, H, 3.0%. ¹H NMR (CDCI₃, 295 K) δ/ppm: 1.85 (s, [18H], CH₃), 2.55 (m, [2H], TeCH₂), 3.14 (t, [4H], TeCH₂CH₂). IR (cm-¹ , Nujol): 397 (m), 383 (s), 351 (m). Raman (cm^-1): 396 (w), 378 (w), 348 (s).

EXAMPLE 6

[SnCI₄{ⁿBuTe(CH₂)₃TeⁿBu}]

This is an example of an alkyltelluroether precursor for depositing a metal telluride. SnCI₄ (0.130 g, 0.5 mmol) was added to solution of^,BuTe(CH₂)₃Te"Bu (prepared according to Example 1) (0.205 g, 0.5 mmol) in anhydrous CH₂CI₂ (10 mL) either at room temperature or cooled to 0°C (ice bath) with constant stirring. An orange solution was obtained immediately. After stirring for 30 mins., the solution was concentrated in vacuo yielding brown precipitate which was collected by filtration, washed with hexane and dried in vacuo. Yield: 0.20 g, 60%. ¹H NMR (CD₃CN) δ/ppm: 1.00 (t, [6H] CH₃), 1.49 (m, [4H], CH₂), 1.70 (br, [4H], CH₂), 3.2-3.6 (br m, [10H], CH₂). IR (Nujol) (ν/ατΓ¹: 292 (sh), 307 (s) Sn-CI.

EXAMPLE 7

"BuSe(CH₂)₃SeⁿBu

This is an example of a selenoether ligand used to prepare a metal halide complex and to demonstrate the highly selective chemical vapour deposition. Freshly ground selenium powder (5.0 g, 0.063 mol) in dry tetrahydrofuran (140 mL) was frozen in a liquid nitrogen bath. "BuLi (40 mL of 1.6 mol dm^-3 solution in diethyl ether, 0.063 mol) was added and the mixture allowed to thaw, and then stirred at room temperature for 2 h to give a colorless solution. 1 ,3-Dichloropropane (3 ml_, 3.57 g, 0.03 mol) was added dropwise to the mixture which was then refluxed 1 h. Hydrolysis (aqueous saturated NaCI, 100 ml_) was followed by separation, extraction with diethyl ether and drying (MgS0₄). The solvent was removed by distillation and the residue fractionated in vacuo to give pale yellow oil. Yield: 5.0 g, 50%. ¹H NMR (CDCI₃) δ/ppm: 0.90 (t, [6H], CH₃), 1.39 (m, [4H], CH₂), 1.62 (m, [4H], CH₂), 197 (m, [2H], CH₂), 2.54 (m, [4H], CH₂Se), 2.62 (s, [4H], SeCH₂). ¹³C{ H} NMR (CDCI3) δ/ppm: 13.59 (CH₃), 23.02 (CH₂), 23.56 (CH₂Se, J_Sec = 60 Hz), 23.75 (CH₂Se, ¹J_Sec = 60 Hz), 31.26 (CH₂), 32.71 (CH₂). ⁷⁷Se{¹H} NMR (neat) 5/ppm: 156.

EXAMPLE 8

nBuSe(CH₂)₂SeⁿBu

This is an example of a selenoether ligand used to prepare a metal halide complex and to demonstrate the highly selective chemical vapour deposition. Prepared as in Example 8, but using 1 ,2-dichloroethane. Yield: 5.0 g, 50%. ¹H NMR (CDCI₃) #ppm: 0.92 (t, [6H], CH₃), 1.42 (m, [4H], CH₂), 1.66 (m, [4H], CH₂), 2.62 (m, [4H], CH₂Se), 2.84(s, [4H], SeCH₂). ¹³C{¹H} NMR (CDCI3) tfppm: 13.59 (CH₃), 23.02 (CH₂), 23.80 (CH₂Se, ¹J_SeC = 60 Hz), 23.93 (CH₂Se, J_Sec = 61 Hz), 32.78 (CH₂). ⁷⁷Se{¹H} NMR (neat) #ppm: 205.

EXAMPLE 9 [SnCI₄{ⁿBuSe(CH₂)₂SeⁿBu}]

This is an example of a metal halide complex used to demonstrate the highly selective chemical vapour deposition. SnCI₄ (0.260 g, 1.00 mmol) was added to solution of ⁿBuSe(CH₂)2SeⁿBu (0.300 g, 1.00 mmol) in anhydrous CH₂CI₂ (10 ml_) at room temperature with constant stirring. A pale yellow solution was obtained immediately. After stirring for 30 mins., the solution was concentrated in vacuo yielding an off-white precipitate which collected by filtration, was washed with hexane and dried in vacuo. Crystals were obtained by cooling the CH₂CI2 filtrate from the reaction synthesis at ca. -18^°C. Yield: 0.35 g, 62%. Anal. Calcd for

C 20.9, H 3.6. Found: C 20.7, H 3.8%. ¹H NMR (CDCI₃, 298 K) δ/ppm: 0.91 (t, [6H], CH₃), 1.42 (m, [4H], CH₂), 1.78 (m, [4H], CH₂), 3.03 (s, [4H], SeCH₂), 3.28 (m, [4H], SeCH₂CH₂Se), 5.30 (CH₂CI₂); (193 K) δ/ppm: 0.91 (t, [6H], CH₃), 1.42 (m, [4H], CH₂), 1.76 (m, [4H], CH₂), 3.15 (m, [4H], SeCH₂), 3.60 (m, [4H], SeCH₂CH₂Se), 5.34 (CH₂CI₂). ¹¹⁹Sn NMR (CH₂CI₂/CDCI₃, 298 K): no resonance observed; (193 K) δ/ppm: -626, -649 (ratio -3:1). ⁷⁷Se{¹H} NMR (CH₂CI₂, 298 K): no resonance observed; (193 K) δ/ppm: 201 , 231 (ratio -3:1). IR (Nujol) v/crn^-1: 264 (w), 309 (s), 320 (s) Sn-CI. Raman ν/ατΓ¹: 236 (s), 264 (s), 319 (s) Sn-CI. Crystals of this compound suitable for single- crystal X-ray analysis were obtained by cooling the filtrate (CH2CI2) from the complex preparation. Data collection used a Bruker-Nonius Kappa CCD d iff ractometer fitted with monochromated Μο-Κ radiation (λ=0.71073 A), with the crystals held at 120 K in a nitrogen gas stream. Structure solution and refinement were straightforward, with H atoms introduced into the model in idealized positions. Crystal structure of

(1): formula = C-ioH CUSeaSn, M = 560.69, crystal system monoclinic, space group C2/c (no. 15), a = 9.186(2), b = 11.811(4), c = 17.1785(10) A, β = 102.432(4)°, 1820.0(7) A³, μ = 5.972 mm^-1, total no. of reflections measured = 7590, Rjnt = 0.0455, 2079 unique reflections, 79 independent parameters, R1 (/ > 2σ/) = 0.0336, R1 (all data) = 0.040, wR2 (/ > 2σ/) = 0.075, wR2 (all data) = 0.079.

EXAMPLE 10

[SnCI₄{ⁿBuSe(CH₂)₃SeⁿBu}]

This is an example of a metal halide complex used to demonstrate the highly selective chemical vapour deposition. SnCI₄ (0.130 g, 0.5 mmol) was added to solution of ^/,BuSe(CH₂)2SeⁿBu (0.157 g, 0.5 mmol) in anhydrous CH2CI2 (10 mL) at room temperature with constant stirring. A yellow solution was obtained immediately. After stirring for 30 mins., the solution was concentrated in vacuo yielding pale yellow precipitate which was collected by filtration, washed with hexane and dried in vacuo. Yield: 0.19 g, 65%. Calc. For CiiH₂ Cl₄Se₂Sn: C 22.9, H 4.2. Found: C 23.6, H 4.5%. ¹H NMR (CDCI₃, 298 K) δ/ppm: 0.98 (t, [6H], CH₃), 1.48 (m, [4H], CH₂), 1.83 (m, [4H], CH₂), 2.53 (m, [2H], CH₂), 3.30 (m, [4H], CH₂Se), 3.41 (m, [4H], SeCH₂). ¹¹⁹Sn NMR (CH₂CI₂/CDCl₃,298 K): no resonance observed; (190 K) δ/ppm: -695 (¹J_Snse = 505 Hz). ⁷⁷Se{¹H} NMR (CD₂CI_2l 185 K) δ/ppm: 290. IR (Nujol) v/crrT¹: 311 (br) Sn-CI. Raman v/cm^-1: 270 (s), 319 (s) Sn-CI. Thermogravimetric analysis (performed in a dry, N₂ purged glove box) shows complete sublimation, with T_sub = 563 K.

EXAMPLE 11

[BiCI₃(TeⁿBu₂)₃]

This is a alkyltelluroether complex used to demonstrate the highly ^elective chemical vapour deposition of a metal telluride. BiCI₃ (0.15 g, 0.48 jmmol) was dissolved in CH₃CN (10 mL) and the solution cooled to 0 °C. A jsolution of TeⁿBu₂ (0.35 g, 1.44 mmol) in CH₃CN (10 mL) was slowly added to ^he cooled BiCI₃ solution causing an immediate orange colour which darkened to red. The solution was stirred at 0 °C for 30 min then the volatile j

components were removed under vacuum, resulting in a viscous red oil which was dried under vacuum for 1 h. Yield = 0.39 g, 79 %. Required for 24H54BiCI₃Te₃: C, 27.7; H, 5.2. Found: C, 27.6; H, 5.3 %. ¹H NMR (CDCI₃): 0.96 (t, [3H], CH₃), 1.46 (m, [2H], CH₂), 1.81 (q, [2H], CH₂), 3.24 (t, [2H], CH₂Te). ¹³C{¹H} NMR (CDCI₃): 11.9, 13.5, 25.1 , 33.6. ¹²⁵Te{¹H} NMR (CDCI₃): 238.5. IR (Nujol /cm^"1): 248 (Bi-CI).

EXAMPLE 12

[GaCI₃(SeⁿBu₂)]

This is an example of a metal halide complex used to demonstrate the highly selective chemical vapour deposition. GaCI₃ (0.44 g, 2.5 mmol) was dissolved in anhydrous CH₂CI₂ (10 mL), and a solution of Se"Bu₂ (0.48 g, 2.5 mmol) in anhydrous CH₂CI₂ (5 mL) was added with stirring. After 30 min, all volatiles were removed in vacuo to give a pale yellow oil. Yield = 0.75 g, 82%. Anal. Calcd for C₈Hi₈CI₃GaSe: C, 26.0; H, 4.9. Found: C, 26.7, H, 5.7%. ¹H NMR (CDC , 295 K): 0.98 (f, [6H], CH₃), 1.50 (m, [4H], CH₂), 1.86 (m, [4H], CH₂), 3.16 (f, [4H], SeCH₂). ⁷⁷Se{¹H} NMR (CD₂CI₂, 295 K): 135. ⁷¹Ga NMR (CD₂CI₂₎ 295 K): 244 (Wi_/2 - 9000 Hz). IR (cm^'1, neat film): 395 (s), 371 (s), 356 (s). Raman (cm^-1): 396 (w), 373 (w), 355 (s).

EXAMPLE 13

|[GaBr₃(SeⁿBu₂)]

This is an example of a metal halide complex used to demonstrate the highly selective chemical vapour deposition. This was prepared similarly from SeⁿBu₂ and GaBr₃ (0.100 g, 0.32 mmol) in anhydrous CH₂CI₂. Orange oil.

Yield = 0.152 g, 94%. Anal. Calcd for C₈H₁₈Br₃GaSe: C, 19.1 ; H, 3.6. Found: i

jc, 19.6; H, 3.7%. ¹H NMR (CDCI_3> 295 K): 0.99 (f, [6H], CH₃), 1.49 (m, [4H], CH₂), 1.87 (m, [4H], CH₂), 3.08 (t, [4H], SeCH₂). ⁷⁷Se{¹H} NMR (CDCI₃, 295 K): 146. ⁷¹Ga NMR (CDCI₃, 295 K): 125 (Wi_/2 -4200 Hz). IR (cm^"1, neat film): 299 (s), 237 (m). Raman (cm^-1): 285 (m), 235 (s).

EXAMPLE 14

Metal Telluride Film Characterization

This Example describes the instruments used for collection of X-Ray (diffraction patterns of the metal telluride films produced from the alkyltelluroether precursors. Data were collected in grazing incidence (θι=3°) using a Bruker D8 with GADDS diffractometer or using a Rigaku SmartLab diffractometer (Cu KQI). Scanning electron microscopy was performed on i

[samples of the metal telluride films at an accelerating voltage of 10 kV using a Zeiss EVO LS 25, and energy dispersive X-ray data were obtained on the metal telluride films with an Oxford INCAx-act X-ray detector attached.

EXAMPLE 15

Substrate preparation and pre-treatment

This Example describes the preparation and pre-treatment of the substrates onto which the metal tellurides were deposited. TiN films with thickness of 100 nm were deposited on a p-type Si (100) wafer by the medium frequency magnetron sputtering method at room temperature (type: Leybold HELIOS Pro). The films were deposited under a Ti (99.99% purity) larget with a DC power of 3000 W in a N2/Ar atmosphere. The N2 and Ar flow rates were maintained at 30 and 35 seem respectively. A high drive speed of 180 rpm was applied to enhance the film uniformity. The deposition rate was found to be 0.161 nm s^_1. S1O2 films with thickness of 1 pm were also formed by the medium frequency magnetron sputtering method using a pure Si (99.99% purity) target with a DC power of 2000 W in an O₂/Ar atmosphere. The O2 and Ar flow rates were maintained at 20 seem and 40 seem respectively. With the same drive speed of 180 rpm, the deposition rate was 0.3 nm s^~1. The patterned samples were fabricated via a photolithographic process followed by a reactive-ion etching of SiO₂. The pattern was pre- designed on a mask with template hole-sizes ranging from 1 μητι to 100 pm. The photolithography was carried out using an EVG 620TB with a positive resist S1813. The etching was performed by a RIE80+ with CHF₃ and Ar. The etching rate was found to be 22 nm s^~1.

The silica tile substrates (ca. 1 χ 5 χ 25 mm) used for the depositions were previously cleaned with acetone and demineralised water and dried at 100^°C overnight. Prior to low pressure chemical vapour deposition experiments the silicon tiles (1 x 5 x 25mm) were suspended over 40% HF solution for 15 mins., then immediately transferred to a Schlenk tube and heated in vacuo at 110°C for ca. 6 hours to ensure complete removal of surface bound H2O (this completely eliminated tin oxide formation during subsequent deposition experiments). Patterned TiN/Si02 substrates were similarly etched with HF vapour, but for three mins. only.

EXAMPLE 16

Low Pressure Chemical Vapour Deposition onto un-patterned substrates using alkyltelluroether precursor products according to Examples 3, 4 and 11.

The alkyltelluroether precursor (5 - 100 mg) and substrates were loaded into a closed-end silica tube in a glove-box (precursor at the closed end, followed by either Si, S1O2 or TiN substrates positioned end-to-end through the heated region). The tube was set in a furnace such that precursor was outside the heated zone, the tube was evacuated, then heated to 773 K (actual temperature in the hot zone ca. 767 K) under 0.05 mmHg and the furnace was allowed to stabilize. The tube position was then adjusted so that the precursor was moved towards the hot zone (T ca. 465 K based on temperature profiling carried out after deposition). At this point the sample jposition was maintained until the solid precursor had melted and completely [evaporated (no residual precursor remained), ca. 30 mins. The tube was then jcooled to room temperature and transferred to the glove box where the tiles [were removed and stored under an N₂ atmosphere prior to analysis. The (highest degree of substrate coverage was found just outside the furnace hot zone and ~100 mm from the precursor, where the temperature was ca. 753 - |773 K, and these were the films selected for further study. Similar [experiments were conducted at 50 degree intervals between 723 and 823 K 'and using variable amounts of precursor to control the film thickness.

The alkyltelluroether precursors produced according to Examples 3 and 4 gave Ga₂Te₃, the alkyltelluroether precursor produced according to Example 11 gave Bi₂Te3, the alkylselenoether precursors according to Examples 9 and 10 gave SnSe₂ films, while the alkylselenoether precursors according to Examples 12 and 13 gave Ga₂Se₃ films, with no significant differences in appearance or properties observed across the deposition temperatures used. Deposited films were generally very well adhered to the substrates. Excellent reproducibility was obtained and metal telluride and metal selenide films were visually very similar between depositions conducted across the temperature range. Similar characterization data were obtained from several different samples of the metal telluride and metal selenide films. EXAMPLE 17

Low Pressure Chemical Vapour Deposition onto patterned TiN/Si0₂ or Si/Si0₂ substrates using alkylselenoether precursor produced according to Examples 9 and 10

TiN/Si0₂ and Si/Si02 patterned substrates (1 x 5 x 25 mm), the latter previously pre-treated by HF vapor-etching for 3 mins. and dried in vacuo at 110°C for ca. 6 hours, were loaded with 5 mg of alkylselenoether precursor into a closed-end silica tube in a glove-box as described above, and depositions were performed similarly. A similar process was able to be used for the alkyltelluroether precursor described in Examples 3, 4 and 11.

EXAMPLE 18

Hall measurements on metal telluride films obtained using the procedure described in Example 15 and using the alkyltelluroether precursor described in Example 3.

Hall measurements were performed at room temperature on a Nanometrics HL5500PG with a current of 1 mA. For these measurements, the metal chalcogenides film was deposited on a Si0₂/Si substrate to insulate the current to the substrate. Experiments were conducted under a magnetic field of 0.5 T at 300 K. Hall measurements for Ga₂Te₃ obtained from Example 3: p- type semiconductor; resistivity 195±10 Qcm; carrier density of 5 ^χ 10¹⁵ cm^-3. A similar process was able to be used for the Bi₂Te3 film obtained using the alkyltelluroether precursor described in Example 11. The resistivities for the i .

Bi₂Te₃ films: 5.65 x 1CT (±0.016) Ω cm; n-type semiconductor; carrier density of 1.95 x 10²⁰ cm^-3; Seebeck coefficient: -108 (film thickness = 0.872 μητι). A similar process was able to be used for the SnSe2 film obtained using the alkylselenoether precursors described in Examples 9 and 10. The resistivities for the SnSe2 films were found to be 210 (±10) mQ cm; n-type semiconductor; carrier density of 5.0 * 10¹⁸ cm^-3.

The moisture-sensitive alkyltelluroether precursors [GaCI₃(TeⁿBu2)] ;[(GaCI₃)2{ⁿBuTe(CH₂)₃TeⁿBu}] and [(GaCI₃)₂{^fBuTe(CH₂)₃Te^fBu}], prepared according to Examples 3, 4 and 5 were obtained in good yield by direct reaction of GaCI₃ with the ligand in anhydrous ChfeCb. The solids were stored in a freezer and manipulated in an N₂ purged, dry (< 1 ppm H₂0) glove-box and were characterized by IR, Raman, variable temperature ¹H, ⁷¹Ga and ¹²⁵Te{¹H} NMR spectroscopy and microanalysis as appropriate. The spectroscopic features of the new complexes were in accord with those of related complexes in the literature. The crystal structure of the precursor produced according to Example 5 showed a dinuclear molecule with three CI ligands on each gallium and a bridging ditelluroether.

The alkyltelluroether precursor [BiCI₃{TeⁿBu2}₃] prepared according to Example 11 was obtained similarly from BiCI₃ and TeⁿBu2 in anhydrous CH₂CI₂ and characterised by IR, ¹H and ¹²⁵Te{¹H} NMR spectroscopy.

The moisture-sensitive alkylselenoether precursors [SnCI₄{''BuSe(CH₂)nSe'^,Bu}], prepared according to Examples 9 and 10, were obtained in good yield by direct reaction of SnCU with the ligand in anhydrous CH2CI2. The solids were stored and manipulated in an N2 purged, dry (< 1 ppm H₂0) glove-box and were characterized by IR, Raman, variable temperature ¹H, ⁷⁷Se{¹H} and ¹¹⁹Sn NMR spectroscopy and microanalysis as appropriate. The spectroscopic features of the new complexes were in accord jwith those of related complexes in the literature. The crystal structure of the [precursor produced according to Example 9 showed a discrete mononuclear molecule with four mutually cis CI ligands and a chelating diselenoether. The [complex had crystallographic two-fold symmetry (the Sn atom lies on the C₂ axis) which placed the "Bu groups in the DL configuration (i.e. the substitutents were on opposite sides of the SnSe₂ plane), and the bond distances and angles around the tin atom were in accord with similar Sn(IV) selenoether species.

In order to further illustrate the present invention, reference will now be made to the following Figures in which:

Figure 1 shows the crystal structure of [(GaCbH'BuTeiCH^aTe'Bu}]. Carbon atoms are unlabelled and hydrogen atoms have been omitted for clarity-

Figure 2 shows the X-ray diffraction pattern from Ga₂Te₃ deposited by low pressure chemical vapour deposition on TiN from 100 mg [GaCl3(TeⁿBu2)] (Example 3) at 773 K;

Figure 3 shows a scanning electron micrograph image of deposited thin film of Ga₂Te₃ deposited by low pressure chemical vapour deposition on TiN from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 773 K Figure 4 shows the X-ray diffraction pattern obtained from Ga₂Te₃ deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 723 Kj

Figure 5 shows a scanning electron micrograph image of the Ga₂Te₃ film deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 723 K;

Figure 6 shows the X-ray diffraction pattern from Ga₂Te₃ deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 823 K;

Figure 7 shows a scanning electron micrographs from Ga₂Te₃ deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 823 K-,

Figure 8 shows the X-ray diffraction pattern from Ga₂Te₃ deposited on Si0₂ from 50 mg [(GaCI₃)₂{ⁿBuTe(CH₂)₃TeⁿBu}] (Example 4) at 773

Figure 9 shows scanning electron micrograph images of Bi₂Te₃ deposited on Si0₂ from 100 mg [BiCI₃(TeⁿBu₂)₃] (Example 11) and 723 K;

Figure 10 shows the X-ray diffraction pattern from Bi₂Te₃ deposited on Si0₂ from 100 mg [BiCI₃(TeⁿBu₂)₃] (Example 11) and 723 K;

Figure 11 shows the Raman spectrum of Bi₂Te₃ deposited on Si0₂ from 100 mg [BiCI₃(TeⁿBu₂)₃] (Example 11) and 723 K;

Figure 12 shows the crystal structure of the precursor produced according to Example 9 and with the atom numbering scheme;

Figure 13 shows scanning electron micrograph images of hexagonal

SnSe₂;

Figure 14 shows the X-ray diffraction patterns of a thick film and a thin film of SnSe₂; Figure 15 shows the Raman spectrum of SnSe₂ thin film;

Figure 16 shows X-ray photoelectron spectra obtained from a representative deposited film of SnSe₂ on a Si0₂ substrate (a) Sn 3d and (b) Se 3d ;

Figure 17 shows a scanning electron micrograph image showing selective growth of SnSe₂ onto the Si0₂ on a patterned Si (left) / Si0₂ (right) isubstrate;

Figure 18 shows photolithographically patterned Si0₂ / TiN substrates;

Figure 19 shows scanning electron micrograph images and energy dispersive X-ray element maps of SnSe₂ deposited selectively onto TiN within 80 μητι diameter holes on TiN/Si0₂;

Figure 20 shows scanning electron micrograph images and energy dispersive X-ray element maps of SnSe₂ deposited selectively onto TiN within 5 μητι diameter holes on TiN/Si0₂;

Figure 21 shows a scanning electron micrograph image of SnSe₂ deposited selectively onto TiN within 5 μΐτι diameter holes on TiN/Si0₂*

Figure 22 shows scanning electron micrograph images Ga₂Te₃ deposited preferentially onto TiN within holes on TiN/Si0₂;

Figure 23 shows scanning electron micrograph images and energy dispersive X-ray element maps of Bi₂Te₃ deposited selectively onto TiN within 80 μιη diameter holes on TiN/Si0₂;

I Figure 24 shows a scanning electron micrograph image images and energy dispersive X-ray element maps of Bi₂Te₃ deposited selectively onto |TiN within 2 μιτι diameter holes on TiN/Si0₂; and

Figure 25 shows a scanning electron micrograph image of ΒΪ2Τβ3 deposited selectively onto ΤΊΝ within 2 μηπ diameter holes on TiN/Si0₂.

Referring now to the drawings, Figure 1 is a view of the crystal structure of the precursor in Example 4.

Low pressure chemical vapour deposition of the alkyltelluroether precursor in Example 3 and Example 4 was undertaken with the furnace temperature set at 723 and 823 K, leading to clean evaporation of the precursor compound and deposition of yellow film onto the Si0₂ substrate. Similar behaviour was also observed on TiN tiles.

Figure 2 shows the X-ray diffraction pattern from a reflective grey film of Ga₂Te3 deposited by low pressure chemical vapour deposition on TiN from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 773 K, 0.1 mmHg onto Si0₂. This confirms a cubic lattice with space group F-43m. Figure 3 shows a scanning electron micrograph image of the same thin film of Ga₂Te₃ deposited by low pressure chemical vapour deposition on TiN from 100 mg [GaCl3(TeⁿBu₂)] (Example 3) at 773 K.

Figure 4 shows the X-ray diffraction pattern obtained from Ga₂Te₃ deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 723 K, 0.1 mmHg onto Si0₂. This confirms a cubic lattice with space group F-43m.

I Figure 5 shows a scanning electron micrograph image of the same Ga₂Te₃ film deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 723 K, 0.1 mmHg.

Figure 6 shows the X-ray diffraction pattern from Ga₂Te₃ deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 823 K, 0.1 mmHg onto Si0₂. This confirms a cubic lattice with space group F-43m. Figure 7 shows a scanning electron micrograph from the same Ga₂Te₃ deposited on Si0₂ from 100 mg [GaCI₃(TeⁿBu₂)] (Example 3) at 823 K.

Figure 8 shows the X-ray diffraction pattern from a silvery grey Ga₂Te₃ film deposited on Si0₂ from 50 mg [(GaCI₃)₂{ⁿBuTe(CH₂)₃TeⁿBu}] (Example 4) at 773 K, 0.1 mmHg.

Low pressure chemical vapour deposition of the alkylselenoether complexes in Examples 9 and 10 was undertaken with the furnace temperature set at a range of temperatures (50 degree intervals) between 673 and 823 K, leading to clean evaporation of the precursor compound and deposition of reflective, silvery-black films onto the Si0₂ substrate. Similar behaviour was also observed on TiN tiles.

Figure 9 shows scanning electron micrographs of the films of Bi₂Te₃ obtained by low pressure chemical vapour deposition from the alkyltelluroether precursor described in Example 11 , revealing the rhombohedral single crystals coating the Si0₂ surface of the substrate, as well as an isolated single crystal. Figure 10 shows the X-ray diffraction pattern obtained from the Bi₂Te₃ thin film grown as described, while the Raman spectrum is shown in Figure 11.

Figure 12 is a view of the crystal structure of the precursor in Example 10 with atom numbering scheme. H atoms are omitted for clarity and ellipsoids are drawn at the 50% probability level ellipsoids. The molecule has 2-fold symmetry. Symmetry operation: a = 1 - x, y, 1/2 - z.

Low pressure chemical vapour deposition of both alkylselenoether complexes in Examples 9 and 10 was undertaken with the furnace temperature set at a range of temperatures (50 degree intervals) between 673 and 823 K, leading to clean evaporation of the precursor compound and deposition of reflective, silvery-black films onto the S1O2 substrate. Similar behaviour was also observed on ΤΊΝ tiles and clean, dried (after etching with HF vapour) Si tiles. Initially depositions used ca. 50 to 100 mg of precursor, producing films of thickness ca. 40 to 60 μηη for compositional and structural characterization. Later depositions were reagent-limited (2 - 5 mg) to produce films with thicknesses in the range 0.5 to 2 μιτι. Scanning electron microscopy analysis on the SnSe₂ films showed a regular morphology formed of hexagonal plate crystallites (Figure 13a and b) and cross-sectional SEM images of typical films grown at between 673 and 823 K using 100 mg of precursor showed these were ~40 to 60 μηη thick. In these films the growth direction of the crystallites is quite random, but with a significant percentage aligned approximately perpendicular to the substrate surface. In contrast, reagent-limited films grown using 0.005 g of precursor (30 mins.) were much thinner as expected (1 to 2 μπι), and scanning electron microscopy image Figure 13c shows the majority of crystallites lying flat on the substrate surface, consistent with the preferred orientation seen by XRD analysis (below); the individual crystallites are ca. 1.6 μηι χ 2.0 μηη across the hexagon as shown in Figure 13d. Atomic force microscopy measurements were consistent with the scanning electron microscopy data, revealing that the thicker SnSe2 film surfaces are considerably rougher than the 0.5-2 μπι samples. Route mean square roughness measurements on the latter are ca. 130 nm (2 x 2 micron scan).

Referring to Figure 14, X-ray diffraction measurements on the materials deposited from the precursors produced according to Example 9 and 10 at all temperatures examined confirmed them to be crystalline hexagonal SnSe2 in all cases, consistent with space group P-3m1 , a = 3.82- 3.83 A; c = 6.14-6.16 A (literature values for bulk SnSe₂: a = 3.81 A; c = 6.14 A) with no evidence for other phases. There is no significant variation in the lattice parameters of this phase with deposition temperature. Strong evidence was seen from the X-ray patterns for preferred orientation of the crystallites in the thick films (in the range 40 to 60 μητι), however this is much more pronounced in the thin (1 to 2 μπι) films. The X-ray pattern for the thin films is shown in Figure 14, with intense 001 and 002 peaks, suggests that there is a large enhancement along the c-axis. For thick films there is also some preferred orientation observed from the diffraction data. In this case the pattern is closer to the normal powder distribution of intensities as crystallites can be aligned at any angle parallel or perpendicular to a single direction in the plane of the film, but enhancement of the 100 and 110 peaks indicates [suppression of the peaks related to c-axis alignment as shown in Figure 14.

Referring to Figure 15, Raman spectra recorded from the thin film sample obtained using Examples 9 and 10 each show one intense (and sharp) band at 182.4 cm^-1 as shown in Figure 15, which is assigned to the Ai_g Raman-active mode, and measurements taken at several locations on the sample showed no significant variation in the peak width. These data are also consistent with crystalline hexagonal SnSe₂.

Figure 16 shows the X-ray photoelectron spectroscopic data obtained from a representative deposited film of SnSe₂ on Si0₂ substrate, (a) Se 3d and (b) Sn 3d using Examples 9 and 10. More specifically, referring to Figure 16, X-ray photoelectron spectroscopic measurements on unetched ~40 to 60 μιη samples showed only one Sn and Se environment, with binding energies corresponding to those reported for SnSe₂. For unetched SnSe₂ samples C (39.8 wt%) were also evident, but there is no evidence for Sn0₂, elemental : Sn or elemental Se. Argon ion etching for 60 seconds resulted in a significant reduction in the carbon content (to 13.0 wt%). The 1 :2 Sn:Se ratio was ; unaffected by etching.

Selective deposition For many electronic applications, it is desirable to be able to deposit the chalcogenide alloy selectively onto specific regions of a patterned substrate, e.g. in trenches or holes. Variations in the morphology may also be expected to occur on different substrate types. Hence, deposition experiments were performed under the same conditions onto S1O2, Si and TiN. While the observed morphology was essentially the same for each substrate type, for SnSe2 the SEM data suggested denser film growth onto TiN and SiO₂ compared to Si. On this basis a series of reagent-limited low pressure chemical vapour deposition experiments using 2 - 5 mg of precursor (deposition time = 30 mins.) were undertaken onto photolithographically patterned substrates formed of SiO2 Si. Scanning electron micrograph images of the resulting film (Figure 17) show that SnSe2 film growth onto the SiO₂ is preferred, resulting in very high selectivity. For device applications selective deposition onto a conducting surface such as TiN is particularly advantageous. Patterned SiO2 TiN substrates were prepared by growing a layer of SiO₂ (1 μητι) onto TiN and photolithograhically etched to form an array of holes with a range of diameters from 1 to 100 μητι (Figure 18). Low pressure chemical vapour deposition of SnSe2 using these structured substrates resulted in remarkably high selectivity for film growth onto the exposed (conducting) TiN regions within the holes, but not onto the S1O2. This was observed both for the large (50 - 100 μιη diameter) and also for the smaller (5 μιη diameter) holes, as illustrated in Figures 19 and 20 respectively. Figure 17 shows a scanning electron microscopy image showing selective growth of SnSe₂ onto the Si0₂ on a patterned Si (left) / Si0₂ (right) substrate.

Figure 18 shows an illustration of the photolithographically patterned Si02/TiN substrates (the Si0₂ top layer was grown to 1 μπί thickness)

Figure 19 shows a scanning electron microscopy image (a) and energy dispersive X-ray element maps (b) - (d) confirming the selective deposition of SnSe₂ occurring only within the holes (80 μητι diameter) with growth occurring preferentially onto the TiN surface.

Figure 20 shows a scanning electron microscopy image (a) and energy dispersive X-ray element maps (b) - (d) confirming the selective deposition of SnSe₂ occurring only within the 5 μιτι diameter hole, i.e. onto the exposed TiN surfaces.

Figure 21 shows a scanning electron microscopy image confirming the selective deposition of crystalline SnSe₂ occurring only within the 5 μιη diameter hole, i.e. onto the exposed TiN surfaces.

This unexpected selectivity of the film growth is also observed for 2 μΐη diameter holes, although at this scale the selectivity is limited by the size of the individual SnSe₂ crystallites (~1.6 x 2.0 μιη across the hexagon), hence while nucleation appears to initiate on the TiN, this then nucleates further crystallite growth onto the Si0₂. The reasons for this observed highly selective film growth onto the TiN regions using Si0₂ TiN substrates and onto the Si0₂ surfaces on the Si/Si0₂ patterned tiles most likely arises from differences in the nature of the surfaces. Atomic force microscopy measurements confirm that the surface roughness of the different types of substrate are essentially invariant, however, a strong correlation is observed between the contact angle of a water droplet on the surface and the selectivity of the SnSe₂ deposition on the substrate surfaces. The measured contact angles increase from Si to Si0₂ to TiN (Θ/⁰: 29, 58, 74 respectively) and selectivity increasing across this same series. This is consistent with precursor adsorption and crystallite nucleation favoring the more hydrophobic substrates. This remarkable selectivity for film deposition from the single source selenoether ligand complexes onto the highly conducting TiN is very attractive for potential applications of chalcogenide materials in electronic devices.

Figure 22 shows that preferential deposition onto the conductive TiN rather than Si0₂ is also evident for Ga₂Te₃ grown from the precursor described in Example 3, while Figures 23 and 24 shows that very highly selective growth of Bi₂Te3 into the TiN holes both at 80 μΐη and 2 μιτι diameter on a patterned TiN/Si0₂ substrate using the precursor described in Example 11 , while Figure 25 shows the highly crystalline nature of the Bi₂Te₃ deposited under these conditions.

Importantly, the precursors exhibit a very high degree of selectivity onto lithographically patterned substrates, with deposition strongly preferred onto the (conducting) TiN on Si0₂ TiN surfaces, and onto the Si0₂ on Si/Si0₂ substrates.

The combination of the highly selective growth onto the conducting TiN surfaces within the lithographically formed holes and the stoichiometric, single phase metal telluride film deposition are highly relevant to the prospective application of these and related single source precursors for metal telluride materials in electronics.

In all aspects of the invention a combination of two or more single source metal halide alkyltelluroether precursors may be used. For example, a combination may be used to produce ternary or higher metal telluride materials. Ternary or higher metal telluride materials may be useful in industry, for example, in the production of phase change memory materials or i

thermoelectric materials. Further, an alkyltelluroether precursor may be used I in combination with an analogous alkylselenoether precursor, to form a selenide-doped metal telluride. Such selenide-doped metal tellurides may be useful in thermoelectric applications.

It is to be appreciated that the Examples and the Figures given above have been given by way of example only and that modifications may be effected. Individual components shown in the Examples and the drawings are not limited to use in their Examples and drawings, and they may be used in other Examples and other drawings and in all aspects of the invention.

Claims

1. An alkyltelluroether precursor for use in the single source chemical vapour deposition of a metal telluride, which alkyltelluroether precursor comprises an alkyltelluroether ligand bonded to a metal halide, which alkyltelluroether precursor comprises at least one alkyl group containing at least two carbon atoms, and which alkyltelluroether precursor has the general formula:

MXn(alkyltelluroether)y

where M = metal

X = a halide

n = 3 or 4, and

y = 1 , 2 or 3

alkyl = butyl, propyl, ethyl, trimethylsilyl,

cyclohexyl, cyclopentyl or benzyl.

2. An alkyltelluroether precursor according to claim 1 in which n = 3, and in which M = a p-block element.

3. An alkyltelluroether precursor according to claim 2 in which the p-block element is Ga, In, Al, As, Sb or Bi.

4. An alkyltelluroether precursor according claim 1 in which n = 4, and in which M = a p-block element.

5. An alkyltelluroether precursor according to claim 4 in which the p-block element is Sn or Ge.

6. An alkyltelluroether precursor according to any one of the preceding claims in which X = a chloride or a bromide.

7. An alkyltelluroether precursor according to any one of the preceding claims in which the alkyltelluroether is a mono-telluroether TeR₂, a di- telluroether RTe(CH₂)_nTeR where n = 1 , 3, 4 or 5, or a tri-telluroether MeE(CH₂TeR)₃ where E = C or Si, or RTe(CH₂)₃Te(CH₂)3TeR, and where R for all of the said alkyltelluroethers = alkyl, cycloalkyl, trimethylsilyl or substituted alkyl.

8. An alkyltelluroether precursor according to any one of the preceding claims in which the butyl is n-butyl, t-butyl, or s-butyl.

9. An alkyltelluroether precursor according to any one of the preceding claims in which the propyl is n-propyl or i-propyl.

10. An alkyltelluroether precursor according to claim 7 in which the alkyltelluroether is a di-telluroether and in which the di-telluroether is BuTe(CH2)nTeBu, where Bu = n-butyl, t-butyl or s-butyl.

11. An alkyltelluroether precursor according to claim 7 in which the alkyltelluroether is a di-telluroether, and in which the di-telluroether is PrTe(CH2)_nTePr, where Pr = i-propyl or n-propyl.

12. A process of producing a metal telluride using at least one alkyltelluroether precursor according to Claim 1 , which process comprises placing the precursor together with a substrate into a chemical vapour deposition apparatus, and heating to a predetermined temperature and pressure until the precursor has evaporated and the metal telluride has been deposited on the substrate.

13. A process according to Claim 12 in which the pre-determined temperature and pressure of 600-900 K, 0.1 mmHg, until the precursor had completely evaporated.

14. A process according to Claim 12 or Claim 13 in which the substrate is lithographically patterned TiN/Si0₂ or Si/SiC^.

15. A process according to any one of claims 12-14 in which there is only one of the alkyltelluroether precursors.

16. A process according to any one of claims 12-14 in which there are two of the alkyltelluroether precursors.

17. A process according to any one of claims 12-14 in which the metal telluride is a selenide-doped metal telluride, and in which the process comprises using the alkyl teiiuroether precursor according to Claim 1 , together with the analogous alkyl selenoether precursor.