ATOMIC LAYER DEPOSITION METHOD OF METAL (II), (0), OR (IV) CONTAINING FILM LAYER

Abstract

The present disclosure relates to the use of a M (II) primary precursor of formula (I):

M(OCR.sup.1R.sup.2R.sup.3) L   (I)

wherein: M is Sn or Ge or Pb; L is a ligand displaying ALD reactivity for a secondary precursor; R.sup.1, R.sup.2, and R.sup.3 are each independently selected from: H or a linear or branched alkyl groups, and wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is a linear or branched alkyl group, or an adduct of a metal (M) (II) precursor of formula (I), in the atomic layer deposition (ALD) of a M (II), M (0), or a M (IV) containing film layer on a substrate.

Claims

1. Use of a metal (M) (II) primary precursor of formula (I):
M(OCR.sup.1R.sup.2R.sup.3) L   (I) wherein: M is Sn or Ge or Pb; L is a ligand displaying ALD reactivity for a secondary precursor; R.sup.1, R.sup.2, and R.sup.3 are each independently selected from: H or a linear or branched alkyl groups, and wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is a linear or branched alkyl group, or an adduct of a metal (M) (II) precursor of formula (I) in an atomic layer deposition (ALD) of a M (II), M (0), or a M (IV) containing film layer on a substrate.

2. The use as claimed in claim 1, in which the metal (M) containing film layer is a M (II) containing film layer.

3. The use as claimed in claim 2, in which the M (II) containing film layer is an Sn (II) containing film layer.

4. The use as claimed in claim 3, in which the Sn (II) containing film layer is an Sn (II) oxide film layer.

5. The use as claimed in claim 4, in which the Sn (II) oxide film layer is a crystalline Sn (II) oxide containing film layer.

6. The use as claimed in 1, in which the metal (M) containing film layer is a multicomponent metal (M) containing film layer comprising at least one additional metal (M′).

7. The use as claimed in claim 6, in which the at least one additional metal (M′) is selected from one or more of: Ti, In, Ga, Zn, Cu, Sr, Ba, Mg, W, Pb, Se, S, Te, Bi, Fe, Ni, Co, Al, Si, Sb, K, Na, Ca, Sr, Ba, Li, V and La, or any combination thereof.

8. The use as claimed in claim 1, in the atomic layer deposition (ALD) of a metal (M) and F containing film layer.

9. The use as claimed in claim 8, in the atomic layer deposition (ALD) of a Sn and F containing film layer.

10. The use as claimed in claim 1, in which L is an amide, alkoxide, aminoalcohol, aminoamide, alkoxyether, cyclopenadienyl (Cp), or Op derivative, or halide.

11. The use as claimed in claim 10, in which L is an amide ligand or an alkoxide ligand.

12. The use as claimed in claim 11, in which L is an alkoxide ligand of formula (OCR.sup.1′R.sup.2′R.sup.3′), wherein R.sup.1′, R.sup.2′, and R.sup.3′ are each independently selected from: H or a linear or a branched alkyl group, and wherein at least one of R.sup.1′, R.sup.2′ and R.sup.3′ is a linear or branched alkyl group.

13. The use as claimed in claim 12, in which L is an alkoxide ligand of formula (OCR.sup.1′R.sup.2′R.sup.3′), in which (OCR.sup.1′R.sup.2′R.sup.3′) is the same as (OCR.sup.1R.sup.2R.sup.3) group of the metal (M) (II) containing primary precursor of formula (I).

14. An atomic layer deposition (ALD) method for forming a film layer of a metal (M) containing film layer, in which the film layer is a M (II), M (0), or a M (IV) containing film layer on a surface of a substrate, the method comprising: heating a substrate in a processing chamber; introducing a M (II) primary precursor of formula (I):
M(OCR.sup.1R.sup.2R.sup.3) L   (I) wherein: M is Sn or Ge or Pb; L is a ligand displaying ALD reactivity for a secondary precursor; R.sup.1, R.sup.2, and R.sup.3 are each independently selected from: H or a linear or branched alkyl groups, and wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is a linear or branched alkyl group, or an adduct of a M (II) containing primary precursor of formula (I) to the processing chamber in a first dose stage for a predetermined first dose time; subsequently purging the processing chamber in a first purge stage to remove remaining M (II) primary precursor; introducing a secondary precursor to the processing chamber in a second dose stage for a predetermined second dose time; and subsequently purging the processing chamber in a second purge stage to remove the secondary precursor; optionally repeating one or more of: the first dose stage, first purge stage, second dose stage and second purge stage; to produce a M (II), M (0), or a M (IV) containing film layer on the surface of the substrate.

15. The atomic layer deposition method as claimed in claim 14, in which R.sup.1, R.sup.2, and R.sup.3 are each independently selected from: H or linear or branched C.sub.1-4 alkyl groups, and wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is a linear or branched C.sub.1-4 alkyl group.

16. The atomic layer deposition method as claimed in claim 15, in which the film layer is a crystallized film layer.

17. The atomic layer deposition method as claimed in claim 15, in which the M (II) primary precursor is selected from: Sn(O.sup.iPr).sub.2, Sn(O.sup.tBu).sub.2, Sn(OC(H)MeEt).sub.2, Sn(OC(H)Me.sup.iPr).sub.2, and Sn(OCMe.sub.2Et).sub.2

18. The atomic layer deposition method as claimed in claim 17, in which the M (II) primary precursor is selected from: Sn(O.sup.tBu).sub.2, Sn(OC(H)MeEt).sub.2 and Sn(OCMe.sub.2Et).sub.2.

19. The atomic layer deposition method as claimed in claim 14, in which the processing chamber is heated to a temperature within a range of between 70° C. and 250° C.

20. The atomic layer deposition method as claimed in claim 19, in which the processing chamber is heated to a temperature within a range of between 130° C. and 210° C.

21. An atomic layer deposition (ALD) method for forming a film layer of a metal (M) containing film layer, in which the film layer is a M (H), M (0), or a M (IV) containing film layer on a surface of a substrate, the method comprising: heating a substrate in a processing chamber; contacting a surface of the substrate with a M (H) primary precursor of formula (I):
M(OCR.sup.1R.sup.2R.sup.3) L   (I) wherein: M is Sn or Ge or Pb; L is a ligand displaying ALD reactivity for a secondary precursor; R.sup.1, R.sup.2, and R.sup.3 are each independently selected from: H or a linear or branched alkyl groups, and wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is a linear or branched alkyl group, or an adduct of a M (H) containing primary precursor of formula (I) to the processing chamber in a first dose stage for a predetermined first dose time; either optionally purging the processing chamber in a first optional purge stage to remove remaining M (H) primary precursor, or optionally moving the substrate relative to the precursor source in a first optional movement stage; contacting the surface of the substrate with a secondary precursor in a second dose stage for a predetermined second dose time; and either optionally subsequently purging the processing chamber in a second optional purge stage to remove the secondary precursor, or optionally moving the substrate relative to the precursor source in a second optional movement stage; optionally repeating one or more of: the first dose stage, first optional purge stage, first optional movement stage, second dose stage and second optional purge stage, and second optional movement stage; to produce a M (II), M (0), or a M (IV) containing film layer on the surface of the substrate.

Description

BRIEF DESCRIPTION OF FIGURES

[0091] FIG. 1a is a schematic illustration of the atomic layer deposition (ALD) process, FIG. 1b is a schematic illustration of the spatial atomic layer deposition (ALD) process;

[0092] FIG. 2 is a graph of thermogravimetric analysis of Sn (II) oxide precursors used in the method of the present disclosure;

[0093] FIG. 3 is a graph of isothermogravimetric analysis of Sn (II) oxide precursors used in the method of the present disclosure;

[0094] FIG. 4 is a graph of X-ray diffraction patterns of deposited film layer using Sn(O.sup.tBu).sub.2 precursors at temperatures between 130° C. and 250° C. in the method of the present disclosure;

[0095] FIG. 5 is a graph illustrating the relationship between the growth per cycle of the deposited film and deposition temperature of Sn(O.sup.tBu).sub.2 on a substrate;

[0096] FIGS. 6a and 6b are graph of Raman spectra of SnO films deposited using Sn(O.sup.tBu).sub.2 at temperatures of 170° C. (FIGS. 6a) and 210° C. (FIG. 6b); and

[0097] FIG. 7 is a graph illustrating the relationship between the thickness of deposited film using Sn(O.sup.tBu).sub.2 at a temperature of 170° C. and the number of cycles of ALD; and

[0098] FIG. 8 is a graph of X-ray diffraction patterns of films deposited using Sn(OC(CH.sub.3).sub.2CH.sub.2CH.sub.3).sub.2 precursors at temperatures of 170° C. and 210° C. in the method of the present disclosure.

EXAMPLE 1

Synthesis of Sn (II) Alkoxide Primary Precursors

[0099] There are a number of synthetic routes for the preparation of Sn (II) alkoxides, including salt metathesis, ligand metathesis, alcohol exchange and direct reaction of tin metal with the respective alcohol.

[0100] Sn (II) alkoxide primary precursors are readily synthesized through direct amide ligand displacement reactions, as illustrated in the following scheme:

##STR00001##

[0101] The synthesis of a number of specific examples of Sn (II) oxide primary precursors 1 to 5 suitable for use with the ALD method of the present disclosure is described in detail.

[Sn(O.SUP.i.Pr).SUB.2.]∞ (1)

[0102] ##STR00002##

[0103] A stirring solution of [Sn{N(SiMe.sub.3).sub.2}.sub.2] (0.88 g, 2 mmol) in hexane (50 mL) was cooled and added to a −78° C. solution of 2-propanol (0.24 g, 4 mmol) in hexane (20 mL) affording a colorless solution. After removal of the volatiles, the white powder was redissolved in hexane, filtered through Celite® and the volume reduced. Colorless crystals were afforded at −28° C. (0.37 g, 80%).

[0104] .sup.1H NMR (500 MHz, C.sub.6D.sub.6); 4.62 (sept, 2H, CH(CH.sub.3).sub.2, 1.34 (d, 12H, CH.sub.3). .sup.13C{.sup.1H} NMR (75.5 MHz, C.sub.6D.sub.6); 65.6 (2C, CH(CH.sub.3).sub.2), 28.2 (4C, CH(CH.sub.3).sub.2). .sup.119Sn NMR (111.8 MHz, C.sub.6D.sub.6); −211

[Sn(O.SUP.t.Bu).SUB.2.].SUB.2 .(2)

[0105] ##STR00003##

[0106] A stirring solution of [Sn{N(SiMe.sub.3).sub.2}.sub.2] (0.88 g, 2 mmol) in hexane (50 mL) was cooled and added to a −78° C. solution of tert-butanol (0.30 g, 4 mmol) in hexane (20 mL) affording a colorless solution. After removal of the volatiles, the white powder was redissolved in hexane, filtered through Celite® and the volume reduced. Colorless crystals were afforded at −28° C. (0.48 g, 91%).

[0107] .sup.1H NMR (500 MHz, C.sub.6D.sub.6); 1.45 (s, 18H, CH.sub.3). .sup.13C{.sup.1H} NMR (75.5 MHz, C.sub.6D.sub.6); 72.8 (2C, C(CH.sub.3).sub.3), 32.4 (6C, C(CH.sub.3).sub.2). .sup.119Sn NMR (111.8 MHz, C.sub.6D.sub.6); −91

[Sn(O.SUP.s.Bu).SUB.2.] (3)

[0108] ##STR00004##

[0109] A stirring solution of [Sn{N(SiMe.sub.3).sub.2}.sub.2] (0.88 g, 2 mmol) in hexane (50 mL) was cooled and added to a −78° C. solution of sec-butanol (0.30 g, 4 mmol) in hexane (20 mL) affording a colorless solution. After removal of the volatiles, the viscous clear liquid was redissolved in hexane, filtered through Celite® and the solvent removed. Distillation at 150° C. into liquid N.sub.2 (10.sup.−2 mbar) afforded a colorless liquid. (0.37 g, 70%)

[0110] .sup.1H NMR (500 MHz, C.sub.6D.sub.6); 4.26-4.33 (m, 2H, CH(CH.sub.3), 1.70-1.80 (br m, 2H, CH.sub.2), 1.50-1.60 (br m, 2H, CH.sub.2), 1.36 (d, J=6.2 Hz, 6H, OCH(CH.sub.3)), 0.98, (t, 7.6 Hz, 6H, CH.sub.2CH.sub.3). .sup.13C{.sup.1H} NMR (75.5 MHz, C.sub.6D.sub.6); 71.4 (2C, CH(CH.sub.3)), 35.1 (2C, CH.sub.2), 26.1 (OCH(CH.sub.3)), 11.0 (2C, CH.sub.2CH.sub.3). .sup.119Sn NMR (111.8 MHz, C.sub.6D.sub.6); −141

[Sn{OCH(CH.SUB.3.)CH(CH.SUB.3.).SUB.2.}.SUB.2.] (4)

[0111] ##STR00005##

[0112] A stirring solution of [Sn{N(SiMe.sub.3).sub.2}.sub.2] (0.88 g, 2 mmol) in hexane (50 mL) was cooled and added to a −78° C. solution of 3-methyl-2-butanol (0.35 g, 4 mmol) in hexane (20 mL) affording a colorless solution. After removal of the volatiles, the viscous clear liquid was redissolved in hexane, filtered through Celite® and the solvent removed. Distillation at 170° C. into liquid N.sub.2 (10.sup.−2 mbar) afforded a viscous colorless liquid. (0.38 g, 64%)

[0113] .sup.1H NMR (500 MHz, C.sub.6D.sub.6); 4.0-4.08 (m, 2H, OCH(CH.sub.3)), 1.66-1.76 (m, 2H, CH(CH.sub.3).sub.2), 1.29 (d, J=5.6 Hz, 6H, OCH(CH.sub.3)), 1.03 (d, J=6.2 Hz, 6H, CH(CH.sub.3)), 0.98 (d, J=6.2 Hz, 6H, CH(CH.sub.3)).

[0114] .sup.13C{.sup.1H} NMR (75.5 MHz, C.sub.6D.sub.6); 74.1 (2C, OCH), 36.8 (2C, OCH(CH.sub.3)), 22.6 (2C, CH(CH.sub.3).sub.2), 18.8 (2C, CH(CH.sub.3).sub.2), 18.0 (2C, CH(CH.sub.3).sub.2). .sup.119S.sub.n NMR (111.8 MHz, C.sub.6D.sub.6); −154

[Sn{OC(CH.SUB.3.).SUB.2.CH.SUB.2.CH.SUB.3.}.SUB.2.] (5)

[0115] ##STR00006##

[0116] A stirring solution of [Sn{N(SiMe.sub.3).sub.2}.sub.2] (0.88 g, 2 mmol) in hexane (50 mL) was cooled and added to a −78° C. solution of 2-methyl-2-butanol (0.35 g, 4 mmol) in hexane (20 mL) affording a colorless solution. After removal of the volatiles, the viscous clear liquid was redissolved in hexane, filtered through Celite® and the solvent removed. Distillation at 120° C. into liquid N.sub.2 (10.sup.−2 mbar) afforded a colorless liquid. (0.39 g, 67%)

[0117] .sup.1H NMR (500 MHz, C.sub.6D.sub.6); 1.71 (q, J=7.5 Hz, 4H, CH.sub.2), 1.41 (s, 12H, C(CH.sub.3).sub.2), 1.05 (t, J=7.5 Hz, 6H, CH.sub.2CH.sub.3). .sup.13C{.sup.1H} NMR (75.5 MHz, C.sub.6D.sub.6); 39.7 (2C, CH.sub.2), 32.0 (br, 4C, C(CH.sub.3).sub.2), 9.74 (2C, CH.sub.2CH.sub.3)

[0118] .sup.119Sn NMR (111.8 MHz, C.sub.6D.sub.6); −98

EXAMPLE 2

Mass Loss-Temperature Thermogravimetric Analysis

[0119] The mass loss/temperature plots for Sn (II) oxide primary precursors 1-5 is shown in FIG. 2. It is shown that each of the exemplified Sn (II) oxide primary precursors displays a loss of mass greater than would be expected for the decomposition to any of metallic tin, tin(II) oxide or tin(IV) oxide (see also Table 1).

[0120] It has been found that the degree of volatility appears to be higher in the isopropoxide and tert-butoxide systems 1 and 2 than is evident for the remainder of the series.

[0121] All of the exemplified Sn (II) oxide primary precursors display similar thermogravimetric analysis (TGA) traces, with a sharp loss of mass to ca. 90-95% of the entire mass loss, after which a second smaller loss of mass occurs. All of the exemplified Sn (II) oxide primary precursors 1 to 5 display suitable stabilities and volatilities for ALD applications.

TABLE-US-00001 TABLE 1 Expected Residual Mass (%) Compound Residual Mass (%) SnO SnO.sub.2 Sn 1 22.5 56.9 63.6 50.1 2 17.1 50.8 56.9 44.8 3 3.7 50.8 56.9 44.8 4 9.8 46.0 51.4 40.5 5 2.6 46.0 51.4 40.5

EXAMPLE 3

Isothermal Thermogravimetric Analysis

[0122] Due to the higher observed volatilities of [Sn(O.sup.iPr).sub.2] (1) and [Sn(O.sup.tBu).sub.2] (2) as discussed in Example 2, isothermal analyses were undertaken at temperatures of 70° C., a temperature representative of a heated precursor source. For the remaining three complexes, 3, 4, and 5, isothermal experiments were undertaken at temperatures of 100° C., again representative of elevated temperature precursor sources. The results are shown in FIG. 3 and Table 2.

[0123] As is evident from the isothermal plots (FIG. 3) and evaporation rates (Table 2) for the exemplified Sn (II) oxide primary precursors, despite a lower “source” temperature, [Sn(O.sup.iPr).sub.2] (1) and [Sn(O.sup.tBu).sub.2] (2) displayed the highest volatility, the latter by a large margin. With an evaporation rate of 128.4 μg min.sup.−1 cm.sup.−1, [Sn(O.sup.tBu).sub.2] 2 exhibits almost twice as much volatility as [Sn(O.sup.iPr).sub.2] (65.0 μg min.sup.−1 cm.sup.−1). After a change in temperature to 100° C., the three exemplified Sn (II) oxide primary precursors display decreasing evaporation rates in the order [Sn{OC(CH.sub.3).sub.2CH.sub.2CH.sub.3}.sub.2] (5)>[Sn(O.sup.sBu).sub.2] (3)>[Sn{OCH(CH.sub.3)CH(CH.sub.3).sub.2}.sub.2] (4), with evaporation rates of 60.8, 40.4 and 32.4 μg min.sup.−1 cm.sup.−1 respectively.

TABLE-US-00002 TABLE 2 Compound Evaporation rate (μg min .sup.−1cm.sup.−2) 1 65.0 2 128.4 3 40.4* 4 32.4* 5 60.8* *Isothermal carried out at 100° C.

EXAMPLE 4

Deposition With Sn (II) Oxide Primary Precursors

Deposition With [Sn(O.SUP.t.Bu).SUB.2.].SUB.2

[0124] Existing methods for the deposition of SnO via ALD involved the use of Sn(dmamp).sub.2 as the first precursor with H.sub.2O as the secondary precursor such as methods disclosed in Han et al, “Growth of p-Type Tin (II) Monoxide Thin Films by Atomic Layer Deposition from Bis (1-dimethyl amino-2-methyl-2-propoxy)tin and H.sub.2O, Chem. Mater., 2014, 26, 6088-6091.

##STR00007##

[0125] The resultant film layer (using Sn(dmamp).sub.2) was found to exhibit crystallinity when the operating temperature was between 150-210° C., with decreasing growth per cycle (GPC) with increasing temperature. Growth rates of ca. 0.18 Å/cycle at 170° C. and 0.05 Å/cycle at 210° C. have been reported. It has been found that films deposited at 210° C. display optimum properties of SnO and subsequent device performance However, due to slow deposition rates, Sn(dmamp).sub.2 is commercially unattractive, particularly at 210° C.

[0126] ALD experiments using [Sn(O.sup.tBu).sub.2].sub.2 as the primary precursor were undertaken at a number of different operating temperatures (130° C., 150° C., 170° C., 210° C. and 250° C.) of the processing chamber. The results are shown in FIG. 4. The results showed that successful deposition of SnO was achieved.

[0127] The resultant deposited films were characterized by p-XRD, Raman spectroscopy and variable-angle spectroscopic ellipsometry. The results are shown in FIGS. 4, 5, 6a and 6b.

[0128] The thickness of each deposited film was determined by variable-angle spectroscopic ellipsometry and was found to decrease with increasing temperature of the processing chamber with values of 25.19 (130° C.), 15.78 (150° C.), 12.95 (170° C.), 6.75 (210° C.) and 5.01 nm (250° C.) respectively.

[0129] Powder X-ray diffraction patterns of the SnO films deposited at temperatures between 130° C. and 250° C. (FIG. 4) confirm that crystalline SnO was deposited at temperatures between 150° C. and 210° C. (150° C., 170° C. and 210° C.).

[0130] All of the crystalline SnO films deposited were found to display highly oriented SnO, with the (001) and (002) reflections present at 2θ values of ˜18.3° and ˜37.1° (see FIG. 4). Basic analysis of the peak broadening within the patterns indicate rough estimates of ca. 7.5 (150° C.), 8.0 (170° C.) and 5.8 nm (210° C.) for the mean crystallite dimensions along the C-axes at each temperature. The crystallites were found to reach a maximum value of ca. 8 nm. The thicknesses of all deposited films were shown to be consistently higher than those reported by Han et al. for the published precursor [Sn(dmamp).sub.2].

[0131] Raman spectroscopy (FIGS. 6a and 6b) was also undertaken on crystalline films grown from [Sn(O.sup.tBu).sub.2] primary precursors (after 425 cycles of ALD) at temperatures of 170° C. and 210° C. and confirms the presence of SnO deposited film and a lack of SnO.sub.2. The presence of the SnO A.sub.1g stretch can clearly be observed at 210 cm.sup.−1, consistent with SnO films previously characterized.

[0132] A study to determine an accurate growth rate and extent of ALD behavior was undertaken at 170° C. (FIG. 7). Growth was found to follow a largely linear trajectory consistent with a self-limiting ALD process. The growth per cycle was confirmed to considerably exceed that observed for Sn(dmamp).sub.2 at the same deposition temperature, using the same deposition parameters. Growth rates using Sn(dmamp).sub.2 as the primary precursor in ALD deposition were reported to be between ca. 0.16 Å/cy at 170° C., and increased to 0.18 Å/cy through optimization. In contrast, it has been found that the growth rate at the same temperature using Sn(O.sup.tBu).sub.2 was found to occur at a rate of 0.32 Å. As such, the growth rates for SnO deposition using the Sn (II) oxide primary precursors of the method of the present disclosure were found to be significantly higher that the growth rates for deposited films formed from [Sn(dmamp).sub.2] precursors at each respective temperature (see FIG. 5). It therefore appears that the film layers formed using the Sn (II) containing precursors of the present disclosure are more commercially attractive than known Sn (II) containing precursors, such as Sn(dmamp).sub.2.

Comparative Example

ALD Without an H.SUB.2.O Pulse

[0133] A standard ALD process using Sn(O.sup.tBu).sub.2 as a primary precursor was undertaken at 170° C. without the presence of an H.sub.2O pulse. It was found that no deposition was observed on the substrate, and spectroscopic ellipsometry confirmed only a marginal <1 nm change to the surface of the SiO.sub.2, which is most likely due to a monolayer of adsorbed precursor affecting the refractive index of the substrate. This study proves that no CVD-style deposition is occurring, and the process is an ALD process.

Depositions with [Sn{OC(CH.SUB.3.).SUB.2.CH.SUB.2.CH.SUB.3.}.SUB.2.] (5)

[0134] ALD deposition was carried out at reactor temperatures of 170° C. and 210° C. and successful deposition occurred at both temperatures. Films deposited at the higher temperature of 210° C. were found to display crystallinity (FIG. 8). Highly oriented material was observed, with the p-XRD pattern clearly displaying peaks consistent with the (001) and (002) planes of SnO. The amorphous films were determined to have a thickness of 20.7 nm after 425 ALD cycles, giving an estimated growth per cycle of 0.49 Å, whilst the crystalline films determined to consist of SnO by p-XRD were shown to have a thickness of 11.3 nm, with a growth rate of 0.27 Å/cy. Estimations of crystallite dimensions in the C-axis for the crystalline film were found to be ca. 7.7 nm, consistent with results outlined previously. Direct comparison of deposition between the published standard Sn(dmamp)2 and novel precursor Sn{OC(CH.sub.3).sub.2CH.sub.2CH.sub.3}.sub.2 at 210° C. shows a significant increase in growth rate from 0.05 Å/cy with the published precursor to 0.27 Å/cy with Sn{ OC(CH.sub.3).sub.2CH.sub.2CH.sub.3}.sub.2. This is of particular relevance as films deposited at 210° C. have been shown to display excellent electrical properties for use as p-type channel layers in thin-film transistors.

EXAMPLE 5

Ge(O.SUP.t.Bu).SUB.2

[0135] ##STR00008##

[0136] Preparation: A stirring solution of [Ge{N(SiMe.sub.3).sub.2}.sub.2] (0.39 g, 1 mmol) in hexane (50 mL) was cooled and added to a −78° C. solution of tert-butanol (0.2 mL, 2 mmol) in hexane (20 mL) affording a colorless solution. After removal of the volatiles, the white powder was redissolved in hexane, filtered through Celite® and the volume reduced. Colorless crystals were afforded at −28° C.

[0137] .sup.1H NMR (500 MHz, C.sub.6D.sub.6); 1.48 ppm (s, 18H, CH.sub.3). .sup.13C{.sup.1H} NMR (75.5 MHz, C.sub.6D.sub.6); 34.3, 32.4 (6C, C(CH.sub.3).sub.2).

[0138] Ge(O.sup.tBu).sub.2 may be used as a precursor in ALD as discussed herein and as set out in the Examples above. Mass loss as determined by thermogravimetric analysis is almost complete by 150° C.

[0139] The disclosures of the published documents referred to herein are incorporated by reference in their entirety.

[0140] This application claims the priority of GB1913951.8 and the entire content of the priority application is incorporated by reference in this international application.