Methods for depositing metal-containing films on substrates

Abstract

Methods are disclosed depositing a M-containing film layer on a substrate, the method comprising: providing a substrate, providing a primary precursor of formula (I): [M(OCR1R2R3)NR4R5], and contacting a surface of the substrate with the primary precursor, wherein: M is Sn or Ge or Pb. The method may be an atomic layer deposition (ALD) method. Secondary precursors may included a source of O, Se, S, Te, N, and / or P. Substrates bearing film layers deposited according to the method may be useful as metal oxide semiconductor devices.

Description

[0001]METHODS FOR DEPOSITING METAL-CONTAINING FILMS ON SUBSTRATES FIELD OF THE INVENTION The present invention relates to methods for depositing a metal-containing film layer on a substrate, and to atomic layer deposition (ALD) methods for depositing a film layer of a metal (M) containing film layer on a surface of a substrate. The present invention also relates to substrates having deposited on at least one surface thereof an M-containing film layer obtainable by such methods and metal oxide semiconductor devices comprising at least one such substrate. BACKGROUND OF INVENTION Atomic layer deposition (ALD) is a specific deposition technique comprising the controlled introduction of both a primary precursor and a secondary precursor on to the surface of a substrate. The primary precursor may be a metal-containing precursor and the secondary precursor may be a simple molecule such as H2O, H2S, NH3, or alternatively plasma / ozone. The precursors may be introduced to the reaction chamber in a sequential fashion, with each introduction followed either by a purge step (so as to avoid precursor mixing) or by moving the substrate relative to the precursor flow. A schematic representation of the two main types of the ALD process is shown in Figure 1. Figure 1a shows ALD with purge stages and Figure 1b shows spatial ALD. The first cycle of the ALD process usually involves introducing a reactive primary metal- containing precursor into the processing chamber containing the substrate. The reactive primary precursor reacts with the surface of the substrate, resulting in a chemisorbed, surface-bound metal-ligand species. The layer of chemisorbed surface-bound metal-ligand species is usually of the order of an atomic monolayer in thickness as once all of the reactive surface sites on the substrate are taken, excess primary precursor may not decompose or react in the vapour phase. As a result, the primary precursor reacts with the surface of the substrate in a self-limiting manner. The excess primary precursor and any liberated ligand species may be removed from the processing chamber by the purging step or by moving the substrate to another station. The second cycle of the ALD process involves introducing a secondary precursor that reacts with the primary precursor on the surface of the substrate liberating the remaining ligand species and usually leaving a metal containing layer on the surface. The system is once again purged to remove any excess secondary precursor from the processing chamber. The process may be repeated as often as necessary to produce controlled thickness layers. WO-A-2021 / 058986 discloses the use of a M (II) primary precursor wherein M is Sn, Ge or Pb with a ligand displaying reactivity for a secondary precursor in the atomic layer deposition (ALD) of a M (II), M (0), or a M (IV) containing film layer on a substrate. US-A-2012 / 171378 and EP-A-2532767 disclose the synthesis of metal chalcogenides using a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, or a wet solution processes using ligand exchange reactions of organosilyltellurium or organosilylselenium with a series of metal compounds, including disclosing a method for depositing a Ge containing layer involving a precursor Ge(OR)2, wherein R is an alkyl group. WO-A-2013 / 118937 discloses a method for forming zinc tin oxide thin films using zinc and tin precursors by means of chemical vapor deposition (CVD) or atomic layer deposition (ALD), and to a method for manufacturing a thin film transistor (TFT) element using the method. The precursors may include Sn(OANR1R2)2 where A is an alkylene group that may be substituted by halogen. WO-A-2011 / 057114 discloses hafnium- or zirconium-containing compounds that may be used to deposit hafnium- or zirconium- containing layers using vapor deposition methods. WO-A-2008 / 057616 discloses antimony, germanium and tellurium precursors useful for CVD / ALD of corresponding metal-containing thin films and compositions including such precursors, methods of making such precursors, and films and microelectronic device products manufactured using such precursors, as well as corresponding manufacturing methods. ALD enables films to be efficiently deposited in a highly conformal ABABAB fashion on the surface of a substrate through the sequential introduction of precursors into the processing chamber. ALD can therefore be used to provide uniform deposition of precursors onto the surface of a substrate without “infilling” of trenches or holes. The ALD method is highly controllable and can enable deposition of precursors on to a substrate with a linear relationship between the number of cycles and the resultant film thickness. Unfortunately, there has been limited success in the use of M(II) and especially Sn (II) complexes as ALD precursors. It has been found that M(II) and Sn (II) chemistry is challenging and to date precursor development for most elements has focussed on the formulation of monomeric metal complexes in the belief that it will aid volatility and reactivity. Conventionally, the few Sn (II) precursors known comprise ligands with large steric bulk in order to reduce or avoid polymerisation of Sn (II) complexes. However, the presence of ligands with large steric bulk has also been found to reduce the reactivity of the primary Sn (II) precursor towards a secondary precursor. Secondary precursors for metal oxide materials may include H2O, H2O2, ozone or plasma. It is desirable for a number of commercial processes to use a primary precursor which displays reactivity towards H2O, particularly for oxidatively sensitive materials such as SnO or SnOx, where preservation of the +2 oxidation state of Sn is required. However, this requires the primary Sn (II) precursor to have high reactivity. It has also been found that the other common secondary precursors such as H2O2, ozone or plasma may undesirably result in the deposition of SnO2 (n-type) on the surface of the substrate. As such, there is a need to identify Sn (II) precursors that are both volatile and reactive towards an oxygen source, whilst also resisting oxidation to the more thermodynamically stable Sn (IV) oxide. It is also desirable to identify Sn (II) precursors which can be deposited via ALD onto a surface of a substrate to provide a crystalline film of SnO with the required electrical properties. Amorphous films of SnO have been found to exhibit poor conductivity and are therefore not always optimum for use within electronic devices. There is therefore a need for improved methods for forming metal containing layers on substrate surfaces. It is an aim of the present invention to address this need. SUMMARY OF INVENTION The present invention according provides, in a first aspect, a method for depositing a M- containing film layer on a substrate, the method comprising: a. providing a substrate, b. providing a primary precursor of formula (I): [M(OCR1R2R3)NR4R5] (I), and c. contacting a surface of the substrate with the primary precursor, wherein: M is Sn or Ge or Pb; R1, R2, and R3 are each independently selected from H or a substituted or unsubstituted C1 to C12alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, or halide; and R4 and R5 are each independently selected from H or a substituted or unsubstituted C1to C12 alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, alkylhalide, alkylamine, alkylether, halide, silicon-based group or R4 and R5 together with the N to which they are attached form an optionally substituted 3, 4, 5 or 6 membered ring. Optionally, the silicon-based group may be a silylamide. Suitably, at least one of R1, R2, or R3 is a substituted or unsubstituted C1 to C6 alkyl group. Suitably, the alkoxide ligand (OCR1R2R3) is a chelating or a monodentate ligand. The alkoxide ligand (OCR1R2R3) may be selected from OMe, OEt, OnPr, OiPr, OtBu, OCMe Et, OC(H)MeEt, OC(H) i t t i 2 MePr, OC(H)MeBu, OCMe2Bu, OC(H)Pr2, OC(CF3)3 or may be a chelating alkoxides for example OCH2CH2OMe, OCH(Me)CH2OMe, OCMe2CH2OMe, or OCMe2CH2OEt. Suitably, the amide ligand (NR4R5) may be a chelating or a monodentate ligand. The amide ligand (NR4R5) may be selected so that R4 and R5 are independently selected from Me, Et, nPr, iPr, tBu, CMe2Et, C(H)MeEt, C(H)MeiPr, C(H)MetBu, CMe2tBu, C(H)iPr , C(CF ) , SiMe , SiMe Et, i t i 2 3 3 3 2 SiMe2Pr, SiMe2Bu, SiEt2Me, SiEt3, and Si(Pr)3. In some embodiments, R4 or R5 may be a substituted or unsubstituted C1to C12(optionally C1to C8) alkyl group and the other of R4 or R5 may be a silylamide (e.g. SiMe3, SiMe2Et, SiMe iPr, SiMe tBu, SiEt Me, SiEt , Si i 2 2 2 3 (Pr)3). For example, In other embodiments, R4 or R5 may both be selected from silicon based groups so that the amide ligand may be a disilylamide. The disilylamide may be acyclic, for example: N(SiMe3)2, N(SiEt3)2, N(SiMe3)(SiEt3), N(SiMe2tBu)2 and N(SiMe3)(SiMe2tBu)2. For example, . The disilylamide may be cyclic, and R4 and R5 together with the N to which they are attached may form an optionally substituted 3, 4, 5 or 6 membered ring. For example, R4 and R5 together with the N to which they are attached may be {N(SiMe2)2CH2CH2}, {N(SiMe2)2CH2CH2CH2}, {N(SiMe2)2CH2CMe2CH2}, {N(SiMeEt)CH2CH2}, {N(SiEt2)2CMe2CH2}, or Preferably, M may be M(II). Preferably, M may be Sn (II) or Ge (II) or Pb (II). Suitably, the optionally substituted 6 membered ring may be 2,6-dimethylpiperidine or any tautomer or isomer thereof, or may be 2,2,6,6-tetramethylpiperidine or any tautomer or isomer thereof. The Sn containing film layer may be selected from: a Sn (II) oxide, an (SnO) film layer, a SnO2layer, a Sn2O3layer, a SnS layer, a SnS2layer, a Sn2S3layer, a SnExlayer (preferably a Sn(II)Ex layer) where E is selected from chalcogenide or pnictogen and x is 1 or 2, or a Sn2E3 layer where E is selected from chalcogenide or pnictogen. The term “chalcogenide” is used herein to refer to group 16 elements of the periodic table. Preferably, the chalcogenide is selected from oxides, sulphides, selenides, and tellurides. Preferably, the Sn (II) containing film layer is Sn (II) oxide. The Sn (II) oxide thin may be a crystalline Sn (II) oxide film layer. The term “pnictogen” is used herein to refer to group 15 elements of the periodic table. Preferably, the pnictogen is nitrogen or phosphorus. In one embodiment, M may be Ge. The Ge containing film layer may be selected from: a Ge (II) oxide (GeO) film layer, a GeO2layer, a GeS layer, a GeS2layer, a GeExlayer (preferably a Ge(II)Exlayer) where E is selected from chalcogenide or pnictogen (preferably nitrogen or phosphorus) and x is 1 or 2, or a Ge2E3 layer where E is selected from chalcogenide or pnictogen. Preferably, the Ge (II) containing film layer is Ge (II) oxide. The Ge (II) oxide film layer may be a crystalline Ge (II) oxide film layer. In one embodiment, M may be Pb. The Pb containing film layer may be selected from: a Pb (II) oxide (PbO) film layer, a PbO2layer, a PbS layer, a PbS2layer, a PbExlayer where E is selected from chalcogenide or pnictogen (preferably nitrogen or phosphorus) and x is 1 or 2, or a Pb2E3 layer where E is selected from chalcogenide or pnictogen. Preferably, the Pb (II) containing film layer is Pb (II) oxide. The Pb (II) oxide film layer may be a crystalline Pb (II) oxide film layer. Suitably, the primary precursor may be of formula (II): [Sn(OCR1R2R3)NR4R5] (II). Suitably, R1, R2, and R3 are each independently selected from H or a substituted or unsubstituted C1 to C8 alkyl group, optionally a halo-substituted or unsubstituted C1 to C8 alkyl group. Suitably, R4 and R5 may be independently selected from H or a substituted or unsubstituted C1to C8alkyl group, or silicon-based group, optionally a halo-substituted or unsubstituted C1 to C8 alkyl group. Suitably, at least one of R4 and R5 may be independently selected from R6NR7R8 or R6OR7, wherein R6 either indicates the bond to N or is an alkylene group selected from a substituted or unsubstituted C1 to C8 alkylene group, optionally a halo-substituted or unsubstituted C1to C8alkylene group; and R7 and R8 are independently selected from a substituted or unsubstituted C1 to C8 alkyl group, optionally a halo-substituted or unsubstituted C1 to C8 alkyl group. Suitably, R4 and R5 may be independently selected from R19 or R15SiR16R17R18, wherein R15 either indicates the bond to N or is an alkylene group selected from a substituted or unsubstituted C1 to C8 alkylene group, optionally a halo-substituted or unsubstituted C1 to C8 alkylene group; R16, R17and R18 are independently selected from a substituted or unsubstituted C1to C8alkyl group, and R19 is selected from a substituted or unsubstituted C1 to C8 alkyl group. Suitably, the primary precursor may be selected from [Sn(OMe)NMe2], [Sn(OEt)NMe2], [Sn(OiPr)NMe2], [Sn(OtBu)NMe2], [Sn(OCMe2Et)NMe2], [Sn(OC(H)MeEt)NMe2], [Sn(OC(H)MeiPr)NMe ], [Sn(OC(H)MetBu)NMe ], [ t 2 2 Sn(OCMe2Bu)NMe2], [Sn(OC(H)iPr )NMe ], [Sn(OC(CF ) )NMe ] t t 2 2 3 3 2 , [Sn(OBu)NMe2], [Sn(OBu)NMeEt], [Sn(OtBu)Net2] [Sn(OtBu)NMeiPr], [Sn(OtBu)NMetBu], [Sn(OtBu)NMeCF3], [Sn(OtBu)NEtiPr], [Sn(OtBu)NEttBu], [Sn(OtBu)N(Me)CH2CH2NMe2], [Sn(OtBu)N(Et)CH t 2CH2NMe2], [Sn(OBu)N(Me)CH2CH2NMeEt], [Sn(OtBu)N(Me)CH2CH2NEt2], [Sn(OtBu)N(Et)CH2CH2NMeEt], [Sn(OtBu)N(Et)CH t 2CH2NEt2], [Sn(OBu)N(Me)CH2CH2OMe], [Sn(OtBu)N(Me)CH t 2CH2OEt], [Sn(OBu)N(Et)CH2CH2OMe], [Sn(OtBu)N(Me)CH2CH2OtBu], [Sn(OtBu)N(Et)CH2CH2OMe], [Sn{OtBu}{HMDS}]2, [Sn{OtBu}{N(CH2SiMe2)2)}]2, or mixtures thereof. A preferred primary precursor is of formula (III): [Sn{OtBu}(NMe2)]. Thus, in a preferred embodiment, there is provided a method for depositing a M-containing film layer on a substrate, the method comprising: providing a substrate, providing a primary precursor of formula (III): [Sn{OtBu}(NMe2)] (III), and contacting a surface of the substrate with the primary precursor. The M containing film layer is preferably of predetermined, uniform depth across a surface of a substrate. Suitably, the metal (M) containing film layer is a M (II) containing film layer. Suitably, the M (II) containing film layer is an Sn (II) containing film layer. Suitably, the Sn (II) containing film layer is an Sn (II) oxide film layer. Suitably, the Sn (II) oxide film layer is a crystalline Sn (II) oxide containing film layer. In one embodiment, the metal (M) containing film layer may be a multicomponent metal (M) containing film layer comprising at least one additional metal (M’). For example, the at least one additional metal (M’) may be 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. The additional metal may derive from an additional primary precursor acting as a source of the additional metal that may be mixed with the primary precursor according to formula (I). In one embodiment, the primary precursor may be used in the atomic layer deposition (ALD) of a metal (M) and F containing film layer, for example a Sn and F containing film layer, for example SnO2:F. Thus, the surface of the substrate may also be contacted with a source of a halogen, preferably a source of fluorine. Examples of a source of fluorine may include HF, SF6, AlF3 or BF3, organic F-containing compounds (e.g. hexafluropentanedione) or mixtures thereof. Suitably, the method further comprises contacting the surface of the substrate with a secondary precursor. Suitably, the secondary precursor comprises a source of O, Se, S, Te, N, and / or P. The secondary precursor may be selected from (for oxides): water, a source of water (e.g. a monohydrate of a carboxylic acid, urea monohydrate), oxygen, ozone, hydrogen peroxide, and peroxide-containing compounds;, ammonia, plasmas of hydrogen and ammonia; (e.g., for other elements) hydrogen sulfide, hydrogen selenide, phosphine (PH3), and / or nitrogen. The secondary precursor may be any suitable precursor exhibiting high reactivity to the primary precursor, for example the secondary precursor may be selected from: H2O, H2O2, plasma (for example O2, H2, NH3, Ar, N2), carboxylic acids, nitrous oxide, hydrogen, oxygen, ozone or ammonia. An adduct may be formed comprising the M containing primary precursor together with at least one additional compound. The adduct is preferably a neutral adduct. The volatility of the adduct may be better than the volatility of the M containing primary precursor. The adduct may ensure that the M (II) containing primary precursor is monomeric. The at least one additional compound may comprise pyridine or one or more chelating amines. The substrate surface may be a temperature at which the primary precursor interacts and reacts on the surface. Suitably, the substrate surface may at a temperature in the range 50 oC to 500 oC, optionally 60 oC to 400 oC, optionally 70 oC to 300 oC. More suitably, the substrate surface may be at a temperature in the range 90 oC to 250 oC. Preferably, the processing chamber is heated to a temperature within the range of from 70 oC to 250 oC, preferably from 90 oC to 250 oC, more preferably from 120 oC to 250 oC, for example from 150 oC to 210 oC. The method may be chemical vapour deposition (CVD). Most preferably, the method may be an atomic layer deposition (ALD) method. The ALD process may involve either optionally purging the processing chamber in a first purge stage to separate the surface of the substrate and excess primary precursor, or the purge stage may mean optionally moving the substrate relative to the precursor source in a first optional movement stage. The ALD process may also involve 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. The ALD process may optionally involve 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 / or second optional movement stage. Thus, the present invention according provides, in a second aspect, an atomic layer deposition (ALD) method for depositing a film layer of a metal (M) containing film layer on a surface of a substrate, the method comprising: d. providing a substrate e. in a first dose stage, contacting a surface of the substrate with a primary precursor of formula (I) for a predetermined first dose time: [M(OCR1R2R3)NR4R5] (I), f. optionally, subsequently performing a first purge stage to separate the surface of the substrate and excess primary precursor; g. in a second dose stage, contacting a surface of the substrate with a secondary precursor for a predetermined second dose time; h. optionally, subsequently performing a second purge stage to separate the surface of the substrate and excess secondary precursor; i. optionally repeating one or more of: the first dose stage, first purge stage, second dose stage and / or second purge stage; wherein: M is Sn or Ge or Pb; Preferably, M is Sn, more preferably M is Sn(II). R1, R2, and R3 are each independently selected from H or a substituted or unsubstituted C1to C12 alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, or halide; and R4 and R5 are each independently selected from H or a substituted or unsubstituted C1to C12alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, halide, a silicon-based group, or R4 and R5 together with the N to which they are attached form a 3, 4, 5 or 6 membered ring. The first purge stage may include either purging the processing chamber in order to remove excess primary precursor or it may involve moving the substrate relative to the precursor source in order to separate excess primary precursor and the substrate surface. Similarly, the second purge stage may include either purging the processing chamber in order to remove excess primary precursor or it may involve moving the substrate relative to the precursor source in order to separate excess primary precursor and the substrate surface. Optionally moving the substrate relative to the precursor source may involve moving the substrate in the processing chamber or moving the precursor source(s) (e.g. precursor inlets) relative to the substrate or both. In spatial ALD, the precursor flows may be kept separated by a flow of inert gas that fulfils the purge function. The method may be carried out in a processing chamber in which the substrate may be situated. The processing chamber may be heated to any suitable temperature. Suitably, the processing chamber may be heated to a temperature within the range of between 90 oC and 250 oC, more preferably between 120 oC and 250 oC, for example between 150 oC and 210 oC. The pressure within the processing chamber may be within the range of from about 0.1 mbar to 50 mbar (10 Pa to 5 kPa). In some embodiments of the method (especially in spatial ALD) deposition may occur at around atmospheric pressure (about 101 kPa). The method may be carried out within the processing chamber under a flow of inert gas, such as argon or nitrogen. The primary precursor or adduct may be introduced at any suitable flow rate into the processing chamber. The primary precursor or adduct may be introduced within (e,g, entrained within) a flow of inert gas, such as argon or nitrogen. The primary precursor or adduct may be injected as a liquid into the processing chamber. The primary precursor may be delivered to the processing chamber as an aerosolised or sprayed solution in an inert solvent. The primary precursor may be introduced to the processing chamber over any suitable dose period e.g. to ensure that the deposition of the primary precursor on to the substrate surface has been saturated so that no or few other reactive sites remain on the substrate surface. For example, the dose period of the primary precursor within the processing chamber may be at least 50 milliseconds, preferably at least 500 milliseconds, preferably at least 1 second, preferably at least 2 seconds, more preferably at least 5 seconds. It is to be understood that the deposition may be achieved using a short residency time of the precursor or adduct with an increased number of deposition cycles. The methods of the present invention relate to the use of the primary precursor according to formula (I) in the deposition of a MO (or MOx) containing thin film layer, for example SnO, which is very advantageous because it has the potential to be used as a p-type semiconducting layer in a number of electronic devices, such as p-type metal oxide semiconductor (PMOS) and Complementary Metal Oxide Semiconductor (CMOS) devices. Thus, in a third aspect, the invention provides a substrate having deposited on at least one surface thereof an M-containing film layer obtainable by a method of the first or second aspects. Preferably, in an aspect, the invention provides a substrate having deposited on at least one surface thereof an M (II)-containing film layer obtainable by a method of the first or second aspects. In a fourth aspect, the invention provides a substrate metal oxide semiconductor device comprising at least one substrate according to the third aspect. In a fifth aspect, the invention provides a Sn(II) compound of formula [Sn{OtBu}(NMe2)]. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the various aspects of the invention or of the dependent claims may be combined with features of the other aspects or independent claims as appropriate, and in combinations other than those explicitly set out in the discussion of the various aspects or claims, as supported by the description. DEFINITIONS The term “atomic layer deposition (ALD)” is used herein to refer to any variant of ALD, including plasma-enhanced, thermal, spatial ALD and liquid injected ALD. The time a surface is exposed to a precursor in referred to as a dose or pulse time. The time in between doses of precursor (i.e. the time taken to evacuate or purge the chamber) is referred to as a purge time. The dose-purge-dose-purge sequence of a binary ALD process constitutes an ALD cycle. This cycle can be repeated as many times as required in order to deposit a film having a predetermined thickness on the surface of the substrate. If the purge step or substrate movement has not removed all excess primary precursor from vicinity of the substrate surface prior to introduction of the secondary precursor, precursor mixing may occur, in a non-surface limited fashion, resulting in chemical vapour deposition (CVD)-type growth of the layer on the surface of the substrate. “Substituted,” when used in connection with a chemical substituent or moiety (e.g., an alkyl group), means that one or more hydrogen atoms of the substituent or moiety have been replaced with one or more non-hydrogen atoms or groups, provided that valence requirements are met and that a chemically stable compound results from the substitution. “Optionally substituted” refers to a parent group which may be un-substituted or which may be substituted with one or more substituents. Suitably, unless otherwise specified, when optional substituents are present the optional substituted parent group comprises from one to three optional substituents thus the group may be substituted with 0, 1, 2 or 3 of the optional substituents. Suitably, the group is substituted with 1, 2 or 3 of the optional substituents. Complexes as disclosed herein (and other complexes according to the formulae herein) may be monomers, or dimers (or optionally trimers or other oligomers) and references to complexes or specific complexes are intended to refer to monomers or dimers or any one of these structures (unless the context otherwise suggests). Complexes may be dimers or monomers in the gas phase. Complexes XI and XII are generally dimers in the solid state (see Figures 9 and 10, for example showing the dimeric structures). Complexes 1 to X may be dimers (or monomers) in the solid state. Optional substituents may be selected from C1-10 alkyl, C1-8 alkyl, C1-6 alkyl, C1-4 alkyl, C2- 7 alkenyl, C2-7 alkynyl, C1-12 alkoxy, C5-20 aryl, C3-10 cycloalkyl, C3-10 cycloalkenyl, C3-10 cycloalkynyl, C3-20heterocyclyl, C3-20heteroaryl, acetal, acyl, acylamido, acyloxy, amidino, amido, amino, aminocarbonyloxy, azido, carboxy, cyano, ether, formyl, guanidino, halo, hemiacetal, hemiketal, hydroxamic acid, hydroxyl, imidic acid, imino, ketal, nitro, nitroso, oxo, oxycarbonyl, oxycarboyloxy, sulfamino, sulfamyl, sulfate, sulfhydryl, sulfinamino, sulfinate, sulfino, sulfinyl, sulfinyloxy, sulfo, sulfonamido, sulfonamino, sulfonate, sulfonyl, sulfonyloxy, uredio groups. In some aspects, the optional substituents are 1, 2 or 3 optional substituents independently selected from C1-10alkyl, C1-8alkyl, C1-6alkyl, C1-4alkyl, OC1-12alkyl, and halogen. More suitably, the optional substituents are selected from C1-6 alkyl and OC1-12 alkyl; more suitably, the optional substituents are selected from C1-4 alkyl and OC1-6 alkyl. “Independently” or “Independently selected” is used in the context of statement that, for example, “each R9, R10is independently H, C1-8alkyl…” and means that each instance of the functional group, e.g., R11, is selected from the listed options independently of any other instance of R9or R10in the compound. Hence, for example, H may be selected for the first instance of R9 in the compound; methyl may be selected for the next instance of R9 in the compound; and ethyl may be selected for the first instance of R10 in the compound. C1-8alkyl: refers to straight chain and branched saturated hydrocarbon groups, having from 1 to 8 carbon atoms, and C1-6 alkyl to straight chain and branched saturated hydrocarbon groups, having from 1 to 6 carbon atoms. Suitably a C1-7 alkyl; suitably a C1-6 alkyl; suitably a C1-5alkyl; more suitably a C1-4alkyl; more suitably a C1-3alkyl. Examples of alkyl groups include methyl (Me), ethyl (Et), n-propyl (Pr), i-propyl (iPr), n-butyl (Bu), s- butyl, i-butyl, t-butyl (tBu), pent-1-yl, pent-2-yl, pent-3-yl, 3-methylbut-1-yl, 3-methylbut- 2-yl, 2-methylbut-2-yl, 2,2,2-trimethyleth-1-yl, n-hexyl, n-heptyl, n-octyl and the like. “Alkylene” refers to a divalent radical derived from an alkane which may be a straight chain or branched, as exemplified by –CH2CH2CH2CH2-. The alkylene may have the number of carbons as discussed above for alkyl groups. “Aryl” refers to fully unsaturated monocyclic, bicyclic and polycyclic aromatic hydrocarbons having at least one aromatic ring. Aryl groups as used herein preferably are preferably “C5-20 Aryl” a fully unsaturated monocyclic, bicyclic and polycyclic aromatic hydrocarbons having at least one aromatic ring and having a specified number of carbon atoms that comprise their ring members (e.g., C5-20aryl refers to an aryl group having from 5 to 20 carbon atoms as ring members). The aryl group may be attached to a parent group or to a substrate at any ring atom and may include one or more non-hydrogen substituents unless such attachment or substitution would violate valence requirements. Suitably, a is selected from a C6-12 aryl, more suitably, a C6-10 aryl. Examples of aryl groups include phenyl. “Halogen” or “halo”: refers to a group selected from F, Cl, Br, and I. Preferably, the halogen or halo is F or Cl. In some aspects, preferably the halogen is F. In other aspects, suitably the halogen is Cl. As used herein the term “comprising” means “including at least in part” and is inclusive or open ended. When interpreting each statement in this specification that includes the term “comprising,” features, elements and / or steps other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner. It should be understood that while various aspects in the specification are presented as “comprising,” this includes aspects that “consist essentially of” or “consist of” that aspect. The term “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention. When the phrase “consisting essentially of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause. The term “consisting of” excludes any element, step, or ingredient not specified in the claim; “consisting of” defined as “closing the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase “consists of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. Embodiments of the present invention will be described in more detail with reference to the accompanying Figures, in which: BRIEF DESCRIPTION OF FIGURES Figure 1a is a schematic illustration of the atomic layer deposition (ALD) process, Figure 1b is a schematic illustration of the spatial atomic layer deposition (ALD) process; Figure 2 are thermogravimetric analysis ( TGA) plots showing the % mass loss vs temperature for the Sn(II) oxide primary precursors I-V and VI-X. Figure 3 shows isothermal-TGA plots showing the rate of mass loss for complex III at 75, 100 and 125 °C respectively. Figure 4 shows PXRD plots of SnO deposited by ALD at deposition temperatures of 125 (blue), 150 (red) and 175 oC (green) respectively on to silicon substrates. Figure 5 shows Raman spectra of SnO deposited by ALD at deposition temperatures of 125, 150 and 175 oC respectively on to silicon substrates. Figure 6 shows a plot of growth per cycle as a function of number of cycle, for ALD processes performed at a deposition reactor chamber temperature of 125 and 150 °C respectively. Figure 7a and 7b show graphs showing the linear relationship between film thickness and number of cycles expected of a true ALD process at both 125 °C and 150 °C respectively, over 50, 100, 200 and 400 ALD cycles. Figure 8a and 8b show saturation curves for both the precursor (III) and for the co- reagent (H2O) in the ALD process at 150 °C. Figure 9 shows the solid state molecular structure of complex XI [Sn{OtBu}{HMDS}]2 (with hydrogen atoms omitted for clarity). Figure 10 shows the solid state molecular structure of complex XII [Sn{OtBu}{N(CH2SiMe2)2}]2 (with hydrogen atoms omitted for clarity). Embodiments of the present invention will now be described further, with reference to the Examples, below. Examples Synthesis of Sn (II) Alkoxide Amine Primary Precursors There are several synthetic routes for the preparation of Sn (II) alkoxides-amide, including salt metathesis, ligand metathesis and alcohol exchange with the respective alcohol. Sn (II) alkoxide amine primary precursors are readily synthesized through direct amine ligand displacement reactions, as illustrated in scheme 1: [Sn{OC(CF3)3}(NMe2)] (IV)Scheme 1: Synthesis of complexes I to X. The synthesis of a number of specific examples of Sn(II) oxide primary precursors I to X suitable for use with the ALD method of the present invention is described in detail. General Experimental Synthesis of [Sn{OEt}NMe2] (I): Anhydrous Ethanol (0.230 g, 5 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (1.034 g, 5 mmol) in hexane (40 ml). Upon addition a sticky white semi-solid was produced, after stirring at room temperature for 1 hour the solid disappeared producing a clear colourless liquid. The solution was filtered through Celite® and the solvent was removed in vacuo to produce a sticky white solid. Small white crystals were collected by re-dissolving the product in 15 ml hexane and leaving to crystallize at -28°C for several weeks (0.434 g, 41.8%). 1H NMR (400MHz, Benzene-d6) δ = 4.17 (q, J = 6.8 Hz, 2H, CH2CH3), 2.45 (s, 6H, NMe2), 1.35 (t, J = 6.8 Hz, 3H, CH2CH3). 13C NMR (101 MHz, Benzene-d6) δ = 60.28 (CH2CH3), 41.08 (NMe2, 22.62 (CH2CH3). 119Sn NMR (186 MHz, Benzene-d6) δ = 30 Found: C, 23.40; H, 5.09; N, 6.70 %, C4H11N1O1Sn requires C, 23.11; H, 5.33; N, 6.74 %. Synthesis of [Sn{OiPr}NMe2] (II): Anhydrous iso-propanol (0.120 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a pale-yellow liquid. Short path distillation at 150°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a pale-yellow liquid (0.238 g, 53.6%). Crystals were collected by re-dissolving the product in 5 ml hexane and leaving to crystallize at -28°C for several weeks. 1H NMR (400MHz, Benzene-d6) δ = 4.45 (sept, J = 6 Hz, 1H, CHMe2), 2.44 (s, 6H, NMe2), 1.33 (d, J = 6 Hz, 6H, CHMe2). 13C NMR (101 MHz, Benzene-d6) δ = 66.03 (CHMe2), 41.23 (NMe2), 29.68 (CHMe2).119Sn NMR (186 MHz, Benzene-d6) δ = 31. Found: C, 27.16; H, 6.11; N, 6.24 %, C5H13N1O1Sn requires C, 27.07; H, 5.91; N, 6.31 %. Synthesis of [Sn(OtBu)NMe2] (III): Anhydrous tert-butanol (0.148 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a viscous pale-yellow liquid. Short path distillation at 150°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a viscous clear colourless liquid (0.41 g, 87.2%). 1H NMR (400MHz, Benzene-d6) δ = 2.45 (s, 6H, (NMe2), 1.39 (s, 9H, CMe3). 13C NMR (101 MHz, Benzene-d6) δ = 70.59 (CMe3), 41.26 (NMe2), 35.87 (NMe2). 119Sn NMR (186 MHz, Benzene-d6) δ = 31. Found: C, 30.66; H, 6.37; N, 5.72 %, C6H15N1O1Sn requires C, 30.55; H, 6.41; N, 5.94 %. : Anhydrous nonafluoro-tert-butyl alcohol (0.472 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a white solid. Short path distillation at 150°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a white crystalline solid (0.718 g, 90.2%). Crystals were collected by re-dissolving the product in 5 ml hexane and leaving to crystallize at -28°C overnight. 1H NMR (400Mhz, Benzene-d6) δ = 2.08 (s, 6H, NMe2). 19F NMR (470 MHz, Benzene-d6) δ = 73.77 (s, 9H, {OC(CF3)3}). 13C NMR (101 MHz, Benzene-d6) δ = 123.85 (C(CF3)3), 120.54 (C(CF3)3), 39.88 (NMe2). 119Sn NMR (186 MHz, Benzene-d6) δ = -61. Found: C, 18.48; H, 1.34; N, 3.37 %, C6H6N1O1Sn requires C, 18.12; H, 1.52; N, 3.52 %. (V): Anhydrous 2-methyl-2-butanol (0.176 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a viscous pale-yellow liquid. Short path distillation at 175°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a viscous clear colourless liquid (0.446 g, 89.2%). 1H NMR (400MHz, Benzene-d6) δ = 2.46 (s, 6H, NMe2), 1.60 (q, J = 8 Hz, 2H, CH2CH3), 1.32 (s, 6H, CMe2), 1.05 (t, J = 8.0 Hz, 3H, CH2CH3) 13C NMR (101 MHz, Benzene-d6) δ = 72.40 (CMe2), 41.19 (NMe2), 40.12 (CH2CH3), 33.36 (CMe2), 9.59 (CH2CH3). 119Sn NMR (186 MHz, Benzene-d6) δ = 28. Found: C, 33.35; H, 6.79; N, 5.58 %, C7H17N1O1Sn requires C, 33.64; H, 6.86; N, 5.60 %. Synthesis of [Sn{OCHMeEt}NMe2] (VI): Anhydrous 2-butanol (0.148 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a clear colourless liquid. Short path distillation at 150°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a clear colourless liquid (0.365 g, 77.3%). 1H NMR (400Mhz, Benzene-d6) δ = 3.96 (sept, J = 6.0 Hz, 1H, CHMeEt), 2.26 (s, 6H, NMe2), 1.48 – 1.32 (m, 2H, CH2CH3), 1.11 (d, J = 6.0 Hz, 3H, CHMeEt), 0.83 (t, J = 7.4 Hz, 3H, CH2CH3). 13C NMR (101 MHz, Benzene-d6) δ = 71.30 (CHMeEt), 41.33 (NMe2), 35.71 (CH2CH3), 27.48 (CHMeEt), 11.15(CH2CH3). 119Sn NMR (186 MHz, Benzene-d6) δ = 27 Found: C, 30.37; H, 6.24; N, 6.11 %, C6H15N1O1Sn requires C, 30.55; H, 6.41; N, 5.94 %. (VII): Anhydrous 3-methyl-2-butanol (0.176 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a cloudy colourless liquid. Short path distillation at 175°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a clear colourless liquid (0.33 g, 65.9%). 1H NMR (400MHz, Benzene-d6) δ = 4.04 – 3.98 (m, 1H, OCHMeiPr), 2.45 (s, 6H, NMe2), 1.71 (ddd, J = 9.1, 6.8, 3.5 Hz, 1H, (CHMe2)), 1.24 (d, J = 6.2 Hz, 3H, OCHMe), 1.05 (d, J = 2.1Hz, 3H (CHMe2)), 1.04 (d, J = 2.1 Hz, 3H, (CHMe2)). 13C NMR (101 MHz, Benzene-d6) δ = 74.38 (OCH), 41.44 (NMe2), 37.63 (CHMe2), 24.52 (OCHMe), 19.20 (CHMe2)), 18.68 (CHMe2)). 119Sn NMR (186 MHz, Benzene-d6) δ = 24 Found: C, 33.23; H, 6.57; N, 5.45 %, C7H17N1O1Sn requires C, 33.64; H, 6.86; N, 5.60 %. Synthesis of [Sn{OCHMetBu}NMe2] (VIII): Anhydrous 3,3-dimethyl-2-butanol (0.204 g, 2 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (0.414 g, 2 mmol) in hexane (20 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a cloudy colourless liquid. Short path distillation at 175°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a cloudy colourless viscous liquid (0.311 g, 58.9%). 1H NMR (400Mhz, Benzene-d6) δ = 3.83 (q, J = 6.2 Hz, 1H, CHMetBu), 2.45 (s, 6H, NMe ), 1.21 (d, J = 6.2, 3H, C t 2 HMe), 1.03 (s, 9H, CHBu). 13C NMR (101 MHz, Benzene-d6) δ = 77.55 (CH), 41.62 (NMe2), 36.80 (CMe3), 26.83 (CMe3), 23.06 (CHMe). 119Sn NMR (186 MHz, Benzene-d6) δ = 21 Found: C, 36.42; H, 7.35; N, 5.55 %, C8H19N1O1Sn requires C, 36.40; H, 7.26; N, 5.31 %. Synthesis of [Sn{OCMe i 2Pr}NMe2] (IX): Anhydrous 2,3-dimethyl-2-butanol (0.511 g, 5 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (1.034 g, 5 mmol) in hexane (40 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a cloudy colourless liquid. Short path distillation at 175°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a cloudy colourless viscous liquid (0.925g, 70.1%). 1H NMR (400Mhz, Benzene-d6) δ = 2.45 (s, 6H, NMe2), 1.70 (sept, J = 6.8, 1.1 Hz, 1H, CHMe2), 1.28 (d, J = 1.0 Hz, 6H, OCMe2), 1.06 (dt, J = 6.9, 0.9 Hz, 6H, CHMe2). 13C NMR (101 MHz, Benzene-d6) δ = 74.54 (OCMe2), 41.74 (OCMe2CH), 41.59 (NMe2), 31.79 (OCMe2), 18.78 (CHMe2). 119Sn NMR (186 MHz, Benzene-d6) δ = 28 Found: C, 36.54; H, 7.01; N, 5.31%, C8H19N1O1Sn requires C, 36.40; H, 7.26; N, 5.31 %. Synthesis of [Sn{OCHiPr2}NMe2] (X): Anhydrous 2,3-dimethyl-3-pentanol (0.581 g, 5 mmol) was added dropwise to a stirred solution of [Sn(NMe2)2] (1.034 g, 5 mmol) in hexane (40 ml). After stirring at room temperature for 1 hour the solution was filtered through Celite® and the solvent was removed in vacuo to produce a cloudy colourless liquid. Short path distillation at 175°C into a cooled receptacle (liquid N2) under reduced pressure (10-2 mbar) afforded a cloudy colourless viscous liquid (0.803g, 57.8%). 1H NMR (400Mhz, Benzene-d6) δ = 3.48 (dd, J = 5.5, 4.0 Hz, 1H, OCH(CHMe2)2), 2.53 (s, 6H, NMe2), 1.93 – 1.81 (m, 2H, OCH(CHMe2)2), 1.08 – 0.99 (m, 12H, CHMe2). 13C NMR (101 MHz, Benzene-d6) δ = 84.11 (OCH(CHMe2)2), 41.73 (NMe2), 33.06 (OCH(CHMe2)2), 21.25 (CHMe2), 18.95 (CHMe2). 119Sn NMR (186 MHz, Benzene-d6) δ = 1.20 Found: C, 38.76; H, 7.48; N, 4.97 %, C9H21N1O1Sn requires C, 38.89; H, 7.61; N, 5.04 %. M(II) heteroleptic silylamide / alkoxide precursors Scheme 2: Synthesis of complexes XI and XII. Complexes XI and XII are examples for M(II) heteroleptic silylamide / alkoxide precursors. These precursors may be formed either by direct reaction of the bis-silylamide complexes with one molar equivalent of selected alcohol, in an analogous fashion to the synthesis of complexes I-X (Scheme 1), or by the metathesis of the bis-silyl amides with the bis- alkoxide starting materials as shown in Scheme 2. The synthesis, and characterisation data of the complexes XI and XII are set out below. Synthesis of [Sn{OtBu}{HMDS}]2(XI) [Sn{HMDS}2] (1 mmol, 0.439 g) and [Sn{OtBu}2] (1 mmol, 0.265 g) were dissolved in hexane (10 mL) and left stirring for 12 hours. The resulting pale orange solution was then filtered and concentrated, yielding colourless crystals after being stored at -28ºC overnight (98%). HMDS refers to hexamethyldisilazane. 1H (500 MHz, C6D6): δH 0.41 (s, 9H, SiMe3), 0.53 (s, 9H, SiMe3), 1.37 (s, 9H, CMe3). 13C{1H} (125 MHz, C6D6): δC6.7 (SiMe3), 7.4 (SiMe3), 33.2 (CMe3), 76.2 (CMe3). 119Sn{1H} (187 MHz, C6D6): δSn41 EA-Found: C, 39.8; H, 8.09; N, 4.17 %, C11H27N1O1Sn requires C, 39.31; H, 8.10; N, 4.17 The solid state molecular structure of complex XI (with hydrogen atoms omitted for clarity) is shown in Figure 9. Synthesis of [Sn{N(CH2SiMe2)2}2] (1 mmol, 0.435 g) and [Sn{OtBu}2] (1 mmol, 0.265 g) were dissolved in hexane (10 mL) and left stirring for 12 hours. The resulting pale green solution was then filtered and concentrated, yielding pale green crystals after being stored at -28ºC overnight (94%). 1H (500 MHz, C6D6): δH0.46 (s, 12 H, SiMe2), 0.90 (s, 4H, SiCH2), 1.36 (s, tBu). 13C{1H} (125 MHz, C6D6): δC 4.9 (SiMe2), 11.3 (SiCH2), 33.2 (CMe3), 76.5 (CMe3). 119Sn{1H} (187 MHz, C6D6): δSn 67. EA-Found: C, 34.26; H, 7.19; N, 4.06 %, C10H25N1O1Sn requires C, 34.30; H, 7.20; N, 4.00 %. The solid state molecular structure of complex XII (with hydrogen atoms omitted for clarity) is shown in Figure 10. Thermogravimetric Analysis TGA plots showing the % mass loss vs temperature for the Sn(II) oxide primary precursors I-V and VI-X are shown in Figure 2 Mass Loss-Temperature Thermogravimetric Analysis The mass loss / temperature plots for Sn(II) oxide primary precursors I-V and VI-X are shown in Figure 2. It is shown that each of the exemplified Sn (II) oxide primary precursors displays a loss of mass significantly greater than that which would be expected for the decomposition to any of metallic tin, tin(II) oxide or tin(IV) oxide (see also Table 1). Compound Onset % Non-volatile Expected % for Temperature Residue Sn / SnO / SnO2(Temp.) I 101 °C 4 (198 °C) 57.2 / 64.8 / 72.5 II 93 °C 5.3 (176 °C) 53.5 / 60.7 / 67.9 III 73 °C 3 (155 °C) 50.3 / 57.1 / 63.9 IV 72 °C 1.3 (146 °C) 29.8 / 33.9 / 37.9 V 107 °C 2.5 (197 °C) 47.5 / 53.9 / 60.3 VI 121 °C 12.8 (253 °C) 50.3 / 57.1 / 63.9 VII 115 °C 12.8 (289 °C) 47.5 / 53.9 / 60.3 VIII 149 °C 22.5 (275 °C) 45.0 / 51.0 / 57.1 IX 144 °C 7.6 (258 °C) 45.0 / 51.0 / 57.1 X 150 °C 29.5 (325 °C) 42.7 / 48.5 / 54.2 § The temperature at which 1% mass loss has occurred Table 1: Onset of volatilisation temperature, % non-volatile residue and temperature, and expected % mass residues for formation of Sn / SnO / SnO2 respectively. 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 5 a second smaller loss of mass occurs. The exemplified Sn(II) oxide primary precursors I to V display suitable stabilities and volatilities for ALD applications. Isothermal Thermogravimetric Analysis As a result of the high volatilities observed for [Sn{OtBu}(NMe2)] (III), as discussed above, isothermal analyses at 75 °C, 100 °C and 125 °C respectively was undertaken, each temperature representative of a heated precursor source. The results are shown in Figure 3 and Table 2. As is evident from the isothermal plots (Figure 3) and evaporation rates (Table 2) for the exemplified Sn (II) oxide primary precursor (II), varies significantly with temperature with no indication of thermal decomposition. The highest volatilies were observed for III at 125 °C with a rate of mass loss of 674 μg min–1 cm–1 displayed. With an evaporation rate of 674 μg min–1 cm–1, [Sn{OtBu}(NMe2)] (III) displays a significantly greater volatility than the related homoleptic alkoxide [Sn(OtBu) –1 –1 2] (128.4 μg min cm ). At temperatures of both 75 °C and 100 °C [Sn{OtBu}(NMe2)] (III) displays evaporation rates of 472 and 58 μg min–1 cm–1 respectively. Temperature of Isothermal Rate of Mass loss (mg / min) TGA 75 °C 0.058 100 °C 0.472 125 °C 0.674 Table 2: Table showing the rate of mass loss for complex III at 75, 100 and 125 °C respectively, as determined by isothermal TGA. While the mass residues for complexes I to V are significantly lower than residues expected for Sn, SnO or SnO2, the degree of volatility appears to be higher in the tert- butoxide systems III and IV. This is typified by complex III which shows a mass loss of 674 μg min-1 (at 125 °C). Deposition with [Sn{OtBu}(NMe2)] (III): Reported ALD methods for the deposition of SnO via ALD involved the use of Sn(dmamp)2 as the first precursor with H2O 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 H2O, Chem. Mater., 2014, 26, pp.6088-6091. The resulting film layer (formed using Sn(dmamp)2) was found to exhibit crystallinity at deposition operating temperature (substrate temperatures) between 150-210 °C, with an observed decrease in the growth per cycle (GPC) as the temperature increased. Growth rates of ca.0.18 Å / cycle at 170 °C and 0.05 Å / cycle at 210 oC have been reported, with optimum deposition and superior device performance observed for thin films deposited at 210 °C. However, with associated growth rates, this precursor commercially unattractive, particularly at 210 °C. ALD experiments using [Sn{OtBu}(NMe2)] (III) as the primary precursor were undertaken at several different processing chamber operating reactor temperatures, specifically 125 °C, 150 °C and 175 °C respectively. The resultant deposited films were characterised by p-XRD, Raman spectroscopy and variable-angle spectroscopic ellipsometry. The results are shown in Figures 4 and 5. The results showed that successful deposition of SnO as achieved. Powder X-ray diffraction patterns of the SnO films deposited at temperatures between 125 °C and 175 °C (Figure 4) confirm that crystalline SnO was deposited at these temperatures. While 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 Figure 4). Basic analysis of the peak broadening within the patterns (Scherrer equation) indicate approximate crystallite sizes of ca.16.8 nm (150 °C) and 18.6 nm (175 °C) for the mean crystallite dimensions along the C-axes at each temperature. Raman spectroscopy (Figure 5) was also undertaken on crystalline films grown from [Sn(OtBu)2] primary precursors (after 400 cycles of ALD) at temperatures of 125 °C, 150 °C and 175 °C and confirms the presence of SnO deposited film and a lack of SnO2. The presence of the SnO A1g stretch can clearly be observed at 210 cm–1, consistent with SnO films previously characterised. Materials deposited at 125 °C were identified as SnO by Raman spectroscopy, however PXRD analysis indicated only a small degree of crystallinity. The thickness of the as deposited film was determined by variable-angle spectroscopic ellipsometry for a 400 cycle and are shown in table 3. Temperature of deposition Film Thickness (nm) (400 cycles) 125 °C 45nm 150 °C 46nm 175 °C 50nm Table 3: Film thickness, as determined by variable-angle spectroscopic ellipsometry, verse deposition temperature, in a typical 400 cycle ALD process. 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)2], with a growth per cycle (GPC) of approx.1Å per cycle (see table 4) Cf a GPC of 0.18 Å reported by Han et al. Figure 6, shows a plot of growth per cycle verse number of cycle, and clearly shows the consistency in growth rate per cycle expected for a true ALD process. Reactor Temperature 125 150 175 GPC (Å / cyc) 1.19 0.97 0.96 Table 4: Experimentally determined growth per cycle values as at reactor / deposition temperatures. Figure 5, shows the linear relationship between film thickness and the number of ALD cycles at both 125 and 150 °C, showing the consistency in growth rate per cycle expected for a true ALD process. Figures 6 shows a plot of growth per cycle as a function of number of cycle, for ALD processes performed at a deposition reactor chamber temperature of 125 and 150 °C respectively. Figure 7a and 7b are graphs showing the linear relationship between film thickness and number of cycles expected of a true ALD process at both 125 °C and 150 °C respectively, over 50, 100, 200 and 400 ALD cycles. For a typical ALD process, the film thickness remains unchanged and the film uniformity is consistent when saturation is achieved. Figures 8 and 8b show examples of the saturation curves determined for both precursor III and H2O. In both cases of the Sn(II) oxide precursor (III) the saturation at (150 °C) was determined to have been achieved after a ALD pulse length of approx.4-6 seconds. While this is different to comparative saturation pulse lengths of 5 seconds reported by Han et al. using Sn(dmamp)2, the growth rate using precursor (III) is significantly enhanced (1Å per cycle). In contrast, saturation of the co-reagent (H2O) used in this process was achieved after a pulse of 1 second, at 150 °C, indicating a much enhanced surface reactivity of the chem-absorbed surface species, using the Sn(II) precursor (III) comparative to Sn(dmapmp)2, where surface saturation was achieved only after a 3 second pulse. In both cases the achievement of surface saturation is consistent with a surface self-limiting process, i.e. ALD. Comparative Example – ALD without an H2O pulse A standard ALD process using [Sn(OtBu)2] as a primary precursor was undertaken at 125 , 150 and at 175 °C without the presence of an H2O pulse. PXRD and ellipsometry was used to determine that in the absence of H2O that no deposition was observed on the substrate. Spectroscopic ellipsometry indicated only a marginal <1 nm change to the surface of the SiO2, which is most likely due to a monolayer of adsorbed precursor affecting the refractive index of the substrate. This study provide evidence that the process is an ALD process. All publications mentioned in the above specification are herein incorporated by reference. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

Claims

CLAIMS 1. A method for depositing a M-containing film layer on a substrate, the method comprising: a. providing a substrate, b. providing a primary precursor of formula (I): [M(OCR1R2R3)NR4R5] (I), and c. contacting a surface of the substrate with the primary precursor, wherein: M is Sn or Ge or Pb; R1, R2, and R3 are each independently selected from H or a substituted or unsubstituted C1 to C12alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, or halide; and R4 and R5 are each independently selected from H or a substituted or unsubstituted C1to C12 alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, alkylhalide, alkylamine, alkylether, halide, silicon-based group or R4 and R5 together with the N to which they are attached form an optionally substituted 3, 4, 5 or 6 membered ring.

2. A method as claimed in claim 1, wherein at least one of R1, R2, or R3 is a substituted or unsubstituted C1to C6alkyl group.

3. A method as claimed in either claim 1 or claim 2, wherein the alkoxide (OCR1R2R3) is a chelating or a monodentate ligand.

4. A method as claimed in any one of the preceding claims, wherein the amide ligand (NR4R5) is a chelating or a monodentate ligand.

5. A method as claimed in any one of the preceding claims, wherein M is M(II).

6. A method as claimed in any one of the preceding claims, wherein M is Sn (II) or Ge (II) or Pb (II).

7. A method as claimed in any one of the preceding claims, wherein the primary precursor is of formula (II): [Sn(OCR1R2R3)NR4R5] (II).

8. A method as claimed in any one of the preceding claims, wherein R1, R2, and R3 are each independently selected from H or a substituted or unsubstituted C1 to C8 alkyl group, optionally a halo-substituted or unsubstituted C1 to C8 alkyl group.

9. A method as claimed in any one of the preceding claims, wherein R4 and R5 are independently selected from H or a substituted or unsubstituted C1 to C8 alkyl group, or silicon-based group, optionally a halo-substituted or unsubstituted C1to C8alkyl group.

10. A method as claimed in any one of the preceding claims, wherein R4 and R5 are independently selected from R6NR7R8 or R6OR7, wherein R6 either indicates the bond to N or is an alkylene group selected from a substituted or unsubstituted C1 to C8 alkylene group, optionally a halo-substituted or unsubstituted C1 to C8 alkylene group; and R7 and R8 are independently selected from a substituted or unsubstituted C1to C8alkyl group, optionally a halo-substituted or unsubstituted C1to C8alkyl group.

11. A method as claimed in any one of the preceding claims, wherein R4 and R5 are independently selected from R19 or R15SiR16R17R18, wherein R15 either indicates the bond to N or is an alkylene group selected from a substituted or unsubstituted C1 to C8 alkylene group, optionally a halo-substituted or unsubstituted C1to C8alkylene group; R16, R17and R18 are independently selected from a substituted or unsubstituted C1to C8 alkyl group, and R19 is selected from a substituted or unsubstituted C1 to C8 alkyl group.

12. A method as claimed any one of the preceding claims, wherein the primary precursor is selected from [Sn(OMe)NMe2], [Sn(OEt)NMe2], [Sn(OiPr)NMe2], [Sn(OtBu)NMe2], [Sn(OCMe2Et)NMe2], [Sn(OC(H)MeEt)NMe2], [Sn(OC(H)MeiPr)NMe ], [S t t 2 n(OC(H)MeBu)NMe2], [Sn(OCMe2Bu)NMe2], [Sn(OC(H)iPr2)NMe2], [Sn(OC(CF3)3)NMe2], [Sn(OtBu)NMe2], [Sn(OtBu)NMeEt], [Sn(OtBu)NEt2] [Sn(OtBu)NMeiPr], [Sn(OtBu)NMetBu], [Sn(OtBu)NMeCF3], [Sn(OtBu)NEtiPr], [Sn(OtBu)NEttBu], [Sn(OtBu)N(Me)CH2CH2NMe2], [Sn(OtBu)N(Et)CH2CH2NMe2], [Sn(OtBu)N(Me)CH2CH2NMeEt], [Sn(OtBu)N(Me)CH t 2CH2NEt2], [Sn(OBu)N(Et)CH2CH2NMeEt], [Sn(OtBu)N(Et)CH2CH2NEt2], [Sn(OtBu)N(Me)CH2CH2OMe], [Sn(OtBu)N(Me)CH CH OEt], t 2 2 [Sn(OBu)N(Et)CH2CH2OMe], [Sn(OtBu)N(Me)CH2CH2OtBu], [Sn(OtBu)N(Et)CH2CH2OMe], [Sn{OtBu}{HMDS}]2, [Sn{OtBu}{N(CH2SiMe2)2}]2, or mixtures thereof.

13. A method as claimed any one of the preceding claims, wherein the metal (M) containing film layer is a M (II) containing film layer.

14. A method as claimed in claim 13, wherein the M (II) containing film layer is an Sn (II) containing film layer.

15. A method as claimed in claim 14, wherein the Sn (II) containing film layer is an Sn (II) oxide film layer.

16. A method as claimed in claim 15, wherein the Sn (II) oxide film layer is a crystalline Sn (II) oxide containing film layer.

17. A method as claimed any one of the preceding claims, wherein the metal (M) containing film layer is a multicomponent metal (M) containing film layer comprising at least one additional metal (M’).

18. A method as claimed claim 17, wherein the at least one additional metal (M’) is selected from one or more of: Ti, In, Ga, Zn, Cu, Sr, Ba, Mg, W, Bi, Fe, Ni, Co, Al, Si, Sb, K, Na, Ca, Sr, Ba, Li, V and La, or any combination thereof.

19. A method as claimed in any one of the preceding claims, further comprising contacting the surface of the substrate with a secondary precursor.

20. A method as claimed claim 19, wherein the secondary precursor comprises a source of O, Se, S, Te, N, and / or P.

21. A method as claimed in either claim 19 or claim 20, wherein the secondary precursor is selected from (oxides): water, water producing material etc (e.g. monohydrate of carboxylic acids, urea monohydrate, oxygen, ozone, hydrogen peroxide, and peroxide containing materials (e.g. adducts of amines), ammonia, plasmas of H and ammonia, hydrogen sulfide, hydrogen selenide, phosphine (PH3), and / or nitrogen.

22. A method as claimed in any one of the preceding claims, wherein the substrate surface is at a temperature in the range 70 oC to 300 oC.

23. A method as claimed in any one of the preceding claims, wherein the substrate surface is at a temperature in the range 90 oC to 250 oC.

24. A method as claimed any one of the preceding claims, wherein the method is an atomic layer deposition (ALD) method.

25. An atomic layer deposition (ALD) method for depositing a film layer of a metal (M) containing film layer on a surface of a substrate, the method comprising: a. providing a substrate b. in a first dose stage, contacting a surface of the substrate with a primary precursor of formula (I) for a predetermined first dose time: [M(OCR1R2R3)NR4R5] (I),c. optionally, subsequently performing a first purge stage to separate the surface of the substrate and excess primary precursor; d. in a second dose stage, contacting a surface of the substrate with a secondary precursor for a predetermined second dose time; e. optionally, subsequently performing a second purge stage to separate the surface of the substrate and excess secondary precursor; f. optionally repeating one or more of: the first dose stage, first purge stage, second dose stage and second purge stage; wherein: M is Sn or Ge or Pb; R1, R2, and R3 are each independently selected from H or a substituted or unsubstituted C1 to C12alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, or halide; and R4 and R5 are each independently selected from H or a substituted or unsubstituted C1 to C12 alkyl group, alkoxide, aminoalcohol, aminoamide, alkoxyether, halide, silicon based group, or R4 and R5 together with the N to which they are attached form an optionally substituted 3, 4, 5 or 6 membered ring.

26. A substrate having deposited on at least one surface thereof an M-containing film layer obtainable by a method of any one of claims 1 to 25.

27. A metal oxide semiconductor device comprising at least one substrate as claimed in claim 26.

28. A Sn(II) compound of formula [Sn{OtBu}(NMe2)].

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