WO2011124913A1

WO2011124913A1 - Process for preparing a device

Info

Publication number: WO2011124913A1
Application number: PCT/GB2011/050679
Authority: WO
Inventors: Matthew Suchomel; Matthew Rosseinsky; Hongjun Niu; Paul Chalker; Lei Yan
Original assignee: The University Of Liverpool
Priority date: 2010-04-07
Filing date: 2011-04-06
Publication date: 2011-10-13
Also published as: GB201005741D0

Abstract

The present invention relates to a process for preparing a functional device which comprises a substrate and an element composed of a strontium-hafnium- titanium oxide or strontium- zirconium- titanium oxide. The process involves exposing the substrate to discrete volatalised amounts of a strontium precursor, a hatnium or zirconium precursor an a titaniuim precursor in sequential steps.

Description

PROCESS FOR PREPARING A DEVICE

The present invention relates to a process for preparing a functional device which comprises a substrate and an element composed of a strontium-hafnium-titanium oxide or strontium-zirconium-titanium oxide.

The silicon dioxide (Si0₂) gate layer in a MOS (metal-oxide-semiconductor) field effect transistor device may be substituted by an oxide material with a higher dielectric constant (high-k). However there are few oxide materials which satisfy the requirements of dielectric constant, thermal stability and band gap, whilst providing an interface suitable for integration by silicon processing (see J Robertson, J. Appl. Phys. 104, 7 (2008)). These oxides include Zr0₂ (see M N S Miyazaki et al, Microelectronic Engineering 59, 6 (2001) and R N Wen-Jie Qi et al, Appl. Phys. Lett. 77, 3 (2000)), Hf0₂ (see T M R C Smith et al, Adv. Mater. Opt. Electron. 10, 10 (2000); E C E P Gusev et al, Microelectronic Engineering 59, 9 (2001); and R H D C Gilmer et al, Appl. Phys. Lett. 81, 3 (2002)), A1₂0₃ (see E C M Copel et al, Appl. Phys. Lett. 78, 3 (2001) and C P E Ghiraldelli et al, Thin Solid Films 517, 3 (2008)) and LaA10₃ (see S K Seung-Gu Lim et al, J. Appl. Phys. 91, 6 (2002); H B L L Yan, et al, Appl. Phys. A 77, 4 (2003); and H L Wenfeng Xiang et al, J. Appl. Phys. 93, 4 (2003)). SrHf0₃ is attracting increasing interest as a candidate for a high-k material (B M C Rossel et al, Appl. Phys. Lett. 89, 3 (2006); G K G. Lupina et al, Appl. Phys. Lett. 93, 3 (2008) and C R M Sousa et al, J. Appl. Phys. 102, 6 (2007)). SrTi0₃ and Sr_1-xBa_xTi0₃ are attractive candidates for a gate dielectric because of their large permittivity.

Thus it is generally desirable to identify techniques for growing specific mixed oxides such as strontium-titanium mixed oxides on a substrate for use as a functional device.

The present invention seeks to improve the preparation of a strontium-hafnium- titanium or strontium-zirconium-titanium oxide-based functional device by exploiting saturating surface reactions which control the growth of oxide films with improved properties such as conformality.

Viewed from a first aspect the present invention provides a process for preparing a functional device comprising a substrate and an element composed of a mixed metal oxide of formula SrMi_-xTi_x0₃ (wherein x is 0<x<l and M is Hf or Zr), wherein the process comprises: exposing discrete volatilised amounts of a strontium precursor, of a hafnium or zirconium precursor and of a titanium precursor to the substrate in sequential exposure steps in a contained environment. Preferably each discrete volatilised amount is fed to the contained environment in a pulse. The pulse length may be in the range 1ms to 30s.

The process may further comprise: feeding an oxidising agent to the contained environment during one or more (preferably each) of the exposure steps or in one or more of the intervals between the exposure steps. The oxidising agent may be fed into the contained environment continuously or in a pulse during the exposure step.

Preferably the process further comprises: feeding the oxidising agent into the contained environment in a pulse during each exposure step.

The oxidising agent may be selected from the group consisting of oxygen (eg oxygen plasma), water vapor, hydrogen peroxide (or an aqueous solution thereof), ozone, an oxide of nitrogen (such as N₂0, NO or N0₂), a halide-oxygen compound (for example chlorine dioxide or perchloric acid), a peracid (for example perbenzoic acid or peracetic acid), an alcohol (such as methanol or ethanol) and radicals (such as oxygen radicals and hydroxyl radicals).

A preferred oxidising agent is oxygen plasma.

The process may further comprise: purging the contained environment during one or more (preferably each) of the exposure steps or in one or more of the intervals between the exposure steps. Purging may be carried out by an inert gas flow. The inert gas flow may be fed into the contained environment in a pulse during the exposure step.

Preferably the process further comprises: purging the contained environment with an inert gas flow in a pulse during each exposure step.

Preferably the sequential exposure steps are cyclical. The number and order of each of the steps of exposing discrete volatilised amounts of a strontium precursor, a hafnium or zirconium precursor and a titanium precursor to the substrate in the sequential exposure steps may be empirically determined to achieve a desired stoichiometry and incorporation rate. The number of cycles is determined generally by the desired oxide thickness. Typically the sequential exposure steps are cycled 2 to 100 times.

Preferably the process of the invention comprises a cycle of sequential exposure steps (A), (B) and (C), wherein

step (A) comprises: feeding the discrete volatilised amount of strontium precursor into the contained environment and purging the strontium precursor from the contained environment, step (B) comprises: feeding the discrete volatilised amount of hafnium or zirconium precursor into the contained environment and purging the hafnium or zirconium precursor from the contained environment,

step (C) comprises: feeding the discrete volatilised amount of a titanium precursor into the contained environment and purging the titanium precursor from the contained environment.

Particularly preferably step (A) comprises: feeding the discrete volatilised amount of strontium precursor into the contained environment, purging the strontium precursor from the contained environment and feeding an oxidising agent into the contained environment and purging the contained environment.

Particularly preferably step (B) comprises: feeding the discrete volatilised amount of hafnium or zirconium precursor into the contained environment, purging the hafnium or zirconium precursor from the contained environment, feeding an oxidising agent into the contained environment and purging the contained environment.

Particularly preferably step (C) comprises: feeding the discrete volatilised amount of a titanium precursor into the contained environment, purging the titanium precursor from the contained environment and feeding an oxidising agent into the contained environment and purging the contained environment.

Each of steps (A), (B) and (C) may be independently cyclical. Preferably the ratio of the number of cycles of step (B) to the number of cycles of step (C) is in the range 3:1 to 1 :3 (eg 3:1, 2:1, 1:1, 1 :2 or 1 :3). Particularly preferably the ratio of the number of cycles of step (B) to the number of cycles of step (C) is in the range 1:1 to 1 :3.

Alternatively preferably the process of the invention comprises a cycle of sequential exposure steps (Α'), (Β'), (A") and (C), wherein

each of steps (Α') and (A") comprises: feeding the discrete volatilised amount of strontium precursor into the contained environment, purging the strontium precursor from the contained environment, feeding an oxidising agent into the contained environment and purging the contained environment,

step (Β') comprises: feeding the discrete volatilised amount of hafnium or zirconium precursor into the contained environment, purging the hafnium or zirconium precursor from the contained environment, feeding an oxidising agent into the contained environment and purging the contained environment,

step (C) comprises: feeding the discrete volatilised amount of a titanium precursor into the contained environment, purging the titanium precursor from the contained environment, feeding an oxidising agent into the contained environment and purging the contained environment.

Each of steps (Α'), (Β'), (A") and (C) may be independently cyclical. Preferably the ratio of the number of cycles of step (Α') to the number of cycles of step (Β') is 3:1.

Preferably the ratio of the number of cycles of step (A") to the number of cycles of step (C) is 3: 1.

Preferably the ratio of the number of cycles of step (Β') to the number of cycles of step (C) is in the range 3 : 1 to 1 :3 (eg 3 : 1 , 2: 1 , 1 : 1 , 1 :2 or 1 :3). Particularly preferably the ratio of the number of cycles of step (Β') to the number of cycles of step (C) is in the range 1 :1 to 1 :3.

The contained environment is typically a reaction chamber.

Each precursor may be a volatile liquid or solid, a solid dissolvable or suspendable in a solvent medium for flash vaporization or a sublimable solid. Volatilsation of the precursor may be heat-assisted or photo-assisted. Each discrete volatilised amount may be fed into the contained environment in the gaseous phase (eg as a vapour). The contained environment may be at a temperature in the range 100 to 700°C, preferably 150 to 500°C.

The process may further comprise: pre-treating (eg pre-heating) the substrate.

The process may further comprise: a post-treatment step. The post-treatment step may be a post-annealing (eg rapid thermal post-annealing) step, oxidizing step or reducing step. The step of post-annealing is typically carried out at a temperature in excess of the temperature at which the sequential steps are carried out in the contained environment. For example, post-annealing may be carried out at a temperature in the range 500°C to 900°C for an annealing period of a few seconds to 60 minutes in an air flow.

Each precursor may be a complex featuring one or more bonds between the metal and each of one or more organic ligands (eg coordination bonds between the metal and a heteroatom such as oxygen or nitrogen or bonds between the metal and carbon). The precursor may be a metal organic or an organometallic complex.

The titanium precursor may be a titanium (III) or titanium (IV) precursor. Preferably the titanium precursor is a titanium halide, titanium β-diketonate, titanium alkoxide (such as wo-propoxide or tert-butoxide), dialkylamino titanium complex, alkylamino titanium complex, silylamido titanium complex, cyclopentadienyl titanium complex, titanium dialkyldithiocarbamate or titanium nitrate. The titanium of the titanium precursor may have one or more (for example four) organic ligands which may be the same or different selected from the group of organic ligands defined by formulae (I) to (IV) (preferably one of formulae (I) to (IV)) as follows:

(I) [R¹C(0)-CH-C(0)R²]^"

(wherein each of 1 2

R and R which may be the same or different is an optionally fluorinated, linear or branched C_1-12 alkyl group);

(II) [X(R³)_w(R⁴)_y(R⁵)z]

(wherein X is a heteroatom;

R³ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a Si(R⁶)₂ or Si(R⁶)₃ group;

R⁴is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a Si(R⁷)₂ or Si(R⁷)₃ group;

R⁵ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a Si(R⁸)₂ or Si(R⁸)₃ group;

each of R , R and R is independently H or a linear or branched C_1-12 alkyl, C_6-12 aryl, C_3-i₂ allyl or C_3-12 vinyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups;

w is an integer of 1 or 2;

y is an integer of 0 or 1 ; and

z is an integer of 0 or 1);

(III) [S₂CN(R⁹)(R¹⁰)]

(wherein each of R⁹ and R¹⁰ is independently an optionally fluorinated, linear or branched C_\. n alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups);

(IV) [Cp]

(wherein Cp denotes a single or fused cyclopentadiene moiety optionally ring-substituted partially or fully by one or more of the group consisting of an optionally substituted, acyclic or cyclic, linear or branched alkyl, alkenyl, aryl, alkylaryl, aralkyl or alkoxy group or a thio, amino, cyano or silyl group).

Preferably the titanium of the titanium precursor has four organic ligands selected from the group of organic ligands defined by formulae (I) to (IV) (preferably one of formulae

(I) to (IV)).

Preferably the ligand of formula (I) is an optionally methylated and/or optionally fluorinated (eg optionally tri- or hexa-fluorinated) acetylacetonato, heptanedionato or octanedionato ligand. For example, the ligand of formula (I) may be a 1,1,1-trifluoropentane- 2,4-dionato, l,l,l,5,5,5-hexafluoropentane-2,4-dionato or 2,2,6,6-tetramethyl-3,5- heptanedionato ligand.

Preferably either or both of R¹ and R² are trifluorinated or hexafluorinated.

Preferably R¹ is a C_1-6 perfluoroalkyl. Preferably R² is a Ci_-6 perfluoroalkyl.

Preferably X is O. Particularly preferably X is O, y is 0, z is 0, w is 1 and R³ is an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups. For example, the ligand of formula

(II) may be a hexafluoroisopropoxy, 2-dimethylaminoethanolate, 2-methoxyethanolate or 1 - methoxy-2-methyl-2-propanolate ligand.

Preferably X is N. Particularly preferably X is N, y is 1, w is 1, z is 1 and each of R³, R⁴ and R⁵ is independently H, an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups.

Alternatively particularly preferably, X is N, y is 1 , w is l, z is l, R³ is Si(R⁶)₂ or Si(R⁶)₃, R⁴ is Si(R⁷)₂ or Si(R⁷)₃ and R⁵ is Si(R⁸)₂ or Si(R⁸)₃, wherein each of R⁶, R⁷ and R⁸ is independently methyl, propyl or butyl.

Preferably each of R³ _, R⁴ and R⁵ is independently methyl, ethyl, propyl, butyl or pentyl, particularly preferably methyl, propyl or butyl, more preferably «-butyl, tert-butyl, wo-propyl or ethyl.

Preferably the titanium of the titanium precursor has two ligands of formula (IV). The cyclopentadiene moieties of the two ligands of formula (IV) may be bridged. The bridge may be a substituted or unsubstituted C_1-6-alkylene group which is optionally interrupted by a heteroatom (such as O, Si, N, P, Se or S). Preferably the ligand of formula (IV) is a cyclopentadienyl, indenyl, fluorenyl, pentamethylcyclopentadienyl, iert-butylcyclopentadienyl or trusopropylcyclopentadienyl ligand.

Preferably in a titanium precursor the (or each) ligand of formula (IV) is a

cyclopentadienyl ligand of formula (V)

[C₅(Rⁿ)_mH₅__m] (V)

(wherein m is an integer in the range 0 to 5 and

each R¹¹ which may be the same or different is selected from the group consisting of a C].i₂ alkyl, C1.12 alkylamino, C_1-12 dialkylamino, C_1-12 alkoxy, C_3-10 cycloalkyl, C₂.₁₂ alkenyl, C_7-12 aralkyl, C_7-12 alkylaryl, C_6-12 aryl, C_5-12 heteroaryl, C_1-10 perfluoroalkyl, silyl, alkylsilyl, perfluoroalkylsilyl, triarylsilyl and alkylsilylsilyl group).

Preferably the (or each) R¹¹ group is methyl, ethyl, propyl (eg isopropyl) or butyl (eg tert-butyl).

The titanium precursor may be Ti(OC₂H₅)₄, Ti(OⁱPr)₄, Ti(O^lBu)₄, Ti(OⁿBu)₄ or Ti(OCH₂(C₂H₅)CHC₄H₉) .

The titanium precursor may be titanium nitrate.

The titanium precursor may be iiz^'(/^'50-propoxy) )w(2,2,6,6-tetramethyl-3,5- heptanedionato) titanium or trw(2,2,6,6,-tetramethyl-3,5-heptanedionato) titanium or adducts or hydrates thereof.

The titanium precursor may be tetra&w(diethylamido) titanium,

tetra&zs(dimethylamido) titanium, tetra£« ethylmethylamido) titanium,

tetraAw(isopropylmethylamido) titanium, ¾z^*5(diethylamido)&z5^,(dimethylamido) titanium, >zs(cyclopentadienyl)Ms(dimethylamido) titanium, trz^',y(dimethylamido)(N,N,N'- trimethylethyldiamido) titanium or tert-butylzrw(dimethylamido) titanium or adducts or hydrates thereof.

The titanium precursor may be titanium (n⁵-C₅H₅)₂, titanium (r|⁵-C₅H₅)(ri⁷-C₇H₇), (η⁵- C₅H₅) titanium Z₂ (wherein Z is alkyl (eg methyl), benzyl or carbonyl),

^(tertbutylcyclopentadienyl) titanium dichloride, bw(pentamethylcyclopentadienyl) titanium dichloride or (C₅H₅)₂ titanium (CO)₂ or adducts or hydrates thereof.

The titanium precursor may be a titaniumdialkyldithiocarbamate.

The titanium precursor may be TiCl₄, TiCl₃, TiBr₃, Til₄ or Til₃. The hafnium precursor may be a hafnium (IV) precursor. Preferably the hafnium precursor is a hafnium β-diketonate, hafnium alkoxide, dialkylamino hafnium complex, alkylamino hafnium complex or cyclopentadienyl hafnium complex.

The hafnium of the hafnium precursor may have one or more (for example four) organic ligands which may be the same or different selected from the group of organic ligands defined by formulae (VI) to (VIII) (preferably one of formulae (VI) to (VIII)) as follows:

(VI) [R¹²C(0)-CH-C(0)R¹³]-

(wherein each of R¹² and R¹³ which may be the same or different is an optionally fluorinated, linear or branched C_1-12 alkyl group);

(VII) [X(R¹⁴)_w(R¹⁵)_y(R¹⁶)_z]

(wherein X is a heteroatom;

R¹⁴ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR )₂ or (SiR¹⁷)₃ group;

R¹⁵ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR )₂ or (SiR¹⁸)₃ group;

R¹⁶ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR¹⁹)₂ or (SiR¹⁹)₃ group;

each of R¹⁷, R¹⁸ and R¹⁹ is independently H or a linear or branched C_1-12 alkyl, C _-12 aryl, C_3-12 allyl or C_3-12 vinyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups;

w is an integer of 1 or 2;

y is an integer of 0 or 1 ; and

z is an integer of 0 or 1);

(VIII) [Cp]

Preferably the hafnium of the hafnium precursor has four organic ligands selected from the group of organic ligands defined by formulae (VI) to (VIII) (preferably one of formulae (VI) to (VIII)).

Preferably the ligand of formula (VI) is an optionally methylated and/or optionally fluorinated (eg optionally tri- or hexa-fluorinated) acetylacetonato, heptanedionato or octanedionato ligand. For example, the ligand of formula (VI) may be a 1,1,1 - trifluoropentane-2,4-dionato, l,l,l,5,5,5-hexafluoropentane-2,4-dionato or 2,2,6,6- tetramethyl-3,5-heptanedionato ligand.

Preferably either or both of R and R are trifluorinated or hexafluorinated.

Preferably R¹² is a C_1-6perfluoroalkyl. Preferably R¹³ is a C_1-6 perfluoroalkyl.

Preferably X is O. Particularly preferably X is O, y is 0, w is 1, z is 0 and R¹⁴ is an optionally fluorinated, linear or branched CM₂ alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups. For example, the ligand of formula (VII) may be an isopropoxy, 2-dimethylaminoethanolate, 2-methoxyethanolate or 1-methoxy- 2-methyl-2-propanolate ligand.

Preferably X is N. Particularly preferably X is N, y is 1, w is 1, z is 1 and each of R¹⁴, R¹⁵ and R¹⁶ is independently H or an optionally fluorinated, linear or branched Ci_-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups.

Preferably each of R¹⁴ R¹⁵ and R¹⁶ is independently methyl, ethyl, propyl, butyl or pentyl, particularly preferably methyl, propyl or butyl, more preferably «-butyl, tert-butyl, wopropyl or ethyl.

The hafnium of the hafnium precursor may have one or two ligands of formula (VIII).

Preferably the hafnium of the hafnium precursor has two ligands of formula (VIII). The cyclopentadiene moieties of the two ligands of formula (VIII) may be bridged. The bridge may be a substituted or unsubstituted C_1-6-alkylene group which is optionally interrupted by a heteroatom (such as O, Si, N, P, Se or S). Preferably the ligand of formula (VIII) is a cyclopentadienyl, indenyl, fluorenyl, methylcyclopentadienyl, pentamethylcyclopentadienyl or triisopropylcyclopentadienyl ligand.

Preferably in a hafnium precursor the (or each) ligand of formula (VIII) is a cyclopentadienyl ligand of formula (IX)

[C₅(R²⁰)_mH₅-_m] (IX)

(wherein m is an integer in the range 0 to 5 and

each R which may be the same or different is selected from the group consisting of a C_1-12 alkyl, C_1-12 alkylamino, C_1-12 dialkylamino, C_1-12 alkoxy, C_3-10 cycloalkyl, C_2-12 alkenyl, C_7-12 aralkyl, C_7-12 alkylaryl, C_6-12 aryl, C_5-12 heteroaryl, C_1-10 perfluoroalkyl, silyl, alkylsilyl, perfluoroalkylsilyl, triarylsilyl and alkylsilylsilyl group).

Preferably the (or each) R group is methyl, ethyl, propyl (eg z^'sopropyl) or butyl (eg tert-butyl), particularly preferably methyl.

The hafnium precursor may be i /(/₁s^,opropoxy)bi5(2,2,6,6-tetramethyl-3,5- heptanedionato) hafnium.

The hafnium precursor may be &zs(methylcyclopentadienyl) dimethylhafnium,

Z)w(methylcyclopentadienyl) methoxymethylhafnium or methylcyclopentadienyl hafnium trz^'s(dimethylamide) or adducts or hydrates thereof.

The hafnium precursor may be tetrafo^'s(dimethylamido) hafnium,

tetra£/s(diethylamido) hafnium or tetra&z ethylmethylamido) hafnium or adducts or hydrates thereof.

The hafnium precursor may be hafnium (IV) zso-propoxide, hafnium (IV) tert- butoxide, tetrafo 2-methyl-2-methoxypropoxy) hafnium, 6zXz^'sopropoxy)0zX2-methyl-2- methoxypropoxy) hafnium or 0z5^,(tert-butoxy)0z ^,(2-methyl-2-methoxypropoxy) hafnium or adducts or hydrates thereof.

The hafnium precursor may be HfCl₄.

The zirconium precursor may be a zirconium (IV) precursor. Preferably the zirconium precursor is a zirconium β-diketonate, zirconium alkoxide, dialkylamino zirconium complex, alkylamino zirconium complex or cyclopentadienyl zirconium complex. The zirconium of the zirconium precursor may have one or more (for example four) organic ligands which may be the same or different selected from the group of organic ligands defined by formulae (X) to (XII) (preferably one of formulae (X) to (XII)) as follows:

(X) [R²¹C(0)-CH-C(0)R²²]-

(wherein each of R²¹ and R²² which may be the same or different is an optionally fluorinated, linear or branched C_1-12 alkyl group);

(XI) [X(R²³)_w(R²⁴)_y(R²⁵)_z]

(wherein X is a heteroatom;

R²³ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR²⁶)₂ or (SiR²⁶)₃ group;

R²⁴ is H or an optionally fluorinated, linear or branched CM₂ alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR ⁷)₂ or (SiR²⁷)₃ group;

R²⁵ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR²⁸)₂ or (SiR²⁸)₃ group;

each of R²⁶, R²⁷ and R²⁸ is independently H or a linear or branched C_1-12 alkyl, C_6-12 aryl, C_3-i₂ allyl or C_3-12 vinyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups;

w is an integer of 1 or 2;

y is an integer of 0 or 1 ; and

z is an integer of 0 or 1);

(XII) [Cp]

(wherein Cp denotes a single or fused cyclopentadiene moiety optionally ring-substituted partially or fully by one or more of the group consisting of an optionally substituted, acyclic or cyclic, linear or branched alkyl, alkenyl, aryl, alkylaryl, aralkyl or alkoxy group or a thio, amino, cyano or silyl group). Preferably the zirconium of the zirconium precursor has four organic ligands selected from the group of organic ligands defined by formulae (X) to (XII) (preferably one of formulae (X) to (XII)).

Preferably the ligand of formula (X) is an optionally methylated and/or optionally fluorinated (eg optionally tri- or hexa-fluorinated) acetylacetonato, heptanedionato or octanedionato ligand. For example, the ligand of formula (X) may be a 1,1,1 - trifluoropentane-2,4-dionato, l,l,l,5,5,5-hexafluoropentane-2,4-dionato or 2,2,6,6- tetramethyl-3,5-heptanedionato ligand.

Preferably either or both of R²¹ and R²² are trifluorinated or hexafluorinated.

Preferably R²¹ is a C_1- perfluoroalkyl. Preferably R²² is a Ci_-6 perfluoroalkyl.

Preferably X is O. Particularly preferably X is O, z is 0, y is 0, w is 1 and R²³ is an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups. For example, the ligand of formula

(XI) may be a isopropoxy, 2-dimethylaminoethanolate, 2-methoxyethanolate or l-methoxy-2- methyl-2-propanolate ligand.

Preferably X is N. Particularly preferably X is N, y is 1, w is 1, z is 1 and each of R²³ _, R²⁴ and R²⁵ is independently H or an optionally fluorinated, linear or branched _\. alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups.

Preferably each of R²³ _; R²⁴ and R²⁵ is independently methyl, ethyl, propyl, butyl or pentyl, particularly preferably methyl, propyl or butyl, more preferably «-butyl, tert-butyl, z^'sopropyl or ethyl.

The zirconium of the zirconium precursor may have one or two ligands of formula

(XII) .

Preferably the zirconium of the zirconium precursor has two ligands of formula (XII). The cyclopentadiene moieties of the two ligands of formula (XII) may be bridged. The bridge may be a substituted or unsubstituted C_1-6-alkylene group which is optionally interrupted by a heteroatom (such as O, Si, N, P, Se or S).

Preferably the ligand of formula (XII) is a cyclopentadienyl, indenyl, fluorenyl, pentamethylcyclopentadienyl or triisopropylcyclopentadienyl ligand. Preferably in a zirconium precursor the (or each) ligand of formula (XII) is a cyclopentadienyl ligand of formula (XIII)

[C₅(R²⁹)_mH₅__m] (XIII)

(wherein m is an integer in the range 0 to 5 and

each R²⁹ which may be the same or different is selected from the group consisting of a C_1-12 alkyl, C_1-12 alkylamino, C_1-12 dialkylamino, C_1-12 alkoxy, C_3-10 cycloalkyl, C_2-12 alkenyl, C_7-12 aralkyl, C_7-12 alkylaryl, C_6-12 aryl, C_5-12 heteroaryl, C_1-10 perfluoroalkyl, silyl, alkylsilyl, perfluoroalkylsilyl, triarylsilyl and alkylsilylsilyl group).

The zirconium precursor may be c (z5opropoxy)0 5^,(2,2,6,6-tetramethyl-3,5- heptanedionato) zirconium.

The zirconium precursor may be >zs(methylcyclopentadienyl) dimethylzirconium, 6w(methylcyclopentadienyl) methoxymethylzirconium or methylcyclopentadienyl zirconium tm(dimethylamide) or adducts or hydrates thereof.

The zirconium precursor may be tetrafo dimethylamido) zirconium,

te/ra&z diethylamido) zirconium or tetra&w(ethylmethylamido) zirconium or adducts or hydrates thereof.

The zirconium precursor may be zirconium (IV) wo-propoxide, zirconium (IV) tert- butoxide, tetra£zs(2-methyl-2-methoxypropoxy) zirconium, 0w( jO-propoxy)6w(2-methyl-2- methoxypropoxy) zirconium or ^z5^,(tert-butoxy)&w(2-methyl-2-methoxypropoxy) zirconium or adducts or hydrates thereof.

The zirconium precursor may be ZrCl₄ or ZrBr₄.

The strontium precursor may be a strontium (II) precursor. Preferably the strontium precursor is a strontium halide, strontium β-diketonate, strontium alkoxide (such as iso- propoxide or tert-butoxide), dialkylamino strontium complex, alkylamino strontium complex, silylamido strontium complex, cyclopentadienyl strontium complex or strontium nitrate.

The strontium of the strontium precursor may have one or more (for example four) organic ligands which may be the same or different selected from the group of organic ligands defined by formulae (XIV) to (XVI) (preferably one of formulae (XIV) to (XVI)) as follows: (XIV) [R³⁰C(O)-CH-C(O)R³¹]^"

30 31

(wherein each of R and R which may be the same or different is an optionally fluorinated, linear or branched C_1-12 alkyl group);

(XV) [X(R³²)_w(R³³)_y(R³⁴)_z]

(wherein X is a heteroatom;

R³² is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR³⁵)₂ or (SiR³⁵)₃ group;

R^JJ is H or an optionally fluorinated, linear or branched Ci_-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR³⁶)₂ or (SiR³⁶)₃ group;

R³⁴ is H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups or a (SiR³⁷)₂ or (SiR³⁷)₃ group;

each of R , R and R is independently H or a linear or branched C_1-12 alkyl, C_6-12 aryl, C_3-12 allyl or C_3-i₂ vinyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups;

w is an integer of 1 or 2;

z is an integer of 0 or 1 ; and

y is an integer of 0 or 1);

(XVI) [Cp]

Preferably the strontium of the strontium precursor has two organic ligands selected from the group of organic ligands defined by formulae (XIV) to (XVI) (preferably one of formulae (XIV) to (XVI)).

Preferably the ligand of formula (XIV) is an optionally methylated and/or optionally fluorinated (eg optionally tri- or hexa-fluorinated) acetylacetonato, heptanedionato or octanedionato ligand. For example, the ligand of formula (XIV) may be a 1,1,1,5,5,5- hexafluoropentane-2,4-dionato, 6,6,7,7,8, 8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato or 2,2,6,6-tetramethyl-3 ,5 -heptanedionato ligand.

Preferably either or both of R³⁰ and R³¹ are trifluorinated or hexafluorinated.

Preferably R³⁰ is a C^perfluoroalkyl. Preferably R³¹ is a C_1-6perfluoroalkyl.

Preferably X is O. Particularly preferably X is O, y is 0, z is 0, w is 1 and R is an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups. For example, the ligand of formula

(XV) may be a hexafluorowopropoxy, 2-dimethylaminoethanolate, 2-methoxyethanolate or 1 -methoxy-2-methyl-2-propanolate ligand.

Preferably X is N. Particularly preferably X is N, y is 1, w is 1, z is 1 and each of R R³³ and R³⁴ is independently H or an optionally fluorinated, linear or branched C_1-12 alkyl group optionally substituted by one or more alkoxy, amino, alkylamino or dialkylamino groups.

Preferably each of R³² _; R³³ and R³⁴ is independently methyl, ethyl, propyl, butyl or pentyl, particularly preferably methyl, propyl or butyl, more preferably «-butyl, fert-butyl, wopropyl or ethyl.

Preferably the ligand of formula (XVI) is a cyclopentadienyl, indenyl, fluorenyl, pentamethylcyclopentadienyl or triisopropylcyclopentadienyl ligand, particularly preferably a cyclopentadienyl or indenyl ligand.

The strontium of the strontium precursor may have one or two ligands of formula

(XVI) . Preferably the strontium of the strontium precursor has two ligands of formula (XVI). The cyclopentadiene moieties of the two ligands of formula (XVI) may be bridged. The bridge may be a substituted or unsubstituted C_1-6-alkylene group which is optionally interrupted by a heteroatom (such as O, Si, N, P, Se or S). The cyclopentadiene moieties of the two ligands of formula (XVI) may be the same or different. Preferably each of the cyclopentadiene moieties of the two ligands of formula (XVI) is cyclopentadienyl or indenyl. Preferably the cyclopentadiene moieties of the two ligands of formula (XVI) are

cyclopentadienyl and indenyl respectively.

Preferably in a strontium precursor the (or each) ligand of formula (XVI) is a cyclopentadienyl ligand of formula (XVII) [C₅(R^J*)_mH₅-_m] (XVII)

(wherein m is an integer in the range 0 to 5 and

Preferably the (or each) R group is methyl, ethyl, propyl (eg z^'sopropyl) or butyl (eg tert-butyl). Particularly preferably each R group is methyl.

The strontium precursor may be strontium nitrate.

The strontium precursor may be 0w(l,l,l-trifluoropentane-2,4-dionato) strontium, bis(\, 1 , 1 ,5,5,5-hexafluoropentane-2,4-dionato) strontium, 6w(2,2,6,6-tetramethyl-3,5- heptanedionato) strontium or 6/5(6,6,7,7,8, 8, 8-heptafluoro-2,2-dimethyl-3,5-octanedionato) strontium or adducts or hydrates thereof.

The strontium precursor may be strontium (C5(CH₃)₅)₂, bis((tert- Bu)₃cyclopentadienyl) strontium or 0w(n-propyltetramethylcyclopentadienyl) strontium or adducts or hydrates thereof.

The strontium precursor may be bw[N,N,N',N',N"-pentamethyldiethylenetriamine] strontium, [tetramethyl-n-propylcyclopentadienyl] [Ν,Ν,Ν',Ν',Ν"- pentamethyldiethylenetriamine] strontium or [0/sopropyl][indenyl] strontium or adducts or hydrates thereof.

In addition to one or more of the ligands mentioned hereinbefore, the metal in a precursor may have one or more additional ligands selected from anionic ligands, neutral monodentate or multidentate adduct ligands and Lewis base ligands. The metal may have 1 to 4 (eg two) additional ligands. For example, the (or each) additional ligand may be a β- diketonate (or a sulfur or nitrogen analogue thereof), halide, amide, alkoxide, carboxylate, substituted or unsubstituted C_1-6-alkyl group (which is optionally interrupted by a heteroatom such as O, Si, N, P, Se or S), benzyl, carbonyl, aliphatic ether, thioether, polyether, C_1-12 alkylamino, C_3-10 cycloalkyl, C_2-12 alkenyl, C_7-12 aralkyl, C_7-j₂ alkylaryl, C_6-12 aryl, C_5-12 heteroaryl, C_1-10 perfluoroalkyl, silyl, alkylsilyl, perfluoroalkylsilyl, triarylsilyl,

alkylsilylsilyl, glyme (such as dimethoxyethane, diglyme, triglyme or tetraglyme), cycloalkenyl, cyclodienyl, cyclooctatetraenyl, alkynyl, substituted alkynyl, diamine, triamine, tetraamine, phosphinyl, carbonyl, dialkyl sulfide, vinyltrimethylsilane, allyltrimethylsilane, arylamine, primary amine, secondary amine, tertiary amine, polyamine, cyclic ether or pyridine aryl group. The additional ligand may be pyridine, toluene, tetrahydrofuran, bipyridine, a nitrogen-containing multidentate ligand (such as Ν,Ν,Ν',Ν',Ν"- pentamethyldiethylenetriamine (PMDETA) or Ν,Ν,Ν',Ν'-tetramethylethylenediamine) or a Schiff base. The neutral monodentate or multidentate adduct ligand may derived from a solvent (eg tetrahydrofuran).

Preferred adduct ligands are dimethoxyethane, tetrahydrofuran, tetrahydropyran, diethylether, dimethoxymethane, diethoxymethane, dipropoxymethane, 1 ,2-dimethoxyethane, 1 ,2-diethoxyethane, 1 ,2-dipropoxyethane, 1,3-dimethoxypropane, 1,3-dipropoxypropane, 1,2- dimethoxybenzene, 1 ,2-diethoxybenzene and 1,2-dipropoxybenzene.

The precursor may be dissolved, dispersed or suspended in a solvent such as an aliphatic hydrocarbon or aromatic hydrocarbon (eg xylene, toluene, benzene, 1 ,4- tertbutyltoluene, 1,3-diisopropylbenzene, tetralin or dimethyltetralin) optionally together with a stabilizing agent (eg a Lewis-base ligand), an amine (eg octylamine, NN- dimethyldodecylamine or dimethylaminopropylamine), an aliphatic or cyclic ether (eg tetrahydrofuran), a glyme (eg diglyme, triglyme, tetraglyme), a C_3-12 alkane (eg hexane, octane, decane, heptane or nonane) and a tertiary amine.

Unless specified otherwise, the term alkyl used herein may be a linear or branched, acyclic or cyclic, C_1-12 alkyl and includes methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, pentyl, wopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. Preferably each group C ₁₂ alkyl mentioned herein is preferably Ci_-8 alkyl, particularly preferably Ci_-6 alkyl.

Unless specified otherwise, the term aryl used herein may be a substituted, monocyclic or polycyclic C_6-12 aryl and includes optionally substituted phenyl, naphthyl, xylene and phenylethane.

In a preferred embodiment, M is Hf.

In a preferred embodiment, M is Zr.

Preferably 0.01<x<0.99, particularly preferably 0.05<x<0.95, more particularly preferably 0.2<x≤0.8, yet more particularly preferably 0.3<x<0.7, even more preferably 0.4<x<0.6, yet even more preferably 0.45<x<0.55. In a preferred embodiment, x is about 0.5.

In a preferred embodiment, the mixed metal oxide (in the form of a bulk material) exhibits a dielectric constant (typically at 10kHz) of greater than 35, preferably a dielectric constant in the range 36 to 200, particularly preferably in the range 45 to 125, more preferably in the range 60 to 100.

In a preferred embodiment, the mixed metal oxide (in the form of a bulk material) exhibits a band gap of 3.1 OeV or more, preferably a band gap in the range 3.10 to 6.1 OeV, particularly preferably in the range 3.24 to 3.80eV, more preferably in the range 3.40 to 3.50eV.

The functional device may be an electrical, electronic, magnetic, mechanical, optical or thermal device. For example, the element may be a gate dielectric in a field effect transistor device (eg a MOSFET device) or in a high frequency dielectric application. For example, the element may be a capacitor (eg in a memory device such as DRAM or RAM), a voltage regulator, an electronic signal filter, a microelectromechanical device, a sensor, an actuator, a display (eg a TFT or OLED), a solar cell, a charged couple device, a particle and radiation detector, a printed circuit board, a CMOS device, an optical fibre or an optical waveguide. For example, the element may be an optical fibre or in an optical waveguide.

The mixed metal oxide may be present in the element in a multiphase composition. Preferably the mixed metal oxide is substantially monophasic.

The substrate may be a semiconductor such as an oxide semiconductor, an organic semiconductor, a III-V semiconductor (eg GaAs, InGaAs, GaN or InGaN), a II- VI semiconductor (eg ZnSe or CdTe) or a transparent conducting oxide (eg Al:ZnO, indium tin oxide or fluoride-doped tin oxide).

The substrate may be (or contain) silicon, doped silicon, silicon nitride or silicon dioxide. Typically the substrate is silicon.

The substrate may be composed of material selected from the group consisting of germanium, silicon, silicon dioxide, doped silicon, GaAs, InGaAs, GaN, InGaN, ZnSe, CdTe, TiN, ZnO, Al:ZnO, indium tin oxide, fluoride-doped tin oxide, platinum, Ru0₂, Ir0₂, SrRu0₃, LaSrCo0₃, Ir0₂/Ir and Ru0₂/Pt.

The substrate may be an electronic substrate which may comprise one or more electronic parts, devices or structures (eg a printed circuit board).

The substrate may be conductive. For example, the substrate may a conductive mixed metal oxide such as a metal-doped metal oxide (eg Nb doped SrTi0₃). An electrode may be placed on or applied to (eg deposited on) the element. The electrode may be composed of an elemental metal or metal alloy. For example, the electrode may be (or contain) tantalum, titanium, gold or platinum.

In a preferred embodiment, the functional device is a field effect transistor device wherein the substrate is a substrate layer and the element is a gate dielectric fabricated on the substrate layer, wherein the field effect transistor further comprises: a gate on the gate dielectric.

Preferably the field effect transistor device is a MOSFET device. The field effect transistor device may be present in a CPU or GPU.

The gate dielectric is typically a gate dielectric layer. The thickness of the gate dielectric layer may be 3.0nm or more. The gate dielectric layer may be deposited on the substrate layer. For example, the gate dielectric layer may be deposited epitaxially on the substrate layer.

The present invention will now be described in a non-limitative sense with reference to Examples and the following Figures in which:

Figure 1 : X-ray diffraction pattern of a SrHf0₃ film grown from a 3 : 1 Sr:Hf deposition ratio annealed in air at 600°C for 30 minutes;

Figure 2: Atomic force micrographs: left - as deposited SrHf0₃ film; right - film after annealing in air at 600°C for 30 minutes; and

Figure 3: Capacitance dispersion of a SrHf0₃ MOS capacitor as a function of frequency.

Example 1 : Process for Preparing Sr(Hf-xTiy )C)₃

A film of the mixed oxide Sr(Hf]_-xTi_x)0₃ is prepared on a substrate in a reactor (Oxford Instruments Opal Reactor) using the following precursors:

Precursor PI : bz_>s(2,2,6,6-tetramethylheptane-3,5-dionato) strontium (source temperature 170°C)

Precursor P2: &z^■5^,(methyl-η5-cyclo entadienyl)methoxymethyl hafnium (source temperature 80°C)

Precursor P3: Titanium (IV) isopropoxide (source temperature 50°C). The reactor is maintained at a pressure of 1-2 mbar and the temperature of the substrate is 300°C. The purge gas is argon at a flow rate of 200sccm.

The duration of the steps in each deposition cycle for n cycles is as follows:

{[PI, 2s / purge 2s / H₂0, 0.5s / purge 3.5s], [P2, 2s / purge 2s / H₂0, 0.5s / purge 3.5s]_x, [P3, 2s / purge 2s / H₂0, 0.5s / purge 3.5s]_y}_n (x:y ~ 1:1 to 1:3)

Example 2: Process for Preparing Sr(Zri_.xTix)0₃

A film of the mixed oxide Sr(Zr_1-xTi_x)0₃ is prepared on a substrate in a reactor (Oxford Instruments Opal Reactor) using the following precursors:

Precursor PI : bzs(2,2,6,6-tetramethylheptane-3,5-dionato) strontium (source temperature 170°C)

Precursor P2: 6w(methyl-r|5-cyclopentadienyi) methoxymethyl zirconium (source temperature 70°C)

Precursor P3: Titanium (IV) isopropoxide (source temperature 50°C).

The reactor is maintained at a pressure of 2 mbar and the temperature of the substrate is 325°C. The purge gas is argon at a flow rate of 300sccm.

The duration of the steps in each deposition cycle for n cycles is as follows:

{[PI, 2s / purge 2s / H₂0, 0.5s / purge 3.5s], [P2, 2s / purge 2s / H₂0, 0.5s / purge 3.5s]_x, [P3, 2s / purge 2s / H₂0, 0.5s / purge 3.5s]_y}_n (x:y ~ 1:1 to 1 :3)

Example 3 : Process for Preparing Sr(Hfi-yTiy)O

A film of the mixed oxide Sr(Hf_1-xTi_x)0₃ is prepared on a substrate in a reactor (Oxford Instruments Opal Reactor) using the following precursors:

Precursor PI : Sr(t-Bu₃Cp)₂ Precursor P2: Hf(HNEtMe)₄

Precursor P3: Ti(OMe₃)₄

The reactor is maintained at a pressure of 1-2 mbar and the temperature of the substrate is 275°C. The purge gas is argon at a flow rate of 200sccm.

The duration of the steps in each deposition cycle for n cycles is as follows:

{[PI, Is / purge 2s / H₂0, 0.5s / purge 5s], [P2, Is / purge 2s / H₂0, 0.5s / purge 5s]_x, [P3, Is / purge 2s / H₂0, 0.5s / purge 5s]_y}_n (x:y ~ 1 :1 to 1 :3) .

Precursor PI : Sr(t-Bu₃Cp)₂ (source temperature 120°C)

Precursor P2: )Zί'(methyl-η5-cyclopentadienyl)methoxymethylhaIhium (source temperature 80°C)

Precursor P3: Titanium(IV) isopropoxide (source temperature 50°C).

The reactor is maintained at a pressure of 150 - 200mbar and the temperature of the substrate is 250°C. The purge gas is argon at a flow rate of 200sccm.

Oxygen plasma is generated using a 300W power source, 60sccm of 0₂ and lOsccm of Ar.

The duration of the steps in each deposition cycle for n cycles is as follows:

{[3[P1, 10s / purge 5s / 0₂ plasma, 3s / purge 5s], [P2, 3s / purge 2s / H₂0, 0.5s / purge 3.5s]]_x,3[[Pl, lOs / purge 5s / 0₂ plasma, 3s / purge 5s], [[P3, 3s / purge 5s / 0₂ plasma, 3s/ purge 5s]]_y}n

(x:y ~ 3:l, 2:l, 1:1, 1:2 or 1:3).

Example 5: SrHfC Films Grown on SidOO^{^}) Substrates Examples 5 relates to an investigation of a half cycle of the sequential exposure steps of an embodiment of the process of the invention which lead to the deposition of a SrHf0₃ film on Si(100) substrates.

The deposition of SrHf0₃ was investigated at a substrate temperature of 250°C using an Oxford Instruments Opal Reactor to explore the relationship between its crystalline phase and permittivity. A growth temperature of 250 °C was chosen as the optimum for matching the deposition rates of SrO and Hf0₂. The metal precursors used were Sr(z,soPr₃Cp)₂ and (MeCp)₂Hf (OMe)Me with an oxygen plasma as the oxidant. The plasma was generated using a 300W power source, a frequency of 13.56MHz, 60sccm of 0₂ and lOsccm of Ar. The Sr and Hf sources were evaporated at 120^°C and 100^°C respectively. An argon carrier gas flow rate of 200 cm min was used with a reactor pressure of 5 mbar. The number of cycles was in the range of 50-150, yielding film thicknesses of 15-57 nm. The [precursor

/purge/oxidant/purge/-] pulse sequences were «[Srl0s /5s/0.02s/5s] and m[Hf 3s /5s/0.02s/5s] (where n and m varied depending on the desired Sr.Hf ratio). The different precursor ratios used were: 3 : 1 , 3 :2. 5:2 and 7:2. Samples were prepared as thin sections so that energy- dispersive X-ray analysis could be carried out. This showed that for films deposited with a 3 : 1 (Sr:Hf) cycle ratio a Sr:Hf composition of 1 : 1 was observed. The need for a 3 : 1 ratio is attributed to the growth rate of Hf0₂ using (MeCp)₂Hf (OMe)Me being faster than the growth rate of SrO using Sr(iPr₃Cp)₂.

Films deposited using the 3 : 1 Sr:Hf ratio were selected for subsequent physico- chemical and electrical characterisation. X-ray diffraction analysis of a film grown at 250 °C did not reveal any diffraction features indicating that it was essentially amorphous as deposited. Figure 1 shows that (after annealing in air at 600 °C for 30 min) the film showed diffraction features that correspond to either the cubic or orthorhombic phase of SrHf0₃. These phases are indistiguishable for the thin films investigated using XRD. The c-lattice constant of the SrHf0₃ films determined by XRD was 4.06 A. This is in agreement with structural parameters for bulk SrHf0₃ (cubic, Pm3m =4.08A).

Atomic force microscopy (figure 2) showed that (after annealing in air) the SrHf0₃ films are smooth with a root mean square (rms) roughness of 7.0A over a 5x5 um² area. The darker areas of contrast that appear after annealing accompany the crystallisation process but represent a roughening of approximately only 1 A peak-to-valley for a film thickness of 57nm.

The retention of a smooth morphology is a significant advantage for dielectrics used in MOS gate-stack applications. Metal-oxide-semiconductor (MOS) capacitors were fabricated to assess the dielectric properties of the SrHf0₃ films after air annealing at 600 °C. The performance of MOS field effect transistors can be significantly impaired by dielectric relaxation effects. This is a potential issue for most crystalline, high-k dielectrics compared with Si0₂. Capacitance-frequency (C-f) data from a typical MOS capacitor

[Au/SrHf0₃/Si/Al] is shown in Fi gure 3. The SrHf0₂ film thickness of 57 nm was chosen to minimise the contribution from a Si0₂ interlayer. The C-f data shows a shallow frequency dispersion without any low-frequency (<lkHz) 'sheath-like' grain boundary contributions. A relative permittivity (κ) of 21 was extracted from the accumulation capacitance at 100 kHz. This was derived after accounting for the presence of a 3.2 nm Si0₂ interlayer as quantified by X-ray reflectivity and ellipsometery. The thickness of the interlayer is attributed to the affects of annealing in air. This permittivity value is in close agreement with SrHf0₃ films deposited on Si by alternative deposition techniques such as MBE.

In summary, stoichiometric strontium hafnate thin films have successfully been deposited by employing a plasma-assisted cyclical deposition process. The film composition can be controlled by altering the Sr:Hf ratio by varying the relative numbers of cycles of strontium and hafnium deposition. Perovskite structure SrHf0₃ films crystallized after annealing at 600°C. The crystalline SrHf0₃ dielectric has a high relative permittivity (κ) of 21 measured at a 100 kHz bias voltage.

Claims

1. A process for preparing a functional device comprising a substrate and an element composed of a mixed metal oxide of formula SrM_1-xTi_x0₃ wherein x is 0<x<l and M is Hf or Zr, wherein the process comprises:

exposing discrete volatilised amounts of a strontium precursor, of a hafnium or zirconium precursor and of a titanium precursor to the substrate in sequential exposure steps in a contained environment.

2. A process as claimed in claim 1 wherein each discrete volatilised amount is fed to the contained environment in a pulse.

3. A process as claimed in claim 1 or 2 further comprising:

feeding an oxidising agent into the contained environment in a pulse during each exposure step.

4. A process as clained in claim 3 wherein the oxidising agent is oxygen plasma.

5. A process as claimed in any preceding claim further comprising:

purging the contained environment with an inert gas flow in a pulse during each exposure step.

6. A process as claimed in any preceding claim wherein the sequential exposure steps are cyclical.

7. A process as claimed in any preceding claim comprising a cycle of sequential exposure steps (A), (B) and (C), wherein

step (A) comprises: feeding the discrete volatilised amount of strontium precursor into the contained environment, purging the strontium precursor from the contained environment and feeding an oxidising agent into the contained environment and purging the contained environment.

step (B) comprises: feeding the discrete volatilised amount of hafnium or zirconium precursor into the contained environment, purging the hafnium or zirconium precursor from the contained environment, feeding an oxidising agent into the contained environment and purging the contained environment.

step (C) comprises: feeding the discrete volatilised amount of a titanium precursor into the contained environment, purging the titanium precursor from the contained

environment and feeding an oxidising agent into the contained environment and purging the contained environment.

8. A process as claimed in claim 7 wherein each of steps (B) and (C) is cyclical and the ratio of the number of cycles of step (B) to the number of cycles of step (C) is in the range 3:1 to 1 :3.

9. A process as claimed in any of claims 1 to 6 comprising a cycle of sequential exposure steps (Α'), (Β'), (A") and (C), wherein

10. A process as claimed in claim 9 wherein each of steps (Α') and (Β') is cyclical and the ratio of the number of cycles of step (Α') to the number of cycles of step (Β') is 3:1.

11. A process as claimed in claim 9 or 10 wherein each of steps (A") and (C) is cyclical and the ratio of the number of cycles of step (A") to the number of cycles of step (C) is 3:1.

12. A process as claimed in claim 9, 10 or 11 wherein each of steps (Β') and (C) is cyclical and the ratio of the number of cycles of step (Β') to the number of cycles of step (C) is in the range 3:1 to 1 :3.

13. A process as claimed in any preceding claim wherein the titanium precursor is a titanium halide, titanium β-diketonate, titanium alkoxide, dialkylamino titanium complex, alkylamino titanium complex, silylamido titanium complex, cyclopentadienyl titanium complex, titanium dialkyldithiocarbamate or titanium nitrate.

14. A process as claimed in any preceding claim wherein the hafnium precursor is a hafnium β-diketonate, hafnium alkoxide, dialkylamino hafnium complex, alkylamino hafnium complex or cyclopentadienyl hafnium complex or the zirconium precursor is a zirconium β-diketonate, zirconium alkoxide, dialkylamino zirconium complex, alkylamino zirconium complex or cyclopentadienyl zirconium complex.

15. A process as claimed in any preceding claim wherein the strontium precursor is a strontium halide, strontium β-diketonate, strontium alkoxide, dialkylamino strontium complex, alkylamino strontium complex, silylamido strontium complex, cyclopentadienyl strontium complex or strontium nitrate.