Lesley M. Smith

Novel Mononuclear Alkoxide Precursors for the MOCVD of ZrO2 and HfO2 Thin Films

Thin films of ZrO 2 and HfO 2 have been deposited by liquid injection metal-organic (MO)CVD using a range of new alkoxide precursors, [Zr(O t Bu) 2 (mmp) 2 ] (1), [Hf(O t Bu) 2 (mmp) 2 ] (2), [Zr(mmp) 4 ] (3), and [Hf(mmp) 4 ] (4): (mmp = 1-methoxy-2-methyl-2-propanolate, OCMe 2 CH 2 OMe). The complexes are mononuclear and volatile, and are significantly less reactive to air and moisture than existing Zr and Hf alkoxide precursors such as [Zr(O t Bu) 4 ] and [Hf(O t Bu) 4 ]. The ZrO 2 and HfO 2 films were grown over a wide range of substrate temperatures (350-650 °C), and analysis by laser Raman spectroscopy shows that the films were deposited in the thermodynamically stable α- or monoclinic phase.

Response behaviour of tin oxide thin film gas sensors grown by MOCVD

Abstract Tin oxide is the most widely studied semiconducting oxide for use in gas sensor applications. However, the majority of previous study has been centred around porous media produced as thick films or thin sputtered films. This paper concerns the behaviour of relatively non-porous thin films grown by metal-organic chemical vapour deposition (MOCVD) and presents their response behaviour to the hazardous gases H2S, CH4 and NO2. The films were produced from tetratertiarybutoxytin at 350°C. They were found to act as selective H2S sensors at room temperature and show sensitive responses to all three gases above 200°C. The response to all gases is a reduction in resistance and the effect of water vapour on the response is small.

Deposition of HfO2 and ZrO2 films by liquid injection MOCVD using new monomeric alkoxide precursors

Thin films of ZrO2 and HfO2 have been deposited by liquid injection MOCVD using the new alkoxide precursors [Zr(OBut)2(dmop)2] (1) and [Hf(OBut)2(dmop)2] (2) [dmop = 2-(4,4-dimethyloxazolinyl)-propanolate]. The crystal structures of 1 and 2 have been determined, and they are shown to be six-coordinate monomeric complexes. They are volatile, and are significantly less reactive to air and moisture than existing Zr and Hf alkoxide precursors such as [Zr(OBut)4] and [Hf(OBut)4]. The ZrO2 and HfO2 thin films were deposited over substrate temperatures ranging from 350–550 °C. Analysis by X-ray diffraction shows that the films were deposited in the thermodynamically stable α- or monoclinic phase, and Auger electron spectroscopy shows that the ZrO2 and HfO2 films are non-stoichiometric and that carbon (1.9–8 at%) was present in the oxide films.

MOCVD of indium phosphide and indium gallium arsenide using trimethylindium-trimethylamine adducts

It is not yet clear which is the best indium precursor to use for MOCVD of InP and InGaAs. Trimethylindium, triethylindium and adducts of the metal alkyls with group Vb alkyls have been used. For this work indium phosphide and gallium indium arsenide have been grown using trimethylindium-trimethylamine. This adduct has the advantage over the more usual phosphorus alkyl adducts in having a greater volatility. Indium phosphide has been grown under optimum conditions with 298 K and 77 K are 5000 and 46000 cm2 s-1 V-1. Indium gallium arsenide lattice matched to indium phosphide has a carrier concentration of 2 × 1015 cm-3 electron and mobilities at 298 and 77 K of 8000 and 54000 cm2 s-1 V-1 n-type. Control of alloy composition is good. Photoluminescence at 2 K indicates material of good quality and reasonably low compensation.

Vapour pressure measurement of low volatility precursors

The introduction of new chemicals into semiconductor production processes is an expensive, time consuming exercise. A key parameter required to ensure equipment set up is well suited to the source from the outset of trials is reliable precursor volatility data. In this paper we present details of a newly commissioned vapour pressure (VP) measurement system and latest vapour pressure values for the technologically interesting Hf and Ta precursors pentakis(dimethylamido)tantalum (PDMAT) and tetrakis(ethylmethylamido)hafnium (TEMAH). Calibration data is also presented to illustrate the accuracy of the equipment.

Deposition of hafnium silicate films by liquid injection MOCVD using a single source or dual source approach

Two approaches have been investigated for the MOCVD of high-κ hafnium silicate (HfSixOy) films for gate dielectric applications. The first approach using the novel “single source” precursor [Hf(OSiButMe2)4(Et2NH)], gave a level of Si (∼10 at%) which showed little variation over a range of growth temperatures and oxygen partial pressures. The second, more flexible approach, uses two separate Hf and Si sources, Hf(NMe2)4 and ButMe2SiOH, and allows good control of the Si concentration in HfSixOy, depending on the relative precursor ratios, up to a maximum level of 18 at%. The dielectric properties of the HfSixOy films deposited by this method were shown to be very good. In the dual source process it is proposed that an intermediate containing direct Hf–OSiButMe2 bonds is formed in situ in the gas phase. The crystal structure of [Hf(OSiButMe2)4(Et2NH)] is also reported.

Deposition of LaAlO3 films by liquid injection MOCVD using a new [La–Al] single source alkoxide precursor

The new bimetallic alkoxide complex [LaAl(OPri)6(PriOH)]2 has been synthesised from the reaction between LaCl3, KAl(OPri)4 and KOPri in PriOH/toluene. The complex is volatile and has been used as a “single-source” precursor for the deposition of LaAlO3 by liquid injection MOCVD. The crystal structure of [LaAl(OPri)6(PriOH)]2 has also been determined.

Oxygen incorporation in aluminium-based semiconductors grown by metalorganic vapour phase epitaxy

1H nuclear magnetic resonance (NMR) spectroscopy has been used to characterize and quantify Me2AlOMe impurity added intentionally to Me3Al. This has allowed the correlation of varying alkoxide content in Me3Al with the oxygen content of AlAs measured directly by secondary ion mass spectrometry (SIMS), and with the photoluminescence (PL) efficiency of a GaAs/AlGaAs multi quantum well structure.

Adducts of trimethylgallium and perdeuteriotrimethylgallium with amine ligands and some dimethylgallium organyl pnictides (N, P, As). X-ray crystal structures of [Me3Ga·NH(C6H11)2] and [Me3Ga·NH(CHMe)(CH2)3CHMe]

Abstract The adducts Me3Ga·L [where L = NH(C6H11)2 (1), NHCHMe(CH 2 ) 3 C HMe (2), N(CH2CH2)3CH (3) and 0.5 N(CH2CH2)3N (4)] have been prepared by displacement of either (a) ether from Me3Ga·Et2O or (b) diphos from (Me3Ga)2·diphos (diphos = bisdiphenyl phosphino ethane) and the X-ray crystal structures of 1 and 2 determined. (CD3)3Ga and the adducts (CD3)3Ga·L [L= NMe3, NH(C6H11)2, NHCHMe(CH 2 ) 3 C HMe and N(CH2CH2)3CH], were similarly prepared from [(CD3)3Ga]2·diphos. The covalently bonded dimethylgallium organyl pnictides (Me2GaL′)n [L′= NPri2, NCHMe(CH 2 ) 3 C HMe, PMe2 and AsMe2] were prepared by reactions of either (c) Me2GaCl and LiL′ or (d) Me3Ga·Et2O and HL′. All compounds were characterized by elemental analyses, IR, NMR and mass spectroscopy. The Ga geometry in both 1 and 2 is distorted tetrahedral.

Synthesis of ultra-high purity trialkylgalliumMOVPE precursors. Crystal structures of triethylgallium and triisopropylgalliumadducts with macrocyclic tertiary amines

A synthesis and purification route has been developed for base-free trialkylgallium compounds which avoids the use of traditional ether solvents. The R3Ga compound (R = Et, Pri) is synthesised in triethylamine, NEt3, which leads to the adducts R3Ga(NEt3). The NEt3 ligand can be readily displaced by the addition of low volatility bidentate, tetradentate or hexadentate tertiary amines to give adducts of the type (R3Ga)xL (x = 2, 4, 6), from which base-free R3Ga compounds are obtained by mild thermal dissociation. The synthesis and characterisation of these adducts are described and crystal structures reported for the adducts between R3Ga (R = Et, Pri) and the multidentate macrocyclic amines 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane. These are the first reported structural studies of the Et3Ga and Pri3Ga molecules in the solid state.