MOCVD of High-K Dielectrics and Conductive Metal Nitride Thin Films
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Abstract 2 A known liquid mixture of [(CH 3CH 2)2N]3Ta=NCH 2CH 3 and [(CH 3CH 2)2N] 3Ta[rl CH 3CH 2N=CH(CH 3)] was studied to deposit Ta20 5 and TaN thin films by CVD. Films were deposited at temperatures below 400'C using oxygen for oxide and ammonia for nitride, respectively. XRD analysis revealed that as-deposited amorphous tantalum oxide films were converted to hexagonal Ta2O5 after annealing under oxygen, while tantalum nitride thin films contained cubic TaN as deposited. The low viscosity, thermal stability, and sufficient volatility of the precursor allows direct liquid injection to deliver the precursor, which results in high deposition rate and uniformity of the deposited films.
Introduction As the size of integrated circuit devices decreases, chemical vapor deposition (CVD) shows a unique advantage over physical vapor deposition (PVD) for device fabrication in terms of its excellent step coverage for trench, via, and stacked cell structures for applications in microelectronics devices. In general, liquid precursors are preferred to solid precursors for CVD applications due to the ease and reproducibility of the precursor delivery. Ta2O5 is considered a promising material as a gate oxide and as a DRAM storage capacitor due to its relatively high dielectric constant.' For the CVD of Ta2 0 5 thin films, various precursors have been studied thus far. Tantalum halides (TaX5, X = F2 , Cl3 ) are solid and suffer from low volatility and difficulty in delivery. A solid metal-organic complex Ta(NMe 2)5 has been reported to provide Ta2O5 films with significant levels of carbon and nitrogen impurities.4 A dinuclear solid complex [Ta(OMe)5 ]2 has also been studied. 5 The most commonly studied liquid precursor [Ta(OEt)5] 2 has a marginal vapor pressure and deposits films containing carbon impurities.' It has recently been reported that mononuclear complexes of the type Ta(OEt) 4(L), where L = dimethylaminoethoxide 6 and 13-diketonate,7 have improved volatility for CVD applications. As copper emerges as a substitute for aluminum in multilevel metallization of semiconductor devices, CVD precursors for conductive TaN are also actively being sought due to the excellent barrier properties of TaN against the copper diffusion into silicon substrates at high temperatures.' So far, a number of precursors have been evaluated for TaN CVD. None have shown the combination of being a stable liquid, ease of synthesis and suitability for low temperature CVD processing to provide pure TaN. Solid tantalum halides (TaX5 , X = Br9 , Cl'0 ) are not desirable as mentioned above. Reaction of solid Ta(NMe 2)5 with ammonia yields nonconductive Ta3N 5." Liquid alkylamide type complexes have also been studied. An unstable 13 Mat. Res. Soc. Symp. Proc. Vol. 606 © 2000 Materials Research Society
liquid Ta(NEt 2)5 has been used as a single-source to produce tantalum carbonitride.' 2 The quality of TaN films deposited from Ta(NEt 2)5 was improved by using ammonia as a reactant gas.'3 Tsai, et. al. reported the deposition of low resistivity TaN fi
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