Thermally Induced Atomic Transport in Nanometric LaAlON Films on Si

Abstract

The thermal stability of nanometric lanthanum aluminum oxynitride films on silicon was investigated in vacuum and oxygen. Isotopic enrichment of the films with 15 N and of the annealing atmosphere with 18 O combined with nuclear reaction analysis and Rutherford backscattering spectrometry provides direct evidence of atomic transport starting at 600°C. Oxygen exchange and nitrogen replacement are identified. Interfacial silicon oxide growth takes place as the interfacial N concentration falls below 5 ϫ 10 21 cm −3 . Complementary X-ray photoelectron spectroscopy shows changes in chemical bonding as a function of annealing temperature and ambient. Nanometric LaAlO 3 films on silicon have received attention due to the technological need to replace silicon oxynitride as gate dielectric in advanced metal oxide semiconductor field effect transistors. 1-5 Though a hafnium-based material has been announced as first-generation replacement of SiON, the authoritative International Technology Roadmap for Semiconductors 6 lists lanthanumbased dielectrics as potential successors for which research is in need. LaAlO 3 presents suitable dielectric constant ͑k Ն 20͒, bandgap ͑E g = 5.6 eV͒ and band offsets with respect to silicon ͑⌬E C,V Ͼ 1 eV͒. In addition, the presence of a rare earth element such as La at the interface between the gate dielectric and gate electrode has led to an appropriate threshold voltage in n-type metal-oxidesemiconductor ͑NMOS͒ devices. 7 However, pure LaAlO 3 films on silicon present insufficient thermal stability to withstand device fabrication. Thermally induced crystallization and transport of La, Al, and Si have been reported. 8,9 Such instabilities were suppressed with the incorporation of ϳ3 atom % N in the bulk of lanthanum aluminum oxide during deposition 10 or by thermal nitridation in NH 3 . 8 In this letter we provide specifics of N and O transport, exchange, and chemical bonding modification upon thermal annealing of nanometric LaAlON films on silicon in vacuum or oxidizing ambient. In particular, we determine a threshold nitrogen concentration for the beneficial increase in thermal stability which is of relevance for ongoing research on this material. ExperimentalLaAlON films, 6 nm thick as determined by X-ray reflectivity, were sputter deposited on HF-last p-type Si͑100͒ using a LaAlO 3 target in a Ar/N 2 ͑150:5 sccm͒ radio frequency plasma at 5 ϫ 10 −2 mbar with a power density of 1 W cm −2 . For characterization purposes ͑see below͒, the N 2 supply gas was enriched to 99 atom % in the 15 N isotope. Rapid thermal annealing ͑RTA͒ was performed ex situ in vacuum ͑10 −7 mbar͒ or in 0.5 mbar of O 2 , at 600°C for 20 min, 800°C for 5 min, or 1000°C for 10 s. The O 2 supply gas was enriched to 97 atom % in the 18 O isotope, whose natural abundance is 0.2 atom %, allowing the distinction between oxygen atoms incorporated from the gas phase during thermal annealing and those originally existing in the films.The amounts of 15 N, 18 O, and 27 Al in the films were determined by nuclear reaction anal...

Thermal Annealing Effects on the Atomic Layer Deposited LaAlO[sub 3] Thin Films on Si Substrate

“…In many cases, inevitable interface layer formation between the amorphous LaAlO 3 thin films and Si substrate during film deposition and postdeposition annealing ͑PDA͒ have been reported. 1,2,[5][6][7][8][9] Interface layer formation normally has an adverse effect on the device performance. In this study, the equivalent oxide thickness of a LaAlO 3 film increased from 2.23 to 2.46 nm after PDA at 800°C.…”