Atomic Transport in LaAlO[sub 3] Films on Si Induced by Thermal Annealing

Abstract

LaAlO 3 films sputter-deposited on Si were submitted to rapid thermal annealing at 800 and 1000°C. Atomic transport and chemical changes were investigated using ion beam analysis and X-ray photoelectron spectroscopy. Annealing induced La and Al losses or their migration into a newly formed interfacial layer and Si migration into the film. The mechanism of Si incorporation into the film is influenced by the annealing atmosphere. These instabilities were hampered by a thermal nitridation in NH 3 at 700°C performed prior to rapid thermal annealing, indicating a possible route for producing a thermally stable La-based highgate dielectric.Several different materials holding dielectric constants substantially higher than that of SiO x N y ͑3.8 Ͻ Ͻ 7.8͒ were proposed as alternatives for gate dielectric in next generations of metal-oxidesemiconductor field effect transistors ͑MOSFET͒. 1-3 These materials, usually called high-dielectrics, must withstand all manufacturing steps of MOSFET technology, including those performed at temperatures much higher than that used during the high-film deposition. One critical thermal step is dopant activation, usually accomplished by rapid thermal annealing ͑RTA͒ at 1050°C. 1-3 This step may modify structurally and chemically the films, having deleterious consequences in the electrical characteristics of the formed MOS capacitors. Lanthanum aluminate is a potential candidate for gate dielectric due to its wide band gap ͑5.6 eV͒ and high dielectric constant ͑ = 20-25͒ as compared to SiO x N y . 3-5 Besides, it is predicted to be thermodynamically stable on Si. 6 However, some unexpected physical instabilities, such as metal migration into the substrate, substrate-Si migration into the high-film, as well as chemical reaction leading to the formation of a lanthanum ͑alumi-no͒silicate interfacial layer were recently observed. 7,8 In this paper, we systematically investigate atomic transport and chemical reactions that take place in lanthanum aluminate films on Si following RTA in controlled atmospheres. ExperimentalLaAlO films were sputter-deposited on HF last p-type Si͑100͒, using a LaAlO 3 ceramic target in a 5 ϫ 10 −2 mbar Ar plasma excited by a 13.56 MHz radio frequency with a power density of 1 W/cm 2 . Ex situ post-deposition RTA was performed in vacuum ͑ϳ10 −7 mbar͒ or in 10 mbar of O 2 . Annealing times varied with respect to the temperature of treatments: 60 s for 800°C and 20 s for 1000°C. The quantities of La and O in the films were determined by Rutherford backscattering spectroscopy ͑RBS͒, 9,10 while Al quantification by nuclear reaction analysis ͑NRA͒. 11,12 The results are expressed in areal densities units ͓͑at. cm −2 ͔͒, which correspond to the integral of the atomic densities ͓͑at. cm −3 ͔͒ over the film thickness. The sensitivities of RBS and NRA for these elements are better than 5 ϫ 10 14 cm −2 . 9,11 A selected sample was thermally nitrided at 700°C during 30 min in 20 mbar of NH 3 enriched to 10% in the 15 N isotope. Following nitridation, the sample was submitted to ...

Effects of Nitrogen Incorporation in Lanthanum-Based Dielectric Films

“…The third nitrogen behavior was investigated by deposition of LaAlO 3 films (22 nm), prior to PDA in 20 mbar of 15 NH 3 during 30 min at 700 • C [10]. These LaAlON films were then submitted to a rapid thermal annealing (RTA) in 10 mbar of 18 [11].…”

Thermally Induced Atomic Transport in Nanometric LaAlON Films on Si

“…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.…”

“…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.…”

Effect of nitrogen incorporation on the thermal stability of sputter deposited lanthanum aluminate dielectrics on Si (100)

“…7 While the pseudobinary alloys meet many of the requirements for the gate dielectric implementation, 1 the carrier mobility degradation and the degradation of transistor performance due to crystallization and metal penetration into the underlying channel is a major concern. 7-9 The incorporation of nitrogen into the high-dielectric film or at the high-dielectric interface with the Si substrate could be advantageous and has been found to be effective in suppressing crystallization, 10 decreasing dopant penetration into bulk silicon, 11 inhibiting interfacial reaction with the Si substrate, 11,12 and improving the electrical performance of the device. 13,14 In this letter, we have evaluated the effect of nitrogen incorporation on the thermal stability of sputter deposited lanthanum aluminate ͑LaAlO͒ dielectric 15-20 on a Si ͑100͒ substrate, before and after a 1000°C, 10 s N 2 RTA.…”

“…8 The lack of crystallization and the associated grain boundaries for metal atom penetration into the silicon substrate could be another reason for the suppression of penetration of the metal species from LaAlON thin films compared to LaAlO. 9,12,16 Capacitor measurements of the sputtered 12 nm LaAlON dielectric after a 400°C, 30 min forming gas ͑N 2 90% : H 2 10%͒ annealing treatment ͑not shown͒ indicate an effective dielectric constant of ϳ 12 and a leakage current density of Ͻ1 ϫ 10 −6 A/cm 2 between +4 and −4 V gate voltage.…”