Physical-Chemical Evolution of Hf-aluminates upon Thermal Treatments
- PDF / 1,079,956 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 185 Views
D2.10.1
Physical-Chemical Evolution of Hf-aluminates upon Thermal Treatments B. Crivelli, M. Alessandri, S. Alberici, D. Brazzelli, A. C. Elbaz, S. Frabboni1, G. Ghidini, J. W. Maes2, G. Ottaviani1, G. Pavia, C. Wiemer3 STMicroelectronics, Via C.Olivetti 2, 20041 Agrate Brianza (MI), Italy 1 Department of Physic and Unita’ INFM – University of Modena, 41100 Modena, Italy 2 ASM International, B-3001 Leuven, Belgium 3 Laboratorio MDM-INFM, Via C.Olivetti 2, 20041 Agrate Brianza (MI), Italy ABSTRACT This study presents an investigation on physical-chemical stability of (HfO2)x(Al2O3 )1-x alloys upon prolonged post-deposition annealings. Two different Hf-aluminates were deposited by ALCVDTM, containing 34% and 74% Al2O3 mol% respectively. Post-deposition annealings (PDA) were carried out in O2 or N2 atmosphere, at 850°C and 900°C for 30 minutes. Interfacial layer (IL) increase after PDA was detected on all the samples, but with small differences between N2 and O2 treatments. Stack composition was characterized by means of XRR, XRF, RBS and TOF-SIMS. Growth of interface layer was justified by limited oxygen incorporation from external ambient. Silicon diffusion from the substrate into high-k material and aluminum/hafnium redistribution were observed and associated to annealing temperature. XRD and planar TEM analysis evidenced first grain formation and then, in the case of Hf-rich samples, almost complete crystallization. Overall, Hf-aluminates were found to remain XRD amorphous during high temperature prolonged treatments up to 900°C for 74% and 850°C for 34% alloys respectively. Differently from HfO2, (HfO2)0.66(Al2O3 )0.34 alloy was observed to crystallized in orthorhombic phase. Hf-aluminates were also electrically characterized by means of C(V) and I(V) measurements on basic capacitors. Variations in material electrical properties were found consistent with change in physical-chemical film structure. Increase in k value up to 30 was observed on Hf-rich samples crystallized in orthorhombic phase. INTRODUCTION The continuous scaling down of transistor and memory devices toward 65 nm technology node demands for the replacing of ultra thin SiO2 based dielectrics with high-k materials. Considering basic selection criteria such as stability with silicon, proper band offsets and appropriate k value, hafnium based films were proposed as possible candidates for those applications1. However, one additional and critical requirement for high-k implementation in microelectronic is the material stability during device fabrication. Thermal and chemical stability together with resistance to oxygen diffusion are actually major concerns. Previous study demonstrated that hafnium oxide crystallizes in monoclinic phase at very low temperature, in the range of 300-400°C2. Beside crystallization phenomena, upon prolonged postdeposition annealings, HfO2, as well as other high-k materials, resulted partially permeable to oxygen diffusion and subjected to chemical evolution even under low O2 partial pressure regimes. Increase in thermal sta
Data Loading...
