Study of interface formation of (Ba,Sr)TiO 3 thin films grown by rf sputter deposition on bare Si and thermal SiO 2 /Si
- PDF / 1,203,153 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 65 Downloads / 185 Views
T7.12.1/N9.12.1
Study of interface formation of (Ba,Sr)TiO3 thin films grown by rf sputter deposition on bare Si and thermal SiO2/Si substrates. N.A. Suvorova, A.H. Mueller, A. A. Suvorova1, M. Saunders1 and E.A. Irene Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599, U.S.A. 1 Centre for Microscopy and Microanalysis, University of Western Australia, Crawley 6009, WA, Australia ABSTRACT (Ba,Sr)TiO3 (BST) thin films were deposited by ion beam sputtering on both bare and oxidized Si. Spectroscopic ellipsometry (SE) model results have shown an increase in the SiO2 layer thickness for bare substrates and those with a 1 nm initial oxide layer, and a decrease for thicker (3.5 nm) initial SiO2 films. This result was confirmed by high resolution electron microscopy (HREM) analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO2. From high-frequency capacitance-voltage (C-V) analysis, a decrease in the interface trap density Dit of an order of magnitude was observed for oxidized Si substrates.
INTRODUCTION With dielectric thickness scaling to 1-2 nm, the silicon/dielectric interface becomes an important issue in CMOS technology. Typically, high static dielectric constant (high-K) dielectrics react with Si and SiO2 to form undesirable interface layers that degrade the overall electrical properties [1-3]. In order to maintain the high quality interface and still provide a high overall capacitance for the gate dielectric film stack an ultrathin SiO2 layer can be used as an underlayer of a high-K film. The present study is aimed at the optimization of the SiO2 underlayer in terms of minimizing its effect on K yet maintaining interface quality. In-situ characterization of BST films grown on bare and thermally oxidized Si substrates has been accomplished using spectroscopic ellipsometry (SE). Electrical characterization has been used for ex-situ studies of capacitors prepared completely in vacuo. Composition and structural properties have been correlated with analytical electron microscopy and Rutherford Backscattering Spectroscopy (RBS).
EXPERIMENTAL DETAILS BST films were prepared by reactive ion beam sputtering of a Ba0.5 Sr0.5 TiO3 target in an O2 partial pressure of 1×10-4 torr using a Kr+ ion beam [2,3]. Prior to deposition p-Si wafers were RCA cleaned and HF dipped and thermally oxidized in a conventional furnace in dry O2 at 1000°C and 700°C to yield about 3.5 nm and 1.0 nm SiO2 respectively. BST deposition was monitored using in-situ SE from which optical constants and thicknesses of the grown films were obtained. The films were deposited at a substrate temperature of 50°C and 450° C and followed by annealing at 450°C and 650°C in an oxygen background of 1×10-4 torr. Iridium
T7.12.2/N9.12.2
electrodes were deposited in vacuo by rf sputtering at room temperature through a shadow mask. C-V measurements of capacitors were performed at 1MHz. RBS was utilized to characterize the composition of the BST films. Samples
Data Loading...
