Leakage Current and Dielectric Properties of Ba 0.5 Sr 0.5 TiO 3 Films Deposited by RF Sputtering at Low Substrate Tempe
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Leakage Current and Dielectric Properties of Ba0.5Sr0.5TiO3 Films Deposited by RF Sputtering at Low Substrate Temperature Nicholas Cramer1, Thottam S. Kalkur2, Elliot Philofsky1 and Lee Kammerdiner1 1 Applied Ceramics Research, 1420 Owl Ridge Road, Colorado Springs, CO 80919 2 Dept. of Electrical and Computer Engineering, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80918 ABSTRACT Most studies of Ba0.5Sr0.5TiO3 (BST) thin film deposition have focused on chemical vapor deposition or spin-on techniques. Both these techniques require high substrate temperature (greater than 600 °C), either during the deposition or during an anneal after deposition. A few groups have reported on sputtered films, but most of these studies also used high-temperature processes. While such temperatures are compatible with poly-Si plug DRAM and related technologies, they are far above the limits for technologies that require the deposition of non-refractory metals before the deposition of the ceramic film. For example, the use of Al metalization before the deposition of BST would limit the BST processing temperature to about 450 °C. A process compatible with such a temperature limit is reported. Such a process makes fabrication of high quality BST thin films difficult, primarily due to the need for oxidation and grain growth in the ceramic. The leakage current and dielectric properties of BST films deposited in such a process are reported and are shown to be sufficient for practical device applications. INTRODUCTION A low temperature process for Ba0.5Sr0.5TiO3 (BST) thin-film deposition is required for applications that are on-chip and post-metalization [1]. Chemical Vapor Deposition (CVD) techniques usually involve substrate temperatures in excess of 600 °C, and spin-on techniques usually require crystallization/oxidation anneals in excess of 800 °C [2,3]. A low temperature sputtering process has the significant drawback limiting the growth of BST grains, which leads to lower relative permittivity (K) and higher leakage current. Therefore, a such a process cannot be expected to produce films with qualities as good as other, higher temperature processes. However, low temperature sputtered BST can still produce films with sufficiently high K-values as to be a suitable replacement for such dielectrics and silicon dioxide and silicon nitride. EXPERIMENTAL DETAILS Construction of the bottom electrode was performed on 4” silicon(100) wafers that had been thermally oxidized to an oxide thickness of 500 nm. DC sputter deposition of a TiO2 adhesion layer was performed at ambient temperature. A sputtering gas of 50/50 Ar/O2 and 16 mTorr total pressure was used to deposit a 15 nm thick film of TiO2. A 200 nm Pt film was then added by DC sputtering at ambient temperature using an atmosphere of 8 mTorr Ar. The resulting Pt film was strongly (111) textured, as was confirmed by x-ray diffraction. Oxidation of the Ti film was necessary to prevent Ti diffusion through the Pt film at elevated temperature and to improve the quality of the Pt surfa
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