Sputter Deposition Processes For Thin Film Oxide Dielectrics
Barron, Sara Cordero
As new semiconductor systems are developed and implemented in niche or mainstream applications, the need for new dielectric materials becomes prevalent. Sputter deposition is a versatile approach to preparing candidate materials for thin film dielectrics, affording a large processing space for optimization. The choices made for these sputtering parameters can effect significant variation in dielectric properties. We find that for the complex amorphous dielectric oxide of Zr sub(0.2) Sn sub(0.2) Ti sub(0.6) O sub(2) , the dielectric constant is strongly dependent on substrate temperature during reactive sputter deposition, with epsilon-r ~55 if deposited at 150 to 280 degree C; at higher and lower temperatures, the dielectric constant falls to ~30-35. A high quality dysprosium-substituted titania is prepared by reactive RF sputter deposition on unheated substrates. Preparation by thermal oxidation of a sputtered metal film, however, results in an oxide with a defect polarization along phase boundaries. Finally, we develop a methodology to co-sputter dielectric oxides in a composition gradient. When deposited from an oblique sputtering source, such as that used in composition spreads, dielectric thin films exhibit an abnormal low frequency polarization. We implement a negative electrical bias to the substrate, which eliminates the void-mediated polarization and recovers the intrinsic properties of the dielectric. The validity of this technique is demonstrated in the model system Ta sub(2)O sub(5) . Implementation of the technique and its implications for resputtering are considered in the mixed TaO sub(x) - GeO sub(x) dielectric system.
dissertation or thesis