Effects of RF Sputtering Parameters on C-axis Aligned Crystalline (CAAC) InGaZnO 4 Films Using Design of Experiment (DOE) Approach

Abstract

The influence of deposition parameters on the properties of RF sputter deposited c-axis aligned crystalline (CAAC) IGZO was studied using both single parameter and design of experiment (DOE) analysis (target composition near InGaZnO4). Use of a 3-level, 6 factor Box-Behnken DOE enabled efficient sampling of the large processing parameter space. Deposition temperature and power, oxygen fraction in the sputter gas, and the ensuing Zn composition were identified as the key parameters correlated with c-axis texture in the films. CAAC formation commenced at a deposition temperature of 250\degC reaching maximum surface normal alignment near 315\degC. Crystallinity and alignment increased rapidly with oxygen fraction becoming nearly independent of fraction between 10% and 50%. Zinc loss during deposition at high temperatures and low oxygen partial pressures correlated with lower crystallinity, suggesting a strong composition dependence of CAAC formation in IGZO alloys. In contrast, increased deposition power improved alignment. Optimal deposition conditions were identified and related to a proposed nucleation and growth model.