Indium-tin-oxide coatings for applications in photovoltaics and displays deposited using rotary ceramic targets: Recent insights regarding process stability and doping level

摘要

Several aspects related to high power sputtering with industrial scale sintered ceramic rotary indium-tin-oxide (ITO) targets are presented in the first part of this paper. In particular, the process stability and target integrity upon sputtering with ≥20 kW/m power load and the influence of the gap size between cylindrical segments are discussed. Results show that, in order to avoid nodule formation and deposition rate fluctuations, direct current (DC) power load needs to be limited well below 20 kW/m over long sputter runs. Additional work demonstrates that at a gap size at or below 0.15 mm, strongly adhering deposits form readily between cylindrical segments which are not observed with standard 0.35 mm gaps. The influence of Sn doping level on electro-optical properties of thin films targeting an application such as hetero-junction c-Si solar cells is also investigated. Again, rotary targets operated at high power (10 kW/m) are used, including standard grade ITO containing 10 wt.% SnO_2 and another composition with only 3 wt.% SnO_2. The influence of H_2 and different concentrations of O_2 in the sputter gas is analysed for both target materials. Results indicate that although coatings derived from the lower-doped ITO exhibit considerably less absorption in the NIR due to lower carrier concentrations, their resistivity is nearly 30% higher than that from the standard ITO coating.