Conductive SnO2-x thin films deposited by thermal ALD with H2O reactant

In this study, SnO2-x films were deposited by a thermal atomic layer deposition (ALD) method with H2O as a reactant. The electrical property of the films was assessed with the intention of applying them as a channel for a back-end-of-line (BEOL) compatible transistor. Under the thermal budget constraint (<450 °C) required for a BEOL transistor, the effect of ALD process parameters and post-annealing conditions on the carrier concentration and mobility of the films was investigated. While the as-deposited films were amorphous, more distinctive recrystallization could be observed with the deposition temperature of 200 °C combined with the annealing ambient of N2. As a result, the mobility of 21.55 cm2/Vs and 3.3 × 1019 cm−3 carrier concentration were achieved with an 18-nm thick n-type SnO2-x film. However, it was also observed the mobility of the N2-annealed SnO2-x decreased by ∼50% of an initial value upon exposure to humidity for 2–3 days. 5-Nm Al2O3 on SnO2-x as a capping layer could prevent the degradation, suggesting the presence of a more conductive path near the surface. This work demonstrates SnO2-x deposited by a thermal ALD can exhibit an excellent electrical property suitable for various electronic devices such as a BEOL compatible transistor.