Plasma enhanced atomic layer deposition of ZnO with diethyl zinc and oxygen plasma: Effect of precursor decomposition

Although atomic layer deposition (ALD) of ZnO using diethyl zinc (DEZ) precursor has been extensively reported, variation in growth-per-cycle (GPC) values and the range of substrate temperature (T_sub) for ALD growth between related studies remain unexplained. For identical processes, GPC for the characteristic self-limiting ALD growth is expected to be comparable. Hence, a significant variation in GPC among published ZnO ALD studies strongly suggests a concealed non-ALD growth component. To investigate this, the authors report plasma-enhanced ALD growth of ZnO using DEZ precursor and O₂ inductively coupled plasma. The effect of T_sub on ZnO GPC was studied with deposition cycles (1) 0.02 s–15 s–6 s–15 s, (2) 0.10 s–15 s–15 s–15 s, and (3) 0.20 s–15 s–30 s–15 s, where the cycle parameters t₁–t₂–t₃–t₄ denote duration of DEZ pulse, post-DEZ purge, plasma exposure, and postplasma purge, respectively. The non-ALD growth characteristics observed at T_sub ≥ 60 °C are discussed and attributed to DEZ precursor decomposition. The authors demonstrate ZnO growth at T_sub = 50 °C to be self-limiting with respect to both t₁ and t₃ giving GPC of 0.101 ± 0.001 nm/cycle. The effect of precursor decomposition related (non-ALD) growth at T_sub ≥ 60 °C is illustrated from comparison of optical dielectric function, electrical resistivity, and surface roughness of ZnO films deposited at T_sub = 50, 125, and 200 °C.