Highly-conformal p-type copper(I) oxide (Cu ₂ O) thin films by atomic layer deposition using a fluorine-free amino-alkoxide precursor

A highly-conformal and stoichiometric p-type cuprous copper(I) oxide (Cu ₂ O) thin films were grown using atomic layer deposition (ALD) by a fluorine-free amino-alkoxide Cu precursor, bis(1-dimethylamino-2-methyl-2-butoxy)copper (C ₁₄ H ₃₂ N ₂ O ₂ Cu), and water vapor (H ₂ O). Among tested deposition temperatures ranging from 120 to 240 °C, a self-limited film growth was clearly confirmed for both precursor and reactant pulsing times at 140 °C. Between 140 and 160 °C, the process exhibited an almost constant growth rate of ∼0.013 nm/cycle and a negligible number of incubation cycles (approximately 6 cycles). The Cu ₂ O films deposited at the optimal temperature (e.g. 140 °C) showed better properties in view of their crystallinity and roughness compared to the films deposited at higher temperatures. Rutherford backscattering spectrometry showed that the film deposited at 140 °C was almost stoichiometric (a ratio of Cu and O ∼2: 1.1) with negligible C and N impurities. X-ray photoelectron spectroscopy further revealed that Cu and O in the film mostly formed Cu ₂ O bonding rather than CuO bonding. Plan-view transmission electron microscopy analysis showed formation of densely packed crystal grains with a cubic crystal structure of cuprous Cu ₂ O. The step coverage of ALD-Cu ₂ O film was remarkable, approximately 100%, over 1.14-μm-high Si nanowires with an aspect ratio (AR) of 7.6:1 and onto nano-trenches (top opening width: 25 nm) with an AR of 4.5:1. Spectroscopic ellipsometry was employed to determine optical constants, giving optical direct band gap of 2.52 eV. Finally, Hall measurement confirmed that the ALD-Cu ₂ O film had p-type carriers with a high Hall mobility of 8.05 cm ² /V s.