Highly-conformal p-type copper(I) oxide (Cu2O) thin films by atomic layer deposition using a fluorine-free amino-alkoxide precursor

Abstract

A highly-conformal and stoichiometric p-type cuprous copper(I) oxide (Cu2O) 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 (C14H32N2O2Cu), and water vapor (H2O). Among tested deposition temperatures ranging from 120 to 240 degrees C, a self-limited film growth was clearly confirmed for both precursor and reactant pulsing times at 140 degrees C. Between 140 and 160 degrees C, the process exhibited an almost constant growth rate of similar to 0.013 nm/cycle and a negligible number of incubation cycles (approximately 6 cycles). The Cu2O films deposited at the optimal temperature (e.g. 140 degrees 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 degrees C was almost stoichiometric (a ratio of Cu and O similar to 2: 1.1) with negligible C and N impurities. X-ray photoelectron spectroscopy further revealed that Cu and O in the film mostly formed Cu2O 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 Cu2O. The step coverage of ALD-Cu2O film was remarkable, approximately 100%, over 1.14-mu m-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-Cu2O film had p-type carriers with a high Hall mobility of 8.05 cm(2)/V s. (C) 2015 Elsevier B.V. All rights reserved.