The effect of oxygen remote plasma treatment on ZnO TFTs fabricated by atomic layer deposition

Abstract

We deposited ZnO thin films by atomic layer deposition (ALD) and then investigated the chemical and electrical characteristics after plasma treatment. The chemical bonding states were examined by X-ray photoelectron spectroscopy (XPS). The XPS spectra of O 1s showed that the intensity of oxygen deficient regions of the ZnO film decreased from 27.6 to 19.4%, while the intensity of the oxygen bound on the surface of the ZnO film increased from 15.0 to 21.9% as plasma exposure times increased. The ZnO film exhibited a decrease in carrier concentration from 4.9 x 10(15) to 1.2 x 10(14) cm(-3) and an increase in resistivity from 1.2 x 10(2) to 9.8 x 10(3) Omega cm as the plasma exposure times increased. To verify the changes in the chemical and electrical properties of the ZnO films caused by the oxygen remote plasma treatment, ZnO thin film transistors were fabricated and their electrical properties were investigated. We found that the I-on/Ioff ratio increased from 7.3 x 10(4) to 8.6 x 10(6), the subthreshold swings improved from 1.67 to 0.45 V/decade, and the saturation mobility (mu(sat)) decreased from 1.63 to 0.72 cm(2)/V s as plasma exposure times were increased.