Spatial Atmospheric Atomic Layer Deposition of In x Ga y Zn z O for Thin Film Transistors A. Illiberi,* ,† B. Cobb, † A. Sharma, † T. Grehl, ‡ H. Brongersma, ‡,§ F. Roozeboom, †,§ G. Gelinck, † and P. Poodt † † Holst Centre/TNO, High Tech Campus 31, 5600 AE Eindhoven, The Netherlands ‡ ION-TOF GmbH, Heisenbergstrasse 15, 48149, Muenster, Germany § Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands ABSTRACT: We have investigated the nucleation and growth of InGaZnO thin films by spatial atmospheric atomic layer deposition. Diethyl zinc (DEZ), trimethyl indium (TMIn), triethyl gallium (TEGa), and water were used as Zn, In, Ga and oxygen precursors, respectively. The vaporized metal precursors have been coinjected in the reactor. The metal composition of InGaZnO has been controlled by varying the TMIn or TEGa flow to the reactor, for a given DEZ flow and exposure time. The morphology of the films changes from polycrystalline, for ZnO and In-doped ZnO, to amorphous for In-rich IZO and InGaZnO. The use of these films as the active channel in TFTs has been demonstrated and the influence of In and Ga cations on the electrical characteristics of the TFTs has been studied. KEYWORDS: atomic layer deposition, atmospheric pressure, thin film transistors, indium gallium zinc oxide, amorphous semiconductors, nucleation ■ INTRODUCTION Amorphous oxide semiconductors (AOS) are emerging as a novel class of materials for thin-film-transistor (TFT) displays because of their superior electrical properties compared to a- Si:H and better uniformity over large areas than poly-Si based TFTs. 1−4 AOS are based on ternary and quaternary zinc compounds (e.g., InGaZnO, ZnSnO), and their electrical properties can be fine-tuned by varying the composition ratio of metal ions. Amorphous indium gallium zinc oxide (a- InGaZnO) is the most widely utilized AOS for the active channel in TFTs due to its reasonably large mobility (μ > 10 cm 2 /(V s)), low off-currents due to good controllability of the carrier concentration over a wide range (10 15 −10 19 cm −3 ), and long-term stability. 5,6 The growth of a-IGZO was initially studied using pulsed layer deposition (PLD). 5 PLD allows facile screening of different stoichiometry of the film composition but suffers from poor control of film thickness and composition over a large area. Hence, sputtering is currently most widely used, 1 even though sputtering suffers from a low deposition rate (∼0.1 nm/s) and the presence of high-energy species (e.g., ions) can induce defects at the dielectric/semiconductor interface. Solution processing methods have been proposed to decrease the production costs of a-InGaZnO, but TFTs with nonoptimal electrical properties have been achieved so far. 7 In this work, we propose the use of spatial atmospheric atomic layer deposition (S-ALD). S-ALD has emerged as a potentially disruptive manufacturing method for the display industry, combining high deposition rates (up to nm/s) with excellent control of film composition and superior uniformity over a large area and even nonflat substrates. 8 Selective S-ALD of metal oxides on patterned surfaces has been recently demonstrated. 9 In this Article, we investigate the nucleation and growth of a-InGaZnO by S-ALD and its application as an active channel of TFTs. Conventionally, the ALD technique is characterized by a time-sequenced introduction of the precursors in the deposition zone, where selective and self-limiting half-reactions occur on the substrate, thus allowing a digital control of the film thickness. S-ALD of metal oxides is performed by sequentially exposing the substrate to an oxygen and a metal precursor which are spatially separated in the ALD injector. Time- consuming purge steps are no longer needed and deposition rates up to a hundred times faster than conventional ALD can be achieved. 10,11 By coinjecting the evaporated metal precursors in the same deposition region, multimetal oxides with uniform distribution of the metal elements along the growth direction have been grown by S-ALD. 12,13 ■ EXPERIMENTAL SECTION A schematic and a description of the S-ALD deposition equipment used in this work can be found in ref 10. Diethyl zinc [Zn(C 2 H 5 ) 2 , (DEZ)], trimethyl indium [In(CH 3 ) 3 , (TMIn)], triethyl gallium Received: November 20, 2014 Accepted: January 21, 2015 Published: January 21, 2015 Research Article www.acsami.org © 2015 American Chemical Society 3671 DOI: 10.1021/am508071y ACS Appl. Mater. Interfaces 2015, 7, 3671−3675