AVS 56th International Symposium & Exhibition
    Thin Film Thursday Sessions
       Session TF-ThP

Paper TF-ThP9
High Rate Deposition of SnO2-based Transparent Conductive Films by Reactive Sputtering with Impedance Control Method

Thursday, November 12, 2009, 6:00 pm, Room Hall 3

Session: Aspects of Thin Films Poster Session
Presenter: Y. Muto, Aoyama Gakuin University, Japan
Authors: Y. Muto, Aoyama Gakuin University, Japan
Y. Nishi, Aoyama Gakuin University, Japan
K. Hirohata, Aoyama Gakuin University, Japan
N. Tsukamoto, Aoyama Gakuin University, Japan
N. Oka, Aoyama Gakuin University, Japan
Y. Sato, Aoyama Gakuin University, Japan
Y. Iwabuchi, Bridgestone Corporation, Japan
H. Kotsubo, Bridgestone Corporation, Japan
Y. Shigesato, Aoyama Gakuin University, Japan
Correspondent: Click to Email
SnO2-based transparent conductive oxide (TCO) films have been used as transparent electrodes especially for solar batteries. Recently, because of the toxicity and shortage problems of In, SnO2 is considered to be one of the ITO-alternatives. Most of the TCO films have been deposited by magnetron sputtering using oxide ceramic targets in industry, however, the deposition rate is not so high and also the cost for the high quality ceramic targets is high in general. On the other hand, reactive sputtering using metal or alloy targets should be one of the most promising techniques to achieve much higher deposition rate for various industrial applications because sputtering yield of the metallic surface is much larger than the one of the oxide surface and also the higher sputtering power density can be applied for metallic targets because of their higher thermal conductivity. The reactive sputtering process is strongly affected by the O2 flow ratio; where the deposition rate exhibits hysteresis with respect to the O2 reactive gas flow rate. Such behavior originates in the oxidation state of the target surface, resulting in the marked decrease in deposition rate with the increasing O2 flow (transition region). Therefore, the sputtering conditions should be precisely controlled so as to obtain high-quality SnO2-based TCO films by reactive sputtering with a high deposition rate and with high reproducibility.

In this study SnO2 films doped with Sb or Ta (ATO or TTO, respectively) were deposited on unheated or heated glass substrates at 200oC by the reactive sputtering with Sb-Sn or Ta-Sn alloy targets using a plasma control unit (PCU) and mid-frequency (mf, 50kHz) pulsing. PCU feedback system (Fraunhofer Institut fur Elektronenstrahl-und Plasmatechnik, FEP) monitors the oxidation states of target surface by observing in cathode voltage (impedance control method) [1]. The mf pulsing possesses the approximate shape of a square wave which make it possible to reduce arcing on the target when high power density is applied. In the case of the ATO films deposition on heated substrate at 200oC in the “transition region”, the deposition rate was 280 nm/min where the lowest resistivity of the ATO films was 4.6×10-3 Ωcm and the optical transmittance was more than 80% in the visible region.

[1] M. Kon, Y. Shigesato, et. al, Jpn. J. Appl. Phys. 41, 814 (2002).