Paper PS-TuM11
Characteristics of Reactive Ion Etching Processes for ITO and ZnO

Tuesday, November 11, 2014, 11:20 am, Room 308

With the increasing demand for high-resolution optoelectronic devices and their applications, micro-pattern formation of transparent conducting oxides (TCOs), especially that of tin-doped indium oxide (ITO), has been required more frequently than before in the development of such devices. Since ITO contains indium, which is one of minor metals whose global production is typically small and are generally traded at high prices, less expensive alternative materials for TCOs are highly sought after. Zinc oxide (ZnO) is a possible candidate for such TCOs alternative to ITO.

Micro-pattern formation of thin film materials may be achieved by reactive ion etching (RIE), which uses chemically reactive plasmas that typically allow high selectivity of etching of specific materials over others and high controllability of micro/nano-scale structure formation. RIE has been widely used in fabrication processes of semiconductors. For high-resolution optoelectronic devices, there has been a considerable demand for RIE processes of ZnO with CH₄ based plasmas, which is a non-corrosive gas and expected to yield high etching rates for ZnO. The RIE process of ZnO with CH₄ based plasmas, however, has also various problems such as carbon deposition during the etching processes. To further develop RIE technologies of ZnO by CH₄ based plasmas, a better understanding of elemental processes of plasma-surface interactions of CH₄ based plasmas with ZnO.

In this study, sputtering yields and surface reaction characteristics of ITO and ZnO by energetic chemically reactive CH_x ions (CH⁺ and CH₃⁺) as well as inert-gas ions (Ar⁺, Ne⁺ and He⁺ ions) were examined with the use of a mass-selected ion beam system. It has been found that, for physical sputtering, sputtering yields of ZnO are much higher than those of ITO. For ZnO, etching by CH₃⁺ proceeds faster than Ar⁺ physical sputtering, which indicates that the etching rate is enhanced by chemical interactions of CH_x⁺ with ZnO. The chemical effect is more pronounced at a lower incident energy. With a fewer hydrogen atoms in the incident ion (i.e., in the case of CH⁺ ion incidence), however, carbon deposition tends to take place on the ZnO surface. Similar beam-surface interactions of ITO with CH_x ions as well as inert-gas ions were also examined and compared with those of ZnO. Mechanisms of chemical reactions of CH_x ions with ZnO and ITO will be discussed in the presentation.