Applications of Ar Gas Cluster Ion Beam to Oxide Thin Films

Abstract

The electronic structure of a Ta 2 O 5 thin film on SiO 2 /Si (100) after Ar Gas Cluster Ion Beam (GCIB) sputtering was investigated using X-ray photoemission spectroscopy and compared with those obtained via mono-atomic Ar ion beam sputtering. The Ar ion sputtering had a great deal of influence on the electronic structure of the oxide thin film. Ar GCIB sputtering without sample rotation also affected the electronic structure of the oxide thin film. However, Ar GCIB sputtering during sample rotation did not exhibit any significant transition of the electronic structure of the Ta 2 O 5 thin films. Ar GCIB can be useful for potential applications of oxide materials with sample rotation. 1．IntroductionIon beam sputtering has been widely used in secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) for depth profiling or surface cleaning. One of the drawbacks of ion beam sputtering is an induced matrix effect such as surface segregation, surface composition change and surface damage, which causes difficulties in characterization of organic/inorganic interfaces and oxide materials [1,2]. Therefore, the surface matrix effects caused by ion beam sputtering should be minimized to use facile surface analysis. C 60 ion sputtering has been used for low damage surface cleaning and depth profiling of many organic materials, but the depth profiling of organic has not been successful because of a composition change due to preferential sputtering as well as degradation of chemical states of C 1s, N 1s, and O1s [3]. Recently, Ar GCIB has attracted a lot of attention as a promising method for depth profiling of organic thin films due to extremely low degradation of surface during depth profiling [4,5]. The effects of an Ar GCIB sputtering process on the structural and chemical properties of an organic material as well as the energy level alignment at the interface between the organic semiconductor and the electrode were studied. The molecular structure and the orientation of pentacene stayed the same after the Ar GCIB process. Furthermore, there was no change in the chemical bonding states in the organic materials including pentacene and poly (3, 4-ethylene dioxy thiophene) polymerized with poly (4-styrene sulfonate) (PEDOT: PSS). The Ar GCIB sputtering process did not cause any variation in the primary valence band structure including the chemical state and the configuration of pentacene/PEDOT:PSS and pentacene/Au. The Ar GCIB sputtering is a damage-free process for organic thin films [6,7]. In our previous work, we applied GCIB sputtering to measure the damage profile on Si (100) surfaces [8]. The damage thickness was about 10 nm, 6.4 nm and 4.2 nm for 20, 10, and 5 keV Ar GCIB sputtering, respectively. We also applied Ar GCIB sputtering to SiO 2 thin films [9]. The Ar GCIB sputtering at surface normal incidence had a deal of influence on the surface potential and the chemical structure of a SiO 2 thin film. However, the Ar GCIB sputtering at the grazing incidence...