XPS investigation of monatomic and cluster argon ion sputtering of tantalum pentoxide

Robin Simpson,Richard G White,John F Watts,Mark A Baker

doi:10.1016/j.apsusc.2017.02.006

Robin Simpson, Richard G White + Show 2 more

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https://doi.org/10.1016/j.apsusc.2017.02.006

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Abstract

In recent years, gas cluster ion beams (GCIB) have become the cutting edge of ion beam technology to sputter etch organic materials in surface analysis. However, little is currently known on the ability of argon cluster ions (Arn+) to etch metal oxides and other technologically important inorganic compounds and no depth profiles have previously been reported. In this work, XPS depth profiles through a certified (European standard BCR-261T) 30nm thick Ta2O5 layer grown on Ta foil using monatomic Ar+ and Ar1000+ cluster ions have been performed at different incident energies. The preferential sputtering of oxygen induced using 6keV Ar1000+ ions is lower relative to 3keV and 500eV Ar+ ions. Ar+ ions exhibit a steady state O/Ta ratio through the bulk oxide but Ar1000+ ions show a gradual decrease in the O/Ta ratio as a function of depth. The depth resolution and etch rate is substantially better for the monatomic beam compared to the cluster beam. Higher O concentrations are observed when the underlying Ta bulk metal is sputtered for the Ar1000+ profiles compared to the Ar+ profiles.

Highlights

Tantalum pentoxide, Ta2O5, is technologically significant due to its dielectric properties [1] and applications in microelectronics [2] and optics [1,3]
Ta2O5 grown on Ta foil is a wellestablished standard material for the determination of ion etch rate and depth resolution in compositional depth profiles obtained in electron spectroscopy [4]
In order to establish the Ta chemical states observed during depth profiling of the Ta2O5 layer, a methodical approach was adopted in fitting the Ta 4f spectra, using the known binding energies for the metallic tantalum doublet and well reported peak positions of the Ta2O5 doublet

Summary

Introduction

Ta2O5, is technologically significant due to its dielectric properties [1] and applications in microelectronics [2] and optics [1,3]. Ta2O5 grown on Ta foil is a wellestablished standard material for the determination of ion etch rate and depth resolution in compositional depth profiles obtained in electron spectroscopy [4]. Many authors use the European standard (BCR-261T), which has a certified thickness of Ta2O5 grown on Ta foil as a reference to estimate the etch rate when performing XPS/AES depth profiles on other metal oxide thin films [5]. XPS studies of the preferential sputtering of oxygen from Ta2O5 have been performed by a number of workers [7,8,9,10,11,12]. Hofmann and Sanz performed the earliest in-depth study and they gave the steady-state TaOx stoichiometry (using 3 keV Ar+) to be TaO1.05 [7]. Holloway and Nelson sputtered Ta2O5 at varying incident Ar+ energies between 0.5 and 5 keV and reported that greater preferential sputtering of

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