Real time observation of glass-like carbon formation from SU-8 using X-ray and ultraviolet photoelectron spectroscopy
Abstract
The structural development and change in elemental composition of SU-8 3005 photoresist into glass-like carbon due to pyrolysis up to 1000~ is investigated utilising in-situ x-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) under ultra-high vacuum (UHV). XPS spectra were analysed in order to investigate changes to elemental composition and physical structure. Peak asymmetry in the measured C 1s spectra is found to be a clear indicator of a transition in both physical structure and increased electrical conductivity. The in-situ XPS measurement of pyrolysis is effective in isolating changes in oxygen composition solely due to the pyrolysis process. Oxygen concentration, C 1s peak asymmetry and C 1s peak positions are strong indicators of semiconducting SU-8 transitioning to conducting glass-like carbon. For SU-8 pyrolysed above temperatures of 500~, a clear development is observed in the material structure and composition towards a carbon rich conducting network indicative of glass-like carbon. UPS spectra were analysed to investigate the changes in secondary electron cut-off (SECO) and valence band maximum (VBM) as the SU-8 layer is heated in UHV. The changes in SECO and VBM correlates well with the XPS data and a zero binding energy state is observed at 1000~.
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