Real time observation of glass-like carbon formation from SU-8 using X-ray and ultraviolet photoelectron spectroscopy

The structural development and change in elemental composition of SU-8 3005 photoresist into glass-like carbon due to pyrolysis up to 1000 ° C 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 ° C, 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 ° C. • In-situ observation of glass-like carbon formation. • X-ray photoelectron spectroscopy showing transformation of non - conductive SU-8 to a conductive thin film. • Observation of structural oxygen reduction between 300 and 600 °C leading to the formation of a carbon rich network. • Appearance of various features in UPS data in-line with compositional changes observed in XPS data. • Appearance of zero binding energy state at 1000 ° C.