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

TL;DR

This study uses in-situ X-ray and ultraviolet photoelectron spectroscopy to observe the transformation of SU-8 photoresist into glass-like carbon during pyrolysis up to 1000°C, revealing structural and compositional changes.

Contribution

It provides the first in-situ analysis of SU-8 pyrolysis, identifying key spectral indicators of transition to glass-like carbon and elucidating the evolution of electrical properties.

Findings

Oxygen content decreases with temperature.

Peak asymmetry indicates structural transition.

Conductivity increases as carbon network develops.

Abstract

The structural development and change in elemental composition of SU-8 3005 photoresist into glass-like carbon due to pyrolysis up to 1000~$\degree$C is investigated utilising \textit{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 \textit{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~$\degree$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~$\degree$C.