Abstract
Structuring or removal of the epoxy based, photo sensitive polymer SU-8 by inductively coupled plasma reactive ion etching (ICP-RIE) was investigated as a function of plasma chemistry, bias power, temperature, and pressure. In a pure oxygen plasma, surface accumulation of antimony from the photo-initiator introduced severe roughness and reduced etch rate significantly. Addition of SF6 to the plasma chemistry reduced the antimony surface concentration with lower roughness and higher etch rate as an outcome. Furthermore the etch anisotropy could be tuned by controlling the bias power. Etch rates up to 800nmmin−1 could be achieved with low roughness and high anisotropy.
Highlights
SU-8 is an epoxy based, photo sensitive polymer developed by IBM in the late 1980s [1]
Since severe roughening of the surface was observed after etch, root mean square surface roughness (Rrms) and surface composition were measured by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS)
Our experiments showed a dependency of the etch rate on all parameters, see Fig. 3
Summary
SU-8 is an epoxy based, photo sensitive polymer developed by IBM in the late 1980s [1]. SU-8 negative photo resist is derived from EPONTMresin [2], where the monomer consists in average of eight epoxy groups and eight aromatic benzene groups as indicated by the name. The viscous polymer contains between 5% and 10% photo-initiator enabling cross linking by standard I-line lithography. SU-8 in microtechnology was developed for use in LIGA1 [3] where the polymer is used to define a structured mold.
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