Increased plasma etch resistance of thin polymeric and photoresist films

Plasma etch rate measurements of thin polymeric films are presented. Four commonly used polymers were etched (1) poly-methyl-methacrylate (PMMA), (2) poly-hydroxyethyl-methacrylate (PHEMA), (3) poly-hydroxystyrene (PHS), and (4) a commercial photoresist (GKRS). Their etch rates (ER) in a plasma reactor and their glass transition temperature (Tg), were both studied as functions of the initial film thickness. The results clearly show a strong relation between the ER and the initial polymer thickness. The etch rate is decreasing as the initial polymer thickness is decreasing for films thinner than ∼200 nm. By correlating the plasma ER rate with the Tg of the polymeric films, a clear inverse relation is revealed, namely that the ER decreases when the Tg increases.