Reactive ion etch studies of DUV resists

The morphology and degradation of the polymeric DUV resist of polyhydroxystyrene/t-butyl acrylate copolymers after CF4/O-2/Ar/CHF3 reactive ion etching(RIE) was studied. The surface pitting in the area of 10 nm with spikes as large as 85 nm were found. DUV resists with higher t-butylacrylate content in the main chain were susceptible to main chain scission and surface pitting. The entrapment of volatile fragments by the deposited amorphous fluorocarbon polymer during the RIE process leads to surface distortions. Pre-hardening of the resist by electron beam reduces the surface pitting by two fold. Negative resist based on polyhydroxystyrene homopolymer with minimum volatile produced very smooth films with a tenfold reduction in roughness factor. The future design of positive resist should include the RIE performance factor of minimal outgassing and minimum sidewall surface roughness.