Photoresists based on coconut and castor oil

The development of photoresists with decreased feature sizes and their application in photolithog. has become an active field of research. Neg. photoresists reproduce the geometric patterns of illumination masks by the crosslinking of polymers, yielding insol. 2.5-dimensional surface structures. Advancing our work on water-developable poly(2-oxazoline)-based neg. photoresists, we here present poly(2-oxazoline)-based photoresists from renewable resources. The 2-oxazoline monomers used in the synthesis of the photoresist were synthesized in a one-pot solvent-free reaction of ethanol amine with fatty acids from natural resources, namely undecenoic acid (castor oil) and decanoic acid (coconut oil). The microwave-assisted polymns. were performed at a scale of 300 g in an ionic liq., maximizing the efficiency of energy input, solvent recyclability and polymer recovery, chiefly due the pptn. of the copolymers from the ionic liq. upon cooling. The copolymer was characterized by structural anal. Crosslinking of the copolymers in the film state can be realized by the reaction with a tetrathiol after UV activation of a photoinitiator. If the UV irradn. is applied through a mask aligner system, the geometric patterns can be reproduced after development, notably with a resoln. higher than 1 μm at a film height of 100 nm. The adhesion of the resist on various substrates (cross-hatch tests) and its surface profiling (surface roughness) were found to be in the targeted range.