2019 Volume 40 Issue 3 Pages 121-130
Cresol formaldehyde novolac resins (Cre/Form) are used as photo-resist materials because they can be applied minutely onto hard silicon wafers, which are used in the process of making integrated semiconductor circuits. Resins with high hardness cannot be applied minutely onto flexible bases, such as polyimide films. To develop novolac resins for photo-resists having flexibility beyond that of Cre/Glu novolac resin using glutaraldehyde (Glu) as a crosslinking agent,5-hydroxymethylfurfural (HMF) derived from fructose (Fru) one of a monosaccharide was used as a crosslinking agent.Synthesis of m-cresol 5-hydroxymethylfurfural novolac resins (m-Cre/HMF) was carried out in a stepwise reaction of m-Cre and HMF obtained at the first step. The obtained m-Cre/HMF novolac resin had Mw from 1200 to 2900, and the dissolving rate for alkaline aq. solution (DR) decreased with increasing Mw. To prepare cast films, resins meeting the condition of DR below 500Å/s were chosen. Cast films of thickness 5 μm onto the polyimides were prepared by spin-coating, heatsetting and then exposing to developer solution. The flexibility of the obtained resins was evaluated by observation with a microscope for their bent parts. The m-Cre/HMF novolac resin showed higher flexibility than that of Cre/Glu novolac resin. The lithography performance of the m-Cre/HMF novolac resin coated onto the silicon wafers in 1.5 μm thickness was examined. The residual membrane thickness was high (99%) and the resist pattern could be drawn up in 5 μm width clearly.
