Novolak resins with high thermal stability, high resolution, improved photospeed and etch characteristics for advanced photoresist applications

Abstract Novolak resins provide the best overall performance for “g” and “i”‐line photoresists. There is a continuing need for advanced novolak designs that will provide improved lithographic, thermal, and etch characteristics that may be reproducibly synthesized. A novolak synthesis process was developed using the solution condensation technique. Cresol mixtures with m‐cresol and 3,5‐xylenol at specific ratios provide reproducible novolaks with controlled molecular weights. In order to achieve high thermal and etch performance, while retaining photospeed and resolution characteristics, three basic approaches were investigated: (1) increase in molecular weight, which produces novolaks with T g ranging from 120 to 130°C with relatively slow dissolution rates; (2) incorporation of multi‐hydroxyphenols such as resorcinol to tailor the dissolution rate, resolution, thermal, etch, and adhesion characteristics; (3) partial esterification of multi‐hydroxy novolaks giving a T g range of 140 to 150°C. Lithographic evaluation of the novolak resins was performed by formulating with a 2,1,4‐diazonaphthoquinone (DNQ) sensitizer. Results on resin synthesis, molecular weights, lithographic, thermal, and etch characteristics are discussed.