Improvement in dissolution contrast of positive-tone photo-definable poly(benzoxazole) materials

Positive-tone photo-definable poly(benzoxazole) (PBO) has been widely used as dielectric for re-distribution layer of wafer level chip size package. This material can simplify the manufacturing process and ensure the reliability owing to its good mechanical properties and high thermal stability. However, lithographic performance of conventional photo-definable PBO is not enough mainly due to low dissolution contrast, and the pattern formation on the substrate with deep gap structure is often difficult. Then, in order to improve lithographic performance by enhancing dissolution contrast, we re-designed photo-definable component. As a result, dissolution contrast could be doubled in comparison to conventional PBO by applying contrast activator or more effective diazonaphthoquinone (DNQ) and we could obtain lithographic pattern on the substrate with deep gap structure without residue at the bottom of the gap. In addition, modified PBO also showed good cured film properties even when cured at low temperature below 250 °C.