Advanced Optical Metrology for Stability Monitoring of Polyimide Curing Process

Polyimide (PI) has been widely used as a dielectric material due to its excellent electrical insulation properties, mechanical properties, and thermal resistance for advanced packaging applications such as wafer-level fan-out packaging [1]. Conventionally, imidization degree of polyimide is identified by Fourier-transform infrared spectroscopy (FTIR). Unfortunately, FTIR is hard to tell the difference when curing temperature above certain degree (or when imidization degree >90%). As a result, chemical resistance of highly cured PI can only be judged by practical chemical destructive tests. Here we introduce one methodology, Advanced Optical Metrology (AOM), to determine the variation of highly cured polyimide film property. No matter highly cured PI film changed its curing temperature or went through different chemical treatment, AOM has great sensitivity to capture its minor difference compared to baseline condition. This work also collected polyimide optical intensity data by AOM and demonstrated its correlation to chemical resistance. Taking advantage of this correlation, this methodology is suitable for PI imidization stability monitoring and prevent PI damage in the following process.