Soft mask-based dry etching of parylene AF4 for advanced packaging applications

In this work, an alternative dry etching approach for parylene AF4 is presented based on a photoresist soft mask, which results in a relatively simpler, faster, cheaper and environmentally friendly process in comparison to the typical dry etching process with a hard mask. 2.5 µm thick parylene AF4 was deposited on a silicon (Si) substrate by vapor deposition polymerization (VDP). A 5 µm thick photoresist was used as a soft mask, while parylene AF4 patterning was done using an oxygen (O2)-argon (Ar) inductively coupled plasma reactive ion etching (ICP-RIE) process. The AF4:photoresist selectivity was around 1 while the AF 4 etching rate was roughly 275 nm/min for an Ar/02 ratio of 0.1 at 20mTorr and ICP:CCP powers of 1000W:50W respectively. The influence of the ICP plasma parameters on the AF 4 etching rate was investigated and the results suggested a predominant oxygen radicals-based reactive chemical etching mechanism.