Air-Gap Fabrication Using a Sacrificial Polymeric Thin Film Synthesized via Initiated Chemical Vapor Deposition

Thin films of a sacrificial polymer based on poly(cyclohexyl methacrylate) (PCHMA) were synthesized using initiated chemical vapor deposition (iCVD). iCVD is able to make cross-linked PCHMA in situ on a substrate in one step without using any solvents. Although cross-linked, the polymer was found to decompose cleanly, leaving behind a maximum of 0.3% of residue by thickness upon completion of thermal annealing. Cross-linking renders the polymer stable in practically all solvents, so photoresist used for patterning can be removed by dissolution instead of ashing. The high etch rate in oxygen reactive-ion etching in addition to the stability in solvents eliminates the need of a hard mask during etching. This represents an improvement over previously reported spin-on sacrificial materials. Infrared spectroscopy and solubility tests confirm the identity of the iCVD polymer and its stability in solvents. The onset of thermal decomposition is 270°C, allowing the polymer to survive high-temperature processing steps. Fabrication using conventional lithographic, etching, and deposition techniques resulted in void structures having feature sizes of a minimum of . This work represents a novel approach for air-gap fabrication using a sacrificial polymer, combining the rationale behind cross-linking and the technique required for thin-film deposition.