Highly controllable and reliable ultra-thin Parylene deposition

Thanks to the excellent barrier property and fabrication accessibility, Parylene has been actively used in the microelectromechanical system. An ultra-thin Parylene film with thickness smaller than 100?nm is usually required to precisely tune the surface property of substrate or protect the functional unit. The commercially available regular Parylene deposition is a dimer mass determined chemical vapor deposition process with a high output (i.e. a low deposition precision in term of thickness control), around 1.6?μm/g (the ratio of film thickness to the loaded dimer mass) for the machine in the author’s lab. Therefore, it is hard to controllably and reliably prepare a Parylene film with thickness smaller than 100?nm, which requires a dimer mass less than 62.5?mg. This paper reported a method to prepare ultra-thin Parylene films with the nominal thickness down to 1?nm. A home-made deposition chamber was put inside and connected with the regular machine chamber through a microfabricated orifice with feature size smaller than 1?mm. According to the free molecular flow theory, the pressure inside the deposition chamber can be predictably and controllably reduced, thereby an ultra-low output of Parylene deposition, as low as 0.08?nm/g, was successfully obtained. The deposition precision was increased by 4 orders of magnitude compared to that of a direct Parylene deposition. This highly controllable and reliable ultra-thin Parylene deposition technique will find promising applications in flexible electronics and biomedical microdevices.