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.
Additional Information© The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Received: 30 August 2018; Accepted: 8 October 2018; Published: 10 October 2018. Authors' contributions: YL and WW drafted the manuscript. YL, WW and YT conceived of the study. HL and DK worked on the model calculation. YL and WD carried out the deposition experiment. All authors read and approved the final manuscript. The authors thank Prof. Ying Yan at Dalian University of Technology for her help in analysis of the AFM measurements. The authors declare that they have no competing interests. Ethics approval and consent to participate: Not applicable. Funding for this research was provided by and thank the financial supports from the scholarship from the Major State Basic Research Development Program (973 Program) (Grant No. 2015CB352100) and the National Natural Science Foundation of China (Grant Nos. 81471750 and 91323304).