Infrared laser deposition of Teflon coatings on microstructures

Abstract

Polytetrafluoroethylene (PTFE, trade name Teflon®) has a wide range of unique and desirable physical, electrical and chemical properties. Its tribological properties are well-suited to anti-stiction applications, and its chemical inertness commends it as a barrier and passivation layer. However, conventional thin-film techniques are not suited for depositing Teflon® films on microstructures. Spin coating is impossible because of the well-known insolubility of PTFE. Plasma polymerization of fluorocarbon monomers, ion beam and rf sputtering produce PTFE films that are deficient in fluorine. Pulsed laser deposition (PLD) using excimer and Ti:sapphire lasers is unsatisfactory because UV or near-IR laser ablation "unzips" the PTFE, and requires high-temperature annealing to re-polymerize the deposited monomeric film. We have demonstrated that a completely dry, vapor-phase coating technique -resonant infrared pulsed laser deposition (RIR-PLD) at a wavelength of 8.26 µm -produces crystalline, smooth Teflon® films at low process temperatures. Indeed, the films as deposited by RIR-PLD exhibit a surprising degree of crystallinity even at room temperature. The stoichiometry and local electronic structure are preserved during the laser vaporization process, as demonstrated by IR absorption and X-ray photoelectron spectroscopy. Films deposited on microscale structures show good adhesion, excellent smoothness, and a high degree of conformability to the structures. We also discuss experiments planned for the near future to compare the tribological properties of the PTFE films deposited by RIR-PLD with those of other tribological coatings. We will also discuss the implementation of RIR-PLD in practical processing schemes for MEMS applications, including the challenge in adapting existing solid-state mid-IR laser technology for this purpose.

Micromachining of polyurethane (PU) polymer using a KrF excimer laser (248nm)

“…Currently, the modern materials in MEMS devices are limited due to fabrication process limitations. MEMS devices and hard disks are generally coated with "Teflon-like" materials which require micromachining and micro-processing to obtain the required high surface-to-volume ratio, a prerequisite for micro-electromechanical systems (MEMS) (Papantonakis 2006). For micromachining patterns with the help of laser micro-drilling, the process of laser micro-drilling can be a serial process with one hole drilled at a time or a mask imaging process where many holes can be drilled simultaneously (Zheng 2001).…”