Adhesion force and Nanotribological Characteristics of Chemical Vapor Deposited Fluorocarbon Films
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Adhesion force and Nanotribological Characteristics of Chemical Vapor Deposited Fluorocarbon Films Nam-Kyun Kim1, Tae-Gon Kim1 Jin-Goo Park1 Woon-Bae Kim2, Hyung- Jae Shin2 1 2
Dept. of Metallurgy and Materials Eng., Hanyang University, Ansan, 425-791, Korea Samsung Advanced Institute of Technology, Suwon, 440-600, Korea
ABSTRACT In this study, Adhesion force and Nanotribological Characteristics of fluorocarbon (FC) films on Al deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) were evaluated. The contact angle of FC thin films on Al was measured to be around 110o. The surface energy was calculated to be 15 dynes/cm from the measurements of contact angles of polar and nonpolar solutions on surfaces. The contact angle hysteresis, which is an indicator for the surface heterogeneity, was lower than 30o. The friction force of FC films coated surfaces was three times lower than bare Al. The adhesion force of bare Al was measured to be around 9.6nN. The presence of FC films on Al reduced it to below 4nN. Fourier transform infra-red (FTIR) spectra showed the presence of fluorocarbon groups such as –CFn- and =CF=CF2. INTRODUCTION Fluorocarbon (FC) film coating has been widely reported as one of effective methods to prevent “in use stiction” or to reduce the friction of nanostructure, because of a low coefficient of friction, low adhesion force and its high hydrophobicity [1]. Adhesion of surfaces in nanostructure is a serious failure mechanism in surface-nano-machined devices which cause destruction of structures when surfaces are brought into contact. It results in significant yield loss and reliability problems associated with the system. PTFE-based materials, such as FC films, are the most popular way to reduce the problem of adhesion between surfaces. Their hydrophobic properties make them excellent anti-stiction layers, therefore, when used in a nano manufacturing process, the interaction of such PTFE-like films with the surface of nano structures can modify the film’s chemical and physical properties and consequently, prolong their lifetime as an anti-adhesion layer. These films are being challenged more and more by novel deposition techniques such as self assembled monolayer (SAM) [2] spin coating, and chemical vapor deposition (CVD). Liquid phase depositions such as spin coating and SAM can not be used for the nano structure and are not compatible with wafer scale manufacturing process due to its lacks of reproducibility and controllability. Vapor deposition method, therefore, has been used for the deposition of FC films on nanofabricated complex structure. Also, the thickness and patterns could be easily controlled by CVD during the nanofabrication. The objective of this study was to characterize chemical, optical and nano-mechanical behaviors of FC films deposited perfluoropolymer films as an anti-adhesion layer by PECVD. 2. EXPERIMENTS 2.1. Sample preparation and procedure Aluminum coated wafers (300-nm thick) were prepared by the sputtering technique. These
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wafers were cut into
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