ADHESION/STICTION AND FRICTION STUDIES OF NANO/MICRO-TEXTURED SURFACES PRODUCED BY CRYSTALLIZATION OF AMORPHOUS SILICON Hengyu Wang 1 , Li Cai 2 , Dehua Yang 3 , Thomas Wyrobek 3 , and Min Zou *, 1 1 Department of Mechanical Engineering, 2 Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701 3 Hysitron, Inc., 10025 Valley View Road, Minneapolis, MN 55344 ABSTRACT This paper reports a new method of nano/micro surface- texturing and the results of systematic studies of adhesion/stiction and friction properties on the textured surfaces produced by this method. Nano/micro-textured surfaces with various roughnesses were produced by low temperature aluminum-induced crystallization of plasma enhanced chemical vapor deposited (PECVD) amorphous silicon. Adhesion/stiction experiments on these nano/micro- textured and non-textured surfaces were performed using two diamond tips under predefined displacement profiles with different maximum indentation displacements. Friction experiments on the textured and non-textured surfaces were conducted using the same tips under various normal contact forces. The adhesion/stiction forces and coefficients of friction (COF) of the textured surfaces were found to be much smaller than those of non-textured surfaces. Keywords: surface-texturing, nano-texture, micro-texture, crystallization of amorphous silicon. INTRODUCTION Surface phenomena such as adhesion/stiction and friction are major factors that affect the product reliability microelectromechanical systems (MEMS) due to the large surface area to volume ratio of these structures [1, 2]. These issues will be escalated as microsystems technologies begin to transition into nanoscale. One approach of reducing adhesion/stiction and friction is to texture the contacting surfaces. Random surface texturing has been accomplished through different etching processes for MEMS applications [3, 4]. However, the surfaces produced have fractal geometries with multi-scale random roughness, which limits their benefits in MEMS/NEMS (Nanoelectromechanical systems). Nano scale surface textures are very desirable because they have additional benefits of making the surfaces more hydrophobic, therefore, reducing the meniscus component of adhesion/stiction and friction forces. This paper reports a new surface texturing method which uses low temperature aluminum induced crystallization of amorphous silicon. This method has a potential to adjust textures from nano to micro scale. Adhesion/stiction and friction studies on the nano/micro- textured surfaces with different surface roughness produced by this method are also presented. SURFACE-TEXTURING METHOD In this study, single crystal silicon wafers (100) with thermally grown silicon oxide layers were selected as substrates for surface texturing. The thick thermal oxide layers were used to prevent the crystal orientation of the silicon substrates from affecting the crystallization of amorphous silicon. Amorphous silicon and then aluminum films were deposited on the substrates using PECVD and physical vapor evaporation, respectively. The samples were then divided into three groups and heated at 300ºC for 10, 40, and 70 seconds, respectively, to create nano/micro-textured surfaces through crystallization of amorphous silicon. The aluminum films were then removed by selective chemical etching. The samples were then characterized using optical microscopy, scanning electron microscopy (SEM), x-ray diffraction, and scanning probe microscopy (SPM). SEM images show that crystal silicon bumps with sizes varying from 100 nm to 2 μm were formed on these samples depending on annealing time. SPM results show that the 70 s annealed sample has the highest surface roughness and the 10 s annealed sample has the lowest (Fig. 1). (a) (b) (c) Fig. 1 SPM of the textured samples (10 x 10 μm). (a) 10 s, (b) 40 s, (c) 70 s annealing. RESULTS OF ADHESION AND FRICTION STUDIES Adhesion/stiction and friction studies of the textured samples and non-textured samples were performed using a TriboIndenter (Hysitron, Inc.) with two diamond tips, each attached to a transducer that has normal and lateral force and displacement sensing capabilities. The nominal tip radius of curvature of the tips used was 5 μm, and 100 μm, respectively. Adhesion/stiction tests were performed by setting the diamond tips to follow predefined displacement profiles. A typical displacement profile includes allowing the tip to 1 Copyright © #### by ASME Proceedings of WTC2005 World Tribology Congress III September 12-16, 2005, Washington, D.C., USA WTC2005-63723 1 Copyright © 2005 by ASME