Korean J. Chem. Eng., 25(2), 386-389 (2008) SHORT COMMUNICATION 386 † To whom correspondence should be addressed. E-mail: jyi@snu.ac.kr Highly selective modification of silicon oxide structures fabricated by an AFM anodic oxidation Inhee Choi and Jongheop Yi † School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Seoul 151-742, Korea (Received 25 June 2007  accepted 24 July 2007) Abstract−Anodic oxidation via atomic force microscopy is a promising method for creating submicron-sized silicon dioxide patterns on a local surface. The area patterned by AFM anodic oxidation (AAO) has different chemical prop- erties from the non-patterned area, and thus site-selective modification of patterned surfaces is quite possible. In this study, we combined the AAO with self-assembly method and/or wet chemical etching method for the fabrication of positive and/or negative structures. These locally modified surfaces could be used to the site-selective arrangement and integration of various materials based on a pre-described pattern. Key words: AFM, Anodic Oxidation, Etching, Pattern, Self-assembly INTRODUCTION The fabrication of submicron-sized structures, especially those that are silicon-based, has attracted considerable attention due to the potential applications of such structures, including micro/nano- electromechanical systems (MEMS and NEMS) [1] and miniaturized devices [2]. For this purpose, a wide variety of fabrication methods have been developed to generate patterns on the nano- and micros- cales. Conventional pattern-description techniques such as photoli- thography (e-beam lithography, x-ray lithography, and focused ion beam lithography) and soft lithography ( µ -contact printing and capil- lary lithography), have been widely explored by many researchers. The application of such methods, however, is restricted due to their inherent limitations, which include high costs to reduce pattern size and requirement of complex systems that are derived by photo-mask design. Yet, in the case of nano-probe based patterning methods, such as dip pen lithography [3], nano-scratch [4] and anodic oxi- dation [5], submicron-sized patterns can be easily fabricated on a local area without an intended mask. Therefore, the ability to achieve patterns rapidly and reproducibly by using simple and flexible tech- niques can advance the integration of fabricated structures into micro/ nano-systems. In this study, we demonstrated a highly controllable surface mod- ification method by employing AAO and further chemical treat- ment. The following three factors were major concepts in perform- ing this method: (1) silicon oxide structures can be readily formed by AFM tip-induced local oxidation on a silicon surface, (2) silicon oxide structures have a high affinity to the silane moieties [6], and (3) silicon and silicon oxide have different etching rates in a specific etchants [7]. Based on these facts, constructive and destructive mod- ification of pre-fabricated silicon oxide structures were successfully achieved by the treatments of organosilanes and etchants. EXPERIMENTAL 1. Materials The following materials and chemicals were used: p-type and <100>-oriented silicon wafers with LPCVD (low pressure chemical vapor deposition) silicon nitride as a resist, and KOH, IPA (isopropyl alcohol), HF and 3-aminopropyltriethoxysilane (APTES) as chem- icals for the site-selective modification. Prior to use in the experi- ments, the wafers were cut into 1×1 cm 2 pieces and cleaned in ace- tone, alcohol, and deionized (DI) water under sonication to remove small particles and organic contaminants, followed by drying in a stream of N 2 . 2. Formation of Local Silicon Oxide Structures: AFM Anodic Oxidation Pattern inscription was carried out by pre-controlled, automated AFM oxidation [8], as shown in Scheme 1. A silicon cantilever coated with Ti-Pt (NSC36 series, MikroMasch) was used to pattern the substrates. Here, the contact mode was used to oxidize locally the silicon surface, which was performed under ambient conditions (23- 25 o C and 60-70% relative humidity). During scanning at a rate of 10-20 µm/s, a positive bias of 10-20 V relative to the tip (cathode) was applied to the silicon nitride substrate (anode). 3. Constructive Modification of Silicon Oxide Structures To perform an upward modification of silicon oxide structures, a 10 mM APTES solution in ethanol was added dropwise onto the pre-patterned region for 1 hr and the substrates were then rinsed with ethanol. The fabricated structure was directly characterized by using an AFM apparatus. Topographic and lateral images were simul- taneously obtained in a single scan. 4. Destructive Modification of Silicon Oxide Structures Destructive modification of the locally oxidized patterns was per-