Manila Journal of Science 10 (2017), pp. 114-125 Surface Analysis of Silicon (100) Wafer After Contact Electrification Using Kelvin Force Microscopy Jose M. Esmeria, Jr.,1, 2 Romeric Pobre1 1Physics Department, De La Salle University, 2401 Taft Avenue, Manila 1004, Philippines 2 Reliability Engineering Department, TDK Philippines Corporation (TPC), 119 East Science Avenue, SEPZ, Biñan, Laguna 4024, Philippines. *Corresponding Author: [email protected] ABSTRACT Contact electrification was demonstrated on Si (100) wafer, and surface charge images at submicron scale were analysed using Kelvin force microscopy (KFM). Potential map images have shown carpet-like patterns on the (100) plane of Si wafer. Individual potential spikes that appeared on the surface are indicative of the presence of charges arising from contact electrification. It was clearly shown that positive and negative surface potential maps on Si (100) wafer with low resistivity have minimal change in the order of ±2.5 mV after 4800 seconds of noncontact electrification. The mechanism for the slow discharged on the Si (100) wafer can be modelled like a clamped capacitor direct current (D.C.) electric circuit. Keywords: Surface interfaces, Contact electrification, Triboelectricity. Copyright © 2017 by De La Salle University SURFACE ANALYSIS OF SILICON (100) WAFER ESMERIA & POBRE 115 INTRODUCTION force, room humidity, and ground continuity of the material (Hogue, 2004). A significant number of researches have Triboelectric charging between two been done for the last 50 years in contact different metals is widely accepted as an electrification (CE). CE or triboelectricity has exchange of electrons due to their work function beneficial applications in medical sensors difference. This difference is brought about by , body implants, pharmaceuticals and the difference of the individual Fermi levels of photocopying (Lacks & Mohan Sankaran, both metals where some electrons flow from 2011), and microelectric generators (Zhou metal with higher Fermi level into the other et al., 2013). However, charges generated metal (Williams, 2012). It was also reported through CE are a prelude to a charge device that triboelectric charging for polymers model (CDM) type of electrostatic discharge can be best explained by two well-known (ESD) damage to electronic devices. Typical mechanisms, one involving electron transfer ESD damage associated with CDM is <125 V and the other due to the presence of ions on for class C1 devices (“Part 5: Device Sensitivity the surface of the material. Electron transfer and Testing » Electro Over-Stress (EOS) /ESD on an insulator was reported to be a function of Association, Inc.,” n.d.). Moreover, HDD read/ its physical condition, and surface impurities, write sensors have even lower threshold at <1 such as ion contaminants, could well influence V (Baril, Nichols, & Wallash, 2002). CE is a tribocharging (Diaz & Felix-Navarro, 2004). well-known phenomenon, but the fundamental The use of atomic force microscopy has mechanisms behind CE are not yet fully made advances in the in the study of contact understood (Lacks & Mohan Sankaran, electrification at nanometer levels (Gady, 2011). Current understanding of CE revolves Reifenberger, & Rimai, 1998). By attaching around the idea that when two materials are 5-µm spheres on the AFM tip, these spheres brought into surface contact and made to act as CE applicators on dielectric substrates. separate, each surface will produce uniform With this early setup, contact electrification but oppositely electric charge distribution. was studied using force interactions between Depending on the type of material, electric the sphere and the sample. Later, potential charges may decay rapidly upon contact to mapping (Melitz, Shen, Kummel, & Lee, ground (or ionization) for dissipative materials 2011) by Kelvin force microscopy or KFM—a or charges may stay longer for insulators. A special function of atomic force microscope or common way to determine material’s charge AFM—were mostly utilized to characterize affinity—either positive or negative—is surface electric potentials. KFM was also thru the use of triboelectric series (Diaz & instrumental in demonstrating mosaic Felix-Navarro, 2004). Triboelectric series is patterns of both positive and negative charge based from empirical method that sequences for each material after contact for polymer materials based from their charge transfer specimens (Baytekin, Patashinski, Branicki, & from the positive (+top) to the negative Baytekin, 2011). Aside from the mosaic charge (−bottom). When two different materials patterns, of both positive and negative charge contact and separates (CE), the material distributions, the study also showed material listed at positive (+) side will likely be charged transfer and changes in surface composition positively and the negative (−) side will be occurred after contact electrification. Another charged negatively. However, the amount of study suggested that these mosaic patterns electric charge generated on the surface of two are thought to be an outcome of some complex materials after CE is dependent on the applied mechano-chemical reactions (Sakaguchi, ( ) Therefore, it is in the interest of this work ( ) = [ + + ] to study the effects of contact electrification 1 2 ( ) of aTherefore, semicond uctorit is in surface the interest using of a thiscommon work () = − 2[ + + ] (4.0) touchto -studyup tool the and effects propose of contact a model electrification for the 1 2 Therefore, it is in the interest of this work ( ) chargeof a semiconddecay atuctor the surfacesurface using of Si a commonsample( ) = [ + −+2 ] to study the effects of contact electrification 1(4.0) touch-up tool and propose a model for the 2 of aafter semicond CE.uctor surface using a common − 2 charge decay at the surface of Si (4.0)sample Thus, potential map images have two touch -up tool and propose a model for the after CE. components: tip bias ( and ) and 116 MANILA JOURNAL OF SCIENCE chargeKF Mdecay at the surface VOLUMEof Si sample 10 (2017) Thus, potential map images have two after CE. capacitance gradient ( ( )) . 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