Electrical Characteristics and Surface Properties of Polycrystalline Silicon Exposed to Morphological Alteration with Applications in Micro- and Nanotechnology

As scaling in microelectronic devices occurs, it is important to understand the impact of surface forces and material properties on the reliability of micro- and nanotechnology. In order to characterize surface forces and electrical properties of polycrystalline silicon, a specialized microdevice was fabricated using surface micromaching. Processing conditions were varied to expose the material to morphological alteration, a common issue in micro- and nanotechnology. The impact of morphological alteration on surface properties and electrical characteristics of polycrystalline silicon was investigated.;Micro- and nanoscale surface adhesion forces of polycrystalline silicon were characterized as a function of morphological alteration caused by exposure to electrochemical corrosion. On the microscale, surface roughness increases by 9.1% due to deepened grain boundaries. On the nanoscale, roughness decreased by 80% when sharp nanoasperities, the dominant morphological features, were etched away by corrosion. The two distinct trends in surface roughening are due to the relevant morphological features impacted by corrosion on each scale. Exploration of the impact of these morphological trends on surface forces revealed that, as acid exposure time is increased, microscale adhesion decreased by 69% while nanoscale adhesion increased 170%. The dominant mechanisms of contact adhesion, van der Waals and capillary forces, are inversely related to surface roughness. Thus, as microscale roughness increases, intermolecular forces decrease. As nanoscale roughness decreases, intermolecular forces are strengthened.;Experiments were also conducted to elucidate the impact of morphology on resistance, capacitance, and electrostatic actuation efficiency of polycrystalline silicon. Results show that sheet resistance of polysilicon increased by 45%, indicating increased porosity at a granular level. Furthermore, capacitance is seen to increase with acid exposure due to increases in surface area available for charge storage. A custom MEMS device was used to measure the effect of electrical property changes on the efficiency of a conventional electrostatic actuator. Key results show that actuation efficiency decreases by 60%. Morphological damage to the polysilicon film results in charge storage at non-preferred areas. This storage reduces the amount of charge available at the actuation components.;Results from the experimental examination of surface properties and electrical characteristics of polycrystalline silicon are interpreted in light of the galvanic corrosion mechanism, the primary components of adhesion, and the principals of charge flow.