Virtual NanoFab A Silicon NanoFabrication Trainer Nick Reeder, Sinclair Community College Andrew Sarangan, University of Dayton Jamshid Moradmand, Sinclair Community College Challenge: Providing Hands-on Silicon Nanofabrication Experience • The facilities needed to do silicon nanofab are very expensive. Solution: Virtual Nanofab • • • Software that we’re developing to teach students about the steps involved in processing a silicon wafer. Please take a copy of the installation disc! System Requirements: – – – – Operating system: Windows XP or higher Memory: 2 GB RAM Hard drive: 300 MB of free space If your computer does not have National Instruments LabVIEW installed, you must install the free LabVIEW run-time engine, which is included on the installation disc. Example: Fabricating a MOSFET • MOSFET = Metal-oxide-semiconductor field effect transistor MOSFET in Virtual NanoFab The structure shown required about 25 steps. User Operations • • Thermal oxidation Photolithography • • • • • Removing material • • • Wet etch Dry etch Depositing layers of material • • • • Spin coat Mask Expose Develop E-beam evaporation Chemical Vapor Deposition (CVD) Sputtering Ion implantation (“doping”) Thermal Oxidation • Grows a layer of silicon dioxide (SiO2) on the wafer surface. • Key properties of SiO2: – Impervious to ion implantation. – Can be etched away by immersion in hydrofluoric acid (HF), which does not etch silicon. Thermal Oxidation in Virtual NanoFab Photolithography • Steps in photolithography: – Spin-coat photoresist. – Create and place mask. Mask defines which areas will be exposed to UV light and which areas will be shaded. – Expose with UV light. – “Develop” the photoresist: UV-exposed areas are removed, while shaded areas remain. Photolithography in Virtual NanoFab 1. Before exposing: 2. After exposing (but before developing): 3. After developing: Exposure with Uneven Layer Thicknesses Note that resist above silicon is more fully exposed than resist above aluminum. Removing material • Methods of removing material – Wet etching • • Low-tech Immerse wafer in a bath of liquid acid or solvent – Dry etching • • High-tech Expose wafer to plasma beam Etching in Virtual NanoFab SiO2 (blue) after wet etch with hydrofluoric acid: note tapered sidewalls and undercut of photoresist (pink). SiO2 after dry etch with CF4 plasma: note vertical sidewalls. Depositing Layers • Methods of depositing materials – Electron-beam evaporation – Chemical vapor deposition (CVD) – Sputtering Deposition in Virtual NanoFab Evaporated titanium (gray): accumulates only on horizontal surfaces. Chemical-vapor-deposited titanium: adheres to vertical surfaces as well as horizontal. Ion Implantation • Modifies the electrical characteristics of the silicon wafer: key to the operation of semiconductor devices such as diodes and transistors. • Implanting boron results in “p-type” doping. • Implanting phosphorus results in “n-type” doping. Ion Implantation in Virtual NanoFab Other Features • Maintains history of user operations. • “Reference & Videos” page provides chapters explaining theory, along with videos of operations being performed in the lab.