Virtual NanoFab A Silicon NanoFabrication Trainer Nick Reeder, Sinclair Community College Andrew Sarangan, University of Dayton Jamshid Moradmand, Sinclair Community College
Jan 16, 2016
Virtual NanoFabA Silicon NanoFabrication Trainer
Nick Reeder, Sinclair Community CollegeAndrew 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
• Spin coat• Mask• Expose• Develop
• Removing material • Wet etch• Dry etch
• Depositing layers of material• 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 NanoFab1. 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.