virtual nanofab a silicon nanofabrication trainer nick reeder, sinclair community college andrew...
TRANSCRIPT
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.