1. Virtual NanoFab A Silicon NanoFabrication Trainer
Nick Reeder, Sinclair Community College
Andrew Sarangan, University of Dayton
Jamshid Moradmand, Sinclair Community College

2. Challenge: Providing Hands-on Silicon Nanofabrication Experience
The facilities needed to do silicon nanofab are very expensive.

3. 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.

4. Example: Fabricating a MOSFET
MOSFET = Metal-oxide-semiconductor field effect transistor

5. MOSFET in Virtual NanoFab
The structure shown required about 25 steps.

6. User Operations Thermal oxidation Photolithography Removing material
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”)

7. 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.

8. Thermal Oxidation in Virtual NanoFab

9. 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.

10. Photolithography in Virtual NanoFab
Before exposing:
After exposing (but before developing):
After developing:

11. Exposure with Uneven Layer Thicknesses
Note that resist above silicon is more fully exposed than resist above aluminum.

12. Removing material Methods of removing material Wet etching Dry etching
Low-tech
Immerse wafer in a bath of liquid acid or solvent
Dry etching
High-tech
Expose wafer to plasma beam

13. 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.

14. Depositing Layers Methods of depositing materials
Electron-beam evaporation
Chemical vapor deposition (CVD)
Sputtering

15. Deposition in Virtual NanoFab
Evaporated titanium (gray): accumulates only on horizontal surfaces.
Chemical-vapor-deposited titanium: adheres to vertical surfaces as well as horizontal.

16. 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.

17. Ion Implantation in Virtual NanoFab

18. Other Features Maintains history of user operations.
“Reference & Videos” page provides chapters explaining theory, along with videos of operations being performed in the lab.