1/28/09
Nanomaterials manufacturing approaches
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Limitations of top-down fabrication:
• Due to diffraction effects, the practical limit for optical lithography is around 100 nm.
• Electron beams, of smaller wavelengths can be used to define smaller features and
feature sizes smaller than 20 nm can be patterned.
• But e-beam projection systems using masks have not been fully developed yet – instead,
“direct-write” e-beam lithography has been used.
• While optical lithography works in parallel over the wafer (with high throughput),
direct-write e-beam lithography works as a series process (with low throughput).
Limitations of bottom-up fabrication
• Getting the structures to grow exactly how and where it is wanted to be
• Making complicated patterns
• Fabricating robust structures
Some common strategies are:
• Use catalysts, stress fields, diffraction gratings to achieve selective growth in specific
locations
• Use top-down processes in conjunction with bottom-up processes, and build on silicon
substrates
Requirements for nanomaterials building
- Tools are needed to analyze, visualize, and manipulate very small features
- In addition to standard integrated circuit processing tools, others such as atomic force
microscopes (AFM) are utilized
- Requires very clean environment: “clean room”
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