PATTERN TRANSFER

Optical lithography

Lithography defines where later fabrication operations should occur.

1. Film Material on substrate

2. Photoresist Light-sensitive layer

3. Exposure Pattern through mask

4. Development Create resist pattern

5. Etch Transfer pattern

6. Resist Removal Leave patterned material

Lithography does not usually create the final mechanical structure by itself. It tells later processes where to act.

PHOTORESIST

Positive vs. negative photoresist

Not all photoresists respond to light the same way.

Exposed regions become soluble and wash away during development. Shipley resist is a common example.

Pattern matches the mask

Exposed regions become insoluble and remain after development, while unexposed resist washes away. SU-8 is a common example.

Pattern is inverted from the mask

Positive → matches the mask.

Negative → inverts the mask.

MATERIAL REMOVAL

Uses liquid chemistry to remove selected material.

Uses gas or plasma-based processes to remove selected material.

Both appear as important micromachining methods for pattern transfer and silicon material removal.

Choosing how material is removed affects the geometry that can be fabricated.

UNIT 11 STUDY COMPLETE

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You've covered Lithography & Etching.