- Asked 2/19
- 2079 Asoj · 3 marks
- 2078 Baisakh · 3 marks
Define photolithography and its types
Short answer
Photolithography transfers a mask pattern onto photoresist. Types: positive resist (exposed dissolvesol) vs negative (exposed hardens); exposure: contact, proximity, projection printing; radiation sources include UV, DUV, EUV, e-beam.
Define photolithography and its types.
Photolithography
Photolithography is the process of transferring a circuit pattern from a photomask to a layer of photoresist on a wafer using light, so that the pattern can then be etched or doped into the wafer. It is the basic patterning step in IC fabrication.
Types
- By resist type
- Positive: exposed resist becomes soluble and is removed, so the pattern equals the mask.
- Negative: exposed resist hardens, unexposed part is removed, so the pattern is the inverse of the mask.
- By exposure method
- Contact printing: mask touches the wafer; good resolution but damages mask and wafer.
- Proximity printing: a small gap (10-25 µm) separates them; no damage but diffraction limits resolution.
- Projection printing: a lens projects the mask image (steppers and scanners, 4x-5x reduction); the standard in modern fabs.
- By radiation source
- Optical (UV, DUV, EUV): i-line 365 nm, KrF 248 nm, ArF 193 nm, EUV 13.5 nm.
- Electron-beam (direct write) for masks and research; X-ray and ion-beam lithography for very fine features.
✓ Answer checked by Claude Opus 5.5 (high effort)