chemically amplified resist

**Chemically Amplified Resist (CAR)** — the photosensitive material used in lithography where a single photon triggers a catalytic chain reaction, amplifying the chemical change to enable high-sensitivity patterning. **How It Works** 1. Photon absorption generates a photoacid (PAG — Photo Acid Generator) 2. During post-exposure bake (PEB), the acid catalytically deprotects many polymer units 3. One acid molecule triggers 100–1000 deprotection events (amplification!) 4. Development: Deprotected polymer dissolves in developer (positive tone) or crosslinks (negative tone) **Why Amplification?** - ArF (193nm) photons have limited energy - EUV (13.5nm) photons are scarce (low source power) - Amplification lets fewer photons create sufficient chemical change **EUV Resist Challenges** - Need high sensitivity (few photons per pixel at 13.5nm) - Need low line-edge roughness (LER) — photon shot noise causes random variations - Trade-off triangle: Sensitivity ↔ Resolution ↔ LER (can't optimize all three simultaneously) **Next-Generation Resists** - Metal oxide resists (e.g., Inpria's tin-oxide): High EUV absorption, better resolution - Dry develop resists: No liquid developer needed - These may enable High-NA EUV lithography **Photoresist** is the recording medium of lithography — its performance directly limits how small features can be reliably printed.