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.