1. Wafer processing - I Clean room environment Semiconductor clean room: - controlled temperature (20ºC), air pressure, humidity (30%) - controlled airbone particulates - controlled vibration - controlled lighting INESC: 250 m 2 Class 10 and 100 clean room 250 m 2 Class 10000 (grey area) Class 100: 0.5  m)/ft 3

3. Wafer processing - II resist coating 1- Vapor priming for improved resist adhesion to substrate - Resist adhesion to Si wafers is poor - Dehydration bake to remove adsorbed water from the surface - surfactant to promote adhesion : HMDS (hexamethyldisilazane) Vapor priming is better than spin coating with a liquid solution because lower contamination ~1 monolayer

4. 2- Spinning resist and soft baking Wafer processing - II resist coating SVG Resist coater and developer track: Track system for spin coating of photoresist (1.2 to 2  m thick) and for development of post-exposed wafers. (cassettes of 25 Si wafers  6 inch) Requirements: Good control of thickness, uniformity, viscosity, particle contamination Typical resist thickness: 0.6-2  m Soft baking: remove solvents and stress and promote adhesion to wafer

5. Wafer processing - II Coating and developing Exposure (c)  6 inch Si wafers

6. Wafer processing - III exposure Heidelberg Instruments Direct Write Laser Lithography System: Direct write lithography system utilizing a HeCd laser ( =442 nm (g-line) / write lens NA= 0.85) capable of critical dimensions down to 0.8  m. System works with mask designs in GDS2 format. INESC

7. Wafer processing - IV development Positive resists Negative resists (INESC) Solved in the exposed regions Remain in the exposed regions Selective dissolving of resist

9. Resist profiles