4. For a photo mask, SiO2 thin film is used as the phase-shifting layer. If we use ArF laser as the exposure source, estimate the film thickness. What will be the thickness if we use Si3N4 film? 5. In a 10-mask process, the yield for a 10mmx10mm chip is found to be 40%. If the air stream under laminar flow conditions is at 20m/min, estimate the clean room classification of the fabrication plant. 4. For a photo mask, SiO2 thin film is used as the phase-shifting layer. If we use ArF laser as the exposure source, estimate the film thickness. What will be the thickness if we use Si3N4 film? 5. In a 10-mask process, the yield for a 10mmx10mm chip is found to be 40%. If the air stream under laminar flow conditions is at 20m/min, estimate the clean room classification of the fabrication plant