This paper discusses the types and formation of immersion defects. It is shown that drying stains and water marks are the main immersion defects. The immersion defects are related to resist leaching, water penetration and droplet formation. It is shown that scanner immersion hood design based on an actuated air gap and air curtain droplet clean-up minimizes defect counts. Additionally, pre-and post soaks steps in the track can reduce drying stains and water marks. The defect performance is evaluated on XT:1250i and XT:1400i systems. It is shown that the immersion defect density can go as low as 0.01 /cm<sup>2</sup>, which is well below the ITRS 2005 number of 0.03 /cm<sup>2</sup>.