Study on the reduction of defects in immersion lithography

ArF Immersion lithography is expected to be a production-worthy technology for sub-60nm DRAM. It gives wider process window and better CD uniformity at the cost of defects and overlay accuracy. It is generally mentioned that immersion defects are generated during exposure and removed through pre-soak and post-soak process. A lot of efforts are being made towards less defect generation during exposure and more defect removal through pre-soak and postsoak process. We have experienced a variety of immersion defects and classified them into four types: bubble defect, water mark defect (T-top & Stain), swelling defect and bridge defect (Macro & Micro). We have worked very hard to reduce each immersion defects with immersion exposure and system. In this paper, we investigate method to reduce each immersion defects: bubble, water mark, swelling and bridge through our experiment.