Study On Optimization Of The Key Region Of The Immersion Flow Field In Immersion Lithography

Immersion lithography has been applied widely as a method for extending optical lithography resolution to 45 nm and below, which has been met the need of the fast development of integrated circuit. During the exposure process, yield of exposed wafer is mainly decided by the pressure and velocity of the key region (exposure region) of immersion flow field. And the pressure and velocity of the key region are depended on the immersion unit which is between exposure projection lens and wafer and is used for carrying off the containment and small bubbles produced by exposure process by dispensing immersion fluid into immersion field and collecting pollutant immersion fluid. However, the flow of the immersion fluid will casue much pressure to the exposure lens, resulting in the deformation of the lens and thus defection of wafer. So, optimizing the immersion flow field, especially the key region, is very significant.In this paper, the requirements for immersion flow field are:the velocity of the key region is between 50mm/s and 100mm/s and its fluctuation is below ±5mm/s; the pressure of the key region is between OPa and 1000Pa and its fluctuation is below± 100Pa; and there is no back flow. In order to reach those requirements, this paper accomplished tasks as below.Firstly, the 3D-CFD models of immersion lithography was established, the CFD study of the influencement of dispensing velocity, collecting pressure and the dispensing and collecting angle to the key region of immersion flow field was accomplished, and a better region was confirmed as the key region for exposure.Secondly, the technology of flow visualization for immersion lithography was systematacially studied and the experimental platforms both for velocity and pressure detection were set up. The immersion flow field was visualized by some colored fluid; the velocity of immersion flow field was detected by PIV which are composed of a high-speed camera, a semiconductor lasor, a light sheet and a picture processing system, and the pressure of immersion field by pressure senors.Then, the experimental model was designed and the experimental study of the influencement of dispesing velocity, collecting pressure and the dispensing and collecting angle to the key region of immersion flow field was accomplished. The experimental results were compared with the the CFD results, and a set of optimal parameters was come up with.Finally, an optimal immersion unit was designed according to the CFD and experimental results. The performance of the immersion unit was detected, which proved that all the requirements have been met and the scanning velocity reachs 550mm/s with little disturbence to the immersion flow field.