Fritz Gans

Simulation-based method for sidelobe supression

We present a new method of sidelobe suppressor placement based on fast lithographic simulation. Experimental results of printing 0.18 micron contact holes using a 5.5 percent transmittance attenuated phase shift mask with different settings of partial coherency are shown. Very asymmetric side lobes appear in some of these results. To explain these experimental results simulations were performed that take koma lens aberrations into account. A good agreement between experiment and simulation can be obtained them, Using these simulations a new algorithm has been implemented to place absorbing assist pattern for sidelobe suppression suitable in size and position. Then the process window of a double contact was determined using aerial image simulation. Process windows with koma lens aberrations and different settings of the partial coherency are then compared.

Absorbing assist pattern technique (A2PT) for effective sidelobe control for attenuated phase-shifting masks in optical projection lithography

A novel technique of sidelobe suppression based on absorbing assist pattern is introduced. Chrome shields are placed exactly at the position, where sidelobes appear. The effectiveness of this technique for sidelobe control is demonstrated by simulation and experimental results. The resulting process window enlargement for 180 nm contacts is investigated. Corresponding mask making issues are discussed.