ArF immersion lithography for 65 nm assisted by off-axis illumination

The effect of off-axis illumination for ArF immersion lithography is studied at 65 nm node. Under 3/4 annular and 3/4 quasar illumination, the lithographic performances for dense lines, semi-dense lines and isolated lines in different parameters of the exposure system are studied and the lithographic performances in different illumination modes are compared. The results show that in order to reach the required lithographic performance the system settings could be chosen widely for the acceptable DOF. The DOF due to off-axis illumination increases by 100% ~ 150%, compared to conventional illumination. The better performances are obtained for the isolated lines under the quasar illumination.