The Effect of Condenser Tilt on Optical Projection Lithography

A basic study on the imaging characteristics of wafer steppers influenced by a condenser tilt is presented. The effects of condenser tilt are explored by displacing the source images formed on the entrance pupil plane of a projection lens. The intensity distribution of the wafer surfaces influenced by this condenser tilt is obtained by the two-dimensional aerial intensity simulation method based on Fourier optics. Periodic line pattern images are shown to shift due to the condenser tilt when the image plane is out of focus. It is also suggested that the degree of these image shifts increases as the focal error increases and the pattern feature sizes increases, and these image shifts for large feature sizes are approximated by geometrical shifts.