Investigation of proximity effects in alternating aperture phase shifting masks

This paper investigates proximity effect correction methodologies for alternating aperture phase-shifting masks. A simple approximation is used to investigate the proximity effects: at low sigma, the aerial image intensity on the wafer can be calculated by taking the square of the sum of the amplitudes of each pattern on the mask taken separately. Results show that proximity effects are mainly driven by low sigma illumination and that correcting chrome patterns is less efficient than modifying the diffraction of the patterns by changing the shape of the phase-shifting regions.