Overlay target design method to minimize impact of lens aberrations

摘要

A method of designing an alignment target system to minimize lens aberrations is disclosed. A first layer alignment target's pitch is selected based on the minimum feature size of the circuit. The second layer alignment target's pitch is selected based on the diffraction pattern of the first layer's target and the illumination settings of the second layer. Displacement errors are minimized when the second layer target's 1st diffraction order overlaps the first layer target's 0th diffraction order.