TARGET ACQUISITION AND OVERLAY METROLOGY BASED ON IMAGING BY TWO DIFFRACTED ORDERS

摘要

A system for imaging an acquisition target or an overlay or alignment semiconductor target (404) is disclosed. The system includes a beam generator for directing at least one incident beam (402) having a wavelength lamda towards a periodic target (404) having structures with a specific pitch p. A plurality of output beams (406) are scattered from the periodic target (404) in response to the at least one incident beam (402). The system further includes an imaging lens system (410) for passing only a first and second output beam (412a, 412b) from the target (404). The imaging system is adapted such that the angular separation between the captured beams, lamda, and the pitch are selected to cause the first and second output beams (412a, 412b) to form a sinusoidal image (414). The system also includes a sensor for imaging the sinusoidal image or images (414), and a controller for causing the beam generator to direct the at least one incident beam (402) towards the periodic target or targets (404), and for analyzing the sinusoidal image or images (414).