Patent ID: 7038777

Claim:
A method of determining the state of alignment between a semiconductor wafer and exposure equipment, the wafer having an alignment layer, and a photosensitive layer overlying the alignment layer, the photosensitive layer defining a plurality of exposure fields to be exposed by the exposure equipment, the alignment layer having a plurality of spaced apart surface features grouped together to serve as alignment marks dedicated to the exposure fields, each alignment mark comprising at least a 2×2 array of rows and columns of the surface features, said method comprising the steps of: a) irradiating at least one of the alignment marks dedicated to an exposure field with light beams having a band of wavelengths preselected to prevent interference between light beams reflecting from the photosensitive layer and light beams reflecting from the surface features of the wafer, and to prevent the photosensitive layer from being photo-sensitized; b) collecting the light beams reflected from the alignment mark and producing from the collected light an analog Y-axis photoelectric waveform signal characterizing the rows of surface features of the alignment mark and an analog X-axis photoelectric waveform signal characterizing the columns of surface features of the alignment mark; c) digitizing the analog photoelectric waveform signals, calculating a deviation Δx between the center of the digitized X-axis photoelectric waveform signal and a digital signal representing an X-axis reference mark center, and calculating a deviation Δy between the center of the digitized Y-axis photoelectric waveform signal and a digital signal representing a Y-axis reference mark center; d) repeating steps a) through c) with respect to any other alignment mark dedicated to the exposure field; e) repeating steps a) through d) for each of the other exposure fields; and f) determining the degree to which the wafer is mis-aligned with respect to the exposure equipment based on the deviations Δx and Δy calculated upon performing steps c) through e).