A comparison of electrical and visual alignment test structures for evaluating photomask alignment in integrated circuit manufacturing

Various electrical alignment test structures were designed to conform to the NBS 2 × N probe pad array and are thus compatible with a class of other modular test structures. The object of this study is to determine the feasibility of this new layout, to compare results with visual alignment test structures, and to establish the limits of resolution. The structures can be used to determine the misalignment of two photomask steps and are applicable to two conducting layers that contact each other at a contact window. The electrical data are displayed as wafer vector maps which are useful in quantifying mask alignment problems.