| 摘要 |
An electrical alignment test structure is provided that enables accurate in-process alignment measurements. Embodiments include forming two conductive layers whose alignment is be tested on the surface of a semiconductor substrate, one layer having a generally trapezoidal "shorting bar" with symmetrically stepped sides, and the other layer having a snake-like resistor "sladder" with two symmetrical sets of rung-like segments, whose ends correspond to the steps of the sides of the shorting bar. The ladder and the shorting bar are disposed with the shorting bar between the two sets of segments of the ladder, such that when the two layers are formed properly aligned, an equal number of segments of each set of segments of the ladder makes contact with the shorting bar. Thus, when the two layers are properly aligned, the resistance of each of the two sets of segments of the ladder is about the same. However, when the layers are out of alignment more than a predetermined amount (i.e., the depth of a step of the shorting bar), a different number of segments short to the respective sides of the shorting bar, resulting in each set of segments having a different resistance measured at their ends. Since the resistance of each segment is significant (e.g., over 100 ohms), the resistance difference and, hence, the number of shorted segments on each side can be accurately calculated. Then, knowing the spacing of each step of the shorting bar, the alignment offset of the two layers can be calculated. Furthermore, by comparing the drawn separation of the ladder and the shorting bar with the calculated separation of these components of the actual test structure, quick and accurate measurement of critical dimension (CD) variation is provided.
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