Office of Technology Partnerships (OTP) Data Services
What is claimed is:
1. An improved test structure for providing a plurality of offset measurements of a first portion of a test structure formed in a first operation with respect to a second portion of said structure formed in a subsequent operation, said test structure comprising:
an elongated bridge conductor with taps at either end for forcing a current therethrough;
a first plurality of taps intersecting said bridge conductor at intervals, said taps being connected to pads for measurement of voltage drops along a first group of nonoverlapping contiguous segments of said bridge conductor defined by the intersection of said taps and said bridge conductor, said first plurality of taps being formed in the same operation as said bridge conductor,
a second plurality of taps formed in a second operation and intersecting said bridge conductor, said second plurality of taps also being connected to pads for measurement of voltage drops along a second group of nonoverlapping contiguous segments of said bridge conductor defined by said second set of taps,
said first and second groups of segments including common portions of said bridge conductor,
wherein in use the respective offsets of the second set of taps with respect to the first set of taps are measured by comparison of voltage drops along said bridge conductor with respect to a plurality of intersections of taps formed in said second processing operation, and whereby errors common to the positions of all of the taps of said second set of taps with respect to said first plurality of taps can be effectively distinguished from errors in the position of one or more of said taps formed in said second operation.
2. The test structure of claim 1, wherein a plurality of identical such test structures are formed at spaced locations on a semiconductor substrate, wherein the same tool is used to form the second plurality of taps at each of said plurality of locations, whereby errors in fabrication of said tool used to form said test structures provides a systematic error distinguishable from errors due to misalignment of tools used in said first and second processing operations.
3. The test structure of claim 1, wherein said taps extend transversely across said bridge conductor for optical measurement of their respective spacing.