The Perkin Elmer Model 140 was investigated for second level alignment. Using a photolithographic evaluation mask, inspection of six wafers yielded overlay errors. The average x-translational error was -1.95 urn, the average y-translational error was -.4um, and the average rotational error was -.0005 uradians.
Anastos, Louis G.
"Second Level Alignment of the PE Model 140,"
Journal of the Microelectronic Engineering Conference: Vol. 3
, Article 1.
Available at: http://scholarworks.rit.edu/ritamec/vol3/iss1/1