Optical CD applications for <200 nm lithography control and productivity improvement

As design rules continue to shrink, it is becoming increasingly difficult to evaluate projection-aligners imaging accuracy. Today's DUV scanners meet production requirements for 200 nm or even smaller CDs. With such small CDs, errors associated with metrology start occupying a significant part of total error budget. Optical CD metrology ("OCD") developed by Nikon Precision Inc.(I. Grodnensky et. al., patent pending) has demonstrated its potential of replacing SEM with superior accuracy and throughput. Early studies provided proof of the concept, indicating OCD's versatility to cope with wide range of CDs from sub-half micron to 140 nm or even below and with both isolated and dense pattern structures. In order to evaluate feasibility of using this new technology in the field, various field tests have been conducted for proposed potential applications, such as image-focal-plane analysis, spherical and COMA aberration measurement, across chip line-width variation analysis,etc. This paper will discuss the results to date from such field tests.