Evaluation of the Defense Advanced Lithography Program (DALP) x-ray lithography aligner

A state-of-the-art proximity x-ray lithography aligner was developed for the Defcnse Advanced Lithography Program (DALP) and installed in IBM's Advanccd Lithography Facility (ALF) in 1995. This aligner was designed to satisfy the manufacturing requirements for 250 and 180 nm groundrule electronic devices, such as 256 Mbit and 1 Gbit DRAMs, while connected to synchrotron beamlines which use scanning beam systcms for x-ray flux delivery. The aligner uses an innovative x-ray image sensor (XRIS) to align the mask by detecting its x-ray actinic image, and uses an off-axis alignment system, similar to the alignment system used in Micrascan 3 - II, to align the wafer. As a result, the same wafcr alignment marks can be used by either tool. This facilitates the mix and match between the x-ray aligner and Micrascan 2 -II optical stcppers. A stabilized helium environment is maintained from the beryllium window of the beamline to the exposure plane, including the gap between mask and wafer. The aligner can accept x-ray masks that conform to NIST standards, and has a maximum exposure field of 50 mm by 50 mm. The important lithography performance parameters, ie., ovcrlay, linewidth control and throughput, have been evaluated. The test methodologies and their results will be presented in detail. Potential improvements of the system's performance will also be discussed.