Effects of laser bandwidth on iso-dense bias and line end shortening at sub-micron process nodes

Control of Isolated and Dense line Bias (IDB) and Line End Shortening (LES) in a lithographic process has become increasingly important, particularly for the 65nm node and below. The IDB depends on many factors, for example, focus, lens aberrations, partial coherence and laser spectral bandwidth. This work studies the impact to IDB and LES from changes in laser bandwidth at two sub-micron process nodes. Careful measurements of both FWHM and E95 bandwidth parameters of the laser spectral profile were carried out using two types of spectrometers. The spectral bandwidth was adjusted over a larger range than normally experienced during wafer exposures by carefully varying the laser operating conditions to provide controlled changes in bandwidth while maintaining all other laser performance parameters within specification. Measurements of both linewidth and LES on several substrates were made and correlated with laser bandwidth to determine the sensitivity of IDB and LES to bandwidth variation. The sensitivity of different structures to E95 bandwidth variation was assessed