CD controllability of proximity effect correction in EPL

摘要

In Electron Projection Lithography (EPL) that is designed for 65nm production tool, proximity effect correction (PEC) is an important issue for an accurate feature size control. Reticle resizing method is adopted for its correction. High controllability (ΔCD within +/-10%) of critical dimension (CD) is required after proximity effect correction. For estimating the CD controllability, we have evaluated its dependency on exposure dose and beam blur in resizing method for the first time in EPL using Nikon's EPL experimental column (acceleration voltage=100kV, magnification=1/4, sub field size=250x250μm). Evaluating patterns were the target size of 100nm isolated line and twin lines. Beam blur was controlled by changing focus and was measured by Aerial Image Sensor (AIS). Groups of different biased patterns were located at different distances (0.1-75 μm) from large pattern (60x250μm) on the wafer respectively. As a result, CD variation by proximity effect was 35-40nm for 100nm-isolated. Under our recommended condition that resizing range in plus side was equal to that in minus side (+/-20%), blur latitude and dose latitude satisfied our CD uniformity budget and mask enhanced error factor (MEF) was around 1, then reticle fabrication CD controllability from budget requirement was satisfied. Therefore it was shown that proposed proximity effect correction method achieved high CD controllability.