Key improvement schemes of accuracies in EB mask writing for double patterning lithography

Double pattering or exposure methodologies are being adopted to extend 193nm optical lithography. These methodologies require much tighter image-placement accuracy and Critical Dimension (CD) controls on mask than the conventional single exposure technique. Our experiments indicate that the global image placement drift induced by the time elapsed in mask writing is the dominant factor that degrades image-placement accuracy. In-situ grid measurement method is being proposed to suppress this time dependent drift. Resist charging effect is also an important error factor. While it can be reduced by charge dissipation layer (CDL), further feasibility study is required for using CDL to overcome certain side-effects pertaining to CDL. High dose resist improves local CD uniformity and pattern fidelity. However, mask writing time becomes longer with lower sensitivity. To satisfy conflicting issues, throughput and CD uniformity, high sensitivity CAR which has short acid diffusion length is desirable. Shortening acid diffusion length is essential for achieving good pattern resolution as well as good CD uniformity. This paper will address the results of error source analyses and key schemes of accuracy improvements in photo-mask manufacturing using NuFlare Technology's EB mask writers.