ELECTRON-BEAM LITHOGRAPHY TOOL FOR MANUFACTURE OF X-RAY MASKS

An electron beam lithography system suitable for manufacturing X-ray m asks with critical dimensions down to 0.35 mum is described. The syste m features a 50-kV variable shaped spot (VSS) electron column with a v ariable axis immersion lens (VAIL). This column is capable of maintain ing 0.035-mum edge acuity of the focused spot over a 2.1-mm deflection field. These fields are stitched together over an 84 x 84-mm active p attern area via motion of an xy table. The table position is measured using a laser interferometer. The measurement data are fed back to the magnetic deflection to correct small errors. Maintaining positional a ccuracy of the beam relative to the writing surface relies on a strate gy of measuring and correcting repeatable errors. This is described in detail. Pattern placement accuracy is 0.070 mum (3sigma) and image si ze control is 0.025 mum (3sigma), achieved over the entire 84 x 84-mm pattern area. This performance is achieved with yield better than 90%, as confirmed by routine measurements. The system is currently used to manufacture product X-ray masks with 0.35-mum critical dimensions. Ty pical measurement results on product masks are presented.