ELECTRODYNAMICS OF FAST BEAM BLANKERS

Performance characteristics of an advanced electron beam blanker for l ithography are presented. Various electrodynamic effects are discussed , which must be eliminated to achieve high beam placement accuracy dur ing and after blanking. These electric and magnetic field effects have been measured over six orders of magnitude in time. The fast beam jit ter characteristic of transit time effects in a double-deflection blan ker is captured with nanosecond time resolution. Eddy current effects measured in the micro- to millisecond time domain are shown to be an i nherent problem in earlier double-deflection blanker designs. A conseq uence is beam misplacement after the unblank transition, which can be 0.05 mum even after 500 mus. Several examples of pattern artifacts in purposely underdeveloped resist are given to illustrate graphically th e lithographic consequences of the eddy current effect. All of these e lectrodynamic effects have been addressed with a new ''virtual ground' ' blanker design. The MEBES IV-TFE maskmaker has been upgraded with th is new blanker to meet its accuracy requirements throughout the nano- to millisecond time scale. This enables pattern generation at 160 MHz with 30 nm (3sigma) critical dimension (CD) control for 2.0 mum featur es with addresses up to 0.25 mum. The CD control is tested with patter ns that are fractured with a single pixel placed across the scan bound ary. This situation provides the most extreme test of blanker accuracy at the nanosecond time scale. Blanker eddy current effects are elimin ated from all exposures, including those in underdeveloped resist. The blanker design upgrade has facilitated the fabrication of reticles fo r production 64 Mbit DRAMs and developmental 256 Mbit DRAMs.