Technique for reducing pattern placement error in projection electron- beam lithography

摘要

Electron-beam lithography systems used for transferring images from subfields in a reticle to a wafer. Deflection systems in the electronic lens system are controlled by control systems that include devices to correct misalignment of the electron beams from each of the subfields with the electronic optical axis. In a first embodiment, switches switch between sources to deflect the electron beams to the electronic optical axis and error DACs correct position errors in the sources that are input to the switches. In a second embodiment, the deflection systems deflect the electronic optical axis to coincide with the electron beams from the subfields. In other embodiments, the deflection systems in the electronic lens systems are made insensitive to position errors in deflection control systems by satisfying the condition: G.sub.1 /G.sub.2 =M, where G. sub.1 is the gain of first amplifier amplifying a signal from a DAC which is input to the deflection system deflecting the electron beams from the subfields, G. sub.2 is the gain of a second amplifier amplifying the signal from the DAC which is input to the deflection system deflecting the electron beams to the wafer and M is the magnification of the electronic lens system. Alternatively, the deflection systems deflect the electronic optical axis to coincide with the electron beams from the sub fields. A grillage error DAC supplies a position correction to account for grillage between the subfields. In still other embodiments, a ramp generator supplies a ramp that is input to the deflection systems that are insensitive to position errors in deflection control systems by satisfying the condition: G.sub.1 /G2=M.