High-contrast registration marks for electron-beam pattern exposure on (100) silicon

Abstract

Secondary-electron signals have been measured from 10-μm-square registration marks as a function of electron-beam energy (10∠30 keV). These marks are anisotropically etched holes in (100) silicon which may or may not be covered with SiO2. The uncovered holes are sharp enough to measure electron-beam diameters less than 100 Å. PMMA coating (4000 Å) on the uncovered registration holes reduces signal contrast at 25 kV, incident beam energy from 0.87 to 0.79, and from 0.78 to 0.76 for the mark covered with a SiO2 layer, where perfect contrast is unity. The signal-transition distance from substrate to hole, ε20%–80%, for the mark with a SiO2 cover is degraded to approximately 0.6 μm. However, it is experimentally possible to register vernier patterns to at least ±0.25 μm accuracy, with SiO2-covered holes used as registration marks.