Electron beam induced deposition from W(CO)6 at 2 to 20 keV and its applications

Abstract

Electron beam induced deposition from W(CO)6 was studied for beam energies between 2 and 20 keV and a range of exposure doses, to investigate the dependence of deposit thickness and electrical conductivity on energy and the dependence of deposit conductance on cumulative exposure dose. Larger deposited thicknesses and higher conductivities were produced at the lower beam energies and were attributed to the higher secondary electron yield at lower energies. The deposit thickness was found to scale linearly with exposure dose. The initial dependence of conductance on exposure dose (and deposit thickness) was nonlinear and was attributed to the change from a discontinuous to a continuous film, and to increased backscattering. The subsequent dependence of conductance on exposure dose was linear for deposit thicknesses which were small compared with the electron range, implying that burial precludes the further decomposition of partially decomposed W(CO)6 molecules incorporated in the deposit. Transmission electron microscope examination showed that the structure of the deposits depended on the beam scanning conditions. Deposits were used to form a mask for CF4 plasma etching of Si, while deposits on a doped GaAs substrate were found to form a Schottky contact with an ideality factor of 1.40, enabling the repair of a metal–semiconductor field-effect transistor gate to be demonstrated.