Resolution limits in electron-beam induced tungsten deposition

Abstract

Electron-beam induced deposition of tungsten from the precursor gas W(CO)6 was investigated with the aim of determining the resolution limiting parameters. By exploring the effect of the beam energy and current, the resolution was found to correlate to the expected behavior of the beam diameter. To achieve a more accurate description of the deposition process, the time dependence of the needle height and diameter at the base was determined for deposition times ranging from 5 to 180 s. The measurements enabled a mathematical description of the needle surface as a function of time, and, therefore, the determination of the surface growth. The results exhibit that electron scattering cannot explain the observed growth. For that reason, the surface growth was correlated to the number of secondary electrons (SE) emitted by the primary e beam from the needle surface considering the Gaussian intensity distribution of the e beam and the angle dependence of the SE yield. These assumptions result in a good agreement of the number of SE with the surface growth and demonstrate that the beam diameter mainly limits the deposit resolution. As a consequence, by using a proper e-beam system, a resolution of 1 μm high needles in the order of 50 nm is obtainable.