The application of channeling to masked ion beam lithography

Abstract

Various orientations of undoped single crystal silicon were examined from the standpoint of transmitted half-angle to determine the best orientation for masked ion beam lithography (MIBL). The effect of boron, present at a level of ~10²�/cm³was also determined. Transmitted angular distributions, for particles of incident energy in the range: 80-180 keV, were measured using a movable silicon surface barrier detector with a resolution of $sim$3 keV and an acceptance angle of 0.1°. Planar orientations yielded smaller transmitted half-angles than axial orientations without a significant loss in transmitted yield. The half-angles of particles transmitted along planes, unlike axes, were found to vary with azimuthal angle. The best orientation for use in MIBL was determined to be the {110} planar orientation. Half-angles for particles transmitted along this plane, and for particles transmitted along the {100} plane, were smallest for scans perpendicular to the plane; largest, for scans parallel to it. Scans parallel to the plane were similar in width to scans across axes especially at higher energies and were shown, through calculation, to be consistent with the spreading expected for particles undergoing electronic multiple scattering at a reduced electron density. The presence of boron was found to increase the transmitted half-angle by ~10% over the entire energy range. This relatively small improvement in half-angle does not, by itself, warrant the use of undoped films over boron doped films in an MIBL application.