Fabrication of Multilayer GDP Targets for Foil Thickness Experiments

Four different variations of doped, planar targets were fabricated using multilayer glow discharge polymerization for the foil thickness campaign at the Extended Performance Facility at the University of Rochester. The planar film targets consisted of from one to four layers of CH, CHGe, and CHSi. The composition of Ge and Si was controlled by the flow of dopant gas (either tetramethyl germane or tetramethyl silane) and measured with X-ray florescence. After laser cutting the 200 × 900 × 80-µm film targets out of the larger film, the targets were released from the substrate.

Coating nonuniformity when using an inductively coupled discharge device can be a challenge. We improved the uniformity by rotating the substrate. Film thickness was measured with a chromatic confocal sensor system. Thickness measurements were fit to a Gaussian function, which smoothed the thickness data set and allowed accurate interpolation of thickness measurements.

A challenge for freestanding, planar glow discharge polymer films is intrinsic stress in the coating. Prior to coating the final targets, the coating stress for various deposition parameters was measured. A series of runs with CH, CHGe, and CHSi were coated on thin silicon wafers. The wafers were characterized for bending before and after coating with a stylus profilometer to determine the coating stress using the Stony equation. In general, higher chamber operating pressures resulted in lower stress coatings.