A NOVEL TECHNIQUE FOR CHARACTERIZING THE SURFACE COVERAGE OF THIN-FILM CHEMICAL-VAPOR-DEPOSITION IN ULTRA-HIGH-ASPECT-RATIO MICROSTRUCTURES

A simple technique is introduced for accurately characterizing the surface coverage of chemical vapor deposition (CVD) processes in microstructures with very high aspect ratios. Conventional microfabrication processes are used to produce a planar array of capillary-like silicon structures with entrance dimensions as small as 2 μm and aspect ratios ranging from 10:1 to 200:1. Dielectric or semiconductor films are then deposited on the inner and outer surfaces of the capillary by low pressure chemical vapor deposition (LPCVD). After deposition, the inner surface of the capillary is exposed and the thickness of the CVD film deposited on the interior of the capillary is measured by thin-film spectrophotometry. Thickness measurements are taken along the entire length of the capillary, thus providing a deposition profile for the CVD process under investigation. Deposition profiles were measured in these structures for LPCVD silicon nitride (SiH2Cl2/NH3 precursors), poly silicon (SiH4 precursor), and silicon dioxide (tetraethoxysilane/03 precursors). The deposition uniformity (Uc), defined as the minimum film thickness within the capillary divided by the thickness just outside the capillary entrance, ranged from nearly 0.5 for the SiO2 process to greater than 0.9 for the poly silicon process, suggesting that these CVD processes may be applied to the fabrication of devices requiring conformal thin-film deposition over high-aspect-ratio features. © 1995, American Vacuum Society. All rights reserved.