Plasma enhanced chemical vapor deposition of SiN-films for passivation of three-dimensional substrates

Coating of three-dimensional substrates with passivation layers requires an isotropic deposition process to realize an uniform thickness of the films even at side walls, edges, undercutted surfaces, trenches etc. Our intention was to deposit silicon nitride passivation layers on three-di mensional devices using a microwave electron cyclotron resonance (MW-ECR) p lasma. Besides gas composition: process gas pressure, MW-power and substrat e bias it was possible to vary the distance between the plasma region and s ubstrate and the arrangement of the gas inlets. Silane (SiH4), ammonia (NH3 ), nitrogen (N-2) and argon (Ar) were the available process gases. We varie d all these parameters and geometric conditions to optimize the isotropic d eposition process and the properties of the passivation layers (thickness u niformity on vertical and horizontal surfaces, chemical composition, passiv ation properties, mechanical film stress and electrical dates). Furthermore , the influence of substrate temperature was investigated, because some dev ices were sensitive to heating. The uniformity and quality of the deposited layers were characterized by infrared spectra, refractive indices, etching rates in buffered fluoric acid, measurements of mechanical stress and elec trical dates and inspections by scanning electron microscopy. In our work the optimum conditions for an isotropic deposition process at h igh process pressure (30 Pa) were determined. The uniform coating of three- dimensional substrates could be demonstrated. Different bias voltages cause d clear changes in the film properties. Especially mechanical film stresses could be varied from tension to compression stress. (C) 1999 Elsevier Scie nce S.A. All rights reserved.