MECHANISM OF SINXHY DEPOSITION FROM NH3-SIH4 PLASMA

The plasma-enhanced chemical vapor deposition process for SiNxHy films has been in use for over two decades, but the chemistry of the process has yet to be explained. In the present work, the composition of a 13 MHz NH3-SiH4 parallel plate glow discharge plasma was analyzed by line-of-sight sampling from the film deposition plane into a triple-quadrupole mass spectrometer, which can resolve compositional ambiguities at a given mass number by utilizing collision-assisted secondary cracking. At low RF power, disilane was the main plasma product even when NH3/SiH4 was 25/1, whereas at higher power (0.1 W/cm2 of cross section) disilane was eliminated and tetra-aminosilane, Si(NH2)4, and the triaminosilane radical, Si(NH2)3, became dominant. The concentration of these aminosilanes closely tracked deposition rate, and they are believed to be the principal SiNxHy film precursors. Films deposited with Si(NH2)3 maximized and disilane suppressed in the plasma were excess in N and contained no Si—H bonding, consistent with the precursor composition. Silane utilization was near unity. The composition and properties of films deposited under these “amino-saturated” plasma conditions were examined vs. substrate temperature, Ts. With increasing Ts, there occurred a densification, a loss of H and excess N in a 3/1 ratio, and an increase in tensile stress, suggesting surface and subsurface chemical condensation of the adsorbed precursors via 3Si(NH2)4 → Si3N4 + 8NH3 ↑. Postdeposition flash desorption showed NH3, not H2, to be the main volatile product of condensation. These results demonstrate that plasma chemistry can be manipulated to control film properties in a predictable manner. © 1990, The Electrochemical Society, Inc. All rights reserved.