Fluorinated chemistry for high-quality, low hydrogen plasma-deposited silicon nitride films

Abstract

We have developed a low-temperature (≲300 °C) plasma deposition process to prepare novel fluorine-containing silicon nitride films (p-SiN:F) using SiH4–NF3–N2 discharge mixtures at 14 MHz rf applied frequency. The deposition rate can be extremely high, up to 1600 Å/min. Data indicate p-SiN:F has electrical properties (dielectric constant, breakdown strength, resistivity, etc.) which compare favorably to high-temperature, chemical-vapor-deposited silicon nitride. By controlling the feed chemistry and physical variables of the discharge, a wide variety of film compositions are achieved. Moreover, this chemistry is superior to the only other p-SiN:F which was prepared from a SiF2/SiF4-H2-N2 feed. Two classes of films were identified as stable or unstable to air exposure and the instability of the films correlated with the atom fraction of fluorine initially incorporated. Infrared, Auger electron, and Rutherford backscattering spectroscopy measurements show that low hydrogen concentrations are produced by the introduction of fluorine in the silicon nitride films. More importantly, the concentration of Si–H is extremely low because strong Si–F bonding replaces the weak Si–H bonds that satisfy free Si orbitals found in conventional plasma nitride, and the hydrogen remaining in the film is present as stable N–H bonds. We believe this substitution of silicon-bound hydrogen, caused by the gas phase and surface-driven reactions, is a source of superior film properties. The mechanism for this novel discharge chemistry is discussed.

Chemical Vapor Deposition of Several Silicon-Based Dielectric Films

“…The low reactivity of SiF., however, makes this route unattractive. Along this same line, an attempt to deposit fluorinated silicon nitride by substitution of NF 3 for NH 3 (either partially or totally) in the gas mixture was made by several workers (34,35). It was reported that the presence of NF 3 increased the deposition rate significantly.…”

Material properties of plasma-enhanced chemical vapor deposition fluorinated silicon nitride

“…This is because the Si--F bond is a more thermodynamically stable bond with higher bond energy ( 140 kcal/mol) than the Si--H bond (80 kcallmol). 7 In their experiment, preliminary results obtained from a gm degradation test on devices with fluorinated silicon nitride are indeed promising. s However, the stability of such a fluorinated silicon nitride film was observed to be worse with increasing fluorine concentration.…”

“…Recently, Chang et al have developed a new process of silicon nitride deposition using a gas mixture of SiH 4 -NF3 -NH3 -N z in a plasma reactor. 7 With additional NF 3 , they successfully reduced the Si--H concentration in the deposited silicon nitride films. They believe the reduction of S1--H bonds is a result of the substitution of Si --H bonds with Si--F bonds.…”

Study of SiF4-N2-H2 Plasmas for the Deposition of Fluorinated Silicon Nitride Films

“…The dilution of SiH 4 -N 2 in He plasma [5] causes an H content decrease from typical 20-35 at.% [1,2] to values lower than 10%. Fluorinated silicon nitride produced from SiH4-NH3-NF3 [6], SiH4-N2-NF3 [7], SiH2F2-NH3 [8] and SiF 4 (SiF 2 )-N 2 -H2 [9], generally exhibits less hydrogen incorporation, due to its replacement with F atom. In particular, fluorinated silicon nitride having N/Si ratio of about 0.8 obtained (at 380 OC) by glow discharge in SiF4-N2-H2 gas mixture contains 25 at.% of fluorine [10].…”