Electrical Properties of Vapor-Deposited Silicon Nitride Films Measured in Strong Electric Fields

Abstract

Recently, silicon nitride films have received considerable attention (1-3), mainly for passivating silicon, constructing diffusion masks, and use as gate insulators. The physical and electrical properties of deposited films have been found to vary with reactant composition during growth, temperature, and method of deposition (4-6).Studies of the electrical conductivity of silicon nitride films in strong electric fields can give information concerning the mechanism of the increase of conductivity, the existence and location of trap levels, and dielectric constant. ExperimentalThe substrates used for this study were mechanically polished 2 ohm-cm, p-type silicon. Just before loading into the reactor, the substrates were chemically etched in fresh, concentrated HF and rinsed in deionized water. An rf-heated, horizontal tube reactor was used for the silicon-nitride deposition.A 4~, 2 ohm-cm boron-doped epitaxial layer was deposited at 1135~ by reacting silicon tetrachloride and diborane in hydrogen. The temperature was then reduced to 925~ during the hydrogen purge cycle and silicon nitride was deposited using 150:1 ammoniasilane ratio in a hydrogen ambient. The deposition rate was approximately 10O A/min. The MIS structures for electrical measurements were formed by evaporating aluminum field plates, 30-mil diam over the silicon nitride through a metal mask. Aluminum was also evaporated on the backside of the silicon for contact. The thickness of the nitride films studied ranged from 175 to 500A. The thickness and the index of refraction were measured ellipsometrically. Results and DiscussionPhysical Properties.--Optical measurements were made on samples deposited on silicon blanks by the same process as the samples for electrical measurements. Transmittance curves obtained in the range 2.5-40~ using a Beckman Model IR-121 spectrophotometer indicate a broad absorption peak in the range 10-12~ with a minimum at 11.6~. This absorption is due to the Si-N bond and agrees with that reported by Bean et al. (6). No peaks due to SiO, Sill, or NH were observed. Etch rates of 0.7 and 1.1 A/sec were obtained

Silicon Nitride Films by Direct RF Sputter Deposition

“…This absorption is probably a result of damage caused by particle bombardment of the film during growth (51)(52)(53)(54)(55). Increasing the target voltage to 1.5 kV (Pin ~ 700W) reduced the refractive index to 1.90 and increased the energy gap to ~ 5.5 eV.…”

“…In addition, the films produced at high target voltages were uniformly absorbing in the visible. This absorption is probably a result of damage caused by particle bombardment of the film during growth (51)(52)(53)(54)(55).…”

A Silicon and Aluminum Dynamic Memory Technology

“…In any multilayer dielectric, the differences in conduction between the layers will lead to charging of the interfaces between the dielectrics [34]. For the MONOS dielectric at the gate voltages used in SAMOS, the 3I-nm oxide is essentially nonconductive, while electrons move through the nitride by a number of mechanisms, with Frenkel-Poole conduction predominating [35]. The electrons move across the upper oxide by tunneling.…”