Low hydrogen content silicon nitride deposited at low temperature by novel remote plasma technique

Abstract

A novel remote plasma deposition technique has been used to deposit low hydrogen content silicon nitride at a temperature of 300 °C. This technique uses a remote noble gas discharge to excite nitrogen and silane species which are introduced downstream, out of the plasma region. Optical emission spectroscopy indicates that the downstream interaction creates excited molecular nitrogen with little evidence of atomic nitrogen. Infrared spectroscopy has been used to qualify the hydrogen content in these films. The etch rate in buffered HF of these films is as low as (1)/(20) that of thermal oxide. A surface reaction model for hydrogen removal is proposed. In that model the hydrogen incorporation is controlled by the arrival rate of SiHx species (i.e., the growth rate) and the desorption of NHx groups from the film surface. Electrical results indicate that the fixed charge density in the nitride films is in the low 1011 cm−2 and the interface state density is in the upper 1011 cm−2 eV−1 range. The current–voltage characteristics under ramped bias show no ledges and sustain a current density of 4.6×10−4 A cm−2 at a field of 4.2 MV cm−1. Their analysis shows that conduction is through Poole–Frenkel transport (bulk-trap limited) as in conventional chemical vapor deposited Si3N4. Furthermore, a trilayer oxide–nitride–oxide structure on silicon has been fabricated with no hysteresis observed on capacitance–voltage measurements and a (3–5)×1010 cm−2 eV−1 interface state density.