With the continued miniaturization of devices in the semiconductor industry, atomic layer deposition (ALD) of silicon nitride thin films (SiN_x) has attracted great interest due to the inherent benefits of this process compared to other silicon nitride thin film deposition techniques. These benefits include not only high conformality and atomic-scale thickness control, but also low deposition temperatures. Over the past 20 years, recognition of the remarkable features of SiN_x ALD, reinforced by experimental and theoretical investigations of the underlying surface reaction mechanism, has contributed to the development and widespread use of ALD SiN_x thin films in both laboratory studies and industrial applications. Such recognition has spurred ever-increasing opportunities for the applications of the SiN_x ALD technique in various arenas. Nevertheless, this technique still faces a number of challenges, which should be addressed through a collaborative effort between academia and industry. It is expected that the SiN_x ALD will be further perceived as an indispensable technique for scaling next-generation ultra-large-scale integration (ULSI) technology. In this review, the authors examine the current research progress, challenges and future prospects of the SiN_x ALD technique.

Trisilylamine (TSA), an exemplary chlorine and carbon-free commercial silylamine precursor, is well-known to induce improvements in the process and properties of silicon nitride (SiN_x) thin films grown using atomic layer deposition (ALD). Herein, we report a TSA homolog, tris(disilanyl)amine (TDSA), as a novel chlorine and carbon-free precursor for the deposition of highly etch resistant SiN_x thin films having a high growth rate at a low temperature (<300 °C) using plasma enhanced ALD (PEALD) with hollow cathode plasma (HCP). These improvements in PEALD SiN_x using TDSA may be attributed to higher surface reactivity of the molecule enabled by weaker Si–N bonds, higher molecular polarity and the existence of reactive Si–Si bonds in the molecule. The performance of PEALD SiN_x grown by TDSA has been compared with that of TSA, aminosilanes and chlorosilanes, and explained with the structure–property relationship of the molecule. TDSA grows SiN_x film faster than TSA. Furthermore, the TDSA precursor produces SiN_x films that have lower wet etch rate (WER) when compared to other silylamine precursors like TSA, or other types of silane precursors such as aminosilanes and chlorosilanes. We believe that the result, that TDSA-grown SiN_x films exhibit lower WER than TSA-grown SiN_x films, can be attributed to the abundance of Si in SiN_x films, which thereby offers high resistance to a wet etch.

In this letter, we report GaN MIS-HEMTs with a 16-nm-thick silicon nitride (SiNx) gate insulator and surface passivation layer grown using low-temperature (300 °C) hollow cathode plasma-enhanced atomic layer deposition. Tris(dimethylamino)silane and a remote N2 plasma were used as the silicon precursor and the nitrogen co-reactant, respectively. Though the growth temperature was as low as 300 °C, we obtained excellent film properties such as a high refractive index (2.00), a high film density (2.9 g/cm3), and a low wet etch rate (0.8 nm/min) in 100:1 hydrofluoric acid. High-resolution transmission electron microscopy images of the gate stacks showed ~1.5 nm β-phase Si3N4 crystalline interfacial layer on the GaN surface. The devices showed a negligible hysteresis of ~50 mV, a steep subthreshold slope of 76 mV/dec, and a high ON/OFF drain current ratio of ~109. Additionally, the devices showed a small positive/negative bias temperature threshold voltage (Vth) instability (ΔVth≤ 0.2 V at 25 °C and 150 °C) as well as a mitigated current collapse under an off-state quiescent VDS of 20 V.