Atomic Layer Deposition of Wet-Etch Resistant Silicon Nitride Using Di(sec-butylamino)silane and N₂Plasma on Planar and 3D Substrate Topographies

Abstract

The advent of three-dimensional (3D) finFET transistors and emergence of novel memory technologies place stringent requirements on the processing of silicon nitride (SiN) films used for a variety of applications in device manufacturing. In many cases, a low temperature (<400 °C) deposition process is desired that yields high quality SiN films that are etch resistant and also conformal when grown on 3D substrate topographies. In this work, we developed a novel plasma-enhanced atomic layer deposition (PEALD) process for SiN using a mono-aminosilane precursor, di(sec-butylamino)silane (DSBAS, SiHN(Bu)), and N plasma. Material properties have been analyzed over a wide stage temperature range (100-500 °C) and compared with those obtained in our previous work for SiN deposited using a bis-aminosilane precursor, bis(tert-butylamino)silane (BTBAS, SiH(NHBu)), and N plasma. Dense films (∼3.1 g/cm) with low C, O, and H contents at low substrate temperatures (<400 °C) were obtained on planar substrates for this process when compared to other processes reported in the literature. The developed process was also used for depositing SiN films on high aspect ratio (4.5:1) 3D trench nanostructures to investigate film conformality and wet-etch resistance (in dilute hydrofluoric acid, HF/HO = 1:100) relevant for state-of-the-art device architectures. Film conformality was below the desired levels of >95% and attributed to the combined role played by nitrogen plasma soft saturation, radical species recombination, and ion directionality during SiN deposition on 3D substrates. Yet, very low wet-etch rates (WER ≤ 2 nm/min) were observed at the top, sidewall, and bottom trench regions of the most conformal film deposited at low substrate temperature (<400 °C), which confirmed that the process is applicable for depositing high quality SiN films on both planar and 3D substrate topographies.

Surface reactions of aminosilane precursors during N2 plasma‐assisted atomic layer deposition of SiNx

“…Thus, we further conclude that cumulated double bonded –C x N y species play a negligible role in the overall ALD process. The N/Si ratio obtained from RBS analysis for the DSBAS ALD process was ~1.39, and from SIMS depth profiling for the BDEAS ALD process was ~1.33, which is comparable to previous studies on N 2 ‐plasma‐assisted ALD of SiN x …”

“…A vibrational band at ~2,080 cm −1 was also observed by Kessels et al during SiN x ALD with bis(tert‐butylamino)silane (BTBAS) and N 2 plasma, and the authors assigned this band generically to Si‐NCH complexes formed during the N 2 plasma cycle . Later, a similar observation was made by these authors for SiN x ALD with DSBAS and N 2 plasma . Based on an extensive survey of previous literature, especially on plasma‐deposited SiC x N y and CN x films, we have assigned the band at 2,080 cm −1 to the stretching vibration of C‐ and N‐containing cumulated double‐bonded species.…”

“…While Cl‐containing Si precursors have been widely used in the ALD of SiN x films, these precursors form corrosive byproducts that can damage the underlying films and the reactor walls. Therefore, aminosilane precursors have recently received attention as potential alternatives to chlorosilane precursors . Previous work on plasma‐assisted SiN x ALD has shown that the choice of the Si precursor constrains the choice of the N‐containing plasma: SiN x growth with chlorosilane precursors requires an NH 3 or N 2 /H 2 plasma, and SiN x growth with aminosilane precursors requires an N 2 plasma .…”

A Brief Review of Plasma Enhanced Atomic Layer Deposition of Si3N4

“…(Color online) Cross-sectional TEM image of SiNx thin film deposited on a high aspect ratio structure (AR = 4.5:1) by PEALD using DSBAS and N2 plasma. Reproduced with permission from [33], Copyright 2017, American Chemical Society. Figure 9.…”

“…Studies on SiN x PEALD focusing on the conformality of the film have been reported. For example, Faraz et al deposited a SiN x layer on trench-patterned wafers with an aspect ratio of 4.5 using a PEALD method [33]. Films were deposited by alternating the exposures of di(sec-butylamino)silane (DSBAS) precursor and N 2 plasma (13.56 MHz) at 500 .…”