Atomic layer deposition of thin films: from a chemistry perspective

Abstract

Atomic layer deposition (ALD) has become an indispensable thin-film technology in the contemporary microelectronics industry. The unique self-limited layer-by-layer growth feature of ALD has outstood this technology to deposit highly uniform conformal pinhole-free thin films with angstrom-level thickness control, particularly on 3D topologies. Over the years, the ALD technology has enabled not only the successful downscaling of the microelectronic devices but also numerous novel 3D device structures. As ALD is essentially a variant of chemical vapor deposition, a comprehensive understanding of the involved chemistry is of crucial importance to further develop and utilize this technology. To this end, we, in this review, focus on the surface chemistry and precursor chemistry aspects of ALD. We first review the surface chemistry of the gas-solid ALD reactions and elaboratively discuss the associated mechanisms for the film growth; then, we review the ALD precursor chemistry by comparatively discussing the precursors that have been commonly used in the ALD processes; and finally, we selectively present a few newly-emerged applications of ALD in microelectronics, followed by our perspective on the future of the ALD technology.

Fabrication and integration of photonic devices for phase-change memory and neuromorphic computing

“…SiO 2 protection layer was then removed by HF wet etching. A plasma post-oxidation was performed to form GeO x [172], which was further covered by a 5 nm Al 2 O 3 layer as the bonding interface using atomic layer deposition (ALD) [173,174]. Another Si wafer as the substrate was covered by a 2 µm-thick SiO 2 by thermal oxidation, and was deposited by a 5 nm ALD Al 2 O 3 layer.…”

Preparation of single atom catalysts for high sensitive gas sensing

“…ALD is a cyclic process that relies on the self-limiting surface reaction between gas-phase precursors and solid surfaces [92,154]. This technique offers the capability to uniformly distribute nanoparticles on suitable supports, ranging in size from nanometers to single atoms [155][156][157][158].…”

Material manufacturing from atomic layer

“…Briefly speaking, a typical ALD process is executed in a cyclic manner, where each ALD cycle consists of two or more gas-solid surface chemical reactions performed sequentially. By carefully engineering the precursor molecular structure and deposition conditions [26], self-limited atomic-layer growth of material can be realized in each ALD cycle. This self-limited growth behavior is in stark contrast to a conventional CVD process, where the precursors are continuously and simultaneously supplied so that the film growth is not self-limited.…”

“…For instance, the ALD byproduct may not be sufficiently volatile to liberate from the surface, which could block the reactive sites and therefore reduce the per-cycle film growth [27]; the ALD precursor molecule may partly decompose on the surface, which could lead to impurities in the films [28]. To tackles these issues, one may need to carefully choose the precursor types and deposition conditions, such as temperature, pressure, and perhaps using plasma assisting [26]. With optimized deposition conditions, high-quality heteroepitaxial thin films can also be grown by ALD [29].…”