Basics of Atomic Layer Deposition: Growth Characteristics and Conformality

This chapter introduces some fundamentals and key advantages of the atomic layer deposition (ALD) technique. It provides the standard example of a typical trimethylaluminum (TMA)/H2O ALD cycle, and discusses the essential characteristics of true layer-by-layer growth. The chapter explains how the surface-controlled nature of the reactions ensures atomic-level thickness control and excellent conformality on 3D substrates, and introduces the concept of plasma-enhanced ALD. The chapter also focuses on in situ characterization methodologies that are often used in ALD research. It discusses the advantages of using in situ techniques to determine ALD growth characteristics, and provides examples of quartz crystal microbalance, quadrupole mass spectroscopy, spectroscopic ellipsometry, and optical emission spectroscopy (OES). The chapter further reviews the conformality of ALD and addresses the use of macroscopic and microscopic lateral test structures for quantifying conformality, as well as approaches to characterize conformal ALD in nanoporous materials.