Atomic layer deposition (ALD) is a method that allows for the deposition of thin films with atomic level control of the thickness and an excellent conformality on 3-dimensional surfaces. In recent years, ALD has been implemented in many applications in microelectronics, for which often a patterned film instead of full area coverage is required. This article reviews several approaches for the patterning of ALD-grown films. In addition to conventional methods relying on etching, there has been much interest in nanopatterning by area-selective ALD. Area-selective approaches can eliminate compatibility issues associated with the use of etchants, lift-off chemicals, or resist films. Moreover, the use of ALD as an enabling technology in advanced nanopatterning methods such as spacer defined double patterning or block copolymer lithography is discussed, as well as the application of selective ALD in self-aligned fabrication schemes.

Bottom-up nanofabrication by area-selective atomic layer deposition (ALD) is currently gaining momentum in semiconductor processing, because of the increasing need for eliminating the edge placement errors of top-down processing. Moreover, area-selective ALD offers new opportunities in many other areas such as the synthesis of catalysts with atomic-level control. This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area-selective ALD processes can be improved. A general cause for the loss of selectivity during deposition is that the character of surfaces on which no deposition should take place changes when it is exposed to the ALD chemistry. A solution is to implement correction steps during ALD involving for example surface functionalization or selective etching. This leads to the development of advanced ALD cycles by combining conventional two-step ALD cycles with correction steps in multistep cycle and/or supercycle recipes.

In the past decade, atomic layer deposition (ALD) has become an important thin film deposition technique for applications in nanoelectronics, catalysis, and other areas due to its high conformality on 3-D nanostructured substrates and control of the film thickness at the atomic level. The current applications of ALD primarily involve binary metal oxides, but for new applications there is increasing interest in more complex materials such as doped, ternary, and quaternary materials. This article reviews how these multicomponent materials can be synthesized by ALD, gives an overview of the materials that have been reported in the literature to date, and discusses important challenges. The most commonly employed approach to synthesize these materials is to combine binary ALD cycles in a supercycle, which provides the ability to control the composition of the material by choosing the cycle ratio. Discussion will focus on four main topics: (i) the characteristics, benefits, and drawbacks of the approaches that currently exist for the synthesis of multicomponent materials, with special attention to the supercycle approach; (ii) the trends in precursor choice, process conditions, and characterization methods, as well as underlying motivations for these design decisions; (iii) the distribution of atoms in the deposited material and the formation of specific (crystalline) phases, which is shown to be dependent on the ALD cycle sequence, deposition temperature, and post-deposition anneal conditions; and (iv) the nucleation effects that occur when switching from one binary ALD process to another, with different explanations provided for why the growth characteristics often deviate from what is expected. This paper provides insight into how the deposition conditions (cycle sequence, temperature, etc.) affect the properties of the resultant thin films, which can serve as a guideline for designing new ALD processes. Furthermore, with an extensive discussion on the nucleation effects taking place during the growth of ternary materials, we hope to contribute to a better understanding of the underlying mechanisms of the ALD growth of multicomponent materials.

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