Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Plasma-assisted atomic layer deposition (ALD) is an energy-enhanced method for the synthesis of ultra-thin films with A-level resolution in which a plasma is employed during one step of the cyclic deposition process. The use of plasma species as reactants allows for more freedom in processing conditions and for a wider range of material properties compared with the conventional thermally-driven ALD method. Due to the continuous miniaturization in the microelectronics industry and the increasing relevance of ultra-thin films in many other applications, the deposition method has rapidly gained popularity in recent years, as is apparent from the increased number of articles published on the topic and plasma-assisted ALD reactors installed. To address the main differences between plasma-assisted ALD and thermal ALD, some basic aspects related to processing plasmas are presented in this review article. The plasma species and their role in the surface chemistry are addressed and different equipment configurations, including radical-enhanced ALD, direct plasma ALD, and remote plasma ALD, are described. The benefits and challenges provided by the use of a plasma step are presented and it is shown that the use of a plasma leads to a wider choice in material properties, substrate temperature, choice of precursors, and processing conditions, but that the processing can also be compromised by reduced film conformality and plasma damage. Finally, several reported emerging applications of plasma-assisted ALD are reviewed. It is expected that the merits offered by plasma-assisted ALD will further increase the interest of equipment manufacturers for developing industrial-scale deposition configurations such that the method will find its use in several manufacturing applications.

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Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

The progressively decreasing feature size of the circuit components has tremendously increased the need for the global surface planarization of the various thin film layers that constitute the integrated circuit (IC). Global planarization, being one of the major solutions to meet the demands of the industry, needs to be achieved following the most efficient polishing procedure. Chemical mechanical polishing (CMP) is the planarization method that has been selected by the semiconductor industry today. CMP, an ancient process used for glass polishing, was adopted first as a microelectronic fabrication process by IBM in the 80 s for SiO2 polishing. To achieve efficient planarization at miniaturized device dimensions, there is a need for a better understanding of the physics, chemistry and the complex interplay of tribo-mechanical phenomena occurring at the interface of the pad and wafer in presence of the fluid slurry medium. In spite of the fact that CMP research has grown by leaps and bounds, there are some teething problems associated with CMP process such as delamination, microscratches, dishing, erosion, corrosion, inefficient post-CMP clean, etc.; research on which is still developing. The fundamental understanding of the CMP is highly necessary to characterize, optimize and model the process. The CMP process is ready to make a positive impact on 30% of the US$ 135 billion global semiconductor market. This paper presents an overview of CMP process in general, the science and mechanism of polishing, different metal and dielectric CMP processes. The impact of consumables on the CMP process, post-CMP cleaning, modeling of different CMP processes as well as the future trends are also discussed.

Chemical mechanical planarization for microelectronics applications

Photoelectric detectors are the central part of modern photodetection systems with numerous commercial and scientific applications. p-Type semiconductor materials play important roles in optoelectronic devices. Photodetectors based on p-type semiconductor materials have attracted a great deal of attention in recent years because of their unique properties. Here, a comprehensive summary of the recent progress mainly on photodetectors based on inorganic p-type semiconductor materials is presented. Various structures, including photoconductors, phototransistors, homojunctions, heterojunctions, p-i-n junctions, and metal-semiconductor junctions of photodetectors based on inorganic p-type semiconductor materials, are discussed and summarized. Perspectives and an outlook, highlighting the promising future directions of this research field, are also given.

Photoelectric Detectors Based on Inorganic p-Type Semiconductor Materials.

The combination of hybrid perovskite and Cu(In,Ga)Se2 (CIGS) has the potential for realizing high-efficiency thin-film tandem solar cells because of the complementary tunable bandgaps and excellent photovoltaic properties of these materials. In tandem solar device architectures, the interconnecting layer plays a critical role in determining the overall cell performance, requiring both an effective electrical connection and high optical transparency. We used nanoscale interface engineering of the CIGS surface and a heavily doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layer between the subcells that preserves open-circuit voltage and enhances both the fill factor and short-circuit current. A monolithic perovskite/CIGS tandem solar cell achieved a 22.43% efficiency, and unencapsulated devices under ambient conditions maintained 88% of their initial efficiency after 500 hours of aging under continuous 1-sun illumination.

http://science.sciencemag.org/content/sci/361/6405/904.full.pdf

High-performance perovskite/Cu(In,Ga)Se2 monolithic tandem solar cells

In recent years, the integration of two-dimensional (2D) nanomaterials, especially transition metal chalcogendies (TMCs) and dichalcogendies (TMDCs), into electronic devices have been extensively studied owing to their exceptional physical properties such as high transparency, strong photoluminescence, and tunable bandgap depending on the number of layers Herein, we report the optoelectronic properties of few-layered MoSe2-based back-gated phototransistors used for photodetection The photoresponsivity could be easily controlled to reach a maximum value of 238 AW−1 under near-infrared light excitation, achieving a high specific detectivity Few-layered MoSe2 exhibited excellent optoelectronic properties compared with those reported previously for multilayered 2D material-based photodetectors, indicating that our device is one of the best high-performance nanoscale near-infrared photodetectors based on multilayered two-dimensional materials

https://iopscience.iop.org/article/10.1088/1361-6641/aa6819/pdf

High-performance near-infrared photodetector based on nano-layered MoSe2

Temperature effects of pad conditioning process on oxide CMP: Polishing pad, slurry characteristics, and surface reactions

It is well known that, theoretically, thin-film cadmium telluride (CdTe) solar cell technology can improve on the conversion efficiency and production costs of conventional silicon solar cell technology. Due to the optimal band gap energy (about 1.4 eV) for solar energy absorption, high light absorption capability and lower cost requirements for solar cell production, CdTe has been widely researched as being suitable for commercial cell production. In this study, the sputtering method, which can improve on the cost-efficiency and mass-production of solar cells, was employed to deposit the CdTe thin film with various processing conditions such as sputtering power, and gas pressure. The effects of the processing conditions on the thickness-uniformity and surface morphology of the CdTe thin films were investigated using atomic force microscope (AFM) and ellipsometry for large-area solar cells. The photovoltaic properties of CdTe thin films were analyzed in relation to the different thickness-uniformity and surface morphology caused by the various process conditions. The thickness-uniformity, which was controlled by the process conditions in the sputtering process, was found to affect the photovoltaic properties of the sputtering-deposited CdTe thin films. Higher carrier concentration and better optical absorbance were obtained in CdTe thin films with a good thickness-uniformity.

Influences of thickness-uniformity and surface morphology on the electrical and optical properties of sputtered CdTe thin films for large-area II–VI semiconductor heterostructured solar cells

Structural and surface properties of NiCr thin films prepared by DC magnetron sputtering under variation of annealing conditions

Design of experiment (DOE) method considering interaction effect of process parameters for optimization of copper chemical mechanical polishing (CMP) process

Nam-Hoon Kim

Papers

High-performance near-infrared photodetector based on nano-layered MoSe2

Temperature effects of pad conditioning process on oxide CMP: Polishing pad, slurry characteristics, and surface reactions

Influences of thickness-uniformity and surface morphology on the electrical and optical properties of sputtered CdTe thin films for large-area II–VI semiconductor heterostructured solar cells

Structural and surface properties of NiCr thin films prepared by DC magnetron sputtering under variation of annealing conditions

Design of experiment (DOE) method considering interaction effect of process parameters for optimization of copper chemical mechanical polishing (CMP) process