Thin film technology atomic layer deposition

Suntola T (1995) Atomic layer deposition (Handbook of Thin Film Process Technology), Institute of Physics, Bristol, B15 pp. 1-17... 

Kim H (2003) Atomic layer deposition of metal and nitride thin films. Current research efforts and applications for semiconductor device processing. Journal of Vacuum Science Technology B 21(6), 2231-2261... 

Thin semiconductor films (and other nanostructured materials) are widely used in many applications and, especially, in microelectronics. Current technological trends toward ultimate miniaturization of microelectronic devices require films as thin as less than 5 nm, that is, containing only several atomic layers [1]. Experimental deposition methods have been described in detail in recent reviews [2-7]. Common thin-film deposition techniques are subdivided into two main categories physical deposition and chemical deposition. Physical deposition techniques, such as evaporation, molecular beam epitaxy, or sputtering, involve no chemical surface reactions. In chemical deposition techniques, such as chemical vapor deposition (CVD) and its most important version, atomic layer deposition (ALD), chemical precursors are used to obtain chemical substances or their components deposited on the surface. 

Because of the sequential nature of atomic layer deposition, it is a slow method for preparing thin films. The sequential nature, however, also produces a film of uniform thickness, referred to as a conformal film. This is important when the surface being coated is not atomically flat, but rather, has troughs and islands to be coated. Some of the most important technological materials, such as silicon and germanium, have not shown themselves to be amenable to the atomic layer deposition technique. This points to the need for continued research in the field of precursor synthesis. 

In thin film technology there is a distinction between physical vapor deposition (PVD) and chemical vapor deposition (CVD), a combination of types is available. All methods work in vacuum. The most important physical processes are evaporation and the sputtering. The material is introduced into the system as a solid (target). With an energy introduced into the target, they resolve atoms and molecules form a layer on the substrate. The layer thickness achieved is in the micrometer range. The layer composition substantially corresponds to that of the target. It can be pure metals, alloys, or dielectrics. 

Thin film science and technology is the deposition and characterization of layered structnres, typically less than a micron in thickness, which are tailored from the atomic scale upwards to achieve desired functional properties. Deposition is the synthesis and processing of thin films under controlled conditions of chemical processing. Chemical vapor deposition (CVD) and gas-phase molecular beam epitaxy (MBE) are two processes that allow control of the composition and structure of the films. Characterization is the instrumentation that use electrons, X-ray, and ion beams to probe the properties of the film. Epitaxial films of semiconductors are used for their electronic properties to emit light in the infrared (IR) and the ultraviolet rays. 

---