Atomic Layer Deposition (ALD) is an advanced technique for the fabrication of high-quality thin films for various applications. ALD -deposited thin films are highly uniform and conformal on the whole surface of substrates. In ALD, control of film growth in the nanometer/sub-nanometer thickness regime is achieved by sequential, self-limiting and surface controlled gas-solid reactions between precursor molecules and the substrate surface. Due to the film formation mechanism – the gases won’t react until in touch with the surface which means the film growth proceeds by consecutive atomic layers starting from the surface – the ALD films are dense, crack-, defect- and pinhole-free and the thickness and structural and chemical quality can be precisely controlled on an atomic scale. ALD processes are also repeatable and they can be performed at relatively low temperatures. This gives the possibility to construct not only single material layers but also doped, mixed or graded layers and nanolaminates. The list of ALD materials is wide, ranging from e.g. oxides, nitrides, fluorides and sulfides to ternary compounds, metals (even noble ones) and polymers.
Credit Dr. T. Suntola
The number of ALD applications has grown exponentially over the past few years and nowadays the method is used in e.g. semiconductor industries such as IC (integrated circuits), sensor, III-V device, and MEMS/NEMS (micro/nanoelectromechanical systems) manufacturing, optics and optoelectronics, anti-tarnishing and wear protection, and renewable energy applications such as solar power. Other large scale applications include also corrosion protection, energy storage and production (e.g. advanced thin film batteries and fuel cells), biocompatible coatings for medical devices and implants, water purification, advanced lighting devices such as OLEDs, ecological packaging materials, moisture- and gas-tight encapsulant layers, decorative coatings, anti-cracking layers for glass, and water repelling coatings.
In the MEMS/NEMS field, ALD films are used as electrically insulating or thermally conducting layers, etch stop layers, anti-stiction layers, hermetically sealed layers, biocompatible coatings, optical layers, charge dissipative layers, diffusion barriers or passivation layers, for example.