ALD Precursors
ALD is a gas phase vapor deposition technique that operates in vacuum. The process is based on sequential self-limiting chemical reactions of precursors to form a thin film at the surface of the material being deposited. The reaction sequence can be repeated multiple times to deposit desired thicknesses.
ALD Precursors who uses ALD Precursors
There are a large number of standard precursors available for use in the ALD process. These precursors are formulated to provide the necessary characteristics for ALD growth (volatile, chemically stable to air and moisture, noncorrosive nature, and leave no impurities in deposited films).
Some of the most common materials deposited by ALD include metal oxides, metals, nitrides, sulfides, and semiconductors. Various other materials have been used as ALD substrates including organic materials, inorganic-organic hybrids, and nanoparticles.
Why ALD?
ALD is an ultrathin film growth technique that relies on sequential self-limiting chemical reactions of two (or more) precursors. These precursors react with surface groups on a substrate to create a thin film, which is then purged with an inert gas.
This is a fundamentally different approach to film growth from most other techniques such as sputtering, evaporation, and chemical vapor deposition. In ALD, the self-limiting nature of the reaction between the precursor and the surface enables growth of high aspect ratio structures that cannot be deposited by conventional deposition methods such as sputtering or evaporation. This is a key feature that sets ALD apart from conventional film-growing techniques.
The self-limiting nature of ALD chemistry also allows for the creation of films with extremely high surface conformality. This is in contrast to the roughness and pinhole issues commonly seen in CVD and PVD processes. This is an important characteristic for the use of ALD as a thin film deposition method for semiconductor applications.
However, many ALD processes are prone to reproducibility problems that are not necessarily related to the ALD equipment itself but rather to the nature of the precursors or materials used as substrates. As a result, many of the published ALD results do not form uniform films and may not have all of the desired properties.
One of the more problematic ALD processes is tetrakis(dimethylamino)titanium (TDMAT) and ammonia plasma, which has a wide range of parameters and often yields very poor ALD results. This is because of several factors, some of which are not associated with the ALD equipment itself but rather to the TDMAT precursor itself or to the type of substrate used in the deposition process.
Among these is the presence of undesirable native oxygens on the surface that can cause a significant interference with the Fermi level at the TDMAT/ammonia plasma interface. In addition, this can also prevent the formation of a passivation layer on top of the deposited TiN.
Therefore, the development of a new generation of ALD precursors that meet the requirements for this process is essential to enable continued growth and innovation in this promising area. In particular, precursors with nitrogen-based donor ligands can minimize the incorporation of unwanted elements in the deposited metal oxide or nitride films. ALD precursors with these ligands can be optimized to achieve superior performance in the most challenging applications.
City Chemical LLC sells ALD Precursors in bulk quantities. Visit https://www.citychemical.com/chemical-vapor-deposition to learn more and place order.