Atomic Layer Deposition (or ALD) is an advanced deposition technique that allows for ultra-thin films of a few nanometres to be deposited in a precisely controlled way. Not only does ALD provide excellent thickness control and uniformity but 3D structures can be covered with a conformal coating for high-aspect-ratio structures.
ALD relies on self-limiting surface reactions and therefore generally provides very low pin-hole and particle levels, which can benefit a wide range of applications. The level of film and interface control and high film quality provided are sought after for many applications. The usage of plasma allows for improved film properties, control thereof and a wide range of possible materials. The flexibility of unique surface pre-treatments allows for low damage processing.
Atomic Layer Deposition typically involves a cycle of 4 steps that is repeated as many times as necessary to achieve the required deposited thickness. The example shows ALD of Al2O3 using Al(CH3)3 (TMA) and O2 plasma.
Step 1) Dosing of the substrate with a precursor vapour of TMA, which adsorbs on and reacts with the surface. With the correct choice of precursor and parameters, this reaction is self-limiting.
Step 2) Purging of all residual precursor and reaction products.
Step 3) Low damage remote plasma exposure to the surface with reactive oxygen radicals which oxidize the surface and remove surface ligands, this reaction is self-limiting due to the limited number of surface ligands.
Step 4) Reaction products are purged from the chamber.
Only step 3 varies between H2O for the thermal process or O2 plasma. As the ALD process deposits a (sub)angstrom thickness per cycle, control over the deposition process is obtained at the atomic scale.
In addition to the benefits of thermal ALD, PEALD allows for a wider choice of precursor chemistry with enhanced film quality:
||Load lock or Cassette|
|Substrates||Up to 200mm wafers & pieces directly on stage||Up to 200mm wafers handling and pieces on a carrier plate|
|Bubbled liquid & solid precursors||Up to 4 plus water, ozone and gases||Up to 8 plus water, ozone and gases|
|Max precursor source temperature||200ºC||200ºC|
|MFC controlled gas lines with rapid delivery system; 1) thermal gas precursors (e.g. NH<sub>3</sub>, O<sub>2</sub>) 2) plasma gases (e.g. O<sub>2</sub>, N<sub>2</sub>, H<sub>2</sub>)||2 internally. Up to 8 in externally mounted gas pod||Up to 10 in externally mounted gas pod|
Our Atomic Layer Deposition equipment is built on well over a decade of experience. Key features include of Oxford Instruments systems include: