Sputter deposition
The sputtered ions (typically only a small fraction of the ejected particles are ionized — on the order of 1 percent) can ballistically fly from the target in straight lines and impact energetically on the substrates or vacuum chamber (causing resputtering).
Sputtering is one of the main processes of manufacturing optical waveguides and is another way for making efficient photovoltaic and thin film solar cells.
[4][5] In 2022, researchers at IMEC built up lab superconducting qubits with coherence times exceeding 100 μs and an average single-qubit gate fidelity of 99.94%, using CMOS-compatible fabrication techniques such as sputtering deposition and subtractive etch.
Sputtering sources contain no hot parts (to avoid heating they are typically water cooled) and are compatible with reactive gases such as oxygen.
Also, active control for layer-by-layer growth is difficult compared to pulsed laser deposition and inert sputtering gases are built into the growing film as impurities.
Charge build-up on insulating targets can be avoided with the use of RF sputtering where the sign of the anode-cathode bias is varied at a high rate (commonly 13.56 MHz).
The chemical reaction that the particles undergo is with a reactive gas introduced into the sputtering chamber such as oxygen or nitrogen, enabling the production of oxide and nitride films, respectively.
[12] The introduction of an additional element to the process, i.e. the reactive gas, has a significant influence in the desired depositions, making it more difficult to find ideal working points.
Like so, the wide majority of reactive-based sputtering processes are characterized by an hysteresis-like behavior, thus needing proper control of the involved parameters, e.g. the partial pressure of working (or inert) and reactive gases, to undermine it.
Generally, the influence of the reactive gas' relative pressure and flow were estimated in accordance to the target's erosion and film's deposition rate on the desired substrate.
In ion-assisted deposition (IAD), the substrate is exposed to a secondary ion beam operating at a lower power than the sputter gun.
Any carbon atoms landing on the substrate which fail to bond properly in the diamond crystal lattice will be knocked off by the secondary beam.
HiPIMS utilizes extremely high power densities of the order of kW/cm2 in short pulses (impulses) of tens of microseconds at low duty cycle of < 10%.
In a study on metallic layers prepared by DC sputtering,[18] he extended the structure zone concept initially introduced by Movchan and Demchishin for evaporated films.
[19] Thornton introduced a further structure zone T, which was observed at low argon pressures and characterized by densely packed fibrous grains.
are used for the sublimation of source atoms, the pressure governs via the mean free path the energy distribution with which they impinge on the surface of the growing film.
Since sputter deposition belongs to the group of plasma-assisted processes, next to neutral atoms also charged species (like argon ions) hit the surface of the growing film, and this component may exert a large effect.
Denoting the fluxes of the arriving ions and atoms by Ji and Ja, it turned out that the magnitude of the Ji/Ja ratio plays a decisive role on the microstructure and morphology obtained in the film.
[20] The effect of ion bombardment may quantitatively be derived from structural parameters like preferred orientation of crystallites or texture and from the state of residual stress.
