What is ion sputtering coating for optical lenses?

This issue will continue to introduce another method of coating optical lenses-ion sputtering. In coating technology, sputtering refers to removing particles from solid targets. Therefore, high-energy ions are generated in plasma in vacuum and accelerated in the target direction by external electric field. Ions collide with target atoms to form an impact cascade. If the minimum energy of about 20eV is exceeded, the target material is removed. Some particles leave the target and move to the substrate, where they are deposited as a thin layer.

This coating process for optical lenses is suitable for optics in a wide wavelength range and can be divided into different types, mainly by the ion source used, which can be divided into plasma sputtering and ion beam sputtering.

Plasma sputtering

Plasma sputtering includes various optical lens coating processes, such as magnetron, DC and RF sputtering. The same characteristics of these processes are recovering ions by gas discharge, applying voltage and introducing inert gas (usually argon) to ignite plasma, thus releasing ions that hit the target with high kinetic energy and dissolving sputtering target atoms from the surface.

Magnetron sputtering uses magnetic field to force electrons near the target to move along the target surface in a spiral motion. This process can be used to produce hard and mechanical-resistant optical coatings.

DC sputtering is carried out by applying DC voltage, so that the target forms a negative electrode and the substrate forms a positively charged electrode. Positive (argon) ions from the plasma hit the target and dissolve the target atoms through impact cascade, and the target atoms are deposited on the substrate.

RF sputtering is a high frequency alternating field, which can accelerate plasma (argon) ions and electrons alternately in two directions. In plasma, high-energy electrons reach the free surface faster than ions. This means that each surface of the plasma is negatively charged, so it will generate self-bias. In this method, argon ions are also accelerated to the solid target (cathode) and atoms are knocked out. Non-conductive materials can be atomized because there is no need to release positive charges.

Ion beam sputtering

Ion beam sputtering (IBS) is mainly used for dense layers with low reflection, and IBS uses different ion sources separated from the target and substrate. Heavy monoenergetic ions (for example, 40AR) are generated, focused and directed vertically at the target, and atomized at an energy of usually 5 to 20 keV. Ions hit the target surface, thus triggering the sputtering of target atoms, and the target atoms condense into a dense coating on the substrate. The achievable film thickness on the substrate depends on the ion current, the distance between the substrate and the target, the angle between the support and the target surface, and the atomization time.

Compared with MS sputtering, IBS coating process is technically more complicated, so the cost is higher, and it is mainly suitable for coating systems with high selection and requirements.