Ion Assisted Deposition
Ion Assisted Deposition (IAD) is based on a coating system as described before for Electron Beam Evaporation (EBE) but with an additional plasma source. The plasma is directed onto the calotte and provides a bombardment of the growing layer which results in a denser micro structure and therefore eliminates the thermal drift.
The plasma is generated by a DC-discharge with a RF-heated cathode. Caused by the strong discharge of about 40 amps, the molecules in the vapour are activated and ionized. The reactive argon and oxygen ions hit the substrate with energies up to 150 eV.
IAD still uses the high evaporation rate of EBE what helps to keep the costs down, but it is limited to certain coating materials, for example fluorides cannot be used. By using optimized parameters the internal stress can be minimized. In the VIS/NIR normally the LIDT is close to EBE.
IAD coating machine