IBS(IBD) – Ion beam sputtering (deposition)
IBS | IBD
IBS(IBD) – Ion beam sputtering (deposition) technology is currently one of the most important physical vapor deposition (PVD) technologies for making advanced precision optical coatings. It relies on principle of sputtering target material using collimated and neutralized ion beam. The main difference from other sputtering(deposition) technologies is that plasma is generated in a separate chamber and ions are then extracted using sophisticated grid system. Argon (or xenon) is mainly used as a working gas for plasma generation. Accelerated and neutralized ions hit material target usually at higher than 50° angle to normal, since it allows to achieve higher sputter yield. Knocked out material atoms and molecules have very high kinetic energies (~1<Ek< ~10 eV) and therefore forms very compact and dense films.
Main process parameters, which might be changed and optimized are geometry of the system, ion energy, ion flux, background oxygen pressure.
Since IBS(IBD) process delivers much higher energies of condensing particles, also it has much more precisely controlled process parameters, comparing with electron beam evaporation, ion beam sputtering (ion beam deposition) is very stable technology.
- Flatness and stress
- Available coating materials
Compact and dense layers, which are environmentally stable and do not have spectral shift with change of humidity or temperature;
- Amorphous layer structure, resulting in smooth interfaces, very low surface roughness and respectively low coating scatter usually limited by initial substrate roughness;
- Possible deposition on unheated substrates, so temperature sensitive substrates can be coated;
- Reliable and repeatable batch to batch deposition of complex multilayer coatings with precisely controlled spectral, dispersion properties, like chirped mirrors, interference filters, cut-off filters, etc.;
- High LIDT;
- Low coating defect density.
Ion beam sputtering (ion beam deposition) coatings also has disadvantages – for example high tensions or a.k.a. stress. It could result in flatness deterioration of the final optical component. However, there are several techniques, which allows 3photon coating engineers to relieve stress:
- Depositing SiO2 or any other material coating layer on the rear surface of substrate (wafer), which can also be anti-reflective coating. The stress (tension) caused by optical coating on the front substrate (wafer) surface can be compensated with the stress of similar amplitude induced by coating applied on the rear side of the substrate (wafer)
- Applying special thermal procedures to suppress tensions within as-deposited coatings. This technology allows to keep rear substrate (wafer) surface blank (clear) and allows 3photon coating engineers in many cases to preserve initial flatness of uncoated(bare) substrate.
Sputtering of metal fluorides was demonstrated by several publications. However, due to certain complex issues, usually IBS(IBD) is not considered as an efficient tool for production of coatings for deep UV spectral range (below 200 nm). Recently, more research is emerging, related to sputtering of fluorides for IR coating applications.
- Oxides: Ta2O5, Nb2O5, V2O5, TiO2, ZrO2, HfO2, Al2O3, Y2O3, SiO2, etc.;
- Nitrides: Si3N4, AlN, TiN, etc.;
- Other elements: Al, Si, Pt, etc.;
- Usually these materials are used in metal (non-oxide, non-nitride, non-fluoride, etc.) form, but by introducing these gasses into the chamber or through ion assisting source.