Thin Film Coating

Thin Film Coating

REO utilizes three coating process technologies to produce the highest quality thin films performing a range of functions across the full optical spectrum from the deep UV (190nm) through the long wave IR (14um). Expertise with Ion Beam Sputtering, Ion Assisted Deposition and Thermal Evaporation provide REO an extensive toolbox of available materials and processes suitable for most any application. With a total of 35 coating chambers in operation, REO’s ability to produce the highest performance, lowest loss, most durable thin films across the spectrum is unmatched in the world.

Ion Beam Sputtered Coatings (IBS)

REO pioneered the commercial use of Ion Beam Sputtering in the late 1980’s. With 22 IBS systems in operation today, REO is home to the world’s largest concentration of IBS optical coating technology. Our IBS technology produces thin films with exceptionally low scatter and absorption along with high mechanical durability and environmental stability. Utilizing primarily metal oxide materials, REO has developed the IBS process to produce films which function from the UV through the Mid IR (up to 6um).

Particularly well suited for laser applications, REO's IBS films feature extremely low defect levels along with high laser damage resistance. Our high reflectors for pulsed laser applications at 1064nm may have virtually no defects over a central aperture of several square millimeters and laser damage resistance of up to 60 J/cm2 for 20ns pulse duration, or may be designed to withstand up to 10MW/cm2 for CW applications.  

View IBS Coating Model or click on image below:

Ion Assisted Deposition (IAD)

IAD utilizes the evaporative method described previously, but adds a high energy ion beam that is directed at the part to be coated.  These ions impart energy to the deposited material – acting almost like an atomic sized hammer – resulting in a higher film density than achieved with purely evaporative methods.  The ion beam can also be used to pre-clean or etch the surface of the substrate, which can improve film adhesion.  The combination of a relatively cold deposition process and the ion pre-clean affords the opportunity to coat plastic substrates such as polycarbonate lenses or visors, and even enables deposition on the ends of jacketed fibers and the top of photo-resist masks. 

The higher density of IAD coatings generally gives them more mechanical durability, greater environmental stability and lower scatter than evaporative films.  Furthermore, the amount of energetic assistance can be varied from zero to a maximum level on a layer by layer basis, giving the process tremendous flexibility.  For example, while IAD is not compatible with some of the commonly used materials in the infrared, it can be used solely on the outermost layer to yield an overall coating with superior durability.  The ion energy can also be used to modify the intrinsic stress of a film during deposition.  In some cases, this can change the film stress from tensile to compressive.  This can help to maintain substrate surface figure, especially when depositing thick infrared coatings. Click on image to below to  View IAD Coating Model

Thermal Evaporation

Evaporative coatings are produced in a high vacuum chamber.  Both metals and dielectric coating materials can be utilized with this technique.  The coating material is heated either resistively or through electron beam bombardment until it vaporizes.  The vapor then streams away from the source and recondenses on all surfaces that are in a line of sight with the source. 

Because no energy is applied as the vapor condenses and settles on the surface, thin films formed with this method are porous, of relatively low density, and exhibit a columnar structure.  Substrates are typically heated to several hundred degrees Celsius during the coating process in order to reduce this effect; however, it is by no means eliminated. 

Porosity allows evaporative films to subsequently absorb moisture, meaning that the performance of the coating can shift in use with changes in ambient temperature and humidity.  The low density also compromises mechanical durability to a certain extent, although these films can typically meet most of the MIL-SPEC durability and environmental requirements.  Furthermore, the requirement to heat the components during processing can limit substrate material choice, and also introduce stress in the substrate due to thermal cycling. 

Evaporative coating processes are difficult to automate entirely, and typically need monitoring by an operator.  However, the high deposition rates keep coating run times relatively short, and thus production costs low.  As a result, this method is particularly favored when cost is a significant consideration, and performance and durability specifications are relatively loose.  The other big advantage of evaporative methods is that they are suitable for use with an extremely wide range of coating materials, from fluorides used in the deep ultraviolet, to oxides for visible wavelengths, through semiconductor and sulfide materials often employed in the infrared.  Click on image to below to  View Thermal Evaporation Coating Model

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