Property and Processing Comparison of Optical Coatings Made by Ion Assisted Evaporation and Magnetron Sputtering
- PDF / 1,382,952 Bytes
- 11 Pages / 391.5 x 607.5 pts Page_size
- 73 Downloads / 199 Views
Deposition (PVD) processes: Ion Assisted Evaporation (lAD) and Magnetron
Sputtering (sputtering). The paper emphasizes oxide optical coatings, but the content applies well to other types of PVD coatings discussed in this Proceedings. The plan of the paper is to compare the principal performance features of lAD and sputtering, one-by-one, by presenting a combination of science fundamentals and actual demonstration results. The intent is to provide the reader with a good grasp of what each process can do and to aid in process selection for future coating work. The paper reviews the author's optical coating work, presented as fundamentals that support the approach taken and measurements that show the results obtained. The author has worked "hands on" with these processes for twenty-four years, at three companies, with more than forty different coating chambers. That work covered the entire spectrum from basic research, to applied development, to production-line coating. Since each company used both processes, the comparison is relatively honest and unbiased. Principal performance features compared include: adatom energetics, reactivity, materials compatibility, thickness uniformity, deposition rate, substrate temperature, durability, environmental stability, refractive indices, absorption, scatter, mechanical stress control, and scalability (chamber and substrate size). The analysis of best process for a given application is summarized by assigning a rank of A, B or C to each feature of each process. 41 Mat. Res. Soc. Symp. Proc. Vol. 555 01999 Materials Research Society
PROCESS FUNDAMENTALS Energetic Reactive Processes Both lAD and sputtering are energetic reactive PVD processes [1-4]. The energy delivered to the coating growth surface, per adatom condensed, is much greater than the 0.1 eV obtained with conventional evaporation. Further, the reactive gas (e.g., oxygen) is ionic and activated (02+, O) rather than neutral and molecular (02). The actual physical parameter of importance is likely momentum transfer [5], but the energy concept is often more transparent because ion source output is measured in Amperes of current (number of ions) at a selected energy in Volts (energy of each ion). The following sections examine more closely the energetics and reactivity of each process.
Ion Assisted Evaporation lAD is ion stimulation simultaneous with coating deposition [1-4]. Coating atoms from an electron-beam gun or resistance source arrive at the substrate with low energies (typically 0.1 eV) and largely condense at the point of impact. With continued atom arrival, the adatoms reach critical density, coalesce, shadow neighboring areas, and form a porous columnar microstructure tilted toward the direction of the vapor source. Simultaneous ion bombardment moves atoms to the correct sites and packs them into a denser layer. Argon ions (Ar') with energies in the range of 40 to 100 eV are commonly used, although some ion sources work better at higher energies. Moving an atom requires about 5 eV, so one ion can supply enou
Data Loading...
