Plasma assisted reactive magnetron sputtering
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Load Lock with Single Substrate Handling Sputtering Chamber with rotating multi-Substrate Turn Table Sputter module Single Substrate Load Lock Control panel High Speed Drive Lift Plasma Source Dual Magnetron Substrate Carrier Turn table UV- and VIS Filter Coatings by Plasma Assisted Reactive Magnetron Sputtering (PARMS) M. Scherer, J. Pistner, W. Lehnert Leybold Optics GmbH, Siemensstrasse 88, D- 63755 Alzenau, Germany michael.scherer@leyboldoptics.com Abstract: The advantage of PARMS for the manufacturing of high performance low loss coatings is demonstrated with UV- and VIS band pass filter based on HfO2 respectively Nb2O5 and SiO2. 1. Introduction Reactive sputtering with MF dual magnetron is a highly developed technique and successfully used for many thin film applications. For high performance low loss optical filter coatings based on oxides the reactive process has to avoid any kind of arcing, hard arcs as well as ì-arcs. This requirement is solved by PARMS as well as a high deposition rate for an economic production of high end optical filter coatings. The principle of PARMS is based on a two step process, the reactive deposition of a thin oxide layer with a controlled deficit of oxygen followed by a RF plasma assist process with reactive oxygen for the transformation to a stoichiometric oxide layer. This sequence is repeated until the final layer thickness is stopped by time control or by an optical monitoring system. Details of the PARMS technology are given in references [1-3]. The advantage of PARMS is to avoid non conducting areas on the target surface which results in a fully stable sputtering process free of any arcing and a high sputter yield compared to classical reactive sputtering without a plasma assist process. Two band pass filter coatings, one UV filter based on HfO2/SiO2 and one VIS filter with a high blocking based on Nb2O5/SiO2, demonstrate the capability of PARMS for the economic production of high performance filter coatings. 2. Sputtering equipment The investigations are done in a HELIOS sputtering tool. Figure 1a shows an overview of the tool. Figure 1a: Overview of the HELIOS sputtering tool Figure 1b: Direct optical monitoring The tool is equipped with two dual magnetrons, one with Hf respectively Nb for the high index material and one with Si for the low index material. For plasma cleaning and the plasma assist process a RF plasma source is used. Quartz respectively D263 glass substrates are loaded on substrate carriers and transferred Load Lock Substrate carrier Turn table Monitoring fiber to OMS Monitor glass Sputter module

via a load lock into the turn table. One substrate is used as monitoring substrate for the optical thickness control in intermittent mode shown in figure 1b. Optical thickness was measured in transmittance. The used deposition rate is in the range of 0.5nm/s. 3. UV band pass filter For the production of UV band pass filter coatings down to a wavelength of 250nm we investigated and optimized ZrO2 and HfO2. Hafnium oxide and zirconium oxide are well known candidates with pretty high refractive indices but sometimes difficult to optimize all relevant film properties like losses by absorption...

Even without backside AR the as deposited filter is in the pass band very close to the specification while a post annealing step at 350°C improved the pass band transmittance at 260nm by 3%. Figure 3b shows the low transmittance within the blocking band which is clearly below the specified value of 0.1%. There is a very good spectral correlation between the theory and the experimental filter coating. 4. VIS band pass filter with high blocking The specification of the challenging BP with high blocking is given in table 2. The design consists of a front- and backside design based on Nb2O5 and...