Roelene Botha

Silane injection in a high-density low-pressure plasma system and its influence on the deposition kinetics and material properties of SiO2

High-rate, low temperature deposition is an essential requirement for industrial fabrication technology to be suitable for the deposition of optical and protective coatings. High-density, low-pressure plasmas have received significant attention for such applications due to their ability to create large and controllable ion fluxes onto the substrate. In this study, the high-rate deposition of silica films from a silane and oxygen gas mixture in a high-density plasma system based on a matrix distributed electron cyclotron resonance (MDECR) plasma source is investigated using directional jet injection of undiluted silane. The influence of process parameters such as the microwave power, radio frequency biasing of the substrate holder, and gas flows on the OH content of the oxide films is studied using phase-modulated spectroscopic ellipsometry (SE), Fourier transform infrared (FTIR) spectroscopy, and transmission measurements. The results of the measurements, taken at various points across the wafer, show a d...

Capillary jet injection of SiH4 in the high density plasma chemical vapor deposition of SiO2

In this article, the authors compare the thickness profiles and OH content of SiO2 films deposited using capillary jet injection of silane in a high density plasma chemical vapor deposition (HDP CVD) system with the results of phenomenological modeling using direct simulation Monte Carlo (DSMC) gas flow calculations. A tube with an internal diameter of 1mm is located vertically at 3cm in front of the substrate surface and is used for the injection of the silane. The deposition plasma is characterized using optical emission spectroscopy (OES) and differentially pumped quadrupole mass spectrometry (QMS). Studying the thickness-normalized OH absorption in the deposited film at various points on the substrate, the authors gain insight into the contribution of the water flux to the OH content in the deposited SiO2 film. Gas flow simulations using the DSMC technique are used to study the fluxes of the species onto the substrate plane. From the results the authors conclude that (i) the flux of the H2O onto the s...

Correlation of sidelobe suppression between rugate filters and multilayer mirrors

We present the study of the correlation between refractive index profiles and the optical response of rugate filters and multilayer mirrors. The conventionally used method in multilayer mirrors for ripple suppression in the passband will be compared with a similar simple method to remove the rugate filter sidelobes without apodization. The resulting layers are compared in performance with a typical quintic matching layer. An example based on silicon oxynitride alloys with refractive indices ranging between 1.47 and 1.83 was designed and deposited.

Influence of substrate cleaning on the laser resistance of antireflective coatings

Several studies have reported on the detrimental effects of inadequate cleaning on the performance of optical components exposed to laser radiation. The remaining particulates, contaminants or residue located in the coating or on the substrate surface can absorb laser energy and consequently induce damage. To minimize these contaminants, investigations of various cleaning processes have been performed in both the research and industry communities. Transparent published results and comparisons of the different cleaning processes considered, however, are limited due to proprietary considerations. In addition to this, the manufacturing environment, deposition processes, substrate- and deposition materials all have an influence on the effectiveness of a cleaning process. The purpose of this study was to investigate different cleaning procedures and their influence on the laser resistance of ion-beam sputtered antireflective coatings. For this purpose, a SiO2 / Ta2O5 multilayer antireflective coating for a normal angle of incidence at 1064 nm was deposited onto fused silica substrates. Prior to deposition, the substrates were cleaned with a variety of cleaning solutions and procedures and their roughness and surface quality inspected. All samples were characterized in terms of their laser damage threshold using a 1064 nm ns-pulsed test bench and subsequently visually inspected in order to understand the cause of the damage. In this work, the details of the cleaning steps and the corresponding laser damage performance for the different cleaning processes are presented and compared.

Influence of temperature and environment on the laser damage threshold of ion-beam sputtered anti-reflective coatings at 355 nm wavelength

In this investigation the influence of the local environment on the laser damage threshold of anti-reflective coatings is reported. For this purpose, HfO2 / SiO2 anti-reflective coatings were deposited on fused silica substrates using an ionbeam sputter system. Laser damage threshold measurements were performed using two test procedures, S-on-1 and Ron- 1, at 355 nm for temperatures ranging from room temperature up to 250 °C and in different atmospheres. The two test procedures had comparable LIDT results with a possible pre-conditioning effect evidenced by a broadening of the transition range of the R-on-1 measured samples. It was found that samples measured in normal atmospheric air showed superior laser resistance compared to samples measured under nitrogen purge or in dry air. Samples measured in normal atmospheric air also showed a temperature dependence with an improved laser resistance at 25 °C. No temperature dependence was observed for samples measured under nitrogen purge or in dry air. In this paper, literature showing similar effects is reviewed and the influence of a water epilayer on the coating as a possible cause for the observed results is discussed.

Investigation of the ageing effects exhibited by AR coatings exposed to ultraviolet laser irradiation

Optical coatings used in ultraviolet applications are often exposed to harsh environments operating at elevated temperatures. In order to study the impact of the ageing effects optical coatings experience at various operating temperatures, an ultraviolet laser-induced degradation test system has been developed. It allows for flexible use in both a long-term stability test bench as well as in an LIDT measurement system. This work contains the preliminary results of optical degradation tests at 355 nm performed on anti-reflective coatings. As a subsequent step, the LIDT of the samples were measured using a Q-Switched Nd:YAG laser operating at 1064nm.

Comparative study of the laser damage threshold and optical characteristics of Ta2O5 - SiO2 multilayers deposited using various methods

Manufacturing processes from the private and academic sectors were used to deposit anti-reflective and high-reflective coatings composed of Ta2O5 - SiO2 multilayers. Used deposition techniques included three Ion Assisted Deposition (IAD) systems and an Ion Beam Sputtering (IBS) system. Coatings were performed on fused silica (Corning 7980) substrates polished by two different suppliers. LIDT Measurements were performed using a Q-Switched Nd:YAG laser operating at 1064nm. The paper presents a comparison of the coatings in terms of laser damage threshold values, optical properties and surface quality.