Papers

AVS1996 Session TF-TuA: Industrial-Scale Deposition: Focus on Optical Coatings

Tuesday, October 15, 1996 2:00 PM in Room 107B

Tuesday Afternoon

Start	Invited?	Item
2:00 PM		TF-TuA-1 Industrial Scale Coatings on Glass by In-line dc-Magnetron Sputtering C. Carniglia (BOC Coating Technology) In-line dc-magnetron sputtering is a process that is suited to large scale industrial applications. The use of a load-lock system provides a high throughput of glass while the process section of the system remains under vacuum and runs continuously in a stable fashion. This paper addresses several of the issues of scaling to large area and high volume. A large system must have high speed pumping. A multiposition poppet valve can provide high throughput pumping during pumpdown and reduced pumping while the sputtering process is running. Products for the display market, such as CRTs and FPDs, should be coated in a sputter-up or sputter-sideways configuration. Large sheets of glass for architectural and low-emissivity applications are usually coated in a sputter down arrangement. Typical sputtered coating designs have two or three layers, but designs with as many as seven layers are practical. Gas mixtures are important for controlling the optical properties and coating rates of a wide variety of dielectric, metal and semiconductor materials used in sputter applications. Controlling uniformity across a 3- meter wide substrate is accomplished by adjusting gas flow, magnet strength and anode position. The use of sequencing anodes has provided uniformity within 4% over a 2-meter span. A cylindrical target provides a high level of material utilization. With properly designed magnets, more than 80% of the target material can be utilized. In line and exit optical monitor systems provide important information to enable the operator to control the coating performance. Such systems must be insensitive to focus and tilt of the glass being coated.
2:40 PM		TF-TuA-3 Dual-Frequency Plasma Deposition of Antireflective Coatings on Plastics D. Poitras, J. Klemberg-Sapieha, L. Martinu (Ecole Polytechnique, Canada); N. Yamasaki (Optical Coating Laboratory, Inc.); C. Lantman (Flex Products, Inc.) Optical coatings are used in increasingly demanding applications which require precise optical characteristics, resistance to damage and good adhesion to different types of substrate materials, including polymers. In the present work we investigate optical coatings fabricated by low pressure plasma-enhanced chemical vapor deposition (PECVD), using a dual-mode microwave/radiofrequency (MW/RF) plasma approach. The substrates are exposed to the principal, dense microwave (MW - 2.45 GHz) plasma, while applying an RF-induced negative bias voltage. This technique provides an independent control of the energy and flux of bombarding ions, and it allows one to deposit dense films at ambient substrate temperature and a high rate over large areas.In the first series of experiments we optimized the deposition process for amorphous hydrogenated silicon nitride (SiN) and dioxide (SiO\sub 2\), obtained from silane/NH\sub 3\ or silane/N\sub 2\O mixtures, respectively. Using an average ion energy of about 150 eV, we obtained low-stress (< 100 MPa) films with a refractive index of 1.85 (SiN) and 1.45 (SiO\sub 2\), at deposition rates of several nm/s.Based on the above experiments, we deposit antireflective coatings on polycarbonate, using a four-layer stack design. In the visible, the original reflectance of about 6 % was decreased to less than 1 %. Using spectrophotometry, ellipsometry, X-ray photoelectron spectroscopy, and microscratch testing, we evaluated the effect of film microstructure and interfaces on the optical and mechanical characteristics of the coatings. The results indicate that the MW/RF PECVD approach holds much promise as an emerging industrial process for the fabrication of optical films.
3:00 PM		TF-TuA-4 High Throughput Manufacturing Processes for Optical Coatings in the Display Industry B. Hichwa (Optical Coating Laboratory, Inc.) Optical coatings for display products usually involve Anti-Reflection (AR) coatings on curved CRT displays. This market has segmented into high performance AR coatings sputtered directly onto the workstations and lower performance, spin, spray or dip coatings for less expensive displays. An intermediate performance AR on PET is optically bonded to spherical CRT displays. We will discuss the technical requirements for such coatings and possible manufacturing strategies. In this context we introduce the concept of "Nameplate Capacity", the highest possible throughput of a coating machine on a 24 hour, 7 day a week basis. This includes all maintenance and clean-up procedures. In-line coaters, in statistical process control, operate from 40 to 80% of "Nameplate", while batch coaters range from 70 to 95%. We will discuss how this operating viewpoint has led to much improved and reliable deposition processes. With the advent of large format projection LCD displays, an additional family of optical coatings are required. Highly transmissive dichroic color filters are replacing the traditional gel filters. These dielectric interference filters, typically 10 to 30 layers of alternating layers of high and low index of refraction materials, must transmit >95% and be optically flat. The key technical challenges are the reduction of optical scatter and absorption, while maintaining high deposition rates. Thin film processes to produce such low defect coatings are energetic in nature, typically either ion assisted evaporation or enhanced sputtering. The coatings must be nano-engineered to minimize the interfacial roughness and control scatter. In addition, the coating stress must be simultaneously controlled and balanced to meet the system flatness requirements. We will discuss the OCLI MetaMode( sputtering process as applied to this application and the associated performance data for the dichroic color filters.
3:40 PM		TF-TuA-6 Industrial Scale Deposition of Optical Coatings P. Denton, F. Zimone, N. Arfsten (Denton Vacuum, Inc.) Issues relating to industrial scale optical coatings are presented. Scale-up factors related to the traditional vacuum deposition techniques such as evaporation and sputtering are reviewed with particular attention paid to the total cost of manufacturing. In addition, the impact of capital costs and prior yield assumptions on project success are considered. As an alternative to large area vacuum deposition, "sol-gel" coatings from solution are discussed in detail. Advantages and disadvantages of large area deposition using atmosphere techniques such as sol-gel chemistry are compared to vacuum technology. Relative capital costs, yield expectation, and running costs of various techniques are compared. Finally a review of high volume smaller area coatings used in the optical memory (compact disc) industry and ophthalmic (eyeglass lens) anti-reflection industry are presented. Market issues that drive product cost and quality are reviewed.
4:20 PM		TF-TuA-8 Controlled Surface Figuring of an Optical Surface to Nanometer Tolerances using a Variable Thickness Coating R. Netterfield, D. Drage, C. Freund, J. Seckold (CSIRO Division of Applied Physics, Australia) Fabry Perot filters are used as the narrow band selecting element in high-resolution remote sensing and imaging astronomical spectrometers. The trend has been to solid etalons and away from air-spaced interferometers which often require complex electronics to control parallelism and spacing of the flat plates. Etalons manufactured from electrooptic material such as lithium niobate (LiNbO3) are scanned electrically. Typically the solid etalon has a thickness in the range 0.2-0.5 mm and a useable diameter of 65 mm. The optical thickness of the etalon must be uniform over the whole working aperture to within nanometres. In this presentation we report on the role that coatings have played in the manufacture of etalons. During the preparation of the substrate, departures from optical thickness uniformity over the aperture have been reduced from several nanometres to about 1 nm (average) by depositing layers with the same refractive index as the substrate to selected parts of the surface. Masks fixed to the etalon surface and stationary masks above which the etalon rotates have been used. Single wavelength and broad band high reflectance coatings have been applied to the surfaces of the etalons. Ion assisted deposition has been used to prepare hard, dense dielectric oxides layers as well as the conducting transparent ITO. No substrate heating has therefore been required. The average roughness of the coated surface is similar to that of the polished substrate (about 0.3 nm rms). Measured finesses over 65 mm diameter apertures of 37 at 633 nm have been achieved.
4:40 PM		TF-TuA-9 Laser Light Scattering Studies of Particulate Contamination in Magnetic Disk Sputtering G. Selwyn (Los Alamos National Laboratory); F. Sequeda (Seagate Corp.) Physical vapor deposition is extensively used for production of magnetic storage disks. Particle contamination is an increasing concern in this field, because of the higher storage densities being employed and the smaller "fly" high of heads. Laser light scattering (LLS) has been used in a production-type sputtering tool, the results of which demonstrate that the mechanism for particle generation, transport and trapping during magnetron sputtering are very different from the more studied cases of wafer particle contamination in plasma etch processes. In magnetron sputtering, particle contamination problems may be linked to portions of the sputtering target exposed to weaker plasma density in which redeposition followed by filament growth and enhanced trapping, leads to faster filament growth. Eventually these filaments effectively "short-circuit" the sheath, causing ion current to flow through these thread-like target features. This, in-turn, causes heating failure of the filament and violent ejection of the filament into the plasma, and onto the substrate. A short video will be used to demonstrate this failure mechanism, and the confirmation of this effect by direct, laser light scattering of the disks during processing.