ICMCTF2000 Session C2: Recent Advances in Optical and Polymer Film Technology

Plasma assisted deposition methods have been widely used so far to synthesize varieties of thin. However, charged particles such as electrons and ions, which are inevitably included in plasma, hit surfaces of thin films while the films are being deposited and deteriorate the characteristics of films. High density radical beam sources have attracted attention because it can avoid these problems mentioned above and afford a new deposition method to deposit high quality thin films at relatively low substrate temperatures.

We have been developing radical beam sources with beam diameters larger than 100mm intending to enhance the productivity of thin films. In this study, an end plate with small orifices was set at the end of a quartz discharge tube to maintain the gas pressure inside the discharge tube high while keeping the pressure inside a deposition chamber low. It has been widely known that dominant species of inductive coupling plasma change from ionic species to radical species when the pressure of the plasma gas in a discharge tube is changed from ca.0.1 Pa to 1-100 Pa. Oxygen plasma was generated inductively by a RF (13.56 MHz) power supply. The appropriate conditions to generate high intensity radical beams were surveyed systematically by changing the diameter and number of turns of the coil, the strength of magnetic field supplied to the discharge tube, shapes of the tube and so on. In particular, when the shape of the discharge tube was changed from a tubular shape to a flat shape the intensity of the radical beam was doubled. Furthermore, the ratio between the intensity of radical species and that of charged species from the radical beam source could be controlled by changing the shapes of the end plate.

We will report the detailed experimental results of the high performance radical beam sources.

In recent years the improvement of energy efficiency has become an urgent issue in the industrial countries. Reflector materials with enhanced reflectivity open up the possibility of increasing the lighting efficiency in order to economize the illumination energy.

Meanwhile large area coating of aluminum strips by EB-PVD in order to achieve enhanced optical reflectivity of up to 96 % has been established by industry for the purpose of reflector mass production. The reflection increasing layer system consisting of the 3 layers aluminum, silicon dioxide and titanium dioxide is coated on aluminum strips which are up to 1250 mm wide. The latest production start of such a new air-to-air coating line allowing strip speeds of at least 20 m/min has occured some months ago.

The process management of the individual EB-PVD process steps and the ellipsometrical online layer measurement at the moved strip will be presented. The highly productive air-to-air coating line for long time deposition cycles of up to 120 production hours without interruption will be introduced. Finally the paper will analyze coating results on anodized as well as lacquered strips and discuss tendencies of product development.

The pulsed reactive sputtering process, in conjunction with reactive gas feedback control systems, now allows the routine deposition of high quality dielectric films. Pulsing the magneton discharge in the mid-frequency range (20-350kHz) prevents arc events at the target and stabilises the deposition process. Feedback control of the reactive gas, using an optical emissions monitor for example, establishes constant conditions at the target, allowing control to be maintained at any point on the hysteresis curve. In many cases, however, it has been found that the optimum properties for films, such as alumina, are obtained when the target is operated in at least a partially poisoned mode. This has a detrimental impact on the deposition rate of the film and can lead to long-term stability problems during deposition. An alternative approach, aimed at overcoming these problems, is to introduce pre-activated oxygen into the chamber via an independent plasma source.

In this study, an inductively coupled plasma (ICP) source has been used to generate activated oxygen for introduction into an otherwise standard closed field unbalanced magnetron sputtering system. A number of alternative mounting arrangements for the ICP unit have been considered. The total flow of reactive gas into the chamber is divided between a piezo valve, which forms part of the feedback control loop, and the ICP. Operating in this manner allows transparent, stoichiometric alumina films to be deposited whilst maintaining the target in a metallic mode. This paper, therefore, compares the ICP enhanced process with the standard deposition process, both in terms of operating parameters and film properties.