The rapidly increasing use of nano scale and ultra-precision structured surfaces is widely spread in many applications ranges and covers photovoltaic thin film, optics, Si wafers, hard disks, MEMS/NEMS, micro fluidics and the micro moulding industries. These industries all critically rely on ultra precision surfaces. There is however a fundamental limiting factor to the manufacture of such surfaces, namely the ability to measure the product rapidly in the manufacturing environment. It has been reported that currently the quality of fabrication depends largely on the experience of process engineers backed up by an expensive trial-and-error approach. Consequently many of these manufactured items suffer from high scrap rates as high as 50-70%.
In the industries those making high volume large area foil products such as paper and packaging products and emerging market sectors such as flexible electronics, the manufacturing processes often involve the deposition and patterning of multi-layer thin films on large area substrates and foils. For these types of product, increased product performance and functionality can come from an increase in the number of layers, or a decrease from micro- to nano-scale in the thickness of individual layers or size of pattern features. To achieve high yield in the coating and patterning processes the films must be uniform and largely perfect over most of the area of the foil. However there is an increased risk of defects forming as the number of interfaces increases in the multi-layer films, and the size and nature of those defects changes as the layer thicknesses shrink to the nano-scale.
Coating defects can be caused by surface anomalies on the foil (e.g. scratches and surface spikes or holes), by contamination in the form of ambient particles or chemical stains only a few atoms thick, and by incorrect process conditions (e.g. particle generation or build-up of reaction by-products). Patterning defects arise from incorrect pattern transfer, e.g. scribing or moulding faults. In order to ensure high product yield the key challenge is to inspect the foil surface at production speed with sufficient resolution to detect i) the presence of problem defects on the starting foil surface and ii) defects as they appear during the coating and patterning processes. Due to the nature of these processes the inspection methods have to be in noncontact with the film surfaces. Effective inspection is the key for further process such as applying local repair techniques to remove the defects from the film surface.
Currently there is no effective inspection methods that can be applied for the above applications. This project attempts to address shortcomings of the techniques that we currently employed for surfae inspections by investigating a high speed on-line surface profile optical measurement technique based on white light spectral interferometry and parallel signal processing using general purpose graphic processing unit (GPGPU). These techniques combined have the potential to be applied to real-time on-line measurement of high precision surfaces such as those resulting from roll-to-roll film processing, lithographic etching processing, doping, CVD/PVD coatings, lapping, and CMP processing on the production line.
The proposed system is a key for mass production of high quality, high efficiency photovoltaic thin film and other roll-to-roll film productions. The success of this product will help us to convert solar power to electricity more efficiently and cost effectively.