On-line surface inspection of roll-to-roll film processing

纳米级和超精密结构表面的应用日益广泛，应用范围广泛，涵盖了光伏薄膜、光学、硅片、硬盘、MEMS/NEMS、微流体和微型模塑等行业。这些行业都严重依赖超精密表面。然而，这种表面的制造有一个基本的限制因素，即在制造环境中快速测量产品的能力。据报道，目前制造的质量在很大程度上取决于工艺工程师的经验，并辅之以昂贵的试错法。因此，许多这些制成品的废品率高达50%-70%。在制造大批量大面积铝箔产品的行业，如纸张和包装产品，以及新兴市场行业，如柔性电子产品，制造过程往往涉及到在大面积基板和箔上沉积和图案化多层薄膜。对于这些类型的产品，产品性能和功能的提高可以通过增加层的数量，或者从微米级到纳米级的单个层的厚度或图案特征的大小来实现。为了在涂层和图案化过程中实现高成品率，薄膜必须均匀且基本上完美地覆盖在箔的大部分区域上。然而，随着多层膜中界面数量的增加，形成缺陷的风险增加，并且这些缺陷的大小和性质随着层厚度缩小到纳米级而改变。涂层缺陷可能由铝箔上的表面异常(例如划痕和表面尖峰或孔洞)、周围颗粒或仅有几个原子厚的化学污渍的污染以及不正确的工艺条件(例如颗粒生成或反应副产物堆积)引起。图案缺陷是由于不正确的图案转移引起的，例如划痕或模压缺陷。为了确保高成品率，关键的挑战是以足够的分辨率以生产速度检查箔表面，以检测i)起始箔表面是否存在问题缺陷以及ii)在涂布和构图过程中出现的缺陷。由于这些工艺的性质，检测方法必须与薄膜表面不接触。有效的检测是进一步处理的关键，例如应用局部修复技术来消除薄膜表面的缺陷。目前还没有一种有效的检测方法可以应用于上述应用。本项目试图通过研究一种基于白光光谱干涉测量和基于通用图形处理单元(GPGPU)的并行信号处理的高速在线表面轮廓光学测量技术来解决我们目前所采用的表面检测技术的缺点。这些技术结合在一起，有可能应用于高精度表面的实时在线测量，如生产线上的卷膜加工、光刻刻蚀加工、掺杂、CVD/PVD涂层、研磨和化学机械抛光加工。该系统是大规模生产高质量、高效率的光伏薄膜和其他卷对卷薄膜生产的关键。该产品的成功将帮助我们更高效、更具成本效益地将太阳能转换为电能。

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.