In the automatic macro inspection, a diffraction light method is very effective. However, this method needs a shorter wavelength illumination for finer wafer patterns. A wavelength of 193 nm will be needed for half pitch 55 nm. Light source and optics for such shorter wavelength is large and expensive, and chemical clean environment is needed. Therefore, the equipment size and costs will increase dramatically. In order to solve this problem and to comply with the process of half pitch 55 nm and below, we have developed the breakthrough technology. The key is the image of polarization fluctuation caused by a wafer pattern structure. The polarized light is affected by the variation of the wafer pattern structure due to a dose or focus shift. The new technology converts the polarization fluctuation into the gray level of the image. At a result, the sensitivity for the dose or focus shift was enough to detect process errors.
Macro defect inspection in the photolithography process has been operated by the operator's naked eye. Operator's inspection performance is not constant and depends on his skill, even if these macro defects are determined as the large scale defect. This paper reports our fully automated macro inspection system and its performance data that were evaluated in the production Fab. Our new system, Nikon AMI-2000, is designed to use the diffraction light imaging which is very effective to detect defocus defects and is designed to use an image processing method. This system has much higher sensitivity than operator inspection, the capability of constant yield management and has a high throughput performance.
Macroscopic defects on a wafer are caused by contamination, inhomogeneous resist-thickness, scratches etc. Many of these effects can be observed directly by human eyes rather than through a microscope. In many lithographic processes visual inspection by human operator is performed on all wafers after the developing process. It is called a 'macro inspection'. However a macro inspection takes skill of detecting defects, because defects can be found under some conditions. We have been developing a new inspection system to replace operator-inspection with instrument-inspection for consistency in results. This system is constructed by a defect detecting technology and an image processing technology.
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