A New Step-By-Step Aligner For Very Large Scale Integration (VLSI) Production
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Abstract
Technological considerations of direct wafer stepping are examined and the requirements of high volume V.L.S.I. production are identified. An advanced step-and-repeat alignment system is presented which fulfills, to a high degree, the criteria developed. Its high numerical aperture 10:1 reduction lens provides high resolution at high contrast level. A new designed illumination system supplies high exposure intensity at excellent uniformity. An automatic step-by-step alignment, focusing and leveling system compensates for irregular wafer topography and its changes during processing. By the capability to follow images already present on the wafer, it allows cross-matching with other exposure systems used for less critical manufacturing steps. The through-the-lens system of feedback-controlled alignment and true focus recognition eliminates from the machine geometric and optical changes such as those caused by temperature variation. Means for protecting both reticle and wafer against such environmental influences as dust, temperature and vibrations are provided. Equipment design permits high throughput for a large variety of die formats. High productivity is achieved by microprocessor-controlled functions and automatic handling as well as specially developed high speed displacement devices. The instrument presented promises new levels of productivity and working line widths while drawing on current knowledge in resist technology and wafer processing.