Resolution and Overlay Precision of a 10 to 1 Step-and-Repeat Projection Printer for VLSI Circuit Fabrication

The continuing increases in packing density and complexity of micro-circuit require very fine control and reduction in pattern geometries on the micro-ithography. Electron-beam, X-ray and ion-beam lithography have been actively investigated to realize VLSI circuit fabrication for the past decade. However, these technologies have many inherent problems to be solved before extensively applied for wafer fabrication. Therefore, volume production of the VLSI should be considered by the improvement of optical lithography, until such problems are successfully solved. In the optical lithography, stepand- repeat projection printing is the most powerful method, since high resolution and overlay precision are obtainable by using high numerical aperture (NA) lens and aligning for each step. Standing on the points of view, the authors have studied the step-and-repeat projection printer (direct stepper) in cooperation with Nippon Kogaku K.K. and VLSI Technology Research Association Cooperative Laboratories. The purposes of this paper are to present a general description and evaluation results of the direct stepper. In addition, future trends in direct stepping will be discussed.