Abstract: Magnification correction for small field scanning of large blanks is provided by adding magnification adjusting elements (lenses) to a double pass Wynne-Dyson lens or other type of one-to-one projection lens. The magnification adjusting optical elements includes two pairs of low power lenses, one associated with each of the input and output prisms of a Wynne-Dyson lens. Movement of the magnification adjusting optics provides positive or negative magnification as needed to correct for any expansion or compaction of the blank relative to the reticle (mask) and hence maintain alignment. Further magnification correction is provided by a small velocity relative movement between the reticle and the blank by means of a secondary stage in the scan direction. This corrects for any alignment error in the scan direction and may be used independently of the optical correction technique with any type of projection lens.

Abstract: A laminar flow diffuser has a plurality of round, thin, stacked plates. A central bore penetrates all the plates with the exception of the bottom plate. The diffuser is secured to the vacuum chamber port. When gas enters the port, it enters the central bore and then flows radially outward through the interplate spaces to the outer circumference of the plates and subsequently into the periphery of the chamber. The diffuser thereby provides a controlled laminar flow which prevents turbulence in the chamber and hence, reduces the possibility of contamination to the workpiece in the chamber. The laminar flow diffuser is easily cleaned, both during its initial assembly and later after use, because it chiefly has flat surfaces which do not harbor dirt or gas.