Device Photolithography: A Computer Controlled Coordinate Measuring Machine

In the design of the mask-making laboratory, the need for a precise positional-measurement system was recognized. This system is needed for alignment and adjustment of the primary pattern generator (PPG), the reduction cameras and the step-and-repeat camera. It is also needed for mask inspection. The measurement system should be at least ten times more precise than the tolerance on the masks being measured, and it should be capable of measuring a large number of points in a reasonable time. For example, the test pattern to align the P P G is an array of 208 points, and this should require no more than two hours to measure. Table I summarizes the requirements on the measurement system. l.i System Description A Do-all Coordinate Measurement Machine (CMM) controlled by a P D P - 8 computer forms the basis for the measurement system to meet these needs. This is shown schematically in Fig. 1. The Do-all machine consists of two air-bearing slides at 90° on black granite ways. The plate to be measured is mounted on one slide (x-axis) and 2193