COMPUTER-CONTROLLED INPLANE ALIGNMENT USING A MODIFIED MOIRE TECHNIQUE

An automatic, accurate mask alignment method, based on a modified moir e technique suitable for x-ray lithography is presented. In this techn ique, the alignment marks are in the form of gratings. The high slope region of the moire signal is used to obtain higher sensitivity and be tter position control accuracy. Automatic alignment is achieved by usi ng the difference of the moire signal and its inverted signal obtained by computer. This difference signal is zero at a point in the higher slope region that is considered the correct alignment point. This diff erence signal is treated as an error signal, which is used for obtaini ng control signal by performing the proportional, integration and diff erential (PID) algorithm. The 12-bit analog-to-digital (A/D) and digit al-to-analog (D/A) convertors are used to interface the piezoelectric- transducer-(PZT)-driven alignment system with the computer. Under the present experimental conditions, accuracy for alignment is of the orde r of +/-0.06 mum.