Device Photolithography: Computer Systems for Pattern Generator Control

Computers are indispensable today in the operation of any sizable mask-making laboratory. Nearly all precision pattern generators are either directly computer controlled or else require input of a form which can be reasonably obtained only through the use of computers. Furthermore, the complexity and sheer volume of masks currently required effectively prohibit nonautomated procedures. The mask-making laboratory system described in this issue relies heavily on the use of computers. The first part of this paper describes a system of programs which links a circuit designer to the maskfabrication processes; the next two sections discuss algorithms and programs for generating input to the primary pattern generator (PPG) and the electron beam machine (EBM). 1.1 Computer-Aided Generation of IC Masks Masks are tools required in the fabrication of integrated circuits and other devices. The starting point in mask design is thus an electrical schematic or logic diagram of the desired device. An engineer or technician first allocates scaled geometric shapes to each of the circuit components; he then arranges and rearranges these shapes 20U