Calculation of the resistance value of laser-trimmable planar resistors in an interactive mask-layout design system

Abstract

The calculation method is especially suited for diffused resistors in integration processes and metal-film resistors in thin-film processes which can be adjusted by laser trimming. The method is based on a special application of Green's boundary formula. By modeling the resistor in a special way, the potential problem is reduced to a single-boundary problem. As a consequence, the calculation time and the necessary computer memory are reduced while the accuracy reduction remains small in practical cases. Therefore, the calculation can be carried out on a small computer, making interactive computer design of laser-trimmable resistors on IC layouts more feasible and less expensive. The computing time typically amounts to a few seconds. The method is illustrated by practical examples.