Carafe calculates the relative likeliness of a GOS fault by taking the area of a transistor's active region and dividing it up by the number of diffusion regions, i.e. source and drain. Figure 4.15 shows how the critical area for a GOS fault is calculated. Both faults 1 and 2 are calculated by taking the area of the transistor (A) and dividing it by the number of diffusion regions (2). To weigh the relative occurrence of GOS faults, use the polysilicon to ndiffusion or polysilicon to pdiffusion defect densities in the fabrication file.
Figure 4.15: Calculation of Critical Area for GOS faults