A method of forming an integrated circuit structure on a chip includes extracting an active layer from a design of the integrated circuit structure, forming a guard band conforming to the shape of the active layer, the guard band surrounds the active layer, and the guard band is spaced from the active layer at a first spacing in the X-axis direction and at a second spacing in the Y-axis direction, removing any part of the guard band that violates design rules, removing convex corners of the guard band, and adding dummy diffusion patterns into the remaining space of the chip outside the guard band. The first and second spacing can be specified as the same spacings in a Spice model characterization of the integrated circuit structure. The dummy diffusion patterns with different granularities can be added so that the diffusion density is substantially uniform over the chip.