Pin Accessibility-driven Placement Optimization with Accurate and Comprehensive Prediction Model

The significantly increased density of pins of standard cells and the reduced number of routing tracks at sub-10nm nodes have made the pin access problem in detailed routing very difficult. To alleviate this pin accessibility problem in detailed routing, recent works have proposed to make a small perturbation of cell shifting, cell flipping, and adjacent cells swapping in the detailed placement stage. Here, an essential element for the success of pin accessibility aware detailed placement is the installed cost function, which should be sufficiently accurate in predicting the degree of routing difficulty in accessing pins. In this work, we propose a new model of cost function that is comprehensively devised to overcome the limitations of the prior ones. Precisely, unlike the conventional cost functions, our proposed cost function model is based on the empirical routing data in order to fully reflect the potential outcomes of detailed routing. Through experiments with benchmark circuits, it is shown that using our proposed cost function in detailed placement is able to reduce the routing errors by 44% on average while using the existing cost functions reduce the routing errors on average by at most 15%.