To reduce the yield loss due to via failures, double vias(hence the term “redundant”) are inserted. The idea is that the chance of contact failure is reduced since there are multiple contacts for the same electrical connection. This does require more routing resources, and standard cell pins must be layed out so as to be able to connect two vias. Traditionally double vias were inserted postroute, and then modified the routing to fix any DRCs. However, nowadys most of the have to option to insert double vias at the initial detail route stage itself. The via redundancy may not be 100% for all the metal layers.