Modelling the influence of pad bending on the planarization performance during CMP

Abstract

One of the major problems with oxide-CMP is the oxide thickness variation after CMP within one die, the socalled Within Die Non-Uniformity (WIDNU). The variations in pattern density of the design layout causes different local removal rates across the die resulting in the WIDNU. In this paper we shown that this is influenced by the pad stack. Depending on the thickness of the top pad the WIDNU can be reduced from about 470 nm until almost zero. This will be related to the bending of the top pad. The modelling will focuss on the two extreme cases of perfect pad bending and no pad bending.