Nanotopography Issues in Shallow Trench Isolation CMP

As advancing technologies increase the demand for planarity in integrated circuits, nanotopography has emerged as an important concern in shallow trench isolation (STI) on wafers polished by means of chemical-mechanical planarization (CMP). Previous work has shown that nanotopography-small surface-height variations of 10-100 nm in amplitude extending across millimeter-scale lateral distances on virgin wafers-can result in CMP-induced localized thinning of surface films such as the oxides or nitrides used in STI. A contact-wear CMP model can be employed to produce maps of regions on a given starting wafer that are prone to particular STI failures, such as the lack of complete clearing of the oxide in low spots and excessive erosion of nitride layers in high spots on the wafer. Stiffer CMP pads result in increased nitride thinning. A chip-scale pattern-dependent CMP simulation shows that substantial additional dishing and erosion occur because of the overpolishing time required due to nanotopography. Projections indicate that nanotopography height specifications will likely need to decrease in order to scale with smaller feature sizes in future IC technologies.