Method for making a semiconductor device by variable chemical mechanical polish downforce

Abstract

A semiconductor substrate has features extending above the surface. In one use, these features are gate stacks in which the gate is polysilicon to be replaced by metal. A dielectric is deposited over the substrate and the gate stacks having contours corresponding to the features. The desired structure prior to replacing the polysilicon gates is for the dielectric to be planar and even with the top of the gate stack. This is difficult to achieve with conventional CMP procedures because of varying polish rates based on the area and density of these features. The desired planarity is achieved by first depositing a conformal sacrificial layer. A CMP step using light downforce results in exposing and planarizing the underlying contours of the dielectric layer. A subsequent CMP step using higher downforce achieves the desired planar structure by providing a greater polish rate for the dielectric layer than for the sacrificial layer.