Nanotopography effects on chemical mechanical polishing for shallow trench isolation

Abstract

Nanotopography is the nanometer-scale height variation that occurs over lateral millimeter length scales on unpatterned silicon wafers. This height variation can result in excess thinning of surface films during chemical mechanical polishing (CMP) of shallow trench isolation (STI) structures. The development of an accurate nanotopography CMP modeling and characterization procedure will allow for the proper diagnosis of potential problems due to wafer nanotopography in a given STI CMP process. In this work, a nanotopography modeling methodology is proposed which relates the length scale of nanotopography features to the length scale of the CMP process. A combined density/step-height polishing model indicates that when the nanotopography features occur over a range comparable to or shorter than the planarization length, appreciable thinning is predicted. A contact wear CMP model similarly shows that as the pad stiffness increases, film thinning also increases. These simulation results indicate that the effect of nanotopography on STI CMP may be a substantial concern.