Semiconductor wafer for improved chemical-mechanical polishing over large area features

In chemical-mechanical polishing of semiconductor wafers, a method of polishing an upper layer of material from a wafer having a separation layer under the upper layer and a large area feature beneath in a cavity in the separation layer, the method comprising the steps of:

• forming a pillar in the cavity, the pillar extending approximately to a top surface of the separation layer;
• depositing the upper layer of material over the separation layer and the large area feature;
• mounting the wafer to a wafer carrier of a chemical-mechanical polishing machine;
• pressing the wafer against a polishing pad of the chemical-mechanical polishing machine in the presence of a slurry, the polishing pad engaging the upper layer on top of the separation layer and the pillar;
• and
• moving at least one of the wafer carrier or the polishing pad to impart relative motion between the wafer and the polishing pad, wherein the pillar supports the polishing pad over the cavity in the separation layer to substantially prevent the polishing pad from penetrating into the cavity.