Image Sensor Extension Pads with Polysilicon Pillars for ILD Uniformity

The patent applies local quality by forming dummy polysilicon structures specifically on the extension pads rather than uniformly across the entire substrate. This localized approach modifies the polishing characteristics only where needed (on the large extension pads) to achieve uniform ILD layer thickness, while leaving other areas unchanged. The dummy structures create local variations in polishing speed that compensate for the nonuniformity caused by large extension pad areas.

The patent converts the harmful effect of large extension pad areas (which cause nonuniform polishing and connection failures) into a beneficial effect. By intentionally adding dummy polysilicon structures on the extension pads, the patent creates controlled local variations that actually improve polishing uniformity. The large extension pad area, which was previously a source of problems, becomes a region where the dummy structures successfully compensate for polishing nonuniformity, thereby improving device reliability.

The patent applies preliminary action by forming the dummy polysilicon structures on the extension pads before depositing the ILD layer and performing CMP. This preliminary modification of the extension pad surface ensures that when the ILD layer is subsequently deposited and polished, the underlying dummy structures already exist to control the polishing rate and achieve uniform thickness. This preliminary action prevents bonding failures by ensuring uniform ILD layer formation prior to subsequent processing steps.