A PH-CONTROLLED CHEMICAL-MECHANICAL POLISHING METHOD FOR THIN BONDED SILICON-ON-INSULATOR WAFERS

A pH-controlled chemical mechanical polishing (CMP) method for fabrica ting largearea ultrathin silicon-on-insulator (SOI) layers with unifor m thickness was developed. Using a polishing reagent with the pH and c olloidal silica concentration lowered, together with grooves fabricate d on the SOI layer to expose the insulating oxide, the polishing rate clearly decreased leaving a uniform 0.1-mu m-thick SOI layer. An SOI l ayer with superior thickness uniformity (+/-0.01 mu m) across 5-by-5-m m SOI-Si islands was obtained. The thickness uniformity across the waf ers was decreased to +/-0.07 mu m. In this technique, the end point fo r polishing was controlled to form thin SOI layers with uniform thickn ess.