Effect of silicon dioxide surface-layer thickness on boron profiles for directly aligned implants into (100) silicon

We report boron profiles as determined by secondary ion mass spectrometry that result from implantation into (100) silicon at (0.0±0.1) degrees through various thicknesses of thermally grown silicon dioxide. The implants were performed at room temperature at 150 keV to a fluence of 4.0×1013/cm2. The oxide surface layers examined were 7.6, 33.6, 101.5, or 140.0 nm thick as determined by ellipsometry. The boron profile for implantation through the 7.6-nm oxide surface layer was only slightly degraded from that seen for accurately aligned implantations into bare (100)-oriented silicon, while implantation through the three thicker oxides results in profiles similar to those obtained from random equivalent implantations into crystalline silicon. The systematics of the dechanneling of the implanted boron as a function of the thickness of the amorphous surface layer are analyzed and discussed.