Ellipsometric study of crystalline silicon hydrogenated by plasma immersion ion implantation

The structure and the optical properties of thin Si layer hydrogenated by shallow plasma ion implantation with different fluences up to 1015 cm−2 are studied using spectroscopic ellipsometry and simulation of the distributions of the ions and implantation induced defects. The implantation was regarded to proceed into Si through the native SiO2. Two-layer optical models are applied for examination of the composition and dielectric function behavior of the formed structures. The native oxide is found to be 3 nm thick. The thickness of the Si modified layer decreased 23 to 14 nm with ion fluence due to increased formation of highly hydrogenated surface region that hinder further H-penetration into the Si bulk, especially at the highest fluence. Shifts of the features in the obtained dielectric functions related with Si interband transitions at about 3.4 and 4.2 eV are found caused by process-induced tensile stress. The modified Si region is related rather to defects created by the ion implantation process than the projected range of hydrogen ions. The overall layer modification can be characterized by a low degree of amorphization (up to 5.8%), creation of structural defects and internal tensile stress.