Homogeneity check of ion implantation in silicon by wide-angle ellipsometry

Ion implantation is playing an important role in the fabrication of semiconductor devices, in which the precise control of the dose-homogeneity of dopants is required. As radiation-caused disorder changes the refractive index of single-crystalline silicon significantly, the relative damage can be sensitively measured by optical techniques like ellipsometry. 2 keV Arsenic, 20 keV Boron and BF₂ ions were implanted at room temperature into single-crystalline silicon. Doses from 5E12 cm^-2 to 5E15 cm^-2 were used to cover the range from slightly damaged to totally amorphized layers. The measurements were performed using wide-angle, fast mapping ellipsometry (WAE) developed in our Institute. The relative damage was characterized via complex pseudo dielectric function or using Bruggeman effective medium approximation combining the dielectric function of single-crystalline and ion implantation-amorphized silicon. The depth distribution of damage was described by a simple box-type optical model using two parameters only: effective thickness and effective damage of the implanted layer. The ellipsometric results were cross-checked using ion backscattering spectrometry combined with channeling. The results show that wide-angle ellipsometry can be a sensitive and cheap tool for homogeneity check after an appropriate calibration.