Controlling the Hydrogen Concentration in Boron- and Gallium-Doped Silicon Wafers

The influence of the thickness of the hydrogen-rich silicon nitride layer on the amount of hydrogen introduced into the bulk of silicon wafers, with boron or gallium as the acceptor dopant species, is investigated using cryogenic Fourier Transform-infrared spectroscopy. Nitride layers with comparable refractive indices are deposited on Czochralski wafers and subjected to a simulated contact firing process. Thus, hydrogenation of wafers is performed with different thicknesses of the respective hydrogen sources. Fourier Transform-infrared spectroscopy at 5.0 K show that the hydrogen concentrations can be varied by altering the film thickness. The effect of a subsequent passivation process, i.e. deposition of a second hydrogen rich dielectric film at an elevated temperature, is also investigated. We observe that the passivation may alter the states of hydrogen in the bulk silicon or cause unintentional introduction of hydrogen. This passivation process also revealed considerable differences between boron and gallium doped wafers; The hydrogen-boron concentration grew more than the corresponding hydrogen-gallium concentration during the passivation process.