Dependence on Ge doping of specific volume change in silica induced by electron-beam irradiation

Because of the increasing use of e-beam lithography in telecom optical applications, e-beam induced refractive index change (RIC) has been further investigated in this paper in Ge-doped silica in comparison with pure silica. We investigated modified chemical vapor deposition (MCVD) Ge-doped SiO2 glasses containing 0, 5, 13 and 25 wt% of Ge. Contrary to ultraviolet (UV) photosensitivity for which Ge doping has a positive effect; here, the densification is diminished and even an expansion process appears for larger Ge content. Comparing RIC, directly measured and deduced from topography change, we conclude that specific volume change is the main contribution to RIC. UV and e-beam induced densification are by different mechanisms.