Sodium distribution in thin-film anodic bonding

Depth profiles of the sodium distribution at bonded interfaces of silicon wafers, bonded with an intermediate borosilicate glass film, are recorded by secondary ion mass spectrometry (SIMS). A layer of dielectric material is present under the thin layer of glass, either a layer of silicon oxide or a combined layer of silicon oxide and silicon nitride. The glass layers are sputtered onto the wafers. Sodium is found to pile-up at interfaces. In the structures where a layer of silicon nitride is included, the amount of pile-up is reduced. Sputtered glass films are analysed with energy dispersive X-ray spectroscopy (EDX), and with a microprobe, in order to estimate the content of sodium in the films. Glass films deposited by e-beam evaporation are included in the EDX measurements for comparison purposes.