Though you used SiO2 target, the sputtered material cannot be SiO2
without fail.
Si, SiO and SiO2 are sputtered from your target.
SiOx is formed more easily instead of SiO2.
So you must use oxigen gas(Ar+O2) for sputtering and meet oxygen
stoichiometric.


Sooje Cho from MEMSware