Oxygen is needed to produce oxide. There is no oxygen in the ultra high vacuum system. Therefore, only evaporation of calcium will occur in this system.
I want to deposit metal only, not oxide of it. My metal grenules may be contained(metal may be oxidised) due to calcium metal box was put in room atmosphere for few minute. So if I put this little oxidised calcium in evaporation. Will my film have unwanted oxides also or metal only.
Well, your first depositions will be contaminated, anyway, just because of residual chamber gas. So perform a few depositions and check if you can get down to acceptable levels. Do not stretch this over several days, though, since Ca will reaccumulate residuals. CaO on the other hand is not exactly famous for its high vapour pressure, so you may be lucky in that regards.