The main reason one uses Argon gas during the annealing treatment of any object regardless of its size and its shape is to prevent it to be oxidized due to residual oxygen may be left  in the annealing chamber. The flow rate of Argon is very important to reduce not only the oxygen partial pressure in contact with the film surface but also its time of exposure to oxygen molecules hitting  the surface. 

Thank u indeed Tarik, as u mentioned the flow rate is very important ,therefore, is there any formula to calculate the suitable value of flow rate or just by trial and error?

Dear Süleyman, the following article may give some idea.

I agree with Tarik

Thanks a lot Dr. Daniela Gogova,