Study of a small vacuum coating system for thermal evaporation

In this research we studied and fabricated a small vacuum coating system which is suitable for small pieces of the samples. It can help us to save in both cost and time for coating materials in each run. The home-built system consists of (1) a two-stage rotary pump used as a roughing and backing pump for a vacuum chamber and (2) a diffusion pump. The ultimate pressure of this diffusion pump is about 10-7 torr. From the result of testing the fabricated vacuum system it is found that the chamber pressure under the atmosphere can get down to 2.2 x 10-2 torr in 6 minutes by the rotary pump. The pressure inside the chamber is continuously lower to achieve 4.5 x 10-5torr in 30 minutes by the diffusion pump. Moreover we did further testing the system by coating pure aluminum (99.999%) on a Si (100) substrate using a resistive heater source made of tungsten with applied voltage and current of about 2.19 V and 110 A respectively. The aluminum surface has been investigated by SEM and AFM.