An apparatus includes a vacuum chamber, a wafer transfer mechanism, a first gas source, a second gas source and a reuse gas pipe. The vacuum chamber is divided into at least three reaction regions including a first reaction region, a second reaction region and a third reaction region. The wafer transfer mechanism is structured to transfer a wafer from the first reaction region to the third reaction region via the second reaction region. The first gas source supplies a first gas to the first reaction region via a first gas pipe, and a second gas source supplies a second gas to the second reaction region via a second gas pipe. The reuse gas pipe is connected between the first reaction region and the third reaction region for supplying an unused first gas collected in the first reaction region to the third reaction region.