To realize precise and high-throughput multiprocesses in a single plasma process chamber with a rapid alternative of multiple gases, gas flow characteristics in a plasma process chamber are investigated and a pulse-controlled gas injection method is developed. It is found that gas replacement characteristics greatly depend on the gas supply method used. An upper shower plate has a great advantage in realizing a rapid gas replacement over the case without using the upper shower plate, resulting from the realization of the down flow pattern of feed gas in the chamber. The pulse-controlled gas injection method employs the intentional overshoot pulse at the beginning of gas supply to rapidly stabilize gas pressure. Interference matrix operation is newly introduced to determine the pulse size for the arbitrary gas flow pattern in the chamber. The optimum pulse size can be successfully obtained in the case of HBr addition to a pure Ar plasma.