Abstract: There is provided a process and its system for fabricating plasma with feedback control on plasma density. This process uses a heterodyne millimeter wave interferometer as a sensor to measure the plasma density in the process container and the plasma density that is needed in the plasma fabricating process, and then provides real-time information of the measurements to a digital control device which makes numerical calculations and then drives the RF power generator to change the RF output power so as to enable the plasma density in the plasma fabricating process to be close to the expected plasma density. The conventional operation parameter method is to control air pressure, RF power, gas flow quantity, temperature and so on. However, it does not control the plasma parameter that has the most direct influence on the process. Therefore, this method cannot guarantee that, in the process of fabricating wafers, different batches of wafers will be operated under similar process plasma conditions.