An apparatus deposits a high quality film onto a transparent substrate in a reactor. The transparent substrate may be made of glass, quartz or a polymer such as plastic. The transparent substrate is heated in a process chamber and a process gas stream is introduced into the process chamber. The apparatus generates a high frequency power output and a low frequency power output from a high frequency power supply and a low frequency power supply, respectively. The high frequency power output is generated at a frequency of about thirteen megahertz or more, and at a power from about one to five kilowatts, while the low frequency power output is generated at a frequency of about two megahertz or less, and at a power from about 300 to two kilowatts. The high frequency power output and the low frequency power output are superimposed and used to excite a plasma from the process gas stream at a pressure between about 0.4 Torr and 3 Torr, and at a temperature between about 250.degree. C. and 450.degree. C. to deposit a smooth thin film onto the transparent substrate.