Some features of magnetron sputtering

In a low pressure sputtering system of the magnetron type for depositing thin solid films, two different discharge modes occur: a positive space-charge-dominated mode and a negative space-charge-dominated mode. The positive space-charge-dominated mode predominates in a weak magnetic field of some few hundred gauss and is widely used for sputtering, although the current density is non-uniform at the cathode surface. The negative space-charge-dominated mode predominates in a strong magnetic field of more than several hundred gauss and is also used for sputtering since the mode shows uniform current distribution at the cathode surface.In the magnetron sputtering system the working pressure is so low that the scattering of sputtered atoms by gas molecules can be neglected. Thus energetic sputtered atoms impinge on the substrates during film growth. This causes some phenomena which are rarely observed in a conventional diode sputtering system, e.g. an abnormal surface texture and an unusual crystalline structure are found in the resultant sputtered films. There is evidence that thin films of compounds normally only formed at high temperature can be synthesized at lower substrate temperatures.