Microwave plasma enhanced low pressure DC sputtering of copper films

This paper reports on d.c. sputtering of copper films using a cylindrical magnetron (CyM) with the discharge enhanced and/or ignited by a microwave plasma produced in an external magnetic field B-e. The sputtering system was optimized with the aim to achieve high deposition rate of films at low argon pressures. It was achieved by enhancing the ionization degree of the discharge plasma by microwaves absorbed in the plasma and by the control of the distribution of B-e(z) along the device axis, i.e. by controlling the transport of the plasma to within a close vicinity of the sputtered target of the CyM. The optimized sputtering system can sputter films at low argon pressures from about 0.1 Pa down to 0.005 Pa and at quite large discharge currents I-d up to 1A, i.e. at quite large deposition rates a(D) of about several hunderds of nanometers per minute. The sputtering system operates at pressures lower than conventional magnetrons, i.e., under conditions when fast neutrals play a significant role. It opens the possibility to produce films of new properties. As an example, the microwave enhanced sputtering discharge was used to deposit Cu films. Resistivity and preferred crystal orientation of Cu films prepared under different argon pressures and at microwave powers ranging from about 100 W to 800 W is reported.