Pulsed DC Gas Flow Sputtering

Implementation of reactive sputtering of dielectrics such as Al2O3 and SiO2 by the use of steady DC power is obstructed by arcing. The arcing appears to be due to breakdown of the dielectric (oxide) films that grow on the metal target surface and which accumulate positive charges on their surfaces due to ion bombardment. The arcing can be greatly alleviated when pulsed DC power is applied. By pulsed DC power we mean that the power (voltage) is applied for a short "on" period (on-time), and then removed for a short "off" period often called ‘reverse time”. Our investigations showed that reactive sputtering of dielectrics can be performed without arcing using pulsing frequencies that exceed the critical frequency, and a duty cycle that is less than the critical duty cycle (Figure 1).

Figure 1. Schematic of an arc-free conditions for reactive sputtering of dielectrics in the 2-D space, created by the duty cycle and pulsing frequency at two different current values. The critical frequency increases with the power (or current) delivered to the target. The critical duty cycle decreases as the target power or current increases. For arc-free operation, the charge deposited on the dielectric surface during the sputtering time must be fully discharged during the reverse time. Therefore, to keep the discharge running without arcs, increasing the time-on (lowering the frequency) requires a corresponding increase in the reverse time. The critical frequency usually lies in the range of 10-350 kHz. Pulsing parameters influence the forms of voltage and current peaks, deposition rate and the properties of the deposited thin films. The influence comes through pulsed plasma (PMP) kinetics.

For more details contact Abe Belkind (abebelk@aol.com)

References:
1. A. Belkind, A. Freilich, and R. Scholl, Electrical Dynamics of Pulsed Plasmas, in 41th Annual Technical Conference Proceedings, Boston, 1998 (Society of Vacuum Coaters, 1998), p. 321.
2. A. Belkind, A. Freilich, and R. Scholl, Pulse duration effects in pulse-power reactive sputtering of Al2O3, Surf.Coat.Technol., 108-109 (1998)558.
3. A. Belkind, A. Freilich, and R. Scholl, Using Pulsed DC Power for Reactive Sputtering of Al2O3., J.Vac.Sci.Technol., A 17 (1999) 1934.
4. A. Belkind, Z. Zhao, D. Carter, L. Mahoney, G. McDonough, G. Roche, R. Scholl and H. Walde, Pulsed-DC Reactive Sputtering of Dielectrics: Pulsing Parameter Effects, in: 43rd Annual Technical Conference Proceeding, Denver, 2000 (Society of Vacuum Coaters, 2000), p. 86.
5. A. Freilich, A. Belkind, K. Becker, and J. Lopez, Substrate Biasing in Pulsed DC Reactive Sputtering of Dielectrics, in: 46th Annual Technical Conference Proceeding, 2003 (Society of Vacuum Coaters, 2003), p. 114.