Conventional planar magnetrons have been characterized with small (0.01 and 0.02 cm diam) Langmuir probes in the plasma region and also extending into the sheath. The plasma potentials, electron temperatures, and electron densities have been measured at low and intermediate magnetron discharge currents. The low currents reduce the effect of the probe on the discharge by reducing probe heating. The pressure range examined was 1.5–30 mTorr in both Ar and He. With Ar, the plasma potential is relatively constant in the abnormal (bright) glow region of the magnetron, and only begins to drop appreciably in the dark space (<1 mm thick) near the cathode. The electron temperatures showed a continual increase as the cathode sheath was approached. Temperatures were measured in the 1–5 eV range at 5–30 mTorr Ar, and as high as 22 eV at pressures of 1.5 mTorr Ar. The measured electron densities were also pressure dependent and were highly peaked in the bright glow region near the cathode surface. The densities fell rapidly through the sheath. Significant departures from a Maxwellian electron energy distribution were found for the He plasmas, with a higher proportion of electrons in the high energy tail. The densities, however, were significantly lower than with Ar.

The current–voltage relationship in a magnetron plasma appears to be strongly dependent on the dynamics of the sputtered particle–gas atom interaction. Large fluxes of energetic (several eV) sputtered atoms from the cathode heat the gas in the near cathode region, resulting in a significant reduction in the local gas density as a function of discharge current (and hence particle flux). This reduction in gas density results in a lower rate of ion formation, and hence a more resistive plasma. Thus, the rate of voltage increase with current in a magnetron is related to the magnitude of the gas density rarefaction, which is dependent on the cathode sputter yield, sputtered atom energy, the cross section for sputtered atom–gas collisions, the molecular velocity of the gas, and the gas density. A model has been developed which describes the observed rate of voltage increase in a magnetron as a function of this thermalization process.

No abstract

No abstract

The development of surface microtexture along with ion-impact-enhanced surface and bulk diffusion processes is important for users of ion beams and plasmas for thin film or material processing. Even in those applications where texturing is not desired, an understanding of the process of texturing will permit proper corrective action when texturing is found to occur. Surface microtexturing produced using ion-beam sputtering and simultaneous deposition of impurities is described both in terms of a simple diffusion model and with regard to detailed studies of the initiation, development, and failure of individual sputter cones. Digital computer calculations are presented which follow surface feature development under sputtering. These calculations appear to confirm the role of ion reflection in the development of cones. A coating associated with the impurity deposition is often observed on individual cones. This coating appears to play a role both in the initial development of cones and in the subsequent evolution of second generation cones in a steady-state process. Surface diffusion, in excess of that expected from thermally activated diffusion alone, has been observed as the ion-beam current density is increased. This impact-enhanced diffusion appears to depend on cooperative effects between multiple ion impacts.