Effects of radio-frequency plasma on structure and properties in Ti film deposition by dc and pulsed dc magnetron sputtering

Abstract

Structure and subsequent properties of films deposited by direct current (dc) magnetron sputtering and pulsed dc magnetron sputtering with or without inductively coupled radio-frequency (rf) plasma using a Ti target have been investigated for various discharge pressures ranging from 0.3 to 2.0 Pa. By cross-sectional scanning electron microscopy, it is found that films deposited by pulsed dc sputtering with an rf plasma at pressures of 0.3 and 1.5 Pa become denser than those deposited by dc sputtering without an rf plasma. Surface roughness also decreases with the presence of rf plasma at all discharge pressures. The change in reflectance correlates well to that in surface roughness. Decrease in resistivity due to the presence of rf plasma is remarkable for discharge pressures of 1.5 and 2.0 Pa and less remarkable for discharge pressures of 0.3 and 0.5 Pa. These result from the increase in crystallinity and film density by the presence of rf plasma in a high pressure range. It is presumed that a Ti film with a fine columnar structure results from the enhancement in the energy transferred to the surface of a growing film due to the increase in ion fraction and ion energy in the combination of pulsed dc and inductively coupled rf discharges. The effects of rf plasma on film structure and properties is more remarkable at higher discharge pressures because in this pressure range, the energy loss that occurred through collision scattering, inducing a voided structure, in conventional dc magnetron sputtering is compensated for effectively by the addition of energy to the particles in rf-plasma-assisted sputtering.