The Effect of Charged Ag Nanoparticles on Thin Film Growth during DC Magnetron Sputtering

Abstract

The possibility that charged nanoparticles (CNPs) are generated in the gas phase during direct current (DC) magnetron sputtering of Ag is studied. Sputtered Ag particles could be captured on an ultrathin amorphous carbon membrane for transmission electron microscopy (TEM) observation. It is confirmed that the average particle size and the total area of deposition under the condition of the positive bias applied to the substrate are bigger than those under the condition of the negative bias applied to the substrate. The results indicate that some of the sputtered Ag particles are negatively charged. To evaluate the contribution of negatively-charged particles to the film growth, Ag thin films were deposited for 30 min on the Si substrate with the substrate biases of −300, 0 and +300 V and analyzed by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and four-point probe. When +300 V was applied to the substrate, the film growth rate was highest with the film thickness of 85.0 nm, the crystallinity was best with the smallest full width at half maximum (FWHM) value of 0.44 and the resistivity was smallest with 3.67 μΩ·cm. In contrast, when −300 V was applied to the substrate, the film growth rate was lowest with the film thickness of 68.9 nm, the crystallinity was worst with the largest FWHM value of 0.53 and the resistivity was largest with 8.87 μΩ·cm. This result indicates that the charge plays an important role in film growth and can be a new process parameter in sputtering.