Postdeposition relaxation of internal stress in sputter-grown thin films caused by ion bombardment

Abstract

Influence of oxygen diffusion on residual stress for tantalum thin films J. Vac. Sci. Technol. B 25, 147 (2007); 10.1116/1.2431179 X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment Appl. Phys. Lett. 85, 5905 (2004); 10.1063/1.1836868Influence of energetic bombardment on stress, resistivity, and microstructure of indium tin oxide films grown by radio frequency magnetron sputtering on flexible polyester substrates A hitherto unreported postdeposition method of relaxing ultrahigh internal stresses prevailing in sputter-grown thin films is the subject of the present research. A significant reduction of stress has been confirmed by x-ray diffraction and independent substrate deflection measurements for HfN films treated with Si ϩ ions of various energies ͑450 keV, 500 keV, and 1.1 MeV͒. The particular sequence of the performed experiments has allowed us to deduce the most likely scenario of the resulting stress relaxation. We argue that the observed reduction of internal stress had been caused by structural changes, namely the transport of interstitial defects occurring within the thermal spikes induced by ion bombardment and an increase in vacancy concentration. Simple theoretical considerations proved that the existence of an amorphous silicon interlayer formed right under the HfN film during the bombardment cannot be the cause of the observed stress relaxation. The employed Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction technique confirmed that the ion bombardment did not seriously affect either the composition, dislocation structure, or texture of nitride films. The relative softening of HfN after ion bombardment was found to be caused by amorphization of the substrate directly under the film. The penetration of incident particles deeper than predicted by a numerical simulation was attributed to a distinct crystallographic texture determined experimentally for HfN films. It was confirmed that modification with Si ϩ ions does not affect the resistivity of HfN films.

Anisotropic elasticity ofIVBtransition-metal mononitrides determined byab initiocalculations

“…However, the main interest in transition metal nitrides is associated with their superior mechanical properties, partially related to electronic structure, 10 that are usually tailored by the selection of specific deposition conditions, 11,12 or modified by post-growth ion treatment. [13][14][15] Surprisingly enough, despite common reference to the "extreme hardness" and "significant Young's modulus" of transition metal nitrides, there is considerable confusion regarding what the acceptable values of the mechanical characteristics are. Various authors have reported inconsistent results for HfN thin films, that are relatively rarely examined, as well as for widely investigated TiN and ZrN.…”

“…The extensive documentation of ultrahigh internal stresses that are generated in TiN, ZrN, and HfN during deposition serves as an example of a field that would be much affected by drastic correction of the accepted values, since the methods of stress evaluation employ equations that inevitably require accurate knowledge of elastic parameters for both the film and substrate. [13][14][15]24,25 Furthermore, there is still uncertainty concerning the origin and scale of the anisotropic lattice distortion and related elastic anisotropy exhibited by the transition of metal nitride films 26 that was never addressed in a systematic manner so far.…”