Ion-assisted film growth: modification of structure and chemistry

Abstract

During film growth from the vapor phase, low-energy ion irradiation can cause large changes in the nucleation and growth kinetics and thus in the resulting structure and composition of the deposited films. In this paper, results on the nucleation characteristics during primary ion-beam deposition of In, defect generation and gas incorporation in sputtered epitaxial films, as well as incorporation of dopant atoms during ion-beam doping of Si-MBE films, are discussed. In the case of In primary ion-beam deposition, carried out in an uhv system, it is shown that breakage of small clusters by the ion beam leads to an apparent enhancement of adatom diffusivities and thus to a uniform island size distribution. For gas incorporation in sputter-deposited epitaxial TiN films, both N and Ar supersaturation of the grown films can be obtained by using a substrate bias during growth. It is also shown that the amount of gas incorporated into the films not only depends on parameters such as ion energy and flux, substrate temperature and growth rate, but also on the orientation of the deposited films. The amount of entrapped gas is observed to decrease as the orientation of the epitaxial films is changed from (110) to (100) to (111). This demonstrates that channeling effects occur even for ion energies as low as a few hundred eV. The results also demonstrate that precipitation of the excess gas can occur, resulting in gas bubble formation within the films. Due to the surface anisotropy of the TiN lattie the bubbles will have a rhombohedral shape with 5–20 nm facets on (100) planes but exhibition (110) and (111) facets.