High density diffusion barrier of ionized metal plasma deposited Ti in Al–0.5%Cu/Ti/SiO2/Si structure

Abstract

The Ti layer deposited by ionized metal plasma deposition technique and the reacted region between Ti and Al-0.5%Cu, in Al-0.5%Cu/Ti/SiO 2 /Si structure, were characterized by scanning transmission electron microscopy ͑STEM͒ and Rutherford backscattering spectroscopy ͑RBS͒. The results indicate that the Ti layer with a column-like structure grew epitaxially in the close-packed ͓001͔ direction. This growth mechanism resulted in a high-density Ti layer in Al-0.5%Cu/Ti/SiO 2 /Si structure. This epitaxially grown Ti layer has anisotropic diffusion properties that can retard the diffusion of Al across the Ti layer in the initial stage of high temperature Al sputtering or reflow processes. But the column-like Ti crystals recrystallized during further processing, altered the ͓001͔ alignment of the crystals to cause the interdiffusion of Ti and Al. The reactions between Ti and Al took place subsequently and formed the intemetallic Al 3 Ti, Al 5 Ti 2 , TiAl, and Ti 3 Al layers from the surface inwards. As the diffusion of Al in Ti, Ti 3 Al, and TiAl decreased in order, the formation of Ti 3 Al and TiAl layers further retarded the diffusion of Al into the SiO 2 layer. It can be concluded that the intermetallic layers play an important role of diffusion barrier that impede the migration of Al across the films.

Roughness and texture correlation of Al films

“…This means that the Ti film texture impacts and controls the Al film texture formation, which is consistent with the work of others. 5,6,8 …”

“…Later, it was found that ionized physical vapor deposition (I-PVD) can improve Al(111) texture furthermore. 5,6,8 The higher energy and density of Ti plasma in the I-PVD method bring denser Ti films with fewer gas atoms and voids. 5 In this work, we studied single Ti films and Al films on TiN and Ti underlayers.…”

“…5,6,8 The higher energy and density of Ti plasma in the I-PVD method bring denser Ti films with fewer gas atoms and voids. 5 In this work, we studied single Ti films and Al films on TiN and Ti underlayers. The Ti films deposited by the I-PVD method are compared with Ti films prepared by conventional PVD methods.…”

Diffusion of Au in the Intermetallic Compound Ti3Al

“…[11] In this context, the mechanisms of self-diffusion in Ti 3 Al have been proposed by Mishin and Herzigh. [12] From experiments on impurity diffusion in Ti 3 Al, it has been found that elements with a comparatively small atomic radius (r) such as Fe (r = 0.127 nm) and Ni (r = 0.125 nm) exhibit fast diffusion by the dissociative diffusion mechanism where they pass through the interstitial octahedral sites, whereas elements with a relatively large atom size such as Nb (r = 0.147 nm) and Ga (r = 0.141 nm) exhibit relatively low diffusivity. [7] However, the diffusion of impurity atoms in intermetallic compounds depends not only on the size of the impurity atoms but also on the impurity sitesubstitution behavior.…”

“…[1,2] Recently, Ti 3 Al has attracted attention for possible use as a conductive diffusion barrier in microelectronics devices such as ferroelectric random access memories. [3][4][5] Therefore, diffusion data of elements contained in integrated circuits are increasingly important. Ru¨sing et al [6] have measured self-diffusivity of Ti and interdiffusivity in binary Ti 3 Al.…”