T-type undercut electrical contact process on a semiconductor substrate

Claim 1

A process for fabricating T-type undercut electrical contact structure on a semiconductor substrate, with said contact structure encapsulated on the bottom and sides by a diffusion barrier, comprising: depositing a first metal layer on said substrate, said first metal layer being oxidizable; depositing a second metal layer on said first metal layer; depositing a third metal layer on said second metal layer, said third metal layer being non-oxidizable, said second metal layer being a material providing a diffusion barrier against migration therethrough from said third metal layer; depositing a fourth metal layer on said third metal layer, said fourth metal layer being oxidizable; removing portions of said fourth metal layer outside of a given contact area; removing portions of said third metal layer outside said contact area; removing portions of said second metal layer outside said contact area; oxidizing portions of said first metal layer outside said contact area and oxidizing the remainder of said fourth metal layer within said contact area; electroplating a fifth metal layer on the sides of said third metal layer between said second and fourth metal layers, said fifth metal layer being a material providing a diffusion barrier against migration therethrough from said third metal layer; removing said portions of said first metal layer outside said contact area and removing said remainder of said fourth metal layer within said contact area, and also removing portions of said first metal layer within said contact area undercut beneath said second and third layers.