Critical challenges for "non-critical" layers

Abstract

Historically, the block layers are considered "non critical", as ones requiring less challenging ground rules. However, continuous technology-driven scaling has brought these layers to a point, where resolution, tolerance and aspect ratio issue of block masks now present significant process and material challenges. Some of these challenges will be discussed in this paper. In recent bulk technology nodes, the deep well implants require an aspect ratio of up to 5:1 in conventional resist leading to small process margin for line collapse and/or residue. New integration schemes need to be devised to alleviate these issues, i.e. scaling down the energy of the implant and the STI deep trench to reduce resist thickness, or new hard mask solutions with high stopping power to be dry etched. Underlying topography creates severe substrate reflectivity issues that affect CD, tolerance, profiles and defectivity. In addition to the CD offset due to the substrate, the implant process induces CD shrinkage and resists profile degradation that affects the devices. Minimizing these effects is paramount for controlling implant level processes and meeting overall technology requirements. These "non-critical" layers will require the development of more complex processes and integration schemes to be able to support the future technology nodes. We will characterize these process constraints, and propose some process / integration solutions for scaling down from 28nm to 20 nm technology node. © 2011 SPIE.