Surfaces and Interfaces for Controlled Defect Engineering
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1070-E01-07
Surfaces and Interfaces for Controlled Defect Engineering Edmund G. Seebauer Chemical & Biomolecular Engineering, University of Illinois, 600 S Mathews Ave, 114 RAL, Box C3, Urbana, IL, 61801 ABSTRACT The behavior of point defects within silicon can be changed significantly by controlling the chemical state at the surface. In ultrashallow junction applications for integrated circuits, such effects can be exploited to reduce transient enhanced diffusion, increase dopant activation, and reduce end-of-range damage. INTRODUCTION Engineering of point defects semiconductors is important for a variety of applications, including ion implantation/annealing technology and crystal growth. In particular, forming increasingly shallow pn junctions in silicon-based microelectronic logic devices is critical as device dimensions continue to diminish. More electrically active dopant is also required in the implanted regions. Current technology for junction formation relies mainly on ion implantation followed by rapid thermal annealing to introduce dopants into the substrate. Post-implant annealing technologies have struggled in their ability to simultaneously increase dopant activation and decrease post-implant diffusion, especially for the key dopant boron. In addition, end-of-range defects left over from pre-amorphizing implants need to be reduced. As junctions move progressively closer to nearby surfaces and interfaces, the possibility arises for using these boundaries themselves for defect engineering. Such engineering could also prove useful in the formation of three-dimensional devices such as FINFETs. However, up until recently the science base required for performing such defect engineering was scanty. However, it has now been shown [1-2] that the behavior of point defects within silicon can be engineered by controlling the chemical state at the surface. Experiments combined with modeling of dopant diffusion/activation have suggested that certain chemical treatments of the surface induce it to act as a large controllable “sink” for defects that removes Si interstitials selectively over impurity interstitials, leading to less diffusion and better dopant activation. In addition, end-of-range damage can be reduced. There are two separate mechanisms for such effects: addition to dangling bonds and electrostatic attraction/repulsion. ADDITION TO DANGLING BONDS The first mechanism for interaction of a surface or interface with bulk defects involves insertion of defects into dangling bonds at the boundary. Various surfaces and interfaces differ markedly in their ability to annihilate defects. For example, an atomically clean surface is chemically active and can annihilate interstitial atoms by simple addition of the interstitials to
dangling bonds. However, if the same surface becomes saturated with a strongly bonded adsorbate, annihilation requires the insertion of interstitials into existing bonds. Such insertion should have a higher activation barrier, and the surface becomes less chemically active toward defects.
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