Edge transistor elimination using ammonia nitrided field oxide in SOI and oxide trench isolated SEG N -channel MOSFETs and electrical effects of a single stacking fault on fully depleted thin-film SOI MOSFETs

Jianan Yang, Purdue University

Abstract

N-channel MOSFETs can suffer from parasitic edge transistor effects, unless several extra processing and masking steps are used. These edge devices increase the off-state current and degrade subthreshold slope of the N-MOSFETs. Parasitic edge transistors of oxide trench isolated N-MOSFETs and Silicon-On-Insulator (SOI) N-MOSFETs, fabricated using Selective Epitaxial Growth/Epitaxial Lateral Overgrowth (SEG/ELO) technology, are caused by the boron out-diffusion during high temperature process steps. Employing a simple ammonia nitridation of the field oxide before the epitaxial growth step, boron out-diffusion into the surrounding oxide was suppressed. The parasitic edge transistors in both oxide trench isolated SEG N-MOSFETs and ELO-SOI N-MOSFETs were eliminated. A unique and simple method is demonstrated for characterizing the electrical impact of a single stacking fault on Fully Depleted Thin-Film SOI MOSFETs. SOI islands are created using the SEG/ELO technology. The stacking faults are observed using a optical Nomarski microscope. Both P and N-MOSFETs, with the presence of a single stacking fault entirely in the channel region, are measured. The influence of a stacking fault on device I-V characteristics is determined and compared to that of nearby identical devices without stacking faults. It is found that the threshold voltage increased and saturation current decreased. MOSFETs with a stacking fault only in the drain edge under the gate are found to have high subthreshold leakages under high drain voltage bias. P-MOSFETs, with a stacking fault crossing the gate and penetrating into the source and drain, have high subthreshold leakage currents. Various physical models are proposed to bring physical insights to the observed phenomena.

Degree

Ph.D.

Advisors

Neudeck, Purdue University.

Subject Area

Electrical engineering

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