Nitrogen interface engineering in Al[sub 2]O[sub 3] capacitors for improved thermal stability

Abstract

Monolayer (ML) quantities of SiNx have been placed at both top and bottom interfaces of Al2O3 capacitors to improve thermal stability and electrical performance. Bottom SiNx was formed with NH3 anneal. Top SiNx was formed with ultrahigh vacuum chemical vapor deposition (UHVCVD) utilizing SiH4 and NH3. Characterization has been done with current–voltage (I–V), capacitance–voltage (C–V) transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) after 1050°C–30s anneal. I–V measurements show leakage current reduction of 50× with 2 ML UHVCVD SiNx at the polycrystalline-Si∕dielectric interface, while C–V measurements show that capacitance equivalent thickness increases just 1.2Å. The leakage current reduction is attributed not only to the increased thickness but also to interface passivation as a result of SiNx deposition. EELS N line profiles show evidence of monolayer quantities of N at both top and bottom interfaces. Good thermal stability beyond the 1050°C-30s anneal for the capacitors with UHVCVD SiNx is also demonstrated. Specifically, leakage current remains below 1×10−8A∕cm2 after four thermal stresses to or exceeding 1000°C.