ELECTRICAL CHARACTERIZATION OF N2O ANNEALED GATE OXIDE

Abstract

Anomalous current spikes, observed in the current-voltage characteristics of MOS capacitors, are investigated. It is found that the current spike detected during the sweep from accumulation to inversion is due to charging and/or discharging of the border traps, which can be generated together with the fast interface traps by Fowler-Nordheim stress and/or plasma damage induced during reactive ion etching. This current peaks when two conditions are fulfilled, both of which are satisfied near mid-gap. First, the surface Fermi level must change sharply with the gate bias stepping. And second, the response time of the border traps should be long. It is further found that non-thermal equilibrium effects, resulting from insufficient generation of minority carriers, will enhance the current spike formation by increasing the trap response time. In addition, generation current will dominate the trapping/detrapping current in the deep inversion region on devices where the generation rate is fast. It is distinguishable from the current associated with trapping/detrapping process since the magnitude of this generation current will not be affected by Fowler-Nordheim stress. N2O-based oxide, as a candidate for the gate dielectric for deep submicron devices, has been unanimously reported to show superior qualities over conventional thermal oxides. The improvement has been attributed to the nitrogen incorporation in the vicinity of oxide-silicon substrate interface, which relieves the compressive stress at the interface, resulting in fewer strained bonds available for defect formation. Electrical properties such as interface trap generation, stress induced leakage current and charge trapping characteristics are studied in our N2O annealed samples. Results, however, show that little improvement is achieved by nitrogen incorporation. The high quality of the starting oxide, which has very few strained bonds near the interface and thus little room for improvement, is thought to be part of the reasons.