Gate oxide with graded nitrogen content to optimize performance
Original Publication Date: 2004-Dec-22
Included in the Prior Art Database: 2004-Dec-22
Scaled FET devices have required increased processing complexity to reduce the 'intrinsic' leakage of the gate-oxide film as it is thinned to increase FET performance. Several methods have been developed to reduce this leakage - the more common ones being incorporation of a nitrogen ion implant before gate-oxide growth and/or growing the gate-oxide in a nitrogen rich environment (e.g. N2O or NO). The nitrogen however has several deleterious effects on FET performance including high PFET threshold voltage shifts due to the increased oxide fixed charge and increased Negative Bias Temperature Instability (NBTI) which affects product speed and guardbands. By growing the gate-oxide in a graded nitrogen content we can obtain the reduced gate oxide leakage without the corresponding PFET VT shift and simultaneously improve the NBTI and PFET hot-carrier characteristics. This disclosure teaches a novel method to modulate nitrogen concentration and an ability to change the nitrogen peak location relative to interface.