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Gate oxide with graded nitrogen content to optimize performance

IP.com Disclosure Number: IPCOM000033670D
Original Publication Date: 2004-Dec-22
Included in the Prior Art Database: 2004-Dec-22
Document File: 5 page(s) / 105K

Publishing Venue

IBM

Abstract

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.

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Gate oxide with graded nitrogen content to optimize performance

Oxide scaling beyond the 2.0nm range is accompanied by exponentially increasing gate tunneling current. In partially depleted SOI, this extra current can affect the body voltage. Higher nitrogen concentrations can be used to offset this effect. The nitrided gate oxide is formed using a novel N2O process which increases nitrogen concentrations over standard N

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O annealing processes and avoids the potential yield complications associated with nitrogen ion implantation. In this process, the N2O is preheated to higher temperaturess to increase the NO formation. This preheated mixture is directed into the lower temperature oxidation chamber. In this way, the advantage of higher temperature NO cracking with the benefit of low temperature oxidation control is achieved. In figure 1 we compare the leakage characteristics of this oxide with oxides grown with standard N2O processes and N2 implanted oxide processes.

Figure 1

The dual step process provides leakage improvements comparable to the ion implanted process. By modulating the time sequencing of the combustion temperature, a 'pseudo' grading effect can be achieved where the nitrogen concentration can be modulated during the oxidation process. The oxidation process is essentially divided into two steps, where

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each step has a different pre-combustion temperature, thus generating a different amount of nitrogen in the gate dielectric. Since nitrogen in the gate dielectric results in flatband shifts, relative amounts of nitrogen can be compared for different processes...