On the Argon Annealing-Based Improvements of the Properties of Ultra-Thin Oxynitrides Nitrided with NH 3
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On the Argon annealing-based improvements of the properties of ultra-thin oxynitrides nitrided with NH3 Anindya Dasgupta, Christos G. Takoudis and Greg Martel1 Department of Chemical Engineering, University of Illinois at Chicago 810 South Clinton Street, Chicago, Illinois 60607 1 SemiTest, Inc., 43 Manning Road, Billerica, MA 01821 ABSTRACT Thermally grown Si3N4 films in NH3 are known to have a higher dielectric constant and a higher N concentration than silicon oxynitrides, although they incorporate hydrogen atoms that induce hot electron carriers during subsequent high temperature processing. Further, a silicon nitride is difficult to grow over about 6 nm thick, due to self-limiting growth. One alternative is SiOxNy post-nitrided with NH3. In this work, we study the scope of improvement of Ar annealed nitrided oxynitrides as a function of annealing temperature and duration. Secondary ion mass spectroscopy (SIMS) studies of the nitrogen and hydrogen profiles suggest increasing N and H removal with increasing annealing time and temperature. Electrical characterizations have been performed to determine the total charge (Qox) and interface trap (Dit) densities at different processing conditions, before and after the annealing step. Post-annealing steps are not found to yield improvements of the electrical properties of these dielectric films. Instead, sometimes Qox is even seen to increase (e.g., after a 30 min Ar anneal at 1000 oC). Therefore, an optimization of such annealing steps is essential in designing nanodielectrics with desired nitrogen amounts and N concentration profiles as well as in understanding related process-structure-function relationships. INTRODUCTION Nitrogen engineering within dielectric SiO2 and SiOxNy films has been the focus of attention over the past decade in the ultra-large-scale-integration era. It is known that incorporation of N imparts many advantages over SiO2, like improved performance as a diffusion barrier of boron from p+ gate layers in subsequent high temperature processing steps, enhanced thickness control due to its self-limiting growth, and increased dielectric constant [1-6]. Moreover, N helps with the reduction of interface state densities, and improves interfacial strains and hot carrier resistance, all of which result in a longer and more dependable device lifetime [1-6]. Engineered N within a SiOxNy dielectric film combines the basic merits of both SiO2 and Si3N4 films while excluding the potential disadvantages that accompany these nano-dielectric structures. Non-stoichiometric SiOxNy films can be grown with either N2O or NO, both of which are known to incorporate relatively low amounts of N near the dielectric/substrate interface. On the other hand, silicon nitrides are highly effective in blocking diffusional dopants during high temperature processing steps; they exhibit superior breakdown homogeneity and wear out characteristics than those of ultrathin SiO2 films. But unlike SiO2, a nitridation process in NH3 forms a poor interface with Si, resulting in B4.10.1 Downl
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