Silicon Oxynitride Formation In Nitrous Oxide (N/sub 2/O): The Role Of Nitric Oxide (NO)

Abstract

lntroductionWe present data showing, for the first time, the effect of N 2 0 flow rate on the thickness and interfacial nitrogen concentration of oxynitride films grown in a conventional furnace at one atmosphere. Our analysis, based on the concentration of nitric oxide (NO), can explain these observations as well as the variation in the published data on the kinetics of film growth. This understanding should facilitate the application of these films as tunnel dielectrics and gate dielectrics to improve device reliability (1,2,). Fig.1 shows our kinetic data with replotted results from three other groups (3,4,5). The time dependence ranges from near saturation (3,5) to an almost linear behavior (4). Our data is intermediate between these two extremes. The vertical displacement is due to differences in the oxide thickness before N 2 0 exposure which does not affect the tendency to thickness saturation. Observing the variation in this data, we decided to examine the chemistry of the process more closely. Experimental ProcedureIn this w rk, we focused on dielectrics equal to or greater than 1001 and selected p g l e growth temperature of 950°C. A thermal oxide, 75 thick, was grown on 125 mm wafers in N d 0 2 at 950OC. This initial oxide was exposed to N2O for times U to two hours. The N20 flow rate was varied from 4 to 1 f S L M . The ox nitride growth runs were camed out with all five boats h l l y loaded. A single test wafer at the center of the load was used for thickness and nitrogen measurement. Loading and flow rate variations produce changes in gas residence time which was found to be a. critical parameter. Thickness was measured with an ellipsometer with fixed wavelength (632.8nm) and refractive index (1.465). The nitrogen profile was measured by SIMS using Cs sputtering and CsN+ detection. Experimental Results and DiscussionFig. 2 shows the time dependence of oxynitride thickness for flow rates of 4 SLM and 14 SLM. The higher flow rate shows a greater tendenc to thickness saturation.This effect is shown more fully in 6f. 3 where a fixed time of 35 minutes was used for oxynitri ation of 7.5 nm oxide. SIMS was used to determine the interfacial nitrogen concentration (Nint) ,as shown in Fig. 4. It has been conjectured that nitric oxide (NO) is the critical species responsible for the interfacial nitrogen concentration (6).We show that this conjecture is consistent with published kinetic data and demonstrate below that the dependence of thickness and Nint on flow rate can be ex lained by variation in the concentration of NO at the w d r with gas residence time.Heat-up of the incoming N20 by the 950°C furnace causes decomposition by the following two reactions (7). N20+ N2+0 U11[21 Remaining atomic oxygen will ra idly recombine into 0 2 . At YOO°C-lOOOoC approximately &% of the incoming N20 decomposes according to reaction [ 11 and 2% decomposes according to [ 21 (8). Extrapolation of published kinetic data from 750°C to 950°C indicates that the half-life of the N20 decomposition by [l] and [2] is approximately ...

Reduction of RIE-damage by N/sub 2/O-anneal of thermal gate oxide

“…2, increasing flow rate increases amount of nitrogen incorporation in the dielectric thus increasing resistance to plasma induced degradation proportionally. The effect of increasing nitrogen incorporation as a result of increased N O flow rate has been reported by Tobin et al [10] and has been attributed to reduced nitric oxide (NO) depletion in a conventional furnace. Our results confirm that increasing N O flow rate is an effective way to increase nitrogen incorporation without increasing the thermal budget.…”

“…This reduction can be attributed to nitrogen related positive charge build-up [19]. Amount of nitrogen incorporated at the interface increases with N O flow rate [10], which results in higher positive charge and, thereby, a reduction in for N-MOSFET's. It is seen that the subthreshold swings of all devices are comparable.…”

“…E XTENSIVE research on N O-based oxynitrides has revealed that these dielectrics are excellent candidates for gate oxide in scaled MOSFET's as well as tunnel oxide for EEPROM applications [1]- [10]. The attractive features of N O oxides include improved hot carrier behavior for N-and P-MOSFET's [1]- [5], superior breakdown properties [6] and improved diffusion barrier properties against boron penetration [7].…”

“…Some of reported approaches include RTP for N O oxide growth [1], N O anneal of a pre-oxide [2]- [4], [8], N O O ambient for oxide growth [9], etc., or combinations thereof. A work by Tobin et al [10] suggested that N O flow rate is a key factor in determining the amount of nitrogen incorporated during an N O process. This work led us to believe that a low Manuscript In this work we have tried to explore two areas: 1) N O oxide versus thermal oxide in terms of plasma induced charging damage and 2) impact of N O process conditions on their robustness.…”

Growth characterization of rapid thermal oxides

“…For O 2 RTO the mean thickness uniformity obtained is better than 2%. 19,22,26,27 McIntosh et al attributed the phenomenon to a relatively stagnant gas flow at the wafer's center. This suggests that the growth characteristics are parabolic like.…”