25-tobin-jap-1994-1811 - F urnace formation of silicon...

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Furnace formation of silicon oxynitride thin dielectrics in nitrous oxide (N,Q): The role of nitric oxide (NO) Philip J. Tobin, Yoshio Okada, Sergio A. Ajuria, Vikas Lakhotia,a) William A.’ Feil, and Rama I. Hedge Advanced Products Research and DeveIopment Laboratory, Motoroia, 3501 Ed Bluestein Boulevard, Austin, Texas 18721 (Received 19 May 1993; accepted for publication 15 October 1993) We have studied the growth kinetics of the N20 furnace oxynitridation process demonstrating the importance of input flow rate, and therefore gas residence time, in determining the final film thickness and the nitrogen concentration. This dependence on residence time can explain the variation in the tendency to thickness saturation observed in the film growth data reported by several groups. Using published gas phase kinetic data, we have shown that, for a 950 “C oxynitridation process, NzO decomposes into N,, O,, and NO before reaching the wafer load. Again using published information, we have derived a simple equation which describes the subsequent reaction between NO and O2 to produce NO1 as the gas flows down the tube. This reaction results in loss of NO by an amount which depends on the gas residence time and therefore on the input gas flow rate and the dimensions of the system. Since it can be argued that NO2 does not contribute to nitridation, this system-dependent loss of NO can explain the variation in the reported film growth data. Combining our experimental data and model, we find that the peak nitrogen concentration in the film depends linearly on the NO gas phase concentration. Further, the oxynitride grows more slowly as the NO concentration increases supporting the idea that oxidation sites are blocked by nitrogen as oxynitridation time increases. I. INTRODUCTION The use of NzO to form thin oxynitride films for ap- plication as gate and tunnel dielectrics has recently at- tracted a great deal of interest.1’2 As an alternative to the use of NH,, this approach appears to offer potential ben- efits such as reduced electron trapping due to lower incor- porated hydrogen and greater process simplicity.2 Both rapid thermal processing and conventional furnace tech- nology have been used to form N20 oxynitrides. The re- ported growth rate data using 100% N20 show a tendency to saturating thickness versus time for both methods of formation3’ t This tendency to saturation has been attrib- uted to the observed accumulation of nitrogen at the inter- face between the dielectric and the substrate which retards reaction of the oxidizing species and the silicon.3 In the current work, we have examined the furnace oxynitridation process in, some detail focusing on the chemistry of the process. We present data showing, for the fh-st time, the effect of NzO 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
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