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19-hegde-apl-1995-2882 - Growth and surface chemistry of...

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Growth and surface chemistry of oxynitride gate dielectric using nitric oxide Rama I. Hegde, Philip J. Tobin, Kimberly G. Reid, Bikas Maiti, and Sergio A. Ajuria Advanced Products Research and Development Laboratory, Motorola, Austin, Texas 78721 ~ Received 15 December 1994; accepted for publication 10 March 1995 ! Oxynitride films grown on preoxidized ~ 100 ! silicon surfaces in a nitric oxide ~ NO ! ambient at 950 °C have been investigated using x-ray photoelectron spectroscopy ~ XPS ! , secondary ion mass spectrometry ~ SIMS ! , atomic force microscopy ~ AFM ! , and cross-sectional transmission electron microscopy ~ XTEM ! . Compared to N 2 O oxynitride, NO oxynitride exhibits very different surface chemistry, interface properties, and growth mechanisms. The etch back of NO and N 2 O oxynitride films allows control of sample thickness for the XPS measurements. NO oxynitride has the interfacial nitrogen (N int ) sharply peaked on the Si substrate side of the interface, while it is broad and on the dielectric side of the interface for the N 2 O oxynitride. The N ~ 1 s ! XPS results reveal a clear distinction between N 2 O oxynitride and NO oxynitride. Near the Si/dielectric interface the NO oxynitride shows primarily Si w N bonds, while the N 2 O films showed a N ~ 1 s ! binding energy peak that is in-between that of Si w N bonds and Si 2 v N O bonds. Furthermore, the NO oxynitride surface roughness as determined by AFM is lower than that of the Si/SiO 2 interface. © 1995 American Institute of Physics. Since the first publications by Fukuda et al. 1 and Hwang et al. 2 in 1990, oxynitrides grown in N 2 O have drawn atten- tion as candidate gate dielectrics and tunnel dielectrics for submicron devices due to process simplicity and excellent reliability. 3–10 More recently, oxynitrides formed using nitric oxide ~ NO ! as the nitrogen source gas have been reported to have properties superior to those achieved with N 2 O. 11–14 Our work on furnace NO oxynitride initially focused on the performance and hot carrier injection ~ HCI ! reliability of lightly doped drain ~ LDD ! MOSFETs and the time depen- dent dielectric breakdown ~ TDDB ! of capacitors with 105 Å active dielectric. 11,12 Generally, the results for NO oxynitride were superior to those obtained with N 2 O oxynitride and this motivated us to examine the physical aspects of NO oxyni- tride more closely. This letter reports on growth kinetics, surface chemistry, and film properties of NO oxynitride films as studied by XPS, SIMS, AFM, and XTEM. NO oxynitride films studied here were processed in a conventional horizontal furnace us- ing a two-step process. 11 First, ; 95 Å of thermal oxide was grown at 900 °C in an oxygen ambient then, the NO oxyni- tride films were grown by annealing this oxide in a diluted NO ambient at 950 °C for 15, 28, or 60 min. For comparison, a 107 Å N 2 O oxynitride was grown by annealing 80 Å ther- mal oxide at 950 °C for 28 min. The thicknesses of the ox- ynitride films were measured by single wavelength ellipsom- etry assuming a refractive index of 1.465. The composition
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