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21-lu-apl-1996-2713 - High resolution ion scattering study...

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High resolution ion scattering study of silicon oxynitridation H. C. Lu, E. P. Gusev, a) T. Gustafsson, and E. Garfunkel Departments of Physics and Chemistry and Laboratory for Surface Modification, Rutgers University, Piscataway, New Jersey 08855 M. L. Green, D. Brasen, and L. C. Feldman b) Bell Laboratories Lucent Technologies, Murray Hill, New Jersey 07974 ~ Received 8 July 1996; accepted 22 August 1996 ! High resolution medium energy ion scattering was used to characterize the nitrogen distribution in ultrathin silicon oxynitrides with sub-nm-accuracy. We show that nitrogen does not incorporate into the subsurface region of the substrate after oxidation of Si ~ 100 ! in NO. Core-level photoemission experiments show two bonding configurations of nitrogen near the interface. Oxynitridation in N 2 O results in a lower concentration and a broader distribution of nitrogen than in the NO case. © 1996 American Institute of Physics. @ S0003-6951 ~ 96 ! 04244-1 # Ultrathin silicon oxynitrides ~ SiO x N y ) are promising di- electrics for sub-0.25 m m ULSI devices. 1–9 They exhibit sev- eral properties superior to thermal O 2 oxides (SiO 2 ), the most important being suppression of boron penetration, en- hanced reliability, and reduced hot-electron induced degradation. 10 Recent publications suggest that the perfor- mance of CMOS-based devices depends on both the concen- tration and distribution of the nitrogen atoms incorporated into the gate dielectric. 5,7,9,11 Both the optimal nitrogen pro- file and even the best method for measuring nitrogen in ul- trathin SiO x N y films are still under debate. Characterizing the nitrogen distribution in ultrathin films with the required sub-nm accuracy is an analytical challenge. Two approaches have been used, secondary ion mass spec- troscopy ~ SIMS ! 2,5,9,12 and HF etch-back methods 3,13,14 In addition to the limited depth resolution of these methods, SIMS analysis is complicated by matrix effects, while HF etching may introduce nonuniform oxide removal ~ especially in the presence of nitrogen-rich regions ! . Nitrogen may be incorporated into SiO 2 using either oxidation/annealing 1–5,12–20 or deposition 6,7,9,21 methods. Thermal oxynitridation of silicon in N 2 O ~ Refs. 3, 4, 8, 13, 14, 17, and 19 ! was proposed 1,2 to place small amounts of N ~ typically on the order of 5 3 10 14 N/cm 2 ) in the oxide re- gion near the interface. Recently, oxynitridation in NO has been reported 5,11,12,15,18 to give rise to a higher nitrogen con- centration. Recent SIMS results on silicon ~ furnace ! oxida- tion of a SiO 2 film in NO were interpreted in terms of a nitrogen distribution sharply peaked on the substrate ~ silicon ! side of the interface rather than in the near-interfacial oxide. 12 In contrast, other studies 18 show that nitrogen is dis- tributed evenly throughout dielectric films grown in NO. In this work, high-resolution ( D E / E ; 0.1%) medium energy ion scattering ~ MEIS !
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