Degradation of oxynitride gate dielectric reliability due to boron diffusion

Abstract

In this letter, we report on the impact of the suppression of boron diffusion via nitridation of SiO2 on gate oxide integrity and device reliability. SiO2 subjected to rapid thermal nitridation in pure nitric oxide (NO) is used to fabricate thin oxynitride gate dielectrics. Both n+ polycrystalline silicon (polysilicon) gated n-MOS (metal–oxide semiconductor) and p+-polysilicon gated p-MOS devices were subjected to anneals of different times to study the effect of dopant diffusion on gate oxide integrity. As expected, an advanced oxynitride gate dielectric will effectively alleviate the boron-penetration-induced flatband voltage instability in p+-polysilicon gated p-MOS capacitors due to the superior diffusion barrier properties. However, such improvements are observed in conjunction with some degradation of the oxide reliability due to the boron-blocking/accumulation inside the gate dielectric. Results show that even though the oxide quality is slightly degraded for NO-nitrided SiO2 with p+-polysilicon gates, p-MOSFETs (metal–oxide semiconductor field effect transistors) with these dielectrics still show improved interface stability as compared to conventional SiO2 due to the reduced boron penetration into the Si/SiO2 interface and underlying channel region.

High resolution ion scattering study of silicon oxynitridation

“…3, 4, 8, 13, 14, 17, and 19͒ was proposed 1,2 to place small amounts of N ͑typically on the order of 5ϫ10 14 N/cm 2 ) in the oxide region near the interface. Recently, oxynitridation in NO has been reported 5,11,12,15,18 to give rise to a higher nitrogen concentration. Recent SIMS results on silicon ͑furnace͒ oxidation of a SiO 2 film in NO were interpreted in terms of a nitrogen distribution sharply peaked on the substrate ͑silicon͒ side of the interface rather than in the near-interfacial oxide.…”

“…10 Recent publications suggest that the performance of CMOS-based devices depends on both the concentration and distribution of the nitrogen atoms incorporated into the gate dielectric. 5,7,9,11 Both the optimal nitrogen profile and even the best method for measuring nitrogen in ultrathin SiO x N y films are still under debate.…”

Excess Si atoms near the pyrolytic-gas-passivated ultrathin silicon oxide/Si(100) interface

“…1. 8,9 This suggests that, in addition to a reduction of the H-related bonds by ultra-dry oxidation, PGP changes parts of the residual H-related single bonds, such as Si-H or Si-OH, into stronger Nrelated double or triple bonds, such as Si-N ϭ O 2 or Si 3 ≡ N. The apparent nitride (e.g., SiO x N y ) inclusions or layers obtained by general oxynitridation methods [17][18][19][20][21][22] are not intentionally produced. That is, instead of H passivation of silicon dangling bonds in the oxide films and near their interfaces, N passivation is aggressively performed in situ by the thermally activated NO 2 and N 2 generated from the pyrolytic N 2 O.…”

Diffusion-reaction mechanisms of nitriding species inSiO2

“…The nitriding species are originated in the decomposition of the N 2 O molecule occurring at typical oxidation temperature, these species being the NO and N 2 molecules. 4,5,6 On the other hand, nitrogen incorporation in SiO 2 can also be performed via annealing in a NH 3 atmosphere, resulting in a relatively high N concentrations into the films. 5 This method provides both nearinterface and near-surface nitridation, which suggests different mechanisms for N incorporation or different nitriding species derived from NH 3 .…”

“…1 According to these studies, the best nitrogen profile for an ultrathin gate oxide would have: (i) a small nitrogen concentration near the SiO 2 /Si interface in order to reduce degradations by hot electrons, 2 and (ii) a larger N concentration near the interface between the dielectric and the polycrystalline silicon (poly-Si) gate electrode, in order to minimize dopant diffusion. 3 The growth of ultrathin oxynitride films depends strongly on the reactant agent (e.g., N 2 O, NO, NH 3 ) and the technique used. Nitrogen can be incorporated into SiO 2 using either thermal oxidation and annealing or chemical and physical deposition methods.…”