514-gusev-ibmjrd-1999-265 - Growth and characterization of...

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by E. P. Gusev H.-C. Lu E. L. Garfunkel T. Gustafsson M. L. Green Growth and characterization of ultrathin nitrided silicon oxide films This paper reviews recent progress in understanding microstructural and growth- mechanistic aspects of ultrathin ( < 4 nm) oxynitride films for gate dielectric applications. Different techniques for characterizing these films are summarized. We discuss several nitridation methods, including thermal (oxy)nitridation in NO, N 2 O, and N 2 as well as a variety of deposition methods. We show that a basic understanding of the gas-phase and thin-film oxygen and nitrogen incorporation chemistries facilitates the processing of layered oxynitride nanostructures with desirable electrical properties. 1. Introduction While “pure” SiO 2 films remained the principal material for gate dielectrics in MIS-based structures for more than three decades, the use of the traditional SiO 2 gate dielectric has become questionable for sub-0.25- m m ULSI devices [1–5]. Increasing problems with dopant (boron) penetration through ultrathin SiO 2 layers and direct tunneling for ultrathin ( , 2 nm) oxide films dictate the search for and aggressive exploration of new materials for future gate dielectric applications with better diffusion barrier properties and higher dielectric constants [6, 7]. At this time, ultrathin silicon oxynitrides (SiO x N y or, more accurately, nitrogen-doped SiO 2 ) are the leading candidates to replace pure SiO 2 [8–24]. Oxynitrides exhibit several properties superior to those of conventional thermal O 2 oxides (SiO 2 ), the more important being suppression of boron penetration from the poly-Si gate and enhanced reliability. Nitrogen also reduces hot- electron-induced degradation [25]. The dielectric constant of the oxynitride increases linearly with the percentage of nitrogen from « (SiO 2 ) 5 3.8 to « (Si 3 N 4 ) 5 7.8 [26, 27], though one should note that most SiO x N y films grown currently by thermal methods are lightly “doped” with N ( , 10 at.%) and therefore have a dielectric constant only slightly higher than that of pure SiO 2 . 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 [14, 16, 18, 28–30]. For example, excessive nitrogen at the interface may reduce peak carrier mobility in the channel of MOSFETs and may allow boron accumulation in the oxide, which, in turn, may result in device instabilities [28]. The optimal nitrogen profile is determined by its specific application, although our incomplete understanding of the atomic-scale structural and electronic properties of dielectrics makes the desired structure an imperfectly defined goal. One possibility is an SiO x N y film with two nitrogen-enhanced layers: first, r Copyright 1999 by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions,
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514-gusev-ibmjrd-1999-265 - Growth and characterization of...

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