Interaction of low-energy nitrogen ions with an Si(111)-7×7 surface: STM and LEED investigations

Abstract

We report on scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) investigations of the interaction of low-energy nitrogen ions with a Si(111)-7 × 7 surface in the initial stage of nitridation. On silicon nitride islands showing a quadruplet LEED pattern a triangular periodicity of white protrusions with an average separation of 10-11 Å was observed in the STM image. Furthermore, the symmetry directions of the white protrusions were rotated about 10 • with respect to those of Si(111) surface, which was consistent with the LEED observation of dominant diffraction spots in that direction. The preferential appearance of dark Si adatoms due to bonding with nitrogen atoms on the center adatom sites compared with corner sites is explained in terms of the thermal stability of the product after nitridation. We also found that elevation of the nitridation temperature to 950 • C dramatically improved the quality of the silicon nitride layer owing to the improved mobilities of reacting species.There have been extensive efforts to deposit ordered silicon nitride layers using various methods, since silicon nitride is a versatile material which is used for high-temperature structural ceramics as well as for electronic device applications. As the size of semiconductor devices becomes small, control and understanding of the chemical reactions on the surfaces at the atomic scale have become an essential part of current research. For nitridation of silicon surfaces a variety of reacting species have been used: gaseous molecules such as NH 3 [1-5], NO [6-8], N 2 [9], N atoms [10-12], plasma [13,14] and ion beams [15]. Among these, a recent report on the ion-induced nitridation of a Si(111)-7 × 7 surface showed a high potential for low-energy nitrogen ions as the reacting species for the growth of silicon nitride film [15]. For the structures and chemical compositions of silicon nitride layers conventional techniques, such as low-energy electron diffraction (LEED), Auger electron spectroscopy and electron energy loss spectroscopy (EELS), have mostly been employed. * Corresponding author However, the local surface structures and chemical reactivity at the atomic scale can be probed directly by scanning tunneling microscopy (STM). In particular, the LEED studies suggested that two different surface structures, 8 × 8 and quadruplet structures, appear on the silicon nitride layer depending upon the annealing temperature and the carbon concentration [10,16]. However, recent STM observations [5,8] of the 8 × 8 structure on silicon nitride could not be explained in terms of the atomic structures proposed based upon the LEED interpretation. In the initial stage of nitridation by NH 3 gas, different reactivities of Si atoms at different adatom sites were observed at room temperature, and this was interpreted in terms of the interactions and charge transfer between sites [3,4].In this paper we investigate the interaction of low-energy nitrogen ions with an Si(111)-7 × 7 surface in the initial stage of nitridation. In...

Structure Determination of theSi3N4/Si(111)-Ahn1, Wu2, Gwo3 et al. 2001Phys. Rev. Lett.633410View full textAdd to dashboardCite

“…However, as an exception, a coherent Si 3 N 4 ͑0001͒͞Si͑111͒ interface can be formed using the thermal nitridation process, where a Si substrate is exposed to various nitrogencontaining gases such as NH 3 [4][5][6], NO [7][8][9], and N 2 [10], or to N atom [11] or ion [12] beams at high substrate temperatures. This is related to a nearly perfect lattice match: The 2 3 2 cell of the Si(111) surface ͑a Si 3.84 Å͒ is only ϳ1.1% bigger than the unit cell of b-Si 3 N 4 ͑0001͒ ͑a b-Si 3 N 4 7.61 Å͒ [13].…”

Crystalline Silicon Nitride Films on Si(111): Growth Mechanism, Surface Structure and Chemistry down to Atomic Scale

“…It can be done by exposing the atomically clean Si substrate to various N 2 compound reactive gases such as NH 3 [11][12][13][14][15][16][17], NO [18][19][20][21] or other gaseous at high nitridation temperatures or by post exposure thermal annealing. In addition, ion bombardment methods [22][23][24][25] or sputter deposition technique have also been employed. However, use the pure nitrogen gas would be the simplest and easiest way for the nitridation of the Si surface.…”

“…The atomic nitrogen exposure on Si(111) and Si(001) surfaces at relatively lower nitridation temperatures leads to the formation of amorphous nitride layer and appears with a highly disorder interface of nitride/Si. However, a crystalline interface and well-ordered films of hexagonal β-Si 3 N 4 films have only been observed for nitridation temperature only above 700°C [13][14][15][16][17][22][23][24][25][26][27]. Epitaxial β-Si 3 N 4 formation on Si(111) by thermal annealing of N-irradiated Si(111) surface has been reported by Yamabe et al [28].…”

Reactions of NH3 on high-temperature silicon surface and structure evolution during silicon nitride film growth

“…The morphology and structure of silicon nitride films have been studied using various surface research methods, such as scanning tunneling microscopy (STM), [10][11][12][13][14][15][16][17][18][19] low energy electron microscopy, 8) low energy electron diffraction, 10,11,20) and core-level photoemission, 21) even some theoretical research. 22,23) These studies have focused on the structural characterization of silicon nitride films obtained at high temperatures and high gas exposure.…”