The Subsurface Hydrogen Barrier Layer in Plasma-Treated Silicon
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THE SUBSURFACE HYDROGEN BARRIER LAYER IN PLASMA-TREATED SILICON A.E. JAWOROWSKI*,
L.S. WIELUNSKI** AND G. BAMBAKIDIS*
Department of Physics, Wright State University, Dayton, Ohio 45435, USA ** Department of Physics, SUNY at Albany, Albany, New York 12222, USA *
ABSTRACT The near-surface hydrogen profile was measured using the 15N hydrogen profiling technique in silicon. By depositing an adlayer of Al on the surface we were able to observe the separation of the near-surface hydrogen profile in silicon from the surface contamination layer. The hydrogen profiling of the near-surface region revealed the existence of a subsurface hydrogen layer which acts as a barrier to the transfer of hydrogen into the bulk. The observed subsurface layer is saturated with molecular hydrogen and its profile drops off sharply with increasing depth. The structure of this molecular hydrogen barrier and its thermal stability were studied. INTRODUCTION Technologically important hydrogen plasma passivation of electrically active defects in semiconductors has created considerable interest [1-9]. In silicon exposed to a hydrogen plasma at low to moderate temperatures (800 0C) data. This lower diffusivity indicates that the atomic hydrogen is being trapped or is recombining into molecules. The preferential formation of relatively immobile hydrogen molecules at low temperatures was concluded by Corbett et al.[lO] from calculations based on the MNDO method and by Mainwood and Stoneham [11,12] using the CNDO method. Recently, the molecular formation process has been modeled by Hall [13] and by Pearton [14] by considering experimental data for diffusion in silicon. Although the recent activity in this field has produced a more consistent picture of the state of hydrogen in crystalline semiconductors, it is evident that the details of the diffusion profiles must be studied and more data obtained before we fully understand the complexity of hydrogen diffusion in these materials [15]. The ISN hydrogen depth profiling technique provides a nondestructive high precision direct method of obtaining the hydrogen concentration versus depth in solids. A hydrogen sensitivity of about 100 at.ppm and a depth resolution of about 30 A in the near-surface region are typical for this profiling technique. Recently, Jaworowski and Corbett [16] measured the near-surface concentration of hydrogen in both plasma passivated and untreated silicon using this technique. They found a near surface enrichment in the hydrogen concentration in plasma passivated silicon and interpreted it in terms of preferential hydrogen molecule formation (self-trapping). Due to the ever-present hydrogen surface contamination, however, this enrichment appeared only as a broadening of the hydrogen surface peak. In a subsequent paper [17] we presented the separation of the near-surface hydrogen profile in silicon from the surface contamination layer. By depositing an adlayer of Al on the surface, the hydrogen profiling of the near-surface region revealed the existence of a subsurface hydrogen l
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