Experiments on Si-rich SiGe layers show an exponential increase in Ge difFusion and an exponential decrease in B difFusion as a function of compressive strain, indicating a linear dependence of activation energy on strain. The efFect arises &om the structural relaxation of the lattice around the defect mediating difFusion (inward for a vacancy, outward for an interstitial). We infer the mechanisms of Ge and B difFusion in strain-f'ree and compressively strained Si(Ge) at T ( 1030'C, and draw some general conclusions on strain-modified diffusion in cryst&»ne solids. PACS numbers: 66.30.Jt Strained SiGe/Si heterostructures and superlattices are an essential component of many advanced Si-based devices, but the kinetic mechanisms of SiGe layer relaxation during thermal annealing are still poorly understood. Most previous work on strained-layer relaxation has focused on the nucleation, growth, and multiplication of dislocation loops during growth and subsequent thermal annealing. However, some workers have reported an alternative, diffusive relaxation process [1,2). In particular, Iyer and LeGoues have reported enhanced Si-Ge interdiffusion which is quenched on formation of a high density of dislocations [2]. This observation was attributed to strain-assisted difFusion, based on the thermodynamic analysis of spinodal decomposition by Cahn and Hilliard [3], but no specific physical mechanism for the enhanced Si-Ge interdifFusion has so far been proposed. This remains a significant challenge for our understanding of difFusion in Si and related materials. Recently, enhanced As difFusion [4] and retarded B diffusion [5,6] have been reported in compressively strained Si-rich SiGe layers. In particular, Moriya et al. presented extensive data showing a large reduction (up to a factor of 10) in the intrinsic difFusivity of B in Si(Ge) under compressive strain. By making the critical assumption that B difFusion is mediated by positively charged point defects, Moriya et al. were able to explain their result in terms of band-gap narrowing [6]. Although this assumption is consistent with early diffusion data [7], it appears to be incorrect. More extensive diffusion studies, using isoconcentration p-type and n-type backgrounds, have shown that the contributions of charged and neutral point defects to intrinsic B difFusion are of similar magnitude [ 8,9]. This conclusion rules out a strong reduction in intrinsic B difFusion due to band-gap narrowing, and points to a more drastic strain-related phenomenon.A hint as to the nature of this phenomenon can be found in recent total-energy calculations [10,11). Antonelli and Bernholc computed the formation energies for self-interstitials (b, Eyl) and vacancies (EEyv) in Si as a function of hydrostatic pressure. A linear increase in AEfl and decrease in bEyv were found with increasing pressure, corresponding to an outward relaxation of the lattice around the interstitial, and an inward relaxation of the vacancy. More recently, the same authors computed the effect of tensile strain in a Si l...

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Surface reaction mechanisms are investigated to determine the activation energies of pure boron (PureB) layer deposition at temperatures from 350 C to 850 C when using chemical-vapor deposition from diborane in a commercial Si/SiGe epitaxial reactor with either hydrogen or nitrogen as carrier gas. Three distinguishable regions are identified to be related to the dominance of specific chemical reaction mechanisms. Activation energies in H 2 are found to be 28 kcal/mol below 400 C and 6.5 kcal/mol from 400 C to 700 C. In N 2 , the value decreases to 2.1 kcal/mol for all temperatures below 700 C. The rate of hydrogen desorption is decisive for this behavior. Pure boron (PureB) layer depositions have in recent years been applied for creating the p þ -region of extremely shallow, less than 10-nm deep, silicon p þ n junction diodes for a number of leading-edge device applications. 1 Particularly impressive performance has been achieved for the application to bulk-Si photodiodes for detecting low penetration-depth beams. [2][3][4][5] Ideal diode characteristics have been achieved for deposition temperatures in the 400 C-700 C range. The option of depositing at temperatures below $500 C, which together with the fact that the deposition is conformal and highly selective to Si, makes PureB technology highly compatible with amorphous-/polysilicon-/ crystalline-silicon thin-film device processing. Moreover, these properties also make it an attractive process for creating junctions on silicon nanowires and advanced CMOS (complementary metal-oxide-semiconductor) transistors including source/drain in p-type FinFETs. 6,7 These applications require a sub-3-nm thick layer to avoid excess series resistance through the high-resistivity PureB layer.In the present work, the deposition is performed in a commercial Si/SiGe epitaxial reactor by exposing the Si surface to diborane (B 2 H 6 ). At 700 C, in the first few seconds of exposure, the boron atoms interact with the Si surface sites to quickly build up something like an atomic layer plane, and upon further deposition, the boron coverage readily exceeds one monolayer (1 ML). After this, the boron atoms will be deposited on a full PureB surface, which is a process that has a much slower, well-controlled deposition rate. In the past, it has been shown that less than 2-nm-thick layers can be deposited with good reliability and uniformity by a suitable adjustment of deposition parameters such as deposition time, temperature, partial pressures, and flow rates. 8 In this paper, an investigation is presented of the surface reaction mechanisms and activation energies of PureB layer deposition in the temperature range of 350 C to 850 C. At the lower temperatures, the carrier gas has a large influence on the ability to create the first full boron coverage of the Si. Nevertheless, by first creating a full PureB coverage at 700 C, which is smooth and uniform, and then proceeding with the low-temperature depositions, the boron-on-boron activation energies could be determined over the whole temp...

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