As silicon-based transistors in integrated circuits grow smaller, the concentration of charge carriers generated by the introduction of impurity dopant atoms must steadily increase. Current technology, however, is rapidly approaching the limit at which introducing additional dopant atoms ceases to generate additional charge carriers because the dopants form electrically inactive clusters. Using annular dark-field scanning transmission electron microscopy, we report the direct, atomic-resolution observation of individual antimony (Sb) dopant atoms in crystalline Si, and identify the Sb clusters responsible for the saturation of charge carriers. The size, structure, and distribution of these clusters are determined with a Sb-atom detection efficiency of almost 100%. Although single heavy atoms on surfaces or supporting films have been visualized previously, our technique permits the imaging of individual dopants and clusters as they exist within actual devices.

Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during initial annealing, due to Si interstitials being emitted from the region of the implant damage. The structural source of these interstitials has not previously been identified. Quantitative transmission electron microscopy measurements of extended defects are used to demonstrate that TED is caused by the emission of interstitials from specific defects. The defects are rodlike defects running along 〈110〉 directions, which consist of interstitials precipitating on {311} planes as a single monolayer of hexagonal Si. We correlate the evaporation of {311} defects during annealing at 670 and 815 °C with the length of the diffusion transient, and demonstrate a link between the number of interstitials emitted by the defects, and the flux of interstitials driving TED. Thus not only are {311} defects contributing to the interstitial flux, but the contribution attributable to {311} defect evaporation is sufficient to explain the whole of the observed transient. The {311} defects are the source of the interstitials.

Copper centers in copper-diffused n-type silicon measured by photoluminescence and deep-level transient spectroscopy Appl. Phys. Lett. 101, 042113 (2012) Bonding and diffusion of nitrogen in the InSbN alloys fabricated by two-step ion implantation Appl. Phys. Lett. 101, 021905 (2012) Shift of Ag diffusion profiles in CdTe by metal/semiconductor interfaces Appl. Phys. Lett. 100, 171915 (2012) Diffusion of co-implanted carbon and boron in silicon and its effect on excess self-interstitials Implanted B and P dopants in Si exhibit transient enhanced diffusion ͑TED͒ during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy ͑MBE͒. Damage from nonamorphizing Si implants at doses ranging from 5ϫ10 12 to 1ϫ10 14 /cm 2 evolves into a distribution of ͕311͖ interstitial agglomerates during the initial annealing stages at 670-815°C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of ͕311͖ defects during Ostwald ripening with an activation energy of 3.8Ϯ0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ϳ3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ϳ10 19 /cm 3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED.

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Si molecular-beam epitaxy (MBE) on smooth Si(100) surfaces is shown to occur at room temperature. %'e demonstrate for the first time that Si deposition becomes amorphous after growth of a limiting epitaxial thickness (h,~;). h,~; is = 10-30 A at room temperature and increases rapidly at higher temperatures with a rate-dependent activation energy in the range 0.4-1.5 eV. The effect is tentatively linked to surface roughening during growth at low temperatures, and is probably general in MBE, also occurring for Si/Si(111), Ge/Si(100), and GaAs/GaAs(100).PACS numbers: 61.50.Cj, 68.55.Bd, 68.55.6i The textbook descriptions of thin-film growth define a minimum temperature T,~; for epitaxial growth: Below T,~; vacuum deposition produces an amorphous overlayer, as opposed to a crystalline epitaxial film above T,~;. This critical temperature is attributed to the point at which, for a given growth rate, surface diffusion of incoming atoms ceases to be thermally activated. In this Letter we present data to show that the notion of a T,~;is not generally appropriate.We demonstrate for the first time the existence of a limiting thickness h, "; for an epitaxial film, beyond which a growing epitaxial film becomes amorphous.The thickness h,~; follows an exponential temperature dependence, which has previously been mistaken for an abrupt cutoff in epitaxy.We have carried out a study of Si molecular-beam epitaxy (MBE) on the Si (100) surface, perhaps the most extensively studied epitaxial system. Since electrical dopants segregate very strongly to the Si surface, the minimum epitaxial temperature T,~; limits both the maximum dopant concentrations achievable and the sharpness of dopant profiles. A large variety of techniques have previously been used to determine the epitaxial temperature in Si MBE; surprisingly, however, no clear consensus has emerged for T,~; , with measured values varying from 300'C to room temperature. We shall show that these discrepancies are attributable to the existence of an amorphous-crystalline transition in a film growing at fixed temperature. This allows us to control Si epitaxy (of limited thicknesses) down to room temperature: We use this to demonstrate fully activated doping with both B and Sb to the 10 -cm level with10-A abruptness.The epitaxy of Si at low temperatures was studied using cross-section and plan-view transmission electron microscopy (TEM) to study Si layers deposited under a variety of typical MBE conditions. Several different MBE chambers were used with pressures typically 10 ' -10 Torr during growth. Deposition rates between 10 and 0.05 As ' were studied using electron guns and Knudsen cells as the Si source; dopants were deposited using either Knudsen cells or heavily doped Si electron guns. The surface was prepared by growth of a buffer at 550-770'C on nominally (100)-oriented Si substrates from which a protective oxide had been sputtered or thermally desorbed. In order to clarify the interface between the high-temperature buffer and the low-temperature epilayer an additional ma...