Hydrogen-induced platelets in silicon studied by transmission electron microscopy

Fully Bottom-Up Waste-Free Growth of Ultrathin Silicon Wafer via Self-Releasing Seed Layer

The fabrication of ultrathin silicon wafers at low cost is crucial for advancing silicon electronics toward stretchability and flexibility. However, conventional fabrication techniques are inefficient because they sacrifice a large amount of substrate material. Thus, advanced silicon electronics that have been realized in laboratories cannot move forward to commercialization. Here, a fully bottom-up technique for producing a self-releasing ultrathin silicon wafer without sacrificing any of the substrate is presented. The key to this approach is a self-organized nanogap on the substrate fabricated by plasma-assisted epitaxial growth (plasma-epi) and subsequent hydrogen annealing. The wafer thickness can be independently controlled during the bulk growth after the formation of plasma-epi seed layer. In addition, semiconductor devices are realized using the ultrathin silicon wafer. Given the high scalability of plasma-epi and its compatibility with conventional semiconductor process, the proposed bottom-up wafer fabrication process will open a new route to developing advanced silicon electronics.

Transmission electron microscopy characterization of low temperature boron doped silicon epitaxial films

Transmission electron microscopy techniques to better understand growth mechanisms and annealing of low temperature silicon epitaxy. HRTEM: thickness measurement, crystal morphology, and defect study. GPA (image processing): strain field analysis.

TEM measurement of hydrogen pressure within a platelet

Proton implantation and thermal annealing of silicon result in the formation of a specific type of extended defect involving hydrogen, named “platelets”. These defects have been related to the exfoliation mechanism on which a newly developed process to transfer thin films of silicon onto various substrates is based. In a previous paper, we have shown that these platelets undergo a quasi-conservative Ostwald ripening upon annealing. The measurement of the pressure within such pressurised gas-filled cavities is important to understand and simulate both the growth of these defects and the exfoliation mechanism. To extract this pressure from TEM studies, we have developed and tested an analogy between the platelets and a well-known 2D defect: a dislocation loop. The comparison between simulations of the image of the strain field surrounding a fictitious dislocation loop and experimental TEM images of the platelets shows that the platelets can be described by a Burgers vector of about 0.6nm. Moreover, this vector can be used to deduce the pressure of the molecular hydrogen within a platelet. A typical value of 10 GPa is found for a platelet of 20 nm in diameter at room temperature. Consequently, the atomic density of hydrogen within a platelet and the total number of hydrogen trapped by a population of platelet can be calculated and give reasonable values when compared to the implanted dose.

Atomic scale structure of (001) hydrogen-induced platelets in germanium

An accurate characterization of the structure of hydrogen-induced platelets is a prerequisite for investigating both hydrogen aggregation and formation of larger defects. On the basis of quantitative high resolution transmission electron microscopy experiments combined with extensive first principles calculations, we present a model for the atomic structure of (001) hydrogen-induced platelets in germanium. It involves broken Ge-Ge bonds in the [001] direction that are dihydride passivated, vacancies, and trapped H(2) molecules, showing that the species involved in platelet formation depend on the habit plane. This model explains all previous experimental observations.

Structural transformation in the formation of H-induced (111) platelets in Si

On the basis of first-principles calculations, we present a structural model for the formation of H-induced (111) platelets in Si, which involves a structural transformation from a double-layer-H2(*) configuration of H2(*) aggregates into an H-saturated internal (111) surface structure. This reaction process preferably occurs at high H plasma treatment temperatures and subsequently generates H2 molecules in the platelet voids, consistent with experiments. Our model also reveals the important features observed in (111) platelets, such as high-resolution transmission electron microscopy images, step structures, lattice dilation lengths, and H vibrational frequencies.

Hydrogen interaction with dislocations in Si

An H plasma has a remarkable effect on dislocation mobility in silicon, reducing its activation energy to 1.2 eV. Applying density functional theory to the interactions of H and H2 with the core of the 90 degrees partial dislocation in Si, we have identified a path for motion involving kink formation and migration at hydrogenated core bonds which conforms exactly to the experimentally measured activation energy.

Structure analysis of defects in nanometer space inside a crystal: creation and agglomeration of point defects in Si and Ge revealed by high-resolution electron microscopy

Recent structural studies of point-defect-agglomerates in Si and Ge by high-resolution transmission electron microscopy (HRTEM) are compiled along with some new results. After examining the wave nature of incident electrons on defect formation during HRTEM observation and the correlated recombination of point defects under electron irradiation, we show that HRTEM is the unique means to analyze the atomic structure of small agglomerates of point defects, nanometer in size, inside a crystal. Emphasis is placed on the extension of studies made possible only by the elaborate and crucial structure determination by HRTEM: the mechanism of agglomeration at the atomic level, the extraction of novel unit structures of point defects, and the electronic structure of the agglomerate. Some examples on the subjects are demonstrated in cases of the [113] and [001] defects. The effect of specimen surfaces on structure determination is also discussed. Finally, a development of TEM technique with in-situ optical spectroscopy is described, which is utilized to pursue interaction of point defects under electron irradiation and thus may reinforce HRTEM experiments.