Silicon-on-insulator (SOI) wafers are precisely engineered multilayer semiconductor/dielectric structures that provide new functionality for advanced Si devices. After more than three decades of materials research and device studies, SOI wafers have entered into the mainstream of semiconductor electronics. SOI technology offers significant advantages in design, fabrication, and performance of many semiconductor circuits. It also improves prospects for extending Si devices into the nanometer region (<10 nm channel length). In this article, we discuss methods of forming SOI wafers, their physical properties, and the latest improvements in controlling the structure parameters. We also describe devices that take advantage of SOI, and consider their electrical characteristics.

Frontiers of silicon-on-insulator

The Smart-Cut® process, based on ion implantation (hydrogen, helium) and wafer bonding, appears more and more as a generic process. The first part of the paper is dedicated to the specific case of thermally-induced splitting. Cavity growth by the Ostwald ripening mechanism and crack propagation are responsible for thermally-induced splitting. In this case, the splitting kinetics are controlled by hydrogen diffusion. In the second part, the latest results concerning new structures are presented.

The generic nature of SmartCut process for thin film transfer

When silicon is implanted with a sufficient concentration of H ions, at low to moderate temperature, and subsequently annealed at high temperature, dome-shaped gas-filled blisters and/or craters of exploded blisters appear on the surface. Under particular conditions, blistering can be produced by plasma hydrogenation as well. The phenomenon is another facet of hydrogen behaviour in silicon, a question with both fundamental and applied implications. Blistering is at the origin of the "ion-cutting" process for the fabrication of silicon-on-insulator and other heterostructures; this process is particularly useful whenever atomically sharp interfaces between layers are required. The novelty and vast potential of this process has spurred since the mid-1990's a burst of experimental activity on blistering. The purposes of those works were either to improve or extend the ion-cut process, or to clarify its underlying mechanisms. In "mechanisms", the plural is used to convey the fact that it is a multi-step phenomenon. Because of this complexity, the theoretical work, in comparison, is far less abundant. Hydrogen blistering of silicon is qualitatively understood in broad terms: H being insoluble in Si, it tends to segregate into cavities which grow and coalesce at high temperature, and the H 2 pressure in the cavities finally deforms the surface. In fact, our understanding of the microscopic mechanisms has progressed much beyond that level thanks to the sophisticated work that has been carried out using techniques such as transmission electron microscopy, Ruther-ford backscattering in the channelling mode, infrared spectroscopy of local vibrational modes, stress and strain measurements, and others. The effects of n- or p-doping, He ion coimplantation, and isotope substitution have also greatly helped in discriminating between different hypotheses. After a review of the most relevant experimental facts, the blistering mechanisms that have been proposed in the literature will be discussed and their conformity with the data assessed. Finally an attempt will be made to identify the key questions and suggest a few avenues for future work.

Hydrogen blistering of silicon: Progress in fundamental understanding

Mechanics of Smart-Cut ® technology

The orientation effect on blistering phenomenon in H implanted Si was studied for (100), (111), and (110) Si wafers. It was found that substrate orientation has no observable effects on the underlying blistering mechanisms. Furthermore, the implantation damage, Si–H complex formation in as-implanted samples and surface roughness of the transferred layer appeared to be unaffected by the orientation. However, the blistering kinetics are orientation dependent, with (100) Si having the fastest blistering rate, and (110) Si the slowest. This dependence was attributed to the different density of ruptured Si–Si bonds of different orientations. The magnitude of the observed in-plane compressive stress in the H-implanted Si wafers is rationalized in terms of the formation of platelets in the samples.

Orientation dependence of blistering in H-implanted Si

Proton implantation and thermal annealing of silicon result in the formation of a specific type of extended defects involving hydrogen, named “platelets” or “cavities.” 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. The density and the size of these platelets depend on the implantation and annealing conditions. In this letter, rigorous statistical methods based on transmission electron microscopy have been used to quantitatively study the thermal behavior of these defects. Upon annealing, it is shown that the cavities grow in size, reduce their density, while the overall volume they occupy remains constant. This phenomenon is due to a conservative ripening of the cavities. The transfer of hydrogen atoms from small to large cavities leads to a decrease of the elastic energy within the implanted layer while the strain locally increases around the projected range of the protons.

L. Laanab

Papers

A transmission electron microscopy quantitative study of the growth kinetics of H platelets in Si