Hydrogen blistering of silicon: Progress in fundamental understanding

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, Rutherford 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.