Hydrogen interactions with silicon-on-insulator materials

The booming of microelectronics in recent decades has been made possible by the excellent properties of the Si/SiO2 interface in oxide on silicon systems.. This semiconductor/insulator combination has proven to be of great value for the semiconductor industry. It has made it possible to continuously increase the number of transistors per chip until the physical limit of integration is now almost reached. Silicon-on-insulator (SOI) materials were early on seen as a step in the logical evolution of integrated circuit technology. The basic advantage of the SOI technology is that it keeps the active elements of the integrated circuits electrically insulated from each other, forming Si islands. This prevents undesired effects like parasitic capacitances or cross-talk between devices and improves critical transistor design parameters such as the current gain or the subthreshold characteristics. It turns out that integrated circuits based on SOI materials are very appropriate for applications at high temperature, in hostile environments or in situations in which severe demands are made on power consumption. Despite these advantages, the development of adequate methods for the fabrication of SOI materials is a relatively recent achievement that in the end has led to the commercial use of SOI-based technology in microelectronics. Nowadays, Unibond is the most successful SOI material. Unibond samples are fabricated by the so-called SmartCut method as described in Chapter 1. SIMOX (separation by implantation of oxygen) is another important SOI material. As the name indicates, a SiO2 layer is formed underneath a crystalline Si layer by oxygen implantation in a Si substrate and subsequent high temperature annealing. In contrast with conventional thermal oxidation of Si to form SiO2 insulating layers, SOI materials are fabricated in rather intrusive ways. This leads to the appearance of new defects in SOI materials, which requires special study. Particularly, the buried oxides of SOI materials are in general more defective than conventional thermal oxides. The interaction with the ubiquitous hydrogen is of importance in view of the large number of degradation effects in which hydrogen is involved. Examples are: trap creation, donor generation at the Si/SiO2 interface, depassivation of dangling bonds, generation of states in the Si band gap or formation of complexes with shallow dopant impurities. In the case of SOI materials, the occurrence of these effects may be enhanced for various reasons, e.g., the presence of hydrogen in large amounts as observed for SIMOX, the presence of H2 cracking sites, the existence of stress in the films or the confined nature of the buried oxide. This thesis intends to be a contribution to the understanding of the defect mechanisms. SIMOX and Unibond samples were brought into contact with hydrogen (or deuterium) by different methods. The interaction of hydrogen with the samples was studied by a number of techniques, in particular thermal desorption spectrometry (TDS), positron beam analysis (PBA) and capacitance-voltage measurements (CV). The first two techniques are not standard in semiconductor research, and it required a technical effort to adapt them to semiconductor studies. In the thesis it is shown that useful information can be obtained with the combined use of these techniques.Applied Science