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Application of low-temperature PECVD is a very tempting option for formation of ultrathin silicon layers for nanoelectronic and nanophotonic applications, as followed by annealing of this layer, regardless if executed as individual process performed in controlled ambient or during following high-temperature processes, allows for phase and content changes in the silicon layer. Understanding complex changes that can take place during such process, which depend on its temperature, conditions (e.g., oxygen availability), and timeframe, is a fundamental requirement for conscious application of such technology. It is worth realizing that nanodevices with their unprecedented variety of structures and devices require many different fabrication technologies. Hence, depending on the application in mind, different results of ultrathin silicon layer annealing may appear advantageous. During high-temperature processing (e.g., annealing) of PECVD ultrathin silicon layer, three competing effects have to be taken into account. These are amorphous silicon recrystallization and oxidation of amorphous and crystalline (as-deposited or just recrystallized from as-deposited amorphous phase) silicon (both of which by nature exhibit different kinetics). So far, most of attention has been paid to silicon recrystallization, which was justified by the fact that under experimental conditions studied (silicon multilayers) oxidation was certainly of less importance. In certain applications, the required device structure consists of single (and not multiple) ultrathin silicon layer, and thus, oxidation effects certainly have to be included into considerations. Understanding dynamics and very complex relations between these individual effects is thus mandatory for using consciously this technique and achieving needed properties of the layer. It has to be stated clearly that although the achieved results, presented in this study, refer to the silicon layers fabricated under certain conditions (particular type of PECVD reactor and process parameters), they can, however, be easily extrapolated for similar cases too. The presented below results are, to our knowledge, the first successful attempt to address these issues.

In this work we have studied relations between three competing effects that take place during high temperature annealing of PECVD ultrathin silicon layer, namely: amorphous silicon recrystallization, amorphous silicon oxidation and oxidation of just received crystalline silicon in the first few minutes of this process. Understanding very complex relations between these kinetics is essential to allow for conscious manipulating of annealing and/or oxidation parameters in order to achieve different results, depending on the application in mind. The presented below results are, to our knowledge, the first attempt to address these issues.

Nanoelectronic and nanophotonic applications have created a pressure on methods of fabrication double dielectric barriers stacks with ultrathin silicon layer located between dielectric layers. Among numerous possible methods, PECVD seems to be very promising. In order to increase possible number of applications, however, the ability to transform continuous silicon layer into nanocrystalline form in dielectric matrix is required. The work described below reports on experimental efforts to form such a structure by controlled high temperature recrystallization and oxidation of ultrathin PECVD silicon layer in the stack. The effects if high temperature annealing has been studied by spectroscopic ellipsometry. The applied model allowed for identification of composition and structural changes within the silicon PECVD layer due to different high temperature annealing processes applied. As a result of this study, it has been proved that it is feasible to fabricate complete two barrier stack consisting of ultrathin dielectric and silicon layers in one PECVD system without exposing samples to the ambient atmosphere. In order to reduce the PECVD silicon layer thickness to approximately 3 nm, we proposed using plasma oxidation in PECVD instead of PECVD oxide deposition. High temperature (especially in 1100°C) annealing in argon proved to allow formation of silicon nanocrystals in oxide matrix. Other effects resulting from high temperature annealing of fabricated stacks are also studied.