Invited Paper PS+TF-ThM5
Plasma Production of Silicon Clusters and Nanocrystalline Silicon Particles : A New Route for Nanostructured Silicon Thin Films
The study of silane plasma deposition is important due to the large number of large area devices based on amorphous silicon. When transferring research results to production, deposition rate, uniformity, and powder formation are key issues. In this respect, the study of square-wave modulated discharges revealed that silicon nanocrystals (powder precursors) can be produced even at room temperature. This result has motivated for the work on plasma conditions near the onset of powder formation, to produce better-structured silicon thin films in which silicon clusters, and crystallites formed in the plasma contribute to deposition. Among the nanostructured materials we produced thus far, most work has focused on polymorphous silicon films because they share the high optical absorption of a-Si:H while having improved transport properties. In this presentation we review our recent work on the production, the characterization, and the study of devices based on this new material. The challenging issue of nanoparticle detection in the plasma is addressed with new techniques such as cavity ring down and impedance measurements. Moreover, in situ ellipsometry was used to study the growth and to determine the thermal gradient for which nanoparticles can reach the substrate. In conclusion, the precise control of the size and concentration of nanocrystalline silicon particles in the plasma opens the way to the nanoelectronics field in which the plasma-produced nanocrystallites can be passivated, coated, and incorporated into devices such as non-volatile memories. This is in our opinion an important challenge for the plasma community in the next few years.