Real-time spectroscopic ellipsometry study of the growth of amorphous and microcrystalline silicon thin films prepared by alternating silicon deposition and hydrogen plasma treatment

The growth of amorphous and microcrystalline silicon (μc-Si) films prepared by alternating the deposition of hydrogenated amorphous silicon (a-Si:H) and hydrogen plasma exposure is studied by in situ spectroscopic ellipsometry. The deposition and etching sequences are clearly identified in the real-time ellipsometric trajectories. Insights into the growth of amorphous and microcrystalline silicon materials are obtained from a detailed study of the effects of varying the deposition and hydrogen plasma treatment times as well as the thickness dependence of the film composition. Indeed, we have found that the composition of amorphous and microcrystalline films slowly changes with the increasing film thickness. However, while a-Si:H films becomes porous and rough with the increasing number of cycles, μc-Si films become denser and their crystalline volume fraction increases. During growth, the transition from a-Si:H to μc-Si deposition occurs through an intermediate highly porous a-Si:H phase. We suggest that this porous phase is a key element in μc-Si nucleation, while both selective etching and chemical annealing have to be considered in the growth of the crystallites. Our results show that it is possible to increase the volume fraction of the crystalline phase by reducing the deposition time within one cycle or by increasing the hydrogen plasma treatment time.