REAL-TIME SPECTROSCOPIC ELLIPSOMETRY STUDY OF THE GROWTH OF AMORPHOUSAND MICROCRYSTALLINE SILICON THIN-FILMS PREPARED BY ALTERNATING SILICON DEPOSITION AND HYDROGEN PLASMA TREATMENT

The growth of amorphous and microcrystalline silicon (mu c-Si) films p repared by alternating the deposition of hydrogenated amorphous silico n (alpha-Si:H) and hydrogen plasma exposure is studied by in situ spec troscopic ellipsometry. The deposition and etching sequences are clear ly identified in the real-time ellipsometric trajectories. Insights in to the growth of amorphous and microcrystalline silicon materials are obtained from a detailed study of the effects of varying the depositio n and hydrogen plasma treatment times as well as the thickness depende nce of the film composition. Indeed, we have found that the compositio n of amorphous and microcrystalline films slowly changes with the incr easing film thickness. However, while alpha-Si:H films become porous a nd rough with the increasing number of cycles, mu c-Si films become de nser and their crystalline volume fraction increases. During growth, t he transition from alpha-Si:H to mu c-Si deposition occurs through an intermediate highly porous alpha-Si:H phase. We suggest that this poro us phase is a key element in mu c-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 t ime within one cycle or by increasing the hydrogen plasma treatment ti me.