Plasma deposition of hydrogenated amorphous silicon studied using in situ multiple total internal reflection infrared spectroscopy

Plasma deposition of hydrogenated amorphous silicon films from SiH ₄/Ar discharges is investigated using in situ multiple total internal reflection Fourier transform infrared spectroscopy (MTIR-FTIR) and spectroscopic ellipsometry (SE). A technique is developed that combines surface-sensitive, attenuated total reflection (ATR-) FTIR and a brief Ar + assisted desorption of the surface hydrides to obtain the surface hydride composition as a function of the substrate temperature and ion flux impinging on the surface. As expected, fewer higher hydrides exist on the surface at elevated deposition temperatures. Based on the IR data, a set of thermally activated surface reactions in which higher hydrides decompose sequentially via reaction with dangling bonds is proposed. The rate of dangling bond generation through ion sputtering is manipulated by varying the plasma power. Monitoring the surface species as a function of ion bombardment over a range of substrate temperature reveals a synergy between thermal activation and ion flux.; In situ MTIR-FTIR is used to monitor the bulk hydrogen concentration in real time while in situ spectroscopic ellipsometry enables the simultaneous determination of the thickness and the index of refraction of films grown under the various conditions. Thus, the relation between the surface reactions, surface composition, and the properties of the bulk film is investigated, with particular focus on understanding the mechanism of H incorporation into the bulk. The H concentration depth profiles in the a-Si:H films are obtained in situ by employing a new technique that combines CF₄ plasma etching with MTIR-FTIR. The CF₄ plasma was used to etch the film in sequential layers from the surface while the average H concentration in each slice of film was monitored using MTIR-FTIR. This procedure yields the H depth profile in the film at a resolution of ∼30 Å. During plasma deposition, when ions and photons interact with growing film, a region just below the H-rich surface layer and approximately 20% of the total film thickness is found to be H-depleted relative to the bulk film. In the absence of ion and photon irradiation, the H-depletion layer is not observed.