EXCIMER-LASER-ASSISTED RF GLOW-DISCHARGE DEPOSITION OF AMORPHOUS AND MICROCRYSTALLINE SILICON THIN-FILMS

We combine the deposition of Hydrogenated amorphous Silicon (a-Si:H) b y rf glow discharge with XeCl-excimer laser irradiation of the growing surface in order to obtain different kinds of silicon films in the sa me deposition system. In-situ UV-visible ellipsometry allows us to mea sure the optical properties of the films as the laser fluence is incre ased from 0 up to 180 mJ/cm2 in separate depositions. For fixed glow-d ischarge conditions and a substrate temperature of 250-degrees-C we ob serve dramatic changes in the film structure as the laser fluence is i ncreased. With respect to a reference a-Si:H film (no laser irradiatio n) we observe at low laser fluences (15-60 mJ/cm2) that the film remai ns amorphous but demonstrates enchanced surface roughness and bulk por osity. At intermediate fluences (80-165 m/Jcm2), we obtain an amorphou s film with an enhanced density with respect to the reference film. Fi nally, at high fluences (165-180 mJ/cm2), we obtain microcrystalline f ilms. The in-situ ellipsometry measurements are complemented by ex-sit u measurements of the dark conductivity, X-ray diffraction, and Elasti c Recoil Detection Analysis (ERDA). Simulation of the temperature prof iles for different film thicknesses and for three laser fluences indic ates that crystallization occurs if the surface temperature reaches th e melting point of a-Si:H (almost-equal-to 1420 K). The effects of las er treatment on the film properties are discussed by taking into accou nt the photonic and thermal effects of laser irradiation.