Excimer surface treatment of sol-gel coatings

Sol-gel coatings are finding increased applications in fields as diverse as traditional optical coatings (eg anti- and high-reflectance) and microelectronic devices. Following the deposition process heat treatment is required to densify or crystallize the films. The disadvantage of conventional heat treatment, by hot plate or oven, is the limit on temperature and time set either by the thermal stability of the material or by interactions between film and substrate. A study has been made of the use of excimer lasers for heat treatment of PZT (pbZrO(3):PbTiO3) sol-gel films, the main application being pyroelectric detector arrays. For PZT,heat treatment is required to convert the deposited amorphous sol-gel film into the perovskite phase. The degree of crystallisation is measured using X-ray diffraction. The aim of this work was to anneal PZT using an excimer laser without causing temperature excess at the surface or inside the substrate. The efficiency of the annealing process varies with the laser wavelength (lambda), the film thickness (e) and the pulse duration. For each thickness modelling has been used to derive the optimum combination of lambda and e. For example, a wavelength of 351nm is matched to a thickness of about 1 mu m and a relatively long pulse (similar to 0.5 mu s). The laser systems and beam homogenizers used for the experiments will be described. Perovskite films have been successfully produced and results will be presented, both theoretical and experimental, covering a range of irradiation conditions. This work has been supported by the European Commission under Brite-Euram contract BE-3723 (MOSTOF). The contribution of R Wright and A. Patel of GEC-Marconi Infra-red who supplied the PZT samples is acknowledged.