Experimental study of the optical properties of LTCVD SiO2

Experimental results are presented on the optical and infrared properties of SiO₂, deposited on Si by means of low temperature thermal decomposition of silane with a mixture of oxygen, in a flowing nitrogen atmosphere. The experimental conditions during the deposition were chosen such that the decomposition of silane was sufficiently low for the growth of uniform and dense layers. Good control on thickness in the range 50 to 230 nm was obtained by selecting proper growth temperature and nitrogen carrier gas flow rate. It was found, experimentally, that the refractive index varies as a function of the SiO₂ thickness up to a certain point and only then attains its constant value. The Infrared absorption spectrum of the above films was studied in the range of 200 cm^-1 to 4000 cm^-1. The position and widths of the absorption bands at nominally 1070, 810 cm^-1 and 465 nm, and the changes in these as a function of thickness were used to shed light on the behaviour of the refractive index. It was also established that the absorption bands obey the Lambert-Bouguer law.