DOWNSTREAM MICROWAVE PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION OF SiO₂ USING O₂/SiH₄ AND N₂O/SiH₄ MIXTURES

Abstract
The deposition of silicon dioxide by downstream microwave plasma-enhanced chemical vapor deposition (PECVD) has been investigated. A comparative study of the properties of oxide layers deposited at a pressure of 200 mtorr with two different oxidizing gases (N₂O or O₂) is reported. Particular emphasis is given to the influence of the substrate temperature and reactive gas ratio R = oxidant flow/silane flow on the deposition rate, mechanical stress, refractive index and etch rate. The results show that the properties of silicon oxide films are dependent on temperature below 400°C. But for this temperature and a gas ratio R=1, films are roughly equivalent and independent of the nature of the oxidizing gas used. Indeed they exhibit similar refractive index (≈ 1,47), etch rate (≈ x 3 current thermal oxide), 2.10⁹ dynes/cm² tensile stress, Si-H and Si-OH bonding present in infrared spectra. Nevertheless, the growth rates are very different for O² and N²O, 5 um/min and 1,5 um/min respectively, but significantly higher that those commonly achieved with classical PECVD methods. Moreover, it is shown that under appropriate process variable conditions, the deposited films are suitable for dielectric passivation applications.