Preparation and optical characterisation of APCVD BPSG thin films used for micromachining applications

APCVD films of borophosphosilicate glass with different content of phosphorus and boron was studied as masks for etching in KOH solution. Via the dopant content (B and P) in the as-deposited glasses we can control the etch rate and the stress in the layers. The effect of the proposed densification treatment on the BPSG films is investigated using spectroellipsometry and Wemple Di Domenico approximation. The experiments lead to the conclusion that the best solution is densified thick multiple layers-SiO/sub 2/-BPSG (4 wt.%P, 11 wt.%B)-SiO/sub 2/. The densification treatment used is compatible with the aluminium metalisation process.