Microstructures etched in doped TMAH solutions

Term-methyl ammonium hydroxide, or TMAH, is an anisotropic silicon etchant that is gaining more and more attention in the fabrication process of mecha nical microstructures and device isolation, as an alternative to the more u sual KOH and EDP etchants [1]: because of its high compatibility with conve ntional IC processes, due to the absence of metal ions in it. The possibili ty to passivate the aluminum metalisation in properly saturated TMAH soluti on has also been demonstrated by doping the solution with appropriate amoun ts of silicon or silicic acid [2, 3]. This increases the range of applicati on of these etchants, simplifying both the post processing and the etch set -up configuration. In this paper we present some different technological so lutions adopted for the fabrication of 3D structures using as anisotropic e tchant eloped TMAH solutions. The effects of the the additives on etch unif ormity and surface roughness are studied. Using the etching results under d ifferent doping conditions of the TMAH solutions, we obtained silicon bulk- micromachined structures with controlled surface roughness. Furthermore the aluminium passivation permits to etch devices with no protection of the me talisation layers as some applications require (i.e. bolometers).