Some particular aspects of the thin membrane by boron diffusion processes

Micromachining techniques have an increasing importance in the development of microsensors applications. For free standing 3D structures bulk and surf ace micromachining are used. This paper presents experimental results conce rning thin membranes, realized by p(+) etch stop techniques. We obtained a concentration of 1 X 10(20) cm(-3) through thermal diffusion from boron(+), solid source by a performed program (thermal cycles). This value is enough for stop-etch layer in anisotropic etching of silicon (100) in KOH solutio n at 80 degrees C. Spreading resistance has measured the boron profile. The wafers were processed in two ways. Some of them were boron diffused over t he entire area of the wafer and other were diffused only in pattern geometr ies, defined in silicon after thermal oxidation. In this case, we have used double side alignments. We define square geometries for the membranes, wit h 1.5 and 2.5 mm(2) areas. The performance result could be noticed from the thickness of the membranes of 10-12 mu m with good uniformity on wafers. ( C) 1999 Elsevier Science S.A. All rights reserved.