1. INTRODUCTION
Anisotropic chemical etching has long been used for
fabricating microstructures such as diaphragms and cantilevers
on a silicon wafer. The demand for more complicated 3-D
microstructures on a silicon chip is increasing in various
applications such as ink-jet printing devices and microfluidic
systems. We think it necessary to know the etching rates for a
number of crystallographic orientations, in order to fabricate
3-D microstructures whose profiles are composed of a number
of facets having different orientations. When the etching rate
is known as a function of orientation, etchant, and etching
conditions, one can design fabrication processes of 3-D
structures by simulating the etched product’s shape using a
variety of mask patterns under different process conditions,
including multiple process steps [ 1][2].
KOH water solution has been most commonly used as an
anisotropic etchant for fabricating microstructures. Thus we
first started to construct an etching rate database with KOH
solutions, and reported that the orientation dependence varies
according to the KOH concentration and etching temperature
[3]. Recently, TMAH water solution has started to be gradually
introduced in industry, despite its expense, taking the place of
KOH solution. This is because it hardly attacks the silicon
dioxide film used as an etching mask and it does not contain
harmful ions that might damage the electrical circuits integrated
on the same chip with micro mechanical structures. Thus we
further investigated the orientation-dependent etching
properties of silicon in TMAH solutions [4]. In this paper, we
discuss the difference in anisotropic etching properties of silicon
between KOH and TMAH systems.