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.
1. INTRODUCTIONAnisotropic chemical etching has long been used forfabricating microstructures such as diaphragms and cantileverson a silicon wafer. The demand for more complicated 3-Dmicrostructures on a silicon chip is increasing in variousapplications such as ink-jet printing devices and microfluidicsystems. We think it necessary to know the etching rates for anumber of crystallographic orientations, in order to fabricate3-D microstructures whose profiles are composed of a numberof facets having different orientations. When the etching rateis known as a function of orientation, etchant, and etchingconditions, one can design fabrication processes of 3-Dstructures by simulating the etched product’s shape using avariety of mask patterns under different process conditions,including multiple process steps [ 1][2].KOH water solution has been most commonly used as ananisotropic etchant for fabricating microstructures. Thus wefirst started to construct an etching rate database with KOHsolutions, and reported that the orientation dependence variesaccording to the KOH concentration and etching temperature[3]. Recently, TMAH water solution has started to be graduallyintroduced in industry, despite its expense, taking the place ofKOH solution. This is because it hardly attacks the silicondioxide film used as an etching mask and it does not containharmful ions that might damage the electrical circuits integratedon the same chip with micro mechanical structures. Thus wefurther investigated the orientation-dependent etchingproperties of silicon in TMAH solutions [4]. In this paper, wediscuss the difference in anisotropic etching properties of siliconbetween KOH and TMAH systems.
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