Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Convex Corner Compensation for a Compact Seismic
Mass with High Aspect Ratio Using Anisotropic Wet
Etching of (100) Silicon
Jyh-Cheng YU
National Kaohsiung First University of Science and Technology
2 Jhuoyue Rd.,Nanzih , Kaohsiung City 811,Taiwan, R.O.C.
Abstract - This paper reports a novel convex corner
compensation design for a compact seismic mass of high aspect
ratio using KOH etching of (100) silicon. Anisotropic wet
etching is often applied to fabricate a seismic mass due to cost
advantage. Dimension of the convex corner compensation
pattern is in proportional to etching depth, which restrain the
miniature of seismic mass and supporting beams. If the width
of the seismic is too small, overlap of compensation pattern
occurs to cause a compensation failure. This study presents a
corner compensation for a mesa with high aspect ratio using
oriented compensating bands augmented with a
mandatory separation and a -oriented beam to the
truncated bands due to the overlap of adjacent
compensation patterns. An empirical equation is presented from
the simulation of anisotropic etching using Intellisuite. The
design can produce a satisfactory wet etching mesa with the
aspect ratio of 0.6, while a typical oriented
compensating bands can only applied to a mesa with a largest
aspect ratio of 0.35. A mesa is etched using 30%, 80°C KOH to
verify the design feasibility.
I. INTRODUCTION
Mesa with thin supported beams is a typical configuration
for inertia sensors [2][3][4] as shown in Figure 1. Wet bulk
micromachining processes of (100) silicon such as KOH and
TMAH are widely used to the fabrication of the seismic mesa
due to cost advantages in comparison with dry etching [1].
However, corner compensation pattern is required in the mask
design for protrusion corners to prevent undercut in wet
chemical etching as shown in Figure 2.
Various compensation patterns were proposed to such as
simple squares, triangles, oriented bands,
oriented band with narrow beams, etc. [5][9]. The
compensation of simple oriented bands is widely
applied because perfect shaped convex corners can be produced.
The width of the band is twice the etching depth and the length
of the band depends on the etch rate of the {411} plane relative
to the {100}. Typical length for KOH etching is about 3.2 times
of etching depth as shown in Figure 3 [6].
Figure 1 Typical configuration of a inertial sensor
{111}
{110}
{001}
151.9°
{411} {411}
{111}
{110}
Figure 2 Appearance of fast etching planes at the convex corner during
anisotropic etching
Figure 3 Dimensions and successive etched shape of the oriented
compensating beam [6]
Since the size of the compensation pattern is in proportional
to etching depth, which refrains from further miniature of the
devices with convex corners. If a typical band
compensation is used, the constraints among the size of the
197