Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Crescent Shaped Alignment Marks Applicable to
Self-alignment of Micro-parts with and without
Positive and Negative Poles
Shouhei Shiga 1 , Dong F. Wang 1 , Takao Ishida 2 , and Ryutaro Maeda 2
1
Micro Engineering & Micro Systems Laboratory, Ibaraki University (College of Eng.), Hitachi, Ibaraki 316-8511 Japan
(Tel: +81-294-38-5024; Fax: +81-294-38-5047; E-mail: dfwang@mx.ibaraki.ac.jp)
2 Ubiquitous MEMS and Micro Engineering Research Center (UMEMSME), AIST, Tsukuba, Ibaraki 305-8564, Japan
Abstract
A “crescent-shaped” binding alignment mark, more
applicable to the self-alignment than reported
“tear-drop/elliptical hole” pattern, has been designed and
comparatively studied with other possible alignment marks. In
order to further apply this novel design to micro-parts with
positive and negative poles on the binding sites, a modified
“crescent-shaped” pattern with an insulated space area, defined
as “crescent-shaped/interval” for self-alignment of micro-parts
with two poles has been therefore proposed and discussed. The
fabrication process using micromachining has been studied and
both the substrates and micro-parts with alignment marks have
been fabricated for next self-alignment verification.
Keywords- Self-alignment; Alignment mark; Crescent-shaped
pattern; Surface energy, Overlap ratio; Crescent-shaped/interval
pattern; Positive and negative poles
I. INTRODUCTION
The integration of micro-parts in alignment with an
integrated circuit is a highly important task in assembly process.
In any case, a uni-directional control is required since dies,
packaging or optical elements, i.e. LED etc., must be positioned
to the corresponding sites of the substrate with the correct
angular orientation.
In stead of complicated robotic manipulation or principled
restriction in traditional lithography, fluidic self-assembly
(FSA) is becoming an emerging technology for its high
efficient in-parallel registration or three-dimensional automatic
alignment. Current self-assembly techniques for micro-scale
parts are based on two major mechanisms. One is
capillary-driven self-assembly [1-2] and the other is
shape-directed self-assembly.
The size effect of square micro-parts on the capillary-driven
interaction between the square micro-parts and the square
binding sites was previously studied [3], and the interaction can
be confirmed until 0.3 mm parts × 0.3 mm binding sites.
A two-dimensional alignment mark of a tear-drop/elliptical
hole with a tip angle of 60 o [4] was developed to increase the
recovery angle and reduce the energy barrier to uni-directional
micro-part alignment. The work reported that the standard
deviation of the aligned angular orientation was 0.9 o and the
lateral accuracy was 15 μm; the re-aligned assembly yield was
100 %.
In this study however, a two-dimensional asymmetric
“crescent-shaped” alignment mark has been newly designed
and a “crescent-shaped/interval” pattern has been further
proposed to be applicable to micro-parts with two poles.
Ⅱ. SELF-ALIGNMENT PRINCIPLE
For the FSA process herein, self-alignment is caused by
capillary force, which occurs between lubricant and SAM.
When micro-parts are introduced onto adhesive droplets on
binding sites (receptor sites), their hydrophobic faces (usually
gold faces) can be attracted to the adhesive droplets. The
Au-patterned side of each micro-part that is shown in Fig. 1 is
hydrophobic and the other side is hydrophilic. In this case
(a)
(b)
Si SAM Lubricant
Fig. 1. Schematic illustrating self-alignment, (a): Parts move and rotate with an
angle of θ for coincidence; (b):Using uni-directional Au pattern, part is
self-aligned to the determined direction.
180