特集2 日仏マイクロメカトロニクス国際共同研究組織(LIMMS

FUJITA Hiroyuki

MITA Yoshio

Tixier-MITA Agnes

UTokyo Repository

研究速報 : Nano-structures fabrication
technique for biological applications
journal or
publication title
生産研究
volume 56
number 1
page range 105-108
year 2004
URL http://hdl.handle.net/2261/00078632
doi: info:doi/10.11188/seisankenkyu.56.105
56巻1号 (2004) SEISAN―KENKYU
‖||11111111111111111111111111111111111 111111111111111111111111111111111111111111111111111111111111111111111111111研 究  速
研 究 速 報
報
Nano-Structures Fabrication Technique for Biological Applications
Agnes Tixier-MITA*, Yoshio M[14** and Hiroyuki FUJITA*
ABSTRACT
We succeeded to realize nano-sffuctures using standard {100}
silicon wafers and anisotropic etching; this technique makes use of
the low etching rate in TMAH of {1ll} planes or silicon, in com-
parison to {100} planes, to adjusting the nanometric dimensions of
the structures. No sub-micron lithography is required in this
technique: it is compatible with normal UV photolithography.
Neither complicated process steps are required: a succession of
oxidation, oxide patterning and anisoffopic etching only are
needed. Nano-holes and nano-wires were made using this tech-
nique and possible applications of the structures are described for
two BIO-MEMS projects.
INTRODUCTION
In the BIO-MEMS field, tiny structures are of great interest
because of their dimensions close to the one of biological materi-
als. Actually, cells dimensions are from few microns, to several ten
microns. Proteins dimensions are until few ten microns. This is the
reason why nano-structures maybe essential to manipulate cells
without damaging them or to be able to analyse closer proteins.
The realization of nano-sffuctures is not directly possible with
normal LfV photolithography (the usual minimum realizable pat-
terns size is few microns). Sub-micronic lithography is possible
using direct writing on the wafer with an electron beam.
However, this is a very expensive technique which is time con-
suming. An other possibility is to perform a quite complicated
process using SOI wafert). But this technique, even if it gives very
precise dimensions, requires expensive equipments and is time
consuming too.
In this article, a cheap, simple and robust technique is proposed
to realize nano-structure. The advantages of this technique are as
follows:
- standard {100} silicon wafers can be used (no SOI needed);
- standard UV photolithography can be used (no EB lithography
*Institue 
of Industrial Sciences, The University of Tokyo
* *Department 
of Electric Engineering, the University of Tokyo
needed):
- the structures are rcalizable using oxidation and anisotropic
etching with KOH and TMAH only.
The key of the technique is to take advantage of the slow silicon
etching rate of the { I I 1 } planes in TMAH, compared to { 100}, to
control the dimensions of the nano-structures very precisely. The
ratio between {l1l} and {100} etching rates is reported IBO?).
The principle of the fabrication technique will be first
described, then two examples of fabricated nano-structures
(nano-holes and nano-wires) will be shown; finally examples of
application in the BIO-MEMS field will be explained.
PRINCIPLE OF THE FABRICATION TECHNIQUE
The principle of the fabrication technique is described on the
scheme Figure 1. The fundamental idea is to fabricate intercon-
nected shapes made by anisotropic etching, in a way that their
interconnections form a nano-structure.
Figure l: Principle of the fabrication technique to realize nano-
sructures.
|||||IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIllllllllllllllllllllllllllllllIIIIIIIIIIIIIIIIIIIIIIIIIIlllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllIIIIIIIIIIIIIIIllIIIIIIIIIIII
Lithography.
oxidation
+
Lithography:
Znd SiOZ mask palterning
研 究
56巻1号  (2004) SEISAN¨KENKYU
速
All masks used for the anisoffopic etchings are in SiO2, realized
by thermal oxidation. SiO2 is used as a mask for two reasons: first,
thermal oxidation is cheap and easy to be made; second, this mask
is almost not etched in TMAH (the ratio of SiO2 etching rate and
Si etching rate in TMAH l5%o at80 C is about 104; and only slow-
ly etched in KOH (the same ratio in KOH 337o at 80C is about
s.10'1.
The first anisohopic etching with KOH allows to obtain patterns
with precise dimensions defined by the SiO2 mask: there is
almost no etching of {111} planes with KOH [12]. The structure
obtained in this way has the same dimensions in width and
length as the SiO2 mask.
The second anisotropic etching with TMAH allows to fabricate
the nano-structures, adjusting their dimensions by controlling the
etching time of the {111} planes. Actually, TMAH slowly etches
the {111} plan of silicon, contrary to KOH which doesn't etch this
plan. This etching rate of {111} plans in TMAH rate l5%o was
measured approximatly, about 0.03,r,m/min at 80 C:. Taking
advantage of this slow etching, it is possible to conffol precisely by
time this under-etching of {111} plan and then the nano-structures
dimensions.
No exffemely precise alignment and lithography is required for
this process as the nanometric dimensions are dependent on the
etching time in TMAH only.In the two process presented in the
following part, and generally speaking for this technique, normal
tIV lithography can be used for the masks, with patterns even larg-
er than several microns or ten microns in dimensions.
During the process, an important step is to protect from
TMAH etching the structures made during the first KOH etching:
that is whv a second oxidation is essential. If there is not such a
Figure 2: Formation of holes, with TMAH etching, at the intercon-
nection between nuo V grooves, when there is or not SiO2
protection of one of the V grooves.
protection, the second V grooves interconnecting the first ones will
create a hole which size will increase very rapidly, following the
{100} plan etching rate, and not the {l1l} plan etching rate. On
Figure 2, a scheme explains this phenomena.
Two types of nano-structures were realized using this technique:
nano-holes and nano-wires.
EXAMPLES OF FABRICATION OF NANO.STRUC.
TURES: NANO-HOLES AND NANO-WIRES
These two structures are not the only one which can be made
with this technique.It is possible to imagine many other one, just
interconnecting in the right way shapes made by anisotropic etch-
ing. The nanometric dimensions of the structures is then adjusted
just by controlling the etching time of {111} plans in TMAH.
With anisotropic etching, it is possible to realize mainly two
kinds of shapes: V grooves shapes and rhombus grooves shapes.
The V groove shape is obtained by direct anisotropic etching of a
{100} silicon wafer through a rectangular mask. The rhombus
groove shape needs a supplementary vertical etching of silicon,
through the mask, before performing the anisotropic etching.
If standard V grooves are used, it is possible to realize holes
with nanometer size, by crossing perpendicularly a front-side V
groove with a backside V groove (Figure 3). At the intersection of
both grooves a tiny hole appears which dimensions depend only on
the etching time of the {111} planes in TMAH. A longer time in
TMAH will enlarge the hole, but with a rate slow enough to be
easily controllable.
V grooves on the frontside
(KOH etching}
holo attho■″o
Figure 3: 3 D scheme of system made with standard V grooves.
Tiny holes are obtained at the intersection between the
front-side V grooves and the backside V grooves.
Silicon wafer
at the t{Y
56巻1号 (2004) SEISAN‐KENKYU
速究 報
|  |
1) SiOZ mask patterning
cross‐sect on A配
2)Si etChing wlh KOH
3)2nd OXidation
4)BackSide si02 mask patternlng
cross-s6ction AA'
cross-sestion BBI
… … … … …
cross-section BB',
… … … …
cross-section AA'
cross secion AAi           cross sed on BB
5)Si etChlng wtth TMAH
亦 猾 ♂ 貯 肛 覺
6)Etchin9 of Si02 in HF
¶
cross-section BB'
cross-section BB'
Figure 4: Detailed process chart of the fabrication of nano-holes.
Figure 5: SEM pictures of holes obtained at the bottom of the front-
side V grooves, according to the scheme Figure 3. The
smallest ones obtained are 90 nm X 180 nm.
Figure 6: 3 D cross-section scheme of a system made with rhombus
channels. They are obtained by adding a step of vertical
etching of the substrate before each step of anisotropic
etching. Nano-wires are made by interconnecting two
rhombus grooves laterally.
1)Si02 mask patterning
十Si etChing wtth RIE
4)2nd Si02 mask patterning
+Si etching wth RIE
6)Longer etching wnh TMAH:
slow etching along{111}planeS.
7)BHF to remove Si02
8) Possible ultra-sonic balh
to recover ths nano-wires
形
5)Si etChing wtth TMAH
Figure 7: Process chart of the nano-wires fabrication. System seen in
cross-section.
Figure 4 shows the detailed process of the sfucture presented on
Figure 3.
One Figure 5 are shown SEM pictures of holes obtained with
this technique, with two different dimensions: 4pm width holes
and one of the smallest holes obtained: 90nm X 180nm.
If a vertical etching of silicon is performed before each
anisoffopical etching, the pattern shape is no more a V groove but
a rhombus3). Taking advantage of this shape, nano-wires can be
obtained by connecting two rhombus grooves together, in the lat-
eral direction (Figure 6 and 7). Here the two anisotropic etching
are both made on the front-side of the wafer. Again, the slow etch-
ing of {111} in TMAH allows precise control of the dimensions by
etching time. Nano-wires can be obtained with dimensions as
small as 100 nm in width and 15pm in length (Figure 8).
Both structures are really suitable for BIO-MEMS applications,
||||||IIIIIIIlllllllllllllllllllllllllllllllllllllllllllllIIIIIIIllll111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111lIIIIIIIIllllllllllllllllllllllllllllllllllllIIIIIlllllllllllllllllllllllll
mado by anis●trop c
etchings.          (m。
]
56巻1号 (2004) SEISAN‐KENKYU
究 速  報 |||||||||II I I I I I I I I I I I I IIIIII I II IIIIIII IIII I I IIII I I I I I I IIII I I I I I I I I  I II I I I I I I I I I I I I II I I I I IIIII IIII III研
Figure 8: SEM picture of the realized nano-wires: 100 nano-
metersin width and from 5 to 15 micrometers in length,
according to the mask pattern dimension.
because of their tiny dimensions.
EMMPLES OF APPLICATIONS
One application with yeast cells and an other with motor protein
are presented here.
The system with holes can be used to catch and to place cells
precisely on a chip, by performing aspiration through the holesa).
The aspiration creates a gentle water flow through each hole and
cells in the water are dragged towards them. Figure 9 shows yeast
cells (6pm in diameter) placed successfully as an iuray on holes.
The system used for this experiment had rectangular holes, Zpmin
width and several microns in length, because of the patterns
design. The design can be improved in order to obtain square
holes. Moreover, if smaller cells have to be placed in array, small-
er holes can be easily realizedjust reducing the etching time in
TMAH.In what concerns the nano-wtes, one possible application
is to recover these wires in solution (by performing ultra-sonic
bath) in order to attach them on motor-molecules. Although a
motor-moecule is too small to observe directly, the motion of
attached objects could indicate the motion of the molecule.
GONC.LUSIONS
In this article a cheap, simple and robust technique to make
nano-structrres with normal {100} silicon wafers and anisotropic
etching was presented. It takes advantage of the slow and con-
ffollable, but not neglectible, etching of {111} plans in TMAH to
adjust the nanometric dimensions of the structures.
Figure 9: Photos of the holes system: a) befote aspiration and b)
after aspiration ofyeast cells.
Two examples of realized nano-structures were described:
nano-holes and nano-wires. These sffuctures are really suitable for
BIO-MEMS applications because of their tiny dimensions, close to
the one of the biological materials.
ACKNOWLEDGMENT
Photomasks fabrication for this project is supported by VDEC
(VLSI Design and Education Center), the University of Tokyo.
(Manuscript received, November 18, 2003)
REFERENCES
1) Fabrication of twin nano-probes for nano-scale measurement;K.
Kakushima, M. Mita, G. Hashiguchi, H. Fujita, J. Endo, Y. Wada;
Technical Digest of the 17'h Sensor Symposium 2000; The
Institute of Electrical Engineers af Japan; pp. 427431; 2000.
2) Anisotropic etching of Si in TMAH Solutions; O. Tabata; znd
Workshop on Physical Chemistry of Wet Etching of Silicon, pp.-,
2000.
3) Fabrication of microchannels by laser machining and anisotropic
etching of silicon; M. Alavi, S. Buttgenbach, A. Schumacher, H-J.
Wagner; Sensors and Actuators A32; pp.299-302,I992.
4) To place cells as an array using aspiration technique; A. Tixier-
Mita, Y. Mita, K. Cozic, M. Frenea, B. Le Pioufle and H. Fujita;
Microtas'2002; pp. 888-89 1, 2002.
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
108
15 μm     Ce::S


研究速報 : Nano-structures fabrication technique for biological applications

https://repository.dl.itc.u-tokyo.ac.jp/?action=repository_action_common_download&item_id=53515&item_no=1&attribute_id=19&file_no=1

研究速報 : Nano-structures fabrication technique for biological applications

Abstract

Similar works

Full text

Available Versions

UTokyo Repository