research activities in 2007 - CSEM

Metal Micro-Parts Fabrication
F. Cardot
Micro-parts realized by metal electrodeposition onto a silicon mold are presented; the versatility of this process is shown.
Combining silicon deep reactive etching (DRIE) and microelectrochemistry
leads to the realization of high resolution
(~1 µm) and high aspect ratio (up to 30:1) electrodeposited
micro-parts. This process is schematically depicted in
Figure 1. A silicon dioxide etching mask, (a) is realized at the
surface of a highly conductive silicon wafer comprising of a
backside electrical contact (b). The silicon is etched by using a
DRIE process (c) and the silicon mold thus created is filled by
using an electrodeposited metal or alloy (d). The wafer is
polished (e) and the electrodeposited micro-parts are released
(f) by etching the silicon wafer in a KOH solution.
46
a
b
c
Si
SiO2
Ti
Figure 1: Schematic of the fabrication process flow of metal microparts
This process can be used to fabricate a large range of microparts.
For example flexible structures such as springs
(Figure 2) or micro-“FlexTec” structures (Figure 3) have been
realized which could find applications in the field of chip
testing or for the realization of miniaturized mechanical
systems.
a b
Figure 2: Spring micro-parts. a) FeNi electrical contact pin;
b) Ni membrane spring.
Figure 3: Nickel micro-FlexTec hinges
d
e
f
Ni
Non-flexible structures like gears (Figure 4), rack and pinion or
turbines (Figure 5) have been produced, which could be used
in the watch industry.
Figure 4: Nickel micro-gears
Figure 5: Nickel turbine and rack and pinion
This process can also be used for the realization of 3D folded
micro-parts as illustrated in Figure 6. Figure 7 presents an
example of a heterogeneous micro-part made of silicon and
metal. An 8 µm diameter NiFe ball has been electrodeposited
at the top of a silicon needle, 80 µm long and 2 µm across.
Figure 6: Nickel folded micro-box
Si
NiFe
2 ・ m
80 ・
m
Figure 7: Electrodeposited FeNi ball on top of a silicon needle
The work has been carried out within the frame of internal
research for developing new technologies for MEMS
fabrication.