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Direct-Writing and Debris-Free Laser Micromachining on Glass by

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					   DIRECT-WRITING AND DEBRIS-FREE LASER
MICROMACHINING ON GLASS BY PHOTO ASSISTED
             CHEMICAL ETCHING

                            Meng-Hua    Yen and Ji-Yen Cheng*
      Institute ofApplied Science and Engineering Research, Academia Sinica, Taiwan
                  *Corresponding Author: ~-~la~l:,jy~heng~gute.si~~~u.edu.~

Abstract
   We have developed a direct-writing microfabrication           system for glass machining by
photo assisted chemical etching (PACE).            The process produces smooth and debris-free
surface.     For the first time, we have succeeded in engraving glass by a direct-writing
approach using a solid-state laser that is easier to maintain than the excimer laser.
Furthermore, very low average power is needed compared to the use of excimer laser in
conventional glass machining process.          In addition, high aspect ratio has been generated
by the photo-assisted       anisotropic   etching.    Since no photomask is needed for the
direct-writing process, the substrate size is not limited by the mask and that substrates
larger than 12 inches can be used in our system.           Economic substrates such as borofloat
glass can be used in the system.        The PACE process is very use&l in the development of
microfluidic devices.

Keywords:         glass micromachining,                   laser direct-writing,           microfabrication,            wet etching

1. Introduction
    The direct-writing     micromachining     of polymers      (PMMA, polyimide,        etc.) and
ceramics by laser ablation has been proved to be a flexible method for the fabrication of
micro-mechanical,      micro-fluidic    or micro-optical    components   [ 1,2].   In particular,
transparent dielectric materials are suitable for a wide field of application due to their
superior chemical, optical and mechanical properties.         However, laser ablation is limited
to photon-absorbing      materials and has difficulties in processing materials which are
transparent at the wavelength of the laser.       In addition, the smooth and debris-free laser
machining on glass has been very difficult.          Recently, Wang et. al. have developed a
laser machining platform suitable for quartz and CaFz using a deep UV excimer laser as
the ablation     source [3].         In this work, we have developed             a direct-writing
microfabrication   system for glass machining by photo assisted chemical etching (PACE).
The process produces smooth and debris-free surface.           We have succeeded in engraving
glass by a direct-writing approach using a solid-state laser that is easier to maintain than
the excimer laser.




                      7th lnternat~onal   Conference   on Miniaturized Chemical and Blochemlcal   Analysts   Systems
                                             October   5-9, 2003, Squaw Valley, Callfornla USA



O-974361 I-0.O/~TAS2003/$15.0002003TRF                                                                                         323
2. Experimental
   The machining process is described as follows.        Borofloat glass and quartz are used
as machining substrate.     A frequency quadrupled Nd:YAG laser (h=266 nm, pulse width
30ns, 30 mW) was used as the light source.         The substrate is put in contact with the
etchant (pyrene solution in acetone or xylene), as shown Fig 1. When the etchant is
excited by the laser energy, the substrate surface is smoothly etched by the transiently
activated etchant.
   The user designs the microfluidic pattern by commercial drawing tool such as Core1
Draw and AutoCAD.          The pattern is then translated to motion command of the X-Y
stages.   The desired microfluidic pattern is then engraved on the substrate surface with
the appropriate 2-dimensional     motion of the stages.    Since no photomask is needed in
the fabrication process, the substrate size is dependent only on the travel range of the
stages.     Substrates larger than 12 inches can be used in our system. Since flexible
pattern fabrication can be achieved on large substrates, the development of a novel device
is very fast and only takes a few hours.    After the trench was fabricated, the substrate is
thermally bonded (570 “C) to a blank borofloat glass to form sealed microchannels.




3. Results and discussion
   Several examples showing our micromachining         capability  are presented.     The
photograph in Fig.2 shows a pattern with 20 mm X 60 mm footprint while keeping 10 pm
feature size. As shown in Fig.2, the long-range accuracy and repeatability is maintained
in the machining system.   As an implication for the possible application, the zigzagged
region can be used for heat transfer reaction such as PCR. Fig 3 (a) and (b) show the




                  7th lnternat~onal   Conference   on Miniaturized Chemical and Blochemlcal   Analysts   Systems
                                         October   5-9, 2003, Squaw Valley, Callfornla USA



324
cross sections of trenches engraved on borofloat and quartz, respectively.     The width is
15 pm and depth is 10 urn. No debris or cracks occurs on the surface around the etched
area as compared to the conventional laser ablation and ultrashort pulse laser ablation [4].
The capability to generate trenches with high aspect ratio is shown in Fig.4 (a).
Debris-free trenches with aspect ratio larger than 4 is obtained.    For comparison, aspect
ratio larger than 0.5 is hard to achieve by wet etching process.    Fig.4 (b) shows a cross
section of a sealed microchannel in borofloat substrate.   The width is 20 pm and depth is
10 urn. The lack of boundary between the two substrates suggests successful bonding.
Dye solution is loaded into the channel to further confirm the sealing.




Fig.2. Photo picture showing a sample pattern that may be used for PCR.
The inset shows magnified view of the zigzagged region.      The overall
footprint is 20 x 60 mm. The channel width and depth is 15 pm and 8
pm, respectively,




Fig.3. SEM pictures showing the cross sections                                             of clean trenches    on
borofloat substrate (a) and quartz (b).




               7th lnternat~onal   Conference   on Miniaturized Chemical and Blochemlcal   Analysts   Systems
                                      October   5-9, 2003, Squaw Valley, Callfornla USA



                                                                                                                325

				
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posted:1/20/2011
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