Abstract
A system for manipulating a small object (3) comprising a substrate
to receive the small object (3), a liquid droplet (4), which carries
the small object (3) on the substrate, and a pre-treated surface structure
of the substrate in the vicinity (1,2) of the placement position (1)
of the small object (3). The small objects (3) like silicon dies in
the range from 100 down to 1 micrometer are fine-placed by an evaporating
droplet (4). The dies will serve as active electronic elements in
large-area displays and other applications.
Claims
1. A system for manipulation of a small object comprising a substrate
to receive the small object (3), a liquid droplet (4) that evaporate,
which droplet (4) carries the small object (3) on the substrate, a
pre-treated surface structure of the substrate in the vicinity (1,2)
of the placement position of the small object (3), wherein the small
object is moved to a well-defined placement position (1) by the evaporation
of the droplet (4).
2. A system for manipulation of a small object as claimed in claim
1, wherein the surface structure of the substrate is pre-treated
chemically in that way, that the final placement position (1) of
the object is modified to make it good-wetting and that the near
vicinity (2) of the placement position of the small object (3) is
poor-wetting to make contrast in wettability on the substrate near
the placement position (1,2) of the small object (3).
3. A system for manipulation of a small object as claimed in claim
2, wherein the contrast in wettability of substrate is provided
by a monolayer of a suitable molecule, which monolayer is made by
micro-contact printing.
4. A system for manipulation of a small object as claimed in claim
1, wherein the small (3) object is pre-treated by a monolayer to
make the side (5) of the object (3) in contact with the substrate
hydrophilic.
5. A system for manipulation of a small object as claimed in claim
1, wherein the small object (3) is pre-treated by a dissolvable
layer.
6. A system for manipulation of a small object as claimed in claim
1, wherein the surface structure of the substrate is pre-treated
physically, in that way that the edge of the fluid meniscus is guided
by grooves and ridges of the physically pre-treated structure to
the final placement position of the small object.
7. A system for manipulation of a small object as claimed in claim
1, wherein the object (3) is aligned to match to the placement position
(1) by means of a magnetic field.
8. A system for manipulation of a small object as claimed in claim
1, wherein the placement position (1) on the substrate has a shape
which corresponds to the shape of the small object (3), so that
the object (3) is aligned to match with the final placement position
(1) during evaporation of the droplet (4).
9. A method of manipulation of a small object having a a substrate
with a pre-treated surface structure to receive the small object
(3), which object (3) is pre-treated by a monolayer to make the
side (5) of the object (3) in contact with the substrate hydrophilic,
placing the small object by rough placement of the object on the
substrate somewhere around the final position (1) of the object
(3), placing a droplet (4) on the substrate in the vicinity of the
final position (1) of the small object, dissolving of the object
(3) in the droplet (4) that the object can freely float in the liquid,
moving the droplet (4) from the poor wetting area to the good wetting
area and positioning the object (3) to the proper position (1) by
the evaporation of the droplet, interconnecting the object (3) by
standard lithographic way.
Description
[0001] Manipulation of small objects is in particular of relevance
in the fabrication of semiconductor devices. Small electronic components
need to be placed accurately on a substrate. Often a crystalline Si
wafer is used as substrate. It appears that the cost of semiconductor
devices is strongly dependent on the size of the substrate, so that
the more semiconductor devices made on the substrate, the lower the
production cost per semiconductor device. The number of semiconductor
devices accommodated on the substrate, given the size of the surface
of the substrate, is increased as smaller sized components are employed.
These components need to be manipulated, for example in that they
need to be picked-up and placed accurately at predetermined positions
on the substrate. The placement of small electronic objects is an
important process in the electronics industry. At this moment the
positioning of these objects is performed by mechanical placement,
so-called pick-and-place. The object size is typically 200 .mu.m and
the placement accuracy of the order of 10 .mu.m and this mechanical
placement technologies are not suited for dies with a size below 100
.mu.m.
[0002] The invention pertains to a system for manipulation of a
small object especially electronic objects by using fluid droplets.
[0003] A system for manipulation of small objects is known from
U.S. Pat. No. 6,294,063. The known system concerns in particular
to the manipulation of encapsulated packets. This means that the
packets always need to me immersed in other layer of material. The
packets could be a solid packet and that solid packet could be a
particle of a cell or any material. The known system comprises a
reaction surface configured to provide an interaction site for the
encapsulated packet. Further an inlet port is provided coupled to
the reaction surface to introduce the encapsulated packet onto the
reaction surface. A programmable manipulation force is generated
to move the packet about the reaction surface by arbitrarily chosen
paths. The manipulation force is generated by way of an electric
field or by way of a light source. The manipulation force may include
a dielectrophoretic force, an electrophoretic force, an optical
force or a mechanical force.
[0004] A drawback of the known system is that an object must first
be immersed to get a packet which can be manipulated but there are
shaped solid objects where a front side, left, right up and down
can be distinguished, of which not the whole object might be immersible.
Further it is often an advantage not to immerse objects. A further
drawback of the known system is that the encapsulated packets can
only be moved over the reaction surface so that the manipulation
and exact positioning becomes more cumbersome as more encapsulated
packets are placed on the reaction surface. The control of the orientation
and rotation of the objects is out of the scope of electrophoretic
manipulation of small objects.
[0005] It is the aim of the present invention is to provide a system
for the placement and interconnection of small objects like silicon
dies in the range of about 1 .mu.m to 100 micrometer on large substrates
with high placement accuracy, speed and reliability and at low cost.
[0006] This aim is achieved by a system for manipulation of small
electronic objects according to the invention comprising a substrate
to receive the small object, a liquid droplet that evaporate, which
carries the small object on the substrate, and a pre-treated surface
structure of the substrate in the vicinity of the placement position
of the small object. Due to the presence of a pre-treated surface
structure, the object is moved to a well-defined position by the
evaporating droplet.
[0007] The system according to the invention for manipulating of
small objects by using fluid droplets operates on the basis of the
physical phenomenon of the surface wetting. The wettability of a
liquid is defined as the contact angle between a droplet of the
liquid in thermal equilibrium on a horizontal surface. Depending
on the type of surface and liquid the droplet may take a variety
of shapes. The wetting angle is given by the angle between the interface
of the droplet and the horizontal surface. The liquid is seemed
wetting between an angle of 90.degree. to 180.degree. and non-wetting
between 0.degree. and 90.degree.. A wetting angle of 180.degree.
degrees corresponds to perfect wetting and the drop spreads forming
a film on the surface.
[0008] The present invention in particular focuses on how to control
the destination of the fluid droplets with the small objects on
the substrate. To this end high wettability spots are introduced
and the shape of the high-wettability spots adds to control of orientation
of the small objects when the fluid is removed by evaporation.
[0009] These and other aspects of the invention are disclosed in
the dependent claims and in the following description in which exemplified
embodiments of the invention are described with respect to the accompanying
drawings. Therein shows:
[0010] FIG. 1 a possible structure of the surface with difference
in wettability around the final placement position of the object;
[0011] FIG. 2 the placement of the object due to droplet evaporation;
[0012] FIG. 3 another method to position the object which is due
to a special shape of the object and substrate;
[0013] FIG. 4 the interconnection of the small object after placement
in standard lithographic way.
[0014] One possibility to manipulate small electronic objects like
silicon dies by liquid droplets is to make contrast in wettability
on the substrate near the placement position of the object. This
contrast gives a self-alignment of the object.
[0015] FIG. 1a sketches a possible structures of the surface of
the substrate wherein the position of the object is the square.
An area 2 of the substrate around the final position of the object
the surface has been modified, to make it poor-wetting. This part
is shown in grey. In the near vicinity 1 of the final placement
position of the object, shown as a white square, the wettability
of the liquid with the substrate is good. It is especially important
that the liquid has a non-zero receding contact angle with the substrate
near the placement position of the object--the grey part--, as will
be further discussed in the embodiments. Other structures are also
possible as shown e.g. in FIG. 1b. The contrast in wettability can
be made e.g. with micro-contact printing a monolayer of a suitable
molecule. With this technology sub-micron resolution has been shown
to be feasible and with wave printing large substrates can be printed
with a very good placement accuracy in the order of about 1 micron.
[0016] Another possibility is to make physical structures, such
as grooves and ridges, to guide the edge of the fluid meniscus to
the desired position.
Embodiment 1
[0017] A first embodiment of the invention is to first place the
objects with a rough placement method, e.g. laser die transfer,
or mechanical placement. With this placement the object is placed
somewhere around the final position of the object on the surface
2 which has been modified to poor-wetting.
[0018] With an ink-jet printer very small droplets can be formed,
with a diameter ranging between 15 and 50 .mu.m. The placement accuracy
of the droplets with industrial ink-jet printers is of order 10-15
micron which is sufficient to place the droplet 4 with liquid also
on the non-wetting part 2 of the substrate. The next aspect is to
dissolve the object 3 in the liquid. This can be done by pre-treatment
of the object 3, e.g. to make the side 5 of the object in contact
with the substrate hydrophilic, by e.g. a monolayer. When the object
3 is in contact with the liquid, the object 3 will preferably move
in the liquid and not adhere to the substrate 2. Another method
to achieve that the object 3 becomes part of the droplet 4, is to
place a dissolvable layer on the object side 5 which is in contact
with the substrate. Due to the contact of the object 3 with the
liquid, the layer on the object side 5 dissolved and the object
3 can float freely in the droplet 4. When the object 3 is floating
in the liquid droplet 4 the liquid will evaporate. As stated above
the properties of the liquid with the substrate are such that the
contact line will not pin, but can recede from the non-wetting area.
Only at the position where the object 3 has to be placed the liquid
has a low contact angle with the substrate and will pin. During
evaporation the object 3 remains floating in the droplet 4 and will
be moved to the placement position during the evaporation of the
solvent. Due to the hydrophilic layer 5 it is energetically more
favourable for the object 3 to adhere to the hydrophilic part of
the substrate. Finally all solvent evaporates and the object 3 is
positioned in place 1. There are no restrictions to a single solvent
but there can be used also solvent mixtures to have a favourable
Marangoni force, i.e. a force due to a difference in surface tension
on the interface of the droplet 4 that can help positioning the
object 3 in place. The transportation fluid should be free of dust
particles and most probably the process should run in a clean-room
environment.
[0019] The complete procedure for the fine placement of an object
3 by a printed liquid droplet 4 is sketched in FIG. 2. First the
object 3 is placed by rough placement of the object 3 with a different
technique on the substrate in the area 2 somewhere around the final
position 1 of the object 3 (FIG. 2a). Then a droplet 4 is placed
(FIG. 2b) and by dissolving of the object 3 in the droplet 4 it
can freely float in the liquid (FIG. 2c). Due to the contrast in
surface energy, the evaporating droplet 4 will move to the area
with the low contact angle and the object 3 is manipulated to the
proper position 1. The sketched thin line represents a good wetting
and the thick line a poor wetting area of the substrate (FIG. 2d-2f).
The layer 5 on the object 3 is a hydrophilic monolayer. During evaporation
the solvent will recede from the area with a high contact angle,
but due to the surface energy contrast, it will stick to the low
contact angle area.
[0020] The orientation of the droplet 4 is important to have a
good match with the shape of the placement position. Therefore the
object 3 can be directed during the evaporation of the solvent by
means of a magnetic field, when the object 3 is provided with a
magnetic layer. By means of magnets the object 3 can be rotated
in the azimuthal direction, while residing inside the droplet 4.
FIG. 3 shows another method to position the object 3. This method
for positioning the object 3 is due to a special shape of the object
3 and the final position 1 on the substrate in combination with
the liquid movement during evaporation as an example is shown in
a side view in FIG. 3a. Another option for rotation of the object
3 in the azimuthal plane is by adapting the shape of the object
3 and wetting region 1 of the substrate like it is shown in FIG.
3b in a top view.
Embodiment 2
[0021] In the first embodiment the object 3 was placed with a "rough"
positioning method on the substrate. In a second embodiment the
objects 3 are already dissolved in the liquid during ink-jet printing.
Objects 3 of very small size of order 5 to 10 micron and smaller
can be dissolved in the droplets 4 and placed on the substrate.
The procedure for placement of the droplet is similar as in FIG.
2 shown.
[0022] The orientation of the object 3 can be done in similar ways
as described in the previous embodiment. A flipping of the object
is also possible by applying a magnetic field. In the shown figures
one object 3 is sketched in the droplet 4. This is an important
aspect. There are several ways to have a droplet 4 with a single
object 3 landing on the substrate. First this can be done by manipulating
the liquid flow inside the ink-jet printer. Another option is to
inspect the droplets 4 during flight and let only those droplets
4 pass that contain an object 3. The other droplets are deflected.
The deflection of droplets is a standard technique in continuous
ink-jet printing. Yet another option is to print the droplets 4
and inspect the substrate after printing. A new droplet 4 is printed
where objects are missing. With multi-nozzle printers one can print
easily about 100 droplets per second. By optical inspection it may
also be possible to remove droplets 4 with more than one object
3. Alternatively, droplets with more than one object can be spotted
on the substrate, and non-sticking objects are later removed.
[0023] An important issue in the placement of objects 3 on a substrate
is the interconnect of the object 3 to the outside world. There
are several options for this which are standard. First it can be
done in the standard lithographic way. This is sketched in FIG.
4. In FIG. 4a the object is shown after placement of the object
3 close to a connecting line 6. On top of the object 3 there is
a conducting part 7. By standard lithography via's 8 are made and
the object 3 is connected.
[0024] As sketched in FIG. 1 a monolayer is made by micro-contact
printing. This monolayer can be removed after deposition of the
small object and before interconnect with e.g. UV-ozone or plasma
treatment. In this way the interconnect will not be hindered by
the monolayer.
[0025] Another option for interconnect is by heating the object
on the substrate and melting a layer of low melting temperature
metal on both object and substrate to form a connection.
[0026] The described systems allow manipulation of small objects
in the range of about 1 .mu.m to 100 .mu.m on large substrates with
high placement accuracy, speed and reliability at low cost. There
are several applications that can benefit from this assembly system.
This assembly is called `Meso-assembly`, which is the placement
and interconnect of dies in the above mentioned range on large substrates.
The most prominent application is active-matrix displays. For example,
PolyLED-TV and Active-Matrix-PolyLED-Mobile, require electronic
switches with high electronic mobilities and high reliability. `Meso-assembly`
is potentially an alternative to low-temperature poly-silicon. Besides
active-matrix displays, also other applications can benefit from
`meso-assembly` technologies like large-area X-ray detectors with
direct conversion, chip-cards and tags, LED chips on silicon submounts
and others. |