Note: Descriptions are shown in the official language in which they were submitted.
CA 02883914 2015-03-04
Selective transferring and bonding of
pre-fabricated micro-devices
Introduction
Selective transferring and bonding of pre-fabricated micro-devices from the
donor substrate to a system
substrate containing backend circuitry allows us to develop more efficient
integration schemes for
optical and electronic systems such as display and LED light panels.
In one embodiment, the donor substrate consists of an array of pre-fabricated
micro-devices and the
system substrate is a substrate with an array of contact pads.
Figure 1: An array of pre-fabricated micro-devices and the array of contact
pads on the system substrate.
To transfer some of the micro-devices from donor substrate to the system
substrate, first they are
aligned and brought together. Using some mechanisms, contact pads apply a
force of F' on all micro-
devices attached to the donor substrate. This force may have different sources
such as electrostatic,
magnetic or adhesion (mechanical, chemical,..). Subsequently, using an
operation such as laser lift-off
(LL0), the sticking force that holds micro-devices to the donor substrate is
manipulated. This
manipulation is selective so that it may change the adhesion of individual or
a group of micro devices. As
Figure 3 shows the net force inserted on the micro-devices is the difference
between F, (i=1,2,3..) and
the F' (Fnet = F - F,). Micro-devices with positive Fnet will be detached and
transferred to the system
(system) substrate.
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-1:1-1 11-1
iI
* # * # # *
F' F, F F, F' F'
Figure 2: Pre-fabricated micro-devices and the array of contact pads are
aligned and brought together. Force F' is applied to
the micro-device arrays.
After transferring the selected micro-devices to the system substrate, an
operation is performed to
create a phase change in the contact pad bonding layer and the micro-device
electrode to permanently
bond the micro-device to the system substrate. While this operation is
performed, force F' holds the
micro-devices on the system contact pads. A variety of operations can be
performed to control the
phase of the bonding layer such as using a global heater.
F2 F4 F6
A A A
L......1 1......J 1,...I
-1-1-' i __
II 1----7----1 i---1---1
!
* * * # # *
F' F' r F' F' r
Figure 3: Micro-devices with net force (F'-Fi) >0 are transferred to the
system substrate.
In one embodiment, force F' applied to the micro-devices from the contact pads
on the system
substrate can be designed to be different for the individual or a group of
contact pads. As it is shown in
Figure 3, in this case the net force inserted on the micro-device "i" is F, =
F', - F. Micro-devices with Fnet
> 0 will be transferred to the system after emoving the donor substrate.
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F1 F2 F3 F4 F5 F6
* A A A A A
i-I-1;
Y * * V 4' t
, ,_ , r_ r_ , i_. ,
F1 r2 r3 F4 r5 r6
Figure 4: Pre-fabricated micro-devices and the array of contact pads are
aligned and brought together. Force F1' is applied to
the micro-devices and can be different for individual or a group of contact
pads.
F2 F4 F6
A A A
....1 -I1- 1-11
:
-
. __________________
,
, : !
.
* * * * * *
. . , . ,
F1 F2 F3 F4 F5 F6,
Figure 5: Micro-devices with net force (FV-Fi) >0 are transferred to the
system substrate.
Following scheme describes exemplary implementations of contact pads on the
system substrate. As
mentioned before, this invention describes a method of selective transferring
and bonding an array of
micro-devices to a system substrate. In one aspect, the system substrate can
have any sizes and may
contain the necessary circuitry to derive the micro-devices or process the
output signal of micro-devices.
In another embodiment the substrates consist of connection pads and metallic
tracks. In both cases, the
pads equipped with a mechanism to electrostatically hold the micro-devices
during the transfer from
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the system substrate to the system substrate. As an example, the micro-devices
can be micro LED
devices and the substrate, the back-plane driver circuitry.
Selective transfer of semiconductor devices using electrostatic force
In this invention, there is at least one conductive area in vicinity of the
pads sharing the same micro-
device which is covered by a dielectric. This area provides electro static
forces required to hold the
micro device in place on the system substrate. This area can have different
shapes, different sections,
and different heights.
In one aspect, the system substrate has an array of contact pads as shown in
Figure 6.
Figure 6: Array of pads on the system substrate. Contact pads are surrounded
by a ring of metal/dielectric bi-layer.
In this case, each contact pad is surrounded by a ring of metal/dielectric bi-
layer. The metallic layer of
these rings can be addressed separately or connected together and controlled
by one signal.
,
Figure 7: Cross section of the contact pads.
In this scheme, micro-devices are aligned with the contact pads and they are
brought in contact with
them (Figure 3)
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L111111111=1.11
Figure 8: First micro-devices and the contact pads are aligned and brought
together.
Different micro-devices can be selected for bonding by applying a voltage to
the bonding pads (here the
metallic ring). The electro-static force produced by the voltage across the
dielectric can temporary holds
the micro-devices in contact with the contact pads (Figure 4).
Figure 9: a voltage is applied to the bonding pads (here the metallic ring) to
temporary holds the micro-device in contact with
the contact pads.
Later on, using some operations such as laser lift-off or heating, the force
holding the micro-devices to
the carrier substrate is manipulated. This manipulation leads to a net force
toward the system (system)
substrate and transferring the selected micro-devices upon removing the
carrier substrate.
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Figure 10: Array of pads on the system substrate. Each contact pad consists of
a metallic electrode and a metal/dielectric
stack part.
In another embodiment shown in Figure 10, each contact pad consists of a
metallic electrode and a
metal/dielectric bilayer section.
In another embodiment shown in Figure 11, each contact pad in the array
consist of a metallic electrode
(in the form of a symmetric cross) and four square metal/dielectric stack at
the edges of the contact
pad.
40 15
ILI P -
Figure 11: Array of pads on the system substrate. Each contact pad consists of
a metallic electrode and four metal/dielectric
stack sections at for edges of the contact pad.
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In this embodiment, the four metal/dielectric bilayers in a single contact pad
can be connected together
or one or more of them can be addressed separately. Similarly to the
embodiments in Figure 6 and
Figure 10, metal/dielectric bilayers, here is called bonding pads, for a
single contact pad can be
addressed separately or connected to the bonding pads of other contact pads
and be addressed
collectively.
In general, a variety of different electrode and bonding pad can be designed
and the scope of the
invention is not limited to the above arrangements.
Selective transfer of semiconductor devices using mechanical force
In another aspect of the invention shown in Figure 12, the electrode pads on
the system substrate can
be patterned to form a trench structure.
Figure 12: Trench pattern on the system electrode pads. Micro-devices on the
carrier substrate are aligned and brought close
to the electrode pads on the system substrate.
First, micro-device arrays are aligned with the pads on the system substrate.
Considering the larger size
of the trenches, micro-devices can be accurately placed into them (see Figure
13). The material of the
system substrate electrode is chosen to have a temperature expansion
coefficient (CTE) lower than that
of the micro-device electrode. Consequently, heating up this setup, result in
a larger expansion of the
micro-device electrodes compared to the trench structures. This will cause a
temporary mechanical
bonding between the micro-device arrays and the system substrate. Later on,
using some methods like
laser lift-off, the force holding micro-devices to the carrier substrate can
selectively be decreased. This
manipulation leads to a net force toward the system (system) substrate and
transferring the selected
micro-devices upon removing the carrier substrate (Figure 15).
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111.111
Figure 13: Micro-devices are placed into the electrode trenches on the system
substrate.
=
,
Figure 14: Micro-devices are placed into the electrode trenches on the system
substrate.
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I ___________
limommil L 1 i
L-m-1 1.....ml 11;1 immormil lii
1 ___________ 17
______________________ r 1 __ r 1 __ r 1 __ r 1 __ E
-u.4
ih441 4; tli:4 44 i4i ii
-.;;4
I-ZTI 11-.TII I
7 _____________________ r
i=In=l 7 ___ r
7 _____________________________________________________________ r
Figure 15: process flow of selective transferring of micro-devices to a system
substrate using mechanical grip and laser lift-off
process
