U.S. patent application number 12/169347 was filed with the patent office on 2009-01-22 for system and method for depositing a seed layer.
Invention is credited to Thomas J. Lindner, Niranjan Thirukkovalur.
Application Number | 20090021563 12/169347 |
Document ID | / |
Family ID | 37083664 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090021563 |
Kind Code |
A1 |
Thirukkovalur; Niranjan ; et
al. |
January 22, 2009 |
System And Method For Depositing A Seed Layer
Abstract
A method for depositing a seed layer for a controllable electric
pathway on a substrate includes selectively dispensing a seed
material from an inkjet material dispenser onto said substrate.
Inventors: |
Thirukkovalur; Niranjan;
(Corvallis, OR) ; Lindner; Thomas J.; (Corvallis,
OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD, INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
37083664 |
Appl. No.: |
12/169347 |
Filed: |
July 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11101668 |
Apr 8, 2005 |
7410893 |
|
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12169347 |
|
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Current U.S.
Class: |
347/85 |
Current CPC
Class: |
H01L 27/1292 20130101;
H01L 21/02658 20130101; H01L 21/76874 20130101; H01L 29/7869
20130101; H01L 21/02491 20130101; H01L 21/0237 20130101; H01L
21/02628 20130101; H01L 21/02554 20130101 |
Class at
Publication: |
347/85 |
International
Class: |
B41J 2/175 20060101
B41J002/175 |
Claims
1-38. (canceled)
39. A system for depositing seed layers on a substrate comprising:
a material reservoir containing seed material; and an inkjet
material dispenser fluidly coupled to said material reservoir;
wherein said inkjet material dispenser is configured to selectively
dispense said seed material onto said substrate to aid in formation
of a controllable electric pathway.
40. The system of claim 39, wherein said seed material comprises
one of a stannous chloride solution or a tin/palladium complex
solution.
41. The system of claim 39, wherein said inkjet material dispenser
comprises one of a thermally actuated inkjet dispenser, a
mechanically actuated inkjet dispenser, an electrostatically
actuated inkjet dispenser, a magnetically actuated dispenser, a
piezoelectrically actuated dispenser, or a continuous inkjet
dispenser.
42. The system of claim 39, further comprising a servo mechanism
controllably coupled to said inkjet material dispenser.
43. The system of claim 42, further comprising a computing device
controllably coupled to said servo mechanism; wherein said
computing device is configured to generate a graphical a seed
pattern and convert said graphical seed pattern to a plurality of
servo commands; said servo commands being configured to
controllably translate said inkjet material dispenser according to
said graphical seed pattern.
44. The system of claim 39, further comprising a substrate
transport system disposed adjacent to said inkjet material
dispenser.
45. The system of claim 44, further comprising a plurality of baths
associated with said substrate transport system.
46. The system of claim 45, wherein said plurality of baths
comprise: a rinsing bath including de-ionized water; a palladium
isolating bath including one of an accelerating solution or a
palladium chloride solution; and a zinc oxide plating solution
including zinc nitrate (Zn(NO.sub.3).sub.2) and dimethylamine
borane (C.sub.2H.sub.10BN).
47-54. (canceled)
Description
BACKGROUND
[0001] Zinc oxide is a transparent semiconducting material that has
applications in liquid crystal displays, photovoltaic devices, and
surface acoustic wave devices. Traditionally, zinc oxide is formed
on a desired substrate through conventional photolithographic
methods or shadow masking. However, traditional methods used for
the deposition of zinc oxide are often expensive, make inefficient
use of materials, and are difficult to change patterning.
SUMMARY
[0002] An exemplary method for depositing a seed layer for a
controllable electric pathway on a substrate comprising selectively
dispensing a seed material from an inkjet material dispenser onto
said substrate.
[0003] In another exemplary embodiment, a system for depositing
seed layer on a substrate includes an inkjet material dispenser
configured to deposit seed layer material onto the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The accompanying drawings illustrate various embodiments of
the present system and method and are a part of the specification.
The illustrated embodiments are merely examples of the present
system and method and do not limit the scope thereof.
[0005] FIGS. 1A and 1B illustrate various embodiments of a
semiconductor device, such as a thin-film transistor.
[0006] FIG. 2 illustrates a schematic view of a seed layer
depositing system, according to one exemplary embodiment.
[0007] FIG. 3 illustrates a method for depositing zinc oxide,
according to one exemplary embodiment.
[0008] FIGS. 4A and 4B illustrate a plurality of methods for
dispensing seed layers on a desired substrate, according to various
exemplary embodiments.
[0009] FIG. 5A is a system view illustrating a deposition of seed
material, according to one exemplary embodiment.
[0010] FIG. 5B is a cross-sectional side view illustrating a
rinsing of a deposited seed material, according to one exemplary
embodiment.
[0011] FIG. 5C is a cross-sectional side view illustrating a
palladium isolating bath, according to one exemplary
embodiment.
[0012] FIG. 5D is a cross-sectional side view illustrating a
palladium coated substrate in a rinsing bath, according to one
exemplary embodiment.
[0013] FIG. 5E is a cross-sectional side view illustrating a zinc
oxide plating bath, according to one exemplary embodiment.
[0014] FIG. 5F is a cross-sectional side view illustrating zinc
oxide deposited on a desired substrate, according to one exemplary
embodiment.
[0015] FIGS. 6A and 6B are scanning electron microscope images of
zinc oxide crystal structures that result from the deposition of
zinc oxide, according to various embodiments.
[0016] FIGS. 7A and 7B are scanning electron microscope images of a
resulting zinc-oxide crystal structure when deposited according to
various embodiments.
[0017] Throughout the drawings, identical reference numbers
designate similar, but not necessarily identical, elements.
DETAILED DESCRIPTION
[0018] An exemplary system and method for depositing seed layers to
be used in performing electroless plating on a desired substrate
are disclosed herein. Specifically, exemplary systems and methods
for depositing zinc oxide on a desired substrate are described in
detail. According to one exemplary method, a seed layer of the
desired zinc oxide deposition is selectively deposited on a
substrate by an inkjet material dispenser. Additionally, an
exemplary system for the deposition of zinc oxide seed layers
including an inkjet material dispenser is disclosed herein.
Embodiments and examples of the present exemplary systems and
methods will be described in detail below.
[0019] As used herein, and in the appended claims, the term
"electroless plating" shall be understood to refer to any
deposition of a metallic coating onto a substrate by a controlled
chemical reduction that is catalyzed by the metal or alloy being
deposited.
[0020] Unless otherwise indicated, all numbers expressing
quantities of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood as being
modified in all instances by the term "about." Accordingly, unless
indicated to the contrary, the numerical parameters set forth in
the following specification and attached claims are approximations
that may vary depending upon the desired properties sought to be
obtained by the present disclosure.
[0021] It should also be understood that various semi-conducting
devices such as transistor structures may be employed in connection
with the various embodiments of the present exemplary systems and
methods. For example, the present systems and methods may be
incorporated to form any number of semiconductor structures, field
effect transistors including thin-film transistors, active matrix
displays, logic inverters, amplifiers, and the like. As illustrated
in FIGS. 1A-1B, exemplary thin-film transistor embodiments may be
formed with the present systems and methods. The thin-film
transistors can be of any type including, but not limited to,
horizontal, vertical, coplanar electrode, staggered electrode,
top-gate, bottom-gate, single-gate, and double-gate transistors,
just to name a few.
[0022] In the following description, for purposes of explanation,
numerous specific details are set forth in order to provide a
thorough understanding of the present system and method for
selectively forming a zinc oxide layer on a desired substrate. It
will be apparent, however, to one skilled in the art, that the
present method may be practiced without these specific details.
Reference in the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure, or
characteristic described in connection with the embodiment is
included in at least one embodiment. The appearance of the phrase
"in one embodiment" in various places in the specification are not
necessarily all referring to the same embodiment.
Exemplary Structure
[0023] FIGS. 1A and 1B illustrate embodiments of bottom-gate
transistors that may be formed by the present exemplary systems and
methods. According to various embodiments, the thin-film transistor
(100) can form a portion of any number of devices including, but in
no way limited to, an active matrix display device, such as an
active matrix liquid crystal display (AMLCD) device; an active
matrix detection device, such as an active matrix x-ray detector
device; a logic gate, such as a logic inverter; and/or an analog
circuit, such as an amplifier. The thin-film transistor (100) can
also be included in an infrared device where transparent components
are used.
[0024] While FIGS. 1A and 1B illustrate only a few bottom-gate
transistors, the present exemplary systems and methods may be used
to form any number of semi-conducting apparatuses containing zinc
oxide in various configurations. As shown in FIGS. 1A and 1B, the
exemplary transistors include a substrate (102), a gate electrode
(104), a gate dielectric (106), a channel (108), a source electrode
(110), and a drain electrode (112). Further, in each of the
bottom-gate transistors, the gate dielectric (106) is positioned
between the gate electrode (104) and the source and drain
electrodes (110, 112) such that the gate dielectric (106)
physically separates the gate electrode (104) from the source and
the drain electrodes (110, 112). Additionally, in each of the
exemplary bottom-gate transistors, the source and the drain
electrodes (110, 112) are separately positioned, thereby forming a
region between the source and drain electrodes (110, 112) for
interposing the channel (108). Consequently, the gate dielectric
(106) is positioned adjacent the channel (108) and physically
separates the source and drain electrodes (110, 112) from the gate
electrode (104). Further, the channel (108) is positioned adjacent
the gate dielectric (106) and is interposed between the source and
drain electrodes (110, 112).
[0025] In each of FIGS. 1A and 1B, the channel (108) interposed
between the source and the drain electrodes (110, 112) may be made
of a semi-conducting material such as zinc oxide to provide a
controllable electric pathway configured to selectively facilitate
a movement of an electrical charge between the source and drain
electrodes (110, 112) via the channel (108). The formation of the
semi-conducting zinc oxide channel (108) along with an exemplary
system configured to form the zinc oxide will be provided below.
While the present exemplary system and method will be described in
the context of forming a zinc oxide channel, any number of seed
layers configured to be used in electroless plating may be formed
according to the present exemplary systems and methods.
[0026] FIG. 2 illustrates an exemplary system (200) that may be
used to form a seed layer on a desired substrate (270) with
subsequent formation of a zinc oxide layer, according to one
exemplary embodiment. As illustrated in FIG. 2, zinc oxide seed
material (260) may be independently applied to a desired substrate
(270) from one or more inkjet material dispenser(s) (250). As
shown, the present system includes a computing device (210)
controllably coupled through a servo mechanism (220) to a moveable
carriage (240) having the inkjet material dispenser (250) disposed
thereon. A material reservoir (230) is also coupled to the moveable
carriage (240), and consequently to the inkjet print head (250). A
transporting medium (280) having the desired substrate (270)
disposed thereon is located adjacent to the inkjet material
dispenser (250). Additionally, as illustrated in FIG. 2, a number
of solution baths (290, 294, 296) are disposed near or on the
transporting medium (280). While the present embodiment is
described, for ease of explanation only, in the context of forming
a zinc oxide channel layer on the desired substrate (270), the
present system and method may be used to form any number of zinc
oxide configurations on any receiving substrates including, but in
no way limited to, printed circuit boards, switches, etc. The
above-mentioned components of the present system will now be
described in further detail below.
[0027] The computing device (210) that is controllably coupled to
the servo mechanism (220), as shown in FIG. 2, controls the
selective deposition of the seed material (260) in preparation of a
zinc oxide deposition. According to one exemplary embodiment, a
representation of a desired structure or trace pattern may be
formed using a program hosted by the computing device (210). That
representation of the desired structure or pattern may then be
converted into servo instructions that are housed in a processor
readable medium or memory (215). When accessed by the computing
device (210), the instructions housed in the processor readable
medium (215) may be used to control the servo mechanisms (220) as
well as the movable carriage (240) and inkjet material dispenser
(250), thereby forming the desired array structure or pattern. The
computing device (210) illustrated in FIG. 2 may be, but is in no
way limited to, a workstation, a personal computer, a laptop, a
personal digital assistant (PDA), or any other processor containing
device.
[0028] The moveable carriage (240) of the present exemplary system
(200) illustrated in FIG. 2 is a moveable material dispenser that
may include any number of inkjet material dispensers (250)
configured to dispense the present seed material (260). The
moveable carriage (240) may be controlled by the computing device
(210) and may be controllably moved by, for example, a shaft
system, a belt system, a chain system, etc. making up the servo
mechanism (220). As the moveable carriage (240) operates, the
computing device (210) may inform a user of operating conditions as
well as provide the user with a user interface. Alternatively, the
desired substrate (270) may be selectively translated under a
stationary inkjet material dispenser (250) by a servo
mechanism.
[0029] As a desired structure or pattern of seed material is
printed on a desired substrate (270), the computing device (210)
may controllably position the moveable carriage (240) and direct
one or more of the inkjet material dispensers (250) to selectively
dispense the seed material (260) at predetermined locations on the
desired substrate (270) as digitally addressed drops, thereby
forming layers of the desired seed material. The inkjet material
dispensers (250) used by the present printing system (200) may be
any type of inkjet dispenser configured to perform the present
method including, but in no way limited to, thermally actuated
inkjet dispensers, mechanically actuated inkjet dispensers,
electrostatically actuated inkjet dispensers, magnetically actuated
dispensers, piezoelectrically actuated dispensers, continuous
inkjet dispensers, etc. For ease of explanation only, the present
exemplary system and method will be described in the context of a
thermally actuated inkjet material dispenser.
[0030] The material reservoir (230) that is fluidly coupled to the
inkjet material dispenser (250) houses the present seed material
(260) prior to printing. The material reservoir may be any
container configured to hermetically seal the present seed material
(260) prior to printing and may be constructed of any number of
materials including, but in no way limited to metals, plastics,
composites, or ceramics. Moreover, the material reservoir (230) may
be an off-axis or on-axis component. According to one exemplary
embodiment illustrated in FIG. 1, the material reservoir (230) is
an on-axis component that forms an integral part of the moveable
carriage (240). A number of exemplary seed materials will be
described in further detail below with reference to FIGS. 4A and
4B.
[0031] Continuing with FIG. 2, the transporting medium supports a
desired substrate (270) configured to receive the seed material
(260). According to one exemplary embodiment, the desired substrate
(270) may include glass and a number of dielectric components as
mentioned above. Alternatively, however, the desired substrate
(270) configured to receive a zinc oxide seed material (260)
according to the present exemplary system and method can include
any suitable substrate material or composition for implementing the
various embodiments. For example, the desired substrate (270) may
include, but is in no way limited to, a silicon wafer, with or
without layers or structures formed thereon, used in forming
integrated circuits, and in particular thin-film transistors as
described herein; glass; quartz; organic substrate materials;
polymeric substrate materials; and the like. Furthermore, other
substrates can be used in connection with the present systems and
methods including, but in no way limited to, fibers, wires, etc. In
general, the films can be formed directly on the lowest surface of
the substrate or on any of a variety of the layers (i.e., surfaces)
as in a patterned wafer, for example.
[0032] Further, as mentioned previously, the present exemplary
system includes a number of solution baths (290, 294, 296) disposed
near or on the transporting medium (280). According to the
exemplary embodiment illustrated in FIG. 2, the solution baths
include a number of rinsing baths (290), a palladium isolating bath
(294), and a zinc oxide bath.
[0033] According to one exemplary embodiment, the plurality of
rinsing baths (290) includes a de-ionized water solution. This
de-ionized water solution is configured to remove excess particles
and/or solutions during the present exemplary method.
[0034] As illustrated in FIG. 2, the present exemplary system (200)
also includes a palladium isolating bath (294). The contents of the
palladium isolating bath (294) vary depending on the content of the
seed material (260). According to the present exemplary embodiment,
the palladium isolating bath (294) may include, but is in no way
limited to, a dilute palladium chloride solution or an accelerator
such as fluoroboric acid and/or sulfuric acid. The appropriate
palladium isolating bath (294) that corresponds with the seed
material (260) will be discussed in further detail below with
reference to FIGS. 4A and 4B.
[0035] The zinc oxide bath (296) illustrated in FIG. 2 includes a
zinc oxide plating solution configured to deposit zinc oxide where
palladium has been isolated on the desired substrate (270).
According to one exemplary embodiment, the zinc oxide plating
solution includes, but is in no way limited to, zinc nitrate and
dimethylamine borane. A number of exemplary methods for selectively
depositing zinc oxide onto a desired substrate (270) will now be
described with reference to FIGS. 3 through 5F.
Exemplary Formation
[0036] FIG. 3 illustrates an exemplary method for depositing zinc
oxide on a desired substrate (270; FIG. 2), according to one
exemplary embodiment. As illustrated in FIG. 3, the present
exemplary method includes designing a desired seed pattern in a
computing device (step 300). Once a desired seed pattern is formed,
the desired substrate is positioned adjacent to the inkjet material
dispenser (250; FIG. 2) of the exemplary system (step 310). With
the desired substrate in a proper position, the seed material is
dispensed onto the desired substrate according to the previously
designed pattern (step 320). After the seed material has been
dispensed, the substrate containing the seed material is prepared
for zinc oxide deposition, according to a number of exemplary
embodiments (step 330). Once prepared, the zinc oxide is deposited
on the desired substrate (step 340). Further details of each of the
above-mentioned steps will be described in further detail
below.
[0037] As mentioned, the present exemplary method begins by first
designing the desired seed pattern on a computing device (step
300). According to one exemplary embodiment, the desired seed
pattern is designed on a trace design application stored in the
memory (215; FIG. 2) of the computing device (step 210; FIG. 2).
Once the desired seed pattern has been developed and graphically
represented on the computing device (210; FIG. 2), the resulting
pattern is converted into a number of sequential servo commands
configured to controllably maneuver the servo mechanisms (220; FIG.
2) and inkjet material dispenser (250; FIG. 2) of the exemplary
system (200; FIG. 2), as will be described in further detail
below.
[0038] With the seed pattern design formed (step 300), the desired
substrate (270; FIG. 2) is positioned adjacent to the inkjet
material dispenser (step 310). As illustrated in FIG. 5A, the
desired substrate (270) is positioned adjacent to the inkjet
material dispenser (250) by the transporting medium (280).
[0039] As illustrated in FIG. 3, with the desired substrate (270)
correctly positioned, the seed material may be selectively
dispensed onto the desired substrate according to a pre-determined
pattern (step 320), prepared in a palladium isolating bath for zinc
oxide deposition (step 330), and be deposited with zinc oxide on
the seed material pattern (step 340). As mentioned previously, the
seed material and subsequent palladium isolating bath may vary
according to a number of exemplary embodiments. Two exemplary seed
material deposition methods are illustrated in FIGS. 4A and 4B.
[0040] According to a first exemplary embodiment illustrated in
FIG. 4A, the exemplary method includes selectively jetting stannous
chloride solution onto the desired substrate (step 400), rinsing
the desired substrate in a rinsing bath (step 410), immersing the
desired substrate in a palladium chloride solution (step 420), and
rinsing the desired substrate in a rinsing bath to remove any
excess palladium chloride (step 430). The above-mentioned steps
will be described in further detail below with reference to FIGS.
5A through 5F.
[0041] As mentioned, the first exemplary method for selectively
depositing seed material begins by selectively jetting stannous
chloride solution onto the desired substrate (step 400). As shown
in FIG. 5A, the inkjet material dispenser (250) may access a
deposit of stannous chloride solution stored in the material
reservoir (230) and selectively deposit the stannous chloride
solution onto the desired substrate (270). According to one
exemplary embodiment, the stannous chloride solution may include
both stannous chloride (Cl.sub.2Sn) and concentrated hydrochloric
acid (HCl). Additionally, according to one exemplary embodiment,
the stannous chloride solution may also include a number of
additives configured to facilitate a jetting of the solution from
an inkjet material dispenser. The additives may include, but are in
no way limited to, pH modifiers, fillers, salts, surfactants,
biocides, buffers, viscosity modifiers, sequestering agents,
stabilizing agents, etc.
[0042] Selective deposition of the stannous chloride solution onto
the desires substrate (270) may be further facilitated by the servo
mechanisms (220) controllably translating the inkjet material
dispenser (250) adjacent to the desired substrate (270). According
to the exemplary embodiment shown, the deposited stannous chloride
solution forms a seed material pattern (500) on the surface of the
substrate. According to one exemplary embodiment, stannous ions are
adsorbed by the desired substrate (S*) according to the following
equation:
S*+Sn.sup.+2(aq).fwdarw.S*.Sn.sup.+2(ad) Equation 1
[0043] Continuing with FIG. 4A, once the stannous chloride solution
has been selectively deposited onto the desired substrate (step
400) the desired substrate is rinsed in a rinsing bath (step 410).
As illustrated in FIG. 5B, the desired substrate (270) having the
seed material pattern (500) formed from stannous chloride is
immersed in a rinsing bath (290). Immersing the substrate (270) in
the rinsing bath (290) removes impurities and excess stannous
chloride solution from the desired substrate (270). Consequently, a
material pattern of stannous or tin ions remain on the desired
substrate (270).
[0044] With the substrate rinsed, it may then be immersed in a
palladium isolating bath containing palladium chloride and
hydrochloric acid (HCl), according to the present exemplary
embodiment (step 420). FIG. 5C illustrates the deposition of the
desired substrate (270) in a palladium isolating bath (294). As
shown, the acidic palladium chloride solution (294) controllably
reacts with the stannous ions via galvanic replacement according to
the following reaction:
S*.Sn.sup.+2(ad)+Pd.sup.+2(aq).fwdarw.S*.Pd(ad)+Sn.sup.+4 Equation
2
As a result of the reaction, palladium ions are reduced to a
colloidal state in the shape of the seed material pattern (510) and
stannous ions are released into the solution.
[0045] With the palladium ions reduced to a colloidal state in the
shape of the seed material pattern (510), the substrate may again
be rinsed to remove excess palladium chloride (step 430; FIG. 4),
thereby preparing the substrate for zinc oxide deposition. As
illustrated in FIG. 5C, the substrate (270) is again immersed in a
rinsing bath (290) containing de-ionized water. Consequently, the
substrate (270) is rinsed causing a seeded material pattern of
catalytic palladium ions (510), as shown.
[0046] With the desired substrate (270) containing a seeded
material pattern of catalytic palladium ions (510), the substrate
is prepared for zinc oxide deposition. Returning to FIG. 3, the
zinc oxide is deposited on the seeded pattern (step 340), according
to one exemplary embodiment, by immersing the rinsed substrate in a
zinc oxide bath. FIG. 5E illustrates the desired substrate (270)
immersed in a zinc oxide bath (296). According to the exemplary
illustrated embodiment, the zinc oxide bath (296) contains a
solution of zinc nitrate (Zn(NO.sub.3).sub.2) and dimethylamine
borane (C.sub.2H.sub.10BN).
[0047] According to one exemplary embodiment, zinc nitrate is
reduced by the dimethylamine borane according to the following
proposed reactions illustrated in Equations 2-6:
Zn(NO.sub.3).sub.2.fwdarw.Zn.sup.2++2NO.sub.3.sup.- Equation 3
(CH.sub.3).sub.2NHBH.sub.3+H.sub.2O.fwdarw.BO.sub.2.sup.-+(CH.sub.3).sub-
.2NH+7H.sup.++6e.sup.- Equation 4
NO.sub.3.sup.-+H.sub.2O+2e.sup.-.fwdarw.NO.sub.2.sup.-+2OH.sup.-
Equation 5
Zn.sup.+2+2OH.sup.-.fwdarw.Zn(OH).sub.2 Equation 6
Zn(OH).sub.2.fwdarw.ZnO+H.sub.2O Equation 7
As illustrated in FIGS. 5E and 5F, once the zinc oxide is formed by
the above reactions, it is then attracted to and is deposited on
the seeded material pattern of catalytic palladium ions (510; FIG.
5C) to form a desired zinc oxide pattern (520).
[0048] FIG. 4B illustrates an alternative method for selectively
dispensing a seed material onto a desired substrate in a designated
pattern (step 320; FIG. 3) and preparing the substrate for zinc
oxide deposition (step 330; FIG. 3), according to a second
exemplary embodiment. As shown in FIG. 4B, the second exemplary
method selectively jets a tin/palladium complex onto the desired
substrate (step 450) followed by a rinsing step (step 460). After
the tin/palladium complex deposition is rinsed, the desired
substrate is then immersed in an accelerating solution to
substantially remove the tin component of the deposited
tin/palladium complex (step 470). With the tin component removed
from the tin/palladium complex, the substrate is again rinsed (step
480) in preparation of a zinc oxide deposition. Further details of
the second exemplary method for dispensing a seed material onto a
desired substrate in a designed pattern will now be described in
further detail below.
[0049] As illustrated in FIG. 4B, the second exemplary method
begins by selectively jetting a tin/palladium complex onto the
desired substrate (step 450). Similar to the first exemplary
method, the tin/palladium complex may be jetted onto the desired
substrate (step 450) by the inkjet material dispenser (250; FIG.
5A). According to this exemplary embodiment, the material reservoir
(230; FIG. 5A) contains a tin/palladium complex solution that
includes tin ions configured to adhere to the substrate upon
deposition. Further, palladium ions are associated with the tin
ions, as deposited.
[0050] Once the tin/palladium complex has been deposited onto the
desired substrate, the substrate is rinsed in a de-ionized water
rinsing bath (step 460; FIG. 4). According to this exemplary
embodiment, the rinsing in de-ionized water removes the
tin/palladium ions that are not adhered to the desired substrate,
according to the designed pattern.
[0051] Once rinsed, the exemplary substrate containing the
tin/palladium ions formed in a desired pattern is immersed in an
accelerating solution to substantially remove the tin ions from the
desired pattern (step 470). More specifically, according to one
exemplary embodiment, the desired substrate, having the
tin/palladium ions formed thereon, is submerged in a solution of
fluoroboric acid and sulfuric acid. According to one exemplary
embodiment, the accelerating solution is configured to form
intermediaries and remove the excess tin ions, thereby exposing the
palladium ions making the deposition catalytically active.
[0052] Once the palladium ions are exposed and catalytically
active, the substrate is again rinsed (step 480) to remove excess
accelerator and/or tin in preparation of being submerged in a zinc
oxide plating bath for the reception of zinc oxide depositions
(step 340; FIG. 3) as described above. A number of exemplary zinc
oxide depositions were performed according to the above-mentioned
exemplary methods. Crystal structures and characteristics of the
experimental depositions will be described in detail below.
EXAMPLES
[0053] According to one exemplary embodiment, the above-mentioned
reactions were confirmed by first immersing a substrate in a
solution of stannous chloride (5 gm/l of SnCl.sub.2 and 5 ml/l of
concentrated HCl)] for approximately one minute followed by a
rinsing of the substrate with a de-ionized water solution. After
deposition of the stannous chloride, the sample was activated by
immersing it in a palladium chloride solution including
approximately 1% PdCl.sub.2 and 0.4% concentrated HCl for about a
minute followed again with rinsing of the substrate with a
de-ionized water solution. During the exemplary experiment, the
sample was kept wet between the sensitization and the activation
steps, as well as before ZnO deposition.
[0054] After the activation and rinsing of the sample, a zinc oxide
bath was prepared with approximately 30 g/L of Zn(NO.sub.3).sub.2
and 6 g/L of DMAB. A constant temperature bath was used to maintain
the temperature of the bath between approximately 55 and 65.degree.
C. Additionally, pH of the freshly prepared bath was approximately
5.8. Once the bath was prepared, two to three samples were
deposited in the bath to receive zinc oxide depositions before the
bath was discarded. During deposition, zinc oxide was formed on the
substrate. After deposition, the pH of the bath was approximately
6.3. Typical bath volume was approximately 50 ml.
[0055] The first zinc oxide deposition attempt was made on a glass
substrate cleaned with hexane followed by iso-propyl alcohol (IPA).
To validate the above-mentioned methods, the substrate was
activated with SnCl.sub.2/PdCl.sub.2 as mentioned above. ZnO was
then deposited after immersion in a zinc oxide bath forming
hexagonal zinc oxide crystal structures, as confirmed by scanning
electron microscope (SEM) images. FIGS. 6A and 6B are SEM images
illustrating the resulting zinc oxide crystal structures.
[0056] Additionally, a first 3M transparency was deposited with a
palladium seed layer as illustrated above and a second 3M
transparency was deposited without the palladium seed layer to
evaluate the effect of the palladium seed layer. FIG. 7A
illustrates the zinc oxide crystals that resulted without the
deposition of a palladium seed layer. As illustrated, the resulting
zinc oxide crystals were not well defined. In contrast, FIG. 7B is
an SEM image of the zinc oxide crystals that result after the
deposition of a palladium seed layer as described above. As noted,
the crystals are more defined after the deposition of the palladium
seed layer, resulting in improved semiconducting behavior.
[0057] The zinc oxide as produced by the present exemplary systems
and methods described herein are expected to provide very
satisfactory electrical performance, specifically in the area of
channel mobility. In addition, for certain zinc oxides described
herein, the channel can be transparent in one, both, or more of the
ultraviolet, visible, and/or infrared portions of the
electromagnetic spectrum, allowing for an entire thin-film
transistor to be optically transparent throughout the visible
region of the electromagnetic spectrum.
[0058] In conclusion, the present systems and methods for forming a
seed layer for use in electroless plating of materials such as zinc
oxide on a desired substrate include patterning a palladium or
other seed layer onto a desired substrate with an inkjet material
dispenser prior to the deposition of a metallic material such as
zinc oxide. According to one exemplary embodiment, the palladium
seed patterning described herein is an additive process which
reduces the overall waste of the system, is modifiable very
rapidly, results in a highly crystalline zinc oxide deposition, and
reduces the overall cost of zinc oxide deposition, compared to
traditional methodologies.
[0059] The preceding description has been presented only to
illustrate and describe exemplary embodiments of the present system
and method. It is not intended to be exhaustive or to limit the
system and method to any precise form disclosed. Many modifications
and variations are possible in light of the above teaching. It is
intended that the scope of the system and method be defined by the
following claims.
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