U.S. patent number RE41,989 [Application Number 12/697,398] was granted by the patent office on 2010-12-07 for method and apparatus for electronic device manufacture using shadow masks.
This patent grant is currently assigned to Advantech Global, Ltd. Invention is credited to Thomas Peter Brody.
United States Patent |
RE41,989 |
Brody |
December 7, 2010 |
Method and apparatus for electronic device manufacture using shadow
masks
Abstract
Electronic devices are formed on a substrate that is advanced
stepwise through a plurality of deposition vessels. Each deposition
vessel includes a source of deposition material and has at least
two shadow masks associated therewith. Each of the two masks is
alternately positioned within the corresponding deposition vessel
for patterning the deposition material onto the substrate through
apertures in the mask positioned therein, and positioned in an
adjacent cleaning vessel for mask cleaning. The patterning onto the
substrate and the cleaning of at least one of the masks are
performed concurrently.
Inventors: |
Brody; Thomas Peter
(Pittsburgh, PA) |
Assignee: |
Advantech Global, Ltd (Tortola,
VG)
|
Family
ID: |
37892393 |
Appl.
No.: |
12/697,398 |
Filed: |
February 1, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
11236937 |
Sep 27, 2005 |
07531470 |
May 12, 2009 |
|
|
Current U.S.
Class: |
438/800;
257/E21.532; 216/12; 438/689; 134/2 |
Current CPC
Class: |
C23C
14/564 (20130101); C23C 14/042 (20130101); B08B
7/0035 (20130101); B08B 13/00 (20130101); H01L
51/0011 (20130101); H01L 27/1214 (20130101); H01L
27/1288 (20130101); H01L 29/78681 (20130101) |
Current International
Class: |
H01L
21/00 (20060101) |
Field of
Search: |
;438/689,800 ;216/12
;134/2 ;257/E21.532 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Zandra V.
Assistant Examiner: Novacek; Christy L
Attorney, Agent or Firm: The Webb Law Firm
Claims
The invention claimed is:
1. A method of forming an electronic device comprising: (a)
sequentially advancing a substrate through a plurality of vacuum
deposition vessels positioned along a fabrication path, wherein
each deposition vessel includes (i) a material deposition source
including deposition material, .Iadd.and .Iaddend.(ii) a first
shadow mask positioned within the deposition vessel, the first
shadow mask having a predetermined pattern of apertures
therethrough, .[.(iii).]. .Iadd.and wherein .Iaddend.a first
cleaning vessel .Iadd.is .Iaddend.positioned adjacent the
deposition vessel.[.,.]. and .[.(iv).]. a second cleaning vessel
.Iadd.is .Iaddend.positioned adjacent the deposition vessel,
wherein: the first cleaning vessel, the deposition vessel and the
second cleaning vessel define a cleaning path that is transverse to
the fabrication path; a second shadow mask is positioned in the
second cleaning vessel, the second shadow mask having the
predetermined pattern of apertures therethrough; the first cleaning
vessel is operative for cleaning the first shadow mask when the
first shadow mask is received therein; and the second cleaning
vessel is operative for cleaning the second shadow mask when the
second shadow mask is received therein; (b) cleaning the second
shadow mask positioned in the second cleaning vessel concurrently
with depositing the deposition material through the predetermined
pattern of apertures of the first shadow mask and onto the
substrate; (c) moving the first shadow mask along the cleaning path
from the deposition vessel to the first cleaning vessel and moving
the second shadow mask along the cleaning path from the second
cleaning vessel to the deposition vessel; and (d) cleaning the
first shadow mask positioned in the first cleaning vessel
concurrently with depositing the deposition material through the
predetermined pattern of apertures of the second shadow mask and
onto the substrate.
2. The method of claim 1, further including: (e) moving the second
shadow mask along the cleaning path from the deposition vessel to
the second cleaning vessel and moving the first shadow mask along
the cleaning path from the first cleaning vessel to the deposition
vessel; and (f) repeating step (b)-(e) at least once.
3. The method of claim 2, further including advancing the substrate
along the fabrication path between deposits of deposition material
onto the substrate.
4. The method of claim 1, further comprising measuring an end point
for cleaning each shadow mask to indicate when the shadow mask is
clean.
5. The method of claim 1, wherein the deposition material is
chemically distinct from a chemical component of each shadow
mask.
6. The method of claim 1, wherein each cleaning vessel includes a
plurality of cleaning chambers, each chamber operative for cleaning
a shadow mask.
7. The method of claim 1, wherein each cleaning vessel includes a
plasma source or a source of gaseous etchant for cleaning the
corresponding shadow mask.
8. The method of claim 7, wherein the etchant is selected from
either: a group consisting of a halogen, a halogen-containing
chemical compound and oxygen; or a group consisting of hydrogen and
a hydrogen-containing chemical compound.
9. The method of claim 1, wherein: the first cleaning vessel and
the deposition vessel are interconnected by a first vacuum valve;
the second cleaning vessel and the deposition vessel are
interconnected by a second vacuum valve; moving the first shadow
mask includes passing the first shadow mask through the first
valve; and moving the second shadow mask includes passing the
second shadow mask through the second valve.
10. The method of claim 1, wherein the cleaning path is
substantially linear.
11. The method of claim 1, wherein a time required for cleaning at
least one shadow mask is either: less than a time required for
depositing the material on the substrate; or does not substantially
exceed a time required for depositing the material on the
substrate.
12. A method of forming an electronic device comprising: (a)
providing a substrate adapted for advancement along a fabrication
path, a first portion of the substrate positioned at a first
process location along the path; (b) providing a deposition source
for depositing a material on the substrate at the first process
location; (c) providing a first shadow mask and a second shadow
mask substantially identical to the first shadow mask; (d)
positioning the first shadow mask between the deposition source and
the first portion of the substrate and positioning the second
shadow mask adjacent the fabrication path; (e) depositing the
material on the first portion of the substrate through the first
shadow mask while concurrently cleaning the second shadow mask; (f)
advancing the substrate along the fabrication path whereupon a
second portion of the substrate is positioned at the first process
location; (g) positioning the second shadow mask between the
deposition source and the second portion of the substrate and
positioning the first shadow mask adjacent to the fabrication path;
and (h) depositing the material on the second portion of the
substrate through the second shadow mask while concurrently
cleaning the first shadow mask.
13. The method of claim 12, wherein the material is deposited and
each shadow mask is cleaned in the presence of a vacuum.
14. The method of claim 12, further comprising providing a first
cleaning vessel for cleaning the first shadow mask and a second
cleaning vessel for cleaning the second shadow mask, wherein each
cleaning vessel includes means for determining completion of a
cleaning process.
15. The method of claim 12, wherein cleaning each shadow mask
comprises (i) exposing the shadow mask to at least one of a plasma
and a chemical etchant, (ii) reactive ion etching or (iii) physical
sputtering.
16. The method of claim 12, wherein a time required for cleaning
either shadow mask is either: less than a time required for
depositing the material on the substrate; or does not substantially
exceed a time required for depositing the material on the
substrate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and systems for fabricating
electronic circuits, and particularly to apparatus and methods
incorporating shadow masks and shadow mask cleaning in the
manufacture of integrated circuits.
2. Description of Related Art
Large area active electronic devices are widely used in flat panel
displays and related technologies. For example, active matrix
backplanes are used in flat panel displays for routing signals to
pixels of the display in order to produce viewable pictures. Active
matrix backplanes, as well as other large area electronic circuits,
are multilayer devices presently manufactured using
photolithography, a pattern definition technique that uses
electromagnetic radiation, such as ultraviolet radiation, to expose
a layer of a photoresist material deposited on the surface of a
substrate. Exemplary photolithographic processing steps to produce
a layer of a multilayer active matrix backplane on a substrate
include: coat with photoresist, prebake, soak, bake, align, expose,
develop, rinse, bake, deposit a layer, lift off the photoresist,
scrub, rinse, and dry.
Photolithography-based manufacturing methods thus include a wide
variety of both additive (material deposition) steps and
subtractive (material removal) steps, requiring large, complex and
expensive fabrication facilities that incorporate many disparate
manufacturing technologies. Furthermore, many photolithographic
manufacturing steps must be carried out in clean room environments,
further driving the manufacturing complexity and costs high.
Alternatively, a vapor deposition shadow mask process is well-known
and has been used for years in microelectronics manufacturing. The
vapor deposition shadow mask process is a significantly less costly
and less complex manufacturing process, compared with
photolithography-based manufacturing. The vapor deposition shadow
mask process can be used to form one or more electronic devices on
a substrate using additive processes only. This is done by
sequentially depositing patterns of materials including conductors,
semiconductors and insulators, through complementary patterns of
apertures in shadow masks positioned between one or more material
deposition sources and the substrate.
One challenge in implementing all-additive process steps for the
volume manufacturing of electronic circuits is that as a shadow
mask is used repetitively for patterning a material onto a
substrate, the mask also accumulates the material on its surface
and in its pattern of apertures, changing the dimensions of the
apertures and thereby degrading mask performance for future
depositions through that mask onto a substrate. Frequent
replacement of a shadow mask, especially a large area mask,
generally is neither practical nor cost-effective for a volume
manufacturing process. Some degraded shadow masks may be cleaned to
remove deposited material from the mask, but shadow mask cleaning
is generally considered incompatible with high volume production of
electronic devices because most mask cleaning methods are very slow
or labor intensive or would require that the mask be removed from a
production line and brought to a separate environment for
cleaning.
Accordingly, a need exists in this art for equipment and methods to
rapidly and cost-effectively clean shadow masks in a volume
manufacturing setting. In addition, a need exists for apparatus and
methods for rapidly replacing a used shadow mask for a fresh shadow
mask in a manufacturing line.
SUMMARY OF THE INVENTION
The invention is a method of forming an electronic device. The
method includes (a) sequentially advancing a substrate through a
plurality of vacuum deposition vessels positioned along a
fabrication path, wherein each deposition vessel includes (i) a
material deposition source including deposition material, .Iadd.and
.Iaddend.(ii) a first shadow mask positioned within the deposition
vessel, the first shadow mask having a predetermined pattern of
apertures therethrough, .[.(iii).]. .Iadd.and wherein .Iaddend.a
first cleaning vessel .Iadd.is .Iaddend.positioned adjacent the
deposition vessel, and .[.(iv).]. a second cleaning vessel .Iadd.is
.Iaddend.positioned adjacent the deposition vessel, wherein: the
first cleaning vessel, the deposition vessel and the second
cleaning vessel define a cleaning path that is transverse to the
fabrication path; a second shadow mask is positioned in the second
cleaning vessel, the second shadow mask having the predetermined
pattern of apertures therethrough; the first cleaning vessel is
operative for cleaning the first shadow mask when the first shadow
mask is received therein; and the second cleaning vessel is
operative for cleaning the second shadow mask when the second
shadow mask is received therein; (b) cleaning the second shadow
mask positioned in the second cleaning vessel concurrently with
depositing the deposition material through the predetermined
pattern of apertures of the first shadow mask and onto the
substrate; (c) moving the first shadow mask along the cleaning path
from the deposition vessel to the first cleaning vessel and moving
the second shadow mask along the cleaning path from the second
cleaning vessel to the deposition vessel; and (d) cleaning the
first shadow mask positioned in the first cleaning vessel
concurrently with depositing the deposition material through the
predetermined pattern of apertures of the second shadow mask and
onto the substrate.
The method can further include (e) moving the second shadow mask
along the cleaning path from the deposition vessel to the second
cleaning vessel and moving the first shadow mask along the cleaning
path from the first cleaning vessel to the deposition vessel; and
(f) repeating step (b)-(e) at least once.
The method can further include advancing the substrate along the
fabrication path between deposits of deposition material onto the
substrate.
The method can further include measuring an end point for cleaning
each shadow mask to indicate when the shadow mask is clean.
The deposition material can be chemically distinct from a chemical
component of each shadow mask.
Each cleaning vessel can include a plurality of cleaning chambers,
with each chamber operative for cleaning a shadow mask.
Each cleaning vessel can include a plasma source or a source of
gaseous etchant for cleaning the corresponding shadow mask. The
etchant can be selected from either a group consisting of a
halogen, a halogen-containing chemical compound and oxygen or a
group consisting of hydrogen and a hydrogen-containing chemical
compound.
The first cleaning vessel and the deposition vessel can be
interconnected by a first vacuum valve. The second cleaning vessel
and the deposition vessel can be interconnected by a second vacuum
valve. Moving the first shadow mask can include passing the first
shadow mask through the first valve. Moving the second shadow mask
can include passing the second shadow mask through the second
valve.
The cleaning path can be substantially linear.
The time required for cleaning at least one shadow mask can be
either less than a time required for depositing the material on the
substrate or does not substantially exceed a time required for
depositing the material on the substrate.
The invention is also a method of forming an electronic device
comprising (a) providing a substrate adapted for advancement along
a fabrication path, a first portion of the substrate positioned at
a first process location along the path; (b) providing a deposition
source for depositing a material on the substrate at the first
process location; (c) providing a first shadow mask and a second
shadow mask substantially identical to the first shadow mask; (d)
positioning the first shadow mask between the deposition source and
the first portion of the substrate and positioning the second
shadow mask adjacent the fabrication path; (e) depositing the
material on the first portion of the substrate through the first
shadow mask while concurrently cleaning the second shadow mask; (f)
advancing the substrate along the fabrication path whereupon a
second portion of the substrate is positioned at the first process
location; (g) positioning the second shadow mask between the
deposition source and the second portion of the substrate and
positioning the first shadow mask adjacent to the fabrication path;
and (h) depositing the material on the second portion of the
substrate through the second shadow mask while concurrently
cleaning the first shadow mask.
The material can be deposited and each shadow mask can be cleaned
in the presence of a vacuum.
The method can further include providing a first cleaning vessel
for cleaning the first shadow mask and a second cleaning vessel for
cleaning the second shadow mask, wherein each cleaning vessel
includes means for determining completion of a cleaning
process.
Cleaning each shadow mask can include (i) exposing the shadow mask
to at least one of a plasma and a chemical etchant; (ii) reactive
ion etching; or (iii) physical sputtering.
The invention is also an apparatus for manufacturing an electronic
device. The apparatus includes (a) a plurality of interconnected
deposition vessels defining an elongated fabrication path; (b)
means for advancing a substrate along the fabrication path; (c) at
least one material deposition source positioned in each deposition
vessel for depositing a material on the substrate when the
substrate is positioned in the deposition vessel; and (d) two
cleaning vessels connected to each deposition vessel, each cleaning
vessel operative for receiving a shadow mask from the corresponding
deposition vessel for cleaning and for passing the shadow mask to
the corresponding deposition vessel for depositing the material
onto the substrate through a pattern of apertures in the shadow
mask.
Each cleaning vessel can be operative for cleaning the shadow mask
by reactive ion etching or by physical sputtering. The substrate
can be either continuous or segmented along the fabrication
path.
The apparatus can further include means for monitoring shadow mask
cleanliness.
Each cleaning vessel can be connected to its corresponding
deposition vessel via a vacuum valve.
The invention is also an apparatus for manufacturing an electronic
device. The apparatus includes a plurality of vacuum deposition
vessels positioned along a fabrication path and configured for
receiving a substrate advanced along the path and a material
deposition source positioned in each deposition vessel. A plurality
of shadow masks is provided and a plurality of shadow mask cleaning
vessels are coupled to each deposition vessel and define therewith
a cleaning path that intersects the fabrication path. For each
deposition vessel, one corresponding cleaning vessel is operative
for cleaning one shadow mask while the corresponding deposition
source is depositing a material through another shadow mask onto a
first portion of the substrate and another cleaning vessel is
operative for cleaning the other shadow mask while the deposition
source is depositing the material through the one shadow mask onto
a second portion of the substrate.
Lastly, the invention is an apparatus for manufacturing an
electronic device. The apparatus includes a plurality of series
connected vacuum deposition vessels and a material deposition
source positioned within each deposition vessel. Means is/are
provided for advancing a substrate along a longitudinal fabrication
path through the plurality of deposition vessels. A vacuum cleaning
vessel is coupled to each deposition vessel and a shadow mask is
associated with each deposition vessel. Means is/are provided for
passing the shadow mask between the deposition vessel and the
corresponding cleaning vessel. The shadow mask is alternately
positioned in the cleaning vessel for cleaning the shadow mask, and
positioned between the deposition source and the substrate in the
deposition vessel for depositing a material from the material
deposition source onto the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a illustrates schematically in plan view a plurality of
process stations in a manufacturing system of the present
invention, wherein a first shadow mask is positioned in a
deposition vessels associated with each station, and a second
shadow mask is positioned in a cleaning vessel;
FIG. 1b illustrates an embodiment of one of the plurality of the
process stations illustrated in FIG. 1a;
FIG. 2 illustrates the plurality of stations of FIG. 1a, wherein
used shadow masks are being replaced with clean shadow masks;
FIG. 3 illustrates the plurality of stations of FIG. 1a wherein the
second shadow mask has replaced the first shadow mask in the
deposition vessel, and the first shadow mask is positioned in a
cleaning vessel;
FIG. 4 illustrates schematically in plan view an embodiment of a
multi-mask process station of the present invention;
FIG. 5 illustrates schematically in plan view an embodiment of a
carousel process station of the present invention; and
FIG. 6 through FIG. 9 illustrate end views of a process station of
the present invention and a sequence of process steps for mask
cleaning according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Certain exemplary embodiments will now be described to provide an
overall understanding of the aspects and features of the methods,
apparatus, and systems disclosed herein. Examples of these
embodiments and features are illustrated in the drawings. Those of
ordinary skill in the art will understand that the apparatus,
systems and methods of use disclosed herein can be adapted and
modified to provide apparatus, systems and methods for other
applications and that other additions and modifications can be made
without departing from the scope of the present disclosure. For
example, the features illustrated or described as part of one
embodiment or one drawing can be used on another embodiment or
another drawing to yield yet another embodiment. Such modifications
and variations are intended to be included within the scope of the
present disclosure.
The present invention relates to methods, apparatus and systems for
the manufacture of electronic devices on substrates, and in
particular to the use of shadow masks in the manufacture of
electronic devices, where cleaning of the masks is integrated into
the manufacturing process and apparatus therefor. Some aspects of
the apparatus and methods for forming electronic devices using
shadow masks are disclosed in U.S. Pat. No. 6,943,066, which is
incorporated herein by reference. By electronic devices, we mean an
assembly of electronic elements that may be any combination of
active electronic elements and passive electronic elements formed
on a substrate. The active elements may include transistors,
diodes, radiation emitters, sensors or any other type of active
element. The passive elements may include electrical conductors,
resistors, capacitors, inductors or any other type of passive
element. By a shadow mask, we mean a sheet of a mask material that
is penetrated by a predetermined pattern of apertures, also called
vias, through which a complementary pattern of a deposition
material supplied by a vapor deposition source (deposition source)
can be deposited onto the substrate (also referred to herein as
patterning the deposition material onto the substrate) in a layer
that contributes to the formation of the electronic device. An
electronic device may be formed from any number of layers.
Typically, each consecutive patterned layer differs from a layer
over which it is patterned with regard to at least one of a
deposition material, a mask pattern and a layer thickness.
With reference to FIG. 1a, an electronic device manufacturing
system 100 of the present invention includes a plurality of process
stations 102. FIG. 1b illustrates a representative one of the
plurality of process station 102. Each process station 102 includes
a vacuum deposition vessel 104 positioned along a longitudinal
fabrication path 106. Each deposition vessel 104 also includes a
material deposition source 108 and a first shadow mask 110 through
which a deposition material from deposition source 108 is patterned
onto a substrate 112 through a pattern of apertures 114 in first
shadow mask 110. Deposition source 108 can be an evaporative
source, a sputtering source or another type of vacuum deposition
source. The deposition material can be any material useful for
forming one or more electronic devices on substrate 112 and that
can be deposited on substrate 112 via deposition source 108 and
apertures 114 of first shadow mask 110. Examples of deposition
materials include conductors, semiconductors and insulators. The
interior of deposition vessel 104 typically is maintained under
high vacuum conditions to perform depositions, at pressures
typically in the range of 10.sup.-5 torr to 10.sup.-7 torr.
Substrate 112 may be a continuous flexible substrate along
fabrication path 106, or may comprise a longitudinal array of
flexible or rigid substrate sections along fabrication path 106.
Substrate 112 may be any type of substrate upon which the
deposition material can be deposited, including polymer, glass,
crystal and metal. Fabrication path 106 may be linear, curved or
bent in any manner consistent with advancing substrate 112 through
the plurality of process stations 102. In one non-limiting
embodiment, an unpatterned portion 116 of substrate 112 enters
fabrication system 100 at an entrance 118, sequentially receives a
patterned layer of a deposition material in the deposition vessel
104 at each station 102, and leaves fabrication system 100 at an
exit 120, with one or more electronic device(s) 122 formed thereon.
At each step in the sequence, substrate 112 is advanced along
fabrication path 106 so that a portion of substrate 112 moves from
one process station 102 to the next process station 102 of the
plurality of process stations 102. Each deposition of a layer of a
deposition material on substrate 112 is an additive step in forming
the one or more electronic device(s) 122.
The plurality of stations 102 may include any number of process
stations required to form one or more desired electronic device(s)
122 on substrate 112. In one non-limiting embodiment, the plurality
of process stations 102 includes six process stations, forming at
least one active electronic device 122 on substrate 112 by
patterning in sequence along fabrication path 106 a first
insulator, a semiconductor, a first conductor, a second conductor,
a second insulator and a third conductor. The electronic device can
be a thin-film transistor (TFT) backplane for a flat panel display,
wherein the electronic elements of the electronic device can be
cadmium selenide thin film transistors. The description of the
electronic device being a TFT backplane, however, is not to be
construed as limiting the invention since it is envisioned that the
plurality of stations 102 of manufacturing system 100 can be
utilized to produce other types of electronic devices.
Each time a shadow mask 110 is used to pattern a deposition
material onto a substrate 112 during a deposition, a layer of the
deposition material is also deposited as a film on the surface of
the mask (on the mask) 110. With each additional deposition through
mask 110 onto substrate 112, the film on mask 110 increases in
thickness, eventually degrading the performance of mask 110 as the
pattern of apertures 114 becomes obscured, distorted, or otherwise
changed by the film. Changes in mask 110 due to accumulated
deposition material may include filling of apertures 114 with the
deposition material, warping of mask 110, reduced thermal stability
of mask 110 due to differential thermal expansion properties
between the film and mask 110, and partial or complete delamination
of the film from the mask 110. Thus, there is a requirement to
periodically replace shadow mask 110 or to clean shadow mask 110 to
sustain patterning performance in manufacturing system 100.
Frequent replacement of shadow masks 110 is generally economically
infeasible in volume manufacturing environments. Therefore, the
present invention includes methods, apparatus and systems for
cleaning shadow masks 110 for volume manufacturing of electronic
devices on substrates.
Shadow masks 110 used for forming layers of deposition materials in
the manufacture of electronic devices typically require frequent
cleaning. For example, suppose a shadow mask having a 50 micrometer
diameter circular aperture therein is used for patterning a
substantially 50 micrometer diameter, 0.5 micrometer thick pad of a
deposition material on a substrate. If the maximum tolerance of the
pad diameter is 10% from its nominal 50 micrometer diameter, and
the deposition material deposits isotropically on the mask surface
and inside the aperture during a deposition, each deposition of a
pad will reduce the effective inner diameter of the aperture by one
micrometer, whereupon the aperture will decrease in diameter to its
diametric tolerance limit after five depositions. To avoid this
problem, although a mask may require cleaning only after a
plurality of depositions therethrough, it may be desirable to clean
the mask after every deposition. Frequent mask cleaning may
increase performance consistency between consecutive depositions
through the mask and may optimize the performance lifetime of a
mask by providing consistent cycling of the mask through deposition
and cleaning cycles, as well as by avoiding stresses from
accumulated multiple layers of deposited material. An embodiment
wherein a shadow mask used for patterning onto a substrate is
exchanged with a clean shadow mask after each deposition through
the mask will now be described.
Each process station 102 includes a first mask cleaning vessel 124
and a second mask cleaning vessel 126. Each first cleaning vessel
124 and second cleaning vessel 126 is operative for cleaning a mask
by removing a film of deposition material from the mask
substantially without damaging the mask. In FIGS. 1a and 1b, first
mask 110 is illustrated positioned in deposition vessel 104, and a
second shadow mask 128 having the pattern of apertures 114 is
positioned in second cleaning vessel 126. Second shadow mask 128
can be substantially identical to first shadow mask 110. First
cleaning vessel 126, deposition vessel 104 and second cleaning
vessel 128 define a cleaning path 130 along which first mask 110
and second mask 128 can be translated. Cleaning path 130 can be
linear or is folded.
Mask 128 positioned in second cleaning vessel 126 can be cleaned
concurrently with a deposition being performed through first mask
110 in deposition chamber 104. FIGS. 1a, 2 and 3 illustrate a
portion of a fabrication process for forming an electronic device
in system 100. Following a first deposition of a deposition
material in deposition vessel 104 concurrent with the cleaning of
second mask 128 in the second cleaning vessel 126, illustrated in
FIGS. 1a and 1b, first mask 110 is transported 132 from deposition
vessel 104 to first cleaning vessel 124, and second mask 128 is
transported 134 from second cleaning vessel 126 to deposition
vessel 104, as illustrated in FIG. 2.
In addition, as also illustrated in FIG. 2, substrate 112 is
advanced in a process direction 136 along fabrication path 106,
whereupon a new section 138 of substrate 112 is introduced to
system 100 at entrance 118 and a section of substrate bearing one
or more completed electronic device(s) 122 exits the system 100 at
exit 120. When substrate 112 is advanced in process direction 136,
each portion of substrate 112 positioned for a deposition in
deposition vessel 104 at a first station 140 of the plurality of
stations 102 is moved and repositioned for a next deposition in the
deposition vessel 104 of an adjacent, second station 142 of the
plurality of stations 102. That is, substrate 112 is advanced
stepwise. In one embodiment, substrate 112 is flexible and is
advanced through the system 100 from a cylindrical supply reel (not
shown). In another embodiment, substrate 112 comprises individual
sections of substrate material that are advanced individually
through system 100. Several means for advancing the substrate along
the fabrication path are known in the art, including traction on
the substrate, conveyor systems and robotic substrate handling
systems. For example, substrate 112 can be continuous along
fabrication path 106 and can be advanced along fabrication path 106
using traction rollers.
When translation of first mask 110 to first cleaning vessel 124 and
second mask 128 to deposition vessel 104 is complete and substrate
112 has been advanced, as illustrated in FIG. 3, first mask 110 is
cleaned in the first cleaning vessel 124 concurrently with a
deposition being performed in deposition vessel 104 using second
mask 128. Following this deposition in deposition vessel 104 and
the cleaning of first mask 110 in first cleaning vessel 124,
substrate 112 is again advanced along fabrication path 106 and the
translation direction of first mask 110 and second mask 128 along
cleaning path 130 is reversed with respect to the translation
described in association with FIG. 2, whereupon first mask 110 is
returned to deposition vessel 104 and the second mask 128 is
returned to second cleaning vessel 126. By repeating the above
sequence, first mask 110 and second mask 128 are thus cleaned and
used for patterning onto the substrate 112 in an alternating
manner. Each process station 102 can be operated independently or
synchronously with regard to which of its respective masks is used
for depositing on the substrate or being cleaned at a particular
time. For example, whereas FIG. 1a illustrates all of process
stations 102 having their second masks 128 being cleaned in second
cleaning vessels 126 concurrently with depositions in deposition
vessels 104, in another embodiment, each of one or more of the
plurality of process stations 102 may have its first mask 110 being
cleaned in its corresponding first deposition vessel 124
concurrently with a deposition occurring in its corresponding
deposition vessel 104, while other process stations 102 have their
second masks 128 being cleaned in their corresponding second
cleaning vessels 126.
A maximum throughput rate (minimum time) for forming electronic
devices using manufacturing system 100 is determined by the sum of
a first, longest time required to perform a deposition in one of
process stations 102, a second time required to advance a portion
of the substrate 112 from one process station 102 to a next process
station 102 along fabrication path 106, and a third time required
to cycle the portion of the substrate 112 through any pressure,
temperature and chemical environment changes required for it to be
advanced. Desirably, the minimum time is not limited by a time
required to clean a mask or by the time required to cycle a mask
between a cleaning vessel and an associated deposition vessel. That
is, a cleaning cycle is desirably faster than a deposition cycle.
In one embodiment, the time from the beginning of a deposition onto
a first portion of a substrate in a deposition vessel 104 to the
beginning of a next deposition on a second portion of the substrate
in deposition vessel 104 (a station cycle time) is less than two
minutes. In another embodiment, the cycle time between deposition
events in the same deposition vessel 104 is less than 30
seconds.
In some situations, the time required to clean a mask may exceed
the time required for a deposition. Long cleaning times for masks
can be accommodated in a manufacturing system of the present
invention by providing more than two masks at a process station
along a fabrication path. FIG. 4 illustrates in plan view a
multi-mask process station 150 of a manufacturing system of the
present invention. One or more processed stations 150 can replace a
corresponding number of process stations 102 in electronic device
manufacturing system 100. Multi-mask station 150 includes a first
cleaning vessel 152 and a second cleaning vessel 154, each having
two cleaning chambers 156. A shadow mask 158 is associated with
each cleaning chamber 156, each cleaning chamber 156 being adapted
for independently cleaning a respective mask 158 and for transport
of the respective mask 158 along a cleaning path 160 between the
cleaning chamber 156 and a deposition vessel 162, the deposition
vessel 162 being positioned along a fabrication path 164 for
advancing a substrate 166. In addition to the sequence described in
association with FIGS. 1-3 for transporting masks alternatingly
between cleaning vessels and a deposition vessel, operation of
multi-mask station 150 includes, within each of the first cleaning
vessel 152 and the second cleaning vessel 154, alternately
transporting a mask 158 from each of the two cleaning chambers 156
thereof to the deposition vessel 162, thereby increasing the time
available to clean each mask 158, since each mask 158 is used only
every fourth deposition in deposition vessel 162.
In one embodiment, alternately transporting a mask from each of the
two cleaning chambers 156 comprises translating 168 the two
cleaning chambers 156 as a unit so that the two cleaning chambers
156 are alternately positioned along the cleaning path 160,
depending on which of the two cleaning chambers 156 contains the
mask to be next used for a deposition. In FIG. 4 the first cleaning
vessel 152 and the second cleaning vessel 154 are illustrated on
opposite ends of cleaning path 160. In another embodiment, the two
cleaning chambers 156 of each of the first cleaning vessel 152 and
the second cleaning vessel 154 are fixed in position and each mask
158 is independently transported between each cleaning chamber 156
and the cleaning path 160, for transport to and from the deposition
chamber 162.
Another type of multi-mask process station is the mask carousel
process station 200 shown in FIG. 5. Mask carousel station 200
includes a first carousel cleaning vessel 202 and a second cleaning
vessel 204, with each cleaning vessel including a plurality of
cleaning chambers 206 arranged about an axis 208 and having one or
more shadow masks 210 associated therewith. The plurality of
cleaning chambers 206 of each cleaning vessel 202 and 204 is
configured to rotate about axis 208 to sequentially position each
mask 210 positioned in cleaning chamber 206 for transport along a
cleaning path 212 that extends between first cleaning vessel 202
and second cleaning vessel 204 via deposition vessel 214.
Desirably, more than one mask 210 in at least one of first and
second cleaning vessels 202 and 204 is cleaned simultaneously.
Cleaning of a shadow mask using methods, apparatus or systems of
the present invention may be performed using any suitable
nondestructive cleaning method compatible with coupling to a means
for rapidly transporting the mask between a cleaning vessel and a
vacuum deposition vessel between depositions in the deposition
vessel. Suitable cleaning methods include plasma-based processes
such as Reactive Ion Etching (RIE), physical sputtering and ion
milling, as well as photochemical etching, thermal, laser ablative,
and chemical etching methods. RIE is a chemically selective etching
process in which a surface to be cleaned is exposed, under moderate
vacuum conditions typically in the range of 20 torr to 10.sup.-3
torr in the cleaning vessel, to a plasma including gaseous chemical
species that react rapidly with the material to be removed from the
mask surface, while reacting much more slowly or being unreactive
with an underlying material. Reaction products are volatile in the
plasma environment and pumped away. Physical sputtering is a less
chemically selective plasma process, typically performed at lower
pressures than RIE, with the etching performed by surface
collisions of energetic but chemically inert chemical species.
Depending on the chemical composition of the mask and of the
material to be removed, RIE gases typically are gaseous or
volatilizable chemical compounds, or elemental oxidizing gases
including fluorine, chlorine, bromine, iodine and oxygen, or
reducing gases including hydrogen and hydrogen-containing
compounds. Masks may be made from any material that can be
fabricated as a thin sheet having a pattern of apertures suitable
for patterning a deposition material onto a substrate, and mask
construction materials may be selected for inertness under RIE,
relative to an etching gas. Thus, it may be desirable to
manufacture masks from different materials to pattern different
layers in the formation of an electronic device, depending on a
desired cleaning chemistry. Typically, masks are metallic,
manufactured from pure metals or alloys. Common mask materials
include nickel, copper, and refractory metals.
Referring again to FIGS. 1-3, the pressure and the chemical
environment within each deposition vessel 104 is generally
different from the pressure and the chemical environment within an
associated first and/or second cleaning vessels 124, 126. In
addition, each process station 102 may require a deposition
material that is different from a deposition material required for
deposition at an adjacent process station 102 along the fabrication
path 106. To maintain these differences in environment, the
fabrication system 100 includes suitable means to isolate the
internal working environments of each deposition vessel 104 and its
corresponding first and second cleaning vessels 124, 126.
Deposition vessel 104 of each process station 102 along fabrication
path 106 is isolated from deposition vessel 104 in an adjacent
process station 102 by a station separation means 250 through which
substrate 112 can be translated. In one non-limiting embodiment,
station separation means 250 is a vacuum valve that is closed
between separate sections of substrate 112 along the fabrication
path 106 during a deposition. Also or alternatively, where
substrate 112 is continuous along fabrication path 106, the vacuum
valve seals one or more surfaces of substrates 112. Desirably, the
vacuum valve is adapted for rapid opening and closure, and adjacent
deposition vessels are at substantially the same pressure as one
another before the vacuum valve is opened. In one embodiment, the
vacuum valve is a gate valve.
In another embodiment, depositions in adjacent deposition vessels
104 are performed at a similar pressure and separation means 250 is
a substantially slot-shaped opening through which substrate 112 is
translated along fabrication path 106. In a further embodiment,
separation means 250 is ported to a vacuum source to support the
isolation of deposition vessels 104 in adjacent process stations
102. In another embodiment, each separation means 250 is ported to
a separate vacuum source so that a plurality of separation means
250 can be differentially pumped along the fabrication path
106.
Each cleaning vessel 124, 126 is isolated from its associated
deposition vessel 104 by a vacuum valve 252 through which a mask
can be translated. Each vacuum valve 252 can be ported to a vacuum
source to enhance isolation of deposition vessel 104 from its
corresponding cleaning vessels 124, 126. In another embodiment,
each vacuum valve 252 is ported to a separate vacuum source so that
a plurality of vacuum valves 252 can be differentially pumped along
cleaning path 130. In one embodiment, vacuum valve 252 is a load
lock.
FIG. 6 illustrates another embodiment of a process station 300 of
the present invention. Process station 300 includes a deposition
vessel 302, a first cleaning vessel 304, a second cleaning vessel
306, a first valve 308 for isolating the first cleaning vessel 304
from the deposition vessel 302 and a second valve 310 for isolating
the second cleaning vessel 306 from the deposition vessel 302.
Deposition vessel 302 is positioned along a fabrication path 311
(out of the plane of FIG. 6).
Deposition vessel 300 includes a first shadow mask 312 and
deposition source 314 adapted for patterning a deposition material
316 through mask 312 onto a substrate 317. Deposition vessel 302 is
ported to a vacuum source 318 for establishing and maintaining
vacuum for performing depositions. Each cleaning vessel 304 and 306
includes a cleaning means 320. In one embodiment, cleaning means
320 is RIE. In another embodiment, cleaning means 320 is physical
sputtering. Each cleaning vessel 304 and 306 is ported to a
corresponding vacuum source 322. A second shadow mask 324 is shown
positioned in second cleaning vessel 306 for removing deposited
material 326 from second mask 324. As second mask 324 is cleaned,
removed material 326 is pumped from second cleaning vessel 306 by
its corresponding vacuum source 322.
Each of first valve 308 and second valve 310 is ported to a
corresponding vacuum source 328 for enhancing the isolation of
respective first and second cleaning vessels 304 and 306 from
deposition vessel 302. Each cleaning vessel 304, 306 is adapted for
at least one of rapid flushing with a purging gas, and rapid
pumpdown from a pressure used for mask cleaning, to a lower
pressure suitable for performance of a deposition in deposition
vessel 302.
FIGS. 6-9 illustrate an exemplary cycle of exchanging masks among
deposition chamber 302, first cleaning vessel 304 and second
cleaning vessel 306 during time intervals between depositions in
deposition vessel 302. Referring to FIG. 6, station 300 includes
first mask 312 positioned in deposition vessel 302 and second mask
324 positioned in second cleaning vessel 306. In FIG. 6, a first
deposition is in progress in deposition vessel 302 concurrently
with cleaning second mask 324 in second cleaning vessel 306. First
and second valves 308 and 310 are closed. Turning now to FIG. 7,
following completion of the first deposition, first and second
valves 308 and 310 are opened. First mask 312 is then transported
332 through first valve 308 from deposition vessel 302 to first
cleaning vessel 304 and second mask 324 is transported 332 through
second valve 310 from second cleaning vessel 306 to deposition
vessel 302. Transport of first and second masks 312 and 314 may be
by any suitable means compatible with transport of a thin, flat
object under vacuum through a vacuum valve, including conveyor
belts, rollers, robotic arms or other mechanical means.
For maximum throughput in a manufacturing system of the present
invention for volume manufacturing of electronic devices, it is
generally preferred that mask cleaning does not limit the
production speed. To this end, the cleaning of second mask 324 is
completed and both first and second cleaning vessels 304 and 306
are pumped down to substantially the pressure in deposition vessel
302 before first and second valves 308 and 310 are opened. In
another embodiment, an end point detection means is included in
each cleaning vessel 304 and 306. End point detection supports
maximum throughput of manufacturing system 300 by signaling
manufacturing system 300 to stop cleaning a mask as early as
possible. End point detection also provides quality control for the
cleaning process, preventing either incomplete cleaning of a mask,
or erosion of a mask associated with overcleaning, for example, by
unnecessarily long exposure to a plasma.
Suitable technologies for end-point detection include any
technology that can sense the presence of a predetermined
deposition material on a mask surface. In one embodiment, end point
detection uses an optical sensor to monitor changes in the emission
spectrum of plasma above the surface being cleaned, as a deposition
material is removed from the surface into the plasma. In another
embodiment, a cleaning end point is determined using at least one
of spectroscopic absorption, fluorescence and scattering
measurements of electromagnetic radiation introduced into a
cleaning vessel from an external radiation source. In yet another
embodiment, measurement of an electrical characteristic of the
plasma is used to detect an end point of a cleaning process. In
still another embodiment, an end point is determined by measuring a
physical reference mark on, or aperture through a mask being
cleaned. In yet another embodiment, a mask includes a chemical
component added as an indicator to a material from which the mask
is constructed to assist in end point detection.
In one embodiment, substrate 317 is advanced along fabrication path
311 concurrently with transport of first and second masks 312 and
324 among first cleaning vessel 304, deposition vessel 302 and
second cleaning vessel 306. In another embodiment, advancing
substrate 317 and transporting first and second masks 312 and 324
are performed sequentially. Desirably, the pressure in deposition
vessel 302 is maintained substantially constant during transport of
first and second masks 312 and 324. Turning now to FIG. 8, first
mask 312 is positioned in first cleaning vessel 304, second mask
324 is positioned in deposition vessel 302, and first and second
valves 308 and 310 have been closed 330. Cleaning of first mask 312
in first cleaning vessel 304 is in progress concurrently with a
second deposition occurring in deposition vessel 302. Turning
finally to FIG. 9, after completion of the second deposition using
second mask 324 and cleaning of first mask 312, first and second
masks 312 and 324 are transported in a direction 334 opposite the
transport 332 illustrated in FIG. 7, returning first mask 312 to
deposition vessel 302 and second mask 324 to second cleaning vessel
306, as illustrated in FIG. 6.
Embodiments of the present invention have many advantages,
including, but not limited to, advantages associated with enhanced
manufacturability of electronic devices and reduced cost of
fabrication facilities for electronic devices, particularly for
large area electronic devices. A fabrication system of the present
invention is scalable in a straightforward manner to producing
electronic devices on very large substrates, limited primarily by
the manufacturability of large area shadow masks. Further, by
cleaning the shadow masks frequently and in proximity to a
deposition vessel, manufacturing speed is optimized, the
performance of the shadow masks is maintained over many deposition
cycles, and the risk of damaging a mask associated with
transporting the mask elsewhere for cleaning is eliminated. In
addition, and particularly for multi-mask and carousel embodiments
of the present invention, the inherent redundancy of using a
plurality of masks at each process station enables replacement of a
failed or worn mask without stopping a production line, by
replacing the mask during the time it would have been cleaned.
Another advantage of electronic device manufacturing systems and
methods of the present invention is its unity of manufacturing
technology. Unlike photolithographic manufacturing facilities that
employ many disparate manufacturing technologies and many types of
manufacturing equipment to produce a single type of electronic
device, a manufacturing system of the present invention employs
only material deposition and related mask cleaning technologies to
produce an electronic device. This unity of technology will enable
manufacturing facilities to be constructed for substantially lower
cost than present photolithographic manufacturing facilities. Yet
another advantage of the present invention is that it provides an
electronic device manufacturing system that does not have to be
completely enclosed in a clean room environment, since most or all
manufacturing steps for the electronic devices are performed in a
series of interconnected vacuum vessels.
The invention has been described with reference to the preferred
embodiment. Obvious modifications and alterations will occur to
others upon reading and understanding the preceding detailed
description. It is intended that the invention be construed as
including all such modifications and alterations insofar as they
come within the scope of the appended claims or the equivalents
thereof.
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