U.S. patent application number 09/947648 was filed with the patent office on 2002-01-17 for structures, lithographic mask forming solutions, mask forming methods, field emission display emitter mask forming methods, and methods of forming plural field emission display emitters.
Invention is credited to Alwan, James J., Knappenberger, Eric J., Michiels, John, Wells, David.
Application Number | 20020006583 09/947648 |
Document ID | / |
Family ID | 22497363 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006583 |
Kind Code |
A1 |
Michiels, John ; et
al. |
January 17, 2002 |
Structures, lithographic mask forming solutions, mask forming
methods, field emission display emitter mask forming methods, and
methods of forming plural field emission display emitters
Abstract
The present invention includes structures, lithographic mask
forming solutions, mask forming methods, field emission display
emitter mask forming methods, and methods of forming plural field
emission display emitters. One aspect of the present invention
provides a mask forming method including forming a masking layer
over a surface of a substrate; screen printing plural masking
particles over a surface of the masking layer; and removing at
least portions of the masking layer using the masking particles as
a mask. Another aspect of the present invention provides a method
of forming plural field emission display emitters. This method
includes forming a masking layer over an emitter substrate; screen
printing a plurality of masking particles over the masking layer;
removing portions of the masking layer intermediate the screen
printed masking particles to form a plurality of masking elements;
removing the masking particles from the masking elements; and
removing portions of the emitter substrate to form plural
emitters.
Inventors: |
Michiels, John; (Boise,
ID) ; Wells, David; (Boise, ID) ;
Knappenberger, Eric J.; (Meridian, ID) ; Alwan, James
J.; (Boise, ID) |
Correspondence
Address: |
WELLS ST JOHN ROBERTS GREGORY AND MATKIN
SUITE 1300
601 W FIRST AVENUE
SPOKANE
WA
992013828
|
Family ID: |
22497363 |
Appl. No.: |
09/947648 |
Filed: |
September 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09947648 |
Sep 5, 2001 |
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09458758 |
Dec 10, 1999 |
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09458758 |
Dec 10, 1999 |
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09141809 |
Aug 28, 1998 |
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6228538 |
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Current U.S.
Class: |
430/312 ;
430/313 |
Current CPC
Class: |
G03F 7/00 20130101; H01L
21/3081 20130101; H01J 2329/00 20130101; G03F 7/0015 20130101; H01L
21/31144 20130101; H01L 21/0271 20130101; H01J 9/025 20130101; Y10S
430/15 20130101 |
Class at
Publication: |
430/312 ;
430/313 |
International
Class: |
G03C 005/00 |
Goverment Interests
[0001] This invention was made with Government support under
Contract No. DABT63-97-C-0001 awarded by Advanced Research Projects
Agency (ARPA). The Government has certain rights in this invention.
Claims
1. A lithographic mask forming solution comprising: a
photosensitive material; and a plurality of masking particles
within the photosensitive material.
2. The solution according to claim 1 wherein the photosensitive
material comprises photoresist.
3. The solution according to claim 1 wherein the solution has a
concentration within an approximate range of
1.times.10.sup.8-1.times.10.- sup.9 masking particles per
milliliter of photosensitive material.
4. A structure comprising: a substrate; and a layer of solution
provided over the substrate, the solution comprising a
photosensitive material and a plurality of masking particles.
5. The structure according to claim 4 wherein the layer of solution
is screen printed over the substrate.
6. The structure according to claim 4 wherein the substrate
comprises a field emission display substrate.
7. The structure according to claim 4 wherein the photosensitive
material comprises photoresist.
8. The structure according to claim 4 wherein the substrate
comprises a field emission display substrate and the photosensitive
material comprises photoresist.
9. A structure forming method comprising: providing a solution
including photosensitive material and a plurality of masking
particles; applying the solution over a substrate; removing at
least a portion of the photosensitive material while leaving the
masking particles over the substrate; and processing the substrate
using the masking particles as a mask.
10. The method according to claim 9 wherein the applying comprises
screen printing the solution over the substrate.
11. The method according to claim 9 wherein the substrate comprises
a field emission display substrate.
12. The method according to claim 9 wherein the substrate comprises
a semiconductive substrate.
13. The method according to claim 9 wherein the method comprises an
electronic device forming method.
14. The method according to claim 9 further comprising adhering the
masking particles over the substrate using the photosensitive
material.
15. The method according to claim 9 further comprising removing the
masking particles following the processing.
16. The method according to claim 9 wherein the providing comprises
providing a solution including photosensitive material comprising
photoresist.
17. A structure forming method comprising: providing a solution
including photosensitive material and a plurality of masking
particles within the photosensitive material; screen printing a
layer of the solution over a substrate; curing at least a portion
of the photosensitive material screen printed over the substrate;
removing cured photosensitive material while leaving the masking
particles over the substrate; and processing the substrate using
the masking particles as a mask.
18. The method according to claim 17 wherein the substrate
comprises a field emission display substrate.
19. The method according to claim 17 wherein the substrate
comprises a semiconductive substrate.
20. The method according to claim 17 further comprising adhering
the masking particles over the substrate using the photosensitive
material.
21. The method according to claim 17 further comprising removing
the masking particles following the processing.
22. The method according to claim 17 wherein the providing
comprises providing a solution including photosensitive material
comprising photoresist.
23. A mask forming method comprising: providing a solution
including photosensitive material and a plurality of masking
particles within the photosensitive material; applying the solution
over a substrate; curing at least a portion of the photosensitive
material applied over the substrate; and removing cured
photosensitive material while leaving the masking particles over
the substrate.
24. The method according to claim 23 wherein the applying comprises
screen printing the solution over the substrate.
25. The method according to claim 23 wherein the applying comprises
applying the solution over a semiconductive substrate.
26. The method according to claim 23 wherein the applying comprises
applying the solution over a masking layer substrate.
27. The method according to claim 23 further comprising adhering
the masking particles over the substrate using the photosensitive
material.
28. The method according to claim 23 wherein the providing
comprises providing a solution including photosensitive material
comprising photoresist.
29. A lithographic mask solution forming method comprising:
providing a photosensitive material; providing a plurality of
masking particles; and mixing the masking particles with the
photosensitive material.
30. The method according to claim 29 further comprising mixing the
masking particles with a carrier.
31. The method according to claim 29 wherein the providing the
photosensitive material comprises providing photoresist.
32. A mask forming method comprising: forming a masking layer over
a surface of a substrate; screen printing plural masking particles
over a surface of the masking layer; and removing at least portions
of the masking layer using the masking particles as a mask.
33. The method according to claim 32 wherein the screen printing
comprises offset screen printing.
34. The method according to claim 32 further comprising removing
the masking particles following the removing.
35. The method according to claim 32 further comprising agitating
the masking particles following the screen printing.
36. The method according to claim 32 wherein the screen printing
comprises printing spherical masking particles.
37. The method according to claim 32 wherein the screen printing
comprises printing masking particles within a solution containing
photoresist.
38. The method according to claim 37 further comprising: curing the
photoresist; and removing portions of the photoresist from over the
masking particles and masking layer.
39. The method according to claim 37 wherein the screen printing
comprises printing masking particles within a solution having a
concentration within an approximate range of
1.times.10.sup.8-1.times.10.sup.9 masking particles per milliliter
of photoresist.
40. The method according to claim 32 further comprising guiding the
spherical masking particles over predefined regions of the masking
layer by the screen printing.
41. The method according to claim 32 wherein the removing forms
discrete circular masking elements.
42. The method according to claim 32 wherein the removing comprises
anisotropically etching the masking layer.
43. The method according to claim 32 wherein the forming comprises
forming a masking layer over an emitter substrate of a field
emission display.
44. A mask forming method comprising: forming a masking layer over
a surface of a substrate; forming a layer of masking particles over
a surface of the masking layer; providing the masking particles
over predefined regions of the surface of the substrate during the
forming; and removing at least portions of the masking layer using
the masking particles as a mask.
45. The method according to claim 44 further comprising removing
the masking particles following the removing.
46. The method according to claim 44 further comprising agitating
the masking particles following the providing.
47. The method according to claim 44 wherein the providing
comprises printing the masking particles using a screen.
48. The method according to claim 44 wherein the providing
comprises screen printing masking particles within a solution
containing photoresist.
49. The method according to claim 48 further comprising: curing the
photoresist; and removing portions of the photoresist from over the
masking particles and masking layer.
50. The method according to claim 44 wherein the removing comprises
anisotropically etching the masking layer.
51. The method according to claim 44 wherein the forming comprises
forming a masking layer over an emitter substrate of a field
emission display.
52. A mask forming method comprising: forming a masking layer over
a surface of a substrate; forming a layer of solution including
plural masking particles over a surface of the masking layer;
guiding the masking particles to predefined regions over the
substrate using a screen; and removing at least portions of the
masking layer using the masking particles as a mask.
53. The method according to claim 52 further comprising agitating
the masking particles following the guiding.
54. The method according to claim 52 wherein the forming a masking
layer comprises forming a masking layer over an emitter substrate
of a field emission display.
55. The method according to claim 52 wherein the forming the layer
of solution comprises screen printing masking particles within
photoresist.
56. The method according to claim 55 further comprising: curing the
photoresist; and removing portions of the photoresist from over the
masking particles and masking layer.
57. The method according to claim 52 wherein the removing comprises
anisotropically etching the masking layer.
58. A field emission display emitter mask forming method
comprising: forming a masking layer over a surface of an emitter
substrate; printing a layer of masking particles over a surface of
the masking layer using a screen; removing portions of the masking
layer intermediate the screen printed masking particles; and
removing the masking particles from remaining portions of the
masking layer following the removing of portions of the masking
layer.
59. The method according to claim 58 further comprising removing
the screen following the printing and prior to the removing the
portions of the masking layer.
60. The method according to claim 58 further comprising agitating
the masking particles following the printing.
61. The method according to claim 58 wherein the printing comprises
printing the masking particles within a solution containing
photoresist.
62. The method according to claim 61 further comprising: curing the
photoresist; and removing portions of the photoresist from over the
masking particles and masking layer.
63. The method according to claim 58 wherein the removing portions
of the masking layer comprises anisotropically etching the masking
layer.
64. A method of forming plural field emission display emitters
comprising: forming a masking layer over an emitter substrate;
screen printing a plurality of masking particles over the masking
layer; removing portions of the masking layer intermediate the
screen printed masking particles to form a plurality of masking
elements comprising the masking layer; removing the masking
particles from the masking elements; and removing portions of the
emitter substrate using the masking elements as a mask to form
plural emitters.
65. The method according to claim 64 further comprising removing a
screen following the printing.
66. The method according to claim 64 further comprising agitating
the masking particles following the screen printing.
67. The method according to claim 64 wherein the screen printing
comprises printing masking particles within a solution containing
photoresist.
68. The method according to claim 67 further comprising: curing the
photoresist; and removing portions of the photoresist from over the
masking particles and masking layer.
69. The method according to claim 64 further comprising guiding the
spherical masking particles over predefined regions of the masking
layer by the screen printing.
70. The method according to claim 64 wherein the removing portions
of the emitter substrate comprises removing using the masking
elements.
71. The method according to claim 64 wherein the removing portions
of the masking layer comprises anisotropically etching the masking
layer.
72. The method according to claim 64 wherein the removing portions
of the emitter substrate comprises removing using an isotropic
etch.
73. A method of forming a substantially uniform array of emitters
upon an emitter substrate during field emission display fabrication
comprising: providing an emitter substrate; forming a hardmask
layer over the emitter substrate; providing a solution containing a
plurality of spherical masking particles and photoresist, the
solution having a concentration within an approximate range of
1.times.10.sup.8-1.times.10.sup.9 masking particles per milliliter
of photoresist; forming a layer of the solution including the
spherical masking particles and photoresist upon a surface of the
hardmask layer, the forming of the layer including: guiding the
spherical masking particles to predefined regions over the surface
of the hardmask layer using a screen; removing the screen;
agitating the layer of solution formed upon the surface of the
hardmask layer; and curing the layer of solution following the
agitating; stripping portions of the photoresist intermediate the
spherical masking particles following the forming of the layer of
the solution; etching portions of the hardmask layer intermediate
the screen printed spherical masking particles using an anisotropic
etch thereby forming a plurality of circular masking elements
beneath the spherical masking particles; stripping the spherical
masking particles from the circular masking elements; and etching
portions of the emitter substrate to form plural emitters
corresponding to the circular masking elements using an isotropic
etch.
Description
TECHNICAL FIELD
[0002] The present invention relates to structures, lithographic
mask forming solutions, mask forming methods, field emission
display emitter mask forming methods, and methods of forming plural
field emission display emitters.
BACKGROUND OF THE INVENTION
[0003] Field emission displays are utilized in a variety of display
applications. Conventional field emission displays include a
cathode plate having a series of emitter tips fabricated thereon.
The tips are configured to emit electrons toward a phosphor screen
to produce an image. The emitters or emitter tips are typically
formed from an emitter material such as conductive polysilicon,
molybdenum, or aluminum. Multiple emitters are typically utilized
to excite a single pixel. For example, 120 emitters may be used for
a single pixel. Individual pixels contain a deposited one of red,
green, or blue phosphor.
[0004] One method of fabrication of emitter tips is described in
U.S. Pat. No. 5,391,259 (the '259 patent); assigned to the assignee
hereof and incorporated by reference. A hardmask layer is formed
over emitter material in the disclosed fabrication method. Portions
of the hardmask layer are selectively removed to form a hardmask
utilized for emitter fabrication. One conventional method utilizes
photolithography and etching to selectively remove portions of the
hardmask layer. Following the formation of the hardmask, the
emitter material is etched isotropically to form the tips. For
proper fabrication, it is highly desired that hardmasks be
patterned to a consistent critical dimension. Variations in
critical dimensions or size of the hardmasks can result in
non-uniformity within the formed emitter tips.
[0005] One method for fabricating the hardmask utilized to form the
emitter tips uses spheres or beads as the mask for creating the
hardmask layer mask. The spheres are provided in a liquid medium
such as water. The emitter substrate is dipped into a vat of
solution containing the spheres. The substrate is then withdrawn
from the solution and some of the spheres adhere to the emitter
substrate.
[0006] It is preferred to achieve a homogeneous/uniform
distribution of beads upon the face of the emitter material.
However, homogeneous distribution has been difficult to achieve. A
non-uniform distribution of beads can result in adjacent spheres
touching and subsequent adjoining of emitter tips following emitter
fabrication causing problems with electron optics (e.g., focusing
of electrons). Such joining of emitter tips can result in the
emission of electrons which strike adjacent phosphor patches
resulting in poor color intensity and poor color distribution.
[0007] Further, the spheres may exhibit poor adhesion to the
surface of the substrate when conventional methods of applying the
spheres to the substrate surface are utilized. This drawback is
particularly acute if the spheres are larger than 0.5 microns.
[0008] The present invention provides improvements in device
fabrication while avoiding problems experienced in the prior
art.
SUMMARY OF THE INVENTION
[0009] The present invention includes structures, lithographic mask
forming solutions, and mask forming methods. The invention further
includes field emission display emitter mask forming methods and
methods of forming plural field emission display emitters.
[0010] One aspect of the present invention provides a lithographic
mask forming solution. The solution includes a photosensitive
material and a plurality of masking particles within the
photosensitive material. The photosensitive material comprises
photoresist and the masking particles comprise beads or spheres in
exemplary embodiments. The photosensitive material is cured and
portions of the cured photosensitive material are removed in
preferred aspects of the invention. Masking particles remaining
upon the substrate are thereafter used as a mask to process a
substrate. Uncured photosensitive material is used to improve
adhesion of masking particles to the substrate to be processed.
[0011] A second aspect of the invention provides a structure
forming method including providing a solution comprising a
photosensitive material and a plurality of masking particles. The
method also provides applying the solution over a substrate and
removing at least a portion of the photosensitive material while
leaving the masking particles over the substrate. The solution is
preferably screen printed. The method also includes processing the
substrate using the masking particles as a mask.
[0012] According to another aspect, a method of forming a mask over
a substrate includes forming a masking layer over a surface of a
substrate. Masking particles are screen printed over a surface of
the masking layer and portions of the masking layer are removed
using the masking particles. The removing of portions of the
masking layer forms a mask. This mask includes a plurality of
circular masking elements in some embodiments.
[0013] In another aspect, masking particles are mixed within
photoresist to form a solution which can be screen printed. The
screen printing includes printing masking particles within the
solution containing photoresist. In one embodiment, the solution
has a concentration within the approximate range of approximately
1.times.10.sup.8-1.times.10.sup.9 masking particles per milliliter
of photoresist.
[0014] It is preferred to provide a uniform layer of masking
particles upon the masking layer. To this end, screen printing of
masking particles guides the masking particles to predefined
regions over the substrate. Further, the masking particles are
preferably agitated to space the masking particles from one
another.
[0015] In some aspects of the invention, the solution is permitted
to cure and portions of the photoresist or other photosensitive
material is removed. The masking particles form a mask utilized to
form a hardmask from the masking layer. The hardmask is
subsequently utilized to form a random array of emitters of a field
emission display from an emitter substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Preferred embodiments of the invention are described below
with reference to the following accompanying drawings.
[0017] FIG. 1 is a cross-sectional view of a structure including a
substrate and a solution layer during processing of the
structure.
[0018] FIG. 2 is a cross-sectional view of a processing step of the
structure subsequent to the step of FIG. 1.
[0019] FIG. 3 is a cross-sectional view of a processing step of the
structure subsequent to the step of FIG. 2.
[0020] FIG. 4 is a cross-sectional view of a segment of a field
emission display having plural emitters fabricated in accordance
with processes of the present invention.
[0021] FIG. 5 is a cross-sectional view of a substrate, masking
layer, layer of solution and a screen during fabrication of a
backplate of a field emission display.
[0022] FIG. 6 is a diagrammatic representation of conventional
offset screen printing.
[0023] FIG. 7 is a diagrammatic representation of contact screen
printing.
[0024] FIG. 8 is a top plan view of a predefined region shown at
the processing step of FIG. 5.
[0025] FIG. 9 is a cross-sectional view of a processing step for
forming the backplate subsequent to the step of FIG. 5.
[0026] FIG. 10 is a cross-sectional view of a processing step of
the backplate subsequent to the step of FIG. 9.
[0027] FIG. 11 is a cross-sectional view of a processing step of
the backplate subsequent to the step of FIG. 10.
[0028] FIG. 12 is a cross-sectional view of a processing step of
the backplate subsequent to the step of FIG. 11.
[0029] FIG. 13 is a cross-sectional view of a processing step of
the backplate subsequent to the step of FIG. 12.
[0030] FIG. 14 is a cross-sectional view of emitters formed from an
emitter substrate of a field emission display in accordance with
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] This disclosure of the invention is submitted in furtherance
of the constitutional purposes of the U.S. Patent Laws "to promote
the progress of science and useful arts" (Article 1, Section
8).
[0032] The present application is described with reference to
fabrication techniques for structures which comprise electronic
components or devices. Exemplary electronic components are
fabricated from semiconductive substrates or substrates for flat
panel or field emission display (FED) devices. Such substrates can
comprise silicon, glass, quartz or other materials. Structures are
processed and subsequently utilized in electronic devices of
various configurations.
[0033] During formation of structures such as semiconductive
components or FED emitters, it is often necessary to form masks for
various processing steps. The masks can be utilized to process into
a substrate or form additional layers upon the substrate. Certain
aspects of the present invention are directed towards the formation
of lithographic masks and the formation of solutions utilized to
form lithographic masks.
[0034] Referring to FIG. 1, a structure 1 is illustrated.
Processing of structure 1 is described with reference to formation
of an electronic device or component. For example, structure 1 is
processed to comprise a transistor, memory cell, discrete
component, such as a resistor or FED emitters in exemplary
applications. Structure 1 is fabricated for use in electronic
devices in some applications.
[0035] The depicted structure 1 comprises a substrate 2 and a
solution layer 3 formed over substrate 2. Substrate 2 comprises a
semiconductive substrate, such as monocrystalline silicon, in some
embodiments. In particular, substrate 2 can comprise a field
emission display substrate as described below. Alternatively,
substrate 2 comprises other materials suitable for forming
electronic devices or components.
[0036] Solution layer 3 comprises a medium 4 and a plurality of
masking particles 5 within medium 4. In a preferred embodiment,
medium 4 comprises a photosensitive resin or material. Solution
layer 3 can be formed to comprise the same solution layer as
described below with reference to FIG. 5 (i.e., solution layer 42).
Utilizing such a solution, masking particles 5 comprise spheres and
photosensitive material 4 comprises photoresist. The solution is
formed in the exemplary embodiment to have a concentration within
an approximate range of 1.times.10.sup.8-1.times.10.sup.9 masking
particles per milliliter of photosensitive material or
photoresist.
[0037] In the presently described embodiment, solution layer 3 can
be applied over substrate 2 by any suitable method, such as screen
printing. Conventional offset and contact screen printing methods
are described below with reference to FIG. 6 and FIG. 7. Such
printing techniques are utilized in exemplary processing methods to
form solution layer 3. As described in detail below, screen
printing solution layer 3 is preferred to provide a uniform
distribution of spheres within layer 3 and over substrate 2.
[0038] Following provision of solution layer 3 over substrate 2,
medium 4 comprising photosensitive material is cured or developed.
Exemplary curing methods include exposing solution layer 3 to
ultraviolet light if medium 4 comprises positive photoresist.
[0039] Referring to FIG. 2, portions of photosensitive medium 4 are
removed following curing of exposed portions of medium 4. In
particular, cured portions of photosensitive material 4 can be
stripped or otherwise removed. Masking particles 5 remain over
substrate 2 following the removal of cured portions of medium
4.
[0040] Feet or small portions 6 of photosensitive medium 4 remain
intermediate individual masking particles 5 and substrate 2
following removal of exposed portions of the photosensitive
material. Uncured remaining resin feet 6 assist with adhering
respective masking particles 5 to substrate 2.
[0041] Removal of exposed portions of photosensitive medium 4 forms
a mask 7 comprising masking particles 5 and feet 6. Mask 7
comprises a lithographic mask for processing of structure 1 in the
described embodiment. In particular, masking particles 5 and
corresponding feet 6 of mask 7 define exposed regions 8 upon
substrate 2. Exposed regions 8 of substrate 2 can be processed in
subsequent fabrication steps.
[0042] Referring to FIG. 3, an exemplary fabrication step of
structure 1 is described. In particular, substrate 2 is processed
using masking particles 5 and feet 6 of mask 7 as a lithographic
mask. In FIG. 3, plural diffusion regions 9 are formed within
substrate 2. Exemplary diffusion regions can comprise p type or n
type diffusion regions depending upon the particular structure 1
being processed.
[0043] Such diffusion processing is exemplary and other processing
steps such as deposition can occur using mask 7. Following
formation of diffusion regions 9, or other alternative processing,
masking particles 5 and feet 6 can be stripped from substrate 2.
Acetone is utilized in one embodiment to strip masking particles 5
and feet 6.
[0044] Referring to FIG. 4-FIG. 14, methods of forming masks are
described with reference to field emission display devices.
Further, methods of forming field emission display emitters are
described. The invention is not limited to field emission display
device fabrication as described in the following embodiments and
applications. Aspects of the present invention described below
might be utilized within any masking and etching process.
[0045] Referring to FIG. 4, an exemplary portion of a field
emission display 10 is depicted. The illustrated portion of the
field emission display 10 includes a display segment 12. Display
segment 12 is capable of displaying a pixel of information, or a
portion of a pixel. For example, display segment 12 may be
configured to display one green dot of a red/green/blue fall-color
triad pixel. Field emission display 10 includes a faceplate or
screen 24 and a cathode plate or baseplate 28 spaced therefrom.
Support structures or separators 30 space faceplate 24 from
baseplate 28 and generally define segment 12 in the illustrated
embodiment.
[0046] Baseplate 28 of the described embodiment comprises a matrix
addressable array of cathode emission structures or emitters 16.
Baseplate 28 additionally includes an emitter substrate 14, upon
which the emission structures 16 are created, a dielectric
insulating layer 26, and an anodic grid 18.
[0047] Emitter substrate 14 has been patterned and etched to form
micro-cathodes or emitters 16 as described in detail below. Display
segment 12 includes plural field emission sites 15. Sites 15
correspond to the emitters 16. Dielectric insulating layer 26 is
formed upon substrate 14 intermediate emitters 16 and sites 15.
More specifically, insulator 26 has plural openings at the field
emission sites 15. A vacuum is created between faceplate 24 and
baseplate 28 to provide proper functioning of plural emitters 16 of
the described field emission display 10. Separators 30 function to
support atmospheric pressure which exists on electrode faceplate 24
as a result of the vacuum.
[0048] Emitters 16 are constructed on top of emitter substrate 14.
Emitters 16 are integral with emitter substrate 14 and individually
comprise a cathode for emission of electrons. Alternatively,
emitters 16 form cathodes from one or more deposited conductive
films, such as a chromium amorphous silicon bilayer. Emitters 16
preferably have a fine micro-point in the described embodiment.
[0049] Grid structure 18 surrounds emission sites 15 in the
described embodiment. A power source 20 is utilized to apply a
voltage differential between the cathodes (emitters 16) and anodic
grid 18. In particular, emitters 16 are individually electrically
coupled with a negative terminal of source 20. A positive terminal
of source 20 is coupled with grid 18. Grid 18 serves as a structure
for applying an electrical field potential to appropriate emitters
16. A stream of electrons 22 is emitted from emitters 16 responsive
to the application of a voltage differential via grid 18.
[0050] A second positive terminal of source 20 is connected with
faceplate 24 thereby forming another anode. Faceplate 24 includes a
phosphor coating 25 over surface facing emitters 16. Electrons
ejected from emitters 16 are aimed toward faceplate 24. Further
details of field emission displays are described in U.S. Pat. Nos.
5,229,331 and 5,391,259, both incorporated herein by reference.
[0051] Referring to FIG. 5, fabrication of an exemplary portion of
baseplate 28 of a field emission display is shown. In particular,
methods of forming field emission display masks utilized for
formation of emitters 16 are described. Methods of forming emission
display emitters 16 are also described. The formed emitters 16 are
conical in the described embodiment. Emitters 16 may comprise
protuberances of other shapes in other embodiments.
[0052] The illustrated baseplate 28 includes emitter substrate 14,
a masking layer 40 and a layer of solution 42. A single crystal
silicon layer serves as substrate 14 in one embodiment. Amorphous
silicon or polysilicon deposited upon a glass substrate are other
examples. Other materials are utilized in other embodiments. In
particular, substrate 14 of FIG. 5 can be any material from which
emitters 16 can be fabricated.
[0053] Masking layer 40, also referred to as a hardmask layer,
comprises a masking layer substrate which is deposited or grown on
substrate 14 in the described embodiment. An example material for
layer 40 is silicon dioxide. Masking layer 40 preferably has a
thickness great enough to avoid being completely consumed during
subsequent etching processes. It is also desired to provide a
masking layer 40 which is not excessively thick so as to overcome
adherent forces which maintain the masking layer in the correct
position with respect to emitters 16 throughout the emitter
fabrication process as described hereafter. An exemplary range of
thicknesses of masking layer 40 is 0.05-0.5 microns with a
thickness of 0.2 microns being preferred.
[0054] Solution layer 42 comprises a plurality of masking particles
46 within a medium 48. In one embodiment, masking particles 46 are
initially mixed into a fairly viscous or thixotropic medium 48.
Medium 48 is preferably liquid having an operable viscosity range
from 10 to 1100 centipoise. A viscosity range from 40 to 200
centipoise is preferred at room temperature. Solution layer 42 is
screen printed onto a surface of masking layer 40 and subsequently
cured. As described below, medium 48 is thereafter removed
providing an etch mask for fabricating another mask used to form a
random array of field emitter tips (i.e., emitters).
[0055] Masking particles 46 preferably comprise spherical members
and medium 48 comprises photoresist or photo sensitive material
such as polyimide. Example materials are polystyrene or latex for
spheres 46 and positive photoresist for medium 48. Masking
particles 46 have an exemplary diameter of approximately one micron
(0.04 mils). A preferred spherical diameter range is from 0.5 to
2.0 microns.
[0056] Masking members or particles 46 are typically provided in a
water solution having a density of approximately 10.sup.11 beads or
spheres per milliliter (ml) of solution. Exemplary bead solutions
are available from Bangs Labs IDC Corp. The water solution
containing the beads or masking particles 46 is dissolved in a
carrier, such as isopropyl alcohol, and subsequently combined or
mixed with photoresist in one embodiment of the invention. In one
example, two cubic centimeters (cc) of isopropyl alcohol were added
per one cubic centimeter of bead solution. Then, five cubic
centimeters of photoresist were combined with this solution
providing a ratio of 1:2:5 by volume. An exemplary ratio range of
bead solution to isopropyl alcohol to photoresist is 1:(2 20):(5
50).
[0057] A 1:2:5 mixture of solution yields a bead or masking
particle density of approximately 1.25.times.10.sup.10 beads per
milliliter of solution. An exemplary preferred concentration of
masking particles 46 within medium 48 is within the approximate
range of 1.times.10.sup.8-1.times.10.sup.9 beads/ml immediately
prior to screen printing upon hardmask masking layer 40.
[0058] In one example, approximately 1.times.10.sup.11 spheres were
mixed into approximately 300 ml of Olin HPR504 resist comprising
medium 48. The solution containing spheres 46 and medium 48 was
screen printed onto a glass substrate using conventional screen
printing to form solution layer 42. A 400 mesh screen having a wire
diameter of 0.00075 inches with a patterned emulsion coating of
0.0002 inches was utilized for the screen printing.
[0059] A screen 44 is utilized to screen print the solution layer
42 in accordance with the described embodiment of the present
invention. It is desired to provide solution layer 42 upon masking
layer 42 having a uniform density of masking particles 46. It is
also preferred to provide spacing between adjacent masking
particles 46.
[0060] Screen 44 includes plural mesh portions 45 (one whole mesh
portion 45 is shown in FIG. 5). Mesh portions 45 of screen 44
define predefined regions 50 over masking layer 40 and emitter
substrate 14 (one predefined region 50 corresponding to the
illustrated mesh portion 45 is shown in FIG. 5). Screen 44 includes
mesh portions 45 individually having dimensions of 1.75 mils by
1.75 mils square in one example. Screen 44 is thin as possible in
preferred embodiments. An exemplary preferred thickness for a cured
layer 42 is about five microns.
[0061] Referring to FIG. 6, conventional offset screen printing of
solution to form solution layer 42 is shown. A squeegee 41 is used
to urge solution through mesh portions of screen 44. Solution is
deposited onto screen 44 in front of the direction of travel of
squeegee 41 in the described embodiment. Screen 44 and masking
layer 40 are spaced by a distance d.sub.1 (e.g., 0.04 inches).
Squeegee 41 passes laterally over screen 44 and presses screen 44
to contact the layer being printed upon (e.g., masking layer 40).
Squeegee 41 simultaneously forces the solution containing masking
particles through mesh portions of screen 44.
[0062] Referring to FIG. 7, contact printing of the solution to
form solution layer 42 upon masking layer 40 is shown. Screen 44
contacts masking layer 40 when contact printing is utilized.
Squeegee 41 passes laterally over screen 44 forcing the solution
containing the masking particles through mesh portions of screen
44. Conventional offset printing is the preferred screen printing
method.
[0063] Referring to FIG. 8, a top view of solution layer 42 and
screen 44 are shown. Plural mesh portions 45 (shown in phantom) are
defined by screen 44. Screen 44 also defines plural regions 50 over
the masking layer and the emitter substrate (the emitter substrate
and the masking layer are below solution layer 42 and not shown in
FIG. 8). Predefined regions 50 correspond to mesh portions 45 in
the illustrated embodiment. In accordance with one aspect of the
present invention, mesh portions 45 of screen 44 operate to guide
masking particles 46 to respective predefined regions 50 over
emitter substrate 14 and masking layer 40. The prior art is not
understood to disclose any mechanism to guide masking particles
over the region(s) to be covered with masking particles.
[0064] FIG. 8 illustrates an exemplary number of masking particles
46 within respective predefined regions 50. More or less masking
particles 46 can be provided within individual predefined regions
50. In a preferred embodiment, a two micron pitch of masking
particles 46 is desired if masking particles 46 having a diameter
of one micron are utilized. In this embodiment, the approximate
number of masking particles 46 received through one mesh portion 45
is the area of the mesh portion in square microns divided by four.
Further, FIGS. 5 and 8 diagrammatically illustrate screen printing
of masking particles 46 and are not to scale.
[0065] Referring to FIG. 9, screen 44 is removed from backplate
segment 28 following formation of solution layer 42 over emitter
substrate 14. Screen 44 is ideally removed before substantial
curing of solution layer 42. Masking particles 46 and medium 48
flow to fill the void created by the removal of screen 44.
[0066] Backplate segment 28, including emitter substrate 14,
masking layer 40 and solution layer 42, is preferably agitated
following removal of screen 44 and prior to substantial curing.
Such agitation encourages movement of masking particles 46 apart
from one another and provides spacing intermediate adjacent masking
particles 46. Such agitation also encourages settling of masking
particles 46 upon masking layer 40. Masking particles 46 may also
adhere to masking layer 40 following contacting of the same.
Subsequently, solution layer 42 is cured. An example curing process
includes air drying backplate 28 for twenty minutes in ambient air
at 50% humidity. Masking particles 46 define intermediate portions
54 of medium 48 between adjacent masking particles 46.
[0067] Referring to FIG. 9 and FIG. 10, following curing of
solution layer 42, medium 48, including intermediate portions 54
thereof, is stripped or otherwise removed. In embodiments where
medium 48 comprises positive photoresist, baseplate segment 28 is
flood exposed to ultraviolet light and developed. Media 48,
including intermediate portions 54, is thereafter stripped. A foot
or small portion 52 of medium 48 can remain intermediate individual
masking particles 46 and masking layer 40. Feet 52 of medium 48 are
defined by the diameter of respective masking particles 46. Masking
particles 46 preferably contact masking layer 40. Remaining
portions of medium 48 or feet 52 assist with adhesion of bases of
masking particles 46 to masking layer 40. Masking particles 46 and
feet 52 form a mask 59 upon masking layer 40. In particular,
masking particles 46 and feet 52 define plural exposed portions or
regions 58 of masking layer 40.
[0068] Referring to FIG. 10 and FIG. 11, exposed portions 58 of
masking layer 40 are removed from emitter substrate 14 using
spheres 46 as mask 59. In one embodiment, anisotropic etching is
utilized. An example chemistry includes CF.sub.4, CHF.sub.3,
Ar.sub.2 as described in the '259 patent. Such removal of exposed
portions 58 of masking layer 40 provides masking elements 56
beneath masking particles 46. Masking elements 56 substantially
correspond to, or are defined by, the diameters of respective
masking particles 46. Masking elements 56 are circular in the
described embodiment. Utilization of masking particles 46 in
accordance with the present invention improves critical dimension
control while producing masking elements 56.
[0069] Referring to FIG. 12, the beads or masking particles and the
feet have been stripped from masking elements 56. Acetone is
utilized in one embodiment to strip the masking particles and feet.
Masking elements 56 define a mask 57, which is also referred to
herein as a hardmask. Masking elements 56 define exposed regions or
portions 60 of emitter substrate 14. Exposed portions 60 are
intermediate masking elements 56.
[0070] Referring to FIG. 13, portions of emitter substrate 14,
including exposed portions 60, have been etched (preferably
substantially isotropically) to form plural emitters 16. An example
etching chemistry is SF.sub.6, Cl.sub.2, He as set forth in the
'259 patent. Emitters 16 are formed corresponding to circular
masking elements 56. A timed etch is utilized to form emitters 16
in one embodiment.
[0071] Referring to FIG. 14, a substantially uniform array 62 of
emitters 16 is shown upon emitter substrate 14. The insulating
dielectric layer may be subsequently formed to fabricate the
backplate 28 shown in FIG. 4. Additionally, the anodic grid may be
provided enabling control of the emission of electrons from
emitters 16.
[0072] In compliance with the statute, the invention has been
described in language more or less specific as to structural and
methodical features. It is to be understood, however, that the
invention is not limited to the specific features shown and
described, since the means herein disclosed comprise preferred
forms of putting the invention into effect. The invention is,
therefore, claimed in any of its forms or modifications within the
proper scope of the appended claims appropriately interpreted in
accordance with the doctrine of equivalents.
* * * * *