Electric lamp and discharge devices – Discharge devices having a multipointed or serrated edge...
Reexamination Certificate
1998-02-12
2001-01-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a multipointed or serrated edge...
C313S495000, C445S024000, C445S050000
Reexamination Certificate
active
06175184
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to semiconductor structures for visual displays. More particularly, the present invention relates to a field emission device. In particular, the present invention relates to fabrication of a field emitter tip.
The Relevant Technology
Integrated circuits are currently manufactured by methods in which semiconductive structures, insulating structures, and electrically conductive structures are sequentially constructed in a predetermined arrangement on a semiconductor substrate. In the context of this document, the term “semiconductor substrate” is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term semiconductor substrate is contemplated to include such structures as silicon-on-insulator and silicon-on-sapphire. The term “substrate” refers to any supporting structure. As used herein, “field emission device” is defined to mean any construction for emitting electrons in the presence of an electrical field, including but not limited to an electron emission structure or tip either alone or in assemblies comprising other materials or structures.
Miniaturization of structures within integrated circuits focuses attention and effort to incorporating field emission devices within semiconductor substrates. A field emission device typically includes an electron emission structure, or tip, configured for emitting a flux of electrons upon application of an electric field to the field emission device. An array of miniaturized field emission devices can be arranged on a plate and used for forming a visual display on a display panel. For example, field emission devices may be used in making flat panel displays for providing visual display for computers, telecommunication, and other graphics applications. Flat panel displays typically have a greatly reduced thickness compared to cathode ray tubes.
U.S. Pat. No. 5,635,619 issued to Cloud et al. and U.S. Pat. No. 5,229,331 issued to Doan et al. disclose field emission devices. The foregoing patents are hereby incorporated by reference for purposes of disclosure. A general view of a field emission device (FED) much like those that are disclosed in the foregoing patents to Cloud et al. and Doan et al. particularly as geometries become relatively small, is seen in FIG.
1
. The FED employs a cold cathode and includes a substrate
28
, which can be composed of glass, for example, or any of a variety of other suitable materials. A cathode conductive layer
30
, such as doped polycrystalline silicon, is deposited onto substrate
28
.
At a field emission site location, an emitter tip
14
, which is a micro-cathode, is constructed over substrate
28
. A variety of shapes have been used for emitter tip
14
, so long as the emitter tip
14
tapers to a relatively fine point. Surrounding emitter tip
14
is a low potential anode gate structure
38
, which is separated from cathode conductive layer
30
by means of a dielectric layer
34
.
When a voltage differential is applied between emitter tip
14
and anode gate structure
38
using, for example, voltage source
32
, an electron flux
24
is emitted and accelerates toward an anode panel
26
. The anode panel
26
includes a transparent panel
44
, such as glass; a phospholuminescent panel
48
; and an anode conductive layer
46
, which is electrically connected to source
32
. The electron flux
24
strikes and excites the phospholuminescent panel
48
, thereby causing light
24
to be emitted and to pass through transparent panel
44
.
The coordinated activity of a plurality of emitter tips
14
arrayed over a flat panel display provides a visual display that may be viewed by a user. Each individual or cluster of emitter tips
14
that is provided on a flat panel display may be assigned a unique matrix address. When such a flat panel display is used, the emitter tips
14
are systematically activated by means of their matrix addresses in order to provide the desired visual display.
Significant problems with emitter tip
14
in the above described device are evident in the prior art due to shrinking geometries. As seen in
FIG. 1
, manufacturing processes that are commonly used in the prior art typically form an emitter tip
14
that has a curvilinear vertical profile.
FIG. 2
illustrates an intermediate stage in the formation of emitter tip and further depicts the curvilinear vertical profile thereof. In
FIG. 2
, the intermediate semiconductor structure
10
comprises cathode conductive layer
30
, emitter tip
14
, and a hard mask
16
that covers emitter tip
14
prior to its removal. It can be seen that emitter tip
14
includes wings
18
that cause the vertical profile of emitter tip
14
to be curvilinear instead of rectilinear. Wings
18
are unintentional but persistent products of conventional methods of forming emitter tip
14
. Emitter tips
14
that have pronounced curvilinear vertical profiles have been found to provide sub-grade performance compared to those that are more nearly rectilinear.
Emitter tip
14
is exposed to the etch gas at large, but it encounters two types of etch gas molecules. A primary collision etch gas molecule
8
(its trajectory illustrated) collides with emitter tip
14
by coming from the etch gas at large. A secondary collision etch gas molecule
12
(its trajectory illustrated) comes from the etch gas at large but it collides with and rebounds from hard mask
16
near the intersection of emitter tip
14
and hard mask
16
just prior to its etch collision with emitter tip
14
. Because the etch is selective to hard mask
16
, the secondary collision etch gas molecule
12
rebounds from hard mask
16
and, along with primary collision etch gas molecule
8
, causes an intensified frequency of collisions into emitter tip
14
in the region of the intersection between hard mask
16
and emitter tip
14
. The intensified frequency of collisions into emitter tip
14
by secondary collision etch gas molecule
12
in addition to primary collision etch gas molecule causes increased etching of emitter tip
14
in this region. The increased etching in this region is exacerbated by the increase in surface area that is formed due to both primary- and secondary-collision etch gas molecules. Further, the extinguishment of secondary etch gas molecule
12
causes an etch gas sink which intensifies etching in this region. Hence, wings
18
form because of intensified etching activity in the region of emitter tip
14
near hard mask
16
.
As geometries continue to shrink to the point that the mean free path of secondary etch gas molecule
12
is greater than the distance from its collision point on hard mask
16
to emitter tip
14
, the problem is only made more pronounced. Additionally, as wings
18
begin to form against hard mask
16
, the surface area of emitter tip
14
above wings
18
increases. The increased surface area makes for increased primary and secondary etch gas molecules that collide with emitter tip
14
in this region. This increases etching in this region as compared to the region below wings
18
.
In the prior art, hard mask
16
was formed by patterning a photoresist upon an oxide layer, etching to form hard mask
16
, and stripping the photoresist. Problems of a curvilinear profile arose in part from etching difficulties as emitter tip geometries continued to shrink. Achieving a substantially rectilinear profile became more elusive as geometries shrank and it became more and more challenging to get an undercutting etch beneath hard mask
16
so as to yield an emitter tip having a rectilinear profile. Because an undercutting etch is a preferred method of achieving emitter tip
14
, what is needed in the art is a method of forming a substantially rectilinear profile of an emitter tip as geometries continue to shrink.
SUMMARY OF T
Gerike Matthew J.
Micro)n Technology, Inc.
Patel Nimeshkumar D.
Workman & Nydegger & Seeley
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