Semiconductor device manufacturing: process – Electron emitter manufacture
Reexamination Certificate
2000-04-26
2002-05-14
Niebling, John F. (Department: 2827)
Semiconductor device manufacturing: process
Electron emitter manufacture
C438S034000, C438S673000, C438S712000, C438S713000, C445S049000, C445S050000, C445S051000, C445S024000, C313S309000
Reexamination Certificate
active
06387717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to field emitters and methods of fabricating the same. More particularly, the present invention relates to forming field emission tips by the use of facet etching.
2. State of the Art
Various types of field emitters are used in a variety of devices, from electron microscopes to ion guns. However, one of the most prevalent commercial applications of field emitters is flat panel displays, such as cold cathode field emission displays (“FEDs” ) used for portable computers and other lightweight, portable information display devices.
As illustrated in
FIG. 18
, an exemplary flat panel cold cathode FED
200
comprises a flat vacuum cell
202
having a cathode
204
and an anode
206
spaced apart from one another in a mutually parallel relationship. The cathode
204
comprises a conductive or semiconductive first material
208
, such as silicon, disposed on a substrate
212
, such as a semiconductive or dielectric material, and an array of minute field emission tips
214
distributed across the material
208
. The anode
206
comprises a conductive second material
216
disposed on an interior surface of a transparent plate
218
, and a phosphorescent or fluorescent material
222
coated on the conductive second material
216
. A conductive structural element, called a gate
224
, is disposed in the space between the cathode
204
and anode
206
. The gate
224
is generally formed atop a grid of dielectric material
226
deposited on the cathode
204
. The field emission tips
214
reside within openings in the gate
224
and in the dielectric material
226
, such that the gate
224
surrounds each field emission tip
214
. The gate
224
acts as a low potential anode (i.e., lower potential than the anode
206
), such that when a voltage differential, generated by a voltage source
228
, is applied between the cathode
204
(strong negative charge), the gate
224
(weak positive charge), and the anode
206
(strong positive charge), a Fowler-Nordheim electron emission is initiated resulting in a stream of electrons
232
being emitted from the field emission tips
214
toward the phosphorescent or fluorescent material
222
. The electron stream
232
strikes and stimulates the phosphorescent or fluorescent material
222
. The stimulated phosphorescent or fluorescent material
222
emit photons (light) (not shown) through the conductive second material
216
and the transparent plate
218
to form a visual image.
FIGS. 19-23
illustrate a conventional method of forming a field emission tip. As shown in
FIG. 19
, a substrate of conductive or semiconductive material
252
, such as silicon, is deposited or formed over a dielectric support
254
. A mask material is patterned (such as by lithography) to beneath a mask element
256
at the position of the emission tip
258
to be formed. The conductive or semiconductive material
252
is then etched, such as by a wet etch or an isotropic dry etch, which “undercuts” the mask element
256
to form a sharp field emission tip
258
beneath the mask element
256
, as shown in FIG.
20
. The mask element
256
is then removed, as shown in FIG.
21
. Although such a method is commonly used to form field emission tips
258
, the method has drawbacks. For example, as shown
FIG. 22
, if the etching is halted too soon, inefficient, blunt field emission tips
262
are formed. Further, if the etching is not halted soon enough, the mask element
256
is undermined and the field emission tips
264
formed are short and may be ineffective, as shown in
FIG. 23
(shown with the mask element
256
collapsed onto the conductive or semiconductive material
252
). In other words, the short field emission tip
264
may not be close enough to a gate in a field emission display to generate a sufficient stream of electrons striking the phosphorescent or fluorescent material on the anode to stimulate the material and form a visual image.
Other field emission tip formation techniques which do not involve isotropic etching are also known. For example, U.S. Pat. 5,312,514 issued May 17, 1994 to Kumar (“the Kumar patent” ) relates to forming field emission tips by distributing a discontinuous etch mask material across an electrically conductive material layer. The discontinuity of the etched mask material forms random openings therein. The etch mask material is selected such that the electrically conductive material layer will etch at a faster rate than the etch mask material (at least twice the rate) when the electrically conductive material layer is ion etched. The ion etch is performed until all of the etch mask is removed, which results in v-shaped valleys in the electrically conductive material defining peaked field emission tips therebetween. Further, the Kumar patent discusses using a low work function material for the electrically conductive material layer and also discusses depositing a low work function material over the electrically conductive material after the formation of the field emission tips. Although the method taught in the Kumar patent eliminates the use of an isotropic etch to form field emission tips, it lacks control over the field emission tip distribution and dimensions. The discontinuous layer of etch mask material results in a non-uniform distribution of field emission tips, since the positions of the openings in the discontinuous layer cannot be controlled. Furthermore, the discontinuous layer of etch mask material results in non-uniform dimensions between the field emission tips, since the thickness difference across the discontinuous layer cannot be controlled. In other words, the field emission tips formed in areas where less etch mask material existed over the conductive material will be shorter than in other areas. Moreover, since the etch mask material is a discontinuous layer rather than a patterned mask, the size or diameter of the field emission tips formed cannot be controlled.
Thus, it can be appreciated that it would be advantageous to develop a technique which would result in novel field emission tips having uniform distribution and uniform, precise dimensions.
SUMMARY OF THE INVENTION
The present invention relates to field emitters and methods of fabricating the same, wherein the field emission tips of the field emitters are formed by utilization of a facet etch.
In an exemplary method of the present invention, an etch mask is patterned on a conductive substrate material in the locations desired for subsequently formed field emission tips. The etch mask can be patterned in various shapes in order to achieve a desired field emission tip structure. For example, a circular mask element will result in a conical field emission tip, a triangular mask element will result in a tetrahedral field emission tip, a square mask element will result in a pyramidal field emission tip, and so on. The conductive substrate material is anisotropically etched to translate the shape of the mask into the underlying conductive substrate material, which forms a vertical column having a cross-section with the same shape as the mask element, from the conductive substrate material. The anisotropic etch is conducted for a predetermined duration of time, which will result in a column of a specific height required for the subsequently formed field emission tip. The etch mask element is then removed (optional) and the vertical column is facet etched to form the field emission tip.
The facet etching is generally performed in a chamber in which ions can be accelerated to strike a substrate, such as reactive ion etchers, magnetically enhanced reactive ion etchers, low pressure sputter etchers, and high density source etchers. As opposed to anisotropic etches, such as ion etching or plasma etching processes, in which ions strike the surface of the substrate substantially perpendicular to result in a vertical etch, a facet etch results in ions dispersed in a fashion which results in the ions striking 90 degree features (i.e., corners) of structures on the substrate at a rate wh
Blalock Guy T.
Huang Zhaohui
Tang Sanh D.
Niebling John F.
TraskBritt
Zarneke David A.
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