Etching a substrate: processes – Forming or treating mask used for its nonetching function
Reexamination Certificate
2000-07-17
2002-12-10
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Forming or treating mask used for its nonetching function
C216S041000, C216S056000, C430S004000, C430S005000, C430S023000, C430S024000, C430S313000, C313S402000, C313S403000, C313S407000
Reexamination Certificate
active
06491831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a shadow mask to be used for a cathode ray tube, having a plurality of through-holes, such as dot holes and slot holes, each of which is defined by a greater-size recess formed at a first surface thereof and a smaller-size recess formed at a second surface thereof. The invention further relates to a method of fabricating the shadow mask, and still further to a cathode ray tube including the shadow mask.
2. Description of the Related Art
One of conventional color cathode ray tubes has been suggested in Japanese Unexamined Patent Publication No. 7-65738.
FIG. 1
illustrates the suggested color cathode ray tube. The illustrated color cathode ray tube 11 includes a bulb
12
having a face panel
13
constituting a front surface of the bulb
12
, and a neck portion
12
a,
a fluorescent film
14
formed on an inner surface of the face panel
13
, a shadow mask
15
disposed in facing relation with the fluorescent film
14
and having a plurality of slots, an electron gun
16
disposed in the neck portion
12
a
of the bulb
12
, and a deflecting yoke
18
disposed around the neck portion
12
a
of the bulb
12
for deflecting electron beams
7
emitted from the electron gun
16
.
In operation, the electron gun
16
emits the electron beam
7
, which is deflected by a magnetic field generated by the deflecting yoke
18
. The deflected electron beam
7
passes through the shadow mask
15
, and scans the fluorescent film
14
therewith. In accordance with the scanning path, a certain image is produced on the fluorescent film
14
.
In order to enhance basic characteristics expected in an image display device, such as contrast and brightness, the color cathode ray tube is designed to include, on an inner surface of the pace panel
13
, a black matrix film (not illustrated) comprising non-luminous light-absorbing material, such as black carbon, filling spaces formed between red, green and blue fluorescent luminous pixels, and a metal back film (not illustrated) which is made of an aluminum film and which reflects light independently of the fluorescent film
14
. The above-mentioned fluorescent film
14
is integrally formed with the black matrix film. The shadow mask
15
is disposed in facing relation with the metal back film.
Hereinbelow is explained the shadow mask
15
having a plurality of rectangular slots through which the electron beam
7
passes.
As illustrated in
FIG. 2
, the shadow mask
15
is formed with a plurality of slots
22
each of which has a longer side in a direction of a vertical axis V and a shorter side in a direction of a horizontal axis H. Bridge portions
23
are formed between the adjacent slots
22
in the vertical axis V direction, and connecting portions
24
are formed between the adjacent slots
22
in the horizontal axis H direction.
Each of the slots
22
is a through-hole comprised of a first recess
25
formed at a first surface of the shadow mask
15
, and a second recess
26
formed at a second surface (not seen in
FIG. 2
) of the shadow mask
15
and having a smaller size than the first recess
25
. Herein, the first surface of the shadow mask
15
is defined as a surface facing the fluorescent film
14
, and the second surface is defined as a surface facing the electron gun
16
. The slots
22
are formed by the steps of forming a first photoresist pattern on a first surface of a thin metal plate for forming the first recess
25
, which first photoresist pattern defines a plurality of rectangles each of which has a longer side in the vertical axis V direction and a shorter side in the horizontal axis H direction, forming a second photoresist pattern on a second surface of the thin metal plate for forming the second recess
26
, which second photoresist pattern also defines a plurality of rectangles each of which has a longer side in the vertical axis V direction and a shorter side in the horizontal axis H direction where the longer and shorter sides in the second photoresist pattern are shorter than those in the first photoresist pattern, etching the thin metal plate with the first and second photoresist patterns acting as a mask to thereby form the first and second recesses
25
and
26
, and removing the first and second photoresist patterns.
FIG. 3
is a cross-sectional view taken along the line III—III in
FIG. 2
, illustrating a positional relation between the slot
22
and the incident electron beam
7
passing through the slot
22
. As illustrated in
FIG. 3
, if the electron beam
7
partially strikes an inner surface
26
a
of the second recess
26
, a part of the electron beam
7
is randomly reflected in a direction different from a direction in which the electron beam
7
is originally directed. If the randomly reflected electron beam
7
a
was directed towards the fluorescent film
14
, an undesired image would be generated on the fluorescent film
14
by the randomly reflected electron beam
7
a,
which is a major factor for degrading the contrast of the shadow mask
15
.
The electron beam
7
enters, at a greater incident angle, the slot
22
located farther away from a center of the shadow mask
15
, and accordingly, is reflected at the inner surface
26
a
of the second recess
26
to greater degree, resulting in that the contrast of the shadow mask
15
is considerably degraded.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem of the conventional shadow mask, it is an object of the present invention to provide a shadow mask capable of reducing electron beams reflected from an inner surface of a through-hole towards a fluorescent film to thereby prevent images from being unnecessarily formed on the fluorescent film. It is also an object of the present invention to provide a method of fabricating the shadow mask, and a cathode ray tube including the shadow mask.
In one aspect of the present invention, there is provided a shadow mask to be used for a cathode ray tube, defining a first region where a plurality of through-holes through which electron beams pass are formed, and a second region where no through-holes are formed. Each of the through-holes is defined by a first recess formed at a first surface of the shadow mask and a second recess formed at a second surface of the shadow mask, and has a first wall farther away from a center of the shadow mask than a second wall thereof. The second recess has a smaller size than that of the first recess. The first wall is formed of a first wall portion defined by an inner surface of the first recess and a second wall portion defined by an inner surface of the second recess. Through-holes located at a marginal region of the first region are designed to have the second wall portion designed to reduce electron beams reflected therefrom in directions different from a direction in which the electron beams are originally directed before the electron beams enter the shadow mask.
For instance, the second wall portion of the through-holes located at a marginal region of the first region may be designed to have such a configuration that electron beams reflected therefrom are directed to an inner surface of the first recess. It is preferable that the inner surface of the first recess is designed to have such a configuration that the electron beams directed thereto are reflected therefrom in a direction in which the electron beams are originally directed.
It is preferable that a first boundary between the first and second recesses within the first wall is located lower than a second boundary between the first and second recesses within the second wall on the basis of a bottom of the second recess. It is preferable that the first boundary has a height equal to or lower than 20 &mgr;m on the basis of a bottom of the second recess.
The second wall portion may be designed to have a configuration defined as a function of a horizontal distance between (a) a first boundary between the first and second recesses within the first wall and (b) an outer edge of the second recess, the horizontal distance being defin
Gulakowski Randy
NEC Corporation
Winter Gentle E.
Young & Thompson
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