Etching a substrate: processes – Forming or treating mask used for its nonetching function
Reexamination Certificate
1997-07-02
2001-02-27
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Forming or treating mask used for its nonetching function
C216S100000, C134S002000
Reexamination Certificate
active
06193897
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a shadow mask for a color picture tube and, more particularly, to a shadow mask manufacturing method using photoetching.
The present invention also relates to a cleaning device used in a shadow mask manufacturing process.
Furthermore, the present invention relates to an apparatus for manufacturing a shadow mask.
As shown in
FIG. 1
, a shadow mask type color picture tube has a vacuum envelope
23
consisting of a panel
1
, a cone
20
, and a neck
21
. In this vacuum envelope
23
, a phosphor screen
2
, a shadow mask
3
, and an electron gun
4
are arranged. The phosphor screen
2
is formed on the inner surface of the panel
1
and consists of three kinds of phosphor layers emitting three different colors, respectively. The shadow mask
3
is arranged as a color selection electrode apart from the phosphor screen
2
by a predetermined distance and has a large number of apertures arranged in a predetermined manner and having a predetermined shape. The electron gun
4
is provided in the neck.
In a shadow mask type color picture tube, this shadow mask
3
selects three electron beams
5
emitted from the electron gun
4
so that these electron beams correctly land on the respective predetermined phosphor layers.
The phosphor screen
2
has phosphor dots or stripes and a black matrix burying the portions between these dots or stripes (none of them is shown). This black matrix absorbs landing errors of the electron beams
5
and improves the contrast.
The shapes of the apertures in the shadow mask
3
are roughly classified into a circle and a rectangle. In principle, shadow masks having circular apertures are used in color display tubes for displaying characters and graphics, and shadow masks having rectangular apertures are used in general home color picture tubes.
Recently, a high definition and a high quality are strongly demanded on color display tubes. Accordingly, efforts are being made to decrease the size of apertures in a shadow mask and reduce variations in the aperture size. This is because a shadow mask is used in the formation of a phosphor screen. Generally, in color picture tubes, a phosphor screen for displaying images is formed by photolithography by using a shadow mask as a photomask. For this reason, the size and shape of matrix apertures of a black matrix or of dot-like phosphor layers of three emitting colors constituting this phosphor screen grate depend upon the size and shape of apertures in the shadow mask used. Variations in the size and shape of apertures in the shadow mask appear as unevenness of displayed images and degrade the image quality.
Conventionally, the apertures in shadow masks are formed by photoetching. In particular, apertures are usually formed by a two-stage etching process in display tube shadow masks requiring a high definition and a high quality.
FIGS. 2
to
8
are schematic views for explaining a conventional two-stage etching process.
As a substrate of a color display tube shadow mask, a thin metal plate
7
made from, e.g., an invar material consisting of an Fe—Ni alloy containing such as 36 wt % of Ni or aluminum killed steel is used. This thin metal plate
7
is subjected to degreasing and cleaning to remove, e.g., rolling oil and rust preventing oil.
Photosensitive film formation step
As shown in
FIG. 2
, both two surfaces of the degreased thin metal plate
7
are coated with a photosensitive material made from, e.g., casein or modified PVA. The coated photosensitive material is dried to form resist films
8
as photosensitive films.
Exposure step
As shown in
FIG. 3
, a pair of masters
9
and
19
are prepared. The master
9
has a pattern corresponding to small apertures formed in the surface of a shadow mask, that faces an electron gun. The master
19
has a pattern corresponding to large apertures formed in the surface of the shadow mask, that faces a phosphor screen. These masters
9
and
19
are attached to the resist films
8
on the two surfaces of the thin metal plate
7
. Thereafter, exposure is performed to print the patterns of the masters
9
and
19
onto the resist films
8
. Since a variation in the exposure amount in the exposure area has an influence on the pattern formation dimensions of the resist films
8
, the exposure amount is controlled within a predetermined range.
Development step
The resist films
8
on the both surfaces of which the patterns are transferred are developed by using a developer consisting of water or water and alcohol, thereby removing unexposed portions. Consequently, as shown in
FIG. 4
, resist films
10
and
30
having patterns corresponding to patterns of the pair of masters described above are formed.
First etching step
Thereafter, a protective film
31
is prepared. This protective film
31
consists of an etching-resistant resin film made from polyethyleneterephthalate (PET) or casting polypropylene (CPP) and a pressure-sensitive adhesive applied on the surface of the etching-resistant resin film. As shown in
FIG. 5
, the protective film
31
is adhered by using the pressure-sensitive adhesive to the surface on which the resist film
30
is formed. The surface of the thin metal plate
7
on which the resist film
10
is formed is etched by using a ferric chloride solution as an etching solution. Consequently, small concave holes
12
serving as small apertures to be formed in the surface of a shadow mask, that faces an electron gun are formed in the surface of the thin metal plate
7
on which the resist film
10
is formed.
Etching-resistant layer formation step
Subsequently, the protective film
31
attached on the surface on which the resist film
30
is formed is removed. The resist film
10
on the surface in which the small concave holes
12
are formed is stripped, and the resultant surface is washed with water. Thereafter, as shown in
FIG. 6
, the surface of the thin metal plate
7
in which the small concave holes
12
are formed and the interiors of these small concave holes
12
are coated with varnish, and the varnish is dried to form an etching-resistant layer
13
.
A protective film
11
is adhered to this etching-resistant layer
13
.
Second etching step
Thereafter, the surface of the thin metal plate
7
on which the resist film
30
is formed is etched with an etching solution. Consequently, as shown in
FIG. 7
, large concave holes
32
serving as large apertures formed in the surface of a shadow mask, that faces a phosphor screen are formed on the surface on which the resist film
30
is formed.
Finishing step
The protective film
11
is removed, and the resist film
30
on the surface in which the large concave holes
32
are formed and the etching-resistant layer
13
on the surface in which the small concave holes
12
are formed are stripped off using an aqueous alkali solution. Consequently, as shown in
FIG. 8
, the small concave holes
12
and the large concave holes
32
communicate with each other to form apertures
14
.
A shadow mask is manufactured through the steps described above.
Although this method is generally used, the method has the problem of variations in the size and shape of apertures in a shadow mask. This is caused by some factors described below.
First, etching reproceeds by the etching solution remaining in the concave holes
12
and
32
during cleaning after etching.
This reproceeding will be described below with reference to
FIG. 9
by using the large concave hole
32
as an example.
FIG. 9
is a view for explaining the condition of a thin metal plate immediately after the second etching step. After the second etching step, as shown in
FIG. 9
, an opening diameter De of the concave hole
32
is larger than an opening diameter Dr of the resist film
30
due to side-etching. As a result, an overhanging portion
15
of the resist film
30
is formed around the opening of the concave hole
32
. A relatively large amount of etching solution
16
remains inside the overhanging portion
15
. The etching solution thus remaining in the co
Hirahara Sachiko
Hirosawa Daizi
Nikaido Masaru
Okudo Yukio
Takezawa Hiroharu
Ahmed Shamim
Gulakowski Randy
Kabushiki Kaisha Toshiba
Pillsbury Madison & Sutro LLP
LandOfFree
Shadow mask manufacturing method, shadow mask manufacturing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Shadow mask manufacturing method, shadow mask manufacturing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shadow mask manufacturing method, shadow mask manufacturing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2578894