Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
2001-03-07
2002-12-24
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Screen other than for cathode-ray tube
Reexamination Certificate
active
06497981
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of forming an optical device. More particularly, the present invention relates to a method of forming a color filter array (CFA).
2. Description of Related Art
Color filter array (CFA) is frequently used in optical devices for displaying color images. In such an optical device, each pixel generally corresponds to three neighboring but different color filters. In other words, a specified color is permitted to pass through each filter. A complete color palette can be obtained, for example, by mixing the colors from the three filters such as red (R), green (G) and blue (B). Therefore, the pixel array in an image display device actually consists of an array of three types of color filters such as an array of red filters, an array of green filters and an array of blue filters.
The fabrication of an optical device that displays colorful images normally involves forming a passivation layer such as a silicon oxynitride (SiON) layer over an array of background light sensitive devices. Thereafter, the three color filter arrays are independently fabricated over the passivation layer.
FIGS. 1A through 1C
are schematic cross-sectional views showing the progression of steps for fabricating a conventional tricolor filter array. First, as shown in
FIG. 1A
, a substrate
100
having an array of metallic layers
110
thereon, in which the metallic layers
100
serve as light-sensitive elements, is provided. A passivation layer
120
such as a silicon oxynitride layer is formed over the substrate
100
and the metallic layers
110
. A red negative photoresist layer
130
is formed over the passivation layer
120
. An i-line light source (365 nm)
132
shines on the photomask
134
and exposes a portion of the red photoresist layer
130
. Ultimately, cross-linking of high molecular weight polymer occurs in a light-exposed region
136
of the red photoresist layer.
As shown in
FIG. 1B
, a chemical development of the red photoresist layer is carried out so that red photoresist material outside the exposed region
136
is removed. Thus, a red color filter
140
is produced.
As shown in
FIG. 1C
, the steps illustrated in
FIG. 1B
are repeated twice to form a green color filter
150
and a blue color filter
160
, respectively. Note that only one red/green/blue color filter (
140
/
150
/
160
) is shown in the figure. In fact, an array of red/green/blue color filters covering a wide area is formed.
However, the conventional method of fabricating a color filter array has several problems. First, an I-line light source
132
having a wavelength of 365 nm is used to carry out exposure. However, the silicon oxynitride layer is a poor absorber for light of this wavelength and hence cannot absorb reflected light
132
a
coming from a lower layer. Consequently, a portion of red photoresist
130
outside the desired exposure region
136
is also exposed leading to the formation of cross-linked polymers. After a post-exposure development, a residual patch
130
a
of red photoresist remains over the passivation layer
120
. In the presence of a residual patch
130
a,
subsequent fabrication of the green filter
150
and the blue filter
160
are also affected. Ultimately, image quality of the device will deteriorate.
Second, the conventional method of forming a blue color filter array often leads to color pixel peeling due to insufficient light exposure.
FIGS. 2A and 2B
are schematic cross-sectional views showing a conventional technique for forming a blue color filter array on a substrate and resulting adverse consequence. As shown in
FIG. 2A
, an i-line light source
232
shines through a photomask
234
and exposes a portion of the blue negative photoresist layer
230
on the passivation layer
220
. Since blue negative photoresist has a relatively high i-line absorption coefficient, lower edges of the exposed region
236
in the photoresist layer
230
may not receive sufficient i-line light to trigger cross-linking. Consequently, as shown in
FIG. 2B
, the blue color filter
240
is narrower at its base than at its top after photoresist development. Hence, the chance of this blue color filter
240
peeling off increases considerably (the dashed lines indicate the position of the blue filter before peeling).
In addition, resolution of a light source with a wavelength of 365 nm is relatively low and hence area utilization is unsatisfactory. Furthermore, resolution of the color filters is ultimately limited by the resolution of the light source.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a method of forming a color filter array. A substrate having a passivation layer such as a silicon oxynitride layer thereon is provided. A negative color photoresist layer is formed over the passivation layer. A photolithographic exposure process is conducted using a light source with a wavelength less than or equal to 248 nm so that a pattern for forming the color filter array is imprinted on the negative color photoresist layer.
In the aforementioned photolithographic exposure, a light source having a wavelength less than or equal to 248 nm is used in photolithographic exposure. Since silicon oxynitride material has a higher light absorption capacity for light at such a wavelength, the passivation layer actually serves also as an anti-reflection coating that improves the final quality of the patterned color filter array.
In addition, by using a light source having a wavelength less than or equal to 248 nm rather than an i-line light source, resolution of the photolithographic process is increased. Ultimately, both area utilization and resolution of the color filter panel improves.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5143855 (1992-09-01), Pace et al.
patent: 59-228757 (1984-12-01), None
patent: 10-332920 (1998-12-01), None
Chen Jain-Hon
Yeh Jeenh-Bang
J.C. Patents
United Microelectronics Corp.
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