Etching a substrate: processes – Forming groove or hole in a substrate which is subsequently...
Reexamination Certificate
1999-07-07
2001-10-16
Stinson, Frankie L. (Department: 1746)
Etching a substrate: processes
Forming groove or hole in a substrate which is subsequently...
C216S019000, C438S424000, C438S435000, C438S697000, C438S954000
Reexamination Certificate
active
06303043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a preserve layer. More particularly, the present invention relates to a method of fabricating a preserve layer of a reflection micro-LCD.
2. Description of the Related Art
Reflection micro-LCD is operated by applying voltage to a top metallic layer, which is used for controlling a circuit, in order to generate an electrical field for governing the arrangement of liquid crystals. When lights transmit through liquid crystals to the top metallic layer, the top metallic layer reflects the lights to return the lights through the liquid crystals. Since different arrangements of the liquid crystals represent different optical properties, different pictures can be shown on a display.
In order to prevent moisture and scratches from damaging the surface of the top metallic layer, a preserve layer is formed to protect the top metallic layer. However, the structure and the thickness combination of the preserve layer directly affect the reflectivity of the top metallic layer. Thus, the formation of the preserve layer is a decisive step during the fabrication process of the reflection micro-LCD.
FIGS. 1A through 1B
are schematic, cross-sectional views showing a conventional method of fabricating a preserve layer.
In
FIG. 1A
, a dielectric layer
102
is formed on a substrate
100
. An adhesion layer
104
and a metallic layer
106
are formed in sequence over the substrate
100
. Portions of the top metallic layer
106
, the adhesion layer
104
, and the dielectric layer
102
are removed to form a trench
108
. It is necessary to form the trench
108
completely through the top metallic layer
106
, in order to separate the metallic layer
106
into different regions.
In
FIG. 1B
, a conformal oxide layer
110
is formed over the substrate
100
. The thickness of the oxide layer
110
is 5000 angstroms. A nitride layer
112
having a thickness of 7000 angstroms is formed on the oxide layer
110
to fill the trench
108
. The oxide layer
110
and the nitride layer
112
together form a preserve layer
114
. However, since the preserve layer
114
is particularly thick, the transmissivity of the preserve layer
114
is reduced. Consequently, the reflectivity of the top metallic layer
106
is significantly decreased.
In addition, the conventional method forms the preserve layer
104
with poor planarization. When light transmits through the preserve layer
104
, the transmissivity of the preserve layer
114
is reduced due to poor planarization of the preserve layer
114
. The reflectivity of the top metallic layer
106
is decreased to 30%. Thus, it is difficult to form a top metallic layer
106
with a high reflectivity.
SUMMARY OF THE INVENTION
The invention provides a method of fabricating a preserve layer. A top metallic layer is formed over the substrate. Portions of the metallic layer and the substrate are removed to form a trench. A conformal pad oxide layer is formed over the substrate. A conformal first nitride layer is formed on the pad oxide layer. A spin-on glass layer is formed on the first nitride layer to fill the trench. An etching back step is performed to remove a portion of the spin-on glass layer. The remaining spin-on glass layer fills the trench to the surface of the first nitride layer above the top metallic layer. An oxide layer is formed over the substrate. A second nitride layer is formed on the oxide layer. A preserve layer comprising the pad oxide layer, the first nitride layer, the oxide layer, and the nitride layer is formed.
The present invention uses the spin-on glass layer to fill the trench. The etching back step is performed with a HF solution to remove the spin-on glass layer outside the trench, so as to obtain a planarized surface. Since the etching selectivity between the first nitride layer and the spin-on glass layer is high, the first nitride layer serves as an etching stop layer during the etching back step.
In comparison with the conventional preserve layer, the preserve layer of the invention is thinner. Thus, the preserve layer protects devices without reducing the reflectivity of the top metallic layer. The reflectivity of the top metallic layer is increased by 90%. The performance of the reflection micro-LCD is thus significantly increased.
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.
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Chang Ruoh-Haw
Chen Shu-Jen
Chen Wei-Shiau
Smetana Jiri F.
Stinson Frankie L.
Thomas Kayden Horstemeyer & Risley
United Microelectronics Corp.
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