Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-05-17
2002-07-16
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C216S039000, C438S692000
Reexamination Certificate
active
06421108
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 88106215, filed Apr. 19, 1999, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor process. More particularly, the invention relates to a method for fabricating a passivation layer.
2. Description of the Related Art
The application of semiconductors involves many fields. For example, semiconductors are applicable in the field of liquid crystal display (LCD). A type of LCD, which is called a reflection type LCD, comprises a top metal layer of a typical semiconductor substrate as a light reflection layer. The metal layer can be functioned as a mirror to reflect the incident light thereon, so as to generate a virtual image needed for display.
However, a passivation layer, which is often formed to cover the metal layer as a protection thereof, degrades the reflection effect of the metal layer. This degradation including reduction of intensity of the reflected light, and the reflected light therefore has insufficient intensity for generating the desirable virtual image.
Two conventional methods for fabricating the passivation layer are as follows:
1. Sequentially depositing an oxide layer and a silicon nitride layer over a surface metal layer of a semiconductor substrate. The oxide layer and silicon nitride layer constitute a passivation layer to resist moisture and to prevent the metal layer from being scratched. The passivation layer and the semiconductor substrate to be protected are shown as FIG.
1
. The substrate comprises an inter-metal dielectric layer (IMD)
10
, a titanium nitride/titanium (TiN/Ti) layer
12
, and the top metal layer
14
. The substrate has an opening
16
that exposes a portion of the IMD
10
. The opening
16
is filled up with the passivation layer consisting of the oxide layer
18
and silicon nitride layer
20
.
As shown in
FIG. 1
, the passivation layer does not have a smooth surface, thereby degrading the reflectivity of the top metal layer
14
to only about 30%.
2. Using techniques of spin-on-glass (SOG) and chemical-mechanical polishing the SOG layer to achieve a planarization. As shown in
FIG. 2
, the passivation layer formed by the method comprises a conformal silicon-rich oxide (SRO) layer
38
, a spin-on-glass (SOG) layer
42
, a TEOS layer
44
, and a silicon nitride layer
46
. A substrate, which consists of an IMD
30
, a TiN/Ti layer
32
and a top metal layer
34
, is covered by the passivation layer. The substrate has an opening
36
that exposes a portion of the IMD
30
but that is filled up by the conformal SRO layer
38
and SOG layer
42
. However, the polishing step performed on the SOG layer
42
and stopped on the SRO layer
38
often scratches the SRO layer
38
. Therefore, the polishing step degrades the planarization of the passivation layer and reduces the reflectivity of the top metal layer
34
.
Even if the polishing step is replaced with an etching back step, the thickness of the SOG layer
42
is not easily controlled. Therefore, the etching back step also fails to accomplish the planarization of the passivation layer and to ensure the reflectance of the top metal layer
34
.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method for fabricating a passivation layer. A metal layer is provided. An oxide layer is formed on the metal layer, followed by formation of a first silicon nitride layer, a spin-on-glass (SOG) layer, and a second silicon nitride layer over the SOG layer. The passivation layer is formed comprising the oxide layer, the first silicon nitride layer, the SOG layer and the second silicon nitride layer.
The oxide layer has a thickness of about 675 to about 825 angstroms, and is preferably about 750 angstroms thick. The first silicon nitride layer has a thickness of about 576 to about 704 angstroms, and is preferably about 640 angstroms thick. The SOG layer is formed by a coating method with a thickness of about 1010 to about 1310 angstroms, and preferably, about 1160 angstroms. The second silicon nitride layer has a thickness of about 1080 to about 1320 angstroms, and is preferably about 1200 angstroms thick.
Fabricating the passivation layer comprising the oxide layer, first silicon nitride layer, SOG layer, and second silicon nitride layer ensures the high reflectivity of the metal layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 5849632 (1998-12-01), Tuttle et al.
patent: 5908672 (1999-06-01), Ryu et al.
patent: 5985765 (1999-11-01), Hsiao et al.
patent: 6121151 (2000-09-01), Chen
patent: 6303043 (2001-10-01), Chen et al.
Chen Shuenn-Jeng
Chen Wei-Shiau
Liu Tsan-Wen
J.C. Patents
Nguyen Dung
Sikes William L.
United Microelectronics Corp.
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