Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2000-12-27
2003-09-09
Coleman, William David (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
Reexamination Certificate
active
06617611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display unit and a method of fabricating the same, and more particularly, it relates to a display unit having a display electrode formed on an insulator film and a method of fabricating the same.
2. Description of the Prior Art
A transmission liquid crystal display unit employing a polycrystalline silicon TFT is known in general. For example, Japanese Patent Laying-Open No. 8-152651 (1996) discloses such a transmission liquid crystal display unit.
FIG. 10
is a sectional view showing a pixel part
150
of the conventional transmission liquid crystal display unit disclosed in the aforementioned gazette. The structure of the pixel part
150
in the conventional transmission liquid crystal display unit is now described with reference to FIG.
10
.
In the pixel part
150
of the conventional transmission liquid crystal display unit, a liquid crystal layer
103
filled with liquid crystals is formed between opposed transparent insulating substrates
101
and
102
. The transparent insulating substrate
101
is provided with a display electrode
104
of a liquid crystal cell. The transparent insulating, substrate
102
is provided with a common electrode
105
of the liquid crystal cell. The display electrode
104
and the common electrode
105
are opposed to each other through the liquid crystal layer
103
. An alignment layer
136
a
is provided between the liquid crystal layer
103
and the display electrode
105
, while another alignment layer
136
b
is provided between the liquid crystal layer
103
and the common electrode
105
.
A polycrystalline silicon film
106
defining an active layer of a TFT
141
is formed on the surface of the transparent insulating substrate
101
closer to the liquid crystal layer
103
. A gate insulator film
107
is formed on the polycrystalline silicon film
106
. A gate electrode
108
is formed on the gate insulator film
107
. A drain region
109
and a source region
110
of an LDD structure are formed on the polycrystalline silicon film
106
. The drain region
109
of the LDD structure is formed by a low concentration region
109
a
and a high concentration region
109
b
. The source region
110
of the LDD structure is formed by a low concentration region
110
a
and a high concentration region
110
b
. The drain region
109
and the source region
110
of the LDD structure and the gate electrode
108
form the TFT
141
.
The transparent insulating substrate
101
is provided on a portion adjacent to the TFT
141
with an auxiliary capacitor CS formed through the same step as that for forming the TFT
141
. A storage electrode
111
of the auxiliary capacitor CS is formed in the polycrystalline silicon film
106
and connected with the source region
110
of the TFT
141
. A dielectric film
112
is formed on the storage electrode
111
. A counter electrode
122
of the auxiliary capacitor CS is formed on the dielectric film
112
. The dielectric film
112
, located on an extension of the gate insulator film
107
, is identical in structure to the gate insulator film
107
and formed through the same step as that for forming the gate insulator film
107
. The counter electrode
122
is identical in structure to the gate electrode
108
and formed through the same step as that for forming the gate electrode
108
. Side wall insulator films
113
are formed on the side walls of the counter electrode
122
and the gate electrode
108
. Insulator films
114
are formed on the counter electrode
122
and the gate electrode
108
.
An interlayer isolation film
115
is formed on the overall surfaces of the TFT
141
and the auxiliary capacitor CS. The high concentration region
110
b
forming the source region
110
is connected to a source electrode
119
through a contact hole
117
formed in the interlayer isolation film
115
. The high concentration region
109
b
forming the drain region
109
is connected to a drain electrode
118
forming a drain wire through a contact hole
116
. An insulator film
120
, an SOG film
132
serving as a planarization film and another insulator film
131
are formed on the overall surface of the device including the interlayer isolation film
115
, the drain electrode
118
and the source electrode
119
. The SOG film
132
serving as the planarization film is held between the insulator films
120
and
131
. The display electrode
104
is formed on the insulator film
131
.
The display electrode
104
is connected with the source electrode
119
through a contact hole
121
formed in the insulator film
120
, the SOG film
132
and the insulator film
131
. The aforementioned SOG film
132
fills up steps formed on ends of the auxiliary capacitor CS thereby flattening the surface of the display electrode
104
. An aluminum alloy is generally employed as the material for the drain electrode
118
and the source electrode
119
. Further, an ITO (indium tin oxide) film is generally employed as the material for the display electrode
104
. The display electrode
104
, the drain electrode
118
and the source electrode
119
are generally formed by sputtering.
In the aforementioned structure, the SOG film
132
serving as the planarization film is provided for the following reason: If large steps are caused on the display electrode
104
, liquid crystal molecules cannot be homogeneously oriented in portions of the liquid crystal layer
103
located on the steps. When the liquid crystal molecules are heterogeneously oriented in the liquid crystal layer
103
, the display electrode
104
cannot control light transmission and light interception of the liquid crystal layer
103
, leading to a regular light transmission state. In this case, the contrast is lowered on the step portions regularly in the light transmission state. In the step portions, further, the thickness of the display electrode
104
is so reduced that the resistance value of the display electrode
104
is increased or the display electrode
104
is disadvantageously disconnected. In order to flatten the surface of the display electrode
104
, therefore, the SOG film
132
is provided between the display electrode
104
and the insulator film
131
as the planarization film.
The term “SOG (spin on glass) film
132
” generically indicates a film mainly composed of a silicon dioxide formed from a solution prepared by dissolving a silicon compound in an organic solvent. Spin coating is employed for applying the SOG film
132
. More specifically, the solution prepared by dissolving the silicon compound in the organic solvent is dripped on a substrate while rotating the substrate. Thus, a coating of the solution is formed thickly on concave portions of steps defined on the substrate due to wiring and thinly on convex, to relax the steps. Consequently, the surface of the coating of the solution is flattened. Then, heat treatment is performed for evaporating the organic solvent and progressing polymerization, thereby forming the SOG film
132
having a flat surface.
The SOG film
132
includes an inorganic SOG film containing no organic component in the silicon compound as expressed in the following general formula (1) and an organic SOG film containing an organic component in the silicon compound as expressed in the following general formula (2):
[SiO
2
]
n
(1)
[R
X
SiO
Y
]
n
(2)
where n, X and Y represent integers, and R represents an organic group such as an alkyl group or an aryl group.
The inorganic SOG film contains large quantities of moisture and hydroxyl groups, has high hygroscopicity, is fragile as compared with a silicon oxide film formed by CVD (chemical vapor deposition), and readily cracked in heat treatment when its thickness is in excess of 0.5 &mgr;m.
On the other hand, the organic SOG film has portions where bonds are closed with alkyl groups or aryl groups and is hence inhibited from cracking in heat treatment, and its thickness can be set to about 0.5 to 1 &mgr;m. When employing the organic SOG fil
Hamada Hiroki
Hasegawa Isao
Ide Daisuke
Coleman William David
Sanyo Electric Co,. Ltd.
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