Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2003-02-05
2004-12-07
Zarabian, Amir (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S029000, C438S942000, C438S945000, C438S948000, C438S949000
Reexamination Certificate
active
06828167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor for a liquid crystal display and a method for manufacturing the same, and more particularly, to a thin film transistor for a liquid crystal display and a method for manufacturing the same capable of decreasing the number of required photomasks.
2. Description of the Related Art
In an information-oriented society these days, the role of electronic displays is becoming increasingly important. The electronic displays of all kinds are widely used in various industrial fields.
Generally, the electronic display is an apparatus for visually transmitting a variety of information to a person. That is, an electrical information signal output from various electronic devices is converted into a visually recognizable optical information signal presented on electronic displays. Therefore, the electronic display serves as a bridge for connecting the person and the electronic devices.
The electronic display is classified into an emissive display, in which the optical information signal is displayed by a light-emitting method, and a non-emissive display, in which the optical information signal is displayed by an optical modulation method, including light-reflecting, dispersing and interfering phenomena. Examples of the emissive display, referred to as an active display, include a CRT (Cathode Ray Tube), a PDP (Plasma Display Panel), an LED (Light Emitting Diode) and an ELD (Electroluminescent Display). Examples of the non-emissive display referred to as a passive display, include an LCD (Liquid Crystal Display), an ECD (Electrochemical Display) and an EPID (Electrophoretic Image Display).
The CRT used in an image display such as a television receiver or a monitor, has the highest market share to date with respect to display quality and economical efficiency, but the CRT also has many disadvantages such as heavy weight, large volume and high power consumption.
Meanwhile, due to rapid development of a semiconductor technology, various kinds of electronic devices are now driven by lower voltage and lower power, which produces electronic equipment that is considerably slimmer and lighter. Therefore, a flat panel type display having these slimmer and lighter characteristics, as well as lower driving voltage and lower power consumption characteristics, is very desirable according to the new environment.
The LCD among the various developed flat panel type displays is much slimmer and lighter than any other displays; LCDs also have low driving voltage and low power consumption, as well as displaying quality similar to that of the CRT. Therefore, the LCD is widely used in various electronic equipment.
The LCD comprises two substrates respectively having an electrode, and a liquid crystal layer interposed between the two substrates. In the LCD, a voltage is applied to the electrode to re-align liquid crystal molecules and to control an amount of light transmitted through the molecules. These LCDs are classified into a transmission type LCD, for displaying an image using an external light source, and a reflection type LCD, for displaying an image using natural light.
One of the LCDs, which is mainly used nowadays, is provided with the electrode formed at each of the two substrates and having a thin film transistor for switching power supplied to each electrode. Generally, the thin film transistor (referred to as TFT, hereinafter) is formed at one side of the two substrates.
Generally, a substrate on which TFTs are formed is referred to as a “TFT substrate.” And, such a TFT substrate is generally manufactured by a photolithography process using a photomask; currently, for example, seven sheets of photomasks are required at the present.
FIG. 1
is a sectional view of a conventional reflection type TFT LCD.
Referring to
FIG. 1
, after depositing a single layered metallic film or a double layered metallic film such as chromium (Cr), aluminum (Al), molybdenum (Mo) or an alloy of Mo and tungsten (W) as a gate film on a transparent substrate
10
made of glass, quartz, or sapphire, the gate film is patterned using a photolithography process to form a gate wiring (using a first mask). The gate wiring includes a gate electrode
12
, a gate line connected to the gate electrode
12
and a gate pad
13
that receives a signal from the outside and transmits the received signal to the gate line.
A gate insulating film
14
made of silicon nitride is formed to a thickness of about 4,500 Å on the substrate on which the gate wiring is formed. A semiconductor film made of amorphous silicon is deposited on the gate insulating film
14
and then patterned to form an active pattern
16
of a TFT (using a second mask).
A metal film is deposited on the active pattern
16
and the gate insulating film
14
and then is patterned using the photolithography process to form a data wiring (using a third mask). The data wiring includes a source electrode
18
, a drain electrode
19
and a data pad (not shown) for transmitting an image signal.
After depositing an inorganic passivation film
20
made of silicon nitride on the data wiring and the gate insulating film
14
to a thickness of about 4,000 Å, the inorganic passivation film
20
and the gate insulating film
14
on the source electrode, gate wiring and data pad are dry-etched by the photolithography process (using a fourth mask).
A photosensitive organic passivation film
22
is deposited to a thickness range of about 2-4 &mgr;m on the inorganic passivation film
20
and is then exposed using a photomask (using a fifth mask). At this time, the organic passivation film
22
placed on the source electrode
18
, gate wiring and data pad is fully exposed.
In addition, to make the reflection plate of the pixel region in a light scattering structure, the organic passivation film
22
is again exposed (using a sixth mask). At this time, the organic passivation film
22
of the display region is incompletely exposed in an irregular pattern having a line width corresponding to the resolution of an exposing machine.
Subsequently, the exposed organic passivation film
22
is developed to form an irregular surface having a plurality of concave portions and convex portions in the organic passivation film
22
and a first via hole for exposing the source electrode
18
and a second via hole for exposing the gate pad
13
. In addition, although not shown in the drawings, there is formed a third via hole for exposing the data pad together.
On the organic passivation film
22
, in which the aforementioned via holes are formed, a reflection metal film such as aluminum (Al) is deposited and then patterned to form a pixel electrode
26
, which is connected to the source electrode
18
through the first via hole, and a gate pad electrode
27
, which is connected to the gate pad
13
through the second via hole (using a seventh mask). In addition, there is formed a data pad electrode (not shown), which is connected to the data pad through the third via hole, together. The pixel electrode
26
is formed within the pixel region enclosed by the gate wiring and the data wiring and is provided as a reflection plate.
To manufacture a TFT according to the aforementioned conventional method, the photolithography process is used in the seven layers of the gate wiring, active pattern, data wiring, inorganic passivation film, organic passivation film and pixel electrode and thus at least seven sheets of photomask are needed.
As the number of photomasks used in the photolithography process increases, the more the manufacturing cost and the probability of process error increase. Since this causes an increase in the manufacturing costs, there has been proposed a method for forming the inorganic passivation film as a single layer by deleting the inorganic passivation film in order to simplify the process.
FIGS. 2A
to
4
B are sectional views for describing a method for forming a via hole in a TFT in accordance with another conventional method in which the inorganic passivation film is dele
McGuireWoods LLP
Novacek Christy
Samsung Electronics Co,. Ltd.
Zarabian Amir
LandOfFree
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