Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-11-12
2004-03-02
Thompson, Craig (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
Reexamination Certificate
active
06699738
ABSTRACT:
The present invention claims the benefit of Korean Patent Application No. 71123/2001 filed in Korea on Nov. 15, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor doping method, and more particularly, to a semiconductor doping method and a liquid crystal display device fabricating method using the same.
2. Description of the Related Art
Currently, active matrix liquid crystal display (LCD) devices are commonly used as large-scaled, high picture quality flat panel display devices, and include a pixel thin film transistor formed within each pixel for displaying an actual image and controlling liquid crystal molecules, and a driving circuit thin film transistor for applying a signal to a gate line and a data line to operate the pixel thin film transistor and applying a picture signal to a pixel electrode.
A driving circuit unit may be commonly divided into two types: an external signal driving circuit and an internal signal driving circuit. The external signal driving circuit is formed on an external substrate of a liquid crystal display panel, separately from a pixel driving TFT, and connected to the liquid crystal panel. The internal signal driving circuit is formed integrally with the pixel driving TFT on the liquid crystal display panel. A CMOS (Complimentary Metal Oxide Semiconductor) TFT that uses a polycrystalline silicon (p-Si) with a high junction field effect mobility is commonly used for the internal signal driving circuit. The internal signal driving circuit that uses the CMOS TFT is advantageous because fabrication costs may be reduced, switching effect is improved compared to an external driving type integrated circuit, and fabrication may be accomplished using the same processes for fabricating the pixel driving TFT.
FIG. 1
is a cross sectional view of a liquid crystal display device according to the related art. In
FIG. 1
, the liquid crystal display device is divided into a pixel unit in which liquid crystal molecules are aligned as an external signal is applied thereto, and a driving circuit unit for applying a signal to the pixel unit. The driving circuit unit includes a region “A” where an NMOS TFT is formed and a region “B” where a PMOS TFT is formed.
The NMOS TFT formed within the region “A” of the driving circuit unit and the pixel unit have an LDD (Light Doped Drain) structure that includes a buffer layer
3
stacked on a transparent glass substrate
1
, intrinsic semiconductor layers (i.e., channel layers)
4
a
and
4
b
made of a p-Si, n
−
doped LDD layers
5
a
and
5
b
, and n
+
layers
6
a
and
6
b
formed on the buffer layer
3
, a gate insulation layer
9
formed over the entire substrate
1
upon which the channel layers
4
a
and
4
b
, the LDD layers
5
a
and
5
b
, and the n
+
players
6
a
and
6
b
are formed, gate electrodes
2
a
and
2
b
formed at the channel layers
4
a
and
4
b
on the gate insulation layer
9
, an interlayer
13
stacked throughout the entire substrate
1
upon which the gate electrode electrodes
2
a
and
2
b
are formed, source/drain electrodes
11
a
and
11
b
formed on the interlayer
13
and connected to the n
+
layers
6
a
and
6
b
through a via hole, and a passivation layer
15
stacked throughout the entire substrate with the TFT formed thereon. A pixel electrode
17
is formed on the passivation layer
15
of the pixel unit and is connected to the source/drain electrode
11
a
through a contact hole. The pixel electrode drives a liquid crystal material, thereby displaying image data when a signal is applied thereto.
The PMOS TFT formed at the region “B” of the driving circuit unit includes a buffer layer
3
stacked on a transparent glass substrate
1
, a channel layer
4
c
and a p
+
layer
7
formed on the buffer layer
3
, a gate insulation layer
9
stacked throughout the entire substrate
1
where the channel layer
4
c
and the p
+
layer
7
are formed, a gate electrode
2
c
formed at the region of the channel layer
4
c
on the gate insulation layer
9
, an interlayer
13
stacked throughout the entire substrate
1
upon which the gate electrode
2
c
is formed, source/drain electrode
11
a
and
11
b
connected to the p
+
layer
7
through a contact hole, and a passivation layer
15
stacked throughout the entire substrate with the PMOS TFT formed thereon. The driving circuit CMOS TFT is integrally formed with the pixel TFT and applies a signal to the pixel TFT through the data line and the gate line.
In general, the NMOS TFT formed in the pixel unit and the driving circuit unit is completed by performing n
+
doping after the channel layer and the LDD layer are partially blocked by patterning the photoresist. In case of doping an n-type ion with a relatively big mass such as phosphor ion, the n-type ion penetrates into the photoresist, causing deformation of a chemical structure of the photoresist, thereby influencing display quality of the liquid crystal display device.
For the explanation of the doping phenomenon of the MOS TFT formed at the liquid crystal display device with the driving circuit integrally formed therewith, the MOS FET formed at both the pixel unit and the driving circuit unit is to be illustrated and explained. In this respect, however, considering that the NMOS FET is commonly formed at the pixel unit and the driving circuit unit, only the driving circuit unit will now be explained with omission of description for the pixel unit.
FIGS. 2A-2C
are cross sectional views of an ion doping method according to the related art. In
FIG. 2A
, at regions “A” and “B” of the buffer layer
3
on the substrate
1
, the semiconductor layer (not shown), the gate insulation layer
9
and the gate electrodes
2
b
and
2
c
are formed. When the LDD doping is performed, the gate electrodes
2
b
and
2
c
block the ion doping, thereby forming the channel layers
4
b
and
4
c
. Then, a low concentration of n-type ions is doped at both sides of the channel layers
4
b
and
4
c
, thereby forming the LDD layers
5
b
and
5
c.
In
FIG. 2B
, a photoresist layer
20
is formed at a portion of the LDD layer
5
b
and over the entire region “B” to block a portion of the LDD layer
5
b
and the region “B.” In general, patterning of a photoresist material is completed by soft baking the coated photoresist at a temperature of about 100° C., and photocured by irradiating an ultraviolet light onto the soft baked photoresist material. Then, a high dose of n-type ions are implanted thereon with a high acceleration energy.
In
FIG. 2C
, the portion of the LDD layer
5
b
of the region “A” is changed to an n
+
layer
6
b
, and the photoresist layer is removed. Then subsequent processing, such as interlayer, source/drain, and passivation processes are performed to complete the NMOS TFT of the LDD structure. Although not shown in the drawings, the LDD layer
5
c
of the region “B” is changed to a PMOS TFT according to a p
+
doping.
In the driving circuit integrated liquid crystal panel, in order to form the NMOS TFT of the pixel unit and the NMOS TFT of the driving circuit unit, in a state that a portion of the semiconductor layer is blocked, the high dose of n-type ions uses a high acceleration energy. Since the phosphor is the commonly selected n-type ion used for the n
+
doping and has a relatively large mass, if the high dose/high acceleration energy is performed, the n-type ions penetrate into the photoresist layer, thereby deforming the chemical structure of the photoresist material. The chemical deformation of the photoresist material changes a reaction with a developer, thereby making it impossible to completely strip the photoresist layer
20
after doping. As a result, portions of the photoresist material remain on the gate insulating layer
9
, thereby generating defects in the TFT.
FIGS. 3A-3C
are cross sectional views of another ion doping method according to the related art. In
FIG. 3A
, an LDD doping is performed to form t
Hwang Eui-Hoon
Kim Ki-Jong
LG. Phillips LCD Co., Ltd.
Morgan & Lewis & Bockius, LLP
Thompson Craig
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