U.S. patent application number 09/736308 was filed with the patent office on 2001-08-09 for method of manufacturing thin film transistor.
Invention is credited to Kim, Cheol-Se, Kim, Dong-Hee, Lee, Myeung-Kyu.
Application Number | 20010012650 09/736308 |
Document ID | / |
Family ID | 19634936 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012650 |
Kind Code |
A1 |
Kim, Cheol-Se ; et
al. |
August 9, 2001 |
Method of manufacturing thin film transistor
Abstract
The present invention discloses a method of manufacturing a thin
film transistor, including: preparing a process chamber having a
stage; providing a substrate on the stage of the process chamber;
injecting a first mixed gas of NH.sub.3, N.sub.2 and SiH.sub.4 into
the process chamber; forming a plasma in the process chamber and
forming a silicon nitride film (SiNx) on the substrate; injecting a
second mixed gas of H.sub.2 and SiH.sub.4 into the process chamber
while removing the first mixed gas in the plasma state; forming a
pure amorphous silicon film (a-Si:H) on the silicon nitride film
using the second mixed gas; injecting a third mixed gas of H.sub.2,
SiH.sub.4 and PH.sub.3 into the process chamber while removing the
second mixed gas in the plasma state; and forming a doped amorphous
silicon film (n.sup.+a-Si:H) on the silicon nitride film using the
second mixed gas.
Inventors: |
Kim, Cheol-Se; (Taegu,
KR) ; Kim, Dong-Hee; (Taegu, KR) ; Lee,
Myeung-Kyu; (Kyoungsangbuk-do, KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
19634936 |
Appl. No.: |
09/736308 |
Filed: |
December 15, 2000 |
Current U.S.
Class: |
438/155 ;
257/E21.414; 257/E29.291; 438/162 |
Current CPC
Class: |
H01L 29/78669 20130101;
H01L 29/66765 20130101 |
Class at
Publication: |
438/155 ;
438/162 |
International
Class: |
H01L 021/00; H01L
021/84 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 31, 1999 |
KR |
1999-67845 |
Claims
What is claimed is:
1. A method of manufacturing a thin film transistor, comprising:
preparing a process chamber having a stage; providing a substrate
on the stage of the process chamber; injecting a first mixed gas of
NH.sub.3, N.sub.2 and SiH.sub.4 into the process chamber; forming a
silicon nitride film (SiNx) on the substrate using the first mixed
gas by creating a plasma in the process chamber; injecting a second
mixed gas of H.sub.2 and SiH.sub.4 into the process chamber while
removing the first mixed gas in the plasma state; forming a pure
amorphous silicon film (a-Si:H) on the silicon nitride film using
the second mixed gas; injecting a third mixed gas of H.sub.2,
SiH.sub.4 and PH.sub.3 into the process chamber while removing the
second mixed gas in the plasma state; and forming a doped amorphous
silicon film (n.sup.+ a-Si:H) on the silicon nitride film using the
second mixed gas.
2. The method of claim 1, further comprising, forming a gate
electrode before the step of forming the silicon nitride film; and
forming source and drain electrodes on the doped amorphous silicon
film.
3. The method of claim 1, further comprising, performing a hydrogen
plasma treatment on an interface of the silicon nitride film before
the step of forming the pure amorphous silicon film.
4. The method of claim 1, further comprising, performing a hydrogen
plasma treatment on an interface of the pure amorphous silicon film
before the step of forming the doped amorphous silicon film.
Description
CROSS REFERENCE
[0001] This application claims the benefit of Korean Patent
Application No. 1999-67845, filed on Dec. 31, 2000, under 35 U.S.C.
.sctn. 119, the entirety of which is hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of manufacturing a
thin film transistor, and more particularly, to a method of
manufacturing a thin film transistor for use in a liquid crystal
display (LCD) device.
[0004] 2. Description of Related Art
[0005] Liquid crystal display (LCD) devices are in wide use as
display devices capable of being reduced in weight, size and
thickness. Of these, active matrix LCD devices, where thin film
transistors (TFTs) and pixel electrodes are arranged in the form of
a matrix, have been widely used due to a high resolution and an
excellent performance of implementing moving images.
[0006] FIG. 1 is a cross-sectional view illustrating a liquid
crystal panel of a typical active matrix LCD device. As shown in
FIG. 1, the liquid crystal panel 20 includes lower and upper
substrates 2 and 4 with a liquid crystal layer 10 interposed
therebetween. The lower substrate 2, referred to as an array
substrate, is divided into two regions: a region S; and a region P.
TFTs are arranged on the region S as a switching element, and pixel
electrodes 14 are arranged on the pixel region P. The upper
substrate 4 includes a color filter 8 and a common electrode 12.
Through the pixel electrode 14 and the common electrode 12,
voltages are applied to the liquid crystal layer 10. In order to
prevent a leakage of the liquid crystal, edge portions of the two
substrate 2 and 4 are sealed by a sealant 6. The TFT receives
signals from external drive integrated circuit (IC) to drive the
pixel electrode 14.
[0007] An inverted staggered type TFT is used for a general LCD
device because its simple structure and a high performance. The
inverted staggered type TFT is divided into a back channel etch
type and an etch stopper type. Hereinafter, the back channel etch
type TFT is explained.
[0008] FIG. 2 is a cross-section view illustrating the typical back
channel etch type TFT. As shown in FIG. 2, a gate electrode 30 is
formed on a substrate 1. A gate insulating layer 32 is formed over
the whole surface of the substrate 1 while covering the gate
electrode 30. An active layer 34 and an ohmic contact layer 36 are
sequentially formed on the gate insulating layer 32. Source and
drain electrodes 38 and 40 overlap both end portions of the ohmic
contact layer 36.
[0009] The gate electrode 30 is made of a low resistive material
such as aluminum in order to reduce a RC delay. The gate insulating
layer 34 is deposited at a low temperature of less than 350 and is
made of SiNx or SiO.sub.2. The active layer 34 is made of an
hydrogenated amorphous silicon (a-Si:H). The ohmic contact layer 36
is formed in such a way that a gas containing a boron (B) of a
boron group or a phosphorous (P) of a nitrogen group is ion-doped
into the amorphous silicon layer. The ohmic contact layer 36 is
generally is made of n.sup.+-type hydrogenated amorphous silicon
(n.sup.+ a-Si:H) doped with PH.sub.3 containing a phosphorous (P).
The source and drain electrodes 42 and 44 are made of Cr or Mo.
[0010] In order to form the TFT, a deposition process is repeated
several times, for example, using a plasma-enhanced chemical vapor
deposition (PECVD) technique. The gate insulating layer 32, the
active layer 34 and the ohmic contact layer 36 undergo a deposition
process in the same process chamber.
[0011] FIG. 3 is a graph illustrating a relationship between a
power and each of the layers when the gate insulating layer 32, the
active layer 34 and the ohmic contact layer 36 are deposited.
[0012] In order to form the gate insulating layer 32, a mixed gas
of NH.sub.3, N.sub.2 and SiH.sub.4 is injected into the process
chamber and is decomposed by plasma, so that a silicon nitride film
(SiNx) is formed on the substrate.
[0013] In order to form the active layer 34, NH.sub.3 and N.sub.2
that are used to deposit the gate insulating layer 32 are pumped,
and H.sub.2 are added. The pure amorphous silicon (a-Si:H) is
formed using SiH.sub.4 and H.sub.2.
[0014] Then, in order to form the ohmic contact layer 36, a small
amount of PH.sub.3 is added to the mixed gas of SiH.sub.4 and
H.sub.2 to form an n.sup.+ type amorphous silicon layer
(a-Si:H).
[0015] The active layer 34 generally contains a hydrogen (H).
Electrical characteristics of the amorphous silicon TFTs depend on
a density of state (DOS). The silicon atoms of the active layer 34
have 4 outmost electrons, among them uncombined electrons cause a
dangling bond problem. The dangling bond problem can be solved by
the hydrogen.
[0016] As described above, in order to remove the mixed gases used
to deposit the gate insulating layer, the active layer and the
ohmic contact layer, plasma condition should be released first.
After a predetermined time passes, the mixed gas in the process
chamber is pumped.
[0017] FIG. 4 is a graph illustrating a relationship between an
internal pressure variation of the process chamber and each of the
layers when the gate insulating layer 32, the active layer 34 and
the ohmic contact layer 36 are deposited. After a deposition of the
gate insulating layer 32, if the mixed gas is removed in the state
that the plasma condition is released, an internal pressure of the
process chamber varies suddenly. When the internal pressure of the
process chamber varies, the polymer generated during the deposition
process may fall onto a surface of the gate insulating layer,
leading to inferiority in subsequent process.
[0018] Further, when the active layer is formed, a predetermined
time is required to maintain an initial plasma state. At this time,
the active layer deposited has defects such as a dangling bond. As
a result, an interface between the insulating layer and the active
layer becomes inferior, and therefore current-voltage
characteristics of the TFT are lowered.
[0019] Furthermore, an interface (see a portion "A" of FIG. 2)
between the gate insulating layer and the active layer may have
defects due to a lattice mismatch because of the difference of the
atoms of the insulating layer and the active layer when the thin
films are formed, thereby lowering electrical characteristics of
the TFT. In other words, a threshold voltage of the TFT may
increase, and a switching operation may become impossible, and
there may come the problem in stability. For example, charges are
accumulated on the interface between the gate insulating layer 32
and the active layer 34, lowering an ON current.
SUMMARY OF THE INVENTION
[0020] To overcome the problems described above, preferred
embodiments of the present invention provide a method of
manufacturing a thin film transistor minimizing defects generated
when thin films of the thin film transistor are formed.
[0021] It is another object of the invention to provide a method of
forming thin films for the thin film transistor, which can lower
the manufacturing time.
[0022] In order to achieve the above object, the preferred
embodiments of the present invention provide a method of
manufacturing a thin film transistor, including: preparing a
process chamber having a stage; providing a substrate on the stage
of the process chamber; injecting a first mixed gas of NH.sub.3,
N.sub.2 and SiH.sub.4 into the process chamber; forming a silicon
nitride film (SiNx) on the substrate with the first mixed gas by
creating a plasma state in the process chamber; injecting a second
mixed gas of H.sub.2 and SiH.sub.4 into the process chamber while
removing the first mixed gas in the plasma state; forming a pure
amorphous silicon film (a-Si:H) on the silicon nitride film using
the second mixed gas in the plasma state; injecting a third mixed
gas of H.sub.2, SiH.sub.4 and PH.sub.3 into the process chamber
while removing the second mixed gas in the plasma state; and
forming a doped amorphous silicon film (n.sup.+ a-Si:H) on the
silicon nitride film using the third mixed gas in the plasma
state.
[0023] The method further includes forming a gate electrode before
the step of forming the silicon nitride film; and forming source
and drain electrodes on the doped amorphous silicon film. The
method further includes performing a hydrogen plasma treatment on a
surface of the silicon nitride film before the step of forming the
pure amorphous silicon film. The method further includes performing
a hydrogen plasma treatment on a surface of the pure amorphous
silicon film before the step of forming the doped amorphous silicon
film.
[0024] The method of manufacturing the TFT according to the
preferred embodiment of the present invention has the following
advantages. Firstly, since each of the thin films is deposited in
the plasma state, variation of an internal atmosphere of the
process chamber is minimized, whereupon a processing time becomes
shorten. Secondly, since the thin films deposited are hydrogen
plasma-treated, the hydrogen plasma etches detects on the interface
between the thin films, whereupon defects can be prevented.
Thirdly, since each of the thin films is deposited under the same
pressure, an occurrence of a polymer in the process chamber can be
prevented, and interface characteristics of the thin films can be
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which like reference numerals denote like parts, and in
which:
[0026] FIG. 1 is a cross-sectional view illustrating a liquid
crystal panel of a conventional active matrix liquid crystal
display device;
[0027] FIG. 2 is a cross-sectional view illustrating a conventional
back channel etch type thin film transistor;
[0028] FIG. 3 is a graph illustrating a relationship between a
RF-power and thin film depositions;
[0029] FIG. 4 is a graph illustrating a relationship between an
internal pressure variation of a process chamber and thin film
depositions;
[0030] FIG. 5 is a graph illustrating a relationship between a
RF-power and a thin film deposition according to a preferred
embodiment of the present invention; and
[0031] FIG. 6 is a graph illustrating a variation of an internal
pressure of the process chamber during deposition processes of the
thin films.
DETAILED DESCRIPTION OF PREFFERED EMBODIMENTS
[0032] Reference will now be made in detail to a preferred
embodiment of the present invention, example of which is
illustrated in the accompanying drawings.
[0033] FIG. 5 is a graph illustrating a relationship between a
RF-power and thin film depositions according to a preferred
embodiment of the present invention. As shown in FIG. 5, except for
a process of injecting a first mixed gas of NH.sub.3, N.sub.2 and
SiH.sub.4 into the process chamber in order to deposit a gate
insulating layer, the power maintains ON state through the whole
deposition processes.
[0034] First, the first mixed gas stabilized under a predetermined
pressure is maintained in a first plasma state "A.sub.0" by a
predetermined RF power intensity, and then the gate insulating
layer is deposited. At this point, a deposition temperature of the
thin films is one of the most important parameters to control a
surface reaction of a semiconductor layer during a deposition
process. In other words, since precursors actively react on
hydrogen at a temperature of about 300.degree. C. and also the
number of the silicon dangling bond is decreased at that
temperature, to control a deposition temperature is very
important.
[0035] Subsequently, after depositing the gate insulating layer
using the first mixed gas, the first mixed gas is removed while the
plasma state is maintained (i.e., without OFF of a power). At the
same time, a H.sub.2 gas is injected into the process chamber. That
is, in a second plasma state "A.sub.1", a remove of the first mixed
gas (NH.sub.3+N.sub.2+SiH.su- b.4) and an injection of the H.sub.2
gas are simultaneously carried out. At this time, there is little
variation of the pressure, but the pressure may vary in a range of
less than 200 mTorr.
[0036] At this point, in the second plasma state "A.sub.1", a
hydrogen (H.sub.2) plasma treatment is performed by adjusting radio
frequency energy within the chamber during a predetermined time
period. The hydrogen plasma terminates the dangling bond that may
occur on a surface of the gate insulating layer. In other words,
the hydrogen plasma functions to etch defects that exist on the
surface of the gate insulating layer.
[0037] Subsequently, in the hydrogen plasma state "A.sub.2", a
SiH.sub.4 gas is injected into the process chamber to create a
second mixed gas, so that an active layer is formed using the
second mixed gas (H.sub.2+SiH.sub.4).
[0038] After forming the active layer, the SiH.sub.4 gas is removed
from the second mixed gas, and the active layer is hydrogen
plasma-treated in the third plasma state "A.sub.2".
[0039] Next, the SiH.sub.4 gas and a PH.sub.3 gas are added to the
H.sub.2 gas to create a third mixed gas
(SiH.sub.4+PH.sub.3+H.sub.2), and an ohmic contact layer (n.sup.+
a-Si:H) is formed on the active layer using the third mixed
gas.
[0040] As described above, a method of forming the thin films
according to the preferred embodiment of the present invention does
not turn off a power while depositing the gate insulating layer,
the active layer and the ohmic contact layer, whereby defects due
to a lattice mismatch can be prevented. As a result, since defects
on the interface of each of the thin films are decreased, charges
that are trapped due to defects are decreased, and therefore
trapped charges do not prevent a flow of the charges. This leads to
high electrical characteristics of the TFT.
[0041] FIG. 6 is a graph illustrating a variation of an internal
pressure of the process chamber during a deposition process of the
thin films. As shown in FIG. 6, there is little variation of the
internal pressure during a deposition process of the thin films
(the gate insulating layer, the active layer and the ohmic contact
layer). Therefore, defects that may occur on a surface of the thin
films due to a variation of the internal pressure can be
prevented.
[0042] A method of forming other components such as a gate
electrode, a source electrode and a drain electrode shown in FIG. 2
is same as the conventional art and thus its explanation is
omitted.
[0043] As described herein before, the method of manufacturing the
TFT according to the preferred embodiment of the present invention
has the following advantages. Firstly, since each of the thin films
is deposited in the plasma state, variation of an internal
atmosphere of the process chamber is minimized, whereupon a
processing time becomes shorten. Secondly, since the thin films
deposited are hydrogen plasma-treated, the hydrogen plasma etches
detects on the interface between the thin films, whereupon defects
can be prevented. Thirdly, since each of the thin films is
deposited under the same or similar pressure, an occurrence of a
polymer in the process chamber can be prevented, and interface
characteristics of the thin films can be improved.
[0044] While the invention has been particularly shown and
described with reference to a preferred embodiment thereof, it will
be understood by those skilled in the art that the foregoing and
other changes in form and details may be made therein without
departing from the spirit and scope of the invention.
* * * * *