U.S. patent application number 12/440304 was filed with the patent office on 2010-07-22 for apparatus and method of depositing films using bias and charging behavior of nanoparticles formed during chemical vapor deposition.
This patent application is currently assigned to Seoul National University Industry Foundation. Invention is credited to Yung-Bin Chung, Nong-Moon Hwang, Chan-Soo Kim, Jae-Ik Lee, Woong-Kyu Youn.
Application Number | 20100183818 12/440304 |
Document ID | / |
Family ID | 39157429 |
Filed Date | 2010-07-22 |
United States Patent
Application |
20100183818 |
Kind Code |
A1 |
Hwang; Nong-Moon ; et
al. |
July 22, 2010 |
APPARATUS AND METHOD OF DEPOSITING FILMS USING BIAS AND CHARGING
BEHAVIOR OF NANOPARTICLES FORMED DURING CHEMICAL VAPOR
DEPOSITION
Abstract
Provided are an apparatus and a method of depositing films
capable of controlling deposition rate and film properties using
the charging behavior of nanoparticles formed in gas phase. The
apparatus includes a chamber in which a substrate is loaded, a gas
supply system configured to introduce a reaction gas into the
chamber, a filament configured to emit heat for dissociating the
introduced reaction gas, a power supply configured to apply a
constant alternate current or direct current voltage, and a bias
supply unit configured to apply a bias to at least one of a top, a
side and a bottom of the substrate using a voltage applied from the
power supply while a film is deposited on the substrate from the
dissociated reaction gas, the bias supply unit being separated from
the substrate.
Inventors: |
Hwang; Nong-Moon; (Seoul,
KR) ; Kim; Chan-Soo; (Seoul, KR) ; Lee;
Jae-Ik; (Seoul, KR) ; Chung; Yung-Bin; (Seoul,
KR) ; Youn; Woong-Kyu; (Seoul, KR) |
Correspondence
Address: |
Jae Y. Park
Kile, Goekjian, Reed & McManus, PLLC, 1200 New Hampshire Ave. NW, Suite
570
Washington
DC
20036
US
|
Assignee: |
Seoul National University Industry
Foundation
|
Family ID: |
39157429 |
Appl. No.: |
12/440304 |
Filed: |
September 6, 2007 |
PCT Filed: |
September 6, 2007 |
PCT NO: |
PCT/KR2007/004306 |
371 Date: |
March 6, 2009 |
Current U.S.
Class: |
427/475 |
Current CPC
Class: |
C23C 16/44 20130101;
C23C 16/4401 20130101; H01L 21/0262 20130101; H01L 21/02573
20130101; H01L 21/02532 20130101; H01L 21/0259 20130101 |
Class at
Publication: |
427/475 |
International
Class: |
C23C 4/10 20060101
C23C004/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2006 |
KR |
1020060085819 |
May 10, 2007 |
KR |
1020070045402 |
Claims
1-20. (canceled)
21. A method of depositing films, the method comprising:
controlling a generation behavior associated with a charged
behavior including a size, a number concentration, a charge amount
and a charge ratio of a charged nanoparticle formed in gas phase by
adjusting a process parameter including a reaction temperature, an
amount of a reaction gas and a reaction pressure in a chemical
vapor deposition (CVD) process; and controlling a deposition
behavior of the charged nanoparticle using variations in an
electric field intensity and a polarity through a bias unit.
22. An apparatus of depositing films, the apparatus comprising: a
chamber in which a substrate is loaded and a pressure is maintained
at an atmospheric pressure, a low pressure or a high pressure; a
gas supply system configured to introduce a reaction gas into the
chamber; a heating element configured to emit heat for dissociating
the introduced reaction gas; and a bias supply device configured to
apply an electric field to the substrate, wherein the bias supply
device comprises: a first plate disposed over the substrate; a
second plate disposed under the substrate, and facing the first
plate: a power supply configured to apply a constant AC or DC
voltage to one of the first and second plates; and a ground unit
configured to ground the other of the first and second plates.
23. An apparatus of depositing films, the apparatus comprising: a
chamber in which a substrate is loaded and a pressure is maintained
at an atmospheric pressure, a low pressure or a high pressure; a
gas supply system configured to introduce a reaction gas into the
chamber; a heating element configured to emit heat for dissociating
the introduced reaction gas; and a bias supply device configured to
apply an electric field to the substrate, wherein the substrate is
disposed on a surface of the second plate opposite to the first
plate, the first plate being connected to the ground unit, and the
second plate being connected to the power supply.
24. An apparatus of depositing films, the apparatus comprising: a
chamber in which a substrate is loaded and a pressure is maintained
at an atmospheric pressure, a low pressure or a high pressure; a
gas supply system configured to introduce a reaction gas into the
chamber; a heating element configured to emit heat for dissociating
the introduced reaction gas; and a bias supply device configured to
apply an electric field to the substrate, wherein the bias supply
device draws a charged nanoparticles, which is nucleated and grown
from the dissociated reaction gas, toward the substrate.
25. The apparatus of claim 4, wherein the gas supply system
additionally introduces a carrier gas facilitating the movement of
the charged nanoparticle into the chamber, the gas supply system
comprising a gas flowmeter configured to control a movement rate of
the charged nanoparticle by controlling a flow rate of the carrier
gas.
26. A method of depositing films, the method comprising: loading a
substrate in the chamber and introducing a reaction gas;
dissociating the reaction gas; triggering nucleation in the
dissociated reaction gas; forming a charged nanoparticle through
growth of a nanoparticle generated from the nucleation; and
applying a bias to the substrate to deposit a film by drawing the
charged nanoparticle toward the substrate.
27. The method of claim 6, wherein the depositing of the film is
performed using a hot-filament or hot-wire chemical vapor
deposition (HFCVD or HWCVD) apparatus, a plasma CVD apparatus or an
atmospheric pressure CVD (APCVD) apparatus.
28. The method of claim 6, wherein the charged nanoparticle is
formed in gas phase by adjusting a dissociation degree of the
reaction gas, and an electrical polarity ratio between positively
and negatively charged nanoparticles is controlled.
29. The method of claim 6, wherein the substrate is formed of a
conductive material, and a deposition rate increases by applying a
bias of which a polarity is opposite to a polarity of the charged
nanoparticle dominantly existing in the nanoparticles formed in gas
phase.
30. The method of claim 6, wherein the substrate is formed of one
of a nonconductive material and a plastic, and a deposition rate
increases by applying a bias, of which a polarity is the same as a
polarity of the charged nanoparticle dominantly existing in the
nanoparticles formed in gas phase, to a periphery of the
substrate.
31. The method of claim 6, wherein the substrate is formed of one
of a nonconductive material and a plastic, and a degree of
crystallinity of a film increases by increasing an electrical
polarity ration of the nanoparticles.
32. The method of claim 6, wherein a mixed gas of silane and
hydrogen is used as the reaction gas, and at least one of a
fraction and a size of the nanoparticle charged in gas phase
changes by increasing at least one selected from a dissociation
temperature of the reaction gas, a fraction of the silane in the
mixed gas and a pressure of the mixed gas.
33. The method of claim 6, wherein the bias is applied to a top of
the substrate to thereby change an electrical polarity ratio of the
nanoparticle to be deposited, by changing the charge amount of the
nanoparticle before the nanoparticles are deposited on the
substrate.
34. The method of claim 13, wherein a film deposition is divided
into a nucleation and a growth, and an electrical polarity ratio of
nanoparticles to be deposited changes by changing at least one of a
fraction and a size of the nanoparticle charged in gas phase in
each of the nucleation and the growth and changing the charge
amount of the nanoparticles before the nanoparticles are deposited
on the substrate.
35. The method of claim 6, wherein one of a silicon film, a carbon
nanotube and a nanowire is deposited using the method, and the
silicon film comprises one of a single crystalline silicon film, an
amorphous silicon film and a poly crystalline silicon film.
36. The method of claim 6, wherein a voltage for applying the bias
is in the range of approximately +1,000 V to approximately -1,000
V, and a DC or an AC having a frequency ranging from approximately
0.01 Hz to approximately 10 kHz is applied.
37. The method of claim 6, wherein the bias is applied such that
its polarity is periodically or arbitrarily alternated.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method of depositing
films using the charging behavior of nanoparticles formed during
chemical vapor deposition, and more particularly, to an apparatus
and a method of depositing films capable of increasing deposition
rate and controlling film properties using the charging behavior of
nanoparticles formed in gas phase.
BACKGROUND ART
[0002] Film deposition using chemical vapor deposition (CVD) has a
limitation in that it is difficult to effectively satisfy demands
for increasing deposition rate and improving film properties at the
same time in spite of the increase in energy applied to a reaction
material.
[0003] It was difficult to simultaneously achieve the increase of
film deposition rate and the improvement of film properties by
varying reaction conditions in CVD process, causing difficulties in
satisfying both price and quality. The reason is that it was short
of a definitive understanding of a film deposition mechanism by
CVD. For instance, it was insufficient to understand the reason why
film deposition rates and properties of deposited films are
different according to kinds of substrates, that is to say,
according to an electrical conductive substrate such as a stainless
substrate or an electrical insulation substrate such as a glass
substrate and a silicon wafer, even under the same process
conditions.
[0004] Of many theories for facilitating to understand the
deposition mechanism of CVD process, it is possible to explain the
deposition behavior of films by understanding nanoparticles formed
in gas phase as deposition units and their characteristics, which
differs from a typical theory that deposition units are thought to
be either an atom or a molecule.
[0005] In particular, if characteristics of the nanoparticles can
change by a new method of applying a bias during deposition of
generated nanoparticles, the new method is capable of controlling
the film properties as well as the film deposition rate.
[0006] Accordingly, it is necessary to develop a new technology of
forming films, which can increase a film deposition rate and
control film properties by controlling the deposition behavior of
nanoparticles generated in CVD and the generation behavior using
characteristics of the nanoparticles.
DISCLOSURE
Technical Problem
[0007] To satisfy both demands for increase in film deposition rate
and improvement in film properties at a time, there is required a
method capable of separating a generation step of nanoparticles in
gas phase and a deposition step of the generated nanoparticles and
separately controlling each step. In addition, there is also
required an apparatus of depositing films, which can be used in
implementing this method.
Technical Solution
[0008] A step-by-step control technology for film deposition is
realizable from the understanding about characteristics of
nanoparticles formed in gas phase. It has been regarded that a
conventional film deposition was performed with a deposition
material in units of an atom formed in gas phase. Therefore, a
technology where a generation step of deposition units for a
deposition film and a deposition step of the deposition units can
be separately controlled has not been considered yet.
[0009] Accordingly, the present disclosure suggests a technology
capable of controlling film deposition by separating a generation
step of nanoparticles, i.e., deposition unit of the films, and a
deposition step of the generated deposition units based on a new
paradigm for the deposition units.
[0010] The present disclosure provides a technology of forming
films by respectively controlling a generation step of
nanoparticles and a deposition step of the generated nanoparticles
using the charged behavior of nanoparticles formed in gas phase,
and thus provides a method and an apparatus of depositing films,
which can improve deposition rate and control film properties.
[0011] The present disclosure also provides a technology of
controlling the charged behavior of nanoparticles, which are
deposition units of films, formed in gas phase.
[0012] The present disclosure also provides a technology of
controlling the deposition behavior by application of an electrical
bias affecting the charged behavior of nanoparticles, deposition
units, formed in gas phase.
[0013] The present disclosure also provides a method capable of
improving deposition rate and controlling film properties.
[0014] According to an exemplary embodiment, an apparatus of
depositing films, includes: a chamber in which a substrate is
loaded; a gas supply system configured to introduce a reaction gas
into the chamber; a filament configured to emit heat for
dissociating the introduced reaction gas; a power supply configured
to apply a constant alternate current (AC) or direct current (DC)
voltage; and a bias supply unit configured to apply a bias to at
least one of a top, a side and a bottom of the substrate using a
voltage applied from the power supply while a film is deposited on
the substrate from the dissociated reaction gas, the bias supply
unit being separated from the substrate.
[0015] According to another exemplary embodiment, an apparatus of
depositing films, includes: a chamber in which a substrate is
loaded and a pressure is maintained at an atmospheric pressure, a
low pressure or a high pressure; a gas supply system configured to
introduce a reaction gas into the chamber; a heating element
configured to emit heat for dissociating the introduced reaction
gas; and a bias supply device configured to apply an electric field
to the substrate.
[0016] According to yet another exemplary embodiment, a method of
depositing films, includes: loading a substrate in the chamber and
introducing a reaction gas; dissociating the reaction gas;
triggering nucleation in the dissociated reaction gas; forming a
charged nanoparticle through growth of a nanoparticle generated
from the nucleation; and applying a bias to the substrate to
deposit a film by drawing the charged nanoparticle toward the
substrate.
[0017] The method of depositing films may be performed using a film
deposition apparatus according to exemplary embodiments, and
alternatively the method may be performed using another film
deposition apparatus modified from a typical chemical vapor
deposition (CVD) apparatus, a hot-filament chemical vapor
deposition (HFCVD) apparatus, a plasma CVD apparatus, a
metal-organic chemical vapor deposition (MOCVD) apparatus, or other
apparatuses of forming films where charged nanoparticles are
generated.
[0018] The charged nanoparticle may be formed in gas phase by
adjusting a dissociation degree of the reaction gas, and an
electrical polarity ratio between positively and negatively charged
nanoparticles may be controlled.
[0019] A mixed gas of silane and hydrogen may be used as the
reaction gas, and at least one of a fraction and a size of the
nanoparticle charged in gas phase may change by increasing at least
one selected from a dissociation temperature of the reaction gas, a
fraction of the silane in the mixed gas and a pressure of the mixed
gas.
[0020] The bias may be applied to a top of the substrate to thereby
change an electrical polarity ratio of the nanoparticle to be
deposited, by changing the charge amount of the nanoparticle before
the nanoparticles are deposited on the substrate.
[0021] A film deposition may be divided into a nucleation and a
growth, and an electrical polarity ratio of nanoparticles to be
deposited may change by changing at least one of a fraction and a
size of the nanoparticle charged in gas phase in each of the
nucleation and the growth and changing the charge amount of the
nanoparticles before the nanoparticles are deposited on the
substrate.
[0022] There is provided a film deposition technology associated
with the charged behavior of nanoparticles, i.e., deposition units
of films, formed in gas phase, or to the control of the charged
behavior.
ADVANTAGEOUS EFFECTS
[0023] According to exemplary embodiments, the generation behavior
of nanoparticles, which are charged neutrally, negatively or
positively by reaction gas, can be controlled by varying reaction
conditions of the reaction gas. At the same time, the deposition
behavior can also be separately controlled by applying a bias to a
substrate in consideration of the charged behavior of the charged
nanoparticles, independently of the generation behavior.
Accordingly, it is possible to control film deposition rate and
improve structural properties of films. That is, it is possible to
control properties of a film texture as well as a film deposition
rate by controlling nanoparticles to selectively participate in the
film deposition according to the charged behavior of the
nanoparticles, through the control of electrostatic properties of
deposition sources charged in gas phase, the control of attractive
or repulsive force between the charged deposition sources according
to a bias applied to a periphery of the substrate, and the control
of deposition behavior according to a difference in electrical
conductivity of a substrate.
[0024] In addition, it is possible to control the deposition
behavior of thin films and thick films upon an electrically
insulating substrate such as ceramic substrate through which an
electrical bias does not pass and a plastic substrate requiring a
low reaction temperature as well as an electrically conductive
substrate, by separating a bias supply unit from the substrate and
applying the electrical bias to the substrate from a detached
position. As such, the deposition behavior of thin films can be
effectively controlled by virtue of the improvement of the bias
application.
[0025] Furthermore, the control of the deposition behavior can make
it possible to deposit films having uniform texture, thus
contributing to reduction in haze of the thin films, reduction in
formation of voids, improvement in surface roughness, and
improvement in degree of crystallinity.
[0026] Particularly, contrary to a related art film deposition
process where film deposition is performed without a secondary
process upon deposition units formed in gas phase, exemplary
embodiments can provide such an advantageous merit that a variety
of materials can be used as a substrate by selectively depositing
some deposition units, i.e., nanoparticles, of which charged
behavior differs than that of other deposition units. Further,
according to exemplary embodiment, it is possible to control film
properties and film deposition rate depending on the charged
behavior of various materials generated in gas phase.
DESCRIPTION OF DRAWINGS
[0027] Exemplary embodiments can be understood in more detail from
the following description taken in conjunction with the
accompanying drawings, in which:
[0028] FIG. 1 is a schematic view illustrating an apparatus of
measuring charged nanoparticles formed in gas phase and controlling
the generation of the nanoparticles, which is available in
implementing embodiments;
[0029] FIG. 2 is a schematic view illustrating an apparatus of
depositing films according to an exemplary embodiment;
[0030] FIGS. 3A and 3B are views of a bias supply unit configured
to apply an electrical bias to a substrate during film deposition
according to the exemplary embodiment;
[0031] FIG. 4 is a schematic view illustrating the case that the
bias is applied to a top of the substrate during the deposition
process according to the exemplary embodiment;
[0032] FIG. 5 is a flowchart illustrating a method of depositing
films according to exemplary embodiments;
[0033] FIGS. 6(a) through 6(c) are schematic views illustrating
deposition behaviors caused by interactions between a polarity of a
bias applied to the substrate and polarities of charged
nanoparticles in the method of depositing films according to the
exemplary embodiments;
[0034] FIG. 7 is a schematic view of an apparatus of depositing
films according to another exemplary embodiment;
[0035] FIGS. 8(a) through 8(c) are photographs illustrating a bias
supply device of experimental examples, which is included in the
deposition apparatus of FIG. 7;
[0036] FIG. 9 is a schematic view illustrating a bias supply device
having an alternative structure included in the deposition
apparatus of FIG. 7;
[0037] FIG. 10 is a schematic view of an apparatus of depositing
films according to still another exemplary embodiment;
[0038] FIGS. 11A and 11B are graphs illustrating number
concentration of charged nanoparticles versus particle size, which
are measured under various reaction conditions;
[0039] FIG. 12 is a graph illustrating deposition behaviors
according to a concentration of reaction gas and a bias applied to
a bottom of a substrate in a method of depositing films using the
deposition apparatus of FIG. 2, where the substrate is an
electrical conductor;
[0040] FIG. 13 is a graph illustrating deposition behaviors
according to a concentration of reaction gas and a bias applied to
a bottom of a substrate in a method of depositing films using the
deposition apparatus of FIG. 2, where the substrate is an
electrical insulator;
[0041] FIG. 14 is a graph illustrating film properties obtained by
the different deposition behaviors of the samples in FIG. 13, which
are measured by Raman spectroscopy;
[0042] FIG. 15 is a graph illustrating deposition behaviors
according to a concentration of reaction gas and a bias applied to
a top of a substrate in a method of depositing films using the
deposition apparatus of FIG. 2, where the substrate is an
electrical insulator;
[0043] FIGS. 16A through 16C are schematic views illustrating a
method of applying a bias in experimental examples of a method of
depositing films using the deposition apparatus of FIG. 7;
[0044] FIG. 17 illustrates field emission-scanning electron
microscope (FE-SEM) images comparing thicknesses of the
experimental examples of FIGS. 16A through 16C with that of a
comparative example in the case where the substrate is an
electrical insulator;
[0045] FIG. 18 is a graph illustrating a deposition thickness and a
deposition rate per second for each of the samples of FIG. 17 in
the case where the substrate is an electrical insulator; and
[0046] FIG. 19 is a graph illustrating film properties obtained by
the comparative example and the experimental examples of FIGS. 16A
through 16C, which are measured by Raman spectroscopy.
MODE FOR INVENTION
[0047] Hereinafter, specific embodiments will be described in
detail with reference to the accompanying drawings. The invention
may, however, be embodied in many different forms and should not be
construed as being limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
be thorough and complete, and will fully convey the concept of the
invention to those skilled in the art. In the drawings, shapes of
elements are exaggerated for emphasizing definite explanation. Like
reference numerals in the drawings denote like elements, and thus
their description will be omitted. FIG. 1 illustrates an example of
an apparatus of measuring nanoparticles, which is adapted to
measure charged nanoparticles formed in gas phase and control the
generation of the nanoparticles under reaction conditions of
embodiments, which is available in implementing embodiments.
[0048] Referring to FIG. 1, an apparatus 1 of measuring
nanoparticles includes a gas supply system 4, an atmospheric
pressure chemical vapor deposition (APCVD) chamber 5, a heating
element 6, a differential mobility analyzer (DMA) 8 and a Faraday
cup electrometer (FCE) 9.
[0049] The chamber 5 of FIG. 1 is a horizontal furnace type
chamber. Reaction gas flows into the chamber 5 and thermally
decomposed. A pressure inside the chamber is maintained at an
atmospheric pressure. The chamber 5 is an insulator made of quartz
and may have a tubular shape. Examples of a material that used for
the heating element 6 may include graphite, silicon carbide (SiC),
etc. The heating element 6 may have the shape of a bar, a plate, a
coil, and so forth, and the heating element 6 may be provided
singularly or in plurality.
[0050] The gas supply system 4 for introducing source gas such as
reaction gas and carrier gas into the chamber 5 includes a gas pipe
2 and a flow controller 3.
[0051] Referring to FIG. 1, the DMA 8 classifies charged particles
according to electrical mobility when particles nucleated in gas
phase after thermally decomposed in the chamber 5 are charged while
they colliding against chamber walls, i.e., surface-ionized. The
DMA 8 cannot classify uncharged particles so that it cannot
determine a size and a concentration of the uncharged particles.
The charged nanoparticles existing in gas phase under an
atmospheric pressure or a low pressure inside the chamber 5 are
measured from the atmospheric pressure DMA and the low pressure
DMA. The classified charged particles move to the FCE 9 so that the
charged particles corresponding a voltage intentionally applied
from the outside are measured as a current. The applied voltage
determines a size of the charged nanoparticle, and the charged
current value is converted into a concentration of the charged
nanoparticle.
[0052] As described above, the apparatus 1 of measuring
nanoparticles can control the amount of the neutrally, negatively
or positively charged nanoparticles which are formed in gas phase
during film deposition by changing reaction conditions. Therefore,
the apparatus 1 of measuring nanoparticles is available in
controlling the generation of nanoparticles in gas phase suitable
for deposition purpose according to kinds of deposition material
and substrate.
Embodiment 1
[0053] FIG. 2 illustrates an apparatus of depositing films
according to an exemplary embodiment.
[0054] Referring to FIG. 2, a hot-filament or hot-wire CVD (HFCVD
or HWCVD) apparatus 10, an apparatus of depositing films, includes
a gas supply system 20, a filament 30, a substrate 40 on which a
thin film is formed, a cooler 50 configured to cool the substrate
40, a substrate holder 60, a power supply 70, and a bias supply
unit 80. The gas supply system 20 is configured with a gas pipe and
a gas flowmeter, and supplies source gas such as reaction gas into
a chamber 15 of the HFCVD apparatus 10. The filament 30 is
configured to emit heat so as to dissociate the reaction gas
introduced into the chamber 15. The substrate holder 60 is capable
of adjusting a distance between the substrate 40 and the filament
30 using, for example, an adjustment screw. The power supply 70 is
capable of applying a constant alternative current (AC) voltage or
a constant direct current (DC) voltage. The bias supply unit 80 is
configured to apply a bias to a top, a side or a bottom of the
substrate 40. The bias supply unit 80 is separated from the
substrate 40, and applies an electrical bias to a periphery of the
substrate 40 during deposition process. For instance, FIG. 2
illustrates the bias supply unit 80 designed to apply the bias to
the bottom of the substrate 40.
[0055] By using the HFCVD apparatus 10, it is possible to deposit
one of a silicon film, a carbon nanotube and a nanowire in the
method of depositing films according to the exemplary embodiment.
Particularly, in the case of the silicon film, it is possible to
deposit one of a single crystalline silicon film, an amorphous
silicon film and a poly crystalline silicon film through epitaxial
growth or another kind of growth mechanism.
[0056] In the HFCVD apparatus 10, a graphite heating element or a
metal heating element is used as the filament 30 for dissociating
the reaction gas at a high temperature. Specifically, the filament
30 may be formed of tungsten (W), rhenium (Re), molybdenum (Mo),
rhodium (Rh), platinum (Pt), tantalum (Ta), iridium (Ir) or a
combination thereof. In addition, the filament may be realized with
other heating elements of various materials. The filament 30 may
have the shape of a single wire, a twisted wire or other shapes.
The filament 30 may be provided singularly or in plurality.
[0057] The introduced reaction gas, which is dissociated by the
high temperature filament 30, includes silane compound expressed as
Si.sub.nH.sub.2n+2 (n is a positive integer) as major gas in the
case of depositing a silicon film. Specifically, the silane
compound for the reaction gas may include monosilane, disilane,
trisilane, tetrasilane, etc. For easy handling, the silane compound
for use in the reaction gas may be monosilane, disilane, trisilane
or a combination thereof. However, the reaction gas is not limited
the above-listed one. Thus, the reaction gas may include
fluorosilane, chlorosilane, organic silane, germane, germanium
fluoride, hydrocarbon gas, or other hydrocarbon compounds. In
detail, examples of the fluorosilane expressed as
SiH.sub.2n+2-mF.sub.m (n is a natural number and m is an integer of
0 or more, where m<2n+2) may be SiH.sub.3Cl, SiH.sub.2Cl.sub.2,
SiHCl.sub.3, SiCl.sub.4, Si.sub.2Cl.sub.6, Si.sub.2HCl.sub.5 or
Si.sub.3Cl.sub.8. Examples of the chlorosilane expressed
Si.sub.nH.sub.2n+2-mCl.sub.m (n is a natural number and m is an
integer of 0 or more, where m<2n+2) may be SiH.sub.3Cl,
SiH.sub.2Cl.sub.2 or SiHCl.sub.3, SiCl.sub.4, Si.sub.2Cl.sub.6,
Si.sub.2HCl.sub.5, or Si.sub.3Cl.sub.8. Examples of the organic
silane expressed as Si.sub.nR.sub.2n+2-mH.sub.m may be
Si(CH.sub.3)H.sub.3, Si(CH.sub.3).sub.2H.sub.2 or
Si(CH.sub.3).sub.3H. Examples of the germane expressed as
Ge.sub.nH.sub.2n+2 may be GeH.sub.4 or Ge.sub.2H.sub.6 in the case
of deposing a germanium film. Examples of the germanium fluoride
expressed as Ge.sub.nH.sub.2n+2-mF.sub.m may be GeF.sub.4 and the
like. Examples of the hydrocarbon gas may be methane (CH.sub.4),
ethane (C.sub.2H.sub.6), propane (C.sub.3H.sub.8), ethylene
(C.sub.2H.sub.4), acetylene (C.sub.2H.sub.2), and so forth.
[0058] Although such reaction gas may be used by itself, silane
compound gas may be used as being diluted by adding supporting gas.
Herein, the supporting gas may include: a reactive gas such as
hydrogen, fluorine and chlorine gas; a gas containing a Group Iii
element as a dopant, for example, diborane (B.sub.2H.sub.6) gas and
trimethylboron (B(CH.sub.3).sub.3) gas, or a gas containing a Group
V element as a dopant, for example, phosphine (PH.sub.3) gas; and
an inert gas such as helium, argon and neon; nitrogen gas. A
dilution ratio of the silane compound to the added gas may be in
the range of approximately 0.1% to approximately 100% by volume
percent. Taking into account of an actual semiconductor
film-forming rate, the dilution ratio may be approximately 1% or
more.
[0059] Though a flow rate of the reaction gas may be in the range
of approximately 1 sccm to approximately 1,000 sccm, and an
internal pressure of the chamber 15 may be in the range of
approximately 5 mTorr to approximately 760 Torr, the flow rate and
the internal pressure of the chamber may be appropriately selected
depending on the film-forming rate.
[0060] In performing a method of depositing films using the HFCVD
apparatus 10 according to the exemplary embodiment, the bias supply
unit 80 may be formed of a conductive material, particularly metal,
of which electrical conductivity may be in the range of
approximately 1,000 to approximately 10.sup.7 (.OMEGA.cm).sup.-1.
The substrate 40 and the bias supply unit 80 may have an area
ranging from approximately 1 to approximately 120,000 cm.sup.2. The
bias supply unit 80 may have a larger size than the substrate 40,
but may change its size depending on deposition purposes.
[0061] The bias supply unit 80 may be shaped as a plate structure
illustrated in FIG. 3A or a mesh structure illustrated in FIG. 3B.
Alternatively, the bias supply unit 80 may have a tubular shape. As
illustrated in FIG. 2, the bias supply unit 80 may be designed to
have the shape of the plate structure of FIG. 3A for applying the
bias to the bottom of the substrate 40 on which film deposition is
performed. Alternatively, the bias may be applied to the top of the
substrate 40, as illustrated in FIG. 4. In this case, the bias
supply unit 80 is shaped as the mesh structure of FIG. 3B, and it
is positioned on the top of the substrate 40. The mesh type bias
supply unit 80 may change its aperture size, shape and installation
position depending on deposition purposes. As such, in the
apparatus and method of depositing films according to the exemplary
embodiment, the bias supply unit 80 applying an electrical bias is
separated from the substrate 40, and thus it may positioned over or
under the substrate 40. Furthermore, the bias may be applied to the
side of the substrate 40 according to circumstances. During the
deposition, a polarity of the bias may not be changed, or the
polarity of the bias may be alternated periodically or arbitrarily.
The method of depositing films according to the embodiment using
the HFCVD apparatus 10 will be described with reference to FIGS. 5
and 6.
[0062] First, in operation S1, the substrate 40 is loaded into the
chamber 15, and reaction gas is introduced.
[0063] A temperature of the substrate 40 may be in the range of
approximately 293 to 1,200 K. A temperature of the substrate may be
in the range of approximately 293 to 773 K in consideration of the
heat resistance of the substrate 40 and film properties.
[0064] The substrate 40 may include one of a conductive material, a
nonconductive material and a plastic. A transparent substrate may
include a transparent polymer film substrate as well as a typical
glass substrate. Herein, examples of the transparent polymer film
substrate may be polyethylene terephthalate (PET), polycarbonate,
polyimide (PI) or polyethylenenaphthalate. Examples of the typical
glass substrate may be blue plate glass, borosilicate glass, and
quartz glass. In addition to a substrate of metal having electrical
conductivity and a ceramic substrate, a polymer resin such as cloth
and texture are also available. This is ascribed to the fact that
it is possible to control the deposition behavior of films upon an
electrically insulating substrate such as ceramic substrate through
which an electrical bias does not pass and a plastic substrate
requiring a low reaction temperature as well as an electrically
conductive substrate, by separating the bias supply unit 80 from
the substrate 40 and applying the electrical bias to the substrate
40 from a detached position.
[0065] Specifically, the substrate 40 may also be provided by
forming a metal film such as stainless steel, molybdenum, titanium,
silver and aluminum, upon a surface of a metal substrate such as
stainless steel, molybdenum, titanium, silver and aluminum, a
surface of a glass substrate such as borosilicate glass, blue plate
glass and quartz glass, or a surface of a polymer film. A substrate
obtained by forming a transparent electrode on the glass substrate,
the polymer film and the metal substrate may also be available.
Here, the transparent electrode may include, for example, a
transparent metal or a metal oxide such as tin oxide, indium oxide
and zinc oxide.
[0066] As for a thickness of the substrate 40, a glass substrate
may have a thickness ranging from approximately 0.5 to
approximately 10 mm, a polymer film may have a thickness ranging
from approximately 10 to approximately 500 .mu.m, and a metal film
or a substrate of metal element may have a thickness ranging from
approximately 50 to approximately 50,000 .ANG.. Moreover, when an
amorphous semiconductor thin film is deposited on the substrate 40,
the film may be formed to a thickness ranging from approximately 10
.ANG. to approximately 10 .mu.m (i.e., 100,000 .ANG.), a
film-forming rate may be in the range of approximately 0.1 to
approximately 1,000 .ANG./sec, desirably in the range of
approximately 5 to approximately 30 .ANG./sec.
[0067] A mixed gas of silane and helium may be used as the reaction
gas for silicon film deposition. Nitrogen gas may be added to the
mixed gas of silane and helium and the mixed gas with nitrogen gas
added is then introduced into the chamber 15.
[0068] Thereafter, in operation S2, the reaction gas is dissociated
using the filament 30. The exemplary embodiments described herein
are based on the present inventors' new theory for the film
deposition. So far, it has been believed that film growth was
mainly carried out in units of either an atom or a molecule, and
most of developments for thin film processes are advanced on the
basis of such a belief. Therefore, a condition of causing a
gas-phase nucleation has become a limitation in increasing a
deposition rate. To over come such a limitation, it is necessary to
establish appropriate conditions where thin films with good quality
can grow even under the condition that the nucleation occurs in gas
phase. To this end, it has been announced that it is possible to
deposit the thin film with good quality at a high deposition rate
by making charged clusters, e.g., charged nuclei or nanoparticles
(Nong-Moon Hwang, Doh-Yeon Kim, J. Appl. Phys, 79 234. 2003).
[0069] Meanwhile, a technique, entitled "Ionized Cluster Beam
Deposition (IOCVD)" where charged clusters are intentionally
generated, they are accelerated, and they are thus deposited on a
deposition target has been developed by Yamada, Tagaki et al. In
this technique, however, an adiabatic expansion should be performed
to form the clusters and an electron gun should be used for
ionizing the clusters. Therefore, a deposition apparatus for
realizing this technique must have a complicated structure and
further an ionization efficiency of the generated cluster is too
low, that is, 30% or lower. In addition, since the clusters were
accelerated and deposited according to this technique, a high
vacuum level lower than 0.000001 Torr should be maintained.
[0070] On the contrary, according to the exemplary embodiment, it
is possible to spontaneously generate charged deposition units,
i.e., charged nanoparticles or nanoclusters, by dissociating the
reaction gas simply using the filament 30, without the use of an
additional apparatus for generating the nanoparticles or the
nanoclusters.
[0071] Afterwards, in operation S3, nucleation occurs in a state of
the dissociated reaction gas. Subsequently, in operation S4, the
nanoparticles generated during the nucleation are charged due to
different work function from the inside of the chamber 115 while
the nanoparticles are growing.
[0072] In the exemplary embodiments, characteristics of positive or
negative charges can also be controlled by adjusting a dissociation
degree of the reaction gas. That is, it is possible to control the
charge amount and the polarity ratio of the charged nanoparticles
according to circumstances. As a relative ratio between the
positively and negatively charged nanoparticles changes, a
correlation with the charged behavior of the charged nanoparticles
affected by the relative ratio can be controlled, thus adjusting
deposition rate and film properties.
[0073] Specifically, a mixed gas of silane and hydrogen is used as
the reaction gas. In this case, it is possible to change at least
one of a fraction and sizes of silicon nanoparticles charged in gas
phase by increasing at least one selected from a dissociation
temperature of the reaction gas (i.e., temperature of the filament
30), a fraction of silane in the mixed gas and a pressure of the
chamber 15 caused by the mixed gas.
[0074] For example, the dissociation degree of the reaction gas
depends on the temperature of the filament 30. As the temperature
of the filament 30 increases, the dissociation degree of the
reaction gas increases. Such an increase in the temperature of the
filament 30 changes the dissociation degree of the reaction gas,
which changes electrostatic properties of deposition unit particles
based on the present inventors'.circleincircle. new deposition
theory. In the case of depositing a silicon thin film, the relative
ratio of the negatively charged particles becomes higher than that
of the positively charged particles as the temperature of the
filament 30 increases. The increase in the dissociation degree of
the reaction gas according to the temperature control of the
filament 30 and the related improvement of the thin film properties
differ from the dissociation degree of the reaction gas in a
related art method of using plasma.
[0075] In other words, the method of depositing films according to
the exemplary embodiment includes controlling the generation
behavior associated with charged characteristics such as size,
number concentration, charge amount and charge ratio of the charged
nanoparticles formed in gas phase by adjusting process parameters,
e.g., reaction temperature, the amount of reaction gas, reaction
pressure, in CVD process.
[0076] The electrostatic characteristic caused by the charge amount
of the charged nanoparticles is removed at or accumulated on the
surface of the substrate 40 according to the electrical
conductivity of the substrate 40, which changes an interaction
behavior between the substrate 40 and the charged nanoparticles
depending on the polarities of the charged nanoparticles
successively deposited. Since the electrostatic characteristic
caused by the charge amount of the charged nanoparticles is removed
at the surface of the substrate 40 if the substrate 40 has a high
electrical conductivity, the nanoparticles deposited on the
substrate 40 do not have an effect on nanoparticles to be deposited
later. However, an attractive force or a repulsive force is exerted
on nanoparticles to be deposited later because the electrostatic
characteristic caused by the charge amount of the charged
nanoparticles is accumulated on the surface of the substrate 40 if
the substrate has a low electrical conductivity or is an insulator.
Change in deposition behaviors according to the electrical
conductivity of the substrate 40 will be more fully described in
experimental examples later.
[0077] In operation S5, the bias supply unit 80 applies a bias to
the substrate 40 to draw the charged nanoparticles toward the
substrate 40, thus depositing a film. The deposition behavior is
controlled by continuously or alternately applying a positive or
negative bias. That is, the deposition rate of the charged
nanoparticles and the related structural characteristics of thin
films are controlled by selectively taking positively or negatively
charged nanoparticles through bias application during deposition
process. The method of depositing films according to the exemplary
embodiments may be performed under the condition that a voltage of
the power supply 70 is in the range of approximately +1,000 V to
approximately -1,000 V, and DC or AC with a frequency ranging from
approximately 0.01 Hz to approximately 10 kHz may be applied.
[0078] The method of depositing films according to the exemplary
embodiments includes controlling the deposition behavior of the
charged nanoparticles using electric field intensity and a polarity
change through a bias unit (e.g., the bias supply unit 80 in this
embodiment).
[0079] For example, by applying a bias to the top of the substrate
40, an electrical polarity ratio of nanoparticles to be deposited
may be changed before the nanoparticles are deposited on the
substrate 40. A method of controlling deposition behaviors of
charged nanoparticles according to a position of the bias supply
unit 80 will be more fully described in experimental examples
below. The thin film deposition is divided into two steps, i.e.,
nucleation and growth. The electrical polarity ratio of the
nanoparticles to be deposited may be changed by varying at least
one of a fraction and sizes of the charged nanoparticles in each
step, and varying the charge amount of the nanoparticle before the
nanoparticles are deposited on the substrate 40. For example, it is
possible to decrease the fraction and the sizes of the
nanoparticles in an initial step of the film deposition, i.e., in
the nucleation step, and to increase the fraction and the size of
the nanoparticle in the growth step, and vice versa. The positively
charged nanoparticles to be deposited may be dominant in the
nucleation step and the negatively charged nanoparticles to be
deposited may be dominant in the growth step, and vice versa.
[0080] FIGS. 6(a) through 6(c) are schematic views illustrating
deposition behaviors caused by interactions between a polarity of a
bias applied to the substrate and polarities of charged
nanoparticles in the method of depositing films according to the
exemplary embodiments.
[0081] Referring to FIG. 6(a), when a positive bias, e.g., +150 V,
is applied to the conductive substrate 40 in the case that the
charged nanoparticles 90 have negative polarities, the deposition
rate increases because the nanoparticles 90 are drawn toward the
substrate 40 due to an attractive force. Referring to FIG. 6(b),
when a bias is not applied to the conductive substrate 40, the
deposition rate is equal to that of the related art irrespective of
whether the charged nanoparticles have positive or negative
polarities. Referring to FIG. 6(c), however, when a negative bias,
e.g., -150 V, is applied to the conductive substrate 40 in the case
that the charged nanoparticles 90 have negative polarities, the
deposition rate is too low because the nanoparticles 90 are
repulsed from the substrate 40 due to a repulsive force. As such,
the deposition rate can be controlled by applying the bias to the
substrate 40, making it possible to control the structural
characteristics of the deposited thin film.
[0082] In the method of depositing films according to the exemplary
embodiments, the generation behavior of nanoparticles charged by
reaction gas can be controlled by varying reaction conditions of
the reaction gas. At the same time, the deposition behavior can
also be separately controlled by applying a bias to a substrate in
consideration of the charged behavior of the charged nanoparticles,
independently of the generation behavior. Since the bias supply
unit 80 applying the electrical bias is separated from the
substrate 4, the bias supply unit 80 can be disposed on the top or
the side of the substrate 40 as well as the bottom of the substrate
40 so that it is possible to effectively control the deposition
behavior. This separation of the bias supply unit 80 from the
substrate 40 makes it possible to control the deposition behavior
of thin films and thick films upon an electrically insulating
substrate such as ceramic substrate through which an electrical
bias does not pass and a plastic substrate requiring a low reaction
temperature as well as an electrically conductive substrate.
Furthermore, the control of the deposition behavior can make it
possible to deposit films having uniform texture, thus contributing
to reduction in haze of the thin films, reduction in formation of
voids, improvement in surface roughness, and improvement in degree
of crystallinity.
[0083] The deposition rate of the charged nanoparticles and the
related structural characteristics of thin films are controlled by
selectively taking positively or negatively charged nanoparticles
through bias application during deposition process. For example,
when depositing silicon films, because the charged crystalline
silicon nanoparticles move to a region under the effect of the bias
at a high flow rate, it is possible to obtain a crystalline silicon
film with low impurity content, high degree of crystallinity and
high deposition rate as well.
[0084] Besides the HFCVD apparatus 10, the method of depositing
films as described above may be implemented using another apparatus
of depositing films that falls within a scope of the present
invention, in which a unit of dissociating the reaction gas and a
unit of applying a bias to the substrate are employed. The
apparatus of depositing films, which is available in realizing the
method, may include an HFCVD apparatus, a plasma CVD apparatus, and
an atmospheric pressure CVD (APCVD) apparatus.
Embodiment 2
[0085] FIG. 7 illustrates an apparatus of depositing films
according to another exemplary embodiment.
[0086] Referring to FIG. 7, an APCVD apparatus 110, an apparatus of
depositing films, according to this exemplary embodiment includes a
chamber 115, a gas supply system 120, a heating element 130 and a
bias supply device 190.
[0087] The APCVD apparatus 110 of FIG. 7 is a horizontal furnace
type apparatus. In the chamber 115 of the APCVD apparatus 110,
reaction gas is horizontally supplied and exhausted, and a
substrate 140 is loaded. The internal pressure of the chamber 115
is maintained at an atmospheric pressure. The chamber 115 may be
formed of quartz and shaped as a tube.
[0088] The gas supply system 120 introduces source gas such as
reaction gas and carrier gas into the chamber 115, and includes a
gas pipe and a gas flowmeter. The heating element 130 is configured
to emit heat so as to dissociate the reaction gas introduced into
the chamber 115. Examples of a material that may be used for the
heating element may be graphite, SiC, etc. The heating element 130
may have the shape of a bar, a plate, a coil, and so on. The
heating element 130 may be provided singularly or in plurality. The
heating element 130 shown in FIG. 7 is a bar-shaped SiC heating
element. For instance, six bar-shaped SiC heating elements may be
radially disposed around the chamber 115.
[0089] The bias supply device 190 of the APCVD apparatus 110
according to this exemplary embodiment is disposed over or under
the substrate 140 and applies a bias to the substrate 140 from a
detached position. Specifically, the bias supply device 190
includes a first plate 170 disposed over the substrate 140, a
second plate 175 disposed under the substrate 140 and facing the
first plate 170, a ground unit 180 connected to the first plate 170
through a line 171, and a power supply connected to the second
plate 175 through a line 176.
[0090] The ground unit 180 and the power supply 185 are disposed
outside the chamber 115. The substrate 140 is placed on a surface
of the second plate 175, which is opposite to the first plate 170.
A recess R is provided in the second plate 175 to settle the
substrate 140. The first plate 170 is grounded because it is
connected to the ground unit 180. The power supply 185 applies a
constant AC or DC voltage to the second plate 175, and applies a
bias to the substrate 140 from a detached position thereunder.
[0091] A voltage of the power supply 185 is in the range of
approximately +1,000 V to approximately -1,000 V, and a DC or an AC
having a frequency ranging from approximately 0.01 Hz to
approximately 10 kHz may be applied. The first and second plates
170 and 175 may be formed of a conductive material, particularly
metallic material. The first and second plates 170 and 175 may have
larger sizes than the substrate 140, and may change their sizes
depending on deposition purpose.
[0092] FIGS. 8(a) through 8(c) are photographs of a bias supply
device used in following experimental examples, showing the first
plate 170, the second plate 175 and lines 171 and 176 for
connecting the first and second plates 170 and 175 to the ground
unit and the power supply. The first and second plates 170 and 175
were prepared to have a plate structure of SUS material. In
particular, FIG. 8(c) illustrates a top surface of the second plate
175 where a recess R is provided for settling the substrate
140.
[0093] FIG. 9 is a schematic view of a bias supply device having
alternative structure included in the deposition apparatus of FIG.
7. Referring to FIG. 9, a recess R.circleincircle. for settling the
substrate 140 is provided in a surface of the first plate 170,
which is opposite to the second plate 175. The substrate 140 is
received in the recess R.circleincircle. The power supply 185 and
the ground unit 180 are connected to the first plate 170 and the
second plate 175, respectively. In the bias supply device 190, a
bias is applied to the substrate 140 from a detached position
thereabove. The bias supply device may apply the bias to the
substrate 140 from a detached position thereabove or thereunder.
One of the first and second plates 170 and 175 is connected to the
ground unit 180, and the other is connected to the power supply
185.
[0094] In the APCVD apparatus 110, nucleated and grown
nanoparticles may be positively or negatively charged due to a
different work function from the inside of the chamber through
bipolar charging mechanism. The bias supply device 190 draws the
charged nanoparticles toward the substrate 140. The carrier gas,
e.g., nitrogen gas, introduced by the gas supply system 120
facilitates the charged nanoparticles to move toward the bias
supply device 190. The movement rate of the charged nanoparticles
can be controlled by adjusting a flow rate of the carrier gas
through a gas flowmeter. The charged nanoparticles arriving at the
bias supply device 190 are forced to move toward the substrate 140
so that the nanoparticles are deposited on the substrate 140.
[0095] As described above, since the apparatus of depositing films
according to this exemplary embodiment can apply a bias to the
substrate during film deposition, the crystallized and charged
nanoparticles are drawn toward the substrate and then deposited on
the substrate, which makes it possible to improve the deposition
rate and control the degree of crystallinity as well. Accordingly,
it is possible to obtain a crystalline silicon film in as-depo
state, which is a peculiar effect resulted from the aforementioned
method of depositing films where the deposition of the crystalline
silicon film is accomplished without additional recrystallization
step unlike the related art.
Embodiment 3
[0096] FIG. 10 illustrates an apparatus of depositing films
according to still another exemplary embodiment.
[0097] Referring to FIG. 10, an APCVD apparatus 210, an apparatus
of depositing films, according to this exemplary embodiment
includes a chamber 215, a gas supply system 120, a heating element
130 and a bias supply device 190'. Like reference numerals in FIG.
10 denote like elements of FIG. 7, and thus their description will
be omitted herein.
[0098] The APCVD apparatus 210 of FIG. 10 is a vertical furnace
type apparatus in which the reaction gas is vertically supplied and
exhausted.
[0099] The bias supply device 190' is configured to apply a bias to
the substrate from a detached position thereunder. Specifically,
the bias supply device 190' includes a first plate 170' disposed
over the substrate 140, a second plate 175 disposed under the
substrate 140 and facing the first plate 170' a ground unit 180
connected to the first plate 170' through a line 171, and a power
supply 185 connected to the second plate 175 through a line
176.
[0100] While the charged nanoparticles move downward along the flow
direction of carrier gas, they may encounter the first plate 170'.
Therefore, the first plate 170' may have a mesh shape such that the
charged nanoparticles can pass therethrough. Depending on the
deposition purpose, it is possible to use the first plate 170' by
varying an aperture size, shape and installation position of the
mesh.
[0101] Although FIG. 10 exemplarily illustrates that the ground
unit 180 and the power supply 185 are provided below the chamber
215, the ground unit 180 and the power supply may be provided on
the side of the chamber. Furthermore, although FIG. 10 exemplarily
illustrates that the substrate 140 is disposed in a direction
perpendicular to an extension direction of the chamber 215, the
substrate 140 is disposed in a direction parallel with an extension
direction of the chamber 215.
[0102] The method of depositing films as described in FIG. 5 may
also be performed using the APCVD apparatuses of FIGS. 7 and 10.
The foregoing description for the method of depositing films using
the HFCVD apparatus with reference to FIGS. 2 and 5 is also
available for the method of depositing films using the APCVD
apparatuses of FIGS. 7 and 10 except that the heating element 130
and the bias supply device 190 and 190' are used instead of the
filament 30 and the bias supply unit 80, respectively.
Experimental Example 1
[0103] In this experimental example, the apparatus of measuring
charged nanoparticles illustrated in FIG. 1 was used.
[0104] The temperature of the chamber 5 was in the range of 773 K
to 1,273 K for dissociating reaction gas. A mixed gas of silane
(SiH.sub.4) and nitrogen (N.sub.2) was used as the reaction gas in
which the concentration of silane is approximately 10%. The results
of number concentrations versus sizes of nanoparticles in gas phase
are illustrated in FIGS. 11A and 11B, while changing the
temperature of the chamber 5 from 773 K to 1,273 K using a power
supply. FIG. 11A illustrates a concentration distribution of
negatively charged nanoparticles in the chamber 5, and FIG. 11B
illustrates a concentration distribution of positively charged
nanoparticles in the chamber 5. As the temperature of the chamber 5
increases, the concentration of the negatively charged
nanoparticles increases but that of the positively charged
nanoparticles decreases, as illustrated in FIGS. 11A and 11B.
[0105] As such, it is possible to control the deposition behavior
of films by changing the generation behavior of the charged
nanoparticles generated in the chamber.
Experimental Example 2
[0106] In this experimental example, the HFCVD apparatus 10 of FIG.
2 was used as the apparatus of depositing nanoparticles.
[0107] The temperature of the filament 30 was set to 1,833 K for
dissociating reaction gas. The substrate 40 was formed of stainless
steel with an area of 2 cm.times.2 cm and a thickness of 1 mm. The
temperature of the substrate 40 is set to 393 K. A mixed gas of
silane (SiH.sub.4) and nitrogen (N.sub.2) was used as the reaction
gas in which the concentration of silane was set to 20% and 10%,
respectively. A DC bias of +150 V and -150 V was respectively
applied using the power supply 70. A copper plate was used as the
bias supply unit 80, and disposed below the substrate 40, as
illustrated in FIG. 2. The pressure of the chamber 15 was set to
0.7 Torr, and deposition was performed for 30 minutes. The mass of
the substrate 40 was measured before and after the reaction so that
the deposition amount per unit area according to the bias
application was estimated by a mass difference between the
comparison substrates prepared under the same conditions except the
condition of bias application (the increased mass of the deposited
substrate with the bias applied-the increased mass of the deposited
substrate without the bias applied=the deposition amount according
to the bias application).
[0108] FIG. 12 is a graph illustrating deposition behaviors
according to a concentration of reaction gas and a bias applied to
a bottom of a substrate in the method of depositing films according
to the exemplary embodiments, where the substrate is an electrical
conductor (stainless steel).
[0109] Referring to FIG. 12, the sample (a) is prepared by
depositing nanoparticles under the condition that the concentration
of silane is set to 20% and the bias is set to +150 V. The sample
(b) is prepared by depositing nanoparticles under the condition
that the concentration of silane is set to 20% and the bias is set
to -150 V. The sample (c) is prepared by depositing nanoparticles
under the condition that the concentration of silane is set to 10%
and the bias is set to +150 V. The sample (d) is prepared by
depositing nanoparticles under the condition that the concentration
of silane is set to 10% and the bias is set to -150 V. Here,
heights of bars in FIG. 12 denote increments in the mass of the
silicon thin films of the samples (a), (b), (c) and (d),
respectively.
[0110] As illustrated in FIG. 12, from the results of mass increase
in silicon thin films obtained by applying the bias to the
conductive substrate, it can be appreciated that the deposition
rate of the silicon thin film increases in order by the samples
(a), (b), (c) and (d). In the sample (d), it is observed that the
deposition rate is lower than the case of no bias application,
which may be construed that the charged nanoparticles generated
under the silane concentration of 20% and 10%, respectively, may
exhibit different generation behaviors.
[0111] In the samples (a) and (b) prepared under the silane
concentration of 20%, negatively charged nanoparticles are mainly
generated, and also small amount of positively charged
nanoparticles are generated so that the deposition rate increases
by the positive bias. In the samples (c) and (d) prepared under the
silane concentration of 10%, negatively charged nanoparticles are
more generated than the samples (a) and (b), and thus the
negatively charged nanoparticles, majority of the generated
nanoparticles, are repulsed from the substrate when the bias of
-150 V is applied, which makes it difficult to deposit the
nanoparticles on the substrate. In this case, the amount of the
positively charged nanoparticles which can be easily deposited is
extremely small so that they hardly contributes to the increase in
deposition rate.
[0112] Resultantly, in the case where the substrate is formed of
stainless steel with high electrical conductivity, it is possible
to increase the deposition rate by applying a bias of which a
polarity is opposite to a polarity of the nanoparticles dominantly
existing in the charged nanoparticles according to variations in
charged behaviors of the charged nanoparticles generated depending
on the dissociation condition (i.e., concentration of silane) of
the reaction gas. In addition, a relative ratio of the positively
or negatively charged nanoparticles increases as the concentration
of the reaction gas increases.
Experimental Example 3
[0113] In this experimental example, the HFCVD apparatus 10 of FIG.
2 was used as an apparatus of depositing nanoparticles.
[0114] The temperature of the filament 30 was set to 1,833 K for
dissociating reaction gas. The substrate 40 was formed of
polyethylene terephthalate (PET) with an area of 3 cm.times.6 cm
and a thickness of 0.5 mm. The temperature of the substrate 40 is
set to 353 K.
[0115] A mixed gas of hydrogen (H.sub.2) and silane (SiH.sub.4) was
used as the reaction gas in which the concentration of silane was
set to 20% and 10%, respectively. A DC bias of +150 V and -150 V
was respectively applied using the power supply 70. A copper plate
was used as the bias supply unit 80, and disposed below the
substrate 40, as illustrated in FIG. 2. The pressure of the chamber
15 was set to 0.7 Torr, and deposition was performed for 30
minutes. The mass of the substrate 40 was measured before and after
the reaction so that the deposition amount per unit area according
to the bias application was estimated by a mass difference between
the comparison substrates prepared under the same conditions except
the condition of bias application (the increased mass of the
deposited substrate with the bias applied-the increased mass of the
deposited substrate without the bias applied=the deposition amount
according to the bias application).
[0116] FIG. 13 is a graph illustrating deposition behaviors
according to a concentration of reaction gas and a bias applied to
a bottom of a substrate in a method of depositing films using the
deposition apparatus of FIG. 2, where the substrate is an
electrical insulator (e.g., PET).
[0117] Referring to FIG. 13, the sample (a) is prepared by
depositing nanoparticles under the condition that the concentration
of silane is set to 20% and the bias is set to +150 V. The sample
(b) is prepared by depositing nanoparticles under the condition
that the concentration of silane is set to 20% and the bias is set
to -150 V. The sample (c) is prepared by depositing nanoparticles
under the condition that the concentration of silane is set to 10%
and the bias is set to +150 V. The sample (d) is prepared by
depositing nanoparticles under the condition that the concentration
of silane is set to 10% and the bias is set to -150 V. Here,
heights of bars in FIG. 13 denote increments in the mass of the
silicon thin films of the samples (a), (b), (c) and (d),
respectively.
[0118] As illustrated in FIG. 13, from the results of mass increase
in the silicon thin film obtained by applying the bias to the
nonconductive substrate, it can be appreciated that the deposition
rate of the silicon thin film increases in order by the samples
(b), (d), (a) and (c). In the samples (a) and (c), it is observed
that the deposition rate is lower than the case of no bias
application.
[0119] This result is caused by that the PET with low electrical
conductivity is used as the substrate unlike the experimental
example 2. The charges of the deposited nanoparticles do not escape
from the PET substrate 40, electrical insulator, and accumulated on
the substrate 40. Thus, the deposition rate is reduced due to a
repulsive force between the previously deposited nanoparticles and
nanoparticles to be deposited later. Accordingly, the deposition
rate is lowest in the sample (c) in which the negatively charged
nanoparticles dominantly exist. The deposition rate of the sample
(a) where positively charged nanoparticles increase is also lower
than the case of no bias application. In the case where the bias of
-150 V is applied, i.e., in the samples (b) and (d), the
application of a negative bias increases the deposition rate
because the deposition of positively charged nanoparticles, of
which the amount is relatively smaller than that of negatively
charged nanoparticles, becomes a rate determining step of the
deposition rate.
[0120] Particularly, the deposition rate is higher in the sample
(b) than the sample (d) because a relative generation ratio of the
positive charged nanoparticle to the negatively charged
nanoparticle is higher and the dissociated amount is greater in the
sample (b) than the sample (d).
[0121] FIG. 14 is a graph illustrating film properties resulted
from the difference of deposition behaviors in the samples of FIG.
13, which are measured by Raman spectroscopy.
[0122] Referring to FIG. 14, the degree of the crystallinity is
highest in the ample (d) because a repulsive force between the
charged nanoparticles with the same polarity is strongest during
the deposition of the thin film. That is, the reason is that a
ratio of negatively charged nanoparticles to positively charged
nanoparticles is higher in the samples (c) and (d) obtained under
the condition of the silane concentration of 10% than the samples
(a) and (b) obtained under the condition of the silane
concentration of 20%.
[0123] Resultantly, in the case where the substrate is formed of
PET, i.e., an electrical insulator, it is possible to increase the
deposition rate by applying a bias of which a polarity is the same
as a polarity of the nanoparticles dominantly existing in the
charged nanoparticles according to variations in charged behaviors
of the charged nanoparticles generated depending on the
dissociation condition (i.e., concentration of silane) of the
reaction gas. It is apparent that it is possible to increase the
degree of crystallinity of a thin film when a generation ratio
between the positively and negatively charged nanoparticles
increases due to a high dissociation degree of the reaction gas
under the same condition.
Experimental Example 4
[0124] Like the experimental example 3, the HFCVD apparatus 10 of
FIG. 2 was used. The temperature of the filament 30 was set to
1,833 K for dissociating reaction gas. The substrate 40 was formed
of polyethylene terephthalate (PET) with an area of 3 cm.times.6 cm
and a thickness of 0.5 mm. The temperature of the substrate 40 is
set to 353 K. A mixed gas of hydrogen (H.sub.2) and silane
(SiH.sub.4) was used as the reaction gas in which the concentration
of silane was set to 20% and 10%, respectively. A DC bias of +150 V
and .circleincircle.50 V was respectively applied using the power
supply 70. Hitherto, the conditions are the same as those of the
experimental example 3.
[0125] Instead, a copper mesh was used as the bias supply unit 80
and disposed over the PET substrate 40. A wire of the copper mesh
had a diameter of 0.4 mm, and an aperture between wires per square
centimeter was 64. The pressure of the chamber 15 was set to 0.7
Torr, and deposition was performed for 30 minutes. The mass of the
substrate 40 was measured before and after the reaction so that the
deposition amount per unit area according to the bias application
was estimated by a mass difference between the comparison
substrates prepared under the same conditions except the condition
of bias application (the increased mass of the deposited substrate
with the bias applied-the increased mass of the deposited substrate
without the bias applied=the deposition amount according to the
bias application).
[0126] FIG. 15 is a graph illustrating deposition behaviors
according to a concentration of reaction gas and a bias applied to
a top of a substrate in a method of depositing films using the
deposition apparatus of FIG. 2, where the substrate is an
electrical insulator.
[0127] Referring to FIG. 15, the sample (a) is prepared by
depositing nanoparticles under the condition that the concentration
of silane is set to 20% and the bias is set to +150 V. The sample
(b) is prepared by depositing nanoparticles under the condition
that the concentration of silane is set to 20% and the bias is set
to -150 V. Here, heights of bars in FIG. 15 denote increments in
the mass of the silicon thin films of the samples (a) and (b),
respectively.
[0128] As illustrated in FIG. 15, in both the samples (a) and (b),
it is observed that the deposition rate is lower than the case of
no bias application. The deposition rate is much lower in the case
of applying a positive bias, i.e., the sample (a), than the case of
applying a negative bias, i.e., the sample (b). The reason is that
most of the charged nanoparticles, i.e., basic units of silicon
thin film deposition, are captured by the copper mesh to which the
bias is applied, before they are deposited on the substrate. It is
apparent that it is possible to control the deposition rate using
such a method of applying the bias.
Experimental Example 5
[0129] Like the experimental example 2, the HFCVD apparatus 10 of
FIG. 2 was used as an apparatus of depositing nanoparticles.
[0130] The temperature of the filament 30 was set to 2,173 K for
dissociating reaction gas. The substrate 40 was formed of stainless
steel with an area of 2 cm.times.2 cm and a thickness of 1 mm. The
temperature of the substrate 40 is set to 523 K.
[0131] A mixed gas of hydrogen (H.sub.2) and methane (CH.sub.4) was
used as the reaction gas in which the concentration of methane was
set to 20%. A DC bias of +25V, +0 V and .circleincircle.00 V was
respectively applied using the power supply 70. A copper plate was
used as the bias supply unit 80, and disposed below the substrate
40, as illustrated in FIG. 2. The pressure of the chamber 15 was
set to 170 Torr, and deposition was performed for 30 minutes.
[0132] As a result, the growth of carbon nanotubes is actively
performed in the case of applying +25 V rather than the case of
applying .circleincircle.00 V. It is construed that this is
resulted from the fact the nanoparticles formed in gas phase are
negatively charged.
Experimental Example 6
[0133] In this experimental example, the APCVD apparatus 110 of
FIG. 7 was used as an apparatus of depositing films.
[0134] The highest temperature at a center C of the chamber 115 was
set to 1.073 K, and the temperature decreases as far away from the
center C. The substrate 140 was loaded in a left position with
respect to the center C of the chamber 115. The position where the
substrate 140 was loaded was set to a temperature of 933 K. A mixed
gas of 90%-heliumn (He) and 10%-silane (SiH.sub.4) was used as the
reaction gas. The first and second plates 170 and 175 were formed
of SUS material. The substrate 140 was placed on the second plate
175, as illustrated in FIG. 7. The pressure of the chamber 115 was
set to 760 Torr, and deposition was performed for 30 minutes. The
experiment was performed under the condition that the flow rate of
carrier gas, e.g., nitrogen gas, was 1,000 sccm and the flow rate
of the reaction gas was 10 sccm. Three kinds of voltages were
applied by the power supply 185, as illustrated in FIGS. 16A
through 16C.
[0135] FIG. 16A illustrates the case that the power supply 185
applies +50 V DC bias. Since a positive polarity is applied to the
second plate 175, a negative polarity is relatively applied to the
first plate 170. The negatively charged nanoparticles 192 are drawn
toward the second plate 175 so that the negatively charged
nanoparticles 192 are mainly deposited on the substrate 140 placed
on the second plate 175. On the contrary, the positively charged
nanoparticles 193 are drawn toward the first plate 170 so that
positively charged nanoparticles 193 are difficult to be deposited
on the substrate 140.
[0136] FIG. 16B illustrates the case that the power supply 185
applies -50 V DC bias. Since a negative polarity is applied to the
second plate 175, a positive polarity is relatively applied to the
second plate 175. The positively charged nanoparticles 193 are
drawn toward the second plate 175 so that positively charged
nanoparticles 193 are mainly deposited on the substrate 140 placed
on the second plate 175. On the contrary, the negatively charged
nanoparticles 192 are drawn toward the first plate 170 so that the
negatively charged nanoparticles 192 are difficult to be deposited
on the substrate 140.
[0137] FIG. 16C illustrates the case that DC voltages of +50 V and
-50 V are alternately applied at every 5 seconds. When the DC bias
of +50 V is applied, the negatively charged nanoparticles are
mainly deposited on the substrate 140. In contrast, when the DC
bias of -50 V is applied, the positively charged nanoparticles are
mainly deposited on the substrate 140. Therefore, the polarity of
the nanoparticle deposited on the substrate depends on the polarity
of the bias.
[0138] To analyze the deposition rate of each deposition sample, a
section of the sample was observed with a field emission scanning
electron microscope (FE-SEM). The degree of crystallinity was
measured with a Raman spectroscopy.
[0139] FIG. 17 illustrates FE-SEM images comparing thicknesses of
the experimental examples of FIGS. 16A through 16C with that of a
comparative example in the case where the substrate is an
electrical insulator. FIG. 18 is a graph illustrating a deposition
thickness and a deposition rate per second for each of the samples
of FIG. 17 in the case where the substrate is an electrical
insulator.
[0140] In this case, the substrate is an insulator of quartz
glass.
[0141] In FIGS. 17 and 18, from the result of change in a thickness
of the silicon thin film obtained by applying the bias to the
insulating substrate, it can be observed that the deposition rate
of the silicon thin film increases in order by the sample (c), the
sample (b), the sample of the comparative example, and the sample
(a). In the sample of the comparative example, it is observed that
the deposition rate is higher than the sample (a) where the bias of
+50 V is applied.
[0142] Such a result is caused by that the quartz glass with low
electrical conductivity was used as the substrate and the
positively charged particles existed more than the negatively
charged particles in the chamber, which were observed from DMA
experimental results. In general, the deposition rate decreases due
to a repulsive force when the deposited nanoparticles and the
nanoparticles to be deposited have the same polarities. In the
samples (a) and (b), the deposition is performed in this manner.
The nanoparticles having a polarity opposite to that of the
deposited nanoparticle are deposited on the substrate due to an
attractive force so that the substrate is neutralized again. The
particles having the polarity responsive to the applied bias are
deposited on the substrate again. The reason why the deposition
rate of the sample (a) is lower than that of the sample (b) is that
the negatively charged particles are fewer than the positively
charged particles and the fewer particles determine the deposition
rate. The sample (c) exhibits excellent the deposition rate because
all the positively and negatively charged particles existing in the
chamber are used as deposition sources due to the alternative
application of voltages. In the sample of the comparative example,
the particles are randomly deposited on the substrate according to
Brownian motion.
[0143] FIG. 19 illustrates measurement results of Raman
spectroscopy showing film properties of the samples of FIG. 17
according to deposition behaviors.
[0144] Referring to FIG. 19, it is observed that amorphous silicon
is deposited in the case where the bias is not applied, i.e., in
the case of the comparative example. In contrast, the crystallinity
can be observed when the bias is applied according to the
embodiments. When the bias voltage is applied, it is observed that
the degree of crystallinity increases in order by the case of
depositing negatively charged particles as deposition sources, the
case of depositing positively charged particles as deposition
sources, and the case of alternately depositing positively and
negatively charged particles as deposition sources.
[0145] As described above, a film deposition is performed by
drawing charged silicon particles, which have been crystallized
already in a chamber, toward a substrate by applying a bias.
Therefore, it is apparent that it is possible to obtain a
crystallized silicon film for a short time at a low temperature
through one-step, which was impossible in the related art.
[0146] Although the apparatus and method of depositing films using
a bias and a charging behavior of nanoparticles formed during a
chemical vapor deposition have been described with reference to the
specific embodiments, they are not limited thereto. Therefore, it
will be readily understood by those skilled in the art that various
modifications and changes can be made thereto without departing
from the spirit and scope of the present invention defined by the
appended claims.
* * * * *