U.S. patent application number 11/973525 was filed with the patent office on 2008-02-14 for rare earth element-doped silicon oxide film electroluminescence device.
This patent application is currently assigned to Sharp Laboratories of America, Inc.. Invention is credited to Robert A. Barrowcliff, Wei Gao, Sheng Teng Hsu, Tingkai Li, Yoshi Ono.
Application Number | 20080035946 11/973525 |
Document ID | / |
Family ID | 39060193 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080035946 |
Kind Code |
A1 |
Gao; Wei ; et al. |
February 14, 2008 |
Rare earth element-doped silicon oxide film electroluminescence
device
Abstract
A method is provided for forming a rare earth (RE) element-doped
silicon (Si) oxide film with nanocrystalline (nc) Si particles. The
method comprises: providing a first target of Si, embedded with a
first rare earth element; providing a second target of Si;
co-sputtering the first and second targets; forming a Si-rich Si
oxide (SRSO) film on a substrate, doped with the first rare earth
element; and, annealing the rare earth element-doped SRSO film. The
first target is doped with a rare earth element such as erbium
(Er), ytterbium (Yb), cerium (Ce), praseodymium (Pr), or terbium
(Tb). The sputtering power is in the range of about 75 to 300 watts
(W). Different sputtering powers are applied to the two targets.
Also, deposition can be controlled by varying the effective areas
of the two targets. For example, one of the targets can be
partially covered.
Inventors: |
Gao; Wei; (Vancouver,
WA) ; Li; Tingkai; (Vancouver, WA) ;
Barrowcliff; Robert A.; (Vancouver, WA) ; Ono;
Yoshi; (Camas, WA) ; Hsu; Sheng Teng; (Camas,
WA) |
Correspondence
Address: |
SHARP LABORATORIES OF AMERICA, INC.;C/O LAW OFFICE OF GERALD MALISZEWSKI
P.O. BOX 270829
SAN DIEGO
CA
92198-2829
US
|
Assignee: |
Sharp Laboratories of America,
Inc.
|
Family ID: |
39060193 |
Appl. No.: |
11/973525 |
Filed: |
October 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11334015 |
Jan 18, 2006 |
7297642 |
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11973525 |
Oct 9, 2007 |
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11066713 |
Feb 24, 2005 |
7259055 |
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11334015 |
Jan 18, 2006 |
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11058505 |
Feb 14, 2005 |
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11334015 |
Jan 18, 2006 |
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Current U.S.
Class: |
257/98 ; 257/646;
257/E33.001 |
Current CPC
Class: |
H01L 21/3115 20130101;
H05B 33/145 20130101; Y02E 10/544 20130101; H01L 31/03046
20130101 |
Class at
Publication: |
257/098 ;
257/646; 257/E33.001 |
International
Class: |
H01L 33/00 20060101
H01L033/00; H01L 23/58 20060101 H01L023/58 |
Claims
1-17. (canceled)
18. An electroluminescence (EL) device comprising: a bottom
substrate; a silicon-rich silicon oxide (SRSO) film including: a
first thickness overlying the substrate doped with a first
concentration of a rare earth (RE) element; a second thickness,
overlying the first thickness, doped with a second concentration of
the RE element; and, a top electrode overlying the SRSO film.
19. An electroluminescence (EL) device comprising: a bottom
substrate; a silicon-rich silicon oxide (SRSO) film including: a
first thickness overlying the substrate doped with a first rare
earth (RE) element; a second thickness, overlying the first
thickness, doped with a second RE element; and, a top electrode
overlying the SRSO film.
20. A silicon-rich silicon oxide (SRSO) film comprising: a first
thickness doped with a first concentration of a rare earth (RE)
element; and, a second thickness, overlying the first thickness,
doped with a second concentration of the RE element.
21. A silicon-rich silicon oxide (SRSO) film comprising: a first
thickness doped with a first rare earth (RE) element; and, a second
thickness, overlying the first thickness, doped with a second RE
element.
Description
RELATED APPLICATIONS
[0001] The application is a continuation-in-part of a pending
application entitled HIGH-LUMINESCENCE SILICON ELECTROLUMINESCENCE
DEVICE, Tingkai Li et al., Ser. No. 11/066,713, filed on Feb. 24,
2005, which is incorporated herein by reference.
[0002] The application is a continuation-in-part of a pending
application entitled WIDE WAVELENGTH RANGE SILICON
ELECTROLUMINESCENCE DEVICE, Tingkai Li et al., Ser. No. 11/058,505,
filed on Feb. 14, 2005, which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention generally relates to integrated circuit (IC)
fabrication and, more particularly, to a sputter deposition
procedure for making a rare earth element-doped silicon-rich
silicon oxide (SRSO) film with nanocrystalline (nc) Si particles,
for use in electroluminescence (EL) applications.
[0005] 2. Description of the Related Art
[0006] The observation of visible luminescence at room temperature,
emanating from porous silicon (Si), has spurred a tremendous amount
of research into using nano-sized Si to develop a Si-based light
source. One widely used method of fabricating nanocluster Si
(nc-Si) is to precipitate the nc-Si out of SiOx (x<2), producing
a film using chemical vapor deposition (CVD), radio frequency
(RF)-sputtering, and Si implantation, which is often called
silicon-rich silicon oxide (SRSO). Er implantation, creating
Er-doped nanocrystal Si, is also used in Si based light sources.
However, state-of-the-art implantation processes have not been able
to distribute the dopant uniformly, which may be important for
high-efficiency light emission. Ion implantation also increases
costs. Interface engineering may also be important for the device
performance, but it is very difficult to achieve using ion
implantation. All these drawbacks limit future device
applications.
[0007] Other work (Castagna et al., "High Efficiency Light Emission
Devices in Silicon") describes a silicon-based light source
consisting of a MOS structure with nc-Si particles and Er implanted
in a thin oxide layer. After annealing at 800.degree. C. for 30
minutes under nitrogen flux, the device shows 10% external quantum
efficiency at room temperature, which is comparable to that of
light emitting diodes using III-V semiconductors. However, the
stability of the device is poor. Another device structure consists
of a 750 .ANG. thick silicon-rich oxide (SRO) gate dielectric layer
doped with rare earth ions (Er, Tb, Yb, Pr, Ce) via ion
implantation. After similar annealing, the device shows much more
stable properties but the efficiency drops off to 0.2%
[0008] Undoped silicon nano particles possess a wide wavelength
distribution in its light emission spectrum, due to its particle
size distribution. On the other hand, RE doped SRSO emits light in
discrete wavelengths correspondent to the intra 4f transitions of
the RE atoms. For example, the main emission wavelengths for
terbium, ytterbium, and erbium-doped SRSO are located at the
wavelengths of 550 nm, 983 nm, and 1540 nm respectively. The
monochromaticity of the RE-related light emission from doped
silicon nano particles provides much better control over the
wavelength, giving it wider application in optical
communications.
[0009] To fabricate doped silicon-rich oxide, RE ion implantation
has previously been explored. Although ion implantation provides
for purity and flexibility, it is expensive and the dosage that can
be implanted is limited. Dopant concentration in any particular
depth direction is difficult to control and the concentration of
dopant is not uniform.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method of depositing
RE-doped SRSO by a sputtering process. The doped SRSO film, in
turn, can be annealed into a film that contains actively doped
silicon nano particles imbedded in silicon oxide matrix for
electroluminescence (EL) applications. In one aspect for example,
terbium (Tb)-doped SRSO is deposited in Edwards 360 reactive DC
sputtering system by using a specially designed RE-embedded Si
target. The annealed film shows very strong Tb-related
photoluminescence (PL) signals, making it useful in EL device
applications.
[0011] Accordingly, a method is provided for forming a rare earth
(RE) element-doped silicon (Si) oxide film with nanocrystalline
(nc) Si particles. The method comprises: providing a first target
of Si, embedded with a first rare earth element; providing a second
target of Si; co-sputtering the first and second targets; forming a
Si-rich Si oxide (SRSO) film on a substrate, doped with the first
rare earth element; and, annealing the rare earth element-doped
SRSO film. The first target is doped with a rare earth element such
as erbium (Er), ytterbium (Yb), cerium (Ce), praseodymium (Pr), or
terbium (Tb).
[0012] The sputtering power is in the range of about 75 to 300
watts (W). In one aspect, different sputtering powers are applied
to the two targets. In another aspect, deposition is controlled by
varying the effective areas provided by the two targets. For
example, one of the targets can be partially covered. This control
creates doping profiles that are not available using ion
implantation. For example, a uniformly doped SRSO film can be
formed in a single co-sputtering process. As another example, a
first thickness of SRSO film can be formed having a first RE first
doping concentration, and a second thickness of SRSO film can be
formed overlying the first thickness, having a first RE second
doping concentration, different from the first concentration.
[0013] Additional details of the above-described process and EL
devices fabricated using the above-mentioned process are provided
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a partial cross-sectional view of a silicon-rich
silicon oxide (SRSO) film.
[0015] FIG. 2 is a partial cross-sectional view of a variation of
the SRSO film of FIG. 1
[0016] FIG. 3 is a partial cross-sectional view of an
electroluminescence (EL) device.
[0017] FIG. 4 is a partial cross-sectional view of a variation of
the EL device of FIG. 3.
[0018] FIG. 5 is a graph depicting EL measurements of an exemplary
EL device.
[0019] FIG. 6 is a plot depicting the realtionship between PL,
sputtering power, and annealing conditions.
[0020] FIG. 7 is a flowchart illustrating a method for forming a RE
element-doped Si oxide film with nc Si particles.
[0021] FIG. 8 is a schematic block diagram of a DC sputtering
system using a Si target and a RE-doped Si target.
DETAILED DESCRIPTION
[0022] FIG. 1 is a partial cross-sectional view of a silicon-rich
silicon oxide (SRSO) film. The SRSO film 100 comprises a first
thickness 102 doped with a first concentration of a rare earth (RE)
element. A second thickness 104, overlies the first thickness 102,
and is doped with a second concentration of the RE element. In one
aspect, the first concentration of RE dopant is greater than the
second concentration. In another aspect, the second concentration
of RE dopant is greater than the first. The film of FIG. 1 is
intended to depict a simple exemplary RE doping profile that can be
obtained using a two-target sputtering process to deposit the
RE-doped SRSO film 100. Other, more complicated, profiles may be
created using the same basic methodology.
[0023] As in all the SRSO films described below, SRSO film 100 is
primarily silicon dioxide, with extra Si. After annealing, the Si
atoms agglomerate together to form Si nano particles imbedded in a
silicon oxide matrix. The silicon richness can be represented by
refractive index of the film n. For pure SiO2, n=1.46. For SRSO
film 100, n varies from 1.5 to 2.2. Further, the SRSO film 100 is
doped with an RE concentration in the range of 2 to 10%.
[0024] FIG. 2 is a partial cross-sectional view of a variation of
the SRSO film of FIG. 1. The SRSO film 200 comprises a first
thickness 202 doped with a first RE element. A second thickness 204
overlies the first thickness 202, and is doped with a second RE
element. The film of FIG. 2 is intended to depict a simple
exemplary RE doping profile that can be obtained using a
three-target sputtering process to deposit the RE-doped SRSO film
200. More than three targets can be used to create more complex
profiles.
[0025] FIG. 3 is a partial cross-sectional view of an
electroluminescence (EL) device. The EL device 300 comprises a
bottom substrate 302. A silicon-rich silicon oxide (SRSO) film 304
includes a first thickness 306 overlying the substrate 302, doped
with a first concentration of a rare earth (RE) element. A second
thickness 308 of SRSO overlies the first thickness, and is doped
with a second concentration of the RE element. In one aspect, the
first concentration of RE dopant is greater than the second
concentration. In another aspect, the second concentration of RE
dopant is greater than the first. A top electrode (TE) 310 overlies
the SRSO film 304.
[0026] In one aspect, the substrate 302 is either an n-type or
p-type Si substrate. In other aspects, the substrate 302 or the top
electrode 310 can be a transparent material such as ITO, ZnO:Al, or
Au. Other materials that can be used for the substrate and top
electrode include aluminum (Al), zinc oxide (ZnO), chromium (Cr),
Pt, Ir, AlCu, Ag, YBCO, RuO.sub.2, and La.sub.1-xSr.sub.xCOO.sub.3.
The device of FIG. 3 is intended to depict a simple exemplary EL
device that can be obtained using a two-target sputtering process
to deposit the RE-doped SRSO film 304.
[0027] For light generated using Er doping, the light at IR
wavelengths can be detected through a silicon substrate 302. In
this case, the top electrode can be opaque. For the light generated
via Tb emission, the wavelength is around 550 nm, in the visible
range. The top electrode in this case must necessarily be a
transparent for the light to be detected, as visible-range light
cannot be detected through a Si substrate.
[0028] FIG. 4 is a partial cross-sectional view of a variation of
the EL device of FIG. 3. The EL device 400 comprises a bottom
substrate 402 and a SRSO film 404. A first thickness 406 of SRSO
overlies the substrate 402, and is doped with a first rare earth
(RE) element. A second thickness 408 of SRSO overlies the first
thickness 406, and is doped with a second RE element. For example,
the first RE can be Er and the second RE can be Tb. A top electrode
410 overlies the SRSO film 404.
Functional Description
[0029] By using a specially designed RE-imbedded target with
another, pure silicon target, RE-doped SRSO film can be deposited
in different concentration profiles, to fabricate SRSO films with
varied dopant concentrations. As an example, the fabrication of a
Tb-doped silicon nano-particle SRSO thin film is presented below.
The deposition and annealing conditions are listed in Table 1. The
sputtering power can be changed to alter the silicon richness,
while maintaining the Tb/Si ratio. PL measurements associated with
these samples, with a variety of annealing conditions (from
as-deposited to 1000.degree. C.) are also presented. TABLE-US-00001
TABLE 1 Deposition and post annealing conditions for Tb-doped SRSO
films Sputtering Annealing power Pressure Temperature Gas
temperature 75-300 W 7-8 mtorr 225.degree. C. 15% 900-1100.degree.
C. O.sub.2/Ar
[0030] FIG. 5 is a graph depicting EL measurements of an exemplary
EL device. The device tested has a Si substrate, covered with a 2.8
nm layer of silicon dioxide. A Tb-doped SRSO film overlies the
silicon dioxide, and an ITO top electrode covers the SRSO film. The
SRSO was sputtered at a power level of 300 W, annealed in an oxygen
atmosphere at 950.degree. C., for 4 minutes. The emissions at 550
nm prove that Tb is incorporated into the film. Quite different
from EL emission from silicon nano-particles, RE-related EL
emission have discrete wavelengths that correspondent to the
intra-4f transition in the RE atoms. The graph shows that
post-deposition annealing does not shift the emission wavelengths,
which is another proof of RE involvement. Conventional silicon nano
particle films, without RE dopants, normally show a shift in
emission wavelength as a result of varied annealing conditions.
[0031] FIG. 6 is a plot depicting the realtionship between PL,
sputtering power, and annealing conditions. The peak PL intensity
(at 544 nm) changes with annealing conditions and sputtering power.
A systematic shift of the maximum PL intensity is associated with a
higher sputtering power when the annealing temperature is
increased. The maximum PL occurs at an annealing temperature of
1000.degree. C. using MRL equipment, in N.sub.2, with an annealing
time of 10 minutes (m), when the sputtering power is 125 W. At a
sputtering power of 75 W, the composition of the film is basically
SiO.sub.2 with no extra silicon. The PL intensity decreases with an
increase in annealing temperature. These relationships show the
versatility of the RE-doped sputtering method, and point to new
silicon nano-particle based EL device applications.
[0032] In one simple aspect, a RE-doped SRSO film with different
doping concentrations can be deposited by using different
sputtering power on two targets, and/or by partially covering one
of the targets. In another aspect, the doping concentration can be
varied across the SRSO film thickness, by varying the sputtering
power during the deposition, or by varying the exposed area of
either one of the target during the deposition. In this manner, the
doping concentration can be manipulated to achieve dopant profile
engineering and/or interface engineering.
[0033] FIG. 8 is a schematic block diagram of a DC sputtering
system using a Si target and a RE-doped Si target. The ions are
supplied by a plasma that is induced in the sputtering equipment. A
variety of techniques are used to modify the plasma properties,
especially ion density, to achieve the desired sputtering
conditions. The target can be biased with a direct current (DC)
voltage (DC sputtering). Alternating radio frequency (RF) current
can also be used to bias the target. Magnetron sputtering systems
use magnetic fields to control and confine ion flow. While DC
sputtering equipment is the simplest and cheapest to use, the
present invention sputtering process can be enabled with any
sputtering process.
[0034] Although the sputtered atoms are ejected from the target in
a gas phase, they condense back into a solid phase upon colliding a
substrate, which results in deposition of a thin film of sputtered
material.
[0035] FIG. 7 is a flowchart illustrating a method for forming a RE
element-doped Si oxide film with nc Si particles. Although the
method is depicted as a sequence of numbered steps for clarity, no
order should be inferred from the numbering unless explicitly
stated. It should be understood that some of these steps may be
skipped, performed in parallel, or performed without the
requirement of maintaining a strict order of sequence. The method
starts at Step 700.
[0036] Step 702 provides a first target of Si, embedded with a
first rare earth element. Some exemplary rare earth elements
include erbium (Er), ytterbium (Yb), cerium (Ce), praseodymium
(Pr), and terbium (Tb). However, the method is not limited to
merely these examples. Step 704 provides a second target of Si.
Step 706 provides a substrate. For example, the substrate can be
doped Si, or doped Si with an overlying layer of silicon oxide
having a thickness in the range of about 1 to 10 nm. Step 708
co-sputters the first and second targets. Step 710 forms a SRSO
film on the substrate, doped with the first rare earth element.
Step 712 anneals the rare earth element-doped SRSO film.
[0037] In one aspect, Step 708 co-sputters the first and second
targets using a sputtering power in the range of about 75 to 300 W.
In another aspect, Step 708 uses an environmental pressure in the
range of about 7 to 8 milli-Torr. Typically, the substrate is
heated to a temperature of about 225.degree. C., and the first and
second targets are co-sputtered using an Ar atmosphere, with about
15% oxygen.
[0038] In one aspect, equal sputtering power is applied to the two
targets. Alternately, Step 708 sputters the first target at a first
sputtering power and the second target at a second sputtering
power, different than the first sputtering power. A similar effect
can be achieved by providing a first target with a first effective
area in Step 702, and providing a second target in Step 704 with a
second effective area, different than the first area. For example,
one target can be made with a smaller surface area or partially
covered.
[0039] Using one of the above-mentioned techniques, Step 710 may
form a SRSO film with a RE doping profile that includes a first
thickness of SRSO film having a first RE first doping
concentration. A second thickness of SRSO film overlies the first
thickness, having a first RE second doping concentration, different
from the first concentration.
[0040] In a different aspect, Step 712 anneals at a temperature in
the range of about 900 to 1100.degree. C., for a duration in the
range of 10 to 30 minutes. The annealing is done in an atmosphere
that may include N.sub.2, inert gases, water vapor, oxygen, or a
combination of the above-mentioned elements. The atmosphere chosen
is often dependent upon the degree of oxidation desired.
[0041] As noted in the explanation of FIG. 6 above, in one aspect
Step 708 decreases the sputtering power. Then, Step 712 decreases
the annealing temperature and increases the annealing time, in
response to decreasing the sputtering power. Alternately, if Step
708 increases the sputtering power, then typically, Step 712
increases the annealing temperature and decreases the annealing
time, as a response to increasing the sputtering power.
[0042] In one aspect, Step 710 forms a uniformly doped SRSO film as
a result of a single co-sputtering process (Step 708). This is a
result that cannot be achieved using ion implantation.
[0043] In one variation of the method, an additional step, Step
705, provides a third target of Si, embedded with a second rare
earth element. Then, Step 708 co-sputters the first, second, and
third targets, and Step 710 forms a SRSO film doped with the first
and second rare earth elements. For example, Step 710 may form a
SRSO film with a RE doping profile that includes a first thickness
of SRSO film doped with the first RE first element and a second
thickness of SRSO film, overlying the first thickness, doped with
the second RE element. It should be noted that Step 708 does not
necessarily apply power to all three targets simultaneously. For
example, the above-mentioned doping profile is achieved by
initially co-sputtering just the first and second targets, and
later, co-sputtering just the second and third targets.
[0044] A sputter deposition method has been provided for the
fabrication of a rare earth element-doped SRSO film with
nanocrystalline Si. Some process specifics have been given to
illustrate the method. However, the invention is not limited to
just these examples. Other variations and embodiments of the
invention will occur to those skilled in the art.
* * * * *