U.S. patent application number 09/827582 was filed with the patent office on 2001-11-22 for method of self-assembly silicon quantum dots.
This patent application is currently assigned to National Science Council. Invention is credited to Lee, Si-Chen, Meng, Chao-Yu, Shih, An.
Application Number | 20010042502 09/827582 |
Document ID | / |
Family ID | 21659772 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042502 |
Kind Code |
A1 |
Shih, An ; et al. |
November 22, 2001 |
Method of self-assembly silicon quantum dots
Abstract
A method of self-assembling silicon quantum dots comprises the
steps of providing a substrate, forming a thin amorphous Si film,
and forming a plurality of Si quantum dots by controlling the
energy and the shooting numbers of an excimer laser during an
annealing process, wherein the excimer laser emits light on the
thin amorphous Si film.
Inventors: |
Shih, An; (Changhua Hsien,
TW) ; Meng, Chao-Yu; (Taichung, TW) ; Lee,
Si-Chen; (Taipei, TW) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
National Science Council
|
Family ID: |
21659772 |
Appl. No.: |
09/827582 |
Filed: |
April 5, 2001 |
Current U.S.
Class: |
117/3 ; 117/11;
257/E21.134; 257/E29.071; 257/E33.005 |
Current CPC
Class: |
H01L 29/127 20130101;
H01L 21/02601 20130101; H01L 21/02686 20130101; B82Y 30/00
20130101; H01L 21/02532 20130101; H01L 33/0054 20130101; B82Y 10/00
20130101; H01L 33/06 20130101; H01L 21/0262 20130101 |
Class at
Publication: |
117/3 ;
117/11 |
International
Class: |
C30B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2000 |
TW |
89109546 |
Claims
What is claimed is:
1. A method of self-assembling silicon quantum dots comprising the
steps of: providing a substrate and forming a thin amorphous Si
film; and forming a plurality of Si quantum dots by controlling the
energy and the shooting numbers of an excimer laser during
annealing process, wherein the excimer laser emits light on the
thin amorphous Si film.
2. A method of self-assembling silicon quantum dots according to
claim 1, wherein the substrate comprises one selective of glass
substrate, insulating layer on semiconductor substrate.
3. A method of self-assembling silicon quantum dots according to
claim 1, further including a step of forming an amorphous Si film
on the substrate by utilizing a CVD.
4. A method of self-assembling silicon quantum dots according to
claim 1, further including a step of forming a large-area amorphous
Si film into a large-area Si quantum dots by utilizing a scanner
during annealing process.
5. A method of self-assembling silicon quantum dots according to
claim 1, wherein the thickness of amorphous Si film is less than 50
nm.
6. A method of self-assembling silicon quantum dots according to
claim 5, as the thickness of amorphous Si film is between 1 nm and
50 nm, the laser energy is set to a range from 100 mJ/cm.sup.2 to
500 mJ/cm.sup.2 and the shooting number is set to a range from 1 to
200.
7. A method of self-assembling silicon quantum dots according to
claim 5, as the thickness of amorphous Si film is less than 1.5 nm,
the laser energy is set to a range from 220 mJ/cm.sup.2 to 300
mJ/cm.sup.2 and the shooting number is set to a range from 1 to
10.
8. A method of self-assembling silicon quantum dots according to
claim 3, wherein the CVD comprises one selective of PECVD and
LPCVD.
9. A method of self-assembling silicon quantum dots according to
claim 8, further including a step of forming a hydrogenated
amorphous Si film by utilizing PECVD and then removing the H atoms
in the hydrogenated amorphous Si film to form the amorphous Si film
by annealing process.
10. A method of self-assembling silicon quantum dots according to
claim 8, further including a step of forming the amorphous Si film
directly by utilizing LPCVD.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of self-assembling
silicon quantum dots, and especially relates to the self-assembling
silicon quantum dots on an amorphous silicon film by an excimer
laser.
[0003] 2. Description of Prior Art
[0004] In recent years, semiconductor quantum dots have been
extensively applied in the field of photonics devices, such as
photo-detectors, light emitting diodes (LEDs), semiconductor laser
diodes (LDs), single electron devices, and others. A large number
of experimental and theoretical studies have investigated
semiconductor quantum dots.
[0005] Quantum dots are usually formed by using quantum well
structure. U.S. Pat. 5,229,320 disclosed "Method For Forming
Quantum Dots". With reference to FIG. 1A to FIG. 1D, a film a of
quantum well formed on a substrate and then a layer 10 of
photoresist formed thereon. Finally, the quantum dots 32 formed on
a film of quantum well by the electron-beam lithography. However,
the methods cause a lot of surface states, and the surface states
became the main source of non-radiative recombination center.
Further, the surface state reduced the optical property of quantum
dots. For example, the intensity of luminance resulting from
conventional quantum dots is lower than that resulting from quantum
well. The optical linewidth caused by the conventional quantum dots
is wider than that caused by the quantum well. In addition, the
method of electron-beam lithography is slow and has difficulty
manufacturing a large-area device.
[0006] Quantum dots can also be formed in the Stranski-Krastanov
mode (SK mode) by MBE or MOCVD. However, the quantumdots formed by
MBE or MOCVD are restricted to the material of InAs/GaAs or
SiGe/Si, and confined to the substrate.
SUMMARY OF THE INVENTION
[0007] In accordance with the present invention, the object is
attained by a method of self-assembling quantum dots. A thin Si
film forms on a substrate and then the thin Si film (<100 nm) is
formed into poly-Si quantum dots by utilizing an excimer laser to
proceed with the annealing process.
[0008] The present invention has an advantage in that the quantum
dots of Si are simply and quickly formed by the self-assembling
method. Further, utilizing a laser scanner on a large-area film of
Si can form a large-area device of Si quantum dots.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] This and other objects and features of this invention will
become clear from the following description, taken in conjunction
with the preferred embodiments with reference to the accompanied
drawings in which:
[0010] FIG. 1A to FIG. 1D is a cross-sectional view of the
conventional method of fabricating quantum dots;
[0011] FIG. 2A to FIG. 2D is a cross-sectional view of the
embodiment of present invention;
[0012] FIG. 3 shows a SEM picture of the poly-Si pillars after
annealing process utilizing excimer laser;
[0013] FIG. 4 shows a SEM picture of the poly-Si quantum dots after
annealing process utilizing excimer laser;
[0014] FIG. 5 shows a SEM picture of the poly-Si quantum dots
formed by self-assembling during annealing process;
[0015] FIG. 6 is a photoluminescence spectrum emitted from
self-assembled quantum dots at low temperature.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] As shown in FIG. 2A to FIG. 2D, the method of
self-assembling quantum dots of the preferred embodiment of the
present invention comprises the steps listed below.
[0017] (1) With reference to FIG. 2A, a thin film made of
amorphous-Si is formed on a substrate.
[0018] A Corning 7059 glass substrate 100 is positioned in the
PECVD and the substrate heated to 250.degree. C. The pressure in
the reaction chamber of the PECVD is kept at 0.45 torr, and
SiH.sub.4 and H.sub.2 flow in the reaction chamber, these deposit a
thin layer (<100 nm)--a hydrogenated amorphous silicon (refer to
a-Si:H) film 200. The flow rate of SiH.sub.4 is 5 sccm, and the
flow rate of H.sub.2 is 2 sccm. The growth rate of the a-Si:H film
200 is 0.27 nm/sec, and the concentration of H.sub.2 in the a-Si:H
film 200 is measured by secondary ion mass spectrometry (refer to
SIMS) is 3.9.times.10.sup.21 cm.sup.-3.
[0019] (2) With reference to FIG. 2B, after depositing a layer of
quantum well, the H atoms are removed from the film by the
annealing process.
[0020] The a-Si:H film 200 positioned in a reaction chamber filled
with N.sub.2 is heated to 550.degree. C. during the annealing
process for two hours. All the H atoms in the a-Si:H film 200 are
expelled, and an amorphous Si film 210 is formed.
[0021] (3) With reference to FIG. 2C, the Si quantum dots are in
the form of self-assembling by utilizing an excimer laser.
[0022] The amorphous Si film 210 is positioned in a reaction
chamber, wherein the temperature is kept at room temperature and
the pressure is less than 8.times.10.sup.-6 torr. A pulsed laser
300 emitted from a pulsed KrF excimer laser is incident on the
amorphous Si film 210 at room temperature (Under the conditions of
.lambda.=248 nm, pulse duration=28 ns, and frequency=1 Hz). The
laser emitted from the excimer laser 300 is incident on the surface
of an amorphous Si film 210 to proceed with the laser annealing
process, and then the poly-Si quantum dots are produced by
self-assembling.
[0023] (4) FIG. 2D shows the cross-sectional view of the Si quantum
dots formed by the laser annealing process. As shown in FIG. 2D,
after proceeding with the laser annealing process, the amorphous Si
film forms the poly-Si quantum dots 220 by self-assembling.
[0024] FIG. 3 shows a SEM picture of an amorphous Si film of
thickness 50 nm forming on a glass substrate after the annealing
process utilizing an excimer laser. The operational conditions of
the excimer laser are that the laser energy is 125 mJ/cm.sup.2 and
the shooting numbers are 50. As shown in FIG. 3, the amorphous Si
film forms a plurality of pillars by the annealing process
utilizing the excimer laser but doesn't form quantum dots. The
diameter of the pillar is about 230 nm, and the height is about 25
nm.
[0025] FIG. 4 shows a SEM picture of an amorphous Si film of
thickness 50 nm forming on a glass substrate after the annealing
process utilizing an excimer laser. The operational conditions of
the excimer laser are that the laser energy is 225 mJ/cm.sup.2 and
the shooting number is 1. As shown in FIG. 4, the amorphous Si film
forms a plurality of pillars by annealing process utilizing the
excimer laser. An atomic force microscope can measure the
dimensions of the pillars. The diameter of the protrusion is about
230 nm, and the height is about 25 nm. Because the dimensions of
the pillars are too large, the amorphous Si film hasn't formed the
poly-Si quantum dots.
[0026] FIG. 5 shows a SEM picture, wherein an amorphous Si film of
thickness 1.5 nm forms on a glass substrate formed the
self-assembly quantum dots after annealing process utilizing an
excimer laser. The operational conditions of the excimer laser are
that the laser energy is 250 mJ/cm.sup.2 and the shooting number is
1. As shown in FIG. 5, the amorphous Si film forms the
self-assembling Si quantum dots by annealing process utilizing the
excimer laser. The diameter of the quantum dot is about 14.2 nm,
and the height is about 3.7 nm. FIG. 6 is a photoluminescence
spectrum (refer to PL spectrum) emitted from self-assembled quantum
dots at low temperature. As shown in FIG. 6, several peaks higher
than the energy state of Si appear in the spectrum. Quantum dots of
zero dimension exist as part of the phenomenon of quantum energy
state.
[0027] The inferences of the preferred embodiment of the present
invention concluded from FIG. 3 and FIG. 4 are that (A) the pillars
will become larger with increased laser energy; (B) the pillars
will become larger with increased shooting numbers. The inference
of the preferred embodiment of the present invention concluded from
FIG. 4 and FIG. 5 is that (C) the pillars change into quantum dots
as decreasing the thickness of the amorphous Si film.
[0028] In the present invention, the quantum dots annealed from
amorphous Si film with a thickness of 1.about.50 nm are formed in
the following conditions:
[0029] the laser energy being 100.about.500 mJ/cm.sup.2; and
[0030] the shooting number of pulsed laser being 1.about.200.
[0031] In the present invention, the quantum dots annealed from
amorphous Si film with thickness under 1.5 nm are formed in the
following conditions:
[0032] the laser energy being 220.about.300 mJ/cm.sup.2; and
[0033] the shooting number of pulsed laser being 1.about.10.
[0034] In the embodiment of the present invention, a large-area
structure of self-assembling Si quantum dots is annealed from the
amorphous Si film by utilizing an excimer laser and a scanner.
[0035] In the present invention, it can use an insulating layer,
such as Si.sub.3N.sub.4, SiO.sub.2, or semiconductor substrate,
such as Si, GaAs, etc., instead of using the glass substrate.
[0036] In the present invention, it can also use a low pressure
chemical vapor deposition (LPCVD) instead of the plasma enhanced
CVD (PECVD) to directly form an amorphous Si film on a substrate at
about 550.degree. C.
[0037] In the present invention, the H atoms are removed from the
a-Si:H film during the annealing process, and the temperature is
set to a range from 500.degree. C. to 600.degree. C.
[0038] While the preferred forms of the present invention have been
described, it is to be understood that modifications will be
apparent to those skilled in the art without departing from the
spirit of the invention. The scope of the invention, therefore, is
to be determined solely by the following claims.
* * * * *