U.S. patent application number 11/003249 was filed with the patent office on 2005-06-30 for ceramic thin film on various substrates, and process for producing same.
Invention is credited to Aktik, Cetin, Scarlete, Mihai.
Application Number | 20050139966 11/003249 |
Document ID | / |
Family ID | 29555369 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139966 |
Kind Code |
A1 |
Scarlete, Mihai ; et
al. |
June 30, 2005 |
Ceramic thin film on various substrates, and process for producing
same
Abstract
A thin film of an amorphous silicon-based material on a
substrate. The thin film has the property of any one of a carrier
concentration of 10.sup.13 to 10.sup.18 cm.sup.-3 in a depletion
zone next to the substrate, an electron mobility of 5 to 30
cm.sup.2V.sup.-1s.sup.-1, a dangling bond concentration of
10.sup.12 to 10.sup.19 cm.sup.-3, no solvent-related defects, or a
residual hydrogen concentration of 0 to 25 atomic %. The thin film
may be used to fabricate many devices such as solar cells,
light-emitting diodes, transistors, photothyristors, and integrated
monolithic devices on a single chip.
Inventors: |
Scarlete, Mihai; (Roxboro,
CA) ; Aktik, Cetin; (Sherbrooke, CA) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
29555369 |
Appl. No.: |
11/003249 |
Filed: |
December 3, 2004 |
Current U.S.
Class: |
257/632 ;
438/62 |
Current CPC
Class: |
Y10T 428/265 20150115;
C23C 16/325 20130101; Y10T 428/31504 20150401; C23C 16/46
20130101 |
Class at
Publication: |
257/632 ;
438/062 |
International
Class: |
H01L 021/00; H01L
023/58 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2002 |
CA |
2,387,274 |
Claims
1. A film of an amorphous silicon-based material on a substrate,
the film having a carrier concentration of 10.sup.13 to 10.sup.18
cm.sup.-3 in a depletion zone next to the substrate.
2. The film according to claim 1, wherein the carrier concentration
is 10.sup.13 to 10.sup.17 cm.sup.-3 in a depletion zone next to the
substrate.
3. The film according to claim 1, wherein the carrier concentration
is 10.sup.13 to 10.sup.16 cm.sup.-3 in a depletion zone next to the
substrate.
4. The film according to claim 1, wherein the amorphous
silicon-based material is an amorphous silicon carbide.
5. The film according to claim 1, wherein the amorphous
silicon-based material is an amorphous silicon carbonitride.
6. The film according to claim 1, wherein the amorphous
silicon-based material is an amorphous silicon nitride.
7. The film according to claim 1, wherein the amorphous
silicon-based material is an amorphous silicon oxynitride.
8. The film according to claim 1, wherein the amorphous
silicon-based material is an amorphous silicon
oxy(carbo)nitride.
9. The film according to claim 1, wherein the amorphous
silicon-based material is an amorphous silicon oxycarbide.
10. The film according to claim 1 further comprising a dopant.
11. The film according to claim 10, wherein the dopant is selected
from the group consisting N, B, O, H, Cl, Al, Ga, In, Tl, P, As,
Sb, O, S, Se, Te, and Bi.
12. The film according to claim 1, wherein the substrate is
selected from the group consisting of quartz, metal, ceramic,
electronic-grade sintered alumina, polished alumina, silicon single
crystal wafer, graphite, and stainless steel.
13. The film according to claim 1, wherein the film has a thickness
of at least 100 .ANG..
14. The film according to claim 1, wherein the film has a grain
size of 2-10 nm.
15. The film according to claim 1, wherein the film has a grain
size of 2-5 nm.
16. The film according to claim 1, wherein the film has a grain
size of 2-3 nm.
17. A film of an amorphous silicon-based material on a substrate,
the film having an electron mobility of 5 to 30
cm.sup.2V.sup.-1s.sup.-1.
18. The film according to claim 17, wherein the electron mobility
is 10 to 25 cm.sup.2V.sup.-1s.sup.-1.
19. The film according to claim 17, wherein the electron mobility
is 15 to 20 cm.sup.2V.sup.-1s.sup.-1.
20. The film according to claim 17, wherein the amorphous
silicon-based material is an amorphous silicon carbide.
21. The film according to claim 17, wherein the amorphous
silicon-based material is an amorphous silicon carbonitride.
22. The film according to claim 17, wherein the amorphous
silicon-based material is an amorphous silicon nitride.
23. The film according to claim 17, wherein the amorphous
silicon-based material is an amorphous silicon oxynitride.
24. The film according to claim 17, wherein the amorphous
silicon-based material is an amorphous silicon
oxy(carbo)nitride.
25. The film according to claim 17, wherein the amorphous
silicon-based material is an amorphous silicon oxycarbide.
26. The film according to claim 17 further comprising a dopant.
27. The film according to claim 26, wherein the dopant is selected
from the group consisting N, B, O, H, Cl, Al, Ga, In, Tl, P, As,
Sb, O, S, Se, Te, and Bi.
28. The film according to claim 17, wherein the substrate is
selected from the group consisting of quartz, metal, ceramic,
electronic-grade sintered alumina, polished alumina, silicon single
crystal wafer, graphite, and stainless steel.
29. The film according to claim 17, wherein the film has a
thickness of at least 100 .ANG..
30. The film according to claim 17, wherein the film has a grain
size of 2-10 nm.
31. The film according to claim 17, wherein the film has a grain
size of 2-5 nm.
32. The film according to claim 17, wherein the film has a grain
size of 2-3 nm.
33. A film of an amorphous silicon-based material on a substrate,
the film having a dangling bond concentration of 10.sup.12 to
10.sup.19 cm.sup.-3.
34. The film according to claim 33, wherein the dangling bond
concentration is 10.sup.13 to 10.sup.18 cm.sup.-3.
35. The film according to claim 33, wherein the dangling bond
concentration is 10.sup.14 to 10.sup.17 cm.sup.-3.
36. The film according to claim 33, wherein the amorphous
silicon-based material is an amorphous silicon carbide.
37. The film according to claim 33, wherein the amorphous
silicon-based material is an amorphous silicon carbonitride.
38. The film according to claim 33, wherein the amorphous
silicon-based material is an amorphous silicon nitride.
39. The film according to claim 33, wherein the amorphous
silicon-based material is an amorphous silicon oxynitride.
40. The film according to claim 33, wherein the amorphous
silicon-based material is an amorphous silicon
oxy(carbo)nitride.
41. The film according to claim 33, wherein the amorphous
silicon-based material is an amorphous silicon oxycarbide.
42. The film according to claim 33 further comprising a dopant.
43. The film according to claim 42, wherein the dopant is selected
from the group consisting N, B, O, H, Cl, Al, Ga, In, Tl, P, As,
Sb, O, S, Se, Te, and Bi.
44. The film according to claim 33, wherein the substrate is
selected from the group consisting of quartz, metal, ceramic,
electronic-grade sintered alumina, polished alumina, silicon single
crystal wafer, graphite, and stainless steel.
45. The film according to claim 33, wherein the film has a
thickness of at least 100 .ANG..
46. The film according to claim 33, wherein the film has a grain
size of 2-10 nm.
47. The film according to claim 33, wherein the film has a grain
size of 2-5 nm.
48. The film according to claim 33, wherein the film has a grain
size of 2-3 nm.
49. A film of an amorphous silicon-based material on a substrate,
the film having no solvent-related defects.
50. The film according to claim 49, wherein the solvent-related
defects are voids in the film due solvent evaporation or solvent
trapped in the film during deposition.
51. The film according to claim 49, wherein the amorphous
silicon-based material is an amorphous silicon carbide.
52. The film according to claim 49, wherein the amorphous
silicon-based material is an amorphous silicon carbonitride.
53. The film according to claim 49, wherein the amorphous
silicon-based material is an amorphous silicon nitride.
54. The film according to claim 49, wherein the amorphous
silicon-based material is an amorphous silicon oxynitride.
55. The film according to claim 49, wherein the amorphous
silicon-based material is an amorphous silicon
oxy(carbo)nitride.
56. The film according to claim 49, wherein the amorphous
silicon-based material is an amorphous silicon oxycarbide.
57. The film according to claim 49 further comprising a dopant.
58. The film according to claim 57, wherein the dopant is selected
from the group consisting of N, B, O, H, Cl, Al, Ga, In, Tl, P, As,
Sb, O, S, Se, Te, and Bi.
59. The film according to claim 49, wherein the substrate is
selected from the group consisting of quartz, metal, ceramic,
electronic-grade sintered alumina, polished alumina, silicon single
crystal wafer, graphite, and stainless steel.
60. The film according to claim 49, wherein the film has a
thickness of at least 100 .ANG..
61. The film according to claim 49, wherein the film has a grain
size of 2-10 nm.
62. The film according to claim 49, wherein the film has a grain
size of 2-5 nm.
63. The film according to claim 49, wherein the film has a grain
size of 2-3 nm.
64. A film of an amorphous silicon-based material on a substrate,
the film having a residual hydrogen concentration of 0 to 25 atomic
%.
65. A film of an amorphous silicon-based material on a substrate,
the thin film having a residual hydrogen concentration of 0 to 20
atomic %.
66. A film of an amorphous silicon-based material on a substrate,
the thin film having a residual hydrogen concentration of 0 to 15
atomic %.
67. The film according to claim 64, wherein the amorphous
silicon-based material is an amorphous silicon carbide.
68. The film according to claim 64, wherein the amorphous
silicon-based material is an amorphous silicon carbonitride.
69. The film according to claim 64, wherein the amorphous
silicon-based material is an amorphous silicon nitride.
70. The film according to claim 64, wherein the amorphous
silicon-based material is an amorphous silicon oxynitride.
71. The film according to claim 64, wherein the amorphous
silicon-based material is an amorphous silicon
oxy(carbo)nitride.
72. The film according to claim 64, wherein the amorphous
silicon-based material is an amorphous silicon oxycarbide.
73. The film according to claim 64 further comprising a dopant.
74. The film according to claim 73, wherein the dopant is selected
from the group consisting of N, B, O, H, Cl, Al, Ga, In, Tl, P, As,
Sb, O, S, Se, Te, and Bi.
75. The film according to claim 64, wherein the substrate is
selected from the group consisting of quartz, metal, ceramic,
electronic-grade sintered alumina, polished alumina, silicon single
crystal wafer, graphite, and stainless steel.
76. The film according to claim 64, wherein the film has a
thickness of at least 100 .ANG..
77. The film according to claim 64, wherein the film has a grain
size of 2-10 nm.
78. The film according to claim 64, wherein the film has a grain
size of 2-5 nm.
79. The film according to claim 64, wherein the film has a grain
size of 2-3 nm.
80. A semiconductor device comprising a film of an amorphous
silicon-based material on a substrate, the film having a carrier
concentration of 10.sup.13 to 10.sup.18 cm.sup.-3 in a depletion
zone next to the substrate.
81. The semiconductor device according to claim 80, wherein the
device is a p-type or an n-type.
82. The semiconductor device according to claim 80, wherein the
device is selected from the group consisting of a solar cell, a
light-emitting diode, a Schottky diode, a transistor, a
photothyristor and an integrated monolithic device on a single
chip.
83. A semiconductor device comprising a film of an amorphous
silicon-based material on a substrate, the film having an electron
mobility of 5 to 30 cm.sup.2V.sup.-1s.sup.-1.
84. The semiconductor device according to claim 83, wherein the
device is a p-type or an n-type.
85. The semiconductor device according to claim 83, wherein the
device is selected from the group consisting of a solar cell, a
light-emitting diode, a Schottky diode, a transistor, a
photothyristor and an integrated monolithic device on a single
chip.
86. A semiconductor device comprising a film of an amorphous
silicon-based material on a substrate, the film having a dangling
bond concentration of 10.sup.12 to 10.sup.19 cm.sup.-3.
87. The semiconductor device according to claim 86, wherein the
device is a p-type or an n-type.
88. The semiconductor device according to claim 86, wherein the
device is selected from the group consisting of a solar cell, a
light-emitting diode, a Schottky diode, a transistor, a
photothyristor and an integrated monolithic device on a single
chip.
89. A semiconductor device comprising a film of an amorphous
silicon-based material on a substrate, the film having no
solvent-related defects.
90. The semiconductor device according to claim 89, wherein the
device is a p-type or an n-type.
91. The semiconductor device according to claim 89, wherein the
device is selected from the group consisting of a solar cell, a
light-emitting diode, a Schottky diode, a transistor, a
photothyristor and an integrated monolithic device on a single
chip.
92. A semiconductor device comprising a film of an amorphous
silicon-based material on a substrate, the film having a residual
hydrogen concentration of 0 to 25 atomic %.
93. The semiconductor device according to claim 92, wherein the
device is a p-type or an n-type.
94. The semiconductor device according to claim 92, wherein the
device is selected from the group consisting of a solar cell, a
light-emitting diode, a Schottky diode, a transistor, a
photothyristor and an integrated monolithic device on a single
chip.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation-in-part
application of co-pending U.S. application Ser. No. ______ [not yet
assigned], filed Nov. 22, 2004, entitled "Ceramic Thin Film On
Various Substrates, And Process For Producing Same", which is the
371 National Phase of International Application No.
PCT/CA03/000763, filed May 23, 2003, which was published in English
under PCT Article 21(2) as WO 03/100123 A1. All of these
applications are incorporated herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a thin film of an amorphous
silicon-based material on a substrate.
BACKGROUND OF THE INVENTION
[0003] Kitabatake et al., disclose in U.S. Pat. No. 6,270,573, CVD
and CVD-related methods of producing silicon carbide substrates,
including the growing of silicon carbide film by supplying separate
silicon atoms and carbon atoms on a surface. The silicon-carbon
bond formation occurs mainly on the surface of the substrate, a
step that usually requires high temperatures, in this particular
case the required temperature being 1300.degree. C. MBE and MO-CVD
may use species that contain a limited number of pre-existing Si--C
bonds in the precursor, this number being usually related to
precursor synthesis requirements. Further, MBE and MO-CVD rely
mainly on the creation of Si--C bonds on the surface of the
substrate and prevent rearrangement of Si--Si/C--C bonds
adventitiously produced in the process to the desirable Si--C
bonds. The rate of SiC production is limited to the number of Si--C
bonds produced on the surface of the substrate. The synthesis of
the material is based on Si--H and C--H bond-dissociation and Si--C
bond production, inducing a significant concentration of residual
chemical defects, including residual dangling bonds.
[0004] Kong et al. (European Patent No. EP 0,970,267) describe a
susceptor design for silicon carbide resulting in minimizing or
eliminating thermal gradients between the two surfaces of a
substrate wafer. The CVD and CVD-related deposition procedures of
Kong et al., require strict control of the temperature field and
the gas flow at the surface of the substrate, where the Si--C bond
formation is occurring.
[0005] Grigoriev et al. (Grigoriev, D. A., Edirisinghe, M. J., Bao,
X., Evans, J. R. G. and Luklinska, Z. B. (2001) "Preparation of
silicon carbide by electrospraying of a polymeric precursor,"
Philosophical Magazine Letters (UK), 81, 4, 2001 by Dept. of
Mater., Queen Mary Univ. of London, UK) present silicon carbide
coatings and films prepared for the first time by electrostatic
atomization of a solution of a polymeric precursor and deposition
onto alumina and zirconia substrates. In the method of Grigoriev et
al., the polymeric source already contains most of the Si--C bonds
required for the formation of the SiC film; however, the molecular
source is carried to the surface inside cages of solvent molecules,
implicitly leading to contamination of the film, shrinking and
outgassing phenomena, due to solvent evaporation and polymer
cracking. These effects will be present in any polymer-source
method (for example, spin-coating, spraying, laser ablation, etc.).
The synthesis of material directly from a condensed source (the
liquid solution of the polymer in aerosol, or "spray"-form) as
opposed to the synthesis from a gaseous precursor, prevents a
submicron-level roughness required for the efficient exploitation
of semiconductor/electronic properties of the SiC-material.
[0006] Lau et al. (Lau, S. P., Xu, X. L., Shi, J. R., Ding, X. Z.,
Sun, Z. and Tay, B. K. (2001) "Dependences of amorphous structure
on bias voltage and annealing in silicon-carbon alloys," Materials
Science & Engineering, B85 (16), Sch. of Electr. &
Electron. Eng., Nanyang Technol. Inst., Singapore) report amorphous
silicon-carbon alloy films that have been obtained by a filtered
cathodic vacuum arc (FCVA) technique. They have observed that the
disorder of the Si--C network increased with using the high bias
voltages during the deposition. This high disorder in the film with
high bias voltages induces the smaller nanometer crystallites after
annealing at 1000.degree. C. rather than low bias. The Raman peaks
shift to the high frequency with increasing the annealing
temperature up to 750.degree. C. due to the increase of nanometer
grain size at the same bias. A sharp transition from
nanocrystalline to polycrystalline can be observed when the films
are annealed under 1000.degree. C. The nanometer crystallites of
Si--C alloy used to obtain an increase of grain-size via annealing
induced new Si--C bond formation in the bulk of the material.
However, there was no redistribution of pre-existent Si--C bonds in
a polymeric residue.
[0007] Jana of al. (Jana, T., Dasgupta, A. and Ray, S. (2001)
"Doping of p-type microcrystalline silicon carbon alloy films by
the very high frequency plasma-enhanced chemical vapor deposition
technique" Journal of Materials Research, 16(7) 2001, 2130-5,
Energy Res. Unit, Indian Assoc. for the Cultivation of Sci.,
Calcutta, India) present the synthesis of p-type silicon-carbon
alloy thin films by very high frequency plasma-enhanced chemical
vapor deposition technique using a SiH.sub.4, H2, CH.sub.4, and
B.sub.2H.sub.6 gas mixture at low power (55 mW/cm.sup.2) and low
substrate temperatures (150-250.degree. C.). Effects of substrate
temperature and plasma excitation frequency on the optoelectronic
and structural properties of the films were studied. A film with
conductivity 5.75 Scm.sup.-1 and 1.93 eV optical gap E.sub.04 was
obtained at a low substrate temperature of 200.degree. C. using
63.75 MHz plasma frequency. The crystalline volume fractions of the
films were estimated from the Raman spectra. They observed that
crystallinity in silicon carbon alloy films depends critically on
plasma excitation frequency. When higher power (117 mW/cm.sup.2) at
180.degree. C. with 66 MHz frequency was applied, the deposition
rate of the film increased to 5.07 nm/min without any significant
change in optoelectronic properties. The introduction of the dopant
is based on bond-dissociation and bond reconstruction, increasing
the concentration of residual chemical defects, such as residual
dangling bonds.
[0008] Yamamoto et al. (Yamamoto et al., Diam. Relat. Mater., vol.
10 (no. 9-10), 2001, pp. 1921-6) present a doping procedure whereby
amorphous SiCN films were prepared on Si (100) substrates by
nitrogen ion-assisted pulsed-laser ablation of a SiC target. The
dependence of the formed chemical bonds in the films on nitrogen
ion energy and the substrate temperature was investigated by X-ray
photoelectron spectroscopy (XPS). The fractions of sp.sup.2 C--C,
sp.sup.3 C--C and sp.sup.2 C--N bonds decreased, and that of N--Si
bonds increased when the nitrogen ion energy was increased without
heating during the film preparation. The fraction of sp C--N bonds
was not changed by the nitrogen ion irradiation below 200 eV. Si
atoms displaced carbon atoms in the films and the sp.sup.3 bonding
network was made between carbon and silicon through nitrogen. This
tendency was remarkable in the films prepared under substrate
heating, and the fraction of sp.sup.3 C--N bonds also decreased
when the nitrogen ion energy was increased. Under the impact of
high-energy ions or substrate heating the films consisted of
sp.sup.2 C--C bonds and Si--N bonds, and the formation of sp.sup.3
C--N bonds was difficult. The Yamamoto procedure proposes a doping
step separate from the synthesis step.
[0009] Budaguan et al. (Budaguan, B. G.; Sherchenkov, A. A.;
Gorbulin, G. L.; Chernomordic, V. D. (2001) "The development of a
high rate technology for wide-bandgap photosensitive a-SiC:H
alloys," Journal of Alloys and Compounds, 327(30) Aug., 146-50,
Inst. of Electron Technol., Moscow, Russia) discuss in their paper
the deposition process and the properties of a-SiC:H alloy
fabricated for the first time by 55 kHz PECVD. It was found that 55
kHz PECVD allows an increase in the deposition rate of a-SiC:H
films.
[0010] Modiano et al. (Japanese patent No. 145138/95) present a
process for producing silicon carbide fibers having a C/Si molar
ratio from 0.85 to 1.39, comprising the steps of rendering
infusible the precursory fibers made from an organosilicon polymer
compound, then primarily baking the infusible fibers in a hydrogen
gas-containing atmosphere. This process for producing silicon
carbide thin films comprises the steps of imparting semiconductor
properties to passivating or dielectric thin films from volatile
precursory species produced from organosilicon polymer
compounds.
[0011] Yang et al. (Yang, Lixin; Chen, Changqing; Ren, Congxin;
Yan, Jinlong; Chen, Xueliang, "Synthesis of SiC Using Ion Beam and
PECVD", International Conference on Solid-State and Integrated
Circuit Technology Proceedings, pp. 811-814) present a process for
producing silicon carbide thin films comprising the steps of
conferring semiconductor properties to passivating or dielectric
thin films from volatile precursory species produced from
organosilicon polymeric compounds.
SUMMARY OF THE INVENTION
[0012] According to one aspect of the present invention, there is
provided a film of an amorphous silicon-based material on a
substrate, the film having a carrier concentration of 10.sup.13 to
10.sup.18 cm.sup.-3 in a depletion zone next to the substrate.
[0013] According to another aspect of the present invention, there
is provided a film of an amorphous silicon-based material on a
substrate, the film having an electron mobility of 5 to 30
cm.sup.2V.sup.-1s.sup.-1.
[0014] According to still another aspect of the present invention,
there is provided a film of an amorphous silicon-based material on
a substrate, the film having a dangling bond concentration of
10.sup.12 to 10.sup.19 cm.sup.-3.
[0015] According to yet another aspect of the present invention,
there is provided a film of an amorphous silicon-based material on
a substrate, the film having no solvent-related defects.
[0016] According to a further aspect of the present invention,
there is provided a film of an amorphous silicon-based material on
a substrate, the film having a residual hydrogen concentration of 0
to 25 atomic %.
[0017] According to yet a further aspect of the present invention,
there is provided a semiconductor device comprising a film of an
amorphous silicon-based material on a substrate, the film having a
carrier concentration of 10.sup.13 to 10.sup.18 cm.sup.-3 in a
depletion zone next to the substrate.
[0018] According to still a further aspect of the present
invention, there is provided a semiconductor device comprising a
film of an amorphous silicon-based material on a substrate, the
film having an electron mobility of 5 to 30
cm.sup.2V.sup.-1s.sup.-1.
[0019] According to another aspect of the present invention, there
is provided a semiconductor device comprising a film of an
amorphous silicon-based material on a substrate, the film having a
dangling bond concentration of 10.sup.12 to 10.sup.19
cm.sup.-3.
[0020] According to yet another aspect of the present invention,
there is provided a semiconductor device comprising a film of an
amorphous silicon-based material on a substrate, the film having no
solvent-related defects.
[0021] According to another aspect of the present invention, there
is provided a semiconductor device comprising a film of an
amorphous silicon-based material on a substrate, the film having a
residual hydrogen concentration of 0 to 25 atomic %.
[0022] In an embodiment, the semiconductor device is a solar cell,
light-emitting diode, Schottky diode, a transistor, a
photothyristor or an integrated monolithic device on a single
chip.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In the accompanying drawings, which illustrate an exemplary
embodiment of the present invention:
[0024] FIG. 1a is a schematic diagram of a Polymer Source Chemical
Vapor Deposition (PS-CVD) reactor;
[0025] FIG. 1b is a diagram of the temperature-profile in the
reactor;
[0026] FIG. 2 is a schematic diagram of the FT-IR cell for
monitoring the production of thin film by the PS-CVD process;
[0027] FIG. 3 is an infrared spectrum of a gaseous precursor formed
during deposition of an amorphous silicon carbide thin film
prepared by the PS-CVD process;
[0028] FIG. 4 is a representation of the set of chemical reactions
leading to an n-type amorphous silicon carbide thin film from a
generic polysilane precursor;
[0029] FIG. 5 is a series of substrates that may support a thin
film produced by the PS-CVD process;
[0030] FIG. 6 is a thermogram from a thermogravimetric analysis of
a polymeric source subjected to the PS-CVD process;
[0031] FIG. 7 illustrates a simple Schottky solar cell;
[0032] FIG. 8 illustrates a p-n junction barrier photovoltaic cell
based on amorphous silicon carbide thin film;
[0033] FIG. 9 illustrates a stacked p-n junction solar cell based
on amorphous silicon carbide thin film;
[0034] FIG. 10a illustrates an energy band diagram of Schottky
structure before intimate contact between metal and
semiconductor;
[0035] FIG. 10b illustrates an energy band diagram of Schottky
structure after intimate contact between metal and
semiconductor;
[0036] FIG. 11a illustrates the energy band of a p-n junction solar
cell;
[0037] FIG. 11b illustrates the energy band of a p-n junction solar
cell;
[0038] FIG. 12 is an ERD graph illustrating the relationship
between concentration and depth for an n-type amorphous silicon
carbide thin film;
[0039] FIG. 13 is a graph illustrating the relationship between
carrier concentration and width of the depletion zone for an n-type
amorphous silicon carbide thin film produced by the PS-CVD
process;
[0040] FIG. 14 is a graph illustrating the relationship between
current and voltage for an n-type amorphous silicon carbide thin
film produced by the PS-CVD process;
[0041] FIG. 15 is an image from a scanning electron microscope of
an n-type amorphous silicon carbide thin film;
[0042] FIG. 16 is a spectrum of the photoluminescence of an n-type
amorphous silicon carbide thin;
[0043] FIG. 17 is an EPR spectrum of an n-type amorphous silicon
carbide thin;
[0044] FIG. 18 is an infrared spectrum of a p-type amorphous
silicon carbide thin film on a silicon single crystal wafer;
[0045] FIG. 19a is a graph illustrating the relationship between
the capacitance and voltage of a p-type amorphous silicon carbide
thin film on a silicon single crystal wafer;
[0046] FIG. 19b is a graph illustrating the relationship between
the carrier concentration and depth of a p-type amorphous silicon
carbide thin film on a silicon single crystal wafer;
[0047] FIG. 20 is a UV spectrum of a p-type amorphous silicon
carbide thin film on a silicon single crystal wafer;
[0048] FIG. 21 are .sup.29Si NMR spectra recorded at reaction
temperatures of 300.degree. C., 400.degree. C., 500.degree. C.,
600.degree. C., 700.degree. C., 800.degree. C., and 1100.degree. C.
for an amorphous silicon carbonitride thin film;
[0049] FIG. 22 is a contour plot illustrating the relationship
between the .sup.29Si NMR chemical shifts and reaction temperatures
of an amorphous silicon carbonitride thin film;
[0050] FIG. 23 is an infrared spectrum of an amorphous silicon
carbonitride thin film;
[0051] FIG. 24 is an infrared spectrum of an amorphous silicon
nitride thin film;
[0052] FIG. 25a are infrared spectra of the oxidation of SiON1 in
air for 10 minutes at 300, 550, 600, 700.degree. C.;
[0053] FIG. 25b are infrared spectra of the oxidation of SiON2 in
air at 500.degree. C. for 10, 20, 30, 42 and 52 minutes; and
[0054] FIG. 26 are infrared spectra of amorphous silicon oxycarbide
thin films (a), (b), and (c) annealed at 1100.degree. C. for 8, 16,
and 24 hours, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0055] The present invention is concerned with an innovative method
of forming volatile pyrolysis products from silicon-based polymeric
compounds or sources that are to be used as gaseous precursors to
thin films. This method is herein called Polymer Source Chemical
Vapor Deposition (PS-CVD). The thin films produced by the method
are durable, may be flexible due to their thinness, and may be used
for high-performance semiconductors. Consequently, the present
invention provides a thin film of an amorphous silicon-based
material on a substrate with improved physical characteristics and
properties.
[0056] The term "an amorphous silicon-based material" refers to
both an amorphous and a nanocrystalline silicon-based material. An
amorphous silicon-based material is the non-crystalline form of a
silicon-based material. A silicon-based material normally has a
silicon atom tetrahedrally bonded to four neighbouring atoms. This
is also the case in amorphous silicon-based materials, however,
they do not show long-range order of the tetrahedra in the
crystalline lattice as in crystalline silicon-based materials. In
addition, some silicon and/or carbon atoms may have dangling bonds,
which occur when they do not bond to four neighboring atoms. These
dangling bonds are defects in the continuous random network. A
nanocrystalline silicon-based material is similar to an amorphous
silicon-based material, in that it lacks long-range order (starting
even in the second coordination sphere), as is the case of an
amorphous phase. Where they differ, however, is that
nanocrystalline silicon-based materials have small grains of
crystallites of silicon-based materials ordered in the first
coordination sphere within the totally disordered amorphous phase.
This is in contrast to polycrystalline silicon-based material which
consists solely of crystalline silicon grains separated by grain
boundaries.
[0057] The film comprises a silicon-based material that may be, but
is not limited to, a silicon carbide, a silicon carbonitride, a
silicon nitride, a silicon oxycarbide, a silicon oxynitride, or a
silicon oxycarbonitride, in pure or doped forms. In an embodiment,
the film comprises a dopant/impurity such as N, B, O, H, Cl, Al,
Ga, In, Tl, P, As, Sb, O, S, Se, Te, or Bi.
[0058] The film may be deposited on commonly available substrates
as a completely to partially amorphous semiconductor, at a desired
micron-range thickness, onto a variety of commonly available and
resistant substrates of varying composition, degree of stiffness,
shape, density, or color over a small to an exceptionally large
surface. For example, the substrate may be regular ceramic material
of a complicated shape, quartz, electronic-grade sintered alumina,
polished alumina, silicon single crystal wafer, graphite, stainless
steel, polycrystalline semiconductor and other commonly available
and relatively inexpensive materials, as well as any of the above
materials coated with metals or alloys.
[0059] In an embodiment, the thin film of an amorphous
silicon-based material on a substrate has a carrier concentration
of 10.sup.13 to 10.sup.18 cm.sup.-3 in a depletion zone next to the
substrate, in a preferred embodiment the carrier concentration is
10.sup.13 to 10.sup.17 cm.sup.-3, and in a more preferred
embodiment the carrier concentration is 10.sup.13 to 10.sup.16
cm.sup.-3. The depletion zone is the zone where an electrical field
exists, sweeping the mobile charge carriers. In a further
embodiment the thin film of an amorphous silicon-based material on
a substrate has an electron mobility of 5 to 30
cm.sup.2V.sup.-1s.sup.-1, in a preferred embodiment the electron
mobility is 10 to 25 cm.sup.2V.sup.-1s.sup.-1, and in a more
preferred embodiment the electron mobility is 15 to 20
cm.sup.2V.sup.-1s.sup.-1. Carrier concentration and electron
mobility may be determined by Hall measurements as originally
described by van der Pauw (L. J. van der Pauw, Philips Res. Repts,
13, pp. 1-9, 1958 and L. J. van der Pauw, Philips Tech. Rev, 20,
pp. 220-224, 1958).
[0060] In an embodiment, the thin film of an amorphous
silicon-based material on a substrate has a dangling bond
concentration of 10.sup.12 to 10.sup.19 cm.sup.-3. By contrast,
prior art polycrystalline silicon-based thin films have a dangling
bond concentration of at least 1019 cm.sup.-3 (T. Christidis et
al., 2002, Applied Surface Science, 184, p. 268). A dangling bond
is a defect involving usually an unpaired electron, or an
"unsatisfied" bond. A dangling bond occurs when an atom is missing
a neighbour to which it would be able to bind. Such dangling bonds
are defects that disrupt the flow of electrons as the dangling
bonds may capture electrons. These defects usually segregate to
grain boundaries, crystalline defects, and couple to chemical and
structural impurities. The dangling bonds in the film may be
assigned and their density evaluated via electron paramagnetic
resonance (EPR) (T. Christidis et al., 2002).
[0061] In an embodiment, the thin film of an amorphous
silicon-based material on a substrate has no solvent-related
defects, for example voids in the thin film due to solvent
evaporation or alternatively solvent trapped in the thin film
during the deposition. Solvent-related defects do not occur in the
thin films produced by PS-CVD since no solvent is used as in
traditional deposition methods. Although a unique defect that may
arise in a thin film produced by the PS-CVD process is the
accidental incorporation of a polymer chain.
[0062] In an embodiment the thin film of an amorphous silicon-based
material on a substrate has a residual hydrogen concentration of 0
to 25 atomic %, in a preferred embodiment the residual hydrogen
concentration is 0 to 20%, and in a more preferred embodiment the
residual hydrogen concentration is 0 to 15 atomic %. "Residual
hydrogen" arises due to the nature of the starting materials used
for preparation of the thin films. For example, if polyethylsilane,
(SiC.sub.2H.sub.6).sub.n were used as a polymeric source to produce
a thin film of a-SiC, 50% of the carbon and 100% of the hydrogen
must be removed from the polymeric source to obtain a
stoichiometric product. However, formation of the thin film is not
always stoichiometric, typically resulting in removal of between
50-100% of the carbon and 60-100% of the hydrogen. Anything other
than stoichiometric removal of hydrogen will result in "residual
hydrogen".
[0063] The grain size of the thin films described herein may be 2
to 10 nm. In an embodiment, the grain size of "green" or as
deposited thin film is 2-3 nm, and may be increased to 4-6 nm after
annealing.
[0064] The thin films described herein were prepared by the PS-CVD
process. FIG. 1A illustrates an apparatus used for the PS-CVD
process while FIG. 1B depicts the temperature profile used within
the apparatus. Referring to FIG. 1A, there is a quartz reactor (2),
into which one or several polymer derived precursors (19), enter
through a gas inlet (1). The quartz reactor (2) is also referred to
as the furnace or the PS-CVD reactor. Furthermore, a gaseous
atmosphere (60), either inert or active, also enters through the
gas inlet (1). The inert atmosphere may include argon, nitrogen or
other inert gases while the active atmosphere may include gases
such as ammonia, carbon monoxide or similar gases. Before operation
the reactor (2) is purged with a selected atmosphere (60).
[0065] The gas inlet (1) has a high-vacuum seal to minimize the
ingress of oxygen impurities from the surrounding air drawn into
the reactor (2). The total pressure in the reactor is measured with
a pressure controller (3) that also controls the flowrate into the
reactor (2). The outside of the reactor is heated with electric
heating elements (4), which surround the reactor (2) to produce a
temperature gradient as illustrated in FIG. 1B. There are
additional heating elements (4) near the inlet of the reactor (2),
while there are fewer surrounding the deposition area of the
reactor. The PID (Proportional-Integral-Derivative) temperature
controller (5) ensures that the temperature within the reactor (2)
is in the appropriate range for the polymer-derived precursor (19)
used, the type of gaseous atmosphere (60) and substrate (6) to be
coated. The substrate (6) is placed in the deposition area of the
reactor (2). Typically the substrate (6), is a piece or part made
of silicon, quartz, metal, ceramics, or other materials described
herein. The gas phase near the gas outlet (9), of the reactor (2),
is analyzed by a FT-IR spectrometer (7). The FT-IR spectrometer (7)
allows the in situ verification of the deposition process and the
presence of oxygen impurities. A silicon-based film (8) is
deposited on the substrate (6) through the pyrolysis of the silicon
based polymeric sources and their chemical rearrangement. The
deposited film can be a single or multiple layered film.
[0066] Referring to FIG. 2, there is represented a cross-sectional
view of a FT-IR cell based on a silicon single crystal wafer (68),
which is designed for the monitoring of a film (8) deposited on the
substrate (6) by the PS-CVD process. The substrate (6) with a
coating (8) is held in place, the thickness of the deposited layer
has been exaggerated so that the upper half and lower half of the
FT-IR cell actually sit one on top of the other and are sealed by
the represented O-ring (67). There is a protective gas swept
through the FT-IR cell from an inlet (64) to an outlet (65), which
maintains the appropriate inert atmosphere. The IR beam (61) is
projected onto the substrate and it is bent and reflected through
the deposited film (8), and the collected through a microscope
objective (62) and detected by a MCT (mercury-cadmium-tellurium,
Hg--Cd--Te) detector (63). The FT-IR cell is mounted on an
adjustable 2D micrometric stand (66) which allows the FT-IR to be
adjusted appropriately with respect to the IR beam (61).
[0067] Referring to FIG. 3, the in situ FT-IR spectrum analysis of
a gaseous precursor at the outlet (9) of the reactor (2) shows the
numerous peaks that correspond to the SiH bonds formed when
chemical change in the structure of the solid polymeric source
produces a polymer derived precursor (19). The increasing
temperature near the inlet of the reactor (2) breaks down the
polymeric source into various subunits to produce the gaseous
precursor (19).
[0068] The PS-CVD process distinguishes itself from other forms of
chemical vapor deposition because the synthesis is based on
high-density gaseous precursors (for example, MW higher than 298
amu, from TGA-MS experiments) allowing high mass transport to the
substrate.
[0069] The PS-CVD process distinguishes itself from other forms of
chemical vapor deposition since the synthesis is based on polymeric
gaseous precursors that produce in situ reactive networking
functionalities (Si--H bonds, as captured in the FT-IR analysis of
the trapped gas phase precursor).
[0070] The PS-CVD process distinguishes itself from other forms of
chemical vapor deposition since the Si--H networking
functionalities required for the SiC-synthesis are 3-6 times more
productive than in regular CVD procedures due to the high-mass of
the individual networking precursors thereby resulting in high
deposition rates.
[0071] The PS-CVD process distinguishes itself from other forms of
chemical vapor deposition since the networking functionalities do
not require the intermediate production of dangling bonds, a
process replaced by a thermodynamically-driven redistribution of
pre-existent Si--C bonds in the polymeric-source and in the in situ
formed gaseous precursor. This process may result in a lower
concentration of residual dangling bonds in the material.
[0072] The PS-CVD process further distinguishes itself from other
forms of chemical vapor deposition because it does not require the
following more sophiscated driving forces:
[0073] a) ion implantation, ion beam enhanced deposition, reactive
ion beam sputtering and plasma enhanced chemical vapor deposition
(PECVD);
[0074] b) RF power as described in "High temperature annealing of
hydrogenated amorphous silicon carbide thin films" INS 01-17
6910830 A2001-11-6855-060 (PHA) NDN-174-0691-0829-5 Yihua Wang;
Jianyi Lin; Cheng Hon Alfred Huan; Zhe Chuan Feng; Soo Jin
Chua;
[0075] c) IR and UV laser photolysis as described in "Laser
gas-phase photolysis of organosilicon compounds: approach to
formation of hydrogenated Si/C, Si/C/F, Si/C/O and Si/O phases" INS
00-50 6791677 A2001-03-8250F-001 (PHA) NDN-174-0679-1676-1 Pola,
J., Proceedings of the Indian National Science Academy, Part A
(Physical Sciences); and
[0076] d) electron cyclotron resonance as described in "Application
of electron cyclotron resonance chemical vapor deposition in the
preparation of hydrogenated SiC films. A comparison of phosphorus
and boron doping" INS 98-04 5814339 A98058115H-021 (PHA);
B9803-0520F-017 (EEA) NDN-174-0581-4338-2, S. F. Yoon and R.
Ji.
[0077] Referring to FIG. 1B, the temperature profile within and
along the length of the reactor (2) is represented. The input zone
(10) shows a constant lower temperature associated with the gas
inlet (1). In the heating zone (11), there is an increase in the
temperature due to the large amount of heating elements (4) at the
inlet. In the heating zone (11), the rearrangement of the
silicon-based polymeric sources occurs which leads to the formation
of the poly(carbosilane) species. The next temperature is that of
the pyrolysis zone (12), where there is direct precursor formation
and doping occurring. This is followed by a reduction in the number
of heating elements (4) in the deposition zone (13) which
consequently cools the particularly zone of the reactor (2) thus
lowering the temperature. The deposition zone (13) is represented
by a constant temperature wherein the silicon-based film is being
deposited on the substrate (6). Finally, there is the gas exit zone
(14), where the temperature falls at the gas outlet (9) of the
reactor (2) and approaches that of the ambient temperature outside
the reactor (2). The temperature in the reactor varies between
100.degree. C. and 1000.degree. C. depending on the stage and the
specific local requirements of the process steps in the
aforementioned reactions. The gaseous species are monitored by
FT-IR spectroscopy (7) of samples extracted near the reactor outlet
(9). The amorphous silicon-based thin films may also be
characterized by IR spectroscopy while the concentration of
adventitious oxygen in the thin film can be measured by using a
Czochralski silicon window as a standard (Scarlete, M., J.
Electrochem. Soc., 1992, 139(4), p. 1207).
[0078] The PS-CVD design allows the use of a broad series of
polymeric precursors for use in the synthesis of silicon-based thin
films including, but not limited to, oxides, nitrides, carbides and
variously weighted combinations in homogeneous phases or
multi-layered structures. The resulting films are of considerable
interest as electronic and optoelectronic materials as well as for
protective coatings. A large variety of appropriate silicon-based
polymeric sources that do not present Kumada-type rearrangements,
but can be cracked, vaporized directly or via an intermediate
liquid phase, or chemically transformed in gaseous species in the
reactor, may be used, such as polysilanes, polycarbosilanes,
polycarbosilazanes, polysiloxanes and polysiloxazanes. Other
appropriate polymeric sources may be used, such as carbon nitride
polymeric sources and boron nitride polymeric sources. Possible
carbon nitride polymeric sources (CxNy) may be, for example,
polyepoxy-, polyamides, polyamines, polyimides, polyureas and
polyurethanes. It is noted that polyamides, polyamines, polyimides
and polyureas may be used in mixtures with other polymeric sources
and as a possible source of nitrogen in the reaction. Polymers
sources with other backbones are envisaged, comprising: Al, B, Ge,
Ga, P, As, N, In, Sb, S, Se, Te, In and Sb.
[0079] In the PS-CVD process, gaseous precursors from polymeric
sources are to be produced first directly from the solid phase via
sublimation, or via an intermediate liquid phase subsequently
subjected to vaporization, contrary to the classical polymeric
route. A definite advantage of this process is a purification that
involves the polymer source during the sublimation process. The
purification reduces the effect of adventitious oxidation on the
initial solid polymeric source by the decreased capacity of
oxidized backbones to produce volatile material (e.g., at the
limit, a high degree of oxidation produces SiO.sub.2 with
negligible volatility). The oxidized material is therefore
concentrated in the solid residue, while the precursors reaching
the substrate are purified this way. This purification helps to
produce films that have very few chemical impurities and
consequently fewer surface and bulk defects.
[0080] The tolerance of the polymeric source to cracking, thermal
pyrolysis, and/or depolymerization processes is related directly to
silicon-carbon, silicon-nitrogen and silicon-oxygen relative bond
stability under given thermal and pyrolysis conditions. The PS-CVD
process was tested by subjecting the above-mentioned silicon-based
polymers to various thermal budgets controlling the
depolymerization conditions, for example, thermal cracking,
chemical decomposition and polymeric disproportionation).
[0081] PS-CVD further allows the polymeric source to self-adjust to
the temperature field because each polymeric source will develop a
set of gaseous precursors adapted to the particular thermal
conditions (various gradients and temperature-cycles produce
different gaseous precursors, thermodynamically stable under the
specific conditions). This self adjustment is different for
different polymeric sources. The objective of the PS-CVD process is
to create at the outset, in the gas phase, the majority of the
required bonds that will constitute the solid silicon-based film.
Consequently, the role of the chemical reactions occurring on the
substrate is limited to the completion of the remaining small
number of bonds required for the silicon-based structure. This
technique facilitates a high rate of mass transfer during
desublimation of the large precursor molecules, thereby increasing
the growth rate of silicon-based material on the substrate. This
technique permits much lower operating temperature during growth of
the silicon-based thin film than standard industrial practices. For
this reason the nature of the substrate is less important, in terms
of thermal stability, size or shape. A large number of the SiC,
SiO, or SiN bonds pre-exist in the polymeric precursor.
Furthermore, the gaseous precursor is deposited in chemical chains,
similar to physical chains, that then rearrange and bind to one
another. The bond formed between the precursor and the substrate is
a van der Waals physical bond. Consequently, the lower operating
temperature provides an environment for lowering the amount of
unintentional impurities in the deposited film. Desublimation is
herein defined as a change of phase from a gaseous species directly
to a solid species.
[0082] An example of a chemical reaction in the PS-CVD process is
represented in FIG. 4. The first reaction of the deposition
involves significantly higher a-SiC deposition rates compared to
traditional CVD methods because of chemically-synchronized Si--C
bond redistribution in organo-polysilanes. Still referring to FIG.
4, in the first chemical reaction (15), a thermally activated
methylene insertion into silicon-silicon bonds takes place to
produce poly(carbosilane) precursor. This intramolecular reaction,
known as the Kumada rearrangement, (Shiina, K.; Kumada, M., 1958,
J. Org. Chem., 23, p. 139), provides the structural framework of
silicon carbide, (Scarlete, M.; Brienne, S.; Butter, S. S. and
Harrod, J. F., 1994, Chem. Mater., 6, p. 977). By simply heating
the polymer precursor, a very large number of Si--C bonds are
appropriately redistributed at a very fast rate.
[0083] The second reaction (16) also represented in FIG. 4 leads to
the introduction of nitrogen atoms as donor impurities into the
silicon carbon precursors. The formation of the aminocarbosilane
precursor in reaction (16), occurs via a reaction with ammonia,
found either in the atmosphere or in the polymer derived
source.
[0084] While still referring to FIG. 4, the third reaction (17)
results in high molecular weight species through the formation of
secondary amine species, leading to increased desublimation
capacity. The formation of the secondary amine species is via the
Si--H/N--H dehydrogenation.
[0085] The fourth reaction (18) governs the formation of the film
derived from the third reaction (17) onto the substrate (6). This
example illustrates the formation of high molecular mass ternary
amine species by transamination, the amine species being direct
precursors are deposited via desublimation to yield an n-type a-SiC
film on the substrate.
[0086] FIG. 5 shows various types of substrates that may be coated,
with a-SiC film deposited by the PS-CVD process, as well as, their
nature and complexity. The a-SiC thin film can be deposited on a
regular ceramic material of a complicated shape, quartz,
electronic-grade sintered alumina, polished alumina, silicon single
crystal wafer, graphite, and other commonly available and
relatively inexpensive materials. As seen in FIG. 5, several of the
materials have been coated on one side (the dark surface) by the
PS-CVD process while the other side was masked during deposition. A
pale surface remained after mask removal. Therefore, the PS-CVD
process is also compatible with conventional techniques such as
masking understood by those skilled in the art.
[0087] The PS-CVD process of the present invention further
distinguishes itself from other forms of CVD because it does not
require solvent to dissolve the precursor, the evaporation of these
solvents in other CVD methods produces defects on the surface of
the coating they produce, this is one reason why the PS-CVD process
produces films with fewer and essentially no surface defects.
[0088] This invention incorporates the theoretical concept of
"anticeramic yield" of the gaseous precursors. The traditional
method for producing silicon-based materials from polymeric sources
is through rearrangement of the solid residue left after pyrolysis
of the precursor sources, with a typical ceramic yield amounting to
80% solid (F. Cao et al., 2001, Korean Journal of Chemical
Engineering, 18, p. 761). Recent efforts relating to traditional
methods are directed towards maximization of the amount of polymer
remaining as a solid, thereby increasing the yield to higher
values. The theory applying to the PS-CVD process generally
involves the opposite: to maximize the fraction of polymer that is
vaporized for the formation of the desired new gaseous precursor
leading to the deposit of an amorphous silicon-based material. As
such, almost the entire polymer source is vaporized with the net
result that the ceramic yield is almost nil while the polymer
transforms itself into a new gaseous source resulting in almost
100% anticeramic yield. For example, this phenomenon is illustrated
by the TGA of a polymeric source subjected to the PS-CVD process,
shown in FIG. 6.
[0089] Generally, the PS-CVD process according to the present
invention:
[0090] 1) allows for the hydrogenation, heat treatment and makes
full use of many different types of gaseous reactants such as,
B.sub.2H.sub.6, NH.sub.3, PH.sub.3, AsH.sub.3, BCl.sub.3,
B.sub.2Cl.sub.6, NCl.sub.3, PCl.sub.3, AsCl.sub.3, CO, O.sub.2,
O.sub.3, CO, CO.sub.2, as well as H.sub.2 or D.sub.2, pure or inert
carried gases such as Ar or N.sub.2, or similar mixtures, with the
inert gases varying from 0.1 to 99.0% in volume;
[0091] 2) may accommodate a wide variety of heat sources and
treatment lengths for the polymeric precursors or for the deposited
film under the gaseous atmospheres, for as little as 1 second and
up to, but not limited to, tens of hours, and leading to a wide
variety of passivating, semiconductor, and dielectric thin film
materials;
[0092] 3) allows secondary annealing under BH.sub.3,
B.sub.2H.sub.6, NH.sub.3, PH.sub.3, AsH.sub.3, BCl.sub.3,
B.sub.2Cl.sub.6, NCl.sub.3, PCl.sub.3, AsCl.sub.3, CO, O.sub.2,
O.sub.3, CO, CO.sub.2 or H.sub.2 gases for several seconds, thereby
increasing the crystallinity and/or the degree of reticulation of
the deposited film;
[0093] 4) may make use of standard heating methods as well
electronic beams, X-rays, UV and IR radiation microwave power,
laser beams and other energy transfer mechanisms to produce objects
and substrates in flat, or tubular or complex shapes including, but
not restricted to, rods, cylinders, spheres, and ceramic boats;
and
[0094] 5) produces substrates with varying conductor, semiconductor
or dielectric properties, including, but not restricted to
polycrystalline or amorphous silicon; quartz; graphite; metals;
electronic-grade or refractive ceramic materials, such as alumina
or sintered oxides, nitrides, phosphides; as well as
A.sub.2B.sub.6, A.sub.3B.sub.5, ternary and quaternary compounds in
this class.
[0095] The thin films described herein may be used as active,
passivation, dielectric or protective coatings for semiconductor
discrete or integrated devices, or implantable materials.
[0096] The thin film possesses highly desirable electronic,
optoelectronic and photonic properties that make it highly suitable
for standard, cost-effective fabrication of a variety of electronic
and optoelectronic devices, including photovoltaic cells. The
amorphous silicon-based thin film may an n-type and/or p-type mono
or heterojunction with a donor concentration of 10.sup.13 to
10.sup.18 cm.sup.-3.
[0097] By means of p-n homo- or heterojunctions and using a variety
of flexible or rigid substrates, it is possible to fabricate solar
cells, light-emitting diodes, transistors, photothyristors, and
similar devices. Using high breakdown electrical field and high
electron saturation velocity, it is further possible to produce
high frequency, high power and high temperature electronic and
optoelectronic devices. By combining optical and electronic
properties, the materials may also serve to fabricate integrated
monolithic devices on a single chip.
[0098] Referring to FIG. 7, there is represented a simple Schottky
solar cell. The cell comprises one layer only of an amorphous
silicon-based material (22), a metallic substrate (20) acting as
anode (when layer (22) is n-type) or cathode (when layer (22) is
p-type). The suitable metal is an inexpensive conductive material
and its thickness or uniformity of thickness is not critical (viz.
aluminum foil). The ohmic contact layer (21) deposited by physical
evaporation or other physico-chemical means provides effective
contact with the overlying semiconductor layer as well as the
underlying metallic substrate. The substrate may consist of
aluminum or similar conductor (200 nm) if n-type, or
aluminum/nickel (100 nm/100 nm) if p-type; the surface of which
must be cleaned by chemical etching or mechanical means to avoid
oxidation with respect to layer (22). Alternatively, layers (20)
and (21) could be made or fabricated as one composite layer over
which layer (22) could be deposited. The semiconductor layer of an
amorphous silicon-based material of n- or p-type (22) with free
carrier density between 10.sup.13 and 10.sup.18 cm.sup.-3 and 0.2
to 1 .mu.m thickness, produced by the PS-CVD process, acts as the
heart of the cell. The top layer may be gold (Au) layer (23) of 5
to 10 nm thickness acting as cathode if the semiconductor is n-type
or as anode if it is p-type. The gold deposited mechanically or
chemically onto n-type semiconductor. The gold layer is
sufficiently thin as to allow light to reach the semiconductor.
[0099] FIG. 8 is a p-n junction barrier photovoltaic cell based on
an amorphous silicon-based thin film with multiple layers produced
by the process of the invention. In this photovoltaic cell, a
metallic substrate is acting as an anode (24). Layer (25) is a
metallized (aluminum) ohmic contact layer (.about.100 nm). These
layers are followed by an n-type amorphous silicon-based thin film
(.about.750 nm) layer (26), p-type amorphous silicon-based thin
film (.about.250 nm) layer (27), a nickel ohmic layer (28) and an
aluminum top contact layer (29) serving as cathode which covers
approximately 10 percent of illuminated surface.
[0100] FIG. 9 represents a stacked p-n junction solar cell, the
multiple layers produced by the method of the invention. The layers
of FIG. 9 (with reference numbers followed by the layer
thicknesses, listed from bottom to top) are: (30) metallic
substrate acting as cathode; (31) aluminum-nickel ohmic contact
layer (.about.100 nm/.about.100 nm); (32) p-type a-Ge layer
(.about.200 nm); (33) n-type a-Ge layer (.about.200 nm); (34)
p-type a-Si (.about.200 nm); (35) n-type a-Si (.about.200 nm); (36)
p-type amorphous silicon-based thin film (.about.200 nm); (37)
n-type amorphous silicon-based thin film (.about.200 nm); and (38)
top aluminum anode contact, covering about 10 percent of the
surface.
[0101] In any semiconductor junction, such as in a Schottky
junction shown FIG. 10B or a p-n junction such as shown in FIG.
11B, there is an internal electrical field, E.sub.bi, called
"built-in electrical field", that prevents the charge carriers
(electrons and holes) to stay in the a region of the material
called the "depleted zone." If the depletion region of thickness W,
is illuminated by photons with energies greater than
(E.sub.c-E.sub.v), the region develops pairs of "electron-hole"
which are separated by the internal electrical field. The electrons
are attracted towards the semiconductor while holes are directed
towards the metal, creating a photocurrent when the device is
connected to an external load. The structure is called a
photovoltaic cell or solar cell.
[0102] The current generated in an amorphous semiconductor is
mainly due to a drift component because the diffusion component is
not significant due to low mobilities of the charge carriers. In
order to collect efficiently the photon energies in an amorphous
semiconductor junction, the depleted region width must be as large
as possible. The depleted zone width, W, is given by:
W=(.epsilon.V.sub.bi/qN.sub.D).sup.1/2
[0103] where .epsilon. is the dielectric constant of the
semiconductor, q is the electron charge, N.sub.D is the electron
concentration, and V.sub.bi is the built-in voltage given by:
V.sub.bi=(.PHI..sub.B-(E.sub.C-E.sub.F)
[0104] The width of the depletion region can be increased by
lowering the free carrier concentration of the material.
[0105] If a p-n junction (FIG. 11) is used instead of a Schottky
one, the depletion region width can be increased (in this case,
each type of material has its own depleted zone), therefore
increasing the efficiency of the photovoltaic cell.
[0106] In the Schottky structure (FIG. 8), the energy band diagram
is shown in FIG. 10B before the intimate contact between the metal
and the semiconductor. The work function, .PHI..sub.s (41m) is the
energy difference between the vacuum level (39) and the Fermi
level, EF (40). The vacuum level (39) is the zone where the
electron is free from the semiconductor atoms and has no kinetic
energy. In elemental solids such as a metal, represented in FIG.
10A, the values of the work function .PHI.m (41m) are well
established, (see for example Weast, R. C. (1990), CRC Handbook of
Chemistry and Physics, 70th Edition, CRC Press, E-93).
[0107] FIG. 10A illustrates the work function of a semiconductor
(41s) normally denoted by .PHI..sub.S. The energy difference
between the vacuum level (39) and the bottom of the conduction band
(42), denoting electron affinity (.chi.), is used as reference
since the Fermi level depends on the carrier concentration in the
semiconductor. However, .PHI..sub.s still represents the energy
required to remove an electron from the semiconductor. Referring to
FIG. 11 and 10B, the conduction level (42) E.sub.c, the valence
level (43) E.sub.v; the affinity (44) .chi.; the work function (45)
.PHI..sub.s; and the energy gap (46) E.sub.G are of the
semiconductor layer (22).
[0108] The Fermi level represents the energy for which the
probability to find a free electron in equilibrium and near zero
Kelvin equals 0.5. The probability of finding an electron at a
given energy level is obtained according to the Fermi-Dirac
function:
F(E)=1.div.[1+exp(E-E.sub.F)/kT]
[0109] The Fermi level in a semiconductor depends on the free
carrier concentration, and it is closer to the conduction band than
the valence band in n-type semiconductor. Assuming that
(.PHI..sub.m>.PHI..sub.s, and that the metal-semiconductor
system at equilibrium of FIG. 11A, the Fermi level is at the same
both in the metal and the semiconductor. Therefore, an internally
built-in electric field (E.sub.bi) develops between the metal and
the semiconductor. The field is oriented from the positive charges
to the negative charges, that is, towards the metal. The resulting
built-in voltage is equal to [(.PHI.m-.PHI.s)/q]. A depletion
layer, of thickness W (53b), is formed where there are no free
charges. The potential energy barrier for electrons moving from the
metal to the semi-conduction is known as the Schottky barrier
height, .PHI..sub.B, and is given by:
(.PHI..sub.B=(.PHI..sub.m-.chi.). Under reverse bias or zero bias
electrical conditions, there is no net current flowing through the
metal-semiconductor junction.
[0110] For photon energies greater than E.sub.G, the electron-hole
pairs are generated in the depleted zone.
[0111] In the p-n structure of FIG. 11B, where the p-type amorphous
silicon-based thin film (47) and the n-type amorphous silicon-based
thin film (48) are represented. The principal electronic phenomena
takes place in the depleted zones (52) and (53). In this case, the
built-in voltage V.sub.bi depends on the carrier concentration in
the semiconductor:
V.sub.bi=(kT/q)Ln(N.sub.AN.sub.D/n.sub.i.sup.2)
[0112] where k is the Boltzmann constant, T the temperature,
N.sub.A the hole concentration and n.sub.i the intrinsic carrier
concentration.
[0113] The depletion region widths are given by:
W.sub.n=(.epsilon.V.sub.bi/qN.sub.D).sup.1/2
W.sub.p=(.epsilon.V.sub.bi/qN.sub.A).sup.1/2
[0114] With the conduction level (49) E.sub.c, the Fermi Level (50)
E.sub.F and the valence level (51) also represented in FIG.
11B.
EXAMPLES
[0115] The following examples are provided to illustrate the
invention. It will be understood, however, that the specific
details given in each example have been selected for the purpose of
illustration and are not to be construed as limiting in scope of
the invention.
Example 1
Synthesis of an n-Type Amorphous Silicon Carbide (N-Doped) Thin
Film Via the PS-CVD Process
[0116] Synthesis--Charges of polydimethylsilane and in-house
prepared polymethylsilane (M. Scarlete et al., 1995, Chem. Mater.,
6, p. 1214) have been pyrolyzed in a single-zone Lindberg ceramic
furnace. The synthesis was performed in a 2" quartz tube attached
to a silicone-based hydraulic lock bubbler and to a vacuum line
capable of providing a reduced pressure of 5*10.sup.-2 torr. The
synthesis was performed in a gaseous atmosphere of UHP--Ar or in
home purified NH.sub.3. The purification of NH.sub.3 was obtained
via passing the gas through a 1000 mm column of KOH and a 250 mm
column of a mixture of 3 and 4 .ANG. molecular sieves. The furnace
was operated via a PID Eurotherm temperature-controller proving
.+-.0.5.degree. C. in the range of 110 to 1100.degree. C. at 10
torr above the atmospheric pressure. The atmosphere of the
pyrolysis was carefully purified from oxygen and water vapours via
a series of evacuations/Ar-fillings. The temperature cycle during
the pyrolysis was the following:
[0117] a) a temperature slope of 4.degree. C./min in the 110 to
450.degree. C., in order to allow silane-carbosilane transformation
via Kumada rearrangement (Shiina, K. and Kumada, M., J. Org. Chem.,
1958, 23, p. 139);
[0118] b) a 20 min carbosilane annealing at 450.degree. C.;
[0119] c) a temperature slope of 10.degree. C./min in the range of
450 to 1050.degree. C. to allow nitridation and cracking of the
polymer via reaction with the NH.sub.3-enriched inert gas; and
[0120] d) a 30 min annealing at 1050.degree. C.
[0121] The process can be configured in a single-zone furnace,
using the temperature cycle above, or in a three-zone furnace.
[0122] Various substrates have been placed downstream of the gas
flow in a cooler region of the furnace, in order to collect the
desublimation products of the gaseous species produced during the
pyrolysis. Among the substrates used were 1-10 .OMEGA.cm, type P(B)
[100] silicon single crystal wafers, electronic-grade alumina
ceramic, quartz and steel plates. The native oxide from the silicon
substrate was removed by etching in an acidic 10:3:1
DI-H.sub.2O:CH.sub.3COOH:HF solution for 15-30 sec, then dried in
acetone in an ultrasound bath for 0.5-2 minutes prior to
introduction in the pyrolysis furnace. The acetone sonication step
was used to prepare all substrates. All manipulations prior to
pyrolysis were conducted under continuous inert gas flow.
[0123] Characterization--The a-SiC film has been characterized by
FT-IR spectroscopy having a peak at approximately 800 cm.sup.-1
with the FWHH around 150 cm.sup.-1 in the green or as deposited
material. Subsequent to annealing, the FWHH decreases to 100
cm.sup.-1.
[0124] An elastic recoil detection (ERD) study was performed to
reveal that the thin film had a C/Si ratio of 1-1.4, a residual
hydrogen concentration of 0 to 15%, and a residual oxygen
concentration of 0 to 15% (FIG. 12).
[0125] Film Properties--The carrier concentration in an n-type
semiconductor of an amorphous silicon carbide thin film was
measured by the capacitance-voltage (CV) method (Schroder. D. K.,
1990, Semiconductor Materials and Device Characterization, Wiley
Interscience, p. 41) using a Schumberger* impedance analyzer
Solartron* 3200. The voltage was varied between -6 and 0 V and the
resulting capacitance was observed to increase with increasing
voltages. On a sample film, six Schottky diodes were fabricated
using mercury as anode metal. The mercury probe used provided a
diode area of 0.453 mm.sup.2. The capacitance is given by:
C=.epsilon.A/w
[0126] where A is the diode area. In the presence of an applied
voltage V, the depletion region width is given by:
W=((.epsilon.(V.sub.bi-V))/qN.sub.D).sup.1/2
[0127] The derived value for N.sub.D (electron concentration) in
the diode was 9.times.10.sup.17.+-.0.2.times.10.sup.17 cm.sup.3.
*Trademark
[0128] The electron mobility was measured using the Van der Pauw
method (Van der Pauw, L. J., 1958, Phil. Tech. Rev., 20, p. 220).
The measured mobility was defined as a Hall mobility since the
technique is based on the Hall effect. The measurements were
carried out with a current of 1 mA and a magnetic field of 5 kG.
The correction factor f derived was 0.67, the derived resistivity
was 22.32 .OMEGA.cm.sup.-1, the derived mobility was 4.48
cm.sup.2V.sup.-1s.sup.-1, and the carrier concentration was
6.25.times.10.sup.16 cm.sup.-3.
[0129] Referring to FIG. 13, the carrier properties of an n-type
amorphous silicon carbide thin film produced by the PS-CVD process
are represented. The graph represents the donor concentration, n
(cm.sup.-3) versus the width of the depletion zone, W (.mu.m). We
observed that the sample tested has a low donor concentration,
which can be below 10.sup.13 but range to 10.sup.15 cm.sup.-3. A
preferred range is that less than 10.sup.14 cm.sup.-3. These low
donor level values were before any doping. The width of the
depletion zone (W) which is measured in (.mu.m) is a function of
the material connected at the junction, in the case of FIG. 11,
that of an n-type film with the substrate. W must not be confused
with the film thickness. Thicker films (above 20 .mu.m) were
required for the method of detection used to quantify the carrier
concentration in the depletion zone and the thin films obtained by
this method (100 .ANG. to 0.1 .mu.m) have the same type of curve as
found in FIG. 6 at the far lower thicknesses.
[0130] FIG. 14 represents the semiconductor properties of an n-SiC
PS-CVD film which is a qualitative indication of the quality of the
film, indicated by the curve of current versus voltage.
[0131] An image from scanning electron microscopy (FIG. 15)
indicates that the thin film had a thickness of 73 nm, and a
deposition rate of 25 nm/min.
[0132] The excitation of the n-type a-SiC with photons at 3.25 eV
induced photoluminescence of the material at room temperature (FIG.
16). The maximum is located in the blue region, with a tail
extending to the red region practically covering the whole visible
spectrum.
[0133] An EPR spectrum of dangling bonds and other paramagnetic
centers of the thin film is presented in FIG. 17. The noisy
spectrum qualitatively indicated a somewhat low dangling bond
concentration.
Example 2
Synthesis of a p-Type Amorphous Silicon Carbide (B-Doped) Thin Film
Via the PS-CVD Process
[0134] Synthesis--Charges of poly(dimethylsilane) (PDMS) were
pyrolyzed in a Lindberg* BlueM single-zone furnace. The furnace was
operated via a PID Eurotherm temperature-controller providing an
accuracy of .+-.0.5.degree. C. in the ranger of 110 to 1100.degree.
C. The furnace was equipped with a 2.5" quartz tube attached to a
silicone-based hydraulic lock bubbler and a vacuum line capable of
providing 5*10.sup.-2 torr vacuum as measured with a Welch
Pirani-gauge. The atmosphere prior to pyrolysis was carefully
purged of moisture and oxygen via a series of evacuations and
UHP-Ar fillings. The residual oxygen level obtained after the
purging procedure was measured using an Innovative Technology gauge
and was found to be below 1 ppm. Once purged, a partial pressure of
BCl.sub.3 was created in the reactor. *Trademark
[0135] The substrates used were p-type (B doped) (100) oriented
single crystal silicon substrates, electronic grade quartz
substrates, and Ni coated (200 nm) quartz substrates. The latter
permits bulk resistivity measurements since Ni forms an ohmic
contact on an amorphous silicon carbide semiconductor layer. Native
oxide on the silicon substrate was removed by etching in an acidic
10:3:1H.sub.2O/CH.sub.3COOH/HF solution for 15-30 sec, then dried
in acetone, in a ultrasound bath for 15 minutes prior to
introduction into the pyrolysis furnace. The quartz substrates were
cleaned in the acetone sonication bath for 15 min.
[0136] Characterization--Vibrational spectroscopy has been used to
analyze the layer deposited on Czochralski-silicon single crystal
wafer. The IR absorption of the deposited film at 803 cm.sup.-1 in
FIG. 18 is characteristic of silicon carbide. XRD showed no signal
associated to crystalline material, therefore the obtained film
contained amorphous silicon carbide. Adventitious oxygen
incorporation in the film was readily observed in the IR spectrum
of the film due to the strong absorptivity of the
.nu..sub.as(Si--O). The oxygen content of the film was calculated
as being in the range of 4.times.10.sup.17-10.sup.18 cm.sup.-3 by
the external reference method (ASTM F-118 procedure).
[0137] Film properties--Hall measurements were performed on quartz
substrates that were previously covered with 200 nm of high purity
Ni via vapor deposition. The type of conductivity and the
concentration of charge carriers was determined by measurement of
the CV profiles (FIGS. 19a and 19b) of the layers. Quartz
substrates were used for metal-deposition via vaporization, then
the metalized substrate was used for the PS-CVD deposition of
a-SiC(B). A Schottky contact was formed on the a-SiC(B) layer by a
mercury probe having an area of 0.453 mm.sup.2. A Schlumberger*
S1260 impedance analyzer was used to measured the capacitance with
an applied sinusoidal voltage having an amplitude of 15 mV and a
frequency of 1 MHz. The concentration of charge carriers was
determined to be 2*10.sup.17 cm.sup.-3. *Trademark
[0138] The UV spectrum (FIG. 20) was measured on a Hewlet Packard
HP8452 UV/Vis spectrophotometer and the optical band gap was
calculated from the obtained spectra assuming that strong optical
absorption marks the energy level of band to band transitions. The
.lambda..sub.max is located around 270 nm and the optical bandgap
of the sample was calculated to be 2.82 eV using the intercept of
the line corresponding to high absorption rate with the x axis.
[0139] Other generic properties of the p-type amorphous silicon
thin film have not yet been measured, but they are expected to be
similar to those of the n-type amorphous silicon thin film since
the boron concentration is low.
Example 3
Synthesis of an Amorphous Silicon Carbonitride Thin Film Via the
PS-CVD Process
[0140] Synthesis--In-house prepared polymethylsilane and
poly(dimethyl)silane were pyrolyzed under NH.sub.3. The
nitrogen-containing amorphous layers were deposited on
electronic-grade substrates such as silicon single crystal wafers,
quartz, and alumina. The pyrolyses were conducted at 5-20 torr
above the atmospheric pressure and were undertaken in a Lindberg
single-zone, programmable furnace equipped with a Eurotherm PID
temperature controller with a maximum temperature of
1100.+-.0.5.degree. C. The temperature cycle during the PS-CVD
process was the following: 4.degree./min 110-450.degree. C., 30 min
at 450.degree. C., 4-8.degree. C./min up to 1050.degree. C., and 30
min at 1050.degree. C. (batch process).
[0141] Characterization--Prior to analysis of the film, the
products of the chemical reactions involving the
carbon-for-nitrogen exchange were followed in the ceramic residue
of the polymer. There was continuous C/N replacement activated by a
critical temperature necessary for the displacement level. CP-MAS
NMR analysis (FIG. 21) indicated a large, continuous transformation
of the polymer into silicon carbonitride and eventually into
silicon nitride. Table 1 and FIG. 22 quantify the results of the
NMR studies.
1TABLE 1 SiN.sub.2C.sub.2 SiN.sub.2CH SiN.sub.4 High desity
T[.degree. C.] (-5 ppm) (-22 ppm) (-43 ppm) (-50 < -0 ppm) 300
-5 ppm -20 ppm -38 ppm -- 24.4% 56.5 19.0 -- 400 -10 ppm -6 -23 ppm
-43 ppm -- 6.9% 8.9 59.4 24.8 -- 500 -11 ppm 29 ppm -25 -22 -45 -43
-41 -50 ppm 2.3% 4.8.0% 13.8 9.2 36.6 12.1 5.9 15.2 600 -- -30 ppm
-45 ppm -42 -60 ppm -52 -- 4.2% 54.9% 29.0 2.2% 9.7 700 -- -- -47
-44 -40 -58 ppm -51 -- -- 11.4 42.4 21.6 7.8% 16.8 800 -- -- -47
-43 -40 -61 -56 -51 -- -- 41.0 14.5 6.0 4.8 10.7 23. 1100 -- -- -45
-42 -39 -63 -56 -50 -- -- 25.8 15.8 13.8 7.51 15.2 16.0
[0142] Once the possibility of the N-for-C displacement was proven
as a chemical possibility, the polymer was subjected to PS-CVD
under similar conditions. The FT-IR spectrum of the thin film is
shown in FIG. 23, where the broad absorption at around 850
cm.sup.-1 is assigned to the formation of SiC.sub.xN.sub.y silicon
carbonitride species.
[0143] Film properties--The silicon carbonitride thin film
deposited on silicon, quartz, and alumina substrates were
characterized electrically. The carrier concentrations of the films
were found to be in the range of 10.sup.14-10.sup.16 cm.sup.-3 in
the bulk. The corresponding calculated resistivities of the films
deposited on quartz, alumina and electronic-grade ceramics vary
between 3-50 .OMEGA.cm.
[0144] No residual Si--H and C--H were observed in the FT-IR
spectrum of the material, although the presence of 0 to 15 atomic %
of molecular hydrogen trapped in the film cannot be excluded, based
on similar characteristics found in other silicon-based thin films
produced by the PS-CVD method.
Example 4
Synthesis of an Amorphous Silicon Nitride Via the PS-CVD
Process
[0145] Synthesis--An appropriate time-dependent temperature
gradient was programmed in the furnace, so that quantitative
polysilazane formation was promoted. Possible ranges for the
gradients are 1-5.degree. K min.sup.-1 and 3-50.degree. K cm.sup.-1
where the temperature increases in a 2 inch/150 cm horizontal
quartz reactor. A second step involves pyrolysis of the
polysilazane in the reaction zone where the temperature is
relatively constant. This step may be optionally followed by a
transamination processes induced directly in the deposition zone,
via a carefully monitored (flow, pressure--parameters and PID
temperature parameters where P=1-25, I=10-250, and D=0.1-10)
reaction under pure electronic-grade gaseous ammonia introduced in
the temperature zone at a pressure level of 1 to 50 torr over
atmospheric pressure. The resultant precursor gaseous species were
transported in the deposition zone, where they are desublimed onto
the substrate that can be placed in a horizontal, vertical or a
tilted position, can be mobile or immobile during the deposition.
The resultant material is a-Si.sub.xN.sub.y, with a x/y ratio in
the range of 0.75 to 1. The thickness of the resulted film may be
adjusted in the 100 .ANG.-1 .mu.m via single/multiple layered
deposition.
[0146] Characterization--A representative IR spectra is presented
is FIG. 24. The major peak was observed at 896 cm.sup.-1. This peak
was believed to be the product of overlap of several other peaks.
These included the 850 cm.sup.-1 and 940 cm.sup.-1 peaks associated
with the Si--N stretching mode, and the Si--O symmetric stretching
mode at 1040 cm.sup.-1. The presence of a large shoulder on the
main absorption peak verifies the presence of more than one
absorbance and is in the range of the Si--O symmetric stretching
mode. The peak found at 478 cm.sup.-1 was associated with the Si--N
breathing mode, 680 cm.sup.-1 with the Si--H wag, and 1159
cm.sup.-1 with the N--H.sub.2 bend. The large peak at 2300
cm.sup.-1 was due to an excess of CO.sub.2 in the machine during
the sample scan compared to the background scan. The presence of
oxygen observed in the IR may be due to oxygen contamination during
the synthesis process or surface oxide formation upon handling the
sample. The amount of residual bonded-hydrogen, evidenced as Si--H
and C--H bonds is function of the PS-CVD parameters, and appears to
decrease with the increase temperatures of the zones 2 and 3 of a
three-zone reactor. Residual carbon (Auger) is in the order of 0-5
atomic %.
Example 5
Synthesis of an Amorphous Silicon Oxynitride Thin Film Via
PS-CVD
[0147] Synthesis--Silicon nitride thin films were produced by the
PS-CVD process in various reaction conditions. An organosilicon
polymer was used as the silicon source and NH.sub.3 as the nitride
source. All nitride depositions were performed in a one zone
furnace equipped with a 2" quartz tube attached to a silicone-based
hydraulic lock bubbler and to a vacuum line capable of providing a
reduced pressure of 5*10.sup.-2 torr. When not in use the tube was
maintained at a temperature of 110.degree. C. The gaseous
atmosphere consisted of a diluted mixture of in house purified
NH.sub.3 in a UHP-Ar carrier. The purification of NH.sub.3 was
attained via passing the gas through a 1000 mm column of KOH and a
250 mm column of a mixture of 3 and 4 .ANG. molecular sieves.
[0148] The atmosphere of the pyrolysis was carefully purified from
oxygen and water vapor via a series of evacuations by vacuum pump
and N.sub.2 flushings. In the first series of experiments the
system was evacuated and then filled with nitrogen. An ammonia flow
was introduced into the system throughout the temperature cycle at
an approximate rate of 1 "bubble" per second. In these initial
experiments the ammonia flow was gauged by counting bubbles/time in
the silicone-based hydraulic lock bubbler. The temperature of the
furnace increased at a constant rate until it reached a maximum
temperature of 550.degree. C.
[0149] The films were deposited on both n- and p-type polished
silicon (100) wafers and quartz substrates. Two sample sizes were
employed, 2.5.times.2.0 cm and 10.times.2.5 cm. Prior to
deposition, substrates were immersed in acetone and placed in a
sonic bath for four minutes. They were then rinsed with acetone and
dried in a stream of nitrogen.
[0150] The successful production of silicon nitride was followed by
oxidation of the films. The nitride samples were oxidized in open
air. The thermal profile of the PS-CVD process was varied in
separate trials. In the first trial, the IR spectra were taken
after thermal annealing of the sample for 10 minutes at
temperatures ranging between 300 and 700.degree. C. In the second
trial, the sample was oxidized at a constant temperature of
500.degree. C. and the progression of oxidation was monitored by
FTIR analyses.
[0151] Characterization--The silicon oxynitride films were analyzed
using IR spectroscopy as seen in FIGS. 25a and 25b. The samples
will be referred to as SiON1, which was oxidized at constant
temperature (FIG. 25b) and SiON2, which was oxidized at various
temperatures (FIG. 25a). In sample SiON2, the main peak shifted
from 958 to 1082 cm.sup.-1 upon exposure to temperatures up to
700.degree. C. with a total oxidation time of 50 min. This main
peak shift according to W. L. Scopel et al., 2003, Physical
Review--Section B--Condensed Matter, 68, p. 155332 indicates the
oxidation of the nitride. Shoulders present in the as deposited
nitride due to the Si--O and Si--N stretching vibrations absolved
into the main peak as oxidation proceeded, which indicated the
formation of one phase oxynitride. Moreover, the appearance and
increase of the Si--O bending mode in both samples in the range of
478 to 517 cm.sup.-1 indicates increased oxygen incorporation. The
single sharp absorption band at 1100 cm-1 as in a SiO.sub.2 network
was not observed, rather a broad band was seen with the shoulder at
lower wavenumbers, which was explained by the presence of Si--N
bonding.
[0152] In the case of SiON1, the shift in wavenumbers of the main
peak from 896 to 1050 cm.sup.-1 indicated oxidation of the nitride.
The oxynitride produced by annealing at 400.degree. C. stopped
incorporating oxygen after one hour but oxidation resumed once the
temperature was increased to 500.degree. C. This indicated that as
temperature is increased the rate of reaction also increases.
[0153] Film properties--The optical band gap of the film calculated
from the UV spectrum was found to be 4.92 eV compared to the
literature value of 5.0 eV (Klaus Mogenson, Peter Friis, Jorg
Hubner, Nickolaj Peterson, Anders Jargenson, Pieter Telleman, Jorg
P. Kutter, Optics Letters, 26(10), 2001).
[0154] A Scanning Electron Microscope (SEM) thickness profile of a
representative sample nitride showed that the thickest region in
the film is 600 nm and that the thickness falls off gradually with
few inconsistencies.
Example 6
Synthesis of a Silicon Oxy(Carbo)Nitride Thin Film Via the PS-CVD
Process
[0155] Synthesis--For the initial nitridation procedure, commercial
poly(dimethylsilane) from Gelest was used. The experiments were
performed in a Minibrute parallel diffusion three-zone furnace at
5-10 torr above atmospheric pressure capable of operating up to
1500.degree. C. It was equipped with a 2" quartz tube attached to a
silicone-based hydraulic lock bubbler, and to a vacuum line capable
of providing a reduced pressure of 5*10.sup.-2 torr. The gaseous
atmosphere consisted of a diluted mixture of in house purified
NH.sub.3 in a UHP-Ar carrier. The purification of NH.sub.3 was
attained via passing the gas through a 1000 mm column of KOH and a
250 mm column of a mixture of 3 and 4 .ANG. molecular sieves. The
atmosphere of the pyrolysis was carefully purified from oxygen and
water vapour via a series of consecutive evacuations/Ar-fillings.
The residual oxygen level obtained after the flushing procedure was
measured with an Innovative* Technology gauge and found to be below
5 ppm. Silicon and quartz substrates were used for the PS-CVD
deposition. A continuous flow of anhydrous ammonia was introduced
into the system before heating and during the full temperature
cycle. The pyrolysis cycle performed under pure ammonia flow led to
a deposit consistent with a silicon carbonitride species.
Trademark
[0156] The silicon carbonitride thin film was further thermally
oxidized in a second Minibrute furnace in conjunction with a
three-inch Quartz tube with ends open to the atmosphere. The IR
spectrum of the silicon carbonitride thin film was taken after
heating for 10 minutes at a variety of temperatures between 200 and
720.degree. C. The sample was further annealed for a period of one
to ten hours in the furnace at 700.degree. C. and their respective
IR spectra were taken.
Example 7
Synthesis of an Amorphous Silicon Oxycarbide Via the PS-CVD
Process
[0157] Synthesis--Silicon oxycarbide is an amorphous metastable
phase wherein the silicon atoms are bonded to oxygen and carbon
simultaneously. In silicon oxycarbides, high temperature properties
and chemical stability have been reported, exceeding those of
ordinary vitreous silica. Silicon oxycarbide materials have also
the potential for use in a variety of protective applications
within the semiconductor industry. Using PS-CVD technique, silicon
oxycarbides of various compositions have been deposited on highly
resistive single crystal silicon wafers, using different conditions
to vary the oxygen content in the films.
[0158] An appropriate time-dependent temperature gradient was
programmed in the furnace to enhance quantitative polycarbosilane
formation. Possible ranges for the gradients were 1-10 Kmin.sup.-1
and 3-50 Kcm.sup.-1 in a 2 inch/150 cm horizontal quartz reactor.
The resultant polymeric gaseous species were transported in the
deposition zone.
[0159] The polycarbosilane was oxidized via a carefully monitored
(flow, pressure, and FT-IR) reaction with oxygen carrying species
including, but not limited to, O.sub.2, O.sub.3, CO at a partial
pressure level of 10.sup.-4-10.sup.-1 torr in a UHP-Ar (or N.sub.2)
carrier flow. The oxygen carrying species were introduced directly
in the deposition zone.
[0160] The controlled oxidation products were desublimed onto the
substrate that may be placed in a horizontal, vertical, or a tilted
position, and may be mobile or immobile during the deposition. The
resultant material was a SiO.sub.xC.sub.y glass with an oxygen
content in the range from x=10.sup.-3 to x=1.3 measured using an
external standard of Cz-silicon single crystal via ASTM F-1188.
[0161] Characterization--FIG. 26 represents the FT-IR spectra of
three samples, (a), (b) and (c), of a synthesized silicon
oxycarbide film annealed for increasing time periods of 8, 16 and
24 hours, respectively. It must be noted, that the interstitial
oxygen peak found in sample (a) at approximately 1100 cm.sup.-1,
increased as the film is annealed for longer periods. This
indicated the conversion limited resistance of the film to
oxidation.
[0162] Film properties--The thickness of the resultant film can be
adjusted in the 100 .ANG.-1 .mu.m range via single/multiple layered
deposition.
[0163] Although various embodiments of the invention are disclosed
herein, many adaptations and modifications may be made within the
scope of the invention in accordance with the common general
knowledge of those skilled in this art. Such modifications include
the substitution of known equivalents for any aspect of the
invention in order to achieve the same result in substantially the
same way. Numeric ranges are inclusive of the numbers defining the
range. In the claims, the word "comprising" is used as an
open-ended term, substantially equivalent to the phrase "including,
but not limited to".
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