U.S. patent application number 11/968546 was filed with the patent office on 2009-12-31 for superhard dielectric compounds and methods of preparation.
This patent application is currently assigned to Arizona Board of Regents, a body corporate of the state of Arizona, acting for and on behalf of. Invention is credited to John Kouvetakis, John Tolle, Levi Torrison, I.S.T. Tsong.
Application Number | 20090324475 11/968546 |
Document ID | / |
Family ID | 23283252 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090324475 |
Kind Code |
A1 |
Kouvetakis; John ; et
al. |
December 31, 2009 |
Superhard dielectric compounds and methods of preparation
Abstract
Novel superhard dielectric compounds useful as gate dielectrics
in microelectronic devices have been discovered. Low temperature
methods for making thin films of the compounds on substrate silicon
are provided. The methods comprise the step of contacting a
precursor having the formula H.sub.3X--O--XH.sub.3, wherein X is
silicon or carbon with a compound comprising boron or nitrogen In a
chemical vapor deposition (CVD) chamber or with one or more atomic
elements in a molecular beam epitaxial deposition (MBE) chamber.
These thin film constructs are useful as components of
microelectronic devices, and specifically as gate dielectrics in
CMOS devices.
Inventors: |
Kouvetakis; John; (Mesa,
AZ) ; Tsong; I.S.T.; (Tempe, AZ) ; Torrison;
Levi; (Mesa, AZ) ; Tolle; John; (Gilbert,
AZ) |
Correspondence
Address: |
MCDONNELL BOEHNEN HULBERT & BERGHOFF LLP
300 S. WACKER DRIVE, 32ND FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
Arizona Board of Regents, a body
corporate of the state of Arizona, acting for and on behalf
of
|
Family ID: |
23283252 |
Appl. No.: |
11/968546 |
Filed: |
January 2, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10492271 |
Apr 8, 2004 |
7374738 |
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PCT/US02/32499 |
Oct 10, 2002 |
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11968546 |
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60328967 |
Oct 11, 2001 |
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Current U.S.
Class: |
423/277 ;
423/327.1 |
Current CPC
Class: |
C04B 2235/96 20130101;
H01L 21/28202 20130101; C04B 2235/422 20130101; C23C 16/32
20130101; C04B 35/5805 20130101; C23C 16/308 20130101; C04B 35/5603
20130101; C04B 2235/465 20130101; C04B 2235/402 20130101; H01L
21/02269 20130101; H01L 21/28238 20130101; C23C 16/38 20130101;
C04B 35/597 20130101; H01L 21/02271 20130101; C04B 2235/44
20130101; C23C 16/30 20130101; C01B 21/0826 20130101; H01L 21/02145
20130101; C04B 2235/428 20130101; H01L 29/518 20130101; H01L
21/02216 20130101; C04B 2235/483 20130101; H01L 21/3145 20130101;
H01L 21/02115 20130101; H01L 21/28185 20130101; C04B 2235/40
20130101; C04B 2235/9653 20130101; H01L 21/28194 20130101; C04B
2235/421 20130101; C23C 16/34 20130101 |
Class at
Publication: |
423/277 ;
423/327.1 |
International
Class: |
C01B 35/10 20060101
C01B035/10; C01B 33/26 20060101 C01B033/26 |
Goverment Interests
STATEMENT OF GOVERNMENT FUNDING
[0002] The U.S. Government through the US, Army Research Office
provided financial assistance for this project under Grant No.
DAAD19-00-1-0471 and through the National Science Foundation under
Grant No. DMR-9986271, Grant No. DMR 9902417 and Grant No. ECS
0000121. Therefore, the United States Government may own certain
rights to this invention.
Claims
1. A compound of the formula XqYpZtO wherein X is selected from the
group consisting of silicon or carbon, Y is selected from the group
consisting of boron or nitrogen, Z is selected from the group
consisting of gallium or aluminum, O is oxygen, wherein q and p are
independently 1, 2 or 3 and t is zero or 1, provided that when X is
silicon, and t is zero, Y is not nitrogen.
2. (canceled)
3-5. (canceled)
6. The compound of claim 1 wherein X is Si and Y is boron.
7. The compound of claim 6 having the formula Si.sub.2B.sub.2O.
8. (canceled)
9. The compound of claim 1 wherein X is silicon and Y is
nitrogen.
10. The compound of claim 1 wherein X is carbon and Y is boron.
11. The compound of claim 10 having the formula
C.sub.2B.sub.2O.
12-64. (canceled)
65. The compound of claim 1 wherein at least one of p and q are 1
or 2.
66. The compound of claim 1 wherein Z is aluminum.
67. The compound of claim 1 wherein t is 0.
68. The compound of claim 6 having the formula SiB.sub.2O.
69. The compound of claim 1 wherein X is silicon, Y is nitrogen,
and Z is aluminum.
70. The compound of claim 69 having the formula Si.sub.2N.sub.3AlO.
Description
CROSS REFERENCE
[0001] This application claims priority from U.S. Provisional
Patent Application Ser. No. 60/328,967 filed Oct. 11, 2001, the
disclosure of which is incorporated by reference herein in its
entirety.
FIELD OF INVENTION
[0003] This invention relates generally to certain super-hard
dielectric compounds useful as gate dielectrics in microelectronic
devices. Low temperature methods for depositing thin films of these
compounds onto silicon substrates are presented.
BACKGROUND
[0004] Recently, the challenge of creating smaller dimensions in
microelectronic devices has demanded the use of new materials for
the gate dielectric--either thinner silicon oxide layers or new
compounds having a higher dielectric constant.
[0005] Silicon dioxide (SiO.sub.2) is a classical refractory
material and the most common gate dielectric in microelectronic
devices. Its structure is made up of SiO.sub.2 tetrahedra in which
each oxygen forms two bonds with neighboring Si atoms
((SiO4).sup.-4 tetrahedra connected through bridging oxygens). The
performance of SiO.sub.2-containing devices is limited by dopant
diffusion out of poly-Si and direct tunneling through SiO.sub.2,
and when off-state, power dissipation becomes comparable to active
power.
[0006] Current efforts are focused on replacing SiO.sub.2 with
nitride (Si.sub.3N.sub.4) or oxynitride (SiOxNy) films with K
.about.5-7.5 [1-6] or with alternative higher K (.about.20-30)
films [7,8]. In recent years, nitride oxides (silicon oxynitrides)
have been widely investigated as possible substitutes for SiO.sub.2
because of their higher stability and durability, their ability to
prevent boron diffusion, and their higher dielectric constant. The
introduction of three-coordinate nitrogen into SiO.sub.2 increases
the cross-linking in the structure, resulting in a compound having
higher density, strength, and hardness in comparison to the pure
silicon oxide. Compounds in the Si--O--N system exhibit good
thermal, chemical, and mechanical stability, as well as diffusive
barrier and dielectric properties [9]. In addition,
Si.sub.2N.sub.2O has superior oxidation resistance and thermal
shock resistance compared to Si.sub.3N.sub.4. Most of the reported
Si--O--N systems are amorphous and appear to have a higher
dielectric constant than the pure oxide.
[0007] However, crystalline materials with well-defined
compositions and structures have been sought which will give
significant improvements in mechanical and electrical properties
over more amorphous forms of these compounds. The synthesis of
phases with well-defined composition and structure is desirable
because it may lead to significant improvements and/or
controllability in the mechanical, electrical, and dielectric
properties [10,11].
[0008] One such phase is stoichiometric, silicon oxynitride
(Si.sub.2N.sub.2O), a refractory material having all the
aforementioned and desirable properties. Si.sub.2N.sub.2O has the
high-pressure B.sub.2O.sub.3 structure [12] and is composed of
SiN.sub.3O tetrahedral, corner-linked by O and N atoms. This
structure is illustrated in FIG. 2. In this structure, the oxygen
bridges two Si (as in SiO.sub.2) and the N and Si atoms are,
respectively, in three and four fold coordination as in
Si.sub.3N.sub.4 [13].
[0009] The synthesis of this compound and the search for related
silicon-based dielectric materials has been the focus of intense
research because of their potential for enhanced performance
compared to SiO.sub.2 and Si.sub.3N.sub.4 based devices [14,15].
However, despite their attractive properties, a suitable synthesis
technique for silicon oxynitrides and related dielectrics at
relatively low processing temperatures, as required in silicon
device technology, is still lacking.
IN THE DRAWINGS
[0010] FIG. 1 is a ball-and-stick model illustrating the unit cell
structure of Si.sub.2B.sub.2O.
[0011] FIG. 2 is a ball-and-stick model illustrating the structure
of Si.sub.2N.sub.2O.
[0012] FIG. 3 is a Rutherford Back Scattering (RBS) spectrum of a
Si.sub.2N.sub.2O film deposited at 850.degree. C. The RBS
simulation by RUMP, shown as a dashed line, gives the atomic
compositions of Si, O, and N.
[0013] FIG. 4 illustrates the L.sub.2,3 ionization edge of Si and
the K ionization edges of O and N (inset) in an EELS spectrum of
Si.sub.2N.sub.2O.
[0014] FIG. 5 is a SIMS elemental depth profile of Si.sub.2N.sub.2O
showing a uniform distribution of the elements.
[0015] FIG. 6 is a FTIR spectrum of a Si.sub.2N.sub.2O showing the
N--Si--O absorption peaks corresponding to stretching (900
cm.sup.-1) and bending (470 cm.sup.-1) modes.
[0016] FIG. 7 is AFM image of the Si2B2O film surface showing
relatively flat morphology and an array of indentations used to
determine the microhardness. Inset is an enlarged view of typical
nanoindentation.
SUMMARY
[0017] Novel superhard dielectric compounds useful as gate
dielectrics in microelectronic devices have been discovered. Low
temperature methods for making thin films of the compounds on
substrate silicon are provided. The methods comprise the step of
contacting a precursor having the formula H.sub.3X--O--XH.sub.3,
wherein X is silicon or carbon with a compound comprising boron or
nitrogen in a chemical vapor deposition (CVD) chamber or with one
or more atomic elements in a molecular beam epitaxial deposition
(MBE) chamber. These thin film constructs are useful as components
of microelectronic devices, and specifically as gate dielectrics in
CMOS devices.
[0018] Compounds having a formulae XqYpZtO wherein X is silicon or
carbon, Y is boron or nitrogen, Z is gallium or aluminum, O is
oxygen and q and p are each an integer having a value of 1, 2 or 3
and t is zero or 1, provided that when X is silicon, and t is zero,
Y is not nitrogen are presented. Also presented are
non-stoichiometric compounds having the formulae XqYpZtO wherein X
is silicon or carbon, Y is boron or nitrogen, Z is gallium or
aluminum, O is oxygen wherein one or more of the values of q, p or
t are non-integral.
[0019] In certain preferred embodiments of the invention the
compounds have a dielectric constant between 3 and 7, most
preferably between about 5.5 and 6.6.
[0020] In certain other preferred embodiments the compounds have a
hardness of between about 17 to 25 GPa.
[0021] In one preferred embodiment of the present invention X is Si
and Y is boron and most preferably have the formula
Si.sub.2B.sub.2O or SiB.sub.2O.
[0022] In other preferred embodiments of the present invention, X
is carbon and Y is boron and most preferably has the formula
C.sub.2B2O.
[0023] In other preferred embodiments X is silicon, Y is nitrogen
and Z is aluminum, most preferably the compound having the formula
Si.sub.2N.sub.3AlO.
[0024] Most preferably the non-stoichiometric compounds of the
present invention are silicoxynitrides wherein X is silicon, Y is
nitrogen and the values of q, p and t are non-integral.
[0025] In an important aspect of the present invention, the
compounds are provided as thin films deposited on a silicon
substrate. Preferably thin films of the compounds of the present
invention have a thickness of between about 5 and 500 rim. Most
preferably the silicon substrate, a silicon wafer, e.g., is
Si(100), Si(111) or doped Si(111) as generally utilized as
semiconductor devices. In certain preferred embodiments, the
silicon substrate comprises a native oxide layer. In other
preferred embodiments, the silicon substrate is cleaned prior to
deposition of film. In yet other preferred embodiments the silicon
substrate comprises compliant buffer layers. Substrates other than
silicon generally employed in semiconductor devices may likewise be
utilized.
[0026] In an important aspect of the present invention,
microelectronic devices comprising the present thin film of any of
the compounds of the present invention deposited on a suitable
substrate are provided. Because of their dielectric and other
physical properties, thin films of the compounds of the present
invention are useful gate dielectrics in microelectronic devices
CMOS, e.g., and may be incorporated into semiconductor devices
generally as substrates for other components of integrated circuits
by methods known in the art.
[0027] In another important aspect of the invention, low
temperature methods for preparing thin film of the present
superhard dielectric compounds are provided. These low-temperature
methods are compatible with current silicon processing
technologies. Methods are provided for preparing thin films of
compounds having a formulae XqYpZtO wherein X is silicon or carbon,
Y is boron or nitrogen, Z is gallium or aluminum, O is oxygen and q
and p are each an integer having a value of 1, 2 or 3 and t is zero
or 1 comprising the step of contacting precursor having the formula
H.sub.3X--O--XH.sub.3 with a reactive species containing Y or Z in
the presence of substrate under conditions whereby thin film of the
compound is deposited on the substrate. Methods are provided for
contacting the precursor and reactive species in a chemical vapor
deposition (CVD) chamber or a molecular beam epitaxial (MBE)
chamber. The thin films prepared by the methods generally have a
thickness between about 5 and 500 run. Preferably, the substrate is
Si(100), Si(111) or doped Si(111). Other substrates known to the
art and used as substrate in preparation of thin film devices may
also be employed. In certain preferred embodiments of the
invention, the substrate comprises a native oxide layer. In certain
other preferred embodiments, the substrate is cleaned prior to
deposition of thin film compounds. In yet other preferred
embodiments the substrate may comprise a compliant buffer
layer.
[0028] In certain preferred embodiments of the method of the
present invention, methods are presented for preparing a compound
having the formula XqYpO wherein X is silicon, Y is boron, O is
oxygen and q and p are each an integer having a value of 1 or 2,
comprising the step of contacting a precursor having the formula
H.sub.3X--O--XH.sub.3 with a reactive compound having the formula
(YL.sub.3).sub.v wherein L is hydrogen or halide and v is 1 or 2 in
the presence of substrate in a chemical vapor deposition chamber
under conditions whereby thin film of said compound is deposited on
said substrate. Thin films made by this preferred method are
presented. Microelectronic devices comprising the deposited thin
films are presented.
[0029] In a preferred embodiment of this method, low temperature
methods for depositing superhard dielectric thin films of
Si.sub.2B.sub.2O on a silicon substrate are presented. In these
embodiments, essentially equimolar amounts of precursor
H.sub.3SiOSiH.sub.3 and (BH.sub.3).sub.2 are contacted in a CVD
chamber at a temperature at about 700.degree. C. to 1000.degree.
C., most preferably about 700.degree. C., in the presence of the
silicon substrate under conditions whereby the H.sub.3SiOSiH.sub.3
and B.sub.2H.sub.6 react to form thin film of Si.sub.2B.sub.2O on
the silicon substrate. In these preferred embodiments, films of
Si.sub.2B.sub.2O having a thickness of about 5 to 500 nm may be
formed on silicon substrate, Si(100) or Si(111) or doped Si(111),
for example. The substrate may comprise a native oxide layer, or
may be cleaned before the deposition of film. Thin film of
Si.sub.2B.sub.2O on a silicon substrate thin film of
Si.sub.2B.sub.2O are provided.
[0030] In another preferred embodiment, low temperature methods for
depositing superhard dielectric thin films of SiB.sub.2O on a
silicon substrate are presented. In these embodiments, equimolar
amounts of precursor H.sub.3SiOSiH.sub.3 and (BH.sub.3).sub.2 are
contacted in a CVD chamber at a temperature between about
500-650.degree. C. in the presence of the silicon substrate under
conditions whereby the H.sub.3SiOSiH.sub.3 and B.sub.2H.sub.6 react
to form thin film of Si.sub.2B.sub.2O on the silicon substrate. In
these preferred embodiments, films of SiB.sub.2O having a thickness
of about 5 to 500 nm may be formed on silicon substrate, Si(100) or
Si(111) or doped Si(111), for example. The substrate may comprise a
native oxide layer or may be cleaned before the deposition of film
34. Thin film of SiB.sub.2O on a silicon substrate is provided.
[0031] In an important aspect of the invention, microelectronic
devices comprising thin film of silicoxyborides, most specifically
SiB.sub.2O or Si.sub.2B.sub.2O are given.
[0032] In yet another preferred embodiment, low temperature methods
for depositing superhard dielectric thin films of Si.sub.2N.sub.2O
on a silicon substrate are presented. In these preferred
embodiments, essentially equimolar amounts of precursor
H.sub.3SiOSiH.sub.3 and NH.sub.3 are contacted in a CVD chamber at
a temperature between about 650.degree. C. to 850.degree. C. in the
presence of the silicon substrate under conditions whereby the
H.sub.3SiOSiH.sub.3 and NH.sub.3 react to form thin film of
Si.sub.2N.sub.2O on the silicon substrate. In this preferred
method, thin film of Si.sub.2N.sub.2O having a thickness of about 5
to 500 nm may be formed on a silicon substrate, Si(100) or Si(111)
or doped Si(111), for example. The substrate may comprise a native
oxide layer or may be cleaned prior to deposition of film. Thin
film of Si.sub.2N.sub.2O on a silicon substrate prepared by these
methods are given.
[0033] In another important aspect of the invention microelectronic
devices comprising thin film of Si.sub.2N.sub.2O made by the
methods of the present invention are presented.
[0034] In yet another preferred embodiment of the present
invention, methods for depositing superhard thin films of
B.sub.2C.sub.20 on a silicon substrate are presented. In these
preferred methods, essentially equimolar amounts of
H.sub.3COCH.sub.3 and BCl.sub.3 are contacted in said chamber at a
temperature between about 650.degree. C. to 850.degree. C. in the
presence of the silicon substrate under conditions whereby the
H.sub.3COCH.sub.3 and BCl.sub.3 react to form thin film of B2C20 on
the silicon substrate. B2C20 films formed by these methods may have
a thickness of about 5 to 500 nm. The substrate is preferably
silicon, Si(100) or Si(111) or doped Si(111), for example. The
substrate may comprise a native oxide layer or may be cleaned prior
to deposition of film. Thin film of B.sub.2C.sub.20 on silicon
substrate are provided.
[0035] In yet another important aspect of the invention,
microelectronic devices comprising thin film of borocarboxyoxides,
specifically thin film B.sub.2C.sub.20 are given.
[0036] In another preferred embodiment of the method of the present
invention, methods are presented for preparing thin film of a
compound of the present invention having a formula XqYpZtO wherein
X is silicon or carbon, Y is boron or nitrogen, Z is gallium or
aluminum, O is oxygen and q and p are each an integer having a
value of 1, 2 or 3 and t is zero or 1 and for preparing
non-stoichiometric compounds XqYpZtO wherein one or more of the
values of q, p or t are non-integral. The method comprises the step
of directing Y atoms at a precursor having the formula
H.sub.3X--O--XH.sub.3 in a molecular beam epitaxial chamber in the
presence of a silicon substrate under conditions whereby the
precursor and Y atoms combine to form thin film on the substrate.
Preferably the substrate is Si(100), Si(111) or doped Si(111) and
may comprise a native oxide layer or be cleaned by methods known in
the art prior to deposition. Thin film of these compounds on a
silicon substrate are provided. Substrates other than silicon known
to the art may also be employed as substrate.
[0037] In another important aspect of the invention,
microelectronic devices comprising thin film of a compound made by
these methods are provided.
[0038] In preferred embodiments of the method of this present
invention, superhard thin films of non-stoichiometric
siliconoxynitrides are prepared. In this preferred method, atomic
nitrogen generated in a molecular beam deposition chamber is
directed at precursor H.sub.3SiOSiH.sub.3 in the presence of
silicon substrate under conditions whereby the precursor and
nitrogen atoms react to form thin film of non-stoichiometric
silicon oxynitrides on the silicon substrate. Preferably the
temperature of the chamber is about 850.degree. C. to 950.degree.
C. The substrate may be Si(100), Si(111), doped Si(111) or other
substrate known to the art and may comprise a native oxide layer,
compliant buffer or may be cleaned prior to deposition of the thin
film. Preferably the temperature of said chamber is between about
850 to 950.degree. C. and the substrates is highly doped Si(111).
Thin film of non-stoichiometric silicoxynitrides deposited on a
silicon substrate by these methods are provided.
[0039] In yet another important aspect of the invention,
microelectronic devices comprising a thin film of
non-stoichiometric silicoxynitride made by the present methods are
provided.
[0040] In certain preferred instances of the invention, methods for
depositing superhard thin films of Si.sub.2N.sub.3AlO on a silicon
substrate are given. In these methods atomic nitrogen and atomic
aluminum are directed at precursor is H.sub.3SiOSiH.sub.3 in a
molecular beam deposition chamber in the presence of a silicon
substrate under conditions whereby the disiloxane reacts with
nitrogen atoms and aluminum atoms to form thin film of
Si.sub.2N.sub.3AlO on the silicon substrate. In these instances,
the silicon substrate may comprise compliant buffer layers
comprising in situ generated SiAlONS and related Al silicon
oxynitrides. Thin film of Si.sub.2N.sub.3AlO on a silicon substrate
are provided.
[0041] In yet another important aspect of the present invention,
microelectronic devices comprising thin film of Si.sub.2N.sub.3AlO
are provided.
[0042] In an important aspect of the invention, compounds having
the formula H.sub.3XOXH.sub.3 wherein X is silicon or carbon are
presented as precursors in the preparation of the compounds of the
present invention. In preferred instances, H.sub.3SiOSiH.sub.3 is
presented as a precursor in the preparation of the compounds of the
silicon-based compounds of the present invention. In other
preferred instances, H.sub.3COCH.sub.3 is presented as a precursor
in the preparation of the compounds of the carbon-based compounds
of the present invention.
[0043] In an important aspect of the present invention, methods are
provided for preparing disiloxane having the formula
H.sub.3SiOSiH.sub.3. The method comprises the steps of contacting a
halosiloxane, preferably Cl.sub.3SiOSiCl.sub.3, with a salt of
gallium tetrahydride, preferably LiGaH.sub.4, and capturing gaseous
H.sub.3SiOSiH.sub.3 generated during the reaction between
halosiloxane and the hydride. Disiloxane prepared by this method
may be used as a precursor for the preparation of thin films of the
compounds of the present invention. Preferred compounds made from
siloxane prepared by the method of the present invention are
Si.sub.2N.sub.2O, non-stoichiometric siloxynitrides,
silicoborohydrides, most preferably SiB.sub.2O and
Si.sub.2B.sub.2O, and Si.sub.2N.sub.3AlO.
[0044] In yet another aspect of the compounds of the present
invention may be used as superhard coatings in a variety of
applications.
DETAILS OF THE INVENTION
[0045] While the present invention will be described more fully
hereinafter with reference to the examples and accompanying
drawings, in which aspects of the preferred manner of practicing
the present invention are shown, it is to be understood at the
outset of the description which follows that persons of skill in
the appropriate arts may modify the invention herein described
while still achieving the favorable results of this invention.
Accordingly, the description which follows is to be understood as
being a broad, teaching disclosure directed to persons of skill in
the appropriate arts, and not as limiting upon the present
invention.
[0046] This invention provides novel superhard compounds having
dielectric constants that make them useful as gate dielectrics in
CMOS devices and as superhard coatings in a variety of
applications. In certain preferred instances, the compounds
comprise a Si--O backbone structure and a light element boron or
nitrogen. In other instances the compounds comprise a C--O backbone
structure and a light element, boron or nitrogen. Compounds having
the Si--O backbone and nitrogen and aluminum are also provided.
[0047] Generally, the crystalline structures of these compounds are
compact which gives them their hardness and electronic properties.
Preferred compounds Si.sub.2B.sub.2O and SiB.sub.2O, for example,
are isoelectronic to carbon (i.e., four valence electrons per atom)
and they crystallize with highly dense diamond-like structures in
which all the constituent elements are tetrahedrally coordinated.
This leads to superior properties such as superhardness and high
stability at extreme conditions. In fact, such materials may be
alternatives to diamond in high performance applications.
Si.sub.2B.sub.2O has a structure that consists of SiB.sub.2O
tetrahedra linked at their corners by O and B atoms. This is
essentially the Si.sub.2N.sub.2O structure with all the N atoms at
the trigonal sites replaced by sp.sup.2 hybridized B (FIG. 1).
Alternate structure related to diamond that is denser and harder
may also be possible. In this structure all the elements occupy
exclusively tetrahedral sites as in diamond. This structure is
feasible since SiB.sub.2O is isoelectronic to diamond and is in
essence a stoichiometric hybrid between Si and B.sub.2O. The latter
is a highly sought binary phase of boron with 3-D diamond-like
structure that has been predicted to have extreme hardness and
other important electronic and mechanical properties.
[0048] C.sub.2B.sub.2O is the carbon analogue of Si.sub.2B.sub.2O.
This system is a stoichiometric hybrid between diamond and the
superhard phase B.sub.2O phase. C.sub.2B.sub.2O in the diamond
cubic structure but has superior properties such as superhardness
as well as higher resistance to oxidation and higher thermal
stability than diamond. Si.sub.2N.sub.2O another preferred
embodiment has the high pressure B.sub.2O.sub.3 structure and it is
composed of SiN.sub.3O tetrahedra linked at their corners by O and
N atoms (FIG. 2). Each oxygen is connected to two Si (as in
SiO.sub.2) and the N and Si atoms are, respectively, three and four
fold coordinate as in Si.sub.3N.sub.4.
[0049] Certain preferred compounds of the present invention are
silicon-based oxygen and boron-containing compounds having the
formula Si.sub.aB.sub.bO.sub.d, Most preferably Si.sub.2B.sub.2O or
SiB.sub.2O. Other preferred compounds are, non-stoichiometric
silicon-based oxygen and nitrogen-containing compounds,
siliconoxynitrides having the formula Si.sub.aN.sub.bO. In yet
other preferred embodiments carbon-based compounds having the
formula C.sub.aB.sub.bO, most preferably C.sub.2B.sub.2O are
provided. In certain other preferred embodiments of the present
invention, compounds having the formula
Si.sub.aN.sub.bZ.sub.cO.sub.d wherein Z is aluminum is provided.
Most preferably the compound has the formula
Si.sub.2N.sub.3AlO.
[0050] A highly practical and a low-temperature chemical vapor
deposition (CVD) method, involving an entirely new approach based
on a stoichiometric heterogeneous reaction from gaseous reactants,
is described for depositing Si.sub.2N.sub.2O films (5-500 nm) on Si
substrates. A new and practical method for depositing superhard
thin films of refractory and dielectric silicon oxynitrides, via
CVD and MBE reactions of the molecular precursor
H.sub.3Si--O--SiH.sub.3, is demonstrated. Specifically,
stoichiometric Si.sub.2N.sub.2O and non-stoichiometric
SiO.sub.xN.sub.y films were deposited on Si substrates at
600-850.degree. C., and characterized for their phase, composition,
and structure by RBS, EELS, FTIR, FESEM, and HRTEM. The leakage
current density voltage J.sub.L-V) characteristics and the
capacitance-voltage (C-V) as a function of frequency were
determined on MOS (Al/Si.sub.2N.sub.2O/SiO/p-Si) structures. The
leakage current density, J.sub.L at -6V (+6V) for a 20 nm
Si.sub.2N.sub.2O film was 0.1 nA/cm.sup.2 (0.05nA/CM.sup.2). The
dielectric permittivity, K, estimated from the capacitance density
in accumulation, was 6 and frequency dispersionless. From the
negative flat ban shift (.DELTA.V.sub.fb) of 150 mV, the positive
fixed charge density (N.sub.f) at the Si(100)/SiO interface was
calculated to be 2.3.times.10.sup.11/CM.sup.3. The microhardness of
Si.sub.2N.sub.2O was determined to be 18 GPa.
[0051] The key aspect of this deposition technique is the use of a
completely inorganic source (H.sub.3Si--O--SiH.sub.3) that
incorporates the crucial Si--O--Si building block of the target
solids, and which does not possess the typical impurity elements
such as Cl and C that are potentially detrimental to the electrical
and dielectric properties of the material. Moreover, its
stoichiometric reaction with NH.sub.3 leads to the complete
elimination of its H ligands to yield high purity Si--O--N films.
This precursor compound also offers an ideal synthetic route for
the formation of technologically important oxynitrides, with
controlled stoichiometries, and at low temperatures compatible with
silicon processing technology.
[0052] A novel low-temperature (600-850.degree. C.) chemical vapor
deposition (CVD) method, involving the reaction between disiloxane
(H.sub.3Si--O--SiH.sub.3) and ammonia (NH.sub.3) is presented to
deposit stoichiometric, Si.sub.2N.sub.2O, and non-stoichiometric,
SiO.sub.xN.sub.y, silicon oxynitride films (5-500 nm) on Si
substrates. The gaseous reactants are free from carbon and other
undesirable contaminants. The deposition of Si.sub.2N.sub.2O on Si
[with (100) orientation and a native oxide layer of 1 nm] was
conducted at a pressure of 2 Torr and at extremely high rates of
20-30 nm per minute with complete hydrogen elimination.
[0053] The deposition rate of SiO.sub.xN.sub.y on highly-doped Si
[with (111) orientation but without native oxide] at 10.sup.-5 Torr
was 1.5 nm per minute, and achieved via the reaction of disiloxane
with N atoms, generated by an RF source in an MBE chamber. The
phase, composition and structure of the oxynitride films were
characterized by a variety of analytical techniques. The hardness
of Si.sub.2N.sub.2O, and the capacitance-voltage (C-V) as a
function of frequency and leakage current density-voltage
(J.sub.L-V) characteristics were determined on MOS
(Al/Si.sub.2N.sub.2O/SiO/p-Si) structures. The hardness,
frequency-dispersionless dielectric permittivity (K), and J.sub.L
at 6V for a 20 nm Si.sub.2N.sub.2O film were determined to be 18
GPa, 6, and 0.05-0.1 nA/cm.sup.3, respectively.
[0054] Additionally, the deposition of non-stoichiometric
SiO.sub.xN.sub.y is also demonstrated. The films are characterized
by Rutherford backscattering spectroscopy (RBS), secondary ion mass
spectrometry (SIMS), high-resolution transmission electron
microscopy (HRTEM) and spatially-resolved electron energy loss
spectroscopy (EELS), Fourier transform infrared spectroscopy
(FTIR), field-emission scanning electron microscopy (FESEM), a
Triboscope attached to an atomic force microscope (AFM) for
hardness, and electrical and dielectric methods.
[0055] The synthetic reaction is similar to that for
Si.sub.2N.sub.2O and is illustrated by the equation (1):
H.sub.3SiOSiH.sub.3+B.sub.2H.sub.6.fwdarw.H.sub.2+Si.sub.2B.sub.2O
(1)
[0056] Also presented are methods for preparing the carbon analogs
of the silicon-based compounds utilizing the precursor dimethyl
ether, H.sub.3COCH.sub.3 in the CVD or MBE chamber. Compounds made
by these methods are, for example, C.sub.2B.sub.2O.
[0057] The thin films are characterized by Rutherford
backscattering spectroscopy (RBS), secondary ion mass spectrometry
(SIMS), high-resolution transmission electron microscopy (HRTEM)
and spatially-resolved electron energy loss spectroscopy (EELS),
Fourier transform infrared spectroscopy (FTIR), field-emission
scanning electron microscopy (FESEM), a Triboscope attached to an
atomic force microscope (AFM) for hardness, and electrical and
dielectric methods.
[0058] Determination of the hardness of the compounds give values
of GPa of between about 17 to 25 Gpa. These values illustrate the
usefulness of the compounds as superhard coatings in a variety of
applications. FIG. 7 is AFM image of the preferred embodiment
Si2B20 film surface showing relatively flat morphology and an array
of indentations used to determine the microhardness. Inset is an
enlarged view of typical nanoindentation.
Chemical Precursors
Disiloxane
[0059] The key feature in the method for deposition of thin films
of the present invention comprising silicon is the use of the
simple disiloxane (H.sub.3Si--O--SiH.sub.3) precursor [16]. The
major advantage of utilizing H.sub.3Si--O--SiH.sub.3 is the
presence of the Si--O--Si framework in the molecule, which provides
both the building block for the desired 3-D network and essentially
fixes the necessary Si to 0 ratio. Additionally, the
H.sub.3Si--O--SiH.sub.3 compound is stable and volatile with a
boiling point of -15.degree. C. The vapor pressure at -82.degree.
C., 145.degree. C. and -23.degree. C. are 15, 195 and 563 Torr,
respectively [16]. The precursor can be stored almost indefinitely
in stainless steel containers and like most silanes, ignites
spontaneously but not explosively upon contact with air. Moreover,
it does not contain carbon or any other potentially impure elements
(e.g., Cl, F) in the molecular structure. The deposition of
Si.sub.2N.sub.2O films is illustrated in the following reaction
(2):
H.sub.3Si--O--SiH.sub.3+NH.sub.3.fwdarw.6H.sub.2+Si.sub.2N.sub.2O
(2)
[0060] Moreover, the use of active N species in place of NH.sub.3,
with controlled energies, may also be used to tailor the N to 0
ratio in a desired material. Therefore, nonstoichiometric films
(SiO.sub.xN.sub.y), with composition and property intermediate to
those of stoichiometric Si.sub.3N.sub.4 and stoichiometric
SiO.sub.2, may be readily engineered. Disiloxane is commercially
available and also may be prepared by methods disclosed in the
present invention.
Dimethyl Ether
[0061] The deposition of thin films of the present invention
comprising carbon proceeds through the use of the dimethyl ether
precursor. Dimethyl ether is commercially available. The simple
dimethyl ether precursor may be used in either the CVD chamber or
the MBE chamber to make the carbon analogues of the compounds of
the present invention. Carbon analogues of the silicon compounds
have similar hardness and dielectric properties.
[0062] The deposition of B.sub.2C.sub.20 films is illustrated in
the following reaction (3):
H.sub.3C--O--CH.sub.3+BCl.sub.3.fwdarw.B.sub.2C.sub.2O+6HCl (3)
EXPERIMENTAL SECTION
Example 1
[0063] This example illustrates the deposition of Si.sub.2N.sub.2O
films on silicon substrate in a chemical vapor deposition (CVD)
chamber using siloxane as precursor.
[0064] The deposition of Si.sub.2N.sub.2O films was carried out in
a CVD reactor consisting of a cold-wall quartz tube fitted with a
recirculating jacket. The reactor wall temperature was maintained
at 700.degree. C. by recirculating preheated ethylene glycol. The
Si substrate was p-Si wafer having resistivity of 4.5.times.10-3
ohm/cm. The substrates were inductively heated using a high-grade,
single-wafer graphite susceptor. Prior to its initial use, the
susceptor was out-gassed at 1100.degree. C. under high vacuum
(10.sup.-3 Torr), and then coated with Si via SiH.sub.4
decomposition. The pumping system was comprised of a high capacity
turbo-molecular pump and a corrosion-resistant pump. The former was
used to obtain high vacuum before and after each deposition, and
the latter was used during deposition. A typical reactor base
pressure was 5-6.times.10.sup.-7 Torr. The gaseous reactants,
H.sub.3Si--O--SiH.sub.3 and NH.sub.3, were diluted with research
grade N.sub.2 and introduced into the reactor through precalibrated
mass flow controllers. The deposition was conducted at a pressure
of 2 Torr and temperatures between 600-850.degree. C. Under these
conditions, stoichiometric Si.sub.2N.sub.2O films ranging in
thickness between 5 and 500 run, were deposited on Si [with an
orientation of (100) and a native oxide layer of 1 nm] at extremely
high rates of 20-30 nm per minute.
Physico-Chemical Characterization of Si.sub.2N.sub.2O Films
Prepared in Example 1
[0065] RBS in the random mode was routinely used to obtain the Si,
N, and O concentration and to estimate the film thickness. A
typical plot is illustrated in FIG. 2. Additionally, elastic N and
O resonance nuclear reactions at 3.72 MeV and 3.0 MeV,
respectively, were used to establish the precise Si.sub.2N.sub.2O
elemental ratios. Since forward recoil experiments indicated that
the hydrogen content was at background levels, the elimination of
the Si--H and N--H bonds from the reactants occurred completely
during growth.
[0066] SIMS was used to confirm the presence of the desired
elements and the absence of carbon impurities, and to demonstrate
that the elemental content was homogeneous throughout the material.
A representative SIMS depth profile, showing the highly uniform
elemental distribution in the film thickness direction, is given in
FIG. 5.
[0067] HRTEM (not shown here) indicated that the films were highly
uniform in thickness and displayed flat and smooth surface
morphology. The selected area electron diffraction (SAED) and
high-resolution images confirmed that the material was amorphous.
Spatially-resolved EELS, used to examine the elemental content at
the nanometer scale and characterize the local bonding environment
of the atoms, showed that the constituent elements appeared at
every nanometer step probed; this consistent with a single-phase
material. The absolute elemental concentration (determined by EELS)
was close to the stoichiometric value for Si.sub.2N.sub.2O, which
corroborated the RBS results. An EELS spectrum featuring the
ionization edges of the elements is shown in FIG. 4. The near-edge
fine structure is indicative oa a 3-D Si.sub.2N.sub.2O network.
[0068] The FITR spectrum in FIG. 6 exhibited phonon modes
consistent with the single-phase Si.sub.2N.sub.2O. A strong,
well-defined peak centered at 900 cm.sup.-1 and a weak peak at 470
cm-I corresponds to the N--Si--O stretching and bending modes,
respectively, of the Si.sub.2N.sub.2O phase [15]. Note, the 900
cm.sup.-1 peak is located at frequencies intermediate to those of
the corresponding stretching odes for stoichiometric SiO.sub.2
(.about.980 cm.sup.-1) and Si.sub.3N.sub.4 (.about.850 cm-1).
Moreover, in the region between 2100 cm-1 and 2000 cm-1, of the
spectrum, additional peaks attributable to Si--H vibrations are
absent. This is consistent with the RBS result of complete
elimination of H ligands from the precursor.
[0069] The hardness of the films was determined using a Hysitron
Triboscope attached to a Nanoscope III AFM (digital instruments).
The hardness is defined as the applied load divided by the surface
area of the impression when a pyramidal shaped diamond indentor is
pressed normally into the film. Pure quartz (SiO.sub.2) was used as
a standard and its hardness was measured to be close to 9.5 GPa.
For example, the hardness of single-crystal Al2O3 (sapphire) was
measured to be 22 GPa. Using the same experimental conditions, the
hardness of the Si.sub.2N.sub.2O films are was approximately 18
GPa.
Characterization of Electrical and Dielectric Properties of
Si.sub.2N.sub.2O Films Prepared in Example 1.
[0070] Including tile native oxide layer (SiO.sub.2; x.about.1) of
1 nm [8], the observed Si.sub.2N.sub.2O film thicknesses by FESEM
were 20 nm, 30 nm, 37.5 nm, and 65 nm, in agreement with RBS and
HRTEM results. From the four-point probe measurement of the
electrical resistivity of the Si wafer, the dopant density was
estimated to be 2.5.times.10.sup.19 cm.sup.-3 [16]. For the room
temperature electrical and dielectric measurements, aluminum (Al)
top electrodes (100 nm thick and 530 um diameter) were deposited
onto samples through a shadow mask by e-beam evaporation. Also, 100
nm Al films were deposited on the backside of Si to improve the
bottom contacts. The samples were placed in an analytical probe
system equipped with a chuck (3190 MC Systems), and the top
electrodes were contacted with microprobes (1097 MODEL; mc
Systems). The high frequency (1-100 KHz, ac.sub.osc 20 mV)
capacitance-voltage (C-V) characteristics and the dc
current-voltage (I-V) characteristics of the capacitors were
measured using a multi-frequency LCR meter (HR Impedance analyzer,
4284A) and current meter (HPn4140B), respectively.
[0071] The leakage current densities, J.sub.t (with 10 s delay), at
-6V (-10V) and +6 V (+10V) for a 20 nm Si.sub.2N.sub.2O film were
0.1 nA/cm.sub.3 (100 nA/cm.sup.3) and 0.05 nA/cm.sup.3 (3
nA/cm.sup.3), respectively. This asymmetry in the magnitude of
J.sub.L for positive and negative gate voltages stems from the
asymmetry if the band alignment and band bending at the
Si/SiO.sub.x and Al/Si.sub.2N.sub.2O interfaces, and the consequent
asymmetry in the transmission probability [19-22].
[0072] The C-V measurements were carried out on MOS
(Al/Si.sub.2N.sub.2O/SiO/P--Si) structures. From the measured
capacitance densities in accumulation (C.sub.acc/A) at -5V, which
were dispersionless in the frequency range measured, the total
equivalent SiO.sub.2 thickness or EOT.sub.tot (i.e.,
EOT.sub.tot-.di-elect cons..sub.0K.sub.SiO2/(C.sub.acc/A)) and
K.sub.SI2N2O as a function of Si.sub.2N.sub.2O thickness were
calculated and are tabulated in Table I. Note, for these
calculations the K of the interfacial SiO layer was estimated to be
7.8 (assuming a linear extrapolation between the K of 11.7 for Si
and 3.9 for SiO.sub.2) and quantum corrections were not
applied.
[0073] From the slope of a Schotzky plot (I/C2 versus V), with data
from the depletion region (+I to +5V) of the C-V curve for a 20 nm
film at 100 KHz, the dopant density was calculated using the
following equation [19] (4):
N A = 2 qK s A 2 d ( 1 / C 2 ) / dV = 2.8 .times. 10 19 cm - 3 ( 4
) ##EQU00001##
where K.=11.7, A=0.0022 cm.sup.2 and
(1/C.sup.2)/dV=9.7.times.10.sup.16. Note, this value of NA is in
agreement with that derived from the four-point probe method.
[0074] Considering this doping level (2.8.times.10.sup.19/cm of
p-Si, the work function of Al (4.2 eV), and the electron affinity
of Si (4.05 eV), the ideal flat band, V.sub.fbo=.PHI..sub.MS was
calculated to be -0.85 V. At 100 KHz, the actual V.sub.fb for the
Al/Si.sub.2N.sub.2O/SiO/P--Si structure was -1V. This corresponds
to a negative flat band Shift
(.DELTA.V.sub.fb=V.sub.fb-.PHI..sub.MS) of 150 mV. Therefore, the
positive fixed charge density
N.sub.f=(.DELTA.V.sub.fbC.sub.acc)/qA) at the SiOSi interface was
estimated to be 2.3.times.10.sup.11/cm.sup.2. The potential origin
of this positive charge can be correlated with roughness at the
Si(100)/SiO interface and the non-stoichiometry of SiO.sub.x.
[19,21,23].
[0075] Table 1 gives the measured and estimated parameters, from
C-V data at a frequency of 100 KHz, for Si.sub.2N.sub.2O film with
different thickness. Note, .PHI..sub.MS=-0.85 V, dopant density of
p-Si is 2.8.times.10.sup.19/cm.sup.3, and electrode area=0.00216
cm.sup.2.
TABLE-US-00001 TABLE 1 Thickness of Si.sub.2N.sub.2O, nm t.sub.SiO,
nm (C.sub.acc/A), fF/um.sup.2 EOT.sub.tot, nm KSi.sub.2N.sub.2O 20
1 2.45 14.1 5.9 37.5 1 1.29 26.7 5.7 65 1 0.8 43.4 6.0
Example 2
[0076] This Example illustrates the deposition of
non-stoichiometric Si--O--N Films on Si substrated prepared MBE
chamber utilizing siloxane as precursor.
[0077] The deposition of non-stoichiometric, silicon oxynitride
(SiO.sub.xN.sub.y) films, via reactions of the
H.sub.3Si--O--SiH.sub.3 precursor with N atoms generated by an RF
source in an MBE chamber, was carried out. The base pressure of the
chamber was 10.sup.-10 Torr, which increased to 10.sup.-4 Torr
during the deposition. The plasma source power was operated at 400
W with a typical N pressure of 10.sup.-7 Torr. The SiO.sub.xN.sub.y
films were deposited at 900.degree. C. on highly-doped Si (111)
substrates, which were previously flashed at 1050.degree. C. and
10.sup.-10 Torr to remove the native oxide layer. The duration of
each deposition was 30 to 45 minutes, yielding an average growth
rate of 1.5 nm per minute.
Characterization of Non-Stoichiometric; Si--O--N Films Made by the
Method of Example 2.
[0078] RBS analysis of these films illustrated in FIG. 3 revealed
that the Si, N and O concentrations were 45 at. %, 50 at. % and 5
at. %, respectively, indicating that the oxygen content in these
films were substantially lower than that of Si2N2O (which is 20 at.
%). The FTIR spectrum showed the characteristic stretching mode at
845 cm.sup.-1 which is lower in energy with respect to
Si.sub.2N.sub.2O but almost identical to that of beta
Si.sub.3N.sub.4. This data indicates that the bonding arrangement
of this SiO.sub.xN.sub.y material is based predominately on the
Si.sub.3N.sub.4 network with some of the lattice sites occupied by
oxygen atoms. The dramatic deviation from tile ideal
Si.sub.2N.sub.2O stoichiometry is attributed to displacement of
oxygen from the H.sub.3Si--O--SiH.sub.3 precursor by the highly
reactive N atoms. Therefore, by judicious adjustments in the growth
parameters, particularly the flux of the nitrogen beam, the O
content in the films may be precisely tuned. Consequently this
method provides a simple and convenient pathway leading to the
formation of non-stoichiometric gate dielectric films with
composition and properties intermediate to those of Si.sub.3N.sub.4
and SiO.sub.2.
Example 3
[0079] This example illustrates the deposition of C.sub.2B.sub.2O
films on silicon substrate in a chemical vapor deposition (CVD)
chamber using dimethylether as precursor.
[0080] The deposition of C.sub.2B.sub.2O films is carried out in a
CVD reactor under the reaction conditions given in Example 1. The
Si substrate is p-Si wafer. The gaseous reactants,
CH.sub.3--O--CH.sub.3 and BCl.sub.3 are diluted with research grade
N.sub.2 and introduced into the reactor through pre-calibrated mass
flow controllers. The molar ratio of BCl.sub.3 to precursor is
approximately 2:1. The deposition is conducted at a pressure of 2
Torr and temperatures between 600-850.degree. C. Under these
conditions, stoichiometric C.sub.2B.sub.2O films ranging in
thickness between 5 and 500 run, is deposited on Si.
Example 4
[0081] This Example illustrates tile deposition of Si2B20 films on
silicon substrate in a chemical vapor deposition (CVD) chamber
using disiloxane as precursor.
[0082] Thin films with composition close to the desired
Si.sub.2B.sub.2O were deposited on Si(100) at 735.degree. C. with
rates ranging from 15 nm to 20 nm per minutes. An exactly
stoichiometric mixture of the reactant gases and a deposition
temperature above 700.degree. C. were necessary to obtain films
with Si.sub.2B.sub.2O stoichiometry.
Example 5
[0083] This Example illustrates the deposition of SiB.sub.2O films
on silicon substrate in a chemical vapor deposition (CVD) chamber
using disiloxane as precursor.
[0084] Thin films with composition close to SiB.sub.2O were
deposited on Si(100) under essentially same conditions as described
in Example 4, but the temperature was lowered to 500 to 650.degree.
C. It is proposed that the Si deficiency in this relative to the
Si.sub.2B.sub.2O compound prepared in Example 4 is due to
incomplete reactions and possible elimination of SiH.sub.4 from the
thermal disproportionation of the precursor as is illustrated in
Equation (4):
H.sub.3Si--O--SiH.sub.3+B.sub.2H.sub.6 H.sub.2+SiB.sub.2O+SiH.sub.4
(5)
Nevertheless, the SiB.sub.2O composition in itself is unique
because it is also isoelectronic to diamond and may crystallize
with the diamond structure.
Characterization of Si.sub.2B.sub.2O and SiB.sub.2O
[0085] The elemental concentrations of Si.sub.2B.sub.2O and
SiB.sub.2O were determined by RBS. SIMS was also used to confirm
the presence of the desired elements and the lack of impurities,
and to show that the elemental content was homogeneous through the
material. FTIR showed bands corresponding to Si-0, B--O and Si--B
lattice modes a result, consistent with the structure illustrated
in FIG. 1. Cross-sectional TEM revealed that the as-deposited
samples were amorphous. More crystalline samples may be prepared by
reducing the growth rates and by conducting post-growth annealing.
The hardness of Si.sub.2B.sub.2O was measured to be 17 GPa. The
hardness of SiB.sub.2O was measured to be 12 GPa.
Example 6
[0086] This Example illustrates the preparation of thin film
Si.sub.2AlN.sub.3O in a MBE chamber.
[0087] Precursor disiloxane was bombarded with nitrogen atoms and
aluminum atoms in a MBE chamber under condition described in
Example 2. The hardness of Si.sub.2AlN.sub.3O is 25 Gpa.
Example 7
[0088] This Example illustrates the preparation of thin film
B.sub.2C.sub.20 on a silicon substrate.
[0089] Precursor H.sub.3COCH.sub.3 and BCl.sub.3 are contacted in
essentially equimolar amounts in a CVD chamber according to the
method described in Example 1. The chamber was maintained at a
temperature of about 700.degree. C. to 850.degree. C. The thickness
of the deposited B.sub.2C.sub.20 film was about 5 to 500 nm on
Si(100) substrate. Si(III) and doped Si(111) may also be employed
in this example and said substrate may comprise a native oxide
layer or be cleaned by methods known in the art prior to deposition
of B.sub.2C.sub.2O film.
Example 8
[0090] This example illustrates the preparation of disiloxane
H.sub.3SiOSiH.sub.3.
[0091] Commercially available Cl.sub.3SiOSiCl.sub.3 is diluted in
diethyl ether and cooled to 78.degree. C. Solid LiGaH4 is added to
the Cl.sub.3SiOSiCl.sub.3/solution through a solid addition funnel.
Gaseous O(SiH.sub.3) is formed immediately and it is removed and
purified by trap-to-trap distillation. The yield is typically
30-50%. The compound is identified by mass spectrometry and IR
spectroscopy and shown to be identical with commercially available
disiloxane.
[0092] Those skilled in the art will appreciate that numerous
changes and modifications may be made to the preferred embodiments
of the invention and that such changes and modifications may be
made without departing from the spirit of the invention. It is
therefore intended that the appended claims cover all such
equivalent variations as fall within the true spirit and scope of
the invention.
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