U.S. patent application number 09/871958 was filed with the patent office on 2001-09-27 for method for fabricating a semiconductor structure having a crystalline alkaline earth metal oxide interface with silicon.
This patent application is currently assigned to MOTOROLA, INC.. Invention is credited to Curless, Jay A., Droopad, Ravindranath, Hallmark, Jerald A., Ooms, William J., Overgaard, Corey Daniel, Ramdani, Jamal, Wang, Jun, Yu, Zhiyi.
Application Number | 20010023660 09/871958 |
Document ID | / |
Family ID | 23046026 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023660 |
Kind Code |
A1 |
Yu, Zhiyi ; et al. |
September 27, 2001 |
Method for fabricating a semiconductor structure having a
crystalline alkaline earth metal oxide interface with silicon
Abstract
A method for fabricating a semiconductor structure comprises the
steps of providing a silicon substrate (10) having a surface (12);
forming on the surface of the silicon substrate an interface (14)
comprising a single atomic layer of silicon, oxygen, and a metal;
and forming one or more layers of a single crystal oxide (26) on
the interface. The interface comprises an atomic layer of silicon,
oxygen, and a metal in the form XSiO.sub.2, where X is a metal.
Inventors: |
Yu, Zhiyi; (Gilbert, AZ)
; Droopad, Ravindranath; (Tempe, AZ) ; Overgaard,
Corey Daniel; (Phoenix, AZ) ; Ramdani, Jamal;
(Gilbert, AZ) ; Curless, Jay A.; (Tempe, AZ)
; Hallmark, Jerald A.; (Gilbert, AZ) ; Ooms,
William J.; (Chandler, AZ) ; Wang, Jun;
(Gilbert, AZ) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
MOTOROLA, INC.
1303 E. Algonquin Road
Schaumburg
IL
|
Family ID: |
23046026 |
Appl. No.: |
09/871958 |
Filed: |
June 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09871958 |
Jun 4, 2001 |
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09273929 |
Mar 22, 1999 |
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6241821 |
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Current U.S.
Class: |
117/108 |
Current CPC
Class: |
C30B 29/16 20130101;
C30B 29/30 20130101; C30B 23/02 20130101; C30B 25/02 20130101 |
Class at
Publication: |
117/108 |
International
Class: |
C30B 025/00; C30B
023/00; C30B 028/12; C30B 028/14 |
Claims
What is claimed is:
1. A method of fabricating a semiconductor structure comprising the
steps of: providing a silicon substrate having a surface; forming
on the surface of the silicon substrate an interface comprising a
single atomic layer of silicon, oxygen, and a metal; and forming
one or more layers of a single crystal oxide on the interface.
2. The method of fabricating a semiconductor structure of claim 1
wherein the forming the interface step includes forming a 2.times.1
reconstruction.
3. The method of fabricating a semiconductor structure of claim 1
wherein the forming an interface step includes forming the
interface in an ultra-high-vacuum system.
4. The method of fabricating a semiconductor structure of claim 1
wherein the forming an interface step includes forming the
interface in a chemical vapor deposition system.
5. The method of fabricating a semiconductor structure of claim 1
wherein the forming an interface step includes forming the
interface in a physical vapor deposition system.
6. The method of fabricating a semiconductor structure of claim 1
wherein the forming an interface step comprises forming a single
atomic layer of silicon, oxygen, and an alkaline-earth-metal.
7. The method of fabricating a semiconductor structure of claim 6
wherein the alkaline-earth-metal is selected from the group of
barium and strontium.
8. The method of fabricating a semiconductor structure of claim 1
wherein forming an interface step comprises the steps of: forming a
half of a monolayer of an alkaline-earth-metal; forming a half of a
monolayer of silicon; and forming a monolayer of oxygen.
9. A method of fabricating a semiconductor structure comprising the
steps of: providing a silicon substrate having a surface; forming
amorphous silicon dioxide on the surface of the silicon substrate;
providing an alkaline-earth-metal on the amorphous silicon dioxide;
and heating the semiconductor structure to form an interface
comprising a single atomic layer adjacent the surface of the
silicon substrate.
10. The method of fabricating a semiconductor structure of claim 9
wherein the heating step includes forming the interface with a
2.times.1 reconstruction.
11. The method of fabricating a semiconductor structure of claim 9
wherein the steps of providing an alkaline-earth-metal and heating
the semiconductor structure are accomplished in an
ultra-high-vacuum system.
12. The method of fabricating a semiconductor structure of claim 9
wherein the steps of providing an alkaline-earth-metal and heating
the semiconductor structure are accomplished in a chemical vapor
deposition system.
13. The method of fabricating a semiconductor structure of claim 9
wherein the steps of providing an alkaline-earth-metal and heating
the semiconductor structure are accomplished in a physical vapor
deposition system.
14. The method of fabricating a semiconductor structure of claim 9
wherein the heating step includes forming an interface having a
single atomic layer of silicon, oxygen, and an
alkaline-earth-metal.
15. The method of fabricating a semiconductor structure of claim 14
wherein the alkaline-earth-metal is selected from the group of
barium and strontium.
16. The method of fabricating a semiconductor structure of claim 9
wherein heating step includes forming an interface step comprises
the steps of: forming a half of a monolayer of an
alkaline-earth-metal; forming a half of a monolayer of silicon; and
forming a monolayer of oxygen.
17. A method of fabricating a semiconductor structure comprising
the steps of: providing a silicon substrate having a surface;
providing an alkaline-earth-metal on the surface of the silicon
substrate; and providing silicon and oxygen to form an interface
comprising a single atomic interface with the surface of the
silicon substrate.
18. The method of fabricating a semiconductor structure of claim 17
wherein the providing silicon and oxygen step comprises forming an
interface having a 2.times.1 reconstruction.
19. The method of fabricating a semiconductor structure of claim 17
wherein the steps of providing an alkaline-earth-metal and
providing silicon and oxygen are accomplished in an
ultra-high-vacuum system.
20. The method of fabricating a semiconductor structure of claim 17
wherein the steps of providing an alkaline-earth-metal and
providing silicon and oxygen are accomplished in a chemical vapor
deposition system.
21. The method of fabricating a semiconductor structure of claim 17
wherein the steps of providing an alkaline-earth-metal and
providing silicon and oxygen are accomplished in a physical vapor
deposition system.
22. The method of fabricating a semiconductor structure of claim 17
wherein the providing silicon and oxygen step comprises forming a
single atomic layer of silicon, oxygen, and an
alkaline-earth-metal.
23. The method of fabricating a semiconductor structure of claim 22
wherein the alkaline-earth-metal is selected from the group of
barium and strontium.
24. The method of fabricating a semiconductor structure of claim 17
wherein the providing silicon and oxygen step comprises the steps
of: forming a half of a monolayer of an alkaline-earth-metal;
forming a half of a monolayer of silicon; and forming a monolayer
of oxygen.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to a method for
fabricating a semiconductor structure including a crystalline
alkaline earth metal oxide interface between a silicon substrate
and other oxides, and more particularly to a method for fabricating
an interface including an atomic layer of an alkaline earth metal,
silicon, and oxygen.
BACKGROUND OF THE INVENTION
[0002] An ordered and stable silicon (Si) surface is most desirable
for subsequent epitaxial growth of single crystal thin films on
silicon for numerous device applications, e.g., ferroelectrics or
high dielectric constant oxides for non-volatile high density
memory and logic devices. It is pivotal to establish an ordered
transition layer on the Si surface, especially for subsequent
growth of single crystal oxides, e.g., perovskites.
[0003] Some reported growth of these oxides, such as BaO and
BaTiO.sub.3 on Si(100) was based on a BaSi.sub.2 (cubic) template
by depositing one fourth monolayer of Ba on Si(100) using reactive
epitaxy at temperatures greater than 850.degree. C. See for
example: R. McKee et al., Appl. Phys. Lett. 59(7), pp 782-784 (Aug.
12, 1991); R. McKee et al., Appl. Phys. Lett. 63(20), pp. 2818-2820
(Nov. 15, 1993); R. McKee et al., Mat. Res. Soc. Symp. Proc., Vol.
21, pp. 131-135 (1991); U.S. Pat. No. 5,225,031, issued Jul. 6,
1993, entitled "Process for Depositing an Oxide Epitaxially onto a
Silicon Substrate and Structures Prepared with the Process"; and
U.S. Pat. No. 5,482,003, issued Jan. 9, 1996, entitled "Process for
Depositing Epitaxial Alkaline Earth Oxide onto a Substrate and
Structures Prepared with the Process". However, atomic level
simulation of this proposed structure indicates that it likely is
not stable at elevated temperatures.
[0004] Growth of SrTiO.sub.3 on silicon (100) using an SrO buffer
layer has been accomplished. T. Tambo et al., Jpn. J. Appl. Phys.,
Vol. 37 (1998), pp. 4454-4459. However, the SrO buffer layer was
thick (100 .ANG.), thereby limiting application for transistor
films, and crystallinity was not maintained throughout the
growth.
[0005] Furthermore, SrTiO.sub.3 has been grown on silicon using
thick metal oxide buffer layers (60-120 .ANG.) of Sr or Ti. B. K.
Moon et al., Jpn. J. Appl. Phys., Vol. 33 (1994), pp. 1472-1477.
These thick buffer layers would limit the application for
transistors.
[0006] Therefore, a method for fabricating a thin, stable
crystalline interface with silicon is needed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1-2 illustrate a cross-sectional view of a clean
semiconductor substrate having an interface formed thereon in
accordance with the present invention;
[0008] FIGS. 3-6 illustrate a cross-sectional view of a
semiconductor substrate having an interface formed from a silicon
dioxide layer in accordance with the present invention; and
[0009] FIGS. 7-8 illustrate a cross-sectional view of an
alkaline-earth-metal oxide layer formed on the structures
illustrated in FIGS. 1-6 in accordance with the present
invention.
[0010] FIGS. 9-12 illustrate a cross-sectional view of a perovskite
formed on the structures of FIGS. 1-8 in accordance with the
present invention.
[0011] FIG. 13 illustrates a side view of the atomic structure of
one embodiment of the layers of FIG. 12 in accordance with the
present invention.
[0012] FIG. 14 illustrates a top view along view line AA of FIG. 13
of the interface.
[0013] FIG. 15 illustrates a top view along view line AA of FIG. 13
including the interface and the adjacent atomic layer of the
substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] To form the novel interface between a silicon (Si) substrate
and one or more layers of a single crystal oxide, various
approaches may be used. Several examples will be provided for both
starting with a Si substrate having a clean surface, and a Si
substrate having silicon dioxide (SiO.sub.2) on the surface.
SiO.sub.2 is amorphous rather than single crystalline and it is
desirable for purposes of growing additional single crystal
material on the substrate that a single crystal oxide be provided
as the interface.
[0015] Turning now to the drawings in which like elements are
designated with like numbers throughout, FIGS. 1 and 2 illustrate a
semiconductor structure including a Si substrate 10 having a clean
surface 12. A clean (2.times.1) surface 12 may be obtained with any
conventional cleaning procedure, for example, with thermal
desorption of SiO.sub.2 at a temperature greater than or equal to
850.degree. C., or by removal of the hydrogen from a hydrogen
terminated Si(1.times.1) surface at a temperature greater than or
equal to 300.degree. C. in an ultra high vacuum. Hydrogen
termination is a well known process in which hydrogen is loosely
bonded to dangling bonds of the silicon atoms at surface 12 to
complete the crystalline structure. The interface 14 of a
crystaline material may be formed by supplying (as shown by the
arrows in FIG. 1) controlled amounts of a metal, Si, and O.sub.2,
either simultaneously or sequentially to the surface 12 at a
temperature less than or equal to 900.degree. C. in a growth
chamber with O.sub.2 partial pressure less than or equal to
1.times.10.sup.-9 mBar. The metal applied to the surface 12 to form
the interface 14 may be any metal, but in the preferred embodiment
comprises an alkaline-earth-metal, such as barium (Ba) or strontium
(Sr).
[0016] As the application of the Ba, Si, and O.sub.2 form
BaSiO.sub.2 as the interface 14, the growth is monitored using
Reflection High Energy Electron Diffraction (RHEED) techniques
which are well documented in the art and which can be used in situ,
i.e., while performing the exposing step within the growth chamber.
The RHEED techniques are used to detect or sense surface
crystalline structures and in the present process change rapidly to
strong and sharp streaks by the forming of an atomic layer of the
BaSiO.sub.2. It will of course be understood that once a specific
manufacturing process is provided and followed, it may not be
necessary to perform the RHEED techniques on every substrate.
[0017] The novel atomic structure of the interface 14 will be
described in subsequent paragraphs.
[0018] It should be understood by those skilled in the art that the
temperatures and pressures given for these processes are
recommended for the particular embodiment described, but the
invention is not limited to a particular temperature or pressure
range.
[0019] Referring to FIGS. 3-6, another approach comprises forming a
Si substrate 10 having a surface 12, and a layer 16 of SiO.sub.2
thereupon. The layer 16 of SiO.sub.2 naturally exists (native
oxide) once the Si substrate 10 is exposed to air (oxygen) or it
may be formed purposely in a controlled fashion well known in the
art, e.g., thermally by applying (arrows) oxygen onto the surface
12. The novel interface 14 may be formed at least in one of the two
suggested embodiments as follows: By applying an
alkaline-earth-metal to the surface 18 of SiO.sub.2 layer 16 at
700-900.degree. C., under an ultra high vacuum. More specifically,
the Si substrate 10 and the amorphous SiO.sub.2 layer 16 are heated
to a temperature below the sublimation temperature of the SiO.sub.2
layer 16 (generally below 900.degree. C.). This can be accomplished
in a molecular beam epitaxy chamber or Si substrate 10 can be at
least partially heated in a preparation chamber after which it can
be transferred to the growth chamber and the heating completed.
Once the Si substrate 10 is properly heated and the pressure in the
growth chamber has been reduced appropriately, the surface 12 of
the Si substrate 10 having SiO.sub.2 layer 16 thereon is exposed to
a beam of metal, preferrably an alkaline-earth-metal, as
illustrated in FIG. 5. In a preferred embodiment, the beam is Ba or
Sr which is generated by resistively heating effusion cells or from
e-beam evaporation sources. In a specific example, Si substrate 10
and SiO.sub.2 layer 16 are exposed to a beam of Ba. The Ba joins
the SiO.sub.2 and converts the SiO.sub.2 layer 16 into the
interface 14 comprising BaSiO.sub.2in a crystalline form.
Alternatively, an alkaline-earth-metal may be provided to the
surface 18 at lower temperatures, annealing the result at
700-900.degree. C., in an ultra high vacuum.
[0020] Once the interface 14 is formed, one or more layers of a
single crystal oxide may be formed on the surface of the interface
14. However, an optional layer of an alkaline-earth-metal oxide,
such as BaO or SrO, may be placed between the interface 14 and the
single crystal oxide. This alkaline-earth-metal oxide provides a
low dielectric constant (advantageous for certain uses such as
memory cells) and also prevents oxygen from migrating from the
single crystal oxide to the Si substrate 10.
[0021] Referring to FIGS. 7 and 8, the formation of
alkaline-earth-metal oxide layer 22 may be accomplished by either
the simultaneous or alternating supply to the surface 20 of the
interface 14 of an alkaline-earth-metal and oxygen at less than or
equal to 700.degree. C. and under O.sub.2 partial pressure less
than or equal to 1.times.10.sup.-5 mBar. This alkaline-earth-metal
oxide layer 22 may, for example, comprise a thickness of 50-500
.ANG..
[0022] Referring to FIGS. 9-12, a single crystal oxide layer 26,
such as an alkaline-earth-metal perovskite, may be formed on either
the surface 20 of the interface 14 or the surface 24 of the
alkaline-earth-metal oxide layer 22 by either the simultaneous or
alternating supply of an alkaline-earth-metal oxide, oxygen, and a
transition metal, such as titanium, at less than or equal to
700.degree. C. under an oxygen partial pressure less than or equal
to 1.times.10.sup.-5 mBar. This single crystal oxide layer 26 may,
for example, comprise a thickness of 50-1000 .ANG. and will be
substantially lattice matched with the underlying interface 14 or
alkaline-earth-metal oxide layer 22. It should be understood that
the single crystal oxide layer 26 may comprises one or more layers
in other embodiments.
[0023] Referring to FIG. 13, a side view (looking in the
<{overscore (l)}10> direction) of the atomic configuration of
the Si substrate 10, interface 14, and alkaline-earth-metal metal
oxygen layer 26 is shown. The configuration shown comprises, in
relative sizes, for illustrative purposes, from larger to smaller,
barium atoms 30, silicon atoms 32, oxygen atoms 34, and titanium
atoms 36. The Si substrate 10 comprises only silicon atoms 32. The
interface 14 comprises metal atoms (which in the preferred
embodiment are illustrated as barium atoms 30), silicon atoms 32,
and oxygen atoms 34. The alkaline-earth-metal metal oxygen layer 26
comprises barium atoms 30, oxygen atoms 34, and titanium atoms
36.
[0024] Referring to FIG. 14, a top view of the interface along view
line AA of FIG. 13, shows the arrangement of the barium, silicon,
and oxygen atoms 30, 32, 34.
[0025] Referring to FIG. 15, a top view along line AA of FIG. 13,
shows the interface 14 and the top atomic layer 11 of the Si
substrate 10.
[0026] For this discussion, a monolayer equals 6.8.times.10.sup.14
atoms/cm.sup.2 and an atomic layer is one atom thick. It is seen
that the interface 14 shown in the FIGS. comprises a single atomic
layer, but could be more than one atomic layer, while the Si
substrate 10 and the alkaline-earth-metal metal oxide layer may be
many atomic layers. Note that in FIG. 13, only four atomic layers
of the Si substrate 10 and only three atomic layers of the
alkaline-earth-metal metal oxide layer 26 are shown. The interface
14 comprises a half monolayer of the alkaline-earth-metal, a half
monolayer of silicon, and a monolayer of oxygen. Each barium atom
30 is substantially equally spaced from four of the silicon atoms
32 in the Si substrate 10. The silicon atoms 32 in the interface 14
are substantially on a line and equally spaced between the
alkaline-earth-metal atoms in the <110> direction. Each
silicon atom 32 in the top layer of atoms in the Si substrate 10 is
bonded to an oxygen atom 34 in the interface 14 and each silicon
atom 32 in the interface 14 is bonded to two oxygen atoms 34 in the
interface 14. The interface 14 comprises rows of barium, silicon,
and oxygen atoms 30, 32, 34 in a 2.times.1 configuration on a (001)
surface of the Si substrate 10, 1.times. in the <{overscore
(l)}10> direction and 2.times. in the <110> direction. The
interface 14 has a 2.times.1 reconstruction.
[0027] A method for fabricating a thin, crystalline interface 14
with silicon 10 has been described herein. The interface 14 may
comprise a single atomic layer. Better transistor applications are
achieved by the interface 14 being thin, in that the electrical
coupling of the overlying oxide layers to the Si substrate 10 is
not compromised, and in that the interface 14 is more stable since
the atoms will more likely maintain their crystalinity in
processing.
* * * * *