U.S. patent application number 11/523105 was filed with the patent office on 2008-05-29 for active regions with compatible dielectric layers.
Invention is credited to Pushkar Ranade.
Application Number | 20080121932 11/523105 |
Document ID | / |
Family ID | 39200833 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080121932 |
Kind Code |
A1 |
Ranade; Pushkar |
May 29, 2008 |
Active regions with compatible dielectric layers
Abstract
A method to form a semiconductor structure with an active region
and a compatible dielectric layer is described. In one embodiment,
a semiconductor structure has a dielectric layer comprised of an
oxide of a first semiconductor material, wherein a second (and
compositionally different) semiconductor material is formed between
the dielectric layer and the first semiconductor material. In
another embodiment, a portion of the second semiconductor material
is replaced with a third semiconductor material in order to impart
uniaxial strain to the lattice structure of the second
semiconductor material.
Inventors: |
Ranade; Pushkar; (Hillsboro,
OR) |
Correspondence
Address: |
INTEL/BLAKELY
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Family ID: |
39200833 |
Appl. No.: |
11/523105 |
Filed: |
September 18, 2006 |
Current U.S.
Class: |
257/192 ;
257/183; 257/E21.426; 257/E21.431; 257/E29.068; 257/E29.266;
257/E29.286 |
Current CPC
Class: |
H01L 21/31604 20130101;
H01L 29/785 20130101; H01L 21/02236 20130101; H01L 29/41783
20130101; H01L 29/6653 20130101; H01L 29/0847 20130101; H01L
21/02148 20130101; H01L 21/02183 20130101; H01L 21/0254 20130101;
H01L 29/78654 20130101; H01L 29/16 20130101; H01L 29/66545
20130101; H01L 21/02159 20130101; H01L 21/02164 20130101; H01L
29/1054 20130101; H01L 29/41766 20130101; H01L 29/66795 20130101;
H01L 21/28264 20130101; H01L 21/02178 20130101; H01L 29/513
20130101; H01L 29/7833 20130101; H01L 21/0217 20130101; H01L
21/02238 20130101; H01L 21/02546 20130101; H01L 29/66636 20130101;
H01L 29/0653 20130101; H01L 29/165 20130101; H01L 29/20 20130101;
H01L 29/512 20130101; H01L 21/0228 20130101; H01L 29/267 20130101;
H01L 29/517 20130101; H01L 29/66492 20130101; H01L 29/66522
20130101; H01L 21/02189 20130101; H01L 29/0649 20130101; H01L
27/0886 20130101; H01L 29/6656 20130101; H01L 29/205 20130101; H01L
21/02192 20130101; H01L 21/02197 20130101; H01L 21/28255 20130101;
H01L 29/4238 20130101; H01L 21/02532 20130101; H01L 29/0673
20130101; H01L 21/02181 20130101; H01L 21/47 20130101; H01L
21/31055 20130101; H01L 29/66651 20130101; H01L 21/02543 20130101;
H01L 29/66628 20130101; H01L 29/7851 20130101; H01L 21/02549
20130101; H01L 21/28167 20130101; H01L 29/66553 20130101; H01L
29/7848 20130101 |
Class at
Publication: |
257/192 ;
257/183; 257/E29.068 |
International
Class: |
H01L 29/78 20060101
H01L029/78 |
Claims
1. A semiconductor structure comprising: a substrate comprised of a
first semiconductor material; an active region above said
substrate, wherein said active region is comprised of a second
semiconductor material, and wherein the composition of said second
semiconductor material is different from that of said first
semiconductor material; and a dielectric layer directly above said
active region, wherein said dielectric layer is comprised of a
layer of oxide of said first semiconductor material directly above
said active region.
2. The semiconductor structure of claim 1 wherein said first
semiconductor material is comprised of silicon, and wherein said
layer of oxide is selected from the group consisting of a layer of
silicon dioxide or silicon oxy-nitride.
3. The semiconductor structure of claim 2 wherein the atomic
concentration of silicon atoms in said first semiconductor material
is greater than 97%.
4. The semiconductor structure of claim 1 wherein said second
semiconductor material is comprised of a material selected from the
group consisting of gallium nitride, gallium phosphide, gallium
arsenide, indium phosphide, indium antimonide, indium gallium
arsenide, aluminum gallium arsenide, indium gallium phosphide,
germanium or silicon/germanium with an atomic concentration of
germanium atoms greater than 5%.
5. The semiconductor structure of claim 4 wherein said first
semiconductor material is comprised of silicon, and wherein said
layer of oxide is selected from the group consisting of a layer of
silicon dioxide or silicon oxy-nitride.
6. The semiconductor structure of claim 1 wherein said dielectric
layer further comprises a layer of a high-K dielectric material
above said layer of oxide of said first semiconductor material.
7. The semiconductor structure of claim 6, wherein said first
semiconductor material is comprised of silicon, wherein said layer
of oxide is selected from the group consisting of a layer of
silicon dioxide or silicon oxy-nitride, and wherein said high-K
dielectric material is selected from the group consisting of
hafnium oxide, hafnium silicate, lanthanum oxide, zirconium oxide,
zirconium silicate, tantalum oxide, barium strontium titanate,
barium titanate, strontium titanate, yttrium oxide, aluminum oxide,
lead scandium tantalum oxide, lead zinc niobate or a combination
thereof.
8. A semiconductor device comprising: a substrate comprised of a
first semiconductor material; an active region above said
substrate, wherein said active region is comprised of a second
semiconductor material, and wherein the composition of said second
semiconductor material is different from that of said first
semiconductor material; a gate dielectric layer directly above said
active region, wherein said gate dielectric layer is comprised of a
layer of oxide of said first semiconductor material directly above
said active region; a gate electrode above said gate dielectric
layer; a pair of tip extensions on either side of said gate
electrode and in said active region; a pair of gate isolation
spacers adjacent to the sidewalls of said gate electrode and above
said pair of tip extensions; and a pair of source/drain regions on
either side of said pair of gate isolation spacers and in said
active region.
9. The semiconductor device of claim 8 wherein said first
semiconductor material is comprised of silicon, and wherein said
layer of oxide is selected from the group consisting of a layer of
silicon dioxide or silicon oxy-nitride.
10. The semiconductor device of claim 9 wherein the atomic
concentration of silicon atoms in said first semiconductor material
is greater than 97%.
11. The semiconductor device of claim 8 wherein said second
semiconductor material is comprised of a material selected from the
group consisting of gallium nitride, gallium phosphide, gallium
arsenide, indium phosphide, indium antimonide, indium gallium
arsenide, aluminum gallium arsenide, indium gallium phosphide,
germanium or silicon/germanium with an atomic concentration of
germanium atoms greater than 5%.
12. The semiconductor device of claim 11 wherein said first
semiconductor material is comprised of silicon, and wherein said
layer of oxide is selected from the group consisting of a layer of
silicon dioxide or silicon oxy-nitride.
13. The semiconductor device of claim 8 wherein said gate
dielectric layer further comprises a layer of a high-K dielectric
material above said layer of oxide of said first semiconductor
material.
14. The semiconductor device of claim 13, wherein said first
semiconductor material is comprised of silicon, wherein said layer
of oxide is selected from the group consisting of a layer of
silicon dioxide or silicon oxy-nitride, and wherein said high-K
dielectric material is selected from the group consisting of
hafnium oxide, hafnium silicate, lanthanum oxide, zirconium oxide,
zirconium silicate, tantalum oxide, barium strontium titanate,
barium titanate, strontium titanate, yttrium oxide, aluminum oxide,
lead scandium tantalum oxide, lead zinc niobate or a combination
thereof.
15. The semiconductor device of claim 8 wherein said pair of
source/drain regions is comprised of a third semiconductor
material, and wherein the composition of said third semiconductor
material is different from that of said second semiconductor
material.
16. A semiconductor device comprising: a substrate comprised of a
first semiconductor material; an active region above said
substrate, wherein said active region is comprised of a second
semiconductor material, and wherein the composition of said second
semiconductor material is different from that of said first
semiconductor material; a gate dielectric layer above said active
region; a gate electrode above said gate dielectric layer; a pair
of tip extensions on either side of said gate electrode and in said
active region; a pair of gate isolation spacers adjacent to the
sidewalls of said gate electrode and above said pair of tip
extensions; and a pair of source/drain regions on either side of
said pair of gate isolation spacers and in said active region,
wherein said pair of source/drain regions is comprised of a third
semiconductor material, and wherein the composition of said third
semiconductor material is different from that of said second
semiconductor material.
17. The semiconductor device of claim 16 wherein the atomic
concentration of silicon atoms in said first semiconductor material
is greater than 97%.
18. The semiconductor device of claim 17 wherein said second
semiconductor material is comprised of a material selected from the
group consisting of gallium nitride, gallium phosphide, gallium
arsenide, indium phosphide, indium antimonide, indium gallium
arsenide, aluminum gallium arsenide, indium gallium phosphide,
germanium or silicon/germanium with an atomic concentration of
germanium atoms greater than 5%.
19. The semiconductor device of claim 16, wherein said gate
dielectric layer is comprised of a material selected from the group
consisting of silicon dioxide, silicon oxy-nitride, hafnium oxide,
hafnium silicate, lanthanum oxide, zirconium oxide, zirconium
silicate, tantalum oxide, barium strontium titanate, barium
titanate, strontium titanate, yttrium oxide, aluminum oxide, lead
scandium tantalum oxide, lead zinc niobate or a combination
thereof.
20.-45. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The invention is in the field of Semiconductor
Structures.
[0003] 2) Description of Related Art
[0004] For the past several decades, semiconductor devices such as
Metal Oxide Semiconductor Field-Effect Transistors (MOS-FETs) have
been fabricated using doped crystalline silicon for active regions,
e.g. channel regions, and amorphous silicon dioxide for dielectric
regions, e.g. gate dielectric layers. The beauty of the
silicon/silicon dioxide pairing is that the silicon dioxide can be
formed directly on the surface of a crystalline silicon substrate
via heating the substrate in the presence of oxygen. The process is
very controllable and can reliably provide silicon dioxide films as
thin as 2-3 monolayers thick.
[0005] In the drive for ever-faster semiconductor devices, however,
it may be desirable to utilize a channel material other than
crystalline silicon. One caveat is that very few other
semiconductor materials, if any, form as compatible a surface
amorphous oxide layer as does the crystalline silicon/silicon
dioxide pairing. This has made the utilization of channel materials
other than silicon quite daunting. Thus, a method to form active
regions with compatible dielectric layers, and the resultant
structures, is described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIGS. 1A-B illustrate cross-sectional views representing
semiconductor structures having active regions with compatible
dielectric layers, in accordance with an embodiment of the present
invention.
[0007] FIGS. 2A-N illustrate cross-sectional views representing the
formation of a planar MOS-FET having active regions with compatible
dielectric layers, in accordance with an embodiment of the present
invention.
[0008] FIGS. 3A-C illustrate cross-sectional views representing the
formation of a tri-gate MOS-FET having active regions with
compatible dielectric layers, in accordance with an embodiment of
the present invention.
DETAILED DESCRIPTION
[0009] A process for fabricating semiconductor devices, and the
resultant devices, is described. In the following description,
numerous specific details are set forth, such as specific
dimensions and chemical regimes, in order to provide a thorough
understanding of the present invention. It will be apparent to one
skilled in the art that the present invention may be practiced
without these specific details. In other instances, well-known
processing steps, such as patterning steps or wet chemical cleans,
are not described in detail in order to not unnecessarily obscure
the present invention. Furthermore, it is understood that the
various embodiments shown in the figures are illustrative
representations and are not necessarily drawn to scale.
[0010] Disclosed herein are semiconductor structures having active
regions with compatible dielectric layers and methods to form the
same. Controlled thermal or native growth of an oxide, via
consumption of the top surface of a semiconductor substrate in an
oxidation process, can provide a reliable dielectric layer.
However, it may be desirable to retain the reliable dielectric
layer, yet replace the portion of the semiconductor substrate
directly under the reliable dielectric layer with a different
semiconductor material. This subsequent replacement of a portion of
the semiconductor substrate with a different semiconductor material
directly below the dielectric layer may enable the formation of a
new active region with a reliable dielectric layer. Thus, a
structure may be formed wherein a dielectric layer comprising an
oxide of a first semiconductor material is retained directly above
a second, and different, semiconductor material. This process and
the resulting structure can be particularly beneficial in cases
where the oxide of the second semiconductor material has inferior
characteristics to the oxide of the first semiconductor material,
but incorporation of the second semiconductor material is
nonetheless desirable. Furthermore, a portion of the second
semiconductor material may be replaced with a third semiconductor
material in order to impart uniaxial strain to the lattice
structure of the second semiconductor material. The combination of
incorporating an optimal semiconductor material to form an active
region and applying uniaxial strain to that active region can lead
to increased charge carrier mobility in the channel region of a
semiconductor device. Thus, optimization of high performance
semiconductor devices may be achieved.
[0011] The controlled consumption of the top surface of a
semiconductor substrate via an oxidation process can provide a
reliable (i.e. uniform thickness and consistent composition)
dielectric layer on the surface of that substrate. For example,
thermal or native growth of silicon dioxide on the surface of a
crystalline silicon substrate provides a reliable dielectric layer
as thin as 3-10 Angstroms (i.e. 1-3 monolayers). The resulting
oxide layer may be used as a gate dielectric layer, or a component
thereof, in a semiconductor device. In accordance with an
embodiment of the present invention, a silicon dioxide layer is
formed on the surface of a crystalline silicon substrate by heating
the crystalline silicon substrate in the presence of an oxidizing
agent, such as O.sub.2, H.sub.2O, or O.sub.3. In accordance with an
alternative embodiment of the present invention, a native layer of
silicon dioxide is formed upon exposure of a crystalline silicon
substrate to a water pulse in an atomic layer deposition (ALD)
chamber. A bi-layer dielectric layer can be formed by depositing a
layer of a high-K dielectric material directly above the native
silicon dioxide layer.
[0012] In some applications, a crystalline silicon substrate may
not be the most desirable material for use as an active region
(e.g. a channel region) in a semiconductor device. For example, in
accordance with an embodiment of the present invention, it is
desirable to use germanium as the channel material in a P-type
device, while it is desirable to use a III-V material as the
channel material in an N-type device. In another embodiment, one of
germanium or a III-V material is used for both the P-type device
and the N-type device. By incorporating these channel materials
into such devices, the hole mobility and the electron mobility,
respectively, may be optimized for improved device performance.
However, the oxidation of the surfaces of germanium and III-V
materials tends to provide oxide layers that are unstable and/or
non-uniform in thickness or composition. It may therefore be
desirable to combine a semiconductor material with an oxide layer
of a different semiconductor material. Thus, in accordance with an
embodiment of the present invention, a semiconductor material that
would otherwise provide an inferior oxide layer is combined with a
reliable oxide layer, wherein the oxide layer is an oxide of a
different semiconductor material.
[0013] In order to provide a semiconductor structure comprising a
second semiconductor material in combination with an oxide layer of
a first semiconductor material, a replacement approach may be
utilized. In effect, the oxide layer may be formed above a first
semiconductor material, a portion of which is then removed to form
a trench between the oxide layer and the first semiconductor
material. A second semiconductor material may then be formed in the
trench. Thus, in accordance with an embodiment of the present
invention, a portion of a semiconductor substrate comprised of a
first semiconductor material is replaced with a second
semiconductor material (i.e. an active region) directly between a
pre-formed oxide layer and the semiconductor substrate.
[0014] A semiconductor region formed on or in a crystalline
semiconductor material may impart a strain to the crystalline
semiconductor material, and hence may be a strain-inducing
semiconductor region, if the lattice constant of the semiconductor
region is different from the lattice constant of the crystalline
semiconductor material. The lattice constants are based on the
atomic spacings and the unit cell orientations within each of the
semiconductor region and the crystalline semiconductor material.
Thus, a semiconductor region comprising different species of
lattice-forming atoms than the crystalline semiconductor material
may impart a strain to the crystalline semiconductor material. For
example, in accordance with an embodiment of the present invention,
a semiconductor region that comprises only silicon lattice-forming
atoms imparts a strain to a crystalline semiconductor material
comprised of germanium lattice-forming atoms. Furthermore, a
semiconductor region comprising the same species of lattice-forming
atoms as the crystalline semiconductor material, but wherein the
species of lattice-forming atoms are present in different
stoichiometric concentrations, may impart a strain to the
crystalline semiconductor material. For example, in accordance with
an embodiment of the present invention, a semiconductor region that
comprises Si.sub.xGe.sub.1-x lattice-forming atoms (where
0<x<1) imparts a strain to a crystalline semiconductor
material comprised of Si.sub.yGe.sub.1-y lattice-forming atoms
(where 0<y<1, and x.noteq.y).
[0015] As an example of an embodiment of the present invention,
FIGS. 1A-B illustrate cross-sectional views representing
semiconductor structures having active regions with compatible
dielectric layers. Referring to FIG. 1A, a semiconductor structure
100 is comprised of a substrate 102, which is comprised of a first
semiconductor material. An active region 104 is above substrate 102
and the active region is comprised of a second semiconductor
material. In accordance with an embodiment of the present
invention, the composition (i.e. the atomic make-up) of the second
semiconductor material is different for that of the first
semiconductor material. A dielectric layer 106 is directly above
active region 104 and may comprise a layer of oxide of the first
semiconductor material. A conductive region 108 is above dielectric
layer 106, which isolates conductive region 108 from active region
104.
[0016] Substrate 102 may comprise any semiconductor material that
can withstand a manufacturing process. In an embodiment, substrate
102 is comprised of a crystalline silicon or silicon/germanium
layer doped with a charge carrier, such as but not limited to
phosphorus, arsenic, boron or a combination thereof. In one
embodiment, the concentration of silicon atoms in substrate 102 is
greater than 97%. In another embodiment, substrate 102 is comprised
of an epitaxial layer grown atop a distinct crystalline substrate,
e.g. a silicon epitaxial layer grown atop a boron-doped bulk
silicon mono-crystalline substrate. Substrate 102 may comprise an
insulating layer in between a bulk crystal substrate and an
epitaxial layer to form, for example, a silicon-on-insulator
substrate. In an embodiment, the insulating layer is comprised of a
material selected form the group consisting of silicon dioxide,
silicon nitride, silicon oxy-nitride or a high-k dielectric
layer.
[0017] Active region 104 may comprise any semiconductor material in
which charges can migrate. In an embodiment, active region 104 is
comprised of a III-V material such as, but not limited to, gallium
nitride, gallium phosphide, gallium arsenide, indium phosphide,
indium antimonide, indium gallium arsenide, aluminum gallium
arsenide, indium gallium phosphide or a combination thereof. In
another embodiment, active region 104 is comprised of germanium or
silicon/germanium with an atomic concentration of germanium atoms
greater than 5%. Active region 104 may incorporate charge-carrier
dopant impurity atoms. In one embodiment, active region 104 is a
crystalline silicon/germanium active region of the stoichiometry
Si.sub.xGe.sub.1-x, where 0.ltoreq.x.ltoreq.1, and the
charge-carrier dopant impurity atoms are selected from the group
consisting of boron, arsenic, indium or phosphorus. In another
embodiment, active region 104 is comprised of a III-V material and
the charge-carrier dopant impurity atoms are selected from the
group consisting of carbon, silicon, germanium, oxygen, sulfur,
selenium or tellurium.
[0018] Dielectric layer 106 may comprise any dielectric material
suitable to insulate a conductive region 108 from active region
104. Furthermore, dielectric layer 106 may comprise a layer of
oxide of a semiconductor material different than that of the
semiconductor material of active region 104. In an embodiment,
dielectric layer 106 is comprised of an oxide of a semiconductor
material. In one embodiment, dielectric layer 106 is comprised of
silicon dioxide or silicon oxy-nitride. In an embodiment,
dielectric layer 106 is comprised of an oxide layer of the
semiconductor material of substrate 102. In a specific embodiment,
substrate 102 is comprised of silicon and dielectric layer 106 is
comprised of silicon dioxide or silicon oxy-nitride. In an
embodiment, dielectric layer 106 is comprised of an oxide layer
that is directly above active region 104. In one embodiment,
dielectric layer 106 is comprised of an oxide layer of the
semiconductor material of substrate 102, active region 104 is
comprised of a semiconductor material different from the
semiconductor material of substrate 102, and the oxide layer of
dielectric layer 106 is directly on the top surface of active
region 104. In a specific embodiment, dielectric layer 106 is
comprised of a silicon dioxide or silicon oxy-nitride, substrate
102 is comprised of silicon, and active region 104 is comprised of
germanium or a III-V material. Alternatively, dielectric layer 106
may be comprised of a high-K dielectric layer. In one embodiment,
the high-K dielectric layer is selected from the group consisting
of hafnium oxide, hafnium silicate, lanthanum oxide, zirconium
oxide, zirconium silicate, tantalum oxide, barium strontium
titanate, barium titanate, strontium titanate, yttrium oxide,
aluminum oxide, lead scandium tantalum oxide, lead zinc niobate or
a combination thereof.
[0019] Conductive region 108 may comprise any material suitable to
conduct a current. In an embodiment, conductive region 108 is
comprised of doped polycrystalline silicon. In another embodiment,
conductive region 108 is comprised of a metal layer such as, but
not limited to, metal nitrides, metal carbides, metal silicides,
hafnium, zirconium, titanium, tantalum, aluminum, ruthenium,
palladium, platinum, cobalt, nickel or conductive metal oxides,
e.g. ruthenium oxide.
[0020] Referring to FIG. 1B, additional features useful for the
fabrication of a semiconductor device 110 may be incorporated into
semiconductor structure 100. A pair of tip extensions 112 are
formed in active region 104 and are separated by a channel region
114, which comprises a portion of active region 104. Conductive
region 108 may be a gate electrode, the top surface of which may be
protected by a gate electrode protection layer 116 and the
sidewalls of which are protected by a pair of gate isolations
spacers 118. The pair of gate isolation spacers 116 is above the
pair of tip extensions 112. A pair of source/drain regions 120 is
formed in active region 104 on either side of gate isolation
spacers 118. The pair of source/drain regions 120 may be raised
above the top surface of active region 104, as depicted in FIG. 1B.
Dielectric layer 106 may be a gate dielectric layer and may be
comprised of two distinct dielectric layers, a lower layer 106A and
an upper layer 106B, also depicted in FIG. 1B.
[0021] The pair of tip extensions 112 may comprises portions of
active region 104 that incorporate charge-carrier dopant impurity
atoms. In one embodiment, active region 104 is a crystalline
silicon/germanium active region of the stoichiometry
Si.sub.xGe.sub.1-x, where 0.ltoreq.x.ltoreq.1, and the
charge-carrier dopant impurity atoms are selected from the group
consisting of boron, arsenic, indium or phosphorus. In another
embodiment, active region 104 is comprised of a III-V material and
the charge-carrier dopant impurity atoms are selected from the
group consisting of carbon, silicon, germanium, oxygen, sulfur,
selenium or tellurium.
[0022] Gate electrode protection layer 116 and the pair of gate
isolation spacers 118 may comprise any materials suitable to
isolate gate electrode. The same species of material, however, need
not be used for both gate electrode protection layer 116 and gate
isolation spacers 118. In an embodiment, gate electrode protection
layer 116 and gate isolation spacers 118 are comprised of
insulating materials. In a particular embodiment, gate electrode
protection layer 116 and gate isolation spacers 118 are comprised
of a material selected from the group comprising silicon dioxide,
silicon oxy-nitride, carbon-doped silicon oxide, silicon nitride,
carbon-doped silicon nitride or a combination thereof.
[0023] The pair of source/drain regions 120 may comprises portions
of active region 104 that incorporate charge-carrier dopant
impurity atoms. In one embodiment, active region 104 is a
crystalline silicon/germanium active region of the stoichiometry
Si.sub.xGe.sub.1-x, where 0.ltoreq.x.ltoreq.1, and the
charge-carrier dopant impurity atoms are selected from the group
consisting of boron, arsenic, indium or phosphorus. In another
embodiment, active region 104 is comprised of a III-V material and
the charge-carrier dopant impurity atoms are selected from the
group consisting of carbon, silicon, germanium, oxygen, sulfur,
selenium or tellurium. Alternatively, the pair of source/drain
regions 120 may comprise a semiconductor material that is different
from the semiconductor material of active region 104. In an
embodiment, the lattice-constant of the semiconductor material of
source/drain region is different from the lattice-constant of the
semiconductor material of active region 104 and, thus, the pair of
source/drain regions 120 is a pair of uniaxial strain-inducing
source/drain regions. In one embodiment, active region 104 is
comprised of Si.sub.xGe.sub.1-x and the pair of source/drain
regions 120 is comprised of Si.sub.yGe.sub.1-y where 0.ltoreq.x,
y.ltoreq.1 and x.noteq.y. In another embodiment, active region 104
is comprised of Al.sub.xGa.sub.1-xAs, In.sub.xGa.sub.1-xAs,
In.sub.xGa.sub.1-xP or Al.sub.xIn.sub.1-xSb and the pair of
source/drain regions 120 is comprised of Al.sub.yGa.sub.1-yAs,
In.sub.yGa.sub.1-yAs, In.sub.yGa.sub.1-yP or Al.sub.yIn.sub.1-ySb,
respectively, where 0.ltoreq.x, y.ltoreq.1 and x.noteq.y.
[0024] Dielectric layer 106 may be comprised of two distinct
dielectric layers, a lower layer 106A and an upper layer 106B. In
an embodiment, lower layer 106A is comprised of comprised of an
oxide of a semiconductor material. In one embodiment, lower layer
106A is comprised of silicon dioxide or silicon oxy-nitride. In an
embodiment, lower layer 106A is comprised of an oxide layer of the
semiconductor material of substrate 102. In a specific embodiment,
substrate 102 is comprised of silicon and lower layer 106A is
comprised of silicon dioxide or silicon oxy-nitride. In an
embodiment, lower layer 106A is comprised of an oxide layer that is
directly above active region 104. In one embodiment, lower layer
106A is comprised of an oxide layer of the semiconductor material
of substrate 102, active region 104 is comprised of a semiconductor
material different from the semiconductor material of substrate
102, and lower layer 106A is directly on the top surface of active
region 104. In a specific embodiment, lower layer 106A is comprised
of a silicon dioxide or silicon oxy-nitride, substrate 102 is
comprised of silicon, and active region 104 is comprised of
germanium or a III-V material. In an embodiment, upper layer 106B
is comprised of silicon dioxide or silicon oxy-nitride. In an
alternative embodiment, upper layer 106B is comprised of a high-K
dielectric layer. In one embodiment, the high-K dielectric layer is
selected from the group consisting of hafnium oxide, hafnium
silicate, lanthanum oxide, zirconium oxide, zirconium silicate,
tantalum oxide, barium strontium titanate, barium titanate,
strontium titanate, yttrium oxide, aluminum oxide, lead scandium
tantalum oxide, lead zinc niobate or a combination thereof. In a
particular embodiment, semiconductor substrate 102 is comprised of
silicon, lower layer 106A is comprised of silicon dioxide or
silicon oxy-nitride, and upper layer 106B is comprised of a high-K
dielectric layer.
[0025] Semiconductor structures having active regions with
compatible dielectric layers may be used to form semiconductor
devices. In one embodiment, the semiconductor device is a planar
MOS-FET, a memory transistor or a micro-electronic machine (MEM).
In another embodiment, the semiconductor device is a non-planar
device, such as a tri-gate or FIN-FET transistor, an
independently-accessed double-gated MOS-FET, or a gate-all-around
MOS-FET with a nanowire channel. FIGS. 2A-N illustrate
cross-sectional views representing the formation of a planar
MOS-FET having active regions with compatible dielectric layers, in
accordance with an embodiment of the present invention. In one
embodiment, such a process enables the formation of a high quality
dielectric layer (comprising an oxide of a first semiconductor
material) on an active region (i.e. the second, replacement
semiconductor material) comprised of a semiconductor material that
does not typically yield an oxide of high quality. As will be
appreciated in the typical integrated circuit, both N-- and
P-channel transistors may be fabricated in a single substrate or
epitaxial layer to form a CMOS integrated circuit.
[0026] Referring to FIG. 2A, a gate dielectric layer 206 is formed
above a substrate 202. Substrate 202 may comprise any material
discussed in association with substrate 102 from FIGS. 1A-B.
Likewise, gate dielectric layer 206 may comprise any material
discussed in association with dielectric layer 106 from FIG. 1A.
Gate dielectric layer 206 may be formed from an oxide of substrate
202 by any technique suitable to provide a reliable (i.e. uniform
composition and thickness) dielectric layer above the top surface
of substrate 202. In accordance with an embodiment of the present
invention, gate dielectric layer 206 is formed by consuming a
portion of the top surface of substrate 202. In one embodiment,
gate dielectric layer 206 is formed by oxidizing the top surface of
substrate 202 to form an oxide layer comprised of an oxide of the
semiconductor material of substrate 202. In a particular
embodiment, gate dielectric layer 206 is formed by heating
substrate 202 in the presence of an oxidizing agent, such as
O.sub.2, H.sub.2O or O.sub.3, until a desired thickness of an oxide
layer is formed. In a specific embodiment, substrate 202 is
comprised of silicon, gate dielectric layer 206 is comprised of a
layer of silicon dioxide, the formation of the layer of silicon
dioxide is carried out at a temperature in the range of 600-800
degrees Celsius for a duration in the range of 1 minute-1 hour, and
the layer of silicon dioxide is formed to a thickness in the range
of 5-15 Angstroms. In another embodiment, gate dielectric layer 206
is formed by oxidizing the top surface of substrate 202 in the
presence of a nitrogen-containing gas to form an oxy-nitride layer
comprised of an oxy-nitride of the semiconductor material of
substrate 202. In a particular embodiment, gate dielectric layer
206 is formed by heating substrate 202 in the presence of an
oxidizing agent, such as O.sub.2, H.sub.2O or O.sub.3, and ammonia
until a desired thickness of an oxy-nitride layer is formed. In a
specific embodiment, substrate 202 is comprised of silicon, gate
dielectric layer 206 is comprised of a layer of silicon
oxy-nitride, the formation of the layer of silicon oxy-nitride is
carried out at a temperature in the range of 600-800 degrees
Celsius for a duration in the range of 1 minute-1 hour, and the
layer of silicon oxy-nitride is formed to a thickness in the range
of 5-15 Angstroms. In an alternative embodiment, gate dielectric
layer 206 is formed by a deposition process. In one embodiment, the
deposition process is selected from the group consisting of a
chemical vapor deposition process, an atomic layer deposition
process or a physical vapor deposition process.
[0027] Referring to FIG. 2A', gate dielectric layer 206 may be
comprised of two distinct dielectric layers, a lower layer 206A and
an upper layer 206B. Lower layer 206A and upper layer 206B of gate
dielectric layer 206 may comprise any material discussed in
association with lower layer 106A and upper layer 106B from FIG.
1B. In accordance with an embodiment of the present invention,
subsequent to the formation of lower layer 206A comprised of an
oxide or oxy-nitride layer above substrate 202 (as discussed
above), upper layer 206B may be formed above lower layer 206A.
Upper layer 206B may be formed by any technique suitable to provide
a reliable (i.e. uniform composition and thickness) dielectric
layer above the top surface of lower layer 206A. In an embodiment,
upper layer 206B is formed by a deposition process. In one
embodiment, the deposition process is selected from the group
consisting of a chemical vapor deposition process, an atomic layer
deposition process or a physical vapor deposition process. In an
alternative embodiment, gate dielectric layer 206 comprising two
distinct dielectric layers, i.e. lower layer 206A and an upper
layer 206B, may be formed in a single process step (i.e. in a
single reaction chamber without requiring multiple introductions of
substrate 202 into the reaction chamber). In one embodiment, a
native layer of oxide (i.e. lower layer 206A) is formed upon
exposure of substrate 202 to a water pulse in an atomic layer
deposition (ALD) chamber. An upper layer 206B of a dielectric
material may then be deposited above the native oxide layer by a
sequencing of dielectric precursor introductions into the ALD
chamber. In a particular embodiment, substrate 202 is comprised of
silicon, lower layer 206A is a native silicon dioxide layer with a
thickness in the range of 3-10 Angstroms, and upper layer 206B is a
high-K dielectric layer selected from the group consisting of
hafnium oxide, hafnium silicate, lanthanum oxide, zirconium oxide,
zirconium silicate, tantalum oxide, barium strontium titanate,
barium titanate, strontium titanate, yttrium oxide, aluminum oxide,
lead scandium tantalum oxide, lead zinc niobate or a combination
thereof.
[0028] A gate electrode 208 may then be formed above gate
dielectric layer 206, as depicted in FIG. 2B. For illustrative
purposes, gate dielectric layer 206 is depicted as a single layer
film (i.e. as illustrated in FIG. 2A), but it should be understood
that it may comprise more than one layer, as discussed in
association with FIG. 2A'. Gate electrode 208 may comprise any
material discussed in association with conductive region 108 from
FIGS. 1A-B. Gate electrode 208 may be formed by any technique
suitable to provide a conductive region above the top surface of
gate dielectric layer 206 without detrimentally impacting gate
dielectric layer 206. In accordance with an embodiment of the
present invention, gate electrode 208 is formed by depositing a
blanket film and then subsequently patterning the blanket film to
form a conductive structure of a desired shape and dimension. In
one embodiment, gate dielectric layer 206 is also patterned during
the patterning of gate electrode 208 to expose the top surface of
substrate 202, as depicted in FIG. 2B. In a specific embodiment,
gate dielectric layer 206 is patterned with a wet chemical cleaning
process step that comprises the application of an aqueous solution
of hydrofluoric acid, ammonium fluoride or both. A gate electrode
protection layer 216 may be formed above gate electrode 208, also
depicted in FIG. 2B. Gate electrode protection layer 216 may
comprise any material discussed in association with gate electrode
protection layer 116 from FIG. 1B. In accordance with an embodiment
of the present invention, gate electrode protection layer 216 is an
artifact from the patterning process steps used to for gate
electrode 208. In an alternative embodiment, gate electrode
isolation layer 216 is formed post-patterning above gate electrode
208 by a chemical vapor deposition process.
[0029] Referring to FIG. 2C, a pair of sacrificial gate isolation
spacers 222 may be formed adjacent the sidewalls of gate electrode
208. Sacrificial gate isolation spacers 222 may comprise any
material discussed in association with gate isolation spacers 118
from FIG. 1B. In accordance with an embodiment of the present
invention, sacrificial gate isolation spacers 222 are used to
protect gate electrode 208 during the subsequent substrate etch
step discussed below. Thus, in an alternative embodiment, gate
electrode 208 is robust against the substrate etch step and a pair
of sacrificial gate isolation spacers 222 is not required. The pair
of sacrificial gate isolation spacers 222 may be formed by any
technique suitable to provide total coverage of the sidewalls of
gate electrode 208. In an embodiment, sacrificial gate isolation
spacers 222 are formed by depositing, and subsequently
anisotropically etching, a blanked dielectric film. In another
embodiment, sacrificial gate isolation spacers 222 are formed by
consuming/passivating a portion of gate electrode 208 in an
oxidation process.
[0030] FIG. 2C is a cross-sectional view along the A-A' axis of the
top-down view illustrated in FIG. 2C'. As depicted, shallow-trench
isolation regions 224 and 226 may be formed in substrate 202. In
accordance with an embodiment of the present invention, in order
for gate electrode 208 and underlying gate dielectric layer 206 to
remain in tact during a subsequent substrate etch step,
shallow-trench isolation region 226 must be present. Isolated
devices may also comprise shallow-trench isolation region 224 and
this feature will be included onward for illustrative purposes.
However, it is to be understood that in the case of nested
structures, shallow-trench isolation region 224 need not be present
and substrate 202 may be extended along the dashed lines shown in
FIG. 2C'. As would be apparent to one of ordinary skill in the art,
shallow-trench isolation regions 224 and 226 would typically have
been formed in substrate 202 prior to the formation of dielectric
layer 206. For example, in accordance with an embodiment of the
present invention, shallow-trench isolation regions 224 and 226 are
formed by filling trenches created in substrate 202 with a
dielectric material, e.g. a silicon dioxide material deposited by a
chemical vapor deposition process.
[0031] Referring to FIG. 2D, a portion of substrate 202 may be
removed to form a trench 228 directly between substrate 202, gate
dielectric layer 206, and shallow-trench isolation regions 224. A
portion of gate dielectric layer 206, gate electrode 208,
sacrificial gate isolation spacers 222 and gate electrode
protection layer 216 is suspended over trench 228, but another
portion of these structures is secured by shallow-trench isolations
regions 226 (shown in FIG. 2C'), as depicted by the dashed lines.
Trench 228 may be formed by any technique suitable to selectively
remove a portion of substrate 202 without significantly impacting
gate dielectric layer 206 or gate electrode 208, such as a dry etch
or a wet etch process. In accordance with an embodiment of the
present invention, gate electrode protection layer 216 and
sacrificial gate isolation spacers 222 protect gate electrode 208
during the formation of trench 208. In one embodiment, trench 228
is formed by a dry plasma etch step utilizing gases selected from
the group consisting of NF.sub.3, HBr, SF.sub.6/Cl or Cl.sub.2. In
a specific embodiment, portions of substrate 202 are removed
uniformly, leaving a trench 228 with equal depth in all locations,
as depicted in FIG. 2D. In another embodiment, a wet etch step
utilizing aqueous solutions of NH.sub.4OH or tetramethylammonium
hydroxide is used to form trench 228. In one embodiment, these wet
etchants are inhibited by high density planes of substrate 202
(e.g. the <111> plane in a silicon substrate), and trench 228
thus assumes a tapered profile, as depicted in FIG. 2D'. In a
specific embodiment, trench 228 is formed by applying an aqueous
solution of NH.sub.4OH with a concentration in the range of 10-30%
at a temperature in the range of 20-35 degrees Celsius to a
substrate 202 comprised of crystalline silicon and a tapered
profile results with a surface angle of 55 degrees. For
illustrative purposes, however, the uniform trench 228 of FIG. 2D
is shown in subsequent steps. Trench 228 may be formed to a depth
sufficient to remove all channel activity from substrate 202 and/or
sufficient to accommodate source/drain regions comprised of a
different semiconductor material, as discussed below. In one
embodiment, trench 228 is formed to a depth in the range of
800-1200 Angstroms.
[0032] Referring to FIG. 2E, active region 204 is formed in trench
228, directly between substrate 202 and gate dielectric layer 206.
Active region 204 may be comprised of any material discussed in
association with active region 104 from FIGS. 1A-B. Additionally,
active region 204 may incorporate charge-carrier dopant impurity
atoms. In one embodiment, active region 204 is a crystalline
silicon/germanium active region of the stoichiometry
Si.sub.xGe.sub.1-x, where 0.ltoreq.x.ltoreq.1, and the
charge-carrier dopant impurity atoms are selected from the group
consisting of boron, arsenic, indium or phosphorus. In another
embodiment, active region 204 is comprised of a III-V material and
the charge-carrier dopant impurity atoms are selected from the
group consisting of carbon, silicon, germanium, oxygen, sulfur,
selenium or tellurium. In accordance with an embodiment of the
present invention, active region 204 is comprised of a
semiconductor material with a composition different than the
semiconductor material of substrate 202 and is compatible with
dielectric layer 206.
[0033] Active region 204 may be formed by any technique suitable to
form a highly uniform (i.e. low surface defect density, e.g. less
than 106 dislocations/cm.sup.2 at the surface of active region 204)
crystalline layer. In one embodiment, active region 204 is a
uniform epitaxial layer. In another embodiment, active region 204
is a graded epitaxial layer, wherein the grading process minimizes
surface defects. In an alternative embodiment, the defect density
of active region 204 at the interface of substrate 202 is greater
than 108 dislocations/cm.sup.2, but at the top surface of active
region 204 is less than 10.sup.5 dislocations/cm.sup.2. In an
embodiment, active region 204 is deposited by a process selected
from the group consisting of chemical vapor epitaxy, molecular-beam
epitaxy or laser-abolition epitaxy. In one embodiment, a wet
chemical clean is carried out immediately prior to the deposition
of active region 204. In a specific embodiment, the wet chemical
cleaning process step comprises the application of an aqueous
solution of hydrofluoric acid, ammonium fluoride or both.
[0034] In the case where sacrificial gate isolation spacers 222
were employed to protect gate electrode 208 during the formation of
trench 228 and/or during the deposition of active region 204, these
spacers may be removed following the deposition of active region
204, as depicted in FIG. 2F. In accordance with an embodiment of
the present invention, sacrificial gate isolation spacers 222 are
removed to enable the optimization of the tip implant step
discussed below. In one embodiment, sacrificial gate isolation
spacers 222 are removed with a wet chemical cleaning process step
that comprises the application of an aqueous solution of
hydrofluoric acid, ammonium fluoride or both to expose the
sidewalls of gate electrode 208.
[0035] Referring to FIG. 2G, a pair of tip extensions 212 may be
formed by implanting charge-carrier dopant impurity atoms into
active region 204. The pair of tip extensions 212 may be formed
from any of the charge-carrier dopant impurity atoms discussed in
association with the pair of tip extensions 112 from FIG. 1B. In
accordance with an embodiment of the present invention, gate
electrode 208 acts to mask a portion of active region 204, forming
self-aligned tip extensions 212. By self-aligning tip extensions
212 with gate electrode 208, channel region 214 may be formed in
the portion of active region 204 that is underneath gate electrode
208 and gate dielectric layer 206, as depicted in FIG. 2G. In one
embodiment, the charge carrier dopant impurity atoms implanted to
form the pair of tip extensions 212 are of opposite conductivity to
channel region 214. In a specific embodiment, the pair of tip
extensions 212 is formed by implanting charge-carrier dopant
impurity atoms with an energy in the range of 0.2 keV-10 keV at a
dose in the range of 5E14 atoms/cm.sup.2-5E15 atoms/cm.sup.2 to
form a dopant concentration in the range of 1E20
atoms/cm.sup.3-1E21 atoms/cm.sup.3 and to a depth in the range of
5-30 nanometers. In order to activate the charge carrier dopant
impurity atoms implanted active region 204 to form the pair of tip
extensions 212, any suitable annealing technique may be used. In
accordance with an embodiment of the present invention, the
annealing technique employed to cause the charge carrier dopant
impurity atoms of the pair of tip extensions 212 to become
substitutionally incorporated into the atomic lattice of active
region 204 is selected from the group consisting of thermal
annealing, laser annealing or flash annealing.
[0036] A pair of gate isolation spacers may then be formed. In one
embodiment, referring to FIG. 2H, a dielectric material layer 230
is deposited by a chemical vapor deposition process and is
conformal with the sidewalls of gate electrode 208 and the top
surface of active region 204. Dielectric material layer 230 may be
comprised of any of the materials discussed in association with the
pair of gate isolation spacers 118 from FIG. 1B. Dielectric
material layer 230 may be deposited to a thickness selected to
determine the final width of the pair of gate isolation
spacers.
[0037] Referring to FIG. 2I, a pair of gate isolation spacers 218
may be formed from dielectric material layer 230 by an anisotropic
etch process. In one embodiment, dielectric material layer 230 is
dry etched by a remote plasma etch or a reactive ion etch process.
In another embodiment, dielectric material layer 230 is patterned
to form the pair of gate isolation spacers 218 by using a vertical
dry or plasma etch process comprising fluorocarbons of the general
formula C.sub.xF.sub.y, where x and y are natural numbers. The pair
of gate isolation spacers 218 may sit above the top surface of
active region 204 and may have a width at the top surface of active
region 204 substantially equal to the original thickness of
dielectric material layer 230. In accordance with an embodiment of
the present invention, the pair of gate isolation spacers 218
resides above the pair of tip extensions 212, as depicted in FIG.
2I. In one embodiment, the pair of gate isolation spacers 218 forms
a hermetic seal with gate electrode 208 and the top surface of
active region 204 to encapsulate gate dielectric layer 206.
[0038] The structure described in association with FIG. 2I may then
undergo typical process steps to complete the formation of a
MOS-FET, such as an implant step to form a pair of source/drain
regions in active region 204 and a silicidation step.
Alternatively, strain-inducing source/drain regions may be formed
in active region 204. Referring to FIG. 2J, a pair of etched-out
regions 240 is formed in active region 204 and are aligned with the
outer surfaces of the pair of gate isolation spacers 218, leaving
protected the portions of the pair of tip extensions 212 that are
underneath the pair of gate isolation spacers 218. In one
embodiment, gate electrode protection layer 216 protects gate
electrode 212 during the formation of etched-out regions 240. In
accordance with an embodiment of the present invention, etched-out
regions 240 are formed to a depth such that substrate 202 is not
exposed and in the range of 600-1100 Angstroms. In a specific
embodiment, portions of active region 204 are removed
isotropically, leaving etched-out regions 240 with curvature, as
depicted in FIG. 2J. In another embodiment, a wet etch step
utilizing aqueous solutions of NH.sub.4OH or tetramethylammonium
hydroxide is used to form etched-out regions 240. In one
embodiment, these wet etchants are inhibited by high density planes
of active region 204, and the etched-out regions 240 thus assume a
tapered profile. For illustrative purposes, however, the curved
etched-out regions 240 of FIG. 2J are shown in subsequent
steps.
[0039] A strain-inducing source/drain region formed in an
etched-out portion of a crystalline semiconductor material may
impart a uniaxial strain to the channel region of the crystalline
semiconductor material. In turn, the crystalline semiconductor
material may impart a uniaxial strain to the strain-inducing
source/drain region. In one embodiment, the lattice constant of the
strain-inducing source/drain regions is smaller than the lattice
constant of the crystalline semiconductor material and the
strain-inducing source/drain regions impart a tensile uniaxial
strain to the crystalline semiconductor material, while the
crystalline semiconductor material imparts a tensile strain to the
strain-inducing source/drain regions. Thus, when the lattice
constant of a strain-inducing source/drain region that fills an
etched-out portion of a crystalline semiconductor material is
smaller than the lattice constant of the crystalline semiconductor
material, the lattice-forming atoms of the strain-inducing
source/drain region are pulled apart (i.e. tensile strain) from
their normal resting state and hence induce a tensile strain on the
crystalline semiconductor material as they attempt to relax. In
another embodiment, the lattice constant of the strain-inducing
source/drain regions is larger than the lattice constant of the
crystalline semiconductor material and the strain-inducing
source/drain regions impart a compressive uniaxial strain to the
crystalline semiconductor material, while the crystalline
semiconductor material imparts a compressive strain to the
strain-inducing source/drain regions. Thus, when the lattice
constant of a strain-inducing source/drain region that fills an
etched-out portion of a crystalline semiconductor material is
larger than the lattice constant of the crystalline semiconductor
material, the lattice-forming atoms of the strain-inducing
source/drain region are pushed together (i.e. compressive strain)
from their normal resting state and hence induce a compressive
strain on the crystalline semiconductor material as they attempt to
relax.
[0040] Therefore, referring to FIG. 2K, a pair of source/drain
regions 220 is formed in etched-out regions 240. The pair of
source/drain regions 220 may be comprised of any material discussed
in association with the pair of source/drain regions 120 from FIG.
1B. Additionally, in accordance with an embodiment of the present
invention, the pair of source/drain regions 220 have a composition
different from the composition of the semiconductor material of
active region 204 and impart a uniaxial strain to channel region
214. The pair of source/drain regions 220 may be formed by any
technique suitable to form a highly uniform (i.e. low surface
defect density, e.g. less than 10.sup.6 dislocations/cm.sup.2 at
the surface of the pair of source/drain regions 220) crystalline
layer. In one embodiment, the pair of source/drain regions 220
comprises a uniform epitaxial layer. In another embodiment, the
pair of source/drain regions 220 comprises a graded epitaxial
layer, wherein the grading process minimizes surface defects. In an
embodiment, the pair of source/drain regions 220 is deposited by a
process selected from the group consisting of chemical vapor
epitaxy, molecular-beam epitaxy or laser-abolition epitaxy. In one
embodiment, a wet chemical clean is carried out immediately prior
to the deposition of the pair of source/drain regions 220. In a
specific embodiment, the wet chemical cleaning process step
comprises the application of an aqueous solution of hydrofluoric
acid, ammonium fluoride or both. The pair of source/drain regions
220 may incorporate charge-carrier dopant impurity atoms. In one
embodiment, the pair of source/drain regions 220 is a crystalline
silicon/germanium region of the stoichiometry Si.sub.xGe.sub.1-x,
where 0.ltoreq.x.ltoreq.1, and the charge-carrier dopant impurity
atoms are selected from the group consisting of boron, arsenic,
indium or phosphorus. In another embodiment, the pair of
source/drain regions 220 is comprised of a III-V material and the
charge-carrier dopant impurity atoms are selected from the group
consisting of carbon, silicon, germanium, oxygen, sulfur, selenium
or tellurium. The charge-carrier dopant impurity atoms may be
incorporated into the pair of source/drain regions 220 at the same
time as the formation of the pair of source/drain regions 220 (i.e.
in situ) or as a post ion-implantation step.
[0041] The structure described in association with FIG. 2K may then
undergo typical process steps to complete the formation of a
MOS-FET, such as a silicidation step. Alternatively, subsequent to
the formation of the pair of source/drain regions 220, process
steps compatible with a replacement gate process scheme may be
carried out. In accordance with an embodiment of the present
invention, an interlayer dielectric layer 250 (e.g. a layer of
silicon dioxide) is formed over the pair of source/drain regions
220, shallow-trench isolation regions 224, the pair of gate
isolation spacers 218 and gate electrode protection layer 216
and/or gate electrode 208, as depicted in FIG. 2L. The interlayer
dielectric layer 250 may then be polished back and the gate
electrode protection layer 216 removed with a chemical-mechanical
polish step to reveal gate electrode 208, as depicted in FIG. 2M.
In one embodiment, gate electrode protection layer 216 acts as a
polish-stop layer and a wet etch process is subsequently used to
remove gate electrode protection layer 216 in order to reveal the
top surface of gate electrode 208.
[0042] Referring to FIG. 2N, gate electrode 208 may be removed and
replaced with an alternative gate electrode 260. In accordance with
an embodiment of the present invention, alternative gate electrode
260 is comprised of any material described in association with
conductive region 108 from FIGS. 1A-B. Additionally, subsequent to
the removal of gate electrode 208 and prior to the replacement with
alternative gate electrode 260, an additional dielectric layer 270
may be added to gate dielectric layer 206. In accordance with an
embodiment of the present invention, additional dielectric layer
270 may be comprised of any material discussed in association with
upper layer 106B from FIG. 1B. The additional dielectric layer 260
may be formed by an atomic layer or chemical vapor deposition
process and may therefore also form on the inner walls of the pair
of gate isolation spacers 218, as depicted in FIG. 2N.
[0043] Thus, referring to FIG. 2N, a planar MOS-FET comprising an
active region with a compatible gate dielectric layer may be
formed. The planar MOS-FET may be an N-type or a P-type
semiconductor device and may be incorporated into an integrated
circuit by conventional processing steps, as known in the art. As
will be appreciated in the typical integrated circuit, both N-- and
P-channel transistors may be fabricated in a single substrate or
epitaxial layer to form a CMOS integrated circuit.
[0044] The present invention is not limited to the formation of
planar MOS-FETs comprising active regions with compatible gate
dielectric layers. For example, devices with a three-dimensional
architecture, such as tri-gate devices, may benefit from the above
process. As an exemplary embodiment in accordance with the present
invention, FIGS. 3A-C illustrate cross-sectional views representing
the formation of a tri-gate MOS-FET having active regions with
compatible dielectric layers.
[0045] Referring to FIG. 3A, the foundation of a single substrate
tri-gate MOS-FET 300 is formed. Tri-gate MOS-FET 300 is comprised
of a three-dimensional substrate 302. Three-dimensional substrate
302 may be formed from any material described in association with
substrate 102 from FIGS. 1A-B. A gate dielectric layer 306 is
formed around three-dimensional substrate 302. Gate dielectric
layer 306 may be formed from any material described in association
with dielectric layer 106, lower layer 106A and upper layer 106B
from FIGS. 1A-B. A gate electrode 308 is formed above gate
dielectric layer 306. Gate electrode 308 may be formed from any
material described in association with conductive region 108 from
FIGS. 1A-B. Gate dielectric layer 306 and gate electrode 308 may be
protected by a pair of gate isolation spacers 318.
[0046] Referring to FIG. 3B, a portions of three-dimensional
substrate 302 may be removed to form trench 328. Trench 328 may be
formed by any technique described in association with the formation
of trench 228 from FIGS. 2D and 2D'. Referring to FIG. 3C,
three-dimensional active region 304 is formed selectively in trench
328 and on the remaining portion of three-dimensional substrate
302. Thus, a method to form a tri-gate MOS-FET device comprising an
active region with a compatible gate dielectric layer has been
described. The tri-gate MOS-FET may be incorporated into an
integrated circuit by conventional processing steps, as known in
the art.
[0047] Thus, a method to form a semiconductor structure with an
active region and a compatible dielectric layer has been disclosed.
In one embodiment, a semiconductor structure has a dielectric layer
comprised of an oxide of a first semiconductor material, wherein a
second (and compositionally different) semiconductor material is
formed between the dielectric layer and the first semiconductor
material. In another embodiment, a portion of the second
semiconductor material is replaced with a third semiconductor
material in order to impart uniaxial strain to the lattice
structure of the second semiconductor material.
* * * * *