U.S. patent application number 10/428903 was filed with the patent office on 2003-10-09 for nitrogen-rich barrier layer and structures formed.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Buchanan, Douglas Andrew, Copel, Matthew Warren, Holl, Mark Monroe Banaszak, Litz, Kyle Erik, McFeely, Fenton Read, Varekamp, Patrick Ronald.
Application Number | 20030190821 10/428903 |
Document ID | / |
Family ID | 26742237 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030190821 |
Kind Code |
A1 |
Buchanan, Douglas Andrew ;
et al. |
October 9, 2003 |
Nitrogen-rich barrier layer and structures formed
Abstract
The present invention discloses a method for forming a layer of
nitrogen and silicon containing material on a substrate by first
providing a heated substrate and then flowing a gas which has
silicon and nitrogen atoms but no carbon atoms in the same molecule
over said heated substrate at a pressure of not higher than 500
Torr, such that a layer of nitrogen and silicon containing material
is formed on the surface. The present invention is further directed
to a composite structure that includes a substrate and a layer of
material containing nitrogen and silicon but not carbon overlying
the substrate for stopping chemical species from reaching the
substrate. The present invention is further directed to a structure
that includes a semiconducting substrate, a gate insulator on the
substrate, a nitrogen-rich layer on top of the gate insulator, and
a gate electrode on the nitrogen-rich layer, wherein the
nitrogen-rich layer blocks diffusion of contaminating species from
the gate electrode to the gate insulator.
Inventors: |
Buchanan, Douglas Andrew;
(Cortlandt Manor, NY) ; Copel, Matthew Warren;
(Yorktown Heights, NY) ; McFeely, Fenton Read;
(Ossining, NY) ; Varekamp, Patrick Ronald;
(Croton-on-Hudson, NY) ; Holl, Mark Monroe Banaszak;
(Ann Arbor, MI) ; Litz, Kyle Erik; (Ann Arbor,
MI) |
Correspondence
Address: |
Randy W. Tung
Tung & Associates
Suite 120
838 W. Long Lake Road
Bloomfield Hills
MI
48302
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
26742237 |
Appl. No.: |
10/428903 |
Filed: |
May 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10428903 |
May 2, 2003 |
|
|
|
08982150 |
Dec 1, 1997 |
|
|
|
6566281 |
|
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60062424 |
Oct 15, 1997 |
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Current U.S.
Class: |
438/790 ;
257/E21.269; 257/E21.639; 438/791; 438/793; 438/794 |
Current CPC
Class: |
H01L 21/823857 20130101;
H01L 21/3145 20130101; H01L 21/02271 20130101; H01L 21/0214
20130101 |
Class at
Publication: |
438/790 ;
438/791; 438/793; 438/794 |
International
Class: |
H01L 021/31; H01L
021/469 |
Claims
1. A method for forming a layer of nitrogen-containing material on
a substrate comprising the steps of: providing a substrate, heating
the substrate to a temperature not less than 400.degree. C., and
flowing a gas comprising nitrogen-containing molecules over a
surface of said substrate at a sub-atmospheric pressure, said
molecules being without carbon such that said nitrogen-containing
molecules form a layer of nitrogen-containing material on said
surface.
2. A method for forming a layer of nitrogen-containing material
according to claim 1 further comprising the step of flowing a gas
which has silicon and nitrogen atoms in the same molecule and is
without carbon over a surface of said substrate at a
sub-atmospheric pressure forming a layer of nitrogen and silicon
containing material on said surface.
3. A method for forming a layer of nitrogen-containing material
according to claim 1 further comprising the step of flowing a gas
comprising nitrogen-containing molecules at a pressure of not
higher than 500 Torr.
4. A method for forming a layer of nitrogen-containing material
according to claim 1 further comprising the step of flowing a gas
comprising nitrogen-containing molecules at a pressure between
about 1 m Torr and about 500 Torr.
5. A method for forming a layer of nitrogen-containing material
according to claim 1 further comprising the step of heating the
substrate to a temperature between about 400.degree. C. and about
900.degree. C.
6. A method for forming a layer of nitrogen-containing material
according to claim 1 wherein said nitrogen-containing molecules
pyrolize and react at said surface forming said layer of
nitrogen-containing material.
7. A method for forming a layer of nitrogen-containing material
according to claim 2, wherein said nitrogen and silicon containing
molecules pyrolize and react at said surface forming said layer of
nitrogen and silicon containing material on said surface.
8. A method for forming a layer of nitrogen-containing material
according to claim 1, wherein said gas comprising
nitrogen-containing molecules is flowed over a surface of said
substrate in a chemical vapor deposition process.
9. A method for forming a layer of nitrogen-containing material
according to claim 2, wherein said gas which has a silicon and
nitrogen atoms in the same molecule is flowed over a surface of
said substrate in a chemical vapor deposition process.
10. A method for forming a layer of nitrogen-containing material
according to claim 1 further comprising the step of flowing a gas
selected from the group consisting of (SiH.sub.3).sub.3N,
SiH.sub.4, Si.sub.2H.sub.6, Si.sub.2H.sub.2Cl.sub.2, NH.sub.3, NO,
N.sub.2O, N.sub.2H.sub.4 and O.sub.2.
11. A method for forming a layer of nitrogen-containing material
according to claim 1 further comprising the step of flowing a gas
of (SiH.sub.3).sub.3N over the surface of said substrate.
12. A method for forming a layer of nitrogen-containing material
according to claim 1, wherein said nitrogen-containing molecules
contain pendant groups of SiH.sub.3.
13. A method for forming a layer of nitrogen-containing material
according to claim 1, wherein said nitrogen-containing molecules
contain nitrogen covalently bonded to SiH.sub.3.
14. A method for forming a layer of nitrogen-containing material
according to claim 1, wherein said substrate is selected from the
group consisting of crystalline silicon, polycrystalline silicon,
amorphous silicon, silicon germanium alloy, silicon dioxide or
other dielectric materials and substrates covered with a dielectric
material.
15. A method for forming a layer of nitrogen and silicon containing
material on a substrate comprising the steps of: providing a
substrate maintained at a temperature not less than 400.degree. C.,
and flowing a gas which has silicon and nitrogen atoms in the same
molecule over a surface of said substrate at a pressure of not
higher than 500 Torr, said molecules being without carbon such that
a layer of nitrogen and silicon containing material is formed on
said surface.
16. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of providing a substrate maintained at a temperature
between about 400.degree. C. and about 900.degree. C.
17. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of flowing a gas which has silicon and nitrogen atoms in
the same molecule at a pressure between about 1 m Torr and about
500 m Torr.
18. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15, wherein said gas has
silicon and nitrogen atoms in the same molecule and pyrolizes and
reacts at said surface forming said layer of nitrogen and silicon
containing material on said surface.
19. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of flowing a gas selected from the group consisting of
(SiH.sub.3).sub.3N, SiH.sub.4, Si.sub.2H.sub.6,
Si.sub.2H.sub.2Cl.sub.2, NH.sub.3, NO, N.sub.2O, N.sub.2H.sub.4 and
O.sub.2.
20. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of flowing a gas of (SiH.sub.3).sub.3N (trisilylamine)
over the surface of said substrate.
21. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15, wherein said gas has
silicon and nitrogen atoms in the same molecule and is flowed over
the surface of said substrate in a chemical vapor deposition
process.
22. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15, wherein said
nitrogen and silicon containing molecules further contain pendant
groups of SiH.sub.3.
23. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15, wherein said
nitrogen and silicon containing molecules further contain nitrogen
covalently bonded to SiH.sub.3.
24. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15, wherein said
substrate is selected from the group consisting of crystalline
silicon, polycrystalline silicon, amorphous silicon, silicon
germanium alloy, silicon dioxide or other dielectric materials and
substrates covered with a dielectric material.
25. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of forming a nitrided oxide layer on said substrate prior
to said gas flowing step.
26. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of forming a nitrided oxide layer to a thickness of less
than 10 nm on said substrate prior to said gas flowing step.
27. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of reacting said layer of nitrogen and silicon containing
material with ammonia and thereby converting said material to
stoichiometric nitride.
28. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of reacting said layer of nitrogen and silicon containing
material with ammonia at a temperature less than 700.degree. C. and
converting said material to stoichiometric nitride.
29. A method for forming a layer of nitrogen and silicon containing
material on a substrate according to claim 15 further comprising
the step of reacting said layer of nitrogen and silicon containing
material with a material selected from the group consisting of
N.sub.2H.sub.4, O.sub.2, N.sub.2O and NO.
30. A composite structure comprising: a substrate, and a layer of
material containing nitrogen and silicon and without carbon
overlying said substrate for stopping chemical species from
reaching said substrate.
31. A composite structure according to claim 30 further comprising
a nitrided oxide layer formed between the substrate and the layer
of material containing nitrogen and silicon.
32. A composite structure according to claim 30 further comprising
a nitrided oxide layer having a thickness of less than 10 nm formed
between the substrate and the layer of material containing nitrogen
and silicon.
33. A composite structure according to claim 30, wherein said layer
of material containing nitrogen and silicon and without carbon is a
stoichiometric nitride.
34. A composite structure according to claim 30, wherein said
substrate is selected from the group consisting of crystalline
silicon, polycrystalline silicon, amorphous silicon, silicon
germanium alloy, silicon dioxide or other dielectric materials and
substrates covered with a dielectric material.
35. A composite structure according to claim 30, wherein said
substrate is a dielectric material layer.
36. A composite structure according to claim 30, wherein said
substrate is a gate insulator and said structure is positioned
within said layer of material containing nitrogen and silicon in
intimate contact with a gate electrode.
37. A composite structure according to claim 36, wherein said layer
of material containing nitrogen and silicon blocks diffusion of
contaminating species from the gate electrode to the gate
insulator.
38. A composite structure according to claim 30, wherein said
structure is included in a field effect transistor.
39. A composite structure according to claim 30, wherein said
structure is included in one of SRAM, CMOS, DRAM, SDRAM, CCD and
flash EEPROM.
40. A semiconductor structure comprising: a semiconducting
substrate, a gate insulator on said substrate, a nitrogen-rich
layer on top of said gate insulator, and a gate electrode on said
nitrogen-rich layer, whereby said nitrogen-rich layer blocks
diffusion of chemical species from said gate electrode to said gate
insulator.
41. A semiconductor structure according to claim 40, wherein said
nitrogen-rich layer is a material containing nitrogen and silicon
and is without carbon.
42. A semiconductor structure according to claim 40 further
comprising a nitrided oxide layer between said gate insulator and
said nitrogen-rich layer.
43. A semiconductor structure according to claim 42, wherein said
nitrided oxide layer has a thickness of less than 10 nm.
44. A semiconductor structure according to claim 40 further
comprising a nitrided oxide layer between said gate insulator and
said substrate.
45. A semiconductor structure according to claim 44, wherein said
nitrided oxide layer has a thickness of less than 10 nm.
46. A semiconductor structure according to claim 40, wherein said
nitrogen-rich layer is a stoichiometric nitride.
47. A semiconductor structure according to claim 40, wherein said
nitrogen-rich layer contains at least 20 atomic % nitrogen.
48. A semiconductor structure according to claim 40, wherein said
nitrogen-rich layer has a thickness of at least 5 .ANG..
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to co-pending U.S.
provisional application Serial No. 60/062,424 filed Oct. 15,
1997.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a method for
forming a layer of nitrogen and silicon containing material on a
substrate and more particularly, relates to a method for forming a
layer of nitrogen and silicon containing material on a substrate by
flowing a gas which has silicon and nitrogen atoms in the same
molecule over a heated substrate at a pressure of less than 500
Torr wherein the molecules do not contain carbon.
BACKGROUND OF THE INVENTION
[0003] In the recent advancement in semiconductor fabrication
technologies, semiconductor devices are continuously being made
smaller such that a larger number of devices can be packaged on the
same chip real estate. The continuing miniaturization of devices,
such as very large scale integrated (VLSI) and ultra large scale
integrated (ULSI) devices, demands that each component must be
reduced in dimensions. For instance, as the lateral dimensions of a
semiconductor device are reduced, the thickness of each of the
component layers such as an insulating layer or a conducting layer
must be reduced accordingly. As the characteristic dimensions of
complementary metal oxide semiconductor (CMOS) technology decrease,
more stringent demands are being placed on the silicon dioxide gate
insulator layer in the field effect transistor. In addition to its
normal function as a circuit element in the device, the gate
insulator layer must also protect the silicon substrate from
possible diffusion of chemical species originating from a
polysilicon gate electrode through the gate insulator/silicon
substrate interface. Such chemical species include dopant atoms
such as boron which can diffuse from the gate electrode through the
gate insulator into the silicon substrate and thus, result in a
device that no longer performs within specification. Another
chemical species, hydrogen, which is normally present in the gate
electrode, is also highly mobile and can react at the silicon
substrate/gate insulator interface during the operation of the
device. Such reaction may result in a degradation of the gate
insulating layer leading to a reduced lifetime of the device.
Traditionally, as long as the gate insulating layer is sufficiently
thick, the layer serves to protect the substrate from the diffusive
chemical species. However, with the thickness of gate insulators in
modern ULSI devices shrinking to dimensions of 3 nm or less, the
protection of the substrate is no longer assured. Other remedies
must be provided for such devices in order to guarantee the
fabrication of a transistor that operatesment.
[0004] Different ways to increase the chemical isolation provided
by a thin gate insulator in a modern semiconductor device have been
proposed by others. One of the methods for suppressing diffusive
chemical species from the gate electrode is to introduce a very
small amount of nitrogen into the silicon dioxide normally used as
the gate insulator. Nitrogen acts as a barrier to a number of
elemental species such as B, H, and alkali metals such as Li, Na,
K, etc. Traditionally, small amounts of nitrogen can be
incorporated into silicon dioxide in an uncontrolled manner, i.e.,
through high temperature annealing of the oxide in a
nitrogen-containing gas such as NO, N.sub.2O or NH.sub.3. The high
temperature required for the annealing process is normally greater
than 800.degree. C. A nitrided oxide is thus formed which has been
shown to slightly suppress boron penetration and improve hot
carrier reliability.
[0005] It is known that the optimal nitrogen concentration and
distribution in the oxide required to maximize both the suppression
of boron penetration and the improvement of hot carrier reliability
is different. For instance, to improve the hot carrier reliability,
the introduction of a small amount, i.e., <2 atomic %, of
nitrogen near the substrate/insulator interface is required. The
amount of nitrogen at the interface cannot exceed 2 atomic %,
however, without adversely affecting the device characteristics. On
the other hand, the ability to suppress boron penetration is
directly proportional to the total nitrogen concentration and as
such, the amount of nitrogen should be as large as possible. This
presents a direct conflict with the effort of improving the hot
carrier reliability of the device.
[0006] Furthermore, even though the distribution of nitrogen atoms
within the oxide is not important with regard to the suppression of
boron diffusion, it is desirable to keep boron atoms as far away
from the substrate interface as possible. By utilizing the
conventional high temperature nitridation annealing process,
nitrided oxides with optimal nitrogen content at the
substrate/dielectric interface and maximum hot carrier reliability
can be obtained. However, there are no existing methods that will
also produce a high concentration of nitrogen at the
electrode/dielectric interface. As a result, it is presently not
possible to simultaneously optimize the hot carrier reliability and
the suppression of boron penetration.
[0007] As the gate dielectric layer becomes thinner, i.e., when the
oxide layer is thinner than 30 .ANG., another undesirable effect of
a large increase in electron tunneling can cause degradation of the
oxide and reduced lifetime. It is therefore desirable to provide a
barrier layer for blocking hydrogen from attacking the oxide layer
when the oxide layer is less than approximately 30 .ANG.. The
barrier layer should be advantageously positioned in between the
gate dielectric and the gate electrode. The small amount of
nitrogen that is incorporated into the oxide via the conventional
nitridation annealing method will not act as a significant barrier
to hydrogen diffusion from the gate electrode.
[0008] It is therefore an object of the present invention to
provide a method for forming a layer of nitrogen and silicon
containing material on a substrate that does not have the drawbacks
nor shortcomings of the conventional high temperature nitridation
annealing method.
[0009] It is another object of the present invention to provide a
method for forming a layer of nitrogen and silicon containing
material on a substrate wherein the substrate is maintained at a
temperature of not less than 400.degree. C. to enable a pyrolysis
reaction.
[0010] It is a further object of the present invention to provide a
method for forming a layer of nitrogen and silicon containing
material on a substrate by first heating the substrate and then
flowing a gas which has silicon and nitrogen atoms in the same
molecule over the surface of the substrate.
[0011] It is another object of the present invention to provide a
method for depositing a layer of nitrogen and silicon containing
material on a substrate wherein trisilylamine vapor
[(SiH.sub.3).sub.3N] is flowed over a heated substrate.
[0012] It is still another object of the present invention to
provide a composite structure which includes a substrate and a
layer of material containing nitrogen and silicon without carbon
overlying the substrate for stopping chemical species from reaching
the substrate.
[0013] It is yet another object of the present invention to provide
a composite structure that includes a substrate, a nitrided oxide
layer on the substrate and a layer of nitrogen and silicon
containing material on top of the nitrided oxide layer for stopping
chemical species from diffusing to said substrate.
[0014] It is still another object of the present invention to
provide a semiconductor structure that includes a nitrogen-rich
layer between a gate electrode and a gate insulator on a
semiconducting substrate wherein the nitrogen-rich layer blocks
diffusion of chemical species from the gate electrode to the gate
insulator.
[0015] It is yet another object of the present invention to provide
a semiconductor structure that includes a semiconducting substrate,
with a gate insulator which may include a nitrided oxide layer, a
nitrogen-rich layer and a gate electrode sequentially deposited or
grown on the semiconducting substrate such that the diffusion of
chemical species from the gate electrode to the gate insulator is
inhibited.
SUMMARY OF THE INVENTION
[0016] The present invention discloses a method for forming a layer
of nitrogen and silicon containing material on a substrate by
flowing a gas which has silicon and nitrogen atoms in the same
molecule over the surface of a heated substrate wherein the
molecules do no contain carbon such that the layer of nitrogen and
silicon containing material formed will stop diffusing species from
reaching the substrate.
[0017] In a preferred embodiment, a method for forming a layer of
nitrogen-containing material on a substrate can be carried out by
the operating steps of first providing a substrate, then heating
the substrate to a temperature of not less than 400.degree. C., and
then flowing one or more gases one of which includes
nitrogen-containing molecules over a surface of the substrate at a
sub-atmospheric pressure. The nitrogen-containing molecules do not
contain carbon. The gas can be flowed over the surface of the
substrate at a pressure between about 1 m Torr and about 500 Torr,
while the surface of the substrate can be maintained at a
temperature between about 400.degree. C. and about 900.degree. C.
The nitrogen-containing molecules pyrolize and react at the surface
to form the layer of nitrogen-containing material. The process can
be advantageously carried out in a chemical vapor deposition
chamber, wherein the gases flowed therethrough can be selected from
the group consisting of (SiH.sub.3).sub.3N, SiH.sub.4,
Si.sub.2H.sub.6, Si.sub.2H.sub.2Cl.sub.2, NH.sub.3, NO, N.sub.2O,
N.sub.2H.sub.4 and O.sub.2.
[0018] In another preferred embodiment, a method for forming a
layer of nitrogen and silicon containing material on a substrate
can be carried out by the operating steps of first providing a
substrate that is maintained at a temperature of not less than
400.degree. C., and then flowing a gas which has silicon and
nitrogen atoms in the same molecule but with no carbon atoms in the
molecule over the surface of the substrate at a pressure of not
higher than 500 Torr.
[0019] The present invention is further directed to a composite
structure which includes a substrate and a layer of material
containing nitrogen and silicon without carbon overlying the
substrate for stopping chemical species from reaching the
substrate. The composite structure may further include a nitrided
oxide layer that has a thickness of less than 10 nm deposited or
grown between the substrate and the layer of material containing
nitrogen and silicon. The layer of material containing nitrogen and
silicon but not carbon may be stoichiometric nitride. The substrate
in the composite structure may be selected from the group
consisting of crystalline silicon, polycrystalline silicon,
amorphous silicon, silicon germanium alloy, silicon dioxide or any
other dielectric materials and substrates covered with a dielectric
material. When the substrate is a gate insulator, the composite
structure can be positioned with the layer of material containing
nitrogen and silicon in intimate contact with a gate electrode
layer. The composite structure may further be advantageously used
in a CMOS device.
[0020] The present invention is further directed to a semiconductor
structure that includes a semiconducting substrate, a gate
insulator on the substrate, a nitrogen-rich layer on top of the
gate insulator and a gate electrode on the nitrogen-rich layer,
whereby the nitrogen-rich layer blocks diffusion of chemical
species from the gate electrode to the gate insulator. The
nitrogen-rich layer in the semiconductor structure may be a
material containing nitrogen and silicon but not carbon. The
semiconductor structure may further include a nitrided oxide layer
placed between the substrate and the gate insulator. The nitrided
oxide layer may have a thickness of less than 10 nm, while the
nitrogen-rich layer may be a stoichiometric nitride. The
nitrogen-rich layer may contain at least 20 atomic % of nitrogen
and have a thickness of at least 5 .ANG..
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other objects, features and advantages of the
present invention will become apparent from the following detailed
description and the appended drawings in which:
[0022] FIG. 1 is an enlarged, cross-sectional view of a
semiconductor structure utilizing the present invention novel
nitrogen-rich diffusion barrier layer.
[0023] FIG. 2A is an enlarged, cross-sectional view of the present
invention semiconducting substrate.
[0024] FIG. 2B is an enlarged, cross-sectional view of the present
invention semiconducting substrate of FIG. 2A having a gate
dielectric layer deposited or grown on top.
[0025] FIG. 2C is an enlarged, cross-sectional view of the present
invention semiconductor structure of FIG. 2B having a nitrogen and
silicon containing diffusion barrier layer deposited on top.
[0026] FIG. 2D is an enlarged, cross-sectional view of the present
invention semiconductor structure of FIG. 2C having a final gate
electrode layer formed on top of the nitrogen and silicon
containing diffusion barrier layer.
[0027] FIGS. 3 and 4 are graphs illustrating X-ray photoemission
data obtained on present invention devices during various stages of
preparation.
[0028] FIG. 5 is a graph illustrating the effect of a nitrided
oxide suppressing the diffusion of boron atoms at various annealing
temperatures.
DETAILED DESCRIPTION OF THE PREFERRED AND THE ALTERNATE
EMBODIMENTS
[0029] The present invention discloses a method for forming a layer
of nitrogen and silicon containing material on a substrate by first
heating the substrate to a temperature of at least 400.degree. C.
and then flowing a gas which has silicon and nitrogen atoms in the
same molecule over the heated substrate at a pressure of not higher
than 500 Torr, wherein the molecules do not contain carbon such
that the layer of nitrogen and silicon containing material formed
is a diffusion barrier layer on the surface of the substrate.
[0030] The present invention novel structure that has a
nitrogen-rich barrier layer can be advantageously used in a
semiconductor structure such as that shown in FIG. 1. A preferred
embodiment of the present invention structure 10 is shown in FIG. 1
in a CMOS transistor pair. The present invention novel structure 10
is built on a substrate 12 which can be P-type crystalline silicon
into which trenches 14 are first formed. An insulating material
such as silicon dioxide is then used to fill the trenches 14, in
order to provide isolation between the two transistors, i.e., a
p-FET (field effect transistor) 20 and an n-FET 30. The substrate
12 is then doped by an ion implantation method to create a deep
implanted area of p-type silicon 18 and n-type silicon 22. An
insulating layer 24 is then formed on the surface of the substrate
12. The insulating layer 24 is normally formed of silicon dioxide
or any other suitable dielectric material. A nitrogen-rich layer 26
is then deposited followed by the deposition of a conducting gate
electrode layer 28. The conducting gate electrode layer 28 is
normally composed of polysilicon. The insulating layer 24, the
nitrogen-rich layer 26 and the polysilicon layer 28 are then etched
to form the stack shown in FIG. 1. After the formation of the
stack, an ion implantation process is carried out to dope shallow
regions of n-type silicon 32 and p-type silicon 34. The
semiconductor device 10 is therefore completed for a CMOS
transistor pair of an n-FET 30 and a p-FET 20.
[0031] The fabrication details of the present invention
nitrogen-rich layer 26 are illustrated below and in appended
drawings of FIGS. 2A-2D. As shown in FIG. 2A, a substrate 40 is
first provided. The substrate 40 should be formed of a
semiconducting material since the present invention nitrogen-rich
layer is essentially located in a metal-insulator-semicondu- ctor
capacitor structure. The substrate 40 can be advantageously made of
doped crystalline silicon or polycrystalline silicon. The substrate
40 may also be formed by any other semiconducting material. In the
next fabrication step, as shown in FIG. 2B, a capacitor is
fabricated by the deposition or growth of an insulating layer 42 on
top of the semiconducting substrate 40. The insulating layer 42 is
typically pure silicon dioxide or silicon dioxide that contains a
small amount, i.e., smaller than 2 atomic %, of nitrogen. It should
be noted that this amount of nitrogen is not adequate to stop the
diffusion of chemical species from the gate electrode 28 to the
substrate 12. The insulating layer 42 therefore, cannot be utilized
as a substitute for the present invention nitrogen-rich layer. It
should be noted that the insulating layer 42 does not have to be a
homogenous material. Instead, it can be suitably formed of an
insulating stack of materials such as silicon dioxide and a metal
oxide. It is also possible that the subsequently formed
nitrogen-rich layer 44 shown in FIG. 2C, can be used to completely
replace the insulating layer 42 as long as the nitrogen-rich layer
is insulating.
[0032] The present invention novel nitrogen-rich layer 44 can be
deposited by a novel method of surface pyrolysis of molecules that
contain at least Si and N atoms, but do not contain carbon atoms.
Optionally, the nitrogen-rich layer 44 can be altered by reacting
it with oxidizing or nitridizing species such as NH.sub.3,
N.sub.2H.sub.4, O.sub.2, N.sub.2O, NO, etc. The reaction can be
conducted either during the deposition with the Si--N containing
molecules or can be carried out as a post processing step.
[0033] The present invention novel nitrogen-rich layer 44 should
only contain nitrogen, silicon, oxygen, and optionally, small
amounts of hydrogen. After the nitrogen-rich layer 44 is formed, it
acts as an insulator, a semiconductor, or a conductor as determined
by its stoichiometry. One of the benefits achievable by the present
invention is that the stoichiometry can be completely
user-controlled.
[0034] The process utilized for producing the structure shown in
FIG. 2C involves a low temperature and low pressure chemical vapor
deposition (CVD) process for producing a nitrided film, and then a
low temperature reaction of the film with a nitridizing and/or
oxidizing gas. The present invention novel process therefore can be
executed by either one of two methods. It can be executed by two
distinct and separate processing steps, or can be executed by CVD
and nitrification/oxidation reaction carried out concurrently.
[0035] In one preferred embodiment, the present invention
deposition process for the nitrogen-rich layer can be carried out
by exposing the substrate 40 on which the gate oxide layer 42 is
formed to trisilylamine vapor (TSA=[(SiH.sub.3).sub.3N]). A novel
feature of the gas molecules of trisilylamine is that they contain
only silicon, nitrogen and hydrogen. It is the unique discovery of
the present invention method that any other precursor that contains
carbon in any form cannot be used for the present invention method
since carbon would inevitably be incorporated into the film and
therefore degrade the operation of the device. As a result, none of
the many silicon-containing organic amines can be used in the
present invention novel method. Another novel feature of
trisilylamine is that this molecule enables a lower temperature
route to the formation of a silicon and nitrogen containing layer
via low pressure chemical vapor deposition than any other precursor
known.
[0036] The present invention novel method can be advantageously
performed in a stainless steel cold-wall reactor such that the wall
deposition of TSA can be minimized. A commonly used quartz tube hot
wall LPCVD furnace could serve equally well, but would require the
standard practice of removing the deposited material from the sides
of the tube on a regular basis. The TSA gas pressure can be
suitably chosen in the range between about 1 m Torr and about 500
Torr, while the substrate can be heated to a temperature in the
range between about 400.degree. C. and about 900.degree. C.
Formation of the nitrogen-rich film by the present invention novel
method to a suitable thickness, i.e., 5-100 .ANG. can be normally
achieved in 5 minutes, depending on the pressure and temperature
employed.
[0037] The final step in the fabrication of the present invention
capacitor is the deposition of a conducting layer 46 on top of the
nitrogen-rich layer 44. This is shown in FIG. 2D. The conducting
layer 46 can be composed of doped or intrinsic polysilicon, or any
other conducting material which contains chemical species that
could degrade the performance or lifetime of the semiconductor
device if they were to diffuse through the insulating layer into
the substrate.
[0038] The chemical nature of the present invention novel
nitrogen-rich film can be verified by an X-ray photoemission test
and furthermore, can be illustrated by the X-ray photoemission
spectra shown in FIGS. 3 and 4. The graph shown in FIG. 3 contains
six traces each representing X-ray photoemission data of the layer
after each processing step. The traces directly show the bonding
configurations of the silicon atoms within the layer. The traces
were obtained after performing a deposition such as previously
described on a silicon substrate coated with a thin, previously
grown nitrided oxide layer. The thickness of the nitrided oxide
layer will always be less than 10 nm, and in one preferred
embodiment is approximately 1.0 nm. A thin nitrided oxide layer is
specifically chosen in this experiment in order to show the maximum
effect which the chemical manipulations that are performed on the
overlayer have on the oxide/substrate interface. It has been found
that the thinner the nitrided oxide layer is, the more vulnerable
its interface with the substrate will be to chemical effect by the
post processing of the deposited overlayer.
[0039] Referring now to FIG. 3, trace 1 was obtained on a silicon
substrate after the growth of approximately 10 .ANG. silicon
dioxide. The large peak at 64 eV is from the oxide film, while the
smaller peak at 68 eV shows the presence of a pure silicon
substrate under the film. After deposition of the
nitrogen-containing film, which was accomplished by pyrolysis of
trisilylamine vapor on the surface of the oxide at 515.degree. C.,
trace 2 was obtained. At this point of the process, the TSA layer
contains approximately 25 atomic % nitrogen due to the
stoichiometry of the particular precursor used and thus the film is
fairly conductive. When the TSA layer is thick enough, i.e., larger
than 25 .ANG., the signals from the oxide and the substrate
underneath are completely attenuated. However, it is possible to
observe the signal from the oxide layer underneath if the TSA layer
is made thin enough. Trace 2 shows a peak characteristic of silicon
with no direct bonding to nitrogen, as well as a feature
characteristic of Si--N bond formation. This spectrum, along with
the intensity of the N 1 s XPS spectrum, indicates that the
stoichiometry of the nitrogen-containing film is approximately
Si.sub.3N.
[0040] In one preferred embodiment of the present invention,
approximately three monolayers of the nitrogen-rich film are used
to provide an effective barrier to boron diffusion. If it is
necessary to make the nitrogen-containing film insulating, it could
be oxidized or subjected to further nitridation. The thickness of
the nitrogen-rich film shown in FIG. 3, trace 2, of approximately
50 .ANG. is substantially larger than would be required in the
actual implementation of the present invention method. A thicker
film was specially chosen for this demonstration, as it requires
more stringent conditions for conversion to a stoichiometric
nitride, since the stoichiometric nitride formed at the surface of
the nitrogen-rich film serves as a diffusion barrier and thus
shields the bottom of the nitrogen-rich film from the nitriding
agent. It is therefore demonstrated that an entire nitrogen-rich
film of the present invention having an excessive thickness can be
transformed to stoichiometric nitride under conditions which do not
perturb the stoichiometry of the nitrided oxide/silicon substrate
interface. It is therefore concluded that all of the possible post
processing reactions which could be used for the nitrogen-rich film
will pose no inherent problem. The X-ray photoemission spectra
therefore amply demonstrate this effect.
[0041] The majority of the 50 .ANG. thick nitrogen-rich film in
FIG. 3 is converted to stoichiometric nitride upon reaction with
ammonia at a temperature of less than 500.degree. C. This
temperature would be sufficient for the preferred embodiment of the
process, if only a three monolayer film were used. The 50 .ANG.
thick film can be completely transformed to stoichiometric silicon
nitride at a temperature of approximately 700.degree. C. However,
even this process is insufficient to perturb the original oxide
film. It has also been observed that, even subjecting the test
structure to the 700.degree. C. NH.sub.3 reaction conditions for a
prolonged period of time, no additional nitrogen is incorporated
into the gate oxide layer underneath. It is therefore concluded
that the stoichiometry of the deposited buffer layer can be
manipulated without altering the gate insulator layer. It should be
further noted that, in addition to nitriding the nitrogen-rich
buffer layer, it is also possible to oxidize the film to any
desired extent by the use of, for instance, molecular oxygen,
N.sub.2O or NO. This can be conducted either in a separate
processing step, or concurrently with the deposition of the
nitrogen-rich film.
[0042] When the sample is annealed to 750.degree. C., i.e., FIG. 3
trace 3, hydrogen is removed from the trisilylamine film. Traces 4,
5 and 6 illustrate that annealing in ammonia at increasing
temperatures of 560.degree. C., 630.degree. C. and 690.degree. C.,
respectively, results in the incorporation of additional nitrogen
into the film. As a result, the film is converted to the insulator
silicon nitride (Si.sub.3N.sub.4). Alternatively, it may be
desirable to keep the nitrogen concentration of the film at 25
atomic %, and instead anneal in oxygen. The results obtained by
such a method are shown in FIG. 4.
[0043] As shown in FIG. 4, wherein trace 1 is equivalent to trace 3
of FIG. 3, trace 1 shows a TSA film deposited at 503.degree. C.
after annealing for removal of hydrogen. Traces 2-7 further
illustrate TSA films annealed in oxygen at 454.degree. C.,
505.degree. C., 566.degree. C., 703.degree. C., 770.degree. C. and
850.degree. C., respectively. Utilizing this process, a silicon
oxynitride film can be fabricated without reducing the nitrogen
concentration significantly. The silicon oxynitride film has the
same diffusion barrier characteristic, in addition to being a good
insulating layer.
[0044] An example of how the present invention novel method and
structure would prove beneficial is demonstrated in FIG. 5. The
presence of nitrogen in the gate oxide of a CMOS FET is used to
stop boron atoms which are present in a heavily doped p+
polysilicon gate electrode from diffusing through the gate oxide
into the n-type Si substrate. One way to monitor the presence of
boron in the substrate is by monitoring the changes in the flatband
voltage of a capacitor-like device structure. The flatband voltage
(Vfb) is known to be directly proportional to the difference
between the workfuncton of the gate and that of the substrate.
Since the workfunction of doped Si is primarily determined by the
doping concentration, any change in the dopant concentration will
be reflected by a change in Vfb. An example of this is shown in
FIG. 5, where the change in Vfb is monitored for two different
kinds of 35 .ANG. oxides, as a function of annealing time at a
given temperature. This annealing process is required for CMOS
device manufacture in order to activate the boron atoms that were
previously implanted into the polysilicon gate electrode. This
figure shows that boron is diffusing through the oxide and into the
substrate, causing a change in Vfb. The diffusion of boron occurs
to a much lesser extent in the N.sub.2O grown oxide vs. the pure
thermal oxide, due to the presence of N atoms blocking the B
diffusion. A small change in Vfb is still observed in the N.sub.2O
grown oxide, however, since the percentage of N atoms in this layer
is quite low. Using the present invention novel method and
structure, it would be possible to significantly increase the time
or temperature of the boron activation anneal, and at the same time
keep the boron atoms completely inside the polysilicon gate
electrode.
[0045] The advantage and uniqueness offered in our novel structure
and method is the precise control of the location of and the N
concentration in the N-containing layer. In the example above,
nitrogen is added to the oxide via a simple thermal process which
allows for little or no control over where the nitrogen is
incorporated. Indeed, in the example above, nitrogen is located
close to the oxide-substrate interface, where it can adversely
affect FET characteristics, such as the initial flatband voltage.
Ideally, it is desirable to control the location of the
N-containing layer, which is accomplished via the deposition of a
N-containing layer on top of a gate oxide, as well as to tailor the
N concentration independently, which can be performed via judicious
choice of the deposition molecules and conditions.
[0046] The present invention novel method and device formed have
therefore been amply demonstrated by the above descriptions and the
appended drawings of FIGS. 1-5. The present invention novel method
solves the problems of the conventional method by providing a low
temperature CVD-based process for the deposition of
nitrogen-containing layers at the electrode-dielectric interface.
When the present invention nitrogen-rich layer is combined with a
substrate already possessing a nitrided oxide layer, a greatly
improved device can be produced which possesses a small amount of
nitrogen near the substrate, and a large controllable amount of
nitrogen near the gate electrode. For instance, the small amount of
nitrogen located near the substrate may be approximately 2 atomic
%, while the larger controllable amount of nitrogen near the gate
electrode may be approximately 25 atomic %. Since the CVD process
can be conducted at low temperatures, it does not cause a
redistribution of the nitrogen previously incorporated in the oxide
near the substrate interface. The present invention novel method
therefore enables the two different functions of the introduced
nitrogen to be optimized independently.
[0047] The present invention novel basic structure embodied in the
preferred embodiment has been shown in FIG. 2D. The novel feature
consists of a thin nitrogen-containing silicon layer that is
inserted between a gate dielectric layer and a gate electrode, for
blocking diffusion of contaminating species from the electrode into
the dielectric. The novel diffusion barrier layer can be fabricated
advantageously by a chemical vapor deposition method. The diffusion
barrier layer can be as thin as one or two atomic layers, or can be
increased as required. Even though the structure depicted in FIG.
2D has a superficial similarity to a so-called "stacked gate
dielectric" device, the function of, and the typical width
envisioned for, the deposited layer put it in an entirely different
category. For instance, in a stacked gate structure, a
stoichiometric silicon nitride layer is typically of similar
thickness to the silicon dioxide layer in the gate insulator, and
both make substantial contributions to the total capacitance of the
gate dielectric. In contrary, the present invention novel diffusion
barrier layer is intended only to minimally impact the total
capacitance of the gate dielectric, while intended primarily for
the purpose of blocking impurity diffusion into the oxide and
substrate.
[0048] While the present invention has been described in an
illustrative manner, it should be understood that the terminology
used is intended to be in a nature of words of description rather
than of limitation.
[0049] Furthermore, while the present invention has been described
in terms of a preferred and an alternate embodiments, it is to be
appreciated that those skilled in the art will readily apply these
teachings to other possible variations of the inventions. For
example, a nitrogen-containing layer for the purpose of blocking
the diffusion of contaminants could be used in static random access
memory (SRAM), dynamic random access memory (DRAM), synchronous
dynamic random access memory (SDRAM), flash electrically eraseable
programable read only memory (EEPROM) and charge coupled devices
(CCD) as well as in CMOS FETs.
[0050] The embodiment of the invention in which an exclusive
property or privilege is claimed are defined as follows:
* * * * *