U.S. patent application number 09/031526 was filed with the patent office on 2001-08-09 for capacitor having tantalum oxynitride film and method for making same.
Invention is credited to AL-SHAREEF, HUSAM N., DEBOER, SCOTT JEFFREY, GEALY, DAN, THAKUR, RANDHIR P.S..
Application Number | 20010011740 09/031526 |
Document ID | / |
Family ID | 21859947 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011740 |
Kind Code |
A1 |
DEBOER, SCOTT JEFFREY ; et
al. |
August 9, 2001 |
CAPACITOR HAVING TANTALUM OXYNITRIDE FILM AND METHOD FOR MAKING
SAME
Abstract
A capacitor has a tantalum oxynitride film. One method for
making the film comprises forming a bottom plate electrode and then
forming a tantalum oxide film on the bottom plate electrode.
Nitrogen is introduced to form a tantalum oxynitride film. A top
plate electrode is formed on the tantalum oxynitride film.
Inventors: |
DEBOER, SCOTT JEFFREY;
(BOISE, ID) ; AL-SHAREEF, HUSAM N.; (BOISE,
ID) ; THAKUR, RANDHIR P.S.; (CUPERTINO, CA) ;
GEALY, DAN; (KUNA, ID) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Family ID: |
21859947 |
Appl. No.: |
09/031526 |
Filed: |
February 26, 1998 |
Current U.S.
Class: |
257/306 ;
257/E21.008; 257/E21.274; 257/E21.648; 438/240; 438/386; 438/393;
438/396 |
Current CPC
Class: |
H01L 27/10861 20130101;
H01L 27/10852 20130101; H01L 23/5252 20130101; H01L 27/112
20130101; H01L 28/65 20130101; H01L 21/02337 20130101; H01L
27/11206 20130101; H01L 28/40 20130101; H01L 2924/0002 20130101;
H01L 21/31604 20130101; G11C 17/16 20130101; H01L 21/31637
20130101; H01L 21/0234 20130101; H01L 21/02271 20130101; H01L
21/02326 20130101; H01L 28/84 20130101; H01L 21/02183 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/306 ;
438/393; 438/386; 438/396; 438/240 |
International
Class: |
H01L 021/8242; H01L
021/20; H01L 031/119 |
Claims
What is claimed is:
1. A method for fabricating a capacitor on an integrated circuit,
comprising the steps of: forming a bottom plate electrode; forming
a tantalum oxide film on the bottom plate electrode; annealing the
tantalum oxide film in an environment containing oxygen;
introducing nitrogen into the tantalum oxide film to form a
tantalum oxynitride film; and forming a top plate electrode on the
tantalum oxynitride film.
2. The method of claim 1, wherein the annealing step is performed
after the introducing step when the introducing step is performed
at temperatures greater than approximately 600 degrees Celsius.
3. The method of claim 1, wherein the step of forming the tantalum
oxide film comprises the steps of: forming tantalum on the bottom
electrode; and oxidizing the tantalum.
4. The method of claim 1, wherein the step of forming the tantalum
oxide film comprises the step of forming tantalum oxide film by
chemical vapor deposition with tantalum and oxygen sources.
5. The method of claim 4, wherein the step of forming the tantalum
oxide film by chemical vapor deposition with tantalum and oxygen
sources comprises the step of forming tantalum oxide film by low
pressure chemical vapor deposition with tantalum (V) ethoxide and
oxygen at a temperature between approximately 400 and 500 degrees
Celsius.
6. The method of claim 1, wherein the step of introducing nitrogen
into the tantalum oxide film to form the tantalum oxynitride film
comprises the step of annealing the tantalum oxide film to form a
tantalum oxynitride film Ta.sub.xN.sub.yO.sub.z, wherein
(y+z)/x>2.5.
7. The method of claim 1, wherein the step of introducing nitrogen
compromises the step of implanting nitrogen ions into the tantalum
oxide film to form the tantalum oxynitride film.
8. The method of claim 1, wherein the step of introducing nitrogen
compromises the step of annealing the tantalum oxide film in a
nitrogen atmosphere in the presence of a plasma.
9. The method of claim 1, further comprising the step of silicon
nitridation.
10. The method of claim 9, wherein the step of silicon nitridation
comprises the step of exposing the capacitor to a combination of
silicon and nitrogen sources.
11. The method of claim 10, wherein the step of exposing comprises
the step of exposing the capacitor to a combination of silicon and
nitrogen sources, wherein the silicon source is one of a group
consisting of: silane, disilane and dichlorosilane.
12. The method of claim 10, wherein the step of exposing comprises
the step of exposing the capacitor to a combination of silicon and
nitrogen sources, wherein the nitrogen source is one of a group
consisting of: N.sub.2, NH.sub.3, N.sub.2H.sub.4, N.sub.2O, and
monomethyl hydrazene (MMH).
13. The method of claim 10, wherein the step of exposing
compromises the step of exposing the capacitor to disilane and
ammonia combined respectively in a one to five ratio.
14. The method of claim 10, wherein the step of exposing is
conducted for less than approximately the incubation time so that
an insubstantial amount of silicon nitride is formed on the
capacitor.
15. A method for fabricating a capacitor in an integrated circuit,
comprising the steps of: forming a bottom plate electrode; forming
a tantalum oxide film on the bottom plate electrode; annealing the
tantalum oxide film in an environment containing oxygen;
introducing nitrogen into the tantalum oxide film to form a
tantalum oxynitride film; forming a top plate electrode on the
tantalum oxynitride film; and wherein the step of introducing
nitrogen comprises the step of annealing the tantalum oxide film in
a nitrogen atmosphere at a temperature range between approximately
25 and 1100 degrees Celsius.
16. The method of claim 15, wherein the step of annealing comprises
the step of annealing the tantalum oxide film in a nitrogen
atmosphere that is one of a group consisting of: N.sub.2, NH.sub.3,
and N.sub.2H.sub.4.
17. The method of claim 15, wherein the step of annealing comprises
the step of annealing the tantalum oxide film in a nitrogen
atmosphere at a temperature range between approximately 200 and 825
degrees Celsius at a pressure range between approximately 1 and 50
atmospheres.
18. The method of claim 15, wherein the step of annealing in an
environment containing oxygen is performed after the step of
annealing in a nitrogen atmosphere when the step of annealing in a
nitrogen atmosphere is performed at temperatures greater than
approximately 600 degrees Celsius.
19. A method for fabricating a capacitor in an integrated circuit,
comprising the <steps of: forming a bottom plate electrode;
forming a tantalum oxide film on the bottom plate electrode;
annealing the tantalum oxide film in an environment containing
oxygen; introducing nitrogen into the tantalum oxide film to form a
tantalum oxynitride film; forming a top plate electrode on the
tantalum oxynitride film; and wherein the step of introducing
nitrogen comprises the step of annealing in a furnace having an
ammonia atmosphere at a temperature range between approximately 500
and 1050 degrees Celsius, and at a pressure less than 5 torr, for
approximately five minutes.
20. The method of claim 19, wherein the step of annealing in an
environment containing oxygen is performed after the step of
annealing in a nitrogen atmosphere when the step of annealing in a
nitrogen atmosphere is performed at temperatures greater than
approximately 600 degrees Celsius.
21. A method for fabricating a capacitor in an integrated circuit,
comprising the steps of: forming a bottom plate electrode; forming
a tantalum oxide film on the bottom plate electrode; annealing the
tantalum oxide film in an environment containing oxygen;
introducing nitrogen into the tantalum oxide film to form a
tantalum oxynitride film; forming a top plate electrode on the
tantalum oxynitride film; and wherein the step of introducing
nitrogen comprises the step of rapid thermal processing in a
nitrogen atmosphere at a temperature between approximately 700 and
1050 degrees Celsius for a time between approximately 10 and 120
seconds.
22. The method of claim 21, wherein the introducing step is
performed before the annealing step.
23. A method for fabricating a capacitor, comprising the steps of:
forming a bottom plate electrode; forming a tantalum oxynitride
film on the bottom plate electrode; and forming a top plate
electrode on the tantalum oxynitride film.
24. The method of claim 23, wherein the step of forming tantalum
oxynitride film comprises the step of forming tantalum oxynitride
film by metal organo chemical vapor deposition with tantalum and
nitrogen sources.
25. The method of claim 24, wherein the step of forming tantalum
oxynitride film by metal organo chemical vapor deposition comprises
the step of forming tantalum oxynitride film by metal organo
chemical vapor deposition wherein the nitrogen source is introduced
to the capacitor in the presence of a remote plasma.
26. The method of claim 24, wherein the step of forming tantalum
oxynitride film by metal organo chemical vapor deposition comprises
the step of forming tantalum oxynitride film by metal organo
chemical vapor deposition wherein the nitrogen source is introduced
to the capacitor in the presence of a plasma for enhanced
deposition.
27. The method of claim 24, wherein the step of forming tantalum
oxynitride film by metal organo chemical vapor deposition comprises
the step of forming tantalum oxynitride film by metal organo
chemical vapor deposition with a nitrogen source at a temperature
between approximately 300 and 600 degrees Celsius to form amorphous
tantalum oxynitride; and wherein the nitrogen source is one of a
group consisting of hydrazene and hydrazene derivatives.
28. A method of fabricating a capacitor in an integrated circuit,
comprising the steps of: forming a bottom plate electrode; forming
a tantalum oxide film on the bottom plate electrode; annealing the
tantalum oxide film in an environment containing oxygen;
introducing nitrogen into the tantalum oxide film to form a
tantalum oxynitride film; forming a top plate electrode on the
tantalum oxynitride film; and wherein the step of introducing
nitrogen comprises the step of annealing in a nitrogen atmosphere
and a plasma.
29. The method of claim 28, wherein the step of annealing comprises
the step of annealing in nitrogen atmosphere and a plasma that is
one of a group consisting of: high density plasma, remote plasma,
radio frequency plasma, and electron cyclotron resonance
plasma.
30. The method of claim 31 wherein the step of annealing comprises
the step of annealing in a nitrogen atmosphere that is one of a
group consisting of: N.sub.2O, NH.sub.3, NO, and
N.sub.2H.sub.4.
31. A capacitor, comprising: a bottom plate electrode; a tantalum
oxynitride film on the bottom plate electrode; and a top plate
electrode on the tantalum oxynitride film.
32. The capacitor of claim 31, wherein the bottom plate electrode
comprises a material selected from the group consisting of:
polysilicon, crystalline silicon, hemispherical grain polysilicon,
germanium, silicon-germanium, ruthenium, ruthenium oxide, iridium,
iridium oxide, platinum and rhenium.
33. The capacitor of claim 31, wherein the bottom plate electrode
is doped.
34. The capacitor of claim 31, wherein the bottom plate electrode
has a shape selected from the group consisting of: fin-type,
stacked-type, container-type, crown-type and trenched-type.
35. The capacitor of claim 31, wherein the bottom plate electrode
has a topography selected from the group consisting of
single-sided, double-sided, and roughened.
36. The capacitor of claim 31, wherein the tantalum oxynitride is
amorphous.
37. The capacitor of claim 31, wherein the tantalum oxynitride is
crystalline.
38. A memory, comprising: a memory array having a plurality of
capacitors, each capacitor comprising, a bottom plate electrode, a
tantalum oxynitride film on the bottom plate electrode, and a top
plate electrode on the tantalum oxynitride film; a control circuit,
operatively coupled to the memory array; and address logic,
operatively coupled to the memory array and the control logic.
39. The memory of claim 38, wherein the bottom plate electrode
comprises a material selected from the group consisting of:
polysilicon, crystalline silicon, hemispherical grain polysilicon,
germanium, silicon-germanium, ruthenium, ruthenium oxide, iridium,
iridium oxide, platinum and rhenium.
40. The memory of claim 38, wherein the bottom plate electrode is
doped.
41. The memory of claim 38, wherein the bottom plate electrode has
a shape selected from the group consisting of: fin-type,
stacked-type, container-type, crown-type and trenched-type.
42. The memory of claim 38, wherein the bottom plate electrode has
a topography selected from the group consisting of single-sided,
double-sided, single-sided roughened, and double-sided
roughened.
43. The memory of claim 38, wherein the tantalum oxynitride is
amorphous.
44. The memory of claim 38, wherein the tantalum oxynitride is
crystalline.
45. A system, comprising: a memory including, a memory array having
a plurality of capacitors, each capacitor comprising, a bottom
plate electrode, a tantalum oxynitride film on the bottom plate
electrode, and a top plate electrode on the tantalum oxynitride
film, a control circuit, operatively coupled to the memory array,
and address logic, operatively coupled to the memory array and the
control logic; and a processor coupled to the memory.
46. The system of claim 45, wherein the bottom plate electrode
comprises a material selected from the group consisting of:
polysilicon, crystalline silicon, hemispherical grain polysilicon,
germanium, and silicon-germanium.
47. The system of claim 45, wherein the bottom plate electrode is
doped.
48. The system of claim 45, wherein the bottom plate electrode has
a shape selected from the group consisting of: fin-type,
stacked-type and trenched-type.
49. The system of claim 45, wherein the bottom plate electrode has
a topography selected from the group consisting of single-sided,
double-sided, and roughened.
50. The system of claim 45, wherein the tantalum oxynitride is
amorphous.
51. The system of claim 45, wherein the tantalum oxynitride is
crystalline.
52. A method of operating an antifuse, comprising the steps of:
applying a voltage across the electrodes of a capacitor having a
tantalum oxynitride film; forming a hole in the tantalum oxynitride
film; creating a resistance between approximately 1000 and 6000
ohms.
53. The method of claim 52, further comprising the step of
programming a redundant element in a memory.
54. A method of forming an antifuse, comprising the steps of:
forming a bottom plate electrode; forming a tantalum oxide film on
the bottom plate electrode; annealing the tantalum oxide film in an
environment containing oxygen; introducing nitrogen into the
tantalum oxide film to form a tantalum oxynitride film; and forming
a top plate electrode on the tantalum oxynitride film.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to semiconductor structures
and methods for fabricating such structures in semiconductor
integrated circuits and, in particular, to forming capacitors for
memory cells having high dielectric constant materials therein.
BACKGROUND OF THE INVENTION
[0002] Dynamic random access memories (DRAMs) are the most widely
used form of memory integrated circuits to date. DRAMs are composed
of memory cell arrays and peripheral circuitry required for cell
access and external input and output. Each memory cell array is
formed of a plurality of memory cells for storing bits of data.
Typical memory cells are formed of a capacitor, for storing
electric charges and a transistor, for controlling charge and
discharge of the capacitor. Of primary concern is maximizing the
storage capacitance of each memory cell capacitor, particularly in
light of the demand for 256 Mb DRAMs today and higher densities in
the future without increasing the chip space required to form the
array. There is a need to decrease the chip space required to form
each memory cell while maximizing the capacitance of the memory
cells. The importance of high density DRAMs cannot be overstated in
today's competitive microelectronics market. Devices are becoming
smaller, but they are required to provide much more
performance.
[0003] One way to achieve greater capacitance per unit area is to
roughen the surface of the capacitor plate, increasing the surface
area. As can be seen from the following equation (I), the most
important parameters involved in achieving maximum charge, Q,
stored on the capacitor are the thickness of the capacitive
dielectric film (t.sub.cdf), the area of the capacitor (A), and the
dielectric constant (.epsilon.). The voltage applied across the
capacitor plates is V.
Q=(.epsilon..multidot.A.multidot.V)/t.sub.cdf (I)
[0004] Increasing the capacitor area (A) by forming the storage
capacitor in a trench shape etched in the substrate is well known
in the art, as well as using a stacked capacitor structure.
Stacked-type capacitors feature a major part of the capacitor
extending over the gate electrode and field isolating film of the
underlying transistor. Such structures are generally composed of a
lower plate electrode (consisting of a base portion and a standing
wall portion), a capacitive dielectric film, and an upper plate
electrode. Other complex topographical lower plate electrode
configurations have also been used to maximize the capacitive area
(A) of a memory cell, such as fin-type, double-sided, and roughened
lower plate electrode structures produced using hemispherical grain
(HSG) polysilicon.
[0005] In addition to increasing the capacitive surface area (A) of
a memory cell, as can be seen from the above equation (I), the
thickness of the capacitive dielectric film (t.sub.cdf) must be
minimized to maintain the maximum charge stored on the capacitor.
However, the capacitive dielectric film must also prevent direct
electrical contact between the lower and upper electrodes to
prevent the charge from decaying.
[0006] It is also desirable to utilize a capacitive dielectric film
having as high of a dielectric constant (.epsilon.) as possible to
further increase the capacitance per unit area of a memory cell.
One material that has a high dielectric constant is tantalum oxide,
such as tantalum penta oxide (Ta.sub.2O.sub.5). Ta.sub.2O.sub.5
potentially has a dielectric constant (.epsilon.) of about 22,
which is significantly greater than conventional silicon oxide,
which has a dielectric constant (.epsilon.) of only about 3.9.
[0007] A capacitor of a memory cell formed with Ta.sub.2O.sub.5
insulator includes an electrode. To attain adequate step coverage
for the electrode on an integrated circuit, the electrode may be
initially formed with an organometallic precursor that contains
carbon.
[0008] After the capacitor is formed, the integrated circuit is
subject to a high temperature processing step, such as
borophosphosilicate glass (BPSG) reflow or polysilicon activation.
During such heating, in the memory cell capacitor, carbon from the
electrode diffuses into the Ta.sub.2O.sub.5 insulator. The carbon
in the Ta.sub.2O.sub.5 insulator forms a leakage mechanism that
renders the capacitor unusable. A relatively high leakage current
flows through the capacitor even when relatively small voltage is
applied across the capacitor. Therefore, there is a need for a
capacitor that has a relatively high capacitance per unit area, to
ensure high device density, and a relatively low leakage current.
There is also a need for a dielectric material having a high
dielectric constant that is substantially unaffected by subsequent
high temperature processing steps.
SUMMARY OF THE INVENTION
[0009] A capacitor has a tantalum oxynitride film. One method for
making the film comprises forming a bottom plate electrode and then
forming a tantalum oxide film on the bottom plate electrode.
Nitrogen is introduced to form a tantalum oxynitride film. A top
plate electrode is formed on the tantalum oxynitride film. In
another embodiment, an anti-fuse is formed in the same manner.
[0010] In one embodiment, the step of forming the tantalum oxide
film comprises the steps of forming tantalum on the bottom
electrode, and oxidizing the tantalum. In another embodiment,
tantalum oxide film is formed by chemical vapor deposition with
tantalum and oxygen sources. In yet another embodiment, the
tantalum oxide film is annealed to form a tantalum oxynitride film
Ta.sub.xN.sub.yO.sub.z, wherein (y+z)/x>2.5.
[0011] In another embodiment, the method of forming the capacitor
includes the step of forming a bottom plate electrode. A tantalum
oxynitride film is formed on the bottom plate electrode. A top
plate electrode is formed on the tantalum oxynitride film. In one
embodiment, the tantalum oxynitride film is formed by metal organo
chemical vapor deposition with a nitrogen source that is hydrazene
at a temperature between approximately 400 and 600 degrees Celsius
so as to form amorphous tantalum oxynitride.
[0012] In another embodiment, the invention is a capacitor that has
a bottom plate electrode, a tantalum oxynitride film and a top
plate electrode. In one embodiment, the tantalum oxynitride film is
amorphous.
[0013] In one embodiment, the capacitor may be used in a memory
array of a memory. The memory comprises the memory array, a control
circuit, operatively coupled to the memory array, and address
logic, operatively coupled to the memory array and the control
logic.
[0014] In yet another embodiment, the capacitor may be used in the
memory array of a system. The system comprises a memory and a
processor coupled to the memory.
[0015] In yet a further embodiment, an antifuse is operated by
applying a voltage across the electrodes of the capacitor having a
tantalum oxynitride film. A hole is formed in the tantalum
oxynitride film.
[0016] It is an advantage of the present invention that the
capacitor has a high dielectric constant. It is also a benefit of
the present invention that it is less affected by heat so as to
have reduced leakage current. It is a further advantage of the
invention that the capacitor has enhanced reliability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a cross-sectional representation of a polysilicon
electrode stacked, double-sided capacitor memory cell formed
according to the method of the invention, wherein the capacitor is
stacked on a source/drain region of an underlying access
transistor.
[0018] FIG. 1B is a cross-sectional representation of a trench-type
capacitor memory cell formed according to the method of the
invention.
[0019] FIG. 2 is a graphical representation of voltage versus
capacitance for planar tantalum penta oxide capacitive dielectric
films formed according to the method of the invention compared to
conventional silicon nitride capacitive dielectric films.
[0020] FIG. 3A is an Auger plot of atomic concentrations in a
memory cell having a tantalum oxide dielectric.
[0021] FIG. 3B is an Auger plot of atomic concentrations in a
memory cell having a tantalum oxynitride dielectric
[0022] FIG. 4 is a block diagram of a memory having a capacitor in
accordance with the present invention.
[0023] FIG. 5 is a block diagram of the memory of FIG. 4 coupled to
an external system.
DESCRIPTION OF THE EMBODIMENTS
[0024] In the following detailed description of the invention,
reference is made to the accompanying drawings which form a part
hereof, and in which is shown, by way of illustration, specific
embodiments in which the invention may be practiced. In the
drawings, like numerals describe substantially similar components
throughout the several views. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention. Other embodiments may be utilized and structural,
logical, and electrical changes may be made without departing from
the scope of the present invention. The terms wafer and substrate
used in the following description include any structure having an
exposed surface with which to form the integrated circuit (IC)
structure of the invention. The term substrate is understood to
include semiconductor wafers. The term substrate is also used to
refer to semiconductor structures during processing, and may
include other layers that have been fabricated thereupon. Both
wafer and substrate include doped and undoped semiconductors,
epitaxial semiconductor layers supported by a base semiconductor or
insulator, as well as other semiconductor structures well known to
one skilled in the art. The term conductor is understood to include
semiconductors, and the term insulator is defined to include any
material that is less electrically conductive than the materials
referred to as conductors. The following detailed description is,
therefore, not to be taken in a limiting sense.
[0025] FIGS. 1A and 1B represent, generally, capacitors 100 of
memory cells formed in accordance with the method of the invention.
The following description details process steps utilized to form
the capacitors 100. In particular, the process steps described are
directed towards forming a tantalum oxynitride film 102 between
bottom and top plate electrodes 104, 106, respectively, of a
capacitor 100.
[0026] FIG. 1A is a cross-sectional representation of a stacked,
double-sided capacitor 100 formed according to the method of the
invention, wherein the capacitor 100 is stacked on a source/drain
region 108 of an underlying access transistor. The access
transistor comprises source/drain regions 108 on both sides of a
gate structure, which includes a polysilicon gate 110 and gate
oxide 112. The access transistor is fabricated in an active area of
an underlying substrate 101 that is defined by field oxide 114.
Typically, the gate oxide 112 and the field oxide 114 are formed
using a conventional method, such as LOCal Oxidation of Silicon
(LOCOS). The capacitor 100 is supported over the source/drain
region 108 by an insulating material 116, such as
borophosphosilicate glass (BPSG), which reflows easily to produce
rounded comers over the gate 110, allowing better step
coverage.
[0027] FIG. 1B is a cross-sectional representation of a trench-type
capacitor 100 formed according to the method of the invention,
wherein the trench shape is defined by sidewalls 118 and a bottom
surface 120. FIGS. 1A and 1B are meant to be illustrative,
generally, of various capacitor 100 shapes and electrode 104, 106
topographies that increase the surface area of the capacitor 100.
The capacitor 100 shape and topography of the electrodes 104 and
106 in a capacitor 100 are not critical to practicing the
invention. The capacitor 100 may also be formed as a fin-type,
container-type, or crown-type capacitor. The scope of the invention
is not meant to be limited to those capacitors 100 illustrated.
[0028] In one embodiment, polysilicon, crystalline silicon,
hemispherical grain polysilicon, germanium, silicon-germanium,
ruthenium, ruthenium oxide, iridium, iridium oxide, platinum,
rhenium, and combinations thereof (deposited using chemical vapor
deposition) is used as electrode 104, 106 material in a capacitor
100. An increased surface area polysilicon bottom plate electrode
104 is formed over a supporting semiconductor structure, as well
known to one skilled in the art. The shape of the bottom plate
electrode 104 may be stacked-type and trench-type structures, as
illustrated in FIGS. 1A and 1B, to provide an increased capacitive
surface area for the capacitor 100. The topography of the bottom
plate electrode 104 may include single-sided, double-sided, and
roughened lower plate electrode 104 topographies produced using
hemispherical grain (HSG) polysilicon. The lower plate 104 may be
roughened on one side or both sides. The bottom plate electrode 104
can be doped or undoped, and rough or smooth. Phosphorus is a
common dopant for a bottom plate electrode 104.
[0029] After cleaning the bottom plate electrode 104, such as with
a hydrofluoric acid (HF) solution, the bottom plate electrode 104
is subjected to a surface treatment. The capacitor 100 is then
annealed, such as by rapid thermal nitridation (RTN), rapid thermal
oxidation (RTO), rapid thermal oxynitridation (RTN.sub.2O), dry
oxidation or high pressure oxidation.
[0030] A tantalum oxide film, such as tantalum penta oxide
(Ta.sub.2O.sub.5), is then formed on the bottom plate electrode.
The tantalum oxide film is preferably stoichiometric.
Stoichiometric films have a lower defect density, resulting in a
decreased leakage current. This is essential for optimum electrical
properties, particularly in capacitors 100.
[0031] Tantalum oxide film deposition is accomplished in a manner
known to those skilled in the art. In one embodiment, inorganic or
organic precursors, both liquids and/or solids, may be used for
starting materials. Then, tantalum is deposited on the bottom
electrode 104 of the capacitor 100. Then the tantalum is oxidized
to form the tantalum oxide film. Alternatively, the tantalum oxide
film can also be formed by chemical vapor deposition (CVD) with
tantalum and oxide sources. In one embodiment, using tantalum (V)
ethoxide (Ta(OC.sub.2H.sub.5).sub.5) and oxygen (O.sub.2) sources,
a film of Ta.sub.2O.sub.5 can be deposited on the capacitor 100
with low pressure CVD (LPCVD) at a temperature between
approximately 400 and 500 degrees Celsius.
[0032] The thickness of tantalum oxide film is approximately 30 to
200 angstroms, and typically 90 angstroms. The formation of
tantalum oxide films is further described in P. C. Fazan et al., "A
High-C Capacitor (20.4 fF/.mu.m.sup.2) with Ultrathin
CVD--Ta.sub.2O.sub.5 Films Deposited on Rugged Poly-Si for High
Density DRAMs," IEEE, pp. 263-266, 1992, and P. C. Fazan et al.,
"Ultrathin Ta.sub.2O.sub.5 Films on Rapid Thermal Nitrided Rugged
Polysilicon for High Density DRAMs," International Conference on
Solid State Devices and Materials, pp. 697-698, 1992, both
incorporated herein by reference.
[0033] After formation of the tantalum oxide film, the capacitor
100 is annealed in an environment containing oxygen. This anneal
crystallizes and fills vacancies in the tantalum oxide film. This
oxygen anneal may be performed after the subsequently described
introduction of nitrogen, such as by anneal, if the nitrogen
introduction is performed at a temperature of greater than
approximately 600 degrees Celsius. In one embodiment, to form
partially crystallized tantalum oxynitride, the oxygen anneal is
performed after the nitrogen anneal, when the nitrogen introduction
is performed at a temperature between approximately 500 and 750
degrees Celsius. In another embodiment, to form fully crystallized
tantalum oxynitride, the oxygen anneal is performed after the
nitrogen anneal when the nitrogen introduction is performed at a
temperature between approximately 750 and 1050 degrees Celsius.
[0034] Subsequently, the tantalum oxide is transformed into
tantalum oxynitride (Ta.sub.xN.sub.yO.sub.z) film 102, where
preferably (y+z)/x>2.5, by introducing nitrogen into the
tantalum oxide film. In one embodiment, the transformation is
accomplished annealing the tantalum oxide, in a furnace or with
rapid thermal processing (RTP), in a nitrogen atmosphere at a
temperature ranging between approximately 25 and 1100 degrees
Celsius. The nitrogen atmosphere may be nitrogen (N.sub.2), ammonia
(NH.sub.3), or hydrazene (N.sub.2H.sub.4).
[0035] In one embodiment, the capacitor 100 is annealed in nitrogen
atmosphere at a temperature range between approximately 200 and 825
degrees Celsius, and at a pressure range between approximately 1
and 50 atmospheres. As a result, the tantalum oxynitride is formed
to be amorphous. Amorphous tantalum oxynitride has a higher
dielectric constant than crystalline tantalum oxynitride, and
therefore can form capacitors having higher capacitance per area.
Amorphous tantalum oxynitride can also be formed at temperatures
between approximately 350 and 575 degrees Celsius, and pressures
between approximately 10 milliTorr and 400 Torr. Preferably, the
pressure is between approximately 1 atmosphere and 30
atmospheres.
[0036] In another embodiment, the capacitor 100 is annealed in an
ammonia environment in a furnace at a temperature range between
approximately 500 and 1050 degrees Celsius and at a pressure less
than 5 torr for approximately 5 minutes. Alternatively, the
capacitor 100 can be furnace annealed between approximately 1 and
60 minutes at a pressure between approximately 10 milliTorr and 1
atmosphere. In another embodiment, the capacitor 100 is annealed in
a nitrogen environment, such as ammonia, with RTP between
approximately 700 and 1050 degrees Celsius for a time between
approximately 10 and 120 seconds. As a result of annealing, the
tantalum oxide film is converted to a tantalum oxynitride film
102.
[0037] In yet a further embodiment, the capacitor 100 is annealed
in a nitrogen atmosphere in the presence of a plasma. The plasma
may be a plasma for enhanced deposition, such as high density
plasma (HDP), a radio frequency (RF) plasma, or an electron
cyclotron resonance (ECR) plasma, or a remote plasma. The nitrogen
atmosphere may include the previously described nitrogen sources,
N.sub.2O, NO, O.sub.3, O.sub.2 or a combination thereof.
[0038] In yet another embodiment, the tantalum oxide film can be
transformed into tantalum oxynitride film 102 by implanting
nitrogen ions into the tantalum oxide. Ion implantation of nitrogen
is known to persons skilled in the art.
[0039] In an alternative embodiment, the tantalum oxynitride film
102 can be directly formed by CVD, such as metal organo CVD
(MOCVD), with tantalum and nitrogen sources, in a manner known to
those skilled in the art. The tantalum source may be tantalum (V)
ethoxide (Ta(OC.sub.2H.sub.5)). The nitrogen source may be N.sub.2,
NH.sub.3, N.sub.2O, N.sub.2H.sub.4, monomethyl hydrazene (MMH), or
other nitrogen sources. The nitrogen source may be introduced to
the capacitor 100 in the presence of one of the plasmas described
above. Typically, the tantalum oxynitride film 102 formed by the
methods described above has a crystalline structure.
[0040] However, it may be desirable to create tantalum oxynitride
film 102 that is amorphous. To form an amorphous tantalum
oxynitride film 102, a volatile nitrogen source such as hydrazene,
or hydrazene derivatives such as monomethyl hydrazene (MMH), is
used. As a result, the MOCVD process can be performed at relatively
lower temperatures of between approximately 300 and 600 degrees
Celsius to form the amorphous tantalum oxynitride film 102.
Preferably, the temperature ranges between 400 and 550 degrees
Celsius.
[0041] In another embodiment, to diminish the amount of carbon that
subsequently enters the tantalum oxynitride film 102 to form a
leakage mechanism, silicon is preferably formed on the tantalum
oxynitride film 102. Thus, in one embodiment, a silicon nitridation
process is used. The memory cell 100 is exposed to a combination of
silicon and nitrogen sources. The silicon sources include silane,
disilane and dichlorosilane. The nitrogen sources include N.sub.2,
NH.sub.3, N.sub.2H.sub.4, N.sub.2O, and MMH. In one embodiment, the
silane and nitrogen are respectively disilane and ammonia combined
in a one to five ratio. In another embodiment, this process is
conducted for a sufficiently small period of time, such as less
than the incubation time, so that no, or an insubstantial amount
of, silicon nitride is actually formed on the capacitor 100.
[0042] After tantalum oxynitridation film 102 formation, the top
electrode 106 is formed. In one embodiment, the top electrode 106
is formed from titanium nitride (TiN) either formed by CVD with an
organic precursor such as tetradimethyl amino titanium (TDMAT), or
by a high-temperature CVD process with inorganic precursors such as
TiCl.sub.4 and NH.sub.3. Alternatively, the top electrode 106 may
be initially formed with tungsten nitride. Subsequent processing of
the capacitor 100 is completed in a manner known to those skilled
in the art. For example, the capacitor 100 is later subjected to
high temperature processing steps, such as BPSG reflow or
polysilicon activation.
[0043] The resulting capacitor 100 has reduced leakage current when
a dielectric that is tantalum oxynitride film 102 is used rather
than tantalum oxide film. This beneficial property is illustrated
in FIG. 2 which shows the voltage required to induce a leakage
current density of 3.times.10.sup.-7 A/cm.sup.2 in a capacitor 100.
FIG. 2 illustrates that such current density occurs in a capacitor
100 having a tantalum oxide film dielectric with the application of
zero volts (201). However, at least 0.8 volts must be applied
across a memory cell 100 with a tantalum oxynitride film 102
dielectric to induce the same current density (202). Thus, the
tantalum oxynitride film 102 in a capacitor 100 reduces the leakage
current density.
[0044] These benefits arise because the formation of the tantalum
oxynitride film 102 and introduction of silicon, described above,
diminish the amount of carbon that enters the tantalum oxynitride
film 102 during the high temperature processing steps. FIGS. 3A and
3B are Auger plots of the relative concentrations of atomic
concentrations of a capacitor 100 having dielectrics that are
respectively tantalum oxide and tantalum oxynitride. FIG. 3A and 3B
show that the concentration of carbon carbide in the capacitor 100
having a tantalum oxynitride film 102 (304) is substantially less
then for a capacitor 100 having a tantalum oxide film (302).
[0045] Additionally, the capacitors 100 made with the
aforementioned process have significantly enhanced reliability
resulting from the use of the tantalum oxynitride film 102.
Specifically, the capacitor 100 has enhanced time-dependent
dielectric breakdown and rupture voltage.
[0046] FIGS. 2 and 3 are illustrative of the present invention.
However, different results may occur if process parameters, such as
the length and temperature of the high temperature processing
steps, vary.
[0047] The present invention can be performed in a single tool
without exposing the capacitor 100 to the atmosphere. For example
the nitridization of the bottom electrode 104, oxidation of the
tantalum, and the nitridization of the tantalum oxide can be
accomplished in a single tool. As a result, undesired effects, such
as oxidation of the bottom electrode, can be diminished. Also, the
stoichiometry of the tantalum oxynitride film 102 can be more
tightly controlled.
[0048] The aforementioned processes may be used to form capacitors
100 in a memory array 402 of a memory 400, such as a dynamic random
access memory, as illustrated in FIG. 4. The memory 400 may include
a memory array 402, control logic 404, and address logic 406
coupled in a manner known to one skilled in the art and exemplified
in FIG. 4. The memory 400 may be coupled to an external system 524,
such as a processor, as illustrated in FIG. 5.
[0049] The capacitor 100 made according to the present invention
may also be used as an antifuse, for example, for programming
redundant elements in a memory 400. The antifuse is activated in
the following manner. A large voltage is applied across the
electrodes 104, 106 of the capacitor 100. A hole is formed in the
tantalum oxynitride film 102. As a result, the capacitor 100
becomes a resistor having a resistance between approximately 1000
and 6000 ohms, typically about 3000 ohms. The resistance may also
range between approximately 500 and 7000 ohms. The antifuse is
superior to other antifuse structures because it has a relatively
lower resistance.
CONCLUSION
[0050] It is an advantage of the present invention that it forms a
capacitor having relatively high capacitance to area ratio. It is
also a benefit of the present invention that it is less affected by
heat so as to have a diminished leakage current. It is also an
advantage of the invention that the capacitor has enhanced
reliability. It is a further benefit of the present invention that
it can be performed in a single tool without exposing the memory
cell 100 to the atmosphere. It is to be understood that the above
description is intended to be illustrative, and not restrictive.
Many other embodiments will be apparent to those of skill in the
art upon reviewing the above description. The scope of the
invention should, therefore, be determined with reference to the
appended claims, along with the full scope of equivalents to which
such claims are entitled.
* * * * *