U.S. patent application number 10/385029 was filed with the patent office on 2003-09-04 for atomic layer deposition of capacitor dielectric.
Invention is credited to Breiner, Lyle, Doan, Trung T., Ping, Er-Xuan, Zheng, Lingyi A..
Application Number | 20030166318 10/385029 |
Document ID | / |
Family ID | 25540784 |
Filed Date | 2003-09-04 |
United States Patent
Application |
20030166318 |
Kind Code |
A1 |
Zheng, Lingyi A. ; et
al. |
September 4, 2003 |
Atomic layer deposition of capacitor dielectric
Abstract
A process of forming a capacitor structure over a semiconductor
substrate by atomic layer deposition to achieve uniform thickness
in memory cell dielectric layers, particularly where the dielectric
layer is formed in a container-type capacitor structure. In
accordance with several embodiments of the present invention, a
process for forming a capacitor structure over a semiconductor
substrate is provided. Other embodiments of the present invention
relate to processes for forming memory cell capacitor structures,
memory cells, and memory cell arrays. Capacitor structures, memory
cells, and memory cell arrays are also provided.
Inventors: |
Zheng, Lingyi A.; (Boise,
ID) ; Ping, Er-Xuan; (Meridian, ID) ; Breiner,
Lyle; (Meridian, ID) ; Doan, Trung T.; (Boise,
ID) |
Correspondence
Address: |
Killworth, Gottman, Hagan & Schaeff, L.L.P.
Suite 500
One Dayton Centre
Dayton
OH
45402-2023
US
|
Family ID: |
25540784 |
Appl. No.: |
10/385029 |
Filed: |
March 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10385029 |
Mar 10, 2003 |
|
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09994547 |
Nov 27, 2001 |
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6551893 |
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Current U.S.
Class: |
438/239 ;
257/E21.013; 257/E21.018; 257/E21.293; 257/E21.647; 438/253;
438/255; 438/393; 438/396 |
Current CPC
Class: |
H01L 28/90 20130101;
H01L 28/84 20130101; H01L 21/0228 20130101; H01L 21/02211 20130101;
H01L 21/3185 20130101; H01L 21/0217 20130101; H01L 27/1085
20130101 |
Class at
Publication: |
438/239 ;
438/253; 438/255; 438/393; 438/396 |
International
Class: |
H01L 021/8242; H01L
021/20 |
Claims
What is claimed is:
1. A process for forming a dielectric layer over an electrode
layer, said process comprising the acts of: chemisorbing a first
precursor over a surface of said electrode layer; reacting a second
precursor with said chemisorbed precursor to form said dielectric
layer; and maintaining a substantially flat temperature
distribution across said electrode layer as said first precursor is
chemisorbed and said second precursor is reacted with said
chemisorbed precursor.
2. A process for the fabrication of a capacitor formed over a
semiconductor substrate comprising: forming a lower electrode
layer; forming a dielectric layer over said lower electrode layer
through an atomic layer deposition process where a first precursor
is chemisorbed over a surface of said lower electrode layer, a
second precursor is reacted with said chemisorbed precursor to form
said dielectric layer, and a substantially flat temperature
distribution is maintained across said semiconductor substrate as
said first precursor is chemisorbed and said second precursor is
reacted with said chemisorbed precursor; and forming an upper
electrode layer over said dielectric layer.
3. A process for the fabrication of a capacitor formed over a
semiconductor substrate comprising: forming a lower electrode
layer; forming a silicon nitride dielectric layer over said lower
electrode layer through an atomic layer deposition process where a
silicon-containing precursor is chemisorbed over a surface of said
lower electrode layer and a nitrogen-containing precursor is
reacted with said chemisorbed silicon-containing precursor to form
said silicon nitride dielectric layer; maintaining a substantially
flat temperature distribution across said semiconductor substrate
as said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor; and forming an upper electrode layer
over said dielectric layer.
4. A fabrication process as claimed in claim 3, wherein said
silicon-containing precursor is selected from SiCl.sub.4,
SiHCl.sub.3, SiH.sub.2Cl.sub.2, Si.sub.2H.sub.6, SiCl.sub.6, and
SiH.sub.4, and combinations thereof and said nitrogen-containing
precursor is selected from NH.sub.3, N.sub.2H.sub.2 and
combinations thereof.
5. A fabrication process where a capacitor structure is formed over
a semiconductor substrate by: forming an insulating layer over said
semiconductor substrate; forming a container in said insulating
layer; forming a lower electrode layer along an inner surface of
said container, wherein said lower electrode layer extends beyond
said inner surface of said container; forming a dielectric layer
over said lower electrode layer through an atomic layer deposition
process where a first precursor is chemisorbed over a surface of
said lower electrode layer, a second precursor is reacted with said
chemisorbed precursor to form said dielectric layer, and a
substantially flat temperature distribution is maintained across
said semiconductor substrate as said first precursor is chemisorbed
and said second precursor is reacted with said chemisorbed
precursor; and forming an upper electrode layer over said
dielectric layer.
6. A process as claimed in claim 5, wherein said lower electrode
layer extends along an upper surface of said insulating layer.
7. A process as claimed in claim 5, wherein said lower electrode
layer extends from said inner surface in the direction of an upper
surface of said insulating layer along an extension of said
container.
8. A process as claimed in claim 5, wherein said lower electrode
layer extends along an upper surface of said insulating layer and
from said inner surface in the direction of said upper surface of
said insulating layer along an extension of said container.
9. A fabrication process as claimed in claim 5, wherein said
dielectric layer is formed on said lower electrode layer.
10. A fabrication process as claimed in claim 5, wherein said lower
electrode layer covers the entire inner surface of said
container.
11. A fabrication process as claimed in claim 5, wherein said
dielectric layer covers the entire lower electrode layer.
12. A fabrication process as claimed in claim 5, wherein said upper
electrode layer covers the entire dielectric layer.
13. A fabrication process as claimed in claim 5, wherein said
atomic layer deposition process is characterized by a semiconductor
substrate temperature of between about 350.degree. C. to about
700.degree. C. and a pressure of about 1 Torr to 120 Torr.
14. A fabrication process where a capacitor structure is formed
over a semiconductor substrate by: forming an insulating layer over
said semiconductor substrate; forming a container in said
insulating layer; forming a lower electrode layer along an inner
surface of said container, wherein said lower electrode layer
extends beyond said inner surface of said container; forming a
dielectric layer over said lower electrode layer and an upper
surface of said insulating layer through an atomic layer deposition
process where a first precursor is chemisorbed over a surface of
said lower electrode layer and an upper surface of said insulating
layer, a second precursor is reacted with said chemisorbed
precursor to form said dielectric layer, a substantially flat
temperature distribution is maintained across said semiconductor
substrate as said first precursor is chemisorbed and said second
precursor is reacted with said chemisorbed precursor, and said
dielectric layer exhibits uniform thickness across said lower
electrode layer and said upper surface of said insulating layer;
forming a reoxidized layer over said dielectric layer by subjecting
said dielectric layer to a reoxidation process, wherein said
dielectric layer is formed such that said uniform thickness is
sufficient to prevent oxidation of said lower electrode layer as a
result of said reoxidation process; and forming an upper electrode
layer over said reoxidized layer.
15. A fabrication process as claimed in claim 14, wherein said
dielectric layer is formed in an atomic layer deposition chamber
and said reoxidized layer is formed in said chamber or external to
said chamber.
16. A fabrication process where a capacitor structure is formed
over a semiconductor substrate by: forming an insulating layer over
said semiconductor substrate; forming a container in said
insulating layer; forming a lower electrode layer along an inner
surface of said container, wherein said lower electrode layer
extends beyond said inner surface of said container; forming a
silicon nitride dielectric layer over said lower electrode layer
through an atomic layer deposition process where a
silicon-containing precursor is chemisorbed over a surface of said
lower electrode layer and a nitrogen-containing precursor is
reacted with said chemisorbed silicon-containing precursor to form
said silicon nitride dielectric layer; maintaining a substantially
flat temperature distribution across said semiconductor substrate
as said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor; and forming an upper electrode layer
over said dielectric layer.
17. A fabrication process as claimed in claim 16, wherein said
silicon-containing precursor is selected from SiCl.sub.4,
SiHCl.sub.3, SiH.sub.2Cl2, Si.sub.2H.sub.6, SiCl.sub.6, and
SiH.sub.4, and combinations thereof and said nitrogen-containing
precursor is selected from NH.sub.3, N.sub.2H.sub.2 and
combinations thereof.
18. A fabrication process where a capacitor structure is formed
over a semiconductor substrate by: forming a BPSG insulating layer
over said semiconductor substrate; forming a container in said BPSG
insulating layer; forming an HSG polysilicon lower electrode layer
along an inner surface of said container, wherein said lower
electrode layer extends beyond said inner surface of said
container; forming a silicon nitride dielectric layer on said HSG
lower electrode layer through an atomic layer deposition process
where a silicon-containing precursor is chemisorbed over a surface
of said HSG lower electrode layer and a nitrogen-containing
precursor is reacted with said chemisorbed silicon-containing
precursor to form said silicon nitride dielectric layer;
maintaining a substantially flat temperature distribution across
said semiconductor substrate as said silicon-containing precursor
is chemisorbed and said nitrogen-containing precursor is reacted
with said chemisorbed silicon-containing precursor; forming a
reoxidized layer over said silicon nitride dielectric layer by
subjecting said silicon nitride dielectric layer to a reoxidation
process; forming a polysilicon upper electrode layer over said
reoxidized layer.
19. A fabrication process where a capacitor structure of a memory
cell is formed by: providing a semiconductor substrate including a
semiconductor structure defining a transistor and a pair of
transistor node locations; forming a BPSG insulating layer over
said semiconductor substrate; forming a container in said BPSG
insulating layer over one of said transistor node locations;
forming an HSG polysilicon lower electrode layer along an inner
surface of said container, wherein said lower electrode layer
extends beyond said inner surface of said container; forming a
silicon nitride dielectric layer on said HSG lower electrode layer
and over a portion of an upper surface of said BPSG insulating
layer through an atomic layer deposition process where said silicon
nitride dielectric layer has a thickness of 50 .ANG. or less; a
silicon-containing precursor is chemisorbed over a surface of said
HSG lower electrode layer and said portion of said upper surface of
said BPSG insulating layer, a nitrogen-containing precursor is
reacted with said chemisorbed silicon-containing precursor to form
said silicon nitride dielectric layer, a substantially flat
temperature distribution is maintained across said semiconductor
substrate as said silicon-containing precursor is chemisorbed and
said nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor, and said silicon nitride dielectric
layer exhibits uniform thickness across said HSG lower electrode
layer and said portion of said upper surface of said BPSG
insulating layer; forming a reoxidized layer over said silicon
nitride dielectric layer by subjecting said silicon nitride
dielectric layer to a reoxidation process, wherein said silicon
nitride dielectric layer is formed such that said uniform thickness
is sufficient to prevent oxidation of said HSG lower electrode
layer as a result of said reoxidation process; and forming a
polysilicon upper electrode layer over said reoxidized layer.
20. A fabrication process where respective capacitor structures are
formed over a plurality of semiconductor substrates in a multiple
wafer batch-type furnace by: forming respective insulating layers
over said semiconductor substrates; forming respective containers
in said insulating layers; forming respective lower electrode
layers along respective inner surfaces of said containers, wherein
said lower electrode layer extends beyond said inner surface of
said container; forming respective dielectric layers over said
lower electrode layers through an atomic layer deposition process
where a first precursor is chemisorbed over a surface of respective
lower electrode layers, a second precursor is reacted with said
chemisorbed precursor to form said dielectric layers, and a
substantially flat temperature distribution is maintained across
said semiconductor substrates as said first precursor is
chemisorbed and said second precursor is reacted with said
chemisorbed precursor; and forming respective upper electrode
layers over said dielectric layers.
21. A fabrication process where respective capacitor structures are
formed over a plurality of semiconductor substrates in a multiple
wafer batch-type furnace by: forming respective insulating layers
over said semiconductor substrates; forming respective containers
in said insulating layers; forming respective lower electrode
layers along respective inner surfaces of said containers, wherein
said lower electrode layer extends beyond said inner surface of
said container; forming respective dielectric layers over said
lower electrode layers through an atomic layer deposition process
where a first precursor is chemisorbed over a surface of respective
lower electrode layers, a second precursor is reacted with said
chemisorbed precursor to form said dielectric layers, said
dielectric layer exhibits uniform thickness across said lower
electrode layer and an upper surface of said insulating layer, and
a substantially flat temperature distribution is maintained across
said semiconductor substrates as said first precursor is
chemisorbed and said second precursor is reacted with said
chemisorbed precursor; forming respective reoxidized layers over
said dielectric layers by subjecting said dielectric layers to a
reoxidation process, wherein said dielectric layers are formed such
that said uniform thickness is sufficient to prevent oxidation of
said lower electrode layer as a result of said reoxidation process;
and forming respective upper electrode layers over said reoxidized
layers.
22. A fabrication process where respective capacitor structures are
formed over a plurality of semiconductor substrates in a multiple
wafer batch-type furnace by: forming respective insulating layers
over said semiconductor substrates; forming respective containers
in said insulating layers; forming respective lower electrode
layers along respective inner surfaces of said containers, wherein
said lower electrode layer extends beyond said inner surface of
said container; forming respective silicon nitride dielectric
layers over said lower electrode layers through an atomic layer
deposition process where a silicon-containing precursor is
chemisorbed over a surface of respective lower electrode layers, a
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor to form said silicon nitride
dielectric layers, and a substantially flat temperature
distribution is maintained across said semiconductor substrates as
said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor; and forming respective upper
electrode layers over said dielectric layers.
23. A fabrication process where respective capacitor structures are
formed over a plurality of semiconductor substrates in a multiple
wafer batch-type furnace by: forming respective BPSG insulating
layers over said semiconductor substrates; forming respective
containers in said BPSG insulating layers; forming respective HSG
lower electrode layers along respective inner surfaces of said
containers, wherein said lower electrode layer extends beyond said
inner surface of said container; forming respective silicon nitride
dielectric layers over said HSG lower electrode layers through an
atomic layer deposition process where a silicon-containing
precursor is chemisorbed over a surface of respective HSG lower
electrode layers, a nitrogen-containing precursor is reacted with
said chemisorbed silicon-containing precursor to form said silicon
nitride dielectric layers, and a substantially flat temperature
distribution is maintained across said semiconductor substrates as
said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor; forming respective reoxidized layers
over said silicon nitride dielectric layers by subjecting said
dielectric layers to a reoxidation process; and forming respective
upper electrode layers over said reoxidized layers.
24. A fabrication process where respective capacitor structures of
an array of memory cells are formed in a multiple wafer batch-type
furnace by: providing a plurality of semiconductor substrates
including respective semiconductor structures defining a plurality
of transistors and respective pairs of transistor node locations;
forming respective BPSG insulating layers over said semiconductor
substrates; forming respective containers in said BPSG insulating
layers; forming respective HSG lower electrode layers along
respective inner surfaces of said containers, wherein said lower
electrode layer extends beyond said inner surfaces of said
containers; forming respective silicon nitride dielectric layers
over said HSG lower electrode layers and a portion of respective
upper surfaces of said BPSG insulating layers through an atomic
layer deposition process where said dielectric layer has a uniform
thickness of 50 .ANG. or less, a silicon-containing precursor is
chemisorbed over a surface of respective HSG lower electrode layers
and said portions of respective upper surfaces of said BPSG
insulating layers, a nitrogen-containing precursor is reacted with
said chemisorbed silicon-containing precursor to form said silicon
nitride dielectric layers, a substantially flat temperature
distribution is maintained across said semiconductor substrates as
said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor, and said silicon nitride dielectric
layer exhibits uniform thickness across said HSG lower electrode
layer and said portion of said upper surface of said BPSG
insulating layer; forming respective reoxidized layers over said
dielectric layers by subjecting said dielectric layers to a
reoxidation process, wherein said dielectric layers are formed such
that said uniform thickness is sufficient to prevent oxidation of
said lower electrode layer as a result of said reoxidation process;
and forming respective upper electrode layers over said reoxidized
layers.
25. A fabrication process where a memory cell is formed by:
providing a semiconductor substrate including a semiconductor
structure defining a transistor and a pairs of transistor node
locations; forming an insulating layer over said semiconductor
substrate; forming a container in said insulating layer over one of
said transistor node locations; forming a lower electrode layer
along an inner surface of said container, wherein said lower
electrode layer extends beyond said inner surface of said
container; forming a silicon nitride dielectric layer over said
lower electrode layer and a portion of an upper surface of said
insulating layer through an atomic layer deposition process where a
silicon-containing precursor is chemisorbed over a surface of said
lower electrode layer and said portion of said upper surface of
said insulating layer, a nitrogen-containing precursor is reacted
with said chemisorbed silicon-containing precursor to form said
silicon nitride dielectric layer, a substantially flat temperature
distribution is maintained across said semiconductor substrate as
said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor, and said silicon nitride dielectric
layer exhibits uniform thickness across said lower electrode layer
and said portion of said upper surface of said insulating layer;
forming a reoxidized layer over said dielectric layer by subjecting
said dielectric layer to a reoxidation process, wherein said
dielectric layer is formed such that said uniform thickness is
sufficient to prevent oxidation of said lower electrode layer as a
result of said reoxidation process; and forming an upper electrode
layer over said reoxidized layer.
26. A fabrication process where an array of memory cells are formed
on a semiconductor die by: providing a semiconductor substrate
including a semiconductor structure defining a plurality of
transistors and respective pairs of transistor node locations;
forming an insulating layer over said semiconductor substrate;
forming respective containers in said insulating layer over
selected ones of said transistor node locations; forming respective
lower electrode layers along inner surfaces of selected ones of
said containers, wherein said lower electrode layers extend beyond
said inner surfaces of said containers; forming respective silicon
nitride dielectric layers over said lower electrode layer and a
portion of an upper surface of said insulating layer through an
atomic layer deposition process where a silicon-containing
precursor is chemisorbed over a surface of said lower electrode
layer and said portion of said upper surface of said insulating
layer, a nitrogen-containing precursor is reacted with said
chemisorbed silicon-containing precursor to form said silicon
nitride dielectric layer, a substantially flat temperature
distribution is maintained across said semiconductor substrate as
said silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor, and said silicon nitride dielectric
layer exhibits uniform thickness across said lower electrode layer
and said portion of said upper surface of said insulating layer;
forming a reoxidized layer over said dielectric layer by subjecting
said dielectric layer to a reoxidation process, wherein said
dielectric layer is formed such that said uniform thickness is
sufficient to prevent oxidation of said lower electrode layer as a
result of said reoxidation process; and forming an upper electrode
layer over said reoxidized layer.
27. A fabrication process where an array of memory cells are formed
on a plurality of semiconductor die in a multiple wafer batch-type
furnace by: providing a plurality of semiconductor substrates
including respective semiconductor structures defining a plurality
of transistors and respective pairs of transistor node locations;
forming respective insulating layers over said semiconductor
substrates; forming respective containers in said insulating layers
over selected ones of said transistor node locations; forming
respective lower electrode layers along inner surfaces of selected
ones of said containers, wherein said lower electrode layers extend
beyond said inner surfaces of selected ones of said containers;
forming respective silicon nitride dielectric layers over said
lower electrode layer and a portion of an upper surface of said
insulating layers through an atomic layer deposition process where
a silicon-containing precursor is chemisorbed over a surface of
said lower electrode layer and said portion of said upper surface
of said insulating layer, a nitrogen-containing precursor is
reacted with said chemisorbed silicon-containing precursor to form
said silicon nitride dielectric layer, said silicon nitride
dielectric layer exhibits uniform thickness across said lower
electrode layer and said portion of said upper surface of said
insulating layer, and a substantially flat temperature distribution
is maintained across said semiconductor substrates as said
silicon-containing precursor is chemisorbed and said
nitrogen-containing precursor is reacted with said chemisorbed
silicon-containing precursor; forming respective reoxidized layers
over said dielectric layers by subjecting said dielectric layers to
a reoxidation process, wherein said dielectric layers are formed
such that said uniform thickness is sufficient to prevent oxidation
of said lower electrode layer as a result of said reoxidation
process; and forming respective upper electrode layers over said
reoxidized layers.
28. A fabrication process as claimed in claim 26, wherein said
dielectric layer has a uniform thickness of 50 .ANG. or less.
Description
CROSS-REFERENCE TO RELATED APPLCIATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/994,547, filed Nov. 27, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to memory cell capacitor
structures and, more particularly, to a fabrication process where a
capacitor dielectric is formed by atomic layer deposition.
[0003] Silicon nitride is commonly employed as the dielectric in
memory cell capacitor structures. Unfortunately, conventional
process technology is limited in its ability to manufacture
suitable reduced-thickness dielectric layers with good uniformity.
Accordingly, there is a need for an improved memory cell capacitor
dielectric layer manufacturing process.
BRIEF SUMMARY OF THE INVENTION
[0004] This need is met by the present invention wherein a
capacitor dielectric is formed by atomic layer deposition. The
present inventors have recognized that it is difficult to achieve
uniform thickness in memory cell dielectric layers, particularly
where the dielectric layer is formed in a container-type capacitor
structure. The present invention is also applicable to trench-type
capacitor structures. Generally, as device size shrinks, thinner
dielectric layers are needed to ensure adequate memory cell
capacitance. As dielectric layer thickness decreases,
non-uniformity leads to reoxidation punch-through and corresponding
device degradation. Also, as the dielectric layer thickness
decreases, the leakage current attributable to the dielectric layer
tends to increase dramatically, deteriorating device
performance.
[0005] The present invention addresses these problems by providing
a manufacturing process where the dielectric layer is formed
through atomic layer deposition (ALD). In accordance with several
embodiments of the present invention, a process for forming a
capacitor structure over a semiconductor substrate is provided.
Other embodiments of the present invention relate to processes for
forming memory cell capacitor structures, memory cells, and memory
cell arrays. Capacitor structures, memory cells, and memory cell
arrays are also provided. Accordingly, it is an object of the
present invention to provide an improved memory cell capacitor
dielectric layer manufacturing process. Other objects of the
present invention will be apparent in light of the description of
the invention embodied herein.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0006] The following detailed description of the preferred
embodiments of the present invention can be best understood when
read in conjunction with the following drawings, where like
structure is indicated with like reference numerals and in
which:
[0007] FIGS. 1 and 2 illustrate a memory cell capacitor structure
fabrication scheme according to one embodiment of the present
invention;
[0008] FIG. 3 illustrates a memory cell capacitor structure
fabrication scheme according to an alternative embodiment of the
present invention;
[0009] FIG. 4 illustrates a memory cell array;
[0010] FIG. 5 is a schematic diagram of an ALD apparatus according
to the present invention; and
[0011] FIG. 6 is an elevation view of an ALD apparatus for a
large-scale production system according to present invention.
DETAILED DESCRIPTION
[0012] Referring to FIGS. 1 and 2, according to one embodiment of
the present invention, a capacitor structure of a memory cell may
be formed by providing a semiconductor substrate 10 including a
semiconductor structure defining a transistor 12 and a pair of
transistor node locations 14. An insulating layer 16, e.g. a BPSG
layer, is formed over the semiconductor substrate 10. A container
18 is formed in the insulating layer 16 over one of the transistor
node locations 14. A lower electrode layer 20, typically a HSG
polysilicon layer, is formed along an inner surface of the
container 18. A dielectric layer 22 is formed on the lower
electrode layer 20 and over a portion of an upper surface of the
insulating layer 16. A reoxidized layer 24 is formed over the
dielectric layer 22 by subjecting the dielectric layer 22 to a
reoxidation process. Finally, an upper electrode layer 26,
typically a polysilicon layer, is formed over the reoxidized layer
24, typically covering the entire dielectric layer 22.
[0013] The lower electrode layer 20 typically covers the entire
inner surface of the container 18. The dielectric layer 22, which
is typically formed directly on the lower electrode layer 20,
completely covering the lower electrode layer 20, exhibits uniform
thickness across the lower electrode layer 20 and the upper surface
of the insulating layer 16. The dielectric layer 22 is formed such
that the uniform thickness is sufficient to prevent punch-thru
oxidation, i.e., incidental oxidation of the lower electrode layer
20 during reoxidation of the dielectric layer and other device
components. As will be appreciated by those practicing the present
invention and familiar with semiconductor device fabrication, a
reoxidation step is commonly incorporated in semiconductor device
fabrication schemes.
[0014] The dielectric layer 22 is formed through an atomic layer
deposition (ALD) process. The thickness of a silicon nitride
dielectric layer is typically 50 angstroms or less. Conventional
process technology, such as low pressure chemical vapor deposition
(LPCVD) is not well-suited for fabrication of silicon nitride
dielectric layers of such thicknesses because dielectric quality
deterioration and oxidation punch-through become problems at layer
thicknesses of 50 angstroms or less. Oxidation punch-through of
LPCVD silicon nitride dielectric layers occurs because the silicon
nitride on the underlying BPSG insulating layer is thinner than
that on the HSG lower electrode. The difference in thickness is
attributable to the difference in LPCVD nucleation incubation times
for silicon nitride over BPSG and HSG, respectively. Specifically,
the nucleation incubation time is longer for silicon nitride on
BPSG than for silicon nitride on HSG. Data has also shown that the
quality of the silicon nitride layer formed according to the
present invention is superior to that of the silicon nitride layer
formed by the LPCVD method. Therefore, according to the present
invention, capacitor performance is maintained even as the
dielectric thickness goes below 50 angstroms.
[0015] According to the deposition process of the present
invention, a first precursor, e.g., a silicon-containing precursor,
is chemisorbed over a surface of the lower electrode layer 20 and
the upper surface of the insulating layer 16. A second precursor,
e.g., a nitrogen-containing precursor, is then reacted with the
chemisorbed precursor to form the dielectric layer 22, e.g., a
silicon nitride dielectric layer. The specific processing steps
utilized to introduce the first and second precursors and cause
their chemisorption/reaction are beyond the scope of the present
invention and may be gleaned from any one of a number of teachings
related to atomic layer deposition. For the purposes of describing
and defining the present invention, it is noted that the precise
mechanism by which the molecules of the first precursor adhere to
the surface of the semiconductor substrate is not the subject of
the present invention. The mechanism is merely described herein as
chemisorption--a term intended to cover absorption, adsorption, and
any other similar mechanisms by which the precursor may form a
monolayer upon the surface of the semiconductor substrate 10.
[0016] Generally, in atomic layer deposition, assuming that two
precursor gases A and B are used, precursor gas A is introduced
into a reaction chamber of an ALD device and atoms of the precursor
gas A are chemisorbed on a substrate in the chamber. Next,
un-absorbed precursor gas A is purged with an inert gas such as Ar
or nitrogen N.sub.2 and precursor gas B flows into the chamber. A
chemical reaction between the precursor gases A and B occurs only
on the surface of the substrate on which the precursor gas A has
been adsorbed, resulting in formation of an atomic layer on the
substrate. Un-reacted precursor gas B and the by-products of the
reaction between two gases A and B are purged. The thickness of the
film can be increased by repeating these steps to deposit
successive atomic layers. In this manner, the thickness of the thin
film can be adjusted in atomic layer units according to the number
of repetitions. Atomic layer deposition processes according to the
present invention are typically characterized by semiconductor
substrate temperatures of between about 350.degree. C. to about
700.degree. C. and reactor chamber pressures of about 1 Torr to
about 120 Torr. A substantially flat temperature distribution can
be maintained across the semiconductor substrate as the first
precursor is chemisorbed and the second precursor is reacted with
the chemisorbed precursor.
[0017] The ALD method, when used for depositing a thin film on a
substrate, can ensure near perfect step coverage regardless of the
morphology of the substrate. The composition of the atomic layer
depends upon the nature of the reaction between the precursor gases
A and B. In the present invention, where the object is to form a
silicon nitride film in a capacitor structure, the first precursor
gas typically comprises a silicon-containing gas and the second
precursor gas typically comprises a nitrogen-containing gas.
Suitable silicon-containing precursors include, but are not limited
to, SiCl.sub.4, SiHCl.sub.3, SiH.sub.2Cl2, Si.sub.2H.sub.6,
SiCl.sub.6, and SiH.sub.4. Suitable nitrogen-containing precursors
include, but are not limited to, NH.sub.3 and N.sub.2H.sub.2.
[0018] In some cases, for example where N.sub.2H.sub.2 is utilized
as the precursor, it may be helpful to generate a plasma in the
reaction chamber to help break-up the precursor, generating
nitrogen radicals encouraging reaction of the two precursors at the
surface of the substrate on which the layer is to be formed.
Alternatively, a laser source or an infrared radiation source may
be employed to help generate nitrogen radicals. Use of the plasma,
the laser source, or the infrared radiation source also allows the
process to operate at reduced chamber and substrate
temperatures.
[0019] FIG. 5 is a schematic diagram of a single wafer process ALD
apparatus 50 according to the present invention. As shown in FIG.
5, the ALD apparatus comprises a vacuum chamber 52 and a heater 54
for heating a substrate 56 placed in the vacuum chamber 52 to an
appropriate temperature. The substrate 56 is seated on a substrate
holder (not shown) placed on top of the heater 54, and heated
evenly by the heater 54. Also, a showerhead 58 through which a
predetermined precursor gas flows into the vacuum chamber 52, is
installed facing the surface of the substrate 56.
[0020] The present invention can be utilized in any standard hot
wall batch-type ALD furnace. Batch type furnaces enable processing
of multiple wafers in a single batch process, increasing
manufacturing throughput. FIG. 6 is an elevation view of an
batch-type ALD apparatus 60 for a large-scale production system
according to present invention. In this embodiment, preprocessed
substrates a-j are loaded onto a cassette or stacking mechanism 62
in a reaction chamber 64 of the ALD apparatus 60 through a cassette
load lock (not shown). Alternatively, an entire cassette of
substrates may be introduced into the chamber 64. Specific
structure for accomplishing this sort of loading and interfacing is
well-known in the art of production systems. Once loaded the
substrates a-j are subject to processing according to the present
invention and removed from the chamber 64. In this manner,
respective capacitor structures according to the present invention
may be formed over a plurality of semiconductor substrates.
Similarly, the present invention relates to fabrication of a memory
cell and, on a larger scale, to fabrication to an array of memory
cells on a semiconductor die and to respective arrays of memory
cells on a plurality of semiconductor die.
[0021] Although the present invention has been illustrated with
reference to the specific memory cell structure of FIGS. 1 and 2,
it is contemplated that the present invention is applicable to a
variety of memory cell arrangements. For example, FIG. 3, where
like structure is indicated with like reference numerals,
illustrates the process of the present invention as applied to an
alternative memory cell structure.
[0022] FIG. 4 illustrates a memory cell array 2. The memory cell
array 2 includes a plurality of memory cells 4. Each memory cell 4
includes a capacitor structure and a transistor structure, as
discussed above with reference to FIGS. 1-3. Conventional source
regions S, drain regions D, bit lines BL, and word lines WL are
also illustrated in FIG. 4. It is noted that although the present
invention is illustrated with reference to the structures of FIGS.
1-4, the present invention is applicable to a variety of types of
memory cell structures and memory array arrangements.
[0023] For the purposes of describing and defining the present
invention, it is noted that a "semiconductor substrate" denotes any
construction comprising a semiconductor material. Examples of
semiconductor substrates include semiconductor wafers or other bulk
semiconductor materials (either alone or in assemblies comprising
other materials), and semiconductor material layers (either alone
or in assemblies comprising other materials).
[0024] It should be further noted that, for the purposes of
defining and describing the present invention, "on" a substrate or
layer denotes formation in contact with the surface of the
substrate or layer and "over" a substrate or layer denotes
formation above or in contact with the surface of the substrate or
layer. For the purposes of describing and defining the present
invention, it is noted that a layer formed "in" a region or other
layer may be formed at a surface of the region/layer or within the
region/layer between its upper and lower surfaces. A layer formed
"at" a surface of a region/layer may be formed directly on the
surface or may be partially embedded in the region/layer so as to
define a portion of the surface of the region/layer.
[0025] Having described the invention in detail and by reference to
preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims. More
specifically, although some aspects of the present invention are
identified herein as preferred or particularly advantageous, it is
contemplated that the present invention is not necessarily limited
to these preferred aspects of the invention.
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