U.S. patent application number 14/037633 was filed with the patent office on 2014-01-30 for semiconductor structures comprising conductive material lining openings in an insulative material.
This patent application is currently assigned to Micron Technology, Inc.. Invention is credited to Fred Fishburn, Terrence McDaniel, Sandra Tagg.
Application Number | 20140027913 14/037633 |
Document ID | / |
Family ID | 35943845 |
Filed Date | 2014-01-30 |
United States Patent
Application |
20140027913 |
Kind Code |
A1 |
McDaniel; Terrence ; et
al. |
January 30, 2014 |
SEMICONDUCTOR STRUCTURES COMPRISING CONDUCTIVE MATERIAL LINING
OPENINGS IN AN INSULATIVE MATERIAL
Abstract
Semiconductor devices have conductive material lining a first
opening in an insulative material and in contact with a metal
silicide layer at the base of the opening overlying an active area
within a silicon material and lining a second opening in the
insulative material in direct contact with a polysilicon plug
having substantially no metal silicide situated thereon.
Inventors: |
McDaniel; Terrence; (Boise,
ID) ; Tagg; Sandra; (Boise, ID) ; Fishburn;
Fred; (Morgan Hill, CA) |
Assignee: |
Micron Technology, Inc.
Boise
ID
|
Family ID: |
35943845 |
Appl. No.: |
14/037633 |
Filed: |
September 26, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13246146 |
Sep 27, 2011 |
8580666 |
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14037633 |
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|
11512004 |
Aug 29, 2006 |
8026542 |
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13246146 |
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10932327 |
Sep 1, 2004 |
7605033 |
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11512004 |
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Current U.S.
Class: |
257/754 |
Current CPC
Class: |
H01L 21/28052 20130101;
H01L 21/32134 20130101; H01L 23/48 20130101; H01L 27/10894
20130101; H01L 21/76843 20130101; H01L 21/02068 20130101; H01L
27/10888 20130101; H01L 2924/0002 20130101; H01L 21/2855 20130101;
H01L 21/76846 20130101; H01L 29/4933 20130101; H01L 2924/0002
20130101; H01L 21/76895 20130101; H01L 2924/00 20130101; H01L
21/76897 20130101 |
Class at
Publication: |
257/754 |
International
Class: |
H01L 23/48 20060101
H01L023/48 |
Claims
1. A semiconductor device, comprising: a conductive material lining
a first opening in an insulative material, wherein the conductive
material is in contact with a metal silicide material at a base of
the first opening overlying an active area within a silicon
material, and the conductive material lining a second opening in
the insulative material, wherein the conductive material is in
direct contact with a polysilicon plug having substantially no
metal silicide situated thereon.
2. The semiconductor device of claim 1, wherein the conductive
material comprises, in sequence, a titanium material, a metal
nitride, and a conductive metal.
3. The semiconductor device of claim 2, wherein the titanium
material comprises nitrogen.
4. The semiconductor device of claim 2, wherein the conductive
metal comprises tungsten.
5. The semiconductor device of claim 1, wherein the conductive
material overlies the insulative material and electrically
interconnects the metal silicide at the base of the first opening
with the polysilicon plug in the second opening.
6. The semiconductor device of claim 2, wherein the titanium
material is in direct physical contact with the metal silicide
layer at the base of the first opening and the polysilicon plug in
the second opening.
7. The semiconductor device of claim 1, wherein the first opening
is in a periphery area of a memory device and the second opening is
in a memory cell array area of the memory device.
8. A semiconductor device, comprising: at least one doped
polysilicon plug over a substrate; a metal silicide overlying an
active area within a silicon material over the substrate; an
insulative material over at least a portion of the substrate; and a
conductive material in electrical contact with the at least one
doped polysilicon plug, the metal silicide, and the insulative
material.
9. The semiconductor device of claim 8, wherein the conductive
material lines a first opening in the insulative material and
wherein a surface of the metal silicide is within the first
opening.
10. The semiconductor device of claim 8, wherein the conductive
material lines a second opening in the insulative material and
wherein a surface of the doped polysilicon plug is within the
second opening.
11. The semiconductor device of claim 8, wherein the at least one
doped polysilicon plug is substantially free of metal silicide.
12. The semiconductor device of claim 8, wherein the conductive
material comprises titanium, a metal nitride over the titanium, and
a conductive metal over the metal nitride.
13. The semiconductor device of claim 12, wherein the conductive
metal comprises tungsten.
14. The semiconductor device of claim 8, wherein the conductive
material overlies at least a portion of the insulative
material.
15. The semiconductor device of claim 8, wherein the conductive
material comprises nitrogen and titanium.
16. The device of claim 8, wherein the substrate comprises a doped
diffusion region proximate the at least one doped polysilicon
plug.
17. The device of claim 8, further comprising at least one
additional doped polysilicon plug over the substrate, the at least
one additional doped polysilicon plug electrically insulated from
the conductive material by the insulative material.
18. A semiconductor device, comprising: a first doped polysilicon
plug disposed over a first doped diffusion region of a substrate; a
second doped polysilicon plug disposed over a second doped
diffusion region of the substrate; a metal silicide overlying an
active area within a silicon material over the substrate; an
insulative material over the second doped polysilicon plug and at
least a portion of the substrate; and a conductive material in
electrical contact with the first doped polysilicon plug, the metal
silicide, and the insulative material and insulated from the second
doped polysilicon plug.
19. The semiconductor device of claim 18, further comprising a
memory cell disposed over the substrate and between the first doped
polysilicon plug and the second doped polysilicon plug.
20. The semiconductor device of claim 18, wherein the first doped
polysilicon plug is in electrical contact with a bit line.
21. The semiconductor device of claim 18, wherein a portion of the
conductive material is in electrical contact with the first doped
polysilicon plug, and another, discontinuous portion of the
conductive material is in electrical contact with the metal
silicide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/246,146, filed Sep. 27, 2011, pending, which is a
continuation of U.S. patent application Ser. No. 11/512,004, filed
Aug. 29, 2006, now U.S. Pat. No. 8,026,542, issued Sep. 27, 2011,
which is a divisional of U.S. patent application Ser. No.
10/932,327, filed Sep. 1, 2004, now U.S. Pat. No. 7,605,033, issued
Oct. 20, 2009. The disclosure of each of the previously-referenced
U.S. applications is hereby incorporated in its entirety by
reference.
FIELD
[0002] The invention relates generally to semiconductor processing
methods of forming integrated circuitry including DRAM integrated
circuitry, and, more particularly, to processes for forming a metal
plug structure for contacting polysilicon plugs in a memory cell
array and active areas including word lines and doped regions in a
periphery area of a memory device.
BACKGROUND
[0003] A dynamic random access memory (DRAM) device is commonly
used in electronic systems to store data. A typical DRAM device
includes memory cells arranged in an array and a peripheral circuit
around the memory cell array, with each memory cell generally
consisting of a capacitor coupled through a transistor gate
electrode or word line stack to a bit or digit line. The doped
regions or active areas of a transistor fabricated in a
semiconductive substrate are typically contacted using polysilicon
(poly) plugs, which may connect with a capacitor, a bit line, or
other conductor layers.
[0004] In the formation of local interconnects in memory devices,
it is difficult to form low resistance peripheral contacts while
maintaining high quality array contacts.
[0005] In a conventional process flow for fabricating a DRAM
device, contact openings are formed through insulative layers in
the DRAM peripheral area to active areas in the substrate and in
the DRAM array area poly plugs are connected to diffusion regions,
and filled with conductive material to form peripheral and array
contacts. A problem faced in making a DRAM local interconnect
contact is that there are subsequent temperature steps, which make
it difficult to put down chemical vapor deposition (CVD) films
early in the DRAM fabrication process flow. Although films such as
physical vapor deposition (PVD) TiN can withstand high process
temperatures, they are high in resistivity, making them undesirable
for forming contacts on a silicon substrate.
[0006] CVD titanium (CVD Ti) provides a desirable film for
fabricating a low resistivity resistance contact. However, problems
such as delamination of subsequently deposited film layers that are
formed over a CVD Ti layer can develop. In addition, a CVD Ti layer
deposited onto amorphous silicon highly doped poly plugs exposed in
the memory cell array results in the formation of titanium silicide
(TiSi.sub.x) in the poly plugs resulting in the development of
voids within the plugs. Further, due to die shrinkage, there is a
trend to fabricate DRAM word lines (gate stacks) of tungsten rather
than tungsten silicide, due to the lower resistivity of tungsten.
However, in utilizing titanium to form interconnects to the
tungsten layer of a gate stack, it is difficult to selectively
remove portions of the titanium layer to form the gate contacts
without adversely affecting the exposed tungsten of the stack.
[0007] It would be desirable to provide a process that overcomes
such problems.
DISCLOSURE
[0008] The present invention provides methods for forming memory
devices and integrated circuitry, for example, DRAM circuitry,
structures and devices resulting from such methods, and systems
that incorporate the devices.
[0009] In one aspect, the invention provides methods for forming a
memory device. In one embodiment, the method includes: providing a
substrate having a memory cell array area and a peripheral
circuitry area, the memory cell array including at least one word
line with an adjacent source/drain region in a silicon substrate
and a polysilicon plug over the source/drain region adjacent a gate
stack, the peripheral circuitry including an active area in the
silicon substrate, and a dielectric layer overlying the memory cell
array area and the peripheral circuitry area; forming a first
opening in the dielectric layer at the peripheral circuitry area to
expose the active area in the silicon substrate, chemical vapor
deposition of a titanium layer over the dielectric layer and into
the first opening to form a titanium silicide layer over the
silicon substrate; removing the titanium layer selective to the
titanium silicide layer; forming a second opening in the dielectric
layer at the memory cell array area to expose the polysilicon plug;
and forming metal contacts within the first and second openings to
the active area and the exposed polysilicon plug.
[0010] Preferably, the CVD titanium layer is selectively removed by
applying a sulfuric acid solution onto the substrate, preferably
containing at least about 50% sulfuric acid. It is also preferred
that the metal contacts are formed by physical vapor deposition
(PVD, sputtering) of titanium (Ti), which can be conducted in an
atmosphere of nitrogen, to form a PVD Ti layer, which can
incorporate nitrogen, followed by a metal nitride layer (e.g.,
tungsten nitride), and a conductive metal layer (e.g., tungsten).
In another embodiment, the metal contacts can be formed by CVD of
titanium to form a CVD Ti layer with nitrogen incorporated into the
layer.
[0011] In another aspect, the invention provides processing methods
for forming integrated circuitry. In one embodiment, the method
includes forming memory circuitry and peripheral circuitry over a
substrate, the memory circuitry comprising at least one word line
with an adjacent source/drain region in a silicon substrate and a
polysilicon plug over the source/drain region adjacent the gate
stack, and the peripheral circuitry comprising an active area in
the silicon substrate and an overlying dielectric layer (e.g.,
BPSG), depositing a second dielectric layer (e.g., TEOS oxide) over
the first dielectric layer and the memory circuitry; forming a
first opening in the first and second dielectric layers at the
periphery circuitry area to expose the active area in the silicon
substrate; chemical vapor deposition of a titanium layer over the
second dielectric layer and into the first opening to form a
titanium silicide layer over the silicon substrate; removing the
titanium layer selective to the titanium silicide layer, preferably
by the application of sulfuric acid (H.sub.2SO.sub.4); forming a
second opening in the second dielectric layer at the memory cell
array area to expose a polysilicon plug; and forming metal contacts
within the first and second openings to the active area and the
exposed polysilicon plug, preferably by physical vapor deposition
of titanium (Ti), which can be conducted in an atmosphere of
nitrogen, to form a PVD Ti layer over the second dielectric layer
and into the first and second openings over the exposed polysilicon
plug and the titanium silicide layer and sidewalls of the first and
second openings. In another embodiment, the metal contacts can be
formed by initially depositing a CVD Ti layer with nitrogen
incorporated into the layer.
[0012] In another aspect of the invention, a method of forming a
metallized contact to an active area in a silicon substrate in a
periphery area and a metallized contact to a polysilicon substrate
in a memory cell array area is provided. An embodiment of the
method of forming the metallized contacts includes etching through
an insulating layer to form a contact opening to expose the active
area of the periphery area; chemical vapor deposition of a titanium
layer over the substrate and into the first opening to form a
titanium silicide layer over the silicon substrate; applying a
sulfuric acid solution to the substrate to remove the titanium
layer selective to the titanium silicide layer; etching through the
insulating layer to form a bit line opening to expose a polysilicon
plug in the memory cell array area; physical vapor deposition of
titanium to form a PVD Ti layer (which can incorporate nitrogen)
over the substrate into the contact opening over the titanium
silicide layer and into the bit line opening over the exposed
polysilicon plug, and over the sidewalls of the openings; and
depositing a metal layer over the PVD Ti layer to form metallized
contacts in the contact opening at the periphery area and the bit
line opening at the memory cell array area.
[0013] A further aspect of the invention is directed to memory
devices. In one embodiment, the memory device includes a memory
cell array area comprising a word line with an adjacent
source/drain region in a silicon substrate and a polysilicon plug
over the source/drain region; a periphery area comprising an active
area (e.g., source/drain region) in the silicon substrate; a first
dielectric layer overlying the periphery area; a second dielectric
layer overlying the first dielectric layer and the memory cell
array area; and a bit line formed over the second dielectric layer
and within a first opening through the second dielectric layer to a
polysilicon plug in the memory cell array area, and within a second
opening through the first and second dielectric layers to a
titanium silicide layer over the active area in the periphery area;
the bit line comprising a titanium layer, preferably deposited by
PVD (which can be conducted in the presence of a nitrogen gas),
overlying the polysilicon plug, the silicide layer, and sidewalls
of the first and second openings, and a metal layer over the PVD Ti
layer. In another embodiment of the memory device, the periphery
area further includes a word line with a tungsten layer, and the
bit line is formed within a third opening through the first and
second dielectric layers to the tungsten layer of the word
line.
[0014] In yet another aspect, the invention provides interconnects.
One embodiment of an interconnect according to the invention
comprises a titanium layer deposited by PVD, which can be conducted
in the presence of nitrogen, overlying a dielectric layer, and
overlying sidewalls and a polysilicon plug at a bottom of a bit
line opening through the dielectric layer in a memory cell array
area, and overlying sidewalls and a titanium silicide layer
overlying an active area in a silicon substrate at a bottom of a
contact opening through the dielectric layer in a periphery area.
In another embodiment, the titanium layer of the interconnect is
deposited by CVD in the presence of nitrogen.
[0015] A further aspect of the invention provides buried bit line
memory circuitry. In one embodiment, the circuitry comprises a bit
line over a dielectric layer and contacting a polysilicon plug in a
memory cell array area and a titanium silicide layer overlying an
active area in a silicon substrate in a periphery area, the bit
line comprising a titanium layer deposited by physical vapor
deposition (PVD Ti). In another embodiment, the bit line comprises
a titanium layer deposited by CVD in the presence of nitrogen. The
bit line can further comprise an overlying metal layer, for
example, a metal nitride barrier layer and a conductive metal
layer. In another embodiment, the bit line further contacts a
tungsten layer of a word line in the periphery area.
[0016] In yet another aspect, the invention provides integrated
circuitry, such as DRAM integrated circuitry. In one embodiment,
the integrated circuit comprises a word line with an adjacent
source/drain region in a silicon substrate and a polysilicon plug
over the source/drain region adjacent the DRAM word line in a
memory cell array area; a word line with an adjacent source/drain
region in a silicon substrate in a periphery area; and a bit line
formed over a dielectric layer overlying the memory cell array area
and within a bit line opening through the dielectric layer to the
polysilicon plug, and within first and second contact openings
through the dielectric layer over the periphery area, the first
contact opening to a titanium silicide layer over the active area
and the second contact opening to a tungsten layer of the word
line; the bit line comprising a titanium layer deposited by
physical vapor deposition (PVD Ti), which can be conducted in an
atmosphere of gaseous nitrogen, overlying the dielectric layer, the
polysilicon plug, the silicide layer, and sidewalls of the first
and second openings. In another embodiment, the bit line comprises
a titanium layer deposited by CVD in the presence of nitrogen.
[0017] In a further aspect of the invention, electronic systems
incorporating the integrated circuits are provided. In one
embodiment, the system comprises a processor, and an integrated
circuit (e.g., a memory circuit such as a DRAM memory circuit) in
communication with the processor, the integrated circuit comprising
a bit line over a dielectric layer and contacting a polysilicon
plug in a memory cell array area and a titanium silicide layer
overlying an active area in a silicon substrate in a periphery
area, the bit line comprising a titanium layer deposited by
physical vapor deposition (PVD Ti), which can be conducted in the
presence of a nitrogen gas.
[0018] In another embodiment, the system comprises a
microprocessor, and a memory device coupled to the microprocessor,
the memory device including a memory cell array comprising a word
line with an adjacent source/drain region in a silicon substrate
and a polysilicon plug over the source/drain region adjacent the
word line; a periphery area comprising an active area in the
silicon substrate; a dielectric layer overlying the memory cell
array and the periphery area; and a bit line formed over the
silicon substrate and within a first opening through the dielectric
layer to the polysilicon plug in the memory cell array area, and
within a second opening through the dielectric layer to a silicide
layer over the active area in the periphery area; the bit line
comprising a PVD Ti layer, which can incorporate nitrogen,
overlying the polysilicon plug, the silicide layer, and sidewalls
of the first and second openings, and a metal layer over the PVD Ti
layer. In another embodiment, the bit line can comprise a CVD Ti
layer that includes nitrogen.
[0019] Advantageously, the invention provides a method for
simultaneously forming low resistance peripheral contacts to active
areas (e.g., source/drain regions) in the periphery of a memory
device, and suitable contacts to highly doped polysilicon (poly)
plugs in the memory array area, while eliminating problems such as
voids and opens in the poly plugs, and delamination of subsequently
deposited films caused by CVD deposited titanium layers and their
related stresses. The contacts produced according to the invention
also demonstrate improved temperature stability in later process
steps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Preferred embodiments of the invention are described below
with reference to the following accompanying drawings, which are
for illustrative purposes only. Throughout the following views,
reference numerals will be used in the drawings, and the same
reference numerals may be used throughout the several views and in
the description to indicate same or like parts.
[0021] FIG. 1 is a diagrammatic, cross-sectional view of a
semiconductor construction at a preliminary processing stage of an
exemplary application of the present invention, showing a wafer
fragment comprising example DRAM integrated circuitry in
fabrication.
[0022] FIGS. 2-7 are views of the wafer fragment of FIG. 1 at
sequential processing steps subsequent to that of FIG. 1 according
to an embodiment of a method of the invention.
[0023] FIG. 8 is a block diagram of a circuit module according to
an embodiment of the present invention.
DETAILED DESCRIPTION
[0024] The invention will be described generally with reference to
the drawings for the purpose of illustrating the present preferred
embodiments only and not for purposes of limiting the same. The
figures illustrate processing steps for use in the fabrication of
semiconductor devices in accordance with the present invention. It
should be readily apparent that the processing steps are only a
portion of the entire fabrication process.
[0025] In the context of the current application, the terms
"semiconductor substrate," "semiconductive substrate,"
"semiconductive wafer fragment," "wafer fragment," or "wafer," will
be understood to mean any construction comprising semiconductor
material including, but not limited to, bulk semiconductive
materials such as a semiconductor wafer (either alone or in
assemblies comprising other materials thereon), and semiconductive
material layers (either alone or in assemblies comprising other
materials). The term "substrate" refers to any supporting structure
including, but not limited to, the semiconductive substrates, wafer
fragments or wafers described above.
[0026] The following description with reference to the figures
provides an illustrative example in the fabrication of DRAM
integrated circuitry (IC) construction. Such description is only
for illustrative purposes and the present invention can be utilized
to provide other integrated circuitry in other constructions and
devices. The present invention is not limited to the described
illustrative devices.
[0027] Steps in an embodiment of a method for fabricating local
interconnect contacts according to an embodiment of the invention
are illustrated in FIGS. 1-7. The illustrated example is of the
fabrication of bit line contacts to a poly plug of a memory array
and to active areas in a periphery area of a memory device.
[0028] FIG. 1 depicts a wafer fragment 10 at a preliminary
processing step. As shown, a DRAM memory cell array 12 and a DRAM
peripheral logic circuitry (periphery) area 14 where control
circuitry is formed outside of and around the memory cell array 12,
have been fabricated on the substrate 16 of the wafer fragment
10.
[0029] The substrate 16 can comprise an unprocessed semiconductor
wafer or other substrate, the wafer with various process layers
formed thereon including one or more semiconductor layers or other
formations, and active or operable portions of semiconductor
devices. A semiconductor device can comprise a transistor,
capacitor, electrode, insulator, or any of a variety of components
commonly utilized in semiconductor structures. In the illustrated
example, the substrate 16 comprises a semiconductive material such
as monocrystalline silicon that is lightly doped with a
conductivity enhancing material.
[0030] The memory cell array 12 includes a series of four word
lines or gate stacks 18a-18d, which are conventional as shown and
formed over the substrate 16. The word lines or gate stacks 18a-18d
generally include a gate dielectric layer 20 over the substrate 16,
an overlying conductive polycrystalline silicon (poly) layer 22, an
overlying conductive metal (e.g., tungsten) or metal silicide layer
24, and an insulative cap 26 and sidewall spacers 28 (e.g., silicon
nitride, SiN). Two memory cells (word lines) 18b, 18c electrically
connect doped source/drain diffusion regions 30a-30c and, as
depicted, share a source/drain region 30b that will electrically
connect with a bit (digit) line, as described herein. The memory
cell array 12 further includes highly doped, polysilicon (poly)
plugs 32a-32c. The poly plugs can be further identified as poly
plugs 32a, 32c, which will connect with subsequently foimed memory
cell capacitors, and poly plug 32b, which will connect with a
subsequently formed bit (digit) line.
[0031] The DRAM periphery area 14 comprises a tungsten gate stack
or word line 34 (including tungsten layer 24) and an active area
(source/drain region) 36 in the silicon substrate 16.
[0032] A first dielectric (insulative) layer 38 overlies the
substrate 16, and can be, for example, silicon dioxide (SiO.sub.2),
silicon dioxide deposited by decomposition of
tetraethylorthosilicate (TEOS oxide), phosphosilicate glass (PSG),
borosilicate glass (BSG), borophosphosilicate glass (BPSG), a
spin-on dielectric (SOD), or other dielectric material, in a single
layer or multiple layers, with the first dielectric layer 38 being
BPSG in the illustrated example. The first dielectric layer 38 can
be deposited by chemical vapor deposition or other suitable
technique.
[0033] Overlying the first dielectric layer 38 and the DRAM array
12 is a second dielectric (insulative) layer 40, which can be, for
example, SiO.sub.2, TEOS oxide, PSG, BSG, BPSG, SOD, and the like,
being TEOS oxide in the present example. The second dielectric
layer 40 is formed over the DRAM array 12 to insulate the poly
plugs 32a-32c.
[0034] Referring now to FIG. 2, according to the present invention,
with the second dielectric layer 40 insulating the poly plugs
32a-32c of the memory array 12, a directional dry etch (e.g., a
reactive ion etch (RIE)) or other suitable process through a
photomask (not shown) is conducted in the peripheral circuitry area
14 to etch through the dielectric layers 38, 40 to form respective
peripheral contact or plug openings 42, 44, also referred to herein
as source/drain (S/D) contact opening 42 and gate contact opening
44. As shown, the contact opening 42 extends to and exposes the
active area (source/drain region) 36 in the silicon substrate 16,
and gate contact opening 44 extends to the tungsten layer 24 of the
gate stack (word line) 34. The source/drain (S/D) contact opening
42 has sidewalls 46 defined by the dielectric layers 38, 40, and a
bottom or base 48 defined by the exposed surface of the silicon
substrate 16 containing the source/drain (S/D) region 36. The gate
contact opening 44 includes sidewalls 50 defined by the sidewall
spacers 28 and the second dielectric layer 40, and a bottom or base
52 defined by the exposed surface of the tungsten layer 24 of the
gate stack 34. After formation of the gate contact opening 44, the
photoresist mask is removed.
[0035] Referring to FIG. 3, a titanium (Ti) layer 54 is then formed
by chemical vapor deposition (CVD) over the surface of the second
dielectric layer 40 as well as over the sidewalls 46, 50 and bottom
48, 52 of the contact openings 42, 44. Typically, a sufficient
thickness of the titanium layer 54 is about 1-1,000 .ANG.. The
titanium layer 54 can be deposited using a standard chemical vapor
deposition (CVD) process. For example, a plasma enhanced chemical
vapor deposition (PECVD) process can be conducted using a gas
mixture comprised of TiCl.sub.4, Ar, H.sub.2, and He, a reaction
gas temperature of about 650.degree. C., an RF power of about 400
W, and a chamber pressure of about 4 Torr.
[0036] During the titanium CVD process, the titanium reacts with
the exposed silicon substrate 16 and remains unreacted over the
exposed dielectric layers 38, 40 and the exposed tungsten layer 24
of the periphery gate stack 34. The reaction of the titanium with
the silicon substrate 16 at the bottom 48 of the S/D contact
opening 42 results in the formation of a film of titanium silicide
(TiSi.sub.x) 56 at the interface between the CVD titanium layer 54
and the doped polysilicon substrate 16. The silicide layer 56
enhances conductivity of a subsequently formed S/D contact within
the opening 42 by providing a low resistivity conductive film
between the silicon substrate 16 and the overlying contact.
[0037] To eliminate problems such as the delamination of
subsequently formed layers over a chemical vapor deposition
titanium (CVD Ti) base layer, the unreacted titanium layer 54 is
then stripped by a selective wet etch, resulting in the structure
depicted in FIG. 4. Sulfuric acid (H.sub.2SO.sub.4) is applied to
selectively remove the unreacted titanium layer 54 without
detrimentally removing the titanium silicide (TiSi.sub.x) layer 56
over the silicon substrate 16 at the bottom 48 of the S/D contact
opening 42, or other exposed materials such as dielectric materials
(i.e., dielectric layers 38, 40) or the tungsten layer 24 of the
periphery gate stack (word line) 34 which is exposed within the
gate contact opening 44. The unreacted titanium (Ti) layer 54
overlying the sidewalls 46, 50 of the contact openings 42, 44, the
tungsten (W) layer 24 in the gate contact opening 44, and over the
surface of the second insulative layer 40, is removed selective to
the TiSi.sub.x layer 56 at the bottom 48 of the S/D contact opening
42 and the W layer 24 of the gate stack 34 (i.e., with minimal
removal of the TiSi.sub.x layer 56 or the W layer 24, and maximal
removal of the Ti layer 54).
[0038] The sulfuric acid (H.sub.2SO.sub.4) solution can be applied
over a range of concentrations, preferably, from an about 50 wt %
to 100 wt % concentration (or 50% to 100% H.sub.2SO.sub.4).
Sulfuric acid is commercially available in a number of different
concentrations including 78 wt %, 93 wt %, 96 wt %, 98 wt % to 99
wt %, and 100 wt %.
[0039] To selectively wet etch the unreacted titanium layer 54, the
wafer fragment 10 can be immersed in or sprayed with the sulfuric
acid solution, exposed to vapors of the sulfuric acid solution, and
the like. Processing time is generally a few seconds to an hour or
longer, and can vary according to the concentration and the
temperature of the sulfuric acid solution, and the thickness of the
titanium layer 54. Preferably, the sulfuric acid is heated to a
temperature of about 100.degree. C. to 140.degree. C., preferably
about 120.degree. C. As an example, wafer fragment 10 bearing an
about 85 .ANG. titanium layer 54 can be immersed in an about 98%
sulfuric acid solution at about 120.degree. C. for about 5 to 10
minutes to remove the unreacted titanium layer 54.
[0040] Referring now to FIG. 5, after the removal of the unreacted
titanium layer 54, a photoresist mask 58 is deposited onto the
second dielectric layer 40 and patterned, and a directional etching
process (e.g., RIE) or other suitable process is used to etch
through the second dielectric layer 40 to define a bit (digit) line
opening 60 to the poly plug 32b of the memory array 12. After
formation of the bit line opening 60, the photoresist mask 58 is
removed.
[0041] As illustrated in FIG. 6, the buried bit (digit) line
material layer 62 is now deposited over the surface and to
simultaneously fill the bit line opening 60 and the peripheral
contact openings 42, 44. The results in the formation of a bit line
contact 64 that is electrically coupled to the poly plug 32b and
the shared diffusion region 30b of the memory array 12 and, in the
DRAM periphery area 14, peripheral contacts (plugs) 66, 68 to the
source/drain (S/D) region 36 and to the tungsten (W) layer 24 of
the gate electrode 34, respectively.
[0042] An exemplary conductive (bit line) material layer 62 is
foamed by depositing, in sequence, a conductive barrier layer 70 to
prevent migration of an overlying conductive metal (e.g., tungsten
layer) into the poly plug 32b, a second conductive barrier layer
72, and a conductive metal layer 74. In a preferred embodiment, the
conductive barrier layer 70 comprises titanium formed by a physical
vapor deposition (PVD Ti) process involving reactive sputtering
from a titanium target as known and used in the art, which can be
conducted in an atmosphere of gaseous nitrogen (N.sub.2) to include
nitrogen in the PVD Ti layer. Exemplary PVD process conditions for
sputtering titanium include a deposition temperature of about
200.degree. C., an inductive coil power (RF) of about 2.8 kW, a
target power (DC) of about 2.5 kW, a pressure of about 10 to 20
mTorr, with argon (Ar) and nitrogen (N.sub.2) flows at 0-1,000 seem
and 0-1,000 seem, respectively. The resulting PVD Ti layer 70 is
deposited over the surface and the sidewalls and base of the
contact openings 42, 44, 60. A preferred thickness for the PVD Ti
layer 70 is about 1-1,000 .ANG.. In another embodiment, a titanium
layer 70 can be deposited by a chemical vapor deposition (CVD)
process as known and used in the art, preferably in the presence of
a nitrogen source to form a CVD Ti layer.
[0043] An overlying tungsten nitride (WN) layer 72 can be deposited
onto the titanium layer 70 (e.g., PVD Ti layer) by a standard PVD
process. A tungsten (W) layer 74 can then be deposited over the
surface of the WN layer 72 and to fill the contact openings 42, 44,
60 by a conventional chemical vapor deposition (CVD) process. The
resulting conductive (bit line) material layer 62 comprises a
three-layer stack of (PVD) titanium/tungsten nitride/tungsten (PVD
Ti/WN/W).
[0044] Advantageously, the PVD Ti layer 70 has a greater tolerance
to high process temperatures than CVD Ti. In addition, sputtering
titanium (Ti) to produce the PVD Ti layer 70 deposits a reduced
amount of Ti onto the surface compared to a CVD Ti layer resulting
in very little titanium silicide (TiSi.sub.x) in the highly doped,
poly plug 32b, thus eliminating the problem of void formation
within the poly plug. Although a PVD Ti layer has a higher
resistance on a silicon substrate (12) than a CVD Ti layer, since
the PVD Ti layer 70 is deposited onto a low resistance TiSi.sub.x
layer 56 in the bottom of the S/D contact opening 42 and does not
directly contact the silicon substrate 16, the contact resistance
is low.
[0045] As illustrated in FIG. 7, the deposited conductive (bit
line) material layer 62 is then patterned and etched by a standard
process to foini buried bit (digit) lines 76a-76c.
[0046] The resulting semiconductor structure 78 includes a buried
bit (digit) line 76a and a high quality and reliable bit (digit)
line contact 64 to the highly doped, polysilicon (poly) plug 32b
without causing voids or opens in the poly plug 32b as with a CVD
Ti layer. The structure also includes, in the periphery area 14, a
buried bit (digit) line 76b and a low resistance contact 66 to the
active area S/D region 36 in the polysilicon substrate 16 with the
TiSi.sub.x layer 56 in the bottom of the contact, and a buried bit
(digit) line 76c and gate contact 68 to the tungsten (W) layer 24
of the gate stack 34.
[0047] Although conductive materials such as CVD Ti make low
resistance contacts on a silicon substrate (16), they will void out
highly doped poly plugs 32b due to the formation of TiSi.sub.x in
the plugs. In the present invention, the formation of the low
resistance TiSi.sub.x layer 56 over the slightly doped silicon
substrate 16 in the peripheral contact opening 42, enables a
conductive material such as Ti, which provides a good contact and
will not void out the highly doped poly plugs but has a high
resistance on the silicon substrate 16, to be successfully
deposited as a PVD Ti layer 70 in forming both the bit line contact
64 to the poly plug 32b and the peripheral contact 66 to the S/D
region 36 in the silicon substrate 16.
[0048] The resulting semiconductor structure 78 can be used in a
variety of applications including, for example, programmable memory
devices, programmable resistor and capacitor devices, optical
devices, and sensors, among others.
[0049] FIG. 8 is a block diagram of an embodiment of a circuit
module 80 in which the present invention can be incorporated. Such
modules, devices and systems (e.g., processor systems)
incorporating the module are described and illustrated in U.S. Pat.
No. 6,437,417 (Gilton) and U.S. Pat. No. 6,465,828 (Agarwal), the
disclosures of which are incorporated by reference herein. In
brief, two or more dies may be combined into a circuit module 80 to
enhance or extend the functionality of an individual die. Circuit
module 80 may be a combination of dies representing a variety of
functions, or a combination of dies containing the same
functionality. One or more dies of the circuit module 80 can
contain circuitry, or integrated circuit devices, that includes at
least one contact in accordance with the embodiments of the present
invention. The integrated circuit devices can include a memory
device that comprises a semiconductor structure as discussed in the
various embodiments in accordance with the invention.
[0050] Some examples of a circuit module include memory modules,
device drivers (on a BIOS or EPROM), power modules, communication
modems, processor modules, and application-specific modules, and
may include multilayer, multi-chip modules. Circuit module 80 may
be a subcomponent of a variety of electronic systems, such as a
clock, a television, a cell phone, a personal computer, an
automobile, an industrial control system, an aircraft, among
others. Circuit module 80 will have a variety of leads 82 extending
therefrom and coupled to dies 84 providing unilateral or bilateral
communication and control.
[0051] The circuit module 80 can be incorporated, for example, into
an electronic system that comprises a user interface, for example,
a keyboard, a monitor, a display, a printer, and speakers, etc. One
or more circuit modules can comprise a microprocessor that provides
information to the user interface, or is otherwise programmed to
carry out particular functions as is known in the art. The
electronic system can comprise, for example, a computer system
including a processor and a memory system as a subcomponent, and,
optionally, user interface components, and other associated
components such as modems, device interface cards, etc. Examples of
memory circuits include, but are not limited to, DRAM (Dynamic
Random Access Memory), SRAM (Static Random Access Memory), Flash
memories, a synchronous DRAM such as SGRAM (Synchronous Graphics
Random Access Memory), SDRAM (Synchronous Dynamic Random Access
Memory), SDRAM II, and DDR SDRAM (Double. Data Rate SDRAM), as well
as Synchlink or Rambus DRAMs and other emerging memory
technologies.
[0052] In compliance with the statute, the invention has been
described in language more or less specific as to structural and
methodical features. It is to be understood, however, that the
invention is not limited to the specific features shown and
described, since the means herein disclosed comprise preferred
forms of putting the invention into effect. The invention is,
therefore, claimed in any of its forms or modifications within the
proper scope of the appended claims appropriately interpreted in
accordance with the doctrine of equivalents.
* * * * *