U.S. patent application number 11/509066 was filed with the patent office on 2007-03-01 for mixed metal nitride and boride barrier layers.
Invention is credited to Brian A. Vaartstra, Donald L. Westmoreland.
Application Number | 20070045856 11/509066 |
Document ID | / |
Family ID | 23022472 |
Filed Date | 2007-03-01 |
United States Patent
Application |
20070045856 |
Kind Code |
A1 |
Vaartstra; Brian A. ; et
al. |
March 1, 2007 |
Mixed metal nitride and boride barrier layers
Abstract
Mixed metal aluminum nitride and boride diffusion barriers and
electrodes for integrated circuits, particularly for DRAM cell
capacitors. Also provided are methods for CVD deposition of
M.sub.xAl.sub.yN.sub.zB.sub.w alloy diffusion barriers, wherein M
is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, or W; x is greater than zero; y
is greater than or equal to zero; the sum of z and w is greater
than zero; and wherein when y is zero, z and w are both greater
than zero.
Inventors: |
Vaartstra; Brian A.; (Nampa,
ID) ; Westmoreland; Donald L.; (Boise, ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
23022472 |
Appl. No.: |
11/509066 |
Filed: |
August 24, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10642607 |
Aug 19, 2003 |
7101779 |
|
|
11509066 |
Aug 24, 2006 |
|
|
|
10185009 |
Jul 1, 2002 |
6664159 |
|
|
10642607 |
Aug 19, 2003 |
|
|
|
09268326 |
Mar 16, 1999 |
6445023 |
|
|
10185009 |
Jul 1, 2002 |
|
|
|
Current U.S.
Class: |
257/771 ;
257/295; 257/751; 257/770; 257/E21.17; 257/E29.146 |
Current CPC
Class: |
H01L 21/7687 20130101;
H01L 23/485 20130101; H01L 21/76843 20130101; H01L 27/10811
20130101; H01L 2924/0002 20130101; Y10S 438/932 20130101; H01L
2924/00 20130101; H01L 27/10888 20130101; H01L 28/90 20130101; H01L
29/456 20130101; H01L 2924/0002 20130101; H01L 21/28556 20130101;
H01L 27/10855 20130101; H01L 21/76897 20130101; H01L 28/75
20130101 |
Class at
Publication: |
257/771 ;
257/770; 257/295; 257/751 |
International
Class: |
H01L 23/48 20060101
H01L023/48; H01L 23/52 20060101 H01L023/52; H01L 29/94 20060101
H01L029/94 |
Claims
1-91. (canceled)
92. A method of depositing an amorphous alloy, comprising the steps
of: placing an object within a vapor deposition chamber; injecting
gaseous precursors of a metal, aluminum, nitrogen and boron into
said chamber, wherein each of said gaseous precursors is
transferred from a respective bubbler, each said respective bubbler
and said chamber being at about a same pressure; and depositing an
amorphous alloy layer from said precursors on said object.
93. The method of claim 92, wherein said metal precursor is
titanium and a single gas serves as said metal precursor and said
nitrogen precursor.
94. The method of claim 93, wherein said metal and nitrogen
precursor is of the formula Ti(NR.sub.2).sub.4, where R is selected
from the group consisting of one or more of hydrogen, an alkyl
group and an aryl group.
95. The method of claim 93, wherein said metal and nitrogen
precursor is Ti(N(CH.sub.3).sub.2).sub.4.
96. The method of claim 92, wherein said wafer is heated to a
temperature of approximately 250-550.degree. C.
97. The method of claim 92, wherein said aluminum precursor is
selected from the group consisting of DMEAA,
dimethylaluminumhydride ethyldimethylamine adduct, dimethyl
aluminum hydride, an alkyl aluminum compound, an alkylaminealuminum
compound, and any adducted complexes of the above-named
aluminum-containing compounds.
98. The method of claim 92, wherein said metal precursor is
selected from the group consisting of tetrakisdiethylamidotitanium,
bis(2,4-dimethyl)(1,3-pentadienyl)titanium, titanium tetrachloride,
titanium tetrabromide, titanium tetraiodide, and
cyclopentadienylcycloheptatrienyltitanium.
99. The method of claim 92, wherein said metal precursor is
selected from the group consisting of metal halide compounds and
organometallic compounds.
100. The method of claim 92, wherein said boron precursor is a
boron reactant gas.
101. The method of claim 92, wherein said nitrogen precursor is a
nitrogen reactant gas.
102. The method of claim 92, wherein said amorphous alloy layer
comprises M.sub.xAl.sub.yN.sub.zB.sub.w, wherein M is said first
metal, x, y and z are each greater than zero, and w is between
about 0.35 and about 1.4.
103. The method of claim 92, wherein said precursors are introduced
into said chamber substantially simultaneously.
104. A method of depositing a layer on a semiconductor wafer,
comprising: placing said wafer within a vapor deposition reactor;
heating said wafer to a temperature of about 250.degree. C. to
about 550.degree. C.; establishing a pressure of 100 millitorr to
10 torr within said reactor; injecting a gaseous organometallic
precursor from a first bubbler into said reactor; injecting an
aluminum precursor from a second bubbler into said reactor, said
first bubbler and said second bubbler being at a pressure
substantially the same as that within said reactor; and depositing
a layer comprising M.sub.xAl.sub.yN.sub.zB.sub.w, wherein M is a
first metal, x, y and z are each greater than zero, and w is
between about 0.35 and about 1.4.
105. The method of claim 104, wherein said aluminum precursor is
selected from the group consisting of DMEAA,
dimethylaluminumhydride ethyldimethylamine adduct, dimethyl
aluminum hydride, an alkyl aluminum compound, an alkylaminealuminum
compound, and adducted complexes of any of the above-named
aluminum-containing compounds.
106. The method of claim 104, wherein said first metal is titanium
and is deposited from a titanium precursor selected from the group
consisting of tetrakisdiethylamidotitanium,
bis(2,4-dimethyl)(1,3-pentadienyl)titanium, titanium tetrachloride,
titanium tetrabromide, titanium tetraiodide,
cyclopentadienylcycloheptatrienyltitanium, and a precursor of the
formula Ti(NR.sub.2), where R is selected from the group consisting
of one or more of hydrogen, an alkyl group and an aryl group.
107. The method of claim 104, wherein said organometallic precursor
comprises titanium and nitrogen.
108. The method of claim 107, wherein said organometallic precursor
is Ti(N(CH.sub.3).sub.2).sub.4.
109. The method of claim 107, wherein said organometallic precursor
is of the formula Ti(NR.sub.2).sub.4, where R is selected from the
group consisting of one or more of hydrogen, an alkyl group and an
aryl group.
110. The method of claim 104, wherein said aluminum precursor is
selected from the group consisting of DMEAA,
dimethylaluminumhydride ethyldimethylamine adduct, dimethyl
aluminum hydride, an alkyl aluminum compound, an alkylaminealuminum
compound, and any adducted complexes of the above-named
aluminum-containing compounds.
111. The method of claim 104, wherein said selected organometallic
precursor is selected from the group consisting of
tetrakisdiethylamidotitanium,
bis(2,4-dimethyl)(1,3-pentadienyl)titanium, titanium tetrachloride,
titanium tetrabromide, titanium tetraiodide, and
cyclopentadienylcycloheptatrienyltitanium.
112. The method of claim 104, wherein said organometallic precursor
is selected from the group consisting of metal halide compounds and
organometallic compounds.
113. The method of claim 104, wherein said boron is included in
said layer comprising M.sub.xAl.sub.yN.sub.zB.sub.w by utilizing a
boron reactant gas.
114. The method of claim 104 wherein said nitrogen is included in
said layer comprising M.sub.xAl.sub.yN.sub.zB.sub.w by utilizing a
nitrogen reactant gas.
115. The method of claim 104, wherein said precursors are
introduced into said reactor substantially simultaneously.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to integrated circuits and
more particularly to the use of amorphous ternary aluminum nitride
and boride alloy materials for diffusion barrier layers in such
circuits.
BACKGROUND OF THE INVENTION
[0002] In semiconductor devices, it is common for the design to
require interfaces of silicon and a metal such as aluminum or
tungsten. For example, aluminum and tungsten are commonly used as
the material of choice for electrical contacts, which contacts
interface with electrically active areas made of doped silicon. It
is also common in the fabrication of semiconductor devices to
anneal the devices at elevated temperatures, such as 500.degree. C.
At these temperatures, the metal and silicon will rapidly
interdiffuse into each other at the interface. Even at room
temperature, the metal and silicon will interdiffuse over time.
Such interdiffusion changes the semiconductive properties of the
silicon and causes defective devices.
[0003] Capacitors are used in a wide variety of integrated circuits
and present special interdiffusion concerns. Capacitors are of
particular concern in DRAM (dynamic random access memory) circuits.
The electrodes in a DRAM cell capacitor must protect the dielectric
film (e.g., Ta.sub.2O.sub.5 and (Ba, Sr)TiO.sub.3) from interaction
with surrounding materials and from the harsh thermal processing
encountered in subsequent steps of DRAM process flow. In order to
function well as a bottom electrode, the electrode film or film
stack must act as an effective barrier to the diffusion of oxygen
and silicon. Oxidation of the underlying Si results in decreased
series capacitance, thus degrading the capacitor.
[0004] It is common practice to provide diffusion barriers in
semiconductor devices. A thin film of titanium nitride (TiN) or
titanium tungsten (TiW) is conventionally used as diffusion
barrier. Conventional barrier materials, however, tend to be
polycrystalline with grain boundaries through which diffusion of Si
and O atomic species can occur.
[0005] The conventional diffusion barriers for silicon/metal
interfaces and capacitor dielectrics, while generally relatively
effective at room temperature, can fail at more elevated
temperatures. Many preferred semiconductor fabrication processes,
such as deposition, reflow, and annealing, require elevated
temperatures. Thus conventional diffusion barriers can create
limits on the processes that can be used to fabricate a
semiconductor device. There is a need for a diffusion barrier that
is more effective than conventional polycrystalline barriers,
especially at elevated temperatures.
[0006] What is needed are improved diffusion barrier layers and
fabrication methods that offer a combination of good conformality,
high conductivity, and excellent barrier properties for protecting
against interdiffusion at capacitor dielectrics and silicon/metal
interfaces in semiconductor devices, particularly during high
temperature fabrication processes.
SUMMARY OF THE INVENTION
[0007] The present invention provides mixed-metal nitride, boride
and boride-nitride alloy barrier layers of the formula
M.sub.xAl.sub.yN.sub.zB.sub.w, wherein M is Ti, Zr, Hf, V, Nb, Ta,
Cr, Mo, or W; x is greater than zero; y is greater than or equal to
zero; the sum of z and w is greater than zero; and wherein when y
is zero, z and w are both greater than zero, and when M is Ti, w is
greater than 0.
[0008] The preferred metals (M) are Ti, Zr, Hf, Ta, Nb, Mo and W.
Preferably, when M is Ti, Zr, Hf, Ta, or Nb, x+y=1, and z+w/2=1;
and when M is Mo or W, x+y=1, and z+2w=1. Most preferably, M is Ti,
Zr, Hf, Ta, or Nb and M.sub.xAl.sub.yN.sub.zB.sub.w has the formula
M.sub.0.7Al.sub.0.3N.sub.0.3B.sub.1.4, or M is Mo, or W, and
M.sub.xAl.sub.yN.sub.zB.sub.w has the formula
M.sub.0.7Al.sub.0.3N.sub.0.3B.sub.0.35.
[0009] The invention also provides semiconductor capacitors and
methods for fabricating capacitors and other devices containing
M.sub.xAl.sub.yN.sub.zB.sub.w barrier layers in order to protect
capacitor cell dielectrics, such as SiO.sub.2, Ta.sub.2O.sub.5,
SrTiO.sub.3 ("ST"), (Ba,Sr)TiO.sub.3 ("BST"), Pb(Z,Ti)O.sub.3
("PZT"), SrBi.sub.2Ta.sub.2O.sub.9 ("SBT") and Ba(Zr,Ti)O.sub.3
("BZT").
[0010] The mixed-metal nitride and boride layers of the invention
provide excellent barrier protection, conductivity as capacitor
electrodes, and conformality, and so may be employed either as
capacitor electrodes, or as separate barrier layers formed adjacent
to conventional capacitor electrodes, either a top these electrodes
or interposed between the electrode and the capacitor dielectric.
Preferably, the M.sub.xAl.sub.yN.sub.zB.sub.w layer according to
the invention comprises a thin barrier film between a cell
dielectric and an underlying polysilicon (poly) plug or drain in a
DRAM cell array, as well as acting as a lower electrode.
[0011] The barrier layers and methods of the invention are also
useful in any device containing a Si/metal interface, and any other
semiconductor device where protection against degradation through
diffusion and thermal effects is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic of a chemical vapor deposition system
suitable for use in the method of the present invention.
[0013] FIG. 2 is a schematic of an alternative chemical vapor
deposition system suitable for use in the method of the present
invention.
[0014] FIG. 3 is a diagrammatic cross-sectional view taken along a
portion of a semiconductor wafer at an early processing step
according to one embodiment of the present invention.
[0015] FIG. 4 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 3.
[0016] FIG. 5 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 4.
[0017] FIG. 6 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 5.
[0018] FIG. 7 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 6.
[0019] FIG. 8 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 7.
[0020] FIG. 9 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 8.
[0021] FIG. 10 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 9.
[0022] FIG. 11 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 10.
[0023] FIG. 12 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 11.
[0024] FIG. 13 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 12.
[0025] FIG. 14 is a diagrammatic cross-sectional view taken along a
portion of a semiconductor wafer at a processing step according to
another embodiment of the present invention.
[0026] FIG. 15 is a diagrammatic cross-sectional view taken along a
portion of a semiconductor wafer at processing step according to
still another embodiment of the present invention.
[0027] FIG. 16 is a diagrammatic cross-sectional view taken along a
portion of a semiconductor wafer at processing step according to
yet a further embodiment of the present invention.
[0028] FIG. 17 is a diagrammatic cross-sectional view of a portion
of a semiconductor wafer at a processing step subsequent to that
shown in FIG. 16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The mixed metal boride, nitride, and boride-nitride barrier
materials of the invention generally have the formula
M.sub.xAl.sub.yN.sub.zB.sub.w, wherein M is Ti, Zr, Hf, V, Nb, Ta,
Cr, Mo or W, and x, y, z, and w are any suitable value such that x
is greater than zero; y is greater than or equal to zero; the sum
of z and w is greater than zero; and wherein when y is zero, z and
w are both greater than zero, and when M is Ti, w is greater than
0. The preferred metals ("M") are Ti, Zr, Hf, Ta, Nb, Mo and W.
Preferably, when M is Ti, Zr, Hf, Ta, or Nb, x+y=1, and z+w/2=1,
and when M is Mo or W, x+y=1, and z+2w=1. Most preferably, M is Ti,
Zr, Hf, Ta, or Nb and M.sub.xAl.sub.yN.sub.zB.sub.w has the formula
M.sub.0.7Al.sub.0.3N.sub.0.3B.sub.1.4, or M is Mo, or W, and
M.sub.xAl.sub.yN.sub.zB.sub.w has the formula
M.sub.0.7Al.sub.0.3N.sub.0.3B.sub.0.35.
[0030] The M.sub.xAl.sub.yN.sub.zB.sub.w barrier material can be
deposited by a sputter process from metal nitride and metal boride
targets, or sputtered from metal targets in the presence of boron
and nitrogen containing gases, such as diborane, ammonia and
nitrogen. The barrier material can also be deposited by chemical
vapor deposition utilizing a volatile source for M and Al and a
reactive gas source for N and B. Examples of metal sources for Al
deposition include, such as, dimethylaluminumhydride (DMAH) and
triethylaluminum (TEAL). Sources for M include any metal halide or
organometallic compound suitable for a CVD process. The
M.sub.xAl.sub.yN.sub.zB.sub.w barrier material can also be
deposited by liquid spin-on or dip coat processes utilizing a
metalorganic solution that is baked and annealed after application.
Chemical vapor deposition techniques are preferred, because they
generally are more suitable for deposition on semiconductor
substrates or substrate assemblies, particularly in contact
openings which are extremely small and require conformally filled
layers.
[0031] The methods of the present invention can be used to deposit
a barrier material film on a variety of substrates, such as a
semiconductor wafer (e.g., silicon wafer, gallium arsenide wafer,
etc.), glass plate, etc., and on a variety of surfaces of the
substrates, whether it be directly on the substrate itself or on a
layer of material deposited on the substrate as in a semiconductor
substrate assembly. Metal and other components of the barrier film
may be deposited from either a volatile liquid, a sublimable solid,
or a solid that is soluble in a suitable solvent that is not
detrimental to the substrate, and other layers thereon. Preferably,
however, solvents are not used; rather, the metal components are
liquid and used neat. Methods of the present invention preferably
utilize vapor deposition techniques, such as flash vaporization,
bubbling, etc.
[0032] A typical chemical vapor deposition (CVD) system that can be
used to perform the process of the present invention is shown in
FIG. 1. The system includes an enclosed chemical vapor deposition
chamber 210, which may be a cold wall-type CVD reactor. As is
conventional, the CVD process may be carried out at pressures of
from atmospheric pressure down to about 10.sup.-3 torr, and
preferably from about 10 torr to about 0.1 torr. A vacuum may be
created in chamber 210 using turbo pump 212 and backing pump
214.
[0033] One or more substrates 216 (e.g., semiconductor substrates
or substrate assemblies) are positioned in chamber 210. A constant
nominal temperature is established for the substrate, preferably at
a temperature of about 100.degree. C. to about 600.degree. C., and
more preferably at a temperature of about 250.degree. C. to about
550.degree. C. Substrate 216 may be heated, for example, by an
electrical resistance heater 218 on which substrate 216 is mounted.
Other known methods of heating the substrate may also be
utilized.
[0034] In this process, the precursor composition 240, which
contains one or more metal or metalloid complexes, is stored in
liquid form (a neat liquid at room temperature or at an elevated
temperature if solid at room temperature) in vessel 242. A source
244 of a suitable inert gas is pumped into vessel 242 and bubbled
through the neat liquid (i.e., without solvent) picking up the
precursor composition and carrying it into chamber 210 through line
245 and gas distributor 246. Additional inert carrier gas or
reaction gas may be supplied from source 248 as needed to provide
the desired concentration of precursor composition and regulate the
uniformity of the deposition across the surface of substrate 216.
As shown, a series of valves 250-254 are opened and closed as
required.
[0035] Generally, the precursor composition is pumped into the CVD
chamber 210 at a flow rate of about 1 sccm (standard cubic
centimeters) to about 1000 sccm. The semiconductor substrate is
exposed to the precursor composition at a pressure of about 0.001
torr to about 100 torr for a time of about 0.01 minute to about 100
minutes. In chamber 210, the precursor composition will form an
adsorbed layer on the surface of the substrate 216. As the
deposition rate is temperature dependent, increasing the
temperature of the substrate will increase the rate of deposition.
Typical deposition rates are about 10 Angstroms/minute to about
1000 Angstroms/minute. The carrier gas containing the precursor
composition is terminated by closing valve 253.
[0036] An alternative CVD system that can be used to perform the
mixed metal nitride and boride CVD process of the present invention
is shown in FIG. 2. The system includes an enclosed chemical vapor
deposition chamber 210, which may be a cold wall-type CVD reactor,
in which a vacuum may be created using turbo pump 212 and backing
pump 214. One or more substrates 216 (e.g., semiconductor
substrates or substrate assemblies) are positioned in chamber 210.
Substrate 216 may be heated as described with reference to FIG. 1
(for example, by an electrical resistance heater 218).
[0037] In this process, one or more solutions 260 of one or more
precursor metal or metalloid complexes are stored in vessels 262.
The solutions are transferred to a mixing manifold 264 using pumps
266. The resultant precursor compositions containing one or more
precursor complexes and one or more organic solvents is then
transferred along line 268 to vaporizer 270, to volatilize the
precursor composition. A source 274 of a suitable inert gas is
pumped into vaporizer 270 for carrying a volatilized precursor
composition into chamber 210 through line 275 and gas distributor
276. Reaction gas may be supplied from source 278 as needed. As
shown, a series of valves 280-285 are opened and closed as
required. Similar pressures and temperatures to those described
with reference to FIG. 1 can be used.
[0038] Various combinations of carrier gases and/or reaction gases
can be used in certain methods of the present invention. They can
be introduced into the chemical vapor deposition chamber in a
variety of manners, such as directly into the vaporization chamber
or in combination with the precursor composition. Although specific
vapor deposition processes are described by reference to FIGS. 1-2,
methods of the present invention are not limited to being used with
the specific vapor deposition systems shown. Various CVD process
chambers or reaction chambers can be used, including hot wall or
cold wall reactors, atmospheric or reduced pressure reactors, as
well as plasma enhanced reactors.
[0039] The use of the mixed metal nitride and boride materials and
methods of forming layers and films of the present invention are
beneficial for a wide variety of applications in semiconductor
structures, particularly those using high dielectric materials or
ferroelectric materials. Such applications include capacitors such
as planar cells, trench cells (e.g., double sidewall trench
capacitors), stacked cells (e.g., crown, V-cell, delta cell,
multi-fingered, or cylindrical container stacked capacitors), as
well as field effect transistor devices, and any semiconductor
device having a silicon-metal interface.
[0040] Examples of fabrication processes for capacitors and other
semiconductor devices containing mixed metal nitride, boride and
nitride-boride barrier layers of the formula
M.sub.xAl.sub.yN.sub.zB.sub.w are described below. It is to be
understood, however, that these processes are only examples of many
possible configurations and processes utilizing the barriers or
electrodes of the invention. For example, in the DRAM cell stacked
container capacitor process described next, a mixed metal nitride
and boride material is utilized as a barrier below the bottom
electrode of a capacitor. Alternatively, the top electrode may also
include a barrier material. The invention is not intended to be
limited by the particular processes described below.
[0041] Referring to FIG. 3, a typical semiconductor wafer fragment
at an early processing step is indicated generally by reference
numeral 100. The semiconductor wafer 100 is comprised of a bulk
silicon substrate 112 with field isolation oxide regions 114 and
active areas 116, 118, 120. Word lines 122, 124, 126, 128 have been
constructed on the wafer 100 in a conventional manner. Each word
line consists of a lower gate oxide 130, a lower poly layer 132, a
higher conductivity silicide layer 134 and an insulating silicon
nitride cap 136. Each word line has also been provided with
insulating spacers 138, also of silicon nitride.
[0042] Two FETs are depicted in FIG. 3. One FET is comprised of two
active areas (source/drain) 116, 118 and one word line (gate) 124.
The second FET is comprised of two active areas (source/drain) 118,
120 and a second word line (gate) 126. The active area 118 common
to both FETs is the active area over which a bit line contact will
be formed.
[0043] Referring to FIG. 4, a thin layer 140 of nitride or TEOS is
provided atop the wafer 100. Next a layer of insulating material
142 is deposited. The insulating material preferably consists of
borophosphosilicate glass (BPSG). The insulating layer 142 is
subsequently planarized by chemical-mechanical polishing (CMP).
[0044] Referring to FIG. 5, a bit line contact opening 144 and
capacitor openings 146 have been formed through the insulating
layer 142. The openings 144, 146 are formed through the insulating
layer 142 by photomasking and dry chemical etching the BPSG
relative to the thin nitride or TEOS layer 140. Referring now to
FIG. 6, a layer 150 of conductive material is deposited to provide
conductive material within the bit line contact and capacitor
openings 144, 146. The conductive layer 150 is in contact with the
active areas 116, 118, 120. An example of the material used to form
layer 150 is in situ arsenic or phosphorous doped poly. Referring
now to FIG. 7, the conductive layer 150 is etched away to the point
that the only remaining material forms plugs 150 over the active
areas 116, 118, 120.
[0045] Referring now to FIG. 8, a thin barrier film 151 of a mixed
metal boride, nitride or boride-nitride of the formula
M.sub.xAl.sub.yN.sub.zB.sub.w as defined above is formed as a
barrier layer atop conductive layer 150. Barrier film 151 is
preferably deposited by CVD to form a conformal layer which
protects the subsequently deposited capacitor dielectric against
diffusion from underlying plug 150 and other surrounding materials.
Perhaps more importantly for some applications of the invention,
barrier film 151 also protects the underlying plug 150 from
diffusion of oxygen from the capacitor dielectric.
[0046] The preferred method for depositing barrier layer 15,
includes positioning the wafer assembly within a vacuum CVD reactor
chamber. In one preferred implementation, the CVD reactor will be a
cold wall reactor. Preferably, the substrate will be heated by a
resistive-type ceramic heater to a temperature of 250-550.degree.
C. Hydrogen gas will inlet to the chamber at a rate of
approximately 50-500 sccm. Subsequently, the metal (M), aluminum,
nitrogen, and boron precursors will be admitted into the CVD
chamber. Preferably, if the metal (M) is Ti, the titanium precursor
will be of the formula Ti(NR.sub.2).sub.4, where R is selected from
the group consisting of H an alkyl and/or aryl group. However, any
suitable organometallic or inorganic titanium containing source may
be substituted for Ti(NR.sub.2).sub.4. In such case, the same gas
will serve as both the titanium and nitrogen precursor. Most
preferably, the titanium precursor will be a titanium
organometallic precursor, having the formula
Ti(N(CH.sub.3).sub.2).sub.4, which is commonly referred to as
TDMAT. The aluminum precursor will preferably be
dimethylethylaminealane, commonly known as DMEAA. However, any
suitable organometallic or inorganic aluminum containing source may
be substituted for DMEAA. Both of these reaction precursors are
liquids at room temperature, and must be bubbled with helium, or
otherwise vaporized, such as through injection into a vaporizer to
facilitate transport as gases into the CVD chamber for deposition
on the substrate. Sources as precursors for Ti, Zr, Hf, V, Nb, Ta,
Cr, Mo and W, can be any suitable metal halide or organometallic
compound containing Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W.
[0047] In a particularly preferred CVD process according to the
present invention, a bubbler will be used for each precursor, and
each bubbler will be held at the same pressure as that within the
CVD chamber. A TDMAT bubbler will preferably be maintained at a
temperature of 35-55.degree. C., with helium being flowed through
at a rate of approximately 20-200 sccm. Simultaneously, the DMEAA
vessel will be maintained at a temperature of approximately
5-30.degree. C., with the helium passed through at a rate of 10-100
sccm. Other systems may be utilized for introducing one or more
precursors into the CVD chamber. For example, in addition to the
use of a vaporizer or evaporator, a precursor may be introduced
into the CVD chamber by direct liquid injection. Additionally,
although the use of gaseous precursors is currently preferred,
precursors may be introduced in vapor or liquid form, such as in
liquid source CVD (LSCVD) operations.
[0048] When deposition is to occur, the precursors are bubbled into
the CVD chamber, and are mixed in a gas distributor, such as a gas
"showerhead", and are directed onto the heated substrate.
Deposition may be continued for the desired period of time. The
metal, aluminum, nitrogen, and boron will thus preferably be
deposited generally simultaneously, as an amorphous material. In
one exemplary implementation, where the
M.sub.xAl.sub.yN.sub.zB.sub.w will be deposited upon a wafer, the
deposition may continue for approximately 3-10 minutes, after which
time the gas flows will be stopped, and the substrate allowed to
cool.
[0049] Although the DMEAA precursor gas is described relative to
the exemplary embodiment above, an aluminum precursor, aluminum
alkyls or alkyl hydride compounds, or their Lewis-based adducts may
also be utilized in their place. Other examples of acceptable
aluminum precursors can be, but are not limited to,
trimethylaluminum, tris(dimethylamino)aluminum,
trimethylaminealane, dimethylalane, or
(dimethylethylamine)dimethylalane.
[0050] Other examples of the exemplary products for titanium
precursors are, but are not limited to: the ethyl analog of TDMAT,
tetrakisdiethylamidotitanium (also conventionally known as TDEAT);
bis(2,4-dimethyl-1,3-pentadienyl)titanium (also conventionally
known as BDPT); titanium tetrachloride; titanium tetrabromide;
titanium tetraiodide; and cyclopentadienylcycloheptatrienyltitanium
(also conventionally known as CpTiChT). Examples of exemplary
products for other metal precursors include CpZr(BH.sub.4).sub.2,
CpHf(BH.sub.4).sub.2, TaCl.sub.5, WF.sub.6, and MoF.sub.6.
[0051] Examples of reactive gas sources for nitrogen and boron
include, but are not limited to NF.sub.3, N.sub.2 (especially with
plasma assist), NH.sub.3, hydrazine, methyl hydrazine,
B.sub.2H.sub.6, and BCl.sub.3.
[0052] Following chemical vapor deposition of a mixed metal nitride
and boride barrier film 151, a layer 152 of conductive material
that will eventually form one of the electrodes of the capacitor is
deposited at a thickness such that the capacitor openings 144, 146
are not closed off. Referring to FIG. 9, the layer 152 may be
formed of various refractive metals, conductive metal oxides, metal
nitrides, noble metals and may include, such as, Pt, Rh, Ir, Ru,
Os, Pd, IrO.sub.2, RhO.sub.2, RuO.sub.2, Ta, TiN, TaN, Ti and
others. The conductive layer 152 is in electrical contact with the
previously formed plugs 150 or, as previously mentioned, the
M.sub.xAl.sub.yN.sub.zB.sub.w layer will itself be the lower
electrode.
[0053] Referring to FIG. 10, the portion of the conductive layer
152 above the top of the BPSG layer 142 is removed through a
planarized etching process, thereby electrically isolating the
portions of layer 152 remaining in the bit line contact and
capacitor openings 144, 146. Referring now to FIG. 11, a capacitor
dielectric layer 154 is provided over conductive layer 152 and
capacitor openings 144, 146.
[0054] Dielectric layer 154 is deposited with a thickness such that
the openings 146 are again not completely filled. Dielectric layer
154 may comprise tantalum pentoxide (Ta.sub.2O.sub.5). Other
suitable dielectric materials such as Strontium Titanate (ST),
Barium Strontium Titanate (BST), Lead Zirconium Titanate (PZT),
Strontium Bismuth Tantalate (SBT) and Bismuth Zirconium Titanate
(BZT) may also be used. Dielectric layer 154 may be deposited by a
low-pressure CVD process using Ta(OC.sub.2H.sub.5).sub.5 and
O.sub.2 at about 430.degree. C., and may be subsequently annealed
in order to reduce leakage current characteristics.
[0055] A second conductive electrode layer 156 is then deposited by
CVD over the dielectric layer 154, again at a thickness which less
than completely fills the capacitor openings 146. The second
conductive layer 156 may be comprised of TiN, Pt, or other
conventional electrode materials, such as many of those previously
described for use as conductive layer 152. In addition to serving
as the top electrode or second plate of the capacitor, the second
conductive layer 156 also forms the interconnection lines between
the second plates of all capacitors.
[0056] Referring to FIG. 12, the second conductive layer 156 and
underlying capacitor dielectric layer 154 are patterned and etched
such that the remaining portions of each group of the first
conductive layer 152, capacitor dielectric layer 154, and second
conductive layer 156 over the bit line contact and capacitor
openings 144, 146 are electrically isolated from each other. In
this manner, each of the active areas 116, 118, 120 are also
electrically isolated (without the influence of the gate).
Furthermore, a portion of the first conductive layer 152 in contact
with the plug 150 over the bit line active area 118 is outwardly
exposed.
[0057] Referring now to FIG. 12, a bit line insulating layer 158 is
provided over the second conductive layer 156 and into the bit line
contact opening 144. The bit line insulating layer 158 is
preferably comprised of BPSG. The BPSG is typically reflowed by
conventional techniques, i.e., heating to about 800.degree. C.
Other insulating layers such as PSG, or other compositions of doped
SiO.sub.2 may similarly be employed as the insulating layer
158.
[0058] Referring to FIG. 13, a bit line contact opening 160 is
patterned through the bit line insulating layer 158 such that the
barrier film 151 above plug conductive layer 150 is once again
outwardly exposed. Then a bit line contact is provided in the bit
line contact opening 160 such that the bit line contact is in
electrical contact with the outwardly exposed portion of the
barrier film 151 above conductive plug layer 150. Thus, the plug
150 over the active area 118 common to both FETs acts as a bit line
contact. The DRAM array and associated circuitry may then be
completed by a variety of well established techniques, such as
metalization, and attachment to peripheral circuitry.
[0059] Another specific example of where a film formed from the
M.sub.xAl.sub.yN.sub.zB.sub.w materials of the present invention is
useful is the ferroelectric memory cell 310 of FIG. 14. The memory
cell 310 includes a ferroelectric material 311, which is prepared
by depositing one or more of the materials discussed herein
preferably using chemical vapor techniques, between two electrodes
312 and 313, which are typically made of platinum, although other
metals such as gold or aluminum can also be used. The bottom
electrode 313 is typically in contact with a silicon-containing
layer 314, such as an n-type or p-type silicon substrate, silicon
dioxide, glass, etc. A conductive mixed metal nitride and boride
barrier layer 315, preferably deposited by CVD, is positioned
between the bottom electrode 313 and the silicon-containing layer
314 to act as a barrier layer to diffusion of atoms such as silicon
into the electrode and ferroelectric material.
[0060] Yet another specific example of where a film formed from the
material of the present invention is useful is the structure shown
in FIG. 15. The substrate 416 may be in the form of an n-channel
MOSFET (n-channel metal-oxide semiconductor field-effect
transistor), which may be used in a DRAM memory device. As shown,
substrate 416 is a p-type silicon having two n-type silicon islands
420 and 422, representing the transistor source and drain. Such a
construction is well known. The gate for the transistor is formed
by a metal/polysilicon layer 424 deposited over a silicon dioxide
layer 426. A relatively thick layer of an insulating silicon
dioxide 428 overlies the active areas on substrate 416.
[0061] To connect the MOSFET of FIG. 15 with conductive paths on
the surface of the device, contacts 430 and 432 have been etched
through oxide layer 428 down to the surface of substrate 416. A
metal or metal silicide layer 434, such as titanium silicide, is
deposited and formed at the base of contacts 430 and 432. A thin,
conformal barrier layer of a mixed metal boride and nitride 436 is
deposited by CVD over the walls of the contacts. Because of the
presence of the conductive barrier layer, the electrical contact
path is excellent and the aluminum metal 438 which is deposited
over the mixed metal boride and nitride barrier layer 436 is
prevented from attacking the substrate surfaces.
[0062] In still another example, as depicted in FIG. 16, after
deposition of the M.sub.xAl.sub.yN.sub.zB.sub.w barrier layer 516
within the opening within layer 514, a conductive layer 518 may be
deposited to fill the cavity formed in layer 514 over the substrate
contact region 515. Conductive layer 518 may be, for example,
aluminum or tungsten. Subsequently, layers 516 and 518 may removed,
such as by being patterned and etched in a desired manner to form
interconnects between substrate regions. Alternatively, conductive
layer 518 and barrier layer 516 could be etched away to form a
conductive plug structure as shown in FIG. 17.
[0063] The mixed-metal nitride and boride barrier layer and
electrode materials according to the invention have excellent
conductivity, and therefor reduce depletion effects and enhance
frequency response. The materials possess excellent barrier
properties for protection of cell dielectrics and substrate during
oxidation/recrystallization steps for dielectrics and during BPGS
reflow and other high temperature steps after capacitor formation.
In addition, the barriers according to the invention also
substantially prevent diffusion to protect cell dielectrics from
interaction with Si and other surrounding materials which may
degrade the dielectric materials or produce an additional SiO.sub.2
dielectric layer. Thus, the barriers/electrodes of the invention
are not limited to use as barrier films for bottom electrodes, but
may also be employed both as top and bottom electrodes, and as
additional barrier layers applied to any other top and/or bottom
electrodes. The compositions and methods of forming barrier films
of the present invention are also beneficial for a wide variety of
thin film applications in integrated circuit structures,
particularly those using high dielectric materials and/or
silicon-metal interfaces. The method of the preferred embodiments
of the invention prevent degradation of an electrical connection
between a conductive layer and a semiconductor substrate by
providing a diffusion barrier between the two regions.
[0064] Accordingly, the above description and accompanying drawings
are only illustrative of preferred embodiments which can achieve
and provide the objects, features and advantages of the present
invention. It is not intended that the invention be limited to the
embodiments shown and described in detail herein. The invention is
only limited by the spirit and scope of the following claims.
* * * * *