U.S. patent application number 09/397763 was filed with the patent office on 2001-08-16 for forming a conductive structure in a semiconductor device.
Invention is credited to BECK, JAMES, HU, YONGJUN JEFF, PAN, PAI HUNG, RATAKONDA, DEEPA, THAKUR, RANDHIR P.S., WEIMER, RONALD A..
Application Number | 20010014522 09/397763 |
Document ID | / |
Family ID | 21859302 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014522 |
Kind Code |
A1 |
WEIMER, RONALD A. ; et
al. |
August 16, 2001 |
FORMING A CONDUCTIVE STRUCTURE IN A SEMICONDUCTOR DEVICE
Abstract
A conductive structure for use in a semiconductor device
includes a multilayer structure. A first layer includes a material
containing silicon, e.g., polysilicon and silicon germanide. A
barrier layer is formed over the first layer, with the barrier
layer including metal silicide or metal silicide nitride. A top
conductive layer is formed over the barrier layer. The top
conductive layer can include metal or metal silicide. Selective
oxidation can be performed to reduce the amount of oxidation of
selected materials in a structure containing multiple layers, such
as the multilayer conductive structure. The selective oxidation is
performed in a single-wafer rapid thermal processing system, in
which a selected ambient, including hydrogen, is used to ensure low
oxidation of a selected material, such as tungsten or a metal
nitride.
Inventors: |
WEIMER, RONALD A.; (BOISE,
ID) ; HU, YONGJUN JEFF; (BOISE, ID) ; PAN, PAI
HUNG; (BOISE, ID) ; RATAKONDA, DEEPA; (BOISE,
ID) ; BECK, JAMES; (BOISE, ID) ; THAKUR,
RANDHIR P.S.; (CAPERTINO, CA) |
Correspondence
Address: |
DAN C HU
TROP PRUNER HU & MILES PC
8554 KATY FREEWAY
SUITE 100
HOUSTON
TX
77024
|
Family ID: |
21859302 |
Appl. No.: |
09/397763 |
Filed: |
September 15, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09397763 |
Sep 15, 1999 |
|
|
|
09031407 |
Feb 26, 1998 |
|
|
|
Current U.S.
Class: |
438/591 ;
118/724; 257/E21.2; 257/E21.201; 257/E21.301; 257/E29.157; 438/653;
438/655 |
Current CPC
Class: |
H01L 21/28061 20130101;
H01L 21/32105 20130101; H01L 21/2807 20130101; H01L 29/4941
20130101 |
Class at
Publication: |
438/591 ;
438/653; 438/655; 118/724 |
International
Class: |
H01L 021/3205; H01L
021/4763; H01L 021/44 |
Claims
What is claimed is:
1. A method of forming a multi-layer conductive structure in a
semiconductor device, the method comprising: forming a first layer
containing silicon; depositing a metal layer over the first layer;
and annealing the metal layer in an ambient having a composition
selected from a group consisting of nitrogen, NH.sub.3, and
hydrazine, wherein a second layer containing silicide is formed
over the first layer after annealing.
2. The method of claim 1, wherein the second layer contains a metal
silicide nitride composition.
3. The method of claim 1, further comprising forming a top
conductive layer over the second layer.
4. The method of claim 3, wherein the first layer, second layer,
and top conductive layer form the multi-layer conductive
structure.
5. A method of forming a conductive structure in a semiconductor
device, the method comprising: forming a lower electrically
conductive layer on a support surface; forming an electrically
conductive barrier layer over the lower layer; and forming an upper
conductive layer over the barrier layer, the upper conductive layer
including metal silicide.
6. The method of claim 5, wherein the lower layer includes
silicon.
7. The method of claim 5, wherein the lower layer includes a
material selected from the group consisting of polysilicon, SiGex,
and amorphous silicon.
8. The method of claim 5, wherein the barrier layer includes a
metal silicide composition.
9. The method of claim 5, wherein the barrier layer includes a
metal silicide nitride composition.
10. The method of claim 5, wherein the upper conductive layer
includes a material selected from the group consisting of TiSix,
CoSix, NiSix, and PdSix.
11. A method of forming a conductive structure in a semiconductor
device, comprising: forming a first electrically conductive layer
on a base; forming a barrier layer over the first layer, the
barrier layer including a metal silicide; and forming a second
electrically conductive layer over the barrier layer.
12. The method of claim 11, wherein the barrier layer includes
tungsten silicide.
13. The method of claim 11, wherein forming the barrier layer
includes using chemical vapor deposition.
14. The method of claim 11, wherein forming the barrier layer
includes using physical vapor deposition.
15. The method of claim 11, wherein forming the barrier layer
includes depositing a metal on a layer containing silicon and
controlling the metal-silicon structure in a preselected
ambient.
16. The method of claim 15, wherein the preselected ambient
includes NH.sub.3.
17. The method of claim 15, wherein the preselected ambient
includes hydrazine.
18. The method of claim 15, wherein the preselected ambient
includes nitrogen.
19. A method of oxidizing layers formed on a base of a
semiconductor device, the layers including a first layer containing
silicon, the method comprising: generating a predetermined mixture
of H.sub.2 and H.sub.2O; providing the mixture to a single-wafer
thermal processing chamber; and heating the chamber to selectively
oxidize the first layer over one or more other layers.
20. The method of claim 19, further comprising: generating a flow
of a mixture containing H.sub.2O vapor and H.sub.2 by injecting an
inert gas.
21. The method of claim 20, wherein the inert gas includes
Argon.
22. The method of claim 19, further comprising: filling a vessel
with deionized water; and heating the vessel to evaporate a portion
of the water.
23. The method of claim 22, wherein injecting the inert gas
includes injecting the inert gas into the vessel.
24. The method of claim 19, wherein heating the processing chamber
includes heating the processing chamber to a temperature between
about 950.degree. C. and 1100.degree. C.
25. The method of claim 19, wherein generating the mixture of
H.sub.2 and H.sub.2O includes injecting H.sub.2 and O.sub.2 vapor
into a heating element.
26. The method of claim 25, wherein the heating element includes a
torch heater assembly.
27. The method of claim 26, further comprising maintaining the
torch heater assembly at a temperature above about 900.degree. C.
to provide ignition energy.
28. The method of claim 19, wherein the one or more other layers
include tungsten.
29. The method of claim 19, wherein the one or more other layers
include a metal nitride.
30. The method of claim 34, wherein the one or more other layers
include a stack containing second and third layers formed over the
first layer, the second and third layers both being electrically
conductive.
31. An oxidation system for oxidizing layers formed on a base of a
semiconductor device, a first layer containing silicon, the
oxidation system comprising: a source of H.sub.2 vapor; a source of
H.sub.2O vapor; a flow controller connected to deliver a mixture of
H.sub.2O and H.sub.2; and a process chamber in which the
semiconductor device is placed, the process chamber connected to
receive the mixture of H.sub.2O and H.sub.2 to perform selective
oxidation of the first layer over the other layers.
32. The system of claim 31, wherein the source of H.sub.2O vapor
includes a vessel containing water heated to evaporate a portion of
the water.
33. The system of claim 32, wherein the inert gas is injected into
the vessel.
34. The system of claim 32, wherein the H.sub.2 vapor is injected
with the inert gas.
35. The system of claim 31, wherein the H.sub.2O/H.sub.2 mixture
has a partial pressure ratio of between about 2.3 and 2.8.
36. The system of claim 35, wherein the process chamber is heated
to a temperature between about 950.degree. C. and 1100.degree.
C.
37. The system of claim 31, wherein the process chamber is a
single-wafer process chamber.
38. The method of claim 31, wherein the other layers include
tungsten.
39. The method of claim 31, wherein the other layers include a
metal nitride.
40. A selective oxidation system for oxidizing layers formed on a
base of a semiconductor device, a first layer containing silicon,
the system comprising: a source of H.sub.2 vapor; a source of
O.sub.2 vapor; a heating element connected to receive H.sub.2 vapor
and O.sub.2 vapor, the heating element being heated to generate a
mixture of H.sub.2O and H.sub.2 having a predetermined partial
pressure ratio; and a process chamber in which the semiconductor
device is place, the process chamber connected to receive the
mixture of H.sub.2O and H.sub.2 to perform selective oxidation of
the first layer over the other layers.
41. The system of claim 40, wherein the heating element is heated
to above a predetermined temperature to generate H.sub.2O
vapor.
42. The system of claim 40, wherein the heating element includes a
torch heater assembly.
43. The system of claim 42, wherein the torch heater assembly is
maintained at a temperature above about 700.degree. C. to provide
ignition energy.
Description
[0001] This is a divisional of co-pending and commonly assigned
U.S. patent application Ser. No. 09/031,407, entitled "Forming a
Conductive Structure in a Semiconductor Device," filed Feb. 26,
1998.
BACKGROUND
[0002] The invention relates to forming a conductive structure in a
semiconductor device.
[0003] Advanced integrated circuits in a semiconductor device
require high speed interconnecting lines between circuits for
improved device speed. Interconnecting lines are typically made of
metal, e.g., aluminum, titanium. However, in some parts of a
semiconductor device, particularly in regions where components are
densely packed (such as the array of a memory device), or in
regions where further heat steps are needed after formation of the
interconnecting line during the manufacturing process, other
materials are also widely used to form interconnecting lines, e.g.,
doped polysilicon or N+ or P+ diffused regions.
[0004] The different types of interconnecting lines exhibit
different resistivities, with metal generally having the lowest
resistivity. Polysilicon, which is also typically used as the
conductive electrode at the gate of an N-channel or P-channel
metal-oxide-silicon field effect transistor (MOSFET), exhibits a
higher resistivity than metal.
[0005] As the speed requirements of semiconductors increase, the
resistance of interconnecting lines, especially those formed of a
higher resistivity material (such as polysilicon) reduces switching
speeds of circuits in the device. The resistance of a line
increases proportionately with its length. Thus, a polysilicon line
running over a long length and connected to a large capacitive
load, such as a wordline in a memory array connected to multiple
transistors in the array, would cause a high RC delay during
circuit switching.
[0006] One approach to reduce the resistivity of a polysilicon
interconnect line is to use a polycide structure, in which a low
resistance silicide (e.g., WSix) is formed on top of a doped
polysilicon layer. This effectively forms a two-layer interconnect
line in which the silicide layer provides a low resistivity
conductive path.
[0007] Three-layer interconnecting lines have also been proposed,
including a polymetal composite structure having tungsten (W) as
the top layer, tungsten silicide nitride (WSiN) as the intermediate
layer, and polysilicon as the bottom layer. The polymetal structure
has a resistivity lower than the polycide structure that includes
tungsten silicide on polysilicon.
SUMMARY
[0008] In general, according to one embodiment, a method of forming
a conductive structure in a semiconductor device includes forming a
lower electrically conductive layer on a support surface and
forming an electrically conductive barrier over the lower layer.
Further, an upper conductive layer is formed over the barrier
layer, the upper conductive layer including metal silicide.
[0009] Other features and embodiments will become apparent from the
following description and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an enlarged, cross-sectional view of a transistor
in a semiconductor device.
[0011] FIG. 2 is a flow diagram of the fabrication steps for
forming portions of the transistor structure of FIG. 1.
[0012] FIGS. 3, 4, and 5 are block diagrams of single-wafer rapid
thermal processing systems for performing selective oxidation.
[0013] FIG. 6 is graph of an X-ray photoelectron spectrometer (XPS)
surface analysis showing the selective oxidation region for a
multilayer conductive structure.
DETAILED DESCRIPTION
[0014] Referring to FIG. 1, a multilayer, low resistivity
conductive structure is described. The conductive structure can be
used as part of the gate structure of a MOS transistor (as shown)
or as an interconnecting line to connect circuits, such as a
wordline used to connect transistors connected to memory cells in a
memory array.
[0015] In FIG. 1, a transistor 12 is formed on a base 10, which
includes a semiconductor (e.g., silicon) substrate or multilayer
substrate (e.g., silicon-on-insulator or SOI substrate). The
transistor 12 is adjacent a field oxide layer 110. The transistor
includes source and drain regions 108A and 108B and a channel
region 109. If the transistor 12 is used in a memory array, the
source would be connected to a memory cell capacitor structure (not
shown), while the drain would be connected to a digit line (not
shown). The transistor 12 can also have many other uses in a
semiconductor device.
[0016] A gate oxide layer 106 is formed above the channel region
109. A gate stack 112 is then formed over the gate oxide layer 106.
In one embodiment, the gate structure 112 includes three
electrically conductive layers (100, 102, 104) to reduce the
resistivity of the gate. The three-layer structure can also be used
to form an interconnecting line separate from the transistor 12, in
which case the gate oxide layer 106 beneath the stack 112 would be
replaced with other insulating layers.
[0017] The bottom conductive layer 104 is formed of a material that
includes silicon, e.g., doped or undoped polysilicon, silicon
germanium (SiGex), or amorphous silicon. The top conductive layer
100 includes a low resistivity material, which can be metal or
metal silicide. Sandwiched between the top layer 100 and the bottom
layer 104 is a conductive diffusion barrier layer 102 that is
resistant to oxidation, agglomeration, and silicidation.
[0018] The barrier layer 102 acts to prevent agglomeration of
silicon from the bottom layer 104 into the top conductive layer
100. For example, titanium silicide (TiSix) formed on polysilicon
may result in agglomeration of silicon into the TiSix grains, which
can increase resistivity. Silicidation can also occur between
certain top layer and bottom layer materials, such as tungsten (W)
formed on polysilicon, in which formation of higher resistivity
Wsix can occur.
[0019] The barrier layer 102 is formed of a material that includes
metal silicide, metal nitride, or metal silicide nitride, such as
tungsten silicide (Wsix), tungsten silicide nitride (WSixNy),
titanium silicide nitride (TiSixNy), tantalum silicide (TaSix),
tantalum silicide nitride (TaSixNy), molybdenum silicide (MoSix),
and molybdenum silicide nitride (MoSixNy), hafnium silicide
(HfSix), hafnium silicide nitride (HfSixNy), zirconium silicide
nitride (ZrSixNy), niobium silicide (NbSix), niobium silicide
nitride (NbSixNy), and titanium nitride (TiNy).
[0020] Generally, a silicide, nitride, or silicide nitride
composition is resistant to oxidation and is stable at high
temperatures. The ability to withstand high temperatures is
particularly important since the gate structure or interconnecting
line is put through various subsequent high temperature process
steps, including source-drain implant anneal, oxidation, and glass
flow/reflow.
[0021] Metal silicides, nitrides, or silicide nitrides also have
other desirable properties, including low resistivity, ease of
formation, controlled oxidation properties, and stability in an
oxidizing ambient. These materials also have excellent adhesion
characteristics and exhibit low stress contacts.
[0022] The resistivity of a metal silicide, metal nitride, or metal
silicide nitride barrier layer 102 is dependent on several factors,
including the method of formation, annealing times and
temperatures, and chemical purity. The stoichiometry of the
refractory metal silicide, metal nitride, or metal silicide nitride
composition can also affect resistivity; e.g., the x value of an
MSix composition and the x and y values of an MSixNy composition
can affect the resistivity.
[0023] In the barrier layer 102 containing an MSixNy composition,
the value of x for silicon can be set at a value greater than 2,
while the value of y for nitrogen is set in the range between about
0.1 and 0.9, preferably between about 0.5-0.6. With higher y
values, the MSixNy compositions are more stable at higher
temperatures, but the compositions also have higher
resistivities.
[0024] The top conductive layer 100 can be made from low
resistivity materials, e.g., metal or metal suicides, such as
tungsten (W), cobalt (Co), titanium silicide (TiSix), cobalt
silicide (CoSix), nickel silicide (NiSix), or other metal or metal
silicide layers. Typically, the value of x may be greater than or
equal to 2, with the exception of NiSix, where x can be equal to
one. Generally, the metal silicide compositions are more stable at
high temperatures than tungsten or cobalt, which tend to have
relatively high oxidation rates.
[0025] The gate stack 112 and the gate oxide 106 are electrically
insulated by side insulating spacers 114A and 114B and a top
insulating layer 116. The insulating materials can be formed using
silicon nitride (Si.sub.3N.sub.4) or silicon dioxide
(SiO.sub.2).
[0026] Referring to FIG. 2, the fabrication flow of portions of the
transistor 12 shown in FIG. 1 is illustrated. After the field oxide
110 and source-drain regions 108A and 108B are formed in the base
10, the gate oxide 106 is formed on the surface of the base 10
(step 202) by thermal growth or deposition such as chemical vapor
deposition (CVD). The thickness of the gate oxide 106, for current
generation technologies, can typically range from about 30
angstroms (A) to 150 A.
[0027] Next, the bottom conductive layer 104 (which can include
polysilicon, SiGex, or amorphous silicon) is formed, such as by
deposition using a low pressure chemical vapor deposition (LPCVD)
process. The bottom conductive layer 104 can have an exemplary
thickness ranging from about 100 A to 3,000 A. The polysilicon,
SiGex, or amorphous silicon layer 104 can also be doped with a
dopant such as phosphorous or boron to improve electrical
conductivity.
[0028] Next, the barrier layer 102 is formed (step 206) to a
thickness between about 50 A to 500 A, for example. Various methods
can be used to form the diffusion barrier layer 102, including
using chemical vapor deposition (CVD), physical vapor deposition
(PVD), or deposition followed by a high temperature anneal of a
metal (e.g., tungsten or titanium) in an ambient containing
nitrogen, ammonia (NH.sub.3), or hydrazine (N.sub.2H.sub.4) in a
rapid thermal processing (RTP) system.
[0029] Formation of metal silicide barrier layers using CVD may
involve deposition of the metal onto the bottom conductive layer
104 followed by subsequent heating, which causes the metal and
silicon containing material in the layer 104 to react to form a
silicide. This type of silicide formation can yield low resistivity
silicide layers.
[0030] To form a barrier layer 102 having metal silicide nitride
(MSixNy) or metal nitride (MNy), the metal deposition onto the
bottom conductive layer step is followed by a high temperature
(e.g., 600-1000.degree. C.) anneal in an ambient including NH.sub.3
or N.sub.2H.sub.4. The NH.sub.3 or N.sub.2H.sub.4 anneal can be
performed in a rapid thermal processing (RTP) system for a
predetermined amount of time, e.g., between about 1-60 seconds. If
the metal deposited is tungsten on a polysilicon, SiGex, or
amorphous silicon layer, the anneal step forms a barrier layer that
contains Wsix and SiN, with no formation (or very little formation)
of tungsten nitride (WN), as illustrated by the X-ray photoelectron
spectrometer (XPS) profile graph shown in FIG. 6. Wsix and SiN are
more oxidation resistant than WN or tungsten. The high temperature
anneal can also be performed with a titanium on a
silicon-containing material structure. The anneal in the NH.sub.3
or N.sub.2H.sub.4 ambient forms a TiNy barrier layer.
[0031] FIG. 6 shows the percentage of materials present in a
Wsix-polysilicon stack after anneal of a W/poly-Si structure in an
NH.sub.3 ambient at 750.degree. C. The depth (as defined by an axis
generally projecting perpendicularly from the surface of the base
10) begins at the top surface (0 .ANG.) of the stack 112 (without
the top conductive layer 100) and continues downwardly into the
stack. A layer of tungsten is initially deposited on polysilicon.
After anneal in the NH.sub.3, the layers formed include a tungsten
layer 100 at the top and a Wsixny barrier layer 102 between the top
tungsten layer and the bottom conductive layer 104.
[0032] PVD by sputtering or evaporation can also be used to form
metal silicides and metal silicide nitrides. The evaporation method
utilizes simultaneous deposition of the metal and silicon (or
metal, silicon and nitrogen) under high vacuum or sputtering of a
metal silicide composite target. Sputtering of the metal and
silicon (or metal, Si, and N) can be performed using RF or
magnetron sputtering.
[0033] After formation of the barrier layer 102, the metal or metal
silicide conductive layer 100 is formed over the barrier layer 102
(step 208), using either CVD or PVD techniques, for example. The
conductive layer 100 can be formed to a thickness between about 200
A to 2000 A. Following formation of the top conductive layer 100,
the electrically insulating cap layer 116 is formed over the
conductive layer 100 as an etch stop and oxidation barrier (step
210). The insulating layer 116 can be formed using vapor deposited
SiO.sub.2 or Si.sub.3N.sub.4. A dry etch process (such as reactive
ion etching) is then used to form the gate stack (step 212).
[0034] After the gate stack is formed, nitride insulating spacers
114A and 114B can optionally be formed using known methods, such as
by LPCVD or PECVD nitride (step 214). Oxide spacers can also be
used, such as those formed using CVD with tetraethylorthosilicate
(TEOS). Whether this step is performed depends on the type of
materials used in forming the stack 112.
[0035] For example, if a stack having a tungsten conductor on a
titanium nitride barrier is used, then the spacers are useful as
etch barriers as well as oxidation barriers in subsequent
processing steps. The spacers 116A and 116B may also be used with
other stacks that contain a metal conductor on a metal silicide or
nitride barrier.
[0036] The spacer forming step 214 may not be needed when a stack
having a metal silicide conductor on a metal silicide or metal
silicide nitride barrier (e.g., TiSix conductor on Wsix barrier) is
used. With such stacks, the spacer formation is performed after the
source-drain re-oxidation step (216).
[0037] The source-drain re-oxidation step (216) is performed to
remove damage caused by reactive ion etching and patterning of the
gate electrode. The re-oxidation step causes oxide to be thermally
grown on the sidewall of the etched polysilicon, SiGex, or
amorphous silicon electrode, which also serves to thicken the gate
oxide 106 at the gate edge to improve the gate oxide dielectric
strength. The source-drain re-oxidation can be performed in the
following environment: O.sub.2; O.sub.2/H.sub.2; N.sub.2O; NO; or a
selective ambient, such as an H.sub.2O/H.sub.2 ambient in which the
ratio of H.sub.2O to H.sub.2 is controlled to predetermined
ranges.
[0038] If the top conductive layer 100 is formed of a metal
silicide material, and the barrier layer 102 is formed of a metal
silicide or metal silicide nitride material, then the two layers
are relatively resistant to oxidation and any of the source-drain
re-oxidation techniques listed above can be used. However, certain
materials that can be used in the top conduction layer 100, such as
tungsten (W) or titanium (Ti), and certain materials in the barrier
layer 102, such as a metal nitride (e.g., TiN), have relatively
high oxidation rates.
[0039] For example, tungsten oxidation rate is much faster than
that of silicon, and typical oxidation processes can cause the
volume of tungsten oxide (WO.sub.3) to be much larger than that of
W. If WO.sub.3 formation occurs, peeling or morphological
degradation of the tungsten film may occur. Thus, in cases where
the top conduction layer 100 has a relatively high oxidation rate,
a selective oxidation process is preferred over conventional
oxidation or wet oxidation. Similar issues exist when titanium is
used as the top conduction layer 100.
[0040] Possible metal nitride materials (in addition to the
materials discussed above) for the barrier layer 102 include
tungsten nitride (WN) or titanium nitride (TiN), which are
susceptible to relatively fast oxidation. If such barrier layers
are used, then selective oxidation may be particularly
advantageous. However, even if metal silicide top conductive layers
100 or metal silicide or metal silicide nitride barrier layers 102
are used, the selective oxidation process may also help to reduce
the rate of oxidation of those materials.
[0041] Selective source drain re-oxidation can be performed in a
water vapor ambient with controlled amounts of hydrogen added in a
single-wafer rapid thermal processing (RTP) system (e.g., an AG8108
Heat Pulse RTP system) for selective oxidation of silicon over the
metal, metal silicide, metal silicide nitride, or metal nitride top
conducting layer 100 or barrier layer 102. In addition, use of a
single-wafer system, such as the three types shown in FIGS. 3-5,
provide several advantages over use of a furnace that can receive
multiple wafers. In a single-wafer RTP system, better control of
process conditions can be achieved. For example, better uniformity
of temperature can be achieved over the entire surface of the
wafer, which is particularly advantageous when large wafers (e.g.,
300 mm wafers) are used. In addition, better ambient control and
uniformity of oxidation over the entire processed surface of a
wafer can be achieved.
[0042] The described selective oxidation processes (shown in FIGS.
3, 4, and 5) can also be applied to multi-wafer furnace
systems.
[0043] Referring to FIG. 3, an RTP single-wafer system uses an
ambient of argon-hydrogen (Ar--H.sub.2) and water vapor. Other
inert gases besides Ar can also be used. By controlling the ratio
of H.sub.2O to O.sub.2, use of this ambient can reduce oxidation of
a metal (e.g., tungsten) top conductive layer 100 and WN, Wsixny,
TiN, and other metal nitride conductive diffusion barrier layers
102.
[0044] A quartz vessel 300 (which can contain 20 liters of liquid)
is filled approximately half full of deionized water through a
liquid flow controller 304 from a source 306. The vessel 300 is
then heated and maintained at an elevated temperature, e.g.,
between about 95-98.degree. C., through use of an external heating
blanket 314 affixed to the outside of the quartz vessel 300. The
elevated temperature evaporates portions of the deionized
water.
[0045] The temperature of the deionized water in the vessel 300 is
monitored by a thermocouple 308 inserted into a sheath in the
quartz vessel 300. The over temperature trip level of the
thermocouple 308 can be set at about 120.degree. C. The
thermocouple 308 is connected to a temperature and water level
controller 310 for monitoring. The controller 310 adjusts the
temperature of the blanket 314 as the liquid temperature in the
vessel 300 varies. Over temperature thermocouples (not shown) can
also monitor the heater blanket 314 temperature to prevent heater
blanket temperature runaway.
[0046] The level of the deionized water in the vessel 300 is
monitored by a liquid level sensor 312, also connected to the
controller 310. The controller 310 adjusts the flow rate through
the flow controller 304 to maintain the level of the liquid in the
vessel 300. The autofill feature for the deionized water is
disabled during a process run (to perform the source drain
re-oxidation) so as not to disturb the water vapor delivery.
[0047] Delivery of the deionized water vapor is achieved by
injecting an Ar--H.sub.2 mixture into the vessel 300 through a mass
flow controller 322 at a predetermined rate. The Ar--H.sub.2 comes
from a source 318. The H.sub.2 can originate from a pure hydrogen
source or from a breakdown of a hydrogen containing compound such
as NH.sub.3 or N.sub.2H.sub.4. The resulting water and argon vapor
is transported through a line 316 (which can be a {fraction (1/2)}
inch heat taped stainless steel line) maintained at a predetermined
temperature, e.g., about 110.degree. C., to prevent recondensation
of the vapor.
[0048] The vapor in the line 316 flows through a vapor flow
controller 324 to a single-wafer process chamber 302. Other
conventional RTP process gases are also provided through flow
controllers 326 to the processor chamber 302. The flow of H.sub.2O
can be selected to be in the range between about 1 SCCM (standard
cubic centimeters per minute) and 50 SLM (standard liters per
minute), with a preferred range of about 1 SCCM to 10 SLM. The flow
rate of H.sub.2 can be selected to a value in the range between
about 1 SCCM and 50 SLM, with a preferred range of about 1 SCCM to
20 SLM. In the AG8108 system, the H.sub.2O/H.sub.2 partial pressure
ratio can be maintained between about 2.3 and 2.8. However, the
ratios vary according to the specific types of RTP systems used.
The processing temperature in the single-wafer processing chamber
can be maintained between about 950.degree. C. and 1100.degree. C.
Selective oxidation of silicon over tungsten of about 2:1 can be
achieved using the system of FIG. 3.
[0049] Referring to FIG. 4, an alternative single-wafer RTP system
performs source-drain selective re-oxidation using a different
transport system. Elements that are the same as in the RTP system
of FIG. 1 have common reference numerals. As in the RTP system of
FIG. 1, a predetermined amount of deionized water is kept in the
vessel 300 (e.g., half full in a 20-liter vessel). However,
delivery of the deionized water vapor is achieved through the use
of a vapor flow controller 330, rather than through use of the mass
flow controller 322 to pump argon 318 into the vessel 300 to move
vapor through the line 316. The pressure in the water vessel 300
can be approximately 960 Torr, which is sufficient to generate
ample flow through the vapor flow controller 330. The vapor is then
transported through the line 316 to the process chamber 302, with
the line temperature maintained at about 110.degree. C. to prevent
recondensation of the vapor. Hydrogen is passed through one of the
vapor flow controllers 326 to the process chamber 302 to perform
selective oxidation of silicon over other materials.
[0050] Referring to FIG. 5, an RTP system with an external torch
assembly is used to create the water vapor flow for selective
oxidation. Hydrogen (H.sub.2) and oxygen (O.sub.2) are delivered
through vapor flow controllers 350 and 352, respectively, from
sources 354 and 356, respectively. The H.sub.2 and O.sub.2 are
delivered to an injector 360 inserted into the external torch
assembly 358. The torch assembly 358 is maintained at a temperature
of about 900.degree. C. to provide ignition energy. The resulting
water vapor and H.sub.2 mixture is delivered to the single-wafer
process chamber 302 via a quartz tube interface 362.
[0051] As is the case with the RTP system of FIG. 3, the RTP
systems of FIGS. 4 and 5 also maintain a predetermined
H.sub.2O/H.sub.2 partial pressure ratio and temperature.
[0052] In the RTP system of FIG. 5, safety measures are provided by
an external controller 364, which monitors and maintains the
external torch element temperature and provides over temperature
and runaway safeties. The controller 364 can also implement steps
to ensure safety associated with using H.sub.2 as a process gas.
The safety mechanisms implemented include maintaining a particular
H.sub.2/O.sub.2 ratio. Thus, H.sub.2 flow is disabled if no O.sub.2
is present; H.sub.2 is disabled if the torch temperature is below
700.degree. C.; an initial nitrogen (N.sub.2) purge is performed of
the injector 360 before the flow of H.sub.2 is turned on; and
H.sub.2 leak detectors are used to determine when to turn off and
purge the H.sub.2 line if an H.sub.2 leak is detected. The
controller 364 also monitors the temperature of the process chamber
302 to prevent water vapor from being formed if the process chamber
302 is below 700.degree. C. to prevent recondensation of the water
vapor.
[0053] Other embodiments are also within the scope of the following
claims. Although the layers in the multilayer conductive structure
have been described with certain thicknesses for each layer, it is
contemplated that the layer thicknesses can be varied and still
achieve desirable results. The conductive structure described can
be formed with a stack having more than three layers. Further,
various systems and processes have been described with particular
parameters; these parameters can also be varied. The systems
described have components associated with certain, specific
parameters and values, which can be varied.
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