U.S. patent application number 09/296889 was filed with the patent office on 2002-01-31 for chemistry for chemical vapor deposition of titanium containing films.
Invention is credited to IRELAND, PHILIP J., RHODES, HOWARD E., SANDHU, GURTEJ S., SHARAN, SUJIT.
Application Number | 20020013050 09/296889 |
Document ID | / |
Family ID | 23143998 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013050 |
Kind Code |
A1 |
SHARAN, SUJIT ; et
al. |
January 31, 2002 |
CHEMISTRY FOR CHEMICAL VAPOR DEPOSITION OF TITANIUM CONTAINING
FILMS
Abstract
Titanium-containing films exhibiting excellent uniformity and
step coverage are deposited on semiconductor wafers in a cold wall
reactor which has been modified to discharge plasma into the
reaction chamber. Titanium tetrabromide, titanium tetraiodide, or
titanium tetrachloride, along with hydrogen, enter the reaction
chamber and come in contact with a heated semiconductor wafer,
thereby depositing a thin titanium-containing film on the wafer's
surface. Step coverage and deposition rate are enhanced by the
presence of the plasma. The use of titanium tetrabromide or
titanium tetraiodide instead of titanium tetrachloride also
increases the deposition rate and allows for a lower reaction
temperature. Titanium silicide and titanium nitride can also be
deposited by this method by varying the gas incorporated with the
titanium precursors.
Inventors: |
SHARAN, SUJIT; (BOISE,
ID) ; RHODES, HOWARD E.; (BOISE, ID) ;
IRELAND, PHILIP J.; (NAMPA, ID) ; SANDHU, GURTEJ
S.; (BOISE, ID) |
Correspondence
Address: |
MICHAEL G FLETCHER
FLETCHER YODER & VAN SOMEREN
P O BOX 692289
HOUSTON
TX
772692289
|
Family ID: |
23143998 |
Appl. No.: |
09/296889 |
Filed: |
April 22, 1999 |
Current U.S.
Class: |
438/680 ;
257/E21.168; 438/503; 438/507; 438/656; 438/677; 438/685 |
Current CPC
Class: |
C23C 16/34 20130101;
H01L 21/76843 20130101; C23C 16/14 20130101; H01L 21/28568
20130101; C23C 16/42 20130101 |
Class at
Publication: |
438/680 ;
438/685; 438/656; 438/503; 438/507; 438/677 |
International
Class: |
H01L 021/44; H01L
021/20; H01L 021/36 |
Claims
What is claimed is:
1. A chemical vapor deposition process for depositing a titanium
containing film on a substrate, the process comprising the steps
of: a) disposing the substrate inside a reaction chamber; b)
bringing the substrate to a given temperature; c) introducing a
titanium source gas, the titanium source gas being at least one of
titanium bromide and titanium iodide, into the reaction chamber; d)
introducing a reactant gas of at least one of hydrogen, silane,
nitrogen and mixtures thereof into the reaction chamber; and e)
discharging plasma inside the reaction chamber to deposit the
titanium containing film onto the substrate.
2. The process of claim 1, wherein a deposition pressure between
0.2 and 2 Torr is maintained.
3. The process of claim 1, wherein the reaction chamber is a hot
wall reaction chamber.
4. The process of claim 1, wherein the reaction chamber is a cold
wall reaction chamber and the given temperature is in the range of
200.degree. C. to 350.degree. C.
5. The process of claim 1, wherein the given temperature is less
than 400.degree. C.
6. The process of claim 1, wherein the reactant gas comprises
hydrogen.
7. The process of claim 1, wherein the reactant gas comprises
hydrogen and silane.
8. The process of claim 1, wherein the reactant gas comprises
hydrogen and nitrogen.
9. A chemical vapor deposition process for depositing titanium
containing film on a substrate, the process comprising the steps
of: a) disposing the substrate inside a cold wall reaction chamber;
b) bringing the substrate to a temperature less than 400.degree.
C.; c) introducing a titanium source gas into the reaction chamber,
the titanium source gas being one of titanium bromide and titanium
iodide; d) introducing a reactant gas of at least one of hydrogen,
silane, nitrogen and mixtures thereof into the reaction chamber;
and e) discharging plasma inside the reaction chamber to deposit
the titanium containing film onto the substrate.
10. The process of claim 9, wherein the substrate is brought to the
given temperature by heating a substrate holder which secures the
substrate.
11. The process of claim 10, wherein the substrate holder is heated
to the given temperature by halogen lamps.
12. The process of claim 9, wherein the given temperature is in the
range of 200.degree. C. to 350.degree. C.
13. The process of claim 9, wherein a deposition pressure between
0.2 and 2 Torr is maintained.
14. The process of claim 9, wherein the reactant gas comprises
hydrogen.
15. The process of claim 9, wherein the reactant gas comprises
hydrogen and silane.
16. The process of claim 9, wherein the reactant gas comprises
hydrogen and nitrogen.
17. The proceess of claim 9, wherein the plasma is discharged
inside the reaction chamber for less than 200 seconds.
18. A chemical vapor deposition process for depositing
titanium-containing films on a substrate, the process comprising
the steps of: a) disposing the substrate inside a reaction chamber
maintained at a given temperature; b) introducing a titanium source
gas into the reaction chamber; c) introducing a reactant gas into
the reaction chamber; and d) discharging plasma inside the reaction
chamber and applying a voltage to substrate to bias the substrate
to deposit a titanium-containing film onto the substrate.
19. The process of claim 18, wherein a deposition pressure between
0.2 and 2 Torr is maintained.
20. The process of claim 18, wherein the reaction chamber is a hot
wall reaction chamber.
21. The process of claim 18, wherein the reaction chamber is a cold
wall reaction chamber.
22. The process of claim 18, wherein the given temperature is less
than 600.degree. C.
23. The process of claim 18, wherein the given temperature is less
than 400.degree. C.
24. The process of claim 18, wherein the titanium source gas is a
titanium tetrahalide.
25. The process of claim 18, wherein the reactant gas is hydrogen,
silane, nitrogen, or mixtures thereof.
26. The process of claim 18, wherein the reactant gas comprises
hydrogen.
27. The process of claim 18, wherein the reactant gas comprises
hydrogen and silane.
28. The process of claim 18, wherein the reactant gas comprises
hydrogen and nitrogen.
29. The process of claim 18, wherein the surface of the wafer is
negatively biased.
30. The process of claim 18, wherein the voltage applied to the
surface of the wafer is an RF voltage.
31. A chemical vapor deposition process for depositing a
titanium-containing film a substrate, the process comprising the
steps of: a) disposing the substrate inside a cold wall reaction
chamber maintained at a given temperature; b) introducing a
titanium source gas into the reaction chamber; c) introducing a
reactant gas of at least one of hydrogen, silane, nitrogen, and
mixtures thereof into the reaction chamber; and d) discharging
plasma inside the reaction chamber and applying a voltage to the
surface of the wafer to bias the surface to deposit the
titanium-containing film onto the substrate.
32. The process of claim 31, wherein the substrate is brought to
the given temperature by heating a substrate holder which secures
the substrate.
33. The process of claim 32, wherein the substrate holder is heated
to the given temperature by halogen lamps.
34. The process of claim 31, wherein the given temperature is less
than 600.degree. C.
35. The process of claim 31, wherein the given temperature is less
than 400.degree. C.
36. The process of claim 14, wherein the titanium source gas is a
titanium tetrahalide.
37. The process of claim 31, wherein the reactant gas is hydrogen,
silane, nitrogen, or mixtures thereof.
38. The process of claim 31, wherein the reactant gas comprises
hydrogen.
39. The process of claim 31, wherein the reactant gas comprises
hydrogen and silane.
40. The process of claim 31, wherein the reactant gas comprises
hydrogen and nitrogen.
41. The process of claim 31, wherein the substrate is negatively
biased.
42. The process of claim 31, wherein the voltage applied to the
substrate is an RF voltage.
43. An in-situ plasma cleaning process for cleaning contact
openings, the process comprising the steps of: a) disposing a
substrate having contact openings inside a reaction chamber; b)
bringing the substrate to a given temperature; c) introducing a
cleaning agent of at least one of hydrogen, argon, or nitrogen
trifluoride into the reaction chamber; and d) discharging plasma
inside the reaction chamber and applying a voltage to the substrate
to bias the substrate to remove material from within the contact
openings.
44. The process of claim 43, wherein the reactor pressure is
between 0.2 and 2 Torr is maintained.
45. The process of claim 43, wherein the reaction chamber is a hot
wall reaction chamber.
46. The process of claim 43, wherein the reaction chamber is a cold
wall reaction chamber.
47. The process of claim 43, wherein the given temperature is less
than 600.degree. C.
48. The process of claim 43, wherein the given temperature is less
than 400.degree. C.
49. The process of claim 43, wherein hydrogen is added subsequent
to nitrogen trifluoride and argon.
50. The process of claim 43, wherein the voltage applied to the
substrate is an RF voltage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field Of The Invention
[0002] The present invention relates generally to the field of
integrated circuit manufacturing technology and, more particularly,
to an improved method for depositing thin films.
[0003] 2. Background Of The Related Art
[0004] In the manufacturing of integrated circuits, numerous
microelectronic circuits are simultaneously manufactured on
semiconductor substrates. These substrates are usually referred to
as wafers. A typical wafer is comprised of a number of different
regions, known as die regions. When fabrication is complete, the
wafer is cut along these die regions to form individual die. Each
die contains at least one microelectronic circuit, which is
typically replicated on each die. One example of a microelectronic
circuit which can be fabricated in this way is a dynamic random
access memory ("DRAM").
[0005] Although referred to as semiconductor devices, integrated
circuits are in fact fabricated from numerous materials of varying
electrical properties. These materials include insulators or
dielectrics, such as silicon dioxide, and conductors, such as
aluminum or tungsten, in addition to semiconductors, such as
silicon and germanium.
[0006] In the manufacture of integrated circuits, conductive paths
are formed to connect different circuit elements that have been
fabricated within a die. One method to make these connections is
through the use of openings in intermediate insulative layers.
These openings are typically referred to as "contact openings" or
"vias." A contact opening is typically created to expose an active
region, commonly referred to as a doped region, while vias
traditionally refer to any conductive path between any two or more
layers in a semiconductor device.
[0007] After a contact opening, for instance, has been formed to
expose an active region of the semiconductor substrate, an enhanced
doping may be performed through the opening to create a localized
region of increased carrier density within the bulk substrate. This
enhanced region provides a better electrical connection with the
conductive material which is subsequently deposited within the
opening. One method of increasing conductivity further involves the
deposition of a thin titanium-containing film, such as titanium
silicide, over the wafer so that it covers the enhanced region
prior to deposition of the conductive layer. Thin films of
titanium-containing compounds also find other uses as well in the
fabrication of integrated circuits. For example, titanium nitride
is used as a diffusion barrier to prevent chemical attack of the
substrate, as well as to provide a good adhesive surface for the
subsequent deposition of tungsten.
[0008] Indeed, many reasons exist for depositing thin films between
adjacent layers in a semiconductor device. For example, thin films
may be used to prevent interdiffusion between adjacent layers or to
increase adhesion between adjacent layers. Titanium nitride,
titanium silicide, and metallic titanium are known in the art as
materials that can be deposited as thin films to facilitate
adhesion and to reduce interdiffusion between the layers of a
semiconductor device. Other films that may be useful for these
purposes also include titanium tungsten, tantalum nitride, and the
ternary alloy composed of titanium, aluminum, and nitrogen.
[0009] The deposition of titanium-containing films is just one
example of a step in the manufacture of semiconductor wafers.
Indeed, any number of thin films, insulators, semiconductors, and
conductors may be deposited onto a wafer to fabricate an integrated
circuit. As the size of the microelectronic circuits, and therefore
the size of die regions, decreases, the percentage of reliable
circuits produced on any one wafer becomes highly dependent on the
ability to deposit these thin films uniformly across the surface of
the wafer. This includes uniform deposition on horizontal surfaces,
slanted surfaces, and vertical surfaces, including those surfaces
which define the walls and base of contacts and vias. If these thin
films are not deposited in a uniform manner, gaps may be created
which prevent the thin film from fully performing its function. The
likelihood of the existence of these gaps tends to increase as the
films become thinner.
[0010] Films may be deposited by several different methods, such as
thermal growth, sputter deposition, spin-on deposition, chemical
vapor deposition (CVD), and plasma enhanced chemical vapor
deposition (PECVD). In thermal growth, the wafer substrate is
heated at precisely controlled temperatures, typically between 800
and 1200.degree. C., with a choice of ambient gases. The high
temperature promotes the reaction between the ambient gas and the
wafer substrate. For instance, films of silicon dioxide are often
produced by this method. The problem with this method is the
extremely high deposition temperatures required. Extremely high
temperatures are a concern for two reasons. First, high temperature
may be incompatible with or even detrimental to other elements of
the integrated circuit, and, second, excessive cycling from low to
high temperatures can damage a circuit, thereby reducing the
percentage of reliable circuits produced from a wafer. Therefore, a
lower deposition temperature is typically preferred as long as the
characteristics of the deposited film are unaffected.
[0011] In sputter deposition, the material to be deposited is
bombarded with positive inert ions. Once the material exceeds its
heat of sublimation, atoms are ejected into the gas phase where
they are subsequently deposited onto the substrate, which may or
may not be negatively biased. Sputter deposition has been widely
used in integrated circuit processes to deposit titanium-containing
films. The primary disadvantage of sputter deposition is that it
results in films having poor step coverage, so it may not be widely
useable in submicron processes. Films deposited by sputter
deposition on slanted or vertical surfaces do not exhibit uniform
thickness, and the density of films deposited on these surfaces is
usually not as high as the films deposited on horizontal
surfaces.
[0012] In spin-on deposition, the material to be deposited is mixed
with a suitable solvent and spun onto the substrate. The primary
disadvantage of spin-on deposition is that nominal uniformity can
only be achieved at relatively high thicknesses. Therefore, this
method is primarily used for the deposition of photoresist and the
like. It is generally not useful for the deposition of thin
films.
[0013] As previously indicated, the trend for reducing the size of
die regions has dictated the reduction of the thickness of many
deposited films. These thin films need to have improved step
coverage to reduce the number of gaps in the films and to increase
the yield of operable devices. Of the methods discussed above, CVD
and PECVD are best suited to deposit the thinnest films, as films
deposited by sputter deposition on slanted or vertical surfaces do
not exhibit the degree of uniformity obtainable by CVD and
PECVD.
[0014] In CVD, the gas phase reduction of highly reactive chemicals
under low pressure results in very uniform thin films. A basic CVD
process used for depositing titanium involves a given composition
of reactant gases and a diluent which are injected into a reactor
containing one or more silicon wafers. The reactor is maintained at
selected pressures and temperatures sufficient to initiate a
reaction between the reactant gases. The reaction results in the
deposition of a thin film on the wafer. If the gases include
hydrogen and a titanium precursor, a titanium-containing film will
be deposited. For example, if, in addition to hydrogen and the
titanium precursor, the reactor contains a sufficient quantity of
nitrogen or a silane, the resulting titanium-containing film will
be titanium nitride and titanium silicide respectively. Plasma
enhanced CVD is a form of CVD that includes bombarding the material
to be deposited with a plasma to generate chemically reactive
species at relatively low temperatures.
[0015] Chemical vapor deposition is typically carried out in one of
two types of reactor. One type of reactor is called a hot wall
reactor. A hot wall reactor is operated at a low pressure,
typically 1 Torr or less, and high temperatures, typically
600.degree. C. or greater. The other type of reactor is called a
cold wall reactor. A cold wall reactor is operated at atmospheric
pressure and low temperatures, typically 400 to 600.degree. C.
[0016] The primary advantage of the hot wall reactor is that
deposited films exhibit excellent purity and uniform step coverage.
However, the hot wall reactor process is also characterized by low
deposition rates, high temperatures, and the potential for the
occurrence of unwanted reactions on the walls of the reaction
chamber. Conversely, the cold wall reactor exhibits high deposition
rates but poor step coverage.
[0017] Exposure to extreme temperatures and excessive cycling from
low to high temperatures during the fabrication of integrated
circuits can render the circuits useless. Therefore, a process for
depositing films exhibiting uniform step coverage that can be
conducted with a minimum of exposure to elevated temperatures could
have a dramatic impact on the yield of reliable circuits. It has
been thought that PECVD is the best method of achieving this
result. In fact, plasma deposition has been used to produce
titanium-containing films in a cold wall reactor maintained at
approximately 400.degree. C. The result of this deposition is thin
titanium-containing films exhibiting good step coverage and growth
rate.
[0018] However, the current plasma deposition technology does have
its limitations. Because of the higher pressures associated with
deposition in a cold wall reactor, it is difficult to deposit films
that exhibit a high degree of uniform coverage in contacts and vias
having high aspect ratios. This difficulty extends to both the
vertical surfaces of the contacts and vias as well as the
horizontal surfaces at the base of the contacts and vias.
[0019] The present invention may address one or more of the
problems set forth above.
SUMMARY OF THE INVENTION
[0020] Certain aspects commensurate in scope with the originally
claimed invention are set forth below. It should be understood that
these aspects are presented merely to provide the reader with a
brief summary of certain forms the invention might take and that
these aspects are not intended to limit the scope of the invention.
Indeed, the invention may encompass a variety of aspects that may
not be set forth below.
[0021] In accordance with one aspect of the present invention,
there is provided a chemical vapor deposition process for
depositing a titanium containing film on a substrate. The process
includes the steps of: a) disposing the substrate inside a reaction
chamber; b) bringing the substrate to a given temperature; c)
introducing a titanium source gas, the titanium source gas being at
least one of titanium bromide and titanium iodide, into the
reaction chamber; d) introducing a reactant gas of at least one of
hydrogen, silane, nitrogen and mixtures thereof into the reaction
chamber; and e) discharging plasma inside the reaction chamber to
deposit the titanium containing film onto the substrate.
[0022] In accordance another aspect of the present invention, there
is provided a chemical vapor deposition process for depositing film
on a substrate. The process includes the steps of: a) disposing the
substrate inside a cold wall reaction chamber; b) bringing the
substrate to a given temperature; c) introducing a titanium source
gas selected from the group consisting of titanium bromide and
titanium iodide into the reaction chamber; d) introducing a
reactant gas of at least one of hydrogen, silane, nitrogen and
mixtures thereof into the reaction chamber; and e) discharging
plasma inside the reaction chamber to deposit the titanium
containing film onto the substrate.
[0023] In accordance with still another aspect of the present
invention, there is provided a chemical vapor deposition process
for depositing titanium-containing films on a substrate. The
process includes the steps of: a) disposing the substrate inside a
reaction chamber maintained at a given temperature; b) introducing
a titanium source gas into the reaction chamber; c) introducing a
reactant gas into the reaction chamber; d) discharging plasma
inside the reaction chamber and applying a voltage to substrate to
bias the substrate to deposit a titanium-containing film onto the
substrate.
[0024] In accordance with yet another aspect of the present
invention, there is provided a chemical vapor deposition process
for depositing a titanium-containing film on a substrate. The
process includes the steps of: a) disposing the substrate inside a
cold wall reaction chamber maintained at a given temperature; b)
introducing a titanium source gas into the reaction chamber; c)
introducing a reactant gas of at least one of hydrogen, silane,
nitrogen, and mixtures thereof into the reaction chamber; and d)
discharging plasma inside the reaction chamber and applying a
voltage to the surface of the wafer to bias the surface to deposit
the titanium-containing film onto the substrate.
[0025] In accordance with a further aspect of the present
invention, there is provided an in-situ plasma cleaning process for
cleaning contact openings. The process includes the steps of: a)
disposing a substrate having contact openings inside a reaction
chamber; b) bringing the substrate to a given temperature; c)
introducing a cleaning agent of at least one of hydrogen, argon, or
nitrogen trifluoride into the reaction chamber; d) discharging
plasma inside the reaction chamber and applying a voltage to the
substrate to bias the substrate to remove material from within the
contact openings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The foregoing and other advantages of the invention will
become apparent upon reading the following detailed description and
upon reference to the drawings in which:
[0027] FIG. 1 illustrate a semiconductor wafer and its constituent
die regions;
[0028] FIG. 2 is a diagrammatic cross-section of a semiconductor
wafer processed in accordance with the present invention, wherein a
thin film has been deposited onto the surface of a die including
the surfaces of a contact opening;
[0029] FIG. 3 is a diagrammatic cross-section of a semiconductor
wafer processed in accordance with the present invention, wherein a
conductive layer has been deposited onto the thin film previously
deposited; and
[0030] FIG. 4 is schematic diagram of a cold wall reactor used in
chemical vapor deposition processes which has been modified to
discharge plasma into the reaction chamber and which has been
further modified to apply a voltage to the surface of the die.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0031] In the interest of clarity, not all features of an actual
implementation into an integrated circuit process are described in
this specification. This illustration is restricted to those
aspects of an integrated circuit process involving the deposition
of thin films. Conventional details of integrated circuit
processes, such as mask generation, resist casting, resist
development, etching, doping, cleaning, implantation and annealing
are not presented as such details are well known in the art of
integrated circuit manufacture.
[0032] Turning now to the drawings, a typical semiconductor wafer
is illustrated in FIG. 1 and designated by a reference numeral 10.
The wafer 10 includes a number of different regions, known as die
regions 12. Each die region 12 may include an integrated circuit
containing various features and fabricated using various materials
and processes. For the purposes of this discussion, one of the die
regions 12 will be discussed. The die region 12 includes a thin
titanium-containing film. An example of such a film is illustrated
in FIG. 2. Specifically, FIG. 2 illustrates a cross-sectional view
of a die region 12 which includes an enhanced doped region or
active region 24 within a semiconductor substrate 26. The active
region 24 by be formed by an implantation process, for instance.
The bulk substrate 26 is coated with an insulative layer 22, such
as borophosphosilicate glass (BPSG) or phosphosilicate glass (PSG).
The insulative layer 22 is etched to form a contact opening 20
through the insulative layer 22 to the active region 24. Of course
it should be understood that the depiction of a contact opening to
an active region is merely exemplary of a high-aspect ratio feature
and that this discussion applies to other high-aspect ratio
features, such as vias, as well.
[0033] Using the method described in detail below, a layer of
titanium or titanium-containing film 28 is deposited across the
wafer such that it lines the contact opening 20. The film 28
exhibits good adhesion to the contact opening 20 and the active
region 24, along with excellent step coverage. The film 28 also
exhibits good adhesion to a subsequently deposited conductive metal
layer 21 illustrated in FIG. 3.
[0034] By known CVD processes, the only way good step coverage
could be achieved was by deposition in a hot wall reactor. However,
deposition in the hot wall reactor was achieved at low deposition
rates and was often accompanied by unwanted reactions which
occurred at the walls of the reactor. Conversely, use of a
traditional cold wall reactor achieved more favorable deposition
rates but sacrificed good step coverage. When a cold wall reactor
is modified to discharge plasma into the reaction chamber, thin
films are deposited that exhibit good step coverage as a result of
using titanium tetrachloride as the titanium gas source.
[0035] To perform the deposition of the film 28, a cold wall CVD
reactor 30 is advantageously used, as illustrated in FIG. 3,
although a similarly modified hot wall reactor may also be used
under the conditions set forth below to achieve improvements. The
cold wall CVD reactor 30 is modified with an RF generator 32. A
titanium source gas, advantageously obtained from a titanium halide
such as titanium tetrachloride, titanium bromide, or titanium
iodide, and hydrogen are introduced into the reaction chamber 34
through a shower head 31. If so desired, a carrier gas, such as
argon or helium, may be added to the reactant gases. The gases may
or may not be pre-mixed. The gases are generally introduced through
the shower head 31 to achieve good dispersion of the gases, but the
gases can be introduced by other means. Desired reaction pressures
are maintained by conventional pressure control components,
including a pressure sensor 33, a pressure switch 35, an air
operating vacuum valve 37, and a pressure control valve 39. The
carrier gas and the resultant gas, such as HCl when titanium
tetrachloride is used as the titanium precursor, given off during
the reaction escapes from the reaction chamber 34 through an
exhaust vent 42. These gases pass through a particulate filter 44,
and gas removal is facilitated by a roots blower 46.
[0036] In the reactor chamber 34, a substrate holder 36 is heated
to a temperature of less than 600.degree. C., and typically less
than 400.degree. C. In fact, temperatures may be in the range of
200 to 350.degree. C., with pressures in the range of 0.2 to 2.0
Torr. Heating may be achieved through the use of halogen lamps 38,
so that the silicon wafer 10 is heated by convection. As the
reactant gases enter the reaction chamber 34 through the shower
head 31, a voltage is applied between the substrate holder 36 and
the reaction chamber 34 for a period of from about 50 to 150
seconds typically. The voltage may be supplied by an RF generator
32 with one line 48a coupled to a wall of the reaction chamber 34
and another line 48b coupled to the substrate holder 36. The RF
voltage causes the ionization of hydrogen gas present as a reactant
to create a plasma of H.sup.+ ions.
[0037] The plasma is discharged in the space above the wafer 10 to
facilitate the deposition reaction.
[0038] If no further modification to the deposition process is
made, films 28 are deposited at relatively high rates. These films
28 exhibit good step coverage which is not inherent in a cold wall
reactor system in which plasma is not used. However, deposition
along the surfaces of contacts 20 and vias is generally not optimal
because the pressures associated with deposition preclude optimal
deposition in the recesses of these conductive paths, particularly
when a cold wall CVD reactor is employed.
[0039] However, a voltage, such as an RF voltage, may be applied to
the surface of the wafer 10 via a line 48c from the RF generator
32. If this voltage is applied as the plasma is being discharged
above the wafer 10, further improvements in step coverage can be
achieved. In particular, step coverage along the surfaces of the
contact 20 is improved. The applied voltage causes the surface of
the wafer 10 to become biased. The charged surface attracts
oppositely charged species from the space above the wafer 10. The
charged species are drawn to the surface overcoming the pressures
which had previously hindered deposition. Typically the surface of
the wafer 10 is negatively biased to attract the positive metal
cations.
[0040] As a cumulative result of this process, a chemical reaction
occurs which results in the deposition of a titanium-containing
film 28 along the exposed surfaces of the wafer 10. These surfaces
include the vertical and horizontal surfaces of the contact 20. The
deposited films 28 exhibit uniform step coverage. In particular,
the vertical and horizontal surfaces of the contact 20 exhibit
improved step coverage compared to films 28 deposited onto the
surface of a wafer 10 which has not been biased. The films 28 which
are typically deposited by this process using titanium
tetrachloride are generally less than 3000 .ANG. thick, and the
reaction can be characterized as
TiCl.sub.4+2H.sub.2.fwdarw.Ti+4HCl. The deposition of titanium from
titanium tetrachloride in this manner generally requires an
exposure period greater than 200 seconds.
[0041] Optionally, a reducing agent can be introduced into the
reaction chamber 34 along with the titanium precursor and hydrogen.
When this reducing agent is nitrogen, the titanium-containing film
28 which is deposited onto the wafer 10 is composed principally of
titanium nitride, and the reaction can be characterized by
2TiCl.sub.4+4H.sub.2+N.sub.2.fwd- arw.2TiN+8HCl. When the reducing
agent is a silane, the titanium containing film 28 which is
deposited onto the wafer is composed principally of elemental
titanium and titanium silicide, and the reaction can be
characterized by 3TiCl.sub.4+2H.sub.2+2SiH.sub.4.fwdarw.2Ti+TiSi.s-
ub.2+12HCl.
[0042] As mentioned above, the modified reactor may contain
titanium tetrabromide or titanium tetraiodide as the titanium
source gas, instead of titanium tetrachloride. This results in the
deposition of thin titanium films exhibiting good step coverage. It
has been found that this deposition can be achieved at lower
temperatures and in a shorter period of time as compared with known
methods, partly as a result of titanium tetrabromide and titanium
tetraiodide being more reactive than titanium tetrachloride. This
results in a faster deposition rate of the titanium film, and
allows for the reaction to be conducted at lower temperatures. For
instance, the deposition of titanium-containing films exhibiting
good step coverage can be achieved in less than 200 seconds of
exposure at temperatures less than 350.degree. C. The chemical
reaction can be characterized by TiBr.sub.4 (or
TiI.sub.4)+2H.sub.2.fwdarw.Ti+4HBr (or 4 HI).
[0043] The presence of the plasma allows for good step coverage
under the temperature conditions normally employed in a cold wall
reactor. Also, the wafer 10 may be biased as discussed above so
that the material to be deposited is drawn into the contact 20 or
via to improve the step coverage of the deposited film.
Furthermore, as discussed previously, a reducing agent can be
introduced into the reactor chamber along with the titanium
precursor and hydrogen. When this reducing agent is nitrogen, the
titanium-containing film deposited onto the wafer is composed
principally of titanium nitride, and the reaction can be
characterized by 2TiBr.sub.4 (or
2TiI.sub.4)+4H.sub.2+N.sub.2.fwdarw.2TiN+8HBr (or 8 HI ). When the
reducing agent is a silane, the titanium containing film deposited
onto the wafer is composed principally of elemental titanium and
titanium silicide, and the reaction can be characterized by
3TiBr.sub.4 (or
3TiI.sub.4)+2H.sub.2+2SiH.sub.4.fwdarw.2Ti+TiSi.sub.2+12H- Br (or
12 HI).
[0044] As the size of devices decreases the thickness of these
films 28, whether used as diffusion barriers or adhesive layers,
also decreases. By ensuring the highest degree of uniform step
coverage, the likelihood of producing a higher percentage of
reliable devices increases. Additionally, depositing films 28 as
discussed above results in a higher deposition rate. Because the
deposited material is drawn into the contacts 20 and vias, the
films 28 are deposited in a shorter period of time. This ability to
deposit films 28 in a shorter period of time also increases the
likelihood of obtaining a higher yield of reliable circuits. The
barrier properties and adhesive properties of the deposited films
28 are generally at their lowest at elevated temperatures.
Therefore, the longer the period of exposure to elevated
temperatures, the greater the likelihood of producing faulty
devices. Because deposition by the described methods results in
deposition in a shorter period of time, the amount of time the
wafer 10 is exposed to elevated temperatures decreases.
[0045] Furthermore, the methods may serve other uses. For example,
an in-situ plasma cleaning of the surfaces of the contact or via,
in particular the base of these conductive paths, can be conducted.
It is not uncommon for oxides, particularly oxides of silicon, to
form during semiconductor processes. The presence of these oxides
is generally not desired. To conduct the cleaning operation which
removes the unwanted oxides, the deposition process previously
described is employed except that hydrogen, argon, and nitrogen
trifluoride are charged to the reactor. When plasma is then
discharged in the reactor, the oxide of silicon is converted into a
volatile product, such as SiF.sub.4, which is readily removed. If,
in addition to discharging plasma into the reactor, a voltage is
applied to the surface of the wafer to bias that surface
negatively, the cleaning operation's efficiency at removing
unwanted oxide deposits located along the walls and base of
contacts and vias is increased. Without this modification, the
cleaning agents may not overcome the reaction pressures and
penetrate the recesses of the contacts and vias.
[0046] While the invention is susceptible to various modifications
and alternative forms, specific embodiments have been shown by way
of example in the drawings and will be described in detail herein.
However, it should be understood that the invention is not intended
to be limited to the particular forms disclosed. Rather, the
invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the following appended claims.
* * * * *