U.S. patent application number 11/245559 was filed with the patent office on 2007-04-12 for pre-treatment to eliminate the defects formed during electrochemical plating.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Haiyang Gu, Glen T. Mori, Ho Sun Wee, Ming Xi, Jeff Yang, Yohan Zondak.
Application Number | 20070080067 11/245559 |
Document ID | / |
Family ID | 37910217 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070080067 |
Kind Code |
A1 |
Gu; Haiyang ; et
al. |
April 12, 2007 |
Pre-treatment to eliminate the defects formed during
electrochemical plating
Abstract
Embodiments of the invention provide methods for reducing
formation of void-type defects on the surface of a substrate during
electrochemical plating. Embodiments of the invention provide
methods to improve the wetting of a substrate surface prior to
immersion and thereby minimize adhesion of bubbles to the substrate
surface during immersion. A thin uniform metal oxide is formed on a
metal layer on the substrate immediately prior to substrate
immersion. In one aspect, exposing the substrate to an
oxygen-containing gas, e.g. air, forms the metal oxide. The
oxygen-containing gas may be flowed over the substrate or the
substrate may be rotated at a high rate in the presence of an
oxygen-containing gas. In another aspect, non-uniform metal oxides
are first removed from the substrate in an anneal process and a
thin uniform metal oxide is subsequently re-formed. An optimized
substrate immersion method may also be used to further reduce void
defects.
Inventors: |
Gu; Haiyang; (San Jose,
CA) ; Yang; Jeff; (Sunnyvale, CA) ; Wee; Ho
Sun; (Santa Clare, CA) ; Xi; Ming; (Palo Alto,
CA) ; Mori; Glen T.; (Gilroy, CA) ; Zondak;
Yohan; (San Jose, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
APPLIED MATERIALS, INC.
|
Family ID: |
37910217 |
Appl. No.: |
11/245559 |
Filed: |
October 7, 2005 |
Current U.S.
Class: |
205/183 ;
205/205; 257/E21.174; 257/E21.175 |
Current CPC
Class: |
C23C 28/322 20130101;
C23C 14/16 20130101; H01L 21/76873 20130101; C25D 5/34 20130101;
H01L 21/288 20130101; H01L 21/76856 20130101; H01L 21/2885
20130101; C23C 14/5853 20130101; C25D 7/123 20130101; C23C 28/345
20130101; H01L 21/76874 20130101; C23C 28/023 20130101 |
Class at
Publication: |
205/183 ;
205/205 |
International
Class: |
C23C 28/00 20060101
C23C028/00; C25D 5/34 20060101 C25D005/34 |
Claims
1. A method for forming a layer on an electronic device substrate,
comprising: depositing a first metal layer on a substrate; forming
a metal oxide layer on the first metal layer by flowing an
oxygen-containing gas across the first metal layer at a velocity
between about 3 m/sec and about 10 m/s; and plating a second metal
layer on the metal oxide layer.
2. The method of claim 1, wherein the oxygen-containing gas
comprises atmospheric air.
3. The method of claim 1, wherein the humidity of the
oxygen-containing is between about 50% and about 70%.
4. The method of claim 1, wherein the first metal layer is a
copper-containing layer.
5. The method of claim 1, wherein the metal oxide layer formed on
the first metal layer is between about 10 .ANG. and about 20 .ANG.
thick.
6. The method of claim 1, wherein the substrate may include a
material selected from the group consisting of monocrystalline
silicon, polycrystalline silicon, amorphous silicon, strained
silicon, silicon on insulator, doped silicon, silicon germanium,
germanium, gallium arsenide, glass, sapphire, silicon oxide,
silicon nitride, silicon oxynitride and/or carbon doped silicon
oxide.
7. The method of claim 1, further comprising: immersing the first
metal layer into a plating solution using an optimized tilt method,
wherein the optimized tilt method comprises: positioning the
substrate at a first tilt angle from horizontal above the plating
solution; vertically displacing the substrate to immerse the first
metal layer into the plating solution while maintaining the
substrate at the first tilt angle from horizontal; and positioning
the substrate substantially parallel to an anode prior to
plating.
8. The method of claim 7, wherein the optimized tilt method further
comprises rotating the substrate during the immersing the first
metal layer step.
9. The method of claim 7, wherein the optimized tilt method further
comprises altering the position of the substrate from the first
tilt angle from horizontal toward horizontal during said vertical
displacing.
10. The method of claim 7, wherein the optimized tilt method
further comprises altering the position of the substrate to a
second tilt angle measured from horizontal when the substrate
contacts the plating solution.
11. A method for forming a layer on an electronic device substrate,
comprising: depositing a first metal layer on a substrate; forming
a metal oxide layer on the first metal layer by rotating the
substrate from about 500 rpm to about 2000 rpm in the presence of
an oxygen-containing gas; and plating a second metal layer on the
metal oxide layer.
12. The method of claim 11, wherein the oxygen-containing gas
comprises atmospheric air.
13. The method of claim 11, wherein the humidity of the
oxygen-containing is between about 50% and about 70%.
14. The method of claim 11, wherein the first metal layer is a
copper-containing layer.
15. The method of claim 11, wherein the metal oxide layer formed on
the first metal layer is between about 10 .ANG. and about 20 .ANG.
thick.
16. The method of claim 11, wherein the substrate may include a
material selected from the group consisting of monocrystalline
silicon, polycrystalline silicon, amorphous silicon, strained
silicon, silicon on insulator, doped silicon, silicon germanium,
germanium, gallium arsenide, glass, sapphire, silicon oxide,
silicon nitride, silicon oxynitride and/or carbon doped silicon
oxide.
17. The method of claim 11, further comprising: immersing the first
metal layer into a plating solution using an optimized tilt method,
wherein the optimized tilt method comprises: positioning the
substrate at a first tilt angle from horizontal above the plating
solution; vertically displacing the substrate to immerse the metal
layer into the plating solution while maintaining the substrate at
the first tilt angle from horizontal; and positioning the substrate
substantially parallel to an anode prior to plating.
18. The method of claim 17, wherein the optimized tilt method
further comprises rotating the substrate during the immersing the
first metal layer step.
19. The method of claim 17, wherein the optimized tilt method
further comprises altering the position of the substrate from the
first tilt angle from horizontal toward horizontal during said
vertical displacing.
20. The method of claim 17, wherein the optimized tilt method
further comprises altering the position of the substrate to a
second tilt angle measured from horizontal when the substrate
contacts the plating solution.
21. A method for improving the wettability of a substrate with a
metal surface layer, comprising: exposing the metal surface layer
of the substrate to an oxygen-containing gas until a metal oxide
layer that is between about 10 .ANG. and about 20 .ANG. thick is
formed on the metal surface layer of the substrate.
22. The method of claim 21, wherein the process of exposing the
metal surface layer of the substrate to an oxygen-containing gas
comprises exposing the metal surface layer of the substrate to
atmospheric air for longer than about 80 minutes and less than
about 24 hours.
23. The method of claim 22, wherein the metal surface layer is a
copper-containing surface layer.
24. The method of claim 21, wherein the process of exposing the
metal surface layer of the substrate to an oxygen-containing gas
comprises flowing an oxygen-containing gas over the metal surface
layer of the substrate at a velocity of between about 3 m/sec and
about 10 m/s.
25. The method of claim 24, wherein the oxygen-containing gas is
atmospheric air.
26. The method of claim 24, wherein the metal surface layer is a
copper-containing surface layer.
27. The method of claim 21, wherein the process of exposing the
metal surface layer of the substrate to an oxygen-containing gas
comprises rotating the substrate from about 500 rpm to about 2000
rpm in the presence of an oxygen-containing gas.
28. The method of claim 27, wherein the oxygen-containing gas is
atmospheric air.
29. The method of claim 27, wherein the metal surface layer is a
copper-containing surface layer.
30. The method of claim 27, wherein the humidity of the
oxygen-containing gas is between about 50% and about 70%.
31. A method of processing a substrate that has a metal layer
formed thereon, comprising: positioning the substrate in a first
process chamber; causing an oxygen-containing gas to flow across
the substrate until a metal oxide layer about 10 to about 20 .ANG.
thick is formed on the metal layer; immersing the substrate in a
plating solution; and plating a second metal layer on the
substrate.
32. The method of claim 31, wherein the process of causing an
oxygen-containing gas to flow across the substrate comprises
flowing an oxygen-containing gas over the metal surface layer of
the substrate at a velocity between about 3 m/sec and about 10
m/s.
33. The method of claim 31, wherein positioning the substrate
comprises positioning the substrate on a rotatable substrate
support and causing an oxygen-containing gas to flow across the
substrate comprises rotating the substrate from about 500 rpm to
about 2000 rpm in the presence of an oxygen-containing gas.
34. The method of claim 31, wherein the metal layer is a
copper-containing layer.
35. The method of claim 31, wherein the oxygen-containing gas is
ambient air.
36. The method of claim 31, wherein the process of immersing the
substrate in a plating solution comprises: positioning the
substrate at a first tilt angle above a plating solution positioned
in a process chamber; vertically displacing the substrate to
immerse the metal layer into the plating solution while maintaining
the substrate at the first tilt angle; and positioning the
substrate substantially parallel to an anode positioned in the
plating solution prior to plating.
37. The method of claim 36, further comprising rotating the
substrate during immersion.
38. The method of claim 36, further comprising altering the
position of the substrate from the first tilt angle toward
horizontal during said vertical displacing.
39. The method of claim 36, further comprising altering the
position of the substrate to a second tilt angle when the substrate
contacts the plating solution.
40. The method of claim 31, further comprising positioning the
substrate in a second process chamber prior to the immersing the
substrate in a plating solution step, wherein the second process
chamber is adapted to perform the immersing the substrate in a
plating solution step and the plating a second metal layer on the
substrate step.
41. The method of claim 31, wherein causing an oxygen-containing
gas to flow across the substrate further comprises: holding the
substrate in a low-oxygen, hydrogen-enriched environment;
increasing the temperature of the substrate to between about
50.degree. C. and about 100.degree. C.; and exposing the substrate
to an oxygen-containing gas.
42. A method for forming a layer on an electronic device substrate,
comprising: depositing a first metal layer on a substrate; forming
a metal oxide layer between about 10 .ANG. and about 20 .ANG. thick
on the metal layer by exposing the metal layer to an
oxygen-containing gas for longer than about 80 minutes and less
than about 24 hours; and plating a second metal layer on the metal
oxide layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the invention generally relate to a method
for processing a semiconductor substrate to reduce defects formed
during an electroplating process.
[0003] 2. Description of the Related Art
[0004] Sub-quarter micron, multi-level metallization is one of the
key technologies for the next generation of very large scale
integration (VLSI) and ultra large scale integration (ULSI)
semiconductor devices. The multilevel interconnects that lie at the
heart of this technology require the filling of contacts, vias,
lines, and other features formed in high aspect ratio apertures.
Reliable formation of these features is very important to the
success of both VLSI and ULSI as well as to the continued effort to
increase circuit density and quality on individual substrates and
die.
[0005] As circuit densities increase, the widths of contacts, vias,
lines and other features, as well as the dielectric materials
between them, are continually decreasing as the device feature
sizes decrease from 65 nm to 32 nm and beyond. Many conventional
deposition processes do not consistently fill structures with
narrow openings or difficult aspect ratios. As such, there is a
great amount of ongoing effort being directed at the void-free
filling of nanometer-sized structures with narrow opening and/or
high aspect ratios features wherein the ratio of feature height to
feature width could be 4:1 or higher.
[0006] Additionally, as the feature widths decrease, the device
current typically remains constant or increases, which results in
an increased current density for such features. Elemental aluminum
and aluminum alloys have been the traditional metals used to form
vias and lines in semiconductor devices because aluminum has a low
electrical resistivity, superior adhesion to most dielectric
materials, and ease of patterning, and the aluminum in a highly
pure form is readily available. However, aluminum has a higher
electrical resistivity than other more conductive metals, such as
copper (Cu). Aluminum can also suffer from electromigration,
leading to the formation of voids in the conductor.
[0007] Copper and copper alloys have lower resistivities than
aluminum, as well as a significantly higher electromigration
resistance compared to aluminum. These characteristics are
important for supporting the higher current densities experienced
at high levels of integration and increased device speed. Copper
also has good thermal conductivity. Therefore, copper is becoming a
choice metal for filling sub-quarter micron, high aspect ratio
interconnect features on semiconductor substrates.
[0008] Conventionally, deposition techniques such as chemical vapor
deposition (CVD) and physical vapor deposition (PVD) have been used
to fill these interconnect features. However, as the interconnect
sizes decrease and aspect ratios increase, void-free interconnect
feature fill by conventional metallization techniques becomes
increasingly difficult using CVD and/or PVD. As a result thereof,
plating techniques, such as electrochemical plating (ECP) and
electroless plating, have emerged as viable processes for filling
sub-quarter micron sized high aspect ratio interconnect features in
integrated circuit manufacturing processes.
[0009] In an ECP process, for example, sub-quarter micron sized
high aspect ratio features formed into the surface of a substrate
(or a layer deposited thereon) may be efficiently filled with a
conductive material. ECP plating processes are generally two stage
processes, wherein a seed layer is first formed over the surface
features of the substrate and then the surface features of the
substrate are filled via an ECP process. Conventional non-ECP type
processes that are used to deposit the diffusion barrier layer and
seed layer include depositing the seed layer (e.g., copper) by
physical vapor deposition (PVD), chemical vapor deposition (CVD),
or atomic layer deposition (ALD) onto a diffusion barrier layer
(e.g., tantalum or tantalum nitride), generally in a separate
substrate processing tool. The surface features of the substrate
are then exposed to an electrolyte solution in the ECP tool, while
an electrical bias is applied between the seed layer and a copper
anode positioned within the electrolyte solution. The electrolyte
solution generally contains a source of metal that is be plated
onto the surface of the substrate and, therefore, the application
of the electrical bias causes the metal source to be plated onto
the biased seed layer, thus depositing a layer of the ions on the
substrate surface that may fill the features.
[0010] However, the decreasing size of features being filled by ECP
processes in semiconductor processing requires that the plating
process generate minimal void-type defects in order to produce
viable devices. Research has shown that one cause of void-type
plating defects is the presence of air bubbles on the surface of
the substrate being plated. Generally, air bubbles are formed on
the surface of the substrate during the process of immersing the
substrate into the plating solution. More particularly, as the
substrate is transitioned from the air into the plating solution,
small bubbles often adhere to the surface of the substrate. These
air bubbles prevent the electrolyte solution from contacting the
substrate surface at that particular location and, therefore,
prevent plating at that location. This forms a void-type defect in
the plated layer.
[0011] Conventional immersion schemes have attempted to address
this issue by optimizing the way the substrate is introduced into
the ECP electrolyte, such as titling the substrate into the
electroplating bath. The tilting process is generally completed by
loading the substrate into substrate contact ring, or receiving
member, that is pivotally attached to a location next to the
processing solution into which the substrate is to be immersed,
such that the contact ring member may be pivoted to bring the
substrate into the electrolyte gradually. The substrate and contact
ring may also be rotated to reduce the effects seen on the
substrate surface. These processes have not been reliable or
completely effective in removing the void-type defects seen on the
substrate.
[0012] Two defect types commonly found on the substrate surface are
individual voids in the ECP layer, known as "pit" defects, and
arrays of multiple voids, known as "dot line void" defects. Each of
these void-type defects consist of small regions, e.g., <0.1
.mu.m in diameter, of the plated film where no ECP deposited layer
is formed and thus these areas only have the seed layer and barrier
over the exposed feature surfaces. Such void-type defects formed in
the ECP deposited layer may affect the yield and electromigration
results and are a real concern to electronic device
manufacturers.
[0013] Therefore, there is a need for a method for processing a
substrate, wherein the process is configured to minimize the
formation of defects on the surface of the substrate during
electrochemical processing.
SUMMARY OF THE INVENTION
[0014] Embodiments of the invention generally provide methods for
reducing the formation of void-type defects on the surface of a
substrate during electrochemical processing. More particularly,
embodiments of the invention provide methods to improve the wetting
of a substrate surface prior to immersion and thereby minimize
adhesion of bubbles to the substrate surface during substrate
immersion.
[0015] In one embodiment, a thin, uniform metal oxide is formed on
the surface of the substrate immediately prior to immersion of the
substrate to improve wetting of the substrate by the plating
solution. In one aspect, the metal oxide is formed by exposing the
substrate to an oxygen-containing gas, e.g., air, for several
hours. No forced convective flow is used. In another aspect, the
metal oxide is formed by flowing an oxygen-containing gas over the
surface of the substrate. In yet another aspect, the metal oxide is
formed by rotating the substrate at a relatively high rate in the
presence of an oxygen-containing gas.
[0016] In another embodiment, a thin, uniform metal oxide layer is
formed on the surface of the substrate immediately prior to
immersion by first removing any metal oxides formed thereon and
then reforming a uniform metal oxide layer in a controlled manner.
The original metal oxide layer is removed via an anneal process
wherein the heated substrate is held in a low oxygen,
hydrogen-enriched environment. The uniform metal oxide layer is
then formed by maintaining a constant, uniform substrate
temperature while exposing the substrate to an oxygen-containing
gas.
[0017] In another embodiment, an optimized substrate immersion
method involving a first tilt angle and a second tilt angle is used
in conjunction with a substrate with improved wettability to
further reduce void defects. The procedure is designed to immerse a
substrate into a plating solution with minimal bubble formation. In
one aspect, the metal oxide layer is formed by exposure to an
oxygen-containing gas while the substrate is rotated at a
relatively high rate. In another aspect, the substrate is initially
stripped of any metal oxides by an anneal process in a
hydrogen-enriched environment. In another aspect, the wettability
of the substrate surface is improved by exposing the substrate to
an oxygen-containing gas with no forced convective flow for several
hours.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0019] FIG. 1 (Prior Art) is a schematic side view of a void-type
defect in a copper layer plated on an unpatterned substrate.
[0020] FIG. 1A is a schematic top-down partial view of a
copper-plated substrate surface, illustrating pit defects and
dot-line void defects.
[0021] FIG. 2 is a graph of the number of total defects detected on
copper-plated substrates vs. exposure time of the substrate seed
layer to ambient air prior to the plating process.
[0022] FIG. 3 is a schematic cross-sectional view of a solid-liquid
system consisting of a drop of liquid on a solid surface.
[0023] FIG. 3A illustrates a droplet of an aqueous solution in
contact with a solid surface and forming a contact angle that is
greater than 90.degree..
[0024] FIG. 3B illustrates a droplet of an aqueous solution in
contact with a solid surface and forming a contact angle that is
equal to 90.degree..
[0025] FIG. 3C illustrates a droplet of an aqueous solution in
contact with a solid surface and forming a contact angle that is
less than 90.degree..
[0026] FIG. 4 is a graph of the percent concentration of Cu2 and O1
atoms, as measured by X-ray Photoelectron Spectroscopy.
[0027] FIG. 4A illustrates a flowchart of one process sequence for
reducing void-type defects on plated substrates.
[0028] FIG. 4B illustrates a flowchart another process sequence for
reducing void-type defects on plated substrates.
[0029] FIG. 5 illustrates a sectional view of an exemplary plating
cell.
[0030] FIGS. 6-10 illustrate sectional views of an exemplary
plating cell and plating head assembly.
[0031] For clarity, identical reference numerals have been used,
where applicable, to designate identical elements that are common
between figures.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] Embodiments of the invention generally provide various
methods for processing a substrate to reduce the number of
void-type defects formed on the substrate when an electrochemical
plating process is performed on the substrate. The method of the
invention is designed to minimize plating defects by performing one
or more preprocessing steps on a substrate prior to performing the
ECP process.
[0033] "Plating" as used herein, refers to any deposition process
that includes electrochemical plating, electroless plating, or a
combination of both.
[0034] Percent concentrations of gas mixtures, as used herein,
refer to volume percent.
[0035] "Ambient air" as used herein, refers to air that contains
about 21% O.sub.2 (by volume). For example, a volume of air that
has been sealed in a container that also contains substances that
spontaneously react with the gaseous oxygen therein, such as
un-oxidized copper, is not considered "ambient air" after any
significant period of time has elapsed. This is due to the
depletion of oxygen that takes place in such a sealed container via
reaction with the substances therein. A gas may vary from standard
temperature and/or pressure, i.e., 20.degree. C. and 760 Torr
(absolute pressure) and still be considered "ambient air" as long
as it consists of about 21% O.sub.2 and 79% N.sub.2 and other trace
components.
[0036] "Oxygen-containing gas" as used herein, refers to any gas
mixture that contains from about 1% to about 100% O.sub.2.
"Oxygen-depleted" as used herein, refers to having less than about
21% O.sub.2. "Low-oxygen" as used herein, refers to having no
significant amount of oxygen present, i.e., trace quantities of
oxygen at a maximum. "Hydrogen-enriched", as used herein, refers to
having a concentration of H.sub.2 greater than about 0.5%.
[0037] FIG. 1 is a schematic side view of one example of a void
defect 100 that has been formed in a copper layer 104 that is
formed on a substrate surface 101 via an ECP or electroless plating
process. Substrate surface 101 may be any substrate or material
surface formed on a substrate upon which film processing is
performed. For example, a substrate surface on which processing may
be performed include materials such as monocrystalline,
polycrystalline or amorphous silicon, strained silicon, silicon on
insulator (SOI), doped silicon, silicon germanium, germanium,
gallium arsenide, glass, sapphire, silicon oxide, silicon nitride,
silicon oxynitride and/or carbon doped silicon oxides, such as
SiO.sub.xC.sub.y, for example, BLACK DIAMOND.TM. low-k dielectric,
available from Applied Materials, Inc., located in Santa Clara,
Calif., substrate 101 is a silicon substrate. For clarity, in the
example shown in FIG. 1, substrate 101 is illustrated to be
unpatterned, i.e., without typical substrate features such as
apertures, vias, trenches, etc.
[0038] A diffusion barrier layer 102 and a plating seed layer 103
are deposited on substrate 101 prior to the plating process wherein
copper layer 104 is deposited. The diffusion barrier layer 102 and
seed layer 103 are typically deposited by conventional deposition
techniques, such as PVD, ALD or CVD in a separate substrate
processing tool. It has been shown that void defects in plated
copper layer 104, such as void defect 100, are formed only in
copper layer 104 and do not originate from a void or other defect
in underlying layers on the substrate, such as diffusion barrier
layer 102 or plating seed layer 103. This is illustrated in FIG. 1,
wherein the bottom 100a of void defect 100 ends at plating seed
layer 103. Void defects 100 are substantially cylindrical in shape
and are commonly less than 0.1 .mu.m in diameter.
[0039] Void defect 100 may occur in very large numbers on plated
substrates, either individually, in which case they are referred to
as "pit" defects, or they may be formed into arrays of void
defects, which are referred to as "dot line void" defects. FIG. 1A
is a schematic top-down partial view of a copper-plated substrate
surface 110, illustrating each. Region 111, which is 10 .mu.m
square, contains a plurality of pit defects 111a. Region 112, which
is also 10 .mu.m square, contains part of a dot-line void defect
111b, i.e., a substantially linear array of a large number of pit
defects. Pit defects 111a and dot-line void defects 111b may both
affect device yield and electromigration results.
[0040] Occurrence of void defects, i.e., pit and dot-line void
defects, has been shown to be a strong function of how long the
copper seed layer has been exposed to ambient air. This trend is
illustrated in FIG. 2. FIG. 2 is a graph of the number of total
defects detected on copper-plated substrates vs. exposure time of
the substrate seed layer to ambient air prior to the plating
process. The abscissa represents the time, in minutes, that a
freshly deposited copper seed layer on a substrate was exposed to
air prior to electrochemical plating. The ordinate represents the
total number of defects (void-type and all others) detected on a
substrate surface after the plating process. The total number of
pit and dot-line void defects on an ECP-plated silicon substrate
200 mm in diameter may range from as high as the 10's of thousands
to as low as approximately 100 or lower, depending on copper seed
layer exposure time. When the copper seed layer on the substrate is
exposed to ambient air for less than 10 minutes, the number of void
defects is highest, typically in the 10's of thousands. When pit
and dot-line defects occur on a plated wafer in large numbers,
i.e., in the thousands and higher, they typically appear in a
distinctive swirl pattern on the substrate and are collectively
referred to as a "swirl" defect. Void defect counts per substrate
quickly drop in magnitude for copper seed layers exposed to ambient
air for longer times. For copper seed layers exposed to ambient air
for more than approximately 70 or 80 minutes, the swirl pattern is
not present and defect counts repeatably stabilize at approximately
100 per substrate and do not decrease with further exposure to air.
However, copper seed layers exposed for more than approximately 24
hours to ambient air begin showing other defect types when
plated.
[0041] Further, when substrates freshly deposited with copper seed
layers are stored for up to a week in an airtight container, a
similar trend for void defect counts is seen. The first substrates
to be plated, i.e., those with the shortest exposure time to
ambient air, uniformly show the highest void defect counts in the
swirl defect pattern--although at a lower magnitude than substrates
that are plated immediately after seed layer deposition. As with
substrates that are plated with a very fresh seed layer, void
defect counts on stored substrates quickly trend down as a function
of exposure time to ambient air. This indicates that exposure to
ambient air is the most effective measure for eliminating pit and
dot-line defects.
[0042] Tests involving different methods of the immersing
substrates into a plating bath, such as varying substrate rotation
speed and direction, confirm that the swirl defect is primarily
produced during the substrate immersion step of the plating
process. It is believed that gas bubbles trapped on the surface of
the copper seed layer during immersion are the foremost cause of
void defect formation. Hence, the swirl defect can be reduced or
eliminated by minimizing the amount of bubbles generated during
substrate immersion, improving the wetting action of the plating
fluid, and increasing substrate surface wettability.
[0043] Substantial and on-going effort has been directed to
minimizing bubble creation during substrate immersion into plating
baths. Methods developed to date include optimized substrate tilt
angle, substrate rotation speed and substrate velocity during
immersion in the plating solution for minimal flow disturbance and
bubble formation. Optimized substrate immersion methods used in
aspects of the invention are described below in conjunction with
FIGS. 5, 6, 7, 8, 9 and 10.
[0044] Increasing the wetting action of the plating fluid, i.e.
altering the chemistry of the plating fluid so that it more readily
wets the surface of the substrate during immersion, is another
approach for eliminating the swirl defect. Testing has been
performed involving a medium acidity and low acidity plating fluid
and the swirl defect occurs with either plating solution. Further
changes to plating fluid chemistry that improve the wetting of the
plating fluid, such as the addition of surfactants, is problematic.
Such changes may eliminate the swirl defect but create other
serious problems, such as organic contamination of the plated
copper film and/or poor gap fill capabilities. Hence, aspects of
the invention generally do not contemplate altering plating fluid
chemistry.
[0045] It is known that a surface with a higher wettability will
have fewer bubbles adhering to the surface when immersed in a given
liquid, hence, increasing substrate surface wettability is the
third approach for eliminating void-type defects on plated
substrates. Wettability is usually quantified in terms of the
contact angle, also known as the wetting angle, for a drop of a
liquid on a solid in a vapor. FIG. 3 is a schematic cross-sectional
view of a solid-liquid system 300 consisting of a droplet 305 on a
solid 302. The contact angle 301 of solid-liquid system 300 is a
measurement of the angle formed between the surface of solid 302
and the line 303 tangent to the radius 304 of droplet 305 on the
solid 302 from the point of contact 306 with the solid 302. For
ease of measurement of the contact angle 301, the solid 302
typically is a flat, horizontal surface, as shown in FIG. 3. The
contact angle 301 will vary for different systems of liquids and
solids, resulting from the interaction of the surface tension of
the droplet 305 and the surface chemistry of the solid 302. When
contact angle 301 is less than 90.degree. for a solid-liquid system
300, good wetting is produced and the droplet 305 tends to spread
across the surface of solid 302. When contact angle 301 is greater
than 90.degree., wetting is poor, i.e., droplet 305 is repelled by
the surface of solid 302, and droplet 302 tends to bead or shrink
away from solid 302.
[0046] For aqueous solutions, such as plating solutions, a surface
or material that creates a contact angle smaller than 90.degree. is
referred to as hydrophilic and a surface or material that creates a
contact angle larger 90.degree. than is referred to as hydrophobic.
FIG. 3A illustrates a droplet 305a of an aqueous solution in
contact with a solid surface 302a and forming a contact angle 301a
that is greater than 90.degree.. Surface 302a is considered highly
hydrophobic. FIG. 3B illustrates a droplet 305b of an aqueous
solution in contact with a solid surface 302b and forming a contact
angle 301b that is equal to 90.degree.. Droplet 305b demonstrates
significant beading on surface 302b and therefore surface 302b is
considered hydrophobic. FIG. 3C illustrates a droplet 305c of an
aqueous solution in contact with a solid surface 302c and forming a
contact angle 301c that is less than 90.degree.. Droplet 305c
spreads out across surface 302c, therefore surface 302c is
considered hydrophilic.
[0047] It is known that the formation of metal oxide on a freshly
deposited copper seed layer is very fast in the first five minutes
of exposure to ambient air but reaches a saturation depth of about
10 to 20 .ANG. after approximately 90 minutes of exposure. Metal
oxide growth thereafter is relatively slow, as illustrated in FIG.
4. FIG. 4 is a graph of the percent concentration of Cu2 and O1
atoms, as measured by X-ray Photoelectron Spectroscopy (XPS). The
abscissa represents exposure time to ambient air of a fresh,
PVD-deposited copper seed layer on a substrate. The ordinate
represents measured concentration, in atomic percent, of elements
present on the surface of the seed layer. Data set 401 represents
the concentration of Cu2 atoms present on the surface of the
substrate. Data set 402 represents the concentration of O1 atoms
present on the surface of the substrate. As shown in FIG. 4, the
concentration of Cu2 drops quickly in the first 300 seconds, i.e.,
5 minutes, of exposure to ambient air from 48.7% at data point 401
a to 32.5% at data point 401 b. A corresponding increase in the
concentration of O1 atoms takes place in the first 300 seconds of
exposure from 24.3% at data point 402a to 35.6% at data point 402b,
indicating oxidation of the copper seed layer. After 5400 seconds,
i.e., 90 minutes, of exposure to ambient air, the concentration of
Cu2 has only decreased slightly at data point 401c to 29.7% and the
oxygen concentration has only increased slightly at data point 402c
to 40.6%, indicating that the oxidation process has essentially
stopped.
[0048] Referring to Table 1, it is clear that the surface roughness
of a fresh copper seed layer increases significantly with exposure
to ambient air. After 11 minutes of exposure to ambient air, the
root-mean-square (RMS) surface roughness of a PVD-deposited layer
of copper on a substrate is measured to be 0.309 nm. 16 minutes
later, i.e., after 27 minutes of exposure to ambient air, the RMS
surface roughness increases to 0.327 nm. It is believed that this
is due to the formation of the cuprous oxide (Cu.sub.2O) layer
brought about by oxidation. Further, it is known that increasing
the roughness of a metal oxide surface reduces the contact angle of
liquids thereon and improves the wettability of the surface (see
Physical Chemistry of Surfaces, 5.sup.th edition, by Arthur W.
Adamson, John Wiley & Sons, Inc. p. 388). Hence, it is believed
that the reduced numbers of void-type defects detected on
substrates that have been exposed to ambient air for at least about
80 minutes prior to plating is due to improved wettability brought
about by the thin, uniform cuprous oxide layer that forms after
about 80 minutes of exposure to ambient air. The micro-roughness
associated with a fully developed metal oxide layer improves
wettability of the substrate surface and reduces the tendency of
gas bubbles to adhere to the surface of the substrate. With
improved wettability, bubbles are less likely to adhere to the
surface of the substrate during immersion and void-type defects are
not formed. It is also believed that a non-uniform copper surface,
such as a freshly deposited copper seed layer that has only
partially oxidized regions, or oxide islands, on its surface, may
be more likely to drag gas bubbles from the air-liquid interface
during immersion of the substrate. A copper seed layer that has not
formed a 10-20 .ANG. thick cuprous oxide layer is such a
non-uniform copper surface. TABLE-US-00001 TABLE 1 Surface
Roughness of Fresh Copper Seed Layer After Exposure to Air Time of
Air Exposure 11 minutes 17 minutes 27 minutes Surface Roughness
(RMS) 0.309 nm 0.321 nm 0.327 nm
[0049] Embodiments of the invention provide two methods for
producing a thin, uniform cuprous oxide layer on a copper seed
layer quickly and consistently: anneal followed by metal oxide
re-growth and metal oxide growth via forced air exposure. In some
aspects, an optimized substrate immersion method is also used to
further reduce void defects. The optimized tilt method is designed
to immerse a substrate into a plating solution with minimal bubble
formation.
[0050] FIG. 4A illustrates a flowchart of one process sequence 450
for reducing void-type defects on plated substrates. In step 451,
an anneal process, described below, is performed on the substrate
to remove metal oxides from the surface of a substrate with a
freshly deposited seed layer. In step 452, a suitable metal oxide
layer is formed on the surface of the seed layer via exposure of
the seed layer to an oxygen-containing gas. In step 453, the
substrate is immersed in a plating solution. In step 454, the
substrate is plated. Alternatively, the substrate is immersed in
step 453 using an optimized tilt method, described below, to
minimize bubbles created during immersion and to discourage
adhesion of bubbles to the surface of the substrate.
[0051] FIG. 4B illustrates a flowchart of another process sequence
460 for reducing void-type defects on plated substrates. In step
461, a dry spin process, described below, is performed on the
substrate to quickly and consistently form a suitable metal oxide
on the surface of a substrate with a freshly deposited seed layer.
In step 462, the substrate is immersed in a plating solution. In
step 463, the substrate is plated. Alternatively, the substrate is
immersed in step 462 using an optimized tilt method, described
below, to minimize bubbles created during immersion and to
discourage adhesion of bubbles to the surface of the substrate.
Anneal and Metal Oxide Re-Growth
[0052] One method that may be included in embodiments of the
invention involves the removal of metal oxides formed on the
surface of a freshly deposited metal layer, followed by the
controlled formation of a more suitable metal oxide layer prior to
plating. In the case of a copper seed layer, a thin, i.e., 10-20
.ANG. thick, uniform, cuprous oxide layer is desired.
[0053] An anneal chamber may be used to remove metal oxides formed
on a copper seed layer prior to the plating process. Shortly before
plating, the substrate is heated in an air-tight chamber in a
low-oxygen environment. Because metal oxides are being removed from
the surface of the substrate, it is important that the oxygen
concentration in the environment during this process step is very
low, for example at most no more than about 1% and preferably no
more than about 0.1%. In one aspect, the anneal chamber is mounted
on the same substrate processing platform that performs the
substrate plating process to minimize the time between the
formation of the metal oxide layer and the plating process. The
low-oxygen environment may be achieved through pump-down of the
chamber via a vacuum pump and subsequent back-fill of the chamber
with a low-oxygen gas, such as nitrogen or argon. It has been shown
that heat treatments greater than about 150.degree. C. tend to
damage seed layers via recrystallization, resulting in other
defects, such as copper grain pullout during subsequent processes.
Heat treatments less than about 50.degree. C. are generally not
effective for oxide reduction. Hence, in a preferred aspect of the
invention, an anneal process at a temperature less than about
150.degree. C. and more than about 50.degree. C., such as
100.degree. C. for example, is used to remove metal oxides from the
surface of a copper seed layer.
[0054] In one aspect, the substrate annealing environment includes
a forming gas, such as hydrogen, to more completely remove metal
oxide layers on the substrate. When the process temperatures are
relatively low, i.e. no greater than about 100.degree. C., the use
of a forming gas greatly increased the effectiveness of the anneal
process for removing metal oxides. In a preferred aspect of the
invention, a 4% concentration of hydrogen is used because that is
the lower explosive limit of hydrogen. However, use of higher
concentrations of hydrogen is contemplated for faster or more
effective removal of metal oxides during this process step.
[0055] In one typical anneal process for removing metal oxides from
the surface of a substrate, a substrate is positioned in an anneal
chamber. The chamber is pumped down to about 0.1 kPa or less and
back-filled with a purge gas, such as N.sub.2, at about 8 kPa for
about 20 seconds. A forming gas consisting of 4% H.sub.2/96%
N.sub.2 is flowed into the chamber at a flow rate that maintains
the pressure in the chamber at about 2 kPa. The substrate is then
heated to about 100.degree. C. for between about 60 seconds and
about 120 seconds. The anneal time may be reduced if a forming gas
containing more than 4% H.sub.2 is used.
[0056] After removal of some or all metal oxides from the surface
of a substrate, the substrate is cooled and then exposed to an
oxygen-containing gas in a controlled manner. Preferably, the
exposure to the oxygen-containing gas takes place in the same
chamber wherein the anneal process takes place. In one aspect, the
substrate is cooled with a purge gas, such as nitrogen. In another
aspect, a temperature-controlled substrate pedestal may be used to
cool the substrate to the desired oxidation temperature. In the
preferred embodiment, ambient air is used to form the desired metal
oxide layer on the surface of the seed layer, which, in the case of
a copper seed layer, is a cuprous oxide layer 10-20 .ANG. thick. In
another embodiment, an oxygen-depleted gas mixture may be used,
such as a 50% ambient air/50% N.sub.2 mixture. Because it is
believed that too-rapid oxidation of a metal layer may result in
non-uniform growth of a metal oxide layer, a gas mixture with less
oxygen than ambient air may be used to form the desired metal oxide
on the substrate. An oxygen-containing gas with more than about 21%
oxygen may also be used to form the metal oxide layer on the
surface of the substrate. However, it is more difficult to control
the uniformity of the resultant metal oxide layer.
[0057] After removal of unwanted metal oxides via an anneal process
and the subsequent formation of a desired metal oxide on the
surface of the substrate, the substrate is then plated with an
electrochemical or electroless plating process.
Forced Air Exposure
[0058] Another method that may be included in embodiments of the
invention involves the formation of a suitable metal oxide layer on
the surface of a freshly deposited metal layer by causing an
oxygen-containing gas to flow across the surface of the metal
layer. It has been shown that in the case of a copper seed layer, a
10-20 .ANG. thick cuprous oxide layer may be formed thereon in less
than two minutes if ambient air is flowed across the copper seed
layer under certain conditions.
[0059] In one embodiment, the substrate is rotated at high rpm in a
process chamber that is purged with ambient air. This is also known
as a "dry spin" process. It is known in the art that the rotation
of a substrate in a chamber at a relatively high speed, e.g. at
least 500 rpm for a 300 mm circular substrate, creates a vortex
that forces air or any other gases present in the chamber radially
outward across the surface of the substrate. This forced convection
of oxygen-containing gas across the freshly deposited metal layer
greatly increases the rate at which the metal oxide is formed. In
the case of a PVD-deposited copper seed layer, a cuprous oxide
layer of about 10-20 .ANG. thickness is formed in less than two
minutes, rather than the at least 80 minutes required when the
copper seed layer is exposed to ambient air without forced
convection.
[0060] It is important to note that the dry spin chamber must be
continually refreshed with enough ambient air or other
oxygen-containing gas to prevent the environment inside the
processing chamber from becoming oxygen-depleted. In situations
wherein the flow rate of ambient air into the chamber is marginally
adequate, an increase of as little as 30% in the flow rate of
ambient air into the chamber may have a measurable effect on the
number of void-type defects detected on plated substrates. In the
preferred aspect, the chamber in which the dry spin takes place is
open to ambient air and a continuous supply of ambient air is
provided during the dry spin process via a process exhaust system,
wherein oxygen-depleted air is removed from the dry spin chamber
and ambient air is drawn in to the process chamber during substrate
processing. The minimum required exhaust flow for a given chamber
varies depending on several factors, including substrate size,
chamber volume, process chamber humidity and substrate spin speed,
but in general a minimum of three air changes per minute is
desired. One skilled in the art, upon reading the disclosure
herein, can determine the required process exhaust volume for a
given dry spin chamber.
[0061] In one embodiment, a rotatable substrate support spins the
substrate at a desired rpm. In one aspect, the dry spin chamber is
mounted on the same substrate processing platform that performs the
substrate plating process and is used for other process steps
associated with the plating process, such as a pre-rinse chamber, a
spin-rinse-dry chamber, a plating cell or a bevel clean chamber.
Any substrate processing chamber with a rotatable substrate support
and exposure to ambient air may be used for this embodiment. The
substrate may be oriented face-up or face-down during the dry spin
process. In a preferred aspect, a chamber that contains 50% to 70%
humidity when processing substrates is used for the dry spin
process, such as a plating cell or spin-rinse-dry chamber. Humidity
of at least about 50% to 70% has been shown to reduce the time
required for metal oxide formation during the dry spin process
step. In one aspect, the substrate is held in place on a rotatable
substrate support during the dry spin process with a vacuum chuck.
In another aspect the substrate is held in place via centrifugal
clips on the rotatable substrate support. Both methods are known in
the art. In another aspect, the rotatable substrate support may be
adapted with air vanes or impellors to enhance forced convection in
the dry spin chamber. This aspect is useful for situations in which
the process chamber being used for the dry spin process is unable
to adequately perform the dry spin process. Chambers with marginal
exhaust, low humidity and/or no high rpm capability, such as a
plating chamber, may benefit from the enhanced forced convection
generated with air vanes or impellers. The optimal rpm and spin
time for formation of a given metal oxide formation varies as a
function humidity and airflow rate. For the formation of a 10-20
.ANG. thick cuprous oxide layer on a copper seed layer, the
preferred rpm is from about 500 rpm to about 2000 rpm and the spin
time is from about 1 minute to about 2 minutes. Lower humidity in
the dry spin chamber than 50% may require a longer spin time and/or
a higher rpm. For example, when a dry spin process takes place in a
dry chamber, i.e. less than 40% relative humidity, the spin time
may need to be as long as about 4 minutes or longer to produce a
suitable metal oxide layer on a copper substrate.
[0062] In another embodiment, an oxygen-containing gas is fed into
the dry spin chamber in addition to or in lieu of ambient air. This
makes it possible to vary oxygen content in the dry spin chamber as
a means for controlling the formation of a suitable metal oxide on
the surface of a freshly deposited metal layer. In general, other
parameters of the dry spin process are easier to control, such as
substrate rpm, exhaust flow rate and spin time. However, variation
of oxygen content in the dry spin chamber is one method that may be
used for tuning the dry spin process. For example, if a 50%
oxygen/50%ambient air mixture is introduced into the dry spin
chamber, the dry spin time required to form a suitable metal oxide
layer on a freshly deposited seed layer may be reduced.
[0063] In another embodiment, an oxygen-containing gas is flowed
across the surface of the metal layer on a stationary substrate by
forced convection to form a suitable metal oxide prior to plating.
The process may be a single substrate process or batch substrate
process. In the preferred aspect, ambient air is flowed across the
surface of the substrate. An oxygen-containing gas of higher or
lower oxygen content than ambient air may also be used. In one
aspect, the forced convection of the oxygen-containing gas is
generated by a fan. In another aspect, the forced convection of the
oxygen-containing gas is caused by releasing the gas from a
pressurized vessel or other gas source.
[0064] In one aspect, the velocity of the oxygen-containing gas is
used as a process parameter for controlling the formation of the
desired metal oxide. Generally, a higher velocity will reduce the
time required for formation of a metal oxide on the surface of a
freshly deposited metal layer. The optimal velocity and oxygen
content of the oxygen-containing gas for formation of metal oxide
formation varies depending on the metal layer present and relative
humidity of the oxygen-containing gas. For the formation of a 10-20
.ANG. thick cuprous oxide layer on a copper seed layer, the
preferred incident velocity of ambient air on the substrate surface
is at least about 3 m/s to about 10 m/s and the air flow time is
from about 1 minute to about 3 minutes. Lower relative humidity
than 50% in the ambient air or other oxygen-containing gas may
require a longer flow time and/or a higher incident velocity.
Immersion with Optimized Tilt
[0065] As noted above, in order to minimize void-type defects in
plated films, bubbles adhering to the substrate surface during the
process of immersing a substrate into a plating solution contained
in a plating cell should be minimized. Therefore, embodiments of
the invention include a method for immersing a substrate into a
processing fluid that generates minimal bubbles and discourages any
bubbles that are formed from adhering to the substrate surface.
[0066] The immersion method incorporated in some embodiments of the
invention generally includes driving or actuating the substrate
into the plating solution using a combination of a tilt and swing
immersion process. More particularly, the substrate may be tilted
at an angle with respect to horizontal, and then vertically
actuated toward the plating solution while being rotated, which
immerses the substrate and maintains a constant angle between the
substrate and the upper surface of the plating solution. The
combination of the tilt and rotation causes bubbles to be dislodged
from the substrate surface and carried away from the substrate
surface as a result of the buoyancy of the bubbles. Further, the
tilt angle of the substrate may be adjusted during the immersion
process, thus generating a swing or pendulum type motion, which
also urges bubbles attached to the substrate surface to be
dislodged therefrom.
[0067] FIG. 5 illustrates a sectional view of an exemplary plating
cell, hereinafter referred to as plating cell 500, that will
illustrate immersion with optimized tilt. The plating cell 500
generally includes a plating head assembly 600, a frame member 503,
an outer basin 501 and an inner basin 502 positioned within outer
basin 501.
[0068] The plating head assembly 600 includes a receiving member
601 for supporting and rotating a substrate during immersion into
the plating bath and during plating. In this example, receiving
member 601 includes a contact ring 602 and a thrust plate assembly
604 that are separated by a loading space 606. The contact ring 602
may be adapted to make electrical contact around the periphery of
the substrate so that the necessary electrical plating bias may be
applied to the substrate. A more detailed description of the
contact ring 602 and thrust plate assembly 604 may be found in
commonly assigned U.S. patent application Ser. No. 10/278,527,
filed on Oct. 22, 2002 and entitled "Plating Uniformity Control By
Contact Ring Shaping", and commonly assigned U.S. Pat. No.
6,251,236 entitled Cathode Contact Ring for Electrochemical
Deposition, both of which are hereby incorporated by reference in
their entirety to the extent not inconsistent with the present
invention.
[0069] The frame member 503 of plating cell 500 supports an annular
base member 504 on an upper portion thereof. Since frame member 503
is elevated on one side, the upper surface of base member 504 is
generally tilted from the horizontal at an angle that corresponds
to the tilt angle of frame member 503 relative to a horizontal
position. Base member 504 includes a disk-shaped anode 505. Plating
cell 500 may be positioned at a tilt angle, i.e., the frame portion
503 of plating cell 500 may be elevated on one side such that the
components of plating cell 500 are tilted between about 3.degree.
and about 30.degree..
[0070] Inner basin 502 is generally configured to contain a plating
solution that is used to plate a metal, e.g., copper, onto a
substrate during an electrochemical plating process. During the
plating process, the plating solution is generally continuously
supplied to inner basin 502, and therefore, the plating solution
continually overflows the uppermost point 502a, generally termed a
"weir", of inner basin 502 and is collected by outer basin 501 and
drained therefrom for chemical management and recirculation. The
exemplary plating cell is further illustrated in commonly assigned
U.S. patent application Ser. No. 10/268,284, filed on Oct. 9, 2002,
and entitled "Electrochemical Processing Cell", claiming priority
to U.S. Provisional Application Ser. No. 60/398,345, which was
filed on Jul. 24, 2002, both of which are incorporated herein by
reference in their entireties.
[0071] In an exemplary ECP process, a substrate may be transferred
into a plating cell, such as plating cell 500 for example, and
positioned face-down on contact ring 602. Thrust plate assembly 604
holds the substrate in place as described below in conjunction with
FIG. 6. The substrate is then immersed in the catholyte solution
filling inner basin 502 using the optimized tilt immersion method
described below in conjunction with FIGS. 6-10, typically while
being rotated by the contact ring 602 between about 5 rpm and about
60 rpm. The catholyte solution may have between about 5 g/l and 50
g/l of sulfuric acid, a copper concentration between about 25 g/l
and 70 g/l, and a chlorine concentration between about 30 ppm and
about 60 ppm. The catholyte solution may also include additional
additives, such as levelers, suppressors or accelerators. During
plating, a plating bias, typically between about 1 VDC and about 10
VDC, is applied to the substrate. The substrate may be rotated
between about 10 rpm and about 100 rpm during the plating process
step by contact ring 602. Plating takes place for between about 30
sec and about 5 minutes, depending on the thickness of plated film
desired. The plating bias is then removed and the substrate is
positioned above the catholyte solution and uppermost point 502a of
inner basin 502 for removal from plating cell 500. Prior to removal
from plating cell 500, the substrate may be rotated between about
100 and 1000 rpm for between about 1 second and about 10 seconds in
order to remove excess catholyte solution from the substrate. An
exemplary ECP cell and plating process is further described in
commonly assigned U.S. patent application Ser. No. 10/627,336
entitled "Electrochemical Processing Cell," filed on Jul. 24, 2003,
which is hereby incorporated by reference in its entirety to the
extent not inconsistent with the present invention.
[0072] The optimized immersion method that may be used in some
aspects of the invention begins with loading a substrate into
plating head assembly 600. A wafer handling robot is used to
position a substrate on the contact ring 602 via access space 606.
The substrate is placed in a face down, i.e. production surface
facing down, orientation. Once the substrate is positioned on the
contact ring 602, thrust plate assembly 604 may be lowered into a
processing position, i.e., thrust plate 604 may be actuated
vertically in the direction indicated by arrow 610 in FIG. 6, to
engage the backside of the substrate positioned on the contact ring
602.
[0073] Once the substrate is secured to the contact ring 602 by the
thrust plate 604, the lower portion of the plating head assembly
600, i.e., the combination of the contact ring 602 and the thrust
plate 604, may be positioned at a tilt angle. The lower portion of
the plating head assembly is pivoted to the tilt angle via pivotal
actuation of the plating head assembly 600 about a pivot point 608.
The lower portion of plating head assembly 600 is actuated about
pivot point 608, which causes pivotal movement of the lower portion
of plating head assembly 600 in the direction indicated by arrow
609 in FIG. 6. The lower portion of plating head assembly 600 and
the plating surface of the substrate positioned on the contact ring
602 are tilted to the tilt angle as a result of the movement of
plating head assembly 600, wherein the tilt angle is defined as the
angle between horizontal and the plating surface/production surface
of the substrate secured to the contact ring 602. The tilt angle is
generally between about 3.degree. and about 30.degree.. Further,
pivot point 608 is generally positioned such that when the plating
head assembly 600 is tilted, a central vertical axis of the
substrate remains in substantially the same location as when the
substrate was positioned horizontally, i.e., the pivot point 608 is
generally positioned proximate contact ring 602.
[0074] Once the plating head assembly 600 is tilted, it may be
actuated in the Z-direction, i.e., in the direction indicated by
arrow 701, as illustrated in FIG. 7 to begin the immersion process.
Plating head assembly 600 is actuated to bring the substrate
positioned in the contact ring 602 toward the plating solution
contained within the plating cell 500 positioned below plating head
assembly 600. The direction indicated by arrow 701 may be parallel
to the central axis of the substrate, or alternatively, the
direction indicated by arrow 701 may be substantially vertical.
Alternatively, the tilting process may be conducted simultaneously
with the Z-direction actuation.
[0075] As plating head assembly 600 is moved toward plating cell
500, the lower side of contact ring 602, i.e., the side of contact
ring 602 positioned closest to plating cell 500 as a result of the
tilt angle, contacts the plating solution as the plating head
assembly 600 is actuated toward inner basin 502 of plating cell
500. The process of actuating plating head assembly 600 toward
inner basin 502 may further include imparting rotational movement
to contact ring 602. Thus, during the initial stages of the
immersion process, contact ring 602 is being actuated in a vertical
or Z-direction, while also being rotated about a central axis that
intersects the radial center of the substrate, which is also
generally orthogonal to the substrate surface.
[0076] As the substrate becomes immersed in the plating solution
contained within plating cell 500, the Z-motion of plating head
assembly 600 may be slowed and/or terminated and the tilt position
of contact ring 602 is returned to horizontal, as illustrated in
FIG. 8. The slowing or termination of the vertical, or the
Z-direction, movement is calculated to maintain the substrate in
the plating solution contained in cell 500 when the tilt angle is
reduced. Further, the optimized tilt method may include the removal
of the tilt angle, i.e., the return of contact ring 602 to a
substantially horizontal position, simultaneously with the vertical
movement of contact ring 602 into the plating solution. As such, a
substrate immersed by this method may first contact the plating
solution with the substrate being positioned at a tilt angle, and
then the tilt angle may be returned to horizontal while the
substrate continues to be immersed into the plating solution. This
process generates a unique swinging or pendulum type movement that
includes both vertical actuation and tilt angle actuation, which
has been shown to reduce bubble formation and adherence to the
substrate surface during the immersion process. Further, the
vertical and pivotal actuation of the substrate during immersion
process may also include rotational movement of contact ring 602,
which has been shown to further minimize bubble formation and
adherence to the substrate surface during the immersion
process.
[0077] Once the substrate is completely immersed into the plating
solution contained within cell 500, plating head assembly 600 may
be further actuated in a vertical direction, i.e., downward, to
further immerse the substrate into the plating solution, i.e., to
position the substrate further or deeper into the plating solution,
as illustrated in FIG. 9. This process may also include rotating
the substrate, which operates to dislodge any bubbles formed during
the immersion process from the substrate surface. Once the
substrate is positioned deeper within the plating solution, the
plating head assembly 600 may again be pivoted about pivot point
608, so the substrate surface may be positioned in parallel
relationship to the upper surface of the anode 505, as illustrated
in FIG. 10. This final tilting motion of plating head assembly 600
generally corresponds to positioning contact ring 602 in a
processing position, i.e., a position where the substrate supported
by contact ring 602 is generally parallel to anode 505 positioned
in a lower portion of the plating cell 500, which corresponds to
positioning the substrate at a processing angle. The processing
angle generally corresponds to the angle that the upper surface of
the anode 505 makes with respect to horizontal.
[0078] The optimized tilt method is further described in commonly
assigned U.S. patent application Ser. No. 10/781,040 [APPM8266],
filed on Feb. 18, 2004, and entitled "Method For Immersing A
Substrate," which is hereby incorporated by reference in its
entirety to the extent not inconsistent with the present
invention.
[0079] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *