U.S. patent application number 10/744285 was filed with the patent office on 2004-09-09 for composition and method used for chemical mechanical planarization of metals.
Invention is credited to Chang, Song Y., Evans, Mark, Hymes, Stephen W., Tamboli, Dnyanesh.
Application Number | 20040175942 10/744285 |
Document ID | / |
Family ID | 32717930 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040175942 |
Kind Code |
A1 |
Chang, Song Y. ; et
al. |
September 9, 2004 |
Composition and method used for chemical mechanical planarization
of metals
Abstract
Compositions for use in CMP processing and methods of CMP
processing. The composition utilizes low levels of particulate
material, in combination with at least one amino acid, at least one
oxidizer, and water to remove a metal layer such as one containing
copper to a stop layer with high selectivity.
Inventors: |
Chang, Song Y.; (Dublin,
OH) ; Evans, Mark; (Columbus, OH) ; Tamboli,
Dnyanesh; (Dublin, OH) ; Hymes, Stephen W.;
(Briarcliff, TX) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP
2700 CAREW TOWER
441 VINE STREET
CINCINNATI
OH
45202
US
|
Family ID: |
32717930 |
Appl. No.: |
10/744285 |
Filed: |
December 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60437826 |
Jan 3, 2003 |
|
|
|
Current U.S.
Class: |
438/689 ;
257/E21.304; 257/E21.583 |
Current CPC
Class: |
H01L 21/3212 20130101;
C09G 1/02 20130101; C09K 3/1463 20130101; H01L 21/7684 20130101;
B24B 37/044 20130101 |
Class at
Publication: |
438/689 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed is:
1. A composition for use in removing copper from the surface of a
wafer containing copper above a stop layer comprising: an oxidizing
agent; an amino acid; about 5 ppm to less than 1000 ppm particulate
material by weight; and water, wherein the composition facilitates
removal of copper from the wafer surface while maintaining a rate
of removal of copper to stop layer of at least 50:1.
2. The composition of claim 1 wherein the oxidizing agent is
hydrogen peroxide.
3. The composition of claim 1 wherein the amino acid is aminoacetic
acid.
4. The composition of claim 1 wherein the particulate material is
selected from the group consisting of fumed silica, colloidal
silica, fumed alumina, colloidal alumina, cerium oxide, titanium
dioxide, zirconium oxide, polystyrene, polymethyl methacrylate,
mica, hydrated aluminum silicate, and mixtures thereof.
5. The composition of claim 1 wherein the particulate material is
selected from the group consisting of fumed silica, colloidal
silica, fumed alumina, colloidal alumina, cerium oxide, zirconium
oxide, polystyrene, polymethyl methacrylate, mica, hydrated
aluminum silicate, and mixtures thereof.
6. The composition of claim 1 wherein the particulate material is
selected from the group consisting of polystyrene, polymethyl
methacrylate, mica, hydrated aluminum silicate, and mixtures
thereof.
7. The composition of claim 1 wherein the composition maintains a
rate of removal of copper to stop layer of at least 100:1.
8. The composition of claim 1 wherein the composition maintains a
rate of removal of copper to stop layer of at least 300:1.
9. The composition of claim 1 having a pH of about 6.6.
10. The composition of claim 1 having a pH in a range between about
3.5 and about 9.
11. The composition of claim 1 wherein the particulate material has
a particle size in the range of about 4 nm to about 10,000 nm.
12. The composition of claim 1 wherein the particulate material has
a particle size in the range of about 4 nm to about 1000 nm.
13. The composition of claim 1 wherein the particulate material has
a particle size in the range of about 4 mn to about 400 nm.
14. The composition of claim 1 wherein the particulate material has
a concentration in the range of about 5 ppm to about 700 ppm by
weight.
15. The composition of claim 1 wherein the particulate material has
a concentration in the range of about 5 ppm to about 400 ppm.
16. The composition of claim 1 wherein the particulate material has
a concentration in the range of about 5 ppm to about 100 ppm.
17. The composition of claim 1 further comprising a corrosion
inhibitor.
18. The composition of claim 17 wherein said corrosion inhibitor is
1,2,4-triazole.
19. The composition of claim 1 wherein the amino acid is selected
from the group consisting of aminoacetic acid, serine, lysine,
glutamine, L-alanine, DL-alanine, iminoacetic acid, asparagine,
aspartic acid, valine, sarcosine, and mixtures thereof.
20. The composition of claim 1 wherein the amino acid has a
concentration in the range of about 0.05% to about 5% by
weight.
21. The composition of claim 1 wherein the amino acid has a
concentration in the range of about 0.25% to about 2% by
weight.
22. A method of removing copper from the surface of a wafer
containing copper above a stop layer, comprising: contacting a
wafer surface with a polishing pad at an interface between the
wafer surface and the polishing pad; supplying a solution to the
interface, the solution comprising at least one oxidizing agent, at
least one amino acid, at least one particulate material, and water,
wherein the particulate material has a concentration sufficient to
remove copper while maintaining a rate of removal of copper to stop
layer of at least 50:1; and initiating relative motion between the
polishing pad and the wafer surface.
23. The method of claim 22 wherein the particulate material has a
concentration in the range of about 5 ppm to about 4000 ppm by
weight.
24. The method of claim 22 wherein the particulate material has a
concentration in the range of about 5 ppm to less than 1000 ppm by
weight.
25. The method of claim 22 wherein the particulate material has a
concentration in the range of about 5 ppm to about 700 ppm by
weight.
26. The method of claim 22 wherein the particulate material has a
concentration in the range of about 5 ppm to about 400 ppm by
weight.
27. The method of claim 22 wherein the particulate material has a
concentration in the range of about 5 ppm to about 100 ppm by
weight.
28. A method of removing copper from the surface of a wafer
containing copper above a stop layer, comprising: contacting a
wafer surface with a polishing pad at an interface; adding water to
a solution, the solution comprising at least one amino acid, at
least one particulate material, and water, the combination of water
and solution forming a diluted solution; supplying the diluted
solution to the interface, wherein the particulate material in the
diluted solution has a concentration sufficient to remove copper
while maintaining a rate of removal of copper to stop layer of at
least 50:1; and initiating relative motion of the polishing pad and
the wafer surface.
29. The method of claim 28 further comprising adding at least one
oxidizing agent to one of the solution and diluted solution prior
to supplying the diluted solution to the interface.
30. The method of claim 28 wherein the particulate material has a
concentration in the range of about 5 ppm to about 4000 ppm by
weight.
31. The method of claim 28 wherein the particulate material has a
concentration in the range of about 5 ppm to less than 1000 ppm by
weight.
32. The method of claim 28 wherein the particulate material has a
concentration in the range of about 5 ppm to about 700 ppm by
weight.
33. The method of claim 28 wherein the particulate material has a
concentration in the range of about 5 ppm to about 400 ppm by
weight.
34. The method of claim 28 wherein the particulate material has a
concentration in the range of about 5 ppm to about 100 ppm by
weight.
35. A composition for use in removing copper from the surface of a
wafer containing copper above a stop layer consisting essentially
of: an oxidizing agent; an amino acid; about 5 ppm to about 4000
ppm particulate material by weight; and water, wherein the
composition facilitates removal of copper from the wafer surface
while maintaining a rate of removal of copper to stop layer of at
least 50:1.
36. The composition of claim 35 wherein the oxidizing agent is
hydrogen peroxide.
37. The composition of claim 35 wherein the amino acid is
aminoacetic acid.
38. The composition of claim 35 wherein the particulate material is
selected from the group consisting of fumed silica, colloidal
silica, fumed alumina, colloidal alumina, cerium oxide, titanium
dioxide, zirconium oxide, polystyrene, polymethyl methacrylate,
mica, hydrated aluminum silicate, and mixtures thereof.
39. The composition of claim 35 wherein the particulate material is
selected from the group consisting of fumed silica, colloidal
silica, fumed alumina, colloidal alumina, cerium oxide, zirconium
oxide, polystyrene, polymethyl methacrylate, mica, hydrated
aluminum silicate, and mixtures thereof.
40. The composition of claim 35 wherein the particulate material is
selected from the group consisting of polystyrene, polymethyl
methacrylate, mica, hydrated aluminum silicate, and mixtures
thereof.
41. The composition of claim 35 wherein the composition maintains a
rate of removal of copper to stop layer of at least 100:1.
42. The composition of claim 35 wherein the composition maintains a
rate of removal of copper to stop layer of at least 300:1.
43. The composition of claim 35 having a pH of about 6.6.
44. The composition of claim 35 having a pH in a range between
about 3.5 and about 9.
45. The composition of claim 35 wherein the particulate material
has a particle size in the range of about 4 nm to about 10,000
nm.
46. The composition of claim 35 wherein the particulate material
has a particle size in the range of about 4 nm to about 1000
nm.
47. The composition of claim 35 wherein the particulate material
has a particle size in the range of about 4 nm to about 400 nm.
48. The composition of claim 35 wherein the particulate material
has a concentration in the range of about 5 ppm to about 700 ppm by
weight.
49. The composition of claim 35 wherein the particulate material
has a concentration in the range of about 5 ppm to about 400
ppm.
50. The composition of claim 35 wherein the particulate material
has a concentration in the range of about 5 ppm to about 100
ppm.
51. The composition of claim 35 wherein the amino acid is selected
from the group consisting of aminoacetic acid, serine, lysine,
glutamine, L-alanine, DL-alanine, iminoacetic acid, asparagine,
aspartic acid, valine, sarcosine, and mixtures thereof.
52. The composition of claim 35 wherein the amino acid
concentration is within the range of about 0.05% to about 5% by
weight.
53. The composition of claim 35 wherein the amino acid
concentration is within the range of about 0.25% to about 2% by
weight.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This patent document claims the benefit of the filing date
of Provisional U.S. Patent Application No. 60/437,826, entitled
"Composition and Method Used for Chemical Mechanical Planarization
of Metals" and filed on Jan. 3, 2003. The entire disclosure of the
'826 Provisional U.S. Patent Application is incorporated into this
patent document by reference.
FIELD OF THE INVENTION
[0002] The invention is directed to compositions for use in
planarizing a metal surface applied over a dielectric layer, metal
layer, or semi-conductor layer, primarily in connection with the
manufacture of integrated circuits. The invention also is directed
to methods used in effecting the planarization of the metal
surface.
BACKGROUND OF THE INVENTION
[0003] Chemical-mechanical planarization (CMP) is used extensively
as a processing step in various planar fabrication technologies,
such as in the removal and polishing of dielectric, metal and
semi-conductor layers having an uneven or excessively thick
topography on a wafer performed in connection with the manufacture
of semi-conductors. In the semi-conductor application, CMP can be
used to polish dissimilar materials nonselectively, as well as to
nonselectively remove single material overburden. CMP can remove
different thicknesses of a first layer down to a stop layer of a
second material, as well as decrease the thickness of a single
layer without reaching a stop layer. A planarized surface allows
accurate photolithography to take place more readily. Some of the
uses for the CMP process encompass polishing the interconnect areas
of the wafer as well as front end and silicon polishing, and it is
generally employed each time after successive layers are formed on
the wafer. As the name implies, the process involves both a
chemical and a mechanical component. Typically, a wafer is mounted
on a carrier. Pressure is applied to bring the wafer surface within
contact of a polishing pad typically made of a porous or fibrous
polymeric material, which is mounted on a platen, and relative
motion is initiated between the wafer surface and the polishing
pad. At the interface between pad and wafer a liquid is supplied
which facilitates the removal of material on the surface of the
wafer. The liquid may, but is not required to, contain an abrasive
component which contributes to the removal action at the pad-wafer
interface during the planarization procedure.
[0004] The liquid can also contribute to controlling the removal of
material from the wafer by incorporating components which interact
chemically with the metal layer on the surface of the wafer. The
chemical action generally takes one of two forms. In the first,
components in the liquid react with exposed metal on the surface of
the metal layer to create an oxide layer. Oxide layer formation
typically involves the addition to the liquid of an oxidizer such
as hydrogen peroxide, which typically but not necessarily is
combined with the other components of the liquid just prior to use.
The oxide layer formed thereby is then removed by the mechanical
action of a pad or an abrasive component in the liquid. In the
second, the surface is converted by components in the liquid which
become adsorbed onto the surface. In both instances, the chemical
action passivates the surface.
[0005] In addition, the liquid may contain one or more components
which directly act to dissolve abraded material. The components
operate preferably to dissolve particles after they have been
abraded from the wafer surface. Generally, it is not desired for
the dissolution process to occur on the surface of the wafer.
[0006] Where the CMP liquid is formulated to contain an oxidizer,
the oxidizer component may be added just prior to actual use on the
wafer to maximize the working time of the liquid if incorporation
of the oxidizer would tend to destabilize the formulation or any of
the components of the formulation. However, the oxidizer-containing
CMP liquid can also be prepared some time before use if a
non-destabilizing oxidizer can be incorporated.
[0007] Regardless of whether an abrasive is used in the CMP liquid,
the liquid may need to undergo a pH adjustment, for example where a
high zeta potential is attainable to retain colloidal stability. It
is undesirable in an abrasive-containing liquid for the particles
to settle out of the suspension. Electrical charges surrounding the
interface between the particle and the liquid strongly influence
the stability of the colloidal system. The zeta potential measures
the potential of a particle's surface at its shear plane and
provides a general measure of the stability of a colloidal system.
To maintain a stable colloidal system, a high zeta potential of
either positive or negative charge is desired. The zeta potential
of the particular particle decreases to zero at the pH
corresponding to its isoelectric point. Thus, to enhance the
stability of the colloid, the pH of the system should differ from
the pH at the isoelectric point. For example, the isoelectric point
of a silica slurry is at a pH of 2; preferably, then, the silica
slurry is maintained at an alkaline pH to enhance the colloidal
stability. In contrast, the isoelectric point of an alumina slurry
is at a pH of 8; it is preferred to maintain this slurry at an
acidic pH to enhance colloidal stability. Other variables which
affect the colloidal stability of a particulate system include
particle density, particle size, particle concentration, and
chemical environment.
[0008] The abrasive assists in facilitating the replenishment of
fresh wafer surface which can then be further attacked by any of
the oxidizing, chelating and etching components of the liquid.
Nonetheless, the use of an abrasive component in the CMP liquid can
produce undesired results on the wafer surface. The abrasive can
create micro-scratches on any exposed surface of the wafer
resulting in a non optically-flat surface. For example, these
micro-scratches can lead to a defect in later processing whereby a
thin metal line is trapped within the dielectric, causing shorts
between adjacent metal lines or vias. Also, formation of topography
creates preferential sites for subsequent particle adhesion.
Further, residual particles of the abrasive can cause potential
opens or shorts depending on the electrical nature of the
particle.
[0009] The surface of the wafer contains materials having differing
resistances to the effect of abrasive action. As a result, exposing
the wafer surface to the mechanical action of the rotating pad in
the presence of abrasive causes certain regions of the wafer
surface to be more quickly removed than others, creating surface
anomalies and a varying topography. For example, in the case of
copper deposited on a dielectric, the planarization process can
cause the copper to recede below the level of the adjacent
dielectric. This effect on the wafer surface is known as dishing.
It is believed that etching of the metal surface of the wafer is
one of the factors which contributes to undesired dishing. Etching
is the nonselective removal of metal from the surface of a layer,
which tends to both roughen the resultant surface and create a
nonplanar surface. Where an array of copper metal lines is located
on a wafer substrate, the mechanical action of the rotating pad in
the presence of abrasive tends to cause formation of individual
recesses of copper which in turn results in a high polishing rate
of the adjacent dielectric. This thinning of the dielectric in the
array relative to dielectric outside the array is known as
erosion.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to a composition for use
in chemical mechanical planarization which facilitates the removal
of metal from the wafer without significantly contributing to the
undesirable polishing effects attributable to an abrasive
component. The invention also relates to a method of chemical
mechanical planarization utilizing the composition described above.
It is an object of the invention to provide a CMP composition which
provides for tunable metal removal rates, such as for copper. It is
a further object of the invention to provide a CMP composition
capable of being produced in a reduced water content form while
retaining high particle stability. It is a further object of the
invention to provide a CMP composition which produces a highly
uniform metal surface on the wafer with low susceptibility to
dishing and erosion. It is yet a further object of the invention to
provide a method of effecting planarization and removal of a wafer
surface while minimizing formation of micro-scratches onto the
metal surface of the wafer. It is yet a further object of the
invention to provide a CMP composition which can produce a highly
planarized surface on the wafer over a range of operating pH
values. It is yet a further object of the invention to provide a
CMP composition having a low defectivity response.
[0011] The composition attains rates of removal on the order of
compositions having appreciable concentrations of abrasive material
using substantially non-abrasive chemistry. The invention provides
a CMP composition comprising the following components:
[0012] (a) an oxidizing agent;
[0013] (b) an amino acid;
[0014] (c) particulate material in a concentration range at a level
below which any significant abrasive effects attributable to the
particulate material are observed; and
[0015] (d) water.
[0016] Though the particles incorporated into the CMP composition
are present at a level below which any significant abrasive effects
attributable to the particles are observed, rates of copper metal
removal comparable to that of highly loaded abrasive-containing
systems are obtained. Typically the amount of particles in the
formulation is less than about 1000 ppm by weight of the
formulation, and more narrowly in the range of about 5 ppm to about
100 ppm. The particle concentration in the formulation can be
higher, however, up to about 4000 ppm, as long as the ratio of
copper rate of removal (RR) relative to the stop layer rate of
removal (RR), i.e., the selectivity, is at least 50:1, more
narrowly at least 100:1, and most narrowly at least 300:1. As used
herein, reference to copper is meant to encompass materials having
copper as a component, including but not limited to pure copper
metal and copper alloys. Reference to a stop layer is meant to
encompass materials having tantalum as a component, including but
not limited to pure tantalum metal, tantalum nitride, tantalum
carbide, and other tantalum alloys, including tertiary and
quaternary materials containing tantalum. In addition, reference to
a stop layer is also intended to encompass materials such as other
refractory metals, other noble metals, and transition metals and
alloys which have a substantially reduced removal rate relative to
copper in the presence of the formulations recited herein for
planarizing the wafer surface. The stop layer may also include
silicon dioxide and other materials which operate as a dielectric
layer. Optionally, a corrosion inhibitor can also be incorporated
into the composition.
[0017] Because the stop layers, i.e., the dielectric and barrier
layers, generally require abrasives to be removed, the low-particle
concentration composition promotes selectivity. The composition in
the absence of any appreciable amount of particulate material for
the purpose of providing mechanical polishing facilitates removal
of the copper layer from the wafer without significant removal of
the stop layer. The low-particle concentration composition also
tends to have longer shelf stability. Further, because the
composition contains a generally lower concentration of non-aqueous
components, the composition can be more easily concentrated. This
capability more readily permits the composition to be prepared and
shipped in a concentrate form, avoiding the need to ship water to
the purchaser.
[0018] The composition also provides a low defectivity response.
Wafers treated using the compositions exhibit low surface
roughness. Further, corrosion effects, including but not limited to
interfacial corrosion between the barrier and copper layers, and
copper corrosion involving the grain structure, are low.
Micro-scratching is also maintained at minimum levels. Also, the
presence of residual particles on the wafer surface is minimized by
use of the composition.
[0019] Additional objectives and advantages of the invention will
be set forth in the description which follows, and in part will be
understood from the description, or may be learned by practice of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings are incorporated herein and
constitute part of the specification. These drawings illustrate
embodiments of the invention and, in conjunction with the
description provided herein, serve to explain the principles of the
invention.
[0021] FIG. 1 is a schematic view of processing equipment which can
be used in connection with chemical mechanical planarization.
[0022] FIG. 2 is a graph of dishing step height relative to total
copper removal for a particular CMP composition.
[0023] FIG. 3 is a graph of erosion step height relative to total
copper removal for the same composition evaluated in FIG. 2.
[0024] FIG. 4 is a graph of dishing step height relative to total
copper removal for an alternate CMP composition.
[0025] FIG. 5 is a graph of erosion step height relative to total
copper removal for the same composition evaluated in FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0026] In its broader aspects the invention is directed to a
composition for use in planarizing a metal film on a wafer
comprising an oxidizing agent, an amino acid, particulate material
in a concentration range below which any significant abrasive
effects attributable to the particulate material are observed, and
water. The particle concentration usable to facilitate removal of
copper without significant removal of the stop layer is equal to or
less than about 4000 ppm. Typically the particle concentration in
the composition is about 5 ppm to less than 1000 ppm by weight,
more narrowly between about 5 ppm and about 700 ppm, still more
narrowly between about 5 ppm and about 400 ppm, and most narrowly
between about 5 ppm and about 100 ppm. It has been found that the
use in the composition of very low concentrations of particles, up
to a weight percentage which is below a level wherein the particles
could provide any negative observable abrasive effect traditionally
associated with higher abrasive concentration formulas, such as
micro-scratching, selectivity loss or dishing, provides beneficial
effects in copper layer removal from the wafer surface.
[0027] The particle size range of the particles used in the
composition should generally be on the order of about 4 to about
10,000 nm, and more narrowly about 4 nm to about 1,000 nm. Most
narrowly the particle size falls in the range of about 4 nm to
about 400 nm. The effect provided by the particles is generally not
dependent on particle size. However, improved copper removal rates
are observed with colloidal silica particles in the particle size
range of about 4 to 400 nm, and fumed silica with a particle size
in the range of about 40 to about 400 nm.
[0028] Other particles in addition to colloidal silica have utility
in the composition and method of planarizing. Generally, a wide
range of compositions can be used with good effect. Further, the
particles can be obtained through a variety of manufacturing and
processing techniques, including but not limited to thermal
processes, solution growth processes, mining of raw ore and
grinding to size, and rapid thermal decomposition. The materials
can be incorporated into the composition generally as supplied by
the manufacturer. Certain of the particulate materials usable in
the composition have been previously incorporated into CMP slurries
at higher concentrations as abrasive materials. However, other
particulate materials which have not traditionally been used as
abrasives in CMP slurries can also be used to provide advantageous
results. Representative particulate compositions include a variety
of inorganic and organic materials which are inert under the use
conditions of the composition of the invention, such as fumed
silica, colloidal silica, fumed alumina, colloidal alumina, cerium
oxide, titanium dioxide, zirconium oxide, polystyrene, polymethyl
methacrylate, mica, hydrated aluminum silicate, and mixtures
thereof. The particles have particle sizes ranging from about 4 nm
to about 10,000 nm, more narrowly from about 4 nm to about 1,000
nm, and most narrowly from about 4 nm to about 400 nm. The
particles may exist in a variety of physical forms, such as but not
limited to platelet, fractal aggregate and spherical species.
[0029] Colloidal silica is one particulate material which is
commercially available as a pre-dispersion in liquid media,
typically water. Other particulate materials are also available
commercially as pre-dispersions in the same or different liquid
media. The pre-dispersion contains a stabilizer which supplies
counter ions to charge the colloid surface and thereby improve the
colloidal stability. Stabilizers are used in preparing
pre-dispersions for a variety of particulate materials.
[0030] Electric diffusion factors tend to limit the nature of ions
which can be used to charge the colloid surface for applications in
semi-conductor manufacture. Non-limiting examples of materials for
contributing counter ions include ammonium hydroxide, potassium
hydroxide, hydrochloric acid, nitric acid and organic acids. The
concentration range of materials contributing counter ions in the
particle formula varies as a function of the desired pH of the
formula as well as the particle size of the particulate material,
with higher counter ion concentration generally required for
formulations incorporating smaller size particles. Non-limiting
factors which promote colloidal stability are pH values
sufficiently distinct from the pH at the isoelectric point, and a
low particle concentration in the liquid.
[0031] Optionally, the formulation can incorporate a corrosion
inhibitor, which limits metal corrosion and etching during the CMP
process. The corrosion inhibitor forms a protective film on the
metal surface by either physical adsorption or chemical adsorption.
The corrosion inhibitor is incorporated at a concentration level in
the range of about 10 ppm to about 20,000 ppm by weight, more
narrowly about 20 ppm to about 10,000 ppm by weight, and most
narrowly about 50 ppm to about 1000 ppm by weight. The corrosion
inhibitor operates to protect the copper surface from the effects
of etching and corrosion during the CMP process. One preferred
material is 1,2,4-triazole. Other materials which may be
incorporated as corrosion inhibitors include but are not limited to
nitrogenous cyclic compounds such as 1,2,3-triazole,
1,2,3-benzotriazole, 5-methylbenzotriazole, benzotriazole,
1-hydroxybenzotriazole, 4-hydroxybenzotriazole,
4-amino-4H-1,2,4-triazole, and benzimidazole. Benzothiazoles such
as 2,1,3-benzothiadiazole, triazinethiol, triazinedithiol, and
triazinetrithiol can also be used.
[0032] The oxidizing agent facilitates conversion of copper on the
wafer surface to hydrated copper compounds of either CuOH,
Cu(OH).sub.2, CuO, or Cu.sub.2O. The oxidizer can be hydrogen
peroxide, but may be any of a number of materials which perform an
oxidizing function, such as but not limited to ammonium dichromate,
ammonium perchlorate, ammonium persulfate, benzoyl peroxide,
bromates, calcium hypochlorite, ceric sulfate, chlorates, chromium
trioxide, ferric trioxide, ferric chloride, iodates, iodine,
magnesium perchlorate, magnesium dioxide, nitrates, periodic acid,
permanganic acid, potassium dichromate, potassium ferricyanide,
potassium permanganate, potassium persulfate, sodium bismuthate,
sodium chlorite, sodium dichromate, sodium nitrite, sodium
perborate, sulfates, peracetic acid, urea-hydrogen peroxide,
perchloric acid, di-t-butyl peroxide, monopersulfates and
dipersulfates. Preferably the oxidizing agent is incorporated into
the formulation on site at the time of use or shortly prior
thereto. It is also possible to incorporate the oxidizing agent at
the time of combining the other components, though stability of the
thus-formed composition over longer storage conditions must be
taken into consideration. The oxidizing agent is incorporated at a
concentration level in the range of about 0.1% to about 20% by
weight, more narrowly about 0.25% to about 5% by weight.
[0033] At least one amino acid is incorporated into the
formulation. The presence of amino acid in the formulation has been
found to affect the rate of copper removal during the CMP process.
However, increased amino acid levels increase the etching rate of
the copper, which is undesirable. Concentration levels are
therefore adjusted to achieve an acceptable balance between copper
rate of removal and the etching rate. Typically, the concentration
of the amino acid is within the range of about 0.05% to about 5% by
weight, and more narrowly between about 0.25% and about 2% by
weight.
[0034] A variety of amino acids can be used in the preparation of
the CMP formulation. Good results have been obtained using
aminoacetic acid, also known as glycine. Other representative amino
acids which can be used in the composition include but are not
limited to serine, lysine, glutamine, L-alanine, DL-alanine,
iminoacetic acid, asparagine, aspartic acid, valine, sarcosine, and
mixtures thereof.
[0035] Typically, water constitutes a major weight percentage of
the formulation. Generally, water which is acceptable in preparing
formulations will not adversely affect the CMP processing, and will
neither adversely affect the stability of the formulation nor the
surface of the wafer subjected to the CMP processing. Typically,
deionized water is used in preparing the formulation, though
distilled water or reverse osmosis water may also be used.
[0036] The individual formulations described herein can be prepared
from a single oxidizing agent, amino acid, particulate material,
water source and optional additive such as a corrosion inhibitor.
However, the formulation can also incorporate mixtures of each or
all of these components with good effect.
[0037] As an alternative to the inventive formulations, the rate of
removal for copper could be increased by incorporating abrasives
into a CMP formulation. Nonetheless, a high abrasive loading in the
formulation can create micro-scratches, leave residual abrasive or
metal particles on the metal, and promote dishing and erosion on
the wafer surface. The incorporation of both very low levels of
particles and lowered levels of an amino acid in place of high
abrasive loadings or an elevated amino acid concentration provide
an improved rate of removal of the copper layer while at the same
time avoiding the disadvantages attributed to high abrasive loading
and the copper etching associated with elevated levels of the amino
acid. The ability to produce a composition which attains rates of
removal comparable to highly loaded abrasive-containing
compositions but having a low concentration of amino acid and
particle relative to highly loaded abrasive-containing compositions
more readily permits delivery of a concentrated form of the
composition to the customer.
[0038] For formulations containing higher levels of particulates,
maintaining colloidal stability generally requires that the pH be
brought to within a narrow range. However, to control the polish
rate or static etch rate of the formulation in a CMP process, the
pH may preferably need to be set at a different value which is not
consistent with maintaining optimum colloidal stability. The low
particulate concentration in the inventive formulations diminishes
the requirement for operating within a particular pH range to
optimize colloidal stability, and thereby permits more flexibility
in controlling the polish rate and static etch rate.
[0039] The composition of the invention can be employed in CMP
processing equipment without modification of the equipment or the
process methodology. The process and equipment described below is
exemplary; however, variations of the process and equipment have
been used which can also employ the composition of the
invention.
[0040] In referring to FIG. 1, the CMP procedure for polishing a
wafer in commercial practice utilizes a chuck, or carrier 2, which
holds the wafer 4 in position relative to a polishing table, also
known as a platen 6. This particular arrangement of polishing and
holding devices is known as the hard-platen design. In this
arrangement the wafer surface to be polished is secured in the
carrier 2 which holds the wafer 4 in a generally horizontal
orientation, the surface to be polished facing down. The carrier 2
may retain a carrier pad 8 which lies between the retaining surface
of the carrier 2 and the surface of the wafer 4 which is not being
polished. This pad 8 can operate as a cushion for the wafer 4,
though alternate cushioning materials can be utilized.
[0041] Below the carrier is a larger diameter platen 6, which is
also oriented generally horizontally, presenting a surface parallel
to that of the wafer to be polished. The platen 6 is fitted with a
polishing pad 10 which contacts the wafer surface during the
planarization process. Polishing is facilitated by a polishing
composition 12 which is generally applied onto the polishing pad 10
as a stream or in a dropwise fashion. This composition 12 supplies
materials which assist in removing particles from the surface, and
acts as a medium for the convective transport of polish byproducts
to be removed from the vicinity of the wafer surface.
[0042] After the wafer 4 secured into the carrier 2 is aligned
relative to the polishing pad 10 on the platen 6, both the carrier
2 and the platen 6 are caused to rotate around respective shafts 2A
and 6A extending perpendicularly from the carrier and platen. The
parallel relationship between wafer surface and polishing pad is
maintained throughout the process. The rotating carrier shaft 2A
may remain fixed in position relative to the rotating platen 6, or
may oscillate horizontally relative to the platen 6. Polishing
composition 12 is continuously supplied during the planarization
process as either a stream or dropwise. The direction of rotation
of the carrier 2 containing the secured wafer 4 typically, though
not necessarily, is the same as that of the platen 6. The speeds of
rotation for the carrier 2 and platen 6 are generally, though not
necessarily, set at different values. Generally, the carrier 2
rotates at about 30 rpm, while the platen 6 rotates at about 90
rpm. In practice, the carrier rotates over a range of speeds from 0
to 120 rpm, and the platen rotates over a range of speeds from 0 to
150 rpm.
[0043] The rate of removal of material on the surface of the wafer
4 varies as a function of the pressure, or downforce, exerted on
the wafer surface by the respective proximity of the carrier 2 to
the platen 6, and the rotational speeds of the carrier 2 and platen
6. Generally, the pressure exerted on the wafer surface being
polished is in the range of about 0 to 10 psi, with a typical
pressure of about 2.8 psi. Depending on the composition and
thickness of the material being removed by the planarization
procedure, the time required to complete one planarization routine
for a single wafer is on the order of 1 to about 10 minutes.
[0044] Factors which may influence the planarization process
include among others the wafer downforce, platen speed, pad
structure, pad conditioning, the chemistry of the polishing
composition, and the composition supply rate. Planarization is
maximized by employing minimum downforce and high relative rotation
speed. Wafer surface removal rate is maximized by increasing the
downforce and table speed.
EXAMPLES
[0045] The following detailed examples illustrate the practice of
the invention in its most preferred form, thereby enabling a person
of ordinary skill in the art to practice the invention. The
principles of this invention, its operating parameters and other
obvious modifications can be understood in view of the following
detailed procedures.
Example 1
[0046] The rates of removal for several materials on a wafer
surface were evaluated using several formulations. The testing
apparatus was an IPEC 472 unit from SpeedFam-IPEC Corporation,
Phoenix, Ariz. The 22.5 inch (57.21 cm) diameter table was fitted
with a pre-stacked K-grooved IC 1000/SBA IV polishing pad from Rode
Corp., Phoenix, Ariz. 85034. The table was rotated relative to a
smaller diameter rotating carrier to which the 200 mm wafer was
attached. Both the table, also known as the platen, and the carrier
rotated in the same direction, but at different speeds. Polishing
formulation was deposited onto the polishing pad and thereby
conveyed by relative movement of the rotating pad to the carrier
into contact with the wafer surface.
[0047] Several sets of process parameters were utilized during the
course of evaluating various formulations for their ability to
remove material from the wafer surface. The process parameters can
affect the copper removal rate and the parameters for each
evaluation are therefore set out herein. The process parameters
utilized on the test apparatus for the first example are set out
below; as used in other examples these parameters are identified as
OP-I herein. Potential sources of possible removal rate variation,
such as the condition of the polishing pad and pad conditioner,
were also maintained in a generally constant state, as
possible.
1 OP-I Down Force on the Carrier: 3 psi Backfill Pressure on the
wafer: 2 psi Platen Speed: 90 rpm Carrier Speed: 30 rpm Pad Type:
IC 1000 S-IV (Rode Inc., Phoenix AZ 85034) Pad Conditioning 1591 g.
5.08 cm (Morgan Advanced Ceramics Inc., Diamine Division,
Allentown, PA), 75.mu. grid pad, in situ Slurry Flow Rate: 200
ml/min
[0048] Four different wafers were used in the tests, each with an
eight inch (20.3 cm) diameter. The wafers were:
[0049] Cu Blanket Film (Wafered Inc., San Jose, Calif.)
[0050] Ta Blanket Film (Wafered Inc., San Jose, Calif.)
[0051] SiO.sub.2 Blanket Film (Wafered Inc., San Jose, Calif.)
[0052] 854AZ Patterned Film (International SEMATECH, Austin,
Tex.)
[0053] To evaluate the effect of low concentrations of colloidal
silica particles on the copper removing ability of the formulation,
aqueous solutions were prepared according to the following
compositions listed below. Unless otherwise indicated, all
concentrations herein are listed by weight percent.
[0054] Unless otherwise noted herein, hydrogen peroxide was
introduced into the formulations as a 30% solution by weight in
water. Also, 1,2,4-triazole was introduced as a 33% by weight
solution in water, this solution being commercially available from
Ashland Specialty Chemical Co. Unless otherwise noted, the amounts
of component materials in the tables listed below are provided on a
100% actives basis.
2 TABLE 1 Component Formula 1 Formula 2 H.sub.2O.sub.2 1% 1%
Aminoacetic Acid 1% 1% 1,2,4-Triazole 500 ppm 500 ppm SiO.sub.2
0.0% 0.1% Deionized Water Balance Balance
[0055] Test solutions were prepared by dissolving the desired
amount of aminoacetic acid and 1,2,4-triazole in deionized water in
an open container. To the test solution was added the desired
amount of colloidal silica having a pH of 9 and 84 nm particle
size. The colloidal silica was from W. R. Grace with ammonium
hydroxide stabilization. The colloidal silica is in the form of a
suspension having a solids content of 48% by weight silica with the
remainder being water and ammonia, based upon the total weight of
the suspension. The specific gravity of the suspension is 1.35. The
solution containing colloidal silica was homogenized by physical
agitation using a stirring rod for several minutes before adding
H.sub.2O.sub.2 as the oxidizer.
[0056] Generally, the particle size data supplied herein was
provided by the manufacturer of the particulate material. In
instances where the particulate material was supplied in the form
of a powder, particle size was measured using an Accusizer 788/388
ASP device from Particle Sizing System, Santa Barbara, Calif. Mean
particle size and particle size distribution is measured in this
device by registering the scattering intensity from dispersed
particles at a 90 degree angle and then performing an
autocorrelation analysis to yield the mean particle size and
particle size distribution. The Accusizer 788/388 device features
an autodilution chamber, a solid-state He/Ne laser and a
128-channel photon correlator. The device dilutes the injected
sample to a proper concentration, then selects the proper channel
width to record photons scattered from the sample. The
autocorrelation period is ten minutes. Mean particle size and
particle size distribution can be generated on the basis of
intensity average, volume average and number average; intensity
average is reported and the measured particulate materials are
reported herein by mean particle size.
[0057] Formula 3 was prepared by blending formulas 1 and 2 from
Table 1 in varying amounts. Thus, formula 3 was prepared by mixing
200 parts by volume of formula 2 with 1500 parts by volume of
formula 1 into a container.
3 TABLE 1A Component Formula 3 H.sub.2O.sub.2 1% Aminoacetic Acid
1% 1,2,4-Triazole 500 ppm SiO.sub.2 0.012% Deionized Water
Balance
[0058] The electroplated copper, physical vapor-deposited tantalum
and chemical vapor-deposited TEOS-grown silicon dioxide blanket
film wafers were then subjected to the CMP process using OP-I for a
one minute polish period. The respective film removal rates for
each of the three wafers were measured using a Tencor RS35c 4-point
probe for the copper and tantalum metal films and a Philips SD 2000
ellipsometer for the TEOS film.
[0059] The rate of removal value was determined by measuring the
thickness difference of the tested wafer from pre to post-polish.
The thickness of the metal film, T, was measured by applying the
equation T.times.R=resistivity coefficient, wherein T is the film
thickness in .ANG. and R is the sheet resistance in
.OMEGA./.quadrature.. The sheet resistance was measured using a
Tencor RS35c 4-point probe, KLA-Tencor Corporation, San Jose,
Calif. The resistivity coefficient is a constant for a particular
metal film but not for all films of the same metal. In the instant
case for a pure thin copper film, the resistivity coefficient used
was 1.8 .mu..OMEGA.-cm. For a pure thin tantalum film, the
resistivity coefficient used was 177 .mu..OMEGA.-cm. The thickness
of the SiO.sub.2 dielectric film was determined using a Philips
Analytical, Natick, Mass., SD-2000 dual wavelength ellipsometer
with an index of refraction, n, of 1.47 at 632.8 nm and 1.45 at
1540 nm.
[0060] In evaluating metal film thickness, the film was measured
for sheet resistance to determine initial thickness using the
equation above, after which the film was polished using a CMP
protocol for one minute. After the polish step the wafer was
cleaned by spin rinsing and drying, and the sheet resistance was
measured again, to calculate the residual thickness. The amount of
film removed was then determined by calculating the difference in
thickness before and after the polish step.
[0061] The Tencor 4-point probe was also used for determining the
metal static etch rate (SER). The static etch rate for a particular
formula compared with the rate of removal for the same metal
provides a measure of the formula's ability to facilitate metal
polishing without undesirable metal removal via etching. Square
wafer pieces nominally about 3.3 cm on each side were measured for
thickness with the Tencor RS35c probe prior to etching. The pieces
were then suspended by a sample holder in a 250 ml beaker. To the
beaker was then added the test solution which covered the suspended
wafer piece. The solution was agitated using a magnetic stirrer
operating at about 125 rpm during the etch period, nominally 20
minutes at room temperature. To get accurate rate results, at least
about 300 .ANG. of material from the surface should be removed.
[0062] After the etch period was completed, the wafer pieces were
removed, washed in deionized water, and blown dry using compressed
air or nitrogen. The amount of material removed was then determined
by subtracting the pre-measurement average film thickness from the
post-measurement average film thickness.
[0063] Tantalum rate of removal was determined in the same manner
as for copper rate of removal. SiO.sub.2 rate of removal was
determined by use of the Philips SD 2000 ellipsometer.
[0064] The results showing film removal rates of all films and
etching rate of copper are set out below in Table 2. Listed results
for all film removal rates herein were taken as an average of 49
points across the diameters of 2 wafers, the average thus being
based on 98 data points. Listed results for all static etch rates
were taken as an average of 9 measurements across the sample
piece.
4TABLE 2 Formula SER Ta RR SiO.sub.2 RR Cu RR No. (.ANG./Min)
(.ANG./Min) (.ANG./Min) (.ANG./Min) 1 54.3 14 3 337 2 63.0 12.7 0
8266 3 * <15 0 8307 * Test was not performed
[0065] The results demonstrate the substantial improvement in
copper removal rate by the addition of very small amounts of
colloidal silica. Formula 3 containing only 0.012% colloidal silica
produced a copper removal rate more than 24 times greater than
formula 1, which was identical in all respects except for the
presence of colloidal silica. Higher amounts of colloidal silica
incorporated into the formula, as shown in formula 2, provided
comparable copper and tantalum removal rate results to that found
with formula 3. The tantalum rate of removal was considered to be
insignificant, and it can be seen that the formulas containing
colloidal silica removed about the same amount of tantalum as the
base formula containing no colloidal silica. SiO.sub.2 removal was
effectively zero for all formulas.
[0066] The copper to stop layer selectivity, in this instance for
tantalum, was determined by comparing the rate of removal of copper
relative to that of tantalum for each of the formulas where both
copper and tantalum rates of removal were determined. In addition,
the static etch rates for copper generated for formulas 1 and 2
were measured and were found to be very low when compared to the
copper rate of removal. The rate of removal of copper relative to
the static etch rate for copper was determined for formulas 1 and
2. A high ratio of removal rate to etch rate is preferred. The
ratios are provided in Table 2A below.
5TABLE 2A Formula Cu/ Cu RR/ No. Ta RR Cu SER 1 24.1 6.2 2 650.9
131.2 3 553.8 --
[0067] Thus, high Cu: Ta selectivities were obtained using formulas
2 and 3 while still maintaining a relatively low etch rate. Also,
high Cu RR/Cu SER performance was achieved by formula 2.
[0068] Additional formulas having varying concentrations of
particulate material, amino acid and corrosion inhibitor components
were produced by mixing formula 2 from Table 1 above with a 1% (by
weight) H.sub.2O.sub.2 solution at varying relative concentrations
into an open container at room temperature. The following formulas
4 through 11 have the compositions as set out in Table 3 below. The
relative amounts of formula 2 and the H.sub.2O.sub.2 solution were
incorporated into the listed formulas on a percent volume basis.
Table 3 also provides the effective resulting concentration of
oxidizing agent, amino acid, corrosion inhibitor and particulate
material for the various formulas.
6TABLE 3 Formula Formula Formula Formula Formula Formula Formula
Formula Component 4 5 6 7 8 9 10 11 1% H.sub.2O.sub.2 (by volume)
95 90 85 80 75 65 50 25 Formula 2 (by volume) 5 10 15 20 25 35 50
75 Colloidal Silica Content (ppm) 50 100 150 200 250 350 500 750
Aminoacetic Acid Content (ppm) 500 1000 1500 2000 2500 3500 5000
7500 1,2,4-Triazole Content (ppm) 25 50 75 100 125 175 250 375
Total H.sub.2O.sub.2 Content (ppm) 10,000 10,000 10,000 10,000
10,000 10,000 10,000 10,000
[0069] CMP applications were conducted on each of the copper,
tantalum and SiO.sub.2 blanket wafers using the above described
IPEC 472 platform and the OP-I CMP protocol described in Example 1
using formulas 4 through 11 for a one minute run time. For each
formula, the rate of removal results for copper, tantalum and
SiO.sub.2, as well as the copper to tantalum selectivity ratio are
set out in Table 4 below. The rate of removal measurement set out
above was used.
7TABLE 4 Formula Cu RR Ta RR TEOS RR Cu/ Colloidal Silica No.
(.ANG./Min) (.ANG./Min) (.ANG./Min) Ta RR Content (ppm) 4 622 9 0
69.1 50 5 1269 9 22 141 100 6 2965 5 0 593 150 7 2791 13 0 214.7
200 8 2951 9 0 327.9 250 9 4535 13 27 348.8 350 10 5848 12 28 487.3
500 11 6790 18 3 377.2 750
[0070] As the results in Table 4 indicate, the rate of removal of
tantalum and SiO.sub.2 remains low for all formulas. The rate of
removal of copper, on the other hand varied from 622 .ANG./Min to
6790 .ANG./Min. Thus, the rate of removal of copper can be rendered
tunable relative to the tantalum and SiO.sub.2 removal rate.
[0071] Two compositions were also tested for their ability to
provide satisfactory planarization performance with minimum
topography. Formula 2 as prepared above was used to planarize an 8"
SEMATECH 854AZ patterned wafer, which was evaluated for dishing
effects on an isolated 100 .mu.m wide line and for erosion effects
on a 9 .mu.m by 1 .mu.m, 90% metal density array. Planarization was
conducted using CMP protocol OP-II which varied from OP-I in
several respects. The OP-II protocol is set out below.
8 OP-II Down Force on the Carrier: 2 psi Backfill Pressure on the
wafer: 1 psi Platen Speed: 120 rpm Carrier Speed: 30 rpm Pad Type:
IC 1000 S-IV (Rode Inc., Phoenix AZ 85034) Pad Conditioning 1591 g.
5.08 cm (Morgan Advanced Ceramics Inc., Diamine Division,
Allentown, PA), 75.mu. grid pad, in situ Slurry Flow Rate: 200
ml/min
[0072] The patterned wafer was subsequently analyzed for dishing
and erosion effects by measuring the step height magnitude of such
structures on the 854AZ patterned wafer after each polishing step,
using a Tencor P2 profiler from KLA-Tencor Corporation. The dishing
on isolated 100 .mu.m wide lines from the center, mid radius and
edge die of the SEMATECH 854AZ patterned wafer was characterized.
Further, the erosion on a 9 .mu.m by 1 .mu.m, 90% metal density
array from the center, mid radius and edge die of the patterned
wafer was characterized.
[0073] Data generated using formula 2 for the cumulative total
amount of copper removed on an equivalent die location basis on
blanket copper films polished under identical conditions as for
each patterned wafer polish and the dishing step height magnitude
at center, mid radius and edge die locations for the dishing
evaluation are set out in Table 5. The data points were used to
generate the graph as shown in FIG. 2.
[0074] Data generated using formula 2 for the cumulative total
amount of copper removed on an equivalent die location basis on
blanket copper films polished under identical conditions as for
each patterned wafer polish and the erosion step height magnitude
at center, mid radius and edge die locations for the erosion
evaluation are set out in Table 6. The data points were used to
generate the graph as shown in FIG. 3.
9TABLE 5 Dishing Step Height Evaluation (Formula 2) Total Copper
Dishing Step Removed From Height (100.mu. .times. Die Location Die
(.ANG.) 100.mu.) (.ANG.) Center Die 0 6000 6934 200 9459 0 12000
600 13064 900 Middle Die 0 6250 7321 100 10178 0 13025 600 14109
1150 Edge Die 0 6250 6593 100 10180 400 14284 1650 15888 1900
[0075]
10TABLE 6 Erosion Step Height Evaluation (Formula 2) Total Copper
Erosion Step Removed From Height (9.mu. Metal Die Location Die
(.ANG.) 1.mu. Post) (.ANG.) Center Die 0 2700 6934 100 9459 0 12000
275 13064 300 Middle Die 0 2400 7321 100 10178 175 13025 400 14109
400 Edge Die 0 2500 6593 550 10180 175 14284 450 15888 500
[0076] In a separate test, formula 3A was prepared comprising 35
ppm colloidal silica of the type identified above in Example 1,
0.35% aminoacetic acid, 175 ppm 1,2,4-triazole, 1% hydrogen
peroxide and the balance deionized water. This formula was
evaluated for dishing effect using the SEMATECH 854AZ patterned
wafer. Planarization was conducted using the OP-II CMP protocol
above. The wafer was then analyzed for dishing effects at the
center, middle, and edge die locations. Data generated using
formula 3A for the total amount of copper removed and the dishing
step height for the dishing evaluation are set out in Table 7
below. The data points were used to generate the graph as shown in
FIG. 4. Data generated using formula 3A for the total amount of
copper removed and the erosion step height at center, middle and
edge die locations for the erosion evaluation are set in Table 8
below. The data points were used to generate the graph as shown in
FIG. 5.
11TABLE 7 Dishing Step Height Evaluation (Formula 3A) Total Copper
Dishing Step Removed From Height (100.mu. .times. Die Location Die
(.ANG.) 100.mu.) (.ANG.) Center Die 0 5700 6999 150 7946 0 8969 0
10357 125 11862 375 Middle Die 0 6000 7748 0 8763 0 9782 0 11342
200 12869 475 Edge Die 0 6100 7500 150 8887 150 10010 0 11897 600
13638 1100
[0077]
12TABLE 8 Erosion Step Height Evaluation (Formula 3A) Total Copper
Erosion Step Removed From Height (9.mu. Metal Die Location Die
(.ANG.) 1.mu. Post) (.ANG.) Center Die 0 2500 6999 400 7946 300
8969 0 10357 0 11862 150 Middle Die 0 2500 7748 400 8763 0 9782 0
11342 175 12869 325 Edge Die 0 2500 7500 750 8887 200 10010 200
11897 250 13638 500
[0078] In evaluating the topography evolution during polishing on
the as-plated 854AZ patterned wafer, the amount of copper removal
was measured on a blanket copper plated film polished under
otherwise identical conditions. This amount of copper removal was
measured by a 4-point probe but using the five Tencor RS35c
measurements which correspond to the equivalent die location on the
patterned wafer. The cumulative amount of copper removed in each
sequential polish was compared with the height difference of
material in the feature of interest relative to the height of
material just outside the feature of interest, in absolute terms.
For a dishing effect evaluation, the height of the copper in a
trench was compared to the adjacent height of material just outside
the trench. The trench width was 100 .mu.m. For an erosion effect
evaluation, the maximum height of material at the middle of the 90%
metal density array is compared to the height of material just
outside the array. The width of copper lines relative to the
adjacent silica lines was 9 .mu.m to 1 .mu.m. For both the dishing
and erosion effect evaluations, the process started with
significant as-plated topography. The copper removal process
reached a point wherein the copper in the feature was at
substantially the same height as the copper on the surrounding
surface, thus essentially achieving a state without topography but
with remaining copper overburden. Continued polishing then began to
clear copper overburden and remove copper inside the trench feature
relative to material outside the trench on the surrounding wafer,
and the absolute value of this difference in height appeared on the
graphs shown in FIGS. 2, 3, 4 and 5. The build-up of topography
during this clearing process generally increased in a linear
fashion with the extent of total amount of copper removed. The
slope of the topography build-up relative to the copper removed is
termed the dishing or erosion susceptibility for the structure of
interest and can be used as a performance metric. This
susceptibility value is dimensionless. The lower the value of
slope, the lower the amount of topography at any given amount of
copper removed and the better the performance. For the data from
Tables 5 and 6 the magnitude of 100 .mu.m wide line dishing
susceptibility was approximately 0.29 as shown in FIG. 2 and the
magnitude of 90% metal density erosion susceptibility was
approximately 0.07 as shown in FIG. 3. For the data from Tables 7
and 8, the corresponding magnitudes of dishing and erosion
susceptibilities for formula 3A were 0.2 and 0.097 respectively, as
shown in FIGS. 4 and 5 respectively. Both dishing and erosion
susceptibilities were determined by a least squares fit on the data
points of the overpolishing portion of the graphs. The formulas
described were used with the OP-II test protocol. The run times
were varied over the course of the evaluation. Sequential polish
times of 60 sec, 30 sec, 30 sec, and 30 sec were used for the
formula 2 evaluation. Sequential polish times of 60 sec, 60 sec, 30
sec, 30 sec, 40 sec and 40 sec were used for the formula 3A
evaluation, with the interval between the start point (0 .ANG.
copper removed) and the next data entry receiving two polish times
of 60 seconds each.
Example 2
[0079] The ability of different particulate substances in the
composition to enhance the copper removal rate was evaluated. A
single formulation composition as set out in Table 9 below was used
to evaluate various particulate materials.
[0080] The individual formulas were prepared by first blending
aminoacetic acid, 1,2,4-triazole and water, then adding in the
specific particulate material generally in the form of a
pre-dispersion or other water-containing flowable form from the
manufacturer; or alternatively directly from the powder or as a
homogeneous laboratory-prepared mixture of powder and water
optionally containing small amounts of stabilizing additive.
13 TABLE 9 Component Concentration H.sub.2O.sub.2 1% Aminoacetic
Acid 1% 1,2,4-Triazole 500 ppm Particulate Material 0.1% Deionized
Water Balance
[0081] Various formulations were developed by substituting
different particles and evaluating the rates of removal. The CMP
protocol described in Example 1 (OP-I) was utilized for a one
minute run time for formulas 12, 13 and 14 below. The copper film
removal rate was measured using a Tencor RS35c 4-point probe. Each
particulate material for this series of runs was compounded into
the respective formulas from the powder form, and mean particle
sizes were generated using the Accusizer measurement equipment
described above.
[0082] The fumed silica was mixed in the laboratory with deionized
water sufficient to prepare a 20% suspension by weight, with
addition of about 255 ppm phosphoric acid. NH.sub.4OH was also
incorporated to adjust the final pH to approximately 7. The mixture
was agitated using a homogenizer for about 10 minutes. The aluminum
oxide powder was combined in the laboratory with deionized water
sufficient to prepare an 18% solids pre-dispersion with addition of
about 750 ppm phosphoric acid. No further pH adjustment was
employed. The mixture was agitated using a homogenizer for about 10
minutes. The titanium dioxide was pre-dispersed in deionized water
to produce a 10% solids suspension. 300 ppm H.sub.3PO.sub.4 was
introduced into the mixture, and NH.sub.4OH was added as necessary
to adjust the pH to approximately 7. The mixture was agitated using
a homogenizer for 10 minutes. In all cases the oxidizer was added
after the other components were combined. The formula number,
particulate material utilized in the formulation and copper rates
of removal are provided below in Table 10 for fumed silica, fumed
aluminum oxide, and titanium dioxide. The rate of removal
measurement set out in Example 1 was used.
14TABLE 10 Formula Particulate Cu RR No. Material (.ANG./Min.) 12
Fumed SiO.sub.2.sup.1 8984 13 Fumed Al.sub.2O.sub.3.sup.2 4501 14
TiO.sub.2.sup.3 7963 .sup.1Aerosil 90 Product, 250 nm particle
size, available from Degussa Corp., New Jersey .sup.2Aluminium Oxid
C Product, 300 nm, available from Degussa Corp., New Jersey
.sup.3Titan Dioxid P25, 300 nm, available from Degussa Corp., New
Jersey
[0083] A separate group of runs on additional compositions of
particulate materials was generated using another CMP protocol
identified as OP-III with a one minute run time. The relevant
parameters were as follows:
15 OP-III Down Force on the Carrier: 2.8 psi Backfill Pressure: 2
psi Platen Speed: 150 rpm Carrier Speed: 30 rpm Pad Type: IC 1000
S-IV (Rode Inc., Phoenix AZ 85034) Pad Conditioning: 1591 g. 5.08
cm (Morgan Advanced Ceramics Inc., Diamine Division, Allentown,
PA), 75.mu. grid pad, in situ Slurry Flow Rate: 150 ml/min
[0084] The formulas containing the additional particulate materials
used in the OP-III protocol produced copper rate of removal data
which are set out below.
[0085] The CeO.sub.2 was introduced with agitation into the
combination of aminoacetic acid, 1,2,4-triazole and water as a
commercially prepared slurry. The polystyrene latex spheres were
introduced into the combination of aminoacetic acid, 1,2,4-triazole
and water with mechanical stir bar agitation for about 10 minutes.
The formulas containing kaolin and mica powders were prepared in
similar manner to the formula containing polystyrene latex spheres.
In all cases the oxidizer was added after the other components were
combined. The rate of removal measurement set out in Example 1 was
used.
16TABLE 10A Formula Particulate Cu RR No. Material (.ANG./Min.) 15
CeO.sub.2.sup.1 4160 16 Polystyrene 4585 Latex.sup.2 17
Kaolin.sup.3 3711 18 Mica.sup.4 3036 .sup.1Particle size 250 nm,
17.7% slurry, available from Nanophase Materials, Illinois
.sup.2Particle size 1.mu., available from Poly Sciences Inc.,
Illinois .sup.3Particle size 0.3.mu., available from Engelhard, New
Jersey .sup.4Particle size 3-10.mu., available from E M Industries,
New York
[0086] The copper rate of removal results in Tables 10 and 10A
demonstrate the effectiveness of formulations containing a variety
of particle compositions. It should be noted that good rates of
removal were observed using materials such as kaolin and mica,
which have a particulate structure distinct from that of silica and
alumina.
Example 3
[0087] The use of other amino acids in addition to aminoacetic acid
was evaluated. Various formulations containing components identical
but for the amino acid were prepared, having a base composition as
shown below in Table 11. The colloidal silica was the same as that
described previously in Example 1. The test solutions were prepared
by dissolving the desired amount of amino acid and 1,2,4-triazole
in deionized water in an open container. To this solution was added
the colloidal silica. The solution containing the colloidal silica
was homogenized by physical agitation using a stirring rod for
several minutes before adding H.sub.2O.sub.2 as the oxidizer.
17 TABLE 11 Component Concentration H.sub.2O.sub.2 1% Amino Acid 2%
1,2,4-Triazole 500 ppm Colloidal SiO.sub.2 0.1% Deionized Water
Balance
[0088] The formulation numbers and particular amino acids used in
each of the formulations are listed below in Table 12. Table 12
lists the formula number, the particular amino acid used and the
rate of removal of the copper for a one minute run as measured
using a Tencor RS35c 4-point probe. The OP-III CMP protocol
described in Example 2 was used, and the rate of removal
measurement set out in Example 1 was used.
18TABLE 12 Formula Cu RR No. Amino Acid (.ANG./Min.) 19 Serine 8267
20 Lysine 1906 21 Glutamine 5650 22 L-alanine 5588 23 DL-alanine
5739 24 Iminoacetic Acid 1945 25 Asparagine 4260 26 Aspartic Acid
2787 27 Valine 1977 28 Sarcosine 5852
[0089] In the above formulations no pH adjustment was required
except for formulation 24 containing iminoacetic acid, with which
NH.sub.4OH was used to adjust the pH to 7. The pH for the remaining
formulations fell within a range of 5.5 to 7.3.
Example 4
[0090] The effective range of pH for the CMP formulas was also
evaluated. Three aqueous mixtures comprised of 1% H.sub.2O.sub.2,
1% aminoacetic acid, 500 ppm of 1,2,4-triazole, and 0.1% colloidal
SiO.sub.2 of the type described in Example 1 above were prepared.
The initial pH values were all 6.6. One portion (formula 30) was
retained at this pH. Ammonia solution was incorporated into a
separate portion of the original composition to adjust this sample
(formula 31) to a pH of 9. Citric acid was incorporated into a
separate portion to adjust this sample (formula 29) to a pH of 3.5.
The OP-III CMP protocol described in Example 2 was used for a one
minute run time, and the copper rate of removal measurement set out
in Example 1 was used. The test results are set out below in Table
13.
19TABLE 13 Formula Cu RR No. pH (.ANG./Min.) 29 3.5 2281 30 6.6
7229 31 9.0 3109
[0091] Acceptable rate of removal results were observed to be
obtained over a range of pH values.
Example 5
[0092] The effect of copper rate of removal relative to the change
in concentration of the particulate material alone in the formula
was also evaluated. A single base formulation for this example was
developed having the components and concentration values listed in
Table 14 below.
20 TABLE 14 Component Concentration H.sub.2O.sub.2 1% Aminoacetic
Acid 1% 1,2,4-Triazole 500 ppm Colloidal SiO.sub.2 Various loading
levels Deionized Water Balance
[0093] The formulations below were prepared utilizing different
concentrations of colloidal silica and the copper rate of removal
was measured. The colloidal silica was that previously described in
Example 1. The OP-III CMP protocol described in Example 2 was used
for a one minute run time, and the rate of removal measurement set
out in Example 1 was used. The test solutions were prepared by
dissolving the desired amount of amino acid and 1,2,4-triazole in
deionized water in an open container. To this solution was added
the colloidal silica. The solution containing the colloidal silica
was homogenized by physical agitation using a stirring rod for
several minutes before adding H.sub.2O.sub.2 as the oxidizer. Table
15 below shows the various formulations, colloidal silica loading
levels, and copper removal rates.
21TABLE 15 Formula SiO.sub.2 Cu RR No. (ppm) (.ANG./Min.) 32 0 1661
33 5 5531 34 10 6175 35 35 4822 36 1000 7229
[0094] Substantial increases in copper rate of removal were
observed in formulas having even very low levels of colloidal
silica relative to the formula containing no added colloidal
silica.
Example 6
[0095] The ability of a formulation to be diluted was also
evaluated. Formula 37, set out below in Table 16, was initially
prepared as a concentrate but without the H.sub.2O.sub.2 oxidizer
and then diluted with 40 volumes of water sufficient to create a
solution having the same component concentrations as formula 38,
also set out in Table 16. Formula 38 was separately prepared having
the component concentrations appearing in Table 16. The test
solutions were prepared by dissolving the desired amount of amino
acid and 1,2,4-triazole in deionized water in an open container. To
this solution was added the colloidal silica. The solution
containing the colloidal silica was homogenized by physical
agitation using a stirring rod for several minutes. H.sub.2O.sub.2
as the oxidizer was added only to formula 37 after the dilution
with water to form the solution as actually tested.
[0096] The OP-III protocol set out in Example 2 was used to
evaluate the copper rate of removal for formulas 37 and 38 using a
one minute run time. Rate of removal was measured using a Tencor
RS35c 4-point probe, and the rate of removal measurement set out in
Example 1 was used. The copper rates of removal are set out below
in Table 16 for formula 38 prepared with normal dilution of water,
and from the concentrate (formula 37) with subsequent dilution. For
comparison, formula 2 was also prepared as a concentrate, shown
below as formula 39, but without the H.sub.2O.sub.2 as the oxidizer
and the formula prepared as set out above. This formula 39 was then
diluted with 10 volumes of water sufficient to create a solution
having the same component concentrations as formula 2, also set out
below. Formula 2 was separately prepared having the component
concentrations which appear in Table 16. H.sub.2O.sub.2 as the
oxidizer was added only to formula 39 after the dilution with water
to form the solution as actually tested. A modified protocol
(OP-IV) set out below was used to evaluate the copper rate of
removal for diluted formula 39 and formula 2 using a one minute run
time.
22 OP-IV Down Force on the Carrier: 2 psi Backfill Pressure: 1.5
psi Platen Speed: 50 rpm Carrier Speed: 30 rpm Pad Type: IC 1000
S-IV (Rode Inc., Phoenix AZ 85034) Pad Conditioning: 1591 g. 5.08
cm (Morgan Advanced Ceramics Inc., Diamine Division, Allentown,
PA), 75.mu. grid pad, in situ Slurry Flow Rate: 150 ml/min
[0097] Rate of removal was measured using a Tencor RS35c 4-point
probe, and the rate of removal measurement set out in Example 1 was
used. The copper rates of removal are also set out below in Table
16 for formula 2 prepared with normal dilution of water, and from
the concentrate (formula 39) with subsequent dilution.
23TABLE 16 Formula Formula Formula Formula Component 37 38 39 2
H.sub.2O.sub.2 --* 1% --* 1% Aminoacetic 14% 0.35% 10% 1% Acid
1,2,4-Triazole 7000 175 5000 500 (ppm) SiO.sub.2 (ppm) 1400 35
10000 1000 Deionized Water Balance Balance Balance Balance Cu RR
(at same 3223 3346 3661 3284 level of dilution) .ANG./Min. Protocol
OP-III OP-III OP-IV OP-IV *1% H.sub.2O.sub.2 added to the final,
diluted solution
[0098] As can be seen from the above examples, the formulas and
methods set out above demonstrate the ability of CMP formulations
containing low concentrations of particulate material to
effectively remove copper-containing material deposited on the
surface of a wafer down to a stop layer without substantial removal
of the stop layer. The formulas and methods can be practiced over a
range of pH conditions using a range of component materials, and
can further be practiced using dilutions of formula concentrate
without adverse effect.
[0099] Thus it is apparent that there has been provided, in
accordance with the invention, CMP formulas and methods of
planarization utilizing the formulas which fully satisfies the
objects, aims, and advantages set forth above. While the invention
has been described in conjunction with specific embodiments
thereof, it is evident that many alternatives, modifications, and
variations will be apparent to those skilled in the art in light of
the foregoing description. Accordingly, departures may be made from
such details without departing from the spirit or scope of the
general inventive concept.
* * * * *