U.S. patent application number 10/716116 was filed with the patent office on 2004-05-27 for method and system to provide material removal and planarization employing a reactive pad.
Invention is credited to Basol, Bulent M., Talleh, Homayoun, Uzoh, Cyprian E..
Application Number | 20040102049 10/716116 |
Document ID | / |
Family ID | 26929842 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040102049 |
Kind Code |
A1 |
Basol, Bulent M. ; et
al. |
May 27, 2004 |
Method and system to provide material removal and planarization
employing a reactive pad
Abstract
Systems and methods to remove a first material located on a top
surface of a workpiece are presented according to one aspect of the
present invention. According to an exemplary method, the pad
including a second material is positioned proximate to the
workpiece so that a front surface of the pad contacts an exposed
surface of the first material. The front surface of the pad is
mechanically moved against the exposed surface of the first
material to initiate a chemical reaction between the first material
and the second material that yields a reaction product. The
reaction product may be removed by using a chemical solution, by
using the mechanical movement of the pad against the exposed
surface of the first material or both.
Inventors: |
Basol, Bulent M.; (Manhattan
Beach, CA) ; Uzoh, Cyprian E.; (Milpitas, CA)
; Talleh, Homayoun; (San Jose, CA) |
Correspondence
Address: |
Legal Department
Nu Tool, Inc
1655 McCandless Drive
Milpitas
CA
95035
US
|
Family ID: |
26929842 |
Appl. No.: |
10/716116 |
Filed: |
November 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10716116 |
Nov 18, 2003 |
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09969531 |
Oct 1, 2001 |
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6649523 |
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60236505 |
Sep 29, 2000 |
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Current U.S.
Class: |
438/710 ;
257/E21.23; 257/E21.244; 257/E21.304; 257/E21.583 |
Current CPC
Class: |
H01L 21/31053 20130101;
B24B 37/042 20130101; B24D 3/346 20130101; B24B 37/24 20130101;
H01L 21/3212 20130101; C23F 3/00 20130101; B24D 13/14 20130101;
H01L 21/7684 20130101 |
Class at
Publication: |
438/710 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed is:
1. A method of removing a first material located on a top surface
of a workpiece using a pad positioned proximate to the workpiece,
the method comprising: positioning a pad proximate to the workpiece
so that a front surface of the pad contacts an exposed surface of
the first material, the pad comprising a second material;
mechanically moving the front surface of the pad against the
exposed surface of the first material to initiate a chemical
reaction between the first material and the second material, the
chemical reaction yielding a reaction product; removing the
reaction product using a chemical solution, the reaction product
being soluble into the chemical solution and the first material and
second material not being substantially soluble into the chemical
solution.
2. The method according to claim 1, further comprising: depositing
the first material onto a top surface of a workpiece and into
features of the workpiece.
3. The method according to claim 2, further comprising:
mechanically rotating, vertically moving, and laterally moving the
pad relative to the workpiece using a shaft coupled to the pad.
4. The method according to claim 3, wherein the pad is wholly
comprised of the second material.
5. The method according to claim 3, wherein the second material is
stored within the pad.
6. A method of removing a first material located on a top surface
of a workpiece using a pad positioned proximate to the workpiece,
the method comprising: positioning a pad proximate to the workpiece
so that a front surface of the pad contacts an exposed surface of
the first material, the pad comprising a second material;
mechanically moving the front surface of the pad against the
exposed surface of the first material to initiate a chemical
reaction between the first material and the second material, the
chemical reaction yielding a reaction product; removing the
reaction product using the mechanical movement, wherein
mechanically moving the front surface of the pad against the
exposed surface of the first material is not sufficient to remove
the first material but is sufficient to remove the reaction
product.
7. A method of removing a first material located on a top surface
of a workpiece using a pad positioned proximate to the workpiece,
the method comprising: positioning a pad proximate to the workpiece
so that a front surface of the pad contacts an exposed surface of
the first material, the pad comprising a second material;
mechanically moving the front surface of the pad against the
exposed surface of the first material to initiate a chemical
reaction between the first material and the second material, the
chemical reaction yielding a reaction product; removing the
reaction product using a chemical solution and the mechanical
movement, the reaction product being soluble into the chemical
solution and the first material and second material not being
substantially soluble into the chemical solution, wherein
mechanically moving the front surface of the pad against the
exposed surface of the first material is not sufficient to remove
the first material but is sufficient to remove the reaction
product.
8. A system to remove a first material located on a top surface of
a workpiece, the system comprising: a pad positioned proximate to
the workpiece so that a front surface of the pad contacts an
exposed surface of the first material, the pad comprising a second
material; means for mechanically moving the front surface of the
pad against the exposed surface of the first material to initiate a
chemical reaction between the first material and the second
material, the chemical reaction yielding a reaction product; and a
chemical solution to remove the reaction product, the reaction
product being soluble into the chemical solution and the first
material and second material not being substantially soluble into
the chemical solution.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of prior U.S.
Provisional Application Serial No. 60/236,505, filed Sep. 29, 2000,
which is hereby incorporated by reference herein.
TECHNICAL FIELD
[0002] The present invention generally relates to semiconductor
integrated circuit technology and, more particularly, to techniques
for employing a reactive pad in contact with-the surface of a
workpiece during material removal or planarization.
BACKGROUND
[0003] Removal of excess material in a uniform manner from the
surface of coated patterned substrates has wide range of
applications. One of these applications is in the field of
integrated circuit manufacturing. Conventional semiconductor
devices such as integrated circuits generally include a
semiconductor substrate, usually a silicon substrate, and a
plurality of sequentially formed dielectric interlayers such as
silicon dioxide, and conductive paths or interconnects made of
conductive materials. Copper and copper alloys have recently
received considerable attention as interconnect materials because
of their superior electromigration and low resistivity
characteristics. The interconnects are usually formed by filling a
conductor such as copper in features or cavities etched into the
dielectric interlayers by a metallization process. In an integrated
circuit, multiple levels of interconnect networks laterally extend
with respect to the substrate surface. Interconnects formed in
sequential layers can be electrically connected using features such
as vias or contacts.
[0004] In a typical interconnect fabrication process, first an
insulating interlayer is formed on the semiconductor substrate.
Patterning and etching processes are performed to form features
such as trenches, pads and vias etc. in the insulating layer. Then,
copper is deposited on the substrate through a metallization
process to fill all the features. The preferred method of copper
metallization process is electroplating.
[0005] FIG. 1 illustrates a cross-sectional view of a substrate 102
such as a wafer with features 104 such as trenches and vias formed
into its insulating layer. A material 106, such as copper (Cu) is
deposited on the wafer 102 surface over the features 104. In
conventional deposition processes, a barrier layer 108, and then,
in the case of copper 106 deposition, a very thin copper seed layer
to initiate copper growth, are coated onto the insulating layer and
into the features of the insulating layer of the wafer 102. The
goal of a planarization process is to remove the material 106 from
the top surface of the wafer 102, leaving the material 106 only in
the features 104. This is presently achieved by a polishing
technique such as chemical mechanical polishing (CMP),
electropolishing, etching, or a combination of these techniques.
The polishing techniques are conducted to remove the excess
material 106 layer or material overburden and other conductive
layers that are above the top surface of the insulating portions of
substrate 102. FIG. 2 shows the cross-section of the same substrate
102 after the polishing technique(s) are applied and the excess
conductors are removed. The substrate is planarized so that the
material 106 is only in the features 104.
[0006] In most commonly used CMP approaches, the substrate 102
surface is contacted with a pad and the pad is moved with respect
to the substrate surface. This pad is typically made of a polymeric
material which is inert to the material 106. The pad may or may not
contain abrasive particles or gels. The hardness of the pad may
change in accordance with the material to be removed. Companies
such as 3M, Rodel, and Universal Photonics supply CMP-pads of
various types to the industry. The role of the pad is to polish the
surface of the substrate 102 and to remove the material 106 on the
surface with the help of, for example, a chemical solution or a
slurry containing abrasive particles. Therefore, slurry apart, the
role of the pad in prior processes is purely mechanical.
Conventionally, chemical reactions occur between the film to be
removed and the slurry. The reaction products are then removed by
the pad and the abrasive particles.
[0007] There are many challenges with the state-of-the art CMP
techniques. These include but are not limited to: the pads getting
glazed and loosing their efficiency, the stability of the removal
rate from run to run, the cost of the consumables, and the defects
such as dishing and erosion which are well known and characterized
by those skilled in the art and in the field.
[0008] The higher the pressure, the higher the metal removal rates
during CMP operations. Higher polishing pressures of, for example,
three to six pounds per square inch (psi), while practical for
strong dielectric films such as silicon dioxide, are problematic
for many films with low dielectric constants, such as SOX, SILK,
diamond like carbon (DLC), and their likes. This is because they
tend to be more fragile than silicon dioxide. In general, CMP
operations that occur at low pressures, for example, less than
three psi, result in lower metal removal rates, hence lower process
throughput and higher operating costs.
[0009] To this end, it would be desirable to have a more efficient
method and system for providing material removal and planarization
of the surface of a substrate such as a semiconductor wafer
surface.
SUMMARY
[0010] The presently preferred embodiments described -herein
include systems and methods for providing material removal and
planarization of the surface of a workpiece such as, for example, a
semiconductor device or wafer, a packaging substrate, or a magnetic
device, using a reactive pad.
[0011] A method of removing a first material located on a top
surface of a workpiece using a pad positioned proximate to the
workpiece is presented according to one aspect of the present
invention. The pad is positioned proximate to the workpiece so that
a front surface of the pad contacts an exposed surface of the first
material. The pad includes a second material. The front surface of
the pad is mechanically moved against the exposed surface of the
first material to initiate a chemical reaction between the first
material and the second material. The chemical reaction yields a
reaction product. The reaction product is removed using a chemical
solution. The reaction product is soluble into the chemical
solution and the first material and second material are not
substantially soluble into the chemical solution.
[0012] A method of removing a first material located on a top
surface of a workpiece using a pad positioned proximate to the
workpiece is presented according to another aspect of the present
invention. The pad is positioned proximate to the workpiece so that
a front surface of the pad contacts an exposed surface of the first
material. The pad includes a second material. The front surface of
the pad is mechanically moved against the exposed surface of the
first material to initiate a chemical reaction between the first
material and the second material. The chemical reaction yields a
reaction product. The reaction product is removed using the
mechanical movement of the front surface of the pad against the
exposed surface of the first material. The mechanical movement is
not sufficient to remove the first material but is sufficient to
remove the reaction product.
[0013] A method of removing a first material located on a top
surface of a workpiece using a pad positioned proximate to the
workpiece is presented according to a further aspect of the present
invention. The pad is positioned proximate to the workpiece s,o
that a front surface of the pad contacts an exposed surface of the
first material. The pad includes a second material. The front
surface of the pad is mechanically moved against the exposed
surface of the first material to initiate a chemical reaction
between the first material and the second material. The chemical
reaction yields a reaction product. The reaction product is removed
using a chemical solution and the mechanical movement of the front
surface of the pad against the exposed surface of the first
material. The reaction product is soluble into the chemical
solution and the first material and second material are not
substantially soluble into the chemical solution. The mechanical
movement is not sufficient to remove the first material but is
sufficient to remove the reaction product.
[0014] A method of removing a material on a surface of a workpiece
using a reactive pad positioned in very close proximity to the
workpiece is presented according to another aspect of the present
invention. The pad is sufficiently close to the workpiece, while
not touching the workpiece during the material removal process. The
reactive pad and workpiece may vibrate and or move mechanically
with respect to each other during the materials removal process and
the removal rate is independent of the applied pressure.
[0015] A method of removing a material from a surface of a
workpiece using a reactive pad positioned sufficiently near to the
workpiece, such that the reactive pad barely touches the surface of
the material to be removed, and so that the reactive pad is
subjected to near zero deformation or non-significant deformation
with respect to its thickness. The reactive pad and the workpiece
may vibrate or move mechanically with respect to each other during
the material removal process.
[0016] A method of removing a material from a surface of a
workpiece using a combination pad. The combination pad material is
a combination of a reactive pad and a conventional mechanical pad,
such that some portions of the combination pad material include a
reactive pad material and other portions of the combination pad
material include conventional mechanical pad material. During the
material planarization process, the workpiece is positioned very
close to the pad so as to be in contact with the combination pad
material. Both the workpiece and the combination pad material move
with respect to each other.
[0017] A method and arrangement of removing a material from a
surface of a workpiece using a combination of a reactive pad and a
mechanical pad, such that the reactive pad is positioned adjacent
to a mechanical pad. During planarization of the workpiece, the
workpiece may vibrate or move mechanically with respect to the pad.
Some portions of the material on the workpiece are removed using
the reactive pad, while other portions of the material are removed
using the mechanical pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The foregoing and other features, aspects, and advantages
will become more apparent from the following detailed description
when read in conjunction with the following drawings, wherein:
[0019] FIG. 1 is a diagram illustrating a cross-sectional view of
an exemplary substrate with material overburden deposited on the
surface of the substrate;
[0020] FIG. 2 is a diagram illustrating a cross-sectional view of
an exemplary substrate following removal of the material overburden
from the surface of the substrate;
[0021] FIG. 3 is a diagram illustrating a cross-sectional view of
an exemplary substrate with material overburden deposited on a top
surface of the substrate and a reactive pad according to a
presently preferred embodiment of the present invention;
[0022] FIG. 4 is a diagram illustrating a cross-sectional view of
the exemplary substrate and reactive pad of FIG. 3 following
removal of the material overburden from the top surface of the
substrate; and
[0023] FIG. 5 is a diagram illustrating a partial view of a front
surface of an exemplary embodiment of the reactive pad of FIG. 3
that includes a combination of reactive and mechanical pad
material; and
[0024] FIG. 6 is a diagram illustrating a view of a front surface
of an exemplary embodiment of the reactive pad of FIG. 3 that
includes reactive pad material and of a front surface of a
conventional mechanical pad placed alongside the reactive pad.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0025] The present invention will now be described in detail with
reference to the accompanying drawings, which are provided as
illustrative examples of preferred embodiments of the present
invention.
[0026] Referring now to FIG. 3, it is a diagram illustrating a
cross-sectional view of an exemplary material removal system 200
according to a presently preferred embodiment of the present
invention. The system 200 includes a reactive pad 210 to remove a
material 206 overburden from an exemplary substrate 202. The
material 206 is deposited on a top surface 216 of the substrate
202. The material removal system 200 preferably provides planar
polishing of the substrate 202 top surface 216 so that the material
206 only remains in features 204 such as trenches and vias formed
into an insulating layer of the substrate 202. The pad 210 is
mounted on a shaft 212 and can be brought into direct contact with
the material 206 overburden on the top surface 216 of the substrate
202. It should be noted that there may be various methods of
mounting or holding the pad 210, the details of which have not been
shown for clarity. All approaches that are presently used to hold
conventional pads are applicable to holding the pad 210 of the
present invention. Also the relative positions of the substrate 202
and the pad 210 may be reversed, i.e. the surface of the substrate
may be above the surface of the pad 210. The pad 210 may be moved
rotationally, which may be clockwise or counter clockwise, or the
pad 210 can be moved laterally along the x-axis of the substrate
202, or the pad 210 can be both rotated and moved laterally. The
pad 210 may also be moved vertically along the z-axis shown in FIG.
3. It is noted, however, that the above description described
rotation and movement of the pad 210, while assuming that the
substrate 202 Was stationary. It is understood that the system 200,
as described above, will allow for either the pad 210 or the
substrate 202 to move, or for both of them to move, thereby
creating the same relative motion effect. Furthermore the pad 210
may be in the form of a belt and its motion may be linear. For ease
of description, however, the invention was above-described and will
continue to be described in terms of movement of the pad 210.
[0027] The workpiece or substrate 202 may be, for example, a
silicon wafer plated with a conductor metal material 206,
preferably copper or copper alloy. The material 206, such as
copper, is deposited on the substrate 102 surface over the features
204. A barrier layer 224, and then, in the case of copper 206
deposition, a very thin copper seed layer to initiate copper
growth, are coated onto the insulating layer of the substrate 202
and into the features 204 of the insulating layer of the substrate
202. The barrier layer 224, which may also be referred to as a glue
layer 224 since it effectively glues copper to the insulating
layer, can be made up of bilayers such as, for example, a tantulum
(Ta)/tantulum nitride (TaN) bilayer or a titanium (Ta) /titanium
nitride (TiN) bilayer. The pad 210 is preferably capable of
performing planar polishing of the substrate 202 top surface 216 so
that the material 106 is left only in the features 204. It should
be understood that the barrier layer 224 that is over the
insulating layer can also be removed using the pad 210, if the pad
210 is so configured. The pad 210 may also be specifically
configured for the purpose of removing portions of the barrier
layer 224 so that the material 206 is electrically and physically
isolated throughout the features 204. A chemical solution 214 such
as an electrolyte, depicted by arrows 214, is preferably applied
between a front surface 218 of the pad 210 and an exposed surface
220 of the material 206 to aid in material 206 removal.
[0028] The pad 210 removes material 206 overburden from the top
surface 216 of the workpiece or substrate 202 in a chemical way as
well as a mechanical way. The pad 210 preferably contains a
chemical species 222, or is made of a chemical species 222, that
can react with the exposed surface 220 of the material 206. This is
achieved by physical contact and motion between the front surface
218 of the pad 210 and the exposed surface 220 of the material 206
on the top surface 216 of the substrate 202. The chemical reaction
between the pad 210 and the exposed surface 220 of the material 206
may involve an alloying or an exchange reaction. As is known to
those skilled in the art, alloying or exchange reactions may result
from the physical work done against the frictional forces between
the two surfaces 218, 220. One example of such a reaction can be
seen using a reactive pad 210 that includes, for example, very
finely dispersed ferric nitrate as the primary oxidant. During the
polishing step, the ferric ion is reduced to a ferrous ion, while
the copper on the substrate is oxidized to cupric ions. In another
example, in a reactive pad 210 that includes calcium peroxide, the
peroxide oxidizes the copper or metal 206 on the substrate 202, to
form copper oxide. The resulting reduced calcium acts as a very
mild abrasive for the removal of the copper oxide, thus exposing a
new copper layer beneath. This is an example of an in situ
generated abrasive material or particulate during the planarization
process. Any products of the chemical reaction occurring between
the pad 210 chemical species 222 and the material 206 exposed
surface 220 are then removed by the chemical solution 214 present
between the pad 210 and the substrate 202 top surface 216, or are
removed physically by the pad 210, or both chemical and mechanical
mechanisms may help in this removal. When the excess material 206
on the top surface 216 is removed, contact between the pad 210
front surface 218 and the material 206 within the features 204 is
lost, therefore, reaction between the material 206 and the pad 210
stops. This automatically stops material removal and thus avoids
dishing of the material 206 in the feature 204 regions.
[0029] There are several conditions that are to be satisfied for
the material removal process to work properly in a presently
preferred embodiment. First, the chemical species 222 contained on
the pad 210 or on the front surface 218 of the pad 210 that
contacts the exposed surface 220 of the material 206 should react
with the exposed surface 220 of the material 206 to form reaction
products 208. Second,.the products 208 resulting from the chemical
reaction should be chemically different from the material 206 on
the substrate 202 as well as from the chemical species 222
contained on the pad 210. Third, the products 208 resulting from
the chemical reaction, but not the pad 210 or the material 206 on
the substrate 202 top surface 216, should be substantially soluble
in the chemical solution 214, e.g., an electrolyte, or the reaction
products 208 should be such that the products 208 can be easily
removed from the top surface 216 of the substrate 202 by physical
action of the pad 210, by chemical action of the electrolyte 214,
or both.
[0030] As an example referring to FIG. 3, assume that the pad 210
is made of a chemical species 222 material "A." Further assume that
the material 206 that coats the top surface 216 of the substrate
202 is the material "B." To remove the material B 206 from the top
surface 216 of the substrate 202, the front surface 218 of the pad
210 is brought into contact with the exposed surface 220 of the
material B 206 and the pad 210 is preferably moved with respect to
the top surface 216 of the substrate 202. The physical rubbing
between the species material A 222 pad 210 and the material B 206
causes a reaction product A.sub.xB.sub.y 208 formed either on the
exposed surface 220 of the material B 206 or on the front surface
218 of the pad 210, or both. In the reaction product compound
A.sub.xB.sub.y 208, X and Y represent stoichiometric and
non-stoichiometric numbers, as applicable. In one exemplary
scenario, the reaction product A.sub.xB.sub.y 208 is preferably
exposed to an electrolyte solution 214 that does not dissolve
species A 222 or material B 206 appreciably but that chemically
attacks and removes the reaction product A.sub.xB.sub.y 208.
Similarly, in another exemplary scenario, the mechanical action of
the pad 210 by itself may not efficiently remove material B 206,
but the mechanical properties of the reaction product
A.sub.xB.sub.y 208 are such that pad 210 is able to remove
A.sub.xB.sub.y 208 efficiently regardless. In both exemplary
scenarios, the removed reaction product A.sub.xB.sub.y 208 takes
away with it some material B 206 from the top surface 216 of the
substrate 202. A planar material removal process continues until
the front surface 218 of the pad 210 loses contact with the exposed
surface 220 of material B 206. This happens when all, or
substantially all, of the material B 206 is removed from the top
surface 216 and is left only in the-features 204 of the substrate
202, as can be seen in FIG. 4.
[0031] It should be understood that the methods and systems
described herein according to the present invention can be applied
to polish a wide variety of workpieces and to remove many different
materials, including barrier materials, from a wide variety of
workpieces.
[0032] As an example, in the case of copper planarization or
removal by the reactive pad 210, the pad 210 material, normally a
polymer such as polyurethane, polyester, polyether and their
different combinations, may be formulated to incorporate organic or
inorganic agents, or combinations of these that will react with the
metal material 206 to be polished. Organic and inorganic nitrites
and nitrates, in various chemical forms, be it as a powder, micro
or nanogel, can be compounded into the matrix of the pad 210
material.
[0033] In another embodiment, finely dispersed abrasive particles
or powder, such as alumina, silica, silicon carbide, titanium
borides, and others may be compounded in conjunction with the
reactive agents A 222, into the structure of the pad 210. During
the material B 206 removal process, the pad 210 abrades the surface
of the material B 206, e.g. copper, while the reactive agent A 222
chemical interacts with the material B 206 metallic or copper layer
to the Cu.sub.xA.sub.y compound.
[0034] The electrolyte 214, for instance, may be deionized water.
The removal rate of copper 206 from the top surface 216 of the
substrate 202 may be controlled by the chemical activity of
chemical species A 222 at the front surface 218 of the pad 210. It
should be understood that this chemical activity is equivalent to
the concentration of the very reactive components of agent A 222
that participate in the reaction with copper, and not necessarily
the concentration in the pad 210. This removal rate of copper 206
is controlled by chemical activity of species material A 222 at the
exposed surface 220 of copper 206. In one instance, the higher the
chemical activity of the reactive agent A 222, the higher the
removal rate of copper 206. The chemical activity of the reactive
agent A 222 for instance can be increased by increasing the
temperature of the electrolyte 214, by increasing the electrolyte
214 flow rate, or by modifying the electrolyte 214 pH. For
instance, lowering the electrolyte 214 pH from 6.5 to 4 may
increase the activity of agent A 222 by, for example, an order of
three, thus increasing the removal of copper 206.
[0035] Besides electrolyte 214 temperature, pH, and flow rate,
metal 206 removal from the top surface 216 of the substrate 202 may
be increased by adding a third agent C in the electrolyte. For
example, a small amount of ethyl acetate may be added as a catalyst
to the electrolyte to further increase the dissolution of copper
206 or to enhance the formulation of the reaction product 220
A.sub.XB.sub.Y type compound.
[0036] Other reactive agents 222 that may be formulated into the
structure of the pad 210 material, alone or in their various
combinations, include, for example, citric acid, citrates,
oxalates, tartaric acid, tartarates, amines, iodine, iodates,
amines, carbonates, diamines, ethylenediamine tetraacetic acids,
ammonium compounds, chlorates or perchlorates, salicylic acid,
sulfosalicylic acids, organic peroxides or inorganic peroxides,
such as calcium peroxide or organic peroxides. These reactive
agents 222 in the pad 210 may be used to remove other materials 206
such as nickel, aluminum, tungsten, copper alloys, cobalt, silver
alloys, iron, tantulum, titanium, chromium, platinum, and
others.
[0037] Typically, Cu.sup.2+ ions are formed from the chemical
reaction between copper 206 and the reactive agent A 222, which are
readily soluble in the electrolyte, but also Cu.sup.2+ oxides, or
chelates can be formed, which can be removed by the mechanical
action of the front surface 218 of the pad 210 against the exposed
surface 220 of the material B 206 copper.
[0038] In some material B 206 metal removal steps, it is preferable
that reagents, i.e., the byproducts or products of the reaction,
producing uncharged complexes or chelates be formed over the
surface of the metal film 206. The complex is then removed by mild
abrasive action of the pad 210. Without the action of the pad 210,
the uncharged chelate leaves a thin passivating film over the
exposed surface 220 of the metal 206.
[0039] In other pad 210 material formulations, reagents giving
charged complexes or chelates may be preferred, this may include
peroxides, oxalates, tartarates, polyamines, citrates, and others.
In this case, it is preferable that small amounts of a masking
agent such as any of the triazole moieties, for example,
benzotriazole (BTA), be co-compounded into the pad material or be
added into the electrolyte to control the removal rate. Thus at a
lower amount of masking agent, typically below ten (10) parts per
million (ppm), a certain removal rate is obtained, and for instance
at above 50 ppm of the masking material, negligible removal rate is
observed.
[0040] Thus the addition of a masking agent in the electrolyte 214
may be used to control the removal rate of material B 206 metal
film from the substrate. Besides the addition of sulfur bearing
groups such as BTA to control the removal rate, the removal rate
may also be controlled by adding a surfactant or a material that
may increase the viscosity of the electrolyte 214. For example,
glycerol, or members of polyols or the glycerol family, may be
added to the electrolyte 214. The addition of glycerol moderates
the activity of the reactive agent 222 in the pad, nominally by
increasing the viscosity of the electrolyte. Glycerol has an
additional beneficial effect of acting as a lubricant between the
substrate 202 and the front surface 218 of the pad 210.
[0041] In another embodiment of this invention, during the material
206 removal process, the reactive pad 210 is disposed sufficiently
close to the top surface 216 of the workpiece 202, while not
touching the workpiece 202. During the material 206 removal from
the top surface 216 of the workpiece 202, it is preferred that the
workpiece 202 and the pad 210 vibrate, and/or move mechanically
with respect to each other without touching. In this movement
and/or vibration, material 206 removal occurs predominantly by
etching process. Thus, materials 206 on the substrate can be
chemically etched using reactive agents 222 in the reactive pad
210.
[0042] In other embodiments, all that may be needed for material
206 removal is that the workpiece 202 gently touch or brush the
front surface 218 of the reactive pad 210, during the material 206
removal process step. The workpiece 202 is sufficiently close and
lightly to the pad 210 material, such that there is no significant
deformation of the reactive pad 210 material compared to a
conventional CMP process. In this removal configuration, the
removal process is the interplay between etching and mechanical
removal, with minimal damage to the top surface 216 of the
workpiece 202. In these removal processes, there is no significant
deformation of the pad 210 material, the role of the applied
pressure is minimal. Thus the removal rate can be nearly
independent of the applied pressure. This type of planarization
process, where the pad 210 and workpiece 202 are in very close
proximity and float over each other, is very beneficial in the
planarization of comparatively fragile materials 206, such as many
low dielectric constant (K) films.
[0043] In another embodiment according to the present invention, an
arrangement consisting of the combination of a reactive pad
positioned adjacent to a mechanical pad is described. Referring now
to FIG. 5, it is a diagram illustrating a partial view of a front
surface 318 of an exemplary embodiment 310 of the reactive pad 210
of FIG. 3 that includes a combination of reactive and mechanical
pad material. As shown in FIG. 5, strips 302, 304 of reactive 302
and mechanical 304 pad are disposed in as alternating layers. Of
course, different geometrical arrangements or configurations may be
used. For example, reactive pad portions 302 preferably range
between five to seventy percent, the balance being a conventional
mechanical pad portions 304, or vice versa. During the
planarization process, portions of the material B 206 to be removed
are removed by the reactive pad sections 302, while other portions
are removed by the mechanical pad sections 304.
[0044] In other embodiments, a fully reactive pad 410 is positioned
adjacent to, but separately from, a conventional mechanical pad
420. Referring to FIG. 6, it is a diagram illustrating a view of a
front surface 418 of an exemplary embodiment 410 of the reactive
pad 210 of FIG. 3 and of a front surface 428 of the mechanical pad
420 placed alongside the reactive pad 410. During the material 206
removal process step, the workpiece 202 is planarized for some
period or portion of time using the reactive pad 410, and for other
portion of time using the conventional pad 420. For example, for
higher removal rates, the planarization may occur predominantly
over the reactive pad 410 top surface 418. However, when workpiece
202 surface 216 smoothness is of primary importance, an appropriate
combination of planarization times over both pads 410, 420 may be
used. Thus, in some applications, the workpiece 202 may move
sequentially over, or under, both the reactive pad 210 and the non
reactive pad. In other material removal steps, for example,
the,workpiece 202 may reside longer over-the reactive pad 210 than
the non reactive mechanical pad 428 and vice versa during the
material 206 removal process.
[0045] Although the present invention has been particularly
described with reference to the preferred embodiments, it should be
readily apparent to those of ordinary skill in the art that changes
and modifications in the form and details may be made without
departing from the spirit and scope of the invention. It is
intended that the appended claims include such changes and
modifications.
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