U.S. patent application number 10/996165 was filed with the patent office on 2005-06-23 for electroetching methods and systems using chemical and mechanical influence.
Invention is credited to Basol, Bulent M., Lindquist, Paul, Talieh, Homayoun, Uzoh, Cyprian E..
Application Number | 20050133380 10/996165 |
Document ID | / |
Family ID | 28044196 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050133380 |
Kind Code |
A1 |
Basol, Bulent M. ; et
al. |
June 23, 2005 |
Electroetching methods and systems using chemical and mechanical
influence
Abstract
The present invention applies an electrochemical etching
solution to a material layer, preferably a metal layer, disposed on
a workpiece, in the presence of a current. This electrochemical
etching solution supplies to the material on the substrate surface
the species to form an intermediate compound on the surface that
can be more easily mechanically removed as intermediate compound
fragments than the material. By removing the intermediate compound
fragments, the process allows more efficient use of the supplied
current to form another layer of intermediate compound that can
also be mechanically removed, rather than using the current to
result in another compound on the surface of the material that
eventually dissolves into the solution. In another aspect of the
invention, such intermediate compound particulates are externally
generated and used to mechanically remove the surface layer of the
material. Such intermediate particulates do not contaminate, and
thus allow for more efficient material removal, as well as plating
to occur within the same chamber, if desired.
Inventors: |
Basol, Bulent M.; (Manhattan
Beach, CA) ; Uzoh, Cyprian E.; (San Jose, CA)
; Lindquist, Paul; (Milpitas, CA) ; Talieh,
Homayoun; (San Jose, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
28044196 |
Appl. No.: |
10/996165 |
Filed: |
November 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10996165 |
Nov 22, 2004 |
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10117991 |
Apr 5, 2002 |
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6821409 |
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60282202 |
Apr 6, 2001 |
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Current U.S.
Class: |
205/658 ;
257/E21.309 |
Current CPC
Class: |
C25F 7/00 20130101; C25F
3/14 20130101; C25D 17/001 20130101; C25D 5/22 20130101; B23H 5/08
20130101; H01L 21/32134 20130101 |
Class at
Publication: |
205/658 |
International
Class: |
B23H 003/00 |
Claims
What is claimed is:
1. A method of electrochemically removing a conductor of a top
conductive surface of a workpiece, the method comprising the steps
of: applying an electrochemical etching solution to the top
conductive surface of the workpiece in the presence of a current,
thereby causing a portion of the top conductive surface to form
into an intermediate compound, the intermediate compound being more
easily mechanically removed from the top conductive surface than
the portion of the top conductive surface; and mechanically
removing at least a portion of the intermediate compound from the
top conductive surface.
Description
[0001] This application is a continuation of U.S. Pat. No.
6,821,409 issued Nov. 23, 2004 which relates to and claims priority
from U.S. Provisional Patent Application No. 60/282,202 filed Apr.
6, 2001.
FIELD OF THE INVENTION
[0002] The present invention generally relates to semiconductor
integrated circuit technology and, more particularly, to an
electroetching process and apparatus to yield planar layers.
BACKGROUND OF THE INVENTION
[0003] Conventional semiconductor devices 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. The interconnects are usually formed by
filling a conductive material in trenches etched into the
dielectric interlayers. In an integrated circuit, multiple levels
of interconnect networks laterally extend with respect to the
substrate surface. The interconnects formed in different layers can
be electrically connected using vias or contacts. A conductive
material filling process of such features, i.e., via openings,
trenches, pads or contacts, can be carried out by electrodepositing
a conductive material, such as copper, over the substrate including
such features. There are many conventional electrodeposition
methods and tools that deposit conformal layers of Cu on various
substrates.
[0004] The importance of overcoming the various deficiencies of the
conventional electrodeposition techniques, which deposit conformal
coatings, is evidenced by technological developments directed to
the deposition of planar copper layers. In such processes, a pad or
a mask can be used during at least a portion of the
electrodeposition process when there is physical contact or close
proximity, and relative motion between the workpiece surface and
the pad or the mask. For example, U.S. Pat. No. 6,176,992 to
Talieh, entitled "Method and Apparatus for Electrochemical
Mechanical Deposition" and commonly owned by the assignee of the
present invention, describes in one aspect an electro chemical
mechanical deposition technique (ECMD) that achieves deposition of
the conductive material into the cavities on the substrate surface
while minimizing deposition on the field regions by polishing the
field regions with a pad as the conductive material is deposited,
thus yielding planar copper deposits.
[0005] U.S. application Ser. No. 09/740,701 entitled "Plating
Method and Apparatus that Creates a Differential Between Additive
Disposed on a Top Surface and a Cavity Surface of a Workpiece Using
an External Influence," also assigned to the same assignee as the
present invention, describes in one aspect a method and apparatus
for plating a conductive material onto the substrate by creating an
external influence to cause a differential in additives to exist
for a period of time between a top surface and a cavity surface of
a workpiece. While the differential is maintained, power is applied
between an anode and the substrate to cause greater relative
plating of the cavity surface than the top surface.
[0006] U.S. application Ser. No. 09/735,546 entitled "Method and
Apparatus For Making Electrical Contact To Wafer Surface for
Full-Face Electroplating or Electropolishing," filed on Dec. 14,
2000 describes in one aspect a technique for providing full face
electroplating or electropolishing or electroetching. And U.S.
application Ser. No. 09/760,757 entitled "Method and Apparatus for
Electrodeposition of Uniform Film with Minimal Edge Exclusion on
Substrate," filed on Jan. 17, 2001 describes in one aspect a
technique for forming a flat conductive layer on a semiconductor
wafer surface without losing space on the surface for electrical
contacts.
[0007] After depositing copper into the features on the
semiconductor wafer surface using either planar deposition
techniques or the conventional techniques, an electropolishing or a
chemical mechanical polishing step (CMP) may be employed. These
processes planarize the resulting surface, and if continued, the
conductive material is removed off the field regions of the surface
and left only within the features such as vias, contacts, trenches,
bond pads etc. In the electro polishing, which is also referred to
as "electrochemical etching" or "electroetching," both the material
to be removed and a conductive electrode are dipped into the
electro-polishing solution. Typically an anodic (positive) voltage
is applied to the material to be removed with respect to the
conductive electrode. With the applied voltage, the material is
electrochemically dissolved and removed from the wafer surface.
[0008] Also, various other methods and apparatus, which attempt to
improve the efficiency of the polishing process by combining
electroetching with a CMP process step, exist. For example, U.S.
Pat. No. 6,066,030, issued May 23, 2000 to Uzoh et al., generally
employs a single device to carry out sequentially both CMP process
and electroetching process of a substrate. The device includes a
polishing head having a polishing pad and a cathode, which is
arranged adjacent the polishing head while the anode is the
substrate to be polished and electroetched. The electroetching
process requires delivery of an etching or polishing solution to
the substrate surface through the cathode while the tool is rotated
and/or laterally moved across the substrate. The electroetching
step is followed by the CMP process where a polishing slurry is
introduced between the polishing pad and the substrate while the
substrate is rotated.
[0009] To this end, however, there is need for alternative etching
techniques that uniformly etches back conductive films. There is
also a need for a process that yields planar surfaces.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide an
apparatus and process that can more efficiently etch a material
deposited on a workpiece.
[0011] It is an object of the present invention to provide an
apparatus and process that can more efficiently etch a metal
deposited on a workpiece.
[0012] It is a further object of the invention to form at least one
intermediate compound from a material layer of a workpiece such
that the intermediate compound can be more easily mechanically
removed than the material.
[0013] It is a still further object of the present invention to
provide a method of introducing noncontaminating particulates to an
electroetching or chemical mechanical etching process.
[0014] The above object of the invention, among others, either
taken singly or in combination, are achieved by the method and
apparatus according to the present invention. In one aspect the
present invention applies an electrochemical etching solution to a
material layer, preferably a metal layer, disposed on a workpiece,
in the presence of a current. This electrochemical etching solution
supplies to the material on the substrate surface the species to
form an intermediate compound on the surface that can be more
easily mechanically removed as intermediate compound fragments than
the material. By removing the intermediate compound fragments, the
process allows more efficient use of the supplied current to form
another layer of intermediate compound that can also be
mechanically removed, rather than using the current to result in
another compound on the surface of the material that eventually
dissolves into the solution.
[0015] Accordingly, raised surface portions of the material layer
can be removed more quickly than surface portions within grooves or
other cavities on the material layer, thus creating more efficient
removal from the raised surface portions.
[0016] In another aspect of the invention, such intermediate
compound particulates are externally generated and used to
mechanically remove the surface layer of the material. Such
intermediate particulates do not contaminate, and thus allow for
more efficient material removal, as well as plating to occur within
the same chamber, if desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] These and other aspects of an embodiment of the present
invention are better understood by reading the following detailed
description of the preferred embodiment, taken in conjunction with
the accompanying drawings, in which:
[0018] FIGS. 1A-1C shows cross-sectional views of a portion of a
work piece at various levels of detail;
[0019] FIGS. 2-4 illustrate the an exemplary electroetching or
electropolishing system according to the present invention;
[0020] FIGS. 5A-5C illustrate the operation of the present
invention on a workpiece.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0021] As will be described below, the present invention provides a
method and a system to selectively electrochemically etch a
conductive material layer deposited on a surface of a
semiconductor. The invention can be used with ECMD, other plating
systems that yield planar deposits as well as other plating systems
that deposit conformal films. The present invention achieves
electro etching of the conductive material through the combination
of the use of an etching solution and by contacting, sweeping
and/or polishing of the conductive surface with a mask plate with
abrasive surface.
[0022] Reference will now be made to the drawings wherein like
numerals refer to like parts throughout. FIG. 1A shows a
cross-sectional view of a portion of a work piece 100, or a
substrate, such as a portion of a semiconductor wafer. The
substrate 100 comprises a top layer 102 having a top surface 103, a
bottom layer 104 having an upper surface 105 upon which the top
layer 102 formed. The top layer 102 of the substrate 100 may be
comprised of a layer of conductive material and the bottom layer
104 may be comprised of a semiconductor material. In this
embodiment, although the conductive layer 102 is formed on the
substrate 100, it is within the scope of the present invention that
the substrate 100 may be entirely formed from a conductive
material. FIG. 1B is an enlarged partial cross-sectional view of
near surface region of the substrate 100 (shown in FIG. 1A) which
comprises a via feature 106 and a trench feature 108 formed in an
insulating region 109 which is previously formed on the wafer
surface. The substrate 100 may comprise a plurality of via, trench
and other features. As illustrated in FIG. 1B, in order to
exemplify one embodiment of the present invention the surface 103
of the conductive material layer 102 may not be planar, i.e., may
have a surface topography having high and low regions formed during
the deposition of the conductive layer. As shown in detail in FIG.
1C, accordingly, the surface 103 may have raised regions 103a and
recessed regions 103b. It should be noted that the structure in
FIG. 1B may contain barrier/glue layer, seed layers etc., which are
commonly deposited on the substrate surface before the conductive
layer is deposited.
[0023] FIGS. 2-4 schematically show an exemplary electroetching or
electropolishing system 110 of the present invention to etch the
layer 102 of the substrate 100 in a planar fashion. The etching
system 110 in this example embodiment has an electrode 111 and the
substrate 100 and a mask plate portion 112. During the etching
process of the present invention the conductive layer 102 is
electrically connected, preferably with movable connectors, to a
positive terminal of a power supply (not shown), and the electrode
is connected to a negative terminal of a power supply. An etching
solution, as depicted by arrows 124 touches the electrode 111 and
the substrate 100 (see FIGS. 1A-1C). The substrate 100 is held by a
carrier head (not shown) by the bottom layer 104. FIG. 3
exemplifies the mask plate portion 112 which may comprise a top
surface 113 and a bottom surface 114. The mask plate 112 also
comprises an exemplary channel 116 extending between the top and
the bottom surfaces 113, 114 and defined by a `V` shaped sidewall
118. The channel also laterally extends between a closed end 120
and an open end 122. The channels may be of various sizes and
shapes. Holes or other asperities may also be used in place of
channels, although channels are preferred. Channels and other
asperities bring the etching solution in contact with the surface
102. They also control the etching rate at various parts of the
substrate. For example the areas that are exposed the longest to
the electrolyte through the asperities are expected to etch more
during the etching process. Therefore, designing the openings in
the mask plate 112 one can have more etching in the middle of a
substrate, at the edge of the substrate or at any other specific
place on the substrate. The etching rate can be graded throughout
the substrate by grading the opening size and therefore the
exposure time of the substrate surface to the electrolyte. IT
should be noted that during electroetching, most or all of the
etching current passes through the asperites in the mask plate 112
(depending on the distance between the mask plate and the substrate
surface) and therefore removes material from the region on the
substrate surface directly across from the asperity.
[0024] As will be described more fully below, during an etching
process, when needed, the front surface 103 of the substrate 100
may be brought into close proximity, or contact with, the top
surface 113 of the mask plate 112 for planar metal removal. The top
surface of the mask plate is preferably abrasive or contains
abrasive particles or features. As the etching solution 124, is
delivered to the channel 116, the substrate 100 is rotated about a
rotation axis 126 while the front surface 103 contacts the top
surface 113 of the mask plate 112 or is in close proximity of the
top surface 113. For the purpose of clarification, the rotation
axis 126 may be the point at which the closed end 120 of the
channel 116, thereby ensuring that rotation of the substrate 100
will result in the entire front surface 103 of the substrate 100
having uniform contact with the channel 116. As the solution 124 is
delivered and fills the channel 116, it wets the front surface 103
of the substrate 100. The etching solution 124, which may be
continuously delivered under pressure, will then flow through the
channel 116 in the direction of the arrow 128 towards the open end
122 of the channel 116, and exits the plate 112.
[0025] It is noted that the above description described rotation
and movement of the substrate 100, assuming that the plate 112 was
stationary. It is understood that the system 100, as described
above, will allow for either the substrate or the plate to move, or
for both of them to move, thereby creating the same relative
affect. For ease of description, however, the invention was
above-described and will continue to be described in terms of
movement of the substrate.
[0026] The process of the present invention may generally be
described with the following example process. If the conductive
material of the layer 102 is a metal `A` which is formed of atoms
of "A" (for example a conductive element atom in the periodic
system of the elements, such as Cu, Ni, Ag, Sn, etc. or a
conductive alloy). And, if the etching solution comprises a
negatively charged ion, for example ion `D.sup.-n`, such as halide
ion i.e. Cl.sup.-, Br.sup.- or I.sup.-, (each being within Group
VII of the periodic system of elements) or "RD.sup.-n", where R
represents an organic or inorganic group and RD-n is a complexed or
adsorbed charged entity. Ion `D` may have a single electron charge
(n=1) and may be denoted as `D.sup.-` in the exemplary process.
[0027] As shown in FIG. 5A, as the solution 124, containing ion
`D.sup.-`, is delivered to the surface 103, due to the anodic
voltage on the surface 103, `D.sup.-` ions in the solution 124
react with the `A` atoms in the surface 103 and form a compound
layer 130 across the surface 103 and hence on the regions 130a,
130b. Under above given conditions:
[0028] If a single ion `D.sup.-` reacts with `A`, a compound,
denoted with, `AD` forms. This requires one electron transfer. If
the `AD` compound is not soluble in the solution 124 or it is only
slightly soluble it would momentarily suppress the etching process.
The etch process may be continued by (1) transforming the `AD`
compound into a compound that can dissolve in the etching solution,
and by (2) using the mechanical influence of the mask plate 112 to
remove the compound layer from the surface 103 so that a new
compound layer is formed in place of it.
[0029] The transformation of the `AD` compound into a compound that
may dissolve in the solution 124 may occur by attaching more than
one D.sup.- ion to the AD compound. Since the compound is under
anodic voltage, a reaction between the `AD` compound and more `D-`
ions in the solution may continue and the `AD` compound on the
surface may for example transform into `AD.sub.x` (x>1), where x
denotes number of electrons transferred in the reaction and the
number of `D` atoms attached to the newly formed compound. If
`AD.sub.x` compound is soluble in the etching solution, it
dissolves from the surface and process repeats itself. Such etching
of the layer 102 progresses across the surface 103 and may have an
etch rate denoted with R1.
[0030] Meantime however, if the plate 112 is touched to the surface
103, which is illustrated in FIG. 5B, the mechanical influence of
the mask plate 112 may physically dislodge the compound layer 130
in fragments from the raised regions 103a, even when it is in a
chemical form that is not soluble in the etching solution, i.e as
AD in our example. This results in removal of the raised regions
103a in a rate (R2) that is much faster than the etching rate (R1)
of the recessed regions 103b, i.e., R2>R1. Because the portion
of the compound layer 130 which covers the recessed regions 103b of
the layer 102 cannot be readily affected from the mechanical
influence of the mask plate 112, this portion of the compound layer
remains untouched, and gets etched at the rate R1. Once the
compound layer portion of the raised regions is removed, however,
the `AD` compound once again forms over the exposed A material
surface of the layer 102, and process repeats itself.
[0031] As shown in FIG. 5C, as the process of formation and then
removal of the compound layer 130 on the raised regions 103a
continue, the combination of both the slow etch rate across the
recessed regions 103b and faster mechanical removal of the raised
regions results in planarizing the layer 102. As the layer 102
planarized, the raised regions level with the recessed regions and
the R2 etch rate becomes the controlling etch rate across the
surface 103. Since the fragments of the compound layer 130 are less
soluable than the compound layer 130, or not soluble at all, in the
etching solution 124, they remain in the solution for at least a
period of time and can thus additionally function as mild abrasives
to assist polishing of the layer 102.
[0032] It should be noted that the above example used ions with one
negative charge. The same process can use ions with differing
charges. The condition is that there should be more than one
electron transfer in the process and that intermediate compound(s)
formed before the soluble compound is formed should be less soluble
in the etching solution than the soluble compound.
EXAMPLE
[0033] An exemplary Cu etching solution may be an acid solution
(such as sulfuric acid) comprising ionic species of copper
(Cu.sup.++), chlorine (Cl.sup.-) and additives. In accordance with
the principles of the present invention, when an anodic potential
is applied to the substrate 100 with respect to the electrode 111,
in the presence of the solution 124 that fills the channel 116,
chlorine ions in the etching solution 124 reacts with the copper of
the top layer 102 and forms a compound layer, which is a CuCl
compound, on the top surface 103. Other additives in the bath may
also participate in this reaction. This situation is exemplified in
FIG. 5A which essentially shows the structure shown in FIG. 1C but
with the addition of compound layer 130 which is formed as a result
of a reaction between the copper and chlorine ions. The CuCl
compound is not very soluble in the plating solution 124.
Therefore, in this embodiment, CuCl compound is removed off the
front surface 103 of the substrate by sweeping the compound layer
130 with the top surface 113 of the plate 112. This sweeping of the
compound layer 130 with the plate 112 provides necessary mechanical
influence to remove the compound layer 130 from the top layer 102.
As the layer 130 is removed from the surface of the top layer 102,
as illustrate in FIGS. 5B-5C, underlying surface which is under the
compound layer 130 is exposed to the etch solution 124. As in the
previous case, copper of the underlying surface, which is exposed
after the removal of the compound layer 130, reacts with the
chlorine ions in the solution 124 and forms a new compound layer
containing CuCl. Accordingly, the steps forming of the CuCl layer
and then the mechanical removal of it may be repeated until the
copper layer 102 covering the field regions is removed. Because of
the fact that the removed CuCl layer fragments are not very soluble
in the etch solution, the such CuCl fragments function as mild
abrasives enhancing polishing of the top layer 102. In this
respect, the mechanical sweeping action results in forming an
in-situ polishing slurry in the etching solution so that the copper
layer 102 can be polished while being etched back.
[0034] If the plate 112 was not used then the CuCl would eventually
transform into CuCl.sub.2 and dissolve. CuCl.sub.2 formation
requires two electron transfer in comparison to CuCl formation that
requires one electron transfer. This suggests that for the same
amount of charge passing through the electroetching circuit during
electroetching process, use of the mechanical action of the plate
112 would double the removal rate for a flat substrate compared to
the case no mechanical action is required. For a non flat
substrate, regions that are not affected by the mechanical action
of the mask plate would etch slower through CuCl.sub.2 formation,
whereas the regions at the top that get affected etch faster
through formation of CuCl and its physical removal.
[0035] It should be noted that the process can use a deposition
solution as the electroetching solution also provided that the
necessary species are contained in the solution. For example a
sulfuric acid solution with Cu and Cl ions and other additives
having similar such properties can be used to deposit Cu as well as
to electroetch it using the method of this invention. This can be
achieved in one machine by simply changing the polarity of the
voltage applied between the anode and the cathode. And the
deposition/electroetching processes can be repeated as many times
as necessary.
[0036] In another embodiment the intermediate compound such as CuCl
in the above example or other charge carrying complex may be
supplied from another remote source where it is generated. Once
generated it can be supplied to the surface of the substrate to aid
the electroetching process. The insoluble or slightly soluble
compounds of the substrate material to be removed are attractive
polishing compounds for removing the substrate material because
they do not scratch and damage the substrate surface. They are
chemically very compatible with the substrate and the solution and
therefore they do not contaminate. They can be continually
generated as needed. They dissolve in the solution over time
leaving no residues, therefore they are recyclable. The time of
dissolution may vary from a few seconds to many minutes.
[0037] The preferred embodiments described above have been
presented for purposes of explanation only, and the present
invention should not be construed to be so limited. Variations on
the present invention will become readily apparent to those skilled
in the art after reading this description, and the present
invention and appended claims are intended to encompass such
variations as well.
* * * * *