U.S. patent application number 15/263978 was filed with the patent office on 2016-12-29 for techniques and apparatus for anisotropic metal etching.
The applicant listed for this patent is Varian Semiconductor Equipment Associates, Inc.. Invention is credited to Ludovic Godet, Tristan MA, Thomas R. Omstead.
Application Number | 20160379844 15/263978 |
Document ID | / |
Family ID | 55267939 |
Filed Date | 2016-12-29 |
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United States Patent
Application |
20160379844 |
Kind Code |
A1 |
Omstead; Thomas R. ; et
al. |
December 29, 2016 |
TECHNIQUES AND APPARATUS FOR ANISOTROPIC METAL ETCHING
Abstract
In one embodiment, a method for etching a copper layer disposed
on a substrate includes directing reactive ions to the substrate
when a mask that defines an exposed area and protected area is
disposed on the copper layer, wherein an altered layer is generated
in the exposed area comprising a chemically reactive material; and
exposing the copper layer to a molecular species that is effective
to react with the chemically reactive material so as to remove the
altered layer.
Inventors: |
Omstead; Thomas R.;
(Gloucester, MA) ; MA; Tristan; (Lexington,
MA) ; Godet; Ludovic; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Varian Semiconductor Equipment Associates, Inc. |
Gloucester |
MA |
US |
|
|
Family ID: |
55267939 |
Appl. No.: |
15/263978 |
Filed: |
September 13, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14452153 |
Aug 5, 2014 |
9460961 |
|
|
15263978 |
|
|
|
|
Current U.S.
Class: |
156/345.29 |
Current CPC
Class: |
C23F 4/00 20130101; H01J
37/32422 20130101; H01L 21/32139 20130101; H01L 21/76892 20130101;
H01L 21/32135 20130101; H01J 2237/1502 20130101; H01L 21/32136
20130101; H01J 37/32449 20130101; H01J 37/32412 20130101; H01L
21/67069 20130101; H01J 37/32366 20130101; H01J 2237/3341 20130101;
H01J 2237/334 20130101 |
International
Class: |
H01L 21/3213 20060101
H01L021/3213; H01J 37/32 20060101 H01J037/32; C23F 4/00 20060101
C23F004/00; H01L 21/768 20060101 H01L021/768; H01L 21/67 20060101
H01L021/67 |
Claims
1. A processing apparatus, comprising: a plasma chamber configured
to generate a plasma comprising reactive ions; an extraction plate
having an extraction aperture to direct the reactive ions to a
substrate over trajectories that form a non-zero angle with respect
to a perpendicular to a substrate plane; an extraction voltage
supply to impart an ion energy to the reactive ions sufficient to
implant into a metal layer disposed on the substrate to form an
altered layer comprising a chemically reactive material; and a
molecular source to provide a molecular species to the substrate
that is effective to react with the chemically reactive material so
as remove the altered layer from the metal layer.
2. The processing apparatus of claim 1, wherein the plasma chamber
and molecular source comprise separate chambers.
3. The processing apparatus of claim 1, wherein the extraction
plate is configured to modify a shape of a plasma sheath boundary
proximate the extraction aperture, and wherein at least some of the
reactive ions are directed to the substrate over trajectories that
form a non-zero angle with respect to a perpendicular to a
substrate plane.
4. The processing apparatus of claim 1, wherein the reactive ions
comprise oxygen.
5. The processing apparatus of claim 4, wherein metal layer is
copper and the molecular species comprises an acetylacetonate.
6. The processing apparatus of claim 1, wherein the reactive ions
comprise hydrogen.
7. The processing apparatus of claim 6 wherein the molecular
species comprise arsine, trimethylarsine, phosphine, or
trimethylphosphine.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/452,153 filed Aug. 5, 2014, which is herein
incorporated by reference in its entirety.
FIELD
[0002] The present embodiments relate to substrate processing, and
more particularly, to techniques and processing apparatus for
etching metal layers.
BACKGROUND
[0003] As semiconductor devices scale to smaller dimensions, metal
interconnects that form part of device circuitry are also scaling
to smaller dimensions. In order to maintain the
resistance-capacitance (RC) delay at acceptable levels it may be
useful to reduce the materials resistance in a metal interconnect.
However, conventional metal interconnects such as copper
interconnects are formed using a dual Damascene process in which
copper is deposited into patterned features where interconnect
lines are to be formed. This may limit the grain size of the copper
material, which may increase resistivity due to grain boundary
scattering, among other phenomena. This smaller grains size may in
turn raise the RC delay and hence limit the speed of the
circuits.
[0004] In principle, larger-grain metal materials such as copper
may be formed if a metal is deposited as a blanket layer. However,
if metal is first deposited as a blanket layer, formation of
interconnect wiring entails etching of the metal layer after
deposition to pattern the metal layer. It is with respect to these
and other considerations that the present improvements have been
needed.
SUMMARY
[0005] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended as an aid in determining the scope of the
claimed subject matter.
[0006] In one embodiment a method for etching a copper layer
disposed on a substrate includes directing reactive ions to the
substrate when a mask that defines an exposed area and protected
area is disposed on the copper layer, wherein an altered layer is
generated in the exposed area comprising a chemically reactive
material. The method may further include exposing the copper layer
to a molecular species that is effective to react with the
chemically reactive material so as to remove the altered layer.
[0007] In another embodiment a processing apparatus may include a
plasma chamber configured to generate a plasma comprising reactive
ions. The processing apparatus may also include an extraction
aperture to direct the reactive ions to a substrate over
trajectories that form a non-zero angle with respect to a
perpendicular to a substrate plane. The processing apparatus may
also include an extraction voltage supply to impart an ion energy
to the reactive ions sufficient to implant into a metal layer
disposed on the substrate to form an altered layer comprising a
chemically reactive material. The processing apparatus may also
include a molecular source to provide a molecular species to the
substrate that is effective to react with the chemically reactive
material so as remove the altered layer from the metal layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1A depicts a processing apparatus according to
embodiments of the present disclosure;
[0009] FIG. 1B and FIG. 1C depict details of operation of the
processing apparatus of FIG. 1A;
[0010] FIG. 2A to FIG. 2D depict a side view of a substrate that
illustrate exemplary operations involved in a method for etching a
metal layer according to embodiments of the disclosure;
[0011] FIG. 2E depicts a top plan view of the substrate
corresponding to the instance depicted in FIG. 2A;
[0012] FIG. 2F depicts a top plan view of the substrate of FIG. 2E
after processing according to the operations of FIGS. 2A-2D;
and
[0013] FIG. 3A to FIG. 3D depict exemplary operations involved in a
method for etching a metal layer according to further embodiments
of the disclosure.
DETAILED DESCRIPTION
[0014] The embodiments described herein provide techniques and
apparatus for etching metal such as copper to form patterned
features. In various embodiments, methods and apparatus to etch
copper in an anisotropic fashion are provided. In particular, the
copper may be disposed as a pure copper layer or copper alloy layer
on a substrate base. The copper layer may be etched in an
anisotropic fashion when a mask is in place to form a patterned
feature such as an interconnect structure. The copper layer may be
initially formed as a blanket layer before etching where the copper
layer is composed of crystallites having relatively large grain
size at least within a plane of the copper layer. The grain size
within the plane of the copper layer may be larger than a dimension
of a copper feature after etching. For example, a line width of a
copper feature after etching may be less than one half micrometer,
while a grain dimension within a plane of the copper layer before
etching may be greater than one micrometer. Accordingly, the
fabrication techniques for forming patterned copper features that
are provided by the present embodiments provide a manner in which
resistance may be reduced within a patterned copper feature. This
is accomplished by reducing the number of grain boundaries
encountered along a length of a patterned feature by fabricating
the copper feature initially as a blanket layer where the grain
size may be greater in comparison to conventional approaches such
as dual Damascene fabrication. In the dual Damascene approach, for
example, in order to fabricate a copper feature having a linewidth
of 200 nm, copper is deposited within small cavities or trenches
that are 200 nm wide. The processes involved in filling such narrow
cavities and polishing excess metal to remove the metal where
appropriate may inherently limit or reduce the grain size of such
metal.
[0015] As detailed below, in various embodiments, copper etching is
performed by alternately exposing the copper layer to be etched to
an ion beam extracted from a plasma chamber and to molecular
species that may be provided as a molecular beam of undissociated
molecules. In accordance with various embodiments, the ion beam
includes reactive ions that generate an altered layer in exposed
areas of a copper layer. This may be accomplished by providing the
reactive ions at an appropriate energy and ion dose to implant into
the copper layer to form an altered layer, for example, in an
exposed area of the copper layer. Molecules within a molecular beam
that impinge on a surface of the altered layer may then
preferentially react with this altered layer to form a volatile
product that forms a gas phase species that is removed from the
copper layer. By controlling the size and shape of an implant
region, that is, the altered layer, material within the exposed
area of a copper layer may be removed in a manner that results in
an anisotropic etch profile of resulting etched copper features.
The ions and molecular species may be directed to a substrate in
such a matter that generates an anisotropic etch profile in a
copper layer effective to form a copper interconnect having a
critical dimension of less than 1000 nm, such as 100 nm or less in
one example. The etched copper features may thus be fabricated
having shapes and size of copper features that are fabricated by
conventional processing, but having the advantage of providing
lower resistance by virtue of larger grain size.
[0016] FIG. 1A illustrates a processing apparatus 100 consistent
with various embodiments of the disclosure. The processing
apparatus 100 includes a plasma chamber 102 and an extraction plate
104 disposed along a side of the plasma chamber 102. The extraction
plate 104 is disposed between the plasma chamber 102 and a process
chamber 106, which is configured to house a substrate holder 108
and substrate 110. As shown in FIG. 1A the substrate holder may be
movable with the aid of a stage 112 along the X-axis, Y-axis, or
Z-axis, or any combination thereof with respect to the Cartesian
coordinate system shown. In various embodiments, the substrate
holder 108 may be configured to rotate within the X-Y plane or tilt
with respect to the X-Y plane.
[0017] The processing apparatus 100 also includes a plasma source
114, which may be used to generate a plasma in the plasma chamber
102. For example, the plasma source 114 may, in various
embodiments, be an in situ source or remote source, an inductively
coupled plasma source, capacitively coupled plasma source, helicon
source, microwave source, arc source, or any other type of plasma
source. The embodiments are not limited in this context.
[0018] The processing apparatus 100 includes a gas source assembly
116 that includes a gas source 118, which may supply to the plasma
chamber 102 oxygen (O2), hydrogen (H2), or nitrogen (N2) gas in
some embodiments. As detailed below, the gas supplied from gas
source 118 may be used to generate reactive ions in the plasma
chamber 102 that are extracted through an extraction aperture 124
and implanted into the substrate 110 to form an altered layer. For
example, an extraction voltage may be applied by an extraction
voltage supply 132 between the plasma chamber 102 and process
chamber 106 to implant ions into the substrate 110.
[0019] The gas source assembly 116 may also include a gas source
120, which supplies a molecular gas that may be used to react with
an altered layer in the substrate 110 to form a volatile product as
described below. The gas source assembly 116 may include a
controller 122 that is coupled to the gas source 118 and gas source
120, and is configured to control the providing of gaseous species
to the plasma chamber 102.
[0020] FIG. 1B depicts one instance of operation of the processing
apparatus 100 according to an embodiment of the disclosure. In the
scenario of FIG. 1B a plasma 130 is generated in the plasma chamber
102. The plasma 130 may be generated when reactive gas is provided
from gas source 118. In some examples, the plasma 130 may include
oxygen ions, hydrogen ions, or nitrogen ions. However, the
embodiments are not limited in this context. In FIG. 1B, the
extraction voltage supply 132 may apply an extraction voltage as a
positive voltage to the plasma chamber 102 with respect to the
process chamber 106 and also the substrate holder 108. This has the
effect of attracting positive ions from the plasma 130 to the
substrate 110. As shown in FIG. 1B, an ion beam 140 is directed
through the extraction aperture 124 and impinges upon the substrate
110. The extraction voltage applied by the extraction voltage
supply 132 may be sufficient to cause implantation of ions of the
ion beam 140 into the substrate 110 and in particular into a copper
layer provided on the substrate 110, as detailed below. In brief,
however, the ion beam 140 may generate an altered layer within a
copper layer (not shown) disposed on the substrate 110, where the
altered layer is composed of a chemically reactive material.
[0021] As further shown in FIG. 1B the substrate holder 108 may be
scannable along a direction 126 that lies parallel to the Y-axis.
In one implementation the extraction aperture 124 may be an
elongated slot that has a short dimension, or aperture width, along
the Y-axis that is less than the dimension of the substrate 110, as
suggested by FIGS. 1A-1C. In contrast, the long dimension of the
extraction aperture 124 parallel to the X-axis may be equal to or
exceed the dimension of the substrate 110 along the X-axis.
Accordingly, when the substrate holder 108 is scanned a sufficient
distance along direction 126, the entirety of substrate 110 may be
exposed to the ion beam 140.
[0022] FIG. 1C illustrates another instance of operation of the
processing apparatus 100 according to an embodiment of the
disclosure. In the scenario of FIG. 1C no plasma 130 is present in
the plasma chamber 102. However, the gas source 120 may supply
molecular gas 134 to the plasma chamber 102, which may comprise
undissociated, as well as non-ionized, molecules. The molecular gas
134 may stream out of the plasma chamber 102 via the extraction
aperture 124 as the molecular beam 142, which impacts the substrate
110 as shown. Thus, the plasma chamber 102 may act as a source of
ions and as a molecular source. However, in other embodiments, a
plasma chamber 102 and molecular source may be separate
chambers.
[0023] Molecular species within the molecular beam 142 may act as a
molecular etchant in which the molecular species are configured to
react with reactive material in a copper layer on the substrate
110, creating an etch product that results in removal of the
reactive material. In particular, and as detailed below, the
molecular beam 142 may provide molecular species that are
configured to react with the chemically reactive material formed by
ion beam 140 to form a volatile product that may then escape the
surface of the substrate 110. Accordingly, the operations
illustrated in FIGS. 1B and 1C may constitute an exposure that is
effective to etch a copper layer.
[0024] FIG. 2A to FIG. 2D depict a side view of a substrate that
illustrate exemplary operations involved in a method for etching a
metal layer according to embodiments of the disclosure. FIG. 2E
depicts a top plan view of the substrate corresponding to the
instance depicted in FIG. 2A. In some implementations, the
operations depicted in FIGS. 2A-2D may be performed in the
processing apparatus 100, although the embodiments are not limited
in this context. Turning now to FIG. 2A a substrate 200 is shown,
which includes a substrate base 202 upon which a metal layer is
disposed. In some implementations the metal layer is a copper layer
and will be referred to herein as copper layer 204. The copper
layer 204 may be formed as a blanket layer by conventional
deposition processes including physical vapor deposition, chemical
vapor deposition, plating, or other process. The deposition (not
shown) may be carried out in a manner to promote a large
crystallite (grain) size at least within the X-Y plane shown. In
some examples, the copper layer 204 may serve as the basis for
patterned features to be formed such as interconnects in a
semiconductor device. The copper layer 204 may have an appropriate
thickness in the direction parallel to the Z-axis, such as one
micrometer, one half-micrometer, one quarter micrometer, one tenth
micrometer, and so forth. However, the embodiments are not limited
in this context.
[0025] As further illustrated in FIG. 2A, a mask 205 that is
composed of a plurality of mask features 206 is provided on the
copper layer 204. The mask 205 may be used as an etch mask for
etching the copper layer 204 and may be formed from known
materials, such as hard mask materials, oxides, nitrides,
photoresist, or other mask material. The mask features 206 may in
particular serve to define the shape and size of copper features to
be etched from the copper layer 204. Thus, the mask features 206
are characterized by a width D and length L, which may correspond
to dimensions for copper features to be formed by etching the
copper layer 204 when the mask features are present, in a so-called
subtractive etch process. One advantage of forming patterned copper
features by subtractive etching from a blanket layer, such as
copper layer 204 is that the final features formed may retain a
grain size characteristic of the copper layer 204 from which they
are formed. In some cases, the grain size within the X-Y plane may
exceed the width D as well as the length L (see FIG. 2E) of the
mask features 206 that may define the planar dimensions of copper
features to be formed. Accordingly, after formation of such copper
features, the number of grain boundaries that cross a given copper
feature may be low, leading to lower grain boundary scattering and
therefore higher conductivity of the copper features.
[0026] As further shown in FIG. 2A, ions 208 are directed to the
substrate 200. The ions 208 may be provided with sufficient energy
to implant into exposed areas 210 of the copper layer 204. In some
examples the ions 208 may be oxygen, hydrogen, nitrogen, or other
reactive ion that may create an altered layer within the exposed
areas 210. The instance shown in FIG. 2A may represent an early
stage of implantation of the ions 208. Turning now to FIG. 2B there
is shown a later stage of implantation of the ions 208 in which a
sufficient number of ions 208 have been incorporated into the
exposed areas 210 of the copper layer 204 to create an altered
layer(s) 214 as shown
[0027] In some instances, the composition of an altered layer 214
may be such that the altered layer 214 is reactive with a molecular
species to form a volatile compound. For example, the ions 208 may
be oxygen ions in one implementation, and the altered layer 214 may
correspond to a Cu.sub.1O.sub.1 composition, which represents the
CuO composition of a known copper oxide. This type of copper oxide
may react with certain molecules to form volatile products which
may evaporate from a surface of the copper layer 204. However, the
overall composition of the altered layer 214 need not correspond to
the exact stochiometry of a crystalline copper oxide in order for
the altered layer 214 to be reactive with a given molecular
species. Thus, the altered layer 214 may have a composition over a
range of Cu/O ratios that is reactive with a molecular species.
[0028] As further shown in FIG. 2A and FIG. 2B the mask features
206 may attenuate the ions 208 such that the ions 208 do not
implant into the copper layer 204 in the protected areas 212. Thus,
after exposure to the ions 208 an undisturbed copper region may be
preserved under the mask features 206, which is shown as the copper
layer 204 in FIG. 2B.
[0029] Once the altered layer 214 has been formed in the exposed
areas 210, the exposure to ions 208 may be terminated.
Subsequently, the substrate 200 may be exposed to molecular species
that are configured to react with the altered layer 214. This is
shown in the instance depicted in FIG. 2C. As shown therein,
molecular species 220, which may be gas phase species, are provided
to the substrate 200, and impinge upon various features of the
substrate 200. The molecular species 220 may in particular be
composed of at least one molecule that is configured to react with
a reactive material of the altered layer 214. Continuing with the
example in which the altered layer 214 is CuO, the molecular
species 220 may include an acetic acid-based molecule such as an
acetylacetonate. In one particular example, the molecular species
220 may be hexafluoroacetlyacetonate (HFAc), which may react with
CuO in the altered layer 214 according to:
CuO+2HFAc.fwdarw.Cu(HFAc).sub.2+H.sub.2O (1)
where Cu(HFAc).sub.2 may be represented as
##STR00001##
[0030] In other embodiments the molecular species may be a
non-fluorinated species (HAC) that reacts with the copper to form
Cu(Ac).sub.2 where Cu(Ac).sub.2 has the same general structure as
Cu(HFAc).sub.2 except that fluorine is replaced by hydrogen. In
other embodiments, the molecular species may be an alkane based
precursor such as P(CH.sub.3).sub.3 or other Lewis base.
[0031] These compounds are volatile such that the Cu(HFAc).sub.2 or
Cu(Ac).sub.2, for example, may evaporate into the gas phase from
the surface of altered layer 214. FIG. 2D depicts an instance after
the molecular species 220 have reacted with the altered layer 214.
As noted the molecular species 220 and reactive material of the
altered layer 214 may react to form a volatile product that is
removed from the substrate 200, with a result that the copper layer
204 is removed in the exposed areas 210, as shown. This results in
the formation of copper features 222 which may mimic the mask
features 206 in size and shape as in other anisotropic etching
processes. Subsequently, the mask features may be removed, leaving
copper features 222. FIG. 2F depicts a top plan view of the
substrate after etching of the copper layer 204 and removal of mask
features 206. As illustrated, the copper features 222 may retain
the width D as well as the length L (see FIG. 2E) of the mask
features 206, which is indicative of a vertical anisotropic etch
process.
[0032] It is to be noted that in the examples of FIGS. 2A-2D the
material used for the mask 205 may be chosen so as not to be unduly
etched, sputtered, or altered by implantation from the ions 208 and
exposure to the molecular species 220. For example, if the mask
features 206 are composed of silicon nitride, implantation of
oxygen into the mask features 206 may form a silicon oxynitride,
which may be impervious to reaction with an acetylacetonate.
[0033] It is further to be noted that the size and shape of the
altered layer 214 may be defined by the mask features 206 and the
experimental parameters associated with ions 208, such as ion
energy, ion dose, ion incidence angle, and so forth. By appropriate
selection of these parameters, the degree of anisotropic etching,
verticality of sidewalls of copper features 222, and overall
dimensions of copper features 222 may be adjusted. Returning to
FIGS. 1B and 1C, an advantage of performing the operations shown in
FIGS. 2A-2D in an apparatus such as the processing apparatus 100 is
that the anisotropic etching of copper features may be performed
without breaking vacuum in a single apparatus. However, although
the processing apparatus 100 is depicted as having a single chamber
that provides both ions and molecular species, in other
embodiments, molecular species may be provided from a different
chamber. For example, in other apparatus (not shown) the substrate
110 may be exposed to an ion beam while adjacent to a plasma
chamber 102 and may be moved to a different position adjacent a
molecular chamber to receive exposure to molecular species. In
still further embodiments, the ions 208 may be provided to a
substrate in a conventional beamline ion implanter, and the
molecular species may be provided in a separate apparatus.
[0034] Another advantage of using a processing apparatus such as
the processing apparatus 100 to perform the operations generally
depicted in FIGS. 2A to 2D is that the operations may be repeated
in a cyclic fashion multiple times to perform etching of a metal
layer such as copper. For example, a copper layer 204 to be etched
may have a thickness of 200 nm. Furthermore, it may be convenient
to from an altered layer 214 by ion implantation having a thickness
of just 10 nm. Accordingly, a 10 nm thick layer of copper may be
removed in a single exposure cycle, where the single exposure cycle
is composed of an exposure to an ion beam to generate a 10 nm thick
altered layer, and an exposure to a molecular beam that is
effective to remove the 10 nm thick altered layer. This exposure
cycle may be repeated approximately 20 times to remove a 200 nm
film.
[0035] Although the aforementioned embodiments detail examples in
which the altered layer 214 is composed of copper oxide, in other
embodiments an altered layer may be composed of a reactive material
such as a hydride. Thus, in additional embodiments hydrogen ions
such as molecular or atomic hydrogen ions may be implanted into
exposed areas of a copper layer to form a copper hydride in one
operation. In a subsequent operation, a molecular species such as
HAc, HFAc, cyclopentadienyl, arsine, trimethylarsine, phosphine, or
trimethylphosphine may be provided to the surface of the copper
hydride, which may form a volatile product that results in etching
of the copper layer in the exposed areas. In particular
implementations, the arsine, trimethylarsine, phosphine, or
trimethylphosphine molecular species may be provided optionally
with a ligand such as cyclopentadienyl, or other cyclic, aromatic,
alkene or alkyne ligand to generate a volatile etch product. The
embodiments are not limited in this context.
[0036] FIG. 3A to FIG. 3D depict exemplary operations involved in a
method for etching a metal layer in which an exposure cycle
composed of ion implantation and exposure to a molecular etchant is
repeated in cyclic fashion. In this manner, as discussed above, a
metal layer may be etched incrementally, which may be useful under
circumstances in which the thickness of a metal film to be removed
exceeds the implantation range that is conveniently accessible by a
processing apparatus. Moreover, even in circumstances where a
processing apparatus may be capable of implanting reactive ions
through an entire thickness of a metal layer it may nevertheless be
desirable to implant incrementally into a thinner portion of the
metal layer. By reducing the implant depth in a given ion
treatment, the lateral straggle of ions is also reduced. This
lateral straggle, if excessive, may compromise the ability to
control the lateral dimensions of an altered layer to be
removed.
[0037] In the particular example of FIGS. 3A to 3D, two exposure
cycles are shown. However, in other embodiments, a greater number
of exposure cycles may be performed, which may be tailored
according to the thickness of a metal layer to be etched, the
reactive ion used to implant the metal layer, and other
considerations. Moreover, in the example of FIGS. 3A to 3D, instead
of repeating the same ion implantation process in each exposure
cycle, the ion implantation conditions are varied between different
exposure cycles. In particular examples, the ion angular
distribution of ions directed to a metal layer may be varied
between successive exposure cycles. This may provide a finer
control over an etch profile of a metal film to be etched, as
detailed below.
[0038] In FIG. 3A a substrate 300 is illustrated, which includes a
substrate base 302. For the purposes of illustration, it may be
assumed that a copper layer 304 is formed on the substrate base
302. Mask features 206 as described above are also provided on the
copper layer 304 to define a pattern of copper features to be
formed. It may also be assumed that the substrate 300 is subject to
ion implantation in an apparatus such as the processing apparatus
100. Returning also to FIG. 1B, the extraction plate 104 may be
configured to modify the shape of a plasma sheath boundary 136,
such that a meniscus 138 is formed adjacent the extraction aperture
124, as in known extraction plate apparatus. This may cause ions
that are extracted from the plasma 130 through the extraction
aperture 124 to exit the plasma 130 over a range of angles that are
defined by an ion angular distribution. The term "ion angular
distribution" refers to the mean angle of incidence of ions in an
ion beam with respect to a reference direction such a perpendicular
to a substrate, as well as to the width of distribution or range of
angles of incidence centered on the mean angle, termed "angular
spread" for short. The ion angular distribution may involve a mean
angle for ion trajectories of the ion beam that forms a non-zero
angle with respect to a perpendicular to the plane P of the
substrate, where the perpendicular lies parallel to the Z-axis.
[0039] In various embodiments, the ion angular distribution of an
ion beam may be adjusted by adjusting, alone or in combination,
settings of a processing apparatus such as processing apparatus
100. These settings may include RF power supplied to a plasma
chamber that generates the ions, extraction voltage used to
accelerate ions to a substrate, gas pressure in the plasma chamber,
extraction aperture width, and other settings.
[0040] In the example of FIG. 3A, an ion beam 306 is provided to
the substrate having a first ion angular distribution, which is
represented schematically by the arrows. As noted, this ion angular
distribution may be characterized by a mean angle of incidence as
well as an angular spread. In some instances, an extraction plate
may be configured to generate a bimodal ion angular distribution in
which a maximum number of ions are directed to a substrate at two
different angles of incidence. For example, a bimodal distribution
may be characterized by a peak in the number of ions having
trajectories whose angle of incidence is located at +/-20 degrees,
where 0 degrees incidence is parallel to the Z-axis shown in FIG.
3A. In any case, a portion of ions in the ion beam 306 may be
directed at trajectories that form a non-zero angle with respect to
the Z-axis. This may be useful to tailor the shape of an
implantation region and thus the shape of an altered layer that may
be formed by the implantation of reactive ions. As shown in FIG.
3A, ions of the ion beam 306 may be provided with an ion energy and
an ion dose to form an altered layer 308 in exposed areas 310 of
the copper layer 304. In particular, the ion energy and ion dose of
the ion beam 306 that is provided to the substrate 300 may generate
an altered layer 308 that does not extend through the entire
thickness of the copper layer 304. In some examples, the ions of
ion beam 306 may be oxygen ions, and the altered layer 308 may be
composed of CuO. Moreover, the shape of the altered layer 308
adjacent the mask features 206 may not exhibit a vertical profile
that is parallel to the Z-axis.
[0041] FIG. 3B depicts a subsequent operation in which molecular
species 312 are provided that act as a molecular etchant to react
with the altered layer 308 and generate a volatile etch product as
discussed above. For example, an acetylacetonate molecular species
may be provided to react with the altered layer 308 to create a
copper acetonate product that is volatile. This results in the
removal of the altered layer 308 as shown in FIG. 3B. However, in
order to define isolated copper features that are etched completely
to the substrate base 302, further copper etching is to take place.
Moreover, the shape of the etched regions 315 of the copper layer
may be such that the sidewalls are angled or curved with respect to
the Z-axis. Accordingly, it may be desirable to adjust ion
treatment in a subsequent ion implantation operation to account for
this.
[0042] In a next exposure cycle, which may commence with another
ion implantation procedure, the ion angular distribution of ions
may be adjusted from that of the ion beam 306. FIG. 3C depicts an
instance in which an ion beam 320 is directed to the substrate 300.
After sufficient time, the ion beam 320 may create an altered layer
318 that extends through the remaining thickness of the copper
layer 304 in the exposed areas 310 (see FIG. 3A). In addition, as
schematically shown by the arrows, the ion beam 320 exhibits a
different ion angular distribution than that of ion beam 306. In
particular, the ion beam 320 may provide ions having trajectories
that direct ions into corner regions 316 to generate an altered
layer 318 that serves to define a more vertical profile for a
sidewall 314 of a copper feature being formed.
[0043] FIG. 3D depicts a subsequent operation in which molecular
species 322 are provided that act as a molecular etchant to react
with the altered layer 318 and generate a volatile etch product as
discussed above. Thus, the adjustment of the ion angular
distribution for ion beam 320 may result in a vertical shape to the
final copper features formed, which are shown as copper features
324.
[0044] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present disclosure, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
disclosure. Furthermore, although the present disclosure has been
described herein in the context of a particular implementation in a
particular environment for a particular purpose, those of ordinary
skill in the art will recognize that its usefulness is not limited
thereto and that the present disclosure may be beneficially
implemented in any number of environments for any number of
purposes. Accordingly, the claims set forth below should be
construed in view of the full breadth and spirit of the present
disclosure as described herein.
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