U.S. patent application number 11/940361 was filed with the patent office on 2008-10-02 for cmp system having an eddy current sensor of reduced height.
Invention is credited to Jens Heinrich, Axel Kiesel, Mike Schlicker, Uwe Stoeckgen.
Application Number | 20080242195 11/940361 |
Document ID | / |
Family ID | 39719531 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080242195 |
Kind Code |
A1 |
Heinrich; Jens ; et
al. |
October 2, 2008 |
CMP SYSTEM HAVING AN EDDY CURRENT SENSOR OF REDUCED HEIGHT
Abstract
By providing an eddy current sensor element in a polishing tool
at a reduced height level in combination with a corresponding
optical endpoint detection system, standard polishing pads may be
used, thereby enhancing the lifetime of the polishing pad and
increasing tool utilization.
Inventors: |
Heinrich; Jens; (Wachau,
DE) ; Kiesel; Axel; (Chemnitz, DE) ;
Stoeckgen; Uwe; (Dresden, DE) ; Schlicker; Mike;
(Hirschfeld, DE) |
Correspondence
Address: |
J. Mike Amerson;Williams, Morgan & Amerson, P.C.
Suite 1100, 10333 Richmond
Houston
TX
77042
US
|
Family ID: |
39719531 |
Appl. No.: |
11/940361 |
Filed: |
November 15, 2007 |
Current U.S.
Class: |
451/6 ; 451/21;
451/323; 451/527 |
Current CPC
Class: |
B24B 37/013 20130101;
B24B 49/105 20130101 |
Class at
Publication: |
451/6 ; 451/323;
451/21; 451/527 |
International
Class: |
B24B 13/00 20060101
B24B013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2007 |
DE |
10 2007 015 502.8 |
Claims
1. A polishing tool, comprising: a polishing platen having a
surface configured to receive a sub pad and a top pad, said top pad
having a polishing surface and a lower surface in contact with said
sub pad, said sub pad having a first opening covered by a portion
of said top pad; and an inductive sensor positioned in said first
opening, said inductive sensor having a sensing surface that is
positioned at a height level that is less than a height level of
said lower surface of said top pad.
2. The polishing tool of claim 1, wherein said top pad comprises a
substantially transparent window.
3. The polishing tool of claim 2, wherein said window is positioned
above said first opening in said sub pad.
4. The polishing tool of claim 2, wherein said window is positioned
above a second opening formed in said sub pad.
5. The polishing tool of claim 1, wherein said sensing surface is
substantially flush with a surface of said sub pad that is in
contact with said top pad.
6. The polishing tool of claim 1, further comprising a control unit
coupled to said inductive sensor to obtain a signal responsive to
the presence of a conductive material above said top pad.
7. The polishing tool of claim 2, further comprising an optical
measurement system optically coupled to said window for optically
probing a surface portion of a substrate placed on said top
pad.
8. The polishing tool of claim 1, wherein said top pad comprises a
magnetic material at a portion located above said sensing
surface.
9. The polishing tool of claim 1, further comprising a height
adjustment unit coupled to said sensing surface and configured to
vary a height of said sensing surface.
10. The polishing tool of claim 1, wherein a thickness of said top
pad is substantially uniform across said polishing platen.
11. A polishing tool, comprising: a polishing platen having a
surface configured to receive a polishing pad having a
substantially uniform thickness; and an inductive sensor comprising
a sensing surface positioned to extend from said surface of said
platen and to support said polishing pad.
12. The polishing tool of claim 11, further comprising a sub pad
provided below said polishing pad, said sub pad having at least one
opening for receiving said sensing surface.
13. The polishing tool of claim 11, wherein said sensing surface is
covered by a window portion of said polishing pad.
14. The polishing tool of claim 11, further comprising a control
unit coupled to said inductive sensor to obtain a signal responsive
to the presence of a conductive material provided above said
polishing pad.
15. The polishing tool of claim 13, further comprising an optical
measurement system optically coupled to said window for optically
probing a surface portion of a substrate placed on said polishing
pad.
16. The polishing tool of claim 11, wherein said polishing pad
comprises a magnetic material at a portion supported by said
sensing surface.
17. The polishing tool of claim 11, further comprising a height
adjustment unit coupled to said sensing surface and configured to
vary a height of said sensing surface.
18. A polishing pad for a polishing tool, comprising: a base
material configured to be mounted on a polishing platen, said base
material comprising laterally restricted areas having included
therein a magnetic material; and a surface for polishing a
substrate.
19. The polishing pad of claim 18, wherein said magnetic material
is comprised of ferrite particles.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Generally, the subject matter disclosed herein relates to
the field of manufacturing integrated circuits, and, more
particularly, to chemical mechanical polishing (CMP) process tools
used for the formation of advanced metallization structures, such
as so-called damascene structures, in which metal trenches and vias
are formed in an insulating layer, while subsequently filling the
vias and trenches with a metal and planarizing the structure by
removing the excess metal using a polishing process.
[0003] 2. Description of the Related Art
[0004] Typically, the fabrication of modern integrated circuits
requires a large number of individual process steps, wherein a
typical process sequence involves the deposition of conductive,
semiconductive or insulating layers on an appropriate substrate.
After deposition of the corresponding layer, device features are
produced by patterning the corresponding layer with well-known
means, such as photolithography and etching. As a consequence, by
patterning a deposited layer, a certain topography will be created
that also affects deposition and patterning of subsequent layers.
Since sophisticated integrated circuits require the formation of a
plurality of subsequent layers, it has become standard practice to
periodically planarize the surface of the substrate to provide
well-defined conditions for deposition and patterning of subsequent
material layers. This especially holds true for so-called
metallization layers in which metal interconnects are formed to
electrically connect the individual device features, such as
transistors, capacitors, resistors and the like, to establish the
functionality required by the circuit design.
[0005] In this respect, CMP has become a widely used process
technique for reducing "imperfections" in the substrate topography
caused by preceding processes in order to establish enhanced
conditions for a subsequent process, such as photolithography and
the like. The polishing process itself causes mechanical damage to
the polished surface, however, in an extremely low range, i.e., at
an atomic level, depending on the process conditions. CMP processes
also have a plurality of side effects that have to be addressed so
as to be applicable to processes required for forming sophisticated
semiconductor devices.
[0006] For example, recently, the so-called damascene or inlaid
technique has become a preferred method in forming metallization
layers wherein a dielectric layer is deposited and patterned to
receive trenches and vias that are subsequently filled with an
appropriate metal, such as aluminum, copper, copper alloys, silver,
tungsten and the like. Since the process of providing the metal may
be performed as a "blanket" deposition process based on, for
instance, electrochemical deposition techniques, the respective
pattern of the dielectric material may require a significant
over-deposition in order to reliably fill narrow openings and wide
regions or trenches in a common process. The excess metal is then
removed and the resulting surface is planarized by performing a
process sequence comprising one or more mechanical polishing
processes, which also include a chemical component. Chemical
mechanical polishing (CMP) has proven to be a reliable technique to
remove the excess metal and planarize the resulting surface so as
to leave behind metal trenches and vias that are electrically
insulated from each other as required by the corresponding circuit
layout. Chemical mechanical polishing typically requires the
substrate to be attached to a carrier, a so-called polishing head,
such that the substrate surface to be planarized is exposed and may
be placed against a polishing pad. The polishing head and polishing
pad are usually moved relative to each other by individually moving
the polishing head and the polishing pad. Typically, the head and
pad are rotated against each other while the relative motion is
controlled to locally achieve a target material removal. During the
polishing operation, typically a slurry, that may include a
chemically reactive agent and possibly abrasive particles, is
supplied to the surface of the polishing pad.
[0007] One problem involved in the chemical mechanical polishing of
substrates is the very different removal rates of differing
materials, such as of a metal and a dielectric material from which
the excess metal has to be removed. For instance, at a polishing
state where the dielectric material and the metal are
simultaneously treated, i.e., after the major portion of the metal
has already been removed, the removal rate for the metal exceeds
the removal rate for the dielectric material. This may be desirable
because all metal is reliably ablated from all insulating surfaces,
thereby insuring the required electrical insulation. On the other
hand, significant metal removal from trenches and vias may result
in a trench or via that exhibits an increased electrical resistance
due to the reduced cross-sectional area. Moreover, the local
removal rate may significantly depend on the local structure, i.e.,
on the local pattern density, which may result in a locally varying
degree of erosion of the dielectric material in a final state of
the polishing process. In order to more clearly demonstrate a
typical damascene process, reference is made to FIGS. 1a-1c.
[0008] FIGS. 1a-1c schematically show cross-sectional views of a
semiconductor structure 100 at various stages in fabricating a
metallization layer according to a typical damascene process
sequence.
[0009] In FIG. 1a, the semiconductor structure 100 comprises a
substrate 101 bearing circuit features (not shown) and an
insulating cap layer on which metal lines are to be formed. A
patterned dielectric layer 102 is formed over the substrate 101 and
includes openings, for example in the form of narrow trenches 103
and wide trenches 104. The dielectric layer 102 may also comprise
closely-spaced openings 109. The openings for trenches 103, 109 and
104 are patterned in conformity with design rules to establish
metal lines exhibiting the required electrical characteristics in
terms of functionality and conductivity. For instance, the trench
104 is designed as a so-called wide line to provide low electrical
resistance. The deposition of the dielectric material 102 as well
as the patterning of the trenches 103, 109 and 104 is carried out
by well-known deposition, etching and photolithography
techniques.
[0010] FIG. 1b schematically depicts the semiconductor structure
100 after deposition of a metal layer 105, for example a copper
layer when sophisticated integrated circuits are considered. As is
evident from FIG. 1b, the topography of the metal layer 105 will be
affected by the underlying pattern of the dielectric layer 102. The
metal layer 105 may be deposited by chemical vapor deposition,
sputter deposition or, as usually preferred with copper, by
electroplating with a preceding sputter deposition of a
corresponding copper seed layer. Although the precise shape of the
surface profile of the metal layer 105 may depend on the deposition
technique used, in principle, a surface shape will be obtained as
shown in FIG. 1b.
[0011] Subsequently, the semiconductor structure 100 will be
subjected to the chemical mechanical polishing in which, as
previously mentioned, the slurry and polishing pad are selected to
optimally remove the excess metal in the metal layer 105. During
the chemical mechanical polishing, the excess metal is removed and
finally surface portions 120 of the dielectric material 102 will be
exposed, wherein it is necessary to continue the polishing
operation for a certain overpolish time to ensure clearance of the
metal from all insulating surfaces in order to avoid any electrical
short between adjacent metal lines. As previously mentioned, the
removal rate of the dielectric material and the metal may differ
significantly from each other so that, upon overpolishing the
semiconductor structure 100, the copper in the trenches 103, 109
and 104 will be recessed.
[0012] FIG. 1c schematically shows a typical result of chemical
mechanical polishing the structure shown in FIG. 1b. As is evident
from FIG. 1c, during overpolishing of the semiconductor structure
100, different materials are simultaneously polished with different
removal rates. The removal rate is also dependent to some degree on
the underlying pattern. For instance, the recessing of the metals
during the overpolish time, which is also referred to as dishing,
as well as the removal of the dielectric material, also referred to
as erosion, is significantly affected by the type of pattern to be
polished. In FIG. 1c, dishing and erosion at the wide trenches 104,
as indicated by 107 and 106, respectively, are relatively moderate,
whereas at the narrow lines 103, dishing 107 and 106 are
significantly increased. For obtaining a required electrical
conductivity, circuit designers have to take into consideration a
certain degree of dishing and erosion, which may not be compatible
with sophisticated devices.
[0013] Therefore, complex control strategies are typically used in
advanced CMP tools in order to generate in situ measurement data
for estimating an appropriate end point of the polishing process
and/or control the uniformity of the polishing process. For
example, the layer thickness may be monitored at various sites on
the substrate in order to determine the local removal rate during
the process and/or to identify an appropriate point in time for
terminating the process. To this end, optical measurement
techniques, such as spectroscopic ellipsometry or other
reflectivity measurement techniques, may be used. Since the optical
probing of the substrate surface is difficult due to the nature of
the polishing process, significant efforts have been made to
provide appropriate CMP tools comprising optical measurement
capabilities. For this purpose, appropriately configured polishing
pads and platens have been developed that allow optical access to
the substrate surface during polish. This may be accomplished by
providing respective transparent windows in the pad. Respective
optical measurement data may therefore be obtained for a plurality
of dielectric materials and very thin metal layers during
polishing, thereby enabling efficient control and endpoint
detection strategies. For moderately thick initial metal layers as
are typically encountered in forming metallization layers, as
described above, enhanced process control may also be important
during any stage of the polishing process of initially thick metal
layers, which may not be efficiently addressed by presently
available optical systems.
[0014] For this reason, other in situ measurement strategies have
been proposed, such as sensors operating on the basis of inductive
coupling. In this case, eddy currents may be induced in the metal
layer, which may depend on the layer thickness. The response of a
sensing coil to the eddy currents may then be used to evaluate the
local thickness of the layer. Respective sensor systems may be very
efficient for situations as described above with reference to FIGS.
1a-1c, since the metal removal may be monitored by the varying
degree of induced eddy currents. Thus, advanced control regimes may
be used based on optical and inductive regimes, wherein, in
advanced CMP tools, both optical process control and inductive
process control may be provided concurrently. For instance,
respective inductive sensor portions are positioned close to the
substrate surface within the pad window of specifically design
polishing pads, in which the respective distance or "air gap"
between the substrate surface and the sensor portion is reduced by
providing a thinned material portion within the transparent pad
window. This allows an efficient optical and inductive coupling
during sophisticated polishing processes.
[0015] In advanced CMP techniques, an important factor is the cost
of ownership for respective tools, since in the last years CMP
costs have increased significantly. The delivery and management of
slurries, pads, conditioners, cleansers and the like is very cost
intensive. Thus, respective process and control strategies
requiring special and thus expensive consumables, such as polishing
pads, as described above, may have to be enhanced with respect to
consumable consumption and the like, since these factors may
significantly contribute to increased production costs due to
frequent change of consumables, less tool utilization and
availability and the like. In the case described above, the
specifically designed pad may be very expensive and may suffer from
a reduced life time due to window delamination and/or degradation
of the thin material portion in the pad window.
[0016] The present disclosure is directed to various devices that
may avoid, or at least reduce, the effects of one or more of the
problems identified above.
SUMMARY OF THE INVENTION
[0017] The following presents a simplified summary of the invention
in order to provide a basic understanding of some aspects of the
invention. This summary is not an exhaustive overview of the
invention. It is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is discussed
later.
[0018] Generally, the subject matter disclosed herein is directed
to CMP tools and related components, such as polishing pads, sensor
components and the like, which enable an in situ monitoring of the
polishing process, wherein at least an inductive sensor may be
provided that generates a signal related to the amount of
conductive material formed on a surface to be treated. As
previously explained, in highly advanced CMP tools, typically
optical process control and process control based on inductive
sensor concepts, for instance using the eddy current principle, may
be provided concurrently in order to enhance controllability and
flexibility of the respective CMP tools. In these conventional CMP
tools, sophisticated polishing pads may have to be used including
extra thin pad windows for enabling both efficient optical coupling
and efficient inductive coupling. Due to the sophisticated design
of the respective polishing pad, significantly increased cost of
ownership may be encountered, in particular as reduced lifetime of
the corresponding window portions may require more frequent
replacement of a polishing pad. In illustrative embodiments
disclosed herein, a respective inductive sensor is provided that is
appropriately designed to enable the usage of pad windows of
increased thickness and/or standard polishing pads as are typically
used in optical endpoint detection systems of CMP tools without
additional eddy current sensor elements, thereby increasing the
overall lifetime of the polishing pad.
[0019] In one illustrative embodiment disclosed herein, a polishing
tool comprises a polishing platen having a surface configured to
receive a sub pad and a top pad that comprises a polishing surface
and a lower surface in contact with the sub pad, wherein the sub
pad has a first opening covered by a portion of the top pad.
Furthermore, the polishing tool comprises an inductive sensor
comprising a sensing surface positioned to extend from the surface
of the platen into the first opening, wherein the sensing surface
is positioned at a height level that is less than a height level of
the lower surface of the top pad.
[0020] An illustrative polishing tool disclosed herein comprises a
polishing platen having a surface configured to receive a polishing
pad having a substantially uniform thickness. Furthermore, the
polishing tool comprises an inductive sensor comprising a sensing
surface positioned to extend from the surface of the platen and to
support the polishing pad.
[0021] In a further illustrative embodiment, a polishing pad for a
CMP tool comprises a base material configured to be mounted on a
polishing platen, wherein the base material comprises laterally
restricted areas having included therein a magnetic material. The
polishing pad further comprises a surface for polishing a
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The disclosure may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0023] FIGS. 1a-1c schematically illustrate cross-sectional views
of a semiconductor device during various manufacturing stages in
forming an advanced metallization structure using a CMP process for
removing excess material;
[0024] FIG. 2a schematically illustrates a top view of a CMP tool
including an inductive sensor according to illustrative
embodiments;
[0025] FIGS. 2b-2c schematically illustrate cross-sectional views
of a portion of the CMP tool of FIG. 2a according to still other
illustrative embodiments in which a sensor surface of an inductive
sensor element may be positioned at a height level that is reduced
compared to sophisticated conventional CMP tools including optical
and inductive sensor components;
[0026] FIG. 2d schematically illustrates a cross-sectional view of
a CMP tool comprising an optical detection system in combination
with an inductive sensor element, which may be provided in a
respective window of the polishing platen according to illustrative
embodiments; and
[0027] FIGS. 3a-3b schematically illustrate cross-sectional views
of a polishing pad having included therein a magnetic material
according to still other illustrative embodiments.
[0028] While the subject matter disclosed herein is susceptible to
various modifications and alternative forms, specific embodiments
thereof have been shown by way of example in the drawings and are
herein described in detail. It should be understood, however, that
the description herein of specific embodiments is not intended to
limit the invention to the particular forms disclosed, but on the
contrary, the intention is to cover all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Various illustrative embodiments of the invention are
described below. In the interest of clarity, not all features of an
actual implementation are described in this specification. It will
of course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0030] The present subject matter will now be described with
reference to the attached figures. Various structures, systems and
devices are schematically depicted in the drawings for purposes of
explanation only and so as to not obscure the present disclosure
with details that are well known to those skilled in the art.
Nevertheless, the attached drawings are included to describe and
explain illustrative examples of the present disclosure. The words
and phrases used herein should be understood and interpreted to
have a meaning consistent with the understanding of those words and
phrases by those skilled in the relevant art. No special definition
of a term or phrase, i.e., a definition that is different from the
ordinary and customary meaning as understood by those skilled in
the art, is intended to be implied by consistent usage of the term
or phrase herein. To the extent that a term or phrase is intended
to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner
that directly and unequivocally provides the special definition for
the term or phrase.
[0031] The subject matter disclosed herein addresses the issue of
increased production costs and reduced tool availability of
sophisticated CMP tools or any other type of polishing tools in
which advanced in situ process monitoring may be required on the
basis of inductive sensor concepts. As previously explained,
complex polishing processes for removing excess material and
planarizing the surface topography may require precise control of
the removal rate, even prior to a final polishing phase, in order
to reliably control the respective polishing process. For example,
during the removal of excess copper, reliable monitoring of the
remaining amount of copper material may be important, even at an
initial or intermediate process stage, so as to enable high removal
rates without introducing undue process non-uniformities. During a
corresponding polishing process, an optical detection system may be
less efficient, since the corresponding reflectivity may not
efficiently provide information on the remaining material amount,
since the initially present surface topography may increasingly be
planarized, thereby providing a highly uniform scattering behavior
of the respective surface, while the remaining thickness of the
metal may not allow the extraction of information with respect to
the remaining layer thickness. In this case, efficient non-contact
measurement techniques, for instance based on inductive principles
by generating eddy currents in the metal surface to be treated, may
be used for estimating the remaining material thickness, wherein
the respective measurement information may also be used for
determining an appropriate endpoint of, for instance, a polishing
phase with high removal rate and entering a subsequent phase of
reduced removal rate so as to substantially completely clear the
respective dielectric surface and electrically isolating the
respective metal regions contained therein. During this polishing
phase, optical endpoint detection or process monitoring techniques
may be efficiently used, possibly in combination with the inductive
sensor components, so as to obtain a substantially uniform material
removal with an efficient clearance of the respective dielectric
surface portions substantially without significantly contributing
to erosion of the dielectric material and dishing of exposed metal
regions. Thus, in particular, the combination of optical
measurement strategies and inductive sensor concepts may be highly
advantageous in respective manufacturing sequences, in which highly
conductive metals, such as copper, copper alloys, silver, tungsten
and the like, may be formed over a patterned dielectric material,
the surface topography of which has to be planarized in a
subsequent step based on a polishing process. However, in addition
to high process quality of respective process steps, other factors
during the complex manufacturing process for forming microstructure
devices are of comparable importance, such as tool utilization,
tool availability, cost of ownership of respective process tools
and the like, since in addition to a high production yield, the
overall throughput for a given equipment may also determine the
profitability of the entire manufacturing sequence. Since, in
particular, polishing processes in the form of chemical mechanical
polishing or electrochemical mechanical polishing and the like have
significantly gained in importance during the fabrication of
complex semiconductor devices, a significant reduction of cost of
ownership of polishing processes in combination with an increase of
tool availability may contribute to reduced overall production
costs.
[0032] In illustrative embodiments disclosed herein, respective
inductive sensor systems may be provided in sophisticated polishing
tools without requiring extremely sophisticated and thus expensive
and sensitive polishing pads, as is the case in a plurality of
advanced conventional CMP tools, such as the polishing tool
"Reflexion LK," available from Applied Materials Inc. In some
illustrative embodiments, a standard polishing pad including a
standard pad window used for optical process control may be used
wherein the corresponding sensor assembly may be appropriately
adapted to the respective thickness of the standard polishing pad.
In other illustrative embodiments, the corresponding height level
of a respective sensing surface of an inductive sensor may be
appropriately positioned in an adjustable manner so as to provide
enhanced flexibility in selecting an appropriate pad configuration
in sophisticated polishing tools. As a consequence, in advanced
polishing tools, respective optical measurement systems and
inductive sensor systems may be combined without requiring
specifically designed polishing pads.
[0033] It should be appreciated that the subject matter disclosed
herein may be applied to polishing tools, such as electrochemical
mechanical polishing tools and the like, used for the fabrication
of highly complex semiconductor devices, such as CPUs, memory chips
and the like, in which advanced metallization structures have to be
formed for electrically connecting circuit elements, such as
transistors and the like, having critical dimensions of
approximately 50 nm and significantly less. However, the principles
of the subject matter disclosed herein may also be applied to any
situation in which polishing tools may be used, at least
temporarily, for the removal of conductive materials from
respective substrate surfaces, wherein the provision of an
inductive sensor system in combination with a less critical
polishing pad may provide enhanced tool flexibility, in particular
when the corresponding inductive sensor system may be combined with
a respective optical detection system. Thus, unless specifically
pointed out in the specification or the appended claims, the
subject matter disclosed herein should not be considered as being
restricted to polishing processes for forming copper-based
metallization layers.
[0034] FIG. 2a schematically illustrates a top view of a polishing
tool 200 which may represent a CMP tool, an electro CMP tool or any
other polishing tool. The polishing tool 200 may comprise a frame
210 configured to accommodate a polishing platen 220, a polishing
head 230 and a pad conditioner 260, as well as any respective
mechanical, electrical and other components for operating the
respective components 220, 230, 260. It should be appreciated that
the platen 220 may be rotatably supported by respective drive
assemblies (not shown) configured to provide controllable rotation
of the platen 220 in accordance with process parameters. Similarly,
the polishing head 230 may be configured, in combination with any
appropriate mechanical, electrical, hydraulic, pneumatic and other
components, to receive a respective substrate, such as a
semiconductor substrate of 200, 300 or 450 mm diameter, or any
other appropriate size, and to rotate the substrate relative to the
polishing platen 220 in accordance with specified process
parameters, wherein a specific down force may also be applied to
the substrate for obtaining a desired interaction with a
corresponding polishing pad (not shown in FIG. 2a) in combination
with a respective slurry substance, such as a chemical component,
an electrolyte and the like. Similarly, the pad conditioner 260 may
be connected to any appropriate drive assembly in order to provide
the desired positioning of a respective conditioning surface (not
shown) above the polishing platen 220, thereby allowing an
efficient reworking of the corresponding pad surface in order to
maintain substantially uniform process conditions throughout the
processing of a plurality of substrates.
[0035] The polishing tool 200 may further comprise a respective
sensor portion 221 formed in the polishing platen 220, in which may
be provided at least an inductive sensor 240 having a respective
sensing surface 241 that may be positioned close to a corresponding
surface of a substrate to be treated during the operation of the
polishing tool 200. In some illustrative embodiments, the sensor
portion 221 may further be configured to allow optical access of a
corresponding substrate surface during the operation of the tool
200 wherein the sensor portion 221 may have an appropriately
designed surface portion in the respective polishing pad that is
substantially transparent for a respective wavelength range, as
will be described later on in more detail.
[0036] During operation of the polishing tool 200, a substrate may
be loaded onto the polishing head 230 on the basis of well-known
components, such as robot handlers and the like, wherein the
polishing head 230 may itself be configured to provide the
respective substrate handling and transport activities within the
polishing tool 200. Furthermore, the substrate loaded onto the
polishing head 230 may be brought into a respective operating
position and the corresponding relative motion between the
polishing platen 220 and the polishing head 230 may be established
on the basis of respective rotational motions of these components,
wherein prior to and/or during the relative motion, an appropriate
slurry substance may be supplied, which may include a chemical
agent or any other component for enhancing the overall removal
rate, or providing enhanced surface conditions during the
corresponding polishing process. The pad conditioner 260 may be
continuously or temporarily in contact with the corresponding
polishing surface so as to "rework" the respective surface
structure. During operation of the polishing tool 200, the sensor
portion 221 may pass the substrate surface, wherein the sensing
surface 241 may generate eddy currents in the substrate to be
treated when a sufficiently conductive material or a magnetic
material may be provided thereon. For example, the inductive sensor
240 may comprise an exciting coil and a sense coil (not shown),
both of which may be coupled to the sensing surface 241, wherein
the exciting coil may generate a respective varying magnetic field,
which may thus cause respective eddy currents in a conductive
material provided in the vicinity of the sensing surface 241 and in
particular at a surface of the substrate to be treated. Thus, the
electrical response of the respective sense coil may indicate the
amount of conductive material located in the vicinity of the
sensing surface 241, thereby providing an efficient means for
estimating the corresponding polishing process in a highly dynamic
manner. In other cases, the sensor 240 may comprise a single coil
or a system of coils coupled to the sensing surface 241, wherein
the overall inductance of the respective system may be influenced
by the amount of conductive material and thus eddy currents induced
therein. Consequently, upon driving the respective coil with an
appropriate AC signal, the responsiveness of the coil may also be
indicative of the amount of conductive material and thus of the
present state of the polishing process.
[0037] As is evident, during the operation of the polishing tool
200, the respective surface of a polishing pad may interact with
the substrate to be treated and the pad conditioner 260, thereby
restricting the overall lifetime of the respective polishing pad.
Similarly, the surface of the sensor portion 221 may come into
contact with the substrate surface and the pad conditioner 260,
which may significantly influence the status of the respective
material covering the sensor portion 221, which may also be
referred to as a window, as will be described later on in more
detail. In sophisticated applications, the respective window may be
comprised of a substantially transparent material having a
different configuration compared to the remaining polishing
surface, which may therefore be less durable compared to the
remaining surface portion of the polishing pad.
[0038] In conventional devices, a respective pad window may be
provided with an even reduced material thickness in order to reduce
the corresponding gap between a respective sensing surface and the
substrate to be treated. In this case, an even more accelerated
wear of the respective window portion may be observed, thereby also
reducing the overall lifetime of the respective polishing pad, even
though the remaining polishing surface is still in an operable
state. For this reason, the sensing surface 241 as described herein
may be appropriately positioned such that an increased material
thickness may be provided between the surface 241 and the
corresponding substrate, thereby reducing the risk for material
delamination or premature wear of the corresponding window
material.
[0039] FIG. 2b schematically illustrates a cross-sectional view of
a portion of the platen 220 according to illustrative embodiments.
The polishing platen 220 may have formed thereon a polishing pad
250 having a polishing surface 253 for treating a substrate
surface, as previously explained. In the embodiment shown, the
polishing pad 250 may be comprised of a sub pad 251 provided on a
respective surface of the polishing platen 220, and a top pad 252
having the polishing surface 253 and a lower surface 254 which may
be in contact with the sub pad 251. In the embodiment shown, the
sub pad 251 may comprise a respective opening 251A, in which may be
inserted the corresponding sensor surface 241 of the inductive
sensor 240. In the embodiment shown, the sensor 240, or at least
the sensing surface 241 thereof, may be coupled to a corresponding
height adjustment unit 245, which is configured to appropriately
adjust or vary the height level of the sensing surface 241 in
accordance with respective process and device requirements. The
height adjustment unit 245 may be configured to provide the
respective vertical movement on the basis of any appropriate
components, such as electric motors, pneumatic components,
hydraulic components or any combinations thereof, as are well known
for the person skilled in the art. For example, an electric motor
may be coupled to a threaded member for translating the rotational
motion of the electric motor into a corresponding vertical movement
for adjusting the height position of the sensing surface 241. In
one illustrative embodiment, the height adjustment unit 245 may be
configured so as to enable the positioning of the sensing surface
241 at any height level above and below the lower surface 254,
thereby providing the potential for using a variety of different
types of top pads 252 having a respective window portion 252W,
wherein a corresponding material thickness may vary, depending on
the type of pad used. For instance, the top pad 252 may represent a
highly sophisticated polishing pad as may be used in advanced
polishing tools, wherein the window portion 252W may be comprised
of a substantially transparent material so as to also allow the
optical probing of a respective substrate surface during the
processing of the device 200, as previously described. Hence, in
this case, the sensing surface 241 may be positioned close to the
material or in contact thereto of the window portion 252W, thereby
allowing operation of the tool 200 in accordance with conventional
strategies. When significantly enhanced thickness of the window
portion 252W may have to be used, for instance in order to reduce
material delamination or material degradation in the window portion
252W, the sensing surface 251 may be appropriately positioned so as
to accommodate the respective increased material thickness.
[0040] FIG. 2c schematically illustrates a cross-sectional view of
the polishing platen 220 and the inductive sensor element 240
according to further illustrative embodiments. The top pad 252 may
have a substantially uniform thickness 252T across the entire
polishing platen 220 so that the window portion 252W may be
provided with a respective material thickness. The top pad 252 may,
in this case, be provided as a standard polishing pad designed for
advanced polishing tools including optical detection systems, such
as the tool "Reflexion" or "Mirra" available from Applied Materials
Inc. The top pad 252 may be comprised of a microporous polymer
material, such as polyurethane material, with an appropriate
texture formed in the polishing surface 253 in order to generate,
in combination with a respective slurry material, a corresponding
polishing effect. In some illustrative embodiments, the window
portion 252W may be provided as a transparent polyurethane material
to enable optical endpoint technology, as previously described,
while, in other illustrative embodiments, the window portion 252W
may be comprised of the same material as the remaining portion of
the pad 252, when optical access may not be required. Thus, the pad
252 may be provided with any appropriate thickness, for instance 80
mils and the like, substantially without requiring a material
removal above the sensor portion 221, which may otherwise result in
premature failure of the polishing pad 252. Hence, the sensing
surface 241 may be positioned at a height level that substantially
corresponds to the height level of the lower surface 254, thereby
additionally supporting the window portion 252W, which may also
result in enhanced uniform process conditions.
[0041] During operation of the polishing tool 200 comprising the
configuration of the inductive sensor 240, as for instance shown in
FIGS. 2b and 2c, a respective signal may be generated on the basis
of an AC signal inductively coupled into a corresponding substrate
surface, i.e., a conductive material provided thereon or therein,
wherein the corresponding signal may be evaluated by a
corresponding control unit 246. The respective gap between the
sensing surface 241 and a corresponding substrate surface, which
substantially corresponds to the thickness 252T in the embodiment
shown in FIG. 2c or a corresponding thickness of the window portion
252W, as shown in FIG. 2b, may be taken into consideration during
the evaluation of a corresponding sensor signal by using
appropriate calibration techniques, which may include the provision
of a predefined material amount above the window portion 252W so as
to produce respective reference data. Moreover, respective
compensation data may be deduced, which may take into consideration
temperature-related effects and overall pad wear, i.e., a reduced
thickness 252T, which may vary upon processing a plurality of
substrates. Consequently, even for an increased gap width between
the sensing surface 241 and the polishing surface 254 compared to
conventional designs, in which the window portion 252W may have a
significantly reduced material thickness, a reliable sensor signal
may be obtained, thereby enabling advanced process control
strategies while additionally providing a significantly enhanced
overall lifetime of the polishing pad 252 due to the increased
layer thickness and the reduced risk of material delamination at
the window portion 252W.
[0042] Furthermore, in the embodiment described with reference to
FIG. 2b, sophisticated polishing pads 252 may be used, if an
increased signal strength, i.e., an enhanced inductive coupling to
the substrate to be treated, may be required, for instance, when
conductive material layers of reduced thickness are to be treated,
which may otherwise lack pronounced responsiveness to the magnetic
field. In other cases, the tool may be efficiently re-configured
when standard polishing pads may be used, wherein the corresponding
height of the sensor element and thus of the sensing surface 241
may be appropriately adjusted on the basis of the height adjustment
unit 245. In some illustrative embodiments, the height adjustment
unit 245 may be operated in accordance with a corresponding wear of
the polishing pad 252, irrespective of whether a standard pad, such
as is shown in FIG. 2c, or a sophisticated pad, as shown in FIG.
2b, may be used, thereby providing the potential for substantially
maintaining the resulting gap between the sensing surface 241 and
the polishing surface 253. This may be accomplished, for instance,
on the basis of a respective reference substrate, which may be
processed on a regular basis in the tool 200, wherein a deviation
from the expected signal may be compensated for by appropriately
controlling the height adjustment unit 245 so as to obtain a
substantial match between the measured signal and the expected
signal.
[0043] FIG. 2d schematically illustrates the polishing tool 200
according to a further illustrative embodiment, wherein an optical
measurement system 270 may be arranged below the sensor portion
221, i.e., a respective opening provided in the polishing platen
220. The optical system 270 may be attached to a support member 271
which in turn may be mechanically coupled to a drive assembly 222
that is configured to rotate the polishing platen 220. The optical
system 270 may comprise a light source 272 configured to emit a
light beam and to direct the same to the surface of a substrate 231
that is currently being processed. Moreover, the optical system 270
may include a detector 273 that is configured and arranged to
receive a light beam reflected by the surface of the substrate 231.
The respective light beams may be received through a substantially
transparent material provided in the window portion 252W, as
previously explained. The light source 272 and the detector 273 may
be coupled to a control unit 274, which is configured to evaluate
the signal obtained from the sensor 273 and, if required, to
appropriately drive the light source 272. Furthermore, in the
embodiment shown, the control unit 274 and the control unit 246 may
be connected to a tool internal control unit 201, which is
configured to control respective components of the tool 200, such
as a drive assembly 223 for driving the polishing head 230 and a
corresponding drive unit 222 for driving the polishing platen
220.
[0044] Consequently, upon operation of the tool 200 as shown in
FIG. 2d, optical signals in combination with signals obtained by
the sensor 240 may be obtained in order to provide enhanced process
control and/or endpoint detection during processing of the
substrate 231. In the embodiment shown in FIG. 2d, the window
portion 252W may be provided with substantially the same thickness
as the remaining portion of the polishing pad 252, as previously
explained, thereby providing enhanced lifetime of the polishing pad
252 and increased tool availability and utilization due to a
reduced number of pad changes and maintenance activities.
[0045] FIG. 3a schematically illustrates a cross-sectional view of
a portion of a polishing platen 320 having formed thereon a
polishing pad 350, which may be comprised of a sub pad 351 and a
top pad 352, as previously explained. For instance, the top pad 352
may have a substantially uniform thickness, as previously
described, while the sub pad 351 may have a corresponding opening
351A. Furthermore, a respective inductive sensor 340 may extend
into the opening 351A. Furthermore, the top pad 352 may comprise a
portion 352W which may have included therein a magnetic material in
order to enhance the magnetic conductivity of the portion 352W,
thereby effectively reducing a respective air gap between the
sensor 340, i.e., a sensing surface 341 thereof, and the polishing
surface 353. The magnetic material, indicated as 352M, may be
comprised of fine particles including soft magnetic materials, such
as ferrite materials and the like, which may exhibit a high
electrical resistance to reduce the risk of the creation of eddy
currents within the portion 352W. The respective fine particles may
be provided in the form of an appropriate metallic powder or the
like, and may be incorporated during the respective manufacturing
process, wherein an appropriate piece of material may then be
inserted into the portion 352W similarly as is typically done when
providing a substantially transparent material in the portion 352W.
In other illustrative embodiments, the top pad 352 may be formed on
the basis of conventional techniques and the magnetic material 352M
may be locally provided, thereby defining respective portions 352W
within a substantially homogenous material.
[0046] FIG. 3b schematically illustrates the polishing pad 350
mounted on the polishing platen 320 in accordance with further
illustrative embodiments in which a magnetic material 351M may be
provided, additionally or alternatively, in a corresponding portion
351W of the sub pad 351. Hence, the sub pad 352 may be provided
without an opening at the portion 351W so that the corresponding
inductive sensor 340 may be configured such that the sensing
surface 341 thereof may be in contact with the portion 351W,
wherein the magnetic material 351M provides the desired efficient
magnetic coupling through the sub pad 351 and into the top pad 352.
In this case, the mechanical strength of the sub pad 351 may be
increased due to the lack of a corresponding opening required for
the inductive sensor 340. If a corresponding opening has to be
provided for optical access, the respective opening may be designed
to comply with the requirements of the optical measurement system,
while the sensing surface 341 may be covered by the material
including the magnetic substance 351M. It should be appreciated
that embodiments shown in FIGS. 3a and 3b may be combined in any
appropriate manner in order to enhance the magnetic coupling to a
substrate surface to be treated. For instance, in some illustrative
embodiments, the magnetic material 352M may be provided within a
laterally restricted area whose lateral dimension may be less
compared to the sensing surface 341, thereby "focusing" the
respective field lines, which may be advantageous in obtaining a
scan area of reduced lateral dimensions.
[0047] As a result, the subject matter disclosed herein provides an
enhanced sensor configuration for sensor systems in polishing tools
based on inductive coupling, such as eddy currents, in order to
avoid or reduce the necessity for applying highly sophisticated and
thus expensive polishing pads with a reduced material thickness at
respective pad windows. For this purpose, the height level of a
corresponding inductive sensing surface may be reduced compared to
conventional designs or may at least be provided in an adjustable
manner, thereby providing the potential for using standard
polishing pads, which may have a significantly increased lifetime
compared to sophisticated polishing pads including windows of
reduced material thickness. Consequently, the overall cost of
ownership may be reduced and tool availability may be increased
thereby contributing to an enhanced overall throughput.
[0048] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. For example, the process steps
set forth above may be performed in a different order. Furthermore,
no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below.
It is therefore evident that the particular embodiments disclosed
above may be altered or modified and all such variations are
considered within the scope and spirit of the invention.
Accordingly, the protection sought herein is as set forth in the
claims below.
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