U.S. patent application number 16/797925 was filed with the patent office on 2021-08-26 for chemical mechanical polishing using fluorescence-based endpoint detection.
This patent application is currently assigned to INTEL CORPORATION. The applicant listed for this patent is INTEL CORPORATION. Invention is credited to ABDIAS J. ACOSTA, Francoise Bainye Angoua, Ravindranadh T. Eluri, Sashi Shekhar Kandanur, Clark Linde, Rahul N. Manepalli, Srini Raghavan, Dilan Seneviratne.
Application Number | 20210260718 16/797925 |
Document ID | / |
Family ID | 1000004667864 |
Filed Date | 2021-08-26 |
United States Patent
Application |
20210260718 |
Kind Code |
A1 |
Raghavan; Srini ; et
al. |
August 26, 2021 |
CHEMICAL MECHANICAL POLISHING USING FLUORESCENCE-BASED ENDPOINT
DETECTION
Abstract
A polishing tool and methodology are disclosed, particularly
useful for chemical mechanical polish (CMP) applications (e.g.,
polishing and planarizing). In an embodiment, the tool includes a
carrier structure configured to support a workpiece, a polishing
pad configured to rotate and polish at least a portion of the
workpiece, a source configured to generate excitation radiation
directed towards the workpiece, and a detector configured to
receive fluorescence radiation from the workpiece. The fluorescence
radiation is generated by absorption of the excitation radiation by
a polymer material on the workpiece. The polishing tool also
includes a controller configured to, based on a magnitude of the
received fluorescence radiation, change at least one operating
condition of the polishing tool. For instance, the controller can
speed or slow the polishing process, and stop the polishing process
when a target thickness is achieved.
Inventors: |
Raghavan; Srini; (Tucson,
AZ) ; Kandanur; Sashi Shekhar; (Chandler, AZ)
; Manepalli; Rahul N.; (Chandler, AZ) ; Eluri;
Ravindranadh T.; (Tempe, AZ) ; Seneviratne;
Dilan; (Chandler, AZ) ; Linde; Clark;
(Gilbert, AZ) ; ACOSTA; ABDIAS J.; (Maricopa,
AZ) ; Angoua; Francoise Bainye; (Chandler,
AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTEL CORPORATION |
Santa Clara |
CA |
US |
|
|
Assignee: |
INTEL CORPORATION
Santa Clara
CA
|
Family ID: |
1000004667864 |
Appl. No.: |
16/797925 |
Filed: |
February 21, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/042 20130101;
B24B 37/20 20130101 |
International
Class: |
B24B 37/04 20060101
B24B037/04; B24B 37/20 20060101 B24B037/20 |
Claims
1. A polishing tool, comprising: a carrier structure configured to
support a workpiece; a polishing pad configured to rotate and
polish at least a portion of the workpiece; a source configured to
generate excitation radiation directed towards the workpiece; a
detector configured to receive fluorescence radiation from the
workpiece, the fluorescence radiation generated by absorption of
the excitation radiation; and a controller configured to, based on
a magnitude of the received fluorescence radiation, change at least
one operating condition of the polishing tool.
2. The polishing tool of claim 1, wherein the source comprises an
ultraviolet (UV) source.
3. The polishing tool of claim 1, further comprising a first
optical fiber configured to direct the generated excitation
radiation towards the workpiece, and a second optical fiber
configured to collect fluorescence radiation from the workpiece and
to direct the fluorescence radiation towards the detector.
4. The polishing tool of claim 1, wherein the controller is
configured to halt rotation of the polishing pad in response to the
magnitude of the received fluorescence radiation falling below a
threshold value.
5. The polishing tool of claim 1, wherein the controller is
configured to increase or decrease a rotation speed of the
polishing pad based on the magnitude of the received fluorescence
radiation.
6. The polishing tool of claim 1, further comprising a memory
configured to store data that associates given thicknesses of a
polymer material with corresponding fluorescence magnitudes.
7. The polishing tool of claim 6, wherein the controller is
configured to compare the magnitude of the received fluorescence
radiation to the stored data having corresponding fluorescence
magnitudes to determine a thickness of the polymer material present
on the workpiece.
8. A method of polishing a polymer material, the method comprising:
bringing the polymer material, via a carrier structure, into
contact with a polishing pad; rotating the polishing pad to polish
the polymer material; directing excitation radiation towards the
polymer material; receiving fluorescence radiation from the polymer
material, the fluorescence radiation generated from absorption of
the excitation radiation; and adjusting an operating condition of
at least one of the polishing pad and the carrier structure based
on a magnitude of the received fluorescence radiation.
9. The method of claim 8, wherein the polymer material comprises a
polymer film that encapsulates at least a portion of a
semiconductor die.
10. The method of claim 8, wherein directing excitation radiation
comprises directing UV radiation towards the polymer material.
11. The method of claim 8, wherein directing excitation radiation
comprises directing excitation radiation via a first optical fiber
towards the polymer material, and wherein receiving fluorescence
radiation comprises receiving fluorescence radiation via a second
optical fiber from the polymer material.
12. The method of claim 8, wherein the adjusting comprises halting
rotation of the polishing pad.
13. The method of claim 8, further comprising: accessing stored
data from a memory, the stored data including thicknesses of the
polymer material with corresponding fluorescence magnitudes; and
comparing the magnitude of the received fluorescence radiation to
the corresponding fluorescence magnitudes in the stored data.
14. A chemical mechanical process apparatus configured to execute
the method of claim 8.
15. A computer program product including one or more non-transitory
machine-readable mediums encoding instructions that when executed
by one or more processors cause a process to be carried out for
polishing a polymer material, the process comprising: actuating a
carrier structure coupled to the polymer material, to bring the
polymer material into contact with a polishing pad; rotating the
polishing pad to polish the polymer material; receiving
fluorescence data associated with fluorescence radiation from the
polymer material; and adjusting an operating condition of at least
one of the polishing pad and the carrier structure based on a
magnitude of the fluorescence data.
16. The computer program product of claim 15, wherein the adjusting
comprises one or both of: halting rotation of the polishing pad;
increasing a rotation speed of the polishing pad; and decreasing
the rotation speed of the polishing pad.
17. The computer program product of claim 15, wherein the adjusting
comprises actuating the carrier structure to move the polymer
material away from the polishing pad.
18. The computer program product of claim 15, wherein the process
further comprises: accessing stored data from a memory, the stored
data having given thicknesses of the polymer material with
corresponding fluorescence magnitudes; and comparing the magnitude
of the received fluorescence data to the corresponding fluorescence
magnitudes in the stored data.
19. The computer program product of claim 18, wherein the process
further comprises determining a thickness of the polymer material
based on the comparing.
20. A chemical mechanical process apparatus including the computer
program product of claim 15.
Description
BACKGROUND
[0001] Chemical mechanical polishing (CMP) is a process of
smoothing surfaces with the combination of chemical and mechanical
forces. In conjunction with a polishing pad, a chemically reactive
slurry containing an abrasive is used to polish or planarize the
surface of semiconductor wafers, metals, nanofiber materials, and
other substrates. When used for semiconductor wafers, the polishing
pad and wafer are pressed together by a polishing head and the
wafer is held in place by a plastic retaining ring. The polishing
head rotates about an axis of rotation that is different from the
axis of rotation for the wafer. The CMP process can be used to
remove wafer material and reduce irregular topography to provide a
flat or planar wafer. Accordingly, CMP is useful to prepare a wafer
for lithography and formation of circuits. Recently, CMP has been
used for polishing surfaces of polymeric films. There are a number
of non-trivial issues associated with achieving acceptable
polishing results when dealing with polymeric materials.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] FIG. 1 illustrates an example CMP system.
[0003] FIG. 2 illustrates a portion of an example CMP system with
integrated fluorescence detection, in accordance with an embodiment
of the present disclosure.
[0004] FIG. 3 is a graph of measured fluorescence for various
polymer thicknesses, in accordance with some embodiments of the
present disclosure.
[0005] FIGS. 4A-4C illustrate cross-sections of a bridge interposer
fabricated using a CMP process, in accordance with some embodiments
of the present disclosure.
[0006] FIGS. 5A-5C illustrate cross-sections of another bridge
interposer fabricated using a CMP process, in accordance with some
embodiments of the present disclosure.
[0007] FIG. 6 illustrates a fluorescence-integrated CMP process on
a panel that includes multiple bridge interposers, in accordance
with an embodiment of the present disclosure.
[0008] FIG. 7 is a flow chart of an example method for controlling
a CMP process using fluorescence-based measurements, in accordance
with an embodiment of the present disclosure.
[0009] FIG. 8 illustrates an example computer system that can be
used to control a CMP process, in accordance with some embodiments
of the present disclosure.
[0010] The Figures depict various embodiments of the present
disclosure for purposes of illustration only. Numerous variations,
configurations, and other embodiments will be apparent from the
following detailed discussion.
DETAILED DESCRIPTION
[0011] Techniques are disclosed for polishing a polymer material.
The techniques are particularly well-suited to chemical mechanical
polishing (CMP) applications, but other uses will be appreciated in
light of the disclosure. In any such cases, the techniques include
the use of fluorescence-based measurements to provide real-time
thickness observations of a polymer material as it is being
polished. In an embodiment, a CMP tool is programmed or otherwise
configured to bring the polymer material, via a carrier structure,
into contact with a polishing pad, and to rotate the polishing pad
to polish the polymer material. The tool is further configured to
direct excitation radiation towards the polymer material, and
receive fluorescence radiation from the polymer material. The
fluorescence radiation is generated from absorption of the
excitation radiation. The tool is further configured to adjust an
operating condition of at least one of the polishing pad and the
carrier structure based on a magnitude of the received fluorescence
radiation. For instance, the CMP tool may halt rotation of the
polishing pad, increase a rotation speed of the polishing pad,
decrease the rotation speed of the polishing pad, or actuate the
carrier structure to move the polymer material away from the
polishing pad, or some combination of these. Numerous variations
will be appreciated.
General Overview
[0012] As noted above, there are a number of non-trivial issues
associated with achieving acceptable polishing results when dealing
with polymeric materials. For example, existing panel-level polymer
dielectric CMP equipment use time-based recipes to determine
process endpoint. Such time-based approaches fail to guarantee a
suitable uniform polymer dielectric thickness output between
panels, particularly over time. Although there may be any number of
contributors to this non-uniformity, some include variation in
polymer dielectric thickness incoming to the CMP process, as well
as pad-life induced process shifts in the CMP process. So, for
instance, panels with lower incoming polymer dielectric thicknesses
yield lower polymer dielectric thicknesses post CMP. Accordingly,
it is difficult to control the final thickness of a polymer film
when using CMP.
[0013] Thus, and according to an embodiment of the present
disclosure, a CMP system and operating method are provided herein
that integrate fluorescence spectroscopic techniques to detect
real-time thickness changes and provide reliable endpoint thickness
control. Many polymers, such as ones used in semiconductor
fabrication and packaging, exhibit fluorescent properties in
certain wavelength regions. Accordingly, and as will be appreciated
in light of this disclosure, the measured fluorescence from these
polymer materials can be used to determine, or at least estimate, a
thickness of the polymer material. In one embodiment, a substrate
polishing tool includes a carrier structure configured to support a
workpiece, a polishing pad configured to rotate and polish at least
a portion of the workpiece, a source configured to generate
excitation radiation directed towards the workpiece, and a detector
configured to receive fluorescence radiation from the workpiece.
The fluorescence radiation is generated by absorption of the
excitation radiation by a polymer material on the workpiece. The
substrate polishing tool also includes a controller configured to,
based on a magnitude of the received fluorescence radiation, change
at least one operating condition of the substrate polishing tool.
One such example operating condition includes ceasing the polishing
of the workpiece once a desired thickness of a polymer material on
the workpiece has been achieved. Numerous configurations and
variations will be apparent in light of this disclosure.
[0014] While generally referred to herein as "chemical mechanical
polishing" or "CMP" for consistency and ease of understanding the
present disclosure, the disclosed methods are not limited to that
specific terminology and alternately can be referred to, for
example, as polishing, planarization, leveling, smoothing,
recessing, or other similar terms.
[0015] Polishing Tool
[0016] Referring to FIG. 1, a substrate polishing tool 100 is
presented that includes a platen 102 and carrier structure 106. A
polishing pad 104 is supported on platen 102 while a workpiece 108
to be polished is coupled to an underside of carrier structure 106.
Workpiece 108 may be, for example, a semiconductor wafer, a die, or
a panel of connected structures, to name a few examples. Workpiece
108 may be adhered to carrier structure 106 by frictional forces,
an adhesive, magnetics, vacuum, or other suitable means. Carrier
structure 106 may apply a downward force on workpiece 108 during
polishing. During a polishing stage, workpiece 108 is rotated by
carrier structure 106 about first axis 107 and in contact with
polishing pad 104 wet with slurry 112. Polishing pad 104 and platen
102 rotate about a second axis 109. The rotation of workpiece 108
and polishing pad 104 may be in the same direction or in opposite
directions. A slurry feed 112 may be used to dispense slurry 110
onto polishing pad 104, as needed, during polishing.
[0017] Polishing of traditional semiconductor materials such as
silicon, silicon oxide, or silicon nitride typically use
friction-based sensors or reflectance measurements to determine a
remaining thickness of the material as it is being polished.
Although CMP of common crystalline semiconductor materials has been
well established, CMP of polymer materials involves additional
non-trivial challenges. Polymer dielectric films have become widely
used in various semiconductor devices, microelectromechanical
systems (MEMS), and packaging structures. In many applications,
such films need to be planarized like any other dielectric material
when performing a layer-by-layer fabrication process. Controlling
the final thickness of the polymer films can be critical for
certain applications. For example, films that are not polished
enough (e.g., too thick) may provide too much insulating material
that breaks the electrical connection between conductive layers,
while films that are polished too much (e.g., too thin) may cause
damage to underlying structures within or beneath the polymer
film.
[0018] One application of polymer films in the semiconductor
industry is as a fill dielectric material in bridge interposer
structures. The bridge interposer structure provides an
interconnect packaging substrate for multiple die to be packaged
together on the same substrate. Polymer materials are used as the
dielectric around the various conductive pathways and vias of each
metal layer in the interconnect structure. Examples of such bridge
interposer structures are provided in FIGS. 3 and 4 and will be
discussed in turn.
[0019] As further noted above, while traditional CMP processes can
be performed to polish and planarize such polymer dielectric
materials, there is little control of the final thickness beyond a
trial and error process. To this end, tool 100 can be modified
according to an embodiment of the present disclosure, such that the
tool will be configured to execute a thickness determination of
polymer films during the polishing process by using fluorescence
measurements of the polymer film. Polymer-based dielectrics, such
as, for example, Ajinomoto build-up film (ABF), exhibit ultraviolet
(UV) fluorescence for excitation wavelengths between about 340 nm
and 360 nm. Accordingly, a UV source can provide excitation
radiation towards a polymer film while a detector receives the
fluorescence radiation (e.g., around 395 nm for ABF). The magnitude
of the received fluorescence can be used to determine a current
thickness of the polymer film.
[0020] According to one such embodiment, a controller (such as the
controller of the CMP tool, or a dedicated controller that
interfaces with the CMP tool) is programmed or otherwise designed
to control operations of the CMP tool by using the fluorescence
measurements to affect one or more operating conditions of the CMP
tool. For example, the fluorescence measurements may be used to
continually monitor the thickness of a polymer film of a workpiece.
When the thickness reaches a particular threshold (e.g., a desired
final thickness), the controller may halt the rotation of the
polishing pad to cease further polishing of the polymer film and
may further remove the workpiece from the polishing pad, according
to some such embodiments.
[0021] Integrated Fluorescence Endpoint Detection
[0022] FIG. 2 illustrates a portion of a substrate polishing tool
200 that includes polishing pad 104, carrier structure 106, and
workpiece 108 as described above with reference to FIG. 1. In
addition, and according to an embodiment of the present disclosure,
substrate polishing tool 200 includes a window 202 through a
portion of polishing pad 104 to provide optical access to workpiece
108 as it is being polished by polishing pad 104. Window 202 may
extend through an entire thickness of polishing pad 104. In other
examples, window 202 extends through a portion of the thickness of
polishing pad 104 and an optically transparent cap 204 is provided
to prevent any particles or slurry from falling through window
202.
[0023] According to an embodiment, window 202 is provided through
polishing pad 104 in order to allow fluorescence measurements to be
taken from one or more polymer films present on workpiece 108. To
this end, a first optical fiber 206 can deliver excitation
radiation 210 via window 202 and directed towards workpiece 108.
Excitation radiation may be absorbed by the one or more polymer
films on workpiece 108, which generates fluorescence radiation 212
collected by a second optical fiber 208. Either or both first
optical fiber 206 and second optical fiber 208 can represent a
single fiber or a bundle of optical fibers. In some embodiments,
first optical fiber 206 and second optical fiber 208 are angled
from one another in some fashion to reduce the amount of excitation
radiation 210 received by second optical fiber 208. In other
embodiments, communication mediums other than optical fibers can be
used, such as waveguide structures or other radiation transport
mediums. Alternatively, some embodiments don't include optical
fibers or any other communication medium, and instead place the
source 214 and optical detector 216 (to be discussed in turn) close
to the window 202 (e.g., where an output port of source 214 and an
input port of optical detector 216 are adjacent the window 202).
Transparent cap 204 may be a material that is substantially
transparent to the wavelengths of excitation radiation 210 and
fluorescence radiation 212 (e.g., materials that are transparent in
the range of 250 to 700 nanometers, such as plexiglass or optical
glass). Still other embodiments don't include cap 204.
[0024] Excitation radiation 210 may be generated by a source 214
that delivers excitation radiation 210 into first optical fiber 206
(or directly into window 202 in some embodiments where there is no
optical fiber 206). In some embodiments, source 214 is a UV source
that generates excitation radiation 210 having a peak wavelength
between about 340 nm and 360 nm. Other optical sources, such as
visible light or infrared (IR) sources, may be used as well
depending on the fluorescent properties of the material of interest
on workpiece 108. For many polymer materials, fluorescence is
exhibited when absorbing UV light. An optical detector 216 may be
used to receive fluorescence radiation 212 via second optical fiber
208 (or directly from window 202 in some embodiments where there is
no optical fiber 208) and transduce the optical signal into an
electrical signal that represents a magnitude of fluorescence
radiation 212.
[0025] As can be further seen in this example embodiment, the
electrical signal from optical detector 216 is received by a
controller 218. According to some such embodiments, controller 218
controls the operations of tool 200, and the received electrical
signal from optical detector 216 is used by controller 218 to
change one or more operating conditions of substrate polishing tool
200. Since the magnitude of fluorescence radiation 212 is roughly
proportional to the thickness of the polymer material (at least for
thicknesses below a certain amount) on workpiece 108, the magnitude
of fluorescence radiation 212 may be used by controller 218 to
determine (or estimate) a thickness of the polymer material and
take appropriate actions based on the thickness of the polymer
material. For example, controller 218 may cease the rotation of
polishing pad 104 and/or carrier structure 106 in response to the
magnitude of fluorescence radiation 212 being lower than a
threshold value. In another example scenario, controller 218 may
raise carrier structure (with workpiece 108 attached) away from
polishing pad 104 in response to the magnitude of fluorescence
radiation 212 being lower than a threshold value.
[0026] Controller 218 can control other aspects of the processing
as well, as will be appreciated. In some such embodiments,
controller 218 may change the revolutions per minute (RPM) speed of
either or both polishing pad 104 and carrier structure 106 based on
the magnitude of fluorescence radiation 212. The change in RPM
speed may involve continuous monitoring of the magnitude of
fluorescence radiation 212 and subsequent adjustment to the RPM
speed. In some embodiments, the RPM speed may be continually
adjusted until a set-point magnitude of fluorescence radiation 212
(corresponding to a particular thickness of the polymer material)
is reached. For example, if the magnitude of fluorescence radiation
212 is high above the set point (corresponding to a too-thick
polymer film) then the RPM speed may start high or be increased to
polish the polymer material more quickly. As the magnitude of
fluorescence radiation 212 decreases, the RPM speed may similarly
decrease until the setpoint is reached and the polishing operation
is ceased.
[0027] According to some embodiments, data that relates
fluorescence magnitudes to thicknesses for one or more different
polymer materials may be stored in a memory coupled to controller
218. Such correlation data can be established empirically (e.g., by
trial and error) or theoretically (e.g., by computer simulation),
or both. In some cases, the data can be updated or modified by
users, based on empirical analysis. In any such cases, the data may
be accessed by controller 218 to determine the thickness of the
polymer material on workpiece 108 associated with the received
magnitude of fluorescence radiation 212. In some embodiments, a
set-point thickness for the polymer material on workpiece 108 is
provided by a user via a user-interface, and controller 218
controls the operations of substrate polishing tool 200 to ensure
that the set-point thickness is achieved.
[0028] Different polymer materials will exhibit different
fluorescence properties, and thus should be considered to
accurately determine thickness of such materials, based on the
established correlation. FIG. 3 is a graph showing arbitrary
fluorescence counts received for different thicknesses of the
polymer-based dielectric ABF when using excitation light at around
350 nm. The fluorescence radiation was received at around 395 nm.
As will be appreciated, the wavelength of the excitation radiation
and fluorescence radiation can vary greatly depending on the
material being polished (e.g., 250 to 700 nanometers), and the
present disclosure is not intended to be limited to any particular
range of wavelengths.
[0029] As can be seen, a linear dependence on thickness exhibits
for thicknesses below around 20 micrometers. Above this thickness,
the excitation energy is likely unable to penetrate deeper into the
polymer material, thus the fluorescence radiation does not continue
to increase for increasing thicknesses. For thicknesses of ABF
below around 20 micrometers, the fluorescence dependence data
illustrated in FIG. 3 may be saved in a memory and accessed by
controller 218 when comparing magnitudes of actual received
fluorescence radiation 212. Similar such fluorescence vs. thickness
curves can be produced for any number of different polymer
materials and that resulting data may be stored in memory. The
stored data may be indexed by polymer type or by optical
characteristics such as the excitation wavelength used or the
fluorescence wavelength.
[0030] Enhanced CMP Control for Bridge Interposer
[0031] One area that can benefit from accurately controlling the
final polished thickness of polymer materials is the field of
semiconductor packaging. Many semiconductor package schemes use
polymer dielectrics when designing interconnect structures to
connect semiconductor die(s) to a circuit board. One particular
example is a bridge interconnect structure that uses a bridge die
with other surrounding interconnect structures to provide
electrical connections to more than one die on the same substrate.
Polymer-based dielectrics, such as ABF, are used to encapsulate the
bridge die and surrounding interconnect structures. If the
thickness of the polymer dielectric is not well controlled, the
bridge interconnect structure may fail to provide proper electrical
connections to one or more of the semiconductor dies.
[0032] FIGS. 4A-4C illustrate cross sections of an example bridge
interconnect structure during a critical CMP process of its
upper-most polymer layer. It should be understood that the
illustrated cross-sections do not show all layers of the bridge
interconnect structure and that other interconnect layers may be
present beneath the layers shown.
[0033] FIG. 4A illustrates a bridge interconnect structure having a
polymer material 402 laminated or otherwise deposited over a
plurality of interconnect structures 404 and a bridge die 406.
Plurality of interconnect structures 404 represent one or more
conductive traces and conductive vias fabricated on various metal
layers, as would be understood to persons skilled in the relevant
art. Bridge die 406 provides its own plurality of conductive
interconnect structures.
[0034] As observed in FIG. 4A, the lamination or other deposition
process for polymer material 402 leaves an uneven top surface. This
top surface of polymer material 402 is planarized using a CMP
process to provide a smooth, level surface for die coupling. FIG.
4B illustrates the bridge interconnect structure following a
successful CMP process. Note that a final thickness t.sub.1 of
polymer material 402 is achieved. The CMP process may be controlled
using the fluorescence detection techniques described herein to
provide the desired final thickness t.sub.1. Achieving the final
thickness t.sub.1 also provides a thickness t.sub.2 of polymer
material 402 above the top surface of bridge die 406. According to
some embodiments, thickness t.sub.2 should be thick enough to
provide sufficient electrical isolation between conductive
components on the top surface of polymer material 402 and
underlying conductive structures. However, if it is too thick, then
it would become difficult to fabricate vias to contact the
different conductive portions of bridge die 406.
[0035] FIG. 4C illustrates the final bridge interconnect structure
after formation of top-level interconnects 408 and top-level bridge
interconnects 410. Also illustrated are two semiconductor dies
coupled to the various top-level interconnects, which includes
top-level bridge interconnects 410. In some examples, more than two
die are coupled to a single bridge interconnect structure.
[0036] FIGS. 5A-5C illustrate cross sections of another example
bridge interconnect structure during a critical CMP process of its
upper-most polymer layer. Like the previous example, a polymer
material 502 laminated or otherwise deposited over a plurality of
interconnect structures 504 and a bridge die 506. However, in this
example, top-level interconnects 508 and top-level bridge
interconnects 510 are formed before the final lamination of further
polymer material 502. In this design, the final thickness of
polymer material 502 after CMP is even more critical. If polymer
material 502 is too thick, the top surfaces of top-level
interconnects 508 and top-level bridge interconnects 510 will not
be exposed. If polymer material 502 is too thin, portions of
top-level interconnects 508 and top-level bridge interconnects 510
will also be polished away, which can damage the structure.
[0037] FIG. 5B illustrates the bridge interconnect structure
following a successful CMP process. The CMP process may be
controlled using the fluorescence detection techniques described
herein to provide the desired final thickness that exposes the top
surfaces of top-level interconnects 508 and top-level bridge
interconnects 510 without polishing away any substantial portions
of the conductive vias.
[0038] FIG. 5C illustrates the final bridge interconnect structure
after formation of top-level conductive pads 512 and top-level
bridge pads 514 that contact the lower top-level interconnects 508
and top-level bridge interconnects 510, respectively. Also
illustrated are two semiconductor dies coupled to the various
top-level pads, which includes top-level bridge pads 514. In some
examples, more than two die are coupled to a single bridge
interconnect structure.
[0039] FIG. 6 illustrates substrate polishing tool 200 with many of
the same labeled components from FIG. 2. In this example, the
workpiece being polished is a panel 600 that includes a plurality
of bridge interconnect structures. As noted before, only the
top-most levels of the structures are illustrated for clarity, but
other layers may be present as part of the bridge interconnect
structures. Polymer material 602 may be polished across the entire
panel 600 using polishing pad 104. Fluorescence radiation 210 may
be collected from polymer material 602 during the polishing process
to control the operation of substrate polishing tool 200, according
to an embodiment.
[0040] Methodology
[0041] FIG. 7 is a flow chart of a method 700 for polishing a
polymer material using fluorescence-based endpoint detection,
according to an embodiment. The operations of method 700 may be
performed to achieve a desired final thickness of the polymer
material. Any other standard operations may be performed before,
between, or after any illustrated operations of method 700 and have
been omitted merely to focus on the operations most related to the
polishing and fluorescence detection operations. The correlation of
the various operations of method 700 to the specific components
illustrated in FIG. 2 is not intended to imply any structural
and/or use limitations.
[0042] Method 700 begins with operation 702 where the polymer
material is coupled to a carrier structure of a substrate polishing
tool. The polymer material may be laminated or otherwise deposited
film on a workpiece and the workpiece is coupled to the carrier
structure. The workpiece may be a wafer, die, panel, or any other
type of substrate. The polymer may have a rough or uneven top
surface that is to be planarized using the substrate polishing
tool. The workpiece (with the polymer material) may be coupled to
the carrier structure using an adhesive, electrostatic force,
vacuum, or mechanical clamping, to name a few examples.
[0043] Method 700 continues with operation 704 where one or both of
the carrier structure and a polishing pad are rotated to polish the
polymer material. In some embodiments, the carrier structure is
moved towards the polishing pad and applies pressure so that the
polymer material is pushed against the polishing pad during the
polishing process.
[0044] Method 700 continues with operation 706 where excitation
light is generated and directed towards the polymer material. The
excitation light may be UV light generated from a UV source. The
excitation light can be directed towards the polymer material using
one or more optical fibers. Depending on the type of polymer
material, the peak wavelength of the excitation light can change to
maximize the fluorescence radiation from the polymer material. For
example, ABF exhibits fluorescence around 395 nm when absorbing
excitation light around 350 nm. Other polymers may exhibit
fluorescence in different portions of the electromagnetic spectrum.
In some embodiments, the excitation light is directed via an
optical fiber through an opening through the polishing pad to
impinge upon the polymer material during the polishing process.
[0045] Method 700 continues with operation 708 where fluorescence
radiation is received from the polymer material. The fluorescence
radiation may be received via another optical fiber, or from the
same optical fiber used to direct the excitation light towards the
polymer material. The magnitude of the fluorescence radiation may
be used to determine (or at least estimate) a thickness of the
polymer material, at least within a linear operating portion of the
response curve (as seen, for example, by the response curve of FIG.
6 for thicknesses below around 20 micrometers for ABF). Thus, the
received fluorescence radiation allows the substrate polishing tool
to have a real-time observation of the polymer thickness as the
polymer is being polished.
[0046] Method 700 continues with operation 710 where one or more
operating conditions of the substrate polishing tool is adjusted
based on the received fluorescence radiation. Since the magnitude
of the fluorescence radiation is roughly proportional to the
thickness of the polymer material (at least for thicknesses below a
certain amount), the magnitude of fluorescence radiation may be
used by a controller to take appropriate actions based on the
thickness of the polymer material. For example, the rotation of one
or both of the polishing pad and carrier structure may be stopped
in response to the magnitude of the fluorescence radiation being
lower than a threshold value. In another example, the carrier
structure (with the workpiece attached) can be moved away from the
polishing pad in response to the magnitude of the fluorescence
radiation being lower than a threshold value. These adjustments may
be used to put a quick stop to the polishing process once a desired
thickness of the polymer material has been achieved. In some other
embodiments, the RPM of one or both the carrier structure and the
polishing pad is lowered or raised depending on the magnitude of
the fluorescence radiation.
[0047] Example Computing System for Process Control
[0048] FIG. 8 illustrates an example computing system 800 that may
be coupled to one or more substrate polishing tools and may control
operations of the one or more substrate polishing tools, in
accordance with some embodiments of the present disclosure. In some
embodiments, computing system 800 may host, or otherwise be
incorporated into a personal computer, workstation, server system,
laptop computer, ultra-laptop computer, tablet, touchpad, portable
computer, handheld computer, palmtop computer, personal digital
assistant (PDA), cellular telephone, combination cellular telephone
and PDA, smart device (for example, smartphone or smart tablet),
mobile internet device (MID), messaging device, data communication
device, imaging device, wearable device, embedded system, and so
forth. Any combination of different devices may be used in certain
embodiments.
[0049] In some embodiments, computing system 800 may comprise any
combination of a processor 802, a memory 804, a network interface
806, an input/output (I/O) system 808, a user interface 810, a
storage system 812, and a CMP control module 818. As can be further
seen, a bus and/or interconnect is also provided to allow for
communication between the various components listed above and/or
other components not shown. Computing system 800 can be coupled to
a network 816 through network interface 806 to allow for
communications with other computing devices, platforms, or
resources. Other componentry and functionality not reflected in the
block diagram of FIG. 8 will be apparent in light of this
disclosure, and it will be appreciated that other embodiments are
not limited to any particular hardware configuration.
[0050] Processor 802 can be any suitable processor and may include
one or more coprocessors or controllers to assist in control and
processing operations associated with computing system 800. In some
embodiments, processor 802 may be implemented as any number of
processor cores. The processor (or processor cores) may be any type
of processor, such as, for example, a micro-processor, an embedded
processor, a digital signal processor (DSP), a graphics processor
(GPU), a network processor, a field programmable gate array or
other device configured to execute code. The processors may be
multithreaded cores in that they may include more than one hardware
thread context (or "logical processor") per core.
[0051] According to some embodiments of the present disclosure, CMP
control module 818 can be any suitable processor and may include
one or more coprocessors or controllers designed to control the
operations of one or more substrate polishing tools. CMP control
module 818 may receive magnitudes of fluorescence measurements
taken from polymer materials being polished by the one or more
substrate polishing tools, and adjust the operation of the one or
more substrate polishing tools accordingly, according to some of
the embodiments of the present disclosure. In some embodiments, the
operations performed by CMP control module 818 are shared by, or
entirely performed by, processor 802.
[0052] Memory 804 can be implemented using any suitable type of
digital storage including, for example, flash memory and/or random
access memory (RAM). In some embodiments, memory 804 may include
various layers of memory hierarchy and/or memory caches as are
known to those of skill in the art. Memory 804 may be implemented
as a volatile memory device such as, but not limited to, a RAM,
dynamic RAM (DRAM), or static RAM (SRAM) device. Storage system 812
may be implemented as a non-volatile storage device such as, but
not limited to, one or more of a hard disk drive (HDD), a
solid-state drive (SSD), a universal serial bus (USB) drive, an
optical disk drive, tape drive, an internal storage device, an
attached storage device, flash memory, battery backed-up
synchronous DRAM (SDRAM), and/or a network accessible storage
device. In some embodiments, storage system 812 may comprise
technology to increase the storage performance enhanced protection
for valuable digital media when multiple hard drives are included.
According to some embodiments of the present disclosure, either or
both memory 804 and storage system 812 includes data that
associates fluorescence magnitude with thickness for a one or more
different polymer materials.
[0053] Processor 802 may be configured to execute an Operating
System (OS) 814 which may comprise any suitable operating system,
such as Google Android (Google Inc., Mountain View, Calif.),
Microsoft Windows (Microsoft Corp., Redmond, Wash.), Apple OS X
(Apple Inc., Cupertino, Calif.), Linux, or a real-time operating
system (RTOS).
[0054] Network interface 806 can be any appropriate network chip or
chipset which allows for wired and/or wireless connection between
other components of computing system 800 and/or network 816,
thereby enabling computing system 800 to communicate with other
local and/or remote computing systems, servers, cloud-based
servers, and/or other resources. Wired communication may conform to
existing (or yet to be developed) standards, such as, for example,
Ethernet. Wireless communication may conform to existing (or yet to
be developed) standards, such as, for example, cellular
communications including LTE (Long Term Evolution), Wireless
Fidelity (Wi-Fi), Bluetooth, and/or Near Field Communication (NFC).
Exemplary wireless networks include, but are not limited to,
wireless local area networks, wireless personal area networks,
wireless metropolitan area networks, cellular networks, and
satellite networks.
[0055] I/O system 808 may be configured to interface between
various I/O devices and other components of computing system 800.
I/O devices may include, but not be limited to, a user interface
810. User interface 810 may include devices (not shown) such as a
display element, touchpad, keyboard, mouse, and speaker, etc. I/O
system 808 may include a graphics subsystem configured to perform
processing of images for rendering on a display element. Graphics
subsystem may be a graphics processing unit or a visual processing
unit (VPU), for example. An analog or digital interface may be used
to communicatively couple graphics subsystem and the display
element. For example, the interface may be any of a high definition
multimedia interface (HDMI), DisplayPort, wireless HDMI, and/or any
other suitable interface using wireless high definition compliant
techniques. In some embodiments, the graphics subsystem could be
integrated into processor 802 or any chipset of computing system
800.
[0056] It will be appreciated that in some embodiments, the various
components of the computing system 800 may be combined or
integrated in a system-on-a-chip (SoC) architecture. In some
embodiments, the components may be hardware components, firmware
components, software components or any suitable combination of
hardware, firmware or software.
[0057] In various embodiments, computing system 800 may be
implemented as a wireless system, a wired system, or a combination
of both. When implemented as a wireless system, computing system
800 may include components and interfaces suitable for
communicating over a wireless shared media, such as one or more
antennae, transmitters, receivers, transceivers, amplifiers,
filters, control logic, and so forth. An example of wireless shared
media may include portions of a wireless spectrum, such as the
radio frequency spectrum and so forth. When implemented as a wired
system, computing system 800 may include components and interfaces
suitable for communicating over wired communications media, such as
input/output adapters, physical connectors to connect the
input/output adaptor with a corresponding wired communications
medium, a network interface card (NIC), disc controller, video
controller, audio controller, and so forth. Examples of wired
communications media may include a wire, cable metal leads, printed
circuit board (PCB), backplane, switch fabric, semiconductor
material, twisted pair wire, coaxial cable, fiber optics, and so
forth.
[0058] Unless specifically stated otherwise, it may be appreciated
that terms such as "processing," "computing," "calculating,"
"determining," or the like refer to the action and/or process of a
computer or computing system, or similar electronic computing
device, that manipulates and/or transforms data represented as
physical quantities (for example, electronic) within the registers
and/or memory units of the computer system into other data
similarly represented as physical quantities within the registers,
memory units, or other such information storage transmission or
displays of the computer system. The embodiments are not limited in
this context.
Further Example Embodiments
[0059] The following examples pertain to further embodiments, from
which numerous permutations and configurations will be
apparent.
[0060] Example 1 is a polishing tool that includes a carrier
structure supporting a workpiece, a polishing pad, a source, a
detector, and a controller. The polishing pad rotates and polishes
at least a portion of the workpiece. The source generates
excitation radiation directed towards the workpiece while the
detector receives fluorescence radiation from the workpiece. The
fluorescence radiation is generated by absorption of the excitation
radiation. The controller is designed to change at least one
operating condition of the polishing tool based on a magnitude of
the received fluorescence radiation.
[0061] Example 2 includes the subject matter of Example 1, wherein
the source comprises an ultraviolet (UV) source.
[0062] Example 3 includes the subject matter of Example 1 or 2,
further comprising a first optical fiber configured to direct the
generated excitation radiation towards the workpiece, and a second
optical fiber configured to collect fluorescence radiation from the
workpiece and to direct the fluorescence radiation towards the
detector.
[0063] Example 4 includes the subject matter of any one of Examples
1-3, wherein the controller is configured to halt rotation of the
polishing pad in response to the magnitude of the received
fluorescence radiation falling below a threshold value.
[0064] Example 5 includes the subject matter of any one of Examples
1-3, wherein the controller is configured to increase or decrease a
rotation speed of the polishing pad based on the magnitude of the
received fluorescence radiation.
[0065] Example 6 includes the subject matter of any one of Examples
1-5, further comprising a memory configured to store data that
associates given thicknesses of a polymer material with
corresponding fluorescence magnitudes.
[0066] Example 7 includes the subject matter of Example 6, wherein
the controller is configured to compare the magnitude of the
received fluorescence radiation to the stored data having
corresponding fluorescence magnitudes to determine a thickness of
the polymer material present on the workpiece.
[0067] Example 8 is a method of polishing a polymer material. The
method includes bringing the polymer material, via a carrier
structure, into contact with a polishing pad; rotating the
polishing pad to polish the polymer material; directing excitation
radiation towards the polymer material; receiving fluorescence
radiation from the polymer material, the fluorescence radiation
generated from absorption of the excitation radiation; and
adjusting an operating condition of at least one of the polishing
pad and the carrier structure based on a magnitude of the received
fluorescence radiation.
[0068] Example 9 includes the subject matter of Example 8, wherein
the polymer material comprises a polymer film that encapsulates at
least a portion of a semiconductor die.
[0069] Example 10 includes the subject matter of Example 8 or 9,
wherein directing excitation radiation comprises directing UV
radiation towards the polymer material.
[0070] Example 11 includes the subject matter of any one of
Examples 8-10, wherein directing excitation radiation comprises
directing excitation radiation via a first optical fiber towards
the polymer material, and wherein receiving fluorescence radiation
comprises receiving fluorescence radiation via a second optical
fiber from the polymer material.
[0071] Example 12 includes the subject matter of any one of
Examples 8-11, wherein the adjusting comprises halting rotation of
the polishing pad.
[0072] Example 13 includes the subject matter of any one of
Examples 8-12, further comprising: accessing stored data from a
memory, the stored data including thicknesses of the polymer
material with corresponding fluorescence magnitudes; and comparing
the magnitude of the received fluorescence radiation to the
corresponding fluorescence magnitudes in the stored data.
[0073] Example 14 is a chemical mechanical process apparatus that
is designed to execute the method of any one of claims 8-13.
[0074] Example 15 is a computer program product including one or
more non-transitory machine-readable mediums encoding instructions
that when executed by one or more processors cause a process to be
carried out for polishing a polymer material. The process includes
actuating a carrier structure coupled to the polymer material, to
bring the polymer material into contact with a polishing pad;
rotating the polishing pad to polish the polymer material;
receiving fluorescence data associated with fluorescence radiation
from the polymer material; and adjusting an operating condition of
at least one of the polishing pad and the carrier structure based
on a magnitude of the fluorescence data.
[0075] Example 16 includes the subject matter of Example 15,
wherein the adjusting comprises one or both of: halting rotation of
the polishing pad; increasing a rotation speed of the polishing
pad; and decreasing the rotation speed of the polishing pad.
[0076] Example 17 includes the subject matter of Example 15 or 16,
wherein the adjusting comprises actuating the carrier structure to
move the polymer material away from the polishing pad.
[0077] Example 18 includes the subject matter of any one of
Examples 15-17, wherein the process further comprises: accessing
stored data from a memory, the stored data having given thicknesses
of the polymer material with corresponding fluorescence magnitudes;
and comparing the magnitude of the received fluorescence data to
the corresponding fluorescence magnitudes in the stored data.
[0078] Example 19 includes the subject matter of Example 18,
wherein the process further comprises determining a thickness of
the polymer material based on the comparing.
[0079] Example 20 is a chemical mechanical process apparatus that
includes the computer program product of any one of claims
15-19.
[0080] The foregoing description of example embodiments of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Many modifications and
variations are possible in light of this disclosure. It is intended
that the scope of the invention be limited not by this detailed
description, but rather by the claims appended hereto.
* * * * *