U.S. patent application number 09/866985 was filed with the patent office on 2001-12-27 for method of chemical mechanical polishing.
This patent application is currently assigned to Micron Technology, Inc.. Invention is credited to Kim, Sung C., Koos, Daniel A., Sandhu, Gurtej S..
Application Number | 20010055941 09/866985 |
Document ID | / |
Family ID | 25356559 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010055941 |
Kind Code |
A1 |
Koos, Daniel A. ; et
al. |
December 27, 2001 |
Method of chemical mechanical polishing
Abstract
A method of planarizing a substrate employs two separate
chemical mechanical polishing (CMP) steps. In the first CMP step,
the substrate is polished using a first CMP slurry solution and a
polishing pad. A diluting solution is then applied to the polishing
pad to remove slurry of the first CMP step. In the second CMP step,
after applying the diluting solution to the polishing pad to remove
the first slurry, second CMP slurry solution is applied to the
polishing pad to facilitate additional planarization of the
substrate. In a particular embodiment of this invention, the
diluting solution comprises a buffer solution having a pH level
corresponding to a pH level of one of the first or second CMP
slurry solution. In accordance with another aspect of this
embodiment, a plurality of different diluting solutions are applied
to the polishing pad intermediate the respective first and second
CMP steps.
Inventors: |
Koos, Daniel A.; (Tempe,
AZ) ; Kim, Sung C.; (Pflugerville, TX) ;
Sandhu, Gurtej S.; (Boise, ID) |
Correspondence
Address: |
Terril G. Lewis
HOWREY SIMON ARNOLD & WHITE, LLP
750 Bering Drive
Houston
TX
77057-2198
US
|
Assignee: |
Micron Technology, Inc.
|
Family ID: |
25356559 |
Appl. No.: |
09/866985 |
Filed: |
May 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09866985 |
May 29, 2001 |
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09590035 |
Jun 7, 2000 |
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6234877 |
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09590035 |
Jun 7, 2000 |
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09351424 |
Jul 12, 1999 |
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6120354 |
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09351424 |
Jul 12, 1999 |
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08871028 |
Jun 9, 1997 |
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5934980 |
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Current U.S.
Class: |
451/57 ;
257/E21.23; 257/E21.244; 257/E21.304 |
Current CPC
Class: |
B24B 37/042 20130101;
B24B 37/105 20130101; H01L 21/31053 20130101; H01L 21/3212
20130101 |
Class at
Publication: |
451/57 |
International
Class: |
B24B 001/00 |
Claims
What is claimed is:
1. A method of chemically-mechanically planarizing a substrate,
comprising steps of: positioning said substrate against a polishing
pad; supplying first slurry to said polishing pad; planarizing said
substrate with said polishing pad and said first slurry; supplying
a buffer solution to said polishing pad to at least partially
cleanse said polishing pad; supplying second slurry to said
polishing pad; and further planarizing said substrate with said
polishing pad and said second slurry.
2. A method according to claim 1, further comprising supplying a
diluting solution to said polishing pad to cleanse said polishing
pad of at least a portion of said first slurry.
3. A method of polishing a substrate, comprising the steps of:
positioning said substrate against a polishing surface; polishing
said substrate with said polishing surface and a first polishing
solution; using a buffer solution to at least partially cleanse
said polishing surface; and further polishing said substrate with
said polishing surface and a second, different polishing
solution.
4. A method according to claim 3, wherein at least one of said
polishings comprises mechanical planarization.
5. A method according to claim 3, wherein at least one of said
polishings comprises chemical-mechanical planarization.
6. A method according to claim 3, wherein at least one of said
first and said second polishing solutions comprises a slurry
mixture having mechanical particles suspended therein.
7. A method according to claim 3, further comprising providing one
of an acidic or basic pH for said first polishing solution, and the
other one of said acidic or basic pH for said second polishing
solution.
8. A method according to claim 3, further comprising moving said
substrate relative and against said polishing surface during said
cleansing thereof with said buffer solution.
9. A method of planarizing a substrate having at least one layer of
material, said method comprising the steps of: polishing the
substrate using a polishing surface and a first planarization
mixture to remove a first portion of said one layer; using a
diluting solution to cleanse the polishing surface of at least a
portion of said first planarization mixture; and further polishing
the substrate using the polishing surface and a second
planarization mixture to remove a second portion of said one
layer.
10. A method according to claim 9, further comprising moving said
substrate relative and against said polishing surface during the
cleansing thereof with said diluting solution.
11. A method according to claim 10, further comprising providing a
buffer solution as said diluting solution.
Description
[0001] This is a continuation application of U.S. application Ser.
No. 09/351,424, filed on Jul. 12, 1999, now U.S. Pat. No. ______
issued ______, which is a continuation application of U.S.
application Ser. No. 08/871,028, filed on Jun. 9, 1997, now U.S.
Pat. No. 5,934,980 issued Aug. 10, 1999.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to planarization of
a substrate; and more particularly relates to chemical mechanical
polishing (CMP) of a semiconductor substrate employing two separate
chemical mechanical slurry solutions.
[0003] During fabrication of certain semiconductor devices, a metal
layer, e.g., tungsten or aluminum may be deposited upon an
underlying patterned dielectric layer, e.g., phosphosilicate glass
(PSG), borosilicate glass (BSG), borophosphosilicate glass (BPSG)
or silicon dioxide (SiO.sub.2), to form interconnects, for example,
within a semiconductor. In forming the interconnects, chemical
mechanical polishing of the metal layer removes metal material
until reaching the dielectric. Ideally, the polished substrate has
a flat surface, leaving metal in voids of the patterned dielectric
to serve as interconnect plugs. These interconnects should each
have a flat upper surface that is flush with an upper plane defined
by the top surfaces of the patterned dielectric layer. When a
subsequent metal layer is deposited, the deposited metal
electrically connects with ends of the plugs. The interconnect
plugs, therefore, provide electrical connections between the upper
metal to respective semiconductor regions therebelow.
[0004] Available CMP procedures for planarizing a metal layer
relative to a patterned dielectric for the formation of an
interconnect plug often result in undesirable divits, surface
unevenness, or salt residues. Assuming a known planarization
procedure employing two separate CMP slurry solutions, it is
theorized (pursuant this disclosure), that the addition of a second
CMP slurry solution to a polishing procedure while first CMP slurry
solution is still present, may alter a pH of the polishing
procedure. This change in pH level, in-turn, may effect formation
of precipitates, causing the slurry solution to gel and/or provide
salt formations.
[0005] Furthermore, when injecting different slurry solutions onto
a polishing pad at different times during polishing of a
semiconductor substrate, the pH of the combined solutions is not
precisely controlled; rather, the pH level is in a state of
fluctuation as the new slurry solution is dispensed onto the pad
and mixed with solutions already on the pad. Thus, the resulting
CMP process rate and selectivity are not precisely known. For
example, the slurries of certain known CMP processes for polishing
tungsten have been found to chemically attack the tungsten layer
and create undesirable voids within exposed tungsten plugs, or
result in the formation of vias during later process stages.
Additionally, if there is a loss of oxide selectivity (for the
above described example where the oxide layer serves as the
patterned dielectric beneath the tungsten), the lack of oxide
selectively may result in complete removal of certain oxide
portions so as to expose and damage underlying semiconductor
devices beneath the oxide layer--resulting in scrapped
material.
SUMMARY OF THE INVENTION
[0006] The chemical etch rate of certain materials is strongly
dependent on a pH level of the associated slurry solution.
Accordingly, the present invention provides new methods for
polishing of a substrate, which methods provide greater control of
the pH level during the planarization procedures.
[0007] During a polishing procedure, a second slurry solution is
dispensed onto a polishing pad following use of a first slurry
solution, providing a slurry solution transition to alter
characteristics of polishing of a semiconductor substrate. The
second slurry solution may have a pH that is different from the
first solution. Since the polishing pad used for polishing the
substrate has a capacity to absorb slurry, a precise switch from
one pH to another pH during the polishing of the substrate is not
readily available. In accordance with one embodiment of the present
invention, a diluting solution is dispensed onto the polishing pad
as an intermediate step between the application of respective first
and second slurry solutions to the polishing pad. The diluting
solution assists neutralization of the polishing pad before the
application of the second slurry solution.
[0008] In accordance with one aspect of this particular embodiment
of the present invention, a substrate is polished using a first
slurry solution and a polishing pad. Thereafter, the first slurry
solution is substantially removed from the polishing pad using at
least one diluting solution. After this step of applying diluting
solution to the polishing pad to remove the first slurry solutions,
the substrate is further polished using a second slurry
solution.
[0009] In a preferred aspect of this embodiment of the present
invention, the first slurry solution is removed from the polishing
pad using (as the diluting solution) a first buffer solution having
a pH to the same side of 7 as that of the first slurry solution.
Following use of the first buffer solution, a solvent is applied to
the polishing pad for neutralizing a pH level. Preferably, the
buffer solution and/or solvent are applied to the polishing pad
during relative movement of the substrate against the polishing pad
and during mechanical conditioning of the polishing pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will be understood from reading the
following description of particular embodiments, with reference to
the attached drawings as listed below, where:
[0011] FIG. 1 is a partial, cross sectional, simplified view
representative of a chemical mechanical polishing (CMP) machine for
polishing a substrate;
[0012] FIG. 2 is a partial, simplified block diagram view
representative of the CMP polishing apparatus of FIG. 1 for
polishing a substrate;
[0013] FIG. 3 is a simplified flow chart representative of a CMP
procedure of the present invention; and
[0014] FIGS. 4-6 are cross sectional views of an exemplary
substrate for illustrating various stages of a CMP procedure of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] With reference to FIGS. 1 and 2, a chemical mechanical
polishing (CMP) apparatus includes a polishing table 18 coupled to
a table shaft 31 for holding and rotating a polishing pad 16 on an
upper surface of the polishing table 18. Wafer carrier 10 has a
polishing head 27 coupled to an associated shaft 33. Polishing head
27 has a lower surface for seating substrate 12 in face-to-face
relationship with a polishing surface of polishing pad 16. Shaft 33
of wafer carrier 10 can be rotated or moved using known means for
moving a surface of substrate 12 relative polishing pad 16. In
addition, a downward force 11 is typically applied to wafer carrier
10 for pressing the surface of substrate 12 against the polishing
surface of polishing pad 16.
[0016] Although not shown specifically, polishing head 27 of wafer
carrier 10 preferably has a slight recess for receiving substrate
12 therein. During polishing, fluids provide an adhesive force
between substrate 12 and polishing head 27 for keeping substrate 12
adhered to polishing head 27 by way of the surface-tension effects
therebetween. Although, the polishing head, in a preferred
embodiment, has a recess for seating substrate 12; polishing head
27 alternatively employs other known substrate adhesive provisions.
By way of example, polishing head may comprise an intermediate
poromeric material consisting of a fiber reinforced polyurethane
foam as described in U.S. Pat. No. 3,841,031, issued Oct. 15, 1974,
to Robert J. Walsh, entitled "Process for Polishing Thin Elements",
the disclosure of which is hereby incorporated by reference in its
entirety.
[0017] Preferably, wafer carrier 10 can be moved radially in or out
relative the center of polishing table 18. Additionally, head shaft
33 is capable of being rotated at the same time that table shaft 31
of the polishing table 18 is rotated, as shown by the respective
arrows of FIG. 2 of the present application, and includes
provisions to apply force to a substrate for gently holding the
substrate under pressure against a polishing head during rotation
and/or oscillation of head shaft 33 and rotation (or oscillation)
of polishing table 18.
[0018] Solution delivery tube or pipe 23 ( with reference to FIGS.
1 and 2) has an ejection outlet, or nozzle, positioned over the
polishing surface of polishing pad 16 for enabling delivery of
various solutions to the surface of polishing pad 16. FIG. 1 shows
only one solution delivery tube 23 over the polishing table 18;
however, it will be understood that a plurality of solution
delivery tubes 23 (as shown in FIG. 2) could be provided for
delivering one or a plurity of associated solutions to the
polishing surface of polishing pad 16. Such a multiple solution
delivery system is described in U.S. Pat. No. 5,540,810, issued
Jul. 30, 1996, to Gurtej Sandhu et al, entitled "IC Chemical
Mechanical Planarization Process Incorporating Two Slurry
Compositions for Faster Material Removal Times", the disclosure of
which is hereby incorporated by reference in its entirety.
[0019] With reference to FIG. 2, solution delivery tube 23A has one
end disposed over the polishing pad 16 for dispensing a diluting
solution as received from a reservoir 27. Similarly, solution
delivery tube 23B has one end disposed over the polishing pad 16
proximate the outlet of delivery tube 23A to deliver, for example,
a slurry solution from an associated reservoir 25. Not shown,
although implied, are appropriate pumps and valve regulators for
controlling flows of slurry solution and diluting solution through
respective solution delivery tubes 23 onto the polishing surface of
polishing pad 16. Additionally, it will be understood that the
solution supplied to respective delivery tubes 23 may be altered in
known fashion using a control valve in selective communication
between separate supply reservoirs of different solutions.
Additionally, although not shown, solution delivery tube(s) 23, is
(are) mounted to an appropriate control arm that provides variably
controlled positioning of the outlet(s) of tube(s) relative the
polishing surface of polishing pad 16.
[0020] An additional optional element for the CMP polishing
apparatus, as shown in phantom-lines in FIGS. 1 and 2, is
mechanical conditioner unit 15. Face plate 19 of mechanical
conditioner 15 has conditioner tips 21 on a lower surface thereof
for meeting the polishing surface of polishing pad 16. During
conditioning, conditioner tips 21 penetrate the polishing pad 16 to
a depth established in accordance with a height of the conditioner
tips 21, the height of the tips being established relative to a
bottom horizontal surface of face plate 19. The bottom horizontal
surface of face plate 19 acts as a mechanical-stop, keeping the
conditioner tips 21 at a preferred penetration depth. During
mechanical conditioning of the polishing pad 16, polishing table 18
is rotated while conditioner tips 21 of the conditioner 15 are held
against the polishing surface of polishing pad 16. Additionally,
shaft 17 of the mechanical conditioner 15 is rotated, and moved
radially relative polishing table 18 so as to facilitate complete
coverage and conditioning of polishing pad 16.
[0021] CMP machines are available from companies such as
Strausbaugh or Itec/Westech. Exemplary CMP polishing pads are
available from companies such as Rodel, Dupont or Clarino. In one
preferred embodiment and implementation of the invention, the CMP
polishing pad for performing the process of the present invention
is an IC-1000 Rodel polishing pad, configured in a pad stack
arrangement (not shown) with an FR-4 underpad also of Rodel.
Although specific CMP machines, polishing pads, and substrate
mounting techniques have been disclosed for carrying out CMP
procedures of the present invention, it is to be understood that
the methods and techniques of the present invention may be carried
out similarly using alternative CMP machines, polishing pads,
substrate mounting and/or mechanical conditioning tools.
[0022] During polishing of a surface of a substrate 12, the surface
of substrate 12 is held against a polishing surface of polishing
pad 16 and moved relative thereto while chemical mechanical
polishing (CMP) slurry mixtures are dispensed and applied to the
surface of polishing pad 16 for facilitating planarization of
substrate 12. During the polishing procedure, the rotational
movement of polishing pad 16 will cause slurry solution to flow
radially outward. Some of the slurry solution will flow off
polishing pad 16 due to the centrifugal forces of the rotation.
Accordingly, in order to keep an adequate amount of slurry on the
polishing pad during polishing, solution is typically supplied to
polishing pad 16 continually during the CMP operation.
[0023] As used hereinafter, diluting solution refers to a diluent
used to wash away material from the polishing pad, i.e., a liquid
applied to the polishing pad for cleansing the polishing surface.
The diluting solution in one exemplary embodiment comprises a
buffer solution, or alternatively, simply a solvent. A buffer
solution refers to a known solution comprising both a weak acid and
weak base and having the ability to absorb small additions of acids
and bases without giving rise to a significant change in the pH of
the solution. A known solvent generally refers to a liquid capable
of dissolving or dispersing other substances, typically the
substance of greatest proportion in a solution is deemed the
solvent. However, in solutions that contain water, water is
typically deemed the solvent.
[0024] In certain polishing procedures, it is desirable to employ a
first slurry solution during a preliminary polishing step (for
removing, for example, a first layer of material from the substrate
12) followed by a subsequent polishing step that employs a
different slurry solution. During the second polishing procedure,
for example, a subsequent amount of the material is removed from
the substrate.
[0025] For purposes of illustration, with reference to FIGS. 4-6, a
preliminary portion 28 of material 20 (e.g. tungsten) is removed
from substrate 12 by way of a first polishing procedure.
Thereafter, a subsequent portion 26 of material 20 is removed using
a second slurry solution until achieving a desired planar
arrangement of material 20 relative secondary material 22, for
example, tungsten relative a dielectric. During the first polishing
step for the removal of the first portion 28 of material 20, it may
be desirable to employ a first chemical-mechanical polishing (CMP)
slurry mixture for providing an efficient first removal rate for
removal of material 20. Thereafter, the remaining polishing
planarization step could employ a different slurry solution that
provides a reduced etching characteristic for etching of material
20 relative material 22. In such circumstances, the first CMP
polishing step may employ an acidic CMP slurry solution while the
subsequent polishing procedure may employ a basic CMP slurry
solution. When transitioning between the different slurry mixtures,
the subsequent slurry solution has typically been dispensed and
applied to the polishing surface-of polishing pad 16 with residual
remnants of the first slurry solution still present thereon.
Accordingly, when the acidic solution, of the first polishing step,
for example, meets a basic solution of, for example, the second
polishing step, it is theorized (pursuant this disclosure) that
unwanted precipitates result. Such precipitates, e.g., a salt, can
have an adverse impact upon the desired polishing of substrate 12.
Accordingly, the present invention proposes an intermediate step of
applying a diluting solution to a polishing surface of a polishing
pad intermediate the two separate polishing steps of a multiple
step polishing procedure. With reference to FIG. 3, the diluting
solution is applied (step 44) to the polishing pad intermediate a
transition from a first slurry solution to a second slurry
solution.
[0026] The simplified flow chart of FIG. 3 outlines a
chemical-mechanical polishing procedure of the present invention,
which is described herein with reference to the exemplary substrate
depicted in FIGS. 4-5. With reference to FIG. 4, substrate 12 has
been previously processed to define first 22 and second 20 layers
of material over a base substrate 24. In the exemplary embodiment,
base structure 24 comprises a silicon wafer. In alternative
embodiments, base substrate 24 comprises other materials such as
gallium arsenide, aluminum oxide, glass, ceramic, or other similar
substrate material. In addition, although not shown, it will be
understood that base substrate 24 may be representative of a
previously processed substrate, upon which layers 22 and 20 are
provided thereover. In one preferred embodiment of the present
invention, materials 22 and 20 comprise a dielectric material and a
metal respectively. More particularly, dielectric 22 is a silicon
based insulator such as silicon dioxide, or alternatively,
phosphosilicate glass (PSG), borophosphosilicate glass (BSPG) or
silicon nitride; and metal 20 is tungsten, or alternatively,
aluminum, titanium, or titanium nitride. Alternatively, substrate
12 constitutes a base substrate alone (e.g., silicon, gallium
arsenic, aluminum oxide, glass, ceramic) that is to be processed by
the procedure of the present invention, after which additional
materials will be layered thereover.
[0027] In a preliminary step, substrate 12 is secured to the
polishing head 27 of wafer carrier 10. In step 40, the exposed
surface 31 of substrate 12 (facing away from polishing head 27) is
positioned for meeting the polishing surface of polishing pad
16.
[0028] In step 42, a first CMP polishing solution is applied to the
surface of polishing pad 16 while an appropriate force and
respective rotational motions are applied to wafer carrier 10 and
polishing table 18 to facilitate planarization of surface 35 of
substrate 12. The CMP polishing of step 42, using the first CMP
slurry solution, continues until a majority 28 of layer 20 (e.g.
tungsten) is removed from substrate 12, as shown in FIG. 5. In a
preferred embodiment of the present invention, the first CMP slurry
mixture is an acidic pH (pH greater than 7) slurry with alumina
particles and provides efficient removal of tungsten. Such CMP
slurry solutions are available from Rodel, Inc, under the
trademarks of MSW-1000 or MSW-2000.
[0029] After removing the first portion 28 of substrate 12 via the
first CMP polishing step 42, a diluting solution is applied to the
polishing surface of polishing pad 16 for clearing residual slurry
(of the first CMP step) from the polishing surface of polishing pad
16. In a preferred embodiment of the present invention, pad
conditioner 15 scrubs the polishing surface of polishing pad 16
while the diluting solution is dispensed onto the polishing pad 16.
In accordance with one aspect of this preferred embodiment, the
rotation of wafer carrier 10 and polishing table 18 continue during
the cleaning step, enabling removal of residual slurry from
substrate 12 and polishing head 27 at the same time. In alternative
embodiments of the present invention, wafer carrier 10 lifts
substrate 12 from the polishing pad during the pad cleaning
procedure; and/or pad conditioner 15 is not used at all, during the
time that the diluting solution is dispensed upon the polishing
pad.
[0030] As the diluting solution is applied to polishing pad 16, it
is preferably applied, firstly, near the center of the polishing
pad. Thereafter, outlet 25 of solution delivery tube 23 is moved
radially outward away from the center of the pad, in order to
dispense diluting solution upon other circumferential regions of
polishing pad 16. A known mechanical arm is operative to control
the position of the solution dispensing tube 23 relative the
polishing table so as to move outlet 25 of the tube along the
radial direction away from the center of the polishing table during
the polishing pad cleaning step 44. Additionally, and regardless of
the movement of delivery tube 23, as diluting solution is applied
to the polishing surface of polishing pad 16, rotation of polishing
table 18 provides rotational centrifugal forces to flow diluting
solution (as dispensed thereon) along the surface and radially
outward from the center of polishing pad 16 so as to carry-away
residual slurry from polishing pad 16.
[0031] Preferably, the diluting solution is dispensed from delivery
tube 23 by way of a nozzle with sufficient velocity to agitate and
loosen slurry materials on the polishing surface when the diluting
solution strikes the surface of the polishing pad. This fluid
scrubbing action assists cleansing of polishing pad 16.
[0032] In one embodiment of the present invention, the diluting
solution comprises a buffer solution having a pH level the same
side of 7 as that of the first CMP slurry mixture. In other words,
if the CMP slurry solution has an acidic pH level, the diluting
solution used is a buffer solution of acidic pH; likewise, if the
CMP slurry solution has a basic pH level, the diluting solution
used is a buffer solution of basic pH. More preferably, the buffer
solution has a pH level within two of that of the first CMP slurry
solution and prevents precipitates from forming on the polishing
pad when the buffer solution mixes with the residual CMP slurry
(e.g., of the first CMP procedure).
[0033] An exemplary basic buffer solution to be used in connection
with a basic slurry, comprises 1-5 weight percent ammonium
hydroxide and 0.5-2 weight percent ammonium acetate in water
providing a pH of about 8-10 pH.
[0034] In one embodiment and implementation of the present
invention, the above exemplary buffer solution is used as a
diluting solution to cleanse a polishing pad of previous SC-20 (KOH
buffered) slurry, or ILD-1300 (ammonium hydroxide buffered)
slurry.
[0035] An exemplary acidic buffer solution to be used in connection
with an acidic slurry, comprises about 20 parts by volume of
ammonium fluoride solution (80 weight percent in water) and 1 part
hydrofluoric acid (49 weight percent in water) providing a pH of
about 4-5.
[0036] In another embodiment and implementation of the present
inventions, the above exemplary buffer solution is used as a
diluting solution to cleanse a polishing pad of previous acidic pH
slurry, e.g., MSW-1000 or MSW-2000.
[0037] Buffer solution, as the diluting solution, is applied to the
polishing pad at a rate and duration to sufficiently clean the pad
of first CMP solution. In an exemplary procedure of this
embodiment, polishing pad 16 has a diameter of about 20-100 inches
and a rotational speed of about 10-70 rpm, and preferably receives
buffer solution for a duration in the range of 5 to 120 seconds,
and most preferably in the range, from 20 to 30 seconds. The rate
at which the buffer solution is applied to the polishing pad, in
this preferred embodiment, is in the range of 50 milliliters to 1
liter per minute, or more preferably 100 to 300 milliliters per
minute. In a specific exemplary embodiment of the present
invention, the buffer solution is dispensed at a rate of 200
milliliters per minute. Of course, the amount of time that the
buffer solution is applied to the polishing pad can be adjusted in
accordance with the size of the polishing pad, the amount of
solution dispensed per unit time, the rotational speed of the
polishing pad and cleanliness desired.
[0038] After cleaning the polishing surface of polishing pad 16
(per step 44), additional polishing of the substrate is provided in
step 46 using a second CMP slurry solution. In the exemplary
embodiment of the present invention, remaining portion 26 of
substrate 12 is removed using a second CMP slurry solution having
basic pH. Preferably, the second CMP slurry solution comprises
either a potassium hydroxide or ammonium hydroxide buffer based
slurry with silica suspended therein for assisting oxide removal.
Such slurry solutions are available from Rodel, Inc.--i.e.,
tradename SC-20 for a silica based potassium hydroxide buffered
slurry, or tradename ILD-1300 for a silica based ammonium hydroxide
buffered slurry. By sufficiently removing first slurry solution
from polishing pad 16 (e.g., using the associated diluting
solution) before applying the second CMP slurry, precipitation of
unwanted particulate is minimized.
[0039] In one particular embodiment of the present invention, a
single buffer solution (serving as the diluting solution) is
dispensed over polishing pad 16 during cleaning step 44. Such a
procedure can be used when the first CMP slurry mixture of step 42
and the second CMP slurry mixture of step 46 have comparable
chemistries, e.g., both acidic or both basic or, alternatively,
with pH levels within two of each other. In such case, the buffer
solution serves to re-establish the pad's pH condition, to purge
the pad of slurry accumulation or build-up, and to assist
conditioning of the polishing pad.
[0040] On the other hand, if the pH level of the first slurry
solution differs substantially from the pH level of the second
slurry solution, for example, one is acidic and the other basic or,
alternatively, the pH levels differ from each other by more than
two, then undesirable precipitates could be formed if the two
different solutions are combined on the polishing pad, as might
occur during a transition from the first slurry to second slurry
solution. Therefore, in accordance with one preferred embodiment of
the present invention, the polishing surface of polishing pad 16 is
first neutralized before dispensing the second CMP slurry solution
onto the polishing pad.
[0041] In accordance with this one embodiment of the present
invention, assuming first and second CMP slurry solutions of
substantially different pH chemistries, two separate diluting
solutions are applied, at different time intervals, to the
polishing surface of the polishing pad, intermediate the
application of the respective first and second CMP slurry
solutions. After polishing substrate 12 using the first CMP slurry
solution of, for example, acidic pH (i.e. after completing step
42), a buffer solution of (acidic) pH is applied to the polishing
surface of the polishing pad 16. The buffer solution serves as a
first diluting solution for washing away particulate and residual
material of the first CMP procedure. Thereafter, a second diluting
solution is applied to the polishing surface of polishing pad 16
for purging the polishing pad 16 of the first diluting solution and
for neutralizing the associated pH. Preferably, the second diluting
solution comprises a solvent, such as, for example deionized water.
Alternatively, the solvent comprises other suitable pH neutral
solutions, such as, for example, acetone or alcohol. Again, as
similarly described hereinbefore, preferably, the pH neutralization
solution or solvent is dispensed by way of a nozzle onto the
polishing pad 16 with sufficient velocity so as to agitate and
loosen particles and liquids as it impinges the surface and assist
cleansing of previous diluting solution and/or slurry off of the
polishing pad. Pad conditioner 15 and wafer carrier 10 each may or
may not be operative for conditioning polishing pad 16 and
polishing substrate 12 respectively during the application of the
second diluting solution. Once polishing pad 16 has been
neutralized by the appropriate neutralization solution, the second
CMP slurry mixture is dispensed onto polishing pad 16 with reduced
concern of undesirable precipitates or salt formation.
[0042] In accordance with an additional, alternative aspect of this
embodiment of the present invention, step 44 further comprises an
additional step of applying a third diluting solution to polishing
pad 16 following the previous applications of first and second
diluting solutions. The third diluting solution is provided a pH
level that is comparable with the second CMP slurry mixture. In
certain procedures, residual diluting solution on polishing pad 16
may result in undesirable precipitation of materials when the
second CMP slurry mixture is combined therewith. Accordingly, this
alternative procedure preconditions polishing pad 16 with a
solution having a pH level comparable with the pH of the second CMP
slurry mixture.
[0043] In other words, if the second CMP slurry solution is acidic,
then the third diluting solution is a buffer solution of acidic pH;
if the second CMP slurry solution is basic then the third diluting
solution is a buffer solution of basic pH. Accordingly, the third
diluting solution comprises a buffer solution with a pH level the
same side of seven as that of the second CMP slurry mixture, and
more preferably, within two of the pH of the second CMP slurry
mixture. This buffer solution is applied to polishing pad 16 for a
duration sufficient to purge the polishing surface of previous
solutions. Again, wafer carrier 10 and pad conditioner 15 may or
may not be operable (but preferably, they are both operative)
during the application of this third solution to polishing pad 16.
After polishing pad 16 has been preconditioned with the third
diluting solution, the second CMP slurry solution is applied to the
polishing pad 16 to provide additional chemical mechanical
polishing of substrate 12.
[0044] Thus, according to the polishing procedures of the present
invention, a substrate is polished using two different slurry
solutions while avoiding undesirable precipitation and/or salt
formations.
[0045] In the exemplary embodiments of the present invention
described above, the first CMP slurry solution was described as
having an acidic pH while the second CMP slurry solution was
characterized with a basic pH. It will be understood that the
present invention similarly encompasses other CMP slurry sequences
of different pH levels. Such alternative slurry sequences would
employ respective buffer solutions of similar pH levels
corresponding thereto. For example, it may be desirable to first
etch an oxide layer over a metal layer, wherein the first CMP
slurry solution could have a basic pH and the second CMP slurry
solution an acidic pH. When employing three separate diluting
solutions intermediate the slurry transition, the first diluting
solution comprises a buffer solution having a basic pH level that
corresponds to the pH level of the first CMP slurry solution; the
second diluting solution comprises an intermediate pH level
solution (e.g., a neutral solvent); and the third diluting solution
comprises a buffer solution having an acidic pH level that
corresponds to the acidic pH of the second CMP slurry solution.
[0046] Likewise, although the CMP polishing procedures of the
exemplary embodiments described above were described for
planarizing a metal over a dielectric; it is understood that the
scope of the present invention could similarly encompass
planarization of one particular dielectric material relative a
second type of dielectric material. For example, doped glass could
be planarized relative undoped glass, silicon oxide relative
silicon nitride, or gallium-arsenide relative
aluminum-gallium-arsenide. Similarly, the CMP polishing procedure
of the present invention encompasses polishing of one electrically
conductive material relative a second electrically conductive
material--for example, aluminum relative tungsten, tungsten
relative titanium nitride, or copper relative silicon. During such
polishing operations, CMP slurry transitions need not be limited to
acid-base pH transitions. For these particular alternative
applications, it may be desirable to shift from, for example, a
strong acidic to a less acidic CMP slurry mixture. In addition, a
slurry transition may comprise a switch from a silica based CMP
slurry solution to an alumina based CMP slurry solution.
[0047] In each of the above embodiments, an intermediate diluting
solution is dispensed onto the polishing pad, intermediate a slurry
transition, so as to purge previous solutions off of the polishing
pad. This intermediate step offers advantages such as providing
better control of pH levels on the polishing pad and reducing
undesirable artifacts associated with mixing of different CMP
slurry solutions.
[0048] It should be readily understood that the embodiments
described and illustrated herein are illustrative only, and are not
to be considered as limitations upon the scope of the present
invention. Other variations and modifications may be made in
accordance with the spirit and scope of the present invention.
* * * * *