U.S. patent application number 09/887790 was filed with the patent office on 2002-12-26 for method to increase removal rate of oxide using fixed-abrasive.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Economikos, Laertis, Simpson, Alexander.
Application Number | 20020197937 09/887790 |
Document ID | / |
Family ID | 25391865 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020197937 |
Kind Code |
A1 |
Economikos, Laertis ; et
al. |
December 26, 2002 |
METHOD TO INCREASE REMOVAL RATE OF OXIDE USING FIXED-ABRASIVE
Abstract
The invention provides fixed-abrasive chemical-mechanical
polishing processes which are effective in rapidly reducing
thickness of oxide layers, especially siliceous oxides. The
processes of the invention are preferably characterized by at least
one step involving simultaneous use of a fixed-abrasive polishing
element and an aqueous liquid medium containing an abrasive. Where
the original oxide layer has topographic variation, the thickness
reduction technique of the invention may be preceeded by topography
reduction step using a fixed-abrasive and an aqueous medium
containing a polyelectrolyte for at least a portion of the
polishing process involving reduction in the amount of topographic
variation (height differential) across the oxide layer on the
substrate.
Inventors: |
Economikos, Laertis;
(Wappingers Falls, NY) ; Simpson, Alexander;
(Wappingers Falls, NY) |
Correspondence
Address: |
INTERNATIONAL BUSINESS MACHINES CORPORATION
DEPT. 18G
BLDG. 300-482
2070 ROUTE 52
HOPEWELL JUNCTION
NY
12533
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
25391865 |
Appl. No.: |
09/887790 |
Filed: |
June 22, 2001 |
Current U.S.
Class: |
451/41 ;
257/E21.244 |
Current CPC
Class: |
B24B 37/042 20130101;
H01L 21/31053 20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 001/00; B24B
007/19 |
Claims
What is claimed is:
1. A method of reducing thickness of an oxide layer on a substrate
by fixed-abrasive chemical-mechanical polishing, said method
comprising: a) providing a substrate having an oxide layer on a
first surface, b) providing an aqueous liquid medium containing a
first abrasive component, c) contacting said oxide layer of the
substrate with said aqueous liquid medium and with a polishing
member, the polishing member containing a fixed-abrasive component
therein, and d) maintaining the contact of step c) while providing
movement between said substrate and polishing member, whereby said
oxide layer becomes reduced in thickness.
2. The method of claim 1 wherein said oxide layer provided in step
a) is substantially planar.
3. The method of claim 1 wherein said first abrasive component is
ceria.
4. The method of claim 1 wherein said aqueous medium contains about
0.1-50 g/l of said first abrasive component.
5. The method of claim 4 wherein said aqueous medium contains about
0.5-2 g/l of said first abrasive component.
6. The method of claim 1 wherein said aqueous medium has a pH of
about 5-13.
7. The method of claim 1 wherein said thickness is reduced by at
least 1000 .ANG. in step d).
8. The method of claim 1 wherein step d) is conducted until at
least a portion of an underlayer is exposed.
9. The method of claim 1 wherein said fixed-abrasive is ceria.
10. A method of polishing an over-filled oxide topographic feature
on a substrate by fixed-abrasive chemical-mechanical polishing,
said method comprising: a) providing a substrate having an oxide
layer on a first surface, said oxide layer having (i) an overfill
thickness across substantially all of said layer, and (ii) portions
above said overfill thickness which have a height differential
relative to each other, said thickness and height being measured
from a reference plane parallel with a principal plane of said
substrate, b) providing a first aqueous liquid medium containing a
polyelectrolyte, c) contacting said oxide layer with said first
aqueous liquid medium and with a polishing member, the polishing
member containing a fixed-abrasive component therein, d)
maintaining the contact of step c) while providing movement between
the substrate and polishing member, whereby said height
differential becomes reduced, e) providing an second aqueous liquid
medium containing a first abrasive component, f) contacting said
oxide layer from step d) with said second aqueous liquid medium and
with said polishing member, and g) maintaining the contact of step
f) while providing movement between said substrate and polishing
member, whereby said overfill thickness is reduced.
11. The method of claim 10 wherein said oxide layer resulting from
step d) is substantially planar.
12. The method of claim 10 wherein said first abrasive component is
ceria.
13. The method of claim 10 wherein said second aqueous medium
contains about 0.1-50 g/l of said first abrasive component.
14. The method of claim 13 wherein said second aqueous medium
contains about 0.5-2 g/l of said first abrasive component.
15. The method of claim 10 wherein said first aqueous medium
provided in step b) substantially free of abrasive.
16. The method of claim 1 wherein said second aqueous medium has a
pH of about 5-13.
17. The method of claim 10 wherein said thickness is reduced by at
least 1000 .ANG. in step g).
18. The method of claim 10 wherein step g) is conducted until at
least a portion of an underlayer is exposed.
19. The method of claim 10 wherein said fixed abrasive is
ceria.
20. The method of claim 10 wherein said oxide layer contains at
least one topographically non-uniform feature having a height
differential of at least about 2000 .ANG..
21. The method of claim 10 wherein said oxide is a siliceous
oxide.
22. The method of claim 10 wherein said first aqueous medium
contains at least about 0.01 wt. % of said polyelectrolyte.
23. The method of claim 22 wherein said first aqueous medium
contains at least about 0.1 wt. % of said polyelectrolyte.
24. The method of claim 10 wherein said first aqueous medium has a
pH of about 1-13.
25. The method of claim 24 wherein said first aqueous medium has a
pH of about 4-5.
26. The method of claim 10 wherein said polyelectrolyte is selected
from the group consisting of polyacrylic acid, polyethyleneimine,
polymethylmethacrylate, polymethacrylic acid, polymaleic acid, or
mixtures thereof.
27. The method of claim 18 wherein said underlying layer comprises
a nitride.
28. The method of claim 10 wherein step (b) comprises combining an
aqueous liquid medium with a polyelectrolyte precursor
compound.
29. The method of claim 10 wherein said polyelectrolyte comprises
moieties selected from the group consisting of carboxylic acid
moieties, carboxylate moieties and mixtures thereof.
30. The method of claim 29 wherein said precursor compound is a
polyelectrolyte salt.
31. The method of claim 10 wherein said polyelectrolyte is a
hydrolyzed polyacrylamide.
32. The method of claim 1 wherein said aqueous liquid medium
further comprises a polyelectrolyte.
33. The method of claim 10 wherein said second aqueous liquid
medium further comprises a polyelectrolyte.
Description
BACKGROUND OF THE INVENTION
[0001] While a variety of materials configurations exist in
integrate circuit structures, a common element for many integrated
circuit structures is the dielectric-filled isolation trench.
Isolation trenches are widely used to allow the compact arrangement
of electrically active components making up the integrated
circuit(s) without adverse effects on electrical operability.
[0002] When isolation trench structures are formed in a substrate
(e.g., by etching), variation in trench depth often occurs between
the various trenches formed on the same substrate level on
different parts of the wafer. Typically, the variation may be on
the order of about 10% of the intended trench depth. To ensure that
all the trenches (across the entire wafer) are completely filled
with dielectric isolation material, it is typically necessary to
deposit sufficient dielectric material to account for the
non-uniformity of trench depth.
[0003] The necessity to account for variation in trench depth
results in an overfill of the shallower trenches and a fairly thick
deposit over the wafer surface. Additionally, the dielectric
material (typically an oxide) deposited to fill the trenches is
typically conformal to some extent. Thus, the local step topography
(step height) of the trenches is reflected at least to some extent
in the upper surface of the dielectric deposited to fill the
trenches. Large step height is normally encountered in combination
with a high "within" wafer (overfill) thickness. The deeper (or
higher aspect ratio) the trench to be filled, the greater the step
height in the dielectric filling layer and the more overfill is
required to ensure complete filling of the trench structures across
the wafer.
[0004] Another use of dielectric oxides, such as silicon oxides
formed by reacting tetraethylorthosilicate (TEOS) and oxygen or
ozone, is for so-called interlevel dielectric (ILD), e.g., between
metal interconnects of aluminum/copper or tungsten typically for
back end of the line (BEOL) wiring. A general discussion of
interlevel dielectrics can be found in "Fundamentals of
Semiconductor Processing Technology" by El-Kareh, Kluwer Academic
Publishers, (1995), pages 565-571, which discussion is incorporated
herein by reference. Silicon oxide layers and other insulators
obtained by other processes may also be used as interlevel
dielectrics. For example, other widely used materials for such
purposes are boron and/or phosphorous doped silicate glasses.
[0005] Chemical-mechanical polishing (CMP) to remove dielectric
materials has been widely used to improve the quality and
manufacturability of integrated circuit device structures.
Generally, the objective in polishing is to remove the deposited
dielectric material across the wafer so it remains only within the
trenches (or between conductive features, e.g., metal lines) and
presents a planar surface for subsequent processing.
[0006] Often, a reactive ion etching process (to reduce step height
and/or overall thickness in the deposited dielectric material) is
required in combination with a conventional slurry
chemical-mechanical polishing (CMP) process in order to obtain
proper planarization. Reactive ion etch processes are not desirable
from the point of cost and/or process control.
[0007] Conventional fixed-abrasive CMP (alkaline
medium--pH=10.5-12--using a fixed-abrasive) is generally selective
to step height (i.e., capable of reducing step height
differential), but where the overfill is substantial,
fixed-abrasive CMP is not capable of performing the necessary
material removal which results in a non-planar final surface. This
deficiency limits use of fixed-abrasive CMP processes to structures
with small (e.g., less than 200 .ANG.) variation in trench depth or
oxide overfill.
[0008] Recent improvements to fixed abrasive CMP processes
disclosed in U.S. patent application Ser. No. 09/469,922, filed
Dec. 22, 1999, now ______ and 09/702311, filed Oct. 31, 2000, now
______ have improved the ability to planarize structures with more
substantial topography, however, once topography removal has been
achieved, the reduction of the planarized layer thickness (e.g., to
reach an underlying etch stop layer) can become a very slow
process. This problem is especially apparent for highly overfilled
structures.
[0009] It would be undesirable to perform the topography reduction
and thickness reduction in separate tools. Thus, there is a need
for improved fixed abrasive polishing processes which are capable
of more rapidly reducing the thickness of subtantially planarized
oxide layers to produce a substantially planar surface while
avoiding the need for RIE etch back processing or other undesirable
alternatives.
SUMMARY OF THE INVENTION
[0010] The invention provides fixed-abrasive chemical-mechanical
polishing processes which are effective in reducing the thickness
of oxide layers, especially siliceous oxides, and more especially
substantially planar oxide layers. The invention also provides
fixed-abrasive chemical-mechanical polishing processes which are
capable of planarizing oxide materials with even where the starting
oxide layer has significant topographical variation and significant
overfill. The processes of the invention are preferably
characterized by a step involving simultaneous use of a
fixed-abrasive polishing element and an aqueous liquid medium
containing an abrasive for at least a portion of the polishing
process involving reduction in thickness of an oxide layer on the
substrate.
[0011] In one aspect, the invention encompasses method of reducing
thickness of an oxide layer on a substrate by fixed-abrasive
chemical-mechanical polishing, the method comprising:
[0012] a) providing a substrate having an oxide layer on a first
surface,
[0013] b) providing an aqueous liquid medium containing a first
abrasive component,
[0014] c) contacting the oxide layer of the substrate with the
aqueous liquid medium and with a polishing member, the polishing
member containing a fixed-abrasive component therein, and
[0015] d) maintaining the contact of step c) while providing
movement between the substrate and polishing member, whereby the
oxide layer becomes reduced in thickness.
[0016] The oxide layer to be polished in step a) is preferably
substantially planar. The oxide is preferably a dielectric
material, more preferably silica or boron phosphosilicate glass
(BPSG). Preferably, step d) is conducted until an underlayer is
revealed to a desired extent.
[0017] In another aspect, the invention encompasses a method of
polishing an oxide layer on a substrate by fixed-abrasive
chemical-mechanical polishing, the method comprising:
[0018] a) providing a substrate having an oxide layer on a first
surface, the oxide layer having (i) an overfill thickness across
substantially all of the layer, and (ii) portions above the
overfill thickness which have a height differential relative to
each other, the thickness and height being measured from a
reference plane parallel with a principal plane of the
substrate,
[0019] b) providing a first aqueous liquid medium containing a
polyelectrolyte,
[0020] c) contacting the oxide layer with the first aqueous liquid
medium and with a polishing member, the polishing member containing
a fixed-abrasive component therein,
[0021] d) maintaining the contact of step c) while providing
movement between the substrate and polishing member, whereby the
height differential becomes reduced,
[0022] e) providing a second aqueous liquid medium containing a
first abrasive component,
[0023] f) contacting the oxide layer from step d) with the second
aqueous liquid medium and with the polishing member, and
[0024] g) maintaining the contact of step f) while providing
movement between the substrate and polishing member, whereby the
overfill thickness is reduced.
[0025] Preferably, the first aqueous medium is substantially
abrasive-free. If desired, the height differential reduction steps
could be replaced with an alternative method for reducing height
differential.
[0026] These and other aspects of the invention are described in
further detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a schematic cross section of a dielectric
isolation layer to be planarized on a substrate, the layer having
overfill and a height differential between portions.
[0028] FIG. 2 shows a schematic cross section of a dielectric
isolation layer of FIG. 1 after leveling off of the height
differential.
[0029] FIG. 3 shows a schematic cross section of a dielectric
isolation layer of FIG. 2 after further reduction in height to
reveal a stop layer.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The invention provides fixed-abrasive chemical-mechanical
polishing processes which are effective in reducing the thickness
of oxide layers, especially siliceous oxides, and more especially
substantially planar oxide layers. The invention also provides
fixed-abrasive chemical-mechanical polishing processes which are
capable of planarizing oxide materials with even where the starting
oxide layer has significant topographical variation and significant
overfill. The processes of the invention are preferably
characterized by a step involving simultaneous use of a
fixed-abrasive polishing element and an aqueous liquid medium
containing an abrasive for at least a portion of the polishing
process involving reduction in thickness of an oxide layer on the
substrate.
[0031] More specifically, the invention encompasses method of
reducing thickness of an oxide layer on a substrate by
fixed-abrasive chemical-mechanical polishing, the method
comprising:
[0032] a) providing a substrate having an oxide layer on a first
surface,
[0033] b) providing an aqueous liquid medium containing a first
abrasive component,
[0034] c) contacting the oxide layer of the substrate with the
aqueous liquid medium and with a polishing member, the polishing
member containing a fixed-abrasive component therein, and
[0035] d) maintaining the contact of step c) while providing
movement between the substrate and polishing member, whereby the
oxide layer becomes reduced in thickness.
[0036] The processes of the invention may be used to polish various
oxide materials on various substrates, however the processes of the
invention are especially useful in the context of oxide dielectric
materials and substrates used in the production of integrated
circuit devices and/or other microlithographically created
articles. The materials to be polished are preferably oxide
dielectric materials to be configured or removed in the production
of such devices or articles. The processes of the invention are
especially useful for the planarization or removal of siliceous
oxide materials, more especially silicon dioxide materials. The
processes of the invention may also be used with other siliceous
materials such as doped silicon dioxide films (e.g., BPSG, BSG,
etc.). For interlevel dielectric oxides, the oxide is preferably a
silicon oxide (e.g., SiO.sub.2) and/or a silicate containing one or
more elements selected from groups 3A (e.g. boron) and 5A (e.g.
phosphorus or arsenic). The interlevel dielectric may be adjacent
to metal or metal-containing features formed from various materials
such as copper, copper alloy, titanium, titanium nitride, tantalum,
tantalum nitride, aluminum and/or aluminum alloy.
[0037] The oxide layer to be polished in step d) is preferably
substantially free of significant topography (i.e., it is
preferably substantially planar). Where significant topography
exists above any overfill component, alternative techniques are
preferably used prior to step a) above in order to remove such
topography. See especially the discussion of further aspects of the
invention below where the thickness reduction steps are preceded by
topography removal step(s).
[0038] An example of a typical overfilled oxide structure is shown
in FIG. 1. The substrate 20 has a first layer 30 (e.g., a silicon
nitride stop layer) and a trench 45 (e.g., a trench to be filled
with an oxide dielectric isolation material). The oxide layer 40
overfills trench 45 and oxide layer 40 has a depression 46 therein.
The height differential H is the distance between top surface 44
and depression surface 42 measured relative to a reference plane
10. Layer 40 in FIG. 1 may have any height differential typically
found in the manufacture of isolation features, e.g., about 2000
.ANG. or more, especially about 4000 .ANG. or more. A typical
height differential of interest would be on the order of about 4000
to 7000 .ANG.. As noted above, such topography is preferably
removed before use of the thickness reduction technique of the
invention.
[0039] The degree of overfill corresponds to height O which extends
across the entire oxide layer 40. The thickness reduction processes
of the invention are especially useful for reducing the overfill
thickness of substantially planarized layers such as the appearance
of layer 40 in FIG. 2. The methods of the invention may be used
with any overfill thickness. A typical overfill thickness may be on
the order of at least 500 .ANG., more typically at least 1000
.ANG., and especially on the order of 1000-2000 .ANG. where deep
trenches are being filled.
[0040] Oxide material 40 may be provided by various known
techniques such as spin-on-glass (SOG) coating, chemical vapor
deposition (CVD), physical vapor deposition, high density plasma or
other technique. See for example, the various techniques discussed
in "Fundamentals of Semiconductor Processing Technologies", by
Badih El-Kareh, Kluwer Academic Publishing, 1995 or other texts.
Typically, deposition or formation of the dielectric oxide layer 40
over a surface having topography results in topographic variation
in the oxide layer 40. In some instances, topographic variation may
occur in oxide layer 40 even where the structure underlayer 30
contains no topographic variation (not shown), for example, if the
formation of oxide layer 40 is preferential over certain areas of
layer 30 (e.g., due to variation of material composition in regions
of layer 30 and/or due to the nature of the specific dielectric
layer formation step itself. Topographic variation may also occur
in oxide layer 40 where the structure underlayer 30 contains a
topographic variation within a die and across the wafer. This
variation may be attributed to variations in trench 45 depth and
width. Layer 40 may contain one or more such regions having a
height differential, e.g., where a plurality of trenches 45 are to
be filled.
[0041] The abrasive-containing aqueous liquid medium preferably
contains an abrasive suitable for removal of oxide materials as may
be known in the art. The abrasive comprises ceria, more preferably
the abrasive consists essentially of ceria. The concentration of
ceria in the aqueous medium is preferably less than the amount
typically used in conventional slurry-based CMP processes.
Preferably, the abrasive-containing aqueous medium contains about
0.1-50 g of abrasive particles per liter, more preferably about
0.5-2 g/l. The abrasive-containing liquid medium preferably has a
pH of about 5-13, more preferably a pH of about 7-12, most
preferably about 9-11.5. The abrasive-containing liquid medium may
also contain additives such as polyelectrolytes described below
(e.g., polyacrylic acid) to facilitate stopping upon underlayer
exposure.
[0042] The processes of the invention are otherwise not limited to
use of any specific fixed-abrasive CMP set up or apparatus.
Examples of fixed-abrasives and other apparatus are disclosed in
U.S. Pat. Nos. 5,958,794; 5,855,804; 5,972,124; 5,897,426;
5,733,176; 5,919,082; 5,972,792; or 5,782,675, the disclosures of
which are incorporated herein by reference. The fixed abrasive
member preferably uses a ceria abrasive fixed therein.
[0043] The method step d) is preferably conducted until the oxide
layer becomes reduced to a desired thickness and/or until a stop
material (underlayer or metal feature) is exposed to a desired
extent. For example, the structure of FIG. 3 may represent a
desired endpoint for the process.
[0044] As note above, where the oxide layer 40 has substantial
initial topography, the thickness reduction step is preferably
preceeded by a topography reduction step. Thus, the invention
further encompasses an overall method where such topography is
substantially removed followed by the thickness reduction technique
of the invention. A preferred version of such an overall method
comprises:
[0045] a) providing a substrate having an oxide layer on a first
surface, the oxide layer having (i) an overfill thickness across
substantially all of the layer, and (ii) portions above the
overfill thickness which have a height differential relative to
each other, the thickness and height being measured from a
reference plane parallel with a principal plane of the
substrate,
[0046] b) providing a first aqueous liquid medium containing a
polyelectrolyte,
[0047] c) contacting the oxide layer with the first aqueous liquid
medium and with a polishing member, the polishing member containing
a fixed-abrasive component therein,
[0048] d) maintaining the contact of step c) while providing
movement between the substrate and polishing member, whereby the
height differential becomes reduced,
[0049] e) providing a second aqueous liquid medium containing a
first abrasive component,
[0050] f) contacting the oxide layer from step d) with the second
aqueous liquid medium and with the polishing member, and
[0051] g) maintaining the contact of step f) while providing
movement between the substrate and polishing member, whereby the
overfill thickness is reduced.
[0052] The first aqueous liquid medium is characterized by the
presence of a polyelectrolyte and is preferably substantially free
of abrasive. The first aqueous liquid medium preferably contains at
least about 0.01 wt. % of polyelectrolyte, more preferably about
0.05-1.0 wt. %, most preferably about 0.1-0.5 wt. %. The
polyelectrolyte preferably comprises molecules having plural
carboxylic acid, carboxylate ion moieties or other suitable ionic
moieties. If desired, the polyelectrolyte may be formed from a
precursor (e.g., a polyelectrolyte salt such as ammonium
polyacrylate) capable of forming the desired ionic moieties in the
aqueous liquid medium. The polyelectrolyte is more preferably
selected from the group consisting of polyacrylic acid,
polyethyleneimine, polymethylmethacrylate, polymethacrylic acid,
polymaleic acid, hydrolyzed polyacrylamide or mixtures thereof.
More preferably, the polyelectrolyte is polyacrylic acid. The
polyelectrolyte preferably has a weight average molecular weight of
about 500-20000, more preferably about 500-11000. Other
polyelectrolytes, such as those described in U.S. Pat. No.
5,968,280, the disclosure of which is incorporated herein by
reference, may also be used.
[0053] The first aqueous liquid medium preferably has a pH of about
1-13, more preferably about 2-12, most preferably about 4-5 (pH of
4.5 being especially preferred for high selectivity). A pH of about
1-3 is preferred where hydrolyzed polyacrylamide is used as the
polyelectrolyte. Any suitable acid or base may be used for
establishing the pH level of the solution. Where an alkaline pH is
desired, hydroxides such as ammonium hydroxide are preferred for pH
adjustment. For acidic pH, mineral acids are generally preferred
for pH adjustment. The liquid medium may contain other components
known in the art, however the liquid medium preferably consists
essentially of water, base and polyelectrolyte.
[0054] The second aqueous liquid medium (containing abrasive) is
preferably as described above relative to the thickness reduction
method of the invention.
[0055] Preferably, polishing step d) is carried out until a desired
reduction in topography is achieved in oxide layer 40 (e.g., as
shown in FIG. 2). Preferably, polishing step g) is conducted until
an underlayer is revealed (e.g., as shown in FIG. 3).
[0056] The processes of the invention advantageously permit the
rapid removal of blanket oxide layers (e.g., as may occur with
overfill) at rates comparable to conventional slurry-based CMP
processes with minimal or no occurrence of dishing compared to
conventional slurry-based CMP processes.
* * * * *