U.S. patent application number 11/153636 was filed with the patent office on 2006-12-21 for planarization composition.
Invention is credited to Sharad Mathur, Ivan Petrovic.
Application Number | 20060283093 11/153636 |
Document ID | / |
Family ID | 37571957 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060283093 |
Kind Code |
A1 |
Petrovic; Ivan ; et
al. |
December 21, 2006 |
Planarization composition
Abstract
The present invention provides CMP abrasive slurry that is
substantially free of aluminum oxide and comprises liquid and
solids wherein the solids comprises: (a) in an amount of at least
about 90 weight percent based on the solids, at least one
non-spherical component having formula Al.sub.2O.sub.3.xH.sub.2O
where x ranges from 1 to 3; and (b) up to about one weight percent
based on the solids portion of submicron alpha-alumina. The CMP
abrasive slurry may be used to polish metallic or dielectric
surfaces in computer wafers.
Inventors: |
Petrovic; Ivan; (Princeton,
NJ) ; Mathur; Sharad; (Macon, GA) |
Correspondence
Address: |
ENGELHARD CORPORATION;Attention: Chief Patent Counsel
101 Wood Avenue
P.O. Box 770
Iselin
NJ
08830-0770
US
|
Family ID: |
37571957 |
Appl. No.: |
11/153636 |
Filed: |
June 15, 2005 |
Current U.S.
Class: |
51/307 ;
257/E21.304; 51/309 |
Current CPC
Class: |
H01L 21/3212 20130101;
C09G 1/02 20130101 |
Class at
Publication: |
051/307 ;
051/309 |
International
Class: |
B24D 3/02 20060101
B24D003/02 |
Claims
1. CMP abrasive slurry that is substantially free of anhydrous
aluminum oxide and comprises liquid and solids wherein said solids
comprises: (a) in an amount of at least about 90 weight percent
based on said solids, at least one non-spherical component having
formula Al.sub.2O.sub.3.xH.sub.2O where x ranges from 1 to 3; and
(b) up to about one weight percent based on said solids portion of
submicron alpha-alumina.
2. The CMP abrasive slurry of claim 1 consisting essentially of
said at least one non-spherical component having formula
Al.sub.2O.sub.3.xH.sub.2O where x ranges from 1 to 3.
3. The CMP abrasive slurry of claim 1 wherein said non-spherical
component is boehmite.
4. The CMP abrasive slurry of claim 1 wherein said non-spherical
component comprises kaolin coated with boehmite.
5. A method of planarization metal comprising the step of: using
the CMP abrasive slurry of claim 1 to polish metal.
6. The method of claim 5 wherein planarization occurs in pH acidic
conditions.
7. The method of claim 5 wherein said slurry is used to polish
copper.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a novel slurry for
chemical-mechanical planarization (CMP). The present invention is
applicable to manufacturing high speed integrated circuits having
submicron design features and high conductivity interconnect
structures with high production throughput.
[0002] In the fabrication of integrated circuits and other
electronic devices, multiple layers of conducting, semiconducting,
and dielectric materials are deposited on or removed from a surface
of a substrate. Thin layers of conducting, semiconducting, and
dielectric materials may be deposited by a number of deposition
techniques. Common deposition techniques in modern processing
include physical vapor deposition (PVD), also known as sputtering,
chemical vapor deposition (CVD), plasma-enhanced chemical vapor
deposition (PECVD), and now electrochemical plating (ECP).
[0003] As layers of materials are sequentially deposited and
removed, the uppermost surface of the substrate may become
non-planar across its surface and require planarization.
Planarizing a surface, or "planarization" a surface, is a process
where material is removed from the surface of the substrate to form
a generally even planar surface. Planarization is useful in
removing undesired surface topography and surface defects, such as
rough surfaces, agglomerated materials, crystal lattice damage,
scratches, and contaminated layers or materials. Planarization is
also useful in forming features on a substrate by removing excess
deposited material used to fill the features and to provide an even
surface for subsequent levels of metallization and processing.
[0004] Chemical mechanical planarization, or chemical mechanical
planarization (CMP), is a common technique used to planarize
substrates. CMP utilizes a chemical composition, typically a slurry
or other fluid medium, four selective removal of material from
substrates. Considerations in CMP slurry design are discussed in
Rajiv K. Singh et al., "Fundamentals of Slurry Design for CMP of
Metal and Dielectrics Materials", MRS Bulletin, pages 752-760
(October 2002). In conventional CMP techniques, a substrate carrier
or planarization head is mounted on a carrier assembly and
positioned in contact with a planarization pad in a CMP apparatus.
The carrier assembly provides a controllable pressure to the
substrate urging the substrate against the planarization pad. The
pad is moved relative to the substrate by an external driving
force. Thus, the CMP apparatus effects planarization or rubbing
movement between the surface of the substrate and the planarization
pad while dispersing a planarization composition, or slurry, to
effect both chemical activity and mechanical activity.
[0005] Conventional slurries used for CMP processes contain
abrasive particles in a reactive solution. Alternatively, the
abrasive article can be a fixed abrasive article, such as a fixed
abrasive planarization pad, which may be used with a CMP
composition or slurry that does not contain abrasive particles. A
fixed abrasive article typically comprises a backing sheet with a
plurality of geometric abrasive composite elements adhered
thereto.
[0006] Abrasives which are most extensively used in the
semiconductor CMP process are silica (SiO.sub.2), alumina
(Al.sub.2O.sub.3), ceria (CeO.sub.2), zirconia (ZrO.sub.2), and
titania (TiO.sub.2), which can be produced by a fuming or a sol-gel
method, as described in U.S. Pat. Nos. 4,959,113; 5,354,490; and
5,516,346 and WO 97/40,030. There has recently been reported a
composition or a slurry comprising mangania (Mn.sub.2O.sub.3)
(European Pat. No. 816,457) or a silicon nitride (SiN) (European
Pat. No. 786,504).
[0007] U.S. Pat. No. 6,508,952 discloses a CMP slurry containing
any commercially available abrasive agent in particle form, such as
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, CeO.sub.2, SiC,
Fe.sub.2O.sub.3, TiO.sub.2, Si.sub.3N.sub.4, or a mixture thereof.
These abrasive particles normally have a high purity, a high
surface area, and a narrow particle size distribution, and thus are
suitable for use in abrasive compositions as abrasive agents.
[0008] U.S. Pat. No. 4,549,374 discloses planarization
semiconductor wafers with an abrasive slurry prepared by dispersing
montmorillonite clay in deionized water. The pH of the slurry is
adjusted by adding alkali such as NaOH and KOH.
[0009] Demands for electrical processing speed have continued to
increase requiring higher and higher circuit densities and
performance. It is now desirable to fabricate chips with 8 or more
layers of circuit patterns. In principal the requirement for more
layers does not change the nature of planarization, but it does
require more rigorous specifications from the planarization method.
Defects such as scratches and dishing must be lessened or
eliminated. An issue that further increases the technical demand is
the move toward 300 mm wafers. The larger wafer makes it more
difficult to maintain uniformity over larger length scales as
compared to an 8'', or 200 mm, wafer.
[0010] Besides adding layers, increased circuit density can be
achieved by decreasing the space between the individual pathways.
Pathways cannot be too close as electrical spillover can occur
across the SiO.sub.2 dielectric (the wafer oxide) effectively
shorting out the connection. Recent technological advancements
permitting the fabrication of very small, high density circuit
patterns on integrated circuits have placed higher demands on
isolation structures.
[0011] US Patent Application Publication 2003/0129838 (filed Dec.
28, 1999) discloses the following non-plate-like abrasive
materials: iron oxide, strontium titanate, apatite, dioptase, iron,
brass, fluorite, hydrated iron oxide, and azurite.
[0012] U.S. Pat. No. 5,693,239 teaches a CMP planarization
composition comprising water; 1-50 weight percent alpha-alumina or
alpha-aluminum oxide; the remainder of the solids being of a
substantially less abrasive composition chosen from the group
consisting of aluminum hydroxides, gamma-alumina, delta-alumina,
amorphous alumina, and amorphous silica. See also U.S. Pat. Nos.
4,956,015; 6,037,260; and 6,475,607. However, we believe that the
presence of aluminum oxide at even <5 weight percent in the
solids portion of a CMP slurry may scratch the metal surface of the
wafer.
[0013] Japanese Kokai Patent Publication 2000-246649 teaches a
planarization pad containing 5-50% by weight of boehmite abrasive
particles. The reference teaches that if the beohmite weight
percent exceeds 50, the pad's cushioning property drops. The slurry
used with the planarization pad contained 1-15 weight percent of
fine particles such as boehmite. See also Japanese Kokai Patent
Publication 2000-246620.
[0014] U.S. Pat. No. 5,906,949 teaches a CMP slurry containing
abrasive particles mainly made of boehmite for planarizing
dielectric films such as SiO.sub.2 under pH basic conditions. We
believe that this patent's Example 3 results in a boehmite surface
coated alumina.
[0015] U.S. Pat. No. 6,562,091 teaches that a spherical shaped
boehmite did not scratch a wafer during CMP processing; the
spherical particles preferably had a diameter of less than
approximately 50 nm. This was in contrast to the prior art teaching
that an angulated silica particle may scratch a wafer surface
during CMP processing.
SUMMARY OF THE INVENTION
[0016] The present invention provides CMP abrasive slurry that is
substantially free of anhydrous aluminum oxide (generic formula
Al.sub.2O.sub.3) and comprises liquid portion and solids portion
wherein said solids portion comprising:
[0017] (a) in an amount of at least about 90 weight percent based
on said solids portion, at least one non-spherical component having
formula Al.sub.2O.sub.3.xH.sub.2O where x ranges from 1 to 3;
and
[0018] (b) up to about one weight percent based on the said solids
portion of submicron alpha-alumina.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a TEM of one embodiment of the present
invention.
[0020] FIG. 2 illustrates one embodiment of the present
invention.
[0021] FIGS. 3-7 are thermograms (TGA/DTA or TGA/DSC) for boehmites
useful in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention uses a component having the formula
Al.sub.2O.sub.3.xH.sub.2O where x ranges from 1 to 3. When x is 1
in the preceding formula, the resulting product is known as
diaspore and has a Mohs' hardness of about 6.5-7. When x ranges
from greater than 1 to 2, i.e., 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,
1.8, 1.9, or 2, the resulting products are known as boehmite or
pseudoboehmite and have a Mohs' hardness of about 2.5-3. When x is
3 in the preceding formula, the resulting products are known as
gibbsite, doyleite, nordstrandite (all with Mohs' hardness of about
2.5-3), or bayerite, Preferably, the component is boehmite or
pseudoboemite.
[0023] Examples of the phrase "at least one non-spherical component
having the formula Al.sub.2O.sub.3.xH.sub.2O" as used herein
includes but is not limited to the following mixtures of phases:
Al.sub.2O.sub.3.1.2H.sub.2O and Al.sub.2O.sub.3.1.6H.sub.2O,
Al.sub.2O.sub.3.1.2H.sub.2O and Al.sub.2O.sub.3.2H.sub.2O, and
Al.sub.2O.sub.3.1.6H.sub.2O and Al.sub.2O.sub.3.2H.sub.2O, and
Al.sub.2O.sub.3.1.5H.sub.2O and Al.sub.2O.sub.3.3H.sub.2O. One
useful commercially available mixture is about 80 weight percent
boehmite and 20 weight percent gibbsite.
[0024] The value of x in the above formula
Al.sub.2O.sub.3.xH.sub.2O may be conveniently determined by
commercially available thermal analysis instruments (e.g., TGA,
TGA/DTA, TGA/DSC). In FIGS. 3-6, the sample in powdered form,
without any special pre-treatment (drying or humidification), was
heated from room temperature to about 1200.degree. C. at a rate of
20.degree. C./min in 100 mL/min flow of dry air. In FIG. 7, a sol
sample was left to dry in the fume hood for approximately two days,
and then heated as described above. It is apparent that in certain
instances the x, as determined by these common thermal analysis
techniques, may be more than 2 or less than 1 for boehmite or
pseudobeohmite, and may be greater or smaller than 3 for gibbsite,
doyleite, nordstrandite or bayerite. Other useful technique to
identify these alumina hydrate phases is powder X-ray diffraction
(XRD).
[0025] The boehmite is usually produced by a method wherein
gibbsite or the like is subjected to hydrothermal treatment under
pressure at a temperature of about 250.degree. C. or by a method
wherein an organoaluminum compound of the formula Al(OR).sub.3
wherein R is an alkyl group is hydrolyzed.
[0026] The term "non-spherical" as used herein means particles
having a morphology wherein at least one dimension (height, length
and/or width) is substantially larger than another. Thus, a
non-spherical particle morphology may be plate-like, sheet-like,
needle-like, capsule-like, laminar-like, or any other of a myriad
of shapes having at least one dimension substantially larger than
another. Such morphology distinguishes over spherical particles
which are substantially round in appearance and do not have
noticeable elongated surfaces as disclosed in U.S. Pat. No.
6,562,091.
[0027] The advantages of the present non-spherical particle over
the spherical particle of U.S. Pat. No. 6,562,091 are as follows.
First, for a given loading of abrasive solids in a slurry,
non-spherical particles provide much larger effective contact,
i.e., planarization surface. This results in higher material
removal rates. The rationale for this is that a substantially
spherical particle has in the extreme a point contact with the
surface to be polished. In sharp contrast, the present
non-spherical particle expected to be positioned flat during the
planarization process advantageously is in contact with the
polished surface through the largest face. Also, since the applied
pressure from the polisher will be transferred onto the wafer
through the surface rather than through the point, the polish
uniformity and overall planarity are expected to be improved. Such
improvements include reduced erosion, dishing, and field oxide
loss. Secondly, the greater planarization area of the non-spherical
particle allows the use of lower abrasive content in the slurry.
This provides a positive effect on particle related defects such as
scratch and particle residue. Thirdly, the non-spherical particle
will positively contribute to non-Prestonian behavior of the fully
formulated slurry, i.e., that the slurry will not show a linear
increase of the planarization rate with applied pressure. This may
be significant for low pressure planarization such as less than 2-3
psi and also for planarization of next generation copper and low or
ultra low k dielectric devices with planarization pressures as low
as less than one psi.
[0028] FIGS. 3-7 show examples of thermal
analysis-thermogravimetric analysis (TGA) and differential thermal
analysis (DTA) or differential scanning calorimetry (DSC) charts of
possible alumina hydrate abrasives useful in the present invention.
They were obtained using a TA instruments SDT Q600 analyzer by
heating the sample from room temperature to 1 200.degree. C. at a
heating rate of 20.degree. C./min in 100 ml/min flow of dry air.
The results show in FIGS. 3-7 that a distinct three step weight
loss (TGA curve--left Y axis) with correspondence endothermic peaks
as shown by DTA or DSC curve (right Y axis) associated with the
water loss. The first weight loss varies from about 1 to 25 weight
percent and is typically associated with a DTA/DSC peak between
about 60.degree. C. and 1 20.degree. C. The second weight loss is
more consistent ranging from about 12 to 16 weight percent with
associated very sharp DTA/DSC peaks in the range 460.degree. C. to
515.degree. C. The third weight loss, in all cases less than 2
percent, is a very gradual one, taking place at temperatures above
600.degree. C., with a very broad endotherm in the range of
740.degree. C. to about 905.degree. C. While the overall weight
loss at 1 200.degree. C. observed in FIGS. 3-6 is consistent with x
in the above formula Al.sub.2O.sub.3.xH.sub.2O in the range of 1-2,
FIG. 7 shows an overall weight loss of 38.5 percent corresponding
to x>3. This shows that the value of x as determined by routine
thermal analysis may vary significantly for similar samples and is
sensitive to sample treatment prior to the measurement.
[0029] Unlike the boehmite surface coating of U.S. Pat. No.
5,906,949's Example 3, the present non-spherical particles
comprises boehmite substantially throughout the core and surface of
the particle.
[0030] Useful boehmite is commercially available from Sasol.
Examples of useful DISPERAL.RTM. acid dispersible boehmite alumina
systems are in the following Table 1: TABLE-US-00001 TABLE 1
TYPICAL CHEMICAL AND PHYSICAL PROPERTY DISPERAL DISPERAL S DISPERAL
HP 14 DISPERAL 40 Al.sub.2O.sub.3 (%) 77 75 77 80 Na.sub.2O (%)
0.002 0.002 0.002 0.002 Particle Size 25 15 35 50
(d.sub.50)(microns) Crystallite Size 10 10 14 40 [120](nanometers)
Dispersed Particle 80 100 100 140 Size (nanometers)
[0031] Examples of useful DISPERAL.RTM. and DISPAL.RTM. liquid
boehmite alumina systems are in the following Table 2
TABLE-US-00002 TABLE 2 TYPICAL CHEMICAL DISPERAL AND PHYSICAL
Dispersion DISPERAL DISPAL DISPAL DISPAL DISPAL PROPERTY 20/30 AL
25 11N7-12 14N4-25 18N4-20 23N4-20 Al.sub.2O.sub.3 (%) 30 25 12 25
20 20 NO.sub.3 (%) 0.006 -- 0.015 0.240 0.300 0.380 NH.sub.3 (%) --
2 -- -- -- -- pH of dispersion 4 10 7 4 4 4 Dispersed 200 200 180
140 120 100 Particle Size (nanometers)
[0032] Examples of useful DISPERAL.RTM. and DISPAL.RTM. water
dispersible boehmite alumina systems are in the following Table 3:
TABLE-US-00003 TABLE 3 TYPICAL CHEMICAL AND PHYSICAL DISPERAL
DISPERAL DISPAL DISPAL DISPAL DISPAL PROPERTY P2 HP 14/2 11N7-80
14N4-80 18N4-80 23N4-80 Al.sub.2O.sub.3 (%) 72 75 80 80 80 80
Na.sub.2O (%) 0.002 0.002 0.002 0.002 0.002 0.002 NO.sub.3 (%) 4.0
1.3 0.1 0.7 1.1 1.6 Particle Size 45 35 40 50 50 50 (d.sub.50)
(microns) Crystallite Size -- 13 35 25 15 10 [120] (nanometers)
Dispersed 25 100 160 120 110 90 Particle Size (nanometers)
Useful boehmite is also commercially available from Sasol as
CATAPAL.TM.. CATAPAL A, B, C1 or D is spray dried alumina with
increasing crystallite sizes from 40 Angstroms to 70 Angstroms.
CATAPAL 200 has a 400 Angstroms crystallite size. FIG. 1 shows a
TEM of a Sasol boehmite.
[0033] Another embodiment of the present invention is shown in FIG.
2. In FIG. 2, non-spherical abrasive particle 10 comprises core 12
that is at least partially coated with aluminum hydroxide layer 14.
Useful core material 12 includes those disclosed in our pending
patent application U.S. Ser. No. 10/792,738 filed Mar. 5, 2004
incorporated herein by reference in its entirety. Laminar clays
such as kaolin, vermiculite and montmorillonite (that can be
exfoliated) and modifications of such clays that preserve the clay
shape such as acid leached kaolin, mica, talc, graphite flake,
glass flake, and synthetic polymer flake are useful.
[0034] These non-spherical particles are primary in the slurry.
Thus, the phrase "non-spherical particle" as used herein does not
cover a non-spherical agglomeration of spherical particles.
[0035] In addition to having a non-spherical morphology, the
present abrasive particles are preferably softer than the silica,
alumina or ceria abrasives typically used for CMP. Accordingly, the
non-spherical abrasive particles have a Mohs hardness of about 1-5
to 6. For reference, Table 4 below sets forth the various metals
and abrasive particles: TABLE-US-00004 TABLE 4 MICROHARDNESS
MATERIALS MOHS [kg mm.sup.-2] Copper 2.5-3.0 80 Tantalum 6.5 230
Tungsten 7.5-8.0 350 Hydrated SiO.sub.2 4-5 400-500 SiO.sub.2 6-7
1200 Copper Oxide 3.5-4.0 -- Kaolin (hydrous) 2-3 -- Kaolin
(calcined) 4.0-6.0 alpha-Alumina 9.0 2000 ZrO.sub.2 6.5 -- Diamond
10.0 10000
[0036] It is believed that a non-spherical abrasive having a Mohs
hardness between about 1-6 is hard enough to provide the necessary
mechanical action of a CMP slurry, yet defects such as scratching,
dishing, and over planarization action can simultaneously be
avoided.
[0037] In general, the non-spherical particle abrasive will
comprise up to 20 by weight percent of the slurry although abrasive
solids contents up to 60 wt. % may be prepared. More typically,
amounts of less than 15% by weight and more preferably, an abrasive
content in amounts of from 0.5-8 wt. % are utilized.
[0038] Kaolin clay particles are preferred for core material 12.
While hydrous kaolin can be utilized, it has been found that if the
kaolin has been calcined, a better planarization rate results.
However, the overall performance of hydrous kaolin is better than
calcined kaolin and thus, hydrous kaolin is preferred. Calcination
of the kaolin to undergo a strong endothermic reaction associated
with dehydroxylation results in metakaolin. Kaolin clay calcined
under conditions more severe than those used to convert kaolin to
metakaolin, i.e., kaolin clay calcined to undergo the
characteristic kaolin exothermic reaction, results in the spinel
form of calcined kaolin and also mullite if more extreme conditions
are utilized. Generally, calcination of the hydrous kaolin at
temperatures of 1200.degree. F. and higher results in the
dehydroxylation of hydrous kaolin to metakaolin. Calcination
temperatures of 1400-2200.degree. F. can be used to produce a
kaolin clay that has been calcined through its characteristic
exotherm to spinel form kaolin. At the higher temperatures, e.g.
above 1900.degree. F., formation of mullite occurs. Any and all of
these forms of kaolin clay can be utilized as the abrasive of this
invention. All of these materials are available commercially from
the present assignee, Engelhard Corporation, Iselin, N.J.
[0039] Hydrous kaolin is typically prepared through combination of
unit operations that modify the particle size distribution and
remove coloring impurities from kaolin. These unit operations are
facilitated by using aqueous suspensions of kaolin in water.
Examples of unit operations that change the particle size
distribution are centrifuges, delamination or milling devices and
selective flocculation. Examples of unit operations that result in
removal of coloring impurities are flotation and magnetic
separation. Further, reductive and/or oxidative bleaching can be
used to render coloring impurities colorless. In addition,
filtration may be utilized to substantially remove water from
kaolin following which the high solids filtration product slurry
can be spray dried. The spray dried portion can be added back to
the high solids filter product slurry to further raise the solids
content of the slurry. The filtration product may not be dispersed
and thus the filtercake can be dried and pulverized to obtain what
is referred to as acid dried kaolin product in the industry.
Additionally, the kaolin may be modified by thermal or chemical
treatments. Typically, the kaolin is pulverized prior to and after
the calcinations operation. Treated kaolin can be slurried to
further effect modifications to the particle size distribution
through the unit operations mentioned above.
[0040] Other useful non-spherical abrasive particles for core
material 12 are brucite (magnesium hydroxide), hydrotalcite, and
nanotalc. The preceding materials are commercially available. Other
useful non-spherical abrasive particles are disclosed in commonly
assigned U.S. Pat. No. 6,187,710 incorporated herein by reference
in its entirety. This patent teaches in one embodiment clay
minerals made up of elementary three-layer platelets consisting of
a central layer of octahedrally oxygen-surrounded metal ions
(octahedron layer), which layer is surrounded by two tetrahedrally
surrounded, silicon atom-containing layers (tetrahedron layer),
characterized in that the dimensions of the clay particles vary
from 0.1 micron to one micron. In the octahedron layer, at most 30
at. % of the metal ions has been replaced by ions of a lower
valency and in the tetrahedron layers, at most 15 at. % of the
silicon ions has been replaced by ions of a lower valency. The
patent teaches in another embodiment that the silicon (germanium)
in the tetrahedron layer can be replaced by trivalent ions. In the
octahedron layer, aluminum, chromium, iron (III), cobalt (III),
manganese (III), gallium, vanadium, molybdenum, tungsten, indium,
rhodium, and/or scandium are preferably present as trivalent ions.
As divalent ions, magnesium, zinc, nickel, cobalt (II), iron (II),
manganese (II), and/or beryllium are preferably present in the
octahedron layer. In the tetrahedron layer, silicon and/or
germanium is present as tetravalent component and preferably,
aluminum, boron, gallium, chromium, iron (III), cobalt (III),
and/or manganese (III) are present as trivalent component.
[0041] The aluminum hydroxide layer material 14 may be as described
above. The partial aluminum hydroxide coating generally has a
thickness of about up to 0.5 micron. Any known coating process may
be used for coating the aluminum hydroxide 14 onto core material
12.
[0042] In general, CMP slurry compositions include abrasives for
mechanical action and at least one of: oxidizers, acids, bases,
complexing agents, surfactants, dispersants, and other chemicals
for providing a chemical reaction such as oxidation on the surface
to be polished.
[0043] Non-limiting examples of available bases include KOH,
NH.sub.4OH, and R.sub.4NOH. Acids also can be added, which can be
exemplified by H.sub.3PO.sub.4, CH.sub.3COOH, HCl, HF and so on.
Available as such supplementary oxidizing agents are
H.sub.2O.sub.2, KIO3, HNO.sub.3, H.sub.3PO.sub.4,
K.sub.2Fe(CN).sub.6, Na.sub.2Cr.sub.2O.sub.7, KOCl,
Fe(NO.sub.3).sub.2, NH.sub.2OH, and DMSO. Divalent acids, such as
oxalic acid, malonic acid, and succinic acid can be used as
additives for the planarization composition of the present
invention.
[0044] Additional suitable acid compounds that may be added to the
slurry composition include, for example, formic acid, acetic acid,
propanoic acid, butanoic acid, pentanoic acid, hexanoic acid,
heptanoic acid, oxtanoic acid, nonanoic acid, lactic acid, nitric
acid, sulfuric acid, malic acid, tartaric acid, gluconic acid,
citric acid, phthalic acid, pyrocatechoic acid, pyrogallol
carboxylic acid, gallic acid, tannic acid, and mixtures
thereof.
[0045] Suitable corrosion inhibitors that may be added to the
slurry composition include, for example, benzotriazole,
6-tolylytriazole, 1-(2,3-dicarboxypropyl) benzotriazole, and
mixtures thereof.
[0046] Carboxylic acids, if added, may also impart corrosion
inhibition properties to the slurry composition.
[0047] To increase the selectivity of tantalum and tantalum
compounds relative to silicon dioxide, fluorine-containing
compounds may be added to the slurry composition. Suitable
fluorine-containing compounds include, for example, hydrogen
fluoride, perfluoric acid, alkali metal fluoride salt, alkaline
earth metal fluoride salt, ammonium fluoride, tetramethylammonium
fluoride, ammonium bifluoride, ethylenediammonium difluoride,
diethylenetriammonium trifluoride, and mixtures thereof.
[0048] Suitable chelating agents that may be added to the slurry
composition include, for example, ethylenediaminetetracetic acid
(EDTA), N-hydroxyethylethylenediaminetriacetic acid (NHEDTA),
nitrilotriacetic acid (NTA), diethylklenetriaminepentacetic acid
(DPTA), ethanoldiglycinate, and mixtures thereof. The chelating
agents may aid in the softening of the metallic surface or even
help to protect low lying features or surfaces of particular
composition. The idea of protection mechanisms may lead to
significant improvements.
[0049] Suitable amines that may be added to the slurry composition
include, for example, hydroxylamine, monoethanolamine,
diethanolamine, triethanolamine, diethyleneglycolamine,
N-hydroxylethylpiperazine, and mixtures thereof.
[0050] Suitable surfactant compounds that may be added to the
slurry composition include, for example, any of the numerous
nonionic, anionic, cationic, or amphoteric surfactants known to
those skilled in the art.
[0051] The pH of the slurry is vital to the performance of all
slurry components. The acidity level of a solution can control
reaction rates at the surface, formation constants of metal
complexing agents, rates of surface oxidation, solution ionic
strength, aggregation size of slurry particles, and more.
Examination of various acids, bases, and pH buffers are a
prospective area for CMP development.
[0052] A boehmite slurry may be conveniently prepared by dispersing
a boehmite abrasive in water, and adjusting the pH, if needed, by
adding acid or a base. This mixture is then agitated for a period
of time to ensure desired solids dispersion and form a particle
slurry. To this particle slurry, active CMP slurry components such
as oxidizer or other complexing agent, chelating agent, passivating
agent and surfactant are added. Other active components may be also
added on as needed basis to ensure optimal performance of the fully
formulated CMP slurry. The pH of the final slurry then may be
adjusted by adding acid or base.
[0053] Removing excess metal or other contamination from smaller
and smaller spaces between individual pathways presents ever
increasing challenges for CMP processing. Copper metal has a
smaller intrinsic resistance and capacitance than Cu/Al alloy,
which is currently used as the conducting medium. Therefore, a
smaller electrical potential is required to send a signal through a
copper line, reducing the tendency for electrical spillover. In
effect, by using Cu-only, the circuit pathways can be placed closer
together.
[0054] However, the use of Cu also has disadvantages. Copper does
not adhere well to oxide surfaces. Copper is also susceptible to
bulk oxidation as, unlike WO.sub.3 or Al.sub.2O.sub.3, a CuO or
CuO.sub.2 surface layer still allows O.sub.2 and H.sub.2O to
penetrate into the bulk metal. Moreover, Cu atoms are mobile and
can migrate into the SiO.sub.2 wafer material ultimately causing
the transistors in the circuit to fail. Therefore, a thin layer of
low dielectric material, typically composed of tantalum, tantalum
nitride, or titanium nitride, is placed between the wafer oxide and
conducting Cu layers. The buffer layer promotes Cu adhesion,
prevents oxidation of the bulk Cu metal, prevents Cu ion
contamination of the bulk oxide, and further lowers the dielectric
between the circuits (i.e. allows the circuits to be even more
closely spaced).
[0055] One of the uses of CMP technology is in the manufacture of
shallow trench isolation (STI) structures in integrated circuits
formed on semiconductor chips or wafers such as silicon. The
purpose of an STI structure is to isolate discrete device elements
(e.g., transistors) in a given pattern layer to prevent current
leakage from occurring between them.
[0056] An STI structure is usually formed by thermally growing an
oxide layer on a silicon substrate and then depositing a silicon
nitride layer on the thermally grown oxide layer. After deposition
of the silicon nitride layer, a shallow trench is formed through
the silicon nitride layer and the thermally grown oxide layer and
partially through the silicon substrate using, for example, any of
the well-known photolithography mask and etching processes. A layer
of a dielectric material such as silicon dioxide is then typically
deposited using a chemical vapor deposition process to completely
fill the trench and cover the silicon nitride layer. Next, a CMP
process is used to remove that portion of the silicon dioxide layer
covering the silicon nitride layer and to planarize the entire
surface of the article. The silicon nitride layer is intended to
function as a planarization stop that protects the underlying
thermally grown oxide layer and silicon substrate from being
exposed during CMP processing. In some applications, the silicon
nitride layer is later removed by, for example, dipping the article
in an HF acid solution, leaving only the silicon dioxide filled
trench to serve as an STI structure. Additional processing is
usually then performed to form polysilicon gate structures.
[0057] The use of Cu and accompanying low dielectric buffer layer
demand enhanced performance from planarization techniques. The new
techniques are called Cu-CMP but in principle do not differ
significantly from previous planarization methods. The CMP process
must be able to remove the soft Cu metal overburden, yet limit Cu
dishing, scratching, and removal of the low dielectric buffer
layer. Simultaneously, tolerances are more rigorous because of more
closely spaced circuit patterns. The ability to produce layers that
are thin, flat, and defect free is of paramount importance.
[0058] As is also known in the art, one method for forming
interconnects in a semiconductor structure is a so-called dual
damascene process. A dual damascene process starts with the
deposition of a dielectric layer, typically an oxide layer,
disposed over circuitry formed in a single crystal body, for
example silicon. The oxide layer is etched to form a trench having
a pattern corresponding to a pattern of vias and wires for
interconnection of elements of the circuitry. Vias are openings in
the oxide through which different layers of the structure are
electrically interconnected, and the pattern of the wires is
defined by trenches in the oxide. Then, metal is deposited to fill
the openings in the oxide layer. Subsequently, excess metal is
removed by planarization. The process is repeated as many times as
necessary to form the required interconnections. Thus, a dual
damascene structure has a trench in an upper portion of a
dielectric layer and a via terminating at the bottom of the trench
and passing through a lower portion of the dielectric layer. The
structure has a step between the bottom of the trench and a
sidewall of the via at the bottom of the trench.
[0059] The abrasive particles of the current invention can be used
in CMP of copper in applications other than logic (such as
microprocessors) or memory (such as flash memory) devices where
copper is used in the interconnect metallic layers. For example,
improving the thermal and electrical characteristics of the
packaging of the device may involve use of a copper layer that
needs to be planarized. The structure of the interconnect copper
layer in the integrated circuit device and the copper layer in
packaging may be different leading to different requirements on
thickness of layer to be removed, planarity, dishing and
defectivity. Also Micro-ElectroMechanical Systems (MEMS) may have a
copper layer that may require planarization using CMP. Abrasive
particles of the current invention can be used in CMP slurries for
this application also.
[0060] A review of CMP processing is provided in "Advances in
Chemical-Mechanical Planarization," Rajiv K. Singh and Rajiv Bajaj,
MRS Bulletin, October 2002, pages 743-747. In general, while the
CMP process appears quite simple, achieving a detailed
understanding has been limited primarily by the large number of
input variables in the planarization process. Among such variables
are slurry variables such as particles and chemicals, pad
variables, tool variables such as down pressure and linear
velocity, and substrate variables such as pattern density. The
article provides a good review of the process variables and
emerging applications for CMP technology and is herein incorporated
by reference.
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