Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MODIFYING THE SURFACE OF A SEMICONDUCTOR WAFER
Background of the Invention
The invention relates to modifying a semiconductor wafer.
S Wafers used in the fabrication of semiconductors often require surface
modification, e.g., polishing and planarization, at some point during the
fabrication
process. Traditional polishing methods include moving an abrasive substrate
and
the wafer in relation to each other, typically in the presence of a water-
based
solution.
Polishing processes can be used to remove the highest points from the
surface of a wafer. Polishing operations are performed on unprocessed and
partially processed wafers. A typical unprocessed wafer is crystalline silicon
or
another semiconductor material, e.g., gallium arsenide. A typical wafer, when
ready for polishing has a top layer of a dielectric material such as glass,
silicon
dioxide or a metal conformally overlying one or more patterned layers. The
underlying patterned layers create local protrusions. Polishing smoothes the
local
features so that ideally the surface of the wafer is flat or planarized.
In some cases, polishing is achieved through the solution working in
combination with the fixed abrasive article in a chemical mechanical polishing
process. As an example, the chemical polishing of a silicon dioxide substrate
occurs when a basic compound in a solution reacts with the silicon dioxide to
form
a surface layer of silicon hydroxides. The mechanical process occurs when an
abrasive article removes the metal hydroxides from the surface of the
substrate.
A number of chemical mechanical polishing techniques exist. Some
chemical mechanical polishing techniques include orbiting or oscillating
motions
of either the article to be polished or of the polishing pad, or both. Other
chemical
mechanical polishing techniques include a belt-shaped polishing pad that is
advanced translationally under the article to be polished, and the article to
be
polished is rotated, oscillated or both across the surface of the belt-shaped
pad.
In some chemical mechanical polishing techniques a slurry is distributed
between a pad and the surface to be polished. These slurries often contain
water
and abrasive particles.
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In other chemical mechanical polishing techniques, the abrasive is fixed on
a substrate and a polishing solution is distributed between the fixed abrasive
and
the surface to be polished.
Often the polishing pad and the substrate to be polished are hydrophobic,
which inhibits wetting. Wetting facilitates the transport of fresh chemistry
into the
region between the abrasive surface and the surface of the wafer to be
planarized.
The polishing liquid can also assist in the removal of debris and soluble
material
removed from the surface of the substrate being polished. Surfactants present
in
the composition can inhibit the removal rate. When a solution does not wet the
abrasive surface, the polishing process can also be inhibited.
SUNINIARY
In one aspect, the invention features a method of modifying a surface of a
semiconductor wafer, the method including (a) contacting the wafer with a
fixed
abrasive article in the presence of a composition that includes water and a
polar
component having from 1 to 10 functional groups selected from the group
consisting of-OH, -OOH, =O, and combinations thereof, and from 1 to 10
consecutive groups selected from the group consisting of -CHZ-, -CH20-, -C2H40-
,
-C3II60- and combinations thereof; and (b) relatively moving the wafer and the
fixed abrasive article to modify the surface of the wafer. In some
embodiments,
the polar component includes no greater than 8 carbon atoms. In other
embodiments, the polar component is selected from the group consisting of
alcohols, glycols, ketones, ethers, acetates, and combinations thereof.
In another embodiment, the polar component includes an alcohol selected
from the group consisting of methanol, ethanol, propanol, isopropanol,
butanol,
isobutanol and mixtures thereof. In some embodiments, the polar component is
selected from the group consisting of acetone, ethyl acetate, cellosolve
acetate, and
mixtures thereof.
In one embodiment, the fixed abrasive article includes a three-dimensional
textured abrasive surface having a plurality of abrasive particles and a
binder
arranged in a pattern. In some embodiments, the fixed abrasive comprises
particles
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selected from the group consisting of ceria, silica, alumina, titania,
zirconia,
manganese oxide, and mixtures thereof.
In other embodiments, the method includes chemically and mechanically
modifying the surface of the wafer.
In another embodiment, the fixed abrasive article includes a backing and an
abrasive coating on a surface of the backing, and the abrasive coating
includes
abrasive particles and a binder.
In another aspect, the invention features a method of modifying a surface of
a first article, the method includes (a) contacting the first article with a
fixed
abrasive article in the presence of a composition that includes water and a
polar
component having from 1 to 10 functional groups selected from the group
consisting of-OH, -OOH, =O, and combinations thereof, and from 1 to 10
consecutive groups selected from the group consisting of -CHZ-, -CH20-, -C2H40-
-C3II60- and combinations thereof; and (b) relatively moving the first article
and
the fixed abrasive article to modify the surface of the first article. In one
embodiment, the polar component includes no greater than 8 carbon atoms. In
other embodiments, the polar component is selected from the group consisting
of
alcohols, glycols, ketones, ethers, acetates, and combinations thereof.
In some embodiments, the polar component includes an alcohol selected
from the group consisting of methanol, ethanol, propanol, isopropanol,
butanol,
isobutanol and mixtures thereof. In another embodiment, the polar component is
selected from the group consisting of acetone, ethyl acetate, cellosolve
acetate, and
mixtures thereof.
In another embodiment, the fixed abrasive article includes a three-
dimensional textured abrasive surface comprising a plurality of abrasive
particles
and a binder arranged in a pattern.
The composition used in the method preferably exhibits reduced surface
tension relative to water and is able to wet hydrophobic substrates. The
method is
particularly well suited to wetting abrasives that include hydrophobic oxide
abrasives, e.g., cerium oxide particles. The method also facilitates web
polishing
by maintaining the solution within the confines of the web such that it does
not
seep underneath the web where it might cause mechanical difficulties. The
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improved wetting also provides good rates of removal of surface material. The
composition also provides good low vibration and friction during chemical
mechanical planarization operations.
Other features and advantages of the invention will be apparent from the
following description~of the preferred embodiments thereof, and from the
claims.
Detailed Description
The inventors have discovered that aqueous polishing solutions tend to
form large beads of liquid when in contact with a hydrophobic web. The large
beads tend to be mobile on the abrasive surface during polishing. As a result,
under the action of the polishing head the solution travels beyond the edge of
the
abrasive surface and seeps between the abrasive surface polishing pad and the
sub
pad on which the fixed abrasive polishing pad sits. This can cause the
polishing
pad to stick to the sub pad, which in turn causes mechanical problems.
The method of modifying a surface of a semiconductor wafer includes
contacting the wafer with a fixed abrasive article in the presence of a
composition
that includes water and a polar component, and moving at least one of the
wafer
and the fixed abrasive article relative to each other so as to modify the
surface of
the wafer. The method preferably modifies the surface of the wafer to achieve
a
surface that is more planar or uniform, or less rough, or a combination
thereof,
relative to the wafer surface prior to treatment.
The polar component preferably provides a composition that is capable of
sufficiently wetting the hydrophobic substrate to be modified as well as the
fixed
abrasive pad. The polar component includes from 1 to 10 functional groups
selected from the group consisting of-OH, -OOH, =O, and combinations thereof,
and from 1 to 10 consecutive groups selected from the group consisting of -CHz-
, -
CH20-, -CzH40-, -C3Hb0- and combinations thereof. Preferably the polar
component includes no greater than 8 carbon atoms.
Examples of useful polar components include alcohols, e.g., methanol,
ethanol, propanol, isopropanol, n-butanol, sec-butanol, tent-butanol,
isobutanol,
and octanol; acetates including methyl acetate, ethyl acetate, and cellosolve
acetate; ketones, e.g., acetone; ketone alcohols, e.g. diacetone alcohol;
ethers
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including, e.g., methyl ether; alkylene glycols or thioglycols containing a Cz
- C6
alkylene group, e.g. ethylene glycol, propylene glycol, tripropylene glycol,
butylene glycol, pentylene glycol and hexylene glycol; poly(alkylene-glycol)s
and
thioglycols, e.g. diethylene glycol, thiodiglycol, polyethylene glycol and
polypropylene glycol; polyols, e.g. glycerol and 1,2,6-hexanetriol; and lower
alkyl
glycol and polyglycol ethers, e.g.2-methoxyethanol, 2-(2-
methoxyethoxy)ethanol,
2-(2-ethoxyethoxy)ethanol, 2-(2-butoxyethoxy)ethanol,3-butoxypropan-1-ol, 2-[2-
(2-methoxyethoxy)-ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]-ethanol; cyclic
esters and cyclic amides, e.g. substituted pyrollidones; sulpholane; multiple
functionality polar components; and mixtures thereof.
The pH of the composition is selected to be suitable for the substrate being
modified. Useful compositions have a pH of greater than 1.5, more preferably
from about 3 to about 12.5, most preferably from about 5 to about 12.
Additives
can be included in the composition to achieve a desired pH. Examples of such
additives include bases, e.g., potassium hydroxide and ammonium hydroxide, and
acids, e.g., KI03, potassium phthalate, phthalic acid, phosphoric acid, nitric
acid,
and sulfuric acid. Buffers can also be included in the composition to maintain
the
desired pH.
The composition may also include other components including, e.g., liquid
etchants, e.g., strong acids (e.g., sulfuric acid and hydrofluoric acid) and
oxidizing
gents (e.g., peroxides), lubricants and combinations thereof. Examples of
suitable
lubricants include metal salts of fatty acids including, e.g., zinc stearate,
calcium
stearate and lithium stearate, graphite, mica, molybdenum disulfide, talc,
polyamides, boron nitride, sulfides, waxes, silicone compounds, polyvinyl
acetate,
polyvinyl alcohols, polymers, and combinations thereof.
The method is suitable for use with a variety of fixed abrasive articles.
Examples of useful fixed abrasive articles include those fixed abrasive
articles that
are in the form of a pad or a web, e.g., a continuous belt. The fixed-abrasive
article
preferably includes a number of abrasive particles in a binder attached to a
substrate, e.g., a backing. The abrasive particles in the binder may be in the
form
of an abrasive coating (e.g., a continuous or discontinuous coating), abrasive
composites (e.g., shaped bodies) or a combination thereof. The abrasive
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components (e.g., the particles and the composites) may be arranged in a
pattern or
random configuration. The fixed abrasive article can be textured such that it
includes raised portions and recessed portions. The fixed abrasive article can
also
be three-dimensional such that it includes numerous abrasive particles
extending
throughout at least a portion of its thickness such that removing some of the
abrasive particles during the surface modifying process exposes additional
abrasive
particles capable of performing the surface modifying function. Examples of
useful fixed abrasive articles are described in U.S. Patent Nos. 5,958,794,
5,692,950 and 5,990,012.
The abrasive article may include any number of different abrasive particles.
Suitable abrasive particles include, e.g., ceria, silica, alumina, iron oxide,
chromic,
titanic, tin oxide, zirconia, manganese oxide and combinations thereof. Other
useful abrasive particles include fused aluminum oxide, heat treated aluminum
oxide, white fused aluminum oxide, black silicon carbide, green silicon
carbide,
titanium diboride, boron carbide, silicon nitride, tungsten carbide, titanium
carbide,
diamond, cubic boron nitride, hexagonal boron nitride, garnet, fused alumina
zirconia, alumina-base sol gel derived abrasive particles and combinations
thereof.
The movement of at least one of the abrasive article and the wafer relative
to each other to modify a surface of the wafer can be rotational, e.g., in a
circular,
spiral, elliptical, or non uniform fashion, in a figure eight or a corkscrew,
translational, vibrational, oscillatory, or a combination thereof. Preferably
the
movement includes rotation of one or both of the fixed abrasive article and
the
wafer. For example, the wafer and the abrasive article can be rotated in a
circular
fashion and in the same direction. Alternatively, the wafer and the fixed
abrasive
article can be rotated in opposite directions. Examples of suitable methods
for
relatively moving at least one of a fixed abrasive article and a wafer
relative to
each other so as to modify a surface of the substrate are described in U. S.
Patent
Nos. 5,871,390, 5,961,372, 6,000,997, 5,851,136, 5,335,453, WO 99/06182,
5,759,918 and 5,938,884.
The method may be used to modify the surface of a variety of articles
including, e.g., semiconductor wafers and components of semiconductor wafers.
The semiconductor wafer may be in a variety of forms including, e.g., a blank
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wafer (i.e., a wafer prior to processing, e.g., prior to adding topographical
features
such as metallized and insulating areas) or a processed wafer (i.e., a wafer
that has
been subjected to one or more processing steps to add topographical features
to the
wafer surface). The wafer can include a number of materials including, e.g.,
silicon, silicon dioxide, silicon nitride, gallium arsenide, copper, aluminum,
tungsten, titanium, titanium nitride, polymer, and combinations thereof.
The invention will now be described by way of the following examples.
All ratios and percentages are by weight unless otherwise indicated.
EXAMPLES
EXAMPLE 1
The chemicals set forth in Table 1 were added at 10 % by volume to
distilled water and then placed on SWR 159 cerium oxide fixed abrasive (3M,
St.
Paul, Minnesota). The wetting nature was observed and is reported in Table 1.
TABLE 1
Chemical Observation
Distilled Water Solution forms beads
on the
surface of the substrate.
Acetone Solution forms a smooth
film on
the surface of the
substrate
Methanol Solution forms a smooth
film on
the surface of the
substrate
Ethanol Solution forms a smooth
film on
the surface of the
substrate
Butanol Solution forms a smooth
film on
the surface of the
substrate
Isopropanol Solution forms a smooth
film on
the surface of the
substrate
Ethyl Acetate Solution forms a smooth
film on
the surface of the
substrate
Cellosolve Acetate Solution forms a smooth
film on
the surface of the
substrate
Tripropylene Glycol Solution forms a smooth
Methyl film on
Ether the surface of the
substrate
Polyethylene Oxide Solution forms a smooth
film on
the surface of the
substrate
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Other embodiments are within the following claims. For example
although the method has been described with respect to a semiconductor wafer,
the
article to be modified can be a variety of articles and can include materials
such as
silicon, silicon dioxide, silicon nitride, gallium arsenide, copper, aluminum,
tungsten, titanium, titanium nitride, polymers, and combinations thereof.
_g_
