Hs3313371345

M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of Engineering
Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 3, Issue 3, May-Jun 2013, pp.1337-1345
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CHEMICAL MECHANICAL POLISHING BY COLLOIDAL SILICA
SLURRY
M.SIVANANDINI, DR. SUKHDEEP S DHAMI , DR. B S PABLA
Mechanical Department, National Institute of Technical Teachers Training and Research,Chandigarh-160019
ABSTRACT
Chemical Mechanical Polishing is a
unique process enabling technology that allows
chip makers to readily drive lithographic
patterning steps to smaller dimensions, an ages
old, “retro” technology related to glass polishing
and metallographic finishing, thus enabling
optical lithography to work. It represents a
situation that is a true paradigm shift from the
typical way in which technological advancements
become main stream in high-technology
semiconductor manufacturing processes.
Colloidal nano-abrasives with different particle
sizes are required for slurries in different CMP
processes. Colloidal silica is used as polishing
slurry for producing reflecting surfaces for
mirrors, lenses and the planarization of
computer chips. Industrial use of colloidal
silica’s is growing steadily in both traditional
areas and ever-increasing numbers of novel
areas. Colloidal silica’s are found in fields as
diverse as catalysis, metallurgy, electronics,
glass, ceramics, paper and pulp technology,
optics, elastomers, food, health care and
industrial chromatography, polishing
sophisticated microcircuit parts to outer space
and play vital role in the safe reentry of space
vehicles and the development of Western for
that matter, world civilization. The paper
focuses a brief overview of chemical mechanical
polishing using colloidal slurry.
Keywords - Chemical Mechanical Polishing,
Colloidal silica, Nanoabrasives, Slurry,
Semiconductor
I. INTRODUCTION
Chemical mechanical polishing (CMP)
technology was first put forward by Monsanto [1-
3] in 1965. It is an indispensable process step in
semiconductor device fabrication, common
technique used in wafer polishing for dynamic
memory, microprocessor applications and glass
mechanical polishing. It is one of the key new
nanotechnology fabrication processes, a true
advance that could be made to work despite
enormous odds and technical difficulties early on.
Chemical mechanical polishing (CMP) is widely
used in the semiconductor industry [4-7] to produce
mirror like surfaces with no measurable subsurface
damage. The application of scientific technological
results in the domain of glass polishing with
suspensions of rare earth oxides and micro
heterogeneous suspensions with particle
dimensions of 0.1–0.5 μm diameter and new or
tested abrasive ultra disperse powders (UDP) have
been attempted in electronics. The Chemical
mechanical polishing performances can be
optimized by process parameters such as
equipment and consumables (pad, backing film,
and slurry). One of the critical consumables in the
CMP process is slurry (typically containing both
abrasives and chemicals acting together), that
directly affects CMP efficiency and the yield.
Slight changes in slurry properties due to
contamination, chemical degradation, abrasive
content or applied shear can change polish
performance and impact yield. Correlation of
slurry property measurements with evaluations of
wafer polish rate, planarity and defectivity provides
insight into the root cause of degradation in
polishing. The conventional slurry consists of
abrasive particles of the solid state suspended in a
liquid state chemical solution [8] containing one or
more of various chemicals such as oxidizers, pH
stabilizers, metal ion complexants and corrosion
inhibitors [9]. An abrasive in the slurry provides
both mechanical action with nanometer-sized
abrasive particles and chemical action from the
solution additives with a synergistic effect that
causes material removal [10,11].Through chemical
and physical actions, the abrasive-liquid
interactions play an important role in determining
the optimum abrasives’ type, size, shape and
concentration [12]. The slurry designed for optimal
performance should produce reasonable removal
rates, acceptable polishing selectivity with respect
to the underlying layer, low surface defects after
polishing and good slurry stability. Choosing slurry
which provides good removal rates without causing
defects is of utmost importance in CMP. Colloidal
sized SiO2, CeO2 and Al2O3 particles are used in
the manufacturing of CMP slurries. They are
applied in different fields, but SiO2 is promising.
Alumina particles find limited used in the
manufacturing of slurries for tungsten CMP; they
are slowly falling out of vogue because of their
hardness[13], Today, silica particles are
predominantly used in the preparation of slurries
for dielectric as well as metal CMP. The use of
industrial sols–gels of silicon acid (Monsanto

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Comp, Dupoint, Nalco Ch et al.) and of
compositions based on aerosol type UDP SiO2
(Siemens,Degussa) and Al2O3 (Union Carbide
Corp.) led to the development of colloidal silica.
Robert Walsh (Monsanto), patent and publications
of other authors (H. Dersin, I.S. Basi, R.L.
Lachapelle, et al.) up to the beginning of eighties
contributed to development in microelectronics
with the development of colloidal silica sol and
silica gel. In this paper a brief review of CMP
process using colloidal silica slurry is presented.
II. COLLOIDAL SILICA SLURRY
The silica slurries are typical consumable
materials for CMP. The colloidal silica and fumed
silica are known as the representative CMP slurry
materials. Colloidal silica polishing suspensions are
unique because they provide both dispersing action
as well as a chemical mechanical polishing (CMP)
action. It is effective as an additive for the
intermediate diamond polishing of metals and is
also the best polishing abrasive for eliminating
subsurface and surface because of its CMP
polishing action. These polishes are chemically
stabilized to produce a nearly “perfect suspension”;
can also have additives that minimize the effect of
particle aggregation of crystallization. The
distribution of colloidal silica has an important
effect on polishing rate and polished surface
roughness.
In 2001, the effects of temperature, slurry
pH, applied pressure and polishing rotation rate on
the material removal rate during chemical
mechanical polishing (CMP) of 4H-silicon carbide
wafers using colloidal silica slurry and
polyurethane/polyester fiber polishing pads have
been studied by Neslen C.L et al [14]. The wafers
were polished for 30 or 60 mins using a Strasbaugh
Precision Polishmaster with a random motion
polishing armature. Polishing at wafer temperatures
of 230
C and 650
C were performed and found that
increased temperatures had no significant
improvements in removal rate. The polishing slurry
pH levels for the 90 rpm study were similar to 60
rpm, showed that material removal rate was not
affected by pH. Increased applied pressure resulted
in accelerated removal of wafer material. The
average removal rate over the four-hour period
using a 9.9 pH polishing slurry was 139 Å/hour
while an pH 11 polishing slurry was only 108
Å/hour., the variability in the removal rate during
150 rpm was high and ranged from 298 Å/hour
during the second 30 min polish to 1860 Å/hour
during the last 30 min polishing interval due to the
inability to maintain a constant amount of polishing
solution on the pad during the polishing interval.
Excessive pressure resulted in damage of polishing
pad and increased wafer preparation costs.
Polishing pad rotational speeds had the greatest
impact on wafer material removal rates with an
associated increase in removal rate variability. The
authors concluded that additional rotational speed
studies would be useful to maximize material
removal rate with decreased variability
The effects of phosphoric acid addition on
slurry for chemical–mechanical planarization
(CMP) of copper and tantalum nitride were
investigated by [15]. Alumina or colloidal silica as
an abrasive, organic acid as a complexing agent,
Hydrogen peroxide (H2O2) an oxidizing agent, a
film forming agent, a pH control agent and
additives, phosphoric acid (H3PO4) as accelerator
of the tantalum nitride as well as hydrogen
peroxide as stabilizer were used. Experiments were
performed on G&P Technology POLI-500CEk
chemical–mechanical polisher ,Rodel IC-1400 k-
groove polyurethane pad with the head speed and
the table speed 40 rpm, down pressure of the head
7 psi , slurry flow rate 150 ml/min, polishing for 1
min on electroplated copper, sputtered tantalum
nitride, PETEOS wafer with 10,000 A° thickness.
Zeta potential and particle size measurement of the
slurries were carried out by using the Brookhaven
ZetaPlus instrument. An acceleration of the
tantalum nitride CMP was verified by
electrochemical curves recorded with an EG and G
273A potentiostat. The slurry of 5.0% by wt.
abrasive, 5.0% by wt hydrogen peroxide, 0.5% by
wt. phosphoric acid had good H2O2 stability and
TaN acceleration and dispersion ability. Hence
slurry including phosphoric acid was proposed.
Hong Lei prepared novel colloidal SiO2
slurry, a carboxylic acid containing a long alkyl
chain as lubricant additive, for the chemical–
mechanical polishing of disk substrates with NiP
plated [16]. Polishing tests were conducted with
SPEEDFAM-16B-4M CMP equipment
(SPEEDFAMCo. Ltd., Japan ) for four slurries,
each with a different mean particle diameter of 15,
30, 50 and 160 nm, processing pressure of 70
g/cm2
, rotating speed of 25 rpm, processing
duration of 8.5 min and slurry supplying rate of
300 ml/min on work pieces of 95 mm/1.25mm
aluminum alloy substrates with NiP plated about 85
wt. % nickel and 15 wt. % phosphorus element.
Prepared slurry of 6 wt. % SiO2 particles with an
average diameter of 30 nm, 1 wt. % ferric oxidizer
and 2 wt. % lubricants in DI water at pH value of
1.8, exhibited smoother polished surface. The
abrasive particle size, contents of oxidizer,
lubricant additive and abrasive particle contained in
the prepared colloidal SiO2 slurry as well as pH
value of the slurry, had strong impact on the
average roughness (Ra), the average waviness (Wa)
and material removal rate. Better surface quality
resulted, with smaller SiO2 size, moderate SiO2
concentration, lower oxidizer content, higher
lubricant content and moderate pH value under the

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testing conditions, while the high material removal
rate with large size SiO2 , high particle, oxidizer
contents and low lubricant content.
The chemical mechanical polishing
(CMP) of aluminum and photo resist using
colloidal silica-based abrasive (average ∼20 nm
diameter,Ace Hitech) ,effects of varying slurry pH,
silica concentration and oxidizer concentration on
surface roughness(Rv) and removal rate were
investigated by [17] in order to determine the
optimum conditions for these parameters.
Experimentation was conducted on a modified
Motopol 2000 polishing system from Buehler Co.
with Polytex Supreme pad from Rodel. H3PO4 and
KOH were added to adjust the pH of colloidal
silica with de-ionized water. In the Al CMP, H2O2
was used as an oxidizer. In all experiments, the
polishing pressure was 30 kPa, the linear polishing
velocity was 15 m/min and the slurry flow rate of
12 ml/min with polishing times of 4 and 1 min for
Al and PR respectively. The measurement was
carried out under a sampling length of 10 mm, a cut
off length of 0.08 mm and a scanning speed of
25m/s by Dektak (Veeco Instruments).The removal
rate of Al was measured by a four-point probe
(Chang Min Tech) and PR removal rate was
measured under a wave length of 480 nm and a
reflective index of 1.63 by a NanoSpec
(Nanometrics). The Rv values of the Al and PR
surfaces before the CMP were 39.4 and 7.85 nm,
respectively. The results of the CMP of the
aluminum with the colloidal silica-based slurry
were good with small micro-scratch size when Rv
≤ 10 nm and large removal rate for the slurry pH of
2–4 and the oxidizer H2O2 concentration 1–3% by
vol. The colloidal-based silica slurry produced a
desirable fine Al surface with few micro-scratches
similar to filtered alumina-based slurry, but
produced a photo resist surface with many micro-
scratches as shown in table.1. The Fig1a, 1b and
Fig 2a, 2b represent roughness and removal rate of
Al and PR as function of slurry pH and SiO2
concentration.
Table: 1
Fig 1.a
Fig 1.b
Fig.2 a
Fig.2 a
Fig. 2b
New semi-abrasive free slurry for copper
chemical mechanical planarization (CMP) was
investigated through the addition of acid colloidal
silica below 0.5% by wt, hydrogen peroxide and
other additives by [18]. The additives as stabilizers
for hydrogen peroxide as well as accelerators in
tantalum nitride CMP were also evaluated.
Experimentation was carried on G&P Technology
POLI-500CETM chemical mechanical polisher
using Rodel IC-1400 k-groove polyurethane pad.
Electroplated copper wafer with 1600 nm,
sputtered tantalum nitride wafer, PETEOS wafer

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with 1000 nm thickness were used for polishing.
SKW 6-3 copper wafer was used as a patterned
wafer with 0.25 μm minimum feature size. For the
polishing, down pressure of the head 4.3 psi, slurry
flow rate 300 ml/min, head speed and table speed
was set at 50 rpm. The Zeta potential and particle
size measurement of the slurries were carried out
using Brookhaven ZetaPlus instrument.
Electrochemical curves were recorded with EG&G
273A Potentiostat. Metal impurities measurement
of the slurry was carried out by PerkinElmer ICP-
Mass instrument. Zeta potential change of colloidal
silica in slurries with and without the addition of
additives as a function of pH is shown in Fig. 3.
When surfactant was added to colloidal silica
slurry, zeta potential increased from 0 and a sudden
reversal of charges was observed in pH 2–3 range.
Particle dispersion with the chemical-added
colloidal silica slurry in pH 2.5 was stable during
90 days. A copper wafer dipped in chemical added
colloidal silica slurry was clearer than a wafer
dipped in the slurry without the chemicals. Good
hydrogen peroxide stability, excellent colloidal
silica dispersion ability and easiness of post-CMP
cleaning were provided by the semi-abrasive free
slurry. The extent of enhancement in tantalum
nitride CMP was verified through an
electrochemical test. Ammonium and amine
became very stable, indicating that decomposition
rate was below 0.001 wt%/day. So this type of
slurry was formulated in a single package rather
than conventional, uncomfortable two-package
system due to unstable hydrogen peroxide.
Figure 3 Zeta potentials of copper, colloidal silica
and chemical added colloidal silica
Shao-Yu Chiu et al. [19] investigated the removal
mechanism of Cu-CMP on the characteristics of
colloidal-silica-based slurry. All polishing
experiments were performed with (100) oriented,
6-inch-diameter p-type Si wafers. The polishing
sample was stacked with 900-nm-thick, 50-nm-
thick Cu and Ta respectively. Multi-step chemical
mechanical polishing (CMP) with different copper
removal rates and polishing pads was used to
eliminate topography efficiently and to reduce
micro-scratches on copper films. Cu-CMP was
performed with a Westech Model 372M polisher
using a Politex Regular E. pad. Polishing
parameters such as down force, platen/carrier
rotary speed, back pressure and slurry flow rate
were set to be 5 psi, 42/45 rpm, 2 psi and 150
ml/min respectively. Polishing slurries with diluted
colloidal silica (<50 nm in size) 10% by wt, 10 wt.
%H2O2 (30 wt. % semiconductor grade), Potassium
hydroxide (KOH), ammonium hydroxide (NH4OH)
and tetra-methylammonium hydroxide (TMAH)
were used as slurry pH adjusters. A laser
diffraction particle size analyzer, UP-150 was used
to measure the aggregation size of abrasives in
slurries. In colloidal-silica-based slurry, the
polishing behaviors of copper, tantalum and silicon
dioxide were found to relate to alkaline additives.
The size of cations from alkaline additives
influenced the zeta potential of slurries, so as to
vary the material removal rate. It was found that the
polishing behavior of Cu, Ta and oxide was deeply
dependant on the slurry pH and the surface charge-
related interactions between the slurry and the
polishing substrate. The maximum removal rate of
Cu was above130 nm/min at pH2. As slurry pH
increased into neutral regime, the removal rate of
Cu dropped by formation of Cu oxide passivation
(Cu2O, CuO). The attraction and expulsive force
affected the impacting frequency between colloidal
silica abrasives and the wafer surface. The iso-
electric potential of colloidal-based slurries was
around pH2 which led to higher Ta removal rate.
NH3 dissolved Cu oxide passivation and formed Cu
(NH3)4
2+
to enhance the removal rate of copper.
The removal rate was about 225nm/min for Cu and
80nm/min for Ta at pH9.2. With more NH4OH
added into the slurry at pH10, the removal rate was
enhanced to 1490 nm/min for Cu and 100nm/min
for Ta. Large-size cations led to less impacting
frequency between the abrasives and the substrate,
to get lower removal rate. KOH was found to be a
suitable pH adjuster for the colloidal-silica-based
slurry. High or low removal selectivity of Ta/Cu
and SiO2/Cu during the two-step Cu-CMP process
could be achieved by modified colloidal-silica-
based slurries with proper alkaline additives and
pH values.
The effects of varying the size and the
concentration of the abrasive in colloidal silica
slurry and the concentration of tetra-methyl
ammonium hydroxide (TMAH) were investigated
in terms of the oxide film loss, the removal rate, the
roughness of the film surface and polysilicon-to-
oxide film removal selectivity. These effects were
investigated [20] performing chemical mechanical
polishing (CMP) experiments under polishing
pressure 13.8 to 41.4kPa, relative velocity between
the pad and the wafer 0.539 m/s and the polishing
time 30 s on conventional 8” silicon wafers

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prepared by using the single side polishing method.
Nanoscale colloidal silica slurries (PL-3 and PL-7,
Fuso Chemical Inc., Japan) containing two
different spherical abrasive particles with primary
sizes of 30 and 70 nm were used in these
experiments. The colloidal silica slurry was
dispersed in deionized water and stabilized by
adding 0.06 wt% of a commercially available
nonionic organic polymer (poly(acrylamide),
PAAM) along with quaternary ammonium
hydroxide compound (TMAH) up to 0.52 wt% ,
wet etchants for polysilicon, a cellulosic polymer
(hydroxyethyl cellulose, HEC), molecular weight
of 50,000, at a constant concentration of 0.001wt%
was optionally added. The morphology of the
colloidal silica abrasives was observed with a high-
resolution transmission electron microscope
(HRTEM; JEM-2010, JEOL, Japan). The
secondary particle size was measured by using
acoustic attenuation spectroscopy (APS-100, Matec
Applied Sci., U S A.). The surfactant pH was
measured with an advanced benchtop pH meter
(Orion-525A, Thermo Orion, U.S.A.). The
rheological behavior of the slurry suspensions
examined with a controlled-stress viscometer
(MCR300, Paar Physica, Germany). Average size,
pH and conductivity increased with the TMAH
concentration. The removal rate of the polysilicon
film reduced with high pH value in the range of 10
to 12 due to change in the polysilicon surface from
hydrophobic to hydrophilic. The abrasive behavior
in the slurry was less affected by abrasive size and
TMAH concentration. Higher polysilicon to oxide
removal selectivity was directly related to the
zetapotential curves of the oxide , polysilicon films
and the modified abrasive particles in the colloidal
silica slurry. It was found that with increasing
TMAH concentration, the removal rate and the
polysilicon-to-oxide selectivity were reduced after
an initial increase, regardless of the abrasive size in
the slurry. Within a TMAH concentration range of
0.06 to 0.52 wt%, the removal selectivity at a lower
abrasive concentration for abrasive size of 30 nm
was slightly higher than for higher abrasive
concentration in case of a smaller abrasive, but in
the case of a larger abrasive the removal selectivity
was almost independent of the abrasive
concentrations. The oxide removal rate was
maintained at 40 to 60 °A/min during the polishing
process. At a lower TMAH concentration the
surface roughness, became worse. The results
qualitatively suggested a mechanism in which OH−
ions bonded to the Si surfaces of the abrasives in
the slurry and attached to the surface of the
polysilicon film.
In paper [21], the polishing mechanism of
LN , discussed based on the results of an integrated
analysis considering mechanical, chemical and
thermal factors. Research and development CMP
equipment, POLI-400 (G&P Technology Co.), was
used in the experiments. The slurry was formulated
by adding colloidal silica abrasive (average ~120
nm diameter, pH 10.7, Ace Hitech Co.) and a
foamed crosslinked polymer pad, IC 1400 k-groove
(Rohm & Hass Corp.), was used. The Material
Removal Rate (MRR) was investigated by XPS and
nano-indenter analysis. The MRR increased with
low pH slurry in both cases with H3PO4 and HNO3.
HNO3 had a stronger effect on the MRR than
H3PO4. High quality surfaces (Ra < 2 nm) were
obtained with pH 3 and 7. The higher abrasive
concentration and low pH slurry induced high
MRR. The flow rate was controlled from 50
cc/minute to 500 cc/minute (50, 100, 300, 500
cc/minute) in the experiments. As the flow rate
decreased, the material removal rate increased due
to frictional heat, the thermal energy and chemical
activation energy. The reaction layer formed on the
LN surface showed a variation of hardness with
NbO2, Nb2O5 and changed MRR.
The optimum condition selection of ultra precision
wafer polishing and the effect of polishing
parameters on the surface roughness, temperature
variation were evaluated by Eun-Sang Lee et
al.[22] using central composite designs such as the
Box-Behnken method, one of response surface
analyses. The polishing process was performed
over the whole wafer surface when the polishing
pad rotational velocity and wafer rotational
velocity was same. silicon wafer 4-inch,
environmental temperature 21.5℃, humidity 43%,
Polyurethane based Suba 600 made by Rodel Inc.
as polishing pad and commercial colloidal silica
based slurry with particle size in the 50- 70 nm
range were used. Pressure, wheel speed and process
time which were used as factors in this experiment
affected surface roughness of wafer under the final
polishing processes. A second-order regression
equation for the surface roughness was developed
from the experimental data. The regression
equation induced by response surface model was
evaluated to select proper polishing conditions with
constraints of the surface roughness. The effect of
changing final polishing parameters on the surface
roughness has been investigated and the ideal
optimum condition has been researched. At each
ranges of pressure, with increase in wheel speed
and process time, surface roughness decreased
initially and then increased. Optimum condition for
surface roughness was 0.2MPa of pressure, 30 rpm
of wheel speed and 10 minutes of process time.
The frictional heat between polishing pad and
wafer during the final wafer polishing increased
with range increment of each process parameters.
As the temperature increased, there was increase of
the effect by a chemical reaction and a variation of
pH so that the removal rate of wafer increased in
proportion to the temperature. The temperature

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elevation affected the increase of the removal
rate.
Chemical mechanical polishing (CMP) of
commercially pure Titanium (Ti) was carried out
using two types of slurries, acidic (pH of 3.2
adjusted by H3PO4 and NH4 H2 PO4 ) and basic(pH
of 9.8) colloidal silica (MasterMet 2, Buehler, IL,
USA) with a mean grain size of 0.06μm containing
H2O2 up to 3％ by wt termed as 3BCS and 3ACS
respectively. Experiments were performed on the
automatic polisher for 15 minutes under a polishing
pressure of 1 kg/cm2
, slurry dropped on a buffing
cloth (Chemomet I, Buehler, IL, USA). The
specimens Titanium ingots, 16 mm in diameter
(equivalent to JIS Class 2; T-Alloy M, GC Corp.,
Tokyo, Japan) were ultrasonically cleaned in
acetone for 5 minutes after CMP and then dried by
blowing air. Polishing behavior and surface
properties were investigated by [23] using a
commercial atomic force microscope (AFM)
(JSPM- 4210, JEOL, Tokyo, Japan), EPMA
(EPMA-8705-HII, Shimadzu,Kyoto, Japan), X-ray
photoelectron spectroscopy (XPS) (Quantum 2000,
ULVAC-PHI Inc., Chigasaki, Japan). Multiple
analysis of variance showed the effects H2O2
concentration and slurry pH on weight loss were
highly significant (p<0.01). Surface roughness
gradually decreased with increased concentration
of H2O2, independent of slurry pH. Weight loss of
Ti polished using the basic slurry was larger than
that using the acidic one and surface roughness was
less than 2 nm with basic slurry of 3 wt％ H2O2.
The thicknesses of their oxide films were estimated
to be 6.7 nm and 7.7 nm respectively. H2 O2
concentration, up to 6％by vol, resulted in higher
Ti oxidation rate and increased removal rate.
Higher pH values (2 to 6) resulted in increased Ti
removal rate. Chemical species of three kinds,
OH－, O2－ and H2O were detected on the Ti
surfaces with peak binding energy values of
530.3, 532.0 and 533.2 eV respectively. Fig 4
shows the Elemental analysis of the polished
surfaces by EPMA. Results of this study showed
that CMP using colloidal silica containing H2O2
successfully created a mirror-polished surface
without contaminated and reacted layers.
Fig. 4 SE images of the surfaces polished with
CMP and O Kα line profiles. The location of an O
Kα profiling was indicated by a line on the
corresponding SE image. (a) Treated with colloidal
silica slurry of pH 3.2 (ACS) and ACS containing 3
wt％H2O2 (3ACS). (b) Treated with colloidal silica
slurry of pH 9.8 (BCS) and BCS containing 3 wt％
H2O2 (3BCS).
The material removal rate (MRR) was
investigated by [24] to learn how long the CMP
process continues to remove a damaged layer by
mechanical polishing using 100 nm diamond and
the dependency of mechanical factors such as
pressure, velocity and abrasive concentration using
a single abrasive slurry(SAS) and focused on the
epi-ready surface with a mixed abrasive slurry
(MAS). A 6H-SiC wafer, crystallized by physical
vapor transport (PVT), colloidal silica slurry,
POLI-400 (G&P Technology CO.) was used during
the experiments. With the increased pressure,
velocity and concentration of an abrasive the MRR
also increased. SAS (only colloidal silica and
nanodiamond abrasive) and MAS (colloidal silica +
nanodiamond) were used for the SiC CMP. The
surface roughness was improved with MAS up to
2.4 Å as analyzed from AFM images. The
scratches were not completely removed and the
MRR decreased with increase in the abrasive
concentration (0.25 mg/h).The addition of
nanometre sized diamond in the MAS provided a
strong synergy between mechanical and chemical
effects. Through the experiments, chemical effect
(KOH based) was essential and the atomic-bit
mechanical removal was found to be efficient to
remove residual scratches. With increased
concentration of nano-diamond, surface roughness
and the condition of scratches were improved,
MRR was increased up to 0.6mg/h. SiC CMP
mechanism was quite different from that of
relatively softer materials to gain both high quality
surfaces and a high MRR. The reaction of wafer
surfaces by X-ray Photoelectron Spectroscopy
(XPS spectra ) of SiC substrate submerged into the
KOH based slurry for 24 hours is shown in fig 5

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Fig.5 XPS spectra of : (a) Survey and (b) Si 2p
from SiC surface of as-received and dipped in
KOH based slurry.
Xiaokai Hu et al [25] studied monodisperse
colloidal silica nanoparticles ranging from 60 to
130 nm in diameter as abrasives in chemical
mechanical planarization/polishing (CMP) process
of integrated circuit (IC) manufacturing. The
physicochemical properties of the silica
synthesized were characterized by the X-ray
diffraction (XRD) patterns and thermal analysis.
Three inch polished silicon wafers (P type and (1 1
1) orientation) were subjected to CMP testing on a
CETR CP-4 machine (CETR, Inc., Campbell, CA)
using the slurry consisting of colloidal silica with
pad made of IC1000 type with grooves, from Rohm
& Haas Co. The material removal rate (MRR) was
determined on the basis of weight loss before and
after polishing and the surface quality were
evaluated by means of the atomic force microscopy
(Q-ScopeTM250 AFM) and scanning electron
microscopy. The silica nanoparticles, amorphous in
structure as compared to crystalline quartz,
possessed a relative density of 93%. The as-grown
large sized silica nano particles applied as abrasives
in CMP slurry to polish silicon wafer, achieved
MRR of 430 nm/min and RMS roughness of less
than 0.97 nm.
The effect of particle size from 40 to 120
nm and surfactant from nonionic to anionic and
cationic on MRR and surface roughness by
chemical mechanical polishing (CMP) of glass
using colloidal silica-based slurry was explored by
Zefang Zhang et al. [26]. Four colloidal silica-
based slurries with different particle sizes from 40
to 120 nm and three typical surfactants from
nonionic to anionic and cationic were used to
investigate their effects on glass CMP. The
surfactants were selected from cationic surfactant
cetyl tri methyl ammonium bromide (CTAB),
anionic surfactant OROTAN 1124 [poly-(acrylic
acid) sodium] and nonionic surfactant AEO∼ 9
(Peregal). Two inch glass substrates of chemical
composition of SiO2 (70–73%), Na2O and K2O
(13–15%), CaO (7–12%) were polished using a
CMP tester (CETR CP4) with an IC1010 grooved
pad (Dow Electronics). The pad was conditioned
prior to each polishing for 5 min using a 4 inch
diamond grit conditioner. The polishing process
parameters at room temperature were set as
follows: pad and wafer rotation speed rotation
speed 100 rpm, relative velocity 134 cm/s, down
force 5 psi, feed rate of the slurry 120 ml/ min and
polishing time 10 min. The surface roughness was
measured from an area of 10μm×10 μm using AFM
and found surface finish of glass surfaces was
independent of the particle size. The material
removal rate strongly depended on the particle size
and the types of surfactants. The root mean square
roughness was independent of particle size and
correlated to surfactants. MRR increased with
0particle size from 40 to 60 nm but decreased with
particle size changing from 60 to 120 nm. On the
basis of polishing results, it was concluded that the
main polishing mechanism was changed from
indentation mechanism to surface-area mechanism
at the critical point of 60 nm, with the variation of
particle size. In the surfactant test, nonionic
surfactant AEO ∼ 9 showed the highest MRR,
while anionic OROTAN 1124 gave the best surface
quality. Cationic Cetyl tri methyl ammonium
bromide (CTAB) showed the lowest MRR and
worst surface quality. The molecular structure,
charge type and lubricating effect of the surfactants
played an important role in the dispersion of
abrasive particles and in the CMP performance.
Chemical mechanical polishing (CMP)
experiments were performed to study the effects of
polish pressure, pad rotational speed, polish head
rotational speed and slurry supply velocity on the
flatness, surface finish of the polished optical
silicon substrates and on the material removal rate
(MRR) [27]. Single-crystal (100) silicon substrates
with a thickness of 6 mm and a diameter of 76.2
mm(3 in.) were polished on an Okamoto SPP-
600S CMP machine, a conditioning head, a
polishing head and a ϕ600-mm polishing platen
with fabric cloth pad (3M 300LSE) on it.
Commercial colloidal silica slurry
(NYACOL®9950) was diluted with DI water and
stirred by a magnetic stirrer during the polishing
experiments. Both the specially designed carrier
and the substrate were mounted onto a backside
film of the polishing head prior to each test holding
under vacuum pressure of -90 KPa. Oscillation
motions of the polishing head and conditioning
head relative to the pad were applied with an
oscillation speed of two strokes per minute and an
oscillation width of 10 mm. The optimal process
parameter setting obtained from the design of
experiments were average MRR for the optical
silicon substrates polished at a polish pressure of
9,800 Pa was 88% higher than that at 4,900 Pa and
at a pad rotational speed of 20 rpm was 171%
higher than that at 40 rpm due to the distribution of
colloidal silica slurry in the perimeter area of the
polishing pad. The combination of a polish head
rotational speed of 20 rpm and a slurry supply
velocity of 100 ml/min resulted in the lowest
average flatness value. The goal to attain optical
silicon substrates with nanometric surface
roughness and micrometric flatness by an
optimized CMP process with a high MRR with

1344 | P a g e
reduced polishing time to only 15 min from over 8
h has been achieved.
III. CONCLUSIONS
The silica based compositions are applied
successfully for the finish polishing of Si, Ge,
GaAs, InP, variety of materials, metals, dielectrics
and other semiconductors in industries.
Experimental, theoretical ideas were considered to
develop new efficient colloidal compositions.
Investigations into the kinetics and mechanisms of
the processes proceeding by the CMP and the
development of polishing compositions and
technology (including equipment upgrading) will
progress further. The persistence of the CMP in
semiconductor technology, its competitiveness and
its compatibility with other nanotechnologies over
a long time, infer new scientific and technological
breakthroughs. Further research regarding the
influence of the diverse mixed conditions will be
continued. Imagination is the only limit to the
range of uses that scientists will find for old and
new forms of colloidal silica to contribute to CMP
and the quality of life of people around the world.
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June 2011 / Accepted: 20 September 2011
/ Published online: 4 October 2011 #
Springer-Verlag London Limited 2011

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