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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  1. 1. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451337 | P a g eCHEMICAL MECHANICAL POLISHING BY COLLOIDAL SILICASLURRYM.SIVANANDINI, DR. SUKHDEEP S DHAMI , DR. B S PABLAMechanical Department, National Institute of Technical Teachers Training and Research,Chandigarh-160019ABSTRACTChemical Mechanical Polishing is aunique process enabling technology that allowschip makers to readily drive lithographicpatterning steps to smaller dimensions, an agesold, “retro” technology related to glass polishingand metallographic finishing, thus enablingoptical lithography to work. It represents asituation that is a true paradigm shift from thetypical way in which technological advancementsbecome main stream in high-technologysemiconductor manufacturing processes.Colloidal nano-abrasives with different particlesizes are required for slurries in different CMPprocesses. Colloidal silica is used as polishingslurry for producing reflecting surfaces formirrors, lenses and the planarization ofcomputer chips. Industrial use of colloidalsilica’s is growing steadily in both traditionalareas and ever-increasing numbers of novelareas. Colloidal silica’s are found in fields asdiverse as catalysis, metallurgy, electronics,glass, ceramics, paper and pulp technology,optics, elastomers, food, health care andindustrial chromatography, polishingsophisticated microcircuit parts to outer spaceand play vital role in the safe reentry of spacevehicles and the development of Western forthat matter, world civilization. The paperfocuses a brief overview of chemical mechanicalpolishing using colloidal slurry.Keywords - Chemical Mechanical Polishing,Colloidal silica, Nanoabrasives, Slurry,SemiconductorI. INTRODUCTIONChemical mechanical polishing (CMP)technology was first put forward by Monsanto [1-3] in 1965. It is an indispensable process step insemiconductor device fabrication, commontechnique used in wafer polishing for dynamicmemory, microprocessor applications and glassmechanical polishing. It is one of the key newnanotechnology fabrication processes, a trueadvance that could be made to work despiteenormous odds and technical difficulties early on.Chemical mechanical polishing (CMP) is widelyused in the semiconductor industry [4-7] to producemirror like surfaces with no measurable subsurfacedamage. The application of scientific technologicalresults in the domain of glass polishing withsuspensions of rare earth oxides and microheterogeneous suspensions with particledimensions of 0.1–0.5 μm diameter and new ortested abrasive ultra disperse powders (UDP) havebeen attempted in electronics. The Chemicalmechanical polishing performances can beoptimized by process parameters such asequipment and consumables (pad, backing film,and slurry). One of the critical consumables in theCMP process is slurry (typically containing bothabrasives and chemicals acting together), thatdirectly affects CMP efficiency and the yield.Slight changes in slurry properties due tocontamination, chemical degradation, abrasivecontent or applied shear can change polishperformance and impact yield. Correlation ofslurry property measurements with evaluations ofwafer polish rate, planarity and defectivity providesinsight into the root cause of degradation inpolishing. The conventional slurry consists ofabrasive particles of the solid state suspended in aliquid state chemical solution [8] containing one ormore of various chemicals such as oxidizers, pHstabilizers, metal ion complexants and corrosioninhibitors [9]. An abrasive in the slurry providesboth mechanical action with nanometer-sizedabrasive particles and chemical action from thesolution additives with a synergistic effect thatcauses material removal [10,11].Through chemicaland physical actions, the abrasive-liquidinteractions play an important role in determiningthe optimum abrasives’ type, size, shape andconcentration [12]. The slurry designed for optimalperformance should produce reasonable removalrates, acceptable polishing selectivity with respectto the underlying layer, low surface defects afterpolishing and good slurry stability. Choosing slurrywhich provides good removal rates without causingdefects is of utmost importance in CMP. Colloidalsized SiO2, CeO2 and Al2O3 particles are used inthe manufacturing of CMP slurries. They areapplied in different fields, but SiO2 is promising.Alumina particles find limited used in themanufacturing of slurries for tungsten CMP; theyare slowly falling out of vogue because of theirhardness[13], Today, silica particles arepredominantly used in the preparation of slurriesfor dielectric as well as metal CMP. The use ofindustrial sols–gels of silicon acid (Monsanto
  2. 2. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451338 | P a g eComp, Dupoint, Nalco Ch et al.) and ofcompositions based on aerosol type UDP SiO2(Siemens,Degussa) and Al2O3 (Union CarbideCorp.) led to the development of colloidal silica.Robert Walsh (Monsanto), patent and publicationsof other authors (H. Dersin, I.S. Basi, R.L.Lachapelle, et al.) up to the beginning of eightiescontributed to development in microelectronicswith the development of colloidal silica sol andsilica gel. In this paper a brief review of CMPprocess using colloidal silica slurry is presented.II. COLLOIDAL SILICA SLURRYThe silica slurries are typical consumablematerials for CMP. The colloidal silica and fumedsilica are known as the representative CMP slurrymaterials. Colloidal silica polishing suspensions areunique because they provide both dispersing actionas well as a chemical mechanical polishing (CMP)action. It is effective as an additive for theintermediate diamond polishing of metals and isalso the best polishing abrasive for eliminatingsubsurface and surface because of its CMPpolishing action. These polishes are chemicallystabilized to produce a nearly “perfect suspension”;can also have additives that minimize the effect ofparticle aggregation of crystallization. Thedistribution of colloidal silica has an importanteffect on polishing rate and polished surfaceroughness.In 2001, the effects of temperature, slurrypH, applied pressure and polishing rotation rate onthe material removal rate during chemicalmechanical polishing (CMP) of 4H-silicon carbidewafers using colloidal silica slurry andpolyurethane/polyester fiber polishing pads havebeen studied by Neslen C.L et al [14]. The waferswere polished for 30 or 60 mins using a StrasbaughPrecision Polishmaster with a random motionpolishing armature. Polishing at wafer temperaturesof 230C and 650C were performed and found thatincreased temperatures had no significantimprovements in removal rate. The polishing slurrypH levels for the 90 rpm study were similar to 60rpm, showed that material removal rate was notaffected by pH. Increased applied pressure resultedin accelerated removal of wafer material. Theaverage removal rate over the four-hour periodusing a 9.9 pH polishing slurry was 139 Å/hourwhile an pH 11 polishing slurry was only 108Å/hour., the variability in the removal rate during150 rpm was high and ranged from 298 Å/hourduring the second 30 min polish to 1860 Å/hourduring the last 30 min polishing interval due to theinability to maintain a constant amount of polishingsolution on the pad during the polishing interval.Excessive pressure resulted in damage of polishingpad and increased wafer preparation costs.Polishing pad rotational speeds had the greatestimpact on wafer material removal rates with anassociated increase in removal rate variability. Theauthors concluded that additional rotational speedstudies would be useful to maximize materialremoval rate with decreased variabilityThe effects of phosphoric acid addition onslurry for chemical–mechanical planarization(CMP) of copper and tantalum nitride wereinvestigated by [15]. Alumina or colloidal silica asan abrasive, organic acid as a complexing agent,Hydrogen peroxide (H2O2) an oxidizing agent, afilm forming agent, a pH control agent andadditives, phosphoric acid (H3PO4) as acceleratorof the tantalum nitride as well as hydrogenperoxide as stabilizer were used. Experiments wereperformed on G&P Technology POLI-500CEkchemical–mechanical polisher ,Rodel IC-1400 k-groove polyurethane pad with the head speed andthe table speed 40 rpm, down pressure of the head7 psi , slurry flow rate 150 ml/min, polishing for 1min on electroplated copper, sputtered tantalumnitride, PETEOS wafer with 10,000 A° thickness.Zeta potential and particle size measurement of theslurries were carried out by using the BrookhavenZetaPlus instrument. An acceleration of thetantalum nitride CMP was verified byelectrochemical curves recorded with an EG and G273A potentiostat. The slurry of 5.0% by wt.abrasive, 5.0% by wt hydrogen peroxide, 0.5% bywt. phosphoric acid had good H2O2 stability andTaN acceleration and dispersion ability. Henceslurry including phosphoric acid was proposed.Hong Lei prepared novel colloidal SiO2slurry, a carboxylic acid containing a long alkylchain as lubricant additive, for the chemical–mechanical polishing of disk substrates with NiPplated [16]. Polishing tests were conducted withSPEEDFAM-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 70g/cm2, rotating speed of 25 rpm, processingduration of 8.5 min and slurry supplying rate of300 ml/min on work pieces of 95 mm/1.25mmaluminum alloy substrates with NiP plated about 85wt. % nickel and 15 wt. % phosphorus element.Prepared slurry of 6 wt. % SiO2 particles with anaverage diameter of 30 nm, 1 wt. % ferric oxidizerand 2 wt. % lubricants in DI water at pH value of1.8, exhibited smoother polished surface. Theabrasive particle size, contents of oxidizer,lubricant additive and abrasive particle contained inthe prepared colloidal SiO2 slurry as well as pHvalue of the slurry, had strong impact on theaverage roughness (Ra), the average waviness (Wa)and material removal rate. Better surface qualityresulted, with smaller SiO2 size, moderate SiO2concentration, lower oxidizer content, higherlubricant content and moderate pH value under the
  3. 3. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451339 | P a g etesting conditions, while the high material removalrate with large size SiO2 , high particle, oxidizercontents and low lubricant content.The chemical mechanical polishing(CMP) of aluminum and photo resist usingcolloidal silica-based abrasive (average ∼20 nmdiameter,Ace Hitech) ,effects of varying slurry pH,silica concentration and oxidizer concentration onsurface roughness(Rv) and removal rate wereinvestigated by [17] in order to determine theoptimum conditions for these parameters.Experimentation was conducted on a modifiedMotopol 2000 polishing system from Buehler Co.with Polytex Supreme pad from Rodel. H3PO4 andKOH were added to adjust the pH of colloidalsilica with de-ionized water. In the Al CMP, H2O2was used as an oxidizer. In all experiments, thepolishing pressure was 30 kPa, the linear polishingvelocity was 15 m/min and the slurry flow rate of12 ml/min with polishing times of 4 and 1 min forAl and PR respectively. The measurement wascarried out under a sampling length of 10 mm, a cutoff length of 0.08 mm and a scanning speed of25m/s by Dektak (Veeco Instruments).The removalrate of Al was measured by a four-point probe(Chang Min Tech) and PR removal rate wasmeasured under a wave length of 480 nm and areflective index of 1.63 by a NanoSpec(Nanometrics). The Rv values of the Al and PRsurfaces before the CMP were 39.4 and 7.85 nm,respectively. The results of the CMP of thealuminum with the colloidal silica-based slurrywere good with small micro-scratch size when Rv≤ 10 nm and large removal rate for the slurry pH of2–4 and the oxidizer H2O2 concentration 1–3% byvol. The colloidal-based silica slurry produced adesirable fine Al surface with few micro-scratchessimilar to filtered alumina-based slurry, butproduced a photo resist surface with many micro-scratches as shown in table.1. The Fig1a, 1b andFig 2a, 2b represent roughness and removal rate ofAl and PR as function of slurry pH and SiO2concentration.Table: 1Fig 1.aFig 1.bFig.2 aFig.2 aFig. 2bNew semi-abrasive free slurry for copperchemical mechanical planarization (CMP) wasinvestigated through the addition of acid colloidalsilica below 0.5% by wt, hydrogen peroxide andother additives by [18]. The additives as stabilizersfor hydrogen peroxide as well as accelerators intantalum nitride CMP were also evaluated.Experimentation was carried on G&P TechnologyPOLI-500CETM chemical mechanical polisherusing Rodel IC-1400 k-groove polyurethane pad.Electroplated copper wafer with 1600 nm,sputtered tantalum nitride wafer, PETEOS wafer
  4. 4. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451340 | P a g ewith 1000 nm thickness were used for polishing.SKW 6-3 copper wafer was used as a patternedwafer with 0.25 μm minimum feature size. For thepolishing, down pressure of the head 4.3 psi, slurryflow rate 300 ml/min, head speed and table speedwas set at 50 rpm. The Zeta potential and particlesize measurement of the slurries were carried outusing Brookhaven ZetaPlus instrument.Electrochemical curves were recorded with EG&G273A Potentiostat. Metal impurities measurementof the slurry was carried out by PerkinElmer ICP-Mass instrument. Zeta potential change of colloidalsilica in slurries with and without the addition ofadditives as a function of pH is shown in Fig. 3.When surfactant was added to colloidal silicaslurry, zeta potential increased from 0 and a suddenreversal of charges was observed in pH 2–3 range.Particle dispersion with the chemical-addedcolloidal silica slurry in pH 2.5 was stable during90 days. A copper wafer dipped in chemical addedcolloidal silica slurry was clearer than a waferdipped in the slurry without the chemicals. Goodhydrogen peroxide stability, excellent colloidalsilica dispersion ability and easiness of post-CMPcleaning were provided by the semi-abrasive freeslurry. The extent of enhancement in tantalumnitride CMP was verified through anelectrochemical test. Ammonium and aminebecame very stable, indicating that decompositionrate was below 0.001 wt%/day. So this type ofslurry was formulated in a single package ratherthan conventional, uncomfortable two-packagesystem due to unstable hydrogen peroxide.Figure 3 Zeta potentials of copper, colloidal silicaand chemical added colloidal silicaShao-Yu Chiu et al. [19] investigated the removalmechanism of Cu-CMP on the characteristics ofcolloidal-silica-based slurry. All polishingexperiments were performed with (100) oriented,6-inch-diameter p-type Si wafers. The polishingsample was stacked with 900-nm-thick, 50-nm-thick Cu and Ta respectively. Multi-step chemicalmechanical polishing (CMP) with different copperremoval rates and polishing pads was used toeliminate topography efficiently and to reducemicro-scratches on copper films. Cu-CMP wasperformed with a Westech Model 372M polisherusing a Politex Regular E. pad. Polishingparameters such as down force, platen/carrierrotary speed, back pressure and slurry flow ratewere set to be 5 psi, 42/45 rpm, 2 psi and 150ml/min respectively. Polishing slurries with dilutedcolloidal silica (<50 nm in size) 10% by wt, 10 wt.%H2O2 (30 wt. % semiconductor grade), Potassiumhydroxide (KOH), ammonium hydroxide (NH4OH)and tetra-methylammonium hydroxide (TMAH)were used as slurry pH adjusters. A laserdiffraction particle size analyzer, UP-150 was usedto measure the aggregation size of abrasives inslurries. In colloidal-silica-based slurry, thepolishing behaviors of copper, tantalum and silicondioxide were found to relate to alkaline additives.The size of cations from alkaline additivesinfluenced the zeta potential of slurries, so as tovary the material removal rate. It was found that thepolishing behavior of Cu, Ta and oxide was deeplydependant on the slurry pH and the surface charge-related interactions between the slurry and thepolishing substrate. The maximum removal rate ofCu was above130 nm/min at pH2. As slurry pHincreased into neutral regime, the removal rate ofCu dropped by formation of Cu oxide passivation(Cu2O, CuO). The attraction and expulsive forceaffected the impacting frequency between colloidalsilica abrasives and the wafer surface. The iso-electric potential of colloidal-based slurries wasaround pH2 which led to higher Ta removal rate.NH3 dissolved Cu oxide passivation and formed Cu(NH3)42+to enhance the removal rate of copper.The removal rate was about 225nm/min for Cu and80nm/min for Ta at pH9.2. With more NH4OHadded into the slurry at pH10, the removal rate wasenhanced to 1490 nm/min for Cu and 100nm/minfor Ta. Large-size cations led to less impactingfrequency between the abrasives and the substrate,to get lower removal rate. KOH was found to be asuitable pH adjuster for the colloidal-silica-basedslurry. High or low removal selectivity of Ta/Cuand SiO2/Cu during the two-step Cu-CMP processcould be achieved by modified colloidal-silica-based slurries with proper alkaline additives andpH values.The effects of varying the size and theconcentration of the abrasive in colloidal silicaslurry and the concentration of tetra-methylammonium hydroxide (TMAH) were investigatedin terms of the oxide film loss, the removal rate, theroughness of the film surface and polysilicon-to-oxide film removal selectivity. These effects wereinvestigated [20] performing chemical mechanicalpolishing (CMP) experiments under polishingpressure 13.8 to 41.4kPa, relative velocity betweenthe pad and the wafer 0.539 m/s and the polishingtime 30 s on conventional 8” silicon wafers
  5. 5. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451341 | P a g eprepared by using the single side polishing method.Nanoscale colloidal silica slurries (PL-3 and PL-7,Fuso Chemical Inc., Japan) containing twodifferent spherical abrasive particles with primarysizes of 30 and 70 nm were used in theseexperiments. The colloidal silica slurry wasdispersed in deionized water and stabilized byadding 0.06 wt% of a commercially availablenonionic organic polymer (poly(acrylamide),PAAM) along with quaternary ammoniumhydroxide compound (TMAH) up to 0.52 wt% ,wet etchants for polysilicon, a cellulosic polymer(hydroxyethyl cellulose, HEC), molecular weightof 50,000, at a constant concentration of 0.001wt%was optionally added. The morphology of thecolloidal silica abrasives was observed with a high-resolution transmission electron microscope(HRTEM; JEM-2010, JEOL, Japan). Thesecondary particle size was measured by usingacoustic attenuation spectroscopy (APS-100, MatecApplied Sci., U S A.). The surfactant pH wasmeasured with an advanced benchtop pH meter(Orion-525A, Thermo Orion, U.S.A.). Therheological behavior of the slurry suspensionsexamined with a controlled-stress viscometer(MCR300, Paar Physica, Germany). Average size,pH and conductivity increased with the TMAHconcentration. The removal rate of the polysiliconfilm reduced with high pH value in the range of 10to 12 due to change in the polysilicon surface fromhydrophobic to hydrophilic. The abrasive behaviorin the slurry was less affected by abrasive size andTMAH concentration. Higher polysilicon to oxideremoval selectivity was directly related to thezetapotential curves of the oxide , polysilicon filmsand the modified abrasive particles in the colloidalsilica slurry. It was found that with increasingTMAH concentration, the removal rate and thepolysilicon-to-oxide selectivity were reduced afteran initial increase, regardless of the abrasive size inthe slurry. Within a TMAH concentration range of0.06 to 0.52 wt%, the removal selectivity at a lowerabrasive concentration for abrasive size of 30 nmwas slightly higher than for higher abrasiveconcentration in case of a smaller abrasive, but inthe case of a larger abrasive the removal selectivitywas almost independent of the abrasiveconcentrations. The oxide removal rate wasmaintained at 40 to 60 °A/min during the polishingprocess. At a lower TMAH concentration thesurface roughness, became worse. The resultsqualitatively suggested a mechanism in which OH−ions bonded to the Si surfaces of the abrasives inthe slurry and attached to the surface of thepolysilicon film.In paper [21], the polishing mechanism ofLN , discussed based on the results of an integratedanalysis considering mechanical, chemical andthermal factors. Research and development CMPequipment, POLI-400 (G&P Technology Co.), wasused in the experiments. The slurry was formulatedby adding colloidal silica abrasive (average ~120nm diameter, pH 10.7, Ace Hitech Co.) and afoamed crosslinked polymer pad, IC 1400 k-groove(Rohm & Hass Corp.), was used. The MaterialRemoval Rate (MRR) was investigated by XPS andnano-indenter analysis. The MRR increased withlow pH slurry in both cases with H3PO4 and HNO3.HNO3 had a stronger effect on the MRR thanH3PO4. High quality surfaces (Ra < 2 nm) wereobtained with pH 3 and 7. The higher abrasiveconcentration and low pH slurry induced highMRR. The flow rate was controlled from 50cc/minute to 500 cc/minute (50, 100, 300, 500cc/minute) in the experiments. As the flow ratedecreased, the material removal rate increased dueto frictional heat, the thermal energy and chemicalactivation energy. The reaction layer formed on theLN surface showed a variation of hardness withNbO2, Nb2O5 and changed MRR.The optimum condition selection of ultra precisionwafer polishing and the effect of polishingparameters on the surface roughness, temperaturevariation were evaluated by Eun-Sang Lee etal.[22] using central composite designs such as theBox-Behnken method, one of response surfaceanalyses. The polishing process was performedover the whole wafer surface when the polishingpad rotational velocity and wafer rotationalvelocity was same. silicon wafer 4-inch,environmental temperature 21.5℃, humidity 43%,Polyurethane based Suba 600 made by Rodel polishing pad and commercial colloidal silicabased slurry with particle size in the 50- 70 nmrange were used. Pressure, wheel speed and processtime which were used as factors in this experimentaffected surface roughness of wafer under the finalpolishing processes. A second-order regressionequation for the surface roughness was developedfrom the experimental data. The regressionequation induced by response surface model wasevaluated to select proper polishing conditions withconstraints of the surface roughness. The effect ofchanging final polishing parameters on the surfaceroughness has been investigated and the idealoptimum condition has been researched. At eachranges of pressure, with increase in wheel speedand process time, surface roughness decreasedinitially and then increased. Optimum condition forsurface roughness was 0.2MPa of pressure, 30 rpmof wheel speed and 10 minutes of process time.The frictional heat between polishing pad andwafer during the final wafer polishing increasedwith range increment of each process parameters.As the temperature increased, there was increase ofthe effect by a chemical reaction and a variation ofpH so that the removal rate of wafer increased inproportion to the temperature. The temperature
  6. 6. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451342 | P a g eelevation affected the increase of the removalrate.Chemical mechanical polishing (CMP) ofcommercially pure Titanium (Ti) was carried outusing two types of slurries, acidic (pH of 3.2adjusted by H3PO4 and NH4 H2 PO4 ) and basic(pHof 9.8) colloidal silica (MasterMet 2, Buehler, IL,USA) with a mean grain size of 0.06μm containingH2O2 up to 3% by wt termed as 3BCS and 3ACSrespectively. Experiments were performed on theautomatic polisher for 15 minutes under a polishingpressure of 1 kg/cm2, slurry dropped on a buffingcloth (Chemomet I, Buehler, IL, USA). Thespecimens Titanium ingots, 16 mm in diameter(equivalent to JIS Class 2; T-Alloy M, GC Corp.,Tokyo, Japan) were ultrasonically cleaned inacetone for 5 minutes after CMP and then dried byblowing air. Polishing behavior and surfaceproperties were investigated by [23] using acommercial atomic force microscope (AFM)(JSPM- 4210, JEOL, Tokyo, Japan), EPMA(EPMA-8705-HII, Shimadzu,Kyoto, Japan), X-rayphotoelectron spectroscopy (XPS) (Quantum 2000,ULVAC-PHI Inc., Chigasaki, Japan). Multipleanalysis of variance showed the effects H2O2concentration and slurry pH on weight loss werehighly significant (p<0.01). Surface roughnessgradually decreased with increased concentrationof H2O2, independent of slurry pH. Weight loss ofTi polished using the basic slurry was larger thanthat using the acidic one and surface roughness wasless than 2 nm with basic slurry of 3 wt% H2O2.The thicknesses of their oxide films were estimatedto be 6.7 nm and 7.7 nm respectively. H2 O2concentration, up to 6%by vol, resulted in higherTi oxidation rate and increased removal rate.Higher pH values (2 to 6) resulted in increased Tiremoval rate. Chemical species of three kinds,OH-, O2- and H2O were detected on the Tisurfaces with peak binding energy values of530.3, 532.0 and 533.2 eV respectively. Fig 4shows the Elemental analysis of the polishedsurfaces by EPMA. Results of this study showedthat CMP using colloidal silica containing H2O2successfully created a mirror-polished surfacewithout contaminated and reacted layers.Fig. 4 SE images of the surfaces polished withCMP and O Kα line profiles. The location of an OKα profiling was indicated by a line on thecorresponding SE image. (a) Treated with colloidalsilica slurry of pH 3.2 (ACS) and ACS containing 3wt%H2O2 (3ACS). (b) Treated with colloidal silicaslurry of pH 9.8 (BCS) and BCS containing 3 wt%H2O2 (3BCS).The material removal rate (MRR) wasinvestigated by [24] to learn how long the CMPprocess continues to remove a damaged layer bymechanical polishing using 100 nm diamond andthe dependency of mechanical factors such aspressure, velocity and abrasive concentration usinga single abrasive slurry(SAS) and focused on theepi-ready surface with a mixed abrasive slurry(MAS). A 6H-SiC wafer, crystallized by physicalvapor transport (PVT), colloidal silica slurry,POLI-400 (G&P Technology CO.) was used duringthe experiments. With the increased pressure,velocity and concentration of an abrasive the MRRalso increased. SAS (only colloidal silica andnanodiamond abrasive) and MAS (colloidal silica +nanodiamond) were used for the SiC CMP. Thesurface roughness was improved with MAS up to2.4 Å as analyzed from AFM images. Thescratches were not completely removed and theMRR decreased with increase in the abrasiveconcentration (0.25 mg/h).The addition ofnanometre sized diamond in the MAS provided astrong synergy between mechanical and chemicaleffects. Through the experiments, chemical effect(KOH based) was essential and the atomic-bitmechanical removal was found to be efficient toremove residual scratches. With increasedconcentration of nano-diamond, surface roughnessand the condition of scratches were improved,MRR was increased up to 0.6mg/h. SiC CMPmechanism was quite different from that ofrelatively softer materials to gain both high qualitysurfaces and a high MRR. The reaction of wafersurfaces by X-ray Photoelectron Spectroscopy(XPS spectra ) of SiC substrate submerged into theKOH based slurry for 24 hours is shown in fig 5
  7. 7. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451343 | P a g eFig.5 XPS spectra of : (a) Survey and (b) Si 2pfrom SiC surface of as-received and dipped inKOH based slurry.Xiaokai Hu et al [25] studied monodispersecolloidal silica nanoparticles ranging from 60 to130 nm in diameter as abrasives in chemicalmechanical planarization/polishing (CMP) processof integrated circuit (IC) manufacturing. Thephysicochemical properties of the silicasynthesized were characterized by the X-raydiffraction (XRD) patterns and thermal analysis.Three inch polished silicon wafers (P type and (1 11) orientation) were subjected to CMP testing on aCETR CP-4 machine (CETR, Inc., Campbell, CA)using the slurry consisting of colloidal silica withpad made of IC1000 type with grooves, from Rohm& Haas Co. The material removal rate (MRR) wasdetermined on the basis of weight loss before andafter polishing and the surface quality wereevaluated by means of the atomic force microscopy(Q-ScopeTM250 AFM) and scanning electronmicroscopy. The silica nanoparticles, amorphous instructure as compared to crystalline quartz,possessed a relative density of 93%. The as-grownlarge sized silica nano particles applied as abrasivesin CMP slurry to polish silicon wafer, achievedMRR of 430 nm/min and RMS roughness of lessthan 0.97 nm.The effect of particle size from 40 to 120nm and surfactant from nonionic to anionic andcationic on MRR and surface roughness bychemical mechanical polishing (CMP) of glassusing colloidal silica-based slurry was explored byZefang Zhang et al. [26]. Four colloidal silica-based slurries with different particle sizes from 40to 120 nm and three typical surfactants fromnonionic to anionic and cationic were used toinvestigate their effects on glass CMP. Thesurfactants were selected from cationic surfactantcetyl tri methyl ammonium bromide (CTAB),anionic surfactant OROTAN 1124 [poly-(acrylicacid) sodium] and nonionic surfactant AEO∼ 9(Peregal). Two inch glass substrates of chemicalcomposition of SiO2 (70–73%), Na2O and K2O(13–15%), CaO (7–12%) were polished using aCMP tester (CETR CP4) with an IC1010 groovedpad (Dow Electronics). The pad was conditionedprior to each polishing for 5 min using a 4 inchdiamond grit conditioner. The polishing processparameters at room temperature were set asfollows: pad and wafer rotation speed rotationspeed 100 rpm, relative velocity 134 cm/s, downforce 5 psi, feed rate of the slurry 120 ml/ min andpolishing time 10 min. The surface roughness wasmeasured from an area of 10μm×10 μm using AFMand found surface finish of glass surfaces wasindependent of the particle size. The materialremoval rate strongly depended on the particle sizeand the types of surfactants. The root mean squareroughness was independent of particle size andcorrelated to surfactants. MRR increased with0particle size from 40 to 60 nm but decreased withparticle size changing from 60 to 120 nm. On thebasis of polishing results, it was concluded that themain polishing mechanism was changed fromindentation mechanism to surface-area mechanismat the critical point of 60 nm, with the variation ofparticle size. In the surfactant test, nonionicsurfactant AEO ∼ 9 showed the highest MRR,while anionic OROTAN 1124 gave the best surfacequality. Cationic Cetyl tri methyl ammoniumbromide (CTAB) showed the lowest MRR andworst surface quality. The molecular structure,charge type and lubricating effect of the surfactantsplayed an important role in the dispersion ofabrasive particles and in the CMP performance.Chemical mechanical polishing (CMP)experiments were performed to study the effects ofpolish pressure, pad rotational speed, polish headrotational speed and slurry supply velocity on theflatness, surface finish of the polished opticalsilicon substrates and on the material removal rate(MRR) [27]. Single-crystal (100) silicon substrateswith a thickness of 6 mm and a diameter of 76.2mm(3 in.) were polished on an Okamoto SPP-600S CMP machine, a conditioning head, apolishing head and a ϕ600-mm polishing platenwith fabric cloth pad (3M 300LSE) on it.Commercial colloidal silica slurry(NYACOL®9950) was diluted with DI water andstirred by a magnetic stirrer during the polishingexperiments. Both the specially designed carrierand the substrate were mounted onto a backsidefilm of the polishing head prior to each test holdingunder vacuum pressure of -90 KPa. Oscillationmotions of the polishing head and conditioninghead relative to the pad were applied with anoscillation speed of two strokes per minute and anoscillation width of 10 mm. The optimal processparameter setting obtained from the design ofexperiments were average MRR for the opticalsilicon substrates polished at a polish pressure of9,800 Pa was 88% higher than that at 4,900 Pa andat a pad rotational speed of 20 rpm was 171%higher than that at 40 rpm due to the distribution ofcolloidal silica slurry in the perimeter area of thepolishing pad. The combination of a polish headrotational speed of 20 rpm and a slurry supplyvelocity of 100 ml/min resulted in the lowestaverage flatness value. The goal to attain opticalsilicon substrates with nanometric surfaceroughness and micrometric flatness by anoptimized CMP process with a high MRR with
  8. 8. M.Sivanandini, Dr. Sukhdeep S Dhami , Dr. B S Pabla / International Journal of EngineeringResearch and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp.1337-13451344 | P a g ereduced polishing time to only 15 min from over 8h has been achieved.III. CONCLUSIONSThe silica based compositions are appliedsuccessfully for the finish polishing of Si, Ge,GaAs, InP, variety of materials, metals, dielectricsand other semiconductors in industries.Experimental, theoretical ideas were considered todevelop new efficient colloidal compositions.Investigations into the kinetics and mechanisms ofthe processes proceeding by the CMP and thedevelopment of polishing compositions andtechnology (including equipment upgrading) willprogress further. The persistence of the CMP insemiconductor technology, its competitiveness andits compatibility with other nanotechnologies overa long time, infer new scientific and technologicalbreakthroughs. Further research regarding theinfluence of the diverse mixed conditions will becontinued. Imagination is the only limit to therange of uses that scientists will find for old andnew forms of colloidal silica to contribute to CMPand the quality of life of people around the world.REFERENCES[1] Walsh R J, Herzog A.H “Process forpolishing semiconductor materials” [p]U.S.3170273,1965.2.23[2] Chen W C, Lin S C, Dai Bau ,Tong Tsai,Ming Shih “Chemical MechanicalPolishing of low dielectric constantpolymers: hydrogen silesquioxane andmethyl silesquioxane”[J]. J.Electrochem.Soc, 1999, 146(8) 3004-3008.[3] Hara Tohru,Tomisawa Tomohiro,KurosuToshiaki ,Doy Toshiro K “ChemicalMechanical polishing of polyarylether lowdielectric constant layers by manganeseoxide slurry”[J] J. Electrochem. Soc 1999146(6) : 2333-23336[4] J.F. Luo, and D.A. Dornfeld, IEEE Trans.Semiconduct. Manufact 16[1] (2003) 45-56.[5] Y.L. Liu, K.L. Zhang, and F. Wang,Micro electronic Engineering 66[1-4](2003) 438-444.[6] P.B. Zantye, A. Kumar, and A.K. Sikder,Materials Science and Engineering R45[3-6] (2004) 89-220.[7] P.H. Chen, B.W. Huang, and H.-C. Shih,Thin Solid Films 476[1] (2005) 130-136.[8] Y. Kamigata, Y. Kurata, K. Masuda, J.Amanokura, M. Yoshida, M. Hanazono,Mater. Res. Soc. Symp. Proc. 671 (2001)M13.[9] Muthukumaran, A. (2008): “ChemicalSystems for Electrochemical MechanicalPlanarization of Copper and TantalumFilms”, Doctoral Dissertation, TheUniversity of Arizona.[10] M.R. Oliver, “Chemical-MechanicalPlanarization of SemiconductorMaterial”, Springer-Verlag, Berlin,Germany (2004).[11] G. Yehiel and R. Kistler, Electrochemical198th Society Meeting Abstracts, 2000-2,496 (2000).[12] R. Carpio, J. Farkas, R. Jairath, Thin SolidFilms 266 (1995) 238.[13] Lei Hong, Chu Yuliang,Tu ,Xifu”Preparation of ultra-fined Al2O3 slurryand its polishing properties on diskCMP”,[J] Journal of FunctionalMaterials,2005, 36(9):1 425–1 428. (inChinese)[14] C.L. Neslen, W.C. Mitchel, R.L.Hengehold “Effects of Process ParameterVariations on the Removal Rate inChemical Mechanical Polishing of 4H-SiC”, Journal of Electronic Materials,Vol.30, No. 10, 2001[15] Nam-Hoon Kim, Jong-Heun Lim, Sang-Yong Kim, Eui-Goo Chang “Effects ofphosphoric acid stabilizer on copper andtantalum nitride CMP” , Materials Letters57 (2003) 4601– 4604[16] Hong Lei, Jianbin Luo “CMP of hard disksubstrate using a colloidal SiO2 slurry:preliminary experimental investigation” ,Wear 257 (2004) 461–470[17] Yoomin Ahn, Joon-Yong Yoon , Chang-Wook Baek, Yong-Kweon Kim“Chemical mechanical polishing bycolloidal silica-based slurry for micro-scratch reduction” , Wear 257 (2004)785–789[18] Nam-Hoon Kim, Jong-Heun Lim, Sang-Yong Kim, Eui-Goo Chang “Semi-abrasive free slurry with acid colloidalsilica for copper chemical mechanicalplanarization” , Journal Of MaterialsScience: Materials In Electronics 16(2005) 629– 632[19] Shao-Yu Chiu , Ying-Lang Wang, Chuan-Pu Liu, Shih-Chieh Chang, Gwo-JenHwang, Ming Shiann Feng, Chia-FuChen, “High-selectivity damascenechemical mechanical polishing” ThinSolid Films 498 (2006) pp.60 – 63[20] Kyung-Woong Park, Hyun-Goo Kang,Manabu Kanemoto and Jea-Gun Park“Effects of the Size and the Concentrationof the Abrasive in a Colloidal Silica(SiO2) Slurry with Added TMAH onRemoval Selectivity of Polysilicon andOxide Films in Polysilicon ChemicalMechanical Polishing” , Journal of the
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