An Approach to Slurry Characterization for CMP

An Approach to Slurry Characterization for CMP

An Approach to Slurry Characterization for CMP


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<strong>An</strong> <strong>Approach</strong> <strong>to</strong> <strong>Slurry</strong> <strong>Characterization</strong> <strong>for</strong> <strong>CMP</strong>Yoshitaka Morioka, Masaharu Kinoshita, Shinichi HabaNitta Haas Incorporated172,IKEZAWA,YAMATOKORIYAMA,JAPANPhone:+81-743-56-8241, Fax:+81-743-56-1297e-mail: , ymorioka@nittahaas.co.jp mkinoshita@nittahaas.co.jpAbstractNodular colloidal silica is proposed <strong>to</strong> be used as a consumable material <strong>for</strong> the<strong>CMP</strong>. The typical spherical colloidal silica slurry is effective in decreasing thedefect level of the interlayer dielectric (ILD) film during <strong>CMP</strong>, but the removalrate is also decreased. Hence, the nodular colloidal silica slurry has beendeveloped <strong>for</strong> the purpose of improving the per<strong>for</strong>mance on <strong>CMP</strong> process. Thesurface characteristics of the silica particles are considered <strong>to</strong> affect the removalrate of ILD film and the planarity of W <strong>CMP</strong> process etc. These <strong>CMP</strong>per<strong>for</strong>mances are recognized <strong>to</strong> depend on the different characteristics betweenthe spherical colloidal and fumed silica.KEYWORDS: <strong>CMP</strong>, removal rate, nodular colloidal silica slurry, sphericalcolloidal silica, fumed silica, p-TEOS, surface morphology, W <strong>CMP</strong>1. IntroductionThe silica slurries are typical consumable materials <strong>for</strong> <strong>CMP</strong>. The colloidalsilica and fumed silica are known as the representative <strong>CMP</strong> slurry materials.During the ILD film <strong>CMP</strong> using the colloidal silica slurry, the surface showsbetter quality than that using the fumed silica slurry. It is considered that thespherical shape of colloidal silica particles is effective <strong>for</strong> polishing withoutcausing defects and scratches. However, the removal rate of the colloidal silicaslurry would be decreased due <strong>to</strong> the lower friction between the silica particlesand the substrate during <strong>CMP</strong>.[1] In order <strong>to</strong> overcome the low removal ratedisadvantage of the colloidal silica slurry, the nodular shaped colloidal silicaslurry has been developed <strong>for</strong> improving the removal rate of ILD film polishing.The nodular colloidal silica slurry is made by the sol-gel method. It is consideredthat the nodular shape of colloidal silica is <strong>for</strong>med at the particle growth step.Additionally, it is confirmed that the surface of the nodular colloidal silicaconsists of a more porous layer than that of the typical colloidal silica.[2]However, the nodular colloidal silica polishing per<strong>for</strong>mance on the semiconduc<strong>to</strong>rsubstrate, in comparison <strong>to</strong> the typical colloidal silica, has not been reported.In this study, the relationship between the <strong>CMP</strong> per<strong>for</strong>mance and the surfaceshape of the particle, the dispersibility and the associative ratio of nodularcolloidal silica are discussed by comparing the nodular colloidal silica with thetypical spherical colloidal silica. It is considered that the surface shapes ofsilica particles should affect the removal rate during <strong>CMP</strong>. The surface oftypical colloidal silica is covered with many silanol bonds which are sensitive <strong>to</strong>the pH change, and particularly, can be swollen by neutralization at high pH usingan alkaline additive. [3] There<strong>for</strong>e, the pH change should be one of the effectivefac<strong>to</strong>rs on the <strong>CMP</strong> per<strong>for</strong>mance because of the silica particle surface morphologyvariation.In this study, we confirmed the effect of the associative ratio and the surface153 PacRim-<strong>CMP</strong> 2004

morphology of the nodular colloidal silica with the pH change on the <strong>CMP</strong>per<strong>for</strong>mances of ILD film and tungsten. The pH values <strong>for</strong> the optimum polishingcondition are also proposed.2. Experiments and ProceduresFor the evaluation of <strong>CMP</strong> <strong>for</strong> p-TEOS film, all silica slurries were prepared using12 wt% silica solid contents and adjusted using 29 wt% NH 4 OH or 0.5N HCl frompH 2.0 <strong>to</strong> pH 10.5.For the evaluation of <strong>CMP</strong> <strong>for</strong> tungsten, the abrasive concentrations of silicaslurries were diluted at 1wt%,3wt% and 5wt% using Iodate oxidizer.IC1400 from Nitta-Haas was used as the polishing pad.Ecomet 3 was used <strong>for</strong> ILD and tungsten <strong>CMP</strong>.3. Results and DiscussionFig. 1 shows the removal rate of p-TEOS <strong>CMP</strong> with silica slurries between pH2.0 and pH 10.5.180The removal rate of nodular colloidal silicaNodular colloidal silica160is maximized <strong>to</strong> 127 nm/min at pH 2.0 andSpherical colloidal silica140 Fumed silicaminimized <strong>to</strong> 33 nm/min at pH 7.0. The120removal rate of spherical colloidal silica is100also maximized <strong>to</strong> 94 nm/min at pH 2.0 and80minimized <strong>to</strong> 22 nm/min at pH 7.0. The60removal rate of fumed silica is 55 nm/min40at pH 2.0, minimized <strong>to</strong> 31 nm/min at pH204.0, and maximized <strong>to</strong> 154 nm/min at pH00 2 4 6 8 10 1210.5. The increase tendencies of removalpHrates at pH 10.5 compared <strong>to</strong> lower pHFig. 1Dependence of Removal rate on pHdepends on the chemical etching of p-TEOSfilm in the alkaline condition.It is found that the tendencies of removal rates of all samples are different withpH change and are also reversed in the acidic and alkaline conditions.This means that the mechanical characteristics of silica particles are also variedwith the pH change, and the <strong>CMP</strong> per<strong>for</strong>mance might depend on the surface shapesof the abrasive silica particles in the slurry. In particular, the removal rate ofnodular colloidal silica becomes lower compared with that of spherical colloidalsilica and fumed silica in the alkaline condition. It is considered that thisphenomenon should be affected by the friction <strong>for</strong>ce between the nodular colloidalsilica and TEOS film which might decrease during <strong>CMP</strong> because the surface ofnodular colloidal silica is swollen with NH 4 OH.In order <strong>to</strong> evaluate the physical removal rate fac<strong>to</strong>r of p-TEOS film, the <strong>CMP</strong>test was carried out using various silica abrasive concentrations.Fig. 2(a) shows the FESEM image ofnodular colloidal silica treated with HCl atpH 2.0. The surface of nodular particlestreated with HCl is covered by the porousand the rough layers, and it is not likely <strong>to</strong>100nm100nmbe swollen. Fig. 2(b) shows the FESEMimage of nodular colloidal silica treated(a) pH 2.0 (b) pH 10.5with NH 4 OH at pH 10.5. The surface ofFig. 2 Dependence of Colloidal Silicanodular particles treated with NH 4 OH isSurface on pHRemoval rate (nm/min)154

covered with the smooth layer which isswollen completely.Fig. 3 shows the relationship between the removal rate of tungsten and theabrasive concentration and the abrasive size in the slurries.The effect of nodular colloidalsilica <strong>for</strong> the tungsten <strong>CMP</strong> wasevaluated using the iodate oxidizer(KIO 3 ) <strong>for</strong>mulated at pH 4.2. The largeabrasive size(70nm)is higher removalrate of W film and p-TEOS film thansmall size(30nm). For instance, usingthe samall abrasive size is higherselectivity than large one.There<strong>for</strong>e, using small abrasive size isable <strong>to</strong> get the better planarity thanlarge one.Correlation of RR and %-SiO 2 , particle size00.00 1 2 3 4 5 64. ConclusionThe above results depend on the morphology of silica particles in the acidiccondition and the shapes of silica particles. It is confirmed that the nodularparticle has the non spherical shape which improves the <strong>CMP</strong> removal rate ofp-TEOS film and tungsten.The removal rate of p-TEOS film using the nodular colloidal silica slurry inalkaline conditions is lower than that using the spherical colloidal silica slurry.These results depend on the different morphology of silica particles. This meansthat the surface morphology of nodular colloidal silica varies more easily inalkaline conditions compared with that of typical spherical colloidal silica, andthe morphology of nodular colloidal silica in the alkaline condition is completelydifferent from that in the acidic condition. For tungsten <strong>CMP</strong>, which is generallyper<strong>for</strong>med in the acidic condition, it is also confirmed that the nodular colloidalsilica slurry per<strong>for</strong>ms a higher planarity compared with the ordinary silica slurry.The nodular colloidal silica slurry is proposed <strong>to</strong> be treated at pH 2 in the acidiccondition <strong>for</strong> obtaining the best mechanical polishing per<strong>for</strong>mance of the p-TEOSfilm and tungsten.W, TEOS - Removal rate ( A/min )Reference[1] T. Doi: Details of Semiconduc<strong>to</strong>r <strong>CMP</strong> Technology( Kogyo Tyosakai, 2000 ) p.80 [ in Japanese ].[2] S. Sakka: Sol-gel hou no kagaku ( The science of sol-gel method )( Agune Shoufusha, 1988 ) p.43 [ in Japanese ].[3] R. K Iler: The Chemistry of Silica ( J. Wiley, New York 1979 ) Chap. 4,p.350.30002500200015001000500SiO 2 ( wt.% ) ( W-RR/TEOS-RR )30nm : W-RR30nm : TEOS-RR70nm : W-RR70nm : TEOS-RR30nm : Selectivity70nm : SelectivityFig. 3 Dependence of RR on%SiO2, and size155 PacRim-<strong>CMP</strong> 2004

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