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Characteristics of Acid-Proof Coated Layer for Metal CMP Slurry

Characteristics of Acid-Proof Coated Layer for Metal CMP Slurry

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<strong>Characteristics</strong> <strong>of</strong> <strong>Acid</strong>-Pro<strong>of</strong> <strong>Coated</strong> <strong>Layer</strong><strong>for</strong> <strong>Metal</strong> <strong>CMP</strong> <strong>Slurry</strong>So-Young Yoon*, Jung-Soo An, Joo-Han LeeIndustrial Tools Technology Development, Ehwa Diamond Ind. Co., Ltd., Osan, KoreaE-mail : syyoon@ehwadia.co.krThe <strong>CMP</strong> process is consist <strong>of</strong> four main processes ; polishing pad, slurry, elasticsupporter and pad conditioning. Conditioners play an important role in keeping designedcharacteristic <strong>of</strong> pad. In the metal <strong>CMP</strong> process, acid-pro<strong>of</strong> characteristic is required touse the conditioner. As we plate the conditioner by Rh and Pd, we confirmed that acid –pro<strong>of</strong> characteristic is improved to ceria, W-slurry and Cu-slurry, and we are expecting tohave longer life-time because <strong>of</strong> this result. We got the same result from the all the tests ;change <strong>of</strong> plated layer surface, hardness, interface gap between diamond and matrix, andpush-pull strength ; to evaluate the acid-pro<strong>of</strong> characteristic, and we confirmed thepossibility to predict the characteristic that can be happen in the <strong>CMP</strong> process practically.Especially, as we got the numerical value <strong>of</strong> push-pull strength, it will be usefulin<strong>for</strong>mation about the corrosion.Key Words : <strong>Metal</strong> <strong>CMP</strong>, <strong>Metal</strong> <strong>Slurry</strong>, Pad Conditioner, <strong>Acid</strong>-Pro<strong>of</strong> Coating1. INTRODUCTIONChemical mechanical planarization(<strong>CMP</strong>), a surface planarization process, has enabled theproduction <strong>of</strong> advanced semiconductor devices by producing a globally planar wafer surface. The<strong>CMP</strong> process requires a poly-urethane polishing pad; a slurry composed <strong>of</strong> abrasive, chemicals, andwater; and pad conditioner etc [1-3]. In the <strong>CMP</strong> process, chemical reaction occurs betweenchemicals(slurry) and the wafer. Consequently, the reaction product would gradually accumulate ontothe holes and grooves <strong>of</strong> the pad surface leading to the so-called glazing <strong>of</strong> the pad [4]. There<strong>for</strong>e,<strong>CMP</strong> pad conditioner used to regenerate a new pad surface and recover its role in the process isnecessary.The general <strong>CMP</strong> pad conditioner is manufactured by nickel plating or metal powder brazing inorder to fix the diamond particle. Up to now, the researches regarding the factors(diamond size, grade


and separation, amount <strong>of</strong> protrusion <strong>of</strong> the diamond, substrate design and planarity etc.) which has aneffect on the life time and per<strong>for</strong>mance in the Oxide <strong>CMP</strong> process have been per<strong>for</strong>med steadily and ithas been progressed a lot [5-6]. However, it leaves something to be desired about the research <strong>of</strong> thelifetime in <strong>Metal</strong> <strong>CMP</strong> process.In order to use diamond conditioner in <strong>Metal</strong> <strong>CMP</strong> process which is using a strong acid slurry, themetal bond layer which is retentive <strong>of</strong> diamonds must not react with acid. The main reason <strong>for</strong> it is thatcorrosion <strong>of</strong> metal bond layer lead to decrease <strong>of</strong> retention and it cause diamond pulling out from thebody. Accordingly, it makes a scratch on the wafer in <strong>CMP</strong> process. Consequently, the high corrosionresistance to strong acid is essential to metal bond layer.The conditioner that is used in <strong>Metal</strong> <strong>CMP</strong> process is also based on nickel which is metal bond.However Ni-base bond has insufficient resistance <strong>for</strong> <strong>Metal</strong> <strong>CMP</strong> process which is using strong acid.In this reason, it is general to have acid-pro<strong>of</strong> coating on the surface <strong>of</strong> metal bond layer so that it canbe protected from a corrosion <strong>of</strong> metal bond layer and increasing a lifetime <strong>of</strong> conditioner as well. Inthis study, we evaluated a chemical-pro<strong>of</strong> characteristic <strong>for</strong> acid-pro<strong>of</strong> coating layer which is coated afew μm thickness by Rhodium(Rh) and Palladium(Pd). And they are respect to a tungsten, copperslurry and ceria slurry which is increasing a frequency <strong>of</strong> use recently in <strong>Metal</strong> <strong>CMP</strong> process. At thesame time, we studied to find out a possibility <strong>of</strong> application to chemical-pro<strong>of</strong> material which issuitable <strong>for</strong> <strong>Metal</strong> <strong>CMP</strong> process and acid-pro<strong>of</strong> coating conditioner by evaluating an adhesion betweenacid-pro<strong>of</strong> layer and metal bond layer.2. EXPERIMENTALIn our experiment, the conditioner used Ф20 pallet type as a substrate, and adhered the diamond byNi-plating. We used low grit ranged diamond, 165~181μm, to have certain exposure height, andmanufactured exposure height to be 50~60μm. And Rhodium(Rh) and Palladium(Pd) are used as aacid-pro<strong>of</strong> coating materials, and the thickness <strong>of</strong> coating was ~1±0.1μm.In the corrosion experiment to evaluate the chemical-pro<strong>of</strong> characteristic <strong>of</strong> the conditioner, we usedHitachi Co., <strong>for</strong> ceria slurry, Cabot Co., <strong>for</strong> W-slurry and Rohm & Haas Co. <strong>for</strong> Cu-slurry and we keptthe temperature 25℃ and pH 6.5~6.8, 6.9~7.2, 5.4~5.7 each.We measured the variation <strong>of</strong> the surface corrosion <strong>of</strong> the acid-pro<strong>of</strong> coating, hardness, interfacegap between diamond and matrix, push-pull strength at intervals in 50 hours up to 200 hours. Thespecimen <strong>for</strong> measuring push-pull strength was adhered 20 particles <strong>of</strong> diamond in 2 row at interval<strong>of</strong> 5mm in fixed exposure height. We have used remodeled push-pull gauge basically FB-20K, madeby IMADA Co., and outline <strong>of</strong> the usage is as below.In addition, we dressed specimens, which had experienced, in tough condition to figure out thepossibilities <strong>of</strong> fracture and pulling out in practice. In dressing, we used polisher made by Struers Co.and the condition is showing at the table below. The pad was IC 1000 <strong>of</strong> Rohm & Haas Co..


DiamondForcePush-pullGaugeMatrix(pure Ni)Fig. 1. The Schematic <strong>for</strong> push-pull strength measurement.Table 1. Experiment conditions <strong>for</strong> dressing.ConditionerMatrixCoating Down Force Spindle Speed Table Speed TimematerialNickel - 50 N 150 rpm 60 rpm 60 minNickel Rhodium(Rh) 50 N 150 rpm 60 rpm 60 minNickel Palladium(Pd) 50 N 150 rpm 60 rpm 60 min3. RESULTS AND DISCUSSIONFig. 2~4 show conditioner’s surface which was dressed <strong>for</strong> 1hour on pad after soaking 200 hours inthe ceria slurry, W-slurry and Cu-slurry(<strong>Metal</strong> slurry). The fracture and pulling out did not happen tonickel plated layer, which is not coated by acid-pro<strong>of</strong>, and plated layer, which was coated by rhodiumand palladium. Fig. 2 shows the surface <strong>of</strong> the plated layers to ceria slurry. As you can see at Fig. 2(b),you can notice that there is serious corrosion at the surface <strong>of</strong> nickel-plated layer which is not coatedby acid-pro<strong>of</strong>. Rhodium and palladium plated layers. This kind <strong>of</strong> surface corrosion is result <strong>of</strong>reaction with additive <strong>of</strong> slurry and it cause a micro scratch on the wafer by decreasing <strong>of</strong> surfacehardness which might lead to fall <strong>of</strong>f the plating layer or it cause a mixture <strong>of</strong> unexpected impurities.In worse case, they can lead to pulling out the diamond and it make macro scratch. We can see thatplating layer <strong>of</strong> Rd and Pd has been corroded minutely however it is very small compare to nickelplatedlayer. The Fig. 3 and Fig. 4 are showing the results <strong>of</strong> surface corrosion <strong>of</strong> plated layers.In the W-slurry at Fig 3, nickel-plated layer was corroded minutely, and Rh coating and Pd coatingwas not much changed. At the Fig 4, all three kinds <strong>of</strong> plated layers were not corroded.Among the 3 kinds <strong>of</strong> metal slurry, the surface corrosion in the ceria slurry was remarkable.There<strong>for</strong>e, we investigated that how the surface corrosion is affected to hardness. Fig. 5 describes thechange <strong>of</strong> hardness <strong>of</strong> matrix in metal slurry. The result <strong>of</strong> surface corrosion and the variation <strong>of</strong>


hardness were accorded, and the hardness variation <strong>of</strong> nickel plated layer, which was corrodedseriously in the ceria slurry, was the highest as 13%. Although the hardness <strong>of</strong> acid-pro<strong>of</strong> Rh coatingand Pd coating layers was decreased according to increase the digestion time, it was not much big asthe change <strong>of</strong> hardness <strong>of</strong> nickel-plated layer(Rh 5%, Pd 6%).(a)(b)(c)(d)Fig. 2. Conditioner’s surface after soaking <strong>for</strong> 200 hours in the ceria slurry(X100, OM).(a) Initial condition, (b) Non-coating, pure Ni, (c) Rh coating, (d) Pd coatingThe change <strong>of</strong> hardness in W-slurry and Cu-slurry decreased 7% and 5 % each and acid-pro<strong>of</strong> Rhcoating and Pd coating layers were not very big. And the change <strong>of</strong> hardness <strong>for</strong> Rh and Pd had almostsame corrosion trend like in the ceria slurry.(a) (b) (c)Fig. 3. Conditioner’s surface after soaking <strong>for</strong> 200 hours in the W-slurry(X100, OM).(a) Non-coating, pure Ni, (b) Rh coating, (c) Pd coating


(a) (b) (c)Fig. 4. Conditioner’s surface after soaking <strong>for</strong> 200 hours in the Cu-slurry(X100, OM).(a) Non-coating, pure Ni, (b) Rh coating, (c) Pd coatingHardness(Hv)660640620600580560540520500480pH : 6.5 ~ 6.8460-50 0 50 100 150 200 250Time(hr.)Non-coating, pure NiNi + Rh coatingNi + Pd coatingHardness(Hv)660640620600580560540520500480pH : 6.9 ~ 7.2460-50 0 50 100 150 200 250Time(hr.)Non-coating, pure NiNi + Rh coatingNi + Pd coating(a)(b)Hardness(Hv)660640620600580560540520500480pH : 5.4 ~ 5.7460-50 0 50 100 150 200 250Time(hr.)Non-coating, pure NiNi + Rh coatingNi + Pd coating(c)Fig. 5. Change <strong>of</strong> hardness according to the slurry.(a) in ceria slurry, (b) in W-slurry, (c) in Cu-slurryThe weak part <strong>of</strong> surface corrosion is the interface between diamond and matrix. Fig. 6 shows theinterface <strong>of</strong> diamond and matrix after soaking <strong>for</strong> 200 hours in the ceria slurry and then dressing <strong>for</strong>one hour. As we can notice by Fig. 6, we can confirm that the interface gap is the biggest at Non-


coating Ni that was corroded seriously and the specimen which is acid-pro<strong>of</strong> coated by Rd and Pd didnot have the change <strong>of</strong> interface gap. The meaning <strong>of</strong> big interface gap is high possibility <strong>of</strong> falling thediamond <strong>of</strong>f. So, we predicted the diamond retention by using push-pull gauge whether the difference<strong>of</strong> interface gap have an effect on pulling out a diamond.DiamondMatrix : NiInterfaceMatrix: pure NiDiamond(a)(b)DiamondDiamondMatrix : RhMatrix : Pd(c)(d)Fig. 6. Interface gap between diamond and matrix after digestion <strong>for</strong> 200 hours in the Cuslurry(X2000,SEM).(a) Initial condition, (b) Non-coating, pure Ni, (c) Rh coating, (d) Pd coatingFig. 7 shows the push-pull strength results <strong>of</strong> diamond <strong>for</strong> the metal slurry. The push-pull strength isthe <strong>for</strong>ce to fall <strong>of</strong>f or fracture a diamond by giving a horizontal <strong>for</strong>ce to matrix and the bigger thevalue is the stronger bonding strength is between diamond and matrix. As you can see at Fig. 7, thecase <strong>of</strong> nickel-plated layer in the ceria slurry the push-pull strength value is decreased 12%, and pushpullstrength value <strong>for</strong> both acid-pro<strong>of</strong> Rh and Pd changed 5%. As you saw in Fig.6, it because the gapwhich occurred between the interface <strong>of</strong> diamond and matrix let down the diamond retention.Even though all three plated layers were not much changed in the W-slurry and Cu-slurry, Rh andPd coated conditioner’s push-pull strength value were more stable than non coating nickel plating.


Push-pull strength(x100g)43424140393837363534ceria slurryW-slurryCu-slurryPush-pull strength(x100g)43424140393837363534ceria slurryW-slurryCu-slurry330 50 100 150 200Time(hr.)330 50 100 150 200Time(hr.)(a)(b)Push-pull strength(x100g)43424140393837363534330 50 100 150 200Time(hr.)ceria slurryW-slurryCu-slurry(c)Fig. 7. Change <strong>of</strong> Push-pull strength according to acid-pro<strong>of</strong> materials.(a) Non-coating, pure Ni, (b) Rh coating, (c) Pd coating4. CONCLUSIONTo evaluate chemical-pro<strong>of</strong> characteristic, surface condition, interface gap between diamond andmatrix, hardness, push-pull strength were almost accorded. Now that the push-pull strength waspossible to evaluate numerically, it was very useful in<strong>for</strong>mation to estimate the holding <strong>for</strong>ce betweendiamonds and plated-layer.In the metal <strong>CMP</strong> process using ceria slurry, the acid-pro<strong>of</strong> chemical characteristics <strong>of</strong> Rh and Pdcoated products are expected to improve 2 to 3 times more than the nickel-plated conditioners. Inaddition, we can confirm that acid-pro<strong>of</strong> coating Rh and Pd are more stable than nickel-plated layers


in W-<strong>Slurry</strong> and Cu-slurry as well. As a result, we could expect longer lifetime due to improvement <strong>of</strong>acid-pro<strong>of</strong> characteristic by per<strong>for</strong>ming acid-pro<strong>of</strong> Rd or Pd coating.REFERENCES[1]. T. Dyer and J. Schlueter, “Characterizing <strong>CMP</strong> pad conditioning using diamond abrasives”, Micro,Vol. 20, p. 47-54, 2002.[2]. S. Nag and A. Chatterjee, “Shallow trench isolation <strong>for</strong> sub-0.25-μm IC technologies”, Solid StateTechnology, p. 129, 1997.[3]. K. Smekalin, “<strong>CMP</strong> dishing effects in shallow trench isolation”, Solid State Technology, p.187,1997.[4]. S. Sivaram, H. Bath, R. Leggett, A. Maury, K. Monnig and R. Tolles, Solid State Technology, Vol.35, p.87, 1992.[5]. J. Zimmer and A. Stubbmann, Proc. NCCAVS <strong>CMP</strong>’98 Symposium, pp. 88, 1998.[6]. C.C. Garretson, S.T. Mear, J.P. Rudd, G. Prabhu, T. Osterneld and D. Flynn, Proc. <strong>CMP</strong>-MIC, p. 1,2000.

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