Tungsten CMP Processes

Tungsten CMP is most widely used for the formation of studs in contacts and vias. There are some reports of tungsten CMP utilized for the formation of interconnections however, the relatively high resistivity of tungsten (5.65 pfl-cm) compared to aluminum (2.66 pQ-cm) or copper (1.67 pQ-cm), limits the use of 

Extr lation of the Tafel regions back gives and at the intersection point. (From Ref. (22), adt ted by permission of Prentice-Hall, Inc.) 

In contrast to the Ce(N03)3/HN03 slurry, the HjOj slurry does not passivate the tungsten surface. Passivation in the H2O2 slurry is not expected because the slurry pH of 5.1 is above the pH where tungsten passivation occurs. The lack of a passivation film is suggested by the relatively high etch rates in the H2O2 slurry. In addition, the potentiodynamic scans in the static solution do not indicate passivation. Finally, the fact that abrasion does not 

Potentiodynamic scans of tungsten during abrasion in four slurries. (From Ref, (21).) 

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A similar but more detailed comparison of IC1400 and Politex pads in a tungsten CMP process was given by Stein et al. [24]. Overall, the process differences observed were the same as in the previous study cited (i.e., the... 

Lin BT, Lee SN, Tseng SM, Ho PH. Novel tungsten CMP process with diluted slurry. Proceedings of the 16th International VMIC. 1999. p 636-641. 

Kaufinan et al. describe a successful tungsten CMP process as a competition between the formation and removal of a surface layer of WO3 that forms naturally in the slurry solution. A bare tungsten surface is not thermodynamically stable in the low pH slurry described by Kaufman et al., and the chemicals quickly oxidize the tungsten surface to WO3 according to the reduction-oxidation reaction ... 

Robert Lum, Sourabh Mishra, Fritz Redeker, Brian Brown, Kapila Wijekoon, Ronald Lin, Savitha Nanjangud, Defects characterization and productivity optimization of tungsten CMP process , presented at 1999 SEMICON Korea, Seoul, Korea, February 22-24, 1999. 

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