Tungsten oxide erosion

Fig. 26. Degree of oxide erosion as a function of polishing time in tungsten CMP [12]. Reproduced by permission of the Electrochemical Society, Inc.

Chekina et al. [8] have applied contact wear methods to the modeling of surface evolution in both oxide and dual material (tungsten-oxide) CMP to predict erosion and dishing or recess. The formulation uses calculation of... 

The main cause of anode wear is electrochemical oxidation or sulfur attack of anodic surfaces. As copper is not sufficiently resistant to this type of attack, thin caps of oxidation and sulfur-resistant material, such as platinum, are bra2ed to the surface, as shown in Eigure 15a. The thick platinum reinforcement at the upstream corner protects against excessive erosion where Hall effect-induced current concentrations occur, and the interelectrode cap protects the upstream edge from anodic corrosion caused by interelectrode current leakage. The tungsten undedayment protects the copper substrate in case the platinum cladding fails. 

The cathodes can be of the hot type such as tungsten, carbon or molybdenum, cathodes which obviously must be used in a non oxidizing atmosphere. Under certain conditions of oxidizing atmosphere one can use zirconium or hafnium cathodes. The so-called cold cathodes are generally made of copper is -i - ). Heat losses at the cathode are generally quite low (less than 15% of power input to the arc). For a tungsten cathode tip, erosion with current is of g/Clb... 

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