Pad wear

PadProbe allows either continuous or periodic in situ, in-process control of two crucial CMP parameters pad life (dynamics of pad wear) and pad condition (dynamics and level of pad friction). Data obtained from such a... 

FIGURE 4.14 Pad wear during continuous conditioning (from Ref. 22). 

Pad wear (cut) rate, which can be defined as the pad thickness loss over a period of continuous conditioning. It characterizes the abrasiveness, or aggressiveness, of the conditioner. 

Computerized real-time measurements and analysis of the coefficient of friction, contact high-frequency acoustic emission, and pad wear allow the effective evaluation of consumables, understanding of tribological interactions at the polishing interface, process development, dynamic characterization of the polishing process, including rate and nonuniformity of material removal, and so on. The application of tribometrology not only is restricted to research and development departments but also proves very useful in the device production facilities. 

FIGURE 5.8 Comparison of NCP and ICIOOO pad wear rates (total conditioning time = 4h under 5lbs downforce) (a) NCP pad wear rate 14.3 pm/h, (b) ICIOOO pad wear rate 44.0 pm/h. 

Figure 5 illustrates endpoint time versus pad wear. In order to eliminate the effect of topological density differences, pad life wear versus endpoint time was examined on two different device types. Note Typical pad changes occur after a wafer count of 400. 

A well-known problem in CMP is that the pad wears over long periods of time as the number of wafers processed on the pad increases. Various strategies have emerged to address this concern, including ex-situ and in-situ pad conditioning, and run by run control. In previous work, we have demonstrated run by run control on blanket wafers, in which polish time and other process parameters are adjusted for the next or later wafer based on measurements on a previous wafer to compensate for removal rate and uniformity degradation [10,11]. In practical use, however, such run... 

T. Smith, D. Boning, J. Moyne, A. Hurwitz, and J. Curry, Compensating for CMP Pad Wear Using Run by Run Feedback Control, VLSI Multilevel Interconnect Conference, pp. 437-440, Santa Clara, CA, June 1996. 

Potassium titanate whiskers were found to improve the tribological properties of NAO friction materials. These soft, synthetic refractory materials stabilize friction level, reduce pad wear, noise, fade, thermal conductivity, control porosity, and provide thermal reinforcement. Fibrous potassium titanates are being replaced by platelet and powder versions because of health concerns associated with respirable fibers. 

Pad wear occurs during pre-CMP conditioning and during CMP. Pad life is also related to the chemical attack of water molecules, transferring wafer elements. Pad wear is mainly dominated by mixed wear modes. 

The definition of a suitable conditioning process has outputs of MRR (both value and uniformity), pad wear, and conditioner lifetime (including the probability of diamond dropout). The input parameters are grouped by... 

Some process designs try to use conditioning as an independent process variable, attempting to compensate for variations in other process conditions by adjusting the aggressiveness of the conditioning steps. Caution must be used, if that is the intent, to ensure that the effects of the conditioning recipe (on MRR, pad wear, etc.) have been well identified across all of the interactive... 

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