Abrasion Modes

Section 4.4.2 further separates the polishing mode of abrasion into two submodes, that of Hertzian indentation based wear and fluid-based wear. The difference between these two polishing modes is the nature of the slurry fluid layer between the pad and the wafer. This area of CMP is still poorly understood, yet has important implications as to the removal mechanisms of CMP. 

---

Frictional Forces and Lubrication Frictional forces are a measure of how much contact the pad makes with the surface, which is important in determining the abrasion mode. Friction and lubrication also affect the amount of heat that is produced during polishing and thus affect the temperature. 

Abrasion Mode Mass Removed via Scale of Mass Removal... 

In this chapter, we shall first propose a model to explain the removal and planarization mechanisms of copper CMP. Next, we discuss surface layer formation during copper CMP, which is important for planarization, followed by copper dissolution during CMP, which is iii5)ortant to maintain high removal rates. Next a comparison of copper CMP to the Preston equation is made, followed by a discussion of the abrasion mode during copper CMP. Lastly, we investigate the dishing and erosion behavior of copper CMP. 

As discussed in Section 4.4.1, one indication of the mode of abrasion is the stress in the polished film. The development of a compressive stress in the copper film suggests a ductile grinding abrasion mode. Figure 7.29 shows the change in stress in copper films polished in slurries of 1 vol% NH4OH with (1) colloidally dispersed alumina, (2) 0.3 pm alumina, and (3) 3.0 pm alumina using a Suba IV pad. The benefit to the colloidally suspended alumina is that the particles do not agglomerate, and therefore maintain a smaller size distribution. However, the colloidal suspension may be affected by the introduction of polish by-products... 

In 1999, Luo and Domfeld [110] proposed that there are two typical contact modes in the CMP process, i.e., the hydro-dynamical contact mode and the solid-solid contact mode [110]. When the down pressure applied on the wafer surface is small and the relative velocity of the wafer is large, a thin fluid film with micro-scale thickness will be formed between the wafer and pad surface. The size of the abrasive particles is much smaller than the thickness of the slurry film, and therefore a lot of abrasive particles are inactive. Almost all material removals are due to three-body abrasion. When the down pressure applied on the wafer surface is large and the relative velocity of the wafer is small, the wafer and pad asperity contact each other and both two-body and three-body abrasion occurs, as is described as solid-solid contact mode in Fig. 44 [110]. In the two-body abrasion, the abrasive particles embedded in the pad asperities move to remove materials. Almost all effective material removals happen due to these abrasions. However, the abrasives not embedded in the pad are either inactive or act in three-body abrasion. Compared with the two-body abrasion happening in the wafer-pad contact area, the material removed by three-body abrasion is negligible. 

Attrition in fluidized bed systems leads primarily to a loss of bed material since the cyclones, which are mostly used for the collection of entrained material, are not able to keep the attrition-produced debris inside the fluidized bed system. The material loss through the cyclone is, therefore, usually taken as the attrition rate. This means that among the attrition modes discussed in Sec. 2, namely fragmentation and abrasion, it is abrasion which is the attrition mode of interest for fluidized bed systems. 

The primary failure modality identified clinically for restorations in posterior teeth is loss of material through abrasion. The complex nature of this failure mode in composite materials makes it difficult to correlate this phenomenon with any one mechanical property. A number of studies have suggested improvements in the system by using various mechanical properties as evidence. These studies have identified major factors such as ceramic filler loading and type of filler [186-191]. Some effects have been identified related to the... 

Major causes for coating failure are surface cracking and undetected pinholes or voids. These can be repaired and serious problems avoided. Coatings generally fail in different modes, these are chemical failure, abrasion failure, adhesive failure, cohesive failure and undercoat corrosion. For performance evaluation of coatings on experimental basis on these parameters various ASTM and BS specifications are presently being used. 

Since from the outset attempts to determine the hardness of minerals have involved various techniques, ranging from scratch through abrasion to indentation, it will be useful to examine these three measurement groups, and to distinguish them according to the nature of action on the material under test, and also to present attempts to relate them to the results obtained by different methods. Specified in Table 4.1.1 are the most important methods, classified according to the mode of action on the sample under test. 

---