This study examined the friction and wear of brake friction materials containing two different abrasives: zircon and quartz. Commercial grade abrasives with two different sizes (fine and coarse) were compared in terms of the effects of the size, shape, and toughness of the abrasive particles on the friction and wear of the friction material and counter discs. The results showed that the morphology of the abrasives has a considerable effect on the friction effectiveness and wear of the friction couple. The level of friction was higher in the case of using quartz than zircon, and smaller particles were more effective in increasing the coefficient of friction. The toughness of the abrasives also played important roles in determining the friction effectiveness. Improved heat resistance at elevated temperatures was achieved when coarse zircon was used. The wear of the friction material was also dependent on the morphology and toughness of the abrasives and the large abrasive particles produced more wear on the gray iron disc.

INTRODUCTIONChemical-mechanical polishing (CMP) has been an important process in dielectric planarization, shallow trench isolation, and the metal damascene process. Although CMP provides the best planarity in comparison to the other techniques, this technique is hampered by pattern dependencies, which cause some regions on a die to be thinner than the other regions due to differences in underlying topography. Several studies 1-10 have proposed models for the pattern density effect on CMP. The early pattern density modeling investigations were mainly at a local level with some simple pattern structure. 7-9 This is because chip-level modeling requires a more sophisticated modeling algorithm and intensive computing for handling complex chip layout patterns. Locallevel CMP modeling is useful to understand the basic concept of CMP pattern dependency. However, chip-level modeling is essential for the actual chip design and process development. Implying, results of chip-level modeling can be useful to obtain planarity information before actual wafer processing, to effectively fill dummies to widen the CMP process window, to improve planarization ability, and to find the thickest and thinnest oxide positions within the die and hence to predict the intradie thickness variation range. Recently, results of an MIT density model 1-6 showed some degree of success in chip-level modeling by introducing concepts of interaction distance (or planarization length) and effective pattern density. From these concepts, they presented some possibility of predicting post-CMP oxide thickness for arbitrary die layouts. Also, it was recently notified that topographic profile differences between high-density plasma (HDP) and conformal chemical vapor deposition (CVD) oxide would result in a different pattern density for each oxide from that of the design layout. 10 But there are few experimental data for these deposition profile effects on CMP. Furthermore, there are fewer results on the applications of these concepts to the conventional test chip. In this paper, new test masks for characterizing and modeling patTest masks for characterizing pattern-dependent variation of the remained thickness after chemical-mechanical polishing (CMP) were designed by taking the experimentally obtained interaction distance into consideration. Polishing behaviors were characterized by taking into consideration layout pattern density and pitch variations using these masks. Deposition profile effects were also compared between plasma-enhanced tetra ethyl ortho silicate (PETEOS) and high-density plasma (HDP) oxide. Both the measured post-CMP thickness and the expected oxide pattern density after the consideration of deposition profile effects showed a good correlation with respect to the pitch variation for a constant layout pattern density. Also, the relationship between remained thickness and true layout pattern density was deduced. Chip-level CMP modeling was investigated to obtain the post-CMP thickness distributions across a die from its design layout and a...