Particle-Containing Pads

FIGURE 5.23 Removal rate and WIWNU as a function of polishing time without pad conditioning [80]. 

In addition to the self-refreshing function, the fixed abrasive pads also give better planarization behavior [79,80,82,83], lower WIWNU and WIDNU 

FIGURE 5.24 MRR comparison of oxide wafer polishing on particle-containing pad with DI water and on IC1400 pad with fumed silica slurry at pH = 10.8 [81]. 

FIGURE 5.25 Material removal selectivity of TEOS, Ti, and TiN to W for polishing on the fixed abrasive pad [80]. 

FIGURE 5.26 Erosion as a function of pattern density after CMP. FAP Polishing with fixed abrasive pad. Slurry Polishing with abrasive-containing slurry and conventional pad [80]. 

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Only slurry that enters the pad/wafer gap can remove material, but most of it apparently is not utilized (PhUipossian and Mitchell, 2003). Slurry that has been advected under the wafer can be carried around by the platen several times, either re-entering the gap or joining the bow wave on each pass. Within the gap, the slurry chemistry alters the surface of the wafer. However, material removal not caused directly by the chemistry is accomplished by the simultaneous action of pad asperities that contact the wafer surface and slurry or slurry particles contained in the contact area. This lubricated three-body contact (pad asperities, wafer, slurry, and slurry particles) is thought to be the dominant material removal mechanism in many processes (Wang et al., 2007 Borucki and PhUipossian, 2007). Since the contact area between the pad and the wafer is very small, typically much less than 1% of the wafer surface (Elmufdi and Muldowney, 2006 Sun et al., 2010 Jiao et al., 2012), it is likely that very little of the slurry is directly involved in material removal. 

Some friction materials may contain other potentially harmfiil materials. Lead has been found in some secondary linings. Class B and C organic disk pads, and other friction materials as lead metallic particles, oxides, and sulfides. Several original equipment and aftermarket suppHers are known to have a pohcy against incorporation of lead or other potentially harmfiil materials in thek products. 

Chemical-mechanical planarization occurs when the surface of the wafer to be polished is forced against a polishing pad. Aqueous slurry that contains abrasive particles is placed on a polishing pad. The wafer is moved relative to the slurry-covered pad and the rate at which material is removed is often described by the heuristic equation called Preston s law ... 

FIGURE 5.15 Section of an ICIOOO pad, partially covered with abrasive particles, after CMP with a 12% slurry containing 200-nm abrasives [66]. 

Charns L, Sugiyama M, Philipossian A. Mechanical properties of chemical mechanical polishing pads containing water-soluble particles. Thin Solid Films 2005 485 188-193. 

The effect of temperature of slurry containing ceria particles (average diameter 440 nm and lEP 8.5), on the removal rates of TEOS oxide and silicon nitride was found to be weak as seen in Figure 1. This is similar to the effect of temperature of a silica based slurry on silica pK)lishing in the temperature range of 20-50 °C for the slurry with the pad maintained between 25-30 C [2]. The pad hardness decreases with an increase in temperature [2] and the associated reduction in removal rate may have compensated for any increased chemical removal caused by the increased temperature. 

For example, brake linings contain finely divided, hard, abrasion resistant particles (Tab. 11-1, Chapter 11) in a complex matrix that provides the bonding in the lining itself and with the metallic supports. The formulation, containing all components, may also include such materials as metallic, mineral and, synthetic fibers. During production of the break drums, discs, or shoes, the blend is pressed onto the structural supports with specially designed presses to produce uniform, homogeneous wear pads. 

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