Nonporous pad

Pad porosity is inversely related to its density. Many physical properties of the polyurethan pad are strongly dependent upon its porosity (or density). The hardness and Young s modulus (elastic or storage modulus) of porous pads have a clear linear correlation with the density (or porosity) of the pads [1]. It is obvious that nonporous (noncell) pads have much smaller variability in density and other physical properties compared to porous pads. Nonporous pads have much higher strength, modulus, hardness, and elongation than porous pads. 

List and explain the advantages and disadvantages of nonporous pad versus porous pad in terms of polishing performance. 

The physical and mechanical properties of a polishing pad are determined not only by the chemical composition of the pad materials but also by its microstructures. As described in Table 5.1, each type of pad has its unique microstructure that ranges from large open pores to nonporous solids. Some representative microstructures of pad surfaces are shown in Fig. 5.1. 

Pad Porosity/Density Type I, II, and III pads all have pores although their microstructures are different. Type IV pads (noncell, nonporous, solid) do not have native porous microstructure except those generated by the conditioning process. Typical physical properties of ICIOOO pad (type III, porous) and IC2000 pad (type IV, noncell, nonporous, solid) are listed in Table 5.2. 

When MRR of oxide wafer polishing on porous ICIOOO pad and on nonporous NCP pad is compared, it shows that MRR on nonporous NCP pad is slightly lower than that on porous ICIOOO pad, and WTWNU of MRR is comparable for NCP and ICIOOO pads (see Fig. 5.4). The WIWNU of MRR on NCP pad is much lower than that on ICIOOO pad. This demonstrates better... 

In order for the water to affect hydrogen bonding within the urethane, the water must first diffuse into the pad material. The diffusion coefficient of water in a film (nonporous) of polyurethane has been measured as approximately 1x10 cmVsec. The diffusion constant is important because it determines how rapidly water will affect G. In the case of the IClOfX) pad (Figure 4.21), a sharp decline in G (almost a 2x reduction) is experienced during... 

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