Pad material

Rinse and buff immediately after the bulk CMP step. Rinsing removes the residual slurry and the polishing by-products including abraded film from the wafer, abraded polish pad material, and agglomerated slurry. Buffing removes most of the particles that are adhering to the surface as well as many mechanically embedded particles. 

A number of additional wafer-level variations in the removal rate may result from the variation in the Preston coefficient across the surface of the wafer. Because depends on the slurry, pad, material, and process parameters in a poorly understood fashion, it is not clear where all of these dependencies ultimately reside. 

These two equations show that the pad deformation is proportional to the applied load and inversely proportional to the pad material stiffness (represented by the Young s modulus). The equations involve complete elliptic integrals that can be readily evaluated numerically. The relative deformation represented by Eqs. (24) and (25) is plotted in Fig. 13, where the inner region corresponds to Eq. (24) and the outer corresponds to Eq. (25). 

Summary of Expected Pad Material Property Effects on the CMP Process... 

Additional insight was obtained from conditioning studies conducted on class IV pads. A pad of the type described in Ref. [3] was prepared from a solid urethane sheet and used in an oxide CMP process. Pad material properties and process conditions employed are given in Tables VI and VII, respectively. 

Bajaj, R., Desai, M., Jairath, R., Stell, M., Tolies, R. (1994). Effect of polishing pad material properties on chemical mechanical polishing (CMP) processes. Proc. MRS Spring Meeting. 

Scratches can also be caused by particles by another means. Since in CMP the slurry (particles included) stays on the polish pad, and the polish pad material is removed by the end effector, the end product of this complicated slurry-pad material reaction is a kind of substance with unknown characteristics and sizes. These substances can be the cause of the scratches. Figure 18 shows such substances collected by an end effector [16]. If the end effector is not properly cleaned, these particles can become hardened and cause severe scratches. To prevent this, a high-pressure water spray nozzle or a rotating brush can be used. 

In the cold pad-batch process, the padded material is rolled without heating and stored at room temperature for 8-24 h. 

Separator or Release Sheets. Separator or release sheets are used to free the reverse side of a laminate either from pressure padding material or the adjacent laminate normally they are paper of the glassine type, coated with release agents. 

Sisal fiber finds use in a variety of items such as in the manufacture of binder twine and baler twine, mattings, rugs, marine ropes, padding material for cars, upholstery, etc. 

FIGURE 4.7 Stribeck curves for polishing using different pad materials and groove patterns (from Ref 6). 

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. 

The first term is for the conventional Hooke s law—Young s modulus expansion/compression of an elastic pad material with Young s modulus E,... 

In general, polishing pads are composed of either a matrix of cast polyurethane foam with filler material to control hardness or polyurediane impregnated felts. Polyurethane is utilized because urethane chemistry allows the pad characteristics to be tailored to meet specific mechanical properties needs. Jairath et al. describe the manufacture of pad material as follows ... 

A cross section of resulting pad material is shown in Figure 4.10. In this section, we shall review the properties that make a pad useful as a polishing surface. 

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... 

Figure 4.22 Schematic description of the effect of water on pad materials.

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