Stiffness, pad

Experimental [66] and theoretical [47] studies of the actual contact area Ac show that during CMP it is only a few tenths of a percent of the total wafer area Aw, and increase with applied pressure P. Stiff pads have a smaller contact area than compliant ones at any given pressure. This has been modeled [47], for pads with Young s modulus E, as Equation 5.1... 

Qualitatively, since the contact area increases linearly with applied pressure, the effective pressure is constant for a given pad. Soft, compliant pads have a larger contact area and lower effective pressure whereas hard, stiff pads have a smaller contact area and higher effective pressure. Thus soft pads push abrasive particles against the wafer over a larger area but with less force than hard pads do. 

But Uie powen of invention are most wonderful. What ilo you think of a steebpeduted bullet Chat pene tndes two feet sin inches of solid oak being stopped by a stiff pad of felt and some other oompoeition not only siop(], but all crumbled out of sliape t This has been done, and a little tailor of Man helm, Germany, is the inventor. 

A planarization monitor has been applied to the copper system to investigate pattern dependencies during copper overburden planarization. Conventional profilometry and a noncontact, acousto-optic measurement tool, the Insite 300, are utilized to quantify the planarization performance in terms of the defined step-height-reduction-ratio (SHRR). Illustrative results as a function of slurry, pad type and process conditions are presented. For a typical stiff-pad copper CMP process, we determined the planarization distance to be approximately 2mm. 

Using a new planarization monitor, the planarization efficiency and planarization distance were computed for a copper CMP process. The influence of polish pad, slurry and process conditions was demonstrated. Results indicate that harder, stiffer pads can extend planarization performance to wider structures given a suitable choice of slurry. Process conditions play a relatively minor role. The planarization of copper during the as-plated copper overburden removal was found to exhibit similar behavior to the planarization of oxide topography in oxide CMP, with a planarization distance of approximately 2mm for a typical stiff-pad copper CMP process. 

The solution (pad bath) contains one or more of the amino resias described above, a catalyst, and other additives such as a softener, a stiffening agent, or a water repeUant. The catalyst may be an ammonium or metal salt, eg, magnesium chloride or ziac nitrate. Synthetic fabrics, such as nylon or polyester, are treated with amino resias to obtaia a stiff finish. Cotton (qv) or rayon fabrics or blends with synthetic fibers are treated with amino resias to obtain shrinkage control and a durable-press finish. 

Resilient but rigid foundations such as by providing spring mounts or rubber pads for machines on the floor or for components and devices mounted on the machine so that they are able to absorb the vibrations, caused by resonance and quasi resonance effects, due to filtered out narrow band ground movements. The stiffness of the foundation (coefficient of the restoring force, k) may be chosen such that it would make the natural frequency of the equipment... 

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). 

Oil film thickness is critical in bearing stiffness calculations. In a tilt-ing-pad bearing, one can change this thickness in a number of ways ... 

With P=0 we get a30=6jiwR2K x. Hence a is finite even for zero external load P, owing to the adhesion forces. The detachment of tip and sample, the so-called pull-off, requires a tensile force Pa(i which characterises the adhesion force Pad=-(3l2)nwR. With 8 denoting the deformation of the tip-sample contact as measured in the vertical direction, the corresponding stiffness kts=dPld8 of the contact is given by... 

Combined Measurement of Friction and Stiffness on a Model Brake Pad... 

Multilayer or stacked pads are commonly used in the CMP processes for better polishing performance such as uniform material removal and good planarization across the wafer surface. A multilayer or stacked pad usually consists of a stiff, hard top layer and a soft, flexible subpad, and possibly some medium layer(s), as shown in Fig. 5.3. 

Hardness of polyurethane pads can vary from shore D values of less than 15 (very soft and flexible pads) to greater than 65 (very stiff and rigid pads), and Young s (elastic) modulus of polyurethane pads can vary from a low of 1 MPa (very soft, flexible, and elastomeric pads) to greater than 1 GPa (very stiff and rigid pads). Usually, hardness increases with the increase in Young s modulus. 

S.2.4.3 Pad Hardness, Young s Modulus, Stiffness, and Thickness Effects Pad hardness has an influence on many aspects of polishing performance. A harder... 

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