Pad thickness

3 Pad Thickness Typical polishing pads for CMP are about 1.3 mm (0.05 in.) thick. Slightly thicker pads (2.0mm or 0.08 in. in thickness) have also 

TABLE 5.2 Typical Physical Properties of ICIOOO and IC2000 Pads [1]. 

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Use completely welded full wrap-around reinforcement pads at branch connections with pad thickness equal to header wall thickness. 

Lupeol, isolated from the stem bark of Crataeva magna (Lour.) DC. (Capparaceae), reduces the foot-pad thickness and complement activity in arthritic rats (75). Oleano-lie acid saponins isolated from the roots of Momordica cochinchinensis (Lour.) Spreng. is anti-pruritic in rodent (76). 

A.W, Maximum allowable oil pad thickness, in. lSG - Difference in specific gravity relative to water of oil and water phases It, Oil viscosity, cp... 

Graph results and dioose reasonable size which does noi violate gas capacity or oil pad thickness constraints. Possible choices from l ig. 7 are 90-in. x 20-ft, 96-in x 7-ft, 6-in., and 102-in. x 15-ft ... 

Real-time monitoring of the pad thickness and surface conditions allows extended pad use, as long as both these parameters are above the critical threshold, thus increasing pad life. Such an increase in pad life translates into... 

Pad wear (cut) rate, which can be defined as the pad thickness loss over a period of continuous conditioning. It characterizes the abrasiveness, or aggressiveness, of the conditioner. 

Thus CMP pads play an important role in dishing of patterned wafers. The model presented here parameterizes CMP pads using Young s modulus, Poisson s ratio, and pad thickness plus an unusual fcstretch term. Control of these parameters could lead to improvements in dishing and erosion outcomes during polishing. 

For very wide trenches (a large multiple of the pad thickness, depending on the hardness of the pad), the pad conforms easily to both the trench sides and the bottom, and except very close to the sides, the contact pressures and polishing rate are nearly equal. The planarization rate (the rate at which the step height is reduced) is therefore very low, and we could describe the feature as being larger than the pad planarization length. 

For somewhat narrower trenches (a small multiple of the pad thickness) that are also deep relative to the pad roughness, the pad initially spans the gap, the entire load is carried by the trench sides, and none is carried by the bottom. The sides therefore polish more quickly than on a blanket wafer, the bottom does not polish at all, and the planarization rate is high. Eventually, the unsupported area of the pad, which projects or bends into the recess, makes... 

Pad Thickness Units of (pm) or (mils). Pad thickness is related to compressibility. The thicker the pad, the more the pad compresses to conform to the surface. Pad thickness must be balanced to obtain optimum planarity and uniformity, as discussed above. Since pad conditioning (see Chapter 4) has become essential, the choice of pad thickness, with pad conditioning and life in mind, becomes an important COO issue. 

By modifying the parameters in Equation (7.15), the effect of both pad compressibility and roughness may be taken into account. The pad is compressed as it pushes against the wafer as it rides over a recess, some of the compression is relieved. Consequently, the entire thickness of the pad does not deform. A near surface effective thickness / < /, the pad thickness, should therefore be used to account for pad compression. Indeed, if values of L = 10 pm, w = PL = 150 kPa-pm and E = 40 GPa are used with the pad thickness of r = 1.25 mm (specified by the manufacturer), a value of y = 10 pm is obtained for the deflection of the pad. However, if due to pad compression, only a near surface layer of thickness / = 1.8 pm is assumed to bend, then the deflection of the pad is equal to 100 nm, which is more in line with the dishing seen in Figme 7.32. 

Figure 1 (left) The bending of the top pad as a function of the distance between the supporting points and for various pad thickness. 

Poland GA, Borrud A, Jacobson RM, et al. Determination of deltoid fat pad thickness Implications for needle length in adult immunization. JAMA 1997 277 1709-1711. 

Time This is the time spent at each region that the disc conditions. Chen [17] stated that the acmal conditioning time is the main determinant of the amount of pad wear. Also, when the conditioner stays at one region for a longer time, local pad thickness would reduce and local conditioner contact pressure also reduces. As a result, MRR gradually reduces with longer conditioning time. 

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