Friction, coefficient of, COF

AFM studies on the thin ( 50 nm) brush layers demonstrate that the dynamics of supramolecular cross-links contribute to the friction of the soft brush surfaces (Fig. 3.11). When the faster 4a cross-linker is added, both the absolute friction values and the coefficient of friction (COF) drop to 30% of those of the uncross-linked PVP control. When the slower cross-linker 4b is added, however, the absolute friction value and the COF increase dramatically both the COF and the absolute friction values for PVP 4b are more than twice that of PVP alone. The absolute lateral force measured is proportional to the normal force applied this is consistent with the model that the more the tip is pressed into the brush layer the more force it takes to drag it laterally through the brushes. 

There have been some efforts in slurry recycling to reduce CoO of CMP consumables. In a recent study [37], the effluent samples were characterized for pH, trace-metal levels, viscosity, specific gravity, mean aggregate particle size, and LPC (>1.0 rm) before and after depth (melt-blown polymeric media) filtration. The study showed that the use of a recycled fumed silica slurry (recycled five times) decreased the CMP removal rate and the coefficient of friction (COF) by 40%. A perfect relationship was observed between the removal rate and COF. It was concluded that the increase in mean aggregate particle size, which lowers the contact area between the abrasive particles and the wafer, had some impact on the removal rate data. In general, there is a stronger emphasis on slurry additives and chemical action in current CMP processing with much lower maximum defectivity performance specifications [2]. 

A real-time measure of the coefficient of friction is essential to a well-controlled CMP process. It is possible that this could be done by a coefficient of friction (COF) probe, mounted on the CMP tool, which could feed back observed values to the process control computer. There are several requirements in making a measurement that truly reflects the process conditions, the first of which is that the probe surface material should be the same as the wafer surface material (so the COF you read reflects what the wafer experiences). That situation, of course, is already inherent in the wafer carrier head, but the signal-to-noise ratio in trying to read the COF off the wafer carrier head is often too great to be of use. 

Coefficient of Friction. Primary Film Test Method ASTM D1894. The coefficient of friction (CoF) test is used to measure the static (starting) and kinetic (sliding) resistance of the film when sliding over another surface, either film-to-film or film-to-metal. Coefficient of fiiction is the ratio of the fiictional force to the force, usually gravitational, acting perpendicular to the two surfaces in contact. The static CoF is representative of the force required to begin movement of the surfaces relative to each other. (See Fig. 3.) The kinetic CoF is representative of the force required to sustain this movement. ]... 

Coefficient of Friction (CoF) The coefficient of frietion is defined as the ratio of the weight of an obj ect being moved along the surfaee of a speeimen to the force that is required to maintain eontaet between the object and the surface. 

When plastics (particularly films) slide over each other, there is a resistance that is quantified in terms of the coefficient of friction (COF). Films with a high COF tend to stick together instead of sliding over one another. Sticking makes the... 

Measurement of coefficient of friction (COF) can be done in many ways. ASTM D1894 is one method. For instance, static COF, the force needed to start movement across a polymeric surface, can be quite high. Dynamic COF, the force required to maintain movement, is always lower. 

The coefficient of friction (COF) measured during the tribological test is presented in figure 1 as a function of the applied load. The two bars represent two independent samples. The reported COFs are the values averaged over the last full turn of the disk at the particular load. It is assumed that, at this time, a... 

By preparing silane SAMs on a silicon surface, the coefficient of friction (COF) is reduced from 0.5-0.6 to 0.1, as reported by many groups [29, 34] using a reciprocating tribometer, and from 0.15 to 0.018, as reported by Tsukruk et al. [35] using FFM. 

A schematic depicting these lubrication regimes is illustrated in fig. 13.1, where p is the coefficient of friction (COF) and h is film thickness. In fig. 13.1, p and h are plotted as functions of the lubrication process parameter, z, defined as follows ... 

The coefficient of friction (COF) of the polymer against the metal surface is independent of pressure. 

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