Stylus Profilometry Force Measurement

Stylus profilometry is a very simple and powerful tool in CMP. Profilometry can be used to determine the surface planarity change before and after CMP. Basically, in this technique, a stylus scans across a pattern feature in contact with a wafer, while the Z motion (height) of the stylus is monitored. This Z motion signal reflects the surface topography scanned. 

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A serious complication of using profilometry to measure volume change becomes apparent when attempting to make measurements on thin films (<10 pm). Here the applied force from the stylus can lead to anomalous results such as a smaller PPy (DBS) film thickness in the expanded (reduced) state than in the contracted (oxidized) state. This is due to the lower stiffness (Young s modulus of elasticity) in the reduced state compared to the oxidized state resulting in the stylus sinking into the softer polymer. This is not a problem for relatively thick films provided absolute values are not required profilometry can serve as a useful tool to observe the actuation of thick conducting polymer films. 

In all tests a load of 75 N was applied to the pin giving a contact pressure of 1 MPa. Stylus profilometry was used to assess the depth of the wear scar produced at four places on each track and the results averaged to determine the wear. Friction coefficients were determined by dividing the measured frictional force by the applied normal load. 

The ablation depths are measured by profilometry (optical interferometer, mechanical stylus [59], atomic force microscopy [60]) and starts sharply at the threshold fluence. Similar conclusions can be drawn from reflectivity [61] or acoustic measurements [62]. The problem with these measurements is that either single- or multi-pulse experiments are used to determine the ablation depths and threshold which might give different results. 

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