Micro-scratch

In micro-scratch experiments single scratches of characteristic and realistic phenotype can be generated. The indentation depth depends on the applied force and the indentation body (indenter). Indentation depth is usually in the range of 1 xm and smaller. A diamond indenter (radius at the peak 1-2 xm) is pushed onto the sample surface applying a defined force to generate the scratch while the sample is moved in a linear direction at constant velocity underneath the indenter (see Fig. 1). The applied normal force... 

Lin M, Chang C-Y, Liao DC, Wang B, Henderson AImproved STI-CMP Technology for micro-scratch issue. Proceedings of the CMP-MIC 1999. 

Fig. 7. Defect and micro-scratch counts in an extended run over 3 days with on oxide wafers using AEP ring and a 2 platen polish process.

The AFM analysis on the Si02 film revealed that the 10%of particles wore pit type. These particles were micro scratches same as Si wafer surfece. Many micro scratches occurred on die Si02 and Si surfece induced some secondary particles in slurry during polishing. Particles were easily washed away widi DI water. 

Typical slurries for polishing Si02 are KOH or NH4OH based at high pH (10-12) with equal or slightly harder material such as silica. Careful particle size control of the slurry using filtration is required to minimize defects such as micro scratches and gouging. ... 

Though both the optical and force plots show all three zones, the borderlines between them, defining the critical loads (times) or micro-scratching and delamination, can be determined with higher accuracy by utilizing additional electrical and acoustic measurements. 

FIG. 4—Micro-scratch test data for thin hard coatings. 

Gitis, N. and Vinogradov, M., patent of Micro-scratch Test Indentation and Method of Micro-scratch Testing, 1999. 

Figure 1.11 SEM images of micro-scratch at post-STI CMP process [10].

As observed in the scanning electron microscope (SEM) image, any macro-scratch can be observed right after the STI CMP step, but most of the polishing scratches can be seen after the oxide deglazing step since the wet etch step can make any tiny microscratch more visible by isotropic etching (Figure 1.13). A very tiny micro-scratch can be observed on the nitride surface, but the scratch on the oxide surface is expanded due to the additional wet etch step. 

The polishing scratch mechanism in dielectric CMP is illustrated in Figure 1.18. From the top view, an arc shaped chatter-mark is created behind the abrasive contact region because of the maximum shear stress in the tensile region. In this case, the concave side of the arc shape of the micro-scratch will face the direction of travel... 

Otherwise, micro-scratches and other defects can be less critical. Also, post-CMP cleaning and surface contamination play a minor role. Small scratches can be tolerated... 

Specific cases of fracture onset are observed when metals and high-strength ceramics are micro-scratched while in contact with metal melts. Of special interest is the investigation of the surface damage occurring under a combination of the medium effects and electric polarization. In this case, there is a possibility of using electrical-chemical-mechanical treatment, namely, liquid metal embrittlement in the absence of a liquid or a metal phase. The latter is achieved by the reduction of the active ions on the treated surface. 

Figure 1. Block diagram of the micro-scratch apparatus.

For the micro-scratch experiments presented here, the instrument configured for a maximum of 100 milli-Newtons (mN) normal force with 5 micro-Newtons (tiN) resolution, and 90 micrometers (pm) vertical displacement with 2 nanometer (nm) resolution. A variety of normal force and displacement ranges and system resolutions can be constructed depending on the application. The resolution for the sensor of tangential force measurement is 20 pN. 

The AFM used in these experiments is a precision large stage M-5 instrument from Park Scientific Instruments. The stage motion is calibrated with NIST traceable standards and the absolute reproducibility is within a few microns. The micro-scratch instrument and the AFM are in perfect registry so that images and morphological calculations are precisely related to the micro-mechanical measurement (i2). 

Figure 2. Force and displacement vs. scratch distance during a micro-scratch experiment.

There may be other ways to evaluate plastic resistance of coatings based on the data of micro-scratch experiment. Nevertheless, mar resistance can be evaluated or ranked mechanistically and objectively with the area under the plastic deformation curve and the critical normal force before fracture. 

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