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Application of Atomic Force Microscopy (AFM) for Surface Characterization
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Gold is an indispensable element for the metallization of optoelectronic and high-frequency devices due to its low electrical resistivity, to its excellent mechanical robustness, as well as to the increased resistance to oxidation and to electromigration. During physical analysis, the gold metallization has often to be selectively removed at low temperature and without damaging neither the dielectrics nor the semiconductor.

Figure 1 shows a 400 nanometer thick gold layer evaporated on a silicon substrate. After 40 minutes of etching in an 0.005 Mole aqueous solution of potassium iodide and iodine (I2/I-) this topographic image has been taken by an Atomic Force Microscope in tapping mode with a magnification of 20,000.

The operation of photonic devices at high junction temperatures as encountered in field applications leads to the regrowth of the gold grains with time. It has been shown that this time-dependent coarsening of the metallization texture results in a relevant degradation of the etching rate of the I2/I- solution.

Fig2: Atomic Force Microscope
Fig3: In tapping mode the cantilever (tip) oscillates at a frequency near to the resonance touching softly the sample surface. The system detects the variations in topography by changes in the cantilever oscillation frequency or amplitude

Last change: 21 December 2005    Author:  Mauro Ciappa