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Characterization of integrated circuit aluminium bonding pads by nanoindentation and scanning force microscopy

Surface and Coatings Technology
Publication Date
DOI: 10.1016/s0257-8972(97)00435-0
  • Ic Bonding Pads
  • Nanoindentation
  • Scanning Force Microscopy
  • Vickers Hardness
  • Mathematics


Abstract The mechanical properties of thin films and surface modified layers can be measured by a variety of different techniques, with nanoindentation being one of the most recent developments in this growing field. It is particularly suited to the characterization of bonding pads used to connect individual microcircuits and chips. Such pads are commonly made of aluminium and have a thickness of approximately 1 μm. By using a depth-sensing indentation method it is possible to obtain quantitative values for the hardness and modulus, and thus gain better insight into the response of a bonding pad material to controlled deformation at such small scales. The nano hardness tester (NHT) is a recently developed instrument using an already established method where an indenter tip with a known geometry is driven into a specific site of the material to be tested, by applying an increasing normal load. When reaching a preset maximum value, the normal load is reduced until partial or complete relaxation occurs. At each stage of the experiment the position of the indenter relative to the sample surface is precisely monitored with a differential capacitive sensor, giving a load/displacement curve characteristic of the sample material. By consequently measuring the topography of the residual indent using a surface imaging technique (e.g., scanning force microscopy) and combining this information with the indentation data, it is possible to gain a fuller understanding of the material response, as well as additional information on surface roughness and frictional properties, the latter being of particular importance in bonding applications. Experimental results are presented for a variety of integrated circuit bonding pads, these confirming the ability of the NHT to becoming a common test in quality assurance and process development of thin films and coatings for the microelectronics industry.

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