Mapping the phase of the cantilever oscillation during an atomic force microscopy (AFM) scan can create a phase image that reveals submicron surface variations. A Digital Instruments (Santa Barbara, CA) applications engineer created images of a bond pad on an integrated circuit at the Microscopy Society of America conference held last summer in Kansas City, MO. A conventional TappingMode AFM topographical scan does not show any unusual features, but the phase image reveals light contrast from the areas of the pad contaminated with polyimide. (A phase shift of 120° over a 1.5 µm area was used to create the image.)
According to Monte Heaton at Digital Instruments, the phase imaging technique can detect differences in composition, adhesion, friction, viscoelasticity, and other contrasts in surface characteristics. The technique can image soft, adhesive, or loosely bound samples and can be implemented on the company's MultiMode or Dimension series scanning probe microscopes equipped with an appropriate electronics module.