title: Detection of buried reference structures by use of atomic force acoustic microscopy.
abstract: The miniaturization of micro- and nanoelectronic components requires new methods for the inspection of buried inner structures at the nanoscale. We used the atomic force acoustic microscopy technique (AFAM) to image subsurface defects. This technique combines high lateral resolution with the capability to determine local elastic properties of materials near the surface. As the structures buried near the surface change the effective tip-sample contact stiffness it is possible to detect them. For the verification of the detection capabilities of AFAM we fabricated well-defined buried void structures with different geometries and dimensions. Large, thin, plate like structures of silicon nitride with a local filling were our first test samples. Then, sets of nine small, square, thin plates with thicknesses increasing stepwise from 30 to 270 nm were etched in a thinned silicon wafer. The last two samples contained wedge structures of widths varying between 1.6 and 10 μm. Our results showed that it was possible to detect buried void structures at depths between 180 and 900 nm. We also observed that the depths at which the buried defects can be detected by the use of the AFAM method depend on the defect dimensions and geometry, and on the mismatch in the elastic properties of the sample and the defects. The experimental results obtained for the groups of small, thin plates were verified by quantitative analysis via finite element method (FEM) simulations.
authors.affiliation: Fraunhofer Institute for Non-Destructive Testing, Dresden Branch (IZFP-D), Maria-Reiche-Strasse 2, D-01109 Dresden, Germany. andre.striegler@izfp-d.fraunhofer.de
authors.forename: Andre
authors.initials: A
authors.lastname: Striegler
authors.forename: Bernd
authors.initials: B
authors.lastname: Koehler
authors.forename: Beatrice
authors.initials: B
authors.lastname: Bendjus
authors.forename: Mike
authors.initials: M
authors.lastname: Roellig
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Kopycinska-Mueller
authors.forename: Norbert
authors.initials: N
authors.lastname: Meyendorf