Optical Characterization of Electronic Packages with Confocal Microscopy

New electronic packages and electronic systems with integrated micromechanical functions (MEMS) or integrated optical functions (MOEMS) need for their geometrical characterization measurement systems which can operate in the nanometer scale. At present, different optical scanning techniques are used to measure surface features of packages, substrates and other devises. Therefore a laser beam follows the object surface in a meander pattern. Because of the necessary movement of the plane-table or the sensor the measurement result is superimposed by the drive characteristics. For very smooth surfaces as silicon or glass this can result in a strong failure. In contrast to this the confocal microscopy provides a high resolution surface plot in one shot without movement of the device. This paper shows the benefits of such a measurement principle. The confocal microscope can measure optically complex surface structures while maintaining high vertical and lateral resolution. The physical filtering principle leads to a significant reduction of optical artefacts and a robust and predictable height signal in cases, where other optical methods fail. In addition the confocal microscopy allows to measure through transparent layers as passivations or optical windows in hermetic packages. For such applications a non-destructive testing becomes possible. The confocal microscopy is best used for the development of new products with functional microstructures, for the failure analysis and the industrial quality assurance. Application data demonstrate the capabilities of this technique compared to conventional scanning profilers on one side and the scanning electron microscopy (SEM) on the other side.