Examination of CCDs using voltage contrast with a scanning electron microscope

The voltage contrast mode of a scanning electron microscope (SEM) is utilized to observe charge-coupled devices (CCDs) which have been cross sectioned. A new cross sectioning technique which uses anisotropic etching to accurately define the axis along which fracture occurs is presented. Lapping is not required in this technique, as smooth surfaces result from the controlled fracturing. SEM imaging of the region just beneath a CCD double-level, polycrystalline silicon electrode structure revealed a region of contrast which appeared and disappeared under the presence and absence of an applied pulsed bias. Application of a pulsed bias to the CCD output gate is seen to result in the transient charging of the output floating diffusion, while application of a dc bias is seen to not result is such charging.