Focused-ion-beam preparation of wedge-shaped cross sections and its application to observing $p–n$ junctions by electron holography

The preparation of well-defined cross-sectional samples is critical for the quantitative analysis of $p–n$ junctions in semiconductor devices by electron holography. A wedge is a good shape for the geometry of the cross section that is suitable for mapping and characterizing one-dimensional $p–n$ junctions, especially those with lower doping levels. The method we used to prepare such cross sections involved focused-ion-beam milling and we describe it in detail. Following this, we could easily fabricate well-defined wedge-shaped cross sections with different given angles within a very short time. The use of such cross sections allowed us to clearly map implanted Si/Si $p–n$ junction structures with lower dopant concentrations with off-axis electron holography.