Zhouguang Wang

Electron holographic characterization of electrostatic potential distributions in a transistor sample fabricated by focused ion beam

A cross-sectional sample of a silicon-metal-oxide semiconductor field-effect transistor, which was directly cut from an integrated circuit wafer, has been prepared carefully using a focused-ion-beam technique and examined by means of off-axis electron holography. In the reconstructed phase image, heavily doped source, and drain regions are revealed clearly as bright contrast, from which an n-channel transistor is identified. In addition, two-dimensional phase distributions around both source and drain regions show a core area with relatively high phase in the heavily doped region, which may be attributed to the effect of doping atoms and residual defects and strains remaining after implantation. The electrostatic potentials across the core area and depletion layer are estimated and discussed. This work demonstrates the feasibility of using a focused-ion-beam technique to prepare electron holographic sections of a wide range of semiconductor devices.

Long-range order parameter of single L10-FePd nanoparticle determined by nanobeam electron diffraction : Particle size dependence of the order parameter

The long-range order (LRO) parameter (S) of single isolated L10-FePd nanoparticle was determined by quantitative analysis of nanobeam electron diffraction (NBD) intensities and intensity calculations considering the multiple scattering of electrons. The obtained order parameters of the nanoparticles larger than 8nm are distributed around the mean LRO parameter (S¯=0.79) which was determined by selected area electron diffraction intensity analysis, while the parameters slightly decreased gradually as the particle size decreased below about 8nm (S=0.60–0.73). The low degree of order in very small particles is responsible for the coercivity decrease of the L10 nanoparticles in smaller-sized regions. Quantitative NBD intensity analysis is quite useful for the determination of the LRO parameter of individual L10-FePd single crystalline nanoparticle. Experimental conditions required for NBD analysis are presented in detail and the possible experimental errors of the determined LRO parameters are discussed.

Characterizing an implanted Si/Si p–n junction with lower doping level by combined electron holography and focused-ion-beam milling

A Si/Si p–n junction with very low doping level was made via a standard device fabrication process by implanting As ions at 25 keV into a p-type Si substrate with a boron concentration of 1015 cm−3, followed by heat annealing at 1035 °C for 33 s. To characterize this junction, a pair of 45° wedge-shape cross sections was prepared simultaneously by focused-ion-beam milling and examined using off-axis electron holography. The reconstructed phase images clearly show the phase shift induced by the electrostatic potential drop across the p–n junction, indicating that the junction has been mapped successfully. Quantitative measurements from the phase images give the potential values of 12.21±0.40 and 11.50±0.27 V, respectively, for the n- and p-type sides of the junction, 0.71±0.05 V for the potential drop across the junction and 50.10±3.88 nm for the total electric dead layer thickness. This work demonstrates that electron holography is a powerful technique for characterizing low dopant level p–n junctions in ...

Determination of order parameter of L10-FePd nanoparticles by electron diffraction

Long-range order (LRO) parameters of two-dimensional dispersed single-crystalline 10-nm-sized FePd nanoparticles with the L10 structure have been determined accurately by electron diffraction in transmission electron microscopes (TEMs) under accelerating voltages of 300kV and 1kV. Diffraction patterns by exciting hh0 systematic reflections effectively reduced the numbers of diffracted beams and simplified the thickness dependence of intensity ratio I110∕I220 for 110 and 220 reflections. Mean thickness of the nanoparticles was estimated to be 7.8nm by electron holography. The relation between the intensity ratio and the order parameter was calculated on the basis of multiple-scattering intensity calculation. By comparing the relation and experimentally obtained intensity ratios, the order parameters of 0.65 and 0.79 were obtained using 300-kV TEM for FePd nanoparticles after annealing at 873K for 3.6 and 36ks, respectively. Also, the order parameter of 0.82 was obtained using 1-MV TEM for the same specimen...

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.

In-situ TEM observation of electromagnetic field in some real materials

Electromagnetic fields presents in some real materials have been observed using electron holography and a simple method named the Shadow Image Distortion (SID) method which we have developed. The in-situ electron holography observation of the electric field surrounding a ceramic particle showed the rapid degradation of dielectric properties of the particle at an elevated temperature. The cross sectional view of mean electrostatic potential distributions in a silicon device has been observed. In-situ electron holography and SID observations showed the electrostatic potential distribution across a reverse biased p-n junction in a compound semiconductor. The SID method using a dedicated tool allowed single-step imaging of 2D maps of electromagnetic field.