SEM techniques for characterization of GaN nanostructures and devices

High resolution electron beam induced current (EBIC) analyses were carried out on InAs quantum dots (QDs) grown on GaAs substrate, in a scanning electron microscope (SEM) and a conducting atomic force microscope (C-AFM) hybrid system. This scanning near-field EBIC microscope allows one to image a sample conventionally by SEM, to investigate by AFM the local topography and to simultaneously perform EBIC imaging. The EBIC capabilities of this combined instrument are evidenced by imaging plastic slip lines created by nanoindentation, and its performance in resolution is demonstrated to be of the order of 20nm by imaging the induced current flowing through the InAs∕GaAs QDs and the ringlike structures that surround them. The influence of the presence of QDs on the minority carrier diffusion length is also investigated. It is shown that the presence of QDs close to the surface sample increases the diffusion length.

In the scanning electron microscope (SEM), specially designed microrobots can act as a flexible assembly facility for prototype microsystems, as probing devices for in-situ tests in various applications or just as a helpful teleoperated tool for the SEM operator when examining a few samples. Several flexible microrobots of this kind have been developed and tested. Driven by piezoactuators, these few cubic centimeters small mobile robots perform manipulations with a precision of up to 20 nm and transport the gripped objects at speeds of up to 3 cm/s. New microrobot prototypes being employed in the SEM are described in this paper. The SEM's vacuum chamber has been equipped with various elements to enable the robots to operate. In order ot use the SEM image for automatic real-time control of the robots, the SEM's electron beam is actively controlled by a PC. The latter submits the images to the robots' control computer s ystem. For obtaining three- dimensional information in real time, a triangulation method with the luminescent spot of the SEM's electron beam is being investigated. Finally, the strategies of a micro force sensing and control methods required for handling techniques with two robots are discussed.

3D-investigations of electrically active interfaces in ZnO varistor materials have been performed using electron beam induced current (EBIC) contrast in the scanning electron microscope in combination with the focused ion beam workstation (FIB). The EBIC measurements were performed with spatial resolution better than 100 nm and the depth dependence of the signal was studied by variation of the acceleration voltage. The FIB was used for characterization of the subsurface geometry of electrically active grain boundaries. Experimental EBIC profiles, obtained by scanning the electron beam across grain boundaries, were compared with computer simulations using three different models for the electron–hole generation function. The EBIC contrast has been found to depend strongly on the geometric properties, i.e., the tilt of the grain boundary, and on asymmetries in the depletion region at the boundary. Calculations of the EBIC contrast taking these two effects into account show good agreement with experimental data. The “hot electron effect” close to the electrical breakdown voltage has been experimentally observed. The possibility to study asymmetry in the depletion region and the influence of the applied bias on the electrical properties of individual interfaces using the EBIC technique has been demonstrated.

A novel analytical method applying combined electron beam induced current (EBIC) imaging based on scanning electron microscopy (SEM) and focused ion beam (FIB) cross sectioning in a SEM/FIB dualbeam system is presented. The method is demonstrated in several case studies for process characterization and failure analysis of thin film technology based Solar cells, including Silicon (CSG), Cadmium Telluride (CdTe) and Copper Indium Selenide (CIS) absorbers. While existing techniques such as electro-, photoluminescence spectroscopy and lock-in thermography are able to locate the larger, electrically active defects reasonably fast on a large area, the FIB-SEM EBIC system is uniquely capable of detecting sub-micron, sub-surface defects and of analysing these defects in the same system. In combination with a FIB, the localized region of interest can be easily cross sectioned and additional EBIC analysis can be applied for a three dimensional analysis of the p/n junction.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

Atomic force microscopy (AFM) was combined with scanning electron microscopy (SEM) to investigate electronic devices. In general, under observation using an optical microscope, it is difficult to position the cantilever at an arbitrary scan area of an electronic device with a microstructure. Thus, a method for positioning the cantilever is necessary to observe electronic devices. In this study, we developed an AFM/SEM system to evaluate an electronic device. The optical beam deflection (OBD) unit of the system was designed for a distance between the SEM objective lens and a sample surface to be 2 cm. A sample space large enough to place an actual device was created, using a scan unit fabricated with three tube scanners. The scanning ranges of the scan unit are 21.9 µm × 23.1 µm in the XY plane and of 2.5 µm for the Z axis. The noise density in the OBD unit was measured to be 0.29 pm/Hz0.5, which is comparable to noise density values reported for commercial AFM systems. Using the electron beam of SEM, the electron beam induced current (EBIC) is generated from a p–n junction of a semiconductor. Using the EBIC, the cantilever was positioned at the p–n-junction of a Si fast recovery diode (FRD). In addition, scanning capacitance force microscopy (SCFM) and Kelvin probe force microscopy (KFM) were combined with the AFM/SEM system. The SCFM and KFM signals were in qualitative agreement with the expected carrier density distribution of the p and n-regions of the Si-FRD.

Electron beam induced current, cathodoluminescence and scanning photoluminescence study of GaN layers

EBIC study of recombination activity of oxygen precipitation related defects in si

Applications of the scanning electron microscope EBIC mode to semiconductor device evaluation and failure analysis

Electron beam-induced current (EBIC) imaging is a well-established scanning electron microscope (SEM) technique used to analyze the behavior of microelectronic devices including solar cells. Recently, the application of EBIC imaging in an aberration-corrected scanning transmission electron microscope (STEM) has been demonstrated and offers great potential for the in situ study of electronic materials, correlating charge transport properties to atomic structural and elemental information. This work presents two ways to implement EBIC imaging in conventional SEM and STEM systems: one relying on the instrument's inherent scanning and imaging electronics and the other involving third-party systems usually available in electron microscopes. The implementation of lock-in EBIC in systems equipped with a fast beam blanker is also described. In addition, this work shows and discusses the different mechanisms at play in EBIC imaging and their dependence on beam energy, sample impedance, and electrical measurement configuration, providing researchers with the basic information needed to apply the technique to their research.

Particulate growth processes in Ar+SiH4 RF plasmas are studied using ultraviolet light-absorption and scanning electron microscopic (SEM) methods. Measurements of particulate size and density using the SEM method show that they grow through three phases: nucleation, rapid growth and growth saturation. Such features of temporal evolutions of their size and density are very similar to those for He+SiH4 RF plasmas previously obtained by SEM and in situ laser light scattering methods. It is also found that particulates in two different size ranges coexist after the initiation of the rapid growth phase, and their coagulation plays an important role in this phase. Close similarities among spatial profiles of Si emission intensity, Si density, and amount of particulates are revealed in wide discharge-parameter ranges of 1–100% SiH4, 11–20 Pa, and 40–100 W. These results suggest that many short-lifetime neutral radicals such as SiHn (n=0–2) contribute to nucleation and subsequent initial growth of a particulate, since other short-lifetime radicals are also expected to have similar spatial profiles.

Analysis of Cu(In,Ga)(S,Se) 2 thin-film solar cells by means of electron microscopy

Low dose 60Co gamma-irradiation effects on electronic carrier transport and DC characteristics of AlGaN/GaN high-electron-mobility transistors

Electron-beam-induced current (EBIC) measurements in the scanning electron microscope have been correlated to analytical transmission electron microscopy observations on a faceted Σ = 3 twin boundary in aluminium-doped silicon. A microfaceted region, where about 1010 cm−2 aluminium-containing oxynitride nanoprecipitates were also present, exhibited no EBIC contrast. On an atomic scale, the microfacets were along no other planes than the (11―1) and (11―2) twin planes, and all the observed nanoprecipitates were situated at facet intersections. Given the EBIC detection limit, the concentration of electrically active bonds along these edges was estimated to be less than about 3%, which, on the one hand, corroborates the absence of deep levels predicted by Kohyama et al. in 1990 for these defects and, on the other hand, shows that the electrical activity of the oxide-based precipitates is small.

In a-Si:H/c-Si hetero-junction solar cells, front surface texturization is used to maximize light absorption, while care should be taken to avoid high number of generated dangling bonds, which deteriorate the electronic properties of the device through surface recombination losses at the amorphous/crystalline silicon interface. Thus, a balance between light absorption and recombination of minority carrier has to be satisfied. This work concerns the study of the optoelectronic properties of a-Si:H/c-Si hetero-junction involving two texturization processes of silicon substrates based on a cupper-assisted etching and a CP4 etching. Obtained results show that the optical properties are more interesting with samples etched in cupper solution. However, the highest effective carriers’ lifetime, measured by the photoconductive decay (PCD) and μW-PCD methods are more interesting in samples etched with a CP4 solution. We confirm these results through the determination of the surface recombination velocity of minority carriers, which was obtained from a developed theoretical procedure and PCD measurements. Therefore, we obtain a recombination velocity of 500 cm.s−1 in the case of the CP4 etching. However, it is three times greater in the case of Cu etching. We discuss these results in link with the morphology of fabricated samples performed with 2D and 3D AFM characterization, as well as surface profiling and RMS values.