Dependence of cathodoluminescence on layer resistance applied for measurement of thin-layer sheet resistance.

The dependence of spatially and spectrally resolved cathodoluminescence in a scanning electron microscope on resistances in semiconductor structures, especially on the layer resistance, is reported. This previously unstudied dependence is utilized for thin-layer sheet-resistance measurement. The method is illustrated by an assessment of lateral confinements in semiconductor-laser heterostructures.

Depth measurements of etch-pits in GaN with shape reconstruction from SEM images.

The method, which allows shape reconstruction by reading the intensity from the scanning electron microscopy image, is presented and discussed in details. The method is applied to read the morphology of etch-pits, which were formed on the GaN surface by etching in molten KOH-NaOH eutectic mixture to delineate dislocations. The etch-pit depth distributions are obtained and used to determine densities of pits related to screw, mixed or edge-type dislocations. The results are compared with atomic force microscopy.

Identification of electron beam vibration sources by separation of magnetic distortion from electric distortion on scanning electron microscope imaging.

Different types of distortions in scanning electron microscopy require different methods of their elimination, and therefore influence of these types on particular elements of the SEM system should be known. The proposed method allows for separation of the direct influence of the magnetic field on the electron beam in the SEM chamber from its influence in the SEM column and from the distortions generated in the SEM scanning block. For this purpose, a series of distorted images is registered for several working distances (between the final aperture of the electron column and the specimen) and for several energies of the electrons. Magnitudes of the distortions are measured on these images. For each applied electron energy, the dependence of the results versus the working distance is approximated with the second-order polynomial function. The analysis of the polynomial coefficients allows for the separation of the above-mentioned kinds of distortions. The presented method enables a selection of the most efficient solution to the distortions reduction. It utilizes the SEM itself and does not need any additional equipment.

Transmission electron microscopy characterization of Au/Pt/Ti/Pt/GaAs ohmic contacts for high power GaAs/InGaAs semiconductor lasers.

We report on transmission electron microscopy studies of Au/Pt/Ti/Pt(10-30 nm) contact structures for high power GaAs/InGaAs semiconductor lasers. The studies showed that annealing at 450 degrees C of contact structures causes the reaction of whole Pt with substrate components (Ga and As) and the formation of Pt-GaAs interlayers with smooth interfaces as required for such structures. Annealing of the structures at 470 and 490 degrees C unfavourably affects the contact structure. At this condition, the strong downward diffusion of Au and Pt from the top layers causes a formation of Au-Pt pits, which break the Ti barrier. Transmission electron microscopy observation revealed that Au/Pt/Ti/Pt(10-30 nm) system annealed at 450 degrees C is appropriate for practical applications. The EDS technique used to identify the phase composition in the Pt(30 nm)/GaAs structure (specially produced for the EDS analysis) annealed at 450 degrees C showed that two layers were formed as a result of the reaction of the whole Pt layer with GaAs, and they consist of Ga, Pt and As. The top layer has the highest concentration of Ga. However, the bottom layer, which is close to the substrate, has the highest concentration of As.

Transmission electron microscopy study of erbium silicide formation from Ti/Er stack for Schottky contact applications.

In this paper, we present results of transmission electron microscopy studies on erbium silicide structures fabricated under various thermal conditions. A titanium cap has been used as a protective layer against oxidation during rapid thermal annealing of an erbium layer in a temperature range of 300-700 degrees C. Both layers (200 nm Ti and 25 nm Er) were deposited by electron-beam sputtering. The investigations have shown that the transformation of the 25-nm-thick erbium into erbium silicide is completed after annealing at 500 degrees C. At higher temperatures, the formation of a titanium silicide layer above erbium silicide is observed. The lowest Schottky barrier has been measured in the sample annealed at 700 degrees C.

New approach to cathodoluminescence studies in application to InGaN/GaN laser diode degradation.

Cathodoluminescence (CL) studies are widely applied in semi-conductor science and technology. However, for structures with a p-n junction the CL spatial distribution can be strongly affected by internal current flows of the electron beam induced current generated within the structure. This influence is the investigated in application to CL studies of degradation in aged laser diodes with InGaN multiquantum wells.

Selective etching of dislocations in GaN and quantitative SEM analysis with shape-reconstruction method.

Due to the differences in etch-pit morphologies, chemical etching offers a possibility to determine densities of dislocations in respect to their type. In the present paper we propose a method, which implements a simple shape-from-shading procedure, i.e. with results derived from image brightness dependence on surface slope. It allows estimation of etch-pit depth distributions from scanning electron microscopy micrographs. This method is used to obtain depth distributions from GaN surface after etching in molten KOH-NaOH eutectic mixture. Depth distributions are used to estimate densities of etch-pits related to a given dislocation type. The distributions are compared with dislocation densities determined with transmission electron microscopy.

Transmission electron microscopy characterization of the erbium silicide formation process using a Pt/Er stack on a silicon-on-insulator substrate.

Very thin erbium silicide layers have been used as source and drain contacts to n-type Si in low Schottky barrier MOSFETs on silicon-on-insulator substrates. Erbium silicide is formed by a solid-state reaction between the metal and silicon during annealing. The influence of annealing temperature (450 degrees C, 525 degrees C and 600 degrees C) on the formation of an erbium silicide layer in the Pt/Er/Si/SiO(2)/Si structure was analysed by means of cross-sectional transmission electron microscopy. The Si grains/interlayer formed at the interface and the presence of Si grains within the Er-related layer constitute proof that Si reacts with Er in the presence of a Pt top layer in the temperature range 450-600 degrees C. The process of silicide formation in the Pt/Er/Si structure differs from that in the Er/Si structure. At 600 degrees C, the Pt top layer vanishes and a (Pt-Er)Si(x) system is formed.

Elimination of scanning electron microscopy image periodic distortions with digital signal-processing methods.

Electromagnetic interference is one of the main distortion sources in scanning electron microscopy. Electromagnetic interference-generated scanning electron microscopy image distortions are usually visible as edge blur (at low scan rates) or vibration (at high scan rates). Hardware solutions to this problem, e.g. electrostatic and magnetic shielding, are expensive and, in some cases, difficult to implement. The current investigations led to a significant decrease in the periodic distortions by a novel adaptation of software-based digital signal processing to scanning electron microscopy problems, without any hardware modification.

In situ electron beam induced current measurements of the local thickness in semiconductor devices.

A quantitative electron beam induced current method is shown, applicable in situ for electron beam current measurement on a semiconductor sample without the need for a Faraday cup. As a validation technique, the measurement of top overlayer thickness in the semiconductor structure was chosen for two reasons. First, the measured thickness is easily verified using the same electron microscope in the secondary electron mode by measuring the layer thickness at the layer edges. Second, the measurement of a layer thickness and its local variations constitute an important issue in semiconductor processing and characterization. The proposed method is used in the planar view of the sample, and also for locations far from the layer edges. Quasi-three-dimensional maps of the thickness spatial distribution are presented.

Buried amorphous-layer impact on dislocation densities in silicon.

The impact of amorphous layers on dislocation densities in silicon piezo-resistors was investigated by means of transmission electron microscopy and chemical etching. Mechanical bevel polishing at a shallow angle and selective etching were applied to assess the dislocation depth distributions. It was found that, despite the presence of additional defects after recrystallization, the initial presence of a buried amorphous layer reduced, after annealing, the dislocation density in the depletion region of a p-n junction, compared with the case of a shallower, surface amorphous layer.