FBH research: 13.02.2012

New tool for materials characterization at FBH

In the framework of the EFRE project "Application center for high frequency technologies" the Ferdinand-Braun-Institut recently installed a materials analytics tool for characterization of degradation processes in semiconductor devices (Fig. 1). The centerpiece of the tool is an Ultra+ high resolution scanning electron microscope (SEM) with a thermal field emission electron gun from Carl Zeiss NTS which is capable of high-resolution imaging of surfaces. During installation, a lateral resolution of 1.0 nm was demonstrated.

The SEM is equipped with several systems for the analysis of structural and optical properties of semiconductor layers and devices. Among these is an energy-dispersive X-ray spectrometer (EDXS) from Bruker Nano with an energy resolution of 125 eV for quantitative determination of composition of compound materials as well as a system for detection of electron-induced currents (EBIC) allowing for failure analysis of transistors and semiconductor laser diodes.

Moreover, a cathodoluminescence system from Gatan is attached to the microscope for characterization of the optical properties of laser chips in the temperature range from 80 K to 300 K before and after life testing. The Mono-CL4-system provides fast spectral mappings in the wavelength range of 200 nm to 1100 nm. This allows also for high spatial resolution to detect areas where material properties have changed due to the high electrical and optical load during operation.

Some examples illustrate the capabilities of the new tool that considerably improves the equipment potential for characterization of semiconductor layer structures and devices at FBH. Fig. 2 shows the vertical and lateral structure of a laser with an integrated Bragg grating for wavelength stabilization with a high resolution. The contrasts are caused by the different material composition of the etched grating and the waveguide layers showing self organization during growth in the second epitaxial step. The new SEM enables an improved material contrast together with a very good lateral resolution. In Fig. 3(a) 20 µm thick HVPE-GaN layer is depicted which was grown on a structured sapphire substrate. Fig. 3(a) is a cathodoluminescence (CL) image with dark spots at dislocation positions (defect density 1,3 x 108 cm-2) and Fig. 3(b) shows the surface structure with regular growth terraces and small pits where the dislocations terminate at the surface.