D. Dietzel

Radiometric Analysis of Laser Modulated IR Properties of Semiconductors

A photothermal technique for the characterization of semiconductor materials is presented, in combination with the theoretical description of the signal generation process of the effects of the charge carrier density on the IR optical properties. It relies on the excitation of charge carrier density waves by modulated laser irradiation in the visible spectrum, leading to periodical variations of the IR optical properties. The detection is based on sensing the ir transmission of the semiconductor sample. The modulated laser irradiation in the visible simultaneously leads to small temperature variations and additional signal contributions due to the modulation of the internal IR radiation, which can be minimized and eliminated by appropriate focussing conditions. A principal understanding of the signal generation mechanism has been achieved by time-dependent measurements with a gradually increasing intensity of the external IR radiation source, while frequency-dependent measurements of the modulated IR transmission signal provide quantitative information on the semiconductor properties.

Imaging of ferromagnetic-resonance excitations in Permalloy nanostructures on Si using scanning near-field thermal microscopy

The investigated structures were Permalloy (Py) stripes of 3×0.3μm2 and a thickness of 24nm. Two samples with lattices of stripes of 2μm distance between the stripes and a lattice constant of 5μm are reported in this paper. One of the samples had crossed perpendicular lattices. The samples were prepared using standard lithography lift-off processes and comprised large arrays of at least 1000 stripes, such that enough material was available to perform conventional ferromagnetic-resonance (FMR) measurements. The overall anisotropy and resonance line behavior of the samples were determined by conventional FMR measurements. The origin of the FMR modes was then deduced locally resolved in single stripes using a scanning thermal microscope (SThM), which features a lateral resolution of 100nm and a temperature resolution of the order of a few millikelvins, mounted on a conventional FMR setup. The technique is based on the detection of the dissipated heat due to microwave absorption while in FMR. This setup provi...

Double modulated thermoreflectance microscopy of semiconductor devices

Photothermal microscopy based on combined optical and electrical excitation has been applied to insulating lines and conducting channels on SIMOX mesas prepared by focused ion beam implantation. The double excitation technique permits imaging of electrical properties of the implanted structures yielding complementary information achievable by a single excitation defect tracing. In addition, the contrast of the images of implanted structures can be increased considerably. The best contrast for the observation of insulating lines adjacent to a conducting channel has been achieved by recording the modulated reflectance signal at the fourth harmonic of the modulation frequency used for electrical and optical excitation. The contrast enhancement is found to be mainly due to thermal origins caused by the photoinduced currents, which can act as an additional heat source.

Contrast enhancement of modulated optical reflectance microscopy of semiconductor devices

Photothermal microscopy based on combined optical and electrical excitation has been applied to insulating lines prepared by focused ion beam implentation on oxygen implanted mesas. The double excitation technique permits to image electrical properties of the implanted structures which are complementary to simple defect tracing when a single excitation is applied. In addition, the contrast of imaging of implanted structures can be increased considerably. Apart from combining modulated optical excitation with electrical direct current voltages, double modulation configurations can improve the contrast further, by detecting either on a higher harmonic of the single excitation frequency or on the sum or difference of two different excitation frequencies. The influence of different parameters characterizing the experimental configuration gives information on the physical processes of the signal generation, indicating that the observed contrast enhancement is mainly of thermal origin related to the photoinduced currents.

Analysis of focused ion beam implantation of semiconductors by thermal microscopy

Implantation effects produced by focused ion beams in semiconductor materials have been analyzed with the help of thermal microscopy, based on thermal waves and laser-modulated optical reflectance (thermoreflectance). Implantation profiles related to variations of the ion dose and to the halos of neutrals and differently charged particles are interpreted with respect to the local thermal and electronic transport properties. For the signal excitation, different schemes have been applied: modulated laser beam irradiation; and additional electrical AC heating, giving improved signal contrast and improved lateral resolution for imaging applications on semiconductor devices.

Plasma etching and ion implantation on silicon, characterized by laser-modulated optical reflectance

Plasma etching and ion implantation lead to changes of the electronic and thermal properties of semiconductor materials, which have been measured with the help of the modulated optical reflectance. Imaging based on modulated optical reflectance applied to control etching and ion implantation in the production of semiconductor devices is more efficient at higher modulation frequencies where both thermal waves and charge carrier waves contribute to the measured signal.

Charakterisierung technischer Schichtsysteme mittels IR-Radiometrie thermischer Wellen

Reale technische Schichtsysteme und Oberflächen, wie CVDund PVDFilme und plasmagespritzte Beschichtungen werden mittels IR-Radiometrie thermischer Wellen in Bezug auf die Tiefenprofilierung ihrer thermischen Eigenschaften untersucht. Obwohl solche Systeme, bedingt durch Oberflächenrauheit, Reibungsverschleiß und leichte Transparenz im sichtbaren wie im infraroten Spektralbereich, erheblich vom idealen Zweioder Dreischichtenmodell des Festkörpers mit glatter und opaker Oberfläche abweichen, können aus den Messungen wertvolle Informationen über die thermischen und optischen Eigenschaften und den Zustand der Oberflächen gewonnen werden. Der besondere Vorteil ist dabei, daß die IR-Radiometrie im industriellen Umfeld eingesetzt werden kann, absolut kontaktlos arbeitet, ohne besondere Probenvorbereitung und über größere Entfernungen hinweg.

Optical properties in the visible and infrared spectrum of fiber-reinforced composites determined by combined photoacoustic and IR detection (abstract)

Carbon based fiber-reinforced composites are mostly used because of their particular mechanical properties combining a low specific weight with good elastic properties, namely from stability and break resistance. This combination allows applications which are not realizable with other materials. Other advantages are a low thermal expansion and a relatively high-temperature stability, which are the important properties for heat shields, e.g., when high heat pulses have to be absorbed. Such materials can be slightly transparent, both in the visible and the IR spectrum, which makes the thermal characterization extremely difficult. For this work, a measurement system has been developed which combines IR radiometric and photoacoustic detection in two geometrical configurations: (i) In the reflection configuration of thermal waves, where modulated heating in the visible spectrum and IR detection of the thermal wave take place at the same surface, the phase retardation measured by photoacoustics depends on the a...

Systematical analysis of laser beam modulated optical reflectance signals

Based on silicon as semiconductor reference material, the performance of the laser modulated optical reflectance signal is analyzed with respect to variations of the technical parameters of the measuring system and with respect to variations of the charge carrier lifetime related to ion implantation.

Photothermal characterization of protective layers and surface modifications

Protective layers, such as CVD and PVD coatings on steel substrates, surface modifications related to friction wear, and the effects of mechanical and thermal cycling of SMA samples have been analysed with respect to the depth profile of the thermal properties by using IR detection of thermal waves. The advantage of IR detection of thermal waves is that this method is most appropriate for remote sensing under industrial conditions, working absolutely contactless with remote detection and without any sample preparation.