Didier Marty-Dessus

Surface temperature measurement for space charge distribution measurements with thermal methods

The implementation of space charge measurements based on thermal perturbation on thin films requires an improvement of the temperature distribution estimation at the surface and in the depth of dielectric materials for getting reliable space charge profile measurements. Absolute temperature variations are needed, both in time and space. The present contribution addresses surface temperature measurements based on either thermoelectric or bolometric effects. Both responses have been measured on copper-coated silicon nitride layers and gold-coated polypropylene films heated with a Nd:YAG laser pulse. It is shown that high temporal resolution thermal response can be obtained through the bolometric response and that the information appears nearly independent on the nature of the coating electrode. The setup developed provides good signal to noise ratio for heated electrodes of a few ohm resistance. Strategies are still to develop to get the temperature profile in the insulating sample layer.

Defect detection in silicon wafer by photoacoustic imaging

Photoacoustic imagery is a non-destructive testing technique, which allows in-depth images in thick samples to be realized. Image representing cuts at different depths were obtained by modifying the laser source modulation frequency, and this technique was applied to defect localization within a silicon wafer.

Virtual Space Charge Model for a Frequency-Based Characterization of Insulators.

As insulators are stressed with a strong electric field, they store electric charges that can be represented as space charge distributions. We propose a simple equivalent model of these distributions in order to characterize the internal residual field in a thin polymeric insulator using a frequency-based technique called focused laser intensity modulation method (FLIMM). This approach shows its ability to follow simple evolutions resulting for example from an increasing of stressing field or of the poling duration time, avoiding in a first approximation the use of complex mathematical algorithms.

Space charge formation in polyimide films and polyimide/SiO2 double-layer measured by LIMM

For Polyimides (PI) used as insulating inter-layers or passivation layers in microelectronics and power electronics, reliability and failure mechanisms are intimately linked to phenomena such as non-linear conduction, distortion of field distribution and electrical ageing that have all some relation to space charge processes. Knowledge about these space charge distributions is therefore of importance to optimize structures and designs involving PIs. However, in the thickness scale of interest for such applications, of the order of 10 μm, no results were reported for PI, and only scarce studies for other materials. Space charge measurements carried out on PI using the laser intensity modulation method (LIMM) are reported in this work. PI-containing metal-insulator-semiconductor structures were pre-stressed under DC fields up to 2 MV/cm. The impact of the doping type of the substrate (either n-type or, p-type silicon) has been evaluated to address the mechanisms of space charge formation. The nature of electrode substrate substantially impacts the measured charge amount and charge nature, pointing towards charge injection as the origin of space charge build-up. The interpretation is substantiated by results obtained using a SiO2 layer as a barrier against electronic injection from the substrate into the PI layer.

Towards space charge measurements by (F)LIMM under DC electric field

An evolution of a conventional thermal wave technique for space charge investigation in insulations is presented. Based on a laser diode as source of heat, the set-up has been modified in order to be able to stress electrically samples under study with an external electric field while doing measurements for space charge investigation. After a short presentation of the fundamentals related to the technique, its evolutions towards “on-line” studies are evoked, in particular the fundamental equations associated in this new configuration. In the experimental part of the text are described the new challenges arising with the modified set-up and the solutions proposed. At the end, the conclusion is two folds: the modified bench is not only consistent with the classical one, but also allows a thermal calibration of the technique that will enhance the accuracy of results to come.