| AVS 60th International Symposium and Exhibition | |
| Atom Probe Tomography Focus Topic | Tuesday Sessions |
| Session AP+AS+SS-TuA |
| Session: | Microstructural and Interface Analysis of Metals Subjected to Various Conditions |
| Presenter: | B. Mazumder, University of California, Santa Barbara |
| Authors: | B. Mazumder, University of California, Santa Barbara X. Liu, University of California, Santa Barbara F. Wu, University of California, Santa Barbara U.K. Mishra, University of California, Santa Barbara J.S. Speck, University of California, Santa Barbara |
| Correspondent: | Click to Email |
Al2O3 has emerged as an appropriate gate dielectric for III-nitride based electronic devices. Major growth challenges for such high-k/GaN interfaces include unwanted GaN oxidation, impurity etc during deposition may result in the formation of electrically active defects. In addition to prior structural investigations of such systems, the relation between atomic structure, chemistry and electrical properties of these interfaces is poorly understood. Atom probe tomography (APT) was used to determine structural information related to interface abruptness, layer composition including impurity content. It is quite challenging to analyze dielectric/insulating oxides multilayers using atom probe. Micro fractures, irregular evaporation etc due to the evaporation field difference between the layers can make the analysis challenging. Additionally, experimental parameters including tip temperatures, laser energy, and detection rate all strongly impact the field evaporation and subsequent data analysis. In this study we have reported reliable and reproducible data with high measurement yield by optimizing experimental parameters and using a suitable capping layer.
Ga-face ((0001) c-plane) GaN samples were grown by metal organic chemical vapor deposition (MOCVD). Al2O3 layers were grown on GaN, both by MOCVD and atomic layer deposition (ALD) system for a comparative study . These samples were then analyzed in Local Electrode Atom Probe 3000X HR. The experimental parameters were optimized for the oxide/semiconductor system. Initially the measurement yield was very low with a metal cap layer (Ni, Cr). Replacing it by a low temperature GaN cap layer the measurement yield was increased substantially. Thorough compositional analysis and roughness measurements were done and it was found that the interface is relatively rough and not atomically abrupt. However no presence of GaxOy was found in both the cases. Qualitative estimation of carbon impurities within dielectric was done for both the samples and was found to be in the order of 1019/cm3, however the MOCVD sample shows higher carbon concentration than those grown by ALD. From the C-V measurements the volume trap charge density was estimated to be around 2 x1019 cm-3and 3.9 x1019 cm-3 for ALD and MOCVD samples respectively, those are of the same order as the carbon concentration determined from the atom probe measurements. By varying the growth temperature the amount of C impurity was controlled. In conclusion, atom probe was successfully used to investigate the dielectric/III-V system in depth, which provides valuable feedback for growth optimization required for better device fabrication.