The reduction of surface "native" oxides from GaAs substrates following reactions with trimethylaluminum ͑TMA͒ precursor is studied using medium energy ion scattering spectroscopy ͑MEIS͒ and x-ray photoelectron spectroscopy ͑XPS͒. MEIS measurements after one single TMA pulse show that ϳ65% of the native oxide is reduced, confirmed by XPS measurement, and a 5 Å thick oxygen-rich aluminum oxide layer is formed. This reduction occurs upon TMA exposure to as-received GaAs wafers.
The 4H–SiC/SiO2 interface is a major obstacle that hampers SiC device applications. The nature of the transition region stoichiometry and structure need to be elucidated to both understand and improve such devices. In this paper, we use medium energy ion scattering on device grade structures to examine critical aspects of this dielectric/semiconductor structure. Our findings indicate no excess C greater than 1.8×1014 cm−2 from the oxide surface down to a few monolayers beneath the SiC/SiO2 interface, setting limits on the previously predicted nonstoichiometric transition region on the dielectric side.
Combining Cs+ bombardment with positive secondary molecular ion detection (MCs+) can extend the analysis capability of secondary ion mass spectrometry (SIMS) from the dilute limit (<1 at. %) to matrix elements. The MCs+ technique has had great success in quantifying the sample composition of III–V semiconductors. However, the MCs+ has been less effective at reducing the matrix effect for group IV materials, particularly Si-containing compounds. The lack of success in quantifying group IV materials is primarily attributable to the high Cs surface concentrations overloading the sample surface and lowering ion yields. The Cs overload issue is caused by the mobility and relocation of the implanted Cs to the surface during an analysis. Critical to understanding the material-dependent success of the MCs+ technique and elucidating the Cs mobility is understanding how Cs is incorporated and distributed into the sample and how the Cs surface concentration affects the ionization processes. The authors provide both new insight for improving the MCs+ technique by investigating the Cs retention, distribution, and ion yield differences between group III–V and IV materials and a greater understanding of the temperature-dependent mobility and relocation of the implanted Cs. There have been many studies on improving the MCs+ technique; however, our novel approach to use temperature as a means of controlling the Cs mobility has not been previously explored. Cesium build-up curves were acquired to assess the in situ Cs incorporation differences. By utilizing the newly developed variable temperature stage on our SIMS, cesium build-up curves were acquired over a wide range of temperatures (−150 to 300 °C) to show the temperature-dependent relocation of Cs and the effect it has on the ionization processes. Additionally, Cs ionization and neutralization were quantified as a function of Cs fluence and temperature. The Cs retention and distribution differences were determined ex situ by measuring the Cs concentration using heat-treatment x-ray photoelectron spectroscopy and heat-treatment medium energy ion scattering. These results allow for a more thorough understanding of the material-dependent success of the MCs+ technique, the Cs+-sample interaction, and the temperature component of the Cs mobility.
Silicon Carbide (4-H SiC) is a promising candidate for high power and high temperature MOS devices. However, the performance and wide-scale application of such devices is hindered by the poor quality of SiO 2 /SiC interface. Much work has been done in the past decade to improve the interface quality. Among them, post-oxidation nitridation passivation shows great enhancement and promising results.In this talk, two nitridation processes on thermally oxidized (0001) 4H-SiC will be discussed: namely nitric oxide (NO) anneal [1] (NO gas, atm. pressure, 1175 o C, 2hrs) and nitrogen plasma anneal (N 2 plasma, 2.7 Torr, 1165 o C, 20hrs). The NO anneal process results in a decreased interface trap density (D IT ) of ~ 1.0E+12 cm -2 eV -1 at 0.1eV below conduction band and fieldeffect channel mobility at about 40 cm 2 /Vs [1][2], barely adequate for device applications. Further understanding of the beneficial effects of nitrogen and new methods of nitrogen injection are potentially useful in still further improvement.We report, D IT and channel mobility as a function of interfacial nitrogen content by varying the NO annealing time. A continuous decrease in D IT and increase in mobility is observed as the interfacial N concentration increases. The dependence suggests that N is passivating Coulomb scattering centers which limit the mobility.An alternate passivation technique, which reduces the incremental oxidation associated with the NO process, is the use of a nitrogen plasma. Here, microwaves create atomic nitrogen to achieve the nitridation annealing condition with little or no additional oxidation. Results for electrical characterization will be discussed in detail and compared with standard NO results. The strong dependence of mobility on nitrogen content described above, indicates that the plasma/gas comparison is only valid for accurately known nitrogen content.Medium energy ion scattering spectroscopy (MEIS) allows for such accurate elemental concentration calculation at near surface region. Quantitative measurement of nitrogen incorporation at the SiO 2 /SiC interface by the above nitridation processes will be presented and compared to other analyzing techniques such as SIMS.978-1-4244-6031-1/09/$26.00 ©2009 IEEE
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