4H‐SiC MISFETs with nitrogen‐containing insulators have been fabricated and characterized. Several techniques have been explored to incorporate nitrogen in the gate insulator in order to improve the density of interface states and thereby the channel mobility. The techniques are N2O‐grown oxides, the oxidation of a surface layer co‐implanted with N+ and Al+, deposited SiO2 annealed in N2O and NO, and deposited SiNx /SiO2 annealed in N2O. By optimizing the formation process of the gate insulators, MIS capacitors with N‐containing insulators have demonstrated an interface state density close to the conduction band edge below 2 × 1011 cm–2 eV–1 which is one or two orders‐of‐magni‐ tude lower than that of MOS capacitors with oxides grown in dry O2. The channel mobility of the n‐channel 4H‐SiC(0001) MISFETs with N‐containing insulators is increased to about 30 cm2/Vs. In addition, an even higher channel mobility of 50 cm2/Vs has been realized by utiliz‐ ing N‐containing insulators adequately processed on the 4H‐SiC (000$ \bar 1 $) face. From the experimental results, the dominant scattering mechanisms in SiC MISFETs have been identified; Coulomb scattering and electron trapping at interface states dominate the channel mobility in SiC MOSFETs with thermally‐grown and deposited SiO2. The application of N‐containing insulators to p‐channel 4H‐SiC MIS devices is also discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The recombination activity of interstitial chromium (Cri) and pairs of interstitial chromium and substitutional boron (CriBs) in crystalline silicon is studied by combining temperature- and injection-dependent lifetime and deep-level transient spectroscopy measurements on intentionally chromium-contaminated n- and p-type silicon wafers. Cri as well as CriBs pairs are found to be one order of magnitude less recombination active than widely assumed. In the case of Cri, a defect energy level of EC−Et=0.24 eV, an electron capture cross section of σn=2×10−14 cm2, and a hole capture cross section of σp=4×10−15 cm2 are determined. For CriBs pairs, measurements on boron-doped p-type silicon result in Et−EV=0.28 eV, σn=5×10−15 cm2, and σp=1×10−14 cm2. Theoretical calculations using the Shockley–Read–Hall theory show that it depends crucially on the doping concentration whether Cri or CriBs is the more active recombination center. Using a calibration function calculated from the defect parameters determined in this study, lifetime changes measured before and after thermal dissociation of CriBs pairs can be used to determine the interstitial chromium concentration in boron-doped silicon.
Through a combined application of two characterization methods, deep-level transient spectroscopy and lifetime spectroscopy, the lifetime-limiting defect level in intentionally aluminum-contaminated Czochralski silicon has been analyzed and a complete set of defect parameters could be obtained. This aluminum-related defect center is found to be located at an energy level of Et−EV=0.44±0.02eV and exhibits an asymmetric capture cross section, with σp=3.6×10−13cm2 and σn=3.1×10−10cm2 being the hole and electron capture cross sections, respectively. The investigated defect center is attributed to the aluminum-oxygen complex (Al–O).
Several alternative oxidation techniques are developed and tested with the aim to reduce the high density of interface traps Dit in n‐type 4H‐SiC MOS capacitors. A lamp furnace in combination with a microwave plasma is employed to grow thin oxide layers, which are used for an insulating stack (SiO2 and Al2O3). The treatment of the oxide with nitrogen is another way to lower Dit. We introduce N atoms prior to the oxidation by ion implantation. During the oxidation process, the implanted N‐profile is redistributed; a considerable amount of the implanted N is accumulated at the SiC/SiO2‐interface, which leads to a strong reduction of Dit and a large negative flatband voltage. The negative flatband voltage can largely be compensated by coimplantation of aluminum. A model is proposed, which explains the passivation of interface traps in n‐type 4H‐SiC MOS capacitors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
3C‐SiC/SiO2 capacitors are fabricated by over‐oxidation of an implanted Gaussian nitrogen (N) profile and investigated by conductance spectroscopy. An unexpected double peak structure is observed in the conductance spectra indicating two types of independent traps at different energy positions in the bandgap, which change their charge state with identical time constant. A theoretical model is developed assuming two independent distributions of interface traps in the bandgap of 3C‐SiC with different trap parameters. The experimental G /ω – V and C – V spectra are simulated and the trap parameters are determined on the basis of this model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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