Investigation Of Electrical Properties Of SiC MOS Interface Modified By NH₃ Plasma Post-oxidation Annealing

As a promising third generation semiconductor, silicon carbide ?SiC? has great physical properties, such as large band gap energy and high thermal conductivity. In addition, SiC is the only compound semiconductor material which can form SiO₂ layer by oxidation. However, the current fabrication of SiC MOSFET exists the problem of low inversion channel mobility, which is attributed by high SiO₂/SiC density of interface traps ?Dit?.Thus, the problem of reducing interface traps is always the key topic in the SiC MOS device research field.In this thesis,4H-SiC MOS devices are fabricated with electron cyclotron resonance ?ECR? ammonia plasma post-oxidation annealing ?POA?. Through current-voltage measurements, the dielectric breakdown voltage of samples with treatment was increased from 9.6 MV/cm to 9.85 MV/cm, and barrier height between SiO₂ and 4H-SiC with treatment was increased from 2.4 eV to 2.56 eV. In addition, through the CCTDDB measurement, the lifetime under the normal operating conditions ?typically 3 MV/cm? of the samples with ammonia plasma treatment is almost 50000 hours, which is 50 times larger than as-oxidized sample. Through capacitance-voltage measurement, the distribution of Dit, in the range of 0.06 ?1.2 eV below conduction band was extracted. The result indicated significant decrease of Dit, throughout the whole upper band gap, and indeed an order of magnitude in deeper band level. Through secondary ion mass spectrometry measurement, the depth profiles of H, N, C was extracted. It indicated that ECR microwave ammonia plasma POA introduced a large number of N and H mainly near the SiO₂/SiC interface, which ensured quality of oxide layer.The test results indicated that ECR microwave ammonia plasma POA could reduce Dit, significantly, and enhance the dielectric properties and reliability of SiC MOS device. This work provides a new SiO₂/4H-SiC interface passivating route, which could play a role of N and H in the meantime and significantly improve the interfacial properties.