590-RM - tF eF gooperD trFX edvnes in ig wy ehnology physF...

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phys. stat. sol. (a) 162 , 305 (1997) Subject classification: 73.40.Qv; S6 Advances in SiC MOS Technology J. A. C ooper, Jr. School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA (Received January 31, 1997) Silicon carbide (SiC) is the only compound semiconductor whose native oxide is SiO 2 . This places SiC in a unique position to compete with silicon in applications involving high power, high voltages, or high temperatures. SiC MOS technology has made substantial progress in recent years. This article aims to summarize the present status of this field, including MOS analysis techniques, oxida- tion procedures, experimental results, reliability considerations, alternative insulators, and remain- ing questions. In addition, we hope to convince the reader of the following: 1. Great care must be exercized in interpreting MOS data on wide bandgap semiconductors. This is due to the extremely long response times for interface states deep in the bandgap. 2. Recent results do not support the argument that interface quality on p-type SiC is inferior to that of n-type. 1. Introduction Silicon has become the predominant commercial semiconductor material for two reasons. First, silicon melts at a moderate temperature (1410 ± C), so that growth of large boules of single-crystal material from the melt is feasible and relatively cheap. Second, silicon can be thermally oxidized to form SiO 2 , an excellent insulator suitable for fabricating stable metal oxide semiconductor (MOS) devices. Silicon carbide (SiC) exhibits much greater physical and thermal stability than silicon. This is both a blessing and a curse –– a blessing because it makes SiC suitable for ex- treme applications such as high-temperature and high-power devices; a curse because it makes it impractical to grow SiC from the melt. This latter fact results in substrates which are very small and very expensive compared to silicon, a dilemma which is the subject of other articles in this volume. On the positive side, SiC is the only compound semiconductor whose native oxide is SiO 2 . This places SiC in a unique position in the family of semiconductor materials and makes it possible to fabricate all of the standard silicon MOS device structures. Thermal oxidation of SiC is similar to silicon and utilizes the same equipment, although at slightly higher temperatures. The MOS properties of thermally oxidized SiC are not yet as good as silicon, but steady improvements are being mande. These improvements and the technology behind them are the subject of this article. 2. MOS Measurement Techniques for Wide Bandgap Semiconductors The most important figures-of-merit for MOS interfaces are: 1 the density of interface traps, symbol D IT (in eV ² 1 cm ² 2 ), 2. the density of fixed positive charges at the inter- face, symbol Q F (in cm ² 2 ), 3. the density of border traps in the insulator adjacent to the J. A. C ooper, Jr .: Advances in SiC MOS Technology 305 20 physica (a) 162/1
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interface, symbol N OT (in cm ± 2 ) 4. the density of mobile ions in the insulator, symbol N IONS (in cm ± 2 ), 5. insulator leakage current as a function of electric field and tempera-
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590-RM - tF eF gooperD trFX edvnes in ig wy ehnology physF...

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