Accession Number : ADA338756

Title :   Defects and Impurities in 4H- and 6H-SiC Homoepitaxial Layers: Identification, Origin, Effect on Properties of Ohmic Contacts and Insulating Layers and Reduction

Descriptive Note : Quarterly rept. 1 Oct-31 Dec 97

Corporate Author : NORTH CAROLINA STATE UNIV AT RALEIGH

Personal Author(s) : Davis, R. F. ; Aboelfotoh, M. O. ; Baliga, B. J. ; Nemanich, R. J.

PDF Url : ADA338756

Report Date : DEC 1997

Pagination or Media Count : 24

Abstract : A hot wall chemical vapor deposition system has been constructed to deposit thin films of 4H- and 6H-SiC and AlN. The design incorporates a separate load lock from which the growth chamber and a RHEED chamber are attached. Operation awaits the completion of the laboratory upfitting to address the safety requirements necessary to use silane. MOS capacitors were fabricated on 6H- and 4H-SiC with an average effective charge density of 5x10(exp 11)x10(exp -12)/sq cm. Related MOSFETs exhibited excellent gate controlled linear and saturation regimes of operation. The threshold voltage was 2-5 volts for all 4-H and 6H-SiC FETs. Maximum inversion layer mobilites of 60 sq cm/V.s and 72 sq cm/V.s were determined for the MOSFETs fabricated on 4H- and 6H-SiC, respectively. Aluminum nitride thin films were also grown by GSMBE on 4H and 6H-SiC substrates. Streaked RHEED patterns indicated smooth films and, for the first time, contained surface reconstruction streaks. The smooth surface character was confirmed via atomic force microscopy which showed root mean square values typically between 0.5 nm and 1 nm. X-ray diffraction showed the films to be highly c-axis orientedand single phase. The major impurities in the films were oxygen and carbon, as revealed by secondary ion mass spectrometry. Thermal and plasma enhanced chemical vapor deposition were employed with oxygen and nitrous oxide to deposit a silicon oxide on 6H-SiC(0001). The resulting morphology was compared with an analogous oxide produced via thermal oxidation and with the base SiC substrate. The RMS values of the surface roughness of the initial insulator and the control wafers were 0.93 and 0.95 nm, respectively, as measured via atomic force microscopy. The RMS values for PECVD (200-400 deg C) and thermal CVD (400-600 deg C for oxygen-silane) and 800-1000 deg C for nitrous oxide-silane ranged from 1.43 to 1.93 nm.

Descriptors :   *LAYERS, *EPITAXIAL GROWTH, *IMPURITIES, *CRYSTAL DEFECTS, *SILICON CARBIDES, THERMAL PROPERTIES, REQUIREMENTS, ALUMINUM COMPOUNDS, INSULATION, PLASMAS(PHYSICS), THRESHOLD EFFECTS, THIN FILMS, X RAY DIFFRACTION, SURFACE ROUGHNESS, VOLTAGE, CHEMICAL VAPOR DEPOSITION, SUBSTRATES, CARBON, METAL OXIDE SEMICONDUCTORS, NITRIDES, OXYGEN, OXIDATION, THERMOCHEMISTRY, SILANES, SAFETY, INVERSION, CHARGE DENSITY, WAFERS, CHAMBERS, NITROUS OXIDE, MOSFET SEMICONDUCTORS, ELECTRIC CONTACTS, CAPACITORS, MASS SPECTROMETRY.

Subject Categories : Inorganic Chemistry
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE