Electrical Properties of Mg-Implanted 4H-SiC

Because Al and B (elements of III group) in SiC are deep-level acceptors and these acceptors cannot reduce the resistivity of p-type SiC very much, Mg (element of II group) that may emit two holes into the valence band is investigated. A p-type 4H-SiC layer is obtained by 1800 °C annealing of the Mg-implanted layer, not by 1600 and 1700 °C annealing. It is found that a Mg acceptor level in 4H-SiC is too deep to determine the reliable density and energy level of the Mg acceptor using the frequently-used occupation probability, i.e., the Fermi-Dirac distribution function. Using the distribution function including the influence of the excited states of the Mg acceptor, therefore, its density and energy level can be determined to be approximately 1×1019cm-3and 0.6 eV, respectively. Judging from the Mg implantation condition, the obtained values are considered to be reliable.

Characterization Of SiO2/Si Interface Using Secondary Ion Mass Spectrometry(Sims) And Laser Post-Ionization Sputtered Neutral Mass Spectrometry(Snms)

SIMS has inherent difficulties with quantification because of the so called “matrix effect”. Many factors contribute to the matrix effect, e.g. differing concentration of oxygen, sputtering rate differences in the hetero-layers, etc. In the case of MOS(metal-oxide-semiconductor) structures, the oxide layer gives rise to a large matrix effect. It is thus very difficult to use SIMS to evaluate the relationship between the electrical properties of the LSI devices and the impurity profiles present in such systems.So we have been studying laser post-ionization SNMS, which consists of TOF-SIMS apparatus and excimer laser, in order to quantify the impurity profiles around SiO2/Si interface. Depth profiles of implanted Cu with 1×1015 atoms/cm2 in SiO2(100 nm)/Si system taken by Monte-Carlo simulation ,SIMS and laser post-ionization SNMS are shown in Fig.l. In this implantation condition the Cu+:Cu2+:Cu3+ percentage ratios of the charge distributions were 44:42:14. Fig. 1(a) shows the theoretical depth profiles expetted from this implantation condition by Monte-Cairo simulation.