Kazuto Kawakami

Influence of Crystal Originated Particles on Gate Oxide Breakdown.

Defects causing gate oxide breakdown in Czochralski silicon were evaluated using a location marking technique by copper plating. The cross sectional structure of the defect was observed by a combination technique of focused ion beam (FIB) etching at the marked location and transmission electron microscopy (TEM) and found to have similar appearances and sizes to those of crystal originated particles (COPs) observed by atomic force microscopy (AFM). Correlation between locations of the defects at a wafer surface determined using the copper plating and those of COPs determined using a particle counter was investigated for various electric field applied for the copper plating. We found that COPs are one of the major factors causing gate oxide breakdown at fields around 4 MV/cm, while other factors become dominant when a higher electric field is applied.

Defects in Czochralski-Grown Silicon Crystals Investigated by Positron Annihilation

Positron lifetime and Doppler broadening experiments were performed on Czochralski-grown silicon crystals. A monoenergetic positron beam was also used to measure the diffusion length of positrons in the wafer. From the measurements, it was observed that the value of diffusion length of positrons decreased at the region where micro-defects were formed during the crystal growth process. It was also found that the line shape parameter S decreased and the lifetime of positrons increased at the region. These results can be attributed to the annihilation of positrons trapped by vacancy oxygen complexes which are formed in association with the microdefects.

Oxygen microclusters in Czochralski-Grown Si probed by positron annihilation

Trapping of positrons by oxygen microclusters in Czochralski-grown Si was studied. Lifetime spectra of positrons were measured for Si specimens annealed in the temperature range between 450°C and 1000°C. Positrons were found to be trapped by oxygen microclusters, and the trapping rate of positrons into such defects increased with increasing annealing temperature. In order to investigate the clustering behaviors of oxygen atoms in more detail, vacancy-oxygen complexes, VnOm (n,m=1, 2,...), were introduced by 3 MeV electron irradiation. The concentration of monovacancy-oxygen complexes VOm (m=2, 3,...) increased with increasing annealing temperature. These facts were attributed that the oxygen microclusters, Om, were introduced by annealing above 700°C.