Yoshimaro Fujii

Evaluation of the bonded silicon on insulator (SOI) wafer and the characteristics of PIN photodiodes on the bonded SOI wafer

Electrical properties of the bonded silicon on insulator (SOI) wafer and characteristics of PIN photodiodes fabricated on the SOI layer were evaluated. A trap with deep energy level (about Ec-Et=0.55 eV) was observed in the SOI layer with 100 /spl mu/m- and 30 /spl mu/m-thickness using the deep level transient spectroscopy (DLTS) method. No trap was detected in the SOI layer with 10 /spl mu/m-thickness. This deep trap was not observed before the wafer bonding process and thus the trap is generated during the wafer bonding process. From primary mode lifetime (/spl tau//sub 1/) measurements, it is considered that the trap will works as the generation center or the recombination center. For PIN photodiodes on the SOI layer in which the trap was detected, the increases of dark current were observed. Spectral responses of photodiodes on the SOI layer were almost the same as that on the normal FZ-Si wafer. We fabricated PIN photodiodes with good spectral response. >

Automatic Determination of In-Depth Profiles of Recombination Lifetime in Epitaxial Si Layer with P+-N−-N+ Stripe Test Pattern Diodes

Recombination lifetime of a epitaxial layer (epilayer) is automatically measured by using the conductivity modulation technique. A lateral p + -n − -n + diode test structure on the surface of the epilayer is formed to evaluate the minority carrier lifetime. Depth profiles of the recombination lifetime are obtained from current-voltage curves of a lateral p + -n − -n + diode and a vertical n + -n − -n + structure between the substrate and the top surface. We measure the lifetime in epilayers with and without a buffer-layer. In addition, photo-response of photodiodes with and without the buffer-layer is measured. Profiles of the recombination lifetime depend on the thickness of the epilayer but not on the thickness of the buffer-layer. Minority carrier lifetime in the epilayer, and the leakage current and the photo-response of photodiodes are improved by the buffer-layer formation between epilayer and substrate.