Komatsu Electronic Metals Co., Ltd.

Mitsuo Kono

Shiro Yoshino

Kei Matsumoto

Hiroyuki Kawahara

Noriyuki Uemura

Seiichi Shimura

In the wafer-bonding method of fabricating an SOI (silicon-on-insulator) substrate, even if there exists thickness variation in the silicon layer, devices fabricated onto the silicon layer, in accordance with the present invention, have a decreased threshold voltage variation. According to the present invention, after bonding two wafers, the thickness of the thinned silicon layer atop the SOI substrate is measured to precisely determine the local thickness distribution. However, the fabricated devices' threshold voltage depends upon the doping concentration as well as the thickness of the silicon layer. Shielding masks of photoresist are thereafter formed selectively on a portion of the silicon that are thicker. Then, through the masks as shielding, impurities are implanted into the silicon layer to adjust the doping concentration therein. Accordingly, the doping concentration is varied corresponding to the thickness, with the result that the threshold voltage variation nearly approaches zero.

Method for fabricating an SOI substrate

A simple method for evaluating the dielectric breakdown of an oxide layer on a silicon wafer is disclosed. The SPV method is utilized to measure a diffusion length L.sub.on of minority carriers when the silicon wafer is illuminated by white light from another source and a diffusion length L.sub.off of the minority carriers when the silicon wafer is not illuminated by white light from another source. A diffusion length L.sub.safe, which is determined by trap sites in the silicon wafer, is calculated from an equation L.sub.safe =(L.sub.off.sup.-2 -L.sub.on.sup.-2).sup.-1/2. Since L.sub.safe has a strong correlation with the dielectric breakdown of the oxide layer, the dielectric breakdown of the oxide layer can be easily evaluated by L.sub.safe during the fabrication of the silicon wafer.

Method for analysis of silicon wafers

An epitaxial wafer capable of removing impurities and oxide layers thereon having a high dielectric strength is disclosed. A substrate wafer 1 in which laser-scattering centers have a density of higher than 5.times.10.sup.6 /cm.sup.3 is provided. An epitaxial layer 3 is formed by epitaxial growth on a completely clean surface of the substrate. The surface of the epitaxial layer consists of a non-defect layer which is provided for device active regions. Moreover, a high density of laser-scattering centers are distributed near the interface of the epitaxial layer and the substrate wafer and the interior of the substrate, thus providing for a wafer capable of removing impurities.

Growing community of inventors

Hadano, Japan

Mitsuo Kono