Method for fabricating an SOI substrate

Chemistry: molecular biology and microbiology – Process of mutation – cell fusion – or genetic modification – Introduction of a polynucleotide molecule into or...

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438406, 438517, H01L 2176

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active

058664688

ABSTRACT:
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.

REFERENCES:
patent: 4263057 (1981-04-01), Ipri
patent: 4851366 (1989-07-01), Blanchard
patent: 5308776 (1994-05-01), Gotou
patent: 5686364 (1997-11-01), Ohki et al.

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