| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of minimizing or eliminating dependence of threshold voltage of an ultrathin SOI/MOS transistor on film thickness. SOLUTION: An SOI substrate is prepared, thickness of an upper silicon film of the SOI substrate is reduced into approx. 10 to 50 nm, and an absorbing layer is formed on the upper silicon film. Phosphorous ions are implanted through the absorbing layer so that concentration of the phosphorous ions in the upper silicon film is adjusted to approx. 5×10<10> to 5×10<13> ion/cm<2> , or boron ions are implanted into the upper silicon film so that the concentration of the ions is adjusted to approx. 1×10<17> to 5×10<18> ion/cm<3> . Thereafter, arsenic ions are implanted so that the concentration of the ions is adjusted to approx. 0 to 5×10<11> ion/cm<2> , or the boron ions are implanted into the upper silicon film so that the concentration of the boron ions of the upper silicon film is adjusted to approx. 1×10<9> to 2×10<10> ion/cm<2> .
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