| 摘要 |
A semiconductor device fabrication method by which CMOS transistors with low-resistance metal gate electrodes each having a proper work function can be fabricated. A HfN layer in which nitrogen concentration in an nMOS transistor formation region differs from nitrogen concentration in a pMOS transistor formation region is formed. A MoN layer is formed over the HfN layer and heat treatment is performed. Nitrogen diffuses from the MoN layer into the HfN layer in which nitrogen concentration is low and a work function is set by the HfN layer according to nitrogen concentration which depends on the nitrogen content of the HfN layer before the heat treatment and the amount of nitrogen that diffuses into the HfN layer. On the other hand, nitrogen hardly diffuses from the MoN layer into the HfN layer which originally has a certain nitrogen content, and a work function is set by the HfN layer according to nitrogen concentration in the HfN layer before the heat treatment. By controlling the nitrogen content of each layer and the amount of nitrogen that diffuses, a low-resistance metal gate electrode having a predetermined work function can be formed in each of the nMOS transistor formation region and the pMOS transistor formation region.
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