Semiconductor device and manufacturing method thereof

A semiconductor device having a first conductive type transistor and a second conductive type transistor formed on a substrate,

• the first conductive type transistor comprising:
• a first lower gate electrode portion formed on the substrate, the first lower gate electrode portion comprising silicon including first impurity ions;
• a first intervening layer formed on the first lower gate electrode portion, the first intervening layer comprising silicon including at least one of oxygen and nitrogen;
• and
• a first upper gate electrode portion formed on the first intervening layer, the first upper gate electrode portion comprising silicon including the first impurity ions, and
• the second conductive type transistor comprising:
• a second lower gate electrode portion formed on the substrate, the second lower gate electrode portion comprising silicon including second impurity ions;
• a second intervening layer formed on the second lower gate electrode portion, the second intervening layer comprising silicon including at least one of oxygen and nitrogen;
• and
• a second upper gate electrode portion formed on the second intervening layer, the second upper gate electrode portion comprising silicon including the second impurity ions.