Gate all-around field effect transistor and method for fabricating the same

A method for fabricating a gate all-around field effect transistor, comprising:

• sequentially forming a first sacrificial layer, a channel layer and a protective layer on a substrate;
• performing a first patterning process on the first sacrificial layer, the channel layer and the protective layer to form a fin structure;
• forming a composite field oxide layer to cover the fin structure and the substrate and to surround the fin structure;
• performing a second patterning process on the composite field oxide layer to remove one portion of the composite field oxide layer in a channel region and retain another portion of the composite field oxide layer in a drain region and a source region on two sides of the channel region;
• removing the protective layer, the first sacrificial layer and the one portion of the composite field oxide layer in the channel region to release the channel layer;
• forming a gate stack layer on the another portion of the composite field oxide layer in the drain region and the source region, the substrate in the channel region and a surface of the channel layer;
• performing a third patterning process on the gate stack layer to remove the gate stack layer from the drain region and the source region;
• performing a fourth patterning process on the composite field oxide layer to form a drain opening in the drain region and a source opening in the source region;
• and
• forming a drain electrode in the drain opening and a source electrode in the source opening and electrically connecting the drain electrode and the source electrode to the protective layer.