Formation of a semiconductor device with a gate containing a metal oxide layer using an oxidation process

A method for forming a semiconductor device structure, comprising:

• forming a fin structure over a substrate, wherein the fin structure has a plurality of sacrificial layers and a plurality of semiconductor layers laid out alternately;
• removing the sacrificial layers to form a plurality of semiconductor nanostructures made up of remaining portions of the semiconductor layers;
• forming a gate dielectric layer to wrap around the semiconductor nanostructures;
• forming a first work function layer over the gate dielectric layer;
• forming an oxygen-containing layer over the first work function layer, wherein the oxygen-containing layer is thinner than the first work function layer;
• and
• forming a second work function layer over the oxygen-containing layer, wherein the oxygen-containing layer is thinner than the second work function layer.

A method for forming a semiconductor device structure, comprising:

• forming a channel structure over a substrate;
• forming a gate dielectric layer along a top and sidewalls of the channel structure;
• forming a first metal-containing layer over the gate dielectric layer;
• introducing oxygen into the first metal-containing layer to transform an upper portion of the first metal-containing layer into a metal oxide layer;
• and
• forming a second metal-containing layer on the metal oxide layer, wherein the first metal-containing layer has a first average grain size, the second metal-containing layer has a second average grain size, and the first average grain size is greater than the second average grain size.