Work function adjustment in high-k metal gate electrode structures by selectively removing a barrier layer

A method, comprising:

• forming a first gate electrode structure above a first semiconductor region of a semiconductor device and a second gate electrode structure above a second semiconductor region, said first and second gate electrode structures comprising a gate insulation layer including a high-k dielectric material, a metal-containing cap material formed on said gate insulation layer and a placeholder material, at least said second gate electrode structure comprising an etch stop liner located between said metal-containing cap material and said placeholder material;
• removing said placeholder material in said first and second gate electrode structures;
• forming one or more first material layers in said first and second gate electrode structures, said one or more first material layers comprising a work function metal for said first gate electrode structure;
• removing said one or more first material layers selectively from said second gate electrode structure by using a wet chemical agent based on ammonium hydroxide to etch at least one of said one or more material layers;
• and
• forming one or more second material layers in said second gate electrode structure, said one or more second material layers comprising a work function metal for said second gate electrode structure.