Metal gate stack having TaAlCN layer

A method comprising:

• forming a gate stack over a substrate;
• at least partially removing the gate stack, thereby forming an opening;
• depositing a multi-function layer in the opening, wherein the multi-function layer includes nitrogen and one of titanium or tantalum;
• and
• depositing a work function layer over the multi-function layer, wherein the work function layer includes nitrogen and one of titanium or tantalum, and further wherein a concentration of the nitrogen of the work function layer is less than a concentration of the nitrogen of the multi-function layer.

A method comprising:

• forming a dummy gate stack over a substrate;
• and
• replacing at least a portion of the dummy gate stack with a metal gate stack, wherein the replacing includes:
• depositing a multi-function layer that includes nitrogen and one of titanium or tantalum,
• depositing a work function layer over the multi-function layer, wherein the work function layer includes nitrogen and one of titanium or tantalum, and further wherein a concentration of the nitrogen of the work function layer is less than a concentration of the nitrogen of the multi-function layer,
• depositing a conductive layer over the work function layer, and
• performing a planarization process to remove any excess multi-function layer, work function layer, and conductive layer.