MOS device with multi-layer gate stack

A semiconductor device, comprising:

• a substrate having therein a source region and a drain region separated by a channel region extending to a first surface of the substrate;
• a multilayered gate structure located above the channel region and having one or more regions containing a mobile impurity, wherein the gate structure comprises:
• a gate oxide in substantial contact with the channel region;
• a first conductor overlying the gate oxide;
• a second conductor overlying the first conductor;
• and
• an impurity absorption layer located above or below the first conductor, adapted to significantly inhibit movement of the mobile impurity.

A method for forming a semiconductor device with a multi-layered gate structure resistant to migration of a mobile species and overlying a channel region of the device, comprising:

• providing a semiconductor substrate having an upper surface;
• forming on the upper surface a stack of overlying layers in various orders, comprising:
• a gate oxide layer having an interface in contact with the upper surface;
• a first conductor layer;
• a second conductor layer;
• and
• an absorption layer for reducing migration of the mobile species toward the interface, wherein the absorption layer is formed either after the gate oxide and before the first conductor layer and lies therebetween or formed after the first conductor layer and before the second conductor layer and lies therebetween;
• and then
• removing portions of the stack of layers lying laterally outside a region desired to be the channel region of the device, thereby forming the multi-layered gate structure overlying the channel region of the device.