Technique for forming an oxide/nitride layer stack by controlling the nitrogen ion concentration in a nitridation plasma

A method of forming an insulation layer, the method comprising:

• forming a silicon dioxide layer with a first thickness on a silicon-containing semiconductor region provided on a substrate;
• oxidizing said silicon-containing semiconductor region in a nitrogen-containing plasma ambient by oxygen residuals present in said plasma ambient to increase said first thickness to a second thickness;
• and
• increasing the nitrogen ion concentration in said plasma ambient when said second thickness substantially corresponds to a threshold value.

A method of forming a gate insulation layer of a field effect transistor, the method comprising:

• forming a dielectric oxide layer with an initial thickness on an active region formed on a substrate, said initial thickness being less than a desired design thickness of said gate insulation layer;
• introducing said substrate into a nitrogen-containing plasma ambient of controlled pressure;
• and
• reducing said pressure during exposure of said substrate to said plasma ambient.

A method of controlling a nitrogen concentration during the formation of an insulation layer, the method comprising:

• exposing a substrate to a nitrogen-containing plasma ambient, said substrate having formed thereon an oxide layer of a first thickness;
• monitoring the thickness of said oxide layer and generating a monitor signal indicating the monitored thickness;
• and
• controlling at least one process parameter which determines a nitrogen ion density of said plasma ambient on the basis of said monitor signal.