Diffusion barrier layer formation

A method of forming a titanium nitride diffusion barrier, the method comprising:

• exposing a deposition surface to a pulse of a titanium-containing precursor gas to initiate
• a nucleation of the titanium nitride diffusion barrier in the deposition surface, wherein the deposition surface comprises sidewalls and a bottom of a contact opening;
• exposing the deposition surface to a first pulse of a nitrogen-rich plasma to form a first titanium nitride layer with a first nitrogen concentration in the deposition surface;
• exposing the first titanium nitride layer to a second pulse of the nitrogen-rich plasma to form a second titanium nitride layer with a second nitrogen concentration directly above and in contact with the first titanium nitride layer;
• exposing the second titanium nitride layer to a third pulse of the nitrogen-rich plasma to form a third titanium nitride layer with a third nitrogen concentration directly above and in contact with the second titanium nitride layer;
• and
• exposing the third titanium nitride layer to a fourth pulse of the nitrogen-rich plasma to form a fourth titanium nitride layer with a fourth nitrogen concentration directly above and in contact with the third titanium nitride layer,
• wherein the first, second, third, and fourth titanium nitride layers form a multi-layer titanium nitride diffusion barrier exhibiting gradually decreasing levels of fluorine diffusivity, the fluorine diffusivity of the first, second, third, and fourth titanium nitride layers is inversely proportional to a duration of the first, second, third, and fourth pulses of nitrogen-rich plasma and to a nitrogen concentration of the first, second, third, and fourth titanium nitride layers.