Diffusion barrier layer formation

1. 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; and

wherein the first, second, third, and fourth pulses have gradually increasing durations of approximately 3 seconds, 5 seconds, 5 seconds, and 10 seconds, respectively.

2. The method of claim 1 , wherein the first, second, third, and fourth pulses comprise a relatively short and timed injection interval of the nitrogen-rich plasma.

3. The method of claim 1 , wherein the pulse of the titanium-containing precursor gas have a duration of approximately 2 seconds.

4. The method of claim 1 , wherein the first, second, third, and fourth pulses of the nitrogen-rich plasma causes nucleation and densification of the titanium nitride diffusion barrier to gradually increase to control a reactivity between fluorine and titanium during the last deposition cycles to prevent fluorine diffusion, and allows the formation of a thinner titanium nitride diffusion barrier for decreasing vertical resistance.

5. The method of claim 4 , wherein causing the nucleation and densification of the titanium nitride diffusion barrier to gradually increase reduces the amount of deposition cycles required to form the titanium nitride diffusion barrier, and causes oxidation of the titanium nitride diffusion barrier to decrease.

6. The method of claim 1 , further comprising:

purging the reaction chamber with an inert gas before each of the first, second, third, and fourth pulses of the nitrogen-rich plasma.

7. 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; and

wherein the first, second, third, and fourth pulses of the nitrogen-rich plasma have a gradually decreasing duration of approximately 10 seconds, 5 seconds, 5 seconds, and 3 seconds, respectively.

8. The method of claim 7 , wherein the first, second, third and fourth pulses of the nitrogen-rich plasma causes nucleation and densification of the titanium nitride diffusion barrier to gradually decrease to control the reactivity between fluorine and titanium during the first deposition cycles to prevent fluorine diffusion, and allows the formation of a thinner titanium nitride diffusion barrier for decreasing vertical resistance.

9. The method of claim 8 , wherein causing nucleation and densification of the titanium nitride diffusion barrier to gradually decrease reduces the amount of deposition cycles required to form the titanium nitride diffusion barrier, and causes oxidation of the titanium nitride diffusion barrier to decrease.