Methods for growing low-resistivity tungsten for high aspect ratio and small features
The present invention addresses this need by providing methods for depositing low resistivity tungsten films in small features and features having high aspect ratios. The methods involve depositing very thin tungsten nucleation layers by pulsed nucleation layer (PNL) processes and then using chemical vapor deposition (CVD) to deposit a tungsten layer to fill the feature. Depositing the tungsten nucleation layer involves exposing the substrate to alternating pulses of a boron-containing reducing agent and a tungsten-containing precursor without using any hydrogen gas, e.g., as a carrier or background gas. Using this process, a conformal tungsten nucleation layer can be deposited to a thickness as small as about 10 Angstroms. The feature may then be wholly or partially filled with tungsten by a hydrogen reduction chemical vapor deposition process. Resistivities of about 14 μΩ-cm for a 500 Angstrom film may be obtained.
1. A method of forming a tungsten layer in feature on a substrate, said feature including a feature opening, the method comprising:
forming a conformal tungsten nucleation layer in at least the feature by exposing the substrate to alternating pulses of a boron-containing reducing agent and a tungsten containing precursor at a substrate temperature of between about 250° C.-350° C., wherein no hydrogen is flowed during or between the pulses.
2. The method of claim 1 wherein the feature opening prior to forming the conformal nucleation layer is less than about 400 Angstroms.
3. The method of claim 2 further comprising, after forming the conformal nucleation layer, simultaneously exposing the substrate to a tungsten-containing precursor and a second reducing agent to thereby deposit a bulk tungsten layer by a chemical vapor deposition process in at least the feature.
4. The method of claim 3 wherein the second reducing agent is hydrogen.
5. The method of claim 1 wherein the substrate temperature during formation of the tungsten nucleation layer is between about 250° C. and 325° C.
6. The method of claim 1 wherein the substrate temperature during formation of the tungsten nucleation layer is about 300° C.
7. The method of claim 1 wherein the tungsten nucleation layer is deposited to a total thickness of between about 10-20 Angstroms.
8. The method of claim 1 wherein the tungsten nucleation layer is deposited to a total thickness of between about 10-15 Angstroms.
9. The method of claim 1 wherein the aspect ratio of the feature is at least about 10:1.
10. The method of claim 1 wherein the feature has an opening width of no more than about 300 Angstroms.
11. The method of claim 3 wherein the substrate temperature during the chemical vapor deposition process is about 395° C.
12. A method of forming a tungsten layer comprising in a feature on a substrate:
forming a conformal tungsten nucleation layer in at least the feature by alternating pulses of a boron-containing reducing agent and a tungsten containing precursor at a substrate temperature of between about 250° C.-350° C., wherein no hydrogen is flowed during or between the pulses; and
after forming the conformal nucleation layer, substantially filling the feature with a tungsten bulk layer by simultaneously exposing the substrate to a tungsten-containing precursor and hydrogen thereby deposit tungsten by a chemical vapor deposition process in at least the feature.
13. The method of claim 12 wherein the substrate temperature during formation of the tungsten nucleation layer is between about 250° C. and 325° C.
14. The method of claim 12 wherein the substrate temperature during formation of the tungsten nucleation layer is about 300° C.
15. The method of claim 12 wherein the tungsten nucleation layer is deposited to a total thickness of between about 10-20 Angstroms.
16. The method of claim 12 wherein the tungsten nucleation layer is deposited to a total thickness of between about 10-15 Angstroms.
17. The method of claim 12 wherein the aspect ratio of the feature is at least about 20:1.
18. The method of claim 12 wherein the feature has an opening width of no more than about 400 Angstroms.
19. The method of claim 12 wherein the substrate temperature during the chemical vapor deposition process is about 395° C.
20. The method of claim 12 wherein the total thickness of tungsten deposited is about 500 Angstroms.
21. The method of claim 20 wherein the resistivity of the deposited film is no more than about 14 μΩ-cm.