Low dielectric constant (low-k) dielectric and method of forming the same
A method of forming a low dielectric constant (low-k) dielectric is disclosed. The method includes providing a substrate and forming a dielectric including porogens over the substrate. While subjecting the dielectric to a first pressure, the dielectric is exposed to ultraviolet (UV) radiation. The dielectric is also subject to a second pressure less than 1×10 −3 Torr. While subjecting the dielectric to the second pressure, the dielectric is exposed to vacuum UV (VUV) radiation having one or more photon energies greater than 7 eV. Since it is difficult for VUV radiation to travel through a medium at a pressure greater than 10 Torr without being absorbed by intermittent materials, subjecting the dielectric to the second pressure creates a medium wherein the dielectric can be exposed to the VUV radiation. By exposing the dielectric to UV and VUV radiation, the dielectric can achieve a reduced dielectric constant and increased mechanical properties.
1. A method comprising:
providing a substrate;
forming a dielectric comprising porogens over the substrate;
subjecting the dielectric to a first pressure greater than 10 Torr;
while subjecting the dielectric to the first pressure, exposing the dielectric to ultraviolet (UV) radiation having one or more photon energies less than or equal to seven electronvolts (7 eV);
subjecting the dielectric to a second pressure less than 1×10 −3 Torr;
while subjecting the dielectric to the second pressure, exposing the dielectric to vacuum UV (VUV) radiation having one or more photon energies greater than 7 eV.
2. The method of claim 1 , wherein the dielectric comprises an organosilicate.
3. The method of claim 2 , wherein a dielectric constant of the dielectric is at least two percent (2%) lower than before being exposed to the UV radiation and the VUV radiation.
4. The method of claim 2 , wherein an elastic modulus of the dielectric is at least five percent (5%) higher than before being exposed to the UV radiation and the VUV radiation.
5. The method of claim 1 , wherein:
the UV radiation has one or more photon energies between 3 eV and 7 eV; and
the VUV radiation has one or more photon energies between 7.25 eV and 12 eV.
6. The method of claim 5 , wherein the dielectric comprises an organosilicate.
7. The method of claim 1 , wherein:
the UV radiation has one or more photon energies between 5.5 eV and 7 eV; and
the VUV radiation has one or more photon energies between 8 eV and 9.5 eV.
8. The method of claim 7 , wherein the dielectric comprises an organosilicate.
9. The method of claim 7 , wherein the dielectric is not heated by an external heat source during the exposure to the UV radiation and the exposure to the VUV radiation.
10. The method of claim 1 , wherein the VUV radiation has one or more photon energies between 8.3 eV and 8.9 eV.
11. The method of claim 10 , wherein the UV radiation has one or more photon energies between 6 eV and 6.5 eV.
12. The method of claim 11 , wherein the dielectric comprises an organosilicate.
13. The method of claim 12 , wherein the dielectric is not heated by an external heat source during the exposure to the UV radiation and the exposure to the VUV radiation.
14. The method of claim 13 , wherein the second pressure is between 1×10 −4 Torr and 1×10 −7 Torr.
15. The method of claim 11 , wherein the UV radiation has one or more photon energies of about 6.2 eV.
16. The method of claim 10 , wherein the VUV radiation has one or more photon energies of about 8.8 eV.
17. The method of claim 1 , wherein:
the first pressure is greater than 10 Torr and less than or equal to 1000 Torr; and
the second pressure is less than 1×10 −4 Torr.
18. The method of claim 1 , wherein the dielectric is exposed to the UV radiation before it is exposed to the VUV radiation.
19. The method of claim 1 , wherein the VUV radiation is normally incident on a surface of the dielectric.
20. The method of claim 1 , wherein the dielectric is not heated by an external heat source during the exposure to the UV radiation and the exposure to the VUV radiation.
21. The method of claim 1 , wherein the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared.
22. The method of claim 1 , wherein the VUV radiation has a photon fluence greater than or equal to 1×10 16 photons per centimeter squared.
23. The method of claim 1 , wherein the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared and less than or equal to 1×10 16 photons per centimeter squared.
24. The method of claim 1 , wherein the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared and less than or equal to 1×10 17 photons per centimeter squared.
25. The method of claim 1 , wherein the VUV radiation has a photon fluence greater than or equal to 1×10 15 photons per centimeter squared and less than or equal to 1×10 16 photons per centimeter squared.
26. The method of claim 1 , wherein:
a dielectric constant of the dielectric is at least two percent (2%) lower than before being exposed to the UV radiation and the VUV radiation; and
the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared and less than or equal to 1×10 16 photons per centimeter squared.
27. The method of claim 1 , wherein:
a dielectric constant of the dielectric is greater than or equal to 2.4 and less than or equal to 2.75 after being exposed to the UV radiation and the VUV radiation; and
the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared and less than or equal to 1×10 16 photons per centimeter squared.
28. The method of claim 1 , wherein:
a dielectric constant of the dielectric is greater than or equal to 2.43 and less than or equal to 2.74 after being exposed to the UV radiation and the VUV radiation; and
the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared and less than or equal to 1×10 16 photons per centimeter squared.
29. The method of claim 1 , wherein:
the first pressure is greater than 10 Torr and less than or equal to 1000 Torr;
the second pressure is between 1×10 −4 Torr and 1×10 −7 Torr; and
the VUV radiation has a photon fluence greater than or equal to 1×10 14 photons per centimeter squared and less than or equal to 1×10 17 photons per centimeter squared.