| AVS 60th International Symposium and Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Wednesday Sessions |
| Session EL+AS+EM+SS+TF-WeA |
| Session: | Spectroscopic Ellipsometry: Perspectives and Novel Applications |
| Presenter: | L.S. Abdallah, New Mexico State University |
| Authors: | L.S. Abdallah, New Mexico State University S. Zollner, New Mexico State University C. Lavoie, IBM A. Ozcan, IBM M. Raymond, GLOBALFOUNDRIES |
| Correspondent: | Click to Email |
Nickel silicides are widely used in semiconductor manufacturing as contacts in CMOS device processing to achieve highly stable low-resistance contacts between copper back-end metallization and front-end silicon transistors. We provide a comprehensive analysis of the dielectric function and optical conductivity for nickel platinum silicides with different platinum concentrations (0 to 30 at.% Pt). Our goal is in-line process control of Ni-Pt alloy deposition and silicide formation using spectroscopic ellipsometry.
Previously, we determined the optical constants of Ni1-xPtx metal alloys. We deposited 100 Å Ni1-xPtx alloy films with different Pt compositions (0 to 25 at.% Pt) on a thick layer of SiO2 to prevent the reaction between the metal and the silicon. Ellipsometric measurements were performed on these samples from 0.6 to 6.6 eV using a broad range of angles of incidence (20 to 80°). Using a thick transparent layer of SiO2 as well as using a broad range of angles of incidence, we vary the optical path length and thus obtain more information about our metal films.
After determining accurate optical constants of Ni1-xPtx, alloys with the same thickness were deposited directly on Si to study the optical constants of silicides. Ellipsometric measurements were performed over the same photon energy range (0.6 to 6.6 eV), but using a smaller range of incident angles because of the absence of SiO2 underneath the metal (no sharp interference fringes).
During Ni1-xPtx deposition on Si, some metal atoms will diffuse into the Si substrate even at room temperature, creating a metal-rich silicide. Annealing the samples at 500˚ C for 30 s creates a monosilicide layer with a thickness of about 200 Å . No unreacted metal remains. We include a 10 Å layer of SiO2 as a native oxide in our model. To obtain the correct silicide thickness, we tried different thicknesses (all around 200 Å) and then we picked the thickness that eliminates Si substrate artifacts.
The imaginary part of the resulting dielectric function of monosilicides shows metallic Drude behavior with two additional peaks at 1.5 eV and 4.5 eV due to interband electronic transitions. Our results will be compared to previous measurements and electronic structure calculations on NiSi and PtSi. In our results, absorption peaks broaden with increasing Pt content in the silicides, similar to our earlier results for Ni1-xPtx metal alloys.