| AVS 55th International Symposium & Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuA |
| Session: | Practical Surface Analysis |
| Presenter: | E. Martinez, CEA-LETI, France |
| Authors: | E. Martinez, CEA-LETI, France F. Pierre, CEA-LETI, France D. Mariolle, CEA-LETI, France N. Benedetto, CEA-LETI, France J.P. Barnes, CEA-LETI, France R. Gassilloud, CEA-LETI, France O. Renault, CEA-LETI, France F. Martin, CEA-LETI, France F. Bertin, CEA-LETI, France A. Chabli, CEA-LETI, France N. Chevalier, CEA-LETI, France |
| Correspondent: | Click to Email |
The scaling of metal-oxide-semiconductor devices faces the challenge of metal gate integration to replace poly Silicon metallization. These metal gates will provide lower electrical resistivity and thinner EOT by removing depletion. New materials based on tungsten alloys are being investigated because of high thermal stability and corrosion resistance. W and WSi are good candidates because of a middle-gap work function that is shifted to P+ or N+ by ion implantation. Before integration in sub-45 nm nodes, the effective work function of the metal gate must be accurately evaluated. Complementary surfaces characterization techniques such as Kelvin Force Microscopy (KFM) and Ultraviolet Photoelectron Spectroscopy (UPS) can be used. Due to extreme surface sensitivity, surface preparation is mandatory before carrying out the measurements. Auger and TOF-SIMS depth profiles evidence the presence of native tungsten and silicon oxides on top of W and WSi materials, respectively. Removal of these oxides must be performed before KFM or UPS measurements, in order to estimate the real metal work function. We investigate here the impact of surface treatments, such as chemical etching, ion sputtering, and thermal annealing on the work function measurement. For WSi metal gates, HF based chemical etching is used to partially remove SiO2. For W metal gates, annealing at 700°C is performed to evaporate WO3. Subsequent X-ray Photoelectron Spectroscopy (XPS) is carried out to follow the evolution of the chemical surface composition. A detailed analysis of Si2p and W4f core levels evidences partial removal of native oxides. Gentle argon sputtering is finally performed to fully remove the superficial oxide. UPS and KFM measurements are performed after these surface treatments. A crossed study of the results obtained by these techniques will be commented. AFM and SEM results will highlight the roughness and morphology of the surface after each surface treatment.