| AVS 62nd International Symposium & Exhibition | |
| Selective Deposition as an Enabler of Self-Alignment Focus Topic | Thursday Sessions |
| Session SD+AS+EM-ThM |
| Session: | Fundamentals of Selective Deposition |
| Presenter: | Yves J. Chabal, University of Texas at Dallas |
| Authors: | L.-H. Liu, University of Texas at Dallas T. Peixoto, University of Texas at Dallas W. Cabrera, University of Texas at Dallas D. Dick, University of Texas at Dallas J.-F. Veyan, University of Texas at Dallas D.J. Michalak, Intel Corporation R. Hourani, Intel Corporation M.D. Halls, Schrodinger, Inc. S.P. Pujar, Wageningen University, Netherlands H. Zuilhof, Wageningen University, Netherlands Y.J. Chabal, University of Texas at Dallas |
| Correspondent: | Click to Email |
The ability to process silicon nitride and oxide films and chemically functionalize their surfaces by wet chemical methods is critical for selective deposition. The nature of HF-etched silicon nitride surface is complex and somewhat controversial. We have therefore performed an extensive study of HF etching of both Si3N4 and SiO2 surfaces, combining spectroscopic techniques (Infrared absorption, X-ray photoemission, Low energy ion scattering), imaging (atomic force microscopy) and contact angle measurements with first principles calculations, as a function of HF concentration. We have also performed post-treatment in cold and hot water, and chemical functionalization with a range of organic molecules to help determine the chemical nature of the HF-etched surfaces.
The nature of silicon nitride surfaces is complex. We find that immediate rinsing in deionized water after HF wet-chemical etching yields smooth silicon nitride surfaces with clear evidence for Si-F surface termination. Low energy ion scattering experiments and XPS measurement as a function of gentle sputtering with Gas cluster ion beams (GCIB) confirm that the F is all located at the surface (i.e. not distributed into the bulk), and in the form of Si-F with high temperature stability (up to 600 oC in ultra-high vacuum). Hydrolysis in water is very slow at room temperature, but can be achieved at high temperature (~90 % removal at 70 oC for 30 min). However, water is found to etch silicon nitride, as evidence by a loss of Si3N4 phonon absorption, suggesting that the removal of the surface fluorine may not only be due to surface reaction through a direct exchange mechanism via pentavalent Si intermediate, but also to the hydrolyzation of Si3N4 itself through back-bond chemical attack by water. In addition to F, we find that there is also surface -NH2 species, as evidenced by IR active -NH2 bending modes at 1550 cm-1, which we estimate to be only ~20 % monolayer from analysis of reaction with aldehyde molecules. However, this coverage appears sufficient to protect the Si3N4 surface. Finally, LEIS and XPS indicate that there is oxygen at the surface, which could either be in the form of -OH or Si-O-Si. Functionalization with alkylsiloxanes reveals that ~50 % of the surface contains Si-OH. In summary, the sum of the concentrations (50 %, 20 %, 50 % in ML), i.e. exceeding 1 ML, suggests that the etched surface may be atomically rough. Overall, these findings provide a method for selective deposition by using first aldehyde reaction for Si3N4 functionalization, followed by silane reaction for SiO2 functionalization.