Optimization and upscaling of spin coating with organosilane monolayers for low-k pore sealing

- SAMs are spin coated onto 300 mm low-k wafers. After SAMs deposition, ∆k is 0.1 and decreases to 0.03 after annealing.
- Solvent dielectric constant affect the pre-condensation of SAMs and therefore sealing.
- RBS measurements shows that SAMs seal against MnN by CVD but not TNT by PVD.

For porous low-k film to be integrated into the next generation of interconnects, the pores need to be sealed against metal ions and barrier precursors. Self-assembled monolayers (SAMs) from organosilane precursor are spin coated onto 300 mm k = 2.2 low-k wafers. Two solvents, propylene glycol monomethyl ether acetate (PGMEA) and methanol with different dielectric constant of 8.3 and 20.1, are evaluated in terms of SAMs layer quality and sealing efficiency at coupon level. SAMs deposited from PGMEA show better sealing than SAMs deposited from methanol and therefore are selected for upscaling. Full wafer spin coating results show that a concentration of 0.05 mM or below results in a partial coverage and a tilt angle as high as 70° from the backbone to the normal. Aggregation is observed for all tested concentrations and is worse for higher concentrations, which is possibly induced by the non-negligible presence of water in PGMEA solvents. In order to test the sealing efficiency of the SAMs layer against metal barrier precursors, MnN films by chemical vapor deposition (CVD) and TaNx/Ta (TNT) films by physical vapor deposition (PVD) are deposited on SAM coated low-k wafers. HfO2 is also deposited by Atomic layer deposition (ALD), which is not considered as a barrier but to test the sealing against ALD precursors. Depth profiling Rutherford Backscattering Spectrometry (RBS) measurements indicate an effective sealing of SAMs against CVD and ALD precursors but not against PVD barrier.

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