A protocol has been developed to selectively process low-k SiCOH dielectric substrates in order to activate or deactivate them toward the deposition of thin solid films by chemical (CVD or ALD) means. The original SiCOH surfaces are hydrophobic, an indication that they are alkyl- rather than silanol-terminated and that, consequently, they are fairly unreactive. However, the chemical-mechanical polishing (CMP) sometimes done during microelectronics fabrication renders them hydrophilic and reactive. It was shown here that silylation of the CMP-treated surfaces with any of a number of well-known silylation agents such as HMDS, ODTS, or OTS caps the reactive silanol surface groups and turns them back to being hydrophilic and unreactive. Further exposure of any of the passivated surfaces to a combination of ozone and UV radiation reinstates their hydrophilicity and chemical activity. Importantly, it was also demonstrated that all these changes could be induced without altering the original mechanical, optical, or electrical properties of the samples: atomic force microscopy (AFM) images show no increase in roughness, ellipsometry measurements yield the same values for the index of refraction and dielectric constant, and infrared absorption spectroscopy attests to the preservation of the organic fragments present in the original SiCOH samples. The chemical selectivity of the resulting surfaces was tested for the atomic layer deposition (ALD) of HfO2 films, which could be grown only on the UV/O3 treated substrates.
Keywords: atomic layer deposition; low-k dielectrics; ozonolysis; selective deposition; silylation; surface chemistry; ultraviolet photoactivation.