Surface properties restoration and passivation of high porosity ultra low-k dielectric (k?2.3) after direct-CMP
Surface hydrophilisation and effective k-value degradation have been reported in literature after direct-CMP of high porosity SiOC films (without a protective capping layer). In the sequel, attempts to restore ultra low-k (ULK) material initial properties after a standard CMP and post-CMP cleaning process are reported. Annealing treatment has shown to be valuable to remove residual organics and water absorbed at the ultra low-k material surface after direct-CMP. However, as the hydrophilicity of the polished surface remains unchanged, it does not prevent moisture uptake, leading to an increase in k-value with time. Therefore, in order to restore hydrophobic properties and to stabilize the surface in time, three silylating agents  containing chlorosilane reactive groups (SiMenCl3?n) as well as hydrophobic methyl functions (CH3) in their structure  have been employed in liquid, gas or dense CO2 phases on the CMP-induced damaged ULK layers. While each of these organic treatments is efficient to restore hydrophobicity on post-CMP ULK surfaces, only one of them proved to be able to keep the k-value low (comparable to the ULK pristine k-value) and stable in time, without inducing significant change in porosity of the ULK material.
k-value ulk post-cmp hydrophobicity silylation