In semiconductor industry adhesion promoters (such as HMDS) are applied on various surfaces to improve adhesion between the surface and the photoresist:

On SiO2 and many metals surfaces, the air humidity forms polaric OH-bonds. Such substrates are hydrophilic, but reveal a bad wetting and adhesion of the unpolaric resist. Adhesion promoters make hydrophilic surfaces hydrophobic thus improving the resist adhesion. [...] The methyl groups of the HMDS fragment hereby form a hydrophobic surface thus improving resist wetting and adhesion. (source)

But why should non polar (hydrophobic) substances wet non polar substrates better than polar substrates? (in the opposite case of polar substances it is clear why)

  • $\begingroup$ You mean if the polar substance can't move to get away from the nonpolar liquid, what should keep the latter from forcing itself on the former? A static dipole should be able to induce a dipole moment in the hydrophobic, and attraction should follow? $\endgroup$
    – Karl
    Dec 4, 2016 at 14:44


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