Enhancement in mechanical properties of silica low-k thin films using wet chemical technique
Silica low-k films have been deposited on silicon wafer using sol-gel spin-on method. The tetraethyl orthosilicate (TEOS) has been used as a precursor solution. In order to improve the properties, the deposited films have been surface treated by wet chemical treatment at different trimethylcholosilane (TMCS) volumetric concentrations in hexane. The presence of hydrophobic (CH3) groups observed around 2900 cm-1 confirms the surface modification of films. Further, the water contact angle of as-deposited and surface treated film at 20% TMCS concentration in hexane have been found to be 83º to 104º, respectively. This significant change in water contact angle after surface modification confirmed the change in surface of film from hydrophilic to hydrophobic. The mechanical properties of films have been determined by using nano-indentation techniques. The depth of penetration of indent in film surface has been observed to be decrease from 75 nm to 45 nm after surface modification at 20% TMCS concentration in hexane. This shows the improvement in mechanical properties of film after surface modification. The Young’s modulus and hardness of surface modified films at 20% TMCS have been observed to be 78 GPa and 3.45 GPa, respectively.
Porous low-k; ULSI; TMCS; Contact angle; Nano-indentation
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