27 May 1996 Importance of chemistry at the resist-wafer interface for mechanical and lithographic adhesion
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Abstract
Simple geometric considerations suggest that the interface between a photoresist and a wafer surface will be increasingly important in semiconductor lithography as critical dimensions in X-ray and other lithographies drop below 0.25 micrometers . A sensitive, qualitative adhesion test, indentation debonding, was used to compare directly the adhesion of a photoresist to a silicon native oxide throughout various wafer preparation procedures prior to exposure. It is argued and shown that hexamethyldisilazane (HMDS), a commonly used primer, is unlikely to be the optimal choice at feature dimensions below 0.25 micrometers . Application of HMDS left solely methyl groups at the surface of the wafer allowing only for Van der Waals forces for interactions with the polymer. This actually weakened the potential for chemical bonding between the resist and the wafer, in agreement with others. It is also shown that the bonding sites available at the surface of the native oxide varied with cleaning preparation of the wafer and with time of storage between the final cleaning step and lithography. HMDS was not adept at covering the variable native oxide, and this may have allowed for contaminant species such as water or aqueous bases to more easily compete with the polymer for surface sites. A monomolecular layer of organotrimethoxysilane was found to be superior at normalizing the variability of the substrate and also offered the ability to design the functional moieties of the monolayer preferentially to interact with the resist backbone. If designed properly, the increased interaction of the monolayer primer with the polymer can be enhanced while concurrently decreasing the potential for interference from competing monomeric contaminants such as water or aqueous developers. This improves both mechanical and lithographic adhesion.
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Paul M. Dentinger, Paul M. Dentinger, James Welch Taylor, James Welch Taylor, } "Importance of chemistry at the resist-wafer interface for mechanical and lithographic adhesion", Proc. SPIE 2723, Electron-Beam, X-Ray, EUV, and Ion-Beam Submicrometer Lithographies for Manufacturing VI, (27 May 1996); doi: 10.1117/12.240476; https://doi.org/10.1117/12.240476
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