The product is used to augment the adhesion of photoresist on silicon and SiO2 surfaces.
The effectiveness of HMDS on adhesion is correlated with the reactivity of this compound with surface hydroxyl groups to form a new siloxane end product, i.e. Si-O-Si(CH3)3. This newly formed termination on the substrate renders the surface more hydrophobic in character and leads to greater wettability by photoresist. The latter condition is a crucial factor in good bonding. As a result of these altered characteristics due to the surface chemistry, the treated silicon surfaces become highly compatible with both negative and positive photoresists.
HMDS preparations are generally applied to the silicon wafer while spinning, prior to the application of photoresist. As an alternative procedure, the wafers may be immersed in HMDS preparations and allowed to dry after removal.