ADHESION PROMOTERS
Use of adhesion promoters
While the purpose of substrate cleaning is to remove all substances that do not
belong to the substrate, an adhesion promoter is intended to chemically modify the
substrate surface itself with regard to optimised paint wetting
and adhesion.
SiO2 or silicates in the form of
quartz, glasses or silicon with (native) oxide as well as most
base metals form polar OH bonds on their surface after sufficiently long exposure to
air humidity. The
substrate in question is therefore hydrophilic (water-loving) and
therefore shows a poor affinity to the non-polar resin molecules of the
photoresist.
In order to make such a substrate surface hydrophobic (water
repellent and therefore attractive to photoresist),
molecules with non-polar groups can be chemically bonded to it using adhesion promoters such as HMDS or TI Prime.