Hexamethyldisilazane (HMDS) is an adhesion promoter between photoresist and the silicon wafer.

Allows easy stripping of hard to remove photoresists and other materials plus improved adhesion

Advanced adhesion promoter for Hybrid Polymers

In fabricating a semiconductor device or package, adhesion of the materials used to one another is one of the most important considerations. Typically, multiple layers of polymers, metals, and inorganic glasses are used, and these layers must adhere well to each other to survive reliability testing. The adhesion of CYCLOTENE Advanced Electronics Resin* (BCB) to various materials is thus of vital importance in fabricating a reliable device.

Two adhesion promoter solutions are available from The Dow Chemical Company, AP8000 and AP3000. Both are based on organosilane primer chemistry.
These adhesion promoters are supplied as dilute solutions of the organosilane compounds in 1-methoxy-2-propanol. They are ready to use, and dilution or mixing may result in reduced adhesion. Table 1 shows the composition and sales specs of the two products.
During the manufacture of AP3000 and AP8000, the silanes are hydrolyzed by a proprietary process. This converts some of the alkoxysilane or acetoxy silane groups to silanols (Si-OH), which partially condense to form siloxane oligomers. It is the silane oligomers containing silanol groups that are believed to be the active components in the adhesion promoter solutions.
AP3000 and AP8000 are the only adhesion promoters recommended for use with BCB. In particular, hexamethyldisilazane (HMDS) is not effective as a BCB adhesion promoter.