For protective paint coatings to be effective for a longer duration of time, they must have good adhesion properties. Adhesion is a widely used term in the field of chemistry and there are several domains that define it differently. When used in reference to paint systems, adhesion is defined by three main properties: adsorption, chemical, and mechanical interlocking. The paint system is mainly defined as a simple three layered system comprising of the paint film, the interface, and the substrate. The performance and durability of any paint genre depends mainly on two basic properties: cohesion and adhesion. While cohesion is associated with the strength of the bonds between the various molecules of the coating film, adhesion is the strength of the bonds forming between one material and another. To ensure a strong adhesive coating in paints, Hexamethyl Disilzane (HMDS) is widely used as an adhesive promoter and Hexamethyl Disiloxane (HMDSO) is commonly use as a plasma polymerized agent that is useful in manufacture of HMDS.
As stated earlier, a painted surface has a three component layer: paint, substrate, and the substrate interface. A technique has been developed for making comparative evaluations of the adhesion of photo resists to various substrates. Adhesive promoters usually have a high affinity for the substrate and the applied adhesive. Many substrates like e.g. silicon, silicon nitride and base metals (like aluminum, copper) show generally good resist adhesion features Hexamethyl Disilazane, with the molecular formula of C6H19NSi2, HMDS readily react with the substrate material removing absorbed water and reducing surface energy which, in turn promotes photo resist adhesion to the substrate. The component silizanes bond to the oxygen-atoms of the oxidized substrates in the wafer (a thin slice with parallel faces cut from a semiconductor crystal) while the non-polar methyls provide a hydrophobic layer with good resist adhesion and wetting features. Applying HMDS to dehydrated wafers is one common method for achieving the surface hydrophobicity required to prevent photo resist delimitation.
Hexamethyl Disiloxane (HMDSO) is commonly utilized as a major source of the trimethylsilyl functional group, including HMDS in the process of organic synthesis. For instance, HMDSO converts carboxylic acids and alcohol into various types of silyl esters and silyl ethers in the presence of a suitable acid catalyst. Studies suggest that different HMDSO/O2 ratios when mixed together can produce a plasma-polymerized coating from that provides a varying degree of corrosion protection.
The quality of the coating of Hexamethyl Disilazane (HMDS) causes surface dehydration and results in chemical bonding to surface hydroxyl ions and not feebly bound surface moisture. The coating can remain stable for several weeks. Not only this, as it is stored in the system under vacuum, the chemical does not degrade from exposure to moisture in the air and the operators are not exposed to fumes from the HMDS or carrier solvent; making it a perfect suitor as an adhesive promoter agent in paint and coating system.