Tuesday, 19 April 2016

Reaction of Hexamethyldisilazane with silica / water

Reaction of Hexamethyldisilazane with silica:

Researchers have been made to study the reaction of Hexamethyldisilazane (HMDS) with OH groups with silica that can be examined by infrared spectroscopy method. This reaction frees the OH groups and results in kinetics. The reaction produces mainly hexamethydisiloxane (HMDSO) and ammonia with a small quantity of nitrogen and methane. When temperature is maintained lower than 300°C no methane is produced. Moreover, ammonia is the first product produced and subsequently HMDSO is produced. As the temperature increases, the amount of nitrogen produces increases and that of ammonia and HMDSO decreases. Reaction of pendant silyl groups with surface acidic hydroxyls to eliminate methane and the concentration of residual silyl moieties on the silica surface both increase with temperature of reaction.

HMDS is used for deactivating materials that support in gas chromatography by many Hexamethyldisilazane Makers. Kinetic studies have been made to get comprehension about the reaction of HMDS with silica and the optimum conditions in which the reactions take place the best.

Study of HMDS:

Four important chemical properties have been deduced from such studies- 1) The freely vibrating hydroxyl groups can occur in either in Si-OH or [Si-(OH)2] configurations, 2) The freely vibrating hydroxyl groups are monoenergetic (i.e. all the OH groups show the same reactivity), 3) Due to the monoenergetic nature of the OH groups, physical absorption results in same fraction of the hydroxyl group being covered for a given pressure and temperature, and 4) The mutually H-bonded OH groups on the surface are essentially nonreactive towards the various bonding agents.

Another such study outlines the kinetics for the reaction of HMDS with silica which is mainly a two-steps process. The first step is a rate determining step that produces trimethylsilylation on the surface of silanol and forms trimethylaminosilane. The second step is where a trimethylaminosilane reactive intermediate reacts to form a trimethylsilyl surface chemical and ammonia. This two step process was mainly applied to analyze the data of the kinetics of HMDS reaction with smoked silica in the field of spectroscopy.

Absorbs Techniques:

Hexamethyldisilazane reacts with many substrate surfaces to enhance their adhesive power. When HMDS reacts with the substrate, it absorbs the excess water in them, reduced surface energy and increases the photoresist adhesion on the surface. The silizane components bond with the oxygen-atoms of the substrates and the methyls offer hydrophobic layers that have good wetting and adhesive characteristics. This dehydration reaction of HMDS on wafers (semiconductor slices) is carried out using two techniques: Liquid Priming and Vapor Priming. It is commonly know that HMDS is very sensitive to the presence of water and degrades in humid air. Studies have been made to understand the reaction of HMDS in dry and humid air in the presence of absorbent surfaces. Studies show that HMDS hydrolyzes in humid air and produces trimethylsilanol (TMS) and ammonia (NH3). Chemcon Speciality Chemicals.Pvt.Ltd is suppliers and Manufacturers of of Speciality Chemicals.