Friday, 27 November 2015

Hexamethyl Disilazane & Pharma Intermediate

Hexamethyl Disilazane, which is also known as HMDS, is a special organosilicon compound that is a derivative of ammonia. It is different from the traditionally known compound because it has trimethylsilyl groups in place of the two hydrogen atoms. It is a colorless liquid that is a popular reagent and precursor to many bases, making the compound a very popular ingredient in different types of organic synthesis and organometallic chemistry. HMDS has many uses as a chemical intermediate, release agent, lubricant, coupling agent, deactivator for chromatographic support materials, silylating agent in pharmaceuticals, adhesion promoter for photoresists on silicon (electronics), as reagent for temporary protection of reactive sites in manufacture of betalactum antibiotics, etc. Amongst these, the main applications of HMDS are in electron microscopy and in semiconductor electronics industry.

Major Applications of HMDS

HMDS represents an attractive to critical point drying (CPD) in the imaging of cells on coal, negating the need for expensive equipment. Coal, a popular choice in scanning electron microscopy, is easily fragmented into sub-micron particles, which can be problematic in critical point drying procedures.  Alternatively, HMDS was found to be easily used as an ideal substitute to critical point drying that takes place at the time of sample preparation. Even though critical point drying is a popular method of drying up biological specimens that are used for scanning electron microscopy, drying up of specimens by HMDS evaporation is also a very good alternative. Hexamethyldisilazane evaporation is not used frequently however experts have suggested that this is also a great method for drying up of specimens. Hardly any differences are observed during the process and furthermore this method is proved to be much more helpful as far as drying up of whole-mount cells for AFM and TEM are concerned.
Not only this, in the semiconductor industry, with the use of HMDS as semiconductor, companies have been able to enable powerful yet small chips inside computers, tablets and smartphones to work better on a consistent basis. HMDS 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.

A few experiments were also made to verify the hydrophobicity and adsorption properties of HMDS thin films and the results pointed out that HMDS films can be used: for ultraviolet protection of flexible organic substrates, such as PP, for sensor and/or preconcentrator development, due to their adsorption properties, and in spatial applications due to resistance for O2 attack in hostile conditions, such as plasma etching. Thus, with many applications as described above, HMDS has found its way to be a major player as a Pharma Intermediate.