Hexamethyl Disilazane is a commonly used pharmaceutical intermediate which is instrumental in the success of various manufacturing processes carried out in large pharma industry. However, not many people know the fact that, HMDS is used heavily in the semiconductor electronics industry as CVD/ALD precursors and photoresist adhesion promoters mainly for ultra-low K dielectrics, low temperature oxides and litho spacers. 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. For making these applications a success, HMDS is tested against powerful quality control systems.
Applications of HMDS as adhesion promoters
Electronic grade HMDS (Hexamethyl disilazane) functions as an exceptional adhesion promoter because it is critical to the process of bonding of silicon dioxide surfaces to photoresists. Several substrates including base metals, silicon, and silicon nitride are known to display exceptionally well resist adhesion characteristics, whereas this adhesion is lower in the case of glass, precious metals like gold, silver and even SiO2. Therefore, it is very important to keep the right measures in mind if you wish to enhance the overall adhesive strength through the promoters. For ensuring a consistent resist film, various kinds of promoters are used. HMDS along with Ti-Prime are two of the most commonly used adhesion promoters.
Hexmethyl Disilazane easily binds to all types of surfaces that are free from moisture through its Si-atoms. This is the reason why there is a very thin oxide layer present on all kinds of silicon surfaces. HMDS as a promoter is the perfect match for silicon substrates. It is never recommended that you go for a spin coating of hexamethyl disilazane. HMDS is not just very costly but is in huge demand as well and therefore it is important to use it in the apt quantity.
Some of the popular semiconductor substrate surfaces are completely hydrophilic in nature mainly because they have a surface layer which is completely absorbed. Therefore, if it is not properly removed just before the photoresist is done, this layer will permit the etch chemicals and developer to go through the substrate/resist interface and will cause huge undercutting or complete damaging of the film.
Major things to consider
Before priming wafers with (HMDS / HMDZ) CAS No. : 999-97-3 the entire surface needs to be entirely dehydrated. Therefore it is done by baking the substrate at a temperature of 140 to 160 degree Celsius. During the next step, the surface is completely exposed to the HMDS’s vapor phase. This is simply done using a single wafer chamber or a priming oven. Hexamethyl disilazane is sometimes also applied in its liquid form, however in this case the results can be a bit unpredictable. If you want to measure the hydrophobicity on the surface area then you can do so by positioning a small water droplet on the surface and monitoring its state.
These are some of the key HMDS applications in the semiconductor electronics industry. HMDS is a very good adhesion promoter which improves the quality of substrates significantly.