page_title: Chemistry of photolithography
section_title: HMDS
hierarchical_section_title: Chemistry of photolithography / HMDS
caption_attribution_description: chemical structure of Bis(trimethylsilyl)amine (HMDS)
context_page_description: Photolithography is a process in removing select portions of thin films used in microfabrication. Microfabrication is the production of parts on the micro- and nano- scale, typically on the surface of silicon wafers, for the production of integrated circuits, microelectromechanical systems, solar cells, and other devices. Photolithography makes this process possible through the combined use of hexamethyldisilazane, photoresist, spin coating, photomask, an exposure system and other various chemicals. By carefully manipulating these factors it is possible to create nearly any geometry microstructure on the surface of a silicon wafer. The chemical interaction between all the different components and the surface of the silicon wafer makes photolithography an interesting chemistry problem. Current science has been able to create features on the surface of silicon wafers between 1 and 100 μm.
context_section_description: A common method to increase adhesion of photoresist on the silicon wafer surface is to treat the wafer with Hexamethyldisilazane (HMDS). A new silicon wafer has a polar surface and has some adsorbed water on the surface. The wafer can undergo a dehydration bake to remove adsorbed water, and followed by the HMDS treatment also known as the priming stage. HMDS can be dispensed in liquid form onto the wafer using a syringe while the wafer is attached to a vacuum chuck in a spin coater. HMDS can also be applied in gas form in the process known as the vapor prime. The HMDS promotes good photoresist-to-wafer adhesion because it ensures the wafer surface is hydrophobic. After HMDS treatment the silicon surface oxide becomes silated, leaving a non-polar surface. The pristine silicon (100) face has a surface energy value of 56.9 mN/m, which is reduced to a value of 44.1 mN/m after HMDS treatment 
  The molecular formula for hexamethyldisilazane is C₆H₁₉NSi₂.
caption: 3D image of HMDS
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