Photoresist: Cleaning, Spinning & Descum

To more effectively coat and pattern substrates such as silicon wafers and glass with photoresist, plasma treatment is used extensively to enhance three crucial steps: Cleaning, Spinning and Descum. An essential first task is to ensure that the substrate surface is free of contamination that might otherwise obstruct subsequent process steps and diminish the overall quality of the patterned substrate. Cleaning is often performed using strong oxidizing agents like piranha, a mixture of sulfuric acid and hydrogen peroxide requiring complex handling and safety measures.  In many cases, new silicon wafers and glass slides do not require cleaning with unnecessarily dangerous chemicals. Plasma treatment oxidizes and removes organic contamination, offering a safe and equally effective alternative in such cases.

In addition to cleaning, plasma treatment introduces polar functional groups, increases surface energy and induces high surface wettability. This surface treatment improves the ability of many photoresists to spread evenly over substrates during the spinning step. An even coating is important for creating channels or patterns with consistent depths and feature sizes. Hydrophobic recovery of substrates can occur immediately after plasma treatment (or piranha). The small size of Harrick plasma cleaners facilitates the rapid movement of substrates from treatment to photoresist spinning. Finally, plasma treatment can be used following UV exposure and development for descum, the removal of nanoscale photoresist remnants in the patterned regions. If a patterned substrate is underexposed or underdeveloped, the small amount of remaining photoresist can interfere with subsequent processes and reduce the substrate quality. Harrick Plasma cleaners are used to descum without significantly affecting the bulk of the photoresist.

Below, you will find articles in which silicon, glass or other substrates are plasma treated before and after spin coating with photoresist.

Relevant Articles from Harrick Plasma Users

  • An H, Chen L, Liu X, Zhao B, Ma D, and Wu Z. “A method of manufacturing microfluidic contact lenses by using irreversible bonding and thermoforming”. J. Micromech. Microeng. (2018) 28: 105008. 10.1088/1361-6439/aaceb7
  • Cheng DF, and McCarthy TJ. “Using the Fact that Wetting Is Contact Line Dependent”. Langmuir (2011) 27: 3693—3697. 10.1021/la2001893
  • Chung BG, Manbachi A, Saadi W, Lin F, Jeon NL, and Khademhosseini A. “A Gradient-generating Microfluidic Device for Cell Biology”. J. Vis. Exp. (2007) 7: e271. 10.3791/271
  • Kelemen L, Valkai S, and Ormos P. “Parallel photopolymerisation with complex light patterns generated by diffractive optical elements”. Opt. Express (2007) 15: 14488—14497. 10.1364/oe.15.014488
  • Limbut W, Loyprasert S, Thammakhet C, Thavarungkul P, Tuantranont A, Asawatreratanakul P, Limsakul C, Wongkittisuksa B, and Kanatharana P. “Microfluidic conductimetric bioreactor”. Biosens. Bioelectron. (2007) 22: 3064—3071. 10.1016/j.bios.2007.01.001
  • Nandagopal S, Lin F, and Kung SKP. “Microfluidic-Based Live-Cell Analysis of NK Cell Migration In Vitro”. Methods Mol. Biol. (2016) 1441: 75—86. 10.1007/978-1-4939-3684-7_7

Harrick Plasma is a leading supplier of plasma equipment to the research community. We have been providing quality tabletop plasma devices specifically designed for laboratory and R&D use for over 30 years.