Fabricating Soft Lithography SU-8 Molds for Microfluidic Devices

Microfluidic devices are increasingly popular due to their precise manipulation of small amounts of fluids through narrow channels. This is advantageous in various applications and scientific fields, such as chemistry, biology, and medicine.

Most microfluidic devices depend on standard photolithography as a microfabrication method to process photoresists for the electronics industry and to pattern substrates. However, soft lithography complements photolithography as it enables processing of different materials, such as polymers and gels.

Soft lithography is not an independent method of microfluidic device fabrication. Instead, it must be used with another lithography technique, frequently e-beam or photolithography, to produce the necessary mold or stamp.

This article discussed the main steps in fabricating SU-8 molds for soft lithography, which is utilized to create microfluidic devices.

Fabricating Soft Lithography SU-8 Molds for Microfluidic Devices

Image Credit: Platypus Technologies, LLC

SU-8 Mold Fabrication

This article considers the process for creating SU-8 epoxy resin molds with a silicon wafer. However, alternative methods and materials are available, depending on suitability or preferences. 

Wafer preparation

Wafer preparation is required before the addition of a SU-8 photoresist. This preparation includes cleaning the wafer with acetone and heating the wafer to remove all surface moisture. The SU-8 resin connection with the substrate should be improved.

Spin coating

The creation of a photoresist layer is required for mold creation. The most widely used method is spin coating, which yields the required uniform layer on top of a substrate.

A pool of SU-8 photoresist is positioned in the middle of the substrate on a rotating platform. The platform's rotation speed and acceleration establish the photoresist layer's thickness.

Soft baking the photoresist

Once the photoresist layer has undergone the spin-coating process, the soft baking process is employed for the evaporation of the solvent and hardening of the SU-8 photoresist. This is the first of three baking processes involved in mold development.

Photomask Alignment and UV Exposure

A photomask is aligned with the substrate to ensure the desired pattern can be generated on the surface. SU-8 is a negative photoresist, meaning that it will become hard following exposure to UV light, with the part not exposed dissolving. 

Post-exposure baking

The second baking process occurs following the exposure of the substrate to UV light. The photoactive components are activated during UV exposure, but energy is required for the reaction to progress further. In post-exposure baking, this required energy is generated and aids the development of the substrate’s mechanical properties.

Development

The wafer is submerged in a solvent to reveal the design patterned on the substrate and dissolve the photoresist parts not subjected to UV light.

Hard baking

Hard baking is the third process in fabricating a SU-8 mold. It is carried out to enhance the mechanical properties of the substrate and decrease the likelihood of the material cracking. This stage is optional.

Checking

Ultimately, the completed SU-8 mold must be checked to verify it is suitable for its intended application and satisfies any regulatory requirements. This is typically performed using a microscope, but additional observation may occur using an optical or a mechanical profiler.

Platypus Technologies

Platypus Technologies provides various photolithography services and supplies negative and positive photoresists (including SU-8 wafers) for various applications across the electronics industry.

Contact a member of Platypus Technologies today to learn more about SU-8 photolithography or the fabrication of SU-8 epoxy molds.

References and Further Reading

  1. https://www.sciencedirect.com/topics/materials-science/soft-lithography
  2. https://www.researchgate.net/publication/350182349_Fabrication_Methods_for_Microfluidic_Devices_An_Overview 

This information has been sourced, reviewed and adapted from materials provided by Platypus Technologies, LLC.

For more information on this source, please visit Platypus Technologies, LLC.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Platypus Technologies, LLC. (2023, May 09). Fabricating Soft Lithography SU-8 Molds for Microfluidic Devices. AZoNano. Retrieved on May 19, 2024 from https://www.azonano.com/article.aspx?ArticleID=6444.

  • MLA

    Platypus Technologies, LLC. "Fabricating Soft Lithography SU-8 Molds for Microfluidic Devices". AZoNano. 19 May 2024. <https://www.azonano.com/article.aspx?ArticleID=6444>.

  • Chicago

    Platypus Technologies, LLC. "Fabricating Soft Lithography SU-8 Molds for Microfluidic Devices". AZoNano. https://www.azonano.com/article.aspx?ArticleID=6444. (accessed May 19, 2024).

  • Harvard

    Platypus Technologies, LLC. 2023. Fabricating Soft Lithography SU-8 Molds for Microfluidic Devices. AZoNano, viewed 19 May 2024, https://www.azonano.com/article.aspx?ArticleID=6444.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Your comment type
Submit

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.