Two-step photolithography to fabricate multilevel microchannels.

Area of Science:

• Materials Science
• Microfluidics
• Lithography

Background:

• Controlling feature thickness in microchannels is crucial for microfluidic device performance.
• Traditional photolithography methods face challenges in achieving precise thickness control for complex structures.

Purpose of the Study:

• To investigate the variation of photoresist thickness in patterned microchannels using a two-step photolithography technique.
• To understand the factors influencing photoresist thickness during the two-step process.
• To demonstrate the application of this method in fabricating microfluidic devices.

Main Methods:

• Utilized a two-step photolithography process to pattern microchannel features in photoresist.
• Analyzed the influence of first-step pattern dimensions (thickness and width) and second-step spin-coated film thickness on the final photoresist thickness.
• Investigated the role of capillary pressure in determining photoresist film thickness within critical pattern widths.

Main Results:

• The final photoresist thickness is a function of both the initial photoresist pattern and the subsequent spin-coated layer.
• Thickness variation is significant within critical pattern widths where capillary pressure dominates.
• Successfully fabricated multilevel channel features using the developed two-step photolithography method.

Conclusions:

• Two-step photolithography offers a viable method for precise control over photoresist thickness in microchannel fabrication.
• This technique facilitates the creation of complex microfluidic architectures, including multilevel channels.
• Demonstrated the utility of this approach by fabricating a functional cross-flow filter with dual pore sizes.