Buried Channel for In-chip Microfluidic Applications

Microfluidic technology offers a diversity of tools for manipulating small volumes of fluids in channels with dimensions of the order of tens micrometres. It has emerged in the last two decades with many advances accomplished and the concept of lab-on-a-chip expanded to diverse areas of application. The development of microfluidic tools based on lithographic techniques enables the integration with electronic and optical elements necessary for the construction of different devices with a broad range of applications.

In this work, we developed a buried channel process to fabricate microfluidic channels in 8 inch silicon wafers. Using this technology, we were able to create a system of complex microchannels in the bulk silicon substrate, considerably below its surface. The microgeometries are fabricated by starting with a deep reactive ion etching of a small trench, followed by a passivation step of the walls formed, by depositing SiO₂. In a subsequent step, the SiO₂ layer at the bottom of the trench is removed by anisotropic etching keeping the walls passivated and the silicon protected. Then, with isotropic Si etching (using XeF₂), the main channel is created inside the bulk silicon with hundreds of micrometres of diameter. The optimized process leads to the fabrication of microchannels with a low surface roughness with different diameters and geometries meeting the needs of the desired applications.

The network of microchannels that can be formed at different depths in bulk silicon, are then sealed and can be integrated with electronic parts in order to create a final device with great value for different applications, such as in-chip cooling mechanisms, lab-on-chip sensors, microreactors and micro probes.