**11. Conclusion**

surface of each micro-well is the only region fully exposed to the UV lights. The SU-8 resin attached to the opposite side of the UV-exposed surface will be partially cured. As a result, the interior surface of each micro-well will be polymerized into a hard and thick layer. The thickness of this polymeric layer can be easily increased by increasing the duration of the UV exposure. In general, this polymeric layer can be as thin as a membrane or as thick as the

In step 5, the uncured UV-opaque SU-8 resin attached to each of the micro-well is removed from the micro-well by melting at an elevated temperature. The SU-8 resin attached to the opposite side of the UV-exposed surface will remain uncured and melted into a liquid when the wafer is subjected to a strong heat. As a result of this heat, the UV-exposed surface will be significantly hardened. Traces of the uncured photosensitive resin which remain attached to the micro-well array can be stripped off by developing in 1-methoxy-2-propanol acetate.

In step 6, a hole is formed on the tip of each conical micro-well by dry etching. This step is intended to turn each conical micro-well into a micro-funnel. A hole can be formed on the tip of each conical micro-well by dry-etching the wafer in oxygen plasma for 100 seconds using a Trion RIE/PECVD tool. The oxygen plasma also sharpens the tip of each micro funnel during the dry etching process. In the present study, the process parameters were 90% O2, 10% CF4,

**Figure 4** shows one of the micro-funnels which have been fabricated using the abovementioned method. The micro-funnels were designed to have a sharp tip and wide top, that is a low aspect ratio geometry. This design allows a larger amount of drug to be encapsulated per microfunnel. The conical geometry used in this study had a volume in excess of 24.4 nl. In addition, the micro-funnels were found to have sufficient mechanical strength for inserting into the

application demands, depending on the duration of UV exposure.

an RF power of 100 w, and a chamber pressure of 1.6 Torr.

**10. Results and discussions**

12 Lab-on-a-Chip Fabrication and Application

**Figure 4.** Photo illustrating a fabricated micro-funnel.

For the first time, this article has presented a method that enables concave or convex microstructures with shells elements or hollow space to be photo-lithographically fabricated. The method comprises four basic stages. The first stage involves preparation of a composite containing a mixture of SU-8 monomer and a UV-opaque impurity. The second stage involves fabrication of an embossing stamp for casting the desired 3D patterns. In the third stage, the desired 3D hollow or suspended micro-structures are cast using the embossing stamp. In the final stage, features requiring with suspended or hollow parts are selectively polymerized by UV exposure. The concepts of this technology have been demonstrated by fabrication of prototypes.
