Is it possible to use RIE etching system for etching more than 200 micrometers in depth. I know that for deep etching it is used DRIE etching system but it is more expensive. The difference between DRIE and RIE etching systems is only the rate and the etching speed. Is there any other difference between them? If I would like to create micro-channels with a size equal to 300 micrometers I have to use DRIE etching system. Does it exist another cheaper technology for creation of masters not using silicon as a material. I would like to create polymer micro-channels.
Hi Tihomir,
if you are looking to machine a master for a polymer microfluidic network, there are many alternatives cheaper and easier than DRIE.
The most common option in the literature is a one step photolithography process with thick resists, like SU8 (negative photoresist) or AZ 40XT (positive). To achieve the thicknesses you mentioned, probably you need to spin coat the resist at a very slow speed, or use more than one step of deposition. Microchem SU8 2100 will probably be the best.
Usually, the most expensive step is the realization of the optical mask, but, for the feature size you mentioned, you can print it on a transparency for few euros with a common high-resolution printer, and attach it to an UV-transparent glass block with tape to hold it.
With this technique, you can achieve probably a master with a better surface roughness (about 10 nm), and sharper corners than with DRIE.
Another common option is to use micro-milling: you can either mill directly polymers (like PMMA, COC, or PC), or metals (like aluminum, brass, steel [more difficult], ...).
This results in a master having a greater roughness (of the order of 200 nm), and roundings around the corners (depending on the size of the tools you are using). If you mill a metal master, it can be easier to add a polishing step to improve the surface roughness without affecting significantly the dimensions of the structures. The sidewalls could be very step, even better than the one achieved with SU8, but adding a draft angle could be not a bad idea depending on the replication method you choose and the number of reps you want to achieve.
Good results can be achieved also with small and relative inexpensive machines.
Laser ablation and 3D printing are two other alternatives. There are many review of the fabrication processes of polymer microchannels, and I believe one of the best is Becker and Gartner, "Polymer microfabrication methods for microfluidicanalytical applications", Electrophoresis 21, 12 (2000). Even if it is relatively old, it is very complete and shows clearly all the possibilities to machine the master, replicate the structures, and assemble the final device. Below the link to the article in the journal website.
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