Tuning of resist slope with hard-baking parameters and release methods of extra hard photoresist for RF MEMS switches

We have studied the properties of photoresist (resist) as a sacrificial material for fabricating suspended metal bridges and developed a process to release RF MEMS switches by dissolving thermal cross-linked extra hard photoresist. At the edges of the patterned photoresist, the contact angle with the substrate can be tuned using hard-baking parameters. From the experiment we have found that the resist angle reduces both with baking temperature and time. The baking temperature has a stronger effect on resist slope than the baking time has. It is also observed that at a certain baking temperature, and after a certain time, the resist angle does not reduce further. The RF MEMS switch with photoresist as the sacrificial layer can be released by plasma ashing to strip the initial resist skin, followed by dissolution of the bulk resist in Microposit 1165 solution with heating. The heating of the Microposit 1165 solution accelerates and improves the dissolving process. The Piranha solution is also very effective in dissolving hard resist for releasing RF MEMS switches.