Air-bridges, air-ramps, planarization, and encapsulation using pyrolytic photoresist in the fabrication of three-dimensional microstructures

Abstract

Pyrolyzation of photolithographically patterned photoresist on semiconductor substrates such as silicon, gallium arsenide, and indium phosphide, results in a convex-shaped, chemically inert, temporary form that functions as a mold upon which to lift-off evaporated thin films such as metals. The pyrolyzation process is simply a bake on a standard laboratory hot-plate that is ramped from room temperature to 300 °C air. The pyrolytic-photoresist form is subsequently removed in an oxygen plasma stripper leaving behind the three-dimensional lifted off thin films of free-standing, convex-shaped, full-arch air-bridges or half-arch air-bridges that we call air-ramps. Some applications are interconnects for high-speed devices; inter-level interconnects; out-of-plane coils for out-of-plane inductors; microdomes for eletromagnetic shielding; electrodes for field-emitter tips; and microelectromechanical structures. Pyrolyzing photoresist does not alter the good planarization capabilities of photoresist. Because pyrolytic photoresist is a version of the earliest form of synthetic thermoset resin called Bakelite, it can also be used as a reasonably good encapsulation material.

Characterization and optimization of dry releasing for the fabrication of RF MEMS capacitive switches

“…Based on equations (3)-(7), the mean stress and the stress gradient can be obtained by the curve-fitting method with the following steps. First, σ 1 can be calculated according to equation (5) after measuring the deflection z of a cantilever beam at different positions; then based on equation 3and the calculated σ 1 , the radius of the curved cantilever beam R can be calculated; after that, s can be obtained based on equation (6) and the values of R, L and z tip ; finally, σ 0 is calculated according to equation (7).…”

“…These measured deflections can be obtained from figure 11. According to equations (5) and (7), the fitted mean stress σ 0 and stress gradient σ 1 are σ 0 = 21.8 MPa and σ 1 = 3.6 MPa, respectively. The residual stress and stress gradient can affect the characteristics of the RF switch, especially the pull-in voltage.…”

“…The main advantage of dry releasing is that stiction problems are easily avoided. Several researchers have discussed the dry release of metal structures in oxygen plasma [5,6], but no detailed investigation of the effect of the process parameters has been carried out.…”

Fabrication challenges for indium phosphide microsystems

“…It is attractive due to its robustness, processing ease, and photopatternable formulations. Other very common methods include pyrolyzed photoresist films, which offer ease of patterning, but somewhat unstable electrical characteristics due to the high carbon-containing compounds [118,119].…”