Cleanroom G07 LISE
XeF2 etching is an isotropic process widely used for releasing MEMS structures including switches, cantilevers, bridges, mirrors, membranes, channels, and thermal isolation cavities. Its merits include highly selective etching, no stiction problems as existed with wet etching, and long under cuts. Our system is homemade. A cycling process is applied in the following order:
* supplying high pressure N2 gas to XeF2 storage bottle flowing the mixture of XeF2 and N2 into the etch chamber
* pumping out vapor by-products
* starting the next cycle.
For safety concerns, the upper cabinet holds the etch chamber, the XeF2 bottle, and the gas lines and is vented to the acid exhaust pipe of the cleanroom. The cabinet normally is at a slightly lower pressure than the ambient. During process and stand-by modes, the cabinet doors are closed. At the end of every run, the etch chamber is pump-purged with N2 for 3 cycles to minimize harmful residuals.
Materials can be etched: XeF2 is widely used to etch Si and it also etches Ge, Mo and SiGe as well as transitional metals W, Ti, Ta, TiN and TaN under certain conditions such as high temperatures.
Materials that won’t be etched with XeF2: Al, Ni, Cr, Pt, Ga, MgO, ZnO, AlN, GaAs, resist, and PDMS
The etching selectivity of different materials relative to Si:
Si 1:1; Mo 2:1; Ge>1:1; SiGe>1:1; Thermal SiO2 1:1000; CVD or PECVD SiO2 1:1000; Si3N4 >1:1000
This system is able to handle sample sizes of 6″ in diameter or smaller.