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In MEMS fabrication, the end pointing is commonly achieved by using optical emission spectroscopy OES, simple reflectometry or possibly just by timing or parameter setting. In the presentation, we discuss some critical issues of optical spectroscopy and reflectometry(those methodologies require etchstop layer) with highlighting Claritas solution for structure with low open area.The key limitation of OES, reflectivity, etch time or parameter setting end point is that no information can be obtained about the etch rate or etch depth as the process progresses. The exposed stop layer is then removed usually with a wet etch. The use of an etch stop layer is inefficient, since in order to use this method additional fabrication steps are required. More critically, the stop layer material left behind (beneath the masked region) can affect the performance of the device being manufactured. Fully integrated interferometric end-point detection (IEPD) unit which monitors in-situ the etching process depth, requires no etch stop layer, provides a sensible solution to this issue.