Ultra low leak detection method for MEMS devices

A new leak detection method for miniature MEMS (micro-electro-mechanical-systems) packages is presented. It has the remarkable advantage to simultaneously reveal both extremely fine and gross leaks. It is shown that a cumulative chemical reaction, such as the oxidation of thin copper layers, can be used to detect a test gas (oxygen) and that the oxidation level of these layers can be assessed by simple optical transmission measurements in the infrared region. Copper test patterns deposited and micro-structured inside the devices cavity are further shown to be capable of detecting leak rates as low as 5/spl times/10/sup -16/ mbarl/s as needed to guarantee the hermeticity of wafer level packaged small size devices.