Test structure to monitor the release step in a micromachining process
View Patent ↗Electrical and visual test structures monitor the degree of removal of conductive sacrificial layers used in micromachining processes that fabricate micro-electromechanical systems (MEMS).
1. A micro-electromechanical test apparatus, comprising:
an insulating substrate;
a first conductive structural element having a first anchor portion fixed to the substrate and a first bridge portion cantilevered from the anchor portion over the substrate;
a second conductive structural element insulated from the first conductive structural element and having a second anchor portion fixed to the substrate and a second bridge portion cantilevered from the second anchor portion over the substrate; and
an electrical resistance measuring device connected to the first and second conductive structural elements adapted to detect the presence of an incompletely removed conductive sacrificial layer contacting the first and second conductive structural elements under the bridge portions.
2. The system of claim 1 , in which the first bridge portion comprises a first plurality of conductive fingers and the second bridge portion comprises a second plurality of conductive fingers interleaved with the first plurality of conductive fingers.
3. The system of claim 1 , further comprising:
a structural insulating layer situated between the first and second bridge portions.
4. A method of detecting the presence of an incompletely etched conductive sacrificial layer in a micromachining process, comprising the steps of:
forming an insulating substrate;
forming a first conductive structural element having a first anchor portion fixed to the substrate and a first bridge portion cantilevered from the anchor portion over the substrate;
forming a second conductive structural element insulated from the first conductive structural element and having a second anchor portion fixed to the substrate and a second bridge portion cantilevered from the second anchor portion over the substrate; and
detecting electrical resistance between the two conductive structural elements suspended above the insulating substrate to detect the presence of the incompletely etched conductive sacrificial layer contacting the first and second conductive structural elements under the bridge portions.
5. A micro-electromechanical test apparatus, comprising:
an insulating substrate;
a first conductive layer formed on the substrate;
a second conductive layer formed on the substrate and insulated from the first conductive layer;
a first structural element having a first anchor portion fixed to the first conductive layer and a first bridge portion cantilevered from the anchor portion over conductive layers and the substrate;
an electrical resistance measuring device connected to the first and second conductive layers adapted to detect the presence of an incompletely removed conductive sacrificial layer contacting the first and second layers under the bridge portion.
6. The apparatus of claim 5 , further comprising:
a second structural element separated from the first structural element and having a second anchor portion fixed to the second conductive layer and a second bridge portion cantilevered from the second anchor portion over the substrate; and
a third structural element suspended above the substrate and separating the first and second structural elements.