An innovative methodology for monitoring the sacrificial layer removal process in MEMS structures

TY - JOUR

T1 - An innovative methodology for monitoring the sacrificial layer removal process in MEMS structures

AU - Barati, Hamed

AU - Barazandeh, Farshad

AU - Akbari, Mohammad

PY - 2024/2

Y1 - 2024/2

N2 - The sacrificial layer is a key component for the fabrication of a released structure in the MEMS sensors and actuators. Wet etching is a practical microfabrication process that minimizes costs compared to dry etching. Since the sacrificial layer exists between the structural layer and the substrate, characterization of the etching process is unavailable to observe and evaluate directly. This research, for the first time, presents a methodology for monitoring sacrificial layer removal. It takes advantage of using a transparent substrate (during process development) to observe the removal process from the backside. This method can be used as a separate test during surface micromachining to monitor and optimize the release process of the MEMS device. To evaluate the efficiency of the method, the copper sacrificial layer was selected. The removal process was investigated for typical structures used in MEMS sensors and actuators including the etch-holes, the cantilever beams, comb fingers, and the pads. The experimental test showed the removal of the sacrificial layer, the non-uniformity of the etching, and all the veritable chemical reactions and phenomena under the structural layer. In addition, the etch-rate were obtained in the order of 0.35-5.5 μm min−1 for various structural features. The procedure developed in this research is an approach to the process monitoring of the sacrificial layer removal. Therefore, it can be used to organize the quality control in the released structures of MEMS and optimization in batch processing. This method can be adopted for non-metallic sacrificial layers and dry etching as well.

AB - The sacrificial layer is a key component for the fabrication of a released structure in the MEMS sensors and actuators. Wet etching is a practical microfabrication process that minimizes costs compared to dry etching. Since the sacrificial layer exists between the structural layer and the substrate, characterization of the etching process is unavailable to observe and evaluate directly. This research, for the first time, presents a methodology for monitoring sacrificial layer removal. It takes advantage of using a transparent substrate (during process development) to observe the removal process from the backside. This method can be used as a separate test during surface micromachining to monitor and optimize the release process of the MEMS device. To evaluate the efficiency of the method, the copper sacrificial layer was selected. The removal process was investigated for typical structures used in MEMS sensors and actuators including the etch-holes, the cantilever beams, comb fingers, and the pads. The experimental test showed the removal of the sacrificial layer, the non-uniformity of the etching, and all the veritable chemical reactions and phenomena under the structural layer. In addition, the etch-rate were obtained in the order of 0.35-5.5 μm min−1 for various structural features. The procedure developed in this research is an approach to the process monitoring of the sacrificial layer removal. Therefore, it can be used to organize the quality control in the released structures of MEMS and optimization in batch processing. This method can be adopted for non-metallic sacrificial layers and dry etching as well.

KW - MEMS

KW - coppersacrificiallayer

KW - micro-fabricationtechniques

KW - processmonitoring

KW - releasing

KW - copper sacrificial layer

KW - process monitoring

KW - micro-fabrication techniques

UR - http://www.scopus.com/inward/record.url?scp=85185408656&partnerID=8YFLogxK

U2 - 10.1088/1402-4896/ad2662

DO - 10.1088/1402-4896/ad2662

M3 - Journal article

SN - 0031-8949

VL - 99

JO - Physica Scripta

JF - Physica Scripta

IS - 3

M1 - 035942

ER -