Development and Optimization of Contact Module Process for Micro-Bridge Structure based MEMS/Sensor Application*

In this work, trench first process integration scheme was used to develop MEMS contact module, and local surface planarization was realized by the optimized design and process control. Thin electrode layer was deposited on the sidewall and bottom of contact hole to form the electrical connection from micro-bridge surface to bottom readout circuit without any metal or dielectric plug filling in the contact. Dark spot problem was found in non-uniformity electrical output map for one of the products with large scale array, which was corresponding to the increase of contact parasitic resistance. Failure analysis was done, and it was found seriously bottom and sidewall lateral corrosion problem on the bottom of the contact structure, which had caused thinning or even discontinuity of the electrode layer. After comparative experiments design and results analysis, contact wet cleaning process was found to be the root cause. During contact wet cleaning process, the reactive solution in the deep contact may not easily be removed, and the residue solution will damage the metal on the bottom and sidewall of contact and cause lateral corrosion problem. Based on the analysis results, optimized process has been developed, and the wafer-level yield test result shows that the dark spot problem has been greatly improved.