Comparative Study of Top Electrode and Bottom Electrode Sensing Resistor Schemes for MEMs Based Bolometer Application

In this work, CMOS compatible MEMs based bolometer process was developed on 200mm std CMOS Cu BEOL. As to the micro-bridge structure, TaN was used as electrode material, and alpha-Si film was used as the sacrificial material fabricated by low Temperature PECVD technology. No metal or dielectric material plug was used for the anchor supporting structure, which make the process much more controllable and flexible. For one of the Sensor product application, B-doped alpha-Si film was used as sensing material fabricated by PECVD and in situ doping process. The sensing resistor, which is the most important structure of this product, was fabricated with different approaches. In the top electrode scheme, TaN was used as electrode layer on top of sensing material whose pattern was to define the sensing resistor. In the bottom electrode scheme, TaN electrode layer was located on bottom of sensing material. The two schemes were comparatively studied to show their advantages and drawbacks. Conclusion was made that both the scheme can match the product requirements, and bottom electrode scheme was the better choice for its well control for sensing material loss and uniformity of sensing resistor, which was most important to the performance and yield of MEMs based IR sensor products.