MEMS-on-CMOS integration of a holographic 8M-pixel SLM device using KrF-lithography

We discuss the process integration to manufacture a spatial light modulator (SLM) device for application in mixed and augmented reality. The MEMS-part of the device is integrated on an external 180nm CMOS. The SLM consists of an 8MPixel micro mirror array with a pixel size of 4μm x 6μm. To provide the vertical strokes necessary for RGB color image generation, a comb-drive actuator concept was developed. Besides the yoke and the stator of the comb-drive, the actuator uses a double spring structure to reduce tilting of the mirror and other stress-induced effects. At the beginning of the product development we used iLine-lithography only, while later for the final device we switched to KrF-lithography to provide the necessary feature size down to 200nm as well as better CD-uniformity and overlay specification. We describe the process development, with focus on the lithography and etching processes for the actuator. Especially the different processes for patterning the Titanium-Aluminum structures of ultra-thin springs as well as the yoke and the stator with their high aspect ratios, which are specific for MEMS processing. Finally we achieved post-etch CD-uniformity <10nm per wafer for all metal structures as well on-product-overlay accuracy <15nm.