Polarization- and wavelength-sensitive sub-wavelength structures fabricated in the metal layers of deep submicron CMOS processes

摘要

Sub-wavelength structures in metal films have interesting optical properties that can be implemented for sensing applications: gratings act as wire grid polarizer, hole arrays with enhanced transmission can be used as spectral filters. This paper demonstrates the feasibility of these nanostructures using 180 nm and 90 nm complementary metal-oxide semiconductor (CMOS) processes. The metal layers of the process can be used for optical nanostructures with feature sizes down to 100 nm. We describe the design and simulation of these metal structures using the finite-difference time-domain (FDTD) method. The spectral response of the test structures was measured for different polarizations, where the gratings showed typical features of wire grid polarizers. Using a 180 nm CMOS image sensor process, an image sensor with 6 μm pixel size was designed and fabricated with different polarization selective structures allowing for polarization imaging. A polarization camera using this image sensor is demonstrated, visualizing stress birefringence as an application example. Finally, first results on the fabrication of hole arrays with a period of 320 nm are presented, showing color filters with enhanced transmission.