Machine Vision System Utilizing Black Silicon CMOS Camera for Through-Silicon Alignment

Abstract

Current development trends concerning miniaturizing of electronics and photonics systems are aiming at assembly and 3-D co-integration of a broad range of technologies including MEMS, microfluidics, wafer level optics, and silicon photonics. To this end, on-chip integration using silicon-photonics platform offers a wide range of possibilities addressing passive optics functionality, active optoelectronic devices, and compatibility with CMOS fabrication. On the other hand, the hybrid technology enabling volume manufacturing of such system-on-chip components, it is still in an early development stage. Here, a new type of machine vision system enabling precision stacking and bonding processes of III–V components on silicon photonics chips is introduced. In particular, we focus on the ability to see through substrates with high resolution, which is crucial for the alignment of the markers used for assembly of integrated components on silicon wafer. The system is based on the use of a black silicon enhanced CMOS sensor with extended wavelength response beyond transparency cutoff wavelength for silicon substrate. We study the use of the camera system as a microscope with bottom coaxial infrared (IR) illumination scheme and demonstrate the ability of through-silicon vision for one- and two-layered silicon photonic integrated circuit (PIC) samples. The ability of observing objects with dimensions down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \mu \text{m}$ </tex-math></inline-formula> is confirmed. This resolution is close to diffraction limit and corresponds to the dimensions of optical waveguide structures on the PICs surface. In addition, we demonstrate the implementation of a 2-D Fourier transform-based autofocusing technique for through-silicon IR microscopy. These building blocks offer a solution for advanced photonic integration processes and other through-silicon vision-related applications, which is instrumental for a large variety of assembly, lithography, and wafer bonding setups.