A Substrate-Agnostic, Submicrometer PSAS-to-PSAS Self-Alignment Technology for Heterogeneous Integration

This article presents a novel substrate-agnostic self-alignment technology with submicrometer alignment accuracy targeted for heterogeneous integrated systems. This self-alignment technology, referred to as PSAS-to-PSAS self-alignment, incorporates positive self-alignment structures (PSAS) or reflowed patterned photoresist structures that couple with other PSAS to achieve submicrometer alignment accuracy without the need for an advanced placement tool. The PSAS-to-PSAS self-alignment technology is non-substrate invasive and hence does not consume any substrate real estate. These PSAS structures can also be fabricated atop any material substrate; hence, this technology is suitable for heterogeneous integrated systems where a variety of different material substrates may be incorporated. This article discusses this PSAS-to-PSAS self-alignment technology and it provides a design analysis relating the inter-substrate gap between aligning substrates and the dimensions of the PSAS structures. The fabrication of the PSAS on two separate substrates is then performed, followed by a manual assembly process to couple the PSAS on one substrate to the PSAS on the other aligning substrate. Vernier scales are incorporated on these substrates to measure the misalignment between said substrates; submicrometer alignment is recorded. As these structures may also enable a non-permanent system configuration, alignment repeatability measurements were also performed.