Challenges of photolithography processing on glass wafers within a 300mm CMOS wafer fab

With the emergence of derivatives technologies which purpose is to serve different markets compared to standard CMOS technology such as bio sensors, photonics chips or optical devices, the microelectronics industry is facing new challenges. Whereas standard CMOS processes are classically done on silicon, new optical applications require the use of transparent glass substrates. This can be achieved by transferring processes initially done on silicon substrates onto glass substrates (via bonding for example) or by performing processes directly on glass substrates. For microelectronics tools that have been specifically designed to handle silicon wafers, processing glass wafer is already a real challenge. For photolithographic process, which required precise control of CD, the understanding of the impact of substrate characteristics onto photolithographic performance is key. In this paper, we will discuss different problematics encountered by performing photolithography directly on glass wafer and explain, thanks to a study of thermal behavior of glass substrate during lithographic bakes, how the substrate characteristics and especially the coefficient of thermal expansion is responsible for wafer warpage during bake. Finally, we will propose different solutions to improve lithographic performances on glass wafer.