“Front-end-ization” of the back-end

Abstract

The trend towards 3D stacking and Cu Pillar bumping has significantly altered the requirements for manufacturing tools in the back-end. Techniques and processes are beginning to resemble the front-end of 20 years ago but with updated and more affordable cost-of ownership capabilities. As an example, steppers would have been unheard of in the back-end. Today steppers are critical to achieve yield for devices ranging from fan-out wafer level chip scale packaging to Cu Pillar bumping. Re-distribution layer pitch has shrunk dramatically over the last few years, customers are demanding less than 5μm spacing and 5μm width. It is impossible to maintain effective CD over a 300mm wafer without a stepper on a three layer process. On wafer requirements, 0.5μm resolution inspection was state of the art 25 years ago. Today, fine pitch Cu Pillar is driving inspection of Cu bumps at similar resolution but at a significantly higher throughput and a much lower Cost-of-ownership (COO). Other traditional Front-end capabilities such as Metrology and Advanced Process Control (APC) that are being adopted by the back-end will also be discussed.