"Front-end-ization" of the Back-End

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 5 mu m spacing and 5 mu m width. It is impossible to maintain effective CD over a 300mm wafer without a stepper on a three layer process. On wafer requirements; 0.5 mu m 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.