STI CMP stop in Silicon Nitride controlled by FullVision™ endpoint

Abstract:
For each new CMOS manufacturing technology node, control of the step height between active area and isolation area becomes more and more critical for transistor performance. The main contributor of the step height is the Shallow Trench Isolation Chemical Mechanical Planarization (STI CMP). The remaining silicon nitride thickness post CMP is the main parameter that will guarantee the step height in dense area. In this paper, a new method is proposed to improve CMP process stability by stopping STI CMP process by endpoint. Accurate endpoint process control for CMP is necessary for stopping in materials. Hence, the FullVision(TM) optical endpoint technology system is selected and used to control this silicon nitride thickness film. This FullVisionTM system is a white-light endpoint which collects full spectra of wafers in-situ during polishing. Different algorithms and library wafers have been evaluated in order to achieve a single algorithm for all sets of product /masks. Finally, a gain of 50% is achieved on the step height lot to lot variation. Keywords: Step Height, Shallow Trench Isolation, Chemical Mechanical Planarization, FullVision(TM) endpoint system, White-light endpoint, Stop-in-nitride polish.