The Study And Improvement On 90nm STI CMP Process

Shallow Trench Isolation(STI) became the mainstream isolation method in deep sub-micron ULSI process for its great isolation performance and almost no field erosion. The new type of CeO2 slurry which is more stable and high selectivity on SiO2 and Nitride, promoted the STI CMP process. Of course CMP process generate its specific defect to wafer, as scratch, particle, slurry residue, etc, especially dishing means lot to device, dishing is critical control for process under 90 nm, while scratch will lead to failure of reliability, both of defect are to be reduced keeping at a low level. CMP is a global planarization technology; many factors can affect the planarization result, as the polish head speed, pressure, the character of polish pad, and slurry flow rate, etc. STI CMP has critical requirement on uniformity; a worse polish uniformity can lead to device function fail.In this thesis, according to a 90 nm product, the several typical inline issues will be analyzed, by multiple experiments, improvement solutions are proposed:1. On same 90 nm process, CeO2 slurry leads to better planarization and less dishing, baseline parameter setting was summarized base on large amount of experiment data, which could be reference for new technology development.2. A solution of reducing micro scratch is proposed on a two-step STI CMP, by studying the source of micro scratch and found it came from CeO2 step, it’s easily to generate slurry crystal along with the process time, reducing the process time of CeO2 step can improve the micro scratch performance significantly.3. AMAT 300 MM Reflection polish head pressure control mode is studied, and by optimizing the pressure, planarization and Nitride uniformity is improved.4. In a new 90 nm process development, compare the result of endpoint polish mode and time polish mode, found by time polish has better result on the new production.