Abrasive Free Polishing for ULSI Cu Damascene Interconnect

• Main Authors: Jeng - Yu Fang, 方政煜
• Other Authors: Ming — Shiann Feng
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/73541769938010128517

碩士 === 國立交通大學 === 材料科學與工程系 === 89 === For improving the effectiveness of semiconductor device, instead of aluminum interconnection by copper material has become necessary in ULSI IC process. It is because copper has higher electron migration and lower resistance. However, although chemical mechanical polishing is the important technology to approach globe planar polished copper surface, there are still many issues existing for solving, like scratches, dishing, and uniformity. In this study, we discuss the way for approach the goal of scratch — free surface in copper damascene CMP. Generally, the abrasives applied to first step copper CMP are almost pure aluminum powders. Owing to its large size and irregular morphology, there will exist much and deep scratches on polished surface leading to damage of device. For achieving the goal of scratch free, the first way is applying abrasive free polishing instead of pure aluminum system. The planarization efficiency of abrasive free polishing is affected by the properties of polishing pad and passivation. The harder pad has less deformation effect during polish and faster remove of passivation, those will lead to clearly different removal rate between protrudent and recess areas. By the way, the required planar surface will be achieved. Therefore, in all experiments the polishing pad is used by Rodel IC — 1400. Besides, the oxidizer is fixed to be pure nitric acid aqueous, the inhibitors are selected by BTA and PEG. While abrasive free slurry formulated by nitric acid and BTA, the uniformity of polishing rates are not satisfied. By means of the observation of hydrophobic phenomenon on polished copper surface, it impacted that the surface tension existing between slurry and copper surface is too small leading to bad wettability of abrasive free slurry. For improving the wettability of abrasive free slurry, surfactant PEG is added into original polishing slurry. Besides, the second way to achieve scratch free copper surface is applied modified colloidal silica instead of pure aluminum powder. From sol — gel production, silica abrasives would have higher suspension and become circular morphology. Furthermore, the colloidal silica abrasives were coated a thin alumina layer that would retain the chemical characteristic of aluminum powders. By the modified surface, we hope to avoid the scratches produced from irregular morphology. In this partial section, the oxidizer is fixed to be hydrogen peroxide. From the analysis of electrochemical measurement, it was found that copper would be oxidized to different oxidizing state as the concentration of hydrogen peroxide increase. Unfortunately, the scratches still exist after polish. The goal of experiment is to find out the reason of scratch existance and the affection of copper oxidized behavior to planarization efficiency. Finally, we discuss the potassium iodate system with colloidal silica abrasives in order to understand the relation between selectivity and dishing. From the results of experiments, if the selectivity of tantalum to copper closes to 1, the dishing shift after second step polish would be nearly unapparent. It impacted that if the selectivity of copper, tantalum, and dielectric layer closes to 1, the control of end point could be neglected.