Tungsten chemical mechanical polishing (CMP) has been used for metal interconnect formation in semiconductor manufacturing for a long time. Its application continues to the advanced device manufacturing with transistor scaling. However, the defect concerns of the tungsten CMP process have become critical to manufacturing such as metal flake defects that can cause electrical shorts between contacts. Although there are many published studies on tungsten CMP fundamentals, process applications and CMP-induced defects, the mechanism of thin metal flake formation in nanoscale (nano-flake defect) has not been clearly known to industry. In this study, nano-flake defects are identified after tungsten contact CMP, and mechanism of its formation is explored. Significant CMP dishing at wide contact area removes all tungsten and open barrier metal. Friction force by 3-body interaction among wafer, abrasive particle and pad asperity breaks the adhesion of barrier material from intermetallic dielectric material. And it allows re-deposition of barrier metal to the wafer surface. Insufficient CMP in-situ cleaning results in residual nano-flake defects at the end of CMP process. Analysis of device macros, thickness of flake, cross sectional analysis by transmission electron microscope (TEM) and topographical analysis support this suggested mechanism.
The advanced node semiconductor device fabrication needs tungsten chemical mechanical polishing as a critical process to enable transistor formation as well as metal interconnection. Accordingly, CMP induced defect concerns have drawn attention to the process integration. Tungsten voids by CMP are one of the major defects to detract device yield. Their formation mechanism has been known as electrochemical corrosion or an optical induced corrosion phenomenon associated with polishing slurry chemistry. However, this paper proposes a new mechanism of tungsten void formation. Different from known corrosion mechanisms, it is observed that tungsten void frequency has strong correlation with CMP in-situ cleaner brush lifetime. At early brush life, tungsten void forms more frequently. Moreover, this paper reveals that CMP brush cleaning play a critical role in the formation of tungsten voids. Tungsten etch rate dependence on brush condition, tungsten void defect density correlation to brush life, and surface chemical analysis of tungsten blanket wafers show that tungsten voids are induced by combined effect of friction force and oxidation in brush cleaner module, which is a new approach to the formation mechanism of tungsten void defect.
Tungsten contact chemical mechanical polishing is a critical process in advanced node semiconductor device manufacturing that enables metal interconnection. It is essential for device performance, and any defects caused by the tungsten CMP process have a direct effect on product yield. Among these defects, the highest yield killer is microscratches. Microscratches are a well-studied CMP produced defect; however, this paper provides a new look at controlling microscratches in a manufacturing environment. Specifically, the bulk tungsten slurry is the cause for nearly all scratches at tungsten contact CMP. This paper studies the effects of abrasive size on defect performance and suggests causes for variation in size of slurry particles outside of manufacturing variability. While tungsten removal rate is not affected by abrasive size, the defectivity performance relies heavily on the ability to remove large particles from suspension. Current filtration solutions are not completely effective in preventing large particles from contacting the wafer, so the burden falls on preventing their formation. Factors such as age of material, storage temperature and agitation induced agglomeration will be studied to characterize the effects on particle size. Volume manufacturing data will be used to support the claims made in this paper.
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