Influence of overpolish time on the performance of W Damascene technology

In this paper a metal-chemical mechanical polishing (CMP) process for so-called inverse metallization processes is described. The influence of a critical process parameter, overpolish time on pattern dependent erosion and dishing for a 0.25 mu m W Damascene process, is investigated in detail. Material removal rate and uniformity (WIWNU) were 150-250 nm/min and 3% (1 sigma), respectively. Further it was found that the pad temperature close to the contact area between pad and wafer indicates the end point of polishing. Feature size and pattern density effects on the CMP performance are as expected. At proper rpm and pressure settings, the effects are sufficiently small for application in integrated circuit processing. However, surprisingly, with overpolishing erosion and dishing increase rapidly, while at the end point the effects are negligible: 10% overpolishing gave satisfactory results; 25% overpolishing was not acceptable. Overpolishing of 10% was needed to obtain good (electrical) yield (measured on meander-comb structures with pitch down to 0.8 mu m and length up to 3 m). The main dishing and erosion arise after the end point of polishing. This is crucial for process optimization and metal CMP modeling.