Real-Time Shear and Normal Force Trends in Tungsten Chemical Mechanical Planarization with Different Conditioning Discs

Abstract

In-situ conditioning is known to increase material removal rate (RR) during chemical mechanical planarization (CMP), because it roughens the pad surface that is in contact with the wafer. Previous studies have shown that the conditioning disc changes the pad surface micro-texture and affects the thermal, kinetic and tribological attributes of the CMP process. This study focuses on two different diamond discs for in-situ conditioning during tungsten CMP, and shows how real-time force data improves our understanding of the effects from using one disc versus the other. Shear and normal forces were analyzed through spectral analysis, variance and force scatter plots. Frequency signatures that appear regardless of the type of disc used were likely attributed to vibrations of the polisher and the harmonics of these vibrations. A new parameter, directivity ( ), was employed, which highlighted the significant differences in shear force variance between the two discs. Above all, this study confirmed that high correlated with high RR.Compared to a related study on copper CMP with these discs, the trends between and RR seemed to continue to hold.

Insights into the Tribological and Kinetic Attributes of Retaining Rings in Chemical Mechanical Planarization

“…As seen in Fig. 4, a plot of directivity, 10,11 or , (defined as the ratio of measured variances in shear force to those of normal force) of all data points (regardless of ring or slurry types) vs. the pseudo-Sommerfeld number follow a common trend. It must be noted that a directivity value of unity indicates that the fluctuations in shear and normal force are identical.…”

Tribological, Thermal, Kinetic, and Pad Micro-Textural Studies Using Polyphenylene Sulfide Retaining Rings in Interlayer Dielectric Chemical Mechanical Planarization

“…44 Directivity itself (taken from the science of characterizing old Italian violins, which believe it or not, have many similarities to CMP tools) [45][46][47][48][49][50] is defined as the ratio of measured variances in shear force to variances of normal force at a given polishing PV condition. 44,[51][52][53][54][55] Here, the fluctuating components of shear and normal forces are the key factors and not their absolute values. In this case, the ordinate and the abscissa are independent of one another, and because we use linear scales, there are no distortions or optical illusions that would have been caused by the logarithmic scales.…”

Correlating Removal Rate to Directivity in Copper Chemical Mechanical Planarization

“…(13,14) Peckler et al also observed that Δ was affected by a CMP consumable, this time being the pad conditioner. (15) Separately, Peckler et al found that Δ somewhat increased with P × v and found a loose correlation between Δ and copper RR. (16) Mariscal et al also found a correlation between Δ and RR, but for a tungsten CMP application.…”

“…(12)(13)(14)(15)(16)(17) Previous work has focused on the vibrations that occur in various CMP processes. (12)(13)(14)(15)(16)(17)(18)(19)(20)(21) Fukuroda et al, Hetherington et al, Kojima et al and Rao et al studied vibrations in CMP and found that they could be used as an end-point detection technique for polishing different materials. (18)(19)(20)(21) However, the authors did not correlate the vibrations to RR.…”

“…Of the works that have studied vibrations in CMP, several have focused on Δ's role in the process. (12)(13)(14)(15)(16)(17) Philipossian et al…”