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

Abstract

The effect of two different commercially-available CVD-coated diamond conditioning discs on copper CMP was investigated tribologically and kinetically with the intent of correlating pad surface micro-texture to polish performance. Data analyses were particularly focused on in-situ shear and normal force measurements taken during polishing at several pressures (P) and sliding velocities (V), including Fast Fourier Transform (FFT) analysis of the data. One of the two discs consistently resulted in greater variances of shear force with increasing P and V indicative of increased pad-slurry-wafer stick-slip events. This trend correlated to higher values of coefficient of friction (COF) and removal rate (RR). By dividing the shear force variance by the normal force variance, a new parameter, termed directivity, was used to further emphasize the improved performance of the above-mentioned disc. Lastly, the tribological and kinetic data, combined with data regarding the pad's micro-texture and its extent of contact with the wafer, showed that at all values of P and V, higher values of directivity correlated to more contacting pad asperities, a greater asperity density and a thinner micro hydrodynamic lubrication layer, thus highlighting the potential importance of directivity in future studies.

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.…”

Correlating Removal Rate to Directivity in Copper Chemical Mechanical Planarization

“…(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. (17) Mariscal el al.…”

“…(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…”

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.…”