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

Abstract

We have successfully applied the Stribeck+ curve to determine the tribological mechanism involved in the ring-slurry-pad interface during CMP at various pressures and velocities. Using two types of slurries (one for copper and another for inter-layer dielectric polishing) and two differently designed rings made of polyether ether ketone (PEEK), one with sharp slots and the other with rounded slots. We find "boundary lubrication" as the initial dominant lubrication mechanism followed by a transition to "mixed lubrication" as pseudo-Sommerfeld numbers increase. Coefficient of friction (COF) values for the ring with sharp slots are larger than their rounded counterparts. COF values are also higher for inter-layer dielectric (ILD) processes as compared to copper. In all cases, COF values are directly correlated with average pad surface temperature. The trend in Stribeck+ curves are explained by plotting a new parameter, referred to as directivity, which shows the cluster shape evolution to be a real phenomenon (and not an optical illusion due to the log-log nature of the curve, nor the inherent dependence of the two axes on one another) caused by force fluctuations at the extreme ranges of velocity and pressure. Raw data from the Stribeck+ curves are used to construct a new "kinetic" plot to help infer the relative wear rate of the ring thus allowing one to choose process parameters that balance it against wafer removal rate. Validation studies involving extended wear of eight differently formulated retaining rings show a correlation between wear rate and the "inferred" wear rate which renders credibility to our approach regarding the above-mentioned "kinetic" plots.

Enhancing resistance of poly(ether ketone ketone) to high‐temperature steam through crosslinking and crystallization control

“…Poly(aryl ether ketone)s (PAEKs) are a family of high‐performance thermoplastics that offer excellent chemical and thermal resistance, good mechanical properties, and manufacturability into end‐use components for critical applications. They find widespread use in the medical, semiconductor manufacturing, aerospace, automotive and petrochemical industries. Poly(ether ether ketone) (PEEK) (Figure (a)) is the most widely available of the PAEK family, has the largest production volume, and performs well in most sealing and connector applications that involve contact with drilling fluids and sour (sulfur containing) crude oil under high‐pressure and high‐temperature conditions.…”

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.…”

“…This is important because a recent study by our team has shown that, for a total of eight retaining rings each made of a different engineered plastic material and processed differently, Δ seems to correlate nicely with the corresponding ring wear rate (RWR). 51 This suggests that, in principle, one can reduce RWR by 4X by simply wearing the ring under conditions corresponding to Step No. 2 of Table II where vibrations ought to also be minimal.…”

Correlating Removal Rate to Directivity in Copper Chemical Mechanical Planarization

“…(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…”