Christopher Wargo

Tribological, Thermal, and Wear Characteristics of Poly(phenylene sulfide) and Polyetheretherketone Retaining Rings in Interlayer Dielectric CMP

Retaining rings made of poly(phenylene sulfide) (PPS) and polyetheretherketone (PEEK) with two different slot designs were subjected to a 4 h wear test. During the chemical mechanical planarization (CMP) process, the PPS retaining ring induced a higher coefficient of friction (COF) by ∼0.1 than the PEEK retaining rings. In addition, the PPS retaining ring exhibited a higher wear rate than the PEEK retaining rings by ∼28%. Although the retaining ring slot design did not significantly affect the COF and wear rate, retaining rings with sharp slot edges resulted in higher pad surface abruptness.

PVA Brush Technology for Next Generation Post-CMP Cleaning Applications

With semiconductor industry’s transition from 32nm to 22nm and smaller technology nodes, and introduction of advanced devices and new materials such as copper/ultra low-k dielectric, chemical mechanical planarization (CMP) processes are becoming much more demanding. The above requires most stringent management of CMP consumables, including CMP slurry and slurry filters, pads, pad conditioners, retaining rings, polyvinyl alcohol (PVA) post-CMP (PCMP) cleaning brushes, and PCMP cleaning chemistries. It is essential to characterize CMP consumables individually and then as a set in small-scale real applications, to optimize consumables set for consistent and low cost of ownership CMP processes. PCMP cleaning consumables including PVA brushes must evolve to provide significantly improved cleaning effectiveness and consistency in the above applications. This paper presents new developments in the design and characterization of CMP consumables with specific emphasis on the PCMP cleaning PVA brushes tailored to the needs of specific challenges of real life applications. One such example was the wafer edge cleaning challenges seen in some PCMP cleaning applications of advanced devices. Modified nodule shape PVA brushes were designed to cater to this need and to provide optimum cleaning contact area as well as contact force at the brush-wafer interface. A number of commercially available slip-on-the-core (SOTC) and molded-through-the-core (MTTC) design PVA brushes were analyzed to obtain tribological and DI water flow distribution data using a bechtop tribometer (CETR, Campbell, CA, USA, Model – Modified CP-4). Results are presented and discussed for the effects of PCMP cleaning chemistries on the brush PVA properties, dynamic skin-friction at a wide range of brush rotational speeds (50-800 rpm). The above test also included long term soak tests of PVA brushes in several common acidic and alkaline PCMP chemistries (in typical real-application dilutions), and observation of the PVA as well as the PCMP clean solutions at the beginning and end of the test. Some of the chemistries showed significant attack on the brush PVA under extended exposure, especially once used in higher concentrations. Present study demonstrates the usefulness of new brush designs and characterization methods for PVA brushes for advanced PCMP applications. Abstract #1480, 218th ECS Meeting,

Retaining Ring Design Impact on CMP Process Stability and Optimization

The focus of this work is wafer retaining rings and their impact on chemical mechanical planarization (CMP) process stability, yield, and overall cost of ownership (CoO). The study looks at various CMP retaining ring materials and processing methods. Tribological investigations as well as wafer processing are critical to understand the retaining ring and polishing pad environment. Interactions at the ring/pad interface have a major effect on the planarization and defectivity of a polished wafer. Shear and normal forces at this interface, as well as temperature and lubrication regimes, were monitored to establish an empirical model. All process conditions equal, the material properties of retaining rings govern the coefficient of friction (COF) in the ring and pad contact area. Present study demonstrates a lower COF to be an indicator of extended ring lifetime, decreasing WTWNU and removal rate (RR) variation. The study correlates the findings on wafer level data from high volume manufacturing fabs with empirical data generated using applications lab tribological equipment to understand the on-wafer performance as a function of retaining ring material. The studys further aim is to understand for specific applications, the material interactions on-wafer using various retaining ring materials. CMP process optimization can be attained with a better understanding of retaining ring design and material characteristics, as well as polishing head and slurry parameters.