Yaw S. Obeng

Dynamic Mechanical Analysis (DMA) of CMP pad materials

In the semiconductor industry, there is a need to establish fundamental, mechanism-based, correlation(s) between process conditions, consumables (e.g., pads and slurries), and observed process performance in Chemical-Mechanical Polishing (CMP). In this paper, we present recent results of studies on polyurethane-based CMP pads in static and dynamic conditions using Dynamic Mechanical Analysis (DMA) to monitor modulus and energy damping changes. Two-layered, composite IC1000 on Suba IV pads, [IC1000 (cast and cured polyurethane elastomer) / Suba IV (polyurethane impregnated polyester felt)], were analyzed: prior to use (fresh); after a 24-hr soak in silica-containing oxide slurry (basic); and after oxide polishing (used). Upon comparison it was observed that a characteristic transition feature due to water is present at sub-ambient temperatures in both the slurry soaked and used pads. Exposure of as-received pads to basic oxide slurry results in a broad, high temperature transition thought to be the result of chemical-induced disruption of macrostructural units. Polishing (load-enhanced chemical exposure) introduces further changes to the polymer network represented by an apparent degradation to the structural species responsible for the high temperature transition in Suba IV.

Metrology of Psiloquest's Application Specific Pads (ASP) for CMP Applications

There is a need to develop a metrology metrics for evaluation of pad CMP performance before putting them in to service. This has been attempted on Psiloquests application specific pads (ASP) in which the pad surface is tuned to match the mechanical properties of the target substrate. The ASP is made up of thermoplastic foams co extruded with condensed polyolefin. The chemical and mechanical properties of the pad-wafer interface are tuned by coating the pad with ceramic thin films by surface coating method such as chemical vapor deposition (CVD). The surface of the pad is characterized using metrology techniques such as ultra sound reflectivity, XPS and nanoindentation. The cross section of the pads was characterized using SEM. The mechanical properties of bulk pad materials were studied using Dynamic Mechanical Analysis (DMA). A test was performed on the pads to measure the static coefficient of friction (COF) and wear rate. The pads were polished using CETR CP-4 bench top CMP tester to evaluate the dynamic COF, Acoustic Emission (AE) signal and removal rate during a simulated Tungsten CMP process. The thickness of the ceramic coating on the surface of the ASP played an important role in determining these tribological properties. The results of the various static and dynamic tests performed on the pad were cross tabulated to evaluate their correlation.

‘Back end’ Chemical Cleaning in integrated Circuit Fabrication: a Tutorial

The applications of wet chemical cleaning at the ‘back-end’ of Integrated Circuit (IC) or Metal-Oxide Semiconductor (MOS) fabrication are reviewed from chemical, environmental and cost perspectives. The various classes of commercially available “solvents” and “cryogenic” cleans are reviewed from the perspective of process suitability, impact on device yield and waste management. Strategies for minimizing processing concerns, as well as alternatives to organic solvent based wet chemical processing will also be discussed. Bulk photoresist (PR) stripping, post metal definition-, and post window etch cleaning are used to illustrate the discussion. The use of radiotracing as a diagnostic tool in understanding the mechanism for metallic contamination during solvent cleans is also discussed. Data suggesting how the chemistry and solvent composition affects alkali metal (for example, sodium) contamination of dielectric- and barrier films during IC processing will also be presented.