Subrahmanya Mudhivarthi

Effect of temperature on copper damascene chemical mechanical polishing process

The effects of different process parameters on tribology and surface defects were studied till date, but there has been minimal study to understand the effect of temperature on the copper chemical mechanical polishing (CMP) process. The effect of temperature on tribology and surface defects during copper CMP employing different pad materials and slurries has been explored. From the results, it was seen that the coefficient of friction and removal rate increased with an increase in slurry temperature during polishing. The experimental data indicated that the increase in temperature results in an increase in amounts of metal dishing and metal loss. The dishing and metal loss in the interconnect features initially increased with an increase in temperature and then decreased at elevated temperatures. With an increase in temperature the copper films peeled off from the wafer due to low adhesion with low-k dielectric material at higher temperatures. The electrical properties of the planarized devices showed dra...

Novel Hybrid Abrasive Particles for Oxide CMP Applications

In the present research, novel abrasive particles are investigated in order to carry out CMP at relatively low down force (low mechanical stress) yet achieve desirable removal rates and superior post CMP surface quality (reduced scratches). Hybrid abrasives are developed where the composition of the polymeric particles formed via colloidal precipitation is modified with inorganic segments to reduce surface damage during CMP. The composition is controlled by changing the time for condensation and hydrolysis of the inorganic oxide. Characterization of these particles is performed by FTIR spectroscopy, dynamic light scattering, and electron microscopy (TEM/SEM). Tribological characteristics during polishing employing these novel particles are studied on a bench-top CMP tester. Surface roughness and defectivity are estimated using Atomic Force Microscopy (AFM).

Metrology and characterization of application specific chemical mechanical polishing pads

There is a need for metrology, characterization, and optimization of chemical mechanical polishing (CMP) pad architecture before being put into service. A polishing pad which is made up of polyolefin material instead of conventional polyurethane has been developed. The surface of the pad has been modified to match the hardness of the surface of the material that is being polished. In this research, we coated the pad with tetraethylorthosilicate using plasma enhanced chemical vapor deposition for varying durations of time for optimum pad output. The pad was then extensively characterized using the several standard metrology techniques such as scanning electron microscopy, x-ray photoelectron spectroscopy, nanoindentation, etc. The CMP performance evaluation of all the candidate pads along with in situ measurement of dynamic coefficients of friction, material removal rate, and acoustic emission was done using CETR CP-4™ bench top CMP tester. There was a correlation and interdependence of the pad coating tim...

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.

Some Tribological Aspects of Thin Film Copper During CMP

The effect of various process parameters like pressure, velocity and process consumable characteristics like pad properties and slurry chemistries on copper during Chemical Mechanical Planarization (CMP) process have been extensively researched. However, the thermal aspects of CMP have not been understood in detail. In this research, we present the effect of slurry temperature on the coefficient of friction and the resulting micro-structural changes in the copper material due to the polishing process. We also investigated the work hardening effect of polishing on copper thin film. From the results, it was found that temperature has an effect on the coefficient of friction but the effect of process parameters influences the effect of temperature. The effect of temperature on coefficient of friction is also dependent on the material of polishing pad. From XRD measurements more crystallinity was observed for the sample polished at 29°C as compared to other samples. The mechanical properties of copper investigated before and after CMP show improved mechanical properties with polishing. Significant change was observed among the mechanical properties of samples polished at different temperatures.Copyright