Chemical Mechanical Polishing – How Technology Is Improving?

By Author: Vishal Khosla
Total Articles: 19
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Incorporation of the latest technology in chemical mechanical polisher ensures accurate real-time polish control of every wafer without compromising throughput. Growing number of film layers in the devices requires greater productivity, removal uniformity and lower costs on the part of CMP technology.

Chemical Mechanical Polishing (CMP) offers planarization solutions for shallow trench isolation (STI), copper damascene, oxide, polysilicon and tungsten applications. Industries require ultra-quick planarizing platens and polishing heads that ensure superior uniformity.

The instrument must have technology to virtually eliminate watermark defects and bring drastic reduction in particle contamination. There should be a suite of endpoint methods, advanced process control methodologies and in-line metrology that ensures top-notch within-wafer and wafer-to-wafer process control. It must provide for repeatability for all planarization applications.

Latest technology supports accurate real-time polish control of every wafer without compromising throughput. Broadband spectroscopy may be used to significantly improve ...
... the process and minimize wafer scrap that is caused by drifts in consumable sets.

Increasingly complex devices require incorporation of a wide variety of materials. A growing number of film layers demands on CMP technology for better greater productivity, removal uniformity and lower costs. For any polisher to be cost-effective, lower costs and higher productivity is necessary.

A chemical mechanical polisher must be extensible to other applications and future technology nodes. It must complement pad conditioning and dedicated slurry delivery for each wafer. A state-of-the-art polisher has advanced head and process controls including in-platen metrology that ensures precise control of final thickness.

The system must have a mechanism for post-polish cleaning. Incorporation of a proven cleaning and rinsing technology provides for quick, effective watermark-free drying. The CMP involves planarization steps needed to meet the stringent planarity or defect requirements. Several slurry technologies are used for the objective including Aluminum CMP, poly-open-polish, etc.

CMP technology has allowed for scaling of transistor level devices, leading to the shrinking of device structure and improvement in performance. This requires CMP slurries that help meet the planarity and defect requirements for device performance.

Industrial applications require slurries that can remove layers of silicon nitride at relatively high rates of removal. The common steps in the nitride slurries require a high silicon nitride removal rate with tunable selectivity to silicon dioxide. Nitride slurries are applied for poly open polish, advanced transistor build and double patterning technology. The process removes the nitride layer cap from the surface.

Polish rates depend on the kinetics of the hydrolysis of the nitride film. Polish conditions and pad choice also have a role to play. Promotion additives are based on several organic acids. Nitride and oxide removal rates may depend on the concentration of a specific phosphonic acid. Nitride selectivity can be tuned with additive concentrations and abrasive.

A nitride slurry platform utilizes uniquely modified colloidal silica. Additives to selectively suppress the removal of polysilicon are put up in the slurry for achieving the performance desired for RMG build. It is essential for POP to be able to selectively suppress the removal of polysilicon relative to the other dielectric films present. Various technologies can be used as tandem for optimum performance.

When using chemical mechanical polisher, it is critical to obtain acceptable film removal, while limiting unwanted defect performance. It must be easy to interchange various wafer holders, allowing to polish samples from 1inch to 6 inch without changing the tester.

Author of this article is associated with Rtec Instruments, a California based company that deals in chemical mechanical polisher, surface profiler, ball on disk tester, high temperature tribometer, nano indentation, atomic force microscope and other instruments. For details, please visit rtec-instruments.com.