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Latest development from Strasbaugh reduces potential for metallic contamination

Quadrant EPP : 07 October, 2002  (New Product)
The latest refinement in the Strasbaugh precision wafer surfacing equipment reduces metal particle contamination. For its CMP Planarizers, including models 6EG, 6EC and 6DS-SP, Strasbaugh replaced the titanium top plate in the wafer carrier assembly with a top plate made of a high-performance plastic, Techtron polyphenylene sulfide.
The primary function of chemical-mechanical processing is to smooth a nominally macroscopically flat wafer. This planarization is necessary so that subsequent processes can begin from a flat surface. The wafer, held face down on a rotating carrier fixture, is pressed against a polishing pad attached to a rotating disk. Depending on wafer composition, various abrasive slurry compounds and chemistries, generally based on di-ionized water, are used to polish the surface of the wafer by a combination of mechanical friction and chemical etching. CMP generally involves several polishing steps, and intermediate cleanings using DI water. Thus, CMP is an extremely wet environment, often with a high or low pH factor.

In the Strasbaugh equipment, wafers are held in a chuck, which is attached to the carrier top plate. The carrier top plate firmly holds the carrier in the polishing fixture. For use with 200-mm diameter wafers, the top plate diameter is about 10 in. and for 300-mm wafers the top plate is about 14-in. The plates are 0.5 in. thick. Key requirements to be met by the top plate material include dimensional stability, high rigidity, high strength, corrosion resistance, flatness, and long service-life. Techtron PPS, produced by Quadrant Engineering Plastic Products, has excellent resistance to the very wet and pH environments, typically 2-12, of CMP. Also, Techtron PPS has high compressive strength and high shear strength, both of which are important properties for the top plate. Another benefit of Techtron PPS is its excellent dimensional stability, which results from Quadrant's proprietary stress-relieving manufacturing process, and the material's inherent low coefficient of thermal expansion and that it absorbs virtually no moisture. In addition, Techtron PPS has excellent resistance to long-term embrittlement, which is a key factor for long service life of the top plates.

'With the prevalent use of chemical-mechanical processing in the integrated circuitry industry,' says William Kalenian, Project Manager at Strasbaugh, 'new sophistication in both equipment and process technologies are essential to prevent the deposition of metallic impurities on IC wafers. These contaminants can require components to be put through cost-increasing processing steps. Such advancements, as our switching to a high-performance plastic top-plate, help make the Strasbaugh wafer polishing equipment more effective in low-cost, high-yield CMP productivity.'

Strasbaugh, San Luis Obispo, CA, is a global supplier of precision surfacing equipment for the semiconductor, telecommunications and precision optics industries. Strasbaugh's 6EG 300-mm CMP Planarizer is an economical, small-footprint, single spindle/table CMP system for both 200- and 300-mm failure analysis, research, and low-volume production.

The 6EC CMP system is a semi-automatic 200-mm tool for CMP research, failure analysis, and low-volume production. The 6DS-SP is a dual spindle/table, full-automatic, CMP production unit for 200-mm and smaller wafers.
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