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Giuseppe Fazio & Massimo Strada, ST Microelectronics, Central R&D, Agrate Brianza, Italy

ABSTRACT

In the modern fab process control is very important. The process control may be improved by modifications to equipment. The wafer-cleaning process is one of the most important and critical steps in semiconductor manufacturing. In this process two or more chemicals are mixed and it is very important to have the correct concentrations. Repeatability and reproducibility in concentration impact on the process quality. The chemical input usually is guaranteed by mechanical flow controllers installed in every chemical line, where a narrowing regulated by a valve provides the correct flows entering the DIW line. The performance of such flow controllers is affected by several variables: chemical pressure or DIW flow, which could generate fluctuations during the chemical injection phase. In order to reduce these phenomena and to insure good reproducibility and stability during a chemical preparation, in STMicroelectronics R2 Central R&D the standard mechanical flow controllers were replaced with new models, electronically operated. Several experiments were performed loading test wafers in the tank with RCA recipes, in order to define the etch rate obtained with the two flow regulators and various chemistry titrations in order to define the process reproducibility. The tests performed yielded very good results in term of accuracy and reproducibility of the chemical preparation, and the new electronic chemical flow controllers ensured a very stable process.