Many plasma coating systems used in the semiconductor industry have to undergo thorough cleaning on a regular basis after each stage of production. Currently this is mainly carried out using perfluorinated compounds (PFCs) and nitrogen trifluoride (NF3) gases, which are up to 17,000 times as damaging to the environment and climate as the greenhouse gas CO2.
Solvay, Texas Instruments, Muegge and Fraunhofer EMFT are working on the project ecoFluor to develop an environment-friendly alternative which only has the greenhouse potential of CO2: the gas mixture used by the cooperation partners – Solvaclean®, consisting of fluorine, nitrogen and argon – dispenses entirely with the highly environmentally harmful gases PFCs and NF3. The project is funded partially under the BMBF program “r+Impuls – Innovative technologies for resource efficiency – Impulses for industrial resource efficiency”, which in turn is embedded in the framework program “Research for Sustainability” (FONA).
In the first year of the project, Fraunhofer EMFT was mainly responsible for optimizing the new gas mixture in terms of etching rate, process stability and particle contamination. In the second year, the process was transferred to Texas Instruments in Freising. A mix ratio of 30% fluorine in nitrogen and argon was established as the best known method. Texas Instruments set up the relevant gas supply and tested the Solvaclean fluorine gas mixture (Solvaclean®N) in production systems. The result was a slightly improved cleaning performance and a reduction in the time required as compared to the standard process using NF3.
A pilot production test on an Applied Materials Producer system with more than 70,000 processed wafers – and therefore approx. 70,000 cleaning cycles – showed that the cleaning processes using the Solvaclean®N fluorine gas mixture achieved the same particle levels as with the standard Ar/NF3 method. The first components containing PECVD-based SiO² layers produced using environment-friendly cleaning chemicals have already been supplied to the semiconductor market by Texas Instruments. This means that an F2-based, climate-friendly cleaning process has been qualified for Ar/NF3-based cleaning processes with remote plasma system (RPS).
In a second production test on a LAM Novellus Sequel PECVD system (silane-based oxide/ nitride), the standard cleaning process based on C2F6/O2 was replaced with an environment-friendly and climate-friendly Solvaclean®NO in-situ plasma cleaning process. This cleaning process was also qualified after processing of more than 25,000 wafers. By comparison with the PFC-based cleaning process, this resulted in fluorine savings of over 80%. In order to be able to increase efficiency even further in the future, a new type of microwave-based remote plasma source produced by Muegge GmbH will be tested at Texas Instruments. Preliminary development work for this was carried out at Fraunhofer EMFT as part of the ecoFluor project.
Other semiconductor manufacturing sites in Germany are currently investing in their gas and water supply so as to be able to use the Solvaclean® cleaning system.