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 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. 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. This established a mix ratio of 30% fluorine in nitrogen and argon as the best known method. At its production site in Freising, Texas Instruments has assembled a gas supply unit and tested the Solvaclean fluorine gas mixture on a number of production units. Initial tests show a slightly improved cleaning performance, and a reduction in the time required as compared to the standard process using C2F6. An initial durability test with more than 500 processed wafers and therefore approx. 250 cleaning cycles also showed that cleaning processes using the Solvaclean fluorine mixture do not cause increased particle contamination in the cleaning plasma source and the process chamber.
The new cleaning process went into pilot use in mid-November, with the aim of securing approval for industrial production by the end of 2017.