Industrial tested Environmental friendly Fluorine mixture cleaning process to replace C3F8,C2F6, CF4 and NF3 as cleaning gas

Michael Pittroff; Robert Wieland
(EMFT, Hansastr. 27d, Munich)

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Abstract – Since the beginning of the 1980’s per fluorinated carbons (PFC’s) such as C2F6 and CF4 have been used as cleaning gases in thin film deposition technology and since the 1990’s NF3 has been used in the same way. PFC’s and NF3 have long atmospheric lifetimes and therefore high global warming potentials. The main applications of these gases are to remove residual films left behind after a chemical vapor deposition process (CVD). The most important materials to remove are dielectric layers like silicon oxides (SiO2), carbon-containing silicon oxides, silicon nitrides (Si3N4) and, to a certain extent, conducting films like doped poly-silicon and silicide layers. According to the World Semiconductor Council the semiconductor industry in 2013 used 7512 t NF3, 1133 t CF4 and 708 t C2F6 on a global basis. Approximately 72% of all semiconductor industry gaseous emissions are caused from these three gases (C2F6, CF4 and NF3). Fraunhofer EMFT and Solvay Special Chem have developed an alternative cleaning process, which can be a replacement for the currently used PFC’s and NF3 in semiconductor CVD tools. The target of this work was to find viable alternative gas mixtures for the semiconductor industry, which could be used as a “drop in” to avoid additional high investment costs from equipment modification. Our study has demonstrated that these more environment friendly gas mixtures also provide a more efficient and faster cleaning behavior for most applications. A cleaning efficiency gain of a factor 1.3 up to 1,7 can be expected, relative to the F2-amount required for cleaning; this gain in efficiency depends on the cleaning gas to be replaced and on the reactor type. A shorter cleaning time can lead directly into a higher equipment throughput and more cost effective usage of thin film tools. Industrial tests on Applied Producer and Novellus Sequel were performed for different processes. The long term tests at the CVD tool, was equipped with a mass spectrometer, to verify the end point of the chamber cleaning and to gain an overview of the waste gases going into the abatement system. In addition an endpoint system based on an optical spectrometer was tested as well. Long term behavior of piping used with fluorinated gas mixtures was as well monitored.

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