Surface reaction pathways of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione on clean and pre-oxidized Ni(110) surfaces

Ni contamination of Si surfaces is an increasing problem for very large scale integrated manufacturers seeking sub-0.25 $μ$m features. Dry etching methods are considered important, potential processes for removal of this contaminant. We and others have recently proposed a chemical vapor etching (CVE) treatment using oxygen and hexafluoropentanedione that could be used to remove Ni. In this article, we have used temperature programmed desorption to examine the surface kinetic pathways of Ni removal by CVE. Ni was successfully dry etched from the pre-oxidized surface by the desorption of $Ni(CF3COCHCOCF3)2$ between 280 and 480 K with a maximum desorption rate around 390 K. However, above 500 K, a variety of decomposition products appeared and etching ceased. Analysis of the clean (i.e., fully reduced surface) showed these products to be a result of the scission of bonds attached to the $β$-carbon: $C–CF3,$ C–CH and C=O. Furthermore, stabilization of radical species like $CF3$ on the clean surface resulted in some unexpected decomposition products observed desorbing between 360 and 540 K. Otherwise, some Ni-fluoride desorption was observed on both surfaces above 800 K and Auger revealed carbon on both surfaces after flashing to 900 K. From these results, it is clear that we need to understand the $β$-scission process better before we can determine how clean etching can be achieved.