Backside and Bevel Contamination Removal

Abstract

challenge. Initiated by copper integration for BEOL interconnects the phenomena expanded with the HK / Metal Gate stack use. Therefore, the backside and bevel cleaning became a key parameter to insure both tools integrity and wafers yield while reducing as more as possible the cross contamination risk. The main parameter to avoid the contamination transfer across all the different clean room equipments is to strictly manage the backside and bevel areas on the wafers. Thus, the use of single side processor tools which achieve the specific treatment of the backside and bevel areas drastically increases. Up to now, diluted-HF mixtures are mainly used in production plants demonstrating a good efficiency to remove contamination on dielectric surfaces. Thus, a very large range of contaminant materials can be addressed with a performance level which has been widely evidenced on BEOL applications as well on more FEOL embedded specific materials (ie: Hf, La, W). Nevertheless, the fundamental mechanism which drives the diluted-HF mixtures efficiency remains only based on a lift-off effect as the contaminant can be caught in the liquid phase after a fixed amount material etching. Most of the time there is no direct solubilisation of the contaminant from the surface. For silicon surface without any dielectric coverage the efficiency of a single diluted HF mixture can be very poor especially towards noble metals contamination. Various on-going developments (ie on MRAM technology or 3D integration or Imagers) in which pure FEOL tools are used on MEOL or BEOL levels required more efficient cleaning towards a larger range of metal contamination on backside and bevel areas.