XPS Analysis on Fluorine Removal by Plasma Cleaning
Lorenza Lombardi, Fulvio Fontana, IBM Microelectronics
Surface contamination on aluminum bond pads, introduced in chip Fab process during CF4/O2 reactive ion etching (RIE) used for pads stripping, can have an adverse effect on gold-wirebonds on serniconductor chips, accelerating corrosion that leads to device failure in timeunder stress conditions.
The purpose of this study was to investigate the capability of Hydrogen plasma cleaning to remove the fluorine compounds from the aluminum bonding pads, using a DOE approach to find the best plasma parameters setting. X-Ray photoelectron spectroscopy (XPS) was used to characterize the surface IC's bonding pads before and after the plasma cleaning runs.
XPS analyses indicated that there were fluorine compounds, mainly in the form of Al(OF)x and AlFx and there was evidence of CFx compounds too. It was determined that fluorine contamination is not present on the silicon oxide surface around pads. DOE results showed that H2 plasma cleaning is able to significantly reduce fluorine contamination and main parameters are H2 flow rate and good exposure of parts to plasma beam.