Deposition of hydrogen chloride gas on copper wafer depending on humidity and HCl concentration

Residual volatile HCl acid remaining on the wafer surface after certain microelectronic fabrication can lead to the yield defectiveness of integrated circuits made of copper (Cu). The control of HCl contamination is a key point to avoid the yield loss. In order to elucidate the deposition mechanism of HCl on copper surface, Cu-coated wafers were exposed to HCl at different HCl airborne concentrations (20–450 ppbv) and at different relative humidity (<1%–70% RH). Liquid phase extraction (LPE) and ionic chromatography (IC) allow to quantitatively determine the amount of deposited chloride at given time, humidity and HCl airborne concentration. Below a threshold of 1.25 × 1015 Cl atom.cm−2, a linear behavior of HCl deposition on Cu-coated wafer is observed depending on airborne concentration and time regardless of the humidity (dry <1% RH up to humid 70% RH). In particular, at high humidity (70% RH), a plateau of 1.5 × 1015 Cl atom.cm−2 on Cu surface is steadily maintained whatever the increase of either exposure time or HCl airborne contamination. Besides, the key role of humidity (RH%) in the formation of various Cu compounds and the oxidation states of Cu at given exposure conditions are also elucidated by XPS measurements. An empirical-mathematical model of deposition HCl on Cu was established, which could be served as an industrial tool to predict the contamination transfer to wafer during storage in FOUPs.