Plasma damage reduction by using ISSG gate oxides

Almost all processing steps involving the use of plasma can lead to gate oxide damage. Among these, damage due to inter metal dielectric (IMD) deposition has been of particular concern. At least two mechanisms can lead to gate oxide damage during this process step, that is non-conformal oxide coverage of exposed metal lines and photoemission due to UV photons generated inside the plasma. In particular, the gate oxide can be damaged even by very small tunneling currents, because it is weakened by the relatively high temperature used during IMD deposition. In this work, we have studied the damage induced during IMD deposition by using high density plasma (HDP) tools and different recipes for both the IMD and the gate oxide. In particular, we show that in situ steam generation (ISSG) gate oxides are by far more tolerant to plasma-induced damage than conventional ones. This assertion is demonstrated by using a damaging fluorinated silica glass (FSG) step, in conjunction with both conventional and ISSG gate oxides.