Electrically active defects generated by MERIE and RIE-mode plasmas in thin SiO2-Si structures

The effect of both RIE and high-density nonuniform magnetically enhanced re active ion etching (MERIE)-type plasmas on the properties of thin oxide (11 -13 nm) MOS capacitors as well as FETs without gate has been investigated. The results reveal the vulnerability of the oxide and its interface with Si to the plasma process - the interface is much more sensitive. The creation of defects in the form of fixed oxide charge, bulk traps, slow states and interface states is;found. The damage level is a function of both the disch arge conditions (including plasma exposure time) and the initial Si-SiO2 st ructure parameters, the plasma conditions having a priority impact. The dam age process is very rapid particularly in the first seconds (up to 30 s) of plasma exposure. The effects become highly process dependent as the plasma time increases. The plasma induced defects degrade the inversion carrier m obility and change the dominant scattering mechanism in the inversion chann el. The damage leads to an excess leakage current and decreases the breakdo wn fields. A strong linear correlation between plasma induced leakage curre nt and plasma created positive charge is detected. It is established that t he build-up damage depends on plasma nonuniformity, but the non uniformity is neither the only nor the dominating factor. The nature of process induce d defects and the influence of plasma components are discussed. It is propo sed that generated interface states are mainly attributed to VUV and ion bo mbardment, whereas the high values of positive oxide charge are due to the charging effect. The type of plasma induced defects (oxide traps or interfa ce states) and the energy distribution of interface states strongly depend on the relative contribution (or domination) of the different plasma compon ents. A room temperature annealing of MERIE-type plasma induced interface states is established. The reduction depends only on the starting postplasma treat ment level of interface states and the effects responsible for this reducti on take place very close to the Si-SiO2 interface. (The fixed oxide charge is stable and it does not change at all.) The process seems to be controlle d by moisture transport to the Si-SiO2 interface. By means of X-ray photo e lectron spectroscopy it is found that 5 min exposure of thin thermal SiO2 t o N-2-RIE mode plasma causes structural modifications, which manifest only as a deterioration of oxide quality without actual nitration of the oxide. The presence of a small constant amount of SiO species through the oxide an d a broadening of Si-SiO2 interface region are detected. The nature of the electrically active plasma induced defects by both plasma processes - RIE and MERIE is equal - the bond defects in the oxide and at the interface: the oxide charge is associated with E' centers and the inter face states with Pb centers. (C) 2000 Elsevier Science Ltd. All rights rese rved.