Chlorine (Cl2 or BCl3, with additions of Ar or N2), fluorine (SF6/Ar) and methane/hydrogen (CH4/H2/Ar or CH4/H2/N2) based plasmas have been examined as a function of composition, source and sample chuck power, and pressure, for dry etching of the typical luminescent sulphide phosphors (ZnS, SrS), conductive electrode materials [indium tin oxide, (ITO) and TiW] and insulators (Al2O3, alumina/titania-ATO) used in thin film electroluminescent displays. It is necessary to have both a high ion flux and an ion energy above a particular threshold (typically ⩾125 eV) in order to achieve practical etch rates for the high bond strength materials such as Al2O3, alumina/titania and SrS. The fastest etch rates for ZnS, Al2O3 and aluminum tin oxide are obtained with Cl2/Ar for SrS with SF6/Ar and for ITO with CH4/H2/Ar.
A number of different plasma chemistries have been investigated for the etching of oxides (indium tin oxide for conductive electrodes; alumina/titania and Al2O3 for insulators) and phosphors (SrS, ZnS) used in thin film electroluminescent displays. Under high ion density conditions, such as in an electron cyclotron resonance source, maximum etch rates above 1500 Å/min are obtained for ZnS in Cl2/Ar, BCl3/Ar, and SF6/Ar, for SrS in SF6/Ar and CH4/H2/Ar, for ITO in CH4/H2/Ar and for ATO in SF6/Ar. The etching is ion activated under most conditions, producing good feature anisotropy. Near-surface stoichiometry could generally be maintained on the etched surfaces of all materials except SrS where we invariably detected strong preferential loss of S. An optimized process for etching a typical metal-insulators-semiconductor-insulator-metal stack would involve switching plasma chemistries for each individual layer, but we have successfully patterned such a stack using only the CH4/H2/Ar chemistry.
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