A Dry-patterned Cu(Mg) Alloy Film as a Gate Electrode in a Thin Film Transistor Liquid Crystal Displays (TFT-LCDs)

Abstract

The annealing of a Cu(4.5at.% Mg)/<TEX>$SiO_2$</TEX>/Si structure in ambient <TEX>$O_2$</TEX>, at 10 mTorr, and <TEX>$300-500^{\circ}C$</TEX>, allows for the outdiffusion of the Mg to the Cu surface, forming a thin MgO (15 nm) layer on the surface. The surface MgO layer was patterned, and successfully served as a hard mask, for the subsequent dry etching of the underlying Mg-depleted Cu films using an <TEX>$O_2$</TEX> plasma and hexafluoroacetylacetone [H(hfac)] chemistry. The resultant MgO/Cu structure, with a taper slope of about <TEX>$30^{\circ}C$</TEX> shows the feasibility of the dry etching of Cu(Mg) alloy films using a surface MgO mask scheme. A dry-etched Cu(4.5at.% Mg) gate a-Si:H TFT has a field effect mobility of 0.86 <TEX>$\textrm{cm}^2$</TEX>/Vs, a subthreshold swing of 1.08 V/dec, and a threshold voltage of 5.7 V. A novel process for the dry etching of Cu(Mg) alloy films, which eliminates the use of a hard mask, such as Ti, and results in a reduction in the process steps is reported for the first time in this work.