Ultra low density of interfacial traps with mixed thermal and plasma enhanced ALD of high-k gate dielectrics

Anomalous growth per cycle was observed using in situ ellipsometry during the initial cycles of plasma enhanced atomic layer deposition (ALD) of high-k dielectrics, while thermal atomic layer deposition of these oxides exhibited linear growth per cycle. The anomalous growth per cycle was attributed to oxidation of the substrate by plasma oxygen. Thermally grown films have a lower capacitance density and higher leakage current but lower density of interfacial traps compared to plasma enhanced grown films. For plasma enhanced films, the leakage current is dominated by direct tunnelling while trap assisted tunnelling seems to be dominant in thermally grown films. Initiating the oxide growth with thermal atomic layer deposition and then switching to the plasma enhanced process protects the substrate surface from plasma oxygen and lowers the density of interfacial traps (D-it). Starting with ten cycles of thermal atomic layer deposition of ZrO2 enhances the capacitance density while decreasing the D-it. The lowest value of D-it was obtained with twenty cycles of thermal atomic layer deposition (1.8 x 10(10) cm(-2) eV(-1)). The mid-gap D-it reduces systematically with an increasing number of thermal ALD cycles. Furthermore, the frequency dispersion in accumulation is reduced with an increasing number of thermal ALD cycles up to twenty.