Effect of hydrogen peroxide on hydrofluoric acid etching of high-k materials: ESR investigations

Oxides and silicates of zirconium and hafnium are being actively considered for use as gate dielectrics in MOS devices. Because of their higher dielectric constant (k ∼ 16-22), they permit the use of thicker layers without sacrificing the capacitance value. Wet chemical etching is the method of choice for patterning these oxides. The etching process has to be selective to zirconium/hafnium oxides over silicon dioxide, which may be present in other areas. In this paper, work done on HF etching of ZrO₂ and HfO₂ in presence of hydrogen peroxide is presented and discussed. It was found that addition of hydrogen peroxide to HF solutions lower the etch rate of ZrO₂ and HfO₂ films. Electron spin resonance (ESR) spectroscopy was used to probe the reasons for the decrease in etch rates in this solution.