The etch rate of HfO2 etch processing has been feedback controlled in inductively coupled Cl2/N2/Ar plasmas. The ion current and the root mean square rf voltage on the wafer stage, which are measured using a commercial impedance meter connected to the wafer stage, are chosen as controlled variables because the positive-ion flux and ion energy incident upon the wafer surface are the key factors that determine the etch rate. Two 13.56 MHz rf generators are used to adjust the inductively coupled plasma power and bias power which control ion density and ion energy, respectively. The adopted HfO2 etch processing used rather low rf voltage. The ion-current value obtained by the power/voltage method is underestimated, so the neural-network model was developed to assist estimating the correct ion-current value. The experimental results show that the etch-rate variation of the closed-loop control is smaller than that of the open-loop control. However, the first wafer effect cannot be eliminated using closed-loop control and thus to achieve a constant etch rate, the chamber-conditioning procedure is required in this etch processing.
The etch selectivity of HfO2 to Si reported to date is poor. To improve the selectivity, one needs to either increase the etch rate of HfO2 or decrease the etch rate of Si. In this work, the authors investigate the etch selectivity of HfO2 in Cl2∕N2 plasmas. In particular, the effects of in situ N2 plasma treatment of HfO2 and Si were investigated. The silicon substrate was exposed to nitrogen plasma and was nitrided, which was confirmed by x-ray photoelectron spectroscopy. The nitrided Si etching was suppressed in Cl2∕N2 plasmas. The effectiveness of nitridation was studied with varying the plasma power, bias power, pressure, and N2 plasma exposure time. The results show that the etch resistance increased with increased power and decreased pressure. A minimum exposure time was required to obtain etch resistant property. The applied bias power increased the etch rate of Si substrate, so it should not be used during N2 plasma treatment. Fortunately, the etch rate of HfO2 was increased by the nitridation process. Therefore, HfO2∕Si selectivity can be improved by nitridation and became higher than 5 under proper exposure condition.
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