Effect of O2 Gas during Inductively Coupled O2/Cl2 Plasma Etching of Mo and HfO2 for Gate Stack Patterning

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In this study, we investigated the etching characteristics of Mo and HfO2 single layers and Mo/HfO2 stacked structure for metal electrode/high-$k$ gate stack patterning in O2/Cl2 inductively coupled plasmas and the effects of O2 addition on the etch rates and etch selectivity of the Mo to the HfO2 layer. By controlling the process parameters such as the O2/Cl2 flow ratio, the top electrode power and the dc self-bias voltage ($V_{\text{dc}}$), the Mo/HfO2 etch selectivity as high as ${\cong}67$ could be obtained. Addition of O2 gas to the O2/Cl2 chemistry improved the Mo/HfO2 etch selectivity because the O2 gas in a certain flow ratio range reduced the HfO2 etching reactions due to less chlorination of Hf but enhanced the Mo etch rate presumably due to effective formation of highly volatile Mo–O–Cl etch by-products.
2008-08-25