Additive-Gas Effects on Cl2 Plasma-Based Copper-Etch Process and Sidewall Attack
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The influence of the additive gas in Cl2 plasma-based copper etch and sidewall attack was investigated. The additive gas, such as Ar, N2, and CF4, drastically changed the plasma-phase chemistry, i.e., the Cl radical concentration, and the ion-bombardment energy, which resulted in changes of the copper chlorination rate and the sidewall roughness. The addition of Ar increased the Cl concentration, which increased the copper chlorination rate and the sidewall attack. The addition of N2 enhanced ion bombardment, which increased the copper chlorination rate. Meanwhile, the addition of N2 diluted the Cl concentration and formed a copper nitride passivation layer, which protected the sidewall and reduced roughness. The addition of CF4 induced a fluorocarbon passivation layer, which decreased the copper chlorination rate in the vertical direction but protected the sidewall from vigorous Cl attack and resulted in a smooth sidewall surface. Therefore, the additive gas not only affected the Cu chlorination rate but also influenced sidewall roughness. © 2007 The Electrochemical Society.
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