Dependences of bottom and sidewall etch rates on bias voltage and source power during the etching of poly-Si and fluorocarbon polymer using SF6, C4F8, and O2 plasmas

The dependences of bottom and sidewall etch rates on the bias voltage and source power in four plasma/substrate systems constituting the advanced Bosch process were investigated using a Faraday cage and a step-shaped substrate specially designed for the accurate observation of lateral and vertical etch rates. The four systems, established by combining discharge gases and substrates, were SF6/poly-Si, SF6/fluorocarbon polymer, O-2/fluorocarbon polymer, and C4F8/Si. For etch ksystems using SF6/poly-Si, SF6/polymer, and O-2/polymer, the degree of anisotropy showed a higher dependence on the bias voltage than on the source power. As the bias voltage was increased, the degree of anisotropy obtained in SF6/poly-Si decreased while that for the SF6/Polymer and O-2/polymer increased. The contribution of spontaneous etching by reactive radicals to the etch rates increased in the order of SF6/polymer<O-2/polymer<SF6/poly-Si, while that of ion-enhanced chemical etching by ions to the degree of anisotropy increased in the inverse order. For C4F8/Si, the redeposition of bottom-emitted particles on the sidewall had a significant effect on the etch characteristics of the sidewall. The sidewall etch rate was dependent on the bottom etch rate and showed different trends with bias voltage and source power. Based on these findings, optimum conditions for bias voltage and source power for each step of the advanced Bosch process, which are required for improved anisotropy, are proposed. (C) 2004 American Vacuum Society.