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, O2/fluorocarbon polymer, and C4F8/Si. For etch systems using SF6/poly-Si, SF6/polymer, and O2/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 O2/polymer increased. The contribution of spontaneous etching by reactive radicals to the etch rates increased in the order of SF6/polymer