Si Etching with Low Ion Energy in Low-Pressure Electron Cyclotron Resonance Plasma Generated by Longitudinal and Multipole Magnetic Fields

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Abstract
Si etching at the low pressure of 5×10-5 Torr was studied employing a multipolar electron cyclotron resonance (ECR) plasma stabilized further by longitudinal magnetic field. Even at low pressure, the negative ion generated in the NF3 plasma greatly reduced the self-bias voltage. The self-bias of 25 V provided an anisotropic etching feature in NF3 alone. A further reduction of the bias voltage was made by changing the mirror magnetic field through control of the electron incoming flux, and at the lowest, the voltage of 14 V was attained. In this condition, the etched profile of the side wall became concave. However, the 20% O2 addition to the NF3 achieved the directional feature in the condition.

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