Paper PS2+MS-MoM12
High-rate Deep Anisotropic Silicon Etching with the Expanding Thermal Plasma Technique

Monday, October 15, 2007, 11:40 am, Room 607

Emerging microsystem and 3D interconnect technologies require high anisotropic etch rates to accommodate Si etch depths exceeding 200-300 µm and aspect ratios higher than 10. Using inductively coupled plasma (ICP) reactors there has been a steady improvement of the performance of deep anisotropic Si etching, however, it is unclear whether sufficiently high etch rates can be obtained by continuous innovation of the existing ICP technology. Following our work on high-rate deposition of a wide variety of materials, we have explored deep anisotropic Si etching with the expanding thermal plasma (ETP) technique using fluorine-based chemistries. The ETP technique consists of a remote high-density plasma source and due to a low downstream electron temperature (< 0.3 eV) it has a good control of the plasma chemistry and ion energy. Both a cryogenic etching process and a time-multiplexed etching process were developed using SF₆-O₂ and SF₆-C₄F₈ etch chemistries, respectively. The ion energy was controlled by employing several substrate biasing schemes, including rf and pulse-shape biasing. In this contribution we will present data on etch rates, anisotropy, and selectivity with regard to the hard mask and it will be demonstrated that etch rates up to 12 μm/min and selectivities higher than 300 can be obtained by the ETP technique. Insight in feature profile control will also be presented and it will be shown that feature profiles are comparable to those obtained with ICP reactors. This novel, ETP-based deep anisotropic silicon etching technique might therefore be an attractive alternative for the fabrication of silicon microstructures with high-aspect-ratio features.