High-performance and damage-free neutral beam etching for advanced ULSI devices

A novel 50 nm-width MOS gate etching process was established using a newly developed neutral beam etching system by optimizing the gas chemistry and the electrode bias condition. In a comparison of poly-Si gate etching using either SF₆ or Cl₂ gas chemistries, opposite etching characteristics were observed in the pattern profile. Consequently, the use of a mixture of these gases was proposed in order to achieve fine control of the etching profiles. The energy of the neutral beam was increased by applying a 600 kHz RF bias to the bottom electrode. The RF bias was very effective in increasing the etch rate and the anisotropy of the poly-Si gates, with no deterioration of the neutralization efficiency. The oxide leakage current achieved for a MOS capacitor etched by the neutral beam was one order of magnitude lower than that achieved by conventional plasma etching.