Paper PS2-TuM13
The Effect of Oxygen Addition in a Chlorine Plasma during Shallow Trench Isolation Etch

Tuesday, October 16, 2007, 12:00 pm, Room 607

Shallow trench isolation has been widely used to electrically isolate adjacent transistors. The mixtures of chlorine and oxygen have been one of the most commonly used chemistries for the shallow trench isolation etching process. In this work, an electron cyclotron resonance high density plasma is used to study the effect of oxygen addition in a chlorine plasma during the etching of silicon. To quantitatively assess the effect of oxygen addition, the plasma density and the electron temperature were characterized by using a Langmuir probe. The plasma species, including the etching by-products, were studied using the quadrupole mass spectrometry and the optical emission spectroscopy. The silicon etching rate was measured in-situ by using laser interferometry. Scanning electron microscopy was used to observe the topography change of the etched blanket films. The silicon etching rates were found to increase with the square root of the ion energy with a 9 eV threshold energy, suggesting the etching reaction is limited by the momentum transfer from the ions to the surface. With a relatively small amount of oxygen addition to the chlorine plasma, the etching rate remained approximately constant while the by-product identity and its distribution changed significantly. The dominant ionic etching by-products in chlorine plasmas were SiCl⁺ and SiCl₃⁺, but changed to SiCl⁺, SiOCl₂⁺, and SiCl₃⁺ with the oxygen addition. The roughness of the etched surface increased significantly with oxygen addition. The significant changes of the by-products distribution and the etched surface topography suggest that the etching mechanism changes with the oxygen addition to the chlorine plasmas.