Nitridation of Si surface at the bottom of submicron trench using nitrogen neutral beam

The nitridation of silicon at the bottom of nanoscale trench patterns using a nitrogen neutral beam (NB) extracted with a low acceleration voltage of less than 100 V was studied at room temperature. By X-ray photoelectron spectroscopy (XPS) analysis, the formation of a Si₃N₄ layer was confirmed at the bottom of the trench when the acceleration voltage was higher than 20 V. The XPS depth profile suggested that nitrogen was diffused to a depth of 180 nm. In contrast, the bottom of the trench was not nitrided by the low-energy N⁺ ions produced by inductively coupled plasma (ICP). It is suggested that most of the N⁺ ions bombarded the top corner of the trench owing to the concentrated electric field around it. On the other hand, the neutral N₂ or N beam was not affected by the local electric field concentration, and it was able to reach bottom of the deep trench. (author)