Profile control of high aspect ratio trenches of silicon. I. Effect of process parameters on local bowing

A cryogenic etching method with SF6/O2 chemistry plasma in an Alcatel inductively coupled plasma reactor is used to achieve deep trenches with high aspect ratio (depth/width >10) and high anisotropy. The mean etch rate in 2 μm wide and 100 μm deep trenches is about 3.5 μm/min. The slope of the trenches can be adjusted from 88° to 90° by selecting appropriate process conditions and selectivity (silicon/SiO2 mask) is higher than 400:1. However, profiles still present a defect: they need to be improved, mainly by reducing the local bowing effect. Local bowing is lateral etching located on the sidewalls and resulting in profiles destruction. This article deals with the study of the local bowing and profile improvement by changing process parameters. We investigated the effect of the process parameters (pressure, bias voltage, temperature, gas flow rates, etc.), and the mechanisms responsible for local bowing are discussed and evaluated. The final aim is to find the cause of the appearance of local bowing and ...