Articles you may be interested inProfile control of high aspect ratio trenches of silicon. II. Study of the mechanisms responsible for local bowing formation and elimination of this effect J.A cryogenic etching method with SF 6 /O 2 chemistry plasma in an Alcatel inductively coupled plasma reactor is used to achieve deep trenches with high aspect ratio ͑depth/width Ͼ10͒ and high anisotropy. The mean etch rate in 2 m wide and 100 m deep trenches is about 3.5 m/min. The slope of the trenches can be adjusted from 88°to 90°by selecting appropriate process conditions and selectivity ͑silicon/SiO 2 mask͒ 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 thus the means to reduce or eliminate it. We especially showed that local bowing depends on the efficiency of the trench passivation mechanism and on ion energy and density: ions seem to be responsible of the destruction of the passivation layer.

We are interested in etching very deep anisotropic trenches (∼100 μm) with high aspect ratios (depth/width) (∼20–50) and high etch rates (∼5 μm/min). A high density plasma helicon reactor using SF6/O2 chemistry and a cryogenic chuck has been used for etching very narrow trenches from 1.2 to 10 μm wide on n-type Si wafers with a SiO2 mask. The first results show significant features that demonstrate the feasibility of this method. Two-micron-wide trenches have been etched to a depth of 80 μm at an average etch rate of 2.7 μm/min. The resulting profiles are highly anisotropic and selectivity of Si/SiO2 is remarkably high (>500).

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