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Recessed oxide regions in a silicon substrate are produced by taking advantage of the preferential thermal oxidation of N+ doped silicon, which leads to an oxide covered structure with a planar surface.
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Silicon Structure With Recessed Isolation Regions
Recessed oxide regions in a silicon substrate are produced by taking
advantage of the preferential thermal oxidation of N+ doped silicon, which leads
to an oxide covered structure with a planar surface.
Into silicon substrate 1 with a buried, highly N+ doped layer 2, trenches 3 are
etched to penetrate into layer 2 (Fig. 1A). This is followed by thermal oxidation in
a water vapor atmosphere. In a first oxidation step, the furnace temperature is
set to < 800 degrees C, at which the N+ doped silicon is oxidized much faster
than the other more lowly doped silicon areas, so that mainly the bottoms of the
trenches are oxidized, while the substrate surface is covered only with a thin
SiO(2) layer 4.
The first oxidation step is completed when the oxide forms mesatype
elevations 5 (step height approximately 200 nm) on top of trenches 3 in the
silicon (Fig. 1B). In a second oxidation step, the furnace temperature is raised to
> 900 degrees, at which the surface of oxide layer 4 is grown to the level of the
mesa-type elevations 5, resulting in a planar surface 6 (Fig. 1C).
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