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A planar insulating cap is formed over a trench filled with polysilicon by first forming a silicon dioxide (SiO2) film which is etched away and then forming a final SiO2 film.
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Planar Self-aligned Trench Cap
A planar insulating cap is formed over a trench filled with polysilicon by first
forming a silicon dioxide (SiO2) film which is etched away and then forming a
final SiO2 film.
Referring to Fig. 1, a deep trench is formed in substrate silicon (Si) 2. Films
of SiO2 4 and silicon nitride (Si3N4) 6 are then conformally grown on the
exposed Si 2, poly-silicon 8 is deposited by a conformal deposition process to fill
the trench, and a planarizing etch removes the excess silicon as shown in Fig. 1.
The top surface of the poly-silicon 8 within the trench is oxidized to the
thickness of oxide 10 desired in a final cap oxide as shown in Fig. 2. This oxide
film 10 is then completely etched away using a buffered hydrofluoric acid (HF)
As shown in Fig. 3, the poly-silicon is again oxidized to form SiO2 film 12 to
the same thickness as previous oxide film 10 resulting in the insulating cap 12 on
the top of the filled trench. Thus, surfaces of films 12 and 6 are nearly in the