Formation of removable shroud by anisotropic plasma etch
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United States of America Patent
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May 2, 2006
Grant Date -
Dec 29, 2005
app pub date -
Jun 25, 2004
filing date -
Jun 25, 2004
priority date (Note) -
Expired
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Abstract
Isotropic etching of sacrificial oxide that is adjacent to a trench fill step in an STI wafer can lead to undesired etching away of a sidewall of the trench fill material (e.g., HDP oxide). A sidewall protecting method conformably coats the trench fill step and sacrificial oxide with an etch-resistant carbohydrate. In one embodiment, conforming ARC fluid is spun-on and hardened. A selective, dry plasma etches the hardened ARC over the sacrificial oxide while leaving intact part of the ARC that adheres to the trench fill sidewall. The remnant sidewall material defines a protective shroud which delays the subsequent isotropic etchant (e.g., wet HF solution) from immediately reaching the sidewall of the trench fill material. The delay length of the shroud can be controlled by tuning the etchback recipe. In one embodiment, the percent oxygen in an O.sub.2 plus Cl.sub.2 plasma and/or bias power during the plasma etch is used as a tuning parameter.
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