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Optimized Shallow Trench Isolation Structure and Its Process for Eliminating Shallow Trench Isolation Induced Parasitic Effects

IP.com Disclosure Number: IPCOM000108059D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Wen, DS: AUTHOR

Abstract

The conventional shallow trench isolation (STI) structure suffers several parasitic effects which may increase leakage current or reduce device reliability. The shallow trench isolation structure forms a 90-degree corner at the trench edge. Because the oxidation rate is slower at the corner, a sharply wedged silicon is formed after thermal oxidation and a thinner gate oxide is grown at the corner. The enhanced electrical field, due to the sharp corner and the thinner gate oxide, tends to lower the intrinsic gate oxide breakdown voltage and reduce the gate oxide integrity. Furthermore, the area containing the thinner gate oxide may form a secondary parasitic channel for FET device operation.

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Optimized Shallow Trench Isolation Structure and Its Process for Eliminating Shallow Trench Isolation Induced Parasitic Effects

       The conventional shallow trench isolation (STI) structure
suffers several parasitic effects which may increase leakage current
or reduce device reliability.  The shallow trench isolation structure
forms a 90-degree corner at the trench edge.  Because the oxidation
rate is slower at the corner, a sharply wedged silicon is formed
after thermal oxidation and a thinner gate oxide is grown at the
corner.  The enhanced electrical field, due to the sharp corner and
the thinner gate oxide, tends to lower the intrinsic gate oxide
breakdown voltage and reduce the gate oxide integrity. Furthermore,
the area containing the thinner gate oxide may form a secondary
parasitic channel for FET device operation. This device has a lower
threshold voltage than the normal device due to the thinner gate
oxide and, therefore, increases the subthreshold leakage.

      The proposed structure is to preserve the corner of trench
before etching the trench, and uses the subsequent thermal oxidation
to separate the active device area and the trench edge.  Fig. 1 shows
the cross-sectional view of the proposed structure.  The process
sequence is described as follows and shown in Fig. 2.

      Grow pad oxide and deposit pad nitride.  A lithographic masking
step to define isolation area.  Etch the dielectic layers (pad oxide
and nitride), and strip the p...