Self-aligned deep trench isolation to shallow trench isolation

Details Self-aligned deep trench isolation to shallow trench isolation Self-aligned deep trench isolation to shallow trench isolation

2000-06-22

2001-10-02

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Grooved and refilled with deposited dielectric material

C438S153000, C438S163000, C438S425000, C257S069000

Reexamination Certificate

active

06297127

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention is integrated circuit processing using shallow trench isolation (STI) to separate circuit elements.
BACKGROUND OF THE INVENTION
STI has come into widespread use in the semiconductor industry because of its space savings as compared with the old LOCOS isolation.
In an active well circuit, where the wells are actively biased to improve the device performance, a solid and constant isolation is needed between the wells. The isolation must be deeper (~2&mgr;m) than the shallow isolation (~0.25 &mgr;m) between devices.
It is not enough, however, to have only deep trenches because device isolation using deep trenches would require body contacts, as in silicon on insulator technology, and would consume a great deal of space.
In addition, it is not practical to have varying widths of deep trenches because of the nature of the filling mechanism. Ordinarily, a deep trench is filled by growth of a layer adhering to the walls of the trench, so that the thickness of the fill layer can be much less than the width of the trench. This mechanism does not work for wide deep trenches. When the width of the trench is greater than twice the depth, the thickness of the fill layer must be at least the depth of the trench; i.e. a wide deep trench would require a 2 &mgr;m thick fill layer.
The combination of shallow and deep trenches has been suggested in the past, but the previous approaches have suffered from various practical problems.
If the deep trenches are not self-aligned to the shallow trenches, the deep trench can overlap the devices that are isolated by the trenches, so that the device size is not correct for that process.
SUMMARY OF THE INVENTION
The invention relates to a shallow trench isolation that is combined with optional deep trenches and the process for forming the isolation.
A feature of the invention is that the deep trenches are self-aligned with the shallow trenches, at the edges of the shallow trenches.
Another feature of the invention is that deep trench width is controlled by the thickness of a temporary sidewall spacer deposited in the interior of the shallow trench.
Another feature of the invention is that the deep trench width is limited by the sidewall deposition thickness of the deep trench fill in the case in which the two deep trenches entirely fill the shallow trench.


REFERENCES:
patent: 5320975 (1994-06-01), Cedarbaum et al.

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