Method of fabricating shallow trench isolation structure

Details Method of fabricating shallow trench isolation structure Method of fabricating shallow trench isolation structure

1999-04-28

2001-06-19

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Grooved and refilled with deposited dielectric material

Reexamination Certificate

active

06248644

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor fabricating method. More particularly, the present invention relates to a method of fabricating a shallow trench isolation (STI) structure.
2. Description of the Related Art
An isolation region is formed in an integrated circuit for the purpose of separating neighboring device regions of a substrate and preventing the carriers from penetrating through the substrate to neighboring devices. For example, isolation regions are used to isolate field effect transistors (FETs) from each other in order to prevent current leakage among the FETs.
Shallow trench isolation (STI) technique is a common method of forming isolation regions. STI structure is formed by first anisotropically etching to form a trench in the substrate, and then depositing oxide in the trench to form an isolation region. Since STI structure is scaleable, it has become widely used for forming sub-micron CMOS circuits.
In
FIG. 1
, a preserve layer
102
is formed on a substrate
100
. A photolithographic and etching process is performed to form a trench
104
in the substrate
100
and the preserve layer
102
. A low-pressure chemical vapor deposition is performed with tetra-ethyl-ortho-silicate (TEOS) serving as a gas source. An oxide layer
106
is formed to cover the preserve layer
102
and fill the trench
104
. The oxide layer
106
is deposited in such way that the oxide layer
106
is conformal to the trench
104
and gradually gets thicker to fill the trench
104
. Thus, a seam
108
is formed in the oxide layer
106
between opposite sidewalls of the trench
104
. A dry densification is performed in nitrogen environment or oxygen environment. A chemical-mechanical polishing and a dip step are performed in sequence. However, the seam
108
is easily exposed after the chemical-mechanical polishing step. The dip step even expends the seam
108
. Thus, defects usually form in the STI structure.
In the conventional STI structure, a seam easily forms in a trench after an oxide layer is deposited in the trench. If a trench with a high aspect ratio is provided, a void may even form in the oxide layer after depositing the oxide layer into the trench. The seam or void is likely to remain in the oxide layer even after the performance of a dry densification. In this manner, after the planarization step, the seam or void is easily exposed. Once the seam or void is exposed, it is easily to be enlarged during a dip step. This, in turn, causes current leakage and device failure to occur.
SUMMARY OF THE INVENTION
The invention provides a method of fabricating a shallow trench isolation structure. A preserve layer is formed on a substrate. A trench is formed in the substrate and the preserve layer. An oxide layer is formed over the substrate to fill the trench. A wet densification step is performed in a moist environment. The oxide layer outside the trench is removed.
In the present invention, a wet densification step is performed in a moist environment. Oxygen radicals are generated in the moist environment during the performance of the wet densification step. The oxygen radicals penetrate into the seam to bond with the dangling bonds along the seam. Thus, portions of the oxide layer beside the seam are bonded and the seam is eliminated. The quality of the STI structure is enhanced.
In addition, the oxygen radicals penetrate into the oxide layer to make contact with the top corner and the bottom corner of the trench
204
. It leads to the occurrence of an additional oxidation step. A right-angled bottom and a right-angled top corner are further oxidized into smooth corners. Thus, the stress of the top and bottom corners is reduced and kink effect does not occur.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


REFERENCES:
patent: 5492858 (1996-02-01), Bose et al.
patent: 5989978 (1999-11-01), Peidous

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