Shallow trench isolation process

Details Shallow trench isolation process Shallow trench isolation process

2002-12-23

2004-06-15

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Grooved and refilled with deposited dielectric material

Reexamination Certificate

active

06750117

ABSTRACT:

BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a shallow trench isolation (STI) process of a semiconductor device.
2. Description of Related Art
STI techniques have turned into important isolation methods in advanced semiconductor processes since STI structures occupy less areas and provide better isolation effects as compared with conventional field oxide (FOX) structures formed with the local oxidation method (LOCOS). A STI process in the prior art is described as follows.
Referring to
FIG. 1A
, a pad oxide layer
110
and a silicon nitride mask layer
120
are sequentially formed on a substrate
100
, and are patterned subsequently. A trench
130
is then formed in the substrate
100
with the patterned silicon nitride mask layer
120
as a mask.
Referring to
FIG. 18
, a silicon oxide liner layer
133
is thermally grown on the surface of the trench
130
, and then a silicon nitride liner layer
140
is formed on the substrate
100
. Thereafter, CVD silicon oxide is filled into the trench
130
to form a STI structure
150
. The filling process (not shown) comprises depositing a CVD oxide layer on the substrate
100
, performing an annealing process to densify the CVD oxide layer, and then removing the CVD oxide layer outside the trench
130
. During the annealing process, the silicon nitride liner layer
140
serves to reduce the stress in the substrate
100
around the trench
130
.
Referring to
FIG. 1C
, the silicon nitride mask layer
120
is removed with an etchant such as hot phosphoric acid. At the same time, however, the silicon nitride liner layer
140
is easily over-etched to form indents
152
. Therefore, the isolating effect of the STI structure
150
is reduced, and a leakage easily occurs in the channel.
SUMMARY OF INVENTION
Accordingly, this invention provides a shallow trench isolation (STI) process that is capable of protecting a silicon nitride liner layer in the trench from the etchant used for removing the mask layer.
A STI process of this invention is described below. A patterned mask layer, such as a patterned silicon nitride mask layer, is formed on a substrate, and then a trench is formed in the substrate with the mask layer as a mask. A portion of the mask layer around the trench is then removed, and a portion of the substrate around the top portion of the trench is removed with the remaining mask layer as a mask. A liner layer is formed in the trench, and then the liner layer on the top portion of the trench is removed with a pre-deposition process of a high-density plasma chemical vapor deposition (HDP-CVD) process. Thereafter, an insulating material like CVD silicon oxide is filled into the trench covering the liner layer remaining in the trench, and the mask layer is removed with an etchant. In the STI process, the liner layer comprises a material that can also be etched by the etchant for removing the mask layer, and can be a silicon nitride liner layer capable of reducing the stress in the substrate around the trench during a densification process of the insulating material.
In another STI process of this invention, a mask layer having an opening therein is formed on a substrate, and then spacers are formed on the sidewalls of the opening. A trench is formed in the substrate with the mask layer and the spacers as a mask. A thermal oxide layer is formed on the surface of the trench with a thermal oxidation process, such that bird's beaks are formed under the spacers. A liner layer is formed in the trench, and then the liner layer on the top portion of the trench is removed with a pre-deposition process of an HDP-CVD process. Thereafter, an insulating material like CVD silicon oxide is filled into the trench covering the liner layer remaining in the trench, and the mask layer is removed with an etchant. In the STI process, the liner layer comprises a material that can also be etched by the etchant for removing the mask layer, and can be a silicon nitride liner layer capable of reducing the stress in the substrate around the trench during a densification process of the insulating material.
Since the liner layer on the top portion of the trench is removed in the aforementioned STI processes of this invention, the liner layer remaining in the trench is covered by the insulating material and isolated from the etchant during the step of removing the mask layer. Therefore, the isolating effect of the STI structure is not reduced, and a leakage does not easily occur in the channel
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.


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