Fabrication method of a device isolation structure

Details Fabrication method of a device isolation structure Fabrication method of a device isolation structure

1999-09-10

2001-07-10

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Implanting to form insulator

C438S444000

Reexamination Certificate

active

06258694

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a fabrication method of a semiconductor device, and more particularly, to a fabrication method of a device isolation structure.
2. Description of the Related Art
Today, development in integrated circuit fabrication is blooming. Minimization of devices is the mainstream. When the size of the device decreases, the integration of the device increases. That is, the isolation between devices must be minimized. Thus, isolation between devices becomes intractable. According to the prior art, a field oxide layer formed by local oxidation is used as the device isolation. However, edge corners of the field oxide (FOX) layer formed by local oxidation are bird's beak-shaped, and stresses may be induced. Due to bird's beak formation, it is difficult to minimize the FOX layer. Thus, it is difficult to adapt the local oxidation process to the sub-half micron process.
SUMMARY OF THE INVENTION
According to this, the invention provides a fabrication method of a device isolation structure to form an embedded FOX layer that shortens a bird's beak region and reduces the stresses. The invention can apply to the fabrication of a high integration device.
The invention provides a fabrication method of a device isolation structure. A patterned mask layer is formed on a silicon substrate. The mask layer has a trench opening that aligns with a desired isolation region that comprises a field oxide region and a bird's beak region. A first dopant is doped into the silicon substrate exposed by the trench opening in a first doping step to dope the silicon substrate of the bird's beak region. The first dopant such as nitrogen can prevent the silicon from being oxidized. A spacer is formed on sidewalls of the mask layer. The mask layer and the spacers are used as a mask to remove portions of the silicon substrate and to form a trench in the silicon substrate. A second dopant is doped into the exposed bottom of the trench in a second doping step to dope the silicon substrate of the field oxide region. The second dopant such as oxygen can benefit the oxidation of the silicon. A field oxide process is performed to form and to fill a field oxide layer in the trench in order to isolate the device.
Since the silicon substrate of the bird's beak region is doped by the first dopant to prevent the silicon from being oxidized, the formation of a bird's beak structure is inhibited, and the length of the bird's beak structure and the stresses are reduced. Additionally, the second dopant doped into the silicon substrate of the field oxide region to benefit the oxidation of the silicon is useful for forming the FOX layer in order to prevent the formation of the FOX layer from being affected by an embedding process.
According to the invention, an embedded FOX layer can have a bird's beak structure that is shorter than the traditional one and reduce stresses. Furthermore, it can adjust the width of a FOX layer according to the width of a trench opening; thus, the FOX layer is adjustable and not affected by the bird's beak-shape structure.
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: 5372950 (1994-12-01), Kim et al.
patent: 5972777 (1999-10-01), Hsu et al.
IBM Tech. Disc. Bull., vol. 27, No. 11, pp. 6703-6704, Apr. 1985.

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