Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-09-14
2001-05-01
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S647000, C438S657000, C438S658000, C438S659000, C438S660000, C438S684000
Reexamination Certificate
active
06225214
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 88113867, filed Aug. 13, 1999, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of deposition. More particularly, the present invention relates to a method for forming a contact plug.
2. Description of the Related Art
In general, contact resistance is dependent upon the contact area or dimensions of the contact window. As dimensions of the contact window shrink, contact resistance will increase correspondingly. For a device having a line width smaller than 0.18 &mgr;m, contact resistance can be so high that special processing steps have to be executed.
In the design of DRAMs, a polysilicon plug is one of the most common contact structures for connecting a conductive layer with an N+ or an N− silicon substrate. The contact is a polysilicon/polysilicon contact region. One of the problems for forming such a contact structure is that a layer of thin native oxide is usually formed at the substrate surface due to exposure to air during processing. Although the thin native oxide layer has little effect on contact resistance when the contact area is large, the presence of a native oxide layer can increase contact resistance considerably when the contact opening is small.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a method for forming a contact plug capable of reducing contact resistance caused by native oxide formation.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method form forming a contact plug. A substrate having a dielectric layer thereon is provided. The dielectric layer has an opening that exposes a thin layer of native oxide. A plurality of conformal doped polysilicon layers each having a different dopant concentration is sequentially formed over the opening. Dopant concentration of the polysilicon stack increases towards the bottom of the opening. A top doped polysilicon layer with a dopant concentration smaller than all of doped polysilicon layers in the polysilicon stack is formed over the polysilicon stack so that the opening is completely filled. Lastly, the top doped polysilicon layer and the polysilicon stack are annealed.
In this invention, the contact plug consists of a stack of conformal doped polysilicon layers inside a contact opening. By forming a polysilicon stack inside a contact opening such that the dopant concentration is higher towards the bottom of the contact opening, contact resistance of the contact plug is reduced.
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: 4829024 (1989-05-01), Klein et al.
patent: 5141892 (1992-08-01), Beinglass
patent: 5326722 (1994-07-01), Huang
patent: 5444302 (1995-08-01), Nakajima et al.
patent: 5759905 (1998-06-01), Pan et al.
patent: 5976961 (1999-11-01), Jung et al.
patent: 6067680 (2000-05-01), Pan et al.
Gurley Lynne A.
Huang Jiawei
J.C. Patents
Niebling John F.
Taiwan Semicondutor Manufacturing Co., Ltd.
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