Semiconductor device manufacturing: process – Forming schottky junction – Compound semiconductor
Reexamination Certificate
2000-05-17
2004-02-10
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Forming schottky junction
Compound semiconductor
C438S655000, C438S682000, C438S787000, C438S791000, C438S902000
Reexamination Certificate
active
06689673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The proposed invention relates to a method for forming a gate with metal silicide and more particularly to a method that effectively eliminates gate edge leakage of the metal silicide gate.
2. Description of the Prior Art
In contemporary semiconductor technology, a gate usually is formed by the following process: as
FIG. 1A
shows, the formation of a dielectric layer
11
and conductor layer
12
on substrate
13
in sequence; as
FIG. 1B
shows, patterning the position of a gate by photoresist
14
; and then as
FIG. 1C
shows, etching these layers to form the required gate and then the removal of photoresist
14
.
Moreover, because some scars
15
are formed on the sidewall of the dielectric layer during the etching process, the quality of dielectric layer
11
is degraded and it is called a “gate edge defect.” A popular method for dealing with this issue is to eliminate these scars
15
by performing an oxidation process after the etching process and before a spacer is formed. Obviously, the efficiency of the oxidation process is more enhanced when the dielectric layer
11
is an oxide layer.
However, when metal silicide is used to reduce resistivity and is formed as a part of gate, a new issue arises because the oxidation process not only repairs scars but also oxidates the metal silicide layers, and then resistivity of the metal silicide layer is increased. In other words, improvement of the dielectric layer accompanies degradation of the metal silicide layers, and then the degraded quality of the gate is unavoidable. In addition, because TiSi
2
is liable to be oxidated more than other popular metals silicide such as CoSi
2
, WSi
2
, PtSi
2
, MoSi
2
, PtSi
2
or TaSi
2
, the issue is more serious when the metal silicide layer is a TiSi
2
layer.
In summary, it is desired to develop a new method that repairs scars without defalcation with the metal silicide layer being oxidated. Particularly, the new method is more important when the metal silicide layer is indispensable.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a manufacturable method for forming a gate with a metal silicide.
Another object of the present invention is to provide a practical method that eliminates the edge defect without increased resistivity of a metal silicide.
A present preferred embodiment of the invention is a method for forming a gate with a metal silicide. In short, the proposed method comprises the following steps: providing a substrate; forming a first dielectric layer on the substrate; forming a polysilicon layer on the first dielectric layer; forming a metal silicide layer on the polysilicon layer; forming a second dielectric layer on the metal silicide layer; etching these layers to form a gate on the substrate; performing a thermal nitridation process to form a metal nitride layer on sidewall of the metal silicide layer; and performing a thermal oxidation process to eliminate the edge defect.
Another preferred embodiment is a re-oxidation process for a Ti-polycide gate. First, a substrate is provided; then, an oxide layer is formed, followed by the formation of polysilicon layer, a Ti-polycide layer and a silicon nitride layer on the substrate in sequence; and then etching a silicon nitride layer, a Ti-polycide layer, a polysilicon layer and an oxide layer to form a gate; next, a thermal nitridation process is performed to treat the gate; finally, a thermal oxidation process is performed to treat the gate.
In short, the nitridation process is the main characteristic of the invention. Herein, a metal nitride layer is formed on the sidewall of the metal silicide layer and then the remainder of the metal silicide layer is not affected by the following oxidation process.
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patent: 6326668 (2001-12-01), Li
Hsu Kirk
Lin Wen-Jeng
Lin Yuang-Chang
Dickinson Wright PLLC
Smith Matthew
United Microelectronics Corp.
Yevsikov V.
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