Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-10-08
2003-11-04
Hu, Shouxiang (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S413000
Reexamination Certificate
active
06642585
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device including a MOS field effect transistor having a gate electrode of a stacked structure including a polycrystalline silicon (polysilicon) layer and a metal layer and a method of manufacturing the same.
In recent years, a MOS field effect transistor (hereinafter referred to as MOS-FET) is being miniaturized, and the operating speed of the MOS-FET is being promoted. With increase in the operating speed, a problem of signal delay, i.e., gate delay, is generated. The gate delay depends on the product between the capacitance and the resistance of the gate wiring. In order to suppress the gate delay, used is a gate electrode of a stacked structure consisting of a polysilicon layer and a metal layer, e.g., a stacked structure consisting of a polysilicon layer and a tungsten (W) layer.
FIG. 1
is a cross sectional view showing the construction of a conventional semiconductor device having a gate electrode of a stacked structure consisting of a polysilicon layer and a tungsten layer. As shown in the drawing, a gate insulating film
101
is formed on a semiconductor substrate
100
, and a gate electrode of a stacked structure consisting of a polysilicon layer
102
and a tungsten layer
103
is formed on the gate insulating film
101
.
In manufacturing a semiconductor device provided with such a gate electrode, the tungsten layer
103
tends to be oxidized under an oxidizing atmosphere or tends to be dissolved in a process solution consisting of sulfuric acid and hydrogen peroxide solution. To overcome these difficulties, the gate electrode is covered with a cap film
104
and a gate side wall film
105
. Each of these cap film
104
and gate side wall film
105
consists of a silicon nitride film. When it comes to the manufacturing process of the device shown in
FIG. 1
, a resist removing step is performed after the etching step by lithography in preparation for a wiring step with, for example, aluminum. In this resist removing step, used is a mixed solution consisting of sulfuric acid and hydrogen peroxide solution.
It should also be noted that it is important to decrease the parasitic resistance in order to achieve further miniaturization of the semiconductor device for increasing the degree of integration and to allow the semiconductor device to be operated at a high speed. In view of these requirements, used is a salicide technology that is effective for decreasing the diffusion layer resistance and the contact resistance. In the salicide technology, a metal such as titanium or cobalt is deposited on a diffusion layer, followed by applying a heat treatment so as to bring about reaction between silicon in the diffusion layer and the deposited metal, thereby forming a silicide layer in the diffusion layer.
The salicide technology includes a selective etching step for selectively removing the unreacted metal, with the silicide formed by the heat treatment left unremoved. A mixed solution consisting of sulfuric acid and hydrogen peroxide solution is used in this selective etching step.
As described above, the gate electrode of a stacked structure consisting of a polysilicon layer and a tungsten layer is treated in a subsequent step with a chemical solution containing hydrogen peroxide solution. What should be noted is that tungsten is dissolved in the particular chemical solution, making it necessary to cover the tungsten layer with an insulating film.
Tungsten is poor in its resistance to oxidation. Therefore, it is desirable for the insulating film to be formed of a material that can be deposited under a reducing atmosphere and that is capable of inhibiting intrusion of an oxidizing agent in the subsequent heating step. In general, the insulating film is formed of silicon nitride.
However, defects such as pin holes tend to be formed by stress in the silicon nitride film. Naturally, defects such as pin holes are formed in many cases in the silicon nitride film covering the gate electrode, making it difficult to prevent a mixed solution consisting of sulfuric acid and hydrogen peroxide solution from permeating through the pin holes so as to dissolve tungsten in the selective etching step with the mixed solution in the subsequent step of forming a silicide layer in the source and drain regions (diffusion layers). It should also be noted that the removing solution for removing the resist film used for the patterning intrudes through the pin holes made in the silicon nitride film used as a gate protective film (cap film and gate side wall film) so as to dissolve tungsten and, thus, to bring about breakage of the gate electrode.
Further, when a silicon nitride film acting as a cap film is deposited on the tungsten layer, tungsten is oxidized by the oxidizing agent within the atmosphere so as to bring about a morphological deterioration of the surface.
Still further, when a silicon nitride film is deposited to form a gate side wall film on the side surface of the gate electrode, an oxidizing agent within the atmosphere tends to intrude through the defects such as pin holes of the silicon nitride film so as to oxidize the tungsten layer included in the gate electrode.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention, which has been achieved in an attempt to overcome the above-noted problems inherent in the prior art, is to provide a semiconductor device, in which the gate electrode of a stacked structure consisting of a polysilicon layer and a metal layer is prevented from being broken or deteriorated, and a method of manufacturing the particular semiconductor device.
According to a first aspect of the present invention, there is provided a semiconductor device, comprising a gate electrode having a stacked structure of a polysilicon layer and a metal layer, and a side wall insulating film formed on a side wall of the gate electrode for protecting the side wall of the gate electrode, the side wall insulating film having a silicon oxide layer and at least two layers of silicon nitride.
According to a second aspect of the present invention, there is provided a semiconductor device, comprising a gate electrode having a stacked structure of a polysilicon layer and a metal layer, a cap insulating film formed on a upper surface of the gate electrode for protecting the upper surface of the gate electrode, the cap insulating film having at least two layers of silicon nitride, and a side wall insulating film formed on a side wall of the gate electrode for protecting the side wall of the gate electrode, the side wall insulating film having a silicon oxide layer and at least two layers of silicon nitride.
According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of forming a gate electrode having a stacked structure of a polysilicon layer and a metal layer on a gate insulating film formed on a semiconductor substrate, forming a side wall insulating film on a side wall of the gate electrode, the side wall insulating film having a silicon oxide layer and at least two layers of silicon nitride.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of forming a gate electrode having a stacked structure of a polysilicon layer and a metal layer on a gate insulating film formed on a semiconductor substrate, forming a first silicon nitride film on a upper surface of the gate electrode, forming a second silicon nitride film on a side wall of the gate electrode, forming a third silicon nitride film to cover the first and second silicon nitride films, and forming a first silicon oxide film on that portion of the third silicon nitride film which is positioned on the side wall of the gate electrode.
According to a fifth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of forming a stacked structure forming a gate electrode and having a polysilicon layer and a metal layer o
Azuma Atsushi
Ohuchi Kazuya
Hu Shouxiang
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
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