Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2000-06-29
2003-02-18
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S197000, C438S301000, C438S303000, C438S305000, C438S306000, C438S307000
Reexamination Certificate
active
06521500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a semiconductor device including a gate oxide film without any constriction and a method of manufacturing the same.
2. Description of the Related Art
A method of manufacturing an n-channel type MOS transistor (hereinafter referred to as an nMOS transistor) will now be explained as an example of a conventional semiconductor device.
A thermal oxide film is formed on a p-type silicon substrate, and a polysilicon film is formed on the thermal oxide film. The polysilicon film and the thermal oxide film are patterned using a photoresist film, thereby to form a gate electrode and a gate oxide film. After this, the photoresist film is removed therefrom. Then, ions are implanted into the surface of the silicon substrate so as to form n-type diffusion layers. Subsequently, a side wall is formed on the side wall of the gate electrode. Ions are implanted into the surface of the silicon substrate while using the gate electrode and the side wall as masks, so as to form n
+
-type diffusion layers for forming a source and drain areas. Heat treatment is carried out so as to activate the impurities, so that a source and drain diffusion layers each comprising the n-type diffusion layer and the n
+
-type diffusion layer can be formed. Then, the gate electrode and the n
+
-type diffusion layers are silicided, and an interlayer insulating film is formed on the silicon substrate. Furthermore, contact holes are formed in the interlayer insulating film, and wiring is formed on the n
+
-type diffusion layers.
According to the above method of manufacturing the semiconductor device, the gate oxide film is exposed to a removing agent when removing the photoresist film, and exposed to a cleaning agent when cleaning the silicon substrate. This causes a constriction (hollow) to be formed in the gate oxide film. If there is any constriction in the gate oxide film, an oxide film formed on the silicon substrate enters the constriction when forming a side wall. In the semiconductor device having such a defective gate oxide film, unnecessary current flows through the gate oxide film when an electric field is applied between the gate electrode and the substrate, resulting in breaking down the gate oxide film.
After the formation of the gate electrode, having formed a thick thermal oxide film, the constriction can be filled with an oxide, etc., and thus restoring the gate oxide film. In order to prevent the restored gate oxide film from being exposed to the release agent for photoresist film or the cleaning agent for silicon substrate during a process following this process of restoring the gate oxide film, it is necessary to remain the thick thermal oxide film on the silicon substrate. In this case, in the state where the thermal oxide film is formed both on a source and drain electrode areas, an ion implantation process is carried out, thus it is difficult to manufacture a semiconductor device in which a pn-junction is formed not far from the surface of the substrate.
Unexamined Japanese Patent Application KOKAI Publication No. S62-241379 discloses a method of manufacturing a semiconductor device, wherein, after the formation of a gate electrode using a photoresist film, a nitride film is formed on the side wall of a gate electrode and the photoresist film is removed therefrom. According to this method, an ion implantation process is carried out in the state where an insulating film is formed both on a source and drain electrode areas, therefore, it is difficult to form the semiconductor device wherein the pn-junction is formed not far from the surface of the substrate.
Unexamined Japanese Patent Application KOKAI Publication No. H4-58566 discloses a method of manufacturing a semiconductor device, wherein, after the formation of a gate electrode, an oxide film is formed on the side wall of the gate electrode. The thickness of the oxide film to be formed on the side wall of the gate electrode is 30 to 100 nm, i.e., it is quite thick. Thus, it is difficult to diffuse an impurity diffusion layer into the lower end of the gate electrode through heat treatment.
It is accordingly an object of the present invention to provide a semiconductor device having a gate insulating film with high reliability and a method of manufacturing the same.
Another object thereof is to provide a semiconductor device, wherein a pn-junction is formed not far from the surface of a substrate, and a method of manufacturing the same.
SUMMARY OF THE INVENTION
In order to achieve the above objects, according to the first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising:
forming a first insulating film on a semiconductor substrate;
forming a conductive film on the first insulating film;
forming an etching mask with a predetermined pattern on the conductive film;
etching the conductive film using the etching mask, so as to form a gate electrode;
removing the etching mask with a removing agent;
forming a second insulating film, with which a constriction formed in the first insulating film by the removing agent is filled and which is incorporated with the first insulating film, on a circumference of the gate electrode;
forming a gate insulating film which insulates between the gate electrode and the semiconductor substrate, by removing the first insulating film using the gate electrode and the second insulating film as masks;
forming a protection film which covers at least a circumference of the gate insulating film, in order to protect the gate insulating film during a step following this step; and
implanting an impurity into the semiconductor substrate using the gate electrode, the second insulating film and the protection film as masks, and forming a source area and a drain area by performing heat treatment.
According to the above method, after the removing of the etching mask with the removing agent, having formed the second insulating film which is incorporated with the first insulating film, the constriction (hollow) made in the first insulating film by the removing agent can be filled. Accordingly, the gate insulating film without any constriction can be formed.
Having formed the protection film in the circumferential section of the restored gate oxide film, it becomes preventable that the gate oxide film is exposed to a chemical agent during a process for removing the etching mask or a process for cleaning the substrate, for example. This prevents any new constriction from being formed. Therefore, a semiconductor device having a gate oxide film with high reliability can be manufactured.
The forming the gate insulating film may include removing the first insulating film and a part of the second insulating film which corresponds to an upper surface of the gate electrode; and
the forming the protection film may include forming the protection film as to cover the first and second insulating films, and the method may comprise:
removing a part of the protection film which corresponds to the upper surface of the gate electrode, thereby to expose the upper surface of the gate electrode; and
forming a silicide layer on the upper surface of the gate electrode.
After the formation of the second insulating film, the second insulating film formed on the upper surface of the gate electrode is removed therefrom. After the formation of the protection film, the protection film is removed from the upper surface of the gate electrode. By doing this, the upper surface of the gate electrode is exposed, and a silicide layer is formed on the gate electrode, resulting in siliciding the gate electrode.
In the method of manufacturing a semiconductor device,
the semiconductor substrate may be a silicon substrate;
the first insulating film and the second insulating film may be thermal oxide films;
the conductive film may be a polysilicon film;
the etching mask may be a photoresist pattern;
the removing agent may be
Smith Matthew
Yevsikov V.
Young & Thompson
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