Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-12-19
2003-10-14
Fahmy, Wael (Department: 2814)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S166000, C438S517000, C438S200000
Reexamination Certificate
active
06632708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having a circuit constructed of a thin film transistor (hereinafter referred to as TFT) and a method of manufacturing the same. For example, the present invention relates to an electro-optical device typified by a liquid crystal display panel and to electronic equipment having such an electro-optical device mounted thereon as its component.
It is to be noted that a semiconductor device as stated herein throughout the present specification denotes a general device which functions by utilizing semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic equipments are all semiconductor devices.
2. Description of the Related Art
A technique for structuring a thin film transistor (TFT) using a semiconductor thin film (having a thickness on the order of about several to several hundred nm) formed on a substrate having an insulating surface has been attracting much attention in recent years. Thin film transistors are widely applied to electronic devices such as an IC or an electro-optical device, and in particular, development of the TFT as a switching element of an image display device is proceeding rapidly.
Typically, an amorphous silicon film, a crystalline silicon film formed from an amorphous silicon film that is crystallized by a known method such as laser light annelaing, or like other film is used as a material of the semiconductor thin film. In particular, the TFT using the crystalline silicon film as an active layer realizes a high electric field mobility, and hence its ability in current driving is high, making it possible to perform fine processing and increasing an aperture ratio of a pixel portion.
An active matrix liquid crystal display device that utilizes such TFTs as switching elements of pixels and as driver circuits is attracting much attention. Utilizing an inexpensive glass substrate rather than an expensive quartz substrate becomes the premise to realize an inexpensive as well as a large screen display device. Furthermore, it is demanded that the highest temperature in a manufacturing process be set at 600 to 700° C. or lower when taking the heat resistance temperature of the glass substrate in consideration.
However, a large quantity of impurity ions of alkali metal such as sodium (Na), or other impurities are contained in the glass substrate. A base film (blocking layer) formed from a silicon oxide film, a silicon nitride film, or the like is therefore formed on the surface of the glass substrate on which the TFTs will be formed in order to prevent the impurity ions of the alkali metal element, etc. from penetrating into the active layer of the TFT.
An electric field is formed in the active layer when a voltage is applied to a gate electrode of the TFT, whereby the impurity ions in the glass substrate are drawn to the active layer. As a result, if the impurity ions pass through the base film and penetrate into a gate insulating film and the active layer, then an electrical characteristic will undergo a fluctuation, thereby leading to the reduction in reliability.
In the case of a top gate TFT, in particular, the film quality of the base film influences the characteristic of the TFT immensely because a channel forming region is in contact with the base film.
Conventionally, the silicon nitride (SiN
x
) film and the silicon oxide (SiO
x
) film are generally used as the base film. Although it is known that an insulating film formed from the silicon nitride (SiN
x
) film is high in its blocking effect of impurity ions, the insulating film has a great number of trap levels and therefore has a huge influence on the characteristic of the TFT. In addition, the silicon oxide film has merits such as a wider band gap, a higher insulation, and a lower trap level compared with the silicon nitride film. The silicon oxide film, however, has demerits in that it is apt to absorb moisture and also has a low blocking effect of impurity ions.
Besides, in the case of using a layered film of the silicon nitride (SiN
x
) film and the silicon oxide (SiO
x
) film as the base film, it is also known that the layered film has an effect on improvement in stability of the TFT characteristic.
When forming the layered film formed of the silicon nitride film and the silicon oxide film on the glass substrate, two film deposition chambers were necessary to exclusively form these films individually because the composition elements of the silicon nitride film and the silicon oxide film are respectively different.
Furthermore, in the case of using two film deposition chambers to form the layered film, a conveying time when conveying the substrate and a heating time for heating the substrate which has grown cold while being conveyed are required, thereby inviting an increase in the processing time.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problem, and therefore has an object to provide a base film formation method having excellent productivity and a base film attained through this formation method.
According to a first aspect of the present invention, there is provided a semiconductor device having a thin film transistor, characterized in that the semiconductor device comprises an insulating film in contact with a substrate and a semiconductor film on the insulating film and in contact thereto, and that the insulating film is a silicon nitride oxide film in which a concentration ratio of nitrogen to a concentration of silicon in the film undergoes a continuous change within a range of 0.3 or more and 1.6 or less. Therefore, from TFT characteristics so far, remarkable progress can be made in an electric characteristic of a TFT using the semiconductor film that is in contact with the silicon nitride oxide film as an active layer.
According to a second aspect of the present invention, there is provided a semiconductor device having a thin film transistor, characterized in that the semiconductor device comprises a layered film including an insulating film in contact with a substrate and a semiconductor film on the insulating film and in contact thereto, and that the insulating film is a silicon nitride oxide film in which a concentration ratio of oxygen to a concentration of silicon in the film undergoes a continuous change within a range of 0.1 or more and 1.7 or less. Therefore, from TFT characteristics so far, remarkable progress can be made in an electric characteristic of a TFT using the semiconductor film that is in contact with the silicon nitride oxide film as an active layer.
According to a third aspect of the present invention, there is provided a semiconductor device having a thin film transistor, characterized in that the semiconductor device comprises an insulating film in contact with a substrate and a semiconductor film on the insulating film and in contact thereto; and that the insulating film is a silicon nitride oxide film in which a concentration ratio of nitrogen to a concentration of silicon in the film undergoes a continuous change within a range of 0.3 or more and 1.6 or less and a concentration ratio of oxygen to a concentration of silicon in the film undergoes a continuous change within a range of 0.1 or more and 1.7 or less. Therefore, from TFT characteristics so far, remarkable progress can be made in an electric characteristic of a TFT using the semiconductor film that is in contact with the silicon nitride oxide film as an active layer.
According to a fourth aspect of the present invention, there is provided a semiconductor device having a thin film transistor, characterized in that the semiconductor device comprises a layered film including a silicon nitride oxide film in contact with a substrate and a semiconductor film on the layered film and in contact thereto, and that the layered film including the silicon nitride oxide film includes one layer of film in which a concentration ratio of nitrogen to a concentration of silicon in the film undergoes a continuous change within a ran
Ishimaru Noriko
Iwai Mitinori
Miwa Masahiko
Sakama Mitsunori
Fahmy Wael
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Semiconductor Energy Laboratory Co,. Ltd.
Trinh (Vikki) Hoa B.
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