Semiconductor device and method for manufacturing the same

Abstract

An object is to provide a semiconductor device including an oxide semiconductor with stable electric characteristics can be provided. An insulating layer having many defects typified by dangling bonds is formed over an oxide semiconductor layer with an oxygen-excess mixed region or an oxygen-excess oxide insulating layer interposed therebetween, whereby impurities in the oxide semiconductor layer, such as hydrogen or moisture (a hydrogen atom or a compound including a hydrogen atom such as H2O), are moved through the oxygen-excess mixed region or oxygen-excess oxide insulating layer and diffused into the insulating layer. Thus, the impurity concentration of the oxide semiconductor layer is reduced.

Description

TECHNICAL FIELD[0001]The present invention relates to a semiconductor device using an oxide semiconductor and a manufacturing method thereof.[0002]Note that the semiconductor device in this specification refers to all the devices which can operate by using semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.BACKGROUND ART[0003]A technique of forming a thin film transistor (TFT) by using a thin semiconductor film that is formed over a substrate having an insulating surface has attracted attention. A thin film transistor is used for a display device typified by a liquid crystal television. Besides a silicon-based semiconductor material which is known as a material for a semiconductor thin film applicable to a thin film transistor, an oxide semiconductor has attracted attention.[0004]As a material for the oxide semiconductor, zinc oxide and a material containing zinc oxide as its component are kno...

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Benefits of technology

[0008]An insulating layer having many defects typified by dangling bonds is formed over an oxide semiconductor layer with an oxygen-excess mixed region or an oxygen-excess oxide insulating layer interposed therebetween, whereby impurities in the oxide semiconductor layer, such as hydrogen or moisture (a hydrogen atom or a compound including a hydrogen atom such as H2O), are moved through the oxygen-excess mixed region or the oxygen-excess oxide insulating layer and diffused into the insulating layer having defects. Thus, the impurity concentration of the oxide semiconductor layer is reduced.

[0010]Further, the mixed region or the oxide insulating layer, which is provided between the oxide semiconductor layer and the insulating layer having defects, includes excess oxygen, and thus have many oxygen dangling bonds as defects and has high binding energy to impurities such as hydrogen or moisture (a hydrogen atom or a compound including a hydrogen atom such as H2O). Therefore, when the impurities are diffused from the oxide semiconductor layer into the insulating layer having defects, the oxygen-excess mixed region or the oxygen-excess oxide insulating layer functions to facilitate the diffusion. On the other hand, when the impurities which have been removed from the oxide semiconductor layer and diffused into the insulating layer having defects move back toward the oxide semiconductor layer, the oxygen-excess mixed region or the oxygen-excess oxide insulating layer functions as a protective layer (a barrier layer) which is bound to and stabilizes the impurities so as to prevent the impurities from entering the oxide semiconductor layer.

[0012]Thus, the oxygen-excess mixed region or the oxygen-excess oxide insulating layer removes impurities, such as hydrogen, moisture, hydroxyl, or hydride (also referred to as a hydrogen compound) which cause variation, from the oxide semiconductor layer, and further functions as a barrier layer which prevents the impurities which have been diffused into the insulating layer having defects from entering the oxide semiconductor layer again. Consequently, the impurity concentration of the oxide semiconductor layer can be kept low.

[0013]From the above, a thin film transistor including an oxide semiconductor layer in which impurities such as hydrogen, moisture, hydroxyl, or hydride (also referred to as a hydrogen compound) which cause variation are reduced has stable electric characteristics, and a semiconductor device including the thin film transistor can realize high reliability.

[0015]The oxide semiconductor layer, the oxygen-excess mixed region, the oxygen-excess oxide insulating layer, and the insulating layer having defects are preferably formed in a film-formation chamber (a process chamber) in which the impurity concentration is lowered by evacuation with a capture-type vacuum pump such as a cryopump. As a capture-type vacuum pump, for example, a cryopump, an ion pump, or a titanium sublimation pump is preferably used. The capture-type vacuum pump functions to reduce the amount of hydrogen, water, hydroxyl, or hydride in the oxide semiconductor layer, the oxygen-excess mixed region, the oxygen-excess oxide insulating layer, and the insulating layer having defects.

Problems solved by technology

However, a deviation from the stoichiometric composition in an oxide semiconductor arises in a thin film formation process.

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