Disclosed in the present invention is a rare-earth doped semiconductor material. Compounds of two rare-earth elements R and R having different functions are introduced into an indium oxide containing material. The coupling of R element ions to an O2p orbit can effectively enhance the transfer efficiency of the rare-earth R as a photogenerated electron transfer center, such that the light stability of a device with a small amount of R doping can be achieved. Compared with single rare-earth element R doping, due to less doping, the impact on a mobility is less, such that higher mobility and light stability devices can be obtained. Further provided in the present invention is a semiconductor-based thin-film transistor, and an application.

A transistor having a minute size is provided. The transistor includes a first conductive layer, a second conductive layer, a third conductive layer, a first insulating layer, a second insulating layer, and a semiconductor layer. The first insulating layer is provided over the first conductive layer and includes an opening reaching the first conductive layer and a depressed portion surrounding the opening in a plan view. The second conductive layer is provided to cover the inner wall of the depressed portion and includes a region facing the semiconductor layer with the first insulating layer therebetween. The semiconductor layer is provided to include a region overlapping with the opening and is in contact with the top surface of the first conductive layer, the side surface of the first insulating layer, the side surface of the second conductive layer, and the top surface of the second conductive layer. The second insulating layer is provided in contact with the top surface of the semiconductor layer. The third conductive layer is provided over the second insulating layer to cover the inner wall of the opening and includes a region facing the semiconductor layer with the second insulating layer therebetween.

A crystalline IZTO oxide semiconductor and a thin film transistor having the same are provided. The thin film transistor includes a gate electrode, a crystalline InZnSn oxide (IZTO) channel layer overlapping the upper or lower portions of the gate electrode and having hexagonal crystal grains, and a gate insulating layer disposed between the gate electrode and the IZTO channel layer, and source and drain electrodes respectively connected to both ends of the IZTO channel layer.

Provided is a method for manufacturing a semiconductor device whose electric characteristics are prevented from being varied and whose reliability is improved. In the method, an insulating film is formed over an oxide semiconductor film, a buffer film is formed over the insulating film, oxygen is added to the buffer film and the insulating film, a conductive film is formed over the buffer film to which oxygen is added, and an impurity element is added to the oxide semiconductor film using the conductive film as a mask. An insulating film containing hydrogen and overlapping with the oxide semiconductor film may be formed after the impurity element is added to the oxide semiconductor film.

An object is to provide a high reliability thin film transistor using an oxide semiconductor layer which has stable electric characteristics. In the thin film transistor in which an oxide semiconductor layer is used, the amount of change in threshold voltage of the thin film transistor before and after a BT test is made to be 2 V or less, preferably 1.5 V or less, more preferably 1 V or less, whereby the semiconductor device which has high reliability and stable electric characteristics can be manufactured. In particular, in a display device which is one embodiment of the semiconductor device, a malfunction such as display unevenness due to change in threshold voltage can be reduced.

A novel method for forming a metal oxide is provided. The metal oxide is formed using a precursor with a high decomposition temperature while a substrate is heated to higher than or equal to 300 C. and lower than or equal to 500 C. In the formation, plasma treatment, microwave treatment, or heat treatment is preferably performed as impurity removal treatment in an atmosphere containing oxygen. The impurity removal treatment may be performed while irradiation with ultraviolet light is performed. The metal oxide is formed by alternate repetition of precursor introduction and oxidizer introduction. For example, the impurity removal treatment is preferably performed every time the precursor introduction is performed more than or equal to 5 times and less than or equal to 10 times.

A method for manufacturing a semiconductor device with high productivity is provided. The method includes a step of forming a first insulator, a second insulator, and a third insulator in this order using a multi-chamber apparatus; a step of forming a fourth insulator, a fifth insulator, a first oxide film, a second oxide film, and a third oxide film in this order using a multi-chamber apparatus; a step of forming a conductive film; a step of processing the first oxide film, the second oxide film, the third oxide film, and the conductive film, thereby forming a first oxide, a second oxide, an oxide layer, and a conductive layer each having an island shape; a step of forming a sixth insulator and an insulating film in this order using a multi-chamber apparatus; a step of planarizing the insulating film; a step of forming, in the insulating film and the sixth insulator, an opening where the second oxide is exposed; a step of forming a seventh insulator and a first conductor; and a step of forming an eighth insulator and a ninth insulator in this order using a multi-chamber apparatus.