Semiconductor device and method for manufacturing the same

Abstract

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.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising a transistor, the transistor comprising:
 a first insulating layer;   a first gate electrode layer over the first insulating layer;   a first gate insulating layer over the first gate electrode layer;   an oxide semiconductor layer over the first gate insulating layer;   a source electrode layer over the oxide semiconductor layer;   a drain electrode layer over the oxide semiconductor layer;   a second gate insulating layer over the oxide semiconductor layer; and   a second gate electrode layer over the second gate insulating layer,   wherein the oxide semiconductor layer comprises indium, gallium, and zinc,   wherein an amount of change in a threshold voltage of the transistor before and after a +BT test at 150° C. for one hour is less than or equal to 2 V, and   wherein an amount of change in a threshold voltage of the transistor before and after a −BT test at 150° C. for one hour is less than or equal to 2 V.   
     
     
         3 . The semiconductor device according to  claim 2 ,
 wherein the oxide semiconductor layer comprises a crystal.   
     
     
         4 . The semiconductor device according to  claim 2 ,
 wherein the first insulating layer comprises a halogen element, and   wherein a peak of a concentration of the halogen element in the first insulating layer measured by secondary ion mass spectrometry is in a range of 1×10 15  cm −3  to 1×10 20  cm −3 .   
     
     
         5 . The semiconductor device according to  claim 2 ,
 wherein each of the source electrode layer and the drain electrode layer comprises a first titanium layer, an aluminum layer over the first titanium layer, and a second titanium layer over the aluminum layer.   
     
     
         6 . The semiconductor device according to  claim 2 ,
 wherein the same potential is supplied to the first gate electrode layer and the second gate electrode layer,   wherein a potential is supplied to the first gate electrode layer in the +BT test so that a potential difference between the first gate electrode layer and each of the source electrode layer and the drain electrode layer is 20V, and   wherein a potential is supplied to the first gate electrode layer in the −BT test so that a potential difference between the first gate electrode layer and each of the source electrode layer and the drain electrode layer is −20V.   
     
     
         7 . The semiconductor device according to  claim 2 ,
 wherein the same potential is supplied to the first gate electrode layer and the second gate electrode layer, and   wherein a potential is supplied to the first gate electrode layer in each of the +BT test and −BT test so that an intensity of an electric field is 2 MV/cm.   
     
     
         8 . A light-emitting display device comprising the transistor according to  claim 2 .