Semiconductor device and manufacturing method thereof

Abstract

Electric characteristics and reliability of a thin film transistor are impaired by diffusion of an impurity element into a channel region. The present invention provides a thin film transistor in which aluminum atoms are unlikely to be diffused to an oxide semiconductor layer. A thin film transistor including an oxide semiconductor layer including indium, gallium, and zinc includes source or drain electrode layers in which first conductive, layers including aluminum as a main component and second conductive layers including a high-melting-point metal material are stacked. An oxide semiconductor layer 113 is in contact with the second conductive layers and barrier layers including aluminum oxide as a main component, whereby diffusion of aluminum atoms to the oxide semiconductor layer is suppressed.

1 . A method for manufacturing a semiconductor device, comprising the steps of:
 forming a source electrode layer and a drain electrode layer, each comprising a first conductive layer and a second conductive layer over the first conductive layer;   oxidizing an edge portion of the first conductive layer;   forming an oxide semiconductor layer to be in contact with the edge portion;   forming a gate insulating film over the oxide semiconductor layer; and   forming a gate electrode over the gate insulating film.   
     
     
         2 . The method for manufacturing a semiconductor device according to  claim 1 , wherein the oxide semiconductor layer includes indium, gallium, and zinc. 
     
     
         3 . The method for manufacturing a semiconductor device according to  claim 1 , wherein the first conductive layer includes aluminum. 
     
     
         4 . The method for manufacturing a semiconductor device according to  claim 1 , wherein the second conductive layer includes at least one selected from the group consisting of titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium. 
     
     
         5 . The method for manufacturing a semiconductor device according to  claim 1 , wherein the oxidizing step is one of an oxygen plasma treatment, an ozone treatment using ultraviolet light, and a treatment using hydrogen peroxide. 
     
     
         6 . A method for manufacturing a semiconductor device, comprising the steps of:
 forming a source electrode layer and a drain electrode layer, each comprising a first conductive layer and a second conductive layer over the first conductive layer;   oxidizing an edge portion of the first conductive layer;   forming an oxide semiconductor layer to be in contact with the edge portion;   performing a plasma treatment on the oxide semiconductor layer in an atmosphere containing N 2 O;   forming a gate insulating film over the oxide semiconductor layer; and   forming a gate electrode over the gate insulating film.   
     
     
         7 . The method for manufacturing a semiconductor device according to  claim 6 , wherein the oxide semiconductor layer includes indium, gallium, and zinc. 
     
     
         8 . The method for manufacturing a semiconductor device according to  claim 6 , wherein the first conductive layer includes aluminum. 
     
     
         9 . The method for manufacturing a semiconductor device according to  claim 6 , wherein the second conductive layer includes at least one selected from the group consisting of titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium. 
     
     
         10 . The method for manufacturing a semiconductor device according to  claim 6 , wherein the oxidizing step is one of an oxygen plasma treatment, an ozone treatment using ultraviolet light, and a treatment using hydrogen peroxide.