Thin film transistor device and method of manufacturing the same, and liquid crystal display device

Abstract

The present invention relates to a thin film transistor device formed on an insulating substrate of a liquid crystal display device and others, a method of manufacturing the same, and a liquid crystal display device. In structure, there are provided the steps of forming a negative photoresist film on a first insulating film for covering a first island-like semiconductor film, forming a resist mask that has an opening portion in an inner region with respect to a periphery of the first island-like semiconductor film by exposing/developing the negative photoresist film from a back surface side of a transparent substrate, etching the first insulating film in the opening portion of the resist mask, forming a second insulating film for covering the first insulating film and a conductive film thereon, and forming a first gate electrode and a second gate electrode by patterning the conductive film.

1 . A thin film transistor device manufacturing method comprising the steps of: 
 forming a first island-like semiconductor film and a second island-like semiconductor film on a surface of a transparent substrate;    forming a first insulating film for covering the first island-like semiconductor film and the second island-like semiconductor film;    forming a negative photoresist film on the first insulating film;    exposing the negative photoresist film via a mask that shields an overall region of the first island-like semiconductor film from a light;    exposing the negative photoresist film from a back surface side of the transparent substrate;    forming a resist pattern, which has an opening portion in an inner region with respect to a periphery of the first island-like semiconductor film, by developing the negative photoresist film;    etching the first insulating film in the opening portion of the resist pattern;    removing the resist pattern;    forming a second insulating film on an overall surface of the transparent substrate on a surface side and then forming a conductive film thereon;    forming a first mask pattern on the conductive film over the first island-like semiconductor film and forming a second mask pattern on the conductive film over the second island-like semiconductor film; and    forming a first gate electrode by etching the conductive film while using the first mask pattern as a mask and forming a second gate electrode by etching the conductive film while using the second mask pattern as a mask.    
     
     
         2 . A thin film transistor device manufacturing method according to  claim 1 , wherein, in the step of exposing the negative photoresist film from the back surface side of the transparent substrate, a light employed in exposure is a g-line, an h-line, an i-line, an excimer laser or a UV light.  
     
     
         3 . A thin film transistor device manufacturing method comprising the steps of: 
 forming a first island-like semiconductor film and a second island-like semiconductor film on a substrate;    forming a semiconductor film for covering the first island-like semiconductor film and the second island-like semiconductor film, and then forming an insulating film on the semiconductor film;    forming a pattern of the insulating film by selectively etching the insulating film over the second island-like semiconductor film;    oxidizing the semiconductor film under the pattern of the insulating film and in other regions to form a first gate insulating film consisting of an insulating film, which is made by oxidizing the semiconductor film, on the first island-like semiconductor film and to form a second gate insulating film consisting of an insulating film, which is made by oxidizing the semiconductor film, and the pattern of the insulating film on the second island-like semiconductor film; and    forming a first gate electrode on the first gate insulating film and forming a second gate electrode on the second gate insulating film.    
     
     
         4 . A thin film transistor device manufacturing method according to  claim 3 , wherein the first island-like semiconductor film and the second island-like semiconductor film are formed of a polysilicon film, and the semiconductor film is made of an amorphous silicon film.  
     
     
         5 . A thin film transistor device manufacturing method according to  claim 3 , wherein, in the step of forming a pattern of the insulating film by selectively etching the insulating film over the second island-like semiconductor film, the semiconductor film is used as an etching stopper in etching the insulating film.  
     
     
         6 . A thin film transistor device manufacturing method according to  claim 3 , further comprising the step of: 
 forming an insulating film for covering the first island-like semiconductor film and the second island-like semiconductor film, prior to formation of the semiconductor film;    wherein the first gate insulating film consists of an insulating film for covering the first island-like semiconductor film and an insulating film made by oxidizing the semiconductor film, and the second gate insulating film consists of an insulating film for covering the second island-like semiconductor film, an insulating film made by oxidizing the semiconductor film, and the pattern of the insulating film.    
     
     
         7 . A thin film transistor device manufacturing method comprising the steps of: 
 forming a first semiconductor film on a substrate;    forming sequentially a first insulating film, a second semiconductor film, and a second insulating film on the first semiconductor film;    forming a pattern of the second insulating film by selectively etching the second insulating film;    selectively etching the second semiconductor film to form an island-like second semiconductor film that does not contain the pattern of the second insulating film and an island-like second semiconductor film that contains the pattern of the second insulating film;    oxidizing the island-like second semiconductor film under the pattern of the second insulating film and other region and also oxidizing the first semiconductor film in a region, which is not covered with the island-like second semiconductor film, via the first insulating film, so as to form a first island-like semiconductor film consisting of the first semiconductor film in a region, which is covered with an island-like second semiconductor film that does not contain the pattern of the second insulating film, and also form a second island-like semiconductor film consisting of the first semiconductor film in a region, which is covered with the island-like second semiconductor film that contains the pattern of the second insulating film, and so as to form a first gate insulating film consisting of an insulating film, which is made by oxidizing the second semiconductor film, and the first insulating film on the first island-like semiconductor film, and also form a second gate insulating film consisting of the pattern of the second insulating film, an insulating film, which is made by oxidizing the second semiconductor film, and the first insulating film on the second island-like semiconductor film; and    forming a first gate electrode on the first gate insulating film and forming a second gate electrode on the second gate insulating film.    
     
     
         8 . A thin film transistor device manufacturing method according to  claim 7 , wherein the first semiconductor film is a polysilicon film, and the second semiconductor film is an amorphous silicon film.  
     
     
         9 . A thin film transistor device manufacturing method according to  claim 7 , wherein, in the step of forming a pattern of the second insulating film by selectively etching the second insulating film, the second semiconductor film is used as an etching stopper in etching the second insulating film.  
     
     
         10 . A thin film transistor device manufacturing method according to  claim 7 , wherein, in the step of selectively etching the second semiconductor film to form an island-like second semiconductor film that does not contain the pattern of the second insulating film and an island-like second semiconductor film that contains the pattern of the second insulating film, the first insulating film is used as an etching stopper in selectively etching the second semiconductor film.  
     
     
         11 . A thin film transistor device comprising: 
 a first thin film transistor including a first island-like semiconductor film having a pair of source/drain regions that are formed to put a channel region therebetween, a first gate insulating film made of a first insulating film formed on the channel region of the first island-like semiconductor film, and a first gate electrode made of a first conductive film formed on the first gate insulating film; and    a second thin film transistor including a second island-like semiconductor film having a pair of source/drain regions that are formed to put a channel region therebetween, a second gate insulating film made of the first insulating film and a second insulating film formed on the channel region of the second island-like semiconductor film, and a second gate electrode made of a second conductive film formed on the second gate insulating film, both the first thin film transistor and the second thin film transistor being formed on a same substrate;    wherein the first thin film transistor has electric- field relaxation electrodes that are formed of the second conductive film over edges of the first island-like semiconductor film on side portions and on the first gate electrode via the second insulating film, and    the second thin film transistor has electric-field relaxation electrodes that are formed of the first conductive film under the second gate electrode and on edges of the second island-like semiconductor film on side portions via the first insulating film.    
     
     
         12 . A thin film transistor device manufacturing method comprising the steps of: 
 forming a first island-like semiconductor film and a second island-like semiconductor film on a substrate;    forming a first insulating film for covering the first island-like semiconductor film and the second island-like semiconductor film;    forming a first conductive film on an overall surface, and then selectively etching the first conductive film so as to form a first gate electrode on the first insulating film over the first island-like semiconductor film;    forming sequentially a second insulating film and a second conductive film on an overall surface;    forming a mask pattern on the second conductive film, and then side-etching the second conductive film while using the mask pattern as a mask so as to form a second gate electrode, which is narrower in width than the mask pattern;    applying an anisotropic etching to the second insulating film while using the mask pattern as a mask and also applying the anisotropic etching to the first insulating film while using the first gate electrode and the mask pattern as a mask so as to thus form a first gate insulating film made of the first insulating film under the first gate electrode and also form a second gate insulating film consisting of the first insulating film and the second insulating film under the second gate electrode;    removing the mask pattern;    forming high-concentration impurity regions on both sides of the first gate electrode by ion-implanting an impurity into the first island-like semiconductor film while using the first gate electrode as a mask, and also forming a pair of high-concentration impurity regions on both sides of the second gate electrode by ion-implanting the impurity into the second island-like semiconductor film while using the second gate electrode and the second gate insulating film as a mask; and    forming a pair of low-concentration impurity regions under the second gate insulating film on both sides of the second gate electrode by ion-implanting the impurity into the second island-like semiconductor film while using the second gate electrode as a mask and under a condition that the ion can transmit through the second gate insulating film in a peripheral portion of the second gate electrode.    
     
     
         13 . A thin film transistor device manufacturing method according to  claim 12 , wherein, in the step of applying an anisotropic etching to the second insulating film while using the mask pattern as a mask and also applying the anisotropic etching to the first insulating film while using the first gate electrode and the mask pattern as a mask, the first insulating film is left such that the first island-like semiconductor film and the second island-like semiconductor film are covered with the first insulating film.  
     
     
         14 . A thin film transistor device manufacturing method according to  claim 12 , wherein, in the step of forming a first conductive film on an overall surface and then selectively etching the first conductive film so as to form a first gate electrode on the first insulating film over the first island-like semiconductor, electric-field relaxation electrodes made of the first conductive film are formed in a region in which the second gate electrode is to be formed and on edges of the second island-like semiconductor film on both sides via the first insulating film.  
     
     
         15 . A thin film transistor device manufacturing method according to  claim 12 , wherein, in the step of forming a mask pattern on the second conductive film, and then side-etching the second conductive film while using the mask pattern as a mask so as to form a second gate electrode, which is narrower in width than the mask pattern, electric-field relaxation electrodes made of the second conductive film are formed over edges of the first island-like semiconductor film on both sides and the first gate electrode via the second insulating film.  
     
     
         16 - 19 . (canceled)