Thin film transistor, manufacturing method of same, and display device

Abstract

According to one embodiment, a thin film transistor includes: a substrate; a semiconductor layer; first and second insulating films; and gate, source and drain electrodes. The semiconductor layer is provided on the substrate. The semiconductor layer is made of an oxide having indium. The semiconductor layer has first and second regions and other region. The first insulating film covers a top face of the other region. The second insulating film covers at least a pair of side surfaces of the semiconductor layer. The second insulating film is formed under a condition different from that for the first insulating film. The gate electrode is provided on the first and second insulating films or below the semiconductor layer. The source and drain electrodes are provided on the first and second regions, respectively. The drain and source electrodes sandwich the pair of the side surfaces of the semiconductor layer.

1 . A thin film transistor comprising:
 a substrate;   a semiconductor layer provided on the substrate, the semiconductor layer being made of an oxide having indium for a main component, the semiconductor layer having a top face facing the substrate and a pair of side face, the top face having a first region, a second region, and an other region except the first region and the second region;   a first insulating film covering the other region of the semiconductor layer;   a second insulating film covering at least the pair of side surfaces of the semiconductor layer, the second insulating film being formed under a condition different from a condition for the first insulating film;   a gate electrode provided on the first insulating film and the second insulating film or provided below the semiconductor layer;   a source electrode provided on the first region; and   a drain electrode provided on the second region, the drain electrode facing the source electrode, the drain electrode and the source electrode sandwiching the pair of the side surfaces of the semiconductor layer.   
     
     
         2 . The transistor according to  claim 1 , wherein the second insulating film is formed using conditions including at least one of:
 a flow ratio smaller than a flow ratio of a source gas in forming the first insulating film;   a film forming rate smaller than a film forming rate in forming the first insulating film; and   a film forming temperature lower than a film forming temperature in forming the first insulating film.   
     
     
         3 . The transistor according to  claim 1 , wherein the second insulating film includes silicon oxide. 
     
     
         4 . The transistor according to  claim 1 , further comprising a gate insulating layer,
 the gate electrode being provided between the substrate and the semiconductor layer, and   the gate insulating layer being provided between the gate electrode and the semiconductor layer.   
     
     
         5 . The transistor according to  claim 4 , wherein a distance between the pair of the side surfaces is shorter than a width of the gate electrode along a first direction from one of the pair of the side surfaces toward the other of the pair of the side surfaces. 
     
     
         6 . The transistor according to  claim 5 , wherein a distance between the pair of the side surfaces is longer than a width along the direction of the first insulating film. 
     
     
         7 . The transistor according to  claim 1 , wherein the gate electrode is provided on at least one of the first insulating film and the second insulating film. 
     
     
         8 . The transistor according to  claim 1 , wherein the second insulating film further covers at least a part of the first insulating film. 
     
     
         9 . The transistor according to  claim 1 , wherein the second insulating film includes a resin containing fluorine at a concentration of 5 wt % or more. 
     
     
         10 . The transistor according to  claim 1 , wherein the semiconductor layer further contains at least one of gallium (Ga), zinc (Zn), tin (Sn), and silicon (Si). 
     
     
         11 . The transistor according to  claim 1 , wherein a thickness of the first insulating film is 10 nanometer or more. 
     
     
         12 . The transistor according to  claim 1 , wherein a thickness of the first insulating film is 50 nanometers or less. 
     
     
         13 . The transistor according to  claim 1 , wherein an oxygen concentration of the second insulating film is higher than an oxygen concentration of the first insulating film. 
     
     
         14 . The transistor according to  claim 1 , wherein
 the first insulating film is formed with a gas containing silicon and oxygen with a first value of a ratio of a silicon quantity to an oxygen quantity; and   the second insulating film is formed with a gas containing silicon and oxygen with a second value of a ratio of a silicon quantity to an oxygen quantity, the second value being lower than the first value.   
     
     
         15 . The transistor according to  claim 1 , wherein
 the first insulating film is formed using a SiH 4  gas and a N 2 O gas with a first value of a ratio of a SiH 4  gas flow rate to a N 2 O gas flow rate; and   the second insulating film is formed using a SiH 4  gas and a N 2 O gas with a second value of a ratio of a SiH 4  gas flow rate to a N 2 O gas flow rate, the second value being lower than the first value.   
     
     
         16 . A manufacturing method for a thin film transistor, comprising:
 processing including:
 forming a semiconductor layer made of an oxide having indium for a main component on a gate electrode on a substrate via a gate insulating layer, forming a first insulating film on a top face except a source electrode contact region and a drain electrode contact region of the semiconductor layer, and forming a second insulating film covering at least a pair of side surfaces of the semiconductor layer under a condition different from a condition for the first insulating film; or 
 forming a semiconductor layer made of an oxide having indium for a main component on a substrate, forming a first insulating film on a top face except a source electrode contact region and a drain electrode contact region of the semiconductor layer, forming a second insulating film covering at least a pair of side surfaces of the semiconductor layer under a condition different from a condition for the first insulating film, and forming a gate electrode on the second insulating film; 
   forming a source electrode on the source electrode contact region of the semiconductor layer; and   forming a drain electrode on the drain electrode contact region of the semiconductor layer so as to face the source electrode to sandwich a part of the side surfaces of the semiconductor layer.   
     
     
         17 . The method according to  claim 16 , wherein the forming the second insulating film includes using conditions including at least one of:
 a flow rate of a gas containing Si, the flow rate being smaller than a flow rate of a source gas containing Si in the forming the first insulating film;   a film forming rate smaller than a film forming rate in the forming the first insulating film; and   a film forming temperature lower than a film forming temperature in the forming the first insulating film.   
     
     
         18 . The method according to  claim 16 , wherein,
 annealing at a highest temperature in forming process of the thin film transistor for 10 minutes or more is performed after the forming the second insulating film; or   annealing at the highest temperature in forming process of the thin film transistor for 10 minutes or more is performed in the forming the second insulating film.   
     
     
         19 . The method according to  claim 16 , wherein the semiconductor layer is formed by processing performed after being formed on the substrate and annealed. 
     
     
         20 . A display device comprising:
 a thin film transistor including:
 a substrate; 
 a semiconductor layer provided on the substrate, the semiconductor layer being made of an oxide having indium for a main component, the semiconductor layer having a top face facing the substrate and a pair of side face, the top face having a first region, a second region, and an other region except the first region and the second region; 
 a first insulating film covering the other region of the semiconductor layer; 
 a second insulating film covering at least the pair of side surfaces of the semiconductor layer, the second insulating film being formed under a condition different from a condition for the first insulating film; 
 a gate electrode provided on the first insulating film and the second insulating film or below the semiconductor layer; 
 a source electrode provided on the first region; and 
 a drain electrode provided on the second region, the drain electrode facing the source electrode, the drain electrode and the source electrode sandwiching the pair of the side surfaces of the semiconductor layer; and 
   a display layer configured to cause at least one of optical emission and a change in an optical property including at least one of birefringence, optical activity, scattering property, diffraction property, and optical absorption, according to at least one of a voltage and a current supplied through the thin film transistor.