Method of forming channel in thin film transistor using non-ionic excited species

Abstract

In the production of channel etch type bottom gate thin film transistors, etching damage in a channel etch step is prevented to improve the transistor performance. The channel etch is performed using non-ionic excited species, such as hydrogen radicals and fluorine radicals, generated by contact-decomposition reaction which utilizes a metal heated by electric resistance heating. Alternatively, in place of the channel etch, a portion of the source/drain semiconductor thin film immediately above the channel is nitrided by a non-ionic nitrogen-containing decomposition product that is produced by contacting molecules of a chemical substance containing nitrogen atoms with a metal heated by electric resistance heating to decompose the chemical molecules.

What is claimed is;  
     
         1 . A method of producing a bottom gate thin film transistor, comprising the steps of: 
 forming a gate electrode on an insulating substrate;    forming a gate insulating film over the gate electrode;    forming a first semiconductor thin film for a channel over the gate insulating film;    forming a second semiconductor thin film for a source and a drain over the first semiconductor thin film;    processing stacked layers of the first semiconductor thin film and the second semiconductor thin film so as to be formed into an island;    subsequent to the step of processing stacked layers, depositing a source/drain electrode metal over the stacked layers of the first semiconductor thin film and the second semiconductor thin film;    etching a region of the deposited source/drain electrode metal, the region being located above the channel, in the depth direction to expose the second semiconductor thin film, whereby a source electrode and a drain electrode are formed; and    etching away the exposed portion of the second semiconductor thin film in the depth direction with the use of a non-ionic excited species to form a channel.    
     
     
         2 . The method according to  claim 1 , wherein the non-ionic excited species is generated by bringing molecules of a chemical substance into contact with a metal heated by electric resistance heating to decompose the molecules of the chemical substance.  
     
     
         3 . The method according to  claim 2 , wherein the non-ionic excited species is a radical.  
     
     
         4 . The method according to  claim 3 , wherein the metal is selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium, or is an alloy comprising at least two metals selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium.  
     
     
         5 . The method according to  claim 4 , further comprising, subsequent to the step of etching away the exposed portion of the second semiconductor thin film, forming a passivation film comprising a silicon nitride film in such a manner that the etched surface is not exposed to atmosphere.  
     
     
         6 . The method according to  claim 5 , wherein the first semiconductor thin film is a thin film comprising silicon; and the second semiconductor thin film is a thin film comprising silicon and an n-type impurity.  
     
     
         7 . The method according to  claim 6 , wherein the silicon comprises amorphous silicon or polycrystalline silicon.  
     
     
         8 . The method according to  claim 1 , wherein the non-ionic excited species is a non-Ionic radical.  
     
     
         9 . The method according to  claim 1 , further comprising, subsequent to the step of etching away the exposed portion of the second semiconductor thin film, forming a passivation film composed of a silicon nitride film in such a manner that the etched surface is not exposed to atmosphere.  
     
     
         10 . The method according to  claim 2 , wherein the metal is selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium, or is an alloy comprising at least two metals selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium.  
     
     
         11 . The method according to  claim 3 , wherein the molecules of the chemical substance comprise hydrogen, ammonia, or a mixture thereof.  
     
     
         12 . The method according to  claim 3 , wherein the non-ionic radical is a hydrogen radical.  
     
     
         13 . The method according to  claim 3 , wherein the non-ionic radical is a halogen radical.  
     
     
         14 . The method according to  claim 13 , wherein the non-ionic halogen radical is a fluorine radical.  
     
     
         15 . The method according to  claim 1 , wherein the step of etching is such that the excited species is generated in a microwave plasma generating chamber provided in isolation from an etching chamber in which the etching is performed, and from the generated excited species, only non-ionic excited species are selected and introduced into the etching chamber.  
     
     
         16 . The method according to  claim 15 , wherein the selected non-ionic excited species is a non-ionic radical.  
     
     
         17 . The method according to  claim 15 , further comprising, subsequent to the step of etching away the exposed portion of the second semiconductor thin film, forming a passivation film comprising a silicon nitride film in such a manner that the etched surface is not exposed to atmosphere.  
     
     
         18 . A method of producing a bottom gate thin film transistor, comprising the steps of: 
 forming a gate electrode on an insulating substrate;    forming a gate insulating film over the gate electrode;    forming a first semiconductor thin film for a channel over the gate insulating film;    forming a second semiconductor thin film for a source and a drain over the first semiconductor thin film;    processing stacked layers of the first semiconductor thin film and the second semiconductor thin film into an island;    subsequent to the step of processing stacked layers, depositing a source/drain electrode metal over the stacked layers;    etching a region of the deposited source/drain electrode metal, the region being located above the channel, in the depth direction to expose the second semiconductor thin film, whereby a source electrode and a drain electrode are formed; and    nitriding the exposed portion of the second semiconductor thin film using a non-ionic nitrogen-containing decomposition product that is produced by decomposing molecules of a chemical substance containing nitrogen atoms.    
     
     
         19 . The method according to  claim 18 , wherein the non-ionic nitrogen-containing decomposition product is generated by bringing a metal heated by electric resistance heating into contact with the molecules of the chemical substance containing nitrogen atoms.  
     
     
         20 . The method according to  claim 19 , wherein the molecules of the chemical substance comprise ammonia.  
     
     
         21 . The method according to  claim 19 , wherein the metal is selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium, or is an alloy comprising at least two metals selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium.  
     
     
         22 . The method according to  claim 19 , wherein the first semiconductor thin film is a thin film comprising silicon; and the second semiconductor thin film is a thin film comprising silicon and an n-type impurity.  
     
     
         23 . The method according to  claim 22 , wherein the silicon comprises amorphous silicon or polycrystalline silicon.  
     
     
         24 . A bottom gate thin film transistor comprising: 
 a gate electrode formed on an insulating substrate;    a gate insulating film formed over the gate electrode;    a channel comprising a first semiconductor thin film stacked over the gate insulating film;    a source region and a drain region each comprising a second semiconductor thin film that is stacked over a region of the first semiconductor thin film exclusive of the channel;    a source electrode and a drain electrode formed on the second semiconductor thin film; and    a passivation film composed of a silicon nitride film formed on the channel;    wherein a portion of the channel contains at least one element selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium, the portion of the channel being adjacent to a surface thereof which is in contact with the silicon nitride film; and the total atomic density of the at least one element is in the range of from 1×10 16 ·cm −3  to 1×10 19 ·cm −3 .    
     
     
         25 . The bottom gate thin film transistor according to  claim 24 , wherein the first semiconductor thin film is a thin film comprising silicon; and the second semiconductor thin film is a thin film comprising silicon and an n-type impurity.  
     
     
         26 . The bottom gate thin film transistor according to  claim 25 , wherein the silicon comprises amorphous silicon or polycrystalline silicon.  
     
     
         27 . A bottom gate thin film transistor comprising: 
 a gate electrode formed on an insulating substrate;    a gate insulating film formed over the gate electrode;    a channel formed of a first semiconductor thin film stacked over the gate insulating film;    a source and a drain each formed of a second semiconductor thin film stacked over the first semiconductor thin film;    a nitrided region in which a portion of the second semiconductor thin film disposed immediately above the channel is nitrided; and    a source electrode and a drain electrode, each formed on a portion of the second semiconductor thin film exclusive of the nitrided region;    wherein a portion of the channel contains at least one element selected from the group consisting of tungsten, tantalum, molybdenum, vanadium, platinum, and thorium, the portion of the channel being adjacent to a surface thereof which faces the nitrided region; and the total atomic density of the at least one element is in the range of from 1×10 16 ·cm −3  to 1×10 19 ·cm −3 .    
     
     
         28 . The bottom gate thin film transistor according to  claim 27 , wherein the first semiconductor thin film is a thin film comprising silicon; and the second semiconductor thin film is a thin film comprising silicon and an n-type impurity.  
     
     
         29 . The bottom gate thin film transistor according to  claim 28 , wherein the silicon comprises amorphous silicon or polycrystalline silicon.  
     
     
         30 . A liquid crystal display device comprising: 
 a first substrate comprising a plurality of scan electrodes, a plurality of data electrodes intersecting the scan electrodes, a plurality of thin film transistors provided at the intersectional positions of the scan electrodes and the data electrodes so that at least one of the plurality of thin film transistors is provided at each of the intersectional positions, and a plurality of pixel electrodes connected to the thin film transistors;    a second substrate comprising a counter electrode opposed to the pixel electrodes; and    a liquid crystal sandwiched between the first substrate and the second substrate;    wherein each of the thin film transistors is a bottom gate thin film transistor according to any one of  claims 24  to  29 .    
     
     
         31 . An organic electroluminescent display device comprising: 
 a first substrate comprising a plurality of scan electrodes, a plurality of data electrodes intersecting the scan electrodes, a plurality of thin film transistors provided at the intersectional positions of the scan electrodes and the data electrodes so that at least one of the thin film transistors is provided at each of the intersectional positions, and a plurality of pixel electrodes connected to the thin film transistors;    a second substrate comprising a counter electrode opposed to the pixel electrodes; and    a layer comprising an organic electroluminescent material, the layer being sandwiched between the first substrate and the second substrate;    wherein each of the thin film transistors is a bottom gate thin film transistor according to any one of  claims 24  to  29 .