Thin film transistor and producing method thereof

Abstract

In producing a thin film transistor used for such devices as a large-sized liquid crystal display panel with a high pixel density, a leftover of an insulating film caused by insufficient etching and a loss of a semiconductor layer caused by overetching are prevented, and a reliable electrical contact between the source and drain electrodes and the semiconductor layer is achieved. These are achieved by (a) forming a contact hole region of a silicon film so that the region has a larger thickness, for example, by making the film to have a plurality of layers, and (b) providing a suicide layer between an electrode metal and the semiconductor layer.

What is claimed is:  
     
         1 . A method of producing a thin film transistor formed on a substrate, said thin film transistor comprising a semiconductor thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate insulating film, a source electrode, and a drain electrode, each of the source electrode and the drain electrode being connected with the semiconductor thin film via a contact hole, said method comprising: 
 a step of increasing a thickness of the semiconductor thin film in at least a region where the contact hole is to be formed for connecting the semiconductor thin film with one of the source electrode and the drain electrode, so that the region where the contact hole is to be formed has a larger thickness than a thickness of the semiconductor thin film in the channel region.    
     
     
         2 . A method of producing a thin film transistor according to  claim 1 , in which said step of increasing a thickness of the semiconductor thin film comprises: 
 a step of increasing a thickness of the semiconductor thin film by repeating a plurality of times a step of forming the semiconductor thin film, so that the thickness of the semiconductor thin film in the region in which the contact hole is to be formed results in larger than a thickness of the other region of the semiconductor thin film.    
     
     
         3 . A method of producing a thin film transistor comprising the steps of: 
 forming a first semiconductor thin film in only each position corresponding to a source electrode and a drain electrode on a substrate,    selectively forming a second semiconductor thin film in a region where the thin film transistor is desired, the second semiconductor thin film formed over the first semiconductor thin film,    forming a gate insulating film over the second semiconductor thin film,    forming a gate electrode on the gate insulating film,    forming an interlayer dielectric layer over the gate insulating film and the gate electrode,    forming a contact hole by dry etching in a position in the gate insulating film and the interlayer dielectric layer corresponding to each of the source electrode and the drain electrode to be formed, and    forming the source electrode and the drain electrode so that the electrodes are connected with the semiconductor thin film via the contact hole.    
     
     
         4 . A method of producing a thin film transistor comprising the steps of: 
 forming a gate electrode in a predetermined position on a substrate,    forming a gate insulating film over the gate electrode,    forming a first semiconductor thin film in only each position corresponding to a source electrode and a drain electrode,    selectively forming a second semiconductor thin film over the first semiconductor thin film,    forming an interlayer dielectric layer over the second semiconductor thin film,    forming a contact hole by dry etching in each position in the interlayer dielectric layer corresponding to the source electrode and the drain electrode, and    forming the source electrode and the drain electrode so that the electrodes are connected with the semiconductor thin film via the contact hole.    
     
     
         5 . A method of producing a thin film transistor comprising the steps of: 
 forming a first semiconductor thin film in a predetermined position on a substrate,    forming a second semiconductor thin film in only each position in the first semiconductor thin film corresponding to a source electrode and a drain electrode,    forming a gate insulating film over the first and second semiconductor thin films,    forming a gate electrode on the gate insulating film,    forming an interlayer dielectric layer over the gate insulating film and the gate electrode,    forming a contact hole by dry etching in each of the positions in the gate insulating film and the interlayer dielectric layer corresponding to the source electrode and the drain electrode, and    forming the source electrode and the drain electrode so that electrodes are connected with the semiconductor thin film via the contact hole.    
     
     
         6 . A method of producing a thin film transistor comprising the steps of: 
 forming a gate electrode in a predetermined position on a substrate,    forming a gate insulating film over the gate electrode,    forming a first semiconductor thin film over the gate electrode,    forming a second semiconductor thin film in only each position in the first semiconductor thin film corresponding to a source electrode and a drain electrode,    forming an interlayer dielectric layer over the second semiconductor thin film,    forming a contact hole by dry etching in each of the positions in the interlayer dielectric layer corresponding to the source electrode and the drain electrode, and    forming the source electrode and the drain electrode so that the source electrode and the drain electrode are connected with the semiconductor thin film via the contact hole.    
     
     
         7 . A method of producing a thin film transistor comprising the steps of: 
 forming a semiconductor thin film having a thickness larger than a required thickness,    reducing the thickness of the semiconductor thin film in an excessive region except each region corresponding to a source electrode and a drain electrode, so that a thickness of the excessive region except each region corresponding to a source electrode and a drain electrode results in the required thickness,    forming a gate insulating film over the semiconductor thin film,    forming a gate electrode on the gate insulating film,    forming an interlayer dielectric layer over the gate electrode and the gate insulating film,    forming a contact hole by dry etching in each of the positions in the interlayer dielectric layer corresponding to the source electrode and the drain electrode, and    forming the source electrode and the drain electrode so that the electrodes are connected with the semiconductor thin film via the contact hole.    
     
     
         8 . A method of producing a thin film transistor comprising the steps 
 forming a gate electrode in a predetermined position on a substrate,    forming a gate insulating film over the gate electrode,    forming a semiconductor thin film having a thickness larger than a required thickness,    reducing the thickness of the semiconductor thin film in a region except each of the regions corresponding to a source electrode and a drain electrode to be formed, so that a thickness of the region except each of the corresponding regions results in the required thickness,    forming an interlayer dielectric layer over the semiconductor thin film,    forming a contact hole by dry etching in each of the positions in the interlayer dielectric layer corresponding to the source electrode and the drain electrode, and    forming the source electrode and the drain electrode so that electrodes are connected with the semiconductor thin film via the contact hole.    
     
     
         9 . A thin film transistor formed on a substrate, comprising a semiconductor thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate electrode, a gate insulating film, a source electrode, and a drain electrode, the electrodes being connected with the semiconductor thin film via a contact hole, said thin film transistor wherein: 
 a thickness of the semiconductor thin film in a region where the contact hole for connecting the semiconductor thin film with one of the source electrode and the drain electrode is to be formed, is larger than a thickness of the semiconductor thin film in the channel region.    
     
     
         10 . A thin film transistor according to  claim 9 , wherein said semiconductor thin film is composed of one of silicon, silicon-germanium, and silicon-germanium-carbon.  
     
     
         11 . A method of producing a thin film transistor comprising on a substrate, a gate electrode, a source electrode, a drain electrode, and a semiconductor film wherein a channel region, a source region and a drain region are provided, said method comprising a step of forming a silicide layer between the semiconductor film and each of the source electrode and the drain electrode.  
     
     
         12 . A method of producing a thin film transistor according to  claim 11 , wherein the silicide layer comprises a silicide of at least one metal selected from the group consisting of titanium, nickel, platinum, and cobalt.  
     
     
         13 . A method of producing a thin film transistor according to  claim 11 , wherein: 
 each of the source electrode and the drain electrode comprises a plurality of metal layers,    a step of forming an undermost layer of the plurality of metal layers is performed prior to the step of forming a silicide layer, the undermost layer being formed in each of the positions where the source electrode and the drain electrode are to be formed, and the undermost layer being a metal layer composed of at least one metal selected from the group consisting of titanium, nickel, platinum, and cobalt, and    the step of forming a silicide layer comprises a step of reacting the metal in the undermost layer with silicon in the silicon film.    
     
     
         14 . A method of producing a thin film transistor comprising the steps of: 
 forming a silicon film in a predetermined region on a substrate,    forming a gate insulating film on an entire area of the silicon film,    forming a first metal film by removing a portion of the gate insulating film located in each position where a source electrode and a drain electrode are to be formed and thereafter forming a first metal film on an entire area of the substrate,    forming a silicide layer in a region where the first metal film is directly in contact with the silicon film, by reacting the first metal film with the silicon film with heat,    forming an interlayer dielectric layer, by firstly removing the first metal film, thereafter forming, in a position on the silicon film where a gate electrode is to be formed, a second metal film composed of a metal resistant to an etching gas for etching the interlayer dielectric layer, and thereafter forming the interlayer dielectric layer on the entire area of the substrate,    forming a contact hole by dry etching the interlayer dielectric layer utilizing the silicide layer and the second metal film as an etch stopper, so as to provide the contact hole in each of the positions corresponding to the gate electrode, the source electrode, and the gate electrode, and    forming a third metal film on the entire area of the substrate and thereafter removing an excessive portion of the third metal film to form the gate electrode, the source electrode, and the drain electrode or an undermost layer thereof.    
     
     
         15 . A method of producing a thin film transistor according to  claim 14 , wherein said silicon film is so formed as to have a thickness of 650 Å or less in the step of forming a silicon film, and the contact hole is so formed that a diameter of an undermost portion of the contact hole results in 4 μm or smaller in said step of forming a contact hole.  
     
     
         16 . A method of producing a thin film transistor according to  claim 15 , wherein the same metal as a metal composing the first metal film is selected for a material for the third metal film prior to the step of forming a contact hole.  
     
     
         17 . A method of producing a thin film transistor comprising the steps of: 
 forming a gate electrode in a predetermined position on a substrate,    forming a gate insulating film over the gate electrode,    forming a silicon film in a predetermined position on the gate insulating film,    forming a first metal film in only each position corresponding to a source electrode and a drain electrode,    forming a silicide layer in a region where the first metal film is directly in contact with the silicon film by reacting the first metal film with the silicon film with heat,    forming an interlayer dielectric layer in an entire area of the silicon film,    forming a contact hole by dry etching the interlayer dielectric layer using the silicide layer as an etching stopper, so as to provide the contact hole in each position corresponding to the source electrode and the gate electrode, and    forming a second metal film on an entire area of the substrate and thereafter removing an excessive portion of the second metal film to form the source electrode and the drain electrode or an undermost layer thereof.    
     
     
         18 . A method of producing a thin film transistor according to  claim 17 , wherein the silicon film is so formed as to have a thickness of 650 Å or less in the step of forming a silicon film, and the contact hole is so formed that a diameter of an undermost portion of the contact hole results in 4 μm or smaller in the step of forming a contact hole.  
     
     
         19 . A method of producing a thin film transistor according to  claim 18 , wherein the same metal as the first metal film is selected for a material for the third metal film prior to said step of forming a contact hole.  
     
     
         20 . A method of producing a thin film transistor comprising the steps of: 
 forming a silicon film in a predetermined position on a substrate,    forming a silicide layer between a first metal film and the silicon film by forming the first metal film in only each position corresponding to a source electrode and a drain electrode on the substrate, and thereafter reacting the first metal film with the silicon film,    forming an insulating film over an entire area of the silicon film, and a second metal film comprising a metal unetched by an etching gas used for etching the insulating film,    forming an interlayer dielectric layer by etching the second metal film except in a position corresponding to a gate electrode, and thereafter forming the interlayer dielectric layer in an entire area of the substrate,    forming a contact hole in each position corresponding to a gate electrode, the source electrode, and the drain electrode, by dry etching the interlayer dielectric layer utilizing the silicide layer and the second metal film left unetched in the position corresponding to the gate electrode as an etch stop,    forming a third metal film on the entire area of the substrate and thereafter removing an excessive portion of the third metal fill to form the gate electrode, the source electrode, and the drain electrode.    
     
     
         21 . A method of producing a thin film transistor according to  claim 20 , wherein said silicon film is so formed as to have a thickness of 650 Å or less in the step of forming a silicon film, and the contact hole is so formed that a diameter of an undermost portion of the contact hole results in 4 μm or smaller in said step of forming a contact hole.  
     
     
         22 . A method of producing a thin film transistor according to  claim 21 , wherein the same metal as the first metal film is selected for a material for the third metal film prior to said step of forming a contact hole.  
     
     
         23 . A method of producing a thin film transistor formed on a substrate, said thin film transistor comprising a silicon thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate insulating film, a source electrode, and a drain electrode, the source electrode and the drain electrode being connected with the silicon thin film via a silicide layer in a contact hole formed in the interlayer dielectric layer and the gate insulating film, said method comprising the steps of: 
 forming a first metal film in a position corresponding to a gate electrode in the gate insulating film after forming a silicide in the contact hole, the first metal film consisting of the same metal as a metal composing the silicide layer and being the undermost layer of the gate electrode with a multiple-layer structure,    forming a second metal film over the first metal film, the second metal film being a second layer in the gate electrode with a multiple-layer structure, having a predetermined thickness, and consisting of a metal which is not etched by an etching gas for the interlayer dielectric layer,    forming the gate electrode serving as a mask, by removing an excessive portion of the first metal film and the second metal film so that the first metal film extends towards at least one of the source electrode and the drain electrode with respect to the most outer edge of the second metal film, and    doping predetermined impurity ions by implanting the ions from an upper direction of the substrate into a semi-finished thin film transistor in which the gate electrode is formed.    
     
     
         24 . A method of producing a thin film transistor according to  claim 23 , wherein said silicon film is so formed as to have a thickness of 650 Å or less in the step of forming a silicon film, and the contact hole is so formed that a diameter of an undermost portion of the contact hole results in 4 μm or smaller in said step of forming a contact hole.  
     
     
         25 . A method of producing a thin film transistor according to  claim 24 , wherein a metal such that a reaction with silicon is highly controllable and a capability of preventing hydrogen in doping is high, is selected for a metal material for forming the silicide and the first metal film.  
     
     
         26 . A method of producing a thin film transistor formed on a substrate, said thin film transistor comprising a silicon thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate insulating film, a source electrode, and a drain electrode, the source electrode and the drain electrode being connected with the silicon thin film via a silicide layer in a contact hole formed in the interlayer dielectric layer and the gate insulating film, said method comprising the steps of: 
 forming a first metal film in a position corresponding to a gate electrode in the gate insulating film after forming a silicide in the contact hole, said first metal film consisting of the same metal as the metal composing the silicide and being the undermost layer of the gate electrode with a multiple-layer structure,    forming a silicon film having a predetermined thickness over the first metal film so that the silicon film extends towards at least one of the source electrode and the drain electrode with respect to the most outer edge of the first metal film,    forming a metal film for forming silicide on the silicon film in a region in the contact hole in which the silicide layer is to be formed,    forming the silicide layer in the contact hole and between the first metal film in the position corresponding to the gate electrode and the silicon film thereover, and    doping predetermined impurity ions by implanting the ions, utilizing the first metal film, the silicide layer, and the silicon film as a mask, from an upper direction of the substrate into a semi-finished thin film transistor in which the gate electrode is formed.    
     
     
         27 . A method of producing a thin film transistor according to  claim 26 , wherein said silicon film is so formed as to have a thickness of 650 Å or less in the step of forming a silicon film, and the contact hole is so formed that a diameter of an undermost portion of the contact hole results in 4 μm or smaller in said step of forming a contact hole.  
     
     
         28 . A method of producing a thin film transistor according to  claim 27 , wherein a metal such that a reaction with silicon is highly controllable and a capability of preventing hydrogen in doping is high, is selected for a metal material for forming the silicide and the first metal film.  
     
     
         29 . A thin film transistor formed on a substrate, comprising a semiconductor thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate electrode, a gate insulating film, a source electrode, and a drain electrode, the electrodes being connected with the semiconductor thin film via a contact hole, said thin film transistor further comprising: 
 a silicide layer between each of the source and drain electrodes and the semiconductor thin film in a region in which the contact hole is to be formed.    
     
     
         30 . A thin film transistor according to  claim 29 , wherein a portion of each of the source electrode and the drain electrode being in contact with the silicide layer in each of the source region and the drain region is composed of the same metal as the metal composing the silicide.  
     
     
         31 . A thin film transistor according to  claim 30 , wherein said silicide layer comprises a silicide of one of titanium, nickel, platinum, and cobalt.  
     
     
         32 . A thin film transistor according to  claim 31 , wherein said silicon thin film has a thickness of 650 Å or less, and said contact hole has a diameter of 4 μm or smaller in an undermost portion of the contact hole.  
     
     
         33 . A thin film transistor according to  claim 29 , wherein said silicide layer comprises a silicide of one of titanium, nickel, platinum, and cobalt.  
     
     
         34 . A thin film transistor according to  claim 33 , wherein said silicon thin film has a thickness of 650 Å or less, and said contact hole has a diameter of 4 μm or smaller in an undermost portion of the contact hole.  
     
     
         35 . A thin film transistor having an LDD structure formed on a substrate, comprising a semiconductor thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate electrode, a gate insulating film, a source electrode, and a drain electrode, the electrodes being connected with the semiconductor thin film via a contact hole, said thin film transistor wherein: 
 a silicide layer is provided between each of the source and drain electrodes and the semiconductor thin film in a region in which the contact hole is to be formed,    the gate electrode has a multiple-layer structure in which an undermost layer consists of the same metal as a metal composing the silicide layer, and an upper layer consists of a metal layer extending towards at least one of the source region and the drain region with respect to the outermost edge of the undermost layer, the gate electrode serving as a mask, and    the semiconductor thin film has an LDD structure in which impurity ions are distributed corresponding to a capability of shielding impurity ions retained by the gate electrode serving as a mask.    
     
     
         36 . A thin film transistor according to  claim 35 , wherein said silicide in each of the gate electrode, the source electrode, and the drain electrode is a silicide of one of titanium, nickel, platinum, and cobalt.  
     
     
         37 . A thin film transistor according to  claim 36 , wherein said semiconductor thin film has a thickness of 650 Å or less, and each of the source electrode and the drain electrode has a diameter of 4 μm or smaller in a portion being in contact with the silicide layer.  
     
     
         38 . A thin film transistor having an LDD structure formed on a substrate, comprising a semiconductor thin film in which a channel region, a source region, and a drain region are to be formed, an interlayer dielectric layer, a gate electrode, a gate insulating film, a source electrode, and a drain electrode, the electrodes being connected with the semiconductor thin film via a contact hole, said thin film transistor wherein: 
 a silicide layer is provided between each of the source and drain electrodes and the semiconductor thin film in a region in which the contact hole is to be formed,    the gate electrode has a multiple-layer structure in which an undermost layer consists of the same metal as a metal composing the silicide layer, and an upper layer consists of the silicide layer extending towards at least one of the source region and the drain region with respect to the outermost edge of the undermost layer, the gate electrode serving as a mask, and    the semiconductor thin film has an LDD structure in which impurity ions are distributed corresponding to a capability of shielding impurity ions retained by the gate electrode serving as a mask.    
     
     
         39 . A thin film transistor according to  claim 38 , wherein said silicide in each of the gate electrode, the source electrode, and the drain electrode is a silicide of one of titanium, nickel, platinum, and cobalt.  
     
     
         40 . A thin film transistor according to  claim 39 , wherein said semiconductor thin film has a thickness of 650 Å or less, and each of the source electrode and the drain electrode has a diameter of 4 μm or smaller in a portion being in contact with the silicide layer.