Patent Application
20130001572
The present invention relates to a display device such as an organic electroluminescence (EL) display device, to a thin-film transistor used for the display device, and to a method of manufacturing thin-film transistors.
In recent years, organic EL display devices including current-driven organic EL elements have been receiving attention as a next-generation display device. Among them, an active-matrix-driven organic EL display device includes a field-effect transistor. As such a field-effect transistor, there is known a thin-film transistor where a semiconductor layer provided on a substrate with an insulating surface becomes a channel-forming region.
A thin-film transistor used for an active-matrix-driven organic EL display device requires at least a switching transistor for controlling timing (e.g. turning on and off) of driving an organic EL element; and a drive transistor for controlling the amount of light emitted from the organic EL element. Such thin-film transistors preferably have their superior transistor characteristics, on which various researches are being performed.
A switching transistor for instance requires the off-current to be further decreased and variations between the on- and off-currents to be reduced. A drive transistor requires the on-current to be further increased and variations in the on-current to be reduced.
Conventionally, as a channel-forming region of such a thin-film transistor, an amorphous (non-crystalline) silicon film for instance has been used; however, an amorphous silicon film has low mobility and resultantly the on-current is small. In recent years, to achieve a desirable drive performance (i.e. on-current) of a thin-film transistor, research and development have been made on crystallization of an amorphous silicon film by heat treatment using a laser beam for instance.
To use this crystallized silicon film for a thin-film transistor, after forming an ohmic contact layer on the channel-forming region, when processing the ohmic contact layer, damage to the channel-forming region remains, which undesirably deteriorate the characteristics of the thin-film transistor.
To reduce such damage, a method has been devised of forming an insulating film in a thin-film transistor (refer to patent literature 1 for instance).
In this conventional configuration, however, an ohmic contact layer directly contacts a crystallized silicon film, causing an electric field to concentrate between them, which undesirably increases the off-current.
The present invention provides a display device including a display element and a thin-film transistor for controlling light emission from the display element. The thin-film transistor includes a gate electrode formed on an insulating substrate; a gate insulating film formed on the substrate so as to cover the gate electrode; a semiconductor layer formed on the gate insulating film; an ohmic contact layer formed on the semiconductor layer; and a source electrode and a drain electrode formed on the ohmic contact layer so as to be spaced from each other. The transistor further includes an etching stopper made of spin-on glass (SOG) on a channel-forming region of the semiconductor layer.
The present invention provides a thin-film transistor used for a display device. The thin-film transistor includes a gate electrode formed on an insulating substrate; a gate insulating film formed on the substrate so as to cover the gate electrode; a semiconductor layer formed on the gate insulating film; an ohmic contact layer formed on the semiconductor layer; and a source electrode and a drain electrode formed on the ohmic contact layer so as to be spaced from each other. The transistor further includes an etching stopper made of SOG on a channel-forming region of the semiconductor layer.
The present invention provides a method of manufacturing thin-film transistors. A thin-film transistor, used for a display device, includes a gate electrode formed on an insulating substrate; a gate insulating film formed on the substrate so as to cover the gate electrode; a semiconductor layer formed on the gate insulating film; an ohmic contact layer formed on the semiconductor layer; and a source electrode and a drain electrode formed on the ohmic contact layer so as to be spaced from each other. The method includes the successive steps of: successively forming the gate electrode, the gate insulating film, and the semiconductor layer on the insulating substrate; then forming an etching stopper made of SOG on a channel-forming region of the semiconductor layer; then successively forming a film for forming the ohmic contact layer so as to cover the etching stopper and an electrode film becoming the source electrode and the drain electrode; and then forming the ohmic contact layer, the source electrode, and the drain electrode by etching.
As described above, the present invention provides thin-film transistors with stable characteristics without greatly increasing the number of processing steps.
Hereinafter, a description is made of a thin-film transistor (hereinafter sometimes abbreviated as TFT), and a method of manufacturing TFTs, according to an embodiment of the present invention with reference to the related drawings.
First, a description is made of a display device according to the embodiment of the present invention, taking an organic EL display device as an example.
Next, a description is made of an example circuit configuration of pixel 2 using
As shown in
In such a configuration, when a gate signal is input into gate wiring 8 and switching transistor 13 is turned on, a signal voltage corresponding to an image signal supplied through source wiring 7 is written into capacitor 14. The retaining voltage written into capacitor 14 is retained through one frame period.
The retaining voltage written into capacitor 14 changes the conductance of drive transistor 12 in an analog fashion to cause a drive current corresponding to the gradation in light emission to flow from the anode of organic EL element 11 to the cathode. The drive current running through the cathode causes organic EL to element 11 to emit light, which is displayed as an image. Consequently, as described above, the display device includes a display element and a thin-film transistor for controlling light emission from the display element.
As shown in
Here, thin-film transistor 30 forming drive transistor 12 is a bottom-gate, n-type thin-film transistor and is formed by successively laminating gate electrode 31, gate insulating film 32, semiconductor layer 33, ohmic contact layer 34, and source electrode 35S and drain electrode 35D, on support substrate 21.
Next, a description is made of a configuration of a thin-film transistor and a method of manufacturing the transistor, according to the embodiment of the present invention using
As shown in
Gate electrode 31 is pattern-formed of electrode material such as molybdenum (Mo) for instance in a strip shape on support substrate 21 made of an insulating substrate such as glass. If the manufacturing process includes a heating step, gate electrode 31 is preferably made of a high-melting-point metallic material resistant to heat alteration.
Gate insulating film 32, formed so as to cover gate electrode 31, is film-formed of a lamination of at least an insulating material such as SiO2, SiN, or SiON by plasma chemical vapor deposition (CVD) for instance in a thickness of approximately 75 nm to 500 nm.
Semiconductor layer 33 composed of source electrode 35S, drain electrode 35D, first semiconductor layer 33a, and second semiconductor layer 33b is formed on gate insulating film 32 so as to cover gate electrode 31.
Consequently, first semiconductor layer 33a laminated on gate insulating film 32 is formed of a crystalline silicon film containing crystalline silicon with a thickness of 30 nm to 500 nm. First semiconductor layer 33a may be formed by crystallizing part of a laminated semiconductor film.
Second semiconductor layer 33b, laminated on first semiconductor layer 33a, is preferably a non-crystalline silicon film with its mobility lower than that of first semiconductor layer 33a to reduce the off-current; however, second semiconductor layer 33b may be a film containing crystalline silicon. Second semiconductor layer 33b, by being formed between ohmic contact layer 34 and first semiconductor layer 33a, moderates an electric field at the drain electrode, thereby reducing the off-current.
Ohmic contact layer 34 is formed on semiconductor layer 33. Specifically, ohmic contact layer 34 is for forming contact between source electrode 35S and drain electrode 35D and semiconductor layer 33 composed of first semiconductor layer 33a and second semiconductor layer 33b, by ohmic connection, where ohmic contact layer 34 is formed of a material that is a non-crystalline silicon film with impurities doped thereinto. Examples of the impurities include a group 5 metal such as phosphorus (P) and a group 3 metal. In the examples shown in
Source electrode 35S and drain electrode 35D are pattern-formed and disposed on ohmic contact layer 34 in a state spaced from each other. Source electrode 35S and drain electrode 35D are formed of a single layer made of a metal such as titanium (Ti), tantalum (Ta), molybdenum (Mo), tungsten (W), aluminum (Al), and copper (Cu); or a laminated film made of two or more layers, with a film thickness of approximately 50 nm to 1,000 nm, by sputtering for instance.
Etching stopper 36 is formed of photosensitive SOG (spin-on glass) (e.g. silsesquioxane) having a siloxane structure, on a channel-forming region of semiconductor layer 33. Etching stopper 36 is formed so as to protect a channel-forming region to prevent the transistor characteristics from fluctuating due to damage to first semiconductor layer 33a caused by penetration of etching through second semiconductor layer 33b when source electrode 35S and drain electrode 35D and ohmic contact layer 34 are etched into a given pattern. Here, Etching stopper 36 desirably has a film thickness of 300 nm or greater for reasons of fixed charge at the interface and in the film.
As described above, thin-film transistor 30, used for a display device, includes gate electrode 31 formed on insulating support substrate 21; gate insulating film 32 formed on support substrate 21 so as to cover gate electrode 31; semiconductor layer 33 formed on gate insulating film 32; ohmic contact layer 34 formed on semiconductor layer 33; and source electrode 35S and drain electrode 35D formed on ohmic contact layer 34 in a state spaced from each other.
Hereinafter, a description is made of a method of manufacturing thin-film transistors using sectional views showing an example manufacturing process.
First, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
Then, as shown in
Further, as shown in
After processing ohmic contact layer 34 and semiconductor layer 33, as shown in
As described hereinbefore, in the present invention, thin-film transistor 30 includes gate electrode 31 formed on insulating support substrate 21; gate insulating film 32 formed on support substrate 21 so as to cover gate electrode 31; semiconductor layer 33 composed of first semiconductor layer 33a and second semiconductor layer 33b formed on gate insulating film 32; ohmic contact layer 34 formed on semiconductor layer 33; and source electrode 35S and drain electrode 35D formed on ohmic contact layer 34 in a state spaced from each other. Thin-film transistor 30 further includes etching stopper 36 made of SOG on the channel-forming region of the semiconductor layer 33. Resultantly, etching stopper 36 prevents the transistor characteristics from fluctuating due to damage to first semiconductor layer 33a caused by penetration of etching through second semiconductor layer 33b when source electrode 35S and drain electrode 35D and ohmic contact layer 34 are processed by etching in a given pattern. Furthermore, using etching stopper 36 and resist mask 39 for processing allows semiconductor layer 33 and ohmic contact layer 34 to be processed at one time, thereby reducing the number of steps of manufacturing thin-film transistors.
As described above, the present invention is useful for providing thin-film transistors with stable characteristics without greatly increasing the number of processing steps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-134877 | Jun 2011 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/001587 | Mar 2012 | US |
| Child | 13616673 | US |
