Liquid crystal display device and method of fabricating the same

A liquid crystal display device includes a plurality of gate lines and data lines on a first substrate defining a plurality of pixel regions, a thin film transistor within the pixel regions, a pixel electrode within the pixel regions, and at least one TiOx layer provided with the thin film transistor.

The present invention claims the benefit of Korean Patent Application No. 81459/2002 filed in Korea on Dec. 18, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and a method of fabricating a display device, and particularly, to a liquid crystal display device and a method of fabricating a liquid crystal display device.

2. Description of the Related Art

In general, flat panel displays, such as liquid crystal display (LCD) devices, commonly include an active device, such as a thin film transistor, provided at pixel regions to drive the display device. In addition, a driving method for the LCD device is commonly referred to as an active matrix driving type method, wherein the active device is disposed at respective pixel regions that are arranged in a matrix configuration to drive corresponding pixels.

FIG. 1is a plan view of an LCD device according to the related art. InFIG. 1, a TFT LCD uses a thin film transistor (TFT)10as an active device. In addition, an N×M matrix configuration of pixels are arranged along longitudinal and transverse directions, and includes the TFT10formed at a crossing region of a gate line3, which receives a scan signal supplied from a driving circuit of an exterior portion of the LCD device, and a data line5, which receives an image signal. The TFT comprises a gate electrode11connected to the gate line3, a semiconductor layer12formed on the gate electrode11, which is activated when the scan signal is supplied to the gate electrode11, and a source electrode13and a drain electrode14formed on the semiconductor layer12. A pixel electrode16, which is connected to the source and drain electrodes13and14to operate a liquid crystal material (not shown) by supplying the image signal through the source and drain electrodes13and14as the semiconductor layer12is activated, is formed on a display area of the pixel.

FIG. 2is a cross sectional view along I–I′ ofFIG. 1according to the related art. InFIG. 2, the TFT10is formed on a first substrate20made of a transparent material, such as glass, and includes the gate electrode11formed on the first substrate20, a gate insulating layer22deposited on an entire surface of the first substrate20upon which the gate electrode is formed11, a semiconductor layer12formed on the gate insulating layer22, source and drain electrodes13and14formed on the semiconductor layer12, and a passivation layer24deposited on an entire surface of the first substrate20. A pixel electrode16, which is connected to the drain electrode14of the TFT10through a contact hole26formed on the passivation layer24, is formed on the passivation layer24.

In addition, a black matrix32, which is formed on a non-display area (i.e., a TFT10forming area) and an area between pixels to prevent light from transmitting to the non-display area, and a color filter layer34for producing R(Red), G(Green), and B(Blue) colors are formed on a second substrate30made of transparent material, such as glass. The first and second substrates20and30are bonded together, and a liquid crystal material layer40is formed therebetween.

FIGS. 3A to 3Iare cross sectional views of a fabrication method of an LCD device according to the related art. InFIG. 3A, a metal layer11ais formed by depositing metal material on the first substrate20, and a photoresist layer60ais formed on the metal layer11aand baked at a certain temperature. Then, light is radiated onto the photoresist layer60athrough a mask70.

InFIG. 3B, a developer is applied to the photoresist layer60a, and a photoresist pattern60is formed on the metal layer11a. For example, when the photoresist is a negative photoresist, portions of the photoresist layer60athat are not exposed to the light are removed by the developer.

InFIG. 3C, an etching solution is applied to the metal layer11a. Accordingly, a portion of the metal layer11ablocked by the photoresist pattern60remains, whereby a gate electrode11is formed on the first substrate20.

InFIG. 3D, a gate insulating layer22is formed on an entire surface of the first substrate20, and a semiconductor layer12ais formed on the gate insulating layer22. Then, a photoresist layer is deposited onto the semiconductor layer12a, and a mask (not shown) is provided such that light is radiated onto the photoresist layer and developed to form a photoresist pattern62on the semiconductor layer12a. Next, an etching solution is applied to the semiconductor layer12asuch that only a portion of the semiconductor layer12aunder the photoresist pattern62remains on the gate insulating layer22.

InFIG. 3E, the photoresist pattern62(inFIG. 3D) is removed. Accordingly, a semiconductor layer12is formed on the gate electrode11.

InFIG. 3F, a metal material is deposited on an entire surface of the first substrate20, and a photoresist pattern (not shown) is formed using a mask (not shown). Then, the metal material is etched using the photoresist pattern (not shown) for forming a source electrode13and a drain electrode14on the semiconductor layer12.

In addition, a passivation layer24is deposited on the first substrate20upon which the source and drain electrodes13and14are formed to protect the TFT. Then, a portion of the passivation layer24overlying the drain electrode14is etched using a photolithographic process to form a contact hole26in the passivation layer24.

InFIG. 3H, a transparent material, such as indium tin oxide (ITO), is deposited onto the passivation layer24, and patterned using a photolithographic process to form the pixel electrode16on the passivation layer24. Accordingly, the pixel electrode16is electrically connected to the drain electrode14through the contact hole26formed in the passivation layer24.

InFIG. 3I, a black matrix32and a color filter layer34are formed on a second substrate30, the first and second substrates20and30are bonded together, and a liquid crystal material layer40is formed between the bonded first and second substrates20and30.

In the fabrication method ofFIGS. 3A to 3I, the source, drain, and pixel electrodes13,14, and16and/or the semiconductor layer12is formed using photolithographic processes that use a photoresist layer. However, use of the photoresist layer in the photolithographic process is problematic. First, the fabrication processes are relatively complex. For example, the photoresist pattern is formed through processes of photoresist coating, baking, exposure, and developing. In addition, in order to bake the photoresist layer, a soft-baking process is performed at a first low temperature and a hard-baking process is performed at a second higher temperature.

Second, a majority of fabrication costs lie with the fabrication of active switching devices. During fabrication of the active switching devices, a plurality of photoresist patterns are required. For example, the cost of forming the photoresist patterns is about 40–45% of the total cost of fabricating the LCD device.

Third, the process for forming the photoresist patterns produces massive amounts of environment pollutants that must be recovered during the fabrication process of the LCD device. In general, the photoresist layer is made by spin coating a photoresist material to achieve a certain thickness. Accordingly, large amounts of the spun-off photoresist material are not used and some amounts are unfortunately released into the environment. In addition, recovery of the spun-off photoresist material increases fabrication costs.

Fourth, since the photoresist layer is applied using the spin coating method, it is difficult to control the thickness of the photoresist layer. Accordingly, thickness of the photoresist layer is non-uniform. Thus, during removal of portions of the non-uniform photoresist layer, residual amounts of the photoresist layer are created that negatively impact operation of the active switching devices.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystal display device and method of fabricating a liquid crystal device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an LCD device fabricated using a pattern forming method to simplify fabrication processes and reduce fabrication costs.

Another object of the present invention is to provide a method of fabricating an LCD device having simplified fabrication processes and reduced fabrication costs.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display device includes a plurality of gate lines and data lines on a first substrate defining a plurality of pixel regions, a thin film transistor within the pixel regions, a pixel electrode within the pixel regions, and at least one TiOx layer provided with the thin film transistor.

In another aspect, a liquid crystal display device includes a plurality of gate lines and data lines on a first substrate defining a plurality of pixel regions, a thin film transistor within pixel regions, a pixel electrode within the pixel regions, and a TiO2layer provided in at least one of the thin film transistor and an upper portion of the pixel electrode.

In another aspect, a liquid crystal display device includes a plurality of gate lines and data lines on a first substrate defining a plurality of pixel regions, a thin film transistor within the pixel regions, a pixel electrode within the pixel regions, and a metal layer provided in the thin film transistor.

In another aspect, a method of fabricating a liquid crystal display device includes forming a gate electrode on a first substrate, forming a TiOx layer on the gate electrode using a Ti masking layer, forming a gate insulating layer on the first substrate, forming a semiconductor layer on the gate insulating layer, forming source and drain electrodes on the semiconductor layer, forming a passivation layer on the first substrate, and forming a pixel electrode on the passivation layer.

In another aspect, a method of fabricating a liquid crystal display device includes forming a gate electrode on a first substrate, forming a TiO2layer on the gate electrode, forming a gate insulating layer on the first substrate, forming a semiconductor layer on the gate insulating layer, forming source and drain electrodes on the semiconductor layer, forming a passivation layer on the first substrate, and forming a pixel electrode on the passivation layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, Ti is stable under atmospheric conditions. However, Ti is converted into TiOx when it is heated in an oxygen atmosphere. Accordingly, since Ti and TiOx have different etching selectivity ratios, TiOx may be formed by oxidizing a portion of Ti and an etching solution may be applied to remove the Ti and to form a TiOx pattern. In addition, when light of a certain wavelength is irradiated onto the TiOx, surface properties of the TiOx may become hydrophilic. Accordingly, the TiOx pattern may be formed by making use of differences between hydrophlicity and hydrophobicity. Thus, a metal layer may be precisely etched using the TiOx pattern.

FIGS. 4A to 4Fare cross sectional views of an exemplary pattern forming method for fabricating an LCD device according to the present invention. InFIGS. 4A to 4F, a metal pattern may be formed to create an electrode, a semiconductor pattern, and an insulating pattern.

InFIG. 4A, a metal layer103may be formed on an entire surface of a substrate101made of insulating material, such as glass or a semiconductor material. Then, a Ti layer110may be formed on an entire surface of the substrate101to overlie the metal layer103. The Ti layer110may be formed using evaporating or sputtering methods.

InFIG. 4B, light, such as ultraviolet light or laser produced light, may be irradiated on an area where a metal pattern will be formed using a mask107. Irradiation of the light results in deposition of energy onto the Ti layer110.

InFIG. 4C, since the irradiation of the light may be performed in an atmospheric or oxidizing atmosphere, portions of the Ti layer110exposed to the light may be oxidized. The oxidation of the Ti layer110may begin at a surface of the Ti layer110and may continue through an entire thickness of the Ti layer110over a period of time. Accordingly,the Ti layer110may include unexposed portions of the Ti layer110ban exposed portion of the Ti layer110a.

InFIG. 4D, the unexposed portions of the Ti layer110bmay be removed to form a patterned TiOx layer110a. The unexposed portions of the Ti layer110bmay be removed using wet or dry etching processes. During the wet etching process, acids, such as HF, may be used, wherein the HF acid may not react with the TiOx layer110a. Accordingly, HF acid etches the Ti layer110b, and leaves the TiOx pattern110aon the metal layer103. In addition, other acids besides HF may be used in order to etch the Ti material. However, it is desirable that H2SO4may not be used since H2SO4may not react with the Ti material.

During the dry etching process, the etching rate of the TiOx using Cl2gas or Cl2mixed gas, such as CF4/Cl2/O2gas, is much lower than the etching rate of the Ti. Accordingly, the Cl2gas or Cl2mixed gas may be mainly used as the etching gas.

InFIG. 4D, when the metal layer103is etched using the wet etching process or the dry etching process, the TiOx pattern110ablocks the etching solution (in case of the wet etching process) or the etching gas (in case of the dry etching process). Accordingly, portions of the metal layer103aunderlying the TiOx pattern110aremain on the substrate101.

InFIG. 4F, the TiOx pattern110aon the metal pattern103amay be etched and removed from the metal pattern103a. The TiOx pattern110amay be etched using the wet and dry etching processes. During the wet etching process, H2SO4(SO4ion is reacted with the TiOx and removed) may be used, and during the dry etching process, Cl2/N2gas or CF4/Cl2gas may be used.

FIGS. 5A to 5Fare cross sectional views of another exemplary pattern forming method for fabricating an LCD device according to the present invention. InFIG. 5A, a metal layer203may be formed by depositing metal material(s) on a substrate201made of insulating material(s), such as glass or semiconductor material(s). Then, TiOx, especially TiO2, may be deposited to form a TiO2layer210on the metal layer203. The TiO2layer210may be formed directly onto the metal layer203through evaporation or sputtering methods, or may be formed by oxidizing Ti using applications of heat and/or light after depositing the Ti onto the metal layer203.

InFIG. 5B, light, such as ultraviolet light or laser light, may be irradiated onto a first area of the TiO2layer210using a mask207to form a patterned area. Accordingly, the first area of the TiO2layer210may become hydrophilic. For example, TiO2material is a photocatalyst material having hydrophobic properties. However, when ultraviolet light or laser light is irradiated onto the TiO2material, an OH group may be formed on a surface of the TiO2material, thereby producing a hydrophilic material. A contact angle may be defined as an angle that makes a thermodynamic balance on a surface of a solid and that may be indicative of surface wettability (i.e., hydrophilicity) of a material. Accordingly, when the ultraviolet light is irradiated onto the TiO2layer210for more than a predetermined time, such as one hour, a contact angle may be gradually reduced to near 0 (i.e., hydrophilicity).

InFIG. 5C, the TiO2layer may be divided into a first TiO2layer210ahaving a hydrophilic surface211and a second TiO2layer210bhaving hydrophobic properties by the irradiation of the ultraviolet light or the laser light. When the H2SO4or an etching solution of alkali is applied to TiO2layers each having different surface properties, the OH group of the first TiO2layer210athat has hydrophilic properties may be combined with SO4ions of the H2SO4. That is, the surface211of the first TiO2layer210bmay be protected by the OH group. Accordingly, the hydrophobic second TiO2layer210bmay be removed by the etching solution, and the first TiO2layer210amay remain on the metal layer203, as shown inFIG. 5D.

InFIG. 5E, the etching solution may be applied to the metal layer203. Accordingly, portions of the metal layer203may be removed that do not underlie the first TiO2layer210a.

InFIG. 5F, the first TiO2layer210amay be removed using a gas, such as Cl2/N2or CF4/Cl2. Accordingly, a metal pattern203amay be formed on the substrate201.

Using the pattern forming method according to the present invention, a pattern may be formed by making use of different etching selectivity rates of a first metal, such as Ti, and of a first metal oxide, such as TiOx, and by making use of surface properties of the first metal oxide. The pattern forming method according to the present invention is advantageous as compared to the pattern forming method according to the related art that uses photolithographic processes including photoresist materials.

First, in the pattern forming method according to the related art, baking processes (soft-baking and hard-baking) are required after applying the photoresist, and an ashing process is required when the photoresist is removed. However, according to the present invention, since a photoresist is not required, the fabrication process is simplified.

Second, in the pattern forming method according to the related art, since the photoresist processing and patterning are additional fabrication processes, expensive equipment for the photoresist processing (i.e., a spin coater) is required during each individual process step in addition to equipment for fabricating the active devices (i.e., thin film transistors). On the contrary, the pattern forming process according to the present invention uses metal and metal oxide materials that may be produced using the same equipment used to fabricate the active devices. For example, when the metal pattern is formed, the metal layer and the Ti layer, which are the objects to be etched, may be formed in a vacuum chamber using similar methods (i.e., evaporation or sputtering). Accordingly, no addition equipment, other than those used to fabricate the active devices, is required. Thus, fabrication costs may be greatly reduced as compared to costs associated with the pattern forming method according to the related art that use the photoresist material.

Third, introduction of environment pollutants may be reduced since large amounts of wasted photoresist material are not produced using the pattern forming method according to the present invention. In addition, fabrication costs may be reduced by not producing the large amounts of wasted photoresist material since the pattern forming method according to the present invention uses metal and metal oxide materials.

FIGS. 6A to 6Gare cross sectional views of an exemplary method of fabricating an LCD device according to the present invention. InFIG. 6A, a metal layer311amay be formed on a first substrate320made of a transparent material, such as glass, by depositing a metal, such as Al, an Al alloy, and Cu, and a metal layer370a, such as Ti, may be formed on the metal layer311a. Next, light, such as ultraviolet light or laser light, may be radiated onto the Ti layer370athrough a mask380. Accordingly, portions of the Ti layer370aexposed to the light may become oxidized and converted into TiOx.

InFIG. 6B, an etching solution (i.e., HF) may be applied, wherein the unexposed portions of the Ti layer370amay be removed leaving a TiOx pattern370on the metal layer311a. When the etching solution is applied, the portion of metal layer311aunderlying the TiOx pattern370remains on the first substrate320. Accordingly, a gate electrode311(inFIG. 6C) and the TiOx pattern are formed on the first substrate320

InFIG. 6C, a gate insulating layer322may be formed on an entire surface of the first substrate320using a chemical vapor deposition (CVD) method, for example, a semiconductor layer312amay be deposited onto the gate insulating layer322, and a Ti layer372amay be formed on the semiconductor layer312a. Accordingly, when light, such as ultraviolet light or laser light, is radiated onto a portion of the Ti layer372ausing a mask382, portions of the Ti layer372aoxidizes to become TiOx.

Then, when an etching solution is applied to the Ti layer372a, the only remaining portion of the Ti layer372ais the oxidized TiOx portion, thereby forming a TiOx pattern. Next, when the semiconductor layer312ais etched using etching gas, the portions of the semiconductor layer312underlying the TiOx pattern372will remain on the gate insulating layer322, as shown inFIG. 6D. Accordingly, the TiOx pattern372may remain on the semiconductor layer312. Alternatively, the TiOx pattern372may be removed form the semiconductor layer312.

Since the semiconductor layer312may include silicon, the TiOx pattern372provided on the semiconductor layer312may react with the silicon to form Ti-silicide. On the other hand, since the Ti-silicide has a resistance lower than a resistance of the semiconductor layer312, an ohmic contact may be formed on the semiconductor layer312beneath subsequently formed source and drain electrodes313and314(inFIG. 6E). That is, the converted TiOx pattern372provided on the semiconductor layer312may remain to function as the ohmic contact layer.

InFIG. 6D, a metal layer313a, such as Cr, Mo, Al, an Al alloy, and Cu, may be formed on an entire surface of the first substrate320upon which the semiconductor layer312may be formed, and a Ti layer373amay be formed on the metal layer313a. Accordingly, when the metal layer313ais etched using the mask384, the source electrode313and the drain electrode314are formed on the semiconductor layer312, and TiOx patterns373and374(inFIG. 6E) may be formed on the source and drain electrodes313and314, respectively. Alternatively, the TiOx patterns373and374may be removed from the source and drain electrodes313and314, respectively. When the metal layer313ais etched the TiOx pattern372formed on some areas of the semiconductor layer312may be removed to form a channel area of the semiconductor layer312.

Although not shown, the gate electrode311, the source electrode313, and the drain electrode314may be formed as a plurality of individual layers each comprising a single metal material, or may be formed as a single layer comprising a plurality of different material layers, such as alloys.

InFIG. 6E, a passivation layer324may be deposited on an entire surface of the first substrate320, and a portion of the passivation layer324provided on the drain electrode314may be removed to form a contact hole326. Next, a transparent electrode316a, such as indium tin oxide (ITO), and a Ti layer376amay be formed on the passivation layer324where the contact hole326has been formed, and the transparent electrode316amay be etched using a mask386to form a pixel electrode316(inFIG. 6F). In general, since the converted TiOx layer has a low light transmittance, the TiOx layer should not exist within an area where the pixel electrode is formed. Accordingly, the TiOx layer formed on the passivation layer324and the pixel electrode316may be removed, as shown inFIG. 6F.

InFIG. 6G, a second substrate330may include a black matrix332and a color filter layer334. Accordingly, the first and second substrates320and330may be bonded together to form an LCD device.

In addition, the present invention may be used together with photolithographic processes using a photoresist layer, as well as a TiOx layer. For example, the TiOx masking layer may be used to form some patterns, and a photoresist layer may be used to form other patterns.

FIGS. 7A to 7Fare cross sectional views of another exemplary method of fabricating an LCD device according to the present invention. InFIG. 7A, a metal layer411amay be formed on a first substrate420made of transparent material, such as the glass, by depositing metal material(s), such as Al, an Al alloy, and Cu, on the first substrate420, and a TiO2layer470ahaving hydrophobic properties may be formed on the metal layer411a. Then, light, such as ultraviolet light or laser light, may be radiated on an upper part of the TiO2layer470ausing a mask480. Accordingly, a surface portion470(inFIG. 7B) of the TiO2layer470amay be converted to have hydrophilic properties.

InFIG. 7B, when H2SO4or an alkali etching solution is applied to the TiO2layer470a(inFIG. 7A), the portion of the TiO2layer470ahaving hydrophobic properties may be removed. Accordingly, the surface portion470bof the TiO2pattern470may remain on the metal layer411a.

InFIG. 7C, the metal layer411amay be etched using an etching solution. Accordingly, a portion of the metal layer411aunderlying the TiO2pattern470may remain on the first substrate420to form a gate electrode411. Alternatively, the TiO2pattern470may be removed from the gate electrode411. Then, a semiconductor layer412aand a TiO2layer472amay be formed on an entire surface of the first substrate420upon which the gate electrode411may be formed. Next, light may be radiated onto a portion of the TiO2layer472ausing a mask482.

Accordingly, the light radiated onto the TiO2layer472amay convert a surface of the TiO2layer472ainto hydrophilic material. Thus, the semiconductor layer412amay be etched after forming a TiO2layer472(inFIG. 7D) having hydrophilic properties by removing the TiO2layer472ahaving hydrophobic properties similar to the processes for forming the gate electrode411.

InFIG. 7D, the semiconductor layer412may be formed on the gate insulating layer422. Accordingly, the TiO2pattern472that remains on an upper part of the semiconductor layer412may react with the silicon of the semiconductor layer412to form Ti-silicide. Thus, an ohmic contact layer472bmay be formed on the semiconductor layer412.

InFIG. 7E, a source electrode413and a drain electrode414may be formed on the semiconductor layer412using processes similar to those shown inFIGS. 7A–7D, wherein TiO2patterns473and474may be forming on the source electrode413and on the drain electrode414. Alternatively, the TiO2patterns473and474may be removed from the source and drain electrodes413and414. Next, a passivation layer424may be deposited on an entire surface of the first substrate420, and a portion of the passivation layer424corresponding to the drain electrode414may be etched to form a contact hole426. In addition, a TiO2pattern476may be formed on the passivation layer424.

Although not shown, the gate electrode411, the source electrode413, and the drain electrode414may be formed as a plurality of individual layers made of a single metal material, or may be formed as a plurality of single layers each made of different alloys.

InFIG. 7F, an ITO layer and TiO2layer may be formed on the passivation layer424, and the ITO layer may be etched making use the hydrophobic and hydrophilic surface properties of the TiO2layer to form a pixel electrode416and a TiO2pattern478connected to the drain electrode414through the contact hole426.

The TiO2material has a resistivity of 103Ωcm and a visible ray transmittance of 85%. Thus, the TiO2pattern476formed on upper part of the passivation layer424and the TiO2pattern478formed on an upper part of the pixel electrode416may not be removed. Alternatively, the TiO2patterns476and478may be removed. Accordingly, adjacent pixel electrodes of neighboring pixel regions are not broken and light transmitted within the pixel regions is not blocked by the TiO2patterns476and478.

InFIG. 7F, a second substrate430may include a black matrix432and a color filter layer434. Then, the first and second substrates420and430may be bonded together to form the LCD device.

According to the present invention, since the TiO2layer formed on the semiconductor layer412reacts with the semiconductor layer412, no additional ohmic contact layers, or processes for forming additional ohmic contact layers may be necessary. Moreover, since the TiO2patterns476and478are transparent and have a relatively high resistivity, removal of the TiO2patterns476and478on the upper part of the passivation layer424and the pixel electrode416may not be necessary.

In addition, the present invention may be used together with photolithographic processes using a photoresist layer, as well as a TiOx layer. For example, the TiOx masking layer may be used to form some patterns, and a photoresist layer may be used to form other patterns.