Abstract:
The present invention discloses a method of manufacturing an active matrix display device, comprising: a) forming a semiconductor layer on an insulating substrate; b) forming a gate insulating layer over the whole surface of the substrate while convering the semiconductor layer; c) forming a gate electrode on the gate insulating layer over the semiconductor layer; d) forming spacers on both side wall portions of the gate electrode while exposing both end portions of the semiconductor layer; e) ion-implaing a high-density impurity into the semiconductor layer to form high-density source and drain regions in the semiconductor layer; f) depositing sequentially a transparent conductive layer and a metal layer on the inter insulating layer; g) patterning the transparent conductive layer and the metal layer to form the source and drain electrodes, the source and drain electrodes directly contacting the high-density source and drain regions and having a dual-layered structure; h) forming a passivation layer over the whole surface of the substrate; i) etching the passivation layer and the metal layer to form an opening portion exposing a portions of the transparent conductive layer, thereby forming a pixel electrode; and j) performing a reflow process to cover the metal layer in the opening portion by the passivation layer.

Description:
CROSS REFERENCE 
     This application claims the benefit of Korean Patent Application No. 2001-10840, filed on Mar. 2, 2001, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thin film transistor, and more particularly, to a method of manufacturing the same. Also, the present invention relates to an active matrix display device having improved reliability and a manufacturing method thereof. 
     2. Description of Related Art 
     A cathode ray tube (CRT) is widely employed as display devices for use in televisions, measuring instruments, information terminals, etc. However, the CTR has disadvantages that it cannot satisfy trends toward miniaturization and lightweight of electronic appliances. 
     Due to such shortcomings of the CRT, flat panel display devices, which are lightweight and small-sized, is being watched with keen interest. 
     FIG. 1 is a cross-sectional view illustrating a TFT array substrate of an active matrix flat panel display device according to a conventional art. A process of manufacturing the conventional TFT array substrate is described below. 
     First, a buffer layer  11  is formed on a transparent substrate  10 . The buffer layer  11  is an oxide layer, and the substrate is a transparent glass substrate or a transparent plastic substrate. A polycrystalline silicon layer is deposited on the buffer layer  11  and then patterned to form a semiconductor layer  12 . 
     Then, a first insulating layer  13  is deposited over the whole surface of the substrate  10  and covers the semiconductor layer  12 . The first insulating layer  13  serves as a gate insulating layer. A first metal layer is deposited on the first insulating layer  13  and then patterned to form a gate electrode  14  over the semiconductor layer  12 . A high-density impurity, for example, an n-type or a p-type high-density impurity is ion-implanted into the semiconductor layer  12  to form high-density source and drain regions  15 - 1  and  15 - 2  on both end portions of the semiconductor layer  12 . 
     Thereafter, a second insulating layer  16  is deposited over the whole surface of the substrate  10  and then patterned to form first and second contact holes  17 - 1  and  17 - 2 . The first contact hole  17 - 1  is formed at a location corresponding to a portion of the source region  15 - 1 , and the second contact hole  17 - 2  is formed at a location corresponding to a portion of the drain region  15 - 2 . The second insulating layer  16  serves as an inter insulating layer. 
     Subsequently, a second metal layer is deposited on the inter insulating layer  16  and then patterned to form source and drain electrodes  18 - 1  and  18 - 2 . The source and drain electrodes  18 - 1  and  18 - 2  contact the source and drain regions  15 - 1  and  15 - 2  through the first and second contact holes  17 - 1  and  17 - 2 , respectively. 
     Next, a passivation layer  19  is formed over the whole surface of the substrate  10  and covers the source and drain electrodes  18 - 1  and  18 - 2 . The passivation layer  19  includes a via hole  20  at a location corresponding to a portion of either of the source and drain electrodes  18 - 1  and  18 - 2 . In FIG. 1, the via hole  20  is formed on a portion of the drain electrode  18 - 2 . 
     A transparent conductive material layer is deposited and then patterned to form a pixel electrode  21 . The pixel electrode  21  contacts the drain electrode  18 - 2  through the via hole  20 . 
     Finally, a planarization layer  22  is deposited and then patterned to form an opening portion  23 . The opening portion  23  exposes a portion of the pixel electrode  21 . Therefore, the TFT array substrate of the flat panel display device is completed. 
     The source and drain electrodes  18 - 1  and  18 - 2  are electrodes to which electrical signals are applied and are made of a low resistive metal to prevent a signal delay. The pixel electrode  21  is made of a low resistive, high transmitting material, for example, a transparent conductive material such as indium tin oxide (ITO). 
     Therefore, when the source and drain electrodes and the pixel electrode are made of metal, they are low in specific resistance but low in transmittance. Alternatively, when the source and drain electrodes and the pixel electrode are made of ITO, they are high in transmittance but high in specific resistance in comparison to metal. Neither of metal and ITO cannot satisfy requirements of the source and drain electrodes and the pixel electrode. 
     Therefore, in conventional manufacturing process of the TFT array substrate of the flat panel display device, the source and drain electrodes are made of metal, and the pixel electrode is made of ITO. As a result, two mask processes are required to form the source and drain electrodes and the pixel electrode. In addition, a process is additionally required that forms the contact hole in the passivation layer to contact one of the source and drain electrodes and the pixel electrode. 
     As described above, the conventional process of manufacturing the TFT array substrate of the flat panel display device is very complicated. Therefore, manufacturing yield is low, and production cost is high. 
     Also, the TFT array substrate of the flat panel display device has a problem in that a contact resistance between the source and drain regions and the source and drain electrodes is very large sufficiently to degrade electric characteristics thereof. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, preferred embodiments of the present invention provide a thin film transistor and a flat panel display device having an improved light transmittance and a low resistance. 
     It is another object of the present invention to provide a thin film transistor and a flat panel display device having a simplified manufacturing process, leading to manufacturing yield and high production cost. 
     It is a still object of the present invention to provides a thin film transistor and a flat panel display device having excellent electric characteristics. 
     In order to achieve the above object, the preferred embodiments of the present invention provide a method of manufacturing an active matrix display device, comprising: a) forming a semiconductor layer on an insulating substrate; b) forming a gate insulating layer over the whole surface of the substrate while covering the semiconductor layer; c) forming a gate electrode on the gate insulating layer over the semiconductor layer; d) ion-implanting a high-density impurity into the semiconductor layer to form high-density source and drain regions in the semiconductor layer; e) forming an inter insulating layer over the whole surface of the substrate; f) etching the inter insulating layer to form contact holes, the contact holes exposing portions of the high-density source and drain regions; g) depositing sequentially a transparent conductive layer and a metal layer on the inter insulating layer; h) patterning the transparent conductive layer and the metal layer to form the source and drain electrodes, the source and drain electrodes contacting the high-density source and drain regions through the contact holes and having a dual-layered structure; i) forming a passivation layer over the whole surface of the substrate; j) etching the passivation layer and the metal layer to form an opening portion exposing a portions of the transparent conductive layer, thereby forming a pixel electrode; and k) performing a reflow process to cover the metal layer in the opening portion by the passivation layer. 
     The present invention further provides a method of manufacturing an active matrix display device having an opening portion, comprising: a) forming a semiconductor layer on an insulating substrate; b) forming a gate insulating layer over the whole surface of the substrate while covering the semiconductor layer; c) forming a gate electrode on the gate insulating layer over the semiconductor layer; d) ion-implanting a high-density impurity into the exposed portions of the semiconductor layers to form high-density source and drain regions; e) forming an inter insulating layer over the whole surface of the substrate, f) etching the inter insulating layer including to form contact holes exposing portions of the high-density source and drain regions; g) depositing sequentially a transparent conductive layer and a metal layer over the whole surface of the substrate; h) coating a photoresist layer over the whole surface of the substrate; i) patterning the photoresist layer using a half-tone mask to from a photoresist pattern, the photoresist pattern exposing a portion of the metal layer over the gate electrode and including a relative thin portion having a thickness thinner than the rest portion thereof at a loation thereof corresponding to the opening portion; j) patterning the transparent conductive layer and the metal layer using the photoresist pattern as a mask to form source and drain electrodes and to expose a portion of the transparent conductive layer corresponding to the opening portion, the source and drain electrodes respectively contacting the high-density source and drain regions through the contact holes and having a dual-layered structure; and k) depositing a passivation layer over the whole surface of the substrate and etching the passivation layer to form the opening portion, thereby forming a pixel electrode. 
     The present invention further provides a method of manufacturing an active matrix display device, comprising: a) forming a semiconductor layer on an insulating substrate; b) forming a gate insulating layer over the whole surface of the substrate while covering the semiconductor layer; c) forming a gate electrode on the gate insulating layer over the semiconductor layer; d) forming spacers on both side wall portions of the gate electrode while exposing both end portions of the semiconductor layer; e) ion-implanting a high-density impurity into the semiconductor layer to form high-density source and drain regions in the semiconductor layer; f) depositing sequentially a transparent conductive layer and a metal layer on the inter insulating layer; g) patterning the transparent conductive layer and the metal layer to form the source and drain electrodes, the source and drain electrodes directly contacting the high-density source and drain regions and having a dual-layered structure; h) forming a passivation layer over the whole surface of the substrate; i) etching the passivation layer and the metal layer to form an opening portion exposing a portions of the transparent conductive layer, thereby forming a pixel electrode; and j) performing a reflow process to cover the metal layer in the opening portion by the passivation layer. 
     The present invention further provides a method of manufacturing an active matrix display device having an opening portion, comprising: a) forming a semiconductor layer on an insulating substrate; b) forming a gate insulating layer over the whole surface of the substrate while covering the semiconductor layer; c) forming a gate electrode on the gate insulating layer over the semiconductor layer; d) forming spacers on both side wall portions of the gate electrode while exposing both end portions of the semiconductor layer; e) ion-implanting a high-density impurity into the exposed portions of the semiconductor layer to form high-density source and drain regions; f) depositing sequentially a transparent conductive layer and a metal layer over the whole surface of the substrate; g) coating a photoresist layer over the whole surface of the substrate; h) patterning the photoresist layer using a half-tone mask to from a photoresist pattern, the photoresist pattern exposing a portion of the metal layer over the gate electrode and including a relative thin portion having a thickness thinner than the rest portion thereof at a loation thereof corresponding to the opening portion; i) patterning the transparent conductive layer and the metal layer using the photoresist pattern as a mask to form source and drain electrodes and to expose a portion of the transparent conductive layer corresponding to the opening portion, the source and drain electrodes respectively directly contacting the high-density source and drain regions and having a dual-layered structure; and j) depositing a passivation layer over the whole surface of the substrate and etching the passivation layer to form the opening portion, thereby forming a pixel electrode. 
     The present invention further provides an active matrix display device, comprising: a semiconductor layer formed on an insulating substrate; a gate insulating layer formed over the whole surface of the substrate and exposing both end portions of the semiconductor layer; a gate electrode formed on the gate insulating layer over the semiconductor layer; spacers formed on both side wall portions of the gate electrode; source and drain regions formed in the exposed portions of the semiconductor layer that are not covered by the spacers; source and drain electrodes directly contacting the high-density source and drain regions and having a dual-layered structure of a transparent conductive layer and a metal layer; a passivation layer formed over the whole surface of the substrate to cover the metal layer for the source and drain electrodes and having an opening portion; and a pixel electrode extending from a portion of the transparent conductive layer forming any one of the soruce and drain electrodes and exposed by the opening portion. 
     The present invention further provides an active matrix display device, comprising: a semiconductor layer formed on an insulating substrate; a gate insulating layer formed over the whole surface of the substrate and covering the semiconductor layer; a gate electrode formed on the gate insulating layer over the semiconductor layer; high-density source and drain regions formed on both end portions of the semiconductor layer; an inter insulating layer formed over the whole surface of the substrate and having contact holes, the contact holes exposing portions of the source and drain regions; source and drain electrodes formed on the inter insulating layer, contacting the high-density source and drain regions through the contact holes and having a dual-layered structure of a transparent conductive layer and a metal layer; a passivation layer formed over the whole surface of the substrate to cover the metal layer for the source and drain electrodes and having an opening portion; and a pixel electrode extending from a portion of the transparent conductive layer forming any one of the soruce and drain electrodes and exposed by the opening portion. 
     The source and drain electrodes comprises a transparent conductive layer and a metal layer in sequentially stacked. The metal layer is made of a material having a lower specific resistance than the transparent conductive layer or one of Al, Al-alloy, Mo, Mo-alloy, Cr, and Ti. The transparent conductive layer is made of one of indium tin oxide, indium zinc oxide, tin oxide and indium oxide. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numerals denote like parts, and in which: 
     FIG. 1 is a cross-sectional view illustrating a thin film transistor (TFT) of an active matrix flat panel display device according to a conventional art; 
     FIGS. 2A to  2 E are cross-sectional views illustrating a thin film transistor (TFT) according to a first preferred embodiment of the present invention; 
     FIGS. 3A to  3 F are cross-sectional views illustrating a process of manufacturing a TFT according to a second preferred embodiment of the present invention; 
     FIGS. 4A to  4 G are cross-sectional views illustrating a process of manufacturing an active matrix flat panel display device according to one embodiment of the present invention; and 
     FIGS. 5A to  5 C are cross-sectional views illustrating a process of manufacturing an active matrix flat panel display device according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to preferred embodiments of the present invention, example of which is illustrated in the accompanying drawings. 
     FIGS. 2A to  2 E are cross-sectional views illustrating a thin film transistor (TFT) according to a first preferred embodiment of the present invention. 
     First, as shown in FIG. 2A, a buffer layer  31  is formed on a transparent substrate  30 . The buffer layer  31  is an oxide layer, and the substrate is a transparent glass substrate or a transparent plastic substrate. A polycrystalline silicon layer is deposited on the buffer layer  31  and then patterned to form a semiconductor layer  32 . 
     Then, as shown in FIG. 2B, a first insulating layer  33  is deposited over the whole surface of the substrate  30  and covers the semiconductor layer  32 . The first insulating layer  33  serves as a gate insulating layer. A first metal layer is deposited on the first insulating layer  33  and then patterned to form a gate electrode  34  over the semiconductor layer  32 . A high-density impurity, for example, an n-type or a p-type high-density impurity is ion-implanted into the semiconductor layer  11  to form high-density source and drain regions  35 - 1  and  35 - 2  on both end portions of the semiconductor layer  32 . 
     Thereafter, as shown in FIG. 2C, a second insulating layer  36  is deposited over the whole surface of the substrate  30  and then patterned to form first and second contact holes  37 - 1  and  37 - 2 . The first contact hole  37 - 1  is formed at a location corresponding to a portion of the source region  35 - 1 , and the second contact hole  37 - 2  is formed at a location corresponding to a portion of the drain region  35 - 2 . The second insulating layer  36  serves as an inter insulating layer. 
     Subsequently, as shown in FIG. 2D, a transparent conductive material layer  38  and a second metal layer  39  are sequentially deposited on the inter insulating layer  36 . The second metal layer  39  is made of a material having a resistance value lower than the transparent conductive material layer such as Al, Al-alloy, Mo, Mo-alloy, Cr, and Ti. The transparent conductive material layer  39  is made of a material such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (TO) and indium oxide (IO). The second metal layer  39  and the transparent conductive material layer  38  are patterned to form source and drain electrodes  40 - 1  and  40 - 2 . Therefore, the source and drain electrodes  40 - 1  and  40 - 2  have a dual-layered structure. The dual-layered source and drain electrodes  40 - 1  and  40 - 2  contact the source and drain regions  35 - 1  and  35 - 2  through the first and second contact holes  37 - 1  and  37 - 2 , respectively. Therefore, the TFT is completed. 
     In the process of manufacturing the TFT according to the first preferred embodiment of the present invention, the source and drain regions  35 - 1  and  35 - 2  are configured to have a single doped region but can have an offset region or a lightly doped drain (LDD) region by, for example, an anodizing process. That is, the first preferred embodiment of the present invention can be applied to the TFT of the offset structure or the LDD structure having dual-layered source and drain electrodes. 
     FIGS. 3A to  3 F are cross-sectional views illustrating a process of manufacturing a TFT according to a second preferred embodiment of the present invention. 
     First, as shown in FIG. 3A, a buffer layer  71  is formed on an insulating layer  70 , and a semiconductor layer  72  is formed on the buffer layer  71 . 
     As shown in FIG. 3B, a first insulating layer  73  is formed over the whole surface of the substrate  70  and covers the semiconductor layer  72 . An oxide layer or a nitride layer is used as the first insulating layer  73 . A first metal layer and a second insulating layer are sequentially deposited on the first insulating layer  73  and then patterned to form a gate electrode  74  and a capping layer  75  over the semiconductor layer  72 . Thereafter, using the gate electrode  74  as a mask, an n-type or a p-type low-density impurity is ion-implanted into both end portions of the semiconductor layer  72  to form low-density source and drain regions  76 - 1  and  76 - 2 . At this moment, the capping layer  75  serves as an impurity barrier to prevent the gate electrode  74  from being ion-implanted and includes SiNx or SiO 2 . 
     Subsequently, as shown in FIG. 3C, a third insulating layer is deposited over the whole surface of the substrate  70  and then etched-back to form spacers  77  on both side wall portions of the gate electrode  74  and the capping layer  75 , so that the gate electrode  74  is perfectly insulated by the capping layer  75  and the spacers  77 . An oxide layer or a nitride layer is used as the third insulating layer. At the same time, the third insulating layer  73  is etched to form a gate insulating layer  73   a,  so that end portions of the low-density source and drain regions  76 - 1  and  76 - 2  are exposed. 
     Next, as shown in FIG. 3D, silicide layers  78 - 1  are formed on the exposed portions of the source and drain regions  76 - 1  and  76 - 2 , respectively. Subsequently, a high-density impurity having the same conductivity as the source and drain regions  76 - 1  and the  76 - 2  is ion-implanted into the exposed low-density source and drain regions  76 - 1  and  76 - 2  to form high-density source and drain regions  79 - 1  and  79 - 2 . 
     Finally, as shown in FIGS. 3E and 3F, a transparent conductive material layer and a second metal layer  80  and  81  are sequentially deposited over the whole surface of the substrate  70  and then patterned to form source and drain electrodes  82 - 1  and  82 - 2 . The source and drain electrodes  82 - 1  and  82 - 2  have a dual-layered structure. The second metal layer  81  is made of a material having a lower resistance value than the transparent conductive material layer  80  such as Al, Al-alloy, Mo, Mo-alloy, Cr, and Ti, and the transparent conductive material layer  80  is made of a transparent conductive material such as ITO, IZO, TO, and IO. Therefore, the TFT according to the second preferred embodiment of the present invention is completed. 
     According to the second preferred embodiment of the present invention, since the source and drain regions are formed in a self-align manner using the spacers, an additional mask process to form an LDD structure is not required. Also, since the source and drain electrodes  82 - 1  and  82 - 2  directly contact the high-density source and drain regions  79 - 1  and  79 - 2  without contact holes, one mask process can be omitted, leading to a simplified manufacturing process. In addition, since the silicide layers  78 - 1  and  78 - 2  are, respectively, formed between the source and drain regions  79 - 1  and  79 - 2  and the source and drain electrodes  82 - 1  and  82 - 2 , a contact resistance can be reduced. Furthermore, the silicide layers  78 - 1  and  78 - 2  serves as an etching barrier for source and drain electrodes  82 - 1  and  82 - 2  to improve an etching selection ratio, and also serves as an impurity barrier during an ion-implanting process for the high-density source and drain regions  79 - 1  and  79 - 2  to minimize damages of the semiconductor layer  72 . 
     The TFT according to the second preferred embodiment of the present invention has an LDD structure or an off-set structure, electric characteristics can be improved. For example, since an off current is reduced, an on/off current ratio can be improved. The off-set structure can also be formed by omitting the low-density ion-implantation step of FIG.  3 B. 
     In the first to second preferred embodiments of the present invention, when the TFT having the source and drain electrodes of a dual-layered structure is applied to the active matrix flat panel display device, the source and drain electrodes come to have a low specific resistance and also improve transmittance of light. Also, since the source and drain electrodes and the pixel electrode are formed through a single mask process, maximum two mask processes are reduced, leading to a simplified manufacturing process. 
     FIGS. 4A to  4 G are cross-sectional views a process of manufacturing an active matrix flat panel display device according to one embodiment of the present invention. 
     A process of manufacturing an active matrix flat panel display device according to one embodiment of the present invention is explained in detail with reference to FIGS. 4A to  4 G. 
     First, as shown in FIGS. 4A and 4B, a buffer layer  202  is formed on a transparent insulating substrate  105 . An oxide layer is used as the buffer layer  202 . A polycrystalline silicon layer is deposited on the buffer layer  202  and then patterned to form a semiconductor layer  210 . 
     A first insulating layer  215  is formed over the whole surface of the substrate  105 . The first insulating layer  215  serves as a gate insulating layer. A first metal layer and a second insulating layer are sequentially deposited on the first insulating layer  215 . An oxide layer or a nitride layer is used as the second insulating layer. The first metal layer and the second insulating layer are patterned to form a gate electrode  220  and a capping layer  225  of the TFT  200  over the semiconductor layer  210 , and a lower capacitor electrode  160  and a dielectric layer  165  of the storage capacitor  150 . 
     Then, an n-type or a p-type low-density impurity is ion-implanted into both end portions of the semiconductor layer  210  which is not covered with the gate electrode  220  to form low-density source and drain regions  214 - 1  and  214 - 2 . 
     Thereafter, a third insulating layer is deposited over the whole surface of the substrate  105  and then etched-back to form spacers  230  on both side wall portions of the gate electrode  220  and the lower capacitor electrode  160 . 
     At the same time, the first insulating layer  215  is etched to form a gate insulating layer  215 , so that portions of the source and drain regions  214 - 1  and  214 - 2  that are not covered with the gate insulating layer  215  are exposed. 
     Subsequently, as shown in FIG. 4C, a second metal layer is deposited over the whole surface of the substrate. The second metal layer is made of a material such as Ni or Cr. The second metal layer is annealed at a low temperature of less than  500 □, so that the second metal layer reacts with silicon to form silicide layers  240  such as a Ni-silicide layer or a Cr-silicide layer on the exposed portions of the low-density source and drain regions  214 - 1  and  214 - 2 . 
     After the rest portion of the second metal layer that does not reacts with the silicon is removed, a high-density impurity having the same conductivity as the low-density source and drain regions  214 - 1  and  214 - 2  is ion-implanted into both end portions of the low-density source and drain regions  214 - 1  and  214 - 2  under the silicide layers  240  to form high-density source and drain regions  216 - 1  and  216 - 2 . Therefore, the source and drain regions of an LDD structure having both the low-density source and drain regions  214 - 1  and  214 - 2  and the high-density source and drain regions  216 - 1  and  216 - 2  are formed. A central portion of the semiconductor layer  210  under the gate electrode  220  acts as an active area (i.e., channel area). 
     Meanwhile, if a process of forming the low-density source and drain regions  214 - 1  and  214 - 2  is omitted after forming the gate electrode  22  and thereafter the high-density source and drain regions  216 - 1  and  216 - 2  are formed, portions of the semiconductor layer  210  under the spacers  230  which is not ion-implanted with impurity serve as an off-set region, so that the source and drain regions having an off-set structure can be formed. 
     Subsequently, the transparent conductive material layer  310   a  and the third metal layer  250   a  are sequentially deposited over the whole surface  105 . 
     As shown in FIG. 4D, the transparent conductive material layer  310   a  and the third metal layer  250   a  are then patterned to form source and drain electrodes  250  and  255  which directly contact the high-density source and drain regions  216 - 1  and  216 - 2 . The source and drain electrodes  250  and  255  therefore have a dual-layered structure. The transparent conductive material layer  310   a  is made of a material such as ITO, IZO or IO, and the third metal layer  250   a  is made of a material having a resistance value lower than the transparent conductive material layer such as Al, Al-alloy, Mo, Mo-alloy, Cr, or Ti. 
     The upper capacitor electrode  170  is formed at the same time as the source and drain electrodes  250  and  255 . Like the source and drain electrodes  250  and  255 , the upper capacitor electrode  170  also has a dual-layered structure. Portions of the transparent conductive material layer  310   a  and the third metal layers  310   a  and  250   a  over the pixel region  140  remains. 
     Subsequently, as shown in  4 E, a fourth insulating layer  260  are deposited over the whole surface of the substrate  105 . The fourth insulating layer  260  serves as a passivation layer and is made of an organic material such as acrylic or polyimide or an inorganic material such as an oxide layer or a nitride layer. 
     Next, as shown in FIG. 4F, a portion of the passivation layer  260  and a portion of the third metal layer  250   a  are etched to expose a portion of the transparent conductive material layer  310   a  over the pixel region  140 , so that an opening portion  266  is formed. The exposed portion of the transparent conductive material layer  310   a  serves as a pixel electrode  265 . 
     In manufacturing the active matrix display device according to the present invention, a manufacturing method according to the second preferred embodiment is used. However, other methods, for example, a manufacturing method according to the first preferred embodiment of the present invention can also be used. 
     Meanwhile, when the passivation layer is made of an organic material such as acrylic or polyimide, after a portion of the passivation layer  260  and a portion of the third metal layer  250   a  over the pixel region  140  are etched to form the opening portion  266 , a reflow process can be carried out to cover and insulate end portions of the third metal layer  250   a.    
     When such a manufacturing process is applied to the organic EL display, an organic EL layer that will be formed in subsequent process contacts only a portion of the transparent conductive material layer  310   a  which serves as the pixel electrode  265 , therefore reliability can be improved. According to the one embodiment, the passivation layer is formed to cover the third metal layer  250   a  by using the reflow process, without additional masking process and therefore open failure in the organic EL layer is prevented. 
     FIGS. 5A to  5 C are cross-sectional views illustrating a process of manufacturing an active flat panel matrix display device according to another embodiment of the present invention. 
     FIG. 5A shows a manufacturing process subsequent to FIG.  4 C. As shown in FIG. 5A, after the transparent conductive material layer  310   a  and the third metal layer  250   a  are sequentially deposited over the whole surface of the substrate  105 , a photoresist layer is deposited to a predetermined thickness on the third metal layer  250   a  and patterned into a photoresist pattern  600  using a half-tone mask to expose a portion of the third metal layer  250   a  corresponding to the TFT. Also, a portion of the photoresist pattern  600  corresponding to the pixel region  140 , i.e., a portion of the photoresist pattern  600  in which an opening portion will be formed, is formed to a relatively thin thickness. A thickness of the portion of the photoresist pattern  600  in which the opening portion will be formed depends on an etching process of the third metal layer  250   a.    
     As shown in FIG. 5B, using the photoresist pattern  600  as a mask, the third metal layer  250   a  is etched to form source and drain electrodes  250  and  255 , and at the same time, a portion of the third metal layer  250   a  in which the opening portion will be formed is removed. A portion of the transparent conductive material layer  310   a  corresponding to the pixel region  140  is exposed. Thereafter, the remaining portion of the photoresist pattern  600  is removed. 
     As shown in FIG. 5C, a planarization layer  260  is formed over the whole surface of the substrate  105 . The planarization layer  260  includes the opening portion  266  on the exposed portion of the transparent conductive material layer  310   a.  At this time, the opening portion  266  is formed to perfectly surround the metal layer  250   a,  whereby an organic EL element is formed only on the transparent conductive material layer  310   a  in subsequent process. Therefore, the active matrix display device according to another embodiment of the present invention is completed. 
     According to another embodiment, the passivation layer is formed to cover the third metal layer  250   a  by using the half-tone mask, without additional masking process and therefore open failure in the organic EL layer is prevented. The passivation layer is made of an organic material such as acrylic or polyimide or of an inorganic material such as silicon oxide or silicon nitride. 
     As described herein before, the TFT and the active matrix display device according to the preferred embodiments of the present invention have the following advantages. 
     The source and drain electrodes of the TFT can have a dual-layered structure without any additional process. When the active matrix display device is manufactured using the TFT having the dual-layered source and drain electrodes, four mask processes are performed, whereupon a manufacturing process is simplified, leading to high manufacturing yield and low production cost. 
     Also, since the capping layer is formed on the gate electrode of the TFT, while an ion-implanting process is performed to form the low-density source and drain regions, it is prevented that the gate electrode is damaged. 
     In addition, due to the silicide layers respectively formed between the source and drain regions and the source and drain electrodes, a contact resistance is reduced, leading to high reliability. Further, since the source and drain electrodes directly contact the source and drain regions without contact holes, a manufacturing process is simplified. 
     Further more, since an LDD region or an off-set region is formed in a self-align manner through the spacers formed both side wall portion of the gate electrode or the anodizing layer surrounding the gate electrode, a manufacturing process is simplified, and electric characteristics such as an on/off current ratio is improved. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.