text: reference will now be made in detail to preferred embodiments of the present invention , example of which is illustrated in the accompanying drawings . [ 0037 ] fig2 a 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 fig2 a , 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 fig2 b , 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 fig2 c , 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 fig2 d , 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 ( i 0 ). 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 . [ 0043 ] fig3 a 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 fig3 a , 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 fig3 b , 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 fig3 c , 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 fig3 d , 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 fig3 e 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 i 0 . 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 ionimplanting 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 . 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 . [ 0052 ] fig4 a 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 fig4 a to 4 g . first , as shown in fig4 a 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 fig4 c , 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 fig4 d , 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 fig4 f , 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 . [ 0070 ] fig5 a 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 . [ 0071 ] fig5 a shows a manufacturing process subsequent to fig4 c . as shown in fig5 a , 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 fig5 b , 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 fig5 c , 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 .