Abstract:
A thin film transistor comprises a gate electrode  18  formed on a substrate  10 , a gate insulation film  20 , a semiconductor layer  22 , a source electrode  36   a  and a drain electrode  36   b . The gate electrode, the source electrode or the drain electrode include a first conductor film  12 , a second conductor film  14  and a third conductor film  16 . The first conductor film is formed of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag, and has the side surfaces sloped. The second conductor film is formed of a film of Mo containing nitrogen, or an alloy of Mo, as a main component, containing nitrogen, and has the side surfaces sloped. The third conductor film is formed of Mo or an alloy of Mo as a main component.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a thin film transistor and a method for fabricating the thin film transistor, more specifically to a highly reliable thin film transistor using low resistance wiring, and a method for fabricating the thin film transistor. 
     Liquid crystal display devices have an advantage that they are thin and light, and can be operated at low voltages with small current consumption. Recently liquid crystal display devices are widely used as displays of personal computers, etc. 
     Generally, the display panels of liquid crystal display devices are each constituted with two transparent glass substrates and liquid crystal sealed between the two transparent glass substrates. On one of the opposed sides of the two glass substrates a black matrix, a color filter, an opposed electrode, an alignment film, etc. are formed, and thin film transistors, picture element electrodes and an alignment film are formed on the other of the opposed sides of the two glass substrates. 
     Polarization plates are adhered respectively to the sides of the two glass substrates, which are opposite to the opposed sides. The polarization axes of the two polarization plates are arranged normal to each other to provide a liquid crystal display of normally white mode. That is, light is transmitted when no electric filed is applied to the liquid crystal, and when an electric field is applied to the liquid crystal, light is shaded. On the other hand, the polarization axes of the two polarization plates are parallel with each other to provide the liquid crystal device of normally black mode. That is, light is shaded with no electric field applied to the liquid crystal, and light is transmitted with an electric field applied to the liquid crystal. 
     A conventional liquid crystal display device will be explained with reference to FIGS. 11A and 11B. FIG. 11A is a plan view of a conventional active matrix substrate of the invert stagger type. FIG. 11B is a sectional view of the active matrix substrate along the line A-A′ in FIG.  11 A. 
     As shown in FIG. 11B, a gate electrode  118  is formed of an Al film  112  and an Mo film  116  on a glass substrate  110 . As shown in FIG. 11A, the gate electrode  118  is connected to a gate bus line  118   a  of the same conductor films. 
     Al film  112  is used as a material of the gate electrode  118  because Al has low electric resistance. In the conventional liquid crystal devices Cr, etc., which are metals of relatively high electric resistance and high melting point, have been used. Recently, in accordance with large scales and higher definition of the liquid crystal display devices, low resistance materials, such as Al, etc., are used. 
     The Mo film  116  is formed on the Al film  112  because Mo has high heat resistance and makes good electric contact with the Al film  112  with the other wiring, etc. The gate bus line  118   a  is connected to TAB through ITO (Indium Tin Oxide) in a region not shown, but is connected to other wiring, etc. through the Mo film  116 . The gate bus line  118   a  can have good electric contact. 
     A gate insulation film  120  is formed on the glass substrate  110  with the gate electrode  118  formed on. An amorphous silicon film  122  is formed on the gate insulation film  120 . A channel protection film  124  is formed on the amorphous silicon film  122 . An n + -amorphous silicon film  126  is formed on the amorphous silicon film  122  with the channel protection film  124  formed on. A source electrode  136   a  and a drain electrode  136   b  are formed of an Mo film  128 , an Al film  130  and an Mo film  134  on the n + -amorphous silicon film  126 . As shown in FIG. 11A, the drain electrode  136   b  functions as a data bus line. 
     A protection film  138  is formed on the gate insulation film  120  with the source electrode  136   a  and the drain electrode  136   b  formed on. A contact hole  140  arriving at the source electrode  136   a  is formed in the protection film  138 . A picture element electrode  142  is formed of ITO on the protection film  138  connected to the source electrode  136   a  through the contact hole  140 . The Al film  130  is connected to the picture element electrode  142  through the Mo film  134 , and the electric contact is good. 
     As described above, in the conventional liquid crystal display device shown in FIGS. 11A and 11B, Al, which is a low resistance metal, is used as a material of the gate bus line and the data bus line, and is suitable for larger scales and higher definition. 
     However, in the liquid crystal display device shown in FIGS. 11A and 11B, the side surfaces of the Mo film  116  of the gate electrode  118  is acute, which makes the step coverage of the gate insulation film  120  poor. Film quality of the gate insulation film  120  is interrupted near the side surfaces of the Mo film  116 . Accordingly, the gate insulation film  120  has low dielectric voltage resistance. 
     The side surfaces of the Mo film  134  of the source-drain electrodes  136   a ,  136   b  are acute, which makes it difficult to form the protection film  138  in good quality. The protection film  128  has low dielectric voltage resistance. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a thin film transistor which uses a low resistance metal as a material of the gate electrodes and wiring but can ensure high reliability, and a method for fabricating the thin film transistor. 
     The above-described object is attained by a thin film transistor comprising a gate electrode formed on a substrate, a gate insulation film formed on the gate electrode, a semiconductor layer formed on the gate insulation film, and a source electrode and a drain electrode formed on the semiconductor layer, the gate electrode, the source electrode or the drain electrode including a first conductor film, a second conductor film formed on the first conductor film, and a third conductor film formed on the second conductor film; the first conductor film being formed of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag, and having side surfaces sloped; the second conductor film being formed of a film of Mo containing nitrogen, or an alloy of Mo containing nitrogen, and having side surfaces sloped; and the third conductor film being formed of Mo, or an alloy of Mo as a main component. The gate insulation film is formed on the gate electrode having the side surfaces generally sloped, whereby film quality of the gate insulation film is prevented from being interrupted near the side surfaces of the gate electrode. The gate insulation film can be highly reliable and can have high dielectric voltage resistance. The thin film transistor can be highly reliable. 
     The above-described object is attained by a thin film transistor comprising a gate electrode formed on a substrate, a gate insulation film formed on the gate electrode, a semiconductor layer formed on the gate insulation film, and a source electrode and a drain electrode formed on the semiconductor layer, the gate electrode, the source electrode or the drain electrode including a first conductor film, and a second conductor film formed on the first conductor film; the first conductor film being formed of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag, and having side surfaces sloped; the second conductor film including a lower layer formed of a film of Mo containing nitrogen or an alloy of Mo, as a main component, containing nitrogen, and an upper layer formed of a film of Mo or an alloy of Mo, as a main component, and side surfaces of the lower layer being sloped. The gate insulation film is formed on the gate electrode having the side surfaces generally sloped, whereby film quality of the gate insulation film is prevented from being interrupted near the side surfaces of the gate electrode. The gate insulation film can be highly reliable and can have high dielectric voltage resistance. The thin film transistor can be highly reliable. 
     The above-described object is attained by a method for fabricating a thin film transistor comprising the steps of forming a gate electrode on a substrate, forming an gate insulation film on the gate electrode, forming a semiconductor layer on the gate insulation film, and forming a source electrode and a drain electrode on the semiconductor layer, the step of forming the gate electrode, or the step of forming the source electrode and a drain electrode including the steps of: forming a first conductor film of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag; forming a second conductor film of Mo containing nitrogen or an alloy of Mo, as a main component, containing nitrogen; forming a third conductor film of Mo or an alloy of Mo as a main component; and etching the second conductor film at a higher etching rate than the first conductor film, and etching the third conductor film at a higher etching rate than the second conductor film to thereby slope side surfaces of the first conductor film and of the second conductor film. The gate insulation film is formed on the gate electrode having the side surfaces generally sloped, whereby film quality of the gate insulation film is prevented from being interrupted near the side surfaces of the gate electrode. The gate insulation film can be highly reliable and can have high dielectric voltage resistance. The thin film transistor can be highly reliable. 
     The above-described object is attained by a method for fabricating a thin film transistor comprising the steps of forming a gate electrode on a substrate, forming an gate insulation film on the gate electrode, forming a semiconductor layer on the gate insulation film, and forming a source electrode and a drain electrode on the semiconductor layer, the step of forming the gate electrode, or the step of forming the source electrode and the drain electrode including the steps of: forming a first conductor film of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag; forming a second conductor film including a lower layer of Mo containing nitrogen or an alloy of Mo, as a main component, containing nitrogen, and an upper layer of Mo or an alloy of Mo as a main component; and etching the lower layer of the second conductor film at a higher etching rate than the first conductor film, and etching the upper layer of the second conductor film at a higher etching rate than the lower layer of the second conductor film to thereby slope side surfaces of the first conductor film and side surfaces of the lower layer of the second conductor film. The gate insulation film is formed on the gate electrode having the side surfaces generally sloped, whereby film quality of the gate insulation film is prevented from being interrupted near the side surfaces of the gate electrode. The gate insulation film can be highly reliable and can have high dielectric voltage resistance. The thin film transistor can be highly reliable. 
     As described above, according to the present invention, the gate electrode is formed of an AlNd film, an Mo film containing nitrogen, which can be etched at a higher etching rate than the AlNd film, and an Mo film, which can be etched at a higher etching rate than the Mo film containing nitrogen, whereby the gate electrode can be formed with the side surfaces generally sloped. The gate insulation film, which is formed on such gate electrode, can be kept from interruption of film quality near the side surfaces of the gate electrode. According to the present invention, the gate insulation film can have high reliability and high dielectric voltage resistance. Accordingly, the thin film transistor can have high reliability. 
     According to the present invention, the same technique that is applied to the gate electrode is applied also to the source/drain electrodes, whereby the source/drain electrodes can be formed with the side surfaces generally sloped. The protection film is formed on such source/drain electrodes, whereby the protection film is kept from interruption of film quality near the side surfaces of the source/drain electrodes. Thus, according to the present invention, the protection film can have higher dielectric voltage resistance, which leads to higher reliability of liquid crystal display devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of the thin film transistor according to one embodiment of the present invention. 
     FIGS. 2A to  2 D are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 1). 
     FIGS. 3A to  3 C are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 2). 
     FIGS. 4A to  4 C are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 3). 
     FIGS. 5A to  5 C are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 4). 
     FIGS. 6A and 6B are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 5). 
     FIGS. 7A and 7B are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 6). 
     FIGS. 8A and 8B are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 7). 
     FIGS. 9A and 9B are sectional views of the thin film transistor according to the embodiment of the present invention in the steps of the method for fabricating the same, which explain the method (Part 8). 
     FIG. 10 is a graph of reliability evaluation results. 
     FIG. 11A is a plan view of the conventional liquid crystal display device. 
     FIG. 11B is a sectional view of the conventional liquid crystal display device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The thin film transistor according to a first embodiment of the present invention and the method for fabricating the same will be explained with reference to FIGS. 1 to  10 . FIG. 1 is a sectional view of the thin film transistor according to the present embodiment. FIGS. 2A to  9 B are sectional view of the thin film transistor according to the present embodiment in the steps of the method for fabricating the same, which shows the method. FIG. 10 is a graph of results of reliability evaluation. 
     (Thin Film Transistor) 
     As shown in FIG. 1, on a glass substrate  10 , a 150 nm-thickness AlNd (Nd: Neodymium) film  12  is formed with the side surfaces sloped. On the AlNd film  12 , a 50 nm-thickness Mo film  14  containing nitrogen is formed with the side surfaces sloped. On the Mo film  14  containing nitrogen, a 30 nm-thickness Mo film  16  is formed. 
     The AlNd film  12 , the Mo film  14  containing nitrogen and the Mo film  16  form a gate electrode  18 . The Mo film  16  is not essentially sloped, but the Mo film  16  is so thin relative to a total thickness of the gate electrode  18  that the side surfaces of the gate electrode  18  are sloped as a whole. 
     A gate insulation film  20  is formed on the glass substrate  10  with the gate electrode  18  formed on. The gate insulation film  20 , which is formed on the gate electrode  18  having the side surfaces sloped, has good film quality. Accordingly, the gate insulation film  20  can ensure higher dielectric voltage resistance. 
     A 30 nm-thickness amorphous silicon film  22  is formed on the gate insulation film  20 . A channel protection film  24  of a 120 nm-thickness SiN film is formed on the amorphous silicon film  22 . The side surfaces of the channel protection film  24  are sloped. 
     A 30 nm-thickness n + -amorphous silicon film  26  is formed on the amorphous silicon film  22  with the channel protection film  24  formed on. 
     A 20 nm-thickness Ti film  28  is formed on the n + -amorphous silicon film  26 . 
     On the Ti film, a 150 nm-thickness Al film  30  is formed with the side surfaces sloped. On the Al film  30 , a 50 nm-thickness Mo film  32  containing nitrogen is formed with the side surfaces sloped. A 30 nm-thickness Mo film  34  is formed on the Mo film  32  containing nitrogen. 
     The Ti film  28 , the Al film  30 , the Mo film  32  containing nitrogen and the Mo film  34  form a source electrode  36   a  and a drain electrode  36   b . The Mo film  34  is not essentially sloped, but the Mo film  34  is so thin relative to the total thickness of the source/drain electrodes  36   a ,  36   b  that the source/drain electrodes  36   a ,  36   b  have the side surfaces sloped as a whole. 
     A protection film  38  of a 330 nm-thickness SiN film is formed on the entire surface. Because of the protection film  38  formed on the source/drain electrodes  36   a ,  36   b  having the side surfaces sloped, the protection film  38  has good film quality. Accordingly, the protection film  38  can ensure high dielectric voltage resistance. 
     A contact hole  40  arriving at the source electrode  36   a  is formed in the protection film  38 . A picture element electrode  42  of a 70 nm-thickness ITO (Indium Tin Oxide) connected to the source electrode  36   a  through the contact hole  40  is formed on the protection film  38 . 
     Thus, the thin film transistor according to he present embodiment is formed. 
     (Method for Fabricating the Thin Film Transistor) 
     Then, the method for fabricating the thin film transistor according to the present embodiment will be explained with reference to FIGS. 2A to  9 B. 
     First, on the glass substrate  10 , the 150 nm-thickness AlNd film  12  is formed by sputtering. As a target, an Al alloy containing Nd is used. 
     Then, the 50 nm-thickness Mo film  14  containing nitrogen is formed on the entire surface by reactive sputtering using N 2  gas. A target is formed of Mo. As a film forming condition, a flow rate ratio between Ar gas and N 2  gas is, e.g., 9:1. A nitrogen content in the Mo film  14  containing nitrogen is, e.g., 0.01 to 0.1 with respect to an Mo amount. 
     Next, the 30 nm-thickness Mo film  16  is formed on the entire surface by sputtering. Thus, the AlNd film  12 , the Mo film  14  containing nitrogen, and the Mo film  16  form a multi-layer film  17  (see FIG.  2 A). 
     Next, a photoresist film is formed on the entire surface by spin coating. Then, the photoresist film is patterned by photolithography. Thus, a photoresist mask  44  for patterning the gate electrode  18  is formed (see FIG.  2 B). 
     Next, with the photoresist mask  44  as a mask, the AlNd film  12 , the Mo film  14  containing nitrogen and the Mo film  16  are wet etched together. As an etchant, an aqueous solution of a mixture of, e.g., 67.3 wt % of phosphoric acid, 5.2 wt % of nitric acid, and 10 wt % of acetic acid is used. This etchant allows the Mo film  16  to be etched at a higher etching rate than the Mo film  14  containing nitrogen, and the Mo film  14  containing nitrogen to be etched at a higher etching rate than the AlNd film  12 . Resultantly, the side surfaces of the AlNd film  12  and the Mo film  14  containing nitrogen can be sloped. Further, the gate electrode  18  can be formed, having the side surfaces sloped as a whole (see FIG.  2 C). 
     The side surfaces of the Mo film  16  are not essentially sloped. In a case that the Mo film  16  is formed in an extreme thickness of above 30 nm, a ratio of the thickness of the Mo film  16  to a total thickness of the gate electrode  18  becomes higher, and the gate electrode  18  cannot have the side surfaces sloped as a whole. On the other hand, in a case that the Mo film  16  is formed in a smaller thickness of below 5 nm, the etchant cannot arrive the Mo film  16 , and the side surfaces of the Mo film  14  containing nitrogen and the AlNd film  18  cannot be sloped. Accordingly, the gate electrode  18  cannot have the side surfaces sloped as a whole. In order to form the gate electrode  18  having the side surfaces sloped as a whole, it is preferable to set a thickness of the Mo film  16  to be, e.g., 5 to 30 nm. 
     Next, the photoresist mask  44  is removed with a remover (see FIG.  2 D). 
     Next, the gate insulation film  20  is formed of a 350 nm-thickness SiN film on the entire surface by plasma CVD (Plasma enhanced Chemical Vapor Deposition). The gate insulation film  20 , which is formed on the gate electrode  18  having the side surfaces sloped as a whole, can have good film quality. The gate insulation film  20  can have high reliability and high dielectric voltage resistance. 
     Then, the 30 nm-thickness amorphous silicon film  22  is formed on the entire surface by plasma CVD. 
     Then, the channel protection film  24  is formed of a 120 nm-thickness SiN film on the entire surface by plasma CVD (see FIG.  3 A). 
     Then, a photoresist film is formed on the entire surface by spin coating. Then, the photoresist film is patterned by photolithography. Thus, the photoresist mask  46  for patterning the channel protection film  24  is formed (see FIG.  3 B). 
     Then, the channel protection film  24  is etched by dry etching with the photoresist mask  46  as a mask (see FIG.  3 C). 
     Next, the photoresist mask  46  is removed with a remover (see FIG.  4 A). 
     Then, the n + -amorphous silicon film  26  is formed by plasma CVD. Phosphorus is used as a dopant. 
     Next, the 20 nm-thickness Ti film is formed by sputtering. 
     Then, the 150 nm-thickness Al film  30  is formed by sputtering. A target is Al. 
     Then, the 50 nm-thickness Mo film  32  containing nitrogen. The Mo film  32  containing nitrogen is formed by, e.g., the same technique as the Mo film  14  containing nitrogen. 
     Next, the 30 nm-thickness Mo film  34  is formed by sputtering. The Mo film  34  is formed by, e.g., the same technique as the Mo film  16  (see FIG.  4 B). 
     Next, a photoresist film is formed on the entire surface by spin coating. Then, the photoresist film is patterned by photolithography. Thus, a photoresist film  48  for patterning the source/drain electrodes  36   a ,  36   b  is formed (see FIG.  4 C). 
     Then, with the photoresist mask  48  as a mask, the Mo film  34 , the Mo film  32  containing nitrogen and the Al film  30  are etched together. An etchant is, e.g., an aqueous solution of a mixture of 67.3 wt % of phosphoric acid, 5.2 wt % of nitric acid and 10 wt % of acetic acid. This etchant allows the Mo film  34  to be etched at a higher etching rate than the Mo film  32  containing nitrogen, and the Mo film  32  containing nitrogen to be etched at a higher etching rate than the Al film  30 . Resultantly, the side surfaces of the Al film  30  and the Mo film  32  containing nitrogen can be sloped as a whole (see FIG.  5 A). 
     Then, with the Al film  30  as a mask, the Ti film  28 , the n + -amorphous silicon film  26  and the amorphous silicon film  22  are etched. Thus, the source/drain electrodes  36   a ,  36   b  having the side surfaces sloped as a whole can be formed (FIG.  5 B). 
     Next, the photoresist mask  48  is removed with a resist remover (see FIG.  5 C). 
     Then, the protection film  38  of a 330 nm-thickness SiN film is formed by plasma CVD. The protection film  38 , which is formed on the source/drain electrodes  36   a ,  36   b  having the side surfaces sloped as a whole, can have good film quality. Thus, the protection film  38  having high reliability and high dielectric voltage resistance can be formed (see FIG.  6 A). 
     Next, a photoresist film is formed on the entire surface by spin coating. Then, the photoresist film is patterned by photolithography to form a photoresist mask  52  with an opening  50  formed in (see FIG.  6 B). 
     With the photoresist mask  52  as a mask, the protection film  38  is etched to form the contact hole  40  arriving at the source electrode  36   a  (see FIG.  7 A). 
     Then, the photoresist mask  52  is removed with a resist remover (see FIG.  7 B). 
     Then the 70 nm-thickness ITO (Indium Tin Oxide) film  41  is formed on the entire surface by sputtering (see FIG. 8 a ). 
     Next, photoresist film is formed on the entire surface by spin coating. Next, the photoresist film is patterned by photolithography. Thus, a photoresist mask  54  for forming a picture element electrode  42  is formed (see FIG.  8 B). 
     Next, with the photoresist mask  54  as a mask, the ITO film  41  is etched to form the picture element electrode  42  of the ITO (see FIG.  9 A). 
     Next, the photoresist mask  54  is removed with a resist remover (see FIG.  9 B). Thus, the thin film transistor according to the present embodiment is fabricated. 
     (Reliability Evaluation Results) 
     Results of reliability evaluation of the thin film transistor according to the present embodiment will be explained with reference to FIG.  10 . An insulation film was formed on a 960-TEG (Test Element Group), and voltages were applied to the insulation film, and test elements which had insulation defects were measured. FIG. 10 shows the measured numbers corresponding to the applied voltages. 
     In the Example, the thin film transistor according to the present embodiment, which includes the gate electrode formed of Mo/MoN/AlNd was tested. 
     In Control  1 , the thin film transistor shown in FIGS. 11A and 11B, which includes the gate electrode formed of Mo/AlNd was tested. In Control  2 , a thin film transistor includes the gate electrode formed of MoN/AlNd. 
     As seen in FIG. 10, in Controls  1  and  2 , insulation detects took place at applied voltages of above about 150 V. 
     In contrast to this, in the Example, no insulation defect took place at a 200 V applied voltage. Based on this, the present embodiment shows that even in a case that low resistance wiring, as of AlNd, is used, an insulation film of high reliability and high dielectric voltage resistance can be formed. 
     As described above, according to the present embodiment, the gate electrode is formed of an AlNd film, an Mo film containing nitrogen, which can be etched at a higher etching rate than the AlNd film, and an Mo film, which can be etched at a higher etching rate than the Mo film containing nitrogen, whereby the gate electrode can be formed with the side surfaces sloped as a whole. The gate insulation film, which is formed on such gate electrode, can be kept from interruption of film quality near the side surfaces of the gate electrode. According to the present embodiment, the gate insulation film can have high reliability and high dielectric voltage resistance. Accordingly, the thin film transistor can have high reliability. 
     According to the present embodiment, the same technique that is applied to the gate electrode is applied also to the source/drain electrodes, whereby the source/drain electrodes can be formed with the side surfaces sloped as a whole. The protection film is formed on such source/drain electrodes, whereby the protection film is kept from interruption of film quality near the side surfaces of the source/drain electrodes. Thus, according to the present embodiment, the protection film can have higher dielectric voltage resistance, which leads to higher reliability of liquid crystal display devices. 
     [Modifications] 
     The present invention is not limited to the above-described embodiment and covers other various modification. 
     For example, in the above-described embodiment, the Mo film containing nitrogen, and the Mo film are separately formed, but they may be continuously formed. That is, a film of the Mo film as an upper layer and the Mo film containing nitrogen as a lower layer may be formed. Such film can be formed by first forming the Mo film containing nitrogen by sputtering at, e.g., a 9:1 flow rate ratio between Ar gas and N 2  gas, and then forming the Mo film with the sputtering set on and with the feed of the N 2  gas stopped. 
     In the above-described embodiment, the AlNd film has a 150 nm-thickness, and the Mo film containing nitrogen has a 50 nm-thickness, but these film thicknesses are not essential. A film thickness of the AlNd film and a film thickness of the Mo film containing nitrogen may be suitably set so that the latter is, e.g., about 0.1 to 0.7 times the former, preferably about 0.3 to 0.5 times the former. 
     In the above-described embodiment, the gate electrode includes the AlNd film  12 . The AlNd film is not essential and may includes Al film. An Al alloy containing at least one element of Sc (Scandium), Ta, Zr (Zirconium), Y (Yttrium), Ni, Nb (Niobium) and B may be used. 
     In the above-described embodiment, the source/drain electrodes  36   a ,  36   b  are formed of the Al film  30 , but may be formed of AlNd. An Al alloy containing at least one element of Sc, Ta, Zr, Y, Ni, Nb and B may be used. 
     In the above-described embodiment, the AlNd film  12  and the Al film  30  are used, but they are not essential. Cu, Ag or others may be used. An alloy film containing Cu as a main component, an alloy film containing Ag as a main component, or others may be used. 
     In the above-described embodiment, the Mo film is used, but the Mo film is not essential. An alloy containing Mo as a main component, e.g., Mo containing Ta, Mo containing W (tungsten), others may be used.