Patent Publication Number: US-2011048953-A1

Title: Metal wire structure with high-melting-point protective layer and its manufacturing method

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a metal wire structure with high-melting-point protective layer and its manufacturing method, and more particularly to an innovative one which prevents the generation of silicide and produces protective effect. 
     2. Description of Related Art 
     The conventional Hot Wire Chemical Vapor Deposition (HWCVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) are widely applied to the manufacturing processes of various films, including: semi-conductors, liquid crystal display (LCD) panels and solar panels, helping to form a thin film on a substrate. Such film is made of Amorphous Silicon (a-Si) or other components (depending on the reactant gases supplied). 
     The major disadvantages of PECVD include: low deposition rate, low productivity, longer deposition time and cost. The disadvantages of HWCVD include: difficult to control the concentration of free radical or the filament temperature, and lower film quality. 
       FIG. 1  depicts a hybrid chemical vapor deposition combining HWCVD and PECVD (patent No. WO 2009/2009499). Of which, a closed reaction chamber  810  comprises: a reaction space  820 , a plasma generating unit  830 , a hot wire device  840 , a substrate  850 , a substrate carrier  860 , a heater  870 , a substrate feeder  875  and a substrate discharger  880 . The plasma generating unit  830  is used to generate plasma-excited atoms of vapor chemicals, and the hot wire device  840  is used to generate thermally-excited atoms of vapor chemicals. For instance, the mixture of hydrogen (H 2 ) and silicon hydride (SiH 4 ) is fed into the reaction space  820  at 1:100; the hot wire device  840  is heated to 1850° C., the plasma generating unit  830  generates the energy of 25 w/100 cm 2  for the substrate, and the heater  870  maintains the temperature of 400° C. With the use of HWCVD and PECVD, a-Si film can be generated on the substrate  850 . 
       FIG. 2  depicts another conventional HWCVD technique (patent No. EP1986242A2), which comprises: a reaction chamber  91 , a gas feed portion  92 , a direct current (DC) power supply  93 , a catalytic hot wire  94 , an exhaust valve  95 , a carrier platform  96  and a heater  97 . The carrier platform  96  is provided with a bottom layer  920 , which can be heated by the heater  97 ; a film  910  is gradually formed on the bottom layer  920 . 
     However, both hot wire device  840  and catalytic hot wire  94  are made of pure tungsten; when silicon hydride (SiH 4 ) is filled into the reaction space  820  and the reaction chamber  91 , and the temperature of hot wire device  840  or catalytic hot wire  94  hasn&#39;t reached the melting point of silicon (about 1410° C.), the gas will contact with the hot wire device  840  or catalytic hot wire  94 , but cannot be fully decomposed, with some residual gas left on the surface of hot wire device  840  or catalytic hot wire  94 . Then, the silicide (e.g. tungsten silicide) is formed, leading to change of the filament resistance. Take catalytic hot wire  94 , for example,  FIGS. 3A and 3B  depicts the outside view of the catalytic hot wire  94  without and with silicide respectively, whilst  FIGS. 4A and 4B  depicts the partially enlarged sectional view of the surface of catalytic hot wire  94  without or with silicide respectively. It can be clearly seen that, when silicide  941  is formed on the surface of the catalytic hot wire  94 , silicide  941  may generate many cracks  942  due to expansion and contraction, as the surface temperature of the catalytic hot wire  94  is at normal temperature in idle state, or at 1850° C. in operating state. In addition, when the silicide  941  is fully covered onto the catalytic hot wire  94 , the function of the catalytic hot wire  94  will be lost, affecting the process of hot wire chemical vapor deposition seriously. 
     Hence, it is important to know how to prevent generation of silicide with fed gas when the temperature of tungsten filament (either hot wire device  840  or catalytic hot wire  94 ) increases from normal temperature to 1850° C. 
     Thus, to overcome the aforementioned problems of the prior art, it would be an advancement if the art to provide an improved structure that can significantly improve the efficacy. 
     SUMMARY OF INVENTION 
     The object of the present invention is to provide a metal wire structure with high-melting-point protective layer and its manufacturing method, which prevents the generation of silicide and produces protective effect to resolve the shortcomings of prior art. 
     In order to achieve the above mentioned object, this invention is provided. A manufacturing method of metal wire structure with high-melting-point protective layer comprising the following steps: 
     preparation step: preparing a core and a discharge device, of which the core in a threaded shape is made of metal material; the discharge device being provided with a positive electrode, a negative electrode, a discharge reaction tank, a discharge processing medium, an electrode fixed portion and a discharge reaction member; the discharge processing medium being placed into the discharge reaction tank, the electrode fixed portion being used to fix the core, which is linked to the negative electrode; the discharge reaction member made of metal being linked to the positive electrode; a preset discharge gap being defined between the core and the discharge reaction member, and filled with the discharge processing medium; the discharge processing medium consisting of either carbon atom or nitrogen atom; 
     discharge step: the discharge device being activated to enable electrical discharge of the core and the discharge reaction member; a local temperature in this discharge process being over 5000° C., so metal atoms of the core impinging dispersedly on an exterior surface of the discharge reaction member, meanwhile the metal atoms of the discharge reaction member being combined with atoms in the discharge processing medium, and impinging dispersedly on the exterior surface of the core, so a protective layer being gradually formed on the exterior surface of the core; 
     finish step: a metal wire structure with high-melting-point protective layer being made which comprises:
         a core which is made of metal material and is shaped as a thread;   a protective layer which is made of either metal carbide or metal nitride; the protective layer being gradually bonded onto an exterior surface of the core until a preset thickness, and then fully covered onto the core through a plating process of discharge reaction at temperature over 5000° C.       

     About the structure of this invention, a metal wire structure with high-melting-point protective layer comprises: 
     a core which is made of metal material and is shaped as a thread; 
     a protective layer which is made of either metal carbide or metal nitride; the protective layer being gradually bonded onto an exterior surface of the core until a preset thickness, and then fully covered onto the core through a plating process of discharge reaction at temperature over 5000□. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of the first prior art. 
         FIG. 2  shows a schematic view of the second prior art. 
         FIG. 3A  shows a perspective view that no silicide is formed on the surface of conventional catalytic hot wire. 
         FIG. 3B  shows a perspective view that silicide is already formed on the surface of conventional catalytic hot wire. 
         FIG. 4A  shows a partially enlarged sectional view that no silicide is formed on the surface of conventional catalytic hot wire. 
         FIG. 4B  shows a partially enlarged sectional view that silicide is already formed on the surface of conventional catalytic hot wire. 
         FIG. 5  is a view illustrating the present invention. 
         FIG. 6  shows a flow chart of the present invention. 
         FIG. 7  shows a schematic view of the processing system of the present invention. 
         FIG. 8  shows a partially enlarged view of  FIG. 7 . 
         FIG. 9A  shows a schematic view of the first discharge process of the present invention. 
         FIG. 9B  shows a schematic view of the second discharge process of the present invention. 
         FIG. 9C  shows a schematic view of the third discharge process of the present invention. 
         FIG. 10  shows a schematic view that the structure of the present invention is applied to HWCVD device. 
         FIG. 11  shows another schematic view that the structure of the present invention is applied to HWCVD device. 
         FIG. 12  shows a partially enlarged view that the structure of the present invention is applied to HWCVD device. 
         FIG. 13  shows an appearance view of common tungsten filament. 
         FIG. 14  shows an appearance view of the present invention. 
         FIG. 15  shows a partially enlarged view of the present invention. 
         FIG. 16  shows an EDS analysis view of the protective layer of the present invention. 
         FIG. 17  shows a schematic view that common tungsten filament is heated to 600° C. 
         FIG. 18  shows a schematic view that the present invention is heated to 600° C. 
         FIGS. 19A ,  19 B,  19 C and  19 D show the surface the metal wire structure with high-melting-point protective layer after completion of discharge that is amplified to 25 times, 50 times, 100 times and 200 times respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a metal wire structure with high-melting-point protective layer and its manufacturing method. Referring to  FIG. 5 , the metal wire structure  100  of the present invention with high-melting-point protective layer comprises: 
     a core  20 , which is made of metal material and is shaped as a thread; 
     a protective layer  30 , which is made of either metal carbide or metal nitride; the protective layer  30  is gradually bonded onto the surface of the core  20  until a preset thickness, and then fully covered onto the core  20  through a plating process of discharge reaction at temperature over 5000° C.; moreover, the cross section of the core  20  is of round (shown in  FIG. 5 ), rectangular, flat or other geometric shapes. 
     Referring to  FIG. 6 , the manufacturing method of the present invention includes the following steps: 
     preparation step  11 : preparing a core  20  and a discharge device  40 , of which the core  20  in a threaded shape is made of metal material; the discharge device  40  is provided with a positive electrode  41 , a negative electrode  42 , a discharge reaction tank  43 , a discharge processing medium  44 , an electrode fixed portion  45  and a discharge reaction member  46 ; the discharge processing medium  44  is placed into the discharge reaction tank  43 , the electrode fixed portion  45  is used to fix the core  20 , which is linked to the negative electrode  42 ; the discharge reaction member  46  made of metal is linked to the positive electrode  41 ; a preset discharge gap S is defined between the core  20  and the discharge reaction member  46 , and filled with the discharge processing medium  44 ; furthermore, the discharge processing medium  44  consists of either carbon atom or nitrogen atom; 
     discharge step  12 : the discharge device  40  is activated to enable electrical discharge of the core  20  and the discharge reaction member  46 ; referring to  FIGS. 9  A,  9 B and  9 C, the local temperature in this discharge process is over 5000° C., so metal atoms of the core  20  impinge dispersedly on an exterior surface of the discharge reaction member  46 , meanwhile the metal atoms of the discharge reaction member  46  are combined with the atoms of the discharge processing medium  44  (i.e. carbon or nitrogen atoms), and impinge dispersedly on the exterior surface of the core  20 , so a protective layer  30  is gradually formed on the exterior surface of the core  20 ; 
     finish step  13 : a metal wire structure  100  with high-melting-point protective layer is made which comprises: 
     a core  20 , made of metal material and shaped as a thread; 
     a protective layer  30 , made of either metal carbide or metal nitride; the protective layer  30  is gradually bonded onto the surface of the core  20  until a preset thickness of protective layer, and then fully covered onto the core  20  through a plating process of discharge reaction at temperature over 5000° C. 
     More specifically, the core  20  is made of W, Pt, Pd, Mo, Ti, Nb, Ta, Co, Ni, Cr, Mn or tungsten alloy, platinum alloy, palladium alloy, molybdenum alloy, titanium alloy, niobium alloy, tantalum alloy, cobalt alloy, nickel alloy, chrome alloy, or manganese alloy. The protective layer  30  is made of either metal carbide or metal nitride containing W, Pt, Pd, Mo, Ti, Nb, Ta, Co, Ni, Cr, Mn, tungsten alloy, platinum alloy, palladium alloy, molybdenum alloy, titanium alloy, niobium alloy, tantalum alloy, cobalt alloy, nickel alloy, chrome alloy, or manganese alloy (e.g.: TiC, TaC, TiN, WC and CrC). 
     In addition, the core  20  and the protective layer  30  can be made of materials with similar thermal expansion coefficient so as to prevent the bonding relation due to thermal expansion. For example: when the core  20  is made of tungsten, the expansion coefficient is about 4.6 (10 −6 /° C.), and the protective layer  30  can be made of WC or TiC, with the thermal expansion coefficient of WC approx. 3.7 to 5.7 (10 −6 /° C.), and that of TiC approx. 5.5 (10 −6 /° C.), showing a similar thermal expansion coefficient of the core  20  and the protective layer  30 . 
     It is assumed that the discharge reaction member  46  is made of titanium, and the discharge processing medium  44  is a solution containing carbon atom; the key feature of the present invention lies in the discharge mechanism, whereby a temperature over 5000° C. is generated during the discharge process, so that the titanium atom of the discharge reaction member  46  and the carbon atom in the discharge processing medium  44  are combined into TiC impinging on the electrode (tungsten is assumed), and closely bonded onto the electrode to form gradually a thin TiC protective layer. The bonding process among atoms presents excellent compactness. In other words, when the metal wire structure  100  of the present invention with a high-melting-point protective layer (it is assumed that the core  20  is made of tungsten), the operating temperature of the energized tungsten filament is about 1850° C.˜2100° C., much lower than the temperature generated by TiC protective layer. So, the TiC protective layer no longer reacts with the reactant gas (e.g. silicon hydride or hydrogen), nor generates silicide. Certainly, the discharge processing medium  44  is also a kind of gas containing nitrogen atom (e.g.: N 2 ), so that the carbon and nitrogen atoms are combined into TiN impinging on the electrode, and closely bonded onto the electrode to form gradually a thin TiN protective layer. 
     In addition, as for the metal wire structure  100  with high-melting-point protective layer after completion of discharge, the surface is shown in  FIGS. 19A ,  19 B,  19 C and  19 D, wherein the surface is amplified to 25 times, 50 times, 100 times and 200 times. 
     The present invention can be applied to a HWCVD device (namely, the catalytic hot wire  94  of prior art can be replaced as a metal wire structure  100  of the present invention with a high-melting-point protective layer); referring to  FIGS. 10 ,  11  and  12 , when silicon hydride (SiH 4 ) (shown by the arrow) is filled into the reaction chamber  91 , and the temperature of the core  20  hasn&#39;t reached the melting point of silicon (about 1410° C.), the protective layer  30  can protect the core  20  not to contact with gas (the melting point of the protective layer  30  is over 5000° C.). Hence, it helps to resolve the shortcomings of prior art that gas cannot be fully decomposed, with some residual gas left on the surface of catalytic hot wire  94  (i.e. generation of silicide). 
     The products of the present invention can be used in some applications such as: 
     [a] Example one: the metal wire structure with high-melting-point protective layer is heated up, then the reactant gas passing through the surface of the protective layer  30  is heated to generate free radical, allowing for technical applications for cleaning the surface of Si, Al and TiN, as well as copper film (i.e. Cu film), etc. The reactant as can be selected optionally from any group of hydrogen (H 2 ), ammonia (NH 3 ), silicon hydride (SiH 4 ), hydrazine (NH 2 NH 2 ) and water (H 2 O). For instance, if the reactant gas is hydrogen (H 2 ) or vapor (H 2 O), it can generate free radical of H atom, if the reactant gas is ammonia (NH 3 ), it can generate free radical of NH and NH 2  atoms. 
     [b] Example two; the metal wire structure with high-melting-point protective layer is heated up, then the reactant gas (CH 4 ) passing through the surface of the metal wire is heated to generate free radical (C atom, etc), allowing for DLC (Diamond-Like Carbon) plating. 
     The actual test results of the present invention are described below: 
       FIGS. 13 and 14  depict separately the perspective view of conventional tungsten filament and the present invention.  FIG. 15  depicts a partially enlarged view of the present invention, wherein 2˜3 μm protective layer  30  of the present invention can be clearly observed. 
       FIG. 16  depicts EDS (Energy Dispersive Spectrometer) analysis of the protective layer  30 , of which carbon atom is 67%, titanium atom 3% and tungsten atom 30%, proving the covering effect of the protective layer  30 . 
     Vickers hardness test results indicate that, the hardness of common tungsten filament is HV400, but that of the present invention increases to HV700; common tungsten filament will be softened when it is heated electrically (DC) up to 600° C. (shown in  FIG. 17 ), but the present invention lacks of such phenomenon when it is heated up to 600° C. (shown in  FIG. 18 ). 
     In addition, the temperature distribution of common tungsten filament is shown in Table 1 and  FIG. 17  (serial number of positions in Table 1 corresponds to that of positions A 1 ˜A 14  in  FIG. 17 ). It can be seen that, the temperature distribution of common tungsten filament is extremely uneven (high temperature concentrated at right side). However, the temperature distribution of the present invention is shown in Table 2 and  FIG. 18  (serial number of positions in Table 2 corresponds to that of positions B 1 ˜B 14 ). It can be seen that, the temperature distribution of the present invention is even. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Temperature distribution of common tungsten filament 
               
            
           
           
               
               
               
            
               
                   
                 Serial No of positions 
                 Temperature(° C.) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Point A1 
                 596 
               
               
                   
                 Point A2 
                 580 
               
               
                   
                 Point A3 
                 552 
               
               
                   
                 Point A4 
                 511 
               
               
                   
                 Point A5 
                 492 
               
               
                   
                 Point A6 
                 490 
               
               
                   
                 Point A7 
                 507 
               
               
                   
                 Point A8 
                 518 
               
               
                   
                 Point A9 
                 328 
               
               
                   
                 Point A10 
                 338 
               
               
                   
                 Point A11 
                 57 
               
               
                   
                 Point A12 
                 68 
               
               
                   
                 Point A13 
                 44 
               
               
                   
                 Point A14 
                 42 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Temperature distribution of the present invention 
               
            
           
           
               
               
               
            
               
                   
                 Serial No of positions 
                 Temperature(° C.) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Point B1 
                 606 
               
               
                   
                 Point B2 
                 600 
               
               
                   
                 Point B3 
                 603 
               
               
                   
                 Point B4 
                 596 
               
               
                   
                 Point B5 
                 598 
               
               
                   
                 Point B6 
                 600 
               
               
                   
                 Point B7 
                 598 
               
               
                   
                 Point B8 
                 577 
               
               
                   
                 Point B9 
                 104 
               
               
                   
                 Point B10 
                 68 
               
               
                   
                 Point B11 
                 49 
               
               
                   
                 Point B12 
                 33 
               
               
                   
                 Point B13 
                 35 
               
               
                   
                 Point B14 
                 29 
               
               
                   
                   
               
            
           
         
       
     
     It is proved experimentally that, in an oxygen-bearing environment, if the catalytic hot wire  94  of prior art is made of tungsten, and the temperature is about 1000° C.˜2000° C., wire rupture may occur; but, due to the protective layer  30 , the core  20  of the present invention will not rupture in an oxygen-bearing environment at 1000° C.˜2000° C. 
     The advantages and efficacies of the present invention can be summarized below: 
     1. Without generation of silicide. In the prior art, when silicon hydride (SiH 4 ) contacts with hot wire device  840  or catalytic hot wire  94  whose temperature hasn&#39;t reached the melting point of silicon (about 1410° C.), the gas cannot be fully decomposed, with some residual gas left on the surface of hot wire device  840  or catalytic hot wire  94 . Namely, silicide  941  is formed. When the silicide  941  is fully covered onto the catalytic hot wire  94 , the function of the catalytic hot wire  94  will be lost, affecting the process of hot wire chemical vapor deposition seriously. With the use of discharge processing method, a protective layer  30  is formed on the exterior surface of the core  20 , thus maintaining the function of the core  20  and preventing reaction of gas with the core  20  against generation of silicide  941 . 
     2. Producing protective effects. In the prior art, the silicide  941  is prone to form many cracks  942  due to expansion and contraction, affecting the function and service life of the catalytic hot wire  94 ; with the use of protective layer  30 , the present invention can prevent the forming of silicide  941  on the core  20  for realizing the protective effects. 
     The aforementioned description of the preferred embodiments shows that the present invention can really meet the above-specified purpose and patent specifications, so the patent application is claimed herein. 
     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.