Abstract:
A hollow target assembly has a support tube, a target body and a plurality of elastic elements. The target body includes a plurality of hollow target materials and they pass through the support tube sequentially and locate at the outer surface of the support tube. By the grooves formed and extended from an end of the inside wall of the hollow target material and the corresponding concaves formed at the outside wall of the support tube, the elastic elements can lean and be positioned in the space generated by the grooves and corresponding concaves. Therefore, the target body and the support tube are brought together closely by these elastic elements in a simple and a low-cost way.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a sputtering target assembly, especially a hollow target assembly using elastic elements to provide good adhesiveness between the support tube and the target body. 
         [0003]    2. Description of the Prior Arts 
         [0004]    The sputtering efficiency of conventional plane target is only from 15% to 40%, which makes it unsuitable for large area deposition. To reduce cost, the rotating target is widely used in large area deposition in place of the plane target because the sputtering efficiency of the rotating target can reach 70% to 90%. 
         [0005]    A rotating target normally comprises a target body and a support tube. The target body covers the outer circumferential surface of the support tube. The target body will generate large amount of heat during the deposition, and the heat needs to be conducted to the cooling medium via the support tube. Therefore, sufficient contact area between the support tube and the target body is necessary to provide good heat conduction. Conventionally, metals with low melting point will be filled to the gap between the target body and the support tube so they can contact with each other nicely. However, the cost for the metals having low melting point is too high, and the inside surface of the target body and the outside surface of the support tube need further metallization. Furthermore, during the deposition and cooling processes, cracks may generate between the target body and the support tube because they have different heat expansion coefficient. 
         [0006]    To solve the above-mentioned problem, U.S. 2008/0003385A1 and WO 2009/036910A1 disclose a support tube that includes a meshing part consisting of at least either a protruding shape or a recessed shape at the interface between the support tube and the target body, as shown in  FIG. 7 . The target body is adhered with the support tube by heat treatment or casting. However, the equipment for heat treatment is expensive and will accordingly increase the production cost. Further, cracks and peelings may occur when the thermal expansion coefficient difference between the support tube and the target body is too large and causes too much stress on the meshing part. When using casting technique to form the target body, the high casting temperature and long time cooling cause the density of the target body to decrease and the microstructure of the target body not uniform so the quality of the deposited film is not good. U.S. 2009/0152108A1 discloses a target arrangement using elastic elements to overcome the gap generated between the support tube and the target body, as shown in  FIG. 8 . However, the support tube and the target body are adhered to each other by the friction of the elastic elements. If not enough elastic elements are used, the friction provided by the elastic elements may not be enough to prevent the target body from moving. How to put enough elastic elements into the gap between the support tube and the target body is a very complicated technique. 
       SUMMARY OF THE INVENTION 
       [0007]    The purpose of the present invention is to provide a hollow target assembly to improve the drawbacks of high cost, complicated process, bad contact between the target body and the support tube, and bad quality of the film deposited by the target material. 
         [0008]    To achieve the aforesaid purpose, the present invention provides a hollow target assembly, comprising: 
         [0009]    a support tube having a head end and a tail end, and concaves formed respectively on the outer surface of the tube at the position close to the head end and the tail end; 
         [0010]    a target body having at least a first hollow target material and a second hollow target material, and grooves are respectively formed on the inner surface of the first and second hollow target materials from their one ends over the axial direction so an open formed on said ends of the first and the second hollow target materials; and 
         [0011]    a plurality of elastic elements; 
         [0012]    wherein the first and second hollow target materials cover the outer circumferential surface of the support tube sequentially and open on the first and second hollow target materials respectively facing the head end and the tail end of the support tube so spaces are formed by the grooves on the inner surface of the first and second hollow target materials and the corresponding concaves on the outer surface of the head and tail end of the support tube, an elastic element is leaned and positioned in each space. 
         [0013]    Preferably, the target body further comprises at least a third hollow target material and said third hollow target material is positioned between the first and the second target material. The third hollow target material forms grooves in the inner surface from one end over the axial direction and corresponding concaves formed on the outer surface of the support tube so the elastic elements are put in the spaces formed by the grooves and corresponding concaves. 
         [0014]    Preferably, the first hollow target material further forms grooves on the end close to the third hollow target material over the axial direction and corresponding concaves formed on the outer surface of the support tube so the elastic elements are put in the spaces formed by the grooves and corresponding concaves. 
         [0015]    Preferably, the elastic element is a resilient sheet and its one end is placed in the groove and the other end is placed in the corresponding concave. In one embodiment, the grooves on the first, second and third target materials respectively form a continuous loop and the concaves on the support tube forms a continuous loop. In another embodiment, the grooves on the first, second and third target materials respectively form a discontinuous loop and the concaves on the support tube form a continuous loop. 
         [0016]    Preferably, the elastic element is a spring and its two ends respectively contact with the bottoms of the groove and the corresponding concave. In one embodiment, the grooves on the first, second and third target materials respectively form a discontinuous loop and the concaves on the support tube form a continuous loop. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is the cross-section view of the first preferred embodiment of the hollow target assembly of the present invention; 
           [0018]      FIG. 2  is the cross-section view of the second preferred embodiment of the hollow target assembly of the present invention; 
           [0019]      FIG. 3  is the cross-section view of the third preferred embodiment of the hollow target assembly of the present invention; 
           [0020]      FIG. 4  is the cross-section view of the fourth preferred embodiment of the hollow target assembly of the present invention; 
           [0021]      FIG. 5  is the top view of the fifth preferred embodiment of the hollow target assembly of the present invention; 
           [0022]      FIG. 6  is the top view of the sixth preferred embodiment of the hollow target assembly of the present invention; 
           [0023]      FIG. 7  is a cross-section view of one hollow target in the prior art; 
           [0024]      FIG. 8  is a cross-section view of another hollow target in the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    The above and other technical features and advantages of the present invention will be described in greater detail with reference to the drawings. 
         [0026]    To reduce the manufacture cost of the rotating target material and to improve the contact between the support tube and the target body, the present invention provides a hollow target assembly comprising a support tube  1 , a target body  2  and a plurality of elastic elements  3  as shown in  FIG. 1 . 
         [0027]    The support tube  1  has a head end  10  and a tail end  11 . Concaves  12  are formed respectively on the outer surface of the support tube  1  at the positions close to the head end  10  and the tail end  11 . The concaves  12  are made as a continuous loop by machining, and the cross section shape of the concaves  12  is rectangular, triangular or of any other shapes. 
         [0028]    The target body  2  comprises a first hollow target material  20  and a second hollow target material  21 . Grooves  23  are respectively formed in the inner surface of the first hollow target material  20  and the second hollow target material  21  from one end  22  of said target materials over the axial direction so an open  24  is respectively formed on the first hollow target material  20  and the second hollow target material  21 . The first and second hollow target materials  20 ,  21  cover the outer circumferential surface of the support tube  1  sequentially and open  24  on the first and second hollow target materials  20 ,  21  respectively facing the head end  10  and the tail end  11  of the support tube  1  so spaces  4  are formed by the grooves  23  on the inner surface of the first and second hollow target materials  20 ,  21  and the corresponding concaves  12  on the outer surface of the head end  10  and tail end  11  of the support tube  1 . 
         [0029]    Elastic elements  3  are leaned from the opens  24  on the first and second hollow target materials  20 ,  21  and placed in the spaces  4  formed by the grooves  23  and the corresponding concave  12 . The support tube  1  and the target body  2  are brought together closely by these elastic elements  3 . 
         [0030]    After the first hollow target material  20  is put through and covers the support tube  1  and the elastic elements  3  are placed in the spaces  4  formed by the grooves  23  and the corresponding concaves  12 , the first hollow target material  20  is heated up to the melting point of a metal. The melting metal is poured into the gap between the support tube  1  and the first hollow target material  20 . The heat source is removed and the temperature of the first hollow target material  20  decreases gradually so the melting metal is coagulated and therefore the first hollow target material  20  and the support tube  1  can adhere together nicely. Afterwards, the second hollow target material  21  is treated in the same manner to adhere with the support tube  1  nicely. In this regard, although the different thermal expansion among the support tube  1 , the target body  2  and the metal will cause gap generated between the support tube  1  and the target body  2  during the deposition or cooling process, the support tube  1  and the target body  2  still can maintain good adhesiveness with each other and the target body  2  will not shift by use of the elastic elements  3 . 
         [0031]    Preferably, the metal is metal having low melting point. More preferably, the metal is indium. 
         [0032]    As shown in  FIG. 1  and  FIG. 4 , the target body  2  further comprises at least a third hollow target material  25  between the first hollow target material  20  and the second hollow target material  21 . The first hollow target material  20  firstly covers the outer circumferential surface of the support tube  1  and stays fixed by use of the elastic elements  3 . The third hollow target material  25  is then put through the support tube  1 . Finally, the second hollow target material  21  is put through the support tube  1  and stays fixed by use of the elastic elements  3 . The amount of the third hollow target material  25  may vary depending on the length of the support tube  1 . Since the first and second hollow target material  20 ,  21  stay in the fixed positions by the elastic elements  3 , the third hollow target material  25  will also stay fixed in the middle of the target body  2  between the first and second hollow target materials  20 ,  21 . 
         [0033]    As shown in  FIG. 2 , the third hollow target materials  25  also form grooves  23  in the inner surface from one end  22  over the axial direction. The corresponding concaves  12  are also formed on the outer surface of the support tube  1 . When the third hollow target materials  25  are put through the support tube  1 , the end  22  having the grooves  23  faces the tail end  11  of the support tube  1 . In this regard, the first, second and third hollow target material  20 ,  21 ,  25  have the grooves  23  for elastic elements  3  placement and accordingly enhance the adhesiveness between the target body  2  and the support tube  1  to provide more efficient heat conductivity. 
         [0034]    During the assembly, the first hollow target material  20  is put through the support tube  1  and the elastic elements  3  are positioned in the spaces  4 . The melting metal is poured into the gap between the support tube  1  and the first hollow target material  20 . After the liquid metal coagulates, the third and second hollow target material  25 ,  21  are sequentially put through the support tube  1  in the same manner. That is, when each of the third or second hollow target material  25 ,  21  is put through the support tube  1 , the elastic elements  3  are then positioned in the spaces  4  formed by the grooves  23  on each hollow target material and the corresponding concaves  12  on the support tube  1 . Afterwards, the melting metal is poured in the gap between the hollow target material and the support tube  1  and cooled; the next third or second hollow target material  25 ,  21  is put through the support tube  1  for the same treatment. 
         [0035]    As shown in  FIG. 3 , the inner surface of the first hollow target material  20  further forms grooves  23  on the other end over the axial direction. The outer surface of the support tube  1  also forms concaves  12  at the corresponding position. The elastic elements  3  are put into the spaces  4  formed by the grooves  23  and the corresponding concaves  12  to enhance the adhesiveness between the target body  2  and the support tube  1 . 
         [0036]    The grooves  23  on the target materials provide spaces for elastic elements  3  placement. However, the grooves  23  should be as small as possible to prevent the impact to the target materials during the processing and to increase the use area of the target materials. The depth of the concave  12  in the circumferential direction is at least as thick as the elastic element  3 , if not thicker, to provide sufficient resistance and prevent the displacement of the elastic element  3 . 
         [0037]    As shown in  FIG. 1  to  FIG. 3 , the elastic element  3  is preferably a curved resilient sheet. When the elastic element  3  is a resilient sheet, the depth of the grooves  23  in the axial direction on the target materials is larger than the distance from the end of the concaves  12  to the nearest end of the support tube  1 . Therefore, one end of the elastic element  3  is placed in the groove  23  and the other end of the elastic element  3  is placed in the corresponding concave  12 . 
         [0038]    As shown in  FIG. 4 , the elastic element  3  is preferably a spring. When the elastic element  3  is a spring, two ends of the spring respectively contact with the bottoms of the groove  23  and the corresponding concave  12 . 
         [0039]    The elastic element  3  preferably has good strength to support the target materials. The elastic element  3  preferably has good conductivity to conduct the heat from the target body  2  to the support tube  1 . Preferably, the elastic element  3  is made by pure copper. 
         [0040]    As shown in  FIG. 5 , the groove  23  on the target material can be made as a continuous loop by machining. The groove  23  can also be made as a discontinuous loop (i.e. a plurality of grooves) as shown in  FIG. 6 . 
       EXAMPLE  
       [0041]    The aluminum zinc oxide is chosen as a sputtering material and forms a target body  2 . The target body  2  contains one first hollow target material  20 , one second hollow target material  21  and three third hollow target material  25 . The outer diameter and the inner diameter of the three kinds of the hollow target materials are respectively 160 mm and 133 mm. Each length in the axial direction of the target materials is 280 mm so the total length of the target body  2  is 1400 mm. Grooves  23  are made as a continuous loop by machining in the inner surface of the first hollow target material  20  and the second hollow target material from an end  22  of said target materials with 10 mm depth in the axial direction and 2 mm in the circumferential direction. The support tube  1  is made by stainless SUS304. The outer diameter and inner diameter of the lined pipe  1  are respectively 132.5 mm and 125 mm. The length of the support tube  1  is 1450 mm. The outer diameter of the support tube 1 is 0.5 mm smaller than the inner diameter of the target body  2  so the target body  2  can easily cover the circumferential surface of the support tube  1 . Concaves  12  are made by machining in the outer surface of the support tube  1  from the position close to the head end  10  and the tail end  11 . The concaves  12  have triangle cross section shape, 3 mm length in the axial direction and 1 mm depth in the circumferential direction. The elastic elements  3  are made by pure copper with 1 mm thickness. The outer surface of the first, second and third hollow target materials  20 ,  21 ,  25  and the inner surface of the support tube  1  are metallized by immunization with melting indium. 
         [0042]    The first hollow target material  20  is put through the support tube  1  and  6  elastic elements are put in the spaces formed by the grooves  23  and corresponding concaves  12 . A heating blanket is used to cover the first hollow target material  20 , and the temperature is kept at 180° C. for 30 minutes so the temperature of the first hollow target material  20  is kept higher than the melting point of indium. The melting indium is poured into the gap between the first hollow target material  20  and the support tube  1 . The heating blanket is removed and the melting indium is gradually coagulated. Afterwards, three third hollow target material  25  and the second hollow target material  21  are sequentially put through the support tube  1  and the step of placing the elastic elements  3  in the spaces formed by the grooves  23  and corresponding concaves  12  and the step of filling melting indium into the gap between the target material and the support tube  1  are repeated after each hollow target material is put through the support tube  1 . 
         [0043]    In conclusion, the hollow target assembly of the present invention uses the spaces  4  formed by the grooves  23  in the outer surface of the target materials and the corresponding concaves  12  in the inner surface of the support tube  1  for elastic elements  3  placement. The elastic elements  3  not only provide good heat conduction but also good adhesiveness between the target body  2  and the support tube  1 . 
         [0044]    What is stated above is only preferred embodiments of the present invention, which is illustrative only and not restrictive. Many changes, modifications, or the equivalents may be made by those skilled in the art without departing from the spirits and scope of the present invention as defined by the claims, but will fall within the scope of protection of the present invention.