Patent Publication Number: US-6909587-B2

Title: Apparatus having a static eliminator for manufacturing semiconductor devices and a method for eliminating a static electricity on a semiconductor wafer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of application Ser. No. 09/635,575; filed Aug. 9, 2000 now U.S. Pat. No. 6,432,727, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus having a static eliminator which eliminates static electricity on a semiconductor wafer and to a method for eliminating static electricity on a semiconductor wafer. 
     BACKGROUND OF THE INVENTION 
     In an exposure process of a semiconductor manufacturing process, an apparatus is used, such as a spin coater or a developer, which treats a semiconductor wafer with rotation. 
     Such an apparatus is shown in  FIG. 6 , which is a cross sectional view of certain component parts of an apparatus  100 . 
     A support portion  106  which supports a semiconductor wafer  104  using a vacuum chuck is located in a cylindrical container  102 . A nozzle  108  is arranged above the semiconductor wafer  104  so that a solution is applied to a surface  104   a  of the semiconductor wafer  104 . When the solutions is dropped on the surface  104   a , the semiconductor wafer  104  is rotated by the support portion  106 . Thereby, the solution is uniformly distributed over the surface  104   a.    
     However, as the wafer  104  is rotated at a high speed, friction occurs between the surface  104   a  and the dropped solution. Static electricity is generated by this friction and the surface  104   a  becomes positively charged. An atmosphere above the semiconductor wafer  104  is negatively charged, as shown in FIG.  6 . 
     According to the publication entitled “BREAK THROUGH”, by Dr. Ohmi at Tohoku University, which was published in April, 1993 (Table-1 at p.26), when a resist was applied to a surface of a semiconductor wafer using a similar apparatus, the surface was positively charged at 3000V or more. 
     Therefore, transistors in the semiconductor wafer might be destroyed and small particles might attach on the surface as a result of the static electricity, which in turn may lead to a reduced throughput and quality. Further, the finer the patterns on the semiconductor wafer, the greater the influence of the static electricity or devices of the semiconductor wafer. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an apparatus having a static eliminator which eliminates static electricity on a semiconductor wafer and a method for eliminating static electricity on a semiconductor wafer. 
     To achieve the object, in one embodiment of the present invention, ions are generated above a semiconductor wafer and the ions are combined with static electricity on the semiconductor wafer such that the static electricity may be consumed by the ions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a cross section view of an apparatus according to a first preferred embodiment of the present invention. 
         FIG. 2  is a cross section view of an apparatus according to a second preferred embodiment of the present invention. 
         FIG. 3  is a cross section view of an apparatus according to a third preferred embodiment of the present invention. 
         FIG. 4  is a cross section view of an apparatus according to a fourth preferred embodiment of the present invention. 
         FIG. 5  is a plane view of a discharge electrode of the fourth preferred embodiment. 
         FIG. 6  is a cross section view of a conventional apparatus. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described hereinafter with reference to the accompanying drawings. The drawings used for this description typically illustrate major characteristic parts in order that the present invention will be easily understood. In this description, one embodiment is shown in which the present invention is applied to an apparatus which treats a semiconductor wafer while rotating the semiconductor wafer, such as a spin coater and a spin developer. However, the invention is not limited to such an apparatus. The present invention may be applied to a single wafer processing apparatus or a batch processing apparatus used for etching or deposition. 
     A cross sectional view of an apparatus  10  is shown in FIG.  1 .  FIG. 1  illustrates an outline of the apparatus. 
     The apparatus  10  includes a cylindrical container  12 , a support portion  14  and a down flow portion  11 . The support portion  14  which supports a semiconductor wafer  16  using a vacuum chuck is located in the cylindrical container  12 . A nozzle (not shown) is arranged above the semiconductor wafer  16  so that a solution is applied to a surface  16   a  of the semiconductor wafer  16 . 
     The apparatus  10  is located in an atmosphere which is fluid toward a predetermined direction. In this embodiment, the predetermined direction means a direction which flows down from the down flow portion  11  to the surface  16   a  of the semiconductor wafer  16 . In the case where the semiconductor wafer is supported perpendicularly, the predetermined direction means a horizontal direction toward to the surface of the semiconductor wafer. The atmosphere which is fluid toward the predetermined direction is formed at least above the semiconductor wafer. 
     The apparatus  10  includes an ion generator  18  which supplies ions into the atmosphere above the semiconductor wafer. The ions from the ion generator  18  reach the surface  16   a  by the flow in the atmosphere. 
     In this embodiment, the ion generator  18  is comprised of a thin needle type electrode. The needle type electrode  18  is sharply pointed as shown in FIG.  1 . The needle type electrode  18  is connected to a first terminal  20   a  of a power supply  20 . The power supply  20  supplies a power supply voltage to the needle type electrode  18 . A second terminal  20   b  of the power supply  20  is connected to a ground. The power supply  20  is a dc type power supply. 
     The needle type electrode  18  is comprised of a conductive material which is 1 centimeters in diameter. In this embodiment, the conductive material is copper. The tip  18   a  of the needle type electrode  18  is located above the semiconductor wafer  16 . The needle type electrode  18  can be attached to the side wall of the apparatus  10 . 
     When a solution is dropped on the surface  16   a  from a nozzle (not shown), the semiconductor wafer  16  is rotated at 1000-6000 rpm by the support portion  14 . As the wafer  16  is rotated at a high speed, friction occurs between the surface  16   a  and the dropped solution. A static electricity is generated as a result of the friction and the surface  16   a  becomes positively charged. 
     Here, the power supply  20  supplies a negative voltage to the needle type electrode  18 . In this preferred embodiment, the negative voltage is between −200V and −500V. Therefore, the atmosphere around the needle type electrode  18  is ionized and a corona discharge occurs therein. 
     As such, positive ions  19   a  and negative ions  19   b  are generated around the needle type electrode  18 . Most of the positive ions  19   a  gather around the needle type electrode  18  since the needle type electrode  18  is supplied with the negative voltage and a strong negative electrical field is formed around the needle type electrode  18 . Part of the positive ions  19   a  may reach the surface  16   a  of the semiconductor wafer  16  as a result of the down flow in the atmosphere. However, as the surface  16   a  is positively charged, the positive ions  19   a  are repelld. The negative ions  19   b  are carried to the surface  16   a  as a result of the down flow. As the surface  16   a  is positively charged, the negative ions  19   b  are combined with positive ions on the surface  16   a . Therefore, the charges are extinguished from the surface  16   a . That is, the static electricity on the semiconductor wafer can be eliminated. 
     According to the first preferred embodiment, it is possible to eliminate the static electricity on the semiconductor wafer using the needle type electrode which is a relatively small addition to the system. That is, an apparatus having a static eliminator which eliminates a static electricity on a semiconductor wafer can be easily realized. 
     As the tip  18   a  of the needle type electrode  18  is located above the middle of the semiconductor wafer  16 , most of the negative ions generated around the needle type electrode can be carried by the down flow to the surface  16   a . As such, the static electricity on the surface is efficiently eliminated. 
     If the surface  16   a  of the semiconductor wafer  16  were negatively charged, the needle type electrode  18  would be supplied with a positive voltage from the power supply  20 . 
     In the case where the support portion  14  can move up and down, the semiconductor wafer  16  is carried to the outside of the cylindrical container  12  so as to expose the surface  16   a , and the charge on the surface is eliminated by the needle type electrode. 
     The present invention may be applied to a batch processing apparatus which simultaneously treats plural semiconductor wafers stored in a wafer cassette. 
     A second preferred embodiment will be described hereinafter, referring to FIG.  2 . The same elements mentioned above are marked at the same symbols and a description thereof is omitted. A cross sectional view of an apparatus  30  is shown in FIG.  2 .  FIG. 2  illustrates an outline of the apparatus. 
     Similar to the first preferred embodiment, the apparatus  30  of this embodiment includes a cylindrical container  12 , a support portion  14 , a down flow portion  11 , an ion generator  22  and a nozzle (not shown). 
     In this preferred embodiment, a second electrode  24  is located over the cylindrical container  12  so as to face toward the tip  22   a  of the needle type electrode  22 . An atmosphere  26  where ions are generated therein is sandwiched between the needle type electrode  22  and the second electrode  24 . In this embodiment, a plate electrode  24  is used as the second electrode. The plate electrode  24  is connected to a second power supply  25  which supplies a voltage power to the plate electrode  24 , as shown in FIG.  2 . Otherwise the plate electrode  24  is directly connected to the ground. The second power supply  25  is also connected to the ground. 
     Similarly, when the surface  16   a  is positively charged by the friction between the surface  16   a  and the solution dropped from the nozzle, the power supply  20  supplies a negative voltage to the needle type electrode  22 . In this preferred embodiment, the negative voltage is between −200 v and −500v. Therefore, the atmosphere around the needle type electrode  22  is ionized and a corona discharge occurs therein. As such, positive ions  19   a  and negative ions  19   b  are generated around the needle type electrode  18 . 
     Also, most of the positive ions  19   a  gather around the needle type electrode  22 . The negative ions  19   b  and electrons gather on the plate electrode  24  which is supplied with a positive voltage (less than 100V). Therefore, the kinetic speed of the negative ions  19   b  and the electrons is slowed down by the plate electrode  24 . The electrons mainly combine with oxygen and become negative ions ( 19   b ). That is, more negative ions can be gained in the atmosphere. 
     The negative ions  19   b  are carried by the down flow to the surface  16   a . As the surface  16   a  is positively charged, the negative ions  19   b  are combined with positive ions on the surface  16   a . Therefore, the charges are extinguished from the surface  16   a . That is, the static electricity on the semiconductor wafer can be eliminated. 
     A third preferred embodiment will be described hereinafter, referring to FIG.  3 . The same elements mentioned above are marked at the same symbols and a description thereof is omitted. A cross sectional view of an apparatus  40  is shown in FIG.  3 .  FIG. 3  illustrates an outline of the apparatus. 
     The apparatus  40  of this embodiment includes a cylindrical container  12 , a support portion  14 , a discharge electrode  28  and a nozzle (not shown). 
     The discharge electrode  28  is comprised of a thin needle type electrode. The needle type electrode  28  is sharply pointed as shown in FIG.  3 . The needle type electrode  28  is connected to a ground. The needle type electrode  18  is comprised of a conductive material. In this embodiment, the conductive material is copper, aluminum or iron. 
     In the case where the surface  16   a  is positively charged by the friction between the surface  16   a  and the solution dropped form the nozzle, the tip  28   a  of the discharge electrode  28  is laid to the surface  16   a  of the semiconductor wafer  16  so that the static charge on the surface  16   a  is discharged. Thereby, the static charge is removed from the semiconductor wafer  16 . 
     In this embodiment, the discharge electrode  28  is approximated at a distance of 2 millimeters from the surface  16   a . Thereby, the static charge on the surface can be discharged. 
     A fourth preferred embodiment will be described hereinafter, referring to FIG.  4  and FIG.  5 . This embodiment is a variation of the third embodiment. The same elements mentioned above are marked at the same symbols and a description thereof is omitted. A cross sectional view of an apparatus  50  is shown in FIG.  4 . 
     In this embodiment, a discharge electrode  32  is comprised of plural needle type electrodes  32   x , as shown in FIG.  4  and  FIG. 5. A  plane view of the discharge electrode  32  is shown in FIG.  5 . 
     The discharge electrodes  32  are comprised of thin needle type electrode  32   x . The needle type electrodes  32   xa  are sharply pointed as shown in FIG.  4 . The needle type electrodes  32   x  are connected to a ground. The needle type electrodes  32   x  are comprised of a conductive material. The conductive material is copper, aluminum or iron. 
     The plural needle type electrodes  32   x  are arranged in a discharge region  34  which has substantially the same width as the semiconductor wafer  16 . Further, the needle type electrodes  32   x  are arranged perpendicular to the semiconductor wafer  16  at regular intervals. Suitable intervals are determined by a voltage applied to the needle type electrodes  32   x  and a distance between the surface  16   a  of the semiconductor wafer  16  and tips  32   xa  of the needle type electrodes  32   x . The needle type electrodes 32   x  are fixed in a support substrate  36 . 
     Also, the apparatus  50  of this embodiment includes a cylindrical container  12 , a support portion  14  and a nozzle (not shown). The support portion  14  can move up and down in order to expose the semiconductor wafer  16  to the outside of the cylindrical container  12 . The discharge electrode  32  is located above the semiconductor wafer  16  so that the discharge electrode  32  does not to interfere with the nozzle. 
     In the case where the surface  16   a  is positively charged by the friction between the surface  16   a  and the solution dropped from the nozzle, the support portion  14  is moved up to expose the semiconductor wafer  16  outside the cylindrical container  12 . 
     The tips  32   xa  of the discharge electrode  32  are approximated at a distance of 2 millimeters from the surface  16   a  of the semiconductor wafer  16 . This, state is then maintained for a few seconds. As such, the static charge on the semiconductor wafer  16  is discharged. Then, the discharge electrode  32  is moved away from the semiconductor wafer  16 . 
     According to this embodiment, as the discharge electrode  32  is comprised of the plural thin electrodes  32   x  which correspond to the whole surface of the semiconductor wafer, the static charge can be removed from the semiconductor wafer in short time, as compared with the third embodiment. 
     The apparatus and methods of the invention for eliminating static electricity on a semiconductor wafer can be applied to each processing step which might generate a static charge on the semiconductor wafer or to each of a predetermined number of processing steps. 
     The present invention has been described with reference to illustrative embodiments, however, this description must not be considered to be confined only to the embodiments illustrated. Various modifications and changes of these illustrative embodiments and the other embodiments of the present invention will become apparent to one skilled in the art from reference to the description of the present invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.