Abstract:
An electroplating apparatus includes: a wafer holder that is detachable from an engaging hole of a cathode holder and capable of moving in a up and down direction; a spring contact type cathode electrode that is fixed to an electrode housing recess on a top surface of the wafer holder and presses against a backside of a wafer placed on the wafer holder; and a suction pad that is fixed to a pad housing recess on a top surface of the wafer holder and suctions the backside of the wafer placed on the wafer holder.

Description:
FIELD OF THE INVENTION 
     The invention relates to an electroplating apparatus used for plating substrates for electronic components, wafers for ICs and wafers for thin-film magnetic heads. 
     BACKGROUND OF THE INVENTION 
     A thin plating film attached to a plating surface (referred to as a front surface) of a wafer is formed by use of an electroplating apparatus. In the electroplating apparatus, a conductive base film is disposed on a front side on which a plating film is being formed and, with the base film as a cathode, a current is flowed in a plating solution to precipitate a plating film on the base film. 
     As an existing electroplating apparatus, an apparatus where the plating is carried out with a front side of a wafer turned downward (referred to as a bottom surface plating method) and an apparatus where the plating is carried out with the front side turned upward (referred to as a top surface plating method) are in use. 
     In the electroplating apparatus for bottom surface plating method, an anode electrode is disposed at a bottom portion of a plating bath, on an upper side thereof a wafer holder is disposed movable up and down, on the wafer holder a wafer is placed with a front side turned downward, after that a cathode holder is inserted in the wafer holder, a spring contact type cathode electrode is brought into contact with a back side of the wafer under pressure and the wafer is energized. 
     In the bottom surface plating method, since a wafer and a wafer holder are manually set to carry out the plating with a front side turned downward, the operating efficiency is not good. In this connection, in order to improve the operating efficiency, an automation apparatus is considered. 
     However, the process of setting a cathode electrode and a wafer can be automated only in a very complicated manner. In a Permalloy plating apparatus where the plating is applied with a magnetic field applied to give the directionality, the automation in the bottom surface plating method is difficult and has not yet been put into practical use. 
     Furthermore, in the plating apparatus for the top surface plating method, an anode electrode is disposed on an upper portion of a plating bath, at a bottom portion thereof a cathode holder having an engaging hole is disposed, a wafer holder is disposed detachably with the engaging hole and a wafer is placed on the wafer holder with a front side thereof turned upward. After that, an electrode housing recess of the wafer holder, in which a spring contact type cathode electrode is accommodated is evacuated to hold the wafer, the electrode is brought into contact with a backside of the wafer and the wafer holder is lifted and inserted into the engaging hole to closely seal the bottom portion. 
     The above-described top surface plating apparatus has problems outlined below. 
     That is, in order to automate an electroplating apparatus, when a wafer is placed on a wafer holder, the wafer has to be assuredly held and a cathode electrode has to be brought into contact with a backside of the wafer at a predetermined contact pressure to enable an assured energization. 
     However, a tip end of the cathode electrode, in consideration of a bending portion, is disposed a little above a top surface of the wafer holder and the cathode electrode applies pressure in a direction in which the wafer is detached from the wafer holder; accordingly, the wafer cannot be brought into contact with a top surface of the wafer holder. As a result, when a vacuum line is operated, the electrode recess cannot be evacuated, the wafer holder cannot assuredly hold the wafer and desired contact pressure of the cathode electrode can be obtained only with great difficulty. 
     In order to overcome the above-mentioned problems, what is mentioned below can be considered. 
     In an electrode housing recess of a wafer holder, a lift unit is disposed to displace a cathode electrode. When a wafer is placed on the wafer holder, the cathode electrode is moved downward so that a tip end thereof may not protrude from a top surface of the wafer holder, after the wafer holder on which the wafer has been placed is inserted in an engaging hole, the lift unit is driven to lift the cathode electrode to bring the tip end thereof into contact under pressure with a backside of the wafer. 
     However, according to the method, the lift apparatus has to be disposed inside of a small wafer holder; accordingly, the apparatus becomes very complicated and is difficult to put into practical use. 
     SUMMARY OF THE INVENTION 
     The present invention, in view of the above-mentioned situations, intends to assuredly hold a wafer to a wafer holder and to enable it to sufficiently energize. 
     An aspect of the present invention includes providing an electroplating apparatus including: a plating bath in which a plating solution is accommodated; a cathode holder having an engaging hole disposed penetrating through a bottom portion of the plating bath; a wafer hold disposed at an upper end of the engaging hole; a wafer holder that is detachable from the engaging hole from a bottom surface side of the cathode holder and can move in an up and down direction; an electrode housing recess disposed on a top surface of the wafer holder; a spring contact type cathode electrode that is fixed to the electrode housing recess and presses against a backside of a wafer placed on the wafer holder; a pad housing recess disposed on a top surface of the wafer holder; and a suction pad that is fixed to the pad housing recess and suctions the backside of the wafer placed on the wafer holder. 
     The spring contact type cathode electrode of an aspect of the invention includes an annular fixing portion and a plurality of upward slopes. The plurality of upward slopes becomes gradually slender as they go from a base end side toward a free end side. The wafer hold can comprise an inner periphery portion of an annular cathode auxiliary electrode. 
     Between the wafer hold and a front side of the wafer, a sealing means is disposed. The sealing means is a seal rubber disposed on a bottom surface of the wafer hold. A tip end of the spring contact type cathode electrode and an upper end of the suction pad protrude from a top surface of the wafer holder and a protrusion amount of the electrode is smaller than a protrusion amount of the suction pad. A protrusion amount of the spring contact type cathode electrode is in the range of 0.1 to 1 mm and that of the suction pad is in the range of 1 to 2 mm. 
     Since an aspect of the present invention is constituted as mentioned above, a wafer placed on a wafer holder is suctioned at a backside thereof by a suction pad and held and fixed to the wafer holder. Furthermore, when the wafer holder is inserted in an engaging hole and the wafer is brought into contact with a wafer hold, a cathode electrode is pressed against a backside of the wafer and bent to sufficiently come into contact with it; and therefore, the energization can be assuredly secured. 
     These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1(A) and 1(B)  are diagrams showing an embodiment of the present invention,  FIG. 1(A)  being a longitudinal sectional view of a bottom portion of a plating bath,  FIG. 1(B)  being a longitudinal sectional view of a wafer holder. 
         FIG. 2  is a longitudinal sectional view showing a state where a wafer holder is inserted in a cathode holder. 
         FIG. 3  is an enlarged diagram of an essential portion of a wafer holder. 
         FIG. 4  is a plan view of a wafer holder. 
         FIG. 5  is a longitudinal sectional view of a plating apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described with reference to  FIGS. 1 through 5 . 
     At a bottom portion  1   a  of a plating bath  1 , a cathode holder  3  having an engaging hole  3   a  is disposed. At an upper end of the engaging hole  3   a , an annular cathode auxiliary electrode  5  is disposed. The electrode  5  inhibits a current of an outer peripheral portion of a wafer W from concentrating; and therefore, a film thickness can be uniformized. An inner peripheral portion  5   a  of the auxiliary electrode  5  projects inside of the engaging hole  3   a  and works as a wafer hold when a wafer holder  10  is inserted in the engaging hole  3   a . On a bottom surface of the inner peripheral portion  5   a , a sealing means is disposed, as the sealing means, for instance, a seal rubber  7  being adopted. Other sealing means are contemplated. 
     Below the cathode holder  3 , a wafer holder  10  is disposed. At a center portion of a top surface  10   a  of the wafer holder  10 , a circular pad housing recess  12  is disposed and outside thereof an annular electrode housing recess  14  is disposed. 
     To the pad housing recess  12 , a suction pad, for instance, a rubber vacuum pad,  16  is fixed. The suction pad  16  is formed in an inverse conical shape and an upper end surface  16   a  thereof slightly protrudes from the top surface  10   a  of the wafer holder  10  ( FIGS. 1 and 3 ). A protrusion amount T 2  is selected in a range where a backside WB of the wafer W can be held in close contact with a top surface  10   a  of the wafer holder  10 . For instance, as the protrusion amount T 2 , 1 to 2 mm is selected. 
     In the electrode housing recess  14 , a spring contact type cathode electrode  18  is fixed. The electrode  18 , as shown in  FIG. 4 , includes an annular fixing portion  18   a  and upward slope portions  18   b . A plurality of, for instance, thirty-four slope portions  18   b  is formed in a circumferential direction at an identical interval along an outer periphery of the fixing portion  18   a.    
     Each of the slope portions  18   b  gradually becomes more slender as it goes from a base end  18   c  side toward a tip end  18   d  side and inclines upward. The tip end  18   d  of the upward slope portion  18   b  protrudes from a top surface  10   a  of the wafer holder  10 . A protrusion amount T 1  thereof is selected in a range where the tip end  18   d , when coming into contact with a backside WB of the wafer W, bends and can obtain a predetermined contact pressure. For instance, as the protrusion amount T 1  thereof, a value smaller than the protrusion amount T 2  of the suction pad  16 , for instance, T 1 =0.1 to 1 mm is selected. 
     When the cathode electrode  18  is formed like a starfish, a cathode electrode  18  having a great bending flexibility and toughness can be obtained. A shape, slope angle and number of the upward slopes  18   b  are appropriately selected as necessary. 
     The wafer holder  10  is provided with a suction path  22  communicated with the suction pad  16  and the suction path  22  is connected to a vacuum line  24 . Furthermore, the wafer holder  10  is provided with a cathode wafer electrode  26  and the cathode wafer electrode  26  is connected to a cathode wafer power supply  28 . To the wafer holder  10 , a means that can move in an up and down direction, for instance, a lift cylinder  30 , is connected. Other means are contemplated. 
     In the drawings, reference numeral  31  denotes a cathode auxiliary electrode power supply;  32 , an anode (plus electrode) disposed in a plating bath  1 ;  34 , a sliding paddle in the plating bath  1 ;  36 , a paddle sliding arm;  38 , an overflow portion that reserves an overflowed plating solution and returns it to a circulating tank (not shown in the drawings);  40 , a plating supply tube for supplying the plating solution from the circulating tank to a plating solution circulation supply  42 ;  44 , a magnet;  46 , a return to the circulating tank; and  47 , an automatic valve. 
     Next, an operation of the embodiment will be described. 
     As shown in  FIG. 1 , when an object to be plated, for instance, a wafer W for ICs, is placed on a wafer holder  10  with a backside WB thereof turned downward, the wafer W comes into contact with an upper end surface  16   a  of a suction pad  16 . The upper end surface  16   a  of the suction pad  16  is separated by T 2  from a top surface  10   a  of the wafer holder  10 ; accordingly, the wafer W does not come into close contact with the top surface  10   a  of the wafer holder  10 . 
     At this time, a protrusion amount T 1  of a tip end  18   d  of a cathode electrode  18  is smaller than the top end surface  16   a  of the pad  16 ; accordingly, the cathode electrode  18  does not come into contact with the wafer W. 
     When a suction driver (not shown) is started operating, evacuation is carried out through a vacuum line  24  and a suction path  22 , the suction pad  16  suctions a backside WB of the wafer W; accordingly, the wafer W is assuredly fixed and held. 
     In this state, a lift cylinder  30  is driven. As shown in  FIG. 2 , a wafer holder  10  is inserted into an engaging hole  3   a  of a cathode holder  3  and a front side WF of the wafer W is pushed against a seal rubber  7 . 
     Thereby, the suction pad  16  is deformed and an upper end surface  16   a  thereof becomes level with the top surface  10   a  of the wafer holder  10 . The tip ends  18   d  of the cathode electrode  18  bends and descends to a position of the top surface  10   a  of the wafer holder  10  to press the backside WB of the wafer W. Between the wafer W and the cathode auxiliary electrode  5 , a seal rubber  7  is used to seal and in this state a bottom portion  1   a  of the plating bath  1  is completely sealed. 
     In the sealed state, a plating solution M is filled in the plating bath  1 , and the respective electrodes  5 ,  18 ,  26  and  32  are energized to plate the front side WF of the wafer W. 
     Upon completion of the plating, the plating solution M in the plating tank  1  is returned to the circulating tank to empty the inside of the plating tank  1 , followed by driving the lift cylinder  30  to lower the wafer holder  10  to extract from the engaging hole  3   a  of the cathode holder  3 . 
     When the lift cylinder  30  reaches an initial position, the suction driver is stopped driving to unleash the suction of the suction pad  16  and a plated wafer W is removed from the wafer holder  10  and stored in a predetermined place. 
     Although an attach and remove operation of the wafer W to and from the wafer holder  10  is automatically carried out with a robot, it goes without saying that the operation can be manually carried out without using a robot. 
     An embodiment of the present invention is not restricted to the above-mentioned one. For instance, the following may be adopted. 
     (1) In the foregoing embodiment, as an object to be plated, a wafer for ICs is used. However, an object to be plated in the present invention includes, in addition to the wafer for ICs, a substrate for electronic components and a wafer for thin-film magnetic heads. The “wafer” referred to here includes all of the above-mentioned objects to be plated. 
     (2) As the wafer hold, in place of an inner periphery portion of the cathode auxiliary electrode, a hold click may be used. A plurality of the hold clicks are disposed at circumferentially spaced intervals, for example, protruding from and along an outer periphery portion of the engaging hole. 
     The above description is considered that of the preferred embodiments only. Modification of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.