BACKGROUND
A uniformity of thickness of electroplated metal layer is one of a major factor for determining a quality of the electroplating. During the electroplating, “edge effect” causes a problem associated with thin middle and thick edge portions of the electroplated metal layer. Unevenness of the thickness of the electroplated metal layer is likely to affect a subsequent manufacturing process or a product performance, thereby reducing an overall process yield.
As shown in FIG. 1, in a deposition process of metal bumps, when a free space of a plating solution is larger than a wafer 2, electric field lines 8 will spread outwardly and tend to concentrate at the edge 221 of the wafer 2, called edge effect. The electric field lines 8 concentrate more at the edge 221 of the wafer 2, with a higher local current density, making higher metal bumps to be formed during the plating. The electroplated metal bumps higher on the edge 221 than in the center of the wafer 2 lead to a bad uniformity of bumps for a whole wafer 2.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
FIG. 1 is a prior art illustrating a cross-sectional view of an electrochemical reactor.
FIG. 2 is a cross-sectional view of an electrochemical reactor, in accordance with one embodiment of the present disclosure.
FIG. 3 is a schematic view of an apparatus for fastening a shield, in accordance with one embodiment of the present disclosure.
FIGS. 4, 6, and 9 are some diagrammatic perspective views of a shield, in accordance with some embodiments of the present disclosure.
FIGS. 5, 7, and 8 are some cross-sectional views of a shield, in accordance with some embodiments of the present disclosure.
DETAILED DESCRIPTION
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
Referring to FIG. 2, FIG. 2 is a cross-sectional schematic view of electrochemical reactor 200. The electrochemical reactor 200 includes an adjustable electric field shaping capability during electroplating. The electrochemical reactor 200 includes a reservoir 20, an anode 4, a cathode 3 and a shield 100. The reservoir 20 is for receiving electrolytic solution (i.e., plating solution) 5. The anode 4 and the cathode 3 are disposed in the reservoir 20, and at least partially immersed in the electrolytic solution 5. A power supply 23 supplies positive and negative electricity to the anode 4 and the cathode 3 respectively to form electric field lines 8 passing through the electrolytic solution 5.
Either the anode 4 or the cathode 3 includes a workpiece holder used to hold a workpiece to be plated. As illustrated in FIG. 2, in this embodiment, the workpiece holder is located at the cathode 3 and is a wafer holder 9 which is used to hold a wafer 2 during electroplating process and is electrically coupled with the negative charge to serve as the cathode 3. In some embodiments, the wafer holder 9 is mechanically driven to rotate as a turntable during the electroplating process. In contrast with the workpiece holder, an electrode holder 102 is configured to hold the other one of the cathode 3 or the anode 4. In this embodiment, the electrode holder 102 is used to fasten the anode 4 and electrically connected to positive charge. At least a part 114 of the anode 4 is exposed by the electrode holder 102 to form the electric field lines 8 passing through electrolytic solution 5 to the cathode 3. The anode 4 is made of metal and can be a soluble anode or an insoluble anode. In this embodiment, the anode 4 is the insoluble anode used to transmit electrical current. Metal ions in the electrolytic solution 5 are resupplied by adding metallic salts. The insoluble anode is in general a good conductor, and would not chemically react with the electrolytic solution 5 to contaminate the fluid and would not be eroded.
The shield 100 is disposed in the reservoir 20, and is located between the anode 4 and the cathode 3. In this embodiment, the shield 100 is attached to the anode 4 and is fastened on the electrode holder 102. Referring also to FIG. 3, the electrode holder 102 can include a fixing member 112 used to allow the shield 100 to be fixed replaceably on the electrode holder 102. In other word, the shield 100 can be removed from the electrode holder 102 easily and be replaced when necessary.
The shield 100 can be made of materials capable of withstanding corrosion by the electrolytic solution 5 and not producing electroplating effect. These materials are dielectric or a composite material including a dielectric coating so as to prevent metal plating onto the shield 100 due to an induced potential change in the reservoir 20, or chemical reaction being produced by the shield 100 causing contamination in the electrolytic solution 5. The materials of the shield 100 include plastics such as polypropylene (PP), Polyvinylchloride (PVC), polyethylene (PE), fluoropolymers, polytetrafluoroethylene (PTFE), or polyvinylidine fluoride. The material blocks a passing of the electric field lines 8 such that the electric field lines 8 are limited to pass through the shield 100 only through an aperture 13.
The shield 100 includes a plate 10 with a surface 14 and a conduit 11. The plate 10 is configured to block a formation of a portion of the electric field lines 8 by the surface 14. The surface 14 is substantially parallel with a surface 22 of the wafer 2 and with a flat surface of the wafer holder 9. The plate 10 includes a thickness TH1 measured from the surface 14 to a back surface 17. The conduit 11 is disposed on the surface 14. As illustrated in FIG. 3, the shield 100 can be fastened by a way of inserting the plate 10 into the fixing member 112 so that the conduit 11 corresponds to a partial region of the part 114 of the anode 4 exposed by the electrode holder 102, and the other region of the part 114 is entirely covered by the surface 14 of the plate 10.
As illustrated in FIG. 2, the conduit 11 includes the aperture 13 and has a height H1. The height H1 is measured along a direction X from the surface 14 to a top surface 12 of the conduit 11. The height H1 makes the conduit 11 a protruding portion. The conduit 11 is coupled with the surface 14, and is used to concentrate the electric field lines 8 to pass through the aperture 13. The aperture 13 passing through the surface 14 and plate 10 penetrates the protruding portion to allow the electric field lines 8 passing through the shield 100. As illustrated in FIG. 2, in this embodiment, the electric field lines 8 start from the anode 4, through the shield 100 via the aperture 13, and pass through the electrolytic solution 5 to reach the wafer 2 on the cathode 3. The aperture 13 is used to shape the electric field lines 8 passing inside the conduit 11. The shield 100 is used to adjust a uniformity of the distribution of the electric field lines 8 reaching the surface 22 of the wafer 2. The distribution of the electric field lines 8 determines the density of a current flowing to the surface 22 of the wafer 2, and further affects a uniformity of a plating layer deposited on the surface 22.
The shield 100 restricts the current flowing along the electric field lines 8 to spread out only from the aperture 13. The shield 100 is a three-dimensional shielding plate; its function is to reduce an exposed area of the anode 4 and to reduce a distance between the cathode 3 and the anode 4. Still referring to FIG. 2, a position where the shield 100 attaches to the anode 4 is such that a center of the aperture 13 of the conduit 11 coincides with or is near to a center line 7 of the wafer 2. The exposed area of the anode 4 is reduced by a covering of the plate 10 such that the shield 100 can concentrate the electric field lines 8 closer toward the center line 7 to make the distribution of the electric field lines 8 more concentrated than the distribution in FIG. 1. Since the shield 100 is directly attached to the anode 4, the electric field lines 8 are restricted to move within the aperture 13 of the conduit 11 immediately after produced by the anode 4, and start to spread outward from the top surface 12 of the conduit 11 till reaching the surface 22 of the wafer 2. The shield 100 reduces the distance between the anode 4 and the cathode 3 by the conduit 11 such that a scattering path of the electric field lines 8 is blocked, hence altering a distributed curvature of the electrical field.
Specifically, the top surface 12 of the conduit 11 is separated from the surface 22 of the wafer 2 by a distance D1. According to a size and condition of the surface 22 of the wafer 2, a relative ratio between the height H1 and the distance D1 can be adjusted. For example, increasing the height H1 of the conduit 11 decreases the distance D1, making the aperture 13 closer to the wafer 2. The scattering path of the electric field lines 8 from the aperture 13 to the wafer 2 is shorter than the scattering path in FIG. 1. In other word, unlike the electric field lines 8 in FIG. 1 that have enough distance to spread outward and then fold back to concentrate on the edge 221 of the wafer 2, the electric field lines 8 in FIG. 2 reach the wafer 2 after spreading outward for just a small distance. Therefore, increasing the height H1 and reducing the distance D1 can reduce the density of the electric field lines 8 reaching the edge 221 of the wafer 2, thus a thickness of the deposited plating layer at the edge 221 is not thicker than that on the other regions. Reducing the scattering path changes a distributed shape of the electric field lines 8 such that the density of the peripheral electric field lines 8 is reduced, making the distribution of the overall electric field lines 8 more uniform so as to lessen the edge effect. Lessening the edge effect can reduce a difference of height between the bumps at the edge 221 of the wafer 2 and the bumps on the other regions; thereby, increasing an overall uniformity of the bump heights for a wafer 2.
A shape and form of the aperture 13 and the conduit 11 of the shield 100 can be changed according to certain need to adjust the uniformity of the electric field lines 8 reaching the surface 22 of the wafer 2. A first embodiment of the shield 100 is described with reference to FIG. 4. A second embodiment of the shield 100 is described with reference to FIG. 5. A third embodiment of the shield 100 is described with reference to FIG. 6. A fourth embodiment of the shield 100 is described with reference to FIG. 7. A fifth embodiment of the shield 100 is described with reference to FIG. 8. A sixth embodiment of the shield 100 is described with reference to FIG. 9. Understandably, this disclosure can provide other embodiments from various combinations of the embodiments mentioned above.
FIG. 4 illustrates a diagrammatic perspective view of the shield 100. The illustration includes a coordinate system with arrows pointing in three directions X, Y, and Z which are orthogonal to each other. Direction Z and direction Y are parallel with the surface 14. In FIG. 4, the shield 100 includes a conduit 11 in a cylindrical form. The conduit 11 includes a height H1 measured from the surface 14 of the plate 10 to a top surface 12 of the conduit 11. The height H1 is measured in a direction orthogonal to the surface 14, i.e. in direction X. The top surface 12 is in a shape of a circular ring. The conduit 11 includes a thickness TH2 measured from an outer surface 15 to an inner surface 16 of the conduit 11 in a direction parallel to the surface 14. The conduit 11 with the aperture 13 in a circular shape passing through it forms a cylinder. In some embodiments, a ratio between a size of the aperture 13 and the height H1 of the conduit 11 is predetermined. The outer surface 15 and the inner surface 16 are parallel with direction X and orthogonal to the surface 14. The top surface 12 of the conduit 11 is parallel with the surface 14 of the plate 10.
In FIG. 5, the shield 100 includes a conduit 11 in a conical form. The aperture 13 in the conduit 11 is also in the conical form. A size of the aperture 13 closer to the surface 14 is smaller than a size of the aperture 13 closer to the top surface 12. The outer surface 15 and the inner surface 16 are parallel with each other. The outer surface 15 and the inner surface 16 slant at an angle T1 with respect to the surface 14, in which T1 is smaller than 90 degree. In some embodiments, the outer surface 15 and the inner surface 16 can tilt at different angles with respect to the surface 14 such that the outer surface 15 and the inner surface 16 are not parallel with each other. The conduit 11 and the aperture 13 are symmetrical about the center line 7.
In FIG. 6, the shield 100 includes a conduit 11 in a rectangular or rhombus form. The top surface 12 is in a shape of a quadrilateral ring. The aperture 13 in the conduit 11 is also in a rectangular or rhombus form. The conduit 11 and the aperture 13 are symmetrical about the center line 7.
In FIG. 7, the height H1 of the conduit 11 measured from the surface 14 of the plate 10 to the top surface 12 changes gradually such that the top surface 12 of the conduit 11 inclines at an angle T2 with respect to the surface 14 of the plate 10. In this case, the conduit 11 and the aperture 13 are asymmetrical about the center line 7. The electric field lines 8 pass through the aperture 13 from the back surface 17 and diverge out of the aperture 13 at the top surface 12. Changing the angle T2 would change a density distribution of the electric field lines 8 scattering from the aperture 13. For example, the electric field lines 8 scattering from the aperture 13 near a side of the conduit 11 with lower height H1 (the left side of FIG. 7) would spread more outwardly and be further away from the center line 7 as compared with the electric field lines 8 scattering from the aperture 13 near the side with greater height H1 (the right side of FIG. 7). That is, in this embodiment, the electric field lines 8 are asymmetric with respect to the center line 7. In some other embodiments, the top surface 12 can include a plurality of angles T2. For example, in a cross sectional view of a plane cut along the center line 7, the top surface 12 can be a symmetrical or asymmetrical V-shape.
In FIG. 8, the shield 100 includes a plurality of conduits 11. The conduits 11 can include similar or different features such as shape, height H1, thickness TH2, tilt angle, or a form of the top surface 12. The conduits 11 are spaced from each other by a distance D. The distance D is measured in a direction parallel with the surface 14. The distance D is a shortest distance from one outer surface 15 to another outer surface 15. Depending on the structure of each conduit 11, the electric field lines 8 can be symmetrical or asymmetrical about the center line 7. In this embodiment, a portion of the electric field lines 8 spreading out from the apertures 13 of the two conduits 11 coincides at a region R close to the center line 7 increasing the current density near the region R.
In FIG. 9, the shield 100 includes the conduit 11. The conduit 11 includes a plurality of apertures 13. The apertures 13 can be of different shapes such as square, rectangle, polygon, oval, or circle. The conduit 11 includes a thickness TH2 measured from an outer surface 15 to an inner surface 16 of the conduit 11. The thickness TH2 can be different for the different aperture 13. For example, in some embodiments, some apertures 13 are closer to the outer surface 15 than other apertures 13. The aperture 13 closer to the outer surface 15 would have smaller thickness TH2. The top surface 12 includes a plurality of apertures 13. A thickness TH3 is a shortest distance measured from an inner surface 16 to another inner surface 16. In various embodiments, the inner surfaces 16 of the different apertures 13 can be parallel, tilted away, or tilted toward each other. The apertures 13 can be symmetric or asymmetric about the center line 7.
In some other embodiments, the outer surface 15 and the inner surface 16 can be in a irregular shape. Depending on an area to be plated, the shapes of the outer surface 15 and the inner surface 16 can be the same or different. The top surface 12 can also be an irregular ring. The conduit 11 can be a cylinder, rectangular prism, triangular prism, or irregular prism. The aperture 13 can be in square, circle, polygon, or other irregular shapes. The shape and size of the aperture 13 can be adjusted according to the predetermined area to be plated.
Different features of the foregoing different embodiments may be configured in different combinations to form other embodiments for adjusting the scattering path and the density of the electric field lines 8. Adjusting the scattering path of the electric field lines 8 can be achieved by different methods. For example, adjusting a tilt angle of the inner surface 16 controls a degree of diffusion of the scattering path. As illustrated in FIG. 5, a greater tilt angle of the inner surface 16 widens the degree of diffusion. Moreover, adjusting the tilt angle of the top surface 12 controls symmetry of diffusion of the scattering path. As illustrated in FIG. 7, a greater tilt angle of the top surface 12 decreases the symmetry of the scattering path.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
Patent Application
20160281257
