Patent Publication Number: US-2016222537-A1

Title: Electroplating apparatus and method

Description:
FIELD 
     The present disclosure relates generally to a method and apparatus for electrochemically plating a semiconductor structure. 
     BACKGROUND 
     Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials as well as organic semiconductors. Semiconductor devices have replaced thermionic devices (vacuum tubes) in most applications. They use electronic conduction in the solid state as opposed to the gaseous state or thermionic emission in a high vacuum. Semiconductor devices are manufactured both as single discrete devices and as integrated circuits (ICs), which consist of a number of devices manufactured and interconnected on a single semiconductor substrate, or wafer. 
     Semiconductor device fabrication is a multiple-step sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications. Among semiconductor fabrication processes, layer deposition processes are utilized to form IC components. One of the most frequently employed layer deposition process is the electro-chemical plating (ECP) process, which deposits a layer of conductive material onto a substrate by electrolytic deposition. 
     A problem confronted by the conventional electroplating apparatus is that the varying of physical properties, dimensional conditions or other parameters associated with components in the electric loop would result in a significant variation in the electric current flowing through the electric loop, thus affecting the plating quality and uniformity. 
    
    
     
       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 schematic diagram illustrating an electroplating apparatus for electrochemically plating a substrate in an electrochemical plating (ECP) process. 
         FIG. 2  is a schematic diagram illustrating an electroplating apparatus for electrochemically plating a substrate in accordance with one embodiment of the present disclosure. 
         FIG. 3  is a schematic diagram illustrating an electroplating apparatus in accordance with one embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional view illustrating a substrate holder and a rotation driver in accordance with one embodiment of the present disclosure. 
         FIG. 5  is a cross-sectional view illustrating a substrate holder and a rotation driver in accordance with one embodiment of the present disclosure. 
         FIG. 6  is a schematic diagram illustrating an electroplating apparatus for electrochemically plating a substrate. 
         FIG. 7  is a schematic diagram illustrating an electroplating apparatus for electrochemically plating a substrate in accordance with one embodiment of the present disclosure. 
         FIG. 8  is a flowchart of a method for electrochemically plating a substrate. 
     
    
    
     DETAILED DESCRIPTION 
     The manufacturing and use of the embodiments of the present disclosure are discussed in details below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. It is to be understood that the following disclosure provides many different embodiments or examples for implementing different features of various embodiments. 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. 
     Embodiments, or examples, illustrated in the drawings are disclosed below using specific language. It will nevertheless be understood that the embodiments and examples are not intended to be limiting. Any alterations and modifications in the disclosed embodiments, and any further applications of the principles disclosed in this document are contemplated as would normally occur to one of ordinary skill in the pertinent art. 
     Further, it is understood that several processing steps (operations) and/or features of a device may be only briefly described. Also, additional processing steps and/or features can be added, and certain of the following processing steps and/or features can be removed or changed while still implementing the claims. Thus, the following description should be understood to represent examples only, and are not intended to suggest that one or more steps or features is required. 
     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&#39;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. 
     Integrated chips (IC) are manufactured by subjecting a semiconductor subject to multiple processing steps. Among these, layer deposition processes are utilized to form IC components such as polysilicon gate material and metal interconnect layers within a cavity of a dielectric layer. Deposition processes include physical vapor deposition (PVD), atomic layer deposition (ALD) and electrochemical plating (ECP). 
     Electrochemical plating (ECP) processes deposit a layer of conductive material onto a substrate by electrolytic deposition, wherein a substrate is submerged into an electroplating solution comprising ions of a material to be deposited. A DC voltage is applied to the substrate, causing it to act as a cathode which attracts cations of the electroplating solution, which reduce and accumulate over the substrate to form a thin film onto the substrate. 
     In reference to the drawings,  FIG. 1  is a schematic diagram illustrating an electroplating apparatus  100  for electrochemically plating a substrate in an electrochemical plating (ECP) process. The electroplating apparatus  100  comprises an electroplating cell  101 , a substrate holder  103 , a rotation driver, a power distribution assembly  106  and an anode  107 . The electroplating cell  101  serves as a container/vessel for containing an electroplating solution  102 . The substrate holder  103  is configured for holding a substrate  104  in the electroplating solution  102 . The rotation driver  105  is configured to rotate the substrate holder  103  and is electrically coupled to the substrate holder  103 . The power distribution assembly  106  is electrically coupled to the rotation driver  105 . In addition, the anode  107  is disposed within the electroplating cell  101  (the anode  107  being immersed in the electroplating solution  102 ). The electroplating apparatus  100  further comprises a power supply unit  108  that is electrically coupled between the anode  107  and the power distribution assembly  106 , thereby forming an electric loop (not shown). The power supply unit  108  is configured to provide a voltage V (not shown) that causes an electric current I 1  to flow through the electric loop. Namely the electric current I 1  would flow from the power supply unit  108  through the anode  107 , the electroplating solution  102 , the substrate  104 , the substrate holder  103 , the rotation driver  105 , the power distribution assembly  106  and back to the power supply unit  108 . The flow of the electric current I 1  through the electric loop would cause the deposition of a conductive material (not shown) of the electroplating solution  102  onto the substrate  104 . 
     As is well known for a skilled person, regarding an electrochemical plating (ECP) process, the plating quality and uniformity depend on the stability and uniformity of current distribution. Given that the voltage V provided by the power supply unit  108  being a fixed value, the electric current I 1  is dependent on the total effective impedance of the electric loop, which includes the effective impedance of the substrate  104 , the substrate holder  103 , the rotation driver  105 , the power distribution assembly  106 , the power supply unit  108 , the anode  107 , the conductive path of the electroplating solution  102  (staring from the anode  107  to the substrate  104 ) and the conductive lines. Therefore, a problem confronted by the conventional electroplating apparatus  100  is that the varying of physical properties, dimensional conditions or other parameters associated with components (e.g., the substrate  104 ) in the electric loop would result in a significant variation in the electric current I 1  flowing through the electric loop, thus affecting the plating quality and uniformity. 
     Furthermore, a significant variation in the electric current flowing through the electric loop of an electroplating apparatus would result in other problems in electroplating a semiconductor substrate (or wafer). Generally an electroplating process performed by an electroplating apparatus would not be carried out before complete immersion of the substrate into the electroplating solution. During a pre-plating step (which is defined as a time period starting from the commencement of immersion to complete immersion of the substrate into the electroplating solution), the electric current would gradually rise to a peak electric current value (as the resistance/impedance between the substrate/electroplating solution interface gets smaller). Accordingly, the detection of the peak electric current value can be used as an indicator of complete immersion of the substrate into the electroplating solution so as to facilitate following electroplating operations. In view of the above, a significant variation in the electric current flowing through the electric loop (resulted from, e.g., wafer-to-wafer variation) would result in a significant variation in the peak electric current value, which in turn affects plating quality or reduces throughput. 
     To address the aforementioned problem that exists in the conventional electroplating apparatus  100 , an electroplating apparatus with an additional current regulating member is proposed.  FIG. 2  is a schematic diagram illustrating an electroplating apparatus  200  for electrochemically plating a substrate in accordance with one embodiment of the present disclosure. Similarly, the electroplating apparatus  200  comprises an electroplating cell  101 , a substrate holder  103 , a rotation driver  105 , a power distribution assembly  106 , an anode  107 , a power supply unit  108  and a current regulating member  109 . The electroplating cell  101  contains an electroplating solution  102  and the substrate holder  103  is configured holding a substrate  104 . The power supply unit  108  may be a DC power supply unit. According to the arrangement shown in  FIG. 2 , the current regulating member  109  is electrically coupled between the rotation driver  105  and the power distribution assembly  106 . However, it should be noted that the current regulating member  109  may be arranged at elsewhere on the electric loop. For instance, in  FIG. 3  (which is a schematic diagram illustrating an electroplating apparatus  300  in accordance with one embodiment of the present disclosure), the current regulating member  109  is electrically coupled between the power supply unit  108  and the anode  107 . Alternatively, the current regulating member  109  may be electrically coupled between the power supply unit  108  and the power distribution assembly  106 . Further alternatively, the current regulating member  109  may be electrically coupled between the substrate holder  103  and the rotation driver  105 . Note that the current regulating member  109  should not be disposed within the electroplating cell  101 . 
     Referring back to  FIG. 2 , a voltage V provided by the power supply unit  108  would cause an electric current I 2  to flow through the electric loop, wherein the electric current I 2  would flow from the power supply unit  108  through the anode  107 , the electroplating solution  102 , the substrate  104 , the substrate holder  103 , the rotation driver  105 , the current regulating member  109 , the power distribution assembly  106  and back to the power supply unit  108 . The flow of the electric current I 2  through the electric loop would cause the deposition of a conductive material of the electroplating solution  102  onto the substrate  104 . 
     The current regulating member  109  serves to provide a predetermined impedance value for the electric loop. The predetermined impedance is such selected that the variation of the electric current I 2  flowing through the electric loop is kept within a smaller range compared to the electric current I 1  flowing through the electric loop (which is measured in the absence of the current regulating member  109 ). The selection of the predetermined impedance is based on the following two criteria: (1) the larger impedance the current regulating member  109  has, the variation of the electric current flowing through the electric loop is more controllable; and (2) the larger impedance the current regulating member  109  has, the greater amount of power it consumes. Preferably, the predetermined impedance value ranges from 0.02 mΩ to 20Ω. More preferably, the predetermined impedance value ranges from 0.05 mΩ to 5Ω. Yet more preferably, the predetermined impedance value ranges from 0.1 mΩ to 1Ω. Most preferably, the predetermined impedance value is 50 mΩ. Note that the total impedance of the electric loop ranges from 1Ω to 50Ω. 
     In one embodiment, the substrate  104  is a semiconductor wafer with conductive elements/features (e.g., conductive plugs, conductive vias, conductive posts, filler materials or conductive traces) provided on an active surface (plating surface) thereof. In one embodiment, the substrate  104  may comprise logic devices, eFlash device, memory device, microelectromechanical (MEMS) devices, analog devices, CMOS devises, combinations of these, or the like. The substrate  104  may comprise bulk silicon, doped or undoped, or an active layer of a silicon-on-insulator (SOI) substrate. Generally, an SOI substrate comprises a layer of a semiconductor material such as silicon, germanium, silicon germanium, SOI, silicon germanium on insulator (SGOI), or combinations thereof. In one embodiment, the substrate  104  includes multi-layered substrates, gradient substrates, hybrid orientation substrates, any combinations thereof and/or the like, such that the semiconductor package can accommodate more active and passive components and circuits. In one embodiment, the electroplating apparatus  200  is employed for electrochemically plating the substrate  104  so as to form copper interconnects, patterns or layers on semiconductor features previously arranged on the active surface of the substrate  104 . 
     In one embodiment, the conductive material that is to be plated onto the substrate  104  may be a metal (such as gold, zinc nickel, silver, copper or nickel), and the anode  107  may be made of the same metal. Also, the electroplating solution  102  may include a metal salt of the same metal. In one embodiment, the conductive material that is to be deposited/plated onto the substrate  104  is copper. Thus, the anode  107  may be made of copper. The electroplating solution  102  may include a mixture of copper salt, acid, water and various organic and inorganic additives that improve the properties of the deposited copper. Suitable copper salts for the electroplating solution  102  comprise copper sulfate, copper cyanide, copper sulfamate, copper chloride, copper formate, copper fluoride, copper nitrate, copper oxide, copper fluorine-borate, copper trifluoroacetate, copper pyrophosphate and copper methane sulfonate, or hydrates of any of the foregoing compounds. The concentration of the copper salt used in the electroplating solution  102  will vary depending on the particular copper salt used. Various acids can be used in the electroplating solution  102 , comprising: sulfuric acid, methanesulfonic acid, fluoroboric acid, hydrochloric acid, hydroiodic acid, nitric acid, phosphoric acid and other suitable acids. The concentration of the acid used will vary depending on the particular acid used in the electroplating solution  102 . 
     In one embodiment, the electroplating solution  102  is a copper sulfate (CuSO 4 ) solution. The substrate  104  and the anode  107  are both immersed in the electroplating solution  102  (CuSO 4  solution) containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. The power supply unit  108  supplies an electric current to the anode  107 , oxidizing the copper atoms that the anode  107  comprises and allowing them to dissolve in the electroplating solution  102 . At the substrate  104  (cathode), the dissolved metal ions (cation Cu 2+ ) in the electroplating solution  102  are reduced to metallic copper onto the substrate  104  by gaining two electrons. At the anode  107 , copper is oxidized at the anode to Cu 2+  by losing two electrons. The result is the transfer of copper from the anode  107  to the substrate  104 . The rate at which the anode  107  is dissolved is equal to the rate at which the substrate  104  is plated. In this manner, the ions in the electroplating solution  102  are continuously replenished by the anode  107 . 
     The electroplating solution  102  may comprise additives that improve certain electroplating characteristics of the electroplating solution, improve the properties of the deposited copper or accelerate the copper deposition rate. One of the key functions of the additives is to level the deposit by suppressing the electrodeposition rate at protruding areas in the surface of the substrate  104  and/or by accelerating the electrodeposition rate in recessed areas in the surface of the substrate  104 . The adsorption and inhibition may be further enhanced by the presence of halogen ions. 
     Common additives for copper electroplating solution include brighteners, suppressors and levelers. Brighteners are organic molecules that tend to improve the specularity (or reflectivity) of the copper deposit by reducing both surface roughness and grain-size variation. Suitable brighteners include, for example, organic sulfide compound, such as bis-(sodium sulfopropyl)-disulfide, 3-mercapto-1-propanesulfonic acid sodium salt, N-dimethyl-dithiocarbamyl propylsulfonic acid sodium salt and 3-S-isothiuronium propyl sulfonate, or mixtures of any of the foregoing compounds. Suppressors are macromolecule deposition inhibitors that tend to adsorb over the surface of the substrate and reduce local deposition rates, increasing the deposition uniformity. Levelers usually have ingredients with nitrogen functional group and may be added to the electroplating solution at a relatively low concentration. Traditional leveling involves the diffusion or migration of strongly current suppressing species to corners or edges of macroscopic objects which otherwise plate more rapidly than desired due to electric field and solution mass transfer effects. The levelers may be selected from the following agents: a polyether surfactant, a non-ionic surfactant, a cationic surfactant, an anionic surfactant, a block copolymer surfactant, a polyethylene glycol surfactant, polyacrylic acid, a polyamine, aminocarboxylic acid, hydrocarboxylic acid, citric acid, entprol, edetic acid, tartaric acid, a quaternized polyamine, a polyacrylamide, a cross-linked polyamide, a phenazine azo-dye, an alkoxylated amine surfactant, polymer pyridine derivatives, polyethyleneimine, polyethyleneimine ethanol, a polymer of imidazoline and epichlorohydrine, benzylated polyamine polymer. 
     Another approach to achieve even deposition of the metal ions (from the electroplating solution  102 ) onto the substrate  104  is to stir the electroplating solution  102  to flow to the substrate  104  with uniform flow velocity. A uniform flow velocity is important during the electroplating process to provide even deposition of the metal ions from the electroplating solution  102  onto the substrate  104 . In one embodiment, the flow velocity of the electroplating solution  102  toward the center of the plating surface of the substrate  104  is controlled to be the same as the flow velocity of the electroplating solution  102  toward the peripheral region of the plating surface of the substrate  104 . Thus, the uniform flow velocity of the electroplating solution  102  (as it flows laterally across the plating surface of the substrate  104 ) results in uniform plating height. In addition, unevenness in the plating thickness due to uneven flow velocity distribution of the plating solution can be mitigated and uniform distribution of the plating thickness can be achieved over the plating surface of the substrate  104 . 
       FIG. 4  is a cross-sectional view illustrating a substrate holder  103  and a rotation driver  105  in accordance with one embodiment of the present disclosure. The substrate holder  103  is controllable to hold the substrate  104  and immerse it into the electroplating solution  102 . In one embodiment, the substrate holder  103  may be a clamshell-type substrate holder comprising a cone member  103   a , cup member  103   b  and seal (flange) member  103   c , wherein the cup member  103   b  and seal member  103   c  are annular in shape. When the substrate  104  is clamped within the cavity formed by the cone member  103   a  and the cup member  103   b , the seal member  103   c  would press against the plating surface  104   a  of the substrate  104  (namely the active surface of the substrate  104 ). This forms a seal between the seal member  103   c  and a perimeter region of the plating surface  104   a  of the substrate  104  while simultaneously forming the electrical connection between a plurality of contacts provided within the substrate holder  103  (not shown) and the plating surface  104   a  of the substrate  104 . The seal with the plating surface  104   a  prevents the electroplating solution  102  from contacting the edge of the substrate  104 , the rest of the edge of the substrate  104  and the plurality of contacts and thus prevents the associated electrolyte contamination from the electroplating solution  102 . (only a targeted portion of the plating surface  104   a  of the substrate  104  is exposed to the electroplating solution  102  during electroplating cycle) 
     In one embodiment, the rotation driver  105  may comprise a rotatable spindle  105   a  and a slip ring assembly  105   b  (which comprises a plurality of slip rings). Slip ring assembly  105   b  mounted on and electrically isolated from the rotatable spindle  105   a  are electrically connected to the substrate holder  103  by electric interconnects/wires (not shown) inside of the rotatable spindle  105   a . Each of the plurality of slip rings of the slip ring assembly  105   b  in combination with a corresponding brush (not shown) enable electrical connection between external electrical components (e.g. power supply unit  108  of  FIG. 2 ) and the substrate holder  103  when the rotatable spindle  105   a  is rotating. One or more slip rings are typically used to provide one or more channels (electrical pathways electrically isolated from one another). For example, four or six slip rings may be used. 
     In one embodiment, the rotatable spindle  105   a  is driven by a motor (not shown). Mounting the cone member  103   a  of the substrate holder  103  on the rotatable spindle  105   a  advantageously allows the substrate holder  103  and the substrate  104  to be rotated after (or before, upon) being immersed in the electroplating solution  102 . This prevents bubble entrapment on the plating surface  104   a  of the substrate  104 , ensures uniformity of the plating and averaging possible disturbances and improves electrolyte transport to the substrate  104 . Further, the thickness profile of the electroplated layer can readily be adjusted by changing the rotational speed of the rotatable spindle  105   a . Different rotational speeds may be employed for different operations. For immersing the substrate, the rotational speed is preferably between about 1 and 150 rpm. For a 200 mm diameter substrate (wafer), the speed is preferably between about 100 and 150 rpm. For a 300 mm diameter substrate (wafer), the speed is preferably between about 50 and 100 rpm. 
     Another approach for preventing bubble entrapment on the plating surface  104   a  of the substrate  104  is angled immersion, which is depicted in  FIG. 5  (which is a cross-sectional view illustrating a substrate holder and a rotation driver in accordance with one embodiment of the present disclosure). The configuration of  FIG. 5  allows immersion of the substrate  104  at an angle with respect to the surface  102   a  of the electroplating solution  102 . Specifically, angled immersion reduces the problems of bubble entrapment on the plating surface  104   a  of the substrate  104 . Depending on the different electroplating processes and the details of the substrate holder  103  (e.g., clamshell-type substrate holder), different angles may be used. Note that electroplating at an angle helps also prevent entrapment of bubbles on the plating surface during electroplating and defects in the plated film are reduced when angled plating is employed. In one embodiment, the angle of the plating surface  104   a  of the substrate  104  with respect to the surface  102   a  of the electroplating solution  102  is preferably about 1 to about 5 degrees. In one embodiment, the angle is about 4 to about 5 degrees. Furthermore, the substrate  104  is preferably moved into the electroplating solution  102  at a speed of between about 5 and 50 millimeters/second. More preferably, the substrate  104  is moved into the electroplating solution  102  at a speed of between about 5 and 25 millimeters/second. Even more preferably, the substrate  104  is moved into the electroplating solution  102  at a speed of between about 8 and 15 millimeters/second. Most preferably, the substrate  104  is moved into the electroplating solution  102  at a speed of about 12 millimeters/second. 
       FIG. 6  is a schematic diagram illustrating an electroplating apparatus  600  for electrochemically plating a substrate. The electroplating apparatus  600  comprises: an electroplating cell  101  (for containing the electroplating solution  102 ). The electroplating apparatus  600  comprises a substrate holder  103  for holding a substrate  104 . The electroplating apparatus  600  further comprises a rotation driver  105  and an anode  107 , wherein a voltage V applied across the rotation driver  105  and the anode  107  causes an electric current I 3  to flow from the rotation driver  105  to the anode  107 . 
       FIG. 7  is a schematic diagram illustrating an electroplating apparatus  700  for electrochemically plating a substrate in accordance with one embodiment of the present disclosure. The electroplating apparatus  700  comprises an electroplating cell  101 , a substrate holder  103 , a rotation driver  105 , an anode  107  and a current regulating member  109 . Similarly, the electroplating cell  101  is used for containing an electroplating solution  102 . The substrate holder  103  is capable of holding a substrate  104  in the electroplating solution  102 . The rotation driver  105  is configured for rotating the substrate  104 . The current regulating member  109  is electrically coupled between the rotation driver  105  and the anode  107 , wherein a voltage V applied across the current regulating member  109  and the anode  107  causes an electric current I 4  to flow from the current regulating member  109  to the anode  107 . The electric current I 4  would flow from the current regulating member  109  through the anode  107 , the electroplating solution  102 , the substrate  104 , the substrate holder  103 , the rotation driver  105  and back to the current regulating member  109 . The flow of the electric current I 4  through the electric loop would cause the deposition of a conductive material of the electroplating solution  102  onto the substrate  104 . 
     The current regulating member  109  serves to provide a predetermined impedance value for the electric loop. The predetermined impedance is such selected that the variation of the electric current I 4  flowing through the electric loop is kept within a smaller range compared to the electric current I 3  flowing through the electric loop (which is measured in the absence of the current regulating member  109 ). Preferably, the predetermined impedance value ranges from 0.02 mΩ to 20Ω. More preferably, the predetermined impedance value ranges from 0.05 mΩ to 5Ω. Yet more preferably, the predetermined impedance value ranges from 0.1 mΩ to 1Ω. Most preferably, the predetermined impedance value is 50 mΩ. The total impedance of the electric loop ranges from 1Ω to 50Ω. 
       FIG. 8  is a flowchart of a method for electrochemically plating a substrate. In operation  801 , a substrate is immersed into an electroplating solution. In operation  802 , an anode is provided and is electrically coupled to the electroplating solution (e.g., being immersed into an electroplating solution). Operation  803  discloses forming an electric loop starting from a power supply to the anode, the electroplating solution, the substrate, and back to the power supply (wherein an electric current flows from the power supply to the anode, the electroplating solution, the substrate, and back to the power supply). In operation  804 , a current regulating member with a predetermined impedance value is provided on the electric loop, wherein the predetermined impedance is such selected that the variation of the electric current flowing through the electric loop is kept within a smaller range compared to that measured in the absence of the current regulating member, wherein the flow of the electric current through the electric loop causes the deposition of a conductive material onto the substrate. Preferably, the predetermined impedance value ranges from 0.02 mΩ to 20Ω. More preferably, the predetermined impedance value ranges from 0.05 mΩ to 5Ω. Yet more preferably, the predetermined impedance value ranges from 0.1 mΩ to 1Ω. Most preferably, the predetermined impedance value is 50 mΩ. The total impedance of the electric loop ranges from 1Ω to 50Ω. 
     In one embodiment, an operation of forming additional multiple conductive metal layers is performed prior to operation  801  (namely, immersing the substrate into the electroplating solution). First, a barrier layer, preferably comprising tantalum, tantalum nitride (TaN), titanium nitride (TiN), or any suitable material, may be pre-deposited over a to-be-plated surface of the substrate. The barrier layer is typically deposited over the to-be-plated surface using physical vapor deposition (PVD) by sputtering or a chemical vapor deposition (CVD) process. The barrier layer limits the diffusion of copper into the semiconductor substrate (because copper reacts with SiO2, it is necessary to form a barrier layer first) and any dielectric layer thereof, thereby increasing reliability. Preferably, the barrier layer has a film thickness between about 25 angstroms and about 500 angstroms for an interconnect structure/feature having sub-micron dimension. In one example, the barrier layer has a thickness between about 50 angstroms and about 3000 angstroms. Second, a copper seed layer may be deposited over the barrier layer using PVD. The copper seed layer provides good adhesion for subsequently electroplated copper. In one example the seed layer has a thickness between about 50 angstroms and about 3000 angstroms. The seed layer may be patterned for subsequent formation of deposited copper. 
     In addition, after electroplating, the plated surface of a substrate may be planarized, e.g., by chemical mechanical polishing (CMP), to define a conductive interconnect feature. Chemical mechanical planarization is a process that can remove topography from a plated surface of the substrate. Chemical mechanical planarization is used to planarize the plated surface for following fabrication processes. Chemical mechanical planarization is the preferred planarization step utilized in deep sub-micron IC manufacturing. For chemical mechanical planarization, the polishing action is partly mechanical and partly chemical. The mechanical element of the process applies downward pressure while the chemical reaction that takes place increases the material removal rate and this is usually tailored to suit the type of material being processed. 
     Some embodiments of the present disclosure provide an electroplating apparatus for electrochemically plating a substrate, comprising an electroplating cell for containing an electroplating solution; a substrate holder for holding a substrate in the electroplating solution; a rotation driver electrically coupled to the substrate holder and configured to rotate the substrate holder; a power distribution assembly electrically coupled to the rotation driver; an anode disposed within the electroplating cell, the anode being immersed in the electroplating solution; a power supply unit electrically coupled between the anode and the power distribution assembly, thereby forming an electric loop; and a current regulating member for providing a predetermined impedance value for the electric loop, wherein a voltage provided by the power supply unit causes an electric current to flow through the electric loop, and the predetermined impedance is such selected that the variation of the electric current flowing through the electric loop is kept within a smaller range compared to that measured in the absence of the current regulating member. 
     Some embodiments of the present disclosure provide an electroplating apparatus for electrochemically plating a substrate, comprising: an electroplating cell for containing an electroplating solution; a substrate holder for holding a substrate in the electroplating solution; a rotation driver electrically coupled to the substrate holder and configured to rotate the substrate holder; an anode disposed within the electroplating cell, the anode being immersed in the electroplating solution, wherein a voltage applied across the rotation driver and the anode causes an electric current to flow from the rotation driver to the anode; and a current regulating member electrically coupled to the rotation driver, wherein a predetermined impedance value of the current regulating member is such selected that the variation in the electric current is kept within a smaller range compared to that measured in the absence of the current regulating member. 
     Some embodiments of the present disclosure provide an electroplating method for electrochemically plating a substrate, comprising: immersing a substrate into an electroplating solution; electrically coupling an anode to the electroplating solution; forming an electric loop in which an electric current flows from a power supply to the anode, the electroplating solution, the substrate, and back to the power supply; and providing a current regulating member with a predetermined impedance value on the electric loop, wherein the predetermined impedance is such selected that the variation of the electric current flowing through the electric loop is kept within a smaller range compared to that measured in the absence of the current regulating member, wherein the flow of the electric current through the electric loop causes the deposition of a conductive material onto the substrate. 
     The methods and features of this disclosure have been sufficiently described in the above examples and descriptions. It should be understood that any modifications or changes without departing from the spirit of the disclosure are intended to be covered in the protection scope of the disclosure. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As those skilled in the art will readily appreciate from the disclosure of the present disclosure, processes, machines, manufacture, composition of matter, means, methods or steps presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such as processes, machines, manufacture, compositions of matter, means, methods or steps/operations. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure.