BACKGROUND
The present disclosure relates to a metal plating system, and more specifically, to a metal plating system including gas bubble removal unit.
Copper metallization is a key component for integrated circuits (ICs). As the industry demand for smaller sized ICs increases, plating-related defects in metal vias and interconnect lines are becoming more prominent. These plating defects ultimately affect the reliability of the ICs.
One such plating defect that has increased over the years is referred to as “hollow metal.” Hollow metal describes various point defects, such as voids, porosity etc., which occur in the metal vias and connection lines of the ICs. One cause of hollow metal may be attributed to conventional plating tools used to perform the metallization electroplating applied to IC wafer surfaces. More specifically, conventional plating tools dispose the wafer surface in a metallization solution in a downward-facing position towards an opposing anode of the plating tool. The plating process forms various metal vias and/or metal connections on the downward-facing surface. While the wafer is immersed, gas bubbles, such as air, may be trapped in the trenches and via holes trapping as a result of insufficiently fast and incomplete wetting of the trenches and vias with plating solution before plating starts. Hydrogen and/or air bubbles may also be formed in the solution during plating. They may be trapped in the trenches and vias. The bubbles also rise toward the surface and may encounter the wafer. The trapped bubbles may not be removed when using the currently used rotating disc configured plating tool. However, the trapped bubble may adhere to the bottom or side wall of the trenches and vias. These bubbles may block metal ions from reaching the conduction seed layer and forming the metal conductor by properly filling the trenches and vias. Accordingly, non-plated sections beneath the bubbles may occur, which ultimately causes hollow sections in the metal lines or vias, i.e., the hollow metal.
SUMMARY
According to an embodiment, an electroplating apparatus includes an anode configured to electrically communicate with an electrical voltage and an electrolyte solution. A cathode module includes a cathode that is configured to electrically communicate with a ground potential and the electrolyte solution. The cathode module further includes a wafer in electrical communication with the cathode. The wafer is configured to receive metal ions from the anode in response to current flowing through the anode via electrodeposition. The electroplating apparatus further includes at least one agitating device interposed between the wafer and the anode. The agitating device is configured to apply a uniform agitation across a cathode module including a wafer surface and a shearing force to gas bubbles trapped in the trenches and vias created on a surface of the wafer facing the agitating device. In addition this agitating device will help to maintain an uniform diffusion layer over the large cathode i.e., wafer, surface which eventually enables plating having a uniform metal/alloy plating thickness. Uniform plating across the wafer surface results in uniform planarization by chemical mechanical polishing (CMP).
According to another embodiment, an agitating device to remove bubbles adhered to a surface of a wafer undergoing an electroplating process comprises a frame having an upper portion facing a wafer and a lower portion opposing the upper portion. The upper portion has a slot formed therethrough. The slot is configured to stream an electrolyte solution toward and past the surface of the wafer at an increased velocity.
Additional features are realized through the techniques of the various embodiments described herein. For a better understanding of the features, refer to the description and to the drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. Various forgoing and other inventive features are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1A is a block diagram illustrating an electroplating apparatus according to an exemplary embodiment of the present disclosure;
FIG. 1B is a block diagram illustrating an IC wafer according to an embodiment of the present disclosure;
FIG. 2 is a block diagram illustrating an electroplating apparatus according to another embodiment of the present disclosure;
FIG. 3 is a block diagram illustrating an electroplating apparatus according to yet another embodiment of the present disclosure;
FIG. 4 is a block diagram illustrating an electroplating apparatus according to still another embodiment of the present disclosure;
FIGS. 5A-B illustrate examples of an agitating device according to an embodiment of the disclosure;
FIG. 6 illustrates an example of a plating tool including a filter unit according to an embodiment of the disclosure;
FIG. 7 is a block diagram illustrating an electroplating apparatus including an ultrasonic transducer according to another embodiment of the present disclosure;
FIGS. 8A-8C illustrate a process flow of electroplating a wafer according to an embodiment of the disclosure;
FIG. 9 is a line graph illustrating an current profile corresponding to applying a voltage potential to the wafer during a plating process according to an embodiment of the disclosure; and
FIG. 10 is a flow diagram illustrating a method of electroplating a wafer according to an embodiment of the disclosure.
DETAILED DESCRIPTION
Referring now to FIG. 1A, an electroplating apparatus 100 according to an exemplary embodiment of the present disclosure is illustrated. The electroplating apparatus 100 includes a power supply 102, a container 104 and a plating tool 106. The plating tool 106 includes an anode 108 and a cathode module 110, each in electrical communication with the power supply 102. The anode 108 and the cathode module 110 may be formed of various shapes including, but not limited to, square and circular.
The power supply 102 includes a positive terminal 115 and a negative terminal 116. The power supply 102 may include a voltage source, a current source, or a voltage source and a current source. The power supply 102 is configured to output an electrical voltage, a current, or a voltage and a current. The power supply 102 may execute a voltage scan with a predetermined scan rate. The power supply 102 may also supply a constant voltage. In addition, the power supply 102 may generate a voltage output and then switched to a current output or vice versa. The voltage and current output may be a direct current (DC), a pulse or combination of different waveforms. The current may also have a value selected to achieve a desired current density.
The current may be supplied according to a constant electrical potential condition, under constant electrical current condition or combination thereof (see FIG. 9).
The container 104 may contain an electrolyte solution 117 capable of conducting an electrical current that induces a metallization plating process. The electrolyte solution 117 may comprise cupric ions and/or chlorine ions and sulfate ions that render the electrolyte solution 117 to be electrically conductive. According to at least one exemplary embodiment, the electrolyte solution 117 includes, but is not limited, to sulfuric acid (H2SO4), copper sulfate pentahydrate, 2N hydrochloric acid, sodium sulfate, etc. An electrolyte solution of sulfuric acid may range from 2-50 grams/liter (g/L), copper sulfate pentahydrate may range from 20-300 g/L and organic additives used as accelerator, levelers, suppressors and wetting agents. A solution of 2N hydrochloric acid may range from 0-5 milliliters/liters (ml/L), and a solution of sodium sulfate may range from 80-200 g/L. It can be appreciated that other solutions of acids, bases or salts may be used as the electrolyte solution 117. In addition, the electrolyte solution 117 may comprise either H2SO4 or chloride (Cl), and metal ions. The electrolyte metal ions comprises, for example, copper (Cu). In another embodiment, the solution comprises an acid copper plating solution including (1) a dissolved copper salt (e.g., as copper sulfate), (2) an acidic electrolyte (e.g., as sulfuric acid) in an amount sufficient to impart conductivity to the bath and (3) additives (e.g., surfactants, brighteners, levelers and suppressants). The bath may also contain a wetting agent to increase wettability of the wafer. Various wetting agents may be used including, but not limited to, anionic agents, cationic agents, amphoteric wetting agents that ionize when mixed with water, and non-ionic wetting agents.
In response to current flowing through the anode 108, metal ions from the anode 108 are transferred to the downward-facing surface of the wafer 113 via an electrodeposition process. As a result, copper vias and/or copper connection lines may be formed on the downward-facing surface of the wafer 113 and in the etched trenches and vias which are metalized with a very thin conducting seed layer, as discussed in greater detail below with respect to FIG. 1B. A seed layer formed on a top of the surface of the cathode and inside the vias and trenches. The seed layer may be formed from tantalum nitride, tantalum copper (Cu) or Cu alloys seed like Cu alloyed with easily oxidized metal e.g. Cu—Mn, Cu—Al, Cu—Zn, Cu—Ga and similar alloy or other suitable conducting seed layer. Although copper is referenced as an example when describing the various embodiments, the plating process described herein may be utilized with other metals including, but not limited to, gold (Au), silver (Ag), nickel (Ni), iron (Fe), palladium (Pd), and alloys plating thereof.
The plating tool 106 is in electrical communication with the power supply 102 and is in fluid communication with the electrolyte solution 117. In at least one embodiment illustrated in FIG. 1A, the anode 108 may be connected to an inner surface of the container 104 and immersed in the electrolyte solution 117. An electrically conductive wire 118 has one end connected to the anode 108 and an opposing end connected to the positive terminal 115 of the power supply 102. The anode 108 may be formed of any metal configured to transfer metal ions to the downward-facing surface of the wafer 113 via electrodeposition. In at least one exemplary embodiment, the anode 108 is formed of copper (Cu).
The cathode module 110 includes a cathode 111 coupled to a supporting plate 112. Various means may be used to connect the cathode 111 to the supporting plate 112 including, but not limited to, mechanical pins, fasteners, and a non-soluble conductive adhesive. Further, the cathode 111 may be connected to the supporting plate 112 using a universal joint 400. The universal joint 400 allows the cathode module 110 to move in a plurality of directions with respect to the axis (A). For example, the cathode module 110 may rotate about the axis, while still capable of tilting left, right or moving up and down.
The supporting plate 112 may be configured to rotate about an axis (A) extending perpendicular to cathode module 110. Hence, the cathode 111 may be rotated when the plate 112 rotates. The cathode module 110 further includes an interconnect (IC) wafer 113 connected in electrical communication to the cathode 111. A conductive alloy seed layer 114 may be formed on the IC wafer. Accordingly, the IC wafer 113 may rotate along with the supporting plate 112 and the cathode 111. In at least one embodiment, the supporting plate 112 may be selectively rotated. The cathode module 110, including the wafer 113, may be formed in various shapes including, but not limited to square, circular and other.
Referring now to FIG. 1B, an IC wafer 300 is illustrated according to an embodiment. The IC wafer 300 may be formed from a semiconductor material, such as silicon. The IC wafer 300 includes a base layer 302 and a dielectric layer 304. The base layer 302 and dielectric layer 304 may be insulated from one another by an insulating layer 306 interposed therebetween. One or more trenches 308 and/or vias 309 may be formed in the dielectric layer 304. In at least one embodiment, the vias 309 may extend through the insulating layer 306 and into the base layer 302. The trenches 308 and/or vias 309 may be lined with a liner 310. The liner 310 may be formed from tantalum (Ta) or tantalum nitride (TaN). A copper (Cu) seed layer 312 may be formed on top of the liner 310. Accordingly, one or more air and/or hydrogen bubbles 314 may become trapped against the lower surface of the wafer 300, in a trench 308, and/or inside a via 309.
Referring again to FIG. 1A, the cathode 111 is in electrical communication with the negative terminal 116 of the power supply 102 via a second electrically conductive wire 119. An electrochemical circuit may be achieved when the anode 108 and the cathode 111 are introduced to the electrolyte solution 117 as described above. Accordingly, the electrical current output from the power supply 102 travels through the electrolyte solution 117 and to the anode 108, which induces an electrochemical metallization plating process such that metal ions from the anode 108 are transferred to the downward-facing surface of the wafer 113 via electrodeposition. As a result, metal vias and/or metal connection lines are formed on the downward-facing surface the wafer 113.
The plating tool 106 further includes at least one agitating device 120 configured to prevent air, hydrogen and/or other gas bubbles from becoming trapped inside the trenches and vias located beneath the cathode module 110 and adhering to the downward-facing surface of the wafer 113. The agitating device 120 may include a static agitating device that remains fixed or a dynamic agitating device that moves. When the wafer 113 is static, the dynamic agitating device will remove one or more bubbles from the wafer 113. When the wafer 113 is dynamic, a static agitation device will also maintain a constant well defined diffusion layer across the plating surface of the wafer 113.
Referring to at least one embodiment illustrated in FIG. 1A, for example, the agitating device 120 is fixated within the solution 117 and is disposed a predetermined distance below the wafer 113. The distance between the agitating device 120 and the wafer 113 may range from about 1 millimeter (mm) to about 5 mm. In at least one embodiment, the agitating device 120 may include a slot 122. The slot 122 is configured to flow one or more streams of solution 117 therethrough and toward the downward-facing surface of the wafer 113. The streamed solution 117 dislodges and directs bubbles away from the cathode module 110. Further, the flowed solution exerts a force on bubbles adhered to the downward-facing surface the wafer 113. The force causes the bubbles to loosen from the downward-facing surface and escape from beneath the cathode module 110. Accordingly, the wafer 113 may be plated without the formation of hollow metal since the bubbles 314 are removed from the downward-facing surface.
The plating system 106 may further include a pump configured to force the electrolyte solution through the slot 122. Accordingly, the stream generated by the pump may have an increased velocity that weakens the adhering force of the bubbles against the down-facing surface of the wafer 113. However, it is appreciated that the pump may be located outside of the container 104, and may include a tube system (not shown) that conveys solution to the slot 122. Although the pump may assist in flowing the stream of solution through the slot 122, it is appreciated that the pump is not required. For example, the rotation of the cathode module 110 may generate a shearing force that induces a partial vacuum between the wafer 113 and the agitating device 120 such that solution and gas bubbles are drawn from the vias and trenches.
The electroplating apparatus 100 may further include a filter unit 123 that is disposed between the anode 108 and the cathode module 110, and that extends between opposing inner walls of the container 104. The filter unit 123 may include a sac filter or a membrane, and is configured to separate a solution inside the container into a plating solution including additives and a virgin made solution (VMS) excluding the additives. The anode 108 may be disposed in the VMS, while the cathode module 110 is disposed in the plating solution 117. The additives may include brightener, suppressor, leveler, surfactant, wetting agent.
Referring to FIG. 2, a plating tool 106′ is illustrated according to another embodiment. The plating tool 106′ operates similar to the plating tool 106 described above. In this embodiment, however, the cathode module 110 is not rotated and remains stationary. Further, the agitating device 120 is disposed a short distance beneath a center region of the wafer 113. The agitating device 120 is configured to reciprocate at a predetermined frequency in a lateral direction with respect to the surface of the wafer 113. In at least one embodiment, the agitating device 120 may reciprocate at substantially the center of the cathode module 110. According to another the embodiment, the agitating device 120 may reciprocate and move all the way past, i.e., beyond, the edge of the wafer 113. The agitating device 120 may be reciprocated at frequency ranging from about 0.01 Hertz (Hz) to about 5 Hz, and more specifically 0.5 Hz-1.0 Hz. In the embodiment of FIG. 2, the agitating device 120 excludes a slot such that the portion near the wafer 113 is uniformly solid. The motion of the agitating device 120 induces waves in the solution 117, which exerts a force on bubbles trapped against the downward-facing surface of the wafer 113. As a result, the bubbles may be removed from the vias and trenches and forced away from beneath the wafer 113 such that they may continue rising toward the upper surface of the solution 117. In at least one embodiment, the agitating device 120 is coupled to an electrical motor (not shown) that is configured to reciprocate the agitating device 120 back and forth as described above.
In another embodiment, a plating tool 106″ may include a plurality of agitating devices 120A-120C, as illustrated in FIG. 3. Each agitating device 120A-120C may be spaced apart from one another by a predetermined distance and may reciprocate back and forth similar to the agitating device 120 described with respect to FIG. 2. However, the reciprocal motion of the plurality of agitating devices 120A-120C generates a greater shear force onto bubbles trapped beneath the wafer 113 and in the trenches and vias compared to the force generated by the single agitating device 120 illustrated in FIG. 2. The increased shear force, therefore, further weakens the adhesion force of bubbles against the wafer 113, and may further prevent hollow metal from forming during the plating process.
Referring to FIG. 4, a plating tool 106′″ is illustrated according yet another embodiment. The plating tool 106′″ operates similar to the plating tool 106′ described above with respect to FIG. 2. In this embodiment, however, the agitating device 120 is configured to move dynamically from one end of the wafer 113 to an opposing end. The agitating device 120 may also move all the past, i.e., beyond, the edge of the wafer 113. More specifically, the agitating device 120 is shown in phantom traveling beneath from a first end of the wafer 113 to an opposite end. As a result, the agitating device 120 can exert a shearing force across the entire downward-facing surface of the wafer 113, thereby increasing the possibility that bubbles trapped along the entire downward-facing surface can be pulled out and forced away from the wafer 113. In at least one embodiment, the agitating device 120 is coupled to an electrical motor (not shown) that is configured to sweep the agitating device 120 between opposing ends of the wafer 113.
Turning now to FIGS. 5A-5B, various agitating devices to prevent adherence of air and/or hydrogen bubbles to a wafer, e.g., inside one or more trenches and/or vias, during a plating process are illustrated. FIG. 5A illustrates an agitating device 500 according to a first embodiment. The agitating device 500 includes opposing first and second ends 510. A slotted portion 502 is connected deliberately between the first and second ends 510 The agitating device 500 may be formed from various electrically insulated materials including, but not limited to, plastic or metal coated with plastic/polymer such as, for example, Teflon™. The upper and lower sections of paddle 504, 506 may each have a triangular cross-section where the outer edges of the section extend toward the slotted portion 502. The triangular cross-section permits minimal resistance against the solution.
Referring to FIG. 5B, an agitating device 500′ is illustrated, which is similar to the agitating device 500 described above with respect to FIG. 5A. The agitating device 500′ of FIG. 5B, however, includes one or more slots formed in the agitating device 500′. According to the embodiment illustrated in FIG. 5B, a slot 508 is formed through the upper section of the paddle 504. When utilized with the plating tool 106, the slot 508 permits surrounding solution 117 to stream therethrough at an increased velocity and toward the downward-facing surface of the wafer 113. As discussed above, the streamed fluid exerts a force on bubbles adhered to the downward-facing surface and in the trenches and vias. The force from the stream causes the bubbles to dislodge and to break away from the downward-facing surface and escape from beneath the wafer 113. Accordingly, the wafer 113 may be plated without the formation of hollow metal since the bubbles are removed from the downward-facing surface. Although not illustrated, additional slots may be formed in the agitating device 120.
In at least one embodiment, the slot 508 is shaped such that a slot opening increases as the slot 508 extends toward the middle of the upper section 504. The slot 508, for example, may be formed to have a diamond-shape such that the slot-opening gradually increases as the slot 508 extends toward the center. Bubbles which adhere to the downward-facing surface of the wafer 113 congregate most at the center of the wafer. Forming a slot 508 having a slot opening that increases at the center of the upper section 504 permits the agitating device 500′ to be positioned such that maximum velocity of the stream flowing through the slot 508 is focused at the center of the downward-facing wafer 113 where the highest concentration of bubbles typically exist. It is appreciated that the slot 508 may have a shape other than the described above. The slot 508 is shaped in such a fashion so that a substantially uniform shear force is generated between the solution and the wafer when the wafer is rotated throughout the entire 360° circle. For example, the slot may 508 be shaped in such a way that the plating solution velocity is highest near the center of the wafer. The slot 508 may also be formed such that a force may be delivered therethrough to dislodge any bubbles on the downward facing surface.
Referring now to FIG. 6, a plating tool 106 is provided with a buffle unit 600 which is configured to provide more uniform current distribution between the anode 108 and the cathode module 110 of the plating tool 106. As a result of the increase in uniform current distribution, a resistance drop in a seed layer between an edge and a center of the wafer is compensated, e.g., reduced. More specifically, the buffle unit 600 is interposed between the anode 108 and the lower section 506 of the agitating device 120. The buffle unit 600 may be formed from any electrically insulated material including, but not limited to, plastic. The buffle unit 600 includes a plurality of holes that are sized to assure a higher current in the center of the wafer to compensate for the drop of current in the very thin seed layers between the edge and center of the cathode module 110.
Turning to FIG. 7, a plating tool 106″″ is illustrated according to yet another embodiment. The plating tool 106″″ operates similar to the plating tool 106′ described above with respect to FIG. 2. However, the cathode module 110 further includes one or more ultrasonic transducers 700 coupled thereto. The ultrasonic transducer 700 may convert electricity into sound waves/pulses at a predetermined frequency and intensity. As the wafer 113 is immersed in the solution 117, ultrasonic transducer 700 may generate the sound waves, which vibrate the wafer 113. The vibrations weaken the adhesion force of the bubbles attached to the downward facing surface of the wafer 113, thereby dislodging bubbles such that they may be separated and removed from the wafer 113. The ultrasonic transducer 700 may be combined with the reciprocating agitating device 120 and/or the high velocity solution steamed through the slot 508 to assist in further weakening the adhesion force of the bubbles.
Referring now to FIGS. 8A-8C, a process flow illustrates a process of electroplating a wafer 113 according to an embodiment of the disclosure. As illustrated in FIG. 8A, a cathode module 110 is coupled to an axis (A) via a universal joint (400). The cathode module 110 includes a wafer 113, which rotates when the cathode module 110 rotates about the axis (A). The cathode module 110 may be rotated at a predetermined speed, for example 90 rotations per minute (RPM).
Turning to FIG. 8B, the cathode module 110 may be tilted while continuing to rotate about the axis (A) via a universal joint 400. As the cathode module 110 is titled, the cathode module 110 may be moved toward a plating solution 117. Prior to contacting the cathode module 110 with the plating solution 117, a constant biased potential may be applied to the wafer 113. In addition, one or more ultrasonic transducers 700 can be mechanically attached at the back of the wafer by a lever 800, which may be initiated to output pulses at a predetermined frequency that vibrate the cathode module 110. Accordingly, the wafer 113 may be vibrated at a predetermined frequency prior to being immersed in the plating solution 117.
Referring to FIG. 8C, the cathode module 110 may be introduced into the plating solution 117 while tilted, vibrating and biased at the predetermined electrical potential. After the wafer 113 is immersed in the plating solution 117, the cathode module 110 may be leveled and the ultrasonic transducers 700 may be switched off Accordingly, the cathode module 110 may continue to rotate such that the wafer 113 is rotated while being electroplated, as discussed in detail above.
The wafer 113 may be electroplated according to an electrical current profile. An example of a current profile is illustrated in FIG. 9. More specifically, FIG. 9 shows an initial increase of current due to the potentiostatic entry of a wafer into a plating solution, such as a copper bath. The potentiostatic entry of the wafer assists to protect the seed layer from corrosion by the plating solution. At the end of potentiostatic entry, a short pulse (for example 0.01-0.5 seconds) is used to achieve optimum nucleation and liner seed repairing. The high current density is used for plating overburden followed by a low current density step to fill trenches and vias. Accordingly, the majority of trapped air bubbles will be removed when the wafer is still in the tilted position.
Turning now to FIG. 10, a flow diagram illustrates a method of electroplating a wafer according to an embodiment of the disclosure. At operation 1000, the wafer is rotated at a predetermined speed, such as 90 RPMs. At operation 1002, the wafer is tilted at a predetermined angle. For example, the wafer may be tilted at an angle ranging from 0.5-5 degrees with respect to the plating solution. At operation 1004, a constant potential may be applied to the wafer. For example, the wafer may be biased with a constant potential that is less than the hydrogen evolution over-potential. At, operation 1006, the wafer may be vibrated at a predetermined frequency and intensity. For example, one or more ultrasonic transducers may generate ultrasonic waves that vibrate the wafer. At operation 1008, the wafer is introduced into the plating solution while the wafer is tilted, rotated, electrically biased, and vibrating. Accordingly, a potentiostatic entry, referred to as a “hot entry,” is achieved. At operation 1010, the wafer may be leveled with respect to the plating solution when a predetermined amount of the wafer is immersed in the plating solution. At operation 1012, the wafer continues to rotate while being electroplated until the method ends. Accordingly, the surface of the wafer may be uniformly plated, while preventing the formation of hollow metal.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the operations described therein without departing from the scope of the claims. For instance, the operations may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the scope of the claimed features.
While various embodiments have been described, it will be understood that those skilled in the art, both now and in the future, may make modifications to the embodiments which fall within the scope of the following claims. These claims should be construed to maintain the proper protection for the invention.
Patent Application
20140262803
